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A car of mass 1.5 tonnes pass over a bridge formed the arc of a circle of radius 20m.
a) Find the force exerted by the car on the road at the top of the bridge if the car is travelling at 10m/s.
b) What speed would cause the car to be on the point of lifting up off the bridge at its highest point
What I've done:
F = mv^2 / r
F = 1500 * 10^2 / 20
F = 7500 N
---- Don't know if this is anything (the answer in the book is 7200N)
tan(t) = v^2/rg
tan(t) = 10^2/20*9.8
tan(t) = 0.510
(t) = tan^-1(0.510)
(t) = 27.02 deg
Force of car on road = mg sin (t)
= 1500*9.8sin (27.02)
= 6678.23 N
However as I said previously the answer is 7200 N.
b) No idea really... not sure of the formula to use
The answer for b) is 14m/s. | <urn:uuid:f40bcc9f-e755-4396-9e7c-29650ddb9f00> | 2.828125 | 257 | Q&A Forum | Science & Tech. | 122.214382 |
Rationalizing Maxwell's Equations
Maxwell's equations in Gaussian units are shown at the right. Gaussian units are based on the cgs system of mechanical units, and were long dominant for theoretical investigations. Absolute electrostatic units (esu) are used for electrical quantities, absolute electromagnetic units (emu) for magnetic quantities. The electric field E and the magnetic flux density B are the basic vectors; D and H are obtained from them by adding the polarization P or subtracting the magnetization M, respectively. If P and M are proportional to the applied field, then D and B are related to E and H through the dielectric constant κ and the permeability μ as shown. The sources of the fields are charges and currents. The equivalent charge density and current due to polarization and magnetization are ρb and Jb, where the "b" stands for "bound." The divergence of D and the curl of H give the "free" charge and current densities, respectively, while the divergence of E and the curl of B give the total charge and current densities. The Lorentz force on a point charge q is also given, where E and B are the effective fields on the charge q, where polarization and magnetization are zero. The energy definitions of resistance R, capacitance C and inductance L are shown. Charges are in esu, currents in esu/s in these equations. The universal constant c = 2.9979 x 1010 cm/s, the speed of light.
The factors of 4π in the equations come from the 4π steradians of solid angle surrounding a point. If the radial electric field from a point charge q is q/r2, then the flux of the electric field across a sphere of radius r with center at the charge is 4πr2(q/r2) = 4πq. This implies that div E = 4πρ when the divergence theorem is used to turn this into a differential relation.
The factors of 4π in Maxwell's equations can be eliminated by a scale change on the fields and their sources, otherwise retaining the form of each equation. This is called "rationalization" of the units, which is a convenience in theoretical studies, especially of electromagnetic waves and radiation. The greatest convenience is the elimination of the 4π in the definitions of D and B. The name was probably chosen to encourage the step, by disparaging "irrational" units, but has no other significance. Rationalization was encouraged by Oliver Heaviside and H. A. Lorentz, after which the resulting system of units is named. Heaviside-Lorentz units (hlu) are rationalized Gaussian units. The engineer's Giorgi or MKSA units have also been rationalized.
What we need to do can be found from the equation div D = 4πρ, or from its equivalent in the absence of polarization, div E = 4πρ. If we multiply ρ by a constant α, we must also divide E by the same constant, so that the equation F = qE is preserved. Therefore, we write div (E/√4π) = √4π ρ. In terms of the new field E' = E/√4π and new charge density √4π ρ, we have div E' = ρ', which is what we desire. Therefore, to rationalize the Gaussian units, we multiply the measures of the sources by √4π, and divide the measures of the fields by the same factor. As you can easily check, this removes the factors of 4π from Maxwell's equations while preserving the form of each equation. The primes refer to hlu, the unprimed quantities to Gaussian.
To avoid confusion, we must state that we are working with the measures of the quantities in terms of their units. This is the number in expressions like 2.5 ft. To convert to inches, we multiply the measure by 12: 12 x 2.5 ft = 30 in. The unit has changed from 1 ft to 1 ft/12 = 1 in in the process. Of course, to convert units, we use factors of unity, such as 12 in / 1 ft, and this factor, multiplying the combination of measure with the unit, takes care of both.
The equations that result are shown at the right. The factor √4π = 3.544907. In free space, where ρ = 0, J = 0, P = 0 and M = 0, they are exactly the same as in Gaussian units, so not a lot has been gained here. From what we have said, the hlu of charge is (1/3.545) esu (statcoulomb), and the hlu of potential is 3.545 esu (statvolt). The hlu of magnetic flux density is 3.545 gauss. Therefore, the charge on the electron is -1.703 x 10-9 hlu, and the hlu of potential is 1063.5 V. The practical current corresponding to 1/c hlu is 10/3.545 = 2.821 A.
The effect on resistance, capacitance and inductance can easily be found by the equations defining them. It is convenient to define a resistance that is c times the actual esu resistance, v = (cR) x (i/c), relating v and i/c. Then, W = cR(i/c)2 becomes W = (cR/4π)(√4πi/c)2, or (cR)' = (cR)/4π. 1 hlu of resistance cR' is 377.1 Ω in practical units. Similarly, U = Cv2/2 gives U = 4πC(v/√4π)2/2, or C' = 4πC. Finally, from U = Li2/2 we find U = L/4π(√4π i)2/2, or L' = L/4π. Just as cR is sometimes used instead of R, so c2L may be used instead of L, but the conversion is the same. The 4π's, banished from Maxwell's equations, pop up elsewhere!
Coulomb's Law in hlu is F = qq'/4πr2 dyne. The capacitance of a parallel-plate capacitor of area A and spacing d is C = A/4πd cm in Gaussian units, so it is C' = A/d in hlu. Similarly, a sphere of radius a has C = a in Gaussian, C' = 4πa in hlu. These, and many other similar results, are easily obtained from what we have said. Note that the hlu cm of capacity is not equal to the esu cm of capacity! It is very easy to convert between hlu and Gaussian units, since only factors of √4π are required. A theoretical argument can use hlu, then convert ot Gaussian at the end. Conversions from Gaussian to practical units are, of course, well known.
Composed by J. B. Calvert
Created 9 October 2002
Last revised 10 October 2002 | <urn:uuid:6d9b9a3b-7674-4194-ac02-f974b8015b00> | 3.640625 | 1,515 | Academic Writing | Science & Tech. | 71.204025 |
ABSTRACT. One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding Universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model, we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics - inflation + cold dark matter - holds the promise of extending our understanding to an even more fundamental level and much earlier times, as well as shedding light on the unification of the forces and particles of nature. As we enter the 21st century, a flood of observations is testing this paradigm.
Table of Contents | <urn:uuid:f1931f08-c6a4-4e0d-9295-81002f26847a> | 3.375 | 251 | Academic Writing | Science & Tech. | 30.978169 |
A new generation of robotic explorers are going to search for water on Mars.
The rover is a mobile geology lab
Mark Adler, deputy manager on the US space agency (Nasa) mission, talks to BBC News Online's Helen Briggs about what they might encounter.
HB: How does each rover work?
MA: It's a solar powered robot. At about 9 am it will wake up and by 2-3 pm in the afternoon it will send back what it has done. It then goes to sleep and our job begins here on Earth.
We have about 19 hours to figure out the data and send a series of instructions to the rover next morning.
HB: How similar are they to Pathfinder's Sojourner, the first Martian rover?
MA: Pathfinder was quite similar in terms of its landing system for entry and descent to the surface of Mars. From that point on it looks a lot different to Pathfinder.
The purpose of that mission overall was a technology demonstrator, but it did do some good science.
Mars Exploration Rovers (Mer) is a science mission. Once the landers have delivered the rovers, they are discarded. Now the rovers are completely independent - they can go off to do work and have no reason to go back to the landers.
HB: Will the Mer mission be looking directly for evidence of life?
MA: Our rovers' main science objective is to understand the water environment of Mars. They're not looking for life, they're looking for ancient environments that could have harboured life.
What we learnt from Viking is that it is very difficult to come up with specific experiments to look for something you don't really know what to look for.
This is taking a more measurable approach - trying to understand Mars as a global environment and using the rovers to look at the local environment.
To answer those (life) questions definitively we need to bring samples back (to Earth).
What we want to do is find the right places to go to Mars using our orbiters and landers, then go to these places and bring samples back.
Even if the rovers don't strike gold, sending a set of instruments to Mars has always taught us new things.
HB: Do you think this latest mission will capture the public imagination?
MA: Part of the mission is to inspire the next generation. The mission is an independent rover that can go off over the hill to explore the other side. The public will participate through the website.
We're going to two new places where we haven't been before. Meridiani has chemical evidence of a mineral - haematite - we believe could have formed in water. The evidence comes from Mars Global Surveyor.
Gusev is a morphological site, a crater that could have been a large lake in the ancient history of Mars. The instruments will tell us if it was a lake.
Within weeks, there will be some preliminary answers. There may well be argument about the data for years afterwards. | <urn:uuid:8287d1bd-8218-43bb-80f2-2799a114a967> | 3.640625 | 621 | Audio Transcript | Science & Tech. | 60.433342 |
Google Coding Conventions
Only deviations from the Google style guide will be documented here.
We use JsDoc comments as outlined in the Google style guide with but we name the variable name directly after the @param tag and the type without curly braces.
Generally we encourage inline comments. These help readers of your code to understand the logic without having to understand every line of code. It's also a good practice to write inline comments before you write code so that you first think about the logic and semantics you want to implement and then about the syntax.
We do not generally use the @protected and @private markers that Google recommends. We do, however, implement the following nomenclature for class members (properties and methods):
- We group members by visibility and class (static) vs. object (instance) membership:
- private static class variables (start with underscore)
- private instance variabes (start with underscore)
- protected instance variables (discouraged)
- public static class variables or instance variables are not allowed!
- public static methods
- public methods
- protected static methods
- protected methods
- private static methods (start with underscore)
- private methods (start with underscore)
- Sections are divided with a three line // style comment indicating the class member category.
- An underscore at the start of the name marks a class member private. You are not supposed to use such a member outside scope even if the visibility is not enforced by closure.
- Protected class members are named like public methods but they must not be used outside of the inheritance hierarchy of the current class. | <urn:uuid:c36995a3-4761-477f-a692-61036530c058> | 2.90625 | 334 | Documentation | Software Dev. | 25.023897 |
Astronomers have just released the highest-resolution images ever taken of the Sun's corona, or million-degree outer atmosphere, in an extreme-ultraviolet wavelength of light. The 16-megapixel images were captured by NASA's High Resolution Coronal Imager, or Hi-C. The Hi-C telescope provides five times more detail than the next-best observations by NASA's Solar Dynamics Observatory.
ALBUQUERQUE, N.M. — Researchers creating electricity through photovoltaics want to convert as many of the sun's wavelengths as possible to achieve maximum efficiency. Otherwise, they're eating only a small part of a shot duck: wasti... Read Post
GOES-14 has been brought into service again on October 25th, 2012 for SRSOR imaging of Hurricane Sandy. (h/t to Al Lipton) Here’s a super high resolution visible light image of Sandy from today at 19:41UTC: Click image to enlarge to... Read Post
A huge storm on the sun this past week unleashed what some have called the most massive eruption of solar plasma ever seen. NASA astronomers said the huge June 7 solar eruption, called a coronal mass ejection, probably wasn't the... Read Post | <urn:uuid:dd404fe6-93c0-4fe5-a6db-a5c8eae3a56e> | 2.9375 | 255 | Content Listing | Science & Tech. | 50.592433 |
What are Ice Jams?
Spring is the time of year when ice-covered rivers begin to thaw. As this ice breaks up into chunks, they move downstream and can jam in areas where the water flow bends, near bridges and abutments or in shallow areas. The restricted ice can then act as a dam, causing water to back up behind it. River levels behind the ice jam can rise rapidly, often flooding areas upstream. And ice jams that break can quickly release water, causing flash floods and sending huge chunks of ice downstream in the torrent.
NOAA's National Weather Service continuously monitors conditions that lead to flooding and issues forecasts, watches, and warnings when necessary. Weather.gov and NOAA Weather Radio All Hazards are some of your best sources of such critical flood alert information.
Each year, more than 100 deaths occur due to flooding. Why? Because people underestimate the force and power of water. Just six inches of fast-moving flood water can knock you off your feet, and a depth of two feet will float your car! Never try to walk, swim or drive through water-covered roads. Remember: Turn Around Don't Drown™.
This month’s expert: Larry Wenzel , National Hydrologic Outreach Program Leader, NOAA's National Weather Service, Hydrologic Services Division. | <urn:uuid:10e9a76d-4887-4cf7-9eba-37575261c846> | 3.421875 | 270 | Comment Section | Science & Tech. | 59.574167 |
Attaching a short DNA molecule to two metal electrodes, researchers in the Netherlands have found evidence that DNA acts as a semiconductor for electrical charge. The figure shows the electrodes as two gray cliffs on either side of a chasm. In the experiment, the electrodes were separated by just 8 nanometers (billionths of a meter). The DNA (the colorful rope across the canyon) was double-stranded with a length of 10.4 nanometers (billionths of a meter).
The research provides insights into a heavily debated question: Is DNA a conductor for electrical charge? The present work indicates that the DNA strands are semiconductors with large band gaps (typically around several volts), with a band gap indicating the amount of voltage required to boost an electron from the valence band (a state in which an electron is attached to a particular atom) to a conduction band (a state in which an electron can move freely in the material).
Therefore, by applying a sufficiently high voltage, one can greatly influence the flow of electrons in the DNA strand or any other wide bandgap semiconductor. Such work is leading to a new field called "DNA electronics," which may lead to intriguing new designs for biosensors and other devices
These experiments were performed by scientists at the DIMES institute of the Delft Institute of Technology in the Netherlands.
Figure copyright 2000 by the DIMES Institute, Delft Institute of Technology, the Netherlands. Journalists have permission to use these images if the source is acknowledged.
1) Danny Porath, Alexey Bezryadin, Simon de Vries and Cees Dekker; Direct measurements of electrical transport through DNA molecules, in the journal Nature, 10 February 2000.
2) A.Bezryadin, C. Dekker, and G. Schmid, Electrostatic trapping of single conducting nanoparticles between nanoelectrodes, in Applied Physics Letters, v. 71, p. 1273 (1997) | <urn:uuid:b6518aef-a91f-4d9b-bb2c-3e7376edbc0a> | 3.609375 | 399 | Knowledge Article | Science & Tech. | 37.207235 |
Sometimes both heaven and Earth erupt.
Colorful aurorae erupted unexpectedly earlier this month, with
green aurora appearing near the horizon and brilliant bands of
red aurora blooming high overhead.
A bright Moon lit the foreground of this picturesque scene,
while familiar stars could be seen far in the distance.
With planning, the careful astrophotographer shot this image mosaic in the field of
White Dome Geyser in
Yellowstone National Park
in the western USA.
Sure enough, just after midnight,
White Dome erupted -- spraying a stream of water and vapor many meters into the air.
Geyser water is heated to steam by
scalding magma several
kilometers below, and rises through rock
cracks to the surface.
About half of all known geysers occur in
Yellowstone National Park.
that created these aurorae has since subsided, eruptions of White Dome Geyser continue about every 30 minutes.
Credit & Copyright: | <urn:uuid:d930dc1d-b461-4e13-b8a2-95623013e3d9> | 2.9375 | 208 | Knowledge Article | Science & Tech. | 35.465302 |
Python's Apache interpreter is available as an Apache module, mod_python. This module reduces the time it takes to deliver a given page to a client. It is also capable of a great deal more, including interacting with Apache itself in various powerful ways. This article gives you just a taste of what mod_python can do.
I'm sure many of you are coming from a CGI background and have several CGI scripts sitting around. Fortunately for you, mod_python can emulate a CGI enviroment and run your old scripts. Create a directory called pycgi. Create a .htaccess file and add this to it:
We'll now create a simple "CGI" script:
import cgi formData = cgi.FieldStorage() if 'name' in formData: name = formData [ 'name' ].value else: name = 'John Doe'
print 'Content-type: text/html' print print 'Hello, ', name + '.'
You should not, however, rely on this method. It has a few problems, and mod_python offers much more efficient methods of doings things, as I explained at the beginning of the article. Let's not waste a perfectly good Apache module on CGI emulation.
Instead, we'll move on to mod_python's publisher handler. The publisher handler allows us to easily deliver Python powered pages to clients. Instead of having a separate page for everything, mod_python's publisher handler allows us to have a Python function for everything.
Create a directory named pypublish. We'll use this to play around with the publisher handler. Create a .htaccess file with this in it:
Now create a file named test.py and fill it with this:
def index(): return "This is only a test." def peyton(): return "Peyton wrote this."
Obviously, it contains two functions. Let's see how those functions relate to the script's output. Open up your Web browser and head over to the page you just created:
The peyton function is now executed. This interesting feature can be convenient in developing applications.
Now let's make a script that is a bit more complicated. Let's process data from a form - a task vital to functional websites. We'll create a form that asks for the reader's favorite color, the time he or she woke up and his or her favorite language. All this will go in the index function. When the form is submitted, the data will be sent to the process function to be made pretty and displayed. Create a file appropriately named form.py:
def index(): out = "<form method='POST' action='form.py/process'>" out = out + "What is your favorite color?<br>" out = out + "<input type='text' name='color'><br>" out = out + "What time did you wake up this morning?<br>" out = out + "<input type='text' name='waket'><br>" out = out + "What is your favorite language?<br>" out = out + "<select name='flang'><option>Python</option></select><br>" out = out + "<input type='submit' value='Process'>" out = out + "</form>" return out def process ( color, waket, flang ): return "Your favorite color is " + color + ", you woke up at " + waket + " and you like " + flang + "."
The index functon contains no suprises. It just displays form data, so I won't bother going into detail there. The process function, however, is a bit different. As you can see, it takes three arguments. Notice that the three arguments correspond to the names of the form fields. The way the publisher handler handles this is pretty interesting. Try switching around the arguments or even taking out a few (just remember to take out the variable in the return statement, too). The function still executes fine. The publisher handler automatically puts in the correct arguments. Pretty neat, huh? | <urn:uuid:929f79dd-70ae-4379-87a9-d9baea47a6ad> | 2.78125 | 846 | Documentation | Software Dev. | 59.132344 |
How do you compute the volume of a cat?
Dunking it in water doesn’t work– you only get the volume of the rat-like creature that lives inside the cat; much like the feeble alien within a Dalek. (And, if your answer had anything to do with contour integrals, get real.)
Here is a low-tech method that works: Using successive approximation, determine the smallest box that the cat will fully enclose itself in, and measure the size of that box. Cats tend to leave a few appendages hanging out of the corners– you may need to assist with folding the cat into the box for the final stages of approximation.
This cat is approximately 648 cubic inches in volume. | <urn:uuid:6ec954bc-07f1-4cae-8b71-9ba4512a0b9d> | 2.8125 | 151 | Tutorial | Science & Tech. | 53.522858 |
and Without Sex
this glass water tank there are living organisms that may look like
plants but they are animals that can be found in tide pools along
the California coast. Many of these species spend their lives stuck
to rocks or separated from potential mates, and have developed unique
strategies to reproduce. Some reproduce sexually to create genetically
different individuals. Some simply divide in two, creating genetically
identical individuals called clones. And some can do both. | <urn:uuid:6d3e3167-a7f5-47f5-8a87-9e2dc2038f59> | 2.984375 | 95 | Knowledge Article | Science & Tech. | 28.596208 |
An example for both is the ArrayList class. It functions like an array (and is actually implemented using one), but provides precise control over where in the array you can access.
ArrayList<String> myList = new ArrayList<String>();
myList.add("hello"); // somehow the string "hello" gets added to the ArrayList
System.out.println(myList.get(0)); // somehow the zeroth element inside myList gets extracted. No need to know where in myList this is actually stored
System.out.println(myList.get(1)); //The get method has complete control over where you can retrieve data from. The get method generates an exception because there is one string in myList even though the actual implementation could have a slot for a second string | <urn:uuid:0eae18ce-1060-4aad-8768-94ea775813a2> | 3.1875 | 168 | Comment Section | Software Dev. | 53.669672 |
Zebra Mussel Watch
The zebra mussel, a black-and-white striped bivalve mollusk, came to North American waters from Europe in international shipping ballast water. Since first discovered in Lake St. Clair in June 1988, the zebra mussel has spread rapidly throughout the Great Lakes and the Arkansas, Cumberland, Hudson, Illinois, Mississippi, Mohawk, Niagara, Ohio, St. Lawrence, and Tennessee Rivers. The mussel is expected to spread to other fresh water bodies and waterways throughout North America in the next several decades.
The zebra mussel is clogging power plant, industrial and public drinking water intakes, fouling boat hulls, and disrupting aquatic ecosystems throughout its range. Economic impacts of the zebra mussel in North America over the next decade are expected to be in the billions of dollars.
Zebra mussels are fingernail-size clams with yellowish or brownish shells marked with wavy bands. Their larvae are too small to be seen, but live for weeks in any water left in boats. As zebra mussels grow, they form clumps that damage boats, kill native clams, foul beaches with stinky razor-sharp shells, and clog water intake pipes.
IF YOU HAVE BOATED RECENTLY IN A ZEBRA MUSSEL INFESTED AREA, PLEASE FOLLOW THESE DIRECTIONS:
Zebra mussels are on the move. These pests are easily transported by people, boats, and fishing gear. Please assist us in stopping them.
To find more detailed information about zebra mussels, visit Dr. Jefferey Ram's Zebra Mussel Page
The above information was provided by the Glen Canyon National Recreation Area, www.nps.gov/glca | <urn:uuid:537e8be1-8444-49f2-af9c-41e0be447956> | 3.65625 | 364 | Knowledge Article | Science & Tech. | 43.837623 |
The job of the manifest file is to indicate to the device the name and version of the MIDlet suite in the JAR and to specify which of the class files it contains correspond to the individual MIDlets. In order to make use of this information, however, the device must download the JAR and extract the manifest. Having done this, it can then display the values associated with the
MIDlet-Vendor attributes and the optional
MIDlet-Icon attributes. These attributes allow the user to decide whether the MIDlets should be installed. However, the JAR for a MIDlet suite might be quite large and may take some time to retrieve over the relatively slow networks to which mobile devices typically have access. If the only useful description of its content were in the JAR itself, a lot of time might be wasted transferring large files that are immediately rejected as uninteresting.
To solve this problem, some of the attributes from the manifest file, together with extra information, is duplicated in the JAD file. Instead of downloading the whole JAR, a MIDP device first fetches its JAD file, which is much smaller than the JAR and can be transferred quickly. The device then displays the JAD file's contents to the user so that she can decide whether to fetch the JAR file. The JAD contains some attributes that come from the manifest file and others that do not appear in the manifest. The common attributes are as follows:
These attributes (with the possible exception of the last one) can all be presented to the user as an aid to deciding whether the content of the corresponding JAR file is interesting enough to download. The first three of these attributes are mandatory in both JAR and JAD files, and the MIDP specification requires that their values be identical. The remaining attributes are all optional. If they appear in both the manifest and the JAD file, the value in the JAD file takes precedence over that in the manifest (and at this stage, the device can see only the value in the JAD file).
The JAD file also contains two other attributes that are not present in the manifest file:
The Mobile Information Device Profile and MIDlets, Part 5
The Mobile Information Device Profile and MIDlets, Part 4
The Mobile Information Device Profile and MIDlets, Part 3
The Mobile Information Device Profile and MIDlets, Part 1
MIDlet-Jar-Size attribute can be displayed to the user to help determine how long it will take to fetch the JAR; it also enables the user to guess whether the device has enough free space to install the JAR. Assuming the user decides to install the MIDlet suite, the next step is to fetch the JAR itself, which can be found by using the value of the
Suppose a company called "Wireless Java Inc." creates a suite of MIDlets called
WirelessTrader that allow a user to do online stock trading from a MIDP device. The suite contains two MIDlets, one for trading, the other for simply browsing through stock prices. The main classes for these two MIDlets are called
com.wireless.BrowseMIDlet, and they make use of common code in the
com.wireless.Utils class. The manifest for this suite would look something like this:
MIDlet-Name: WirelessTrader MIDlet-Vendor: Wireless Java Inc. MIDlet-Version: 1.0.1 MIDlet-Description: A set of MIDlets for online trading. MIDlet-Icon: /com/wireless/icons/wireless.png MIDlet-Info-URL: http://www.wireless.com/trader/info.html MIDlet-Data-Size: 512 MicroEdition-Profile: MIDP-1.0 MicroEdition-Configuration: CLDC MIDlet-1: StockTrader,/com/wireless/icons/trader.png,com.wireless.TradeMIDlet MIDlet-2: StockBrowser,/com/wireless/icons/browser.png,com.wirelessBrowseMIDlet
In the JAR, this file would appear as
META-INF/MANIFEST.mf. The JAR would also include the following files:
Note the following about the attributes in the manifest file and the content of the JAR:
The JAR contains the two MIDlet class files and the class file for
com.wireless.Utils, which contains code that is used by both MIDlets. This latter file, however, does not need to be referenced from the manifest file. The JAR also contains the three icons that are referred to from the manifest file.
MIDlet-Iconattribute contains the absolute path of the icon file for the MIDlet suite, relative to the JAR file itself.
Each MIDlet has an attribute that describes it; the attribute's name is of the form
nis an integer. The value of this attribute has the following form:
nameis the name of the MIDlet within the MIDlet suite.
iconis the full path of the icon that the device may use along with the MIDlet name when displaying the content of the MIDlet suite to the user.
classis the name of the MIDlet's main class. The icon is optional; if no icon is required, it should be omitted:
Note that even if an icon is specified, the device is not obliged to display it. The same applies to the MIDlet suite icon defined by the optional
The JAD file for this suite can be constructed like this:
MIDlet-Name: WirelessTrader MIDlet-Vendor: Wireless Java Inc. MIDlet-Version: 1.0.1 MIDlet-Description: A set of MIDlets for online trading. MIDlet-Info-URL: http://www.wireless.com/trader/info.html MIDlet-Data-Size: 512 MIDlet-Jar-Size: 10312 MIDlet-Jar-URL: http://www.wireless.com/trader/Midlets.jar
This file contains the information that the device displays to the user, together with the URL of the MIDlet suite JAR. In this case, the common attributes have the same values in the manifest and the JAR, but it is possible to override the
MIDlet-Data-Size attributes by specifying different values in the JAD file.
In order to be fully portable, the JAD file should be encoded using ISO-8859-1, because all MIDP implementations are required to support this character encoding. The successful use of any other encoding depends on the target device, which may not support the encoding, and the way in which the JAD file is transported to the device. If, for example, the file is fetched using HTTP, the Content-Type header can be used to specify the encoding as described in the later section "Delivery and Installation of MIDlets." In some cases, it is useful to be able to include in the JAD file Unicode characters that are not available in the ISO-8859-1 encoding or that are not easy to access from a standard keyboard. The MIDP reference implementation allows you to use Unicode escape sequences of the form
\uxxxx to overcome encoding limitations. For example, the following line includes the copyright character (Unicode value
00A9) in the MIDlet suite description:
MIDlet-Description: A set of MIDlets for online trading. \u00A9 Wireless Java Inc.
Although this feature is available in the MIDP reference implementation, it is not mentioned in the MIDP specification, so there is no guarantee that real devices will actually support it.
At runtime, a MIDlet can access files from its JAR using the
getResourceAsStream( ) method of
java.lang.Class. Any file in the JAR, apart from class files, can be accessed this way. This is typically how you would include images or text files that should be displayed in the user interface, an example of which will be shown in Chapter 4. A MIDlet can also define its own private attributes in the manifest file and the JAD and retrieve them at runtime, as you'll see in "Developing MIDlets" later in this chapter.
