text large_stringlengths 148 17k | id large_stringlengths 47 47 | score float64 2.69 5.31 | tokens int64 36 7.79k | format large_stringclasses 13 values | topic large_stringclasses 2 values | fr_ease float64 20 157 |
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Active Regions on the Sun
An active region on the Sun is an area with an especially strong magnetic field. Sunspots frequently form in active regions. Active regions appear bright in X-ray and ultraviolet images. Solar activity, in the form of solar flares and coronal mass ejections (CMEs), is often associated with active regions. | <urn:uuid:57f6734e-3c65-4896-92cc-202b470013c7> | 3.4375 | 70 | Knowledge Article | Science & Tech. | 42.136932 |
|Opening Tag||Content||Closing Tag|
The advantage to logical markup is that, regardless of how the affected text appears, it is always considered to be what the markup says it is. For example, a variable is always a variable, regardless of the font that any particular browser uses to represent it. The disadvantage to logical markup is that you cannot be sure how the text will appear (which may be important).
Conversely, the advantage to physical markup is that you can be sure of what the text will look like: when you want a typewriter font for a piece of text, you'll get typewriter font. The disadvantage to physical markup is that you may not be able to tell, just by looking at the font, what the text is supposed to represent (which may be important).
The syntax is: | <urn:uuid:ffde8265-df81-4c6f-9e04-51c7ae7e2492> | 3.0625 | 168 | Documentation | Software Dev. | 44.263571 |
Invasive aquatic plants
Some of the most worrying species of invasives in Ireland are aquatic plants. In many cases the plant fills an empty niche and then expands rapidly and competes for additional niches. Oftentimes the native species are ousted and the ecology of the waterway can be changed dramatically. This can lead to waterways becoming completely choked by a single species impeding navigation, angling and other recreation.
Invasive aquatic animals
As most of the fish in Ireland were introduced by man throughout the history of the country many fish species could be regarded as invasive. Those which are well established are considered to be naturalised species having reached some sort of equilibrium in the environment.
Those fish which are still considered invasive species due to their recent arival or continued spread through our water courses are:
In more recent times we have had new invertebrate species released into Irish waterways. These include Zebra Mussel and Bloody Red Shrimp.
Zebra Mussels have colonised many waterways and causing significant ecological and economic impacts.
Bloody Red Shrimp has been confirmed in Lough Ree on the Shannon River system. Crangonyx pseudogracilis is another freshwater shrimp which is colonising Irish water courses. Now Asian clam and killer shrimp threaten our waterways. | <urn:uuid:a10646ea-151c-49b9-b6b0-70256c8ddc54> | 3.03125 | 260 | Knowledge Article | Science & Tech. | 23.395815 |
This page compares quaternion multiplication and orthogonal matrix multiplication as a means to represent rotation.
If you are not familiar with this subject you may like to look at the following pages first:
We want to be able to represent 3D solid body movements (rotations and translations) in one operation.
Initially it would seem that multivectors based on 3D vectors would be ideal for this because such a multivector contains a 3D bivector (which could represent rotations) and a 3D vector (which could represent translations). However there are problems with this approach, one problem is that multivectors are not always invertible, whereas 3D isometry translations do always have an inverse.
There are subsets of multivectors that do always have an inverse (such as a * a†=1) but this restriction means that the vector part is no longer independent of the bivector. this means we have to go to higher dimensional multivectors to represent independent rotation and translation.
In order to explore this subject I have calculated the condition a * a†=1 for multivectors based on various dimensional vectors on these pages:
- Isometry properties of multivectors based on 2D vectors.
- Isometry properties of multivectors based on 3D vectors.
- Isometry properties of multivectors based on 4D vectors.
- Isometry properties of multivectors based on 5D vectors. | <urn:uuid:1f94f55f-5072-4d5c-8334-50e30e24f3ff> | 2.890625 | 300 | Knowledge Article | Science & Tech. | 28.328176 |
Data types are a subtree of the ABAP type hierarchy. Data types are only
type descriptions. Data types do not have any attached memory for storing working data, but they may require space for administration information. A data type characterizes the technical properties of all
data objects that have this type. In ABAP, data objects occur as attributes of data objects, but they can also be defined as stand-alone data types.
The definition of stand-alone data types is based on a set of
predefined data types. Stand-alone
data types can either be defined internally in the program using the statement
TYPES in the global declaration section of a program, in the declaration section of a class, locally in procedures, or for all programs in the
ABAP Dictionary. Data types in the ABAP Dictionary are either created directly as
repository objects or in a type group.
Predefined and self-defined data types can be used to generate data objects and for
typing. For the latter in particular,
predefined generic data types are available. A
generic data type is a data type that does not determined all the properties of a
data object. Generic data types can only be used for typing
formal parameters and field symbols.
Data types can be divided into elementary, reference, and complex types.
- Elementary types are 'atomic'
in the sense that they are not composed of other types. They are further classified into elementary types of fixed length and of variable length.
- There are eight predefined elementary data types of fixed length in ABAP. There are four
character-type types: text fields
(c), numeric text fields
(n), date fields (d), and time fields (t). There are three
numeric types: Integer
(i), floating point numbers (f), and packed numbers (p).
Byte-like type: Byte fields
(x). The data types c,
n, x, and
p are generic in terms of length. p is also generic in terms of the number of decimal places.
- Reference types describe data objects that contain references to other objects (data objects and instances of classes), which are known as
reference variables. There are
no predefined reference types in ABAP. A reference type must either be defined in the ABAP program or
in the ABAP Dictionary. Reference types form a hierarchy, which represents the hierarchy of the objects to which the references can point.
- Complex data types are composed
of other types. They enable the administration and processing of semantically related datasets under
one name. A data object of a complex type can be accessed overall or by component. With the exception
of the structure sy,
there are no predefined complex data types in ABAP. A complex type must either be defined in the ABAP program or in the ABAP Dictionary. There are two types of complex data type:
- A structured type is a sequence
of any elementary reference or complex data types. Structures are used for grouping together work areas that logically belong together.
- Table types consist of a sequence of any number of lines of the same data type. Table types are characterized by a
row type, which can be any elementary data type, a reference data type, or a complex data type. They are also characterized by the
table type, which defines how tables can be accessed, and by a
table key, which is used to identify the table rows. | <urn:uuid:89344548-645c-4027-82bd-d71082de395b> | 3.625 | 719 | Documentation | Software Dev. | 34.184182 |
Dated 2005, a
white paper from International Partnerships in Ice Core Sciences (IPICS)
IPICS 2k Array: a network of ice core climate and climate forcing records for
the last two millennia” contains an interesting graphic. A couple of
horizontal lines have been added to help illustrate the point. It clearly shows
that over the last 200 years of the last millennium Antarctica temperatures have
fluctuated but that the temperatures in the late 20th century were matched in
about 1830 and 1940. There are two distinct temperature minimums at around 1865
and 1955. It is also important to note that the continent wide ice core records
do not demonstrate the same positive trend of the southern hemisphere
By inspection, if
the record had been extended to beyond the year 2000, it is likely that the
apparent peak in the 1990’s, where the smoothed curve stops, would have turned
over and matched fairly closely, or possibly been lower than the other two
maxima. Bear in mind that Antarctica is a significant proportion of the Earth's
land area, being approximately double the size of Australia, half as big again
as the USA or nearly fifty times that of the UK.
has released a paper on this work. It contains a slightly extended
graph, and indeed the late twentieth century peak does turn over and plummets.
An excellent critique can be found
Here is the graphic from the paper -
Schneider, D. P., E. J. Steig, T. D. van Ommen, D. A. Dixon, P. A. Mayewski, J.
M. Jones, and C. M. Bitz (2006), Antarctic temperatures over the past two
centuries from ice cores, Geophys. Res. Lett., 33, L16707,
Now compare the continent wide Antarctic
temperature reconstruction with the accepted carbon dioxide record:
It is rather difficult to conclude that
atmospheric carbon dioxide is driving temperature.
However, Schneider et al conclude:
Interesting. It seems that peer review
missed this one. | <urn:uuid:478d5d65-46d2-498b-b4ea-8f1cc7ab9f98> | 3.125 | 438 | Personal Blog | Science & Tech. | 56.567725 |
JLoom is a modular template language for text generation. Parameters can be any Java type, even Generics or Varargs.
Here are some key features of "JLoom":
JSP like Syntax
· The syntax and semantics of JLoom templates are similar to Java Server Pages (JSP). If you already know JSP you will have no problem to write JLoom templates.
· JLoom doesn't have include-tags like JSP - which just insert other JSPs without encapsulation and parametrization. Instead of include-tags, JLoom supports modular composition of templates.
· Templates are full encapsulated like classes with parametrization and compiletime type-checking.Parameters are not restricted to String types - they can be any Java type, even Generics or Varargs.
· You can make a top-down/bottom-up design of the text-processing in your application. The modular templates strongly improve the maintainability of your code and eliminate redundancy.
· In addition you can organize your templates hierarchically in packages. And you can make modular extensions of the language with macros.
· JLoom is easy to learn. The syntax is clean and uniform. Because it is build upon Java it can concentrate on its core function: building a bridge from Java to text-generation.
· If you are already familiar with Java syntax, there is not much to learn. The operators, rules for assignments and expressions are the same. And you can make use of the most recent Java (currently Java 1.5) syntax features, like Generics, Varargs, Autoboxing, etc.
· The basic syntax is simpler than JSP Syntax. But it is very powerful by allowing the definition of new syntax elements. This is done by writing macros, which are nothing else than JLoom templates themselves. The basic JLoom syntax is extended by such macros, e.g. all these commands are macros: exec, import, for, if, incIndent, decIndent.
· You can extend the language by writing your own custom macros, which are just JLoom templates - simple and powerful.
· Like JSP, JLoom can be used to generate dynamic web content. And you can use both together: a JSP which accepts the HTTP requests, handles HTTP specific things like setting the content type and delegates the HTML generation to a JLoom template.
· But JLoom can be used for arbitrary purposes. Generating of source code, XML (alternative to XSLT), documentations, Emails, configuration files, scripts are just some other examples.
· Everywhere you have text-generation in your application, JLoom can help you to get an easy maintainable and extendable solution.
· JLoom lets you control the indention of the generated text - this is especially useful for code generation. JLoom uses itself (JLoom macros) to create the generator classes and therefore the generated Java code has correct indention.
· JLoom generates text extremely fast. Like in JSP, JLoom generation is done in two phases. In the first phase the template is parsed and compiled into a Java class. This phase takes place only one time after creating/changing the template. Subsequent generations just "throw out" the text.
· Java 1.5 | <urn:uuid:3526b111-030a-4be6-8b34-8d56d5cc7f78> | 2.71875 | 699 | Knowledge Article | Software Dev. | 42.431156 |
Chapter 12 - Vorticity in the Ocean
12.2 Conservation of Vorticity
The angular momentum of any isolated spinning body is conserved. The spinning body can be an eddy in
the ocean or the Earth in space. If the the spinning
body is not isolated, that is, if it is linked to another body, then angular momentum can be
transferred between the bodies. The two bodies need not be in
physical contact. Gravitational forces can transfer momentum between bodies in space. We will return to
this topic in Chapter 17 when we discuss tides in
the ocean. Here, let's look at conservation of vorticity in a spinning ocean.
Friction is essential for the transfer of momentum in a fluid. Friction transfers
momentum from the atmosphere to the ocean through the thin, frictional,
Ekman layer at the sea surface. Friction transfers
momentum from the ocean
to the solid Earth through the Ekman layer at the seafloor. Friction along the sides of subsea mountains
leads to pressure differences on either side of the
mountain which causes another form of drag called form drag. This is the
same drag that causes wind force on cars moving at high speed. In the vast interior
of the ocean, however, the flow is frictionless, and vorticity is conserved. Such a flow is said to be
||Figure 12.2 Sketch of the production of relative vorticity by the changes in the
height of a fluid column. As the vertical fluid column moves from left to right, vertical stretching
reduces the moment of inertia of the column, causing it to spin faster.
Conservation of Potential Vorticity
The conservation of potential vorticity
couples changes in depth, relative vorticity, and changes in latitude. All three interact.
- Changes in the depth H of the flow causes
changes in the relative vorticity. The concept is analogous with the way
figure skaters decreases their spin
by extending their arms and legs. The action increases their moment of inertia
and decreases their rate of spin (Figure 12.2).
- Changes in latitude require a corresponding change in ζ. As a column of
water moves equatorward, f decreases, and ζ must
increase (Figure 12.3). If this seems somewhat mysterious, von Arx (1962)
suggests we consider a barrel of water
at rest at the north pole. If the barrel is moved southward,
the water in it retains the rotation it had at the pole, and it will appear
to rotate counterclockwise at the new latitude where f is
|Figure 12.3 Angular momentum tends to be conserved as
columns of water change latitude. This causes changes in relative vorticity
columns. From von Arx (1962).
Consequences of Conservation of Potential Vorticity
The concept of conservation of potential vorticity has far reaching consequences, and its
application to fluid flow in
the ocean gives a deeper understanding of ocean currents.
1. In the ocean f tends to be much larger
ζ and thus f/H = constant. This requires that the flow
in an ocean of constant depth be zonal. Of course, depth is not constant,
but in general, currents tend to be east-west rather than
north south. Wind makes small changes in ζ,
leading to a small meridional component to the flow (see Figure
2. Barotropic flows are diverted by seafloor features. Consider what happens
when a flow that extends from the surface to the bottom encounters a subsea ridge (Figure 12.4).
As the depth decreases, ζ + f must
also decrease, which requires that f decrease,
and the flow is turned toward the equator. This is called topographic steering.
If the change in depth is sufficiently large, no change in latitude will
be sufficient to conserve potential vorticity,
and the flow will be unable to cross the ridge. This is called topographic
|Figure 12.4 Barotropic flow over a sub-sea ridge is turned
equatorward to conserve potential
vorticity. From Dietrich, et al. (1980).
3. The balance of vorticity provides an alternate explanation for the
existence of western boundary currents (Figure 12.5). Consider the gyre-scale
in an ocean basin, say in the North Atlantic from
10°N to 50°N. The wind blowing over the Atlantic adds negative
vorticity. As the water flows around the gyre, the vorticity of the gyre
nearly constant, else the flow would spin up or
slow down. The negative vorticity input by
the wind must be balanced by a source of positive vorticity.
The source of positive vorticity must be boundary currents: the wind-driven
flow is baroclinic, which is weak near the bottom, so bottom friction
cannot transfer vorticity out of the ocean. Hence, we must decide which boundary
contributes. Flow tends to be zonal, and east-west boundaries
will not solve the problem. In the east, potential vorticity is conserved:
the input of negative relative vorticity is balanced by a decrease in potential
vorticity as the flow turns southward. Only in the west is vorticity not
in balance, and a strong
source of positive vorticity is required. The vorticity
is provided by the current shear in the western boundary current as the current
rubs against the coast causing the northward velocity to go to zero
at the coast (Figure 12.5, right).
In this example, friction transfers angular momentum from the wind to the
ocean and eddy viscosity - friction - transfers angular momentum from the
ocean to the solid Earth.
||Figure 12.5 The balance of potential vorticity
can clarify why western boundary
currents are necessary. Left: Vorticity
input by the wind ζt balances
the change in relative vorticity ζ in the
east as the flow moves southward and f decreases;
but the two do not balance in the west where ζ must
decrease as the flow moves northward and f increases. Right: Vorticity
in the west is balanced by relative vorticity ζb generated
by shear in the western boundary current. | <urn:uuid:5eefb76d-c616-48bf-8efe-184ab64809f4> | 4.25 | 1,363 | Academic Writing | Science & Tech. | 51.931263 |
Ask a question about 'N-Acetyltransferase'
Start a new discussion about 'N-Acetyltransferase'
Answer questions from other users
is an enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
the transfer of acetyl
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...
groups from acetyl-CoA
Acetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. In chemical structure, acetyl-CoA is the thioester...
to arylamines. They have wide specificity for aromatic amine
An aromatic amine is an amine with an aromatic substituent - that is -NH2, -NH- or nitrogen group attached to an aromatic hydrocarbon, whose structure usually contains one or more benzene rings. Aniline is the simplest example....
s, particularly serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, and can also catalyze acetyl transfer between arylamines without CoA. EC 188.8.131.52.
The following is a list of human gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s that encode N-acetyltransferase enzymes:
Serotonin N-acetyl transferase also known as arylalkylamine N-acetyltransferase or AANAT is a protein that, in humans, is encoded by the AANAT gene.-Function:...
| arylalkylamine N-acetyltransferase
N-terminal acetyltransferase complex ARD1 subunit homolog A is an enzyme that in humans is encoded by the ARD1A gene.-Further reading:...
| ARD1 homolog A, N-acetyltransferase (S. cerevisiae)
|| glucosamine-phosphate N-acetyltransferase 1
Heparan-alpha-glucosaminide N-acetyltransferase is an enzyme that in humans is encoded by the HGSNAT gene.-External links:...
| heparan-alpha-glucosaminide N-acetyltransferase
|| MAK10 homolog, amino-acid N-acetyltransferase subunit (S. cerevisiae)
|| N-acetyltransferase 1 (arylamine N-acetyltransferase)
N-acetyltransferase 2 , also known as NAT2, is an enzyme which in humans is encoded by the NAT2 gene.- Function :...
| N-acetyltransferase 2 (arylamine N-acetyltransferase)
N-terminal acetyltransferase B complex catalytic subunit NAT5 is an enzyme that in humans is encoded by the NAT5 gene.-Further reading:...
| N-acetyltransferase 5 (GCN5-related, putative)
|| N-acetyltransferase 6 (GCN5-related)
N-acetyltransferase 8 is a protein that in humans is encoded by the NAT8 gene....
| N-acetyltransferase 8 (GCN5-related, putative)
|| N-acetyltransferase 8-like (GCN5-related, putative)
N-acetyltransferase 9 is an enzyme that in humans is encoded by the NAT9 gene.-Further reading:...
| N-acetyltransferase 9 (GCN5-related, putative)
N-acetyltransferase 10 is an enzyme that in humans is encoded by the NAT10 gene.-Further reading:...
| N-acetyltransferase 10 (GCN5-related)
|| N-acetyltransferase 11 (GCN5-related, putative)
|| N-acetyltransferase 12 (GCN5-related, putative)
|| N-acetyltransferase 13 (GCN5-related)
|| N-acetyltransferase 14 (GCN5-related, putative)
|| N-acetyltransferase 15 (GCN5-related, putative) | <urn:uuid:2b7ef311-48d7-4cca-8105-a122d3b2d045> | 3.390625 | 1,123 | Q&A Forum | Science & Tech. | 27.788933 |
Stag beetle (Lucanus cervus)
|Size||Male body length: 25-75 mm|
Female body length: 30-45 mm
Ths stag beetle is listed under Annex II of the EC Habitats Directive and Appendix III of the Bern Convention. Protected in the UK under Schedule 5 of the Wildlife and Countryside Act 1981, as amended.
The stag beetle (Lucanus cervus) is arguably the most spectacular looking beetle in Britain; the male looks like something from a prehistoric age. The giant antler-like mandibles are used in courtship displays, and wrestling with other males. Although rather fearsome in appearance, the mandibles cannot be closed with any force. You are more likely to be nipped sharply by the female stag beetle, a smaller insect than the male that lacks the huge jaws. The stag beetle, superficially, appears black all over but, in certain lights, it can be seen to have dark maroon or brown wing cases. The impressive mandibles also have a reddish sheen to them. The wing cases are glossy; the head and thorax are a dull black.
The stag beetle is nothing like as common as it used to be, but is still widespread in southern England, especially the Thames valley, north Essex, south Hampshire and West Sussex. It also occurs fairly frequently in the Severn valley and coastal areas of the south-west. Elsewhere in Britain it is extremely rare or even extinct. This beetle is found throughout Europe, and East Asia as far as Japan, although it is rare or declining in some countries.
Stag beetles are found in gardens, wooded parks and pasture woodland; anywhere where there is a good supply of dead wood.
Despite it being such a large and spectacular insect, surprisingly little is known about the habits of the stag beetle. In 1998 the People's Trust for Endangered Species (PTES) invited the public to look for the beetles, asking questions about where they were finding them, the type of wood it was found near, was it eating and so-on. The 'Stag Hunt' revealed that the beetles lay their eggs both in rotting log piles and in the roots of an assortment of rotten trees, including oak, apple, ash and cherry. They seem to have a preference for oak, especially those growing along riverbanks. They also prefer warm places on sandy or light soils, and are now mostly reported from urban and suburban gardens. In fact, seventy percent of the beetles reported were found in gardens.
The larvae of the stag beetle live within their rotting logs for up to four years before pupating and emerging as adults at the beginning of the flight season the following year. However, the adults have a much shorter life than the larvae, and only survive for a few months. It used to be thought that adult stag beetles died at the end of the year but, as a result of the survey, it seems some beetles can survive the winter. The main message from the survey was, sadly, that the beetle seems to have declined in numbers greatly, especially in some areas.
As the beetle grubs take so long to develop, they become extremely vulnerable to tree clearance and the 'tidying up' of wood in parks and especially gardens; the over-zealous tidying of dead timber and stumps is thought to be the chief reason why this spectacular beetle seems to be in decline; although facts about its true status are still unclear. Elsewhere, there may also be a threat caused by the collection of the beetles for sale; to date no evidence of such a trade has been found in the UK. There are a number of websites that offer specimens for sale in the US for about $10 per animal. Whether they are collected from the wild or bred for the purpose is not clear, but if it does occur this practice is probably limited to European countries.
The stag beetle is listed as a priority species under the UK Biodiversity Action Plan (UK BAP), and is included in English Nature's Species Recovery Programme. The People's Trust for Endangered Species is leading a number of programmes to raise the profile of this insect, and have now organised two national surveys to find out more about stag beetle distribution and behaviour and encourage the public to become more sympathetic towards them; the huge response to the first PTES survey suggests that the beetles now have an enthusiastic fan club who may lobby local authorities and owners of large gardens to 'spare that rotten tree!'
With regard to the fear that trade in the insects might present a threat, the PTES lobbied the government's advisors and, since April 1998, the stag beetle has been protected under Schedule 5, Section 9.5 of the Wildlife and Countryside Act 1981, which means that all trade in the species is illegal and those suspected of trading in the species can be prosecuted.
For more on the People's Trust for Endangered Species:
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
- Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Mandibles: the pair of mouthparts most commonly used for seizing and cutting food, common to the centipedes, millipedes and insects.
- Pupating: the process of forming a pupa, the stage in an insect's development, when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
- Thorax: part of the body located near the head in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs. | <urn:uuid:6b60000c-e76d-45a8-a60e-78141b1b08a4> | 3.15625 | 1,194 | Knowledge Article | Science & Tech. | 46.720107 |
Buff-tailed bumblebees are the UK's largest bumblebee species. The queen is the only one that has the buff-coloured tail, the workers all have white tails. The queen emerges in the spring after hibernating through the winter, and goes looking for a nest site. At the height of its success, a buff-tailed bumblebee colony may contain 150 workers.
Scientific name: Bombus terrestris
Large earth bumblebee
The life and death of a bumble bee colony.
David Attenborough describes life at the heart of the hive, exploring the fascinating world of the bee colony. This is one of nature's most highly organised and well constructed ways of life. It's a life cycle story that has provided a rich thematic backdrop to many a work of fiction exploring the nature of humanity and society.
Thermal cameras show how bumblebees leave a warm glow.
New camera technologies have enabled scientists and film-makers to study and reveal the secret inner workings of animals' lives. Here, a thermal camera shows the mechanical technique used by a chilly bumblebee to get to a flight-ready temperature. The camera then also shows how heat from the bumblebee is left behind in the flowers visited by the hot-bodied bee.
The following habitats are found across the Buff-tailed bumblebee distribution range. Find out more about these environments, what it takes to live there and what else inhabits them.
Discover what these behaviours are and how different plants and animals use them.
Additional data source: Animal Diversity Web
Bombus terrestris, the buff-tailed bumblebee or large earth bumblebee is one of the most numerous bumblebee species in Europe. The queen is 2–2.7 cm long, while the workers are 1½–2 cm. The latter are characterized by their white-ended abdomens and look (apart from their yellowish bands being darker in direct comparison) just like those of the white-tailed bumblebee, B. lucorum, a close relative. The queens of B. terrestris have the namesake buff-white abdomen ("tail") tip; this area is white like in the workers in B. lucorum.
Such bees can navigate their way back to the nest from a distance as far away as 13 kilometres (8.1 mi), although most forage within 5 km from their nest.
Take a trip through the natural world with our themed collections of video clips from the natural history archive.
Bees are amazing - not only do they fulfil a vital role in our ecosystem, they are one of the most complex and sophisticated living things in the history of evolution.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so. | <urn:uuid:1a67c67d-2e2c-4367-82a3-db7586a496b5> | 3.953125 | 626 | Knowledge Article | Science & Tech. | 51.961565 |
How JVM will find is loading file is class or interface. How it will find extended/implemented files.
Well, I'm not sure if I understand your question correctly, but this is what I think:
1) When we write a class or interface, we clearly mention in code that whether it is a class or interface right? So, I don't think JVM should face any issues while identifying if it is class or interface.
2) JVM couples classpath and package hierarchy (i.e. import and package statements) to search classes.
How JVM will find is loading file is class or interface.
By searching in the classpath.
How it will find extended/implemented files.
It's not clear what you're asking here. If you're asking, given a particular class or interface, how does the JVM find all its subclasses or subinterfaces, the answer is that it doesn't. If B extends A, the JVM doesn't know that until it loads B when our code first uses it. It doesn't find B when it loads A. | <urn:uuid:515e7669-d6f9-4ed6-bbc3-6fe0648fa333> | 2.734375 | 230 | Q&A Forum | Software Dev. | 77.591578 |
A vulture doing what vultures do. An unfortunate rabbit was hit by a car and the vulture was "cleaning up." Vultures are amazing. They can eat spoiled meat and not get sick. Scientists are studying them to find out why/how to try to help people not get sick when spoiled meat is consumed. Vultures also have black feet. However, their urine is so acidic that it turns their legs/feet white with a bleaching effect. This is to kill germs they pick up from the carrior they land on. (Info learned at Bird of Prey Show, Callaway Gardens, Ga)
If you think this observation is inaccurate, please add an ID, participate in the quality assessment above, or describe the inaccuracy in a comment. | <urn:uuid:03e24609-2f22-49e7-b420-62a0aac2ed54> | 2.703125 | 160 | Knowledge Article | Science & Tech. | 61.174749 |
The discovery gleans important clues about the last universal common ancestor, the mysterious great-grandparent of all living things.
Discovering life's last universal common ancestor, or LUCA for short, is one of the great unresolved quests of science. Researchers scouring for traces of the elusive LUCA look for shared traits that exist between all three of the major branches of life: archaea, bacteria and eukaryotes (the cells that make up plants, animals, fungi, algae and everything else).
Now scientists based at the University of Illinois think they may have uncovered a breakthrough: a primitive organelle that can be found within all types of organisms, reports Physorg.com.
Click "source" for entire article.
Related article: "Last universal common ancestor more complex than previously thought" | <urn:uuid:d201475f-4492-48e4-86a6-9ec568e2951f> | 2.9375 | 163 | Truncated | Science & Tech. | 29.621237 |
THE HOLE in the ozone layer above Antarctica returned in the spring of 1989. But researchers in the US also found that ozone was significantly depleted far beyond the boundaries of that hole (Nature, vol 342, p 233).
According to the scientists, from the US National Oceanic and Atmospheric Administration's Aeronomy Laboratory, and the University of Colorado (both in Boulder), 'the geographic extent of the ozone loss (is) larger than that generally identified (and) ozone is lost earlier in the year than previously reported'.
They base their conclusions on measurements made by the ER2 research aircraft on a flight between California and Chile. The measurements show that at all southern latitudes down to 50 degrees, as much as 15 per cent of the stratospheric ozone was lost in August, and 30 per cent in September. This is outside the region subject to polar temperatures.
