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- Open Access
Open questions: some unresolved issues in biodiversity
© Magurran; licensee BioMed Central Ltd. 2013
Received: 21 November 2013
Published: 6 December 2013
Biodiversity - or biological diversity - is a term now so familiar that politicians use it to persuade us that they really care about the natural world. Many papers, and indeed entire journals, are devoted to explaining how species coexist, why some localities are more diverse than others, and to tracking the rate at which biodiversity is being lost. It might seem that there is little to add to the debate. Yet, while there has been remarkable progress in understanding how ecological communities are structured, and how best to protect them, there are still many unresolved issues. Here are just three of them.
Relative abundance of species
It must always have been obvious to observers that species vary in their abundances. Darwin remarked on the ‘beautiful diversity and proportion of kinds’ in his Origin of Species. We know that all ecological communities are characterized by a few common and typically many rare species. Although this pattern is ubiquitous, ecologists still struggle to provide a convincing explanation why species abundances are as uneven as they are. Dozens of models have been proposed (the first in 1932). Some of these take account of biological interactions such as competition, while others reflect the statistical behavior of large numbers. Since models can be based on conflicting assumptions yet generate patterns seen in the real world, a good ‘fit’ to empirical data does not in itself vindicate the theory underpinning the model. There is still a need for a much better understanding of the processes that influence the relative abundance of species, and that determine which species are abundant and which ones are rare. This will likely take account of species traits, and the positioning of a species in its range (populations tend to be larger when taxa are close to the center of their range). But the spatial and temporal context of a community is also important as species turnover in space and time plays a crucial role in maintaining the diversity of an assemblage. Understanding the processes that shape diversity over both macroecological and local assemblage scales will play an essential part in this .
Anthropogenic change and biodiversity
Many diversity measures have been developed with the goal of finding a metric that can quantify the effects of impacts such as pollution on natural communities. This quest has been only partially successful. One reason is that community responses to different types of disturbance can be complex . Moreover, even the best known predictive framework, the Intermediate Disturbance Hypothesis, has been subject to growing criticism . A further problem is that a diversity metric reported in isolation is uninformative. It is only when there are good comptive data on species identities and abundances in an undisturbed community that meaningful conclusions can be drawn.
Biodiversity offsetting is increasingly hailed as a way of balancing the demands of development and conservation. It provides compensation for damaged sites. For example, if habitat such as woodland is destroyed to make way for housing or industry, offsetting means that equivalent habitat must be created or restored to protect the same level of biodiversity. In principle this sounds encouraging, but there are considerable challenges even when developers are keen to abide by the spirit as well as the letter of local guidelines. For example, some ancient habitats are irreplaceable, and it may be difficult or impossible to recreate ecological communities that have been established over decades and form part of important ecological networks. The Lawton report discusses many of the concerns that biodiversity offsetting raises, and makes recommendations for dealing with them. In short, given the knowledge gaps that exist in relation to the processes that shape biodiversity, and how natural systems respond to impacts, biodiversity offsetting is not an easy solution, and substantial uncertainties remain.
- McGill BJ: Linking biodiversity patterns by autocorrelated random sampling. Am J Bot. 2011, 98: 481-502. 10.3732/ajb.1000509.View ArticlePubMedGoogle Scholar
- Dornelas M: Disturbance and change in biodiversity. Phil Trans R Soc B Biol Sci. 2010, 365: 3719-3727. 10.1098/rstb.2010.0295.View ArticleGoogle Scholar
- Fox JW: The intermediate disturbance hypothesis should be abandoned. Trends Ecol Evol. 2013, 28: 86-92. 10.1016/j.tree.2012.08.014.View ArticlePubMedGoogle Scholar
- Lawton JH, Brotherton PNM, Brown VK, Elphick C, Fitter AH, Forshaw J, Haddow RW, Hilborne S, Leafe RN, Mace GM, et al: Making Space for Nature: a Review of England’s Wildlife Sites and Ecological Network. http://archive.defra.gov.uk/environment/biodiversity/documents/201009space-for-nature.pdf,
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. | <urn:uuid:eec8a2b0-d8d9-4a3e-af5d-3560ef6bf000> | 3.359375 | 1,125 | Truncated | Science & Tech. | 35.405049 | 95,517,688 |
Biogeoscientists show evidence of 90 billion tons of microbial organisms—expressed in terms of carbon mass—living in the deep biosphere, in a research article published online by Nature, July 20, 2008. This tonnage corresponds to about one-tenth of the amount of carbon stored globally in tropical rainforests.
Biogeoscientists show evidence of 90 billion tons of microbial organisms—expressed in terms of carbon mass—living in the deep biosphere, in a research article published online by Nature. This tonnage corresponds to about one-tenth of the amount of carbon stored globally in tropical rainforests.
Research at the University of Liverpool has found how Saharan dust storms help sustain life over extensive regions of the North Atlantic Ocean.
Working aboard research vessels in the Atlantic, scientists mapped the distribution of nutrients including phosphorous and nitrogen and investigated how organisms such as phytoplankton are sustained in areas with low nutrient levels.
As part of the Agency's user-driven approach to preparing new Earth Explorer missions to advance our understanding of the Earth system, six candidate missions will be presented to the science community at a User Consultation Meeting in January 2009.
Antarctic worms, sea spiders, urchins and other marine creatures living in near-shore shallow habitats are regularly pounded by icebergs. New data suggests this environment along the Antarctic Peninsula is going to get hit more frequently. This is due to an increase in the number of icebergs scouring the seabed as a result of shrinking winter sea ice. The results are published this week in the journal Science.
A team of researchers from the University of Manchester (United Kingdom), the National Institute of Applied Sciences in Lyon (France) and the ESRF has revealed how a growing crack interacts with the 3D crystal structure of stainless steel. By using a new grain mapping technique it was possible to determine the internal 3D structure of the material without destroying the sample. Afterwards, a crack was initiated in the stainless steel, and the scientists were able to study how the crack grew between the grains.
FRESNO, CA - Horticultural crops account for almost 50% of crop sales in the United States, and these crops are carefully managed to ensure good quality. But more information is needed about the crops' growth and response to seasonal and climatic changes so that management practices such as irrigation can be precisely scheduled. Existing research can be difficult to generalize because of variations in crops, planting densities, and cultural practices. | <urn:uuid:ac1c47e2-b430-478a-94b8-8f536ef87360> | 2.96875 | 515 | Content Listing | Science & Tech. | 28.642002 | 95,517,689 |
Chemists from the University of Würzburg have developed a boron-based molecule capable of binding nitrogen without assistance from a transition metal. This might be the first step towards the energy-saving production of fertilisers.
Whether wheat, millet or maize: They all need nitrogen to grow. Fertilisers therefore contain large amounts of nitrogenous compounds which are usually synthesised by converting nitrogen to ammonia in the industrial Haber-Bosch process, named after its inventors. This technology is credited with feeding up to half of the present world population.
Air consists of nearly 80 percent nitrogen (N2) which is, however, extremely unreactive, because the bond between the two nitrogen atoms is very stable. The Haber-Bosch process breaks this bond, converting nitrogen to ammonia (NH3) which can be taken up and used by plants. This step requires very high pressures and temperatures and is so energy intensive that it is estimated to consume 1% of the primary energy generated globally.
Bacteria lead the way
"So we were looking for a way to split nitrogen that is more energetically favourable," explains Professor Holger Braunschweig from the Institute of Inorganic Chemistry at Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany. Certain bacteria show that this actually works: They are capable of doing so at normal pressure and temperatures by using the nitrogenase enzyme which catalyses the reaction with the help of the transition metals iron and molybdenum.
"We have been unsuccessful in reproducing a kind of nitrogenase so far," Braunschweig says. "So we started to look for an alternative: a molecule that is capable of catalysing the reaction and is not based on transition metals."
His team has been studying specific boron-containing compounds, the so-called borylenes, for years. They are considered potential candidates for such a catalyst. But how exactly would the corresponding borylene molecule have to be structured for this purpose?
The candidates must be a good match for nitrogen
The iron and molybdenum in the nitrogenase are known to give away electrons to the nitrogen molecule, a process called reduction. This causes the bond between the two N atoms to break. However, this only works because the transition metals are a good match for the nitrogen molecule: Their orbitals, the space where the electrons passed during reduction can be found, overlap considerably with those of the nitrogen due to their spatial layout.
Based on quantum mechanical predictions, Dr. Marc-André Légaré from the Institute of Inorganic Chemistry designed a borylene with a similar orbital arrangement. The results of his investigations were then synthetically tested at the JMU institute.
And successfully so, as the borylene produced in this manner was capable of fixing nitrogen – and that at room temperature and normal air pressure. "For the first time, we were able to demonstrate that nonmetallic compounds are also capable of accomplishing this step," Légaré emphasises.
Merely a first step
However, this does not mean that the Haber-Bosch process is about to be abolished. For one thing, it is not certain that the reduced nitrogen can be detached from the borylene without destroying it. However, this step is necessary to recycle the catalyst so that it is available to bond to the next nitrogen molecule subsequently.
"Whether this will ultimately yield a method that is more favourable energetically is still an open question," says Professor Braunschweig. "It is only the very first step, albeit a major one, on the way to reaching the ultimate goal."
The results of the study, which was carried out in collaboration with the research group of Professor Bernd Engels of the JMU Institute for Physical and Theoretical Chemistry, will be published in the renowned Science magazine.
Marc-André Légaré, Guillaume Bélanger-Chabot, Rian D. Dewhurst, Eileen Welz, Ivo Krummenacher, Bernd Engels and Holger Braunschweig: Nitrogen Fixation and Reduction at Boron; Science; 23. February 2018.
Prof. Dr. Holger Braunschweig, Chair of Inorganic Chemistry II, JMU, T +49 931 31-85260, firstname.lastname@example.org
http://www.braunschweiggroup.de/ Website of Braunschweig's team
Robert Emmerich | Julius-Maximilians-Universität Würzburg
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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Spawning of the cobia,Rachycentron canadum, in the Chesapeake Bay area, with observations of juvenile specimens
- Edwin B. Joseph, John J. Norcross, William H. Massmann
- Chesapeake science SCOPUS
- Coastal and Estuarine Research Federation in 1964
- Cited Count
- Springer JSTOR
Pelagic eggs collected in Atlantic coastal waters adjacent to Chesapeake Bay have been identified as those of the cobia,Rachycentron canadum (Linnaeus). The egg diameters ranged from 1.16 mm to 1.42 mm with a mean of 1.27 mm. The single large oil globule had a mean diameter of 0.38 mm. The presence of gravid females and the appearance of cobia eggs in plankton collections indicated that spawning occurs between mid June and mid August. Sampling in 1960 showed spawning maxima to be in June and July. Although virtually all of the cobia eggs were collected in the Atlantic, knowledge of the current patterns in the survey area led to the conclusion that spawning occurred in lower Chesapeake Bay or in the immediate vicinity of the Virginia Capes. The color pattern and fin shape is described and illustrated from two juvenile cobia collected in August 1962. Observations made before capture of the juveniles point out that certain adult behavioral characteristics are already well established in the first few months of juvenile existence.
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The Universe is home to numerous exotic and beautiful phenomena, some of which can generate almost inconceivable amounts of energy. Supermassive black holes, merging neutron stars, streams of hot gas moving close to the speed of light ... these are but a few of the marvels that generate gamma-ray radiation, the most energetic form of radiation, billions of times more energetic than the type of light visible to our eyes. What is happening to produce this much energy? What happens to the surrounding environment near these phenomena? How will studying these energetic objects add to our understanding of the very nature of the Universe and how it behaves?
The Fermi Gamma-ray Space Telescope, formerly GLAST, is opening this high-energy world to exploration and helping us answer these questions. With Fermi, astronomers at long last have a superior tool to study how black holes, notorious for pulling matter in, can accelerate jets of gas outward at fantastic speeds. Physicists are able to study subatomic particles at energies far greater than those seen in ground-based particle accelerators. And cosmologists are gaining valuable information about the birth and early evolution of the Universe.
For this unique endeavor, one that brings together the astrophysics and particle physics communities, NASA has teamed up with the U.S. Department of Energy and institutions in France, Germany, Japan, Italy and Sweden. General Dynamics was chosen to build the spacecraft. Fermi was launched June 11, 2008 at 12:05 pm EDT.
For the first time ever, scientists using NASA's Fermi Gamma-ray Space Telescope have found the source of a high-energy neutrino from outside our galaxy. This neutrino traveled 3.7 billion years at almost the speed of light before being detected on Earth. This is farther than any other neutrino whose origin scientists can identify.
+ Read More
On June 11, NASA's Fermi Gamma-ray Space Telescope celebrates a decade of using gamma rays, the highest-energy form of light in the cosmos, to study black holes, neutron stars, and other extreme cosmic objects and events.
+ Read More
Both instruments on Fermi have been returned to operational status and are actively collecting science data. For the LAT, this data will be used to monitor performance as the instrument returns to normal operating temperatures. GBM has returned to full functionality. | <urn:uuid:e4a9b3cc-9dda-45f6-bec4-25d283eb044a> | 3.96875 | 481 | About (Org.) | Science & Tech. | 37.88094 | 95,517,725 |
The java.sql package contain a prepared statement, This prepared statement interface is available from the Statement interface. This is used to pass parameters at runtime. In this Tutorial we want to describe you a code that helps you in understanding JDBC Insert Prepared Statement. For this we have a class Jdbc Insert Prepared statement, Inside this class we have a main method that include the list of following steps -
import a package java.sql - this provides you a network interface that help in communicating between front end and backend in database.
Loading a driver followed by calling a class.forname( ),this class accept a driver class as argument. The Driver Manager call getConnection (),which returns you a connection object and this is used to built a connection between url and database.
prepareStatement ( ) : This method is useful when you want to execute the same statement object many times, This reduces the time of execution to use the same object.The method accept a sql object as parameter, that include the list of inserted values into the table set The String( ) : Set String XXX is defined in prepared statement to substitute a value in the question mark placeholder as string,int .In the code, we substitute a question mark value as string.executeUpdate ( ) :This method provides you the numbers of affected rows in the table and execute the statement in a given code.executeQuery ( ):This method provides you a set of records retrieved from a table in the database. The select statement is used to obtain the records from the result set.
next ( ) : This method retain you the next elements in a series.
Finally the print print the No, Name from a employee table present in database. In case there is an exception in try block, the subsequent catch block check and handle the exception.
No Name Girish Tewari Rohini Indian Komal Singh Rohini Indian Sandeep kumar Rohini Indian Amit Singh Rohini Indian Girish Tewari Rohini Indian Darshan Tewari Rohini Indian Rakesh Kanwal Delhi Indian | <urn:uuid:4c625fc5-b3d5-4c69-a7e5-4ab166304347> | 3.40625 | 420 | Tutorial | Software Dev. | 38.557997 | 95,517,745 |
- Inside the Discovery of the Higgs Boson
- Sprecher: Jonathan Keeble
- Spieldauer: 10 Std. und 19 Min.
- Ungekürztes Hörbuch
- Erscheinungsdatum: 22.07.2014
- Sprache: Englisch
- Anbieter: Audible Studios
The discovery of the Higgs boson made headlines around the world. Two scientists, Peter Higgs and François Englert, whose theories predicted its existence, shared a Nobel Prize. The discovery was the culmination of the largest experiment ever run, the ATLAS and CMS experiments at CERN's Large Hadron Collider.
But what really is a Higgs boson and what does it do? How was it found? And how has its discovery changed our understanding of the fundamental laws of nature? And what did it feel like to be part of it?
Jon Butterworth is one of the leading physicists at CERN and this book is the first popular inside account of the hunt for the Higgs. It is a story of incredible scientific collaboration, inspiring technological innovation and ground-breaking science. It is also the story of what happens when the world's most expensive experiment blows up, of neutrinos that may or may not travel faster than light, and the reality of life in an underground bunker in Switzerland.
This book will also leave you with a working knowledge of the new physics and what the discovery of the Higgs particle means for how we define the laws of nature. It will take you to the cutting edge of modern scientific thinking.
Jon Butterworth is one of the leading physicists on the Large Hadron Collider and is Head of Physics and Astronomy at UCL. He writes the popular Life & Physics blog for the Guardian and has written articles for a range of publications including the Guardian and New Scientist.
Jon has appeared on BBC Radio 4's Today Programme, Material World, The Infinite Money Cage, BBC Newsnight, Horizon, Channel 4 News, and Al Jazeera. He frequently gives public lectures including at the Welcome Institute and the Royal Institution.
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Von "muratvogt" Am hilfreichsten 27.01.2015
just fine but a little to high for me.
I really liked it. but this book is not the easiest to undertsand (happens sometimes when reading a book about particle phisics)
but written good. read even better. so i will listen to it another time. | <urn:uuid:7bc190f5-d930-4cde-91eb-6ea0a90b8844> | 2.875 | 548 | Product Page | Science & Tech. | 57.590916 | 95,517,753 |
Connections Between Atmospheric Ozone, The Climate System and UV-B-Radiation in The Arctic
The global three-dimensional distribution of atmospheric ozone is highly controlled by atmospheric dynamics. In its turn, ozone affects the global climate system through its absorption bands in the ultraviolet and infrared parts of atmospheric spectra, and through infrared emission by ozone molecules. The considerable increase in tropospheric ozone concentrations, especially in mid-latitudes, since the 19th Century and the decreasing trend of stratospheric ozone in high and mid-latitudes during recent decades emphasise the central role of atmospheric ozone in global change. These changes are not only important for the biosphere, but also for the global climate system.
KeywordsPotential Vorticity Total Ozone Stratospheric Ozone Polar Vortex Total Ozone Column
Unable to display preview. Download preview PDF.
- Bojkov, R. and C. Zerefos, 1993, Atlas of G030S total ozone maps for the European Arctic Stratospheric Ozone Experiment, WMO GAW Report No. 31, 167 p.Google Scholar
- Harwood, R., E. Carr, I. MacKenzie, J. Waters, E. Fishbein, D. Flower, I. Froidevaux, R. Jarnot, W. Read, G. Peckham, W. Lahoz and P. Ricaud, 1994, Contributions from microwave limb sounder to our understanding of middle atmosphere composition and dynamics, Annales Geophysicae, Supplement III to Volume 12, p. C607.Google Scholar
- Huovila, S. and A. Tuominen, 1990, On the influence of radiosonde lag errors on upper-air climatological data in Finland 1951–1988, Finnish Meteorological Institute, Meteorological Publications 14, 29 p.Google Scholar
- Larsen N., B. Knudsen, I. Mikkelsen, T. Jorgensen and P. Eriksen, 1994, Ozone depletion in the Arctic stratosphere in early 1993, submitted to the Geophys. Res. Lett.Google Scholar
- Rummukainen, M., B. Knudsen and P. von der Gathen, 1994, Dynamical diagnostics of the edges of the polar vortices, Annales Geophysicae, in press.Google Scholar
- Taalas, P. and E. Kyrö, 1992 b, Two years of regulär ozone soundings in the European Arctic, Sodankylä, J. Geophys. Res. D97, 8093–8098.Google Scholar
- Taalas, P., 1992, On the behaviour of tropospheric and stratospheric ozone in Northern Europe and in Antarctica 1987–90. Finnish Meteorological Institute, Contributions No. 8, 88 p.Google Scholar | <urn:uuid:c15414fb-2431-40cf-93a1-7bf6417f806f> | 2.953125 | 591 | Truncated | Science & Tech. | 46.513004 | 95,517,772 |
Great loess: layers of ancient dust give clues to mountains birth.
Deserts covered Central Asia as early as 22 million years ago
The great Asian deserts developed 22 million years ago at the latest, 14 million years earlier than had been thought. So concludes a new analysis of Chinese soils, filling in another piece of the puzzle of the Himalayas’ birth.
Today, huge deserts characterize the vast landmasses inside Asia, the largest continent on Earth. Here, cut off by the Himalayas from the humidity of the Indian Ocean and far from any other seas, the climate is extreme. Winters are ice-cold, summers blazing hot and moisture scarce.
The loess was deposited from 22 to 6.2 million years ago between layers of red clay. Each layer contains about 65,000 years’ worth of deposits. Such large layers imply that extensive deserts existed nearby: the Asian interior.
"The deserts would have been relatively cold, like the Gobi today, as opposed to the Sahara," explains Bill Ruddiman of the University of Virginia, one of the team. Cold, dry, winter monsoon winds transported the desert dusts to their long-term resting place.
The Qinan basin’s stripy landscape was produced by a climate of dry winter monsoons punctuated by moist summer monsoons. The reddish clay layers were produced locally during more humid periods, when weaker winter monsoons meant that desert dust didn’t make it to the Loess plateau, the researchers believe.
"To block the moisture, there must have been some sort of a mountain range in place 22 million years ago", says Jay Quade, a desert geoscientist at the University of Arizona in Tucson. The existence of the central Asian deserts 22 million years ago offers an independent perspective on the uplift of the Himalayas, the details of which are still controversial.
Before now, little was known about the region’s climate that far back in time. Most of the studies on Chinese loess have centred on the Quaternary period, less than 1.6 million years ago. Previously, the oldest reliably dated loess finds were only about 6 million years old.
HEIKE LANGENBERG | © Nature News Service
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
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03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences | <urn:uuid:75f767dc-a7bf-4b12-8146-a18d78ae7a7a> | 3.96875 | 1,039 | Content Listing | Science & Tech. | 44.923916 | 95,517,773 |
In this section, we are going to describe the action tag. The action tag is a generic tag that is used to call actions directly from a JSP page by specifying the action name and an optional namespace. The body content of the tag is used to render the results from the Action. Any result processor defined for this action in struts.xml will be ignored, unless the executeResult parameter is specified.
Add the following code snippet into the struts.xml file.
|<action name="actionTag" class="net.roseindia.actionTag">
Create an action class as shown below:
Now create a jsp page using
tag as shown in the success.jsp
page. The action tag is used to call actions directly from a JSP page
by specifying the action name and an optional namespace.
Output of the success.jsp | <urn:uuid:e75b763b-6f06-4844-aeb8-93282e028415> | 2.8125 | 179 | Documentation | Software Dev. | 62.137002 | 95,517,777 |
+44 1803 865913
Series: Biodiversity of Poland Volume: 7
By: Wladislaw Wojewoda
812 pages, no illustrations
Language: Bilingual in English and Polish
About 400 genera and 2,650 species known in Poland are included in this book. Some of them are invalid according to the ICBN. Some of the taxa are uncertainly classified, and others are mistakenly recorded from Poland. The true number of Basidiomycete taxa known from Poland is about 2,550.
Over 2,100 species of agaricoid and boletoid fungi (Moser 1983) and about 2,000 species of aphyllophoroid, gasteromycetoid, tremelloid, auricularoid, dacryomycetoid and tulasnelloid fungi (Julich 1984) are known in Europe. Most certainly this number is still not inclusive, as in fact more fungi occur in Europe. In the former German Federal Republic, 3,515 species Basidiomycetes (Krieglsteiner 1991) were known through 1991, about a thousand more than those known in Poland in 2003. Because Poland and the western part of Germany are comparable in terms of area, climate and nature preservation, the same number of species might be expected to grow in Poland.
The genera and species are alphabetized. Presently accepted Latin names and the most important synonyms are given for each taxon. The affiliations to families and orders and the number of species known in Poland are given for the genera. The most important Polish names are given. The habitats in which the fungi grow, plant community, substratum, mode of nutrition and fructification time are characterized.
For threatened species, the threat categories assigned in Poland and other European countries are given from the literature (red books, red lists).
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Scientific luminaries has put forward a new theory of the origin of life on Earth. Sensational views publishes News Ufa ToDay.
Scientists have learned that the first people came to light thanks to the moon. It has affected the fact that plants appeared on land.
Known version, life first appeared in the sea 750 million years ago. Many organisms exist in the water over millions of years. But 430 million years ago first plants moved into the coastal area.
According to experts, the Moon, have a huge impact on the tides, was the reason that the organisms began to live on land. In those days, the satellite was much closer to our planet and tides, with low tides were much stronger.
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The Iceland plume is a postulated upwelling of anomalously hot rock in the Earth's mantle beneath Iceland. Its origin is thought to lie deep in the mantle, perhaps at the boundary between the core and the mantle at approximately 2,880 km depth. Opinions differ as to whether seismic studies have imaged such a structure. In this framework, the volcanism of Iceland is attributed to this plume, according to the theory of W. Jason Morgan.
According to the plume model, the source of Icelandic volcanism lies deep beneath the center of the island. The earliest volcanic rocks attributed to the plume are found on both sides of the Atlantic. Their ages have been determined to lie between 58 and 64 million years. This coincides with the opening of the north Atlantic in the late Paleocene and early Eocene, which has led to suggestions that the arrival of the plume was linked to, and has perhaps contributed to, the breakup of the North Atlantic continent. In the framework of the plume hypothesis, the volcanism was caused by the flow of hot plume material initially beneath thick continental lithosphere and then beneath the lithosphere of the growing ocean basin as rifting proceeded. The exact position of the plume at that time is a matter of disagreement between scientists, as is whether the plume is thought to have ascended from the deep mantle only at that time or whether it is much older and also responsible for the old volcanism in northern Greenland, on Ellesmere Island, and at Alpha Ridge in the Arctic.
As the northern Atlantic opened to the east of Greenland during the Eocene, North America and Eurasia drifted apart; the Mid-Atlantic Ridge formed as an oceanic spreading center and a part of the submarine volcanic system of mid-oceanic ridges.The initial plume head may have been several thousand kilometers in diameter, and it erupted volcanic rocks on both sides of the present ocean basin to produce the North Atlantic Igneous Province. Upon further opening of the ocean and plate drift, the plume and the mid-Atlantic Ridge are postulated to have approached one another, and finally met. The excess magmatism that accompanied the transition from flood volcanism on Greenland, Ireland and Norway to present-day Icelandic activity was the result of ascent of the hot mantle source beneath progressively thinning lithosphere, according to the plume model, or a postulated unusually productive part of the mid-ocean ridge system. Some geologists have suggested that the Iceland plume could have been responsible for the Paleogene uplift of the Scandinavian Mountains by producing changes in the density of the lithosphere and asthenosphere during the opening of the North Atlantic.
An extinct ridge exists in western Iceland, leading to the theory that the plume has shifted east with time. The oldest crust of Iceland is more than 20 million years old and was formed at an old oceanic spreading center in the western fjord (Vestfirðir) region. The westward movement of the plates and the ridge above the plume and the strong thermal anomaly of the latter caused this old spreading center to cease 15 million years ago and lead to the formation of a new one in the area of today's peninsulas Skagi and Snæfellsnes; in the latter there is still some activity in the form of the Snæfellsjökull volcano. The spreading center, and hence the main activity, have shifted eastward again 7–9 million years ago and formed the current volcanic zones in the southwest (Reykjanes, Hofsjökull) and northeast (Tjörnes). Presently, a slow decrease of the activity in the northeast takes place, while the volcanic zone in the southeast (Katla, Vatnajökull), which was initiated 3 million years ago, develops. The reorganisation of the plate boundaries in Iceland has also been attributed to microplate tectonics.
Geophysical and geochemical observations
Information about the structure of Earth's deep interior can be acquired only indirectly by geophysical and geochemical methods. For the investigation of postulated plumes, gravimetric, geoid and in particular seismological methods along with geochemical analyses of erupted lavas have proven especially useful. Numerical models of the geodynamical processes attempt to merge these observations into a consistent general picture.
An important method for imaging large-scale structures in Earth's interior is seismic tomography, by which the area under consideration is "illuminated" from all sides with seismic waves from earthquakes from as many different directions as possible; these waves are recorded with a network of seismometers. The size of the network is crucial for the extent of the region which can be imaged reliably. For the investigation of the Iceland Plume, both global and regional tomography have been used; in the former, the whole mantle is imaged at relatively low resolution using data from stations all over the world, whereas in the latter, a denser network only on Iceland images the mantle down to 400–450 km depth with higher resolution.
Regional studies from the 1990s and 2000s show that there is a low seismic-wave-speed anomaly beneath Iceland, but opinion is divided as to whether it continues deeper than the mantle transition zone at roughly 600 km depth. The velocities of seismic waves are reduced by up to 3% (P waves) and more than 4% (S waves), respectively. These values are consistent with a small percentage of partial melt, a high magnesium content of the mantle, or elevated temperature. It is not possible to unambiguously separate out which effect causes the observed velocity reduction.
Numerous studies have addressed the geochemical signature of the lavas present on Iceland and in the north Atlantic. The resulting picture is consistent in several important respects. For instance, it is not contested that the source of the volcanism in the mantle is chemically and petrologically heterogeneous: it contains not only normal peridotite, but also eclogite – a fertile rock originating from subducted slabs – both of which contribute to the melts. The origin of the latter is assumed to be metamorphosed, very old oceanic crust which sank into the mantle several hundreds of millions of years ago during the subduction of an ocean, then upwelled from deep within the mantle.
Studies using the major and trace-element compositions of Icelandic volcanics showed that the source of present-day volcanism was about 100 °C greater than that of the source of mid-ocean ridge basalts.
The variations in the concentrations of trace elements such as helium, lead, strontium, neodymium, and others show clearly that Iceland is compositionally distinct from the rest of the north Atlantic. For instance, the ratio of He-3 and He-4 has a pronounced maximum on Iceland, which correlates well with geophysical anomalies, and the decrease of this and other geochemical signatures with increasing distance from Iceland indicate that the extent of the compositional anomaly reaches about 1,500 km along the Reykjanes Ridge and at least 300 km along the Kolbeinsey Ridge. Depending on which elements are considered and how large the area covered is, one can identify up to six different mantle components, which are not all present in any single location.
Furthermore, some studies show that the amount of water dissolved in mantle minerals is two to six times higher in the Iceland region than in undisturbed parts of the mid-oceanic ridges, where it is regarded to lie at about 150 parts per million. The presence of such a large amount of water in the source of the lavas would tend to lower its melting point and make it more productive for a given temperature.
The north Atlantic is characterized by strong, large-scale anomalies of the gravity field and the geoid. The geoid rises up to 70 m above the geodetic reference ellipsoid in an approximately circular area with a diameter of several hundred kilometers. In the context of the plume hypothesis, this has been explained by the dynamic effect of the upwelling plume which bulges up the surface of the Earth. Furthermore, the plume and the thickened crust cause a positive gravity anomaly of about 60 mGal (=0.0006 m/s²) (free-air).
Since the mid-1990s several attempts have been made to explain the observations with numerical geodynamical models of mantle convection. The purpose of these calculations was, among other things, to resolve the paradox that a broad plume with a relatively low temperature anomaly is in better agreement with the observed crustal thickness, topography, and gravity than a thin, hot plume, which has been invoked to explain the seismological and geochemical observations. The most recent models prefer a plume that is 180–200 °C hotter than the surrounding mantle and has a stem with a radius of ca. 100 km. Such temperatures have not yet been confirmed by petrology, however.
Challenges to the plume model
The weak visibility of the postulated plume in tomographic images of the lower mantle and the geochemical evidence for eclogite in the mantle source have led to the theory that Iceland is not underlain by a mantle plume at all, but that the volcanism there results from processes related to plate tectonics and is restricted to the upper mantle.
Subducted ocean plate
According to one of those models, a large chunk of the subducted plate of a former ocean has survived in the uppermost mantle for several hundred million years, and its oceanic crust now causes excessive melt generation and the observed volcanism. This model, however, is not backed by dynamical calculations, nor is it exclusively required by the data, and it also leaves unanswered questions concerning the dynamical and chemical stability of such a body over that long period or the thermal effect of such massive melting.
Upper mantle convection
Another model proposes that the upwelling in the Iceland region is driven by lateral temperature gradients between the suboceanic mantle and the neighbouring Greenland craton and therefore also restricted to the upper 200–300 km of the mantle. However, this convection mechanism is probably not strong enough under the conditions prevailing in the north Atlantic, with respect to the spreading rate, and it does not offer a simple explanation for the observed geoid anomaly.
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A team from Purdue and Northwestern universities analyzed the fault motion for eight years using global positioning system measurements and found that it is much less than expected given the 500- to 1,000-year repeat cycle for major earthquakes on that fault. The last large earthquakes in the New Madrid seismic zone were magnitude 7-7.5 events in 1811 and 1812.
Estimating an accurate earthquake threat for the area, which includes parts of Illinois, Indiana, Tennessee, Arkansas and Kentucky, is crucial for the communities potentially affected, said Eric Calais, the Purdue researcher who led the study.
"Our findings suggest the steady-state model of quasi-cyclical earthquakes that works well for faults at the boundaries of tectonic plates, such as the San Andreas fault, does not apply to the New Madrid fault," said Calais, who is a professor of earth and atmospheric sciences. "At plate boundaries, faults move at a rate that is consistent with the rate of earthquakes so that past events are a reliable guide to the future. In continents, this does not work. The past is not necessarily a key to the future, which makes estimating earthquake hazard particularly difficult."
The team determined that the ground surrounding the fault system is moving at a rate of less than 0.2 millimeters per year and there is likely no motion. A paper detailing the work is published in the current issue of Science magazine.
Seth Stein, co-author of the paper, said this surface movement represents energy being stored that could be released as an earthquake.
"Building up energy for an earthquake is like saving money for a big purchase," said Stein, the William Deering Professor of Earth and Planetary Sciences at Northwestern University. "You put money in over a long period of time and then spend it all at once and have to start saving again."
With an earthquake, it is elastic deformation that must be built up. This can be measured using GPS through movements on the surface, he said.
"The slower the ground moves, the longer it takes until the next earthquake, and if it stops moving, the fault could be shutting down," Stein said. "We can't tell whether the recent cluster of big earthquakes in the New Madrid is coming to an end. But the longer the GPS data keep showing no motion, the more likely it seems."
The U.S. Geological Survey-funded study used data recorded at nine GPS antennas mounted in the ground in the earthquake zone.
"GPS technology can measure movement to the thickness of a fishing line," Stein said. "Use of GPS to study earthquakes shows the impact a new technology can have. It lets us see that the world is different than we thought it was."
In the Midwest there are other faults that show no activity today but have evidence of earthquakes occurring within the past 10,000 to 1 million years, Calais said.
"If other faults in the central and eastern U.S. have been active recently, geologically speaking, they could potentially be activated again in the future," he said. "We need to develop a new paradigm for how earthquakes happen at faults that are inside continents."
Calais and Stein are exploring possible explanations for the behavior of faults like the New Madrid. One possibility is that earthquakes in these areas occur in clusters and then migrate to a nearby fault.
"There is the possibility that seismicity migrates with time as earthquakes trigger earthquakes on nearby faults," Calais said. "Geologists studying the seismic history of faults have found that there have been earthquakes on several faults in the central and eastern U.S. and that they seem to produce bursts of earthquakes and then turn off."
The team is doing additional analysis and modeling to study this further.Writer: Elizabeth K. Gardner, 765-494-2081, email@example.com
Elizabeth K. Gardner | EurekAlert!
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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4 recent findings that explain why crocodiles are smarter than you think
Crocodile stories keep surfacing lately in Costa Rica. One hung out shoreside with tourists in Guanacaste on Wednesday. A couple weeks ago a croc crashed a hospital in Ciudad Neily. In late April, a man made the misguided decision to wade into the famously crocodile-infested waters of the Río Tárcoles.
As humans keep encroaching on crocodile habitats, these types of encounters make sense. The reptiles have been around for millions of years, and waaaay back in the day nobody threatened these big fellas. Now in some parts of the world they’ve been hunted to near-extinction. And their livelihood appears threatened by climate change. One croc in Russia was even hospitalized recently after a large woman fell on top of it.
But with so many years on planet Earth, don’t expect crocodiles to allow puny humans to destroy everything so easily. A round-up by The American Scholar shows the latest documented croc characteristics after 65 million years of evolution. We’ve written about some of these crocodile discoveries before. It’s why the prehistoric creature is one of the coolest animals around.
Here are four of the newest findings that show why crocodiles are more intelligent than you realize:
1. They can climb trees. And they use tree climbing as part of their own neighborhood watch system, according to a recent study. The arboreal crocs have been seen in Costa Rica’s Santa Rosa National Park and in many other crocodile habitats worldwide. Baby crocodiles have been spotted 30-feet up in the air.
