HDTenEightyP/NetNews huggingface dataset:
From: gilligan@bldrdoc.gov (Jonathan M. Gilligan)
Newsgroups: sci.physics,alt.sci.physics.new-theories
Subject: Re: The Speed of Gravity Waves
Date: 10 Apr 92 22:33:23 GMT
Followup-To: sci.physics
Organization: National Institute of Standards and Technology

In article <22642@dog.ee.lbl.gov> sichase@csa2.lbl.gov writes:
>There recently was a discussion of gravity waves and I asserted that 
>the speed of such waves must necessarily be Cem, the speed of electromagnetic
>waves, by virtue of the masslessness of the graviton.  I have since learned
>that my answer was not complete.  Here is as better explanation:

(discussion of Brans-Diske models omitted)

>A definitive test would be produced by LIGO in coincidence with optical 
>measurements of some catastrophic event which generates enough gravitational
>radiation to be detected.  Then the "time of flight" of both gravitons and
>photons from the source to the Earth could be measured, and strict direct
>limits could be set on Cgw. 

I would think that some information could be gleaned from the spindown
of pulsars due to gravitational radiation. But I'm ignorant of such things.
Can someone who knows comment?

---Jon
Newsgroups: sci.physics
From: jeroen@dxcern.cern.ch (Jeroen Belleman)
Newsgroups: sci.physics
Subject: Re: van de Graaff generators
Date: 14 Apr 92 12:02:04 GMT
Organization: CERN European Laboratory for Particle Physics

In article <10390@inews.intel.com> bhoughto@hopi.intel.com (Blair P. Houghton) writes:
>In article <1992Apr10.085039.10688@dxcern.cern.ch> jeroen@dxcern.cern.ch (Jeroen Belleman) writes:
>>Can anyone suggest a method to measure the output voltage? I do not
>>think suitable probes exist.
>
>There isn't really an "output voltage."  The potential on
>the sphere is a function of the charge it holds and the
>capacitance between it and the grounds around the room.
>

So? Can anyone suggest a way to measure the potential of the sphere?
The capacitance of the sphere is hardly affected by any grounds around
the room. The nearest ground is about 70cm away, normally.

>>So far, I get fat sparks from a polished 4cm diameter metal pipe over
>>a little more than 10cm. The more diffuse sparks from the pipe's end
>>easily exceed 50cm. You can make you own voltage estimates from that.
>
>Drat.  I forgot the breakdown voltages for air.  The
>potential at the time of the spark is of course just the
>distance (cm) times the breakdown voltage (KV/cm).
>

No sir, it's electric field strength that gives the breakdown voltage
between two electrodes, not simply their potential difference and
distance. For a given distance, sharp electrodes will cause
breakdown for much lower potential differences than blunt ones.
Besides, the capacitance change caused by a small nearby electrode
is negligible. ('Small', that is to say, compared to the size of
the high voltage electrode.)

>As you can see, by varying the capacitance (a smooth surface
>nearby; a sharp surface at a greater distance) your generator
>can operate at different potentials.
>
>If you integrate the charging current to get the charge you
>can determine the capacitance.
>

The charging current is constant and independent of the terminal
voltage. (Excuse me, potential.) It's breakdown of the air
insulation that limits the potential. The relatively simple
geometry of the setup enables me to calculate the capacitance.
It's about 18pF. If I integrate the 9uA charging current over
the time it takes to get the first discharge (about 1 second),
that gives me a peak potential of 500kV. I don't really believe
that. That's why I'm looking for a different way to measure it.

