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WHAT IS GEOMETRY? Geometry is the field of mathematical knowledge dealing with spatial relationships. The earliest written records -- dating from Egypt and Mesopotamia about 3100 BC -- demonstrate that ancient peoples had already begun to devise mathematical rules and techniques useful for surveying land areas, constructing buildings, and measuring storage containers. Beginning about the 6th century BC, the Greeks gathered and extended this practical knowledge and from it generalized the abstract subject now known as geometry, from the combination of the Greek words geo (Earth) and metron (measure).
WHAT IS GLOBAL WARMING DOING TO THE OCEANS? It's raising the oceans' temperatures ever so slowly, but also, it's making it easier for them to absorb Carbon Dioxide (CO2). Large amounts of CO2 are absorbed by the ocean, up to a million tons an hour worldwide. This changes the chemistry of the ocean, making it slightly more acidic. This can harm the environment as far as many marine animals and plants are concerned, causing devastation in ecosystems like coral reefs. However, because more acidic seawater absorbs less low- and mid-frequency sound (the frequencies at which many animals communicate), water becomes better able to transmit certain frequencies, meaning that equally loud noises can be heard farther away in water with lower pH levels.
The American Geophysical Union, American Mathematical Society, American Statistical Association, Biophysical Society, Mathematical Association of America, and Society for Industrial and Applied Mathematics, contributed to the information contained in the TV portion of this report. | <urn:uuid:42817b51-ab7a-483b-9eac-acfe50b3050e> | 3.203125 | 314 | Knowledge Article | Science & Tech. | 21.693839 |
Results from our forum
... cores are putted in that solutions it will loose or get water or doesn't loose or gain water. So the objective of this experiment is to find the hydric potencial of the potato. When the concentration of the solution is lower than the potato, water gets out from the potatoe. when the concentation ...
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Hamilton, J., Zangerl, A.R., Berenbaum, M.R., Sparks, J.P., Elich, L., Eisenstein, A. and DeLucia, E.H. 2012. Elevated atmospheric CO2 alters the arthropod community in a forest understory. Acta Oecologica 43: 80-85.
The authors write that "the response of complex plant and animal communities to global change is highly variable (Tylianakis et al., 2008)," but they note that "recent studies have documented that loss of foliage to arthropod herbivores decreases under elevated CO2 in woody communities (Hamilton et al., 2004; Knepp et al., 2005; Stiling and Cornelissen, 2007)," and they say that the fitness and in some cases the population size of herbivorous insects may decline in communities exposed to elevated CO2 (Hillstrom and Lindroth, 2008; Hillstrom et al., 2010)," although they indicate that the "effects of elevated CO2 on naturally occurring arthropod assemblages have not yet been widely characterized."
What was done
Working at the Duke Forest FACE facility in the Piedmont region of North Carolina (USA) - where three 30-meter-diameter plots of an expansive stand of loblolly pine had their atmospheric CO2 concentrations boosted by approximately 200 ppm, and where three other such plots were maintained at the normal ambient CO2 concentration - Hamilton et al. counted the numbers of different types of arthropods found in each of the six plots every two weeks throughout June and July of 2005, in order to be able to assign them to different feeding guilds. In addition, they say that "stable isotope data for spiders collected in ambient and elevated CO2 plots were analyzed to determine the extent to which herbivorous prey species moved into and out of the elevated CO2 plots."
What was learned
The seven U.S. scientists say their isotopic data "gave no indication that the treatment plots represented a 'boundary' to the movement of insects." In addition, they determined there was no detectable effect of elevated CO2 on the total number of individual arthropods in the two sets of treatment plots. However, they say "there was an increase in the numbers of individuals collected in primarily predaceous orders (Araneae and Hymenoptera; from 60% to more than 150%) under elevated CO2 and a decrease in the numbers in primarily herbivorous orders (Lepidoptera and Coleoptera; from -30 to -45%)."
What it means
In the closing sentence of their paper, Hamilton et al. conclude what is pretty obvious, i.e. that "decreases in herbivorous arthropods and increases in predaceous arthropods may contribute to reduced herbivory under elevated CO2 in forest systems," which is basically what has also been observed in the other studies that have experimentally explored the subject, all of which bodes well for earth's forests in a CO2-enriched world of the future.
Hamilton, J.G., Zangerl, A.R., Berenbaum, M.R., Pippen, J.S., Aldea, M. and DeLucia, E.H. 2004. Insect herbivory in an intact forest understory under experimental CO2 enrichment. Oecologia 138: 566-573.
Hillstrom, M.L. and Lindroth, R.L. 2008. Elevated atmospheric carbon dioxide and ozone alter forest insect abundance and community composition. Insect Conservation and Diversity 1: 233-241.
Hillstrom, M.L., Vigue, L.M., Coyle, D.R., Raffa, K.F. and Lindroth, R.L. 2010. Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO2 and host species. Agricultural and Forest Entomology 12: 285-292.
Knepp, R.G., Hamilton, J.G., Mohan, J.E., Zangerl, A.R., Berenbaum, M.R. and DeLucia, E.H. 2005. Elevated CO2 reduces leaf damage by insect herbivores in a forest community. New Phytologist 167: 207-218.
Stiling, P. and Cornelissen, T. 2007. How does elevated carbon dioxide (CO2) affect plant-herbivore interactions? A field experiment and meta-analysis of CO2-mediated changes on plant chemistry and herbivore performance. Global Change Biology 13: 1-20.
Tylianakis, J.M., Didham, R.K., Bascompte, J. and Wardle, D.A. 2008. Global change and species interactions in terrestrial ecosystems. Ecology Letters 11: 1351-1363.Reviewed 27 February 2013 | <urn:uuid:afaf1484-f0c7-4dfa-8259-b430ca2df263> | 2.890625 | 1,025 | Knowledge Article | Science & Tech. | 55.975996 |
Mathematics » Content » The Number System
Apply and extend previous understandings of multiplication and division to divide fractions by fractions.
- CCSS.Math.Content.6.NS.A.1 Interpret and compute quotients of fractions, and solve word problems involving division of fractions by fractions, e.g., by using visual fraction models and equations to represent the problem. For example, create a story context for (2/3) ÷ (3/4) and use a visual fraction model to show the quotient; use the relationship between multiplication and division to explain that (2/3) ÷ (3/4) = 8/9 because 3/4 of 8/9 is 2/3. (In general, (a/b) ÷ (c/d) = ad/bc.) How much chocolate will each person get if 3 people share 1/2 lb of chocolate equally? How many 3/4-cup servings are in 2/3 of a cup of yogurt? How wide is a rectangular strip of land with length 3/4 mi and area 1/2 square mi?.
Compute fluently with multi-digit numbers and find common factors and multiples.
- CCSS.Math.Content.6.NS.B.2 Fluently divide multi-digit numbers using the standard algorithm.
- CCSS.Math.Content.6.NS.B.3 Fluently add, subtract, multiply, and divide multi-digit decimals using the standard algorithm for each operation.
- CCSS.Math.Content.6.NS.B.4 Find the greatest common factor of two whole numbers less than or equal to 100 and the least common multiple of two whole numbers less than or equal to 12. Use the distributive property to express a sum of two whole numbers 1–100 with a common factor as a multiple of a sum of two whole numbers with no common factor. For example, express 36 + 8 as 4 (9 + 2)..
Apply and extend previous understandings of numbers to the system of rational numbers.
- CCSS.Math.Content.6.NS.C.5 Understand that positive and negative numbers are used together to describe quantities having opposite directions or values (e.g., temperature above/below zero, elevation above/below sea level, credits/debits, positive/negative electric charge); use positive and negative numbers to represent quantities in real-world contexts, explaining the meaning of 0 in each situation.
- CCSS.Math.Content.6.NS.C.6 Understand a rational number as a point on the number line. Extend number line diagrams and coordinate axes familiar from previous grades to represent points on the line and in the plane with negative number coordinates.
- CCSS.Math.Content.6.NS.C.6a Recognize opposite signs of numbers as indicating locations on opposite sides of 0 on the number line; recognize that the opposite of the opposite of a number is the number itself, e.g., –(–3) = 3, and that 0 is its own opposite.
- CCSS.Math.Content.6.NS.C.6b Understand signs of numbers in ordered pairs as indicating locations in quadrants of the coordinate plane; recognize that when two ordered pairs differ only by signs, the locations of the points are related by reflections across one or both axes.
- CCSS.Math.Content.6.NS.C.6c Find and position integers and other rational numbers on a horizontal or vertical number line diagram; find and position pairs of integers and other rational numbers on a coordinate plane.
- CCSS.Math.Content.6.NS.C.7 Understand ordering and absolute value of rational numbers.
- CCSS.Math.Content.6.NS.C.7a Interpret statements of inequality as statements about the relative position of two numbers on a number line diagram. For example, interpret –3 > –7 as a statement that –3 is located to the right of –7 on a number line oriented from left to right.
- CCSS.Math.Content.6.NS.C.7b Write, interpret, and explain statements of order for rational numbers in real-world contexts. For example, write –3 oC > –7 oC to express the fact that –3 oC is warmer than –7 oC.
- CCSS.Math.Content.6.NS.C.7c Understand the absolute value of a rational number as its distance from 0 on the number line; interpret absolute value as magnitude for a positive or negative quantity in a real-world situation. For example, for an account balance of –30 dollars, write |–30| = 30 to describe the size of the debt in dollars.
- CCSS.Math.Content.6.NS.C.7d Distinguish comparisons of absolute value from statements about order. For example, recognize that an account balance less than –30 dollars represents a debt greater than 30 dollars.
- CCSS.Math.Content.6.NS.C.8 Solve real-world and mathematical problems by graphing points in all four quadrants of the coordinate plane. Include use of coordinates and absolute value to find distances between points with the same first coordinate or the same second coordinate.
Apply and extend previous understandings of operations with fractions.
- CCSS.Math.Content.7.NS.A.1 Apply and extend previous understandings of addition and subtraction to add and subtract rational numbers; represent addition and subtraction on a horizontal or vertical number line diagram.
- CCSS.Math.Content.7.NS.A.1a Describe situations in which opposite quantities combine to make 0. For example, a hydrogen atom has 0 charge because its two constituents are oppositely charged.
- CCSS.Math.Content.7.NS.A.1b Understand p + q as the number located a distance |q| from p, in the positive or negative direction depending on whether q is positive or negative. Show that a number and its opposite have a sum of 0 (are additive inverses). Interpret sums of rational numbers by describing real-world contexts.
- CCSS.Math.Content.7.NS.A.1c Understand subtraction of rational numbers as adding the additive inverse, p – q = p + (–q). Show that the distance between two rational numbers on the number line is the absolute value of their difference, and apply this principle in real-world contexts.
- CCSS.Math.Content.7.NS.A.1d Apply properties of operations as strategies to add and subtract rational numbers.
- CCSS.Math.Content.7.NS.A.2 Apply and extend previous understandings of multiplication and division and of fractions to multiply and divide rational numbers.
- CCSS.Math.Content.7.NS.A.2a Understand that multiplication is extended from fractions to rational numbers by requiring that operations continue to satisfy the properties of operations, particularly the distributive property, leading to products such as (–1)(–1) = 1 and the rules for multiplying signed numbers. Interpret products of rational numbers by describing real-world contexts.
- CCSS.Math.Content.7.NS.A.2b Understand that integers can be divided, provided that the divisor is not zero, and every quotient of integers (with non-zero divisor) is a rational number. If p and q are integers, then –(p/q) = (–p)/q = p/(–q). Interpret quotients of rational numbers by describing real-world contexts.
- CCSS.Math.Content.7.NS.A.2c Apply properties of operations as strategies to multiply and divide rational numbers.
- CCSS.Math.Content.7.NS.A.2d Convert a rational number to a decimal using long division; know that the decimal form of a rational number terminates in 0s or eventually repeats.
- CCSS.Math.Content.7.NS.A.3 Solve real-world and mathematical problems involving the four operations with rational numbers.1
Know that there are numbers that are not rational, and approximate them by rational numbers.
- CCSS.Math.Content.8.NS.A.1 Know that numbers that are not rational are called irrational. Understand informally that every number has a decimal expansion; for rational numbers show that the decimal expansion repeats eventually, and convert a decimal expansion which repeats eventually into a rational number.
- CCSS.Math.Content.8.NS.A.2 Use rational approximations of irrational numbers to compare the size of irrational numbers, locate them approximately on a number line diagram, and estimate the value of expressions (e.g., π2). For example, by truncating the decimal expansion of √2, show that √2 is between 1 and 2, then between 1.4 and 1.5, and explain how to continue on to get better approximations. | <urn:uuid:28652538-dff7-426f-81ee-f12619be9be4> | 4.28125 | 1,887 | Tutorial | Science & Tech. | 68.592938 |
Peter Andreas Grünberg
Grünberg, Peter Andreas (pāˈtər ändrāˈäs grünbĕrkˈ) [key], 1939– German physicist, b. Pilsen, Germany (now Plzeň, Czech Republic). After receiving his Ph.D. at the Darmstadt Univ. of Technology in 1969, he was a postdoctoral fellow of the National Research Council of Canada at Carleton Univ. in Ottawa. Grünberg joined the Institute of Solid State Research at Research Centre Jülich in Germany in 1972, where he became a leader in the field of thin-film and multilayer magnetism. This led to his discovery in 1988 of giant magnetoresistance (GMR), so called because tiny changes in a magnetic field produce large changes in electrical resistance. For this discovery, which led to the development of spintronics, he shared the 2007 Nobel Prize in physics with Albert Fert, who had independently discovered the same effect.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
See more Encyclopedia articles on: Physics: Biographies | <urn:uuid:0fd2c8d7-4e67-447f-93b7-eb3682329b4b> | 3.15625 | 245 | Knowledge Article | Science & Tech. | 46.273722 |
. "3. Global Change Leading to Biodiversity Crisis in a Greenhouse World: The Cenomanian-Turonian (Cretaceous) Mass Extinction." Effects of Past Global Change on Life. Washington, DC: The National Academies Press, 1995.
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Effects of Past Global Change on Life
and deeper portions of epicontinental seas during accelerated outgassing associated with large-scale middle Cretaceous plate reorganization and development of the Pacific superplume (Larson, 1991a,b). These trace elements could have been concentrated as oxides and carbonates in basinal Cretaceous sediments in the presence of at least moderate amounts of benthic oxygen, especially during high sea-level and offshore sediment starvation; trace elements could also have been sequestered in solution in low-oxygen to anoxic water masses (OMZs). Expansion and benthic touchdown of the oceanic oxygen minimum zone during the Cenomanian-Turonian OAE would have remobilized sequestered trace elements from the seafloor and caused progressive advection of potentially toxic chemicals through the water column, with profound effects on the global marine biota. If the base of the food chain was affected by these advection events, it would have caused a far-reaching set of negative ecological feedback loops within the trophic web. The precise correlation of the first five C-T extinction steps, and two of the succeeding steps, with trace element enrichment horizons in epicontinental and continental shelf deposits of four continents, strongly supports the hypothesis of advection and trace element poisoning as a partial cause of C-T mass extinction. The relatively shallow water trace element enrichment layers found to be associated with C-T extinction events in high-resolution stratigraphic analysis, probably represent depositional sites of advecting trace elements from deeper ocean sources, situated at and above the oceanic redoxcline between the OMZ and the mixing zone.
A third hypothesis for C-T mass extinction, which draws on events described in the two previous hypotheses, focuses on the extraordinary rates and magnitudes of ocean-climate changes associated with the 1.46-m.y.-long C-T boundary interval, and their effects on a global biota narrowly adapted for the most part to the equable greenhouse environments that had been developing throughout the early and middle Cretaceous. Data from Pueblo, Colorado (Figures 3.3 and 3.4) are characteristic of many global boundary sections and show a series of exceptionally rapid, large-scale shifts in organic carbon values (representing rapid shifts in benthic oxygen levels); in d13C values (representing changes in carbon cycling) within the global positive d13C excursion; in d18O values (possibly representing rapid salinity and/or temperature changes); and in trace element values (probably representing one or more oceanic advection sequences). Virtually all late Cenomanian extinction events, and some lesser ones in the early Turonian, are correlative with one or more of these rapid, large-scale geochemical fluctuations. Whereas these geochemical signals can be strongly modified by diagenetic processes, the fact that similar changes occur in virtually all well-studied global C-T boundary sections suggests that they represent a primary ocean-climate signal. Major changes in ocean chemistry and temperature around the C-T boundary could well have been the primary cause of extinction events as they progressively exceeded the narrow adaptive ranges of many stenotopic Cenomanian-Cretaceous lineages. Of special interest in this theory is the general correlation of many apparently rapid environmental fluctuations with bedding rhythms representing 41,000- and 100,000-yr Milankovitch climate cycles (Barron et al., 1985; Fischer et al., 1985; Kauffman, 1988a; Glancy et al., 1993; Figures 3.3 and 3.5 herein). On the one hand this may suggest diagenetic modification of a primary signal in carbonate-rich versus carbonate-poorer facies of the C-T boundary interval, but to the degree that it represents a primary signal, it suggests that the Milankovitch climate cyclicity may have acted as an independent catalyst that drove an environmentally perched, greenhouse ocean-climate system to even greater levels of change, at rates dictated by the climate cycles themselves.
Finally, the possibility of extraterrestrial influences on the C-T mass extinction cannot be ruled out. The precise correlation of the first five late Cenomanian extinction events, or steps, with Ir enrichment of two to four or five times background levels leaves open the possibility of extraterrestrial sources for the iridium. Orth et al. (1989, 1990, 1993) have been cautious in suggesting extraterrestrial origins, pointing out instead an apparent similarity of the overall C-T trace element suite to those originating from deep mantle outgassing, and the fact that the C-T boundary interval was also a time of major plate rearrangement and superplume development (Larson, 1991a,b). On the other hand, four temporally clustered late Albian to late Cenomanian terrestrial impact craters are known with age error bars that overlap the C-T boundary (Grieve, 1982), suggesting an impact storm, or shower (sensu Hut et al., 1987); this is a conservative estimate of terrestrial impacts, when considering the amount of Cenomanian surface that has been subducted or is now covered by younger sediments/strata, vegetation, ice, and especially water. Because impacting is predictably spatially random (Grieve, 1982), and the late Cenomanian world was 80 to 82% covered by water near eustatic highstand, it is likely that at least four of five potential impactors would have fallen in the world seas and oceans during this impact shower. This statistically projects at least 20 impacts during the Cenomanian and early Turonian interval, the majority of which would be aquatic. Oceanic impacting would cause repeated, short-term stirring events. This hypothesis further predicts an extended duration for the Cenomanian impact shower, with high probability that it would overlap the C-T mass extinction interval. Recent discoveries of possible microtektites (Colombia) and multilamellate shocked quartz grains (Colorado) at two | <urn:uuid:5ed2ad98-08b4-495a-941a-a29d8d3e974d> | 3.296875 | 1,345 | Academic Writing | Science & Tech. | 21.078076 |
Q: What are the physical and/or chemical processes that take place when the creases in clothes are removed by ironing? Is the process independent of the type of material ironed?
A: Fabrics contain fibres, each of which is composed of many long-chain molecules lying alongside one another and loosely bonded together. If these bonds are undone and remade elsewhere the molecules (and the fibres they make up) may be forced to run straight and true.
Ironing a cotton shirt provides an example of the process. Cotton is made up of cellulose molecules, polysaccharides composed of a long chain of glucose-like subcomponents. Hydroxyl groups stick out from the sides of the cellulose molecules and attach to those of neighbouring cellulose molecules by hydrogen bonds.
These bonds can be broken with enough heat and a little water, which causes swelling. Remember how hard it is to get the wrinkles out of a ...
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As a Scotsman I have to correct a statement in the item about the cosmic "smoke ring" - a form of wave known as a soliton (9 April, p 15).
The Scottish engineer John Scott Russell saw his soliton from the Forth and Clyde Canal, not the Union Canal, as you state. The Forth and Clyde Canal runs from Bowling on the river Clyde, past Glasgow to Grangemouth on the Firth of Forth. The Union Canal runs westward from Edinburgh and links with the Forth and Clyde Canal at the famous Falkirk Wheel.
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Have you ever gotten an e-mail with a list of math instructions that amazingly ends up telling you your age or some other vital statistic?
I just got one that first had me select the number of times I wanted to
eat chocolate in a week (within specific parameters) and then followed it with a list of math directions that accurately ended up with my age.
Not being much of a mathematician, I couldn’t figure out how it worked, so I asked my genius friend Lee Kraftchick, who is a Dade County assistant attorney by day but a mathematician at heart, to explain the pattern. (It’s good to have a friend who can do percentages for you.)
Below is the puzzle, and then his explanation for how it actually works.
Your Age by Chocolate Math
Work this out step by step; it should only take a minute or so. Be sure you don’t read the bottom until you’ve worked it out!
1. Pick the number of times a week that you would like to eat something chocolate — more than once but less than 10.
2. Multiply this number by 2 (just to be bold).
3. Add 5.
4. Multiply it by 50. Go ahead, use a calculator if you want.
5. If you have already had your birthday this year add 1762. If you haven’t, add 1761.
6. Now subtract the four digit year that you were born. You should have a three digit number.
Look at that number. The first digit of this was the number of times you said you wanted to eat chocolate every week.
The next two numbers are YOUR AGE!
So how does this work?
It’s actually pretty easy, according to my friend Lee.
It’s a simple math formula that winds up subtracting your birth year from the current year. It uses some numbers to distract you and make you think it is individualized because it allows you to pick the number of times that you want chocolate.
The instructions result in the following formula:
First pick a number from 1-10, call this number “a”
a times 2
Plus 1761 if birthday has passed, 1762 if birthday has not yet occurred
minus year born
((a x 2) + 5) x 50 + 1761= 100a + 250 + 1761= 100a + 2011= 2000 +100a +11 [third digit is 100a]
subtract the third digit= 100a= 2011
2011- year you were born= your age.
Now go eat a piece of chocolate.
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The Semantic Web: A Primer
by Edd Dumbill | Pages: 1, 2
Semantic Web Technologies (con'td)
The W3C's Resource Description Framework is one of the cornerstones of Semantic Web work. While its somewhat unwieldy syntax often attracts negative attention from XML developers, the real value of RDF is the data model. It defines a very simple data model of triples (subject, predicate, object), where subject and predicate are URIs, and the object is either a URI or a literal. With this simple model, objects and their properties may be represented. Although the XML serialization of RDF (the "Syntax" of the RDF Model & Syntax specification) is referred to as RDF/XML, other syntaxes are being proposed to try and overcome the awkwardness of the existing syntax. For example, RDF models could just as easily be serialized using SOAP's serialization rules (see presentation at WWW9 by Henrik Frystyk-Nielsen). It is in this simple data model where the power of RDF truly lies. As long as information on the web can be reduced to triples like this, it doesn't really matter which XML serialization format is used. What isn't negotiable here though is the role of the URI as a universal identifier.
The table below shows an hypothetical RDF/XML snippet, and the generated triples in the data model.
<contact rdf:about="edumbill"> <name>Edd Dumbill</name> <role>Managing Editor</role> <organization>XML.com</organization> </contact>
Once we have the data model, there's a need to describe the characteristics of the objects being modeled. For instance, we want to say that a "Contact" must have a name, role, and organization property. This is where RDF schemas come in -- they define an RDF vocabulary that can be used to express the "Contact" class. This allows all users of a resource of type "Contact" to have an agreed expectation of its properties and relationship to other resource types.
RDF schemas differ somewhat from XML schemas (such as DTDs or W3C XML Schemas) in that they do not define a permissible syntax but instead classes, properties, and their interrelation: they operate directly at the data model level, rather than the syntax level. Scaled up over the Web, RDF schemas are a key technology, as they allow machines to make inferences about the data collected from the web.
In fact, work is now underway to take RDF Schemas one step further in the description of ontologies. (An ontology is essentially a formal description of objects and their interrelationships.) The MIT/LCS has begun to define DAML (DARPA Agent Markup Language), a language for expressing ontologies. Although DAML is very much a work in progress, real work can be done now with RDF Schemas, see the section on Redfoot below.
The hardest problem in this area is not the infrastructure, but the actual ontologies themselves. Until an industry-wide ontology exists for, say , vehicle parts, there is a limit to the utility of the SW in the auto manufacturing industry. Organizations such as the Dublin Core Metadata Initiative have been developing such vocabularies for some time now, and they've made progress both in terms of the ontologies themselves and also tools to manage and maintain them.
Work on XML protocols -- the use of XML for messaging and remote procedure calls -- approaches the Semantic Web from the other end of the spectrum. Avoiding grand schemes for the classification of everything, it is focused on standardizing XML-based interactions between computers. A key component of XML protocol technology is the description and discovery of web services available via XML protocols such as SOAP, since systems require the ability to conduct electronic transactions with other systems of which they have no prior knowledge.
This requirement has led to the creation of technologies such as Web Services Description Language (WSDL), which describes the characteristics of the interface offered by a web service, and ADS, which allows the advertisement and discovery of such services. ADS, by offering techniques for embedding such descriptions inside normal web content, fits neatly into the Semantic Web vision. (For more on WSDL and ADS, see our XML Protocol Technology Reference.) The recently announced UDDI effort also provides an API for registries of web e-business services. Although the Semantic Web vision focuses on decentralized technology as opposed to centralized registries, the emphasis on machine discovery of resources is a common theme.
While the XML protocol-related technologies solve narrow problems in order to achieve results over the next year, they represent use-cases for the Semantic Web, and one expects that mature SW technologies will cater for the solution of problems such as these.
The major center of Semantic Web-related development thus far has been in the area of RDF. The creation of semantically-richer documents is a relatively easy task, so most of the effort has been concentrated on accumulating the data, storing it and querying it. RDF/XML provides a useful intermediate syntax which, when combined with tools like XSLT, allows multiple data sources to be combined.
Further details on RDF tools and applications can be obtained from the W3C's RDF home page, and the RDF category of XMLhack. In this section I will concentrate on introducing tools useful for making a relatively speedy start with Semantic Web development.
Redland: Redland is an RDF application framework with C and Perl APIs. As a framework, most of its components are pluggable. For instance, you can choose which RDF parser you use (an important factor at this stage in RDF's development, where the emphasis on conformance for RDF parsers is not as high as it is for XML parsers). Storage mechanisms are also pluggable: currently, in-memory storage and Berkeley DB are supported. Beta-level software.
Redfoot: Redfoot is a 100% Python application framework for distributed RDF applications. It provides a web interface to its RDF import, editing, and viewing functions. It also has support for RDF Schemas. One of its more intriguing features is emerging support for peer-to-peer exchange of RDF data -- peered Redfoots (Redfeet?) will be able to discover the contents of each other's stores. Easy customization of the web interface makes this a good choice for experimentation with RDF. Alpha/beta-level software.
Wraf: The Web Resource Application Framework is another RDF application framework, this time written in Perl. It also offers a web interface to RDF storage, editing and querying. Alpha-level software.
RSS 1.0: This work on the next generation of web site metadata distribution employs RDF for its data model and syntax. Of particular interest is its use at the W3C, where XSLT is used to extract the RSS information from the front page. Dan Connolly has documented how this was done. If you want to experiment with scraping data from XHTML pages, this is an interesting starting point.
Describing and retrieving photos using RDF and HTTP: This note, written by W3C staff, describes the creation of a system allowing the description and retrieval of photographs using RDF. The RDF itself is embedded in the comment portion of JPEG files using a custom editor application, and it's retrieved through an extension to a web server. This illustrates another good starting point for doing Semantic Web development using existing web technologies: attempting to combine this work with a framework such as Redfoot would be an interesting line of investigation.
The Semantic Web has already been the subject of much bluster among the XML developer community and will doubtless continue to be so. Arguments rage over the usefulness of the technology, the difficulty of using RDF, and so on. However, the Semantic Web vision of a machine-readable web has possibilities for application in most web technology -- while some complain about its lack of definition, its broad scope properly reflects the quietly radical effect it will have on the Web. | <urn:uuid:de9de1db-5435-43b9-9f79-2e4aff32ed26> | 3.078125 | 1,710 | Documentation | Software Dev. | 39.235579 |
A Productive Star Formation Factory
W3 is a region where many massive stars are forming in a string of stellar clusters, located about 6,000 light years from Earth in the Perseus arm of the Milky Way galaxy. W3 is part of a vast molecular cloud complex that also contains the W4 superbubble (not seen in this image). Scientists believe that the extraordinary amount of star formation in W3 has possibly been influenced by neighboring W4, an inflating bubble of gas over 100 light years across. W4 may directly trigger the birth of W3's massive stellar clusters as it expands and sweeps up molecular gas into a high-density layer at its edge, within which stars can form. Another possible scenario is that W4's expansion has caused a domino effect of star formation, forming the cluster IC 1795 (seen as a clump of X-ray sources in the bottom left corner of this image) which in turn triggered formation of the young, massive clusters in W3.
In this composite image of one of the many star-forming complexes of W3, called W3 Main, green and blue represent lower and higher-energy X-rays, respectively, while red shows optical emission. Hundreds of X-ray sources are revealed in this central region of W3 Main. These bright point-like objects are an extensive population of several hundred young stars, many of which were not found in earlier infrared studies. These Chandra data show that W3 Main is the dominant star formation region of W3. Because its X-ray sources are all at the same distance, yet span a range of masses, ages, and other properties, W3 is an ideal laboratory for understanding recent and ongoing star formation in one of the Milky Way's spiral arms. | <urn:uuid:c82f6341-5493-47bc-84df-dae30ae17382> | 3.359375 | 357 | Knowledge Article | Science & Tech. | 46.175459 |
Silver crystals are beautiful and easily grown metal crystals. You can watch crystal growth under a microscope or let the crystals grow overnight for larger crystals.
Time Required: Instantly to Overnight
- Suspend a piece of copper wire in 0.1M silver nitrate in a test tube. If you coil the wire you will get high surface area and more visible growth.
- Place the tube in a darkened location. Try to avoid high-traffic (high-vibration) areas.
- Crystals should be visible to the naked eye on copper wire after about an hour, but larger crystals and noticeable blue coloration of liquid will occur overnight.
