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The IRAS Asteroid and Comet Survey is the largest, most uniform
and least biased survey ever conducted of asteroids and comets.
Because the emission observed is thermal, the present survey is not
plagued by the albedo bias to which visible wavelength analogues are
susceptible. Asteroids and comets are bright infrared sources,
particularly at 25 microns.
The IRAS hours and weeks-confirmation strategy was developed to discriminate against moving sources. However, to provide data for the study of the properties of known and newly-discovered asteroids, all sources with infrared colors typical of Solar system objects were recorded in auxiliary files at both seconds and hours-confirmation, with an emphasis on completeness.
In addition to data for 25 comets and 1811 known asteroids, a search for sources moving across the sky more rapidly than about 1' per hour resulted in the discovery of six new comets, an extensive cometary debris trail, and two Apollo asteroids, one of which may be an extinct cometary nucleus. Asteroids and comets moving more slowly than 1' per hour would hours-confirm and thus reside in the Working Survey Database.
Thirteen Asteroid and Comet data products were generated, of which four - the IRAS Asteroid Catalog, the Asteroid Statistics Catalog, the Low-Resolution Spectrometer Spectra of Selected Asteroids, and the IRAS Comet Catalog - are bound together with the Asteroid and Comet Explanatory Supplement and a User's Guide to the data products (see reference). The complete set of data products is listed in Table 8-1 of that volume. The NSSDC holds seven data products:
This catalog is available on the ADC Selected Astronomical Catalogs, Volume 2 CD-ROM and via the ADC FTP server. Supplementary asteroid data are provided in the Minor Planet Survey Database.
Version and release date: 1.0, 1986 Oct | <urn:uuid:15c8dc73-3a3d-46bf-b908-0a631c767eff> | 2.859375 | 393 | Knowledge Article | Science & Tech. | 27.895568 |
XSL Transformation is widly known tecnique for converting XML files to XHTML output. XSLT is designed for use as part of XSL, which is a stylesheet language for XML. XSL specifies the styling of an XML document by using XSLT to describe how the document is transformed into another XML document that uses the formatting vocabulary.
Here is sample XML document that will be used further.
Here is sample XSL Transformation
By using following sample c# code we can effectivly load xml document, and transform it's content into xhtml by using given xslt transformation:
Now since we know how to transform xml data with xsl stylesheet and produce valid html code, we can continue with introducing XSL Extension Objects.
Extension objects are used to extend the functionality of style sheets. Extension objects are maintained by the XsltArgumentList class.
The following are advantages to using an extension object rather than embedded script:
XSLT extension objects are added to the XsltArgumentList object using the AddExtensionObject method. A qualified name and namespace URI are associated with the extension object at that time. In this example we are using ResourceReader object
Let's add this object to XsltArgumentList so we can use latter in xsl transformation for reading string values from resources
And modified xslt stylesheet will look like this
And the rest is history. Cheers! | <urn:uuid:9dd63720-3113-43f3-a282-dd19dde081bf> | 3.15625 | 298 | Documentation | Software Dev. | 42.855491 |
Mission Type: Lander, Orbiter
Launch Vehicle: Proton booster plus upper stage and escape stages; 8K82K + Blok D (Proton-K no. 255-01)
Launch Site: Tyuratam (Baikonur Cosmodrome), USSR; NIIP-5 / launch site 81P
Spacecraft Mass: Orbiter/bus and descent module: about 4650 kg at launch (orbiter/bus: 3440 kg, descent module/lander: 1210 kg)
Spacecraft Instruments: Orbiter: 1) three-component magnetometer; 2) infrared radiometer; 3) radiotelescope; 4) infrared photometer/CO2 absorption strips; 5) ultraviolet photometer; 6) imaging system (two cameras); 7) photometer in visible part of electromagnetic spectrum; 8) cosmic-ray particle detector; 9) energy spectrometer; 10) spectrometer to determine water vapor; and 11) Stereo antenna
Lander: 1) gamma-ray spectrometer; 2) x-ray spectrometer; 3) thermometer; 4) wind velocity recorder; 5) barometer; 6) imaging system (two cameras); 7) penetrometer (on mobile PROP-M); and 8) gamma-ray densitometer (on PROP-M)
Spacecraft Dimensions: Combined orbiter/bus and descent module: 4.1 m high, 5.9 m across the 2 solar-panel wings, and a base diameter of 2 m. Landing capsule: spherical with a diameter of 1.2 m.
Spacecraft Power: Orbiter/bus: 2 solar panels; Lander: batteries (charged by the orbiter/bus prior to separation)
Antenna Diameter: 2.5 m (high-gain antenna)
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi
National Space Science Data Center, http://nssdc.gsfc.nasa.gov/
Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.
Mars 2 was the first of two orbiter-lander-combination spacecraft sent to Mars by the Soviets during the 1971 launch window. The orbiters were roughly cylindrical structures fixed to a large propellant-tank base. The landers were egg-shaped modules with petals that would open on the Martian surface. The 1,000-kilogram landers (of which about 350 kilograms was the actual capsule) were fastened to the top of the bus and protected by a braking shell for entry into the Martian atmosphere. After jettisoning the shell, the landers would deploy parachutes to descend to the Martian surface.
On the Mars 2 trip to the Red Planet, controllers performed two successful midcourse corrections on 17 June and 20 November 1971, respectively. On 27 November 1971, Mars 2 implemented its final midcourse correction, after which the lander probe separated to initiate atmospheric entry. At this point, the onboard computer was designed to implement final corrections to the trajectory, spin the lander around its longitudinal axis, and fire a solid-propellant engine to initiate reentry in a specific direction.
During the flight, after the final midcourse correction, the trajectory of the spacecraft was so accurate that there was no need for further corrective measures. Because of pre-programmed algorithms that assumed a deviated trajectory, the lander was put into an incorrect attitude after separation to compensate for the "error." When the reentry engine fired, the angle of entry proved to be far too steep. The parachute system never deployed, and the lander eventually crashed onto the Martian surface at 4? north latitude and 47? west longitude. It was the first human-made object to make contact with Mars.
Meanwhile, the Mars 2 orbiter successfully entered orbit around Mars at 20:19 UT on 27 November 1971. Parameters were 1,380 x 25,000 kilometers at 48.9? inclination.
The Mars 2 and 3 orbiters sent back a large volume of data covering the period from December 1971 to March 1972, although transmissions continued through August. It was announced that Mars 2 and 3 had completed their missions by 22 August 1972, after 362 orbits completed by Mars 2 and 20 orbits by Mars 3.
The Mars 2 and 3 probes sent back a total of 60 pictures. The images and data revealed mountains as high as 22 km, atomic hydrogen and oxygen in the upper atmosphere, surface temperatures ranging from -110 ?C to +13 ?C, surface pressures of 5.5 to 6 mb, water vapor concentrations 5000 times less than in Earth's atmosphere, the base of the ionosphere starting at 80 to 110 km altitude, and grains from dust storms as high as 7 km in the atmosphere. The data enabled creation of surface relief maps, and gave information on the Martian gravity and magnetic fields. | <urn:uuid:d24666e5-cf4e-4c2a-a7ed-3e39b607f34f> | 3.15625 | 1,027 | Knowledge Article | Science & Tech. | 50.848701 |
Programs which give users access to privileges of any sort need to be able to authenticate the users. When you log into a system, you provide your name and password, and the login process uses those to authenticate the login -- to verify that you are who you say you are. Other forms of authentication than passwords are possible, and it is possible for the passwords to be stored in different ways.
PAM, which stands for ``Pluggable Authentication Modules'', is a way of allowing the system administrator to set authentication policy without having to recompile programs which do authentication. With PAM, you control how the modules are plugged into the programs by editing a configuration file.
Most Red Hat Linux users will never need to touch this configuration file. When you use RPM to install programs that need to do authentication, they automatically make the changes that are needed to do normal password authentication. However, you may want to customize your configuration, in which case you need to understand the configuration file.
There are four types of modules defined by the PAM standard. auth modules provide the actual authentication, perhaps asking for and checking a password, and set ``credentials'' such as group membership or kerberos ``tickets''. account modules check to make sure that the authentication is allowed (the account has not expired, the user is allowed to log in at this time of day, etc.). password modules are used to set passwords. session modules are used once a user has been authenticated to make it possible for them to use their account, perhaps mounting the user's home directory or making their mailbox available.
These modules may be stacked, so that multiple modules are used. For instance, rlogin normally makes use of at least two authentication methods: if ``rhosts'' authentication succeeds, it is sufficient to allow the connection; if it fails, then standard password authentication is done.
New modules can be added at any time, and PAM-aware applications can then be made to use them. For instance, if you have a one-time-password calculator system, and you can write a module to support it (documentation on writing modules is included with the system), PAM-aware programs can use the new module and work with the new one-time-password calculators without being recompiled or otherwise modified in any way.
Each program which uses PAM defines its own ``service'' name. The login program defines the service type login, ftpd defines the service type ftp, etc. In general, the service type is the name of the program used to access the service, not (if there is a difference) the program used to provide the service.
The directory /etc/pam.d is used to configure all PAM applications.
(This used to be
/etc/pam.conf in earlier PAM versions; while the pam.conf file is still read if no
/etc/pam.d/ entry is found, its use is deprecated.) Each application (really, each service) has its own file. A file looks like this:
#auth required /lib/security/pamsecuretty.so auth required /lib/security/pampwdb.so shadow nullok auth required /lib/security/pamnologin.so account required /lib/security/pampwdb.so password required /lib/security/pamcracklib.so password required /lib/security/pampwdb.so shadow ¬ nullok useauthtok session required /lib/security/pampwdb.so
The first line is a comment. Any line that starts with a # character is a comment. Lines two through four stack up three modules to use for login authorization. Line two makes sure that if the user is trying to log in as root, the tty on which they are logging in is listed in the /etc/securetty file if that file exists. Line three causes the user to be asked for a password and the password checked. Line four checks to see if the file /etc/nologin exists, and if it does, displays the contents of the file, and if the user is not root, does not let him or her log in.
Note that all three modules are checked, even if the first module fails. This is a security decision---it is designed to not let the user know why their authentication was disallowed, because knowing why it was disallowed might allow them to break the authentication more easily. You can change this behavior by changing required to requisite; if any requisite module returns failure, PAM fails immediately without calling any other modules.
The fifth line causes any necessary accounting to be done. For example, if shadow passwords have been enabled, the pam_pwdb.so module will check to see if the account has expired, or if the user has not changed his or her password and the grace period for changing the password has expired.
The sixth line subjects a newly-changed password to a series of tests to ensure that it cannot, for example, be easily determined by a dictionary-based password cracking program.
The seventh line (which we've had to wrap) specifies that if the login program changes the user's password, it should use the pam_pwdb.so module to do so. (It will do so only if an auth module has determined that the password needs to be changed---for example, if a shadow password has expired.)
The eighth and final line specifies that the pam_pwdb.so module should be used to manage the session. Currently, that module doesn't do anything; it could be replaced (or supplemented by stacking) by any necessary module.
Note that the order of the lines within each file matters. While it doesn't really matter much in which order required modules are called, there are other control flags available. While optional is rarely used, and never used by default on a Red Hat Linux system, sufficient and requisite cause order to become important.
Let's look at the auth configuration for rlogin:
auth required /lib/security/pamsecuretty.so auth sufficient /lib/security/pamrhostsauth.so auth required /lib/security/pampwdb.so shadow nullok auth required /lib/security/pamnologin.so
That looks almost like the login entry, but there's an extra line specifying an extra module, and the modules are specified in a different order.
First, pam_securetty.so keeps root logins from happening on insecure terminals. This effectively disallows all root rlogin attempts. If you wish to allow them (in which case we recommend that you either not be internet-connected or be behind a good firewall), you can simply remove that line.
Second, pam_nologin.so checks /etc/nologin, as specified above.
Third, if pam_rhosts_auth.so authenticates the user, PAM
immediately returns success to rlogin without any password checking
being done. If
pam_rhosts_auth.so fails to authenticate the user, that failed authentication is ignored.
Finally (if pam_rhosts_auth.so has failed to authenticate
the user), the
pam_pwdb.so module performs normal password authentication.
Note that if you do not want to prompt for a password if the securetty check fails, you can change the pam_securetty.so module from required to requisite
The pam_pwdb.so module will automatically detect that you are using shadow passwords and make all necessary adjustments. Please refer to Section 11.5 for more information on the utilities that support shadow passwords.
This is just an introduction to PAM. More information is included in the /usr/doc/pam* directory, including a System Administrators' Guide, a Module Writers' Manual, an Application Developers' Manual, and the PAM standard, DCE-RFC 86.0. In addition, documentation is available from the Red Hat web site, at http://www.redhat.com/linux-info/pam/. | <urn:uuid:9331b09c-259f-49c1-8d55-bc09af163792> | 3.171875 | 1,697 | Documentation | Software Dev. | 44.404333 |
image credit: Jeff Schmaltz, MODIS Rapid Response System, Goddard Space Flight Center; image source; larger image
The Arctic Oscillation
Great Britain is usually exempt from the cold winter weather in other countries of the same latitude. (Warm air from the Gulf Stream keeps temperatures mild; read more here.) However, as the image above shows, Britain's winter was much colder than usual. One reason for this change is The Arctic Oscillation, the process of alternating pressure regions in the northern hemisphere. For more on Britain's recent and upcoming weather, check out this article from the Guardian discussing El Nino.
Atmospheric Dry Spell Eases Global Warming
This article from NPR offers insight into a few factors affecting global temperatures. For more on how changing temperatures might affect you, see these pages on stronger hurricanes (NOVA) and the nor'easters (NOAA). | <urn:uuid:86562b12-a563-40ce-a90f-51de4ee6eabc> | 3.796875 | 184 | Content Listing | Science & Tech. | 35.463571 |
Algae may help corals withstand warmer waters
HONG KONG (Reuters) - Certain types of algae can help corals withstand higher sea temperatures and prevent them from bleaching, scientists in Australia have found.
Coral reefs are vulnera"le to climate change and without rapid genetic adaptation, they will not survive projected sea temperature increases over the next 50 years, experts say.
But in an article published in latest issue of the Proceedings of the Royal Society B: Biological Sciences, the researchers said they may have found an answer to why some corals continue to thrive in warmer waters when others die.
The answer appears to lie in a heat-tolerant single-celled algae which lives in coral tissue, said Ray Berkelmans at the Australian Institute of Marine Science.
In the study, the researchers tagged and analyzed some 480 coral colonies in the Keppel Islands of the Great Barrier Reef and found that some 94 percent of them contained a heat-sensitive strain of the algae, named C2.
But after a natural bleaching event in 2006, those corals that managed to survive were dominated instead by the heat-tolerant algae strain, called type D.
"The hypothesis is that C2 was dominant in the tissues, but present in background levels that are sometimes hard to detect were the D-type," Berkelmans explained.
"With the dominant algae being expelled (because of warmer temperatures), the more heat-tolerant algae had the chance to reoccupy the space. And as the coral recovers, the previously low-density algae became more dominant."
Some algae produce toxic compounds in warmer waters and corals start expelling them to try to survive. But very often, corals die before they are able to get rid of all the bad algae.
Looking ahead, Berkelmans said his team would continue to study corals that managed to survive bleaching.
"Is it because they have background levels of type D algae? And if so, we have to protect these a little bit more so they can repopulate at great speed," he suggested.
(Reporting by Tan Ee Lyn; Editing by Alex Richardson) | <urn:uuid:77ae3099-9edc-4805-b9aa-a773dd9aeca7> | 3.53125 | 443 | Truncated | Science & Tech. | 38.271744 |
Inscribed and Central Angles Showing that an inscribed angle is half of a central angle that subtends the same arc
Inscribed and Central Angles
⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles.
- What I want to do in this video is to prove one of the more
- useful results in geometry, and that's that an inscribed angle
- is just an angle whose vertex sits on the circumference
- of the circle.
- So that is our inscribed angle.
- I'll denote it by psi -- I'll use the psi for inscribed angle
- and angles in this video.
- That psi, the inscribed angle, is going to be exactly 1/2 of
- the central angle that subtends the same arc.
- So I just used a lot a fancy words, but I think you'll
- get what I'm saying.
- So this is psi.
- It is an inscribed angle.
- It sits, its vertex sits on the circumference.
- And if you draw out the two rays that come out from this angle
- or the two cords that define this angle, it intersects the
- circle at the other end.
- And if you look at the part of the circumference of the circle
- that's inside of it, that is the arc that is
- subtended by psi.
- It's all very fancy words, but I think the idea is
- pretty straightforward.
- This right here is the arc subtended by psi, where psi is
- that inscribed angle right over there, the vertex sitting
- on the circumference.
- Now, a central angle is an angle where the vertex is
- sitting at the center of the circle.
- So let's say that this right here -- I'll try to eyeball
- it -- that right there is the center of the circle.
- So let me draw a central angle that subtends this same arc.
- So that looks like a central angle subtending that same arc.
- Just like that.
- Let's call this theta.
- So this angle is psi, this angle right here is theta.
- What I'm going to prove in this video is that psi is always
- going to be equal to 1/2 of theta.
- So if I were to tell you that psi is equal to, I don't know,
- 25 degrees, then you would immediately know that theta
- must be equal to 50 degrees.
- Or if I told you that theta was 80 degrees, then you would
- immediately know that psi was 40 degrees.
- So let's actually proved this.
- So let me clear this.
- So a good place to start, or the place I'm going to
- start, is a special case.
- I'm going to draw an inscribed angle, but one of the chords
- that define it is going to be the diameter of the circle.
- So this isn't going to be the general case, this is going
- to be a special case.
- So let me see, this is the center right here of my circle.
- I'm trying to eyeball it.
- Center looks like that.
- So let me draw a diameter.
- So the diameter looks like that.
- Then let me define my inscribed angle.
- This diameter is one side of it.
- And then the other side maybe is just like that.
- So let me call this right here psi.
- If that's psi, this length right here is a radius -- that's
- our radius of our circle.
- Then this length right here is also going to be the radius of
- our circle going from the center to the circumference.
- Your circumference is defined by all of the points that are
- exactly a radius away from the center.
- So that's also a radius.
- Now, this triangle right here is an isosceles triangle.
- It has two sides that are equal.
- Two sides that are definitely equal.
- We know that when we have two sides being equal, their
- base angles are also equal.
- So this will also be equal to psi.
- You might not recognize it because it's
- tilted up like that.
- But I think many of us when we see a triangle that looks like
- this, if I told you this is r and that is r, that these two
- sides are equal, and if this is psi, then you would also
- know that this angle is also going to be psi.
- Base angles are equivalent on an isosceles triangle.
- So this is psi, that is also psi.
- Now, let me look at the central angle.
- This is the central angle subtending the same arc.
- Let's highlight the arc that they're both subtending.
- This right here is the arc that they're both going to subtend.
- So this is my central angle right there, theta.
- Now if this angle is theta, what's this angle going to be?
- This angle right here.
- Well, this angle is supplementary to theta,
- so it's 180 minus theta.
- When you add these two angles together you go 180 degrees
- around or they kind of form a line.
- They're supplementary to each other.
- Now we also know that these three angles are sitting
- inside of the same triangle.
- So they must add up to 180 degrees.
- So we get psi -- this psi plus that psi plus psi plus this
- angle, which is 180 minus theta plus 180 minus theta.
- These three angles must add up to 180 degrees.
- They're the three angles of a triangle.
- Now we could subtract 180 from both sides.
- psi plus psi is 2 psi minus theta is equal to 0.
- Add theta to both sides.
- You get 2 psi is equal to theta.
- Multiply both sides by 1/2 or divide both sides by 2.
- You get psi is equal to 1/2 of theta.
- So we just proved what we set out to prove for the special
- case where our inscribed angle is defined, where one of the
- rays, if you want to view these lines as rays, where one of the
- rays that defines this inscribed angle is
- along the diameter.
- The diameter forms part of that ray.
- So this is a special case where one edge is
- sitting on the diameter.
- So already we could generalize this.
- So now that we know that if this is 50 that this is
- going to be 100 degrees and likewise, right?
- Whatever psi is or whatever theta is, psi's going to be 1/2
- of that, or whatever psi is, theta is going to
- be 2 times that.
- And now this will apply for any time.
- We could use this notion any time that -- so just using that
- result we just got, we can now generalize it a little bit,
- although this won't apply to all inscribed angles.
- Let's have an inscribed angle that looks like this.
- So this situation, the center, you can kind of view it as
- it's inside of the angle.
- That's my inscribed angle.
- And I want to find a relationship between this
- inscribed angle and the central angle that's subtending
- to same arc.
- So that's my central angle subtending the same arc.
- Well, you might say, hey, gee, none of these ends or these
- chords that define this angle, neither of these are diameters,
- but what we can do is we can draw a diameter.
- If the center is within these two chords we
- can draw a diameter.
- We can draw a diameter just like that.
- If we draw a diameter just like that, if we define this angle
- as psi 1, that angle as psi 2.
- Clearly psi is the sum of those two angles.
- And we call this angle theta 1, and this angle theta 2.
- We immediately you know that, just using the result I just
- got, since we have one side of our angles in both cases being
- a diameter now, we know that psi 1 is going to be
- equal to 1/2 theta 1.
- And we know that psi 2 is going to be 1/2 theta 2.
- Psi 2 is going to be 1/2 theta 2.
- So psi, which is psi 1 plus psi 2, so psi 1 plus psi 2 is going to
- be equal to these two things.
- 1/2 theta 1 plus 1/2 theta 2.
- psi 1 plus psi 2, this is equal to the first inscribed
- angle that we want to deal with, just regular psi.
- That's psi.
- And this right here, this is equal to 1/2 times
- theta 1 plus theta 2.
- What's theta 1 plus theta 2?
- Well that's just our original theta that
- we were dealing with.
- So now we see that psi is equal to 1/2 theta.
- So now we've proved it for a slightly more general case
- where our center is inside of the two rays that
- define that angle.
- Now, we still haven't addressed a slightly harder situation or
- a more general situation where if this is the center of our
- circle and I have an inscribed angle where the center isn't
- sitting inside of the two chords.
- Let me draw that.
- So that's going to be my vertex, and I'll switch colors,
- so let's say that is one of the chords that defines the
- angle, just like that.
- And let's say that is the other chord that defines
- the angle just like that.
- So how do we find the relationship between, let's
- call, this angle right here, let's call it psi 1.
- How do we find the relationship between psi 1 and the central
- angle that subtends this same arc?
- So when I talk about the same arc, that's that right there.
- So the central angle that subtends the same arc
- will look like this.
- Let's call that theta 1.
- What we can do is use what we just learned when one side of
- our inscribed angle is a diameter.
- So let's construct that.
- So let me draw a diameter here.
- The result we want still is that this should be 1/2 of
- this, but let's prove it.
- Let's draw a diameter just like that.
- Let me call this angle right here, let me call that psi 2.
- And it is subtending this arc right there -- let me do
- that in a darker color.
- It is subtending this arc right there.
- So the central angle that subtends that same arc,
- let me call that theta 2.
- Now, we know from the earlier part of this video that psi
- 2 is going to be equal to 1/2 theta 2, right?
- They share -- the diameter is right there.
- The diameter is one of the chords that forms the angle.
- So psi 2 is going to be equal to 1/2 theta 2.
- This is exactly what we've been doing in the last video, right?
- This is an inscribed angle.
- One of the chords that define is sitting on the diameter.
- So this is going to be 1/2 of this angle, of the central
- angle that subtends the same arc.
- Now, let's look at this larger angle.
- This larger angle right here.
- Psi 1 plus psi 2.
- Right, that larger angle is psi 1 plus psi 2.
- Once again, this subtends this entire arc right here, and it
- has a diameter as one of the chords that defines
- this huge angle.
- So this is going to be 1/2 of the central angle that
- subtends the same arc.
- We're just using what we've already shown in this video.
- So this is going to be equal to 1/2 of this huge central angle
- of theta 1 plus theta 2.
- So far we've just used everything that we've learned
- earlier in this video.
- Now, we already know that psi 2 is equal to 1/2 theta 2.
- So let me make that substitution.
- This is equal to that.
- So we can say that si 1 plus -- instead of si 2 I'll write
- 1/2 theta 2 is equal to 1/2 theta 1 plus 1/2 theta 2.
- We can subtract 1/2 theta 2 from both sides, and
- we get our result.
- Si 1 is equal to 1/2 theta one.
- And now we're done.
- We have proven the situation that the inscribed angle is
- always 1/2 of the central angle that subtends the same arc,
- regardless of whether the center of the circle is inside
- of the angle, outside of the angle, whether we have a
- diameter on one side.
- So any other angle can be constructed as a sum of
- any or all of these that we've already done.
- So hopefully you found this useful and now we can actually
- build on this result to do some more interesting
- geometry proofs.
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about the site | <urn:uuid:fcf126cf-8849-4aef-9f58-91a0b671c84b> | 4.09375 | 3,235 | Truncated | Science & Tech. | 79.858043 |
A transformation in which
a figure grows smaller.
Compressions may be with respect to a point (compression
of a geometric figure) or with respect to the axis of
a graph (compression
of a graph).
Note: Some high
school textbooks erroneously use the word dilation to
refer to all transformations in which the figure changes size,
whether the figure becomes larger or smaller. Compression (or contraction)
refers to transformations in which the figure becomes smaller.
Dilation properly refers only to transformations in which the figure
Unfortunately the English language has no word that refers collectively
of a geometric figure, dilation
of a graph | <urn:uuid:a92d9dc1-9f60-42be-a2f6-c8cf2cec1cff> | 3.09375 | 139 | Structured Data | Science & Tech. | 25.023088 |
Life in a Drop of Water
by Mike Morgan
How often have we seen, in books aimed at the amateur microscopist, that one drop of sediment and water from the pond, would yield a wealth of organisms to view and wonder at?
I tried this, observing over a period of one hour, 25 microlitres of sediment/pond water.
Indeed there were a wealth of organisms to wonder at. I decided to split these observations into different articles, covering the types seen. The first will show the types of Rotifer observed and I will follow this with articles showing the protozoa and algae / desmids.
Three types of rotifer were seen. The most abundant was Brachionus sp. and I was able to see the rotifer both with and without her carrying her eggs (image above and left respectively).
Next to appear was Anuraeopsis. There is only one British and Irish species of this rotifer, i.e. Anuraeopsis fissa. The asexual eggs are very distinctive in being tear-drop shaped and are carried attached to an anal appendage or egg carrier.
The third rotifer observed was Rotaria neptunia. The telescopic nature of the rotifer's movement was clearly seen, as were the 3 toes and 2 spurs on the foot.
The more observant may notice a few other organisms, captured alongside the rotifers. The ubiquitous Paramecium, for one! My next two articles will cover the various protozoa and algae seen in what, for me, was a very exciting hour's viewing of that "drop of water".
Further reading: A Key to British Freshwater Planktonic Rotifera by Rosalind M Pontin. Freshwater Biological Association.
See a video clip showing the birth of a live rotifer of the genus Rotaria.
Please report any Web problems
or offer general comments to the Micscape Editor,
via the contact on current Micscape Index.
Micscape is the on-line monthly
magazine of the Microscopy UK web
site at Microscopy-UK | <urn:uuid:bea94844-ca90-4f4e-8ab3-29604fe22595> | 2.9375 | 440 | Personal Blog | Science & Tech. | 48.515739 |
NOTE: Hover over the bold words for definitions or see the Glossary.
Rafinesque described this species in 1820. As with most species of the genus Lampsilis, the wavyrayed lampmussel exhibits sexual dimorphism in shell shape. Females are relatively circular, while males are more elliptical. The periostracum is a shiny golden yellow with wavy green rays usually distributed over the entire shell surface. The nacre is white to bluish white and may be iridescent in fresh shells. The pseudocardinal teeth are triangular; two in the left valve, one in the right. Lateral teeth are slightly curved.
This species is distributed from the Great Lakes, through the Ohio and Mississippi river drainages, and into the Tennessee River Basin (Parmalee and Bogan 1998). In addition to the species' current North Carolina distribution, its historical distribution in North Carolina included the French Broad and Pigeon river basins. Distribution by County: Cherokee Co. (Hiwassee River); Macon Co. (Little Tennessee River); Swain Co. (Little Tennessee River); Mitchell Co. (Nolichucky River Basin); Yancey Co. (Nolichucky River Basin). NOTE: All headwater areas that flow into these occupied habitats should receive special management.
This species is typically found in rivers and streams with coarse sand and gravel beds.
Fish hosts for this species include the small and largemouth bass (Zale and Neves 1982, Watson 1999). The sexual dimorphism in shell shape suggests that this species, like many other members of the genus Lampsilis, is bradytictic. Females in the Little Tennessee River display exceptional variability in the types of mimics used to attract the fish host.
General Life History For Mussels | <urn:uuid:dfaa178f-69e9-4b78-bb65-472ad2c5abd8> | 2.984375 | 375 | Knowledge Article | Science & Tech. | 37.661379 |
Fluid dynamics of flapping wings associated with change of domain topology
Seminar Room 1, Newton Institute
We re-examine the clap-fling-sweep mechanism employed by some insects to increase lift. As argued by Lighthill (J Fluid Mech 60(1):1-17, 1973), this mechanism can create a circulatory motion even in a totally inviscid fluid, due to a topological change of the solid boundary that represents the wings surfaces. During the stroke, the wings first clap together behind the insect's back, then open in a fling motion around the `hinge' formed by the two trailing edges, and finally separate at the hinge and sweep apart.
In a two-dimensional approximation, we use two different conformal mappings in simply and doubly connected domains, respectively, to calculate the complex potential at all stages of the process. The results indicate that circulation (equal in magnitude and opposite round the two wings) can be generated in an inviscid fluid, and that this circulation appears when a solid body immersed in the fluid breaks into two pieces (when fling gives way to sweep). Bound vortex sheets produced during fling are still carried by the just-separated wings. This is accompanied by a continuous time evolution of the velocity everywhere in the fluid, although the pressure field jumps instantaneously at the moment of wing separation.
In a viscous fluid, the flow during the break is essentially different because, locally, the Reynolds number is very low near the hinge point. We describe it by local similarity solutions to the Stokes equation (J Fluid Mech 676:572-606, 2011).
Three-dimensional effects are present in the flow. We study them by performing numerical simulations of the Navier-Stokes equations using a Fourier spectral method with volume penalization. The flow before the break is found to be in a good agreement with the two-dimensional approximation. After the wings move farther than one chord length apart, the three-dimensional nature of the flow becomes essential (J Fluids Struct 27(5-6):784-791, 2011). | <urn:uuid:2e8a4728-e673-40d5-bd9e-faef96e8c33a> | 2.8125 | 437 | Academic Writing | Science & Tech. | 37.933166 |
Name: Jason M.