Jeroen Belleman (Getting a sore throat from breathing too much ozone)
jeroen@dxcern.cern.ch
jeroen@cernvax.cern.ch
From: jim@cs.UAlberta.CA (Jim Easton)
Newsgroups: sci.physics
Subject: Re: Question about dimmer switch and lamp.
Date: 13 Apr 92 20:19:04 GMT
Organization: University of Alberta, Edmonton, Canada

usenet@crd.ge.com (Required for NNTP) writes:

>>In article <1020006@hpdmd48.boi.hp.com> rrr@hpdmd48.boi.hp.com (Rudi Rynders) writes:
>>
>>    Given an incandescent lamp with a dimmer switch. The lamp is on.
...
>>    switch up, no matter how slow, the light always comes on rather
>>    suddenly and much brighter than in the reverse process .

>This is not a physics problem, it is an electrical engineering problem.
>If you were the incandescent lamp with a Variac, it would turn off and on
>at the same point, smoothly and without hysteresis. The reason it behaves
>as described by Rudi is that residential dimmers do not use variable
>transformers, but do use a semiconductor switch called a Triac to apply
>the 60Hz power to the lamp for variable portions of the cycle. That is, at
>half power, full voltage is applied for half of each 60Hz cycle. The
>triggering circuit for this Triac has considerable hysteresis, which
>accounts for the behavior documented above.

I beg to differ.  The reason that you don't observe the effect with
a variac is that a variac is a low impedance (constant voltage) source
and the bulb can draw as much current as it needs when the filament is
cold (and has a low resistance).

The triac on the other hand is a high impedance source and with a 
variable resistance, as represented by a lightbulb at different
temperatures, will create a bistable system. I can state with some
confidence that it has nothing to do with the hysteresis of the
triac for two reasons;

1) One observes the same effect if the dimmer is a rheostat.

2) the triac hysteresis is repeated 60 times a second but the bulb
   can stay in one of its two states essentially forever.

	Jim
Newsgroups: sci.physics
From: natelson@burst.Princeton.EDU (Douglas Natelson)
Subject: ir reflectivity
Originator: news@ernie.Princeton.EDU
Organization: Princeton University
Distribution: sci.physics
Date: Fri, 10 Apr 1992 20:32:27 GMT

Hi.

Hi.  For my independent work, I've performed reflectivity measurements
of some substances (bismuth, antimony, yttrium, dysprosium) in the ir,         
range (~ 600 cm^-1 to 8000 cm^-1).  My problem is that I can't find any
reference reflectivity spectra to compare my results with, and I'm also
having a tough time finding good (interesting) materials to look at.
If anyone out there could direct me to a reference work which contains
information of this nature, I'd greatly appreciate it.

My e-mail address is natelson@phoenix.princeton.edu .
l 
					Thanks,
					   Doug Natelson
From: hall@vice.ICO.TEK.COM (Hal Lillywhite)
Newsgroups: sci.physics
Subject: Re: simple question
Date: 8 Apr 92 16:55:30 GMT
Organization: Tektronix Inc., Beaverton, Or.

In article <9204080901.aa00587@Paris.ics.uci.edu> kibler@turing.ICS.UCI.EDU (Dennis Kibler) writes:
>How is radioactive dating done?

> I understand that by knowing the current % (say Z) of X in Y,
>and the half-life of X, that we can project backwards
>and figure out the % (say Z') of X in Y at any previous time.
>So to figure out the age of Y  we need to know the original
>percentage of X in Y.  But how is that known?

> Let me put it in a more concrete form. Suppose we use carbon
>dating to measure the age of a fossilized plant. I don't
>understand why we aren't measuring the age of the carbon,
>created I presume at the some time before the age of the earth,
>rather than the age of the plant.


Actually the carbon used for dating is being created all the time
and that is why it can be used for such dating.  C14 is created by
cosmic ray bombardment of the atmosphere.  Being radioactive it
decays of course.  However it is replaced by the constant creation
of new atoms, resulting in an approximately constant ratio of C12 to
C14 atoms in the biosphere.  However when an organism dies the
carbon atoms in its body cease to be replaced with new ones.  After
death the percent of C12 atoms stays constant while the percent of C14 
atoms decreases as they decay radioactively (I am talking about what
percent C12 or C14 are of the entire sample).  Therefore if we can 
get a relatively undisturbed sample of old biological material we can
determine its age by measuring the ratio of C12 to C14.  If the ratio 
is the same as the atmosphere today, the sample is very young.  If 
there is very little C14 the sample is old.  A few relatively simple
mathematical calculations will tell us how old.
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Right handed neutrino
Date: 7 Apr 92 21:10:13 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

