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Chemists who study the earth by analyzing its minerals,
rocks, the crust, salts and other lithospheric properties. They use reactions
such as chemical weathering, dissolution, hydration, dehydration, oxidation to
explore the relationship between chemical processes and reactions with the
atmosphere and hydrosphere.
[Environmental Chemistry; Manahan, Stanley E.; Lewis
Publishers; Boca Raton; page 451-2; 1994.] [Atmospheric Change; Graedel, T. E.;
W. H. Freeman and Company; New York; page 10; 1993.] | <urn:uuid:13ff63e2-efab-4cf6-931b-6e738f1e65a8> | 2.921875 | 125 | Knowledge Article | Science & Tech. | 38.200556 |
No. I'm not making that up. It's what the article says. Really:
sulfur is commonly known to have a standard atomic weight of 32.065. However, its actual atomic weight can be anywhere between 32.059 and 32.076, depending on where the element is found. (Emphasis added)Oh wait.... they're talking about "weight". Not mass. Silly me.
Oh wait. Silly them. Get outside of a gravitational field and there's no weight! Thus these ranges are a bit off.
Oh wait... that's still not what they're talking about? Well why didn't they say that?
What's really going on is that some people are wanting to include the ranges of stable isotopes (different atoms altogether) of certain, common elements. So.... they're not really changing anything. They're just pulling a bit of info off of the table of isotopes and including it on the periodic table.
No big deal really. Except now students are going to be a lot more confused about what number to plug into the formula they don't understand either. Yes. Let's compound the problems early. | <urn:uuid:9238e5a7-44ad-4a56-9750-7f1f1a475035> | 3.140625 | 239 | Personal Blog | Science & Tech. | 78.706381 |
The Early History of Seismometry (to 1900)
James Dewey and Perry Byerly
The Tilt Controversy
For a seismograph to be effective, its response characteristics must be known. We have seen that the British seismologists in Japan attempted to simplify the problem of the seismograph response by building relatively long-period instruments, and assuming that the seismogram trace was proportional to the ground displacement. The general problem of the response of a damped oscillatory system to ground motion of arbitrary period was considered theoretically by Perry and Ayrton (1879). Poincaré (1888) and Lippmann (1890) presented short notes on the integration of a seismogram trace to obtain ground displacement.
In the 1890's, however, the possibility arose that all of the theories of seismograph response just mentioned were fundamentally wrong. For these theories assumed that a seismograph pendulum responds to linear motion which is in the plane of oscillation of the pendulum and perpendicular to the line joining the pendulum's center-of-mass with the pendulum's axis-of-rotation. That is, a common pendulum which oscillated in an east-west plane was expected to respond to linear horizontal motions occurring in the east-west plane. The alternative theory, which became very widespread in the 1890's, was that horizontal and common pendulums were responding largely to tilting, which was in turn due to vertical displacements of the Earth's surface. As the Earth's surface tilted up and down, the pendulum would attempt always to point in the direction of gravity (or to point along the projection on the pendulum's plane-of-oscillation of the direction of gravity).
At first, the implications of recording tilting instead of displacements do not seem to have been understood among seismologists in Europe. We shall see, however, that calculated ground displacements commonly varied by several orders of magnitude according as the seismograph was assumed to be responding to horizontal displacements or to tilts due to vertical displacements. To be confident of any seismographic measurements of the amplitude of ground motion in an earthquake, it was necessary to determine the importance of tilting in earthquake motion.
An instrument for recording tilt in an earthquake was suggested as early as 1703 (De la Haute Feuille, 1703), but the idea that seismographs should record tilting in earthquakes was not widely accepted until European seismologists began recording teleseisms. Then, it was assumed without much argument, at first, that the recorded waves represented tilt, rather than horizontal motions (Ehlert, 1897a; Schlüter, 1903, p. 301-325). Perhaps this was because the earliest records of a teleseism, those of von Rebeur, were obtained with instruments which were built to measure changes in the direction of the vertical. Furthermore, the recorded motion, consisting of long-period sinusoidal oscillations, suggested a wave motion not unlike waves on the surface of the sea, which seemed to imply considerable tilting (Agamennone, 1894).
While the European seismologists were interpreting their first seismograms of teleseisms, John Milne, still in Japan, had independently concluded that tilting had a significant effect on the response of a seismograph in an earthquake. During the Mino-Owari earthquake of October 28, 1891, Milne (1893d) had observed horizontal-pendulum seismometers located at a distance of 140 miles from the epicenter and was convinced from watching the pendulums that the instruments were being tilted. A comparison of seismograms from different horizontal instruments suggested that record amplitudes were proportional to the static tilt sensitivities of the instruments rather than to their static displacement sensitivities. In order to obtain a more accurate measure of tilt, Milne (1893e) set up a beam balance, arranged so that the motion of the balance's vertical pointer was amplified and recorded on a smoked-glass plate. Milne believed that the beam would remain horizontal in an earthquake while the Earth tilted beneath it. The balance was in stable equilibrium, so that one would expect it to respond also to horizontal displacements of the ground, like any other pendulum. Nevertheless, Milne seemed to assume that the records given by the instrument represented only tilt. Significant "tilting" was recorded by the balance seismograph. Milne was forced to the "unpleasant conclusion ... that all the records hitherto published in Japan where vertical motion has been recorded are of but little value" (Milne, 1893e, p. 103-104).
Figure 25. Schlüter's klinograph (modifed from Schlüter, 1903). The frame rotates on an agate edge S, which rests on an agate plate, not shown. S is made to coincide with the frame's center of mass by adjusting the weights L. Light is reflected off the mirror M onto a moving photographic surface. The mirror is mounted so as to apply a slight restoring force to the klinograph.
Soon, however, the "tilting hypothesis" met objections. A major difficulty was the large vertical displacement required to produce a tilting of the magnitude which seismologists believed they were recording. Under the assumption that his seismographs were recording only tilt, Cancani (1894) calculated that the ground rose and fell forty centimeters during the passage of waves of sixteen-second period from a distant earthquake. The improbability of such large vertical motion occurring in the unfelt waves of a distant earthquake was emphasized by Schmidt (1896). The same record which Cancani thought represented tilting due to a vertical displacement of forty centimeters, Schmidt pointed out, could also represent a horizontal displacement of much smaller amplitude. (In this case, using Schmidt's formulas, the horizontal amplitude would be less than a millimeter.) Feeling that a horizontal displacement of a millimeter was more probable than a vertical displacement of forty centimeters, Schmidt concluded that the common and horizontal pendulums were indeed recording horizontal oscillations from teleseisms.
Schmidt's conclusion was not accepted by many seismologists, at first, and a controversy arose over the presence or absence of large tilts in earthquake waves. (Ehlert (1897a) summarizes the arguments which were used "for" and "against" tilting.) Although the large vertical displacements required to produce significant tilting were not perceptible to human beings, Ehlert (1897a) argued that the vertical displacements might still exist, but that their periods were too long to be noticed by humans. At this time, there were no long period vertical seismographs, and seismologists do not seem to have considered the possibilities of directly recording the vertical displacements believed to be responsible for tilting.
In 1899, W. Schlüter (1903) began recording in Göttingen with a tilt-measuring device, which he called a "klinograph". The instrument was similar to a beam balance, with the difference that the horizontal axis of rotation of the moving frame, or beam, passed through the center of mass of the frame (Figure 25). In this situation, the frame would not respond to linear displacements. By virtue of its rotational inertia, however, the frame would respond to a rotational motion in a vertical plane, i.e., tilting. In order to stabilize the klinograph, Schlüter adding a restoring force to one end of the beam. The instrument recorded photographically.
Schlüter operated his klinograph simultaneously with a horizontal pendulum seismograph. He calculated the tilt sensitivities of the two instruments and found them to be of the same order of magnitude. If an earthquake were recorded on the horizontal pendulum seismograph, and if the seismogram from this instrument represented tilting of the ground, then the earthquake would be well recorded on the klinograph. Contrary to what he had expected, Schlüter found that the klinograph recorded nothing at times when the horizontal pendulum seismograph recorded large earthquakes. He concluded that the horizontal pendulum was responding only to horizontal displacements, for which the klinograph had no sensitivity. Tilting, if it existed, was too small to affect either his klinograph or contemporary horizontal pendulum seismometers.
Schlüter's experiment, and theoretical considerations such as those of Schmidt, were accepted by many as strong evidence in favor of the viewpoint that seismographs responded largely to linear motion rather than tilting, except for waves of very long period (Wiechert, 1903). The experiment provided justification for neglecting the effect of tilt in theoretical studies of seismograph response. Those (such as Galitzin, 1902) who doubted the validity of Schlüter's experiment found the theory of a pendulum responding to both tilt and displacements to be so complicated that they were forced to neglect the effect of tilt as a matter of convenience (Galitzin, 1904). [However one of the authors of this paper (P B.), remembers when Father Macelwane changed the interpretation charts for the Berkeley Bosch-Omori pendulums to correspond to response to tilt rather than displacement. This was in 1923.]
From the Bulletin of the Seismological Society of America. Vol. 59, No. 1, pp. 183-227. February, 1969. | <urn:uuid:d020d1af-fea4-432c-83e3-e2004534103b> | 3.875 | 1,918 | Academic Writing | Science & Tech. | 32.065954 |
The influence of Great Earthquakes on volcanic eruption rate along the Chilean subduction zone
Watt, Sebastian F.L., Pyle, David M. and Mather, Tamsin A. (2009) The influence of Great Earthquakes on volcanic eruption rate along the Chilean subduction zone. Earth and Planetary Science Letters, 277, (3-4), 399-407. (doi:10.1016/j.epsl.2008.11.005).
Full text not available from this repository.
Seismic activity has been postulated as a trigger of volcanic eruption on a range of timescales, but demonstrating the occurrence of triggered eruptions on timescales beyond a few days has proven difficult using global datasets. Here, we use the historic earthquake and eruption records of Chile and the Andean southern volcanic zone to investigate eruption rates following large earthquakes. We show a significant increase in eruption rate following earthquakes of MW > 8, notably in 1906 and 1960, with similar occurrences further back in the record. Eruption rates are enhanced above background levels for ~ 12 months following the 1906 and 1960 earthquakes, with the onset of 3–4 eruptions estimated to have been seismically influenced in each instance. Eruption locations suggest that these effects occur from the near-field to distances of ~ 500 km or more beyond the limits of the earthquake rupture zone. This suggests that both dynamic and static stresses associated with large earthquakes are important in eruption-triggering processes and have the potential to initiate volcanic eruption in arc settings over timescales of several months.
|Keywords:||seismic triggering; volcanic eruption; Chile; Andean southern volcanic zone; great earthquake; eruption rates|
|Subjects:||Q Science > QE Geology|
|Divisions:||University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
|Date Deposited:||21 Jun 2011 13:02|
|Last Modified:||23 Jul 2012 03:16|
|Contributors:||Watt, Sebastian F.L. (Author)
Pyle, David M. (Author)
Mather, Tamsin A. (Author)
|Date:||30 January 2009|
|RDF:||RDF+N-Triples, RDF+N3, RDF+XML, Browse.|
Actions (login required) | <urn:uuid:234e2040-2a7d-4d83-bd3f-21b05c90bb67> | 3.078125 | 495 | Academic Writing | Science & Tech. | 48.927759 |
Soil Changes Over Time Within a Dry Meadow, Long Term Soil Organic Matter Study, RussiaEntry ID: RAS.SCG.DryMeadow
Abstract: This experiment began in 1965. The present cutting meadow was formed
on land that was ploughed in 1890-1900, then used only for hay harvest
without any treatment. The soil at the site developed on loess-like
loams, underlain by moraine. The climatic region of the sit falls
within the cold temperate boreal boudaries. The studied soil has no
equivalents in USDA, FAO. Under the Russian ... classification system
these soils are called Soddy soils. All information about this soil
can be found in Yakimenko E (1987) Pochvovedenie, 1987 no. 5 (English
The experiment consists of straw incorporation & FYM on an arable,
meadow cut for hay. The measurements made (data available),
methodology, and frequency are as below:
a) Vegetation measurements made and frequency
Yield: Biweekly in summer, otherwise monthly.
Total above-ground dry matter: biweekly in summer, otherwise monthly.
Total dry matter offtake: biweekly in summer, otherwise monthly.
Carbon content of offtake: biweekly in summer, otherwise monthly.
Nitrogen content of offtake: biweekly in summer, otherwise monthly.
b) Soil sampling
Details of soil sampling method: Five-ten sections were made.
Samples taken according to genetic horizons by auger (100 cu cm) from
every section. In the transect, soil samples were taken for every 5 cm
of depth, and every 20 cm along its length. Soil is separated into
Details of measuring depths and soil layers: Asod 1-5 cm; A1
10-15,20-25 cm; B1 30-40 cm; B2 50-60,70-80 cm; BC 100-110 cm.
c) Soil measurements made and frequency
Total carbon: Once every 3-5 years
Method of measuring total carbon: Acid-dichromate digestion
Biomass carbon: Once only
Method of measuring biomass carbon: Burning to ashes
Carbon measurements in other organic matter fractions: Once every
Method of measuring carbon in other organic matter fractions:
Humic and fulvic acids were extracted by treatment with
Na4P2O7. Carbon contentwas determined by acid-dichromate digestion of
Total nitrogen: Every 3-5 years
Method of measuring total nitrogen: By treatment with H2SO4.
Soil bulk density or weight: Every 3-5 years.
Method of measuring soil bulk density or weight: Bulk density was
determined by excavation of a core with metal glass. Soil weight
(specific gravity) was determined by pycnometers.
Other nutrients: pH (salt extract), soluble P.
Atmospheric inputs: Chemical composition of atmospheric deposits
(rain and snow) was determined in the open plots and was taken into
account when soil properties were discussed.
Other measurements: Content of exchangeable cations in the soil.
Total amount of
SiO2,Al2O3,FeO3,MnO,MgO,CaO,Na2O,K2O,P2O5 and Fe and Mn content in
the acid extract (1H H2SO4) in the soil, grain-size
compound, amount of Fe-Mn neoformations and their compound bulk
density and soil weight; water permeability; pH (water extract).
d) Details of the meteorological station
Nearest meteorological station to the site: Nebolsin (most
meteorological data comes from the Moscow University Meteorological
e) Meteorological data available and frequency
Rainfall: Monthly in the growing season. Also total snowfall in summer.
Air temperature: Monthly in the growing season
This information was compiled for the GCTE-SOMNET Database, Pete
Smith, Pete Falloon, David Powlson, and Jo Smith. Soil Science
Department, IACR-Rothamsted, UK.
(Click for Interactive Map)
Start Date: 1965-01-01
Vertical Resolution: 5 cm
Temporal Resolution: varies by specific measurement
AGRICULTURE > AGRICULTURAL CHEMICALS > FERTILIZERS
AGRICULTURE > AGRICULTURAL PLANT SCIENCE > CROP/PLANT YIELDS
AGRICULTURE > SOILS > CALCIUM
AGRICULTURE > SOILS > CARBON > BIOMASS CARBON
AGRICULTURE > SOILS > CARBON > TOTAL CARBON
AGRICULTURE > SOILS > CATION EXCHANGE CAPACITY
AGRICULTURE > SOILS > MAGNESIUM
AGRICULTURE > SOILS > MICRONUTRIENTS/TRACE ELEMENTS
AGRICULTURE > SOILS > NITROGEN
AGRICULTURE > SOILS > ORGANIC MATTER
AGRICULTURE > SOILS > PHOSPHORUS
AGRICULTURE > SOILS > POTASSIUM
AGRICULTURE > SOILS > SOIL SALINITY/SOIL SODICITY
AGRICULTURE > SOILS > SOIL BULK DENSITY
AGRICULTURE > SOILS > SOIL CHEMISTRY > ALUMINUM
AGRICULTURE > SOILS > SOIL CHEMISTRY > SILICON
AGRICULTURE > SOILS > SOIL CHEMISTRY
AGRICULTURE > SOILS > SOIL PH
AGRICULTURE > SOILS > SOIL TEXTURE
ATMOSPHERE > ATMOSPHERIC TEMPERATURE > AIR TEMPERATURE
ATMOSPHERE > PRECIPITATION > RAIN
LAND SURFACE > SOILS > CALCIUM
LAND SURFACE > SOILS > CARBON > BIOMASS CARBON
LAND SURFACE > SOILS > CARBON > TOTAL CARBON
LAND SURFACE > SOILS > CATION EXCHANGE CAPACITY
LAND SURFACE > SOILS > MAGNESIUM
LAND SURFACE > SOILS > MICRONUTRIENTS/TRACE ELEMENTS
LAND SURFACE > SOILS > NITROGEN
LAND SURFACE > SOILS > ORGANIC MATTER
LAND SURFACE > SOILS > PHOSPHORUS
LAND SURFACE > SOILS > POTASSIUM
LAND SURFACE > SOILS > SOIL SALINITY/SOIL SODICITY
LAND SURFACE > SOILS > SOIL BULK DENSITY
LAND SURFACE > SOILS > SOIL CHEMISTRY > ALUMINUM
LAND SURFACE > SOILS > SOIL CHEMISTRY > SILICON
LAND SURFACE > SOILS > SOIL CHEMISTRY
LAND SURFACE > SOILS > SOIL PH
LAND SURFACE > SOILS > SOIL TEXTURE
Quality a) Details of the plots
Width of smallest plot is 50 m
Length of smallest plot is 100 m
Slope: 3-4% . Shape: Uniform
Width of Discard Strip around plot: 10-20 m
b) Details of replication, randomization and controls
There are at least 5 replicates in the experiment. The experiment has
... a randomized plot design. The experiment has a restricted randomized
plot design. Soil was sampled from sections (in this investigation)
which were distributed in chess order. Earlier replicates distributed
by random plot design. The control plot is a forest (pine) ecosystem
of the same age as the dry meadow . Standard statistical tests were
used: Mean values, error of mean values, dispersion, coefficient of
Access Constraints none
Data Set Progress
Role: DIF AUTHOR
Phone: (301) 614-6898
Email: Tyler.B.Stevens at nasa.gov
NASA Goddard Space Flight Center Global Change Master Directory
Province or State: MD
Postal Code: 20771
Role: TECHNICAL CONTACT
Phone: (095) 923 18 86
Phone: (095) 923 31 11
Fax: (095) 923 1886
Email: egc at geoenv.msk.su
Scientific Centre for Geoecology, Russian Academy of Sciences, Ulansky Line 13, bd 2,
Postal Code: 101000
Dry meadow as a biogeoceonos. Nauka, Moscow, 1978.
Skvoztsova, E & Yakimenko, E. (1991) Impact of forest and meadow
vegetation on the microstructure. Pochvovedenie (Soviet Journal of Soil
Science), 1991, N11.
Soil formation in the forest Ecosystems. Nauka, 1989.
Yakimeno, E. (1987) Pedogenesis under dry meadows. Pochvovedenie (Soviet
Journal of Soil Science), 1987, N5.
Creation and Review Dates
DIF Creation Date: 2000-02-17
Last DIF Revision Date: 2008-01-31
Future DIF Review Date: 2001-02-17 | <urn:uuid:d9cafd2f-c4db-4c42-bcbf-0c51d3f70c8d> | 3.0625 | 2,006 | Academic Writing | Science & Tech. | 36.834163 |
This tiny pond creature has 15,600 chromosomes. From Ed Yong:
Within its cell, Oxytricha contains two nuclei, which enclose its DNA. One of these—the micronucleus— contains the complete edition of Oxytricha’s genome, just like the single nucleus within our own cells. That’s the tidy encyclopaedia shelf. But while the material in our nucleus must be constantly decoded and transcribed so that we can live, Oxytricha’s micronucleus is largely inactive. The encyclopaedia’s are barely read.
Instead, it relies on a second structure called the macronucleus. That’s the messy drawer. All of the DNA in the micronucleus is copied thousands of times over, and shunted into the macronucleus. In the process, it is broken up at tens of thousands of places, rearranged, and pruned. What’s left is a collection of thousands of “nanochromosomes” that contain all the information Oxytricha needs to survive. This is the stuff that gets decoded and transcribed, used and reused while the originals gather dust.
Sequencing this almighty mess must have been a devilish task, but Etienne Swart from Princeton University rose to the challenge. Leading a team of US and Swiss scientists, he has sequenced Oxytricha’s complete macronuclear genome. …
The team found around 15,600 of these nanochromosomes. On average, each is around 3,200 DNA ‘letters’ long, and around 80 percent of them contain just a single gene.
More at the link. | <urn:uuid:6f23eab9-3dce-4dc8-82c5-d324e76dbdde> | 3 | 362 | Truncated | Science & Tech. | 50.244118 |
When I was at school I learned about "implicit coordinates" for curves in a plane. Essentially these mapped the path in terms of arc length $s$ from a fixed point, and direction of travel $\psi$ measured against a fixed line (so the curve has to be sufficiently smooth). The point was that these data could be measured by a person travelling along the path. They were handy for computing curvature, and solving chase problems, I recall.
A question was posed about curves parameterised by arc length, which put me in mind of this. I did a search online, as I wanted to mention it in a comment, and came up with nothing resembling what I remembered.
I may have the name wrong, of course, or such co-ordinates may now be called something else. But a good reference would be helpful.
As noted in comments below, the term is intrinsic coordinates. Good references still welcome, though the correct terminology does open up various online resources. I learned about these at school, and afterwards they went nowhere, or so it seemed. Yet they always seemed interesting. I suppose the way that Riemann Surfaces are made up from local bits (the direction gives you a piece which is locally nearly straight) - and generalisations of the same in various manifolds and geometries are where it went. Yet the particular expression here, which is effectively how to map a curve using a car with a milometer and a compass always seemed very real. | <urn:uuid:0642d5c2-106a-47f6-959a-3dcde60583d3> | 2.875 | 303 | Q&A Forum | Science & Tech. | 48.462018 |
Salpingoeca cells appear as sessile, thecate trophic cells and naked, free-swimming or creeping zoospores.
Trophic cells are roughly spherical, and reside in a theca (labelled "lorica" in the illustrations) that may or may not have a stipe. The theca, which is visible by light microscopy, is the main diagnostic character for the genus and family; in Codosigidae, no theca can be seen in the light microscope, while in Acanthoecidae the cell is surrounded by a lorica of siliceous strips ("costae"). The anterior end of the cell shows a single flagellum and a ring of tentacles. Under most light microscopes, the tentacle ring appears as a solid collar around the flagellum. In disturbed cells, both the flagellum and the collar may be shed or retracted.
Zoospores are similar to the sessile cells but are naked. During settlement, zoospores may produce fine pseudopodia at the posterior end of the cell, by which the cell slowly creeps to the position at which it will secrete its theca and become sessile.
Salpingoeca: Index | Introduction | Appearance | Ultrastructure | Reproduction and Life History | Similar genera | Classification | Taxonomy and Nomenclature | Cultures | References | Internet resources | <urn:uuid:9391157b-cdf9-49e5-9ca4-791faeb78b7a> | 3.46875 | 296 | Knowledge Article | Science & Tech. | 23.40991 |
Ten squares form regular rings either with adjacent or opposite
vertices touching. Calculate the inner and outer radii of the rings
that surround the squares.
One side of a triangle is divided into segments of length a and b
by the inscribed circle, with radius r. Prove that the area is:
Find the exact values of some trig. ratios from this rectangle in
which a cyclic quadrilateral cuts off four right angled triangles. | <urn:uuid:746d0f14-1071-4730-85da-5824a605ea10> | 3.859375 | 93 | Tutorial | Science & Tech. | 56.424219 |
Lets say I want to design a Nomarski prism that would split the ordinary and extraordinary beam by an angle of 0.32 mrad. I used a raytracer to find the internal angle between the quartz wedges.
However I couldn't decide how thick the quartz wedges should be.
The original patent mentions the thickness but I don't understand the sentence: http://www.google.co.uk/patents?id=QI5kAAAAEBAJ&zoom=4&dq=nomarski%20patent%202924142&pg=PA6#v=onepage&q=Fig.%204&f=false
The picture shows the Nomarski prism from the side. The optical axis of the system is horizontal. The internal angle between the wedges (or blades) is $\alpha$. The optic axis (note the difference between optical axis of the system and optic axis of the crystal) of the first prism Q2 is perpendicular to the screen. The wedge Q1 has its axis inclined in-plane.
Q2 is 0.5mm thick at the center. Q1 is 1mm thick at the center.
Both compensate their birefringence.
This last expression isn't clear to me. I have the feeling that I understand this only vaguely.
Is the birefringence in Q2 stronger because of the orientation of the optic axis? (Probably yes)
Why does the birefringence need to be compensated? (must have something to do with the adjusting the bias by shifting the Nomarski prism transversal to the optical axis in the microscope)
How is the total thickness of the prism (here 1.5mm) chosen? Can a thinner Nomarski prism be used with higher angles? | <urn:uuid:2a3605cf-e5e5-45c7-b732-25488c64c856> | 3.296875 | 375 | Q&A Forum | Science & Tech. | 69.747882 |
The area of smashing particles is surrounded by detectors. Whatever is captured by detectors is a particle (I would say "by definition" for simplicity). It causes some reaction inside detector. For instance, it can be a trace of bubbles in Wilson camera. The shape and other parameters of this trace depend of the type of particle. It has been known from numerous experiments that there is only a limited number of trace types, and hence there is only limited number of particles that can be detected directly (i.e. each type of trace is associated with some particle type, like electron or proton. All electrons result in similar shapes of trace when crossing the Wilson camera). So, the first "class" of particles comprise of those instances that can be detected directly. Let's call the "real" particles.
There is also another "class" of particles that cannot be detected directly. Physicists think that they are particles too for two reasons:
- Physicists developed a model that explains why this particle decays into certain combination of "real" particles that can be detected directly.
- Quantitative predictions of this model are consistent with experimental data.
Examples of such particles are W and Z bosons, as well as number of so called "resonances" (presumably short-living particles) etc. And also Higgs boson of course.
In fact, collider is a kind of a black box: there are "real" particles on input and output, but we can only guess what happens inside. "Guessing" process is explained in principle by @zhermes.
This, in turn, brings us to another question:
Why some particles cannot be detected directly?
There might be a number of reasons for that:
a) our detectors are not good enough
b) particles are too short-living (which is in fact equivalent to reason (a))
c) for some "fundamental" reasons (usually quantum mechanical arguments are used)
Frankly speaking, I do not know for what reason, for instance, W and Z bozons cannot be detected directly.
And last (but not least): I admit that possibly those non-"real" particles are not in fact particles as per rigorous definition (field configurations that realise irreducible representations of Poincare group in Minkowsky space or something like that). I admit that they might be "shattered fragments" of "real" particles.
But modern physics is unable to establish that. Because our models were developed based on collider-type experiments (i.e. "real" particles in and out of the black box). And all models are based on "black box" logic - quantization. Do you know what quantization is? it is a set of numbers connecting inputs and ouptuts of the black box. Vicious circle. That's why these models are useless for identifying the properties of the isolated and not moving "real" particles (mass, charge ets.). | <urn:uuid:b6f38db0-b5ab-4433-a144-d3e5609d52b3> | 3.109375 | 611 | Q&A Forum | Science & Tech. | 44.825113 |
There is considerable disagreement as to the proper grouping and status of divisions within this heterogeneous assemblage of organisms, some of which, as indicated below, are animal in nature. As a matter of convenience in discussing the more important marine members, we shall here employ only names of more or less familiar usage in biology and oceanography. Many of the members included are classified as animals in zoological texts, but in consideration of their holophytic nature (faculties of photosynthesis) it is most convenient for oceanographic studies to include them a priori among the producers. For more detailed treatment of the systematics of the various divisions, the reader is referred to Fritsch (1935) and the relevant works included in the discussions under the separate groups.
In contrast to the algae previously discussed, the members of this assemblage of plants and plantlike animals are primarily floating forms and will be taken up in the order of their importance in the economy of the sea.
Diatoms. The plants here included are all microscopic in size, the larger species viewed individually appearing only as tiny points. Some earlier authors of marine botany included them with the brown algae. A comprehensive treatment of the group is given by Hustedt (1930). In structure they are unicellular, but individuals may form chains or groups of various types. Examples of types representing the common genera are
Characteristic types of diatoms. a, Corethron; b, Nitzschia closterium; c, Planktoniella; e, Coscinodiscus; f, Fragilaria; g, Chaetoceros; h, Thalassiosira; i, Asterionella; j, Biddulphia; k, Ditylum, l, Thalassiothrix; m, Navicula; n, o, Rhizosolenia semispina, summer and winter forms.
Since these plants as a group may be considered the most important in the economy of the sea, it is imperative that we treat them in considerable
The shell structure of diatoms (fig. 71) may be likened to a box with a telescoping lid, because it consists of two nearly equal halves fitted one over the other. The pieces corresponding to the top and bottom of the box are known as the valves, and these are each joined by connecting bands that overlap and together form the girdle. The larger half of the shell is known as the epitheca, and the smaller half, which fits into it, as the hypotheca. The protoplasm lies wholly within the shell, but for exchange of metabolic products it is exposed by a slit (raphae) in the valve of some types and by small pores in others.
The gross structure of a simple diatom (Coscinodiscus). a, valvular view; b, girdle-view section of cell wall.
Reproduction in diatoms. a,b, cell division; c, diminution of size resulting from cell division in three generations.
Diatoms may possess only one or many chromatophores, which may vary in color from yellow to olive-green or brown. Authorities are in poor agreement as to the nature of the pigments present, but there is some indication that the common pigments are masked by the accessory brown pigment diatomin, which may be identical with fucoxanthin of the brown algae. An important product of assimilation is an oil that is frequently visible as droplets within the diatom.
Methods of Reproduction. The most common method of propagation among the diatoms is by simple cell division (fig. 72a). This method has a far-reaching effect on the population in two distinct ways. First, it is conducive to a rapid production of enormous numbers when
Reproduction in diatoms. a, auxospore formation in Thalassiosira aestivalis (after Gran and Angst); b, increase in cell size following auxospore formation in Melosira nummuloides (after Fritsch); c, resting spores in mother cells, Chaetoceros vanhurckii; d, resting spore of Chaetoceros diatema; e, resting spore of Chaetoceros radicans; f, microspores in Ditylum; g, microspores in Chaetoceros didymus (after Gran and Angst).
Diatoms may also produce what are known as microspores (fig. 73b). These were early observed by Murray, Gran, and others. They consist of small protoplasmic spheres occupying the shell, and may escape as biciliated spores. The significance of these bodies is not fully known.
Resting spores of characteristic structure (fig. 73c) are also formed in most pelagic neritic species, especially of the centric types, by the cell contents becoming condensed and surrounded by a heavy, siliceous wall. They may be produced at the initial appearance of unfavorable living conditions, and may drift for some time within the old frustule or sink to the bottom to survive the unfavorable seasons of inadequate nutrients, cold, or of varying salinity so characteristic of many coastal areas. Gran (1912) has reported them from Arctic collections in which they were enclosed in ice.
Winter and summer forms of oceanic diatom species have been reported. These are cases of marked dimorphism in which the coarse winter forms have been looked upon as a means of survival from one favorable season to another. However, the dimorphism may be only an adjustment to changes of viscosity inherent with seasonal temperature changes.