The creatures climb trees to bask in the sun, which regulates the body temperature of the cold-blooded species. But the study also notes that the crocs use the higher ground to keep watch over their surroundings since they tend to be skittish and flee from their heights when the researchers moved too closely. Escape is easy for a croc way up high and out on a limb — the reptile after spotting a threat can roll off the branch and fall into the waters below.
2. They use tools. Is that a log or a crocodile? We’ve all asked this question (hopefully before it was already too late!). Turns out crocs are aware that they are masters of disguise. The same scientists who published the paper that crocodiles can climb, also learned that the reptiles balance twigs on their nose to blend with their surroundings. The authors observed that “the crocodiles remained perfectly still for hours, and if they did move to change position, they did it in such a way that the sticks remained balanced on their snouts.”
The Los Angeles Times explains the scenario in more detail:
Were the sticks purely there by coincidence? Was it just part of the camouflage? Or could these reptiles actually be using these sticks as lures?
After studying the habits of these reptiles at four sites in Louisiana for a year, the scientists confirmed that alligators and crocodiles do indeed use twigs to lure unsuspecting birds to their doom.
Here was the really strange part: The reptiles were covering their snouts with sticks only during spring nesting season, when demand for twigs was high and birds would grab every little woody scrap they could get their beaks on to build their nest.
3. They eat veggies. Crocodiles haven’t gone full-on vegan just yet. But they’re maybe feeling it out a little bit. Experimenting a little and trying to find themselves. Yes, crocodilians still consume huge amounts of meat. But research shows that the reptiles also have a hankering for nuts, berries, legumes and grains. The seeds they excrete or regurgitate help plants thrive across wide-ranging territories.
4. They’ve made impressive allies. As we reported in May, at La Selva biological reserve in Puerto Viejo, Sarapiquí, butterflies and bees have been filmed drinking caiman tears. La Selva Director Carlos de la Rosa said the butterfly fed for 15 minutes out of the eye socket of the caiman, a crocodilian species (though not a true crocodile), while the relaxed reptile failed to even blink. The butterfly and bee were seeking the salt from their tears, a scarce resource in their environment. De la Rosa added that the tears could contain proteins and other micronutrients that help the insects survive.
How does this benefit the reptile? Well, it actually might not matter much at all to the sun-bathing beast. Or, as de la Rosa intends to find out, the relationship could be essential for the ecosystem. If the teardrop dinners are not just casual cravings, but in fact are frequently observed phenomena it would be a sign that the top predator’s tears are a key piece of La Selva’s ecosystem and its sustainability.
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Inventors: Belbruno JJ
, Tanski SE
Devices For Detecting Airborne Contaminants, And Associated Methods
Publication date: 2015
A device for detecting an airborne contaminant includes (a) a reactive polymer film having affinity for binding with the airborne contaminant, (b) an electrically conductive polymer film in contact with the reactive polymer film and having electrical property sensitive to binding of the airborne contaminant to the reactive polymer film, and (c) two electrodes in electrical contact with the electrically conductive polymer film for measuring the electrical property to detect the binding of the airborne contaminant to the reactive polymer film. Another device for detecting an airborne contaminant includes (a) a polymer film molecularly imprinted with the airborne contaminant, and (b) color reporting molecules having color sensitive to binding of the airborne contaminant to the polymer film. A method for manufacturing a device for detecting an airborne contaminant includes depositing, using one or more inkjet print heads, a polymer film and at least two electrodes onto a substrate.
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Mercury – The Smallest Planet of Solar System
Mercury, the smallest planet, goes whizzing around the Sun at a dazzling 31 miles per second. The planet travels so fast that it makes a complete loop in only 88 days. People have known about Mercury for thousands of years. It is named for the Roman god, Mercury, the fastest of all the gods.
Mercury is the densest planet next to Earth. It has a solid core and crust. Its core is made of metal – mostly iron. Its crust is made of rock. Because Mercury is so small, it has a very weak magnetic field. Gases, like oxygen or hydrogen, blow away into outer space. Mercury doesn’t have a blanket of gases to protect it like Earth. Instead, it has a very thin atmosphere. When comets and meteors enter the Earth’s thick atmosphere, they usually burn up long before they reach Earth. When comets and meteors enter Mercury’s atmosphere, they don’t slow down. Instead, they slam into the planet, causing craters and pock marks.
Fun Facts about Mercury for Kids
- Mercury has extreme temperatures because it is so close to the Sun and because it has almost no atmosphere. The sunny portion of the planet has a temperature of 800 degrees. The other side of the planet is -300 degrees. Ouch!
- Mercury can be seen from Earth. Look for it just as the Sun rises in the morning or as the Sun is setting at night. It looks like a bright star that sits close to the Sun.
- Mercury is just a bit larger than our moon.
- Some of the craters on Mercury are very deep. Scientists believe there is frozen ice in deep craters at the poles.
- One crater is over 8 miles long.
- If you weigh 60 pounds on Earth, you’d weigh only 18 pounds on Mercury.
- Whiz: fly or flash past
- Dense: heavy, solid
- Magnetic field: force that causes gravity
- Crater: deep, round hole
Learn More All About Mercury, the Smallest Planet of Solar System
Take a peek at this Mercury video:
A video documentary all about Mercury.
Question: Does Mercury have volcanoes on it?
Answer: Mercury’s crust is too hard and thick for volcanoes to form. There are no tectonic plates that move like there are on Earth. Scientists believe Mercury might have a molten, or liquid metal, crust, but the molten liquid can’t erupt through the surface.
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Scientists Decode the Origin of Universe’s Heavy Elements in the Light from a Neutron Star Merger
Berkeley Lab scientists play key role in explaining a historic discovery
October 16, 2017
Contact: Glenn Roberts, science writer, 510-486-5582, email@example.com
Sometimes – even in matters of science – you have to be lucky.
On Aug. 17, scientists around the globe were treated to near-simultaneous observations by separate instruments: One set of Earth-based detectors measured the signature of a cataclysmic event sending ripples through the fabric of space-time, and a space-based detector measured the gamma-ray signature of a high-energy outburst emanating from the same region of the sky.
These parallel detections led astronomers and astrophysicists on an all-out hunt for more detailed measurements explaining this confluence of signals, which would ultimately be confirmed as the first measurement of the merger of two neutron stars and its explosive aftermath.
Just a week earlier, Daniel Kasen, a scientist in the Nuclear Science Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and an associate professor of physics and astronomy at UC Berkeley was attending a science conference in Seattle.
A hypothetical question was posed to attendees as to when would astronomers detect an astrophysical source that produced both a strong disruption in the space-time continuum – in the form of gravitational waves – and see an associated burst of light.
The likely target would be the violent merger of a neutron star, which is the ultradense remnant of an exploded star, with another neutron star or a black hole. Such events have been theorized to seed the universe with heavy elements like gold, platinum, and radioactive elements like uranium.
|An animation for a model of a kilonova associated with a neutron star merger (right), showing fast effects in blue and slower effects in red, and associated graph that shows how the model matches with data from the observed kilonova. (Credit: Daniel Kasen/Berkeley Lab, UC Berkeley)|
Most scientists in the room expected that, based on the planned sensitivity of future instruments, and the presumed rarity of neutron star mergers, such a historic discovery might – with some luck – be more than a decade away.
So Kasen, who had been working for years on models and simulations to help understand the likely signals from merging neutron stars, was stunned when data on a neutron star merger and its aftermath began to pour in just a week later.
“It seemed too good to be true,” said Kasen. “Not only had they detected gravitational waves, but from a neutron star merger that was so close, it was practically in our backyard. Almost everybody on Earth with a telescope started pointing at the same part of the sky.”
LIGO and VIRGO – a network of Earth-based gravitational wave detectors capable of observing some of the universe’s most violent events by detecting ever-so-slight changes in laser-measured distances caused by passing gravitational waves – had picked up an event.
A couple of seconds later, a brief burst of gamma rays were detected by an instrument aboard the Fermi Gamma-ray Space Telescope. Less than 12 hours after that, astronomers spotted the first glimpse of visible light from the event.
When Kasen saw the email alerts rolling in about the various observations, he couldn’t help but feel a sense of unease. “For years we had been studying what colliding neutron stars would look like, with nothing to go on but our theoretical imagination and computer modeling,” he said. “Now, real data was flooding in, and it was going to test everything we had predicted.”
Over the following days and weeks, an influx of observations provided data confirming that the brilliant burst behaved remarkably like the theorized merger of two neutron stars.
Computer simulations had suggested that, during such a merger, a small fraction of neutron star matter would be flung into surrounding space. Models predicted that this cloud of exotic debris would assemble into heavy elements and give off a radioactive glow over 10 million times brighter than the sun. The phenomenon is called a kilonova or macronova.
Jennifer Barnes, an Einstein postdoctoral fellow at Columbia University, who as a UC Berkeley graduate student worked with Kasen to compute some of the first detailed model predictions of kilonovae, said, “We expected from theory and simulations that kilonovae would be tinged red if heavy elements were produced, and would shine blue if they weren’t.
She added, “Understanding this relationship allowed us to more confidently interpret the emission from this event and diagnose the presence of heavy elements in the merger debris.”
Kasen, Barnes, and two other Berkeley Lab scientists were among the co-authors of several papers published today in the journals Nature, Science, and the Astrophysical Journal. The publications detailed the discovery, follow-up observations, and theoretical interpretation of this event.
Simulations related to the event were carried out at the Lab’s National Energy Research Scientific Computing Center (NERSC).
Peter Nugent, a senior staff scientist in the Computational Research Division at Berkeley Lab and an adjunct professor of astronomy at UC Berkeley, also closely followed the alerts related to the Aug. 17 observations.
At the time, he was assisting with the final preparations for the startup of the Zwicky Transient Facility (ZTF) at the Palomar Observatory in Southern California. Berkeley Lab is a member of the collaboration for ZTF, which is designed to discover supernovae and also to search for rare and exotic events such as those that occur during the aftermath of neutron star mergers.
“This event happened too early by three months,” Nugent said, as the soon-to-launch ZTF is designed to quickly follow up on LIGO/VIRGO gravitational wave measurements to look for their visible counterparts in the sky.
Nugent said that, at first, he thought that the multiple observations of the object (known as an optical transient) associated with the neutron star merger and gamma-ray burst was just a common supernova. But the object was evolving too quickly and had an incredibly blue light signature that pointed to a different type of event than the supernovae normally associated with the type of galaxy hosting this event.
Also, Nugent said, “We didn’t expect an event this close. It’s almost akin to having a supernova blow up in Andromeda,” which is about 2.5 million light years away from our Milky Way galaxy. “We hope this means there are going to be more of these events. We now know the rate is not zero.”
Nugent contributed to an analysis in one of the papers in the journal Science that concludes there may be “many more events” like the observed merger, and that neutron star mergers are likely “the main production sites” for heavy elements in the Milky Way. The observation could also provide valuable clues about how scientists might look for other neutron star mergers in optical surveys without a LIGO/VIRGO detection.
“How the heaviest elements came to be has been one of the longest standing questions of our cosmic origins,” Kasen said. “Now we have for the first time directly witnessed a cloud of freshly made precious metals right at their production site.”
The debris cloud from the merger mushroomed from about the size of a city shortly after the merger to about the size of a solar system after only one day, Kasen said. It is also likely that only a few percent of the matter in the merging neutron stars escaped the central site of the merger; the rest likely collapsed to form a black hole.
It is expected that the escaping debris will be very long-lived, diffusing across the galaxy over a billion years and enriching stars and planets with the heavy elements like those we find on Earth today.
“For me, it is the astronomical event of a lifetime,” Kasen said “It’s also an incredible moment for the field of scientific computing. Simulations succeeded in modeling what would happen in an incredibly complex phenomenon like a neutron star merger. Without the models, we all probably all would have been mystified by exactly what we were seeing in the sky.”
Future advances in computing, and new insights from the Facility for Rare Isotope Beams (FRIB) at Michigan State University on exotic reactions that produce heavy nuclei, should provide even more insight as to how the heavy elements came to be, and the extreme physics of matter and gravity that occurs in mergers.
Kasen is also the lead investigator on a DOE Exascale Computing Project that is developing high-performance astrophysical simulation codes that will run on the next generation of U.S. supercomputers. He is also a member of a DOE-supported SciDAC (Scientific Discovery through Advanced Computing) collaboration that is using computing to simulate supernovae, neutron star mergers, and related high-energy events.
“Before these observations, the signals from neutron star mergers were mainly theoretical speculation,” Kasen said. “Now, it has suddenly become a major new field of astrophysics.”
The National Energy Research Scientific Computing Center is a DOE Office of Science User Facility.
Berkeley Lab’s contributions to the simulations and observations were supported by the U.S. Department of Energy’s Office of Science.
Listen to Nugent talk about the recent discovery:
View a related UC Berkeley video:
About NERSC and Berkeley Lab
The National Energy Research Scientific Computing Center (NERSC) is a U.S. Department of Energy Office of Science User Facility that serves as the primary high-performance computing center for scientific research sponsored by the Office of Science. Located at Lawrence Berkeley National Laboratory, the NERSC Center serves more than 6,000 scientists at national laboratories and universities researching a wide range of problems in combustion, climate modeling, fusion energy, materials science, physics, chemistry, computational biology, and other disciplines. Berkeley Lab is a DOE national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California for the U.S. DOE Office of Science. »Learn more about computing sciences at Berkeley Lab. | <urn:uuid:4fb3f679-7df3-48fe-b1b8-df93debe50f8> | 3 | 2,166 | News (Org.) | Science & Tech. | 32.005632 | 95,517,873 |
Astronomers think that acidification inhibits the formation of stars and planets in the dust clouds. Now it is a case of waiting for precise measurements from the SRON-built HIFI space instrument that will be launched on the Herschel space telescope next year. Van der Tak: ‘I have already submitted my observation proposal’.
The formation of stars and planets in the universe is a delicate process. Clouds of gas and matter rotate and draw together under the influence of gravity. Pressure and temperature then rise, which eventually leads to the kindling of a new star with planets potentially orbiting it. Yet why does this happen at some locations in the universe and not at others? What are the conditions for star and planet formation? How does this process start and when does it stop? Astronomers are fumbling in the dark.
‘The quantity of charged molecules in the dust cloud appears to have an inhibitory effect’, says Floris van der Tak. ‘These ensure that the magnetic fields can exert a greater influence on the cloud, as a result of which the entire cloud becomes agitated and the star-forming process is disrupted’. Observing these charged molecules directly is difficult. The ratio of acidic water molecules to ordinary water molecules is a measure of the quantity of charged molecules.
However, it is difficult to observe water molecules from under an atmosphere that is itself predominantly made up of water molecules. ‘It is like looking for stars in the daylight.’ On Earth it can only be done from a high mountain where the air is rarefied. Such a spot is the 4092 metre-high top of the Hawaiian volcano Mauna Kea, where the James Clerk Maxwell Telescope is located. Van der Tak focused this telescope on the Milky Way galaxies M82 en Arp 220, where he discovered areas rich in acidic water molecules.
‘Amazingly, what causes these acid water molecules to be present in both Milky Way galaxies is completely different’, says Van der Tak. ‘In Arp 220 they develop under the influence of X-rays in the vicinity of the central supermassive black hole. In M82, the cause is the ultraviolet radiation emitted by hot young stars in the star-forming area. Therefore, in these particular galaxies the process of star formation inhibits itself, due to more and more charged molecules being created.’
The astronomer will be able to deploy even heavier equipment for his research in the not too distant future. Next year, the European Space Agency (ESA) is launching the Herschel space telescope with the SRON-constructed Heterodyne Instrument for the Far Infrared (HIFI) attached to it. And in the 5000 metre-high and completely arid Atacama Desert in Chile, a start has been made on the construction of ALMA, 66 smart telescopes that can together produce detailed maps of the Milky Way galaxies. SRON is one of the partners involved in developing the detectors for these telescopes.
The results of the research of Floris van der Tak and his collegues Susanne Aalto of the Chamlers University of Technology, Onsala Sweden and Rowen Meijerink of the University of California are published this week in the scientific journal Astronomy & Astrophysics.
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C# provides function types to fit a variety of scenarios, called delegates, events, and lambda functions. In this course, Joe Marini explores these key elements, starting with delegates, which allow developers to easily separate functional pieces of a program. Joe shows how to create both anonymous and composable delegates, using a shipping costs calculator as a practical example. Next, he covers using events to broadcast and listen to messages both inside and outside a program, switching functionality on and off on demand. Finally, the course explores lambda functions: concise ways to declare small and focused or one-off functions, which keep your program code tight and efficient.
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Layers of the Atmosphere
Types of Clouds
The mesosphere is the the third layers out of the four, it stretches from 50km to 80km. "meso" means middle, which this layer is.
From NASA Marshall Space Flight Center on flickr
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When two uncharged objects are placed in a vacuum with no external fields, we wouldn’t expect them to have any force between them other than gravity. Quantum electrodynamics says otherwise. It shows that tiny quantum oscillations in the vacuum will give rise to an attraction called the Casimir force.
Scientists at the RIKEN Advanced Science Institute in Wako, and co-workers at the National Academy of Sciences of Ukraine (NASU), have shown for the first time that the Casimir force has a complex dependence on temperature1. They propose a related experiment that could clarify the theory around this important interaction, which has widespread applications in physics and astronomy, and could eventually be exploited in nano-sized electrical and mechanical systems.
“The Casimir force is one of the most interesting macroscopic effects of vacuum oscillations in a quantum electromagnetic field,” says Franco Nori from RIKEN and the University of Michigan in the USA. “It arises because the presence of objects, especially conducting metals, alters the quantum fluctuations in the vacuum.”
The Casimir force was first predicted in 1948, but has only recently been measured in the laboratory because experiments are difficult—the force is negligible except when the distance between objects is very small. More experiments are needed to understand how the force depends on temperature, an important practical consideration.
“As the temperature increases, metal objects in a vacuum experience two competing effects,” explains Sergey Savel’ev from RIKEN and Loughborough University in the UK. “They lose some of their electrical conductivity, which tends to cause a decrease in the Casimir force. At the same time they are bombarded with more radiation pressure from the thermal heat waves, and this increases the Casimir force.”
Nori and co-workers derived the temperature dependence for Casimir attractions between a thin film and a thick flat plate, and between a thin film and a large metal sphere. They found that the Casimir force will tend to decrease near room temperature, but can increase again at higher temperatures as the thermal radiation effects take over.
RIKEN’s Valery Yampol’skii, who also works at NASU, says that “if these temperature effects were observed in an experiment, they would resolve some fundamental questions about electron relaxation in a vacuum”. Such an experiment would be near-impossible with pieces of bulk metal, but could be done using extremely thin metal films.
1. Yampol’skii, V.A., Savel’ev, S., Mayselis, Z.A., Apostolov, S.S. & Nori, F. Anomalous temperature dependence of the Casimir force for thin metal films. Physical Review Letters 101, 096803 (2008).
The corresponding author for this highlight is based at the RIKEN Digital Materials Team
Further reports about: > Casimir force > NASU > Quantum electrodynamics > RIKEN > bulk metal > dependence on temperature > electrical conductivity > gravity > nano-sized electrical and mechanical systems > quantum electromagnetic field > quantum fluctuations > radiation pressure > thermal heat waves > tiny quantum oscillations > vacuum
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(əkì´´nōdûr'mətə) [Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea stars (starfish), or reduced to minute spicules in the skin, as in sea cucumbers. The skin usually has warty projections or spines, or both. Echinoderms display pentamerous radial symmetry, that is, the body can be divided into five more or less similar portions around a central axis. Unlike other radially symmetrical animals, they develop from a bilaterally symmetrical larva and retain some degree of bilateral symmetry as adults. There is no head; the surface containing the mouth (the underside, in sea stars and most others) is called the oral surface, and the opposite side, which usually bears the anus, the aboral surface. There are five living classes of echinoderms.
The radially symmetrical body cavity contains a system of water-filled canals unique to echinoderms. Called the water-vascular, or ambulacral, system, it connects with the tube feet, or podia, which are extensions of the body wall that generally protrude through holes in the skeleton. The areas with such holes are called ambulacra. The tube feet often have suction cups on their tips and are used for locomotion in most echinoderms; they also function in feeding, respiration, and sensory reception.
The water-vascular system consists of a circular passageway, the ring canal, that surrounds the digestive tract and five radial canals that radiate from the ring canal like spokes of a wheel. Each radial canal underlies an ambulacral area. The ring canal is usually connected to a porous plate in the body wall, the madreporite, by a lime-walled tube called the stone canal. The position of the madreporite varies in the different groups. Seawater enters the system through the madreporite, which is regulated by the animal. Short lateral canals equipped with valves lead from the radial canals into the tube feet. Generally a muscular, water-filled bulb, the ampulla, is connected to each tube foot. When the valve closes and the ampulla contracts, water is squeezed into the tube foot, causing the foot to extend. The foot is retracted by the contraction of the attached muscles, thereby forcing the water back into the ampulla. Sea stars, sea cucumbers, and sea urchins move by alternately extending and retracting groups of tube feet, gripping with the suction cups and pulling themselves along. Because the tube feet are very thin-walled, their surface is suitable for the diffusion of oxygen into the body cavity and the diffusion outward of carbon dioxide and wastes.
The tube feet perform at least part of the respiratory function in most echinoderms; however, many groups have developed auxiliary respiratory structures. Echinoderms have no special excretory organs. Circulation occurs in an open system of channels and sinuses and in the body cavity, which is lined with flagellated cells that create an internal current. The cavity contains large phagocytic cells (amoebocytes) that function in the transport of food and the storage of insoluble wastes. There is a simple nervous system sensitive to temperature, light, and vibrations, with the various body projections serving as sensory receptors. Echinoderms have extensive powers of regeneration of lost or injured parts.
Most species reproduce sexually, and species have separate sexes. Fertilization is external; the gametes are simply shed into the water at spawning time. The floating embryo develops into a ciliated, free-swimming, bilaterally symmetrical larva, which undergoes metamorphosis into the radially symmetrical adult.
Sea stars, or starfish, vary in shape from nearly circular, to pentagonal, to the familiar starlike and flowerlike forms with five or more tapering arms. The arms are extensions of the body; each contains an extension of the body cavity, a radial canal, and body organs. Each arm has an ambulacral groove on the undersurface; in the furrow of the groove is the ambulacral area, or ambulacrum, with holes for the tube feet. The margins of the groove have spines that can close over the ambulacrum. The tip of each arm bears a tube foot that functions as a sensory receptor for chemical and vibratory stimuli, and some have a red pigment spot that serves as a simple eye. The outer surface consists of a latticework of lime ossicles, or plates, between which project thin-walled fingerlike extensions called papulae. The papulae and the tube feet are the principal sites of respiratory exchange. In some groups of sea stars there are also body wall projections called pedicellaria, equipped with tiny pinchers that are operated by muscles and are used to clean the body surface and capture very small prey. Sea stars crawl about on rocks or muddy bottoms, feeding on a variety of living and dead animals. Many feed largely on bivalve mollusks and are notorious as destroyers of commercial oyster beds. There are two or more gonads in each arm; at spawning time these may nearly fill the arms. The swimming larva settles and goes through a sessile (attached) stage while changing to the adult form.
The brittlestars, or serpent stars, are so called for their long, slender, fragile arms, which are set off sharply from the circular, pentagonal, or slightly star-shaped body disk. The arms of brittlestars are flexible and appear jointed because of the conspicuous plates of the outer surface. They bear a row of spines along each edge. In one group, the basket stars, they are repeatedly branched, forming a large mass of tentaclelike limbs. Each arm contains a radial canal (or one of its branches), but it does not contain body organs. Brittlestars feed on detritus and small organisms. The mouth leads to a large saclike stomach that fills most of the body cavity. There is no intestine or anus, and solid waste is extruded through the mouth. The stomach is folded into ten pouches, between which lie ten respiratory sacs that open by slits onto the oral surface. The cells lining the sacs have flagellae, which create a current of water moving in and out. Respiratory exchange occurs chiefly through the thin lining of the sacs.
Echinoids—sea urchins, heart urchins, and sand dollars—are echinoderms without arms and with a spiny shell, or test, formed of tightly fused skeletal plates. The sea urchins (regular echinoids) are hemispherical in shape, round on top and flat on the lower surface. They have very long, prominent spines and are often brightly colored. The test of a sea urchin is divided into ten parts from pole to pole, like the sections of an orange. Five of these are ambulacra, with openings for tube feet; these alternate with wider sections, called interambulacra, that lack tube feet. However, spines and pedicellaria are found over the entire surface of the test. Urchins move by pushing against the substratum with the spines and extending the tube feet in the direction of movement. If turned over they can right themselves by means of the tube feet on the aboral surface. The mouth, located in the center of the undersurface, is surrounded by a thickened region bearing five pairs of short, heavy tube feet and sometimes five pairs of bushy gills. Within the mouth is an elaborate five-sided jaw structure called Aristotle's lantern that can be partially extruded from the mouth. It is able to grind up calcareous exoskeletons of plants and animals. The anus is at the center of the aboral surface and is surrounded by a thin-walled area without skeletal plates.
Sand dollars and heart urchins (irregular echinoids) have a dense covering of short spines, and locomotion is exclusively by movement of the spines. There are two groups of podia-bearing ambulacra, one arranged in a petallike pattern on the upper surface and the other forming a similar pattern on the lower surface. The upper tube feet function as respiratory organs (there are no gills around the mouth), and the lower ones are specialized for gathering food particles. Sand dollars are extremely flattened and oval in outline; the anus is on the oral surface. Heart urchins are somewhat flattened and are heart-shaped; a deep ambulacral groove running from top to bottom creates a secondary bilateral symmetry. The anus is on the aboral surface, opposite the groove.
The sea cucumbers are long-bodied echinoderms with the mouth at or near one end and the anus at or near the other. Because of their elongation along the oral-aboral plane, they lie on their sides rather than on the oral surface. In nearly all sea cucumbers the skeleton is reduced to microscopic ossicles imbedded in the leathery skin. Sea cucumbers have no arms, but tube feet around the mouth have been modified to form a circle of 10 to 30 tentacles of varying lengths and shapes that function in gathering food particles from the ocean bottom. The gut of the sea cucumber terminates in a chamber called the cloaca that opens into the anus. Two unique structures called respiratory trees, found in most sea cucumbers, also terminate in the cloaca. These are systems of highly branched tubes, one on either side of the body. The animal pumps water into the respiratory trees by contracting the cloaca, and oxygen diffuses through from the walls of the trees into the fluid of the body cavity. The madreporite in most sea cucumbers opens into the body cavity rather than to the outside and receives its fluid from the cavity. In a few sea cucumber species there is a large mass of tubules at the base of the respiratory tree that can be shot out of the anus if the animal is irritated. The extruded tubules, which may engulf and incapacitate an intruder, break off; they are then regenerated by the sea cucumber. In other species the respiratory trees, gonads, and part of the digestive tract are shot out through the anus; this evisceration is followed by regeneration of the lost organs.
The sea lilies and feather stars are members of an ancient group of stalked, sessile, detritus-feeding echinoderms. Most of the sea lilies remain stalked throughout life; their movements include bending the stalk and the arms and crawling. Feather stars break off the stalk and become free-living as adults. Crinoids, whether free or stalked, always have the oral side upward, and the ring of arms about the mouth gives them a flowerlike appearance. They have at least 10 arms, but some sea lilies have up to 40 and some feather stars up to 200 arms. The stalk and the arms have a jointed appearance, and each arm has a row of projections, the pinnules, on either side, giving a feathery appearance. A ciliated ambulacral groove runs along each arm and branches into the pinnules; the groove contains feathery, tube feet arranged in triads. These react to the presence of minute food particles in the water by bending inward, sweeping the particles into the groove, where they are trapped in mucus and swept by the cilia toward the mouth. Gametes develop in some of the pinnules, which rupture at spawning time. The free-swimming larva eventually settles and develops a stalk and a crown.
The sea daisies, which were discovered in 1986, have disk-shaped flat bodies and are less than 0.39 in. (1 cm) in diameter. The two known species were located on wood found in deep waters off the coasts of New Zealand and the Bahamas. They have a water-vascular system, with tube feet on the body surface around the edge of the disk. They have no obvious arms or mouth, and appear to absorb nutrients through the membrane surrounded their bodies.
Echinoderms are found in seas and oceans all over the world. They include starfish, sea urchins, brittlestars, sea cucumbers, and sea lilies and...
This phylum contains approximately 6000 living species of exclusively marine animals. The group has an extensive evolutionary history extending...
Any of various marine invertebrates (phylum Echinodermata) characterized by a hard spiny covering, a calcite skeleton, and five-rayed radial body s | <urn:uuid:8240dd92-ec9c-4f4a-b7e9-da570e17a65f> | 3.703125 | 2,686 | Knowledge Article | Science & Tech. | 38.975449 | 95,517,928 |
A Quicktime Movie of Winter/Spring Birds in SW Ohio. CLICK on the image above! From my SW Ohio Bird Photo Collection
3.Sources of blooms
a. Dinoflagellates (Karenia brevis)
a.To marine organisms
5.Impact on Southwest Florida
b.When are toxins released
c.What causes final “die off” of bloom
Since the first recorded Florida red tide outbreak in 1844, this very dangerous and harmful algae bloom has been studied by scientists. Amazingly, there is still much to learn about the dynamics of this devastating phenomenon. Over the last century red tide blooms have affected almost every county along Florida’s Gulf Coast along with the Florida Keys and some coastal counties along the Atlantic. With blooms ranging from several months to sometimes over a year, scientists are working to develop a complete understanding of the physical, chemical and biological parameters that lead to red tide's formation and persistence. It has shown to be a very versatile algae, making it able to infest both saltwater as well as freshwater rivers and estuaries. This paper will focus on the causes, effects, and management issues the Florida red tide brings to the affected areas, along with the remaining questions scientists still have regarding the harmful algae bloom.
Burkholder JM, Noga EJ, Hobbs CH, Glasgow HB. New “Phantom” Dinoflagellate is the Causative Agent of Major Fish Estuarine Fish Kills. Nature, 1992. Vol. 358: 407-10.
Curriero, F.C. The Association Between Extreme Precipitation and Waterborne Disease Outbreaks in the United States. American Journal of Public Health, 2001. Vol. 91: 1194-1199
Fish and Wildlife Research Institute. Florida Fish and Wildlife Conservation Commission. 2006. http://www.floridamarine.org/.
Morris, J. Glenn. Harmful Algal Blooms: An Emerging Public Health Problem with Possible Links to Human Stress on the Environment. Annu. Rev. Energy Environment, 1999. Vol. 24: 367-90.
Start: Solutions to Avoid Red Tide, Inc. 2004-2006. http://www.start1.com/redtide/default.aspx.
Steidinger, K., et al. Harmful Algal blooms in Florida. HAB Task Force Technical Advisory Group, 1999.
Tomerlin, A., Adams, C. The Economics of Harmful Algal Blooms (HABs). Florida Sea Grant Program, 1999. Vol. 98.
Twilley, Robert R., et al. Confronting Climate change in the Gulf Coast Region: Prospects for Sustaining Our Ecological Heritage. Union of Concerned Scientists & Ecological Society of America, 2001.
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RadarScope: What's Roosting Near the Radar?
by David Moran, on Dec 11, 2017 1:08:15 PM
During the morning hours right before sunrise, expanding rings can sometimes be seen on radar images. These are called Roosting Rings and are a result of birds in flight near the radar. Let's take a look at what they look like on RadarScope.
As birds begin to migrate to the south, certain species tend to gather at known roosting sites. These areas are often detected by radar as the birds take flight in the morning. Their flight is indicated by rings on various radar products that eventually disappear once the birds fly above or below the radar beam. Below is an example of a roosting ring. High reflectivity values may indicate areas where birds are tightly clustered together.
Roosting Ring Reflectivity
These rings are only seen during their morning flight and not their evening return due to atmospheric conditions that typically occur in the early hours of the day. On a calm night, a temperature inversion (in which temperature increases with height) develops near the surface. It causes the radar beam to refract downward, enabling echoes at lower levels to be detected. In the evening, these inversions typically are not present or are very weak, and as a result, these rings are not observed.
Other radar products can also be used to observe these roosting rings. In the example below, Super Resolution Velocity is shown. The left half of the circle (red shades) is moving westward away from the radar whereas the right half is moving eastward toward the radar (green shades). For perspective, the radar is located just to the east of the ring.
Roosting Ring Velocity
Dual polarization data can also tell us information about the ring. One of the dual-polarimetric variables that we can use is known as Differential Reflectivity. It is related to the logarithm of the ratio of the power received from the horizontally polarized pulse to the power received from the vertically polarized pulse. If the Differential Reflectivity is positive then the object observed by the radar is horizontally oriented; if the Differential Reflectivity is negative, it is vertically oriented. With the ring discussed here, values are a mixture of both positive and negative, indicating various orientations.
Roosting Ring Differential Reflectivity
These images of a roosting ring are just one example of a nonmeteorological echo that can be observed by radar. Analyzing values of these products within this phenomena can provide even more insight into what the radar is seeing, including the orientation of the birds as well as the variety of sizes and shapes of the birds within these rings. Biologists have even been known to use the same radar we use to study weather echoes to study bird migration. | <urn:uuid:a28701f4-c9bd-462b-899f-b34c62edf45b> | 4.09375 | 575 | News (Org.) | Science & Tech. | 38.058526 | 95,517,957 |
Anderson said increased fuel loads in the forest are a result of fire suppression, a practice that, when combined with a projection of increasingly drier climates ahead, spells a recipe for increasing disaster for forested ecosystems.
While grazing and fire suppression have kept incidents of wildfires unusually low for most of the last century, the amounts of combustible biomass, temperatures and drought are all rising. The result, Anderson said, is a “fire deficit” in which current conditions and past fire suppression practices have pushed fire regimes out of equilibrium with climate.
“In the near future, since our forests and their fuel loads are not in balance with their natural fire regimens, we can expect to see additional huge fires such as last year’s Wallow Fire that burned 540,000 acres in Arizona and Las Conchas Fire that burned 156,000 acres in New Mexico,” he said.
Anderson and a team of researchers combined resources to examine existing records on charcoal deposits in lakebed sediments, which established a baseline of fire activity throughout the region. The team published its findings last week in the journal of The Proceedings of the National Academy of Sciences. The full research study is available online.
“We were able to link fire to changing climate in the West for much of the last 3,000 years,” Anderson said. “With the increase of Euro-Americans in the West, the patterns began to change, first with large fires associated with indiscriminant land clearance, railroad construction and so on, then later with fire suppression.”
Wildfires have been debated for years as either a destructive force of nature that should be eradicated or natural disturbance that keep ecosystems healthy. National policy over the last century had been to respond rapidly to suppress all wildfires, but with increasing occurrence of catastrophic wildfires in the region such practices have come into question. In recent years local forest managers have been given more latitude to evaluate which fires to suppress while ensuring public safety.
Anderson’s research could lead the way to reshaping policy on wildfire response and natural resource management, but he cautioned such a change might be too little too late.
“The fire deficit situation is unsustainable, now and long into the future,” he said. “If it is not addressed quickly—and many of us believe it is too late already—it will likely lead to widespread and long-enduring changes in forest types across the West.”CONTACT:
Cynthia Brown | Newswise Science News
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
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May explain life extension via calorie restriction
Researchers at Harvard Medical School (HMS) have discovered that a gene in yeast is a key regulator of lifespan. The gene, PNC1, is the first that has been shown to respond specifically to environmental factors known to affect lifespan in many organisms. A team led by David Sinclair, assistant professor of pathology at HMS, found that PNC1 is required for the lifespan extension that yeast experience under calorie restriction. A yeast strain with five copies of PNC1 lives 70 percent longer than the wild type strain, the longest lifespan extension yet reported in that organism. Their findings are reported in the May 8 Nature.
The PNC1 protein regulates nicotinamide, a form of vitamin B3. Sinclairs group previously found that nicotinamide acts as an inhibitor of Sir2, the founding member of a family of proteins that control cell survival and lifespan. Sir2 extends lifespan in yeast by keeping ribosomal DNA stable. PNC1 converts nicotinamide into nicotinic acid, a molecule that does not affect lifespan. In doing so, it keeps nicotinamide from inhibiting Sir2, allowing the yeast to live longer.
