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The StreamReader class is a subclass of Codec and defines the following methods which every stream reader must define in order to be compatible with the Python codec registry.
All stream readers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.
stream must be a file-like object open for reading (binary) data.
The StreamReader may implement different error handling schemes by providing the errors keyword argument. These parameters are defined:
'strict'Raise ValueError (or a subclass); this is the default.
'ignore'Ignore the character and continue with the next.
'replace'Replace with a suitable replacement character.
The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the StreamReader object.
The set of allowed values for the errors argument can be extended with register_error().
|[size[, chars, [firstline]]])|
chars indicates the number of characters to read from the stream. read() will never return more than chars characters, but it might return less, if there are not enough characters available.
size indicates the approximate maximum number of bytes to read from the stream for decoding purposes. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. size is intended to prevent having to decode huge files in one step.
firstline indicates that it would be sufficient to only return the first line, if there are decoding errors on later lines.
The method should use a greedy read strategy meaning that it should read as much data as is allowed within the definition of the encoding and the given size, e.g. if optional encoding endings or state markers are available on the stream, these should be read too.
Changed in version 2.4: chars argument added. Changed in version 2.4.2: firstline argument added.
size, if given, is passed as size argument to the stream's readline() method.
If keepends is false line-endings will be stripped from the lines returned.
Changed in version 2.4: keepends argument added.
Line-endings are implemented using the codec's decoder method and are included in the list entries if keepends is true.
sizehint, if given, is passed as the size argument to the stream's read() method.
Note that no stream repositioning should take place. This method is primarily intended to be able to recover from decoding errors.
In addition to the above methods, the StreamReader must also inherit all other methods and attributes from the underlying stream.
The next two base classes are included for convenience. They are not needed by the codec registry, but may provide useful in practice.
See About this document... for information on suggesting changes. | <urn:uuid:62b4d00e-eb80-465e-bbe2-72619ecdf69e> | 2.859375 | 608 | Documentation | Software Dev. | 44.868324 |
The module pdb defines an interactive source code debugger for Python programs. It supports setting (conditional) breakpoints and single stepping at the source line level, inspection of stack frames, source code listing, and evaluation of arbitrary Python code in the context of any stack frame. It also supports post-mortem debugging and can be called under program control.
The debugger’s prompt is (Pdb). Typical usage to run a program under control of the debugger is:
>>> import pdb >>> import mymodule >>> pdb.run('mymodule.test()') > <string>(0)?() (Pdb) continue > <string>(1)?() (Pdb) continue NameError: 'spam' > <string>(1)?() (Pdb)
pdb.py can also be invoked as a script to debug other scripts. For example:
python -m pdb myscript.py
When invoked as a script, pdb will automatically enter post-mortem debugging if the program being debugged exits abnormally. After post-mortem debugging (or after normal exit of the program), pdb will restart the program. Automatic restarting preserves pdb’s state (such as breakpoints) and in most cases is more useful than quitting the debugger upon program’s exit.
New in version 2.4: Restarting post-mortem behavior added.
The typical usage to break into the debugger from a running program is to insert
import pdb; pdb.set_trace()
at the location you want to break into the debugger. You can then step through the code following this statement, and continue running without the debugger using the c command.
The typical usage to inspect a crashed program is:
>>> import pdb >>> import mymodule >>> mymodule.test() Traceback (most recent call last): File "<stdin>", line 1, in ? File "./mymodule.py", line 4, in test test2() File "./mymodule.py", line 3, in test2 print spam NameError: spam >>> pdb.pm() > ./mymodule.py(3)test2() -> print spam (Pdb)
The module defines the following functions; each enters the debugger in a slightly different way:
The debugger recognizes the following commands. Most commands can be abbreviated to one or two letters; e.g. h(elp) means that either h or help can be used to enter the help command (but not he or hel, nor H or Help or HELP). Arguments to commands must be separated by whitespace (spaces or tabs). Optional arguments are enclosed in square brackets () in the command syntax; the square brackets must not be typed. Alternatives in the command syntax are separated by a vertical bar (|).
Entering a blank line repeats the last command entered. Exception: if the last command was a list command, the next 11 lines are listed.
Commands that the debugger doesn’t recognize are assumed to be Python statements and are executed in the context of the program being debugged. Python statements can also be prefixed with an exclamation point (!). This is a powerful way to inspect the program being debugged; it is even possible to change a variable or call a function. When an exception occurs in such a statement, the exception name is printed but the debugger’s state is not changed.
Multiple commands may be entered on a single line, separated by ;;. (A single ; is not used as it is the separator for multiple commands in a line that is passed to the Python parser.) No intelligence is applied to separating the commands; the input is split at the first ;; pair, even if it is in the middle of a quoted string.
The debugger supports aliases. Aliases can have parameters which allows one a certain level of adaptability to the context under examination.
If a file .pdbrc exists in the user’s home directory or in the current directory, it is read in and executed as if it had been typed at the debugger prompt. This is particularly useful for aliases. If both files exist, the one in the home directory is read first and aliases defined there can be overridden by the local file.
With a lineno argument, set a break there in the current file. With a function argument, set a break at the first executable statement within that function. The line number may be prefixed with a filename and a colon, to specify a breakpoint in another file (probably one that hasn’t been loaded yet). The file is searched on sys.path. Note that each breakpoint is assigned a number to which all the other breakpoint commands refer.
If a second argument is present, it is an expression which must evaluate to true before the breakpoint is honored.
Without argument, list all breaks, including for each breakpoint, the number of times that breakpoint has been hit, the current ignore count, and the associated condition if any.
Specify a list of commands for breakpoint number bpnumber. The commands themselves appear on the following lines. Type a line containing just ‘end’ to terminate the commands. An example:
(Pdb) commands 1 (com) print some_variable (com) end (Pdb)
To remove all commands from a breakpoint, type commands and follow it immediately with end; that is, give no commands.
With no bpnumber argument, commands refers to the last breakpoint set.
You can use breakpoint commands to start your program up again. Simply use the continue command, or step, or any other command that resumes execution.
Specifying any command resuming execution (currently continue, step, next, return, jump, quit and their abbreviations) terminates the command list (as if that command was immediately followed by end). This is because any time you resume execution (even with a simple next or step), you may encounter another breakpoint–which could have its own command list, leading to ambiguities about which list to execute.
If you use the ‘silent’ command in the command list, the usual message about stopping at a breakpoint is not printed. This may be desirable for breakpoints that are to print a specific message and then continue. If none of the other commands print anything, you see no sign that the breakpoint was reached.
New in version 2.5.
Continue execution until the line with the line number greater than the current one is reached or when returning from current frame.
New in version 2.6.
Set the next line that will be executed. Only available in the bottom-most frame. This lets you jump back and execute code again, or jump forward to skip code that you don’t want to run.
Evaluate the expression in the current context and print its value.
print can also be used, but is not a debugger command — this executes the Python print statement.
Creates an alias called name that executes command. The command must not be enclosed in quotes. Replaceable parameters can be indicated by %1, %2, and so on, while %* is replaced by all the parameters. If no command is given, the current alias for name is shown. If no arguments are given, all aliases are listed.
Aliases may be nested and can contain anything that can be legally typed at the pdb prompt. Note that internal pdb commands can be overridden by aliases. Such a command is then hidden until the alias is removed. Aliasing is recursively applied to the first word of the command line; all other words in the line are left alone.
As an example, here are two useful aliases (especially when placed in the .pdbrc file):
#Print instance variables (usage "pi classInst") alias pi for k in %1.__dict__.keys(): print "%1.",k,"=",%1.__dict__[k] #Print instance variables in self alias ps pi self
Execute the (one-line) statement in the context of the current stack frame. The exclamation point can be omitted unless the first word of the statement resembles a debugger command. To set a global variable, you can prefix the assignment command with a global command on the same line, e.g.:
(Pdb) global list_options; list_options = ['-l'] (Pdb)
Restart the debugged Python program. If an argument is supplied, it is split with “shlex” and the result is used as the new sys.argv. History, breakpoints, actions and debugger options are preserved. “restart” is an alias for “run”.
New in version 2.6. | <urn:uuid:a63c50f5-4c11-4e36-a721-82a0229f4a22> | 3.453125 | 1,825 | Documentation | Software Dev. | 57.084643 |
i am having trouble understanding how java's input output system works, as the sun's tutorial is helpful with swing stuff its is extramly vague with I/O.
and yes i have many books on java yet all fail to describe java's I/O effectively for the noob :P
has any one a clue on a any good books or resoures's on the internt which deal with I/O as i would like to figure it out my self with out u peopole doing my work for me because i cant get a job with other people doing my work.
im basicly coding a simple note pad application yet dont know y you need to
"throws IOException" ect
so please, if any one know of any good resources with examples i would be thankful
so yes i am obioulsly refering to Files, FileReader, FileWriter ect
NOT the obvious console I/O System.out.print
It's pretty easy stuff if you just read through the API a bit and test some stuff out. All you really need is a BufferedReader/BufferedWriter.
IOExceptions are necessary because there are many different things that can go wrong while trying to use a stream. For instance, you may try to create a FileReader with a file that does not exist, so an IOException will be thrown.
you don't need to declare your method to throw IOExceptions, you can catch them if you want. They have to be caught somewhere after all.
ok cool it makes sence that a exception has to be throwen like u stated, but as i said sun's tutorial is very vage as to how to correctly use (code) I/O and the jave api is obviously daughting for a noob such as myself.
so do u know of any good resources which teach the use of I/O with or without working examples ?????
i posted that twice,
as the sun's tutorial is helpful with swing stuff its is extramly vague with I/O.
jesus christ didnt u read my posts,
no offence but i said it not once but twice. *sigh*
First of all, I suggested reading the API at first, not the tutorials. Second, there is no need to get pissy. If you can't read an API/tutorial (oh by the way, have you heard of search engines?) enough to learn what should be a very basic concept for someone wanting to use file I/O, then maybe you need to spend more time learning the language and less time demanding exactly what you said you didn't want:
i would like to figure it out my self with out u peopole doing my work for me because i cant get a job with other people doing my work.
exactly which tutorial didn't make sense? I haven't found many that didn't help me at least a little bit.
drain this is the New to Java section
try to remember that next time.
you obviously understand java, but maby your english needs a little attention
mike: yeah i get what u mean but i just need that extra bit of background. so if you have any books or documents u can recommend for the New to Java sort of person that would be good.
thanks any way
The only java book i've ever read is Introduction to Java Programming by Liang, but I have no idea how this compares to other java books. It was just the recommended book on my course. To be honest if I ever don't know how to use something i've always used the sun API and tutorials. The API lists all the methods for a particular class and explains what they do. This is usually enough to know how to use a class, but they sometimes stick the tutorial in if its more complex.
I will now quote the API.
= new BufferedReader(new FileReader("foo.in"));
will buffer the input from the specified file. Without buffering, each invocation of read() or readLine() could cause bytes to be read from the file, converted into characters, and then returned, which can be very inefficient.
Create a buffering character-input stream that uses a default-sized input buffer.
Read a line of text.
Creates a new FileReader, given the name of the file to read from.
ill check out that book and see how i go
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A Swiss marine biologist and an Australian quantum physicist have found that a species of shrimp from the Great Barrier Reef, Australia, can see a world invisible to all other animals.Dr Sonja Kleinlogel and Professor Andrew White have shown that mantis shrimp not only have the ability to see colours from the ultraviolet through to the infrared, but have optimal polarisation vision -- a first for any animal and a capability that humanity has only achieved in the last decade using fast computer technology.Prof. White notes, "Some of the animals they like to eat are transparent, and quite hard to see in sea-water - except they're packed full of polarising sugars - I suspect they light up like Christmas trees as far as these shrimp are concerned." "And of course," Dr Kleinlogel concludes, "they can still flirt with each other using fancy polarisation cues!"
"they can still flirt with each other using fancy polarisation cues!"
These critters see 12 primary colors.What would it take to genetically engineer equivalent visual range into a human?
Text and signs viewable by only those with the right eyes? | <urn:uuid:fd7886f8-4b1b-4b4f-a141-1c140a215df4> | 2.796875 | 247 | Comment Section | Science & Tech. | 43.138 |
Parallel programming isn’t always just a simple matter of writing loops that run at the same time. While that might work for certain individual algorithms, bigger software systems are certainly more complex and require a type of parallel programming that goes beyond simple loops and spawning C++ threads.
Instead, most systems are more likely to be along the lines of, “Step A must precede all steps, but Steps B and C can run in parallel.” And you might even have more complexity like, “Step B1 follows step B, and Step C1 follows both Step B1 and C.” Such systems can be diagrammed using a directed graph. A directed graph is a type of graph that contains nodes with arrows pointing between nodes. In this case, each node represents a task to perform.
Modeling such systems directly can be difficult and result in bugs. And that’s where the graph classes in Threading Building Blocks help. TBB includes several classes as part of the tbb:flow namepsace, such as a basic graph class, and a basic node class.
The Importance of Communications Between Nodes
Nodes can provide functions that execute, or they can serve as message handlers. The idea here is that you can have your nodes communicate with each other and send data back and forth between them. This goes beyond the simple matter of having them execute in an order determined by the graph. Helping with this are other node classes derived from the basic node class. (In fact, the basic node class really provides nothing more than a virtual destructor.)
In addition to the node class, there are two other classes that serve as abstract bases: sender and receiver. These classes give a node communication capabilities. Both are template classes and abstract; as such you need to derive new classes from them.
Send, Receive, Continue Classes
The receiver class includes a virtual abstract function called try_put. This is called to “put” an item into this receiver. Similarly, the sender class includes a function called try_get. This is called to get an item from this sender. (That seems a bit backwards to me in terms of nomenclature, but that’s okay.)
A class called continue_receiver is derived from receiver, which takes as a template parameter a continue_msg. This abstract class provides the methods necessary for executing nodes in order without having to pass messages between them. The idea is simple: This class includes an abstract function called execute, as well as the try_put function. Additionally, it includes a constructor that has as a parameter the number of preceding nodes. When those preceding nodes call try_put this number of times, the execute function gets called. (By providing this count, you can have the node wait for more than one node.)
But remember, continue_receiver is an abstract class. There’s also a class called continue_node. This class is derived from continue_receiver, as well as graph_node. It includes the continue_receiver functionality I just described; and by deriving it from graph_node, it can serve as a node inside a graph. But beyond that it also implements the sender abstract class. Why? Because while this node will execute after other nodes, it in turn might need to notify nodes after it to execute as well. In other words, this class servers as both a receiver and a sender, and can therefore function inside a graph, waiting for its time to run, and then notifying subsequent nodes of this same class to run.
That’s the basics of how this works. We don’t have room to get into actual code yet, and there are still more classes to explore. But next week I’ll look at some simple code to demonstrate what I’ve covered so far. I encourage you to take a look at the documentation.
Have you worked with the graphs at all? Have you run into any stumbling blocks or problems? Let me know in the comments below. | <urn:uuid:bcf9cadf-1770-495a-903c-f1c23d2e1209> | 3.703125 | 831 | Documentation | Software Dev. | 53.698994 |
This is not how you actually hold a corer – I was too busy posing to keep my hands in the proper position! You’re supposed to have one facing up, one facing down.
My hydrology class went out coring trees to study dendrochronology! Dendrochronology is the study of trees through time . To take a core sample, you gently screw this hollow tube into the tree, and then insert an extractor that much resembles a long-handled ice tea spoon, which grips onto the end of the core and pulls it out.
Much as it seems really invasive, they’ve apparently figured out a way that this doesn’t harm the tree. I like to think of it like getting an ear piercing with a hollow needle, or a biopsy.
Then we let the cores dry out in the lab, and our professor used a planer saw to flatten them out. Then the real work of counting and measuring rings began!
The youngest rings are the smallest, because a tree grows from the inside-out. When the tree has grown larger, the total growth for the tree is spread out over a larger area – this results in smaller rings. In addition to marking the years on the core-holder, you also mark the core with a certain number of dots – one for a decade, two for a half-century, three for a century, etc..
Once you get close to the tree’s center, the rings become much larger. In this picture, you can see how the rings near 1810 are curving, instead of being perpendicular to the core – this means that we missed the core. These rings aren’t very useful to measure, because it’s difficult to get a good reading on their actual width.
We correlated this data with historical precipitation data, to see how the growth reacted to precipitation. Our correlation was quite poor, since our measuring tools were fairly low-grade. (Plus, we’re newbs.) But, with the proper measuring tools, many more data points, and a lot more practice, a good correlation can be established. The relationship from this correlation can then be used as a proxy to establish possible precipitation values for the years before historical measurements exist. In addition to being a useful tool for looking at a particular region’s specific precipitation and plant growth patterns, this is one of the primary methods current climate change studies rely upon to establish past climate figures. | <urn:uuid:ba50dd69-570b-4b33-8c01-a2ef5dfa9c55> | 3.5625 | 507 | Personal Blog | Science & Tech. | 55.929889 |
INDEX FOR THIS PAGE
Nomenclature of Alkyl Halides
Nature of the C-X Bond
Halogenation of Alkanes
Mechanism of Halogenation
Energetics of Halogenation
Regioselectivity of Bromination
Regioselectivity of Chlorination Compared to Bromination
Resonance Stabilization of the Allyl Radical
NOMENCLATURE OF ALKYL HALIDES
- Essentially, the naming of alkyl halides is not different
from the naming of alkanes. The halogen atoms are treated as substituents
on the main chain, just as an alkyl group, and have no special priority over
- The name of a chlorine substituent is "chloro",
that of a bromine substituent "bromo" and so on.
- You sould practice naming a variety of haloalkanes.
POLARITY AND STRENGTH OF THE
- Carbon-halogen bonds are very substantially polar covalent,
with carbon as the positive and halogen as the negative end of the dipole.
Conosequently, the carbon attached to the halogen is electrophilic.
We shall see in the next chapter how nucleophiles react at the carbon of an
- The carbon-fluorine bond is the strongest, especially since
fluorine is the most electronegative of the halogens, resulting in a larger
contribution of the polar (ionic) structure to the resonance hybrid. The larger
contribution of the ionic structure not only makes the molecule more polar,
it also makes the bond more stable because the ionic structure is lowered
in energy. However, all of the C-X bonds are significantly polar.
- The C-X bond dissociation energies (D), which you do not
need to memorize, are C-F 108; C-Cl 85; C-Br 70; C-I 57 (these are for CH3-X
RADICALS: DEFINITION: SPECIES
WHICH HAVE AN UNPAIRED ELECTRON (AN ODD NUMBER OF ELECTRONS)
FORMATION OF RADICALS BY HOMOLYSIS
THE METHYL RADICAL
The methyl radical is
an example of a very simple organic radical. The carbon atom has only three
hydrogens bonded to it, so it is trigonally hybridized. It therefore is planar
and has the odd (unpaired) electron in the 2p AO. This odd electron is
what makes the radical very reactive.
RELATIVE STABILITIES OF METHYL,
PRIMARY, SECONDARY, AND TERTIARY RADICALS.
NOTE THAT THE D'S OF C-H BONDS DECREASE PROGRESSIVELY
AS THE NUMBER OF ALKYL GROUPS ATTACHED TO THE RADICAL CENTER IN THE PRODUCT
RADICAL IS INCREASED. THE D IS DECREASED BECAUSE THE PRODUCT RADICAL IS BEING
STABILIZED BY THE ALKYL GROUPS.
HYPERCONJUGATIVE RESONANCE STABILIZATION
OF A RADICAL CENTER BY ATTACHED ALKYL GROUPS
THE HALOGENATION REACTION
- A very simple example of the halogenation of alkanes is
the chlorination of methane, as shown in the illustration below. The products
are HCl and chloromethane.
- The REACTION TYPE is SUBSTITUTION, since a
hydrogen of methane is replaced by a chlorine atom. The MECHANISTIC TYPE,
as we will see, is Homolytic or Radical. The overall designation of
the reaction, then, is SH (S WITH A SUBSCRIPT H).
- Virtually any C-H bond in which the carbon atom is tetrahedrally
hybridized can be chlorinated, so that chloromethane can be further converted
to dichloromethane, and this on to trichloromethane (chloroform), and finally
to tetrachloromethane (carbon tetrachloride). You may recognize these chlorinated
compounds as common solvents, both in the laboratory and in commercial uses.
- In the chlorination of alkanes more complex than methane
or ethane, more than one monochloroalkane can be formed. We will refer to
the preference for the formation of one constitutional isomer over the other
as regiospecificity. For example, propane can be converted to both 1-chloropropane
and 2-chloropropane. Actually, both are formed, but the 2-chloropropane is
slightly, but only slightly, preferred. Thus, the reaction is not very stereooregiospecific.
MECHANISM OF CHLORINATION OF METHANE
The mechanism for the chlorination
of methane is representative of the chlorination of any alkane or indeed of
the halogenation of an alkane:
- This is our first example of a reaction mechanism in which
radicals are involved. The definition of a radical is any species which has
an unpaired or odd electron. There are two radical species involved in
this mechanism, the chlorine atom and the methyl radical. The naming of
organic radicals is simple, it is essentially the name of the corresponding
substituent with the name radical being appended to it.
- The overall reaction is said to be a homolytic substitution
reaction, as noted previously, because the bonds which are broken are broken
homolytically, i.e., one electron departing with each component of the bond.
In homolytic cleavages radicals are always formed, so the reaction mechanism
can also be called radical substitution.
- One specific way in which radical reactions can occur is
by means of a radical chain reaction. It is important to keep in mind
that not all radical reaction mechanisms are radical chain mechanisms.
A radical chain mechanism is one in which a particular set or two or three
steps is repeated over and over without the necessity of generating more radicals.
This is seen in steps 2 and 3 of the mechanism above. The stage of the reaction
which represents the chain is called the propagation cycle. It is so
called because in it, the observed products (HCl and chloromethane) are propagated
or made. An efficient set of progpagation reactions is essential to a successful
radical chain mechanism.
- Overall, this or any, radical chain mechanism consists of
three discrete stages or parts. The first part is called initiation.
In the initiation stage of the mechanism (step 1), the radicals which are
necessary to enter the propagation cycle are generated. This typically involves
the homolytic cleavage of a covalent bond, and so it requires energy. In this
case, it is the Cl-Cl bond which is cleavaged homolytically.It is for this
reason that the chlorination reaction requires the input of either heat or
- As noted above, the second stage or part of the radical
chain mechanism is the propagation cycle. An efficient propagation
cycle uses a relatively few radicals to generate a large amount of product.
It is desirable that for each radical produced in the initiation reaction,
hundreds or even thousands of product molecules be generated before the radical
- The third and final stage of the radical chain mechanism
is termination. Termination is the undesirable but unavoidable coupling
between two radicals which destroys the chain carrying radicals and stops
the current radical chain. It is thus the competitor of propagation. Because
of this continuing consumption of radicals, initiation must continue to progressively
generate more radicals. For a chain reaction to be effective, propagation
by the radicals must be much more efficient than coupling between them.These
coupling reactions are extrememly fast, because no bond is broken and one
bond is formed. However, since the radical concentrations are extremely small,
the probability of one radical meeting another is much less than for a radical
to meet a molecule of chlorine or methane.
OF THE REACTION AND THE INDIVIDUAL PROPAGATION STEPS
- First we note that the overall reaction is strongly exothermic
and proceeds to the right. If it were endothermic it would not proceed toward
products, no matter what the reaction mechanism. Of course, it is really the
free energy change which determines the position of the equilibrium between
reactants and products, but the enthalpy change is normally the largest component
- Then, we note that both propagation steps are exothermic.
This is , of course, a necessary but not sufficient condition for a rapid
rate. However, radical reactions which are exothermic typically are very fast.
It is important to note that both propagation steps are required to be very
fast, since they must follow each other sequentially in the chain process.
- The hydrogen abstraction step (abstraction in this
context means "pulling off") of the reaction is favorable because
the HCl bond is stronger than virtually any C-H bond of an alkane.
- The second propagation step, in which methyl radicals abstract
a chlorine atom from chlorine molecules, is even more favorable, because the
relatively weak Cl-Cl bond is much weaker than the C-Cl bond formed. This
weak Cl-Cl bond is also the main reason the overall reaction is favored.
- Of course, the termination steps are always powerfully exothermic,
and the initiation is normally strongly endothermic.
REGIOSELECTIVITY IN BROMINATION
- There are primary,secondary, and teritary hydrogens in the
alkane illustrated and five possible products of monobromination (not to mention
many more di-, tri-, and polybromination bproducts). However, essentially
only one product is formed, that being from substitution of the tertiary hydrogen
by bromine. This highly regiospecific reaction is therefore synthetically
quite useful. In contrast, chlorination gives all five products in significant
amounts and is nearly useless for laboratory synthetic purposes.
- In general, tertiary hydrogens are most reactive to bromination.
Secondary hydrogens are much less reactive, and primary ones are virtually
unreactive, as are the hydrogens of methane.
- In sharp contrast, any of these types of hydrogen can be
readily chlorinated, and the preferences are still tertiary>secondary>primary>methane,
but the selcectivity is low. Note that vinyl C-H are very difficult even to
WHAT IS THE BASIS FOR THE SELECTIVITY
To understand the high selectivity of bromination and also
the preference for tertiary over secondary, etc. hydrogens we should construct
a TS model for the hydrogen abstraction step. This is the step of interest because
once the hydrogen is removed, giving an alkyl radical, the bromine will be abstracted
by the radical site. Thus, whichever hydrogen is abstracted will be replaced
directly, at the same carbon, by bromine.
- The TS model is constructed in the usual way, using resonance
theory and modeling the TS as a resonce hybrid of reactant-like and product-like
structures. The DL/PC structure reveals partial bonds between H and Br and
also between R and H, with partial radical character at both bromine (as in
the reactant) and carbon (as in the product).The TS thus has alkyl radical
- It has already been established that tertiary alkyl radicals
are more stable than secondary than primary than methyl, so as the R group
(alkyl) is varied from tertiary to secondary to primary, the TS becomes less
stable, the activation energy higher, and the rate lower.
- This explains the sequence of reactivity, but not the degree
of selectivity, which is high for bromine. To explain this, we need to use
the Hammond Postulate as applied to this reaciton step. Since the H-Br bond
strength is only about 87 kcal/mol and since any C-H bond of the tertiary,
secondary, etc. types is stronger than this, the reaction is endothermic,
and according to the Hammond Postulate, the TS more closely resembles the
product. In the product-like structure, the radical character is on the alkyl
group. Thus, we have extensive radical charcter development in the
TS for the hydrogen abstraction step of bromination, which means the preference
for tertiary hydrogens is relatively great.
REGIOSELECTIVITY IN CHLORINATION
- As we have earlier noted, chlorination has the same qualitative
sense of selectivity as bromination, i.e., tertiary>secondary>primary,
but the selectivity is very much lower.
- The TS model is essentially like that for bromination, having
alkyl radical character, thus explaining the preference for tertiary hydrogens.
- The low selectivity is explained by the circumstance that
the TS has only a low level of radical character. The basis for this conclusion
is that the hydrogen abstraction step when chlorine atoms is involved is exothermic,
since the H-Cl bond formed is relatively strong (D=103 kcal/mole), and stronger
than any of the C-H bonds of alkanes except that of methane. Thus, an application
of the Hammond Postulate to this TS reveals that it should have only a low
level of radical character, i.e., it looks more reactant-like.
STATISTICAL EFFECTS IN CHLORINATION
- The chlorination of isobutane, in contrast to the bromination,
which gives only tert-butyl bromide, gives rise to a mixture of isobutyl and
tert-butyl chlorides, with the former (isobutyl chloride) actually predominating.
How can it be explained that primary hydrogens are actually more reactive
than tertiary ones?
- The answer lies in statistical or probability factors.
In isobutane there is only one tertiary hydrogen but nine primary ones.
The probability of a chlorine atom colliding with and abstracting a primary
hydrogen is therefore nine times as great as with a tertiary hydrogen. Since
the selectivity for a tertiary hydrogen over a primary one is relatively small
in chlorination, it may be no surprise that the statistical factor
of 9 which operates to prefer primary hydrogen abstraction is dominant over
the small chemical selectivity which favors the tertiary hydrogen.
- If we compare the reactivity per hydrogen, we do
see that there is an inherent preference for abstracting a tertiary hydrogen.
- In the case of bromination, the chemical selectivity is
so high that it overwhelms the statistical factor of 9.
- Allylic hydrogens are hydrogens, such as the methyl hydrogens
of propene, which are attached to a carbon atom which, in turn, is attached
to a carbon-carbon double bond(see illustration below).
- Allylic hydrogens are especially easily halogenated by a
free radical chain mechanism because their C-H bond dissociation energyies
are relatively low, i.e., these bonds are weak and easy to break homolytically.
We will see in a minute that this is because the allylic radicals produced
upon homolysis are highly resonance stabilized.
- If we consider propene itself, there are three equivalnet
allylic hydrogens with D's of 86 kcal/mol, i.e., they are weaker than even
tertiary C-H bonds. The other three bonds are of the vinyl type (i.e.,
they are directly attached to a carbon atom of the double bond) and have D's
of ca. 106 kcal/mol, i.e., they are stronger than even the C-H bonds of methane
and also of than that of HCl. Therefore, these particular bonds are not easy
to halogenate, even by chlorination. Therefore, the only monohalogenation
product of propene which is observed is 3-chloropropene or allyl chloride.
- The mechanism of chlorination or bromination is the same
as before, the free radical chain mechanism. You should write this out for
the specific case of propene.
- Any hydrogen atom which is of the general allylic type is
especially easily halogenated, e.g., in the illustration below, the allylic
halogens hydrogens of cyclohexene.
- The biggest problem with allylic halogenation is the electrophilic
addition of the halogen to the C=C double bond. For bromination, this is usually
overcome by using, instead of molecular bromine (dibromine), the compound
N-bromosuccinimide (NBS), which is a less toxic and more conveniently handled
solid, which produces bromine only very gradually in solution. Under these
conditions (very low bromine concentration), allylic bromination by a free
radical mechanism is normally predominant over electrophilic addition of halogen.