Above Antarctica itself, chemical reactions that ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:5ffed3a7-eb51-41a7-9eb8-d1e424f66b00> | 4.15625 | 210 | Truncated | Science & Tech. | 42.140574 |
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RECEIVE OUR FREE NEWSLETTERON SCIENCE
University of Toronto
Scientists explore the physics of bumpy roads
August 9th, 2009
Just about any road with a loose surface - sand or gravel or snow - develops ripples that make driving a very shaky experience. A team of physicists from Canada, France and the United Kingdom have recreated this "washboard" phenomenon in the lab with surprising results: ripples appear even when the springy suspension of the car and the rolling shape of the wheel are eliminated. The discovery may smooth the way to designing improved suspension systems that eliminate the bumpy ride.
"The hopping of the wheel over the ripples turns out to be mathematically similar to skipping a stone over water," says University of Toronto physicist, Stephen Morris, a member of the research...
Click here for more articles from University of Toronto
Source: VerticalNews Science (2009-08-09) | <urn:uuid:1f5e95d9-b257-4e27-9d9c-bda94048d182> | 3.015625 | 194 | Truncated | Science & Tech. | 30.707755 |
In case you have missed this important event last week…
(Photo note: An image taken by the Mars rover Opportunity, shown by NASA during a press conference Thursday, Oct 7, 2004, shows a bizarre, lumpy rock informally named Wopmay on the lower slopes of Endurance Crater. Scientists believe the lumps in Wopmay were formed by one of two processes. Either they were caused by the impact that created the football field-sized crater, or they arose when water soaking the rock dried up, said the scientists)
(Photo note: The Mars Descent Imager (MARDI), a camera on board the Curiosity designed to take photos during the descent to Mars, took this image of the heat shield plummeting to the Martian surface)
(Photo note: A close-up of one of the rover’s wheels. Curiosity is currently driving around the Gale Crater, a place NASA scientists believe could harbor signs of microbial life, from the past or present)
NASA successfully landed the latest of its Mars Rover called Curiosity in Mars last week. With this, they have 3 rovers (Spirit and Opportunity which landed back in 2004) on the planet exploring the surface and geology. The mission’s scientific objective was to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars.
The much-celebrated Mars rover Curiosity is headed for Mount Sharp, where it will help scientists explore the question of life on Mars as it climbs up and up. Meanwhile, however, NASA’s budget for planetary exploration is slated to go down, down, down.
Scientists are basking in the success of Curiosity’s stunning landing earlier this week, proving that a complicated system involving a parachute and a sky crane can safely deliver a 2,000-pound vehicle to Mars. The $2.6 billion Curiosity will spend years roaming the planet, snapping photos and gathering scientific data.
Given the budget constraints facing the space agency, however, there are limits on what the rover, and NASA, will be able to do on the surface of the Red Planet. Although astronauts brought back thousands of moon rocks during the Apollo Mission, there’s never been a sample of Martian material returned to Earth. Such a mission is considered a priority, so scientists can do more detailed chemical analyses.
After the Moon, we have been eyeing Mars as the next frontier and a place where humans may be able to adapt as their next home. Who knows what lays thereafter – new mining colonies perhaps or as a “jumping stone” to explore other planets? And inspire future generation of space explorers and scientists to think beyond and ahead. And with 2 rovers on the planet, why we need another rover on the planet?
From Associated Press:-
NASA’s new robot rover named Curiosity landed safely early Monday in a huge crater near the equator of Mars and will soon begin its scientific studies. This marks NASA’s seventh landing on the red planet and is its 19th Mars mission, including those by orbiters and other spacecraft.
Why Mars Again?
The big unknown remains. Scientists want to know if any form of life ever existed there, and that means microscopic organisms. Curiosity is the most ambitious effort ever to burrow into that question, though it is not equipped to look for actual microbes. During its two-year exploration, it will try to answer whether the giant crater had the right conditions to support that type of life.
What will Curiosity do?
Curiosity carries a toolbox of 10 instruments, including a rock-zapping laser and a mobile organic chemistry lab. It also has a long robotic arm that can jackhammer into rocks and soil. It will hunt for the basic ingredients of life, including carbon-based compounds, nitrogen, phosphorus, sulfur and oxygen, as well as minerals that might provide clues about possible energy sources.
And talking about the mission to Mars, if you recalled in 2010, President Obama talked about a manned mission to Mars by year 2030 whilst at the same time, cancelled the project to return to the Moon citing that the project was too costly, “behind schedule, and lacking in innovation”. With the latest successful landing of the Curiosity Rover, it will be interest how this mission to take man to the Red Planet going to take place in the next few years. It is also going to be very interesting how we are going to push the current innovation to make space exploration cheaper, safer and longer lasting.
(Our very own Planetarium Space Theater – it is a good platform to generate keen deep interest on space exploration and science. The other is the Langkawi National Observatory which has good stellar and solar telescopes. Image source: National Planetarium)
Looking back at Malaysia, no doubt we started with the wrong foot with teaching of Science and Mathematics in Bahasa Malaysia instead of the more “universal” language of English (we still have a chance to correct this mistake) but it is good that we have also started to expose Malaysians (especially the young ones) on the science of astronomy, mechanical, robotics, computing and others that is crucial for future space explorations. The sight on a greater exploration of the space should be there for all and we should start with the right language of science and mathematics.
P.s. Have a nice weekend and happy holidays to all. Hope that you will miss the madness at the highway and arrive safely at your destination.
- Mars rover “dreams” on Red Planet (cbsnews.com)
- 5 new Mars photos released (cbsnews.com)
- Mars Curiosity Rover ‘brain transplant’ a success: Nasa – Firstpost (firstpost.com)
- Mars Curiosity rover is ready to roll, says Nasa (guardian.co.uk)
- Mars rover Curiosity’s set to take a spin in coming days (latimesblogs.latimes.com)
- NASA’s Mars rover Curiosity getting “brain transplant” (gizmag.com)
- Mars as you’ve never seen it: Nasa’s Curiosity Rover transmits more stunning images of the red planet (dailymail.co.uk)
- NASA eager to take Mars rover Curiosity for a drive (latimesblogs.latimes.com) | <urn:uuid:26320d2a-ab04-4d6f-abf1-d05a8bcae644> | 3.203125 | 1,303 | Personal Blog | Science & Tech. | 47.481287 |
Mous Chahine is a senior research scientist at NASA’s Jet Propulsion Laboratory in California.
He told us about research using an instrument called the Atmospheric Infrared Sounder – AIRS – that works aboard NASA’s Aqua satellite. AIRS tracks carbon dioxide, a greenhouse gas known to cause global warming.
There is no area on Earth immune from the effects of carbon dioxide regardless of whether that area produces carbon dioxide or not. From AIRS, we have made one discovery. It is that carbon dioxide is not well mixed. It is lumpy. We can look at the carbon dioxide emitted from Asia moving across the Pacific to North America, where we add more carbon dioxide, and then to Europe. It goes round and around.
Dr. Chahine said AIRS also tracks water vapor in the atmosphere, which he called the planet’s most potent greenhouse gas. He said warming global temperatures mean more evaporation from the oceans. This water vapor gets stored in Earth’s upper atmosphere, heating up the Earth even more.
If the carbon dioxide is causing global warming of, say, one degree, the resulting water vapor in the atmosphere will multiply it so that the net is two and a half degrees, not just one.
He explained that AIRS tracks carbon dioxide using spectra, or colors.
We make the measurement in the infrared. This is the region in which we get heat emitted from the atmosphere. If we have more carbon dioxide, we have more energy emitted, and the satellite will measure more energy. What we do is take those measurements which we call spectra [infrared colors], and we unscramble it to see how much change from carbon dioxide, clouds, or water vapor.
Chahine said carbon dioxide is the most demanding gas to study.
Because we are asked to measure it one part per million. With AIRS we have shown we can do it between one and two. We have to be very careful, very attentive – this is a message to my colleagues. Treat your instrument with infinite care, it will pay off.
Chahine said AIRS has produced six years worth of global carbon dioxide data – the longest-running measurement. He said that a future project for AIRS is identifying Earth’s natural carbon dioxide ‘sinks’ – that is, CO2 storage spots like oceans and forests that might help keep Earth cool.
Our thanks today to NASA’s Aqua Mission, improving our knowledge of our home planet through satellite observations. | <urn:uuid:f3b66f15-3a8e-4daf-a83f-cc6e23885ce5> | 4.3125 | 519 | Audio Transcript | Science & Tech. | 49.770143 |
See also:physical and
See also:mechanical science, the
See also:term given to the resistance which every material
See also:surface presents to the sliding of any other such surface upon it . This resistance is due to the roughness of the surfaces; the minute projections upon each enter more or less into the minute depressions on the other, and when motion occurs these roughnesses must either be worn off, or continually lifted out of the hollows into which they have fallen, or both, the resistance to motion being in either case quite perceptible and measurable .
See also:Friction is preferably spoken of as " resistance " rather than " force," for a reason exactly the same as that which induces us to treat stress rather as molecular resistance (to
See also:change of
See also:form) than as force, and which may be stated thus: although friction can be utilized as a moving force at will, and is continually so used, yet it cannot be a
See also:primary moving force; it can transmit or modify motion already existing, but cannot in the first instance cause it . For this some
See also:external force, not friction, is required . The
See also:analogy with stress appears
See also:complete; the motion of the "
See also:link " of a machine is communicated to all the other parts, modified or unchanged as the case may be, by the stresses in those parts; but the actual setting in motion of the driving link itself cannot come about by stress, but must have for its production force obtained directly from the
See also:expenditure of some form of energy . It is important, however, that the use of the term " resistance " should not be allowed to mislead . Friction resists the motion of one surface upon another, but it may and frequently does confer the motion of the one upon the other, and in this way causes, instead of resists, the motion of the latter . This may be made more clear, perhaps, by an
See also:illustration . Suppose we have a
See also:leather strap A passing over a fixed cylindrical
See also:drum B, and let a pulling force or effort be applied to the strap . The force applied to A can
See also:act on B only at the surfaces of contact between them . There it becomes an effort tending either to move A upon B, or to move the
See also:body B itself, according to the frictional conditions . In the
See also:absence of friction it would simply cause A to slide on B, so that we may
See also:call it an effort tending to make A slide on B .
The friction is the resistance offered by the surface of B to any such motion . But the value of this resistance is not in any way a
See also:function of the effort itself,—it depends chiefly upon the pressure normal to the surfaces and the nature of the surfaces . It may therefore be either less or greater than the effort . If less, A slides over B, the
See also:rate of motion being deter-
See also:mined by the excess of the effort over the resistance (friction) . But if the latter be greater no sliding can occur, i.e . A cannot, under the
See also:action of the supposed force, move upon B . The effort between the surfaces exists, however, exactly as before,—and it must now tend to cause the motion of B . But the body B is fixed,—or, in other words, we suppose its resistance to motion greater than any effort which can tend to move it,—hence no motion takes place . It must be specially noticed, however, that it is not the friction between A and B that has prevented motion, this only prevented A moving on B; it is the force which keeps B stationary, whatever that may be, which has finally prevented any motion taking place . This can be easily seen . Suppose B not to be fixed, but to be capable of moving against some third body C (which might, e.g., contain cylindrical
See also:bearings, if B were a drum with its
See also:shaft), itself fixed,—and further, suppose the frictional resistance between B and C to be the only resistance to B's motion . Then if this be less than the effort of A upon B, as it of course may be, this effort will cause the motion of B .
Thus friction causes motion, for had there been no frictional resistance between the surfaces of A and of B, the latter body would have remained stationary, and A only would have moved . In the case supposed, therefore, the friction between A and B is a necessary
See also:condition of B receiving any motion from the external force applied to A . Without entering here on the mathematical treatment of the subject of friction, some general conclusions may be pointed out which have been arrived at as the results of experiment . The "
See also:laws" first enunciated by C . A . Coulomb (1781), and after-wards confirmed by A . J . Morin (1830-1834), have been found to hold
See also:good within very wide limits . These are: (1) that the friction is proportional to the normal pressure between the surfaces of contact, and therefore
See also:independent of the
See also:area of those surfaces, and (2) that it is independent of the velocity with which the surfaces slide one on the other . For many
See also:practical purposes these statements are sufficiently accurate, and they do in fact sensibly represent the results of experiment for the pressures and at the velocities most commonly occurring . Assuming the correctness of these, friction is generally measured in terms simply of the
See also:total pressure between the surfaces, by multiplying it by a " coefficient of friction " depending on the material of the surfaces and their state as to smoothness and
See also:lubrication . But beyond certain limits the " laws " stated are certainly incorrect, and are to be regarded as mere practical rules, of extensive application certainly, but without any pretension to be looked at as really general laws .
Both at very high and verylow pressures the coefficient of friction is affected by the intensity of pressure, and, just as with velocity, it can only be regarded as independent of the intensity and proportional simply to the total load within more or less definite limits . Coulomb pointed out long ago that the resistance of a body to be set in motion was in many cases much greater than the resistance which it offered to continued motion; and since his
See also:time writers have always distinguished the " friction of
See also:rest," or static friction, from the " friction of motion," or kinetic friction . Ile showed also that the value of the former depended often both upon the intensity of the pressure and upon the length of time during which contact had lasted, both of which facts quite agree with what we should expect from our know-ledge of the physical nature, already mentioned, of the causes of friction . It seems not unreasonable to expect that the influence of time upon friction should show itself in a comparison of very slow with very rapid motion, as well as in a comparison of starting (i.e. motion after a long time of rest) with continued motion . That the friction at the higher velocities occurring in
See also:engineering practice is much less than at
See also:common velocities has been shown by several
See also:modern experiments, such as those of
See also:Galton (see
See also:Report Brit . Assoc., 1878, and Proc . Inst . Mech . Eng., 1878, 1879) on the friction between
See also:brake-blocks and wheels, and between wheels and rails . But no increase in the coefficient of friction had been detected at slow speeds, until the experiments of Prof . Fleeming Jenkin (Phil . Trans., 1877, pt .
2) showed conclusively that at extremely low velocities (the lowest measured was about •0002 ft. per second) there is a sensible increase of frictional resistance in many cases, most notably in those in which there is the most marked difference between the friction of rest and that of motion . These experiments distinctly point to the conclusion, although without absolutely proving it, that in such cases the coefficient of kinetic friction gradually increases as the velocity becomes extremely small, and passes without discontinuity into that of static friction . (A . B . W . K.; W . E .
FRIBOURG [Ger. Freiburg]
FRIDAY (A.S. frige-dreg, fr. frige, gen. of frigu, ...
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M.Elizabeth Chemistry 2010-2011
Spring Semester March 8 - March 21
Chemical Reaction Rates and Equilibrium
- GUHS Chemical Reaction Rates and Equilbrium SG word
- Kinetics Equilibrium Bell Ringer Part 1 Part 2 Part 3 Part 4 Part 5
- Kinetics Online Quiz 1 Equilibrium Online Quiz 2
- Reaction Rate Standard Notes word
- Equilibrium Standard Notes word
- Equilibrium Notes word
- Glencoe Kinetics ppt
- Reaction Rate ppt
- Glencoe Equilibrium ppt
- Kinetics and Equilibrium 2011 ppt
Mark Rosengarten Rate Of Reaction music video
Mark Rosengarten Equilibrium Shifts music video
Reaction Rate Video Notes
Equilibrium Video - Notes Taking Guide pdf
- Lab: Equilibrium Datasheet pdf
- Lab: Le Chatelier’s Principle pdf
- Calculating Keq pdf
- Le Chatelier’s Principle pdf
>> Reaction Rate Crossword word
>> Equilibrium Constant and Calculations word
>> LeChatelier's Principle Practice word
>> Collision Theory Questions word
>> Rate Graphing and Analysis Practice word
Online Resources (Web Sites)
Chemical Kinetics link
Kinetics with Canadian Connections link
8. Chemical reaction rates depend on factors that influence the frequency of collision of reactant molecules. As a basis for
understanding this concept:
a. the rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time.
b. reaction rates depend on such factors as concentration, temperature, and pressure.
c. catalysts increases the reaction rate. A catalyst increases the rate of a chemical reaction without taking part in the net
reaction. A catalyst lowers the energy barrier between reactants and products by promoting a more favorable pathway for the
reaction. Surfaces often play important roles as catalysts for many reactions. One reactant might be temporarily held on the
surface of a catalyst. There the bonds of the reactant may be weakened, allowing another substance to react with it more quickly.
Living systems speed up life-dependent reactions with biological catalysts called enzymes.
Chemical equilibrium is a dynamic process that occurs when there is not changes in a product or reactant concentration that
undergo reversible reactions with several factors affecting equilibrium that must be considered when writing expressions used to
quantify a state of equilibrium. Changes in heat accompanying chemical reactions and spontaneity of chemical reactions are key
topics, along with physical states of substances undergoing chemical reactions, for example gases respond to changes in pressure
and volume. Calculation of concentration and molarity for solutions, particularly for aqueous solutions and use of exponents are
needed to solve quantitative problems.
When a stress is applied to a chemical reaction in equilibrium, a shift will occur to partly relieve the stress.
9. Chemical equilibrium is a dynamic process at the molecular level. As a basis for understanding this concept: a. Students know
how to use Le Chatelier’s principle to predict the effect of changes in concentration, temperature, and pressure. Le Chatelier’s
principle can be introduced by emphasizing the balanced nature
of an equilibrium system. If an equilibrium system is stressed or disturbed, the system will respond (change or shift) to partially
relieve or undo the stress. A new equilibrium will eventually be established with a new set of conditions. When the stress is
applied, the reaction is no longer at equilibrium and will shift to regain equilibrium.
For instance, if the concentration of a reactant in a system in dynamic equilibrium is decreased, products will be consumed to
produce more of that reactant. Students need to remember that heat is a reactant in endothermic reactions and a product in
exothermic reactions. Therefore, increasing temperature will shift an endothermic reaction, for example, to the right to regain
equilibrium. Students should note that any endothermic chemical reaction is exothermic in the reverse direction.
Pressure is proportional to concentration for gases; therefore, for chemical reactions that have a gaseous product or reactant,
pressure affects the system as a whole. Increased pressure shifts the equilibrium toward the smaller number of moles of gas,
alleviating the pressure stress. If both sides of the equilibrium have an equal number of moles of gas, increasing pressure does
not affect the equilibrium. Adding an inert gas, such as argon, to a reaction will not change the partial pressures of the reactant or
product gases and therefore will have no effect on the equilibrium.
9. b. Students know equilibrium is established when forward and reverse reaction rates are equal.
Forward and reverse reactions at equilibrium are going on at the same time and at the same rate, causing overall concentrations
of each reactant and product to remain
constant over time.
9. c.* Students know how to write and calculate an equilibrium constant expression for a reaction.
Because the concentrations of substances in a system at chemical equilibrium are constant over time, chemical expressions
related to each concentration will also be constant. Here is a general equation for a reaction at equilibrium:
aA + bB ↔ c C + d D
The general expression for the equilibrium constant of a chemical reaction is Keq, defined at a particular temperature, often 25°
C. Its formula is | <urn:uuid:48e7e5ca-5785-4d51-a661-7209d86bb8e1> | 3.84375 | 1,121 | Content Listing | Science & Tech. | 31.524893 |
Euler found four whole numbers such that the sum of any two of the
numbers is a perfect square. Three of the numbers that he found are
a = 18530, b=65570, c=45986. Find the fourth number, x. You could
do this by trial and error, and a spreadsheet would be a good tool
for such work. Write down a+x = P^2, b+x = Q^2, c+x = R^2, and then
focus on Q^2-R^2=b-c which is known. Moreover you know that Q >
sqrtb and R > sqrtc . Use this to show that Q-R is less than or
equal to 41 . Use a spreadsheet to calculate values of Q+R , Q and
x for values of Q-R from 1 to 41 , and hence to find the value of x
for which a+x is a perfect square.
The diagram illustrates the formula: 1 + 3 + 5 + ... + (2n - 1) = n² Use the diagram to show that any odd number is the difference of two squares.
Find the frequency distribution for ordinary English, and use it to help you crack the code.
Start with a diagram of a cube just passing under a ribbon.
And maybe put the cube exactly in the middle, just to start
Next choose a size for the cube, any size, and calculate how
long the ribbon would be if that was the biggest cube that would
Was it 104 cm ? Adjust the cube size and try again ? | <urn:uuid:4c1760ea-e8fb-453c-817a-33f0800e9beb> | 3.46875 | 332 | Tutorial | Science & Tech. | 95.968399 |
Whirl a conker around in a horizontal circle on a piece of string.
What is the smallest angular speed with which it can whirl?
How do you write a computer program that creates the illusion of stretching elastic bands between pegs of a Geoboard? The answer contains some surprising mathematics.
Can you explain what is happening and account for the values being
Make a poster using equilateral triangles with sides 27, 9, 3 and 1 units assembled as stage 3 of the Von Koch fractal. Investigate areas & lengths when you repeat a process infinitely often.
Explain how to construct a regular pentagon accurately using a
straight edge and compass. | <urn:uuid:09f42814-7d54-460a-903a-6ee145c27322> | 3.25 | 136 | Content Listing | Science & Tech. | 52.875872 |
The Role of Ice in the Ocean: Pt. III: Shrinking Ice: Impacts
NASA/Goddard Space Flight Center Scientific Visualization Studio
Benjamin Jones - USGS
Footage Search - Daniel Zatz, Ernie Kovacs
As Arctic ice continues to melt, it will cause ripple effects across the planet. When the polar regions warm, even just a degree, it disturbs atmospheric and oceanic patterns.
The patterns of the jet stream will be affected, which may lead to more extreme summer and winter weather events in Europe, Asia, and North America. Not only will our weather change, but sea level will rise too.
Sea ice melt itself does not cause sea levels to rise because the ice is already in the water. But the melting of ice on a land surface, like Greenland, does because new water is flowing into the ocean. In addition, as ocean water warms, it expands, which also raises sea level.
Warmer air temperatures will accelerate the melting of Greenland's ice sheet, which contains enough ice to raise global sea levels by more than 20 feet.
Sea ice creates a unique ecosystem that supports millions of plants and animals, from krill and ice algae to cod and walruses. Both the topside and underside of the ice provide places for animals to hunt, hide, rest, mate, and give birth.
Without sea ice, arctic plants and animals must either adapt or migrate. If they can't, they will go extinct.
If that isn't enough, people who live in coastal communities within the Arctic Circle are also battling erosion along their coastlines.
Sea ice serves as a buffer against wave action. Without it, the wind blows across a larger region of open water, resulting in stronger winds and bigger waves that erode the shoreline.
These communities must relocate inland or their homes and land could be washed out to sea.
For ice in the Arctic, it's a race against time. If humans do not change what we are doing to the global climate, the ice will continue to disappear and life as we know it will be altered. | <urn:uuid:e2139735-b834-4749-9cc0-b874c74b3da0> | 4.09375 | 433 | Knowledge Article | Science & Tech. | 50.347346 |
On this page, you will find information on uniform random number
generators (RNGs). We will not (yet) discuss cryptographic generators,
nor non-uniform random numbers. For those two topics and for code
for RNGs, we refer to our Links
This page has been written by Peter
Uniform RNGs produce numbers with certain distribution properties.
Roughly speaking, these numbers should behave similar to realizations
of independent, identically distributed random variables.
We may distinguish between hard- and software RNGs and, among the
algorithms, between deterministic and non-deterministic algorithms.
Deterministic RNGs are usually called pseudo-random number generators.
We will simply use the term "RNG" for all of those. Links
to some hardware RNGs are to be found via our Links
Every RNG has its deficiencies. No RNG is appropriate for all tasks.
For example, several good RNGs from the toolbox of stochastic simulation
are unsuited for cryptographical applications, because they produce
predictable output streams. On the other hand, cryptographic RNGs
are usually (but not always) too slow for doing Monte Carlo simulations.
A good RNG has been thoroughly analyzed theoretically and is backed
by convincing practical evidence like extensive statistical testing.
In stochastic simulation, in order to verify our simulation results,
we should be able to choose from a whole arsenal of widely different
RNGs. The reason behind this argument is the possibility that the
intrinsic structure of our RNG might interfere with our simulation
problem and yield wrong results.
There are two big families of RNGs, linear generators and nonlinear
ones. Cryptographers stay away from the linear algorithms because
of predictability reasons, but in Monte Carlo simulations, linear
RNGs are the best-known and most widely available ones. If one has
to generate huge samples of random numbers as efficiently as possible,
then one will use linear RNGs like the extremely fast and reliable
RNGs available from Makoto Matsumoto, see TT800
and the Mersenne Twister,
or the (single or combined) multiple recursive generators
studied and implemented by Pierre L'Ecuyer,
see his publications page,
or one of Li-Yuan Deng's huge RNGs.
Sometimes, you will run into trouble with linear RNGs, because
those algorithms produce linear point structures in every dimension
and this fact may interfere with your simulation problem. For this
reason, nonlinear generators have been introduced. In general, they
are much slower than linear generators of comparable size (by a
factor of, say 5 to 10), but they allow you to use larger samples.
At present, there is no equivalent to the huge linear generators
of Matsumoto and L'Ecuyer available in the nonlinear family, with
one notable exception. You may use AES as a highly efficient nonlinear
RNG with a huge period. Together with Stefan Wegenkittl, I have
submitted AES to state-of-the-art statistical tests. AES has passed
with flying colours, see our recent ACM
TOMACS article titled "Empirical Evidence Concerning AES".
In the pLab project we have investigated the most promising
nonlinear type, inversive
RNGs (keywords: ICG, EICG). These generators have properties that
differ strongly from those of traditional generators like
linear generators (keyword: LCG), or from shift register generators.
Implementations in C of inversive and also of linear RNGs are available
on our Software
page. Appropriate parameters for ICGs are availabe from the Winter
Simulation Conference 1995 survey paper by Peter Hellekalek
and in the form of extensive tables
The following table is an index to the available information.
Further information on multiple
recursive generators (MRGs) and combined
LCGs and a basic
introduction in "linear" methods in general is available,
see also the survey
paper written for practitioners.
Randomness in Practice: Travelling around in Buenos Aires, Argentina, comes close to a random walk, even for local people.
In order to find your way around this mega-city, there now is
viaja fácil, a website that will tell you how to get from
point A to point B. Highly recommended!
If you need code for RNGs, please see our Software
back to the top
Research supported by and | <urn:uuid:001acfd9-c382-470a-997a-36617040f90c> | 3.15625 | 973 | Content Listing | Science & Tech. | 30.28158 |
Nowadays, much of the world is lit up twenty-four hours a day. This has consequences for invertebrates. We’ve all seen moths and other insects buzzing around streetlights, but the effects of artificial lighting extends much deeper. According to Thomas Davies, Jonathan Bennie and Kevin Gaston of the University of Exeter, even ground-dwelling invertebrates are affected.
The researchers set pitfall traps in the grass either directly under streetlights or midway between them (the darkest area of the street). Occupants of the traps were collected thirty minutes before sunrise and before sunset so that both diurnal and nocturnal creatures were represented.
More organisms were collected under streetlights than between them. Interestingly, the pitfall traps under streetlights yielded significantly more carnivores and scavengers than pitfall traps between lights. This was true for both daytime and nighttime sampling. In other words, it wasn’t just that some creatures were attracted to the streetlights while they were turned on. Different communities of invertebrates were living near streetlights twenty-four hours a day. | <urn:uuid:36416f23-34bb-4834-ac46-51bba976d588> | 3.703125 | 225 | Personal Blog | Science & Tech. | 37.375695 |
The speech-recognition algorithms behind Google Voice Search analyze thousands of hours of human speech to pick out patterns. Babies may use the same technique. Google speech recognition guru Mike Cohen and linguist Sheila Blumstein discuss how humans and computers learn language.