Date: March 2004
I have been wondering how long the cells in our bodies
stay with us. I mean, I know that our cells are dividing and eventually
are passed from our bodies. I found that red blood cells have a life
span of 120 days, but what about the rest of our cells. How often do we
(basically) get a new body? I have also learned that nerve cells don't
come and go like red blood cells. Is this true and are other cells the
Very good questions! I mammals we probably know the most about blood cells
( a type of connective tissue) since they have been studied so much. It
turns out that there is a complete scale of life-times for cells. Some
cells are in what we call G-0 because they seldom if ever divide ( some
nerve cells are like this). Cells that are dividing can produce more of
themselves or can divide and mature (differentiate) into another cell type.
Cells that can consistently produce both themselves and produce cells that
differentiate are often called "stem cells". Under favorable stimuli, a
population of hundreds of stem cells can give rise to billions of mature
functional cells...like red cells which last about 115-120 days. Some stem
cell lines are more "committed" to making a certain line of cells.
blood cells are produced from a certain "cell line" of stem cells in a
mature person. Cells of a very early embryo are capable of producing any
cell in your body. Stem cells of a mature person typically produce a
certain line of cells. Cells that line the inside and outside of our bodies
are often rapidly dividing every 20 or so hours. So your skin cells, the
lining of your intestine, and your blood cells are very actively living
dying and being replaced....As to the question of what you are...think of
this...about 75% of your body is water and every month or so almost all the
water in your body is replaced, about 7% of your body weight is blood fluid
and blood cells, most of which are replaced in three months. And the
mitochondria that provide most of the energy in most of the cells of our
body are actually bacterial descendents that live in perfect harmony. Then
subtract the non-cellular bone matrix and there isn't much left of us to
By the way...it is my belief that any nucleated cell can
divide...and even dedifferentiate under the correct circumstances...but no
one I know of has done so with animal cells...plants can be stimulated to do
so but not yet animals.
Different cell types have different longevities. The cells on your skin and in your mouth
for example have a very fast rate of mitosis. The cells lining your stomach also divide
to replace the ones that are eaten away by stomach acid. The cells in your clavicle
(collar bone) have a very low rate of mitosis. Your bone marrow does replenish your
red blood cells every 3 months. But some cells never divide again once they are made.
Some of the cells of the nervous system fit that bill. Recently however, nervous system
stem cells have been discovered in an adult, so there must be some new nervous tissue
cells made. So, there is not a consistent rate of replacement. Your body doesn't
completely replace itself, although most of it does.
Click here to return to the Molecular Biology Archives
Update: June 2012 | <urn:uuid:d7240d33-5082-4853-96d8-8771f40e6738> | 3.0625 | 743 | Knowledge Article | Science & Tech. | 63.979624 |
I have a biology final coming up and I would really appreciate it if someone could answer this question for me. Thank you very much!
The equation for photosynthesis is 6CO2 + 6H2O = C6H12O6 +6O2, which shows that energy is stored in the form of glucose, a 6 carbon sugar. This forms chains of starch, which are kept as a long term energy store.
Yes, but will you LOVE ME? Tomorrow?
In any case plants really store energy just as people do, they create more plant tissue. In this tissue are sugars, starches and fats, which are typically those items people who write tests are looking for. But there are plants that can break down protein as well. These plants "store" energy in proteins as do human beings as well as in the other reserves.
Humans are less able than plants to "store sugars". But we can tolerate for short periods of time increased levels of sugars in our blood streams. We can store starches in our gut for short periods of time.
We can store protein for as long as a decade without reprocessing it.
Plants can store protein for perhaps hundreds of years, though I don't know of a species of protein processing plant that does so.
Typically plants cannot process their own proteins, but I suspect there are plants that can, given there are literally over a billion species.
Of the well known plants that can "store" protein an example would be the venus fly trap, which can take it's time eating an ant. Another example would be the "Pitcher plant" which likewise can be more or less aggressive in eating a wasp.
Photosynthesis is the process plants and some algae use to convert light energy to chemical energy stored as sugar. Plants need only carbon dioxide (CO2) and water (H2O) for photosynthesis to work. This occurs in plant leaves, specifically the leaf cells' chloroplasts. Chloroplasts are full of chlorophyll, a green pigment key to photosynthesis. The energy stored during photosynthesis starts the flow of energy and carbon down the food chain. All the energy we consume through food is a direct or indirect result of the energy stored by photosynthesis.
The Chemical Reaction
The formula that describes photosynthesis is
6CO2 + 6H20 + light energy = C6H1206 + 602
What this chemical equation means is that photosynthesis combines light energy with six molecules of carbon dioxide and six molecules of water to produce six molecules of oxygen and a molecule of sugar.
The only thing i know about storage of energy are when the glucose are converted into starch molecules and starch grains form in the chloroplast | <urn:uuid:d3c3516c-65ee-44a6-b9a8-d6761ce311f7> | 3.609375 | 559 | Q&A Forum | Science & Tech. | 52.108364 |
|Global annual mean temperature anomalies as measured by surface data (black bars) and the MSU satellite unit (gray bars) using the MSU-2R technique. Temperatures on the vertical axis are times 100 degrees C. (Illustration from Hurrell and Trenberth, "Satellite versus surface estimates of air temperature since 1979," Journal of Climate 9(9), 1996.)|
A flurry of papers over the past several years in the Journal of Climate, Climatic Change, and other literature has tried to pin down the causes of the MSU/surface disagreement. At last month's meeting of the American Meteorological Society (AMS) in Long Beach, California, an afternoon session was devoted to the discrepancies. The lively session provided a thorough airing of the issues at hand, but no clear resolution.
Two key players in the debate are NCAR's James Hurrell and Kevin Trenberth. They have collaborated on a series of recent papers (including two presented at AMS) aimed at reconciling the patterns of difference between the surface and the MSU data. "We need both surface and MSU records to get a proper perspective on what's going on," says Trenberth. "Although the MSU data are excellent for many purposes, we think there are some substantive problems with the trends as depicted by MSU."
John Christy (University of Alabama at Huntsville) and Roy Spencer (NASA) have led the development of temperature-trend retrieval from MSU data. Both presented papers at AMS on their most recent work. Christy maintains that the MSU data are solid. "Since the MSU measures temperatures through a deep layer of the atmosphere, the only proper comparison is with temperature profiles from radiosondes. Our extensive comparisons show no significant disagreements." Christy believes the main difference between surface and MSU readings lies in the very real distinction between surface and tropospheric temperature, an area now receiving increased scrutiny.
In the MSUs' favor is their strong correlation with global radiosonde records. Christy notes the minimal difference in decadal temperature trends between MSU-2R and radiosonde data across North America, the Arctic, and the tropics. In all three regions, Christy has found a difference of 0.027degreesC or less per decade between the radiosonde and MSU trends.
Although it has longevity on its side, the earth's surface temperature record has well-documented flaws. Tom Karl (National Climatic Data Center) found in 1994 that about 10% of the half-degree C warming seen at the surface this century could be due to error induced by the uneven distribution of weather stations across land and by their absence over the oceans, where sea-surface temperatures (SSTs) are routinely used as a substitute for surface air temperature. Karl believes the error could be proportionately greater over shorter intervals of a decade or two.
Adding to the murkiness, a number of recent earth-system upheavals have had global impact; in particular, the major El Niño/Southern Oscillation (ENSO) event of 1982-83 and volcanoes El Chich—n (1982) and Mt. Pinatubo (1991). Philip Jones (University of East Anglia) estimates that the effect of these transitory events could be twice as large in the troposphere as at the surface, with El Niño warming and volcanic cooling both amplified aloft.
Correction factors must be applied to each MSU to account for different satellite orbits and orbital shifts over time. Moreover, as much as 20% of the MSU-2R readings above land areas, and up to 10% above oceans, come from surface-based emissions. Hurrell and Trenberth argue that unusual land characteristics at the time of satellite transition, such as those caused by persistent droughts or floods, may have altered the surface emissions and biased the MSU-2R trends.
Christy's MSU-to-radiosonde comparisons show little disagreement in the tropics, although Hurrell and Trenberth question the reliability of radiosonde records there, where site changes and other confounding events are frequent. Instead of satellite transitions, Christy suspects natural features are responsible for the 1981 and 1991 temperature drops. He cites a 1981 African volcano, Nyamuragira, along with 1982's El Chich—n and 1991's Mt. Pinatubo. However, MSU temperatures have been slow to return to their pre-Pinatubo values, while surface temperatures have rebounded completely. Indeed, even with the influence of ENSO and volcanoes factored out, the MSU and surface readings continue to reflect increasing disparity over time.
Improved computer models may help clarify things. Hurrell and Trenberth are now using NCAR's latest community climate model, CCM3 (part of the NCAR climate system model), and new global reanalyses produced by the National Center for Environmental Prediction and NCAR's Scientific Computing Division. Christy has reservations about using climate models to project global temperature trends: "These vertical variations being modeled are very small, and they are affected by such factors as volcanic aerosols, which are not included explicitly in CCM3 and similar models." Trenberth argues that volcanic effects are reflected in the sea-surface data used as input to study the 1979-95 period. "CCM3 is indeed suitable for this research, and it in fact accounts for the vast majority of the temperature variability we've found."
Some of the work by Hurrell and Trenberth has focused on differences in the vertical profiles between land and ocean. The strongest surface warming of the past few years has been found over Northern Hemisphere continents, particularly in winter, while MSU's slight cooling trend has been centered above the oceans. Hurrell points out that wintertime cold fronts sweeping from land to sea are modulated near the relatively warm ocean yet maintain their strength higher up. In contrast, over land, inversions often trap cold air near the surface while the troposphere above remains warmer. The prevalence of these inversions means that a reduction in their number or strength (through increased low-level water vapor, for example) could produce a significant warming of average surface temperature with little change at higher levels. Moreover, the inversions are often too shallow to be diagnosed or tracked by computer models.
Those involved in the global temperature game, and others on the sidelines, are paying keen attention as the latest numbers roll in. Says Spencer: "The surface and satellite records cannot continue to diverge indefinitely. They should gradually come closer to one another." Both records are now seen as critical to unraveling global change, especially with an atmosphere acting contrary to some modeling results and theoretical assumptions. As Christy puts it: "Do we have an atmosphere that's less rigid than we think?" | <urn:uuid:e9c9ad88-6550-45dd-8462-1e337f874011> | 3.359375 | 1,393 | Knowledge Article | Science & Tech. | 31.935713 |
The Prolog Language
Prolog (for PROgramming in LOGic) is a logic programming language loosely based on first-order logic. It was invented by Alain Colmerauer and Phillipe Roussel at the University of Aix-Marseille in 1971. Since then a large number of good implementations of the language have become available.
See http://vl.fmnet.info/logic-prog/ for more details. | <urn:uuid:42241b82-0311-4b1d-b254-7819899e46d1> | 3.390625 | 93 | Knowledge Article | Software Dev. | 45.815 |
"Electronegativity is the power of an atom when in a molecule to attract eletrons to itself." The electronegativity will depend upon a number of factors including other atoms in the molecule, the number of atoms coordinated to it, and the oxidation number for the atom. There are a number of ways to produce a set of numbers which represent electronegativity scales. The Pauling scale is perhaps the most famous.
He noticed that the bond energy E(AB) in a molecule AB is always greater than the mean of the bond energies E(AA) + E(BB) in the homonuclear species AA and BB. His argument was that in an "ideal" covalent bond E(AB) should equal this mean, and that the "excess" bond energy is caused by electrostatic attraction between the partially charged atoms in the heternuclear species AB. In effect, he was saying that the excess bond energy arises from an ionic contribution to the bond. He managed to treat this ionic contribution by the equation
E(AB) = [E(AA).E(BB)]1/2 + 96.48(ΧA - ΧB)2
in which E(AB) is expressed in kJ mol-1 (1 electron volt, 1eV, = 96.48 kJ mol-1) and ΧA - ΧB represents the difference in "electronegativity" between the two elements, whose individual electronegativities are given the symbols ΧA and Χ. Using this equation, Pauling found that the largest electronegativity difference was between Cs and F. Pauling set F arbitrarily at 4.0 (today, the value for F is set to 3.98) and this gives a scale in which the values for all other elements are less than 4 but still with a positive number.
Most values are taken from reference 1 and where values are missing from reference 2. Values for Group 18 elements and for elements 95-102 are taken from reference 3. Pauling electronegativities are published in many sources and essentially identical data are to be found in references such as 4 and 5.
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:afe16325-19f2-4b77-8b4d-5cbb3028ea27> | 3.59375 | 485 | Knowledge Article | Science & Tech. | 51.085632 |
Logic Devices from Neuronal Cultures
(to design a novel neuronal device click here)
Neurons in the brain perform amazing calculations in a flash, but if you put them into a dish they become sluggish and 'stupid' - i.e. their response repertoire is very limited. Our principal question is how the connections between the neurons be manipulated so as to improve their computational capacity.
In the current project, we used 1D cultures and took one step up the dimensionality scale to create "function-follows-structure" neuronal devices. For example the triangular diode alternates between one and two dimensional patterns to create an asymmetric connectivity between ensembles of neurons. The transmission of signals along a line that includes these devices is necessary if we want to measure the performance of our devices - this is how we are able to control their input, located in a defined area of the culture, and measure their output, located at a different area.
Nine separate neuronal devices patterned on a single 13mm coverslip (4 Thresholds on the left column, 4 AND gates on the center column and on the right a composite Diode consisting of 8 daisy-chained triangles). Dark field illumination, bright areas are concentrations of neurons. NeuronTimeLapse.wmv - Hippocampal neurons growing on patternned glass coverslip (field of view is centered on a connection between two triangles, see Left figure). In a few hours cell bodies send axons and connect between themselves. Threshold
Two parallel straight lines connected with a thin line(<50µm). Here, Input signals of population activity were observed at the right line and the resulting output signals were measured at the left line. Only signals whose strength surpassed a limit propagated to the other side.
A pair of straight lines served as inputs, interconnected at one end with a thick perpendicular line. At the other end they were connected via two thin lines to a central region serving as Output. When the two Input regions were disconnected (via local application of TTX - red arrow) they fired independently and no Output response was observed (0^1=0, 1^0=0). When both Input regions fired synchronously, the Output region responded (1^1=1).
A series of concatenated isosceles triangles, each one connected at its tip to the base of the consecutive triangle. The Input and Output was measured from two consecutive triangles. Only signals that originated in the lower triangle propagate upwards while signals originating in the upper triangle are blocked when trying to propagate backwards.
Neuronal Devices expressing GFP provide insight on how structure affects function. In the Threshold (left) the thin section limit the number of axons that connect the lines. In the Diode, the triangles funnel axons forward to the next triangle (cyan tracks) and backward crossings are less likely (red tracks). OscillatorA neuronal Oscillator can be assembled by combining diodes into a closed loop. Usually, signals in a closed loop propagate in both directions and at a point of rendevouz both fronts "annihilate" due to the refractoriness property of bursts (neurons have to "rest" between bursts). Here, the diodes determine a single direction of propagation and by the time a signal completes a cycle along the Oscillator, the refractory period is over and the burstis free to repeat itself. In the movie (Oscillator.wmv) the center region of the oscillator is imaged while a signal completes a single anti-clockwise loop.
Our primary goal is to understand how computation comes about from an ensemble of neurons. We believe that building these logic devices not only provides a methodology for precise monitor and control over neural networks but also insight on how they function. For example, the existence of a threshold level for activation turns out to play a central role in neuronal computation. We encounter this phenomenon for the case of neuronal ensembles and also in other, percolating neuronal network systems that we investigate in the lab. | <urn:uuid:4ccbe4c3-a5c8-4eca-a3e2-8446e542d7fc> | 2.984375 | 837 | Academic Writing | Science & Tech. | 34.218072 |
Protected by the following WLT projects:
The Morelet’s Crocodile is also known as an Alligator, an Agarei, Brown Crocodile or Swamp Crocodile. These crocodiles are relatively small, usually less than 3m in length. They have a broad snout, and are greyish brown in colour with dark bands and spots on their bodies and tails.
Morelet's Crocodiles are generally shy and timid although the larger ones can be considered dangerous to humans. They eat a variety of prey, including aquatic invertebrates, fish, small reptiles and mammals and birds.
The females lay 20-45 eggs in a mound nest before the onset of the rainy season (April – June). These crocodiles are the only New World crocodiles that are exclusively mound nesting. The mounds occur near the water or on floating vegetation. Females guard the nest during the incubation period (around 80 days) and respond to the vocalisation of hatchlings and open up the mounds.
This species is primarily a freshwater crocodile, living in swamps, marshes, ponds, lagoons and forested areas, although sometimes it can be found in brackish water around coastal areas. Morelet's crocodiles occur in areas of Central America including Mexico, Belize and Guatemala.
Threats and Conservation
In the 1940's and 1950s the Morelet's Crocodile was almost hunted to extinction due to its valuable hide. It has since been made illegal to hunt these animals and the species has steadily recovered. Although there are thought to be over 10,000 adult specimens in the wild the crocodile still faces threat from habitat loss and illegal poaching and is thus listed in the IUCN red list of threatened species as Conservation Dependent . | <urn:uuid:67395444-2d92-4b1f-8254-e4bbf7adc7ff> | 3.921875 | 366 | Knowledge Article | Science & Tech. | 41.693136 |
Science Fair Project Encyclopedia
In optics Spherical aberration is an imperfection of telescopes and other instruments, which makes their focussing less than ideal due to the spherical shapes of the lenses and mirrors. This is an important effect, as spherical shapes are much easier to produce than aspherical and so most lenses have spherical shapes.
The effect is proportional to the fourth power of the diameter and inverse proportional to thrird power of the focal length, so it's much more pronounced at short focal ratios, i.e. fast lenses.
For small telescopes using spherical mirrors with focal ratios shorter than f/10. Light from a distant point source (such as a star) is not all focused at the same point. Particularly, light striking the inner part of the mirror focuses further from the mirror than light striking the outer part of the mirror. As a result the image cannot be focused as sharply as if the aberration were not present. Because of spherical aberration telescopes shorter than f/10 are usually made with non-spherical mirrors or with correcting lenses.
In lens systems, the effect can be minimized using special combinations of concex and concave lenses, as well as using aspherical lenses .
- Aberration in optical systems
- Schmidt corrector plate
- Parabolic reflector
- Ritchey-Chrétien telescope
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:77ec8e40-2cc3-4619-8dd1-29f3d651e793> | 4.21875 | 307 | Knowledge Article | Science & Tech. | 40.71562 |
[Very incomplete. Please extend as you learn more.]
The parser is written using
- Alex, for lexical analysis. Source file compiler/parser/Lexer.x
- Happy, for the parser itself. Source file compiler/parser/Parser.y.pp. Note the .pp suffix; it is run through cpp to yield Parser.y.
- RdrHsSyn, for Haskell support functions. Source file compiler/parser/RdrHsSyn.lhs
Making a parser parse precisely the right language is hard. So GHC's parser follows the following principle:
- We often parse "over-generously", and filter out the bad cases later.
Here are some examples:
- Patterns are parsed as expressions, and transformed from HsExpr.HsExp into HsPat.HsPat in RdrHsSyn.checkPattern. An expression like [x | x<-xs] that doesn't look like a pattern is rejected by checkPattern.
- The context of a type is parsed as a type, and then converted into a context by RdrHsSyn.checkContext. For example, when parsing
f :: (Read a, Num a) => a -> athe parser can only discover that (Read a, Num a) is a context, rather than a type, when it meets the =>. That requires infinite lookahead. So instead we parse (Read a, Num a) as a tuple type, and then convert it to a context when we see the =>.
Sometimes the over-generous parsing is only dealt with by the renamer. For example:
- Infix operators are parsed as if they were all left-associative. The renamer uses the fixity declarations to re-associate the syntax tree.
There are plenty more examples. A good feature of this approach is that the error messages later in compilation tend to produce much more helpful error messages. Errors generated by the parser itself tend to say "Parse error on line X" and not much more.
The main point is this. If you are changing the parser, feel free to make it accept more programs than it does at the moment, provided you also add a later test that rejects the bad programs. Typically you need this flexibility if some new thing you want to add makes the pars ambiguous, and you need more context to disambiguate. Delicate hacking of the LR grammar is to be discouraged. It's very hard to maintain and debug. | <urn:uuid:6d9ce047-b222-40c5-adc7-181e11d2a594> | 2.90625 | 519 | Documentation | Software Dev. | 61.305189 |
Hello math experts, thanks for giving me the opportunity to post here.
My maths education is limited to a 16 yr old's so your help is much appreciated.
In my attachment, I have measured A, B and C in 112 different subjects. Using these measurements, I hope to come up with an approximate index that can be used to compare between subjects.
To approximate the arc length, I am going to average A and B. C will be the chord length of that curve. My question is: how can I measure the central angle of that curve given these values? It does not have to be exact, just an estimation that can be used to subjectively describe if one subject is more curved than the other.
In fact, it doesn't even have to be the central angle. Just a discrete value of some sort. Even something as simple as a ratio?
Please help! Thank you. | <urn:uuid:38022e3b-4a67-4349-9566-4483f8808d74> | 3.15625 | 184 | Q&A Forum | Science & Tech. | 66.329789 |
A neuroscientist has linked the brains of two rats together, so when one of them pushes a lever - the other one does, too!
The rats were trained to push a lever when a light went on, but after a while, electrodes were placed in the rodent's brains.
Soon they had one rat pushing a level because of the light, and another rat pushing the lever only as a response to the brain stimulation it felt from its partner rat.
Tags: brains, experiment, links, rats, science, two
We're not sure what the need was, but we're pretty sure the crabs didn't like this experiment.
The Queen's University Belfast shocked a group of crabs to see if they experienced pain. As one (with common sense) would expect, the crabs wanted to avoid the shocks.
The message behind the experiments is a bit confusing…
Tags: belfast, business, crabs, experiment, food, northern ireland, pain, science, seafood
Next stop, Planet of The
Scientists are discovering that baboons can pick up on the first steps of reading, determining four letter combos as real words or made up mumbo jumbo.
The study was done in France but the words the primates used were in English. The study shows that the baboons got an average of 75 percent of the four letter words correct, giving clues to how humans process reading at a young age.
The key to the success is that the baboons pick up on patterns. They recognize what letters normally form words (i.e. SH) and what combinations don't (i.e. FX).
The best part of the experiment for the primates? FREE FOOD!
The baboons aren't forced into the test, but they are allowed to choose when they want to perform the task instead.
Some baboons perform the test 3,000 a day! On the low end, a measly 400! HA!
Tags: baboons, experiment, reading, science, study
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Luis Acosta / AFP - Getty Images
This combination of pictures shows the moon in various stages of a total lunar eclipse as seen from Mexico City on Dec. 21. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer.
Jose Cabezas / AFP - Getty Images
A double expousure picture shows the moon and the monument of The Savior of The World during a total lunar eclipse as seen from San Salvador, El Salvador on Dec. 21.
Kim Shiflett / NASA
Space shuttle Discovery waits to roll back from Launch Pad 39A to the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida in the early morning hours of Dec 21, with the beginning of the total lunar eclipse clearly in view.
Once inside the VAB, Discovery's external fuel tank will be examined and foam reapplied where 89 sensors were installed on the tank's aluminum skin for an instrumented tanking test on Dec. 17. The sensors were used to measure changes in the tank as super-cold propellants were pumped in and drained out. Data and analysis from the test will be used to determine what caused the tops of two, 21-foot-long support beams, called stringers, on the outside of the intertank to crack during fueling on Nov. 5. Discovery's next launch opportunity is no earlier than Feb. 3, 2011.
Patrick Pleul / AFP - Getty Images
This combo of photos shows, left, the full moon behind clouds and, right, the earth's shadow casting over the moon a few minutes later during a lunar eclipse on early Dec. 21, seen from the northeastern German town of Petersdorf.
Seth Wenig / AP
The moon on its way to being totally eclipsed is seen with the Chrysler Building in the foreground in New York, Tuesday, Dec. 21. A total lunar eclipse occurs when the Earth casts its shadow on the full moon, blocking the sun's rays that otherwise reflect off the moon's surface.
Don Emmert / AFP - Getty Images
A halo or icebow appears around the moon in the sky above a home in the Bronx borough of New York City Dec. 20. The phenomenon is caused by the refraction of the light of the moon by ice crystals in the air.
Juan Carlos Ulate / Reuters
The moon is seen over a Christmas tree during a total lunar eclipse as seen from San Jose, Dec. 21.
Bill Ingalls / Nasa / Handout / EPA
The Washington Monument as the full moon is shadowed by the Earth during a total lunar eclipse on the arrival of the winter solstice, Dec. 21 in Washington D.C. From beginning to end, the eclipse lasted about three hours and twenty-eight minutes.
Desiree Martin / AFP - Getty Images
The volcano Teide is pictured on Dec. 21 during a total lunar eclipse, in the National Park of Teide on the Spanish Canary Island of Tenerife.
Doug Murray / Reuters
The Moon is engulfed in the Earth's shadow as it nears the peak of a rare winter solstice total lunar eclipse as viewed through a telescope from Palm Beach Gardens Dec. 21.
Did you watch the total lunar eclipse? For more incredible space images view our Year in Space slideshow.
Astrophysicist Neil deGrasse Tyson walks you through the stunning beauty of the first lunar eclipse to land on the winter solstice since 1638. | <urn:uuid:5461a9ba-d428-4ad2-8952-0d5db25e0e1b> | 2.765625 | 713 | Content Listing | Science & Tech. | 59.347941 |
Cosmic dust clouds ripple across
this infrared portrait
of our Milky Way's
galaxy, the Large Magellanic Cloud.
In fact, the remarkable composite image from the
Space Observatory and the
Spitzer Space Telescope
show that dust clouds fill this neighboring dwarf galaxy, much like
dust along the plane of the Milky Way itself.
The dust temperatures
tend to trace star forming activity.
Spitzer data in blue hues indicate warm dust heated
by young stars.
Herschel's instruments contributed the image data shown in red and
green, revealing dust emission from cooler and intermediate regions
where star formation is just beginning or has stopped.
Dominated by dust emission, the Large Magellanic Cloud's
infrared appearance is different
from views in optical images.
But this galaxy's well-known
Tarantula Nebula still stands out,
easily seen here as the brightest region to the left of center.
A mere 160,000 light-years distant,
the Large Cloud of Magellan
is about 30,000 light-years across.
JPL-Caltech / STScI | <urn:uuid:915ae4f3-4af1-4af9-9a04-e32cb8148bd0> | 4 | 235 | Knowledge Article | Science & Tech. | 44.094232 |
Posted by U15626221 (U15626221) on Friday, 22nd February 2013
I don't understand the topic of gas exchange, can someone explain clearly but in detail please, a few example would help too. Much appreciated :D
Posted by The Bitesize Science Teacher (U14392404) on Friday, 22nd February 2013
You have answers to this here: www.bbc.co.uk/dna/mb...
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so. | <urn:uuid:2d7d9c58-9d8e-4b87-bfa2-7197166968c2> | 2.6875 | 168 | Q&A Forum | Science & Tech. | 73.596475 |
SAVING THE Devils River minnow
In just about 50 years, the Devils River minnow has gone from being one of the most abundant native fishes in southern Texas to one of the rarest fishes in the world. Requiring clean spring waters for survival, populations of this tiny, shiny minnow have declined drastically as stream modifications and pollution have increased. Sadly, the fish has even been eliminated from the upper and lower portions of its namesake — the Devils River. The Devils River minnow is part of a unique fish fauna in the area where the Chihuahuan Desert, Edwards Plateau, and South Brush Texas ecosystems join. Badly hurt by human water use and introduced species, half the native fishes in this region are considered imperiled, and four species have already gone extinct.
Although first proposed for endangered status under the Endangered Species Act in 1978, the Devils River minnow wasn’t listed until 1999 — at which point it earned only threatened status and was given no habitat protections. The U.S. Fish and Wildlife Service’s final recovery plan for the minnow, approved in 2005, relies exclusively on voluntary measures for the species’ protection and is insufficient to prevent the fish's extinction, much less promote its recovery.
Shortly after the minnow's recovery plan was approved, the Center, Forest Guardians, and Save Our Springs Alliance filed a lawsuit against the Service to challenge the minnow's lack of designated critical habitat, as well the fact that it has been granted only threatened — rather than endangered — status. We continue to work for river protection to save the habitat of the Devils River minnow and many other imperiled species.
Contact: Jeff Miller
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atmospheric and cloud processes
...greater than 100 percent, with respect to a flat surface of H2O. The development of clouds in such a fashion, which occurs only in a controlled laboratory environment, is referred to as homogeneous nucleation. Air containing water vapour with a relative humidity greater than 100 percent, with respect to a flat surface, is referred to as being supersaturated. In the atmosphere,...
Nucleation processes are classed as heterogeneous or homogeneous. In the former, the surface of some different substance, such as a dust particle or the wall of the container, acts as the centre upon which the first atoms, ions, or molecules of the crystal become properly oriented; in the latter, a few particles come into correct juxtaposition in the course of their random movement through the...
Before ice can form, water must supercool and ice crystals nucleate. Homogeneous nucleation (without the influence of foreign particles) occurs well below the freezing point, at temperatures that are not observed in water bodies. The temperature of heterogeneous nucleation (nucleation beginning at the surface of foreign particles) depends on the nature of the particles, but it is generally...
...nucleation). The nuclei consist predominantly of silicate minerals of terrestrial origin, mainly clay minerals and micas. At still lower temperatures, ice may form directly from water vapour ( homogeneous nucleation). The influence of the atmospheric water vapour depends mainly on its degree of supersaturation with respect to ice.
What made you want to look up "homogeneous nucleation"? Please share what surprised you most... | <urn:uuid:8991ff78-7af2-4917-a140-daa8dca8354b> | 3.640625 | 366 | Knowledge Article | Science & Tech. | 37.165477 |
Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES)
Simultaneous Determination of Manganese and Nickel in Steel by Inductively Coupled Plasma Atomic Emission Spectrometry:
pp. 106-108, 479-482, 486-487, and 492-494 in Harris text
- To simultaneously determine the mass percentages of manganese and nickel in a sample of steel.
- To become familiar with the operation of an inductively coupled plasma atomic emission spectrophotometer.
This experiment will be an introduction to the inductively coupled plasma atomic emission spectrometer (ICP-AES), also known as ICP-OES for optical emission spectrometer. The first commercial ICP-AES was made available in 1975, and it is now commonly used as a very powerful instrument for the determination of one or more elements in a sample. The ability to simultaneously determine the concentrations of multiple elements in a sample is what sets the ICP-AES apart from the less expensive atomic absorption (AA) spectrometer.