Next time, learn MIDlet Execution Environment and Lifecycle.
Kim Topley has more than 25 years experience as a software developer and was one of the first people in the world to obtain the Sun Certified Java Developer qualification.
View catalog information for J2ME in a Nutshell
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Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes.
A brief description of how these devices detect smoke, exploring the two most common types used today: photoelectric and ionization detectors. Part of Marshall Brain's HowStuffWorks.com. Assumes ...
Online exhibits including Marie Curie and the Discovery of Radioactivity, the History of the Transistor, Albert Einstein, the Discovery of the Electron; Heisenberg, and Sakharov.
Enrico Fermi received the Nobel Prize for Physics in 1938 for his work on the artificial radioactivity produced by neutrons, and for nuclear reactions brought about by slow neutrons. A good biography ...
Irene Joliot-Curie (1897 - 1956) did important work on natural and artificial radioactivity, transmutation of elements, and nuclear physics; she shared the Nobel Prize for Chemistry in 1935 with her ...
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Photograph by Evan Hurd/Getty Images
2001: The Institute for Genomic Research, founded by Venter, helps sequence the genome of the anthrax strain mailed in the attacks that killed five people evidence that eventually leads the FBI to the source.
2004: Sorcerer II, Venters 95-foot sailboat, leaves Halifax, Nova Scotia, on a two-year circumnavigation of the globe in search of new microbial species for DNA sequencing.
2005: Venter starts the for-profit Synthetic Genomics Inc. (SGI) to work on solving global problems, such as fossil-fuel dependence, environmental degradation and disease epidemics.
2007: He establishes another first by mapping the 6-billion-letter code of his own diploid genome (DNA from both chromosome pairs, one from each parent), discovering a genetic predisposition for blue eyes, antisocial behavior and heart disease.
2008: Using a computer code and four bottles of chemicals, Venters lab creates the largest man-made DNA structure by synthesizing and assembling the 582,970-base-pair genome of a bacterium.
2009: He announces SGI will receive $300 million from Exxon Mobil to engineer algae cells that turn sunlight and carbon dioxide into biofuel.
2010: Venters team uses a synthetic genome to boot up the worlds first man-made bacterial cell. Mycoplasma mycoides JCVI-syn1.0 becomes the first living organism to have its own website encoded in its chromosomes. | <urn:uuid:d3d15d1b-1c5a-401f-947f-5cc07c56f232> | 2.921875 | 309 | Listicle | Science & Tech. | 38.142204 |
Atomic radius (empirical)
These values derived by J.C. Slater are an empirical set of atomic radii derived by the careful comparison of bond lengths in over 1200 bond types in ionic, metallic, and covalent crystals and molecules (reference 1).
The idea is that for a bond A-B, the atomic radius of A added to the atomic radius of B will give a reasonable estimate for the A-B separation in whatever environment. A single set of radii is very useful for most purposes, however, for very accurate work adjustments would have to be made to the values quoted to reflect the specific environment of the element (such as coordination number). Values are given to an accuracy of about 5 pm.
WebElements now has an online chemistry shop at which you can buy periodic table posters, mugs, T-shirts, games, molecular models, and more. | <urn:uuid:9d02d049-b5b7-40dc-8cde-82d281985b6f> | 3.125 | 183 | Knowledge Article | Science & Tech. | 38.781034 |
Building Resilience in a Changing Climate
What is Adaptation?
Lying to the young is wrong.
Proving to them that lies are true is wrong.
that God's in his heaven
and all's well with the world
They know what you mean.
They are people too.
Tell them the difficulties
can't be counted,
and let them see
what will be
these present times.
Say obstacles exist they must encounter,
The hell with it.
Who never knew
the price of happiness
will not be happy.
Forgive no error
it will repeat itself,
will not forgive in us
what we forgave.
Translated by Robin Milner-Gulland and Peter Levi
Adapting, adaptation, adaptedness—all, according to Merriam-Webster’s, mean change to better match present or future circumstances. Adaptation can mean adjusting to environmental conditions to avoid negative impacts or can mean to embrace positive consequences of change. By looking at present and likely future environmental conditions, we can see that the past is no longer a good guide for the future. The science tells us the climate is changing (e.g. temperatures and sea levels are rising and precipitation patterns are changing). As humans we know what it means to have our natural environment change and to be able to prepare for it through changes in our built environment: we know that the seasons will cause us to need a variety of clothes and housing because winter is colder and summer is warmer. Change, then, can and does affect us in both our natural environment and in our built or human environment. And knowledge around what is likely coming can help us to prepare effectively and become less vulnerable.
Adaptations we make to climatic change need to be aimed at making systems more resilient and healthy now and in the long run. Resilient, healthy systems can better withstand perturbations of all types than systems that are unbalanced or at the edge of their survival. Making a system more resilient can mean reducing pressures that are already stressing the system. It can mean fishing for new species that are becoming established in a new region and reducing pressure on a stressed species; providing greenways and migration routes for plants and animals that need to move to better match the environment that is best for them; or restoring natural floodways to allow the natural system to better protect the built environment. It can mean investing in long-term projects that reduce vulnerability (of people, infrastructure, or even investments) rather than increasing it. It can mean investing in educating the public to increase their awareness and availability of more environmentally friendly choices and options open to them.
The purposes of the Adaptation Network are fourfold:
- Identify who "on the ground" at local, state, regional, national/binational, and international levels is doing and planning to do adaptation, including stakeholder consultation on policy and implementation.
- Amplify and strengthen the work of those on the ground and increase their number by networking them with each other and ensuring best practices are known and shared. Also informing the media, policymakers, and the public about them and their work and plans.
- Permit change in US policy on climate change by demonstrating that there exists a significant constituency of voters who understand climatic change, the anthropogenic influences on it, and endorse fiscally intelligent responses proposed to it.
- Counteract the widespread misperception that if one strongly feels we need adaptation, one is against the equally strong need for mitigation. Mitigation thinking can be summed up in the call to "Stop Global Warming." Yes, we may be able to slow or stop warming-but 100 years from now or more. Adaptation thinking can be summed up as "Climate is changing now. What actions make sense to take now to help people and animals and the planet that we will be glad we took 100 years from now?" It is harder to face what is needed now than to think about the more distant future.
Other activities and actions will evolve as the network evolves but we feel we need to take action now and bring together others of like-mind to assist our communities and natural resources to be more resilient to changes that are here now and that we are fairly certain are coming. Join Us?
Adaptations are always regional and local
Because climate change impacts are regionally and locally specific, so will the adaptations that are undertaken to address those impacts need to be regionally and locally specific. At present, the information that is generally available around climate change, the global climate model projections, tend to be on rather large geographical scales larger than the decisions that need to be made around adaptation. Until appropriately downscaled information is available to all regions and localities, it can be difficult to know what parts of the present climate are likely to change or continue in your region. As coastal managers, you may for example wonder if recently experienced flooding from sea level rise might become a more regular event. If you knew the relative rate of sea level rise in your area you could have a better understanding of what is likely coming your way in the future.
When making a decision to adapt to some future climatic condition, it is unwise to make that decision based on any extremely specific projected value (e.g. of temperature, precipitation, or sea-level rise) or future date. A more skillful approach is to look at the trends that the models are suggesting along with the trends that are beginning to show themselves in your region and plan accordingly. Trends will continue for generations—even if mitigation is extremely successful.
For decision-making, trends are one important factor. Another is vulnerability. Mapping projected and observed trends against already identified vulnerabilities will give some indications of where to start thinking about developing adaptation options. Other approaches to developing adaptation action plans are scenario building, hazard planning, and what ifs/how much (would have to happen to see a particular negative impact or reach a threshold). There are many approaches to planning or choosing adaptive activities. All have their appropriate place in a planning repertoire.
Who should consider adaptation activities?
A variety of levels of decision-makers make adaptation decisions. Cities and towns may look at areas of present vulnerability--for example, where it always floods during heavy rains, and make changes to the drainage of particular locations because they have learned that the problem will likely increase or become more frequent. States or regions may look to changes in laws or regulations that could for example, make developing long-term plans and systems work differently (e.g. a reservoir, infrastructural planning that includes likely climate projections in their tolerances, etc.). Homeowners may, for example, decide to plant not the traditional horticultural choices but instead choose options that grow more readily in the new projected environment. We may work with other citizens in a town to develop neighborhood resiliency plans. State and National agencies may support adaptation by offering grants to develop local models aimed at supporting choices of local decision-makers.
Along with diverse levels of decision-makers, there is also a variety of time scales or timelines along which decisions can be made. If you are a farmer and plant annual crops you will be making decisions on an annual basis. If you are planning the development and implementation of a bridge or other long-lived infrastructure, e.g. a port, you will need to be planning on a much longer timeframe. It is important to recognize that the future will be different from the past and include those future differences in our planning and hazard mitigation efforts.
When deciding to adapt to climate changes, we need to be cognizant of not choosing an adaptation just because it is easy now if in fact it could make the problem worse in the long run. It is important that short-term decisions be consistent with the longer-term perspective of adaptation demands, and with reducing societal vulnerability and building the resilience of natural systems. It would be a waste of money and time to make adaptations to immediate problems that do not translate into long-term solutions, or worse create new long-term problems.
A few other considerations that should be included in any adaptation planning process:
- After you have decided on the need for an adaptive action, consider the costs (both economic and who is impacted). What are the costs, who should pay them, how should responsibility be shared, who can help? Are there groups missing from the discussion e.g. those likely impacted (vulnerable groups) or those who have expertise to assist in the process (corporations)? Equity issues might need to be included in your calculations as well as the costs of doing nothing.
- What might be some of the unintended or unexpected consequences from your adaptive action? Try to think outside of the box and anticipate and address any possible problems.
- What is the relationship between adaptations that occur in different sectors? For example, an adaptation that requires a release of water from a reservoir to deal with reduced runoff from lack of rain to support a fishery could cause a water shortage for agriculture or human use.
- Any adaptation action needs to consider the relationship between adaptation and mitigation. Is your adaptation making mitigation harder or easier to attain? An adaptation to heat stress could be to provide air conditioners to needy residents. That could be helpful to the health concerns of heatwaves but would lead to problems in the energy sector that is already stressed on hot days and make the overall problem worse by increasing emissions of greenhouse gases.
These considerations and others support a significant level of planning and feedback prior to and following implementation of any adaptive decisions. Feedback can include evaluating the present success of the adaptive action and future assessments to be certain that the action of choice continues to work as the future projections become the now environment. Adaptation is not really anything new, it is just better planning and using different information (future projections) in recognition that the future will be different than the past. All adaptive actions should try to fall into the win-win-win category: where there is a benefit now, a benefit in the future, and could still be a benefit whether the climate changes as projected or we are surprised.
Article submitted to URI Coastal Resources Center journal: Basins and Coasts, Nov 07
PO Box 117
Berkeley Springs, WV 25411 | <urn:uuid:449c3f5c-99a9-4f08-981d-186d697c7bb3> | 3.390625 | 2,089 | Academic Writing | Science & Tech. | 34.798363 |
A Brief History of Time
We've always talked about our hardware upgrades and how well they perform. Our hardware architecture is, no doubt, critical to the success of the site, but the software that actually runs AnandTech.com is equally important. Recently, we performed a major architecture shift from a ColdFusion based back-end to Microsoft.NET. We thought that this would be an interesting article, to highlight the history of AnandTech.com from a software perspective.
In this article, we will discuss background information on the following platforms:
is a web-based language that focuses on the RAD development of dynamic web content. ColdFusion started off based on a C++ runtime that interpreted code within HTML templates and compiled it into PCODE, which was then interpreted by the ColdFusion runtime and delivered to the web server and, in turn, to the end user requesting the page. ColdFusion back then was similar to PHP and ASP. Recently, Macromedia decided to take the ColdFusion language to a standards based platform, JAVA. ColdFusion runs on top of almost any J2EE server; we used the ColdFusion standalone version, which uses Macromedia JRUN as the J2EE server. ColdFusion templates are written in CFML (ColdFusion Markup Language) and then compiled down to JAVA byte code and executed by the J2EE server. Macromedia used to be the only game in town, in terms of ColdFusion. Now, a company named New Atlanta
makes a ColdFusion server that also runs on .NET.
The .NET platform is the new framework for building Windows based and web-based applications from Microsoft. It not only replaces the older ASP platform, but introduces some up-to-date languages that run on the Common Language Runtime, which is the backbone of .NET. The three main languages used with .NET are: C# (similar to C++), VB.NET (somewhat similar to VB) and J# (fairly close to JAVA). The beauty of this architecture is that it brings different developers together on a single platform. Those who wrote mostly in C++ or JAVA will probably choose C#; and those who are familiar with VB or more verbose languages will probably choose VB.NET. J# is there for the JAVA developer. Whatever language in which you write your code, it is compiled into an intermediate language, CIL (Common Intermediate Language), which is then managed and executed by the CLR. ASP.NET is simply another .NET based environment that allows you to write in any of the languages that run on the CLR. Its syntax is similar to ASP. | <urn:uuid:35151954-dc9e-4b9c-a546-5b61194508a5> | 2.75 | 563 | Truncated | Software Dev. | 49.509403 |
Jellyfish Rule! --- Moon Jellyfish [LiveScience 2011-04-28]
The moon jellyfish is believed to have been introduced into many new environments by ships, when the jellyfish's stationary developmental stage, called a polyp, attached to their hulls or came in via the ballast water, which ships dump once they arrive at their destination.
Jellyfish are simple, successful and, occasionally, deadly creatures. The Australian box jellyfish has enough toxin in each of its tentacles to kill 60 people. Some jellyfish create spectacular blooms when fields of polyps, their stationary life stage, simultaneously bud off into free-floating medusae. These blooms are blamed for the deaths of swimmers, clogged fishing nets and power plant intakes, and in certain parts of the world, like Japan, they appear to be on the rise.
But these problems are associated with only a subset of the creatures we call "jellyfish" – a catch all term for an amazingly diverse group of organisms. It includes corals, true jellies and others with stinging cells, as well as the stingless comb jellies, which swim using tiny hairs, called cilia.
What they also are is beautiful, as the following images attest.
- Red Giant: Big Red Jellyfish (Tiburonia granrojo)
- Haunting Eyes: Sea Wasp (Chironex fleckeri)
- Ocean Mixers: Golden Jellyfishes (Mastigias sp.)
- Moon Jellyfish (Aurelia aurita)
- Oldest Known Jellyfish Fossils
- Monster Jellyfish: Australian spotted jellyfish (Phyllorhiza punctata)
- Jellies from Above: Blooms of Moon Jellyfishes
- Nomura's Jellyfish (Nemopilema nomurai)
- Blooms of Nomura's Jellyfishes
- Mating Ritual: Box Jellyfish (Copula sivickisi)
- Jellyfish Introductions: Moon Jellyfish (Aurelia aurita) | <urn:uuid:da2ba035-7894-47e2-8d8c-0593cd2b550a> | 3.5 | 431 | Knowledge Article | Science & Tech. | 23.993445 |
Needs Summary: This article does not have a summary. Summaries give a brief overview of the topic and are automatically included on some listing pages that link to this article.
The width property is a standard HTML attribute. The value of this attribute is usually an integer.
It is very common to see HTML tags like images, iframes or object elements have width (and height) attributes.
<img src="smiley.gif" alt="Smiley face" height="42" width="42">
This property is an integer value. Although an HTML author can specify the width as a percentage, this property always specifies the width in pixels in C++. In Microsoft Internet Explorer 5 it is possible to set the width property, but doing so has no effect on the rendering of the frame.
This article contains content originally from external sources.
Portions of this content come from the Microsoft Developer Network: [Windows Internet Explorer API reference Article] | <urn:uuid:f95faae6-a2e8-40d5-ac3f-78aa48441da2> | 2.90625 | 196 | Documentation | Software Dev. | 44.776088 |
About Recombinant DNA
Recombinant DNA is the technology that allows us to insert genes from one organism into another to make it produce a protein product, copy the gene multiple times, or give it a new trait. The discovery of recombinant DNA was considered the "birth" of modern biotechnology.
Deoxyribonucleic acid, or DNA, is the blueprint for life. Inside every cell in your body, DNA contains the code that determines who you are and what traits you have. Recombinant DNA is DNA from two different sources that has been combined in vitro (outside living organisms). There are three main reasons for creating recombinant DNA: (i) to create a protein product, (ii) to create multiple copies of genes, and (iii) to insert foreign genes into other organisms to give those organisms a new trait (Campbell & Reece, 2002).
Recombinant DNA is used widely today to create large amounts of protein for treating certain illnesses. In 1982, insulin became the first recombinant DNA drug to hit the market (NHGRI, 2003). A person with diabetes does not produce adequate insulin. Insulin, a protein, can now be produced in large quantities by bacteria that have been given the human insulin gene (Hormones, n.d.; Stanford University, 2002; G. Stein & J. Stein, 2002). Another example of a protein that is made by bacteria for medical use is human growth hormone (Hanna, 2004; G. Stein & J. Stein, 2002).
The creation of multiple copies of a gene is valuable for genetic research. The availability of multiple copies of a gene has many advantages including the determination of the nucleotide sequence of a gene (Campbell & Reece, 2002).
Inserting genes that originated in one organism into another organism is proving indispensable in agriculture and other fields. In agriculture, adding genes to plants to make them draught or insect resistant is already common practice (Anunson et al, 1999; Campbell & Reece, 2002). Another use is the creation of bacteria that will help clean up toxic waste. A bacteria has been created using recombinant technology that can digest oil from an oil spill (Campbell & Reece, 2002).
Here is an overview of how a gene from an organism can be inserted into a bacterium. First, the gene of interest must be identified. For example, the insulin gene would have to be localized in the human genome. Then a plasmid has to be isolated from bacteria cells. A plasmid is a circular, double-stranded DNA sequence that replicates in bacteria and is separate from the bacterial chromosome. The gene is inserted into the plasmid, and the plasmid is taken up by a bacterium. The bacteria reproduce, and start creating the desired protein (Campbell & Reece, 2002).
A illustration showing showing how human insulin can be produced by bacteria using recombinant DNA (MIT, 1989).
Bacterial Plasmids (Kimball, 2004).
Restriction enzymes, discovered in 1968, are important parts of this process (NHGRI, 2003). In nature, restriction enzymes are a bacterium’s self-defense. A restriction enzyme cuts in between a certain sequence of nucleotides, called the restriction sight, which is 4-8 nucleotides long. Every time that sequence occurs in the bacterium’s own DNA, methyl groups (-CH3) are added to adenines or cytosines which prevent the restriction enzyme from working. Any time foreign DNA, such as a phage (a bacterial virus), enters the bacterium, the bacterium’s restriction enzyme would cut the phage’s DNA into pieces. Although not all bacteria have restriction enzymes, there are wide varieties of restriction enzymes that have been discovered and continue to be discovered (Campbell & Reece, 2002).
Restriction enzymes are used to cut open a plasmid and the same enzyme is used to cut the desired gene out of the chromosome. This makes two matching cuts, and when the gene and plasmid are combined, they form a temporary bond. Another enzyme, DNA ligase, is used to create a permanent seal (Campbell & Reece, 2002).
An example of how a restriction enzyme might work. The restriction site is g-g-a-t-c-c (Kimball, 2004).
This is an example of using restriction enzymes to insert DNA into a plasmid. The restriction site is g-a-a-t-t-c (MIT, 1989).
To simplify things, the foregoing has described recombinant DNA in terms of one cell, one restriction enzyme, etc. When scientists are attempting to make recombinant DNA, it is done on a much larger scale. Millions of plasmids are mixed with millions of genes. Millions of restriction enzymes are dumped in to make millions of cuts. Plasmids bind to plasmids, plasmids bind to genes, genes bind to genes, plasmids bind to multiple genes, and the whole thing is a mess (Campbell & Reece, 2002).
To solve this problem, a cool trick is used. The starting plasmids (the
ones that are going to be modified) are called cloning vectors, which is a
molecule of DNA that can carry foreign DNA into a cell and replicate there.
These plasmids include a gene that confers resistance to ampicillin. They
also contain a second gene (for example lacZ). The restriction site, where
the restriction enzyme will make a cut, is in the lacZ gene. If foreign DNA
is inserted into the lacZ gene where the restriction enzyme made its cut,
the lacZ gene will no longer work. The restriction enzymes are mixed with
the plasmids, and then the desired genes, the genes we want to combine with
the plasmids, are added. Then the bacteria are induced to take up the plasmids.
Changes in heat, or chemicals that are added, are ways to make bacteria do
this. After the bacteria are induced to take up the plasmids, the bacteria
are grown on a medium of ampicillin and a substance that reacts to the protein
product of lacZ. A bacteria colony that took up a plasmid with an intact lacZ
gene, meaning that it is not a recombinant plasmid, will turn blue. Bacteria
that did not take up any plasmids will not be able to grow on the ampicillin.
Therefore, only bacteria that took up a plasmid will be growing, and only
bacteria that had something inserted into the lacZ gene will be white (Campbell & Reece,
Anunson, A., Baker, D., Cracraft, J. (1999). Gene School. Retrieved August 30, 2004, from The ThinkQuest Library: http://library.thinkquest.org/28599/agriculture.htm?tqskip1=1
Campbell, N., & Reece, J. (2002). Biology: Sixth Edition. San Francisco: Benjamin Cummings.
Hanna, K. (2004). Genetic Enhancement. Retrieved July 25, 2004, from National Institute of Health (NIH), National Human Genome Research Institute Web site: http://www.genome.gov/pfv.cfm?pageid=10004767
Hormones. (n.d.). Retrieved August 10, 2004, from http://www.schoolscience.co.uk/questions/4/biology/
Investigating Proteins. (n.d.). Unilever Education Advanced Series:
Protein. Retrieved August 10, 2004, from http://www.schoolscience.co.uk/content/5/chemistry/
Kimball, J. W. (2004, September 3). Recombinant DNA and Gene Cloning. Retrieved
July 17, 2004, from
Massachusetts Institute of Technology, MIT. (1989). Cloning Genes. Retrieved
September 9, 2004, from
National Human Genome Research Institute Web (NHGRI). (2003). Genetic Timeline. Retrieved July 24, 2004, from National Institute of Health (NIH), National Human Genome Research Institute Web site: http://www.genome.gov/Pages/Education/GeneticTimeline.pd
Stanford University (2002). Recombinant insulin to treat diabetes. Retrieved July 24, 2004, from Stanford University, Introduction to Biology Web site: http://www.stanford.edu/class/bio4/ClassLinks/october2.htm
Stein, G., & Stein, J. (2002). Molecular biology. Retrieved July 24, 2004, from AccessScience@McGraw-Hill: http://www.accessscience.com, DOI 10.1036/1097-8542.430300. | <urn:uuid:072d0a61-3367-45ea-a61e-a5a34ee248dc> | 4.0625 | 1,848 | Knowledge Article | Science & Tech. | 54.24249 |
Quasars have remained enigmatic ever since their discovery in 1963 because of the way they emit prodigious amounts of energy yet are very compact. Their star-like appearance gave birth to the name quasi-stellar object, later shortened 'to 'quasar'. The most widely accepted theory to explain quasars is that they are powered by supermassive black holes in the cores of galaxies.
This HST image of the quasar PKS 2349 shows evidence that it is merging with a companion galaxy. The bright central object is the quasar itself, which is several billion light years away. The wisps next to it are remnants of a bright galaxy that has been disrupted by the gravitational pull between it and the quasar.
Credit: J. Bahcall (Institute for Advanced Study, Princeton), and NASA | <urn:uuid:6567fe32-da36-4956-9b93-92989fbf4593> | 4.21875 | 165 | Knowledge Article | Science & Tech. | 43.85093 |
[Tkinter-discuss] How can I edit a string inside a textbox?
fredrik at pythonware.com
Thu Dec 6 12:27:17 CET 2007
Alex Garipidis wrote:
> I have a Tkinter Textbox in my application. I want to scan the
> textbox for a symbol, defined by me as a "mark", and
> change the word that is inside or next to that symbol.
> This is what i mean:
> If a user types this to the textbox:
> "Hello @everybody, how are you doing?"
> I want to scan this string for the "@" character (or something
> else) and edit the word next to it (or "inside" it, e.g.
> "@everybody@"), "everybody" in this case, and make it have
> a color for example or make it underlined.
to find things in a text widget, use the "search" method:
pos = text.search(string, start)
where "string" is the string you want to search for, and start is the
starting position (e.g. 1.0 or INSERT).
to search for things that match "@word", where "word" is an arbitrary
string of letters or digits, you can use a regular expression, e.g.
pos = text.search("@\w+", 1.0, regexp=True)
search only returns where the match begins; to find the end of "@word",
you can search from the given position to the first thing that isn't a
end = text.search("\W", pos + " 1 char", regexp=True)
to change the appearance of a block of text, register the style using
tag_config, and then use tag_add to apply the style tag to the block, e.g.:
# do this when you create the widget
# do this to apply this style to a range of text
text.tag_add("mystyle", pos, end)
hope this helps!
More information about the Tkinter-discuss | <urn:uuid:5c4dde72-9d2a-438a-ab33-c9531776dd57> | 2.9375 | 459 | Comment Section | Software Dev. | 78.164567 |
Hi guys, i need help with this problem that i seriously have no idea with.
with t=0 representing the year 1990.
1. What is the population of elk in the year 2004
2. Determine the years between 1990 and 2020 in which the elk population is at its maximum
3 Explain the period of the function in context of the problem
4 Graph the function showing the elk population from 1990 to 2020. identify the points on the graph you determined in parts 1 and 2. | <urn:uuid:9560a553-2f06-434f-b5d8-8cfb543c4a99> | 2.6875 | 104 | Q&A Forum | Science & Tech. | 86.124397 |
What does potential at a point exactly mean? My teacher tells me that current flows from higher potential to lower potential but when I ask him the reason, he fails to give me a convincing answer.
And can anyone explain how electric potential is related to potential energy & work done?
Further, when I referred a Physics textbook it said that since Coulomb's force & Gravitational force are mathematically similar, electric potential is a charge's equivalent of a the potential energy of mass. Hence I related Electric potential to the potential energy of a ball for example. A ball falls from a height to the ground because of Potential energy- so similarly, current flows from higher to lower potential. Is this analogy correct?
Even if the above analogy is correct, I still cannot understand why current flows between two electrodes of an electrochemical cell. The only explanation my teacher offers is that there is a potential difference & thus current flows from higher to lower potential. This explanation is not of any help since I don't understand what potential is in the first place !!!
If the analogy is valid, then how do the electrons in the Electrochemical cell move without an electric field to impart the electric potential energy? (as in gravitational energy where the potential energy is present only if gravitational force is present? In space, no object of any mass has weight)
Can someone help me? | <urn:uuid:75b4b29a-54ac-4154-84a6-8edadcee8eb4> | 3.03125 | 275 | Q&A Forum | Science & Tech. | 40.369829 |
Can any one please explain this piece of code I found in the linux kernel source. I see a lots of code like this in linux and minix kernel but dont seem to find what it does (even if C compilers ...
On the Wikipedia page for Windows, it states the Windows is written in Assembly for the bootloader and task switcher, and C and C++ for kernel routines. IIRC, you can call C++ functions from an ...
I have a very abstract question about a kernel module writing estimate. How much dev-hours/months may required to write or, especially, port an existant kernel driver for a new PCI HBA from one ...
I'm a very ambitious university student who wishes to learn pretty much everything there is to know about computers (bash me if you want, I love learning). Recently I thought it would be a fun project ...