RESONANCE STABILIZATION OF
THE ALLYL RADICAL
- Considering the illlustration given below, we note that
the allyl radical has two equivalent resonance structures. Therefore,
resonance stabilization is particularly strong.
- Note from the diagram that the MO's of the allylic pi system
are delocalized over three carbons, so that it is impossible to designate
the electrons as being shared by only two atoms, as in a classical covalent
- The radical character appears equally upon the two terminal
allylic carbons, but not at all on the central carbon. thus, the allyl
radical reacts at the terminal carbon when it behaves as a radical, e.g.,
abstracting chlorine from chlorine molecules.
- The strong resonance stabilization of the allyl radical
is the reason that the D for the allylic hydrogens of propene and other allylic
hydrogens is much smaller than for typical hydrogens attached to carbon.
- Allylic radicals are more stable than tertiary radicals,
than secondary, than primary , than methyl radicals.
Regiochemistry of Allylic Halogenation
It is important to note that, because allylic radicals are
delocalized over three carbon atoms and have radical character at two carbons
(the terminal ones), when an unsymmetrical alkene is NBS brominated, two products
can and do result.
BACK TO THE TOP OF THIS PAGE
ON TO NUCLEOPHILIC SUBSTITUTION
BACK TO ALKENES
BACK TO THE BAULD HOME PAGE | <urn:uuid:79eb465c-0df0-49fd-85d2-e2f70abaf9cf> | 2.890625 | 4,022 | Tutorial | Science & Tech. | 27.69974 |
Citizen science occurs when data for scientific research is collected by members of the public in a voluntary capacity. Public participation in environmental projects, in particular, has been described as a global phenomenon.But there is a stigma associated with these types of projects. The data collected are often labelled untrustworthy and biased. Research in this area continues to show however, that data collected by what is essentially a non-professional workforce, are comparable to those collected by professional scientists.
via Citizen science can produce reliable data.
The official name of the latest rover we’ve sent to Mars is not Curiosity. It’s Mars Science Laboratory. And one of the mobile lab’s primary jobs — besides photography and interplanetary telegraphy and being, generally, spunky — is to do the very scientific job of assessing the soil on Mars. Curiosity has made its mission mainly to see what Mars is made of (and how its soil varies, and whether that soil could have once supported life).
via Um, What’s That Bright, Shiny Thing Curiosity Just Found on Mars? – Megan Garber – The Atlantic.
Maybe it’s a litter from a Martian!
An immunity booster to take on HIV and a lab-on-a-chip device to identify chemical warfare agents have featured in this year’s Eureka awards, which celebrate innovators in Australian science.This year’s Australian Museum Eureka Prize, the 23rd, awarded $180,000 in prize money to scientists and researchers tackling some of the world’s most challenging and controversial issues.
via Scientists say eureka on HIV and chemical warfare.
LONDON, Nov. 8, 2010 Reuters Life! — Scientists using tarantulas to unpick human fear have found that the brain responds differently to threats based on proximity, direction and how scary people expect something to be.A Chilean rose tarantula is shown at the environment reserve in Mexico state, one of 500 tarantulas abandoned at the airport in Mexico City this week when their owner failed to complete import paperwork. REUTERS/Henry Romero HR/HBResearchers from the Cognition and Brain Sciences Unit in Cambridge, England used functional magnetic resonance imaging, or fMRI, to track brain activity in 20 volunteers as they watched a tarantula placed near their feet, and then moved closer.Their results suggest that different components of the brains fear network serve specific threat-response functions and could help scientists diagnose and treat patients who suffer from clinical phobias
via NewsDaily: Tarantulas help scientists break down human fear. | <urn:uuid:87b4d662-aabf-4bad-b138-399473a36b72> | 3.109375 | 526 | Content Listing | Science & Tech. | 37.289823 |
Whales communicate using melodic sounds or "songs" that can travel more than 100 meters. Oceangoing ships produce noise, mainly from their propellers, that interfere with the ability of whales to communicate. Other types of ships create additional layers of noise. Oil-exploration ships, for example, use reflection seismology to map the ocean floor. Research has shown that these additional noises can interfere with a whale's ability to communicate, causing confusion for the whale.
Published on Aug 20, 2012 by NMANewsDirect | <urn:uuid:fb6a4741-cec0-434d-8c93-48fcb6b3fd22> | 3.546875 | 108 | Truncated | Science & Tech. | 31.636444 |
Then supposing that the earth does weigh relatively the same, how does it effect the rotation of the earth, orbit of the earth when we do remove weight from our sphere by sending things into space?
Also, the rotation of the Earth has been slowing throughout its history. The first days were only 6.5 hours!
"The Geophysical Effects of the Earth's Slowing Rotation!"
Did the fast spinning Earth have a ring around it when it was very young?
When the Earth was very young, its faster rotation caused it to have a much larger equatorial circumference than it has at the present time. It may have been spinning fast enough to have a "Saturn type ring" around it.
It is well known that the rotation of planet Earth is gradually slowing. For four and one half billion years, its entire lifetime, its rate of rotation has been gradually slowing. As the Earth loses its kinetic energy due to all forms of friction acting on it; tides, galactic space dust, solar wind, space weather, geomagnetic storms, etc., like any flywheel, it will slow down. (The space surrounding the planet is far from empty).
...over the course of the planet's entire lifetime, it has had very profound effects on the geophysics of the planet.
It has caused mountains to rise, earthquakes, etc. to occur as we will see. This article is about, factoring in the tremendous geophysical activity that was caused, by the Earth's slowing rotation, in the interior of the planet, its crust, oceans and atmosphere over its entire lifetime.
Tracing these tiny milliseconds back for 4.5 billion years adds up to a very significant amount of time for a solar day. I have determined that the day/night rotation was 63,000 seconds shorter than the present 86,400 seconds it is today. This would put the Earth's rotation at about 6.5 hours per day/night cycle, when it was created, 4.5 billion years ago. (This is a much faster rate of rotation than the Cassini-Huygens mission (2003 to 2004) determined Saturn's 10.5 hours rotation period to be.) | <urn:uuid:9fbb58a7-07aa-4102-b3ef-b2aee710d81f> | 3.53125 | 446 | Comment Section | Science & Tech. | 66.803423 |
Computing (FOLDOC) dictionary
Jump to user comments
The standard function in the C
language library for printing formatted output.
The first argument is a format string which may contain
ordinary characters which are just printed and "conversion
specifications" - sequences beginning with '%' such as %6d
which describe how the other arguments should be printed, in
this case as a six-character decimal integer padded on the
right with spaces.
Possible conversion specifications are d, i or u (decimal
e.g. 1.23E-22), g or G (f or e format as appropriate to the
value printed), c (a single character), s (a string), %
(i.e. %% - print a % character). d, i, f, e, g are signed,
the rest are unsigned.
The variant fprintf
prints to a given output stream and
sprintf stores what would be printed in a string variable. | <urn:uuid:67b941f0-7a8a-4a01-9959-c9292e338b9f> | 3.984375 | 207 | Documentation | Software Dev. | 62.862783 |
Richard Gerber has worked on numerous multimedia projects, 3D libraries, and computer games for Intel. Andrew Binstock is the principal analyst at Pacific Data Works and author of "Practical Algorithms for Programmers". They are the authors of Programming with Hyper-Threading Technology.
Parallel programming makes use of threads to enable two or more operations to proceed in parallel. The entire concept of parallel programming centers on the design, development, and deployment of threads within an application and the coordination between threads and their respective operations. This article examines how to break up traditional programming tasks into chunks that are suitable for threading. It then demonstrates how to create threads, how these threads are typically run on multiprocessing systems, and how threads are run using HT Technology.
Designing for Threads
Developers unacquainted with parallel programming are generally comfortable with traditional programming models such as single-threaded declarative programs and object-oriented programming (OOP). In both cases, a program begins at a defined point -- such as main() -- and works through a series of tasks in succession. If the program relies on user interaction, the main processing instrument is a loop in which user events are handled. From each allowed event -- a button click, for example -- an established sequence of actions is performed that ultimately ends with a wait for the next user action.
When designing such programs, developers enjoy a relatively simple programming world because only one thing is happening at any given moment. If program tasks must be scheduled in a specific way, it's because the developer chooses a certain order to the activities, which themselves are designed to flow naturally into one another. At any point in the process, one step generally flows into the next, leading up to a predictable conclusion, based on predetermined parameters -- the job completed -- or user actions.
Moving from this model to parallel programming requires designers to rethink the idea of process flow. Now, they must try to identify which activities can be executed in parallel. To do so, they must begin to see their programs as a series of discrete tasks with specific dependencies between them. The process of breaking programs down into these individual tasks is known as decomposition. Decomposition comes in three flavors: functional, data, and a variant of functional decomposition, called producer/consumer. As you shall see shortly, these different forms of decomposition mirror different types of programming activities.
Decomposing a program by the functions it performs is called "functional decomposition", also called "task-level parallelism". It is one of the most common ways to achieve parallel execution. Using this approach, individual tasks are catalogued. If two of them can run concurrently, they are scheduled to do so by the developer. Running tasks in parallel this way usually requires slight modifications to the individual functions to avoid conflicts and reflect that these tasks are no longer sequential.
If discussing gardening, functional decomposition would suggest that gardeners be assigned tasks based on the nature of the activity: If two gardeners arrived at a client's home, one might mow the lawn while the other weeded. Mowing and weeding are separate functions broken out as such. To accomplish them, the gardeners would make sure to have some coordination between them, so that the weeder is not sitting in the middle of a lawn that needs to be mowed.
In programming terms, a good example of functional decomposition is word processing software, such as Microsoft Word. When a very long document is opened, the user can begin entering text right away. While the user is doing this, document pagination occurs in the background, as can readily be seen by the quickly increasing page count that appears in the status bar. Text entry and pagination are two separate tasks that, in the case of Word, Microsoft has broken out by function and run in parallel. Had it not done this, the user would be obliged to wait for the entire document to be paginated before being able to enter any text. Many of you will recall that this wait was common on early PC word processors.
Producer/consumer (P/C) is so common a form of functional decomposition that it is best examined by itself. Here, the output of one task, the producer, becomes the input to another, the consumer. The important aspects of P/C are that both tasks are performed by different threads and the second one -- the consumer -- cannot start until the producer finishes some portion of its work.
Using the gardening example, one gardener prepares the tools -- puts gas in the mower, cleans the shears, and other similar tasks -- for both gardeners to use. No gardening can occur until this step is mostly finished, at which point the true gardening work can begin. The delay caused by the first task creates a pause for the second task, after which both tasks can continue in parallel. In computer terms, this particular model occurs frequently.
In common programming tasks, P/C occurs in several typical scenarios. For example, programs that must rely on the reading of a file are inherently in a P/C scenario: the results of the file I/O become the input to the next step, which might well be threaded. However, that step cannot begin until the reading is either complete or has progressed sufficiently for other processing to kick off. Another common programming example of P/C is parsing: an input file must be parsed, or analyzed semantically, before the back-end activities, such as code generation in a compiler, can begin.
The P/C model has several interesting dimensions absent in the other decompositions:
- The dependence created between consumer and producer can cause formidable delays if this model is not implemented correctly. A performance-sensitive design seeks to understand the exact nature of the dependence and diminish the delay it imposes. It also aims to avoid situations in which consumer threads are idling while waiting for producer threads.
- In the ideal scenario, the hand-off between producer and consumer is completely clean, as in the example of the file parser. The output is context-independent and the consumer has no need to know anything about the producer. Many times, however, the producer and consumer components do not enjoy such a clean division of labor, and scheduling their interaction requires careful planning.
- If the consumer is finishing up while the producer is completely done, one thread remains idle while other threads are busy working away. This issue violates an important objective of parallel processing, which is to balance loads so that all available threads are kept busy. Because of the logical relationship between these threads, it can be very difficult to keep threads equally occupied in a P/C model. | <urn:uuid:8b7bc43b-6426-4a0e-ab3c-be45d4a71560> | 3.84375 | 1,354 | Knowledge Article | Software Dev. | 34.606902 |
Actinopterygii (ray-finned fishes) > Beloniformes
(Needle fishes) > Exocoetidae
Etymology: Parexocoetus: Greek, para in the side of + Greek, exos = outside + Greek, koite = hole (Ref. 45335).
Environment / Climate / Range
Marine; pelagic-neritic; oceanodromous (Ref. 51243); depth range 0 - 20 m. Tropical; 30°N - 23°S, 20°E - 178°W
Size / Weight / Age
Maturity: Lm ? range ? - 13 cm
Max length : 11.0 cm SL male/unsexed; (Ref. 2797)
Indo-Pacific: widespread from East Africa, including the Red Sea and the Gulf, to southern Japan, Marshall Islands, Fiji, the Arafura Sea (Ref. 9819) and Queensland, Australia. Migrated to eastern Mediterranean through the Suez Canal (Ref. 6523). Presence in Somalia to be confirmed (Ref. 30573). Records from the Atlantic (as Parexocoetus mento atlanticus) are in error.
Found in near-shore surface waters, never spread to open sea (Ref. 9839). Capable of leaping out of the water and gliding above the surface (Ref. 30573).
Parin, N.V., 1996. On the species composition of flying fishes (Exocoetidae) in the West-Central part of tropical Pacific. J. Ichthyol. 36(5):357-364.
IUCN Red List Status (Ref. 90363)
Threat to humans
Fisheries: minor commercial
ReferencesAquacultureAquaculture profileStrainsGeneticsAllele frequenciesHeritabilityDiseasesProcessingMass conversion
Estimates of some properties based on empirical models
Phylogenetic diversity index (Ref. 82805
= 0.6250 [Uniqueness, from 0.5 = low to 2.0 = high].
Bayesian length-weight: a=0.00389 (-0.16711 - 0.17489), b=3.12 (3.03 - 3.21), based on all LWR estimates for this BS (Ref. 93245
Trophic Level (Ref. 69278
): 3.3 ±0.4 se; Based on size and trophs of closest relatives
Resilience (Ref. 69278
): High, minimum population doubling time less than 15 months (Preliminary K or Fecundity.).
Vulnerability (Ref. 59153
): Low vulnerability (10 of 100) . | <urn:uuid:62799c87-e163-4617-8341-d7fed4c81a53> | 2.984375 | 568 | Knowledge Article | Science & Tech. | 63.045 |
This problem was posted by our own Agnishom in another thread.
A triangle has sides of length at most 2, 3 & 4. What is the maximum area the triangle can have?
Let's see if geogebra 4.27 can lend some insight into the problem.
1) Hide the xy axes.
2) Place point A anywhere on the screen.
3) Use the circle with center and radius tool and click on point A and enter a radius of 2.
4) Use the point on object tool to create a point B on the circle's circumference. See the first drawing.
5) Use the circle with center and radius tool and click on point B and enter a radius of 3. A second circle will be created.
6) Use the point on object tool to create a point C on the larger circle's circumference. See the second drawing.
7) Use the polygon tool and click A, B, C, and back to A. A triangle will be created with sides AB = 2 and BC = 3. Move the three vertices around to see that those sides are constant. See fig 3.
You can see on the left the brown algebra pane which gived the sides and the areas of that triangle.
8) Set rounding to 15 decimal places in options. Play with points B and C carefully with your mouse or shift right, left arrows and try get the largest area for poly1 while keeping b < = 4.
It is not too difficult to reach poly1 = 2.999992275497143. if you are lucky you will even get poly1 = 3. No matter how hard you try you will not get an area bigger than 3. Once you are satisfied with your value use the angle tool to measure angle ABC. I got α = 89.86997934032091°. Hence the assumption of 90°, which yields sides of 2,3, √(13), with a maximum area of 3.
What has been accomplished here? For one thing we have a conjecture for the 3rd side and the conjecture that this has to be a right triangle. This helps in looking in the literature for a possible answer based on that. Or might guide us in looking for an answer.
If we are are unable to find the maximum we at least have a good estimate. | <urn:uuid:886100d0-07c2-4ae9-9ff6-96243dc71bb4> | 3.109375 | 483 | Q&A Forum | Science & Tech. | 85.620122 |
Perl Style: Program Perl, Not C/BASIC/Java/Pascal/etc
- `Just because you can do something a particular way doesn't mean
you should do it that way.' --Programming Perl
- If you find yourself writing code that looks like C code, or BASIC, or
Java, or Pascal, you are probably short-changing yourself. You need to
learn to program idiomatic Perl -- which does not mean obfuscatory Perl.
It means Perl in its own idiom: native Perl.
- Fall not into the folly of avoiding certain Perl idioms for fear
that someone who maintains your Perl code won't understand it because
they don't know Perl. This is ridiculous! That person shouldn't be
maintaining a language they don't understand. You don't write your
English so that someone who only speaks French or German can understand
you, or use Latin letters when writing Greek.
Forward to Elegance
Back to Everyone Has an Opinion
Up to index
Copyright © 1998, Tom Christiansen
All rights reserved. | <urn:uuid:4491b615-13ce-4801-bfab-6a3bef7f3674> | 2.6875 | 226 | Knowledge Article | Software Dev. | 61.955298 |
A butterfly is a flying insect of the order Lepidoptera belonging to one of the superfamilies Hesperioidea (the skippers) and Papilionoidea (all other butterflies). Many butterflies have remarkable colors and patterns on their wings. People who study or collect butterflies (or the closely related moths) are called lepidopterists. Butterfly watching is growing in popularity as a hobby.
The four stages in the lifecycle of a butterfly
Unlike many insects, butterflies do not experience a nymph period, but instead go through a pupal stage which lies between the larva and the adult stage (the imago).
- Larva, known as a caterpillar
- Pupa (chrysalis)
- Adult butterfly (imago)
Butterfly eggs consist of a hard-ridged outer layer of shell, called the chorion. This is lined with a thin coating of wax which prevents the egg from drying out before the larva has had time to fully develop. Each egg contains a number of tiny funnel-shaped openings at one end, called micropyles; the purpose of these holes is to allow sperm to enter and fertilize the egg. Butterfly and moth eggs vary greatly in size between species, but they are all either spherical or ovate.
Larvae, or caterpillars, are multi-legged eating machines. They consume plant leaves and spend practically all of their time in search of food. As they mature their skin is shed several times.
When the larva has eaten enough it will form a chrysalis (butterflies do not spin cocoons, moths do.) The larva usually moves to the underside of a leaf. To form a cocoon it spins a silk-like thread around itself. A chrysalis is formed by hardening bodily secretions. A larva completely covered by a cocoon or chrysalis is called a pupa. Inside its protective shell the larva will transform into a butterfly (or moth), a process known as metamorphosis.
The adult, sexually mature stage of the insect is known as the imago. As Lepidoptera, butterflies have four wings that are covered with tiny scale. However, unlike moths, the fore and hindwings are not hooked together, permitting a more graceful flight. A butterfly has six legs. The larva also has six true legs and a number of prolegs. After it emerges from its pupal stage it cannot fly for some time because its wings have not yet unfolded. A newly emerged butterfly needs to spend some time ‘inflating’ its wings with blood and letting them dry, during which time it is extremely vulnerable to predators.
Many species of butterfly are sexually dimorphic. Some butterflies, such as the Monarch butterfly, are migratory.
Butterflies are often confused with moths, but there are a few simple differences between them, including color, habits, and pupating appearance.
Butterflies live primarily on nectar from flowers. Some also derive nourishment from pollen, tree sap, rotting fruit, dung, and dissolved minerals in wet sand or dirt. Butterflies are also pollinators.
Although the butterflies are classified in two superfamilies – Hesperioidea and Papilionoidea – these are sister taxa, so the butterflies collectively are thought to constitute a true clade. Some modern taxonomists place them all in superfamily Papilionoidea, distinguishing the skippers from the other butterflies at the series level only. There is only one family in the Hesperioidea (or series Hesperiiformes), the skipper family Hesperiidae. The families in the Papilionoidea (or Papilioniformes) are:
- Swallowtails and Birdwings, Papilionidae
- Whites or Yellow-Whites, Pieridae
- Blues and Coppers or Gossamer-Winged Butterflies, Lycaenidae
- Metalmark butterflies, Riodinidae
- Snout butterflies, Libytheidae
- Brush-footed butterflies, Nymphalidae
Some older taxonomies recognize additional families, for example Danaidae, Heliconiidae and Satyridae, but modern classifications treat these as subfamilies within the Nymphalidae.
There are between 15,000 and 20,000 species of butterflies worldwide. Some well known species include:
- Small Tortoiseshell, Nymphalis urticae
- Small White, Artogeia rapae
- Green-veined White, Artogeia napi
- Monarch butterfly, Danaus plexippus
- Red Admiral, Vanessa atalanta
- Painted Lady or Cosmopolite, Vanessa cardui
- Peacock, Inachis io
- Xerces Blue, Glaucopsyche xerces
- Gulf Fritillary, Agraulis vanillae
- Black Swallowtail, Papilio polyxenes
- Spicebush Swallowtail, Papilio troilus
- Karner Blue, Lycaeides melissa samuelis (endangered)
- Morpho genus
- Troides genus (birdwings; the largest butterflies)
Butterflies (and their immature stages) have many natural enemies such as:
- Lizards, frogs, and toads
- Praying mantises
Ants will sometimes attack a larva in hordes. However, there are actually some species of ants that keep myrmecophilous (ant loving) butterfly larvae as cattle, taking a larva into their nest, feeding it leaves on one end and milking it for honeydew on the other. This symbiotic relationship can turn to the larvae becoming myrmecophageous (ant-eating). The ants actually tolerate the larvae even while they eat the ant pupae.
Some butterflies have evolved “eye” like markings on their wings, scaring off some birds. Also, since some birds attack the eyes of an animal first, the butterfly has a chance of escaping in the confusion when the bird simply pokes a hole in one of the wings.
An erroneous etymology claims that the word butterfly came from a metathesis of “flutterby”; however, the Old English word was buttorfleoge and a similar word occurs in Dutch, apparently because butterflies were thought to steal milk. | <urn:uuid:015bdd0e-6401-4a84-90b7-77def68529b5> | 3.796875 | 1,336 | Knowledge Article | Science & Tech. | 26.871379 |
Water Thermometer - Sick Science!
Watch the temperature rise with this homemade thermometer
Is it possible to make a thermometer out of water? Absolutely! The best part about our Water Thermometer experiment is that you have all the materials you need in your own home. That's right, you'll be measuring temperature with this amazing homemade tool in no time.
- Glass bottle
- Modeling clay
- Food coloring
- Container of hot water
- Container of cold water
- Heavy glove
- Fill the glass bottle up to the bottom of its neck with cold water.
- Add a few drops of food coloring to the water in the bottle. You pick the color!
- Place a straw (make sure it's long enough) into the bottle. Pack clay around the straw and bottle neck. Make as tight of a seal as possible.
- Now that you've made your thermometer, set the bottom of the bottle into the container of hot water. What happens to the water inside the bottle?
- Make sure you are wearing a heavy glove and remove your water thermometer from the hot water.
- Put the water thermometer into the container of cold water. What happens to the water inside the bottle this time?
- Try experimenting with other water temperatures.
How does it work?
June 8th, 2011
Click the thumbnail below to see the video.
nandini - September 27, 2012
i have never thought that theres a water therometer.by this i came to know so thanks a lot | <urn:uuid:bacfe451-46be-4a30-a5a6-534e929c16e1> | 3.375 | 320 | Tutorial | Science & Tech. | 59.769417 |
Did Earth encounter pieces of an alien visitor Wednesday night? Apparently so! It appears tiny pieces of Comet Hartley 2 may have presented a spectacular and startling sky show across the country. NASA meteor experts had predicted it was a long shot, but the evenings of November 2nd and 3rd might display a meteor shower from dust which puffed off this visiting comet as it passed within twelve million miles of Earth. And indeed, the Center for Astrophysics has collected several sightings of bright meteors called fireballs, which result when comet dust burns up in Earth’s atmosphere.
Helga Cabral in Seascape, California, reported after 9 pm Wednesday night, “I saw a bright white ball and tail, arcing towards the ocean. It was quite beautiful and it looked like it was headed out to sea and so picture perfect it could have been a movie!” Three thousand miles away just north of Boston, Teresa Witham witnessed a similar cosmic event.
“I was in the Revere area about 7:15 last night, driving north on Route 1, when a brilliant object with a tail passed in front of me — very similar in appearance to a shooting star but it appeared much lower to the Earth than a typical shooting star would be. If it weren’t for the fact that I had my daughter with me, I’d begin to believe I’d imagined it.”
Comet Hartley 2 has put on quite a nice show for amateur astronomers over the past few weeks, sporting a vivid green coma or halo around it and a golden auburn tail of dust. NASA’s Deep Impact/EPOXI probe will present dramatic close-up images of the comet when it zooms past the nucleus on November 4th.
When a comet approaches the Sun, it heats up unevenly, throwing off dust, ice and bits of rock. When the Earth encounters some of this space debris, it is seen as a beautiful meteor shower.
“Many people don’t realize that the famous periodic meteor shower in August, the Perseids, is the remains of Comet Swift-Tuttle and the Orionids, appearing in late October, are leftovers from Comet Halley,” said Tim Spahr, Director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA.
So for the next two evenings, we may see more of Comet Hartley 2. And if you have dark skies and a small telescope or binoculars, try to find Comet Hartley 2 itself. It will be near the bright star Procyon in the constellation Canis Minor near Orion the Hunter, which will be high overhead in the early hours before dawn.
- adapted from a news announcement from: Harvard-Smithsonian Center for Astrophysics
Tags: comet Hartley, meteor
Posted in Meteors, Solar System | 20 Comments » | <urn:uuid:4de75d94-748a-4e4f-86a5-204df0d66dda> | 3.046875 | 603 | Personal Blog | Science & Tech. | 49.898435 |
A trend line should always pass through ate least two actual data points on a scatter plot. True or false?.?
I don't even know whether it is multiplication, addition etc. This is something to do with Integers. I am taking Basic College Mathematics.
how to solve algebraic equation using elimination method
I can find the vertex, focus and directrix but I can't find the rest of the points on the graph!
y=-x-4 in coordinate plane
solve the inequality, 2(3x-2) is grater or equail to 22
After a 20% reduction, you purchase a new suit for $276. What was the price of the suit before the reduction? A) First write an equation you can use to answer this question. Use x as your variable...
I just need to know the answer and if there is only one correct answer or multiple ones
Imagine a plane and a cone intersecting to form a parabola. Explain why the plane has to intersect the axis of the cone.
This a math homework problem and i don't understand it.
Find two numbers such that 6 times the first added to 5 times the second equals -9, and 5 times the first added to 8 times the second equals 4.
I'm not sure how to answer this problem so any help on how to solve this problem would be appreciated. Thanks!
write the equation of a hyperbola in standard form whose center is (-2, -4), a focus at (-2, 6), and eccentricity of 5/4.
please show work so i can understand how you solved it. thanks!
Answer this question step by step please. Thank you!
Find the value of 3x+5(x+9)-4x, when x=-5.
how can i simplify this
y = 2x + 8 I know it's going to be above the line and it is going to be dashed, but I don't know how to find the origin. Does it included the origin or does not include the origin?
I dont know know any specifect details. | <urn:uuid:a63bee1e-aa18-4f1d-83ef-31dd71fdfb99> | 2.828125 | 436 | Q&A Forum | Science & Tech. | 78.659155 |
Short Summaries of Articles about Mathematics
in the Popular Press
"Quadramagicology," by Dana Mackenzie. New Scientist, 20/27 December 2003,pages 50-53.
This article discusses magic squares, which are square arrays of numbers inwhich the rows, columns, and diagonals add up to the same number. Althoughmagic squares have been looke upon as fun puzzles rather than real mathematics,Mackenzie says that this has now changed. "[M]athematicians have begun asystematic exploration of the rich vein of magic squares that lies beneaththose found by amateurs," he writes. "Using powerful tools from algebra andgeometry, they can now predict exactly how many magic squares of a given typeare out there."
--- Allyn Jackson | <urn:uuid:5c125b0f-370c-4d32-b026-cc166e339733> | 2.90625 | 160 | Content Listing | Science & Tech. | 35.177576 |
Say I have three unicellular organisms: a eukariote, a bacterium and an archaeon. If I cut off nutrition from them at the same time, how long will it take for them to die? What will their death look like, and do they actually need to die? If so, why?
This is very dependent on the organism within each of the groups you mention. While for the most part, archea are the extremophiles and have the ability to withstand many extreme conditions, nutrient limitation survival greatly varies. I think you could easily find organisms in each group that could withstand nutrient limitation well.
A good example would be yeast, which is a single celled organism you may have actually worked with. If you take laboratory yeast, in their diploid state, and starve them, they will undergo meiosis, and in their spore form, live for a very very long time without nutrients, protected by their ascus (which is actual their dead mother cell).
Yeast can also completely desiccate and still live. When you pick up an active yeast packet for baking, those yeast have not only been starved, but have been completely sucked dry of their water. Yet when you add water back, they live (though a great number of them will die).
I think in general, most single celled organisms have a certain tolerance for low nutrient conditions. This does happen to them a lot. All it means is they slow their cell cycle down, stop dividing, and just undergo a caution period. There is all sorts of signaling in the cells that sense the nutrients, and slow growth based on their conditions. | <urn:uuid:f7122e74-1182-4ace-bb17-188983bafb04> | 3.09375 | 335 | Q&A Forum | Science & Tech. | 58.325588 |
Night 5 Reading:Acceleration
Acceleration can be defined as a change in velocity over a period of time. Usually, we think of this as a change in speed. Remember, velocity is a vector with both a magnitude and a direction. So there are two ways to change the velocity of an object. We can change either the speed or the direction of that speed (or both at the same time!)
Like velocity, acceleration is a vector with a magnitude and a direction. If the direction of the velocity is not changing, then we can express the acceleration as the rate of change of the speed,
Where a is acceleration, v is velocity, and t is time.