Many diatoms grow normally on the bottom in the littoral zone, where they may or may not be attached by stalks or glide freely over the bottom. These benthic forms produce the heavily shelled types with most exquisite designs. Diatoms may also grow in profusion on other plants and animals. The littoral genus Licmophora frequently occurs on pelagic copepods, and the massed growth of Cocconeis ceticola flourishing on the skin of whales that have spent considerable time in the cold antarctic waters has, by its yellow color, given rise to the name “sulphur-bottom” for the blue whale.
Dinoflagellata. These are frequently spoken of collectively as the dinoflagellates (fig. 74). Space will not permit the amount of discussion that this diverse group of organisms requires for adequate treatment (see Kofoid and Swezy, 1921, Kofoid and Skogsberg, 1928, Fritsch, 1935). It is a group concerning which it is not easy to make generalizations without the danger of introducing errors. The members are of great importance in the economy of the sea. A large number are holophytic and rank second to the diatoms as producers in the marine plankton. They are therefore best studied with the phytoplankton. Others are holozoic or animal-like in nutritional requirements, ingesting particulate food and possessing other characteristics that place them clearly with the animals. Some are saprophytic, living upon dead organic matter. All are important as food to filter- and detritus-feeding animals.
Typically, the dinoflagellates are unicellular, some being armored with plates of cellulose, others unarmored or naked. All possess two flagella for locomotion, an important feature in the holophytic forms, for
Dinoflagellates and other phytoplankton organisms. a, Ceratium tripos; b, Dinophysis; c, Ornithocercus; d,e, Triposolenia, front and side views; f, Peridinium; g, Amphisolenia; h, Goniaulax; i, Ceratium fusus.
Methods of Reproduction. Among the dinoflagellates, reproduction is accomplished mainly by processes of cell division, which in some instances result in a chain of individuals clinging loosely together. Temporary structural variations may normally occur in individual cells at opposite ends of the chain. The progressive size reduction that is
Dinoflagellates are found in all seas, but the greatest development of species is met with in the warmer waters, where a number of very bizarre forms are to be found. Owing to the destructibility of their cellulose plates by bacteria and other agencies, they are not preserved in bottom deposits. Important genera are Ceratium, Peridinium, Dinophysis, Gonyaulax.
Phaeocystis. Phaeocystis is a brown, flagellated plant, neritic in habit, that forms colonies in gelatinous, lobed globules visible to the naked eye. The large numbers produced may at times render the surface water quite brown and become a serious cause of clogging in silk plankton nets. Reproduction is accomplished by formation of flagellated spores that escape from the colonies.
Coccolithophoridae. Among the smallest (5 to 20 microns) of autotropic organisms of the sea are the biflagellated (some marine forms are not flagellated) forms of this group (fig. 74). Usually they are not caught by the ordinary net, through the meshes of which they readily escape, and when caught special care must be taken that their calcareous protecting armor is not dissolved by the preservative, leaving only an indefinable mass. The soft parts are shielded by tiny calcified circular plates or shields of various design and projections called coccoliths, or rhabdoliths. These shields had been found in enormous numbers in marine bottom deposits before the organisms of which they are a part were discovered by the Challenger and identified from their living habitat in the plankton, where they were found entangled in protoplasmic strands of pelagic protozoa or in the stomachs of salps and pteropods. Typically, the coccolithophoridae belong to the open sea, but they may occasionally reproduce in large numbers in coastal waters; at one time, according to Gran (1912) numbers of 5 to 6 million per liter gave the waters of Oslo Fjord a milky appearance. Some also occur in fresh water.
Though minute in size, they are of great importance as food to filter-feeding organisms, and also as contributors to calcareous bottom sediments. They occur in geological formations dating from the Cambrian period. Common genera among these organisms are Coccolithus, Pontasphaera, and Rhabdosphaera.
Halosphaera. Halosphaera is a unicellular, microscopic plant of the order Heterococcales (fig. 74). Earlier authors have included it with the green algae. It occurs at times in vast numbers in the plankton, floating mostly near the surface. Halosphaera virides occurs over the whole Atlantic and is abundant both in the warmer waters of the Gulf Stream system and in high southerly latitudes, where the Discovery investigations in the Antarctic found it second in importance to the diatoms. Meringosphaera of this order also occurs in marine plankton.
According to Gran, Halosphaera is practically the only open-sea form in which the predominantly green color of land plants is to be found. Notwithstanding the vast numbers that are often found, it does not reproduce by the quick method of simple binary fission, as in diatoms, but, after having grown for some time to its maximum size, the cell contents are transformed into a large number of zoospores. These swimming spores escape and through some unknown method are transformed back into tiny globular forms that gradually increase to normal size by successively shedding their weakly silicified investing membranes. Resting spores may also be produced.
Silicoflagellates. These flagellate organisms (fig. 74) deserve mention only briefly, since they do not usually occur in sufficiently large numbers to enter materially into the economy of the sea. However, they are such persistent members of plankton communities from nearly all colder seas that their starlike, open, siliceous shells attract a good deal of interest. Many occur in bottom sediments, and their development is shown in fossil marine deposits. That they contribute at least in a small way to the food of animals is shown by their frequent occurrence in food vacuoles of tintinnids. | <urn:uuid:fd0d8c1d-3fbd-4fa6-97fd-1cdb89d967df> | 3.140625 | 2,608 | Academic Writing | Science & Tech. | 31.13524 |
Natural Gas Energy
The United States and the rest of the world have a very clear dependency on oil as a source of energy. Drilling for oil, however, sometimes has unexpected consequences. Natural gas is one of the main byproducts of drilling for oil (Taylor, 2009). At this point, oil companies do not do anything with the natural gas that they uncover. Instead of using it as a source of alternative energy, it is burned to dispose of it (Taylor, 2009). Gas flares result from the burning of natural gases. Using the Defense Meteorological Satellite Program, the Department of Defense created a gas flare layer in Google Earth that shows gas flares around the world (Taylor, 2009). Google Earth gives a geospatial dimension to the waste of natural gas energy.
The gas flare layer does a nice job of pointing out a large waste of energy that should be stopped but gives no information on the research being done on natural gas energy. There should be more of an emphasis, in this layer or other layers, on informing users of the benefits of using natural gas and the harm oil companies are doing by wasting all of this valuable resource.
The picture above is a screenshot from the gas flares layer in Google Earth. The various colored points represent locations where gas flares have occurred.
Taylor, F. (2009, June 2). Huge Waste of Energy Visible in Google Earth. Google Earth Blog. Retrieved from http://www.gearthblog.com/blog/archives/2009/06/huge_waste_of_energy_visible_in_go o.html | <urn:uuid:b0bc4a6d-9810-4bb2-aea9-b1a9bc9a43be> | 3.4375 | 320 | Knowledge Article | Science & Tech. | 52.710147 |
There are an estimated 1.618 million web sites dedicated to recreational mathematics. Many of them feature interesting and useful material, but there is mammoth duplication of content. I strongly desire not to contribute to the clutter, hoping to offer perspectives sufficiently unique that they will not be encountered elsewhere.
Doubtless these materials will interest only a small percentage of visitors. No advanced learning is required here, however; a reasonable awareness of high-school math is sufficient.
The articles in this section are designed to be assimilated in numeric sequence. Each page features ideas or methods previously introduced.
Black Box math challenge
square root iteration
pencil and paper | <urn:uuid:a2213b54-cdfe-48d5-83c4-086be7f76c9b> | 2.796875 | 130 | Personal Blog | Science & Tech. | 20.015833 |
In general if A, B and C are the three components of a
vector (so F = <A, B, C>, then the curl is the
curl(F) = <dC/dy - dB/dz, dA/dz - dC/dx, dB/dx - dA/dy>
where dC/dy is the derivative of C with respect to y, and so on.
Here all derivatives are zero except dA/dy, dB/dx and dC/dx. You should be able to figure out these derivatives.
This is a simple computation with proper substitution of limits.
Direct computation is quite complicate but we can use divergence theorem which states that
Flux = (S) ∫∫ F dot n dS = (W) ∫∫∫ divF dV,
i.e. the flux over the closed surface S is equal to the tripple integral over the enclosed volume W of the divergence of F. | <urn:uuid:fcd1fb77-8225-41c4-a119-6fc0deb32cec> | 2.734375 | 210 | Q&A Forum | Science & Tech. | 78.778571 |
Nowadays, the determination of the humidity of air in the atmosphere is done on a global scale by satellite measurements.
But of course the technique of humidity measurements did not start in space.
The first measurements were performed on the ground.
These ordinary techniques are still used today as ground-based measurements.
The question of how much water is present in the atmosphere is as important for short-term weather forecasts as for long-term projections on the future of our climate.
Where the water is to be found in the
atmosphere can also be just as
important. The water vapor concentration at the equator can be 500 times bigger than the water concentrations at the North or the South
Poles. At the same time, the concentration varies strongly at one location, depending on season and daytime.
In addition to the spatial dimensions
of altitude, latitude, and longitude, the water
vapor concentration in the Earth´s atmosphere changes in a very irregular way with time.
Rise of a balloon sonde
Meteorologists have long measured water
vapor in the air. Every day, standard measurements of temperature, pressure and water
vapor concentration are performed.
Often balloon sondes are used for these measurements.
In this procedure, measurement equipment is attached to a
ballon, which is released into the air and rises up
to 10 km, all the while measuring a so-called vertical profile of water
vapor and other meteorological data above a certain point on the Earth
surface and relaying the
data via radio back to the
surface. The equipment
used nowadays on sondes and
at the surface is a psychrometer, or a
Long ago, the meteorologists used a
Degreased hair has the characteristic that its length changes with
humidity, and this was used to determine the water content of
Most of these instruments have to be calibrated.
This means that for the case of a hair-hygrometer (hygro is Greek for moisture), the length of a hair has to be measured at an exactly known water
vapor concentration in a lab. From this model value, the actual value of the concentration in the atmosphere can be calculated if you measure the length of the same hair somewhere
else in the atmosphere. Nowadays, much more advanced and precise equipment is used.
Even so, scientists are regularly
discovering sources of systematic error in these modern measurement techniques
(one was recently found of up to 10%), due to different conditions during the calibration in the lab and in the real
atmosphere, and thus instruments are
constantly improving. For this reason, it is important to use as many techniques as possible, in our case to measure the humidity of air.
Water vapor measurement of a balloon sonde at the Royal Dutch Meteorological Institute (KNMI) on 25th October 1995.
Measurements (Remote Sensing)
Measurements of water vapor concentrations by means of equipment on a satellite is one of the most recent alternatives to ground-based measurements.
Since it is like taking measurements from a great distance,
many people call it "remote sensing". Satellites fly over every point of the Earth within the time
frame of a couple of days, and can therefore give
full coverage of the global water vapor
concentration over the earth's
surface. The disadvantage is that a "point" for a satellite is usually an area of several hundreds
of square kilometers. So one can only measure the average humidity of a very large area.
The measurement of a "vertical profile", like in balloon sonde measurements, is very difficult as well, because you look through the entire atmosphere and cannot distinguish between certain altitudes.
The latest satellite techniques try to tackle this problem by not looking straight down on the Earth surface, but in a certain diagonal angle. By changing this angle, the direction of where the satellite is "looking" is changed continually.
The satellites that were used until today could either look perpendicular on the Earth, or take measurements diagonally. A new satellite,
though, is in production:
The newest satellites can look at the Earth surface
both sideways through the atmosphere and straight at it.
Where the two looking directions cut each other, the solar intensity in the volume can be determined.
Picture-insert comes from IFE/Bremen
|Spectrometer measurements from satellites
The radiation from the sun consists of photons with different energies. Every energy is represented by a certain wavelength of the light.
Depending on the characteristics of a compound in the atmosphere,
such as a molecule of water or carbon dioxide, it is able to absorb light only in certain energies or on certain wavelengths.
In a spectrometer, this characteristic of the compound is used to identify the compound by the means of the absorption spectrum.
If a spectrometer is used from a satellite, it can measure the spectrum of the light that is scattered back from the Earth and it can identify all kinds of compounds from this spectrum.
This method is also used to determine the amount of water
vapor in the atmosphere, because, as is seen in chapter 2, water
vapor only absorbs light in certain areas.
When the spectrometer counts the photons that come from the Earth, and the photons that water can absorb are missing, you can tell that there was water
vapor in the atmosphere at the time.
A simplified picture:
The sun radiates from space (black) into the atmosphere (blue). The "light particles" (the photons, the yellow beam) reach the Earth surface (brown). We now look at the light particles that bounce back from the surface, that are reflected. Particle
no. 1 reflects and reaches the satellite (blue-green), which receives a signal (becomes red). The same happens with photon
no. 2. No. 3, though, encounters a water molecule on the way to the satellite.
This absorbs the energy of the photon, and the satellite
no longer detects the photon. The more
water molecules there are in the air, the
fewer photons will reach the satellite.
If the number of photons with a wavelength
absorbed by water reaching the satellite from the Earth is compared to the number of photons which is emitted by the sun, it is possible to derive the concentration of water molecules in the atmosphere.
This is only the overall concentration in the area that the satellite covers on the moment the spectrum is taken.
Because more than 99% of the water vapor in the Earth atmosphere is in the 5000 meter above the surface,
and the atmosphere itself is over a hundred kilometers thick and satellites are usually at an altitude of about a thousand kilometers, you can imagine that the photon-counter in the spectrometer must be very precise. To achieve this, the track of the satellite must be calculated in advance by a computer.
Click to enlarge!
Global water vapor measurements in July with the satellites SSM/I, TOVS und TRIOS
Source: David L. Randel et.al., BAMS - June, 1996 Vol 77, No 6
|Meaning of the water
In the chapters "Water vapor - A greenhouse gas" and "Absorption", we already saw that the water molecule absorbs photons in the far ends of the energy spectrum, especially in the infrared,
which is the wavelength emitted back from the Earth.
The greater the number of the warmth-absorbing water molecules, the more heating of the atmosphere
occurs. This is called the greenhouse effect.
Carbon dioxide, produced when fossil fuels like oil or
coal are burned, and methane, primarily emitted by rotting plant
material and animals, are both molecules that absorb in the areas in the infrared spectrum where water does not.
The increasing concentrations of carbon dioxide and methane cause an additional warming, which causes even more water
vapor to get in the atmosphere. The water concentration is
a thousand times higher than the methane concentration, which makes water by far the most important greenhouse gas.
When it is possible to precisely determine the water
vapor concentration on every spot in the atmosphere, it will be possible to quantify the human contribution in the form of CO2 and methane to the greenhouse effect.
One would expect a constant global water vapor
concentration if no human influence was to be detected.
Only if the water vapor concentration could be
determined in a very precise way on every point in the atmosphere, will
it be possible to quantify the human contribution to the greenhouse effect.
The precision of the determination of water
vapor concentrations by means of satellite measurements at the time is about 30 to 40%, sometimes even worse. This is mainly due to the complex spectrum that water has in relation to other gases in the atmosphere. In addition, most of the water is near the Earth surface, which is very far from the satellite and therefore hard to detect. The determination of water
vapor concentrations in a way which is more reliable, say within 5% precision, is still very far away.
It is very hard to quantify water
vapor in the atmosphere.
Its concentration changes continually with time, location and altitude.
To measure it at the same location every day, you would need a hygrometer, which in earlier days made use of the moisture-sensitivity of a hair, and by now of for instance condensators.
A vertical profile is obtained with a weather balloon.
To get a global overview, only satellite measurements are suitable.
From a satellite, the absorption of the reflecting sunlight due to water
vapor molecules is measured.
The results are pictures of global water
vapor distributions and their changes.
The measurement error, however, is still about 30 to 40%.
text: Ruediger Lang
FOM-Institute for Atomic and Molecular Physics
Atmospheric Photophysics Group
translation: Heleen de Coninck - MPI Mainz 16/10/01
Edited by Stephen Gawtry - University of | <urn:uuid:9c8a7262-07ac-447e-94ca-d4720c91372d> | 3.828125 | 2,073 | Knowledge Article | Science & Tech. | 35.200708 |
In this tutorial, you've looked at the methods available for debugging Perl scripts. You started by looking at the methods used in traditional Perl development environments. In general, these involve the use of either the
print() function and monitoring the output or the use of the standard debugger provided with Perl. Both methods have limitations.
Using EPIC, the Perl development environment plug-in for Eclipse, you can debug Perl scripts and Perl CGI applications. You gain all of the functionality you might expect in a debugger, including step-by-step processing, variable monitoring and the ability to set breakpoints and monitor the execution of the script. You can also debug CGI scripts through Eclipse/EPIC through a proxy functionality that runs the scripts in Eclipse while providing the output from the script direct to a Web browser, including the built-in Web browser provided within Eclipse. Finally, you can also debug regular expressions, within a script and on an ad-hoc basis during development.
You can see from the functionality provided by EPIC detailed in this tutorial, and from the functionality you examined in the "Build Perl applications with Eclipse" tutorial, that the plug-in provides a complete environment for developing and testing Perl applications from within Eclipse. | <urn:uuid:cd6f1ce9-767b-4e1c-8514-904ab1397267> | 3.140625 | 247 | Tutorial | Software Dev. | 31.470186 |
1 [intransitive and transitive]HBMB
if an animal or plant reproduces, or reproduces itself, it produces young plants or animals:
The turtles return to the coast to reproduce.
to make a photograph or printed copy of something:
Klimt's artwork is reproduced in this exquisite book.
to make something happen in the same way as it happened before [= repeat; ↪ copy]:
British scientists have so far been unable to reproduce these results.
to make something that is just like something else [↪ copy]:
With a good set of speakers, you can reproduce the orchestra's sound in your own home. | <urn:uuid:2013e737-5813-416d-b228-06ab0303a2c7> | 3.0625 | 135 | Knowledge Article | Science & Tech. | 36.075663 |
Hydropower, also called "hydraulic power" or "water power," is energy that is derived from harnessing the force of moving water. It is often used for irrigation, the operation of machines and commercial electricity production, through the use of dams or tidal, wave or ocean power schemes.
U.S. natural gas prices are rising, while wind and solar are growing rapidly. The global transition to mostly renewable grid power may now be unstoppable.
45 | April 3, 2013 3:00am |
As people push against the limits of what nature freely offers us in terms of fresh water, climate stability and more, how can we use our resources to achieve the greatest return for society?
3 | April 1, 2013 3:00am |
The ice is vanishing in the world's longest continental mountain range, threatening the water supply for tens of millions of people in South America.
1 | January 23, 2013 2:28pm |
Building a smarter city rests on a solid business plan. But drafting a viable one is trickier than you might expect.
November 12, 2012 12:17pm |
Europe's largest economy shows that solar power can succeed even in northern climates.
8 | November 6, 2012 3:00am |
Throw jeans in a hot wash and they'll come out smaller. Why should creatures in a warming ocean be any different?
11 | October 5, 2012 3:14am |
Many banks are wary to finance renewable energy projects, and that hesitation can stall or even stop new projects. Insurers have stepped in to help mitigate the risks and establish the appropriate...
4 | September 17, 2012 9:22pm |
Archeologists think they've unearthed King Richard III - under a parking lot. The long missing "my kingdom for a horse" monarch has probably resurfaced as a famous skeleton. Bring on the DNA!
September 12, 2012 11:46am |
A chart illustrates the dramatic changes within the nation's power sector over the past several decades. The upshot? Natural gas isn't the only rising star.
4 | August 22, 2012 12:04pm |
The force of 8,000 locomotives will soon be captured and converted to energy to power homes in Maine.
3 | July 25, 2012 3:06am |
First the Queen did it on the River Thames near Windsor Castle. Now a London park heads to the river to turn the ancient Archimedes screw upside down and generate electricity. Watch videos.
5 | July 19, 2012 8:50am |
BARCELONA -- Starlab is a Catalan-based private company that converts technology into profits, global innovation and mind-controlled robots.
April 2, 2012 3:07am |
The growing city of Atlanta, Georgia is not built near a source of water. It's a major problem that demonstrates a coming urban, environmental and economic crisis.
1 | March 21, 2012 8:10am |
MADRID -- As Spain falls deeper into recession and drought, farmers and researchers work together to innovate and diversify farming practices.
March 2, 2012 4:34am |
What's good for Her Majesty could also be good for the common folk of Britain.
4 | January 20, 2012 5:59am |
Global investment into renewable power sources surpassed investment into fossil fuel power plants in 2010, according to a Bloomberg report.
3 | November 27, 2011 6:14pm |
Would you prefer products made via renewable energy? A new certification aims to harness consumer purchasing power for companies who harness the wind, from big banks to building blocks.
3 | November 22, 2011 4:00am |
The N. Atlantic island has been trying to lure industry with 100 percent renewable, stably priced electricity. A Jersey City IT firm serving NY, London financial districts is moving in. Is IBM next?
October 5, 2011 12:00am |
As more electric cars hit the road, more wind power may be able to hit the grid. Two studies explore how.
2 | September 23, 2011 10:44am |
The ancient Archimedes' screw is coming into its own as a hydroelectric technology. The Queen buys two to power Windsor Castle.
3 | September 9, 2011 2:16am | | <urn:uuid:7b5a5606-ee3c-4bc2-b7e4-c60481c0a925> | 2.9375 | 888 | Content Listing | Science & Tech. | 63.03127 |
The Satanic Leaf-tailed Gecko - First described in 1888 and re-discovered in Madagascar in 1998. It is the smallest of 12 species of nocturnal bizarre looking leaf-tailed geckos. They are only found in primary, undisturbed forests in Madagascar, so their populations are very sensitive to habitat destruction.
ET salamander - Discovered in Ecuador in 2009.This genus of salamanders has fully webbed feet which help them climb high into the canopy of tropical forests; they also have no lungs and breathe instead through their skin.
Pinocchio frog - The frog was discovered in 2008 during an expedition to the Foja Mountains in the Papua province of Indonesia. The frog has a long, Pinocchio-like protuberance on its nose that points upwards when the male is calling but deflates and points downwards when he is less active.
Large tree frog - The six inch long tree frog with enormous eyes was discovered next to a clear running mountain river in Papua New Guinea’s in 2008. It belongs to a group of frogs with an unusual vein-like pattern on the eyelid and its tadpoles have enormous sucker-like mouths that allow them to graze on exposed rocks in torrential stream environments.
Chinchilla tree rat: Discovered between 1997 and 1998 in the mountains of Peru. The chinchilla tree rat was discovered in the Vilcabamba mountain range, very close to the world famous ruins of Macchu Picchu. The discovery was certainly very unique as typically it’s unusual to discover a species of this size (similar to that of a domestic cat).
Tube-nosed fruit bat - This is a previously seen but still undescribed species endemic to Papua New Guinea found by researchers in 2009. It is likely restricted (endemic) to hill forests on the island. Fruit bats are important seed dispersers in tropical forests.
Smoky honeyeater - Also found on an expedition to the Foja Mountains of Papua province, Indonesia, on the island of New Guinea in 2005. The honeyeater was discovered at an altitude of 1,650 m (5,445 feet) above sea level, This medium-sized, sooty-gray songbird has a short black bill, and each eye is surrounded by an orange-red patch of bare skin, below which hangs a pendant wattle. It is these features that distinguish it from the more widespread Common Smoky Honeyeater.
Gola malimbe bird - Flocks were discovered in Guinea, Africa in 2003. Previously it was known only from eastern Sierra Leone, Liberia, and western Cote d'lvoire.
Walking shark - Discovered in Cenderawasih Bay, Indonesia in 2006. The shark can swim. However, it prefers to walk along the shallow reef flats on its fins, preying on shrimp, crabs, snails, and small fish.
Colurful paracheilinus nursalim fish - Discovered in west Papua, Indonesia in 2006. The males go through an amazing courtship ritual in which "electric" colours are flashed periodically to attract nearby females.
Suckermouth catfish - The catfish was discovered during a survey in Suriname in 2005. The suckermouth exhibited by these catfish allow them to adhere to objects in their habitats, even in fast-flowing waters.
The Peacock katydid - Observed in Guyana's Acarai Mountains in 2006. It is a large rainforest insect that employs two effective strategies to protect itself from predators: at a casual glance it looks just like a dead, partially damaged leaf, but if threatened is suddenly reveals a pair of bright eye spots and starts jumping excitedly, which gives the impression of a giant head of a bird suddenly pecking at the attacker.
The RAP katydid – Discovered in 2002 in Ghana and Guinea. The species is a sit-and-wait predator, hiding on the underside of leaves, and attacking small insects that make the mistake of landing on the leaf.
Colourful platycypha eliseva dragonfly - Discovered in the Democratic Republic of Congo in 2004. Males of this species have a unique combination of colors which differentiate it from other species.
Simandoa conserfariam beetle – These interesting insects are known from a single cave in Guinea's Simandoa Range, where they were discovered them in 2002. They feed on the droppings of giant fruit bats that inhabit the cave.
Fish-hook ant - Observed in Virachey National Park, Cambodia in 2007. The large ant, measuring 1.5 cm, has a curved spine that can easily slice through skin and tend to hold on for a while.
Tiger ant - Observed in Papua New Guinea in 2009. This ant may not be as big as a tiger but it's just as ferocious and dangerous to small invertebrates in the leaf litter of rainforests. This tiny ant (about 2 mm long) walks around with its mandibles held wide open so that it can capture small invertebrates with a lightning fast snap.
The Emperor scorpion - An 8-inch long scorpion observed in Ghana in 2006. Despite their enormous size they feed primarily on termites and other small invertebrates, and its venom is not particularly harmful to humans.
Goliath bird eating spider - The largest spider in the world, reaching the weight of 170g and leg span of 30 cm was observed by scientists in Guyana in 2006. They live in burrows on the floor of lowland rainforests and despite the name feed primarily on invertebrates.
Atewa dinospider- An ancient arachnid discovered during a a 2006 expedition to Ghana’s Atewa Range Forest Reserve. The strange little creature looks like a cross between a spider and a crab, and males have their reproductive organs on their legs. They are considered quite rare, with only 57 other species known from this group throughout the world. | <urn:uuid:25b122ab-2571-48f7-b80f-10736d4aa254> | 3.421875 | 1,239 | Listicle | Science & Tech. | 48.547732 |
Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat. It is the two-dimensional analog of the length of a curve (a one-dimensional concept) or the volume of a solid (a three-dimensional concept).
The area of a shape can be measured by comparing the shape to squares of a fixed size. In the International System of Units (SI), the standard unit of area is the square metre (m2), which is the area of a square whose sides are one metre long. A shape with an area of three square metres would have the same area as three such squares. In mathematics, the unit square is defined to have area one, and the area of any other shape or surface is a dimensionless real number.
There are several well-known formulas for the areas of simple shapes such as triangles, rectangles, and circles. Using these formulas, the area of any polygon can be found by dividing the polygon into triangles. For shapes with curved boundary, calculus is usually required to compute the area. Indeed, the problem of determining the area of plane figures was a major motivation for the historical development of calculus.
For a solid shape such as a sphere, cone, or cylinder, the area of its boundary surface is called the surface area. Formulas for the surface areas of simple shapes were computed by the ancient Greeks, but computing the surface area of a more complicated shape usually requires multivariable calculus.
Area plays a important role in modern mathematics. In addition to its obvious importance in geometry and calculus, area is related to the definition of determinants in linear algebra, and is a basic property of surfaces in differential geometry. In analysis, the area of a subset of the plane is defined using Lebesgue measure, though not every subset is measurable. In general, area in higher mathematics is seen as a special case of volume for two-dimensional regions.
Every unit of length has a corresponding unit of area, namely the area of a square with the given side length. Thus areas can be measure in square metres (m2), square centimetres (cm2), square millimetres (mm2), square kilometres (km2), square feet (ft2), square yards (yd2), square miles (mi2), and so forth. Algebraically, these units can be thought of as the squares of the corresponding length units.
The SI unit of area is the square metre, which is considered an SI derived unit.
The conversion between two square units is the square of the conversion between the corresponding length units. For example, since
the relationship between square feet and square inches is
where 144 = 122 = 12 × 12. Similarly:
Though the are has fallen out of use, the hectare is still commonly used to measure land:
The acre is also commonly used to measure land areas, where
An acre is approximately 40% of a hectare. | <urn:uuid:f880aa5a-7d89-4343-8e2b-7e36ee7c5850> | 4.03125 | 640 | Knowledge Article | Science & Tech. | 37.113922 |
Elliptic and circular orbits are found for points lying on an ellipse perturbed by Gaussian errors. The Akaike information criterion is then used to judge which of the models is more complex. The controls allow you to change the magnitude of the errors and the shape of the unperturbed curve.
This Demonstration, based on the paper Kepler versus Akaike, uses the example of the Earth's orbit to show how the Akaike information criterion works for distinguishing between two models with different numbers of parameters. The points shown could be thought of as measurements of the planet's position relative to the Sun. The problem is that a circular orbit, predicting constant distance between the bodies, is always considered as the simpler one. However, the measurement error and the fact that the real orbit is not a circle causes the AIC to select the ellipse most of the time, even though it has more parameters. | <urn:uuid:1fe04f73-a26e-42d3-8fcf-522da5aeb026> | 3.375 | 187 | Documentation | Science & Tech. | 40.267097 |
On Mon, Feb 9, 2009 at 3:41 PM, Steven Buehler wrote:
> Ok, I just saw a post about using view's in mysql. I tried to look it up
> and found how to use it, but my question is: what is a view and why would
> you use it?
The problem with any definition of an object in a database is that
there are multiple definitions. Usually on the one hand you have the
definition from abstract relational theory, and on the other hand you
have the definition from actual working databases. So I am not going
to bother with a definition, I will try to explain how a view works
internally inside database code.
The easiest way to understand a view is to consider a view as a macro
that gets expanded during the execution of every query that references
that view in its FROM. Lets take for example the view that your DBA
has defined for you using:
CREATE VIEW x AS SELECT * FROM y INNER JOIN z ON y.id = z.id;
Then you query that view with the query:
SELECT a FROM x;
What the database will do for you behind the scenes is expand your
usage of the view. In effect, the database will replace "x" with its
definition. So your query SELECT a FROM x; gets expanded to:
SELECT a FROM (SELECT * FROM y INNER JOIN z ON y.id = z.id);
Notice that I have done nothing but replace x with its definition
between parenthesis. And this results in a valid query that can be
executed. And that is exactly what the database will do. It will do
this substitution and then it will run the result of that substitution
as if it were the query that you submitted.
Obviously a bit more will go on behind the scenes to handle things
like permissions and optimizations (especially if you get to databases
that have more functionality then MySQL), but this is really all there
is to it. A view is a simple macro that assigns an alias to a select
statement, and when you reference that alias the select statement will
get substituted back in.
Jochem van Dieten | <urn:uuid:c387aa61-025b-4316-a955-27e16f2e8c74> | 3.21875 | 460 | Comment Section | Software Dev. | 59.758962 |
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The Math Forum is a research and educational enterprise of the Drexel University School of Education. | <urn:uuid:86560cff-78e1-4436-a664-5339a983ab80> | 3.734375 | 156 | Tutorial | Science & Tech. | 49.725873 |
Tag: "hemisphere" at biology news
Wetlands clean selenium from agricultural runoff
...ealthy." Terry noted that the air in the northern hemisphere
already contains about 10,000 metric tons of volatile selenium from volcanoes, soil and plants. "The amount of dimethyl selenide released by wetlands would be negligible in comparison," he said. The researchers are studying ways - including using ge...