I want to learn kernel programming but before that I want to have firm understanding of data structures and algorithms in C. I am a beginner in this field. Can you refer any book or resources that ... | <urn:uuid:dc1a1f4d-6734-4a34-8bf4-ea788b4ccacf> | 2.703125 | 219 | Q&A Forum | Software Dev. | 70.764685 |
This is one of my favorite things about ants -- the ant death spiral. Actually, it's a circular mill, first described in army ants by Schneirla (1944). A circle of army ants, each one following the ant in front, becomes locked into a circular mill. They will continue to circle each other until they all die. How crazy is that? Sometimes they escape, though. Beebe (1921) described a circular mill he witnessed in Guyana. It measured 1200 feet in circumference and had a 2.5 hour circuit time per ant. The mill persisted for two days, "with ever increasing numbers of dead bodies littering the route as exhaustion took its toll, but eventually a few workers straggled from the trail thus breaking the cycle, and the raid marched off into the forest."
Folks interested in things like self-organization, emergant properties, complex systems, etc. etc. like to point to this as a cautionary tale. I even found a reference to a group programming robots to interact like ants that accidentally produced this behavior in their robots. Apparently you can also reproduce this behavior in the lab by placing a glass jar into the surface. The ants will eventually circle the jar and continue to do so even after the jar has been removed. I assume just army ants. Wow, I wish we had an army ant colony in the lab.
Anyway, in tribute to this fabulously bizarre phenomenon, I made some Ant Death Spiral T-shirts. Check them out!
- Schneirla, T. C. (1944). A unique case of circular milling in ants, considered in relation to trail following and the general problem of orientation. American Museum Novitates, (1253), 1--26.
- Google Video -- Crazy Ants in Panthanal - Why do they walk like this?
- Beebe, W. 1921. Edge of the Jungle. Henry Holt, New York
- Couzin ID, Franks NR (2003) Self-organized lane formation and optimized traffic flow in army ants. Proc R Soc Lond B 270:139–146
- Army Ants Trapped by Their Evolutionary History
- Experiments in Path Optimization via Pheromone Trails by Simulated Robots, Jason L. Almeter September 17, 1996 | <urn:uuid:cf6553e2-7741-4022-9a3e-aa2bedcd016e> | 2.6875 | 472 | Personal Blog | Science & Tech. | 60.387434 |
Science Fair Project Encyclopedia
The name is derived from the Greek words kopros meaning "dung" and lithos meaning "stone".
Coprolites are also trace fossils and vary in size from the small fecal pellets of a sea-snail to the large droppings of crocodiles, dinosaurs, or mammals. Typical sizes vary from less than 5 mm (0.2") to 5 cm (2"), although they may exceed 30 cm (12") in length. There is a large variety of shapes: cigar-shaped, lens-shaped, kidney-shaped, cone-shaped, round, oval, cylindrical, or spiral-shaped, depending upon the type of animal which produced them, although as with other trace fossils, the specific animal is usually not known.
The recognition of coprolites is aided by their structural patterns, such as spiral or annular markings, their content, such as undigested food fragments, and also by associated fossil remains. The smallest coprolites are often difficult to distinguish from inorganic pellets or from eggs. Most coprolites are composed chiefly of calcium phosphate, along with minor quantities of organic matter. By analysing coprolites sometimes the diet of the animal which produced them may be determined.
Coprolites have been recorded in deposits ranging in age from the Ordovician period to recent times and are found worldwide. Some of them are useful as index fossils, such as 'Favreina' from the Jurassic period of Haute-Savoie in France.
Some marine deposits contain a high proportion of fecal remains, however, animal excrement is easily fragmented and destroyed and so usually has little chance of becoming fossilized.
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details | <urn:uuid:757d82d3-76ea-4463-acd7-d0a002736e94> | 3.875 | 378 | Knowledge Article | Science & Tech. | 36.343097 |
Pliocene Climate Lessons
An ongoing reconstruction of a warmer Earth 3 million years ago helps test climate-change forecasts
The middle portion of the Pliocene Epoch—about three million years ago—is the most recent period when global temperatures were sustained at levels comparable to those we may see at the end of this century due to climate change. One way to seek a more accurate view of a warmer Earth is to look closely at that time. Paleoclimate studies of the mid-Pliocene are also emerging as a ground truth for testing the accuracy of computer models used to predict Earth’s future climate.
Go to Article | <urn:uuid:8fee3722-7c1a-48be-96fe-979ae6a2db57> | 3.484375 | 129 | Truncated | Science & Tech. | 24.595 |
Simply begin typing or use the editing tools above to add to this article.
Once you are finished and click submit, your modifications will be sent to our editors for review.
...poses environmental challenges, especially in regions where it occurs. Even so, oil shales and tar sands are abundant, and advances in recovery technology may yet make them attractive alternative energy resources.
An industrially advanced society uses energy and materials in large amounts. Transportation, heating and cooling, industrial processes, communications—in fact, all the physical characteristics of modern life—depend on the flow and transformation of energy and materials through the techno-economic system. These two flows are inseparably intertwined and form the lifeblood of...
Practical efforts to harness fusion energy involve two basic approaches to containing a high-temperature plasma of elements that undergo nuclear fusion reactions: magnetic confinement and inertial confinement. A much less likely but nevertheless interesting approach is based on fusion catalyzed by muons; research on this topic is of intrinsic interest in nuclear physics. These three methods are...
What made you want to look up "energy source"? Please share what surprised you most... | <urn:uuid:f5f459dd-7280-4a04-b08c-4935b655d985> | 2.875 | 231 | Truncated | Science & Tech. | 28.548333 |
Understanding the relative importance of these two factors is key to designing effective conservation strategies. It may be common sense to focus on boosting numbers if demographics matter more, and to put together breeding programmes that expand the remaining gene pool if genetics rule, but accurately pointing the finger at the primary cause of decline is rarely a simple task.
The cheetah is the poster child for this problem, Wootton told attendees of the 2012 Ecological Society of America annual meeting in Portland, Oregon, on 6 August. Africa’s most at-risk cat species has lost much of its habitat and its former genetic diversity. Consequently, no one knows which factor will more strongly influence its fate.
He and Pfister wanted to do experiments in which they could manipulate both the genetic structures and the sizes of populations. Cheetahs being impractical subjects, they opted instead for the sea palm, Postelsia, a type of kelp that occurs along the western coast of North America. Postelsia barely disperses at all. It grows in clumps on wave-swept rocky shores, reproducing by dribbling spores onto rocks directly below it. Waves remove the adult plants each year, leaving room for spores to grow. As a result, each clump is often genetically isolated from those just metres away.
Wootton and Pfister bred sea-palm populations with varying degrees of genetic diversity. They transplanted them onto rocky patches of shoreline in batches of different sizes. After 12 years, smaller populations were less likely to have survived than larger ones, and, among the populations that did disappear, smaller ones did so more quickly. Crucially, genetic diversity did not influence the odds of a population’s survival.
Wootton found a cut-off point, between 10 and 100 individuals, where the risk of becoming locally extinct changed dramatically. “The rule of thumb when I was a student was that 50–100 individuals was a viable population size,” he says. “Our experiments support that.”
How widely applicable are the findings? The sea palm is edible and heavily harvested, so the results have direct implications for its management. But it is also stationary, whereas many vulnerable species — speedy cheetahs especially — are mobile.
“It’s hard to know [how broadly applicable the results are] because it’s the first experiment of its kind,” Wootton points out. Meanwhile, Robert Paine, an ecologist at the University of Washington in Seattle, who has worked with Wootton and Pfister, praises the new study, describing it as dealing with a very real question with broad application.
Some other studies have claimed that genetic diversity is the more important factor, but these typically report only a correlation between low diversity and species endangerment, Wootton says. “I’d say if you have a limited budget, you should probably study the ecology and the demographics first rather than doing molecular analysis.” | <urn:uuid:dee41189-7556-48fd-96d1-82e77dddea00> | 3.734375 | 609 | Knowledge Article | Science & Tech. | 35.216859 |
Definitions for absorption, electric
The Standard Electrical Dictionary
A property of the static charge. When a Leyden jar is being charged it dilates a little and the capacity increases, so that it can take a little more charge for a given potential difference existing between its two coatings. This phenomenon occurs with other static condensers, varying in degree with the dielectric. With shellac, paraffin, sulphur and resin, for instance, the absorption is very slight; with gutta-percha, stearine, and glass, the absorption is relatively great. The term is due to Faraday. Iceland spar seems almost or quite destitute of electric absorption.
Use the citation below to add this definition to your bibliography:
"absorption, electric." Definitions.net. STANDS4 LLC, 2013. Web. 19 May 2013. <http://www.definitions.net/definition/absorption, electric>. | <urn:uuid:1f67f55a-2156-4fad-9c4d-fda3a88e8594> | 2.875 | 195 | Structured Data | Science & Tech. | 43.155256 |
Another Newbie question :)
Keith.Wansbrough at cl.cam.ac.uk
Wed Nov 5 12:27:35 EST 2003
> I seem to understand the basic idea behind the fold function, i think but do
> not seem to be able to write them myself. My understanding is that it works
> by replacing every constructor with a fold ?
I think you mean "replaces every constructor with a function or
Think of a list [1,2,3]. Recall this is "syntactic sugar"
(abbreviation) for 1:(2:(3:)). That looks like
Recall (+) is the function that takes two arguments and returns their
foldr (+) 0 [1,2,3]
What happens is that (:) is replaced by the first argument (+) and
is replaced by the second argument 0, as follows:
This is just 1+(2+(3+0)), which is 6.
You can see this from the definition of foldr:
foldr :: (a -> b -> b) -> b -> [a] -> b
foldr f z = z
foldr f z (x:xs) = f x (foldr f z xs)
where clearly every is replaced by z and every : by f.
A similar fold can be written for any datatype; it just takes a
different number of arguments, one for every constructor. The general
term is "catamorphism". E.g.:
data Expr = Num Int
| Plus Expr Expr
| Times Expr Expr
foldExpr :: Int -> (b -> b -> b) -> (b -> b -> b) -> b
foldExpr n p t (Num i ) = n i
foldExpr n p t (Plus e1 e2) = p (foldExpr n p t e1) (foldExpr n p t e2)
foldExpr n p t (Times e1 e2) = t (foldExpr n p t e1) (foldExpr n p t e2)
Hope this helps.
> Could anyone please point me in the direction of a suitable resource of
> attempt to explain this to me :)
You could try googling for "catamorphism", or looking at some of Erik
Meijer et al's papers on "bananas, lenses, and barbed wire" and so on.
More information about the Haskell-Cafe | <urn:uuid:a1a4af3a-9e0e-4c13-b7d0-3b250c368ad2> | 3.578125 | 532 | Comment Section | Software Dev. | 86.086212 |
Mishka Henner, Astronomical, twelve 506 paged volumes of black pages with planets and the sun on 11 of the pages. The Solar System is mostly pretty empty.
Top: Jupiter on page 283 of volume 2
Bottom: The Earth on page 155 of volume 1
Each page = 1,000,000 km. A picture of each planet in the Solar System is on a page equivalent to its distance from the Sun, with black pages in between. The Sun is on pages 2 & 3 of volume 1, Pluto is on page 503 of volume 12 (Earth: page 155 of volume 1. Jupiter: page 283 of volume 2. Uranus: page 383 of volume 6. Neptune: page 53 of volume 10). I did not know that Uranus and Neptune were so MUCH farther away than Jupiter and Saturn. According to this, it’s 6,069,000,000 km from the Sun to Pluto, which was maybe Pluto’s distance from the sun when he first made the books.
The index sheet, giving the relative distances of the planets from the sun
The related video | <urn:uuid:6d7115ab-d4be-408f-8fde-4bca9c8a1794> | 2.84375 | 229 | Personal Blog | Science & Tech. | 73.415 |
"In a stunning first for neuroscience, researchers have created an electronic link between the brains of two rats, and demonstrated that signals from the mind of one can help the second solve basic puzzles in real time — even when those animals are separated by thousands of miles."
posted by sarastro
on Feb 28, 2013 -
The Timeline of the Far Future
is a Wikipedia article which serves as a gateway to a ton of fascinating scientific topics on the far edge of human understanding: ~50,000 years from now the Earth will enter a new Glacial period
; ~100,000 years from now the Earth will likely have experienced a supervolcanic
eruption; ~10,000,000 years from now the East African Rift
divides the continent of Africa in to two land masses; ~20,000,000,000 years from now the Universe effectively dies due to The Big Rip
posted by codacorolla
on Jan 22, 2013 -
Prototypes are usually the missing links in the evolution of human technology, the dead-ends of ideas that give way to the refinement of the final physical product. Prototypes aren't just for Darth Vader
. While the legal back and forth between Apple and Samsung continues, a treasure trove
of prototype designs
for Apple devices has been released to the public, showing insights into various design approaches and feature enhancements, including larger form-factor
and without kickstands
and landscape ports
and iPhones that parody the Sony logo
, show a different layout for camera elements
, and look remarkably like fourth-generation models
, as far back as 2005. On the other hand, some have made prototypes into the end goal itself, such as the folks at Dangerous Prototypes
, a site which features a new open-source electronic hardware project
each month. Some are just gratuitous fun
, while others are a bit more practical, such as one project that recycles old Nokia displays
and another that provides access to infrared signal
, useful for hacking together remote controls for all sorts of IR-based devices. Other prototypes of tomorrow's technology
are less concerned with shrinking down the guts of the invention itself, to make it disappear, but rather on how
with and integrate
physical representations of these ideas into our daily lives. Above all else, prototypes are always forward-looking and are therefore inherently optimistic expressions of human creativity: Even children
are getting into imagining the world of tomorrow.
posted by Blazecock Pileon
on Aug 1, 2012 -
Where forward thinking terrestrials exchange ideas and information about the state of the species, their planet and the universe, living the lives of science fiction today. A growing number of universities, architecture and design schools are conducting projects
on this site. Hundreds of art treasures, educational videos and narratives are found in their galleries
. Every SpaceCollective member is provided with a personal time capsule
, preserving their contributions for the edification of each other as well as future times and beings.
posted by netbros
on Apr 7, 2009 -
Miracles You’ll See In The Next Fifty Years
Some more up-to-date predictions: science
, space travel
, mental health
, smart machines
, robots, mind uploading
What is your prediction
posted by MetaMonkey
on Oct 5, 2006 -
What Comes Next?
Big scientists answer some big questions: apparently Elvis may still be alive in a parallel universe.
posted by Holly
on Feb 10, 2005 -
Life in the future.
In the year 2,000 "everything will be so easy that people will probably die from sheer boredom." Workweeks will be 24 hours and the home computer will be the new status symbol.
posted by caddis
on Jan 12, 2005 -
Evolution is a process
that hasn't stopped just because humans now rule the planet. What will animals look like in 200,000 years? The Discovery Channel's Animal Planet
asks experts to predict the future of life on Earth.
posted by hipnerd
on Dec 31, 2002 -
Alternate universes may exist besides our own in some ghostly manner. Various science-fiction series explore parallel universes
, but what do serious physicists think? Hugh Everett III's doctoral thesis outlines a controversial theory in which the universe at every instant branches into countless parallel worlds
. Physicist Andrei Linde's theory of self-reproducing universes
implies that new universes are being created all the time through a budding process. Stephen Hawking's quantum cosmology
also suggests the possibility of other universes connected by wormholes. Some scientists feel that the famous photon double slit experiments
proves the existence of parallel universes in which a photon from one universe interacts with a photon from another. Black hole theory suggests that black holes may be portals to parallel universes
Science-fiction stories about parallel universes always delight the mind. Two of my favorite SF novels on parallel universes are Heinlein's Job
and Number of the Beast
. Several others intrigue me, such as The Neoreality Series
, and Parallelities
. Science books on the subject include a famous book
by David Deutsch.
Do you have any favorite books on parallel universes or parallel realities, fiction or nonfiction?
What do you think? No doubt, scientists and science-fiction authors
will continue to explore the concept in the decades to come.
posted by Morphic
on Oct 21, 2002 -
Genetic engineering leaves mice impervious to pain.
By removing a protein called "DREAM", scientists were able to create rodents that didn't mind extreme heat, pressure and inflammation. This could provide hope for those suffering, or a strange removal from the experience of living, and classic human traits like bravery, strength, volition, and empathy, depending on your view.
posted by mdn
on Jan 15, 2002 -
Miracles of the Next Fifty Years
-- a reprint of an article from the February 1950 issue of Popular Mechanics. At times laughably naive, other times pretty accurate (the author predicts that cancer won't be cured by 2000, but it won't be far off), it's a fun piece of George-Jetson-meets-Ozzie-and-Harriet gee-whizness.
posted by RylandDotNet
on Jun 2, 2001 -
Why the Future Doesn't Need Us
is the cover story in this month's 'Wired'. It was written by Bill Joy, chief scientist at Sun. In it he makes a very convincing case for strict regulation of genetics, nanotech, and robotics, given that any of these could cause the extinction of the human species in the next 30 years. What do you think?
posted by Sean Meade
on Mar 22, 2000 - | <urn:uuid:5cbf8340-66b8-4364-b856-1f978ded162d> | 3 | 1,400 | Comment Section | Science & Tech. | 37.661744 |
strand synthesis uses a single, dimeric DNAPol III enzyme
Models of DNA synthesis often show it as occurring independently on the leading and lagging strands, with separate DNAPol IIIs on each. However, replication at any one fork is under the control of a single, dimeric DNAPol III holoenzyme [the two donut-shaped rings] that replicates both parental DNA strands simultaneously. The process occurs consistent with the requirement that new strand synthesis always occurs 5'3'.
Synthesis off the leading strand (below, blue) occurs in the 5'3' direction, which is oriented towards the replication fork (lower DNA molecule, red strand).To achieve the same orientation on the lagging strand, the lagging strand loops around the subunit (above, blue). This allows either parental strands to enter the alternate subunits of the polymerase in the same 5'-3' orientation as well as the same right-to-left direction. It also means that lagging strand synthesis will trail a series of Okazaki fragments as succesive segments of the parental strand pass through the polymerase.
imagine the top subunit rotated 180o to the left,
the Okazaki fragments will be directed away from the
replication fork, in the manner seen in the simplified | <urn:uuid:c4d1c467-88a2-4e0a-9bca-7ab1daae6899> | 3.09375 | 268 | Knowledge Article | Science & Tech. | 30.715909 |
AERIAL land photographs are vital for hundreds of scientific, commercial and military projects. Now similar panoramas of the seafloor may be possible, thanks to a scanning laser system described at a conference last week. Such images "would radically change the way we now think about and work in the submarine environment", Ian MacDonald, a geochemist at Texas A&M University, told the Oceans 95 conference in San Diego.
The problem is that seawater scatters and absorbs visible light in the same way as thick fog. So while bright lights show nearby objects underwater, scattered light obscures anything lying more than a few metres away, even in clear water. But MacDonald described a scanning laser system developed by the engineering company Westinghouse that can map the seabed through up to 25 metres of water.
In an attempt to minimise interference from scattered light, designers of conventional undersea cameras separate the illuminating lamp ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:ae51b7b1-b7c9-4a17-8ab1-cf6dfd363c78> | 3.609375 | 215 | Truncated | Science & Tech. | 36.203732 |
In America, the kind Nycticeius gathers two species of Chauve-souris of the family of the Vespertilionidae;
- Nycticeius humeralis (Rafinesque, 1818) - evening bat
- Nycticeius cubanus (Cuban Evening Beats) - evening bat of Cuba.
DescriptionThe evening bat is a small brown bat weighing 7 to 15 grams.
DistributionOne finds it in most of the United States; in almost all the Middle-West and south-east.
Dans of many sectors (particularly littoral states of Gulf) they are very common, but can have populations reduced in some states.
LifestyleThe summer, this species spent the day in the cavities of old trees, but one finds some sometimes in more artificial habitats. The colonies living in the trees are generally small, but certain groups living in buildings reach almost the 1.000 individuals.
La evening bat is often regarded as migrating, but of recent work suggest that some individuals can be sedentary, even in the north of their surface of distribution. In winter, the individuals are gathered in their cavities or buildings, but they can leave and drive out the least cold nights. heats.
FoodThis bat particularly seems to appreciate the Coléoptère S, but they also consumes and moths (Lepidoptera) moindrement Diptère S (flies.) and other insects.
reproductionThe cycle of reproduction of this species is known little about, but at others Vespertilionidé S of moderated zone, the coupling is done in autumn, the Sperme being stored in the reproductive bodies of the female until spring when the Ovulation and the Fécondation occur. The female is generally confined of two young people, in June, who will be able to drive out as of their third week after the birth.
Close speciesThe evening bat of Cuba, which is known only on the island of Cuba resembles NR. humeralis, but is definitely smaller and light (4 to 7 grams). It is a species which was studied little.
ThreatsThe Pesticide S, the lack of old dead or hollow trees, the buildings not allowing the installation or the life of colonies, the luminous Pollution are threats for this species, as for the majority of the bald person mouse living in the hollow shafts.
External bondsAugust 1st
|Random links:||Avenay | Juan Sutter | Fontainebleau (Quebec) | Municipalities of Piauí by population | Vrhpolje | Sohodolls | Angela_Aames| | <urn:uuid:507a1cb1-d63d-4e51-a30a-3ede89cc95f0> | 3.0625 | 548 | Knowledge Article | Science & Tech. | 38.492733 |
Texas 80-Meter Wind Map and Wind Resource Potential
The U.S. Department of Energy's Wind Program and the National Renewable Energy Laboratory (NREL) published an 80-meter (m) height wind resource map for Texas. This map is a key piece of understanding the state's wind resource potential from a development, policy, and a jobs and economic development impact perspective.
About the 80-Meter Texas Wind Resource Map
The wind resource map shows the predicted mean annual wind speeds at an 80-m height, presented at a spatial resolution of about 2 kilometers that is interpolated to a finer scale for display. Areas with annual average wind speeds around 6.5 meters per second and greater at 80-m height are generally considered to have a resource suitable for wind development. Utility-scale, land-based wind turbines are typically installed between 80 and 100 m high.
Texas Wind Resource Potential
The chart to the right shows the wind resource potential above a given gross capacity factor at both 80-m and 100-m heights for Texas.
NREL estimated the windy land area and wind energy potential in various capacity factor ranges for each state using AWS Truepower's gross capacity factor data. The table lists the estimates of windy land area with a gross capacity of 30% and greater at an 80-m height and the wind energy potential from development of the "available" windy land area after exclusions.
"Installed capacity" refers to the potential megawatts of rated capacity that could be installed on the available windy land area, and "annual generation" refers to the estimated annual wind energy generation in gigawatt-hours that could be produced from the installed capacity. NREL reduced the wind potential estimates by excluding areas unlikely to be developed, such as wilderness areas, parks, urban areas, and water features (see Wind Resource Exclusion Table for more detail). Additional wind potential tables are included for various capacity factor ranges.
These maps and wind potential estimates resulted from a collaborative project between NREL and AWS Truepower. This is the first comprehensive update of the wind energy potential by state since 1993. NREL has worked with AWS Truepower for almost a decade on updating wind resource maps for 36 states and producing validated maps for 50-meter heights. The U.S. Department of Energy's Wind Powering America initiative supported the mapping efforts.
Note: Wind resource at a micro level can vary significantly; therefore, you should get a professional evaluation of your specific area of interest. | <urn:uuid:df1fdb11-861a-47b0-9e08-7568602603c1> | 2.96875 | 510 | Knowledge Article | Science & Tech. | 35.463571 |
Triton is the largest moon of Neptune, with a diameter of 2,700 kilometers. It was discovered by William Lassell, a British astronomer, in 1846 scarcely a month after Neptune was discovered.
Triton is colder than any other measured object in the Solar System with a surface temperature of -235 C (-391 F). It has an extremely thin atmosphere. Nitrogen ice particles might form thin clouds a few kilometers above the surface. The atmospheric pressure at Triton's surface is about 14 microbars, 1/70,000th the surface pressure on Earth.
Triton is the only large satellite in the Solar System to circle a planet in a retrograde direction -- in a direction opposite to the rotation of the planet. It also has a density of about 2.1 grams per cubic centimeter. This means Triton contains more rock in its interior than the icy satellites of Saturn and Uranus do.
The relatively high density and the retrograde orbit has led to the suggestion that Triton may have been captured by Neptune as it traveled through space several billion years ago. If that is the case, tidal heating could have melted (as seen in the above image) Triton in its originally eccentric orbit, and the satellite might even have been liquid for as long as one billion years after its capture by Neptune. Triton is scarred by enormous cracks (shown below). Voyager 2 images showed active geyser-like eruptions spewing nitrogen gas and dark dust particles several kilometers into the atmosphere. | <urn:uuid:67fcc7b8-a6c2-4813-a296-2775ab1c4f8b> | 4.34375 | 313 | Knowledge Article | Science & Tech. | 41.1676 |
Bats of the genus Pteronotus (Chiroptera: Mormoopidae) are known to inhabit high-temperature roosts. This study examines the thermal ecology of a colony of three different species of Pteronotus in a sea cave on the Osa Peninsula of Costa Rica. Previous work found the cave to be inhabited by three species of the same genus: P. personatus, P. parnelli, and P. gymnonotus, and documented that temperatures in the cave at low tide with bats present can exceed 40° C. This high ambient temperature makes this cave one of the few locations where bats have been documented to roost at temperatures warmer than their body temperature. However, the cave fills with seawater during high tide, which potentially creates a cooling effect. We explored whether temperatures in the cave fluctuated significantly with tide levels and the presence or absence of roosting bats. Hobo data loggers were placed in the cave for several days to continually record changes in ambient temperatures within the different parts of the cave at different combinations of tides and bats. Upon entering the cave, temperatures of roosting individuals (during the day), and the cave ceiling (at night) were also recorded using an infrared thermometer.
Temperatures on the ceiling of the cave, which was entirely covered with roosting individuals, at low tide were measured at 40-41°C. However, during low-tides at night (with bats absent), temperatures were only 37-39°C in the equivalent parts of the cave. Ambient air temperatures collected by the Hobo data loggers detected no significant effect of tide levels (low vs. high) on ambient temperature. Results from sensors placed near the bottom of the cave showed significantly lower temperatures when bats were present, but when sensors were elevated ~8m, it was found that temperatures in the upper parts of the cave were significantly higher with bats present. These patterns are likely related to the properties of the cave walls to absorb and radiate heat generated by the bats. In the upper areas of the cave, where bats roost, the presence of bats clearly elevates temperatures. The genus Pteronotus may use these high temperatures as a means of thermal competition to exclude species with lesser heat tolerance from using the otherwise highly-desirable roosting habitat. | <urn:uuid:aec61249-6e34-42f1-99e3-caa3b20778fb> | 3.578125 | 480 | Academic Writing | Science & Tech. | 29.588175 |
We work in three dimensions, with similar definitions holding in any other number of dimensions. In three dimensions, a form of the type
is called a differential form. This form is called exact on a domain in space if there exists some scalar function defined on such that
throughout D. This is equivalent to saying that the vector field is a conservative vector field, with corresponding potential .
In one dimension, a differential form
is exact as long as has an antiderivative; in this case let be the antiderivative of . Otherwise, if does not have an antiderivative, we cannot write and so the differential form is inexact.
Two and three dimensions
Hence, it follows that in a simply-connected region R of the xy-plane, a differential
is an exact differential if and only if the following holds:
For three dimensions, a differential
is an exact differential in a simply-connected region R of the xyz-coordinate system if between the functions A, B and C there exist the relations:
- ; ;
- Note: The subscripts outside the parenthesis indicate which variables are being held constant during differentiation. Due to the definition of the partial derivative, these subscripts are not required, but they are included as a reminder.
These conditions are equivalent to the following one: If G is the graph of this vector valued function then for all tangent vectors X,Y of the surface G then s(X, Y) = 0 with s the symplectic form.
These conditions, which are easy to generalize, arise from the independence of the order of differentiations in the calculation of the second derivatives. So, in order for a differential dQ, that is a function of four variables to be an exact differential, there are six conditions to satisfy.
In summary, when a differential dQ is exact:
- the function Q exists;
- independent of the path followed.