The principle of the ICP-AES is quite simple. The sample is exposed to the extremely high temperature of an argon plasma (up to 10 000 K) that breaks the sample into atoms, ionizes these atoms, and electronically excites the resulting ions. When the excited electrons in these ions fall back to lower energy levels, they emit light. The wavelengths of light emitted by a particular element serve as a “fingerprint” for that element. Therefore by measuring the wavelengths of light emitted by our sample, we can identify the elements in the sample; and by measuring the amount of light emitted by a particular element in our sample, we can determine the concentration of that element.
The diagram above shows the basic design of the ICP-AES instrument. The sample solution is pumped by a peristaltic pump into the nebulizer where it is broken into an aerosol of fine droplets by a fast stream of argon gas. From the nebulizer it passes through the spray chamber (which eliminates the larger droplets) and on to the quartz plasma torch. The plasma ionizes and excites the atoms of the sample. Emitted light from the ions in the plasma then passes through the entrance window to the monochromator where it is separated into its various wavelengths (colors). The monochromator is a high-resolution “Echelle” design that makes use of both a diffraction grating and a prism to generate a two-dimensional pattern of individual wavelengths of light. This light hits the charge-coupled device (CCD) detector, similar to what you find in a digital camera, where thousands of individual picture elements (pixels) capture the light and turn it into a digital signal that we can measure.
The figure above shows both a diagram of the plasma torch and a picture of the torch compartment on our instrument. A plasma is simply a conducting gas consisting of a combination of positively charged ions and their respective electrons. In our case the plasma is made up of argon ions and electrons. The plasma is initiated by a spark from a tesla coil, and is maintained by a high-frequency electrical current in the induction coil powered by an RF (radio frequency) power supply operating with a power of 0.5 to 2.0 kW at 40.68 MHz. The RF current in the coil generates a magnetic field that causes the ions and electrons to flow in a circular path. This induced current results in collisions between particles and extreme ohmic heating to temperatures of 6000 to 10000 K. A tangential flow of argon gas protects the quartz torch from overheating in this extreme environment.
The picture below shows our Varian ICP-715-ES spectrometer. The cooling unit to the left of the instrument maintains a constant flow of chilled water through the induction coil. Note also the “quick plasma off” button on the front of the instrument that allows the user to extinguish the plasma torch at a moment’s notice.
Overall the ICP-AES is a very easy instrument to use, even for beginners, yielding very accurate results. As previously mentioned, ICP-AES is most useful if multiple elemental determinations must be completed on a single sample. Detection limits are typically in the low parts-per-billion range (1 ppb = 1 ng/mL), and sometimes as low as a few parts per trillion (pg/mL). The addition of an autosampler can increase both productivity and precision. The downside of this instrument is the expense. Aside from the initial purchase price ($60k to $150k), the instrument is very expensive to run due to the high rate of argon consumption (~18 L/min).
Method of Standard Additions:
In this experiment we will be making use of the method of standard additions for calibration of the instrument. Normally, calibration is performed by running a series of pure standard solutions of known concentration through the instrument (Mn and Ni standards in our case) and generating a calibration curve of signal versus concentration. Then we run our sample through the instrument and determine the concentration of our analyte by matching our sample signal to the calibration curve generated with the standards. Ideally, our standard solutions should be similar to our sample solution since other components of the sample solution (the matrix) can interfere with our analyte signal (a matrix effect). Many times, however, it is difficult to prepare standard solutions with a matrix similar to that of our sample. Instead, we can add known amounts of standard directly to the sample solution. In this way the standard is put in the same matrix environment as the analyte in the sample. We then are interested in the increase in signal due to the addition of the standard. Typically we add several different amounts of standard solution to our sample and then generate a curve of signal versus the added analyte concentration. Our original analyte concentration in the sample can then be determined by calculating the x-intercept of the resulting curve. Study the standard additions plot below until you understand why we can say the concentration of analyte in our original sample is 18 ppm. | <urn:uuid:b24d7262-50e0-49a0-9d6a-7987b9c4afdd> | 2.8125 | 1,273 | Tutorial | Science & Tech. | 38.058912 |
Home > News > Terahertz rays see into the nanoworld
October 23rd, 2003
Terahertz rays see into the nanoworld
A new form of imaging that could be particularly valuable in medicine can be used to see nanoscale objects, US researchers report. Terahertz (THz) promises an alternative to techniques such as X-ray, magnetic-resonance and ultrasound imaging, being potentially cheaper, safer, more detailed and more penetrating. All this makes it very attractive for studying body tissue, to look at, say, wound healing or tumor development..
NanoInk, Inc. Assets To Be Sold May 18th, 2013
Beautiful "flowers" self-assemble in a beaker: Elaborate nanostructures blossom from a chemical reaction perfected at Harvard May 17th, 2013
Scientists capture first direct proof of Hofstadter butterfly effect May 17th, 2013
DNA-Guided Assembly Yields Novel Ribbon-Like Nanostructures: Approach could be useful in fabricating new kinds of materials with engineered properties May 16th, 2013 | <urn:uuid:64be5d8f-127b-45cc-883d-a0fc521e8b1d> | 3.015625 | 231 | Content Listing | Science & Tech. | 24.168027 |
|Jan12-12, 09:24 AM||#1|
When a high voltage is applied across the electrodes of the discharge tube, and the pressure of the gas inside the tube is lowered, the electrical energy knocks out some of the electrons from the atoms. These constitute the cathode rays. How does electrical energy knocks out electrons is something I want to know. Please explain.
physics news on PhysOrg.com
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>> New X-ray method shows how frog embryos could help thwart disease
>> Bringing life into focus
|Jan12-12, 11:51 AM||#2|
Usually the electrons are emmited due to thermal transmission (hot cathode) similar to common vacuum tube technolgy. Wiki articles:
As a bit of trivia, there was a CRT used as a memory storage device, called a Williams Tube.
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Researchers have designed a new kind of adaptive material with tunable transparency and wettability features - imagine a tent that blocks light on a dry and sunny day, and becomes transparent and water-repellent on a dim, rainy day. Or highly precise, self-adjusting contact lenses that also clean themselves.
The new material was inspired by natural dynamic, self-restoring systems, such as the liquid film that coats your eyes - tears. Individual tears join up to form a dynamic liquid film with an obviously significant optical function that maintains clarity, while keeping the eye moist, protecting it against dust and bacteria, and helping to transport away any wastes – doing all of this and more in literally the blink of an eye.
Animal and dairy scientists presenting at the Lactation Biology Symposium in Phoenix, Arizona have discovered that drinking milk at an early age can help mammals throughout their lives. The presentations focused on epigenetics, or how gene expression changes based on factors like environment or diet. Epigenetic changes modify when or how certain traits are expressed.
But understanding exactly how milk affects the body is a complicated story of hormones, antibodies and proteins, as well as other cells and compounds researchers have not yet identified.
Health plans that offer low premiums and high deductibles believe that patients with deductibles of $1,000 or more for individual coverage (or twice that for family coverage) will shop around for the best price to get their health care.
A model based on global population data spanning the years from 1900 to 2010 has caused a research team to predict the opposite of what Doomsday Prophets of the 1960s and beyond insisted would happen - the number of people on Earth will stabilize around the middle of the century and perhaps even start to decline.
The results coincide with the United Nation's downward estimates, which claim that by 2100 Earth's population will be 6.2 billion, if low fertility and birth rate continues on its current path, below the 7 billion we are at now.
NASA's Hubble Space Telescope has found the farthest supernova so far. Supernova UDS10Wil, nicknamed SN Wilson after American President Woodrow Wilson, exploded more than 10 billion years ago.
SN UDS10Wil is a Type Ia supernovae. These beacons can be used as a yardstick for measuring cosmic distances. One of the debates surrounding Type Ia supernovae is the nature of the fuse that ignites them. This latest discovery adds credence to one of two competing theories of how they explode. Although preliminary, the evidence so far favors the explosive merger of two burned out stars; small, dim, and dense stars known as white dwarfs, the final state for stars like our Sun.
If objects from space kindled life on Earth, how did it happen?
The terrestrial or extra-terrestrial case for important ingredients that led to the building blocks of life is a hot debate. A new paper says that adenosine triphosphate, similar to what is now found in all living cells and vital for generating the energy that makes something alive, could have been created when meteorites containing phosphorus minerals landed in hot, acidic pools of liquids around volcanoes, which were likely to have been common across the early Earth.
Building on work done by Dominic ffytche et al in 2000, which delineates more than a dozen types of hallucinations, particularly in relation to people with Charles Bonnet syndrome (a condition that causes patients with visual loss to have complex visual hallucinations), a new paper in Brain outlines case studies of hallucinations of musical notation, and commented on the neural basis of such hallucinations.
While ffytche believes that hallucinations of musical notation are rarer than some other types of visual hallucination, Professor Oliver Sacks M.D. details eight examples of people who have reported experiencing hallucinations of musical notation, including:
Bodily fluids contain lots of information about the health of people, that is why medical doctors routinely have blood and urine analyzed.
But bodily fluids can do more than mark infectious diseases or cancer and organ failure, researchers at ETH Zurich and at the University Hospital Zurich have shown they can take advantage of modern high-resolution analytical methods to provide real-time information on the chemical composition of exhaled breath.
Yes, your breath has an identifiable individual chemical pattern. Call it a a 'breathprint'?
The first published results from the Alpha Magnetic Spectrometer (AMS) physics experiment on the International Space Station were announced today and though the result is the most precise measurement to date of the ratio of positrons to electrons in cosmic rays, we still have not caught our first glimpse into dark matter.
The AMS experiment, constructed at universities around the world and assembled at the European Organization for Nuclear Research (CERN), is the world's most precise detector of cosmic rays. It was installed on the Space Station May 19th, 2011 after having been brought into orbit on the last flight of NASA's space shuttle Endeavour. To date it has measured over 30 billion cosmic ray events.
Food so cheap that poor people can be fat is a miracle only dreamed about by philosophers ad economists throughout history. It was previously believed that the labor force needed to produce enough food would outstrip the food they could produce, something like how trying to exceed the speed of light adds too much mass.
are the quintessential bad boys of neurobiology.
These clumps of misfolded proteins found in the brains of people with Alzheimer's disease and other neurodegenerative disorders muck up the seamless workings of the neurons responsible for memory and movement, and researchers around the world have devoted themselves to devising ways of blocking their production or accumulation in humans.
Understanding how amyloids form requires an understanding of the biology of proteins, which are essentially strings of smaller components called amino acids attached end to end. Once they're made, these protein strings twist and fold into specific three-dimensional shapes that fit together like keys and locks to do the work of the cell.
PubMed Central is costing biomedical journal sites readership and that effect is increasing over time.
The bulk of modern biomedical studies are controlled by the government, which means taxpayer-funding, so it makes sense that the results would be available to the public, but Phillip M. Davis writing in The FASEB Journal says that PubMed draws readership away from the scientific journal even when journals themselves are providing free access to the articles.
Male and female blue tits look a lot alike to us but in the UV-range, visible to birds, the male is much more colorful.
Two new symbionts living in the gut of termites have been discovered. These single-cell protists, Cthulhu macrofasciculumque and Cthylla microfasciculumque, help termites digest wood. And now they have a name inspired by science fiction.
The current situation and future prospects for biosimilars is similar to that of small molecule drugs, according to an analysis by Research and Markets: they get to benefit from patent expiry. On this basis, prospects for biosimilars might look good, with the vast majority of leading originator brands in the global biologics market expected to lose some degree of protection by 2019. | <urn:uuid:ae1f10d3-da04-4520-9e95-941f48f95a54> | 2.953125 | 1,473 | Content Listing | Science & Tech. | 31.630072 |
|PL/SQL User's Guide and Reference
10g Release 1 (10.1)
Part Number B10807-01
return_value := SCN_TO_TIMESTAMP(number);
SCN_TO_TIMESTAMP takes an argument that represents a system change number (SCN) and returns the timestamp associated with that SCN. The returned value has the datatype
This function is part of the flashback query feature. System change numbers provide a precise way to specify the database state at a moment in time, so that you can see the data as it was at that moment.
Call this function to find out the date and time associated with an SCN that you have stored to use with flashback query.
DECLARE right_now TIMESTAMP; yesterday TIMESTAMP; sometime TIMESTAMP; scn1 INTEGER; scn2 INTEGER; scn3 INTEGER; BEGIN -- Get the current SCN. right_now := SYSTIMESTAMP; scn1 := TIMESTAMP_TO_SCN(right_now); dbms_output.put_line('Current SCN is ' || scn1); -- Get the SCN from exactly 1 day ago. yesterday := right_now - 1; scn2 := TIMESTAMP_TO_SCN(yesterday); dbms_output.put_line('SCN from yesterday is ' || scn2); -- Find an arbitrary SCN somewhere between yesterday and today. -- (In a real program we would have stored the SCN at some significant moment.) scn3 := (scn1 + scn2) / 2; -- Find out what time that SCN was in effect. sometime := SCN_TO_TIMESTAMP(scn3); dbms_output.put_line('SCN ' || scn3 || ' was in effect at ' || TO_CHAR(sometime)); END; / | <urn:uuid:7ee95074-e3ec-4d7c-997f-3ff7005a73fa> | 3.125 | 414 | Documentation | Software Dev. | 56.8696 |
New data suggests that Mercury has undergone much more dynamic
processes than previously believed and that its core is unlike any
of the other rocky planets in our solar system.
Nasa's Messenger spacecraft, which has been in orbit around
the solar system's smallest and innermost planet for just over a
year, has beamed back plenty of surprises for scientists here on
"I thought the surface of Mercury would turn out to be complex
and the interior simple," said planetary scientist Maria Zuber of
MIT, who is a member of the Messenger team and co-author of two new
papers on the planet that appear March 21 in Science.
"Instead, our data has been such a surprise that we kept thinking
we were interpreting it wrong." Continue reading | <urn:uuid:0975ac71-a43c-4549-8bf4-a741e31d89bd> | 3.265625 | 156 | Truncated | Science & Tech. | 28.74814 |
Bryogeography of the Hypopterygiaceae
The moss family Hypopterygiaceae contains eight genera. This page discusses the bryogeography of the family with hypotheses as to how some the family's current distribution arose. The bulk of the information is taken from Chapter 7 of Kruijer's monograph listed in the references at the end of this page.
The genus Hypopterygium, on which the family name is based, contains seven species and, as a genus, is widespread. The following map shows the parts of the world in which the genus is found.
To say that the genus is found in all those areas is not to say that all species are widespread. Hypopterygium tamarisci is very widespread and found in most of the areas marked above, except Hawaii and the north-west of North America. By contrast, Hypopterygium sandwicense is known only from Hawaii.
Cyathophorum is another genus with seven species and has the following distribution.
The combined distribution of the two species of Lopidium covers much of the area occupied by Cyathophorum but with a presence in more of continental Africa as well as Madagascar and parts of South America. Each of the remaining five genera contains only one species. Dendrocyathophorum is found from Papua New Guinea through to SE Asia, China and Japan. Arbusculohypopterygium is found only in South America while Canalohypopterygium, Catharomnium and Dendrohypopterygium are restricted to New Zealand and some adjacent islands.
The spores of the Hypopterygiaceae generally have diameters in the 9-25 micrometre range, though sometimes up to 35 micrometres. In theory the bulk of the spores of the Hypopterygiaceae are small enough to be carried several thousand kilometres by air streams. The vegetative propagules are larger and capable of only short distance dispersal. Spores of several members of the Hypopterygiaceae were included in experiments on UV tolerance and resistance to frost and drought. The experiments indicated that some of those Hypopterygiaceae could survive transport between, say, Australia and New Zealand, during winter in streams of moist air. However, the spores would be very unlikely to survive a trip between Australasia and South America. Overall, long-distance dispersal would appear to be rare in the Hypopterygiaceae so that the diversity in, and distribution of, the family has been brought about by a combination of plate tectonics and continental drift.
The family is of Gondwanan origin. There are several pieces of evidence that support this hypothesis. Research supports the idea that the genera Arbusculohypopterygium, Canalohypopterygium and Dendrohypopterygium are ancient members of the family and these are endemic to New Zealand or South America. There is a high diversity at both the generic and species level in New Zealand and at the species level in Australasia and Indo Malaysia. Much of the family's present distribution is on Gondwanan fragments. Regarding a more precise location for the family's origin, the number of New Zealand endemics suggests that the family originated in eastern Gondwana. Before Gwondana broke up New Zealand was part of eastern Gondwana and was located near what is now Marie Byrd Land in Antarctica. The evidence suggests that the ancestral Hypopterygiaceae were probably found in active mountain ranges on the continental margin, in cool, temperate conditions and occupied humid, terrestrial habitats at low altitudes. Today the terrestrial Arbusculohypopterygium, Canalohypopterygium and Dendrohypopterygium are largely found in such habitats, though occasionally at higher altitudes. Ancestors of the ancient genera now found in New Zealand must have been in what is now New Zealand before its separation from Gondwana. Since the New Zealand micro-continent separated from Gondwana between 84 and 86 million years ago the family Hypopterygiaceae would be at least 84 million years old.
As the fragments of the original Gondwanan home of the Hypopterygiaceae drifted their separate ways species evolved independently in each fragment. Over time increasing areas of the Gondwanan fragments moved into warm-temperate zones and the descendents of the originally cool-temperate Hypopterygiaceae moved into higher altitudes. The move into warm-temperate zones, with the consequent higher rainfall and humidity meant that more exposed habitats could be occupied and descendents of the terrestrial species now colonized plants and rocks as well. The increase in angiosperm diversity also created a variety of woody substrates. The gametophytes of the three ancient genera are dendroid, with a fan of leafy branches atop a robust stem that is several to many centimetres tall. Such a growth habit is advantageous to terrestrial bryophytes growing on the forest floor, since the photosynthesizing leaves are kept above the terrestrial leaf litter layer. Such stems confer no advantage to bryophytes growing on boulders or tree trunks. Amongst the species that evolved later are non-dendroid forms, with gametophytes that are fan-like or just simple leafy stems.
In his monograph Kruijer gives possible hypotheses for the present distribution of each species. It would take too much space to include all those hypotheses on this web page, so a few examples will suffice.
The Hypopterygiaceae would have reached Asia once Gondwanan fragments had migrated close enough to make the dispersal distance no longer a challenge. There are two possibilities as to migration routes into Asia. One is that ancestors of the current Asian Hypopterygiaceae were carried north on the Indian subcontinent and then moved further into Asia once India collided with Eurasia. Another possibility is that those ancestors island-hopped north from Australasia.
Included in the current distribution of Hypopterygium tamarisci are the Neotropics, southern South America and Africa. During the early Cenozoic period the northern part of South America was close to western Africa and this species may then have reached the Americas from Africa. Alternatively, the species may have reached southern South America from the east Gondwanan Hypopterygiaceae homeland via Antarctica and then migrated north. There is insufficient evidence to decide between the two hypotheses.
Of the two Lopidium species, Lopidium concinnum occurs in Australia, New Zealand, Chile, Bolivia and Brazil and Lopidium struthiopteris is found in Australia, Africa, southern India, Sri Lanka, many areas of South-East Asia, southern China, Japan, Melanesia and Polynesia. In Australia the genus is found in Tasmania and, on the mainland, in eastern Australia between the coast and the Great Dividing Range. However, the only place where the Australian ranges of the two species overlap is near the border between New South Wales and Queensland. Otherwise, in Australia, Lopidium concinnum is found to the south and Lopidium struthiopteris to the north. In Kruijer's view the current world distributions of the two species reflect the occurrence of Lopidium concinnum in the cooler southern areas in Cretaceous Gondwana and the other's occurrence in the warmer north at that time.
Hypopterygium sandwicense occurs only in the Hawaiian islands, more precisely on the islands of Hawaii and Maui and is reported to be rare on the latter. Presumably propagules of an ancestor reached the islands. Earlier in this page it was said that long distance dispersal was probably rare in the Hypopterygiaceae but rare does not mean impossible. Over a long period of time the chance of a rare event happening increases. | <urn:uuid:9c66a5b2-c4c2-4dd5-a27f-050b7d98ac0a> | 3.171875 | 1,632 | Knowledge Article | Science & Tech. | 23.745306 |
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The bitand operator is an alternative representation of the &operator (bitwise AND).
The bitwise AND operator compares each bit of the first operand to the corresponding bit of the second operand When both bits are 1, the corresponding result bit is set to 1. Otherwise, the corresponding result bit is set to 0.
In order to use the bitand operator, you need to check the Enable new operator names option (the -Vn compiler switch, available on the Compatibility page of the Project > Options dialog box). | <urn:uuid:6f35f999-7a1a-45c1-9c22-ae957260fa45> | 2.8125 | 119 | Documentation | Software Dev. | 30.842174 |
Science Keywords>LAND SURFACE
North American ASTER Land Surface Emissivity DatabaseEntry ID: naalsed
Abstract: The North American Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) Land Surface Emissivity Database (NAALSED) covers the continent with 3,327 1 degree (°) x 1° tiles of 100-meter (m) resolution data. The data are placed in geographic coordinates (latitude, longitude) and distributed as Hierarchical Data Format Version 5 (HDF5) files.
Each NAALSED product contains several ... layers of related data such as Emissivity, Temperature, and a top of atmosphere Normalized Difference Vegetation Index (NDVI). Additional supporting layers include a regional version of the ASTER Global Digital Elevation Model (GDEM) V001 resampled to 100-m, a land water map, pixel geographic coordinates, and the number of observations used as input. The NAALSED parameters are averaged for every clear-sky pixel available in the ASTER mission record from 2000 through 2010. A New ASTER Cloud Mask Algorithm (NACMA) 2 was developed specifically to identify inputs to the ASTER Land Surface Emissivity Aggregation Algorithm (ALSEA) 1 that generates the parameter means and standard deviations in each tile. A full description of the methodology used to generate NAALSED is written in the references below.3
SPECIAL NOTE: The Emissivity Science Data Set in the NAALSED product is multidimensional, i.e., the emissivity layer is a stack of layers including mean and standard deviation for each of the five spectral Bands. MATLAB routines were used to write the data layer, which are executed in column-major rather than row-major order. "Column-major" means that arrays are read up and down instead of back and forth, resulting in an image with values rotated 90 degrees and flipped horizontally.
Please note NAALSED is affected as any other ASTER product by the loss of stable SWIR data from April 2008 forward.
1 Hulley, G.C., S.J. Hook, and , A.M. Baldridge, 2008, ASTER Land Surface Emissivity Database of California and Nevada, Geophysical Research Letters, Vol. 35, L13401, doi:10.1029/2008GL034507
2 Hulley G.C., and S.J. Hook, 2008, A New Methodology for Cloud Detection and Classification with Advanced Spaceborne Thermal Emission and Reflection (ASTER) Data , Geophysical Research Letters, Vol. 35, L16812, doi:10.1029/2008GL034644
3 Hulley, G. C. and S. J. Hook, 2009 The North American ASTER land surface emissivity database (NAALSED) version 2.0, Remote Sensing of Environment, vol. 113, no. 9, pp. 1967-1975, September
4 Hulley, G.C., and S.J. Hook, 2010, Generating Consistent Land Surface Temperature and Emissivity Products Between ASTER and MODIS Data for Earth Science Research, IEEE Transactions on Geoscience and Remote Sensing, DOI: 10.1109/TGRS.2010.2063034.
5 Hulley, G. C., S. J. Hook, and A. M. Baldridge, 2009. Validation of the North American ASTER Land Surface Emissivity Database (NAALSED) Version 2.0., Remote Sensing of Environment, 113, 2224-2233.
V003 data set release date: 2002-05-03
Data Set Characteristics:
Geographic Extent: (80°North, -171°West) (22°North, -54°West)
Scene Coverage: 1º x 1º tiles
Image Dimensions: 1,000 x 1,000
Tile Volume: ~40 MB
File Format: Hierarchical Data Format Version 5 (HDF5)
Map Projection: Geographic Lat/Lon
(Click for Interactive Map)
Data Set Citation
Dataset Originator/Creator: Hulley, G.C. and S.J. Hook
Dataset Title: NAALSED
Dataset Series Name: North American Advanced Spaceborne Thermal Emission and Reflection radiometer Land Surface Emissivity Database
Dataset Release Date: 2012-02-03
Dataset Release Place: Sioux Falls, SD, USA
Dataset Publisher: NASA LP DAAC
Version: V003Online Resource: https://lpdaac.usgs.gov
Start Date: 2000-11-10Stop Date: 2010-12-31
Latitude Resolution: 100 m
Longitude Resolution: 100 m
Horizontal Resolution Range: 100 meters - < 250 meters
BIOSPHERE > VEGETATION > VEGETATION INDEX
LAND SURFACE > LAND TEMPERATURE > LAND SURFACE TEMPERATURE
LAND SURFACE > SURFACE RADIATIVE PROPERTIES > EMISSIVITY
LAND SURFACE > SURFACE RADIATIVE PROPERTIES > THERMAL PROPERTIES
LAND SURFACE > TOPOGRAPHY > TERRAIN ELEVATION
LAND SURFACE > TOPOGRAPHY > TOPOGRAPHICAL RELIEF
Quality Users are advised that ASTER SWIR data acquired from late April 2008 to the present exhibit anomalous saturation of values and anomalous striping. This effect is also present for some prior acquisition periods. Please refer to the ASTER SWIR User Advisory Document (https://lpdaac.usgs.gov/sites/default/files/public/aster/docs/ASTER...) for more details.
Access Constraints None.
Use Constraints None.
Data Set Progress
Distribution Media: HTTP
Distribution Size: ~40 MB Tiles
Distribution Format: HDF5
Role: TECHNICAL CONTACT
Phone: (Toll Free) (866) 573-3222
Phone: (605) 594-6116
Fax: (605) 594-6963
Email: LPDAAC at usgs.gov
LP DAAC User Services U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center 47914 252nd Street
City: Sioux Falls
Province or State: SD
Postal Code: 57198-0001
Hulley, G.C., S.J Hook, and A.M. Baldridge (2008), ASTER Land Surface Emissivity Database of California and Nevada, Geophysical Research Letters, 35, doi:10.1029/2008GL034507
Hulley, G.C., and S.J Hook (2008), A New Methodology for Cloud Detection and Classification with Advanced Spaceborne Thermal Emission and Reflection (ASTER) Data, Geophysical Research Letters, 35, doi:10.1029/2008GL034644
Hulley, G. C. and S. J. Hook (2009), The North American ASTER land surface emissivity database (NAALSED) version 2.0, Remote Sensing of Environment, 113, 9
Hulley, G.C., and S.J. Hook (2010), Generating Consistent Land Surface Temperature and Emissivity Products Between ASTER and MODIS Data for Earth Science Research, IEEE Transactions on Geoscience and Remote Sensing, doi:10.1109/TGRS.2010.2063034
North American ASTER Land Surface Emissivity Database (NAALSED) publication references: [available online at http://emissivity.jpl.nasa.gov/pubs]
Extended Metadata Properties
(Click to view more)
Creation and Review Dates
DIF Creation Date: 2012-01-03
Last DIF Revision Date: 2013-01-31 | <urn:uuid:de65aac3-9a03-4877-ad59-b2fbe7cb6964> | 2.703125 | 1,678 | Structured Data | Science & Tech. | 51.924961 |
The broad concept of Oecophoridae, as treated by Clarke (1941), Hodges (1974) and others has been narrowed to include only two subfamilies: Oecophorinae and Stathmopodinae (Hodges, 1998). The family lacks autapomorphies and has been defined by two polymorphic parallelisms and one reversal: 1) second abdominal sternum with a pair of venulae or a pair of venulae and a pair of apodemes, 2) abdominal terga with or without spiniform setae, and 3) the hindwing with Rs and M1 separate. The family also has the gnathos broadly fused with the tegumen and that is tapered to a slender or rounded apex with the dorsomedial surface covered with small dentate or slender projections. Oecophoridae are also characterized by strongly recurved labial palpi.
Oecophoridae has a worldwide distribution and is one of the largest families of Gelechioidea, including more than 3,150 species in about 326 genera. Larvae have diverse feeding habits with some feeding mainly on dead plant tissue and others in fruits and flowers, as well some species being predatory on Homoptera.
Hodges (1998) defined this subfamily by the abdominal terga lacking spiniform setae or having these setae in a broad band. He noted that most characters were variable, but that the labial palpus is often very slender and long.
Larvae feed mainly on dead plant tissue, especially on leaf litter in Australia. Larvae have a variety of habits, some living in portable cases, others tunneling into wood or flowers, and some tying leaves. Pupation occurs in the larval shelter (Scoble, 1992).
Although this subfamily occurs worldwide, it is the most diverse group of Lepidoptera in Australia (Common, 1990; Hodges, 1998). Oecophorinae includes about 3,000 species in 300 genera (Hodges, 1998), although a large number of species in Australia and other regions are undescribed.
Hofmannophila pseudosptretella is a widespread pest of stored products, including grain, dried fruit, seeds, and furs (Scoble, 1992).
Refererences: Clarke (1941, 1963), Common (1990, 1994, 1997), Hodges (1974), Leraut (1989, 1993), Lvovskii (1981), Meyrick (1922), Patocka (1989), Stehr (1987), Toll (1964).
The family group name has been credited to Meyrick (1913) rather than Janse (1917), and this taxon is sometimes given family status (Koster and Sinev, 2003). Hodges (1998) defined this subfamily by the automorphy of the abdominal terga having spiniform setae on their posterior margins. Additionally, the wall of the aedeagus has a ventrodistal, sclerotized projection. The female genitalia have paired signa, with sclerotized plates having a mesial, inwardly directed flange, and often with secondary signa consisting of rows of conical projections that are directed inwardly. Most species have slender wings and closely appressed scales on the head and distinctive hind legs bearing whorls of stout setae (Scoble, 1992; Hodges, 1998). Most species have raised hind legs when at rest, and a large number are brightly colored and diurnal (Scoble, 1992).
Larvae have quite variable habits, feeding on fruits and flowers, sporangia of ferns, dead plant tissue, and as predators on scale insects, aphids, and eggs of spiders (Scoble, 1992; Hodges, 1998; Koster and Sinev, 2003). Some species are pests of cultivated plants, e.g., persimmon and carob (Koster and Sinev, 2003).
Species in this subfamily are pantropical/subtropical, especially diverse in the Afrotropical and Indo-Australian Regions. The subfamily includes about 150 species in 26 genera (Hodges, 1998).
References: Common (1990), Hodges (1978), Janse (1917), Kasy (1973), Meyrick (1913), Walsingham (1889). | <urn:uuid:148a876e-e5ac-469e-a790-4ccc0875d163> | 3.28125 | 920 | Knowledge Article | Science & Tech. | 39.390791 |
A Nasa animation demonstrates the agency's plan to capture an asteroid in the moon's orbit. The idea is for a robot to catch a small asteroid by pushing or pulling it into a stable orbit. This would allow astronauts to explore the rock and test samples. Nasa hopes to achieve this by 2021. The mission forms part of a long-term goal to send astronauts to Mars
Defend the space base station from asteroids that are about to hit. Do this using your spaceship.