Since velocity is the rate of change of position, we could also think of acceleration as the rate of change of the rate of change. Acceleration is how much we speed up (or down) in a given second.
If you were watching a car advertisement, they might tell you that a car can go from 0 to 60 miles per hour in 6 seconds. Thus the units for acceleration might be given as miles/hour/second. Although useful for cars and aircraft, in science we usually express velocity in terms of meters/second. Thus the units for acceleration would be meters/second/second. We can actually simplify this to meters/seconds squared.
Δv = 50.0 m/s
Δt = 20. s
a = ?
In this case, you might note that the time only has two significant figures due to the location of the decimal point (although velocity has three).
t = 4 s
Δv = ?
Notice how in the units, one factor of time (seconds) cancels out, leaving m/s as the units.
Constant Acceleration: When the acceleration is constant we can easily use the above equation to determine the change in velocity. If the acceleration is changing, we would have to use slightly more complex methods to find the change in velocity. Analytically, we could use calculus. Or, using a computer or a calculator we could use any of several approximation algorithms to find the change in velocity, similar to finding the change in position. In the case for a non-constant acceleration, we could even calculate the rate of change of the acceleration, which is called the jerk, as when you sharply tug or jerk a rope.
Circular Motion acceleration. The equation for acceleration for a circular path in the simplest case for non-linear acceleration. This is called an acceleration in a centripetal direction, or centripetal acceleration. We will return to this case when we study circular motion.
Most real-world accelerations are combinations of changes in speed and changes in direction. Another simple acceleration to analyze is when the object is vibrating back and forth. Often, the position of the object will follow a path similar to a sine wave. In this case, the acceleration is also a sine wave, a case we will explore when we get to vibratory motion.
Constant acceleration: graphs
When the acceleration is constant and positive then the a vs t graph will look like this.
Since there is a constant acceleration, the velocity will increase as a linear function with respect to time and will appear like this. Of course, if one were to calculate the slope of the v vs t graph, one would find the acceleration.
As we can see, the velocity is constantly increasing. What this means is that the distance traveled per second is constantly increasing. Likewise, the slope of our position vs time graph is constantly increasing, and will appear like the graph below. In this case the shape of the curve is a parabola, not a line. And the function which describes the graph is not linear but quadratic. Any quadratic term will have a squared term in it.
Recap of average velocity vs instantaneous velocity: Since the velocity is changing, the instantaneous velocity is not the same as the average velocity. We found the average velocity by finding the slope of the line created by two points. Since the velocity is changing, in this case we actually are finding the slope of a chord of this graph. As the chords become smaller we approach the limit for the instantaneous velocity.
At the limit, we no longer have a chord of a finite length. Instead, we take a line which is tangent to the curve, and find the slope of this tangent line.
We will save a presentation of the equations for position under constant acceleration for the next lesson. | <urn:uuid:46bf0e03-c2c8-41eb-9bf6-899d25054903> | 4.375 | 930 | Personal Blog | Science & Tech. | 48.831461 |
|IDL Reference Guide: Procedures and Functions|
The ROUND function rounds the argument to its closest integer.
Result = ROUND(X [, /L64 ] )
Returns the integer closest to its argument. If the input value X is integer type, Result has the same value and type as X. Otherwise, Result is returned as a 32-bit longword integer with the same structure as X.
The value for which the ROUND function is to be evaluated. This value can be any numeric type (integer, floating, or complex). Note that only the real part of a complex argument is rounded and returned.
If set, the result type is 64-bit integer no matter what type the input has. This is useful for situations in which a floating point number contains a value too large to be represented in a 32-bit integer.
This routine is written to make use of IDL's thread pool, which can increase execution speed on systems with multiple CPUs. The values stored in the !CPU system variable control whether IDL uses the thread pool for a given computation. In addition, you can use the thread pool keywords TPOOL_MAX_ELTS, TPOOL_MIN_ELTS, and TPOOL_NOTHREAD to override the defaults established by !CPU for a single invocation of this routine. See Thread Pool Keywords for details.
Print the rounded values of a 2-element vector:
PRINT, ROUND([5.1, 5.9])
Print the result of rounding 3000000000.1, a value that is too large to represent in a 32-bit integer:
PRINT, ROUND(3000000000.1D, /L64) | <urn:uuid:05434eb8-7ee3-4399-9442-e65c40a6428e> | 3.390625 | 355 | Documentation | Software Dev. | 65.564537 |
LOHAFEX was an experiment initiated by the German Federal Ministry of Research and carried out by the German Alfred Wegener Institute (AWI) 2009 to study sea fertilization in the South Atlantic. It was also an Indo-German cooperation project. The word itself is also an acronym and portmanteau word composed from the Indian word for iron, FEX LOHA for "Fertilization EXperiment". LOHAFEX should be a contribution to POGO, the Partnership for Observation of the oceans (P artnership for O bservation of the G lobal O Ceans). AWI in the expedition under the name ANT XXV / 3 is performed. These reports were also published weekly on the website of the Institute.
As part of the experiment, the German research vessel Polarstern deposited 6 tons of iron in the form of ferrous sulfate in an area of 300 square kilometers. It was expected that the iron sulphate would distribute through the upper 15 m of the water layer and trigger algal bloom. A significant part of the carbon dioxide dissolved in sea water would then be bound by the emerging bloom and sink to the ocean floor.
The ship left Cape Town 7 January 2009. The expedition ended after 70 days on 17 March 2009 in Punta Arenas, Chile.
The technique to fertilize the ocean with iron sulphate is controversial, the Federal Environment Ministry called for a halt to the experiment, partly because environmentalists feared damage to marine plants and pets by an artificial algal bloom. Most critics feared long-term effects which would not be detectable durung short-term observation. Other critics feared the entry into large-scale manipulation of ecosystems with these large geo-engineering experiments.
LOHAFEX was not the first experiment of its kind. In 2000 and 2004, comparable amounts of iron sulfate were discharged from the same ship ( EisenEx experiment). 10 to 20 percent of the algal bloom died off and sank to the sea floor. This removed carbon from the atmosphere.
As a side effect, the sinking algae stimulate the growth of zooplankton that feed on them. These in turn are eaten by krill, and these in turn are eaten by fish. Thus, the iron sulfate also contributes to the protection of species at.
- "Alfred-Wegener-Institut für Polar- und Meeresforschung (AWI) ANT-XXV/3". Retrieved 9 August 2012.
- "LOHAFEX über sich selbst". Retrieved 9 August 2012.
- "http://commonsblog.wordpress.com/2009/01/12/polarsternreise-zur-manipulation-der-erde/". Retrieved 9 August 2012.
- "Geo-Engineering in the Southern Ocean" (pdf). Retrieved 9 August 2012.
- "Dem Klima zuliebe das Meer düngen?". Retrieved 9 August 2012. | <urn:uuid:c4375fb6-9ba4-4cfa-a444-bc8763692629> | 3.375 | 622 | Knowledge Article | Science & Tech. | 53.021752 |
A variety of research activities on the organisms in the Ross Dependency was undertaken to determine the biological research potential of the organisms. Most work focused on photoreceptors of different invertebrates and fishes. The studies included work on:
a) Glyptonotus antarcticus: The dorsal and ventral eyes of this big isopod were prefixed, postfixed, dehydrated and embedded for ... transmission electron microscopy (TEM). Additional eyes were prepared for TEM of the inner and outer surfaces. Groups of 4 animals were adapted to 0°C, 5°C and 10°C and their eyes were also prepared for TEM. Another experiment involved painted one eye black and exposing the other to 200 lux for 1 week. Both eyes were analysed with TEM.
b) Orchomenella plebs: Freshly caught amphipods were exposed to bright sunlight for 1, 2 and 3 hours. Their eyes, as well as those of fully dark adapted ones were prepared for TEM. This species can also recover when placed in 10°C for 7h and then returned to 0°C water. Eyes of animals adapted to 5°C and 10°C and those that had recovered afterwards in 0°C were prepared for TEM.
c) The compound eyes of approx 100 facets belonging to a tiny (1-2mm) parasitic isopod from fish and invertebrate hosts were prepared for TEM.
d) Retinae of 3 species of fishes (Trematomus bernacchii, Trematomus brochgrevinkii and Dissostichus mawsoni) were fixed for TEM. The eyes of the Trematomus species were prepared for gas-chromatographical analyses of the fatty acid composition. Observations were carried out on the antifreeze behaviour of D. mawsoni aqueous and vitreous humor.
e) The microfauna and flora of Deep Lake and Skua Lake were studied in culture. Numerous drawings of the microorganisms were prepared.
f) A number of organisms were collected for identification including benthic marine organism from under the 3-5m thick sea ice, marine mite species, skua egg shells, moss samples (from the top of Mt Erebus) and bacteria which were attempted to be cultured from snow samples. | <urn:uuid:4bebf6a6-c7dc-4dcf-9ab0-6a5a461e3182> | 2.921875 | 484 | Academic Writing | Science & Tech. | 46.927975 |
Scarp within Chasma BorealeHiRISE Image PSP_001412_2650
This image is of the north polar layered deposits (PLD) and underlying units exposed along the margins of Chasma Boreale. Chasma Boreale is the largest trough in the north PLD, thought to have formed due to outflow of water from underneath the polar cap, or due to winds blowing off the polar cap, or a combination of both. At the top and left of the image, the bright area with uniform striping is the gently sloping surface of the PLD. In the middle of the image this surface drops off in a steeper scarp, or cliff. At the top of this cliff we see the bright PLD in a side view, or cross-section. From these two perspectives of the PLD it is evident that the PLD are a stack of roughly horizontal layers. The gently sloping top surface cuts through the vertical sequence of layers at a low angle, apparently stretching the layers out horizontally and thus revealing details of the brightness and texture of individual layers. The surface of the PLD on the scarp is also criss-crossed by fine scale fractures. The layers of the PLD are probably composed of differing proportions of ice and dust, believed to be related to the climate conditions at the time they were deposited. In this way, sequences of polar layers are records of past climates on Mars, as ice cores from terrestrial ice sheets hold evidence of past climates on Earth. Further down the scarp in the center of the image the bright layers give way suddenly to a much darker section where a few layers are visible intermittently amongst aprons of dark material. The darkest material, with a smooth surface suggestive of loose grains, is thought to be sandy because similar exposures elsewhere show it to be formed into dunes by the wind. An intermediate-toned material also appears to form aprons draped over layers in the scarp, but its surface contains lobate structures that appear hardened into place and its edges are more abrupt in places, suggesting it may contain some ice or other cementing agent that makes it more competent, or resistent. At the base of the cliff, especially visible on the right side of the image, are several prominent bright layers with regular, rectangular-shaped polygons. Due to similarities in brightness and surface fracturing with the upper PLD, these bottom layers are also likely to be ice rich. The presence of sandy material sandwiched in between the upper PLD and these bottom layers suggests that the climate was once much different from the times during which the icier layers were deposited. The scattered bright and dark points are boulder-sized blocks that are likely pieces of the fractured PLD or other darker layers that have broken off and fallen downhill. At the bottom and right of the image, the floor of Chasma Boreale is dark, with a knobby texture and irregular polygons. Several circular features surrounded by an area that is slightly smoother, lighter, and raised relative to the chasm floor may be impact craters that have been modified after their formation in ice-rich ground.
Image PSP_001412_2650 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 14, 2006. The complete image is centered at 84.7 degrees latitude, 4.0 degrees East longitude. The range to the target site was 320.9 km (200.6 miles). At this distance the image scale ranges from 32.1 cm/pixel (with 1 x 1 binning) to 128.4 cm/pixel (with 4 x 4 binning). The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 12:52 PM and the scene is illuminated from the west with a solar incidence angle of 67 degrees, thus the sun was about 23 degrees above the horizon. At a solar longitude of 135.3 degrees, the season on Mars is Northern Summer.
Images from the High Resolution Imaging Science Experiment and additional information about the Mars Reconnaissance Orbiter are available online at:
For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. | <urn:uuid:f300dcf7-e36c-4a78-bca2-2f141be1d99a> | 3.28125 | 942 | Knowledge Article | Science & Tech. | 46.635651 |
When I saw the tape of Judy K's class I realized that I was part of the problem. I realized that I tended to react with a head nod or a verbal "good" or "what about this...?" to most student comments. What I observed Judy doing was eliciting all the possible student responses before she made any comment other than, "Any more ideas?" It was clear that the expectation (culture) in her classroom was that all student ideas would be put on the table before any were discussed. It was powerful. As soon as I started to do the same thing, the discussion dynamic shifted.
As is apparent from our lesson plans and implementations, there are many ways of presenting this problem. Following are highlights from our reflections that focus on important moments in teaching the lesson.
In Resnick's problem-solving sessions (1988), children frequently failed because
they lacked sufficient prior knowledge of relevant mathematical content. We have
found that in order for this cylinder lesson to be effective, introducing it at
an appropriate point in the curriculum is critical. Unfortunately, because
of the constraints of our project, some of us had to teach the lesson at an
artificial point in the curriculum, without having time to cover all the
needed prerequisites. Depending on the level, these mathematical prerequisites
can be introduced in prior lessons or activities. In these clips,
Susan Boone elicits her students' prior knowledge
through questioning [view clip],
and Susan Stein asks her students to write down what
they know about circles and related concepts
[view clip] and then has the
class review by sharing what they have written.
In our workshop we tackled the problem of maximizing the volume of the cylinders over a family of rectangles having constant perimeter. Most of us, however, felt that it was best to defer the study of constant perimeter, starting instead with constant area and two-dimensional sheets of paper, and hence working with the constant lateral surface of three-dimensional cylinders.
In general, we began by showing students the two pieces of paper, rolling them from different sides to form a tall, narrow cylinder and a short, stout cylinder, and posing a variation of the following question: "Which cylinder would you predict will hold more, and why?" Student predictions are important, since they engage students more fully in the problem, give them a stake in what happens, and make them more likely to care about the results.
Again, this lesson lends itself well to moments that stimulate conversation. Predictions offer one such moment, and we found it particularly important in discussing these hypotheses to stop and let students verbalize their thinking. Most students thought that the two cylinders would have the same volume, but regardless of the prediction, the reasoning behind it provided a powerful connection to the remainder of the lesson. Some students struggled to come up with explanations for their hypotheses, but it is exactly this struggle that advances their mathematical thinking (Stigler & Hiebert, 1998) [view clip].
Sharing the reasoning behind students' predictions created a rich climate for
mathematical discussion in which every explanation could be valued. Susan Boone
reassured her students that no matter what prediction and reasoning they came up
with, "you can't be wrong" [view clip].
At this stage in an inquiry, the key is for students to be able to form opinions
about the problem based on their reasoning and prior knowledge, as depicted in this
clip from Susan Stein's class [view clip].
Art Mabbott used this moment in the lesson to paraphrase a student's prediction,
providing the mathematical term "wider diameter."
Some teachers chose to ask students to write out their thoughts and explanations. This can help students to be more reflective and to create more coherent reasoning. In our experience, students felt more confident in explaining their results with the entire group if they first shared them with their own team members.
Even after the demonstration, some students were still baffled by the outcome, especially if they had originally predicted the cylinders would have the same volume. Such surprise and perplexity are a sign of readiness to grow, and provide the kind of discrepancy that can focus a discussion (Atkins, 1999). During such a discussion, teachers can assess students' learning, and students have an opportunity to use their mathematical vocabulary to construct complex arguments.
Other students were intrigued by the result, and generated other questions: "Why is this happening?" "If we use the same lateral surface area, can we make other cylinders that will follow the same pattern?" "Is there an upper limit to the volume -- a biggest volume?" "How do we know?" Students can be led to formulate such questions by making physical models of several more cylinders with the same constant lateral surface area, and conducting the experiment with these new models, as Jon Basden illustrates [view clip]. In addition, building the family of physical models -- the original two cylinders and at least two more sets -- can give students a tactile experience, letting them see and feel the connections among the dimensions of the rectangles, the sizes of the cylinders, and the cylinder volumes. In cutting the original paper in different places to make cylinders of different sizes, students grasp the notion that the area of the paper is kept constant the entire time [view clip]. Ideally students will ask how to generalize the problem to other cylinders, experiencing ownership and creating a powerful motivation to pursue the problem further, although the teacher often reformulates it to spur the next phase of investigation.
Most students organized their data by making a chart. They chose several values for length and width, in each case keeping the surface area of the paper, and hence the lateral surface area of the cylinders, constant. The next step involved calculating the volume for the different numbers created in the chart. When Cynthia Lanius presented this problem at our first workshop, we responded to this part of the problem in ways that every teacher hopes to see in the classroom: almost all of us spontaneously picked up a tool of choice to determine which of the cylinders would have the greatest volume. One of us chose a drawing tool and started making visual models so as to "see" the problem better. Others pulled out graphing calculators to observe the behavior of the function. Still others began entering data into spreadsheets to generate the graphs, or constructed the problem using the Geometer's Sketchpad. Annie Fetter created two sketches that connect the changing rectangle dimensions to the graphs of the respective volumes. Much discussion ensued, with people moving back and forth among a variety of tools and problem-solving methods.
At this stage of the lesson, technology can help with the number-crunching, creating more time for discourse in the classroom (Goldenberg, 1996), as for example in Art Mabbott's classroom.
Students might use a graphing calculator to create the chart, enter formulas to find the needed values, and graph the numbers, as in Susan Boone's class. Other tools and software, such as spreadsheets or the Geometer's Sketchpad, may be substituted if they are available.
Finally, the interpretation of the graphs and the explanation of the behavior observed offered other important opportunities for discourse. In Judith Koenig's class, connecting the graphs and the problem helped students solidify their knowledge and make connections among mathematical ideas [view clip]. Art Mabbott ended his class by reviewing the questions the class was investigating [view clip].
A version of this cylinder problem was showcased as the Math Forum's
October 25, 1999 Middle School
Problem of the Week. | <urn:uuid:e9d16233-8674-4076-94aa-ad4aea5dfa47> | 3.453125 | 1,539 | Knowledge Article | Science & Tech. | 39.383421 |
Definition We say that the sequence has finitely many non zero terms iff there exists such that for all .
This is just what all mathematicians interpret with the expression the sequence has finitely many non zero terms.
Question: Has the zero sequence finitely many non zero elements?. You are going to say yes.
I have a sequence which has (only) three non-zero terms. Can the sequence be 0? No
I have a sequence which has no terms* which aren't zero. The sequence could be 0, but nothing else.
I have a sequence which has only no terms which aren't zero. The sequence has to be zero.
So W is a subspace because it contains only 0.
* a zero number of non-zero terms. zero is a finite number. Reference Plato | <urn:uuid:6e8aab4e-57f4-4b45-9f9d-efbd1d260c68> | 2.890625 | 168 | Q&A Forum | Science & Tech. | 64.885733 |
Use the information to describe these marbles. What colours must be
on marbles that sparkle when rolling but are dark inside?
This problem looks at how one example of your choice can show something about the general structure of multiplication.
This ladybird is taking a walk round a triangle. Can you see how much he has turned when he gets back to where he started?
More than $30$ solutions were sent in but the activity had asked for some kind of proof and many solutions unfortunately consisted of examples of numbers only, so here are the ones that said a bit more.
Firstly Amrit from Newton Farm Nursery, Infant and Junior School in the United Kingdom who wrote;
Every odd number can be written in the form $2a + 1$, so let the two odd numbers be $2a + 1$ and $2b + 1$. Thus their sum is $2(a + b + 1)$. As every even number can be written in the form $2n$, the sum of two odd numbers is always even.
From James from St. Johns School in Northwood, England we had;
They always add up to an even number because if you add together the even numbers that are one less than each number you'll have an even number. Then if you add together the two that are left you get an even number. If you do this with three odd numbers it would give you an odd number because you'll have three left to add together. If you add up an even number of odd numbers you get an even
number but if you have an odd number of odd numbers you get an odd number.
From Madison at Norwayne School in the USA we had:
Any odd number always ends up in pairs of two when added together. Like if you take $3$ and $9$ they end up in pairs of two. Or if you take $5$ and $9$ they end up in pairs of two. The reason for that is if you add any odd number with a other odd number then the sum is even. So you can split the sum up into to even group.
From Peter at the British International School in Istanbul in Turkey we were sent:
An odd number actually is an "even number plus $1$" (or minus $1$). So if you add two odd numbers. Both "$1$"s from both numbers togeher make a "$2$", which is an even number; and the remaining part of the both numbers were even anyway, so the total is always even. This is best shown by the picture of Abdul with the orange and green coloured squares.
Christopher from Lyngby/Lundtofte
in Denmark sent in some good material but unfortunately I could not open open the file. Thanks to all of you who submitted solutions. | <urn:uuid:9c7ce040-be65-46e8-bc06-e36264836775> | 3.515625 | 580 | Q&A Forum | Science & Tech. | 68.625776 |
How do wood decomposition relate to other traits in the tree? Answered by Benjamin G. Jackson and co-workers in the Early View paper “Are functional traits and litter decomposability coordinated across leaves, twigs, and wood? A test using temperate rainforest tree species”. Here’s Benjamin’s short summary and his pedagogic figure showing the results:
Dead wood represents an important pool of carbon and nutrients entering the decomposer subsystem in forested ecosystems. However, our understanding the factors regulating wood decomposition remain poorly characterized. In our study we ask two main questions:
- Do tree species with leaves that decompose rapidly also have wood that decomposes rapidly?
- Do the same functional traits that control leaf litter decomposition control the decomposition of wood?
We addressed these questions by comparing how traits and litter decomposition vary across 27 co-occurring tree species from temperate rain forests in New Zealand. For each tree species, we quantified the functional traits of their green leaves and leaf, twig and wood litter and then decomposed the three litter types under controlled conditions. Below we show how the main findings of our study fit into the broader picture emerging from recent research into plant functional traits and litter decomposition. | <urn:uuid:5e66ec2b-44b2-40f2-8b06-9967324228fc> | 3.140625 | 259 | Academic Writing | Science & Tech. | 32.556839 |
There’s a little bit of buzz burbling around over Al Gore’s scientific goof during a Conan O’Brien interview. Discussing geothermal energy, he said the following:
It definitely is, and it’s a relatively new one. People think about geothermal energy — when they think about it at all — in terms of the hot water bubbling up in some places, but two kilometers or so down in most places there are these incredibly hot rocks, ’cause the interior of the earth is extremely hot, several million degrees, and the crust of the earth is hot …
Of course the interior of the earth is extremely hot, but not that hot. It’s several thousand degrees rather than several million. If the earth were several million degrees it would be a rapidly diffusing cloud of metallic vapor. Even the center of the sun is only perhaps 13 million degrees C.
But I’ll let him slide; pretty much everyone blanks out from time to time. And it gives us a chance to do a little thinking about just how much thermal energy is in the earth.
First of all, just because something is hot doesn’t mean you can squeeze energy out of it. You can only squeeze energy out of temperature gradients – you need something hot and something cold. This is why we can’t just set up a temperature-to-energy machine in the desert and have free energy. In your car, for instance, you need both the heat of the burning gasoline and the much cooler ambient temperature from the outside air via your radiator to turn the hot gasoline vapors into forward progress. Power plants frequently have large cooling towers for that very reason. It’s not the energy of the hot substance, it’s the process of moving that heat to a cooler place that creates useful work. Think of it in the same way as water flowing downhill can turn a paddlewheel – it won’t work unless the water starts off high and ends up low.
But that’s not a problem here. The interior of the earth is hot and the exterior is much colder. The difference in temperature is such that the efficiency of heat-to-work conversion could be near 100% in theory, though in practice it would be much lower. And we’re not likely to run out of geothermal heat any time soon. As a slightly wild Fermi calculation, assume that the earth is uniformly iron at 3000 C. The specific heat of liquid iron is about 611 J/kg K, so cooling the earth to room temperature this yields about 1.8 million joules of energy per kilogram. Multiply by the mass of the earth, and the total energy content might be in the neighborhood of 10^31 joules. The total energy consumption of the world’s human population is in the vicinity of 5e20 joules per year.
Divide out, the earth’s geothermal energy could support that consumption rate for about 21 billion years. We’re not likely to use it up.
So why isn’t it in widespread use? After all, every nation has domestic access to it – all you have to do is drill straight down. The main problem is that the temperature really doesn’t start getting ramped up until dozens of miles down. Drilling a hole that deep and pumping water (or whatever) down and up is technically unfeasible. Geothermal is at its best at those places which are close to geological activity that brings the heat closer to the surface. Volcanic and other geologically active locations often do very well with geothermal power. Iceland in particular produces vast quantities of usable energy from the internal heat of the earth. Most other places are much farther from the hot regions of the earth’s interior and geothermal is correspondingly much more difficult to get.
Sadly Al Gore’s hopes for geothermal as a major clean energy technology are probably futile until deep drilling develops into a much more mature form. It would be nice if that happened; the energy to be tapped is pretty close to inexhaustible. | <urn:uuid:b0db3486-b10f-4d46-a919-e2a1b4eece48> | 3.09375 | 855 | Personal Blog | Science & Tech. | 55.69625 |
Scientists say a modification to the design of lithium-ion batteries could allow batteries that can charge and discharge in a matter of seconds. Writing in the journal Nature, the team from MIT describe modifying the surface of a sample of lithium iron phosphate to improve the mobility of the lithium ions in the material. Before the processing step, a battery made from one sample of the lithium iron phosphate took six minutes to charge. After processing, batteries using the material were able to charge in under twenty seconds.
Fast-charging and discharging batteries could be of use in a variety of applications, from portable electronics to advanced cars. We'll talk about the work, and how soon it might be able to find its way into consumer products.
Produced by Charles Bergquist, Director and Contributing Producer | <urn:uuid:5a63e6fd-e612-4829-bef4-e49183e924ad> | 3.46875 | 157 | Truncated | Science & Tech. | 34.837269 |
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migration of marine organisms
In coastal waters many larger invertebrates (e.g., mysids, amphipods, and polychaete worms) leave the cover of algae and sediments to migrate into the water column at night. It is thought that these animals disperse to different habitats or find mates by swimming when visual predators find it hard to see them. In some cases only one sex will emerge at night, and often that sex is...
The most productive waters of the world are in regions of upwelling. Upwelling in coastal waters brings nutrients toward the surface. Phytoplankton reproduce rapidly in these conditions, and grazing zooplankton also multiply and provide abundant food supplies for nekton. Some of the world’s richest fisheries are found in regions of upwelling—for example, the temperate waters off Peru and...
What made you want to look up "coastal ecosystem"? Please share what surprised you most... | <urn:uuid:616e5b90-d95a-4a67-ab75-47573cd10497> | 3.53125 | 237 | Truncated | Science & Tech. | 48.732016 |
These two images show atmospheric soundings taken on February 13, 2007 at Wilmington, Ohio, showing measurements of temperature, dewpoint and wind from the surface to several kilometers up in the atmosphere. We will focus on the red line, which shows the atmospheric temperature profile. Both graphs show the freezing line highlighted in yellow. Notice that at 7 am (on the left), almost the entire temperature profile is below freezing, including at the surface. The exception is about 1.5 kilometers off the surface, where there is a very small portion of the atmosphere is above freezing. At this time, snowflakes falling into this small layer did not have time to melt, and continued falling to the surface as snow. 12 hours later (on the right), a much thicker portion of the atmosphere has warmed above freezing. This allowed for total melting of snowflakes as they fell into this layer. The subfreezing portion of the atmosphere below this warm layer was not deep enough to cause the liquid drops to refreeze, and precipitation fell as rain instead of sleet. Since the surface itself was below freezing, the rain instantly froze when it hit solid objects, resulting in ice accumulation across much of southwest and central Ohio. You may have noticed that the sounding on the right stops about 4 km off the surface.. This is because ice accumulation on the weather balloon forced it down. | <urn:uuid:45f6d70e-3c4c-4e9a-adb3-f8229fbd1edf> | 3.625 | 275 | Knowledge Article | Science & Tech. | 47.423846 |
Uh, what do a and b represent here? Vectors, you say? Does that mean the same thing as "line segments?"
A Vector is a line segment where the first endpoint is in the origin (0, 0). This means that a Vector only represent the direction and length of a line. So a and b represents the direction and length of the two line segments.
what does "dot" mean?
dot stands for dot product, also called scalar product. Is one of two ways you can multiply vectors. Is defined as "the product of two vectors to form a scalar, whose value is the product of the magnitudes of the vectors and the cosine of the angle between them"
And what does "|a|" mean? From context, I assume it represents a "normalized" vector, but I don't know what that is. You show me the calculations for normalization later on in your post, but I have no idea what you're doing or why.
|a| means the length of vector a. Let's look at the formula:
a dot b = |a||b|cos angle
we wan't to solve this to get angle:
cos(angle) = (a dot b) / (|a| |b|)
Normalizing a vector means making the length of the vector equal 1. This makes |a| |b| become 1*1. So if a and b is normalized the formula becomes:
cos(angle) = (a dot b)/(1 * 1)
cos(angle) = (a dot b)
finally to solve the equation:
angle = Math.acos(a dot b).
(a dot b) returns a single value not a vector.
The Vectors are normalized by dividing x and y with the length of the Vector.
"Subtract x,y,z?" Hah? It looks to me like A and B are points, here, since they're derived by subtracting one point from another, but I'm not sure how you do that. Subtract A1.x from A2.x and A1.y from A2.y?
Yes, subtracting the points. So
C = B - A
C.x = B.x - A.x
C.y = B.y - A.y
Wich makes C a Vector. Because we have moved the line segment (A, B) so that it A starts in origo (0, 0).
What is this "z" I keep hearing about?
That is the third dimension
I was not sure if you used 2d or 3d lines. The algorithm is identical.
What does "/=" do?
This is java code. "A.x /= ALength" is the same as A.x = A.x / ALength". It's just a little less code.
Finally, exactly what angle does this calculation produce?