John Lacey | EurekAlert!
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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“The jury is still out on whether nanotechnology will prove to be an environmental protector or, in fact, a polluter,” says Aleksandra Kordecka, Chemicals Campaigner at Friends of the Earth Europe. Her comment reflects the current debate that has polarised the scientific community worldwide.
Leading scientists and academics will come together to present both sides of the issue at a panel discussion to take place on 12 September at 10 a.m. at the University of York. Sponsored by Elsevier, the event is part of the renowned annual event of the British Association for the Advancement of Science – the BA Festival of Science, 9-15 September.
Panelists, including Professor Tony Ryan, ICI Professor of Physical Chemistry and Director of the Polymer Centre at the University of Sheffield; Dr. Gareth Wakefield, nanotechnology consultant; Melanie Smallman, Director of nanotechnology activist group Small Talk, and Aleksandra Kordecka, Chemicals Campaigner at Friends of the Earth Europe, will debate the latest developments in nanotechnology and their potential for creating environmentally friendly products and processes.
"Not many new technologies come along with the claim that they can actually benefit the environment,” said Jonathan Wood, Deputy Editor of Elsevier’s Nano Today. ”Can nanotechnologies really lead to a cleaner, more efficient and less wasteful future? This panel discussion, and the varied opinions of the expert panellists, is sure to provide a lively and timely debate on this controversial subject."
Lisa Hendry | alfa
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A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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NASA Earth Observation Programs and Small Satellites
NASA’s strategic goal in Earth science is motivated by the fundamental question: “How is the Earth changing and what are the consequences for life on Earth?” NASA’s mission in Earth science as mandated by the U.S. Space Act is to “ ldots conduct aeronautical and space activities so as to contribute materially to ldots the expansion of human knowledge of the Earth and of phenomena in the atmosphere and space”. Therefore, NASA’s role is unique and highly complements those of other U.S. Federal agencies by continually advancing Earth system science from space, creating new remote sensing capabilities, and enhancing the operational capabilities of other agencies and collaborating with them to advance Earth science goals. NASA’s Earth Science Division (ESD) currently has a system of spacecraft collecting observations of the Earth system and in the months and years ahead will deploy new satellites and constellations with advanced measurement capabilities. Small satellites (~500 kg or less) have been crucial contributors to achieving NASA’s Earth science measurements and will continue to be so in the future. The U.S. National Research Council (NRC) is just now completing its first decadal survey for Earth science and applications from space. This survey will be used to set priorities for future missions to 2017 and beyond. Current status of ESD flight programs, preparations for the NRC decadal survey, and the role of small satellites will be discussed.
KeywordsTotal Solar Irradiance Small Satellite Future Mission Earth Science Division Flight Program
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Carbon Sequestration in loblolly pine plantations: Methods, limitations, and research needs for estimating storage poolsThis article is part of a larger document. View the larger document here.
Globally, the species most widely used for plantation forestry is loblolly pine (Pinus taeda L.). Because loblolly pine plantations are so extensive and grow so rapidly, they provide a great potential for sequestering atmospheric carbon (C). Because loblolly pine plantations are relatively simple ecosystems and because such a great volume of knowledge has been gained about the species, the quantification of C dynamics of loblolly pine stands will be relatively easy. Here, we evaluate the state of science that relates to quantifying standing C pools in managed loblolly pine stands. We consider the accuracy and precision with which aboveground and belowground pools can be estimated, the portability of these tools across different stand types, and the intensity and efficacy of the measurement techniques. We emphasize the need to develop standard and relatively inexpensive measurement protocols.
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- Open Access
Sheath capacitance observed by impedance probes onboard sounding rockets: Its application to ionospheric plasma diagnostics
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. 2010
- Received: 18 August 2009
- Accepted: 28 January 2010
- Published: 31 August 2010
Ion sheath which is formed around an electrode significantly affects the impedance of the probe immersed in a plasma. The sheath capacitances obtained from impedance probe measurements were examined for application to plasma diagnoses. We compared analytical calculations of the sheath capacitance with measurements from impedance probes onboard ionospheric sounding rockets. The S-520-23 sounding rocket experiment, which was carried out in mid-latitude, demonstrated that the observed sheath capacitances agreed well with those of the calculations. We concluded that the sheath capacitance measurements allow for estimation of the electron temperature and the electron density of a Maxwellian plasma. On the other hand, the sheath capacitances obtained from the S-310-35 rocket experiment in the auroral ionosphere showed lower values than expected. Auroral particles precipitations should modify the probe potential.
In-situ plasma diagnoses are essential for clarifying various aspects of phenomena found in space and laboratory plasmas. A radio frequency (RF) probe technique is a powerful tool for measuring the plasma parameters (e.g., Jackson and Kane, 1959). Over the past several decades, numerous investigations have been conducted on the impedance of an electrode immersed in a plasma in order to achieve accurate plasma diagnoses.
The observed antenna impedance reflects various physical properties of the ambient plasma as well as the electron density. Evaluations of the observed impedance are actively discussed subjects these days. Tsutsui et al. (1997) examined antenna impedance measured by the Geotail spacecraft in the Earth’s magnetosphere, where the electron densities are too low to observe the resonances. Béghin et al. (2005) computed the self-impedance and mutual-impedance to model the electric antennas onboard the Cluster satellites. Impedance measurements in a laboratory plasma showed resonances of a long dipole antenna (Blackwell et al., 2007). Miyake et al. (2008) developed an analysis tool of antenna impedance via Particle-In-Cell (PIC) simulation. A Plasma-Fluid Finite-Difference Time Domain (PF-FDTD) simulation was applied to estimate the collision frequency in the ionosphere (Ward et al., 2005; Spencer et al., 2008). In addition, unique characteristics of the probe impedance in a thermal magnetized plasma were found by laboratory experiments (Suzuki et al., 2009).
In actual situations, for evaluating the probe impedance it is essential to consider the effect of an ion sheath surrounding the probe. This paper deals with the capacitance of the ion sheath measured by impedance probes. The ion sheath is formed around the probe due to the difference between the thermal velocity of electrons and ions. The sheath capacitance significantly affects the probe impedance at lower frequencies in comparison to that around the UHR frequency. Derivation of the electron temperature from the sheath capacitance was originally proposed by Oya and Aso (1969). Watanabe (2000) reported that sheath thickness was changed with the auroral energetic electron flux. Sheath capacitance has also been studied in terms of its capacitively coupled plasma (e.g., Chen, 2006).
The purpose of this study is to evaluate the sheath capacitance obtained from impedance probe measurements in order to utilize it for ionospheric plasma diagnostics. We applied an analytical formula of the sheath capacitance with a step sheath model. Although our calculation method of the sheath capacitance is fundamentally the same as that of the report by Oya and Aso (1969), we have made some modifications on the evaluation of the probe potential. We examined the sheath capacitance observed from impedance probes onboard the two sounding rockets, S-520-23 and S-310-35. First, we show analysis of the sheath capacitance in a quiet state of the ionospheric plasma to confirm the validity of the analytical model. We also provide observations of the sheath capacitance under disturbed conditions.
2. Sheath Capacitance in Impedance Probe Measurements
3. Outline of the Sounding Rocket Experiments and Instruments
3.1 Sounding rocket S-520-23 experiment
Wind measurement for Ionized and Neutral atmospheric Dynamics study (WIND) campaign was carried out to investigate the momentum transfer between the ionospheric plasma and the neutral atmosphere. The S-520-23 sounding rocket was launched from the Uchinoura Space Center (31.15°N, 131.04°E in geodetic coordinates), Japan on 2nd September 2007, at 19:20 LT (LT = UT + 9 h). The pay-load reached an apex altitude of 279 km at 268 sec after the launch. The Lithium Ejection System (LES) installed on the S-520-23 rocket was designed to release Li gas three times in the descending phase. The resonantly scattered light of the Li clouds was successfully observed from several ground sites to measure thermospheric neutral wind accurately.
All instruments performed successfully during the rocket flight. Many interesting results were achieved by the neutral wind, the electron density, the electron temperature, the plasma wave, and the electric field measurements. The present paper focuses on the sheath capacitance measured by the impedance probe instrument.
3.2 Sounding rocket S-310-35 experiment
The sounding rocket S-310-35 experiment was performed as a part of the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, whose objectives and results were described in detail in Abe et al. (2006a) and references therein. The sounding rocket was launched from the Andøya rocket range (69.29°N, 16.01°E in geodetic coordinates) in Norway on 13th December 2004, at 01:33 LT (LT = UT + 1 h).
While an auroral breakup was occurring simultaneously with the launch, the sounding rocket flew through the auroral active region. There were two auroral active arcs which crossed the rocket trajectory. The second arc around 124–131 km altitude was within the range of sheath analysis. We should also mention that observations by the N2 temperature instrument (NTV), which emitted the artificial electron beam (Kurihara et al., 2006), onboard the rocket affected the electron densities and the probe potentials below about 115 km altitude in the ascent (see Wakabayashi and Ono, 2006).
3.3 Impedance probe onboard the sounding rockets
While other impedance measurement system found that for sufficiently dense plasma, the parallel circuit resonance appeared at less than the UHR frequency due to the stray capacitance (Kiraga, 2003), the NEI systems from the rocket flights S-520-23 and S-310-35 have not observed the parallel circuit resonance. Pre-flight environmental tests performed in the space plasma simulation chamber at ISAS/JAXA also ensured the reproducibility of the results with well defined, sharp absolute minimum which can be assigned to the upper hybrid frequency. Data pertinent to space ambient plasma show up the same signature of the upper hybrid frequency. The NEI instruments onboard the S-520-23 and S-310-35 rockets therefore realized the accurate measurements of the electron density without the effect of the stray capacitance.
The NEI systems of S-310-35 and S-520-23 are designed to measure the equivalent probe capacitance over the frequency ranges of 300 kHz–10.3 MHz and 300 kHz–12.0 MHz, respectively. The frequency resolution of the impedance probe onboard S-310-35 was 10.0 kHz from (0.3–4.3) MHz and 20 kHz from (4.3–10.3) MHz. In the case of S-520-23, the frequency resolution was 9.4 kHz from (0.3–2.0) MHz, 20.0 kHz from (2.0–4.0) MHz, 50.0 kHz from (4.0–8.0) MHz, and 100.0 kHz from (8.0–12.0) MHz. The time resolution of the impedance probes was about 500 msec.
The observed frequency variations of the equivalent probe capacitance provide the sheath capacitances and the UHR frequencies. In the following analysis, we identified the equivalent probe capacitance measured at around the 300 kHz, which was sufficiently lower than the observed SHR frequencies, as the sheath capacitance. Electron densities along the rocket trajectory were calculated from the observed UHR frequencies and International Geomagnetic Reference Field (IGRF) model. We also used the electron temperature data measured by the fast Langmuir probes onboard the rockets to obtain the Debye length. The Langmuir probe data were running averaged to reduce the effects of the rocket wake.
4. Observations of the Sheath Capacitance
4.1 Observations during the ascent of the S-520-23 sounding rocket
The sensor of the impedance probe was extended at 56.5 sec after the rocket launch, and measurements were successfully operated above 93.1 km. During the ascending phase of the S-520-23 sounding rocket, measurements were performed under quiet plasma conditions. Although the impedance probe was exposed to the sun during the observations, the effects of photoelectrons on the probe potential are negligible in the ionosphere.
4.2 Observations during the descent of the S-520-23 sounding rocket
In the descent of the S-520-23 sounding rocket, LES released Li gas. As the Li releases were strongly disturbing the equivalent probe capacitance, it became difficult to deduce the electron densities by detecting the UHR frequencies after the each Li release. On the other hand, the equivalent probe capacitances measured at lower frequency than SHR frequency were not so fluctuated as capacitance curves around the UHR frequency even after the Li releases.
The most likely interpretation is that Li release caused increases of the plasma density. The observed sheath capacitance variation corresponded to the increase of the electron density of about 1–2 orders of magnitude. The effects of the chemical release on the ionosphere are intriguing (e.g., Szuszczewicz et al., 1996). Uemoto et al. (2010) includes detailed observations and discussion of the electron density after the Li releases.
Here, we should emphasize the practicality of the plasma diagnosis from the sheath capacitance. In rocket observations, instruments sometimes fail to measure plasma parameters due to artificial interferences. Analysis of the sheath capacitance in addition to the UHR frequency will contribute to improvement of the success rate of plasma measurements.
4.3 Observations in the auroral ionosphere
5.1 Validation of the calculation method
We also found a slight difference of the sheath capacitance in the plasma frequency range of more than 4.5 MHz, even though fpe> fce was satisfied (see Fig. 7(b)). The difference appeared periodically around the apex of the rocket flight. The periodic variation was caused by the rocket spin. The effect of rocket wake became significant near the apex and descending phase due to the rocket attitude. Since the electron temperature data were running averaged, the calculated sheath capacitances do not reflect the electron temperatures in the wake. There are some physical issues regarding how to evaluate the temperature in the wake. It is beyond the scope of this article to examine the sheath capacitance measured in the wake region.
5.2 Effect of the auroral particles precipitation
As shown in Fig. 6, the sheath capacitances measured by the S-310-35 rocket were significantly lower than that of the calculations. Note that the plasma frequencies were higher than the cyclotron frequencies except for the altitudes below 100 km, due to the ionization by auroral particles precipitation (Wakabayashi and Ono, 2006). This indicates that the difference between the observations and calculations was not derived from the condition fpe< fce as discussed in Section 5.1.
We examined the sheath capacitance measured by using impedance probe techniques. The sheath capacitance was analytically calculated from the Debye length. Such calculations are a simpler method in comparison with the PIC simulations (Miyake et al., 2008), and as a result, our method does not then require enormous computer facility.
We have compared the sheath capacitances observed by the impedance probes onboard the sounding rockets with the calculated sheath capacitances. When a condition of fpe> fce was satisfied, the equivalent probe capacitance observed at a sufficiently lower frequency than the SHR frequency showed a constant value which equaled to the sheath capacitance. The observed sheath capacitances agreed well with the calculations. This indicates that the calculation methodology of the sheath capacitance described in Section 2 is valid; and the Debye length can be estimated from the observed sheath capacitance. The advantages of this technique are summarized as follows: (a) the sheath capacitance in addition to the UHR frequency provides plasma parameters, (b) the electron density, the electron temperature and the probe potential measured via other instruments can be cross-checked with analysis of the sheath capacitance, and (c) the analysis method is simple. Since the detection of the UHR frequencies sometimes becomes hard due to plasma disturbances (e.g., effect of Li release and electron beam emission) in sounding rocket experiments, plasma diagnosis technique from the sheath capacitance is valuable. In future experiments, we propose to design the impedance probe to measure the sheath capacitance with high time resolution. This improvement allows the impedance probe to realize both high-accurate measurements of the electron density from the UHR frequency and high-resolution plasma diagnostics from the sheath capacitance.
In the case of fpe < fce, the plasma resonance clearly appeared. As a result, it became difficult to separate the sheath capacitance from the observed the equivalent probe capacitance. For accurate plasma diagnostics from the sheath capacitance obtained by the impedance probe, it is necessary that the plasma frequency is larger than the cyclotron frequency.
Observations in the auroral ionosphere indicated that the probe potential was shifted from the analytical solution of the floating potential due to the non-Maxwellian velocity distribution. Strong precipitation of energetic electrons in the auroral arc should have caused the lower probe potential. Quantitative discussion of the response of the probe potential to the total flux of precipitating auroral particles remains a future issue to examine.
The sounding rocket experiments were conducted by the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA) as international projects. We thank all members of the rocket experiments. Pre-flight operation tests of the impedance probes were supported by the Space Plasma Laboratory, ISAS/JAXA. The impedance probes were manufactured by System Keisoku Co., Ltd. This work is supported by the Global COE Program “Global Education and Research Center for Earth and Planetary Dynamics” at Tohoku University.
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3D model (JSmol)
|Molar mass||125.13 g·mol−1|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
5-Methylcytosine is a methylated form of the DNA base cytosine that may be involved in the regulation of gene transcription. When cytosine is methylated, the DNA maintains the same sequence, but the expression of methylated genes can be altered (the study of this is part of the field of epigenetics). 5-Methylcytosine is incorporated in the nucleoside 5-methylcytidine.
In 5-methylcytosine, a methyl group is attached to the 5th atom in the 6-atom ring (counting counterclockwise from the NH nitrogen at the six o'clock position, not the 2 o'clock). This methyl group distinguishes 5-methylcytosine from cytosine.
While trying to isolate the bacterial toxin responsible for tuberculosis, W.G. Ruppel isolated a novel nucleic acid named tuberculinic acid in 1898 from Tubercle bacillus. The nucleic acid was found to be unusual, in that it contained in addition to thymine, guanine and cytosine, a methylated nucleotide. In 1925, Johnson and Coghill successfully detected a minor amount of a methylated cytosine derivative as a product of hydrolysis of tuberculinic acid with sulfuric acid. This report was severely criticized because their identification based solely on the optical properties of the crystalline picrate, and other scientists failed to reproduce the same result. But its existence was ultimately proven in 1948, when Hotchkiss separated the nucleic acids of DNA from calf thymus using paper chromatography, by which he detected a unique methylated cytosine, quite distinct from conventional cytosine and uracil. After seven decades, it turned out that it is also a common feature in different RNA molecules, although the precise role is uncertain.
The function of this chemical varies significantly among species:
- In bacteria, 5-methylcytosine can be found at a variety of sites, and is often used as a marker to protect DNA from being cut by native methylation-sensitive restriction enzymes.
- In plants, 5-methylcytosine occurs at CpG, CpHpG and CpHpH sequences (where H = A, C or T).
- In fungi and animals, 5-methylcytosine predominantly occurs at CpG dinucleotides. Most eukaryotes methylate only a small percentage of these sites, but 70-80% of CpG cytosines are methylated in vertebrates.
While spontaneous deamination of cytosine forms uracil, which is recognized and removed by DNA repair enzymes, deamination of 5-methylcytosine forms thymine. This conversion of a DNA base from cytosine (C) to thymine (T) can result in a transition mutation. In addition, active enzymatic deamination of cytosine or 5-methylcytosine by the APOBEC family of cytosine deaminases could have beneficial implications on various cellular processes as well as on organismal evolution. The implications of deamination on 5-hydroxymethylcytosine, on the other hand, remains less understood.
5-methylcytosine is resistant to deamination by bisulfite treatment, which deaminates cytosine residues. This property is often exploited to analyze DNA cytosine methylation patterns with bisulfite sequencing.
- Matthews AP (2012). Physiological Chemistry. Williams & Wilkins Company/. p. 167. ISBN 1130145379.
- Johnson TB, Coghill RD (1925). "The discovery of 5-methyl-cytosine in tuberculinic acid, the nucleic acid of the Tubercle bacillus". J Am Chem Soc. 47 (11): 2838–2844. doi:10.1021/ja01688a030.
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- Hotchkiss RD (1948). "The quantitative separation of purines, pyrimidines and nucleosides by paper chromatography". J Biol Chem. 175 (1): 315–332. PMID 18873306.
- Squires JE, Patel HR, Nousch M, Sibbritt T, Humphreys DT, Parker BJ, Suter CM, Preiss T (2012). "Widespread occurrence of 5-methylcytosine in human coding and non-coding RNA". Nucleic Acids Res. 40 (11): 5023–5033. doi:10.1093/nar/gks144. PMC . PMID 22344696.
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Latest posts by H. Sterling Burnett (see all)
- Paris Climate Participants Miss Targets While U.S. Reduces Its Emissions - July 12, 2018
- Pope Francis’s Misguided War on Fossil Fuels - July 6, 2018
- Climate Fight Loses a Warrior - July 1, 2018
As temperatures continue to dip and snow accumulates, support for claims human caused global warming is causing winters to disappear are melting like ice under a heat lamp.
All fifty states are expecting to see snowfall in the next seven days with most of them already having experienced modest to record amounts of snow as this particularly wicked winter just refuses to let up.
Cold temperature records were tied or broken at more than 2000 locations in the past week. According to the weather website, sunshine hours, the National Oceanic and Atmospheric Administration (NOAA) recorded 2,634 record low-high temperatures were broken or tied between February 19, 2015 and February 25, 2015. In other words, 2,634 locations experienced daily highs lower than ever recorded on that date since record keeping began. Over the same time period, 272 locations registered record low temperatures at least one day during the week. All these records are falling without the influence of the polar vortex that set thousands of record lows throughout the nation, even into the summer, of 2014.
On Friday the 27th every area east of the Rocky Mountains, excepting Florida, experienced below average temperatures. According to the Weather Channel, cities breaking daily low or daily low high temperatures in New England and the Northeastern U.S. included: Burlington, Vermont (minus 19 degrees), Bridgeport, Connecticut (0 degrees — the latest in a 0 degree temperature was ever recorded), Concord, New Hampshire (minus 20 degrees), Pittsburgh (minus 9 degrees) and Rochester, New York (minus 9 degrees).
Both Bangor, Maine and Syracuse, New York saw more below zero temperatures in February 2015, than they had experienced in any previous February. In Syracuse, the temperature dipped below zero for a record 20 times topping the previous calendar-year record of 19 below zero days in 1948, while Bangor, Maine saw 17 subzero days.
With an average temperature of 24 degrees for the month, 11 degrees below the normal February average, New York City set a record for the coldest February ever. The cold brought winter related health problems in tow. The New York Times reported, “Dr. John Marshall, the head of emergency medicine at Maimonides Medical Center in Brooklyn, said his hospital was averaging 336 patients a day this winter, 20 more than last winter. On Jan. 19, he saw something unlike anything he had seen before. In a single hour, 30 people showed up after having slipped on ice, most of them with wrist and arm fractures, with some ankles thrown in.”
Nor were the Midwest and the Great Lakes states spared the record chill with low records being set or tied in among other locations, Cincinnati, Ohio (minus 7 degrees), Columbus, Ohio (minus 11 degrees), Chicago (minus 10 degrees, Dubuque, Iowa (minus 17 degrees), Detroit (minus 2 degrees), Erie, Pennsylvania (minus 7 degrees), Flint, Michigan (minus 17 degrees), Grand Rapids, Michigan (minus 10 degrees) and Indianapolis, Indiana (minus 5 degrees) all broke low temperature records.
Some cities, including Cleveland and Toledo in Ohio set broke low temperature records on multiple days.
For South Bend, Indiana, Feb. 12 to Feb. 27, was the coldest recorded for this period in history with an average temperature of 11.4 degrees.
The Weather Channel reports, “subzero readings stretched across 22 states from the interior Northeast to the Plains, Great Lakes and Upper Midwest. Temperatures dropped below minus 20 degrees in 7 states (North Dakota, South Dakota, Iowa, Wisconsin, Minnesota, Michigan and New York). Wind chills bottoming out at more than 40 below zero in parts of North Dakota and northern Minnesota Sunday morning. Bottineau, North Dakota saw the lowest actual air temperature in the Lower 48, dipping to minus 32 degrees.
Farther South, Joplin, Missouri (8 degrees), Paducah, Kentucky (11 degrees) set record low temperatures between the 19th and the 25th. On Friday the 27th, Oklahoma (23 degrees) and Dallas, Texas (30 degrees) each set records for the lowest maximum temperature recorded on the date.
As is often the case, in winter, cold temperatures were accompanied with snowfall, in many areas, record snowfall. Boston’s snow woes have been well-documented this winter, but Boston is not the only city, nor the Northeast the only region slammed in February. Accumulating snow and ice brought the roof down on a skating rink in Canton, Massachusetts narrowly avoiding crushing a children’s hockey team and assembled parents and employees.
Also in New England, snowfall measured at Warwick New Hampshire’s Green Airport topped 31.8-inches breaking the old record of 30.9 in set in 1962.
Indianapolis set a new snowfall record for March 1st with 5.9 inches of snowfall, the most ever on March 1st.
According to the National Weather Service, much of Alabama experienced record or near record snowfalls last week. Prior to February 25, Huntsville, AL had received just 6 tenths of an inch of a snowfall all winter, but on the 25th, Huntsville got hammered with 8.1 inches of snow it the second-snowiest day in the city’s history, surpassed only by the 15.7 inches of snow that fell on December 31, 1963.
Record snows fell across much of Alabama with three locations in Marshall County reported 11 or more inches of snow. Other areas receiving high snowfall included Athens (8.5 inches), Eva (9 inches), Moulton (9 inches), Phil Campbell (10 inches) and Rainsville (8.5 inches).
Farther west in Texans and New Mexican’s have also experienced record late-season snowfalls with attendant weather related disasters. Area’s north and west of Ft. Worth experienced record amounts of snow, with some regions getting more than seven inches of snow. Mixed with the snow was freezing rain and ice. As a result of the unusual late February weather, more than 1,000 flights were cancelled out of D/FW International Airport. North Texas experienced more than 1,000 reported accidents, with 617 traffic related calls between 9:00 am and 6:00 pm on Friday in Ft. Worth alone. Interstates 35, 30 and 75 as well and numerous side-streets were closed at times Thursday through Saturday and there were two weather related traffic deaths.
Across New Mexico, residents woke up to more snowfall than some areas had in nearly a decade. The Albuquerque metro area received 1-2 inches per hour for several hours, resulting in a total 8.6 inches, the 9th heaviest snowfall since 1931. The last time more than 8 inches fell in a two day period was in 2006.
H. Sterling Burnett
Environment & Climate News | <urn:uuid:006cd873-0cee-44fd-b47e-7140488b8ba6> | 2.890625 | 1,472 | Content Listing | Science & Tech. | 52.595366 | 95,518,050 |
Peter L. Peres [plp at ACTCOM.CO.IL] says
The keys to larger C projects are header files and build scripts.
The bug that causes you trouble is a very sane and useful ANSI C feature: Symbols declared in a module are not visible to other modules unless they are declared in the module that uses them as external or as function prototypes.
For example a function int foo(void); shall appear as int foo(void); in the main file, and a global variable int bar shall appear as extern int bar; in same. Of course you don't write them there, you include a library header file instead.
In other words, when making a library, you put the functions in the library, and prototypes for all the public functions in it, and 'external' definitions for all the public data in it, in a corresponding header file (usually called like the libarary but with suffix .h). The IMPORTANT part is that there should be NO actual functions NOR data declarations in the header. Anything not declared in the header will remain private to the libary. However some compilers do not like name clashes between same-named symbols located in different libraries (even if they are not public).
Then in your main program, you #include "path/to/header" and the functions are visible. The library is usually compiled separately or automatically (it's a DLL of sorts at the object file level). You must understand the semantics of the double ticks (as opposed to angled brackets) here, and apply some serious path rewriting for DOS under certain circumstances.
Now you need to tell the compiler about all the files it needs to build the executable. Sometimes you tell this the linker. In other words, pass all the required libraries (already compiled into relocatable object form) to the linker, or pass all the source file names to the compiler. I don't know what compiler you are using but sane (i.e. Unixish) compilers allow you to string everything onto the command line. DOS compilers have a limit on the command line length so they often use a command file which contains the actual list of files to use.
A tool that does almost all of this (the invocation of the toolchain parts) for you is called a make tool and YOU WANT ONE BADLY. There are free ones and there are non free ones. The 'standard' make tool is called... make. See Linux... Another make tool is a batch script of whatever shell you are using (yes, you can do it in DOS if you HAVE to).
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<A HREF="http://techref.massmind.org/techref/language/ccpp/largeproj.htm"> The C and C++ Programming Languages </A>
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Species Detail - Brazilian Giant-rhubarb (Gunnera manicata) - Species information displayed is based on all datasets.
Terrestrial Map - 10kmDistribution of the number of records recorded within each 10km grid square (ITM).
Marine Map - 50kmDistribution of the number of records recorded within each 50km grid square (WGS84).
Invasive Species: Invasive Species || Invasive Species: Invasive Species >> Medium Impact Invasive Species || Invasive Species: Invasive Species >> Regulation S.I. 477 (Ireland)
Linden ex André
17 May (recorded in 2013)
24 September (recorded in 2006)
National Biodiversity Data Centre, Ireland, Brazilian Giant-rhubarb (Gunnera manicata), accessed 18 July 2018, <https://maps.biodiversityireland.ie/Species/42049> | <urn:uuid:b20248c6-a7d8-4120-910d-2bfb719eb34e> | 2.640625 | 188 | Structured Data | Science & Tech. | 24.989091 | 95,518,074 |
The Silky Seven: Genetic Analysis Reveals Anteater Species Diversity
Credit: Quinten Questel (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
This is a story that begins in 1758 with the publication of the tenth edition of Systema Naturae, the magnum opus of Swedish naturalist Linnaeus (Carl Nilsson Linnaeus, 1707-78), the father of taxonomy.
Among the 4,200-odd species of animals described by Linnaeus in his book (as well as over 9,000 plant species) was the silky anteater Cyclopes didactylus. Known in Brazil as tamanduaí, or pygmy anteater, it is a cute, shy, small animal with two toes, a short snout, nocturnal habits and a preference for inhabiting tree crowns, where it feeds solely on ants.
It is found in tropical forests in South and Central America, as well as in the few remaining fragments of Atlantic rainforest in Northeast Brazil. All populations of this animal are practically identical, and for 259 years, they were believed to constitute a single species. Now, we know there are at least seven.
The descriptions of six new species of anteater derive from research conducted by Flávia Miranda, a veterinarian affiliated with the Federal University of Minas Gerais’s Biodiversity & Molecular Evolution Laboratory (LBEM-UFMG) in Brazil. Miranda was part of the team of taxonomists, zoologists and geneticists from UFMG and the University of São Paulo who studied the biology and ecology of the new species. They also sequenced the nuclear and mitochondrial DNA of 287 specimens.
The results are in the article “Taxonomic review of the genus Cyclopes Gray, 1821 (Xenarthra: Pilosa), with the revalidation and description of new species”, published in Zoological Journal of the Linnean Society.
Six populations of C. didactylus were discovered in the nineteenth and early twentieth centuries, with habitats ranging from southern Mexico to northern Bolivia, and eastwards in the Brazilian Amazon (Pará and Maranhão States) and Northeast (Alagoas State).
All the collected specimens appeared to be practically identical. Any morphological differences were too slight to justify the creation of a new species, so all were considered subspecies of C. didactylus, the only species in the family Cyclopedidae.
This was the state of knowledge until 2005, when Miranda, the vet, entered the picture. She has worked with the order Xenarthra for over 20 years and leads Project Anteater, whose mission is the conservation of sloths, anteaters and armadillos.
In 2005 Miranda took part as an expert on xenarthrans in a meeting of the International Union for Conservation of Nature (IUCN) to verify the status of C. didactylus with a view to its conservation.
One of the points raised was whether a population of silky anteaters still existed in Northeast Brazil. No sightings had been reported for years. “I said I’d received a specimen in the conservation breeding facility where I was working in Recife in 2000,” Miranda told Agência FAPESP. This justified a trip to check out the area where it had been found.
Miranda decided to survey populations of anteaters in the Northeast and Amazon regions. In the ensuing two years, she carried out fieldwork in Pará and Maranhão. She also reconnoitered the banks of the São Francisco River in Alagoas. She reported sightings and collected specimens, steadily becoming more convinced that distinct species were indeed involved.
“I realized there were differences in coloring,” she said. “The animals I saw in Maranhão were entirely different from those I saw in the Xingu area. Were they the same species? Did the apparent morphological similarity of individuals in the various populations mask profound differences at the molecular level?”
The advent of molecular biology has shown taxonomists that not everything is identical, however much it may appear so. Miranda spent the last ten years organizing and undertaking expeditions to all parts of Brazil where sightings of silky anteaters had been reported. There have been ten expeditions, to Santa Isabel do Rio Negro (Amazonas State), Oriximiná (Pará), the Parnaíba River Delta (Piauí State), Maranhão, Amapá, and Surinam, among other places.
“It was always very hard to spot the animals in the forest. Imagine a little creature that weighs only 250 g, lives in the crowns of tall trees beside creeks or in mangroves and flooded areas, never comes down to the ground, never vocalizes, and is active only at night. I’d been in the field for two years before I made my first sighting.”
Miranda undertook 17 expeditions to collect specimens in Brazil and Suriname, measuring and photographing them, and taking blood samples for molecular analysis. Sex and geographic location were recorded. Age was determined on the basis of body mass, fur density, and fur length. Morphological and morphometric information was also sought from 20 natural history collections in several countries.
Analysis of the animals’ nuclear and mitochondrial DNA removed all doubt about the existence of several species in the genus Cyclopes, supported by morphological and morphometric differences, as well as geographic location.
The researchers plan to assess conservation of the population of silky anteaters in Northeast Brazil, which is threatened above all by deforestation. “The idea is to classify the population in the Northeast as an evolutionarily significant unit, or ESU,” Miranda said.
So many millions of years of separation between species would be more than sufficient for these anteaters to have accumulated various modifications. However, this is not what has happened. The genus Cyclopes has proved extremely conservative throughout its evolutionary history, changing very little or not all in morphological terms.
“The reason for this may be the life habits of these animals. All species occupy a similar and highly specialized ecological niche with no competition,” Miranda said.
Reference: Miranda, F. R., Casali, D. M., Perini, F. A., Machado, F. A., & Santos, F. R. (n.d.). Taxonomic review of the genus Cyclopes Gray, 1821 (Xenarthra: Pilosa), with the revalidation and description of new species. Zoological Journal of the Linnean Society. https://doi.org/10.1093/zoolinnean/zlx079
Synthetic Material That Detects Enzymatic ActivityNews
Scientists integrate protein and polymer building blocks to create stimulus-responsive systemsREAD MORE
Bioethics Council Rules Heritable Genome Editing "Ethically Acceptable" In Certain CircumstancesNews
A leading UK bioethics advisory body has weighed in on the debate around human genetic modification, concluding that heritable genome editing – modifying the DNA of an egg, sperm or embryo with changes that will be passed on to future generations – could be ‘morally permissible’ in humans, provided key ethical tests are met.
Genetic Factors Leading to Rare Bone Fusion Disorder IdentifiedNews
Genome sequencing establishes multiple genes responsible for a rare condition that cause bone fusionREAD MORE | <urn:uuid:8db01b4b-6aac-4be8-86a0-30de2e270c16> | 3.203125 | 1,580 | News Article | Science & Tech. | 33.579574 | 95,518,081 |
|Messier 51 with supernova SN2011dh. Companion galaxy NGC 5195 at bottom.|
In fact, when this supernova first exploded, it was emitting as much energy individually as the rest of the hundreds of billions stars in M51 combined. The reasons it doesn't appear as bright as the rest of the galaxy are 1) it was about five days old by the time I took this picture, so it had begun to fade a little. And 2) most of that energy is not in the visible portion of the spectrum. Remind me sometime when it's not so late to explain the details behind a supernova type IIa.
As an aside, you can't see them in this picture because of the exposure settings I chose, but I caught two extremely faint satellite trails in my exposures, one of which neatly passed diagonally from lower-left to upper-right between M51 and the star on the right. | <urn:uuid:afbed7ce-e76e-4000-b2e1-77d4989334b9> | 2.609375 | 191 | Personal Blog | Science & Tech. | 58.941923 | 95,518,083 |
Global Earth Observation and Monitoring
of the atmosphere
Terrain below site
|Description:||Percentage of terrain within 10 km radius from the site that lies at lower altitudes than the site itself based on GLOBE 30'' (arc-seconds) topography data. For an elevated site this percentage will be large (close to 100 %), while for sites within valleys or basins this percentage will be small. For sites within homogeneous terrain the percentage will be 50 %. Such sites can be assumed to be more representative for a larger area, while for sites in more complex terrain small circulation systems might influence the surface concentration field and introduce large heterogeneities.|
Please contact Stephan Henne
in case of any questions. | <urn:uuid:183720be-38d8-4978-a1cd-9f8a2c980027> | 2.65625 | 150 | Knowledge Article | Science & Tech. | 26.060435 | 95,518,087 |
This specific ISBN edition is currently not available.View all copies of this ISBN edition:
New from the world's number-one programming authorin this book, bestselling programming author herb schildt provides more than 200 practical, self-contained recipes for experienced c++ programmers. Each chapter contains a series of real-life programming tasks, followed by code solutions and concise but detailed discussions on the technique used. This guide will be essential to every c++ programmer's toolkit.