In thermodynamics, when dQ is exact, the function Q is a state function of the system. The thermodynamic functions U, S, H, A and G are state functions. Generally, neither work nor heat is a state function. An exact differential is sometimes also called a 'total differential', or a 'full differential', or, in the study of differential geometry, it is termed an exact form.
Partial differential relations
Substituting the first equation into the second and rearranging, we obtain:669
Since and are independent variables, and may be chosen without restriction. For this last equation to hold in general, the bracketed terms must be equal to zero.:669
Setting the first term in brackets equal to zero yields:670
A slight rearrangement gives a reciprocity relation,:670
There are two more permutations of the foregoing derivation that give a total of three reciprocity relations between , and . Reciprocity relations show that the inverse of a partial derivative is equal to its reciprocal.
If, instead, a reciprocity relation for is used with subsequent rearrangement, a standard form for implicit differentiation is obtained:
Some useful equations derived from exact differentials in two dimensions
Suppose we have five state functions , and . Suppose that the state space is two dimensional and any of the five quantities are exact differentials. Then by the chain rule
but also by the chain rule:
which implies that:
Letting , gives:
using ( gives the triple product rule:
- Çengel, Yunus A.; Boles, Michael A. (1998) . "Thermodynamics Property Relations". Thermodynamics - An Engineering Approach. McGraw-Hill Series in Mechanical Engineering (3rd ed.). Boston, MA.: McGraw-Hill. ISBN 0-07-011927-9.
- Perrot, P. (1998). A to Z of Thermodynamics. New York: Oxford University Press.
- Zill, D. (1993). A First Course in Differential Equations, 5th Ed. Boston: PWS-Kent Publishing Company. | <urn:uuid:c4854a7e-2324-4c87-a9d0-633a89def7f1> | 3.4375 | 842 | Knowledge Article | Science & Tech. | 43.51895 |
From optical and infrared galaxy surveys we know that the distribution of visible mass in the local Universe is far from uniform. Over the characteristic distance of 100 Mpc the number density of galaxies in galaxy superclusters and voids may vary by an order of magnitude. Some huge mass agglomerations (M>1015 Msun) in the local Universe are the nearby Virgo cluster, more distant Great Attractor and Perseus-Pisces supercluster.
It is now widely accepted that practically every galaxy in the local Universe has a supermassive black hole and some of these black holes are AGNs with different luminosities. Therefore, it is quite natural to assume that the volume number density of X-ray emitting AGNs is proportional to the volume number density of galaxies.
The recent hard X-ray all sky survey performed with the INTEGRAL observatory (Krivonos et al., 2007; astro-ph/0701836) made it possible to obtain a census of AGNs covering the whole sky. The effective depth of the survey allows one to effectively probe the nearby Universe up to distances of 100 Mpc. The image above shows the AGN volume density in different directions of the sky. The value in each pixel of the map represents the number density of sources in a solid angle confined by cone with a half-opening angle of 45 degrees.
The image demonstrates the strong anisotropy in the distribution of nearby AGNs. The large-scale feature in the north-east direction is consistent with the projected position of the Virgo cluster and Great Attractor while the southern-west structure is consistent with the Perseus-Pisces supercluster. The green contour represents another indicator of mass agglomerations for comparison: the surface density of IRAS PCSz galaxies at distances <70 Mpc.
(Credit: R.Krivonos and INTEGRAL team, IKI,Moscow/MPA, Garching)
Download the picture [PNG format: 42 kb].
The POM Archive
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Triangles, Sines, and Areas
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|Trig/Calc, difficulty level 3. Show that the area of any triangle is .5*b*c*sin(A).|
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William Thomson called them “beautiful and ingenious geometrical constructions,” and in variance to their rather humdrum name dygograms are certainly charming to the eye. But these geometric constructions can conveniently generate and then calculate the magnetic deviation of a ship compass at a location.
With our electronic calculators and computers, we take for granted the effortless arithmetic and trigonometric calculations that so vexed our ancestors. Pre-calculated tables for roots and circular functions, generated through hard work, were often used to create tables of magnetic deviations for specific ships and locations. To reduce the chance of misreading these tables, a few types of graphical diagrams, not just dygograms, were invented to provide fast and accurate readings of magnetic deviation. These graphical calculators are the focus of this part of the essay.
6 Comments »
The Scottish mathematician and lawyer Archibald Smith first published in 1843 his equations for the magnetic deviation of a ship, or in other words, the error in the ship’s compasses from permanent and induced magnetic fields in the iron of the ship itself. This effect had been noticed in mostly wooden ships for centuries, and broad attempts to minimize it were implemented. But the advent of ships with iron hulls and steam engines in the early 1800s created a real crisis. A mathematical formulation of the deviation for all compass courses and locations at sea was needed in order to understand and compensate for it, and Smith became the preeminent expert in this sphere of activity. With Capt. Frederick J. Evans he extended his mathematical treatment to detailed procedures for measuring the magnetic parameters for a ship, and he also invented graphical methods for quickly calculating the magnetic deviation for any ship’s course once these parameters were found, constructions called dynamo-gonio-grams (force-angle diagrams), or dygograms for short.
Today, radio navigational systems such as LORAN and GPS, and inertial navigation systems with ring and fiber-optic gyros, gyrocompasses and the like have reduced the use of a ship’s compass to worst-case scenarios. But this triumph of mathematics and physics over the mysteries of magnetic deviation, entered into at a time when magnetic forces were barely understood and set against the backdrop of hundreds of shipwrecks and thousands of lost lives, is an enriching chapter in the history of science. Part I of this essay presents a brief sketch of the problem and the analysis and solutions that were developed to overcome it. Part II sets out with a discussion of Smith’s graphical methods of computing the magnetic deviation and concludes with a list of the references cited in the essay.
6 Comments »
An operational calculus converts derivatives and integrals to operators that act on functions, and by doing so ordinary and partial linear differential equations can be reduced to purely algebraic equations that are much easier to solve. There have been a number of operator methods created as far back as Leibniz, and some operators such as the Dirac delta function created controversy at the time among mathematicians, but no one wielded operators with as much flair and abandon over the objections of mathematicians as Oliver Heaviside, the reclusive physicist and pioneer of electromagnetic theory.
14 Comments » | <urn:uuid:865aadf3-296d-4cb0-a3cf-7a2a2dfa05bd> | 3.46875 | 665 | Content Listing | Science & Tech. | 23.284208 |
The MK Spectral classification system was founded by W.W. Morgan and P.C. Keenan in the year 1943, with the publication of the first photographic spectral classification atlas, An Atlas of Stellar Spectra (Morgan, Keenan & Kellman 1943). Since that time, the MK system has been extensively revised and refined by Morgan, Keenan and others. In the late 1970's, two important spectral atlases, summarizing the development of the MK system up until that time, were published. These atlases, the Revised MK Spectral Atlas for Stars Earlier than the Sun by Morgan, Abt & Tapscott (1978) and An Atlas of Spectra of the Cooler Stars: Types G,K,M,S and C, by Keenan & McNeil (1976), are the inspiration for this new digital spectral classification atlas. Indeed, some of the pages in this atlas are "digitized" versions of pages from those two atlases.
The MK spectral classification system is a natural, empirical system of spectral classification which uses in the classification process only the directly observable features in the spectrum. The MK system is defined by a set of standard stars, and classification on the system is carried out by the comparison of the program star with the standard stars, taking into account all of the features in the spectrum. The use of standards is vital because it maintains the autonomy of the system as well as ensuring that different observers will classify stars on the same system.
When the MK system was first defined, it was based on photographic spectra in the blue-violet part of the spectrum. This was done by necessity, as photographic emulsions in the 1940's were sensitive only to blue-violet light. However, it was a fortunate choice, as the blue-violet portion of the spectrum (essentially from the Ca II K-line to H) contains a high density of astrophysically important atomic lines and molecular bands, which allow accurate classification of the star in a two-dimensional temperature, luminosity grid. Classification systems can and have been set up in the red, IR and the ultraviolet. These should remain independent of the traditional MK system, as different parts of the spectrum can sample different levels in the atmosphere of the star.
The current spectral atlas should be considered an ongoing work which will likely be completed only in a number of years. The spectra in this atlas have been obtained with the Gray/Miller spectrograph on the 0.8 meter telescope of the Dark Sky Observatory, using a CCD detector. Two spectral resolutions have been used in this atlas. Most of the illustrations use spectra obtained with the 1200g/mm grating, which gives a spectral resolution of 1.8 Å/2 pixels and a spectral range of 3800 Å - 4600 Å, but some illustrations, especially those of the later-type stars (K, M, C and S) use spectra obtained with the 600g/mm grating. These have a resolution of 3.6 Å/2 pixels, and a spectral range of 3800 Å - 5600 Å. The higher resolution spectra are presented in a rectified intensity versus wavelength format, in which the spectral continuum has been normalized to unity. The 3.6 Å resolution spectra, for the most part, are presented in a flux versus wavelength format; this format provides additional information on the energy distribution of the star, and is to be preferred for the cooler stars, as these stars have essentially no continuum points in their spectra. For ease of illustration, the fluxes have been normalized to unity at one consistent point in the spectrum.
Since the publication of the two most recent photographic spectral atlases mentioned in the paragraphs above, the MK system has undergone extensive revision and refinement. Important work in refining and extending the MK system to dimensions beyond the traditional two-dimensional temperature/luminosity grid has been carried out by Keenan and co-workers in the addition of abundance indices for the late-type stars, by Gray (1989), in the extension of the MK system to metal-weak F and G-type stars, by Henry, Kirkpatrick & coworkers in their careful redefinition and extension of the MK system to the M-type dwarfs and most lately the "L-type" stars, and by Walborn in the classification of the O-type stars. Later editions of this atlas will attempt to illustrate more fully these developments. | <urn:uuid:1e8a7187-3451-4aa7-9e9c-807537677a2d> | 3.140625 | 918 | Knowledge Article | Science & Tech. | 44.45205 |
What does logic mean to us and is that different to mathematical logic? We will explore these questions in this article.
Learn about the link between logical arguments and electronic circuits. Investigate the logical connectives by making and testing your own circuits and fill in the blanks in truth tables to record. . . .
Investigate circuits and record your findings in this simple introduction to truth tables and logic.
Moiré patterns are intriguing interference patterns. Create your own beautiful examples using LOGO!
Can Jo make a gym bag for her trainers from the piece of fabric she has? | <urn:uuid:829674cb-8121-46bf-837a-9f1863e28df3> | 3 | 118 | Tutorial | Science & Tech. | 50.808068 |
I understand that a water heater element is basically just adding energy to the mass of water in the container. So does that mean that the heater element only has to keep adding energy while the water around it becomes hotter than the element itself? Or does the element warm up together with the water until both reach 100C?
The water will not warm up, if the heater has the same temperature as the water. It needs to be hotter than the current water temperature. You can not "add" thermal energy to the water by connecting an object that is in thermal equilibrium with the water.
In practice the element will get very hot without any water cooling it and it will eventually switch off to prevent any damage. If you add water this process is slowed down a lot, as the water has a high heat capacity but until the heater switches off it will always be warmer than the water.
The amount of heat flowing per time depends on the temperature difference as stated by Fourier's law: $$\partial Q \propto \Delta T$$ | <urn:uuid:1913283c-20b6-4ad9-945e-e25bfea13d91> | 2.96875 | 210 | Q&A Forum | Science & Tech. | 50.746909 |
Reader Scott writes in with a good question that I’ve heard posed by several people in various places, because it really goes to the core of the counterintuitive nature of relativity.
Okay, let’s assume I’m in a spacecraft moving at a speed of c-1 m/s. That’s one m/s less than the speed of light. Would I be able to move from the back of the ship to the front at 1 m/s? Would I even be able to survive at that speed?
Here’s my reply, extended a bit to include the relevant equations and go into a little more detail. The derivations will all wait until later:
Yes indeed. The question at issue is your speed with respect to a particular reference frame. Let’s pretend that you’re on an airplane flying at 500 mph with respect to the ground. There’s nothing stopping you from walking forward at 1 mph with respect to the plane. And that also happens to mean that you’re walking at 501 mph with respect to an observer on the ground. Assuming the plane ride is nice and smooth and the windows are closed, you wouldn’t even be able to tell the difference between that and walking in a plane parked on the runway. This is fundamental in modern physics: there’s no preferred inertial reference frame, the laws of physics work the same way in all of them.
An inevitable consequence of this are the relativistic effects of time dilation and length contraction. This implies that in fact velocities don’t add in such a simple way. So when you walk at 1 m/s in a ship going 299999999 m/s with respect to the ground (pretending the speed of light is exactly 300000000 m/s for simplicity), you appear to yourself to be walking at 1 m/s inside the ship, just as in any other case. The guy on the ground will (crunching some numbers) see you as walking at about 299999999.00000000667 m/s. This comes from the Einstein velocity addition formula, which for a guy walking at speed v in a plane with speed u means his velocity s with respect to the ground is
The “why” for all of this is tricky, but within reach for an interested person with a decent grasp of algebra. Of course there’s lots of good websites, but it’s probably hard to beat Einstein’s own book “Relativity: The Special and the General Theory“. And I myself will write up the derivations here one of these days.
Thanks for reading! | <urn:uuid:164f798c-469f-4e77-a27b-b78b7d5bbca4> | 2.734375 | 551 | Personal Blog | Science & Tech. | 70.235802 |
Creating and Modifying FOREIGN KEY Constraints
You can create a FOREIGN KEY constraint as part of the table definition when you create a table. If a table already exists, you can add a FOREIGN KEY constraint, provided that the FOREIGN KEY constraint is linked to an existing PRIMARY KEY constraints or UNIQUE constraint in another, or the same, table. A table can contain multiple FOREIGN KEY constraints.
If a FOREIGN KEY constraint already exists, you can modify or delete it. For example, you may want the FOREIGN KEY constraint of the table to reference other columns. However, you cannot change the length of a column that is defined with a FOREIGN KEY constraint.
To modify a FOREIGN KEY constraint, you must first delete the existing FOREIGN KEY constraint and then re-create it with the new definition.
Delete a FOREIGN KEY constraint to remove the requirement for referential integrity between the foreign key columns and the related primary key, or UNIQUE constraint, columns in another table.
To create a FOREIGN KEY constraint when you create a table
To create a FOREIGN KEY constraint on an existing table
To delete a FOREIGN KEY constraint
When a FOREIGN KEY constraint is added to an existing column or columns in the table, by default, the Database Engine examines the existing data in the columns to make sure that all values, except NULL, exist in the columns of the referenced PRIMARY KEY or UNIQUE constraint. However, by specifying WITH NOCHECK, the Database Engine can be prevented from checking the data in the column against the new constraint and made to add the new constraint regardless of the data in the column. The WITH NOCHECK option is useful when the existing data already meets the new FOREIGN KEY constraint, or when a business rule requires the constraint to be enforced only from this point forward.
However, you should be careful when you add a constraint without checking existing data because this bypasses the controls in the Database Engine that enforce the data integrity of the table.
To prevent checking of existing data when you create a FOREIGN KEY constraint
You can disable existing FOREIGN KEY constraints forspecific operations, such as INSERT operations, UPDATE operations, and replication processing.
INSERT and UPDATE statements
Disabling a FOREIGN KEY constraint enables data in the table to be modified without being validated by the constraints. Disable a FOREIGN KEY constraint during INSERT and UPDATE statements if new data will violate the constraint or if the constraint should apply only to the data already in the database.
Any cascading actions defined on a related primary key will not be performed on rows that contain foreign keys that are disabled.
Disable a FOREIGN KEY constraint during replication if the constraint is specific to the source database. When a table is replicated, the table definition and data is copied from the source database to a destination database. If the FOREIGN KEY constraints are specific to the source database but are not disabled during replication, they may unnecessarily prevent new data from being entered in the destination database. For more information, see Controlling Constraints, Identities, and Triggers with NOT FOR REPLICATION.
To disable a FOREIGN KEY constraint for INSERT and UPDATE statements
To disable a FOREIGN KEY constraint for replication
To obtain information about FOREIGN KEY constraints
To obtain information about columns that make up a FOREIGN KEY constraint | <urn:uuid:c4121b30-4f0e-4abf-8575-540f94fabe17> | 2.75 | 716 | Documentation | Software Dev. | 27.52833 |
Ask a question about 'Undecane'
Start a new discussion about 'Undecane'
Answer questions from other users
is a liquid alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
with the chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
. It is used as a mild sex attractant for various types of moths
Moths may refer to:* Gustav Moths , German rower* The Moths!, an English indie rock band* MOTHS, members of the Memorable Order of Tin Hats...
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
es, and an alert signal for a variety of ants. It has 159 isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
Undecane may also be used as an internal standard in gas chromatography when working with other hydrocarbons. Since the boiling point of undecane (196°C) is well known, it may be used as a comparison for retention times in a gas chromatograph for molecules whose structure has been freshly elucidated. For example, if one is working with a 50 m crosslinked methyl silicone capillary column with an oven temperature increasing slowly, beginning around 60°C, an 11-carbon molecule like undecane may be used as an internal standard to be compared with the retention times of other 10-, 11-, or 12- carbon molecules, depending on their structures.
- Undecane at Dr. Duke's Phytochemical and Ethnobotanical Databases | <urn:uuid:71012352-4172-4513-af7b-af6801c1e257> | 3.21875 | 453 | Q&A Forum | Science & Tech. | 35.626546 |
Summary: Twenty-five years ago, NASA made its only visit thus far to the planet Uranus. Voyager 2 returned unexpected images of an active planet and moons with dramatic surface features. The visit expanded our knowledge of the planets and helped astrobiologists understand whether or not planets and moons in the outer Solar System could be habitable.
These two pictures of Uranus -- one in true color (left) and the other in false color -- were compiled from images returned Jan. 17, 1986, by the narrow-angle camera of Voyager 2. Image credit: NASA/JPL
As NASA's Voyager 2 spacecraft made the only close approach to date of our mysterious seventh planet Uranus 25 years ago, Project Scientist Ed Stone and the Voyager team gathered at NASA's Jet Propulsion Laboratory, Pasadena, Calif., to pore over the data coming in.
Images of the small, icy Uranus moon Miranda were particularly surprising. Since small moons tend to cool and freeze over rapidly after their formation, scientists had expected a boring, ancient surface, pockmarked by crater-upon-weathered-crater. Instead they saw grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda's surface in the past. The images raised questions about whether or not these small and sometimes active bodies could be targets in the search for habitable environments in the Solar System.
The scientists were also shocked by data showing that Uranus' magnetic north and south poles were not closely aligned with the north-south axis of the planet's rotation. Instead, the planet's magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet's interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.
Miranda, innermost of Uranus' large satellites, is seen at close range in this Voyager 2 image, taken Jan. 24, 1986, as part of a high-resolution mosaicing sequence. Image credit: NASA/JPL
"Voyager 2's visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the Solar System with Earth," said Stone, who is based at the California Institute of Technology in Pasadena. "Even though similar in many ways, the worlds we encounter can still surprise us."
Voyager 2 was launched on Aug. 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometers (2 billion miles) away from the Sun. Voyager 2 made its closest approach – within 81,500 kilometers (50,600 miles) of the Uranian cloud tops – on Jan. 24, 1986.
Before Voyager 2's visit, scientists had to learn about Uranus by using Earth-based and airborne telescopes. By observing dips in starlight as a star passed behind Uranus, scientists knew Uranus had nine narrow rings. But it wasn't until the Voyager 2 flyby that scientists were able to capture for the first time images of the rings and the tiny shepherding moons that sculpted them. Unlike Saturn's icy rings, they found Uranus' rings to be dark gray, reflecting only a few percent of the incident sunlight.
The complex terrain of Ariel is viewed in this image, the best Voyager 2 color picture of the Uranian moon. Image credit: NASA/JPL
Scientists had also determined an average temperature for Uranus (59 Kelvin, or minus 350 degrees Fahrenheit) before this encounter, but the distribution of that temperature came as a surprise. Voyager showed there was heat transport from pole to pole in Uranus' atmosphere that maintained the same temperature at both poles, even though the Sun was shining directly for decades on one pole and not the other.
By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.
Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometers (9 billion miles) away from the Sun. Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometers (11 billion miles) away from the Sun.
"The Uranus encounter was one of a kind," said Suzanne Dodd, Voyager project manager, based at JPL. "Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune. Currently both Voyager spacecraft are on the cusp of leaving the Sun's sphere of influence and once again blazing a trail of scientific discovery." | <urn:uuid:ead4d981-ba86-44ee-bd2b-d40ae2d4b0e7> | 3.84375 | 1,026 | Knowledge Article | Science & Tech. | 43.656405 |
genecutl at mendel.berkeley.edu
Sat Feb 26 13:45:06 EST 1994
In article <1994Feb26.164754.16156 at nessie.mcc.ac.uk>,
se040 at sna.co.umist.ac.uk (Mark Joseph Johnston) wrote:
> I am a computer science student working on genetic algorithms and want to ask
> a "silly" question.
> Recessive genes are generally not "good" for the organism, yes?
> If so why do they exist? Why do two alleles exist together?
> Is it to conserve genetic diversity (without manifesting a trait
> with a poor survival value??
> Forgive my ignorance.
You're asking your question as if life was designed rather than evolved.
If a detrimental mutation occurs which is recessive, it will only be
selected against in homozygotes. Heterozygotes for the recessive
mutation will experience no negative selection. Because of this, the
allele can persist for a very long time in the gene pool despite its
detrimental effects on homozygotes.
In simpler words, they happen at random and it's hard as hell to get
rid of them.
The question about maintaining genetic diversity is meaningless. A
species does not decide to maintian genetic diversity. Genetic diversity
or not is effected by selection on specific phenotypes. Given a closed
population with a low mutation rate, a loss of genetic diversity would
More information about the Bioforum | <urn:uuid:6f392dae-832f-4ea1-953c-109442eecace> | 2.8125 | 328 | Comment Section | Science & Tech. | 48.528285 |
Click image for description
| Orbital characteristics (Epoch J2000)
| Semi-major axis
|| 1,426,725,413 km|
9.537 070 32 AU
| Orbital circumference
|| 8.958 Tm|
|| 0.054 150 60
|| 1,349,467,375 km|
9.020 632 24 AU
|| 1,503,983,449 km|
10.053 508 40 AU
| Orbital period
|| 10,757.7365 d|
| Synodic period
|| 378.09 d
| Avg. Orbital Speed
|| 9.638 km/s
| Max. Orbital Speed
|| 10.182 km/s
| Min. Orbital Speed
|| 9.136 km/s
|| 2.484 46°|
(5.51° to Sun's equator)
| Longitude of the|
| 113.715 04°
| Argument of the|
| 338.716 90°
| Number of satellites
| Physical characteristics
| Equatorial diameter
|| 120,536 km |
| Polar diameter
|| 108,728 km|
|| 0.097 96
| Surface area
|| 4.27×1010 km2|
|| 7.46×1014 km3|
|| 5.6846×1026 kg|
| Mean density
|| 0.6873 g/cm3|
(less than water)
| Equatorial gravity
|| 8.96 m/s2|
| Escape velocity
|| 35.49 km/s
| Rotation period
|| 0.444 009 259 2 d|
(10 h 39 min 22.400 00 s) 1
| Rotation velocity
|| 9.87 km/s = 35,500 km/h|
(at the equator)
| Axial tilt
| Right ascension|
of North pole
| 40.59° (2 h 42 min 21 s)
| Avg. Cloudtop temp.
|| 93 K
| Surface temp.
| Atmospheric characteristics
| Atmospheric pressure
|| 140 kPa
| Water vapor
Saturn is the sixth planet from the Sun. It is a gas giant, the second-largest planet in the solar system after Jupiter. Saturn has large rings made mainly out of ice and space debris. It was named after the Roman god Saturn. Its symbol is a stylized representation of the god's sickle (Unicode: ♄).
Saturn's shape is visibly flattened at the poles and bulging at the equator (an oblate spheroid); its equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation and fluid state. The other gas planets are also oblate, but not so much so. Saturn is also the only one of the Solar System's planets less dense than water, with an average specific density of 0.69. This is only an average value, however; Saturn's upper atmosphere is less dense and its core is considerably more dense than water.
Saturn's interior is similar to Jupiter's, having a rocky core at the center, a liquid metallic hydrogen layer above that, and a molecular hydrogen layer above that. Traces of various ices are also present. Saturn has a very hot interior, reaching 12000 K at the core, and it radiates more energy into space than it receives from the Sun. Most of the extra energy is generated by the Kelvin-Helmholtz mechanism (slow gravitational compression), but this alone may not be sufficient to explain Saturn's heat production. An additional proposed mechanism by which Saturn may generate some of its heat is the "raining out" of droplets of helium deep in Saturn's interior, the droplets of helium releasing heat by friction as they fall down through the lighter hydrogen.
Saturn's atmosphere exhibits a banded pattern similar to Jupiter's, but Saturn's bands are much fainter and they're also much wider near the equator. Saturn's cloud patterns were not observed until the Voyager flybys. Since then, however, Earth-based telescopy has improved to the point where regular observations can be made. Saturn exhibits long-lived ovals and other features common on Jupiter; in 1990 the Hubble Space Telescope observed an enormous white cloud near Saturn's equator which was not present during the Voyager encounters and in 1994 another, smaller storm was observed. Astronomers using infrared imaging have shown that Saturn has a warm polar vortex, and is the only planet in the solar system known to do so.
Since Saturn does not rotate on its axis at a uniform rate, two rotation periods have been assigned to it, like in Jupiter's case: System I has a period of 10 h 14 min 00 s (844.3°/d) and encompasses the Equatorial Zone, which extends from the northern edge of the South Equatorial Belt to the southern edge of the North Equatorial Belt. All other Saturnian latitudes have been assigned a rotation period of 10 h 39 min 24 s (810.76°/d), which is System II. System III, based on radio emissions from the planet, has a period of 10 h 39 min 22.4 s (810.8°/d); because it is very close in value to System II, it has largely superseded it.
While approaching Saturn in 2004, the Cassini spacecraft found that the radio rotation period of Saturn had increased slightly, to approximately 10 h 45 m 45 s (± 36 s). The cause of the change is unknown.
Saturn is probably best known for its planetary rings, which make it one of the most visually remarkable objects in the solar system. See rings of Saturn for a list of the planet's rings.
The rings were first observed by Galileo Galilei in 1610 with his telescope, but he clearly did not know what to make of them. He wrote to the Grand Duke of Tuscany that "Saturn is not alone but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac, and the middle one [Saturn itself] is about three times the size of the lateral ones [the edges of the rings]." He also described Saturn as having "ears." In 1612 the plane of the rings was oriented directly at the Earth and the rings appeared to vanish, and then in 1613 they reappeared again, further confusing Galileo.
The riddle of the rings was not solved until 1655 by Christiaan Huygens, using a telescope much more powerful than the ones available to Galileo in his time.
In 1675 Giovanni Domenico Cassini determined that Saturn's ring was actually composed of multiple smaller rings with gaps between them; the largest of these gaps was later named the Cassini Division.
Physical characteristics of the rings
The rings can be viewed using a quite modest modern telescope or with a good pair of binoculars. They extend from 6,630 km to 120,700 km above Saturn's equator, and are composed of silica rock, iron oxide, and ice particles ranging in size from specks of dust to the size of a small automobile. There are two main theories regarding the origin of Saturn's rings. One theory, originally proposed by Édouard Roche in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by tidal forces (see Roche limit). A variation of this theory is that the moon disintegrated after being struck by a large comet or asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material that Saturn formed out of. This theory is not widely accepted today, since Saturn's rings are thought to be unstable over periods of millions of years and therefore of relatively recent origin.
