The most common cause of a fatality in a bike crash is a head injury, of which 45-88% are preventable by wearing a helmet.
The helmet issue is almost as controversial as the one about global warming.You cite the bike helmet safety institute, which sounds kind of biased. Here are some other links:
There is no direct evidence that the wearing of cycle helmets has led to fewer deaths amongst cyclists.
P.S. If you're in or near a city, wear a helmet. I've been hit by cars three times in four years. None actually hurt me, but... well... I can't count on luck forever.
I wouldn't put too much faith in a helmet. If you feel better wearing one then by all means do so, but a cycling helmet is designed to handle the impact of falling from your bike while cycling at low speeds, not a collision with a car at high speed. In most accidents that involve a car, the helmet will either prevent you from getting a few bruises or will do nothing to save your life. The area inbetween where it makes the difference between brain injury or not is rather small.
If you want to protect yourself with a helmet, use the kind that is used by motorcyclists. Better, cycle defensively. Anticipate that you are almost invisible to car drivers and you can cycle 10 thousands of kilometers without significant accidents.
Now I've always been under the impression that by using a voltage divider you create a new "ground" which is the center point where your dropping resisitors meet.
Yes, but only as long as you don't draw any significant amount of current from your circuit. Moreover, your circuit will be eating power even when you don't actually use any. Finally, You can't have +5V and -5V, and then +12V simultaneously.
Of course you can make a range of voltages available with reasonable efficiency, but you need to chop the voltage (creating AC) and lead it through some kind of transformer. That's what all those portable electronic devices do that run off a single AA battery.
I think it was actually OS8 or 9 rather than OSX---the hardware drivers didn't work under OSX. And it was two PhDs, me being one of them.:-)
I think Ph.D. means Philosophiae Doctore, so the D doesn't stand for degree. But our Ph.D.s were not for the English or Latin language, so you're probably right.
They are so lazy that if they thought about it for a minute they would realize that the five minutes it takes to learn OSX (and two days to move files)
Some time ago, two physicists, both with a PhD degree, were cursing about a Mac that served in our laboratory while trying to figure out how to open that CD-ROM tray. Click on CD icon. Nothing. Special menu. Nothing. Search in the help function. Nothing. The button was sitting on the keyboard, which was about 2 meters away from the console. Not documented anywhere!
Compare the submission guidelines for sending an article to any The Physical Review journals in any of the TeX variants they prefer to that of doing a submission with MS Word.
You forgot to mention that they have a Word to LaTeX convertor, and that they subsequently convert everything to the XYVision content-management and typesetting system, which is not LaTeX (although they might have a TeX engine for the equations) As much as I like LaTeX, it is not suitable for producing a journal that has hundreds of authors in every issue with a team of editors. A funny macro by an author on page 1 could interfere with the typesetting of another article on page 187, go try and debug that.
It only takes 64GBs to hold every possible combination of password up to 14 characters using the following (include the space as part of the character set):
The website you refer to is about Windows password hashes.:) Here on/. we all know that Windows is full of bad implementations. The paper explains that in that particular hashing algoritm, the 14 characters are converted to uppercase and treated as two separate passwords of 7 characters, reducing the problem to 2^37 possible passwords rather than 2^82 as you would think from the password length (e.g. if a 128-bit MD5 sum is calculated)
The passwords are enclosed in [] and the script displays the password in "black-on-black", so that you can copy-paste it without anybody looking over your shoulders seeing it, or you remembering it.
And the master password to this file hasn't ever changed... heh
What allowances are you thinking of? I can't think of any. All variables are really pointers inside at the system level as it is
For example,
void f(int* a, int* b, int n) { for (int i=0; i < n; ++i) a[i] = b[i]; }
The compiler might parallellize this under the assumption that a and b really are different arrays. You'd get unpredictable results if you do
int x[100]; f(&x[1], &x[0], 99);
This code should copy the value of x[0] into the rest of the array, but a parallellizing compiler would do something completely different. This can't happen if there aren't any pointers in the language.
By the way, I'm not a fortran fan. I don't usually program for supercomputers and I have heard someone defend fortran-77 because "you can read the code like English without all that cryptic syntax".
i cant recall one bit of spam that came from the EU
I think the issue is about zombies; internet-connected home computers with a trojan that sends spam with a different From address. Trace the IP addresses in the headers and see whether they really don't come from within the EU. (Spamcop.net can do this job for you, and detect forged headers)
A balanced line is three wires: one signal, one inverted signal (180 degrees out of phase), and one ground. Simply passing wires through a shield does not make a balanced cable.