Kinect uses depth sensors, cameras and microphones to track the movements of players, and it's surprisingly good at weeding out distractions. Ira Flatow and guests discuss the development of the gaming technology -- and how movement can influence players' moods.
The British poet and alchemist Thomas Norton used the word "attoms" in his 1477 poem, The Ordinal of Alchemy. Historian Howard Markel explains how Norton came to use the word, and points out earlier philosophers who raised the concept of indivisible units of matter.
Some airport body scanning machines use X-rays to generate images. How much radiation is a traveler exposed to? Should frequent fliers opt for a pat down instead? Radiation expert David Brenner explains the possible public health concerns of scanning millions of passengers.
Why does a saxophone sound different from an oboe? How do tiny flutes produce such loud sounds? Dr. John Powell, author of How Music Works: The Science and Psychology of Beautiful Sounds explains musical acoustics and more.
Scientists at CERN, the European nuclear research facility, say they have produced and trapped molecules of antihydrogen, a form of antimatter. Physicist Jeffrey Hangst explains how they were made and captured. Will trapping antimatter help scientists learn about the construction of the universe?
Kelly Ward, senior software engineer for Walt Disney Animation Studios, was tasked with bringing Rapunzel's locks to life in Disney's new movie, Tangled. The hair had to look realistic, but not too real -- otherwise Rapunzel would be towing 80 pounds of hair behind her.
When it comes to comets, gassy is good, or at least informative, says astronomer Michael A'Hearn. NASA's Deep Impact probe has been snapping pictures of Hartley 2 -- a small comet that is spewing a lot of gas and dust for its size. What do researchers hope to learn from the comet?
Lichens grow practically everywhere, but they have been neglected by scientists for years, says James Lendemer, a lichenologist with New York Botanical Garden. Lendemer took Science Friday on a trip to the Tannersville Cranberry Bog in Pennsylvania to explore the diversity of lichens living there.
It's been 75 years since Albert Einstein decried the "spooky action at a distance" of quantum entanglement. Tom Siegfried, editor-in-chief of Science News, explains how quantum mechanics is being put to use, even though scientists still don't quite understand how it works.
Why do humans have consciousness? In his new book, Self Comes To Mind, neurologist Antonio Damasio argues that consciousness gave humans an evolutionary advantage. Damasio describes the differences between self and mind, and traces the evolutionary path of the human brain.
Harvard researchers have developed a Web tool for volunteers to record what they're doing and how they feel while doing it. The goal? To measure happiness. Doctoral student Matt Killingsworth describes some early results suggesting many people aren't "living in the moment."
Subra Suresh, former dean of engineering at MIT, was sworn in last month as director of the National Science Foundation, which doles out billions of dollars for basic research each year. Suresh talks about his priorities and how the NSF's budget is likely to fare with the new Congress.
This week, a group of scientists called the "rapid response team" has promised to speak up about climate change and take skeptics head-on, even if that means participating in political debates. But does this verge on advocacy? And is that a problem? Ira Flatow and guests discuss.
Host: Marc Pelletier How to fund the development of your own technology through SBIR funding. Guest: Lisa Kurek of Biotechnology Business Consultants We invite you to read, add to, and amend our show notes. Comments and suggestions on Futures in Biotech. For a free audiobook, visit... | <urn:uuid:d89dd8aa-9d5a-4028-8e30-1e60ea7da0bf> | 2.78125 | 867 | Content Listing | Science & Tech. | 48.604716 |
Biology of Subterranean Termites in the Eastern United States B 1209
- Full Text
Dan Suiter, Extension Entomologist
This publication was reviewed on Mar 30, 2012.
Subterranean termites are social insects that live in societies whose members are mostly mature individuals. Their colonies, which can contain thousands to millions of termites, are formidable, even though each individual termite is soft-bodied and delicate. This publication contains comprehensive information about subterranean termites in the Eastern U.S.
Publication Full Text
There is no HTML version of this publication.
Click the link above to view the PDF version.
If you have questions please contact this site's system administrator. | <urn:uuid:0c942845-c1ca-4d5d-9965-eb5e794a305c> | 3.359375 | 145 | Truncated | Science & Tech. | 32.965495 |
- all programs must start with “begin” and end with “end”
- all commands must be ended by “;”
- all variables must be declared just after “begin” in the following format;
int: i num;
- three types exist; “int”, “float”, “char”
- variables names may be any alphanumeric string, but they must start with a letter
- statements between “begin” and “end” can be either a variable declaration or an assignment
- an assignment includes four type of operators; +,-,*,/.
- the number of variables or constants in an expression is unlimited
- the presedence of operators given as..............
Your PL should include a well-defined regular grammar for variable names, rules for
variable declarations including their type, at least 4 arithmetic and 3 logical operators with
their precedence and associativity rules with and without parenthesis, indefinite number of
assignments with expressions having unlimited number of operands.
How can i do? I have to use C language and ANTLR | <urn:uuid:9ec3b137-5a7b-4afc-82f8-d83bdc6dccd8> | 3.53125 | 241 | Comment Section | Software Dev. | 47.475736 |
The body of a Python compound statement cannot be empty; it must always contain at least one statement. You can use a pass statement, which performs no action, as a placeholder when a statement is syntactically required but you have nothing to do. Here's an example of using pass in a conditional statement as a part of somewhat convoluted logic to test mutually exclusive conditions:
if condition1(x): process1(x) elif x>23 or condition2(x) and x<5: pass # nothing to be done in this case elif condition3(x): process3(x) else: process_default(x)
Note that, as the body of an otherwise empty def or class statement, you may use a docstring, covered in "Docstrings" on page 72; if you do write a docstring, then you do not need to also add a pass statement, although you are still allowed to do so if you wish.
The try and raise Statements
Python supports exception handling with the try statement, which includes try, except, finally, and else clauses. A program can explicitly raise an exception with the raise statement. As I discuss in detail in "Exception Propagation" on page 126, when an exception is raised, normal control flow of the program stops, and Python looks for a suitable exception handler.
The with Statement
In Python 2.5, a with statement has been added as a more readable alternative to the try/finally statement. I discuss it in detail in "The with statement" on page 125. | <urn:uuid:84f99695-8b16-43b7-9312-6231cbca6578> | 3.234375 | 320 | Documentation | Software Dev. | 44.625813 |
What do you mean by properties in C#?
Interview question and answer by: Abhisek
| Posted on: 1/21/2010 | Category: C# Interview questions
| Views: 3097 |
Property acts as a cross link between the field and the method . Actually it behaves as a field. We can retrieve and store data from the field using property.
The compiler automatically translates the field like property into a call like special method called as 'accessor" . In property there are two accessor and that are used to save value and retrieve value from the field. The two properties are 'get' and 'set'.
The get property is used to retrieve a value from the field and the set property is used to assign a value to a field .
Depending on there use properties are categorised into three types,
ReadWrite Property :- When both get and set properties are present it is called as ReadWrite Property.
ReadOnly Property :- When there is only get accessor it is called as ReadOnly Property.
WriteOnly Property :- When there is only set accessor, it is called as WriteOnly Property.
| Alert Moderator
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Combinatorial species(This article is about a concept in combinatorial mathematics. There is also an article on the concept of species used in biology.)
For example, the "species of permutations" maps each finite set A to the set of all permutations of A, and each bijection from A to another set B naturally induces a bijection from the set of all permutations of A to the set of all permutations of B. Similarly, the "species of partitions" can be defined by assigning to each finite set the set of all its partitions, and the "power set species" assigns to each finite set its power set.
- Need to explain how to add, multiply, compose, and differentiate combinatorial species. | <urn:uuid:d0cef789-2774-4e31-a19f-b4c74d70a1b1> | 3.234375 | 151 | Knowledge Article | Science & Tech. | 37.022462 |
Copyright © 2007 Dorling Kindersley
Neither plants nor animals, the fungi kingdom includes toadstools, puffballs, and MOLDS. Fungi feed on living or dead organisms by making them rot. Fungi are visible only when spore-bearing fruiting bodies form.
Fungi absorb nutrients from plant or animal matter around them, which may be living or dead. They produce long, slender threads called hyphae that spread through their food. The hyphae release enzymes that break down the food into substances that the fungi can easily absorb.
Most fungi reproduce by releasing tiny spores that then germinate (sprout) and grow into a new fungus. The spores are produced by, and released from, a fruiting body that is visible above the ground. Some fungi drop spores, which are blown away by the wind. Others shoot them out in an explosive burst.
Toadstools are brightly colored and poisonous to eat, but mushrooms are usually edible and dull in color. Both toadstools and mushrooms are fruiting bodies (spore-bearing structures) produced by fungi. They belong to the same group, the Basidiomycetes, so scientists make no distinction between the two.
Scientists are continually revising the classification of the fungi kingdom (with more than 100,000 species), but currently they divide it into three groups:
Fungi called molds produce the woolly or furry growths found on rotting foods, such as bread and fruit. The growths are formed by threadlike hyphae that grow upward and release spores from their tips. These spores then sprout on other foods. | <urn:uuid:f33c3080-839c-4121-b28d-e3f686f5f5db> | 3.796875 | 340 | Knowledge Article | Science & Tech. | 51.261082 |
This page is intended for college, high school, or middle school students.
For younger students, a simpler explanation of the information on this page is
available on the
Weight is the force generated by
the gravitational attraction of the earth on the airplane.
We are more familiar with weight than with the other forces acting on
an airplane, because each of us have our own weight which we can
measure every morning on the bathroom scale. We know when one thing
is heavy and when another thing is light. But weight, the
gravitational force, is fundamentally different from the aerodynamic
forces, lift and drag.
Aerodynamic forces are mechanical forces and the airplane has to be
in physical contact with the the air which generates the force. The
gravitational force is a field force; the source of the force does
not have to be in physical contact with the object to generate
a pull on the object.
The nature of the gravitational force has been studied by
scientists for many years and is still being investigated by
theoretical physicists. For an object the size of an airplane, the
descriptions given three hundred years ago by Sir Isaac Newton work
quite well. Newton developed his theory of gravitation when he was
only 23 years old and published the theories with his laws
of motion some years later. The gravitational force between two
objects depends on the mass of the objects and the inverse of the
square of the distance between the objects. Larger objects create
greater forces and the farther apart the objects are the weaker the
attraction. Newton was able to express the relationship in a single
Weight is a force, and a force is a
having both a magnitude and a direction associated with it.
For an airplane, weight is always directed
towards the center of the earth. The magnitude of this force
depends on the mass of all of the parts of
the airplane itself, plus the amount of fuel, plus any payload on
board (people, baggage, freight, ...). The weight is distributed
throughout the airplane, but we can often think of it as collected
and acting through a single point called the center
of gravity. In flight, the airplane
about the center of
gravity, but the direction of the weight force always remains toward
the center of the earth. During a flight the aircraft burns up its
fuel, so the weight of the airplane constantly changes. Also, the
distribution of the weight and the
center of gravity
can change, so
the pilot must constantly adjust the controls to keep the airplane
Flying involves two major problems; overcoming the weight of
an object by some opposing force, and controlling the object
in flight. Both of these problems are related to the object's weight
and the location of the center of gravity.
The dream remains that, if we could really understand gravity, we
could create anti-gravity devices which would revolutionize travel
through the sky. Unfortunately, anti-gravity devices only exist in
science fiction. Machines like airplanes, or magnetic levitation
devices, create forces opposed to the gravitational force, but they
do not block out or eliminate the gravitational force.
You can view a short
of "Orville and Wilbur Wright" discussing the weight force
and how it affected the flight of their aircraft. The movie file can
be saved to your computer and viewed as a Podcast on your podcast player.
Forces on an Airplane:
Forces on a Glider:
- Beginner's Guide Home Page | <urn:uuid:71eda039-4e70-4eaf-8c02-89781f859d8c> | 4.1875 | 739 | Knowledge Article | Science & Tech. | 45.66866 |
January 6, 2004: Trailing 200,000-light-year-long streamers of seething gas, a galaxy that was once like our Milky Way is being shredded as it plunges at 4.5 million miles per hour through the heart of a distant cluster of galaxies. In this unusually violent collision with ambient cluster gas, the galaxy is stripped down to its skeletal spiral arms as it is eviscerated of fresh hydrogen for making new stars.See the rest:
This galaxy has a strange shape reminiscent of the wake around a boat sailing across a lake. The analogy is apt because the galaxy is plowing through hot gas in the center of a galaxy cluster
The galaxy will be stripped of the hydrogen gas needed to make successive generations of stars. In that sense the galaxy will grow old prematurely. It will be left with aging stars, but no bright blue, new star clusters.
To analyze the galaxy astronomers made a variety of diagnostic observations from telescopes that record the galaxy's appearance in X-ray, optical, and radio light. The observations discovered bright star clusters on the galaxy's leading edge; the galaxy has a tail of gas; and the galaxy is surrounded by its own gas, which is leaking from it.
Though such "distressed" galaxies have been seen before, this one's demise is unusually swift and violent. That's because the galaxy belongs to a cluster of galaxies that slammed into another cluster about 100 million years ago.
Views of the early universe show that spiral galaxies were once much more abundant in rich clusters of galaxies. But they seem to have been vanishing over cosmic time. This result helps explain why.
Credit: NASA, W. Keel (U Alabama), F. Owen (NRAO), M. Ledlow (Gemini Obs.), and D. Wang (U Mass.) | <urn:uuid:f891eb65-ea44-4737-8ac4-d2337dc73307> | 3.234375 | 372 | Knowledge Article | Science & Tech. | 57.211077 |
One can improve performance on many systems by overlapping communication and computation. This is especially true on systems where communication can be executed autonomously by an intelligent communication controller. Multi-threading is one mechanism for threads achieving such overlap. While one thread is blocked, waiting for a communication to complete, another thread may execute on the same processor. This mechanism is efficient if the system supports light-weight threads that are integrated with the communication subsystem. An alternative mechanism that often gives better performance is to use nonblocking communication. A nonblocking communicationcommunication, nonblocking nonblocking post-send initiates a send operation, but does not post-send complete it. The post-send will return before the message is copied out of the send buffer. A separate complete-send complete-send call is needed to complete the communication, that is, to verify that the data has been copied out of the send buffer. With suitable hardware, the transfer of data out of the sender memory may proceed concurrently with computations done at the sender after the send was initiated and before it completed. Similarly, a nonblocking post-receive initiates a receive post-receive operation, but does not complete it. The call will return before a message is stored into the receive buffer. A separate complete-receive complete-receive is needed to complete the receive operation and verify that the data has been received into the receive buffer.
A nonblocking send can be posted whether a matching receive has been posted or not. The post-send call has local completion semantics: it returns immediately, irrespective of the status of other processes. If the call causes some system resource to be exhausted, then it will fail and return an error code. Quality implementations of MPI should ensure that this happens only in ``pathological'' cases. That is, an MPI implementation should be able to support a large number of pending nonblocking operations.
The complete-send returns when data has been copied out of the send buffer. The complete-send has non-local completion semantics. The call may return before a matching receive is posted, if the message is buffered. On the other hand, the complete-send may not return until a matching receive is posted.
There is compatibility between blocking and nonblocking communication functions. Nonblocking sends can be matched with blocking receives, and vice-versa. | <urn:uuid:c48dd902-24f9-4984-bcdd-326a230f6b86> | 2.984375 | 475 | Knowledge Article | Software Dev. | 27.925444 |
Type of particle accelerator that imparts a series of relatively small increases in energy to subatomic particles as they pass through a sequence of alternating electric fields set up in a linear structure. The small accelerations add together to give the particles a greater energy than could be achieved by the voltage used in one section alone. One of the world's longest linacs is the 2-mi (3.2-km) machine at the Stanford Linear Accelerator Center, which can accelerate electrons to energies of 50 billion electron volts. Much smaller linacs, both proton and electron types, have important practical applications in medicine and industry.
Learn more about linear accelerator with a free trial on Britannica.com.
The Stanford Linear Accelerator Center (SLAC) is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Department of Energy Office of Science. The SLAC research program centers on experimental and theoretical research in elementary particle physics using electron beams and a broad program of research in atomic and solid-state physics, chemistry, biology, and medicine using synchrotron radiation. The 2.0 mile (3.2 kilometer) long underground accelerator is the longest linear accelerator in the world, and is claimed to be "the world's straightest object. SLAC's meeting facilities also provided a venue for the homebrew computer club and other pioneers of the 1980s home computer revolution, and later SLAC hosted the first webpage in the U.S. The above-ground klystron gallery atop the beamline is the longest building in the United States.
Founded in 1962, the facility is located on 426 acres (1.72 square kilometers) of Stanford University-owned land on Sand Hill Road in Menlo Park, California—just west from the University's main campus. The main accelerator, a 2.0 mile-long RF linear accelerator, which can accelerate electrons and positrons up to 50 GeV, has been operational since 1966. It is buried 30 feet (10 meters) below ground and passes underneath Interstate 280. As of 2005, SLAC employs over 1,000 people, some 150 of which are physicists with doctorate degrees, and serves over 3,000 visiting researchers yearly, operating particle accelerators for high-energy physics and the Stanford Synchrotron Radiation Laboratory (SSRL) for synchrotron light radiation research.
Research at SLAC has produced three Nobel Prizes in Physics:
In the early-to-mid 90s, the Stanford Linear Collider or SLC, investigated the properties of the Z boson using the Stanford Large Detector.
In the July, 2008 the Department of Energy announced it intends to change the name of SLAC. The reasons given include better representing the new direction of the lab and being able to trademark the name, which Stanford University legally opposes.
Presently no beam enters the south and north arcs in the machine, which leads to the Final Focus, therefore this section is mothballed to run beam into the PEP2 section from the beam switchyard.
SLAC plays host to part of the GLAST project, a collaborative international project also known as The Gamma Ray Large Area Space Telescope, the principle objectives of which are:
The Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) is located on the grounds of SLAC.
Research and Markets Offers Report: 2013 In-Depth Research Report on the Global and Chinese Linear Accelerator Industry
Jun 15, 2013; Wireless News06-15-2013Research and Markets Offers Report: 2013 In-Depth Research Report on the Global and Chinese Linear...
Dose linearity and uniformity of Siemens ONCOR impression plus linear accelerator designed for step-and-shoot intensity-modulated radiation therapy.(Original Article)
Jul 01, 2007; Byline: Janhavi. Bhangle, V. Sathiya Narayanan, Shrikant. Deshpande For step-and-shoot type delivery of intensity-modulated... | <urn:uuid:d6f469c1-89ad-4425-890f-b1c0b3e5f7fe> | 3.421875 | 826 | Knowledge Article | Science & Tech. | 38.458535 |
Have you ever heard the expression, "solid as a rock"? As it turns out, rocks are not entirely solid. Rocks actually have tiny pockets of air inside them. This is obvious when you look at a piece of volcanic rock (often called basalt), which is full of visible holes. But dense rocks, such as granite, have tiny air pockets inside them, too. These pockets of air are just much smaller.
If you picked up one volcanic rock as well as one granite rock of the same size, you would notice they don't weigh the same. The granite is heavier than the volcanic rock. The many large holes of air in the latter make it less dense—and more porous—than the granite, which also makes it lighter. Something that has more holes in it is more porous. So "porosity" is one characteristic that can help tell you what kind of rock you have.
Rocks—and most other objects, for that matter—are made up of particles of varying sizes that are packed together. In between the particles are spaces that are filled with gas, air or liquid. Particles' shapes and sizes affect how they aggregate, including how tightly they can pack together, which affects a rock's porosity—a property that is the ratio of the volume of a rock's empty spaces to its total volume.
In general, larger particles cannot pack together as well as smaller particles can, which means that packing larger particles together leaves more space for air to fill between the particles. You can imagine this if you have one cup full of marbles and another cup full of sand. You'll be able to see many more spaces between the marbles than between the grains of sand.
• Three clear plastic cups
• Measuring cup
• Rocks that can be sorted into one of three size groups (ideally all of the same type of rock, such as granite)
• Screen (optional)
• Make sure that the rocks are sorted into three different groups by size. The greater the difference in size between the rocks is, the easier it'll be to interpret your results. There should be enough of each group of rocks to completely fill a plastic cup.
• Fill each clear plastic cup to the top with one of the groups of rocks. How much space do you see between the rocks in the different cups?
• Fill the measuring cup with one cup of water.
• Pour the water into one of the cups of rocks, filling the cup to the top.
• How much water is left in the measuring cup? Subtracting the amount left in the measuring cup from one cup will tell you how much volume the air between the rocks took up. How much volume did the air take up?
• To each of the two other cups of rocks, again measure one cup of water, fill each cup of rocks with water, and determine how much volume the air took up.
• How much air did the cup with the largest rocks have compared with the cup with the smallest rocks? How did the volume of air in those cups compare with the volume of air in the cup with the medium-size rocks?
• Extra: You can calculate the porosity of each of the cups of different size rocks you used in this activity. To do this, divide the volume of air taken up by each cup of rocks by the total volume of water the cup could hold (without rocks in it). For example, if the air took up one half cup and the cup could hold one cup total, the porosity would be 50 percent. What is the porosity of each of the cups of the different-size rocks?
• Extra: Soil is a mixture of rocks, minerals and organic matter. Porosity is also a property of soil. Try the same activity using different types of soil: clay, loam, sandy, silty, potting soil, compost, etcetera, but put a screen on top of the cup to keep organic matter from floating out as you pour the water into the cup. Do different types of soils have different porosities? | <urn:uuid:41cce175-e778-4696-abc7-f1e170143d11> | 4.65625 | 834 | Tutorial | Science & Tech. | 62.062587 |
Optical Illusion Heart-Sick Science!
Poets and other artists of language have said that love is blind. Well, we've got an optical illusion that is going to take that play on words and put it to the test. All you need to do is bring your eyeballs and we'll teach you a fun trick to play on your eyes. Don't worry, studies have shown that the only permanent effect of this experiment is an eagerness to try some science.
- Your eyeballs
- A computer
- Start the player in the "Video" tab on this screen.
- Stare at the + in the middle of the screen.
- Don't look away.
- Keep staring!
- What happened to the pink dots that were there before? They disappeared.
- What happened to the dots after they were removed, when the frame changed? The dots were green!
How Does It Work?
The dots perceived disappearance is actually a visual phenomenon called Troxler's fading or Troxler's effect. When your sight is fixed on a certain point, visual stimuli in your peripheral vision will fade away and disappear after about 20 seconds or so. In this experiment, your sight is fixated on the + at the middle of the screen. As your brain becomes focused on that point, the pink dots in your periphery slowly fade and finally disappear. The effect is easy to do in this particular experiment because of the low amount of contrast between the light pink dots and the gray background.
Troxler's effect does not explain the green dots that appear after the frame has changed, though. The green dots are explained by afterimage. This phenomenon is caused by the sensitive photoreceptors (or light receivers), primarily the cone cells, in your eyes. These cone cells adapt to the colors that they are being presented with, in this case pink. When the image is removed, the adapted cells receive less of those colors in the original image. This makes them extra sensitive to the original image's negative. For our pink heart experiment, the cones are extra sensitive to green.
For another optical illusion demonstrating optical afterimages, check out Flag Afterimage - Sick Science.
- Trying to make my own on paper Review by Intisar Munir
Thought this was a good experiment. Did the same made dots on white paper with a center point. Had students stare at the middle. Dots vanish.
Good project teaching patience and self-control.
(Posted on February 16, 2011) | <urn:uuid:13ae1a4c-3321-4ec7-9d7d-15c9152be33b> | 3.578125 | 515 | Personal Blog | Science & Tech. | 60.565809 |
What is Direct Current (DC)?
Direct Current (DC) flows in the same direction all the time through an electric circuit. Electrons flow continuously through the circuit from the negative terminal of the battery to the positive terminal. Even when no current is flowing through the wire, the electrons in the wire are moving at speeds up to 600 miles (1000 kilometers) per second but in random directions because the wire has a finite temperature. Since one electron is moving back along the wire at the same time another is moving forward, no net charge is transported along the wire. If a battery is hooked to the ends of the wire, the electrons get pushed all in the same direction along the wire. The speed of the electrons along the wire is less than an inch (few millimeters) per second. So it takes any single electrons a long time to get all the way around the circuit. But there are so many electrons that they bump into one another, like dominoes, and there is a net shift of electric charges around the circuit that can happen at speeds up to the speed of light.
What is Alternating Current (AC)?
The outlets in our homes provide alternating current (AC). 60 times every second the electrons in the wire change direction. The electrical devices we use don't care which direction the electrons are moving, the same amount of current flows through a circuit regardless of the direction of the current.
Space Weather Effects?
Electric power distribution networks are set up to handle the AC voltages that we use in our homes. Magnetic storms induce DC currents in these networks. | <urn:uuid:d76e68be-288b-4e42-a907-7a1717748f3c> | 3.8125 | 319 | Knowledge Article | Science & Tech. | 49.688083 |
From sea shells and spiral galaxies to the structure of human lungs, the patterns of chaos are all around us.
Fractals are patterns formed from chaotic equations and contain self-similar patterns of complexity increasing with magnification. If you divide a fractal pattern into parts you get a nearly identical reduced-size copy of the whole.
The mathematical beauty of fractals is that infinite complexity is formed with relatively simple equations. By iterating or repeating fractal-generating equations many times, random outputs create beautiful patterns that are unique, yet recognizable.
We have pulled together some of the most stunning natural examples we could find of fractals on our planet.
This variant form of cauliflower is the ultimate fractal vegetable. Its pattern is a natural representation of the Fibonacci or golden spiral, a logarithmic spiral where every quarter turn is farther from the origin by a factor of phi, the golden ratio. | <urn:uuid:07d772fb-6330-4350-acae-4e0be0f9a2be> | 2.921875 | 187 | Personal Blog | Science & Tech. | 25.760319 |
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Nitrogen fixation along rainfall and disturbance gradients in Southern Africa and its relation with phosphorus concentration and water availability.
Aranibar, Julieta1, Macko, Stephen1, Dowty, Peter1, Shugart, Herman1, 1
ABSTRACT- Nutrient cycles are coupled at many levels, and affect primary productivity and the possibility of vegetation to act as a sink for increased atmospheric CO2. Nitrogen (N) may limit primary productivity under future climate conditions, and it is a limiting factor in some Southern African ecosystems. The dominant trees of many African savannas are legumes, which are commonly associated with N fixing bacteria of the Rhizobium type. It is reasonable to expect that these plants will fulfill the N requirements to increase productivity under elevated CO2 or precipitation. However, the dominant legumes of many Southern African savannas (such as Burkea africana and Acacia sp) have not been previously found to nodulate. Nitrogen fixation can be limited by low phosphorus (P) and molybdenum availability. 15N is generally more abundant in soils than in atmospheric N2. For this reason, differences in 15N natural abundance (del15N ) of presumed N fixing plants and non-N fixing plants can be used to asses N fixation. In this study, the ability of Southern African legumes to fix N was tested with the del15N method. Leaves from 11 sites along rainfall and fire gradients in Southern Africa were analyzed for del15N and C, N and P concentration, with an Optima isotope ratio mass spectrometer coupled with an elemental analyzer, and an Alpkem autoanalyzer. The contribution of N to each ecosystem was calculated with biomass estimations of N fixing species at each site. It was expected that the drier ends of the transect, dominated by Acacia sp, would present higher rates of N fixation. Leaf P concentration was expected to explain the patterns of N fixation, enhancing it under disturbed conditions that mobilize this nutrient, such as fires. Nitrogen fixing trees were present in the moist end of the transect, but absent in dryer sites, even during an extremely wet year. Only forbs and cyanobacterial soil crusts were able to fix N in arid areas. Our results suggest that long-term water availability determines the pool of species present at each ecosystem and their ability to fix N, which does not change even if short-term water availability increases. Under increased precipitation or atmospheric CO2 given by climate change, there should be a shift in species composition before the N requirements can be fulfilled to increase productivity in these ecosystems.
