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Current Topic: Physics

Sam's Laser FAQ - Preface, Introduction, What is a Laser?, Safety
Topic: Physics 1:14 pm EDT, Sep 12, 2010

Safety, Info, Links, Parts, Types, Drive, Construction

yeah this is a good place for laser info.

today building a voltage regulating, current limiting laser diode power supply.



Sam's Laser FAQ - Preface, Introduction, What is a Laser?, Safety

[0808.3867] Minimal Dark Matter predictions and the PAMELA positron excess
Topic: Physics 11:57 am EDT, Sep  2, 2008

We present Minimal Dark Matter and its univocal predictions for Dark Matter observables. During the idm2008 conference, PAMELA presented preliminary results showing an excess in the positron fraction: we find a good agreement, with a modest astrophysical boost factor.

someone found a possible candidate for dark matter. and in his paper makes a pretty compelling case.


[0808.3867] Minimal Dark Matter predictions and the PAMELA positron excess

0806.2442 Observation of a push force on the end face of a nm fiber taper exerted by outgoing light
Topic: Physics 4:17 pm EDT, Jun 22, 2008

Abstract: There are two different proposals for the momentum of light in a transparent dielectric of refractive index n: Minkowski s version nE/c and Abrahm s version E/ nc , where E and c are the energy and vacuum speed of light, respectively. Despite many tests and debates over nearly a century, momentum of light in a transparent dielectric remains controversial. In this Letter, we report a direct observation of the inward push force on the end face of a free nm fiber taper exerted by the outgoing light. Our results clearly support Abraham momentum. Our experiment also indicates an inward surface pressure on a dielectric exerted by the incident light, different from the commonly recognized pressure due to the specular reflection. Such an inward surface pressure by the incident light may be useful for precise design of the laser-induced inertially-confined fusion.

The momentum of a photon traveling inside a transperent dielectric:

p = E/(nc)

p - momentum
E - energy
n - index of refraction
c - speed of light


0806.2442 Observation of a push force on the end face of a nm fiber taper exerted by outgoing light

Fermilab physicists discover 'triple-scoop' baryon
Topic: Physics 6:27 pm EDT, Jun 13, 2007
cascade-b particle

Physicists of the DZero experiment at the Department of Energy's Fermi National Accelerator Laboratory have discovered a new heavy particle, the Ξb (pronounced "zigh sub b") baryon, with a mass of 5.774±0.019 GeV/c2, approximately six times the proton mass. The newly discovered electrically charged Ξb baryon, also known as the "cascade b," is made of a down, a strange and a bottom quark. It is the first observed baryon formed of quarks from all three families of matter. Its discovery and the measurement of its mass provide new understanding of how the strong nuclear force acts upon the quarks, the basic building blocks of matter.

If you'd like to read the actual article check this arxiv link


Fermilab physicists discover 'triple-scoop' baryon

Topic: Physics 6:21 pm EDT, Jul 28, 2005

Going into physics was the biggest mistake of my life. I should've declared CS. I still wouldn't have any women, but at least I'd be rolling in cash.

Okay science is still funny.


Guardian Unlimited | Life | Why Einstein may have got it wrong
Topic: Physics 9:17 pm EDT, Apr 11, 2005

] A century after Albert Einstein published his most famous
] ideas, physicists will today commemorate the occasion by
] trying to demolish one of them.
] Astronomers will tell experts gathering at Warwick
] University to celebrate the anniversary of the great
] man's "miracle year" that the speed of light - Einstein's
] unchanging yardstick that underpins his special theory of
] relativity - might be slowing down.

Guardian Unlimited | Life | Why Einstein may have got it wrong

Physics Today
Topic: Physics 9:55 am EST, Mar 14, 2005

] Hans Bethe, eminent physicist and winner of the 1967
] Nobel Prize in Physics, died on 6 March 2005 in Ithaca,
] New York. A few of his many contributions will be
] highlighted on the Physics Today website over the next
] few days.

For the next few days Physics Today will be highlighting papers and ideas championed by Hans Bethe... I recomend all of them.

Physics Today

Building a Cyclotron on a Shoestring
Topic: Physics 7:17 pm EST, Nov 29, 2004

] Starting when he was an undergrad, Tim Koeth built a 12−inch
] cyclotron. Now he is in grad school and his creation is used
] in a senior−level lab class.

Yeah. Nerds rule. $15,000 for a cyclotron isn't bad... but they got the 2.5 ton magnet for free. I wonder if someone could do it for cheaper. Still it's wicked hot chowdah.

Building a Cyclotron on a Shoestring

The physics of traffic jams
Topic: Physics 5:14 pm EDT, Sep 15, 2004

] German scientists have shown that the changeover from
] free-flowing traffic to a traffic jam (in which cars on a
] highway are greatly slowed or halted, at least
] temporarily) conforms to the well-known physics of phase
] transitions, an example of which is the transition from
] water to ice. In other words, traffic jams are not random
] patterns, but are deterministic in nature; that is, when
] a parameter exceeds a threshold value--such as the flux
] of cars--then local perturbations can grow, possibly
] leading to jams, analogous to the nucleating effect of
] tiny ice grains in a body of water being frozen. Once
] formed the jam moves along the highway as if it were a
] kind of "solid," with identifiable edges and with a
] "vapor" of comparatively free cars in front of and behind
] it. The information gained in this sort of research, the
] researchers believe, might lead to more accurate traffic
] forecasts and could be used in future "intelligent"
] transport systems.

The physics of traffic jams

[hep-ex/0307083] Evidence for the positive-strangeness pentaquark θ+ in photoproduction with the SAPHIR detector at ELSA
Topic: Physics 2:47 pm EDT, Sep  3, 2003

Evidence of five (5!!!) quark baryon found at the ELectron Stretcher Accelerator (ELSA) in Bonnn, Germany.

The SAPHIR collaboration announced evidence for Theta-plus with a mass of 1540 MeV and a width of less than 25 MeV, compatible with experimental results from SPring-8, ITEP and Jefferson Lab.

This exotic particle is allowed under the rules of Quantum Chromodynamics (QCD It is composed of two up quarks, two down quarks and one anti-strange quark (uudd s-bar). It is called "exotic" because the antiquark is of a different flavor than the other quarks composing the baryon.

It's structure is interesting. It seems like it's got properties of both mesons and bayrons... I'll be reading this paper and posting a follow up.

More info here to be found:

[hep-ex/0307083] Evidence for the positive-strangeness pentaquark θ+ in photoproduction with the SAPHIR detector at ELSA

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