« previous1 next » | <urn:uuid:c59f61ac-e338-498f-92d9-2c662e13c336> | 3.5625 | 101 | Truncated | Science & Tech. | 64.08697 |
Csóka, GY., and Kovács, T. 1999. Xylophagous insects. Forest Research Institute. Erdészeti Turományos Intézet. Agroinform Kiadó, Budapest. 189 pp.
The xylophagous insects in their different developmental stages are eaten by many species of animals. In this chapter we discuss the most characteristic groups of these predators, without the intention of listing them completely. The adults flying at dusk are mainly preyed on by bats. Bats only consume the less chitinized, more easily digestible parts (such as the abdomen) of larger beetles, such as some longhorn beetles for example. The daily food consumption of bats can reach 20-25 % of their body weight. Fragments of xylophagous insects can also be found in pellets of a range of owl species. Wild boars, badgers and foxes frequently look for larger xylophagous larvae in fallen decaying wood. Where they occur, brown bear and martens also feed on these larvae. The xylophages represent a high percentage in the diet of the insectivorous mammals (hedgehogs, moles and shrews). Not only the species known as insectivores feed on them; small rodents, such as forest mice (Apodemus for example) also eat a lot of them.
Although a hidden way of life provides some level of protection from some native enemies, not even the larvae that develop deep in the heartwood are completely safe. The larger woodpeckers, such as the Great Spotted Woodpecker (Dendrocopus major) in the photo are able to excavate large larvae feeding deep in the heartwood.
This is an indirect indication that the larvae are very rich in nutrients and energy, otherwise it would not be profitable to look for them with very high energy investment. Feeding on larvae which are smaller but occurring in large numbers can also be profitable. According to some observations one woodpecker can consume up to 100 bark beetle larvae per day. Larvae developing deep in the heartwood are also threatened by parasitoids. The larvae of the large parasitic wasp Ephialtes mesocentrus develop in larvae of larger longhorn beetles living in hardwood trees such as oak, beech and hornbeam. The female parasitoid, when looking for a host for her offspring, touches the surface of the wood and finds the location of the larval chambers by detecting the very fine tremors and noises made by the longhorn larvae. After detecting the larva she bores with her ovipositor until she reaches the host, up to 3-4 cm deep inside the tree. Then she lays her egg into the cerambycid larva. Her offspring finally will kill the host. Rhyssa persuaria, a parastic wasp of woodwasp larvae, has practically the same life cycle. Unfortunately this species has become rare in the last decades. The smaller parasitoids often attack the host in groups, as can be demonstrated by the pupae of the small parasitoid wasps killed the larva of Currant Clearwing (Synanthedon tipuliformis). The larvae of these small parasitoids often enter via the tunnels made by the xylophagous insect itself. In many cases the parasitoids find these fine holes by detecting the presence of the symbiotic fungus of the xylophages (in the case of woodwasps for example). So the mutualist sometimes "betrays" its partner.
The largest European wasp species (Megascolia flavifrons) has a very special life history. The female uses her sting to paralyse the host (larvae of stag beetle and rhinoceros beetle) and lays a single egg on the surface of it. The wasp larva feeds as an ectoparasite, finally killing the host and leaving its larval skin behind. Unfortunately, as large, old and decaying trees become rare both the hosts and the huge wasp are becoming less and less common.
The larvae developing beneath the bark are preyed on by the larvae of Cardinal Beetles (Pyrochroa coccinea). Both larvae and adults of many rove beetle (family Staphylinidae) are predaceous. Some tiny species of this group are specialised for entering bark beetle galleries and feeding on their eggs, larvae and pupae. The beetle Clerus mutillarius and its relatives are very efficient predators of bark beetles and other smaller xylophagous insects. According to some observations the larvae of a species of this group consumes 10-15 bark beetle larva during its larval development and up to 160 bark beetles in its adult stage. Some of these predators resemble the appearance of their most common prey. The evident advantage of this special mimicry is that the prey will recognise the danger too late and will often not be able to escape from the predator. Ants prey on many insects - including xylophagous insects - up to several magnitudes larger then themselves. | <urn:uuid:36705671-4adc-4ef2-8041-8897a51eb14a> | 3.609375 | 1,053 | Knowledge Article | Science & Tech. | 42.495317 |
Aerodynamic drag is the resistance (retarding effect) applied to a body as it passes through the air. It is made up of two components, caused by pressure and by friction. Resistance caused by pressure occurs because there is a difference in air pressure between the front and rear surfaces of the body. This has to be overcome to keep the body moving through the air, and is particularly significant in the case of relatively flat-surfaced, bulky objects such as motor vehicles. If the body moving through the air is slim and streamlined, however, like a modern aircraft, resistance due to friction represents a higher proportion of total aerodynamic drag. It is caused by the airflow rubbing against the surfaces as it passes over them.
Aerodynamic drag increases at the same rate as the square of the air speed. In other words if the speed doubles, the drag increases fourfold; if it quadruples, it increases sixteen-fold. See also: cd value. | <urn:uuid:59771d48-e3c3-479a-b308-64490c393bf5> | 3.828125 | 194 | Knowledge Article | Science & Tech. | 44.174672 |
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.
psychological testing and measurement
...of odours), it constitutes an ordinal scale. An interval scale has equal units and an arbitrarily assigned zero point; one such scale, for example, is the Fahrenheit temperature scale. Ratio scales not only provide equal units but also have absolute zero points; examples include measures of weight and distance.
What made you want to look up "ratio scale"? Please share what surprised you most... | <urn:uuid:1b399ee3-5693-494f-b543-bda92700de32> | 3.03125 | 122 | Knowledge Article | Science & Tech. | 38.66125 |
Interesting things occur when solutes are added to water. Freezing is inhibited and temperature decreases. Practical applications can be had from these properties. Duration: 4:37.
VIDEO CHECK QUESTIONS
8.4a What happens to the rate of freezing when a solute such as NaCl is added to the water?
8.4b How can you increase the rate of freezing when you have a solute added in the water?
8.4c Why is salt put onto icy roads?
All video check questions can be downloaded from the EXTRAs menu. | <urn:uuid:c97086f5-88bc-4609-a87b-d0fc8baca9ac> | 3.046875 | 120 | Tutorial | Science & Tech. | 67.969545 |
An aqueous antifreeze solution is 58.0% ethylene glycol (C2H6O2) by mass. The density of the solution is 1.075 g/cm3. Calculate molality, molarity, and mole fraction of ethylene glycol.
y=x is a particular solution for 2(x^2)y''+xy'+y=0 find the full solution
2 Hailstone Sequences [12 marks] A hailstone sequence is a sequence of integers found by applying the following rule: Hailstone Iteration: For an integer n in a hailstone sequence, the next item in the sequence is 3n + 1 if n is odd, or n / 2 if n is even. For example, the...
which of the following statements describes an aspect of the U.S. Constitution that makes it a conservative document that limited cultural change?
WHY DOES THE CONDUCTIVITY OF A SOLUTION CHANGE OVERNIGHT
The indicator propyl red has Ka = 3.3 10-6. What would be the approximate pH range over which it would change color? | <urn:uuid:3e6a3890-ae88-45fe-9941-66f52ca5b933> | 2.921875 | 236 | Content Listing | Science & Tech. | 65.040538 |
wchar_t* wcstok (wchar_t* wcs, const wchar_t* delimiters);
Split wide string into tokens
A sequence of calls to this function split wcs into tokens, which are sequences of contiguous wide characters separated by any of the wide characters that are part of delimiters.
On a first call, the function expects a C wide string as argument for wcs, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of last token as the new starting location for scanning.
This is the wide character equivalent of strtok (<cstdlib>), and operates in the same way (see strtok for more details).
- C wide string to truncate.
Notice that the contents of this string are modified and broken into smaller strings (tokens).
Alternativelly, a null pointer may be specified, in which case the function continues scanning where a previous successful call to the function ended.
- C wide string containing the delimiter wide characters.
These may vary from one call to another.
A pointer to the last token found in the wide string.
A null pointer is returned if there are no tokens left to retrieve.
/* wcstok example */
int main ()
wchar_t wcs = L"- This, a sample string.";
wchar_t * pwc;
wprintf (L"Splitting wide string \"%ls\" into tokens:\n",wcs);
pwc = wcstok (wcs,L" ,.-");
while (pwc != NULL)
pwc = wcstok (NULL,L" ,.-");
Splitting wide string "- This, a sample string." into tokens:
- Split string into tokens (function
- Get span until character in wide string (function
- Locate characters in wide string (function | <urn:uuid:1c1f593b-9d31-4f24-8840-0b2a561f8d88> | 3.09375 | 418 | Documentation | Software Dev. | 62.345673 |
Most of the time the Sun is quiet, shining in space beaming out light and heat. But every eleven years it gets cranky – covered in dark spots and fiery eruptions. This is a time called solar maximum, or solar max for short.
The Sun, like all stars, is a big ball of plasma – mostly hydrogen and helium. Because the Sun is so big – 100 million times bigger than Earth – it has a lot of gravity. The gravity squeezes the plasma so hard that it gives off heat and light. Scientists call this nuclear fusion.
Nuclear fusion also makes magnetism, making the Sun a giant magnet in space.
As the Sun spins around in space, the magnetism inside the Sun becomes more and more twisted. After 11 years of twisting the magnetism begins to snap apart – like a rubber band that’s been twisted too much.
When the magnetism snaps, sunspots (dark patches) appear on the surface of the Sun. Prominences and flares are also common, which look like loops and tongues of fires erupting from the Sun.
Flares cause pieces of the Sun – called radiation – to blast into space.
Luckily, our planet has a strong magnetic barrier that protects us from this radiation. Sometimes the radiation causes satellites to turn off or cause electricity supplies to black out. It can also make beautiful lights in the night sky close to the North and South Poles, called aurora.
There are many telescopes and spacecraft watching the Sun. For example, the SOHO spacecraft has been doing it since 1995.
Another spacecraft called Genesis captured pieces of the Sun and brought them back to Earth.
In 2018, scientists will send a spacecraft called Solar Probe+ to travel into the Sun. They don’t expect it to return.
This article appeared in the January 2011 edition of Scientriffic. | <urn:uuid:f898e34d-5e55-42f5-af52-8d07f9eb2170> | 3.90625 | 383 | Personal Blog | Science & Tech. | 61.456914 |
Read more: "Climate change: It's even worse than we thought"
If we stopped pumping more CO2 into the atmosphere now, we'd have a very good chance of avoiding a big hike in temperature. But there is no sign of that happening. Annual emissions fell only slightly after 2008 - the biggest financial crisis since the Great Depression - and are now climbing more rapidly than ever (see diagram). So far they are near the top of the IPCC's worst-case emissions scenario. "Our emissions are not slowing," says Paul Valdes of the University of Bristol, UK. "That's the most scary aspect of our future."
The only international agreement to limit greenhouse-gas emissions, the Kyoto protocol, excluded developing countries and involved only minor cuts. The US never signed up and Canada has withdrawn. Hopes for a more effective and inclusive agreement have faded.
Meanwhile China, now the world's biggest ...
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content. | <urn:uuid:6e826f14-7a65-4343-8a4b-c5e43875329a> | 2.921875 | 212 | Truncated | Science & Tech. | 49.758023 |
Image Formation in Plane Mirrors
Visit The Physics Classroom's Flickr Galleries and enjoy a photo overview of the topic of reflection and mirrors.
Other Multiple Mirror Systems
Besides right angle mirror systems, there is a wealth of other multiple mirror systems that involve two or more mirrors. If two plane mirrors are placed together on one of their edges so as to form a right angle mirror system and then the angle between them is decreased, some interesting observations can be made. One observes that as the angle between the mirrors decreases, the number of images that can be seen increases. In fact as the angle between the mirrors approaches 0 degrees (i.e., the mirrors are parallel to each other), the number of images approaches infinity.
The generation of two images is not difficult to explain; each of the two mirrors produces an image due to the single reflection of light off one of the mirror faces to an observer's eye. The remaining images are produced as the result of multiple reflections of light off more than one of the faces. Right angle mirrors will allow a maximum of two reflections of light from the object. But as the angle decreases, three, four, and even more reflections can occur.
Determining the image locations for such multiple mirror systems can become complicated. First determine the location of the primary images using the principle that the image distance to the mirror is the same as the object distance to the mirror. Each primary image forms a secondary image as a result of a double reflection. By extending one of the mirror lines, a primary image can be reflected (a geometry term, not a physics term) across the second mirror line to form a secondary image - an image of an image. As an example, consider the diagram below for an object placed between two plane mirrors that make a 60-degree angle. Images I1 and I2 are primary images formed by the two plane mirrors. Image I3 was found by reflecting image I2 across the extension of the top mirror. And image I4 was found by reflecting the image I1 across the side mirror. The process can be repeated to determine the location of an image of an image of an image.
Ray diagrams for these multiple mirror systems are drawn much like they were for right angle mirror systems. Once you have located the images, begin by drawing a line of sight towards the image; this would be the reflected ray that ultimately travels to your eye. For a secondary image, this reflected ray is associated with an incident ray that had reflected off the other face of the mirror. The law of reflection can be used to determine the direction it was traveling as it was incident upon this face of the mirror. Repeat this process to determine the point of reflections on each face, tracing the path of light back to its origin - the object itself. A completed ray diagram for a secondary image on a 60-degree mirror system is shown below.
Flickr Physics Photo
When the two mirrors are aligned at a 0-degree angle with each other (i.e., a parallel mirror system), there are an infinite number of images. Each image is the result of an image of an image, or an image of an image of an image or an image of an image of ... . The diagram below shows the multiple images for a parallel mirror system. Images I1 and I2 are primary images. Image I1 is the image resulting from the reflection of the object O across mirror M1 and image I2 is the image resulting from the reflection of the object O across mirror M2. Image I3 is an image of image I1, found by reflecting image I1 across mirror M2. Image I4 is an image of image I2; found by reflecting image I2 across mirror M1. This process could continue indefinitely, producing images of images for an infinite number of images.
Multiple mirror systems are merely the extension of what we have already learned about plane mirrors. The locating of images is an extension of the principle that the image distance to the mirror is the same as the object distance to the mirror. Drawing ray diagrams for multiple mirror systems is an extension of the line of sight and law of reflection principles.
Flickr Physics Photo
1. Rose Inhatt stands between a set of parallel plane mirrors (M1 and M2) as shown in the diagram below. There is a flower on Rose's hat that is located a distance of 0.4 m from M1 and a distance of 1.0 m from M2. Since the mirrors are parallel, Rose will see an infinite number of images of the flower as she looks in mirror M2. These images stretch towards infinity. Some of the images are closer to the mirror than others.
Determine the distance between mirror M2 and the...
a. ... nearest image ____________
b. ... second nearest image____________
c. ... the third nearest image ____________ | <urn:uuid:fe98da02-3504-494d-96a5-56bbb66acc82> | 4.15625 | 988 | Tutorial | Science & Tech. | 51.624385 |
AcetylcholinesteraseJune 2004 Molecule of the Month by David Goodsell
doi: 10.2210/rcsb_pdb/mom_2004_6 (PDF Version, ePub Version )
Every time you move a muscle and every time you think a thought, your nerve cells are hard at work. They are processing information: receiving signals, deciding what to do with them, and dispatching new messages off to their neighbors. Some nerve cells communicate directly with muscle cells, sending them the signal to contract. Other nerve cells are involved solely in the bureaucracy of information, spending their lives communicating only with other nerve cells. But unlike our human bureaucracies, this processing of information must be fast in order to keep up with the ever-changing demands of life.
Nerves communicate with one another and with muscle cells by using neurotransmitters. These are small molecules that are released from the nerve cell and rapidly diffuse to neighboring cells, stimulating a response once they arrive. Many different neurotransmitters are used for different jobs: glutamate excites nerves into action; GABA inhibits the passing of information; dopamine and serotonin are involved in the subtle messages of thought and cognition. The main job of the neurotransmitter acetylcholine is to carry the signal from nerve cells to muscle cells. When a motor nerve cell gets the proper signal from the nervous system, it releases acetylcholine into its synapses with muscle cells. There, acetylcholine opens receptors on the muscle cells, triggering the process of contraction. Of course, once the message is passed, the neurotransmitter must be destroyed, otherwise later signals would get mixed up in a jumble of obsolete neurotransmitter molecules. The cleanup of old acetylcholine is the job of acetylcholinesterase.
Acetylcholinesterase in Action
Acetylcholinesterase is found in the synapse between nerve cells and muscle cells. It waits patiently and springs into action soon after a signal is passed, breaking down the acetylcholine into its two component parts, acetic acid and choline. This effectively stops the signal, allowing the pieces to be recycled and rebuilt into new neurotransmitters for the next message. Acetylcholinesterase has one of the fastest reaction rates of any of our enzymes, breaking up each molecule in about 80 microseconds.
Acetylcholinesterase was first studied by using the form found in electric fish, such as the torpedo ray. These fish have massive arrays of nerve-like structures in the organs that generate electricity, so acetylcholinesterase is particularly abundant. The form shown here, from PDB entry 1acj, forms a dimer in the crystal structure. It normally has lipids attached to the protein chains, which anchor the enzyme to the cell membrane. The lipids were removed in the crystal structure, however, to allow crystallization. The active site is found in a deep pocket, just big enough for the acetylcholine to slip down inside. At the base of the pocket is a triad of three amino acids--serine-histidine-glutamate--that is almost identical to the triad used in the serine proteases like trypsin and chymotrypsin.
Since acetylcholinesterase has an
essential function, it is a potential weak point in our nervous system. Poisons
and toxins that attack the enzyme cause acetylcholine to accumulate in the nerve
synapse, paralyzing the muscle. Over the years, acetylcholinesterase has been
attacked in many ways by natural enemies. For instance, some snake toxins attack
acetylcholinesterase. The picture at the top shows a view straight down the
active site tunnel, from PDB entry 1b41, showing the
active site serine in red. The middle picture shows how a lethal toxin from the
eastern green mamba blocks the active site and poisons the action of the enzyme.
For more information on snake toxins, take a look at the Protein of the Month at
the European Bioinformatics Institute.
Doctors are now willfully poisoning acetylcholinesterase in an attempt to reverse the symptoms of Alzheimer's disease. People with Alzheimer's disease lose many nerve cells as the disease progresses. By taking a drug that partially blocks acetylcholinesterase, the levels of the neurotransmitter can be raised, strengthening the nerve signals that remain. One drug being used in the way is shown at the bottom, from PDB entry 1eve. It inserts into the active site pocket and temporarily blocks entry of acetylcholine. Other poisons, as shown on the next page, take a more permanent approach.
Exploring the Structure
The nerve toxin sarin and insecticides such as
malathion directly attack the active site machinery of acetylcholinesterase. The
structure shown here, from PDB entry 1cfj, shows the
active site triad of acetylcholinesterase after being poisoned by sarin. In the
normal reaction, the serine amino acid forms a bond to the acetyl group of
acetylcholine, breaking the molecule. Then, in a matter of microseconds, a water
molecule breaks the new bond, releasing acetic acid and restoring the serine to
its original form. Sarin, however, transfers a nasty methylphosphonate group
(MeP in the picture) to the serine. The phosphonate is far more stable and will
disable the enzyme for hours or days.
This picture was created with RasMol. You can create similar pictures by clicking on the accession codes and picking one of the options under View Structure.
Further reading on acetylcholinesterase
P. Taylor (1991) The Cholinesterases. Journal of Biological Chemistry 266, 4025-4028.
P. Taylor and Z. Radic (1994) The Cholinesterases: From genes to Proteins. Annual Review of Pharmacology and Toxicology 34, 281-320.
K. L. Davis (2002) Current and Experimental Therapeutics of Alzheimer Disease. In Neuropsychopharmacology, K.L. Davis, D. Charney, J.T. Coyle, C. Nemeroff editors. Lippincott, Williams and Wilkins, publishers.
J. L. Sussman, M. Harel, F. Frolow, C. Oefner, A. Goldman, L. Toker and I. Silman (1991) Atomic structure of acetylcholinesterase from Torpedo californica: a prototypic acetylcholine-binding protein. Science 253, 872-879.
© 2013 David Goodsell & RCSB Protein Data Bank | <urn:uuid:8193161b-d4d0-4139-96ea-f467b0da9b04> | 3.203125 | 1,432 | Knowledge Article | Science & Tech. | 33.377597 |
Magma mixing at the El Hierro submarine eruption
The eruption started from a submarine fissure system on 10 October extending in a N-S direction in the submarine prolungation of El Hierro's southern rift zone, beginning at about 6 km distance from La Restinga at depth of 1000 m, until the closest vent at about 2 km distance and depth of ca. 300 m.
Above the vents, floating (still hot) scoria and bombs of up to 30 cm diamenter were first observed and sampled on 15 Oct.
The shape and texture of these scoria, with quenched surfaces due to rapid cooling with sea water, were similar to the scoria composing the cinder cones dotting the rift zone on land. This suggests that the eruption is a submarine equivalent of basaltic strombolian fissure eruptions.
The fragments were mainly black and of basanitic composition, i.e. extremely poor in silica (even less than basalt). They contain 43‐45% de SiO2 and about 2% of volatiles (H2O, CO2, Cl, S, ...) and were erupted at temperatures around 1200 ºC. Their density was about 2,700 kg/m3. A second juvenile magma component was observed as white pumice, often contained INSIDE and mechanically mixed with the black basanite lava: the white lava was analyzed to contain 63-72% silica (i.e. trachyte - rhyolite), 4-5 % volatiles, erupted at 850‐900 ºC and had densities of 2,300 kg/m3.
This felsic (=silica-rich material) was only observed in the first days of the eruption and constituted less than 10% of the total observed magma. The apparent mixing of magma might very well have been a trigger of the eruption.
New research on these floating rocks have shown that these rocks are highly radioactive to their content of Uranium and Thorium. The white part is probably a remain of mesozoic limestone (=skarn?). The white area of the rocks is rich in Uranium. So probably there was a kind of mixture and hydrothermal effects on magma from very deep areas in the earth crust.
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Cliquez ici pour recommander cette page à un ami | <urn:uuid:e737b328-314a-4728-9beb-3f383f78a3dc> | 3 | 499 | Knowledge Article | Science & Tech. | 57.891317 |
Source code: Lib/tokenize.py
The tokenize module provides a lexical scanner for Python source code, implemented in Python. The scanner in this module returns comments as tokens as well, making it useful for implementing “pretty-printers,” including colorizers for on-screen displays.
To simplify token stream handling, all Operators and Delimiters tokens are returned using the generic token.OP token type. The exact type can be determined by checking the token string field on the named tuple returned from tokenize.tokenize() for the character sequence that identifies a specific operator token.
The primary entry point is a generator:
The tokenize() generator requires one argument, readline, which must be a callable object which provides the same interface as the io.IOBase.readline() method of file objects. Each call to the function should return one line of input as bytes.
The generator produces 5-tuples with these members: the token type; the token string; a 2-tuple (srow, scol) of ints specifying the row and column where the token begins in the source; a 2-tuple (erow, ecol) of ints specifying the row and column where the token ends in the source; and the line on which the token was found. The line passed (the last tuple item) is the logical line; continuation lines are included. The 5 tuple is returned as a named tuple with the field names: type string start end line.
Changed in version 3.1: Added support for named tuples.
Token value used to indicate a comment.
Token value used to indicate a non-terminating newline. The NEWLINE token indicates the end of a logical line of Python code; NL tokens are generated when a logical line of code is continued over multiple physical lines.
Token value that indicates the encoding used to decode the source bytes into text. The first token returned by tokenize() will always be an ENCODING token.
Another function is provided to reverse the tokenization process. This is useful for creating tools that tokenize a script, modify the token stream, and write back the modified script.
Converts tokens back into Python source code. The iterable must return sequences with at least two elements, the token type and the token string. Any additional sequence elements are ignored.
The reconstructed script is returned as a single string. The result is guaranteed to tokenize back to match the input so that the conversion is lossless and round-trips are assured. The guarantee applies only to the token type and token string as the spacing between tokens (column positions) may change.
It returns bytes, encoded using the ENCODING token, which is the first token sequence output by tokenize().
tokenize() needs to detect the encoding of source files it tokenizes. The function it uses to do this is available:
It will call readline a maximum of twice, and return the encoding used (as a string) and a list of any lines (not decoded from bytes) it has read in.
It detects the encoding from the presence of a UTF-8 BOM or an encoding cookie as specified in PEP 263. If both a BOM and a cookie are present, but disagree, a SyntaxError will be raised. Note that if the BOM is found, 'utf-8-sig' will be returned as an encoding.
If no encoding is specified, then the default of 'utf-8' will be returned.
Open a file in read only mode using the encoding detected by detect_encoding().
New in version 3.2.
Example of a script rewriter that transforms float literals into Decimal objects:
from tokenize import tokenize, untokenize, NUMBER, STRING, NAME, OP from io import BytesIO def decistmt(s): """Substitute Decimals for floats in a string of statements. >>> from decimal import Decimal >>> s = 'print(+21.3e-5*-.1234/81.7)' >>> decistmt(s) "print (+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))" The format of the exponent is inherited from the platform C library. Known cases are "e-007" (Windows) and "e-07" (not Windows). Since we're only showing 12 digits, and the 13th isn't close to 5, the rest of the output should be platform-independent. >>> exec(s) #doctest: +ELLIPSIS -3.21716034272e-0...7 Output from calculations with Decimal should be identical across all platforms. >>> exec(decistmt(s)) -3.217160342717258261933904529E-7 """ result = g = tokenize(BytesIO(s.encode('utf-8')).readline) # tokenize the string for toknum, tokval, _, _, _ in g: if toknum == NUMBER and '.' in tokval: # replace NUMBER tokens result.extend([ (NAME, 'Decimal'), (OP, '('), (STRING, repr(tokval)), (OP, ')') ]) else: result.append((toknum, tokval)) return untokenize(result).decode('utf-8') | <urn:uuid:4b7a8542-e96a-4b38-9af0-aa33cd10d5d9> | 3.15625 | 1,151 | Documentation | Software Dev. | 52.143485 |
Who would ever think that building something to function deep in Antarctica in the middle of winter would be the cheap option?
New Scientist reports that astronomers at the University of New South Wales, Australia, have proposed building a new telescope (an "Extremely Large Telescope," no less, with at least a 30 meter mirror) at Dome C, an Antarctic plateau at 75° south and over three kilometers above sea level. Preliminary tests of the location, using an 85 milllimeter scope, showed that the plateau had extremely low atmospheric "jitter" because the location has very low wind speeds and little turbulence in the air. The researchers claim a two-meter telescope in that location -- a moderate size for a professional device -- would be able to image galactic phenomena with a clarity comparable to Hubble. A larger scope would be far better. Dome C could be home to the first serious Earth-based terrestrial planet-finder scope.
According to PhysOrg, the UNSW proposal has another interesting feature: much of it would be built of "icecrete" -- snow compressed to concrete-hardness.
Although a Dome C telescope would be inaccessible during use -- the temperatures that deep in the Antarctic during winter plunge as low as -86° C (-122° F) -- it could be serviced during the summer for far less expense than a trip to an orbital telescope.
here's a neat story about "icecrete" nee 'pykrete' :D
"Pykrete is a super-ice, strengthened tremendously by mixing in wood pulp as it freezes. By freezing a slurry of 14 percent wood pulp, the mechanical strength of ice rockets up to a fairly consistent 70 kg/sq cm. A 7.69 mm rifle bullet, when fired into pure ice, will penetrate to a depth of about 36 cm. Fired into pykrete, it will penetrate less than half as far about the same distance as a bullet fired into brickwork. Yet you can mold pykrete into blocks from the simplest materials and then plane it, just like wood. And it has tremendous crush resistance: a one-inch column of the stuff will support an automobile. Moreover, it takes much longer to melt than pure ice. But as strong and eco-friendly as it is, pykrete remains forgotten today save among glaciologists, who express bafflement over why no one has made use of it. "I don't really know why it has languished in obscurity," admits Professor Erland Schulson, director of the Ice Research Laboratory at Dartmouth College."
That's very cool, glory -- thanks for that info! | <urn:uuid:4c515207-8eae-4175-924d-23638c6c5341> | 3.375 | 531 | Personal Blog | Science & Tech. | 44.326519 |
Jan 31 2013
I know almost nothing about fluid dynamics but my article about wingtip vortices two weeks ago piqued my interest in the subject.
Last weekend I learned about this amazing phenomenon, the von Kármán vortex street, animated above by Cesareo de La Rosa Siqueira.
Von Kármán vortex streets occur when a fluid flows past a stationary object and generates a long line of vortices that swirl in opposite directions. The phenomenon was named for Theodore von Kármán, the man who described it, and is probably called a street because it looks like one.
We usually don’t see von Kármán vortex streets in the wind, but it’s important that engineers plan for them. If a tall structure is uniformly straight the vortices can make it fall down. Click here to read about a famous mistake.
On a small scale, von Kármán vortex streets make telephone wires sing in the wind. On a large scale they’re visible from outer space when clouds blow past a tall island.
Here’s a picture taken from the space shuttle that shows cloud cover blowing past Rishiri Island, Japan. When the wind encounters Mt. Rishiri the clouds form a von Kármán vortex street on the downwind side.
Pretty cool, huh?
There are more than twenty islands that reliably generate von Kármán vortex streets. Click here to see more pictures from NASA.
(Vortex animation by Cesareo de La Rosa Siqueira via Wikimedia Commons. Space shuttle photo from NASA via Wikimedia Commons. Click on the images to see the originals) | <urn:uuid:dbaa9aca-9707-4869-b9ad-8598e27b8646> | 3.265625 | 346 | Personal Blog | Science & Tech. | 57.513156 |
Four years ago, Rodrigo Quian Quiroga from Leicester University showed that single neurons in the brain react selectively to the faces of specific people, including celebrities like Halle Berry, Jennifer Aniston and Bill Clinton. Now, he’s back, describing single neurons that respond selectively to the concept of Saddam Hussein or Oprah Winfrey. This time, Quiroga has found that these neurons work across different senses, firing to images of Oprah or Saddam as well as their written and spoken names.
In one of his volunteers, Quiroga even found a neuron that selectively responded to photos of himself! Before the study began, he had never met the volunteers in the study, which shows that these representations form very quickly, at least within a day or so.