Three inferior prefrontal regions of the brain found receptive to somatosensory stimuli
...derlying frontal operculum. In contrast, the left hemisphere
equivalent only reached statistical significance in one comparison. A second strong area of activation localized to the OFC. In all cases the activation included the right anterior orbital gyrus and the neighboring lateral orbital gyrus. Additional...
Large-scale climate change linked to simultaneous population fluctuations in arctic mammals
...nter weather in Greenland and much of the northern hemisphere
is the North Atlantic Oscillation (NAO). "The North Atlantic Oscillation can be pictured as a fluctuating pressure corridor that squeezes and channels the westerly winds between North America and northern Europe, influencing the direction and speed ...
Wild plant or food plant?
...after the last ice age, inhabitants of the western hemisphere
began to select and cultivate food plants. Plant remains at archaeological sites may not be well preserved, but features often contain phytoliths, tiny silica dioxide deposits from plant tissues. These destinctive microfossils have been used increas...
Large volcanic eruptions affect the 'greener greenhouse'
Last year, scientists discovered that the northern hemisphere
was becoming increasingly greener due to increased... following Pinatubo, the land mass of the northern hemisphere
actually acted as a "carbon sink," where more carbon was taken in than was given out. The Pinatubo ...
New research sheds light on earth's largest animals
...eet and 80 tons, while blue whales in the southern hemisphere
may reach 100 feet and 120 tons. An estimated 7,0008,000 true blue whales are thought to live throughout the world. Mate's research is funded by the Marine Mammal Endowment at Oregon State University and by the Office of Naval Research....
Researchers link migratory birds' winter, summer ranges
...me of the most severe deforestation in the western hemisphere
has occurred in Haiti on the island of Hispaniola, and our results suggest a possible connection between this and declines in the southern breeding population of black-throated blue warblers." The project initially developed as a collaborative effor...
Gondwana split sorts out mammalian evolution
...go during the Cretaceous in Gondwana (the southern hemisphere
super-continent that incorporated Africa, Antarcti...here, as is commonly believed, but in the southern hemisphere
instead, in Gondwana," says Springer. "Furthermore, our study provides the first convincing molecul...
DNA deletion offers new evidence of mammals' origins
...here did each group originate? One in the southern hemisphere
and the other in the northern hemisphere. On the classic trees, the northern and southern groups are mixed up." Geological evidence supports the phylogenies as well. Mammals first appeared in the fossil record about the time continents were splittin...
A bizarre new predatory dinosaur unearthed on Madagascar
...n as abelisauroids, and recovered only on southern hemisphere
landmasses. In particular, the fossils of Masiaka...atory dinosaurs spread across much of the southern hemisphere
toward the end of dinosaur times, paralleling the Late Cretaceous radiations of small-bodied theropo...
New predatory dog-sized dinosaur unearthed on Madagascar
...atory dinosaurs spread across much of the southern hemisphere
toward the end of dinosaur times, paralleling the Late Cretaceous radiation's of small-bodied theropods (such as dromaeosaurids and ornithomimids) in the northern hemisphere. In addition, the broad geographic distribution of these small-bodi...
October Geology and GSA Today highlights
...mely fast supercooling of water in the anti-Jovian hemisphere
of Europa: A speculative model for the fracturing pattern and ascent of brines along cracks. Roberto Oyarzun et al. Europa, the icy moon of Jupiter, displays a complex array of fractures, including roughly concentric and arcuate fractures. The geome...
Turning down the Sun
...un, on the other hand, shines more in the northern hemisphere
in June, more in the southern hemisphere
in December. Surely, thought Caldeira, these very different phenomena couldn't exactly cancel each o...
Plankton are not affected by ozone depletion
...f phytoplankton growth over a year in the southern hemisphere
before and after the ozone hole appeared in the 19...tions before the hole appeared. Over the southern hemisphere
ecosystem as a whole, they found that primary phytoplankton production decreased by only about 1 per...
On the scent
...on to its own side of the brain. Because the right hemisphere
of the brain controls emotional processing, this c...nal reaction to an odour actually depends on which hemisphere
does the processing," Cahill concludes. He hopes to use brain imaging to watch how the two hemispher...
One theory solves two ancient climate paradoxes
...ing the earth 70 degrees gives large parts of each hemisphere
24 hours of sunlight for three months. If this sunlight were to fall on land, temperatures would be hotter than 125 degrees Fahrenheit in summer, but, because land cools very rapidly, during the three-month, 24-hour night, the temperatures would plum...
USGS reports that West Nile virus goes beyond crows
...le virus will find a permanent home in the western hemisphere
and what impact it will have on our native species. Periodically, the USGS issues Wildlife Health Alerts to keep natural resource agencies appraised of wildlife health or disease issues that may threaten free-ranging and captive wildlife. USGS, ...
Massive pollution documented over Indian Ocean
... becarried to the Indian Ocean during the northern hemisphere
winter by monsoonwinds from the northeast. Preliminary results indicate that aerosols in thepolluted region scatter the incoming solar radiation and reduce the amount ofenergy absorbed by the ocean surface by as much as 10 percent. "If you c...
The Sagan criteria for life revisited
... -- Earth. Above: This view of Earth's southern hemisphere
centered on the South Pole was created using images from the Galileo spacecraft taken during the December 1990 flyby. When the Galileo spaceprobe swooped by Earth in 1990, all its instruments were pointed towards us. As Galileo flew toward our pla...
INDOEX Researchers Document The Impact Of Pollutants On Climate Processes Over The Tropical Indian Ocean
... becarried to the Indian Ocean during the northern hemisphere
winter by monsoonwinds from the northeast. The Indian Ocean Experiment is investigating how thesepollutants are transported through the atmosphere and how they affect theatmospheric composition and solar radiation processes over the ocean. A majorobj...
1 2 3 | <urn:uuid:df237288-0e95-4b15-8e0b-b1cde99ecc29> | 3.09375 | 1,493 | Content Listing | Science & Tech. | 41.222291 |
Recent headlines have referred to the fact that the arctic ice has melted to a record low and many are using this as evidence to support the theory of global warming.
The earth is tilted on an axis of 23.5 degrees in relation to its orbit of the sun. This means that in winter the sun is below the horizon in Arctic, plunging the whole region into perpetual darkness and causing temperatures to plummet to around 40 to 60 degrees below zero. At this time the whole of the arctic sea freezes over, but during the summer the opposite occurs. The sun is constantly above the horizon and temperatures reach into the 30’s causing the sea ice to melt. Lately the sea ice has been melting more and more, leading some to claim that the reason is manmade global warming.
The problem is that the people who make these claims, and the authors of the articles that report on the shrinking sea ice do not take into account the history of the Arctic and the natural cycle of the sea ice. Only by studying historic records could we understand the natural variations, and put the current levels into context.
Walt Meier, a scientist at the National Snow and Ice Data Center in Boulder, Colorado, took the first steps to comparing current data with previous records and concluded that “in the context of what’s happened in the last several years and throughout the satellite record, it’s an indication that the Arctic sea ice cover is fundamentally changing.”
Unfortunately Walt just didn’t look back far enough. The “satellite record” which he used only started in 1979 when the polar orbiting satellites were brought online. His study of the 33 years of records showed that there was no change in the amount of Arctic sea ice until the late 1990’s and this lends itself to support a different theory, that the sea ice is melting at the moment because the North Atlantic Ocean is in the warming phase of its long term cooling and warming cycle known as the Atlantic Multidecadal Oscillation (AMO).
In the mid 1980’s Dr. William Gray of Colorado State University used this cycle of warming and cooling to correctly forecast the era of increased hurricane activity we are experiencing now. Another natural result of the warming and cooling cycle will be a that the sea ice melts quicker, but to test this theory we must look for historic references to the amount of sea ice present in the Arctic during a previous warming phase in the Atlantic.
During the 1930’s the North Atlantic was in such a phase, and it was reported that the Soviet ice-breaker ships were able to sail waters that had never before been open for travel, the ship Sadko even managed to sail within 500 miles of the North Pole. And the average coal shipping season at Spitsbergen, Norway almost doubled in length from 95 days from 1909-1912 to 175 days from 1930 to 1938 due to the lack of sea ice.
Maybe global warming should not be given as much credit as it is for the current extreme weathers that are being experienced around the world.
By. Charles Kennedy of Oilprice.com | <urn:uuid:4aa78f2b-bb53-43a6-a49f-1eb8c0e51ac0> | 3.734375 | 636 | Nonfiction Writing | Science & Tech. | 48.816946 |
Opening the fifth door of our advent calendar, we don’t find a recipe of how to do something cool with Perl 6 – rather an explanation of how some of the intuitiveness of the language works.
As an example, consider these two lines of code:
say 6 / 3; say 'Price: 15 Euro' ~~ /\d+/;
They print out
15, respectively. For a Perl programmer this is not surprising. But look closer: the forward slash
/ serves two very different purposes, the numerical division in the first line, and delimits a regex in the second line.
How can Perl know when a
/ means what? It certainly doesn’t look at the text after the slash to decide, because a regex can look just like normal code.
The answer is that Perl keeps track of what it expects. Most important are two things it expects: terms and operators.
A term can be literal like
"a string". After parser finds such a literal, there can either be the end of a statement (indicated by a semicolon), or an operator like
/. After an operator, the parser expects a term again.
And that’s already the answer: When the parser expects a term, a slash is recognized as the start of a regex. When it expects an operator, it counts as a numerical division operator.
This has far reaching consequences. Subroutines can be called without parenthesis, and after a subroutine name an argument list is expected, which starts with a term. On the other hand type names are followed by operators, so at parse time all type names must be known.
On the upside, many characters can be reused for two different syntaxes in a very convenient way. | <urn:uuid:30a7cc5e-cc0b-48db-9c83-2a940d5bd9f0> | 4.03125 | 366 | Documentation | Software Dev. | 56.268067 |
I am not sure where these numbers come from and the answer depends on how you encode the genome data and if you define all the redundancy (unnecessary, repetitive data) as "information".
First of all, the humane genome contains somewhere around 3.1 (men) to 3.2 (women) billion base pairs. Since the X chromosome is three times longer than the Y chromosome, women have a higher total genome length than men.
Source: "Human Genome Assembly Information" from the "Genome Reference Consortium"
A base pair is made of two of the four nucleobases adenine, cytosine, guanine and thymine, but only the four combinations AT, TA, CG and GC are possible as the A and T nucleobases won't bond with the C and G nucleobases and vice versa. These four combinations can be encoded with two bits, so that 6.2-6.4 gigabits or about 750 megabytes are required to store an exact copy of the genome.
Now, even if you need 750 megabytes to store the "raw data" from a human genome, at least a computer scientist will have a hard time defining all of this as "information". E.g. if you record 74 Minutes of complete silence on a CD, the disc contains roughly 750 megabytes of "data" as well, but actually no "information". Large parts of the human genome are repetitive, only a very small part actually differ between different individuals and from the difference, several base pair sequences only occur in a few well-defined varieties.
There is actually some research in the field "how to store a human genome as compact as possible", since genome databases most likely are going to expand rapidly and scientists need efficient ways to share data. Some tools are available for this purpose, e.g. DNAzip, which using a ~5 gigabyte dictionary (permanent data) can compress a human genome down to roughly 4 megabytes.
Source: "Human genomes as email attachments" | <urn:uuid:8b0e2eaa-d207-480f-802f-342ebccb1d6c> | 3 | 415 | Q&A Forum | Science & Tech. | 43.253793 |
Balance of the West Antarctic Ice Sheet
For several decades, measurements of the West Antarctic Ice Sheet showed it to be retreating rapidly. But new data derived from satellite-borne radar sensors show the ice sheet to be growing. Changing Antarctic ice sheets remains an area of high scientific interest, particularly in light of recent global warming concerns.
These new findings are significant because scientists estimate that sea level would rise 56 meters (1620 feet) if the ice sheet collapsed into the sea. Do these new measurements signal the end of the ice sheets 10,000-year retreat? Or, are these new satellite data simply much more accurate than the sparse ice core and surface measurements that produced the previous estimates? Another possibility is that the ice accumulation may simply indicate that the ice sheet naturally expands and retreats in regular cycles. Cryologists will grapple with these questions, and many others, as they examine the new data.
The image above depicts the region of West Antarctica where scientists measured ice speed. The fast-moving central ice streams are shown in red. Slower tributaries feeding the ice streams are shown in blue. Green areas depict
slow-moving, stable areas. Thick black lines depict the areas that collect snowfall to feed their respective ice streams.
- Ian Joughin and Slawek Tulaczyk Science Jan 18 2002: 476-480.
This image originally appeared on the Earth Observatory. Click here to view the full, original record. | <urn:uuid:2842b7ff-8dc0-4dc6-a57f-484d3677710c> | 4.09375 | 293 | Knowledge Article | Science & Tech. | 40.74 |
The largest, most violent star forming region known in the whole
Local Group of galaxies
lies in our neighboring galaxy the
Large Magellanic Cloud (LMC).
Were the Tarantula Nebula at the distance of the
Orion Nebula -- a local star forming region --
it would take up fully half the sky.
30 Doradus, the red and pink gas indicates a massive
emission nebula, although
supernova remnants and
dark nebula also exist there.
The bright knot of stars
left of center
is called R136 and contains many of the most
massive, hottest, and brightest stars known.
above image is one of the largest mosaics ever created by
observations of the
Hubble Space Telescope and has revealed unprecedented details of this enigmatic star forming region.
The image is being released to celebrate the
22nd anniversary of Hubble's launch. | <urn:uuid:f5a68c6d-584d-4742-a0ad-680b83724519> | 3.3125 | 185 | Knowledge Article | Science & Tech. | 38.610833 |
Climate change impacts in Australia
Click here for a comprehensive guide to climate change. This CANA presentation explains the science behind climate change and looks at the impacts, Australia's role, and what you can do.
The CSIRO and Bureau of Meteorology have released the State of the Climate 2012, showing that temperatures in Australia are still rising, as are greenhouse gas emissions. The forthcoming impacts of changed weather, temperature and sea-level rise will be intense and irreversible for Australia -- join the effort to ensure Australia plays its fair part in a global solution to climate change before its too late.
Climate change is likely to lead to:
- More intense storms and tropical cyclones
- Water resources will be further stressed with a greater likelihood of droughts
- The Great Barrier Reef at risk due to rising sea temperatures
- Rising sea levels threatening Kakadu National Park and parts of the east coastline
Climate change is already impacting on agriculture, weather systems and health around the world, including here in Australia. To prepare for the impacts that will come Governments and research institutes have tried to investigate how increasing uncertainty for the climate will affect food prices, homes on the coast, and the spread of disease. Green Cross Australia is helping communities in coastal Queensland share images and stories about the impacts they are already experiencing from rising sea levels in their Witness King Tides project.
A 2002 Climate Change Health Risk Assessment found that heat-related deaths in over 65’s in Australia may double by 2050 as a result of more frequent heat waves.
A report on Climate Change Risks to Australia’s Coast, found that mid-range predictions of sea-level rise this century would mean that “storm events that now happen every 10 years would happen about every 10 days in 2100. The current 1-in-100 year event could occur several times a year.” As an example, the "Pasha Bulka storm" in Newcastle in June 2007 was a 1-in-100 year scale event and saw more than 200,000 homes lose power, thousands of people forced to evacuate their homes, and insured losses exceeded $1.3 billion. The insurance industry has been collecting data on the losses they have incurred from severe weather events in the last ten years, and warn that “small changes to mean climate conditions can have disproportionate changes in damage and losses.”
The Coasts report also identified between 157,000–247,600 homes as potentially exposed to inundation with a sea-level rise scenario of 1.1 metres: nearly a third of these are in coastal NSW, with Lake Macquarie, Wyong and Gosford the worst affected.
Other studies have quantified the increase in heat-related deaths, cases of dengue fever, and water security problems in south-east Australia. While such findings are uncertain to a degree, it is clear that climate change will increasingly impact on Australian households and that reducing greenhouse pollution here and around the world is a risk-averse strategy to ameliorate those impacts.
Australia is a large continent, and each area of the country will be affected differently as world weather patterns are affected by human activity. Click on the below links to see how climate change will affect your region and the rest of Australia.
- The Department of Climate Change and Energy Efficiency aggregates climate change impact assessments Australia wide on their website
- The Coasts and Climate Change Council have released a startling report into the potential impact of sea-level rise and climate change on Australia's coasts
- The Garnaut Review has released an update paper on the latest climate science, available here.
- CSIRO’s Future Climate Change Scenarios by Region: summary and full report
- Tasmanian Coastal Vulnerability to Climate Change and Sea Level Rise
Further information about the impacts of climate change in Australia is archived here.
Climate change impacts globally
In 2009, it was estimated that around 300,000 people are dying as a result of climate change already each year.
Climate change is causing sea-level rise and changes in weather patterns and therefore agriculture and ecosystems world wide. This is already impacting on people's lives, and threatens the existence of entire nations. At a United Nations Security Council meeting in 2011, the impact of climate change on global peace security was discussed, and at the 2011 General Assembly, island nations from around the world used their voices to push for more attention to climate change, as did Suriname and a number of other c countries. You can see the summary of the plenary here.
The current famine in East Africa has been linked to changes in weather patterns and rainfall, and is devastating the lives of millions. You can give to aid gencies currently running appeals, including Oxfam, the Red Cross, Caritas, UNICEF and CARE.
In December 2010, the International Food Policy Research Institute released a report on Food Security, Farming, and Climate Change to 2050 which warned that food prices could rise by 130% by 2050 as a result of climate change. From 2007 to 2008, due partly to the multi-year drought, wheat prices in Australia jumped 42% in one year.
More information about the global impacts of climate change is archived here.
What is the Greenhouse Effect? What does it all mean?
What is a greenhouse gas? What is the greenhouse effect? Is Australia’s climate really changing? To find the answers and more, visit the CSIRO’s Atmospheric Research Group website: CSIRO has answers to your greenhouse questions.
For those who question the link between humans and climate change, New Scientist provides this useful resource.
One of the keys to finding out more about climate change is in recording and analysing the weather. The Commonwealth Bureau of Meteorology records weather information such as rainfall and temperatures from all over Australia, so they’re in a good position to tell us if anything’s changing! See what the Bureau of Meteorology is saying
In 1988 the United Nations Environment Programme (UNEP) and the World Meteorological Association (WMO) established the Intergovernmental Panel on Climate Change (IPCC). The IPCC regularly publishes scientific studies on various aspects of climate change. Their latest Assessment Report was published in 2007, and the next one is due in 2014. For more about the IPCC, go to the IPCC website
The excellent Climate Analysis Indicators Tool (CAIT) from World Resources Institute allows you to easily compare almost any greenhouse statistic across countries http://cait.wri.org
Australia's contribution to climate change
How much greenhouse gas does Australia produce?
The Department of Climate Change and Energy Efficiency produces Australia's greenhouse gas inventories, which are updated quarterly. You can access this information on their website here. In addition, DCEEE also provide forward projections of Australia's emissions.
Currently, Australia is producing more than 500 million tonnes of pollution every year and has the highest emissions per capita of any country in the developed world.
Climate change: who's responsible?
Who's responsible for the global warming we've got already?
Greenhouse gases from human activity have been accumulating in the atmosphere for at least 150 years. Developed countries are responsible for over 70% of the cumulative CO2 emissions since 1950. That's why the United Nations Framework Convention on Climate Change (UNFCCC) says that "the developed country Parties should take the lead in combating climate change". Fair enough. If we created the mess, we should be the first to start fixing it. Australia is a signatory to the UNFCCC, and you can see from the table below we do more than our share of polluting! In fact Australia pollutes IN TOTAL as much greenhouse gas as Indonesia (yes - Indonesia with 10 times our population!) | <urn:uuid:2955f1d4-943c-428b-b883-165f66a1d49b> | 3.6875 | 1,579 | Knowledge Article | Science & Tech. | 36.855952 |
|Why Not to Use Aluminum in Your Langmuir Probes|
I have made a fair number of Langmuir probes during the time I have been running experiments for my thesis. Some of the plasma facing material is aluminum, which I used because it was easy enough to machine that I could do it myself. The benefit of being able to do this myself is that the probe is built more quickly and it is easier to modify compared to the process of having the machine shop do the work. Granted, they do much better work than I possibly can, but for these probes my result is good enough even if it is not perfect.
One problem with using aluminum to make these probes is evident in the figure below. These are photographs of a probe after removing it from the plasma (it ran for a couple days inside the vacuum chamber).
If you noticed the black marks near the center of both images then you have spotted the problem. Those images show the “top” and “bottom” of my planar triple probe. There is no absolute orientation for the probe, so that is essentially a view of both burned sides.
The following figure is a diagram, from the triple probe construction download, that illustrates the basic design features of these probes. The “Head Holder” is the piece that is made from aluminum. It is used to provide centering alignment for the probe head. On a side note, the conducting tips of the probe head are electrically insulated from the probe shaft by alumina. Not to be confused with aluminum, alumina is a hard ceramic with good insulation and vacuum properties. It held its form even under the scorching laid upon it by the aluminum centering piece (head holder).
What Caused the Alumina to Burn?
The burn marks on the probe are likely caused by sputtering from the aluminum. Ions in the plasma impact the aluminum with enough force to knock some of the aluminum atoms out of the solid. In effect, it appears as though the aluminum is arcing out into the ceramic. The problem area is small, as shown in the following image. Notice how far away the burn area is from the probe tips themselves (≈ 7 cm). This is good because the further away the burn is occurring, the less likely there is an effect on the acquired probe signal. While there have been no obvious signal effects, the aluminum pieces are being replaced with stainless steel that is unlikely to demonstrate this behavior. If it does, then I will have to think of something else to remedy the problem.
Significant sputtering does not seem to be a problem for probes in which the volume between the aluminum and ceramic is minimal. The photograph below shows a probe for which there is little to no space between the protruding ceramic and aluminum centering piece. This suggests that using a different material may not solve the problem. It is possible that plasma entering through the gap between the centering piece and ceramic is related to the burn effect.
The lesson is, whether it is the root of my problem or not, that aluminum is not a good material for plasma facing components. Unless, of course, your intention is to sputter, in which case that is a great choice. If there is any interesting (i.e., burn mark) behavior from the stainless pieces I will put some pictures here.
|Initial Posting: Monday, 16 July 2007|
|Last Updated: Thursday, 14 February 2008| | <urn:uuid:4394deeb-3514-4947-abb8-643dd49dd5ba> | 2.8125 | 704 | Personal Blog | Science & Tech. | 49.681776 |
Plant and fungi phenology
Published (reviewed and quality assured)
Justification for indicator selection
Phenology is the timing of seasonal events such as budburst, flowering, dormancy, migration and hibernation. Some phenological responses are triggered by mean temperature, while others are more responsive to day length or weather extremes. Changes in phenology affect the growing season and thus ecosystem functioning and productivity. Changes in phenology are impacting farming, forestry, gardening and wildlife. The timing of tilling, sowing and harvesting is changing, fruit is ripening earlier due to warmer summer temperatures, and grass in municipal parks and on road verges requires more frequent cutting over a longer period. Changes in flowering have implications for the timing and intensity of the pollen season and related health effects. The pollen season is advancing as many species start to flower earlier, and the concentration of pollen in the air is increasing. The increasing trend in the yearly amount of airborne pollen for many taxa is more pronounced in urban than semi-natural areas across the continent.
- DEFRA, 2007. Conserving biodiversity in a changing climate Guidance on building capacity to adapt. DEFRA, UK.
- Nordic Council, 2005. Conservation of Nordic Nature in a Changing Climate. Nordic Council of Ministers, Copenhagen.
- European Commission (2011) Our life insurance, our natural capital: an EU biodiversity strategy to 2020. European Commission (2011) Our life insurance, our natural capital: an EU biodiversity strategy to 2020.
- Trends in spring phenology
Policy context and targets
In April 2009 the European Commission presented a White Paper on the framework for adaptation policies and measures to reduce the European Union's vulnerability to the impacts of climate change. The White Paper stresses the need to improve the knowledge base and to mainstream adaptation into existing and new EU policies. The European Commission will be publishing an EU Adaptation Strategy in 2013. A number of Member States have already taken action, and several have prepared national adaptation plans.
The European Commission and the European Environment Agency have developed the European Climate Adaptation Platform (Climate-ADAPT, http://climate-adapt.eea.europa.eu/) to share knowledge on observed and projected climate change and its impacts on environmental and social systems and on human health; on relevant research; on EU, national and subnational adaptation strategies and plans; and on adaptation case studies.
No targets have been specified.
Related policy documents
Climate-ADAPT: Mainstreaming adaptation in EU sector policies
Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
Climate-ADAPT: National adaptation strategies
Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
DG Climate Action: What is the EU doing about climate change?
Activities of the EU regarding climate change (both mitigation and adaptation)
White paper - Adapting to climate change: towards a European framework for action
EU framework for adaptation to climate change, leading to a comprehensive EU adaptation strategy by 2013
Key policy question
How is climate change affecting the seasonal cycle of plants and fungi in Europe?
Methodology for indicator calculation
A phenological dataset collected during the COST 725 Action ‘Establishing a European phenological data platform for climatological applications’ was analysed, which contained more than 36000 phenological time series for Europe covering 1971–2000.
Methodology for gap filling
- Estrella et al. 2009: Effects of temperature, phase type and timing, location, and human density on plant phenological responses in Europe. Estrella, N., Sparks, T. H. and Menzel, A. (2009) Effects of temperature, phase type and timing, location, and human density on plant phenological responses in Europe. Climate Research 39(3), 235–248. doi:10.3354/cr00818
EEA data references
- No datasets have been specified here.
External data references
Data sources in latest figures
Data sets uncertainty
Generally, observations for popular groups such as vascular plants, birds, other terrestrial vertebrates and butterflies are much better than for less conspicuous and less popular species. Similarly, due to extensive existing networks, a long tradition and better means of detection and rapid responses of the organisms to changes, knowledge on phenological changes are better observed and recorded than range shifts. Projections of climate change impacts on phenology rely crucially on the understanding of current processes and responses. For most cases, only a few years of data are available and do not cover the entire area of the EU but are restricted to certain well monitored countries with a long tradition in the involvement of citizen scientists. Based on these short time series, the determination of impacts and their interpretation thus has to rely on assumptions, and achieving a qualitative understanding of species’ responses is more robust than their quantification. One of the greatest unknowns is how quickly and closely species will alter their phenology in accordance to a changing climatic regime. Even experimental studies seem to be of little help, since they notoriously tend to underestimate the effects of climate change on changes in phenology.
Further information on uncertainties is provided in Section 1.7 of the EEA report on Climate change, impacts, and vulnerability in Europe 2012 (http://www.eea.europa.eu/publications/climate-impacts-and-vulnerability-2012/)
No uncertainty has been specified
Short term work
Work specified here requires to be completed within 1 year from now.
Long term work
Work specified here will require more than 1 year (from now) to be completed.
Responsibility and ownership
EEA Contact InfoHans-Martin Füssel
Typology: Descriptive indicator (Type A – What is happening to the environment and to humans?) | <urn:uuid:183a3a2a-9858-4dee-8044-1a19e82cfeda> | 3.171875 | 1,191 | Structured Data | Science & Tech. | 21.351239 |
The cygwin tools aim to provide a
unix-style API on top of the windows libraries, to facilitate ports of
unix software to windows. To this end, they introduce a unix-style
directory hierarchy under some root directory (typically
everything built against the cygwin API (including the cygwin tools
and programs compiled with cygwin's ghc) will see / as the root of
their file system, happily pretending to work in a typical unix
environment, and finding things like
ever explicitly bothering with their actual location on the windows
GHC, by default, no longer depends on cygwin, but is a native
windows program. It is built using mingw, and it uses mingw's ghc
while compiling your Haskell sources (even if you call it from
cygwin's bash), but what matters here is that - just like any other
normal windows program - neither GHC nor the executables it produces
are aware of cygwin's pretended unix hierarchy. GHC will happily
accept either '/' or '\' as path separators, but it won't know where
or the like. This causes all
kinds of fun when GHC is used from within cygwin's bash, or in
make-sessions running under cygwin.
Don't use absolute paths in make, configure & co if there is any chance that those might be passed to GHC (or to GHC-compiled programs). Relative paths are fine because cygwin tools are happy with them and GHC accepts '/' as path-separator. And relative paths don't depend on where cygwin's root directory is located, or on which partition or network drive your source tree happens to reside, as long as you 'cd' there first.
If you have to use absolute paths (beware of the innocent-looking
ROOT=`pwd` in makefile hierarchies or configure scripts), cygwin provides
a tool called cygpath that can convert cygwin's unix-style paths to their
actual windows-style counterparts. Many cygwin tools actually accept
absolute windows-style paths (remember, though, that you either need
to escape '\' or convert '\' to '/'), so you should be fine just using those
everywhere. If you need to use tools that do some kind of path-mangling
that depends on unix-style paths (one fun example is trying to interpret ':'
as a separator in path lists..), you can still try to convert paths using
cygpath just before they are passed to GHC and friends.
If you don't have cygpath, you probably don't have cygwin and hence no problems with it... unless you want to write one build process for several platforms. Again, relative paths are your friend, but if you have to use absolute paths, and don't want to use different tools on different platforms, you can simply write a short Haskell program to print the current directory (thanks to George Russell for this idea): compiled with GHC, this will give you the view of the file system that GHC depends on (which will differ depending on whether GHC is compiled with cygwin's gcc or mingw's gcc or on a real unix system..) - that little program can also deal with escaping '\' in paths. Apart from the banner and the startup time, something like this would also do:
$ echo "Directory.getCurrentDirectory >>= putStrLn . init . tail . show " | ghci | <urn:uuid:5aca12f6-d8d3-400f-a6d1-769064d90d52> | 2.8125 | 741 | Documentation | Software Dev. | 51.316554 |
Rotation curves of disk galaxies rise steeply in their inner regions and then remain roughly flat out to the last point measured. To explain these observations within the framework of Newtonian gravity, a considerable amount of unseen mass is required.
The idea that unseen matter is needed to account for the rotation velocity curves of disk galaxies was put forward by Freeman (1970):
there must be undetected matter beyond the optical extent of NGC 300; its mass must be at least of the same order as the mass of the detected galaxy.The implications of this idea made it controversial; many wondered if dark matter on galactic scales is unavoidable. Kalnajis (1983) showed that within the radii accessible to optical spectroscopy, the rotation curves of disk galaxies could be well-fit without any dark matter. Indeed, a truncated exponential disk and a de Vaucouleurs bulge can be combined to yield a rotation curve which is flat to about 10% out to four times the disk's scale length r_0 (van Albada et al. 1985). Thus neutral-hydrogen (HI) observations like Freeman's, extending well beyond the optical radii of galaxies, were required to establish the presence of dark matter.
While optical spectroscopy couldn't prove that dark halos exist, rotation curves measured using optical emission lines were important in posing the problem of dark matter in disk galaxies. Results of optical studies are reviewed by Rubin (1983). These show that most disk galaxies have rotation curves which rise at small radii and then level off. For galaxies of a given morphological type (e.g. Sc) the shape of the rotation curve shows a systematic trend with luminosity: low-luminosity galaxies show a fairly gradual rise, while in high-luminosity galaxies the rotation curve rises sharply and then levels off or even drops slightly.