- Place a drop of mercury in a test tube and add 5-10 ml 0.1M silver nitrate.
- Allow the tube to stand undisturbed in a dark location for 1-2 days. Crystals will grow on the surface of the mercury.
- It is easy to watch crystals form on copper wire under a microscope. The heat of the microscope light will cause crystals to form very quickly.
- A displacement reaction is responsible for crystal formation: 2Ag+ + Cu → Cu2+ + 2Ag
What You Need
- 0.1M Silver Nitrate
- Test Tube
- Copper Wire or Mercury | <urn:uuid:93054f00-962a-485e-809b-c8c02bf694b7> | 2.796875 | 266 | Tutorial | Science & Tech. | 60.015385 |
The content on this web page was last updated in December of 2012.
For more information: http://www.nmfs.noaa.gov/stories/2012/11/82corals.html
Update - 2012
November 30, 2012: NOAA Fisheries is proposing Endangered Species Act (ESA) listings for 66 coral species: 59 in the Pacific and seven in the Caribbean.
- In the Pacific, seven species would be listed as endangered and 52 as threatened.
- In the Caribbean, five would be listed as endangered and two as threatened.
- In addition, NOAA Fisheries is proposing that two Caribbean species—elkhorn and staghorn corals—already listed under the ESA be reclassified from threatened to endangered.
In 2009, NOAA received a petition to list 83 species of reef-building corals under the ESA from the Center for Biological Diversity. On February 10, 2010, NOAA found that the Center presented substantial information indicating that listing under the ESA may be warranted for 82 of the 83 petitioned species.
Following the initial finding, NOAA convened a Biological Review Team to initiate a formal status review of the 82 species. The result was a Status Review Report, released in April 2012. The peer-reviewed report incorporated and summarized the best available scientific and commercial data to date.
The agency also conducted a public engagement process between April and July 2012 to gather additional scientific information, allow time for a public review of the Status Review and Draft Management Reports, and to further engage the public. All relevant information gathered was summarized in a new Supplemental Information Report.
Together, the Status Review, Supplemental Information, and Final Management reports form the basis for the proposed listing.
Update - 2004
On March 4, 2004, the Center for Biological Diversity petitioned NOAA's National Marine Fisheries Service (NMFS) to list elkhorn (Acropora palmata) and staghorn (Acropora cervicornis ) corals under the Endangered Species Act (ESA). After further review, NOAA/NMFS determined that these two species of Acropora warranted listing under the ESA. In May 2006, the United States listed Acropora palmata and Acropora cervicornis as vulnerable under the Endangered Species Act due to their widespread decline throughout their Caribbean range.
Should Acropora spp. Be Included on the Endangered Species List?
Elkhorn coral (Acropora palmata) is a branching coral. Branching corals grow in the shallow areas of the reef crest and serve to break up the wave action as it comes onto the reef. The branches of elkhorn coral resemble an elk's rack of antlers, thus its name.
On Jan. 15, 1999, the National Marine Fisheries Service (NMFS) requested comment on the possible listing of elkhorn and staghorn corals as candidates for protection under the Endangered Species Act (ESA). NMFS was considering listing the corals because their populations have been greatly reduced throughout the Caribbean range. Populations declined during the 1980s by up to 96 percent, according to the Federal Register notice. NMFS requested information that would either support or argue against inclusion of these coral species on the candidate list.
Coral-list participants, which generally were equally divided on the issue, discussed the pros and cons of possible ESA protection for the corals, as well as the legal nuances of the act.
The final participant summed up the lengthy discussion by examining the nature of the debate and the conflict between "reductionist" research and "holistic" research.
Click here for a list of discussion participants.
Click here to download the complete unedited discussion (pdf, 127Kb).
Shinn, Eugene. (2004). The mixed value of environmental regulations: do acroporid corals deserve endangered species status? Marine Pollution Bulletin. 49(7-8) pp. 531-533, doi: 10.1016/j.marpolbul.2004.07.007
Bruckner, A.W. , 2002. Proceedings of the Caribbean Acropora Workshop: Potential Application of
the U.S. Endangered Species Act as a Conservation Strategy. NOAA Technical Memorandum
NMFS-OPR-24, Silver Spring, MD 199 pp. http://www.nmfs.noaa.gov/pr/pdfs/species/acropora_workshop_2002.pdf | <urn:uuid:435ca037-6c8e-4b4b-b20c-ff7bfdd97cd8> | 3.25 | 909 | Knowledge Article | Science & Tech. | 45.817088 |
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The Superior Mirage:
This is illustrated in the above diagram. Because of this bending, we see the object floating in the sky, above or even attached to the original object. In cases of strong looming, the image may appear very high in the sky. Looming of a distant ship may be the source of the many legends of flying ghost ships seen by mariners over the centuries. And since the actual ship may be below the geometric horizon, sailors or shoreline viewers might never see it except as a mirage image.
Temperature increases with height.
If the temperature gradient of the layer through which the light travels is constant with height -- that is, the temperature increases at a uniform rate -- no magnification or distortion of the object occurs. However, when the gradient is not uniform, and the temperature increases more rapidly with height as we move away from the surface, then magnification of the object will occur. In many circumstances, we see only a raising of the top of an object to just above its actual position. In such cases, the image appears to be stretched or taller than expected. This situation is called towering.
Superior Mirage Conditions
Towering is quite common in polar regions and during the summer near large bodies of relatively cold water when compared to the overlying air temperatures. Such situations are common along North America's Pacific Northwest coastline during the summer. Towering can make coastal mountains appear to rise and fall in height throughout the course of the day when seen from across cold ocean waters. The illusion formed is of the peaks looming higher, and thus the mountains appear closer than they actually are. This illusion can be quite hazardous to sailors navigating by sight alone by causing them to believe they are closer to shore than they actually are.
The opposite of towering is stooping, a condition where the image appears shorter or further away than it actually is. Stooping occurs when the light from the bottom of the object bends more than the light from the top of the object on its way to the eye. By thus "raising" the lower part of the image more than the upper, the object appears compressed.
We tend to observe mirages most often during the daylight, but superior mirage conditions commonly occur during the night. Indeed, inversion formation is much more frequent during the night hours, at times occurring nightly for long stretches. The advent and spread of artificial light sources during the twentieth century, particularly moving light sources such as the headlights of cars and trucks, can produce some interesting visions.
For example, the superior mirage could be the source for many nighttime UFO sightings. Here's why. The light from headlights on automobiles moving along the highway can be refracted under inversion conditions so that they appear to come from the heavens rather than from the surface where they originated. These images can appear to move quickly across the sky, or they can disappear suddenly as the angle or position of the light beam from the moving vehicle changes.
Since superior mirages are caused by cold air lying beneath relatively warmer air, they are most common and strongest in the Earth's polar regions where the surface is covered by ice or snow or cold seas for most of the year. The arctic mirage is a term that has been applied to superior mirages in northern polar latitudes, particularly when the conditions alter the appearance of the earth's horizon to allow us to see objects that actually are located well beyond or below the geometric horizon.
Also know as the hillingar in Icelandic, the arctic mirage generally forms under conditions of a uniform and widespread temperature inversion. When the temperature rises at a rate of 11 Celsius degrees per 100 metres (6 Fahrenheit degrees per 100 feet), the Earth's horizon will appear flat. If the inversion becomes stronger, the horizon will then appear to rise vertically from the flat position. Thus, when the inversion gradient reaches 18 C deg/100 m (10 F deg/100 ft), the observer will have the illusion of being in a saucer -- that is, the horizon appears as turned upward.
Many beliefs and legends of northern inhabitants and European explorers can be attributed to the arctic mirage, and the exploration of polar regions has been both enhanced and hindered by the condition. Many early explorers reported landscape features in polar regions that never really existed but were mere illusions. [For more on the arctic mirage see: The Arctic Mirage: An Aid to Discovery.]
Arctic-type mirages are not confined only to regions north of 60 degrees latitude, however. Robert Greenler in his book Rainbows, Haloes and Glories reported on one interesting situation of superior mirage viewing on the night of 26 April 1977. When the residents of Grand Haven, Michigan looked westward that night across the relatively cold waters of Lake Michigan, they distinctly saw city lights and a flashing red beacon. But the nearest urban area westward from them was Milwaukee, Wisconsin, 120 km (75 miles) away, well below the geometric horizon and thus normally not visible. Their sightings were later confirmed to have been Milwaukee when a Grand Haven resident timed the blink rate of the flashing red light and linked it to the Milwaukee Harbor entrance beacon. (US Weather Service records also confirm that strong inversion conditions were indeed present that night.) The unseeable had indeed briefly become visible.
When the temperature inversion is not as uniform as that found under arctic mirage conditions, a mirage known as the Fata Morgana or halgerndingar (in Icelandic) may appear. In a Fata Morgana mirage, distant objects and features at the horizon appear as spikes, turrets or towers, objects with great vertical exaggeration rising from the surface.
Charles Earle Funk of Funk & Wagnell's Dictionary fame traced the origin of the name Fata Morgana to Italian poets who named what they saw rising up across the Strait of Messina after the fairy castles of Morgana. Literally, Fata Morgana means the Fairy Morgana, a reference to the English legends of King Arthur's enchanted sister Morgana, who dwelled in a crystal castle beneath the sea.
According to meteorologist William J. Humphreys, Morgana is also a Breton word for sea woman which further connects the name with the mirage. He writes of a mirage appearing as crystal palace rising from beneath the waves of the Strait of Messina and
"molding the bluffs and houses of the opposite shore into wondrous castles that, alike, tower into the sky and sink beneath the surface; nor is it strange that this poetic name should become generic, as it has, for all such multiple mirages, whenever they occur." [Physics of the Air, 1920]
©1999, Jack Stephens Images, All Rights Reserved.
Used with permission.
A striking example of the Fata Morgana photographed in Greenland by Jack Stephens is shown here. Like the arctic mirage, the Fata Morgana can give explorers the appearance of large and significant landmarks such as coastal cliffs or mountains. But in fact, they may only be low hills, beaches or sea ice distorted so that they appear as mountain ranges rising ahead.
Alistair Fraser, an expert on atmospheric optics at Pennsylvania State University, attributes the Fata Morgana to a situation where the temperature increases slowly with height from the surface until it reaches a shallow air layer where the increase in temperature becomes quite rapid. This layer is then topped with another layer of slowly increasing temperature. This atmospheric temperature structure will magnify objects whose light rays pass through the middle layer. Minor spatial variations in the inversion pattern can project a complex image pattern toward the observer. Variations in the degree, thickness or location of the layer may even cause relatively smooth surfaces of water or snow to appear as a line of irregular towers and spires.
Under similar conditions to those which form a Fata Morgan mirage, one may see a Fata Bromosa instead, or even in combined with it. The Fata Bromosa or fairy fog is characterized by less distinct elements than with the Fata Morgana. It generally appears as a flat and uniform image, like an overhanging wall, with strong variation in brightness rather than surface detail. The bright and dark patches are caused by a degree of "fuzziness" in the magnified images as the light rays are distributed more strongly in areas above and below the image than one would expect. Because the image is blurred and brighter than expected, it gives the impression of a luminous fog bank hovering just above the sea, snow or ice surface.
In the winter of 1596, a ship under the command of Willem Barents in search for the Northeast Passage to Asia was ice-bound off the north coast of the Russian arctic island of Novaya Zemlya (latitude 76 degrees North). Barents and his officers were astonished one day in early March to see a distorted sun appear for a short time above the horizon. They had not expected to see the breaking of the long arctic night at this latitude for another few weeks. Yet, there it appeared, approximately 5 degrees of arc higher than its actual position.
Because such mirages were rarely seen by Europeans, Barents' reports were not taken seriously by scientists of his time. Indeed, his observations were not confirmed for over three centuries when, in 1915 and half a world away, Sir Ernest Shackleton briefly observed a distorted sun suddenly visible over the horizon seven days after it had set for the Antarctic winter night.
The Novaya Zemlya mirage requires the sun's rays to travel within an inversion layer for hundreds of kilometres. The layer must have just the right temperature gradient so that the light more or less continuously bends with the curvature of the Earth over that long distance -- 400 km (250 miles) for a 5 degree elevation rise according to calculations by W.H. Lehn -- to allow a sighting of the sun's disk.
With many permanent or long-term scientific settlements in polar regions established over the last fifty years, the Novaya Zemlya mirage has been more frequently observed and even photographed.
Mirages open a whole new aspect to sky watching. Perhaps we have been viewing instances of superior mirages for years without even realizing what we were seeing, or not seeing. Because they were unknown to us, they were often also unseen. What interesting stories may have arisen if the flashing harbour light of Milwaukee had been the only light visible that night to the residents of Grand Haven and had perhaps also been distorted by Fata Morgana conditions? What tales of UFOs may emerge when car headlights located below the horizon are seen under looming and magnification conditions of a strong superior mirage? Could those luminous disks darting around the heavens at unusual speed and motion be only the beams from headlights of a Volkswagen Beetle bent through the air?
Now that you know what to look for, take some time to look closely when conditions are right for superior mirage formation, and you may observe some surprising scenes. And perhaps get a feel for the stuff legends are made of.
For details on mirages, their causes and properties, see
The Mirage: A Primer in the Weather Elements and Phenomena Section,
The Inferior Mirage: Not Just For Deserts Anymore in the Weather Elements and Phenomena Section,
The Arctic Mirage: An Aid to Discovery in the Weather People and History Section.
Did Those Mountains Grow Overnight? in the Weather Almanac Section.
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The BC Weather Book: | <urn:uuid:1d0c53c9-7b81-4812-9dd9-7b98d96538ec> | 3.484375 | 2,394 | Knowledge Article | Science & Tech. | 39.208844 |
As can be seen by observing this graph, we get hyperbolas when we vary
c and let a=b. When c>=-1/2 the hyperbolas are in the first and third
quadrant and when c<-1/2 they lie in the second and fourth quadrant.
The smaller the value of c; the closer the hyperbolas are to the focal
point or the point of symmetry. The larger the value of c; the further
the hyperbolas lie from the focus or focal point. The focal point is the
intersection of the lines x-a=0 and y-b=0. In our case a=b=1, so our focal
point is the intersection of the lines x=1 and y=1. This point is (1,1).
We also notice that as c gets larger (i.e. the hyperbola moves further from the focal point) the hyperbolas seem to be getting straighter.
Next, I conducted an investigation to see what happens when a=c=1 and b varies from -4 to 4. The graph below shows what happens when b is changed.
When b is negative, the hyperbolas are formed around the focus point
in quadrants 2 and 4. As b gets larger, the hyperbolas grow closer together
and the focal radius gets smaller and smaller, but the focal point does
not change. During my investigations of these different graphs, I came
across a very interesting graph. The graph of 0=x-y+1-xy.
When I graphed this function ,I did not get the usual hyperbola, I got
what appeared to be perpendicular lines. Now, let's investigate this function
to see why we get this graph. Upon examining this function , 0=x-y+1-xy,
I know that the graph will have a slop of 1-y and a y-intercept of 1. This
also tells us that no matter what value we put in for y, x=-1 and no matter
what value we put in for x, y=1. This explains the perpendicular lines.
This graph is important because as b gets larger the line y=1 seems to
serve as a horizontal asymptote for the hyperbolas. When b is negative,
except for b=-1, the majority of the hyperbolas lie in quadrants 2 and 4.
When b is positive, the hyperbolas lie quadrants 1 and 3. When b is positive,
we get a new focus that never changes. Now as b gets bigger, the focal
radius becomes longer. While investigating these graphs, I also noticed
that they all had one point in common. This point is (-1,0).
Now, we need to see what happens when we let b=c=1 and vary a from -4 to 4. We get the following graphs.
The changes in a are similar to what we observed in the changes of b.
There is one difference though. As we vary a, the focal point also varies.
While a<-1, the focal point does not seem to change and the focal radius
decreased as a got bigger. When a=-1, we get a similar graph as when
b=-1. The graph of 0=-x+y+1-xy also produces perpendicular lines which
serve as vertical and horizontal asymptotes to the other hyperbolas (i.e.
when a>-1). Thus, we have a horizontal asymptote at y=-1 and a vertical
asymptote at x=1. This time they intersect at (1,-1) instead of (-1,1).
As a increased, the pairs of hyperbolas grew further apart and shifted
upward and to the right. As a result of these changes, the focal point
and radius also change. As in the previous cases, when a<-1 the majority
of the hyperbolas tend to lie in the second and forth quadrants and when
a>=-1 they lie in the first and third quadrant. As in the case when
b was varying, the hyperbolas all have one point in common. In this case,
this point is (0,-1).
In conclusion, when c varies the only thing that changes is the focal radii of pairs of hyperbolas. When b varies, the focal point remains the same no matter where the hyperbolas are located. When a varies, we get sifting and turning. The focal point and radius also change when a changes.
To learn more about this problem, there are many extensions that one can do. One can set the two coefficients that remain constant to be negative and/or to be different values. Another extension would be to change two of the coefficients and let the other one remain constant or to change all three and investigate what happens. These are only a few of the extensions that one can perform; there are many more. | <urn:uuid:d73aa20e-79a9-45b2-b677-fc7db5e22362> | 4.03125 | 1,054 | Academic Writing | Science & Tech. | 75.516923 |
I've been doing revision for my yearlies and I've been struggling with these questions:
1) Prove that, if the difference between the roots of the equation ax^2 + bx + c = 0 is 1, then a^2 = b^2 – 4ac.
2) P is a variable on the curve y = 2x^2 + 3 and O is the origin. Q is the point of the section of OP nearer the origin. Find the locus of Q.
3) Find the equations of the tangents to the curve xy = 6 which are parallel to the line 2y + 3x = 0.
4) The curves y = 2x^2 – x and y^2 = x intersect at (0,0) and at another point Q. Find the angle between the curve at Q.
Could someone please help me out?
Thanx a lot!!!
P.S. I'm really really sorry that I've been posting a lotta questions but I really really need to do good in this exam. | <urn:uuid:681ffa5f-4c00-4fd1-87d6-75678bd0c779> | 2.984375 | 221 | Q&A Forum | Science & Tech. | 101.130142 |
Nanotechnology engineers have 3D printed an ear from calf cells and silver nanoparticles that picks up radio signals at frequencies beyond human capacity. The creation is part of their greater plan to one day build spare parts for humans cyborgs to don.
Rather than simply adding electronics to an ear, the team from Princeton decided to try and integrate the two from the start. They 3D printed hydrogel — a polymer-based gel often used as scaffolding in tissue engineering — with calf cells, and weaved in silver nanoparticles to create an in-built antenna coil that replaces the cochlea. The calf cells matured to become cartilage and the electronics were then encased in a highly supportive ear that mirrors the complex build of the real thing.
The beginning of something wonderful. | <urn:uuid:fadaa8a3-7d21-438c-b424-ec734c9b04d4> | 3.625 | 161 | Personal Blog | Science & Tech. | 41.674103 |
A photomultiplier works by ejecting an electron every time a photon hits, and collecting it after it has been accelerated a great length, to knock out more electrons from more plates, and these are accelerated, and so on, until you get a macroscopic current you can measure. The noise comes from random electrons getting ejected from the plate anyway.
The answer is 1. Doing 2,3,5 increases the signal to noise, and doing 4 does nothing to signal to noise, but probably makes the multiplier stop working. The photomultiplier acts by ejecting electrons when photons hit, and decreasing the temperature will prevent electrons from getting ejected thermally randomly.
Higher voltage will lead to more thermal nucleation, since it will decrease the distance an electron has to go before it is knocked off the plate. Radioactive source is just stupid, you are introducing more noise. A lower "work function" (it's not a function of anything, it's the ionization energy) will mean the electrons have an easier time getting off the metal, so more random electrons ejected.
Option 4 is the only one that requires thinking. It will prevent electrons from reaching the collecting point, but if it doesn't affect the photo-plate it will just change the energy with which the ejected electrons strike, without changing the number of electrons of each type (photon emitted, or thermally emitted). This means it won't affect signal to noise. But it will probably increase signal to noise, because the photomultiplier is already tuned for good signal to noise, so reducing the voltage on the first collection point will perhaps reduce the multiplication to where you won't detect a signal.
Generally these questions are 40 years out of date, and the physics GRE is a joke. I had no idea what a "dynode" is, I guessed from context. | <urn:uuid:a82b24af-4d5a-4a10-8187-c2eae8495bb0> | 3.3125 | 380 | Q&A Forum | Science & Tech. | 41.515995 |
The model-view-controller (MVC) pattern has an interesting, let’s call it sub-pattern, that could be more broadly used. The basic purpose of MVC is to “clean up” the data (model) and interface (view) by delegating all the in-between “dirty” logic to the controller. The controller is aware of both the data and the interface and knows how to handle both: it controls what is happening in them, but from the outside. The controller, if written correctly, can be reused for multiple types of model or view. If we go a step further, we could program multiple controllers that know how to handle different aspects of the functionality: in this way we very much get add-ons that we can attach onto non-intelligent components and make them smarter. By choosing which controllers we attach, we can customize the behaviour of our application. And because the controller is made to work “from the outside” it is isolated from the internal implementation of the components: this could make it instantly reusable.
But it could be interesting to generalize the “add-on” controller pattern and make it work in other situations as well. One interesting area of application could be controlling data: if you use an Object-relational manager (ORM) to read your data (and if you don’t, you should), you already have your data in the perfect form for this – that is, as objects. Likewise if you use a traditional data-access layer and then create business entities as object-oriented structures. Usually, these classes contain much of the business logic inside and this is quite natural to do because business logic represents the behaviour of the data. But it’s not good for reusability: whether you combine the data access and business entities or implement them separately, the business logic is tightly coupled with data/hardcoded inside data so it’s not easy to customize. It would be nice if we could externalize at least some parts of it, but keep it as close to data as possible. Even better would be if we could split the logic and implement different aspects as different components.
If we attached controller objects to our data, they could take the responsibility of providing its behaviour. We could have different controller types for different types of behaviour (status changes, automatic calculations etc.), and if we instantiate them using some kind of configuration engine (or dependency injection framework), they will be easy to replace and thus make your application highly customizable.
Of course, these “data controllers” sound similar to what rules engines do, only more lightweight. But how much of an overhead would they add? As always, it depends on what we do, but I would say not too much. They would contain the code we already have, with probably one layer of isolation because it would be split into distinct classes. Would the instantiated rules waste memory? Probably some: but when you consider that the ORM instantiates each record as an object and has a complex infrastructure for tracking its changes; that for each data binding there is a couple of objects created in the interface; that there can possibly be a control (which is quite a large object) bound to each field… It seems that it shouldn’t make a big difference.
The most sensitive bit is collections: there we can have hundreds of records with one control (a data grid) bound to them. In this case, the overhead of the rules engine could be significant compared to the overhead of the interface – but not in comparison to ORM overhead. Again, this depends on how we implement the rules: the rule could be optimized to utilize a single instance for the whole collection – this can be done using an IBindingList implementation where the collection transmits events for everything happening inside it… Of course, here it is the collection which incurs the overhead, but let’s say we would use it anyway for data binding purposes.
Obviously, there’s a lot of technical issues here. This is partly because the base framework doesn’t have built-in support for what we need. But, it is to be expected that having an ORM (which can be interrogated for data structures and from which we can receive notifications when data is loaded/saved) generally helps.
Of course, I’m still talking hypothetically here: but I’ve already made a couple of small steps in the direction of having a living prototype (in fact, I’m testing an minimal working something as we – uhm, speak). More on that in another post. | <urn:uuid:8b5b8ad0-0fa2-44d0-9332-a5ec040438d8> | 3.109375 | 1,003 | Personal Blog | Software Dev. | 40.877377 |
An optical conveyor belt for moving sub-micron objects has been achieved
by collaborating physicists at the Institute of Scientific Instruments
in Brno, Czech Republic and at the University of St. Andrews in Scotland.
Their set-up used a special type of non-diffracting laser light that
forms a very narrow beam existing over long distance without changing
Two such counter-propagating laser beams establish up a lace-like standing
wave pattern which can suspend and hold tiny polystyrene spheres of
just the right size. The balls, which range in size from 400 nm to one
micron, have a density comparable to water. Previously, scientists have
used such non-diffracting "optical lace" beams to move particles with
the force of radiation pressure, but without the ability to stop them
using only a single beam.
The Czech and Scottish researchers, by contrast, set up a light lace
pattern with numerous knots, corresponding to intensity maxima (antinodes)
of the standing wave. Furthermore a particle can be confined near a
knot and all the knots can then be moved simultaneously over large distances
by changing the relative phases of the counter-propagating laser beams.
Moreover thanks to the self-healing property of the non-diffracting
beams, many particles can be confined simultaneously in the standing
wave structure (near the knots) without significantly spoiling the beam
properties. The positioning accuracy, related to the precision of the
phase shift and the optical trap depth (the size of the knots), is at
the micron level and will get better.
Pavel Zemanek (firstname.lastname@example.org) says that possible applications for
his device include the delivery of biological or colloidal microparticles
or even ultracold atoms. (Cizmar
et al., Applied Physics Letters, 25 April 2005; lab site at http://www.isibrno.cz/omitec/index.php?swt.html
) (A few years we wrote about a different kind of photon conveyor belt: | <urn:uuid:2183357f-9d95-4652-b944-61f4a64ab768> | 3.46875 | 439 | Knowledge Article | Science & Tech. | 41.733974 |
Learn about global warming, carbon footprints and alternative energies.
Global Warming. Global Action. Global Future. Introducing 350.
Reducing Emissions. Carbon Footprint Calculator.
Eat the View campaigns to plant edible landscapes.
Find out about Acton's Solar Panel which feeds clean electricity into the ABRSD grid.
Carbon Rally compares energy-saving activities nationwide.
PC Energy Report 2009 (pdf) describes how powering down your personal computer can save energy and help reduce the effects of global warming.
- What is climate change? Find out at EPA for Kids. Information, links, games and animations from the Environmental Protection Agency.
- Learn about Renewable Energy Basics and Clean Energy Technologies. Check out the Solar Oven Challenge.
- Visit Science Daily to find out about earth, climate and environmental technologies.
- The LoraxTM Project: Student Earth Day and Classroom Activities encourage educators and students to celebrate the Lorax's message and pledge to beautify and conserve their school and environment.
The following books are available at Acton Memorial Library.
||Low Carbon Diet, A 30 Day Program to Lose 5000 Pounds by David Gershon.
"...save energy...save money...save the planet. Be part of the global warming solution!"
||Last Child in the Woods, Saving Our Children from Nature-Deficit Disorder by Richard Louv. |
"The Children in Nature Movement is fueled by this idea: the child in nature is an endangered species, and the health of children and the health of the Earth are inseparable." | <urn:uuid:2b6555b1-ebc4-405c-9861-f89650722a12> | 3.234375 | 320 | Content Listing | Science & Tech. | 43.091573 |
Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °
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Matriculation level - #n+1
1.Which term of the arithmetic progression
is the first negative term?
2. The sum of three numbers in Arithmetic Progression is 54 and their product is 5670. What are the numbers?
3. Find the geometric progression whose 4th term is 8 and 8th term is
4. The sum of the first two terms of a Geometric Progression is -8 and the sum of the first four terms is -80. Find the geometric progression.
5. A ball is dropped from a height of 6 meters and on each bounce, it rebounces to 2/3 of its previous height.
(i) What is the total length covered by the ball in downward path?
(ii) What is the total length covered by the ball in the upward path?
(iii) How far does the ball travel till it stops bouncing?
6. The sum of an infinite series in a geometric progression is 57 and the sum of their cubes is 9747. Find the series.
7. Find the value of
8. Some cubes of sides 5 cm, 6 cm, 7 cm, ....20 cm are arranged in a box such that there is no space left in the box. Find the volume of the box.
9. If 1³ + 2³ + 3³ + ........k³ = 38025, find the value of 1 + 2 + 3 + ......k.
10. How many terms of the series 1³+2³+3³+4³... should be taken to get 25502500?
Character is who you are when no one is looking. | <urn:uuid:4ac461dd-c33c-4edf-b500-6b20c2640505> | 2.703125 | 410 | Comment Section | Science & Tech. | 104.98069 |
space:uk - October 2007, Issue 23
From the UK Space Agency, this issue of Space:UK magazine contains news and features on:
• Plans for missions to the Moon, Mars and beyond.
• Tracking the world’s first spacecraft.
• Satellites to help save lives.
• Getting to grips with space weather.
• How many satellites orbit the Earth?
• Meet the engineer developing the new Mars rover.
• Space traveller’s guide to Saturn’s moons.
HEALTH and SAFETY
Any use of a resource that includes a practical activity must include a risk assessment. Please note that collections may contain ARCHIVE resources, which were developed at a much earlier date. Since that time there have been significant changes in the rules and guidance affecting laboratory practical work. Further information is provided in our Health and Safety guidance. | <urn:uuid:9769369f-2d10-4d68-921b-364020e0a6c8> | 2.75 | 180 | Knowledge Article | Science & Tech. | 46.212922 |
PHP Component and Library API Design Overview
There's been lots of change in the PHP community over the past few years. PHP now has namespaces. More PHP developers are using an IDE. More PHP developers are pulling inspiration from the Java, C#/.NET, and Ruby communities. And even more PHP developers are embracing the object-oriented and, ironically, the functional nature (closures) of PHP. All these changes make for interesting code. What has also happened is that better and more readable code is being produced by this ever growing PHP community. It's been a long time since a€oPHP applicationa€¯ meant a series of transaction scripts as a mix of SQL, CSS, JS, with some PHP sprinkled in, and a couple of few classes for good measure. Of course, that still exists, but you no longer need to go to the ends of the earth to find non-spaghetti code that is understandable within a few minutes.
For the most part, all of these changes are good changes. The number of good/senior/expert level PHP developers is ever increasing and there are more and more a€oenterprise gradea€¯ frameworks and libraries that are being produced. That said, with all of these new changes, the one area which is still fairly inconsistent from project to project is the naming conventions that are employed inside PHP 5.3 project that utilize namespaces. This article will attempt to describe what an API is, how names and object-oriented features affect an API, and how various decisions affect the consumers of a particular API is.