While the largest gaps in the rings, such as the Cassini division and Encke division, could be seen from Earth, the Voyagers discovered the rings to have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise from the gravitational pull of Saturn's many moons in several different ways. Some gaps are cleared out by the passage of tiny moonlets such as Pan, many more of which may yet be undiscovered, and some ringlets seem to be maintained by the gravitational effects of small shepherd satellites such as Prometheus and Pandora. Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; Mimas maintains the Cassini division in this manner. Still more structure in the rings actually consists of spiral waves raised by the moons' periodic gravitational perturbations.
The dark side of the rings
Compare images from the Cassini spacecraft taken in March and October 2004, and a Pioneer 11 picture from 1979:
spacecraft: March 27
; Frontlit rings. Notice both the shadow of Saturn on the rings, and the shadow of the rings onto the planet. The thick B ring is the brightest part of the ring system.
spacecraft: September 1
; Backlit rings, showing the overall darkness of the rings from this angle. The thickest parts of the rings are almost invisible.
The side of Saturn's rings that is lit by the Sun looks very different to the backlit side, which is darker overall and appears almost black in the thick B ring. From Earth, we cannot appreciate this because the Earth cannot view Saturn from an angle that displays the backlit side of the rings, and our only views of it are from spacecraft. In 2004, the Cassini spacecraft revealed the first views of the backlit side in 25 years.
The spokes of the rings
Until 1980, the structure of the rings of Saturn was explained exclusively as the action of gravitational forces. The Voyager spacecraft found dark radial features in the B ring, called spokes, which could not be explained in this manner, as their persistence and rotation around the rings were not consistent with orbital mechanics. It is assumed that they are connected to electromagnetic interactions, as they rotate almost synchronously with the magnetosphere of Saturn. However, the precise mechanism behind the spokes is still unknown.
As of February 2005, the Cassini spacecraft has not observed any spokes in the rings, despite possessing imaging equipment of higher quality than the Voyagers'. It is possible that the spokes appear and disappear seasonally.
Exploration of Saturn
A Hubble Space Telescope image, captured in October 1996 shows Saturn's rings from just past edge-on
Pioneer 11 flyby
Saturn was first visited by Pioneer 11 in 1979. It flew within 20,000 km the planet's cloudtops. Low-resolution images were acquired of the planet and few of its moons. Resolution was not good enough to discern surface features, however. The spacecraft studied also the rings; among the discoveries were the thin F-ring and the fact that dark gaps in the rings are bright when viewed towards the Sun, or in other words, they are not empty of material. It also measured the temperature of Titan.
In November, 1980, Voyager 1 probe visited the Saturn system. It send back the first high-resolution images of the planet, rings, and the satellites. Surface features of various moons were seen first time. Voyager 1 performed a close flyby of Titan greatly increasing our knowledge of the atmosphere of the moon. However, it also proved that Titan's atmosphere is impenetrable in visible waveleghts, so no surface details were seen. The flyby also changed spacecraft's trajectory out from the plane of the solar system.
Almost a year later, in August, 1981, Voyager 2 continued the study of the Saturn system. More close-up images of Saturn's moons were acquired, as well as evidence of changes in the atmosphere and the rings. Unfortunately, during the flyby, the probe's camera stuck and some planned imaging was lost. Saturn's gravity was used to direct the spacecraft's trajectory towards Uranus.
The probes discovered and confirmed several new satellites orbiting near or within the planet's rings.
On July 1, 2004 the Cassini-Huygens spacecraft performed the SOI (Saturn Orbit Insertion) manoeuvre and entered into orbit around Saturn. Before the SOI Cassini had already studied the system extensively. In June, 2004, it had conducted a close flyby of Phoebe sending back high-resolution images and data. The orbiter completed two Titan flybys before releasing the Huygens probe on December 25, 2004. Huygens descended onto the surface of Titan on January 14, 2005 sending flood of data during the atmospheric descent and after the landing. As of 2005, Cassini is conducting multiple flybys of Titan and icy satellites. The primary mission ends in 2008 when the spacecraft has completed 74 orbits around the planet.
For the latest information and news releases, see Cassini website.
Main article: Saturn's natural satellites
Saturn has a large number of moons (34 are currently known or suspected), 30 of which have names. The precise figure will never be certain as the orbiting chunks of ice in Saturn's rings are all technically moons, and it is difficult to draw a distinction between a large ring particle and a tiny moon. Saturn's most noteworthy moon is Titan, the only moon in the solar system to have a dense atmosphere.
Due to the tidal forces of Saturn, the moons are currently not at the same position as they were when they were first formed.
For a timeline of discovery dates, see Timeline of natural satellites.
Best viewing of Saturn
Saturn Oppositions: 2001-2029
While it is a rewarding target for observation for most of the time it is visible in the sky, Saturn and its rings are best seen when the planet is at or near opposition (the configuration of a planet when it is at an elongation of 180° and thus appears opposite the Sun in the sky.) In the opposition on January 13, 2005, Saturn appeared at its brightest until 2031, mostly due to a favourable orientation of the rings relative to the Earth.
Saturn appears to the naked eye in the night sky as a bright, yellowish star varying usually between magnitude +1 and 0 and takes approximately 29 and a half years to make a complete circuit of the ecliptic against the background constellations of the zodiac. Optical aid (a large pair of binoculars or a telescope) magnifying at least 20X is required to clearly resolve Saturn's rings for most people.
Saturn in fiction and film
Saturn is a popular setting for science fiction novels and films, although the planet tends to be used as a pretty backdrop rather than as an important part of the plot.
- In Arthur C. Clarke's novel version of 2001: A Space Odyssey (1968), a spacecraft visits the Saturnian system. Clarke's later novel Imperial Earth (1976) takes place partially at a human colony on Titan.
- Stephen Baxter's novel Titan is focused on the moon Titan, but contains vivid depictions of a journey through the Saturnian system.
- Ben Bova's novel Saturn (2003) is about a spacecraft travelling toward the planet, although Saturn itself does not figure greatly in the story.
- In Isaac Asimov's short story The Martian Way, Martian colonists use a chunk of ice from Saturn's rings to bring water to the dry world.
- Douglas Trumbull's film Silent Running (1972) features an ark-like spacecraft travelling through the Saturnian system.
- The film Saturn 3 (1980) is mostly set on one of Saturn's moons, but also features a journey through the planet's rings.
- Kurt Vonnegut's novel The Sirens of Titan is partly set on Saturn's best known moon.
- Tim Burton's film Beetlejuice is partly set on a fictional Saturn, populated by giant sandworms.
- In Michael McCollum 's novel The Clouds of Saturn , SparrowHawk pilots Larson Sands and Halley Trevanon fight against the Northern Alliance during a time when the Sun has flared out of control and boiled Earth's oceans away.
- In Star Trek, Saturn is used for the Starfleet Academy Flight Range.
Saturn in astrology
| Saturn | Pan | ... | <urn:uuid:0287aac4-5a38-46f0-953f-e098d27e52f9> | 3.234375 | 3,387 | Knowledge Article | Science & Tech. | 58.382442 |
Common Lisp the Language, 2nd Edition
The function make-condition is the basic means for creating condition objects.
make-condition type &rest slot-initializations
Constructs a condition object of the given type using slot-initializations as a specification of the initial value of the slots. The newly created condition is returned.
The slot-initializations are alternating keyword/value pairs. For example:
(make-condition 'peg/hole-mismatch :peg-shape 'square :hole-shape 'round) | <urn:uuid:98c2f656-b85d-43a5-90a8-5074fc28498f> | 3 | 109 | Documentation | Software Dev. | 22.89 |
by Gerald Newton
November 5, 1999
The geometric addition of vectors gives a fast approximation of neutral current in a three phase system. A more precise calculation can be performed using algebra. This can be a long mathematical problem, but by restricting our calculation to A phase at 0 degrees, B phase at 120 degrees, and C phase at 240 degrees the calculation is simplified.
The figure below demonstrates how to break a vector down into its horizontal (X) and vertical (Y) components. The magnitude of the vector is its length in whatever units we chose to represent. In our case that would be amperes.
The following figures demonstrates the algebraic addition of two vectors.
The Pythagorean is used to find the algebraic value
of a vector once its X and Y components are known.
The following demonstrates the use of the Pythagorean
theorem to find the magnitude of the sum of two vectors.
For three vectors the magnitude calculation is similar
to that for two vectors. A third component is added for the third
vector. The process of multiplying the polynomials can be reduced
by using the known angles for the A phase, B phase, and C phase vectors.
The sines and cosines are known for the three angles, 0 degrees, 120 degrees,
and 240 degrees.
Calculator by electrician2.com
||Use the mouse button to lay down up to ten vectors. Click on the Action button to calculate the sum.|
Return to electrician2.com | <urn:uuid:127adf77-3e5b-49ca-815d-12f90423a869> | 3.6875 | 314 | Tutorial | Science & Tech. | 53.393998 |
Reverse transcriptase is an enzyme used by all retroviruses that transcribes the genetic information from the virus from RNA into DNA, which can integrate into the host genome. Usually, transcription only runs from DNA to RNA, catalyzed by RNA polymerase. An example of this kind of enzyme is the reverse transcriptase from the human immunodeficiency virus type 1 (PDB 1HMV, EC 188.8.131.52).
Reverse transcriptase is commonly used in the field of research to be able to apply the Polymerase chain reaction technique to RNA. The classical PCR technique can only be applied to DNA strands, but with the help of reverse transcriptase, RNA can be transcribed into DNA making PCR analysis of RNA molecules possible. The technique is collectively called: Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). | <urn:uuid:9ddd06ce-6f40-4b11-be05-06d1ed44d103> | 3.9375 | 176 | Knowledge Article | Science & Tech. | 39.893889 |
This is Chapter 8 of the Arctic Climate Impact Assessment
Lead Authors: Frederick J.Wrona,Terry D. Prowse, James D. Reist; Contributing Authors: Richard Beamish, John J. Gibson, John Hobbie, Erik Jeppesen, Jackie King, Guenter Koeck, Atte Korhola, Lucie Lévesque, Robie Macdonald, Michael Power,Vladimir Skvortsov,Warwick Vincent; Consulting Authors: Robert Clark, Brian Dempson, David Lean, Hannu Lehtonen, Sofia Perin, Richard Pienitz, Milla Rautio, John Smol, Ross Tallman, Alexander Zhulidov
Changes in climate and ultraviolet radiation levels in the Arctic will have far-reaching impacts, affecting aquatic species at various trophic levels, the physical and chemical environment that makes up their habitat, and the processes that act on and within freshwater ecosystems. Interactions of climatic variables, such as temperature and precipitation, with freshwater ecosystems are highly complex and can propagate through the ecosystem in ways that are difficult to project. This is partly due to a poor understanding of arctic freshwater systems and their basic interrelationships with climate and other environmental variables, and partly due to a paucity of long-term freshwater monitoring sites and integrated hydro-ecological research programs in the Arctic.
This chapter begins with a broad overview of the general hydrological and ecological features of the various freshwater ecosystems in the Arctic, including descriptions of each ACIA region, followed by a review of historical changes in freshwater systems during the Holocene. The chapter continues with a review of the effects of climate change on broad-scale hydro-ecology; aquatic ecosystem structure and function; and arctic fish, fisheries, and aquatic wildlife. Special attention is paid to changes in runoff, water levels, and river- and lake-ice regimes; to biogeochemical processes, including carbon dynamics; to rivers, lakes, ponds, and wetlands; to aquatic biodiversity and adaptive capacities; to fish populations, fish habitat, anadromy, and fisheries resources; and to aquatic mammals and waterfowl. Potential synergistic and cumulative effects are also discussed, as are the roles of ultraviolet radiation and contaminants.
The nature and complexity of many of the effects are illustrated using case studies from around the circumpolar north, together with a discussion of important threshold responses (i.e., those that produce stepwise and/or nonlinear effects).The chapter concludes with a summary of key findings, a list of gaps in scientific understanding, and policy-related recommendations.
Chapter 8: Freshwater Ecosystems and Fisheries
8.2. Freshwater ecosystems in the Arctic
8.3. Historical changes in freshwater ecosystems
8.4. Climate change effects
8.4.1. Broad-scale effects on freshwater systems
8.4.2. Effects on hydro-ecology of contributing basins
8.4.3. Effects on general hydro-ecology
8.4.4. Changes in aquatic biota and ecosystem structure and function
8.5. Climate change effects on arctic fish, fisheries, and aquatic wildlife
8.5.1. Information required to project responses of arctic fish
8.5.2. Approaches to projecting climate change effects on arctic fish populations
8.5.3. Climate change effects on arctic freshwater fish populations
8.5.4. Effects of climate change on arctic anadromous fish
8.5.5. Impacts on arctic freshwater and anadromous fisheries
8.5.6. Impacts on aquatic birds and mammals
8.6. Ultraviolet radiation effects on freshwater ecosystems
8.7. Global change and contaminants
8.8. Key findings, science gaps, and recommendations | <urn:uuid:8a57889c-6cf5-4de2-9308-7e23cc072074> | 2.890625 | 791 | Knowledge Article | Science & Tech. | 38.407642 |
July 26, 2009
Analysis of Alarmism: Ocean Acidification
“Only the unknown frightens men.” Antoine de St. Exupery
Scare Tactics To Create Fear
As public awareness grows that human caused warming is false, the extent and degree of attempts to scare the public increases. The scare preference is for remote geographic areas such as the Arctic or Antarctic or complex obscure topics ideally with global implications, which the public knows little about. The latest scare story is ocean acidification, which combines these traits with the advantage of a word with negative connotations and used before in acid rain.
Like all scares it is based on total acceptance that an increase in atmospheric CO2 is a problem. The claim in this case is it is causing temperature increase, but also changing the chemistry of the oceans. Like all the scares it is pure speculation after you accept the false claim CO2 is causing temperature increase. To counteract suggestions that they are overstating the threat they use a form of the precautionary principle, which holds we must act anyway. So the problem exists, it is just a matter of the extent of the impact. Yet the full impact of ocean acidification and how these impacts may propagate through marine ecosystems and affect fisheries remains largely unknown. (Source)
What Is Ocean Acidification?
Oceans absorb or release CO2 primarily determined by the amount in the atmosphere and the water temperature. The argument is that regardless of what the air temperature does, increased CO2 amount in the atmosphere due to human activity guarantees more going into the oceans. This change results in a change in water chemistry reflected in one measure, the pH.
A solution has a pH level that is a measure of the acidity or alkalinity. The pH scale is from 0 to 14 and a measure of 7 is neutral. The scale is created relative to standard solutions and agreed on internationally. Above 7 the solution is more alkaline and below 7 it is more acid. The oceans are considered to have a pH of 8.2 with a variance of 0.3, so it is an alkaline solution.
The claim of ocean acidification is based on estimates and computer models; these use the very questionable pre-industrial atmospheric level of CO2 to calculate an increase of about 0.1 pH units. Of course, the Intergovernmental Panel on Climate Change (IPCC) attributes the CO2 increase to human production, which is wrong because the global carbon cycle is very vague about sources, storage and length of time in each condition. For example, the error in the estimate of CO2 from the oceans each year is greater than the total human contribution.
The idea that a 0.1 pH unit increase is significant is ludicrous when the estimate has a range of 0.3 units. There is a subtle but important point here because words are part of the scare component. Even if you accept the claimed change it is not acidification, it is proper to say the solution is becoming less alkaline but that doesn’t sound threatening. More problematic is the validity of the measures. Although pH in seawater has been measured for many decades, a reliable long- term trend of ocean water pH cannot be established due to data quality issues, in particular the lack of strict and stable calibration procedures and standards. Moreover, seawater pH is very sensitive to temperature, and temperature is not always recorded or measured at sufficient accuracy to constrain the pH measurement. (Sources: Here and Here)
Even if CO2 increases to 560 ppm by 2050 as the IPCC predict it would only result in a 0.2 unit reduction of pH. This is still within the error of the estimate of global average.
What Is the Real Threat?
So what is threatened by this reduced alkalinity? Most marine life if you read all the stories, but scare stories need one issue people view positively. Coral fits the bill well because the underwater scenes of color and diversity of life mesmerize us all. According to the experts, ocean acidification may render most regions of the ocean inhospitable to coral reefs by 2050, if atmospheric CO2 levels continue to increase. It could lead to substantial changes in commercial fish stocks, threatening food security for millions of people as well as the multi-billion dollar fishing industry. (Source)
Scares Require Dramatic Change Beyond Any Previously Recorded
Scares require dramatic change beyond any previously recorded. “Ocean acidification is more rapid than ever in the history of the earth and if you look at the pCO2 (partial pressure of carbon dioxide) levels we have reached now, you have to go back 35 million years in time to find the equivalents.” Scares also require an impending critical point beyond which remedial action is useless. This so-called “tipping point” is currently estimated to allow a drop of about 0.2 pH units, a value that could be reached in as near as 30 years. It is no surprise the author of these outrageous and incorrect remarks is chair of the EuroCLIMATE program Scientific Committee.
A plot of CO2 levels over the last 600 million years shows current levels are very low at 385 ppm.
Source: Temperature after C.R.Scotese. CO2 after R.A.Bernier.
The only period in 600 million years when CO2 levels were equal to the present was over 300 million years ago. Since that time CO2 levels averaged 1000 to 1200 ppm or 3 to 4 times current levels. How did the plant and animal life survive those levels? It makes a mockery of the claim that even a doubling of atmospheric CO2 is a problem.
More recent measures of pH levels show how current levels and claimed changes are well within natural variability. Here is a reconstruction of pH levels for the South China Seas by Liu et al (2009) that illustrates the point.
Source: Liu et al. (2009) “Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals.”
The Light Of Understanding
Marie Curie one of the greatest scientists of all time said, ”Nothing in life is to be feared. It is only to be understood.” Gradually more and more evidence shows the hypothesis that human CO2 is causing warming or climate change is false. Fear is subsiding as more people including many scientists understand and are speaking out. A surprising one recently was Tom Tripp, a member and lead author of the IPCC since 2004. At the July 2009 Utah Farm Bureau Convention he said there is so much natural variability in weather it makes a scientifically valid conclusion about man-made global warming difficult. Specifically he said, “It may well be, but we’re not scientifically there yet.” That contradicts the message from the reports he helped author. It also disavows the claim the science is settled. The outrage is alarmists continue to present a message of certainty. However, just in case you are wavering the sky is definitely falling and they will continue to produce outrageous unsubstantiated scares to prove it.
Tim Ball, Senior Fellow
has an extensive scientific background in climatology, especially the reconstruction of past climates and the impact of climate change on human history. He is a regular contributing writer for Country Guide magazine and a researcher/author of numerous papers on climate, long-range weather patterns, the impacts of climate change on sustainable agriculture, ecosystems, historical climatology, air quality, untapped energy resources, silting and flooding. He had a long academic career at the University of Winnipeg until he moved to Victoria in 1996. He has a BA from the University of Winnipeg, an MA from the University of Manitoba and a PH.D (Doctor of Science) from the University of London, England. On Dr. Ball as a climate change "denier" - more . . . and more . . . | <urn:uuid:8e207e3e-96b3-4122-986b-8961993e1b9f> | 2.84375 | 1,616 | Nonfiction Writing | Science & Tech. | 44.774863 |
Some things you really can pin on climate change – the heatwave that struck Texas last year, for instance. A long-term rise in temperatures due to greenhouse gas emissions made the hot weather 20 times more likely, modelling suggests.
The same study found that four other extreme weather events last year can be linked to climate change.
Until recently, climate scientists have been reluctant to blame individual weather events on climate change. There have been exceptions: studies have found that the European heatwave in 2003 was twice as likely because of climate change, and that the UK floods in 2000 were also made more likely. But now, for the first time, climate scientists are systematically examining recent extreme weather events to determine whether climate change played a role.
Peter Stott of the UK Met Office in Exeter headed a project looking at six unusual weather events in 2011. "This is the first time this has been done so soon after the events in question," he says.
Five of the six events could be blamed on climate change to some extent. "We can never say 100 per cent absolutely that this is due to climate change," Stott says. "But we are very confident."
In 2011, Texas suffered the hottest and driest growing season since records began in 1895, which resulted in a severe drought. Farmers were forced to sell their cattle because their pastures were so dry they could not feed them. Climate change is expected to bring more drought to the US Southwest, but few states are planning for this eventuality.
A study led by David Rupp of Oregon State University in Corvallis examined the causes of the Texas drought. One major factor was the La Niña in the Pacific, which changed seasurface temperatures and thus rainfall patterns, boosting the chances of a drought in the US Southwest. But that wasn't the only cause.
According to Rupp's models, such a severe heatwave is now 20 times more likely in a La Niña year than it was in the 1960s, when global temperatures were significantly cooler. "Ongoing climate change has exacerbated that existing vulnerability," says Stott.
Europe and UK
Three other events, two in Europe and one in Africa, were also affected by climate change.
In the UK, November 2011 was the second warmest since records began in 1659. "That warm November was about 60 times more likely than in the 1960s," Stott says.
Meanwhile, continental Europe had an unusually warm spring and autumn in 2011. This was partly the result of westerly winds bringing warm air from the tropics, but these circulation patterns cannot explain all the heat. "It wouldn't have been that unusual without the long-term warming," says Stott.
Famine struck East Africa last summer, after both the region's rainy seasons failed and caused a severe drought. Several studies linked this to changes in sea surface temperatures in the western Pacific and Indian Oceans, but it was not clear if this was part of a long-term trend. Stott now says there is "initial evidence" that climate change has, indeed, affected ocean temperatures, and partly caused the drought.
Some events have been made less likely by climate change. December 2010 was the second coldest on record. Greenhouse gases have reduced the odds of such events in the UK. "It's about half as likely," Stott says.
And some events did not appear to be related to climate change at all. Thailand suffered severe floods from July 2011 as a result of a strong monsoon. The capital, Bangkok, was inundated in October. "We didn't find a clear human influence on that weather event," Stott says. Rather, there were changes to the management of rivers, which made the floods more severe than they otherwise would have been.
All the studies rely on the same basic method. The team used models to simulate climate with and without greenhouse-gas emissions, and compared the chances that a given extreme weather event would occur. If it was significantly more likely in the models that included emissions, climate change was judged to have been a factor.
Journal reference: Bulletin of the American Meteorological Society, in press
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Tue Jul 10 17:44:38 BST 2012 by bill
In its 2012 platform document, the Texas GOP rejected "higher-order thinking skills," making it unlikely that the state's leaders will ever accept global climate change, especially anthropomorphic warming. As conservative pundit George WIll put it recently "It's called summer, so get over it."
(long URL - click here)
Thu Jul 12 13:58:40 BST 2012 by Eric Kvaalen
You're somewhat misrepresenting things. "Higher Order Thinking Skills (HOTS)" is a specific programme which the GOP deemed to undermine parental authority. It might be a good programme, but it's not as though the GOP had simply rejected critical thinking! No party would say that.
Tue Jul 10 17:59:32 BST 2012 by Martin
NS banging the same old Global Warming drum again. The headline sounds like a statement of fact but you don't have to read too far down to find the weasel words '...modelling suggests....'. And what were the assumptions upon which this 'modelling' was based? How was a non-biased double blind control established?
Tue Jul 10 19:16:20 BST 2012 by TwoZeroOZ
Did you seriously ask why a "double blind" study was not done?
Do you know what a double blind study is?
Tue Jul 10 19:38:20 BST 2012 by Gesha
No he does not.
Wed Jul 11 05:58:38 BST 2012 by Martin
Would you take a drug whose effect had only been tested by a computer model? Would you trust it if the scientists running the model worked for the pharma company and believed in advance that the drug would work? Would you believe a climate scare story generated by a computer model and sold by 'climate scientists' who are deeply immersed in group think? Climate science needs to conform to the standards of science, not religion.
Wed Jul 11 05:42:44 BST 2012 by Martin
Yes I did. Clearly you do not. Do you seriously believe that computer modelling the earths climate is not affected by the beliefs and prejudices of the 'climate scientists' operating the model? Or for that matter by the prejudices of magazine editors and reviewers who choose which results get published
Wed Jul 11 03:33:03 BST 2012 by Dann
Any scientific discipline that relies as much on probability as it does actual data will always be contentious. Probability is just a more scientific term for uncertainty and assumptions.
Unfortunately, the only way to evaluate the accuracy of a predictive model is to wait and see if it was correct - at which point the predictive model is no longer required. Projecting the model into the past to see if you can 'predict' what has already happened is also fraught with difficulties, as it's possible to accidentally come to the 'right' conclusion based on incorrect assumptions and methodology.
What we need are multiple parallel earths, time machines, and the ability to change past events, in order to look at how certain climatic variables affect the outcome over time. That would be the only sort of double-blind experiment possible for climate change issues. Clearly that's not possible though, so we'll just have to live with the uncertainties and see what happens.
So Heat Waves Were Non Existent 50 Years Ago In Texas?
Thu Jul 12 05:32:34 BST 2012 by Tom Andersen
If you made a model and it predicted 20 times more of a certain kind of event, you would think it would be pretty easy to go back, look at the weather records, and in this case find no comparable texas heat waves in the past. Lets check reality.
(long URL - click here)
'However, the drought is not unprecedented in every way, and much longer droughts have occurred in the past. The worst extended drought remains the massive 1950's event when Texas suffered under drought conditions for 10 years from the late 1940's until the late 1950's.'
It obvious that the down spike in 2011 was bad, but nowhere near out of the ordinary.
So Heat Waves Were Non Existent 50 Years Ago In Texas?
Thu Jul 12 14:18:52 BST 2012 by Eric Kvaalen
You can`t say that the probability is not 20 times as high just because similar heat waves have occurred in the past!
What was the probability of a heat wave like last summer, 50 or 100 years ago?
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refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat,
but this is defined in different ways depending on the context. There is a key distinction between extrinsic curvature
, which is defined for objects embedded in another space (usually a Euclidean space
) in a way that relates to the radius of curvature of circles that touch the object, and intrinsic curvature
, which is defined at each point in a differential manifold. This article deals primarily with the first concept.
The primordial example of extrinsic curvature is that of a circle, which has curvature equal to the inverse of its radius everywhere. Smaller circles bend more sharply, and hence have higher curvature. The curvature of a smooth curve is defined as the curvature of its osculating circle at each point.
In a plane, this is a scalar quantity, but in three or more dimensions it is described by a curvature vector that takes into account the direction of the bend as well as its sharpness. The curvature of more complex objects (such as surfaces or even curved n-dimensional spaces) is described by more complex objects from linear algebra, such as the general Riemann curvature tensor.
The remainder of this article discusses, from a mathematical perspective, some geometric examples of curvature: the curvature of a curve embedded in a plane and the curvature of a surface in Euclidean space.
See the links below for further reading.
One dimension in two dimensions: Curvature of plane curves
For a plane curve C, the mathematical definition of curvature uses a parametric representation of C with respect to the arc length parametrization. It can be computed given any regular parametrization by a more complicated formula given below. Let γ(s) be a regular parametric curve, where s is the arc length, or natural parameter. This determines the unit tangent vector T, the unit normal vector N, the curvature κ(s), the oriented or signed curvature k(s), and the radius of curvature at each point:
The curvature of a straight line is identically zero. The curvature of a circle of radius R is constant, i.e. it does not depend on the point and is equal to the reciprocal of the radius:
Thus for a circle, the radius of curvature is simply its radius. Straight lines and circles are the only plane curves whose curvature is constant. Given any curve C and a point P on it where the curvature is non-zero, there is a unique circle which most closely approximates the curve near P, the osculating circle at P. The radius of the osculating circle is the radius of curvature of C at this point.
The meaning of curvature
Suppose that a particle moves on the plane with unit speed. Then the trajectory of the particle will trace out a curve C in the plane. Moreover, taking the time as the parameter, this provides a natural parametrization for C. The instanteneous direction of motion is given by the unit tangent vector T and the curvature measures how fast this vector rotates. If a curve keeps close to the same direction, the unit tangent vector changes very little and the curvature is small; where the curve undergoes a tight turn, the curvature is large.