Radio-synthesis velocity maps of neutral hydrogen emission provide the most convincing evidence for dark matter (e.g. Carignan & Freeman 1985). In NGC 3198 the rotation curve has been measured to 11 r_0, or about 30 kpc for H_0 = 75 km/sec/Mpc (van Albada et al. 1985). Over such radii most galactic disks are slightly warped, and NGC 3198 is no exception. The warped disk is modeled as a set of concentric circular rings with inclinations varying fairly smoothly from 72 degrees at the center to 76 degrees at the edge. The fitted circular velocity of each ring, plotted against its radius, defines the rotation curve. After rising fairly slowly to a peak value of 157 km/sec at about 3 r_0, the rotation curve does not fall significantly below 150 km/sec out to the last point measured.
The rotation curve of NGC 3198 can be modeled by combining the gravitational forces of
The disk has the usual surface-density profile,
(1) Sigma(R) = Sigma_0 exp(-R/r_0) ,where Sigma_0 is the central surface density and r_0 is the disk scale length. For such a mass distribution the circular speed in the plane of the disk is
2 2 (2) v_d (R) = 4 pi G Sigma_0 r_0 y (I_0(y)K_0(y) - I_1(y)K_1(y)) ,where y = R/(2r_0) and I_n(y) and K_n(y) are modified Bessel functions of the first and second kinds (BT87, Ch. 2.6.3(b)).
The halo is assigned the space density profile
rho_h(0) (3) rho_h(r) = --------------- , 1 + (r/a)^gammawhere r is the spherical radius, a sets the halo length scale, and -gamma is the asymptotic slope of the profile at large r. The core radius of the halo, defined by rho_h(r_core) = rho_h(0)/2^1.5 (roughly, the 3-D equivalent of the `half central surface density' definition used observationally) is
1.5 (1/gamma) (4) r_core = a (2 - 1) .Since the halo is assumed to be spherical the circular speed is
2 M_h(r) 4pi G / 2 (5) v_h (r) = G ------ = ----- | dr r rho_h(r) . r r /
The rotation curve in the plane of the disk is found by adding the disk and halo contributions in quadrature:
2 2 1/2 (6) v_c(R) = (v_d (R) + v_h (R)) .Assuming that the observed disk has a constant M/L ratio, the disk scale length is r_0 = 2.68 kpc. Good fits to the observed rotation curve can be obtained for a wide range of model parameters; even more so than in fitting luminosity profiles, the problem of modeling galactic rotation curves is severely underconstrained. The model with the maximum disk mass has a disk mass-to-light ratio of M/L_B = 3.6, consistent with a disk-type stellar population. But even this choice does not `nail down' the halo model; the slope and scale parameters may be varied in a correlated fashion over the range 1.9 < gamma < 2.9, 7 < a < 12 kpc. The halo core radius is somewhat better determined, with `subjective' 1-sigma limits of r_core = 12.5 +/- 1.5 kpc. Within the last point measured at 30kpc the total disk mass is 3 10^10 solar masses and the total halo mass is about 4 times greater. The detected neutral hydrogen amounts to 5 10^9 solar masses, or about 15% of the maximum disk mass (van Albada et al. 1985).
Rotation curves imply the presence of significant amounts of dark matter but provide little constraint on the shape of the dark matter distribution. A highly flattened and dynamically cold dark matter distribution would run afoul of the same stability problem afflicting ``bare'' disk galaxies, but few other a priori constraints are available.
Gas orbits in the disk plane provide some information about halo shapes. The gas settles onto closed, non-intersecting orbits. In an axisymmetric potential such orbits will be circular, but a non-axisymmetric halo will force the gas onto non-circular orbits. Non-axisymmetric halos may cause oval distortions in some disk galaxies (Kormendy 1982) and kinematic asymmetries in HI maps (e.g. MB87, Fig. 8-31). Asymmetries in the Milky Way's HI kinematics have been attributed to a rotating triaxial halo (Blitz & Spergel 1991). But non-axisymmetric halos will also increase the scatter in the Tully & Fisher (1977) relationship between luminosity and circular velocity; by comparing the observed and predicted scatter, Franx & de Zeeuw (1992) conclude that the potentials of typical disk galaxies can be no flatter than about 0.9:1 in the disk plane. Stronger limits are available in special cases; for example, the potential of the E/S0 galaxy IC 2006 is axisymmetric to better than 0.98:1 (Franx, van Gorkom, & de Zeeuw 1994).
The three-dimensional shape of a disk galaxy's potential can only be inferred from tracers which travel far from the plane of the disk. Polar-ring galaxies are therefore important for discussions of halo shapes; these are S0 galaxies with rings or disks of gas and stars in polar orbits. Such rings probably form via mergers or mass transfers (Schweizer, Whitmore, & Rubin 1983).
Early studies established that the central objects are fairly normal S0 galaxies seen roughly edge-on; in particular, these objects exhibit the rapid rotation characteristic of S0 disks. Observed rotation velocities in the disk plane and in the ring plane are comparable. Simple models in which the potential is halo-dominated then imply that the dark halos of these systems are nearly spherical (Whitmore, McElroy, & Schweizer 1987).
However, more sophisticated models including the gravitational potentials of the central galaxy and polar ring appear to rule out a spherical halo for the polar-ring galaxy NGC 4650A. These models fit the ring with a mass significantly greater than the observed HI mass (Sackett & Sparke 1990); presumably the stellar component of the ring accounts for the difference, though the blue colors of this population (Whitmore et al. 1987) imply a relatively low mass-to-light ratio. Best-fit halo models have minor axis ratios between 0.3:1 and 0.4:1 (Sackett et al. 1994). This is comparable to the axial ratio of the central S0; in this case the dark matter appears to be as strongly flattened as the luminosity!
Besides the apparent coincidence of shapes just mentioned, yet another coincidence demands explanation: Bahcall & Casertano (1985) argue that ``at least one parameter of a two-component mass model must be finely tuned in order to reproduce the observed flatness of... rotation curve[s]''. At small radii, the rotation velocities of disk galaxies are set by the luminous components, while at large radii they are set by the dark matter. It appears that these two components must ``conspire'' to produce rotation curves which remain flat to many times the disk scale length, r_0 (van Albada & Scancisi 1986).
Recent studies have somewhat blunted the teeth of this conspiracy. For one thing, rotation curves are not invariably flat; low-luminosity disk galaxies exhibit gently rising rotation curves, while high-luminosity disk galaxies have rotation curves which peak at about 2 r_0 and gently decline further out (Ruben et al. 1985, Casertano & van Gorkom 1991). Moreover, at least part of the proposed conspiracy may be explained by the dynamical response of a pre-existing dark halo as a disk slowly grows inside it (Blumenthal et al. 1986, Barnes 1987, Athanassoula 1988, Ryden 1991).
But the shapes of halos may provide fresh evidence for conspiracy theorists. Numerical simulations of clustering in a universe full of Cold Dark Matter (Blumenthal et al. 1984) generally yield strongly triaxial halos with minor axis ratios no flatter than about 0.4:1 (Frenk et al. 1988, Dubinski & Carlberg 1991). Halos as flat as the one attributed to NGC 4650A seem to be excluded and may even be dynamically unstable. Moreover, while the gravity of the luminous material may pull the halo in radially, it's much less effective at flattening a dynamically hot mass distribution (e.g. Barnes 1987). Highly flattened yet axisymmetric halos would be easier to explain if dark matter is baryonic and dissipative (e.g. Pfenniger, Combes, & Martinet 1994).
The evidence indicates that dark halos are many times more massive than visible galaxies, that the dark matter is much more extended than the luminous component, that the core radii of dark halos are relatively large, and that halos are somewhat but not extremely flattened (e.g. Trimble 1987, Ashman 1992). These conclusions echo those previously reached -- on the basis of generally weaker evidence -- for halos of elliptical galaxies.
Nonetheless, the above explanations for flat rotation curves would be in trouble if the gas was the only tracer providing evidence for massive halos. But in fact, there is ample evidence for massive halos from other observations (BT87, Ch. 10). In the Milky Way, maximum stellar velocities in the solar neighborhood imply that our galaxy has a potential well deeper than the visible matter alone can generate; velocities of globular clusters and satellite galaxies do not show the fall-off with radius expected in a Keplerian potential, and the tidal forces required to explain the truncations of these systems and the tearing-off of the Magellanic Stream likewise demand more mass than is seen in stars and gas. The present motion of the Milky Way and M31 toward each other implies a total mass at least ten times the luminous mass of these galaxies, and the orbits of binary galaxies seem to be inconsistent with Keplerian potentials. Finally, not only gas and stars but even light seems to respond to the gravitational field of the dark matter in galaxy halos; distortions of background galaxies may be attributed to weak gravitational lensing by halos extending to at least 100 kpc (Brainerd, Blandford, & Smail 1996).
Last modified: April 14, 1997 | <urn:uuid:49e8a0e6-0c85-4cba-b038-5b522e92dc60> | 3.28125 | 2,725 | Academic Writing | Science & Tech. | 52.503037 |
Math.atan --- To Degrees Help
Hi, I've hit a snag. I've got this rather long piece of code that I'm working on, here's the issue area
I'm trying to convert (180/n) to degrees and then take the tangent of it for use in the equation TotalArea. I've been at it for a solid 30 minutes and just can't get it to work. I'm new to java and this is my first time using any of the Math methods (besides Math.pow). The double "TotalArea" has already been predefined earlier, as well as the String "d".
//input number of sides and side length
int n = Integer.parseInt(d); //number of sides
String Ss = JOptionPane.showInputDialog(null, "Enter the length of the side: ", n + "-GON", JOptionPane.QUESTION_MESSAGE);
double s = Double.parseDouble(Ss); //side length
//calculate area and perimeter ----begin problem area
double deg = (Math.toDegrees(180 / n)); //converts radians to degrees
double part = Math.atan(deg); //part is a part of the equation that deals with the tangent of some angle (180/n)
TotalArea = (((s * s) * n)/ (4 * (part)));
System.out.println(TotalArea); //----end problem area
The program compiles without error, i'm just getting the wrong output.
ps. the code is to calculate the area of an N-sided regular polygon where s is the side length and n is the number of sides, if that helps.
Thanks in advance!
Re: Math.atan --- To Degrees Help
That would mean that 180/n is twice the angle subtended at the centre by a side in degrees. If you want to find its tangent you would convert it to radians.
the code is to calculate the area of an N-sided regular polygon where s is the side length and n is the number of sides
Also notice that atan() finds the arctangent (aka inverse tangent - it finds an angle whose tangent is equal to the argument). The comment in the code would indicate you want Math.tan(). But trigonometry would indicate that Math.sin() would be more useful. | <urn:uuid:025693dc-9580-4186-ad09-e98077d05372> | 3.109375 | 513 | Comment Section | Software Dev. | 72.728164 |
What is the phenomenon called when light is bent due to
heat (ie those waves you "see" over your bbq grill or behind a jet engine?
The phenomenon is called refraction. This is due to the differences of the
index of refraction due to temperature differences in the air. On a large
scale, you can get a mirage.
There is a special type of photography called schlieren where regions of
varying refraction in a transparent medium (usually temperature or pressure
differences) are detectable. They are photographed by passing light through
---Nathan A. Unterman---
It's called refraction. The bending of light isn't intrinsically due to
heat; it's because the hot air above your grill, or in a low spot in a
road, is less dense than the surrounding air. The speed of light is
different in these two bodies of air (slower in the denser medium), and the
light bends toward the denser medium.
Richard Barrans Jr., Ph.D.
This is refraction, just like with a glass lens. The hot air over the grill
(behind the engine) is less dense than the rest of the air. The light travels
at a different speed through the less dense air than it does in the more dense
(normal) air. This results in bending the light.
It is called the refraction of light or bending of light due to a change in
medium (what the light is traveling through). The heated air has a
different "density" then the air around it so the light rays bend as they
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:595466d6-b4f5-4835-8b9a-1aa84d781da8> | 3.515625 | 351 | Q&A Forum | Science & Tech. | 65.19651 |
(PHP 4, PHP 5)
base_convert — Convert a number between arbitrary bases
Returns a string containing number represented in base tobase. The base in which number is given is specified in frombase. Both frombase and tobase have to be between 2 and 36, inclusive. Digits in numbers with a base higher than 10 will be represented with the letters a-z, with a meaning 10, b meaning 11 and z meaning 35.
base_convert() may lose precision on large numbers due to properties related to the internal "double" or "float" type used. Please see the Floating point numbers section in the manual for more specific information and limitations.
The number to convert
The base number is in
The base to convert number to
number converted to base tobase
Example #1 base_convert() example
$hexadecimal = 'A37334';
echo base_convert($hexadecimal, 16, 2);
The above example will output:
- intval() - Get the integer value of a variable | <urn:uuid:647739be-72cb-4c8a-b08e-031e98620785> | 3.4375 | 223 | Documentation | Software Dev. | 37.64 |
Atomic physics topics related to nuclear power?
View Single Post
Sep19-06, 10:14 AM
Thanks for clearing that up :)
What process is used to separate for instance plutonium from the waste and how efficient is it? Does a substantial ammount of plutonium get left in the waste after extraction? | <urn:uuid:2c816400-2bbd-421d-992f-da64e01393a0> | 2.71875 | 64 | Comment Section | Science & Tech. | 57.942333 |
Secant right-hand side
In geometry, the relative position of two lines, or a line and a Curve, can be qualified by the adjective secant . This one comes from the Latin secare , which means to cross. In mathematical terms, a line is secant on another line, or more generally with a curve, when it has a nonempty intersection with this one.
To carry out the study of a curve in the vicinity of one of its points P , it is useful to consider the secants resulting from P , i.e. the lines passing by P and another point Q of the curve. It is starting from these secants that the concept is defined of tangent with the curve at the point P : it is about secant the line limit, when it exists, resulting from P when the second point Q approaches P along the curve.
So when Q is sufficiently close to P , the secant can be regarded as an approximation of the tangent.
In the particular case of the curve representative of a numerical function y=f (X) , the Pente of the tangent is the limiting of the slope of the secants, which gives a geometrical interpretation of the Dérivabilité of a function.
Bond between the concepts of secant function and secant lineLet us consider a reality θ. Let us draw a secant line with the Cercle unit (centered with the origin) which passes by the origin and the point (cos θ, sin θ), not of the circle whose vector image forms an angle θ with the directing vector of the x-axis. The absolute Value of the secant trigonometrical of θ is equal to the length of the segment secant line energy of the origin until the line of equation X = 1. If the segment passes by the point (cos θ, sin θ), then the trigonometrical secant of θ is positive, if it passes by the antipodean Point, then the secant of θ is negative.
Approximation by a secantLet us consider the curve of equation there = F ( X ) in a Cartesian Frame of reference, and consider a point P of coordinated ( C , F ( C )), and another point Q of coordinates ( C + Δ X , F ( C + Δ X )). Then the Slope m secant line, not passing P and Q , is given by:
The member of right-hand side of the preceding equation is the report/ratio of Newton in C (or rate of increase). When Δ X approaches zero, this report/ratio approaches the derived number F ( C ), by supposing the existence of the derivative.
- Infinitesimal calculus
|Random links:||University of advanced industrial technologies | Saint-Blaise-of-boxwood | Orthodoxe church autocéphale Ukrainian canonical | Coupe Davis 1986 | Achéménès | Codasyl| | <urn:uuid:5c1d3944-9490-4602-b004-edb73a3bd037> | 4.09375 | 620 | Knowledge Article | Science & Tech. | 46.270048 |
This animated image shows heat rising in convection currents from the
outer boundary of the core and cooling at the surface.
Cooling History, part 2
The heat of a body has the power to control activity because energy must be transported from the warmest spots to the coolest spots by whatever means is possible. The process of cooling causes activities on a planet.
Planetary bodies cool by way of:
- 1.) convection of material inside the body, which brings hot material from the deep interior closer to the surface
- 2.) volcanism, which brings hot material to the surface
- 3.) motions in the atmosphere and oceans, where air/water is carried from the warm equatorial regions to the cooler poles
- 4.) radiation of infrared energy (heat) directly to space from the
If a planet is small, it can cool much faster to space than can a body which is larger.
Earth has had a long a complicated cooling history. An understanding of the Earth's history might begin with the record of geologic time.
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Many kinds of surface features are clues that our lithosphere is sliding. Two types of features can form when plates move apart. At mid ocean ridges, the bottom of the sea splits apart and new crust is...more | <urn:uuid:d8698ae1-cb39-4a90-b8a6-9245ad2c278f> | 4.46875 | 557 | Content Listing | Science & Tech. | 64.32145 |
The Doppler shift is something we are all familiar with. The classic acoustic Doppler shift is observed every time an emergency vehicle goes by with its siren on. When it is approaching the tone sounds higher than when it is receding from us. This is because the sound emitter is moving as it emits and this compresses the wavelength for sound traveling in the same direction as the emitter. For sound emitted in the opposite direction, the sound wave is stretched and the tone lowered. The Doppler shift also effects light, making colors emitted by excited atoms either redder or bluer depending on whether they are receding or approaching.
Although we tend to think of the Doppler shift as something astronomical, with the red shift providing a distance measure for observations, spectroscopists also encounter the Doppler shift every day when measuring the colors of light that atoms (and molecules) absorb. This is because the atoms are moving all the time and the light they would normally absorb at rest is red or blue shifted depending on whether the atom is moving with the light or into the light. Since the atoms are moving in every direction with a distribution of speeds, the atoms absorb a much broader range of colors than its natural properties would lead one to expect, this is called Doppler broadening.
However, the translation movement of the atoms is not the only Doppler shift available, rotation can also lead to a Doppler shift. This rotational Doppler shift is considerably smaller than the translational Doppler shift making it hard to observe. In addition, to observe rotational Doppler broadening the atom must gain or loose a unit of angular momentum during the absorption. Light beams carry their angular momentum in the way the orientation of their electric field changes. Linearly polarized light, where the electric field oscillates in a plane, has no angular momentum. Circularly polarized light, where the electric field traces out a circle, has spin angular momentum. However, the observation of rotational Doppler broadening requires light with orbital angular momentum, called twisted light because the electric field traces out a crazy corkscrew (see the movie*).
To observe the rotational Doppler broadening, researchers illuminated a cell of Rubidium atoms with two twisted light beams. These two beams were aligned such that the translational Doppler shift and a smaller Doppler shift due to the curvature of the light wavefronts exactly canceled out leaving only the rotational Doppler shift. The light beams imparted the atoms with an angular momentum equal to the difference in angular momentum between the two beams. When they had the same angular momentum, no Doppler broadening was observed and the natural absorption of the atom was found. However, as the angular momentum difference between the two beams was increased, the Doppler broadening increased.
The rotational Doppler shift, as seen through the broadening of an atomic absorption line was predicted a while ago. Indirect observations had indicated that it was probably as predicted. However, a direct observation is always the best way to confirm something and it is good to see it happen. It also gave me an excuse to make a cool movie.
*This movie is not just a twisted light beam, however, it shows all the right features. | <urn:uuid:08863c67-c610-4f14-bb09-50025f43da23> | 3.609375 | 678 | Personal Blog | Science & Tech. | 36.223856 |
PORT ANGELES, Wash. — Larry Ward stands on the banks of a gravel-lined channel two miles from the mouth of the Elwha River at what will one day be the point at which adult salmon returning from the ocean come back to spawn, mixing with young smolts on their way out to the open waters.
Ward is the head of the Lower Elwha Klallam Tribe’s new hatchery – which was finished last May. A couple hundred yards from the river, inside the hatchery facility, long concrete troughs hold thousands of juvenile coho salmon, their dappled bodies flickering in the sun.
There are about 600,000 fish in the hatchery – steelhead and coho salmon for now – but Ward wants to see that number increase.
“Ultimately I think we’re looking for thousands of adults coming back to the hatchery, chum salmon, coho, steelhead, hopefully pink and producing upwards of a million and a half or two million fish to be released,” he says.
Part I (Tuesday): Scientists are getting the “before” shot of the Elwha so they can see how things change once the river is dam-free.
Part II (Wednesday): Keeping track of river otters to better understand a changing river and its impact on the forest ecosystem.
Part III (Today): The Lower Elwha Klallam Tribe is counting on hatcheries to hasten the return of its subsistence fisheries.
Across the way from the coho troughs, large asphalt ponds sparkle with steelhead – about 80,000 in each pond. Ward explains that only about 150 wild steelhead return to the Elwha each year. It’s a critically depressed stock, Ward explains.
“That’s why we’ve gone to this extra measure to go out and go through this effort to rear the population captively in the hatchery to try and increase the number of fish that are available,” he says.
The Elwha’s First Class Steelhead
You might look at these captive steelhead as sort of the “freshman class” of the new Elwha. They will be one of the first generations to have access to the waters above the dams when they return from the ocean in a couple years. Ward says hatcheries play a role in speeding up the recovery of salmon stocks in this river once the dams come out. However, this is the largest dam removal in history, so no one really knows how long it will take wild runs of salmon to return to this watershed. Some scientific estimates point to 40 to 60 years. To members of the Lower Elwha Klallam Tribe, whose reservation is at the mouth of the Elwha, that’s too long to wait. They’re hoping the hatchery will restore the salmon fishery here within a decade or so.
Mike McHenry is a fisheries biologist with the Lower Elwha Klallam Tribe. He says there’s been much debate over hatcheries on the Elwha.
“It’s probably one of the most controversial things about the whole Elwha project, this philosophical divide between folks that want to use hatcheries for recovery and those that feel it should be a totally natural recolonization experiment,” he says.
McHenry sits right on the fence on this one. He says hatcheries could be a lifeline for the wild fish population that might suffer during a potentially massive flush of sediment into the river during dam removal. But he and other scientists take issue with the type of fish that will be raised in the hatchery — focusing on one fish in particular: The Chambers Creek steelhead. This fish, from a Tacoma, Wash. stream of the same name, is not native to the Elwha but it’s become popular as a hatchery fish in the Northwest because it grows about twice as fast as wild steelhead and returns early.
McHenry says there’s concern about Chambers Creek steelhead interbreeding with native fish. Chambers Creek smolts also grow faster than wild steelhead and tend to prey on other types of salmon.
Fred Utter is an expert on fish genetics. He worked for the National Marine Fisheries Service for 30 years before becoming a professor at the University of Washington. He says Chambers Creek steelhead are great for maintaining a sport fishery,
“But,” he adds, “It by no means should ever be used as a fish to restore natural populations in the Elwha. I think that would be a serious mistake.”
The Waiting Game
The Lower Elwha Klallam Tribe has been without healthy salmon runs for almost 100 years and they’re tired of waiting. Rob Elofson, a member of the Lower Elwha Klallam Tribe and director of the River Restoration effort, says hatchery-raised Chambers Creek steelhead have been a good supplement to the depleted wild runs, but that’s not a permanent solution. “The idea would be that when our harvest of other salmon in the river reaches a certain point then we can phase out the Chambers Creek.”
As the different runs of salmon balance themselves out, the tribe plans to phase out the entire fish hatchery. But no one knows exactly how long that will take or how hatchery fish might affect the balance of salmon runs here in the long term. As the fish, both hatchery and wild, make it into the upper reaches of the river in the coming years, Elofson’s dream is to follow them.
“I’m hoping that I can go up to Elkhorn and catch a salmon and cook it up for dinner. That would be ideal,” Elofson says, smiling, “because then I’d still be young enough to hike up to Elkhorn.… it’s about 27 miles upstream from the mouth of the Elwha.”
From here on out, all eyes will be on the Elwha as this much-studied, much-debated and much-loved river resumes her natural course from the Olympic Mountains to the Pacific.
(Text and audio by Ashley Ahearn. Video and photos by Katie Campbell.)
Share your experiences as part of EarthFix's Public Insight Network.
Join our Public Insight Network! | <urn:uuid:d0dbbf21-e7eb-427d-91cf-0eea250ae317> | 2.890625 | 1,337 | Truncated | Science & Tech. | 56.804959 |
7 characteristics of Protists
· It is a single celled organism.
· Some are predators and resemble animals.
· All protists are eukaryotic (have a nucleus).
· Protists are classified by the way they obtain energy.
· Biologists identified about 65,000 different types of protozoa, almost half are extinct species from fossils.
· Many species are free living while others are parasites. | <urn:uuid:4d308768-17a5-4fc5-aee7-8d50f3e14eb3> | 3.578125 | 88 | Listicle | Science & Tech. | 32.445132 |
A chacma baboon.
Célérier et al. (2010) uses mice to assess the relatedness of chacma baboons (Papio ursinus) through olfactory cues. But, why mice you asked?
Human noses are often quite weak compared with the rest of the animal kingdom, making it hard for us to find out if baboons can be told apart by smell. Researchers therefore decided to draft much better noses — those of mice. The researchers swabbed the armpits and groins of wild chacma baboons (Papio ursinus) from two different troops of the primates in Namibia. They next tested 24 adult male Swiss mice to scents from 14 adult female baboons. They chose female baboons partly because "some male mice were peeing on male baboon odors as if they were in competition," said researcher Aurélie Célérier, a behavioral biologist at the CNRS and the University of Montpellier II, France.
Their research shows that mice can detect odor differences between individuals of the same sex and age class in another mammal species, and that the mice can perceive a higher similarity between baboons that are related than baboons that are unrelated. These results show that olfactory cues may play a role assessing the degree of relatedness in among individual baboons. Detective mice assess relatedness in baboons using olfactory cues by Célérier et al. (2010) was published on The Journal of Experimental Biology. Also read Detective Mice Help Scientists Study Baboons by Charles Q. Choi on LiveScience. | <urn:uuid:8437db20-ad14-4ab8-80b5-ad9701b40a9c> | 4 | 332 | Personal Blog | Science & Tech. | 42.858064 |
Avian Demography Unit
Department of Statistical Sciences
University of Cape Town
|BIRD NUMBERS||Volume 10 Number 1, July 2001|
16. Notes on the birds and other animals recorded at the Cunene River mouth from 6-8 January 2001
M.D. Anderson*, R.A. Anderson, S.L. Anderson, T.A. Anderson,
The Cunene River is the third-largest Namibian river, emerging in the Atlantic Ocean approximately 1000 km from its source. The banks of the river do not have extensive riparian vegetation and the lagoon and vegetated islands at the mouth are probably the most biologically productive areas on the lower Cunene River. The mouth and lagoon have been described in detail by Simmons et al. (1993) and Simmons et al. (1998).
The Cunene River mouth never supports large numbers of waterbirds, but it is nevertheless an important staging and feeding area for waders, probably as a result of its isolated location along the Atlantic coast. The nearest permanent wetland is Walvis Bay, some 700 km away. The low number of waterbirds can be attributed partly to the relatively small area of the mouth and suitable waterbird habitats. For example, the area of exposed sand and mudflats when the river flow is low is only 125 ha and there are only thin strips of riparian vegetation along the banks and on several small islands (Simmons et al. 1998).
Despite the low numerical abundance of waterbirds, the Cunene River mouth regularly supports the second-largest wetland species total in Namibia and 72 species have been recorded. This wetland is recognized as an Important Bird Area because of significant populations of Damara Tern, White Pelican, Chestnutbanded Plover and a few other species (Simmons et al. 1998).
Although waterbird surveys have been conducted at the Cunene River mouth during the period 1982–2000 (Ryan et al. 1984; Braine 1990; Simmons et al. 1993), it is less frequently counted than other important Namibian wetlands. The aim of this January 2001 study was to count the waterbirds and terrestrial birds at the Cunene River mouth.
The waterbird survey was conducted from 08h15–13h00 on 7 January 2001. We divided into three groups (each comprising three people; two observers and a scribe) and simultaneously counted three separate areas. These areas were (1) the northern and southern beach areas adjacent to the mouth opening, (2) the 1.9 km section of the river from our campsite (17°15'316''S, 11°45'544''E) to the river mouth (17°14'434''S, 11°45'133''E), which included the islands, sandbars, and large lagoon on the southern bank, and (3) the river section from the campsite upstream to opposite the Foz do Cunene (17°16'065''S, 11°47'020''E), a length of 2.3 km. The total straight-line distance of the river that was surveyed was approximately 4.2 km. Simmons et al. (1998) considered the section of the Cunene River up to 4 km from the coast to constitute the river mouth.
The waterbird survey was conducted with the aid of binoculars and spotting scopes. Although we did not have a boat and thus were not able to access the islands and the Angolan bank, an attempt was made to survey these areas from the southern bank. Nevertheless, it is likely that many birds present on the northern bank, islands and reedbeds were not counted and the results of the survey therefore represent a minimum species and population estimate.
All terrestrial birds were also counted during the waterbird survey and additional species recorded during the duration of our three-day stay were also noted. For some waterbirds, such as White Pelican, we conducted additional counts in order to obtain maximum numbers for these species. Notes were also kept of all mammals and reptiles observed.
Dirk Heinrich set up seven mistnets on the mudflats, reedbeds and a small accessible reedbed island throughout the three-day period. On some occasions, strong southwesterly winds prevented continuous netting operations and the nets were then closed. All captured birds were weighed, measured, ringed and released.
During the survey a total of 2452 birds of 61 species were recorded (Table 1). Waterbirds significantly outnumbered terrestrial birds, with only 155 individuals of 20 different terrestrial bird species being recorded – an indication of the extremely arid nature of the surrounding terrestrial habitats (Table 1).
Seven waterbird species were observed which have not been recorded during four previous comprehensive surveys (Ryan et al. 1984; Braine 1990; Simmons et al. 1993), namely Yellowbilled Egret, Dwarf Bittern, Cape Shoveller, African Crake, Wood Sandpiper, Baird’s Sandpiper and Yellow Wagtail. Some species, such as Yellowbilled Egret and African Crake, have been recorded at other localities in the Skeleton Coast Park (Braine 1988). Forty-three species of waterbirds recorded during the previous surveys were not observed during our January 2001 visit.
Unusual birds recording during the survey included Baird’s Sandpiper, Royal Tern, Whitebrowed Coucal, Dwarf Bittern and African Crake. During the waterbird survey, two Baird’s Sandpipers were observed along the camp-Foz do Cunene river section and, later that day, one of these individuals was located again and studied in detail which enabled confirmation of the identity of the species. We observed one (possibly two) Royal Terns on two occasions (6 and 7 January), roosting on sandbars in the mouth area. Although no Swift Terns were present, the presence of many Caspian Terns allowed for a comparison between these two similar species. Royal Terns have previously been recorded at the Cunene River mouth (e.g. Ryan et al. 1984; Komen & Paterson 1999). A coucal, possibly Whitebrowed, first recorded at the mouth during November 2000 by R.E. Simmons (in litt.), was heard calling on two occasions during this survey. Forty-nine individuals of 13 species were caught in the mistnets (Table 2), also providing two species (Dwarf Bittern and African Crake) that were not recorded during the waterbird survey.
The number of waterbirds recorded was lower than several previous counts (Simmons et al. 1993); this may be due to the time of the survey, especially if the Cunene River mouth is more important as a staging area during early and late summer for Palearctic migrants moving north or south along the south-west African coastline. The number of water and terrestrial birds was nevertheless significantly more than the 1412 individuals of 33 species recorded by Simmons (in litt.) on 10/11 November 2000. A comparison with the numbers of waterbirds reported by Ryan et al. (1984), Braine (1990) and Simmons et al. (1993) reveals higher numbers for several species during our survey, namely Whitebreasted Cormorant, Caspian Tern, White Pelican, Egyptian Goose and Redbilled Teal.