Maybe when Vijay said "very heavy right-handed neutrino" he
had read "massive right-handed neutrino."  Any ordinary human
being would interpret these as equivalent, but to a subparticle
bosophysicist "massive" just means "having mass," that is, not 
massless.  This usually confuses me for a while until I
remember what is going on.

After all, we are talking about a field where "high energy"
means ~ 10^-10 joules.

Ben Weiner
From: sichase@csa1.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: simple question
Date: 8 Apr 92 19:23:30 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa1.lbl.gov
NNTP-Posting-Host: 128.3.254.196
News-Software: VAX/VMS VNEWS 1.3-4   

In article <9204080901.aa00587@Paris.ics.uci.edu>, kibler@turing.ICS.UCI.EDU (Dennis Kibler) writes...
>How is radioactive dating done?
> 
> I understand that by knowing the current % (say Z) of X in Y,
>and the half-life of X, that we can project backwards
>and figure out the % (say Z') of X in Y at any previous time.
>So to figure out the age of Y  we need to know the original
>percentage of X in Y.  But how is that known?
> 
There are a variety of methods for doing this.  It depends upon the chemistry
involved.  If you want to date something with Uranium, then you can do chemical
separation of the elements produced in the decay chain by straightforward
methods, and measure the total amount of Uranium vs. decay products.  Assuming
that all of the decay products are from original Uranium, you have an answer.

Sometimes, isotopic separation is required.  For example, for Carbon dating, 
you are interesting in the ratio of C13 to C12.  They are (almost entirely)
indistinquishable by their electronic structure, which means that their
chemistry is identical.  You can do mass spectroscopy, however to measure the
fraction of the carbon which is 13/12 times as massive.  

There are many other variations, but I'm no expert so I'll leave it at this.  


> Let me put it in a more concrete form. Suppose we use carbon
>dating to measure the age of a fossilized plant. I don't
>understand why we aren't measuring the age of the carbon,
>created I presume at the some time before the age of the earth,
>rather than the age of the plant.
> 

Good question.  The half-live of C13 is (roughly - please don't pick nits) 8000
years.  Clearly, if there were no new source of C13, we'd have none left on a 
4.5 Billion year old planet.  But that's not so.  The C13 is constantly being
replenished in the atmosphere by known reactions.  So the atmospheric C13/C12
is (roughly - please don't pick nits) constant over lime. 

But plants only "inhale" CO2 as long as they live.  As soon as a plant dies, 
the C13/C12 ratio begins to decrease as the C13 decays but is not replenished
by atmospheric C13.  This allows you to date the death of the plant, provided
that it did not happen too many C13 half-lives ago.  

-Scott

Newsgroups: sci.physics
From: platt@watson.ibm.com (Daniel E. Platt)
Subject: Re: idealizations??
Date: Wed, 15 Apr 1992 18:28:12 GMT
Disclaimer: This posting represents the poster's views, not necessarily those of IBM
Organization: IBM T.J. Watson Research Center

In article <1992Apr15.173142.6990@cis.uab.edu>, menon@ftp.phy.uab.edu (Govind Menon) writes:
|> The case of the hard sphere and plane is an interesting scenario, but by no 
|> means realistic.  If however, you do wish to conduct a thought experiment, 
|> constrained to idealizations, then permit me if you will to make yet another
|> reasonable assumption.  
|> 

Reasonable assumptions imply that you're looking at a range of phenomena for
which the assumption is adequate.  In biophysics, there might be arguments
where a comment such as 'Consider a spherical frog' makes all the sense in
the world...


|> There is nothing preventing a perfectly spherical and a perfectly planar 
|> material from being infinitely rigid.  Subject to this condition the bodies
|> do not have to deform under infinite pressure at the contact point.  