What Is An API?
Before we jump into naming, it's important to have a common understanding of the actual problem area. When we talk about names, we are really talking about the API. An API is a particular set of rules and specifications that a developer can follow to access and make use of the services and resources provided by another particular software program, component or library. Put another way, it is an interface between various software pieces and facilitates their interaction, similar to the way the user interface facilitates interaction between humans and computers.
For PHP 4 / procedural based libraries, the API is defined by the functions that are declared for usage in that library. It is further described by the global names and global state that the library utilizes to do its job. Typically, API's based on purely function based libraries are far simpler to understand.
Object-oriented API's are a bit more complex. When you build an object-oriented library or component, you are typically designing two API's at the same time, whether or not you know it. This is the nature of object-oriented languages when you employ the use of abstract classes and interfaces in your design.
The first API, the more common of the two, I call the Consumption API. This is the API that answers the question: a€ohow do people consume this thing.a€¯ The answer to this question is generally situated around the great majority of use cases that were identified by the author of the software component/library. In PHP, consumption might look like this:$foo = new SomeCompany\FooComponent\FooComponent($options); $foo-setAdapter(new SomeCompany\FooComponent\Adapter\SomeAdapter($adapterOptions)); $interestingResult = $foo-doSomethingInteresting();
As you can see, no declarative code was required to fulfill the most common use case that was identified as a need for this component's existence. The above API is defined by the totality of all the public (concrete) classes, their public properties and public methods. By examining these elements, a good API design should allow a developer to deduce how the component works without examining any documentation. When that is possible, the API has become the documentation as well as the a€ostorya€¯ behind how the component/library is to be used.
Not all use cases are accounted for in generic components and generic libraries. As developers, we attempt to create generic libraries and components that will solve the majority of problems of the majority of the community. We cannot envision all use cases or even edge cases behind a particular component. That said though doesn't means that the outlying use cases are unimportant or should be unaccounted for. These use cases are handled by the secondary API: the a€oExtension APIa€¯.
The Extension API answers the question: a€osince this component does 90% of what I want, how can I extend it to fulfill the last few of my needs.a€¯ Clearly, it makes sense to leverage tools that do most of what you need especially if they can be extended in ways that are outside of the out-of-the-box feature-set. Object-oriented/class based code is particularly well
Truncated by Planet PHP, read more at the original (another 8587 bytes) | <urn:uuid:7c197ba2-52c0-4544-a689-52edecc99c86> | 2.90625 | 1,006 | Knowledge Article | Software Dev. | 38.386703 |
is to burn. In every complete combustion equation a hydrocarbon(CxHy)
reacts with oxygen (O2)
to produce water (H2O)
and carbon dioxide (CO2).
Combustion reactions that the pattern of : CxHy +
O2(g) --> H2O(g)
25O2 --> 18H2O
reacts with oxygen gas to produce water and carbon
let’s go step by step.
Write the reaction for the complete combustion of propane (C3H8).
|1. Write the formula for the given reactant.
|2. Add oxygen, O2, as a reactant. Don't forget that oxygen is a diatomic molecule.
||C3H8 + O2 -->
|3. Your products are ALWAYS H2O and CO2 in a complete combustion. Write H2O and CO2 on the products side.
||C3H8 + O2 --> H2O + CO2
|4. Balance the equation
||C3H8 + 5O2 --> 4H2O + 3CO2 | <urn:uuid:aee94462-fe50-4803-8eb5-97e0fcbe4edd> | 3.515625 | 239 | Tutorial | Science & Tech. | 73.843006 |
I have revised my views slightly since I began this thread.
A decrease in Cloud Cover is responsible for most of the warming over the last 30 years and last century, and this decrease in Cloud Cover is directly tied to solar activity variations through solar wind variations inflicting changes on GCRs.
There is an overwhelming amount of evidence to support this viewpoint.
Let's start with nine peer reviewed studies that document that the sun was a likely driver of the 20th Century Warming.Palle Bago and Butler 2001
Palle Bago and Butler 2001, using many formulas they derived in their earlier, 2000 paper, calculated that the solar effects, directly and indirectly, caused 0.5 Degrees C of the 0.55 Degree C warming. This means that they found that 91% of the warming over the past 100 years can be explained by solar variability, directly and indirectly alone. They mention that there is a "possibility" that solar attribution could be less during the most recent decades, but they are not definite with this statement. They simply state that the solar contribution an unknown over the last and most recent decades. This probably has to do with the ACRIM and PMOD TSI Composites and the controversy surrounding these datasets which Scafetta 2009 documents.Georgieva et. al 2005
Georgieva et. al 2005 used the Geomagnetic AA Index to quantify the solar impact on Climate Change, rather than the sunspot number, because using the sunspot number to quantify the solar contribution to climate change, as many studies do, leads to an underestimation of the Solar impact on Climate Change.
The above figure from Georgieva et. al shows the Geomagentic AA Index with the broken line, and the Global Temperature Anomalies with the solid line. They find that the correlation coefficient between the AA Index and Global Temperatures is 0.85, meaning that the sun can explain 85% of the variances in temperatures over the last ~150 years. Cliver et. al 1998
Cliver et. al 1998 also used the Geomagnetic AA Index to estimate the solar contribution to climate change.
Above figure: From Cliver et. al 1998. The AA Index is the dotted line, and the solid line are the temperature anomalies.
They found that 50-100% of the warming could be due to the sun, but it should be noted that this analysis does not include other factors like volcanic activity and anthropogenic greenhouse gas emissions when estimating the total contribution. Nonetheless, this study also shows that other studies which do include these factors are only at the lower end of the 50-100% range for the solar contribution over the last 100-150 years. It also supports other studies with a larger solar contribution to climate change because of the remarkable correlation with the AA Index and temperatures.Solheim et. al 2012
Solheim et. al 2012 found that the solar signal is reinforced by the Atlantic Ocean, and this reinforcing signal in the Atlantic Ocean is calculated to be from 63-72% of the variances in temperatures over the entire timeframe. They get a lower solar contribution to land based stations, but the reinforced signal is probably what would lead to a more accurate solar contribution, since most of the world is covered by oceans, and likely, reinforcing the solar signals. Link et. al 2011
The box that represents the % solar contribution from Link et. al 2011 actually represents the probability whether the entire trend over the last 100-150 years is natural. The authors calculate that the probability of the warming being caused by solar activity over this entire timeframe is 40-90%. It should be noted that these probabilities go up significantly over shorter timeframes like 1900-1950 and 1960-2005.Scafetta and West 2008
Scafetta and West 2008 adresses the uncertainty raised in the first paper. If a TSI curve that shows an upward trend from Solar Cycle 21 to 22 is used from the ACRIM TSI composite rather than the flat PMOD TSI composite, then a higher contribution from the sun would be needed. The authors find that up to 69% of the variances in temperatures can be explained by solar activity.
The image above from Scafetta and West 2008 shows the divergence between the PMOD and ACRIM TSI datasets, which makes attribution to past climate change even harder. The red curve is the ACRIM TSI composite, the blue curve is the PMOD TSI Composite, and the black curve and green line are the Global Temperature anomalies. Scafetta and West 2007
The ACRIM verses PMOD controversy continues in this paper. 50% or more of temperatures can be attributed to the solar forcing, depending if the ACRIM TSI composite is used or not. This further adds on to resolving the uncertainty between the PMOD and ACRIM datasets during the ACRIM Gap.
The graph above from Scafetta and West 2007 shows the excellent correlation between solar activity and temperatures. It also shows that a large portion of the warming can be attributed to solar activity. Over the last 30 years, a significant portion of the warming can be attributed to solar activity if the ACRIM TSI composite is used. Ogurtsov 2007
Ogurstov 2007 estimated that the solar contribution directly and indirectly caused about 0.25-0.35 degrees C of the warming that took place during the 20th Century. Using the Skeptical Science trend calculator gives an approxiate warming of 0.6 Degrees C during the 20th Century. This means that 41-59% of the trend upward can be attributed to solar activity over the past 100 years.Blanter et. al 2008
Blanter et. al 2008 found that temperatures correlated remarkably well for all periods between the solar activity indicies and the observed temperatures for stations in Europe and the United States during the 20th Century. They used a finding from a previous study that the temperatures at weather stations correlated remarkably well if they were up to a 1000 km distance from each other. They also state in the abstract that these changes can "possibly" be extended onto a Global scale. Being that they found that solar activity can account for all temperature changes over the 20th Century, I reduced the range slightly from 100% to somwhere in the 90-100% range to account for the anthropogenic forcings.
I will be posting more papers later on this thread that support a natural solar and oceanic cause for recent warming, and not anthropogenic. | <urn:uuid:545e7998-3197-4892-ae19-39e7e3f7d3aa> | 2.953125 | 1,320 | Comment Section | Science & Tech. | 47.938141 |
This is part of 10998521's Mathematics for the Layman project, which you can read more about on his homenode.
Reductio ad absurdum sounds like fancy Latin, but it's actually a very widely-used method of proof. Say you start with some idea that you want to prove: this is the postulate or conjecture. To prove it, we first of all assume the exact opposite. Then, we have to show that this assumption leads to some contradiction: this could be something obvious like 1 = 3, or more subtle. Then, if the opposite is false, that implies that your original postulate was true. Beautifully logical!
As baffo mentions, among the most famous applications of this is the proof that the square root of two is irrational: it can't be written as one integer divided by another. There is a good explanation of this here, and you can see the steps I described above:
- Assume the opposite: That the square root of 2 is rational
- Show that this leads to a contradiction
- Conclude that it must therefore be irrational. | <urn:uuid:c14d8850-e99d-4360-add6-0daaf8a63963> | 3.421875 | 227 | Knowledge Article | Science & Tech. | 50.531577 |
See also the
Browse High School Calculus
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Maximizing the volume of a box.
Maximizing the volume of a cylinder.
Volume of a tank.
What is a derivative?
- Integrals and Trig Functions [4/6/1996]
The integral from pi to zero of the square root of (1-sinX).
- Integrals in Polar Coordinates [04/15/2003]
How can I evaluate an expression like (sin(theta)*(constant)) for
theta = 0...2*Pi?
- Integrals versus Antiderivatives [02/24/2001]
What is the difference between an integral and an antiderivative?
- Integral tan(x)? [6/10/1996]
What is the antiderivative of the function tan(x)?
- Integral using Substitution [4/11/1996]
Evaluate: xdx / (x^2+1)^(1/2), given u^2 = x^2+1.
- Integrate Cos 2a [08/15/2001]
The answer given in the book for integrating cos 2a is sin 2a/2. Does
this follow a pattern?
- Integrating 1/(1+x^n) [11/14/2001]
Are there methods of integrating functions of the form 1/(1+x^n)? I have
solved 1/(1+x^4) and am wondering about solutions for higher powers of x.
- Integrating 1/(sinx)^6 dx [02/25/2002]
What is the integration of 1/(sinx)^6 dx?
- Integrating a Product of Cosines [05/04/2005]
Let n and m be natural numbers. My book says that the integral from
-pi to pi of the function f(x) = cos(nx) * cos(mx) is pi if n = m and
0 else. I can't figure out how to prove this.
- Integrating a Quadruple-Angle Trigonometric Expression or Two [01/13/2011]
A network engineer seeks help integrating a trigonometric expression with a cosine
term in its denominator (or is it the cotangent?). Using double-angle identities and a
substitution, Doctor Ali provides a boost.
- Integrating Exponentials [5/27/1995]
What is the integral of 5^x dx ?
- Integrating exp(-x^2) [11/09/2005]
It seems like all the ways of finding integral exp(-x^2) involve
making it a double integral and using polar coordinates. I was
wondering if there is any way to do it without making it a double
- Integrating with the Arc Length Formula [10/19/1998]
Can you help me integrate functions using the arclength formula, e.g.
x^(2/3)+y^(2/3)=1 and y=e^-x?
- Integrating X^x, Closed Form [10/31/1996]
How do you express the equation y = xcosx in terms of y?
- Integration [5/23/1996]
Integrate the following function: x^2 * e^(-2x^2)
- Integration [5/29/1996]
What does integral of (cos(x).x(cub).sinh(x)square).dx mean, and what's
- Integration [01/08/1998]
What is the integrated area if the anti-derivative is undefined?
- Integration [02/17/1999]
Integrate x*tan^2 x with respect to x.
- Integration [03/30/1999]
Integrate (2 - x^2)^4x dx.
- Integration by Partial Fractions [11/14/1996]
How do you integrate f(x) = x^2/[(x^4) + 1]?
- Integration by Parts [2/15/1995]
I need the integral from 0 to 1 of X^4*exp(-x/2). Can you help?
- Integration by Parts [12/8/1995]
How do you Integrate: x^n/e^x ?
- Integration by Parts [5/24/1996]
How do you integrate x^x?
- Integration by Parts [01/07/1997]
How do you solve Int [sin (ln x)] dx?
- Integration by Parts [05/27/1997]
What is the integral of sec^3(x)?
- Integration by Parts [04/08/1999]
How does one find the integral of [(sec x)^3 dx]?
- Integration by Parts [05/02/1999]
Find the general integral of x*ln(x)-1.
- Integration by Parts [04/10/2008]
How can I integrate e^x(x+1)/(x+2)^2 ?
- Integration Hints [02/23/1999]
Can you help me integrate (cos[x])^4?
- Integration of Natural Logs [02/12/1998]
Why does the natural log of x equal the integral of 1/t dt from 1 to x?
Why is INT[(1/t)dt] from 1 to x the natural log of x, or why was it
defined this way?
- Integration of Sin(x^2) [11/10/1997]
I have been given the solution in the form of Frensel's Sin, but it
explains nothing about how it was integrated. I am not looking for an
equation, I am looking for a reason!
- Integration of Trigonometric Function by Substitution [03/18/1998]
Integrate [tan 2x dx] by u-substitution.
- Integration of Trigonometric Functions [05/28/1999]
How can I integrate sin(x)sin(2x).dx ?
- Integration Over a Complicated Region [11/1/1996]
Given a region defined by five relations simultaneously, find its area.
- Integration Problem [2/22/1995]
How do you integrate the function: (tan 2x)^3 dx, in terms of x?
- Integration Questions [03/09/2001]
Calculate the area of the finite region bounded by the curves y=x^2 and
- Integration Trick [8/13/1996]
If f(x)=1/sin(x), what is the integral of f(x)?
- An Integration with Substitution [06/06/1998]
I'm having trouble with the following integration. Is substitution needed
- Intriguing Limit [04/30/1997]
Why is the following true: lim x --> oo (1-1/x)^x = 1/e?
- Introduction to Line Integrals [02/08/2004]
C is the broken path line that goes from (1,1,2) to (2,0,-1) by
following a line parallel to the x axis from (1,1,2) to (2,1,2) then
parallel to the y axis from (2,1,2) to (2,0,2) then parallel to the z
axis from (2,0,2) to (2,0,-1). Find int_C [ f(x,y,z)*dx + g(x,y,z)*dy
+ h(x,y,z)*dz ]. | <urn:uuid:7f6bc432-3f7b-40c3-a9e1-c5f15186d8c4> | 2.6875 | 1,677 | Q&A Forum | Science & Tech. | 89.95791 |
What caused a giant arrow-shaped cloud on Saturn's moon Titan?
A research group led by Jonathan L. Mitchell, UCLA assistant professor of earth and space sciences and of atmospheric and oceanic sciences, has answered this question by using a global circulation model of Titan to demonstrate how planetary-scale atmospheric waves affect the moon's weather patterns, leading to a "stenciling" effect that results in sharp and sometimes surprising cloud shapes.
"These atmospheric waves are somewhat like the natural, resonant vibration of a wine glass," Mitchell said. "Individual clouds might 'ring the bell,' so to speak, and once the ringing starts, the clouds have to respond to that vibration."
The fascinating clouds, including arrow-shaped ones, that result from the atmospheric waves can cause intense precipitation — sometimes more than 20 times Titan's average seasonal rainfall — and could be essential in shaping Titan's surface by erosion.
The research was published Aug. 14 in the online edition of the journal Nature Geoscience and will be published in an upcoming print edition.
Mitchell and a colleague have described Titan's climate as "all-tropics" — the entire planet experiences the types of weather phenomena that on Earth are confined to the equatorial region.
"Our new results demonstrate the power of this analogy, not only for general features of Titan's climate but also for individual storms," Mitchell said. "In future work, we plan to extend our analysis to other Titan observations and make predictions of what clouds might be observed during the upcoming season.
"Titan's all-tropics climate gives us the opportunity to study tropical weather in a simpler setting than on Earth," he added. "Our hope is that this may help us understand Earth's weather in a changing climate."
NASA's Cassini Spacecraft has been in orbit around Saturn since late 2004 and has revolutionized our understanding of Titan, which is larger in volume than the planet Mercury and the second largest moon in the solar system after Jupiter's Ganymede. Titan has a thick nitrogen atmosphere and experiences rain made of natural methane gas.
"Titan is like Earth's strange sibling — the only other rocky body in the solar system that currently experiences rain," Mitchell said.
Titan is an alien world, but strangely not so different from Earth. Like Earth, the main component of its atmosphere is molecular nitrogen. Water, too, is abundant on Titan, although it is all frozen in the crust at very low temperatures. Methane is thermodynamically active in the lower atmosphere, and much like water vapor on Earth, Titan's methane forms clouds, precipitates and is resupplied from surface sources, Mitchell said. The runoff then weathers the cold surface of Titan, creating what appears to be river patterns.
Scientists think that Earth, shortly after it formed an atmosphere, had large amounts of methane and very little oxygen. Methane provided an important greenhouse warming that probably prevented Earth from staying perpetually in a completely frozen state that otherwise would have resulted from the weaker sunlight from the very young sun, Mitchell said.
"Therefore, by studying Titan's modern climate, we may gain new insights about the way the early Earth's climate was," Mitchell said.
He and his research group have developed an atmospheric model to study the climate and cloud patterns of Titan. - physorg
Illinois couple had seen enough UFOs
Husband was outside on the patio, he started knocking on the door for me to hurry up and come outside, and that there was something in the sky that he didn't know what it was.
I stepped outside on the porch and he pointed up to what he was seeing and I looked in the direction and the only way to say what it looked like is that it was round shaped, glowing red, moving in a North direction than turning slightly to the East for a North East direction, moving at a steady pace then going up higher till it was out of site.
Later on that same evening, about an hour and a half later, directly above us a bright glowing triangle shaped object appeared out of know where. It was visually closer then the red object, it really scared me, because I could make out the outline of it and it was so bright, Ive never seen anything like it, it also was moving in a North East direction and seemed to go up and disappear, we saw one more just like it later on and it also was moving North East and went up and disappeared.
After that last one I went inside, I had decided Id seen enough. These things that we saw were not airplanes, helicopters, balloons etc.. Very strange. - MUFON CMS
'Suicide bomber' bacteria destroys superbug
Experts in the innovative field of “synthetic biology” engineered a strain of E.coli that could detect signs of Pseudomonas aeruginosa, a leading cause of infection that can be fatal to patients with weak immune systems.
Their specially designed bacteria then produced a toxin that is lethal to the bug, before blowing themselves apart like bombs and splattering the substance over the surrounding area.
When added to a culture of P. aeruginosa in lab tests, the artificial E.coli destroyed 99 per cent of its targets and prevented the formation of biofilms - slimy communities of bacteria which are difficult to destroy - by up to 90 per cent.
The method has not been tested in trials on humans or animals, but a study in the journal Molecular Systems Biology indicated it could provide a new approach to tackling drug-resistant infections, where progress using current techniques has ground to a halt.
Researchers at Nanyang Technological University, Singapore, write: “In summary, we engineered a novel biological system, which comprises sensing, killing, and lysing devices, that enables E. coli to sense and eradicate pathogenic P. aeruginosa strains by exploiting the synthetic biology framework.”
P. aeruginosa is a bacteria which infects the lungs and digestive system, particularly in patients who are critically ill or have weakened immune systems.
The strains found in hospitals are often resistant to antibiotics, creating a pressing need for new treatments.
The E.coli strain developed by researchers from the Nanyang Technological University in Singapore uses a protein called LasR to detect chemical signals given off by P. aeruginosa cells when they communicate with each other.
P. aeruginosa naturally produces a toxin known as pyocin, but the scientists engineered the E.coli to produce the same weapon when the pathogen is detected nearby.
The E.coli bacteria then burst themselves open and cover the P. aeruginosa bacteria with pyocin, which eats away at the outer cell wall and causes the insides to spill out. - telegraph
Intense vibration and bright green light
Pennsylvania: In bed w/ MY husband sleeping, awakened by INTENSE vibration, bedroom aglow w/ bright green light. Light then dimmed,then event repeated 3 more times, each time lasting 5-10 seconds. I awoke my husband at the first and he experienced the last 3 events. Heavy cloud cover. No thunder/lightning storm in progress. The vibration/pulse was felt physically. The house did not shake or vibrate. There were no explosions. We both felt an overwhelming fear and agitation and were unable to sleep afterward. There was nothing to be seen or heard. Spoke w/ township workers, no electrical disturbance on our street that night, no evidence of electrical wires having been touched, wires are all clear of tree branches. - MUFON CMS
BBC Wales Interviews Irene Allen-Block - Spirit Rescue International
Irene Allen-Block - Spirit Rescue International - Interview - BBC Wales Radio
Spirit Rescue International™
Providing no-cost professional spiritual help, personal support and guidance
Take the first step towards genuine peace of mind | <urn:uuid:fb38ed93-560b-445a-92e9-04b57503a820> | 3.875 | 1,618 | Content Listing | Science & Tech. | 40.520822 |
- crypt(word, salt) -> string
word will usually be a user's password. salt is a 2-character string
which will be used to select one of 4096 variations of DES. The characters
in salt must be either ".", "/", or an alphanumeric character. Returns
the hashed password as a string, which will be composed of characters from
the same alphabet as the salt. | <urn:uuid:44913c9c-28d7-4b97-bef6-71b16cf8aea2> | 3.546875 | 84 | Documentation | Software Dev. | 72.406098 |
VBS Home page,VBS Course Navigator, Protein Synthesis and DNA replication, DNA Replication, Previous Page, Next Page,top of page
The replication or duplication of DNA depends on one main idea, namely that the nitrogen bases of the nucleotides are complementary to each other on opposite halves of the molecule as shown here. Thus the base adenine(A) in DNA always pairs with thymine(T) and guanine(G) with cytosine(C).
This pairing is due to the shapes of the nucleotide bases which allow hydrogen bonds to form between the complementary bases, holding the two halves of the DNA molecule together.
This idea provided an immediate solution to how DNA replicated. All that should have to happen is the following sequence:
1. The parent DNA molecule unzips exposing the two halves of the DNA molecule
2. Each half of the parent DNA molecule serves as a template for the complementarity bases to be brought into the correct position to make a new complementary half for each of the original parent halves. This theoretical consideration suggested to Watson and Crick that DNA replication is what we now call semiconservative.
Semi conservative DNA replication means that when the two new DNA molecules are formed during DNA replication, each resulting daughter molecule consists of one side from the original parent molecule and a new side synthesized from the parent side which served as a template.
This experiment of Matthew Meselson and Frank Stahl demonstrated that DNA replication was semi-conservative. These scientists grew the bacteria E-coli in media containing nutrients with the isotope Nitrogen 15, 15N as opposed to the normal isotope of nitrogen, 14N. After a time some of the DNA containing the normal isotope is replaced with DNA containing ,15N as new DNA synthesis proceeds.
They cultured the bacteria for a sufficient amount of time that so that they could be sure that all the DNA contained just 15N. Then they took these bacteria and set up cultures using growth medium containing 14N and followed the bacteria through a number of replication cycles.
Meselson and Stahl then knew they could separate DNA's with differing amounts of 15N by using a process called cesium density gradient centrifugation which separates molecules by weight in a solution of cesium chloride. These scientists noted that one would expect a different distribution of DNA's by weight depending on whether the type of replication involved.
For example DNA replication could be conservative, in which case after one replication cycle half the DNA would contain only 14N and thus be lighter and the other half of the DNA would contain only 15N and thus be heavier. Thus there would be two DNA bands, one light and one heavy produced by the centrifugation.
DNA replication could have been dispersive in which case the daughter molecules after one generation would contain roughly equal mixtures of 15N and 14N mixed through each of the halves of the molecule, and there would only be a single DNA band of intermediate weight.
DNA replication could have also been(as does indeed turn out to be the case) semiconservative Again there would only be one DNA band of intermediate weight.
Meselson and Stahl realized that looking at only one replication cycle was not enough, given the equipment available to them in that the results could not distinguish between the dispersive and semiconservative mechanism. But if replication is allowed to continue for another cycle then the dispersive model predicts a single band of DNA, but the semiconservative model predicts a band of intermediate DNA and a band of light DNA containing only 14N.
The results matched the predictions of the semi conservative model but not the dispersive model. The difference in these models is shown in the figure.
DNA replication in both prokaryotes and eukaryotes involves a complex of proteins including several enzymes called DNA polymerases. The DNA polymerases travel up the DNA molecule from an initiation site which is a region along the DNA that the enzyme complex can recognize. | <urn:uuid:31b5b962-e54e-401c-b3cd-ea756f5eaf16> | 4.09375 | 813 | Knowledge Article | Science & Tech. | 29.222305 |
Robert Kaufmann, a professor at Boston University, said he was motivated to conduct the study after a sceptic confronted him, telling him he had seen that temperatures had not risen over the decade.So, that darned coal that emits CO2 which, according to the Fraud, the falsified hypothesis, causes uncontrollable global warming is also emitting sulphur which cancels out the so-called damage of the coal. That's a real travesty, Kevin, because the sulphur is real pollution.
"Nothing that I had read that other people have done gave me a quick answer to explain that seeming contradiction, because I knew that carbon dioxide concentrations have risen," Professor Kaufmann said.
The US-Finnish study, published in the Proceedings of the National Academy of Sciences, named a culprit -- coal. The burning of coal jumped in the past decade, particularly in China. Coal emits sulfur, which stops the sun's rays from reaching the Earth.
UPDATE: Kaufmann report found to be "clown science." HERE
Also see - (2011), Major influence of tropical volcanic eruptions on the stratospheric aerosol layer during the last decade, Geophys. Res. Lett., 38, L12807, doi:10.1029/2011GL047563. (Here)
Latterly reported by WUWT
"New NASA paper contradicts Kaufmann et al saying it’s volcanoes, not China coal"++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
UK Journalist Christopher Booker puts it this way:
But hang on a moment. Aren't these new climate scaremongers the very same people who only a few years back were telling us that the planet was in danger of being fried to a crisp by runaway global warming?
And wasn't it on their say so that the world's politicians, led by our own here in Britain, were committing us to spending hundreds of billions of pounds to save the planet from the catastrophic warming caused by those same evil power stations?
The question this extraordinary turn of events raises is whether any of these supposed experts actually have the faintest idea what they are talking about.
But perhaps the most bizarre thing about this latest twist in the ongoing climate scare story is the way it takes us precisely back to where it all started 40 years ago.
All of us today have become so accustomed to the notion of global warming that it is hard to believe that in the Seventies, U.S. scientists began to warn us the world was heading for a cooling so severe it might even herald a new ice age. | <urn:uuid:447cf1f4-2dca-4583-98f7-9a35abf4e6e5> | 2.90625 | 529 | Personal Blog | Science & Tech. | 51.768317 |
Related Labs, Activities, and Other CoolStuff
Quantitatively confirm the Combined Gas Law with one complete apparatus!
The Combined Gas Law simplifies the Ideal Gas Law and describes a relationship between the pressure, temperature and volume of a gas that is constant. Students can verify this relationship using air and this unique apparatus. Twist the handle to compress the air, and simply read the volume, temperature and pressure from the scales. Repeat and show that the relationship stays the same.
Having trouble viewing this video in YouTube?
Try watching in Teacher Tube instead | <urn:uuid:36a71741-733a-4c10-be76-9829493cb59a> | 3.421875 | 111 | Truncated | Science & Tech. | 33.106449 |
Demand for groundwater has increased as access to surface water supplies has become constrained. Groundwater resources are now being managed through water sharing plans for sustainable long-term usage.
Groundwater is generally seen as a supplementary water resource. However, for many communities in regional NSW, groundwater is the primary source of water for drinking, stock and domestic use, agriculture and other industries. Importantly, too, a range of ecosystems depend on groundwater for their continued survival, including some surface water bodies (wetlands, rivers and lakes) that are connected to groundwater, as well as some terrestrial ecosystems. Significant changes in groundwater quality and quantity have the potential to degrade ecosystems and affect human uses of water. Because of the hidden nature of many groundwater dependent ecosystems, the impacts are likely to be less obvious and well-understood.
Major Uses of Groundwater
Approximately 11% of the water used in NSW comes from groundwater sources. Agriculture and mining are the largest users of groundwater in NSW, with the greatest volume used for irrigation in areas around the main inland alluvial aquifers. For some inland mining operations, groundwater is the only available source of water, but it may also be an obstruction or hazard that must be removed before mining can proceed. For more than 200 towns in NSW, groundwater is the principal source of water supply. An estimated 13% of the groundwater used in NSW goes to domestic and stock purposes.
Levels of Extraction and Recharge
Variability in climatic conditions affects the amount of groundwater used. Extraction may increase substantially in times of drought to offset the lack of surface water, while in periods of high rainfall, groundwater will be recharged more and used less. Due to the heavy competition for surface water supplies in NSW, demand for groundwater resources has generally increased over the past 10 years. Extraction peaked at around 1300 GL in 2002–03, but extraction levels are highly variable from year to year. Typically extraction has generally been between 500 and 1000 GL per year.
Long-term Average Extraction Limits
The intent of water sharing plans for groundwater is to manage the resource sustainably so that extraction remains in balance with yield over the longer term. This means that over-extraction in times of drought, is permissible, providing that extraction drops back below the sustainable yield after the period of drought to allow water levels to recover. This natural flexibility of groundwater systems provides for a reliable and secure water resource. The long-term average extraction limit is the level of groundwater that can be extracted sustainably on an annual basis. At the state scale the overall level of entitlement compared with the long-term average extraction limit is quite low, at around 20%.