That is actually exactly what I am claiming in the special case of a microphone. The microphone (or pick-up element) is not electrically connected to ground, which only serves as a shield. Hence, the two signal wires are completely floating with respect to ground, which is almost equivalent to a balanced output. That is how a dynamic microphone works. On the other hand, a phantom-powered microphone contains a small buffer amplifier that is connected to ground, so there you don't automatically have a balanced output, unless the buffer amplifier is designed to give a balanced output.
But I admit, I don't know much about guitars. Do they typically have some kind of preamplifier?
There's also water. If I spill a Coke on my keyboard, all my data's safe; if I spill one on my notebook, it's all gone.
Of course, you use a ballpoint pen for lab notebooks, not fountain pens or other pens based on water-soluble inks. Of course, this won't help you if you spill vodka.:-)
Anyway, in lab situations you might not have a place nearby to put a laptop and you might be running between different laboratories so a laptop is often not very convenient. I was taught that you should write observations directly in a notebook instead of waiting and writing them down later. Moreover, you are not supposed to change the notes once they are written down, a temptation that might be hard to resist if the notes are in a computer file.
But what about the fact that chicken wire and window-screen wire is often made of steel? Your post implies a copper mesh. Magnetic fields don't usually pass through a surrounding layer of iron/steel, and steel, while not as good a conductor as copper, is nevertheless conductive enough to ground induced milliamps.
I'm quite sure that a small magnet will pick up paper clips right through chicken wire.:-) A reasonably thick layer of iron without holes will probably shield low-frequency magnetic fields. However, iron is too slow to block higher frequencies. That is why a line transformer at 50/60 Hz uses an iron core, while the transformer in a computer power supply, which runs at a few 10s of kHz, uses a ferrite core.
Good EMF shielding is a kind of voodoo science and I don't claim to know it all. But in the lab, I have never succeeded in blocking RF interference by just wrapping cables in aluminium foil. I would guess that a thick sheet of iron will block low-frequency magnetic fields, as well as high-frequency electric fields, but it would be pretty expensive to build a whole room like that, and then still you need somehow to power your equipment.
I'd guess that the interference is coming in through the power lines.
Any audio equipment worth its money ought to have a power supply that adequately prevents line noise from penetrating into the low-voltage circuits. I believe the main issue is that the primary and secondary coils in the transformer should not be too close together, as that would create a capacitative coupling between line voltage and secondary.
Of course, a computer power supply is not rated for use in audio equipment. If you live in a 230 V country, try putting your PC into an ungrounded wall outlet and touch the PC chassis simultaneuously with the ground pin of a wall outlet. Bzzzt! 115 V on the chassis. (The current is not big enough to kill you, but it's quite unpleasant)
Get some wire mesh and surround each light fixture with it, and "ground" the mesh.
Well, in principle, the mesh size should be much smaller than the wavelength of the radiation you want to shield. For example, a microwave oven: 2.5 GHz, 10 cm wavelength, 3 mm mesh size. Now if you want to block audio frequencies, 20 kHz frequency, 15 km wavelength, so a 450 meter mesh size should be enough...
The problem is that you are much closer to the source than the wavelength, i.e. in the near field. You have to block the magnetic component of the field, because that is the one that will generate currents in wires, similar to what happens in a transformer. Blocking the magnetic component is hardest for the low frequencies. I guess you'd need a couple of millimeters of solid metal for that, comparable to the amount of copper that is sitting around the core of a transformer.
There are very few guitars with balanced outputs that I know of.
There's no need for that because the cable from amplifier to guitar is a "dead end", that cannot participate in a ground loop. I'm not that much into indie rock, but I assume that a guitar is nothing more than a microphone from an electrical point of view. Just a device with two wires coming out of it. Guide those two wires through a shielded cables and voilà, you have a balanced signal.
I come from a physical laboratory where we have to measure small
signals with an acceptably low noise despite the presence of laser
flash lamps, or even high-voltage discharges in more or less open
air. The best way to avoid RF interference is not to remove all RF
sources, but to design the electronic circuits correctly.
The main thing that makes electronic circuits sensitive to noise is
ground loops. Often, signals travel through cables that have two
wires or a central wire with a shield surrounding it. Normally,
equipment (whether it is an oscilloscope or consumer-grade audio
equipment) has a common ground, which means that the neutral wire of
each and every input and output is connected. If you have more than
two pieces of equipment interconnected, it is likely that there are
loops in the ground wire, for example the cable from mixer to some
effect generator, and the wire back. All these loops acts as antennas
that can pick up noise. Having shielded cables doesn't help because it
is the shield, that acts as ground wire, that causes the problems.