There's a problem with this in the relativistic limit -- something
infinitely rigid would transmit the signal instantaneously.  An infinitely
rigid ball only makes sense in a limit where the stiffness makes a
transmission speed much greater than any of the other dynamics in the
problem.

Dan
From: gilligan@bldrdoc.gov (Jonathan M. Gilligan)
Newsgroups: sci.physics
Subject: Re: Heard of VIRTUAL PARTICLES???
Date: 10 Apr 92 22:58:27 GMT
Organization: National Institute of Standards and Technology

In article <3581@caslon.cs.arizona.edu> huber@cs.arizona.edu (Eric N. Huber) writes:
>	Now the question comes of do these virtual particles really exist, or
>like i, are they just a figment of our imagination?  The usual experiment I've
>heard of involves a free electrical charge in space.  If virtual particles 
>exist, they should be popping into existance around the electron in the form
>of virtual positrons.  These virtual positive charges will 'shield' the
>electron's charge, and the drop may be measured.  Neat trick!

This test has been made in numerous contexts. Perhaps the most well-known
is that this is simply the vacuum-polarization term in the Lamb shift.
To oversimplify greatly, the e+e- pairs ``popping into and out of existence''
near the nucleus of a hydrogen atom perturb the energy levels of the electron
by screening the nuclear charge. This effect has been measured and is in good
agreement with theory. Similar effects abound in other areas of physics.

It's important to note, though, that all you can do is measure energy levels
and compare them with theory. You can't turn off this phenomenon and compare
results with and without the virtual particles.

---Jon
Newsgroups: sci.physics
From: rescorla@rtnmr.chem.yale.edu (Eric Rescorla)
Subject: Re: simple question
Organization: Rescorla for himself.
Date: Wed, 8 Apr 1992 16:15:32 GMT

In article <9204080901.aa00587@Paris.ics.uci.edu> kibler@turing.ICS.UCI.EDU (Dennis Kibler) writes:
> Let me put it in a more concrete form. Suppose we use carbon
>dating to measure the age of a fossilized plant. I don't
>understand why we aren't measuring the age of the carbon,
>created I presume at the some time before the age of the earth,
>rather than the age of the plant.
The percentage of C14 in the atmosphere is ~constant over time.
As long as you're alive, you exchange carbon with the atmosphere
and maintain the atmospheric concentration of C14 in your system.
When you die, you stop exchanging and that's the zero-time.

-Ekr


-- 
-------------------------------------------------------------------------------
Eric Rescorla, DoD#431, Honda CM400 rider          rescorla@rtnmr.chem.yale.edu
Yale University Department of Chemistry            We hack anything.
My mind is now for rent: C/Unix,Vacuum Tech,Machining,P-Chemist. Hire me, eh? 
From: ric@hpspdla.spd.HP.COM (Ric Peregrino)
Date: Tue, 14 Apr 1992 00:58:49 GMT
Subject: Re: Electrical Conductivity an Intensive Variable?
Organization: HP Stanford Park - Palo Alto, CA
Newsgroups: sci.physics


Please excuse my ignorance, but what's the definition of
intensive in this context?

Just asking,
Ric Peregrino
ric@spd.hp.com
From: sawyer@sscvx1.ssc.gov (Lee Sawyer)
Newsgroups: sci.physics
Subject: Re: Sciencists/politics (was Hawking speaks out ...)
Date: 9 Apr 92 14:35:00 GMT
Distribution: world,local
Organization: Superconducting Super Collider Laboratory
News-Software: VAX/VMS VNEWS 1.4-b1