Given the lines A and B represented by the enpoints (A1, A2) and (B1, B2). This calculation gives you the angle between the lines in the range 0 throug pi. The order of the endpoints matter because it defines the direction of the Vectors. The lines do not have to intersect. You can think of it as the lines are moved to the intersection point of the rays (infinite lines not segments), where the calculations is done.
It gives you the absolute angle of the two vectors A and B. Absolute angle means there are two solutions. The second solution is (2*PI-angle). To find out wich to use you can use the "cross-product"
If you want understand it better you can read up (google) on vector math. I found this when I searched for "angle between lines": http://www.netcomuk.co.uk/~jenolive/vect14.html | <urn:uuid:48ea43da-22ee-44f7-81bf-e3a24219f57f> | 4 | 828 | Comment Section | Software Dev. | 84.258873 |
There is a fertilizer that makes plants grow fast. When you apply this fertilizer, the plant will increase its height by one-half on the first day. On the second day its height increases by one-third of its height of the previous day. On the third day its height increases by one-fourth of its height of the previous day, and so on. How many days does it take to grow to 100 times its original height?
[Problem submitted by Juergen Pahl, LACC Professor of Mathematics.]
Solution for Problem 4:
Let = original height. Then
after one day the height is
after two days the height is
after three days the height is
after four days the height is , etc.
Every day the plant grows by a fixed amount of one half of its original size. Therefore,
after days its height is . | <urn:uuid:97e9c61e-7f13-49a5-b56e-4050311cdaa5> | 3.390625 | 176 | Tutorial | Science & Tech. | 73.26707 |
Fun Demo, But. . .
Thu Jan 22 09:53:13 GMT 2009 by Robin
If this is about charges on electrodes on the boat, then why is there a copper sheet at the bottom of the tank and why is there no visible connection from the electrodes to a external source - they just seem to be connected together?
The Experiment Is Flawed
Sat Nov 28 21:43:20 GMT 2009 by Wai Wong
If meniscus propulsion is possible, then one can made a perpetual motion boat using hydrophilic material at the back and hydrophobic material at the front. The motion of the boat must have been caused by the externally applied electric field.
For detailed analysis, see my post at http://www.physicsforums.com/showthread.php?p=2463599#post2463599
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support. | <urn:uuid:967c5a22-6e67-4466-96ac-291096d68137> | 2.875 | 227 | Comment Section | Science & Tech. | 69.753064 |
Researchers at Wake Forest University's Center of Nanotechnology and Molecular Materials are working with some interesting stuff. They have developed a cloth-like material made from carbon nanotubes that has thermo-electric properties.
Thermoelectric devices (TEDs) have been around since the 19th century. A TED is created when two dissimilar metals are placed in contact and heated. A potential is developed across the junction and associated wires, and current flows from one metal to the other and through a connected load. This effect and the related cooling effect was discovered and analyzed by the French physicist Jean Charles Athanase Peltier and the German physicist Thomas Johann Seebeck. A TED will work the other way: If a current is forced through the junction, one side gets hotter and the other side gets colder. If you stack up plates of dissimilar materials, you can make a small "heat pump" and cool the CPU in your overheating laptop computer.
Materials used for simple TEDs -- like the one in your gas water heater that keeps the valve open as long as the pilot flame remains lit -- are made from inexpensive materials like iron and constantan. The Seebeck constant for an iron-constantan junction is about 55uV/deg-C. For the heat pump version, bismuth and telluride works pretty well, but it's a lot more expensive.
Apply electrical energy, and heat gets pumped from top to bottom.
Apply a temperature differential (hotter on the top), and you get a current flow.
At Wake Forest, they've got a type of TED made of carbon nanotubes and plastic fibers that responds to a temperature differential. Since it's small and can be made inexpensively, the hope is that they can make a thermopile that will produce enough power to be practical. They plan to turn what they've developed in the lab into useful, manufacturable products that could recover waste heat in cars and trucks and produce electricity in usable quantities. Or use your body heat to recharge your cellphone battery. Also you could have clothing that keeps you warmer -- or cooler -- than the ambient temperature as the need dictates. And, of course, there's heating and cooling of buildings.
The research appears in the current issue of Nano Letters, titled "Multilayered Carbon Nanotube/Polymer Composite Based Thermoelectric Fabrics." Wake Forest is in talks with investors to produce its Power Felt product commercially. | <urn:uuid:f46d897d-8191-41bf-bec9-ab2fe0919f97> | 3.71875 | 504 | Knowledge Article | Science & Tech. | 39.340977 |
Revista Brasileira de Ensino de Física
Print version ISSN 1806-1117
MARTINS, Fernando Ramos; PEREIRA, Enio Bueno and ECHER, Mariza Pereira de Souza. Solar energy resources assesment using geostationary satellites in Brazil: Swera Project. Rev. Bras. Ensino Fís. [online]. 2004, vol.26, n.2, pp. 145-159. ISSN 1806-1117. http://dx.doi.org/10.1590/S0102-47442004000200010.
Solar radiation plays a chief role in many human activities like agriculture, architecture, energy planning and policies, etc. It constitutes a clean and renewable source of energy. For better knowledge of the availability of this source of energy, computational models can be used to obtain numeric solution of radiative transfer equations and to estimate the energy fluxes in the Earth's atmosphere. This work reveals what is behind the satellite models and their use to derive the surface solar radiation, having the BRASIL-SR model as a case example. The BRASIL-SR model is currently being applied to map the solar energy potential for Latin America within the SWERA project (Solar and Wind Energy Resource Assessment). The Global Environment Facility (GEF) through a United Nations Environment Program grant supports this project.
Keywords : solar energy; radiative transfer; aerosols; atmosphere; SWERA project. | <urn:uuid:2295ac5e-526e-4360-bdfc-dbe7e6cdb6f6> | 2.953125 | 306 | Academic Writing | Science & Tech. | 41.318182 |
The emergence of nanotechnology is likely to have a significant impact on drug delivery sector, affecting just about every route of administration from oral to injectable. The illustration at left is created for USC's alumni magazine to describe researchers work on nanotechnology drug delivery systems.
The illustration depicts a theoretical, stable, helical nanotube structure, which is analogous to that seen in crystal growth affected by screw dislocations. The structure is composed of 5, 6 and 7 membered-rings. Carbon rings with 5 members are shown in red, 6 in grey and seven in yellow. There is a passing resemblance to the spiral structure of DNA (but a single helix, obviously). Also referred to as "helicoidal graphite".
Nanotube powder is incredibly light and fluffy! This sample is a pile about half an inch wide the way it's stacked in the photo, but it weighs only about 7mg (0.007 grams). A full liter of this stuff would weight only about 25 grams, 40 times less dense than water.
Antibodies are proteins that are generated by the immune system, specifically the white blood cells. They circulate in the blood and attach to foreign proteins called antigens in order to destroy or neutralize them.Monoclonal antibodies are laboratory produced substances that can locate and bind to specific molecules.
Nanoporous materials consist of a regular organic or inorganic framework supporting a regular, porous structure. Pores are by definition roughly in the nanometer range. This is an artistic representation of water molecules in nanoporous material. | <urn:uuid:e1739ebc-433d-4514-817a-5a23fd2d4a48> | 2.765625 | 320 | Knowledge Article | Science & Tech. | 33.331975 |
Chandra observations of merging galaxies
The two images shown above of the early merger Arp 270 (where the galaxy disks are still very distinct) are of approximately equal size. Cool (less than 1 million degree) diffuse gaseous emission is seen associated with the two galaxy disks and several point sources of varying hardness (temperature) are seen scattered within the galaxies. Of great and novel interest are the hard point sources seen where the disks collide. A new idea that is being considered is that they may be due to strong star-formation as the two gaseous disks rotate through each other.
The Mice (Arp 242), so-called because of their distinctive tails, are shown above. The X-ray image is taken from an area far smaller than the optical image, such that the two main X-ray features are from the two galaxy nuclei. The southern nucleus appears harder in X-rays than the northern, and further emission is seen from within the northern tail. The northern galaxy also shows what appears to be a small bipolar X-ray outflow - a great rarity in such a violently evolving classic merger system.
Mkn 266 above consists of two galaxies about to merge (the two nuclei can just be distinguished in the optical image). The Chandra image resolves the two nuclei, with the northern nucleus appearing significantly harder. Interestingly, very soft, diffuse gaseous emission is seen to the north and to the east of the system - thought to be due to a stronger and more evolved and distorted outflow than the type seen in e.g. the Mice. | <urn:uuid:61e47748-6665-4728-b1d4-3aedbe5dc1b4> | 3.3125 | 323 | Knowledge Article | Science & Tech. | 49.30714 |
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The Whitewater-Baldy fire is the largest wildfire in New Mexico’s history and has charred more than 465 square miles of the Gila National Forest since it started back on May 16, 2012 after several lightning strikes in the area. This wildfire produced so much smoke that it was visible even at night to the astronaut photographers on the International Space Station. This image was taken on June 2, 2012 by the crew of Expedition 31 on the ISS, with a Nikon D3S digital camera. A Russian spacecraft docked to the station is visible on the left side of the image.
Credit: NASA Earth Observatory website. | <urn:uuid:dfaeffa0-225e-4d39-a5e9-3667afd30a65> | 2.78125 | 147 | Truncated | Science & Tech. | 47.92947 |
Hide and seek in a warming climate
How are different animal species adapting to a warmer future?
Much of the world’s biodiversity faces an uncertain future as global warming continues across the Earth’s surface.
The scale and pace of the threat posed by a warming climate has alarmed many scientists, leading them to search for areas that may be least affected by having unusual or stable climates. Scientists reason that such areas could provide somewhere for species to expand and contract their populations over long periods or offer shelter from more extreme conditions. They have been termed ‘microrefugia’ but are also known as ‘cryptic refugia’ because of the difficulty in observing them within a landscape.
Before we can identify refugia, we first need to define them in an ecologically meaningful way. Scientists have known for years that refugia exist as patches in variable (heterogeneous) landscapes, but until recently our definitions of microrefugia have lacked precision or were poorly characterised. To address these shortcomings, we have been conducting detailed and intensive field studies over the last three years monitoring the microclimate at a range of sites in the greater Hunter region west of Newcastle.
Every six months, we set off from Sydney to collect data from a total of 150 climate loggers that automatically record hourly temperature and humidity readings. Each field trip takes around a week. The small, button-sized climate loggers have been placed in a variety of sites including rainforest gullies; steep slopes having different aspects; exposed rocky escarpments and even sand dunes. So far, we’ve amassed over six million observations.
Combining these data with detailed information about elevation and the local topographic features that influence temperature has produced a technique that can be widely used to quantify and locate potential microrefugia in a landscape. In short, the technique captures extreme conditions (either very hot or very cool), the degree of stability in these conditions, and how distinct these conditions are from the climatic conditions in the surrounding landscape.
To test and validate the technique, we successfully used it to predict the location of known communities considered to occupy refugia, such as rainforests that have progressively contracted in distribution over the last 2.5 million years, and alpine grasslands that have contracted over the last 15,000 years. So we know the technique works, but can it be applied more widely?
The vast scale of Australian landscapes complicates the incorporation of microrefugia into adaptation plans for future climate change. Indeed, some Australian land management agencies are responsible for land areas larger than certain European countries. This is where computer modelling plays a valuable role. In the past, complex global climate models (GCMs) have been used to identify refugia. A limitation is that many GCMs are based on cells measuring tens to hundreds of kilometres. We now know that temperatures vary at scales of less than one kilometre. In effect, these coarse-scale models can define features that are more correctly termed ‘macrorefugia’, and they certainly have a role in planning for climate change effects.
But another shortcoming is that GCMs fail to accurately estimate surface climate conditions because they are too coarse to take into account the very terrain features that help to decouple upper atmospheric conditions from boundary layer effects. This is a significant weakness because it is the surface climate that most organisms experience and that directly affects their survival: germinating seeds, tender saplings and the majority of terrestrial invertebrates and ground-dwelling vertebrates – all are at the mercy of near-surface temperatures.
Further, GCMs are based on temperature, more specifically ‘average temperature’. This measure has long been held to be important in understanding the distributions of species and in turn their responses to future changes in climate.
Our studies, however, show that it is the extremes and the intervening periods of stability that are more significant in a biologically or ecological sense. We hope that our work will lead to a paradigm shift in which the roles of temperature stability and isolation, rather than long-term averages, are properly considered in understanding ecological communities.
To the future
To test our hypotheses about the roles of temperature extremes and stability, our work at the Museum continues under an ARC-funded project partnered with the University of Technology, Sydney, University of NSW, NSW Office of Water and the Central West Catchment Management Authority. With PhD students, we are planning to conduct intensive biodiversity surveys across the full range of conditions found in the NSW Central West and supplement it with data from collections databases held in museums. The study will include surveys of deep rainforest gullies, exposed mountain ridges and steep rocky slopes.
Some of the questions to be answered include: are microrefugia adequately represented in our reserve network? does climate stability act to stabilise a community? and, are microrefugia more likely to support endemic species? If we are to meet the very real threat to biodiversity posed by climate change, we must work closely with land management authorities to identify microrefugia – not all of which will be represented within existing conservation reserves.
We might not be able to stop the inexorable creep of global warming, but perhaps we can help slow the loss of species through better management of refugia.
Dr John Gollan Research Associate & Dr Mick Ashcroft Spatial Analyst
MB Ashcroft, JR Gollan, DI Warton & D Ramp, 2012. A novel approach to quantify and locate potential microrefugia using topoclimate, climate stability, and isolation from the matrix. Global Change Biology, online 2 March 2012. doi: 10.1111/j.1365- 2486.2012.02661.x
Brendan Atkins , Publications Coordinator | <urn:uuid:f605a7ba-bf66-47e0-aa6c-fbc1d534e41d> | 4.09375 | 1,179 | Academic Writing | Science & Tech. | 24.27234 |
That's a compound line - it's running two commands at once through use of the backticks "`".
Like order of operations - the script will execute what's in the backticks first, and then send its output to the containing statement.
So first it executes
echo $file | sed 's/DIR1/DIR2/'
which is a non-elegant way to substitute all the occurances of "DIR1" in the $file (path) with "DIR2". In this case, DIR1 and DIR2 would be replaced with your source and target root folders.
The output of that statement is the modified file path to point to DIR2/path instead of DIR1/path, so the subsequent statement becomes:
cp DIR1/path DIR2/path
The end result is that a file from the source directory that was found by your 'find' command will be copied to the target directory in the same location. Here's an example of a "real" file as it's transformed by this script:
# we want to syncronize this file: /source/my/dir/testfile to /dest/my/dir/testfile
# so we'll change the script to look like this:
for file in `find /source/* -mtime 0 -name '*' -type f`; do
cp $file `echo $file | sed 's/source/dest/'`
The output of this program will be:
indicating that it copied that file (though it doesn't indicate where to) -- this behavior can easily be modified.
The end result is now you have a copy of the /source/my/dir/testfile in /dest/my/dir/.
So, I'll modify this script to be a little more verbose and a little more parameterized...
# Script to synchronize files modified today from $SRC to $DEST as
# specified by the first and second command-line parameters
SRC = $1
DEST = $2
echo Synchronizing $SRC to $DEST...
for file in `find $SRC/* -mtime 0 -name '*' -type f`; do
dfile = `echo $file | sed 's/$SRC/$DEST/'`
echo copying $file to $dfile
cp $file $dfile
echo Synchronization complete.
Now you can call the program thusly (saved as bsync.sh) using the previous example:
brion> sh bsync.sh /source /dest
Synchronizing /source to /dest...
copying /source/my/dir/testfile to /dest/my/dir/testfile
sed is a Stream EDitor that permits you to, among other things, substitute text in a stream with other text -- in this case, the $SRC with the $DEST directory names in the source file path.
Does that help? | <urn:uuid:a4fde5bd-8775-456b-8171-acc0f2bea5d4> | 3.171875 | 638 | Comment Section | Software Dev. | 65.662321 |
The tornado damage inflicted on Tuscaloosa on April 27, 2011, was just one part of a tornado track roughly 80.3 miles (129.2 kilometers) long and up to 1.5 miles (2.4 kilometers) wide. On May 4, 2011, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite observed another segment of the tornado track, closer to Birmingham, Alabama.
ASTER combines infrared, red, and green wavelengths of light to make false-color images that distinguish between water and land. Water is blue. Buildings and paved surfaces are blue-gray. Vegetation is red. The tornado track appears as a beige stripe running diagonally through this image.
On May 5, the National Oceanic and Atmospheric Administration (NOAA) National Weather Service issued updated information on the violent storms in the Birmingham area. Along the length of its 80-mile path, the tornado that passed through Tuscaloosa and Birmingham caused more than 1,000 injuries and at least 65 deaths. With winds of 190 miles (310 kilometers per hour), the tornado resulted from a supercell thunderstorm that lasted almost seven and a half hours, and traveled from Mississippi to North Carolina, spawning several violent tornadoes.
Between 7:00 a.m. CDT on April 25 and 7:00 a.m. on April 28, a total of 305 tornadoes struck the southeastern and central United States, according to NOAA’s updated survey released May 4. The high-resolution version of this image shows two more tornado tracks, one to the north and one to the south, both running parallel to the tornado track through Tuscaloosa and Birmingham.
- NOAA National Weather Service. (2011, May 5). Weather Forecast Office, Birmingham, Alabama. Accessed May 5, 2011.
- NOAA. (2011, May 4). April 2011 tornado information. Accessed May 5, 2011.
NASA Earth Observatory image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Michon Scott.
- Terra - ASTER | <urn:uuid:83f36da3-5380-47a6-a984-79dcbadc8f52> | 3.109375 | 457 | Knowledge Article | Science & Tech. | 57.657264 |
In chemistry, the addition of a formyl functional group is termed formylation. A formyl functional group consists of a carbonyl bonded to a hydrogen. When attached to an R group, a formyl group is called an aldehyde.
Formylation has been identified in several critical biological processes. Methionine was first discovered to be formylated in E. coli by Marcker and Sanger in 1964 and was later identified to be involved in the initiation of protein synthesis in bacteria and organelles. The formation of n-formylmethionine is catalyzed by the enzyme methionyl-tRNAMet transformylase. Additionally, two formylation reactions occur in the de novo biosynthesis of purines. These reactions are catalyzed by the enzymes glycinamide ribonucleotide (GAR) transformylase and 5-aminoimidazole-4-carboxyamide ribotide (AICAR) transformylase. More recently, formylation has been discovered to be a histone modification, which may modulate gene expression.
Formylation reactions in biology
Formylation in protein synthesis
In bacteria and organelles, the initiation of protein synthesis is signaled by the formation of formyl-methionyl-tRNA ((f-Met)-tRNA). This reaction is dependent on 10-formyltetrahydrofolate, and the enzyme methionyl-tRNA formyltransferase. This reaction is not used by eukaryotes or Archaea, as the presence of (f-Met)-tRNA in non bacterial cells is dubbed as intrusive material and quickly eliminated. After its production, (f-Met)-tRNA is delivered to the 30S subunit of the ribosome in order to start protein synthesis. fMet possesses the same codon sequence as methionine. However, fMet is only used for the initiation of protein synthesis and is thus found only at the N terminus of the protein. Methionine is used in during the rest translation. In E. coli, fMet-tRNA is specifically recognized by initiation factor IF-2, as the formyl group blocks peptide bond formation at the N-terminus of methionine.
Once protein synthesis is accomplished, the formyl group on methionine can be removed peptide deformylase. The methionine residue can be further removed by the enzyme methionine aminopeptidase.
Formyation reactions in purine biosynthesis
Two formylation reactions are required in the eleven step de novo synthesis of inosine monophosphate (IMP), the precursor of the purine ribonucleotides AMP and GMP. Glycinamide ribonucleotide (GAR) transformylase catalyzes the formylation of GAR to formylglycinamidine ribotide (FGAR) in the fourth reaction of the pathway. In the penultimate step of de novo purine biosynthesis, 5-aminoimidazole-4-carboxyamide ribotide (AICAR) is formylated to 5-formaminoimidazole-4-carboxamide ribotide (FAICAR)by AICAR transformylase.
GAR transformylase
PurN GAR transformylase is found in eukaryotes and prokaryotes. However, a second GAR transformylase, PurT GAR transformylase has been identified in E. coli. While the two enzymes have no sequence conservation and require different formyl donors, the specific activity and Km for GAR are the same in both PurT and PurN GAR transformylase.
PurN GAR transformylase
PurN GAR transformylase 1CDE uses the coenzyme N10-formyltetrahydrofolate (N10-formyl-THF) as a formyl donor to formylate the α-amino group of GAR. In eukaryotes, PurN GAR transformylase is part of a large multifunctional protein, but is found as a single protein in prokaryotes.
The formylation reaction is proposed to occur through a direct transfer reaction in which the amine group of GAR nucleophillically attacks N10-formyl-THF creating a tetrahedral intermediate. As the α-amino group of GAR is relatively reactive, deprotonation of the nucleophile is proposed to occur by solvent. In the active site, Asn 106, His 108, and Asp 144 are positioned to assist with formyl transfer. However, mutagenesis studies have indicated that these residues are not individually essential for catalysis, as only mutations of two or more residues inhibit the enzyme. Based on the structure the negatively charged Asp144 is believed to increase the pKa of His108, allowing the protonated imidazolium group of His108 to enhances the electrophillicity of the N10-formyl-THF formyl group. Additionally, His108 and Asn106 are believed to stabilize the oxyanion formed in the transition state.
PurT GAR transformylase
PurT GAR transformylase requires formate as the formyl donor and ATP for catalysis. It has been estimated that PurT GAR transformylase carries out 14-50% of GAR formylations in E. coli. The enzyme is a member of the ATP-grasp superfamily of proteins.
A sequential mechanism has been proposed for PurT GAR transformylase in which a short lived formyl phosphate intermediate is proposed to first form. This formyl phosphate intermediate then undergoes nucleophillic attack by the GAR amine for transfer of the formyl group. A formyl phosphate intermediate has been detected in mutagenesis experiments, in which the mutant PurT GAR transforymylase had a weak affinity for formate. Incubating PurT GAR transformylase with formyl phosphate, ADP, and GAR, yields both ATP and FGAR. This further indicating that formyl phosphate may be an intermediate, as it is kinetically and chemically competent to carry out the formylation reaction in the enzyme. A enzyme phosphate intermediate preceding the formylphosphate intermediate has also been proposed to form based on positional isotope exchange studies. However, structural data indicates that the formate may be positioned for a direct attack on the γ-phosphate of ATP in the enzyme’s active site to form the formylphosphate intermediate.
AICAR transformylase
AICAR transformylase requires the coenzyme N10-formyltetrahydrofolate (N10-formyl-THF) as the formyl donor for the formylation of AICAR to FAICAR. However, AICAR transformylase and GAR transformylase do not share a high sequence similarity or structural homology.
The amine on AICAR is much less nucleophillic than its counterpart on GAR due to delocalization of electrons in AICAR through conjugation. Therefore, the N5 nucleophile of AIRCAR must be activated for the formylation reaction to occur. Histidine 268 and Lysine 267 have been found to be essential for catalysis and are conserved in all AICAR transformylase. Histidine 268 is involved in deprotonation of the N5 nucleophile of AICAR, whereas Lysine 267 is proposed to stabilize the tetrahedral intermediate.
Formylation in Histone Proteins
Formylation has been identified on the Nε of lysine residues in histones and proteins. This modification has been observed in linker histones and high mobility group proteins, it is highly abundant and it is believed to have a role in the epigenetics of chromatin function. Lysines that are formylated have been shown to play a role in DNA binding. Additionally, formylation has been detected on histone lysines that are also known to be acetylated and methylated. Thus, formylation may block other post-translational modifications. Formylation is detected most frequently on 19 different modification sites on Histone H1. The genetic expression of the cell is highly disrupted by formylation, which may cause diseases such as cancer. The development of these modifications may be due to oxidative stress.
In histone proteins, lysine is typically modified by Histone Acetyl-Transferases (HATs) and Histone Deacetylases (HDAC or KDAC). The acetylation of lysine is fundamental to the regulation and expression of certain genes. Oxidative stress creates a significantly different environment in which acetyl-lysine can be quickly outcompeted by the formation of formyl-lysine due to the high reactivity of formylphosphate species. This situation is currently believed to be caused by oxidative DNA damage. A mechanism for the formation of formylphosphate has been proposed, which it is highly dependent on oxidatively damaged DNA and mainly driven by radical chemistry within the cell. The formylphosphate produced can then be used to formylate lysine. Oxidative stress is believed to play a role in the availability of lysine residues in the surface of proteins and the possibility of being formylated.
Formylation in medicine
Formylation reactions as a drug target
Inhibition of enzymes involved in purine biosynthesis has been exploited as a potential drug target for chemotherapy.
Cancer cells require high concentrations of purines to facilitate division and tend to rely on de novo synthesis rather than the nucleotide salvage pathway. Several folate based inhibitors have been developed to inhibit formylation reactions by GAR transformylase and AICAR transformylase. The first GAR transformylase inhibitor Lometrexol [(6R)5,10-dideazatetrahydrofolate] was developed in the 1980s through a collaboration between Eli Lilly and academic laboratories.
Although similar in structure to N10-formyl-THF, lometrexol is incapable of carrying out one carbon transfer reactions. Additionally, several GAR based inhibitors of GAR transformylase have also been synthesized. Development of folate based inhibitors have been found to be particularly challenging as the inhibitors also down regulate the enzyme folypolyglutamate synthase, which adds additional γ-glutamates to monoglutamate folates and antifolates after entering the cell for increased enzyme affinity. This increased affinity can lead to antifolate resistance.
Leigh Syndrome
Leigh syndrome is a neurodegenerative disorder that has been linked to a defect in an enzymatic formylation reaction. Leigh syndrome is typically associated with defects in oxidative phosphorylation, which occurs in the mitochondria.Exome sequencing, has been used to identify a mutation in the gene coding for mitochondrial methionyl-tRNA formyltransferase (MTFMT) in patients with Leigh syndrome. The c.626C>T mutation identified in MTFMT yielding symptoms of Leigh Syndrome is believed to alter exon splicing leading to a frameshift mutation and a premature stop codon. Individuals with the MTFMT c.626C>T mutation were found to have reduced fMet-tRNAMet levels and changes in the formylation level of mitochondrically translated COX1. This link provides evidence for the necessity of formylated methionine in initiation of expression for certain mitochondrial genes.
- Marcker, K; Sanger, F. (1964). "N-formyl-methionyl-S-RNA". J. Mol. Biol. 8: 835–840. PMID 14187409.
- Adams, J.M.; Capecchi, M.R. (1966). "N-Formylmethionyl-sRNA as the initiator of protein synthesis". PNAS 55: 147–155. PMID 5328638. Retrieved 24 February 2013.
- Kozak, M (1983). "Comparison of Initiation of Protein synthesis in Procaryotes, Eucaryotes, and Organelles". Microbiological Reviews: 1–45. PMID 6343825. Retrieved 24 February 2013.
- Voet and Voet (2008). Fundamentals of Biochemistry 3rd edition. New York: Wiley.
- Warren, M.S.; K.M. Mattia, A.E. Marolewski, S.J. Benkovic (1996). "The transformylase enzymes of de novo purine biosynthesis". Pure & Appl. Chem. 68: 2029–2036. Retrieved 24 February 2013.
- Wolan, D; Greasley, S.E., Beardsley, P., Wilson, I.A. (2002). "Structural Insights into the Avian AICAR Transformylase Mechanism". Biochemistry 41: 15505–15513. PMID 12501179.
- Thoden, J.B.; Firestine, S., Nixon, A., Benkovic, S.J., Holden, H.M (2000). "Molecular Structure of Escherichia coli PurT-Encoded Glycinamide Ribonucleotide Transformylase". Biochemistry 39: 8791–8802. PMID 10913290.
- Marolewski, A.E.; Mattia, K.M., Warren, M.S., Benkovic, S.J. (1997). Biochemistry 36: 6709–6716. PMID 9184151.
- Wisniewski, J.R.; Zougman, A., Mann, M. (2002). "N-Formylation of lysine is a widespread post-translational modification of nuclear proteins occurring at residues involved in regulation of chromatin function.". Nucleic Acids Research 36: 570–577. PMID 18056081. Retrieved 24 February 2013.
- Jiang, T; Zhou, X., Taghizadeh, K., Dong, M., Dedon, PC. (2007). "N-formylation of lysine in histone proteins as a secondary modification arising from oxidative DNA damage". PNAS 104: 60–65. PMID 17190813. Retrieved 24 February 2013.
- DeMartino, J.K.; Hwang, I., Xu, L., Wilson, I.A., Boger, D.L. (2006). "Discovery of a Potent, Nonpolyglutamatable Inhibitor of Glycinamide Ribonucleotide Transformylase.". J. Med.Chem. 49: 2998–3002. PMID 16686541. Retrieved 24 February 2013.
- Christopherson, R.I.; Lyons, S.D., Wilson, P.K (2002). "Inhibitors of de Novo Nucleotide Biosynthesis as Drugs". Acc. Chem. Res. 35: 961–971. PMID 12437321.
- Wang, L; Desmoulin, S.K., Cherian, C., Polin, L., White, K., Kushner, J., Fulterer, A., Chang, M., Mitchell, S., Stout, M., Romero, M.F., Hou, Z., Matherly, L.H., Gangjee, A (2011). "Synthesis, biological and antitumor activity of a highly potent 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolate inhibitor with proton-coupled folate transporter and folate receptor selectivity over the reduced folate carrier that inhibits β-glycinamide ribonucleotide formyltransferase.". J. Med. Chem. 54: 7150–7164. PMID 21879757. Retrieved 24 February 2013.
- "Leigh Syndrome". Online Mendelian Inheritance in Man. Retrieved 24 February 2013.