KEY WORDS: nitrogen , fixation, isotopes, legumes | <urn:uuid:c4417cbe-d69e-417a-8629-80342b7f75e0> | 2.75 | 571 | Academic Writing | Science & Tech. | 23.3825 |
Image: Yellow parasitic wasp - Angela Reid-Robertson
These beautiful parasitic wasps occasionally visit our dead mango tree. The long black ovipositor has been adapted to bore through wood in order to parasitise the wood-boring larvae that feed deep inside dead trees. The wasp seems to detect the presence of the larvae by smelling with its antennae and maybe by feeling the larvae's vibrations in the wood.
- Angela Reid-Robertson
- © Angela Reid-Robertson | <urn:uuid:b991c5e4-effc-41ef-ac2f-49f05c074151> | 2.734375 | 102 | Truncated | Science & Tech. | 32.033468 |
Global Warming Movement Falling Apart
August 10, 2007
A few months ago, a study came out that demonstrated global temperatures have leveled off. But instead of possibly admitting that this whole global warming thing is a farce, a group of British scientists concluded that the real global warming won’t start until 2009. Between 2009 and 2014, they predict temperatures will soar past the record warmth of 1998.
Except guess what? A report was released yesterday that NOAA has been using incorrect data! NOAA has admitted this error, the results of which show the 1930s to now be the hottest decade on record. The bottom line is that it hasn’t been nearly as hot as the alarmists thought it was.
But it doesn’t end there. The National Climate Data Center (NCDC) is in the middle of a scandal. Their global observing network, the heart and soul of surface weather measurement, is a disaster. Urbanization has placed many sites in unsuitable locations — on hot black asphalt, next to trash burn barrels, beside heat exhaust vents, even attached to hot chimneys and above outdoor grills!
The data and approach taken by many global warming alarmists is seriously flawed. If the global data were properly adjusted for urbanization and station siting, and land use change issues were addressed, what would emerge is a cyclical pattern of rises and falls with much less of any background trend. | <urn:uuid:6b1f8ba9-a3fa-46c1-9544-1292e3695f88> | 3.046875 | 287 | Personal Blog | Science & Tech. | 53.846923 |
Coral Sex Just Got a Little More Interesting
March 1, 2012
"Once a year, shortly after a full moon, many corals undergo a wild and colorful sex spectacle known as broadcast spawning. During this time, coral colonies spawn like a snowstorm, releasing a blizzard of brightly colored bundles containing eggs and sperm into the open ocean.
Just before that spawning occurs, the coral polyps -- individual organisms that make up coral -- turn pink. Soon after, eggs that range in color from light pink to red are ejected from the polyps, and float upward, like tiny helium balloons, to the water surface, where they bob buoyantly, waiting to get fertilized. But unlike nearly every other animal, these eggs have no protective membrane surrounding them, which means the fertilized embryos are extremely fragile, especially during the first 12 hours of development.
In a study published online Thursday in the journal Science, two Australian scientists have found that when exposed to even small waves, many of these embryos will break into genetically identical pieces, each with the ability to develop into its own larvae. The eggs can clone much like human identical twins."
To read the full text of the article, click here. | <urn:uuid:d6a1efbc-0732-4c2d-b8a9-82105533a6f0> | 3.109375 | 243 | Truncated | Science & Tech. | 34.493408 |
Write a string to a device
#include <sys/modem.h> int modem_write( int fd, char* str );
- The file descriptor for the device that you want to write to; see modem_open().
- The string that you want to write.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The modem_write() function writes the string str to the device specified by the file descriptor fd. Just before writing each character, all buffered input from the same device is flushed. After writing each character, an attempt to read an echo is made. The intent is to write a string without its appearing back in the input stream even if the device is echoing each character written.
If the \ character appears in str, then the character following it is interpreted by modem_write(), and instead of both being written, they're treated as a special escape sequence that causes the following actions to be taken:
|\r||Output a carriage return.|
|\n||Output a newline.|
|\xhh||Output the single character whose hex representation follows as hh.|
|\B||Send a 500 msec break on the line using tcsendbreak().|
|\D||Drop the line for 1 second using tcdropline().|
|\Phh||Pause for hh 1/10 of a second where hh is two hex characters.|
Zero on success, -1 on failure (errno is set ).
- The O_NONBLOCK flag is set for the file descriptor, and the process would be delayed in the write operation.
- The file descriptor, fildes, isn't a valid file descriptor open for writing.
- The write operation was interrupted by a signal, and either no data was transferred, or the resource manager responsible for that file doesn't report partial transfers.
- A physical I/O error occurred. The precise meaning depends on the device.
- An attempt was made to write to a pipe (or FIFO) that isn't open for reading by any process. A SIGPIPE signal is also sent to the process. | <urn:uuid:a8b1803b-9a32-42b3-867d-41a26299e545> | 3.78125 | 464 | Documentation | Software Dev. | 60.0496 |
This chapter explains the meaning of the elements of expressions in Python.
Syntax Notes: In this and the following chapters, extended BNF notation will be used to describe syntax, not lexical analysis. When (one alternative of) a syntax rule has the form
and no semantics are given, the semantics of this form of
are the same as for | <urn:uuid:b3e9f667-c392-4c67-863d-bb5af49619c2> | 3.15625 | 72 | Documentation | Software Dev. | 34.455172 |
Special values defined in numpy: nan, inf,
NaNs can be used as a poor-man’s mask (if you don’t care what the original value was)
Note: cannot use equality to test NaNs. E.g.:
>>> myarr = np.array([1., 0., np.nan, 3.]) >>> np.where(myarr == np.nan) >>> np.nan == np.nan # is always False! Use special numpy functions instead. False >>> myarr[myarr == np.nan] = 0. # doesn't work >>> myarr array([ 1., 0., NaN, 3.]) >>> myarr[np.isnan(myarr)] = 0. # use this instead find >>> myarr array([ 1., 0., 0., 3.])
Other related special value functions:
isinf(): True if value is inf isfinite(): True if not nan or inf nan_to_num(): Map nan to 0, inf to max float, -inf to min float
The following corresponds to the usual functions except that nans are excluded from the results:
nansum() nanmax() nanmin() nanargmax() nanargmin() >>> x = np.arange(10.) >>> x = np.nan >>> x.sum() nan >>> np.nansum(x) 42.0
The default is to 'warn' for invalid, divide, and overflow and 'ignore' for underflow. But this can be changed, and it can be set individually for different kinds of exceptions. The different behaviors are:
- ‘ignore’ : Take no action when the exception occurs.
- ‘warn’ : Print a RuntimeWarning (via the Python warnings module).
- ‘raise’ : Raise a FloatingPointError.
- ‘call’ : Call a function specified using the seterrcall function.
- ‘print’ : Print a warning directly to stdout.
- ‘log’ : Record error in a Log object specified by seterrcall.
These behaviors can be set for all kinds of errors or specific ones:
- all : apply to all numeric exceptions
- invalid : when NaNs are generated
- divide : divide by zero (for integers as well!)
- overflow : floating point overflows
- underflow : floating point underflows
Note that integer divide-by-zero is handled by the same machinery. These behaviors are set on a per-thread basis.
>>> oldsettings = np.seterr(all='warn') >>> np.zeros(5,dtype=np.float32)/0. invalid value encountered in divide >>> j = np.seterr(under='ignore') >>> np.array([1.e-100])**10 >>> j = np.seterr(invalid='raise') >>> np.sqrt(np.array([-1.])) FloatingPointError: invalid value encountered in sqrt >>> def errorhandler(errstr, errflag): ... print "saw stupid error!" >>> np.seterrcall(errorhandler) <function err_handler at 0x...> >>> j = np.seterr(all='call') >>> np.zeros(5, dtype=np.int32)/0 FloatingPointError: invalid value encountered in divide saw stupid error! >>> j = np.seterr(**oldsettings) # restore previous ... # error-handling settings
Only a survey of the choices. Little detail on how each works.
- No dependencies on other tools
- Lots of learning overhead:
- need to learn basics of Python C API
- need to learn basics of numpy C API
- need to learn how to handle reference counting and love it.
- Reference counting often difficult to get right.
- getting it wrong leads to memory leaks, and worse, segfaults
- API will change for Python 3.0!
- avoid learning C API’s
- no dealing with reference counting
- can code in psuedo python and generate C code
- can also interface to existing C code
- should shield you from changes to Python C api
- become pretty popular within Python community
- Can write code in non-standard form which may become obsolete
- Not as flexible as manual wrapping
- Maintainers not easily adaptable to new features
- being considered as the standard scipy/numpy wrapping tool
- fast indexing support for arrays
part of Python standard library
good for interfacing to existing sharable libraries, particularly Windows DLLs
avoids API/reference counting issues
good numpy support: arrays have all these in their ctypes attribute:a.ctypes.data a.ctypes.get_strides a.ctypes.data_as a.ctypes.shape a.ctypes.get_as_parameter a.ctypes.shape_as a.ctypes.get_data a.ctypes.strides a.ctypes.get_shape a.ctypes.strides_as
- can’t use for writing code to be turned into C extensions, only a wrapper tool.
- around a long time
- multiple scripting language support
- C++ support
- Good for wrapping large (many functions) existing C libraries
generates lots of code between Python and the C code
- can cause performance problems that are nearly impossible to optimize
interface files can be hard to write
doesn’t necessarily avoid reference counting issues or needing to know API’s
- Phenomenal tool
- can turn many numpy expressions into C code
- dynamic compiling and loading of generated C code
- can embed pure C code in Python module and have weave extract, generate interfaces and compile, etc.
- Future uncertain–lacks a champion
- Turns pure python into efficient machine code through jit-like optimizations
- very fast when it optimizes well
- Only on intel (windows?)
- Doesn’t do much for numpy?
Fortran: Clear choice is f2py. (Pyfort is an older alternative, but not supported any longer)
- Sage has used cython to wrap C++ (not pretty, but it can be done)
- SIP (used mainly in PyQT)
Placeholder for Methods vs. Functions documentation. | <urn:uuid:be69adcd-fc99-4fed-8bf6-777a595f008b> | 2.890625 | 1,357 | Documentation | Software Dev. | 61.551287 |
|This article does not cite any references or sources. (December 2009)|
Augmented assignment (or compound assignment) is the name given to certain operators in certain programming languages (especially those derived from C). An augmented assignment is generally used to replace a statement where an operator takes a variable as one of its arguments and then assigns the result back to the same variable.
For example, the following statement or some variation of it can be found in many programs:
x = x + 1
This means "find the number stored in the variable x, add 1 to it, and store the result of the addition in the variable x." As simple as this seems, it may have an inefficiency, in that the location of variable x has to be looked up twice if the compiler does not recognize that two parts of the expression are identical: x might be a reference to some array element or other complexity. In comparison, here is the augmented assignment version:
x += 1
With this version, there is no excuse for a compiler failing to generate code that looks up the location of variable x just once, and modifies it in place, if of course the machine code supports such a sequence. For instance, if x is a simple variable, the machine code sequence might be something like
Load x Add 1 Store x
and the same code would be generated for both forms. But if there is a special op code, it might be
meaning "Modify Memory" by adding 1 to x, and a decent compiler would generate the same code for both forms. Some machine codes offer INC and DEC operations (to add or subtract one), others might allow constants other than one.
More generally, the form is
x ?= expression
where the ? stands for some operator (not always +), and there may be no special op codes to help. There is still the possibility that if x is a complicated entity the compiler will be encouraged to avoid duplication in accessing x, and of course, if x is a lengthy name, there will be less typing required. This last was the basis of the similar feature in the ALGOL compilers offered via the Burroughs B6700 systems, using the tilda symbol to stand for the variable being assigned to, so that
LongName:=x + sqrt(LongName)*7;
LongName:=x + sqrt(~)*7;
and so forth. This is more general than just x:=~ + 1; Producing optimum code would remain the province of the compiler.
In general, in languages offering this feature, most operators that can take a variable as one of their arguments and return a result of the same type have an augmented assignment equivalent that assigns the result back to the variable in place, including arithmetic operators, bitshift operators, and bitwise operators.
On the other hand, enthusiastic use of these features (especially with sub-expressions within larger expressions) soon produces sequences of symbols that are difficult to read or understand, and worse, a mistype can easily produce a different sequence of gibberish that although accepted by the compiler does not produce desired results.
The C++ assignment operator is = which is augmented as follows
||Left bit shift|
||Bitwise exclusive OR|
||Bitwise inclusive OR|
Supporting languages
The following list, though not complete or all-inclusive, lists some of the major programming languages that support augmented assignment operators.
See also
- Increment and decrement operators -- special case of augmented assignment, by 1 | <urn:uuid:6028f942-5229-41f0-adf2-c6442b52b192> | 4.0625 | 727 | Knowledge Article | Software Dev. | 29.685965 |
Cpusets: Processor and Memory Placement for Linux 2.6 kernel based systems.Cpusets provide a mechanism for assigning a set of CPUs and Memory Nodes to a set of tasks.
Cpusets are supported in systems using Linux 2.6 kernels. The cpumemset mechanism in Linux 2.4 kernels and the cpuset mechanism in Irix kernels are historical precedents of the cpusets in Linux 2.6. The Linux 2.6 cpusets are a complete reimplementation and redesign of the interface, and have received broad support in the Linux community. The original development of Linux 2.6 cpusets was a joint effort of engineers from SGI and Bull. SGI continues to actively support Linux 2.6 cpusets and also provides an Open Source LGPL licensed user library supporting both more convenient and more advanced uses of cpusets.
The following describes Linux 2.6 cpusets, as supported by the Linux 2.6 kernel and associated user libraries. Some of the following text is borrowed, with minor changes, from the Linux kernel source file Documentation/cpusets.txt.
What are cpusets?Cpusets constrain the CPU and Memory placement of tasks to only the resources within a tasks current cpuset. They form a nested hierarchy visible in a virtual file system, usually mounted at /dev/cpuset. Cpusets provides an essential mechanism for managing dynamic job placement on large systems.
Each task belongs to a cpuset. Each cpuset defines a set of CPUs and a set of Memory Nodes. The tasks in a given cpuset may only execute on the CPUs in its cpuset, and may only allocate memory on the Nodes in its cpuset (with some special case exceptions.)
Requests by a task, using the sched_setaffinity(2) system call to include CPUs in its CPU affinity mask, and using the mbind(2) and set_mempolicy(2) system calls to include Memory Nodes in its memory policy, are both constrained by that tasks cpuset,
The kernel task scheduler will not schedule a task on a CPU that is not allowed in its cpus_allowed vector, and the kernel page allocator will not allocate a page on a node that is not allowed in the requesting tasks mems_allowed vector.
User level code may create and destroy cpusets by name in the cpuset virtual file system, manage the attributes and permissions of these cpusets and which CPUs and Memory Nodes are assigned to each cpuset, specify and query to which cpuset a task is assigned, and list the task pids assigned to a cpuset.
Why are cpusets needed?The management of large computer systems, with many processors (CPUs), complex memory cache hierarchies and multiple Memory Nodes having non-uniform access times (NUMA) presents additional challenges for the efficient scheduling and memory placement of processes.
Frequently more modest sized systems can be operated with adequate efficiency just by letting the operating system automatically share the available CPU and Memory resources amongst the requesting tasks.
But larger systems, which benefit more from careful processor and memory placement to reduce memory access times and contention, and which typically represent a larger investment for the customer, can benefit from explicitly placing jobs on properly sized subsets of the system.
This can be especially valuable on:
The kernel cpuset mechanism provides the minimum essential kernel mechanisms required to efficiently implement such subsets. It leverages existing CPU and Memory Placement facilities in the Linux kernel to avoid any additional impact on the critical scheduler or memory allocator code.
See further the kernel source document Documentation/cpusets.txt for a more detailed describption of Linux 2.6 kernel cpusets.
User library support for cpusets.SGI develops and maintains an Open Source LGPL licensed pair of user level libraries intended to support use of cpusets from C language applications and server programs. These two libraries are intended to be used together.
Documentation for libcpuset is available in the following formats: | <urn:uuid:5e27a2e4-e8f7-4e37-ba75-8fda6da8d4b9> | 2.6875 | 860 | Documentation | Software Dev. | 36.547472 |
Eastern Tiger Salamander
EASTERN TIGER SALAMANDER
Photo Credit: Scott Gravette
SCIENTIFIC NAME: Ambystoma tigrinum tigrinum
DESCRIPTION: The tiger salamander is the most widespread salamander species in North America. There are seven subspecies of tiger salamanders, but the eastern is the only one that occurs in Alabama. This salamander grows to be seven to thirteen inches long. Their coloration is quite variable with a dark gray or gray-brown back and yellowish blotches that extend down the sides. The belly is olive or yellow and may have dark specks. The only other salamander that it might be confused with is the spotted salamander (Ambystoma maculatum). The spotted salamander, however, has two rows of regular, yellow-to-orange spots running parallel down its back. Male and female tiger salamanders are similar in appearance; except the female’s tail is shorter and does not flatten (side to side) like the males during the breeding season. Tiger Salamanders have large robust bodies, broad flattened heads with relatively small eyes, sturdy legs and long tails. Each foreleg has four toes while their hind legs have five toes each. Tiger salamanders have 12-13 costal grooves along the side of the body.
DISTRIBUTION: Eastern tiger salamanders range along the east cost from southern New York to northern Florida, west from Ohio to Minnesota and southward through eastern Texas to the Gulf. In Alabama their distribution is considered to be statewide or nearly so.
HABITAT: Tiger salamanders need two types of habitats to survive – ponds for breeding and soft, moist earth for burrowing. Adult tiger salamanders spend most of their lives in underground burrows, as do other members of the group referred to as “mole salamanders.” These burrows are 2 to 6 inches below the surface and about the diameter of a quarter. Tiger salamanders do not burrow in groups, but several burrows may be in close proximity to each other if the soil is soft and moist.
FEEDING HABITS: Adult tiger salamanders are voracious predators of both terrestrial and aquatic insects, as well as other invertebrates including earthworms, spiders, pill bugs and occasionally eggs or young of amphibians and reptiles. Larvae eat a wide variety of aquatic insects and invertebrates and about anything that will fit in their mouths, including other salamander larvae.
LIFE HISTORY AND ECOLOGY: As adults, tiger salamanders are entirely terrestrial and usually only return to the water to breed. Like all mole salamanders they are very loyal to their birthplace and have been documented to travel up to a half mile in order to reach it. Breeding in Alabama occurs December through February. Males will start moving to breeding ponds following winter rains. They are followed soon after by the females. Tiger salamanders typically choose clear, fish-free ponds that periodically go dry during the summer for breeding. These temporary or ephemeral pools generally produce lush vegetation that tiger salamanders need for cover and egg laying surfaces. Also, the lack of predatory fishes improves survival of larvae. There is no amplexus, or clasping together, during breeding, instead courtship consists of a good deal of nudging, pushing and tail lashing by the male. Finally, males will crawl out ahead of the female and deposit a sperm packet called a spermatophore on the pond bottom. Interested females will glide over the spermatophore and pick it up through a vent on her underside and inseminate their eggs. Over a two or three night period females will lay 200 to 400 eggs, most often in small masses or clusters ranging from 10 to 100 eggs each. Egg masses are usually attached to plants, twigs or stones but may float free if the support is broken. The gelatinous outer covering of the eggs does not become firm as it does in spotted salamander egg masses. Eggs hatch in about 20 to 40 days, depending on water temperatures. Larvae grow rapidly and usually transform, reabsorbing their gills and replacing their tadpole like tails with the rounded tail of an adult terrestrial salamander, in 4.5 to 5 months. Once transformed, young salamanders leave the breeding site during the next wet period.
Tiger salamanders are long-lived, living up to 20 years, but their average lifespan is 5 to 10 years.
Mount, R. H., 1975. The Reptiles and Amphibians of Alabama. Ala. Agri. Expt. Sta., Auburn Univ., Auburn, AL. 347 pp.
New York State Department of Environmental Conservation. “Eastern Tiger Salamander Fact Sheet” (On-Line). Accessed May 15, 2006 at www.dec.ny.gov/animals/7143.html.
Author: Ron Eakes, Wildlife Biologist, Division of Wildlife and Freshwater Fisheries. | <urn:uuid:fa003d0e-750b-4ad1-bd80-f2f89c83a606> | 3.5625 | 1,050 | Knowledge Article | Science & Tech. | 46.189039 |
The Missing Particle
Wishing you all a Magical weekend!
The missing (God) particle’s real name is the Higgs boson, named after British theoretical physicist Peter Higgs who first proposed its existence. It is believed to be the last missing piece to the puzzle of the so-called Standard Model – the 20 fundamental forces and particles that, in various permutations and combinations, account for everything around us – light, magnetism, gravity and all forms of matter.
The Higgs is what supposedly gives mass to fundamental particles, such as quarks and leptons, which in turn constitute neutrons, protons and electrons, which in turn make up atoms and molecules and eventually this page, you and the entire universe. The hadron of the Large Hadron Collider is the classification for neutrons and protons, from the Greek ‘hadros’ for strong, because they are held together in the nucleus of an atom by the strong nuclear force.
The God Particle could well turn out not to be the end of this quest to understand the ultimate nature of matter but instead the beginning of yet another phase.
Particle masses from intersecting braneworlds from Lubos Motl.
“Supersymmetry must exist if the universe is going to make sense”
Fermilab Statement on LHC Magnet Test Failure 27 March 2007. | <urn:uuid:5da05ca2-5f83-4318-bbee-9f19886184fd> | 3.09375 | 285 | Personal Blog | Science & Tech. | 36.774107 |
The Florida panther (Felis concolor coryi) formerly ranged from eastern Texas and western Louisiana into the lower Mississippi River Valley and eastward through Arkansas, Louisiana, Mississippi, Alabama, Florida, Georgia, and parts of Tennessee and South Carolina . Hunting and habitat loss reduced the subspecies to a single population of 30-50 adults in south Florida by the late 1980s . This population generally occurs within the Big Cypress Swamp physiographic region and is centered in Collier and Hendry Counties .
In 1981, two panthers were captured and radio-collared, initiating an extensive monitoring program that continues today (over 116 panthers have been collared since the program’s inception) . By 1990, all extensive panther habitats had been explored and few panthers remained uncollared . Between 1981 and 1990, the panther population was static at 30-50 adults but began to show signs of inbreeding depression in the heart and sperm . To increase genetic diversity, eight reproductive females from a closely related subspecies were translocated from Texas in 1995. The Texas females have produced at least 20 offspring and the hybrid kittens don’t appear to have the heart and reproductive problems seen in the Florida panthers . The population has increased by over 200% between 1995 and 2003 . In 2003, there were 87 known panthers . In addition, the panthers roam over a larger area, including areas in the Everglades, Big Cypress and Fakahatchee once suggested to be unable to support them .
U.S. Fish and wildlife Service. 1993. Florida Panther (Felis Concolor Coryi) Species Account. Website < http://www.fws.gov/endangered/i/a/saa05.html> accessed May, 2006.
Lotz, M., D. Land, M. Cunningham and B. Ferree. 2005. Florida Fish and Wildlife Conservation Commission Florida Panther Annual Report 2—4-2005. Available at <http://www.panther.state.fl.us/news/pdf/FWC2004-2005PantherAnnualReport.pdf>.
Gross, L.J. and Comiskey. 2002. ATLSS PanTrack Telemtry Visualization Tool. U.S. Geological Survey Greater Everglades Science Program 2002 Biennial Report. Available at <http://sofia.usgs.gov/projects/atlss/panthers/telvistool_03geerab.html>.
Pimm, S.L., L. Dollar, and O.L. Bass Jr. 2006. The genetic rescue of the Florida panther. Animal Conservation 9(2):115-122.
McBride, R.T. 2001. Current panther distribution, population trends, and habitat use: report of field work: fall 2000 – winter 2001. Report to Florida Panther SubTeam of MERIT, U.S. Fish and Wildlife Service, South Florida Ecosystem Office, Vero Beach, Florida. www.panther.state.fl.us/news/pdf/rtm2001.pdf. | <urn:uuid:748c832d-2364-4e97-987b-dacc79e8d0f8> | 3.65625 | 641 | Knowledge Article | Science & Tech. | 61.250345 |
Vision is the most precious of our senses, and its appearance in the animal kingdom was almost certainly a major driving force in the radiation of species that occurred around 550 million years ago. Our research addresses both of these issues, firstly by way of understanding the basic cause and potential treatment of inherited retinal diseases, and secondly by investigating the origin and evolution of proteins involved in the visual process. This process is initiated by the capture of photons by the rod and cone visual pigments that are present in the photoreceptors of the retina, and culminates via the phototransduction cascade in a change in membrane potential. In this way, light is converted into an electrical signal. In order to understand the evolution of this process in vertebrates, our studies include ancient groups such as the lampreys, hagfishes, and chimaeras that appeared at the base of the vertebrate radiation, together with more recent divergences among the bony fishes, reptiles, and mammals. Inherited retinal disease is a major cause of blindness. In many cases, the causative mutations are found in these same processes of phototransduction. Therefore, our aim is to identify such mutations and to determine the mechanism of mutant gene action, a necessary precursor to the development of a management strategy or treatment for the disorder.
The key to understanding the structure-function relationship of genes and their role in pathological disease lies at the level of RNA and protein. However, one of the difficulties in achieving this goal is the inability to obtain fresh tissue for RNA or protein work, particularly where tissue biopsy is very invasive (as in the eye or brain) or where the animals are highly endangered. In many cases, only genomic DNA (gDNA) is available to scientific researchers. As an example, we recently obtained the full-length sequences of the visual pigment (opsin) genes in the duck-billed platypus genome. However, to complete the analysis we needed to determine the spectral properties of the pigments. The platypus is an endangered and highly protected species so we were unable to obtain an eye for direct measurement of the pigments, or for the isolation of the spliced opsin transcripts. Nonetheless, by using our SPLICE technique we were able to produce full-length coding sequences with all intronic regions removed, which were subsequently used to express the pigments in vitro. This relatively simple but efficient technique results in the generation of a DNA fragment containing the coding information of any gene from the gDNA of any species for subsequent use by downstream procedures for the assay of gene function.
See “SPLICE: A technique for generating in vitro spliced coding sequences from genomic DNA” on page 785. | <urn:uuid:dadc3ed2-ac59-4b9c-9a0e-ffad8c36c134> | 3.5 | 553 | Truncated | Science & Tech. | 21.755344 |
Good job bringing this to light. People won't realise how huge the problem is and municipalities are woefully ill equipped to...
Agreed; mining can never be sustainable, but then how do you get the metals to make all the things you need in the course of...
Very good piece.
They're cooler than predicted
THOSE studying global warming are often baffled by one observation: in the past three decades, the atmosphere over the tropics has not warmed as much as predicted. Climate change skeptics use this discrepancy in observed and predicted temperatures to argue against human contribution to global warming. A study has now identified the reason for this discrepancy and shown the way to resolve it.
Climate models used since the late 1960s have consistently predicted a rise in temperature both near the surface of the earth and in the atmosphere due to increased greenhouse gas levels. While the temperature near the earth's surface was in sync with what the models predicted, atmospheric data was not. Another prediction that could not be proved in the region was that the rise in temperature in the atmosphere would be higher than at the earth's surface. Data from satellites and weather balloons in the past 30 years showed the tropical atmosphere to be cooler than predicted. It was also cooler than on the surface. Last year, this led David Douglass, a professor of physics at the University of Rochester in the us, and other researchers to suggest in a paper that increase in greenhouse gases was not responsible for global warming.
A paper published in the November 15, 2008, issue of the International Journal of Climatology said Douglass and his collaborators' analysis was flawed and the data they used, old. Global temperature is dependent on natural and man-made factors. Researchers from Lawrence Livermore National Laboratory in the us pointed out that Douglass' paper failed to deduct the effects of natural factors from the temperature data while analyzing temperature rise due to greenhouse gases. The statistical method did not factor in El Nino and La Nina weather phenomena that primarily affect the temperature in the Tropics.