Groundwater Dependent Ecosystems
‘Groundwater dependent ecosystems’ are those that rely in whole or in part, particularly during drought, for their survival on groundwater.
Terrestrial vegetation may depend on diffuse discharges of shallow groundwater to varying degrees, either to sustain transpiration and growth through a dry season or to maintain perennially lush ecosystems in otherwise arid environments.
Wetland ecosystems may depend on groundwater to keep them seasonally waterlogged or flooded. Wetlands provide the most extensive and diverse set of potentially groundwater dependent ecosystems in Australia.
River baseflow systems rely on groundwater for the character and composition of in-stream and near-stream ecosystems.
Aquifer and cave ecosystems are heavily dependent on groundwater for life forms that live in their porous and fissured aquifers. Life in cave aquifers may be as rich as it is above ground.
Terrestrial fauna rely on groundwater as a source of drinking water. Groundwater, as river baseflow or discharge into a spring or pool, is an important source of water across much of the country, particularly in northern and inland Australia and other areas with a semi-arid climate. Its significance is greater for larger mammals and birds, as many smaller animals can obtain most of their water requirements from their food or respiration.
Pastoralists in inland Australia have made extensive use of groundwater to supply drinking water to grazing stock. In addition to watering stock, groundwater is also used by native fauna, such as kangaroos, and pest and feral animals. Provision of water has allowed larger populations of both wildlife and pest animals to be sustained than would otherwise be the case.
Estuarine and near-shore marine systems which may depend on groundwater discharges to provide a suitable habitat include coastal lakes, mangroves, saltmarshes and seagrass beds. Groundwater discharge may be in the form of direct off-shore discharge or baseflow into streams that discharge to the ocean.
Department of Environment, Climate Change and Water | <urn:uuid:c6fc2c68-dea9-4c4a-a873-40a697e18d14> | 3.703125 | 955 | Knowledge Article | Science & Tech. | 26.826884 |
For inquiries contact Stephen
D. McCormick, Conte Anadromous Fish Research Center,
Biological Resources Division, USGS, Turners Falls, MA
Atlantic salmon are known as the "king of fish," an appropriate title for many reasons. Atlantic salmon make a tremendous journey during their lifetime, migrating from the fresh water streams of their youth to feeding grounds in the north Atlantic Ocean and back again to spawn. Their capacity to return back to the same stream where they were hatched has captivated and mystified biologists for hundreds of years. Salmon are among the most beautiful of fish; stream-lined, silver and graceful. They are powerful, too, among the greatest fighters in the fishing world. And perhaps most important of all, Atlantic salmon are a symbol of clean, unspoiled waters that run wild to the sea. For those of us who live near the Connecticut River, Atlantic salmon are also a symbol of clean and wild waters reclaimed.
Spawning female Atlantic salmon build nests (called redds) in the fall. They excavate gravel from the stream bed by turning sideways and lashing up and down with their powerful body and tail. With the encouragement of a male they lay their eggs in the redd. The eggs remain in the gravel through the winter and hatch the following spring. Newly hatched "fry" will stay in the gravel and continue to develop using the energy stored in their yolk and begin to feed.
Salmon fry just after hatching.
Atlantic salmon spend their first few years in small streams and rivers feeding on aquatic insects and other drift' that is brought into their sight by the current. At this time in their life they are known as "parr" and are mostly solitary creatures that defend their feeding territories from other fish that might intrude and compete for food. After reaching a size of about 4 inches, the fish become "smolts" in the spring and begin migrating to the ocean.
Stream-resident parr (below) and seaward-migrating smolt (above).
In southern New England where the growing season is long it may take only two years to become a smolt, but farther north it takes longer: up to 3 years in Northern Vermont, 4 in Nova Scotia and 5 in Newfoundland! During their downstream migration smolts become more sociable, begin schooling and develop the salinity tolerance they will need when they enter the ocean.
Once in the ocean, salmon take advantage of abundant food resources and grow rapidly. Feeding while they migrate, the salmon move toward their major feeding grounds in the North Atlantic near Greenland and Iceland. While in the ocean salmon must avoid many predators such as seals and larger fish in order to survive. After spending one or two years at sea, salmon begin their homeward journey. It is generally thought that salmon use a magnetic or sun compass to find their way to the coast of their natal river, though this is not known for certain. They then use olfactory (smelling) cues learned as smolts to find the river and tributary of their birth. Salmon may reenter fresh water in spring, summer or fall, but spawning occurs in the fall, and the life cycle of the salmon begins anew.
Adult Atlantic salmon on their upstream spawning migration.
Atlantic salmon have been in trouble in New England for many years. Once abundant, populations of Atlantic salmon went extinct on the Connecticut and Merrimac Rivers in the 1800s as result of dam building which blocked access to spawning grounds. More recently, Atlantic salmon in the downeast' rivers in Maine have experienced substantial population declines. It is thought that these recent declines are part of a widespread decline in Atlantic salmon populations that may be caused by poor conditions in the ocean that are related to cyclical temperature patterns. Whatever the reason, these Maine populations have now been classified as threatened. But there is hope for Atlantic salmon too. Twenty-five years ago state and federal fisheries agencies joined forces to restore Atlantic salmon to southern New England. Two to five hundred salmon have been returning to the Connecticut River for each of the last twenty years, though all involved hope these numbers will increase. Last year the first natural spawning of Atlantic salmon in Massachusetts in over 150 years occurred on the Westfield River, a tributary of the Connecticut. In the coming years we can hope to see even more of the "king of fish" returning to the restored waters of the Connecticut.
For more information on Atlantic salmon:
For more information on Pacific salmon:
For more information on migratory and anadromous fish: | <urn:uuid:2968555f-52b0-41f2-b94c-2e169dfe03fd> | 3.15625 | 932 | Knowledge Article | Science & Tech. | 45.954389 |
In our image server example, it is possible that the single file server used to store images could be replaced by multiple file servers, each containing its own unique set of images. (See Figure 4.) Such an architecture would allow the system to fill each file server with images, adding additional servers as the disks become full. The design would require a naming scheme that tied an image's filename to the server containing it. An image's name could be formed from a consistent hashing scheme mapped across the servers. Or alternatively, each image could be assigned an incremental ID, so that when a client makes a request for an image, the image retrieval service only needs to maintain the range of IDs that are mapped to each of the servers (like an index).
Figure 4: Image hosting application with redundancy and partitioning......
Of course there are challenges distributing data or functionality across multiple servers. One of the key issues is data locality; in distributed systems the closer the data to the operation or point of computation, the better the performance of the system. Therefore it is potentially problematic to have data spread across multiple servers, as any time it is needed it may not be local, forcing the servers to perform a costly fetch of the required information across the network.
Another potential issue comes in the form of inconsistency. When there are different services reading and writing from a shared resource, potentially another service or data store, there is the chance for race conditions — where some data is supposed to be updated, but the read happens prior to the update — and in those cases the data is inconsistent. For example, in the image hosting scenario, a race condition could occur if one client sent a request to update the dog image with a new title, changing it from "Dog" to "Gizmo", but at the same time another client was reading the image. In that circumstance it is unclear which title, "Dog" or "Gizmo", would be the one received by the second client.
There are certainly some obstacles associated with partitioning data, but partitioning allows each problem to be split — by data, load, usage patterns, etc. — into manageable chunks. This can help with scalability and manageability, but is not without risk. There are lots of ways to mitigate risk and handle failures; however, in the interest of brevity they are not covered in this article. If you are interested in reading more, you can check out my blog post on fault tolerance and monitoring.
The Building Blocks of Fast and Scalable Data Access
Having covered some of the core considerations in designing distributed systems, let's now talk about the hard part: scaling access to the data.
Most simple Web applications, for example, LAMP stack applications, look something like Figure 5.
Figure 5: Simple Web applications
As they grow, there are two main challenges: scaling access to the app server and to the database. In a highly scalable application design, the app (or Web) server is typically minimized and often embodies a shared-nothing architecture. This makes the app server layer of the system horizontally scalable. As a result of this design, the heavy lifting is pushed down the stack to the database server and supporting services; it's at this layer where the real scaling and performance challenges come into play.
The rest of this article is devoted to some of the more common strategies and methods for making these types of services fast and scalable by providing fast access to data.
Figure 6: Oversimplified Web application
Most systems can be oversimplified to Figure 6. This is a great place to start. If you have a lot of data, you want fast and easy access, like keeping a stash of candy in the top drawer of your desk. Though overly simplified, the previous statement hints at two hard problems: scalability of storage and fast access of data.
For the sake of this example, let's assume you have many terabytes (TB) of data and you want to allow users to access small portions of that data at random. (See Figure 7.) This is similar to locating an image file somewhere on the file server in the image application example.
Figure 7: Accessing specific data
This is particularly challenging because it can be very costly to load TBs of data into memory; this directly translates to disk IO. Reading from disk is many times slower than from memory — memory access is as fast as Chuck Norris, whereas disk access is slower than the line at the DMV. This speed difference really adds up for large data sets; in real numbers memory access is as little as 6 times faster for sequential reads, or 100,000 times faster for random reads, than reading from disk (see The Pathologies of Big Data). Moreover, even with unique IDs, solving the problem of knowing where to find that little bit of data can be an arduous task. It's like trying to get that last Jolly Rancher from your candy stash without looking.
Thankfully there are many options that you can employ to make this easier; four of the more important ones are caches, proxies, indexes and load balancers. The rest of this article discusses how each of these concepts can be used to make data access a lot faster.
Caches take advantage of the locality of reference principle: recently requested data is likely to be requested again. They are used in almost every layer of computing: hardware, operating systems, Web browsers, Web applications and more. A cache is like short-term memory: it has a limited amount of space, but is typically faster than the original data source and contains the most recently accessed items. Caches can exist at all levels in architecture, but are often found at the level nearest to the front end, where they are implemented to return data quickly without taxing downstream levels.
How can a cache be used to make your data access faster in our API example? In this case, there are a couple of places you can insert a cache. One option is to insert a cache on your request layer node, as in Figure 8.
Figure 8: Inserting a cache on your request layer node
Placing a cache directly on a request layer node enables the local storage of response data. Each time a request is made to the service, the node will quickly return local, cached data if it exists. If it is not in the cache, the request node will query the data from disk. The cache on one request layer node could also be located both in memory (which is very fast) and on the node's local disk (faster than going to network storage).
Figure 9: Multiple caches
What happens when you expand this to many nodes? As you can see in Figure 9, if the request layer is expanded to multiple nodes, it's still quite possible to have each node host its own cache. However, if your load balancer randomly distributes requests across the nodes, the same request will go to different nodes, thus increasing cache misses. Two choices for overcoming this hurdle are global caches and distributed caches.
A global cache is just as it sounds: all the nodes use the same single cache space. This involves adding a server, or file store of some sort, faster than your original store and accessible by all the request layer nodes. Each of the request nodes queries the cache in the same way it would a local one. This kind of caching scheme can get a bit complicated because it is very easy to overwhelm a single cache as the number of clients and requests increase, but is very effective in some architectures (particularly ones with specialized hardware that make this global cache very fast, or that have a fixed dataset that needs to be cached). | <urn:uuid:58647d6d-9484-4a7f-8940-80153187973c> | 2.8125 | 1,550 | Personal Blog | Software Dev. | 41.928268 |
Containers (synonym: collection) are objects that hold multiple Entries for any purpose.
Container here only serves to represent the fact that an Entry finds itself in the company of other Entries.
The container is not defined here beyond its property of containing multiple entries, so other behaviors are open.
Containers represent conceptual base class for weblog, archive, syndication feed, thread, ...
For comparison, DublinCore suggests a different(?) model for "containers". Instead of thinking of "an entry is a container of other things", DublinCore treats all resources as "equals". "Containment", per se, is supported by relating an entry to other entries, including, depending on direction, 'isPartOf' or 'hasPart', and 'isReferencedBy' or 'references'.
Containers work the same way. A Container and Entry are peer resources. An Entry is Related to the Container; the relation is "containedBy".
Yes, an Entry can be a Container because it can be Related to multiple Entries, but that's not the goal here. Container is defined here only as a way to allow an Entry to relate indirectly to other Entries that share the same Container.
JasonHx In an Entry-based storage layer, Containers == functional axes in the application == Controllers in MVC terms. Keep in mind that some containers that people may be thinking of are artifacts of the capital-v View. All of the containers above are describable in XPath-like syntax from either the virtual root node of a collection or a given entry:
|Container Use-cases||Non-normative pseudocode containers|
|Current entry notices from one author, like a weblog feed||entry.author.entry(*).since(time)|
|Current entries from one author, like a weblog front page||entry.author.recent(5)|
|Archive entries from one author, like a weblog archive||entry.author.entry(*).sincethrough(starttime, stoptime)|
|Current entries from several authors constituting a thread||entry/#(*).recent(20)|
|An arbitrary group of related entries, like a list or outline.||entry/#list|
|An export file for transferring entries to another host||entry/*?style=csv.xsl|
To generalize, other Containers aren't so obvious but fit the pattern
Results of a search engine query
All entries by author X, anywhere
Word of mouth, so to speak
Citation in another entry
Hypothetical trigger mechanisms, say situational business advice invoked by rules
Hypothetical inference mechanisms, semantic search
Container compared to EchoFeed
[Skware] +1 on this. This matches my thinking over the last few days it relegates the orginisation of the blog to the CMS, allowing things like date archives, heirarchical categorisation, ... to be used. This possibly combined with something similar to Related would easily allow a photoblog that shows multiple photos in a collection, but still allow comments / permalinks to individual entries. It matches human nature to be able to think of a photo album more conceptually than a particular photo. For instance: people remember that the photo they want is in the birthday party collection of photos, rather than remembering that it was the 6th photo taken on the 24th of June 2003.)
[MikeD] How does a 'container' differ from a 'collection'? What happens to each Entry within a Container when you delete the Container? Are there two kinds of Container resources - one that removes contained Entries and one that does not?
[ZhangYining] removal of a container should not remove the entries that were contained in it, coz an entry can be contained in multiple containers.
The definition of Entry assumes that an Entry will never be deleted ie "permalink".
Collection is a synonym for Container.
[PhilWolff] Can a container hold/cite things besides an Echo entry?
This behavior is open, though using Related Entries would have one type of "role" with the Container, and other things would have a different role.
[BillSeitz] - for sites that don't end up with any feed (e.g. Blogger sites, Zeldman's?), would there be other things that would be helpful, like containing each item within "a name" tags? | <urn:uuid:4fb52f01-5e93-43d9-8990-9508a05bb8b9> | 2.875 | 922 | Comment Section | Software Dev. | 41.456611 |
Viruses are not usually regarded as living cells. A virus 'particle' requires a living host cell in order to reproduce. Although we usually think of viruses as causing diseases, they also are an integral part of natural ecosystems controlling the size of bacterial populations by preying on them. This image was provided by Mark Young and George Rice, Montana State University and subsequently colorized is of numerous particles of a virus that infects Sulfolobus. Image copyright: Globe Pequot Press, used under license to MBL (micro*scope). | <urn:uuid:7a242b8f-23e5-4b11-835f-56e736189690> | 3.015625 | 112 | Knowledge Article | Science & Tech. | 24.111884 |
Stolen diamonds can all too easily be sold on to unsuspecting buyers. So to help establish the real owner, Gersan of Liechtenstein has found a way to engrave their name onto jewels without without spoiling their appearance (GB 2361671). First, the gem is coated with a fine layer of gold. It is then mounted in a vacuum chamber where the gold layer acts as an electrode that attracts a high-energy beam of charged ions. The beam can be steered to write the person's name. Molten potassium nitrate is then used to remove the gold coating, leaving the diamond surface smooth except for the owner's name in a 30-nanometre-deep groove. The mark is invisible to the naked eye but shows up under a microscope.
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:c097a652-a54f-43d2-aa39-e60844148952> | 2.953125 | 183 | Truncated | Science & Tech. | 59.814159 |
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Tachyons And Sending Messages Back In Time
Fri Sep 23 21:23:11 BST 2011 by Eric Kvaalen
This doesn't necessarily violate Relativity. It could simply mean that neutrinos are "tachyons", particles that always go faster than light. It's as though they have an imaginary rest mass. But I'm not sure whether that would go with the idea that neutrinos can mutate during flight.
The idea that the neutrinos are tunneling through other dimensions does not mean that "This would explain the measurement without requiring the speed of light to be broken." If they get from A to B faster than light, they are breaking the speed of light, and in the frame of reference of someone moving in the same direction at slightly less than the speed of light they would appear to have been at B before being at A! In other words, they could carry information backwards in time. | <urn:uuid:33af2281-0424-4ee4-b09b-2ae24d3cca68> | 2.9375 | 194 | Comment Section | Science & Tech. | 58.742264 |
Before you can do anything, you must initialize a database storage area on disk. We call this a database cluster. (SQL uses the term catalog cluster instead.) A database cluster is a collection of databases is accessible by a single instance of a running database server. After initialization, a database cluster will contain a database named template1. As the name suggests, this will be used as a template for subsequently created databases; it should not be used for actual work. (See Chapter 5 for information about creating databases.)
In file system terms, a database cluster will be a single
directory under which all data will be stored. We call this the
data directory or data area. It is completely up to you where you
choose to store your data. There is no default, although
locations such as /usr/local/pgsql/data
or /var/lib/pgsql/data are popular. To
initialize a database cluster, use the command initdb, which is installed with PostgreSQL. The desired file system location
of your database system is indicated by the
-D option, for example
$ initdb -D /usr/local/pgsql/data
Note that you must execute this command while logged into the PostgreSQL user account, which is described in the previous section.
initdb will attempt to create the directory you specify if it does not already exist. It is likely that it will not have the permission to do so (if you followed our advice and created an unprivileged account). In that case you should create the directory yourself (as root) and change the owner to be the PostgreSQL user. Here is how this might be done:
root# mkdir /usr/local/pgsql/data root# chown postgres /usr/local/pgsql/data root# su postgres postgres$ initdb -D /usr/local/pgsql/data
initdb will refuse to run if the data directory looks like it it has already been initialized.
Because the data directory contains all the data stored in the database, it is essential that it be secured from unauthorized access. initdb therefore revokes access permissions from everyone but the PostgreSQL user.
However, while the directory contents are secure, the default
client authentication setup allows any local user to connect to
the database and even become the database superuser. If you don't
trust other local users, we recommend you use initdb's
--pwprompt option to assign a
password to the database superuser. After initdb, modify the pg_hba.conf file to use md5 or password instead
of trust authentication before you start the server for the
first time. (Other, approaches include using ident authentication or file system permissions to
restrict connections. See Chapter 6 for more
initdb also initializes the default locale for the database cluster. Normally, it will just take the locale settings in the environment and apply them to the initialized database. It is possible to specify a different locale for the database; more information about that can be found in Section 7.1. One surprise you might encounter while running initdb is a notice similar to this:
The database cluster will be initialized with locale de_DE. This locale setting will prevent the use of indexes for pattern matching operations. If that is a concern, rerun initdb with the collation order set to "C". For more information see the Administrator's Guide.
This is intended to warn you that the currently selected locale will cause indexes to be sorted in an order that prevents them from being used for LIKE and regular-expression searches. If you need good performance in such searches, you should set your current locale to C and re-run initdb, e.g., by running initdb --lc-collate=C. The sort order used within a particular database cluster is set by initdb and cannot be changed later, short of dumping all data, rerunning initdb, and reloading the data. So it's important to make this choice correctly the first time.
If you install Postgres 7.3.2 using Cygwin (as of 2003-05-20), then try to run \"initdb\", you may get an error message indicating that the \"semget\" function cannot be found. After some google-tracking, I discovered that there is a deprecated library of C functions that initdb wants to use called \"cygipc\". I\'m not sure why it\'s not installed with Postgres via Cygwin, but it\'s easy to set up once you know how. (Perhaps because as of Postgres 7.4 the library is no longer going to be used, which is why it\'s deprecated, I guess.)
Download the cygipc library from http://www.neuro.gatech.edu/users/cwilson/cygutils/cygipc/ (I used 1.14) to your root cygwin directory. It is a bz2 file, so you will need to run \"bunzip2 cygipc.bz2\" inside this directory, which turns it into a tar file. Assuming that you have a standard Cygwin directory tree, you can just untar the file and the binaries will automatically go in the proper folders ($CYGWIN_HOME/usr/local/bin, etc).
Then you need to start a daemon so that initdb will have the functions available to it, the recommended way is to simply run \"ipc-daemon &\". Once you have done this, you should be able to run initdb successfully. | <urn:uuid:358b9b75-ff23-47b2-8f3c-0976bd8f4836> | 3.265625 | 1,171 | Documentation | Software Dev. | 49.006712 |
OpenGL (Open Graphics Library) is a standard specification defining a cross-language cross-platform API for writing applications that produce 2D and 3D computer graphics.
This free video tutorial teaches 3D programming in C++ using OpenGL and GLUT. It covers both OpenGL syntax and 3D programming in general. It is designed to be as beginner-friendly as possible.
When playing with OpenGL, most folks quickly tire of simple line-drawn polygon examples and want to play with more challenging concepts--such as putting texture maps onto those shapes. In this...
The Magician Java-OpenGL binding, front-runner in the
cross-platform Java binding-for-OpenGL standardization race,
recently has been withdrawn from the market. Read about other
choices on the...
An introduction to using OpenGL using CsGL - an open source library for using OpenGL in .NET.
A simple demonstration of how to use OpenGL in C#, with the help of the C# Graphics Library.
This tutorial attempts to answer a few of the questions I'm asked on a daily basis. You wanted to know how to tell if you have clicked on an object with your mouse (picking). You wanted to know how...
This article demonstrates how you can take advantage of OpenGL
Utility (GLU) functions to triangulate polygons for use in
Direct3D applications. In this tutorial, we'll generate meshes
This sample uses OpenGl to create a 3-D Scattergraph that the user can view from any angle by rotating with the mouse.
This article will discuss the need for, and creation of, a Singleton Texture Manager in OpenGL.
All the major game developers do it, why can't you? Using OpenGL is not simple, but it's not impossible either. (Some experience in C++ and/or Qt may be required to follow this article.)
How to develop a fantastic 3D screen saver with OpenGL 1.1. This article just gives a description about how to use some new render functions in OpenGL 1.1 with a fantastic 3D screen saver. And give a... | <urn:uuid:89187b81-ea5c-42be-bba1-3a45a34450d2> | 3.234375 | 439 | Content Listing | Software Dev. | 62.298669 |
It is written by the inventors of the java technology, The Java Language Specification, III Edition is a technical reference for the Java language.
In java a layout manager class implements the LayoutManager interface. It is used to determine the position and size of the components within a container.
A locale class in java api represents a specific geographical, political, or cultural region. In java computing, locale defines a set of parameters that defines the user's language, country and any special variant preferences that the user wants to see in their user interface.
a> Logging is the most common concern to keep in mind by the development teams. In java logging is achieved through a logger class which provides an object allowing the applications to log data without regard to the location needed to actually log the data.
Java for Linux
First of all download JDK for the Linux (Fedora Core 3) Operating System.
JSP Tag Libraries
JSP Tag Libraries is the collection of standard tags. JSP tags are the Java components that can be used in a JSP file.
The Java ClassLoader is a an abstract class which extends the Object class. Java class loader is a part of the Java Runtime Environment that dynamically loads Java classes into the Java Virtual Machine.
JSP Standard Tag Libraries
JSTL is developed under the Java Community Process, in the JSR-052 expert group. The purpose of JSTL is to work towards a common and standard set of custom tags.
The long keyword
long is a keyword in java that is used to store 64-bit integer (Java primitive type) value. Keywords are basically reserved words which have specific meaning relevant to a compiler.
If you are facing any programming issue, such as compilation errors or not able to find the code you are looking for.
Ask your questions, our development team will try to give answers to your questions. | <urn:uuid:4409b519-c462-4707-a19c-27f03d76cd82> | 3.1875 | 385 | Knowledge Article | Software Dev. | 45.106506 |
Earth Sciences Research Journal
versão impressa ISSN 1794-6190
CHICANGANA, GERMAN. THE ROMERAL FAULT SYSTEM: A SHEAR AND DEFORMED EXTINCT SUBDUCTION ZONE BETWEEN OCEANIC AND CONTINENTAL LITHOSPHERES IN NORTHWESTERN SOUTH AMERICA . Earth Sci. Res. J. [online]. 2005, vol.9, n.1, pp. 50-64. ISSN 1794-6190.
The Romeral Fault System (RFS) extends 1600 km from Barranquilla-Colombia to Talara city-Peru and before the Pliocene. In the Middle Eocene RFS defi ned the northwestern border of the South America plate, being originated by a triple junction rift - rift - rift occurred from lower to middle Jurassic, when the South American sector separated from Chortis , Oaxaca and Yucatan blocks. From Late Mesozoic until Early Paleocene, the Paleo Pacifi c plate converged on NW South America corner being subducted when an anomalous thick oceanic crust, represented by the Caribbean plate, was accreted extinguishing gradually from the North of Peru to the North of Colombia. The collision generated a transtensive fi eld stress in back arc region, due to the ancestral Central Cordillera rising in continental border. The RFS rocks suffered low grade metamorphism and some rocks of extinct subduction zone suffered metamorphic inversion. During Late Paleogene until Early Miocene, the convergence South America , Farallon and North America plates produced clockwise rotation in Caribbean Plate, which moved to NE producing a dextral displacement in the suture, generating big milonyte belts in the RFS rocks. With the Farallon Plate break, in the Middle Miocene, due to Galapagos triple junction activation, the Caribbean plate moved to the NNE colliding with the south of the North American plate, being trapped between South and North American plates. This caused the Costa Rica-Panama-Choco block (CRCB) collision with the NW of South America plate, deforming the north of the Northern Andes generating a change in the convergence of Nazca plate in this sector. From Late Pliocene, when convergence change fi nish, Carnegie Ridge collision in the south of NW South America confi guring the actual lithosphere geometry and the orogenic styles of the Northern Andes . Based on Petrogenetic correlations supported by interpretation of secondary sources in geology, tectonic, petrogenesis and geophysics, a model for a regional seismotectonic characterization of this zone was done. The deformed zone represents an extinct subduction zone including fore arc basin rocks with fragments of a Lower - Late Cretaceous volcanic arc and some continental fragments of South America plate. I conclude that RFS is a weak rheologic area and a lithosphere contrast between a thick oceanic and the continental crust, presenting a high seismological activity with historically great earthquakes in Colombia and Ecuador.
Palavras-chave : Romeral Fault System; Geodynamic; Caribbean Plate; Lithosphere Delamination; Seismotectonics. | <urn:uuid:abcf5d2c-556a-49f6-8129-bd0d283c2400> | 3.046875 | 669 | Academic Writing | Science & Tech. | 26.849681 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2011 May 25
Explanation: What's that rising from the clouds? The space shuttle. If you looked out the window of an airplane at just the right place and time last week, you could have seen something very unusual -- the space shuttle Endeavour launching to orbit. Images of the rising shuttle and its plume became widely circulated over the web shortly after Endeavour's final launch. The above image was taken from a shuttle training aircraft and is not copyrighted. Taken well above the clouds, the image can be matched with similar images of the same shuttle plume taken below the clouds. Hot glowing gasses expelled by the engines are visible near the rising shuttle, as well as a long smoke plume. A shadow of the plume appears on the cloud deck, indicating the direction of the Sun. The shuttle Endeavour remains docked with the International Space Station and is currently scheduled to return to Earth next week.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U. | <urn:uuid:add30b5a-aafc-42cf-9092-99bb26ea8b5e> | 3.546875 | 260 | Knowledge Article | Science & Tech. | 47.340777 |
Detecting Blooms of the Dinoflagellate
Karenia brevis From Space
Blooms of the toxic dinoflagellate Karenia brevis (formerly
Gymnodinium breve ) occur periodically off the Gulf coast of
Florida in the fall and early
winter. These blooms, often referred to as "red tides" because
their presence discolors the water a reddish hue, pose a
significant risk to human health and detrimentally affect regional
economies and marine resources. The adverse impacts of these
blooms may be mitigated if their presence could be detected early.
Satellite ocean color imagery provides the synoptic and
repeated coverage appropriate to detect these biological events well
offshore where they are thought to initiate. The blooms are likely to
be distinguishable from most other water conditions in ocean color
imagery owing to their relatively unique coloration.
The objective of this project was to develop
a prototype algorithm to detect blooms of the toxic
dinoflagellate Karenia brevis blooms off southwestern
Florida in ocean color imagery.
A supervised, multispectral classification algorithm was
constructed to detect K. brevis blooms in satellite ocean color
imagery. The empirical algorithm is based upon the spectral
signatures of K. brevis blooms and other common oceanic
conditions. The spectral signature of K. brevis blooms was
ascertained from Coastal Zone Color Scanner images
of November 14, 1978 (Tester, et al., 1997; Fig. 1) and October 28, 1983
(Carder et al, 1985), dates with contemporaneous in sea-truth measurements.
Spectral signatures of common oceanographic conditions were obtained from the
literature (Brown and Yoder, 1994). Decision boundary values of the
algorithm were established to allow the blooms to be spectrally
distinguished from the other oceanic conditions.
Fig. 1. True-color composite of Coastal Zone Color Scanner image from
November 14, 1978. Contemporaneous in-situ sampling sites
are indicated by yellow crosses.
Results and Discussion
The classified counterpart of the image presented in Figure 1 is presented
below (Fig. 2). Though the algorithm is preliminary, the results are
encouraging. The K. brevis class is located in the region known
to be occupied by these blooms.
Fig. 2. Classified counterpart of CZCS image presented in Figure 1.
This algorithm was designed for use with CZCS imagery in waters off the
western coast of Florida.
The algorithm has been implemented to use Sea-viewing Wide
Field-of-view Sensor (SeaWiFS) data from the Gulf of Mexico. To see these
results, please click here.
Brown, C.W. and J. Yoder. 1994. Coccolithophorid blooms in the global
ocean. Journal of Geophysical Research 99: 7467-7482.