- Tucker, E.J.; Hershman, S.G., Kohrer, C., Belcher-Timme, C.A., Patel, J., Goldberger, O.A., Christodoulou, J., Silberstein, J.M., McKenzie, M., Ryan, M.T., Compton, A.G., Jaffe, J.D., Carr. S.A, Calvo, S.E., RajBhandary, U.L., Thorburn, D.R., Mootha, V.K. (2011). "Mutations in MTFMT underlie a human disorder of formylation causing impaired mitochondrial translation.". Cell. Metabl. 3: 428–434. PMID 21907147. Retrieved 24 February 2013.
See also | <urn:uuid:e5a803b3-06b3-4fe9-bd2e-f7158e6154cf> | 3.28125 | 3,573 | Knowledge Article | Science & Tech. | 37.624077 |
The phase space dynamics of the discrete dynamical system is just what you describe--- x(n+1) as a function of x(n). The phase space itself is the range of values of the x(n), whatever space they might live on, while the dynamics is the function that specifies the evolution in one step in time.
The connection with mechanical phase space is provided by a Poincare section. The Poincare section describes a dynamical continuous system by its intersections with a given surface in the full phase space. For a 1d motion, you can consider the half-line x=0,p>0, or in canonical action-angle coordinates $\theta$ fixed, J arbitrary. When you have a separable integrable motion, you take any one of the $\theta$ variables and define a surface by setting it to zero. Then the motion will intersect this surface once every period.
In mechanical phase space, the phase-space volume is conserved, but this is not so for maps. The condition of transversal intersection means that the map from the Poincare surface to itself can get
The topological properties of maps on
The properties of maps on spaces are as complicated as you like. The question is then which topological properties are you interested in?
The simplest topological theorems on maps is the Brouwer fixed point theorem, which can be restated as follows:
- Link the points x and f(x) by a path. If you draw a contractible sphere, and you find that as you go around the boundary, this x-f(x) map has a nonzero winding, then there is a fixed point inside this sphere.
The winding of a sphere around another sphere is the index of the map--- it is how many times the sphere covers the other sphere in the map. The Brouwer theorem is classical.
Another classical theorem of this sort is Sharkovskii's theorem:
- There is a linear order on periods of periodic cycles in 1d maps, such that each periodic orbit of length l implies that there is a periodic orbit of length l' whenever l' is greater than l.
Some other results are given by symbolic dynamics, the coarse grained position as a function of time. The notions of the entropy of a dynamical system is related to this. These results are not really topological in character, but they are general, and give qualitative insight, so they are similar.
Many further results can be found here, http://elib.tu-darmstadt.de/tocs/35981431.pdf | <urn:uuid:2d1668da-50de-4764-8fa0-c4e0a0dc0832> | 2.703125 | 542 | Q&A Forum | Science & Tech. | 50.95482 |
Outlying dense plasma
Plots of plasmaspheric ion (right) and electron (below)
density show significant density structure in the plasma
trough region outside the plasmapause. In both panels, the y
axis gives the particle density, while the x axis indicates the
position in L. The top panel shows a well-defined
plasmapause at L ~ 4.2, with structure extending out to the
magnetopause. In the bottom panel, high density structures
can be seen at L ~ 5.5-6 and from
L = 7-9. The structuring in the middle
and outer magnetosphere evident in these data indicates the
presence of dense plasma regions beyond the plasmapause.
These regions consist of material that has
been eroded from the plasmasphere by enhanced convection
and that may be in the form either of detached plasma patches or
of plasma plumes or tails
extending from the main body of the
plasmasphere. The data in the top panel were acquired with
the ion mass spectrometer on the Ogo 5 spacecraft; those in
the bottom panel, with the sweep frequency receiver on the
ISEE 1 satellite. As indicated by the trajectory plot in the
upper righthand corner of the bottom panel, the ISEE
measurements were made in the afternoon-evening sector
of the magnetosphere; the
Ogo data were taken in the morning-noon sector.
Sources: Chappell, C. R., Detached plasma regions in the
magnetosphere, J. Geophys. Res., 79, 1861, 1974 (Ogo plot);
Carpenter, D. L., et al., Plasmasphere dynamics in the
duskside bulge region: a new look at an old topic, J.
Geophys. Res., 98, 19243, 1993 (ISEE plot). | <urn:uuid:0f696c69-037f-487d-9f95-448cee88844a> | 2.734375 | 406 | Knowledge Article | Science & Tech. | 57.358926 |
How warming and steric sea level rise relate to cumulative carbon emissions
Surface warming and steric sea level rise over the global ocean nearly linearly increase with cumulative carbon emissions for an atmosphere-ocean equilibrium, reached many centuries after emissions cease. Surface warming increases with cumulative emissions with a proportionality factor, ΔTsurface:2×CO2/(IB ln 2), ranging from 0.8 to 1.9 K (1000 PgC)−1 for surface air temperature, depending on the climate sensitivity ΔTsurface:2×CO2 and the buffered carbon inventory IB. Steric sea level rise similarly increases with cumulative emissions and depends on the climate sensitivity of the bulk ocean, ranging from 0.4 K to 2.7 K; a factor 0.4 ± 0.2 smaller than that for surface temperature based on diagnostics of two Earth System models. The implied steric sea level rise ranges from 0.7 m to 5 m for a cumulative emission of 5000 PgC, approached perhaps 500 years or more after emissions cease. | <urn:uuid:c962307c-3b06-4c0b-817a-ad5982b02881> | 2.78125 | 214 | Knowledge Article | Science & Tech. | 47.263248 |
Programming - WordFrequency modifications
The purpose of these exercises is to get practice with using some of the basic data structures..
Java: Map Iteration
No direct iteration over Maps -- Get Set of keys or key-value pairs from Mapt.
Key-value pairs are stored in maps..
Example - WordFrequency
This program reads files of words and lists their frequencies.. | <urn:uuid:bec3c6d8-c449-4ae1-9d87-692afd4d29c7> | 2.921875 | 80 | Tutorial | Software Dev. | 47.180526 |
By May 26, 2010, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this photo-like image, Iceland’s Eyjafjallajökull Volcano had slowed its eruption. A tiny, white puff of steam rises from the volcano in this image. Considerable steam had been coming from the crater, said the Icelandic Met Office, but monitoring the eruption became difficult because of windblown ash. The problem is illustrated here. Two broad swaths of tan ash, many kilometers across, obscure the Icelandic coastline and sweep over the Atlantic Ocean.
The ash resembles an eruption plume in color, but it is actually resuspended ash. During Eyjafjallajökull’s eruption, fine powdery ash fell around the volcano and on areas downwind. The ash still rests lightly on the land’s surface and is easily lifted in the wind. On May 26, winds blew toward the south, southeast, picking up a thick cloud of ash near the volcano.
The ash is blowing over the North Atlantic Ocean. The ocean itself is colored with subtle swirls of blue and green, revealing the presence of a large phytoplankton bloom. While volcanic ash can fertilize ocean waters in parts of the world where waters contain little iron, the North Atlantic already contains more than enough iron to sustain large phytoplankton blooms. This bloom is part of the large phytoplankton bloom that covers much of the North Atlantic every spring and summer.
The large image is the highest-resolution version of the image. The image is available in additional resolutions from the MODIS Rapid Response System.
- Sveinbjörnsson, H., Arason, T., and Hreinsdóttir, S. (2010, May 26). Eruption in Eyjafjallajökull. (pdf) Icelandic Meteorological Office and Institute of Earth Sciences, University of Iceland. Accessed May 26, 2010.
- Kuring, N. (2010, May). Seeing past the ash. NASA Ocean Color Web. Accessed May 26, 2010. | <urn:uuid:3a10d7c2-962a-49fd-9d8d-8dc326dcebb6> | 4 | 448 | Knowledge Article | Science & Tech. | 48.581078 |
La Niña, the counterpart to El Niño, alters rainfall patterns over the Pacific and Indian Ocean basins. La Niña develops when stronger-than-average trade winds push the warm surface waters of the equatorial Pacific west. Since cold water rises to replace the warm water, La Niña leaves the eastern and central Pacific Ocean much cooler than normal, while the western Pacific is much warmer than normal. These anomalies in sea surface temperature are mirrored in rainfall patterns, with warmer-than-normal temperatures resulting in enhanced rainfall. In general, La Niña brings unusually heavy rain to the West Pacific, Indonesia, parts of Southeast Asia, and northern Australia.
This image shows the unusual rainfall pattern associated with La Niña. The image was made from the Multi-satellite Precipitation Analysis produced at NASA’s Goddard Space Flight Center, using rainfall measurements collected between December 19, 2007 and January 18, 2008. The image shows rainfall anomalies, or deviations from the average rainfall observed during the same period from 1998 through 2007. Regions that received more rain than average are blue, average rainfall is white, and below-average rainfall is brown. The rainfall pattern revealed by this image is typical of La Niña. A classic horseshoe pattern of above-average rainfall covers parts of the West Pacific, Indonesia and southern Southeast Asia, and northern Australia. A smaller horseshoe-shaped area of below-normal rainfall enfolds the region where ocean temperatures were cooler than average.
Superimposed on the La Niña pattern is the most recent Madden-Julian Oscillation (MJO). The Madden-Julian Oscillation is a large area of thunderstorms that moves slowly eastward from the Indian Ocean into the Pacific Ocean over a period of 30-60 days. In this image, the thunderstorms associated with the most recent Madden-Julian Oscillation were in the process of moving from Southeast Asia and Indonesia into the western Pacific. Since the cluster of thunderstorms had just left the Malaysian Peninsula, the area was unusually dry. In an average La Niña, the peninsula would also be wetter then normal. The Madden-Julian Oscillation was also contributing to the enhanced rainfall north and northeast of Australia. The unusually heavy rains shown in this image caused widespread flooding in northern Australia.
The Multi-satellite Precipitation Analysis used to make this image is based on data collected by the Tropical Rainfall Measuring Mission (TRMM) satellite. TRMM was launched into service with the primary mission of measuring rainfall from space. It can also be used to calibrate rainfall estimates from other sources. TRMM is a joint mission between NASA and the Japanese space agency, JAXA.
- Further Reading
- La Niña, a fact sheet available from NASA’s Earth Observatory. | <urn:uuid:d51fe86b-593b-4872-aa77-0f92ef552d44> | 4.0625 | 570 | Knowledge Article | Science & Tech. | 29.651613 |
The Death Ray Debate
The content of this page is an excerpt from http://www.mlahanas.de/Greeks/Mirrors.htm. Checkout this site for additional, interesting historical context.
A Burning Question by J. L. Hunt
The Greek historian Lucian has recorded that during the siege of Syracuse, Archimedes constructed a burning glass" to set the Roman warships afire. The story has long been dismissed as fantasy and was particularly attacked by the French philosopher-mathematician Rene Decartes, who sought to discredit all claims from antiquity. This story was the subject of an interesting correspondence in the scientific journal Applied Optics in 1976 where arguments pro and con were advanced.
A.C. Claus of Loyola University in Chicago opened the argument by pointing out that a persistent problem with the story was how Archimedes was able to align many mirrors in an array to accomplish this feat. Claus provided a simple method by which this could be done quickly and efficiently by sighting along a stick attached to the mirror.
This letter prompted an immediate response from O.N. Stavroudis of the Optical Sciences Center, University of Arizona, who argued that Claus' explanation was unnecessary because the story was obviously false on physical principles. in support of this he argued that the instrument would have to have a long focal length which was variable, and to have an area sufficient to collect enough energy to do the job.
He calculated that a one foot mirror would provide only 2000 calories per minute even at 100 percent reflection and, argues Stavroudis, this will only raise the temperature by a few degrees per minute.
This argument is incomplete since he said nothing about the nature of the object receiving the focused energy. The total heat delivered by the mirror is not the point. What is important is the size of the image produced by the mirror and the characteristics of the surface being heated, particularly as to how it absorbs and conducts heat. in the ideal case of a perfectly black surface which loses no heat, then the surface temperature will rise to the same temperature as that of the Sun. This is well above the flash-point of wood which as all readers of Science Fiction know is "Fahrenheit 451". All children know that they can set fire to a piece of wood with a magnifying glass. They can do this because the small image of the Sun, which focuses on the wood acquires a high temperature; that amount of heat delivered is of lesser consequence.
Stavroudis addressed himself to the wrong problem and, even so, came up with an incorrect answer. K.D. Mielenz pointed out that Stavroudis's view was negated by experiments done by George Louis LeClerc, Comte de Buffon, in 1747. Buffon recognized that the real problem was the one of having a variable focal length and so the mirror must be an array of individual adjustable elements. What does such an array do to the image quality? The answer is "surprisingly little". Let us look at Buffon's own numbers. He assumed a mirror of 400 feet radius of curvature and a diameter of 10 feet. Such a spherical mirror will produce an image of the Sun about two feet in diameter. if the mirror is made of plane elements of diameter d, then the image is increased in size by about d. If the elements are six inches in diameter then the two foot image is smeared out to two and one half feet.
Buffon assembled 168 mirrors 8 in. by 10 in adjusted to produce the smallest image 150 feet away. The array turned out to be a formidable weapon. At 66 feet 40 mirrors ignited a creosoted plank and at 150 feet, 128 mirrors ignited a pine plank instantly. in another experiment 45 mirrors melted six pounds of tin at 20 feet.
If there is doubt about Buffon's experiment consider the following newspaper report from 1975:
A Greek scientist, Dr. Ioannis Sakkas, curious about whether Archimedes could really have used a "burning glass" to destroy the Roman fleet in 212 BC lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the Sun's rays and direct them at a wooden ship 160 feet away. The ship caught fire at once.....Sakkas said after the experiment there was no doubt in his mind the great inventor could have used bronze mirrors to scuttle the Romans.
See this document in its original web page. | <urn:uuid:f6d3c356-6898-4775-aa03-7b3a01da93e3> | 3.375 | 909 | Knowledge Article | Science & Tech. | 55.680365 |
Suriname was ahead of the curve when it cordoned off what is now some of the world’s largest tracts of unspoiled tropical forest.
In 1998, as proof of its commitment to environmentally-friendly development, the government set aside 10 percent of land — about the size of New Jersey — and created the Central Suriname Nature Reserve. Two years later, UNESCO named the reserve a World Heritage Site. It has remained pristine because the only people who live there are the ones who manage it. In total, Suriname has 12 nature reserves, approximately 14 percent of the land area, and four Multiple Use Management Areas with the goal to preserve the biodiversity.
That’s not unlike the rest of Suriname, which is thickly forested but thinly populated. Much of the countryside is unexplored — a major boon to conservationists.
The “big game” of Amazonia — like the Giant River Otter (Pteronura brasiliensis), Lowland Tapir (Tapirus terrestris), Giant Armadillo (Priodontes maximus) and the American Manatee (Trichechus manatus) — threatened elsewhere — are still abundant, because large parts of their habitat is still intact and undisturbed. The threatened Blue Poison Frog (Dendrobates azureus) can only be found in some of the forest islands in the Sipaliwini savanna in the south of Suriname and is one of the more than 100 IUCN threatened species that occur in Suriname.
Frogs (Atelopus spp.) with fluorescent purple spots were among dozens of startling discoveries made during our recent surveys of two plateaus south of the capital Paramaribo. Besides finding 24 potentially new species, our scientists were the first in more than 50 years to see an armored catfish (Harttiella crassicauda) that was believed extinct.
While the surveys only scratched the surface of what’s hidden, they exposed just how much there is to lose in these unprotected sites.
Small-scale mining is already affecting the two plateaus and threatens similar harm to other forests around Suriname. When undertaken without due care, mining can degrade water quality within a region’s extensive system of waterways and reservoirs. That, in turn, degrades fragile ecosystems. | <urn:uuid:d56ddaf9-9094-47af-83a7-fc8a93de520c> | 3.75 | 487 | Knowledge Article | Science & Tech. | 28.159411 |
This chapter describes a number of modules that are used to parse different file formats.
Python comes with extensive support for the Extensible Markup Language XML and Hypertext Markup Language (HTML) file formats. Python also provides basic support for Standard Generalized Markup Language (SGML).
All these formats share the same basic structure (this isn’t so strange, since both HTML and XML are derived from SGML). Each document contains a mix of start tags, end tags, plain text (also called character data), and entity references.
<document name="sample.xml"> <header>This is a header</header> <body>This is the body text. The text can contain plain text ("character data"), tags, and entities. </body> </document>
In the above example, <document>, <header>, and <body> are start tags. For each start tag, there’s a corresponding end tag which looks similar, but has a slash before the tag name. The start tag can also contain one or more attributes, like the name attribute in this example.
Everything between a start tag and its matching end tag is called an element. In the above example, the document element contains two other elements, header and body.
Finally, " is a character entity. It is used to represent reserved characters in the text sections (in this case, it’s an ampersand (&) which is used to start the entity itself. Other common entities include < for “less than” (<), and > for “greater than” (>).
While XML, HTML, and SGML all share the same building blocks, there are important differences between them. In XML, all elements must have both start tags and end tags, and the tags must be properly nested (if they are, the document is said to be well-formed). In addition, XML is case-sensitive, so <document> and <Document> are two different element types.
HTML, in contrast, is much more flexible. The HTML parser can often fill in missing tags; for example, if you open a new paragraph in HTML using the <P> tag without closing the previous paragraph, the parser automatically adds a </P> end tag. HTML is also case-insensitive. On the other hand, XML allows you to define your own elements, while HTML uses a fixed element set, as defined by the HTML specifications.
SGML is even more flexible. In its full incarnation, you can use a custom declaration to define how to translate the source text into an element structure, and a document type description (DTD) to validate the structure, and fill in missing tags. Technically, both HTML and XML are SGML applications; they both have their own SGML declaration, and HTML also has a standard DTD.
Python comes with parsers for all markup flavors. While SGML is the most flexible of the formats, Python’s sgmllib parser is actually pretty simple. It avoids most of the problems by only understanding enough of the SGML standard to be able to deal with HTML. It doesn’t handle document type descriptions either; instead, you can customize the parser via subclassing.
The XML support is most complex. In Python 1.5.2, the built-in support was limited to the xmllib parser, which is pretty similar to the sgmllib module (with one important difference; xmllib actually tries to support the entire XML standard).
Python 2.0 comes with more advanced XML tools, based on the optional expat parser.
The ConfigParser module reads and writes a simple configuration file format, similar to Windows INI files.
Python’s standard library also provides support for the popular GZIP and ZIP (2.0 only) formats. The gzip module can read and write GZIP files, and the zipfile reads and writes ZIP files. Both modules depend on the zlib data compression module. | <urn:uuid:c145e89e-25f0-4b29-b28b-f0dcbb26f8ac> | 4.0625 | 827 | Documentation | Software Dev. | 55.541649 |
New Genomes Project Data Indicate a Young Human Race
by Brian Thomas, M.S. *
In 2008, an extensive international effort was begun to sequence in unprecedented detail over 1,000 representative human genomes from around the world. The results of three preliminary pilot projects were published in October 2010—one of which uncovered a result that points to a youthful age for the human race.
In this pilot project, researchers examined in great detail the DNA base sequences from two families, including the mother, father, and child of each. A summary of the results appeared in Science, which stated that based on the data, "offspring inherit about 60 mutations that arose in their parents."1
In large measure, the research for the "1000 Genomes Project" is aimed at pinpointing exactly which mutations cause which diseases. Knowing the number of new mutations that arise with each generation can assist with tracking the new diseases that they may cause.
The measurement of close to 60 new mutations occurring within the reproductive cells of each generation is less than a prior estimate of 100.2 This figure can help answer key questions. For example, does this number of mutations provide enough "fuel" for change to have innovated modern humanity from primate ancestors? Also, can the potentially harmful effects of this rate of mutation accumulation be somehow reversed before too many incorrect DNA bases compromise humanity's survival?
Currently, the most accurate way to answer these questions is to use the freely downloadable population genetics modeling program called Mendel's Accountant.3 Developed by a team of scientists, including Cornell University plant geneticist John Sanford, the program calculates the cumulative effects on the fitness (average survivability) of individuals that inherit mutations— some beneficial, some harmful, but mostly neutral—over multiple generations.
The study of mutations that have no, or almost no, effect has presented a longstanding problem for evolutionary biology. Since these near-neutral mutations produce such tiny effects in cells, they do not appreciably affect any trait that is expressed in the organism.4 Therefore, these mutations are undetectable by any imagined natural process and simply add up over the generations.
Mendel's Accountant can simulate, with unprecedented biological accuracy, the result of this accumulation. Assuming a population size of 2,000 individuals, assuming that each mother has six children, and using the rate of 60 mutations per generation in the algorithms, the simulation shows the extinction of the human race after only 350 generations. This also assumes that natural selection would have been effective at removing the least fit from the population every generation.
If this result is anywhere close to correct—that humanity's genetic mutations would have led to extinction within 350 generations—how could that possibly fit within evolution's long ages? But if the total age of the world is about 6,000 years,5 as is consistent with biblical history, then mankind has been here for fewer than 300 generations.6 Thus, the latest and most accurate research into human genetics confirms a straightforward reading of the biblical account of origins and human history.
- Pennisi, E. 2010. 1000 Genomes Project Gives New Map of Genetic Diversity. Science. 330 (6004): 574-575.
- Kondrashov, A. S. 2003. Direct estimate of human per nucleotide mutation rates at 20 loci causing Mendelian diseases. Human Mutation. 21 (1): 12-27.
- Mendel's Accountant: Simulating Genetic Change Over Time. Posted on mendelsaccount.sourceforge.net, accessed November 2, 2010.
- Vardiman, L. 2008. The "Fatal Flaws" of Darwinian Theory. Acts & Facts. 37 (7): 6.
- Beechick, R. 2001. Chronology for everybody. Journal of Creation. 15 (3): 67- 73.
- In reality, the number of generations since creation is smaller, since the average generation time among pre-Flood peoples was 117 years, not 20. Factoring this in yields about 231 generations from creation to 2010 A.D.
*Mr. Thomas is Science Writer at the Institute for Creation Research.
Article posted on November 9, 2010. | <urn:uuid:9fb90f79-99a1-4239-845c-da1437e27c93> | 3.609375 | 853 | Academic Writing | Science & Tech. | 42.585727 |
Shadow Length Change
Why does the length of a shadow change during the day?
Try this (you will need a ruler, pencil and two sheets of paper):
1) draw two upright lines of exactly the same height (about 3cm
in height should do), one line per piece of paper.
2) For one of the lines draw a point or dot at a distance of, maybe
20cm to the right and about 2cm higher than the top of the original
3) Now, draw a line from the dot to the top of the upright line and
continue the line until the line you are drawing is at about the same
height as the bottom of the upright line. The distance of the end of
the line you've just drawn to the bottom of the upright line is the
length of the "shadow" of the upright line.
4) Do the same for the second line, BUT draw the point (or dot) at a
distance of maybe 10cm to the right and 5cm higher than the top of the
upright line. Then draw the line as in #3 above.
5) You should note that the "shadows" are of different lengths. Can you
Greg (Roberto Gregorius)
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:ffa234b5-c914-4155-bf0b-188d73db2f1d> | 3.65625 | 272 | Q&A Forum | Science & Tech. | 63.136776 |
Nanobioscientists like Mike Simpson aim to harness or imitate the complex abilities of bacteria and other single cells to make implantable sensors and actuating devices.
Put a biologist, a physical scientist, and an electrical engineer in the same room, and you have a recipe for an interesting collaboration in nanobioscience. Become a fly on a wall of that room and you might hear statements common to systems biology, invented by physical scientists applying systems analysis tools to biological problems. And you might learn a little about synthetic biology— methods for applying biology's lessons to device design.
What you might hear in that room: "Living cells work using the information processing of gene circuits and networks." "We need to find out how these circuits and networks are built and interconnected to make cells and organisms function." "Let's put the intelligence in genes on an electronic chip." "Our funding agencies want us to create engineered systems that closely mimic the size and functional complexity of biological systems, such as bacteria and other single cells."
In the mid-1990s, ORNL electrical engineer and nanobioscientist Mike Simpson heard University of Tennessee biologist Gary Sayler give a presentation. Simpson and Sayler then talked, and a collaboration began. The result was a silicon chip harboring bacteria engineered to light up in the presence of their favorite food—a pollutant called toluene. The light from an activated fluorescent protein triggered an electronic response. The "critters on a chip" sensor, formally labeled a bioluminescent bioreporter integrated circuit (BBIC), was licensed to Micro Systems TECH for homeland security uses.
Based on research by Simpson's and Sayler's groups and funded by the National Institutes of Health, ORNL recently patented a method for using an implantable BBIC sensor chip for glucose detection. "Sayler's group engineered human mammalian cells to emit light to the circuitry our group designed for an implanted sensor," Simpson says. "The amount of light is related to the glucose level. We have suggested that incorporating our glucose-sensing capability in a closed feedback loop with an implantable insulin pump could lead to an artificial pancreas."
Simpson is intrigued by the infor-mation-processing capabilities that are packed into single cells. "If you compare the information-processing ability of a piece of silicon the same size as an E. coli bacterium, the bacterial cell wins by a lot," says Simpson, who has a joint appointment at the University of Tennessee and Oak Ridge National Laboratory..
He is fascinated by magnetotactic bacteria, which are found in aquatic environments. These aquatic bacteria gather materials to make nanomagnetic particles, assemble them into a rod that aligns itself with the earth's magnetic field, and then start up a protein motor that enables the bacteria to travel, following the magnetic field's curvature. "These bacteria use the magnetic field to guide them down into water where the dissolved oxygen level is just right," Simpson says.
Another micro-organism of interest is the diatom, which builds an elaborate silicon structure in which it lives until the structure divides into two diatom cells. Each of the daughter cells inherits half the structure and must manufacture the other half.
"I am interested in these cells because they perform exquisite controlled synthesis and directed assembly of nanoscale materials," Simpson says. "Understanding how their genetic and biochemical circuits and networks make possible their complex functionality could teach us how to create engineered systems with similar abilities."
Simpson's group, including Tim McKnight and Anatoli Melechko, is collaborating with Mitch Doktycz's group in biomimetics—mimicking cell structure and function in engineered devices.
They can grow an array of vertically aligned carbon nanofibers in any pattern they choose. Thus, they can imitate a cellular membrane by controlling the spacing between the nanofibers so that small molecules will pass through, while larger molecules are excluded. They demonstrated this capability by transporting fluorescently labeled latex beads of different sizes down a microfluidic channel intersected with a stripe of nanofibers and detecting a buildup of the larger beads at the intersection.
For nanobioscientists, Mother Nature is a role model.
Web site provided by Oak Ridge National Laboratory's Communications and External Relations | <urn:uuid:b0b75c20-fda0-4b44-90c1-ba8dbf23f0b3> | 3.421875 | 874 | Knowledge Article | Science & Tech. | 24.414168 |
In recent years, it has been shown that fine particle concentrations in the atmosphere are strongly correlated with increased mortality rates and respiratory disease. One of the major anthropogenic sources of fine particles is coal-fired power generation. This study has been initiated to determine the contribution of coal fired power stations (CFPS) to the levels of atmospheric dust. Sampling has been conducted in the Upper Hunter Valley, Australia, at an existing monitoring site 7km SE of two large CFPS. Time resolved samples have been collected on carbon tape using a Burkard spore sampler. SO₂ at the site has been shown to be predominantly from the CFPS. This has been used as an indicator of when power station impacts are likely to be greatest; sections of the tape have been selectively analysed by Scanning Electron Microscopy to estimate the mass concentration of particles emitted by CFPS. This paper reviews the methodology and presents preliminary results indicating that the maximum contribution due to CFPS is two orders of magnitude less than annual PM₁₀ measured at the site. | <urn:uuid:98bdb88f-1c09-46f4-a1a0-654e7ddae9cb> | 3.03125 | 215 | Academic Writing | Science & Tech. | 27.802727 |
Vertebrates of the class Amphibia including frogs and toads (Anura), salamanders (Urodela), caecilians (Apoda) and extinct forms which are cold-blooded and have life stages in water as eggs and larval forms (tadpoles)until they metamorphose as adults.
Amphibian population declines and deformities due to various causes including land use change, viruses, and fungi. Links to USGS press releases, answers to FAQs (HTML and PDF versions) and photos with downloadable files.
They're abundant in this area, but hard to count reliably. We outline a procedure for estimating the population sizes so that we can determine whether they're increasing or dwindling. We must both listen for their calls and visually confirm them.
Homepage for the Dept. of the Interior's Initiative coordinated by the USGS, for amphibian (frogs, toads, salamanders and newts) monitoring, research, and conservation. Links to National Atlas for Amphibian Distribution, photos, and interactive map serve
Links to information on species of frogs, toads, and salamanders located in the southeastern United States and the U.S. Virgin Islands, with information on appearance, habitats, calls, and status, plus photos, glossary, and provisional data.
Fact sheet (PDF format) on amphibians in Olympic National Park and overview of the habitat, the decline in populations, and rare amphibians in the Pacific Northwest including the giant salamander and tailed frog.
Constructed farm ponds represent significant breeding, rearing, and overwintering habitat for amphibians in the Driftless Area Ecoregion of Minnesota, Wisconsin, and Iowa. Links to fact sheet, brochure, annual reports, field manual, and final report.
The North American Amphibian Monitoring Program (NAAMP) is a long-term monitoring program designed to track the status and trends of frog and toad populations with links to data access, protocol, and how to volunteer as an observer.
Overview of the Southeastern Amphibian Research and Monitoring Initiative, annual report, field methods and protocols, statistical design and analysis, glossary, projects, and lists of frogs, toads and salamanders.
Access to Patuxent Wildlife Research Center fact sheets (PDFs) providing summaries of center studies on coastal ecosystems, birds, amphibians, taxonomy and other subjects and on center activities including partners and volunteer program.