The first and simple step is to have all wires bundled as close
together as possible, such that the area inside the loops is as small
as possible. The next step is to upgrade your equipment to stuff that
has balanced inputs, with those big XLR connectors. Here the shields
are really shields against RF interference, while the signal is
carried by two wires inside the shielded cable. Balanced signals means
roughly that the equipment measures the signals on the two signal
wires completely independent from the ground.
But the motion of water, one of the most labile molecules around, is too fast, and there is argument (at least there was in the mid-90s, when I was going to seminars) about how meaningful the ball-and-stick models of water clusters were.
Well, I did my Ph.D. on ultrafast infrared spectroscopy of water between 1997 and 2001 and things have changed since the mid-90s. The dynamics of the hydrogen-bond network in liquid water happens mainly on a timescale of a few picoseconds, which is actually in agreement with estimates based on NMR measurements several decades ago.
I'm not sure what you mean by "ball-and-stick models". The structure of the hydrogen-bond network changes continuously and rapidly, but it is quite reasonable to visualize the structure at a particular moment with balls and sticks. However, I am skeptical of theories that water molecules form persistant clusters such as 6-rings in liquid water, since one can measure in a number of different ways how fast individual molecules change their orientation. If the molecule were locked in a cluster, this reorientation ought to be much slower because of thermodynamic reasons---it is easier to turn a single molecule than six at the same time.
By the way, it is funny to see what happens when one publishes those kinds of measurements on the memory in the structure of the hydrogen bond network in water and water surrounding other molecules. Somehow, the homeopathy believers use this as a "scientific proof" that water has a memory for dissolved substances, conveniently forgetting that this memory lasts far less than one billionth of a second.
A claim that seems to disagree with everything else that is known should have solid evidence. It is of course possible that these guys are right and that the bookshelves full of other experimental data all are flawed. However, it might also be that the way they measured and modelled ignored some important effect.
From my background, I can mention that the infrared absorptions of the two OH bonds are at a wavenumber of 3650 and 3750 cm-1 (around 2.7 micrometers wavelength). In liquid water, these absorptions shift to a band around 3400 cm-1 (2.95 micron). It is a widely accepted fact that this shift of the OH vibration frequency occurs as a result of the hydrogen bond forming between the H of the OH and the O of the next water molecule:
H-OH... OH2
There is hardly any absorption in liquid water at 3650 and 3750 cm-1, which would strongly suggest that nearly all water molecules have both of their hydrogen atoms bonded to other water molecules (that means four H-bonds per molecule). If the claim in the article were true, half of the OH groups would be free and absorb at a higher wavenumber.
The idea that the OH absorption wavelength depends on whether it has a hydrogen bond is in agreement with a large number of studies in which for example clusters of two, three, four water molecules embedded in another material or in vacuum have different infrared absorptions. They are also in agreement with calculations on what happens with an OH bond when you let it form a hydrogen bond, and with fully quantum-mechanical so-called ab initio calculations of how water molecules should behave, although with the latter, one might object that computers still are not powerful enough to do these calculations with more than a couple of ten molecules at a time.
Systems based on imaging optics (including parabolic reflectors) can't make use of diffuse sunlight;
Although you are correct, it should be noted that an overcast sky provides around 10% of the light intensity in watts per square meter compared to direct sunlight. So if you have a system that works equally well for diffuse as for direct sunlight, and direct sunlight is available 50% of the (day) time, then 90% of the produced electricity will be from the hours with direct sunlight anyway.
Hence, in this example, redesigning your system to work with overcast sky as well will only give you 11% extra yield.
Slashdot Mirror
>That's assuming you haven't updated anything.
On the other hand, regular updating significantly decreases the risk of getting a root compromise. :)
The helmet issue is almost as controversial as the one about global warming.You cite the bike helmet safety institute, which sounds kind of biased. Here are some other links:
Step 1: Take you Fedora or whatever installation cd's with all the original RPM files.
Step 2: Issue the command: rpm -Vp *.rpm
Step 3: All files that have a "5" in front of them have a wrong MD5 checksum.
I wouldn't put too much faith in a helmet. If you feel better wearing one then by all means do so, but a cycling helmet is designed to handle the impact of falling from your bike while cycling at low speeds, not a collision with a car at high speed. In most accidents that involve a car, the helmet will either prevent you from getting a few bruises or will do nothing to save your life. The area inbetween where it makes the difference between brain injury or not is rather small.
If you want to protect yourself with a helmet, use the kind that is used by motorcyclists. Better, cycle defensively. Anticipate that you are almost invisible to car drivers and you can cycle 10 thousands of kilometers without significant accidents.