When the Livermore team modified the statistical test, they found the temperature of the tropical atmosphere to be consistent with climate models that track effects of greenhouse gases. The group used new data, which led to a better consistency between observed and predicted temperatures. The authors concluded that results of these studies should be applied towards improving existing climate monitoring systems. | <urn:uuid:0658efb2-e66f-44b7-a1f1-c5452982a095> | 2.828125 | 475 | Comment Section | Science & Tech. | 36.553256 |
Astronomers using NASA's Spitzer Space Telescope have found a stunning burst of star formation that beams out as much infrared light as an entire galaxy. The collision of two spiral galaxies has triggered this explosion, which is cloaked by dust that renders its stars nearly invisible in other wavelengths of light. Although bright as this is, it pales in comparison to a quasar. The brightest known quasar is 3C 273 in the constellation of Virgo. This quasar's luminosity is about 2 trillion times that of our sun, or about 100 times that of the total light of average giant galaxies like our Milky Way. The starburst newly revealed by Spitzer stands as the most luminous ever seen taking place away from the centers, or nuclei, of merging parent galaxies. It blazes ten times brighter than the nearby Universe's previous most famous starburst that gleams in another galactic smashup known as the Antennae Galaxy.
The new findings show that galaxy mergers can pack a real star-making wallop far from the respective galactic centers, where star-forming dust and gases typically pool.
"This discovery proves that merging galaxies can generate powerful starbursts outside of the centers of the parent galaxies," says Hanae Inami, first author of a paper detailing the results in the July issue of The Astronomical Journal. She adds: "The infrared light emission of the starburst dominates its host galaxy and rivals that of the most luminous galaxies we see that are relatively close to our home, the Milky Way."
Galaxy mergers are now known to be more common than was previously thought. They were even more common in the early universe than they are today. The early universe was smaller, so galaxies were closer together and therefore more prone to smash-ups. Even apparently isolated galaxies can show signs of past mergers in their internal structure.Our own Milky Way contains the debris of the many smaller galaxies it has brushed against and devoured in the past. And it has not stopped munching away at its neighbors: It is currently absorbing the Sagittarius dwarf elliptical galaxy.
Inami, Armus and their colleagues spotted the buried starburst with Spitzer in the interacting galaxies known as II Zw 096. This galactic train wreck - located around 500 million light years away in the constellation Delphinus (the Dolphin) - will continue to unfold for a few hundred million years. Gravitational forces have already dissolved the once-pinwheel shape of one of II Zw 096's pair of merging galaxies.
The ultra-bright starburst region spans 700 light-years or so - just a tiny portion of II Zw 096, which streams across some 50,000 to 60,000 light-years - yet it blasts out 80 percent of the infrared light from this galactic tumult. Based on Spitzer data, researchers estimate the starburst is cranking out stars at the breakneck pace of around 100 solar masses, or masses of our Sun, per year.
"Most of the far-infrared emission in II Zw 096, and hence most of the power, is coming from a region that is not associated with the centers of the merging galaxies," Inami explains. In galaxy mergers, individual stars rarely slam into one another because of the vast distances separating them; even in the comparatively crowded central hubs of spiral galaxies, trillions of kilometers still often yawn between the stars.
Typically the first sign of a collision is a bridge of matter connecting two galaxies as gravity's first gentle tugs tease out dust and gas. As the outer reaches of the galaxies begin to interact, long streamers of gas and dust, called tidal tails, sweep back to wrap around the galactic cores.But giant, diffuse clouds of gas and dust in galaxies do crash together - passing through each other somewhat like ocean waves - and in turn spur the gravitational collapse of dense pockets of matter into new stars. These young, hot stars shine intensely in the energetic ultraviolet part of the spectrum.
In the case of II Zw 096, however, a thick shroud of gas and dust still surrounds this stellar brood. The blanket of material absorbs the stars' light and re-radiates it in the lower-energy, infrared wavelengths that gleam clear through the dust to Spitzer's camera.Merging galaxies such as II Zw 096 also offer a sneak peek at the fate of our Milky Way in some 4.5 billion years when it is expected to plow into its nearest large galactic neighbor, the Andromeda Galaxy. Off-nuclear starbursts such as that in II Zw 096 and the Antennae Galaxy could occur in the vicinity of our Solar System, perhaps, which is located about two-thirds of the way out from the Milky Way's glowing, bulging center. | <urn:uuid:28786f15-21b9-446c-bcf3-4364d7c46c96> | 3.6875 | 975 | Truncated | Science & Tech. | 46.087328 |
In electromagnetism, the permittivity ε of a medium is the ratio D / E where D is the electric displacement in coulombs per square metre (C/m2) and E is the electric field strength in volts per metre (V/m). In the common case of an isotropic medium, D and E are parallel and ε is a scalar, but in more general anisotropic media this is not the case and ε is a rank-2 tensor (causing birefringence).
Permittivity is specified in farads per metre (F/m). It can also be defined as a dimensionless relative permittivity, or dielectric constant, normalized to the absolute vacuum permittivity ε0 = 8.854 10-12F/m.
When an electric field is applied, a current flows. The total current flowing in a real medium is in general made of two parts: a conduction current and a displacement one. A perfect dielectric is a material that shows displacement current only.
In case of lossy medium (i.e. when the conduction currents are not negligible) the total current density flowing is:
where , σ is the conductivity (responsible for conduction current) of the medium and εd is the relative permittivity (responsible for displacement current).
In this formalism the complex permittivity ε* is defined as:
At a given frequency, the imaginary part of ε leads to absorption loss if it is negative (in the above sign convention for frequency) and gain if it is positive. (More generally, one looks at the imaginary parts of the eigenvalues of the anisotropic dielectric tensor.) | <urn:uuid:63b84052-aa89-4609-b157-6dbe8fc24d07> | 3.703125 | 364 | Knowledge Article | Science & Tech. | 42.642473 |
Return a copy of a string with trailing (rightmost) spaces removed.
RTrim[$] removes leading and trailing spaces from a string.
RTrim returns a Variant; RTrim$ returns a String. The stringexpr argument can be any string expression. However, only RTrim can accept a Variant of Null as stringexpr, in which case, a Null is returned.
This example usesRTrim to strip trailing spaces from the variable TestString.
StripTrailSpace = RTrim(TestString) // Strip trailing spaces. | <urn:uuid:da423c0a-d2a1-44a8-8365-cb2b0024bf90> | 2.6875 | 118 | Documentation | Software Dev. | 58.320282 |
Things have changed a lot in Tippecanoe county, Indiana, since the days of the battle of Tippecanoe
. Back then, if Alonzo Chappel's painting
is anything to go by, it was all lush vegetation. Nowadays, and if Bryan Pijanowski
's research is anything to go by, the county involves quite a bit more concrete.
Pijanowski is a researcher at Purdue University
in Indiana, US. He used digitalised aerial images of the county taken in 2005 to measure the number of parking spaces it is home to. The result? Eleven times more than there are families, three times more than there are people.
There are quite a few environmental implications to this. Concrete increases the urban heat island
effect because water from the ground cannot evaporate to cool the atmosphere. Plus the spaces accumulate pollutants, including oil and heavy metals leaked out by the cars that park on them.
Then there's the fact that rain runs off the concrete rather than sinking into the earth, and this can makes floods worse, and increase the erosion of land around paved areas.
"I can't help but wonder: do we need this much parking space?" says Pijanowski. A good question, to be sure. But I can't see supermarkets digging up their parking lots out of environmental concerns.
So what about rehabilitating the concrete space? A few ideas spring to mind:Catherine Brahic, online environment reporter
Labels: green roofs, parking spaces, urban heat island | <urn:uuid:5325567e-e689-4ab1-b564-b2ab3c0de109> | 3.0625 | 317 | Personal Blog | Science & Tech. | 46.754199 |
Heisenberg's uncertainty principle
In 'A brief History of Time' Hawkings explains, that Heisenberg's
uncertainty principle arises because you cannot observe a particle
without disturbing it, which is because you would need to 'touch' it
with something, like a photon or some other particle, and this will
transfer energy to the observed particle.
Further, says Hawkings: 'We could still imagine that there is a set
of laws that determines events completely for some supernatural being,
who could observe the present state of the universe without disturbing it'.
From this it would seem that the uncertainty principle is a sort of
'add on' to quantum mechanics, that has been added for practical reasons.
When I was introduced to quantum mechanics, it was stated as a basic
truth, maybe even THE basic TRUTH about the world: 'Everything is basicly
random, and it is only statistics that makes things look ordered'. But
would it not be more 'fair' to say that the uncertainty principle is
simply a way of taking into account the insecurity our observation
introduces to the measurement?
The observer is part of the observation.
Usually this is stated as: "the observer is part of the experiment."
Look for the book, Margins of Reality, by Robert Jahn; then tell me
what you think...
This has actually been a question of some interest in the philosophy
of quantum mechanics, and there are actually certain conditions
(Bell's inequalities) that predict quite different results for quantum
mechanics as normally understood and for the simplest theories that
assume an underlying determinism (so-called local theories). Experiments
have recently been done that show that the inequalities are actually
violated by the real world, meaning that at least these local deterministic
theories are wrong. But there could still be some kind of determinism
behind quantum mechanics - it is hard for us to find, at least!
In addition to the previous responses: It is incorrect to say that
the uncertainty principle is an "add-on" to quantum mechanics. Quantum
mechanics is a consequence of the uncertainty principle. I think that
the best explanation is in Heisenberg's little book "Physical Principles
of the Quantum Theory."
Jack L. Uretsky
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:06056c4a-19bc-4fa3-af3c-5ef4185b64bf> | 3.3125 | 495 | Q&A Forum | Science & Tech. | 37.592052 |
The physics and mathematics of rocket propulsion
Image from Steve Bowers
A rocket is a device that moves in one direction by squirting part of itself in the other direction. Due to the conservation of momentum, if a rocket craft at rest shoots out a mass m of propellant with velocity Vex (the exhaust velocity), the remainder of the rocket, with mass M, will end up moving at a speed (m/M) × Vex. From this, it is immediately obvious that the more propellant a rocket carries, and the faster it squirts its propellant away, the faster the rocket can go.
One complication is that when a rocket squirts away some of its propellant, this will not just accelerate the rocket's structure and payload, but also all the propellant that has not been used yet. If the total amount of propellant is small compared to the mass of the payload, this will not make much of a difference, but the final velocity will be limited to much less than the exhaust velocity. If the rocket wants to go nearly as fast or faster than it is shooting away its propellant, it will need to carry a mass of propellant much larger than its payload mass. This, in turn, lessens the speed at which initial burns of the propellant can get the rocket going since these initial burns are pushing the mass of the extra propellant along with the rocket. The total amount by which a rocket can change its speed is given by
ΔV = Vex ln(M0/M)
where M0 is the initial mass of the rocket payload + structure + propellant, and M is the total mass remaining after it has burnt its propellant. The function ln is the natural logarithm, or logarithm to the base e ≈ 2.71828. Thus, for a rocket to get moving at the speed of its exhaust velocity, it will need to have an initial mass 2.71828 times larger than its final mass. To go twice as fast as its exhaust velocity, its initial mass will need to be 2.718282 ≈ 7.38906 times larger than its final mass.
Note that the ΔV found for M with empty propellant tanks is the total amount by which a rocket can change its velocity. If it uses all of its ΔV to speed up, it will have no propellant left to slow down again, and will be left forever drifting at its burnout velocity for the rest of time. Rockets without auxilliary forms of propulsion will need to carefully budget their ΔV for their mission.
The force being exerted is the rate at which the momentum changes with time. For a rocket, this is
F = m' × Vex,
where m' is the rate at which the rocket is losing propellant mass (for example, m' might be measured in kilograms of propellant per second).
The acceleration a rocket will experience for a given force is inversely proportional to the rocket's mass,
a = F/M.
Note that since the mass of a rocket will change as it spends propellant, the rocket can accelerate faster near the end of its mission than near the beginning.
| As an example, consider a rocket that shoots out 10 kilograms of propellant per second at an exhaust velocity of 5000 meters per second (typical of high performance chemfuel rockets). This gives a force of 50,000 newtons (1 N = 1 kg/s × 1 m/s = 1 kg × 1 m/s2). If the rocket has a mass of 10,000 kg, it will be accelerated at 5 m/s2, or about half the acceleration due to gravity on the surface of old Earth.|
It takes energy to get propellant moving. The kinetic energy of a mass m moving at a speed Vex is E = ½ m Vex2. Power is the rate at which energy is gained or lost, so the power required to squirt out propellant at a mass flow of m' and an exhaust velocity of Vex is
P = ½ m' Vex2.
Note that the force F = m' × Vex can be substituted into this relationship for power, to relate the power to the force and exhaust velocity
P = ½ F Vex
or the mass flow rate
P = ½ F2/m'.
All this assumes that the rocket shoots its propellant straight backwards, and that all the power goes into moving the propellant and not into residual heat in the exhaust or waste heat in the rocket. If some of the propellant goes to the side (perhaps the exhaust is shot out in a cone instead of straight back, so that some of the propellant goes a bit to one side or the other) it will not get quite as much thrust. This is the nozzle momentum efficiency. If the propellant exhaust stream exits the rocket hotter than it started out in the propellant tanks, it will take more power. This is the nozzle energy efficiency. With well engineered rockets, these are not usually large effects. For example, a rocket that shoots its propellant backward in a cone that is 1/10 as wide as it is long will still have 99.75% as much thrust as if it shot its propellant straight back. Rockets using solid nozzles have efficiencies as high as 70%. Magnetic nozzles can give efficiencies of up to 85% for thermal plasmas, or higher for some athermal plasmas. If the nozzle energy efficiency is denoted ζ and the nozzle momentum efficiency is denoted ξ then
F = ξ m' Vex,
P = ½ m' Vex2 / ζ
P = ½ F Vex / (ζ ξ)
P = ½ F2/(ζ ξ2 m').
Often, a rocket works by heating its propellant until it is a gas or plasma, and then allowing the hot, high pressure propellant to expand away from the rocket in the backward direction, pushing the rocket forward. As the propellant expands, its temperature drops until most of its initial thermal energy has been turned into kinetic energy. If you know the temperature to which the propellant is heated, and the mass of a known quantity of particles of propellant, you can find the exhaust velocity.
If you know the temperature T in kelvin, the efficiency ζ of the rocket, and the molar mass ρ (amount of mass in one mole, and 1 mole = 6.02×1023 particles) of the expelled propellant, the exhaust velocity will be
Vex = √ 3 ζ R T / ρ
where R is the gas constant R = 8.314 J/(mol K). The molar mass of a type of atom is called its atomic weight, and is usually listed in descriptions of that atom or isotope. Be careful - the value for R given above assumes you are measuring ρ in kg/mole, and the molar mass is usually given in grams per mole, so be sure to convert your units.
Often, the temperature will be expressed as an energy τ. If you know the rest mass of a single particle in the spent propellant expressed as an energy ε, then
Vex = c × √ 3 ζ τ / ε ,
where c is the speed of light in vacuum, c = 299,792,458 m/s.
For example, one atom of normal hydrogen has an energy of 938,791 keV due to its rest mass. If a fusion reactor heats hydrogen up to a temperature of 50 keV, and the hydrogen plasma is shot out through a magnetic nozzle at 90% efficiency to form a rocket plume, the exhaust velocity will be
c × √ 3 × 0.9 × 50 / 938,791 = 0.01199 c = 3,600,000 m/s.
Very commonly, a rocket's exhaust will be made of more than one kind of particle. In this case, use the weighted average mass of all the particles in the gas.
| For example, a fusion plasma might consist of 80% helium-3 with a mass of 2,809,440 keV per particle or 0.003016029 kg/mole, and 20% deuterium with a mass of 1,876,140 keV per particle or 0.002014102 kg/mole. The effective mass per particle is then 0.8 × 2,809,440 keV + 0.2 × 1,876,140 keV = 2,622,780 keV, and the effective mass per mole is 0.8 × 0.003016029 kg + 0.2 × 0.002014102 kg = 0.002815644 kg.|
The previous descriptions assume that the exhaust velocity and ΔV are both much less than the speed of light in vacuum. When this assumption breaks down, the analysis will need to be modified.
First calculate a quantity β = Vex/c. The total change in rapidity η available to the rocket is
Δη = β ln(M0/M).
Unlike velocities, at relativistic speeds rapidities do add. So a rocket can accelerate up to any rapidity givin by its Δη, and use any remaining Δη to slow down or change direction. For a given rapidity, the velocity is
V = c × tanh(&eta)
where tanh is the hyperbolic tangent,
and the time dilation factor for the rocket is
γ = cosh(η)
where cosh is the hyperbolic cosine
If you know the total energy E of a particle in the exhaust (including its rest mass-energy), then you can calculate a quantity
γex = E/ε
or, if you know the kinetic energy EK,
γex = 1 + EK/ε
where, as before, ε is the rest mass-energy of one particle. Once you know γex you can find β
| β = √|| |
1 - 1/γex2 .
For a photon rocket, this method works perfectly well - just use β=1; that is, Vex=c.
| For example, protons and antiprotons have rest masses of 938,280 keV each. When they annihilate each other, they produce 1,876,560 keV of energy. This annihilation produces, on average, 1.5 π+ mesons, 1.5 π- mesons, and 2.0 π0 mesons. A π+ or π- meson has a rest mass of 139,570 keV and a π0 has a rest mass of 134,980 keV. In total, then, proton-antiproton annihilation produces 1.5 × 139,570 keV + 1.5 × 139,570 keV + 2.0 × 134,980 keV = 690,000 keV worth of rest mass. Therefore, |
γex = 1,876,560 keV / 690,000 keV = 2.7.
β can be solved for,
β = √ 1 - (1/2.7)² = 0.93.
In actual practice, only the π+ and π- contribute to thrust (the π0 immediately decays into two gamma rays, that cannot be magnetically deflected). This reduces the available Δη by a factor of (1.5 × 139,570 keV + 1.5 × 139,570 keV)/690,000 keV = 61%. | <urn:uuid:4299f5d3-7002-4862-8a97-2743d57091fd> | 4.3125 | 2,444 | Knowledge Article | Science & Tech. | 75.241275 |
Debris in orbit are becoming one of the greatest challenges that we face as we become a space fairing species. You see by the simple fact that something is in orbit means that it has an incredible amount of potential energy, zipping around the earth at Mach 25 ready to wreck anything that might cross its path. Thankfully there’s quite a lot of empty space up there and we’re really good at tracking the larger bits so it’s usually not much of an issue. However as time goes by and more things are launched into orbit this problem isn’t going to get any better, so we need to start thinking of a solution.
Problem is that recovery of space junk is an inherently costly exercise with little to no benefits to be had. A mission to recover a non-responsive satellite or other spacecraft is almost as complex as the mission that launched said object in the first place, even more so if you include humans in the equation. Additionally you can’t send up a single mission to recover multiple other missions as typically satellites are on very different orbits, done so that they won’t collide with each other (although that has happened before). Changing orbits, known as a plane change, is extremely expensive energy wise and as such most craft aren’t capable of changing more than a couple degrees before their entire fuel supply is exhausted. The simple solution is to deorbit any spacecraft after its useful life but unfortunately that’s not the current norm and there’s no laws governing that practice yet.
It’s even worse for geostationary satellites as in that particular orbit things don’t tend to naturally deorbit over time. Instead anything in a geostationary orbit is pretty much going to be there forever unless some outside force acts on them. Geostationary orbits are also particularly valuable due to their advantageous properties for things like communication and location so the problem of space debris up there is of a much bigger concern. Thankfully most geostationary satellites have the decency to move themselves into a graveyard orbit (one just outside geostationary which will eventually see them flung from earth orbit) but this method isn’t guaranteed. Mass that’s already in orbit is incredibly valuable however and DARPA has been working on a potential solution to debris in geostationary orbit.
The DARPA Phoenix program is an interesting idea, in essence a in orbit salvager that cannibalizes other satellites’ parts in order to create new “satlets”. These new satlets won’t be anywhere near as capable as their now defunct donors were but they do have the potential to breathe a whole lot of life back into the hardware that’s just sitting there idle otherwise. Compared to a regular geosynchronous mission something like Phoenix would be quite cheap since a good chunk of the mass is already up in orbit. Such a mission can really only be done in geostationary orbit since all the satellites are in the same plane and the energy required to move between them is minimal. That is our most valuable orbit however so such a mission could prove to be quite fruitful.
Dealing with the ever growing amount of space debris that we have orbiting us is a challenge that we’ve still yet to answer. Programs like DARPA’s Phoenix though are the kinds of projects we’ll need to both reduce the amount of orbital junk we have as well as making the most out of the stuff we’ve already put up there. I’m really keen to see how the Phoenix project goes as it’d would be quite a step forward for on orbit maintenance and construction as well as being just plain awesome. | <urn:uuid:f3c5c3cf-b225-4c64-aa9e-be92bacc98ef> | 3.125 | 758 | Personal Blog | Science & Tech. | 36.800296 |
From W3C Wiki
This is a summary of current thoughts on LTLI (Language Tags and Locale Identifiers)
We are still hard-pressed to come up with a satisfactory definition for a locale. "Locale" is a fairly old concept coming from the field of software localization in the 1980's. Localization is understood to mean doing whatever it takes to adapt a piece of software to a given group of users; we're talking about large groups here, such as a whole country or all the speakers of a certain language. The "locale", then, is the set of "things" common to this group, from the point of view of the software being localized. The most important part of localization is the translation of all text to the language of the users, so that they can understand it. But there are other aspects:
- Traditionally, translating to another language often meant using another character set, which in turn required adapting the software to deal with that character set. Therefore "charset" was deemed to be part of a locale, e.g. in the POSIX locale model.
- Apart from static text, which simply gets translated, software often generates or interprets text by itself. Even primitive applications were often able to interpret the user-provided answers to Yes/No questions (the answer being either "Y" for Yes or "N" for No). Thus the single letters used for Yes and No in a given language became part of the locale data for that language. And similarly for things such as dates, which software would often generate from a binary data value or interpret from user input. The software then needs to know the conventional order of components (year, month, day) and maybe even the names of the months, etc.
- Depending on the particular application, many other things may be subject to adaptation during localization, and may therefore be considered part of the "locale".
- In many systems the notion of locale allows for customization, and thus is not tied to a particular language/country combination. For example, many systems allow customized date or time formats, number formats, choice of measurement system, and so on.
- The concept of locale sometimes has little to do with software localization; it is simply a general bundle of preferences or other information associated with a user, such as the country of residence, the country of citizenship, and so on.
There is general agreement that language is the core part of the locale. Language is always present, which is not the case for any other "aspect" of a locale.
Soon after software localization came internationalization. This consists in making allowance in the design and implementation of software to make subsequent localization easier and more efficient. Text is externalized into resources, making translation easier. But some of the functionality is also generalized, so that it can function in multiple locales. An example would be a date display subroutine, which becomes able to display the date according to many different conventions (different order, month names in multiple languages, character sets). But this date display function then needs to be told which convention to use in any particular call. This leads us to locale identifiers.
Topics to be covered by LTLI
- Language versus locale: should the information be part of one field or separate fields? Proposal for best practice: Use one field for both, except in cases where the notion of locale encompasses extended information (as above).
- Core of a locale: language (mostly). No need (or ability) for LTLI to define the rest.
- BCP 47 as core of locale identifiers.
- Specifying locales - legacy formats (posix example, java / cldr example (centered on language)).
- Canonicalization of other identifiers, e.g. "en_us" to "en-us".
- LTLI and the matching part of BCP 47 - no need to address this.
- Section on "How to reference BCP 47".
- BP: How to specify locale on the web: for browsers / UAs (user settings), for server - client interaction (e.g. web services, language negotiation), web applications, ... | <urn:uuid:dc0b499d-bec4-4102-9930-26ae5e0ebff7> | 3.703125 | 860 | Knowledge Article | Software Dev. | 40.514112 |
The transition from upright to recumbent folding in the Variscan fold belt of southwest England: a model based on the kinematics of simple shear
Sanderson, D.J. (1979) The transition from upright to recumbent folding in the Variscan fold belt of southwest England: a model based on the kinematics of simple shear. Journal of Structural Geology, 1, (3), 171-180. (doi:10.1016/0191-8141(79)90037-3).
Full text not available from this repository.
A transition from upright folds, at high structural levels, to recumbent folds at depth is described from the Variscan fold belt in southwest England. The folds tighten and cleavage intensifies progressively as the axial plane dip decreases. A simple shear model is developed in which the shortening of a multilayer and its folding produces initially upright open folds which tighten as they rotate during increasing shear strain. The model predicts the observed relationship between interlimb angle and axial plane dip and is used to discuss the development of the structure of north Cornwall.
|Subjects:||Q Science > QE Geology
T Technology > TA Engineering (General). Civil engineering (General)
|Divisions:||University Structure - Pre August 2011 > School of Civil Engineering and the Environment
|Date Deposited:||11 Mar 2010|
|Last Modified:||01 Jun 2011 01:25|
|Contributors:||Sanderson, D.J. (Author)
|RDF:||RDF+N-Triples, RDF+N3, RDF+XML, Browse.|
Actions (login required) | <urn:uuid:903345a0-9409-4375-8cee-d2a3712a1a94> | 2.703125 | 360 | Academic Writing | Science & Tech. | 54.79197 |
This website will go over the aspects of building a Jacobs Ladder, playing with it and understanding the physics behind the operation of it. A Jacobs ladder is a really cool device where two parrallel conductors called ladders are connected to a high voltage transformer and an arc jumps between the two electrodes and climbs up the ladder. This is a really cool experiment. For the sake of clarity when the term voltage is tossed around it is implying a differential voltage.
Before undertaking this experiment it must be pointed out that messing around with high voltage equipment can be extremely dangerous and potentially fatal if appropriate steps are not taken into consideration. While this may seem hazardous it is very easy to maintain the safety level required and still have fun making and playing with a Jacobs ladder.
It is a common misconception that the voltage in an electric circuit is destructive to our bodies. The charge that is flowing or the current is damaging to our bodies. However, charge cannot flow without voltage and the higher the voltage is the easier charge will flow. You may have wondered in the past why a bird doesn’t get electrocuted when they sit in a power line that have anywhere from a few thousand volts up to several hundred thousand volts. It turns out that the birds are not completing a circuit or grounded; the charge has nowhere to travel to. For this experiment it is crucial that your body does not complete the circuit for any of the electrical equipment used in this experiment.
The human nervous system operates
on electric signals and it is extremely sensitive to any outside
electricity. When a person uses their body to complete an electric
providing a path for the charge to flow through. The human body has an
resistance to charge flow. When charge flows across a resistive element
causes the resistor to heat up and energy is released in the form of
and heat. If the energy is too great it can cause the resistor to burn
explode. This is one of the things that make electricity very dangerous
if not treated
with caution. The human heart can be stoped with as little as 20
milliamps of charge flowing through it. | <urn:uuid:38cb82a8-a168-4834-be45-455d9eb8e274> | 3.484375 | 434 | Tutorial | Science & Tech. | 45.163947 |
The information on these pages may be out of date, or may refer to
resources that have moved or have been made read-only.
For more information please refer to the Apache Attic
Here is a description of how popping a frame is currently implemented in the DRLVM tool interface (JVMTI). For a definition of the pop frame functionality, consult the JVMTI specification . For generic information on JVMTI in the DRL virtual machine and for definition of related terms, see the developer's guide.
Popping a stack frame becomes necessary when execution is in a native
function and a managed-to-native
frame (M2nFrame) is on the stack. This means that the JVMTI
component pops the M2nFrame and the Java frame above it. A frame is popped
each time the JVMTI function
called. The current pop-frame implementation is based on the exception
handling mechanism for transferring execution control. This way, VM pops
frames on the current thread only. To pop frames on other threads, VM
uses the M2nFrame flag system and callbacks.