Biomonitoring projects studying the status and trends of the nation's environmental resources and programs studying amphibians and birds. Links to long-term programs, resources and references, and related links. | <urn:uuid:21263de2-374b-44a8-8e48-a1b2d61b18ae> | 3.5625 | 548 | Content Listing | Science & Tech. | 27.130789 |
Introduction to RELAX NG (1/2) - exploring XML | 2
Introduction to RELAX NG
While we have seen how elements and attributes are defined, we also need to learn how to specify
cardinality. This is done through special elements, of which we have already seen the
|?||zero or one appearances, either appear all or nothing.|
|*||indicates any number of occurrences|
|+||one to any number of occurrences|
It is also possible to specify alternatives in a grammar, and group elements together:
||||one alternative out of the following set|
|()||a combination of elements, in the given order|
|+||allows child elements to occur in any order|
RELAX NG allows patterns to reference externally-defined datatypes, such as those defined by the W3C XML Schema Datatypes. RELAX NG implementations may differ in what datatypes they support. You must use datatypes that are supported by the implementation you plan to use.
The data pattern matches a string that represents a value of a named datatype.
contains a URI identifying the library of datatypes being used. The datatype library defined by
W3C XML Schema Datatypes would be identified by the URI
type attribute specifies the name of the datatype in the library identified by the
For example, if a RELAX NG implementation supported the datatypes of W3C XML Schema Datatypes,
you could use:
<element name="number"> <data type="integer" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"/> </element>
Datatypes may have parameters. For example, a string datatype may have a parameter controlling the length
of the string. The parameters applicable to any particular datatype are determined by the datatyping vocabulary.
Parameters are specified by adding one or more
param elements as children of the
For example, the following constrains the
<element name="email"> <data type="string"> <param name="maxLength">127</param> </data> </element>
RELAX NG also supports enumerations and lists outside of any supported data type library. Many markup vocabularies have attributes whose value is constrained to be one of a set of specified values. The value pattern matches a string that has a specified value. For example,
<element name="newsletter"> <attribute name="preferredFormat"> <choice> <value>html</value> <value>text</value> </choice> </attribute> </element>
preferredFormat attribute to have the value html or text. This corresponds to the DTD:
<!DOCTYPE newsletter [ <!ELEMENT newsletter EMPTY> <!ATTLIST newsletter preferredFormat (html|text) #REQUIRED> ]>
The list pattern matches a whitespace-separated sequence of tokens; it contains a pattern that the sequence of individual tokens must match. The list pattern splits a string into a list of strings, and then matches the resulting list of strings against the pattern inside the list pattern.
For example, suppose we want to have a vector element that contains two floating point numbers separated by
whitespace. We could use
list as follows:
<element name="vector"> <list> <data type="float"/> <data type="float"/> </list> </element>
This concludes our quick tour of RELAX NG. Review the official specification for some of the less often used features. It will be interesting to see whether RELAX NG or XML Schema will enjoy more success as a replacement for DTDs.
Produced by Michael Claßen
Created: Jul 22, 2002
Revised: Jul 22, 2002 | <urn:uuid:4429de7e-242d-48ab-8135-98d3c00ee669> | 2.984375 | 809 | Documentation | Software Dev. | 29.048846 |
In a previous post, I reported on the baffling new finding that neutrinos appear to travel faster than light. The stuff of science fiction…travel to the past…weird science…Einstein rolling in his grave. (Except that faster-than-light doesn’t necessarily imply the possibility of time travel, and superluminal neutrinos might not violate relativity if they were the hypothetical tachyons.) The result was met with widespread skepticism in the world of physics, and the skepticism still continues. But just as the furor was beginning to die down, the OPERA (Oscillation Project with Emulsion tRacking Apparatus) consortium that runs the neutrino experiment at the Gran Sasso laboratory deep in the Apennine Mountains of central Italy, using neutrinos created 732 kilometers away at CERN, near Geneva, reported an experimental confirmation of their own earth-shattering results.
Originally, the pulses of protons that CERN used to generate the neutrinos through collisions with a stationary target were relatively long, and some critics have claimed that the long pulses, lasting 10.5 microseconds, could have introduced some uncertainty into the process. The OPERA scientists therefore asked CERN to shorten the pulses, and the new pulses have been only three nanoseconds (billionths of a second) long. The original result had been that the neutrinos traveled from CERN to Gran Sasso 60 nanoseconds faster than light would have taken for the same 732 kilometers, with a statistical standard error that was one-sixth as large (hence the result was statistically significant at “six-sigma,” which is extremely significant and its probability of being a fluke was therefore less than one in 3.5 million). The much shorter pulses make the pulse length fall within the standard error, and not a contributor to a possible false finding. Significantly, the new results, based on 20 detected neutrinos from the new and ultrashort pulses, replicated the earlier OPERA finding: The neutrinos still appear to travel faster than light.
What lies ahead? The OPERA scientists are obviously more confident of their results than they had been before. And there appear to be no obvious flaws in their research. At a recent conference at MIT, one of the physicists described the OPERA team as consisting of “Germans, Swiss, and clocks”—accuracy doesn’t get much better. Early concerns that the extremely accurate atomic clocks and GPS used by OPERA were somehow misread or misinterpreted have been easily overturned. But what the world of physics now seeks is a confirmation or refutation of the OPERA results by other research teams.
I just discussed this further work with Professor Stan Wojcicki of Stanford University, one of the founders of the MINOS (Main Injector Neutrino Oscillation Search) project in the United States, which gets its neutrinos from Fermilab, near Batavia, Illinois. Wojcicki told me that the MINOS physicists are now looking through the voluminous data set on neutrino velocities they had accumulated over many years of research. This group did not use a GPS as accurate as that used by OPERA, but the time and space accuracy attained by the group—and their immensely large data set—should still be useful in confirming or challenging the results from Gran Sasso. It is important to note that early analyses of the MINOS data set has indeed indicated that the neutrinos may well travel at speeds higher than that of light. But these results lacked statistical significance (they did not meet the two-sigma, 95% probability standard of proof). It will be fascinating to see what MINOS and other research teams discover over the next few months, and whether we may be forced to update our understanding of Einstein’s special theory of relativity.
Amir D. Aczel is a researcher at the Center for the Philosophy and History of Science at Boston University and the author of 18 books about mathematics and physics, as well as numerous research articles. He is a Guggenheim Fellow and a frequent commentator on science in the media. See more at his website or follow him on Twitter: @adaczel. | <urn:uuid:b70f1b4b-8fd0-40c8-870b-c6fed2a6b5eb> | 3.34375 | 884 | Personal Blog | Science & Tech. | 34.122763 |
No, not that. These (photo by DanielCD):
Blastoids are small but reasonably common Palaeozoic (Silurian to Permian) fossils. The name means, roughly, 'bud-like' and refers to the common resemblance of the fossils to flower buds. However, blastoids were not plants but echinoderms, animals of the same phylum as modern crinoids, starfish and sea urchins.
Most blastoid fossils are less than an inch in diameter, and all have a very clear pentaradial arrangement (the following account is primarily based on Beaver et al., 1967). The theca (the main body) is very solidly built from a very regular arrangement of plates, with five ambulacra (feeding grooves) running down the sides (the ambulacra are what house the tube feet in living echinoderms). At the top of the fossil where the ambulacra meet is a central opening that in life would have led to the mouth, with a number of other openings around it. The largest of these was the anus while the smaller openings are known as the spiracles.
The spiracles are connected to the hydrospires, a series of folds of the internal body wall underlying the ambulacra (reconstruction above from Schmidtling & Marshall, 2010) that are generally believed to have function in respiration. Presumably, water was drawn into the hydrospires on either side of the ambulacra and expelled through the spiracles. Two orders of blastoids are distinguished based on the arrangement of the hydrospires and spiracles. In members of the order Fissiculata, the hydrospires open directly to the outside world through a series of slits in the thecal plates; the spiracles are often small or slit-like and may not be readily distinguishable from the hydrospire slits (as far as I can see, anyway). In members of the order Spiraculata, such as Pentremites, the hydrospire slits were internal and entry to the hydrospires was through minute pores on either side of the ambulacra while the spiracles were much larger and more distinct. The remaining internal anatomy (such as the mode of reproduction) remains largely unknown.
In life the theca was only a small (but significant) part of the whole. A slender stem (up to about 25 cm long) attached the blastoid to the substrate while on either side of each ambulacrum was a row of arm-like structures known as brachioles. The brachioles would have captured food particles in the water, transporting the particles down a groove on the underside to the ambulacrum below. The stem and brachioles were comparatively delicate and rarely preserved but the positions of the brachioles can still be otherwise distinguished by the presence of attachment sockets alongside the ambulacra.
Brachioles are also found in a number of other extinct echinoderm groups (such as cystoids and eocrinoids) but are not found in any living echinoderms. Despite a certain superficial resemblance, brachioles are not comparable to the arms of living crinoids. In recent years, it has been proposed that the echinoderm exoskeleton can be divided on morphological and developmental grounds into two distinct components, the axial skeleton which grows through the alternating addition of plates at the distal points and the extraxial skeleton which can grow through the addition of new plates in between pre-existing ones (David et al., 2000). The axial skeleton makes up the ambulacra and associated structures while the extraxial skeleton makes up the remainder of the body wall. Crinoid arms, which carry the ambulacra along their axis and contain radial extensions of the internal coelom, are made up of both axial and extraxial components. Blastoid brachioles, which sit alongside the ambulacra and do not contain coelomic extensions, are entirely axial*. While many authors have suggested that crinoids may be derived from brachiolar echinoderms (particularly cystoids, some of which have a similar arrangement of thecal plates to early crinoids - e.g. Ausich, 1998), proponents of the extraxial-axial division regard the similarities between the groups as convergent; indeed, the phylogeny proposed by David et al. (2000) would place brachiolar echinoderms such as blastoids entirely outside the echinoderm crown group.
*If I understand things correctly, deriving crinoid arms from blastoid brachioles would be a little like deriving human arms from lemur fingernails.
Ausich, W. I. 1998. Early phylogeny and subclass division of the Crinoidea (phylum Echinodermata). Journal of Paleontology 72 (3): 499-510.
Beaver, H. H., R. O. Fay, D. B. Macurda Jr, R. C. Moore & J. Wanner. 1967. Blastoids. In Treatise on Invertebrate Paleontology pt. S. Echinodermata 1. General Characters. Homalozoa-Crinozoa (except Crinoidea) (R. C. Moore, ed.) pp. S297-S455. The Geological Society of America, Inc. and The University of Kansas.
David, B., B. Lefebvre, R. Mooi & R. Parsley. 2000. Are homalozoans echinoderms? An answer from the extraxial-axial theory. Paleobiology 26 (4): 529-555.
Schmidtling, R. C., II & C. R. Marshall. 2010. Three dimensional structure and fluid flow through the hydrospires of the blastoid echinoderm, Pentremites rusticus. Journal of Paleontology 84 (1): 109-117. | <urn:uuid:2b01ca2c-ae9c-4d17-a5bb-7b1acdcfe4b6> | 3.171875 | 1,253 | Knowledge Article | Science & Tech. | 44.954806 |
1. A black hole is formed when a star is out of nuclear fuel which it needs to exist. It grows smaller and smaller until it collapses under its own weight.
2. While most stars end up as white dwarfs or neutron stars, black holes are the last evolutionary stage in the lifetimes of enormous stars that had been at least 10 or 15 times as massive as our own sun.
3. Our Sun won’t and cannot become a black hole. Only stars with much more mass than the Sun can become a black hole.
4. If someone fell into a black hole their feet would be pulled in faster than their head. They would be stretched like a piece of spaghetti.
5. According to Einstein's theories of relativity, nothing can travel faster than the speed of light. Therefore once something is inside a black hole it can never get out.
6. The black hole emits no light due to its extremely powerful gravitational pull.
7. Planets, light, and other matter must pass close to a black hole in order to be pulled into its grasp.
8. Black holes are small in size, and because they are so small, distant, and dark, black holes cannot be directly observed.
9. Black holes are shaped like a sphere and they can spin.
10. Astronomers believe that one black hole is born every day. | <urn:uuid:d2db4afc-a471-4ac7-8dc0-b345473807d2> | 4.09375 | 280 | Listicle | Science & Tech. | 75.345849 |
Now that we have dealt with the simplicity that Earth Quakes are caused by the interaction of tone of sound and the Earths Magnetic Field and that the Pyramids of Giza and the likes were not built by Egyptians or Aliens but evolved (grew) We can get into more interesting things.
To understand Crop Circle phenomenon you must first understand other phenomenon but before that and to hold your interest here is a thumbnail sketch of Crop circles.
The same forces of our Earth that influences water (waves) and air (wind) are at work creating crop circles.
The seed of the crop when unfolded (think of a snowflake or open flower) has at its centre a nucleus with orbiting nuclei (three nuclei orbits to a nucleus producing six poles.)
The Aura of every seed in this crop is connected as one (protecting the species from evolution.)
Within a crop field there will be accumulations of this energy (Aura) and because forces of equal evolution act upon forces of equal evolution, the Earth forces intermingle with the Aura or forces of the plant. Individually, each plant is affected to eternally change (bend) to the movement direction of Earth energy and contained within the crop's interacting Aura giving the formations of crop circles.
Unlike a tornado you could sit in the dark and not know a crop circle has formed around you. Because all reactions create noise a slight rustle would be heard. However, this would not happen because your Aura or the Aura of say a recording device or the likes would not allow the amalgamation or accumulation of the crop's Aura.
Devices (matter) producing Aura placed throughout a crop field would eliminate crop circles.
Now to understand the above you must first understand - - - to be continued | <urn:uuid:9cba5fe5-4382-4306-8c86-dd033efcefd1> | 2.953125 | 360 | Comment Section | Science & Tech. | 39.662559 |
Teaching python (programming) to children
David Andreas Alderud
aaldv97 at student.remove-this-part.vxu.se
Wed Nov 7 18:07:36 CET 2001
Java, C and C++ got there after a while, but they where not to begin with.
Ada was well documented and with lots of RFC before the actually
implementation of Ada83. Considering that it took 7 years of design before
the next version of Ada to be finnished, it started in '88.
I might be wrong, but I'm not aware of a language that was publicly designed
for years before its first implementation, if you know something I don't,
please enlighten me.
Yes, most languages are designed, but not from start to finnish, more like
version 1.0 and forward, that is not _what I call design_, maybe because I'm
schooled in software architectures, I don't know.
Maybe we have different opinions of design, I think of design as in
More information about the Python-list | <urn:uuid:24fde16a-f047-4a93-85a7-cf84e77002ad> | 2.96875 | 230 | Comment Section | Software Dev. | 62.471152 |
5.4.2. Abundance inhomogeneities
Many studies have suggested that structures seen in planetary nebulae (extended haloes, condensations) have different composition from the main nebular body, indicating that they are formed of material arising in distinct mass loss episodes characterized by different chemical compositions of the stellar winds. However, these differences in chemical composition may be spurious, due inadequacies of the adopted abundance determination scheme. For example, the knots and other small scale structures seen in PNe are possibly the result of instabilities or magnetic field shaping, and their spectroscopic signature could be due to a difference in the excitation conditions and not in the chemical composition. In the following, some examples of such studies are presented, adopting the view of their authors.
a) Extended haloes
NGC 6720, the "ring nebula" is surrounded by two haloes: an inner one, with petal-like morphology, and an outer one, perfectly circular, as seen in the pictures of Balick et al. (1992). Guerrero et al. (1997) have studied the chemical composition of these haloes, and found that the inner and outer halo seem to have same composition, suggesting a common origin: the red giant wind. On the other hand, the N/O ratio is larger in the main nebula by a factor of 2, indicating that the main nebula consists of superwind and the haloes of remnants of red giant wind.
NGC 6543, the "cat eye nebula" also shows two halo structures: an inner one, consisting of perfectly circular rings, and an outer one with flocculi attributed to instabilities (Balick et al. 1992). Unlike what is advocated for NGC 6720, the rings and the core in NGC 6543 seem to have same chemical composition (Balick et al. 2001). It must be noted however, that the abundances may not be reliable, since a photoionization model for the core of NGC 6543 predicts a far too high [O III] 4363/5007 (Hyung et al. 2000). Another puzzle is the information provided by Chandra. Chu et al. (2001) estimated that the abundances in the X-ray emitting gas are similar to those of the fast stellar wind and larger than the nebular ones. On the other hand, the temperature of the X-ray gas (~ 1.7 × 106 K) is lower by two orders of magnitudes than the expected post shock temperature of the fast stellar wind. This would suggest that the X-ray emitting gas is dominated by nebular material. These findings are however based on a crude analysis and more detailed model fitting is necessary.
b) FLIERs and other microstructures
A large number of studies have been devoted to microstructures in PNe, and their nature is still debated. Fast Low Ionization Emission Regions (FLIERs) have first been considered to show an enhancement of N and were interpreted as being recently expelled from the star (Balick et al. 1994). However, Alexander & Balick (1997) realized that the use of traditional ionization correction factors may lead to specious abundances. Dopita (1997) made the point that enhancement of [N II] 6584 / H can be produced by shock compression and does not necessarily involve an increase of the nitrogen abundance. Gonçalves et al. (2001) have summarized data on the 50 PNe known to have low ionization structures (which they call LIS) and presented a detailed comparison of model predictions with the observational properties. They conclude that not all cases can be satisfactorily explained by existing models.
c) Cometary knots
The famous cometary knots of the Helix nebula NGC 7293 have been recently studied by O'Dell et al. (2000) using spectra and images obtained with the HST. The [N II] 6584 / H and [O III] 5007 / H ratios were shown to decrease with distance to the star. Two possible interpretations were offered. Either this could be the consequence of a larger electron temperature close to the star due to harder radiation field. Or the knots close to the star would be more metal-rich, in which case they could be relics of blobs ejected during the AGB stage rather than formed during PN evolution. Obviously, a more thorough discussion is needed, including a detailed modelling to reproduce the observations before any conclusion can be drawn.
d) Planetary nebulae with Wolf-Rayet central stars
About 8% of PNe possess a central star having Wolf-Rayet charateristics, with H-poor and C-rich atmospheres. The evolutionary status of these objects is still in question. A late helium flash giving rise to a "born-again" planetary nebula, following a scenario proposed by Iben et al. (1983), can explain only a small fraction of them. The majority appear to form an evolutionary sequence from late to early Wolf-Rayet types, starting from the AGB (Górny & Tylenda 2000, Peñ at et al. 2001). This seemed in contradiction with theory which predicted that departure from the AGB during a late thermal pulse does not produce H-deficient stars. Recently however, it has been shown that convective overshooting can produce a very efficient dredge up, and models including this process are now able to produce H-deficient post-ABG stars following a thermal pulse on the AGB (Herwig 2000, 2001, see also Blöcker et al. 2001). It still remains to explain why late type Wolf-Rayet central stars seem to have atmospheres richer in carbon than early type ones (Leuenhagen & Hamann 1998, Koesterke 2001). Also, one would expect the chemical composition of PNe with Wolf-Rayet central stars to be different from that of the rest of PNe. This does not seem to be the case, as found by Górny & Stasinska (1995), basing on a compilation of published abundances: PNe with Wolf-Rayet central stars are indistinguishable from other PNe in all respects except for their larger expansion velocities. Peña et al. (2001) obtained a homogeneous set of high spectral resolution optical spectra of about 30 PNe with Wolf-Rayet central stars and reached a similar conclusion, as far as He and N abundances are concerned. Their data did not allow to draw any conclusion as regards the C abundances.
e) H-poor PNe
There are only a few PNe which show the presence of material processed in the stellar interior. They are referred to as H-poor PNe, although the H-poor material is actually embedded in an H-rich tenuous envelope. The two best known cases are A 30 and A 78, whose knots are bright in [O III] 5007 and He II 4686 but in which Jacoby (1979) could not detect the presence of H Balmer lines. With deeper spectra, Jacoby & Ford (1983) estimated the He/H ratio to be ~ 8 in these two objects. Harrington & Feibelman (1984) obtained IUE spectra of a knot in A 30, and found that the high C/He abundance implied by C II 4267 is not apparent in the UV spectra, suggesting that the knot contains a cool C-rich core. Guerrero & Manchado (1996) obtained spectra of the diffuse nebular body of A30, showing it to be H-rich. A similar conclusion was obtained by Manchado et al. (1988) and Medina & Peña (2000) for the outer shell of A 78. However, quantitatively, the results obtained by these two sets of authors are quite different and a deeper analysis is called for.
Three other objects belong to this group: A 58, IRAS1514-5258 and IRAS 18333-2357, the PN in the globular cluster M22, already mentioned in Sect. 3.7.5.
One common characteristic of this class of objects is their extremely high dust to gas ratio, and the fact that the photoelectric effect on the grains provides an important (and sometimes dominant) contribution to the heating of the nebular gas (see Harrington 1996). This may lead to large point-to-point temperature variations (see Sect. 3.7.5) and strongly affect abundance determinations.
Harrington (1996) concludes his review on H-poor PNe by noting that the H-poor ejecta cannot be explained by merely taking material with typical nebular abundances and converting all H to He. There is additional enrichment of C, N, perhaps O, and most interestingly, of Ne. However, more work on these objects is needed - and under way (e.g. Harrington et al. 1997) - before the abundances can be considered reliable. Stellar atmosphere analysis of H-deficient central stars (e.g. Werner 2001) is providing complementary clues to the nature and evolution of these objects.
In conclusion, we have shown how nebulae can provide powerful tools to investigate the evolution of stars and to probe the chemical evolution of galaxies. Nevertheless, is necessary to keep in mind the uncertainties and biases involved in the process of nebular abundance derivation. These are not always easy to make out, especially for the non specialist. One of the aims of this review was to help in maintaining a critical eye on the numerous and outstanding achievements of nebular Astronomy.
ACKNOWLEDGMENTS: It is a pleasure to thank the organizers of the XIII Canary Islands Winterschool, and especially César Esteban, for having given me the opportunity to share my experience on abundance determinations in nebulae. I also wish to thank the participants, for their attention and friendship. I am grateful to Miriam Peña, Luc Jamet and Yuri Izotov for a detailed reading of this manuscript, to Daniel Schaerer for having provided useful information on stellar atmospheres and to André Escudero for having kindly computed a few quantities related to planetary nebulae in the galactic bulge. I would like to thank my collaborators and friends, especially Rosa González Delgado, Slawomir Górny, Claus Leitherer, Miriam Peña, Michael Richer, Daniel Schaerer, Laerte Sodré, Ryszard Szczerba and Romuald Tylenda for numerous and lively discussions in various parts of the World.
Finally, I would like acknowledge the possibility of a systematic use of the NASA ADS Astronomy Abstract Service during the preparation of these lectures. | <urn:uuid:916fdb6e-6ac6-4d6a-8022-bd525f486e14> | 2.78125 | 2,215 | Academic Writing | Science & Tech. | 46.650795 |
Plants and Water on Other Planets
Name: jenny m timis
Date: 1993 - 1999
Do you think that there are plants, water,etc. on other planets?
There is certainly water on other planets (Mars for example),
but much more is needed for life. Most planetary scientists
believe that life probably existed on Mars sometime in the past
even if there's none there now, but there's no scientific evidence
for life existing anywhere except on Earth. That could change soon
with the new missions to Mars. A separate issue is whether or not
other solar systems exist, and, if they do, do they have planets
capable of supporting life. Since there's no scientific evidence
one way or the other, this is largely a matter of personal belief.
I like to think there is life elsewhere.
Click here to return to the Astronomy Archives
Update: June 2012 | <urn:uuid:fecf6849-2fad-4b2d-bf92-281ec33fa120> | 2.6875 | 190 | Audio Transcript | Science & Tech. | 48.335395 |
|The graph on the right shows the amount of longwave radiation
that is emitted to space. An important atmospheric
window exists from 8 to 13 micrometers.
Energy emitted through this window accounts for almost half of longwave radiation emitted to space. CO2 and H2O absorbs radiation at wavelengths longer than the atmospheric window while ozone and methane absorb at wavelengths shorter than the window.
Within the window, some absorption occurs as well (due to CO2 and ozone) but the total absorption is weak in most regions of the globe.
Other important absorbers include CH4, N2O and CFC's.
back to PJW Class home | <urn:uuid:b28dbd03-cbdc-4d52-a6d1-03a05c756ad7> | 3.84375 | 134 | Knowledge Article | Science & Tech. | 49.779765 |
|Home » Howtos » Syntax » Here document|
If you're tempted to write multi-line output with multiple
statements, because that's what you're used to in some other language,
consider using a HERE-document instead.
Inspired by the here-documents in the Unix command line shells, Perl HERE-documents provide a convenient way to handle the quoting of multi-line values.
So you can replace this:
print "Welcome to the MCG Carpark.\n"; print "\n"; print "There are currently 2,506 parking spaces available.\n"; print "Please drive up to a booth and collect a ticket.\n";
print <<'EOT'; Welcome to the MCG Carpark. There are currently 2,506 parking spaces available. Please drive up to a booth and collect a ticket. EOT
EOT in this example is an arbitrary string that you provide to
indicate the start and end of the text being quoted. The terminating string
must appear on a line by itself.
The usual Perl quoting conventions apply, so if you want to interpolate variables in a here-document, use double quotes around your chosen terminating string:
print <<"EOT"; Welcome to the MCG Carpark. There are currently $available_places parking spaces available. Please drive up to booth and collect a ticket. EOT
Note that whilst you can quote your terminator with
cannot use the equivalent
q() operators. So this
code is invalid:
# This example will fail print <<qq(EOT); Welcome to the MCG Carpark. There are currently $available_places parking spaces available. Please drive up to booth and collect a ticket. EOT
Naturally, all of the text you supply to a here-document is quoted by the starting and ending strings. This means that any indentation you provide becomes part of the text that is used. In this example, each line of the output will contain four leading spaces.
# Let's indent the text to be displayed. The leading spaces will be # preserved in the output. print <<"EOT"; Welcome to the MCG Carpark. CAR PARK FULL. EOT
The terminating string must appear on a line by itself, and it must
have no whitespace before or after it. In this example, the terminating
EOT is preceded by four spaces, so Perl will not find it:
# Let's indent the following lines. This introduces an error print <<"EOT"; Welcome to the MCG Carpark. CAR PARK FULL. EOT
Can't find string terminator "EOT" anywhere before EOF at ....
The here-document mechanism is just a generalized means of quoting text, so you can just as easily use it in an assignment:
my $message = <<"EOT"; Welcome to the MCG Carpark. CAR PARK FULL. EOT print $message;
And don't let the samples you've seen so far stop from considering the full range of possibilities. The terminating tag doesn't have to appear at the end of a statement.
Here is an example from
CPAN.pm that conditionally assigns some text to
$msg = <<EOF unless $configpm =~ /MyConfig/; # This is CPAN.pm's systemwide configuration file. This file provides # defaults for users, and the values can be changed in a per-user # configuration file. The user-config file is being looked for as # ~/.cpan/CPAN/MyConfig.pm. EOF
And this example from Module::Build::PPMMaker uses a here-document to
construct the format string for
$ppd .= sprintf(<<'EOF', $perl_version, $^O, $self->_varchname($build->config) ); <PERLCORE VERSION="%s" /> <OS NAME="%s" /> <ARCHITECTURE NAME="%s" /> EOF
perldoc -q "HERE documents" perldoc perlop (see the <<EOF section). Perl for Newbies - Lecture 4 | <urn:uuid:addefc15-1e78-4be9-b4d3-68555c18f293> | 3.3125 | 869 | Tutorial | Software Dev. | 59.682599 |
Those who understand compound interest are destined to collect it. Those who don't are doomed to pay it - or so says a well-known source of financial advice. But what is compound interest, and why is it so important? John H. Webb explains.
In the late 1940s, American painter Jackson Pollock dripped paint from a can on to vast canvases rolled out across the floor of his barn. Richard P. Taylor explains that Pollock's patterns are really fractals - the fingerprint of Nature.
One of the most striking and powerful means of presenting numbers is completely ignored in the mathematics that is taught in schools, and it rarely makes an appearance in university courses. Yet the continued fraction is one of the most revealing representations of many numbers, sometimes containing extraordinary patterns and symmetries. John D. Barrow explains.
Kevin Jones investigates the links between music and mathematics, throwing in limericks, Fibonacci and Scott Joplin along the way. Plus is proud to present an extended version of his winning entry for the THES/OUP 1999 Science Writing Prize. | <urn:uuid:b5379cda-ff6b-42a7-9641-cfac65359e8a> | 3.1875 | 221 | Truncated | Science & Tech. | 51.821011 |
Submitted to: Florida Scientist
Publication Type: Abstract Only
Publication Acceptance Date: January 9, 2008
Publication Date: March 6, 2008
Citation: Sigua, G.C., Paz-Alberto, A.M. 2008. Phytoremediation Potential of Lead-Contaminated Soil Using Tropical Grasses [abstract]. Florida Scientist. 71(1): 1-6.
The global problem concerning contamination of the environment because of human activities is increasing. Most of the environmental contaminants are chemical by-products and heavy metals such as lead (Pb). Lead released into the environment makes its way into the air, soil and water. Lead contributes to a variety of health effects such as decline in mental, cognitive and physical health of the individual. An alternative way of reducing Pb concentration from the soil is through phytoremediation, a method that uses plants to clean up a contaminated area. The objectives of this study were: (1) to determine the survival rate and vegetative characteristics of three grass species such as vetivergrass (Vetiveria zizanioides L.), cogongrass (Imperata cylindrica L.), and carabaograss (Paspalum conjugatum L.) grown in soils with different Pb levels (75 and 150 mg/kg); and (2) to determine and compare the ability of the three grass species as potential phytoremediators in terms of Pb accumulation by plants. The Pb contents of the test plants and the soil were analyzed before and after experimental treatments using an atomic absorption spectrophotometer. This study was laid-out following a 3 x 2 factorial experiment in a completely randomized design. On the vegetative characteristics of the test plants, vetivergrass registered the highest whole plant dry matter weight (33,853 - 39,386 kg/ha). Carabaograss had the lowest herbage mass production of 4,120 kg/ha and 5,720 kg/ha from soils added with 75 and 150 mg Pb/kg, respectively. Vetivergrass also had the highest percent plant survival, which meant it best tolerated the Pb contamination in soils. Vetivergrass registered the highest rate of Pb absorption (10.16 ± 2.81 mg/kg). This was followed by cogongrass (2.34 ± 0.52 mg/kg) and carabaograss with mean Pb level of 0.49 ± 0.56 mg/kg. This can be attributed to the highly extensive root system of vetivergrass with the presence of enormous amount of root hairs. Extensive root system denotes more contact to nutrients in soils, therefore more likelihood of nutrient absorption and Pb uptake. The present study indicated that vetivergrass possessed many beneficial characteristics to uptake Pb from contaminated soil. It was the most tolerant and could grow in soil contaminated with high Pb concentration. Cogongrass and carabaograss are also potential phytoremediators since they can absorb small amount of Pb in soils although cogongrass is more tolerant to Pb-contaminated soil compared with carabaograss. | <urn:uuid:87a08665-bcb0-4272-b3cf-bf5856857ddd> | 2.796875 | 659 | Academic Writing | Science & Tech. | 47.383409 |
Arggghhhh! Nothing gets my goat more than reading a novel or a report that shows a scientific name with both the genus and species names with upper case letters or neither word in italics.