In his original experiments, Quiroga used electrodes to study the activity of individual neurons, in the brains of patients undergoing surgery for epilepsy. As the volunteers saw photos of celebrities, animals and other objects, some of their neurons seemed to be unusually selective. One responded to several different photos of Halle Berry (even when she was wearing a Catwoman mask), as well as a drawing of her, or her name in print. Other neurons responded in similarly specific ways to Jennifer Aniston or to landmarks like the Leaning Tower of Pisa.
The results were surprising, not least because they seemed to support the “grandmother cell theory“, a paradox proposed by biologist Jerry Lettvin. As Jake Young (now at Neurotopia) beautifully explains, Lettvin was trying to argue against oversimplifying the way the brain stores information. Lettvin illustrated the pitfalls of doing so with a hypothetical neuron – the grandmother cell – that represents your grandmother and is only active when you think or see her. He ridiculed that if such cells existed, the brain would not only run out of neurons, but losing individual cells would be catastrophic (at least for your poor forgotten grandmother).
The grandmother cell concept was espoused by headlines like “One face, one neuron” from Scientific American, but these read too much in Quiroga’s work. It certainly seemed like one particular neuron was responding to the concept of Halle Berry. But there was nothing in Quiroga’s research to show that this cell was the only one to respond to Halle Berry, nor that Halle Berry was the only thing that activated the cell. As Jake Young wrote, “The purpose of the neuron is not to encode Halle Berry.”
Instead, our brains encode objects through patterns of activity, distributed over a group of neurons, which allows our large but finite set of brain cells to cope with significantly more concepts. The solution to Lettvin’s paradox is that the job of encoding specific objects falls not to single neurons, but to groups of them. | <urn:uuid:2be2412f-d439-408d-9c06-40280e028e50> | 3.015625 | 585 | Personal Blog | Science & Tech. | 34.479044 |
This will be short but sweet. In the spirit of @J.R answer- (in particular the block section)- the information content of any "word" is most certainly less than that in an equivalent random amount of characters in that word (if one is writing) or syllables (if one is speaking.) As anyone who reads @J.R. block passage will agree, predictability is assured- providing we are on the same rational basis. Nothing more is required- anyone with any questions: look up information theory.
a definite answer as requested.
ok so it seems i need to do all the work:
Entropy is defined in the context of a probabilistic model. Independent fair coin flips >have an entropy of 1 bit per flip. A source that always generates a long string of B's has >an entropy of 0, since the next character will always be a 'B'.
The entropy rate of a data source means the average number of bits per symbol needed to encode it. Shannon's experiments with human predictors show an information rate of between 0.6 and 1.3 bits per character, depending on the experimental setup; the PPM compression algorithm can achieve a compression ratio of 1.5 bits per character in English text.
From the preceding example, note the following points:
The amount of entropy is not always an integer number of bits.
Many data bits may not convey information. For example, data structures often store information redundantly, or have identical sections regardless of the information in the data structure.
Shannon's definition of entropy, when applied to an information source, can determine the minimum channel capacity required to reliably transmit the source as encoded binary digits (see caveat below in italics). The formula can be derived by calculating the mathematical expectation of the amount of information contained in a digit from the information source. See also Shannon-Hartley theorem.
Shannon's entropy measures the information contained in a message as opposed to the portion of the message that is determined (or predictable). Examples of the latter include redundancy in language structure or statistical properties relating to the occurrence frequencies of letter or word pairs, triplets etc. See Markov chain.<
right out of wikipedia: http://en.wikipedia.org/wiki/Entropy_(information_theory)
and seeing as the random generation of an alphabetical character- in english in particular- requires 4.7 bits of information (anyone? anyone?) we simply see that there is no possible way for amount of time it takes "to read X number of characters" to scale linearly or "super-linearly" (whatever that means) with X. In particular note in the block quote of @J.R. above we can remove characters and replace them with others but still not alter the information content of the message. This clearly indicates that- as my own block quote above states- that the brain is engaged in a probabilistic modeling of what the words (spoken or written) actually are- and it is not relying on the input of a certain number of characters to ascertain what is communicated.
to the downvoters: sorry but this is well established- and the question is clearly hinting at some sort of compression algorithm- so perhaps this is not really a neuroscience problem ehh? as my shorter answer was lost somehow on those... | <urn:uuid:74b6aa44-69d7-4d37-8e03-2ccff86a8c08> | 2.984375 | 682 | Q&A Forum | Science & Tech. | 45.603606 |
On 2001-12-08 09:47, SEG9585 wrote:
Since photons in a wave of light always move at the speed of light, if the frequency of one wave was higher than another, wouldnt the higher-frequency's wave take longer to get somewhere than the light with a lower frequency over a long distance, (on a longitudal line). Since the frequency is higher, the waves are shorter and go up and down alot more than the straighter, low-frequency photon flow. This would mean the higher-frequency photon has to travel faster through its waves to keep up with the other wave, which is impossible Can someone clear this up for me?
Also, do waves travel in a mere line up and down, or does it sort of swirl as it travels? | <urn:uuid:62fee08e-f3ce-4009-b327-89b884cbb038> | 3.15625 | 162 | Comment Section | Science & Tech. | 50.926364 |
LINQ stands for Language Integrated Query and it is a set of .Net framework extensions that allow us to query various data sources using a .Net language. There are a couple of different flavors of LINQ:
a) LINQ to SQL: This is for applications that use objects mapped to the database objects.
b) LINQ to Entities: This is for applications that need more flexibility in mapping objects to a RDBMS supported by the ADO.Net data providers.
c) LINQ to XML: This provides an in memory XML API.
d) LINQ to object: This allows us to do queries against the in memory objects.
e) LINQ to Sharepoint: This allows us to query MS Sharepoint lists.
f) LINQ to DataSet: This allows us to query DataSets.
You can get more information on LINQ using these resources: | <urn:uuid:a25045b3-def1-4973-98db-e3ebb3596e83> | 2.921875 | 184 | Knowledge Article | Software Dev. | 61.5325 |
3.1 Systematic Errors
Systematic errors are uncertainties in the bias of the data. A simple example is the zeroing of an instrument such as a voltmeter. If the voltmeter is not correctly zeroed before use, then all values measured by the voltmeter will be biased, i.e., offset by some constant amount or factor. However, even if the utmost care is taken in setting the instrument to zero, one can only say that it has been zeroed to within some value. This value may be small, but it sets a limit on the degree of certainty in the measurements and thus to the conclusions that can be drawn.
An important point to be clear about is that a systematic error implies that all measurements in a set of data taken with the same instrument are shifted in the same direction by the same amount - in unison. This is in sharp contrast to random errors where each individual measurement fluctuates independently of the others. Systematic errors, therefore, are usually most important when groups of data points taken under the same conditions are being considered. Unfortunately, there is no consistent method by which systematic errors may be treated or analyzed. Each experiment must generally be considered individually and it is often very difficult just to identify the possible sources let alone estimate the magnitude of the error. Our discussion in the remainder of this chapter, therefore, will not be concerned with this topic. | <urn:uuid:9094e6b4-5afe-4ecd-b518-999222f1de45> | 3.71875 | 279 | Academic Writing | Science & Tech. | 38.967686 |
Offshore cabled seismic arrays can provide early warning systems.
The oceans are the planetary flywheel for our global climate and the underlying boundaries of tectonic plates are the loci for the formation and destruction of Earth's shallow crust. In concert, these forces generate life but also are deadly when they take the form of massive storms, earthquakes, and tsunamis. The Sumatra 9.3 magnitude earthquake and follow-on tsunami that killed 300,000 people, and the still lingering devastation of Katrina, serve as vivid reminders to the catastrophic loss of life and property resulting from such events. To understand, respond to, and best mitigate these events require long-term observations, sensor arrays in the areas of interest, and real-time communication for rapid-response capabilities.
Within the Pacific Northwest the past few decades have witnessed the impacts of significant storms and moderate earthquakes. For example the 2001 6.8 magnitude Nisqually earthquake resulted in over $2 billion in damages, the 1993 Inauguration Day Storm left more than 1 million people without power and caused ~ $130M in damages, and the 2006 Hanukkah eve storm produced hurricane force winds, left 1.8 million people without power, and caused $267M in damages in Washington and Oregon. It has been estimated that a magnitude 8.5 earthquake associated with the Cascadia Subduction Zone off Washington and Oregon could result in over $12 billion in damages, 8,000 casualties, and 30,000 buildings destroyed. Recognizing the need for offshore seismic arrays in studying and detecting earthquakes Japan has invested millions of dollars in a cabled seismic array off their coast, and NEPTUNE Canada is deploying a seismic array and tsunami detection system mid plate on the Juan de Fuca Ridge. | <urn:uuid:afd2279a-b2ac-4270-bd2b-595b6cb8f02b> | 3.390625 | 357 | Knowledge Article | Science & Tech. | 35.419685 |
Details in radiation belts close to Jupiter are mapped from measurements that NASA's Cassini spacecraft made of radio emission from high-energy electrons moving at nearly the speed of light within the belts.
The three views show the belts at different points in Jupiter's 10-hour rotation. A picture of Jupiter is superimposed to show the size of the belts relative to the planet. Cassini's radar instrument, operating in a listen-only mode, measured the strength of microwave radio emissions at a frequency of 13.8 gigahertz (13.8 billion cycles per second or 2.2centimeter wavelength). The results indicate the region near Jupiter is one of the harshest radiation environments in the solar system.
From Earth-based radio telescopes, the telltale radio emissions would be swamped out by heat-generated radio emissions from Jupiter's atmosphere, but Cassini was close enough to Jupiter in January 2001 to differentiate between the emissions from the radiation belts and those from the atmosphere.
The belts appear to wobble as the planet turns because they are controlled by Jupiter's magnetic field, which is tilted in relation to the planet's poles.
For more information about the Saturn-bound Cassini spacecraft and its observations of Jupiter, see the Cassini home page,http://saturn.jpl.nasa.gov.
Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C. | <urn:uuid:4ec931ba-d1d5-493c-9b14-3b525eb2ea55> | 4.03125 | 323 | Knowledge Article | Science & Tech. | 39.68224 |
- Physik (2) (remove)
- Clustering in heavy ion collisions : why it could happen and how to observe it? (2008)
- We argue that Clustering in heavy ion collisions could be the missing element in resolving the socalled HBT puzzle, and briefly discuss the different physical situations where clustering could be present. We then propose a method by which clustering in heavy ion collisions could be detectedin a model-independent way.
- Nanolesions induced by heavy ions in human tissues: experimental and theoretical studies (2012)
- The biological effects of energetic heavy ions are attracting increasing interest for their applications in cancer therapy and protection against space radiation. The cascade of events leading to cell death or late effects starts from stochastic energy deposition on the nanometer scale and the corresponding lesions in biological molecules, primarily DNA. We have developed experimental techniques to visualize DNA nanolesions induced by heavy ions. Nanolesions appear in cells as “streaks” which can be visualized by using different DNA repair markers. We have studied the kinetics of repair of these “streaks” also with respect to the chromatin conformation. Initial steps in the modeling of the energy deposition patterns at the micrometer and nanometer scale were made with MCHIT and TRAX models, respectively. | <urn:uuid:3f1df0d6-5b37-4c04-b901-4e3f1c9816c3> | 2.734375 | 273 | Content Listing | Science & Tech. | 20.298443 |
DNA from soil mirrors plant taxonomic and growth form diversity
Yoccoz, N.G., Bråthen, K.A., Gielly, L., Haile, J., Edwards, M.E., Goslar, T., Von Stedingk, H., Brysting, A.K., Coissac, E., Pompanan, F., Sonstebo, J.H., Miquel, C., Valentini, A., De Bello, F., Chave, J, Thuiller, W., Wincker, P., Cruaud, C., Gavory, F., Rasmussen, M., Gilbert, M.T.P., Orlando, L., Brochmann, C., Willerslev, E. and Taberlet, P. (2012) DNA from soil mirrors plant taxonomic and growth form diversity. Molecular Ecology, 21 (15). pp. 3647-3655.
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Ecosystems across the globe are threatened by climate change and human activities. New rapid survey approaches for monitoring biodiversity would greatly advance assessment and understanding of these threats. Taking advantage of next-generation DNA sequencing, we tested an approach we call metabarcoding: high-throughput and simultaneous taxa identification based on a very short (usually <100 base pairs) but informative DNA fragment. Short DNA fragments allow the use of degraded DNA from environmental samples. All analyses included amplification using plant-specific versatile primers, sequencing and estimation of taxonomic diversity. We tested in three steps whether degraded DNA from dead material in soil has the potential of efficiently assessing biodiversity in different biomes. First, soil DNA from eight boreal plant communities located in two different vegetation types (meadow and heath) was amplified. Plant diversity detected from boreal soil was highly consistent with plant taxonomic and growth form diversity estimated from conventional above-ground surveys. Second, we assessed DNA persistence using samples from formerly cultivated soils in temperate environments. We found that the number of crop DNA sequences retrieved strongly varied with years since last cultivation, and crop sequences were absent from nearby, uncultivated plots. Third, we assessed the universal applicability of DNA metabarcoding using soil samples from tropical environments: a large proportion of species and families from the study site were efficiently recovered. The results open unprecedented opportunities for large-scale DNA-based biodiversity studies across a range of taxonomic groups using standardized metabarcoding approaches.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Biological Sciences and Biotechnology|
|Copyright:||© 2012 Blackwell Publishing Ltd|
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From this point in, I will define a “set function” as a function whose domain is some collection of subsets . It’s important to note here that is not defined on points of the set , but on subsets of . For some reason, a lot of people find that confusing at first.
We’re primarily concerned with set functions which take their values in the “extended real numbers” . That is, the value of is either a real number, or , or , with the latter two being greater than all real numbers and less than all real numbers, respectively.
We say that such a set function is “additive” if whenever we have disjoint sets and in with disjoint union also in , then we have
Similarly, we say that is finitely additive if for every finite, pairwise disjoint collection whose union is also in we have
And we say that is countably additive of for every pairwise-disjoint sequence of sets in whose union is also in , we have
Now we can define a “measure” as an extended real-valued, non-negative, countably additive set function defined on an algebra , and satisfying . With this last assumption, we can show that a measure is also finitely additive. Indeed, given a collection , just define for to get a sequence. Then we find
If is a measure on , we say a set has finite measure if . We say that has “-finite” measure if there is a sequence of sets of finite measure () so that . If every set in has finite (or -finite) measure, we say that is finite (or -finite) on .
Finally, we say that a measure is “complete” if for every set of measure zero, also contains all subsets of . That is, if , , and , then . At first, this might seem to be more a condition on the algebra than on the measure , but it really isn’t. It says that to be complete, a measure can only assign to a set if all of its subsets are also in . | <urn:uuid:84011f45-600a-43d8-8f09-6e3eb1b302d4> | 2.78125 | 449 | Personal Blog | Science & Tech. | 50.669568 |
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X-rays are high-frequency, and thus high-energy, electromagnetic radiation.
They have wavelengths ranging from 0.01 to 10 nanometres, and thus frequencies from 3×1019 to 3×1016 Hz. They are found to reside between ultraviolet radiation and gamma rays on the electromagnetic spectrum.
Astrophysical sources of X-rays include plasmas with temperatures of 1 to 100 million degrees Celcius, such as the solar corona, supernova remnants and gas in galaxy clusters. In addition to this blackbody radiation from hot gas, high-energy events involving charged particles moving at high speeds within a magnetic field can also generate X-rays. Examples include the aurora of Jupiter, compact galactic objects like neutron stars, cataclysmic variable stars and X-ray binaries, and active galactic nuclei and quasars.
X-rays are commonly regarded to have first been discovered in the laboratory in 1895 when Wilhelm Röntgen conducted experiments with a partially evacuated tube enclosed in thick cardboard. He passed electricity through the tube, and whenever he did this, he noticed that a chemical coated screen on the other side of his laboratory would glow. Within a week he had created an X-ray image of his wife’s hand, showing the bones and her wedding ring. Röntgen dubbed this new form of radiation “X” rays, to denote its mysterious nature, and the name stuck.
Although in 1901 Röntgen received the Nobel prize in physics for his discovery, others had been experimenting with X-rays before him. In 1892 Heinrich Hertz and his student Philipp Lenard were generating X-rays (although they probably did not know it) from cathode ray tubes, and investigating their penetrating ability through different materials. In the preceding year, at Stanford University, Fernando Sanford had created and detected X-rays, as detailed in his Jan 6, 1893, Physical Review Letter. Prior to this, there is evidence to suggest that Nikola Tesla, from 1887 onwards, had worked with X-rays, and before him, from 1881 onwards, the Ukrainian-born Ivan Pulyui had already pioneered the invention and use of X-rays. | <urn:uuid:f52bd792-e64a-4011-9a40-b670077c2393> | 4.09375 | 448 | Knowledge Article | Science & Tech. | 41.456158 |
Barometers measure air pressure, sometimes explained as the weight of the air pressing down on the earth. This pressure helps determine upcoming weather, and aids in forecasting weather trends. When the barometric pressure is high, it inhibits clouds and rain from forming, leading to generally fair weather. Low barometric pressure allows clouds to form, leading to precipitation of many kinds and poor weather. Barometers often use water in a spout to determine the air pressure; in a basic barometer, if the water level is low, the air pressure is high, whereas if the water is high in the spout, air pressure is low. More advanced barometers use antennas and internal measurements to determine the air pressure, and whether it is rising, falling, or remaining steady. For more information on barometric pressure, be sure to check out our Newsletter Archives. | <urn:uuid:4e3f88a8-f81c-4618-aae1-5a28865fc9f6> | 3.75 | 169 | Knowledge Article | Science & Tech. | 33.30446 |
In a polypeptide the main chain N-Calpha and Calpha-C bonds relatively are free to rotate. These rotations are represented by the torsion angles phi and psi, respectively.
G N Ramachandran used computer models of small polypeptides to systematically vary phi and psi with the objective of finding stable conformations. For each conformation, the structure was examined for close contacts between atoms. Atoms were treated as hard spheres with dimensions corresponding to their van der Waals radii. Therefore, phi and psi angles which cause spheres to collide correspond to sterically disallowed conformations of the polypeptide backbone.
In the diagram above the white areas correspond to conformations where atoms in the polypeptide come closer than the sum of their van der Waals radi. These regions are sterically disallowed for all amino acids except glycine which is unique in that it lacks a side chain. The red regions correspond to conformations where there are no steric clashes, ie these are the allowed regions namely the alpha-helical and beta-sheet conformations. The yellow areas show the allowed regions if slightly shorter van der Waals radi are used in the calculation, ie the atoms are allowed to come a little closer together. This brings out an additional region which corresponds to the left-handed alpha-helix.
L-amino acids cannot form extended regions of left-handed helix but occassionally individual residues adopt this conformation. These residues are usually glycine but can also be asparagine or aspartate where the side chain forms a hydrogen bond with the main chain and therefore stabilises this otherwise unfavourable conformation. The 3(10) helix occurs close to the upper right of the alpha-helical region and is on the edge of allowed region indicating lower stability.
Disallowed regions generally involve steric hindrance between the side chain C-beta methylene group and main chain atoms. Glycine has no side chain and therefore can adopt phi and psi angles in all four quadrants of the Ramachandran plot. Hence it frequently occurs in turn regions of proteins where any other residue would be sterically hindered.
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In this second part of a two part series, you'll learn how to use debuggers and optimize performance. It is excerpted from chapter 12 of the book Zend PHP Certification, written by George Schlossnagle et al (Sams; ISBN: 0672327090).
If you're coming from a Java background, you might be used to writing a large infrastructure of classes that rely on each other to perform a particular task.
Don't try this with PHP! PHP's OOP features work best when your framework is small and efficient. Creating objects in PHP is a rather slow process, and, as such, it should be used conscientiously.
Sometimes, it's just not possible to optimize your code beyond a certain point. It might be that your queries are too complicated or that you depend on a slow external resource, such as a web service, over which you have no control.
In these cases, you might want to think about using a caching solution that "saves" the output of an operation and then allows you to access it without performing that operation again.
There are several types of cache; for example, you can save the results of a database query, or even an entire web page. The latter means that you generate your pages normally at predetermined intervals and save them in the cache. When a page is requested by a user, it is actually retrieved from the cache instead of being generated from scratch.
You can find several packages in the PEAR repository that are useful for output caching of various type. Naturally, there are also commercial solutions that perform a similar task, such as the ones provided by Zend.
When PHP runs your scripts, it does so in two steps. First, it parses the script itself, transforming it into a sort of intermediate language referred to as bytecode. Then, it actually interprets the bytecode (which is simpler than PHP itself) and executes it. If your scripts don't change between one execution and the next, the first step could easily be skipped, and only the second step would have to be taken.
This is what "bytecode caches" do. They are usually installed as simple extensions to PHP that act in a completely transparent way, caching the bytecode versions of your script and skipping the parsing step unless it is necessary—either because the script has never been parsed before (and, therefore, can't be in the cache yet) or because the original script has changed and the cache needs refreshing.
A number of commercial and open-source bytecode caches (also called accelerators) are available on the market, such as the one contained in the Zend Performance Suite, or the open-source APC. Most often, they also modify the bytecode so as to optimize it by removing unnecessary instructions.
Bytecode caching should always be the last step in your optimization process because no matter how efficient your code is, it's always going to provide you with the same performance boost. And, as a result, it could trick you into a false sense of security that would prevent you from looking at the other performance optimization techniques available. | <urn:uuid:f035889e-d827-4b39-98b2-8366beb18a18> | 2.875 | 636 | Tutorial | Software Dev. | 45.144336 |
S7 Technical Assistance
Eastern prairie fringed orchid (Platanthera leucophaea)
Determining whether eastern prairie fringed orchid (Platanthera leucophaea) may be present in a proposed project area in the following northeastern Illinois counties: Cook, DuPage, Kane, Lake, McHenry and Will.
|Photo by Mike Redmer
As part of Step 1 of the S7 process, you checked the Illinois species list and found that eastern prairie fringed orchid is present in the county where your proposed project is located. The next step is to determine whether eastern prairie fringed orchid "may be present" in the action area of your proposed project. Below is guidance to help you make that determination.
Habitat: The eastern prairie fringed orchid (orchid) occurs in a wide variety of habitats, from wet to mesic prairie or wetland communities, including, but not limited to sedge meadow, fen, marsh, or marsh edge. It can occupy a very wide moisture gradient of prairie and wetland vegetation. It requires full sun for optimal growth and flowering, which ideally would restrict it to grass and sedge dominated plant communities. However, in some plant communities where there are encroaching species such as cattail and/or dogwood, the orchid may be interspersed or within the edge zones of these communities and thus can sometimes occur in partially shaded areas. The substrate of the sites where this orchid occurs include glacial soils, lake plain deposits, muck, or peat which could range from more or less neutral to mildly calcareous (Bowles et al. 2005, USFWS 1999). In some cases, the species may also occur along ditches or roadways where this type of habitat is present.
Processes that maintain habitats in early or mid-successional phases may be important in providing the sunny, open conditions required by the orchid (USFWS 1999). Sedge meadow and marsh habitats that support this orchid are usually early- or mid- successional because of past grazing, drainage, or soil disturbance. Patch disturbances that expose the soil to this orchid’s seeds, and reduce competition from established plants, may be needed for seedling establishment.
Hawkmoths are the pollinators of this orchid species. In Illinois the hawkmoth, Sphinx eremitus is a confirmed pollinator although there may be others. Eumorpha pandorus and Eumorpha achemon have been confirmed as pollinators in other states. Host plants for the caterpillars of Sphinx eremitus include various species of beebalm (Monarda spp.), mints (Mentha spp.), bugleweed (Lycopus spp.) and sage (Salvia spp.).
Follow the steps below to determine whether the eastern prairie fringed orchid may be present in the action area of your proposed project. This guidance is specific to Cook, Lake, McHenry, DuPage, Kane, and Will counties in northeastern Illinois.
1) Define the action area – all areas to be affected directly or indirectly by the Federal action and not just in the immediate area involved in the action. (For example: downstream areas, adjacent off-site wetlands, etc.)
2) Does the action area support any wet to mesic prairie or wetland
communities including, but not limited to sedge meadow, fen, or marsh edges?
If the answer is yes, go to number 3 (below). If the answer is no, conclude that “the eastern prairie fringed orchid is not present,” document your finding for your records or provide this information to the federal action agency. No further consultation is required.
3) Conduct a floristic quality assessment for the proposed project site during the growing season or use a previous assessment that is not more than three years old and was conducted during the growing season.
4) If any wetland in the action area is determined to be high quality, (a Floristic Quality Index of 20 or greater and/or a Native Mean C of 3.5 or greater) proceed to number 5 (below) or contact the Chicago Field Office for further consultation.
Wetlands that are not high quality will not support eastern prairie fringed orchid. For those wetlands, conclude that “the eastern prairie fringed orchid is not present,” document your finding for your records or provide this information to the federal action agency. No further consultation is required for those wetlands.
5) Compare the plant species list generated for each high quality wetland with our Associate Plant Species List for the Eastern Prairie Fringed Orchid. If four or more associates are listed, then proceed to number 6. If not, high quality wetlands that support three or less eastern prairie fringed orchid associate plant species are unlikely to support eastern prairie fringed orchids. Conclude that “the eastern prairie fringed orchid is not present” and document your finding for your records or provide this information to the federal action agency. No further consultation is necessary for those wetlands.
6) The eastern prairie fringed orchid may be present in your action area. You may either assume that the eastern prairie fringed orchid is present and proceed to Step 2 of the Section 7 Consultation Process or conduct a field search during the bloom date of the orchid; June 28 through July 11. Because northeastern Illinois orchid populations bloom sporadically rather than all plants blooming at the same time, searches should be conducted on a minimum of three non-consecutive days within this time period. Please notify the Chicago Field Office before conducting your survey.
7) If you assume that the eastern prairie fringed orchid may be present in the action area or a field search proves that the orchid is present, the next step in the S7 Consultation Process is to determine whether the proposed action may affect any eastern prairie fringed orchids. Go to Step 2 of the S7 Consultation Process to begin that determination.
Please contact the U.S. Fish and Wildlife Service’s Chicago Illinois Field Office if you for more information or if you have any questions.
Chicago Illinois Field Office
1250 South Grove, Suite 103
Barrington, Illinois 60010
Phone: 847/381-2253, ext. 20
1Swink, F. and G. Wilhelm. 1994. Plants of the Chicago Region, 4th ed. Indiana Academy of Science, Indianapolis. 921pp.
Step 1 of the Section 7 Process
Section 7 Technical Assistance | <urn:uuid:32572c52-4ace-40ed-8aca-40c4ad13e96f> | 2.8125 | 1,392 | Tutorial | Science & Tech. | 44.4152 |
Science Main Index
There are about 300 species of squid. They are native to most of the world's oceans. The squid has a distinct head, eight arms and two tentacles. The mouth of the squid has a sharp horny beak used to kill and tear its prey into small pieces. The main body of the squid is enclosed in the mantle, which has a swimming fin along each side. However, the swimming fin is not the squid's main way of moving through the water. The squid can suck water into the mantle and expel it out in a fast, strong jet. This jet propulsion provides fast, forward movement. Although most squid are less than 2 feet in length, the giant squid can grow up to 43 feet in length. Play the following videos to learn more about the squid. | <urn:uuid:d69842ab-e7cd-49d3-9c5f-5389e50d5a90> | 3.9375 | 159 | Truncated | Science & Tech. | 82.7235 |
| ||Hubble does not travel to stars, planets, and galaxies. It takes pictures of them as it whirls around Earth at 17,500 miles an hour. |
In its 20 years of viewing the heavens, NASA's Hubble Space Telescope has made more than 930,000 observations and snapped over 570,000 images of 30,000 celestial objects.
In its 20-year lifetime the telescope has made more than 110,000 trips around our planet.
With those trips, Hubble has racked up plenty of frequent-flier miles, about 2.8 billion, which is Neptune's average distance from the Sun.
The 20 years' worth of observations has produced more than 45 terabytes of data, enough information to fill nearly 5,800 DVDs.
Each month the orbiting observatory generates more than 360 gigabytes of data, which could fill the storage space of an average home computer.
About 4,000 astronomers from all over the world have used the telescope to probe the universe.
Astronomers using Hubble data have published more than 8,700 scientific papers, making it one of the most productive scientific instruments ever built. In 2009 scientists published 648 journal articles on Hubble telescope data.
Hubble weighs 24,500 pounds -- as much as two full-grown elephants.
Hubble's primary mirror is 2.4 meters (7 feet, 10.5 inches) across -- taller than retired NBA player Gheorghe Muresan, who is 2.3 meters (7 feet, 7 inches) tall. Muresan is the tallest man ever to play in the NBA.
Hubble is 13.3 meters (43.5 feet) long -- the length of a large school bus. | <urn:uuid:6a731d9f-4feb-428d-9080-6fce158b898a> | 3.296875 | 352 | Knowledge Article | Science & Tech. | 69.741545 |
By Curtis C. Ebbesmeyer
Using flotsam to study ocean currents
Beachcombers, scientists and reporters ask if flotsam contributes to the understanding of ocean surface currents. Amongst beached debris — plastic bottles, fishing nets, tires, sea-beans, volcanic pumice, sneakers, gloves, toys, light sticks, rope, beer cans, logs, medical waste, lighters, cigarette butts — lie drifters telling from whence they floated. To messages in bottles (MIBs), add traceable debris from container spills, license tags from lobster pots, and flotsam from myriad other sources.
Much can be learned from this accidental oceanography. Of the hundred million cargo containers shipped overseas annually, several thousand fall overboard. Each container may hold 10,000 sneakers. Until the incident in 1990 in which 80,000 Nike sneakers fell overboard in the mid-North Pacific Ocean, I employed two instruments for learning where surface currents transported drifters: 1) satellite-tracked drifters which transmitted positions daily over intervals of months to a few years; and 2) MIBs which requested beachcombers to report where and when they stranded.
The great sneaker spill revealed another tool. Each Nike shoe carries a code as traceable as a MIB. The code 90 04 06 indicated that Nike Company ordered the 1990 sneakers in April (04) for delivery during June (06). Media and beachcomber reporting provided data regarding where and when 2.5% of the lost sneakers washed up, a percentage matching the 2.8% of the 19,449 MIBs released during 1956-1959 upstream of the sneaker spill.
Unmarked container flotsam may also provide instruments. On January 10, 1992, 28,800 plastic tub toys — turtles, ducks, beavers, and frogs— fell overboard in the mid-Pacific upcurrent of the sneaker spill. Amongst the myriad toys adrift, these four critters which were designed by child psychologist T. Barry Brazelton and manufactured by The First Years, Inc. are unique in Charlotte Lee’s Guinness Book of World Records collection o f 1,900 toy ducks.
The number of toys reported totaled about 3.3% of those spilled. Though the toys carried no traceable ID, I received as many reports as if they had. I tracked the tub toys for 14 years, knowing as much about where the toys drifted as if the same number of MIBs had been released.