Carder, K. L. and R. G. Steward. 1985. A remote-sensing reflectance model
of a red tide dinoflagellate off West Florida. Limnology and
Oceanography 30: 286-298.
Tester, P.A., R.P. Stumpf, and K.A. Steidinger. 1997. Ocean color
imagery: What is the minimum detection level for Gymnodinium breve
blooms? In:B. Reguera, J. Blanco, M. Fernandez, and T. Wyatt (eds),
Harmful Microalgae. Proceedings of the VIII International Conference on
Harmful Algae, Vigo, Spain, 25-29 June 1997. Xunta de Galicia and IOC
of UNESCO Publishers.
Last Revised: March 2, 1998 | <urn:uuid:853ee5c7-5e63-436d-8747-6dc195365d34> | 3.25 | 821 | Academic Writing | Science & Tech. | 44.752631 |
Source code: Lib/pyclbr.py
The pyclbr module can be used to determine some limited information about the classes, methods and top-level functions defined in a module. The information provided is sufficient to implement a traditional three-pane class browser. The information is extracted from the source code rather than by importing the module, so this module is safe to use with untrusted code. This restriction makes it impossible to use this module with modules not implemented in Python, including all standard and optional extension modules.
Read a module and return a dictionary mapping class names to class descriptor objects. The parameter module should be the name of a module as a string; it may be the name of a module within a package. The path parameter should be a sequence, and is used to augment the value of sys.path, which is used to locate module source code.
Like readmodule(), but the returned dictionary, in addition to mapping class names to class descriptor objects, also maps top-level function names to function descriptor objects. Moreover, if the module being read is a package, the key '__path__' in the returned dictionary has as its value a list which contains the package search path.
The name of the module defining the class described by the class descriptor.
The name of the class.
A list of Class objects which describe the immediate base classes of the class being described. Classes which are named as superclasses but which are not discoverable by readmodule() are listed as a string with the class name instead of as Class objects.
A dictionary mapping method names to line numbers.
Name of the file containing the class statement defining the class.
The Function objects used as values in the dictionary returned by readmodule_ex() provide the following attributes:
The name of the module defining the function described by the function descriptor.
The name of the function.
Name of the file containing the def statement defining the function. | <urn:uuid:af1f37c4-2c82-4f22-80a3-32eb2e9924b7> | 2.96875 | 398 | Documentation | Software Dev. | 39.709679 |
Willis Eugene Lamb, Jr. (July 12, 1913 – May 15, 2008) was a physicist who won the Nobel Prize in Physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum".
- In fact, there really is not a new law of nature. It was all in the theory to begin with but nobody worked it out.
- relating his experimental confirmation of the fine structure spectrum of hydrogen, as reported by Jagdish Mehra (2001). The historical development of quantum theory. Springer. p. 1037. ISBN 0387950869.
Last modified on 19 May 2013, at 03:18 | <urn:uuid:8ca8aa79-249f-4bbc-ac14-91870dcac552> | 2.84375 | 131 | Knowledge Article | Science & Tech. | 72.518816 |
The Laws of Thermodynamics
The Zeroth Law of Thermodynamics
The zeroth law expresses that having in existence three systems, A, B, and C, if A is in equilibrium with C and B is in equilibrium with C, then A and B will also be in equilibrium. All three systems will be in equilibrium in temperature. If any of these systems are in contact with other systems, there will be compensation in the temperature level of all the systems involved. That is, they will all have the same temperature.
The First Law of Thermodynamics
The first law of thermodynamics centralizes, generally, on the existence of the property of energy. It states: "For any process involving only the displacement of a mass between specified levels in a gravity field and no externalities to the system, the magnitude of that mass is fixed by the end states of the system and is independent of the details of the process." This law ramifies itself into many other assumptions:
1. Definition of heat.
When two objects that possess different temperatures are brought into contact, a thermodynamic process that establishes an equilibrium of temperatures takes place. Scientists in the XVIII century explained this phenomenon with the concept of "caloric" or heat. This law identified it as a form of energy that could be stored and converted into mechanical energy. It was measured in calories.
2. Uniqueness of work values.
Work is the result of a force acting on a body causing it to move. A specific quantity can be assigned to a work interaction between systems. This number of units of mass is displaced between two specified levels in a gravity field. When work is performed by a system (of a rising weight) it has a positive sign. The unit that identifies work done by energy is the joule.
3. Definition of energy.
When work is done in a system, there is always a change in state. Lets use A as the initial position and B as the final position. In A, there exists a specific amount of energy (EA) that needs work (W) in order for the object to move to B and possess another amount of energy (EB). Therefore, in mathematical terms, EA + W = EB. Its unit of measurement is erg. One calorie is equal to 4.186 x 107 ergs, or 4.186 joules.
4. Conservation of energy.
States that energy can only be modified from one form to another. It cannot be manifested or destroyed. For this reason, the sum of the amount of heat transferred in a system and the work done on the system is equal to an increase in the internal energy in the system. However, this law does not apply to nuclear energy because it is produced when atoms of matter are split or fused. The law of conservation of energy is often combined with the law of conservation of matter. This is because matter can be converted into energy.
5. Impossibility of the perpetual -motion machine of the first kind.
A perpetual- motion machine of the first kind (pmm1) is a hypothetical system in which no energy is required to perform work. In opposition, it is known that a machine needs to have some amount of energy that would be converted to work. Therefore, the ppm1 is an impossible machine.
6. The first law and relativity
According to Einstein's theory of relativity energy of a system is equal to the product of its mass and the square of the speed of light (E = mc2 ). The energy and mass of the system is conserved even when there are processes occurring within the system. Further, if the energy suffers any modifications in the system, then the mass will also be altered.
The Second Law of Thermodynamics
The second law of thermodynamics focuses mainly on the equilibrium states of systems and processes that associate these states with others. The word equilibrium signifies that with time the state of a system will remain unchanged while being isolated from any other systems that may be found in an environment. It states: "Among all the allowed states of a system with specific values of energy, constraints, and numbers of particles, one and only one is a stable equilibrium state." Other hypotheses have been inferred from this law.
1. State principle.
As already known, the equilibrium state of a system corresponds to the values of energy, constraints and numbers of particles in that system. The state principle declares that the values of any property of a system in a state of equilibrium can only be expressed as a function of the values of energy, constraints and numbers of particles.
2. Reversible and irreversible processes.
If a system and its environment can change states and are capable of restoring their original states it is called a reversible process. On the other hand, if a system, for example, changes from its initial state to an equilibrium state without affecting its environment it is said to be an irreversible process.
3. Impossibility of the perpetual-motion machine of the second kind.
A system in a stable equilibrium position cannot produce any work but only receive it. If a system in a stable equilibrium state were to produce work, it would cause the system to change to a non-equilibrium state without affecting its environment. This impossible notion is the premise of the perpetual-motion machine of the second kind (pmm2). It is a device that creates work from a stable equilibrium position.
4. Work done reversibly by a system in combination of a reservoir.
If there are two systems A and B that are in a state of mutual equilibrium each system is in a stable equilibrium position. Furthermore, if the state of one of the two systems is altered, while being in contact A with B, the second system will also alter. A combination of system A and a reservoir can experience work directly through each other or indirectly using an intermediate object.
5. Definition of entropy.
Entropy is a measure of the disorder in the system or the measure of how close the system is to equilibrium. It indicates the degree to which a specific quantity of thermal energy is available for performing work. This means the less entropy, the more available the energy. The second law affirms that entropy cannot decrease for any spontaneous process. As an outcome of this law, an engine can deliver work only when heat is transferred from a hot reservoir to a cold reservoir or heat sink.
The Third Law of Thermodynamics
By virtue of the second law, an absolute zero temperature is included in an absolute temperature scale. The third law of thermodynamics remarks that absolute zero cannot be obtained easily by any procedure. It is only possible to approach absolute zero, but impossible to reach it. This law also defines the term zero entropy by stating that all bodies at absolute zero would have the same entropy.
© 2000 by ThinkQuest team C006011 | <urn:uuid:e0465e74-d703-42a8-b568-d1e8be76c937> | 3.90625 | 1,388 | Knowledge Article | Science & Tech. | 46.567104 |
Now I have Class B variables which I also need to use in Class A. And
also one another Class C, Class A add in Class C (not inherits), and I
want to use Class B variables in Class C.
How can I access?
Short answer: No, you can't do what you propose.
Longer, more detailed explanation:
Classes don't have variables -- objects do. They're called instance variables (or ivars for short) because they're variables that are associated with an instance of a class, which is to say an object. You declare the variables in the class declaration, of course, but they aren't actually created until the class is instantiated, that is, until an instance (an object) of the class is created.
So, if you have this:
ClassA *objectA = [[ClassA alloc] init];
ClassB *objectB = [[ClassB alloc] init];
objectA is an instance of ClassA, and
objectB is an instance of ClassB. Let's also stipulate (as you have in your question) that ClassB is a subclass of ClassA. That is, it's declared like:
@interface ClassA : NSObject
@interface ClassB : ClassA
So to get to your question...
objectA has an instance variable called
foo, plus any that it inherits from NSObject.
objectB has an instance variable called
bar, and it also inherits
foo from ClassA and whatever ClassA gets from NSObject.
objectA does not have an ivar called
bar, and trying to access it would cause an error:
objectA->foo = 1; // OK
objectB->foo = 2; // OK
objectA->bar = 3; // Error!
objectB->bar = 4; // OK
This is because any instance of ClassB is also an instance of ClassA (that's the effect of inheritance) but an instance of ClassA is not necessarily an instance of ClassB. It's okay for code in ClassA to refer to variables or properties in ClassB, but only if it knows that it's dealing with an instance of ClassB. So you could have a method like:
foo += someB->bar;
That's okay because you know that
someB is supposed to be an instance of ClassB. What you can't do in ClassA is:
bar += someB->bar; // Error! ClassA doesn't have a 'bar' ivar!
because, again, ClassA doesn't have an ivar named
By the way, even the first example isn't great form -- unless there's a good reason, it's better to avoid the situation where a class (like ClassA) is dependent on its own subclass (like ClassB). | <urn:uuid:8adcce78-39d8-4b76-a98c-e25d368af2ca> | 2.828125 | 592 | Q&A Forum | Software Dev. | 60.990852 |
Episode 219: Preparation for momentum topic
- understand the term momentum, and the principle of conservation of momentum
- investigate momentum changes experimentally
- solve numerical problems involving collisions and explosions
- gain experience with suitable equipment for measuring speed e.g. motion sensors, light gates
Students should have a simple understanding of Newton’s three laws of motion both at a conceptual and a mathematical level. They should also be able to calculate kinetic energy.
They will also need to be familiar with measuring velocities in an experimental context.
Where this leads
Momentum is a vital concept in mechanics, and any application of physics which involves motion or collisions. This stretches from the most obvious examples of snooker balls and traffic accidents, through pile drivers, bullet-proof vests and laser-induced fusion.
Momentum is in some ways fundamental. When considering quantum physics, students will meet the idea that light has momentum (but it doesn’t make any sense to use the classical physics definition of mv for light that by definition travels at the speed of light, so Einstein’s Relativity theory is needed).
When considering sub-atomic particles, they may use the equation KE = p 2/2m. They will also learn how the momentum of a particle can be read from the curvature of its track. Combining this with the energy from a calorimeter gives the mass and hence the identity of the particle.
Download this episode
Episode 219: Preparation for momentum topic (Word, 32 KB) | <urn:uuid:f2e5ad0b-f004-469a-8053-f13faf495d66> | 4.125 | 316 | Truncated | Science & Tech. | 34.332732 |
for These Tiny Machines
October 16, 2001
CAMBRIDGE - Inside a seemingly sober Harvard laboratory, the Lego mating dance unfolds.
Pale pieces of plastic are riding currents in a twirling flask of warm saltwater. When one piece touches another, it is usually rebuffed, bouncing away. But sometimes the approach is just right, and the two lock together. They are now a couple.
As the dance continues, though, something even more meaningful emerges from these chance encounters. Pairs join pairs. Larger sections come together. Soon the water holds a three-dimensional honeycomb of plastic. And when the honeycomb is allowed to dry, explained researcher David Gracias, it contains a surprise. Since each plastic component was built with wiring inside, the resulting structure forms a complete electrical circuit. The circuit is simple - voltage applied to one piece turns on a light in another - yet it was a dramatic scientific first that caught the eye of the computer industry: This is a circuit that assembled itself.
Since the first human fashioned a crude stone tool in the heart of Africa, people have been building things essentially the same way - making pieces, first of wood or stone, later of metal or plastic, and joining them together. Now, though, scientists have begun pursuing a radical alternative that could fundamentally change everything, including computers, transportation and medicine. Called "self-assembly," the idea is to build components capable of joining together into a complex whole, without an outside builder. It is a concept, they say, that is no stranger than every living thing.
"This is how nature builds all of us," said Gracias, who conducted the circuit experiment in the laboratory of George Whitesides, a Harvard chemist who is one of the leading figures in the movement.
Self-assembly is one of the great miracles of life, and one of its profoundest mysteries. A single acorn placed in the ground is able to assemble itself into a vaulting oak tree that thrives on sunlight. A microscopic cell in the form of a fertilized egg can build itself into a squirrel that bounds from branch to branch. And another speck of biological material, not so different from the squirrel cell, can transform itself into a human being who understands that the squirrel is looking for nuts, and winter is on the way.
Physicists, chemists, and other scientists outside of biology are now looking to these creative miracles that take place in what many observers think will be one of the most active areas of 21st century science - the realm of the nanometer (billionth of a meter) where individual molecules operate.
Nanotechnology is the human tool-making urge taken to its logical extreme, building objects one molecule at a time. In theory, the possibilities include swarms of tiny nano-robots that could be released into a patient's bloodstream to diagnose and fight disease, or materials that are lighter, stronger, or have almost any other property its designer wants.
"We have had the Stone Age, the Bronze Age, and the plastic age," said Shuguang Zhang, who is active in nanotechnology research and is the associate director of MIT's Center for Biomedical Engineering. "The future is the designed material age."
The field is rapidly expanding, with new institutes opening around the country. In the fiscal year 2001, the US government provided $420 million in nanotechnology research grants, according to the National Science Foundation, which has helped fund research at the Whitesides lab.
But even as the nano-technologists have developed machines that let them manipulate individual molecules, they have begun to confront an enormous practical problem: Building something useful, one molecule at a time, takes too long. And, for the solution, they are hoping to copy biology, where fantastic structures build themselves.
"Why recreate the wheel when nature has already created it for you," asked Paul Hyman, a scientist with NanoFrames LLC, a Boston-based company that hopes to use the rod-like tails of viruses to build self-assembling nanoscale construction scaffolds. "I am in awe of what nature has accomplished."
One of the most awe-inspiring examples of self-assembly is the ability of a cell to copy its own DNA, a process that allows one cell to split into two, and leave each with the full genetic instruction book it needs to operate.
DNA is a long molecule that looks like a twisted ladder, with pairs of chemical bases that scientists refer to with letters for simplicity. A "C" is always joined with "G." A "T" is always joined with an "A." The cell is able to split the ladder and then rebuild the other halves so that it now has two copies of the original. Finding the billions of bases needed, and placing them one at a time, would be a daunting task.
But cells takes advantage of a chemical trick, the fact that each base will only lock in with its pair - the C's will only accept G's, for example.
Instead of having to place the right base at each rung, the cell only needs to make sure that the open ladder is exposed to many bases. Correct bases will slide easily into place, like a key into a lock, and the wrong ones will bounce away. A split ladder of DNA could be placed into a soup thick with base pairs, and the other half will quickly assemble itself. Split this ladder, place each in a similar soup, and there would be two identical strands of DNA.
In a cell, the process is much more complex, but it illustrates the central principles of self-assembly - attraction and what scientists call "recognition." Base pairs of DNA are attracted to each other, but they are looking for the right pair to join with: the "G" will reject a "G," a "T," or an "A," but welcome a "C."
The principle does not just apply to DNA. If pieces are attracted to each other, but discriminating, then they will assemble into more complicated wholes.
"People have all of a sudden realized that most of what goes on in living organisms is based on this idea of one thing recognizing another," said James R. Heflin, an associate professor of physics at Virginia Tech who is using self-assembly to create new kinds of solar cells.
For the cells to work, Heflin is using a substance that will assemble itself on a glass slide in a layer just one molecule thick. Such mono-layers are one of the first applications of self-assembly to engineer structures at the nanoscale.
Other researchers, meanwhile, are taking aim at more-complex structures. One intriguing model is the shell of the abalone, which is 3,000 times tougher than naturally occurring minerals made of the same substance, according to Angela Belcher, an assistant professor of chemistry and biochemistry at the University of Texas at Austin.
The abalone secretes proteins, Belcher said, which cause calcium carbonate to form thin layers of crystal that overlap like bricks in a house. This structure is the secret of the shell's strength.
Belcher said that she originally became interested in the abalone shell because it is such a remarkable piece of engineering. The animal is able to build the shell using chemistry that is nontoxic, at normal temperatures, and with materials that are readily available.
Now Belcher's lab wants to try to use proteins to get more exotic materials, such as semiconductors, to grow themselves into useful shapes. Eventually, she hopes to have a library of proteins and techniques that would allow scientists to grow a wide range of useful new materials, all engineered at the molecular level the way nature does.
"I want to do the same thing [the abalone does] with materials that nature hasn't had the opportunity to evolve a way to do," Belcher said. If successful, it would be a new paradigm for manufacturing, in which components aren't built so much as they grow.
The array of self-assembly projects now underway is dizzying, including tiny crystals made by the Quantum Dot Corp. of Haywood, Calif., which could be used for medical imaging; or a technique, used by Alien Technology Inc. of Morgan Hill, Calif. which allows tiny integrated circuits to place themselves in products.
Yet all the techniques that scientists dream of are almost embarrassingly simple compared to the feats accomplished every day by life on Earth.
Biology uses self-assembly in many, many layers. DNA assembles itself, and rules the cell. A group of cells organizes into regions of specialized cells. Specialized cells grow into perfectly designed organs, which join up with other organs. One of these organs is a mind, with a web of cells that is constantly rearranging the pattern that connects them.
Eventually the result is a creature with a mind so stunningly complex that it can look at itself and ask: What built me?
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Astronomy Picture of the Day
Discover the cosmos!Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
Explanation: This cosmic vista stretches almost 20 degrees across the gentle constellation Taurus. It begins at the Pleiades and ends at the Hyades, two of the best known star clusters in planet Earth’s sky. At left, the lovely Pleiades star cluster is about 400 light-years away. In a familiar celestial scene, the cluster stars shine through dusty clouds that scatter blue starlight. At right, the V-shaped Hyades cluster looks more spread out compared to the compact Pleiades and lies much closer, 150 light-years distant. Of course, the Hyades cluster stars seem anchored by bright Aldebaran, a red giant star with a yellowish appearance. But Aldebaran actually lies only 65 light-years away, by chance along the line of sight to the Hyades cluster. Faint dust clouds found near the edge of the Taurus Molecular Cloud are also evident throughout the remarkable 12 panel mosaic. The wide field of view includes the youthful star T Tauri and Hind’s variable nebula about four degrees left of Aldebaran on the sky. | <urn:uuid:d5ee3410-ea38-41a0-a17a-ebd6ff3fdbf5> | 3.1875 | 263 | Personal Blog | Science & Tech. | 52.40254 |
March 20, 1998
AirMISR Flight of 20 March 1998, JPL, Pasadena, CA
A general description of the Airborne Multi-angle Imaging Spectro-Radiometer (AirMISR) is given on the AirMISR page.
The images included below are from AirMISR operational flight No. 4, over Pasadena, California, and includes the location of NASA's Jet Propulsion Laboratory, where AirMISR was built and is maintained. The primary target for the day was the snow-covered area of Mammoth Mountain, at the southern end of the Sierra Nevadas in southern California. However, that area was cloud covered, so the alternative Pasadena target was used. Whenever possible, one or two backup flight plans are prepared in case the primary flight plan is not practicable, usually for weather-related reasons.
Pasadena is situated 20 kilometers north of Los Angeles, at the western end of the San Gabriel Valley, at an elevation of approximately 300 meters. Immediately to the north are the San Gabriel Mountains, which extend up to around 1,600 meters elevation within a short distance from Pasadena. The frontal range of the San Gabriels is visible is some of these AirMISR images, especially the second flight run. Features of the Pasadena area are clearly seen in many of the images, including a maze of city streets, freeways, individual buildings, and even some mountain roads. The nadir view for flight run 1 shows the triangle formed by the 134 Freeway running approximately east-west at the bottom, the 210 Freeway running towards the northwest, and the 2 Freeway running approximately north-south at the left hand side. In the middle of the triangle are the San Rafael Hills, forming a natural boundary between the Pasadena and Glendale communities. To the right of these hills, still within the triangle, is the circular donut appearance of the Rose Bowl, a large stadium in Pasadena with a seating capacity of over 100,000 people, and the adjacent Brookside Golf Course. Just to the north-east of the freeway triangle is the myriad of buildings constituting the Jet Propulsion Laboratory. The downtown area of Pasadena is immediately to the south-east of the bottom right-hand corner of the triangle.
Many of these images contain clouds. Clouds are a vital item of interest in the overall MISR experiment. You can see from the arrays of small thumbnail images presented below that within one flight run the clouds are apparent in some images but almost completely absent in others. In certain instances, the same clouds are in different positions in different images. Although the clouds themselves may have moved during the 11-12 minutes of a flight run, much of the cloud difference between images of the same run is a result of the varying angles of view of the AirMISR camera. In particular, if the camera is pointing towards the north, the clouds will appear to be shifted northward, and vice versa for southerly inclined views. The inclined view also means we can see under the edge of a cloud to the ground surface beneath the cloud, and yet that ground surface is totally obscured in the vertically-downward nadir view. By measuring the degree of these so-called "stereo" effects, and taking into account the aircraft's motion, it is possible to make deductions about both the cloud motion and the cloud height. The ability to make these measurements on a global basis is one of the goals for the spaceborne MISR instrument.
Also of interest is the general texture and structure of the clouds, these being features that have a direct bearing on the amount of sunlight reflected by the clouds, and hence the degree to which the sun's radiation is warming the Earth. A more in-depth discussion of the ways in which MISR will be used to study clouds is given on the MISR science goals page.
The Pasadena flight occurred at around 10 a.m. on 20 March 1998. Each of the images covers an area approximately 10 km on a side, and was acquired from the ER-2 aircraft flying at 20 kilometers altitude. During this flight, three runs were made over the target area. the first was from north to south, the second from south to north, and the third from north to south.
All of the images below are of the AirMISR red "band" (one of AirMISR's four colour channels,) which has a wavelength of 670 nanometers. The images have been flipped and rotated into the correct geographic orientation with north roughly toward the top. Included are both "raw" images and radiometrically calibrated images (radiances.) Subsequent processing will georectify the images, eliminating the effects of rapid aircraft pitch, roll, and yaw changes. From the aircraft altitude of 20,000 meters, the nadir (An) views have a resolution of 7 meters. The D-aft view is ultimately intended to be at 70.5 degrees; however, at the time of this flight the instrument was capable of reaching only 67.5 degrees in this direction because of a temporary mechanical issue. | <urn:uuid:95bbe2bc-c963-420e-a934-ae48d0954584> | 2.84375 | 1,040 | Knowledge Article | Science & Tech. | 46.192336 |
A system of colliding galaxy clusters, nicknamed the Musket Ball Cluster, has been discovered. In these images of the Musket Ball Cluster, the hot gas observed with Chandra is colored red, and the galaxies in the optical image from Hubble appear as mostly white and yellow. The location of the majority of the matter in the cluster (dominated by dark matter) is colored blue. The matter distribution is determined by using data from Subaru, Hubble, and the Mayall Telescope that reveal the effects of gravitational lensing, an effect predicted by Albert Einstein where large masses can distort the light from distant objects.
Photo by X-ray: NASA/CXC/UCDavis/W.Dawson, et al.; Optical: NASA/STScI/UCDavis/W.Dawson, et al.
Using a combination of powerful observatories in space and on the ground, astronomers have observed a violent collision between two galaxy clusters in which so-called normal matter has been wrenched apart from dark matter through a violent collision between two galaxy clusters.
The newly discovered galaxy cluster is called DLSCL J0916.2+2951. It is similar to the Bullet Cluster, the first system in which the separation of dark and normal matter was observed, but with some important differences. The newly discovered system has been nicknamed the “Musket Ball Cluster” because the cluster collision is older and slower than the Bullet Cluster.
Finding another system that is further along in its evolution than the Bullet Cluster gives scientists valuable insight into a different phase of how galaxy clusters — the largest known objects held together by gravity — grow and change after major collisions.
Researchers used observations from NASA’s Chandra X-ray Observatory and Hubble Space Telescope as well as the Keck, Subaru, and Kitt Peak Mayall telescopes to show that hot X-ray bright gas in the Musket Ball Cluster has been clearly separated from dark matter and galaxies.
In this composite image, the hot gas observed with Chandra is colored red, and the galaxies in the optical image from Hubble appear as mostly white and yellow. The location of the majority of the matter in the cluster (dominated by dark matter) is colored blue. When the red and the blue regions overlap, the result is purple as seen in the image. The matter distribution is determined by using data from Subaru, Hubble, and the Mayall Telescope that reveal the effects of gravitational lensing, an effect predicted by Albert Einstein where large masses can distort the light from distant objects.
In addition to the Bullet Cluster, five other similar examples of merging clusters with separation between normal and dark matter and varying levels of complexity have previously been found. In these six systems, the collision is estimated to have occurred between 170 million and 250 million years earlier.
In the Musket Ball Cluster, the system is observed about 700 million years after the collision. Taking into account the uncertainties in the age estimate, the merger that has formed the Musket Ball Cluster is two to five times further along than previously observed systems. Also, the relative speed of the two clusters that collided to form the Musket Ball Cluster was lower than most of the other Bullet Cluster-like objects.
The special environment of galaxy clusters, including the effects of frequent collisions with other clusters or groups of galaxies and the presence of large amounts of hot, intergalactic gas, is likely to play an important role in the evolution of their member galaxies. However, it is still unclear whether cluster mergers trigger star formation, suppress it, or have little immediate effect. The Musket Ball Cluster holds promise for deciding between these alternatives.
The Musket Ball Cluster, which is located about 5.2 billion light-years away from Earth, also allows an independent study of whether dark matter can interact with itself. This information is important for narrowing down the type of particle that may be responsible for dark matter. No evidence is reported for self-interaction in the Musket Ball Cluster, consistent with the results for the Bullet Cluster and the other similar clusters. | <urn:uuid:b603a1da-fc53-426c-9451-b18c48030209> | 3.609375 | 819 | Knowledge Article | Science & Tech. | 37.777783 |
Once more I have to apologise in advance to any statistics practitioners. In the prior article we explored basic statistics terminology and dealt with the expected value or mean of a set of determined values. Here, we extend this to the median, mode, variance and the helpful standard deviation. Hopefully, this article will offer people a bit more grasp with these terms.
In the earlier article we reviewed the 'expected value' or 'mean' of a set of values that we could determine. Those were:
Values: 3, 5, 5, 6, 7, 9, 10, 11, 12, 12, 15, 16
Generally, measured values would have an arbitrary sequence but the values above have been ordered from low to high.
The median value is that value at the middle of the range that has 50 % of its values greater and 50 % of its values lower.
In the above case there isn't a 'midpoint' value because we possess twelve values. And so, we pick the two central values of 10 and 9 and average them to obtain 9.5. That is the median value.
If we had the values: 3, 5, 5, 6, 7, 9, 9, 10, 11, 12, 12, 15, 16, the middle value (of a total number of 13) would be 9 as the median.
Anytime values change a lot the median can be beneficial as a tool that smoothes out the data values. It can serve to track trends in the data by way of documenting the median values. Data values can then be seen as a difference from the median and may provide an idea whether it is migrating beyond this trend.
If the median value is exactly the same as the mean or expected value at that point there is a balanced spread of values. Whenever the median is greater or less than the expected value or mean, then the distribution of the values will be biased either towards the right or left.
When it comes to basic statistics terminology this is basic. If we once more consider the above values measured and adjust one from 15 to 12 we have:
Values: 3, 5, 5, 6, 7, 9, 10, 11, 12, 12, 12, 16
The mode is that value that arises the most times, in the above case it will be 12, which arises in 3 places.
There might be 2 or more modes in a set of values.
If you recall, the mean was additionally known as the 'expected value'. Each determined data value will vary from this mean or expected value by a certain amount. The variance delivers a concept of exactly how 'spread out the data values are' when compared to the mean or expected value.
The overall variance is equal to the average of the sum of the individual variances.
The variance is determined as the square of the deviation between it and the mean or expected value. For example:
If we investigate 6 (the 4th value) the variance will be:
Variance = (6-9.25) x (6-9.25) = (-3.25) x (-3.25) = 10.56
We could calculate this for all of the values, sum them up then divide by the number of values, 12 to get the overall variance.
We could use this basic principle for a simple project activity delay in the last article:
6......................0.3...................6 x 0.3 = 1.8
16....................0.5..................16 x 0.5 = 8.0
20....................0.2...................20 x 0.2 = 4.0
The expected value = 1.8 + 8.0 + 4.0 = 13.8 weeks
The total variance will be the total of the separate variances divided by 3, the number of values.
Overall variance = [(6-- 13.8) x (6-- 13.8) x 0.3 + (16-- 13.8) x (16-- 13.8) x 0.5 + (20-- 13.8) x (20-- 13.8) x 0.2]/3
= [(-7.8) x (-7.8) x 0.3 + (2.2) x (2.2) x 0.5 + (6.2) x (6.2) x 0.2]/3
= [(60.84 x 0.3) + (4.84 x 0.5) + (38.44 x 0.2)]/3
= (18.25 + 2.42 +7.69)/3
This gives a notion of the distribution of values with respect to the 'expected value'.
Notice that in this illustration the 'values' were put forward by an expert's assessment founded upon assumptions, so these are not 'determined data values'. For determined values we would have had to, actually, carry out the activity 3 times in exactly the exact same way and shown that, on those 3 different circumstances, the delays were 6, 16 and 20 weeks. This would not take place in practice.