Although no effort was made to systematically search for and count mammals and reptiles, Tables 3–4 provides a list of these animals that were incidentally observed during our stay.
The Namibian Ministry of Environment & Tourism is thanked for access to the Skeleton Coast National Park. Dr Rob Simmons provided information on the birds of the Cunene River mouth and commented on this manuscript.
Braine S. 1988. Vagrants and range extensions found in and adjacent to the Skeleton Coast Park. Lanioturdus 24: 4–12.
Office Avian Demography Unit
Enquiries/More Information: firstname.lastname@example.org
Document posted: 24-Aug-2001
Office Avian Demography Unit | <urn:uuid:419f405f-a2b6-4780-b11b-30fb31dc2160> | 3.15625 | 1,680 | Academic Writing | Science & Tech. | 51.119259 |
The aftermath of a cosmic cataclysm,
remnant Cassiopeia A (Cas A) is a
11,000 light-years away.
Light from the Cas A supernova,
the death explosion of a massive star,
first reached Earth just 330 years ago.
Still expanding, the explosion's
debris cloud spans
about 15 light-years near the center of this
scene combines color data of the
starry field and fainter filaments of material at optical energies
with image data from the orbiting NuSTAR X-ray telescope.
Mapped to false colors,
the X-ray data in blue hues trace the
fragmented outer ring of the expanding
shock wave, glowing at energies up to
10,000 times the energy of the optical
(Rancho Del Sol Obs.) | <urn:uuid:435163ac-b016-4f15-9742-b48eb3a55f63> | 3.40625 | 173 | Knowledge Article | Science & Tech. | 49.383288 |
Relentless drought extending toll to wildlife
Heat marks set in Texas, Okla.
CANADIAN, Texas - In a muddy pile of sand where a pond once flowed in the Texas Panhandle, dead fish, their flesh already decayed and feasted on by maggots, lie with their mouths open. Nearby, deer munch on the vegetation equivalent of junk food, and wild turkeys nibble on red harvester ants - certainly not their first choice for lunch.
As the state struggles with the worst one-year drought in its history, entire ecosystems, from the smallest insects to the largest predators, are struggling for survival. The foundations of their habitats - rivers, springs, creeks, streams, and lakes - have turned into dry sand, wet mud, trickling springs, or, at best, large puddles.
“It has a compound effect on a multitude of species and organisms and habitat types because of the way that it’s chained and linked together,’’ said Jeff Bonner, a wildlife biologist with the Texas Parks and Wildlife Department.
The National Oceanic and Atmospheric Administration said yesterday that last month was the fourth hottest July on record, and Texas and Oklahoma had their warmest months on record.
Oklahoma also had the country’s highest monthly average temperature ever, according to an associate state climatologist, Gary McManus. Its average last month was 89.1 degrees, topping the mark of 88.1 set in July 1954.
Since January, Texas has gotten only about 6 inches of rain, compared with a norm of about 13 inches, making it the most severe one-year drought on record. Last week, the US Climate Prediction Center said the La Niña weather pattern blamed for the lack of rain might return, and would almost certainly extend the dry spell into next year.
The extreme dry conditions have been made worse by week after week of triple-digit temperatures that have caused reservoirs to evaporate.
Already, some rivers and lakes are at lows not seen since the 1950s - the decade when Texas suffered its worst drought in recorded history.
And in some cases, bodies of water are at their lowest points ever recorded, said Joseph Capesius, chief of the Austin field unit for the US Geological Survey.
Of the state’s 3,700 streams, 15 major rivers, and more than 200 reservoirs, at least seven reservoirs are effectively empty, officials said, and more than half of the streams and rivers are below their normal flow rates.
Fish kills have already happened in parts of the state, including not far from the Panhandle’s Canadian River, which in some places has been reduced to barely a puddle. In West Texas, O.C. Fisher Lake has been so depleted that fish have died from a lack of oxygen, and bacteria have turned the remaining water red.
Without water, animals struggle with thirst. Few plants grow.
Without plants, there are fewer insects. No insects result in low seed production. The animals that rely on seeds and plants for nutrition have low reproduction. Predators that rely on those animals as a food source remain hungry as well, and they reproduce less.
“There’s a domino effect that goes out in however many more branches than you can actually ever keep count of,’’ Bonner said.
The long-term impact from the drought will cross state lines and country borders because Texas is so large and its ecosystems diverse.
For example, birds that migrate south in the winter will find little food and water this year in Texas, so they will have to fly even farther south and expend more energy. As a result, they could reproduce less.
Some of those birds fly to Central America, where there has been a lot of rain and more insects than usual, for part of the year. But because of the drought in Texas and the Plains, there may not be enough birds to consume the insects, Bonner said.
“Now, what happens? Continentally speaking, this big of an area not getting enough water can impact places far and wide.’’
The impact on species also could last for years after the drought officially ends. Quail normally nest in grass grown a year earlier, but because of the drought, there has been almost no grass growth this year. That means many quail won’t be able to nest next year, Bonner said.
With deer, the true impact may not be revealed for six years, when the low reproduction rates caused by the drought will leave an age gap between older bucks and younger deer.
John Baccus, a wildlife biologist at Texas State University in San Marcos, said he is most immediately concerned with bats and songbirds, both of which rely on insects for food. He believes that some females will not have any offspring this year due to a poor diet. Whatever babies are born will probably have a low survival rate because they are entering a world with a scarce food supply.
Already, Baccus said, he has noticed white-tailed deer that are skinnier than usual, their ribs jutting out. As a result, the mothers are producing less milk and the newest crop of fawns will be weaned at subpar weight.
“It’s an ecosystemwide problem,’’ Baccus said. | <urn:uuid:d1943fad-afc5-4c98-86b6-d0ac7da5b05b> | 3.5625 | 1,108 | Truncated | Science & Tech. | 54.309048 |
Scientific notation is used to make extremely large or small numbers more manageable. Numbers written in scientific notation are the products of a digit term and an exponential term and are written in the general form a x 10^n. For example, 0.0000234 is written 2.34 x 10^n and 456,000 is written as 4.56 x 10^5.
So we're going to talk about Scientific notation. Scientific notation is basically a way to take very big numbers or very small numbers and simplify them in a way thatâs easier to write and keep track of. So let's look at how we do that trying to determine proper Scientific notation we need to write a number a times 10 to the b. Now a is going to be a number between 1 and 10, to get that number between 1 and 10, we're going to usually have to move our decimal point to the right or to the left. If we move the decimal point to the right, thatâs going to be a negative exponent. If we move it to the left it's going to be a positive exponent.
Okay let's look at how we do that with some problems. Over here I've got a number 1,100 not a terribly big number not a lot of zeros but to put it in proper Scientific notation we need to move the decimal point, the decimal point is right here, we need to move 1, 2, 3 spots now we have 1.1 times 10 to the third. Sorry 1.1 times 10 to the third okay that was pretty straight forward. Now we've got a very small number with a lot of zeros to the right of the decimal point. So we need to make this number larger by multiplying it by a negative exponent. So if we start with a decimal point we go 1, 2, 3, 4 units to get 5.4 times 10 in this case to the negative 4 since we're moving to the right of a decimal point.
Okay now let's look at a really big number with a lot of zeros and again who wants to write all those zeros? I don't want to write them so let's simplify that okay, we're going to go 1, 2, 3, 4, 5, 6, 7, 8, 9 units to the left of the decimal point. And so we're going to take 7.12 times 10 to the ninth. And we've simplified this very big number with a lot of zeros into a number thatâs much more manageable. Okay and thatâs how we do Scientific notation. | <urn:uuid:f0102cbc-627b-47b3-902a-0cf7ecefd3b8> | 4.21875 | 526 | Tutorial | Science & Tech. | 82.818282 |
crown-of-thorns starfishArticle Free Pass
crown-of-thorns starfish, (Acanthaster planci), reddish and heavy-spined species of the phylum Echinodermata. The adult has from 12 to 19 arms, is typically 45 centimetres (18 inches) across, and feeds on coral polyps. Beginning about 1963 it increased enormously on Australia’s Great Barrier Reef. The population explosion was attributed to the decimation of its chief predator, a large marine snail, the Pacific triton (Charonia tritonis), by shell collectors. Thereafter, the starfish multiplied throughout the southern Pacific (to Hawaii about 1970), seemingly threatening the destruction of coral reefs and islands.
Concern among scientists and environmentalists prompted an attempt to control the animals’ proliferation; many were killed by injection with formaldehyde, while others were simply removed from the reefs and destroyed. In the late 1970s, however, new research data indicated that similar expansions, or blooms, had occurred previously, followed by periods of decline. Thus, it seemed likely that the sudden growth of the starfish population during the 1960s represented a phase in the organism’s natural cycle. Most outbreaks last one to two years, although some have persisted for as long as five years. What causes these dramatic population explosions is unknown; however, authorities hypothesize that the periodic input of high-nutrient loads from land sources and removal of species that prey on adult starfish may be responsible.
What made you want to look up "crown-of-thorns starfish"? Please share what surprised you most... | <urn:uuid:8fdd1991-f885-46a6-8da7-6eac2a42180e> | 3.53125 | 338 | Knowledge Article | Science & Tech. | 37.219752 |
A long straight wire carries a current I
Arectangular wire loop
withits closest edge a distance a
from the wire,
asshown in the figure below. Take a
= 3.5 cm, and
= 6.5 cm.Suppose
the rectangular loop is a conductor
withresistance 45 m
and that the current I
longwire is increasing at the rate of 15 A/s.
Find the induced current in the loop. | <urn:uuid:2518d505-f8b5-4d94-8990-939ed300c9c5> | 3.3125 | 97 | Q&A Forum | Science & Tech. | 73.897273 |
Herb is a bestselling author and consultant on software development topics, and a software architect at Microsoft. He can be contacted at www.gotw.ca.
What does the volatile keyword mean? How should you use it? Confusingly, there are two common answers, because depending on the language you use volatile supports one or the other of two different programming techniques: lock-free programming, and dealing with 'unusual' memory. (See Figure 1.)
Adding to the confusion, these two different uses have overlapping requirements and impose overlapping restrictions, which makes them appear more similar than they are. Let's define and understand them clearly, and see how to spell them correctly in C, C++, Java and C# -- and not always as volatile.
Case 1: Ordered Atomic Variables For Lock-Free Programming
Lock-free programming is all about doing communication and synchronization between threads using lower-level tools than mutex locks. In the past and even today, however, these tools are all over the map. In rough historical order, they include explicit fences/barriers (e.g., Linux's mb()), order-inducing special API calls (e.g., Windows' InterlockedExchange), and various flavors of special atomic types. Many of these tools are tedious and/or difficult, and their wide variety means that lock-free code ends up being written differently in different environments.
The last few years, however, have seen a major convergence across hardware and software vendors: The computing industry is coalescing around sequentially consistent ordered atomic variables as the default or only way to write lock-free code using the major languages and OS platforms. In a nutshell, ordered atomic variables are safe to read and write on multiple threads at the same time without doing any explicit locking because they provide two guarantees: their reads and writes are guaranteed to be executed in the order they appear in your program's source code; and each read or write is guaranteed to be atomic, all-or-nothing. They also have special operations such as compareAndSet that are guaranteed to be executed atomically. See for further details about ordered atomic variables and how to use them correctly.
Ordered atomic variables are available in Java, C# and other .NET languages, and the forthcoming ISO C++ Standard, but under different names:
- Java provides ordered atomics under the volatile keyword (e.g., volatile int), and solidified this support in Java 5 (2004). Java additionally provides a few named types in java.util.concurrent.atomic, such as AtomicLongArray, that you can use for the same purpose.
- .NET mostly added them in Visual Studio 2005, also under the volatile keyword (e.g., volatile int). These are suitable for nearly all lock-free code uses, except for rare examples similar to Dekker's algorithm. .NET is fixing these remaining corner cases in Visual Studio 2010, which is in early beta as of this writing.
- ISO C++ added them to the C++0x draft Standard in 2007, under the templated name atomic<T> (e.g., atomic
). They started to become available beginning in 2008 in the Boost project and other implementations. . The ISO C++ atomics library also provides a C-compatible way to spell those types and their operations (e.g., atomic_int), and these appear to be likely to be adopted by ISO C in the future.
A Word About Optimization
We're going to look at how ordered atomics restrict the optimizations that compilers, CPUs, cache effects, and other parts of your execution environment might perform. So let's first briefly review some basic rules of optimization.
The most fundamental rule of optimization in pretty much any language is this: Optimizations that rearrange ('transform') your code's execution are always legal if they don't change the meaning of the program, so that the program can't tell the difference between executing the original code and the transformed code. In some languages, this is also known as the 'as if' rule -- which gets its name from the fact that the transformed code has the same observable effects 'as if' the original source code had been executed as written.
This rule cuts two ways: First, an optimization must never make it possible to get a result that wasn't possible before, or break any guarantees that the original code was allowed to rely on, including language semantics. If we produce an impossible result, after all, the program and the user certainly can tell the difference, and it's not just 'as if' we'd executed the original untransformed code.
Second, optimizations are permitted to reduce the set of possible executions. For example, an optimization might make some potential (but not guaranteed) interleavings never actually happen. This is okay, because the program couldn't rely on them happening anyway.
Ordered Atomics and Optimization
Using ordered atomic variables restricts the kinds of optimizations your compiler and processor and cache system can do. There are two kinds of optimizations to consider:
- Optimizations on the ordered atomic reads and writes themselves.
- Optimizations on nearby ordinary reads and writes.
First, all of the ordered atomic reads and writes on a given thread must execute exactly in source code order, because that's one of the fundamental guarantees of ordered atomic variables. However, we can still perform some optimizations, in particular, optimizations that have the same effect as if this thread just always executed so quickly that another thread didn't happen to ever interleave at certain points.
For instance, consider this code, where a is an ordered atomic variable:
a = 1; // A a = 2; // B
Is it legal for a compiler, processor, cache, or other part of the execution environment to transform the above code into the following, eliminating the redundant write in line A?
<FONT COLOR="FF000"> // A': OK: eliminate line A entirely</FONT><br> a = 2; // B
The answer is, 'Yes.' This is legal because the program can't tell the difference; it's as if this thread always ran so fast that no other thread accessing a concurrently ever got to interleave between lines A and B to see the intermediate value.
Similarly, if a is an ordered atomic variable and local is an unshared local variable, it is legal to transform
a = 1; // C: write to a local = a; // D: read from a
a = 1; // C: write to a local = <FONT COLOR="FF000">1</FONT>; <FONT COLOR="FF000"> // D': OK, apply "constant propagation</FONT>"
which eliminates the read from a. Even if another thread is concurrently trying to write to a, its as if this thread always ran so fast that the other thread never got to interleave between lines C and D to change the value before we can read our own back into local.
Second, nearby ordinary reads and writes can still be reordered around ordered atomic reads and writes, but subject to some restrictions. In particular, as described in , ordinary reads and writes can't move upward across (from after to before) an ordered atomic read, and can't move downward across (from before to after) an ordered atomic write. In brief, that could move them out of a critical section of code, and you can write programs that can tell the difference. For more details, see .
That's it for lock-free programming and ordered atomics. What about the other case that some "volatiles" address? | <urn:uuid:e4c514eb-e80d-43c9-8fdb-e5c9fc7f1c55> | 3.46875 | 1,571 | Audio Transcript | Software Dev. | 42.094334 |
by Jan Adkins
Meteorologists love hurricanes because they are wonders of nature. But if you're on a ship at sea or in a house on the beach, a hurricane is not so pretty. The screaming winds and enormous waves can overturn a ship. At the shore they can punch out windows, knock down trees, or pluck the roofs from houses.
The most dangerous part of a hurricane's destruction is flooding. Hurricane winds can push the ocean water toward shore, building it up into a huge, rushing tide called a storm surge. Water level at the shore can rise 20 feet in just a few hours. The deadliest hurricane in United States history happened in 1900, when Galveston, Texas, was struck. In the big storm surge more than 6,000 people were killed. These days, with more and more people living in coastal cities, experts predict that if a hurricane hit without warning, the death toll could be even higher.
But scientists have learned a lot about hurricanes since 1900. Meteorologists can now track the path a hurricane takes and predict where it is likely to hit days in advance. When Hurricane Isabel swept toward the North Carolina coast in 2003, the National Hurricane Center was able to make forecasts five days ahead, and scientists were off by only one hour in their prediction of where and when Isabel's eye would make landfall. The information collected by the hurricane hunters improves the accuracy of such forecasts by 30 percent—saving thousands of lives.
- A very powerful storm with extremely strong winds over 75 miles per hour and heavy rains.
- What kind of damage can a hurricane cause?
- What other kinds of storms or weather events can you think of? Describe a few different kinds of storms. What happens when these storms pass through an area? What kind of damage do they cause? How can people protect themselves? Pick two other kinds of storms. Write a few sentences about each of them. | <urn:uuid:13a35ed3-d83b-4501-81e0-e2ad60b6f12e> | 3.6875 | 388 | Tutorial | Science & Tech. | 59.015241 |
SESAME (Spin Echo Scattering Angle Measurement)
The newest LENS beamline, dubbed SESAME (Spin Echo Scattering Angle Measurement), measured its first neutrons on April 21, 2009. Started in the summer of 2006, this beamline has been the vision of IU professor Roger Pynn at CEEM. SESAME will use polarized neutrons to probe in-plane correlations on solid and liquid samples. The process relies upon precise magnetic fields to encode the scattering angle of neutrons into the final polarization of the beam. A 3He analyzer that is currently being designed and built by Dr. Mike Snow, also of CEEM, will be used as a polarizer filter for SESAME.
Several experiments at national labs over the past three years have provided proof-of-principle results for SESAME. The most recent experiments were performed at the NIST Center for Neutron Research and the Los Alamos Neutron Science Center, in which neutron reflectivity was carried out on a nanopatterned silicon stamp. The results have been confirmed through theoretical calculations, and provide a basis for analysis of future experiments on more complicated structures, such as biomembranes and block copolymers.
SESAME is a neutron scattering technique for probing nanometer-to micron-scale correlations of planer structure of a material. Pictured above is a cartoon of neutrons scattering off a biological membrane. SESAME will provide scientists with a method to ensure a high degree of in-plane uniformity in nanoscale materials. | <urn:uuid:bc29b78d-8a7f-4390-9788-137951cf345e> | 3.015625 | 324 | Knowledge Article | Science & Tech. | 26.641246 |
We recommend using at least three classes:
An application class - this will contain your main method and will run the program as well as updating the gui
A board class - this will represent the backend and store the state of the game such as what disks are in what squares
A square/cell/tile class - this represents a single square of the reversi board and can be empty, or have a black or white disk in it
A window opens :
The program will use a GUI as well as console input. To display the GUI, your program must call the update(int grid, boolean gameOver, int gameWinner, boolean moveMade) method on a properly constructed ReversiGUI object. The gui will display a game grid based on the 2D int array you pass it - all values in this array should be one of the class constants defined in ReversiGUI. When the program starts, display an 8x8 grid with the starting initial configuration as defined in the program description above. Nothing really happens yet when you run the program, but at least the user interface shows up.
User Interaction (5 of 45 for design and code correctness):
Allow the user to interact with the game and place disks on squares. To handle GUI input, your program should repeatedly call the getMouseInput() method on a properly constructed ReversiGUI object. This method returns a ReversiAction object that indicates what action the mouse click corresponds to via the ACTION_TYPE instance constant which will correspond to one of the class constants defined in ReversiAction. For now, we are only concerned with ReversiAction.LEFT_CLICK - if it is a left click, we can also get the row and column index of the clicked square from the ROW and COLUMN instance constants. For this part, allow the user to click on any square and simply place a disk there.
Basic game (15 of 45 for design and code correctness):
Get a basic game going by expanding your work from the first two steps. Now only allow users to place disks in squares that correspond to valid moves and flip any disks that this move captured. Note that a player might capture disks on a horizontal, vertical, or diagonal line (or any combination of the three) between the newly placed piece and any of the player's old pieces. Also make sure to check if the game is over after each move. If the game is over, calculate who wins and pass all this information to the gui through the update method.
Basic Buttons :
Get the "New Match" and "Quit Game" buttons working. As before, you can figure out what the user clicked on via the getMouseInput() method. The "New Match" button should initialize a new game with the default starting configuration. The "Quit Game" button should exit your program (make sure to exit the gui as well).
Save Game :
Allow the user to save the game state when the "Save Game" button is pressed. When the save game button is pressed, a dialog will automatically open that prompts the user to save the file. | <urn:uuid:9d0c792a-c288-4030-81cb-4449ef0a8a83> | 2.859375 | 639 | Tutorial | Software Dev. | 49.637252 |
Assertion are simple check assumption made at the beginning of the program to ensure the program is true throughout provided by the Java language. For example, the range of age should be in between 18 and above; or cannot be more than 50.
These are the set of expression used in java that enables you to check the assumption made in a program during throughout the execution of program. An Assertion contain a Boolean expression which is set to be true in the beginning of the program. For Example ,a program has a method that allow the value being passed to it should not be zero and negative, you test this assert by sending a only positive number that is greater than zero by using assert statement in java.
Syntax used to declare Assertion
The Syntax,statement1 is a Boolean expression. When the program is executed ,the statement1 in the assert is checked. If the statement1 returns true, assertion in program is true and the program run without interuption.Incase.,if the statement 1 returns false, the assertion made in the program fail, the program throw assertion error object and program will terminated and an assertion error object is thrown.
An Statement is a error message and statement2 is a Boolean expression. the statement 1 gives you an error message that work only if there is an error in statement1.The statement 1 gives you an error, then it is passed to the Assertion Error constructor of the respective error class, if the statement 2 return false. The constructor changes the value in statement1 into string format and display the message on fail of assertion.
public AssertionError(char message)
The above syntax constructor Assertion Error create its object. The argument passed in the assertion error object contain the error message that will display when an assertion fails.
How to Compile Assertion Files
The Assertion file is compiled with an option ,-source 1.4.The Syntax used in compilation of program is
Javac-source 1.4 AssertDemonstration.java
Where Assert Demonstration is the name of java program using assertion.
-source 1.4 is a command line option to make the compile to accept the code containing assertions.
How to Enable and Disable Assertion
Assertion are disabled at run-time during execution of java program .
The command line prompt -ea or enable assertions is used to enable assertion during run-time execution of the program.
The command prompt -da or disable is used to disable assertion during run-time execution of the program
java -da :AssertDemonstration
Let Us Understand with Example
In this Example We, defined a public class 'Mark Assert Demo' Inside the class we define the static variable i.e. maximum marks to be 100, changes is another static variable, The main static ( ) method has assumption of maximum marks i.e. 40,if the marks come below to 40,the code will show you java.lang.AssertionError and display the Marks is below than 40 on the command prompt.
Output on Command Prompt | <urn:uuid:ad443eb7-7aba-451f-bb79-f9254da9a430> | 3.890625 | 635 | Documentation | Software Dev. | 47.245479 |
It appears easy to understand why there should be a bulge of water, producing a high tide, on the side of the earth facing of the moon. But why is there a bulge on the opposite side as well?
It is obviously not gravity that is doing it but rather, it is the difference in gravitational force across the earth that causes the bulge. This difference in gradational force comes from the moon's pull at various points on the earth.
Because the pull of gravity becomes stronger as the distance decreases, the moon pulls a little harder at point "C" (closest point to the moon) than it does at point "O" (in the center of the earth), and the pull is weaker still at point "F" (farthest point from the moon). If it were not for the earth's gravity, the planet would be pulled apart (above image).
Yet also because of the earth's gravity which pulls us toward the center of the planet we can, mathematically subtract the moon's pull at the center of the earth from the moon's pull at both point "C" and "F". When this vector-based subtraction occurs we are left with two smaller forces; one toward the moon and one on the opposite side point away from the moon (image below) producing two bulges.
As the earth makes one rotation in 24 hours, we pass under these areas where the tidal force pulls water away from the earth's surface and experience high tides. Also, since the difference in gravitation force is constant across the earth, the bulge on both side of the earth is essentially the same. Which explains why consecutive high tides are nearly the same height each time regardless whether the moon is overhead or on the opposite side of the earth. | <urn:uuid:abc476be-62d5-45ee-891a-aba9c60ff102> | 4.375 | 361 | Knowledge Article | Science & Tech. | 52.485261 |
Around 450 million years ago, shallow seas covered the Cincinnati region and harbored one very large and now very mysterious organism. Despite its size, no one has ever found a fossil of this “monster” until its discovery by an amateur paleontologist last year.
UC Paleontologist David Meyer, left and Carlton Brett, right, flank Ron Fine, who discovered the large fossil spread out on the table.
The fossilized specimen, a roughly elliptical shape with multiple lobes, totaling almost seven feet in length, will be unveiled at the North-Central Section 46th Annual Meeting of the Geological Society of America, April 24, in Dayton, Ohio.
Fine is a member of the Dry Dredgers, an association of amateur paleontologists based at the University of Cincinnati. The club, celebrating its 70th anniversary this month, has a long history of collaborating with academic paleontologists.
“I knew right away that I had found an unusual fossil,” Fine said. “Imagine a saguaro cactus with flattened branches and horizontal stripes in place of the usual vertical stripes. That’s the best description I can give.”
The layer of rock in which he found the specimen near Covington, Kentucky, is known to produce a lot of nodules or concretions in a soft, clay-rich rock known as shale. “While those nodules can take on some fascinating, sculpted forms, I could tell instantly that this was not one of them,” Fine said. “There was an ‘organic’ form to these shapes. They were streamlined.” | <urn:uuid:84f13cab-6f59-48a2-9042-18e12dbc6600> | 3.40625 | 337 | Personal Blog | Science & Tech. | 40.595641 |
Comprehensive DescriptionRead full entry
BiologyOccurs in cold brackish and moderately saline water near the coast (Ref. 27547). Enters coastal rivers and may occur as far as 120 miles inland (Ref. 5723). Landlocked in lakes (Ref. 59043). Maximum depth reported at 100m (Ref. 35388). Benthic (Ref. 58426). Movements are limited to short onshore-offshore seasonal movements and mass movements of fry into shallow water in autumn (Ref. 28908, 28910). Moreover, there are no migrations of large numbers; movement into freshwater and long distances up rivers are apparently undertaken by relatively few individuals at a time (Ref. 27547). Diurnal from November to April but is largely nocturnal the rest of the year (Ref. 28905). Feeds on small crustaceans, fishes (Ref. 4968) and molluscs (Ref. 58426). Spawning takes place in shallow waters, male digs a groove in the gravel where pairing and egg laying occur. Move to deeper water in the spring, where they stay in summer (Ref. 35388). Landlocked populations are locally threatened (Ref. 59043). | <urn:uuid:ffdc360c-aced-4425-b515-506eb5a268d2> | 3.25 | 250 | Knowledge Article | Science & Tech. | 60.325507 |
Appendix A. Photographs of feeding fronts of Oreaster reticulatus and Strongylocentrotus droebachiensis.
FIG. A1. (A) A feeding front of the sea star Oreaster reticulatus off St. Croix, U.S. Virgin Islands. The front is moving from left to right. Feeding mounds (fm) of darker sediment surrounded by lighter halos can be seen behind the front on the highly turbated sand bottom. In advance of the front, the sediment appears darker because of a microalgal film which has developed in the absence of sea star grazing in the previous weeks. Average sea star diameter is 0.26 m. (B) A feeding front of the urchin Strongylocentrotus droebachiensis grazing on the kelp Laminaria digitata and L. longicruris near Halifax, Nova Scotia, Canada. The recently created barren ground behind the front (on the right) is denuded of erect macro-algae. Average urchin diameter is 0.04 m. | <urn:uuid:48ece227-a56b-4928-aa35-c5d081e81659> | 2.765625 | 224 | Truncated | Science & Tech. | 58.3025 |
I am doing some research in electromagnetic induction,
and found the following letter from Faraday that appears to contradict
Lenz's law. I doubt very much that Faraday made a mistake here, but I
have been unable to find a plausible explanation for this incongruity.
Could you please help me elucidate this conundrum?
Michael Faraday wrote to R. Phillips on Nov. 29, 1831:
"When an electric current is passed through one of two parallel wires it
causes at first a current in the same direction through the other, but
this induced current does not last a moment, notwithstanding the inducing
current (from the Voltaic battery) is continued all seems unchanged except
that the principal current continues its course, but when the current is
stopped then a return current occurs in the wire under induction of about
the same intensity and momentary duration but in the opposite direction to
that first found. Electricity in currents therefore exerts an inductive
action like ordinary electricity but subject to peculiar laws: the
effects are a current in the same
direction when the induction is established: a reverse current when the
induction ceases and a peculiar state in the interim..."
I don't see a problem here. The induced emf in the undriven wire is
proportional to the rate of change of the flux, so it's nonzero only
while the current in the driven wire is changing.
Faraday's letter refers to two separate wires, not wire loops. As a result,
it can be difficult to relate to Lenz'z Law.
When current begins to flow in the primary wire, the magnetic field around
that wire begins to increase. As the magnetic field increases, it produces
a current in the secondary wire. Because the field is stronger between the
wires than beyond the secondary wire, the secondary current's magnetic field
will oppose the magnetic field between the wires. To do this, both currents
must be in the same direction. This agrees with Lenz's Law.
After the primary current is constant, there is no more change of magnetic
field and no more induced current.
After the primary current is turned off, the primary magnetic field
decreases. The change is opposite the change when turned on. To counter
the decrease of magnetic field between the wires, the induced secondary
current must be opposite what it was at the beginning. Thus, all of
Faraday's letter agrees with Lenz's Law.
I don't think this contradicts Lenz's Law. Basically what Faraday is saying
is that a changing electric current in the first wire induces currents in
the second. As I recall it, Lenz's Law prohibits an induced current in a
conductor (such as the second wire here) from reinforcing the magnetic field
that does the inducing. Recall that the magnetic field from a current
flowing in a straight line is a right-handed circle centered on the wire.
The magnetic field from a current flowing in the same direction along a
parallel path will also be a right-handed circle, opposing the first field
in the regions of greatest overlap.
Bear in mind, though, that it's been a LONG time since I took Physics...
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
Rather than dealing with written arguments and disagreements, be a true
scientist: find out for yourself. There are several ways to try it.
Set up two fairly long adjacent wires, very close but not touching. Have
the "primary wire" connected to an ammeter, resistor (to avoid too much
current), and a power source. Connect the "secondary wire" to just an
ammeter. Make both of them series circuits.
If you have a computer system that with sensors that can measure and record
current as a function of time, have the sensors be the ammeters. Be sure
"positive" current is in the same direction for both wires. After the
computer system is recording, turn on the power source, wait a few seconds,
and then turn off the power source. See what direction the secondary
current flows with respect to the primary current.
If you prefer to use an oscilloscope and square wave function generator, you
can. Use a square wave that is positive, then zero, then positive,.... The
function generator powers the primary wire. Use one oscilloscope channel to
read the current of the primary wire. Use another channel to read the
current of the secondary coil. How you attach the oscilloscope depends on
the individual equipment. Trigger of the primary coil. See how the
secondary current relates to the primary current.