Traceable flotsam provides the times and positions of the release and recovery points. In the 1800s, these data were pioneering, but the main question we ask today is, can the data garnered from drifters contribute anything of value to modern oceanography?
A comparable answer comes from many drifters for which we know the time and location on both sides of the ocean. Those that strand for a time scatter the elapsed times, whereas those that remain adrift cluster around a mean value within narrow statistical confidence limits. Flotsam contributes to oceanography through the statistics of large numbers.
Point measurements of currents circumscribe the ocean’s global conveyor belts, but do drifters actually go all the way around them? Multiple lines of evidence suggest so. Recently, three colleagues and I focused on a segment of a conveyor belt — the North Pacific Sub arctic Gyre — using the tub toys, infant sandals, pumice, MIBs, computer drifters, and spectra of water properties. We combined flotsam with water properties because we consider the ocean to be comprised of discrete slabs of water, each with differing temperatures and salinities produced by varying atmospheric conditions. Drifting objects and spectra yielded means and standard deviations, which were not statistically different at the 95% confidence level. The combined data indicate that within a nine percent uncertainty, a drifter takes on average three years to circle 12,000 kilometers around the Subarctic Gyre.
To gather and interpret traceable flotsam, I established an international network of beachcombers known as the Beachcombers Alert (www.beachcombers.org). Forty newsletters later, the power of the Alert network became evident in the regular reporting of old drift cards and bottles, debris from container spills and crustacean tags. Each year, lobstermen set 10-20 million traps along the US and Canadian east coasts. Each trap sports a tag, and each decade some 14 million tags float free, exceeding the six million historic MIBs released worldwide during 1825-2000.
The Alert network also contributes to traditional oceanographic studies. Most were funded only for a few years after the last drifter release, leaving beachcombers with nowhere to report. During 1976-1980, for example, the National Oceanic and Atmospheric Administration (NOAA) set out tens of thousands of plastic cards in response to significant oil spills along the East Coast from Florida to Massachusetts. Years later, NOAA entrusted me to be the keeper of their drift card records. After a quarter century, reports continue trickling in, occasionally extending the cards’ endurance record. The coating of slowing-growing bryozoans attested to their decades at sea. As of 2006, NOAA’s three oldest cards drifted 28.6, 27.8 and 26.6 years 7- 9 times around the North Atlantic Subtropical Gyre.
Major blocks of ocean surface current data result from releases of more than 100,000 traceable drifters, or a Traceable Drifter Unit (TDU). A review of historical records reveals on the order of ten TDU from university and governmental organizations. Non-conventional programs include the release of beer bottles by the Guinness Brewing Company (2 TDU, 1950s), MIBs with Biblical tracts by a dozen evangelical churches (3 TDU, 1950s), and bottles full of propaganda from the Taiwanese government (1 TDU, 1980s). In present years, crustacean tags, container spills, and MIBs released by mariners annually contribute 3 TDU.
For centuries, drifters have taught us the broad sweep of ocean currents. In the 1800s, drifting derelict vessels revealed the subtropical planetary gyres in the North Pacific and Atlantic and Oceans (Brooks, 1875; Richardson, 1985). By their endurance for as long as a century, flotsam provides a tool for tracing long planetary drifts. Drifters riding the global conveyor belts, for example, require twenty years to circle the earth. We must develop networks, which remain vigilant to collect this flotsam.
Everything afloat has an important story to tell.
Gyre Planetary vortex connecting continents
Brooks, C. W., 1875. Japanese wrecks stranded and picked up adrift in the North Pacific Ocean. Proceedings of the California Academy of Sciences, 6, 50-66. | <urn:uuid:83a6036c-84de-445e-8bbb-672191c695f1> | 2.921875 | 1,419 | Nonfiction Writing | Science & Tech. | 48.526899 |
Wikimedia Commons / United Nations
Your books subtitle is "The Science of Predicting Earths Deadliest Natural Disaster." Yet in the book you refute various ways people have proposed to predict or prevent earthquakes. So what do you mean?
Predicting earthquakes in the sense that its normally usedsaying, well theres going to be an earthquake in this particular place next monththat sort of approach was something that was thought about 50 years ago to be something that would become routine by the 21st century, and that hasnt happened. In the sense that its used in the book title, its really a question of where we might look for places in the world that are particularly at risk from earthquakes and what sorts of solutions can we bring in that will strengthen communities in those vulnerable places.
One of those is California. You mention in the book that some scientists say the fault that caused the great 1906 San Francisco quake, a 7.8, will rupture at about the same magnitude again around the year 2030.
Since its not possible to precisely predict quakes, how did they come up with 2030 in particular?
You focus partly on building structures and cities to withstand earthquakes. What are some ways to go about doing that?
We know that some types of construction are much more secure that others. For example, wooden houses survive much better than brick houses, and good brick houses survive a lot better than mud-brick houses. But if all youve got in the place where you live is mud brick, then its no good to say you should build all your houses out of wood.
So theres quite a lot of effort being spent to try to find ways of strengthening houses that can be applied in areas where there arent a lot of natural resources. These tend to be the vulnerable communities.
So if you had unlimited resources, what would you do to aid earthquake preparedness?
You warn of "rogue quakes." What are those?
A "rogue earthquake" occurs on a fault that wasnt identified as being particularly dangerous. That can happen in areas where earthquakes are very rare. You might get one every several thousands of years, so the last one was long before living memory.
The other sort of case is earthquakes that are a surprise but shouldnt be a surprise, and that was very much the case with Haiti. The fault line that produced the Haiti earthquake was well-known . . . There was a historical record of a devastating earthquake back in the 18th century. But in that case, a lot of people hadnt looked into the history of earthquakes in the area and didnt realize that the fault was as dangerous as it is.
Whats the most interesting thing going on in earthquake research?
For example, one thing that was not really understood some years ago but is now becoming more and more established is that earthquakes tend to happen in clusters. You can look at a particular area and see a pattern whereby you get a number of strong earthquakes in a relatively short period of time, and theres a long gap before the next one. So when youre trying to assess whats going to be the future in that particular place, it depends rather on whether you are in the middle of a cluster. In that case its a short time interval, or if youve reached the end of a cluster, its going to be a long time before the next one is due.
Whether you can actually take advantage of that is another matter. It would be rather dangerous to say, "Im out of a cluster now and I dont have to worry about earthquake," because you might find that you are wrong. But from that sort of observation we might be able to gradually put together a better idea of why earthquakes happen in the patterns that they do. Theres a lot we still dont understand about the mechanics of earthquakes.
Another thing that has been discovered within the last 20 years or so: When the rocks actually break in an earthquake, it was formerly thought that it was a clean breakyou have a fracture that starts and goes from one end of the fault to the other. What weve now discoveredand this has only been possible because of much more sensitive monitoring of earthquakes in the past couple of decadesis that even large earthquakes start off as small ones. You get a very small earthquake in the first second or even fraction of a second in which an earthquake happens, and that triggers a slightly bigger earthquake, which triggers a slightly bigger earthquake, and then suddenly the fault goes bang and the whole fault just unzips. What we dont know at all is why it happens like that and what tells a fault whether its about to have a small or a big earthquake. In a way [that] one seismologist put it recently, we know roughly why earthquakes start, but we dont know why they stop. What is it that stops a small one from growing into a big one in some cases, and why in other cases does it turn into a really big one? | <urn:uuid:5a044cc9-28b2-4a11-9840-aa7fccad227a> | 3.078125 | 1,006 | Audio Transcript | Science & Tech. | 55.984841 |
Web edition: July 19, 2012
Print edition: August 25, 2012; Vol.182 #4 (p. 14)
Some scientists really throw themselves into their research, but Stanford University biophysicist Stephen Quake has taken the all-in approach to a whole new level.
Using his sperm, Quake and colleagues compiled the first-ever genetic blueprint for a single sperm cell. The results shed new light on molecular processes such as mutation and recombination in humans, Quake and his colleagues report in the July 20 Cell.
Figuring out how often humans make mistakes in copying DNA so that single DNA units are changed, or mutated, is important for a variety of reasons, including figuring out how long ago humans diverged from other species, says Laure Ségurel, an evolutionary geneticist at the University of Chicago. “Every calculation is based on this mutation rate,” she says.
In past studies, scientists estimated this rate either by comparing human DNA with that of other species to see how many changes have occurred since that species split from humans, or by studying families to see where children have different DNA than their parents. By studying individual sperm cells, Quake and colleagues calculate the human mutation rate at 2 to 4 changes per 100 million DNA units per generation. That is higher than the rate calculated by looking at families (SN Online: 6/13/11), but consistent with evolutionary estimates.
The new work also offers insights into how humans scramble their DNA so that children inherit different combinations of parental DNA. This process, called recombination, is thought to be directed by a protein called PRDM9, which latches on to DNA and governs where the breaks that allow gene swapping will happen (SN: 8/13/11, p. 17).
But the Stanford researchers found that PRDM9 isn’t always necessary for recombination. Many of the new recombination hot spots fall within transposons — mobile pieces of DNA often called “jumping genes” — that don’t have obvious places for PRDM9 to grab.
Just because PRDM9 doesn’t seem to grasp DNA directly everywhere recombination happens doesn’t mean the protein isn’t involved in every gene swap, says Ségurel.
Regardless of PRDM9’s involvement, the data suggest that transposons may have had an important hand in shaping human evolution, Quake says. “This is a nice mark in the transposon column.”
The work also represents a technical accomplishment: Researchers have begun deciphering the genetic makeup of single cells, such as cancer cells, but this is the first time anyone has compiled a genetic blueprint from a single sperm.
Sperm are challenging for genetic analysis because they contain so little DNA, says Stanford biological engineer Jianbin Wang, a study coauthor. Sperm and eggs each contain half as much genetic material as a typical body cell.
On the flip side, sperm have given scientists an advantage when analyzing the small portion of the genome that contains protein-coding genes, Quake says. With only one copy of each gene per sperm, researchers don’t mix up two copies with each other.
“For 99 percent of the genome it is more challenging,” Quake says of single sperm analysis, “but for 1 percent it’s easier. That’s a pretty important 1 percent.”
J. Wang et al. Genome-wide single-cell analysis of recombination activity and de novo mutation rates in human sperm. Cell Vol. 150, July 20, 2012, p. 402. [Go to]
T. H. Saey. Human mutation rate slower than thought. Science News Online June 13, 2011.
Available online: [Go to]
T. H. Saey. Shuffling the genetic deck. Science News Vol. 180, August 13, 2011, p. 17
Available online: [Go to] | <urn:uuid:428da6a1-006d-438b-82f7-426ed6986b50> | 3.59375 | 817 | Truncated | Science & Tech. | 55.408926 |
An Oceanographer Suggests Creating and Underwater National Park
Narrator: This is Science Today. Coral reefs provide several benefits to their surrounding area, but can suffer because of overfishing. Fish are important because they eat the algae which can overgrow on a coral and eventually kill it. Marine ecologist Stuart Sandin of the University of California , San Diego 's Scripps Institution of Oceanography, says that creating underwater protected areas could benefit both the fish and the corals.
Sandin: You can put in a park in certain regions and the fish stocks will grow up in some marine protected areas. A national park underwater and you just don't allow fishing in that area. If you don't allow fishing, then the fish will start to grow back. You have the fish doing their service eating the algae, protecting the algae from overgrowing the corals or fertilizing the bacteria on the corals.
Narrator: Sandin says this type of protection is necessary in allowing coral reefs to recover.
Sandin: Coral reefs have been around for millions of years, they've done very well through huge sea level changes, temperature changes and if there's one thing they have, it's a capacity to recover. One thing we have to give it is the time to recover at this point.Narrator: For Science Today, I'm Larissa Branin. | <urn:uuid:ecf3f9fb-2153-4bfb-b336-65119d144b4b> | 3.46875 | 279 | Audio Transcript | Science & Tech. | 44.748155 |
Weisbach, Principles of the mechanics of machinery and engineering (Vol.1), 1849.
Table of Contents
Click Adobe PDF icons to download book sections.
- (2.9 MB) Section I. Phoronomy; or The Pure Mathematical Science of Motion.
- Chapter I. Simple Motion
- Chapter II. Compound Motion
- (3.3 MB) Section II. Mechanics in the Physical Science of Motion in General
- Chapter I. Fundamental ideas and fundamental laws of mechanics
- Chapter II. The mechanics of material point
- (8.9 MB) Section III. Statics of Rigid Bodies. Chapters I through IV
- Chapter I. General laws of the statics of rigid bodies
- Chapter II. Centre of gravity
- Chapter III. Equilibrium of bodies rigidly connected and supported
- Chapter IV. Equilibrium in funicular machines
- (10.3 MB) Section III. Continued / Statics of Rigid Bodies. / Chapters V and VI
- Chapter V. On the resistances of friction and rigidity
- Chapter VI. Elasticity and rigidity
- (9.8 MB) Section IV. Dynamics of Rigid Bodies.
- Chapter I. On the equilibrium and pressure of water in vessels
- Chapter II. On the equilibrium of water with other bodies
- Chapter III. On the equilibrium and pressure of air
- Chapter I. The general laws of the efflux of water from vessels
- Chapter II. On the contraction of the fluid vein by the efflux of water through orifices in a thin plate
- Chapter III. On the efflux of water through tubes
- Chapter IV. On the resistance of water in passing through contraction
- Chapter V. On the efflux of water under variable pressure
- Chapter VI. On the efflux of air from vessels and tubes
- Chapter VII. On the motion of water in canals and rivers
- Chapter VIII. Hydrometry or the doctrine of the measurement of water
- Chapter IX. On the impulse and resistance of fluids | <urn:uuid:feadbadc-328f-4c1f-8f22-9156bdd40e1a> | 3.453125 | 433 | Content Listing | Science & Tech. | 61.277115 |
Building a Better Mouth Trap
By now we've all seen them: those awesome, slow-motion images of White Sharks being fed at the surface. The gaping jaws of the Great White Shark have become a potent image of the modern world. Celluloid has popularized and magnified the image of the Great White, which has come to epitomize the ultimate in predation and the archetype of sharkdom. But this popular conception does not do justice to the diversity of sharks and their 'pancake' cousins, the skates, rays, sawfishes, and guitarsharks. Collectively termed elasmobranchs (meaning 'strap-gills'), these cartilaginous fishes are a highly varied group of marine vertebrates, encompassing an amazing range of forms and lifestyles.
Fossil evidence suggests that elasmobranchs have been primarily predatory from their earliest beginnings and throughout their long evolutionary career, from the Middle Paleozoic some 425 million years ago to the present. Over that enormous timespan they have undergone several major adaptive radiations — including some truly bizarre tinkering with shark design — and survived at least eight mass extinctions that many other types of creature did not. The most recent elasmobranch radiation coincided with the mammalian radiation that eventually produced ourselves. Modern elasmobranchs are thus the distillation of millions of years of experiments on how to build a predator. They are a fundamental life form, united by numerous elegant and highly evolved structural, physiological, and behavioral features. While undeniably ancient, there is nothing 'primitive' about today's sharks and rays.
The vast majority of living sharks and rays are predatory. Of some 1,100 species of extant elasmobranchs, only 13 (1.2%) — the Basking Shark (Cetorhinus maximus), Megamouth Shark (Megachasma pelagios), Whale Shark (Rhincodon typus), Manta Ray (Manta birostris) and about 9 species of Devil Rays (genus Mobula) — have forsaken the actively predacious habits of their kin and adapted to a more placid 'grazing' lifestyle. These thirteen species of filter-feeding elasmobranch are not particularly closely related, representing four separate evolutionary lineages. What makes the shift to filter-feeding particularly intriguing is that all four lineages undertook the shift at about the same time, between 60 and 30 million years ago in the Cenozoic Era. Thirty million years may seem an awfully long time in terms of a mortgage, but it represents only 7% of the total period elasmobranchs have existed. What environmental pressures precipitated this profound dietary shift? How have these animals been modified for a filter-feeding mode of life? And, given the groups' enormous long-term success as predators, why have they done so?
Elasmobranch filter-feeding mechanisms can be conveniently divided into two categories: 1) modified gill rakers and, 2) spongy elaboration of the gill bars. Filters of the first category are relatively coarse, being composed of modified dermal denticles (placoid scales), and are found in two cold-water species, the temperate Basking Shark and the deep-sea Megamouth Shark. The gill rakers of the Basking Shark are bristle-like, some 3 inches (7.5 centimetres) long in an average 30-foot (9-metre) specimen and number about 10 per inch (4 per centimetre) of gill bar. In contrast, the gill rakers of Megamouth are papillose ('finger like') with a spongy cartilaginous core, arranged in four rows along each gill bar and about 4 to 6 inches (10 to 15 centimetres) long in a 15-foot (4.5-metre) specimen. Filters of the second category are finer, composed of pinkish-brown spongy tissue arranged in flattened, horizontal plates that bridge the 'gaps' between successive gill bars. This category of filter is found in the Whale Shark and the Manta and Devil Rays, which inhabit primarily tropical to warm-temperate seas with relatively thin plankton biomass. The Basking Shark, Megamouth, Whale Shark, Manta and Devil Rays each has different accessory feeding structures, which are correlated with differing feeding behaviors.
The Basking Shark is a passive filter-feeder, relying on ram-jet ventilation to force plankton-bearing water through its pharynx and out the gills. The Basking Sharks' diet consists almost entirely of a single genus of copepod (Calanus), with a smattering of fish eggs and arrow-worms; this prey specificity suggests that the gill raker filtration system of the Basking Shark may not be as simple as it appears. About 1,500 tons (1,360 tonnes) of water an hour pass through a Basking Shark's gigantic gill slits; periodically (every two to three minutes or so), a feeding Basking Shark flutters its gills sharply, possibly to swallow accumulated planktonic food trapped by the gill rakers. During spring and summer, the planktonic prey of the Basking Shark is abundant, but even under the most favorable conditions, this shark must work hard to make a living. It has been calculated that a 22-foot (6.7 metre) Basking Shark requires about 663 calories per hour just to propel its massive body through the water; when plankton supply falls off during early winter, the Basking Shark can typically consume only 2 pounds of copepods — about 410 calories — an hour. So in winter, a Basking Shark would be using up more energy in swimming than it could get from its food. Since numerous Basking Sharks have been captured in winter without their gill rakers, it has been suggested that when plankton concentrations fall below sustenance levels the Basking Shark sheds its gill rakers and switches to bottom feeding or hibernates until plankton concentration increases again in the spring. If this is true, the seasonal shedding of gill rakers by the Basking Shark would be the only known instance of an annual moult in fishes.
Because most plankton is found near the surface, the mesopelagic Megamouth Shark faces some serious challenges in acquiring enough to eat. Due to its nutrient-poor deep-sea habitat, Megamouth has mushy muscles and a poorly calcified skeleton, making it a rather weak swimmer. The huge, bathtub-sized jaws and supporting arches are highly mobile, suggesting that Megamouth feeds by expanding its pharynx and sucking prey into its mouth. This pharyngeal vacuum may be enhanced by simultaneously raising the huge and highly mobile basihyal ('tongue'). In addition, Megamouth has two sheets of guanine-silvered tissue hanging inside the upper jaw. It has been speculated that Megamouth may be bioluminescent, relying on light to lure its prey (deep-sea shrimp and jellyfishes) within range of its extensible jaws. If true, this deep-sea shark may be the world's largest bioluminescent organism. First captured off Oahu, Hawaii in November 1976, Megamouth has been hailed as the most astounding ichthyological discovery since the 1938 capture of a live coelacanth off East London, South Africa. To date, only 14 specimens of Megamouth are known (from Hawaii, California, Japan, Western Australia, Brazil, Senegal, Indonesia, Philippines). All of this was pretty much academic until October 1990, when a Megamouth Shark made international news. A 16-foot specimen was captured live in a driftnet off Dana Point, California, fitted with two sonic tags, released and tracked for two days. This individual Megamouth Shark remained at a depth of about 50 feet (15 metres) during the night then dived to 490 feet (150 metres) at dawn. Thus, like many other deep-sea creatures, Megamouth is a vertical migrator — following its planktonic prey toward the surface at night and back into deeper water before dawn. In other words, Megamouth is a commuter!
Growing to a length of at least 50 feet (15 metres), the Whale Shark is the largest fish on our planet. Unlike the weakly-muscled Megamouth, the Whale Shark has powerful swimming, throat, and gill pouch musculature. The bellows-like gill pouches make the Whale shark a versatile filter-feeder, enabling it to consume a wide variety of planktonic crustaceans and even small to mid-sized fishes such as sardines, anchovies, and mackerels. Because of its ability to suck food into its mouth, the Whale Shark is not dependent upon forward motion to operate its filters and often assumes a vertical posture when feeding. It has been reported that Whale Sharks enhance the efficiency of vertical feeding by 'bobbing' up and down in 15 to 20-second cycles, pausing at the surface to allow food-bearing water to rush into their mouths and strain through their spongy gill plates; this behavior has been recently filmed by the Cousteau Society off Cuba. There are numerous reports of associations between Whale Sharks and schooling pelagic fishes, particularly skipjack and albacore. These large fishes may be feeding on smaller fishes congregating to feed on the same plankton concentrations as the Whale Sharks. Stewart Springer reported that he once saw several tuna appear to leap into the mouth of a vertically-feeding Whale Shark at the completion of each 'bobbing' cycle. If Whale Sharks actually swallow the large fishes they suck in (accidentally or otherwise), they must add considerably to the Sharks' protein intake!
The exquisitely graceful Manta and Devil Rays rely on ram-jet ventilation to force plankton-bearing water through their ridged gill plates. But unlike the temperate water Basking Shark, these tropical rays have forward extensions of the pectoral wings called 'cephalic fins'; these flexible, horn-like fins may assist Manta and the lesser-known Devil Rays in concentrating plankton and channeling it into their mouths. Their wing-like pectoral fins give these rays extraordinary maneuverability, enabling them to circle and wheel tightly around their planktonic prey. It is possible that such acrobatic behavior may serve to further concentrate plankton and facilitate feeding. When they have finished feeding, Manta Rays can furl the cephalic fins into hydrodynamically-sound 'cutwaters'; I have seen Mantas fold their cephalic fins so that they meet at the midline of the mouth, resembling paddle-shaped 'hands' of a Far Eastern guru reciting mantras ('Mantra Rays'?), then depart rapidly. Unfortunately very little else is known about the feeding behavior of these beautiful rays.
For all their diversity, filter-feeding elasmobranchs share several features in common. Their heads are broad and their mouths have returned to the ancestral terminal position (most modern sharks have 'subterminal' jaws — located on the underside of the head). Teeth are reduced in size and significance — though not necessarily in number: the Whale Shark may have more than 27,000 teeth arranged in some 310 rows. The gill mechanism is elaborated to include sieve-like bristles or spongy filter plates. All filter-feeding elasmobranchs are quite large ... and some are downright gigantic. Large size not only reduces an organism's risk of predation, but also increases swimming efficiency — no small consideration if one's food supply is thinly distributed across entire ocean basins. And last but not least, those filter-feeding elasmobranchs which prey largely on planktonic crustaceans need special enzymes to break-down the chitinous exoskeletons (chitin is a complex heterosaccharide, similar to cellulose, and just as difficult to digest). These are all pretty major modifications. In many ways, these modifications resemble those of the baleen whales — which, by no small coincidence — appeared at about the same time as the filter-feeding elasmobranchs. What environmental conditions might account for such a wholesale shift to filter-feeding?
Sixty million years ago our planet was undergoing some major changes. India and Africa had split away from Gondwanaland, but South America, Antarctica, and Australia retained a land connection. The Atlantic and Southern Indian Ocean widened, while the Pacific diminished. Equatorial energy input from the sun was restricted in ocean basins, rendering oceanic currents rather sluggish. The creation of new seas and reduction in size of older seas disrupted oceanic circling patterns and radically changed the global climate. The general warm and humid conditions typical of Jurassic and early to mid-Cretaceous cooled toward the end of the Cretaceous; the Paleocene continued this trend, but was followed by warming in the Eocene. Mass extinctions, during which many different types of life die out within a relatively short period, occur at roughly 26-million-year cycles. During the Cretaceous Extinction, 15% of marine invertebrate families (about 50% of existing species) died out, including bivalves, gastropods, and cephalopods; many aquatic vertebrates also died out at about this time, including numerous families of bony fishes and marine reptiles. This 'sweeping away' was followed by a 'Post- Cretaceous Explosion' of diversity. Planktonic diatoms underwent major radiations, while copepods, dinoflagellates and coccoliths remained strong. Reef-building corals increased in abundance and diversity, creating more habitats and feeding niches. In response, elasmobranch and especially bony fish diversity flowered.
It was under these conditions that the filter-feeding elasmobranchs evolved. Despite the major physical and behavioral modifications required, filter-feeding has much to recommend it. By feeding directly on the lowest and most productive end of the food chain, filter-feeding elasmobranchs and baleen whales are able to circumvent the fundamental energy problem inherent to most food chains. But evolution is conservative, tending to leave functioning designs well enough alone. The chief benefits associated with a dietary shift from predation to filter feeding are: 1) specialization reduces feeding competition and, 2) large size reduces predation risk and 3) large size allows retention of metabolic body heat, allowing functioning in cold water. The chief drawbacks to filter-feeding are: 1) food supply is thinly distributed, requiring much swimming effort to secure sufficient nourishment and, 2) food supply is subject to wide fluctuations in relative abundance, especially in temperate zones. But to persist over 60 million years the benefits must outweigh the costs, and the compromise be well worth it.
Those four elasmobranch lineages which needed the least modification were 'preadapted' to make the big shift from predation to filter-feeding. (Preadaptation is an unfortunate term, suggesting that organisms somehow evolve features in 'anticipation' of benefit under future environmental conditions; in truth, almost the exact opposite occurs: those organisms which have NOT inherited the potential to take advantage of an environmental change are selected against by the environment ... luck of the genetic draw.) The Basking and Megamouth Sharks are lamnoids (related to the Great White and thresher sharks, respectively), a group characterized by short snouts, long gill slits, and large size. The Whale Shark is an orectoloboid (related to the Nurse and Zebra Sharks), a group which features a near-terminal mouth, broad head, and large gills with powerful muscles. The Manta and Devil Rays are mobulids (related to the sting and eagle rays), a group having relatively short snouts, teeth modified into crushing plates, large gills and body size.
So what precipitated the Big Shift from active predation to a more placid 'grazing' lifestyle? Intense competition for nectonic (swimming) prey at the benthos and throughout the water column and/or a high concentration of plankton — at least seasonally — might have favored the shift from active predation to a filter-feeding mode. Perhaps an opportunistic, short-term seasonal dietary shift in the ancestral types became fixed under conditions of reduced competition. Natural selection then refined each form of filter-feeding elasmobranch, maximizing its planktivorous efficiency. Although they do not fit the popular JAWS image, the filter-feeding elasmobranchs represent some of the latest and most advanced experiments in shark design.
NOTE: In 1999, several of the assumptions behind these calculations were shown by David Sims to be faulty, resulting in an overestimation (by about three times) of the energy Basking Sharks require to swim. [Return to text from footnote] | <urn:uuid:d6880d94-e2c7-4bef-afef-0379048de154> | 3.421875 | 3,527 | Knowledge Article | Science & Tech. | 30.580936 |
Major Section: RULE-CLASSES
See rule-classes for a general discussion of rule classes and
how they are used to build rules from formulas. An example
corollary formula from which a
:forward-chaining rule might be
Example: (implies (and (p x) (r x)) when (p a) appears in a formula to be (q (f x))) simplified, try to establish (r a) and if successful, add (q (f a)) to the known assumptionsTo specify the triggering terms provide a non-empty list of terms as the value of the
:trigger-termsfield of the rule class object.
General Form: Any theorem, provided an acceptable triggering term exists.Forward chaining rules are generated from the corollary term as follows. If that term has the form
(implies hyp concl), then the
concl(formally, lambda expressions) are expanded away, and the result is treated as a conjunction, with one forward chaining rule with hypothesis
hypcreated for each conjunct. In the other case, where the corollary term is not an
implies, we process it as we process the conclusion in the first case.
:trigger-terms field of a
:forward-chaining rule class object
should be a non-empty list of terms, if provided, and should have
certain properties described below. If the
:trigger-terms field is
not provided, it defaults to the singleton list containing the
``atom'' of the first hypothesis of the formula. (The atom of
(not x) is
x; the atom of any other term is the term itself.) If
there are no hypotheses and no
:trigger-terms were provided, an
error is caused.
A triggering term is acceptable if it is not a variable, a quoted
constant, a lambda application, a
let-expression, or a
not-expression, and every variable symbol in the conclusion of the
theorem either occurs in the hypotheses or occurs in the trigger.
:Forward-chaining rules are used by the simplifier before it begins
to rewrite the literals of the goal. (Forward chaining is thus carried
out from scratch for each goal.) If any term in the goal is an
instance of a trigger of some forward chaining rule, we try to
establish the hypotheses of that forward chaining theorem (from the
negation of the goal). To relieve a hypothesis we only use type
reasoning, evaluation of ground terms, and presence among our known
assumptions. We do not use rewriting. So-called free variables in
hypotheses are treated specially; see free-variables. If all hypotheses
are relieved, we add the instantiated conclusion to our known assumptions.
Caution. Forward chaining does not actually add terms to the goals displayed during proof attempts. Instead, it extends an associated context, called ``assumptions'' in the preceding paragraph, that ACL2 builds from the goal currently being proved. The context starts out with ``obvious'' consequences of the negation of the goal. For example, if the goal is
(implies (and (p x) (q (f x))) (c x))then the context notes that
(q (f x))are non-
(c x) is
nil. Forward chaining is then used to expand the context.
For example, if a forward chaining rule has
(f x) as a trigger term
and has body
(implies (p x) (r (f x))), then the context is extended
(r (f x)) to non-
nil. Note however that since
(r (f x))
is put into the context, not the goal, it is not further simplified.
f is an enabled nonrecursive function symbol then this forward
chaining rule may well be useless, since calls of
f may be expanded
Another common misconception is this: Suppose that you forward
chain and put
(< (f x) (g x)) into the context. Then does it go
into the linear arithmetic data base? Answer: no. Alternative
question: do we go looking for linear lemmas about
(g x)? Answer:
no. The linear arithmetic data base is built up by a process very
similar to but independent of forward chaining. | <urn:uuid:7d44b8af-ff7c-499a-9e2b-8ea6a2c94620> | 3.734375 | 924 | Documentation | Software Dev. | 56.262918 |
Now we come to a really nice example of a semigroup ring. Start with the free commutative monoid on generators. This is just the product of copies of the natural numbers: . Now let’s build the semigroup ring on this monoid.