"synopsis" may belong to another edition of this title.
Book Description Tata McGraw-Hill Education Pvt. Ltd., 2008. Softcover. Condition: New. First edition. Your Ultimate "How-To" Guide to C++ Programming! Legendary programming author Herb Schildt shares some of his favorite programming techniques in this high-powered C++ "cookbook." Organized for quick reference, each "recipe" shows how to accomplish a practical programming task. A recipe begins with a list of key ingredients (classes, functions, and headers) followed by step-by-step instructions that show how to assemble them into a complete solution. Detailed discussions explain the how and why behind each step, and a full code example puts the recipe into action. Each recipe ends with a list of options and alternatives that suggest ways to adapt the technique to fit a variety of situations. Whether you`re a beginner or an experienced pro, you`ll find recipes that are sure to satisfy your C++ programming appetite! Topics include: String Handling Standard Template Library (STL) Containers Algorithms Function Objects Binders Negators Adaptors Iterators I/O Formatting Data Learn how to: * Tokenize a null-terminated string * Create a search and replace function for strings * Implement subtraction for string objects * Use the vector, deque, and list sequence containers * Use the container adaptors stack, queue, and priority_queue * Use the map, multimap, set, and multiset associative containers * Reverse, rotate, and shuffle a sequence * Create a function object * Use binders, negators, and iterator adapters * Read and write files * Use stream iterators to handle file I/O * Use exceptions to handle I/O errors * Create custom inserters and extractors * Format date, time, and numeric data * Use facets and the localization library * Overload the [ ], ( ), and -> operators * Create an explicit constructor * And much, much more Table of contents Chapter 1. Overview Chapter 2. String Handling Chapter 3. Working with STL Containers Chapter 4. Algorithms, Function Objects, and Other STL Components Chapter 5. Working with I/O Chapter 6. Formatting Data Chapter 7. Potpourri Index Printed Pages: 0. Seller Inventory # 24036 | <urn:uuid:8b760dee-6319-4906-ac88-1516b58d7188> | 2.578125 | 570 | Product Page | Software Dev. | 38.422792 | 95,518,101 |
The conducting polymers such as polyaniline, polypyrrole and polythiophene
were functionalized with copper phthalocyanine using chemical oxidation method. The obtained polymers viz. PANI-CuPc, PPy-CuPc and PT-CuPc were studied as chemical sensors by their response characteristics after exposure to various chemical vapors such as methanol, ammonia and nitrogen dioxide. The results obtained showed that these polymers have moderate sensitivity towards the methanol as well as ammonia vapors whereas they show tremendous sensitivity towards nitrogen dioxide vapors. The sensitivity factor of as high as 50,000 was obtained for PT-CuPc polymers in nitrogen dioxide. In comparison to this, the sensitivity factors of about 100 and 40 were obtained, when these polymers were
exposed to ammonia and methanol vapors. The very high selectivity towards the nitrogen dioxide was explained on the basis of charge transfer complex formed between, the phthalocyanine donor and nitrogen dioxide acceptor molecules. On the other hand, ammonia becomes a competing electron donor in CuPc containing conducting polymers. The very low response towards the methanol may be explained on the basis very little charge transfer / interaction between CuPc containing polymers and methanol. Thus, CuPc incorporated conducting polymers have much higher selectivity than their original homopolymer.
Thursday, December 01, 2011
Entre las variedades alotrópicas del carbono, se encuentran el diamante y el grafito. Ambas estructuras son sólidas y presentan propiedade...
Hace un siglo, el químico Søren Sørensen inventó lo que se convertiría en una herramienta de diagnóstico crucial: la escala pH. Desde su...
este es un trabajo ke hice para quimica general... algo ke todos hicimos hahaahhah y weno.... me dijeroooon, ke debia postiarloooo NO SE KE... | <urn:uuid:477f8e79-5fb8-4c94-a4f4-e4a567a84cfe> | 2.5625 | 440 | Personal Blog | Science & Tech. | 22.834167 | 95,518,108 |
- Nano Express
- Open Access
Microwave characterisation of carbon nanotube powders
© Porch et al.; licensee Springer. 2012
Received: 22 March 2012
Accepted: 3 July 2012
Published: 1 August 2012
We have used a 3-GHz microwave host cavity to study the remarkable electronic properties of metallic, single-walled carbon nanotubes. Powder samples are placed in its magnetic field antinode, which induces microwave currents without the need for electrical contacts. Samples are shown to screen effectively the microwave magnetic field, implying an extremely low value of sheet resistance (< 10 μΩ) within the graphene sheets making up the curved nanotube walls. Associated microwave losses are large due to the large surface area, and also point to a similar, very small value of sheet resistance due to the inherent ballistic electron transport.
There has been intensive research on the characterisation and application of carbon nanotubes for next-generation electronic devices . Ballistic conduction along single-walled metallic nanotubes is predicted theoretically and has been experimentally verified. Clearly, this has enormous impact for electronic devices fabricated using these remarkable materials, but there are problems in characterising the electronic properties using conventional (i.e. DC) techniques. This is mainly due to the need to make electrical contacts with the ends of the nanotube, which suppresses the measured conductivity, and is further complicated by inter-tube contacts. For example, it has been found that thin film samples have sheet resistances limited by the large junction resistances between adjacent nanotubes .
In this context, we propose a new method to characterise the electronic properties of metallic nanotubes using microwaves as a means of exciting currents, thus negating the requirement for electrical contacts. The method is fast and is performed on a powder sample, so it allows rapid measurements of large numbers of samples and permits in situ changes in electronic properties (e.g. due to surface adsorption of chemical species) without the need to remove the sample from the apparatus. Previous microwave studies of carbon nanotube materials have ranged from the screening efficiency of thin films to the microwave excitation of single nanotubes . In our experiments, powder samples are placed in a region of high microwave magnetic field in a microwave cavity (here, a 3-GHz copper hairpin), and the sample properties are determined using the cavity perturbation technique. We have used a similar method to measure the electronic properties of a range of other material systems (e.g. metal-loaded zeolites ).
The hairpin itself is a 1-mm thick copper strip, with a width of 5 mm, bent into a U shape of length 23 mm and plate separation of 5 mm. The expected resonant frequency of the fundamental mode of the hairpin is, therefore, f0 ≈ c/4 L ≈ 3.26 GHz, in practise about 10% lower due to the end effects of electric and magnetic fields spilling outside of the structure. The microwave magnetic field is largest at the short-circuit end of the hairpin, where the field is also approximately uniform and runs parallel to the plate surfaces. The sample is inserted into this region. The hairpin is surrounded by a cylindrical radiation shield, of length twice that of the hairpin (i.e. 50 mm) and inner radius of 15 mm. This reduces the radiation losses from the hairpin and, thus, preserves a high quality factor, which is desirable for measuring the additional microwave loss contributed by the sample. Microwave power is coupled in and out of the hairpin using an identical pair of loop-terminated RG405 microwave coaxial cables which couple to the microwave magnetic field at the hairpin’s short-circuit end. The transmitted microwave power (i.e. |S21|2) is measured in the frequency domain using an Agilent E5071B network analyser with computer control (Agilent Technologies, Inc., CA, USA). The unloaded quality factor Q of the empty cavity is around 1,500, i.e. large for its small volume (≈ 600 mm3), thus enhancing the sample filling factor for more sensitive measurements of its electronic properties. Cavity couplings are kept weak (i.e. insertion loss > 30 dB at resonance), so that only minor correction factors are needed to extract unloaded Q factors from the raw data.
Results and discussion
A separate calibration experiment involved the insertion of small copper spheres of radii 330 μm into the same H-field position as for the sample. The observed frequency increase of Δf0 = 1.30 ± 0.01 MHz per sphere allows us to determine experimentally Veff = 270 ± 2 mm3, comparing well with the expected value of LWd/2 ≈ 290 mm3. Thus, the observed nanotube frequency shift corresponds to an effective screened volume of ≈ 1.7 mm3.
The inner tube volume within the cavity is ≈ 6.6 mm3, of which ≈ 0.40 mm3 is nanotube material (i.e. a packing fraction of about 6% by volume, based on the sample mass of 1.3 mg). From this, we conclude that the magnetic field is effectively screened within this low density powder, both from within the nanotubes themselves and from a much larger volume (×3) in the space outside. For this to happen, we also conclude that the nanotube sheet resistance must be extremely small, i.e. an upper limit of Rsq ≈ 10 μΩ based on a mean nanotube radius of a ≈ 0.7 nm. Since a trace of metallic Fe is present in the sample, it is prudent to quantify how much this contributes to the microwave screening. The 0.8% atomic ratio of Fe atoms corresponds to a volume of about 0.006 mm3. This is likely to be dispersed as very small particles of radii less than 1 μm. Given that the skin depth of Fe at 3 GHz at room temperature is about 2.8 μm, we would not expect such small particles to screen the microwave magnetic field. Even if the Fe formed a single large particle, which gives rise to the greatest screened volume, the contribution to increase in resonant frequency will be only 0.6% of that observed for the whole CNT sample. Hence, we conclude that the screening effect of the Fe is negligible.
Does such a small value of Rsq contradict the observation of the large microwave losses of Figure 4? The answer can be found in the huge surface area of carbon nanotube powders, e.g. our 1.3-mg sample has a total surface area S ≈ 1.1 m3. Sheet resistance can be extracted from Equation 1b in the limit of strong screening ωτ > > 1, resulting in Rsq ≈ 2πμ0Veff ΔfB / S ≈ 30 μΩ. Therefore, these two independent measurements (one of microwave screening, the other of microwave loss) both point to very small values of sheet resistance due to ballistic transport. In experimental studies of carbon nanotube films, the sheet resistance is found to be of the order of 1 kΩ with similar results for graphene films . In these studies, the intrinsic sheet resistance of the carbon nanotubes can be difficult to extract from the measurements as charge transport is limited by contacts between the nanotubes. Other types of measurement such as the optical conductivities reported in do not circumvent this problem as they characterise relatively large areas of the films. In theoretical studies of devices based on discrete carbon nanotubes and of carbon nanotube films, charge transport is often assumed to be ballistic, and therefore, the sheet resistance is zero. Ballistic transport has been observed in ohmically contacted metallic single wall carbon nanotubes having lengths less than approximately 300 nm .
Not all of the nanotube powders studied to date show such striking behaviour, so future experiments will concentrate on systematic studies of a wider range of materials (semiconducting and metallic), over a wider range of frequencies (particularly from kilohertz to megahertz), also trying to identify the nature of the defects giving rise to the finite sheet resistance. Indeed, isolating metallic samples is, itself, an important problem, and the method we have proposed here may serve as a means of quantifying the volume fraction of metallic nanotubes within a given powder.
- Anantram MP, Léonard F: Physics of carbon nanotube electronic devices. Rep Prog Phys 2006, 69: 507. 10.1088/0034-4885/69/3/R01View ArticleGoogle Scholar
- Fuhrer MS, Nygård J, Shih L, Forero M, Yoon Y-G, Mazzoni MSC, Choi HJ, Ihm J, Louie SG, Zett A, McEuen PL: Crossed nanotube junctions. Science 2000, 494: 288.Google Scholar
- Xu H, Anlage SM, Hu L, Gruner G: Microwave shielding of transparent and conducting single-walled carbon nanotube films. Appl Phys Lett 2007, 90: 183119. 10.1063/1.2734897View ArticleGoogle Scholar
- Yu Z, Burke PJ: Microwave transport in metallic single-walled carbon nanotubes. Nano Lett 2005, 5: 1403. 10.1021/nl050738kView ArticleGoogle Scholar
- Anderson PA, Armstrong AR, Barker PD, Edmondson MJ, Edwards PP, Porch A: Rubidium doped zeolite rho: structure and microwave conductivity of a metallic zeolite. Dalton Trans 2004, 19: 3122.View ArticleGoogle Scholar
- Klein O, Donovan S, Dressel M, Grüner G: Microwave cavity perturbation technique. Int J Infrared Millimeter Waves 1993, 14: 2423. 10.1007/BF02086216View ArticleGoogle Scholar
- Shin DH, Shim HC, Song J-W, Kimb S, Hana C-S: Conductivity of films made from single-walled carbon nanotubes in terms of bundle diameter. Scr Mater 2009, 60: 607. 10.1016/j.scriptamat.2008.12.019View ArticleGoogle Scholar
- De S, Coleman JN: Are there fundamental limitations on the sheet resistance and transmittance of thin graphene films? ACS Nano 2010, 4(5):2713. 10.1021/nn100343fView ArticleGoogle Scholar
- Javey A, Guo J, Paulsson M, Wiang Q, Mann D, Lundstrom M, Dai H: High-field quasiballistic transport in short carbon nanotubes. Phys Rev Lett 2004, 92(1):106804.View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. | <urn:uuid:1021ae84-5a7b-4f5d-bb5f-f5ef96a4b810> | 2.609375 | 2,344 | Academic Writing | Science & Tech. | 50.110167 | 95,518,114 |
They were released three different, independent inventions saving 12%, 15% and 25% energy. Some considered that while the use of these inventions, the total savings will be 12% + 15% + 25% = 52%. Is this true? How much percent of energy will save all three inventions together?
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I longer watch processors for Socket A on ebay, Athlon XP 1.86GHz with a PR rating of 2500+ costs $7 and Athlon XP 2.16Ghz with a PR rating of 3000+ currently cost $16. Calculate: About what percentage of the Athlon XP 2.16Ghz is powerful than Athlon X | <urn:uuid:5d98b3f2-25d9-4a0c-a927-5672873db3d5> | 2.96875 | 632 | Q&A Forum | Science & Tech. | 82.295451 | 95,518,119 |
Reserves are being used increasingly to conserve fish communities and populations under threat from overfishing, but little consideration has been given to how fish behavior might affect reserve function. This review examines the implications of how fish use space, in particular the occurrence and size of home ranges and the frequency and direction of home range relocations. Examples are drawn primarily from the literature on coral reef fishes, but the principles apply to other habitats. Reserves can protect fish species only if individuals restrict their movements to a localized home range during at least part of the life cycle. Home range sizes increase with body size. In small reserves, a significant proportion of fish whose home ranges are centered within the reserve can be exposed to fishing mortality because their home ranges include non-reserve areas. Relocation of home ranges following initial settlement increases exposure to the fishery, especially if habitat selection is frequency-dependent. Distance, barriers, and costs of movement counter such redistribution. These considerations lead to predictions that population density and mean fish size (1) will form gradients across reserve boundaries with maxima in the center of the reserve and minima outside the reserve away from the boundary; (2) will increase rapidly in newly established reserves, only later providing ‘spillover’ to adjacent fisheries as density-dependent emigration begins to take effect; and (3) will be higher in reserves that are larger and have higher area:edge ratios, more habitat types, natural barriers between reserve and non-reserve areas, and higher habitat quality inside than outside the reserve. (4) Species with low mobility and weak density-dependence of space use will show the greatest increase in reserves and the strongest benefit for population reproductive capacity, but those with intermediate levels of these traits will provide the greatest spillover benefit to nearby fisheries.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below | <urn:uuid:0b1aa3c7-5ec8-4bd2-8c21-e5f8573100ac> | 3.859375 | 382 | Academic Writing | Science & Tech. | 3.665277 | 95,518,138 |
+44 1803 865913
By: Nick Harvey(Author), Beverley Clarke(Author)
252 pages, b/w photos, b/w illustrations, tables
Environmental Impact Assessment in Practice is concerned with the process of environmental impact assessment (EIA). In other words, it is a comprehensive analysis of the assessment of the potential environmental impacts of proposed very large projects and complex developments.
Its logical structure mirrors the orderly and thorough processes required of EIA. Part 1 analyses the procedures of conducting an EIA, and raises issues related to practice. Part 2 examines practices for each state and territory in Australia through relevant and well-chosen case examples. It looks at the standard steps for major development proposals: information gathering, to refine the scope of the assessment; the impact assessment (data collection and analysis) and design of mitigation measures; reporting and making public the findings of the assessment, review of the findings and decision-making; and, follow-up, to determine the accuracy of predictions made in the assessment and to establish the effectiveness of the process. Part 3 draws links between the two previous parts, and questions the role that EIA will take in future developments.
Part One: Procedures
2: Environmental Impact Assessment Procedures
3: Innovation in EIA: Australia's 'Second Wave'
4: Strategic Environmental Assessment (SEA) and Its Application in Australia
Part Two: Practices
5: Australian Commonwealth EIA: Procedures and Practice
6: Australian Capital Territory EIA: Procedures and Practice
7: New South Wales EIA: Procedures and Practice
8: Northern Territory EIA: Procedures and Practice
9: Queensland EIA: Procedures and Practice
10: South Australian EIA: Procedures and Practice
11: Tasmanian EIA: Procedures and Practice
12: Victorian EIA: Procedures and Practice
13: Western Australia EIA: Procedures and Practice
Part Three: The Changing Nature of EIA
14: Variation in EIA Legislation and Practice around Australia and the Changing National Role of EIA
15: Conclusion: The Way Ahead
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Up to this point, we’ve quietly ignored a significantly complicating factor in string manipulation: the fact that the rules for text vary considerably among cultures.
There are also lots of different types of rules in operation, from
the characters to use for particular types of separators, to the natural
sorting order for characters and strings. I’ve already called out an
example where the output on my UK English machine was different from that on a U.S. English
computer. As another very simple example, the decimal number we write as
1.8 in U.S. or UK English would be
1,8 in French. For the .NET
Framework, these rules are encapsulated in an object of the type
CultureInfo class makes
certain commonly used cultures accessible through static properties.
CurrentCulture returns the default
culture, used by all the culture-sensitive methods if you don’t supply a
specific culture to a suitable overload. This value can be controlled on a
per-thread basis, and defaults to the Windows default user locale. Another
per-thread value is the
CurrentUICulture. By default, this is based on
the current user’s personally selected preferred language, falling back on
the operating system default if the user hasn’t selected anything. This
culture determines which resources the system uses when looking up
localized resources such as strings.
CurrentUICulture may sound very similar, but are often different. For example, ... | <urn:uuid:56bce0a3-b971-40eb-8d9f-c89afe8aa897> | 3.21875 | 316 | Truncated | Software Dev. | 42.26875 | 95,518,162 |
NASA's Terra satellite passed over Tropical Storm Nuri on Nov. at captured an infrared picture of the storm. The storm looked more like a frontal system as it stretched from northeast to southwest.
The Moderate Resolution Imaging Spectroradiometer or MODIS instrument that flies aboard NASA's Terra satellite flew over Nuri on Nov. 6 at 1240 UTC (7:40 a.m. EST).
The MODIS image showed some strong thunderstorms remaining in a small area around Nuri's center, but the storm appeared stretched out from northeast to southwest. Wind shear was affecting the storm, stretching it out.
The last bulletin on the storm was issued on Nov. 6 at 0300 UTC (Nov. 5 at 10 p.m. EST). At that time, the Joint Typhoon Warning Center (JTWC) noted that Nuri still had maximum sustained winds near 55 knots (63.2 mph/102 kph).
It was located about 130 nautical miles (149 miles/240 km) west-northwest of Chichi-jima, near 29.2 north latitude and 141.0 east longitude. Nuri was moving to the northeast and over open waters of the western North Pacific.
In its final bulletin, JWTC noted that Nuri will become an extra-tropical storm before the end of the day on Nov. 6. Computer models indicate the system will be a strong extra-tropical low pressure area as it continues to move over open waters.
NASA's Goddard Space Flight Center
Rob Gutro | EurekAlert!
New research calculates capacity of North American forests to sequester carbon
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
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Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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16.07.2018 | Earth Sciences | <urn:uuid:c2bfcd4b-882a-4db1-8ce6-12aefdb06639> | 3 | 948 | Content Listing | Science & Tech. | 50.284105 | 95,518,169 |
What's the Latest Development?
Michael Levin, director of Tufts University's Center for Regenerative and Developmental Biology, believes that by better understanding our bodies as hosts of electric current, we might be able to regenerate lost organs and limbs. "He thinks that the key to regeneration—the key to pattern, to shape—may be found in the electrical signals that are transmitted among all our cells, much like the ones and zeros that zip along a computer's hard drive. ... Levin's lab has produced four-headed flatworms and grown an eye from scratch on a tadpole's belly."
What's the Big Idea?
Over the next few years, Levin expects to begin experimenting on mammals. If the experiments go well, human regeneration could become a reality within our lifetime. Already, there is some precedent for our regenerative capacity: "If a child experiences a neat slice through the end of his fingertip, that tip will grow back—a talent that disappears sometime between the ages of seven and eleven. ...were you to lose part of your liver, it would, in fact, regenerate. With the exception of our skin, it's the only human organ that has that capability."
Photo credit: Shutterstock.com | <urn:uuid:c4e80c51-a856-4725-aa0c-35e160455845> | 2.96875 | 249 | Truncated | Science & Tech. | 52.186627 | 95,518,203 |
The study, published on 18th July in the journal PLoS Computational Biology, focuses on the role of oxytocin, a very important hormone recently found be involved in the enhancement of “trust” and love in humans and animals. Oxytocin has long been known to be the trigger that, when released into the blood, causes milk to be let down from the mammary gland.
When oxytocin is released within the brain, it also helps to strengthen the bond between mother and child, but to have these effects, a very large amount must be released abruptly to cause a wave of the hormone that can spread through the brain.
What was not known before this study is exactly how the few thousand neurones, which are specialized to release oxytocin, are marshalled together to produce a sufficiently intense burst of activity to do all of that. In fact, even when a child is not suckling these neurons are continually producing oxytocin but in small amounts and in a much more uncoordinated way. Previous studies on individual neurons have found no obvious way of modifying their behaviour to get the coordinated response needed to produce the large, regular pulses of oxytocin that are needed.
Now this University of Warwick led team of experimental neuroscientists and theoreticians have found a likely answer. The neuroscientists have found that in response to suckling the neurons start releasing oxytocin from their “dendrites” as well as from their nerve endings – this was unexpected because dendrites are usually thought as the part of a neurone which receive, rather than transmit information.
The dendrites usually create a weak network of connections between neurons. However the researchers have now shown that the release of oxytocin from the dendrites allows a massive increase in communication between the neurons. This co-ordinates a “swarm” of oxytocin factories, producing massive intense bursts of oxytocin release at intervals of around 5 minutes or so.
The synchronous activation of the few thousand oxytocin producing neurons is an example of “emergent” process. It develops in just the same way as a flock of birds or insects - closely coordinated action developing without a single leader.
University of Warwick computational biology researcher Professor Jianfeng Feng said:
“We knew that these pulses arise because, during suckling, oxytocin neurons fire together in dramatic synchronized bursts. But exactly how these bursts arise has been a major problem that has until now eluded explanation. This research has allowed us to incorporate all the latest research in a large computational model of the whole population of oxytocin cells.”
“In this model we have shown that the dendritic interactions are enhanced enough to trigger a massive positive-feedback on activity. The model gives us a possible explanation of an important event in the brain that could be used to study and explain many other similar brain activities.”
Peter Dunn | alfa
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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For those that wonder what it would be like to have the sun directly on our Earth, a team of scientists at the German Aerospace Center (DLR) have the answer for you. They have built “Synlight,” an enormous lamp that’s dubbed as an artificial sun to further research if solar power is efficient for vehicles.
Researchers are continuing to figure out the best way to replace fossil fuels in the future. Not only are they a limited resource, but they are hazardous to the environment with carbon dioxide emissions. Every year, reports continue to churn out that worldwide CO2 levels reach their highest point. It has hit 400 parts per million back in 2016, and that is considered a level that cannot be fixed. A recent report by explains how big of a change this has been.
"Current concentrations of CO2 emissions are at their highest in human history, currently hovering around 400 parts per million and continuing to rise. Before the Industrial Revolution, carbon dioxide concentrations had settled into an average of about 280 parts per million."
To put things in a gloomy perspective, that number could rise to 900 parts per million by the end of 2100. Once all fossil fuels have been exhausted in the next 300 years, it could be all the way up to 5,000 parts per million. Obviously, this trend has to change.
One favorite alternative is hydrogen, although it has its pros and cons against electric-fueled vehicles. It is believed that hydrogen fuel cells won’t break down as quickly, mileage is more efficient, and there would be a natural ease of filling up cars like people do with gasoline.
However, more research has to be done. Many argue that it is not much cleaner and hydrogen fuel cells are not very efficient. A strong negative is the amount of electricity required to produce hydrogen. That is why scientists are hoping that solar energy can aid with hydrogen-fueled vehicles.
So what does all that have to do with Synlight? It is an easier and more efficient way to study in Europe. Many parts deal with frequent cloud cover, and the sun is lower in the sky in Germany’s location. When the sun is lower, that means it is less powerful in that area. explains how the oversized lamp works.
"Synlight’s 149 spotlights are similar to those commonly used in cinema projectors. According to DLR, “These enable solar radiation powers of up to 380 kilowatts and two times up to 240 kilowatts in three separately usable irradiation chambers, in which a maximum flux density of more than eleven megawatts per square meter can be achieved."
Of course, this research doesn’t come without a heavy bill. The cost for manufacturing Synergy clocks in at about $3.8 million USD. The electricity the artificial sun uses is, obviously, jarring. A four-hour session of the lights on is equivalent to an entire family’s usage in one year. Despite consumption flaws, it could still be a very important tool in finding alternative fossil fuel resources.
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A new report finds that meat and dairy producers are on track to surpass the oil industry's greenhouse gas emissions. | <urn:uuid:7c50cc8b-e951-4988-b0cd-7667dfe5c8fc> | 4.09375 | 748 | News Article | Science & Tech. | 50.732315 | 95,518,229 |
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The Born Approximation
In the last chapter, we merely reformulated the scattering problem. Instead of solving the scattering problem by finding a solution to a differential equation with the appropriate boundary condition, we will instead try to solve it by finding a solution to an integral equation with the appropriate Green’s function.
KeywordsDifferential Cross Section Born Approximation Identical Particle Coulomb Scattering Screen Coulomb Potential
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In quantum computing and specifically the quantum circuit model of computation, a quantum logic gate (or simply quantum gate) is a basic quantum circuit operating on a small number of qubits. They are the building blocks of quantum circuits, like classical logic gates are for conventional digital circuits.
Unlike many classical logic gates, quantum logic gates are reversible. However, it is possible to perform classical computing using only reversible gates. For example, the reversible Toffoli gate can implement all Boolean functions, often at the cost of having to use ancillary bits. The Toffoli gate has a direct quantum equivalent, showing that quantum circuits can perform all operations performed by classical circuits.
Quantum logic gates are represented by unitary matrices. The most common quantum gates operate on spaces of one or two qubits, just like the common classical logic gates operate on one or two bits. As matrices, quantum gates can be described by sized unitary matrices, where is the number of qubits that the gate act on. The variables that the gates act upon, the quantum states, are vectors in complex dimensions, where again is the number of qubits of the variable: The base vectors are the possible outcomes if measured, and a quantum state is a linear combination of these outcomes.
Quantum gates are usually represented as matrices. A gate which acts on k qubits is represented by a 2k x 2k unitary matrix. The number of qubits in the input and output of the gate have to be equal. The action of the gate on a specific quantum state is found by multiplying the vector which represents the state by the matrix representing the gate. In the following, the vector representation of a single qubit is:
and the vector representation of two qubits is:
where is the basis vector representing a state where the first qubit is in the state and the second qubit in the state .
The Hadamard gate acts on a single qubit. It maps the basis state to and to , which means that a measurement will have equal probabilities to become 1 or 0 (i.e. creates a superposition). It represents a rotation of about the axis . Equivalently, it is the combination of two rotations, about the X-axis followed by about the Y-axis. It is represented by the Hadamard matrix:
The hadamard gate is the one-qubit version of the quantum fourier transform.
Since where I is the identity matrix, H is indeed a unitary matrix.
The Pauli-X gate acts on a single qubit. It is the quantum equivalent of the NOT gate for classical computers (with respect to the standard basis , , which privileges[clarification needed] the Z-direction) . It equates to a rotation of the Bloch sphere around the X-axis by radians. It maps to and to . Due to this nature, it is sometimes called bit-flip. It is represented by the Pauli matrix:
The Pauli-Y gate acts on a single qubit. It equates to a rotation around the Y-axis of the Bloch sphere by radians. It maps to and to . It is represented by the Pauli Y matrix:
The Pauli-Z gate acts on a single qubit. It equates to a rotation around the Z-axis of the Bloch sphere by radians. Thus, it is a special case of a phase shift gate (which are described in a next subsection) with . It leaves the basis state unchanged and maps to . Due to this nature, it is sometimes called phase-flip. It is represented by the Pauli Z matrix:
Note the square roots of the identity matrix
The NOT gate acts on a single qubit.
.?., so this gate is a square root of the NOT gate.
Similar squared root-gates can be constructed for all other gates by finding the unitary matrix that, multiplied by itself, yields the gate one wishes to construct the squared root gate of. All rational exponents of all gates can be created in this way. (Only approximations of irrational exponents are possible to synthesize from composite gates whose elements are not themselves irrational, since exact synthesis would result in infinite gate depth.)
This is a family of single-qubit gates that leave the basis state unchanged and map to . The probability of measuring a or is unchanged after applying this gate, however it modifies the phase of the quantum state. This is equivalent to tracing a horizontal circle (a line of latitude) on the Bloch sphere by radians.
where is the phase shift. Some common examples are the gate (commonly written as T) where , the phase gate (written S, though S is sometimes used for SWAP gates) where and the Pauli-Z gate where .
The swap gate swaps two qubits. With respect to the basis , , , , it is represented by the matrix:
The sqrt(swap) gate performs half-way of a two-qubit swap. It is universal such that any quantum many qubit gate can be constructed from only sqrt(swap) and single qubit gates. The sqrt(swap) gate is not, however maximally entangling, more than one application of it is required to produce a bell state from product states.
Controlled gates act on 2 or more qubits, where one or more qubits act as a control for some operation. For example, the controlled NOT gate (or CNOT or cX) acts on 2 qubits, and performs the NOT operation on the second qubit only when the first qubit is , and otherwise leaves it unchanged. It is represented by the matrix
More generally if U is a gate that operates on single qubits with matrix representation
then the controlled-U gate is a gate that operates on two qubits in such a way that the first qubit serves as a control. It maps the basis states as follows.
The matrix representing the controlled U is
The CNOT gate is generally used in quantum computing to generate entangled states.
The Toffoli gate, also CCNOT gate or Deutsch gate, is a 3-bit gate, which is universal for classical computation. The quantum Toffoli gate is the same gate, defined for 3 qubits. If the first two bits are in the state , it applies a Pauli-X (or NOT) on the third bit, else it does nothing. It is an example of a controlled gate. Since it is the quantum analog of a classical gate, it is completely specified by its truth table. The Toffoli gate is universal when combined with the single qubit Hadamard gate.
|Truth table||Matrix form|
It can be also described as the gate which maps to .
The Fredkin gate (also CSWAP or cS gate) is a 3-bit gate that performs a controlled swap. It is universal for classical computation. It has the useful property that the numbers of 0s and 1s are conserved throughout, which in the billiard ball model means the same number of balls are output as input.
|Truth table||Matrix form|
Deutsch (or ) gate is a three-qubit gate. It is defined as
Unfortunately, a working Deutsch gate has remained out of reach, due to lack of a protocol. However, a method was proposed to realize such a Deutsh gate with dipole-dipole interaction in neutral atoms.
Informally, a set of universal quantum gates is any set of gates to which any operation possible on a quantum computer can be reduced, that is, any other unitary operation can be expressed as a finite sequence of gates from the set. Technically, this is impossible since the number of possible quantum gates is uncountable, whereas the number of finite sequences from a finite set is countable. To solve this problem, we only require that any quantum operation can be approximated by a sequence of gates from this finite set. Moreover, for unitaries on a constant number of qubits, the Solovay-Kitaev theorem guarantees that this can be done efficiently.
One simple set of two-qubit universal quantum gates is the Hadamard gate , the gate , and the controlled-NOT gate .
Another set of universal quantum gates consists of the Ising gate and the phase-shift gate. These are the set of gates natively available in some trapped-ion quantum computers.
Measurement is irreversible and therefore not a quantum gate, because it assigns the observed variable to a singular value. Measurement takes a quantum state and projects it to one of the base vectors, with a likelihood equal to the square of the vectors depth along that base vector. This is a non-reversible operation as it sets the quantum state equal to the base vector that represents the measured state (the state "collapses" to a definite singular value). Why and how this is so is called the measurement problem.
If two different quantum registers are entangled (they cannot be expressed as a tensor product), measurement of one register affects or reveals the state of the other register by partially or entirely collapsing its state too. An example of such a linearly inseparable state is the EPR pair, which can be constructed with the CNOT and the Hadamard gates (described above). This effect is used in many algorithms: if two variables A and B are maximally entangled (the bell state is the simplest example of this), a function F is applied to A such that A is updated to the value of F(A), followed by measurement of A, then B will, when measured, be a value such that F(B) = A. This way, measurement of one register can be used to assign properties to some other registers. This type of value-assignment in theory occurs instantaneously over any distance and this has as of 2018 been experimentally verified for distances of up to 1200 kilometers. That the phenomena appears to violate the speed of light is called the EPR paradox and it is an open question in physics how to resolve this. Originally it was solved by giving up the assumption of local realism, but other interpretations have also emerged. For more information see the Bell test experiments.
If two or more qubits are viewed as a single quantum state, this combined state is equal to the tensor product of the constituent qubits. An entangled state is any state that can not be tensor-factorized (the state can not be separated into its constituent qubits). The CNOT, Ising and Toffoli gates are examples of gates that act on states constructed of multiple qubits.
The tensor product of two n-qubit quantum gates generates the gate that is equal to the two gates in parallel. This gate will act on qubits. For example, the gate is the hadamard gate () applied in parallel on 2 qubits. It can be written as
This "two-qubit parallel hadamard gate" will when applied to, for example, the two-qubit zero-vector () create a quantum state that have equal probability of being observed in any of its four possible outcomes; 00, 01, 10 and 11. We can write this operation as:
Here the amplitude is and the probability is equal to the amplitude squared. The probability to observe any state is the absolute value of the amplitude squared, which in the above example means that there is one in four that we observe any one of the individual four cases. (Remember that amplitudes are complex values, so their squares are not always positive.)
If we have a set of N qubits that are entangled (their combined state can not be tensor-factorized into an expression of the individual qubits) and wish to apply a quantum gate on M < N qubits in the set, we will have to extend the gate to take N qubits. This can be done by combining the gate with an identity matrix such that their tensor product becomes a gate that act on N qubits. The identity matrix () is a representation of the gate that maps every state to itself (i.e., does nothing at all). In a circuit diagram the identity gate or matrix will appear as just a wire.
For example, the hadamard transform () acts on a single qubit, but if we for example feed it the second of the two qubits that constitute the entangled Bell state , we can not write that operation easily. We need to extend the hadamard transform with the do-nothing gate so that we can act on quantum states that span two qubits:
The gate can now be applied to any two-qubit state, entangled or otherwise. The M-gate will leave the first qubit untouched and apply the hadamard transform to the 2nd qubit. If applied to the Bell state in our example, we may write that as:
Because the number of elements in the matrices is , where x is the number of qubits the gates act on, it is intractable to simulate large quantum systems using classical computers. | <urn:uuid:8aed4c76-47d7-4b99-93ca-e14c1c7f44e5> | 3.765625 | 2,699 | Knowledge Article | Science & Tech. | 44.267524 | 95,518,258 |
12 July 2018
Published online 18 January 2018
A climate model that simulates El Niño can help predict droughts in the Arabian Peninsula.
Rainfall and droughts in the Arabian Peninsula are linked to the global climate phenomenon known as the El Niño Southern Oscillation (ENSO), reports a study published in the journal npj Climate and Atmosphere Science, a collaboration between Nature Partner Journals and King Abdulaziz University (KAU) in Saudi Arabia. A climate model adapted by KAU, which simulates the ENSO together with related climate phenomena, was able to reasonably predict rainfall in the region. This could have effects on agricultural sustainability.1
Global climate is affected by changing weather patterns in the Pacific Ocean. Normally, trade winds moving from the eastern Pacific push warm surface waters westwards. Some years, however, these trade winds weaken, causing the warm surface waters to spread eastwards toward the coasts of Central and South America.