One thing to note. If you only have devices that read voltage, you can
create an ammeter with a small resistor. Put the small resistor in series
with the circuit. Read the voltage across that small resistor.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:b1359f04-187c-41e9-a130-cfda6bae7357> | 2.75 | 1,041 | Q&A Forum | Science & Tech. | 52.654332 |
Velocity and Gravity
Every moving object has a particular velocity, which is a three-dimensional vector. The velocity of an object indicates how quickly it is moving in each direction. For example, a velocity of (3, -2, -5) means that an object is moving 3 units per second in the positive x direction, 2 units per second in the downward direction, and 5 units per second in the negative z direction.
The effect of gravity, both in our programs and in the real world, is to decrease the y component of the velocity of each object at a certain rate. In the real world, this rate is 9.8 meters per second per second. In our programs, gravity will be measured in units per second per second.
To simulate gravity, we can adjust the velocity of an object in small steps. We could, for example, decrease the y component of the velocity of each object by 0.01 times the gravity every 0.01 seconds. | <urn:uuid:c2454635-aa36-4493-a134-0fe9caee7ec8> | 4.3125 | 198 | Tutorial | Science & Tech. | 58.813636 |
Awash in a sea of
plasma and anchored in
fields, sunspots are planet-sized,
dark islands in
solar photosphere, the bright surface of the Sun.
because they are slightly cooler than the surrounding surface,
this group of sunspots is captured in a close-up
telescopic snapshot from July 11.
The field of view spans nearly 100,000 miles.
They lie in the center of active region AR1520, now crossing the
Sun's visible face.
In fact, an
X-class solar flare and
coronal mass ejection erupted
from AR1520 on July 12, releasing some of the energy stored in the
region's twisted magnetic fields.
Headed this way, the coronal mass ejection is expected to
arrive today and may trigger
As a result, some weekend auroral displays could grace
planet Earth's skies along with
predawn conjunction of bright planets and crescent Moon.
Credit & Copyright: | <urn:uuid:841d26ad-161e-413c-803b-6c45844491b5> | 3.265625 | 209 | Knowledge Article | Science & Tech. | 49.7 |
Once & Future Climate, Part 1: The Past
Running Time: 00:31:41
Watch as Exploratorium physicists Paul Doherty and Stephanie Chasteen play around with the leading greenhouse gas: carbon dioxide. What is it? How much is there in our atmosphere? What does it do that is so harmful to the environment?
How Climate Change Impacts Penguins
Running Time: 00:33:33
Join Pamela Schaller from the California Academy of Sciences as she discuss penguins and how climate change impacts them.
Penguins in Antarctica
Running Time: 00:26:39
Penguin researcher David Ainley joins us via telephone from his tent at Cape Royds, Antarctica. Dr. Ainley has been studying Adelie penguins for many seasons from his remote encampment.
Global Warming 101: More Questions and Answers
Running Time: 00:09:55
More quick answers to the most frequently asked questions about global warming.
Live Chat from McMurdo Station
Running Time: 00:28:33
What do the kids want to know? Join Kirk Bell's fifth grade class (from Children's Day School in San Francisco)as they chat with Holly Troy in Antarctica. Mr. Troy has spent many seasons at McMurdo station working with scientists.
Understanding the Gulf Stream
Running Time: 00:27:47
Exploratorium biologist Charles Carlson talks about why climate change is causing a crisis with the Gulf Stream.
Once & Future Climate, Part 2: The Present
Running Time: 00:25:43
Join Exploratorium physicists Paul Doherty and Stephanie Chasteen as they examine the past, present, and future of climate change. Watch as Paul and Stephanie demonstrate how you can look at a slice of climate from the past, what a sediment core might look like, and the secrets hidden in an ice balloon!
Drilling Back to the Future: Live from McMurdo Station, Antarctica
Running Time: 00:31:49
Exploratorium physicist Paul Doherty chats with Richard Levy, a geologist, and Ross Powell, who’s the co-director of the ANDRILL project. They are drilling beneath the Antarctic seafloor, and pulling up sediment cores. By looking at the layers of the past, they hope to help us predict our future.
Life at the Poles: Living Organisms and Ecosystems
Running Time: 00:29:33
Join Exploratorium biologist Karen Kalumuck as she investigates the characteristics of living organisms and ecosystems, and how climate change affects them.
Life at the Poles: Enzymes and Proteins
Running Time: 00:24:38
Join Exploratorium biologist Karen Kalumuck as she experiments with enzymes and proteins and shows at what temperatures they function best.
Life at the Poles: From Phytoplankton to Polar Bears
Running Time: 00:30:11
Exploratorium biologist Karen Kalumuck will examine how increasing temperatures affect specific organisms at the poles—from phytoplankton to polar bears!
Once & Future Climate, Part 3: The Future
Running Time: 00:27:15
Join Exploratorium physicists Paul Doherty and Stephanie Chasteen as they examine the past, present, and future of climate change. In this show, Paul and Stephanie discuss the future of our climate. Learn more about the oceans, global warming, feedback effects, glacial ice and sea ice, and some things you can to do help.
Chris Mooney on the Politics of Climate Change
Running Time: 00:37:06
Join us as we chat with Chris Mooney, Washington correspondent for Seed Magazine and author of Storm World: Hurricanes, Politics, and the Battle Over Global Warming and The Republican War on Science. His blog can be found at http://scienceblogs.com/intersection.
The ANDRILL Project
Running Time: 00:38:53
Join us as we talk to scientists from the ANDRILL (ANtarctica DRILLing) project, who are currently on a geological drilling expedition in Antarctica.
Climate Change with Robert Henson
Running Time: 00:34:44
Join us as we talk with Robert Henson, author of The Rough Guide to Climate Change.
Global Warming 101: Five Questions in 10 Minutes
Running Time: 00:16:25
Join Exploratorium staff as they give the quick answers to the most frequently asked questions about global warming: What is a "tipping point"? What are carbon credits? What is carbon neutral? What can I do? What can my kid do?
Sea Ice Versus Land Ice
Running Time: 00:10:32
Join Senior Scientist Paul Doherty as he explains the difference between floating ice and land ice, and why they effect sea levels differently.
Save the World, One Lightbulb At A Time
Running Time: 00:11:46
Join Senior Scientist Paul Doherty as he measures the power used by two lightbulbs--one incandescent and one fluorescent--that make the same amount of light.
Watch Ice Melt!
Running Time: 00:07:54
Join Senior Scientist Paul Doherty as shows how to melt ice unbelievably fast!
Climate Change with Dr. Stephen Schneider
Running Time: 00:38:45
Dr. Stephen H. Schneider joins us to discuss climate change. Dr. Schneider was honored in 1992 with a MacArthur Fellowship for his ability to integrate and interpret the results of global climate research through public lectures, seminars, classroom teaching, and research collaboration with colleagues.
Understanding The Gulf Stream, Part 2
Running Time: 00:29:34
Join Exploratorium staff scientist Charlie Carlson as he continues to examine issues around the Gulf Stream and climate change.
The Impact of Climate Change on Community
Join host Mary Miller and Dr. Mickey Glantz in a discussion on issues around climate change and how it may affect communities. | <urn:uuid:d21d1414-e17b-4483-ae46-4c1f31c9af98> | 2.96875 | 1,231 | Content Listing | Science & Tech. | 51.805005 |
-A bicycle wheel
-2 handles for the axle
-Chain or rope suspended from large stand or ceiling
You can perform this experiment in a couple of different ways. Using the first method, you get the bike wheel spinning and then use the eyebolt in the end of the handle to hang the wheel on a hook which is connected to the end of a rope or chain. The second is to place the wheel on two circles of string hanging from the ceiling or a strong support. Spin the wheel and then cut one of the strings. In both instances the spinning wheel will remain upright. The wheel will also revolve around the remaining string or chain.
What's Going On?
Simply put, spinning objects are very stable and resist change in direction which is perpendicular to the rotation. By spinning the bike wheel, we're giving the bike wheel angular momentum. At this point, the wheel will resist change, but because of gravity it will begin to precess or rotate around the chain. The effect of gravity on a spinning wheel is a slow rotation around the string. This is called precession. The spinning wheel will rotate about an axis at right angles to the force axis. | <urn:uuid:a12354b4-0821-4577-86aa-7c06dc16b7cf> | 3.65625 | 238 | Tutorial | Science & Tech. | 67.355577 |
Question Corner and Discussion Area
Hi. I'm an adult education instructor for SIAST. I'm presently developing multimedia materials in the science area. Part of the program involves showing students how to solve linear equations using a CD ROM format. Does anyone have any suggestions as to how this could be presented using the potential of the CD ROM format. I've thought of using a manipulative approach similar to Alge-Tiles.
Your suggestions would be greatly appreciated. Thanks!
I would like to find a better way of introducing word problems involving linear equations.From Philip Spencer, University of Toronto on July 29, 1997:
To be honest, I can't think of a better way of introducing linear equation word problems than simply stating them, choosing them from some real life application so that students can see the relevance. There are countless applications one can choose from. For example:
You are renovating a house and have a leftover supply of wood trim: 17 long and 9 short. You want to use them up by making decorative window and door frames. A window frame will use up 3 short pieces for the top and sides, and 1 long piece which is cut in two for a double-width sill. A door frame will use up a short piece for the top and two long pieces for the sides. How many window and door frames should you make, to completely use up your leftover trim? (Solve the system of linear equations 3x + y = 17, x + 2y = 9).
A chemical company wants to produce 100 litres of oxygen and 50 litres of pure water. It does so by processing two types of raw material. Each litre of material A produces 0.6 litres of oxygen and 0.2 litres of water. Each litre of material B produces 0.3 litres of oxygen and 0.4 litres of water. How much of each raw material will be required to produce the desired quantities of oxygen and water? (Solve the system 0.6 x + 0.3 y = 100, 0.2 x + 0.4 y = 50).
These are just two off the top of my head. You might want to pick your own real-life situation that's of particular interest or relevance to your students.
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Check out our project guide, which talks about how to do a research paper: http://www.sciencebuddies.org/science-f ... ndex.shtml
The guide will walk through through each step of your project. Just look on the left side under "How to Do a Science Fair Project?" and then "Doing Background Research"
For your report, I'd find some websites about steel and how/why rust occurs. Also do some research on what steel is used for in the world, and why do we care if it rusts or not? Does rusting affect how sturdy it is?
Also research what salt is made from (sodium and chlorine NaCl). If you search for "salt steel rust" in Google I'm sure some websites will pop up.
Here are a couple I found:http://science.howstuffworks.com/question445.htm
Here's a page about why stainless steel does not rust: http://www.scientificamerican.com/artic ... nless-stee
You should be able to find many other websites just by putting in a couple of key words like "steel rust" into Google.
I'm going to move your topic to the Physical Science forum so our experts can better help you.
Good luck and let us know if you have more questions. | <urn:uuid:22ce0dd3-ed89-41f2-830f-af31fdc67e00> | 3.171875 | 279 | Comment Section | Science & Tech. | 85.37391 |
July 16, 2012 The Atlantic Meridional Overturning Circulation (AMOC), driven by temperature and salinity gradients, is an important component of the climate system; it transfers an enormous amount of heat via ocean currents and atmospheric circulation to high northern latitudes and hence has bearing on climate in the region.
Freshening of the surface ocean could weaken the AMOC. But during warm interglacial periods the effect of a fresh surface ocean on the AMOC may be muted. In fact, climate models predict that heat transfer from the North Atlantic to the Arctic may increase over the 21st century. A series of interconnected processes in the North Atlantic, known as polar amplification, could cause the Arctic to warm up faster compared to the rest of the world. It could even lead to ice-free conditions in the Arctic.
Previous paleoclimatic reconstructions indicate that the sub-Arctic may have been warmer by about 5 degrees Celcius (9 degrees Fahrenheit) with little summer sea ice cover during the Eemian, the penultimate interglacial centered around 125,000 years ago. Climate models favoring polar amplification use the Eemian as an analog of the present. In a new study, Bauch et al. compare reconstructed temperatures and water masses from two sediment cores that record the flow of meltwater in the subpolar and polar North Atlantic over the past 135,000 years. They do not find evidence of extreme warmth in the sub-Arctic during the Eemian interglacial period.
In fact, the Arctic may have been colder during the Eemian, with lower heat transfer from the North Atlantic. On the basis of their finding, the authors suggest that previous records may reflect other phenomena and caution against the use of the Eemian as an analog of the present. Their finding also challenges climate models that predict extreme warmth and ice-free conditions in the Arctic in response to greenhouse gas warming in the 21st century.
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- Henning A. Bauch, Evguenia S. Kandiano, Jan P. Helmke. Contrasting ocean changes between the subpolar and polar North Atlantic during the past 135 ka. Geophysical Research Letters, 2012; 39 (11) DOI: 10.1029/2012GL051800
Note: If no author is given, the source is cited instead. | <urn:uuid:2b370b67-c5f5-4db9-bbfc-8ecfeab31d58> | 3.859375 | 488 | Truncated | Science & Tech. | 45.826051 |
FJ is contained in plane R, BC and DE are contained in plane S, and FJ, BC, and DE intersect at A. its hard for me
I dont understand when there's a cirlce and multiple lines crossing what all the rules are for the ratio's of the lines, I remember learning something was one third of something else ? But i dont...
explain how to find the PQ.
7 is on the base of the triangle & 13 is on the right side of the triangle
a 5 foot vertical pole casts a 3 foot shadow a tree casts a 20 foot shadow. find the height of the tree to the nearest tenth
2nd semester dont know where to start
The frustum has: radii of the top circle base is 9. the radii of the bottom circle is 12. The slant height is 6. I know you draw the frustum into a cone by extending it. Then you do the volume...
like square,rectangle,and trapazoid
Identifying points, lines segments and rays
I noticed that the sum of the digits of the number on the page I was reading was 19, and the sum of the next digits on the page was 2. What was the number of the page I was reading?
the perimeter of a triangle is 43ft. The shortest side is one-third of the length of the middle side. The longest side is 3ft more than four times the shortest side. find the lengths of the three...
in regards to geometry
FIND THE LENGTH AND WIDTH?
Find the length of a diagonal of a rectangular box whose edges are 6cm, 8cm, and 10 cm. Write all radicals in simplest form
find the coordinates of the midpoint of the segment wuth the given pair of endpoints J(6,6) and K(2,-4)
need help finding the endpoints
line k passes through the two points (-7,-4) and (8,1) what is the equation of a line perpendicular to line m passing through (0,4)
need the equation
The edge is 12 and the height is 12 for the tetrahedron. I know that tetrahedron consists of 4 equilateral triangles. I have a problem with finding the volume because i had two answers. first...
A person in a 60ft tall tower is looking down 18 degrees at a fire how far away is the fire from the person
absolutely urgent ghavdieveudbekeuehenevv
Hello, I need to reduce the inside diameter of the 5mm thick, flat bar, steel tuning hoop on a conga drum and would like to know how to calculate exactly how much material I need...
The formula to find the perimeter of a rectangle is: P = 2W + 2L. To solve for " W " in this formula, which steps should be followed?
i need the answer | <urn:uuid:db7d3b73-c218-48bd-8b2b-733efff8996b> | 3.234375 | 602 | Q&A Forum | Science & Tech. | 81.15624 |
The Solar System is remarkably regular, its eight planets orbiting the Sun in the same direction in very nearly circular trajectories. Their orbits lie nearly in the same plane, which is aligned with the Sun's equator. These facts point toward a common origin for the Solar System, where everything collapsed from a single protostellar disk.
However, many exoplanetary systems are very different: exoplanets often orbit in highly elliptical orbits, and some "hot Jupiters" (giant planets in very small orbits) even revolve in the opposite direction from their host stars. A current major challenge in astrophysics is to understand why irregular systems exist.
The exoplanet system Kepler-30 could provide some help. A new analysis by Roberto Sanchis-Ojeda and colleagues showed the three known planets in the system orbit in a regular fashion: nearly circular orbits aligned with the rotation of the host star Kepler-30a. The researchers found the Kepler-30 system to be as orderly as the Solar System, leading them to suggest that misaligned hot Jupiter systems arise from interactions among the planets, rather than a different process of planet formation.
The regularity of the largest bodies in the Solar System is striking, especially in contrast with other known exoplanet systems. (In fact, other than Venus and Uranus, planets in the Solar System even rotate around their axes the same direction.) One measure of this regularity is the fact that the planes of our planets' orbits are very close to the Sun's equator. This can be quantified as the stellar obliquity, which is the angle between the star's angular momentum and the angular momentum of each planet. The direction of the angular momentum is found by curling the fingers of your right hand in the direction of rotation or orbit; your thumb points in the direction of the vector. If the angular momentum of the star and a planet's orbit are nearly the same, the stellar obliquity is small.
The eight planets in the Solar System all have small stellar obliquities, but many hot Jupiter systems do not. In some cases, host stars may even rotate in the opposite direction to the revolution of its planets. The most commonly accepted planet formation model predicts that planets and their stars form from a single disk of gas and dust. All the objects in the system revolved the same direction the disk rotated; this provides an excellent explanation for the uniformity of our Solar System.
Rotations can't be measured for every star: starspots need to be present in the data. With only a few exceptions, stars are too far away and too small for direct imaging of their surfaces, so starspots are found via fluctuations in the star's light. To be detected, the starspots have to be significantly larger than sunspots, and so rotation has been measured for only a few stars bearing relatively huge starspots.
Despite this handicap, the researchers determined Kepler-30a's rotation rate to be about 16 days at the latitude of the starspot. (Stars don't rotate at the same rate for every point on the surface, since they are not solid. For example, the Sun rotates once about every 25 days at the equator, but it takes longer at the poles.) From that relatively rapid rotation, they concluded Kepler-3a is younger than the Sun, since stars slow down as they age. (Don't we all?)
Using 2.5 years of Kepler telescope data, the researchers found instances where more than one of the exoplanets passed successively across the same starspot group. This verified both the direction and the plane of orbit for each planet in the system within a range of values, which were consistent with a Solar System-like model. Independent measurements of the planets' orbits showed them to be nearly circular as well.
While Kepler-30 is just one star system, its regularity places it in the same category as the Solar System, making it very different from many exoplanet systems containing hot Jupiters. The authors argue that this could be an indication that hot Jupiters got where they are via orbital interactions with other planets. If other multi-planet systems have similarly low obliquities, then it's unlikely that protoplanetary disks formed out of alignment with the equators of the host stars. The starspot transit method laid out in this paper should help resolve whether all multiple-planet systems are similarly regular to Kepler-30 and the Solar System. | <urn:uuid:fbeff072-2e1b-43db-a4c3-cbd5d4616b89> | 4.15625 | 917 | Knowledge Article | Science & Tech. | 39.066314 |
Millions of years before humans invented sonar, bats and toothed whales had mastered the biological version of the same trick – echolocation. By timing the echoes of their calls, one group effortlessly flies through the darkest of skies and the other swims through the murkiest of waters. It’s amazing enough that two such different groups of mammals should have evolved the same trick but that similarity isn’t just skin deep.
The echolocation abilities of bats and whales, though different in their details, rely on the same changes to the same gene – Prestin. These changes have produced such similar proteins that if you drew a family tree based on their amino acid sequences, bats and toothed whales would end up in the same tight-knit group, to the exclusion of other bats and whales that don’t use sonar.
This is one of the most dramatic examples yet of ‘convergent evolution’, where different groups of living things have independently evolved similar behaviours or body parts in response to similar evolutionary pressures.
It is one of a growing number of studies have shown that convergence on the surface – like having venom, being intelligent or lacking enamel – is borne of deeper genetic resemblance. But this discovery is special in a deliciously ironic way. It was made by two groups of scientists, who independently arrived at the same result. The first authors even have virtually identical names. These are people who take convergence seriously!
Yang Liu from the East China Normal University had previously shown that echolocating bats share very similar versions of Prestin, even species that were only distantly related. This time, he sequenced the gene in even more bats as well as a wide range of whales. These included toothed species (dolphins, porpoises, orcas and sperm whales) that use sonar, and baleen species that don’t.
Based on the DNA sequences of these Prestin versions, Liu drew a mammal family tree (a ‘phylogeny’). It looked much like what you would expect, with the whales and bats clustering in separate family groups. But convert the sequences into amino acids and the picture changes dramatically. Suddenly, the family tree becomes utterly misleading. The echolocating mammals, be they bats or whales, are united as close relatives, to the exclusion of their rightful evolutionary kin.
Ying Li (see what I mean?) from the University of Michigan found a similar result. She sequenced the Prestin gene in the bottlenosed dolphin and compared it to sequences from other mammals. Again, she found that Prestin sequences place the dolphin as a close cousin of echolocating bats rather than species that it’s actually more closely related to, such as cows.
At first, it might seem strange to see such strong convergence at the genetic level. After all, bats and toothed whales echolocate very differently. Bats create their sonar pulses using their voicebox while whales pass air through their nasal bones. Bats send their calls through air and whales send their through water. A single gene can’t have accounted for these differences in production.
Instead, Prestin‘s role is in detecting the rebounding echoes. It is activated in the “outer hair cells” of the ear, which allow mammals to hear high frequencies. In echolocating species, these cells are shorter and stiffer than normal, making them exquisitely sensitive to the ultrasonic frequencies used in echolocation. Li thinks that the Prestin changes might have helped to tune the outer hair cells of echolocators to high-pitched noises.
Liu used his sequences to reconstruct what Prestin would have looked like the ancestor of all bats and the ancestor of all whales. Compared to these original versions, echolocating species have accrued the same set of 14 amino acid changes, whether they have wings or flippers. It seems that there are only very few ways, if not only one, for mammals to hear the ultrasonic sounds needed for biological sonar.
Exactly what these amino acid changes did to the Prestin protein, and how they led to the evolution of echolocation, is a mystery for another time. It will also be interesting to see if these changes have started cropping up in the Prestins of other animals with cruder forms of sonar, like oilbirds, swiftlets, shrews and tenrecs.
Liu et al. Convergent sequence evolution between echolocating bats and dolphins. Current Biology in press.
Li et al. The Hearing Gene Prestin Unites Echolocating Bats and Whales. Current Biology in press.
More on convergent evolution:
- Three desert lizards evolve white skins through different mutations to the same gene
- Elephants and humans evolved similar solutions to problems of gas-guzzling brains
- Venomous shrews and lizards evolved toxic proteins in the same way
- Decay of enamel-forming gene linked to evolutionary loss of enamel | <urn:uuid:727cbd9a-8a88-4bc4-b85e-521a721cac0b> | 3.828125 | 1,050 | Nonfiction Writing | Science & Tech. | 38.563424 |
First of all, the 1976 Viking lander did NOT find organics on Mars. This is not just because the mass-spectrometer they flew was 3 orders of magnitude too insensitive to find organics from either the Atacama desert or the dry valleys of Antarctica, but also because sulfur poisoned the palladium foil that was intended to concentrate the organics for analysis.
The labelled-release experiment of Gil Levin, however, did find evidence of bacterial metabolism. You can read the papers on his website: http://mars.spherix.com/mars.html. It was tested against soils in Antarctica and Atacama, and in both cases found microbes unlike Carl Sagan's mass spectrometer. Carl ran interference and made sure Gil's work didn't get published, but I've told that story elsewhere.
But being a mass spectrometer, and being designed for low-molecular weight gases, Sagan did NOT find perchlorates in the soil either. They would have seen them had they been there. They would have seen the chlorine too--it has an unmistakeable signature. And it would sorta have explained Levin's data because the perchlorate would have oxidized the organics to produce CO2. But they didn't see it. Nothing. Nada, despite there being good explanation if it had existed.
So Carl Sagan argued for super-metallo-peroxides. Why? Because they would produce hydrogen peroxide when water was added, which presumably would evolve carbon dioxide as measured in Gil Levin's experiment without leaving a telltale signature in the mass spec. This theory persisted despite not finding any hydrogen peroxide in the atmosphere which the chemistry required.
So once again. The results of Viking were no organics due to insensitivity and poisoning, and certainly no perchlorates.
Fast forward 32 years to 2008, and we have the Phoenix lander that decided NOT to use mass spectroscopy, but wet chemistry to determine the makeup of Mars soil. In my mind, I can't find a single reason why this is a better measurement. It's less sensitive, less accurate, less general, less power-efficient, less lightweight, less robust, etc. But nothing in the Mars program makes sense without understanding the politics, so I just assume there was someone who had the ear of a congressman. Well, in order to prep the spacecraft for detecting organics, they had to remove finger prints (or as my mechanical engineer used to say, fried chicken grease) from the satellite. How did they do this? Why, with a perchlorate wash of course.
Do you suppose...Nah, the team reported, it couldn't possibly be contamination. Why, it agreed with the Viking results!
Sunday, January 23, 2011
So, did the 1976 NASA mission find evidence of life on Mars? Has anybody?
Friend Rob Sheldon writes, | <urn:uuid:0e3e7414-8e50-40ba-afad-bee09b30a274> | 2.9375 | 593 | Personal Blog | Science & Tech. | 50.852108 |
Telescope spots solar tsunami
Dec. 7, 2006: The prototype of a new solar patrol telescope in New Mexico recorded a tsunami-like shock wave rolling across the visible face of the Sun following a major flare even on Wednesday, Dec. 6, 2006, at 18:28 Universal Time (11:28 MST). The shock wave, known as a Moreton wave, also destroyed or compressed two filaments of cool gas at opposite sides of the solar hemisphere.
"These large scale 'blast' waves occur infrequently, but are very powerful. They quickly propagate in a matter of minutes covering the whole Sun, sweeping away filamentary material," said Dr. K. S. Balasubramaniam, of the National Solar Observatory (NSO) in Sunspot, NM, who is studying these and other phenomena. "It is unusual to see such powerful waves encompassing the whole sun from ground based observatories. Its significance comes from the fact that these waves are occurring near solar minimum, when intense activity is yet to pick up."
This large, "naked eye" sunspot region had an outburst just a day ago, and seems to have built-up tremendous energy in a short period of time. | <urn:uuid:8534f2be-6019-4d52-a6c4-2a832d11877c> | 3.484375 | 249 | Comment Section | Science & Tech. | 44.438238 |
IS THE SPEED OF LIGHT CONSTANT?
Late in life Einstein couldn’t even remember whether he’d been aware, in 1905, of the Michelson-Morley experiment, which showed that the speed of light is constant in all directions. Although we now think of the experiment as having shattered absolute space and time, that result was not at all what Albert Michelson and Edward Morley expected when they did their experiment in 1887, in a basement of the Western Reserve University in Cleveland. They were trying to detect variations in the speed of light to prove the existence of the “luminiferous aether,” a perfectly immobile, transparent, and mysterious substance that was thought to pervade the universe. Physicists had conceived of the ether as a medium that could transmit light waves, the way air or water transmits sound. The ether had to exist, but no one had seen it—it was a bit like dark matter today.
Nineteenth-century scientists believed that space was filled with a mysterious, motionless substance called ether. In 1887 physicist Albert Michelson and chemist Edward Morley set out to find tiny variations in the speed of light caused by Earth’s movement through this ether. They first split a light beam (a) with a half-silvered mirror (b), and the two beams (c and d) then traveled perpendicular paths before recombining. The light waves of each beam mingled, creating a pattern of light and dark lines called fringes (e). Michelson and Morley expected that changing the angles that the beams traveled through the ether would cause fluctuations in the fringe pattern. Instead, they inadvertently proved that there is no ether and set the stage for Einstein’s theory of special relativity, which states that the speed of light is absolute. Sophisticated variations of the experiment are now used to test whether the speed of light remains constant to within one part in a quadrillion.
Because Earth orbits the sun at 18 miles per second, Michelson and Morley reasoned that they should be able to detect an ether wind blowing through their Cleveland basement with the help of an experimental setup called an interferometer. They split a light beam in two with a half-silvered mirror, sent the two halves of light off at right angles, and then bounced them off mirrors about five feet away. The two men expected that light waves traveling against the ether wind, in the same direction as Earth’s motion, would be slowed and would arrive back at the starting point slightly later than the light waves traveling across the wind. When the two beams were recombined, the offset waves would interfere with each other to produce a distinctive pattern of light and dark bands. Michelson and Morley made their measurements with extraordinary care but saw no disruption in the pattern—the light beams traveled the same speed in all directions, impervious to any ether wind.
One null result, of course, did not rid the universe of the ether. Michelson went to his grave in 1931 convinced that it had to exist. But by then Einstein had changed most people’s minds and persuaded them to accept the simple, beautiful truth: The velocity of light, c, really is different from any other velocity. Anyone who measures the speed of any light beam—or any other type of electromagnetic radiation—will get the same value for c: 299,792,458 meters per second. There is no absolute space, Einstein decided, ether-filled or otherwise. Seen in that light, the Michelson-Morley result made perfect sense.
And yet today theorists are questioning the absoluteness of c. Some versions of string theory, the most popular candidate for a unified theory, say there could be extremely feeble force fields left over from the Big Bang that point in different directions in different parts of space. An experiment to measure c might produce variations depending on how the setup was oriented with respect to one of those fields, variations far smaller than Michelson and Morley could have detected.
Several groups are looking for such variations with modern versions of the Michelson-Morley experiment. Peter Wolf, Sebastien Bize, and their colleagues at the Paris Observatory measure c with microwaves oscillating at 12 gigahertz inside a small sapphire crystal. Microwaves reflecting back and forth within the crystal line up and reinforce each other, or resonate—as long as they are moving precisely at c. If c were to change because the orientation of the crystal had changed with respect to some “preferred” direction of space, then the resonant frequency of the sapphire oscillator would change as well. The apparatus containing the crystal is bathed in liquid helium, chilling it to a few degrees above absolute zero to make sure that the crystal doesn’t expand or contract by even a femtometer.
Over a period of months, as Earth spins on its axis and revolves around the sun, the Paris researchers monitor their oscillator, comparing it with the microwaves from a hydrogen maser (microwave laser), which shouldn’t be affected by Earth’s motion. “What we measure is that small frequency difference,” says Bize. “We look for modulations that correlate with the motion of Earth.”
Another group, based at Humboldt University in Berlin, uses a slightly different setup, comparing the outputs of a pair of sapphire oscillators. Over the past several years the two groups have achieved broadly comparable null results. “The speed of light in any two directions is the same to about one part in a quadrillion,” says Holger Müller, a former member of the Berlin team who now works at Stanford. That’s equivalent to knowing the U.S. gross national product to within a penny.
Over vast distances, even such slight variations could become meaningful. If two photons differed that much in velocity, and if they left a galaxy a billion light-years away at the same instant, they would arrive at Earth 30 seconds apart. A few years ago physicist Giovanni Amelino-Camelia at La Sapienza University in Rome had an idea for staging just such a race to test the constancy of c in a new way. Some theories of quantum gravity require space-time itself to be grainy—to be made up of discrete quanta, presumably around 10-35 of a meter across because that’s the scale at which Einstein’s field equations generate their bothersome infinities. (A proton is a hundred million trillion times bigger.) Amelino-Camelia calculated that light photons might navigate this cosmic foam at slightly different speeds, depending not on their direction—the possibility the Michelson-Morley experiments test for—but on their energy.