The magnitude of curvature at points on physical curves can be measured in diopters (also spelled dioptre) — this is the convention in optics. A diopter has the dimension
The signed of the signed curvature k
indicates the direction in which the unit tangent vector rotates as a function of the parameter along the curve. If the unit tangent rotates counterclockwise, then k
> 0. If it rotates clockwise, then k
The signed curvature depends on the particular parametrization chosen for a curve. For example the unit circle can be parametrised by (counterclockwise, with k > 0), or by (clockwise, with k < 0). More precisely, the signed curvature depends only on the choice of orientation of an immersed curve. Every immersed curve in the plane admits two possible orientations.
For a plane curve given parametrically as
the curvature is
and the signed curvature k is
For the less general case of a plane curve given explicitly as the curvature is | <urn:uuid:50dc4b5a-dd95-4caa-9a7a-3d87e98cade8> | 4 | 939 | Knowledge Article | Science & Tech. | 34.517604 |
Just about anything that substantially affects climate change science or policy inevitably affects communication on those issues. The Yale Forum focus in this feature, and the major criterion for inclusion in notable climate developments of 2010, is on key climate happenings influencing public understanding of the subject.
The year now just behind us flew by with record warm temperatures, severe droughts, and numerous other weather anomalies; policy action and inaction; evolving attitudes on geoengineering and adaptation; and evolving attitudes and action by American voters on climate change.
Several ongoing analyses point also to a significant decline in network news and major metropolitan newspaper coverage of climate-related issues in 2010, with experts still debating the exact cause-and-effect relationship, if any, with changing public attitudes on the climate issue. More on that in a future Forum feature.
Some significant 2010 events affecting communications on, and public perceptions of, climate change science and policy follow … all of them contributing to the mosaic of factors likely to influence the trajectory on these issues in the New Year.
What’s with the Weather Extremes?
Widespread reports of unusually severe weather persisted coast-to-coast and across much of the world throughout 2010, reconfirming for some the nonlinear impacts of a changing climate but also buttressing talking points for those inclined to be contrarian by, among other things, conflating short-term weather with long-term climate.
As fire and record heat shut down Moscow and killed thousands, floods devastated Pakistan. The Arctic saw extremely warm temperatures, the Mid-Atlantic states in early 2010 recorded record snowfalls, and record heat in the oceans led to massive bleachings of coral. And, despite the cooling effects of La Niña and natural climate variability, early reports of global temperature indicate that 2010 will tie with 1998 or 2005, as some experts prefer, for the warmest year on record.
These stories provided an opportunity for journalists to give context and deepen readers’ understanding of the kinds of severe weather events that are likely with climate change as levels of heat-trapping gases continue to rise. But financial and institutional pressures consuming many media outlets led to too few seizing those opportunities.
Action … and Non-Action … on Climate Change
In November, voters in California voted overwhelmingly to uphold their state’s landmark Global Warming Solutions Act of 2006. They did so by voting to reject Proposition 23, which would have suspended the state’s landmark A.B. 32 law to bring greenhouse gas emissions back down to 1990 levels. New Mexico, too, took action when it approved a cap-and-trade program that’s one of the most comprehensive greenhouse gas regulations in the country. (New Mexico is also part of the Western Climate Initiative, a consortium of states implementing policies to reduce emissions of heat-trapping gases. A change in governorship in the state could lead to some changes on this issue in coming months.)
In response to increasing despair among climate change policy advocates over the potential for near-term federal or international greenhouse gas reduction requirements, control advocates appear to have warmed-up to the need for increased adaptation efforts, while continuing to pursue mitigation strategies over the longer term. This trend may account in part for some limited, but not insubstantial, increased receptivity to concepts tied to geo-engineering.
With the U.S. Congress having effectively tabled short-term prospects on federal “cap-and-trade” greenhouse gas legislation, these initiatives help set the table for upcoming Supreme Court action on a key climate lawsuit involving greenhouse gases as a public nuisance, a ruling that may open the door to still more legal battles. (See related Yale Forum article.)
Failure to Enact Federal Legislation
It had at least three short-hand names — the climate bill, the cap-and-trade bill, the Waxman-Markey bill — but one official eulogy.
In July, Senate majority leader Harry Reid (D-Nevada) announced that he would abandon plans to move forward in the Senate on federal legislation to control greenhouse gas emissions. Post-mortem analysis points to a multitude of reasons for failure of the legislative effort, high among them the sagging economy, an absence of presidential leadership, opposition from climate skeptics and stiff Republican opposition, and reverberations from the health reform legislative battles. With Republican climate skeptics now taking over as chairs on key House of Representatives committees responsible for energy and policy, few expect meaningful climate change legislation at the federal level any time soon.
Passing of Stanford’s Stephen Schneider
Few voices in climate science have equaled that of Stephen H. Schneider, a member of the National Academy of Sciences and a prominent IPCC author. The high-energy/always “on” Stanford University climatologist passed away in July while on a flight returning from a science meeting in Stockholm.
Equally committed to the hard science and to communicating complexities to non-specialists, Schneider long had been among the most widely recognized and respected — and, by contrarians, among the most controversial — climatologists in the world. His death came at a time when his voice could have been expected to be particularly crucial in upcoming Capitol Hill hearings on climate science. He leaves a gap the climate science community is struggling hard to fill.
America’s First National Oceans Policy Established
In July, President Obama established a sweeping new policy to proactively manage ocean resources. The policy represented a major shift from established practices, but many major news organizations did little actual reporting on it. The dearth of coverage was especially glaring with respect to climate change, since two separate studies published a week later in Nature described news of phytoplankton in 40 percent decline, which scientists blame on rising sea surface temperatures. (The public and policymakers disregard the vital importance of plankton at all of our great risk, scientists emphasize.) Their notable findings saw little coverage among major media, but a few outlets (see here and here) dove into the topic.
For The New York Times, Key Departures
The year 2010 opened with the departure from the nation’s premier “newspaper of record” and leading science section of two by-liners long considered mainstays in reporting on climate science and policy.
Andrew C. Revkin, who reported on climate change for two decades, took a corporate buy-out at the end of 2009. Revkin remains active with the Times online through his DotEarth blog, which was moved from the news section to the Times‘ Opinion section. He remains an active blogger, but many observers agree that the paper’s in-print climate science coverage — quantity and quality — clearly has suffered. Former colleague and one-time “Science Times” Editor Cornelia Dean, who long had reported on science, oceanography, and natural systems for the Times, also left with a buy-out. She too contributed a handful of science reports to the Times in 2010 as a freelance writer.
Geo-Engineering Gets a Serious Once-Over
In December 2009, the American Geophysical Union Council adopted a position statement on geoengineering. In part, the AGU said, “Geo-engineering will not substitute for either aggressive mitigation or proactive adaptation, but it could contribute to a comprehensive risk management strategy to slow climate change and alleviate some of its negative impacts.” Geo-engineering emerged as a serious hot button issue in 2010 with the first ever geo-engineering hearing on Capitol Hill and the approval of a ban on large-scale projects by 193 nations under the global biodiversity treaty. Governance issues of who should have authority over geo-engineering will continue to fuel interest in the coming year.
Media Storm over Hacked E-Mails
As the aftermath over e-mails hacked from prominent climatologists raged, legitimate science news too often was given cursory treatment in early 2010. Even though 2009 had tied as the second warmest year globally since records began in 1880, media outlets throughout the year often zeroed-in on what some say were “cherry-picked” but widely publicized quotes used to imply misdeeds on the part of scientists and the Climactic Research Unit (CRU), University of East Anglia in the United Kingdom.
A series of follow-on investigations, by Penn State and the InterAgency Council and others, held the scientific evidence un-dented, but for some those studies only justified their further muddying of the waters, and the “ghost” of the e-mail controversies continued to color much coverage throughout the year. How those controversies play out in the new U.S. House of Representatives may be one key carryover from 2010.
More Scientific Reports … but Public Opinion Not Swayed
The America’s Climate Choices reports had been billed as among the most comprehensive studies of climate change to date.
The National Research Council issued the four reports in May and June at the request of Congress to provide advice on why the U.S. should act to reduce greenhouse gas emissions and develop a strategy to adapt to the impacts of climate change. The America’s Climate Choices reports were perhaps a missed or lost opportunity because they had the potential, with nearly 100 leading scientists and stakeholders involved, to broadly affect public opinion and climate change communication.
In “Advancing the Science of Climate Change,” the report conclusion didn’t mince words: “Climate change is occurring, is largely caused by human activities, and poses significant risks … for a broad range of human and natural systems.”
Despite strong statements by the nation’s leading scientific body, Americans remained confused, perhaps even more so than in earlier years. Numerous public opinion polls and surveys reflect a decline in general public awareness, interest, and concern over climate change compared with attitudes of two or three years ago. Whether that trend reflects, or is a result of, a decline in mass media coverage of the issue throughout 2010 is unclear; and so, too, is the extent of any relationship with controversies involving the hacked e-mails and IPCC Himalayan glaciers snafu. Experts continue to look into those issues.
A Gallup poll showed 48 percent of Americans now believe global warming is exaggerated, up from 41 percent in 2009. Several polls by George Mason and Yale universities offer similarly grim accounts. A June 2010 survey shows that some 61 percent of Americans believe climate change is happening, but just half of Americans believe it is caused by human activities. In Yale’s study in October 2010, Americans’ Knowledge on Climate Change, 63 percent of Americans believe global warming is occurring but don’t understand why. Roughly half of those polled would fail a basic test assessing their understanding of climate change. On a bright note, the same Yale report indicated that Americans trust scientists and scientific organizations far more than any other source of information.*
Investigation by Virginia Attorney General
Virginia state Attorney General Ken Cuccinelli spent part of his first year in office on a crusade against former University of Virginia researcher Michael E. Mann, now professor and director of the Earth System Science Center at Penn State. Cuccinelli subpoenaed from the University of Virginia documents, e-mails, and more related to grants Mann had received while on its faculty from 1999 to 2005.
From the beginning, the Cuccinelli investigation was widely condemned as a “witch hunt.” Nature published an editorial that said, “Given the lack of any evidence of wrongdoing, it’s hard to see Cuccinelli’s subpoena … as anything more than an ideologically motivated inquisition that harasses and intimidates climate scientists.” A number of leading scientific organizations and academic groups joined in condemning the effort.
A judge dismissed Cuccinelli’s initial efforts because “[t]he nature of the conduct is not stated so that any reasonable person could glean what Dr. Mann did to violate the statute.” Still, Cuccinelli has persisted, in September launching a new effort to obtain documents related to the climate scientist’s work. Further legal actions and decisions are pending, making the issue a clear carry-over story from 2010 to 2011.
*Editor’s Note: The writer of this piece freelanced as development editor of the Advancing the Science report described here. The Yale University study was done by Anthony Leiserowitz, publisher of The Yale Forum. | <urn:uuid:f00339fd-f930-470c-ae5a-a5f1594a8fd5> | 3.265625 | 2,538 | Knowledge Article | Science & Tech. | 26.751721 |
Quantum computation is the current high visibility fad in atomic physics. These computers operate along the same lines as normal computers but every quantum bit (qubit) is both a one and zero at the same time. Only when the final result is desired do we measure the qubit state and receive either a one or a zero. The mathematical operations performed by a quantum computer alter the probability of receiving a one or a zero. The advantage is that quantum computers can potentially perform certain types of calculations much faster than classical computers (database searches and factoring large numbers are examples). The problem is that quantum computers rely on creating and controlling entangled quantum states, which are highly delicate beasts. The traditional approach to this has been to carefully control the interactions between qubits on a pair-wise basis (e.g., only two qubits can interact at a time). Every time you switch the interaction between two qubits on or off you run the risk of destroying that which you are trying to control, thus you can't do many computations in a row. Not only that but you have lost much of the parallelism for which you are doing a quantum computation in the first place.
Now a new approach to the problem is under development. The operations between qubits are still carefully controlled (otherwise no computation would be possible) but the interactions between qubits are not switched on and off, instead they are always on. By developing a method by which quantum calculations can be performed even when an operation on one qubit effects all the remaining qubits has numerous advantages. The biggest fundamental advantage is that the implementation of many common algorithms can be simplified. More practically, this method allows experimental physicists to start using coupled systems such as quantum dots, which have a much better chance of leading to practical computers that can actually scale to the point where they are useful.
One of the distinguishing concepts is that any successful implementation of this algorithm is automatically a programmable multi-bit core much like the processing units of early microprocessors. The big question is can we build it? Well that is a definite maybe, building quantum dots that are coupled together is now a fairly common lab practice. The problem is that these dots are also coupled to the rest of the substrate so the carefully constructed quantum states are easily destroyed by the very material they are built upon. I guess Hannibal can wait a week or two before digging into the new quantum processor core architectures. | <urn:uuid:4b58168e-257a-46d4-8929-4bb7c02b2bee> | 3.4375 | 487 | Nonfiction Writing | Science & Tech. | 32.421667 |
What are These Chytrids?
Barr (1) delineated the order Spizellomycetales from the Chytridiales based on distinctive zoospore ultrastructure. Rhizophlyctis rosea was included in this new order, but recent ultrastructural and molecular analyses demonstrate that R. rosea is a morphogenus distinct from the Spizellomycetales (2). As a consequence a new order has been established which includes four families and four genera, each with distinctive zoospore ultrastructure (2).
Current systematic synthesis of the order Rhizophlyctidales:
The Order Rhizophlyctidales (2) includes four genera:
These Chytrids are Found in Diverse Habitats:
Rhizophlyctidalean chytrids are common in the soil worldwide (2).
(1) Barr, D. J. S. 1980. An outline for the reclassification of the Chytridiales, and for a new order, the Spizellomycetales. Canadian Journal of Botany 58, 2380–2394.
(2) Letcher, P.M., M. J. Powell, Donald J. S. Barr, Perry F. Churchill, William S. Wakefield, and Kathryn T. Picard. 2008. Rhizophlyctidales is a new order in Chytridiomycota. Mycological Research 112: 1031-1048. | <urn:uuid:1f3f8030-c85e-442a-a681-42f2c41d893d> | 3.359375 | 318 | Knowledge Article | Science & Tech. | 41.393618 |
Weather, temperature, carbon, water, soil and all other kinds of climate related open data. Including (but not limited to) data about:
- the atmosphere
- the weather
- air quality
- the ocean
- water levels
- water quality
- carbon emissions
- soil erosion
Existing Lists of Climate Datasets to Migrate Here
13 datasets found.
Climate Data Online: Provides direct access to historical climate data for specific locations and dates. Almanac Data: Provides average and extreme temperature and precipitation values...
About The datasets have been developed in conjunction with Hadley Centre of the UK Met Office. Hosted by the Climate Research Unit at the University of East Anglia. From website: land...
Large volumes of data from various satellite based instruments. Access canned data for research purposes is available on application (automatic acceptance) or via peer-reviewed project...
About data Monthly climate data for thousands of worldwide weather stations. Data are available for each station and also gridded (onto 5x5 degree cells). The Global Historical...
A record of historical temperature anomalies. Global, zoned, and gridded. As the output from a branch of NASA, it's probably public domain, but I couldn't find a statement to that effect.
About Guardian website says: UK and US temperature changes, by weather station, for the last century. The Met Office has released data from 1300 weather stations around the world which...
Global surface temperature anomalies gridded into a 5x5 degree grid. The 1971 to 2000 average is used as the climatology normal.
The Global Surface Temperature Anomaly gives the global anomaly either for each year, or for each month. Hemispheric are also available. It is based on the GHCN dataset
About The datasets have been developed in conjunction with Hadley Centre of the UK Met Office. Hosted by the Climate Research Unit at the University of East Anglia. From website:...
About From the website: HadCRUT3 is a gridded dataset of global historical surface temperature anomalies. Data are available for each month since January 1850, on a 5 degree grid. The...
The data downloadable from this page are a subset of the full HadCRUT3 record of global temperatures, which is one of the global temperature records that have underpinned IPCC assessment...
A historical temperature reconstruction going back to 420,000 years before present based on Vostok ice core data.
About Weatherbase WeatherbaseSM is your one authoritative source for finding monthly weather records and averages for more than 16,439 cities worldwide. Climatological information is one... | <urn:uuid:e1cff353-1262-4181-9e55-d3e49ad1ce8b> | 2.921875 | 537 | Content Listing | Science & Tech. | 34.115431 |
Here is a general implementation. It uses a templatized class, therefore it will get the combinations of any type of variable, not just characters.
The program takes advantage of the next_permutation algorithm and uses a set of bits to determine what to output. The way it works is that you call the NextCombination() function until there are no more combinations left.
I attached the full code, but I'll go over the main() function briefly:
All this does is initialize my vectors that will be used. The "elements" vector is a vector of all of the items I want to take the combination of. The "results" will hold the results of each time I get a combination. Note that the template allows combinations of char type. If I wanted to get the combination of integers, I change the type to <int> (this is done by template magic).
int nItems = 2;
CombinationGenerator<char> CG(elements, nItems);
This declares an instance of a CombinationGenerator class that will generate combinations. The first argument is the vector of all the items, and the second argument is the number I want to choose. For your case, it would be 2 characters. Also note that this is a templatized class that is based on "char", since the items are char items.
int nTries = 0;
// Output our results
int nSize = results.size();
for ( int j = 0; j < nSize; j++ )
cout << results[j] << " ";
cout << endl;
cout << "Number of combinations is " << nTries << endl;
I just call CG.NextCombination() in a loop. The arguments to NextCombination is the vector that will be used to store the next combination.
You should compile and run the program through a debugger. You will see that it will choose 2 letters out of 26 and output all of them. Again, this is a generalized function that will work with any type of data, not just chars. For example you can have a vector of complex structures (call it YourType), and if you want to take the combination of them, do the following:
CombinationGenerator<YourType>(vector_of_YourType, number to_choose);
And call NextCombination() as I did in a loop.
Last edited by Paul McKenzie; April 21st, 2003 at 04:42 AM.
I changed the string to "ABCDEF" and the number of items to choose is 3. The number of combinations is 6! / (3! * 3!) = 20.
Here is the output from the program I posted:
D E F
C E F
C D F
C D E
B E F
B D F
B D E
B C F
B C E
B C D
A E F
A D F
A D E
A C F
A C E
A C D
A B F
A B E
A B D
A B C
Number of combinations is 20
I would just like to say that I found your sample for outputting combinations very elegant. I had not thought of using next_permutation on a vector of bools to provide combinations.
I was wondering if you came up with this yourself, or if it came from some book (and if so, what book did you find it in).
Actually, I learned this in my second Comp Sci. course I took in college. The original code was written in PL/I and there was no official name for doing combinations this way. Just something I also thought was elegant and unique.
For those who want to understand what is really going on, to get the combination of N things taken R at a time, my code creates an array of N bools. I then set the right-most "R" bools to "true" and the other N-R bools are set to "false".
Assume the array of bools is B and the array of original items is O. For each element "i" of the B array, if the value in B[ i ] is "true", you output the corresponding O[ i ] element. Once this loop is done, you have outputted one combination. The next step is now to take the array of bools and get the next permutation of bools. This will move the "true" values around in the bool array. You repeat the loop again, checking it against the O[i] array. Again, you will output another combination.
Combination of 6 things taken 3 at a time.
The O array consists of "ABCDEF" (the 6 items)
The B array consists of 000111 (the '1' is true, '0' is false)
Compare B for 1's:
The first combination would be ---DEF
Permute the bools:
The next combination would be ---CD-F
Permute the bools:
The next combination would be --CDE-
So basically, if you have the code to output a permutation, you also have the code to output a combination. For C++, the next_permutation solves the permutation problem. Then it's all a piece of cake to do the combination using the "marching true values" method (there, I made up a name for it)
If I would like to write it in C, how can i change it ? This use of STL just works in WinConsole to test its algorithm.. i mean in case I want to do something in Borland Builder or something to simulate its flow... | <urn:uuid:dc5c0885-5473-42c3-b1bb-f23c8a55067a> | 3.28125 | 1,192 | Comment Section | Software Dev. | 70.281377 |
Working with controls. Using
Properties, Methods and Events
You use controls to
get user input and to display output. Some of the controls you can use
in your applications include text boxes, command buttons, and list
boxes. Other controls let you access other applications and process
data as if the remote application was part of your code. Each control
has its own set of properties, methods, and events that can be
modified from the properties window or from the code
Properties are simple to understand. Here's an example. A human
being, he/she has eyes, legs, arms, etc. They are all properties of
the human being.
A property describes an object, its behavior and its look. If you
wanted to change the color of the eyes you would just do this:
Human.Eyes = Brown
Human.Weight = 156
If you wanted to change any other properties, you could do that too.
As long as the property is available. For example, you cannot
do this: Human.Beak = True. The nice thing about properties is that
you do not have to know what it takes to actually change the human's
eyes or weight. You just indicate that you want it to change.
An example of this is the Label
The label control has an important property, Caption. Without it, it
would be almost useless. The Caption property sets or returns the text
presently contained in the Label control. The only drawback is that
you cannot directly enter text into the label. The text
control is virtually identical except that you can type in text.
Label.Caption = "This is really easy"
In some cases, properties aren't enough to tell an object what it
should do. It would be nice to give the object direct commands as
well. Visual Basic lets you do this. Let's go back to the Human
example. If you wanted the human to move its arm a method is a nice
and easy way of doing that. The human could have a method called
MoveArm, which we could use like an ordinary command:
As you can see, you don't give a method a value, it will execute like
any other Visual Basic command. As far as this is concerned, you
really don't care what the human has to do to move its arm. All you
want it to do is move its arm.
Q:Ok we used the
properties and the methods of an ďhumanĒ object. In the previous
example we have used the MoveArm method now how will we know when the
human has ended the MoveArm method?
A:By using an event
An event procedure is
simple to understand. These procedures are automatically declared by
Visual Basic for each object that we use and are fired when that event
Draw a button on your
form and then double click it, you will now see a procedure that looks
something like this:
This is an event
procedure and itís fired when Command1 is clicked. You can observe
the parts in the subís name: | <urn:uuid:4bd3b641-616f-4cb4-a31b-38060c16cdf3> | 3.90625 | 648 | Documentation | Software Dev. | 64.592271 |
3.5. Debugging sed scripts
The following two debuggers should make it easier to understand how
sed scripts operate. They can save hours of grief when trying to
determine the problems with a sed script.
(1) sd (sed debugger), by Brian Hiles
This debugger runs under a Unix shell, is powerful, and is easy to
use. sd has conditional breakpoints and spypoints of the pattern
space and hold space, on any scope defined by regex match and/or
script line number. It can be semi-automated, can save diagnostic
reports, and shows potential problems with a sed script before it
tries to execute it. The script is robust and requires the Unix
shell utilities plus the Bourne shell or Korn shell to execute.
(2) sedsed, by Aurelio Jargas
This debugger requires Python to run it, and it uses your own
version of sed, whatever that may be. It displays the current input
line, the pattern space, and the hold space, before and after each
sed command is executed. | <urn:uuid:8c02cbed-2388-4c34-a970-2d6ce91602d2> | 2.8125 | 230 | Tutorial | Software Dev. | 58.854429 |
Solar still built into a pit in the
through the use of a pit (or 'solar still') is a much touted
1) Clear plastic sheet for cooling condensate.
2) Sheet anchor stones (in a shallow ditch).
3) Condensate runs along sheet to drip into can.
4) Collection can, at bottom of dug pit, holds condensate &
5) Drinking tube from can bottom to outside still.
6) Soil or other material, containing all the water you hope to
-- Hints --
Often works better at night.
Make it as big as practical.
Plastic must be steep enough to run not drop, and not touch the pit
A solar still
is a low tech. way of distilling
water, powered by the heat of the
(more precisely, the heat & humidity of
the soil, and relative cool of the plastic). Two basic types of
solar stills are box, and pit. In a solar still, impure water is
contained outside the collector, where it is evaporated by the sun
through clear plastic. The pure water
(and any other included volatile solvent) condenses on
the cool inside plastic surface and drips down off the low
point(pebble), where it is collected and removed. The box type is
Solar stills are used in cases where rain, piped, or well water is
impractical, such as in remote homes or during power outages.
Florida and other hurricane target
areas that frequently lose power for a few days, solar distillation
can provide an alternate source of clean water.
Solar stills are occasionally used on a longer term basis in
depending on environmental conditions, they usually produce a
relatively small amount of water, and even less where the source is
saline or brackish
. If the source is
inadequate, a compromise method is to mix the distilled water with
the brackish or saline water purified with other methods - this
gives a more adequate quantity and re-introduces the other source
contaminants, while still lowering the salinity, and improving the
taste.The Water Pyramid is a larger version, which uses an
inflatable dome as the condensing surface and can be used in
tropical, rural areas.
Knowing how to put together a solar still is often billed as a
useful survival skill
provide an important means of potable water in the event of a
wilderness emergency. Nevertheless, under typical conditions
makeshift solar stills rarely produce enough water for long-term
survival, and the sweat expended in building one can easily exceed
its daily output. Solar stills can extract water from moisture in
the ground but to increase the amount of moisture available to a
solar still, water (fresh or saline
can be added inside or along the edges of the still. Where no water
sources are readily available, shredded vegetation , wet soil/sand,
urine or covered feces, can be used inside the pit. If only the
natural soil moisture is used, the pit must usually be moved as the
productivity drops. To prevent losing moisture by taking apart the
still to retrieve collected water a length of plastic tubing can be
used to sip water as it accumulates.
Besides using stills (which work by controlled evaporation and
condensation of water), filtration, and reverse osmosis are more
difficult but more productive. Water may thus be obtained from
other larger sources (eg the sea as well as fauna and flora, ...)
More information can be found at Drinking
- Solar water
disinfection - uses the sun's infrared energy and heat to
disinfect water, but does not distill (evaporate and condense) the
- Watermaker - A filter to obtain clean
water from seawater; used in large vessels
- Solar cooker -- A similar device
used to cook food.
Jackson, R. D.//van Bavel, C. H. M. (1965)Solar Distillation of
Water from Soil and Plant Materials: A Simple Desert Survival | <urn:uuid:52c97fd0-64c7-4547-8c09-baeae9ad350c> | 3.359375 | 877 | Knowledge Article | Science & Tech. | 42.246346 |
Photograph by Al Giddings
A cloud of hydrothermal fluids streams from a black smoker, or mineral chimney, along the Mid-Ocean Ridge off the west coast of Mexico. Black smokers are common to spreading zones in plate boundaries. Chimneys are made of lead, iron, manganese, and zinc sulfides, through which spew superheated ocean water. They also harbor exotic life-forms, far below the reach of sunlight. | <urn:uuid:83fce49c-cee0-4303-82d3-a8719dd6816a> | 3.078125 | 92 | Truncated | Science & Tech. | 49.0875 |
Global surface temperatures………Credit: Berkeley Earth Project
The Global Warming controversy is ended. Right.
Take a look at the graph above. It shows the results of global temperature measurements over a span of some 100-200 years as compiled by four groups: NASA Goddard Institute for Space Studies, NOAA (National Oceanic and Atmospheric Administration), United Kingdom Meteorology Office Climatic Research Unit (hadCRU), and the Berkeley Earth Surface Temperature Project. Notice that the graph lines are almost identical and they all show a strong trend in global warming.
This is not exactly news, is it? No, but one line in the graph of particular interest is from a report that is making its way toward official release. It’s important because the data for that line on the graph is from those skeptical of scientific measurement of global warming. The Berkeley Earth Surface Temperature Project was begun by University of California physics professor Richard Muller, a man highly critical of the manner in which climate scientists were gathering and manipulating their data. Initial project funding included sources that generally contribute to climate change denial. Muller’ stated goal was to establish an independent source of climate data that would be thoroughly vetted for bias and error.