It is the square root of the variance. For the earlier example we get:
Standard deviation = √9.45 = 3.07
It is a really useful value.
When we measure values there will occur a 68 percent likelihood that each of the data values will fall inside 1 standard deviation of the expected value or mean.
For the instance above:
Expected value or mean = 13.8
Variance = 9.45
Standard deviation = 3.07
68 percent of values will fall within (13.8-- 3.07) and (13.8 + 3.07) = 10.73 to 17.5
In a similar way 95 % of the values will occur within 2 standard deviations and 99.7 % will fall inside 3 standard deviations. So, we would have:
2 standard deviations = 6.14
3 standard deviations = 9.21
95 percent of values will fall inside (13.8-- 6.14) and (13.8 + 6.14) = 7.66 to 19.94
99.7 % of values will land within (13.8-- 9.21) and (13.8 + 9.21) = 4.59 to 23.01
Ideally, this article has presented a modest insight into a few statistical expressions. | <urn:uuid:a3c2c33c-35c0-4d6e-a519-f57427805547> | 3.65625 | 1,329 | Personal Blog | Science & Tech. | 98.343837 |
Archaeognatha (jumping bristletails)
Monura - extinct
Thysanura (common bristletails)
Palaeodictyoptera - extinct
Odonata (dragonflies and damselflies)
Orthoptera (grasshoppers, cricketss, katydids)
Phasmatodea (walking sticks, timemas)
Psocoptera (booklice, barklice)
Hemiptera (true bugs)
Miomoptera - extinct
Megaloptera (alderflies, etc.)
Neuroptera (net-veined insects)
Strepsiptera (twisted-winged parasites)
Mecoptera (scorpionflies, etc.)
Diptera (true flies)
Lepidoptera (butterflies, moths)
Hymenoptera (ants, bees, wasps, etc.)
The scientific study of insects is entomology. More than 800,000 species of insects have been described. There are 5,000 dragonfly species, 20,000 orthopteran, 170,000 lepidopteran, 82,000 hemipteran, 350,000 coleopteran, and 110,000 hymenopteran species.
Insects have segmented bodies, divided into a head, thorax, and abdomen. The head supports a pair of sensory antennae, a pair of compound eyes as well as the mouth, the thorax has six legs, and the abdomen has excretory and reproductive structures. The insect body is supported by an exoskeleton made mostly of chitin. A few small groups with similar body plans, such as springtails (Collembola), are united with the insects as the Hexapoda. The true insects are distinguished from other forms in part by having ectognathous, or exposed, mouthparts.
Most insects also have two pairs of wings, located on the second and third thoracic segments. They are the only invertebrate group to have developed flight, and this has played an important part in their success. The winged insects, and their secondarily wingless relatives, make up the Pterygota. Insect flight is not very well understood, relying heavily on turbulent atmospheric effects. In primitive insects it tends to rely heavily on direct flight muscles, which act upon the wing.
More advanced flyers, which make up the Neoptera, generally have wings which can fold over their back, keeping them out of the way when not in use. In these, the wings are powered mainly by indirect flight muscles, which move them by stressing the thorax. These muscles have adapted to contract when stretched without nervous impulses, allowing the wings to beat much faster than would be otherwise possible.
Insects do not breathe and do not have lungs; a system of airways called trachea allows oxygen to diffuse directly from the air into the tissues. The circulatory system of insects, like that of other arthropods, is open: the heart pumps the hemolymph through arteries to open spaces surrounding the organs; when the heart relaxes, the haemolymph seeps back into the heart.
Insects hatch from eggs, and undergo a series of moults as they develop. In most groups the young, called nymphs, are basically similar in form to the adults, though the wings are not yet developed. This is called incomplete metamorphosis. Complete metamorphosis distinguishes the Endopterygota, which include many of the most successful insect groups. In these, the egg hatches to produce a larva, which is generally worm-like in form and may be fairly helpless. This in turn becomes a pupa, which is often sealed within a cocoon or chrysalis, and undergoes considerable change in form before emerging as an adult.
Many insects are considered pests, because they transmit diseases (mosquitos, flies), damage structures (termites) or destroy agricultural goods (locusts). Others are useful to humans because they pollinate flowering plants (wasps, bees, butterflies) or produce substances such as honey wax or silk. Unique in the animal kingdom are the social insects such as ants or bees that live together in large well-organized colonies, so tightly integrated and genetically identical that they are often considered superorganisms.
For a more complete list of the species of insects that are covered in Wikipedia, see: List of insects.
Animals that feed on insects are said to be 'insectivorous' and are called 'insectivores'. | <urn:uuid:d4a133eb-71cd-4545-a985-bd55ffefe796> | 3.75 | 955 | Knowledge Article | Science & Tech. | 31.469216 |
Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits.
The value of point is a number no less than 1, and no greater than the buffer size plus 1. If narrowing is in effect (see Narrowing), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See Window Point, for more details.
(point) ⇒ 175
This function returns the minimum accessible value of point in the current buffer. This is normally 1, but if narrowing is in effect, it is the position of the start of the region that you narrowed to. (See Narrowing.)
This function returns the maximum accessible value of point in the current buffer. This is
(1+ (buffer-size)), unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (See Narrowing.)
This function returns
(point-max)if flag is greater than 0,
(point-min)otherwise. The argument flag must be a number.
This function returns the total number of characters in the current buffer. In the absence of any narrowing (see Narrowing),
point-maxreturns a value one larger than this.
If you specify a buffer, buffer, then the value is the size of buffer.(buffer-size) ⇒ 35 (point-max) ⇒ 36 | <urn:uuid:9a0a3dd5-66b0-413e-8658-e876f195af9e> | 3.828125 | 473 | Documentation | Software Dev. | 55.441497 |
Effect Of Molten Core Of Earth By The Black Hole At Center Of Universe
Sun Feb 01 11:34:52 GMT 2009 by Shirley Miller
Reading this article made me think about the earth's molten core. Will the gravity pull of the black hole at the center of our Milky Way Galaxy change the shape of the earth in 2012? I read somewhere that the spin of the molten core has changed that is why we are seeing changes in the earth's magnetic fields. The spinning raw egg metaphor made me think of the stresses inside the egg shell. Wouldn't we see more earth quakes on the edges of the tectonic plates and in weak areas such as volcanoes? I also remember as a child hearing that the earth's shape was not round but slightly pear shaped. Is it pear shaped toward the center of the galaxy?
Tue Feb 17 15:08:52 GMT 2009 by Pauline Lisa Doctolero
thank u 4 d big information.......tnxxx u.....
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support. | <urn:uuid:b7602279-d5b0-49d7-8be7-0eeea6fc9993> | 3.265625 | 251 | Comment Section | Science & Tech. | 80.644607 |
The atlas presents an analysis of relative abundances of extant planktic foraminifera (>150 µm) in surface sediments of the Indian Ocean and the North Atlantic, based on CLIMAP data. Relative abundances of each species are plotted against latitude, and winter, summer, mean values, and a seasonality parameter of temperature, salinity, and water density at the sea surface and at 200 m depth, the vertical temperature gradient and the density contrast (stratification) between the sea surface and 200 m depth, based on data from Levitus (1982).
The analysed species are: C. nitida, D. anfracta, G. bulloides, G. falconensis, G. digitata, G. calida, G. siphonifera (syn. G. aequilateralis), G. glutinata, G. conglobatus, G. ruber, G. sacculifer, G. conglomerata, G. crassaformis, G. hirsuta, G. inflata, G. menardii, G. scitula, G. truncatulinoides, G. tumida, G. hexagonus, G. rubescens, G. tenella, H. pelagica, N. dutertrei, N. pachyderma, O. universa, P. obliquiloculata, S. dehiscens, T. humilis, T. quinqueloba; and with sporadic occurrences in a few samples: B. pumilio, G. adamsi, G. uvula (syn. G. bradyi), T. iota, and H. digitata. Some species were not recorded due to their small size (<150µm): G. vivans, G. minuta, O. riedeli, S. globigerus, T. clarkei, T. fleisheri, T. parkerae; or for other reasons: G. cavernula, G. theyeri, and G. ungulata. The biogeographic ranges, suboptima, and optima with respect to the analysed parameters are presented in tabular form for each species with continuous occurrences.
The six dominant species have broad relations with sea surface temperature, with optima in the various biogeographic provinces, or preferences for productive marine environments. Other species show specific relations with combinations of
physical parameters which reflect specialisation and individual niches. A third group is part of bloom successions or seasonal productivity variation and is differentiated by their preferences for conditions in high latitudes and upwelling
zones, tropical environments, or processes related to the deep chlorophyll maximum. Species with known ontogenetic cycles show closest relations with physical conditions in their time of reproduction, suggesting a dominance of
reproduction-related processes for control of relative abundances in sediment assemblages.
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access to all figures and tables | <urn:uuid:3af78c93-c2aa-439f-80cd-f2462438e1ca> | 2.765625 | 631 | Academic Writing | Science & Tech. | 35.589936 |
Japan looks to ancient village wisdom to save biodiversity
Toyooka, Japan (AFP) Oct 27, 2010
Four decades ago the oriental white stork became extinct in Japan, the victim of rapid industrialisation and modern farm practices and heavy pesticide use that destroyed its habitat.
Today, the graceful migratory bird soars again over restored wetlands around the small town of Toyooka in western Japan, now a showcase for an ambitious conservation effort called the Satoyama Initiative.
As Japan hosts a UN conference on biodiversity this week, the high-tech nation is pushing the initiative to promote some of its ancient village wisdom as a way to heal battered environments worldwide.
The initiative draws lessons from before Japan became studded with megacities and crisscrossed by bullet train lines, when most people lived in villages near rice paddies, bamboo groves and forests.
In the pre-industrial age, woodlands gave villagers plants, nuts, mushrooms and wildlife as well as natural medicines, textiles, fuel and timber for building, all usually harvested sustainably over the centuries.
These managed ecosystems -- neither pristine wilderness nor cultivated agricultural landscapes -- are known as "satoyama", a composite of the words for villages (sato) and mountains, woods and grasslands (yama).
Today ecologists, somewhat less poetically, call them "socio-ecological production landscapes".
At the 193-member UN meeting in Nagoya aimed at stemming the loss of plant and animal species, Japan is seeking to sign up groups and countries to exchange conservation lessons and ideas through its Satoyama Initiative.
Japan's centre-left Prime Minister Naoto Kan on Wednesday announced two billion dollars in aid over three years to help poor countries preserve biodiversity, including through the initiative.
"The government of Japan will utilise the wisdom of such traditions, combined with the technology and experience nurtured in our country, to provide assistance to developing countries," Kan said.
In Japan, as elsewhere, the human-influenced natural environments called satoyama have been on the decline as many forests have vanished, agriculture has become modernised, and small farm villages have been abandoned.
Bucking the trend has been Toyooka, a town of about 90,000 people in the west of Honshu island, which prides itself on undoing much of the past damage that had wiped out the oriental white stork.
The bird, which has a wingspan of two metres and is officially designated a national treasure in Japan, became extinct in the country in 1971.
Local farmer Tetsuro Inaba, 68, remembers how when he was a child the birds were still a common sight across the country, before they slowly vanished, with the heavy use of pesticides delivering the final blow.
"When I took over the farm from my father, the farmers here were addicted to pesticides. In hindsight, we used terrifying amounts," he said.
When wild stork numbers in Toyooka fell to just 12 in 1965, the city caught a pair and started an artificial breeding programme. But the conservation attempt failed, and the rest died out in the wild.
"They had lost their reproductive capacity because of the mercury that had accumulated inside their bodies from pesticides," says Inaba.
In 1992, Inaba became a community leader, determined to "live with the storks" -- a species that survived in parts of Russia, China and Korea.
Inaba and other farmers studied how to grow rice without pesticides.
They also rebuilt waterways and flooded some rice fields for longer or all year-round to bring back fish and frogs that are food sources for the storks.
"When I learnt that frogs eat noxious insects, I was very moved. I said to myself 'we can do farming without pesticides'," said Inaba.
As the local habitats slowly recovered, Toyooka released storks into the wild five years ago. They had been bred in captivity from six young birds donated by Russia's far-eastern city of Khabarovsk two decades earlier.
Now, about 50 storks live in local wetlands and fields and 100 in a public park in Toyooka, a fact that the city proudly promotes to attract tourists.
The birds have become the emblem of the local brand of "Stork-Nurturing Rice", popular with ecologically-minded consumers who can order it online.
Inaba said growing organic rice is more challenging than it was when farmers doused fields in pesticides, but said he was determined never to go back.
"I want to pass on the landscape that I saw as a child," said Inaba. "I hope our efforts here will spread to the rest of the country."
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Farming Today - Suppliers and Technology
Rome (AFP) Oct 26, 2010
The genetic diversity of the plants that we grow and eat could be lost forever due to climate change, threatening future food security, the UN's Food and Agricultural Organisation (FAO) said on Tuesday. Experts from the Rome-based organisation warned that the loss of biodiversity will have a major impact on humankind's ability to feed itself in the future as the global population rises to ni ... read more
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“Folds are perhaps the most common tectonic structure developed in deformed rocks” (from Ramsay & Huber 1987) and folds occur in rocks from the millimeter to the lithospheric scale. Understanding the mechanics of folding is therefore essential for understanding tectonic processes in compressional settings. We study folding with analytical and numerical solutions with particular interests in the large-strain, high-amplitude evolution of folds in two (Figure 1 and 2) and three (Figure 3) dimensions.
Figure 1: Quartz vein in shale forming a typical single-layer fold. This feature is the result of a mechanical instability which occurs when mechanically stronger layers (here the quartz vein) are shortened within a mechanically weaker medium (here the shale).
Figure 2: 2D Numerical finite simulation of ductile single-layer folding showing the distribution of strain rates during folding (red = high strain rate, blue = low strain rate).
Figure 3: 3D Numerical simulation of multilayer folding to study fold interference patterns. | <urn:uuid:81db62e5-d895-4b02-9085-cd236c3b32de> | 3.53125 | 214 | Knowledge Article | Science & Tech. | 23.347097 |
People used to establish physical laws on the mathematical frame directly, without considering the existence of the No-Shape-Substance. Such physical laws are separated from nature. By analyzing the interaction between the body and the No-Shape-Substance, we will have a newer and better understanding of physical laws or concepts as inertial mass, Newton's Second Law, kinetic energy equation, mass-energy equation and momentum. And now we are going to uncover the essence of the physical laws.
Comments: 21 Pages.
[v1] 2 Nov 2011
Unique-IP document downloads: 65 times
Add your own feedback and questions here: | <urn:uuid:80d14126-5add-44be-a702-8b96dee87ebb> | 2.71875 | 131 | Truncated | Science & Tech. | 35.101 |
There are numerous examples of sessile animals (sponges, barnacles etc.) but are there any examples of motile plants? If not, why not? Surely mobility would have conferred an evolutionary advantage to some plant species. I am specifically thinking of locomotion here.
It depends how you define locomotion.
If you take it to mean moving from one place to another, then yes, almost all plants do this at some stage during their life cycle. Primarily seeds and pollen move around, and generally they do so by harnessing either natural forces like wind and rain, or by manipulating animals to do the leg-work, e.g.:
If you take it to mean moving around under ones own propulsion, then yes, some plants do this. The example that springs to mind is the gametophyte generation of ferns:
The prothallus (i.e. the gametophyte) has rhizoids on the underside and uses them to slide around and find some space in which to start the next generation. I have seen this happen when fern spores are germinated on agar - when they reach the tiny prothallus stage, they start sliding around to avoid overlapping with one another. I can't find any references for this, but I'll keep looking.
Another example of self-directed locomotion in plants is the motile sperm of bryophytes. The male sex cells have flagella, which they use to propel themselves through water to the female sex cells (reviewed by Renzaglia & Garbary 2001).
Many plants crawl by sending out ground vines and replant themselves in neighboring positions. But that's not what you are asking I think.
I don't know if there are any land dwelling leaf bearing plant forms that move.
In the water most chlorophyll bearing algae have flagellae and can migrate through the water. | <urn:uuid:21fb80b1-9b1a-4ca0-9b6b-a40a395996c9> | 3.5 | 394 | Q&A Forum | Science & Tech. | 50.625455 |
Global environmental challenges
Rather than answering that it was actually a one-time sub editor for The Economist magazine, Herbert Spencer, who coined the phrase, or fighting back with an equally wrong comment about someone being descended from monkeys, Darwin academics are calling for a moratorium on the everyday use and abuse of the great naturalist.
Two-hundred years after he was born, and 150 years after he published “On the Origin of Species”, it’s time to check the facts, as “most of what most people think they know about him is not true,” according to Darwin scholar John van Wyhe, a historian of science at the University of Cambridge.
Visiting Singapore for a Willi Hennig Society-organised talk about Darwin and his contemporary Alfred Russel Wallace, who is also the subject of several myths, van Whye ran through a series of widely-believed Darwin misconceptions that make humankind look pretty slow on the uptake.
First off, he the pointed out that Darwin and Wallace, were not, really, such iconoclasts.
Should the world celebrate the 200th anniversary today of the birth of English naturalist Charles Darwin by working to limit the number of tourists visiting the Galapagos Islands or Antarctica to protect their spectacular wildlife?
Would that help elephant seals like this one above on the Antarctic Peninsula slumber more peacefully? And would it cause less disruption for marine iguanas, below right, on Santa Cruz island in the Galapagos?
Scientists have joined forces to save magical Madagascar by using a new method they hope to apply to other hot spots of biodiversity. For full details you can check my colleague Deborah Zabarenko’s story.
As someone who has had the great privilege of visiting this island continent twice I can only say: “Right on!”
Three giant wind turbines are helping the Galapagos Islands in the Pacific Ocean towards a goal of eliminating use of fossil fuels by 2015 — and no birds have been killed in a six-month pilot scheme despite worries in many nations that big blades and bird brains don’t mix.
The Galapagos are home to mocking birds, finches, petrels, blue-footed boobies, doves, albatrosses and other exotic species many of which only live on the islands. Studies of Galapagos birds helped British 19th century naturalist Charles Darwin work out his theory of evolution. | <urn:uuid:ed05d7ea-bedf-45f8-b9a0-d6e4a1bfb730> | 2.734375 | 501 | Personal Blog | Science & Tech. | 28.491154 |
[Tutor] input and raw input
bkjones at gmail.com
Sat Sep 25 18:36:40 CEST 2010
On Sat, Sep 25, 2010 at 9:40 AM, Evert Rol <evert.rol at gmail.com> wrote:
> > any one have an idea about how we can input many number in the one time
> and change it to list.
> > for example:
> > a=input("Enter the number of your class in the school:") # the number
> can be enter as: 12,13,14 or 12 13 14 with a space in between.
> > now how I can put these numbers into list like b=[12,13,14] with len( a )
> A string has a method split(); that may help you.
> In your case, where you want either a space or a comma as a separator, it
> depends whether both can be used at the same time. If not, you can check for
> the occurrence of one or the other separator and run split() with the
> correct separator. If both can occur in the same line, you may want to use
> the regex module instead: re.split()
No need for the 're' module. Even in the case where both can be used
together, you can still just use string methods:
'12, 13 14'
>>> s.replace(',', '').split(' ')
['12', '13', '14']
> > I tried with that but it's working only for a numbers less than 10 ex.
> 1,2,3 or 1 2 3 but it's not when I go for numbers higher than 10 like in
> example above.
> > a=raw_input("Enter the number of your class in the school:")
> > m=
> > for I range (len( a)):
> > if a[I]==',':
> > pass
> > elif a[I]==' ':
> > pass
> > else:
> > m.append(a[I])
> > m=map(float,m)
> > print m;print len( m )
> > >> [1,2,3]
> > >> 3
> > looking forward to seeing your help,
> > regards,
> > Ahmed
> > _______________________________________________
> > Tutor maillist - Tutor at python.org
> > To unsubscribe or change subscription options:
> > http://mail.python.org/mailman/listinfo/tutor
> Tutor maillist - Tutor at python.org
> To unsubscribe or change subscription options:
Brian K. Jones
My Blog http://www.protocolostomy.com
Follow me http://twitter.com/bkjones
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More information about the Tutor | <urn:uuid:07960603-7683-467a-bb8e-08ee8fbc4a79> | 3.1875 | 645 | Comment Section | Software Dev. | 86.796154 |
An article by David Rose appears today in the Mail on Sunday under the title: ‘Global warming stopped 16 years ago, reveals Met Office report quietly released… and here is the chart to prove it’
It is the second article Mr Rose has written which contains some misleading information, after he wrote an article earlier this year on the same theme – you see our response to that one here.
To address some of the points in the article published today:
Firstly, the Met Office has not issued a report on this issue. We can only assume the article is referring to the completion of work to update the HadCRUT4 global temperature dataset compiled by ourselves and the University of East Anglia’s Climate Research Unit.
Secondly, Mr Rose says the Met Office made no comment about its decadal climate predictions. This is because he did not ask us to make a comment about them.
You can see our full response to all of the questions Mr Rose did ask us below:
Here’s a response to your questions. I’ve kept them as concise as possible but the issues you raise require considerable explanation.
Q.1 “First, please confirm that they do indeed reveal no warming trend since 1997.”
The linear trend from August 1997 (in the middle of an exceptionally strong El Nino) to August 2012 (coming at the tail end of a double-dip La Nina) is about 0.03°C/decade, amounting to a temperature increase of 0.05°C over that period, but equally we could calculate the linear trend from 1999, during the subsequent La Nina, and show a more substantial warming.
As we’ve stressed before, choosing a starting or end point on short-term scales can be very misleading. Climate change can only be detected from multi-decadal timescales due to the inherent variability in the climate system. If you use a longer period from HadCRUT4 the trend looks very different. For example, 1979 to 2011 shows 0.16°C/decade (or 0.15°C/decade in the NCDC dataset, 0.16°C/decade in GISS). Looking at successive decades over this period, each decade was warmer than the previous – so the 1990s were warmer than the 1980s, and the 2000s were warmer than both. Eight of the top ten warmest years have occurred in the last decade.
Over the last 140 years global surface temperatures have risen by about 0.8ºC. However, within this record there have been several periods lasting a decade or more during which temperatures have risen very slowly or cooled. The current period of reduced warming is not unprecedented and 15 year long periods are not unusual.
Q.2 “Second, tell me what this says about the models used by the IPCC and others which have predicted a rise of 0.2 degrees celsius per decade for the 21st century. I accept that there will always be periods when a rising gradient may be interrupted. But this flat period has now gone on for about the same time as the 1980 – 1996 warming.”
The models exhibit large variations in the rate of warming from year to year and over a decade, owing to climate variations such as ENSO, the Atlantic Multi-Decadal Oscillation and Pacific Decadal Oscillation. So in that sense, such a period is not unexpected. It is not uncommon in the simulations for these periods to last up to 15 years, but longer periods are unlikely.
Q.3 “Finally, do these data suggest that factors other than CO2 – such as multi-decadal oceanic cycles – may exert a greater influence on climate than previously realised?”
We have limited observations on multi-decadal oceanic cycles but we have known for some time that they may act to slow down or accelerate the observed warming trend. In addition, we also know that changes in the surface temperature occur not just due to internal variability, but are also influenced by “external forcings”, such as changes in solar activity, volcanic eruptions or aerosol emissions. Combined, several of these factors could account for some or all of the reduced warming trend seen over the last decade – but this is an area of ongoing research.
The below graph which shows years ranked in order of global temperature was not included in the response to Mr Rose, but is useful in this context as it illustrates the point made above that eight of the warmest years on record have occurred in the past decade. | <urn:uuid:e431d0f6-bdc7-4ccb-9c29-7a4ebabbeb73> | 2.9375 | 934 | Comment Section | Science & Tech. | 51.504569 |
This activity is best done with a whole class or in a large group.
Can you match the cards? What happens when you add pairs of the
Dotty Six is a simple dice game that you can adapt in many ways.
This article for teachers describes how number arrays can be a
useful reprentation for many number concepts.
This article for teachers describes how modelling number properties
involving multiplication using an array of objects not only allows
children to represent their thinking with concrete materials,. . . .
Read this riddle and see if you can work out how the trees must be
This article looks at how models support mathematical thinking about numbers and the number system
Can you find different ways of showing the same number? Try this matching game and see!
First or two articles about Fibonacci, written for students.
This article for the young and old talks about the origins of our number system and the important role zero has to play in it. | <urn:uuid:92577955-8cd4-405c-9c24-b63a786243a6> | 3.171875 | 200 | Content Listing | Science & Tech. | 58.544205 |
Last week, AREVA, the French reactor manufacturer, announced that they plan to build a facility to produce medical-grade lead-212. That caught my eye, because lead-212 is a product of the decay of radioactive materials like thorium and radium. Lead-212 can be attached to cell-specific peptides to target and kill cancer cells selectively.
Today, in a blogger conference call with Jacques Besnainou, the CEO of AREVA in North America, the new facility came up. I asked about the source of the lead-212, and Besnainou said that it is from “other processing operations” in France. I pressed on what those operations were, and Besnainou said that AREVA would explain, but he didn’t give any details.
Dan Yurman posted on AREVA’s R&D interest in lead-212 about a year ago. He gave a chart of the the decay chain leading to lead-212 (Pb-212), which I reproduce here. But where does the U-232 come from? It is produced by using thorium fuel in a reactor or the natural radioactive decay of thorium.
The chart also gives the half-lives of the various radionuclides – the numbers followed by y, d, h, m, and s (years, days, hours, minutes, and seconds). The half-life of lead-212 is 10.6 hours, so the process will involve a fast separation of the lead-212 followed by its incorporation into the cancer-treating reagent. This sort of process has been done for many short-lived isotopes for cancer detection and treatment.
The source of the lead-212 is most likely thorium, perhaps irradiated in a reactor, perhaps natural. It’s not surprising that AREVA would have some from “other processing operations”; thorium is often present in uranium ore.
I look forward to AREVA’s telling us exactly what the source is. | <urn:uuid:5d22c939-9e62-436f-b2db-4d33ace622e6> | 3.375 | 420 | Personal Blog | Science & Tech. | 57.425362 |
X-rays From A Young Supernova Remnant
NASA – More than fifty years ago, a supernova was discovered in M83, a spiral galaxy about 15 million light years from Earth. Astronomers have used NASA’s Chandra X-ray Observatory to make the first detection of X-rays emitted by the debris from this explosion.
Named SN 1957D because it was the fourth supernova to be discovered in the year 1957, it is one of only a few located outside of the Milky Way galaxy that is detectable, in both radio and optical wavelengths, decades after its explosion was observed. In 1981, astronomers saw the remnant of the exploded star in radio waves, and then in 1987 they detected the remnant at optical wavelengths, years after the light from the explosion itself became undetectable.
A relatively short observation — about 14 hours long — from NASA’s Chandra X-ray Observatory in 2000 and 2001 did not detect any X-rays from the remnant of SN 1957D. However, a much longer observation obtained in 2010 and 2011, totaling nearly 8 and 1/2 days of Chandra time, did reveal the presence of X-ray emission. The X-ray brightness in 2000 and 2001 was about the same as or lower than in this deep image.
This new Chandra image of M83 is one of the deepest X-ray observations ever made of a spiral galaxy beyond our own. This full-field view of the spiral galaxy shows the low, medium, and high-energy X-rays observed by Chandra in red, green, and blue respectively.
The new X-ray data from the remnant of SN 1957D provide important information about the nature of this explosion that astronomers think happened when a massive star ran out of fuel and collapsed. The distribution of X-rays with energy suggests that SN 1957D contains a neutron star, a rapidly spinning, dense star formed when the core of pre-supernova star collapsed. This neutron star, or pulsar, may be producing a cocoon of charged particles moving at close to the speed of light known as a pulsar wind nebula.
If this interpretation is confirmed, the pulsar in SN 1957D is observed at an age of 55 years, one of the youngest pulsars ever seen. The remnant of SN 1979C in the galaxy M100 contains another candidate for the youngest pulsar, but astronomers are still unsure whether there is a black hole or a pulsar at the center of SN 1979C. Image Credits: X-ray: NASA/CXC/STScI/K.Long et al., Optical: NASA/STScI
- Galactic Views (53) (theneteconomy.wordpress.com)
- Galactic Views (52) (theneteconomy.wordpress.com)
- Galactic Views (42) (theneteconomy.wordpress.com)
Posted in Nature, Science, SPACE WATCH
Tagged Astronomy, Chandra, Chandra X-ray Observatory, Milky Way, NASA, Neutron star, Pulsar, Space, Spiral galaxy, X-ray
Editorial – Just how serious is the scale of this fraud? Some say that the amount tied to LIBOR is $360 trillion; some say $500 trillion, while others put it as high as $800 trillion.
“Manipulating the LIBOR is a big deal, because it affects the cost of money for almost everyone,” writes Gretchen Morgenson. As Dylan Matthews put it, “A bank that mucks with the LIBOR rate isn’t just playing around with esoteric derivatives that will only affect other traders. They’re playing with the real economy that most of us participate in every day.”
So outrage is entirely appropriate. more> http://tinyurl.com/btydxqy
- The Libor Scandal: Three Things to Know (theneteconomy.wordpress.com)
- UBS still plagued by Libor scandal (worldradio.ch)
- Why There Is No Solution To The LIBOR Scandal (businessinsider.com)
- Fair Game: Libor, Mortgage Rates and Wall Street – Fair Game (nytimes.com)
- RBS boss expects bank to be fined over Libor scandal (scotsman.com)
- RBS next for fine over Libor scandal (standard.co.uk)
- RBS expects fine over Libor scandal (walesonline.co.uk)
- Berkshire and the start of Libor lawsuits, MarketWatch
- Libor Review to Look into Scrapping Rate, Kiran Stacey and Caroline Binham,FT/CNBC
- Libor non-scandal of the day, Citigroup edition, Felix Salmon, Reuters
- A Different Take on LIBOR, John Mauldin, Minyanville
- Berkshire Bank Sues 16 Others Over Alleged Libor Manipulation, Alexander Eichler, huffingtonpost.com
SLIDE SHOW (5)
By Charles Murray – The Italian inventor Claudio Torghele spent six years perfecting the mechanized vendor, with the idea that it would do more than simply zap a frozen pizza with microwaves. His machine mechanically mixes the dough from bags of water and flour and then passes it through a series of shaping and pre-heating stations that create a flattened and partially baked pizza base. A conveying tray moves the preheated crust beneath metering devices that squirt on the tomato sauce. Other distribution components add cheese, sausage, ham, and fresh vegetables. The machine then moves its product to an infrared oven for about a minute before putting it in a cardboard container and sliding it through a slot in the front of the machine. more> http://tinyurl.com/bp4nx4e
By Gerry Smith – To help close the digital divide, the Federal Communications Commission is offering phone companies millions of dollars to expand high-speed Internet service to rural Americans.