To pop a frame on the current thread, refer to the following core functions:
||Finds register context for the previous frame using the stack iterator.|
||Transfers control to the saved register context for the popped frame.|
Transfers control to the previous frame. This function is
a simple and fast combination of sequential calls of
The state of a frame with regard to popping is indicated in the
field. This field can have the following values:
||The frame cannot be popped.|
||The frame can be popped but is not.|
||The frame is popped and the state of VM can be unpredictable and unexpected. JVMTI cannot work in this state and waits until the popped frame is resumed and the frame state is changed.|
||The frame is popped now but VM state is OK and JVMTI can work without thread resume.|
In the current implementation, popping a frame goes in the following way:
PopFrame()and does the following:
FRAME_POPABLE, which means that the frame can be popped.
hythread_safe_point()to stop the current thread in the safe point and wait until the thread is resumed by another thread.
JVM Tool Interface Specification, http://java.sun.com/j2se/1.5.0/docs/guide/jvmti/jvmti.html | <urn:uuid:b8b5698d-78c6-4617-93bc-ae5d7f32c2d6> | 2.734375 | 531 | Documentation | Software Dev. | 56.384377 |
|Dickcissel Relative Abundance Map|
|Source: North American Breeding Bird Survey (BBS)|
The Dickcissel is an enigmatic grassland bird, whose status and distribution have always been confounded by its pattern of irregular movements. This species is believed to have originally occupied the tall grass and mixed prairies of the eastern and central Great Plains. Historical changes in its breeding range have been associated with large-scale changes in agricultural land use practices (Hurley and Franks 1976). Deforestation allowed this species to spread eastward during the nineteenth century (Peterjohn and Rice 1991). Additionally, Dickcissels were well established summer residents along the Atlantic coastal plain during that century. This population largely disappeared late in the nineteenth century (Gross 1921), so little is known about its origins, status, and distribution.
Sauer, J. R., B. G. Peterjohn, S. Schwartz, and J. E. Hines. 1995. The Grassland Bird Home Page. Version 95.0. Patuxent Wildlife Research Center, Laurel, MDCautions for this Product:
Analysis and interpretation of BBS data is tricky, because the survey incorporates information from a huge geographic area and the survey varies greatly in quality of information over the area. To document some of the problems with the analyses of BBS data, and help interpret the results presented, a series of help files is provided with information on the survey, discussion of problems with analysis, and details on how the presented information should be interpreted.
For Further Information: | <urn:uuid:3e37d997-8b9e-4fce-b31f-e0a66068eda2> | 3.078125 | 317 | Knowledge Article | Science & Tech. | 37.690269 |
Climate Change in the Mountains: Hazards to Prepare For
My friends and I have been making plans for a group vacation later this year, and we all seem to love the mountains. There's something exhilarating about being so high up near the peaks and breathing the clear, if thin, air. However, as each of us pointed to a favorite mountain range around the globe, I couldn't help but think of the hazards these mountains and the communities that rely on them will experience in coming decades because of climate change.
In many mountain regions, global warming is linked to reduced snow cover, the melting of glaciers, and the degradation of permafrost. High mountain areas are also prone to erosion, since there is lower vegetative cover. As warming increases, there will be less snow and ice holding geologic materials in place, likely leading to more slope failures (PDF). The rock and debris from slope failures can pose a significant threat to human settlements and movement in the mountains. In fact, a team of international scientists just published their findings (PDF) about the critical role of climate change in several recent mountain landslide events around the world.
Also, prolonged periods of higher temperatures may transform areas that are already sensitive to fire – such as coastal areas of California or the Blue Mountains of Australia – into regions of sustained fire hazard. And, of course, one of the biggest impacts in the mountains may be increased desertification in areas that are already dry, like Tibet or Mongolia, and the drying up of essential glacier-fed water supplies in places like the Andes.
Mountains cover about 27% of the world's surface. Approximately 12% of the world's population lives in the mountains, but nearly 50% of the world's people are directly or indirectly dependent on mountain resources. Mountain hazards are likely to impact more and more people as climate change takes its toll on the sensitive and fragile geology of these areas. In the past few weeks, some of our friends and colleagues from around the world ventured into mountain regions to see the impacts of climate change firsthand.
How about you or your family? Have you already started seeing greater hazards in mountain areas you visit or live in? Let us know what you've seen or heard, and why we should be more vigilant in the mountains in a warmer world.
The not so fairways: Wild weather silences golf tournament
New national standards ask schools to teach climate change
Summer gas prices: Here's the reality
Oyster-lovers beware ... this delicacy could become a rarity
Meet a Climate Scientist: John Barnes | <urn:uuid:41606ef1-00f3-4798-ad92-61554199764f> | 3.40625 | 520 | Personal Blog | Science & Tech. | 42.382686 |
Select one of the times from the list on the left and check out what the Earth's climate was like millions of years ago.
Or view an animation that shows how the Earth's climatic belts have changed through time. View Climate Animation
We can determine the past climate of the Earth by mapping the distribution of ancient coals, desert deposits, tropical soils, salt deposits, glacial material, as well as the distribution of plants and animals that are sensitive to climate, such as alligators, palm trees & mangrove swamps.
More Info on how we determined the ancient climate.
ICE HOUSE or HOT HOUSE?
During the last 2 billion years the Earth's climate has alternated between a frigid "Ice House", like today's world, and a steaming "Hot House", like the world of the dinosaurs.
This chart shows how global climate has changed through time. | <urn:uuid:ecfab3ac-2eaa-46a5-a333-2b2ef0097fc4> | 3.421875 | 181 | Structured Data | Science & Tech. | 51.033448 |
Modern Genomics: How to identify microbial species.
Classic methods dependent upon comparative morphology and culturing fall short for the following reasons -
- Prokaryotes are incredibly diverse with relatively little morphological distinction (can't tell them apart under the microscope).
- Fewer than 1% of the known microbes in any given environment can be cultured (the great plate anomaly).
The Answer - Molecular systemetics based upon 16s rRNA sequences (thanks to Carl Woese, the father of modern microbial systematics).
- The 16S rRNA gene is ideal because much of it is conserved due to structural constraints but some of it is not. This allows for variability in the gene sequence useful in making phylogenetic comparisons.
- Because the gene is only about 1550 bp in length and it portions of it are conserved, it is possible to construct primers that will amplify this gene in a major portion of the organisms present in any given environment.
- After PCR amplification, it is possible to sequence the gene and make comparisons with other members of the microbial community or members of its own species.
Sequencing 16s rDNA from individual organisms has given us the ability map phylogenetic relationships between single celled organisms based upon how similar their 16s genes are. A classic example of this is shown below in the "Tree of Life" published by Norm Pace in 1997. | <urn:uuid:3bd9d4b4-d170-4636-84c4-04972ef24a0f> | 3.890625 | 282 | Knowledge Article | Science & Tech. | 27.836079 |
Parameters of Cosmology: Overview
The Big Bang theory of the universe allows plenty of room for variations in the details (parameters) of the actual structure and behavior of our universe. These "free parameters" are important, but must be determined by observations, not theory. The parameters effect very basic aspects of our universe:
- Will the universe expand forever, or will it collapse?
- Is the universe dominated by exotic dark matter?
- What is the shape of the universe?
- How and when did the first galaxies form?
- Is the expansion of the universe accelerating rather than decelerating?
- And more...
Since the CMB radiation was emitted so long ago (and far away), it carries a great deal of information about the properties of our universe which can be measured in no other way. This early radiation was effected everywhere by the physics of matter within the bounds set by the parameters. So we have a large statistical sample of microwave radiation (across the whole sky) to help us determine these parameters.Because WMAP can measure the CMB patterns of radiation with tremendous accuracy, it accurately determines most of the basic parameters of cosmology.
In order to understand how WMAP determines cosmological parameters, we need to give a little background on the physical evolution of the early universe and understand how cosmologists describe the statistical properties of the microwave background radiation. | <urn:uuid:80fd8427-cdde-4bb7-96b0-39962fc19a4a> | 3.21875 | 283 | Knowledge Article | Science & Tech. | 27.583041 |
|What created the circular structure around the south pole of asteroid Vesta?
Pictured above, the bottom of the second largest object in the asteroid belt
was recently imaged for the first time by the robotic
Dawn satellite that arrived last month.
A close inspection of the 260-meter resolution image shows not only hills and
more craters, but ragged circular features that cover most of the lower right of the 500-kilometer sized object.
Early speculation posits that the structure might have been created by a
collision and coalescence with a smaller asteroid.
Alternatively, the features might have originated in an
internal process soon after the asteroid formed.
New clues might come in the next few months as
Dawn spirals down toward the rocky world and obtains images of increasingly high resolution.
MPS, DLR, IDA | <urn:uuid:2824ed70-526b-4190-93e6-fd27b9ff38f5> | 3.84375 | 177 | Content Listing | Science & Tech. | 35.4775 |
Other Worlds, Other Storms
by Patricia d. Lock
Weather is everywhere! We live in it every day, and with weather come storms. What you may not realize, though, is that our neighboring planets and moons have weather and storms much as we do.
We call the study of the planets in relation to each other comparative planetology. The field looks at the different natures of the planets and moons in our solar system to help understand the origin, history, and future of our own planet. Atmospheric scientists study the composition, structure, and motions of atmospheres, both on Earth and off.
“The planets can be thought of as ‘weather’ laboratories, in which different climatic changes and weather occur naturally because the planets have different atmospheres, different surfaces, and different amounts of sunlight,” says atmospheric scientist Dr. Richard Zurek. “All of this gives us a new perspective on the weather and climate of our own planet. The same forces are at work, but in different proportions.”
Planetary Weather Forecasts
- Mercury's weather forecast would be rather like one for the moon. Nothing, nothing, nothing. Its high temperature of greater than 750 degrees F does not allow a permanent atmosphere and, therefore, any weather.
- Venus—Cloudy and hot.
- On Venus, the forecast is cloudy with a high of 840 degrees F. The chance of a breeze is zero percent, with weather at the equator being the same as that at the poles. The sky looks as if a storm is coming, but there are no storms, hurricanes, tornadoes, or jet streams.
- Mars—Cool and windy. Leave the dusting for tomorrow.
- Mars is a bit more hospitable, with sunny days and cool nights. The average temperature is minus 67 degrees F, with lows of minus 207 degrees F in winter and occasional summer highs of a pleasant 80 degrees F. The seasons on Mars are longer than Earth's, as its year is 687 Earth-days long. The most interesting weather on Mars is its huge dust storms. In 2001, a storm raised a cloud of dust that engulfed the entire planet for three months.
- Jupiter—Cloudy with a chance of thunder and lightning.
- Jupiter's weather, while beautiful from a distance, would be rather turbulent for the visitor. The temperature at the top of Jupiter's ammonia clouds is minus 227 degrees F, and winds reach 400 miles per hour. Huge thunderstorms cause lightning over areas the size of the United States. Some of the largest thunderstorms are 50 miles tall and 2,500 miles wide.
- In 2000, scientists watched two of Jupiter's “white oval” storms, each about half the size of Earth, collide and merge to form an even bigger storm. Researchers think that a similar event built Jupiter's Great Red Spot, a storm twice as wide as the Earth that has lasted for more than 300 years.
- Saturn—Windy and cold; winds dropping later.
- Just north of its equator, Saturn's clouds move at more than 1,000 miles per hour, with temperatures of minus 310 degrees F. Saturn's storms behave a lot like the storms on Earth: They are influenced by jet streams and travel large distances, and many are the size of our hurricanes. Saturn recently had an unexpected change in its weather: Winds near the equator slowed from about 1,050 to 600 miles per hour. Saturn's long year, about 30 Earth-years, and the shadow from its rings could possibly account for this change.
- Uranus—Spring is in the air!
- With a “tilt” of almost 90 degrees and a year lasting roughly 84 Earth-years, Uranus has seasons that last for 20 years. The northern hemisphere of Uranus is just now coming out of winter, and huge storms and temperatures of minus 300 degrees F are battering the planet. The hemisphere facing away from the sun is in darkness the entire season.
- Neptune—Stormy and cold, high winds for the rest of the season.
- Neptune is also coming into a spring period, with the change in sunlight causing its cloud bands to get wider and brighter. Massive storm systems have winds that reach 900 miles per hour and temperatures of minus 350 degrees F. Like Uranus's, Neptune's seasons last for decades because its year lasts almost 165 Earth-years. It is remarkable that Neptune exhibits any seasonal change at all, because the sun is 900 times dimmer there than it is on Earth.
- Pluto—Skating, anyone?
- Spacecraft have visited all of the planets except Pluto. With our limited knowledge of it, weather prediction is, at best, a wild guess. The temperature is also a guess, but scientists believe it to be around minus 385 degrees F. It is so cold during the 100 years when Pluto is farthest from the sun that even nitrogen, carbon monoxide, and methane gases freeze onto its surface.
Learning From Our Neighbors
What have we learned? A lot! “Mars told us that there can be global dust storms, and that got people to think about what might happen if an asteroid collided with Earth and threw a massive dust cloud into the atmosphere,” Zurek explains. “Venus tells us that if you have too much carbon dioxide, you can get a runaway greenhouse effect in which the surface becomes very hot.”
According to Zurek, we also know now that Mars is the planet most like the Earth, in that it has a relatively thin atmosphere, has seasons like the Earth, has a day that is just a little longer than ours, and also uses sunlight as its principal energy source. Mars also has a surface temperature that, while cold, is closest to that of Earth.
Where To, Next?
In 2004, the Cassini spacecraft began an in-depth study of the Saturn system and landed a probe on its moon, Titan. Two rovers, two orbiters, and a lander are on their way to Mars. In 2005, an orbiter was launched to make daily weather maps of the Red Planet. (Zurek is the Project Scientist for this mission, the Mars Reconnaissance Orbiter.) There are also plans to revisit Jupiter's moons this decade, and to visit Pluto by 2020.
“It takes a long time to do a space mission, and you always wish you knew more so that you could design the systems better,” Zurek says. “But we make progress step by step.”
So stay tuned for the next storm watch from other worlds.
- Which planet has storms that are like the storms on Earth? What are the similarities between the storms on the different planets?
[anno: Saturn has storms like the storms on Earth. Both planets have storms that are influenced by jet streams and travel large distances. Saturn has storms that are the size of hurricanes on Earth.]
- What kinds of factors affect the weather on a planet?
[anno: Weather on a planet is affected by the planet's atmosphere, or lack of atmosphere, its surface, and the amount of sunlight it receives.]
- Why are scientists interested in studying the dust storms on Mars? What might happen if there were a global dust storm on Earth that lasted for three months? Write a paragraph to explain your answer.
[anno: Scientists are interested in studying the dust storms on Mars because they think that these storms are similar to what might happen on Earth if Earth were hit by an asteroid. If Earth were hit by a dust storm that lasted for three months, it would be very damaging to all the food chains, since the Sun's light would be blocked. If plants could not get enough light to produce food, everything along the food chain would suffer. The planet might also get colder if less sunlight were reaching Earth's surface.] | <urn:uuid:6425bc02-f099-4443-b5ac-6627edf0131d> | 3.59375 | 1,623 | Knowledge Article | Science & Tech. | 62.88407 |
One of the best ways to prevent air pollution is to drive an electric vehicle for short errands and commutes around town. If you can take a train or bus, that works too. If you walk or bicycle, you can get exercise at the same time.
If you do need to drive, please keep the following in mind:
Over one half of car trips in the USA are less than 5 miles. Yet, 82% of these trips are made by personal motor vehicle. The situation is similar in other industrial countries, especially where urban crawl to urban sprawl rules.
Every EV in production today can cover a 5-mile one way range. Thus, it appears that most of the car trips in many industrialized countries could be made with electric vehicles. This idea will likely find opposition from oil conglomerates.
However, since these short trips are responsible for a lot of air pollution, finding a better way to make these short trips could be one of the big ways to prevent air pollution.
While it is true that the electricity used to power the electric vehicle might well come from a coal powered generator, there is the alternative to generate power from other sources. With the internal combustion engine, there is no choice. If you drive one, you will be putting about 20 pounds of CO2 into the atmosphere for every gallon of fuel burned.
The good news is that cleaning the air is simple compared to the math. The decision to drive a gas burner is a personal one. There are alternatives. It is not just up to government, the corporations, or other people. It is up to individuals to fix the air. It is not complicated. It starts with an understanding, and then doing something.
If you care about the air: walk, bike, take the bus, or drive an electric vehicle on those short trips at least part of the time. You might also think about just parking the car or truck once a week at least for a No Driving Day. If everybody simply did that, the CO2 and other pollutants would instantly go down by 16%. | <urn:uuid:cb613af7-c06d-443a-bcf9-1e8eaaaa31ec> | 3.109375 | 418 | Personal Blog | Science & Tech. | 57.938043 |
Climate change and forest health
Examples of forest pest species influenced by climate change*
Some examples of forest insect pests, pathogens and other pests which have been impacted or are predicted to be impacted by climate change are presented below. Information on non-forest pests is also provided to enable a better understanding of the potential impacts of climate change on forest health.
The oak jewel beetle, Agrilus pannonicus, has recently been associated with a European oak decline throughout its natural range and has increased in incidence in several countries including France, Germany, Hungary, Poland, the Netherlands and the UK. Incidences of Agrilus species have increased worldwide (both in their countries of origin and by international movement) and their impacts are being linked to host tree stress potentially caused by climate change. [more...]
The red band needle blight, Mycosphaerella pini, infects and kills the needles of Pinus spp. resulting in significant defoliation, stunted growth and eventually death of host trees. In its native range this fungus normally causes little damage, but since the late 1990s it has been causing extensive defoliation and mortality in young plantations of lodgepole pine (Pinus contorta var. latifolia) in northwestern British Columbia, Canada. The current epidemic coincides with a prolonged period of increased frequency of warm rain events throughout the mid- to late-1990s allowing for the rapid spread and increased rates of infection. Unlike many other pests, changes in precipitation patterns may be more important than changes in temperature for predicting the spread and impact of M. pini. [more...]
In general there is a close correlation between soil temperatures and the distributions of some plant-parasitic species of nematode. Recently, Meloidogyne incognita, previously deemed limited to the Mediterranean area, was found in the Netherlands. It is also believed that a 1 °C rise in temperature would allow Longidorus caespiticola to become established further north in Great Britain. [more...]
* More detailed information, including references, can be found in our publication Climate change impacts on forest health. | <urn:uuid:c948e0cb-84c4-45a6-b1d5-9b4613a93c61> | 3.03125 | 429 | Knowledge Article | Science & Tech. | 27.725884 |
Suspended Sediment and Sedimentation
Silt and mud washing down New Zealand rivers and streams is the most widespread of our land-based effects and the one that we know most about.
Mud and silt is suspended in the water column by rushing flood waters. When they reach the estuary or coast, these waters slow; and the silts and muds start settling to the bottom. There they build up, burying and smothering many creatures that live there.
Storms, tidal currents, and bottom fishing gear like dredges and trawls can stir up and re-suspend these sediments, compounding the original effects.
Currently, New Zealand rivers carry more silt and mud than almost anywhere else in the world. We have only 0.05 percent of the world’s land area, yet our rivers carry nearly 1 percent of the world’s mud and silt load. Some of this is quite natural, given our geology and climate. Much of New Zealand is hilly or mountainous and our position in the south-west Pacific Ocean means we get a lot of rain (including some extreme rainstorms).
However, human activities have increased both the rates and quantities of sediment arriving at our coast.
When Maori arrived, they burnt vegetation and established agriculture around coastal plains and near lakes and rivers. Sediment cores show that this led to increased amounts of silt and mud building up in lakes, estuaries, and harbours.
From the 1840’s onwards, Europeans began logging and clearing the steeper backcountry areas. And since the first and second world wars we have cleared more land and carried out increasingly extensive earthworks to build roads, towns and cities. Our present phase of development is mainly characterised by further intensification of these activities.
Keeping step with this development has been ongoing erosion and sedimentation. Most of this silt and mud eventually reaches our coasts, making the waters murky at times and gradually building up layers of fine sediments on the seafloor.
Effects of sediment on fisheries and ecosystems
Recent research indicates that some of our fisheries and fisheries habitats are not in good shape – a warning that something is wrong in our coastal environment.
As soon as suspended sediment flows into coastal waters it can have immediate, harmful effects on the plants and animals living there.
Sediment in the water can clog the gills of fish, making it harder for them to ‘breathe’, and the reduced visibility can make it harder for some fish to find food. Suspended sediment also makes it harder for filter-feeding shellfish to feed; so cockles, pipi, mussels and scallops can die off if the waters where they live are silty.
Silty water can also reduce the amount of light reaching the seabed and cause seafloor plants like kelp and subtidal seagrass to die off if waters stay silty for too long.
Suspended silts and muds – especially those washed down in floods - may eventually settle to the seabed and the waters will become clear again. However when this happens, these sediments can smother shellfish beds and other living creatures on the seabed, particularly if the silt/mud builds up in thick enough layers.
Layers of silt and mud also prevent shellfish like green lipped mussels attaching to the seabed, because these species need something firm to attach to. Extensive mussel beds in the Firth of Thames are now gone. Initially, this was probably the result of over-fishing. But since fishing has stopped, they have not returned to what is now a very muddy sea bottom.
Sediment settling also affects rocky reef areas because, like the Firth of Thames mussels, kelp spores need a hard surface to attach themselves to. Absence of spores means absence of kelp forests. Baby paua also find it hard to establish on surfaces covered by a fine layer of mud or silt.
But it doesn’t stop there – the direct affects of sediment on marine life can flow-on into other parts of the ecosystem, causing more widespread harm.
For instance, rocky reef ecosystems are supported by the growth of kelp and other seaweeds there. Marine algae are the start of the foodchain – they provide food for many animals that in turn are eaten by larger animals.
By preventing attachment of kelp and seaweed spores, sediment can reduce the growth and extent of kelp forests. Where this happens, the whole productivity of the rocky reef ecosystem is reduced. Lower productivity means fewer of the much sought-after paua and crayfish in some areas, as well as many other popular and biologically important fish species.
Sometimes these indirect (or flow-on) effects of sedimentation become felt over an extensive area. This can happen to species that have a life stage (or stages) that relies on a habitat that is vulnerable and in nearshore waters.
Snapper, trevally, tarakihi, John dory, garfish, parore, blue cod and mullet all rely on habitats that are sensitive to sediment – places like mussel beds, sub-tidal seagrass meadows, sponge gardens and bryozoan and tubeworm mounds. These provide important nursery and rearing areas, rich feeding grounds and safe havens from predators. They also frequently occur in sheltered bays or harbours – the very places most affected by sediment from the land.
When a fishery gets stressed by sediment or other environmental effects, it becomes more vulnerable to further pressure – from fishing, for instance. Sometimes the environmental stress reaches the point where even closing the fishery will not bring it back. This may explain the fact that previously relatively abundant shellfish beds at beaches around the Auckland region have shown no sign of recovery even though harvesting has been banned for many years.
Such declining or closed fisheries can be symptoms of problems in the ecosystem – canaries in the coalmine of our coastal zone. | <urn:uuid:e793e14f-1f9c-4365-90b3-3607575ecca1> | 4.15625 | 1,250 | Knowledge Article | Science & Tech. | 43.085734 |
Read More: Biomagnification, Biomimicry, Ddt, Technology, Ozone Layer, Janine Benyus, David Suzuki Foundation, Environment, Canada's Environment, David Suzuki, Learning From Nature, What Nature Can Teach US, Canada News
We have much to learn by studying nature and taking the time to tease out its secrets. Biomimicry, a word coined by biologist and writer Janine Benyus, means to copy nature. It's a science that asks "What does nature do?" instead of "What's it for?" -- the question usually posed by human endeavour. | <urn:uuid:2a659407-3ab7-4305-8e17-662330e258f1> | 2.8125 | 126 | Content Listing | Science & Tech. | 36.075157 |
Double Integrals 4 Another way to conceptualize the double integral.
Double Integrals 4
⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles.
- I think it's very important to have as many ways as possible
- to view a certain type of problem, so I want to introduce
- you to a different way.
- Some people might have taught this first, but the way I
- taught it in the first integral video is kind of the way that I
- always think about when I do the problems.
- But sometimes, it's more useful to think about it the way I'm
- about to show you, and maybe you won't see the difference,
- or maybe you'll say, oh, Sal, those are just the
- exact same thing.
- Someone actually emailed me and told me that I should make it
- so I can scroll things, and I said, oh, that's not
- too hard to do.
- So I just did that, and I scrolled my drawing.
- But anyway, let's say we have a surface in 3 dimensions.
- It's a function of x and y.
- You give me a coordinate down here, and I'll tell you
- how high the surface is at that point.
- And we want to figure out the volume under that surface.
- We can very easily figure out the volume of a very small
- column underneath the surface.
- So this whole volume is what we're trying to figure out,
- right, between the dotted lines.
- I think you can see it.
- You have some experience visualizing this right now.
- So let's say that I have a little area here.
- We could call that da.
- Let me see if I can draw this.
- Let's say we have a little area down here, a little
- square in the x-y plane.
- And it's, depending on how you view it, this side of it is dx,
- its length is dx, and the height, you could say,
- on that side, is dy.
- Because it's a little small change in y there, and it's a
- little small change in x here.
- And its area, the area of this little square, is
- going to be dx times dy.
- And if we wanted to figure out the volume of the solid between
- this little area and the surface, we could just multiply
- this area times the function.
- Because the height at this point is going to be the
- value of the function, roughly, at this point.
- This is going to be an approximation, and then we're
- going to take an infinite sum.
- I think you know where this is going.
- But let me do that.
- Let me at least draw the little column that I want to show you.
- So that's one end of it, that's another end of it, that's the
- front end of it, that's the other end of it.
- So we have a little figure that looks something like that.
- A little column, right?
- It intersects the top of the surface.
- And the volume of this column, not too difficult.
- It's going to be this little area down here, which is,
- we could call that da.
- Sometimes written like that. da.
- It's a little area.
- And we're going to multiply that area times the height of
- this column, and that's the function at that point.
- So it's f of x and y.
- And of course, we could have also written it as, this
- da is just dx times dy, or dy times dx.
- I'm going to write it in every different way.
- So we could also have written this as f of
- xy times dx times dy.
- And of course, since multiplication is associative,
- I could have also written it as f of xy times dy dx.
- These are all equivalent, and these all represent the volume
- of this column, that's the between this little area
- here and the surface.
- So now, if we wanted to figure out the volume of the entire
- surface, we have a couple of things we could do.
- We could add up all of the volumes in the x-direction,
- between the lower x-bound and the upper x-bound, and then
- we'd have kind of a thin sheet, although it will already have
- some depth, because we're not adding up just the x's.
- There's also a dy back there.
- So we would have a volume of a figure that would extend from
- the lower x all the way to the upper x, go back dy,
- and come back here.
- If we wanted to sum up all the dx's.
- And if we wanted to do that, which expression would we use?
- Well, we would be summing with respect to x first, so we could
- use this expression, right?
- And actually, we could write it here, but it
- just becomes confusing.
- If we're summing with respect to x, but we have the
- dy written here first.
- It's really not incorrect, but it just becomes a little
- ambiguous, are we summing with respect to x or y.
- But here, we could say, OK.
- If we want to sum up all the dx's first, let's do that.
- We're taking the sum with respect to x, and let me, I'm
- going to write down the actual, normally I just write numbers
- here, but I'm going to say, well, the lower bound here is x
- is equal to a, and the upper bound here is x is equal to b.
- And that'll give us the volume of, you could imagine a
- sheet with depth, right?
- The sheet is going to be parallel to the x-axis, right?
- And then once we have that sheet, in my video, I think
- that's the newspaper people trying to sell me something.
- So once we have the sheet, I'll try to draw it here, too, I
- don't want to get this picture too muddied up, but once we
- have that sheet, then we can integrate those, we can
- add up the dy's, right?
- Because this width right here is still dy.