In 2007 or so, NASA plans to launch GLAST, the Gamma Ray Large Area Space Telescope. Its main purpose is to allow astronomers to study such events as gamma-ray bursts, which are mysteriously powerful explosions in distant galaxies. But it could also serve as Amelino-Camelia’s finish line. All the photons in a burst, he reasons, must leave the starting blocks at about the same time. If you compare a lot of high-energy photons with a lot of relatively low-energy ones, you should find that on average, after a billion-year race, the high-energy ones reach GLAST’s detector sooner—by about a millisecond. He and other quantum gravity theorists are pretty excited by that possibility, which just goes to show what they’re up against. | <urn:uuid:76977998-b1f4-4a2b-bad5-6f4344c79ca1> | 4.09375 | 1,566 | Nonfiction Writing | Science & Tech. | 42.738007 |
Signals represent conditions that arise during computation. Each corresponds to one context flag and one context trap enabler.
The context flag is incremented whenever the condition is encountered. After the computation, flags may be checked for informational purposes (for instance, to determine whether a computation was exact). After checking the flags, be sure to clear all flags before starting the next computation.
If the context's trap enabler is set for the signal, then the condition causes a Python exception to be raised. For example, if the DivisionByZero trap is set, then a DivisionByZero exception is raised upon encountering the condition.
Typically, clamping occurs when an exponent falls outside the context's Emin and Emax limits. If possible, the exponent is reduced to fit by adding zeroes to the coefficient.
Can occur with division, modulo division, or when raising a number to a negative power. If this signal is not trapped, returns Infinity or -Infinity with the sign determined by the inputs to the calculation.
Signals when non-zero digits were discarded during rounding. The rounded result is returned. The signal flag or trap is used to detect when results are inexact.
Indicates that an operation was requested that does not make sense. If not trapped, returns NaN. Possible causes include:
Infinity - Infinity 0 * Infinity Infinity / Infinity x % 0 Infinity % x x._rescale( non-integer ) sqrt(-x) and x > 0 0 ** 0 x ** (non-integer) x ** Infinity
Indicates the exponent is larger than Emax after rounding has occurred. If not trapped, the result depends on the rounding mode, either pulling inward to the largest representable finite number or rounding outward to Infinity. In either case, Inexact and Rounded are also signaled.
Signaled whenever rounding discards digits; even if those digits are zero (such as rounding 5.00 to 5.0). If not trapped, returns the result unchanged. This signal is used to detect loss of significant digits.
Occurs when an operation result is subnormal (the exponent is too small). If not trapped, returns the result unchanged.
Occurs when a subnormal result is pushed to zero by rounding. Inexact and Subnormal are also signaled.
The following table summarizes the hierarchy of signals:
exceptions.ArithmeticError(exceptions.StandardError) DecimalException Clamped DivisionByZero(DecimalException, exceptions.ZeroDivisionError) Inexact Overflow(Inexact, Rounded) Underflow(Inexact, Rounded, Subnormal) InvalidOperation Rounded Subnormal
See About this document... for information on suggesting changes. | <urn:uuid:8b1f5709-be3a-4a12-be7b-463d20c30818> | 2.953125 | 560 | Documentation | Software Dev. | 33.318389 |
movie demonstrates the increase in solar
activity from 1996-99. The images we're
taken by the SOHO spacecraft.
to launch movie.)
In the mid-1800s astronomers discovered
from thousands of sunspot sightings that, when they tabulated
and graphed them, their numbers increased and decreased over
time in a repeatable cycle. These extremes represent the amplitude
of the cycle. We now call this the solar activity cycle or
the sunspot cycle.
Solar Maxium (and minimum)
During the last 200 years, the time
between years of maximum activity, which is called the period
of the cycle, has been about 11 years, but sunspot cycles
can be as short as 9 or as long as 15 years. During sunspot
minimum conditions, such as the year 1996, astronomers counted
fewer than 5 sunspots on the surface of the Sun at any one
time. During sunspot maximum conditions in 2000, as many as
246 sunspots could be seen. On March 31, 2001, one very large
sunspot group was visible to the naked eye with the proper
safety precautions. (You should never look directly at the
Sun without proper shielding to avoid eye damage!).
Variations in the Cycle
Ancient Chinese astronomers also
kept track of naked-eye sunspots 4000 years ago, and that's
how we know that sunspots have been a common feature of the
Sun for millennia. We also know from graphs of the sunspot
cycle that sometimes the Sun just stops making them altogether.
This happened in the 1600s, and this was also the time when
Europe was in the grip of what they called a mini-Ice Age.
The Solar Cycle and Weather
Scientists don't fully understand
the connection between the sunspot cycle and weather conditions
here on Earth, but there does seem to be something going on
between them. Scientists have detected correlations between
the ups and downs of the solar activity cycle and the behavior
of a number of terrestrial atmospheric and climate systems.
For example, the ozone hole over Antarctica has an area that
appears slightly larger during sunspot maximum than sunspot
minimum. Traces of the 11-year cycle have also been claimed
to exist in ocean surface temperatures, coral reef layering
and the sizes of northern hemisphere storm systems.
out more about the Sun-Earth Connection at the Sun-Earth
Connection Education Forum Web site.
Text adapted from the
Sun-Earth Connection Tutorial courtesy of NASA, originally
written by Dr. Sten Odenwald. Images and videos courtesy of
NASA unless otherwised noted. | <urn:uuid:c593e01b-7fb4-4dfd-9c9c-6f72e9fffd9f> | 4.09375 | 549 | Knowledge Article | Science & Tech. | 49.899183 |
The role of water
Although water is not directly involved as the transporting medium in mass-wasting processes, it does play an important role. Think about building a sandcastle on the beach. If the sand is totally dry, it is impossible to build a pile of sand with a steep face like a castle wall. If the sand is somewhat wet, however, one can build a vertical wall. If the sand is too wet, then it flows like a fluid and cannot remain in position as a wall.
Dry unconsolidated grains will form a pile with a slope angle determined by the angle of repose. The angle of repose is the steepest angle at which a pile of unconsolidated grains remains stable, and is controlled by the frictional contact between the grains. In general, for dry materials the angle of repose increases with increasing grain size, but usually lies between about 30 and 37o.
Slightly wet unconsolidated materials exhibit a very high
angle of repose because surface tension between the water
and the grains tends to hold the grains in place.
When the material becomes saturated with water, the angle of repose is reduced to very small values and the material tends to flow like a fluid. This is because the water gets between the grains and eliminates grain to grain frictional contact. | <urn:uuid:45aab117-4e0e-4e6c-ab8f-97e50cac2809> | 3.984375 | 269 | Knowledge Article | Science & Tech. | 48.166702 |
How Life could Evolve in a Red Dwarf Star System
On Earth it is believed that life originated or could have originated in caves or round Hydrothermal vents. If life evolved similarly in a Red dwarf star system life could adapt over millions of years to cope with stellar flares. Scientists disagree about whether life could exist in red dwarf star systems. See Proxima Centauri where two scientists are cited, http://www.liebertonline.com/doi/abs/10.1089/ast.2006.0127 A Reappraisal of The Habitability of Planets around M Dwarf Stars and Impact on Expected Magnetospheres of Earth-Like Exoplanets in Close-In Habitable Zones. See also Habitability of red dwarf systems and Aurelia.
The text below assumes those scientsts who think red dwarfs are habitable are correct.
Life in caves
Life in caves could gradually adapt to exploit environments nearer to the cave mouth. In the course of this flares would increasingly become a problem. Life could gradually evolve defences. For example living organisms could evolve opaque protective shells. When they detect that a flare is starting they could retreat into their shells. Probably different organisms would evolve different mechanisms. Resistant organisms could colonize habitats where more susceptible competitors would be killed by flares. Later when the protective mechanisms are sufficiently strong living organisms could live out in the open and evolve Photosynthesis.
Life round hydrothermal vents
Life round hydrothermal vents would face greater difficulties. Most hydrothermal vents are in deep oceans where there is no intermediate habitat between the vents and the ocean surface. On Earth in places like Hawaii and Iceland geological activity typical of hydrothermal vents happens in shallow water. In such places life could also gradually evolve protection against flares. Resistant organisms could colonize habitats where more susceptible competitors would be killed by flares. As resistance progressively evolved life could move progressively into shallower water where there is more light even between flares. Then again photosynthesis could evolve.
Small life and Microscopic life
A smaller living organism has a larger surface area to volume ratio. Therefore smaller plants and animals would need to use proportionately more energy to build protective shells and to carry such shells around if they moved. Small organisms could live in soil in mud, in the shadows of mountains where flares could not reach them or in deep water. Small organisms could also exist in rough terrain where there are places to shelter during flares. Small organisms could live on the surface of mud and soil as well provided they could burrow downwards during flares. Small life could live on the surface of water provided it could dive during flares. Small life, like tardigrades on Earth, could also survive radiation from flares by dehydrating their bodies, and remaining static for sustained periods of time.
Currently scientists believe that small life and microscopic life is probably more common than large life. Such life would be restricted to areas where at least some organisms could survive flares. Alternaively small life would need life chemistry that reacts strongly to the red light that a red dwarf star emits in large amounts and can draw energy from that light. At the same time it would not react fatally with the more intense light emitted during flares. The author is not a biochemist and does not know if this is possible.
Larger organisms
Large organisms may if they are motile retreat into shells. They may also run and find shelter. A large animal or plant with a protective shell may spend its life in open terrain and the shell would protect it during flares. Would their young be large or small? There are two possibilities.
- The first possibility is that young would be large enough to have protective shells as soon as they are independent from their parent or would grow fast after independence. Many animals and plants may produce a few large young rather than many small young. They may have shells at birth or on hatching. Perhaps small dependent young would retreat into their parent's shell during a flare. Perhaps parents would make a shell or a protective burrow for small young before leaving them to fend for themselves. The young may alternatively grow shells after hatching, some young would die if a flare happened before they had grown a shell but sufficiently many young would live until they had a shell before their first flare so the species could continue. (Proxima Centauri flares every few days according to but that site could be controversial This could happen with red dwarf stars that flare less often.)
- The second possibility is that parents would lay eggs or deposit live young in muddy places or other places where a small animal can survive. When the young animals were bigger and had protective shells they would migrate to open terrain.
On Earth mammals have a layer of dead emidermis on the surface of their skin. Also mammalian hair is dead. The sun of the Solar System does not flare and therefore a thick dead layer is not needed on Earth. On a planet orbiting a red dwarf star thick opaque layers of dead skin or scales could protect the living parts of an animal from radiation during flares without restricting movement.
It is quite possible that in a red dwarf ecology larger plants and animals with protective shells or protective outer skins would fill many ecological niches where small organisms are on Earth.
Older Red Dwarf stars
Astronomers believe that red dwarf stars eventually stop flaring. Red dwarfs last for very long periods of time and age very slowly. Proxima Centauri is as old as our sun but is still young by red dwarf standards and is flaring frequently. Life could evolve after the star has stopped flaring provided geological conditions on the planet are favourable for life. Some scientists believe that life requires a geologically active planet like Earth. Barnard's Star is much older than Proxima Centauri and it is believed that this star flared during the 1990's.
Paradoxically there might be a new threat to life when flares become less frequent. While flares are common mechanisms that enable organisms to survive them will remain sharp. Natural selection will weed out organisms with defective mechanisms to resist flares. What will happen if a red dwarf star passes through a stage when it flares on average once every ten thousand years or once every million years? If that happens most organisms may be unable to resist flares when they happen. Organisms that happened to be in places that are sheltered from the flare would survive but plants in those places would not get energy for photosynthesis afterwards.
On Earth many plants can survive if all the parts that are above ground are killed by, for example a forest fire or a plague of locusts. Also seeds below soil level can survive such disasters. Gardeners know that some weeds grow again even after all the parts that are above ground have been removed. If a red dwarf flares rarely plant life could survive similarly.
Devastating ocean waves
The hurricane on Aurelia would generate enormous waves in the ocean and the waves would migrate outwards. Oceanographers should test how high these waves would be in the postulated nearby swamps and delta area. They would be wind driven waves and would not reach from the top of an ocean to the bottom like a tsunami. None the less waves as devastating as those that Earthlings call freak waves might be regular. Simple bacterial and algal life would not be threatened. Oh my poor little Centaurians! I'm not sure if they can exist, though they probably can exist in sheltered areas. Semi aquatic aliens may be able to breathe oxygen dissolved in water and may not be at risk of drowning but they could be dashed to death against rocks etc as easily as humans. I'm going to assume that they evolved round an area like the Mediterranean or Hudson Bay sheltered from the worst waves but conditions would have to remain sheltered for hundreds of millions of years there for complex life to evolve.
Could animals migrate from one sheltered area to another across the wild open ocean and colonize new sheltered areas? Animals might be driven into the open ocean by storms or currents, most would quite likely die but from time to time a breeding pair or a pregnant animal may wash up in another sheltered area of water. Therefore when over long geological epochs one sheltered water area changes and ceases to be habitable for complex life the living organisms could be established elsewhere. | <urn:uuid:f511560d-9839-409c-afb3-4635a5cde446> | 4.15625 | 1,673 | Knowledge Article | Science & Tech. | 44.206793 |
Gray Whiskers stacey.d via Flickr With their strange 60-atom structures, buckyballs could have potential as drug carriers, medical tracers, cancer fighters and other interesting applications in the human body, but studies examining their impact on the body have had mixed results. A group of French researchers set out to study its toxicity and other effects, and came up with a surprising find - not only are buckyballs safe, a buckyball diet doubled the lifespan of lab rats. It's a limited study, and the longer-lasting rats could be the result of a calorie-restricted diet instead, as some skeptics have pointed out. But it raises some interesting questions about the potential health benefits of buckyballs. Computer simulations and other studies have shown buckyballs - more specifically, the fullerene known as C60 - are soluble in fat and can cross cell membranes, which is one reason why they could be useful as drug carriers...
- How buckyballs hurt cellsTue, 27 May 2008, 10:35:33 EDT
- 'Buckyballs' have high potential to accumulate in living tissueThu, 18 Sep 2008, 17:16:51 EDT
- Buckyballs could keep water systems flowingThu, 5 Mar 2009, 6:49:57 EST
- Nanophysics: Serving up Buckyballs on a silver platterMon, 27 Jul 2009, 10:08:44 EDT
- Finding a buckyball in photovoltaic cellTue, 28 Sep 2010, 16:36:52 EDT | <urn:uuid:79fc998a-d567-4fc5-a8ef-ecacb3360ec8> | 3.09375 | 314 | Content Listing | Science & Tech. | 48.258973 |
June 1, 2004: Astronomers unveiled the deepest images from NASA's new Spitzer Space Telescope today, and announced the detection of distant objects — including several supermassive black holes — that are nearly invisible in even the deepest images from telescopes operating at other wavelengths.See the rest:
Supermassive black holes formed early in the universe and accompanied galaxy formation. Hubble research finds that they are common among galaxies. They are millions or billions of times more massive than black holes that are left behind after a star explodes.
AGNs active galactic nuclei are supermassive black holes that are accreting gas. The black hole heats the gas to millions of degrees, where it glows in X-rays. This makes the region around the black hole glow brightly across the universe.
Black holes were well-fed in the early universe. There was a lot of gas from them to accrete from galaxy collisions, which were more frequent when the expanding universe was smaller, so very distant galaxies are more likely to have AGNs.
Black holes can be hidden behind dusty, donut-shaped features, which are common in AGNs. Or, they can be so far away that all their light is stretched into the infrared region of the spectrum. | <urn:uuid:e437963e-08b4-4355-95c9-1670ac01aaff> | 4.3125 | 249 | Knowledge Article | Science & Tech. | 38.527871 |
Degree - The greatest exponent in a polynomial or equation.
- 3x13 + 5x3 (Degree: 13)
- h5 + h4 + h8 + h3 + h12 + h2 + 13h (Degree: 12)
- y = -5b + 19 (Degree : 1; Note, b is raised to the 1st power.)
- ƒ(x) = 5x9 - 5 (Degree: 9)
Why is This Important?
- The degree of a function determines the most number of solutions that the function could have.
- The degree of a function determines the most number of times a function will cross the x-axis.
- y = x (Degree: 1; Only 1 solution)
- y = x2 (Degree: 2; Two possible solutions)
- y = x3 (Degree: 3; Three possible solutions) | <urn:uuid:4db07c60-c3f6-47d3-9d53-0950655d8997> | 3 | 205 | Structured Data | Science & Tech. | 83.323 |
Exploring Hydrocarbon Depletion
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Turns out it's not such a crazy argument after all.
Scientists link melting glaciers to earthquakes
Experts ponder whether tectonic activity increasing
Some scientists theorize that the sudden melting of glaciers due to man-made climate change is lightening the load on the Earth's surface, allowing its mantle to rebound upwards and causing plates to become unstuck.
These scientists point to the historical increase in volcanic and earthquake activity that occurred about 12,000 years ago when the glaciers that covered most of Canada in an ice sheet several kilometres thick suddenly melted.
The result was that most of Canada's crust lifted -and is still rising.
Scientists have discovered that the accelerated melting of the Greenland ice sheet over the last 10 years already is lifting the southeastern part of that island several millimetres every year.
The surface of the Earth is elastic. A heavy load such as a glacier will cause it to sink, pushing aside the liquid rock underneath.
The Greenland glacier is about three kilometres at its thickest and it is believed that its weight has depressed sections of the land under the glacier about one kilometre. In fact, the weight of the glacier is so great that significant portions of Greenland have been pushed well below sea level.
"There is certainly some literature that talks about the increased occurrence of volcanic eruptions and the removing of load from the crust by deglaciation," said Martin Sharp, a glaciologist at the University of Alberta. "It changes the stress load in the crust and maybe it opens up routes for lava to come to the surface.
"It is conceivable that there would be some increase in earthquake activity during periods of rapid changes on the Earth's crust."
Other scientists, however, believe tectonic movements similar to the one that caused the Japanese quake are too deep in the Earth to be affected by the pressure releases caused by glacier melt.
rockdoc123 wrote:Sweet Jesus....the guy is a glaciologist not a structural geologist or rock mechanics expert nor someone who works with geophyisics. What he is suggesting is preposterous from the perspective of rock mechanics and what we know about the response of the asthenosphere to uplift.
And Anthony Watts is just a former TV meteorologist.
rockdoc123 wrote:And Anthony Watts is just a former TV meteorologist.
Ok, you obviously think this fellow is correct. Please explain why with particular attention to the points I raised.
Nuclear fuel has melted through base of Fukushima plant
1:06AM BST 09 Jun 2011
The findings of the report, which has been given to the International Atomic Energy Agency, were revealed by the Yomiuri newspaper, which described a "melt-through" as being "far worse than a core meltdown" and "the worst possibility in a nuclear accident."
A spokesman for Tokyo Electric Power Co. said the company is presently revising the road-map for bringing the plant under control, including the time required to achieve cold shutdown of the reactors.
mhr727 wrote:I personally think its the other way around, the 2 major earthquakes that caused Tsunami,s from what i have read and seen, caused a slight variation in the earths axis and or rotation. i,m curious to see if these factors have increased the rate at which the glaciers are retreating. Everything i read states that since 2004 melting has accelerated. and of course it is too soon since the Japan Earthquake/Tsunami to really notice any change but it may be happening now.
Users browsing this forum: No registered users and 5 guests | <urn:uuid:edbab3b2-ae3c-4cb3-9b4e-9ae681e2a39c> | 3.171875 | 758 | Comment Section | Science & Tech. | 46.099831 |
This is an old physics olympiad problem, I think. The answer hinges on the spheres expanding due to heating. Sphere A raises its center of mass some and sphere B lowers its center of mass some. By conservation of energy sphere A is thus slightly colder, since more of its energy went into its gravitational potential.
It's a bit of a silly problem since the effect is extremely small. We can see this because from common experience if you heat a metal sphere $10 C$, the change in radius is pretty small - so small you probably won't notice without measuring it or else having something with a different expansion coefficient wrapped around the sphere. Meanwhile, if you drop a fist-sized a metal sphere by $1cm$, a distance much larger than such a sphere would expand with a $10 C$ change, the temperature change is much, much smaller than $10 C$. It's smaller than you can even notice, really. So the gravitational potential change is very small compared to the heat, and the difference in temperatures is minute. | <urn:uuid:6442d204-9d23-441a-b9b5-885f555ebb5a> | 3.25 | 211 | Q&A Forum | Science & Tech. | 52.744874 |
Planck's constant, symbolized h, relates the energy in one quantum (photon) of electromagnetic radiation to the frequency of that radiation. In the International System of units (SI), the constant is equal to approximately 6.626176 x 10-34 joule-seconds. In the centimeter-gram-second (cgs) or small-unit metric system, it is equal to approximately 6.626176 x 10-27 erg-seconds.
The energy E contained in a photon, which represents the smallest possible 'packet' of energy in an electromagnetic wave, is directly proportional to the frequency f according to the following equation:
E = hf
E = (6.626176 x 10-34) f
f = E / (6.626176 x 10-34) | <urn:uuid:bbcde94c-cae5-487e-8a76-a1005005b0cc> | 3.40625 | 166 | Knowledge Article | Science & Tech. | 63.458919 |
Our view of the Universe just grew quite a bit more detailed as NASA JPL released the compendium of results from the Wide-field Infrared Survey Explorer orbital telescope. WISE was launched into a 525 km orbit on December 14, 2009 and gathered data until the WISE team ran out of funding on February 17, 2011.
With hardware over 1,000 times more sensitive than prior infrared space surveys, WISE surveyed 99 percent of the sky at 4 different wavelengths. Over 15 terabytes of data and 2.7 million images revealed 560 million stars, galaxies, comets, asteroids, and various other objects too cool or red-shifted to show up in anything but the infrared. Astronomers saw Y-dwarfs for the first time, which are white dwarf stars that have become nearly invisible as they cooled. The first Earth trojan asteroid also revealed itself to WISE—it scouts Earth’s orbit 60 degrees ahead of us around the Sun. | <urn:uuid:091099fe-0559-4a76-9f81-dc3d63849441> | 4 | 195 | Personal Blog | Science & Tech. | 51.135127 |
NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team. Caption by Rebecca Lindsey.
Twelve miles west of Redding, California, a fire touched off by lightning in late June 2008 continued to creep through timber and brush in the Whiskeytown National Recreation area in early July. This false-color image of the area was captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on July 6, 2008. The use of infrared and visible light in the image highlights the contrast between vegetation (red), naturally bare ground (tan), and burned ground (charcoal). According to the July 8, 2008, report from the National Interagency Fire Center, the Whiskeytown Complex fire was 5,050 acres and 50 percent contained.
This image originally appeared on the Earth Observatory. Click here to view the full, original record. | <urn:uuid:b4b7d57f-58a8-4789-9049-8e29eea35f38> | 3.0625 | 203 | Knowledge Article | Science & Tech. | 42.048135 |
sharp view from the
Thermal Emission Imaging System
NASA's Mars Odyssey orbiter is centered on 154 kilometer (96 mile)
wide Gale crater, near the martian equator.
an impressive layered mountain rises about 5 kilometers
(3 miles) above the crater floor.
Layers and structures near its base are thought
to have been formed in ancient times by water-carried sediments.
a spot near
the crater's northern side at the foot of the mountain
has now been chosen
as the target for the
Science Laboratory mission.
Scheduled for launch late this year,
the mission will land
Mars' next visitor from planet Earth in August of 2012,
lowering the car-sized
to the martian surface with a
hovering, rocket-powered skycrane.
Curiosity's science instruments
intended to discover if
Gale once had favorable environmental conditions for
supporting microbial life and for preserving clues about whether life
ever existed on
the Red Planet. | <urn:uuid:bcb37c48-ea00-4bc5-8707-7b22dd6974dc> | 3.5625 | 213 | Knowledge Article | Science & Tech. | 35.621959 |
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A rigorous basis for the new discipline of analysis was achieved in the 19th century, in particular by the German mathematician Karl Weierstrass. Modern analysis, however, differs from that of Weierstrass’s time in many ways, and the most obvious is the level of abstraction. Today’s analysis is set in a variety of general contexts, of which the real line and the complex plane (explained in the...
development of probability theory
During the two decades following 1909, measure theory was used in many concrete problems of probability theory, notably in the American mathematician Norbert Wiener’s treatment (1923) of the mathematical theory of Brownian motion, but the notion that all problems of probability theory could be formulated in terms of measure is customarily attributed to the Soviet mathematician Andrey...
work of Lebesgue
...French mathematician Henri-Léon Lebesgue managed to systematize this naive idea into a new theory about the size of sets, which included integration as a special case. In this theory, called measure theory, there are sets that can be measured, and they either have positive measure or are negligible (they have zero measure), and there are sets that cannot be measured at all.
What made you want to look up "measure theory"? Please share what surprised you most... | <urn:uuid:02e90b13-e298-4230-b474-6c246fa7ada2> | 3.640625 | 309 | Truncated | Science & Tech. | 39.040163 |
Chandra Looks Back At Earth
A team of scientists observed Earth’s north polar region ten times during a four-month period in 2004. As the bright arcs in this sample of images show, they discovered low-energy (0.1 - 10 kilo electron volts) X-rays generated during auroral activity. Other satellite observatories had previously detected high-energy X-rays from Earth’s auroras.
The images – seen here superimposed on a simulated image of the Earth – are from approximately 20-minute scans during which Chandra was pointed at a fixed point in the sky while the Earth’s motion carried the auroral region through the field of view. The color code of the X-ray arcs represents the brightness of the X-rays, with maximum brightness shown in red.
Auroras are produced by solar storms that eject clouds of energetic charged particles. These particles are deflected when they encounter the Earth’s magnetic field, but in the process large electric voltages are created. Electrons trapped in the Earth’s magnetic field are accelerated by these voltages and spiral along the magnetic field into the polar regions. There they collide with atoms high in the atmosphere and emit X-rays (see the accompanying illustration). | <urn:uuid:7d70c302-2d4b-44bf-a303-8b983000eaa5> | 3.890625 | 257 | Truncated | Science & Tech. | 46.202914 |
Mega mushroom expands in Oregon forest
This article was posted on December 7, 2000.
One Thousand Football Fields
Officially known as Armillaria ostoyae, or the honey mushroom, the fungus is 3.5 miles across and takes up 1,665 football fields. The small mushrooms visible above ground are only the tip of the iceberg.
Experts estimate that the giant mushroom is at least 2,400 years old, but could be 7,200 years old.
Previously, the world's largest organism was another Armillaria ostoyae, which covers a mere 1,500 acres near Mt. Adams in Washington state.
Scientists became interested in that section of forest when trees began to die. The honey mushroom uses tentacles, called rhizomorphs, to take water and nutrients from roots, killing trees.
The process benefits the ecosystem by creating clearings where new plants grow. Animals, such as woodpeckers, live in the dead tree trunks. Mushrooms also recycle nutrientsDry Climate Helps
The dry climate of eastern Oregon discourages competition from new growth, leaving space for mushrooms already established.Genetically Closer to People
In other research, scientists have determined that fungi are more closely related to human beings and animals than to other plants.
Moreover, while humans and most species are divided into only two sexes, mushrooms contain over 36,000 sexes. | <urn:uuid:1446307f-5386-4113-9781-32887ed40ee0> | 3.546875 | 282 | Knowledge Article | Science & Tech. | 49.39757 |
The fossilized footprints of dinosaurs tell the story of fumbles,
jaunts, jogs and sprints. But for other groups who swam during the Mesozoic,
the clue to their speed, and also their metabolism, is in their tails.
An evolutionary plus for large fish, cetaceans and some marine reptiles was a tail fin shaped like that of today’s tuna, says Ryosuke Motani of the Royal Ontario Museum in Ontario, Canada. While the unrelated species each have a unique style — think shark vs. dolphin — their similar thunniform, or tuna-like, design, with their tails modeled in the tapered-back wings of a fighter jet, is a prime example of convergent evolution.
Body profiles from left to right of a bluefin tuna Thunnus thynnus, porbeagle Lamna nasus, Heaviside's dolphin Cephalorhynchus heavisidii and an ichthyosaur Stenopterygius quadriscissus. Image by R. Motani.
A decade ago, the forked tails with their crescent-moon shape were believed to help maintain the most efficient and fastest cruising speeds. The more tapered the tail the faster the fish. But then in 1992 the blue marlin was discovered to be a slow cruiser.
Now, by studying the fish’s physical design and its relationship to the medium through which fish travel, Motani has developed a model that shows that in fact the most efficient shape is not always the fastest. And, more importantly, he can take his model back in time to study the speed and energetics of ichthyosaurs, because they too had tuna-like tails.
“Since I saw pictures of a tuna, whale and shark depicted side by side in a college textbook, I always wanted to know what was behind this evolutionary convergence,” Motani says. “It so happened that I went into paleontology to study ichthyosaurs, which is the often-neglected fourth example of this convergence phenomenon. I started to explore the biology of these extinct marine reptiles, and there came a point where I needed to know how fast they swam.”
But while previous models estimated the speed of aquatic reptiles based on an assumption of their metabolic rates, Motani’s model, reported in the Jan. 17 Nature, instead uses external characteristics that can be measured directly from a fossil. He calculated how the mechanical properties of its body shape helped an ichthyosaur move through the fluid medium of the ocean. To determine the predictability of his mathematical model, he compared his results to the steady swimming speeds of 12 different living species of whales, dolphins, fish and other marine cruisers.
When he saw his model fit tightly with the empirical data, he turned to study several specimens of the Early Jurassic ichthyosaur called Stenopterygius.
“You might think it crazy to think about the speed of something long extinct,” he says. “But I thought I might have a chance.”
The tail of a large fish determines the size of its wake and consequently the amount of thrust it can produce. The tips of the tail flukes act as oscillating foils producing an expected power output. Motani developed a few equations to quantify the constraints of swimming for animals with tuna-like tails, tunas being the common reference fish for the design even through they weren’t around until the Pliocene. Ichthyosaurs, he discovered, with lengths ranging from 0.45 meters to 2.4 meters, swam most efficiently at speeds between 1.3 and 1.6 meters per second, slightly slower than whales and dolphins of the same size and more like tunas.
“This is an elegant model that predicts swimming speed and shows clearly why the classic case of convergent evolution is seen in these thunniforms,” says Glenn Storrs, curator of vertebrate paleontology at the Cincinnati Museum Center. “Before people suggested that ichthyosaurs swam in a similar way to tunas, because they had a similar body shape and because they were operating in a similar physical environment. But here Motani took physical measurements, compared them with modern taxa, like tuna and lamnid shark, and demonstrated using his model that yes, they had a similar cruising speed and, ultimately, raised basal metabolic rates — just like tuna.”
Indeed, once Motani had an estimate of ichthyosaur speed, he revisited Judy Massare’s 1988 model determining swimming capabilities for Mesozoic marine reptiles based on assumed metabolic rates. Motani compared his cruising speed of ichthyosaurs with the model based on metabolism and again found a similarity with tuna. Ichthyosaur cruising speed was faster than the speed determined from metabolic rates of cold-blooded reptiles and slower than the higher rates of modern marine mammals. But it was just right for the intermediate rate seen in leatherback turtles and tunas.
Still the true speed of ichthyosaurs may never really be known, says Frank Fish, a zoologist and functional morphologist at West Chester University of Pennsylvania. The tail, he says, is only part of the story. “Did they have drag reduction mechanisms for ichthyosaurs?” he asks. “Something like the surface of the animal’s scale pattern could foster turbulence and keep a layer of water in direct contact with the skin, similar to golf balls with dimples trapping air. That would keep the water from separating from the body and going into outer flow. When that happens drag is high.” Ichthyosaurs also have a large beak, which, if similar to the sword on a swordfish, might act to reduce drag.