But the nation’s two largest phone companies — AT&T and Verizon — have told the FCC to keep the money. more> http://tinyurl.com/c6mxnc6
Posted in Broadband, FCC, Net, telecom
Tagged AT&T, Broadband, Broadband Internet access, Digital divide, FCC, Federal Communications Commission, Internet, United States, Verizon Communications | <urn:uuid:64f8ead4-9ac1-4d13-a662-46ac7dcd157a> | 3.6875 | 1,312 | Content Listing | Science & Tech. | 50.635417 |
The winner of the Best Student Paper award atthe 2011 Annual Meeting was Tara Syc, a student in Steve Szedlmayer’s Auburn University marine fish lab in Fairhope. The title of her talk was “A Comparison of Red Snapper, Lutjanus campechanus, from “old” (2006) to “new” (2009/2010) artificial habitats in the northern Gulf of Mexico.”
Red snapper, Lutjanus campechanus, are a reef associated species that use artificial reefs for both food resources and protection from predators.The species is heavily harvested by both commercial and recreational fishermen and have been managed since 1984. The importance of artificial reefs to the red snapper population has been widely debated for decades. The purpose of my study was to compare the age of red snapper to the age of the artificial reef in an attempt to determine if artificial reefs are allowing for greater red snapper production. If production is occurring, the fish age will be correlated with reef age indicating that fish are settling and staying on the reefs for several years.
A total of 37 artificial reefs were sampled in 2010, with three reef ages examined: 2006 (n =18, 4 year old reefs), 2009 (n = 10, 1 year old reefs), and 2010 (n = 9, 0.5 year old reefs). Red snapper were sampled from April through November 2010 using hook-and-line and a baitedfish trap. The goal of surface sampling was to obtain at least 30 red snapper from each artificial reef. After surface sampling was completed,visual surveys were performed by SCUBA divers to estimate the remaining red snapper densities at reef sites. Once sampling was completed, all fish were brought back to the laboratory and were weighed (0.1 g), measured (mm), and the otoliths were removed for age estimation. The age of redsnapper caught was compared with the age of theartificial reef at the site of capture. Red snappertotal densities per reef were estimated from thecombined captured and diver counted fish.
A total of 1028 red snapper were caught, measured and aged. Mean ± SD age of red snapper showed significant differences whencompared across reef age, with older reefs yielding older fish: 2006 reefs = 3.6 ± 1.2 years, 2009 reefs = 2.0 ± 1.7 years, 2010 reefs = 1.7 ±1.0 years (ANOVA, F2,1025 = 194.23, P <0.0001). A significant positive correlation between fish age and reef age was detected (r2 =0.37, P
< 0.0001). Alternative explanations for the findings were examined including depth differences, distance to other reefs, and growth rates. All of these alternatives were eliminated as factors affecting the age of red snapper on artificial reefs, thereby supporting the conclusion that older reefs are supporting older red snapper. In this study, new artificial reefs were quickly colonized by young fish, and it appears that these fish then stay and grow older as the reef ages.This scenario supports the contention that
artificial reefs in the northern Gulf of Mexico are producing red snapper and not just acting as attractants. | <urn:uuid:fd2a4566-7237-4235-9572-ac03d9c26e83> | 2.90625 | 670 | Academic Writing | Science & Tech. | 56.703403 |
Science Fair Project Encyclopedia
The kimura-gumo (Heptalhela kimurai) is a spider, named after Kimura Arika, who discovered it in 1920. It belongs to the sub-order Liphistiomorphae (primitive burrowing spiders). Their burrows are covered by a camoflaged "pill box" cover.
For photographs of spiders and the entrance to their lairs, see http://www.asahi-net.or.jp/~vp6m-bn/001okinawa.htm
The spider is unusual in that it retains features which were probably typical of ancestral spiders, and which are no longer seen in other living spiders. Thus observation of this species can shed light of the development of all spiders. These ancestral features include the central spinnerets, and signs of segmentation on the abdomen.
The word kumo or gumo in Japanese generically means spider. The kimura spider is near 400 million years old and it is among the most primitive still living spiders. It has spinning glands in the middle of the body. This location is not very effective. It fixes its eggs on the surface with a cobweb, so they are well protected. The spider surrounds underground tunnels also with a cobweb. When it sets out on a hunt, it pulls the thread with it. This helps it in orienting itself.
- Tomo Kočar, Strah je okrogel in ima osem nog (The fear is round and it has eight legs), GEA 12 (2002) 7, pp 46 - 49.
- Yoshikura, M. 1982. Kumo no fushigi (The wonder of spiders). Iwanami-shoten, Tokyo.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:0d2d7442-b0ba-436e-98fa-314265afe529> | 3.34375 | 390 | Knowledge Article | Science & Tech. | 59.526962 |
A dust storm that arose on January 11 spread toward the south and east the next day. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this natural-color image on January 12, 2013.
By the time MODIS captured this scene, the dust stretched from the coast of Pakistan to the Strait of Hormuz. Thick enough to hide the ground below, a river of dust flowed southward past the Dasht-e Lut (Desert of Emptiness) in southeastern Iran. West and south of that desert, mountain ridges poked above the low-lying dust.
Dust storms rank among the leading natural hazards in Iran. Other than the subtropical climate of the Caspian Sea coast, Iran is mostly arid or semiarid. Less than 10 percent of the country’s land is arable.
- CIA World Factbook. (2013, January 2) Iran. Accessed January 14, 2013.
NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response. Caption by Michon Scott.
- Terra - MODIS | <urn:uuid:154f4caa-05f0-41c0-80b6-25b5ed90d815> | 3.90625 | 230 | Knowledge Article | Science & Tech. | 59.567201 |
Handles to derived datatypes can be passed to a communication call wherever a
datatype argument is required.
A call of the form MPI_SEND(buf, count, datatype , ...), where
, is interpreted as if the call was passed a new datatype
which is the
concatenation of count copies of datatype.
MPI_SEND(buf, count, datatype, dest, tag, comm) is equivalent to,
MPI_TYPE_CONTIGUOUS(count, datatype, newtype) MPI_TYPE_COMMIT(newtype) MPI_SEND(buf, 1, newtype, dest, tag, comm).Similar statements apply to all other communication functions that have a count and datatype argument.
Suppose that a send operation MPI_SEND(buf, count, datatype, dest, tag, comm) is executed, where datatype has type map,
and extentextent. (Empty entries of ``pseudo-type'' MPI_UB and MPI_LB are not listed in the type map, but they affect the value ofextent.) The send operation sends entries, where entry is at location
and has type , for andj = 0 ,..., n-1. These entries need not be contiguous, nor distinct; their order can be arbitrary.
The variable stored at address in the calling program should be of a type that matches , where type matching is defined as in section Type matching rules . The message sent contains entries, where entry has type .
Similarly, suppose that a receive operation MPI_RECV(buf, count, datatype, source, tag, comm, status) is executed, where datatype has type map,
with extentextent. (Again, empty entries of ``pseudo-type'' MPI_UB and MPI_LB are not listed in the type map, but they affect the value ofextent.) This receive operation receives entries, where entry is at location
and has type . If the incoming message consists ofk elements, then we must have ; the -th element of the message should have a type that matches .
Type matching is defined according to the type signature of the corresponding datatypes, that is, the sequence of basic type components. Type matching does not depend on some aspects of the datatype definition, such as the displacements (layout in memory) or the intermediate types used.
This example shows that type matching is defined in terms of the basic types that a derived type consists of.A datatype may specify overlapping entries. If such a datatype is used in a receive operation, that is, if some part of the receive buffer is written more than once by the receive operation, then the call is erroneous.... CALL MPI_TYPE_CONTIGUOUS( 2, MPI_REAL, type2, ...) CALL MPI_TYPE_CONTIGUOUS( 4, MPI_REAL, type4, ...) CALL MPI_TYPE_CONTIGUOUS( 2, type2, type22, ...) ... CALL MPI_SEND( a, 4, MPI_REAL, ...) CALL MPI_SEND( a, 2, type2, ...) CALL MPI_SEND( a, 1, type22, ...) CALL MPI_SEND( a, 1, type4, ...) ... CALL MPI_RECV( a, 4, MPI_REAL, ...) CALL MPI_RECV( a, 2, type2, ...) CALL MPI_RECV( a, 1, type22, ...) CALL MPI_RECV( a, 1, type4, ...)Each of the sends matches any of the receives.
Suppose that MPI_RECV(buf, count, datatype, dest, tag, comm, status) is executed, where datatype has type map,
The received message need not fill all the receive buffer, nor does it need to fill a number of locations which is a multiple ofn. Any number,k, of basic elements can be received, where . The number of basic elements received can be retrieved from status using the query function MPI_GET_ELEMENTS.
MPI_GET_ELEMENTS( status, datatype, count)
[ IN status] return status of receive operation (Status)
[ IN datatype] datatype used by receive operation (handle)
[ OUT count] number of received basic elements (integer)
int MPI_Get_elements(MPI_Status status, MPI_Datatype datatype, int *count)
MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
INTEGER STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR
The previously defined
function, MPI_GET_COUNT (Sec. Return status
a different behavior. It returns the number of ``top-level
elements'' received. In the previous example, MPI_GET_COUNT
may return any integer valuek, where
If MPI_GET_COUNT returnsk, then the number of basic
elements received (and the value returned by
MPI_GET_ELEMENTS) is . If the number of basic elements received is not a multiple ofn, that is, if the receive operation has not received an integral number of datatype ``copies,'' then MPI_GET_COUNT returns the value MPI_UNDEFINED.
Usage of MPI_GET_COUNT and MPI_GET_ELEMENT.The function MPI_GET_ELEMENTS can also be used after a probe to find the number of elements in the probed message. Note that the two functions MPI_GET_COUNT and MPI_GET_ELEMENTS return the same values when they are used with basic datatypes.... CALL MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr) CALL MPI_TYPE_COMMIT(Type2, ierr) ... CALL MPI_COMM_RANK(comm, rank, ierr) IF(rank.EQ.0) THEN CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr) CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr) ELSE CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=1 CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=2 CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr) CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr) ! returns i=3 END IF
The extension given to the definition of MPI_GET_COUNT seems
natural: one would expect this function to return the value of the
count argument, when the receive buffer is filled.
Sometimes datatype represents
a basic unit of data one wants to transfer,
for example, a record in an array of records (structures).
One should be able to find out how many components were received
without bothering to divide by the number of elements in each
component. However, on other occasions, datatype is used to
define a complex layout of data in the receiver memory, and does not represent
a basic unit of data for transfers. In such cases, one needs to use
the function MPI_GET_ELEMENTS.
( End of rationale.)
Advice to implementors.
The definition implies that a receive cannot change the value of storage outside the entries defined to compose the communication buffer. In particular, the definition implies that padding space in a structure should not be modified when such a structure is copied from one process to another. This would prevent the obvious optimization of copying the structure, together with the padding, as one contiguous block. The implementation is free to do this optimization when it does not impact the outcome of the computation.
The user can ``force'' this optimization by explicitly including padding as part of the message.
( End of advice to implementors.) | <urn:uuid:07bba630-fe0a-454d-bf7c-877541d7ff9f> | 2.71875 | 1,870 | Documentation | Software Dev. | 45.305926 |
Sea Water Differences by Location
Country: United States
Date: August 2007
There is nothing separating the sea water from Florida and
New York. So, how is it that in Miami I can see the crystal clear
water and view my feet and in New York I cannot? Is there a natural
form of water purification? If so what is it?
Water clarity depends upon a large number of factors which include, but
are not limited to: wave action, water temperature and algal life,
seabed and onshore geology, pollution, nearness of sediment sources such
as rivers, whether the area is sinking or rising from the sea, sun
light, time of depth, water depth, presence of and direction of
currents, marine animals present, range of tides (or no tides).
Depending upon where you are in Florida and New York there is a major
difference in sea bed and onshore geology. Florida is lime and New York
is old glacial deposits. There are also far fewer sources of sediment,
ie. rivers and creeks, in Florida. As I remember it, waves are bigger
and stronger on Long Island's south shore than in much of Florida and
this keeps sediments stirred up.
By the way, if you think New York seawater is cloudy, visit the Texas
and Louisiana Gulf coasts. Long-shore currents and sediments from the
Mississippi and other rivers keeps these waters almost opaque near
Click here to return to the Environmental and Earth Science Archives
Update: June 2012 | <urn:uuid:2f57d7a2-60e9-4cc3-acaf-52db9fe83456> | 3.03125 | 324 | Knowledge Article | Science & Tech. | 44.642017 |
Total-reflectance measurements on a number of igneous rocks and other minerals indicate that reststrahlen features may be of use for remote probes into the nature of the surfaces of the moon and planets. Varying particle size introduces effects such as reduced spectral contrast and in some cases new features that could lead to confusion in identification unless particle size is known. Short-wavelength reflectance measurements offer a method of determining particle size by remote measurements.
W. A. HOVIS, JR. and WILLIAM R. CALLAHAN, "Infrared Reflectance Spectra of Igneous Rocks, Tuffs, and Red Sandstone from 0.5 to 22 µ," J. Opt. Soc. Am. 56, 639-643 (1966) | <urn:uuid:1cdc3e23-1616-4d88-adc9-6caaa99e36a4> | 2.875 | 156 | Academic Writing | Science & Tech. | 52 |
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Description of a pion, the lightest of the meson sub-atomic particles
100 years ago, a group of scientists unknowingly ushered in the Atomic Age. Their work initiated paths of research which changed our understanding of the building blocks of matter.
A great explanation of atoms, including the development of atomic theory and the structure of the atom. From HowStuffWorks.com.
Applets demonstrating Interference Experiments and Bose-Einstein-Condensation from the physics 2000 website
Part of the Physics2000 site. These pages also include information on Energy Levels in the atom and atomic spectra.
BBC new article on the 2004 Physics Nobel Prize, which rewarded the founders of quantum chromodynamics,
A booklet presenting selected properties (atomic number, spin, parity, half life, decay mode) of all known nucleides and their known isomeric states
An amazing optics demonstration, showing views from an astronomic scale down to a sub-atomic view, where the scale factor alters by a power of ten each time.
A site of useful links focusing on nuclear computing, nuclear engineering, fusion, reactors, weapons and waste issues.
A British chemist who studied under Rutherford and brilliantly developed the application of X-ray spectra to study atomic structure; his discoveries resulted in a more accurate positioning of ...
Showing 31 - 40 of 72 | <urn:uuid:c6f75e48-3c15-45c8-a8d9-b4ba2de89145> | 2.796875 | 371 | Content Listing | Science & Tech. | 43.178824 |
Project Coordinator: Hugo Araníbar; email@example.com
Project area: Lake Titicaca; Bolivia and Peru
The Titicaca Flightless Grebe is endemic to the Lake Titicaca catchment in Bolivia and Peru. It is considered Endangered as it has suffered from very rapid population reductions. The species declined by 15% between 2003 and 2005, consistent with a decline of over 50% in ten years. The population is small enough that, if declines continue, this species may soon need uplisting to Critically Endangered. The current population is estimated to be 1600 mature individuals. Threats identified by Armonía include loss of tule-bed breeding habitat, water pollution, hunting, egg collection and over-fishing. The greatest current threat to the species, and the principal cause of the drastic population decline, is drowning in monofilament gill-nets, which have been used on the lake since the early 1990s.
With the support of the Conservation Leadership Programme, Hugo Araníbar and Peruvian biologists conducted an experiment in collaboration with fishermen in the Lake Titicaca National Reserve in Peru, to determine if gill-net color had an effect on by-catch. Red, blue and green nets were tested. By-catch was significantly higher with green nets, the nets most used by fishermen. Red nets significantly reduced by-catch; however, fish-catch also was significantly lower with red nets. By-catch was highest during the breeding season (April-May) when adults as well as young were accidentally caught in the nets.
The next course of action for this species at a medium grant level would be to ensure its protection in the National Reserve in Peru. To save the species throughout Lake Titicaca would require a massive program and substantial support and collaboration by the Bolivian government. | <urn:uuid:890b2514-f2a2-4f01-b84d-b751a8024d8e> | 3.375 | 382 | Knowledge Article | Science & Tech. | 33.664152 |
Steven Strogatz on math, from basic to baffling.
There’s a narrative line that runs through arithmetic, but many of us missed it in the haze of long division and common denominators. It’s the story of the quest for ever-more versatile numbers.
The “natural numbers” 1, 2, 3 and so on are good enough if all we want to do is count, add and multiply. But once we ask how much remains when everything is taken away, we are forced to create a new kind of number — zero — and since debts can be owed, we need negative numbers too. This enlarged universe of numbers called “integers” is every bit as self-contained as the natural numbers, but much more powerful because it embraces subtraction as well.
A new crisis comes when we try to work out the mathematics of sharing. Dividing a whole number evenly is not always possible … unless we expand the universe once more, now by inventing fractions. These are ratios of integers — hence their technical name, “rational numbers.” Sadly, this is the place where many students hit the mathematical wall. | <urn:uuid:f9b433cb-7df9-45b8-9e8e-7dd13e4b1188> | 2.984375 | 240 | Personal Blog | Science & Tech. | 48.581824 |
Publication: Research - peer-review › Journal article – Annual report year: 2011
We present the case of degradation of organic solar cells by sunlight concentrated to a moderate level (similar to 4 suns). This concentration level is not enough for sufficient acceleration of the photobleaching or trap-generation in the photoactive layer and therefore such short treatment (100 minutes) does not affect the short-circuit current of the device. However, a significant degradation of V-OC and FF has been recorded by measurements of the cell current-voltage curves with a variation of light intensity, for the devices before and after the treatment. The same degradation was found to occur after short application of forward voltage biases in the dark. This kind of degradation is found to be repairable, and could even be prevented by simple electrical treatment (short pulses of the reverse bias). Moreover, even the fresh cells can be improved by the same process. Generation and degeneration of shunts in ZnO hole-blocking layer as underlying physical mechanisms for the cell degradation and restoration, respectively, can explain the results.
|Citations||Web of Science® Times Cited: 7|
- Polymer solar cells | <urn:uuid:f0bb723b-7d97-4eef-b58a-e7f027a48dc3> | 2.75 | 242 | Truncated | Science & Tech. | 26.344286 |
The advent of large catalogs with more accurate positions enables the WCSTools
IMWCS program to fit more accurate world coordinate systems to images. There
has always been a question as to how the error in matching images to source
catalogs was split between the uncertainties of the catalog positions, the
uncertainties of the image centroids, nonlinearities in detector and telescope
optics, and nonlinearities in the actual detector chip.
Figure 1 shows an image of a field on the center of the open cluster M67 with sources from the GSC II Catalog plotted over it based on a fit WCS.
Figure 2 compares the results of world coordinate system fits to the field based on sources from the USNO-A2.0, GSC II, 2MASS Point Source, GSC-ACT, and HST GSC and M67 Proper Motion Catalogs. For each catalog, the first column indicates the number of stars matched between the catalog and the image, the second column shows how many catalog stars were found in the image (with an upper limit of 300), and the third column indicates the mean separation between the image and catalog positions for the matched stars after the WCS fit in units of arcseconds times 1000 so that the bars all fit on the same scale.
Note that the proper motion catalog fits significantly better than the other catalogs and that the recent epoch catalogs fit better than the 1950's Palomar Sky Survey-based USNO-A2.0 catalog. Further tests are being undertaken to discover exactly what the position errors really are, but this simple test shows that the better the astrometry in a source catalog, the better it will match an image.
Figure 1 (Click for bigger graph)
Figure 2 (Click for bigger graph) | <urn:uuid:4ddd0cdb-c518-431d-93db-1d627576685a> | 2.890625 | 367 | Academic Writing | Science & Tech. | 38.185996 |
Mark Wilson October 14th, 2012
I begin my Invertebrate Paleontology course by giving each student a common fossil to identify “by any means necessary”. This year I gave everyone a gray little brachiopod, one of which is shown above. They did pretty well. Kevin Silver (’13) got it down to the genus quickly. Turns out a Google image search on “common fossil” is very effective!
This is Mucrospirifer mucronatus (Conrad, 1841), a beautiful spiriferid brachiopod from the Silica Shale Formation (Middle Devonian) of Paulding County, northwestern Ohio. I collected it and many others at a quarry on a crisp October day with my friend and amateur paleontological colleague Brian Bade.
The image at the head of this page is a view of the dorsal valve exterior of Mucrospirifer mucronatus; the image immediately above is the ventral valve exterior. Spiriferid brachiopods like this are characterized by extended “wings” and a long hingeline. Inside was their defining feature: a spiral brachidium that held a delicate tentacular feeding device known as the lophophore.
This is the anterior of our brachiopod. The fold in the middle helped keep incurrent and excurrent flows separate, enabling more efficient filter-feeding. (By the way, have you noted the quirky asymmetry of this specimen?)
Timothy Abbott Conrad (1803-1877) described Mucrospirifer mucronatus in 1841. We met him before when discussing a siliquariid gastropod. He was a paleontologist in New York and New Jersey, and a paleontological consultant to the Smithsonian Institution.
Tillman, J.R. 1964. Variation in species of Mucrospirifer from Middle Devonian rocks of Michigan, Ontario, and Ohio. Journal of Paleontology 38: 952-964. | <urn:uuid:3e7d4e49-3bb7-45ae-8f66-2e8f2a3a3229> | 3.28125 | 420 | Personal Blog | Science & Tech. | 36.136742 |
Why Things Have Color
(see description below the applet)
In this applet, white light entering from the left is dispersed with a prism, passes through the material and is recombined in the second prism. If the material, as modeled by a particle in a box, is absorbing light of a certain color, say green, the transition arrow is green and the spectrum leaving the material has the green removed. The color of the recombined light is the complement of that being absorbed. Since parameters may be entered that do not correspond to absorption of visible light, the arrow at the top shows where in the electromagnetic spectrum the n=1-2 transition of the particle-in-a-box currently lies.
This applet demonstrates elementary numerous aspects of spectroscopy. A longer explanation of ways to use the applet in the classroom is also available. | <urn:uuid:e34dacbd-32de-4a06-86b0-5085bcf2662c> | 3.59375 | 174 | Tutorial | Science & Tech. | 42.432978 |
In HTML, you have 3 basic types of lists. You have an ordered list, an unordered list, and a definition list. An ordered list is basically a numbered list. Do you remember when you were little and your teacher told you to number your paper from one to ten? Well everytime you did that you were making an ordered list. In HTML, when we make an ordered list we open it with the <ol> tag and close it with the </ol> tag. The numbers and line breaks will automatically show up where you put the <li> tag.
Here's an example:
<ol> <li>We love Dream-In-Code!</li> <li>At Dream-In-Code, we have tutorials for most modern programming languages</li> <li>Go Dream-In-Code!</li> <ol>
The next type of list is an unordered list. We all remember those high school days where we had to give that 5 page research paper and we had to give reasons for why we chose that particular side of the situation. Usually when we typed those reasons we did it in a bulleted list. Well guess what, you were making an unordered list! An unordered list begins with the <ul> tag and closes with the </ul> tag. Each item in the list still uses the <li> and </li> tags.
Here's an example:
<ul> <li>We love Dream-In-Code!</li> <li>At Dream-In-Code, we have tutorials for most modern programming languages</li> <li>Go Dream-In-Code!</li> </ul>
One of the great things about the unordered list is you can even make it so that there are no bullets. When coding, there will be some situations where you might need this so why not learn it now. Look at the code below and you'll see where and how to do it.
<ul style="list-style: none; "> <li>We love Dream-In-Code!</li> <li>At Dream-In-Code, we have tutorials for most modern programming languages</li> <li>Go Dream-In-Code!</li> </ul>
That's all you have to do to make an unordered list without bullets.
Finally, we have the definition list. The example I want to give for the definition list is simply a dictionary. Grab a dictionary and usually they will be set up using this same kind of list. For a definition list, you open it with the <dl> tag and end it with the </dl> tag. Then in front of the word to be defined you will use the <dt> tag and then in front of the definition you will use the <dd> tag.
Here's my example for the definition list:
<dl> <dt>Simple</dt> <dd>Easy to understand</dd> <dd>plain</dd> <dd>not complicated</dd> </dl>
I hope that my tutorial has helped someone understand lists a little bit better. | <urn:uuid:14faa69e-5c56-4829-a989-65a145b83305> | 3.484375 | 651 | Tutorial | Software Dev. | 71.235684 |
In contrast to the sparse network of coastal and mid-ocean island tide gauges, measurements of sea level from space by satellite radar altimetry provide near global and homogenous coverage of the world's oceans, thereby allowing the determination of regional sea level change. Satellite altimeters also measure sea level with respect to the centre of the earth. While the results must be corrected for isostatic adjustment (Peltier, 1998), satellite altimetry avoids other vertical land movements (tectonic motions, subsidence) that affect local determinations of sea level trends measured by tide gauges. However, achieving the required sub-millimetre accuracy is demanding and requires satellite orbit information, geophysical and environmental corrections and altimeter range measurements of the highest accuracy. It also requires continuous satellite operations over many years and careful control of biases.
To date, the TOPEX/POSEIDON satellite-altimeter mission, with its (near) global coverage from 66°N to 66°S (almost all of the ice-free oceans) from late 1992 to the present, has proved to be of most value to direct estimates of sea level change. The current accuracy of TOPEX/POSEIDON data allows global average sea level to be estimated to a precision of several millimetres every 10 days, with the absolute accuracy limited by systematic errors.
Careful comparison of TOPEX/POSEIDON data with tide gauge data reveals a difference in the rate of change of local sea level of -2.3 ± 1.2 mm/yr (Mitchum, 1998) or -2 ± 1.5 mm/yr (Cazenave et al., 1999). This discrepancy is caused by a combination of instrumental drift, especially in the TOPEX Microwave Radiometer (TMR) (Haines and Bar-Sever, 1998), and vertical land motions which have not been allowed for in the tide gauge data. The most recent estimates of global average sea level rise from the six years of TOPEX/POSEIDON data (using corrections from tide gauge comparisons) are 2.1 ± 1.2 mm/yr (Nerem et al., 1997), 1.4 ± 0.2 mm/yr (Cazenave et al., 1998; Figure 11.8), 3.1 ± 1.3 mm/yr (Nerem, 1999) and 2.5 ± 1.3 mm/yr (Nerem, 1999), of which the last assumes that all instrumental drift can be attributed to the TMR. When Cazenave et al. allow for the TMR drift, they compute a sea level rise of 2.6 mm/yr. Their uncertainty of ± 0.2 mm/yr does not include allowance for uncertainty in instrumental drift, but only reflects the variations in measured global sea level. Such variations correlate with global average sea surface temperature, perhaps indicating the importance of steric effects through ocean heat storage. Cazenave et al. (1998) and Nerem et al. (1999) argue that ENSO events cause a rise and a subsequent fall in global averaged sea level of about 20 mm (Figure 11.8). These findings indicate that the major 1997/98 El Niño-Southern Oscillation (ENSO) event could bias the above estimates of sea level rise and also indicate the difficulty of separating long-term trends from climatic variability.
Figure 11.10: Estimated sea level rise from 1910 to 1990. (a) The thermal expansion, glacier and ice cap, Greenland and Antarctic contributions resulting from climate change in the 20th century calculated from a range of AOGCMs. Note that uncertainties in land ice calculations have not been included. (b) The mid-range and upper and lower bounds for the computed response of sea level to climate change (the sum of the terms in (a) plus the contribution from permafrost). These curves represent our estimate of the impact of anthropogenic climate change on sea level during the 20th century. (c) The mid-range and upper and lower bounds for the computed sea level change (the sum of all terms in (a) with the addition of changes in permafrost, the effect of sediment deposition, the long-term adjustment of the ice-sheets to past climate change and the terrestrial storage terms).
After upgrading many of the geophysical corrections on the original European Remote Sensing (ERS) data stream, Cazenave et al. (1998) find little evidence of sea level rise over the period April 1992 to May 1996. However, over the time span of overlap between the ERS-1 and TOPEX/POSEIDON data, similar rates of sea level change (about 0.5 mm/yr) are calculated. For the period April 1992 to April 1995, Anzenhofer and Gruber (1998) find a sea level rise of 2.2 ± 1.6 mm/yr.
In summary, analysis of TOPEX/POSEIDON data suggest a rate of sea level rise during the 1990s greater than the mean rate of rise for much of the 20th century. It is not yet clear whether this is the result of a recent acceleration, of systematic differences between the two measurement techniques, or of the shortness of the record (6 years).
Other reports in this collection | <urn:uuid:18f09589-7afe-43dd-a7a8-30c5360fa002> | 3.875 | 1,092 | Academic Writing | Science & Tech. | 49.353337 |
A RIDDLE of the sea is how air-breathing animals manage to dive so far beneath the waves and stay down for so long. Such acts are obviously no problem for fish, which have gills. But people diving without the aid of special gear can stay under for no more than minutes and go down no more than a few hundred feet before facing blackout and eventual death.
Despite the dangers of probing the icy darkness, some birds and mammals and reptiles do so regularly, plunging to depths of up to a mile or more and staying down for as long as two hours on a single breath.
To scientists, long baffled by such feats, the divers often seemed to break the laws of physiology. Now, however, the secrets of these animals are starting to come to light, and the insights promise to help treat and prevent all kinds of human ills.
Among the discoveries are that the divers manage to survive quite differently from land creatures when holding their breath. They tend to rely far less on air stored in their lungs and far more on oxygen stored in their muscles.