- We could add up of all the different dy's, and we
- would have the volume of the whole figure.
- So once we take this sum, then we could take this sum.
- Where y is going from it's bottom, which we said with c,
- from y is equal to c to y's upper bound, to y
- is equal to d.
- Fair enough.
- And then, once we evaluate this whole thing, we have the
- volume of this solid, or the volume under the surface.
- Now we could have gone the other way.
- I know this gets a little bit messy, but I think
- you get what I'm saying.
- Let's start with that little da we had originally.
- Instead of going this way, instead of summing up the dx's
- and getting this sheet, let's sum up the dy's first, right?
- So we could take, we're summing in the y-direction first.
- We would get a sheet that's parallel to the y-axis, now.
- So the top of the sheet would look something like that.
- So if we're coming the dy's first, we would take the sum,
- we would take the integral with respect to y, and it would be,
- the lower bound would be y is equal to c, and the upper
- bound is y is equal to d.
- And then we would have that sheet with a little depth, the
- depth is dx, and then we could take the sum of all of those,
- sorry, my throat is dry.
- I just had a bunch of almonds to get power to be able
- to record these videos.
- But once I have one of these sheets, and if I want to sum up
- all of the x's, then I could take the infinite sum of
- infinitely small columns, or in this view, sheets, infinitely
- small depths, and the lower bound is x is equal to a, and
- the upper bound is x is equal to b.
- And once again, I would have the volume of the figure.
- And all I showed you here is that there's two ways of doing
- the order of integration.
- Now, another way of saying this, if this little original
- square was da, and this is a shorthand that you'll see all
- the time, especially in physics textbooks, is that we
- are integrating along the domain, right?
- Because the x-y plane here is our domain.
- So we're going to do a double integral, a two-dimensional
- integral, we're saying that the domain here is two-dimensional,
- and we're going to take that over f of x and y times da.
- And the reason why I want to show you this, is you see this
- in physics books all the time.
- I don't think it's a great thing to do.
- Because it is a shorthand, and maybe it looks simpler, but for
- me, whenever I see something that I don't know how to
- compute or that's not obvious for me to know how to compute,
- it actually is more confusing.
- So I wanted to just show you that what you see in this
- physics book, when someone writes this, it's the exact
- same thing as this or this.
- The da could either be dx times dy, or it could either be dy
- times dx, and when they do this double integral over domain,
- that's the same thing is just adding up all of these squares.
- Where we do it here, we're very ordered about it, right?
- We go in the x-direction, and then we add all of those up in
- the y-direction, and we get the entire volume.
- Or we could go the other way around.
- When we say that we're just taking the double integral,
- first of all, that tells us we're doing it in two
- dimensions, over a domain, that leaves it a little bit
- ambiguous in terms of how we're going to sum
- up all of the da's.
- And they do it intentionally in physics books, because you
- don't have to do it using Cartesian coordinates,
- using x's and y's.
- You can do it in polar coordinates, you could do it
- a ton of different ways.
- But I just wanted to show you, this is another way to
- having an intuition of the volume under a surface.
- And these are the exact same things as this type of
- notation that you might see in a physics book.
- Sometimes they won't write a domain, sometimes they'd
- write over a surface.
- And we'll later do those integrals.
- Here the surface is easy, it's a flat plane, but sometimes
- it'll end up being a curve or something like that.
- But anyway, I'm almost out of time.
- I will see you in the next video.
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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about the site | <urn:uuid:9a1756e2-d744-4f88-973a-da2d4e8af4c9> | 3.640625 | 2,787 | Truncated | Science & Tech. | 75.531038 |
ESSAY- Invasive pest? Why imported bugs and plants can be good
Here's a fact that I suspect most people don't know: Wherever we humans have gone in the past two centuries, we have increased local and regional biodiversity. Biodiversity, in this case, is defined as increasing species richness. Yet, "the popular view [is] that diversity is decreasing at local scales," UC Santa Barbara biologist Steven Gaines and Brown University biologist Dov Sax report.
Ample scientific evidence shows, however, that this popular view is wrong.
For example, more than 4,000 plant species introduced into North America during the past 400 years grow naturally here and now constitute nearly 20 percent of the continent's vascular plant biodiversity.
The fear among opponents of "invasive species" is the aggressive outsiders will cause a holocaust among the native plants. That might initially seem reasonable because there are a few species– like kudzu, purple loosestrife, and water hyacinth– that grow with alarming speed wherever they show up. But that doesn't mean other species are in danger.
"There is no evidence that even a single long term resident species has been driven to extinction, or even extirpated within a single U.S. state, because of competition from an introduced plant species," Macalester College biologist Mark Davis notes. Yet the spurious threat of extinction persists as one of the chief reasons given for trying to prevent the introduction of exotics.
Meanwhile, there are plenty more examples in which local and regional species richness has been increasing. Introduced vascular plants have doubled the species richness of the plant life on most Pacific Islands. In fact, species richness of some islands has increased so much that they now approach the richness of continental areas. In New Zealand, 2,000 introduced plant species have taken up residence with the islands' 2,000 native species, and only three native plant species have gone extinct. The opening of the Suez Canal introduced 250 new fish species into the Mediterranean Sea from the Red Sea and resulted in only a single extinction.
Researchers find increases in species richness on the local level as well. Gaines and Sax cite studies which find that a corner of West Lancester in Britain has seen a dramatic rise in plant species diversity over the past two centuries, gaining 700 exotics while losing 40 natives. They note that reptile and amphibian diversity has increased slightly in California. Mammal diversity has increased on many oceanic islands, and in Australia and North America. Freshwater fish diversity has increased significantly in many drainages throughout the U.S.
Birds are different. Many species, especially those endemic to isolated islands, have gone extinct, largely due to habitat loss and predation from humans or introduced predators such as rats. Nevertheless, Gaines and Sax note that "net bird diversity (in spite of large changes in species composition) has remained largely unchanged on oceanic islands." In other words, despite extinctions of endemic species, the number of avian species on any given island remains about steady because new species are introduced to them.
So why then are so many ecologists and environmentalists on a jihad against introduced species? Of course, some introduced species do cause harm to the environment. They become pests (which means they set up shop where we don't want them to), or they cause disease in people or creatures we care about. But the vast majority of introduced species blend in more or less unobtrusively with the natives.
The main objection to spreading non-native species seems to be aesthetic. For example, Birmingham University biologist Phillip Cassey and colleagues respond to the evidence of rising local and regional biodiversity by complaining that many of the birds that a visitor from the U.K. would encounter in New Zealand are the same species found back home.
"The same is true for floras and faunas around the world," lament Cassey and colleagues. "It is the biological equivalent of flying from Seattle to Paris and going to Starbucks for your coffee."
Fair enough. But this is not a scientific argument.
Sax and New Mexico University biologist James Brown correctly observe that whether the impacts of introduced species "are considered to be positive or negative, good or bad, is a subjective value judgment rather than an objective scientific finding. Scientists are no more uniquely qualified to make such ethical decisions than lay people."
Cassey may wish to quaff his café au lait at Les Deux Magots while others enjoy their Venti Café Misto in the familiar purlieus of a Parisian Starbucks. Nevertheless, aesthetic reasons are still reasons, and science can be validly deployed in their service. Some people may prefer landscapes restored to a condition prior to the introduction of outside species. As Davis and his colleague Stony Brook University biologist Lawrence Slobodkin point out, architecture uses mathematics, physics, and engineering to achieve aesthetic and social goals. "Perhaps 'ecological architecture' might be a more apt characterization of the work of ecological restoration," they suggest. "Because the term acknowledges the central role played by both values and science."
Ultimately, Davis argues that the good news from biology is that the "globalization of the Earth's biota will not lead to a world composed of zebra mussels, kudzu, and starlings." Instead, while in the future different regions of the world will be more similar in their floras and faunas, Davis concludes, "At the same time, they will become more diverse, in some cases much more diverse."
The top science writer for Reason magazine, Downtown Charlottesville resident Ron Bailey wrote this for Reason. His last essay appearing in the Hook stemmed from his book Liberation Biology: A Moral and Scientific Defense of the Biotech Revolution. | <urn:uuid:bbfae486-f5d1-4924-a812-e8c893608d6a> | 3.296875 | 1,168 | Nonfiction Writing | Science & Tech. | 35.246761 |
Acid rain damages buildings such as this one in Copola, Mexico.
Click on image for full size
Acid rain is a general term used to describe different kinds of acidic air pollution. Although some acidic air pollutants return directly back to Earth, a lot of it returns in rain, snow, sleet, hail, mist or fog, which is why we call it acid rain.
When power plants, factories, houses and cars release pollution into the atmosphere, it contains chemicals known as sulfur dioxide and nitrogen oxides. Sometimes, these chemicals fall directly back to the ground. This is called dry deposition. The rest of the time, they mix with water (moisture) in the air to form acids. Once these acids have formed, they can be transported long distances by the wind before being deposited in rain, snow or hail. This is what we commonly call acid rain.
During the 1970s, scientists in Sweden and Norway began noticing that acid rain was damaging their trees and fresh water. Much of the acid rain was caused by pollution that was transported through the air from other countries, primarily the United Kingdom. After that, acid rain was understood to be an international problem.
Acid rain can have harmful impacts on the ecosystems in the environment. It acidifies the soil and water where it falls, damaging or killing plants and animals. Surface water acidification can lead to a decline in, and loss of, fish populations and other aquatic species including frogs, snails and crayfish. Acid rain affects trees, usually by weakening them through damage to their leaves. Certain types of building stone, such as limestone and marble, can be slowly dissolved in acid rain.
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Biomes are large regions of the world with similar plants, animals, and other living things that are adapted to the climate and other conditions. Explore the links below to learn more about different biomes....more
What do smog, acid rain, carbon monoxide, fossil fuel exhausts, and tropospheric ozone have in common? They are all examples of air pollution. Air pollution is not new. As far back as the 13 th century,...more
Nitric acid is a very strong acid that can burn your skin. Nitric acid has nitrogen, oxygen, and hydrogen atoms in it. There is a very tiny bit of nitric acid gas in Earth's atmosphere. Nitric acid is...more
Sulfuric acid is a very common type of acid. Acid rain has sulfuric acid in it. Acid rain harms plants, fish, and other living things. A type of air pollution causes acid rain. When people burn fossil...more
Rain is precipitation that falls to the Earth in drops of 5mm or more in diameter according to the US National Weather Service. Virga is rain that evaporates before reaching the ground. Raindrops form...more
When you think of chemistry, do you think about mixing colored liquids in test tubes and maybe making an explosion... or at least a nice puff of smoke? Did you know that a lot of chemistry happens in Earth's...more
Ammonia is a kind of gas. Ammonia molecules (NH3) have hydrogen and nitrogen atoms in them. The air you breathe has a tiny bit of ammonia in it. When plants and animals die and decay, they give off ammonia....more | <urn:uuid:28c95630-cfb2-4cd4-84a4-81d0115706b9> | 3.6875 | 744 | Knowledge Article | Science & Tech. | 59.145131 |
Bug of the Week
Milkweed Bug (Family Lygaedidae)
Milkweed bugs (MBs) rated about four lines in a BOTW about Milkweed Critters a little more than a year ago, but these beautiful insects are having a blockbuster year and deserve to be disarticulated from that group and considered in their own right(s).
|LMBs really are beautiful insects.|
Milkweed bugs come in two flavors – Large (¾”) (LMB) and Small (½”) (SMB). MBs are True Bugs, in the Order Hemiptera (“half-wings”). That means you can call them “bugs” without being frowned upon by eminent entomologists. They don’t actually have half-wings, but their front set of wings is half leathery and half membranous (the second set, the flying wings, are 100% membranous). They are in the Seed Bug bunch (Family Lygaedidae), which get their name because they suck juice from seeds. MBs of one kind or another are found on milkweeds across the U.S. and southern Canada, and they are most common in the Southeast.
|The mouthparts are tucked under the body when not in use.|
It’s been speculated that the Hemipteran ancestor had chewing mouthparts, but Hemipterans have strayed rather far since then. MBs’ consist of two, side-by-side tubes; they use one tube to pump digestive enzymes into the tough milkweed seeds and the other to siphon up the softened plant material. Between feedings, the tubes are held out of the way against the underside of the body. If you look closely under the chin of the MB profiled on the pod, you can see the mouthparts tucked between its front legs.
|Two’s company, three’s not a crowd!|
Unlike most insects, MBs are gregarious, and milkweed pods may be covered with adults and nymphs (the nymphs start out solid red-orange and add some black markings each time they molt. Older adults are darker red). One reference theorized that everybody benefits from communal feeding behavior. More feeding tubes = more saliva = more softening = more food. During large outbreaks, milkweed seed production suffers; the inner seeds are safe, but the whole pod seems dysfunctional. Most sources say that MBs have no economic importance, since they don’t attack crops, carry disease, or otherwise cross paths with humans, but people who raise milkweeds or collect seed are not fans.
Both MBs are reported to feed on some nectar, and when food is scarce, MBs may eat other milkweed parts and live or dead invertebrates. SMBs’ tastes may wander to non-milkweed species.
|Older adults are dark red.|
MBs have several ways to protect themselves from predators. If you get too close to a group, the individuals will scatter. When alarmed, MBs drop off the plant into the thicket of grasses at its base. Once on the ground, they lie still for a while before resuming their eating. Predators prefer to kill their food and generally won’t bother an animal that is “dead.”
|A LMB nymph sucks up toxins from the seeds of whorled milkweed.|
These behavioral methods are really unnecessary, because MBs, like Monarchs, taste nasty due to the bitter sap in their favorite food. This begs the question of taste buds among its predators - birds notably lack them, and the BugLady doubts the palettes of praying mantises and garden spiders. MBs are poisonous due to milkweed’s cardiac glycosides (insects that make use of milkweed carbs must either produce chemicals to detoxify them or structures to sequester the toxins). MBs are sequester-ers. At the very least, eating a bunch of MBs will make the predator vomit and develop a strong avoidance reaction to the next MB it lays eyes on (one on-line source warned readers not to let their dogs eat MBs). MBs wear Mother Nature’s warning colors of orange and black, and their habit of feeding in large groups magnifies those colors for near-sighted predators. The bright reddish-orange and black color patterns of the MBs are called aposematic (they are aposematically colored), which, according to Merriam Webster, means “being conspicuous and serving to warn – as in coloration.” There’s some speculation that the non-poisonous box elder bugs are milkweed bug mimics.
|A small milkweed bug has a red “X” on a black body – or a black heart on a red body.|
With one major exception, SMBs (Lygaeus kalmii) and LMBS (Oncopeltus fasciatus) have very similar life stories. Egg to nymph to adult in one to two months, depending on the air temperature. Mating (about 30 minutes in duration in warm weather, with snuggles as long as 10 hours occurring in cool weather) and egg-laying within a week of reaching adulthood (up to 2000 eggs total, half male, half female. The eggs also change color, from pale yellow to almost-red as hatching nears). One or two months of adulthood, and they overwinter as adults. The big difference between SMBs and LMBs is that SMBs can overwinter here in God’s Country and LMBs can’t. SMBs are “permanent residents” and LMBs are migratory, following the milkweed crop north in summer and retreating south in fall. According to Stokes in Observing Insect Lives, about a quarter of LMB adults are migratory – crowded milkweed pods, decreasing northern day lengths, and less reproductive activity send them south, and those that linger, freeze. SMBs crank out the antifreeze and survive northern winters; on warm winter days down south, LMBs may stretch their legs.
Most of what the BugLady has been seeing this year have been LMBs. LMBs (¾”) have a broad, black band across their back, and SMBs (½”) have a red “X” on a black background.
LMBs are available from scientific supply catalogs, along with complete rearing instructions (they’ll eat sunflower seeds and watermelon in captivity) and they are reported to be “easy to dissect.”
|An SMB burrowing into a pod.| | <urn:uuid:f292f8d5-27b2-463d-852b-1605f7020996> | 3.109375 | 1,415 | Knowledge Article | Science & Tech. | 57.779755 |
A module may or may not have a name.
module M; end M.name # => "M" m = Module.new m.name # => ""
A module gets a name when it is first assigned to a constant. Either via the module or class keyword or by an explicit assignment:
m = Module.new # creates an anonymous module M = m # => m gets a name here as a side-effect m.name # => "M"
# File activesupport/lib/active_support/core_ext/module/anonymous.rb, line 19 def anonymous? # Uses blank? because the name of an anonymous class is an empty # string in 1.8, and nil in 1.9. name.blank? end | <urn:uuid:33ff057a-6e21-4ced-94ad-9edd0a72cb31> | 3 | 159 | Documentation | Software Dev. | 74.691824 |
Sunday, December 30th 2012, 2:40 PM EST
CLICK this link for articles about this years Transit of Venus.
1 – Venus transits the sun
As the planets careen around the sun, there is occasionally a fortuitous alignment. In June of 2012 the planet Venus transited the sun, which means it passed in front of Sol from Earth’s perspective. As the planet began its transit, the NASA/JAXA Hinode spacecraft was on hand to take some pictures. This amazing image [featured at the top] shows the sphere of Venus passing into the sun’s corona, silhouetted by the boiling backdrop of glowing plasma.
Enjoy it — Venus won’t transit the sun again until 2117!
Click source to read and see NASA’s 10 most incredible images of 2012 by Ryan Whitwam
Comments section below this advert: | <urn:uuid:d4d3bfee-0d36-4082-9dc7-ee6eb19f9dcf> | 2.953125 | 185 | Personal Blog | Science & Tech. | 58.79451 |
Bezout’s theorem in algebraic geometry is one of those simple facts that manages to capture the heart and style of its field. It states that any two irreducible curves and in usually intersect in points (where the degree of a curve is the degree of the polynomial that defines it).
Now, very few mathematicians will stand for a ‘usually’ in their theorems, and the most basic form of Bezout’s theorem is typically stated differently – so as to be a real theorem. However, my favorite aspect of the theorem is that figuring out how to fix the ‘usually’ has repeatedly foreshadowed the development of algebraic geometry as a whole.
In its simplest cases, Bezout’s theorem is familiar even to most math undergrads. For, if is a degree 1 curve, then it is a line. Restricting the defining equation for to this line gives a polynomial in one variable of (usually) the same degree as , and so by the Fundamental Theorem of Algebra, it (usually) has points. I have glossed over the fact that restricting to the line, which amounts to eliminating a variable, can sometimes cause highest degree terms to vanish; and also that sometimes two roots of a polynomial will coincide. Still, the underlying intuition is the Fundamental Theorem of Algebra, which everyone should find reassuring and familiar.
For higher degrees, the proof is less immediate, but no less intuitive. The two curves always intersect at exactly the proscribed number of points – unless some numbers happen to cancel/coincide.
Geometrically, what is going wrong? There are two kinds of behavior that are causing the theorem to be break down(as I have stated it).
The first is most easily seen in the case of two parallel lines. They both have degree 1, and so Bezout says they should intersect, but Euclid and reality disagree. Higher degree curves can exhibit similar behavior, such as when parallel asymptotes cause an intersection point to be lost.
The second problem is when the two curves intersect too well at a given point of intersection. As a simple example, take to be the curve defined by (also know as the x-axis), and let be defined by (also known as the graph of ). These curves do intersect at , but this is the only place they intersect. This intersection point has multiplicity; that is, it wants to correspond to more than one point ( in this case), but there is no room in the geometric viewpoint to count the same point more than once.
First Fix: Projective Geometry
The first problem is pretty easy to fix. As you might have guessed, the answer is to think of two parallel lines as ‘intersecting at infinity’. can be compactified by adjoining a sphere at infinity. A path leaving has a limit if it has an asymptote. This new space we have constructed is called , and it is the second member of the family of complex projective spaces (the first member is the Riemann sphere).
If we think of our curves and as sitting inside of , then there is a canonical way to extend them to the sphere at infinity. Adding these points at infinity will magically add points of intersection that make Bezout’s theorem (closer to being) true! For example, our two parallel lines now have exactly one intersection point, as we hoped would be true.
This is a basic example of ‘Projective Geometry’, which is the study of varieties not in , but their compactifications in . Theorems tend to be cleaner here, and in general this is seems to be the more natural home for varieties.
Second Fix: Intersection Theory
I claim that projective geometry fixed the problem of points at infinity, so the only remaining problem is that figuring out how to count points with the right multiplicity.
The most basic solution is to notice that any time two curves intersect with multiplicity , you can slide one of the curves a bit in some direction to split the bad point into n points. Thus, Bezout’s theorem is always true, up to an infinitesmal slide. This has the advantage of being conceptually simple, but its not very useful for computations.
We can also develop a rigorous theory for counting intersection multiplicities, appropriately called intersection theory. The details are a bit more technical than I am aiming for with this post, but the idea is that one declares two curves ‘the same’ if you can find an analytic function on the compliment of the first curve that vanishes only on the second curve. This rigid relationship is called ‘linear equivalence’, and its a more algebraic version of the above sliding intuition. The number of intersection points of two curves depends only the linear-equivalence class… except for a small number of exceptions. Thus, we define the intersection number of two curves to be the number of intersections of any two ‘generic’ curves linearly-equivalent to the original pair.
This is mostly just a fancy way of declaring that its ok to slide a curve a small amount in order to resolve a point of multiplicity. However, this is a more effective computational tool, and intersection theory has some nice benefits. For example, intersection theory can be robustly generalized to higher dimensional varieties. Instead of a -valued inner-product like we just constructed, we get a ring called the Chow ring.
Second Fix, Take Two: Schemes
There is a slightly different take on this that isn’t explicitly necessary, but I like since it points us in the direction of another important evolution in algebraic geometry. The above fix was secretly just a weakening of Bezout’s theorem, from talking about curves intersecting, to talking about equivalence classes of curves intersecting.
Let us instead declare that the deficiency was not with the theorem, but with our notion of geometry instead. Perhaps our definition of ‘point’ was too primitive to distinguish between a simple intersection, and one of higher multiplicity. These are bold statements, and they require a bold theory to pull off; but the theory of schemes is just bold enough.
Very crudely, a scheme in this context behaves like a variety, with a distinguished sheaf on it that dictates what the ‘ring of rational functions’ looks like over any (good) open set. With the extra data provided by this sheaf, we can distinguished between two schemes whose underlying variety is the same.
Take for example, a point… a sheaf on a point is the same as a its ring of global sections. This ring can’t be anything; it must be a commutative algebra such that modding out by the Jacobson radical gives . This doesn’t leave room for too much, but we still get multiple different schemes that look like points to the naked eye (ie, as a variety).
Now, there is also a way to intersect schemes, so we can see what happens if we intersect and . We get a point whose global sections looks like (which readers of previous posts might recall is one of my favoritest rings). Ah ha! We get a point of a totally different flavor than what we would have gotten if we’d looked at a simple intersection (its global sections would have been ). By assigning to each distinct flavor of point a ‘multiplicity’ equal to its dimension as a vector space, we can again make Bezout’s Theorem work.
Third Fix…? : Derived Schemes
But wait, I said there were only two things wrong with Bezout’s theorem – what else is there to fix? Well, I have stealthily concealed a third minor error in the statement, to see if readers would ignore it unthinkingly. The trick is that I never forbid that the two curves coincided. Its instinct to dismiss such cases out of hand, since the ‘number’ of intersection points doesn’t make sense.
Perhaps we shouldn’t be so hasty; after all, the other two fixes involved building techniques that turned out to be useful for wholly unrelated reasons. According to Jacob Lurie’s engrossing GRASP lecture, this error can also be fixed, by passing to an even richer version of geometry, known as derived algebraic geometry. I should qualify the following by saying that I know almost nothing about the subject, and so I am parroting cool ideas I have heard others express.
A curve in is the zero-set of some polynomial . Given two polynomials on , their restriction to is the same only if they differ by some multiple of . Thus, the ring of polynomial functions on looks like . If I had another curve , it would be defined by a polynomial , and the ring correspond to the scheme of the intersections of and is . This breaks down if , since quotienting by twice is the same as quotienting by it once.
To fix this, let us first replace rings with topological rings. In practice, topological rings aren’t the right idea to work with, but they will suffice for conveying intuition. A ring then becomes a set of discrete points, with the appropriate ring axioms, etc. We can now think of the act of quotienting by as connecting two points by a line every time a multiple of takes one to the other. We should also add triangles and higher simplices between appropriate compositions. If is nice enough (cancelable), we get a set of contractable pieces, each of which correspond to an element of the quotient. Since we are trying to think of topological rings only up to homotopy, this gives us the old, boring notion of the quotient.
However, if wasn’t nice, then we added some non-trivial loops. The connected components might still be isomorphic to the boring quotient, but suddenly non-trivial first homology has emerged. We can define an Euler characteristic as usual, the alternating sum of dimensions of the homology. Now, if I have two curves that coincide, I can say that their intersection number is the Euler characteristic of the corresponding topological ring, and I can ask if this is equal to the product of the degrees. I believe this is true, though a quick shuffling through my references hasn’t yielded a confirmation.
Derived algebraic geometry is an exciting field that I would like to learn more about. As near as I can tell, it is an attempt to bring the idea of homotopy equivalence into the core of scheme theory, with the goal of explaining such phenomena as stacks that really should have a tangent space that isn’t a vector space, but a complex of vector spaces (up to homotopy). If you are interested in learning more, I would recommend the above GRASP lecture, the (rather long) papers at Lurie’s homepage, and some of Toen’s lecture notes online. | <urn:uuid:072f41cb-592a-4812-89bf-cddece2c3246> | 3.359375 | 2,315 | Personal Blog | Science & Tech. | 45.642923 |
GroovyBeans are JavaBeans but using a much simpler syntax.
Here's an example:
Notice how the properties look just like public fields. You can also set named properties in a bean constructor in Groovy. In Groovy, fields and properties have been merged so that they act and look the same. So, the Groovy code above is equivalent to the following Java code:
Property and field rules
When Groovy is compiled to bytecode, the following rules are used.
- If the property is private, then a Java field is used to represent the property.
- If a public or protected property is declared (properties are public by default), then a public or protected getter and setter are created along with a private Java field.
- If you don't declare getters or setters for public or protected properties, they are automatically created for you at the bytecode level.
- If you create a public or protected property, you can overload any auto-created methods.
So, for example, you could create a read only property or a public read-only property with a protected setter like this:
Note that properties need <i>some</i> kind of identifier: e.g. a variable type ("String") or untyped using the "def" keyword.
Closures and listeners
Though Groovy doesn't support anonymous inner classes, it is possible to define action listeners inline through the means of closures. So instead of writing in Java:
You can do that in Groovy with a closure:
Notice how the closure is for a method on the listener interface (controllerUpdate), and not for the interface itself (ControllerListener). This technique means that Groovy's listener closures are used like a ListenerAdapter where only one method of interest is overridden. Beware: mistakenly misspelling the method name to override or using the interface name instead can be tricky to catch, because Groovy's parser may see this as a property assignment rather than a closure for an event listener.
This mechanism is heavily used in the Swing builder to define event listeners for various components and listeners. The JavaBeans introspector is used to make event listener methods available as properties which can be set with a closure:
The Java Beans introspector (java.beans.Introspector) which will look for a BeanInfo for your bean or create one using its own naming conventions. (See the Java Beans spec for details of the naming conventions it uses if you don't provide your own BeanInfo class). We're not performing any naming conventions ourselves - the standard Java Bean introspector does that for us.