You're talking as if the typical slashdotter would be capable of seducing other women and cheat on his wife... :)
Yes, but only as long as you don't draw any significant amount of current from your circuit. Moreover, your circuit will be eating power even when you don't actually use any. Finally, You can't have +5V and -5V, and then +12V simultaneously.
Of course you can make a range of voltages available with reasonable efficiency, but you need to chop the voltage (creating AC) and lead it through some kind of transformer. That's what all those portable electronic devices do that run off a single AA battery.
I think Ph.D. means Philosophiae Doctore, so the D doesn't stand for degree. But our Ph.D.s were not for the English or Latin language, so you're probably right.
Some time ago, two physicists, both with a PhD degree, were cursing about a Mac that served in our laboratory while trying to figure out how to open that CD-ROM tray. Click on CD icon. Nothing. Special menu. Nothing. Search in the help function. Nothing. The button was sitting on the keyboard, which was about 2 meters away from the console. Not documented anywhere!
You forgot to mention that they have a Word to LaTeX convertor, and that they subsequently convert everything to the XYVision content-management and typesetting system, which is not LaTeX (although they might have a TeX engine for the equations) As much as I like LaTeX, it is not suitable for producing a journal that has hundreds of authors in every issue with a team of editors. A funny macro by an author on page 1 could interfere with the typesetting of another article on page 187, go try and debug that.
The website you refer to is about Windows password hashes. :) Here on /. we all know that Windows is full of bad implementations. The paper explains that in that particular hashing algoritm, the 14 characters are converted to uppercase and treated as two separate passwords of 7 characters, reducing the problem to 2^37 possible passwords rather than 2^82 as you would think from the password length (e.g. if a 128-bit MD5 sum is calculated)
And the master password to this file hasn't ever changed... heh
For example,
The compiler might parallellize this under the assumption that a and b really are different arrays. You'd get unpredictable results if you doThis code should copy the value of x[0] into the rest of the array, but a parallellizing compiler would do something completely different. This can't happen if there aren't any pointers in the language.By the way, I'm not a fortran fan. I don't usually program for supercomputers and I have heard someone defend fortran-77 because "you can read the code like English without all that cryptic syntax".
I think the issue is about zombies; internet-connected home computers with a trojan that sends spam with a different From address. Trace the IP addresses in the headers and see whether they really don't come from within the EU. (Spamcop.net can do this job for you, and detect forged headers)
That is actually exactly what I am claiming in the special case of a microphone. The microphone (or pick-up element) is not electrically connected to ground, which only serves as a shield. Hence, the two signal wires are completely floating with respect to ground, which is almost equivalent to a balanced output. That is how a dynamic microphone works. On the other hand, a phantom-powered microphone contains a small buffer amplifier that is connected to ground, so there you don't automatically have a balanced output, unless the buffer amplifier is designed to give a balanced output.
But I admit, I don't know much about guitars. Do they typically have some kind of preamplifier?
Of course, you use a ballpoint pen for lab notebooks, not fountain pens or other pens based on water-soluble inks. Of course, this won't help you if you spill vodka. :-)
Anyway, in lab situations you might not have a place nearby to put a laptop and you might be running between different laboratories so a laptop is often not very convenient. I was taught that you should write observations directly in a notebook instead of waiting and writing them down later. Moreover, you are not supposed to change the notes once they are written down, a temptation that might be hard to resist if the notes are in a computer file.
I'm quite sure that a small magnet will pick up paper clips right through chicken wire. :-) A reasonably thick layer of iron without holes will probably shield low-frequency magnetic fields. However, iron is too slow to block higher frequencies. That is why a line transformer at 50/60 Hz uses an iron core, while the transformer in a computer power supply, which runs at a few 10s of kHz, uses a ferrite core.
Good EMF shielding is a kind of voodoo science and I don't claim to know it all. But in the lab, I have never succeeded in blocking RF interference by just wrapping cables in aluminium foil. I would guess that a thick sheet of iron will block low-frequency magnetic fields, as well as high-frequency electric fields, but it would be pretty expensive to build a whole room like that, and then still you need somehow to power your equipment.
Any audio equipment worth its money ought to have a power supply that adequately prevents line noise from penetrating into the low-voltage circuits. I believe the main issue is that the primary and secondary coils in the transformer should not be too close together, as that would create a capacitative coupling between line voltage and secondary.
Of course, a computer power supply is not rated for use in audio equipment. If you live in a 230 V country, try putting your PC into an ungrounded wall outlet and touch the PC chassis simultaneuously with the ground pin of a wall outlet. Bzzzt! 115 V on the chassis. (The current is not big enough to kill you, but it's quite unpleasant)
Well, in principle, the mesh size should be much smaller than the wavelength of the radiation you want to shield. For example, a microwave oven: 2.5 GHz, 10 cm wavelength, 3 mm mesh size. Now if you want to block audio frequencies, 20 kHz frequency, 15 km wavelength, so a 450 meter mesh size should be enough...