In article <9382@vice.ICO.TEK.COM>, hall@vice.ICO.TEK.COM (Hal Lillywh writes...
>In article <8APR199214001279@sscvx1.ssc.gov> sawyer@sscvx1.ssc.gov (Lee Sawyer) writes:
> 
>>                                 However can you imagine the response
>> if Leon Lederman or Phillip Anderson spoke on the presidential race ?
>> He would be crucified by the media, if they paid any attention at all.
> 
>Well, pretty much anybody of any stature who speaks out on politics
>will get crucified by the media.  Sometimes you just have to pay the
>price if you are going to make a contribution.  I'm more concerned
>about your last phrase, "If [the media] paid any attention at all."
>Unfortunately movie stars can support political candidates or causes
>and people (including the media) give them coverage as though they
>knew something special.  Scientists usually don't get as much
>attention (unless they speak out in support of some popular or
>politically correct idea).  Jane Fonda has a lot more influence on
>the nuclear power plant issue than do the people who really know
>something about the issue.

  What I imagined by "crucifixion" was MacLaughlin, Barnes, Novack, et al,
 debating whether a scientist has any right to inject their personal
 beliefs into the political dialogue.

  But I agree 100 % that "celebraties" are given widely inflated credence
 on issues that cannot possibly be in their area of expertise. So what do we
 do ? I am all in favor of forming an ACTIVE information service (say,
 within APS) that would force the issue. Have a group of scientists hold
 press conferences, do the things that media seem to feel are important,
 and try to better inform the public. There could be handful of full-time
 folks, who pick particular experts to speak on particular subjects.
 How does this sit with the Net ?

  You know, we really need someone to introduce Robert Parks to the concept
 of vnews, or the new reader of your choice...

 ==============================================================================
         Lee Sawyer     | Dept of Physics          
       (SSCVX1::SAWYER) | Univ of Texas - Arlington    
                        | Arlington, TX            
 ==============================================================================
Newsgroups: sci.physics
From: phyliew@nuscc.nus.sg (Liew Soo Chin (Dr))
Subject: Re: Voltage drop in Silicon diode
Organization: National University of Singapore
Date: Fri, 10 Apr 1992 06:10:39 GMT

raju@bass.bu.edu (rajminder Singh) writes:
: Hi there! I am  taking a course in Solid State Physics but I still 
: haven't been able to answer the basic question of why the voltage drop
: in a Silicon p-n junction is around 0.7 Volts ? Does this vary significantly
: with the doping level ? What about the effect of temperature, current and
: the energy band gap (E) of the material used in the junction ?
: 
	The voltage drop across a pn junction diode depends on the
current, temperature, etc. according to the well-known V-I
characteristic equation, I = I_s [ exp(eV/nkT) - 1 ] (refer to your favorite
text book for a derivation). So the voltage drop is 
	V = (nkT/e) ln(I/I_s + 1).
The parameter n (actually Greek letter eta) is approximately 2 for Si
diodes, and kT/e is about 25 mV at room temperature, so the voltage drop
is approximately (50 mV)*ln(I/I_s). So you can see that for a typical
diode current, V is around 0.7 V for a wide range of values for I_s
(the reverse saturation current). For example, let's say I = 10 mA, then
the voltage drop for various values of I_s are (approximately):
	I_s (A)		V (volt)
	-------		--------
	 1E-9		  0.81
	 1E-8		  0.69
	 1E-7		  0.58 
-- 
---------------------------------------------------------------------
| S. C. Liew, PhD                  |  e-mail: phyliew@nuscc.nus.sg  |
| Department of Physics            |  telephone: (65) 772-2614      |
| National University of Singapore |  fax: (65) 777-6126            |
Newsgroups: sci.physics
From: dougm@cns.caltech.edu (Doug McNought)
Subject: Re: FAQ
Organization: California Institute of Technology
Date: Thu, 16 Apr 1992 01:58:39 GMT


I like the idea. Thanks for volunteering your time.
-doug
--
<><><><><><><><><><><><><><><>Go Orioles<><><><><><><><><><><><><><><><>
<> Doug McNaught                          dougm@descartes.caltech.edu <>
<>  Help!!! I'm addicted to *Spaceward Ho!* Is there a support group? <>
<><><><><><><><><><><><><><><>Go Orioles<><><><><><><><><><><><><><><><>
Newsgroups: sci.physics
From: ST402676@brownvm.brown.edu
Subject: Re: Time
Organization: Brown University
Date: Thu, 9 Apr 1992 18:27:08 GMT

------------------------- Original Article -------------------------

I would want to ask all of you this wery simple (?) question: what is time?