First off, an element of the monoid is an ordered -tuple of natural numbers . Let’s write it in the following, more suggestive notation: . We multiply such “monomials” just by adding up the corresponding exponents, as we know from the composition rule for the monoid. Now we build the semigroup ring by taking formal linear combinations of these monomials. A generic element looks like
where the are integers, and all but finitely many of them are zero.
Assuming everyone’s taken high school algebra, we’ve seen these before. They’re just polynomials in variables with integer coefficients! The addition and multiplication rules are just what we know from high school algebra. The only difference is here we specifically don’t think of as a “placeholder” for a number, but as an actual element of our ring.
But we can still use it as a placeholder. Let’s consider any other commutative ring with unit and pick elements of . Call them , , and so on up to . Since is a commutative monoid under multiplication there is a unique homomorphism of monoids from to sending to . That’s just what it means for to be a free commutative monoid. Now there’s a unique homomorphism of rings from to sending to , because is the semigroup ring of .
The upshot is that is the free commutative ring with unit on generators. Because of this, we’ll usually omit the intermediate step of constructing and just write this ring as .
There are similar constructions to this one that I’ll leave you to ponder on your own. What if we just constructed the free monoid on generators (not commutative)? What about the free semigroup? What sort of rings do we get, and what universal properties do they satisfy? | <urn:uuid:b97e6678-133e-40cd-b317-e5f85a36713f> | 3.390625 | 453 | Personal Blog | Science & Tech. | 53.328328 |
Friday, the fourth and final partial solar eclipse
only visible from high latitudes in the southern hemisphere.
If you missed it, check out
dramatic picture of the
geocentric celestial event from a very high southern latitude
on the continent of Antarctica.
From a camera positioned at
San Martín Station
near the antarctic peninsula mountain range, the picture
looks toward the south and east.
The Sun and
silhouetted lunar disk are seen through thin, low clouds.
Perhaps fittingly, the mountainous slope in the foreground is
part of the larger Roman Four Promontory,
named for its craggy, snow covered face that
resembles the Roman numeral IV.
For 2011, there is actually one more eclipse to go, a
total eclipse of the Moon.
Parts of that eclipse be visible
from most of planet Earth (but not
Credit & Copyright:
Carlos Zelayeta (San Martín Station, Antarctica) | <urn:uuid:c8b7ff8c-ea6e-46a9-a2b5-ac0151cfdc25> | 3 | 207 | Personal Blog | Science & Tech. | 36.5825 |
Defining dynamic properties inside your HTML
<div style="width: expression(document.body.clientWidth/2+'px'); background-color: yellow"> This DIV will always be half the size of the page's width </div>
Now, in the above example, I used the expression:
to derive half of the page's width. But wait, there's a catch! You see, in IE, depending on whether a page contains a valid doctype declaration at the very top of the page, the way to referencing numerous properties of the body changes as a result. Namely, if your page does, the syntax "document.documentElement" needs to be used instead of "document.body":
Taking this unexpected bit of information into account, we can create an expression that works in all types of pages in IE:
expression(document.compatMode=='CSS1Compat'? document.documentElement.clientWidth/2+'px' : body.clientWidth/2+'px');
The above expression tests for the precense of a valid doctype, and switches between the two possible syntax to referencing the desired property in IE. Notice how all the quotes are single (') instead of double (")- this is important, because inside inline styles, using the later would confuse the browser and render the dynamic expression useless!
The expression() function when invoked creates a dependency between your HTML property and dynamic expression specified. If and when the value for the later changes due to select user actions, the function will automatically update your HTML property with this new value. What this means is that if you tried to resize your browser window, for example, the DIV above will automatically resize to be half of the new window's width due to the dependency created between the two values and user actions that may affects one of the two. This is what makes Dynamic Properties such as time saver- it keeps tracks of and adjusts to user actions automatically.
-Positioning an image in the center of the browser window
Without dynamic expressions, the simple task of displaying an image in the center of the window, for example, can be a messy task, partially because you also have to taken into account if the user has resized the window. Using dynamic expressions, it's a more elegant affair:
Example c1: Center Image Dynamic Properties Example:
<img src="myimage.gif" style="width: 120px; height:
150px; position:absolute; left:
Example c1.1: Center Image Dynamic Properties Example Revised:
Defining dynamic properties that rely on the value of other dynamic properties
Here's something you may not have thought of- you can define a dynamic property that changes depending on the value of another dynamic property. The simplest example would be two DIVs, the second being half the width of the first's:
2nd DIV (1/2 the width of the first)
For the second DIV, I set its width to half the width of the first. Notice how I need to retrieve the first DIV's width by accessing it by ID, then its width property, and since this property contains a percentage value, I need to include a "%" prefix at the end of the expression to complete the setting. | <urn:uuid:7fe4d4bc-0b28-4be3-914b-bf5efb03b277> | 2.875 | 674 | Documentation | Software Dev. | 44.602364 |
Video Transcript: Cold Case: Possible Ice Volcano on Titan
Sotra Facula on Titan is the best case yet of a cryovolcano in the outer solar system.
In fact, there appears to be two cryovolcanos separated by a low area where we see some sand dunes.
Here, we see data from radar and the visible and infrared mapping spectrometer.
This is false color to distinguish the different compositions of the surface.
So the green areas are what we think are the volcanic areas, while the blues would be fields of sand dunes.
Now, we change the color scheme. The reds and yellows are highs. The blues are lows.
When we got the topography, we see this tall mountain. It's about a thousand meters tall.
When you have a tall mountain and a deep crater and a lobate flow-like feature coming out of it,
then it's very likely to be a cryovolcano. On Earth, volcanoes are formed by molten rock, or magma,
that when it comes out, it's called lava. On Titan and other icy bodies such as Saturn's moon Enceladus,
we have cryovolcanism, that is very cold volcanism and the material inside these bodies,
the quote, 'magma', is not molten rock. It's actually a watery mixture. It's water with probably ammonia
and maybe methanol and other things. Material is being brought from the interior of the
moon or the planet, to the surface. This is important for a number of reasons and one of them
is that if you still have heat and enough heat to actually cause cryovolcanism to occur and
if you have water, then those are the two ingredients that you need for life. | <urn:uuid:c3cff5da-73fe-4d43-8b74-b0758f87a817> | 3.3125 | 376 | Audio Transcript | Science & Tech. | 57.507847 |
1.3 Who should read this book
Revealing the mystery around the GNU Autotools is likely to raise the interest of a wide audience of software developers, system administrators and technical managers.
Software developers, especially those involved with free software projects, will find it valuable to understand how to use these tools. The GNU Autotools are enjoying growing popularity in the free software community. Developers of in-house projects can reap the same benefits by using these tools.
System administrators can benefit from a working knowledge of these tools -- a common task for system administrators is to compile and install packages which commonly use the GNU Autotools framework. Occasionally, a feature test may produce a false result, leading to a compilation error or a misbehaving program. Some hacking is usually sufficient to get the package to compile, but knowing the correct way to fix the problem can assist the package maintainer.
Finally, technical managers may find the discussion to be an insight into the complex nature of software portability and the process of building a large project. | <urn:uuid:d76ce80f-8dad-4d71-bd55-9bcb4a611a08> | 2.765625 | 211 | Knowledge Article | Software Dev. | 25.798757 |
Getting a head start has its advantages. If you are an early bird, you will get the worm. And if you are in the U. S. Army, you will “do more before 9:00 AM than most people do all day.”
Recent work by UC Berkeley scientists indicates the same is true for genes.1 In prokaryotes, genes encoding collaborative proteins are organized as a contiguous sequence called an operon. Genes located near the start of an operon do more work than most other genes. These first genes are expressed at higher levels because they are transcribed earlier and more often than genes located elsewhere in the operon.
This new insight highlights biochemical information’s elegant organization, helping to further the case for intelligent design. It also provides an effective counter to evidence sometimes cited in favor of biological evolution.
Gene Position in Operons
Genes are not positioned randomly along the DNA molecule. Instead, as I discuss in The Cell’s Design and in an online article, there appears to be a rationale for gene location. The Berkeley researchers demonstrated this concept by showing that a linear relationship exists between the location of the gene in the operon and the amount of protein produced. Genes located near the beginning of the operon produce more proteins than genes at the end of the operon.
To produce a protein, the prokaryote’s cellular machinery reads the entire operon and uses the information contained to generate a particular type of messenger RNA called a polycistronic RNA. This molecule migrates to the ribosome where the proteins are produced simultaneously, ensuring all proteins needed for a specific biochemical task are made at the same time. (Watch the video to get an overview of one of the textbook examples of an operon.)
Operon Structure and the Case for Intelligent Design
Biochemical systems are, in their essence, information based systems.2 Common experience teaches us that information derives from intelligent agency. Therefore, by analogy, one could argue that the information in biochemical systems emanates from a Creator.
But the argument for intelligent design is much deeper than that, as illustrated by operon structure. There is an exquisite biochemical rationale for gene organization along the DNA molecule. The work by the Berkeley investigators indicates that the precise sequencing of operon genes ensure not only that all the right proteins are made, but also that proteins are made at the right levels to support the cell’s metabolic demands.
It looks as if operons are “all that they can be,” and it is rational to see these structures as the work of a Creator. Next week I will discuss what this new insight means for the evolutionary paradigm.
This article is Part 1 (of 2) of "Operon Synteny Brings Order to the Case for Intelligent Design".
To access Part 2, please click on the link below: | <urn:uuid:1989d663-0c03-4b8f-8f04-da3cc1e36931> | 3.875 | 587 | Truncated | Science & Tech. | 33.182579 |
We mapped substantial migration of the river channel between the City of Winslow and the Navajo Nation community of Leupp; in a human lifetime the river has moved more than a mile across its valley floor.
Explains biological soil crusts, organism-produced soil formations commonly found in semiarid and arid environments, with special reference to their biological composition, physical characteristics, and ecological significance.
Home page for Coastal and Marine Geology with links to topics of interest (sea level change, erosion, corals, pollution, sonar mapping, and others), Sound Waves monthly newsletter, field centers, regions of interest, and subject search system.
Interactive map server to view and create maps using available coastal and marine geology data sets of offshore and coastal U.S. and the Gulf of Mexico. Links to available data and metadata that can be downloaded.
USGS responses to and studies of the hazards and impact of major hurricanes, tsunamis, and El Nino storms. Includes links to oblique aerial photography and LIDAR surveys recording coastal changes and other effects of storms and waves.
By measuring the current and historical growth rates of coral skeletons, and using field experiments, we intend to find out whether rising atmospheric CO2 and rising sea levels will cause coral reefs to erode and cease to function. | <urn:uuid:564fb259-c020-43ff-85a9-478c677a931c> | 3.015625 | 267 | Knowledge Article | Science & Tech. | 27.044092 |
Steven Dutch, Natural and Applied Sciences,
University of Wisconsin - Green Bay
First-time Visitors: Please visit Site Map and Disclaimer
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- Fourth planet from the Sun
- Rather eccentric orbit. Average distance from the Sun is 142 million miles
- Perihelion distance 128.6 million miles,
- aphelion distance 160 million miles.
- Takes 687 days to orbit the Sun.
- Distance from Earth varies from 36 million miles (nearest planet after Venus) to over 250
million miles. Proportionately, this six-fold distance variation is the greatest of any planet.
- Diameter 4225 miles.
- Rotates in 24-1/2 hours.
The Climate of Mars
- Mars has an atmosphere which is about 95% carbon dioxide, with small amounts of nitrogen
argon, and oxygen.
- The atmospheric pressure ranges from one-half percent to one percent that of Earth.
- Surface temperatures are in the range -30F to -200F.
- Mars has clouds of mostly water ice but some frozen carbon dioxide.
- Dust storms occur on Mars and sometimes obscure the planet as seen from Earth.
- Mars has two polar ice caps which are thin layers of water ice and carbon dioxide frost.
- The polar caps expand and shrink with the Martian seasons.
Geology of Mars
The Martian Geological Time Scale
Noachian: 4.6 to about 3.5 to 3.8 billion years ago) Named after Noachis
Terra. Heavy cratering but also much evidence of liquid water.
Hesperian: 3.5 to 1.8 billion years ago. Named after Hesperia Planum.
Main epoch of volcanic activity,
which buried many earlier craters.
Amazonian: From the end of the Hesperian to the present. Named after Amazonis Planitia.
Too cold for liquid water at the surface.
Albedo Features on Mars
Below: a map of Martian albedo features compiled from several observers between 1939 and 1941
- Large areas of heavily cratered, probably very ancient crust
- Areas where craters have been obliterated by erosion and deposition
- An enormous rift valley (Vallis Marineris) which is about 5000 km long, about 100 km wide
and nearly 10 km deep.
- Extensive signs of water erosion. Channels and flood plains. Rovers have
found extensive evidence of water-lain sedimentary rocks.
- Enormous volcanoes. Nix Olympica or Olympus Mons is 500 km in diameter and over 20
km high. It is a type of volcano known as a Shield Volcano and is probably made of
basalt. The largest shield volcano on Earth, the island of Hawaii, is only about 300 km in diameter and
- Areas of chaotic terrain, possibly large areas of permafrost melting and ground collapse.
- Mars is far less active than Earth geologically. Judging from cratering, the active erosion
occurred several hundred million years ago.
- There is no known surface water on Mars at present.
- Areas of laminated (bedded) terrain near the poles of Mars may be wind-deposited
- Somewhat denser toward center but not known whether it has a core.
- May have a very weak magnetic field.
Life on Mars
- Early observers thought they could see "canals" on Mars, and some took these to be signs of
intelligent life. Now known that canals are myths.
- Doubtful whether life could evolve on Mars under present conditions but some simple
terrestrial organisms could survive there.
- If life had appeared on Mars in the past, it could have adapted to more severe conditions.
- No certain signs of life have been noted from space images or from the Viking landers, but
the Viking landing sites were chosen for safety and are not the likeliest places to search for life.
- In 1997, a Martian meteorite found in Antarctica was announced to show possible evidence
of ancient Martian life:
- Distinctive organic molecules
- Minerals typical of those formed by terrestrial organisms
- Possible fossil remains of rod-like organisms
- No single piece of evidence is conclusive. Supporters of Martian life believe the best
interpretation of all the evidence together is life
- Skeptics believe the possible fossils are too tiny to contain the molecules necessary for life
- Everyone involved agrees the evidence shows only possible evidence of ancient
The "Canals" of Mars
Schiaparelli's Map of Mars
Percival Lowell's 1896 map of Mars
The Moons of Mars
- Mars has two small moons. Both are rather irregular.
- Phobos measures about 12 by 18 miles
- Circles Mars about 5800 miles from its center or about 3700 miles above its surface.
- It circles Mars in about 7 hours and 40 min., and is unusual in that it circles its home planet
faster than the planet rotates.
- Deimos measures about 7 by 10 miles
- Circles Mars at a distance of 14,600 miles (12,500 miles above the surface).
- It takes about 30 hours to orbit Mars.
- Both satellites would show tiny "disks" from Mars but would appear much smaller than the
Sun would appear (and the Sun would be only 3/4 the size seen from Earth).
- Both satellites are heavily cratered. Phobos shows curious grooves that may be fractures
caused by a large impact.
- The satellites could possibly have formed in orbit around Mars but are more likely captured
- Escape velocity from Phobos is about 25 mph, and from Deimos about 15.
- You could easily throw a baseball free from either.
- An Olympic high jumper could escape from Deimos and could
jump about 3 miles high on Phobos.
- Robert M. Haberle, 1986. The Climate of Mars. Scientific American, vol. 254, no. 5, pp. 54-65
- Raymond E. Arvidson, Alan B. Binder and Kenneth L. Jones, 1978, The Surface of Mars. Scientific American, vol. 238, no. 3, pp. 76-91
- Norman H. Horowitz, 1977, The Search For Life on Mars. Scientific American, vol. 237, no. 5, pp. 52-61
- Conway B. Leovy, 1977, The Atmosphere of Mars. Scientific American, vol. 237, no. 1, pp. 34-43
- Joseph Veverka, 1977, Phobos and Deimos. Scientific American, vol. 236, no. 2, pp. 30-37
- Michael H. Carr, 1976, The Volcanos of Mars. Scientific American, vol. 234, no. 1, pp. 32-43
- James B. Pollack, 1975, Mars. Scientific American, vol. 233, no. 3, pp. 106-117
Return to Planetary Images Index
Access Course Notes on Planetary Geology
Access Astronomy Notes Index
Return to Professor Dutch's Home Page
Created 20 May 1997, Last Update
14 December 2009
Not an official UW Green Bay site | <urn:uuid:c0e172f1-5ffc-4697-a638-7691c4d34e05> | 3.71875 | 1,512 | Knowledge Article | Science & Tech. | 60.540172 |
Basically cybernetics is the study of communication and control processes in biological, mechanical, and electronic systems. The term itself does not imply two or more such system kinds merging together, yet it is most often used by the general populace to describe the combined system of biological-mechanical fusion or biological-electronic fusion.
Below, we offer a selection of links from our resource databases which may match this term.
Related Dictionary Entries for Cybernetics:
Resources in our database matching the Term Cybernetics:
Results by page
In early 2008, the Max Planck Institute for Biological Cybernetics researchers developed an omnidirectional treadmill to facilitate unconstrained walking in all directions through large-scale virtual environments.
This ten year old book, is a bit behind current advances, but is by no means behind the times. If anything, the changes since 1999, have only emphasised the points made in this volume, not diminished them. It argues that we are entering a virtual age, an age where information, minds themselves, are becoming divorced from their physical bodies.
Industry News containing the Term Cybernetics:
By mimicking the way that a living body acquires immunity to disease through vaccination, researchers have designed an artificial immune system to solve optimization problems more effectively than before. The results show that the biologica...
Scientists at the Max Planck Institute for Biological Cybernetics in T?bingen have succeeded in demonstrating for the first time that the activities of large parts of the brain can be altered in the long term. The breakthrough was achieved ...
When observing a fly buzzing around the room, we should have the impression that it is not the fly, but rather the space that lies behind it that is moving. After all, the fly is always fixed in our central point of view. But how does the b...
For the very first time, scientists show what EEG can really tell us about how the brain functions.
The electroencephalogram (EEG) is widely used by physicians and scientists to study brain function and to diagnose neurologic...
A new generation of flight simulators will attempt to make air traffic safer.
Whether for a business trip to a neighbouring country or a holiday in the Caribbean: What most people take for granted, actually poses a great chal... | <urn:uuid:19aa9e38-1055-4229-94e0-598d46f0f3cb> | 2.875 | 475 | Content Listing | Science & Tech. | 40.7532 |
Thousands of pieces of "space junk" orbit our planet.
Click on image for full size
Image courtesy of ESA.
Whether on Earth or in Space, human activity creates waste. Like the Earth's environment, the space environment is getting more and more cluttered. There are currently millions of man-made orbital ruins that make up "space junk". Unfortunately, the past 45 years of space exploration have generated a lot of junk. Orbital debris includes things such as hatches blown off space modules, paint fragments from the space shuttle, or satellites that are no longer in use.
Most space junk is very small (for example, paint flecks). But there are thousands of objects orbiting Earth that are bigger than a baseball. These objects are tracked by ground-based radars.
Human-made debris orbits at a speed of roughly 28,000 km/hr (17,500 miles/hour)! Think of the damage even a small speck of paint could do if it hit a spacecraft at such a high speed! Even an object as small as small as a grape has enough kinetic energy to permanently hurt a medium-sized spacecraft!
Some spacecraft have shielding to protect from damage caused by space junk. It is also sometimes possible for a spacecraft to move out of the way to avoid getting hit by debris. The Center for Orbital and Reentry Debris Studies (CORDS) helps space mission controllers plan so as to avoid impacts between their spacecraft and space junk.
Shop Windows to the Universe Science Store!
Learn about Earth and space science, and have fun while doing it! The games
section of our online store
includes a climate change card game
and the Traveling Nitrogen game
You might also be interested in:
You may think that most objects in space that orbit something else move in circles, but that isn't the case. Although some objects follow circular orbits, most orbits are shaped more like "stretched...more
In February 2009 two satellites in Earth orbit crashed into each other and were destroyed. This was the first time ever for a major collision between two satellites in Earth orbit. The satellites were...more
The Hubble Space Telescope (HST) was one of the most important exploration tools of the past two decades, and will continue to serve as a great resource well into the new millennium. The HST found numerous...more
Driven by a recent surge in space research, the Apollo program hoped to add to the accomplishments of the Lunar Orbiter and Surveyor missions of the late 1960's. Apollo 11 was the name of the first mission...more
Apollo 12 was launched on Nov. 14, 1969, surviving a lightning strike which temporarily shut down many systems, and arrived at the Moon three days later. Astronauts Charles Conrad and Alan Bean descended...more
Apollo 15 marked the start of a new series of missions from the Apollo space program, each capable of exploring more lunar terrain than ever before. Launched on July 26, 1971, Apollo 15 reached the Moon...more
NASA chose Deep Impact to be part of a special series called the Discovery Program on July 7, 1999. The Discovery program specializes in low-cost, scientific projects. In May 2001, Deep Impact was given...more | <urn:uuid:296358bd-19e2-4513-95a1-9977905fed02> | 3.921875 | 654 | Knowledge Article | Science & Tech. | 58.798627 |
The streaming layer provides a framework for pipelined processing of large sequences. Many external memory algorithms implemented with the STXXL streaming layer save a factor at least two in I/Os. The pipelined processing technique is well known in the database world . To the best of our knowledge we are the first who apply this method systematically in the domain of external memory algorithms. We introduce it in the context of an external memory software library.
Usually the interface of an external memory algorithm assumes that it reads the input from external memory container(s) and writes output in external memory container(s). The idea of pipelining is to equip the external memory algorithms with a new interface that allows them to feed the output as a data stream directly to the algorithm that consumes the output, rather than writing it to external memory. Logically, the input of an external memory algorithm does not have to reside in external memory, it could be rather a data stream produced by another external memory algorithm.
Many external memory algorithms can be viewed as a data flow through a directed acyclic graph . The file nodes represent physical data sources and data sinks, which are stored on disks (e.g. in the external memory containers of STL-user layer). A file node outputs or/and reads one stream of elements. The streaming nodes read zero, one or several streams and output zero, one or several new streams. Streaming nodes are equivalent to scan operations in non-pipelined external memory algorithms. The difference is that non-pipelined conventional scanning needs a linear number of I/Os, whereas streaming nodes usually do not perform any I/O, unless a node needs to access external memory data structures (stacks, priority queues, etc.). The sorting nodes read a stream and output it in a sorted order. Edges in the graph denote the directions of data flow between nodes. The question ``When a pipelined execution of the computations in a data flow graph is possible in an I/O-efficient way?'' is analyzed in .
In STXXL, all data flow node implementations have an STXXL stream interface, which is similar to STL Input iterators5. As an input iterator, an STXXL stream object may be dereferenced to refer to some object and may be incremented to proceed to the next object in the stream. The reference obtained by dereferencing is read-only and must be convertible to the value_type of the STXXL stream. The concept of STXXL stream also defines a boolean member function empty() which returns true iff the end of the stream is reached.
Now we tabulate the valid expressions and the expression semantics of STXXL stream concept in the style of STL documentation.
|X, X1, , Xn||A type that is a model of STXXL stream|
|T||The value type of X|
|s, s1, , sn||Object of type X, X1, , Xn|
|t||Object of type T|
|Name||Expression||Type requirements||Return type|
|Constructor||X s(s1,...,sn)||s1, , sn are convertible to X1&, , Xn&|
|Dereference||*s||Convertible to T|
|Member access||s->m||T is a type for which t.m is defined|
|End of stream check||(*s).empty()||bool|
|Constructor||X s(s1,...,sn)||s1, , sn are the input streams of s|
|Dereference||*s||s is incrementable|
|Member access||s->m||s is incrementable||Equivalent to (*s).m|
|Preincrement||++s||s is incrementable||s is incrementable or past-the-end|
The binding of a STXXL stream object to its input streams (incoming edges in a data flow graph ) happens at compile time, i.e. statically. The other approach would be to allow binding at running time using the C++ virtual function mechanism. However this would result in a severe performance penalty because most C++ compilers are not able to inline virtual functions. To avoid this disadvantage, we follow the static binding approach using C++ templates. For example, assuming that streams s1, , sn are already constructed, construction of stream s with constructor X::X(X1& s1,..., Xn& sn) will bind s to its inputs s1, , sn.
After creating all node objects, the computation starts in a ``lazy'' fashion, first trying to evaluate the result of the topologically latest node. The node reads its intermediate input nodes, element by element, using dereference and increment operator of the STXXL stream interface. The input nodes procede in the same way, invoking the inputs needed to produce an output element. This process terminates when the result of the topologically latest node is computed. This style of pipelined execution scheduling is I/O-efficient, it allows to keep the intermediate results in-memory without needing to store them in external memory.
Streaming layer of STXXL library offers generic classes which implement the functionality of sorting, file, and streaming nodes:
As mentioned above, STXXL allows streaming nodes to have more than one output. In this case only one output of a streaming node can have the STXXL stream interface. The other outputs must then be passed to file nodes (e.g. via calling the method push_back of stxxl::vector) or sorting nodes (they have a push_back interface too).
Now we ``pipeline'' the random graph generation example shown in the previous chapter. The data flow graph of the algorithm is presented in Figure 2 in the appendix. Listing 5 shows the pipelined code of the algorithm, the definitions of edge, random_edge, and edge_cmp are in Listing 3. Since the sorter of the streaming layer accepts an STXXL stream input, we do not need to output the random edges. Rather, we generate them on the fly. The random_edge_stream object (model of STXXL stream) constructed in Line 19 supplies the sorter with a stream of random edges. In Line 20, we define the type of the sorter node; it is parameterized by the type of the input stream and the type of the comparison function object. Line 21 creates a SortedStream object attaching its input to the RandomStream. The internal memory consumption of the sorter stream object is bounded to 512 MB. The UniqueStream object filters the duplicates in its input edge stream (Line 23). The generic stream::unique stream class stems from the STXXL library. Line 26 records the content of the UniqueStream into the external memory vector. As in the Listing 4 (Line 27), we cut the vector at the NewEnd boundary. Let us count the number of I/Os the program performs: random edge generation by RandomStream costs no I/O; sorting in SortedStream needs to store the sorted runs and read them again to merge -- I/Os; UniqueStream deletes duplicates on the fly, it does not need any I/O; and materializing the final output can cost up to I/Os. Totally the program incurs only I/Os, compared to for the nonpipelined code in Section 2.3. | <urn:uuid:ae81a86c-6818-4cb9-bc2b-3915739e4ee5> | 3.03125 | 1,552 | Academic Writing | Software Dev. | 51.861687 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
October 26, 1998
Explanation: Space travel entered the age of the ion drive Saturday with the launch of Deep Space 1, a NASA mission designed primarily to test new technologies. Deep Space 1 is bound for asteroid 1992 KD in July 1999. Although the ion drive on Deep Space 1 provides acceleration much smaller than we feel toward Earth, it will gradually give the spacecraft the speed it needs to travel across our Solar System. The propulsion drive works by ionizing Xenon atoms with power provided by large panels that collect sunlight. As these ions are expelled by a strong electric field out the back, the spacecraft slowly gains speed. Pictured above, hot blue ions emerge from a prototype drive that was successfully tested last year at JPL.
Authors & editors:
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U. | <urn:uuid:10c47164-2d85-4d09-9f01-fca2ae923562> | 3.40625 | 216 | Knowledge Article | Science & Tech. | 51.277202 |
Why so blue? Colour change in the chameleon grasshopper (Kosciuscola tristis)
A project undertaken at the Department of Biological Sciences, Macquarie University, and supervised by Marie Herberstein and Kate Umbers
Rapid colour change in insects is extremely rare, yet in Australia such colour change has evolved independently in two disparate lineages. In both the dragonfly genus Austrolestes and the grasshopper genus Kosciuscola, males are able to change colour reversibly from black to bright blue (Veron 1974, Key & Day 1954a, b;). Veron (1974) suggested the dark phase in Austrolestes assisted in thermoregulation at low temperatures but could not explain the bright phase. In Kosciuscola, this colour change is known to be controlled by changes in temperature (Key & Day 1954a, b; Figure 1), though its function remains unknown. Because this colour change is limited to one sex, it is possible that this trait may be under sexual selection. This hypothesis has so far not been tested. The aim of this project is to test the hypothesis that colour change of male K. tristis is a sexual signal. Bright males may gain a fitness advantage by being prefered by females or through detering rivals.
Three studies to date have focused on this unique temperature regulated colour change mechanism, most strikingly seen in male K. tristis (Filshie et al. 1975; Key & Day 1954a, b). Filshie et al. (1975) showed that colour change in male K. tristis is via an intracellular granule migration. Our intracellular images of female K. tristis show the same granule migration (Figure 2 in appendix) but further data suggest a masking pigment in the female cuticle that seems lacking in the male (Umbers unpbl). A male’s colour rapidly changes from black below 10ºC to bright blue above 25ºC (Key & Day, 1954b; Umbers unpbl.). The reversal of this colour change is remarkably slower, up to five hours (Umbers unpbl.). Key and Day (1954b) suggested that this colour change offers a thermoregulatory advantage, by allowing foraging and mate-searching outside optimal temperatures. Our preliminary data show that the bright colour of K. tristis does not reduce heat loading whatsoever (Umbers unpbl.) as suggested previously (Key & Day 1954a, b). Surprisingly, no one has yet proposed a sexual signalling function for this colour change.
The objective of this project is to test if the colour blue and the ability to change from black to bright blue is a sexual signal in the chameleon grasshopper, K. tristis. This overall aim consists of the following hypotheses:
We will address these objectives using a combination of colour analyses, field observations and manipulative field and laboratory experiments.
Filshie B. K., Day M. F. & Mercer E. H. (1975) Colour and colour change in the grasshopper, Kosciuscola tristis Journal of Insect Physiology 21 1763-1770
Key K. H. L. & Day M. F. (1954a) A temperature controlled physiological colour response in the grasshopper Kosciuscola tristis (Sjost) (Orthoptera: Acrididae) Australian Journal of Zoology 2 (3) 309-339
Key K. H. L. & Day M. F. (1954b) The physiological mechanism of colour change in the grasshopper Kosciuscola tristis (Sjost) (Orthoptera: Acrididae) Journal of Australian Zoology 2 (3) 340-363
Veron J. E. N. (1974) The role of physiological change in the thermoregulation of Austrolestes annulosus (Selys) (Odonata) Australian Journal of Zoology 22 457-69 | <urn:uuid:cad8773b-43bf-4e94-ab2d-ec70bde24b0f> | 4.03125 | 832 | Academic Writing | Science & Tech. | 49.635952 |
They do generate heat. They just do not SPEND energy specifically on heating their bodies by raising their metabolisms. This is a form of energy conservation. The metabolic rate they need to live is not nearly enough to heat their bodies.