The Berkeley team, ten scientists led by Robert Rohde, a specialist in climatology with large data sets, included Saul Perlmutter, this year’s Nobelist in physics. The goal was to assemble a merged set of climate data from surface weather stations, check it for various errors, bias, or other distortions, analyze it with new and existing statistical methods, and provide public access to all the data and results. The result of the multi-year project is a database of 1.6 billion records of climate data, and a report that is now available at the website [Berkeley Earth Surface Temperature], which is heading for peer review and publication. Though not final, this is the official report.
The report is based on data collected from about 40,000 weather stations around the world. It will be difficult to impugn the source, as the Berkeley project explicitly stated that the quality of weather station reporting was sufficiently reliable and more importantly did not reflect the contention that modern ‘urban heat islands’ (the heat generated by cities and roads) affected a significant number of measurements. I would say that this data was also subjected to scrupulous statistical analysis, although that will have to wait for the peer review process to be validated. The essential results, in the words of Dr. Muller:
“Our biggest surprise was that the new results agreed so closely with the warming values published previously by other teams in the US and the UK,” said Professor Muller. “This confirms that these studies were done carefully and that potential biases identified by climate change sceptics did not seriously affect their conclusions.”
[Source: BBC News]
The findings of the Berkeley project agree that the global temperature has increased 1 degree Celsius since 1950 and the trend is up. In short, global warming is real.
So here we are in 2011, more than twenty years after the first warnings about the rise in global temperatures, and most people in the United States still think there is no global warming. The Republican Party has virtually enshrined climate change denial as part of its platform. At the same time, the U.S. military is planning for the effects of global warming on world politics and conflict. The energy industry is preparing a full-scale development of the Arctic petrochemical fields as the ice recedes, and plans are already in motion for shipping routes through the Arctic seas. Many countries, especially island states around the world, are making plans for rising coastal waters. This is what some like to call cognitive dissonance, the discrepancy between what people choose to believe and what is actually happening around them.
Will the addition of one more global warming report, albeit from a group inclined to be skeptics, have an impact? Watch your favorite media outlets. Will the results be highlighted? Will they be mentioned even once? Then judge for yourself. | <urn:uuid:297397d1-dea7-4a99-ba62-62e8e5b9a67d> | 2.9375 | 821 | Personal Blog | Science & Tech. | 39.098382 |
The book consists of 25 chapters. The initial five chapters introduce paleobotanical history, principles of geologic age, types of plant fossils, and the techniques employed to study them. Chapter 6 deals with Precambrian paleobotany and chapter 7 with the classification of fossil plants. Major groups of fossil plants are individually treated in chapters 8-19 and 22. Gondwana and Tertiary floras of India are reviewed briefly in chapters 20 and 21. Applied paleobotany is discussed in the final three chapters (23-25).
Paleontologists throughout the world have a great interest in the origin of angiosperms and in fossil angiosperm records. A huge amount of literature on new discoveries has been published in the last two decades, for example, Triassic angiospermid pollen from Arizona (e.g., Review of paleobotany and Palynology, 1988, 55: 337-356) considered to have an affinity with the family Araceae; or the Early Cretaceous origin of Hamamelidaceae based on the discovery of Hamamelidalean Cretaceous fossil flowers with in situ pollen from the Upper Cretaceous of Sweden (1991, Plant Syst. Evol., 175: 101-114). Nine pages in chapter 22 on "Fossil Angiosperms" do not do justice to the subject. The only significant finding included is the case of Eucommiidites which, however, was proven to be gymnosperinous as early as 1961. In comparing angiosperm pollen exine with that of Cheirolepidacea, the term "tectate" (p. 282) should have been "columellate" or "baculate."
It is well established that most sedimented palynomorphs are mainly transported by water. Wind transported palynomorphs have a negligible role in pre-Quaternary sediments. In explaining the role of palynology in oil exploration (chapter 23, pp. 291 and 293), the author's emphasis on the significance of wind dispersed pollen and spores is erroneous. Recycling of palynomorphs is also explained wrongly as due to "their minute size, pollen and spores are susceptible to removal by waters circulating through the rock strata" (p. 292). Recycling of any fossil occurs by the erosion of older strata and its redeposition in younger formations just like any sedimentary particle. Although the term "acritarch" was proposed in 1963, the author has used the old discarded term "Hystricosphaerids" (sic) for these organic walled unicellular marine algal cysts abundant in pre-Jurassic sediments. Veryhachium sp., illustrated on Fig. 23.6: 1, is an acritarch.
Paleobotanical studies of the last century, such as those of Blanford, Feistmantel, Heer, Medlicott, and Supporta, have been mentioned repeatedly in the text but their full references are not listed. Pioneer studies are the foundation for present and future work and should be referred to fully. The following are examples of the numerous errors throughout the book; references not listed, e.g., Srivastav (sic), 1946; technical mistakes, such as Drimys of "Magnoliaceae" (p. 280) should be "Winteraceae"; Terms wrongly explained, e.g., "nomos, meaning distribution" (p. 9) whereas it actually means "knowledge"; misspellings, e.g., Ephedrites (p. 202) for "Ephedripites", Sahnipusham, (p. 267) for "Sahnipushpam", sapropen (p. 289) for "sapropel". Further, several statements lack clarity. For example, "The exact origin of the earth has puzzled man ever since he appeared on the earth's surface" (italics mine) and "A new hypothesis has recently been added" (p. 9) The nature of "new hypothesis" is not mentioned. Several illustrations are similar to those published in earlier paleobotany texts. Geological principles are explained with simple line diagrams but labeling errors make it difficult to understand the figures. For example, the decayed material is labeled in fig. 4.4 as decreasing whereas it actually increases.
The book is printed on nonglare paper with a hardcover binding. The author could have minimized errors by restricting the scope of the book to plant fossils only. Had he expanded upon Indian paleobotany, the book could have been useful for undergraduate students of Indian universities. Poor reproduction of illustrations and light treatment of the subject will not attract students in western countries where better paleobotany textbooks are easily available. - Satish K. Srivastava, Rowland Heights CA (Department of Earth Sciences, USC) | <urn:uuid:62c27231-7701-4a25-bc1c-0b3ce932ef26> | 3.640625 | 1,013 | Academic Writing | Science & Tech. | 39.899178 |
- Roughly 10 billion icy objects outside the orbit of Neptune.
- Although believed to exist since 1930's, only discovered in 1992 because objects are far away and thus faint.
- Most of the bright KBOs are the same as a 100 watt light bulb on the Moon.
- Exception is Pluto because it is covered by bright frost and so reflects 90% of sunlight.
- Objects like the Moon reflect only a few percent.
- That is why scientists originally believed that Pluto was much bigger than it is. | <urn:uuid:d652ae4e-30e1-4af7-93fd-41844355ad8e> | 3.71875 | 107 | Q&A Forum | Science & Tech. | 66.05348 |
- Why Boost?
- What Does Boost Provide?
- What Else?
- Version History
Boost is a free library which is aimed at providing quality software components to developers, whilst using the styles of the Standard Template Library. Some of the components within the library may be put forward as future extensions to the Standard Library.The Boost main pageThe Boost libraries indexCUJ Descriptions of the boost components
The Boost homepage contains extensive documentation on all of the individual components. This article is intended to be an overview of why you should consider using Boost, and the Boost components in preference to other libraries, and to provide a location on CodeProject which can offer links to related documentation.
Boost installation is simple because most of the components within the library reside in their own header files, which should not require modification. The BoostJam build tool is available for the components which do require compilation.
You can download the source zip from SourceForge.
Unzip the entire archive into a directory of your choosing. To start using the components add the Boost directory which includes version numbers to your include path. For the current version of Boost, boost_1_30_0.
Most of the components come with test suites and examples of use.
- Boost is namespace aware. All components within the library are packaged in the "boost" namespace, or a sub-namespace thereof.
- Regular updates. Boost is a library which is growing all the time, the home page and the Boost Announcements Lists show some of the changes in the last few releases.
- Developer support. Questions related to the components can be directed to the Boost users mailing group, or found on the Boost Mail Archives or on one of the specific lists for a particular component.
- Boost supports a variety of compilers, operating systems and standard libraries. It provides workarounds for the broken features of many compilers, perhaps the most significant being the workarounds for problems with templates, including partial template specialisation and member template friends.
- Regression testing. Each update to Boost is heavily regression tested, and the status of the library for all compilers is freely available.
- Many of the people involved with the development of the C++ standard are involved with Boost.
- Simple to install and upgrade. In most cases, installation and upgrading only requires the addition or change of one include path.
- Easy to configure. Compilation options can be specified by changing directives in one or two header files.
What Does Boost Provide?
What follows is a minimal listing of components. There are about 50 major sub-components in Boost at the moment. The following components were those that I felt logically progressed from the components in the STL, were easy to integrate, or were especially significant to most programmers.
Smart pointers are tools that prevent resource leaks (especially in the presence of exceptions), promote the concept of 'Initialisation is Resource Acquisition'. They emulate, to a certain extent, garbage collection like behaviour.
Most of the limitation of std::auto_ptr are relatively well known:
std::auto_ptr's cannot be stored within a standard containers.
std::auto_ptr's cannot (easily) be used to implement the pImpl (pointer-to-implementation) idiom.
std::auto_ptr does not work with arrays.
The 5 types of Boost smart pointers overcome these flaws and provide many extra features.
Boost smart pointer indexComparison of Boost and Loki Smart Pointers
- Custom delete functions can be supplied.
- Detection of incomplete template types.
The New C++: Smart(er) Pointers - Herb SutterIntroduction to uses of the Boost smart pointers
Conversations: Getting to the Point - Herb Sutter and Jim Hyslop
Functors and binders have become a common part of using the STL, but using most standard library implementations it can still be difficult to combine multiple functions. Composers allow functors to be combined in several ways, minimising the amount of times that users have to write their own loops.
The C++ Standard Library - A Tutorial and Reference (Nicolai M. Josuttis)
A component which provides a type safe way to move any type of component, without having to rely upon void pointers or unions. The design principles for this component is at least as significant as the component itself (derivation of a template class from a non template base class). Something similar to boost::any main pageboost::any Theory Introduction to uses of Boost Any
boost::any appears in Alexandrescu’s Modern C++ Design in the guise of Functors and Functor Implementations.
Conversations: I'd Hold Anything for You - Herb Sutter
Bind and Function
Bind and Function are specified as two separate components, but they are extensions (any number of arguments) of binders and functors concept which are currently in place in the Standard Library.
boost::function main page
boost::bind main page
The Lambda Library
The lambda library provides a shortcut for producing binders, functors and composers using expression templates. My personal opinion on the library is that developers would need some practice to recognise it’s use. Libraries like the Lambda library are probably the way of the future for C++, but at the moment, I think I’m prepared to have slower uglier code that I know the next guy can understand.The Boost Lambda Library Index
Further information on the basics of expression templates was published in the March issue of the C/C++ users journal (C++ Expression Templates – Angelika Langer and Klaus Kreft)
The Boost Graph Library (The BGL)
The BGL is a huge library, with a large amount of support material and good sample programs. “The Boost Graph Library, The: User Guide and Reference Manual” has been published by Addison-Wesley in the C++ In Depth Series (The same fantastic series that includes 'Exceptional C++', 'More Exceptional C++' and 'Modern C++ Design'), which I believe is testament to the quality of the library.Boost Graph Library Table of Contents The Boost Graph Library, The: User Guide and Reference Manual
Developed by Code Project regular William E. Kempf, the threads library makes it seem almost as easy to do threads in C++ as it is in Java. It requires linking to an additional library, built with BoostJam.boost::threads indexWilliam E. Kempf on boost::thread
Spirit parser generator framework
Jonathan de Halleux has written an excellent introduction to the Spirit Parser Generator Framework with comprehensive links to relevant material
- Regular Expressions
- File System (Directory Iteration)
- Iterator Adaptors
- Maths and Matrices
- A Template metaprogramming framework
Many of the references in this article come from the C / C++ Users journal website, which is an excellent resource for up to date information on uses, and techniques for using STL and Boost.
Additional information about Boost can be found at Boost Consulting
This article was inspired by an item in the 'Article Requests and Ideas' Forum by John M. Drescher
|30. 6. 2003 Initial Posting|
Andrew is a PhD student at Swinburne University in Melbourne Australia, investigating the control systems of UUV's - Unmanned Underwater Vehicles. He graduated from Swinburne with a Bachelor of Engineering (Robotics and Mechatronics) and a Bachelor of Science(Computer Science & Software Engineering)
His practical experience includes a year developing an industrial computer vision system from scratch, and working as the software architect for the 2004 Swinburne Robocup team (f180 league). | <urn:uuid:05036721-a8b1-40c9-bf20-1c8988b3009b> | 2.78125 | 1,592 | Documentation | Software Dev. | 35.696379 |
About 55 million years ago, in the Eocene, volcanic activity spewed enormous amounts of carbon dioxide into the air. The earth warmed by 4-5 degrees Centigrade. All surface ice melted, and every place on earth became tropical, even Antarctica. Sea levels rose a great deal and a significant amount of land was lost to the sea. It is estimated that sea levels rise some 10 to 20 meters (yards) for every 1 degree C increase in the average surface temperature, over the long term.
But along with all that dramatic change came something else. The seas absorbed a lot of the new carbon dioxide, creating carbonic acid. About 50% of some sorts of sea creatures did not survive the change.
The earth is repeating the experiment today, with human beings spewing out enormous amounts of carbon dioxide. And faster. Much faster indeed than in the Eocene.
Because of acidification and over-fishing, the world could lose a large number of ocean species just in the next 40 years or so. | <urn:uuid:84f205b1-ebac-4b78-9eb6-73c588532aab> | 3.671875 | 208 | Personal Blog | Science & Tech. | 51.37125 |
Dark matter’s tendrils revealed
July 5, 2012 | Source: Nature News
A “finger” of the Universe’s dark-matter skeleton, which ultimately dictates where galaxies form, has been observed for the first time.
Researchers have directly detected a slim bridge of dark matter joining two clusters of galaxies, using a technique that could eventually help astrophysicists to understand the structure of the Universe and identify what makes up the mysterious invisible substance known as dark matter.
The presence of dark matter is usually inferred by the way its strong gravity bends light travelling from distant galaxies that lie behind it — distorting their apparent shapes as seen by telescopes on Earth. But it is difficult to observe this “gravitational lensing” by dark matter in filaments because they contain relatively little mass.
By examining X-rays from plasma in a dark-matter filament, observed by the XMM-Newton spacecraft, the team calculated that no more than 9% of the filament’s mass could be made up of hot gas. The team’s computer simulations suggest that roughly another 10% of the mass could be due to visible stars and galaxies. The bulk, therefore, must be dark matter, says Dietrich.
Japan’s Astro-H X-ray space telescope, due to launch in 2014, will be able to characterize the ionization state and temperature of the plasma in the filament, which will help to discriminate between different models of how the structure formed.
Refining the technique could also help to pin down the identity of dark matter — whether it is a cold (slow-moving) particle or a warm (fast-moving) one, like a neutrino — because different particles will clump differently along the filament. The Euclid space mission, due to launch in 2019, will provide more lensing data. “This will complement direct dark-matter searches, for example at the Large Hadron Collider,” says Alexandre Refregier, a cosmologist at ETH Zurich, the Swiss Federal Institute of Technology in Zurich. | <urn:uuid:4109f2f8-90ad-4ee0-a7f7-bb14c9188045> | 3.15625 | 427 | Truncated | Science & Tech. | 31.141745 |
A computer system designed to analyse the motion of traffic has found a new role: tracking the movement of sperm to help in the treatment of male infertility.
Geoff Hobson developed the traffic tracking system while a professor at the University of Sheffield. He collaborated with Bill Holt of the Institute of Zoology in London to produce the Hobson Sperm Tracker which is now being sold by Hobson's Sheffield-based company, Sense and Vision Electronic Systems.
The sperm tracker can analyse live sperm via a video camera attached to a microscope, which is trained on a sample of semen. Alternatively, video recordings of sperm movement can be fed straight into the system's computer.
The sperms' motion is detected by comparing each frame of the video image with the previous one and registering the difference. The system displays the results as colour tracks superimposed over the microscope image. Information on eight aspects ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:48e6f785-2169-4461-afa5-a286cd68cff4> | 3.265625 | 206 | Truncated | Science & Tech. | 39.628673 |
Evolution by natural selection was an idea revealed to the world 150 years ago tomorrow, by two men, the famous Charles Darwin, and the not so famous Alfred Russel Wallace.
Wallace and Darwin both came up with biology's most important concept and their theory was presented to the Linnean Society in London on 1 July 1858.
The Natural History Museum is marking this anniversary with a small display of original objects that tell how Wallace and Darwin independently developed the same idea.
Original copies of the scientific article they presented in 1858 are on display, as well as objects such as a bird of paradise collected by Wallace and pigeon bones that were prepared by Darwin. The display shows the different ways these two men worked.
Scientists had been looking for an explanation of how and why there was such an amazing variety of life on Earth.
Alfred Russel Wallace
Wallace and Darwin explained this diversity through the idea that species evolve by a process called natural selection.
Natural selection is where the fittest individuals of a species are more likely to survive and reproduce and pass their advantageous characteristics to their offspring.
The idea of natural selection occurred to Wallace while he was suffering from a fever on a remote Indonesian island in February 1858.
Unknown to Wallace, Darwin had worked out the same theory about 20 years earlier, but hadn't published it yet.
In March 1858, Wallace sent his paper on natural selection to Darwin. Darwin's colleagues decided to present the two men's theory to a meeting of the Linnean Society on July 1st.
The society published Darwin and Wallace's ideas a month later and the theory of natural selection went on to change the way the world thought about biology. | <urn:uuid:c81655c9-91cb-4b0b-899d-13cd871cf728> | 4.125 | 346 | Knowledge Article | Science & Tech. | 38.498949 |
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Article looking at the effect of temperature on how fast a beer ages
A great article explaining the reactions that go on to give beer its colour.
How does pressure help get beer out of a keg? Find out in this article
A in-depth guide at what goes on in the brewing process to make your beer, from developing flavours to ensure the right amount of bubbles
This page from Marshall Brain's HowStuffWorks explains how widgets in beer cans work to create bubbles.
Article about beer made with barley grown in space.
Mathematicians analyse beer bubbles to peer deeper into the structure of materials
Beer was tested to see whether it would be safe to drink after experiencing radiation from a nuclear blast.
Researchers are looking at how sound bounces of bubbles in beer. This can tell them how the fluid is moving around the bubbles and has consequences for studying volcanic eruptions or monitoring food ...
Physicist Rik Sargent talks to Josh and Andy from Redemption Brewing who are experts in perfecting their real ale. They discuss how the sugar and alcohol affect the density of the beer and how to ...
Showing 11 - 20 of 41 | <urn:uuid:83b7b164-1971-4707-a3ca-faa2f730c2e0> | 3.1875 | 328 | Content Listing | Science & Tech. | 64.175685 |
|Dec31-12, 03:07 PM||#1|
ice crystal formation
I have a question regarding the following picture of a lattice of ice:
Why does it form the shape that it does? Is it because of the repulsion of charges from the valence electrons?
|Dec31-12, 03:42 PM||#2|
Ice crystal forms that shape due to hydrogen bonds and due to the shape and charge distribution in the water molecule. The shape of the water molecule is due, indeed, to the extra electrons in the valence shell of the oxygen atom.
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|question on crystal formation||General Physics||1| | <urn:uuid:1e03dc28-54f5-473f-b568-96dde64ae8e1> | 2.765625 | 196 | Comment Section | Science & Tech. | 50.540455 |
June 6, 2011
Astronaut James D. Halsell, Jr., mission commander, uses a Hi-8mm camcorder to videotape the Hand Held Diffusion Test Cells (HHDTC), in the Spacelab Science Module aboard the Earth-orbiting Space Shuttle Columbia. Each test cell has three chambers containing a protein solution, a buffer solution and a precipitant solution chamber. Using the liquid-liquid diffusion method, the different fluids are brought into contact but not mixed. Over a period of time, the fluids will diffuse into each other through the random motion of molecules. The gradual increase in concentration of the precipitant within the protein solution causes the proteins to crystallize.
Topics: Health Medical Pharma, Separation processes, Laboratory techniques, Phase changes, James D. Halsell, Spacelab, Space science, crystallization, Space Shuttle, Space Shuttle program, Protein | <urn:uuid:3a51a7cf-8d9e-4a98-9907-0aaa6ae31ad2> | 3.140625 | 183 | Truncated | Science & Tech. | 32.630938 |
Since they are typically observed hiding in dark crevices while opening and closing their mouths in an apparently menacing gesture, it isn’t surprising that moray eels get a bad reputation. The fact that their sharp teeth face backward (causing severe damage to anyone trying to pull their hand out of a moray’s mouth) doesn’t help this reputation, and neither does the recent discovery that morays have a second set of “Alien”-like jaws that drags prey deep into their mouth and throat. The truth isn’t quite so simple. Most people know very little about these amazing animals.
The green moray (pictured above) is the most famous member of this group, but there are more than 200 species in the family Muraenidae. Green morays are not even really green (a yellow mucus deposited on a dark body creates the illusion of green skin). Snyder’s morays are less than a foot long when full grown, while giant slender morays can reach lengths of over 10 feet. Morays live in an impressive variety of habitats, including temperate and tropical seas, depths of several hundred meters, and even freshwater. | <urn:uuid:b4f76ced-ff40-4095-8ff7-12cfb6e0bb9b> | 3.4375 | 244 | Knowledge Article | Science & Tech. | 47.36875 |
According to NASA probes orbiting Mars and amateur astronomers who are not, a large dust storm is developing on the Red Planet. Dust storms are regular features of the Martian climate, and sometimes they reach incredible size. Sometimes, in fact, they envelope the entire planet. The current storm is not presently threatening either NASA rover now operating, but if it envelopes the areas the rovers are exploring, it could hinder rover activity. Because the rovers get their power by collecting sunlight through solar panels significant amounts of dust in the air would cut the power available.
Such huge storms would obviously have an effect on human exploration and settlement of the planet. All equipment would need to be constantly monitored and regularly cleaned. The ideal solution would probably be to completely seal all equipment from the outside environment, but that might not be practical.
Of course, if the terraforming of Mars is successful, soil should some day hold dust to the ground. Huge dust storms would become only an occasional reminder of the planet's wild past. | <urn:uuid:6882d70e-0117-425d-9a56-714638857f94> | 3.859375 | 203 | Personal Blog | Science & Tech. | 38.310178 |
CodePy is a C metaprogramming toolkit for Python. It handles two aspects of metaprogramming:
Both capabilities are meant to be used together, but also work on their own. In particular, the code generation facilities work well in conjunction with PyCuda. Dynamic compilation and linking are so far only supported in Linux with the GNU toolchain.
This sample CodePy program builds a Boost.Python C++ module that returns the string “hello world”:
from cgen import * from codepy.bpl import BoostPythonModule mod = BoostPythonModule() mod.add_function( FunctionBody( FunctionDeclaration(Const(Pointer(Value("char", "greet"))), ), Block([Statement('return "hello world"')]) )) from codepy.toolchain import guess_toolchain cmod = mod.compile(guess_toolchain()) print cmod.greet()
You may notice that the above code snippet refers to Boost.Python. Boost.Python is a Python wrapper generator library for C++. CodePy does not depend on it being available, but its use is strongly encouraged–otherwise the generated sourcecode would need to use another wrapper generator or talk directly to the Python C API to make its functionality accessible from Python. Boost.Python is only used at run time. CodePy has no install-time dependencies
Instructions on how to install Boost.Python are available. As described in the instructions, CodePy looks for the installation location of Boost.Python in $HOME/.aksetup-defaults.py and /etc/aksetup-defaults.py.
Boost.Python is not needed at all if CodePy is used to generate code for PyCuda. | <urn:uuid:0be5af1d-4e3a-4bc5-b0a2-9b9dae021ba2> | 2.78125 | 362 | Documentation | Software Dev. | 40.976353 |
Monday, May 14, 2012 - 13:00 in Biology & Nature
A male robin will be more diligent in caring for its young if the eggs its mate lays are a brighter shade of blue.
- Color of robins' eggs determines parental careMon, 14 May 2012, 16:34:40 EDT
- Mate selection: How does she know he'll take care of the kids?Thu, 18 Jun 2009, 10:39:44 EDT
- Female lizard turns the table: Why exaggerated coloration makes her a good mateThu, 27 Jan 2011, 5:42:36 EST
- Better looking birds have more help at home with their chicksMon, 25 Jun 2012, 8:02:02 EDT
- Female fish abandoned by males to raise offspring on their ownMon, 20 Sep 2010, 10:52:25 EDT | <urn:uuid:173ca56c-62fd-4f77-a089-8b854b5bb398> | 2.828125 | 172 | Content Listing | Science & Tech. | 40.201774 |
We all know the sound well. All is peaceful, driving along in the car or sitting in a room listening to a speaker… and all the sudden “blip bzzzzz blaaaaar bzzzzzz”. Something starts buzzing. We all know why; there’s a mobile phone nearby. This noise has somehow become a part of our everyday lives but why does it happen?
If you were an early mobile phone user you might have noticed that they didn’t have the same effect – so it has to do with the GSM phones that we (mostly) use now. There are three things which need to happen together the cause the buzzing:
1. A pulsing radio transmitter
To connect to the tower and your network, your mobile phone sends out little bursts or pulses of information around 200 times per second (200 Hz). Each of the pulses have a frequency in the radio range, so the signals themselves oscillate millions of times per second – in the MHz range. So this is a ‘pulsing radio transmitter’.
2. Relatively strong power
Compared to original analog phones, newer mobile phones give out a stronger signal strength as they don’t give it out continuously – as I said above it is ‘pulsed’. For most GSM networks the peak power of the pulses is about 8 times the average power. So we have a relatively strong power source.
3. Close to a particular type of electronic element
The particular element in the circuit of a speaker which picks up the signal can vary, but it’s usually some solid state device like a diode or a transistor. When the strong pulsed radio signal is near it, the circuit element can detect the pulses and amplify, then send them to the speaker so we can hear the pulsed signal.
The pulses which are amplified come at 200 Hz, and since Middle C on the piano is 261.63 Hz, it is no surprise that we can hear it!
By now you’re probably wondering, given the title of this post: “Could I use my mobile phone as a particle accelerator??”
Particle accelerators use RF (radio frequency) waves to accelerate particles – similar to the ones that are used by your mobile phone. To give a particle some energy, you need a cavity – which is basically a hollow metal box.
When a wave of the right number of oscillations per second enters the cavity, it bounces back and forth within the cavity, with low loss. In physics we call this a standing wave. As more wave energy enters the cavity, it adds to the standing wave, creating a ‘resonance’.
What happens when we put a particle through the cavity? If we time it just right, the particle will always see a ‘peak’ of the wave and will gain a little bit of energy from it. If we didn’t time it right, the particle would lose energy to the wave and slow down. Fortunately, we’re very good at timing these things precisely!
|An LHC RF cavity which works at 400 MHz. Photo courtesy of CERN.|
The particle only gains a little bit of energy each time, so it’s useful if we have a circular accelerator where the particles go through the cavity again and again, gaining more energy each time. This is what happens in accelerators like the Diamond Light Source (using electrons) or ISIS (using protons), and even in the LHC. We can also use more than one cavity, the one in the picture has (I think) four cavities in one, and we can place them end-to-end. It’s a game of weighing up the cost of more cavities with how long your particles will take to accelerate.
So is it possible to just connect up a mobile phone to the cavity and accelerate particles? It would be great (and make my life as an accelerator physicist a lot easier!) but unfortunately it’s a question of power.