It's really simple! Organisms that have been scientifically described have two names*, a genus name and a species name. The first one is the genus name. It always begins with an upper case letter. The second is the species name. It never has an upper case letter.
For an example, I give you Heterodontus portusjacksoni, better known as the Port Jackson Shark. The whole name is written in lower case letters except the first letter of the genus name. Both names are written in italics. Simple! If you are hand-writing the name and italics cannot be used, underline both words, Heterodontus portusjacksoni.
The genus and species names are usually derived from Latin or Greek but often include a person's name. The genus name Heterodontus comes from the Greek heteros meaning 'different' and dont meaning 'tooth' This refers to the difference between the anterior teeth which are small and pointed and the posterior teeth which are broad and flat. The species name portusjacksoni refers to Port Jackson, better known as Sydney Harbour.
Phew. I feel better now!
*I am ignoring subspecies, races, vars etc. | <urn:uuid:b5bebda8-debb-42b8-bd72-536372906dfc> | 3.046875 | 295 | Personal Blog | Science & Tech. | 52.80055 |
And now to the questions.
Q. Can you give us a brief overview, Robert, of just what your book is about?
A. I'm saying that the next ice age could begin any day. And when it begins it will begin with a bang, practically overnight. People in the north will be buried beneath vast amounts of snow (two stories, three stories, six stories of snow, in one day) while the south will be hammered by ever bigger storms . . . just as is happening today.
Q. What evidence do you see that an ice age is imminent?
A. Look at the headlines. Snow in Guadalajara. Snow in Mexico City. Snow in South Africa. Record snows in Vermont and Washington states. Snow in Louisiana, Alabama, and Mississippi. The coldest December in Moscow since 1882. Record cold and snow in Australia. The worst ice storm ever in Quebec. The worst ever!
Q. But what about global warming?
A. Global warming is a myth. Most of the things we see happening to our weather lately have nothing to do with global warming. They're part of a natural cycle. The fact is that ice ages recur in a dependable, predictable cycle that's about to repeat itself. The next ice age could begin in our lifetimes. The cycle was discovered in the 1970s by a group called CLIMAP (Climate Long- Range Investigation, Mapping, and Prediction). They looked at deep sea cores for the past 500,000 years. During the last half million years, they found, ice ages have begun or ended, abruptly, just like clockwork, about every 11,500 years.
Q. I almost hate to ask this, but when did the last ice age end?
A. That's the problem. The last ice age ended almost exactly 11,500 years ago. Which means that the next ice age could-no, I say should- begin any day.
Q. Okay, let's say that you're right, that today's storms are part of a natural cycle. But still, what causes the cycle?
A. It has to do with our warming seas . . . El Niño, in other words. Ocean temperatures, at least in the Pacific, have been warming for several decades. And I know, I know, we seem to blame everything on El Niño lately. But doesn't anyone wonder why each El Niño seems to be getting worse? I think it's part of the ice-age cycle. We've forgotten that this isn't the first time that our seas have warmed. Ocean temperatures also shot upward some 10o to 18oF about 11,500 years ago just prior to the glaciation that killed the mammoths . . . the same as they're doing today.
Q. This sounds like global warming.
A: At first glance, it does sound like global warming. That's where I think today's scientists have missed the boat.
I think it's caused by underwater volcanism, not by humans. As our seas warm, more and more moisture rises into the sky. Then it condenses and falls to the earth as giant storms and blizzards, the kind of storms and blizzards we've been getting lately. That's what El Niño is all about. My question is, what happens when that moisture begins falling in the winter? Instantaneous ice age. And that's what I'm talking about. Our seas, heated by underwater volcanism, are leading us directly into the next ice age . . . and we don't even know it. I think we're in for the biggest rash of El Niños in 11,500 years.
Q. What makes you think that underwater volcanism is the culprit?
A. Well, scientists have known for years that peaks in volcanism correlate with glaciation.
Just prior to the period of glaciation that killed the mammoths, for example, volcanism increased dramatically. In Alaska and Siberia, large amounts of volcanic ash are interspersed through the piles of mammoth bones themselves.
Q. Does volcanism send so much ash into the sky that it blocks out the sun?
A. That's what scientists thought at first. But then they discovered that there's not enough ash in the stratigraphic record to have done the trick. But I think they missed an important, little-known fact about volcanism. According to experts at NOAA (National Oceanic and Atmospheric Administration), 80% of all volcanic activity occurs underwater. For every volcano you see erupting into the sky, in other words, four volcanoes of equal size should be erupting into the sea. (With new knowledge about underwater volcanoes, this ratio has increased dramatically in the past few years.)
Q. You make it sound as if an ice age could begin almost overnight. But didn't we learn in school that ice ages begin slowly, over tens of thousands of years?
A. We learned wrong. In 1987 a research project called GRIP (Greenland Ice Core Project) began drilling deep cores into the ice in central Greenland. They drilled almost two miles deep, deep enough to reach ice that formed 250,000 years ago.
When they analyzed the cores, they found that every ice age during the past 250,000 years-and there were many-began abruptly.
Q. What do you mean by abruptly?
A. The climate descended from periods of warmth such as today's-let me repeat that, from periods of warmth such as today's-to full-blown glacial severity in less than twenty years. Perhaps in less than ten.
I want people to hear me on this. This is not theory. This is fact. Ice ages begin incredibly fast, and they do it from periods of warmth such as today's.
You do not need cold weather to cause an ice age! During the very depths of the last ice age, the tropics and subtropics were only four degrees colder than today. Temperatures in the equatorial rainforest belt remained much the same as today.
Q. Let's put this in today's terms. How cold would it have to be- today-for an ice age to begin?
A. It's cold enough right now to cause an ice age, said Maurice Ewing, one-time director of Lamont-Doherty Earth Observatory. All we need is more moisture.
And that's why today's giant storms concern me. We're getting the moisture that Ewing was talking about.
Think about what would happen in the north-without lowering the temperature even one degree-if you increased the amount of precipitation. Let it snow two feet a day for 30 days, and you'd have 60 feet of snow! Six stories!
Actually, all you'd need is for a mere two feet of snow to remain on the ground in the north during one entire growing season. Shut down the breadbasket of the world and millions of people would die of starvation.
Ask the people in Grand Forks, North Dakota, who just lived through a winter with the most snowfall on record, and then a 500-year flood. They'll tell you what too much moisture in the winter can do.
Q. Do you see any evidence of too much moisture?
A. Look at the floods. Worldwide flood activity is at it's highest levels since the Middle Ages. Japan, Germany, Italy, Mexico, Canada, Spain, Portugal-in more than 30 countries around the world, flood activity is the worst in 500 years. Same in the United States. Record rains in Minnesota, California, Idaho, Oregon, Washington, the list goes on and on.
Twelve inches of rain in Kentucky in one day. Sixteen inches of rain in North Carolina in one day. This is global warming?
Q. Couldn't it simply be a case of better communications; simply that we're being bombarded with so much news from around the globe that it only seems as if storm activity is worse? Couldn't it be our imaginations?
A. It's not our imaginations. According to Thomas Karl at the National Climatic Data Center, the number of what scientists call extreme precipitation events-blizzards and heavy rainstorms-has jumped almost 20% in the United States just since 1970.
Q. So you're saying that today's record-breaking rainstorms and floods are an indicator of an ice age?
A. Absolutely. Go back to that 16 inches of rain in North Carolina in one day. My question is, what if it had been cold at the time? What if that rain had fallen as snow?
When weather forecasters try to predict how much snow will fall if a rainstorm should turn to snow, they simply add a zero. One inch of rain, therefore, translates into 10 inches of snow. (Or more, if it's fluffy.)
So Kentucky's 12 inches of rain (add a zero) would have been 120 inches of snow. Ten feet. And North Carolina's 16 inches of rain would have been 160 inches of snow. Thirteen feet. One-and-a-half stories.
And that's the point of my book. Two stories, six stories, nine, you pick the number, the point is that vast amounts of snow killed the dinosaurs, vast amounts of snow killed the mammoths, and vast amounts of snow-at least in the north-will soon kill most of us. It's all part of the same natural cycle.
Q. What makes you think that underwater volcanism is heating our seas today?
A. It has to be. After all, above water volcanism, like flooding, is the worst in at least 500 years. (This comes from Dixy Lee Ray's 1993 book Environmental Overkill, and is confirmed by the Smithsonian's 1994 book Volcanoes of the World by Tom Simkin and Lee Siebert.)
If NOAA's 80% ratio is right, shouldn't underwater volcanism also be the greatest in 500 years?
The facts point that way. In 1993, marine geophysicists found 1,133 previously unmapped underwater volcanoes near Easter Island. They're packed into an area of about 55,000 square miles, about the size of New York state.
They were shocked. Until then, scientists had thought there were about 10,000 underwater volcanoes in the entire world. Finding 1,133 new ones-especially in such a small area-blew them away. Closer to home, in 1993 scientists discovered a four-mile-long underwater rift volcano, called Coaxial Volcano, off the coast of Oregon about 270 miles west of Astoria. In 1996 they discovered another one-six miles long-off the coast of Newport, Oregon. And just a couple of months ago they found yet another between the two.
Q. And didn't an underwater volcano recently erupt near Hawaii?
A. Yes. You're talking about Loihi Volcano, which began erupting late last year. It's the largest underwater volcano in the world, and we weren't even monitoring it. This is going on right now! Underwater volcanoes are heating our seas, and they're leading us directly into the next ice age.
And what causes underwater volcanism?
Energy transfer from Sun which is triggered by the emission from Galaxy centre during their alignment.
First great influx of energy causes heating up and partial evaporation of seas. This evaporation keeps Earth's surface temperature contained, like in evaporator of air conditioning plant.If energy flux is large enough, polarity change of the sun causes change of the axis of rotation of Earth.
When alignment subsides Earth core heating /volcanism stops and sudden condensation of massive quantities of airborne water vapour occurs causing diluvial rains and temperature drops in extremely short time. In few days or up to just few weeks occurring imbalance causes heavy snowfalls that rise albedo of Earth's surface which allows more snow to form. Such snow mantle acts like insulator and impedes energy radiation from Earth's surface which, eventually, accumulates enough energy to melt the snow. This occurs first at the equator because the aid of the direct energy radiation form the Sun. Quasi balance is established again.
Human civilisation starts from newly designed beginning. Geneticallywise. That allows new/ old spirit to fill in. Control is maintained.
Otherwise natural development would have continued and humans would spin out of the control. | <urn:uuid:d60185de-e643-460f-81f9-17a513d690c4> | 2.71875 | 2,561 | Audio Transcript | Science & Tech. | 69.25014 |
Multiplication of polynomials
Multiplication of polynomials.
To multiply a polynomial by a polynomial, multiply each of the terms of one polynomial by each of the terms of the other polynomial and combine results.
- The laws of exponents
- The rules of signs
- The commutative and associative properties of multiplication.
Multiply (3x+2)(4x2 - 2x + 10)
(3x+2)(4x2 - 2x + 10)=12x3-6x2+30x+8x2-4x+20=12x3+2x2+26x+20 | <urn:uuid:e7fd15e1-fb43-48ff-baed-3d85e8e476b0> | 3.546875 | 149 | Tutorial | Science & Tech. | 57.203043 |
branch of zoology dealing with the scientific study of insects. The Greek word entomon, meaning `notched,` refers to the segmented body plan of the ... [8 related articles]
Found op http://www.britannica.com/eb/a-z/e/34
entomology 1. The branch of zoology that deals with the study of insects. 2. From French entomologie (1764), coined from Greek entomon, 'insect' plus logia, 'study of'. Entomon is the neuter form of entomos, 'having a notch or cut (at the waist)'; so called by Aristotle in reference to the segmente...
Found op http://www.wordinfo.info/words/index/info/view_unit/737/
Entomology (from Greek ἔντομος, entomos, "that which is cut in pieces or engraved/segmented", hence "insect"; and -λογία, -logia) is the scientific study of insects, a branch of arthropodology. At some 1.3 million described species, insects account for more than two-thirds of all known...
Found op http://en.wikipedia.org/wiki/Entomology
entomology, study of insects, an arthropod class that comprises about 900,000 known species, representing about three fourths of all the classified animal species. Insects are studied because of their importance as pollinators for fruit crops; as carriers of bacterial, viral, and fungal diseases; as...
Found op http://www.infoplease.com/ce6/sci/A0817428.html
Entomology is the branch of zoology dealing with insects. It was started as a science in 1705 by the publication of Ray's 'Methodus Insectorum'.
Found op http://www.probertencyclopaedia.com/browse/BE.HTM
Type: Term Pronunciation: en′tō-mol′ŏ-jē Definitions: 1. The science concerned with the study of insects.
Found op http://www.medilexicon.com/medicaldictionary.php?t=29497
Study of insects
Found op http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0001185.html
1) Bugology 2) Zoological science 3) Zoology
Found op http://www.mijnwoordenboek.nl/EN/crossword-dictionary/entomology/1
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• Juan Nicasio (1) | <urn:uuid:2e37bb85-b103-4038-b6ad-c252a00fcc42> | 3.21875 | 832 | Structured Data | Science & Tech. | 66.106834 |
The Proxy design pattern (GoF ) allows you to provide "a surrogate or placeholder for another object to control access to it". Proxies can be used in many ways. Some of which are:
Commons Proxy supports dynamic proxy generation using proxy factories, object providers, invokers, and interceptors.
Proxy factories encapsulate all necessary proxying logic away from your code. Switching proxying techniques/technologies is as simple as using a different proxy factory implementation class. Currently, Commons Proxy provides proxy factory implementations using JDK proxies, CGLIB , and Javassist . Proxy factories allow you to create three different types of proxy objects:
Object providers provide the objects which will be the "target" of a proxy. There are two types of object providers:
A core object provider provides a core implementation object. Commons Proxy supports many different implementations including:
|Constant||Always returns a specific object|
|Bean||Merely instantiates an object of a specified class each time|
|Cloning||Reflectively calls the public clone() method on a Cloneable object|
|Hessian||Returns a Hessian -based service object|
|Burlap||Returns a Burlap -based service object|
|JAX-RPC||Returns a JAX-RPC -based service object|
|Session Bean||Returns a reference to a Session EJB (stateless session beans only)|
An invoker handles all method invocations using a single method. Commons Proxy provides a few invoker implementations:
|Null||Always returns a null (useful for the "Null Object" pattern)|
|Apache XML-RPC||Uses Apache XML-RPC to fulfill the method invocation|
|Duck Typing||Supports "duck typing" by adapting a class to an interface it does not implement.|
|Invocation Handler Adapter||Adapts the JDK InvocationHandler interface to the Commons ProxyInvoker interface.|
Commons Proxy allows you to "intercept" a method invocation using Interceptors . Interceptors provide rudimentary aspect-oriented programming support, allowing you to alter the results/effects of a method invocation without actually changing the implementation of the method itself. Commons Proxy provides a few interceptor implementations including:
|Executor||Uses an Executor to execute the method in possibly another thread (only void methods are supported).|
|Logging||Logs all method invocations using the Apache Commons Logging API|
|Filtered||Optionally intercepts a method invocation based on a method filter|
|Method Interceptor Adapter||Adapts the AOP Alliance MethodInterceptor interface to the Commons ProxyInterceptor interface.|
The latest version is v1.0. -
For previous releases, see the Apache Archive
Note: The 1.x releases are compatible with JDK1.4+.
The commons mailing lists act as the main support forum. The user list is suitable for most library usage queries. The dev list is intended for the development discussion. Please remember that the lists are shared between all commons components, so prefix your email subject with [proxy].
Issues may be reported via ASF JIRA . Please read the instructions carefully to submit a useful bug report or enhancement request. | <urn:uuid:d5929851-d37d-48cc-84df-1dd901a5afa2> | 2.984375 | 681 | Documentation | Software Dev. | 21.874251 |
In C or C++, it's apparently possible to restrict the number of bits a variable has, so for example:
unsigned char A:1; unsigned char B:3;
I am unfamiliar however with how it works specifically, so a number of questions:
If I have a class with the following variables:
unsigned char A:1; unsigned char B:3; unsigned char C:1; unsigned char D:3;
- What is the above technique actually called?
- Is above class four bytes in size, or one byte in size?
- Are the variables treated as 1 (or 3) bits as shown, or as per the 'unsigned char', treated as a byte each?
- Is there someway of combining the bits to a centralised byte? So for example:
unsigned char MainByte; unsigned char A:1; //Can this be made to point at the first bit in MainByte? unsigned char B:3; //Etc etc unsigned char C:1; unsigned char D:3;
- Is there an article that covers this topic in more depth?
- If 'A:1' is treated like an entire byte, what is the point/purple of it?
Feel free to mention any other considerations (like compiler restrictions or other limitations). | <urn:uuid:789045e0-0dda-4a72-8d9f-90f05bffab21> | 2.96875 | 270 | Q&A Forum | Software Dev. | 57.580529 |
C represented strings as null-terminated arrays of ASCII characters. This meant that you couldn't include '\0' in your strings, and if you forgot the null terminator, you were screwed. I hope you like buffer overflows. And the fact that strings can be changed in-place by any piece of code with a pointer to it should make anybody a little nervous. Strings, in order to behave the way we expect, should be immutable by default.
More recent languages generally agree on these things. Java, Python, and C# (among many others) all represent strings as immutable objects, with the length recorded explicitly -- no null-termination shenanigans. You can share memory among substrings, and pass string values around without having to worry about them being modified from some other thread somewhere. This sort of thing pleases a compiler greatly, and makes programs less bug-prone. This also makes it possible to store only a single copy of short strings, to improve memory efficiency, cache locality, and so on. Plus, you get ridiculously fast string comparisons, since two equal strings will always be represented by the same pointer.
There's one more big wrinkle here, though, and that's Unicode. If we want to represent more characters than the ones that ASCII gives us, we need to be able to use more than one byte per character. And that's a pain in the ass.
You can represent any Unicode character in 32 bits. This gives you a very simple representation, just an array of 32-bit values. It also uses several times more memory than alternatives like UTF-16 and UTF-8, which encode characters with a variable number of bytes. For people using mostly ASCII characters, UTF-8 is going to be the most compact, by far. It also makes random string indexing take O(n) time, because you don't know how wide the characters are until you look at them, so you can't just use O(1) array indexing like you can with fixed-width encodings. Another option, that several systems use, is to use a fixed-width encoding of 16 bits per character, and just ignore the less commonly-used characters. That's vaguely adequate-ish, but it's overkill for ASCII characters, and doesn't support all of Unicode.
So what do we do? For small strings, in European languages, UTF-8 is probably just about right. Having O(n) random indexing doesn't really matter when n is small; cache locality matters more. Most strings are small, so it's important that they be efficient. First rule of optimization: make the common case fast.
How about longer strings? What if we have a 10 MB string, and we want to do random indexing, substring slicing, maybe insert a few characters in the middle... how do we do it efficiently? UTF-32 is preposterously memory-heavy. UCS-2 doesn't support all of Unicode. UTF-8 is memory-efficient, but variable-width. UTF-16 is usually less memory-efficient than UTF-8, and still variable width. That's the worst of both worlds. What do we do?
At this point, we really should stop thinking of strings as arrays of bytes. They're sequences of characters. It's a subtle distinction -- but there are other ways of representing sequences.
Haskell's default strings, for example, are laughably inefficient linked lists of of 32-bit characters. No, seriously. There's a reason people use libraries for more efficient strings. But while this isn't exactly a practical string encoding, it at least illustrates that strings don't have to be arrays.
What would a practical heavyweight string look like? One way to do it would be as a tree of character array chunks. For example, the string "hello, world" might be represented like this:
This is a balanced binary tree, but of course you can pick whatever representation you like. This kind of data structure is called a rope. If you go with ropes as your string representation of choice, you get cheap concatenation and substring slicing.
Ropes also make string modification cheaper. With immutable array-based strings, any time you want to change so much as a single character, you have to allocate a new copy. With any array-based strings, if you want to add or remove characters, you need to copy a bunch of other characters around. With ropes, you can share most of the blocks of characters between the old and new versions of the string, and the insertion and deletion operations are both cheap. Suppose you add an exclamation mark to the end of our string, turning it into "hello, world!" and keep both versions around. You just need to allocate a new block to hold "rld!":
This is the kind of string representation often used in text editors, where they need to support fast and easy string modification. This allows constant- or logarithmic-time concatenation, logarithmic-time modification, and good memory efficiency. The drawback is that it makes our strings more complicated, and makes random indexing an O(lg n) time operation -- worse than the O(1) that people get with fixed-width array-based strings.
But wait! That O(lg n) is still better than the O(n) we would get with variable-width array-based strings, if we went with (say) UTF-8. How can this be?
The answer is that, at each node in the tree, we store the length of the string formed by its children. The tree actually looks something like this:
This way, we can combine efficient string indexing with efficient Unicode encodings. If you encode each of the chunks in UTF-8, then that doesn't change a thing about how you traverse the tree to find the chunk with the nth character. And once you've narrowed it down to a single chunk, the time left for string indexing is proportional to the chunk size -- usually not a very large overhead.
Thus, oddly enough, heavyweight string data types can actually use less memory than simpler ones, by making compact variable-length encodings fast. They give better asymptotic time bounds on most operations. They allow cheap modification of strings, without throwing away immutability. I think that's pretty cool.
(I'm working on an implementation of this in Haskell using the Data.ByteString.UTF8 and Data.FingerTree libraries. It's proving surprisingly straightforward and easy. You just need to combine UTF-8 array strings with a balanced tree that supports caching the value of a monoid at the leaves. That's exactly what a finger tree is all about, so it all fits together nicely. I'll put it up on GitHub sometime in the not-too-distant future.) | <urn:uuid:c111478e-123f-4793-b630-d5490da74131> | 3.59375 | 1,415 | Personal Blog | Software Dev. | 59.902293 |
ThinkProgress did a search of major national newspapers and found that Sandy was mentioned at least 94 times, but terms like climate change, global warming and extreme weather weren't mentioned at all. She suggests two possible reasons for the disconnect: The presidential candidates have been silent on climate change and left it out of the debates for the first time since 1988, and climate denial campaigns try to undermine science. "There is still a gulf between public understanding and the scientific consensus," Leber writes. Al Gore says Sandy was worse because of global warming.
Atmospheric blocking events like the one that intensified Sandy are caused by warming temperatures, melting sea ice and rising ocean levels. Blocking events also shift jet streams further from normal patterns, and climate researcher Jennifer Francis told Andrew Revkin of The New York Times that Sandy's blocking event "may have been boosted in intensity and/or duration by the record-breaking ice loss this summer." Late season hurricanes aren't unusual, she said, but Sandy started during an anomalous jet-stream pattern and an autumn with record-warm sea temperatures in the Atlantic. "It could very well be that general warming along with high sea-surface temperatures have lengthened the tropical storm season," Francis said. | <urn:uuid:ccdedbcc-08be-45ae-9d91-ab82fc26dafc> | 2.703125 | 247 | Personal Blog | Science & Tech. | 31.312716 |
Halloween Worksheets for Math
Halloween Candy Sort - Math for Young Children
Use the Halloween haul to demonstrate sorting and classification to young trick or treaters.
Halloween Math Ideas
Some mathematical suggestions for problem solving with math related to Halloween.
Halloween Related Math Worksheets
Scroll down for a listing of Halloween math worksheets. List includes: Easy Halloween Addition and Subtraction Problems, Halloween Money Problems,Halloween Time Problems, Halloween Multiplication and Division Problems, Halloween Algebra Problems.
Halloween Themed Math Printables
A variety of fun math activites for the Halloween Theme.
Halloween Word Problems: Math
Print these problem solving questions related to Math for your children to solve.
Learning the multiplication fact is fun with Multiplication Ghosts!
Ideal Math! Pumkin size and color, smell and taste make them perfect for children's observation and exploration. In this activity children, suggest, question, predict, and estimate the number of seeds in a set of pumpkins.
Motivating math activities using pumpkins. Skills include: predicting, measuring, sorting, classifying, and finding relationships.
Pumpkin Seed Sort
Estimation, sorting with Pumpkin Seeds. Encourages mathematical thinking! | <urn:uuid:faeebdbc-1e9e-4c94-b603-1350cc1a082c> | 3.359375 | 259 | Content Listing | Science & Tech. | 27.848071 |
Search Loci: Convergence:
Suppose we loosely define a religion as any discipline whose foundations rest on an element of faith, irrespective of any element of reason which may be present. Quantum mechanics for example would be a religion under this definition. But mathematics would hold the unique position of being the only branch of theology possessing a rigorous demonstration of the fact that it should be so classified.
In H. Eves In Mathematical Circles, Boston: Prindle, Weber and Schmidt, 1969.
Gerbert d'Aurillac and the March of Spain: A Convergence of Cultures
Gerbert devised a new kind of abacus which one could use to calculate with the Hindu numerals, a flat board with columns drawn on it, corresponding to ones, tens, hundreds, and so forth. (Some scholars believe he may have been the first person to use the Latin term abacus.) He had a shield-maker construct small pieces of animal horn with the numerals on them; called apices, the pieces could then be placed on the board to represent numbers. A zero was not necessary; the absence of a marker in the tens’ place, for instance, meant that there were no tens. An eleventh-century manuscript found in Limoges illustrates the representation of numbers on such an abacus. (Note that the numerals had changed slightly in the next hundred years.)
Gerbert compiled a list of rules for computing with his abacus, Regula de Abaco Computi, in which he painstakingly explained how to multiply and divide, as well as add and subtract, in the new system. A companion work, Liber Abaci, by his student Bernelin, is often included in the collected works of Gerbert; it predates the book of the same name by Fibonacci by two hundred years.
To see an example of how to add numbers using Gerbert’s abacus, click here. [This is a power point animation of the process.]
And for an example of subtraction, click here. | <urn:uuid:e296596b-c7e6-40f6-9c41-e000dfabcb05> | 3.09375 | 419 | Knowledge Article | Science & Tech. | 44.30125 |
why 360 degrees?
See also the
Dr. Math FAQ:
segments of circles
Browse High School Conic Sections, Circles
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Find the center of a circle.
Is a circle a polygon?
Volume of a tank.
Why is a circle 360 degrees?
- Area under Arc of Circle [02/27/2001]
Calculate the area delimited by the arc of a circle and the chord of that
arc, given only the length of the chord and the length of a line,
perpendicular to the chord, running from the middle of the chord to the
edge of the circle.
- Bounding Rectangle for an Ellipse [6/28/1996]
I would like to know if there is a general equation for a bounding
rectangle of an ellipse.
- Building a Circular Horse Pen [06/16/2002]
My Dad and I are building a round pen for our horse. We have 16
16ft. panels and a 10 ft. gate and a 4ft. gate. (270 ft. total) We
want to use a radius and mark the places to dig holes for each post
that will support the panels, but we don't know how long the radius
should be. Can you help?
- Building a Cone [10/28/2001]
I am trying to find a formula for building a cone for a chimney flashing.
It should be 21" tall with a top opening of 8", a bottom opening of 20",
and a vertical seam overlap of 2".
- Calculating Circle Radius [01/29/2001]
I am trying to find a formula that will give me the radius of a circle,
given only the length of an arc on that circle and the chord length of
- Calculating the Radius from a Chord [08/18/1998]
If I know the chord length and chord height, is there a formula for
determining the radius of the circle?
- Can a Circle be a Polygon? [5/22/1996]
Could a circle be considered a polygon with an infinite number of sides?
- Catenary and Parabola Comparison [04/06/2004]
What is the difference between a catenary and a parabola? I don't
know the difference in shape. Why is the St. Louis arch a catenary
and not a parabola?
- Centering Circles [10/05/2002]
Two metal disks need to be centered on each other, but the circle
with the larger diameter has the center cut out. How can you center
them by knowing the diameters?
- Center of a Circle from Circumference Points [06/25/1999]
How do I figure the center point (Xc,Yc,Zc) of a circle given 2 or more
points on its circumference and its radius?
- Center of Mass of a Semicircle [06/14/1999]
Is there a standard formula I can use to know where the center of mass of
a semicircle is?
- Changing Angle of a Tank [06/11/2003]
Points A and B represent pressure sensors in fixed positions on the
base of a round tank. The chord through CD represents the water level
in the tank. Lines a and b are the heights of water registered by each
- Chord Proofs [10/07/1997]
Prove that in any circle a radius perpendicular to a chord also bisects
the chord... a radius that bisects the chord is perpendicular to the
chord... chords equidistant from the center of the circle are congruent.
- Chords From Inscribed Polygons [07/11/2002]
An regular polygon is inscribed in a circle of known radius. Each
side of the octagon is a chord of the circle. What is the length of
- Circle and Polygons: Lines of Symmetry [04/14/1997]
How many lines of symmetry are there in a circle?
