12,752 research outputs found
Strings in gravity with torsion
A theory of gravitation in 4D is presented with strings used in the material
action in spacetime. It is shown that the string naturally gives rise to
torsion. It is also shown that the equation of motion a string follows from the
Bianchi identity, gives the identical result as the Noether conservation laws,
and follows a geodesic only in the lowest order approximation. In addition, the
conservation laws show that strings naturally have spin, which arises not from
their motion but from their one dimensional structure.Comment: 16 page
Electrodynamics with radiation reaction
The self force of electrodynamics is derived from a scalar field. The
resulting equation of motion is free of all of the problems that plague the
Lorentz Abraham Dirac equation. The age-old problem of a particle in a constant
field is solved and the solution has intuitive appeal.Comment: 5 page
Effects of a torsion field on Big Bang nucleosynthesis
In this paper it is investigated whether torsion, which arises naturally in
most theories of quantum gravity, has observable implications for the Big Bang
nucleosynthesis. Torsion can lead to spin flips amongst neutrinos thus turning
them into sterile neutrinos. In the early Universe they can alter the helium
abundance which is tightly constrained by observations. Here I calculate to
what extent torsion of the string theory type leads to a disagreement with the
Big Bang nucleosynthesis predictions.Comment: accepted by General Relativity and Gravitatio
Leech Parasitism of the Gulf Coast Box Turtle, Terrapene carolina major (Testudines:Emydidae) in Mississippi, USA
Ten leeches were collected from a Gulf Coast box turtle, Terrapene carolina major, found crossing a road in Gulfport, Harrison County, Mississippi, USA. Eight of the leeches were identified as Placobdella multilineata and 2 were identified as Helobdella europaea. This represents the second vouchered report of leeches from a box turtle. Helobdella europaea is reported for the first time associated with a turtle and for the second time from the New World
XUV Frequency Combs via Femtosecond Enhancement Cavities
We review the current state of tabletop extreme ultraviolet (XUV) sources
based on high harmonic generation (HHG) in femtosecond enhancement cavities
(fsEC). Recent developments have enabled generation of high photon flux (1014
photons/sec) in the XUV, at high repetition rates (>50 MHz) and spanning the
spectral region from 40 nm - 120 nm. This level of performance has enabled
precision spectroscopy with XUV frequency combs and promises further
applications in XUV spectroscopic and photoemission studies. We discuss the
theory of operation and experimental details of the fsEC and XUV generation
based on HHG, including current technical challenges to increasing the photon
flux and maximum photon energy produced by this type of system. Current and
future applications for these sources are also discussed.Comment: invited review article, 38 page
Design of a digital ride quality augmentation system for commuter aircraft
Commuter aircraft typically have low wing loadings, and fly at low altitudes, and so they are susceptible to undesirable accelerations caused by random atmospheric turbulence. Larger commercial aircraft typically have higher wing loadings and fly at altitudes where the turbulence level is lower, and so they provide smoother rides. This project was initiated based on the goal of making the ride of the commuter aircraft as smooth as the ride experienced on the major commercial airliners. The objectives of this project were to design a digital, longitudinal mode ride quality augmentation system (RQAS) for a commuter aircraft, and to investigate the effect of selected parameters on those designs
A Science Center for the Advanced Composition Explorer
The Advanced Composition Explorer (ACE) mission is supported by an ACE Science Center for the purposes of facilitating collaborative work. It is intended that coordinated use of a centralized science facility by the ACE team will ensure appropriate use of data formatting standards, thus easing access to the data; will improve communications within and to the ACE science working team; and will reduce redundant effort in data processing
First measurements of the index of refraction of gases for lithium atomic waves
We report here the first measurements of the index of refraction of gases for
lithium waves. Using an atom interferometer, we have measured the real and
imaginary part of the index of refraction for argon, krypton and xenon, as
a function of the gas density for several velocities of the lithium beam. The
linear dependence of with the gas density is well verified. The total
collision cross-section deduced from the imaginary part is in very good
agreement with traditional measurements of this quantity. Finally, as predicted
by theory, the real and imaginary parts of and their ratio
exhibit glory oscillations
On the Interpretation of the Normalization Constant in the Scaling Equation
The scaling equation, Y1 = βYα2, has been used empirically and explored theoretically primarily to determine the numerical value and meaning of the scaling exponent, α. The mathematical interpretation of α is clear—it is the quotient of the relative rate of change of Y1 with respect to the rate of change of Y2. In contrast, the interpretation of the normalization constant, β, is obscure, so much so that some workers have rejected the idea that it has any biological importance. With the notable exception of Steven J. Gould\u27s early work, Huxley\u27s dismissal of β largely relegated the study of its biological role to that of an academic afterthought. Here, we attempt to clarify the meaning of β by using examples from plant biology to illustrate the four primary difficulties that have obscured its importance: (1) the consistency of the units of measurement and the metric being measured (e.g., meters and body length, respectively), (2) the relationship between β and α, (3) the interpretation of scaling equations, and (4) detecting if the numerical value of β has changed and if the change is biologically meaningful. Using examples, we show that β is biologically interpretable and offers a way to quantitatively consider similarities of biological form if (1) it is expressed in terms of the relative magnitudes of Y1 or Y2 for corresponding data points in a set of Y1 = βYα2 equations, (2) the units of measurements are in the same scale, and (3) the corresponding dimensionless numbers are established based on the same units of measurement. We provide examples of where the numerical value of β or differences in the values of β are important, and we propose a research agenda examining the meaning of β values in terms of trait-based ecology
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