An example of spending energy to heat the body is seen in humans shivering. Here muscle is activated not for its usual purpose, but to function as a furnace. "Warm-blooded" and "cold-blooded" is somewhat a misnomer. The correct way to think of it is...
Endotherm or ectotherm. Does the heat primarily come from within (endo) or from the surroundings (ecto). Endothermic animals include mammals. Most of their body heat is generated by their own metabolisms. Ectothermic animals include reptiles and insects. They absorb most of their body heat from the surroundings. This is not the same as saying they let their body temperature fluctuate with their surroundings, some avoid this by moving around to accomodate themselves.
Homeotherm or poikilotherm. Homeotherms want to maintain homeostasis for their body temperatures. They don't want it to change. Poikilotherms do not exhibit this behaviour, instead their body temperatures vary greatly with the environment.
We can have endotherm poikilotherms, such as squirrels, who let their body temperature drop while hibernating. Endotherm homeotherms, such as humans, where temperature is constant by means of complex thermoregulation. Ectotherm homeotherms, such as snakes (moving into shadow or into the sun to regulate temperature), and ectotherm poikilotherms, such as maggots. | <urn:uuid:19a89eb7-7e4d-418f-aa4a-0bab7db6489a> | 3.625 | 354 | Q&A Forum | Science & Tech. | 40.491243 |
look at this cool video and facts that I found on flying snakes.
The image of airborne snakes may seem like the stuff of nightmares (or a certain Hollywood movie), but in the jungles of South and Southeast Asia it is reality.
Flying snake is a misnomer, since, barring a strong updraft, these animals can’t actually gain altitude. They’re gliders, using the speed of free fall and contortions of their bodies to catch the air and generate lift.
Once thought to be more parachuters than gliders, recent scientific studies have revealed intricate details about how these limbless, tube-shaped creatures turn plummeting into piloting. To prepare for take-off, a flying snake will slither to the end of a branch, and dangle in a J shape. It propels itself from the branch with the lower half of its body, forms quickly into an S, and flattens to about twice its normal width, giving its normally round body a concave C shape, which can trap air. By undulating back and forth, the snake can actually make turns. Flying snakes are technically better gliders than their more popular mammalian equivalents, the flying squirrels.
There are five recognized species of flying snake, found from western India to the Indonesian archipelago. Knowledge of their behavior in the wild is limited, but they are thought to be highly arboreal, rarely descending from the canopy. The smallest species reach about 2 feet (61 centimeters) in length and the largest grow to 4 feet (1.2 meters).
Their diets are variable depending on their range, but they are known to eat rodents, lizards, frogs, birds, and bats. They are mildly venomous snakes, but their tiny, fixed rear fangs make them harmless to humans.
Scientists don’t know how often or exactly why flying snakes fly, but it’s likely they use their aerobatics to escape predators, to move from tree to tree without having to descend to the forest floor, and possibly even to hunt prey.
One species, the twin-barred tree snake, is thought to be rare in its range, but flying snakes are otherwise quite abundant and have no special conservation status
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the #1=(programmable . #1#) programming language
What is Common Lisp?
Common Lisp is the modern, multi-paradigm, high-performance, compiled, ANSI-standardized descendant of the long-running family of Lisp programming languages.
Common Lisp is known for being extremely flexible, having excellent support for object oriented programming, and fast prototyping capabilities. It also sports an extremely powerful macro system that allows you to tailor the language to your application, and a flexible run-time environment that allows modification and debugging of running applications (excellent for server-side development and long-running critical software).
Common Lisp is a multi-paradigm programming language that allows you to to choose the approach and paradigm according to your application domain.
This should be all about how to install CL for unix, windows, and OSX.
quicklisp should be here as well
(this-should :be *about* :learning "Common Lisp")
… and maybe swank + slime | <urn:uuid:d0b8c6b8-592a-427c-80a9-0c0adfa05ebe> | 3.0625 | 209 | Knowledge Article | Software Dev. | 29.556735 |
GENESIS SOLAR WIND SAMPLE COLLECTION
Genesis samples are the first extraterrestrial samples returned
to Earth by NASA since the Apollo program, which ended in the early 1970s.
The collectors returned by the Genesis mission contain solar wind atoms which can be analyzed in sophisticated laboratory instruments to measure very precisely the composition of the Sun. Since the Sun contains >99% of the mass in the solar system, knowing its elemental and isotopic composition is a good average measure of the composition of the solar nebula at the time when the planets were forming. Scientists already have rocks from the Moon, Mars and the asteroids and dust specks from comets. Genesis' solar data should allow new insights in tracing the chemical evolution of diverse planetary samples, most of which came from a common starting material, the solar nebula. | <urn:uuid:f1a77167-991e-4854-a50c-62a8d7a02da8> | 3.34375 | 168 | Content Listing | Science & Tech. | 22.791883 |
Neogene-Quaternary Continental Margin Volcanism
Metepec, Puebla, México
12-16 January 2004
- Gerardo J. Aguirre-Diaz
- Centro de Geociencas, Universidad Nacional Autónoma de México, Juriquilla, México;
- José Luis Macías and Claus Siebe
- Instituto de Geofisica, Universidad Nacional Autónoma de México, México D.F., México
Grant Heiken, Freeland, Washington, USA
|Conference participants at Tlamacaz mountaineering lodge on the upper slopes of Popocatépetl. Iztaccíhuatl volcano (5,272 m) in the background. Click on photo for larger image.|
The Mexican volcanic belt crosses México from the Pacific to the Gulf of Mexico and is composed of hundreds of Neogene-Quaternary volcanoes, ranging from humble scoria cones to the great composite cones of Popocatépetl and Citlaltépetl (Orizaba). Holocene and Historic eruptions continue to affect the peoples of México; for example, eruptions changed the course of history between Classic and Post-Classic cultures when the valleys of México and Puebla were subjected to tephra fallout and secondary lahars (volcanic mudflows). Understanding magma evolution and eruption dynamics are critical to México in that modern urban agglomerations ranging in size from 2.2 to 20 million people will be affected by future eruptions.
The purpose of this Penrose Conference was to evaluate the present state of knowledge of the source and evolution of magmas that formed the Neogene-Quaternary continental-margin volcanic belt associated with the Mexican portion of the "Ring of Fire." Discussions included the complexities of volcanic styles that promote explosive eruptions, sector collapse of volcanoes, volcaniclastic sedimentation, and related volcanic hazards. The case of México was compared with continental-margin volcanism at other places in the Americas, such as the Andes in Colombia and the Cordillera and Cascades of the western United States.
Working upward from the roots of continental margin volcanic belts, keynote speakers Charles Langmuir and Gerhard Wörner reviewed the latest interpretations of processes at convergent plate margins. Using compositional data mostly from the trans-Mexican volcanic belt lavas and thermal melting models of the subduction process, Langmuir proposed that controls of the degree of melting include wedge geometry and thermal structure, source compositions, and convergence rates. Working with samples from the well-exposed eruption sequences of the central Andes, Wörner concluded that magma genesis through space and time was controlled by crustal heterogeneity and thickening since the Miocene. The posters covered mostly recent petrological studies of volcanic complexes in México, Central America, the Cascades, and New Zealand. Stephen Grand described a newly funded project to image the Mexican convergent margin with a 50+ seismometer array, a work that should tie well into the many petrological transects of the volcanic belt.
Based on the Smithsonian database for the 1926 Mexican volcanoes, Jim Luhr concluded that the three main magmatic suites in México are (1) calc-alkaline magmas of the trans-Mexican volcanic belt and Northern Mexican Extensional Province, (2) lamprophyres of the western trans-Mexican volcanic belt, and (3) intraplate type mafic alkaline rocks of the Northern Mexican Extensional Province and Pacific Islands. Sixteen posters covered a wealth of new work on the petrology of trans-Mexican volcanic belt volcanoes, including the Chichinautzin volcanic field, which rims the southern end of the Valley of México. Xitle, one of the Chichinautzin monogenetic volcanoes, produced a lava flow with a 14C age of 1665 years B.P., which partly buried Cuicuilco pyramid and now underlies the campus of the National University.
|Conference participants inspecting the 14,000 yr B.P. “Tutti Frutti” sequence at Popocatépetl during the field trip. Click on photo for larger image.|
While pungent smells from Popocatépetl occasionally swept the conference complex at Metepec, Fraser Goff and James Gardner gave keynote lectures on the physical role of gases in continental margin volcanism. Given the great depth of Popocatépetl's crater and the possibility of eruptions at any time, in-situ gas sampling has been impossible. Therefore, most of Goff's data were from simultaneous FTIR and COSPEC measurements of eruption plumes. Like most volcanoes at convergent margins, emissions from Popocatépetl are mostly water vapor with high values of Stotal, F, As, and Hg (with respect to Cl). Over a four-year period, the HCl/SO2 ratio has been increasing and HF/SO2 ratios have been decreasing. CO2 fluxes range from 40,000 t/day to >100,000át/day. Plume emissions also contain SiF4. The observed range of gas ratios indicates temperatures of 200 ▒ 20 °C, which may indicate reaction of gases with conduit walls or with ash particles in the cooling plume.
With an emphasis on rhyolites, James Gardner reviewed the dynamics of bubble growth in magmas, integrating observation with experiments. The pumice, ash, and gases erupted are all products of bubble nucleation, growth, and degassing. Bubble interactions and partial connectivity can produce coexisting bubbles that differ in size by more that 20 times. During the roundtable discussion, it was noted that there is passive degassing between eruptive phases.
Zimmer and Erzinger's continuous measurements of fumaroles at Merapi, Indonesia, demonstrate the influence of rainfall on gas flux and temperatures; during the dry season, fumarole temperatures are constant. Using data from Mount Pinatubo, Philippines, Hammer concluded that the explosive eruption of dense, microlite-rich, partly-degassed tephra, along with vesicular, microlite-free pumice during pulsatory eruptions reflects variable magma travel times.
Having constructed the volcanoes, the meeting moved on to their destruction via sector collapse, avalanches, and lahars. This session was an excellent introduction to the field trip during the last day of the meeting to deposits left by at least three sector collapses of the Paleo-Popocatépetl cone; the youngest of these deposits is ~23,000 yr B.P. Hummocky terrain and debris avalanche deposits south-southwest of Popocatépetl cover over 300 km2 and have a cumulative volume of >30 km3. The youngest of the avalanche deposits are overlain by blast and pyroclastic flow deposits. Preliminary studies indicate that runout was at least 70 km south of the cone. Sector collapse and debris avalanches have occurred at nearly all large Mexican composite cones.
In the Cascade Range of the United States, the dense forest makes documentation of lahar (volcanic mudflow) deposits extremely difficult. Kevin Scott is now documenting the extent and magnitude of lahar deposits with lidar imagery. This application has enhanced evaluation of lahar hazards, which in the past have been very conservative. He explained that lahar mobility is difficult to demonstrate to disaster planners and has found that comparing it with water floods gets the message across. Lahar warnings are possible. Survivors of the Nevado del Ruiz catastrophe felt ground tremors before the lahar arrived. On that basis, acoustic flow monitors have been installed in the valleys around Mount Rainier to provide at least a 45-minute warning to downstream towns.
In the panel discussion it was agreed that the sector collapse, avalanche, and mudflows that were generated by the 1980 eruption of Mount St. Helens was the turning point in recognizing this widespread hazard. Since 1980, 300 sector collapse deposits have been identified at volcanoes along continental margins; their volumes range from 0.1 to 5 km3 (Lee Siebert). Hot research themes include the transition of sector collapse avalanches to debris flows and why some debris avalanches stop and others liquefy and keep moving; for example, the lahars formed during the last eruption of Cotopaxi reached the sea, 300 km downstream. The sedimentary aftermath of a large-scale eruption may be a hazard larger than the eruption itself. James White described eruptions on the North Island of New Zealand that buried entire drainage systems and created lakes. Subsequent failure of the tephra dams produced high-concentration flows that swept downstream areas now occupied by cities.
México has some of the largest ignimbrite deposits in the world. For example, in the Sierra Madre Occidental, ignimbrite sequences can be thousands of meters thick and have volumes of hundreds or even thousands of km3. Most are associated with Miocene calderas and may have been erupted during the opening of the Gulf of California. Much work needs to be done on this province in spite of the difficulties offered by the terrain and isolation. Mike Branney provided a summary of what is known about massive ignimbrite deposits ("large explosive eruptions" were defined by Branney as those with volumes of >1 km3 to >1000 km3). Most are characterized by high mass flux sustained for hours or days and associated caldera collapse. The pyroclastic density currents produced during these eruptions can be fully dilute or granular-fluid-based, based on conditions near the lower flow boundaries. Complex deposit architectures are affected by the nature of the density current and the complexity of underlying terrain.
Within volcanic provinces with large volumes of rhyolite, it is often difficult to distinguish between densely-welded rheomorphic ignimbrites and clastogenic lava flows. Using examples from the Snake River Plain, Bill Bonnichsen described transitions from non-welded ignimbrites to high-grade rheomorphic ignimbrites to clastogenic lava flows and on out to domes having little evidence for fragmentation.
Dealing with a deadly but much smaller-scale eruption type than the large ignimbrites, the session on block and ash flows associated with dome collapse focused on recent eruptions at volcanoes like Colima, México, and Montserrat. Block and ash flows begin with dome collapse and formation of decameter-sized blocks (Marcus Bursik). In the final deposit the same blocks have been fragmented into particles ranging in size from 1 mm to 2 m. High on the dome slopes (~35°), the deposits are 1 to 2 m thick, but in distal regions with slopes of 10° to 20° they are up to 8 m thick. Many are preceded by pyroclastic surges. Much of the mechanical crushing seems to occur at breaks in slope. Bursik also discussed modeling of these flows but emphasized "numerical models are useless without field observation."
The last link in the chain of discussions that began with magma genesis was that of reducing risk at continental-margin volcanoes. The mitigation issues reviewed by Robert Tilling are:
- increasing population growth and air traffic;
- no capability to reliably predict explosive eruptions;
- the fact that most volcanoes are not monitored;
- a low frequency of destructive events; and
- effective communication between scientists, civil authorities, news media, and the population is at risk.
A major quandary concerns monitoring parameters versus time; when do you force local officials to make decisions? There is also the dilemma of acquiring funding for monitoring for infrequent but catastrophic activity. Hazard maps are useful for those who understand how to read them, but don't work well for the public. Public lectures and pamphlets are useful but reach only about 1% of the public. Visualization of processes and videotapes of actual events are more effective, but not if the media will not present them to the public. Methods of reaching the public were discussed during the roundtable, with the suggestion that a system similar to that used by the weather service for tornado warnings be implemented.
Gavilanes noted that mixed signals put the population at risk during eruptions of Volcán de Colima during 1999-2003. There were many conferences in the villages, but conflicting signals from the authorities and the army created confusion and frustration among the residents. He also noted the great need for sociologists to work with volcanologists for effective hazard mitigation.
In slightly less than one week, this dynamic group of 104 workshop participants (including about 30 students) went from the mostly academic pursuit of petrology to the sociological aspects of volcanic disaster mitigation. What was evident is that all of the pieces are available to complete the puzzle, but that the volcanological community has a long way to go to assemble those pieces and to mitigate volcanic hazards. There is hope for increased volcanological research and successful disaster mitigation in México; at this Penrose Conference it was evident that, in addition to the well-respected Mexican volcanological community, there are many talented students at Mexican universities who will carry this work into the future.
For more information on the conference, visit http://tepetl.igeofcu.unam.mx/penrose/index.html. A GSA publication is also in preparation (Volcanic hazards in the México City metropolitan area from eruptions at Popocatépetl, Nevado de Toluca, and Jocotitlán stratovolcanoes and monogenetic scoria cones in the Sierra Chichinautzin volcanic field, by C. Siebe and J.L. Macias).
Additional Sponsoring Organizations:
- International Association of Volcanology and Chemistry of the Earth's Interior
- Coordinación de la Investigación Científica, Universidad Nacional Autónoma de México (UNAM)
- Instituto de Geofísica, UNAM
- Instituto de Geología, UNAM
- Centro de Geociencias (Juriquilla, Querétero), UNAM
- Centro Universitario para la Prevención de Desastres, Benemérita Universidad Autónoma de Puebla
- Gobierno del Estado de Puebla, México
- Volkswagen de México (Puebla)
Gerardo J. Aguirre-Díaz | <urn:uuid:8cb00f1c-d07c-425d-89d2-26b2faa6e023> | 2.875 | 3,054 | Academic Writing | Science & Tech. | 25.943254 |
float opdigits(string name)
This function will return the numeric value of the last set of consecutive digits in a node's name. It is used when building several similar networks. This expression expects a path to a node, if the node doesn't exist, it will return 0.
opdigits(".") means the digits of the node that the expression is in. Tip: It is the same as the variable
opdigits("..") means the digits of the parent of the node. Tip: It is the same as the variable
opdigits("../..") is the digits of the parent of the parent.
opdigits("/obj/geo22") = 22 opdigits("..") = 7 (if the current component is named geo7 for example) | <urn:uuid:3d204b1e-7431-4cd0-a271-33fa95cccdc5> | 3.328125 | 164 | Documentation | Software Dev. | 72.356333 |
From Wikipedia, the free encyclopedia
Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars) causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior.
The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides us with very valuable information about the temperatures and pressures that occur at great depths within the Earth's crust.
Metamorphic minerals are those that form only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet.
Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks, but are not necessarily the result of the process of metamorphism. These minerals formed during the crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are stable only within certain limits, and the presence of some minerals in metamorphic rocks indicates the approximate temperatures and pressures at which they formed.
The change in the particle size of the rock during the process of metamorphism is called recrystallization. For instance, the small calcite crystals in the sedimentary rock limestone change into larger crystals in the metamorphic rock marble, or in metamorphosed sandstone, recrystallisation of the original quartz sand grains results in very compact quartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact.
The layering within metamorphic rocks is called foliation (derived from the Latin word folia, meaning "leaves"), and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as mica and chlorite, to become rotated such that their long axes are perpendicular to the orientation of shortening. This results in a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them.
Textures are separated into foliated and non-foliated categories. Foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage. For example, slate is a foliated metamorphic rock, originating from shale. Non-foliated rock does not have planar patterns of strain.
Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated. Slate is an example of a very fine-grained, foliated metamorphic rock, while phyllite is medium, schist coarse, and gneiss very coarse-grained. Marble is generally not foliated, which allows its use as a material for sculpture and architecture.
Another important mechanism of metamorphism is that of chemical reactions that occur between minerals without them melting. In the process atoms are exchanged between the minerals, and thus new minerals are formed. Many complex high-temperature reactions may take place, and each mineral assemblage produced provides us with a clue as to the temperatures and pressures at the time of metamorphism.
Metasomatism is the drastic change in the bulk chemical composition of a rock that often occurs during the processes of metamorphism. It is due to the introduction of chemicals from other surrounding rocks. Water may transport these chemicals rapidly over great distances. Because of the role played by water, metamorphic rocks generally contain many elements absent from the original rock, and lack some that originally were present. Still, the introduction of new chemicals is not necessary for recrystallization to occur.
Types of metamorphism
Contact metamorphism is the name given to the changes that take place when magma is injected into the surrounding solid rock (country rock). The changes that occur are greatest wherever the magma comes into contact with the rock because the temperatures are highest at this boundary and decrease with distance from it. Around the igneous rock that forms from the cooling magma is a metamorphosed zone called a contact metamorphism aureole. Aureoles may show all degrees of metamorphism from the contact area to unmetamorphosed (unchanged) country rock some distance away. The formation of important ore minerals may occur by the process of metasomatism at or near the contact zone.
When a rock is contact altered by an igneous intrusion it very frequently becomes more indurated, and more coarsely crystalline. Many altered rocks of this type were formerly called hornstones, and the term hornfels is often used by geologists to signify thosefine grained, compact, non-foliated products of contact metamorphism. A shale may become a dark argillaceous hornfels, full of tiny plates of brownish biotite; a marl or impure limestone may change to a grey, yellow or greenish lime-silicate-hornfels or siliceous marble, tough and splintery, with abundant augite, garnet, wollastonite and other minerals in which calcite is an important component. A diabase or andesite may become a diabase hornfels or andesite hornfels with development of new hornblende and biotite and a partial recrystallization of the original feldspar. Chert or flint may become a finely crystalline quartz rock; sandstones lose their clastic structure and are converted into a mosaic of small close-fitting grains of quartz in a metamorphic rock called quartzite.
If the rock was originally banded or foliated (as, for example, a laminated sandstone or a foliated calc-schist) this character may not be obliterated, and a banded hornfels is the product; fossils even may have their shapes preserved, though entirely recrystallized, and in many contact-altered lavas the vesicles are still visible, though their contents have usually entered into new combinations to form minerals that were not originally present. The minute structures, however, disappear, often completely, if the thermal alteration is very profound; thus small grains of quartz in a shale are lost or blend with the surrounding particles of clay, and the fine ground-mass of lavas is entirely reconstructed.
By recrystallization in this manner peculiar rocks of very distinct types are often produced. Thus shales may pass into cordierite rocks, or may show large crystals of andalusite (and chiastolite), staurolite, garnet, kyanite and sillimanite, all derived from the aluminous content of the original shale. A considerable amount of mica (both muscovite and biotite) is often simultaneously formed, and the resulting product has a close resemblance to many kinds of schist. Limestones, if pure, are often turned into coarsely crystalline marbles; but if there was an admixtureof clay or sand in the original rock such minerals as garnet, epidote, idocrase, wollastonite, will be present. Sandstones when greatly heated may change into coarse quartzites composed of large clear grains of quartz. These more intense stages of alteration are notso commonly seen in igneous rocks, because their minerals, being formed at high temperatures, are not so easily transformed or recrystallized.
In a few cases rocks are fused and in the dark glassy product minute crystals of spinel, sillimanite and cordierite may separate out. Shales are occasionally thus altered by basalt dikes, and feldspathic sandstones may be completely vitrified. Similar changes may be induced in shales by the burning of coal seams or even by an ordinary furnace.
There is also a tendency for metasomatism between the igneous magma and sedimentary country rock, whereby the chemicals in each are exchanged or introduced into the other. Granites may absorb fragments of shale or pieces of basalt. In that case, hybrid rocks called skarn arise, which don't have the characteristics of normal igneous or sedimentary rocks. Sometimes an invading granite magma permeates the rocks around, filling their joints and planes of bedding, etc., with threads of quartz and feldspar. This is very exceptional but instances of it are known and it may take place on a large scale.
Regional metamorphism is the name given to changes in great masses of rock over a wide area. Rocks can be metamorphosed simply by being at great depths below the Earth's surface, subjected to high temperatures and the great pressure caused by the immense weight of the rock layers above. Much of the lower continental crust is metamorphic, except for recent igneous intrusions. Horizontal tectonic movements such as the collision of continents create orogenic belts, and cause high temperatures, pressures and deformation in the rocks along these belts. If the metamorphosed rocks are later uplifted and exposed by erosion, they may occur in long belts or other large areas at the surface. The process of metamorphism may have destroyed the original features that could have revealed the rock's previous history. Recrystallization of the rock will destroy the textures and fossils present in sedimentary rocks. Metasomatism will change the original composition.
Regional metamorphism tends to make the rock more indurated and at the same time to give it a foliated, shistose or gneissic texture, consisting of a planar arrangement of the minerals, so that platy or prismatic minerals like mica and hornblende have their longest axes arranged parallel to one another. For that reason many of these rocks split readily in one direction along mica-bearing zones (schists). In gneisses, minerals also tend to be segregated into bands; thus there are seams of quartz and of mica in a mica schist, very thin, but consisting essentially of one mineral. Along the mineral layers composed of soft or fissile minerals the rocks will split most readily, and the freshly split specimens will appear to be faced or coated with this mineral; for example, a piece of mica schist looked at facewise might be supposed to consist entirely of shining scales of mica. On theedge of the specimens, however, the white folia of granular quartz will be visible. In gneisses these alternating folia are sometimes thicker and less regular than in schists, but most importantly less micaceous; they may be lenticular, dying out rapidly. Gneisses also, as a rule, contain more feldspar than schists do, and they are tougher and less fissile. Contortion or crumbling of the foliation is by no means uncommon, and then the splitting faces are undulose or puckered. Schistosity and gneissic banding (the two main types of foliation) are formed by directed pressure at elevated temperature, and to interstitial movement, or internal flow arranging the mineral particles while they are crystallizing in that directed pressure field.
Rocks that were originally sedimentary and rocks that were undoubtedly igneous convert into schists and gneisses. If originally of similar composition they may be very difficult to distinguish from one another if the metamorphism has been great. A quartz-porphyry, for example, and a fine feldspathic sandstone, may both the converted into a grey or pink mica-schist.
Metamorphic rock textures
The five basic metamorphic textures with typical rock types are:
- Slaty: slate and phyllite; the foliation is called 'slaty cleavage'
- Schistose: schist; the foliation is called 'schistosity'
- Gneissose: gneiss; the foliation is called 'gneissosity'
- Granoblastic: granulite, some marbles and quartzite
- Hornfelsic: hornfels and skarn
- ^ Blatt, Harvey and Robert J. Tracy, Petrology, W.H.Freeman, 2nd ed., 1996, p.355 ISBN 0-7167-2438-3
- ^ a b This article incorporates text from the article "Petrology" in the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.
|Wikimedia Commons has media related to: Metamorphic rock|
- Metamorphic textures - Middle East Technical University
- Metamorphism - U. of Alabama
- Types of metamorphism - Tulane U.
- Contact metamorphism example | <urn:uuid:dfe3c9a4-c9a4-4582-bd45-5627b73a040d> | 4.28125 | 2,868 | Knowledge Article | Science & Tech. | 24.171467 |
<language> (GHC) A parallel dialect of Prolog by K. Ueda in which each clause has a guard. GHC is similar to Parlog. When several clauses match a goal, their guards are evaluated in parallel and the first clause whose guard is found to be true is used and others are rejected. It uses committed-choice nondeterminism.
See also FGHC, KL1.
Try this search on Wikipedia, OneLook, Google
Nearby terms: gu « guaranteed scheduling « guard « Guarded Horn Clauses » gubbish » guest book » GUI | <urn:uuid:d087b428-3f2b-4d6b-9bab-adde4b457516> | 2.828125 | 119 | Structured Data | Software Dev. | 61.114167 |
Using a combination of satellite observations and computer modelling, researchers of the Max Planck Institute for Chemistry have studied nitrogen oxides pollution over the Indian Ocean. They showed that the central Indian Ocean in the southern hemisphere is not always as pristine as found earlier during the winter monsoon period, but is polluted during the monsoon transition periods by pollution plumes from Africa and Southeast Asia. Generally, the most polluted region is the Bay of Bengal, which is influenced by Indian and south-east Asian outflow during most of the year and China during part of the year (Geophysical Research Letters, 30 April 2004 and 11 August 2004). Current knowledge of atmospheric chemistry over the Indian Ocean is still limited due to the scarcity of long-term observations covering all seasons. The region is dynamically and chemically active because of the strong tropical sunlight, high humidity and the increasing anthropogenic emissions. The Indian Ocean Experiment (INDOEX) was an international field campaign during the winter monsoon period in 1999 to study how air pollution affects climate processes over the tropical Indian Ocean. Satellite pictures showed a thick haze - one of the now well-known "Atmospheric Brown Clouds" - which spreads thousands of kilometers south of India during this period. The results contrasted the highly polluted northern hemisphere with the more pristine air of the southern hemisphere (Fig. 1a).
Research on southern Asian pollution at the Max Planck Institute for Chemistry since then has focused on other periods of the year. The field campaign MINOS (Mediterranean Intensive Oxidants Study), led by the institute during the summer of 2001, showed that the same monsoon storms which produce the torrential rains also lift insoluble gases like carbon monoxide into the upper troposp
Contact: Dr. Mark Lawrence | <urn:uuid:5c5065ee-4db4-417f-914b-4a09bc5f57a3> | 3.84375 | 350 | Knowledge Article | Science & Tech. | 25.028997 |
Authorizing Users and Roles
ASP.NET is used to control client access to URL resources.
It is configurable for the HTTP method used to make the request
(GET or POST) and can be configured to allow or deny
access to groups of users or roles. The following example shows
access being granted to a user named someone
and a role named Admins. All other users are denied access.
<allow users="email@example.com" />
<allow roles="Admins" />
<deny users="*" />
Permissible elements for authorization directives are either
allow or deny. Each allow or deny
element must contain a users or a roles attribute.
Multiple users or roles can be specified in a single element by
providing a comma-separated list.
<allow users="John,Mary" />
The HTTP method can be indicated using the Verb attribute:
<allow VERB="POST" users="John,Mary" />
<deny VERB="POST" users="*" />
<allow VERB="GET" users="*" />
This example lets Mary and John POST to the protected resources, while only allowing everyone else to use GET.
There are two special usernames:
||Anonymous (unauthenticated) users
These special usernames are commonly used by applications using
forms-based authentication to deny access to unauthenticated users, as shown in the following example:
<deny users="?" />
URL authorization is computed hierarchically and the rules used to determine access are as follows:
What this means is that applications that are not interested in
inheriting their configuration should explicitly configure all of the possibilities relevant to their applications.
- Rules relevant to the URL are collected from across the hierarchy and a merged list of rules is constructed.
- The most recent rules are placed at the head of the list. This means that configuration in the current directory is
at the head of the list, followed by configuration in the
immediate parent, and so on, up to the top-level file for the computer.
- Rules are checked until a match is found. If the match is allowable,
access is granted. If not, access is disallowed.
The default setting in the machine-wide configuration file (machine.config)
is to grant access to all users. Unless an application is configured to the contrary
(and assuming that a user is authenticated and passes the file
authorization ACL check), access is granted.
When roles are checked, URL authorization effectively marches down the list of configured roles and does something that looks like the following pseudocode:
If User.IsInRole("ConfiguredRole") Then
What this means for your application is that you use your own class
that implements System.Security.Principal.IPrincipal to provide
your own role-mapping semantics, as explained in
The following sample uses forms-based authentication services.
It explicitly denies access to firstname.lastname@example.org and anonymous users.
Try logging into the sample with Username="email@example.com" and
Password="password". Access will be denied and you will be redirected
back to the logon page. Now log on as Username="firstname.lastname@example.org" and Password="password". You will see that access is granted.
VB Forms-Based/Cookie Authentication with URL Authorization | <urn:uuid:42fc65a6-d693-4df8-94ec-ea3d19f3185f> | 3.4375 | 724 | Documentation | Software Dev. | 34.586012 |