This phenomenon, known as El Niño, affects the climate by shifting cloud and rainfall eastwards. Eventually, the Pacific trade winds pick up again, sometimes becoming stronger than normal, pushing warm water and its connected weather system toward Asia. This phase of ENSO is called La Niña.
“ENSO tends to control the seasonal rainfall variability and predictability in many regions around the globe,” says KAU climatologist Muhammad Abid. “However, the Arabian Peninsula is not much explored in the climate community.”
Abid and colleagues at KAU’s Center of Excellence for Climate Change Research on Saudi Arabia’s west coast in Jeddah compared observational data and climate simulations of summer rainfall over the Arabian Peninsula for the period from 1981 to 2015.
They found that El Niño affected 71% of drought years in the southern and southwestern parts of the Arabian Peninsula, while La Niña was linked to 38% of this area’s flood years.
Also, KAU’s Atmospheric Global Climate Model, adapted from a model developed by Seoul National University, was able to reasonably predict rainfall in the region. The model, which simulates ENSO weather patterns, had 65% higher predictability for the region’s rainfall during El Niño years compared to La Niña years, meaning that it is better at predicting dry conditions in the region than wetter ones. This may help in the management of regional water resources so that local agriculture is not markedly affected during droughts, Abid explains. But models are mathematical tools, says Abid, whose predictions can never be fully accurate. This could give rise to false alarms, he says. The KAU team hopes to improve their model and to explore what other factors affect rainfall in the Arabian Peninsula.
Climate and earth modeling experts Georgiy Stenchikov and Ibrahim Hoteit from Saudi Arabia’s King Abdullah University of Science and Technology, who were not involved in the study, say the results demonstrate that KAU’s Atmospheric Global Climate Model shows potential for predicting rainfall in the region.
Although it is not surprising that ENSO affects precipitation over the Arabian Peninsula, its apparently strong effect is, says Stenchikov. This could partly be due to the study’s focus on a specific area that is responsive to ENSO. The model could also be exaggerating this link, he says.
Hoteit adds that additional information on the study’s experimental setup would have been useful, such as demonstrating that the model can reproduce realistic ENSO events.
The model’s relatively low resolution also means it will probably be able to resolve large-scale phenomena, such as the large belt of low pressure that extends from Africa to the Indian monsoon region and appears in the southwestern Arabian Peninsula; but will not be able to resolve some regional phenomena that may also contribute to summer rainfall in the region, such as the Tokar Jet: strong summer winds that blow from Africa through a gap in the mountain range lining the west coast of the Red Sea, Hoteit says.
- Abid, M. A. et al. ENSO relationship to summer rainfall variability and its potential predictability over Arabian Peninsula region. NPJ Clim. Atmos. Sci. https://dx.doi.org/10.1038/s41612-017-0003-7 (2018). | <urn:uuid:53555521-2738-4668-a60b-f94b68ce5e67> | 3.5 | 893 | Truncated | Science & Tech. | 36.097126 | 95,518,260 |
Scientists have discovered a monstrous black hole about 13 billion light-years away from Earth, and it is the largest they have ever seen, a new study says.
Scientists may have finally solved the mysterious origin of matter in the Universe, something that had puzzled physicists for many years, according to a new study.
Dark matter may have been responsible for the comet strike that killed off the dinosaurs 66 million years ago, as well as other mass extinction events and geologic upheavals, according to one scientist.
Scientists have re-discovered the famous Higgs boson, the "God particle" believed to be responsible for all the mass in the Universe, using superconductors, researchers announced Thursday.
New technology involved in creating Christopher Nolan's epic Interstellar is shedding light on the powerful effects of real life black holes and paving the way for astrophysics research, a new study explains.
The oldest stars in the sky aren't so old after all. They actually lit up the Universe more than 100 million years later than scientists previously thought, according to a new study.
Back in March, scientists operating the telescope BICEP2 announced that they may have found proof of the Big Bang that created the Universe, while others claimed that their findings could just as well be explained by light scattering off dust between the stars in the Milky Way. And now, new research has confirmed that dust has foiled their "breakthrough" discovery.
A number of holidays are nearly upon us, and you neighborhood is likely looking a lot brighter at night. Little did you know that up above, the Universe has brightened as well. That's because a pair of Galaxies about 130 million light years away just had a get-together, producing some of the most concentrated super-bright X-ray light emissions ever seen.
Construction of the European Extremely Large Telescope (E-ELT) has been given the green light, meaning this "eye of the sky" is a mere 10 years away from peering into the Universe and revealing all its wonders.
New analyses of a primitive meteorite's magnetic fields, frozen within the space rock's grains, are helping to shed light on the solar system's birth and how it has evolved over time, a new study describes.
Last year, a series of sounding rockets were launched to better asses all the light in the known Universe. Based on the resulting data, experts have now determined that there is a lot more infrared light between galaxies than we can account for, leaving astronomers wondering "so where did it all come from?"
Using a novel technique to create a high-resolution map, scientists can now view the adolescent Universe in 3-D, new research describes.
Using a telescope high in Chile's Atacama desert, a group of scientists operating under the POLARBEAR project have made the most accurate measurement yet of cosmic microwave polarization, offering clues about the origins of the Universe, new research describes.
Scientists are focusing on large, star-forming galaxies, whose radiation leaks are shedding light on the beginnings of the Universe as the first stars came into existence, new research says. | <urn:uuid:219a5fd9-9697-4060-8d0e-bcc31173567c> | 3.28125 | 632 | Content Listing | Science & Tech. | 36.82209 | 95,518,265 |
Genome researchers from Bielefeld University’s Center for Biotechnology (CeBiTec) headed by Professor Dr. Alfred Pühler have succeeded in sequencing the genome of the Chinese hamster.
The genome sequencing started with the Chinese hamster (picture). Photo: Bielefeld University. Photo: Kerstin Molthagen
The Chinese hamster supplies the cell cultures used by the pharmaceutical industry to produce biopharmaceutical products such as antibodies used in medicine. This costly project was only possible thanks to a cooperation between Bielefeld University and its international project partners. The researchers have now published their results in the internationally renowned scientific journal ‘Nature Biotechnology‘.
To carry out this project, the CeBiTec research team cooperated with the University of Natural Resources and Life Sciences in Vienna (where the project was headed by Professor Dr. Nicole Borth), the Austrian Centre of Industrial Biotechnology (acib), and two pharmaceutical companies: Novartis (in Switzerland) and Pfizer (in the USA).
Professor Dr. Thomas Noll, Scientific Director of CeBiTec, is confident that the data they have obtained will be of great interest to science and industry. ‘In future, the decoded hamster genome will greatly advance the use of cell lines to produce pharmaceuticals’, says Noll, who runs the Cell Culture Technology research group at the Faculty of Technology and participated in the research project.
The genome of the Chinese hamster is composed of eleven pairs of chromosomes. Decoding such a large genome calls for the generation of large datasets that then have to be processed with bioinformatics. To facilitate the resulting data analysis, the researchers in Bielefeld and their colleagues in this project applied a completely new procedure that sorts the single chromosomes of the genome. The sequencing of the hamster chromosomes was performed by Dr. Karina Brinkrolf at CeBiTec. More than 1.4 billion short DNA sequences were generated with the help of modern instruments for next-generation sequencing. ‘The major challenge in this project was subsequently piecing these short DNA sequences together to form single total sequences of chromosomes’, explains the head of the project Professor Alfred Pühler. This work can only be done with powerful computers. ‘We had to complete the new CeBiTec computer cluster and apply new software before we could determine the genome sequence’, says the bioinformatics expert Dr. Alexander Goesmann who also worked on the project. ‘By decoding the hamster genome sequence’, notes Goesmann, ‘bioinformatics at Bielefeld University has broken new ground.’ With approximately 2.3 billion bases, the magnitude of the genome sequence of the Chinese hamster is comparable to that of the human genome.
The head of the project Alfred Pühler views this research as a milestone in the work at CeBiTec: ‘The decoding of the hamster genome successfully concludes a major CeBiTec project. The hamster sequence is available in the public domain and can be used for research throughout the world.’ The project greatly enhances the status of Bielefeld as a basis for current research on the cell cultures of the Chinese hamster, says Pühler. A further project has already been agreed with the University of Natural Resources and Life Sciences in Vienna and the Austrian Center of Industrial Biotechnology. ‘This places Bielefeld University in a good position to carry on contributing to this highly competitive field of research.’
Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides
16.07.2018 | Tokyo Institute of Technology
The secret sulfate code that lets the bad Tau in
16.07.2018 | American Society for Biochemistry and Molecular Biology
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
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Professor George Eleftheriades and PhD student Michael Selvanayagam have designed and tested a new approach to cloaking—by surrounding an object with small antennas that collectively radiate an electromagnetic field.
The radiated field cancels out any waves scattering off the cloaked object. Their paper ‘Experimental demonstration of active electromagnetic cloaking’ appears today in the journal Physical Review X.
“We’ve taken an electrical engineering approach, but that’s what we are excited about,” says Eleftheriades. “It’s very practical.”
Picture a mailbox sitting on the street. When light hits the mailbox and bounces back into your eyes, you see the mailbox. When radio waves hit the mailbox and bounce back to your radar detector, you detect the mailbox. Eleftheriades and Selvanyagam’s system wraps the mailbox in a layer of tiny antennas that radiate a field away from the box, cancelling out any waves that would bounce back. In this way, the mailbox becomes undetectable to radar.
“We’ve demonstrated a different way of doing it,” says Eleftheriades. “It’s very simple: instead of surrounding what you’re trying to cloak with a thick metamaterial shell, we surround it with one layer of tiny antennas, and this layer radiates back a field that cancels the reflections from the object.”
Their experimental demonstration effectively cloaked a metal cylinder from radio waves using one layer of loop antennas. The system can be scaled up to cloak larger objects using more loops, and Eleftheriades says the loops could become printed and flat, like a blanket or skin. Currently the antenna loops must be manually attuned to the electromagnetic frequency they need to cancel, but in future they could function both as sensors and active antennas, adjusting to different waves in real time, much like the technology behind noise-cancelling headphones.
Work on developing a functional invisibility cloak began around 2006, but early systems were necessarily large and clunky—if you wanted to cloak a car, for example, in practice you would have to completely envelop the vehicle in many layers of metamaterials in order to effectively “shield” it from electromagnetic radiation. The sheer size and inflexibility of the approach makes it impractical for real-world uses. Earlier attempts to make thin cloaks were not adaptive and active, and could work only for specific small objects.
Beyond obvious applications, such as hiding military vehicles or conducting surveillance operations, this cloaking technology could eliminate obstacles—for example, structures interrupting signals from cellular base stations could be cloaked to allow signals to pass by freely. The system can also alter the signature of a cloaked object, making it appear bigger, smaller, or even shifting it in space. And though their tests showed the cloaking system works with radio waves, re-tuning it to work with Terahertz (T-rays) or light waves could use the same principle as the necessary antenna technology matures.
“There are more applications for radio than for light,” says Eleftheriades. “It’s just a matter of technology—you can use the same principle for light, and the corresponding antenna technology is a very hot area of research.”
For more information, contact:Marit Mitchell
Marit Mitchell | EurekAlert!
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
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Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
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It’s September, the month when monarch butterflies are at their peak in the Pacific Northwest.
These are western monarchs, not the eastern monarchs that spend their winters in Mexico. Western monarchs breed in Washington, Oregon, Idaho, and eight other states and then migrate to their winter home in California.
New research shows these monarchs are disappearing even faster than their eastern cousins. Scientists are trying to figure out why. | <urn:uuid:5f855355-1d27-43ab-baf3-7bd8cf66e108> | 3.125 | 88 | News Article | Science & Tech. | 48.805 | 95,518,280 |
Can I ask what is up with the moons today? First we've got Pluto's four little scamps tumbling about like a bunch of circus monkeys. Now, word is that Mars' moon Phobos is falling to pieces. Our Moon better not get any ideas!
Phobos' unfortunate fate is but the latest cosmic upheaval announced today at the annual Meeting of the Division of Planetary Sciences. New modelling work indicates that the shallow grooves lining Phobos' surface — once thought to be impact fractures — are actually planetary stretch marks caused by the gravitational tug of Mars. They're the early signs of a structural failure that will eventually (in 30 to 50 million years or so) yank the miserable Martian satellite apart.
"We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," said NASA astronomer Terry Hurford.
Worse, astronomers now think the moon's interior is nothing more than a bunch of space rubble, packaged under a 100 metre-thick pile of powdery regolith. So if and when Phobos does crack open, our future Martian descendants can expect a real nasty dust storm punctuated by hot falling chunks of garbage moon. Excited to live on the Red Planet yet?
Top: Phobos, I'm sorry for you. Image Credit: Wikimedia | <urn:uuid:024e4313-aec2-40bd-b750-a7adee826f98> | 2.765625 | 272 | News Article | Science & Tech. | 52.482121 | 95,518,312 |
These black holes are at the centers of two galaxies more than 300 million light years from Earth, and may be the dark remnants of some of the very bright galaxies, called quasars, that populated the early universe.
“In the early universe, there were lots of quasars or active galactic nuclei, and some were expected to be powered by black holes as big as 10 billion solar masses or more,” said Chung-Pei Ma, UC Berkeley professor of astronomy. “These two new supermassive black holes are similar in mass to young quasars, and may be the missing link between quasars and the supermassive black holes we see today.”
Black holes are dense concentrations of matter that produce such strong gravitational fields that even light cannot escape. While exploding stars, called supernovas, can leave behind black holes the mass of a single star like the sun, supermassive black holes have presumably grown from the merger of other black holes or by capturing huge numbers of stars and massive amounts of gas.
“These black holes may shed light on how black holes and their surrounding galaxies have nurtured each other since the early universe,” said UC Berkeley graduate student Nicholas McConnell, first author of a paper on the discovery being published in the Dec. 8 issue of the British journal Nature by McConnell, Ma and their colleagues at the university of Toronto, Texas and Michigan, as well as by the National Optical Astronomy Observatory in Arizona.
To date, approximately 63 supermassive black holes have been found sitting in the cores of nearby galaxies. The largest for more than three decades was a 6.3 billion solar mass black hole in the center of the nearby galaxy M87.
One of the newly discovered black holes is 9.7 billion solar masses and located in the elliptical galaxy NGC 3842, the brightest galaxy in the Leo cluster of galaxies, 320 million light years away in the direction of the constellation Leo. The second is as large or larger and sits in the elliptical galaxy NGC 4889, the brightest galaxy in the Coma cluster about 336 million light years from Earth in the direction of the constellation Coma Berenices.
According to McConnell, these black holes have an event horizon – the “abandon all hope” edge from which not even light can escape – that is 200 times the orbit of Earth, or five times the orbit of Pluto. Beyond the event horizon, each black hole has a gravitational influence that would extend over a sphere 4,000 light years across.
“For comparison, these black holes are 2,500 times as massive as the black hole at the center of the Milky Way Galaxy, whose event horizon is one fifth the orbit of Mercury,” McConnell said.
The brightest galaxy in a cluster
These 10 billion solar mass black holes have remained hidden until now, presumably because they are living in quiet retirement, Ma said. During their active quasar days some 10 billion years ago, they cleared out the neighborhood by swallowing vast quantities of gas and dust. The surviving gas became stars that have since orbited peacefully. According to Ma, these monster black holes, and their equally monster galaxies that likely contain a trillion stars, settled into obscurity at the center of galaxy clusters.
Ma, a theoretical astrophysicist, decided to look for these huge black holes in relatively nearby clusters of elliptical galaxies as a result of her computer simulations of galaxy mergers.
Astronomers believe that many, if not all, galaxies have a massive black hole at the center, with the larger galaxies harboring larger black holes. The largest black holes are found in elliptical galaxies, which are thought to result from the merger of two spiral galaxies. Ma found, however, that mergers of elliptical galaxies themselves could produce the largest elliptical galaxies as well as supermassive black holes approaching 10 billion solar masses. These black holes can grow even larger by consuming gas left over from a merger.
“Multiple mergers are one way to build up these behemoths,” Ma said.
To look for these monster black holes, Ma teamed up with observational astronomers, including James Graham, a professor of astronomy at UC Berkeley and the University of Toronto, and Karl Gebhardt, a professor of astronomy at the University of Texas at Austin. Gebhardt had obtained the mass of the previous record holder in galaxy M87.
Using telescopes at the Gemini and Keck observatories in Hawaii and at McDonald Observatory in Texas, McConnell and Ma obtained detailed spectra of the diffuse starlight at the centers of several massive elliptical galaxies, each the brightest galaxy in its cluster. So far, they’ve analyzed the orbital velocities of stars in two galaxies and calculated the central masses to be in the quasar range. Having such huge masses contained within a volume only a few hundred light years across led the astronomers to conclude that the masses were massive black holes.
“If all that mass were in stars, then we would see their light”, Ma said.
Modeling these massive galaxies required use of state-of-the-art supercomputers at the Texas Advanced Computing Center.
“For an astronomer, finding these insatiable black holes is like finally encountering people nine feet tall, whose great height had only been inferred from fossilized bones. How did they grow so large?” Ma said. “This rare find will help us understand whether these black holes had very tall parents or ate a lot of spinach.”
Other coauthors of the Nature paper are Hubble postdoctoral fellow Shelley A. Wright at UC Berkeley and graduate student Jeremy D. Murphy of the University of Texas; Tod R. Lauer of the National Optical Astronomy Observatory; and Douglas O. Richstone of the University of Michigan.
The research was supported by the National Science Foundation, the National Aeronautics and Space Administration and UC Berkeley’s Miller Institute for Basic Research in Science.
Robert Sanders | EurekAlert!
Further reports about: > Astronomy > Astronomy Observatory > Earth's magnetic field > Milky Way > Nature Immunology > black hole > computer simulation > early universe > elliptical galaxies > exploding star > galaxy cluster > gravitational field > massive black hole > optical data > solar masses > supermassive black hole
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
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Physicists have solved a mystery that has puzzled scientists for half a century. They show with the help of powerful microscopes that the distance between graphite oxide layers gradually increases when water molecules are added.
The antibacterial properties of silver-coated textiles are popular in the fields of sport and medicine. A team at Empa has now investigated how different silver coatings behave in the washing machine, and they have discovered something important: textiles with nano-coatings release fewer nanoparticles into the washing water than those with normal coatings.
Physicists have used a scanning tunneling microscope to create quantum dots with identical, deterministic sizes. The perfect reproducibility of these dots opens the door to quantum dot architectures completely free of uncontrolled variations, an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies.
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For his doctoral dissertation in the Goldman Superconductivity Research Group at the University of Minnesota, Yu Chen, now a postdoctoral researcher at UC Santa Barbara, developed a novel way to fabricate superconducting nanocircuitry. However, the extremely small zinc nanowires he designed did some unexpected - and sort of funky - things.
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Using genome sequencing and phylogenetics, researchers have shown that the industrial yeast Pichia kudriavzevii is genetically the same species as Candida krusei.
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Authors: John A. Gowan
Is information destroyed in a black hole? This question is debated in Leonard Susskind's recent book: "The Black Hole War" (Little, Brown, and Co., 2008). From the overview of the "Tetrahedron Model" and Noether's principle of the conservation of symmetry, it appears that information should be destroyed in a black hole. There are several reasons to think so (contrary to the conclusions of Susskind's book). First, on the premise that the universe begins as light, devolves to matter, and finally evolves and resolves to light again, conserving the original perfect symmetry of free electromagnetic energy, information must be destroyed in any physical process which returns matter (and the information which matter contains) to light (because information is an asymmetric state of energy). Such final symmetry-restoring (conserving) reactions and processes include: 1) (actual) matter-antimatter annihilations due to the electromagnetic force; 2) (hypothetical) proton decay due to the strong and weak nuclear forces; 3) (theoretical) "evaporation" of black holes due to "Hawking radiation" (gravitational force); 4) (possible) "Big Crunch" gravitational collapse of the cosmos. (See: "Symmetry Principles of the Unified Field Theory".)
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What is carbon chain? July 6, 2018 WFQ Q10. What is carbon chain? Ans. Carbon atoms often link together like the links of a chain to form very long thin molecules- as in the molecule of propane, which consists of three carbon atoms in a row, with hydrogen atoms attached. | <urn:uuid:ea616fed-d9c9-4c59-977b-ea686708f01b> | 3.015625 | 63 | Q&A Forum | Science & Tech. | 74.861 | 95,518,369 |
Scientists at the Carnegie Institution have discovered concentrations of amino acids in two meteorites that are more than ten times higher than levels previously measured in other similar meteorites. This result suggests that the early solar system was far richer in the organic building blocks of life than scientists had thought, and that fallout from space may have spiked Earth’s primordial broth.
The study, by Marilyn Fogel of Carnegie’s Geophysical Laboratory and Conel Alexander of the Department of Terrestrial Magnetism with Zita Martins of Imperial College London and two colleagues, will be published in Meteoritics and Planetary Science.*
Amino acids are organic molecules that form the backbone of proteins, which in turn build many of the structures and drive many of the chemical reactions inside living cells. The production of proteins is believed to constitute one of the first steps in the emergence of life. Scientists have determined that amino acids could also have formed in some environments on the early Earth, but the presence of these compounds in certain meteorites has led many researchers to look to space as a source.
The meteorites used for the study were collected in Antarctica in 1992 and 1995 and held in the meteorite collection at the NASA Johnson Space Center in Houston, Texas. Antarctica is the world’s richest hunting ground for meteorites, which are naturally concentrated in so-called blue ice regions and held in cold storage by the ice.
For the amino acid study, the researchers took small samples from three meteorites of a rare type called CR chondrites, thought to contain the oldest and the most primitive organic materials found in meteorites. CR chondrites date from the time of the solar system’s formation. During an early phase of their history the meteorites were part of a larger “parent body,” such as an asteroid, which later was shattered by impacts.
The analysis revealed that while one sample showed a relatively low abundance of amino acids, the other two meteorites had the highest ever seen in primitive meteorites—180 and 249 ppm (parts per million). Other primitive meteorites that have been studied generally have amino acid concentrations of 15 ppm or less. Because organic molecules from extra-terrestrial sources have ratios of carbon isotopes different from those of Earthly biological sources, the researchers were able to rule out contamination as a factor in their result.
“The amino acids probably formed within the parent body before it broke up,” says Alexander. “For instance. ammonia and other chemical precursors from the solar nebula, or even the interstellar medium, could have combined in the presence of water to make the amino acids. Then, after the break up, some of the fragments could have showered down onto the Earth and the other terrestrial planets. These same precursors are likely to have been present in other primitive bodies, such as comets, that were also raining material onto the early Earth.”
Conel Alexander | EurekAlert!
New research calculates capacity of North American forests to sequester carbon
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For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
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17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
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Terahertz waves are often used in the checking of passengers and luggage at the airport. They are also in demand in other areas, such as for materials testing in the industry. Physicists at the University of Kaiserslautern (TUK) have now developed a new method for generating such waves. They use a quantum magnetic current flow, so-called spin current, in magnetic metal nanostructures. The cost-effective and material-saving technology has the potential for industry applications. The study was published in the renowned scientific journal "Scientific Reports".
Terahertz (THz) waves lie in the electromagnetic spectrum between microwaves and infrared radiation. They are invisible to the human eye. Since they are low in energy, there is no need for be concerned with their impact on human.
Today, they play a role in medical and communications technology, but also in materials testing. For example, they were used to inspect the plastic insulation on space shuttle. However, powerful radiation sources, i.e. emitters, are needed to generate the waves. This is usually associated with high energy consumption and costs.
A very efficient and at the same time more cost-effective method has now been developed by Kaiserslautern researchers, in which they use a so-called spin current. This is analogous to the electric current, in which electrical charges, namely electrons, flow.
"A spin describes the intrinsic angular momentum of a quasiparticle, such as an electron," says Associate Professor Dr. Evangelos Papaioannou, who is a researcher with his own sub-group in the Magnetism Research Group lead by Professor Burkard Hillebrands in Department of Physics at TUK. "It forms the basis for all magnetic phenomena. Simply said, an electron rotates left or right around its axis like a spinning top."
A special nanostructure has been developed by the research team of Papaioannou for the application of the technique. "It consists of a metal bilayer of magnetic iron and non-magnetic platinum," as the physicist describes the structure. "These are very thin layers that are only a few nanometers thick."
To generate the terahertz waves, the researchers use a femtosecond laser that emits extremely short laser pulses. As a result, the following happens: "When the laser pulses hit the nanostructure they stimulate the electrons in the iron film, creating a spin current," says the Papaioannou. This current flows into the adjacent platinum layer. Here comes a certain physical phenomenon into play, the inverse Spin-Hall Effect. For platinum, this effect has been known for some time. It arises due to the atomic structure of the metal.
"The atomic nuclei of platinum deflect electrons with a left- and right-handed spin in opposite directions, which leads to the transformation of the spin current into an ultrafast transient charge current, which is then the source of terahertz waves”.
As a special feature of the experimental setup, a small silicon lens is attached to the structure. "We are bundling the waves", the Junior Professor continues. In this way, the terahertz waves could be forwarded easily and efficiently in future applications.
In their recently published paper, the researchers have revealed, among other things, how layer thicknesses and the arrangement of materials must be best designed to produce the THz waves. The research field of THz spintronics technology is an emerging field. Only recently, research colleagues in Berlin showed for the first time that terahertz waves can be generated by spin current.
The work of the Kaiserslautern researchers reveals now a way to optimize the emitters so that they can reach their maximum efficiency. This makes them cheaper and more interesting for various fields of application, for example for security techniques, materials testing and information technologies, but also for basic research.
The team of Papaioannou is a part of the State Research Center for Optics and Material Sciences (OPTIMAS), which is funded by the state of Rhineland-Palatinate. Professor R. Beigang and Dr. G. Torosyan also contributed to the study, both are experts in the field of Terahertz. The work was supported by the Deutsche Forschungsgemeinschaft within the scope of the Collaborative Research Center SPIN + X, as well as the Carl-Zeiss Foundation.
The study was published in the prestigious journal Scientific Reports: "Optimized Spintronic Terahertz Emitters Based on Epitaxial Grown Fe / Pt Layer Structures" DOI: 10.1038 / s41598-018-19432-9
Questions can be directed at:
Juniorprof. Dr. Evangelos Papaioannou
Tel.: +49(0)631 205-4099
Melanie Löw | Technische Universität Kaiserslautern
What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
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Physics made easy is an article that summarizes the life of a lecturer who tough physics in a simple way and made very easy but significant nuclei projects that are easily comprehended even today.
On July 2 1906 in Strasbourg, Alsace-Lorraine, Hans Albrecht Bethe was born. He schooled at the Gymnasium from 1915 to 1924 in Frankfurt. Later he studied at the University of Frankfurt for two years. In July 1928 he took his PhD in theoretical physics at Munich after two and a half years study.
He then became an Instructor in physics at Frankfurt for one semester and at Stuttgart for another semester. Between 1929 and 1933 his head office was at the University of Munich. In May 1930, he became Privatdozet.
Throughout this time he had a travel partnership of the International Education Board to travel to Cambridge, England, in the end of 1930. He also traveled to Rome in the spring terms of 1931 and 1932. In the winter semester of 1932-1933, he was involved in acting; he became the Acting Assistant Professor at the University of Tubingen. He lost the post owing the advent of the Nazi regime in Germany.
Physics Made Easy through Hans simplified teachings all over England
Bethe moved to England in October 1933. Here, he held a short-term place as Lecturer at the University of Manchester for one year. In 1935 February, he was chosen as an Assistant Professor at Cornell University, in U.S.A. afterward he was promoted to be a Professor in 1937.
He has lived in England thereafter except for sabbatical leaves and during World War II. His combat work took him initial to the Radiation Lab at the Massachusetts association of Technology.
He started working on microwave radar, next, he went to Los Alamos Scientific Laboratory .Here he engaged in assembling the first atomic bomb. He returned to Los Alamos for partially in 1952. He spent two of his sabbatical leaves in Columbia University, and Copenhagen.
Physics made easy by Bethe Nuclear Project resolution
Bethe’s major effort was concerned with the hypothesis of atomic nuclei. Collectively with Peierls, he came up with theory of the deuteron in 1934 which he advanced in 1949. He affirmed some contradictions in the nuclear mass scale in 1935.
He studied the hypothesis of nuclear reactions in 1935 up to 1938 He predicted several reaction cross sections.
In association with this work, he came up with Bohr’s theory of the compound nucleus in an added quantitative style. This work and also the current information on nuclear theory and experimental outcome, has been summarized in this article physics made easy
Physics Made Easy Ultimatum
Bethe’s effort on nuclear reactions led to the finding of the reactions which supply the energy in the stars. The most significant nuclear reaction in the luminous stars is the carbon-nitrogen cycle, whereas the sun and fainter stars employ the proton-proton reaction.
He was awarded the Nobel Prize for his work on nuclear reactions in general. This just one of the many whom I have noted and explained extensively on this article. This article; Physics made easy gives credit to Hans Bethe`s since he made comprehensible projects though they are so important to be ignored. | <urn:uuid:ad7e2cb2-7126-4b23-8e24-ab9bb9279dc2> | 3.078125 | 677 | Personal Blog | Science & Tech. | 49.690239 | 95,518,407 |
Friday, 20 July, 2018
Cosmobrain (Popularity: )
Lists the 50 brightest stars visible from Earth, and the 50 closest stars to Earth. Proper names, distances, magnitudes, spectral classification and other data are provided for each star.
Stability Analysis (Popularity: )
Performing stability analysis on a set of ordinary differential equations that govern star formation within a galaxy perturbed by a large influx of hydrogen. Using numerical model simulation to determine ...
SpaceWander Virtual Space Trip! (Popularity: )
Multimedia experience of flying by spaceship through the solar system. Visit each planet. Real space pictures from NASA. In English, French, Italian, Spanish and Russian. Recommended for kids.
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In physics and materials science, the Curie temperature (TC), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism. The Curie temperature is named after Pierre Curie, who showed that magnetism was lost at a critical temperature.
The force of magnetism is determined by the magnetic moment, a dipole moment within an atom which originates from the angular momentum and spin of electrons. Materials have different structures of intrinsic magnetic moments that depend on temperature; the Curie temperature is the critical point at which a material's intrinsic magnetic moments change direction.
Permanent magnetism is caused by the alignment of magnetic moments and induced magnetism is created when disordered magnetic moments are forced to align in an applied magnetic field. For example, the ordered magnetic moments (ferromagnetic, Figure 1) change and become disordered (paramagnetic, Figure 2) at the Curie temperature. Higher temperatures make magnets weaker, as spontaneous magnetism only occurs below the Curie temperature. Magnetic susceptibility above the Curie temperature can be calculated from the Curie–Weiss law, which is derived from Curie's law.
In analogy to ferromagnetic and paramagnetic materials, the Curie temperature can also be used to describe the phase transition between ferroelectricity and paraelectricity. In this context, the order parameter is the electric polarisation that goes from a finite value to zero when the temperature is increased above the Curie temperature.
|Manganese bismuthide (MnBi)||630|
|Manganese antimonide (MnSb)||587|
|Chromium(IV) oxide (CrO2)||386|
|Manganese arsenide (MnAs)||318|
|Europium oxide (EuO)||69|
|Iron(III) oxide (Fe2O3)||948|
|Iron(II,III) oxide (FeOFe2O3)||858|
|Yttrium iron garnet (Y3Fe5O12)||560|
- 1 Magnetic moments
- 2 Materials with magnetic moments that change properties at the Curie temperature
- 3 Curie–Weiss law
- 4 Physics
- 4.1 Approaching Curie temperature from above
- 4.2 Approaching Curie temperature from below
- 4.3 Approaching absolute zero (0 kelvins)
- 4.4 Ising model of phase transitions
- 4.5 Weiss domains and surface and bulk Curie temperatures
- 4.6 Changing a material's Curie temperature
- 5 Curie temperature in ferroelectric materials
- 6 Applications
- 7 See also
- 8 Notes
- 9 References
- 10 External links
Magnetic moments are permanent dipole moments within the atom which are made up from electron's angular momentum and spin, by the relation μl = el/2me (me here is mass of electron),(μl = magnetic moment) and (l is angular momentum) this ratio is called as gyromagnetic ratio.
Electrons inside atoms contribute magnetic moments from their own angular momentum and from their orbital momentum around the nucleus. Magnetic moments from the nucleus are insignificant in contrast to magnetic moments from electrons. Thermal contribution will result in higher energy electrons causing disruption to their order and alignment between dipoles to be destroyed.
Ferromagnetic, paramagnetic, ferrimagnetic and antiferromagnetic materials have different structures of intrinsic magnetic moments. It is at a material's specific Curie temperature where they change properties. The transition from antiferromagnetic to paramagnetic (or vice versa) occurs at the Néel temperature which is analogous to Curie temperature.
|Below TC||Above TC|
Ferromagnetism: The magnetic moments in a ferromagnetic material. The moments are ordered and of the same magnitude in the absence of an applied magnetic field.
Paramagnetism: The magnetic moments in a paramagnetic material. The moments are disordered in the absence of an applied magnetic field and ordered in the presence of an applied magnetic field.
Ferrimagnetism: The magnetic moments in a ferrimagnetic material. The moments are aligned oppositely and have different magnitudes due to being made up of two different ions. This is in the absence of an applied magnetic field.
Antiferromagnetism: The magnetic moments in an antiferromagnetic material. The moments are aligned oppositely and have the same magnitudes. This is in the absence of an applied magnetic field.
Materials with magnetic moments that change properties at the Curie temperature
Ferromagnetic, paramagnetic, ferrimagnetic and antiferromagnetic structures are made up of intrinsic magnetic moments. If all electrons within the structure are paired, these moments cancel out due to having opposite spins and angular momentum. Thus even with an applied magnetic field will have different properties and no Curie temperature.
A material is paramagnetic only above its Curie temperature. Paramagnetic materials are non-magnetic when a magnetic field is absent and magnetic when a magnetic field is applied. When the magnetic field is absent the material has disordered magnetic moments; that is, the atoms are asymmetrical and not aligned. When the magnetic field is present the magnetic moments are temporarily realigned parallel to the applied field; the atoms are symmetrical and aligned. The magnetic moment in the same direction is what causes an induced magnetic field.
For paramagnetism this response to an applied magnetic field is positive and known as magnetic susceptibility. The magnetic susceptibility only applies above the Curie temperature for disordered states.
Sources of paramagnetism (materials which have Curie temperatures) include:
- All atoms which have unpaired electrons;
- Atoms where inner shells are incomplete in electrons;
- Free radicals;
Above the Curie temperature the atoms are excited, the spin orientation becomes randomised, but can be realigned in an applied field, i.e. the material becomes paramagnetic. Below the Curie temperature the intrinsic structure has undergone a phase transition, the atoms are ordered and the material is ferromagnetic. The paramagnetic materials' induced magnetic fields are very weak in comparison to ferromagnetic materials' magnetic fields.
Materials are only ferromagnetic below their corresponding Curie temperatures. Ferromagnetic materials are magnetic in the absence of an applied magnetic field.
When a magnetic field is absent the material has spontaneous magnetization which is a result of the ordered magnetic moments; that is, for ferromagnetism, the atoms are symmetrical and aligned in the same direction creating a permanent magnetic field.
The magnetic interactions are held together by exchange interactions; otherwise thermal disorder would overcome the weak interactions of magnetic moments. The exchange interaction has a zero probability of parallel electrons occupying the same point in time, implying a preferred parallel alignment in the material. The Boltzmann factor contributes heavily as it prefers interacting particles to be aligned in the same direction. This causes ferromagnets to have strong magnetic fields and high Curie temperatures of around 1000 K.
Below the Curie temperature, the atoms are aligned and parallel, causing spontaneous magnetism; the material is ferromagnetic. Above the Curie temperature the material is paramagnetic, as the atoms lose their ordered magnetic moments when the material undergoes a phase transition.
Materials are only ferrimagnetic below their corresponding Curie temperature. Ferrimagnetic materials are magnetic in the absence of an applied magnetic field and are made up of two different ions.
When a magnetic field is absent the material has a spontaneous magnetism which is the result of ordered magnetic moments; that is, for ferrimagnetism one ion's magnetic moments are aligned facing in one direction with certain magnitude and the other ion's magnetic moments are aligned facing in the opposite direction with a different magnitude. As the magnetic moments are of different magnitudes in opposite directions there is still a spontaneous magnetism and a magnetic field is present.