The problem is that you are much closer to the source than the wavelength, i.e. in the near field. You have to block the magnetic component of the field, because that is the one that will generate currents in wires, similar to what happens in a transformer. Blocking the magnetic component is hardest for the low frequencies. I guess you'd need a couple of millimeters of solid metal for that, comparable to the amount of copper that is sitting around the core of a transformer.
There's no need for that because the cable from amplifier to guitar is a "dead end", that cannot participate in a ground loop. I'm not that much into indie rock, but I assume that a guitar is nothing more than a microphone from an electrical point of view. Just a device with two wires coming out of it. Guide those two wires through a shielded cables and voilà, you have a balanced signal.
The main thing that makes electronic circuits sensitive to noise is ground loops. Often, signals travel through cables that have two wires or a central wire with a shield surrounding it. Normally, equipment (whether it is an oscilloscope or consumer-grade audio equipment) has a common ground, which means that the neutral wire of each and every input and output is connected. If you have more than two pieces of equipment interconnected, it is likely that there are loops in the ground wire, for example the cable from mixer to some effect generator, and the wire back. All these loops acts as antennas that can pick up noise. Having shielded cables doesn't help because it is the shield, that acts as ground wire, that causes the problems.
The first and simple step is to have all wires bundled as close together as possible, such that the area inside the loops is as small as possible. The next step is to upgrade your equipment to stuff that has balanced inputs, with those big XLR connectors. Here the shields are really shields against RF interference, while the signal is carried by two wires inside the shielded cable. Balanced signals means roughly that the equipment measures the signals on the two signal wires completely independent from the ground.
RTFA. You just turn the clock such that the sun hits it at a different angle.
Well, I did my Ph.D. on ultrafast infrared spectroscopy of water between 1997 and 2001 and things have changed since the mid-90s. The dynamics of the hydrogen-bond network in liquid water happens mainly on a timescale of a few picoseconds, which is actually in agreement with estimates based on NMR measurements several decades ago.
I'm not sure what you mean by "ball-and-stick models". The structure of the hydrogen-bond network changes continuously and rapidly, but it is quite reasonable to visualize the structure at a particular moment with balls and sticks. However, I am skeptical of theories that water molecules form persistant clusters such as 6-rings in liquid water, since one can measure in a number of different ways how fast individual molecules change their orientation. If the molecule were locked in a cluster, this reorientation ought to be much slower because of thermodynamic reasons---it is easier to turn a single molecule than six at the same time.
By the way, it is funny to see what happens when one publishes those kinds of measurements on the memory in the structure of the hydrogen bond network in water and water surrounding other molecules. Somehow, the homeopathy believers use this as a "scientific proof" that water has a memory for dissolved substances, conveniently forgetting that this memory lasts far less than one billionth of a second.
From my background, I can mention that the infrared absorptions of the two OH bonds are at a wavenumber of 3650 and 3750 cm-1 (around 2.7 micrometers wavelength). In liquid water, these absorptions shift to a band around 3400 cm-1 (2.95 micron). It is a widely accepted fact that this shift of the OH vibration frequency occurs as a result of the hydrogen bond forming between the H of the OH and the O of the next water molecule:
There is hardly any absorption in liquid water at 3650 and 3750 cm-1, which would strongly suggest that nearly all water molecules have both of their hydrogen atoms bonded to other water molecules (that means four H-bonds per molecule). If the claim in the article were true, half of the OH groups would be free and absorb at a higher wavenumber.The idea that the OH absorption wavelength depends on whether it has a hydrogen bond is in agreement with a large number of studies in which for example clusters of two, three, four water molecules embedded in another material or in vacuum have different infrared absorptions. They are also in agreement with calculations on what happens with an OH bond when you let it form a hydrogen bond, and with fully quantum-mechanical so-called ab initio calculations of how water molecules should behave, although with the latter, one might object that computers still are not powerful enough to do these calculations with more than a couple of ten molecules at a time.
Although you are correct, it should be noted that an overcast sky provides around 10% of the light intensity in watts per square meter compared to direct sunlight. So if you have a system that works equally well for diffuse as for direct sunlight, and direct sunlight is available 50% of the (day) time, then 90% of the produced electricity will be from the hours with direct sunlight anyway.
Hence, in this example, redesigning your system to work with overcast sky as well will only give you 11% extra yield.