A mobile phone handset has a peak output power of about 2 Watts. The LHC cavities require a power of around 300 kW per cavity – so you would need the same power as 150,000 mobile phones!
So unfortunately, it looks like it isn’t going to happen any time soon. But in the meantime, I find it fascinating that the LHC and my mobile phone are, at least in some way, based on the same technology. | <urn:uuid:45c6515c-bdf3-4f97-a862-c89ddee6f3dc> | 3.375 | 931 | Personal Blog | Science & Tech. | 58.578128 |
loop in python
fredrik at pythonware.com
Tue Aug 23 12:31:03 CEST 2005
Steve Holden wrote:
> If you want a fast language, try Holden. I've just invented it.
> Unfortunately it gets the answer to every problem wrong unless the
> answer is 42, but boy it runs quickly. The code for the whole
> interpreter (it's written in Python) follows:
> print 42
> Why are you looking for a "fast language" without any regard for the
> kind of problems you actually want (or need) to solve?
isn't measuring speed by timing for-loops a 70's thing? I remember doing that
back when I used Z80 BASIC machines (on a 3.58 MHz machine using floating
point variables, each iteration took almost exactly 1 millisecond).
I also remember that the compiler for my first custom language for that machine
contained exactly one optimization: empty loops were replaced with plain assign-
ments. everyone was mightly impressed.
(for another view of Python's performance, see John Walker's floating point
from what I can tell, Python's the fastest interpreter in that test...)
More information about the Python-list | <urn:uuid:c5d793ec-5963-4fde-917f-30f7063e2eab> | 2.71875 | 256 | Comment Section | Software Dev. | 63.611795 |
Until just a few years ago, scientists were unsure why the global energy budget seemed to indicate that an enormous amount of energy couldn’t be accounted for. Incoming and outgoing radiation is fairly straightforward to measure and a simple energy budget is easy to calculate. Accounting for all of the movement of energy within Earth’s climate system imposes a great deal of complexity into the process. Still, numerous attempts were made to try to track down what was growing into a very large amount of energy: was it erroneous measurements or calculations, or did we remain woefully ignorant of significant physical processes?
Then in 2009, two major papers were published that closed the majority of the unaccounted for energy in the climate system. The excess energy was being stored as heat in the ocean, specifically the deep ocean. The volume of the Earth’s oceans is estimated to be 1.332×109 km3. That is obviously a very large volume within which energy can be stored. What has happened over the course of the past century or so is warmer and warmer water has been forced down to the bottom of the world’s oceans. Usually, warm water rises, but the water in question is just above the freezing point of fresh water. At those temperatures, salinity has an increased role in controlling density. Water sinks when sea ice forms because sea ice is made up of only pure water, leaving excess salt in the remaining ocean water. As the salinity increases, the density also increases. Water with higher density than what is surrounding it sinks and then is transported by ocean currents around the world.
It might surprise you to learn that ocean currents can take decades to centuries to complete one cycle around the entire globe. That means that water that was warmed decades ago is now coming back to the places where it originally picked up that warmth. In this case, water is upwelling off the Antarctic peninsula and it is having a very real physical effect on the region. While localized now, that effect will soon cause additional effects across the globe.
One of the 2009 studies had this graph, showing where the excess energy was being stored:
Total Earth Heat Content from 1950 to 2003 (Murphy 2009).
This graph is troubling for a number of reasons. One of the first things to notice is the land and atmosphere haven’t warmed up all that much, since 1950, compared to the ocean. Next, it should be startlingly clear that a great deal of energy wasn’t being properly accounted. Third, if the ocean really is holding all this heat, shouldn’t someone have noticed before last year? Indeed, a number of scientists speculated that the sea level rise recorded in the past 100 years was likely due to this phenomenon occurring. Scientists being the careful people they are didn’t make pronouncements that they knew this was going on because … they didn’t have empirical proof of it.
By now, I hope a couple of things I’ve written about in this piece are starting to come together. The ocean upwelling off the coast of Antarctica is carrying some of the energy it absorbed decades ago. The heat anomaly of the ocean has only increased since then. What might this mean in the future? Well, let’s start answering that by looking at what this means in the present. Here is a graphic put together by Douglas Martinson, a polar scientist at the Lamont-Doherty Earth Observatory who gave a talk at this year’s American Geophysical Union meeting.
The warm upwelled water is being transported around the Antarctic continent by the Antarctic Circumpolar Current, as you can see on the right side of the graphic. Over the past 18 years, Martinson and his colleagues have measured the physical properties of the ocean around Antarctica and came to the startling conclusion that the majority of the heat anomalies they have measured have occurred since 1960. Unfortunately, those anomalies have been growing exponentially ever since. While the rise was tiny at first, exponential growth for 50 years means that now ocean water is a few degrees above freezing. This warm water is coming up and running into ice sheets that are slowly being discharged from the Antarctic interior. Not only do the ice sheets have to contend with anomalously warm air temperatures from above, they also are facing warm water temperatures from below. And since water holds much more energy than air per unit volume, the warmer waters rising from the ocean depths will have a much greater impact, much sooner, on the ice sheets than the warmer air will.
Okay, so what about the future?
As for how fast the ice will melt and in what locations, that depends largely on whether the upwelling warm water comes in contact with the thick ice shelf that crowds the coast and holds the block the glaciers from reaching the sea.
That, in turn, depends on the winds which drive away the surface waters and make it possible for the deeper waters to rise to the surface, said senior researcher Robert Bindschadler of NASA’s Goddard Earth Science and Technology Center and the University of Maryland-Baltimore County.
Now that the upwelling deep sea water is the clear cause of the melting ice shelf, rather than summer melt water, as had been thought in the past, it’s a question of how winds will change in a warming world and whether they will drive more warm water into the ice shelves.
For a short while longer, large-scale effects will remain muted. Warmer waters will likely attack the ice shelves, but since the shelves’ ends are already floating in the ocean, this won’t affect global sea levels. If the ice shelves are melted all the way back to their grounding zones on the Antarctic continent, then larger problems are at hand. If the land-based ice sheets flow toward the ocean faster and faster, and if they come into contact with warmer ocean water, their melting will cause much faster global sea level rise.
As far as the 21st century is concerned, the West Antarctic Ice Sheet (WAIS) is less stable than the Greenland ice sheet. Why? Because its grounding line is actually below sea level. Imagine if the U.S. gulf coast was much colder than it is today, cold enough for ice sheets to be piled up on it. The WAIS is like a hypothetical ice sheet sitting on the New Orleans area. The real-world difference is the WAIS rests on bedrock that is an amazing 2km below sea level! That bedrock is further below sea level than Denver, CO is above it. If warm water ever gets to this area, a vicious cycle will begin. That cycle wouldn’t stop until most or all of the WAIS melted, which could raise global sea levels by 10ft. Moreover, the bedrock also slopes downward inland.
Now I want to tie a number of points raised all together. The WAIS is an unstable ice sheet. Outflow ice shelves extend into the oceans of the Southern Hemisphere. Water is rising from the bottom of those oceans that is warmer than the water already there. If predominant wind currents cause additional warm water to rise faster, the ice shelves floating in the oceans will melt from below. They will melt faster than climate model projections made over the past 20 years have indicated because of the relative lack of understanding of polar weather and climate.
I want to ask you to recall the first graph in this post, the one that shows an increasing amount of heat energy that has been stored in the world’s oceans since 1950. All that anomalous warmth hasn’t had a chance to be transported to the Antarctic yet. Therein lies the scary part to this: Antarctica faces decades of increasingly warm waters rising off its shores. That would be true if we stopped all of our greenhouse forcing tomorrow. We won’t, of course, which means the Antarctic ice sheets face more and more of a threat every year. The world at the end of the 21st century will look quite different than it did at the end of the 20th. How different is up to us.
Cross-posted at SquareState. | <urn:uuid:78363339-5d50-4999-acea-1092055b8700> | 4.125 | 1,643 | Personal Blog | Science & Tech. | 53.239283 |
From Wikipedia, the free encyclopedia
Phononic stop bands are formed for materials with periodic elastic properties. The material does not need to be a crystal.
The basis of phononic crystals dates back to Newton who imagined that sound waves propagated through air in the same way that an elastic wave would propagate along a lattice of point masses connected by springs with an elastic force constant E. This force constant is identical to the modulus of the material. Of course with phononic crystals of materials with differing modulus the calculations are a little more complicated than this simple model.
Based on Newton’s observation we can conclude that a key factor for acoustic band-gap engineering is impedance mismatch between periodic elements comprising the crystal and the surrounding medium. When an advancing wave-front meets a material with very high impedance it will tend to increase its phase velocity through that medium. Likewise, when the advancing wave-front meets a low impedance medium it will slow down. We can exploit this concept with periodic (and handcrafted) arrangements of impedance mismatched elements to affect acoustic waves in the crystal – essentially band-gap engineering.
The position of the band-gap in frequency space for a phononic crystal is controlled by the size and arrangement of the elements comprising the crystal. The width of the band gap is generally related to the difference in the speed of sound (due to impedance differences) through the materials that comprise the composite.
- "Sound ideas". Physics World (2005-12-01). Retrieved on 2008-01-19.
- G.P Srivastava (1990). The Physics of Phonons, CRC Press. ISBN 0852741537. | <urn:uuid:a316a9eb-c552-4bf5-bd7c-5104f22b5f26> | 3.78125 | 338 | Knowledge Article | Science & Tech. | 44.343333 |
Another global issue that has attracted much popular and scientific interest in
recent years is tropical earth, and few processes are likely to have more
dramatic evidence of our ability to transform the face of the earth, and few
processes are likely to have more profound biological consequences. Humans have
been altering and removing the earth’s forest cover for millennia, but nothing
in that long history matches the current pace of forest destruction in the humid
The great blocks of forest that straddle the equator in the Americas, Africa,
and the Asiatic tropics are the most complex and exuberant expression of the
earth’s green mantle. Although they include many different forest formations, it
is possible to divide them into two broad categories; tropical rain forest of
the ever wet tropics and tropical seasonal forest of the seasonally dry tropics.
The sum of the two categories is now generally called tropical moist forest.
Although they clothe only some five per sent of the land surface tropical most
forest are believed species of organisms. That we posses only a very incomplete
inventory of life on the earth reflects in large part how little we know about
tropical forests. Much will remain for eve unknown, because each year a vast
area of forest is converted to other uses. As the forest vanish as, quite
literally, they go up in smoke so too do countless spices of organisms. Current
trends threaten to expunge much of the remarkable cornucopia of tropical life.
The process is irreversible extinction is for ever. | <urn:uuid:360e205f-9b90-42b2-9ada-3ef0123b04ef> | 3.71875 | 322 | Truncated | Science & Tech. | 29.983741 |
Seed dispersal mchanisms
remove.this.ecology at ozemail.com.au
Tue Jul 11 18:38:46 EST 2000
I am working with the native Australian tree species Cadellia pentastylis an
obscure species (and a monotypic genus) belonging to the family Surianaceae.
My question relates to seed dispersal mechanisms and whether the strategy
employed by this species is at all unique.
The small fruits of C. pentastylis remain attached to woody sepals which
swell and twist following pollination and seed maturation. The sepals
enhance seed dispersal as they maintain good bouyancy in the air rotating
like the rotor blades of a helicopter.
Typically plant seeds or fruits themselves develop membranes or wings to aid
dispersal. Is this unusual for sepals to be used in this way? Are there
examples of co-evolution from other continents?
More information about the Plantbio | <urn:uuid:32039f66-377e-43b3-9f8c-39a10efb3f4f> | 3.5 | 209 | Q&A Forum | Science & Tech. | 46.571442 |
||TNC's Need for Ecoregional Planning Tools
Applications of Sites revised
October 11, 2001
Related Online Resources revised
October 11, 2001
The Nature Conservancy (TNC) recently
initiated a new program of ecoregion-based conservation. The goal of this
effort is to assemble regional portfolios of conservation lands that collectively
represent viable examples of all native species and plant communities.
This program aims to increase the efficiency and effectiveness of TNC's
conservation activities through a systematic approach to regional portfolio
assembly coupled to local, on-the-ground implementation.
The initial steps in ecoregional conservation planning involve identifying
an explicit conservation goal, selecting a set of target elements (i.e.,
species and communities), identifying levels of representation for each
target, and then identifying a potential portfolio of sites. In many ecoregions
where TNC works, there are hundreds of target elements to consider, as
well as a variable number of potential conservation sites, each of which
may differ in quality or suitability. To prioritize among potential conservation
sites as the portfolio is assembled, often a hierarchical set of decision
rules is applied. For each ecoregion where TNC works, the general process
of portfolio assembly wll be similar, but the specific combination of goals,
targets, sites, and decision rules likely will be unique.
TNC's Need for Ecoregional Planning
Given the large number of species, communities and potential sites in
many ecoregions, without the aid of computer automation, it is virtually
impossible for conservation planners to evaluate all possible alternative
portfolios that potentially could meet a stated conservation goal. Computer
automation also is needed because the portfolio assembly process is iterative,
and once an initial portfolio is identified, there is an ongoing need to
revise that portfolio. For example, the potential portfolio might change
as a result of revisions to TNC's conservation goal for that ecoregion,
or as a result of new data (e.g., for sites or elements not previously
surveyed; or when the status of an element or site changes because of ownership
changes). Without the aid of computer-based decision rules, it is difficult
to develop an iterative portfolio assembly process that is repeatable,
and the process of reviewing alternative site combinations can be labor
intensive as well as unnecessarily slow. In the last decade, a variety
of computer-based algorithms and analytical approaches for reserve siting
has been developed, however, at the time this project was initiated, these
remained primarily research tools. Based on discussions with various TNC
staff involved with ecoregional planning efforts, in their current form,
none of the existing approaches was well-suited to TNC's planning needs.
From TNC's perspective, the major limitations of current tools fell into
three general categories: those that require high end computing power,
specialized software, and/or a high level of GIS technical expertise (e.g.,
Church et. al. 1996); those with insufficient documentation and/or
inadequate testing of computer code; or those with overly simplistic decision
rules (e.g., "greedy" or rarity-based heuristics).
The following research and development effort for TNC was conducted:
Develop Sites 1.0, with an easy-to-use graphical interface in ArcView to
select and display alternative portfolio solutions.
Adapt the SPEXAN software for selecting reserve sites (written by Ian Ball
and Hugh Possingham of the University of Adelaide in Australia) to accommodate
TNC's portfolio design methodology. The version used in Sites, called
the Site Selection Module, like SPEXAN, explicitly incorporates spatial
design criteria into the site selection process.
Test and apply the planning approach in a structured decision process involving
local TNC staff to develop hypothetical conservation portfolios in two
different ecoregions (Idaho Batholith and the Northern Sierra Nevada).
Produce a web-based tutorial, including a worked example using TNC data
and ecoregions; and conduct a training workshop for TNC staff interested
in learning and applying the regional conservation planning tools to other
Applications of Sites 1.0
The following planning studies that have used Sites 1.0 have been presented
at conferences or published in the peer-reviewed literature (as of October
Sites for Endangered Species Conservation along the Santa Clara River
(large pdf file)
Conservation portfolio for the Middle Rocky Mountains - Blue Mountains
Ecoregion (abstract of poster presented by TNC planning team at the
2000 Society for Conservation Biology conference)
large-scale conservation evaluation and conservation area selection using
a knowledge-based system (paper presented at GIS/EM4 in 2000 by Patrick
Bourgeron of University of Colorado)
Conservation Efforts in the Sierra Nevada Ecoregion. Paper presented
by Bo Wilmer at the 2001 ESRI User
Ecoregions and species assemblages: testing indicators for identifying
areas of conservation concern. Paper presented by Josh
Lawler at the 16th Annual Symposium of the U.S. Chapter of International
Association of Landscape Ecology, Tempe, Arizona, April 2001.
Leslie, Heather, Mary Ruckelshaus,
Ian R. Ball, Sandy Andelman, and Hugh P. Possingham. Using siting algorithms
in the design of marine reserve networks. In press. Ecological Applications.
Beck, M. W. and M. Odaya. 2001. Ecoregional planning in marine
environments: Identifying priority sites for conservation in the northern
Gulf of Mexico. Aquatic Conservation 11: 235-242.
Related Online Resources
These web sites provide further background on the simulated annealing approach
to reserve selection (as of October 11, 2001):
of SPEXAN--home page with descriptions, history, and more publications.
methods for identifying representative reserve networks (pdf file of
a book chapter by Hugh Possingham et al. 2000 that describes simulated
annealing process and spatial design features used in Sites). | <urn:uuid:78775954-50cb-473d-82c3-892ea8d2b116> | 2.703125 | 1,297 | Academic Writing | Science & Tech. | 23.126346 |
Earth's major terrestrial, marine, and freshwater ecosystems are known as biomes. They are classified according to similarities in species composition of plants and animals, and by environmental attributes. These attributes include temperature, precipitation, and soil type in terrestrial biomes and temperature, depth, and salinity in aquatic biomes. There are no hard boundaries between biomes and there is much intermixing of species between them.
Biomes are divided into many kinds of ecosystems and habitats, according to local variations in species composition and physical environment (a cloud forest, mud flat, and meadow, to name a few). However, scientists generally recognize between twelve and fifteen major natural terrestrial biomes, including tropical rain forest, tropical deciduous forest, thorn woodland, tropical savanna , desert, sclerophyllous woodland, subtropical evergreen forest, temperate deciduous forest, temperate rain forest, temperate grassland, boreal forest, and tundra. Some scientists consider cultivated land to be a biome. There are seven major freshwater biomes: ice, spring, river, swamp, marsh, lake, and stream. There are six major marine biomes: coral reef; algal bed; estuary; upwelling zone; continental shelf ; and open ocean.
Significant changes in the global environment and climate are causing major shifts in some biomes, such as glacier movement and polar cap melting, and are threatening the survival of others, such as the deforestation of tropical and temperate rain forests.
Cristina G. Mittermeier and Russell A. Mittermeier
Brown, James H. and M. V. Lomolino. Biogeography, 2nd ed. Sunderland, MA: Sinauer Associates, Inc., 1998. | <urn:uuid:b3c3a25d-1b3e-4a5f-bafa-a7dc94f5552a> | 3.953125 | 360 | Knowledge Article | Science & Tech. | 21.993947 |
image credit: William W Nazaroff (2005); image source; larger image
The Geothermal Power Plant
The above photo shows the Nesjavellir geothermal plant in Iceland, which produces power and hot water for the towns surrounding it. To learn more about how the plant works, see this site from the University of Rochester.
Iceland sits astride the mid-Atlantic ridge, where two tectonic plates are moving apart at about two and a half centimeters per year. Magma--molten rock--wells up in between the plates and heats the bedrock under Iceland. The bedrock heats the groundwater that the plant pipes to the surface to make a mixture of steam and brine (salt water).
For more on tectonic plates and Iceland, including a volcanic island nearby that was formed in 1963, see Physics to Go, Issue 55.
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U.S. Department of Energy: Energy Efficiency & Renewable Energy
Beyond the search for renewable energy sources, a complementary approach is to save energy by using it more efficiently. See this California state government website to find out how changes to your home and your lifestyle can help. To learn more, visit U.S. Department of Energy: Energy Efficiency & Renewable Energy and click on the links under "Renewable Energy" and "Energy Efficiency" on the right. | <urn:uuid:68a8ff1d-96c4-4fbd-9fc3-aa21a17567dd> | 3.8125 | 283 | Knowledge Article | Science & Tech. | 41.483548 |
Hadley Crater Perspective View
About this Image
This computer-generated perspective view of Hadley Crater was created using data obtained from the High-Resolution Stereo Camera (HRSC) on ESA’s Mars Express. Centred at around 19°S and 157°E, this image has a ground resolution of about 19 m per pixel. The ejecta blanket emanating from the deep crater in the middle of the image shows evidence for volatiles, possibly water ice, while the main crater rim to the top (south) of the image shows evidence for so-called “mass wasting”. This is a geomorphic process by which surface materials can move down a slope under the force of gravity. In this case, this process made the southern side of the crater shallower than its northern counterpart. This photo was taken on September 5, 2012.
Credit: ESA/DLR/FU Berlin (G. Neukum) | <urn:uuid:d41119dc-ecb1-4ad3-aa76-578d8e407fed> | 3.828125 | 194 | Truncated | Science & Tech. | 48.255245 |
From the shiny, strong nacre that gives abalone shells an unbreakable, opaline sheen, to the goopy mix of proteins fired by a velvet worm that solidify and trap prey upon impact, nature is packed with inspiration for scientists designing new materials.
Waterproof adhesives and self-cleaning s... Read More
We continue our series of images that have made a difference in microbiology. This one, published by John Cairns in 1963 has earned a most deserved place in textbooks and reviews. It shows a radioautograph of an intact E. coli chromosome in the act of replicating. From this image, Cairns conclud... Read More
A relatively straightforward classroom experiment produces fascinating images by students at the University of Surrey when they imprinted their smartphone onto a bacterial growth medium. Read More
Echinococcus granulosus is a tapeworm parasite that in its larval form can cause hydatid disease, which is characterized by cysts forming within the victim's body. In order to complete its lifecycle, the tapeworm must infect two hosts, a carnivore and a herbivore.
The adult form of Echinococc... Read More
Scanning electron micrograph of HIV particles infecting a human T cell. Credit: NIAID, NIH Read More
Olympus Bioscapes, Honorable Mention, Dr. Petr Znachor, Laboratory of Phytoplankton Ecology, Institute of Hydrobiology,Ceske Budejovice, Czech Republic.
Specimen: Cyanobacterium Anabaena planctonica, Technique: Nomarski contrast, 20x Objective Read More
Marine bioluminescent Photobacterium kishitanii
The genus Photobacterium was first coined by Martin Beijerinck, in 1889, and originally referred to all bacteria capable of light production. Species belonging to Photobacterium are gram negative, rod shaped, chemoorganotrophic, facultative aerob... Read More
Achnanthes longipes (a diatom, Bacillariophyta) (1000x)
Nikon Small World 2012 PHOTOMICROGRAPHY COMPETITION, IMAGE OF DISTINCTION, Dr. Victor Chepurnov, De Water Architect, Ghent, Belgium Read More
Nikon Small World 2012 PHOTOMICROGRAPHY COMPETITION, IMAGE OF DISTINCTION, Wim van Egmond, Micropolitan Museum, Rotterdam, The Netherlands.
Nassula ornata, conjugating ciliates Read More
Nikon Small World 2012 PHOTOMICROGRAPHY COMPETITION, IMAGE OF DISTINCTION, Rogelio Moreno Gill
Euplotes belongs to the class Nassophorea in the phylum Ciliophora; the ciliates, of which there are approximately 8,000 species, are generally considered to be the most evolved and complex of the p... Read More
I am just submitting this as a test submission so that I know how the whole process functions.
Image taken at Pashupathinah Temple in Kathmandu Nepal using a Nikon PS510 Read More
Living green alga Euglena mutabilis. Technique: Differential interference contrast. Credit: Gerd Gunther, Düsseldorf, Germany
Nikon Small World 2012 Honorable Mention. Read More
I comment a bit, as an educator, about the loss of Carl Woese. Not only the importance of his discoveries, but how he went about his work, remains of great value. Read More
A quick demonstration of how my Microbial Mania can impact the holiday season! Read More
Red algae Scagelia, showing reproductive tetraspores and golden diatoms. 2nd place winner of Olympus BioScapes photomicrography contest 2012.
Credit: Dr. Arlene Wechezak, Anacortes, Washington Read More
The winners of Olympus' annual live sciences photography competition are in, with the top 10 submissions revealing an entire world of microscopic wonder.
It's the 10th year of Olympus' BioScapes international digital-imaging competition — where photographers from around the globe can send in ... Read More
Genus Serratia presents special problems of identification because of biochemical and morphological similarity to other genera of the Enterobacteriaceae, notably Klebsiella and Enterobacter. Serratia liquefaciens is an opportunistic pathogen which is capable of colonizing a wide variety of surfa... Read More
please send input as to the nature of this. things I know: zoonotic, fast reproduction, fruiting bodies, possible yeast, cryptococcus? Dicty?some maturing cysts filled with red, one-two red dots. Read More | <urn:uuid:885c5ee6-76d7-4055-b899-d6771913dab1> | 2.75 | 1,020 | Content Listing | Science & Tech. | 25.015996 |
One of the most important features of this universal object is it’s ability to display not only a static text, but expressions as well. Expressions can be located in the object together with text. Let us examine a simple example of how it can be performed. Put the following line into the object:
Hello, World! Today is [DATE].
Thus, when running the report, we can get something like follows:
Hello, World! Today is 01.01.2004.
What lead to such result? During FastReport report building, if an expression enclosed in square brackets is encountered, the engine calculates it’s value and inserts the value into the text (in place of the expression). The “Text” object can contain any number of expressions, together with a usual text. Both single variables and expressions can be enclosed in brackets (for example, [1+2*(3+4)]). Any constants, variables, functions, and DB fields can be used in expressions. We will learn more about these features later, in the chapter.
FastReport automatically recognizes expressions enclosed in square brackets in the text. But what should be done if our object contains square brackets, and we do not want them to be considered as expressions? For example, if we need to display such text as following:
a := 10
FastReport considers as an expression, and displays the following:
a1 := 10
that is not what we want, of course. One of the ways to avoid such a situation is to disable the expression. Just disable the “AllowExpressions” property (“Allow Expressions” in the context menu), therefore all the expressions in the text will be ignored. In our example, FastReport would then display exactly what we need:
a := 10
Sometimes text is required to contain both an expression and a text in square brackets, for example:
a := [myVar]
Disabling of an expression allows us to display square brackets in the required place, but it also disables handling of expression. In this case, FastReport allows you to use another set of symbols to designate the expression. The “ExpressionDelimiters” property, which is equal to “[,]” by default, is responsible for it. In this case, the user can use angular brackets for the expressions, instead of square ones:
a := <myVar>
The “<,>” value must be set in the “ExpressionDelimiters” property. As you can see, the comma divides opening and closing symbols. There is one limitation however: the opening and closing symbols cannot be similar, so “%,%” will not work. One can set several symbols, for example “<%,%>” Thus, our example will look as follows:
a := <%myVar%> | <urn:uuid:a8573f72-ea97-4dab-8883-7ed07f83046d> | 2.765625 | 603 | Documentation | Software Dev. | 49.343278 |
ucleic acid precipitation - why alchohol and low temperature (Jan/29/2002 )
Would anyone out there be able to tell as to why alchohols like isopropanol or ethanol are used to precipitate nucleic acids, and also, why is the precipitation done at low temperatures
Precipitation is probably easier at lower temperatures because of less Brownian motion of the molecules?
I think DNA is not soluble in alcohol because this kind of substance cannot shield the high charge of phosphate groups of the backbone. Water, a molecule that is more polar and has good capacity of shielding charged or polar groups, is more efficient to do that. When you increased the alcohol concentration in water, the DNA becomes progressively less shielded and eventually, precipitate. A good point to note here is that by adding salt, you accentuate a lot this effect (salt ions sequester water molecules wich become less available to solubilize DNA).
For the temperature, it is simply because it reduce the solubility (in general) of dissolved substances. So, it helps to precipitate things (DNA, and unfortunately, salts...). Someone else has given a more in-depht point of view for this explanation.
Regarding temperature dependence of solubility it depends on whether it is endo- or egzotemic process. In the former case, solubility incrises with temperature.
ok i remember something about...
DNA is soluble in water because the water molecules intercalate into the phosphate backbone of the DNA and thus maintain it in a soluble state. When you add salt and alcohol you are essentially removing the water molecules and teh DNA then precipitates. | <urn:uuid:632e0d1e-f2ef-4aa6-ac6d-173ea103afa0> | 2.734375 | 347 | Comment Section | Science & Tech. | 28.673325 |