Similar to ferromagnetic materials the magnetic interactions are held together by exchange interactions. The orientations of moments however are anti-parallel which results in a net momentum by subtracting their momentum from one another.
Below the Curie temperature the atoms of each ion are aligned anti-parallel with different momentums causing a spontaneous magnetism; the material is ferrimagnetic. Above the Curie temperature the material is paramagnetic as the atoms lose their ordered magnetic moments as the material undergoes a phase transition.
Antiferromagnetic and the Néel temperature
Materials are only antiferromagetic below their corresponding Néel temperature. This is similar to the Curie temperature as above the Néel Temperature the material undergoes a phase transition and becomes paramagnetic.
The material has equal magnetic moments aligned in opposite directions resulting in a zero magnetic moment and a net magnetism of zero at all temperatures below the Néel temperature. Antiferromagnetic materials are weakly magnetic in the absence or presence of an applied magnetic field.
Similar to ferromagnetic materials the magnetic interactions are held together by exchange interactions preventing thermal disorder from overcoming the weak interactions of magnetic moments. When disorder occurs it is at the Néel temperature.
The Curie–Weiss law is an adapted version of Curie's law.
The Curie–Weiss law is a simple model derived from a mean-field approximation, this means it works well for the materials temperature, T, much greater than their corresponding Curie temperature, TC, i.e. T ≫ TC; however fails to describe the magnetic susceptibility, χ, in the immediate vicinity of the Curie point because of local fluctuations between atoms.
Neither Curie's law nor the Curie–Weiss law holds for T < TC.
Curie's law for a paramagnetic material:
|χ||the magnetic susceptibility; the influence of an applied magnetic field on a material|
|M||the magnetic moments per unit volume|
|H||the macroscopic magnetic field|
|B||the magnetic field|
|C||the material-specific Curie constant|
|µ0||the permeability of free space. Note: in CGS units is taken to equal one.|
|g||the Landé g-factor|
|J(J + 1)||the eigenvalue for eigenstate J2 for the stationary states within the incomplete atoms shells (electrons unpaired)|
|µB||the Bohr Magneton|
|total magnetism||is N number of magnetic moments per unit volume|
The Curie–Weiss law is then derived from Curie's law to be:
For full derivation see Curie–Weiss law.
Approaching Curie temperature from above
As the Curie–Weiss law is an approximation, a more accurate model is needed when the temperature, T, approaches the material's Curie temperature, TC.
Magnetic susceptibility occurs above the Curie temperature.
An accurate model of critical behaviour for magnetic susceptibility with critical exponent γ:
As temperature is inversely proportional to magnetic susceptibility, when T approaches TC the denominator tends to zero and the magnetic susceptibility approaches infinity allowing magnetism to occur. This is a spontaneous magnetism which is a property of ferromagnetic and ferrimagnetic materials.
Approaching Curie temperature from below
Magnetism depends on temperature and spontaneous magnetism occurs below the Curie temperature. An accurate model of critical behaviour for spontaneous magnetism with critical exponent β:
The critical exponent differs between materials and for the mean-field model as taken as β = 1/ where T ≪ TC.
The spontaneous magnetism approaches zero as the temperature increases towards the materials Curie temperature.
Approaching absolute zero (0 kelvins)
The spontaneous magnetism, occurring in ferromagnetic, ferrimagnetic and antiferromagnetic materials, approaches zero as the temperature increases towards the material's Curie temperature. Spontaneous magnetism is at its maximum as the temperature approaches 0 K. That is, the magnetic moments are completely aligned and at their strongest magnitude of magnetism due to no thermal disturbance.
In paramagnetic materials temperature is sufficient to overcome the ordered alignments. As the temperature approaches 0 K, the entropy decreases to zero, that is, the disorder decreases and becomes ordered. This occurs without the presence of an applied magnetic field and obeys the third law of thermodynamics.
Both Curie's law and the Curie–Weiss law fail as the temperature approaches 0 K. This is because they depend on the magnetic susceptibility which only applies when the state is disordered.
Ising model of phase transitions
The Ising model is mathematically based and can analyse the critical points of phase transitions in ferromagnetic order due to spins of electrons having magnitudes of ±1/. The spins interact with their neighbouring dipole electrons in the structure and here the Ising model can predict their behaviour with each other.
This model is important for solving and understanding the concepts of phase transitions and hence solving the Curie temperature. As a result, many different dependencies that affect the Curie temperature can be analysed.
For example, the surface and bulk properties depend on the alignment and magnitude of spins and the Ising model can determine the effects of magnetism in this system.
Weiss domains and surface and bulk Curie temperatures
Materials structures consist of intrinsic magnetic moments which are separated into domains called Weiss domains. This can result in ferromagnetic materials having no spontaneous magnetism as domains could potentially balance each other out. The position of particles can therefore have different orientations around the surface than the main part (bulk) of the material. This property directly affects the Curie temperature as there can be a bulk Curie temperature TB and a different surface Curie temperature TS for a material.
This allows for the surface Curie temperature to be ferromagnetic above the bulk Curie temperature when the main state is disordered, i.e. Ordered and disordered states occur simultaneously.
The surface and bulk properties can be predicted by the Ising model and electron capture spectroscopy can be used to detect the electron spins and hence the magnetic moments on the surface of the material. An average total magnetism is taken from the bulk and surface temperatures to calculate the Curie temperature from the material, noting the bulk contributes more.
The angular momentum of an electron is either +ħ/ or −ħ/ due to it having a spin of 1/, which gives a specific size of magnetic moment to the electron; the Bohr magneton. Electrons orbiting around the nucleus in a current loop create a magnetic field which depends on the Bohr Magneton and magnetic quantum number. Therefore, the magnetic moments are related between angular and orbital momentum and affect each other. Angular momentum contributes twice as much to magnetic moments than orbital.
For terbium which is a rare-earth metal and has a high orbital angular momentum the magnetic moment is strong enough to affect the order above its bulk temperatures. It is said to have a high anisotropy on the surface, that is it is highly directed in one orientation. It remains ferromagnetic on its surface above its Curie temperature while its bulk becomes ferrimagnetic and then at higher temperatures its surface remains ferrimagnetic above its bulk Néel Temperature before becoming completely disordered and paramagnetic with increasing temperature. The anisotropy in the bulk is different from its surface anisotropy just above these phase changes as the magnetic moments will be ordered differently or ordered in paramagnetic materials.
Changing a material's Curie temperature
Composite materials, that is, materials composed from other materials with different properties, can change the Curie temperature. For example, a composite which has silver in it can create spaces for oxygen molecules in bonding which decreases the Curie temperature as the crystal lattice will not be as compact.
The alignment of magnetic moments in the composite material affects the Curie temperature. If the materials moments are parallel with each other the Curie temperature will increase and if perpendicular the Curie temperature will decrease as either more or less thermal energy will be needed to destroy the alignments.
Preparing composite materials through different temperatures can result in different final compositions which will have different Curie temperatures. Doping a material can also affect its Curie temperature.
The density of nanocomposite materials changes the Curie temperature. Nanocomposites are compact structures on a nano-scale. The structure is built up of high and low bulk Curie temperatures, however will only have one mean-field Curie temperature. A higher density of lower bulk temperatures results in a lower mean-field Curie temperature and a higher density of higher bulk temperature significantly increases the mean-field Curie temperature. In more than one dimension the Curie temperature begins to increase as the magnetic moments will need more thermal energy to overcome the ordered structure.
The size of particles in a material's crystal lattice changes the Curie temperature. Due to the small size of particles (nanoparticles) the fluctuations of electron spins become more prominent, this results in the Curie temperature drastically decreasing when the size of particles decrease as the fluctuations cause disorder. The size of a particle also affects the anisotropy causing alignment to become less stable and thus lead to disorder in magnetic moments.
The extreme of this is superparamagnetism which only occurs in small ferromagnetic particles and is where fluctuations are very influential causing magnetic moments to change direction randomly and thus create disorder.
The Curie temperature of nanoparticles are also affected by the crystal lattice structure, body-centred cubic (bcc), face-centred cubic (fcc) and a hexagonal structure (hcp) all have different Curie temperatures due to magnetic moments reacting to their neighbouring electron spins. fcc and hcp have tighter structures and as a results have higher Curie temperatures than bcc as the magnetic moments have stronger effects when closer together. This is known as the coordination number which is the number of nearest neighbouring particles in a structure. This indicates a lower coordination number at the surface of a material than the bulk which leads to the surface becoming less significant when the temperature is approaching the Curie temperature. In smaller systems the coordination number for the surface is more significant and the magnetic moments have a stronger affect on the system.
Although fluctuations in particles can be minuscule, they are heavily dependent on the structure of crystal lattices as they react with their nearest neighbouring particles. Fluctuations are also affected by the exchange interaction as parallel facing magnetic moments are favoured and therefore have less disturbance and disorder, therefore a tighter structure influences a stronger magnetism and therefore a higher Curie temperature.
Pressure changes a material's Curie temperature. Increasing pressure on the crystal lattice decreases the volume of the system. Pressure directly affects the kinetic energy in particles as movement increases causing the vibrations to disrupt the order of magnetic moments. This is similar to temperature as it also increases the kinetic energy of particles and destroys the order of magnetic moments and magnetism.
Pressure also affects the density of states (DOS). Here the DOS decreases causing the number of electrons available to the system to decrease. This leads to the number of magnetic moments decreasing as they depend on electron spins. It would be expected because of this that the Curie temperature would decrease however it increases. This is the result of the exchange interaction. The exchange interaction favours the aligned parallel magnetic moments due to electrons being unable to occupy the same space in time and as this is increased due to the volume decreasing the Curie temperature increases with pressure. The Curie temperature is made up of a combination of dependencies on kinetic energy and the DOS.
It is interesting to note that the concentration of particles also affects the Curie temperature when pressure is being applied and can result in a decrease in Curie temperature when the concentration is above a certain percent.
Orbital ordering changes the Curie temperature of a material. Orbital ordering can be controlled through applied strains. This is a function that determines the wave of a single electron or paired electrons inside the material. Having control over the probability of where the electron will be allows the Curie temperature to be altered. For example, the delocalised electrons can be moved onto the same plane by applied strains within the crystal lattice.
The Curie temperature is seen to increase greatly due to electrons being packed together in the same plane, they are forced to align due to the exchange interaction and thus increases the strength of the magnetic moments which prevents thermal disorder at lower temperatures.
Curie temperature in ferroelectric materials
T0 is the temperature where ferroelectric materials lose their spontaneous polarisation as a first or second order phase change occurs, that is the internal structure changes or the internal symmetry changes. In certain cases T0 is equal to the Curie temperature however the Curie temperature can be 10 kelvins lower than T0.
|Below T0||Above T0|
|Ferroelectric||↔ Dielectric (paraelectric)|
Ferroelectric and dielectric
Materials are only ferroelectric below their corresponding transition temperature T0. Ferroelectric materials are all pyroelectric and therefore have a spontaneous electric polarisation as the structures are unsymmetrical.
Ferroelectric materials' polarization is subject to hysteresis (Figure 4); that is they are dependent on their past state as well as their current state. As an electric field is applied the dipoles are forced to align and polarisation is created, when the electric field is removed polarisation remains. The hysteresis loop depends on temperature and as a result as the temperature is increased and reaches T0 the two curves become one curve as shown in the dielectric polarisation (Figure 5).
A heat-induced ferromagnetic-paramagnetic transition is used in magneto-optical storage media, for erasing and writing of new data. Famous examples include the Sony Minidisc format, as well as the now-obsolete CD-MO format. Curie point electro-magnets have been proposed and tested for actuation mechanisms in passive safety systems of fast breeder reactors, where control rods are dropped into the reactor core if the actuation mechanism heats up beyond the material's curie point. Other uses include temperature control in soldering irons, and stabilizing the magnetic field of tachometer generators against temperature variation.
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Scientists find 'world's oldest' biological colours
Australian researchers have uncovered the world's oldest biological colour in the Sahara desert, in a find they said Tuesday helped explain why complex lifeforms only recently emerged on earth.
The pink pigments were produced by simple microscopic organisms called cyanobacteria more than 1.1 billion years ago, some 500 million years older than previous colour pigment discoveries.
That makes the samples around fifteen times older than the Tyrannosaurus Rex dinosaur species, according to senior Australian National University researcher Jochen Brocks.
Earth itself is about 4.5 billion years old and researchers said the latest find shed light on why more sophisticated plant and animal life only came into existence 600 million years ago.
Previous research argued that low oxygen levels in the atmosphere held back the evolution of complicated lifeforms, but the discovery of cyanobacteria at such an early date suggests that the organisms crowded out more plentiful food sources such as algae.
Algae, although still microscopic, are a thousand times larger in volume than cyanobacteria, and are a much richer food source, Brocks told AFP.
The cyanobacterial oceans started to vanish about 650 million years ago, when algae began to rapidly spread to provide the burst of energy needed for the evolution of complex ecosystems, where large animals, including humans, could thrive on Earth.
Scientists came across the samples accidently when an oil company drilling in the Taoudeni basin in West Africa sent them rocks for analysis.
The pigments are fossilised relics of chlorophyll, a chemical that allows plants and some microscopic lifeforms to turn light into energy.
Researchers said the pink pigment they discovered would have originally appeared blue-green to the human eye.
The findings were published Tuesday in the journal Proceedings of the National Academy of Sciences.
(2018/07/11 12:17)Click Here for Japanese Translation
AFP-JIJI PRESS NEWS JOURNAL
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- 07/09 12:46 Twitter rooting out fake accounts at record rate-- report
- 07/09 12:43 S. Korea women protest 'spycam porn' in mass rally
- 07/09 12:36 Nadal won't rule out doubles dream team with Federer
- 07/09 12:27 Swedish intellectuals form new literature prize in Nobel protest
- 07/09 12:20 Justin Bieber engaged to model Baldwin-- reports | <urn:uuid:9c43a07b-06c3-42f5-91ca-da44644d02ee> | 3.84375 | 953 | News Article | Science & Tech. | 35.677008 | 95,518,495 |
De Rham cohomology
In mathematics, de Rham cohomology (after Georges de Rham) is a tool belonging both to algebraic topology and to differential topology, capable of expressing basic topological information about smooth manifolds in a form particularly adapted to computation and the concrete representation of cohomology classes. It is a cohomology theory based on the existence of differential forms with prescribed properties.
The integration on forms concept is of fundamental importance in differential topology, geometry, and physics, and also yields one of the most important examples of cohomology, namely de Rham cohomology, which (roughly speaking) measures precisely the extent to which the fundamental theorem of calculus fails in higher dimensions and on general manifolds. — Terence Tao, Differential Forms and Integration
where Ω0(M) is the space of smooth functions on M, Ω1(M) is the space of 1-forms, and so forth. Forms which are the image of other forms under the exterior derivative, plus the constant 0 function in Ω0(M) are called exact and forms whose exterior derivative is 0 are called closed (see closed and exact differential forms); the relationship d 2 = 0 then says that exact forms are closed.
The converse, however, is not in general true; closed forms need not be exact. A simple but significant case is the 1-form of angle measure on the unit circle, written conventionally as dθ (described at closed and exact differential forms). There is no actual function θ defined on the whole circle of which dθ is the derivative; the increment of 2π in going once round the circle in the positive direction means that we can't take a single-valued θ. We can, however, change the topology by removing just one point.
The idea of de Rham cohomology is to classify the different types of closed forms on a manifold. One performs this classification by saying that two closed forms α, β ∈ Ωk(M) are cohomologous if they differ by an exact form, that is, if α − β is exact. This classification induces an equivalence relation on the space of closed forms in Ωk(M). One then defines the k-th de Rham cohomology group to be the set of equivalence classes, that is, the set of closed forms in Ωk(M) modulo the exact forms.
Note that, for any manifold M with n connected components
This follows from the fact that any smooth function on M with zero derivative (i.e. locally constant) is constant on each of the connected components of M.
De Rham cohomology computed
One may often find the general de Rham cohomologies of a manifold using the above fact about the zero cohomology and a Mayer–Vietoris sequence. Another useful fact is that the de Rham cohomology is a homotopy invariant. While the computation is not given, the following are the computed de Rham cohomologies for some common topological objects:
For the n-sphere, Sn, and also when taken together with a product of open intervals, we have the following. Let n > 0, m ≥ 0, and I be an open real interval. Then
Similarly, allowing n > 0 here, we obtain
We can also find explicit generators for the de Rham cohomology of the torus directly using differential forms. Given a quotient manifold and a differential form we can say that is -invariant if given any diffeomorphism induced by , we can . In particular, the pullback of any form on is -invariant. Also, the pullback is an injective morphism. In our case of the differential forms are -invariant since . But, notice that for is not an invariant -form. This with injectivity implies that
Since the cohomology ring of a torus is generated by , taking the wedge products of these forms give all of the explicit representatives for the de Rham cohomology of a torus.
Punctured Euclidean space
Punctured Euclidean space is simply Euclidean space with the origin removed.
The Möbius strip
De Rham's theorem
Stokes' theorem is an expression of duality between de Rham cohomology and the homology of chains. It says that the pairing of differential forms and chains, via integration, gives a homomorphism from de Rham cohomology to singular cohomology groups De Rham's theorem, proved by Georges de Rham in 1931, states that for a smooth manifold M, this map is in fact an isomorphism.
More precisely, consider the map
defined as follows: for any , let I(ω) be the element of that acts as follows:
The theorem of de Rham asserts that this is an isomorphism between de Rham cohomology and singular cohomology.
The wedge product endows the direct sum of these groups with a ring structure. A further result of the theorem is that the two cohomology rings are isomorphic (as graded rings), where the analogous product on singular cohomology is the cup product.
Sheaf-theoretic de Rham isomorphism
The de Rham cohomology is isomorphic to the Čech cohomology H ∗(U, F), where F is the sheaf of abelian groups determined by for all connected open sets U ⊂ M, and for open sets U, V such that U ⊂ V, the group morphism resV,U : F(V) → F(U) is given by the identity map on and where U is a good open cover of M (i.e. all the open sets in the open cover U are contractible to a point, and all finite intersections of sets in U are either empty or contractible to a point).
Stated another way, if M is a compact C m+1 manifold of dimension m, then for each k ≤ m, there is an isomorphism
where the left-hand side is the k-th de Rham cohomology group and the right-hand side is the Čech cohomology for the constant sheaf with fibre
This sequence now breaks up into short exact sequences
Each of these induces a long exact sequence in cohomology. Since the sheaf of C m+1 functions on a manifold admits partitions of unity, the sheaf-cohomology Hi(Ωk) vanishes for i > 0. So the long exact cohomology sequences themselves ultimately separate into a chain of isomorphisms. At one end of the chain is the Čech cohomology and at the other lies the de Rham cohomology.
The de Rham cohomology has inspired many mathematical ideas, including Dolbeault cohomology, Hodge theory, and the Atiyah–Singer index theorem. However, even in more classical contexts, the theorem has inspired a number of developments. Firstly, the Hodge theory proves that there is an isomorphism between the cohomology consisting of harmonic forms and the de Rham cohomology consisting of closed forms modulo exact forms. This relies on an appropriate definition of harmonic forms and of the Hodge theorem. For further details see Hodge theory.
where α is some form, and γ is harmonic: Δγ = 0.
Any harmonic function on a compact connected Riemannian manifold is a constant. Thus, this particular representative element can be understood to be an extremum (a minimum) of all cohomologously equivalent forms on the manifold. For example, on a 2-torus, one may envision a constant 1-form as one where all of the "hair" is combed neatly in the same direction (and all of the "hair" having the same length). In this case, there are two cohomologically distinct combings; all of the others are linear combinations. In particular, this implies that the 1st Betti number of a 2-torus is two. More generally, on an n-dimensional torus Tn, one can consider the various combings of k-forms on the torus. There are n choose k such combings that can be used to form the basis vectors for ; the k-th Betti number for the de Rham cohomology group for the n-torus is thus n choose k.
with d the exterior derivative and δ the codifferential. The Laplacian is a homogeneous (in grading) linear differential operator acting upon the exterior algebra of differential forms: we can look at its action on each component of degree k separately.
If M is compact and oriented, the dimension of the kernel of the Laplacian acting upon the space of k-forms is then equal (by Hodge theory) to that of the de Rham cohomology group in degree k: the Laplacian picks out a unique harmonic form in each cohomology class of closed forms. In particular, the space of all harmonic k-forms on M is isomorphic to The dimension of each such space is finite, and is given by the k-th Betti number.
Letting δ be the codifferential, one says that a form ω is co-closed if δω = 0 and co-exact if ω = δα for some form α. The Hodge decomposition states that any k-form can be split into three L2 components:
where γ is harmonic: Δγ = 0. This follows by noting that exact and co-exact forms are orthogonal; the orthogonal complement then consists of forms that are both closed and co-closed: that is, of harmonic forms. Here, orthogonality is defined with respect to the L2 inner product on Ωk(M):
A precise definition and proof of the decomposition requires the problem to be formulated on Sobolev spaces. The idea here is that a Sobolev space provides the natural setting for both the idea of square-integrability and the idea of differentiation. This language helps overcome some of the limitations of requiring compact support.
- Bott, Raoul; Tu, Loring W. (1982), Differential Forms in Algebraic Topology, Berlin, New York: Springer-Verlag, ISBN 978-0-387-90613-3
- Griffiths, Phillip; Harris, Joseph (1994), Principles of algebraic geometry, Wiley Classics Library, New York: John Wiley & Sons, ISBN 978-0-471-05059-9, MR 1288523
- Warner, Frank (1983), Foundations of Differentiable Manifolds and Lie Groups, Berlin, New York: Springer-Verlag, ISBN 978-0-387-90894-6
- Terence, Tao. "Differential Forms and Integration" (PDF). | <urn:uuid:cfc27c02-56f6-43e2-9a58-1274b424a74a> | 3.328125 | 2,304 | Knowledge Article | Science & Tech. | 42.371608 | 95,518,529 |
By J.D. Capelouto
LONDON (Thomson Reuters Foundation) - People living in arid, drought-ridden areas may soon be able to get water straight from a source that’s all around them — the air, American researchers said Thursday. Scientists have developed a box that can convert low-humidity air into water, producing several litres every 12 hours, they wrote in the journal Science.“It takes water from the air and it captures it,” said Evelyn Wang, a mechanical engineer at the Massachusetts Institute of Technology (MIT) and co-author of the paper. The technology could be “really great for remote areas where there’s really limited infrastructure”, she said.The system, which is currently in the prototype phase, uses a material that resembles powdery sand to trap air in its tiny pores. When heated by the sun or another source, water molecules in the trapped air are released and condensed — essentially “pulling” the water out of the air, the scientists said.
A recent test on a roof at MIT confirmed that the system can produce about a glass of water every hour in 20 to 30 percent humidity.Companies like Water-Gen and EcoloBlue already produce atmospheric water-generation units that create water from air. What is special about this new prototype, though, is that it can cultivate water in low-humidity environments using no energy, Wang said.“It doesn't have to be this complicated system that requires some kind refrigeration cycle,” she said in an interview with the Thomson Reuters Foundation.
An estimated one third of the world’s population lives in areas with low relative humidity, the scientists said. Areas going through droughts often experience dry air, but Wang said the new product could help them still get access to water.“Now we can get to regions that really are pretty dry, arid regions,” she said. “We can provide them with a device, and they can use it pretty simply.”
The technology opens the door for what co-author Omar Yaghi called “personalised water”. Yaghi, a chemistry professor at University of California, Berkeley, envisions a future where the water is produced off-grid for individual homes and possibly farms using the device.“This application extends beyond drinking water and household purposes, off grid. It opens the way for use of (the technology) to water large regions as in agriculture.”In the next few years, Wang said, the developers hope to find a way to reproduce the devices on a large scale and eventually create a formal product. The resulting device, she believes, will be relatively affordable and accessible. (Reporting by J.D. Capelouto; editing by Alex Whiting.; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, climate change, resilience, women's rights, trafficking and property rights. Visit news.trust.org/climate)
This story has not been edited by Firstpost staff and is generated by auto-feed.
Updated Date: Apr 14, 2017 00:30 AM | <urn:uuid:d6b2ea2f-e651-4fca-821c-522d822437a0> | 3.3125 | 653 | Truncated | Science & Tech. | 43.203124 | 95,518,585 |
Hexagonal mesoporous silicates (HMSs) are synthetic silicate materials that have uniform mesopores, comparatively large surface areas, and uniform surface functional groups, which lead to higher adsorption selectivity. Selective adsorption characteristics of HMSs for six types of organic pollutants (2,4-d, mecoprop, 4-chlorophenol, toluene, dichloroacetic acid, and thioflavin T) from synthetic wastewater were investigated. Five different types of HMSs were synthesized by surfactant-templating methods, and three of them were subsequently grafted with organic surface functional groups, i,e. n-octyldimethyl-, 3-aminopropyltriethoxy-, and 3-mercaptopropyl-groups. Titanium-substituted HMS was also made in the same way as pristine HMS. Increasing hydrophobicity of HMSs did not always enhance adsorption of hydrophobic adsorbates, such as toluene. Grafted organic functional groups changed surface charge, which enhanced electrostatic force between HMSs and ionic pollutants. Negatively charged contaminants, i.e. 2,4-d, mecoprop and dichloroacetic acid, were more readily adsorbed on positively charged AM-HMS by electrostatic interaction. Hydrogen bonding and van der Waals interaction between adsorbents and adsorbates, as well as combination of these forces, also enhanced the adsorption capacities of HMSs. In addition to the electrostatic interaction, a cationic dye, thioflavin T, was adsorbed on the surfaces due to hydrogen bonding and van der Waals interaction for hydrophilic surfaces and hydrophobic surfaces, respectively.
Effect of surface functional group on adsorption of organic pollutants on hexagonal mesoporous silicate
P. Patiparn, S. Takizawa; Effect of surface functional group on adsorption of organic pollutants on hexagonal mesoporous silicate. Water Science and Technology: Water Supply 1 July 2006; 6 (3): 17–25. doi: https://doi.org/10.2166/ws.2006.742
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Radioactive decay (also known as nuclear decay or radioactivity) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, gamma ray, or electron in the case of internal conversion. A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emission, or more rarely, proton emission.
Radioactive decay is a stochastic (i.e. random) process at the level of a singular quantum of single atoms, in that, according to quantum theory, it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed. However, for a collection of atoms, the collection's expected decay rate is characterized in terms of their measured decay constants or half-lives. This is the basis of radiometric dating. The half-lives of radioactive atoms have no known upper limit, spanning a time range of over 55 orders of magnitude, from nearly instantaneous to far longer than the age of the universe.
A radioactive nucleus with zero spin can have no defined orientation, and hence emits the total momentum of its decay products isotropically (all directions and without bias). If there are multiple particles produced during a single decay, as in beta decay, their relative angular distribution, or spin directions may not be isotropic. Decay products from a nucleus with spin may be distributed non-isotropically with respect to that spin direction, either because of an external influence such as an electromagnetic field, or because the nucleus was produced in a dynamic process that constrained the direction of its spin. Such a parent process could be a previous decay, or a nuclear reaction.[note 1]
The decaying nucleus is called the parent radionuclide (or parent radioisotope[note 2]), and the process produces at least one daughter nuclide. Except for gamma decay or internal conversion from a nuclear excited state, the decay is a nuclear transmutation resulting in a daughter containing a different number of protons or neutrons (or both). When the number of protons changes, an atom of a different chemical element is created.
The first decay processes to be discovered were alpha decay, beta decay, and gamma decay. Alpha decay occurs when the nucleus ejects an alpha particle (helium nucleus). This is the most common process of emitting nucleons, but highly excited nuclei can eject single nucleons, or in the case of cluster decay, specific light nuclei of other elements. Beta decay occurs in two ways: (i) beta-minus decay, when the nucleus emits an electron and an antineutrino in a process that changes a neutron to a proton, or (ii) beta-plus decay, when the nucleus emits a positron and a neutrino in a process that changes a proton to a neutron. Highly excited neutron-rich nuclei, formed as the product of other types of decay, occasionally lose energy by way of neutron emission, resulting in a change from one isotope to another of the same element. The nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture. All of these processes result in a well-defined nuclear transmutation.
By contrast, there are radioactive decay processes that do not result in a nuclear transmutation. The energy of an excited nucleus may be emitted as a gamma ray in a process called gamma decay, or that energy may be lost when the nucleus interacts with an orbital electron causing its ejection from the atom, in a process called internal conversion.
Another type of radioactive decay results in products that vary, appearing as two or more "fragments" of the original nucleus with a range of possible masses. This decay, called spontaneous fission, happens when a large unstable nucleus spontaneously splits into two (or occasionally three) smaller daughter nuclei, and generally leads to the emission of gamma rays, neutrons, or other particles from those products. | <urn:uuid:579c0435-9e2d-4572-8aa3-09d79ba9e85d> | 4.34375 | 841 | Knowledge Article | Science & Tech. | 28.491638 | 95,518,606 |
How do we measure the brightness of objects in the night sky?
Did this pioneering astronomer invent and use a telescope for the first time?
The pioneer of the sky created the catalogue of deep sky objects.
The life and work of one of the world’s greatest scientific minds
Find out why the hottest planet in the Solar System is so bright in our night sky.
The Polish astronomer who revolutionised our understanding of the Earth’s place in the Solar System.
Where are the stars in various constellations located?
Megan Whewell from the National Space Centre answers this question for us.
Being our next-door neighbour, can we grab stunning views of the surface of Venus?
Venus remains the star of the evening skies, while Saturn and Mars keep close company in the morning
China’s first-ever space laboratory has been predicted to fall to Earth as early as this week, according to Chinese space agency officials
ESA’s Integral space observatory spotted X-rays emitted from a unusual binary star system
Do gravitational waves suggest a bang at the end of the universe? Find out in the latest issue, available now from all good supermarkets and newsagents
On the 31 January 2018, three amazing astronomical phenomena will combine to create a majestic viewing opportunity
Get ready for the first meteor shower of 2018!
NASA’s Chandra X-ray Observatory has imaged the intricate and energetic features within the supernova remnant Cassiopeia A
The supermassive object was observed just 680 million years after the Big Bang
Australia’s new radio telescope has revealed the complexity of the Small Magellanic Cloud’s structure
Since astronomers first measured the size of an extrasolar planet 17 years ago, they have struggled to answer the question: how did the largest planets get to be so large?
Supernovae traditionally occur once at the end of a star’s life, but this particular star has exhibited multiple supernovae over the last three years | <urn:uuid:82a6e9fd-7fd0-4b35-bfa3-952b6be64fd3> | 3.453125 | 410 | Content Listing | Science & Tech. | 33.334091 | 95,518,613 |
Data set ID:
The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan D
esert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities as Brown and Heske (1990a) and Gibbens et al. (1993) suggest? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? Data collected for each captured rodent: habitat, trap night, trap web, recapture, species, sex, age, weight, reproductive status, reproductive condition.
Data file information for the following Jornada data set: SMES rodent trapping data
1995 - 2003: analog tape recorders 2003 - 2007: digital voice recorders
Experimental Design ------------------- A creosotebush shrub study site and a black grama grassland study site have been established at both the Jornada and Sevilleta, for a total of four study sites. The study sites were subjectively chosen to represent typical creosotebush shrub and black grama grassland communities on lower bajada or peidmont slopes at both the Jornada and Sevilleta. The study sites are located in areas that are not grazed by domestic livestock (except the Jornada grassland site; see experimental design below), to eliminate the confounding effects of livestock on vegetation and soil. Each of the four study sites are approximately 1 km by 0.5 km in area. Three rodent trapping webs and four replicate experimental blocks of plots were randomly located at each of the four study sites to measure vegetation responses to the exclusion of small mammals (Figure 2). Treatments within each block include one unfenced control plot, one fenced plot to exclude rodents and rabbits, and one fenced plot to exclude rabbits only. The three treatments were randomly assigned to each of the four possible plots in each block independently. The Jornada grassland site is grazed by cattle, so an additional treatment plot of cattle fencing was randomly assigned to one plot in each of the four blocks. Each of the three or four plots in a replicate block are separated by 20 meters. Each block of plots is situated near a rodent trapping web. Distances between the four replicate blocks of plots at each study site varies among sites from 30 meters to 800 meters, depending upon the random coordinates. Each block of experimental measurement plots consists of one unfenced control plot, and two (or three if cattle are present) fenced animal exclosure plots (Figure 2). Each experimental measurement plot measures 36 meters by 36 meters. A grid of 36 sampling points are positioned at 5.8-meter intervals on a systematically located 6 by 6 point grid within each plot. A 3- meter wide buffer area is situated between the grid of 36 points and the perimeter of each plot. A permanent one-meter by one- meter vegetation measurement quadrat is located at each of the 36 points (Figure 3). The control plots are not fenced. One year of pre-treatment or pre-fencing measurement data will be collected in 1995 from all of the plots. Analysis of the pre-treatment data will reveal any differences between plots that are independent of the treatments. Fences will be constructed in the winter of 1995, and the long-term small mammal exclosure experiment will commence in spring of 1996. One set of exclosure plots will be fenced with three-foot high wire hardware cloth of 1/4-inch mesh size to exclude rodents, and four-foot high poultry-wire fencing of two-inch mesh size to exclude rabbits. The hardware cloth screen will be buried inches to prevent animals from burrowing underneath the fence. The four-foot high poultry-wire fence will be positioned inside of and flush with the screen fence to exclude rabbits from the plot. A six-inch wide strip of metal flashing will be placed along the top of the hardware cloth, and attached outside of the poultry-wire, to prevent rodents from climbing over the fences. Steel fence posts and reinforcing bar (rebar) will be used to support the fences. The second set of exclosure plots will be fenced with poultry-wire to exclude rabbits, but not rodents. Two-inch diameter poultry-wire mesh will allow access for all local rodent species at each site. A four-foot high poultry-wire fence will be positioned around the perimeter of each plot to exclude rabbits. Steel fence posts and rebar will be used to support the fences. Fencing with hardware cloth and poultry wire will impede the ground surface movement of organic litter. Rainfall runoff transports plant litter in ground-surface sheet-flow, and in small ephemeral surface drainages or rills. To alleviate the problem of fences interfering with transport, litter accumulations on the up-slope sides of fences will be manually removed and lifted over the fences once every two months. This procedure will allow for the natural movement of soil surface organic materials on to and off of the fenced plots. Litter catchment screens made of hardware cloth and poultry wire will be placed in all small drainages crossing the up-slope perimeters of each plot, including the unfenced control plots. Litter caught on the screens will be manually lifted over the fences of treatment plots, and placed just across the perimeters of control plots. Use of catchment screens should allow normal litter transport in rills onto and off of the plots. Use of catchment screens on the control plots will account for differences in water flow that the screens might create on the fenced plots. Cattle are present (one-month low intensity winter grazing) at the Jornada black grama grassland site. Barbed-wire strands will be added to the rodent and rabbit, and rabbit only exclosure fences to exclude cattle from those plots. Additionally, a fourth measurement plot was added to each replicate block that will be fenced with barbed-wire to exclude cattle only to measure cattle effects on vegetation and soil. The cattle exclosure treatment is not intended to be part of the overall experimental design, but rather a way a accommodate for the presence of cattle at the site. There are no ungrazed black grama grassland sites at the Jornada that are large enough in area to support the small mammal exclosure study. The same experimental design is proposed for the Mapimi research site, except that a creosotebush study site and a tabosa grassland study site will be installed instead of creosotebush and black grama grassland sites as at Sevilleta and Jornada. Tabosa is the dominant grassland at Mapimi, and no black grama grasslands occur at Mapimi. Additionally, the Mapimi site is grazed by cattle, so a fourth cattle exclosure plot will be included in each block of plots at the creosotebush and tabosa grassland study sites. Rodent trapping webs are being used to determine the composition of rodent species at each study site, and to estimate densities of each species over time. The use of webs and distance measures to estimate rodent densities is statistically more robust than grid plot sampling and mark-release indices (Anderson et al. 1983, Buckland et al. 1993). Each rodent trapping web consists of a series of 12 equally spaced lines radiating from a central point. Each line consists of 12 trap stations. The first trap station is located 5 meters from the center, the next three at 5 meter intervals, and the remaining 8 at ten meter intervals. Each trap line is 100 meters long, and each web is 200 meters in diameter. The above rodent trapping web design has been used for six years at the Sevilleta LTER, and has recently been adopted by the US Centers for Disease Control and Prevention, as a standard technique for monitoring rodent populations. Small Mammals ------------- Rodent populations will be sampled from each of the three webs at each of the study sites twice each year, in the early (April-May) and late (September-October) summer. Sherman (H. B. Sherman Traps, Inc., Tallahassee, FL) live-traps are left open for three consecutive nights, and captured animals are recorded for three consecutive mornings. Each animal caught is identified, measured, and released at the same location where it was captured. Each animal is temporarily marked with a marking pen to determine recapture status for a given three-night sampling period. No permanent marking techniques are used. Rodent trapping is conducted at all 6 webs at a given research site over the same 3 night period. Rodent trapping at the Sevilleta, Jornada, and Mapimi will be conducted at the same time of year. Persons working with rodents in the field will follow safety guidelines developed by the US Centers for Disease Control and Prevention (Mills, et al. in press), to reduce exposure to hantavirus, plague, and other rodent-vectored diseases.