“Visitors to the museum frequently ask me how fast did ichthyosaurs swim and what were their body temperatures,” says Betsy Nicholls, an ichthyosaur expert at the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta. “The great thing about this paper is it presents an alternate method for calculating swimming speeds and body metabolism and the energetics of marine reptiles. Because this paper doesn’t rely on prior assumptions of metabolic rate, it provides an alternate way of checking our assumptions and that’s always helpful.” | <urn:uuid:70cc1770-ee35-4166-8179-529e5107d583> | 3.90625 | 1,326 | Knowledge Article | Science & Tech. | 40.82664 |
Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °
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Oh! So inequality inside parenthesis in the probability arithmetic means sum of probabilities of all events which satisfy the inequality?
I think this would be more clear. Don't you think?
Hopefully it is obvious that
exactly when or or ,
Similarly, you have observed that
exactly when or ,
What anonimnystefy is referring to in post #6 is that
where if is true and 0 if it is false.
This is also equal to
I hope this helps.
Well? Does anyone have an answer?
I am sorry, I do not understand your answer.
They are both 1. But if you multiply 1 by the probability that X is in fact 7 (or 8), and then sum over all values of X, you will get the probability.
Ok, then lets take the k=2.
In that case we have two X which satisfy the inequality in parenthesis: 7 and 8.
Now what is the values of
Can you tell me the values for a and b?
What is the value of Pr(TRUE)???
You need to find the probability that |X-3.2|>=18.3 . You can do that by summind the probabilities of all values of X for which that is hreater than 18.3 (which is in this case 0). And you probably know that 0<=0.01 .
Yes, I read the definition, but it is not enough, I need a practical example.
Which X should I put here to see the truth of this inequality?
That inequality means that the probability of the difference between X and mu being greater or equal to k*sigma is less than or equal to 1/k^2.
I do not understand it.
For example, if we have a pmf table:
Now, how to calculate it for lets say k=10? or for k=100?
What goes for X in the inequality and what is the result of Pr() function? | <urn:uuid:7cee21a7-f9b5-4b31-9a7e-9c12f7bee7c1> | 3.6875 | 495 | Comment Section | Science & Tech. | 83.963399 |
Billiards as dynamical systems
Dynamical systems are defined as the set of prescribed rules to evolve certain state in time. If the rules involve some random or probability feature (e.g., lottery) we say that the dynamical system is stochastic. Otherwise the system is called deterministic. Billiards are very illustrative example of dynamical system. In this case pointwise particles move in straight lines and experience specular collisions in the boundaries (like light in a mirror). The main general properties of billiards motion are illustrated below in a mushroom billiard (semi-circular stem placed on top of a triangular foot, see references at the end).
Another kind of dynamical systems are the so called magnetic billiards. In this case the straight line movement between collision is replaced by a the movement on semi-circles. The physical motivation is the movement of electric charges under the influence of a perpendicular magnetic field.
Chaos in billiards
Non-linear dynamical systems typically present chaos. Its most striking characteristics is its sensitivity to initial conditions. In the simulation below this effect is illustrated: the same position was chosen for the red and blue balls (no interaction between them) and a difference of 0.5% in the direction of movement (first case), and 0.5% in the position (second case). One sees that after some bounces the two trajectories are far away from each other. Chaos introduces unpredictability in fully deterministic dynamical systems.
Chaos and Order coexist
Trajectories in billiards may be chaotic (red) or regular (blue), depending on the initial condition. Regular trajectories perform a periodic or quasi-periodic movement and are restricted to the stem of the mushroom. If one waits long enough, every chaotic trajectories visits every point of the mushroom billiard table. This property is a generic property of Hamiltonian systems (to whom billiards belong). We say that such systems have a mixed phase space.
One interesting problem of nonlinear dynamics which is not completely solved is how the movement of chaotic trajectories in a mixed phase space look like. When chaotic trajectories approach the regular region (located at the mushrooms stem) they spent a very long time close to them before visiting again the rest of the chaotic region (foot of the billiard). During this time the movement is very regular and we call thus the full movement as intermittent (alternates between chaos and regular). This can be seen also in another paradigmatic example of Hamiltonian systems, the [standard map], whose phase space is shown at the right.
How to generate such animations? Making gif animations using Xmgrace.
About mushroom billiards
- L. Bunimovich, Mushrooms and other billiards with divided phase space, Chaos 11 (2001), 802. Kinematics, equilibrium, and shape in Hamiltonian systems: The "lab"effect, Chaos 13 (2003), 903.
- S. Lansel and M. Porter, "Mushroom Billiards", [AMS notices 53, (2006), 334.]
- E. G. Altmann, A. E. Motter, and H. Kantz, "Stickiness in mushroom billiards" [Chaos 15, 033105 (2005)] or pre-print [nlin.CD/0502058]. And "Stickiness in Hamiltonian systems: from sharply divided to hierarchical phase space" [Phys. Rev. E 73, 026207 (2006)] or pre-print nlin.CD/0601008
About chaos in Hamiltonian systems
- E. Ott, Chaos in dynamical systems, Cambridge University Press, Cambridge, 2002.
- A. M. Ozorio de Almeida, Hamiltonian systems: Chaos and quantization, Cambridge University Press, Cambridge, 1992.
- Mackay and Meiss (Eds.), Hamiltonian Dyanmical systems, Adam Hilger, Bristol, 1987.
About intermittent chaos and stickiness
- J.D. Meiss, Symplectic maps, variational principles and transport, Rev. Mod. Phys. 64 (1992), 795.
- J. D. Meiss and E. Ott, Markov-tree model of intrinsic transport in Hamiltonian systems, Phys. Rev. Lett. 55 (1985), 2741.Markov-tree model of transport in area-preserving maps, Physica D 20 (1986), 387.
- G. M. Zaslavsky, Chaos, fractinal kinetics, and anomalous transport, Phys. Rep. 371 (2002), 461.
- E. G. Altmann, Intermittent chaos in Hamiltonian dynamical system [Ph.D. Thesis] (2007).
Questions? Write me: edugalt(AT)pks.mpg.de or visit my homepage http://www.pks.mpg.de/~edugalt/ . | <urn:uuid:98c444a2-423f-4d2f-9358-80141b90e677> | 2.9375 | 1,033 | Knowledge Article | Science & Tech. | 53.069013 |
Joined: 16 Mar 2004
|Posted: Wed Sep 20, 2006 11:30 am Post subject: How Electrons Move Through a Nano-Transistor
|Scientists Attain Control of How Electrons Move Through a Nano-Transistor
Today, all electronics are based on transistors. Danish scientists are leading the field in creating the smallest transistors (called nano-transistors).
Two physicists from the Nano-Science Centre at the University of Copenhagen have now attained unsurpassed control of the migration of electrons in a nano-transistor. By using quantum physics, the scientists have made the electrons ‘communicate’ with each other.
In a recent experiment, carried out at temperatures near absolute zero, the scientists show how electrons, through their so-called spin, establish a quantum mechanic cohesion and thereby help each other through the molecule in the nano-transistor.
This achievement is not only a breakthrough in the fundamental research of nanotechnology; it also influences the development of tomorrow’s electronics, e.g. future super-fast quantum-computers.
The result is attained through an international collaboration with physicists from Harvard University and Universität Karlsruhe, and was published in Nature Physics on the 4th of July 2006.
This story was first posted on 10th July 2006. | <urn:uuid:b6e80455-4a2e-49d4-88bb-88a5f662c849> | 3.453125 | 270 | Comment Section | Science & Tech. | 33.099398 |
We may think of volcanic eruptions as deadly events, but volcanoes have played a major role in shaping the Earth and the life that lives on it. Volcanoes are not all the same. Try creating the different types and find out about the elements that shape them.
Decide whether your lava is runny or sticky and how much water vapour is in your volcano and...
Find out about the different kinds of lava and how they affect volcanic eruptions.
Peer into the dark clouds of toxic gasses that rise thousands of metres above a volcanic eruption.
You might not think it, but lava contains water vapour. What happens when there’s lots of it? | <urn:uuid:084403f2-0921-4b78-97b2-82212b71f161> | 3.53125 | 141 | Content Listing | Science & Tech. | 64.653474 |
|Nov21-12, 01:35 AM||#1|
electric lines of force
can any one tell me how to calculate the electric lines of force of an arbitrary electric charge configuration ?
i have heard that in static case there is no electric field inside a conductor . i now wanna know that is there any dynamical case for the conductor instead of static ?
physics news on PhysOrg.com
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|Nov21-12, 02:39 AM||#2|
it can be very difficult to know the nature of field lines in general case.Even in two charge case,one use prolate ellipsoidal coordinate to draw equipotentials and determining the nature of force lines.In static case,there is no field inside a conductor but in presence of say a time varying magnetic field there can be an electric field inside it.
|Nov21-12, 04:00 AM||#3|
|Nov21-12, 04:39 AM||#4|
electric lines of force
|Nov21-12, 09:39 AM||#5|
From Chabay/Sherwood Electric and Magnetic Interactions:
Step 1: Cut up the charge distribution into pieces and draw E vector for one piece.
-Very small pieces can be approximated by point particles
-Pick out a representative piece, and at the location of interest (where do you want to find the field?) draw a vector E showing the contribution to the electric field of this representative piece. Drawing this vector helps you figure out the direction of the net field at the location of interest. (you are simply using Coloumb's law with one charge being the small piece, and the other you imagine as a positive point charge.)
Step 2: Write an expression for the electric field due to one piece
-invent an integration variable to refer to the various pieces. The integration variable will not appear in the final result, but you will need it to refer algebraically to one of your pieces.
-write algebraic expressions in terms of your integration variable for the vector components of E
-if your representative piece is infinitesimal in size, your integration variable must include infinitesimal increments of the integration variable. For example, if your integration variable is y your expressions must be proportional to delta y.
Step 3: Add up the contributions of all pieces
-Write an expression for the net field as the sum of the contributions of all the pieces. (this is allowable due to the superposition principle) If the individual contributions are infinitesimal, write the sum as a definite integral whose limits are given by the range of the integration variable. If the integral can be done symbolically, do it. If not, choose a finite number of pieces and do the sum with a calculator or computer. (excel is good enough for this)
Step 4: Check the result
-Check that the direction of the net field is qualitatively correct.
-Check units, which should be newtons / coulomb
-look at special cases for which you already know the answer. For example, if you have some net charge, then at an extreme distance you should get something that looks like a single point charge.
I'd add that when you are doing step 2, use proportional reasoning instead of thinking about charge density and such. This allows you to derive charge density and is much more intuitive in my opinion. For example, say your object is a uniformly charged rod. Then it must be the case that
delta x / total length = total charge / delta charge
Delta charge is what goes in your expression for step 2.
As for your second question about conductors, its true inside a conductor in static equlibrium there is a net field of zero. There can also be surface charges on the metal if there is an external charge and yet still be zero inside during static equilibrium. This is called polarization. For the fraction of a second before static equlibrium is reached, the net electric field inside the metal is non-zero.
The "dynamical" case you are looking for is an electric circuit. Inside a conductor in this case there is current, and a non-zero electric field.
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Probaway-Wind is group of methods for converting huge quantities of wind power into available power very cheaply.
The actual device for converting wind to power, which is discussed below, is a group of simple mechanical components with some computer monitoring and control. The solution to the problem of how to get the energy out of the wind and available to a user is presented here.
Technology Review reference to wind, sequestered coal CO2 and breeder reactors as the only hope.
Microwatt (10**-6; watt)
1 µW - approximate consumption of a quartz wristwatch
Milliwatt (10**-3 watt)
5 mW - laser in a CD-ROM drive
20-40 W - approximate power consumption of the human brain
100 W - approximate average power used by the human body
60-100 W - the power of the typical household light bulb
120 W - power output of 1 square meter solar panel in full sunlight
290 W - approximately 1000 BTU/hour
300-400 W typical PC power supply
500 W - power output of a person working hard physically
745.7 W - 1 horsepower
750 W - the amount of sunshine falling on a square meter of the Earth's surface on a clear day
Kilowatt (10**3 watt)
.5 kW - per square meter average at 50 meters above North Dakota
1.366 kW - power received from the Sun at the Earth's orbit by one square meter
2.2 kW - per capita average power use of the world in 2001
3.3-6.6 kW - average photosynthetic power output per square kilometer of ocean
11.4 kW - per capita average power use in the U.S. in 2001
16-32 kW - average photosynthetic power output per square kilometer of land
40 kW to 200 kW - approximate range of power output of typical automobiles
Megawatt (10**6 watt)
1 MW equals approximately 1341 horsepower.
1.3 MW - power output of P-51 Mustang fighter aircraft
2.5 MW - Peak power output of a Blue Whale
3 MW - Mechanical power output of a diesel locomotive
190 MW - peak power output of a Nimitz class aircraft carrier
Gigawatt (10**9 watt)
.5 GW - average power 1 kilometer square kite over North Dakota 340X545 km =183,272km
2.074 GW - peak power generation of Hoover Dam
3 GW - approximate peak power generation of the world's largest nuclear reactor
18.2 GW - electrical power generation of the Three Gorges Dam in China when complete
424.3 GW - average electrical power consumption of the U.S. in 2001.
424.3 GW / .3G people = 46 watts per American
Terawatt (10**12 watt)
0.519 TW - India consumption of elecricity - per capita = .481 k Wh/year
2.170 TW - China consumption of electricity - per capita = 1.662 k Wh/year
3.656 TW - US consumption of electicity - per capita - 12.187 k Wh/year
14.3 TW - world consumption of electricity in k Wh/year 2003 per capita 2,215
1.7 TW - average electrical power consumption of the world in 2001
3.327 TW - average total (gas, electricity, etc) power consumption of the U.S. in 2001.
3.327 TW total power / 6.5 G total people = 5.1 watts per human.
13.5 TW - average total power consumption of the world in 2001
44 TW - average total heat flux from earth's interior
130 TW - global primary production via photosynthesis
50 to 200 TW - Weather: rate of heat energy release by a hurricane
Petawatt (10**15 watt)
1.4 PW - estimated heat flux transported by the Gulf Stream.
4 PW - estimated total heat flux transported by Earth's atmosphere and oceans away from the equator towards the poles.
174.0 PW - total power received by the Earth from the Sun
This winds at sea map created by NASA on September 21, 1996 shows the very large areas where wind is blowing at 4-10 meters per second [the magenta color areas]. This wind speed is very good for creating power but not so strong as to be destructive to well made kites. Any of these areas could supply vast quantities of energy it is just a question of building the equipment to do so.
Liability disclaimer statement: These Probaways contain new and unique information that has been created, tested and retested by me alone. You must approach these findings and materials very carefully as your results may differ greatly from my experience and I can offer no recompensation of any kind for any injuries. | <urn:uuid:a831fba5-958b-4b28-821b-aa388c3044d3> | 2.984375 | 1,006 | Knowledge Article | Science & Tech. | 72.122732 |
Southern AERA Quarterly Activity Bulletin of the South Carolina Department of Natural Resources- Southeast Regional Climate Center
Volume 3, No. 1
The 7th Annual Sky Awareness Week (SAW) celebration will be held April 20-26, 1997. Once again, the theme will be centered on
Since 1991, 42 states and the District of Columbia have issued proclamations in support of this growing national celebration. The National Weather Service, the National Weather Association, the National Science Teachers Association, the International Weather Watchers, and the Weather Channel TM are among the many organizations supporting this effort!
SAW 97 will provide many opportunities for teachers, students, parents, home schoolers, senior citizen centers, nature center staff, meteorologists and others to look toward the sky. In doing so, they can (1) learn how to read the sky (first by learning cloud types and their weather, and then by forecasting from them); (2) understand sky processes (water cycle, sky colors, rainbows); (3) appreciate the sky's natural beauty; (4) protect the sky as a natural resource (it's the only one we have); and (5) learn about sun safety. Also, SAW falls during the same week as National Science and Technology Week and National Mathematics Awareness Week, and around the same time as Earth and Astronomy Day. To enhance multi-disciplinary study, we will be linking dozens of schools across the United States, Canada and elsewhere in a sky data exchange using electronic mail and/or the Internet throughout the school year. SAW 97 encourages people across the Nation and around the world to notice the myriad of cloud types, ranging from fair weather cumulus puffs to high-flying cirrus streamers. Late spring is a time when most people experience their most dramatic and changeable skies. In addition to making their own weather forecasts, just as farmers and explorers used to do, people will notice that the sky is not the same color blue every day. The changes, albeit subtle, are often tied to the movement of weather systems and accumulations and transport of atmospheric pollutants. The list of "things" in the sky also includes birds, airplanes, hot air balloons, and the sun moon and stars. We can appreciate all of these and gain an upbeat feeling just by LOOKING UP!
For more information about SAW 97 contact :
HOW THE WEATHERWORKS
1522 Baylor Avenue
Rockville, MD 20850
A comprehensive sky study guide, cloud charts, cloud postcards, and other low-cost sky related materials are available for purchase.
El Nino/Southern Oscillation
Many climatic hazards affect our lives every year. Climatic hazards familiar to us include hurricanes, tornadoes, and severe winter storms. Although these hazards can have devastating effects on us, we know how to prepare for them and take measures to lessen their impacts. One climatic hazard that is less commonly known is the El Nino/Southern Oscillation (ENSO). Nonetheless it is important to study and understand all climatic hazards. The purpose of this exercise is to introduce and familiarize students with ENSO and its impacts on a global scale as well as on a local scale.
Discussion - Definitions and Background
El Nino is a Spanish word meaning "the Christ Child." The term was originally used by fishermen to describe a disruption in the flow and temperature of ocean currents along the coast of Ecuador and Peru, South America. Oddly enough this event usually occurred around Christmas time, hence giving its name. ENSO occurs typically every four to seven years and lasts an average of a few months. This event has local and global consequences, some of which can be very devastating. The areas that are most directly affected are the countries bordering the tropical Pacific Ocean. However, in addition to the direct impacts there are indirect impacts referred to as teleconnections. These "teleconnections" have been felt in Australia, Indonesia, Southern Africa, India and the United States.
What exactly is the El Nino/Southern Oscillation? The ENSO is the result of interactions between the ocean and the earth's atmosphere. The impacts of the El Nino were first noticed along the west coast of South America. During normal conditions the warm currents on the surface of the ocean are deflected or pushed westward into the eastern Pacific by the equatorial trade winds. The trade winds are driven by a difference in air pressure in the eastern and western portion of the Pacific Ocean. Normally the atmosphere above the eastern portion of the Pacific is dominated by a high pressure zone, while a low pressure zone dominates the west. As the pressure rise in the east, it falls in the west and vice versa. This "seesaw" of relative air pressure is known as the Southern Oscillation.
The trade winds normally blowing from the southeast to the northwest drive the surface ocean currents westward, causing cold, nutrient-rich waters from the ocean depths to rise to the surface. This process, known as upwelling, causes dry arid conditions along the coastal plain as well as providing the base for the fishing economy in Peru.
During El Nino years the trade winds weaken as a result of the pressure in the eastern portion in the Pacific decreasing, as the air pressure in the western portion rises. As the winds weaken or reverse, the warm water found in the eastern Pacific Ocean flows back to the east as a slow-moving wave. These warm surface waters rise over and push below the cold ocean currents which build up along the coast of Peru. As a result the nutrients that provide the base for the anchovy population are killed off. In return, marine birds that feed on the anchovies are also killed. The depletion of the anchovy stock is detrimental to the fishing economy in Peru. Another direct impact includes heavy rains which cause flooding on normally dry land.
The most powerful ENSO ever recorded in the Twentieth Century occurred in 1982-1983. While torrential rains plagued the western Pacific, a serious drought occurred in Indonesia and Australia. The United States weather patterns also changed as a result of the 1982-83 ENSO including severe storms around the Gulf Coast, Midwest and West Coast, as well as causing a hurricane in Hawaii. These weather disruptions had a negative impact on the fishing and agricultural industries, costing the United States millions of dollars. Unusual weather patterns continued through the winter and summer seasons. Heavy rains continued along the Gulf coast and into the Midwest causing significant flooding. Agricultural fields were eroded, cattle and poultry were killed, and buildings and homes were destroyed. For these reasons, ENSO related scientific research has increased. Scientists are using direct global observations to study ENSO and use the data to predict future climatic conditions. Long-term forecasts will make it possible to better prepare for future ENSO conditions.
The 1982-83 ENSO was not predicted and no unusual weather conditions were present before hand to warn scientists of its arrival. The previous El Ninos had been preceded by stronger than normal easterly winds along the equator which the scientists could directly observe. Now, scientists are using historical data and direct global observations and putting them into prediction models using mathematical equations. Two ENSO events, the 1986-87 and the 1991-92 event, were successfully predicted. Models can assist farmers, the fishing industry and government officials to plan ahead for an upcoming ENSO event.
1. What are the indirect impacts of ENSO that affect other parts of the world called?
2. In which direction do the trade winds that influence ENSO blow?
3. What is the process called where cold nutrient rich waters rise up from the depths of the ocean?
4. The atmosphere above the eastern portion of the Pacific Ocean under normal conditions is dominated by a ________ pressure zone, while a _________ pressure zone dominates the west.
5. The "seesaw" effect of air pressure driving the trade winds is known as what?
6. During El Nino years do the trade winds weaken or grow stronger? Why?
7. El Nino's occur on the average every _______ years.
8. What industries are the most severely affected by ENSO?
9. In what country were El Nino conditions first observed?
10. What are some of the impacts of the 1982-1983 ENSO in the United States?
11. Find these words horizontally and vertically in the puzzle:
Southern AER is a quarterly publication of the Southeast Regional Climate Center. Funding is provided by a grant from the National Oceanic and Atmospheric Administration.
Weather and Climate Resources for the Classroom
For El Nino Education Modules on the Internet
For El Nino Theme Pages on the Internet
For Extended Range Predictions of ENSO on the Internet
For Other El Nino Sites and Resources
El Nino Trivia
Did you know that...
Permission is granted for the reproduction of materials contained is this pub lication.
Southeast Regional Climate Center
S.C. Department of Natural Resources
1201 Main Street, Suite 1100
Columbia, South Carolina 29201
The South Carolina Department of Natural Resources prohibits discrimination on the basis of race, color, sex, national origin, disability, religion, or age. Direct all inquiries to the Office of Human Resources, P.O. Box 167, Columbia, SC 29202. | <urn:uuid:fa8a9031-4c2a-4900-be4a-4687e8cf9e41> | 3.25 | 1,923 | Knowledge Article | Science & Tech. | 43.924533 |
|Enlarge ImageA slice through the center of a long-dead brain coral is a slice through human and ocean history. This 1,000-pound coral grew near Bermuda for 200 years. Scientists will analyze the coral's skeleton to decipher ocean temperatures during its lifespan. (Tom Kleindinst, Woods Hole Oceanographic Institution)
|A diver off Bermuda indicates the ?big dead brain? that WHOI scientists recovered for analysis. This coral died 200 years ago, but remained in place to become prime real estate for other marine life to settle on. (Dr. Ross Jones and Alex Venn, Bermuda Biological Staton for Research)
|Enlarge ImageIt?s not easy to get to the center of a half-ton of coral. WHOI engineer Peter Landry (right) works with an employee of Fletcher Granite?s Chelmsford Quarry in North Chelmsford, Mass., to move, position, and slice the huge coral. (Dave Gray, Woods Hole Oceanographic Institution)
|Enlarge ImageWHOI Engineer Peter Landry (left) and WHOI Summer Student Fellow Nicholas Jachowski check the position of the massive coral between heavy braces before it is cut. (Dave Gray, Woods Hole Oceanographic Institution )
|Enlarge ImageA granite quarry worker closely monitors the coral slicing operation. (Dave Gray, Woods Hole Oceanographic Institution)
|Enlarge ImageA heavy cross-section slice of coral skeleton is lifted away. (Dave Gray, Woods Hole Oceanographic Institution)
Anne CohenSometime around the beginning of the 17th century, a tiny drifting larva found the perfect piece
of real estate to settle down, on the shallow seafloor off the island
of Bermuda. It sprouted tentacles to catch prey, revealing itself as a
coral polyp, and a few days later, the small flower-shaped animal began
to build a hard exterior skeleton. The polyp grew and divided,
eventually multiplying into a colony of thousands, with the round shape
and convoluted surface of a brain coral. By the time it died around
1800, it looked like a boulder and weighed more than 1,000 pounds.
Geology & Geophysics Department
and Kate Madin
Two centuries later, Ross Jones (a biologist at the Bermuda
Biological Station for Research) and I found this massive,
while scuba diving off Bermuda. It was just what we were
looking for: a coral with a past. If it were big enough and dead for
long enough, it would have lived through a considerable part the Little
Ice Age, an era between 1350 and 1850 when Earth’s climate was very
different from today’s.
During this period, unforgiving cold gripped the North Atlantic region.
Europe and eastern North America endured cool summers and severe
winters. Rivers froze and glaciers advanced over land that is ice-free
today. The times were marked by persistent crop failures, famine,
disease, and mass migrations. The Norse, for example, abruptly
abandoned their settlements in Greenland.
Meanwhile off Bermuda, each individual polyp in our coral was accreting (growing)
skeleton, in daily increments that built up into seasonal and annual
layers, similar to tree rings. In corals, the chemistry of their skeletons
varies slightly but measurably as the temperature of the waters do. So
the skeleton of this long-lived coral offered a continuous record of
ocean temperatures and environmental conditions off Bermuda throughout
much of the Little Ice Age, a pre-industrial era for which no
instrumental records exist.
Records closeted in skeletons
The Bermuda brain coral, Diploria sp.,
was covered with marine organisms that had attached and burrowed into
its surface. When we cleared off the algae, sponges, burrowing worms,
starfish, and soft corals, we found that the coral’s surface was erodedbut
inside, the skeleton remained intact. The cover of this ancient “book”
was damaged, but its contents were unspoiled.
We recovered the dead coral from the seafloor and sent it back to Woods
Hole Oceanographic Institution. By using a new laser mass spectrometer
technique we developed for very fine-scale sampling of coral, we aim to
do the equivalent of reading the coral “book” page by page: to get a
week-to-week, perhaps even a day-by-day, account of ocean temperatures
over past centuries.
That would give climate scientists better records to
understand the ocean-atmosphere interactions that generate periodic,
short-term climate shifts such as El Niño and the North Atlantic
Oscillation, for example, or abrupt, longer ones, such as the Little
Ice Age. And understanding the oceans’ past behavior offers insights
into how corals and the climate might change as fossil fuel burning and
other human activities increase carbon dioxide levels in the atmosphere.
Until now, we have had few good records of ocean temperatures just before industrial activity
Paleoclimatologists can infer past ocean temperatures over long,
thousand-year timescales by analyzing the chemical composition of
sediments that accumulate on the seafloor over millennia. But in
is hard to resolve a record of short-term and recent changes. Long-dead
corals can provide that record, and they also remain intact, unlike
layers, which are often disturbed by animal movements or currents.
Translating chemistry into temperatures
Corals’ skeletons are made of aragonite, a form of calcium
carbonatethe same substance marble, limestone, chalk, and clamshells
are made of. To grow their skeletons, corals accrete tiny “seed”
crystals at night underneath their tissue; during the day, long aragonite crystals
self-assemble on those seeds from the calcium and carbonate in seawater, just as snow crystals form around tiny ice crystals.
But seawater contains trace amounts of other elements such as strontium
(Sr), magnesium (Mg), and barium (Ba), which become incorporated into
the growing aragonite crystals. These give scientists a handy
Here’s how it works: The relative proportions of minor, or trace
elements (Sr, Mg, and Ba) versus the major element (calcium) that are
incorporated into aragonite as it grows depend on the temperature of
the seawater. Once coral skeletons form, their composition does not
changenot even over centuries. By sampling coral skeleton layers and
measuring their trace element-to-calcium ratios, we can derive a
chronology of ocean temperature, in locations where the corals lived.
For years, WHOI Senior Scientist Stan Hart had been using an instrument
called an ion microprobe, which measures small amounts of isotopes in
samples, to determine the composition of rocks. “Why not use this
instrument for paleoceanography in corals?” he suggested. And so, with
funding from the WHOI Ocean and Climate Change Institute, we
developred microscale analytical techniques for coral
The difficulty is in getting sufficiently small-scale samples.
Previously, we could only analyze samples in bulk. That was kind of
like putting the ancient book in a blender, chapter by chapter, and
getting an average account of the plot’s progress.
Another WHOI colleague, biologist Simon Thorrold, began to use a laser
to take nanoscale samples (called “laser ablation”) of calcium
carbonate in fish ear bones, whose isotopic composition he analyzed in
an ion mass spectrometer. With funding from the WHOI Ocean Life
Institute, Thorrold and I put the two techniques together and developed
a new laser mass spectrometer technique for sampling coral.
The technique lets us analyze samples at distances only 60 micrometers (0.002 inches)
apart within the skeleton, equivalent to just a week’s growth. That is
like reading the book line by line, or word by word. Already, by
analyzing daily growth layers, we have found that corals are sensitive
to tidal and lunar cycles. The chemical compositions of their skeletons
change abruptly with each new and full moon.
Analyzing chemical composition, we found that the seawater during our huge brain coral’s life was about
1.5o C (2.7o
F) colder than it is today, yet the coral grew faster than the corals
there now, thriving in the coldest period of
the Little Ice Age. We think water temperatures now are higher than
optimal for these corals.
What does that mean for this coral’s
brain corals off Bermuda today and tomorrow? If they see much warmer
temperatures, due to global warming, will they be able to thrive and
live long lives also?
Posted: March 9, 2007 | <urn:uuid:f9521219-0c89-402a-b9da-8ed64c27ba41> | 3.28125 | 1,897 | Knowledge Article | Science & Tech. | 35.213038 |
Mixing and Segregation in Chemical Reactors (CSTR versus PFR)
For very fast chemical reactions or viscous liquids, one must take into account the segregation of reactants. The intensity of segregation varies between 0 (perfect mixing) and 1 (no mixing). Mixing intensity can influence reaction rates and selectivities.
This Demonstration displays the segregation intensity versus the mixing time; the blue and red curves correspond to PFR (plug-flow reactor) and CSTR (continuous stirred-tank reactor), respectively. Several conclusions can be drawn from this Demonstration: (1) for fixed values of the mixing time and the reactor residence time, the segregation intensity will be higher for the CSTR, due to the fact that mixing is better in a PFR, where the flow is turbulent; (2) for a fixed residence time, the segregation goes from 0 to unity when the mixing time is varied; indeed, when the mixing time is small or large, the segregation is almost equal to zero or close to unity, respectively; and (3) when the residence time is large, there is a higher chance for mixing to occur in the reactor, since on average reactants are spending more time in the reactor; thus, the segregation takes smaller values corresponding to better mixing.
PFR segregation intensity, , is given by , where is the reactor residence time and is the mixing time.
CSTR segregation intensity, , is given by , where is the reactor residence time and is the mixing time. | <urn:uuid:d7561e98-ce72-48f0-9f59-8698c8b22bd7> | 3.1875 | 306 | Knowledge Article | Science & Tech. | 24.923475 |