 -------------------------------------------------------------

Scott Adams in one of his "Dilbert" comics says:

"Imagine a donut fired from a canon at the speed of light while
rotating. Time is like that, except without the canon and the donut."
From: ric@hpspdla.spd.HP.COM (Ric Peregrino)
Newsgroups: sci.physics
Subject: Re: masers from magnetrons
Date: 15 Apr 92 00:40:40 GMT
Organization: HP Stanford Park - Palo Alto, CA


Careful!! You could fry some eyes with that, not to mention
the FCC might not like you beaming microwaves around! You'd
best know what you're doing!

I'm not trying to disuade you, but please, know what you're
doing before you do it.

Ric Peregrino
ric@spd.hp.com
From: sloan@cis.uab.edu (Kenneth Sloan)
Newsgroups: sci.physics
Subject: Re: Xeroxing mirrors
Date: 13 Apr 92 15:57:46 GMT
Organization: CIS, University of Alabama at Birmingham

In article <8400009@trsvax> pauls@trsvax.tandy.com writes:
>
>Can somebody explain this to me??
>
>I tried to Xerox a flat mirror. The paper came out pitch black.
>
>Well??

What color did you expect it to be?


-- 
Kenneth Sloan                   Computer and Information Sciences
sloan@cis.uab.edu               University of Alabama at Birmingham
(205) 934-2213                  115A Campbell Hall, UAB Station 
(205) 934-5473 FAX              Birmingham, AL 35294-1170
Newsgroups: sci.physics
From: brahm@cco.caltech.edu (David E. Brahm)
Subject: Re: Right Neutrino
Summary: Majorana particles at rest
Organization: California Institute of Technology, Pasadena
Date: Tue, 14 Apr 1992 04:01:55 GMT

I wrote:
* If you give the neutrino a Majorana mass... then when you overtake the
* light left-handed neutrino you will see a light right-handed antineutrino!
* Majorana masses violate any quantum number which the particle carries...
* so "particle" and "antiparticle" are not... well-distinguished...

vijay@wiliki.eng.hawaii.edu (Vijay Fafat) responded:
> What would I see if the same neutrino was AT REST in my frame? ...
> What about its chirality?

The particle would be light (rest-mass is a Lorentz invariant!), and
neither its chirality, nor its helicity, nor its lepton number (i.e.
neutrino vs. anti-neutrino) would be defined.

From Halzen & Martin, p.116: "For a massive fermion... handedness
[chirality] is not a good quantum number... gamma_5 does not commute with
the Hamiltonian...  [H]elicity is conserved but is frame-dependent."
Remember chirality and helicity are not the same thing: chirality is the
eigenvalue of gamma_5, while helicity is the projection of spin onto the
3-momentum unit vector.

> At what point in the experiment does the switch from left- to
> right-neutrino occur?

Its helicity switches as you pass through p=0.

You could ask why I used the terms "neutrino" and "anti-neutrino" in my
original statement if these terms are not well-defined.  I think the answer
is that for large momenta and small Majorana mass, lepton-number is nearly
conserved, i.e. processes which violate it are suppressed by m/p.

--
Staccato signals of constant information,  |  -- David Brahm
A loose affiliation of millionaires and    |  (brahm@coil.caltech.edu)
  billionaires and Baby ...                |---------------------------
These are the days of miracle and wonder,  | I will not post the same
And don't cry, Baby, don't cry, don't cry. |   article 4 times...
Newsgroups: sci.physics