SAS program will be used to analyze data
The Sevilleta LTER site is located at the US Fish and Wildlife Service, Sevilleta National Wildlife Refuge in central New Mexico (Figure 1). The Sevilleta is located at 34 north latitude, and the grasslands and shrublands are at about 1,550 meters in elevation. The grassland and shrubland areas have long- term mean annual precipitation of about 280 mm and mean annual temperature of about 13 C. The Sevilleta is predominantly black grama (Bouteloua eriopoda) and blue grama (Bouteloua gracilis) grassland, with less extensive creosotebush shrub communities. The Jornada LTER site is located at the US Department of Agriculture, Agricultural Research Service, Jornada Experimental Range in southern New Mexico (Figure 1). The Jornada is located at 32 north latitude, and the grasslands and shrublands are at about 1,300 meters elevation. The long-term mean annual precipitation is 230 mm, and the mean annual temperature is 15 C. The Jornada is primarily creosotebush and mesquite (Prosopis glandulosa) shrubland with less extensive black grama grass communities. The grassland site is one kilometer west of the IBPE grassland site, and the creosotebush site is three kilo- meters southeast of the lower trailer. The Mapimi Biosphere Reserve is located in the south-central Chihuahuan Desert in the northeastern portion of the state of Durango, Mexico (Figure 1). The Mapimi site is located at 27 north latitude, and the creosotebush shrublands are at 1,100 meters elevation. Mapimi has a long-term mean annual precipitation of 271 mm, and the average annual temperature is 21C. The Mapimi research site is primarily creosotebush shrubland with mesquite. Tabosa (Hilaria mutica) grasslands occur in the bottoms of basins.
1995-2005 Three nights/site twice each year; April and September/October 2006-2007 Three nights/site in October | <urn:uuid:d4ca0257-60fa-441a-91e9-5965480e6de3> | 3.15625 | 2,516 | Academic Writing | Science & Tech. | 37.642916 | 95,518,627 |
Martian habitats are ideally constructed using only locally available soils; extant attempts to process structural materials on Mars, however, generally require additives or calcination. In this work we demonstrate that Martian soil simulant Mars-1a can be directly compressed at ambient into a strong solid without additives, highlighting a possible aspect of complete Martian in-situ resource utilization. Flexural strength of the compact is not only determined by the compaction pressure but also significantly influenced by the lateral boundary condition of processing loading. The compression loading can be applied either quasi-statically or through impact. Nanoparticulate iron oxide (npOx), commonly detected in Martian regolith, is identified as the bonding agent. Gas permeability of compacted samples was measured to be on the order of 10−16 m2, close to that of solid rocks. The compaction procedure is adaptive to additive manufacturing.
Near-future exploration to Mars connotes the technology of space construction. Permanent human settlement on Mars requires infrastructure to sustain habitats and life. A steady supply of structural materials is integral towards this effort. Of immense consequence is to examine whether such materials can be made solely through in-situ resource utilization (ISRU) and if so, whether energy-intensive processes such as calcination can be avoided. Previous prototyping requires energy-intensive heating1 or use of binders that must be shipped from the Earth2. Ideally, the solution should be as simple as possible.
Much of Martian regolith is formed by basaltic fines containing iron3, 4. The soil consists of substantial nanoparticulate iron oxides and oxyhydroxides, collectively known as npOx, responsible for its reddish hue3,4,5,6,7,8,9,10,11. Some components of npOx are too small to distinguish and are referred to as x-ray amorphous11, 12. A widely used Martian soil simulant, JSC Mars-1a, contains npOx13. A typical Mars-1a particle is composed of two phases: a basaltic body and an npOx rind13. The simulant serves as an analogue for Martian surface soils with high similarity in chemical composition: 45.41 wt% SiO2, 16.73 wt% Fe2O3 and FeO, 8.35 wt% MgO, 6.37 wt% CaO, etc. for average value of Mars regolith, versus 43.48 wt% SiO2, 16.08 wt% Fe2O3 and FeO, 4.22 wt% MgO, 6.05 wt% CaO, etc. for Mars-1a14, 15.
As with most covalently bound silicate materials, basaltic particles do not adhere to each other when compressed, unless if heated to a high temperature16, 17. Nanoparticulate iron oxides, however, may behave differently. Some species of npOx may develop very high specific areas upon external loadings18, 19. Strong bonding can be formed when large specific areas are in contact20,21,22. Based on this consideration, also motivated by the observed cohesion of Martian soils23, 24, we investigated whether a uniaxial load per se is sufficient to form solids capable of infrastructural applications.
Figure 1 shows the experimental results of quasi-statically compacted oven-dried Mars-1a: It is amenable to single-step rapid formation without heating or added binders. Upon a high-pressure compression, Mars-1a particles form a strong solid at ambient, with resultant flexural strengths exceeding that of typical steel-reinforced concrete or many in situ resource utilization (ISRU) created materials formed by adding binders25, 26. It is also more practical and efficient in application compared to other ISRU prototyping utilizing high temperature or laser sintering. Although Mars-1a is one of a multitude of inorganic species known to form intact solids under compression20, 27, its heterogeneity distinguishes npOx as a cement acting under instantaneous mechanical pressure apart from natural, long-term processes, such as fluvial concretion18, 28. This advance offers confidence that the self-cohesive soils seen on Mars may, in fact, be further compressed directly into high-strength structural parts.
Size fractionation and thermal treatment prepared the Mars-1a simulant prior to compaction. A reciprocating sieve separated randomly distributed simulant particles into size bins, as described in detail in the Section of Sieve Analysis in Methods; this was for determining the influence of initial particle size on the sample strength. Thermogravimetric (TGA) and CHNS/O analyses determined the water and organic contents as functions of the drying temperature, respectively (Sections of TGA, Pretreatment and Drying, and Measurement of Carbon Content in Methods; Tables S5 and S6 in Supplementary Material). Drying at 600 °C for 10 hr reduced the water content to <5 wt%. Most Martian soil, by comparison, is dry and contains <5 wt% water, although some regions exceed this29. The carbon content was reduced to within the null margin of error by the thermal treatment, suggesting that the influence of trace organics was trivial30, 31. X-ray diffraction (XRD) analysis of Mars-1a samples (Fig. S15 in Supplementary Material) suggests that the pretreatment does not induce any phase transformation or crystallinity change. A few secondary peaks disappear in the two-theta range of 20° to 30°, probably due to the loss of bonded water.
We compressed the prepared Mars-1a in a uniaxial mode between flat pistons to form solids (Section of Quasi-static Compaction in Methods). Six configurations—two rates of loading and three lateral boundary conditions around the sample—represented the compression process (Sections of Quasi-static Compaction and Impact Compaction in Methods). Loading rates were either quasi-static (with the piston velocity of a few mm/min) or impact (with the hammer velocity of a few m/s). The lateral boundary condition of compaction loading was either rigid (confined by a steel wall), free, or flexible (confined by an elastomeric wall). All boundaries were of cylindrical geometry, with the resulting compacts typically disc-shaped.
Compacted Mars-1a solids were cut into beams and subjected to three-point bending tests (Sections of Materials of Processing System, Flexural Strength Measurement, and Effects of Particle Size on Flexural Strength in Methods). The material was characterized by SEM, TEM, and XRD analyses (Sections of SEM and TEM Characterization and XRD Analysis in Methods).
We mixed neat basalt particles with Mars-1a in various proportions to determine the role that the basaltic phase plays on strength; separately, we investigated goethite and rust fines as analogues to the npOx phase19 (Sections of Compaction of npOx-Related Materials and Addition of Basalt Particles into Mars-1a in Methods). The testing data confirmed that the basaltic phase does not directly contribute to the sample strength, and the npOx phase indeed can behave as a binding agent.
Gas permeability of the compacted Mars-1a was measured, as described in Section of Gas-Permeability Measurement in Methods. Pressurized nitrogen flowed through a solid Mars-1a disc, and the flow rate was monitored. The Rilem-Cerembureau equation32, 33 was employed to calculate the permeability.
Table 1 summarizes the flexural strengths generated by each of the six processing configurations. It is remarkable that the lateral boundary condition of compaction loading significantly influences the strength and the shape of the compacted solid, specifically, the thickness-to-diameter ratio. Compared with the boundary condition, the effect of loading rate is secondary.
Quasi-static Compaction and the Role of npOx
In all loading modes, the flexural strength, R, tends to increase with the peak compressive pressure, P max; however, when the pressure is sufficiently high, further increasing it only causes incremental improvement in R. The optimum peak compressive pressures associated with various boundary conditions are listed in Table 1. For self-comparison purpose, in the current study P max is defined as the peak compressive force divided by the initial sample cross-sectional area.
Very often, strength of a compacted granular material is inversely proportional to the particle size34, e.g. solids formed from nanoparticles35. Under quasi-static loading, Mars-1a did not obey this trend: as the initial particle size changes from less than 20 μm to nearly 100 μm, R remains similar.
The lateral boundary condition of compression loading is a much more important factor than the initial particle size. With the rigid boundary condition, the compacted Mars-1a samples are structurally integral but the flexural strength is relatively low, comparable with ordinary clay bricks38. When the lateral boundary is free or flexible, R is nearly 3 times higher than that of rigid boundary condition. Between the free and flexible boundary conditions, the flexible boundary condition reached high R at much lower P max and the resultant solid thickness was only slightly smaller than that of the rigid boundary condition, much larger than that of the free boundary condition. The strength-wise efficacy of forming inside a flexible boundary is ~150–200% greater than the free boundary for R ~30 MPa, taking into consideration the flexible boundary’s larger sample sizes.
The XRD result is shown in Fig. 2. After compaction, most peaks decrease in height, including the main peaks corresponding to pyroxene minerals39. It may be attributed to the crushing of small crystals. The several minor peaks that grow indicate minute phase transformations of npOx into a denser form, probably goethite or magnetite18. Only mechanical pressure can account for these transformations, because we applied no heat during and after compression. It was reported that milling can transform various FeOOH species into hematite18, 40.
Quasi-statically compacted Mars-1a lost strength when diluted with basalt (Table S3 in Supplementary Material). As the amount of basalt additive exceeds 75 wt%, the compacted material disintegrates spontaneously and R is essentially zero. When goethite particles are compressed with rigid boundary condition, the samples show similar flexural strengths to Mars-1a (Table S2 in Supplementary Material).
Upon impact compaction, the free or flexible boundary condition again yields high R. As shown in Table 1 and Fig. 3, the free boundary condition produced the strongest samples, albeit with higher peak pressure than the flexible boundary condition. When the impact pressure is comparable with the quasi-static pressure, the resultant flexural strength of dynamically formed Mars-1a specimens is higher than those which were quasi-statically formed, implying that the bonding formation process is faster than the characteristic time of impact compaction, around a few milliseconds. Figure 3(A) shows that as the initial particle size, D, decreases from the range of 53–90 μm to 25–45 μm, R significantly increases. This increase differed from the observed R-D relation when the loading was quasi-static.
Figure 3(B) shows that R is determined by the impact energy with other parameters unchanged, no matter whether the impact energy is adjusted by the hammer mass or the impact velocity.
Figure S9 in Supplementary Material shows that the peak stress in the impact pulse is about ~400 MPa for a 120-J drop. It led to a flexural strength ~50 MPa (Fig. 3(B)), significantly greater than R ~30 MPa in the quasi-static case for a similar P max .
The nitrogen permeability of compacted Mars-1a is on the order of ~10−16 m2 (Table S4 in Supplementary Material). It suggests that the compacted material is somewhat similar to dense rocks41, 42, and can be adapted to an atmospheric habitat.
The phenomenon that the flexural strength of quasi-statically compacted Mars-1a, R, is insensitive to the initial particle size, D, may be associated with the high compressive pressure, P max. The crushing pressure of basalt grains is typically 1–10 MPa36, much below P max. Hence, Mars-1a particles are crushed into small pieces. For instance, as D is 25–45 μm, most of the particles are smaller than 10 μm after compaction, as shown in Fig. 2(A) and Fig. S16 in Supplementary Material. Consequently, the properties of compacted solid are unrelated to the initial particle size distribution.
An even dispersion supports the notion of continuous transport of npOx around voids, given that crushing of particles occurs throughout compression. Added basalt essentially served an inert filler material; without sufficient npOx, it cannot be responsible for the strength. The result affirms that npOx binds Mars-1a. Decreasing strength with added basalt also rules out the hypothesis of mechanical interlocking of particles21. Goethite is able to achieve strong bonding by virtue of the relatively high specific area, making it a plausible constituent of npOx.
With the flexible boundary condition, the particle motion is localized. Clearly, during compaction it is critical to allow rotation and transverse motion of Mars-1a particles, so as to maximize the effective contact area and to promote bond formation. Excessive particle motion, however, may introduce defects, which explains why the free boundary compensates with higher pressure to achieve similar R as the flexible boundary.
For impact formation, the particle size dependency of flexural strength may be related to the effects of inertia and npOx availability. Larger particles fall into less-than-optimal arrangements, because rotational inertia depends strongly on the size of particles. Larger particles also have a larger solid volume-to-area ratio, so that less npOx is available to bond simulant particles. The durations of quasi-static and dynamic loadings are separated by about 5 orders of magnitude38.
To explain the permeability of the material, we propose that flow channels of nitrogen are formed by microscopic defects among particles, which, as a first-order approximation, may be modeled as cylindrical tubes carrying Poiseuille flow. Dividing the cross-sectional area of the solid, A s , by the average area of a single particle, A p , we assume that there are ~105 particles over the cross-section. In a face center cubic structure, each particle contributes 1 defect. The radius of each flow channel is r ~10 μm, assuming defect sizes on the order of particle size. Poiseuille’s equation for channel flow can be combined with the Rilem equation to give , where P o is ambient pressure and P i is the upstream pressure. The result is ~10−17 m2, which is in reasonable agreement with the experimental data.
In summary, in ambient environment, Mars-1a Martian soil simulant can develop considerable strength around 30–50 MPa upon one-step high-pressure compaction, with npOx being the bonding agent. The compaction can be performed either quasi-statically or through impact. The processing procedure may be generalized; e.g. the compacted solid can be further strengthened by reinforcements. Although compression-forming represents a novel process for npOx, the process itself may be adapted to a number of other Martian and terrestrial minerals. Such minerals include clays and evaporite salts. Both quasi-static and impact compaction processes are compatible with additive manufacturing, which will be a focus of future study; it is critical to the production of large-sized structural parts, wherein the material may be added incrementally.
Using a drying oven (VWR-1330GM), we subjected 500-ml batches of Mars-1a simulant (Orbitec JSC Mars-1a, <1 mm) to a temperature of 105 °C for 24 hr (Fig. S1 in Supplementary Material). Then, a mechanical sieve (Tyler Rotap RX-29, 350 W) separated the simulant into bin sizes using 90 μm, 53 μm, 45 μm, 25 μm, and 20 μm meshes. The average particle size, D, refers to the arithmetic mean of the bin sizes.
Thermogravimetric Analysis (TGA)
A thermogravimetric analyzer (Perkin Elmer Pyris 1 TGA) heated and weighed 15 mg of nitrogen-purged simulant, using a ramp rate of 5 °C/min to a maximum temperature of 1000 °C held for 20 min. The sample was subsequently furnace-cooled to ambient temperature. Three measurements were averaged and the result is shown in Fig. S2 in Supplementary Material.
Pretreatment and Drying
Mars-1a simulants were transferred in crucibles, protected with aluminum foils, and subjected to 600 °C for 12 hr inside a furnace (Carbolite CTF 12/75/700), followed by furnace-cooling to ambient temperature.
Rigid boundary condition
Mars-1a simulants were transferred inside the chamber of a cylindrical steel mold fitted with a bottom piston. Pistons were either 19.1 mm or 12.7 mm in diameter, with the latter used for higher pressures. The top piston was inserted slowly on top of the simulant, covering the mold (Fig. S3 in Supplementary Material). A uniaxial testing machine (Instron 5582) loaded the assembly to the maximum compression pressure (P max) at a rate of 6 mm/min. The compression pressure was calculated as the compressive force divided by the cross-sectional area of the piston. The peak pressure lasted 5–10 s, and relieved <1 sec. A 1-ton arbor press extracted the solid Mars-1a from the assembly.
Free boundary condition
Compression of Mars-1a simulants without a lateral confinement was achieved by pistons acting on undersized precursors. For the purposes of our geometry, these precursors were disc-shaped pellets with the height of 2–3 mm. Precursors were made by pressing simulant in relatively undersized dies (8.7 or 19.1-mm piston diameter) to 100 MPa. We then reinserted precursors concentrically into larger dies between matching pistons (19.1 or 50.4-mm-diameter, respectively) and loaded the assemblies with the uniaxial testing machine (Instron 5582 or SATEC M600XWHVL, respectively) at 6 mm/min to P max, as depicted in Fig. S4 in Supplementary Material. The compacted sample was then manually removed.
Flexible boundary condition
Mars-1a simulant was transferred inside a flexible tube (Finger Lakes Extrusion Clearflex 70–1 8170–2590) of height 30 mm, fitted on the bottom with a steel piston (19.1 mm diameter) of matching size. The piston translated under force when engaged with the tube, but did not slip; the flexible tube had the outer diameter of 19.1 mm and the thickness of 3.2 mm. The second piston was placed on top of the simulant, and the assembly was loaded to P max using the uniaxial testing machine (Instron 5582) at 6 mm/min (Fig. S5 in Supplementary Material). No hydrostatic control was applied to the exterior of the tube. Typical load-displacement curves are shown in Fig. S6 in Supplementary Material.
Free boundary condition
We generated precursors of thickness 2–3 mm using a steel mold with 8.7 mm piston diameter. Precursors were transferred inside a 19.1-mm-diameter steel mold press-fitted on the outside with a polyurethane jacket (Pleiger Plastics MCTB9595145B), positioned concentrically between matching pistons. The steel mold’s top face was 1 mm lower than that of jacket’s when their bottom faces were flush. To protect hardware, a cushion layer, made of 1 g aluminum foil pressed inside a separate 19.1-mm-diameter mold, was placed above the top piston and another below the bottom piston. The jacketed assembly was then secured inside a fixture, vertically collinear with a guide tube (Fig. S7 in Supplementary Material). The guide tube had dimensions of 76.2 mm outer diameter and 4.8 mm wall thickness. The guide tube lengths were 1.5 m, 0.9 m, or 0.3 m in separate trials, and the longest length was stabilized vertically by securing to the ceiling. A 7.6-kg steel impact hammer fell through the guide tube, striking the assembly on the cushion layer. No simulants escaped the mold assembly during impact. We calculated the impact energy as V = mgh, where V is the gravitational potential energy, m is the mass of the hammer, g is the standard gravity, and h is the drop distance.
Flexible boundary condition
Mars-1a simulant was inserted inside a flexible tube (Saint Gobain Tygon R-3603 AAC00037) and capped on opposite ends with 12.7-mm-diameter steel pistons. The tube was 12 mm in diameter, 24 mm in wall thickness, and 25.4 mm in height. The piston did not slip when engaged with the tube. The total initial height of the simulant inside the tube was ~25 mm. The capped tube was outfitted with an elastomer jacket (Thomas Scientific 9544T65). The jacket had dimensions of 38 mm outer diameter, 19 mm inner diameter, and 74 mm height. The tube containing simulant was pushed down the jacket such that the bottom piston was flush with the jacket. The bottom of the jacketed assembly was then positioned inside a steel cap, of dimensions 38.5 mm inner diameter, 10.4 mm bore depth, and 25.4 mm thickness. To protect the hardware, we formed ~1 g aluminum foil into a 12.7-mm-wide, 2-mm-thick cushion layer at 40 MPa with another die and placed it above the top piston. The entire assembly with the simulant, tube, pistons, jacket, cap, and cushion is shown in Fig. S8 in Supplementary Material. We transferred the assembly inside the chamber of a drop tower (Instron CEAST 9350), with the hammer mass from 2.8 kg to 5.8 kg and the drop distance from 1.8 m to 3.0 m. The hammer mass included the weight of the tup frame, transducer, hammer head, and detachable weights. No simulants escaped from the flexible tube during impact. The compacted sample was harvested by isolating it from surrounding loose material. Figure S9 in Supplementary Material shows a typical impact pulse.
Compaction Condition and Devices
Compaction and testing were performed at ambient; samples remaining overnight were stored at elevated drying temperature of 105 °C. Steel molds used for compression with the rigid boundary condition were of hardness RC 50. Pistons attained a hardness of RC 60, and end faces were regularly polished with 13-μm sandpapers. Clearance between piston and mold amounted to 0.05 mm or less.
Flexural Strength Measurement
Compressed solids were cut and reduced with 26-μm and 13-μm abrasives to beams with dimensions described by Table S4 (Fig. S10 in Supplementary Material). Prior to testing, we lightly chamfered the lengthwise edges using 13-μm abrasive to guard against edge defects.
A fixture held the beam by its ends to represent a simply-supported condition. Distances between the supports were 5.0, 9.8, or 15.2 mm depending on the size of the beam. A single top fixture applied a point load at midspan in all cases. Testing was performed with a 2-kN load cell of 0.2% full-scale sensitivity, on a Type-5582 Instron machine. The flexural test loaded the beam at a rate of 6 mm/min. Figure S11 in Supplementary Material shows a typical load-displacement curve. The flexural strength, R, was calculated as17: , where F m is the peak loading, L is the distance between supports, b is the beam width, and t is the beam depth. Four valid tests constituted the minimum to calculate a standard deviation.
The total time between the heat treatment and the completion of the flexural strength test did not exceed 12 hours. While samples idled, they were maintained inside a sealed container in dry air at 110 °C.
Effects of Particle Size on Flexural Strength
We sieved, dried, and compressed Mars-1a simulant following the procedure described in Sections of Sieve Analysis, Pretreatment and Drying, and Quasi-Static Compaction (Rigid boundary condition) in Methods. Two data series were generated: one compressed at 360 MPa and the other at 720 MPa. We procedurally discarded the high datum and low datum, and at least four data points generated the standard deviations. The two series were combined into one data set by using error propagation43. The results are plotted in Fig. S12 in Supplementary Material.
Compaction of npOx-Related Materials
Rust fines were prepared using steel shavings exposed to aqueous solution of 0.2 M acetic acid in a glass dish exposed under ambient condition for 168 hr. The rust fines were separated from the metal by agitation in a 200 ml beaker filled with ethanol, and then silted for 60 sec. The remaining supernatant fluid was transferred into a second beaker, and silted again for 24 hrs. Once isolated, the fines were further rinsed with distilled water and acetone repeatedly. Oven-drying was performed at 80 °C, 350 °C, or 500 °C overnight prior to compression. Particle sizes of freshly generated rusts was ~30 nm19, bypassing the need for mechanical sieving.
Goethite (Sigma-Aldrich 71063–100 G) was used directly as-supplied. The goethite was not dried prior to compaction, due to the sensitivity of transformation temperature. Like the rust fines, goethite — itself a constituent of rust18— had a relatively small crystallite size and was not sieved.
Both materials were quasi-statically compacted using the rigid boundary condition and tested as described in Section of Flexural Strength Measurement in Methods. The testing results are shown in Table S2 in Supplementary Material.
Addition of Basalt Particles into Mars-1a
Basalt rock (Washougal Quarry) was cleaned with deionized water, dried at 105 °C for 2 hr, and comminuted with a mortar and pestle. The basalt particles were then sieved and dried following the procedure described in Sections of Sieve Analysis and Pretreatment and Drying in Methods. The 25–45 μm size fraction was mixed with the same size fraction of Mars-1 simulant, which had been sieved and dried. The prepared mixture was compressed and tested following the procedure described in Sections of Quasi-Static Compaction (Rigid boundary condition) and Flexural Strength Measurement in Methods. The compositions were 10 wt%, 25 wt%, 50 wt%, or 75 wt% basalt particles, balanced by Mars-1a. The results are summarized in Table S3 in Supplementary Material.
Compressed Mars-1a solids were generated according to the procedure described in Section of Quasi-Static Compaction (Flexible boundary condition) in Methods using the 19.1-mm-diameter mold. The resultant solid was ground into a round disc, with the final pass using 13-μm abrasive. In the final form, the discs were 12.7 mm in diameter and ~3 mm in thickness.
The permeability test stand consisted of a flexible clear tubing connected to a 138-kPa gauge nitrogen gas source. A break in the tubing allowed the disc sample to be inserted and resealed with hose clamps. Vacuum grease (Dow Corning) and a cylindrical piston aided in inserting the disc. The end of the tube led to an upside-down 100-ml graduated cylinder full of water. Leaks were precluding by performing controls with a reference steel piston; no bubbles were observed in the graduated cylinder for 30 min. Permeability was calculated as32: , where μ is the dynamic viscosity of nitrogen at 0.0000176 Pa-s, t is the sample thickness, A is the circular cross-sectional area, P o is ambient atmospheric pressure (~101.3 kPa), and P i is the nitrogen source absolute pressure (~239.3 kPa). Table S4 in Supplementary Material lists the measurement results and the calculated permeability for each sample.
Measurement of Carbon Content
Mars-1a simulant was separately dried at 350 °C and 500 °C for 12 h, and subjected to CHNS/O analysis by using a Perkin Elmer PE2400-Series II Analyzer to detect the remaining carbon content. The results are shown in Table S5 in Supplementary Material, together with the carbon content of as-received Mars-1a.
Flexural strength tests were conducted on compacted samples produced through the procedure described in Section of Quasi-Static Compaction (Rigid boundary condition) in Methods, using Mars-1a particles dried at either 230 °C or 500 °C. The oven-drying procedure followed Section of Pretreatment and Drying in Methods. The decrease in remaining carbon content with increasing temperature is shown in Table S5 in Supplementary Material.
SEM and TEM Characterization
Fracture surfaces of tested Mars-1a samples were observed in a FEI XL30 Scanning Electron Microscope (SEM). Figure 2(A) in the main text and Figs S13 and S14 in Supplementary Material show typical SEM images.
About 20 mg of powders were harvested from the fracture surface of a Mars-1a sample compacted quasi-statically with flexible boundary condition. They were observed under a Hitachi HD-2000 (TEM). The inset in Fig. 2(A) shows a typical TEM image.
X-ray diffraction (XRD) analysis was performed on as-received Mars-1a powders, dried Mars-1a powders, and Mars-1a powders harvested from compacted samples (all about 20 mg) using a Rigaku Miniflex-II XRD machine. Typical results are shown in Fig. 2(B) in the main text and Fig. S15 in Supplementary Material.
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This research was supported by NASA under Grant No. NNX12AI73G. We thank C. Zhang, Y. Zhong, S.W. Hsu, T.-H. Tseng, A. Finch, G. Wang, J.A. Ramirez, C.M. Galarza, and K.S. Vecchio for their help with the experimental work. We are also grateful to P.J. Fox, J.S. McCartney, and D.D.-N. Chow for the useful discussions. | <urn:uuid:26d6dff9-c1ed-4a4d-9ec4-d04b2030a2f3> | 2.703125 | 6,581 | Academic Writing | Science & Tech. | 49.052746 | 95,518,637 |
Evaluation of nuclear effects in the analysis of plastics by neutron activation analysis
Validation of a method for the determination of trace elements in plastic using neutron activation analysis (NAA) required evaluation of nuclear effects. Since plastic is a moderator of neutrons, it is possible that the neutron flux may be affected in such a way as to effectively increase or decrease the measured activity of radionuclides within the plastic. Such effects are likely to depend on the thickness of the sample and so thicknesses of plastic ranging from 1 to 20 mm were used to quantify the effects. A standard containing vanaldium (a thermal neutron absorber) and silver (with epithermal neutron resonances) was used in a sandwich of the plastic. The sandwich was then irradiated and the standard counted. The activity of each radionuclide for each thickness was evaluated. The results showed that a variation of only 10% maximum was observed for thicknesses up to 20 mm. An increase in measured activity was observed for both the thermal and epithermal absorbers.
KeywordsPhysical Chemistry Inorganic Chemistry Radionuclide Activation Analysis Measured Activity
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- 1.P. Bode, M. De Bruin, Th. G. Aalbers, P. J. Meyer,Biol. Trace Element. Research, 26/27 (1990) 377.Google Scholar
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- 3.S. F. Mughabghab, M. Divadeenam, N. E. Holden, Neutron Cross Sections, Vol. 1, Part A, Academic Press, 1981.Google Scholar
- 4.R. Benzing, S. J. Parry, N. M. Baghini, J. A. Davies,The Science of the Total Environment, 130/131 (1993) 267.Google Scholar | <urn:uuid:c17b1238-eeb8-4e37-adc8-45b4c2ba0195> | 2.859375 | 410 | Truncated | Science & Tech. | 59.042088 | 95,518,643 |
The Green Bank Telescope has revealed a never-before-seen river of hydrogen streaming into the nearby galaxy NGC 6946, helping to reveal how certain spiral galaxies keep up their steady pace of star formation.
Using the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT), astronomer D.J. Pisano from West Virginia University has discovered what could be a never-before-seen river of hydrogen flowing through space. This very faint, very tenuous filament of gas is streaming into the nearby galaxy NGC 6946 and may help explain how certain spiral galaxies keep up their steady pace of star formation.
“We knew that the fuel for star formation had to come from somewhere. So far, however, we’ve detected only about 10 percent of what would be necessary to explain what we observe in many galaxies,” said Pisano. “A leading theory is that rivers of hydrogen – known as cold flows – may be ferrying hydrogen through intergalactic space, clandestinely fueling star formation. But this tenuous hydrogen has been simply too diffuse to detect, until now.”
Spiral galaxies, like our own Milky Way, typically maintain a rather tranquil but steady pace of star formation. Others, like NGC 6946, which is located approximately 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus, are much more active, though less-so than more extreme starburst galaxies. This raises the question of what is fueling the sustained star formation in this and similar spiral galaxies.
Earlier studies of the galactic neighborhood around NGC 6946 with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands have revealed an extended halo of hydrogen (a feature commonly seen in spiral galaxies, which may be formed by hydrogen ejected from the disk of the galaxy by intense star formation and supernova explosions). A cold flow, however, would be hydrogen from a completely different source: gas from intergalactic space that has never been heated to extreme temperatures by a galaxy’s star birth or supernova processes.
Using the GBT, Pisano was able to detect the glow emitted by neutral hydrogen gas connecting NGC 6946 with its cosmic neighbors. This signal was simply below the detection threshold of other telescopes. The GBT’s unique capabilities, including its immense single dish, unblocked aperture, and location in the National Radio Quiet Zone, enabled it to detect this tenuous radio light.
Astronomers have long theorized that larger galaxies could receive a constant influx of cold hydrogen by syphoning it off other less-massive companions.
In looking at NGC 6946, the GBT detected just the sort of filamentary structure that would be present in a cold flow, though there is another probable explanation for what has been observed. It’s also possible that sometime in the past this galaxy had a close encounter and passed by its neighbors, leaving a ribbon of neutral atomic hydrogen in its wake.
If that were the case, however, there should be a small but observable population of stars in the filaments. Further studies will help to confirm the nature of this observation and could shine light on the possible role that cold flows play in the evolution of galaxies.
The 100-meter GBT is operated by the National Radio Astronomy Observatory (NRAO) and located in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone, which protect the incredibly sensitive telescope from unwanted radio interference.
Publication: D. J. Pisano, et al., “Green Bank Telescope observations of low column density HI around NGC 2997 and NGC 6946,” 2014, The Astronomical Journal, 147, 48; doi:10.1088/0004-6256/147/3/48
PDF Copy of the Study: Green Bank Telescope observations of low column density HI around NGC 2997 and NGC 6946
Source: National Radio Astronomy Observatory
Image: D.J. Pisano (WVU); B. Saxton (NRAO/AUI/NSF); Palomar Observatory – Space Telescope Science Institute 2nd Digital Sky Survey (Caltech); Westerbork Synthesis Radio Telescope | <urn:uuid:2d2b68b1-f539-47d1-9ddb-ac7b2ea73e82> | 3.765625 | 876 | News Article | Science & Tech. | 40.101567 | 95,518,645 |
Problems for the calculation of the surface area of the solid object
- Tropical, mild and arctic
How many percents of the Earth's surface lies in the tropical, mild and arctic range? The border between the ranges is the parallel 23°27 'and 66°33'.
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Axial section of the cone is equilateral triangle with area 208 dm2. Calculate volume of the cone.
The cuboid has a surface area 1771 cm2, the length of its edges are in the ratio 5:2:4. Calculate the volume of the cuboid.
- Tetrahedral pyramid
What is the surface of a regular tetrahedral (four-sided) pyramid if the base edge a=10 and height v=18?
- Cone A2V
Surface of cone in the plane is a circular arc with central angle of 126° and area 415 dm2. Calculate the volume of a cone.
One cube is inscribed sphere and the other one described. Calculate difference of volumes of cubes, if the difference of surfaces in 254 cm2.
The cube has area of base 225 mm2. Calculate the edge length, volume and area of its surface.
Surface of the sphere is 2820 cm2, weight is 71 kg. What is its density?
How much metal is needed for production 46 pieces of gutter pipes with the diameter 12 cm and length of 4 m? The plate bends add 2% of the material.
- Cuboid diagonal
Calculate the volume and surface area of the cuboid ABCDEFGH, which sides abc has dimensions in the ratio of 9:3:8 and if you know that the wall diagonal AC is 86 cm and angle between AC and the body diagonal AG is 25 degrees.
Right angle prism, whose base is right triangle with leg a = 7 cm and hypotenuse c = 15 cm has same volume as a cube with an edge length of 3 dm. a) Determine the height of the prism b) Calculate the surface of the prism c) What percentage of the cube
Calculate volume and surface area of the cone with diameter of the base d = 15 cm and side of cone with the base has angle 52°.
Gift box has rectangular shape with dimensions of 10×10×9 cm. Warren wants to cover with square paper with sides of 29 cm. How much paper left him?
- Cube zoom
How many percent we increase volume and surface of cube, if we magnify its edge by 38%.
Right triangle with legs 14 cm and 20 cm rotate around longer leg. Calculate the volume and surface area of the formed cone.
The top of the tower is a regular hexagonal pyramid with base edge 8 meters long and a height 5 meters. How many m2 of sheet is required to cover the top of the tower if we count 8% of the sheet waste?
Calculate the surface cube with edge 11 dm.
Jesters hat is shaped a rotating cone. Calculate how much paper is needed to the cap 60 cm high when head circumference is 52 cm.
- Sphere slices
Calculate volume and surface of a sphere, if the radii of parallel cuts r1=31 cm, r2=92 cm and its distance v=25 cm.
