288,559 research outputs found
Graded Lie algebras of maximal class IV
We describe the isomorphism classes of certain infinite-dimensional graded
Lie algebras of maximal class, generated by an element of weight one and an
element of weight two, over fields of odd characteristic.Comment: 38 pages. See also http://www-math.science.unitn.it/~caranti/ and
http://users.ox.ac.uk/~vlee
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Exploring thermal signatures in the experimentally heated CM carbonaceous chondrite Allan Hills 83100
Quasiclassical Green function in an external field and small-angle scattering
The quasiclassical Green functions of the Dirac and Klein-Gordon equations in
the external electric field are obtained with the first correction taken into
account. The relevant potential is assumed to be localized, while its spherical
symmetry is not required. Using these Green functions, the corresponding wave
functions are found in the approximation similar to the Furry-Sommerfeld-Maue
approximation. It is shown that the quasiclassical Green function does not
coincide with the Green function obtained in the eikonal approximation and has
a wider region of applicability. It is illustrated by the calculation of the
small-angle scattering amplitude for a charged particle and the forward photon
scattering amplitude. For charged particles, the first correction to the
scattering amplitude in the non-spherically symmetric potential is found. This
correction is proportional to the scattering angle. The real part of the
amplitude of forward photon scattering in a screened Coulomb potential is
obtained.Comment: 20 pages, latex, 1 figur
Relativistic corrections to the electromagnetic polarizabilities of compound systems
The low-energy amplitude of Compton scattering on the bound state of two
charged particles of arbitrary masses, charges and spins is calculated. A case
in which the bound state exists due to electromagnetic interaction (QED) is
considered. The term, proportional to , is obtained taking into
account the first relativistic correction. It is shown that the complete result
for this correction differs essentially from the commonly used term
, proportional to the r.m.s. charge radius of the system. We
propose that the same situation can take place in the more complicated case of
hadrons.Comment: 19 pages, LaTe
Roughening of ion-eroded surfaces
Recent experimental studies focusing on the morphological properties of
surfaces eroded by ion-bombardment report the observation of self-affine
fractal surfaces, while others provide evidence about the development of a
periodic ripple structure. To explain these discrepancies we derive a
stochastic growth equation that describes the evolution of surfaces eroded by
ion bombardment. The coefficients appearing in the equation can be calculated
explicitly in terms of the physical parameters characterizing the sputtering
process. Exploring the connection between the ion-sputtering problem and the
Kardar-Parisi-Zhang and Kuramoto-Sivashinsky equations, we find that
morphological transitions may take place when experimental parameters, such as
the angle of incidence of the incoming ions or their average penetration depth,
are varied. Furthermore, the discussed methods allow us to calculate
analytically the ion-induced surface diffusion coefficient, that can be
compared with experiments. Finally, we use numerical simulations of a one
dimensional sputtering model to investigate certain aspects of the ripple
formation and roughening.Comment: 20 pages, LaTeX, 5 ps figures, contribution to the 4th CTP Workshop
on Statistical Physics "Dynamics of Fluctuating Interfaces and Related
Phenomena", Seoul National University, Seoul, Korea, January 27-31, 199
Coulomb corrections to bremsstrahlung in electric field of heavy atom at high energies
The differential and partially integrated cross sections are considered for
bremsstrahlung from high-energy electrons in atomic field with the exact
account of this field. The consideration exploits the quasiclassical electron
Green's function and wave functions in an external electric field. It is shown
that the Coulomb corrections to the differential cross section are very
susceptible to screening. Nevertheless, the Coulomb corrections to the cross
section summed up over the final-electron states are independent of screening
in the leading approximation over a small parameter ( is
a screening radius, is the electron mass, ). Bremsstrahlung from
an electron beam of the finite size on heavy nucleus is considered as well.
Again, the Coulomb corrections to the differential probability are very
susceptible to the beam shape, while those to the probability integrated over
momentum transfer are independent of it, apart from the trivial factor, which
is the electron-beam density at zero impact parameter. For the Coulomb
corrections to the bremsstrahlung spectrum, the next-to-leading terms with
respect to the parameters ( is the electron energy) and
are obtained.Comment: 13 pages, 4 figure
Measurement of the SOC State Specific Heat in ^4He
When a heat flux Q is applied downward through a sample of liquid 4He near the lambda transition, the helium self organizes such that the gradient in temperature matches the gravity induced gradient in Tlambda. All the helium in the sample is then at the same reduced temperature tSOC = ((T[sub SOC] - T[sub lambda])/T[sub lambda]) and the helium is said to be in the Self-Organized Critical (SOC) state. We have made preliminary measurements of the 4He SOC state specific heat, C[del]T(T(Q)). Despite having a cell height of 2.54 cm, our results show no difference between C[del]T and the zero-gravity 4He specific heat results of the Lambda Point Experiment (LPE) [J.A. Lipa et al., Phys. Rev. B, 68, 174518 (2003)] over the range 250 to 450 nK below the transition. There is no gravity rounding because the entire sample is at the same reduced temperature tSOC(Q). Closer to Tlambda the SOC specific heat falls slightly below LPE, reaching a maximum at approximately 50 nK below Tlambda, in agreement with theoretical predictions [R. Haussmann, Phys. Rev. B, 60, 12349 (1999)]
Noise and Equivalent Circuit of Double Injection
Measurements of the high‐frequency noise of a silicon double‐injection diode result in 〈i^2〉 = α⋅4kT(1/r)Δf with α=1.04 and in agreement with the literature. A new interpretation demands Nyquist noise with α≡1 in these devices at high frequencies. This is in accord with an equivalent circuit derived for the double‐injection process. Speculations are made on the general validity of Nyquist noise in nonlinear devices at high frequencies. In addition, generation‐recombination noise is suggested as the prime source of the low‐frequency noise
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