Basically the BeanInfo is retrieved for a bean and its EventSetDescriptors are exposed as properties (assuming there is no clash with regular beans). It's actually the EventSetDescriptor.getListenerMethods() which is exposed as a writable property which can be assigned to a closure. | <urn:uuid:b09b6ef7-4dc7-4c07-a0ba-1a3672d05e01> | 2.953125 | 604 | Documentation | Software Dev. | 36.767613 |
We have read a lot of articles and papers about global warming. It is really happening and whether we like it or not we are part of this environmental issue. We might be just an ordinary citizen, but we can do something about it. But really, what is global warming? It is basically the increase in temperature of earth’s atmosphere, land masses and oceans. Global warming is caused by greenhouse gases mainly carbon dioxide which produced or emitted through various human activities. As a result, there are many environmental issues attributed to global warming like climate change. In recent decades there are increase in intensity and frequency of extreme weather events. For this reason Southeast Asia which is known to be vulnerable to climate change has experienced massive flooding, landslides and droughts in various areas. | <urn:uuid:15fdbf2d-6089-4058-ab8a-7a9f7ff24ff0> | 3.25 | 155 | Knowledge Article | Science & Tech. | 35.982516 |
So I took a look at them.
Dan uses the First Law of Thermodynamics.
That’s a start: Energy(in) – Energy(out) = Energy(retained).
Let’s take a look at Energy(Out). A single term: X·T4, where X is Dan’s constant.
Dan helpfully provides a link to Wikipedia’s A very simple model. This shows
(1-a)S = 4εσT4
- S is the solar constant – the incoming solar radiation per unit area—about 1367 W·m−2
- a is the Earth’s average albedo, measured to be 0.3
- σ is the Stefan-Boltzmann constant—approximately 5.67×10−8 J·K−4·m−2·s−1
- ε is the effective emissivity of earth, about 0.612
Dividing both sides by (1-a)S, we get 1 = Y·T4 where Y = 4εσ/(1-a)S.
Plugging in the terms into Y, we get
Y = (4 x 0.612 x 5.67×10−8)/(0.7 x 1367) K−4
= 1.45·10-10 K−4
(or 1·10-10 K−4 to 1 s.f. – we can’t justify more than one significant figure)
Y can’t really be a constant, though, since 1 = Y·T4. If T increases then Y must decrease (and vice versa). Perhaps we should rewrite it as Yi·Ti4 = 1. But for small ΔT Y will not change by much.
So far, so good.
Dan derives his constant in the same way, but then multiplies an additional term (the average sunspot count).
Quoting from his pdf on page 6:
The average sunspot number since 1700 is about 50, the energy radiated from the planet is about 342*0.7 = 239.4 (for the units used) and the earth’s effective emissivity is about 0.61 (http://en.wikipedia.org/wiki/Global_climate_model). Thus, as a place to start, X should be about 50/239.4 times the Stephan-Boltzmann constant times 0.61.
50/239.4*5.67E-8 *0.61 = 7.2E-9
Which then he “refines”, continuing:
With this plugged into the equation, a plausible graph is produced with a dramatic change observed to take place in about 1940. In EXCEL, 7.2E-9 was placed in a cell and the cell (value for X) called by the equation which produced a graph. The graph was observed as the value for X was varied. X was adjusted until the net energy from 1700 to about 1940 exhibited a fairly level trend. This occurs when X is 6.519E-9 (unbeknownst to me at the time, cell formatting rounded it to 6.52E-9).If an average sunspot number of 6.52/7.2*50 = 45.28 had been used, no adjustment would have been needed.
This is, of course, nonsense.
But we will follow this for now to see where it goes.
If we now multiply Y by Dan’s sunspot average count, we get
45.28Y = 45.28 x 1.45·10-10 K−4
= 6.56·10-9 K−4.
This is pretty close to Dan’s value (the difference is probably due to slightly different values of the terms S & ε, which I had used from the model).
To all intents and purposes X = 45.28Y.
Now go back to Dan’s term X·T4, the output energy.
Replacing X with 45.28Y, and remembering that Y·T4 = 1 (so that Y = T-4), we get
X·T4 = 45.28·T-4·T4.
Gosh! The Temperature terms cancel, the Stefan-Boltzmann equation vanishes, and the energy we are left with is ….
45.28 Sunspots ….
We give our consent every moment that we do not resist.
It is worth knowing and abiding by whether you comment on this blog or not.
- The “Mostly” Open Thread” is for general climate discussion that is not relevant to a particular post. Spam and abuse rules still apply;
- The “Challenging the Core Science” Comment Thread is for comments that purport to challenge the core science of anthropogenic climate change.
- The “Spam” Comment Thread is for comments posted by people who think that they can ignore site policy. | <urn:uuid:e41f1a6a-a5e0-40a3-ad90-f07624e9efcc> | 2.78125 | 1,059 | Personal Blog | Science & Tech. | 94.111103 |
How many "finished" or permanent draft complete genome sequences have been published?
How many of them are eukaryotes?
Here are the answers from: GOLD
(Apologies for the Three Domain influence.)
Why are there so few eukaryotes? Because many eukaryotic genomes are very large and it takes a lot more work to sequence that much DNA. Furthermore, many eukaryotic genomes are full of junk DNA and it's difficult to sequence and assemble repetitive regions in order to get a complete chromosome. The bottom line is money—for most labs it's too expensive to sequence the genome of their favorite eukaryote but it can be quite cheap these days to sequence a bacterial genome.
[Hat Tip: Jonathan Eisen] | <urn:uuid:f4ec1b71-3a33-41c5-99df-bcaddcbe8bdc> | 3.015625 | 155 | Personal Blog | Science & Tech. | 33.430085 |
We depend on our cars to take us to work and get our children to school. We rely on our home heating systems to keep us warm in the winter. We take it for granted that we can easily switch on our computer, vacuum cleaner or oven.
Yet scientists say the sources of energy we need to power all these modern conveniences are running dangerously low. We could run out of oil in as little as 40 years, and out of natural gas soon after that [source: The Independent]. These fossil fuels have been percolating beneath the Earth for hundreds of millions of years, and once they're gone, they're going to take millions more years to replenish. Not only are we running out of fossil fuels, but they're adding to our environmental woes by releasing nasty byproducts that increase pollution and contribute to global warming.
Scientists are running a race against time to find cleaner, more efficient, renewable sources of energy. One potential source that we've barely tapped is right underneath our feet. Deep inside the Earth lies hot water and steam that can be used to heat our homes and businesses and generate electricity cleanly and efficiently. It's called geothermal energy -- from the Greek words geo, or "earth," and therme, meaning "heat."
There is plenty of heat in the center of the Earth. The deeper you dig, the hotter it gets. The core, about 4,000 miles (6,437 kilometers) beneath the surface, can reach temperatures of 7,600 degrees Fahrenheit (4,204 degrees Celsius). Part of that heat is left over from the Earth's formation, about 4 billion years ago. The rest comes from the constant decay of radioactive isotopes inside the Earth.
The heat inside the Earth is intense enough to melt rocks. Those molten rocks are known as magma. Because magma is less dense than the rocks surrounding it, it rises to the surface. Sometimes magma escapes through cracks in the Earth's crust, erupting out of volcanoes as part of lava. But most of the time magma stays beneath the surface, heating surrounding rocks and the water that has become trapped within those rocks. Sometimes that water escapes through cracks in the Earth to form pools of hot water (hot springs) or bursts of hot water and steam (geysers). The rest of the heated water remains in pools under the Earth's surface, called geothermal reservoirs. | <urn:uuid:1e7271ff-7a76-4903-8608-1075579a927a> | 3.703125 | 485 | Knowledge Article | Science & Tech. | 58.752046 |
Technically, the file is been read using a charset of UTF-8 as you told the
InputStreamReader to do so. The underlying bytes of the file content are been interpreted using UTF-8. The
readLine() method returns a
String which stores the characters internally in Java's own UTF-16 charset.
What happens thereafter is fully dependent on what you're doing with this
String. If you're writing it back to a file using a
Writer without specifying the charset, then the platform's default will be used. If you're displaying it to the stdout, then the stdout's default charset will be used which is dependent on the runtime environment (command console? IDE? etc). If you're saving it in a database, then it's dependent on the JDBC driver configuration and/or the DB table encoding. Etcetera.
Apparently you're printing it to stdout in Eclipse's console by
System.out.println(). In that case, the GBK charset will be used to display the characters. That would malform any originally read UTF-8 characters which are not covered by GBK. You'd need to configure Eclipse to use UTF-8 as text file encoding. That can be done by Window > Preferences > General > Workspace > Text file encoding. | <urn:uuid:ad16246e-f8d0-4d69-9b57-4a08f8b169bf> | 3.171875 | 272 | Q&A Forum | Software Dev. | 64.173908 |
What's that dark spot on planet Earth?
It's the shadow of the Moon.
above image of Earth was taken last week by
MTSAT during an annular eclipse of the Sun.
The dark spot appears quite unusual as clouds are white and the
oceans are blue
in this color corrected image.
Earthlings residing within the
dark spot would see part of the
Sun blocked by the Moon and so receive less sunlight than normal.
across the Earth at nearly 2,000 kilometers per hour, giving many viewers less than
to see a partially eclipsed Sun.
MTSAT circles the Earth in a
geostationary orbit and so took the above image from about three Earth-diameters away.
Sky enthusiasts might want to keep their eyes
pointed upward this coming week as a
partial eclipse of the Moon will occur on June 4 and a
transit of Venus
across the face of the Sun will occur on June 5. | <urn:uuid:e3eae5d4-e64e-453d-9775-3aa0a5987b40> | 3.578125 | 203 | Truncated | Science & Tech. | 64.59588 |
The organization of gene circuit genotype space favors plasticity-mediated adaptive evolution. Shapes and colors have the same meanings in the diagram as in Figure 1. Starting from the blue genotype network, it is easier to find a genotype that produces a red alternative phenotype than finding the red genotype network. Many genotypes that produce the red alternative phenotype have direct mutational access to the red genotype network. Such genotypes are neighbors of other genotypes that produce the same alternative phenotype. Among genotypes that produce the red alternative phenotype, a high penetrance is associated to easier access to the red genotype network.
Espinosa-Soto et al. BMC Evolutionary Biology 2011 11:5 doi:10.1186/1471-2148-11-5 | <urn:uuid:2ecd22c6-dc92-4e59-9459-8aad2c0db181> | 3.421875 | 159 | Academic Writing | Science & Tech. | 21.825951 |
Hi all the following question is taken from http://www.javacross.com please tell me correct answer. Q].Which of the following makes proper distinction between Collection and Collections in the java standard library a].Collection is a class collections is a Interface b].Collections is a class collection is a Interface c].both Collection and Collections are classes d].both Collection and Collections are Interfaces Thanks in advance.
Joined: Feb 01, 2001
Option b. Collection is the basic interface and collections class provides some algorithms like sort, shuffle methods for the implementations of the Collection interface.
Sun Certified Programmer for Java 2 Platform
Joined: Jan 13, 2001
Hi , can anyone explain what is Collection, collections. Thank you. | <urn:uuid:90fb78e9-f3ba-462d-9ce0-9ed194f4be4e> | 3.015625 | 150 | Q&A Forum | Software Dev. | 53.515143 |
Fuel cells are electrochemical devices that produce electricity and heat from a fuel (often hydrogen) and oxygen. Unlike conventional engines, they do this without burning the fuel and are therefore more efficient, cleaner and carbon neutral. Fuel cells are being developed as a way to both produce and "store" energy in conjunction with renewable energy sources like solar and wind.
Most fuel cells are fueled with hydrogen. Hydrogen can be chemically generated or “reformed” from a range of standard fuels, such as natural gas, gasoline, or methanol. There is no agreement as to the single best fuel.
There are several different kinds of fuel cells. They are known by the electrolyte they contain. The most familiar types are alkaline, molten carbonate, phosphoric acid, proton exchange membrane and solid oxide.
Fuel cells have a number of advantages over other methods of generating power. The main advantage is that fuel cells emit no pollution when used. They also have the potential of using less fuel than competing technologies. Fuel cells are very quiet when operating and they create superior quality electricity.
There are many uses for fuel cells -- currently all of the major carmakers are attempting to commercialize a fuel cell car. Fuel cells are powering buses, boats, trains, planes, scooters, even bicycles. Miniature fuel cells for cellular phones, laptop computers and portable electronics are on their way to market.
In principle, a fuel cell operates like a battery. A battery chemically stores and releases electricity -- a fuel cell produces energy by reacting a fuel with air. A battery will run out of power and have to be recharged or disposed of. A fuel cell will produce energy in the form of electricity and heat as long as fuel is supplied to it.
Hydrogen is the simplest element and most plentiful gas in the universe. It is colorless, odorless and tasteless. Hydrogen is never found alone on earth -- it is always combined with other elements such as oxygen and carbon. Hydrogen can be removed from nearly any hydrogen compound and is the ultimate clean energy carrier. It is safe to produce and its chemical energy can be used in pollution-free ways.
A fuel cell running on pure hydrogen is a zero-emission power source. Fuel cell power plants are so low in emissions that some areas of the United States have exempted them from air permit requirements. Fuel cells are also very quiet, which reduces noise pollution.
Because of its high energy content, hydrogen must be handled correctly, just as gasoline and natural gas require careful management. Hydrogen is no more hazardous than other fuels. | <urn:uuid:3894adb6-2e18-4bc3-96f3-7f7ff7ddfb01> | 3.921875 | 527 | Knowledge Article | Science & Tech. | 37.376218 |
for Microsoft Access
Create complex MS Access databases without being an expert in relational database design! Designer for Microsoft Access asks you plain-language questions about what you want to manage with your database, and creates the tables and relationships automatically. Free trial available
Each table in your database should hold the information on one subject. You might think of a subject as a collection of related information with common characteristics. For example, if you were creating a database to hold information about the operation of your ice cream stand, you might have an IceCream table. If you decided to sell sundaes as well as cones, you might add a Toppings table. Then, to associate ice cream and toppings in particular combinations and record the prices, you might add a Sundaes table.
At this point in the design process, don’t be concerned about having too many tables. It’s much more likely in the early stages that you won’t have enough. Other steps in the process will make it clear whether or not your preliminary set of tables is correct.
Probably the best way to get started on identifying what tables you need is to look at your preliminary list of fields. Look for logical groupings of information.
The name of each table must be unique in the database and each field name must be unique within a table. Table names should normally be plural. Table and field names should be as brief as possible (see below) but also should clearly identify the subject of the table or the data in the field. Avoid abbreviations and acronyms if you can as they can be cryptic to another user of the database. Employees would be a good table name; R2D2 would not be.
Different RDBMS products have different restrictions on the length of table and field names and which characters are allowed. Usually, you can’t go wrong if you use:
Most products are not case-sensitive in table and field names.
Some designers prefer to follow a naming convention that includes a tag that identifies each object (for example, tblEmployees for a table about Employees) and includes information about the data type in the field name (for example, curPayRate for a field of a currency data type). This can be very useful in identifying the different objects in the application (for example, if you wanted to give a table and a query the same name) and becomes almost a necessity if you begin developing code to help control your application. One such convention is the Leszynski Naming Convention (LNC). You can also create your own convention or there may be one already in use at your company. | <urn:uuid:47b0571b-c429-44f3-bed4-52e6d81a8683> | 3.171875 | 536 | Tutorial | Software Dev. | 44.952729 |
More on Java 7 File IO
A reader of my previous blog on Java SE 7's File IO enhancements asked how symbolic links are handled in an OS-agnostic way. Good question! Let's examine that now. Recall Java 7's new Path class, and how it abstracts the details of the path to a directory or file, as in this example:
Path path = FileSystems.getDefault().getPath(".", name); InputStream in = Files.newInputStream(path); BufferedReader reader = new BufferedReader(new InputStreamReader(in)); List<String> lines = new ArrayList<>(); String line = null; while ( (line = reader.readLine()) != null ) lines.add(line); // ...
What my summary left out is that the class
Path represents not only files and directories, but links to files and directories, symbolic or otherwise. In fact, the
Path class detects and handles links automatically, without requiring you to do anything specific when one is encountered in your application. However, you do have options available on how to handle symbolic links when they occur, and you can also create new links in Java for file systems that support them.
Soft or Hard Link?
Like ice-cream, links come in two main varieties: soft (or symbolic) and hard. What's the difference? Symbolic links refer to other files or directories and are generally transparent to applications that use them. They are simply pointers to actual files. Operating systems are usually very lenient with how they are created and used, and therefore problems can arise. One example is a symbolic link that forms a circular reference: An application that recursively walks a directory tree that contains a symbolic link that points back to a higher level in the very same tree will recurse infinitely.
A hard link is more restrictive, and often resolves many of the issues related to soft links. However, because of these restrictions, they are generally used less often than soft links. Hard links have the following restrictions:
- The target of the link must exist
- The target cannot be a directory
- The target must exist on the same partition or volume
Java SE 7 and Links
The Java 7
Files classes work with both soft (symbolic) and hard links. For example, to determine if a
Path is a symbolic link, you pass it to the
// links to /logs/myapplogs/myapplog Path logs = FileSystems.getDefault().getPath("~/MyApp/MyAppLog"); boolean isSoftLink = Files.isSymbolicLink(logs);
To resolve a symbolic link, read the output (yet another
Path object) of a call to
Files.readSymbolicLink(), where the
Path object representing the link is passed as a parameter:
Path target = Files.readSymbolicLink(logs); System.out.println("MyApp log file resides here: " + target.toString() );
To create a symbolic link (not supported on Windows), you use the aptly named
Files.createSymbolicLink() method, and pass two
Path objects. The first represents the link to be created, and the second is the path to the actual target file or directory:
// the link to be created Path link = FileSystems.getDefault().getPath("~/MyApp/MyAppLog"); // the target file (doesn't really need to exist) Path target = FileSystems.getDefault().getPath("/logs/myapplogs/myapplog"); Files.createSymbolicLink(link, target);
You can create a hard link (which is supported by Windows) but the target file must exist in this case:
// the link to be created Path hardLink = FileSystems.getDefault().getPath("/Program Files/MyApp/MyAppLog"); // the target file (MUST EXIST!!) Path target = FileSystems.getDefault().getPath("/WINDOWS/Temp/myapplogs/myapplog"); Files.createLink(hardLink, target);
In any of these examples, if the underlying OS does not support symbolic and/or hard links, or if you violate one of the restrictions of hard links, you will get an
IOException at runtime. Therefore, be ready to handle this situation gracefully in your code.
Diving deeper into Java SE 7's File IO APIs, you can use the
FileVisitor interface to determine if and how links are followed, when to avoid them (i.e. when deleting files), and detect if a circular reference exists. | <urn:uuid:716e4d11-7404-4324-bfad-8b4563e8653d> | 3.21875 | 974 | Documentation | Software Dev. | 50.364435 |
Defining variables in a bash script is so simple! you don't have to worry about the datatype as you do in languages like C/C++. Just go on and define the variable like the following:
#!/bin/bash #Define a string variable, don't forget the quotes!! #if your variable is not string, omit the quotes STR="A Simple String Here" echo $STROK, don't panic about the $ sign in the echo line, here's why: When you want to use a variable's value, you have to add the $ at it's beginning. If you have worked with PHP before, you probably already know this.
Here's another example:
#!/bin/bash #define a string - it holds a directory location LOC="/home/anarion" #another for a file FIL="test.jpg" cp $LOC$FIL ./backup-test.jpgIn the above example, we combined both strings and used them both in a cp command.
Another note on the variables, you can use a program's outputs on-the-fly for another's input like this:
#!/bin/bash echo $(grep "kian" ~kian/names.txt)What this line does is: catch the output of the grep command and use it like a variable - just like our previous examples but this time we don't have a variable name... so it cannot be used in other lines of the script.
Now you should have learned the basic usage of variables in your scripts, in the next part we are going to learn about if statements and a little script to know if user has root privileges or not. | <urn:uuid:3f3cb547-fb3e-4b96-8a31-fa2f7083729f> | 3.234375 | 345 | Tutorial | Software Dev. | 71.750898 |
ANSI Common Lisp 19 Filenames 19.4 Dictionary of Filenames
- Arguments and Values:
host - a string.
just-loaded - a generalized boolean.
Searches for and loads the definition of a logical host named host,
if it is not already defined.
The specific nature of the search is implementation-defined.
If the host is already defined,
no attempt to find or load a definition is attempted,
and false is returned.
If the host is not already defined,
but a definition is successfully found and loaded,
true is returned.
Otherwise, an error is signaled.
Error: The logical host HACKS is not defined.
;; Loading SYS:SITE;HACKS.TRANSLATIONS
;; Loading done.
- Exceptional Situations:
If no definition is found, an error of type error is signaled.
- See Also:
Logical pathname definitions will be created not just by
implementors but also by programmers. As such,
it is important that the search strategy be documented.
For example, an implementation might define that the
definition of a host is to be found in a file called
"host.translations" in some specifically named directory.
- Allegro CL Implementation Details: | <urn:uuid:99cd95ef-8ecf-47d9-9dcd-8efb8ab3ac2d> | 2.765625 | 273 | Documentation | Software Dev. | 41.552114 |
London - Thought all this rain might at least wash away those summer mosquitoes? Think again. A study by the Georgia Institute of Technology in America has discovered why mosquitoes and other small insects can continue to fly through the air undisturbed — even if it’s bucketing down.
They found a mosquito can be hit by a raindrop weighing 50 times its body weight — the equivalent of a grown man being hit by a falling lorry — and simply fly on. It is all down to the mosquitoes’ remarkably tough frames or exoskeletons and the tiny hairs on their wings and bodies which allow water to run off without the insects losing momentum.
Researchers used small acrylic cages covered with mesh to conduct their experiments. Several mosquitoes were placed into each cage, and a water jet was used to simulate a rain stream. Every mosquito survived unharmed. - Daily Mail | <urn:uuid:cea78f5a-915c-4844-9aa0-8ab2d8abf2cf> | 3.25 | 178 | Truncated | Science & Tech. | 48.335395 |
|Scientific Name:||Coregonus oxyrinchus|
|Species Authority:||(Linnaeus, 1758)|
|Taxonomic Notes:||Usually considered to be present in all tributaries of North Sea basin. 'Houtings' from Danish North Sea basin and German rivers from Eider, Elbe west to Ems are C. maraena, a species widespread in Baltic basin.|
|Red List Category & Criteria:||Extinct ver 3.1|
|Assessor/s:||Freyhof, J. & Kottelat, M.|
|Reviewer/s:||Bogutskaya, N., & Smith, K. (IUCN Freshwater Biodiversity Unit)|
The species has not been recorded from its range (Southern North Sea basin: Schelde, Rhine and Meuse drainages) since about 1940. The species relied upon estuaries and brackish water to forage, where pollution was at it its most concentrated and coregonids are very sensitive to pollution. Many surveys have been undertaken since (most recently in 2005) within its previous range, and the species has never been recorded.
|Range Description:||Southern North Sea basin: Schelde, Rhine and Meuse drainages (exceptionally northern France). Ascended Rhine up to Köln [recorded to have reached Strasbourg (France) but this is probably erroneous]. Occasional records from southeast coast of England.|
Regionally extinct:Belgium; France; Germany; Netherlands; United Kingdom
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Last recorded in 1940.|
|Habitat and Ecology:||
In brackish water and main rivers; no evidence that it enters marine waters.
Spawns in October-December in rivers. Young move to brackish habitats where they remain until mature. Feeds on zooplankton, supplemented by benthic invertebrates in adults.
|Citation:||Freyhof, J. & Kottelat, M. 2008. Coregonus oxyrinchus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 25 May 2013.|
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1. IntroductionEither space has mass or it doesn't. A space without mass is a massless space. Massless space is the mathematical limit as a massy space's density goes to zero. The usefulness of this idea and the insights to be gained from it were shown in a previous paper. This paper will show how this can lead to a new understanding of Newton's universal gravitation.
In that paper we showed that treating space as a "body" in the framework of Newton's laws was entirely consistent with those laws. We also showed that the three laws of Newton are really only one.
2. The Problem Won't Go AwayPrevious attempts to cope with the problem of space was to deny its existence as a physical entity. Descartes filled it with material "ethers" consisting of physical "stuff" of various kinds with specific material properties. Newton's "action at a distance", an idea many called "occult" at the time, won out, and has prejudiced our thinking about physics ever since.
But Newton himself was troubled by this, as revealed in a letter:
That gravity should be innate, inherent and essential to matter, so that one body should act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has, in philosophical matters, a competent faculty of thinking, can ever fall into it. Gravity must be caused by an agent, acting constantly according to certain laws, but whether this agent be material or immaterial, I leave to the consideration of my reader.Clearly Newton was admitting that the agent responsible for gravity might actually be immaterial, or massless. Yet physicists continued to assume that space was filled with a "material" substance, the luminiferous ether, and they fully expected it to have at least some small mass density that could be experimentally detected.
In the 18th century physicists discovered electric and magnetic fields, and light as an electromagnetic phenomenon that could propagate through space. That was troublesome, and attempts were made to revive the idea of an ether-filled space to give light something to "wave in". It also provided a medium for fields, that could now be interpreted as stresses and strains in the ether.
Physicists abandoned the ether when relativity theory was adopted. They had enough to do just trying to understand and test the predictions of relativity. But the nagging question "How can bodies exert forces through intervening nothingness" persisted. Independent thinkers tinkered with the ether idea, but were ignored or ridiculed by the larger scientific community. [5, 6, 7]
3. Let's Get Real About SpaceThe answer, it seems to me, is to treat space itself as a legitimate physical entity or "thing", on an equal basis with other concepts of physics, such as mass, energy, momentum, photons, etc. For too long mainstream science has dismissed space as "nothing", and hasn't bothered to investigate the properties of space itself. An example of the confusion this cases in student minds is illustrated by these textbook definitions: "Space is the absence of matter" and "Matter is that which fills space." Very enlightening!
The virtually unknown physicist, Konrad Finagle (1858-1936) explored this notion in his "Theory of the Void". In that work we find this perceptive comment:
Consider what would happen if you took away the space from between matter. Everything in the universe would scrunch together into a volume no larger than a dust speck. We notice that hasn't happened. Why not? Something prevents it. That something is space itself... Space resists being pushed about. Space is what keeps everything from happening in the same place. We should finally admit that even empty space is every bit as real as anything else we talk about in physics. Space is just matter with zero density.
4. Pushing Space AroundFig. 1 was schematic only. Actually space completely surrounds objects. Consider a single object isolated in space. Assume that space exerts force on the body and the body exerts forces on space, in accord with Newton's third law. If space is symmetrically distributed around the body its net force on the body is zero by vector addition.
But now introduce into this picture a second body, B, some distance from the first. The presence of this body destroys the symmetry of space by pushing aside a volume of space equal to its own volume. Now there's a net force on each body due to this asymmetry. Again, Newton's third must be satisfied.
5. The vacuum abhors matterAristotle taught that "Nature abhors a vacuum". Perhaps it is the other way around. Suppose that "The vacuum abhors matter." When a body, like a planet, intrudes into space, pushing space aside, space reacts by trying to re-enter the volume occupied by the planet. This exerts a force all around the planet's volume that only serves to push the matter of the planet more firmly together. This inward rush of space toward the center of the earth is also responsible for the fall of the apple, and all other motion we attribute to "the force of gravity". It also sweeps nearby objects, such as the moon, toward the earth, balancing its centripetal force, and keeping the moon in a stable orbit.
The so-called mutual attraction of the earth and moon is really due to the fact that each body "gets in the way" of part of the inrushing vacuum, lessening its force on each body on the side nearest the other body.
On the grander cosmic scale, we see that this tendency of space to reclaim territory occupied by material objects is responsible for the motion of everything, every where. It's a grand tug of war between the vacuum and intrusive matter, and neither one wins in the short run.
6. Much Ado About
Look around in the universe and what do you see? Well, you see lots of
aggregates of stars called galaxies, that often look like rotating pinwheels.
Of course the rotation is glacially slow, but the evidence is overwhelming that
the most universal feature of the universe is that everything is in rotation.
That's just what our theory would predict. Look at water flowing down a
sink drain. It forms a rotating vortex. In the universe, vacuum flowing toward
masses also forms vortices, or whirlpools as a result of centrifugal forces. | <urn:uuid:9164e927-5886-4450-a0dc-33dcef268d01> | 3.5625 | 1,351 | Academic Writing | Science & Tech. | 49.956158 |