- Pyramid roof
1/3 of area of the roof shaped regular tetrahedral pyramid with base edge 9 m and height of 4 m is already covered with roofing. How many square meters still needs to be covered? | <urn:uuid:1daf3e15-ac89-463d-8a48-f25a3e7cee63> | 3.609375 | 739 | Tutorial | Science & Tech. | 69.964917 | 95,518,647 |
We used local microclimatic conditions and twig sap flow rates to interpret midday stomatal closure in the canopies of two 250-year-old Norway spruce (Picea abies (L.) Karst.) trees at a subalpine site in the Swiss Alps (1650 m a.s.l.). Both trees showed midday stomatal closure on most clear summer days, despite the permanently wet soil. We used a modified Penman-Monteith formula to simulate potential transpiration of single twigs (ETT) based on high-resolution temporal and spatial microclimate data obtained both inside and outside the crowns. Comparison of calculated ETT values and measured twig sap flow rates enabled us to pinpoint the occurrence of midday stomatal closure and the microclimatic conditions present at that time. We found that vapor pressure deficit (and for upper-crown twigs, ETT) largely explained the timing of initial midday stomatal closure but gave no explanation for the different patterns of stomatal behavior after initial closure in upper- and lower-crown twigs. After the initial stomatal closure, upper-crown twigs maintained high transpiration rates by continuously regulating stomatal aperture, whereas stomatal aperture decreased rapidly in lower-crown twigs and did not increase later in the day. Midday stomatal closure in lower-crown twigs occurred on average 1 h later than in upper-crown twigs. However, the microclimate at the time of initial stomatal closure was similar at both crown locations except that lower-crown twigs received significantly less solar radiation than upper-crown twigs both at the time of initial stomatal closure and afterwards. High rates of sap flow in twigs did not always lead to stomatal closure and therefore could not explain the phenomenon. We conclude that stomatal conductance can be modeled accurately only when both local microclimatic conditions and tree water status are known. Further, we hypothesize that both the quantity and quality of light play an important role in the reopening of closed stomata during the day.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below | <urn:uuid:77e7690f-104b-4ad6-b28f-d1716007584f> | 2.59375 | 461 | Academic Writing | Science & Tech. | 28.098372 | 95,518,649 |
Superoxide dismutases (SODs) are a family of metalloenzymes that catalyze the dismutation of superoxide anion radicals into molecular oxygen and hydrogen peroxide. Iron superoxide dismutases (FeSODs) are only expressed in some prokaryotes and plants. A new and highly active FeSOD with an unusual subcellular localization has recently been isolated from the plant Vigna unguiculata (cowpea). This protein functions as a homodimer and, in contrast to the other members of the SOD family, is localized to the cytosol. The crystal structure of the recombinant enzyme has been solved and the model refined to 1.97 A resolution. The superoxide anion binding site is located in a cleft close to the dimer interface. The coordination geometry of the Fe site is a distorted trigonal bipyramidal arrangement, whose axial ligands are His43 and a solvent molecule, and whose in-plane ligands are His95, Asp195, and His199. A comparison of the structural features of cowpea FeSOD with those of homologous SODs reveals subtle differences in regard to the metal-protein interactions, and confirms the existence of two regions that may control the traffic of substrate and product: one located near the Fe binding site, and another in the dimer interface. The evolutionary conservation of reciprocal interactions of both monomers in neighboring active sites suggests possible subunit cooperation during catalysis.
Mendeley saves you time finding and organizing research
Choose a citation style from the tabs below | <urn:uuid:7d4af86d-eed7-4782-8bdd-09cb5e65493c> | 2.703125 | 330 | Academic Writing | Science & Tech. | 10.159929 | 95,518,669 |
What are the positive and negative effects of wildfires? Are the effects primarily restricted to rural areas, and therefore, of little importance to the bulk of society? Defend your statement.© BrainMass Inc. brainmass.com July 21, 2018, 4:12 am ad1c9bdddf
When wildfires occur they destroy the surrounding vegetation. Without trees and shrubs, there is no uptake of carbon dioxide through plant photosynthesis and oxygen is not created. This can have negative implications not only on humans but also on global warming. With less carbon dioxide being taken up by plants, there is more carbon dioxide left in the atmosphere, thus contributing more greenhouse gases to climate change. In addition to the lack of uptake of carbon dioxide, CO2 is also release by the combustion of plant material. When a forest fire occurs it releases all of the carbon that was sequestered by the forest vegetation. This leads to even larger delivery of greenhouse gases to the atmosphere.
When forests are removed by forest fires, water is not as easily retained by the ecosystem because soils and foliage keep up to 50% of rain. This can alter the water balance and lead to increased runoff. This runoff can also carry ash and other materials from the ...
The positive and negative effects of wildfires are examined. The effects primarily restricted to rural areas and little importance to the bulk of society is determined. | <urn:uuid:841cec6e-2877-46e6-b72b-7c62fbcc3cbe> | 3.75 | 277 | Truncated | Science & Tech. | 42.380109 | 95,518,683 |
Get help in your MATLAB Assignments Online
from MATLAB Experts with optimistic results
Python is an interpreted high-level programming language for general-purpose programming. Created by Guido van Rossum and first released in 1991, Python has a design philosophy that emphasizes code readability, notably using significant whitespace
Python is a high-level general purpose programming language that offers multiple paradigms like object-orientation, and structural and functional programming for software development. It works on cross-platform operating systems and can be used across to develop a wide range of applications including those intended for image processing, text processing, web, and enterprise level using scientific, numeric and data from network. BitTorrent, YouTube, Dropbox, Deluge, Cinema 4D and Bazaar are a few globally-used applications based on Python.
Bitcoin Price Prediction | Python
Bitcoin Price Prediction using Tensor Flow(python) used with MATLAB . A deep learning program for highly accurate prediction . | <urn:uuid:2cfd4f97-6093-4f54-aea6-b1206b572cbc> | 2.6875 | 197 | Product Page | Software Dev. | 6.751314 | 95,518,688 |
Can you set the logic gates so that this machine can decide how many bulbs have been switched on?
What will happen when you switch on these circular circuits?
Can you work out what this procedure is doing?
Can you think like a computer and work out what this flow diagram does?
Prove that you can make any type of logic gate using just NAND gates.
Can you work out which of the equations models a bouncing bomb? Will you be able to hit the target?
As a capacitor discharges, its charge changes continuously. Find the differential equation governing this variation.
Put your complex numbers and calculus to the test with this impedance calculation.
In this short problem we investigate the tensions and compressions in a framework made from springs and ropes.
Given the equation for the path followed by the back wheel of a bike, can you solve to find the equation followed by the front wheel?
This article, including exercises, gives a thorough grounding in the topic of AC/DC circuits.
Explore the voltages and currents in this interesting circuit configuration.
What is a random pattern?
Explore the mathematics behind the famous Wheatstone Bridge circuit.
This short question asks if you can work out the most precarious way to balance four tiles.
Which parts of these framework bridges are in tension and which parts are in compression?
In an extension to the Stonehenge problem, consider the mechanical possibilities for an arrangement of frictional rollers.
A series of activities to build up intuition on the mathematics of friction.
A look at power generation using wind turbines.
A preview of some of the beam deflection mechanics you will look at in the first year of an engineering degree
Derive Euler's buckling formula from first principles.
Things are roughened up and friction is now added to the approximate simple pendulum
A look at the fluid mechanics questions that are raised by the Stonehenge 'bluestones'.
An introduction to a useful tool to check the validity of an equation.
At what positions and speeds can the bomb be dropped to destroy the dam?
Explore the power of aeroplanes, spaceships and horses.
Find out how to model a battery mathematically
This is the area of the advanced stemNRICH site devoted to the core applied mathematics underlying the sciences.
What is an AC voltage? How much power does an AC power source supply?
Have you got the Mach knack? Discover the mathematics behind exceeding the sound barrier.
A look at a fluid mechanics technique called the Steady Flow Momentum Equation.
Show that even a very powerful spaceship would eventually run out of overtaking power
An article about the kind of maths a first year undergraduate in physics, engineering and other physical sciences courses might encounter. The aim is to highlight the link between particular maths. . . .
Look at the calculus behind the simple act of a car going over a step.
Can you match up the entries from this table of units?
PhysNRICH is the area of the StemNRICH site devoted to the mathematics underlying the study of physics
engNRICH is the area of the stemNRICH Advanced site devoted to the mathematics underlying the study of engineering
Was it possible that this dangerous driving penalty was issued in error?
See how the motion of the simple pendulum is not-so-simple after all.
This is the technology section of stemNRICH - Core.
How do these modelling assumption affect the solutions?
Explain why, when moving heavy objects on rollers, the object moves twice as fast as the rollers. Try a similar experiment yourself.
Doug has just finished the first year of his undergraduate engineering course at Cambridge University. Here he gives his perspectives on engineering.
Estimate these curious quantities sufficiently accurately that you can rank them in order of size
Given the graph of a supply network and the maximum capacity for flow in each section find the maximum flow across the network.
Bricks are 20cm long and 10cm high. How high could an arch be built without mortar on a flat horizontal surface, to overhang by 1 metre? How big an overhang is it possible to make like this? | <urn:uuid:c2db3186-087f-4499-9599-7383b83029eb> | 3.4375 | 857 | Content Listing | Science & Tech. | 50.700084 | 95,518,707 |
To remove the paradox of classical Fourier theory relating to the instantaneous propagation of thermal disturbances, Cattaneo suggested a generalized Fourier law, which he justified by means of statistical considerations. This constitutive equation relates the heat flux, its time derivative, and the temperature gradient. It is referred to as the Cattaneo–Maxwell relation, since Maxwell previously obtained it but immediately eliminated the term involving the time derivative of the heat flux. It leads to a hyperbolic heat equation.
KeywordsHeat Conductor Constitutive Equation Internal Energy Relaxation Function Maxwell Relation
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Astronomers have mapped the ages of 70,000 stars spanning our galaxy, ushering in a new era of galactic archaeology.
In an archaeological dig, scientists sift through the shards and bones that lay scattered in the dirt. They carefully brush off layers of dust, note each item’s position, and take samples for carbon dating. Now, with a new technique in hand, astronomers are doing much the same, but their dig site is a bit bigger: the Milky Way Galaxy.
At the American Astronomical Society meeting in Kissimmee, Florida, Melissa Ness (Max Planck Institute for Astronomy, Germany) announced her team's release of a catalog that maps the ages of 70,000 red giant stars scattered throughout our galaxy. Like carbon-dating, these luminous beacons and the new method of measuring their ages will revolutionize the field of galactic archaeology.
Digging Up the Milky Way
“Big Data” has become a buzzword everywhere from the corner office to the genetics lab, but astronomy’s been in the business of big data since the advent of the Sloan Digital Sky Survey (SDSS) in 2000. In recent years, the Sloan telescope turned its watchful eye from the farthest reaches of the cosmos to our own galaxy. Since 2011, a survey dubbed APOGEE has sighted 150,000 red giant stars across the Milky Way, splitting starlight across the visible-light range to collect detailed spectra for every star.
But sifting through all that data isn’t easy. And that’s particularly true when it comes to measuring something more indirect like age — stars are secretive about the number of years under their belt.
One way to date a star is to measure the seismic waves that ripple across its surface. These starquakes create pulsations in brightness that change as the star ages. But doing these observations requires time — the kind of time that Kepler had when it stared at hundreds of thousands of stars for four years.
Another way is more indirect. The outer layers of stars like the Sun boil with convective fervor, and when these stars evolve to become red giants, that roiling plasma extends its reach down to scrape the star’s core. Just-fused elements get dredged up from the core and carried to the surface, theoretically revealing how long the star has been around.
Marie Martig (also at the Max Planck Institute for Astronomy) and colleagues took the best of both worlds when they examined 1,475 red giants with both seismic masses from Kepler and dredged-element data from Sloan spectra. This set of overlapping data became the training set for an algorithm dubbed “The Cannon” (named in honor of Annie Jump Cannon). After teaching The Cannon to classify stars’ ages by their spectra, Ness, Martig, and colleagues set it loose on the full dataset. It returned the age for some 70,000 stars strewn throughout the Milky Way.
Star dating, like the carbon dating that revolutionized archaeology, provides astronomers with an essential tool to piece together our galaxy’s history. In a way, it’s still a crude tool — the mass estimates for any given star can be off by as much as 40%. But combined, tens of thousands of stars beat those errors down and provide useful insight. Already, the team has been able to confirm that our galaxy’s spiral disk formed from the inside out, bolstering accepted theory.
The youngest red giant stars assemble along the galactic plane, a skeleton of sorts that’s encased by older stars. Farther from the galaxy’s center, this “backbone” of younger stars flares outward, away from the plane. These patterns are the hallmark of a disk that started small and grew slowly outward, as though whoever was pouring the pancake batter first ladled into the center and then added more and more batter on the outer edges.
These results prove The Cannon works and lay the foundation for future studies, says Daniel Majaess (St. Mary’s University and Mount St. Vincent University, Canada). And Ness, who has already had lots of requests for the catalog, expects those future studies will be coming out soon. | <urn:uuid:eda6f6bd-20d7-49fa-8f2a-5b4184fd5515> | 3.921875 | 876 | News Article | Science & Tech. | 49.216271 | 95,518,730 |
Europe on Thursday launched the first in a constellation of hi-tech satellites designed to monitor Earth for climate change and environmental damage and help disaster relief operations.
Sentinel-1A, a satellite designed to scan the Earth with cloud-penetrating radar, lifted off at 2102 GMT aboard a Soyuz rocket from Kourou, French Guiana, the European Space Agency (ESA) said.
The 2.2-tonne satellite is the first of half a dozen orbital monitors that will be built and launched under the 3.786-billion-euro ($5.19-billion) Copernicus project, a joint undertaking of ESA and the European Union (EU).
Sentinel-1A separated from the rocket’s upper stage 23 minutes and 24 seconds after launch.
It will be followed by a partner, Sentinel-1B, due to be launched towards the end of next year.
Operating 180 degrees apart, at an altitude of about 700 kilometres (435 miles), between them the pair will be able to take a radar picture of anywhere on Earth within six days.
Radar scanning has a range of uses, from spotting icebergs and oil slicks to detecting rogue logging and ground subsidence.
The data will be widely accessible to the public, and is likely to have uses that go beyond the environment, such as in construction and transport.
By mapping areas stricken by flood or earthquake, the monitors will also be able to help emergency teams identify the worst-hit areas and locate roads, railway lines and bridges that are still passable, ESA says.
The others in the series are Sentinel-2, which will deliver high-resolution optical images of forests and land use; Sentinel-3, providing ocean and land data; and Sentinels 4 and 5, which will monitor Earth’s atmospheric composition — the basic component in fine-tuning understanding about greenhouse gases.
The goldmine of data expected to be thrown up by the satellite constellation will be more accessible to the public than any previous Earth-monitoring programme.
The potential applications go beyond stewardship of the environment. They could help shipping firms, farmers and construction companies, too.
“Copernicus is the most ambitious Earth observation programme to date,” ESA said.
“It will provide accurate, timely and easily accessible information to improve the management of the environment, understand and mitigate the effects of climate change and ensure civil security.”
Copernicus replaces Envisat, one of the most successful environmental satellites in space history, whose mission ended in 2012.
It was named last year in honour of the 16th-century Polish astronomer who determined that the Earth orbited the Sun, and not the other way round, as convention had it at the time.
[Image via Agence France-Presse] | <urn:uuid:574bb7ee-4707-4052-b3dc-c6d6b83c3941> | 3.578125 | 581 | News Article | Science & Tech. | 36.356291 | 95,518,764 |
Micron X-ray computed tomography based on micro-particle-induced X-ray emission
- Keizo Ishii
- International Journal of PIXE
- World Scientific Publishing
- Cited Count
- World Scientific
Particle-induced X-ray emission (PIXE) is a phenomenon of atomic inner shell ionization and characteristic X-ray emission due to ion-atomic collisions. The intensity of continuous X-rays in the PIXE energy spectrum is much lower than that of characteristic X-rays. Therefore, PIXE can be used as a semi-monochromatic X-ray source. Furthermore, PIXE produced by a heavily charged particle beam with a diameter of several micrometers (micro-PIXE) can be used as a monochromatic X-ray point source for Xray computed tomography (CT) to investigate internal structures of objects <1 mm. We developed micron X-ray CT based on micro-PIXE with a spatial resolution of about 4 μm. Because the photoelectric effect cross-section is proportional to the fifth power of the atomic number, the distributions of small amounts of heavy elements can be investigated using this CT technique, and the element can be identified using its absorption edge. We applied this CT to observe the internal structure of hair, a head of an ant, and Drosophila. We were able to identify the medulla configuration and cortex of the hair, and the mandibular glands, pharynx, and brain in the ant head. We confirmed a high Mn concentration in the mandibular glands. We used a contrast agent to visualize the internal organs of Drosophila. Furthermore, we applied this CT to research clay particles contaminated by the Fukushima Dai-ichi nuclear accident and confirmed that cesium atoms were distributed on the surfaces of clay particles.
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Package sanitize provides functions to sanitize html and paths with go (golang).
sanitize.Accents(s string) string
Accents replaces a set of accented characters with ascii equivalents.
sanitize.BaseName(s string) string
BaseName makes a string safe to use in a file name, producing a sanitized basename replacing . or / with -. Unlike Name no attempt is made to normalise text as a path.
sanitize.HTML(s string) string
HTML strips html tags with a very simple parser, replace common entities, and escape < and > in the result. The result is intended to be used as plain text.
sanitize.HTMLAllowing(s string, args...string) (string, error)
HTMLAllowing parses html and allow certain tags and attributes from the lists optionally specified by args - args is a list of allowed tags, args is a list of allowed attributes. If either is missing default sets are used.
sanitize.Name(s string) string
Name makes a string safe to use in a file name by first finding the path basename, then replacing non-ascii characters.
sanitize.Path(s string) string
Path makes a string safe to use as an url path. | <urn:uuid:afb2c5e5-dc1f-42fd-8da6-bf3ee39fb93e> | 2.75 | 278 | Structured Data | Software Dev. | 56.803522 | 95,518,773 |
A rocket carrying a NASA spacecraft was launched Wednesday on a first-ever mission to study mysterious clouds that float 50 miles (80 kilometers) above Earth.
The noctilucent clouds, which cluster around the polar regions and can only been seen at night, have appeared more often and grown brighter in recent years. Scientists are puzzled by the changes, but some suggest they may be due to global climate change.
The spacecraft, which will spend two years studying the ice clouds, will try to answer basic questions including why the clouds form and whether human-caused global warming is responsible for the changes. It is dubbed AIM, short for Aeronomy of Ice in the Mesosphere.
"We are exploring clouds literally on the edge of space," principal investigator James Russell of Hampton University said at a press conference earlier this month. | <urn:uuid:ff335190-2b0d-4da0-afb1-d721f597eb03> | 3.734375 | 168 | News Article | Science & Tech. | 42.117956 | 95,518,780 |
Standard Guide for Background Subtraction Techniques in Auger Electron Spectroscopy and X-Ray Photoelectron SpectroscopyÜbersetzen
NORM herausgegeben am 1.11.2016
Bezeichnung normen: ASTM E995-16
Ausgabedatum normen: 1.11.2016
Zahl der Seiten: 6
Gewicht ca.: 18 g (0.04 Pfund)
Land: Amerikanische technische Norm
Kategorie: Technische Normen ASTM
Auger electron spectroscopy, background subtraction, surface analysis, X-ray photoelectron spectroscopy,, ICS Number Code 17.180.30 (Optical measuring instruments)
|Significance and Use|
5.1 Background subtraction techniques in AES were originally employed as a method of enhancement of the relatively weak Auger signals to distinguish them from the slowly varying background of secondary and backscattered electrons. Interest in obtaining useful information from the Auger peak line shape, concern for greater quantitative accuracy from Auger spectra, and improvements in data gathering techniques, have led to the development of various background subtraction techniques.
5.2 Similarly, the use of background subtraction techniques in XPS has evolved mainly from the interest in the determination of chemical states (from the binding-energy values for component peaks that may often overlap), greater quantitative accuracy from the XPS spectra, and improvements in data acquisition. Post-acquisition background subtraction is normally applied to XPS data.
5.3 The procedures outlined in Section are popular in XPS and AES; less popular procedures and rarely used procedures are described in Sections , respectively. General reviews of background subtraction methods and curve-fitting techniques have been published elsewhere 5.4 Background subtraction is commonly performed prior to peak fitting, although it can be assessed (fitted) during peak fitting (active approach (). Some commercial data analysis packages require background removal before peak fitting. Nevertheless, a measured spectral region consisting of one or more peaks and background intensities due to inelastic scattering, Bremsstrahlung (for XPS with unmonochromated X-ray sources), and scattered primary electrons (for AES) can often be satisfactorily represented by applying peak functions for each component with parameters for each one determined in a single least-squares fit. The choice of the background to be removed, if required or desired, before or during peak fitting is suggested by the experience of the analysts, the capabilities of the peak fitting software, and the peak complexity as noted above. , )
1.1 The purpose of this guide is to familiarize the analyst with the principal background subtraction techniques presently in use together with the nature of their application to data acquisition and manipulation.
1.2 This guide is intended to apply to background subtraction in electron, X-ray, and ion-excited Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
|2. Referenced Documents|
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The idea of higher dimensional space can certainly provoke discussion, at KS 23 and KS4 as well at A-level. The image in the article of the carp in the shallow pond, restricted to only two dimensions, is very powerful. As the article says, if you lived in a 2D world, but could move into 3D, you could "magically" appear and disappear from the world by moving in and out of the third dimension. There is a classic book: Flatland: a romance of many dimensions by Edwin A Abbott, which explores ideas like these. It tells the story of a square living in a 2D world and is a worthwhile addition to any school library, with ideas relevant at KS23 and above.
The idea that a "Theory of Everything", explaining all physical phenomena, might be given in an equation "no more than one inch long" really brings home the power of maths. This feature is particularly relevant to A-level maths. Modern physics is founded in mathematics. Newtonian mechanics, relativity and quantum mechanics and superstring theory are mathematical models which attempt to describe the physical world. Physicists express their ideas mathematically then test them against experimental observation and modify them to improve their match with the universe. This is exactly the mathematical modelling process that forms a key part of ASA-level Mathematics. Students making ASA-level choices need to understand just how important maths is in other fields.
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I won't repeat the article from Scientific American; the author (Michael E Mann) says it better than I can. You can read it here. A key discussion in the article is how much global temperatures will rise if atmospheric CO2 doubles from the 280 ppm (parts per million) before industrialisation began to 560 ppm. His estimate: 3 degrees centigrade.
The first chart below from the article shows different estimates of how much the world will warm based on different lines of evidence.
The second chart shows how temperatures will rise depending on just how sensitive the world's climate is to rising CO2. In the article, the author points out that reducing aerosols (emitted along with CO2 by burning coal ) will cause global temps to rise. So ironically, even as China slashes its emissions of CO2 global temps will rise/
Disclaimer. After nearly 40 years managing money for some of the largest life offices and investment managers in the world, I think I have something to offer. These days I'm retired, and I can't by law give you advice. While I do make mistakes, I try hard to do my analysis thoroughly, and to make sure my data are correct (old habits die hard!) Also, don't ask me why I called it "Volewica". It's too late, now.
BTW, clicking on most charts will produce the original-sized, i.e., bigger version. | <urn:uuid:79cced0b-d05d-44ff-967f-5e3e44762319> | 2.53125 | 294 | Personal Blog | Science & Tech. | 57.435784 | 95,518,802 |
Self-assembled graphene and copper nanoparticles composite sensor for nitrate determination
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A new sensor based on decorated copper nanoparticles and self-assembled graphene was fabricated and exemplified with the determination of nitrate solutions. Traditionally, graphene is coated on the sensor by drop-casting, leading to poor adhesion between graphene and the sensor. The self-assembled graphene proposed in this paper not only have a firm connection with the substrate, but also provide a three-dimensional network structure for copper nanoparticles. Copper was found as an effective catalyst for nitrate reduction. The combination of copper nanoparticles and self-assembled graphene can greatly enhance the sensitivity. Thus, low detection limit of 7.89 µM is obtained for nitrate, which to our knowledge, is among the lowest reported in the literatures. This method was employed for the determination of nitrate in lake water and the results were in good agreement with those obtained from a standard analytical procedure.
One of the authors acknowledges the support from China Scholarship Council. The devices are fabricated at Minnesota Nano Center, Minneapolis, MN, USA.
- Bard AJ, Faulkner LR (1980) Electrochemical methods: fundamentals and applications. Wiley, New YorkGoogle Scholar
- World Health Organization (2008) Guidelines for drinking water quality, 3rd edn. World Health Organization, GenevaGoogle Scholar
- Keawkim K, Chuanuwatanakul S, Chailapakul O, Motomizu S (2013) Determination of lead and cadmium in rice samples by sequential injection/anodic stripping voltammetry using a bismuth film/crown ether/Nafion modified screen-printed carbon electrode. Food Control 31:14–21. https://doi.org/10.1016/j.foodcont.2012.09.025 CrossRefGoogle Scholar | <urn:uuid:c9cf4f96-a3fa-450a-95b5-0877a9c1335b> | 2.6875 | 377 | Academic Writing | Science & Tech. | 28.927181 | 95,518,806 |
A giant gas planet -- up to fifty times the mass of Jupiter, encircled by a ring of dust -- is likely hurtling around a star more than a thousand light years away from Earth, according to astronomers, led by the University of Warwick.
A giant gas planet - up to fifty times the mass of Jupiter, encircled by a ring of dust - is likely hurtling around a star more than a thousand light years away from Earth, according to new research by an international team of astronomers, led by the University of Warwick.
Hugh Osborn, a researcher from Warwick's Astrophysics Group, has identified that the light from this rare young star is regularly blocked by a large object - and predicts that these eclipses are caused by the orbit of this as-yet undiscovered planet.
Using data from the Wide Angle Search for Planets (WASP) and Kilodegree Extremely Little Telescope (KELT), Osborn and fellow researchers from Harvard University, Vanderbilt University, and Leiden Observatory analysed fifteen years of the star's activity.
"We found a hint that this was an interesting object in data from the WASP survey," said Hugh Osborn, lead author, who discovered the unusual light curve, "but it wasn't until we found a second, almost identical eclipse in the KELT survey data that we knew we had something special."
They discovered that every two and a half years, the light from this distant star - PDS 110 in the Orion constellation, which is same temperature and slightly larger than our sun - is reduced to thirty percent for about two to three weeks. Two notable eclipses observed were in November 2008 and January 2011.
"What's exciting is that during both eclipses we see the light from the star change rapidly, and that suggests that there are rings in the eclipsing object, but these rings are many times larger than the rings around Saturn," says Leiden astronomer Matthew Kenworthy.
Assuming the dips in starlight are coming from an orbiting planet, the next eclipse is predicted to take place in September this year - and the star is bright enough that amateur astronomers all over the world will be able to witness it and gather new data. Only then will we be certain what is causing the mysterious eclipses.
If confirmed in September, PDS 110 will be the first giant ring system that has a known orbital period.
"September's eclipse will let us study the intricate structure around PDS 110 in detail for the first time, and hopefully prove that what we are seeing is a giant exoplanet and its moons in the process of formation," comments Hugh Oborn.
The researchers suggest that there are moons could be forming in the habitable zone around PDS 110 - pointing to the possibility that life could thrive in this system.
The eclipses can also be used to discover the conditions for forming planets and their moons at an early time in the life of a star, providing a unique insight into forming processes that happened in our solar system.
The research, 'Periodic Eclipses of the Young Star PDS 110 Discovered with WASP and KELT Photometry', is due to be published in the Monthly Notices of the Royal Astronomical Society.
Luke Walton | EurekAlert!
Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
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Ecosystems can be highly dependent on groundwater. Springheads, and wetlands, streams, rivers and lakes may receive groundwater discharge. Groundwater may support shallow-rooted lowland woods and meadows in alluvial settings, or deep-rooted vegetation in arid zones with much deeper water-tables. Understanding how groundwater provides support to ecosystems and the economic consequences of groundwater degradation will emphasise the need for collaborative and integrated actions and basin management for rivers, lakes and aquifers. For further information see IAH’s strategic overview on ecosystem conservation and groundwater.
11 months 2 weeks
Thanks for coming back to me on this. As you know, groundwater can all too often be ‘out of sight and out of mind’ and so can be neglected by those who manage activities that affect the water environment and dependent ecosystems. Groundwater is a fundamental part of the water environment and needs to be managed together with rivers, lakes and estuaries – and of course needs to be taken into account when considering any activities that impact on water in the environment. To do this we need to help all the relevant stakeholders understand how the different parts in this story fit together - and to take the necessary collaborative actions to manage them sustainably.
Groundwater is a major source of urban supply worldwide. However, urbanisation modifies the ‘groundwater cycle’ and can lead to declining aquifer pressures (which can cause land subsidence with building and infrastructure damage) or a rising water-table (which can lead to groundwater flooding with public health hazards and infrastructure damage). Groundwater needs to be used efficiently and sustainably for urban water-supply, and an ‘adaptive management strategy’ should be applied. Integrated approaches to urban water-supply, mains sewerage and sanitation, stormwater drainage, and urban land-use will reduce the cost and improve the resilience of the urban water infrastructure. Cross sector consortia of regulatory agencies and other major stake holders, including groundwater representation, should establish and implement management action plans. For further information see the International Association of Hydrogeologists' Strategic overview on resilient cities and groundwater.
The high quality of most groundwaters, resulting from the self-purification capacity of soils and underlying rocks, has long been a key factor in human health and wellbeing. More than 50% of the world’s population now rely on groundwater for their supply of drinking water. Aquifers used for drinking water supplies should be assessed and monitored for pollution risks. In most cases a properly located and soundly-engineered water-well that prevents direct entry of pollutants, such as pathogenic organisms, fuels or other contaminants, represents a low-cost, reliable and safe source. Collaborative actions by a range of water-users will help protect this vital resource. For further information see IAH’s strategic overview on human health and groundwater.
11 months 1 week
Thanks for your question on this. Clearly good quality, safe drinking water is vital and with so much of the world's population reliant on groundwater it is essential that we protect this resource. Wells need to be sited away from sources of pollution and be designed to prevent entry of pollutants. Protection of groundwater is integral to achieving the SDG targets and ideally there should be ‘groundwater resource status indicators’ to realise these aims. The International Association of Hydrogeologists has published a strategic overview on how groundwater resources underpin the UN Sustainable Development Agenda for 2030. You can find out further information on SDGs and essential indicators for groundwater here. | <urn:uuid:732d0ee2-f7f6-42ea-a2fa-e9dc07bd412c> | 3.9375 | 723 | Comment Section | Science & Tech. | 25.141346 | 95,518,842 |
About the Earth Motor. Basically a motor can do work by generating displacing mechanical pressure waves. This induces a vibratory nature as well as a sound harmonic compression of first and second "mechanical spectral" levels, regions which can be tuned for destructive or constructive interference of waves thus generating nodal points of power. The nodes can yield places of energy or no energy which then can be utilized in real time or collected, recorded and stored. Therefore the motor is capable of sending out or transmitting work to other points in space, but within the confines of a medium.
Tuning & Calibration
The motor is thus tuned to the pressure, density, and temperature of the medium. This calibration determines the speed of the motor, along with an electronic tuning that adjusts the mechanical frequency of transmitting work. The motor is not electromagnetic in nature, in terms of its transmitted work. However, the motor itself is electronic and driven by CMOS and integrated circuit technology.
Motor Work & Power Equations
The equation for the work done is the energy transferred from one place to another. The amount of work done is the force times the distance. The motor power is a measure of how quickly work is being done. Power is expressed as work done divided by time taken. Motion of the medium can effect work perform by the motor thus increasing or decreasing its mechanistic speed. Viscosity can also be used to provide motor attenuation.
Adiabatic Earth Motor AEM generates power waves that can penetrate and travel through all forms of matter, such as a solid, liquid, gas or plasma stream. The energy carried by the motor's oscillating wave converts back and forth between potential energy of the extra compression or lateral displacement stream (with a transverse function) of matter, and the kinetic energy of the displacement velocity of particles of the medium.
The motor does work in a vector from 17m to 17mm. The speed and direction will make up a velocity vector while the wave number and direction create a wave vector. The motor is not isothermal but rather adiabatic.
The periodicy of the motor is yet to be measured but will depend on frequency, amplitude, pressure, speed and direction.
If the medium does not have constant physical properties, the motor can be refracted, and either disperse or focus its work. Refraction has potential space-time applications and the ability to splay energy for work to multiple places at the same time from only one AEM motor. Drawing refraction energy does not tax the AEM in any way, therefore maximum draw is allowable from a maximum number of nodals.
The original AEM did not have internal amplification. The new AEM has provisions for amplification to significantly increase power. The horsepower will vary with the size of the AEM packaging and the size of the motor.
Motor Speed Equation
The speed of the motor is defined according to the Newton-Laplacian equation c = square root of K/rho where K = elastic bulk modulus, c = sound velocity, rho = density. Therefore the motor speed is proportional to the square root of the ratio of the bulk modulus of the medium to its density.
Motor or Engine?
The difference between a motor and an engine is that motors run on electricity while engines run on combustion. | <urn:uuid:7c1d37dd-3c0a-4f78-9faa-6d306b06e220> | 3.609375 | 675 | Knowledge Article | Science & Tech. | 37.733773 | 95,518,849 |
A lightning strike can result in a cardiac arrest and death, and the most lightning strikes occur during warm summer months when people are outside enjoying the weather.
While the southeastern U.S. is no stranger to humid, stormy conditions, widespread wet weather will be more disruptive than usual this week.
An annual event, known as the North America monsoon, will continue to bring the risks of flash flooding, dust storms and lightning strikes over the southwestern United States in the weeks to come.
Violent storms led to an EF2 tornado in the Plains this week, killing an infant and injuring dozens while the aftermath of the devastating Japan flooding proves challenging for rescue efforts.
A lightning strike has sent 15 soldiers to the hospital in Columbia, South Carolina on Thursday. The National Weather Service in Columbia confirmed the strike hit near Fort Jackson during a training exercise.
Following a deadly and destructive tornado from Tuesday night, more severe storms, including the potential for a few tornadoes will affect part of the north-central United States into Thursday night.
Showers and thunderstorms will help ease drought conditions in the southwestern United States into the weekend, but also enhance the risk of flash flooding and dust storms.
Lightning from average thunderstorms continues to be a significant risk to lives this summer. | <urn:uuid:c5617843-89ba-4e0c-9f31-7d02662bf005> | 3.25 | 259 | Content Listing | Science & Tech. | 43.868636 | 95,518,867 |
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Click Here to Read about El Niño and La Nina and their impact on Indian Weather. Feature El-Nino La-Nina Meaning El Nino is a Spanish term which represents “little boy” La Nina is a Spanish term which represents ‘little girl’. Temperature at Sea Surface Temperature at sea surface is warmer than normal sea-surface temperatures. El Nino
The Maharashtra Government had constituted Dharmadhikari committee in 2010 under Justice Chandrashekar Dharmadhikari to suggest measures to curb atrocities against women has recently submitted its one more interim report to the Bombay High Court. The government / court have received several “interim reports” most of which are gathering dust and the full and final report
Big Data is the new reality of everyday living and stands for an immensely huge pool of data which cannot be de-jargoned with ordinary and archaic methods of data interpretation. Such huge data-sets form the basis of all reasonable aspects of society. Data-driven decision-making is gaining leverage and has lent more authenticity to modern ways | <urn:uuid:7cae8448-d409-4e60-bcab-c667c1449722> | 3.1875 | 230 | Truncated | Science & Tech. | 24.260385 | 95,518,884 |
Normal Incidence of action ball game full version Plane Waves shorter oxford textbook of psychiatry pdf at Multiple Dielectric Interfaces.
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Electromagnetics is defined as the study of electric and magnetic phenomena which are caused by the electric charges when they are in rest or when they are in motion.
Wave Characteristics on Finite Transmission Lines.
Gauss's Law and Applications.
Boundary Conditions for Electrostatic Fields.
Poisson's and Laplaces' Equations.Magnetization and Equivalent Current Densities.Faraday's Law of Electromagnetic Induction.Magnetic Field Intensity and Relative Permeability.Fundamental Postulates of Magnetostatics in Free Space.Oblique Incidence of Plane Waves at a Plane Conducting Boundary.Boundary-Value Problems in Cartesian Coordinates.Power Dissipation and Joule's Law.Plane Waves in Lossless Media. | <urn:uuid:6622cc6f-bf85-476b-bc5b-6af4157e97ee> | 3.46875 | 267 | Content Listing | Science & Tech. | 26.759524 | 95,518,890 |