''The field is developing very fast,'' said Dr. Burney J. Le Boeuf, a seal expert at the University of California at Santa Cruz. ''But it's still very difficult.''
Dr. Le Boeuf noted that adult female elephant seals, which are among the deep elite, spend 10 months a year at sea and descend so far so frequently to depths where the pressure is crushing that their lungs are judged to be collapsed up to 95 percent of that time.
''Tell that to a medical guy and they probably won't believe it,'' he said in an interview. ''Collapsing is one thing and reinflating is another, and we don't know how they do it.''
One emerging clue to the formidable powers of the deep divers centers on their use of oxygen. Their muscles tend to hold unusually high concentrations of myoglobin, a protein that picks up life-giving oxygen from the blood and stores it for later use in providing usable energy for muscles (by oxidizing sugars). Thus, their muscles can work unusually long and hard without requiring the animal to breath fresh air.
Dr. Gerald L. Kooyman and Dr. Paul J. Ponganis, physiologists at the Scripps Institution of Oceanography in San Diego, writing in the current issue of The American Scientist, a bimonthly journal, call the high myoglobin levels of deep divers ''perhaps the hallmark characteristic that sets them apart from all land forms.'' Experts say such physiological tricks can be viewed as a living lesson for the practice of medicine.
Dr. Ponganis, a physician who also has a Ph.D. in physiology, said studies of how the animals thrive at low oxygen levels and at reduced blood flows might one day produce better treatments for shock and stroke victims, who can suffer permanent damage when their brains are deprived of oxygen, as well as new ways to preserve human organs slated for transplantation.
''There's lots of potential applications,'' Dr. Ponganis said, although he acknowledged that much remains to be learned.
''In the last decade we've made good progress in understanding how deep they go,'' he said in an interview. ''But we know very little of what they do down there. And when you get to the physiology, we know even less.''
The feats of the animals seem especially impressive when compared with the modest accomplishments of humans.
Correction: November 27, 1997, Thursday An article in Science Times on Nov. 11, about research on mammals able to dive deep in the oceans, misstated the extent to which seven juvenile seals in one study slowed their heart beats while diving. Their mean heart rate fell to 39 beats per minute -- not 68 beats -- from 107 beats on land. | <urn:uuid:8f974932-a676-48a9-a35f-239e5a1ec4bd> | 3.40625 | 777 | Truncated | Science & Tech. | 60.283104 |
Explain the start() and stop() methods of applet life cycle.
Start and Start method of Applet Life Cycle
Start () method: The start method of an applet is called after the initialization method init(). This method may be called multiples time when the Applet needs to be started or restarted. For Example if the user wants to return to the Applet, in this situation the start Method() of an Applet will be called by the web browser and the user will be back on the applet. In the start method user can interact within the applet.
Stop () method: The stop() method can be called multiple times in the life cycle of applet like the start () method. Or should be called at least one time. There is only miner difference between the start() method and stop () method. For example the stop() method is called by the web browser on that time When the user leaves one applet to go another applet and the start() method is called on that time when the user wants to go back into the first program or Applet. | <urn:uuid:29f5a8ac-1053-42d2-8d31-c5f05a9e8234> | 3.078125 | 222 | Q&A Forum | Software Dev. | 58.821117 |
The order Lepidoptera is the second largest order in the class Insecta and includes the butterflies, skippers, and moths.
This order has more than 180,000 species in 127 families and 46 superfamilies.
It is second only to the Coleoptera (the beetles) in number of described species.
Lepidopterans undergo complete metamorphosis going through a four-stage life cycle of egg - larva / caterpillar - pupa/chrysalis - imago/adult.
The larvae have a toughened head capsule, chewing mouthparts, and a soft body, that may have hair-like or other projections, 3 pairs of true legs, and additional prolegs (up to 5 pairs).
Most caterpillars are herbivores, but a few are carnivores (some eat ants or other caterpillars) and detritivores.
For more information about the topic Butterflies, skippers and moths, read the full article at Wikipedia.org, or see the following related articles:
Recommend this page on Facebook, Twitter,
and Google +1:
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This is a drawing of what the surface of a comet might look like.
Click on image for full size
The Comet Nucleus
A comet nucleus is the very center of the comet. It is solid and is made of
a special sort of dust which scientists call "fluffy". They call it fluffy because it is full of holes and could be very light.
At this point, scientists do not know whether the nucleus is very hard, like solid ground, or very soft, like a snowball.
Scientists are going to use the Rosetta mission to land a probe on the surface of a comet! This and other comet missions will certainly help scientists understand the very center of comets!
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This example of Interstellar Dust is a perfect example of the kind of rocky material comets may be made of. The grains themselves seem to be made of smaller grains. There are many holes, or pores. In a...more
The pictures on this page show the nucleus of a comet. These are the best pictures ever made of the nucleus of a comet. The nucleus of a comet is a big lump of ice and dust. This one is about five kilometers...more
Comet Hale-Bopp was one of the brightest comets of all time. Astronomers witnessed the comet spew out intermittent bursts of dust. The surface seemed to be an incredibly dynamic place, with 'vents' being...more
NASA’s Comet Nucleus Tour (called CONTOUR) launched July 3, 2002. The CONTOUR spacecraft will fly by at least two comets. It will take pictures and collect dust from the nucleus of each comet. Learning...more
We are sad to report that CONTOUR is lost in space. The CONTOUR spacecraft was launched July 3, 2002 to explore the nucleus of comets. It was to take pictures and catch dust from the nucleus of at least...more
Stardust is the name of a space mission that studied a comet. Stardust flew very close to the comet in January 2004. It took some very good pictures of the nucleus of the comet. It also grabbed some dust...more
Comet Churyumov-Gerasimenko was discovered in 1969. It is named after the two scientists who found it, Klim Churyumov and Svetlana Gerasimenko. The comet goes around the Sun once every 6.57 years. The...more | <urn:uuid:f7fe1041-3330-468d-87e7-f02e31887536> | 4.21875 | 547 | Content Listing | Science & Tech. | 67.554377 |
This figure illustrates the motions of the interior which help generate the magnetosphere.
Click on image for full size
Image from: Random House Atlas
The Making of Uranus' Magnetosphere
Magnetospheres are generated with 1.) magnetic materials and 2.) with motions within the magnetic material.
The Earth-like planets generate magnetospheres within the iron cores at the center. However, Uranus has almost no iron core.
The magnetic material of Uranus is found within the icy shells inside Uranus. Motions within those shells produce the magnetic field.
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The magnetosphere of Uranus is medium sized, but still much bigger than the Earth's. It holds all of Uranus' moons. It is probably made in the middle of the planet, and with ice, rather than with iron...more
A magnetometer is an instrument for measuring magnetic fields. Many spacecraft carry magnetometers to measure the magnetic fields around planets. When a spacecraft makes those measurements, what do the...more
Uranus has a strange magnetic field. The magnetic poles of Uranus are not at all close to the geographic poles of Uranus. The main magnetic field of Uranus is tilted 59° away from the planet's spin axis....more
Uranus' plasmasphere is tiny. The rings of Uranus sweep away much of the particles in the area. Particles enter the plasmasphere from the atmosphere as well as the magnetotail. Mathematical theory suggests...more
There is not very much radio noise within the magnetosphere of Uranus. Signals are observed with much less power than observed at Saturn, but several times greater than observed at Earth. The signals...more
Besides methane, Uranus' atmosphere contains even more complex molecules such as ethane gas. (These gases are similar to the exhaust gases that come out of cars on earth). These molecules form layers of...more
The mesosphere of Uranus is a region of balance between warming and cooling. That essentially means that nothing happens there. Except for diffusion, the atmosphere is still. Upper reaches of the atmosphere,...more | <urn:uuid:ff2eb967-8f2c-4269-8b1a-023246e81f78> | 3.96875 | 472 | Content Listing | Science & Tech. | 42.607476 |
© 2002, Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112.
|Forward the URL for this issue to a friend.|
by Gibor Basri, UC Berkeley
The Problem with Pluto
Planets and Brown Dwarfs
Born Into the Right Class?
Runts and Runaways
Ask anyone on the street to give an example of a planet, and they'll consider you a bit dim. Perhaps they'll answer with "Earth", or maybe one of the other obvious choices like Venus or Mars. If you ask "How about Pluto?" they may pause, having heard that there is a bit of a debate about that. If you ask, "What is the difference between planets and stars?", the number of people able to answer well drops dramatically, being a subset of the scientifically literate population (which we wish was much larger). Finally, if you ask "What is the exact scientific definition of 'planet'?", it turns out that nobody can answer it, because there really isn't one.
1) Looking (it) Up
Of course, you can certainly look "planet" up in the dictionary (have your students do this). Mine says that a planet is "any heavenly body that shines by reflected sunlight and revolves about the Sun". It also notes that "planet" originally meant any heavenly body that moves with respect to the fixed stars, which included the Sun and Moon. The word itself means "wanderer" in Greek, and other cultures generally have words for "planet" with a similar meaning. So why isn't that good enough for us today? I suppose we can blame Copernicus and Galileo. The former taught us that basing everything on what we at Earth can see is a mistake, and the latter showed that using telescopes gives us far more information about the cosmos than our naked eyes. The discoveries since Galileo (and especially from the last decade) leave us with knowledge that renders the old definition of "planet" completely inadequate.
Nicholas Copernicus (1473-1543) published "On the Revolutions of the Heavenly Spheres" in the year of his death. In this work he proposed that the Earth is not the center of the Universe, but revolves around the Sun as do the other planets.
Galileo Galilei (1564-1642) used his telescope to make observations of the planets that supported the revolutionary ideas of Copernicus.
What's the problem? First of all, we now know that all heavenly bodies shine. It is just a matter of how brightly and with what kind of light. Anything with a temperature above absolute zero will emit light (more technically: electromagnetic radiation). Even you do! Objects at the temperature of people or the planets in our solar system do so primarily in the infrared (what we call "heat radiation": the stuff that night-vision goggles use). It is true that in visible light (the stuff your eye works with), the planets are much brighter from reflected sunlight than from their own luminosity. Actually, Jupiter emits more total radiation from its internal source than the amount of sunlight it reflects, but its internal radiation is mostly infrared. In any case, that is nothing fundamental, since it also depends on the distance of Jupiter from the Sun (ask your students why?). And it is certainly true that the Sun is vastly more luminous than any of the planets.
Red and Pink colors indicate regions where more heat is being emitted and yellow and green are cooler areas. Note that this person was wearing eye glasses when this picture was taken.
Image courtesy Teletherm Infrared, Florida
The bright areas in this infrared image of Jupiter show regions where heat is escaping through gaps in the clouds. Jupiter has an internal heat source, and it emits twice as much heat as it receives from the Sun.
This argument may seem like a quibble, as does the second problem, which is caused by saying that planets must revolve about (orbit) the Sun. There was no problem with that until we began finding planets around other stars (in 1995). Now the count of extrasolar planets is roughly 100, and it will continue to increase rapidly in the foreseeable future. (See http://exoplanets.org/) Of course, one can generalize to "revolves about a star" rather than explicitly mentioning the Sun. We can thus fix the dictionary definition to something like "A planet is an object whose own luminosity is much fainter than the star which it orbits." This seems to improve the dictionary definition to be more in accord with current science. But alas, this is also completely inadequate!
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Amy Maxmen is a freelance science writer based in New York. She received her PhD in Evolutionary Biology from Harvard in 2006. Follow on Twitter
New Yorkers can catch a fleeting glimpse of Nature’s royalty if they hurry. On Saturday I observed dozens of migrating monarch butterflies – glorious kings of the insect world – quivering atop goldenrods on the coast lining Dead Horse Bay in Brooklyn. Other naturalists in the city have reported monarch sightings in Park Slope in Brooklyn and at Robert Moses State Park in Long Island, where a citizen scientist says she spotted about 1,000 monarchs.
You don’t need to understand science in order to appreciate these majestic, orange-and-black patterned beauties gracing our dirty streets, but the biology permitting their voyage is pretty neat.
The stop in New York will be one of many along their approximately 4000 kilometer (or 2485 mile) journey from the eastern United States and southeastern Canada to central Mexico, where they will winter atop mountains in groves of sacred fir trees. The migration is unique among insects, and it piques the curiosity of scientists who try to understand how the creatures find their path without prior experience. Each monarch I spotted in Brooklyn is taking this trip for the first time, and is at least two generations removed from the previous generation of North-South migrants (pdf).
Monarchs orient themselves by the light of the sun, and keep track of time with a circadian clock located in their antennae (pdf). This clock helps them navigate by interacting with the sun-compass, so that the sun’s movement across the daytime sky doesn’t throw them from their course. When biologists removed monarchs antennae, or painted them black to block light input, the butterflies could no longer find their way (pdf).
Like sea turtles and birds, monarchs might also take cues from Earth’s magnetic field. And the fact that each incredible voyage is a monarch’s first and last suggests a genetic basis. Towards this end, Steven Reppert, a neurobiologist at the University of Massachusetts Medical School in Worcester and his colleagues are sequencing the monarch genome. Buried among the credible scientific reasons he lists for sequencing this delicate creature, is “Butterflies enrich our lives.”
So if you inhabit the Big Apple, enrich your life by doing what the Russian novelist and lepidopterist Vladimir Nabokov would do, and head out to the coast or one of the city’s parks. Right now.
Related: Diversity of insect circadian clocks – the story of the Monarch butterfly
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Snapshot 1: it takes five moves to move three cheeses
Snapshot 2: it takes 49 moves to move 10 of 15 cheeses
Snapshot 3: the position after move number 227 with 21 cheeses
It is an unsolved problem in mathematics and computer science to determine the minimum number of moves for all
. For small
, however, the minimum number of moves is known, and the well-known Frame–Stewart algorithm lists the moves to use. Simply stated, the algorithm says: "In order to move
cheeses to a destination stool, first determine a value for
, and then use all four stools to move
cheeses to one of the stools (think of that stool as a "spare stool"), then use the remaining three stools—as in the Towers of Hanoi puzzle—to move
cheeses to the destination stool, and then use all four stools once again to move the
cheeses from the spare stool to the destination stool". See a discussion of the Frame–Stewart algorithm in .
It is important that the reader understand that this algorithm is recursive! Suppose that there are 15 pieces of cheese. In that case, let
. So the algorithm says that you first need to use all four stools to move 10 cheeses. But to do that, you need to determine a
is 4; so you first need to use all four stools to move six cheeses to a spare stool. When
, so in order to move those six, you first need to move three. No recursion is needed to move three cheeses, so the first three can be moved to a spare stool (with five moves). Then you need to move three cheeses, using the three stools that are available, using the Towers of Hanoi algorithm (that will require seven moves). And then you need to move the three cheeses from the spare stool. Now that you have moved six cheeses, you can move four, and after that you can move the six cheeses from the spare stool. All that describes how to move just the first 10 cheeses; now you need to move five; and then 10. I trust you get the idea. See Snapshot 2.
In the Frame–Stewart algorithm, the value of
is determined by a fairly simple rule (see ). For example, if
. However, it turns out that for most values of
there are two possible choices for
, for example,
can be chosen to be either 4 or 5. To make this Demonstration more interesting, a random number generator is used to select the value for
whenever there are two possible values. This Demonstration also randomly decides which stool to use as the "spare stool". Finally, even though the Reve indicated that the cheeses were to end up on the stool "at the other end", this Demonstration chooses the final destination stool randomly as well.
In the Towers of Hanoi puzzle, the required number of moves is much greater than in the Reve's Puzzle. To move 21 discs in the Towers of Hanoi puzzle requires
(2,097,151) moves. As you can see from Snapshot 3, "only" 321 moves are required to move 21 pieces of cheese in the Reve's Puzzle.
There are two sliders. The first slider is used to choose the number of cheeses, from one to 21 (even though the Reve had the pilgrims start with eight pieces of cheese, this Demonstration shows how to move just one to seven pieces as well). The second slider is used to move the pieces.
H. E. Dudeney, The Canterbury Puzzles
, Mineola, New York: Dover Publications, 2002.
K. H. Rosen, Discrete Mathematics and Its Applications
, 5th ed., Boston: McGraw-Hill, 2003. | <urn:uuid:fa095c7e-6a5a-43b5-8433-db9aea047ad0> | 3.515625 | 800 | Tutorial | Science & Tech. | 64.778869 |
This topic describes the syntax of class data fields declarations.
A field is like a variable that belongs to an object. Fields can be of any type, including class types. (That is, fields can hold object references.) Fields are usually private.
To define a field member of a class, simply declare the field as you would a variable. For example, the following declaration creates a class called TNumber whose only member, other than the methods is inherits from TObject, is an integer field called Int.
type TNumber = class var Int: Integer; end;
The var keyword is optional. However, if it is not used, then all field declarations must occur before any property or method declarations. After any property or method declarations, the var may be used to introduce any additional field declarations.
Fields are statically bound; that is, references to them are fixed at compile time. To see what this means, consider the following code.
type TAncestor = class Value: Integer; end; TDescendant = class(TAncestor) Value: string; // hides the inherited Value field end; var MyObject: TAncestor; begin MyObject := TDescendant.Create; MyObject.Value := 'Hello!' // error (MyObject as TDescendant).Value := 'Hello!' // works! end;
Although MyObject holds an instance of TDescendant, it is declared as TAncestor. The compiler therefore interprets MyObject.Value as referring to the (integer) field declared in TAncestor. Both fields, however, exist in the TDescendant object; the inherited Value is hidden by the new one, and can be accessed through a typecast.
Constants, and typed constant declarations can appear in classes and non-anonymous records at global scope. Both constants and typed constants can also appear within nested type definitions. Constants and typed constants can appear only within class definitions when the class is defined locally to a procedure (i.e. they cannot appear within records defined within a procedure).
Class fields are data fields in a class that can be accessed without an object reference (unlike the normal “instance fields” which are discussed above). The data stored in a class field are shared by all instances of the class and may be accessed by referring to the class or to a variable that represents an instance of the class.
You can introduce a block of class fields within a class declaration by using the class var block declaration. All fields declared after class var have static storage attributes. A class var block is terminated by the following:
type TMyClass = class public class var // Introduce a block of class static fields. Red: Integer; Green: Integer; Blue: Integer; var // Ends the class var block. InstanceField: Integer; end;
The class fields Red, Green, and Blue can be accessed with the code:
TMyClass.Red := 1; TMyClass.Green := 2; TMyClass.Blue := 3;
Class fields may also be accessed through an instance of the class. With the following declaration:
var myObject: TMyClass;
This code has the same effect as the assignments to Red, Green, and Blue above:
myObject.Red := 1; myObject.Green := 2; myObject.Blue := 3;
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partial objects are callable objects created by partial(). They have three read-only attributes:
partial objects are like function objects in that they are callable, weak referencable, and can have attributes. There are some important differences. For instance, the __name__ and __doc__ attributes are not created automatically. Also, partial objects defined in classes behave like static methods and do not transform into bound methods during instance attribute look-up.See About this document... for information on suggesting changes. | <urn:uuid:6c36485a-2297-4da7-b4ec-41c3add776f9> | 2.6875 | 101 | Documentation | Software Dev. | 26.669103 |
Comprehensive DescriptionRead full entry
BiologyAdults occur in steep outer reef, occasionally in deep lagoons and along channel walls, usually in current prone habitats and where there are abundant gorgonian and long sea-whip corals on which they lay and guard eggs. Juveniles in small groups often found among large sea fans or black corals. Feed on zooplankton (Ref. 7247). Oviparous, distinct pairing during breeding (Ref. 205). Eggs are demersal and adhere to the substrate (Ref. 205). Males guard and aerate the eggs (Ref. 205). | <urn:uuid:27b20ec1-180d-47ca-9813-9de8efe13481> | 2.890625 | 127 | Knowledge Article | Science & Tech. | 57.309 |
Type Ia supernovae are caused by a completely different mechanism than the more well-known type II supernovae. Type Ia supernovae occur in a multiple (usually binary) star system, where one of the stars is a white dwarf. The white dwarf creates a strong gravitational field, and if its companion star is close enough, it begins to suck matter away from the star in an accretion disk. White dwarfs are composed mainly of carbon and oxygen nuclei. When the increasing mass of the white dwarf reaches about 1.3 times the mass of the sun, it reinitiates nuclear fusion, burning oxygen into carbon. Since the white dwarf is in an electron-degenerate state, the temperature of the star is independent of the pressure. Therefore the white dwarf heats up very quickly but does not expand, which causes it to heat up more, and eventually leads to a runaway fusion extravaganza.
The Chandrasekhar limit dictates that a white dwarf cannot exist as a white dwarf if it is more massive than about 1.4 times the mass of our sun. As it approaches this limit, the temperature rises to an extreme and the star is finally forced to expand. The temperature is once again dependent on pressure, and the expansion produces a cooling that slows down the nuclear fusion, which cannot produce any elements heavier than iron. The energy released in this expansion completely destroys the star (and sometimes its neighbor), by causing the outer layers to be expelled at speeds exceeding 10^4 km/s, or 1/10 the speed of light.
Type Ia supernovae particularly interest astronomers because they are all about the same brightness, or absolute magnitude. This is because the Chandrasekhar limit requires all white dwarfs undergoing this process to be about the same mass. Astronomers can then use these events as standard candles to gauge the distances of galaxies accurately. | <urn:uuid:c0a61700-0b6f-4667-ab6b-9f53b4fcbf1e> | 4.125 | 383 | Knowledge Article | Science & Tech. | 40.347472 |
|The change in motion
is proportional to the motive force impressed; and is made in the direction of the right
[straight] line in which that force is impressed. Hence, p is parallel to Fav and
putting it all together symbolically, we have:
Fav = p/t
The average net force equals the time-rate-of
change of momentum. It is useful to combine the force and time into a single notion
that equals the known momentum change. This concept of change in momentum is called impulse.
Favt = p
This is the measure of the force and the
length of time that the force actually acts.
Momentum, like gravitational potential energy,
spring energy, etc. is a conserved quantity, as the Law of Conservation of
total momentum of objects before = total
momentum of objects after.
Thus along with work and energy, momentum is
an additional factor one considers when analyzing motion problems, particularly problems
involving collisions or explosions. | <urn:uuid:d58964e7-b4ef-4944-9e77-23fc20f8debc> | 3.8125 | 211 | Knowledge Article | Science & Tech. | 37.072601 |
Matter/Anti-matter and Black Holes
If Matter and Anti- matter are oppsite, then would dense
anti-matter create anti-gravity,and would superdense anti-matter create
the oppsite of a black hole?
Matter and anti-matter are made of opposite particles, but these opposite
particles do not have negative masses. An electron and a positron (an
anti-electron) have opposite charge, but they have the same mass. As a
result, gravity is the same for both particles and for antiparticles.
Click here to return to the Physics Archives
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After a decade-long hunt almost as obsessive as Captain Ahab’s search for Moby Dick, a team of researchers and journalists from Japan’s National Science Museum, the Discovery Channel, and Japanese broadcaster NHK have captured video of the mysterious giant squid in its natural habitat, about 9 miles from ChiChi Island and 600 miles south of Tokyo.
This three meter long creature is actually on the small side; giant squids can grow to eight meters (twenty-six feet)!
These real-life underwater giants are believed to be the inspiration for the Kraken, a mythical Nordic sea monster known for attacking ships in the waters off of Scandinavia. Having inspired numerous artists and writers over the centuries, it is no surprise that this fantastical animal has captured the imaginations of scientists as well.
In this gorgeous new Oceana video Alexandra Cousteau delves into Monterey Bay to illuminate the diversity of life at the bottom of the ocean, a crucial habitat that is under the constant threat of obliteration from bottom trawling. Using an ROV the camera captures an otherworldly scene, as scallops flutter by and curlicued basket stars unfurl. Armies of shrimp and brittle stars scamper by, fed by the organic matter from above that drifts down the water column like snowfall, sustaining a remarkably rich community. In shallower waters, coral gardens that take hundreds of years to blossom shelter rockfish and ingeniously disguised crabs, and serve as a nursery for dozens of species of fish. Here octopuses go camouflage against the rocky shale, out of sight of the hungry sperm whales and sea lions from above. Anemone-covered spires upwell nutrient rich waters that feed shoals of krill, which in turn feed blue whales. It is an intricately connected ecosystem and it can be destroyed in an instant by bottom trawling. That’s why Oceana has pushed for an end to bottom trawling in ecologically sensitive areas. And that work has paid off in concrete victories: in 2006 NOAA protected 140,000 square miles of Pacific seafloor from the destructive practice, but more needs to be done. For the most part this world goes unseen by human eyes and it’s why Oceana is working laboriously to document these precious areas before they disappear.
Here's a song that will get stuck in your head and teach you something about the world's oceans at the same time. Our friends over at One World One Ocean put together this parody of Gotye's earworm "Someobody that I Used to Know" for World Oceans Day.
It follows Ferdie and Mitzi on an animated adevnture to some of the world's most famous ocean landmarks: the Mariana Trench, Great Barrier Reef, Sargasso Sea, and more. Check out the video's homepage to learn even more about the amazing places and animals featured in the video.
Do Mitzi and Ferdie remind you of somebody that you know? The nominations are still open for our 4th annual Ocean Heroes Award, and we're looking for juniors and adults that are protecting the oceans that we want to know. You have until June 20th to submit your own Ocean Heroes!
How do you like your oysters? Probably not with a side of fishing line or a plastic bag.
This video, created by Katrin Peters for SOS Plastic, shows a couple on a seemingly romantic date. It’s less appealing, though, when you see what accompanies their dinner:
Part of a global campaign to raise awareness and unite international groups against marine plastic pollution, SOS Plastic aims to show how plastics in the oceans affect the entire world.
Every year we use millions of tons of plastic in packaging, water bottles, single-use bags, fishing line and more. The qualities that are so useful to humans – its durability, light weight, and lack of decomposition – make plastic a dangerous material once it gets into the oceans. Polymers can last for decades, if not centuries, which leads to an enormous accumulation of plastic in the oceans.
In 1992, the EPA found that the majority of the world’s beaches showed some sort of plastic accumulation. You might have seen bottles, bags, or fishing nets washed up on the shore, but the real danger lies in what you can’t see.
When exposed to the sun and water, plastics break apart into tiny pieces, called microplastics. These little bits of trash don’t decompose in the water; instead, they get eaten by plankton then travel up through the food chain. Microplastics carry chemicals at extreme levels that can cause illness in both marine animals and humans when we eat seafood.
Many states and counties are starting to limit or ban plastic bags, like Carmel-by-the-Sea in California. You can help by reducing your plastic use – bring reusable bags to the grocery store or farmer’s market, carry a drink in a stainless steel water bottle, and make sure that when you do use plastics you recycle. Sign the Plastics Pledge today to prevent the ocean from getting trashed.
Drum roll, please: we’re excited to unveil our latest video starring actress and ocean lover, Aimee Teegarden of “Friday Night Lights.”
We traveled with Teegarden up the coast of Southern California, from La Jolla to Santa Barbara Island, filming a video about the need to protect the ocean’s threatened habitats.
Teegarden showed off her surfing skills and also free dove with sea lion pups in a gorgeous kelp forest.
“It’s amazing that hidden treasures like this exist all over the ocean – you just have to look for them. It’s really upsetting to think about an awesome place like the sea lion rookery being destroyed by destructive fishing, pollution, or anything else harmful,” said Teegarden. “This experience made it clear that we need to identify these unique and important areas in the ocean and do whatever we can to save them. I love that Oceana finds the special places like this and then fights to protect them.”
Did you know that protecting our oceans could be an answer to world hunger? A few weeks ago our CEO Andy Sharpless gave a talk at TedxSF about how saving the oceans can help feed the world.
We think it’s a fantastic, thought-provoking presentation, please watch and pass it on:
Earlier this year, Oceana and National Geographic completed an expedition to Sala y GĂłmez Island, an uninhabited Chilean island near Easter Island in the Pacific Ocean.
It was a follow-up to our first journey in October 2010, which was instrumental in the creation of a no-take marine reserve of 150,000 square kilometers around the island. Sala y GĂłmez is part of a chain of seamounts that are vulnerable to fishing activity.
And after months of patiently waiting, we now get to see some of the biodiversity that our colleagues discovered on their expeditions. NatGeo is releasing a documentary about Sala y Gómez, featuring Oceana campaigners as well as Dr. Enric Sala, marine ecologist and National Geographic Explorer-in-Residence, who has called Sala y Gómez “one of the last undisturbed and relatively pristine places left in the ocean.
Check out the trailer:
The dive team glimpses 15 Galapagos sharks and scads of slipper lobsters – and that’s just in this three-minute clip! You can catch the full documentary on January 19th at 8 pm on NatGeo WILD.
At last year’s TEDxOilSpill conference in Washington, D.C., Oceana CEO Andy Sharpless tackled the 10 biggest myths he hears about offshore drilling. His presentation is especially poignant this week considering the government's decision on Friday to re-open the Western Gulf of Mexico for new oil and gas exploration for the first time since the spill.
Check it out and pass it on!
Earlier this year, Oceana Chile sailed to far-flung Alexander Selkirk Island, named for the Scottish sailor who spent four years as a castaway on the island, probably inspiring the story of Robinson Crusoe.
The island is one of three that comprise the Juan Fernández Archipelago, which sits more than 400 miles off the coast of Chile.
Check out the stunning footage they came back with:
As you can see, the expedition team found a surprising abundance and diversity of species around the island, including lobsters and many kinds of fish. While the archipelago has been compared to the Galápagos Islands for its rich biodiversity, it lacks conservation measures against destructive fishing. As a result, Oceana has been working for several years with the fishing communities of Juan Fernández to protect their exceptional marine resources.
Ted Danson was on NBC Nightly News with Brian Williams this weekend, talking about his book, "Oceana: Our Endangered Oceans and What We Can Do to Save Them." Once again he does a fantastic job describing the state of the world's oceans - and why he's optimistic that they can be saved in our lifetimes. If you haven't picked up your copy of "Oceana" today, be sure to order one here! | <urn:uuid:e42e11e3-494c-49cb-a9e8-19fa5c84dd3f> | 2.84375 | 2,026 | Content Listing | Science & Tech. | 47.356644 |