- Circle Center's Cartesian Coordinates [03/24/1999]
How do you find the Cartesian coordinates of a circle's centers if you
know two points on its perimeter?
- Circle Enclosed by Three Circles [08/18/1999]
How can I find the center and radius of a circle that is enclosed by
three other circles that all touch each other at one point?
- Circle Geometry [6/4/1996]
Two circles intersect at A and N. One of their common tangents has points
of contact P and T. Prove that <PAT and <PNT are supplementary.
- Circle in n Sectors [7/8/1996]
A circle is completely divided into n sectors in such a way that the
angles of the sectors are in arithmetic progression...
- Circle Inscribed in a Right Triangle [09/09/1997]
What is the diameter of the circle if the legs of the triangle are known
to be A and B?
- Circle Inscribed in Sector [05/20/1999]
Given a 60-degree arc of a sector of a circle with a radius of 12 inches,
find the area of the circle that can be inscribed in the sector.
- Circle Inscribed in Triangle [04/04/1997]
What is the radius of a circle inscribed in a 3-4-5 right triangle?
- Circle Overlap [11/08/2001]
Circle A and Circle B both have a radius of 1 unit. The centers of each
circle are 1 unit apart as well. Find the area of the union of the two
- Circle Radius from Chord Length and Depth [06/16/1999]
How do you find the radius or diameter of a circle when you only know a
chord length and the depth?
- Circle Regions [01/28/2001]
What is the maximum number of regions you can have with n chords in a
- Circle Revolutions [07/02/2002]
Our teacher gave everyone a CD, and told us to look at the spin of the
smaller inner circle and of the large outer circle. We have concluded
that they both make a revolution in the same amount of time, but they
moving at different speeds. Is that possible?
- Circles around a Larger Circle [07/26/2003]
Is there a formula to determine the diameter of several smaller
circles outlining the circumference of a larger circle?
- Circle Sector Area [03/20/2003]
Do we have to convert degrees to radians when finding the area of a
sector of a circle?
- Circles in a Square [09/15/2001]
A circle of radius 1 is inside a square whose side has length 2. Show
that the area of the largest circle that can be inscribed between the
circle and the square is (pi(17 - 12sqrt(2))).
- Circles Inscribed in Triangles [11/14/1996]
Given two triangles, prove that r1 + r2 + r3 = r.
- Circles of More than 360 Degrees [11/10/2001]
What shape is formed if one cuts along the radius of a circle and adds
degrees by adding a sector?
- Circles within a Circle [10/12/2000]
Given three circles of diameters 3", 2", and 1", the two smaller inside
the largest so that their combined diameters equal the diameter of the
largest circle. What is the greatest possible diameter of a fourth circle
placed in the remaining area?
- Circle Tangent to Line [04/19/2001]
Construct the circle that passes through two given points and is tangent
to a line.
- Circle With Radius of Zero [12/28/2004]
Is it possible for a circle to have a radius that equals zero? Is it
possible for a set of points to occupy the same location?
- Circular Field, Cow, and Length of Rope [9/11/1996]
A cow is tied with a rope to the edge of a circular field 10 ft. in
diameter. How long must the rope be so the cow can graze half the field?
- Circumference and Rotation [10/07/2003]
The wheel on a truck rotates 330 times in a mile. Find the radius of
- Circumference of a Circle Given Chord Length [9/11/1996]
Given the length of a chord of a circle, is it possible to determine the
- Circumference of an Ellipse [5/18/1996]
Is there a formula for determining the circumference or distance around
- Circumference of a Square [05/13/2002]
A circle has a circumference C. Find, in terms of C, the perimeter
of a square having the same area as the circle.
- Circumscribing Tangent Circles [04/13/1999]
Given three circles of various sizes in a plane, circumscribe a circle | <urn:uuid:1bbe4d57-390a-4955-aa9c-1f55796983e7> | 3.75 | 1,961 | Q&A Forum | Science & Tech. | 73.839218 |
Table of Contents [+/-]
MySQL 4.1 introduces spatial extensions to allow the generation,
storage, and analysis of geographic features. Currently, these
features are available for
MyISAM tables only.
This chapter covers the following topics:
The basis of these spatial extensions in the OpenGIS geometry model
Data formats for representing spatial data
How to use spatial data in MySQL
Use of indexing for spatial data
MySQL differences from the OpenGIS specification
The Open Geospatial Consortium publishes the OpenGIS® Simple Features Specifications For SQL, a document that proposes several conceptual ways for extending an SQL RDBMS to support spatial data. This specification is available from the OGC Web site at http://www.opengis.org/docs/99-049.pdf.
If you have questions or concerns about the use of the spatial extensions to MySQL, you can discuss them in the GIS forum: http://forums.mysql.com/list.php?23. | <urn:uuid:dbfe7330-64a4-4697-8945-8a6fece6afe1> | 3.203125 | 209 | Documentation | Software Dev. | 47.675495 |
3.3 m and from Type Ia Supernovae
The use of type Ia supernovae for measuring cosmological parameters is covered elsewhere in this volume by Filippenko (nearby supernovae and determinations of H0) and by Perlmutter (distant supernovae and m and ). Hence, these objects will not be discussed in much detail here, except to highlight their potential, and to summarize some of the main difficulties associated with them so that they can be compared relative to some of the other methods discussed in this review.
The obvious advantage of type Ia supernovae is the small dispersion in the Hubble diagram, particularly after accounting for differences in the overall shapes or slopes of the light curves (Phillips 1993; Hamuy et al. 1995: Reiss, Press & Kirshner 1997). In principle, separation of the effects of deceleration or a potential non-zero cosmological constant is straightforward, provided that (eventually) supernovae at redshifts of order unity can be measured with sufficient signal-to-noise and resolution against the background of the parent galaxies. The differences in the observed effects of m and become increasingly easier to measure at redshifts exceeding ~ 0.5. In principle, the evolution of single stars should be simpler than that of entire galaxies (that have been used for such measurements in the past).
At the present time, however, it is difficult to place any quantitative limits on the expected evolutionary effects for type Ia supernovae since the progenitors for these objects have not yet been unequivocally identified. Moreover, there may be potential differences in the chemical compositions of supernovae observed now and those observed at earlier epochs. In principle, such differences could be tested for empirically (as is being done for Cepheid variables, for example). It is also necessary to correct for obscuration due to dust (although in general, at least in the halos of galaxies, these effects are likely to be small; a minor worry might be that the properties of the dust could evolve over time). In detail, establishing accurate K-corrections for high-redshift supernovae, measuring reddenings, and correcting for potential evolutionary effects will be challenging, although, with the exception of measurements of the cosmic microwave background anisotropies (discussed in Section 9 below), type Ia supernovae may offer the best potential for measuring m and .
The most recent results based on type Ia supernovae (Perlmutter et al. 1997 are encouraging, and they demonstrate that rapid progress is likely to be made in the near future. Currently, the published sample size is limited to 7 objects; however, many more objects have now been discovered. The feasibility of discovering these high-redshift supernovae with high efficiency has unquestionably been demonstrated (e.g. Perlmutter, this volume). However, systematic errors are likely to be a significant component of the error budget in the early stages of this program. | <urn:uuid:9e33147a-8c30-407a-8926-a9eb28a93681> | 3.03125 | 619 | Academic Writing | Science & Tech. | 24.256774 |
Polarization and Direction
Name: Jess V.
Why does the "axis" of a Polaroid lens appear to
shift by a quarter turn (90 degrees) for light traveling in opposite
directions? This behavior does not seem to fit the standard "picket
fence" model for polarized light.
This is not the behavior of a typical polarizing film. Please make sure
you are doing the experiment correctly.
It requires two pieces of polarizing film and a light source such as a
you must know the orientation of at least one film's polarization axis
Put the two pieces of polarizing film in front of the light
Rotate the polarizing film closest to the light so that most of the
light is transmitted through both pieces of film.
Turn the other polarizing film around so that light is passing through it
in the opposite direction. It is very important that you not change the
orientation of the polarization axis of the film when you do this. If
you happen to rotate it about an axis that is at 45 to the true
polarization axis of the film it will appear as though the light
transmitted has changed orientations. If this happens, try turning it
around about an axis 45 away from the one you originally used. This
will either be the polarization axis or at 90 to the polarization axis.
There is no guarantee that the polarization axis is aligned with an edge
(or geometrical axis) of the piece of polarizing film. This will depend
on how it was cut from the original sheet.
Click here to return to the Physics Archives
Update: June 2012 | <urn:uuid:6e1bee14-0bac-46d9-b6d0-de489ea8e009> | 3.015625 | 339 | Q&A Forum | Science & Tech. | 50.707564 |
Can't view YouTube? Download MP4
Challenge Question: Why does the amount of water on the speakers affect how often droplets are ejected?
Challenge Answer: The more water, the larger the surface area of the sphere of water. The speakers exert a force on the sphere of water, increasing the pressure inside the sphere. Pressure is F/A, so a given sound will generate a lower pressure in the sphere. If the pressure per unit area is strong enough to overcome the surface tension of the water, a droplet is ejected. Therefore, more water means larger surface area, which means lower force per unit area on a water droplet.
Challenge Winner: Zach Mitchell from Chapel Hill, NC | <urn:uuid:9020d520-835a-4eb5-b954-78653d7fa9b6> | 4 | 145 | Q&A Forum | Science & Tech. | 48.146923 |
Out In Space
Have you ever looked up at the sky at night and wondered just exactly what is out there? Well, you can start finding the answers to your questions right here! A solar system is made up of planets revolving around a star. It can include moons for each planet, comets, asteroids, meteoroids, and interplanetary dust. There can be many solar systems in one galaxy…and there are also many galaxies in the universe! Click on the links to learn more about what’s out there in space. | <urn:uuid:1a1e67fd-0da0-46ea-9f56-807ed1f8f188> | 2.921875 | 109 | Knowledge Article | Science & Tech. | 58.13 |
Solar power is definitely gaining momentum in the UK. In the past two years alone solar output in the UK has grown by a whopping 41 times! And we at 10:10 couldn’t be happier. In fact, our latest project, called Solar Schools, is all about getting schools across the UK to generate their own power.
Most of the times, pv cells are tucked out of sight and you could be in a solar-powered building without even knowing it! In fact, we bet you’d be surprised to find out that these places have gone solar as well!
No, there isn’t a gigantic solar panel above all of Germany, if that’s what you were wondering. But the country, which was experimenting with feed-in tariffs as far back as 1990, did break a world record in solar energy production during one weekend in spring of this year. At midday on 26 May, Germany's 1.2 million photovoltaic systems produced 22 gigawatts of solar energy per hour. That’s 50% of the entire nation’s needs and the equivalent of 20 nuclear power plants.
Germany's solar capacity is almost that of all the world combined, and they're aiming high with their green aspirations. They are going to invest a whopping $263 billion in transformation of energy sources in order to reach their greenhouse gas reduction target of 35% below 1990 levels by 2020.
Sainsbury’s has experimented with a few different taglines over the years. In the 1880s it was “quality perfect, prices lower”, then in the 1950s with the innovation of self-service shops it was “ help yourself to the best food at Sainsbury’s”. Until recently it was “Try something new today”,but we reckon it should be something along the lines of “Solar-powered quality”! Why? because as of late, Sainsbury’s is the proud owner of the largest solar array in Europe. Around 170 shops in the UK are powered by a grand total of 69,5000 solar panels. Estimated emissions reduction? 6,800 tonnes a year! And they're not stopping there. More panels are on the way to the chain’s branches to help achieve their “20 by 20” sustainability plan goals.
Next time you’re traveling through the newly refurbished and very uniquely designed King’s Cross rail station in London, look up.
What you’ll see above you is the new 240 kWp photovoltaic glazing system forming part of the curved roof of the historic Victorian building that’s recently been transformed into a beautiful futuristic space.The array of pv cells set into nearly 1400 windows is expected to save a massive 100 tonnes of carbon emissions a year while generating 10% of the station’s electricity.
Not the first place that pops to mind when thinking about green technologies, and yet it looks like the Vatican is going to become the first nation state to be completely solar-powered.
The smallest state in the world is spending $660 million on a massive 100 megawatt pv installation that will potentially provide electricity to 40,000 people, which is much more than what the 900 residents of the Vatican require. To top it off, the new acquisition is expected to cut 91,000 tons of carbon emissions and make Vatican city into a net energy exporter.
A 700 year-old fortress? Check! Medieval tower and dungeon? Check! an array of solar panels?? Check! Wait, what?! Yes, it’s a solar castle. Chirk Castle in Wales has been fitted with solar panels thanks to an award from the National Trust’s green energy fund.
The castle is owned by the national trust but some of the descendants of Sir Thomas Myddleton, who bought the castle in 1595, still live in the building. The estimation is that the solar system is expected to generate 8,000 kW of energy and save the castle £3,000 and 4,000kg of carbon in one year. | <urn:uuid:e382aac1-71b2-40cc-b1ac-c3430bb0ec3c> | 2.703125 | 842 | Listicle | Science & Tech. | 66.217701 |
WERE NORTH SLOPE DINOSAURS
"WARM-BLOODED" or "COLD-BLOODED"?
In the past, paleontologists assumed that all dinosaurs were cold-blooded like today's reptiles. But beginning in the 1960s, some scientists began raising the possibility that some dinosaurs were warm-blooded.
In warm-blooded mammals, cross-sections of their bones show many channels for the internal passage of blood. In contrast, cold-blooded reptile bones have far fewer blood channels. Significantly, bones from some types of dinosaurs show a combination of both patterns, with lots of blood channels in the bones of juveniles, and fewer in adults. Dinosaur bones found on the North Slope and studied thus far exhibit the juvenile pattern, but the debate about this matter is far from settled. It may be that dinosaurs had a unique type of metabolism unlike any living animals today. | <urn:uuid:56f0abea-bc7f-4320-8ec0-220c465e73cf> | 3.953125 | 187 | Knowledge Article | Science & Tech. | 42.195815 |
Robert L. Mills
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...in the modern theory of electromagnetism called quantum electrodynamics (q.v.), or QED. Modern work on gauge theories began with the attempt of the American physicists Chen Ning Yang and Robert L. Mills (1954) to formulate a gauge theory of the strong interaction. The group of gauge transformations in this theory dealt with the isospin (q.v.) of strongly interacting particles....
...Harald Fritzsch and Heinrich Leutwyler, together with American physicist Murray Gell-Mann. In particular, they employed the general field theory developed in the 1950s by Chen Ning Yang and Robert Mills, in which the carrier particles of a force can themselves radiate further carrier particles. (This is different from QED, where the photons that carry the electromagnetic force do not...
In the 1950s the American physicists Chen Ning Yang and Robert L. Mills gave a successful treatment of the so-called strong interaction in particle physics from the Lie group point of view. Twenty years later mathematicians took up their work, and a dramatic resurgence of interest in Weyl’s theory began. These new developments, which had the incidental effect of enabling mathematicians to...
...theory relies on a quantum mechanical property called the “mass gap.” The theory was introduced in 1954 by Chinese-born American physicist Chen Ning Yang and American physicist Robert L. Mills, who first developed a gauge theory, using Lie groups, to describe subatomic...
What made you want to look up "Robert L. Mills"? Please share what surprised you most... | <urn:uuid:12b5a28a-8964-4eea-9c01-ed9f72580612> | 3.203125 | 364 | Knowledge Article | Science & Tech. | 58.001902 |
For those who have little or no programming experience at all, you can go to:http://www.krashcourse.com/C++
The software/ebook is entitle C++ Basics for Visual Learners and discusses the basic concepts to C++ like variables, functions, loops, and decision statements. The book doesn't go into advanced topics such as reading and writing data to files. So, if you are looking for something more advanced then this wouldn't be for you but it's a great supplemental guide for those who need help understanding the basic fundamentals of C++.
Herbert Schildt "C++: The Complete Reference" is a good book for more advanced topics as others have stated. | <urn:uuid:d844b652-500b-4471-b557-5a3007478b8b> | 2.75 | 143 | Comment Section | Software Dev. | 57.966905 |
Pumping water from High Plains aquifer reducing stream flows, threatening fish habitat
Suitable habitat for native fishes in many Great Plains streams has been significantly reduced by the pumping of groundwater from the High Plains aquifer -- and scientists analyzing the water loss say ecological futures for these fishes are "bleak."
Results of their study have been published in the journal Ecohydrology.
Unlike alluvial aquifers, which can be replenished seasonally with rain and snow, these regional aquifers were filled by melting glaciers during the last Ice Age, the researchers say. When that water is gone, it won't come back -- at least, until another Ice Age comes along.
"It is a finite resource that is not being recharged," said Jeffrey Falke, a post-doctoral researcher at Oregon State University and lead author on the study. "That water has been there for thousands of years, and it is rapidly being depleted. Already, streams that used to run year-round are becoming seasonal, and refuge habitats for native fishes are drying up and becoming increasingly fragmented."
Falke and his colleagues, all scientists from Colorado State University where he earned his Ph.D., spent three years studying the Arikaree River in eastern Colorado. They conducted monthly low-altitude flights over the river to map refuge pool habitats and connectivity, and compared it to historical data.
They conclude that during the next 35 years -- under the most optimistic of circumstances -- only 57 percent of the current refuge pools would remain -- and almost all of those would be isolated in a single mile-long stretch of the Arikaree River. Water levels today already are significantly lower than they were 40 and 50 years ago.
Though their study focused on the Arikaree, other dryland streams in the western Great Plains -- composed of eastern Colorado, western Nebraska and western Kansas -- face the same fate, the researchers say.
Photo credit: Natural Kansas.org
Article continues: Science Daily | <urn:uuid:fad50cef-08a2-4e24-9e4d-502348a3c849> | 3.09375 | 403 | Truncated | Science & Tech. | 32.877377 |
Find the initial concentration of NO2 if the concentration after 2.00 min is 0.113. k = 0.331 1/(M * s) 2 NO2 (g) + N2 (g) --> 2 N2O (g) + O2 (g)
Dr. Gillian explained that research has identified over 25,000 genes which are responsible for the genetic information which progresses from generation to generation. These genes are:
We conducted a diels-Alder reaction of cyclopentadiene with Maleic Anhydride experiment. Though I was wondering why we added ligroin to the maleic anhydride and ethyl acetate. I know ligroin can be used as a solvent, but I thought that ethyl acetate was the solvent in this exp...
If it had gone down then how would we calculate it
Freezing point of pure water = -2, Freezing point of Unknown solution = -1 Mass of unknown in 50g of water = 1.9964g. Calculate the delta T for the solution of the unknown solid and determine the molecular weight of the unknown solid.
Where reading the poem "LEGAL ALIEN" by Pat Mora . We have to find the rhythm,meter, and assonance . I cant fimd any of that in the poem . Please tell me what each one of them are in the poem .. Reply ASAP please
A reaction involves fictional reagents A & B is begun with the inital concentration of 0.05M A and 0.01M B. The reaction reaches completion in 16 seconds. What is the initial rate of the reaction in respect to A? and what is the order in respect to B
The expression ax^3+2x^2+cx+1 is 5x^3-3 greater than 3x^3+bx^2+d-7x. Find a, b, c, and d.
An aqueous KNO3 solution is made using 73.4g of KNO3 diluted to a total solution volume of 1.86 L. Calculate the molarity of the solution. (Assume a density of 1.05 g/ml for the solution.)
For Further Reading | <urn:uuid:742a845f-e0b7-4ca2-aef3-824d5b56c28d> | 2.6875 | 465 | Comment Section | Science & Tech. | 81.489305 |
A dynamite blast at a quarry launches a chunk of rock straight upward, and 2.0s later it is rising at a speed of 15m/s. Assuming air resistance has no effect, calculate its speed A) at launch and B) 5.0s after lauch
In a historical movie, two knights on horseback start from rest 88.0m apart and ride directly toward each other to do battle. Sir George's acceleration has a magnitude of 0.300m/s (squared), While Sir Alfred's has a magnitude of 0.200m/s (squared). Relative to Sir Geor...
(a) Just for fun, a person jumps from rest from the top of a cliff overlooking a lake. In falling through a distance H, she acquires a certain speed v. Assuming free-fall conditions, how much farther must she fall in order to acquire speed 2v? Express your answer in terms of H.
Two cars cover the same distance in a straight line. Car A covers the distance at a constant velocity. Car B starts from rest and maintains a constant acceleration. Both cars cover a distance of 487 m in 216 s. Assume that they are moving in the +x direction. Determine (a) the...
The magnitudes of the four displacement vectors shown in the drawing are A = 13.0 m, B = 11.0 m, C = 12.0 m, and D = 27.0 m. Determine the magnitude and directional angle for the resultant that occurs when these vectors are added together.
A jetliner, traveling northward, is landing with a speed of 67 m/s. Once the jet touches down, it has 765 m of runway in which to reduce its speed to 5.1 m/s. Compute the average acceleration (magnitude and direction) of the plane during landing (take the positive direction to...
An 18-year-old runner can complete a 10.0 km course with an average speed of 4.58 m/s. A 50-year-old runner can cover the same distance with an average speed of 4.36 m/s. How much later (in seconds) should the younger runner start in order to finish the the course at the same ...
Which is an example of the commutative property? A. 8 + (13) = 13 + (8) B. 11 + (14 + 5) = (11 + (14)) + 5 C. 16 + (16) = 0 D. (22 + 1) = 22 + (1)
What is the football name of this clue, seven squared?
using math expressions, define the following: Ka,pKa, pKb, Kb and pKw
For Further Reading | <urn:uuid:a899a33d-bcde-403a-a881-aa8e2a1743e7> | 3.828125 | 574 | Content Listing | Science & Tech. | 89.265277 |
The World Meteorological Organization (WMO) requires the calculation of averages for consecutive periods of 30 years, with the latest covering the 1961–1990 period. However, many WMO members, including the UK, update their averages at the completion of each decade. Thirty years was chosen as a period long enough to eliminate year-to-year variations.
The latest set of 30-year averages covers the period 1981-2010.
These averages help to describe the climate and are used as a base to which current conditions can be compared. Use the links below to see a selection of station, district and regional averages or UK and regional maps for a wide range of weather elements. | <urn:uuid:7010fe19-4d6a-46c5-95eb-05def6c5f571> | 2.796875 | 136 | Knowledge Article | Science & Tech. | 39.481999 |
How Does the BP Oil Spill Impact Wildlife and Habitat?
Scientists are still assessing the effects of the estimated 170 million gallons of oil that flooded into the Gulf after the explosion of BP's Deepwater Horizon oil rig.
More than 8,000 birds, sea turtles, and marine mammals were found injured or dead in the six months after the spill.
The long-term damage caused by the oil and the nearly 2 million gallons of chemical dispersants used on the spill may not be known for years.
In the months following the Gulf oil disaster, wildlife managers, rescue crews, scientists and researchers saw many immediate impacts of the oil impacting wildlife.
Long Term Impacts
Though oil is no longer readily visible on the surface, it isn’t gone. Scientists have found significant amounts on the Gulf floor, and the oil that has already washed into wetlands and beaches will likely persist for years. We likely will not see the full extent of impacts for many years, which makes creating and implementing successful restoration plans a serious challenge.
Unbalanced Food Web - The Gulf oil disaster hit at the peak breeding season for many species of fish and wildlife. The oil’s toxicity may have hit egg and larval organisms immediately, diminishing or even wiping out those age classes. Without these generations, population dips and cascading food web effects may become evident in the years ahead.
Decreased Fish and Wildlife Populations - Scientists will be watching fluctuations in wildlife populations for years to come. It wasn't until four years after the 1989 Exxon Valdez oil disaster that the herring population collapsed. Twenty years later, it is still has not recovered.
Decline in Recreation - The Gulf Coast states rely heavily on commercial fishing and outdoor recreation to sustain their local economies. According to NOAA, commercial fisheries brought in $659 million in shellfish and finfish in 2008, and just over 3 million people took recreational fishing trips in the Gulf that year. After the spill, recreational fishing from the Atchafalaya Delta to Mobile Bay was shut down from May to August, and state park closures dealt a serious blow to the parks' summer revenue.
Learn More About How Oil Impacts... | <urn:uuid:ff3438d3-d0ad-46b4-867a-4fdee3571334> | 3.734375 | 441 | Knowledge Article | Science & Tech. | 50.590676 |
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Concise explanation of how the solar system started.
Listen the sound a solar flare makes and other read answers to questions on space weather.
Photovoltaic (or PV) cells convert light energy into electricity. This site looks at the development of photovoltaics as a domestic and industrial source of energy, including some quite detailed ...
Extensive overview of our solar system, covering history, mythology, and current scientific knowledge of planets, moons, asteroids in our solar system, with many links.
A very graphic site with short details about the Earth and solar system with pictures starting at Earth diameter and moving away to the edge of the solar system and finally to the local group of ...
An animation (with explanation) of the sun, moon and the earth, showing the arrangement during a solar eclipse , plus a synchronized view from earth.
This website does all the calculations you need to build a scale model of the solar system and visualise the vastness of space.
A description of how a large solar furnace can be constructed
A brief description of how Solar (or photovoltaic) Cells work. Part of Marshall Brain's HowStuffWorks.com.
A brief description of how Solar Yard Lamps work. This site is part of Marshall Brain's HowStuffWorks.com. A good, understandable site.
Showing 21 - 30 of 96 | <urn:uuid:1663a7bc-0f24-4a2d-aeea-176c6198710d> | 3.109375 | 377 | Content Listing | Science & Tech. | 57.735148 |
In this section, you will learn how to remove all white spaces from the given string by using the regular expressions. This section gives you a example for the best illustration about the way of removing all the duplicate white spaces from the given string.
This program takes string from which all duplicate white spaces are removed if any exists in the string. And program shows the final string devoid of duplicate white spaces if any.
Pattern pattern = Pattern.compile("\\s+"):
Above code creates an instance of the Pattern class which compiles the text or regular expression i.e. used to search in the specified string.
Matcher matcher = pattern.matcher(string):
Above code creates an instance of the Matcher class which is used to match the compiled string in the string which is passed through the matcher() method of the above created instance of the Pattern class.
The find() method of the instance of Matcher class is used to check whether the compiled string matches in the specified string or not. This method returns the boolean value either true or false. If the text find in the string then the find() method returns the true value otherwise it returns the false value.
This method returns the whole string after replacing all duplicate white spaces by the single space and then it make a fresh string and return the whole string.
Here is the code of the program:
Ask Questions? Discuss: Removing duplicate white spaces from a String
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If you are facing any programming issue, such as compilation errors or not able to find the code you are looking for.
Ask your questions, our development team will try to give answers to your questions. | <urn:uuid:88d0b0c0-b363-412f-a670-9761a65649d0> | 3.65625 | 341 | Documentation | Software Dev. | 55.759817 |
In the infrared, as in the optical, the means of reporting source
brightnesses and the units employed have varied considerably. In recent years, however,
magnitude systems have been used less frequently, and the most popular unit for expressing brightnesses, both for point source fluxes and surface brightnesses, is steadily becoming the Jansky. We have adopted the Jansky as the standard flux unit (and Jansky/arcsec2
for surface brightness measurements) for NICMOS in our documentation and in observer-oriented software. Here we provide some simple formulae and tables to facilitate the conversion from other units into Jy
. A Unit Conversion Tool is also available on the NICMOS WWW site, at the following URL:
Infrared astronomy really began in the 1960s, when the vast majority of
astronomy was still carried out in the visual region. Flux measurements were routinely reported in the UBV magnitude system, and to attempt to integrate IR astronomy into this system, Johnson (Ap.J., 134
, 69) defined the first IR magnitude system. This involved four new photometric bands, the J, K, L and M bands which were centered on wavelengths of 1.3, 2.2, 3.6 and 5.0 microns. These bands were defined not only by the filter bandpasses, but also by the wavebands of the ‘windows’ of high transmission through the atmosphere. In this system, all measurements were referred to the Sun, which was assumed to be a G2V star with an effective temperature of 5785K, and was taken to have a V–K color of roughly +2.2. From his own measurements in this system, Johnson determined Vega to have a K magnitude of +0.02 and K–L=+0.04.
Until the early 1980s IR astronomical observations were restricted to
spectra or single channel photometry, and most photometry was reported in systems at least loosely based on Johnson’s system. These systems added a new band at 1.6 microns known as the H band and two bands were developed in place of the one formerly defined by Johnson as the L band; a new definition of the L band centered on 3.4 microns, and a rather narrower band known as L' centered on 3.74
As the new science of infrared astronomy rapidly expanded its
wavelength coverage, many new photometric bands were adopted, both for ground-based observations and for use by the many balloon- and rocket-borne observations and surveys. The differing constraints presented by these different environments for IR telescopes resulted in systems with disappointingly little commonality or overlap, and today the IR astronomer is left with a plethora of different systems to work with.
survey results, which were published in 1986, presented observations made photometrically in four bands in the mid- and far-infrared, and mid-infrared spectra, and all were presented in units of Janskys, rather than defining yet another new magnitude system. Since then, IR data from many sites around the world have been increasingly commonly presented in Janskys (Jy), or in Jy/arcsec2
in the case of surface brightness data. IRAS maps are often presented in units of MJy/steradian.
Ground-based mid-IR photometry is usually carried out using the N and
Q photometric bands, which are themselves defined more by the atmospheric transmission than by any purely scientific regard. IRAS
, freed of the constraints imposed by the atmosphere, adopted its own 12 micron and 25 micron bands, which were extremely broad and therefore offered high sensitivity. Similarly, NICMOS, being above the atmosphere, is not forced to adopt filter bandpasses (See Chapter 4
and ) like those used at ground-based observatories, but instead has filters constrained purely by the anticipated scientific demands. Thus in practice NICMOS does not have filters precisely matched to any of the standard ground-based photometric bands. The remaining sections contain simple formulae to convert between systems (magnitudes to Jy, etc.) and look up tables. | <urn:uuid:f6b156c6-0cd1-4c6d-899a-c4f6ba5941bb> | 3.1875 | 857 | Documentation | Science & Tech. | 42.120318 |