3,067 research outputs found
The dressed nonrelativistic electron in a magnetic field
We consider a nonrelativistic electron interacting with a classical magnetic
field pointing along the -axis and with a quantized electromagnetic
field. When the interaction between the electron and photons is turned off, the
electronic system is assumed to have a ground state of finite multiplicity.
Because of the translation invariance along the -axis, we consider the
reduced Hamiltonian associated with the total momentum along the -axis
and, after introducing an ultraviolet cutoff and an infrared regularization, we
prove that the reduced Hamiltonian has a ground state if the coupling constant
and the total momentum along the -axis are sufficiently small. Finally
we determine the absolutely continuous spectrum of the reduced Hamiltonian.Comment: typos correction
Nonuniform viscosity in the solar nebula and large masses of Jupiter and Saturn
I report a novel theory that nonuniform viscous frictional force in the solar
nebula accounts for the largest mass of Jupiter and Saturn and their largest
amount of H and He among the planets, two outstanding facts that are unsolved
puzzles in our understanding of origin of the Solar System. It is shown that
the nebula model of uniform viscosity does not match the present planet masses.
By studying current known viscosity mechanisms, I show that viscosity is more
efficient in the inner region inside Mercury and the outer region outside
Jupiter-Saturn than the intermediate region. The more efficient viscosity
drives faster radial inflow of material during the nebula evolution. Because
the inflow in the outer region is faster than the intermediate region, the
material tends to accumulate in Jupiter-Saturn region which is between the
outer and intermediate region. It is demonstrated that the gas trapping time of
Jovian planets is longer than the inflow time in the outer region. Therefore
the gas already flows to Jupiter-Saturn region before Uranus and Neptune can
capture significant gas. But the inflow in the Jupiter-Saturn region is so slow
that they can capture large amount of gas before the gas can flow further
inward. Hence they have larger masses with larger H and He content than Uranus
and Neptune. I also extend the discussion to the masses of the terrestrial
planets, especially low mass of Mercury. The advantages of this theory are
discussed.Comment: 4 pages, 1 figure, A&A Letters accepte
Interpreting the yield of transit surveys: Are there groups in the known transiting planets population?
Each transiting planet discovered is characterized by 7 measurable
quantities, that may or may not be linked together (planet mass, radius,
orbital period, and star mass, radius, effective temperature, and metallicity).
Correlations between planet mass and period, surface gravity and period, planet
radius and star temperature have been previously observed among the known
transiting giant planets. Two classes of planets have been previously
identified based on their Safronov number. We use the CoRoTlux code to compare
simulated events to the sample of discovered planets and test the statistical
significance of these correlations. We first generate a stellar field with
planetary companions based on radial velocity discoveries and a planetary
evolution model, then apply a detection criterion that includes both
statistical and red noise sources. We compare the yield of our simulated survey
with the ensemble of 31 well-characterized giant transiting planets, using a
multivariate logistic analysis to assess whether the simulated distribution
matches the known transiting planets. Our multivariate analysis shows that our
simulated sample and observations are consistent to 76%. The mass vs. period
correlation for giant planets first observed with radial velocity holds with
transiting planets. Our model naturally explains the correlation between planet
surface gravity and period and the one between planet radius and stellar
effective temperature. Finally, we are also able to reproduce the previously
observed apparent bimodal distribution of Safronov numbers in 10% of our
simulated cases, although our model predicts a continuous distribution. This
shows that the evidence for the existence of two groups of planets with
different intrinsic properties is not statistically significant.Comment: 17 page
Ion structure in warm dense matter: benchmarking solutions of hypernetted-chain equations by first-principle simulations
We investigate the microscopic structure of strongly coupled ions in warm dense matter using ab initio simulations and hypernetted chain (HNC) equations. We demonstrate that an approximate treatment of quantum effects by weak pseudopotentials fails to describe the highly degenerate electrons in warm dense matter correctly. However, one-component HNC calculations for the ions agree well with first-principles simulations if a linearly screened Coulomb potential is used. These HNC results can be further improved by adding a short-range repulsion that accounts for bound electrons. Examples are given for recently studied light elements, lithium and beryllium, and for aluminum where the extra short-range repulsion is essential
Precision Beam Position Monitor for EUROTeV
In the framework of EUROTeV, a Precision Beam Position Monitor (PBPM) has been designed, manufactured and tested. The new PBPM, based on the inductive BPM presently used in the CERN CLIC Test Facility (CTF3), aims to achieve a resolution of 100 nm and an accuracy of 10 μm in a 6 mm aperture. A dedicated test bench has been designed and constructed to fully characterize and optimize the PBPM. This paper describes the final design, presents the test bench results and reports on the beam tests carried out in the CERN CTF3 Linac
A new model for mixing by double-diffusive convection (semi-convection): I. The conditions for layer formation
The process referred to as "semi-convection" in astrophysics and
"double-diffusive convection in the diffusive regime" in Earth and planetary
sciences, occurs in stellar and planetary interiors in regions which are stable
according to the Ledoux criterion but unstable according to the Schwarzschild
criterion. In this series of papers, we analyze the results of an extensive
suite of 3D numerical simulations of the process, and ultimately propose a new
1D prescription for heat and compositional transport in this regime which can
be used in stellar or planetary structure and evolution models.
In a preliminary study of the phenomenon, Rosenblum et al. (2011) showed
that, after saturation of the primary instability, a system can evolve in one
of two possible ways: the induced turbulence either remains homogeneous, with
very weak transport properties, or transitions into a thermo-compositional
staircase where the transport rate is much larger (albeit still smaller than in
standard convection).
In this paper, we show that this dichotomous behavior is a robust property of
semi-convection across a wide region of parameter space. We propose a simple
semi-analytical criterion to determine whether layer formation is expected or
not, and at what rate it proceeds, as a function of the background
stratification and of the diffusion parameters (viscosity, thermal diffusivity
and compositional diffusivity) only. The theoretical criterion matches the
outcome of our numerical simulations very adequately in the numerically
accessible "planetary" parameter regime, and can easily be extrapolated to the
stellar parameter regime.
Subsequent papers will address more specifically the question of quantifying
transport in the layered case and in the non-layered case.Comment: Submitted to Ap
Napoléon et la vitesse
Guillot G. Napoléon et la vitesse. In: Bulletin de l'Académie Vétérinaire de France tome 122 n°10, 1969. pp. 947-958
Scaling exponents for fracture surfaces in homogenous glass and glassy ceramics
We investigate the scaling properties of post-mortem fracture surfaces in
silica glass and glassy ceramics. In both cases, the 2D height-height
correlation function is found to obey Family-Viseck scaling properties, but
with two sets of critical exponents, in particular a roughness exponent
in homogeneous glass and in glassy
ceramics. The ranges of length-scales over which these two scalings are
observed are shown to be below and above the size of process zone respectively.
A model derived from Linear Elastic Fracture Mechanics (LEFM) in the
quasistatic approximation succeeds to reproduce the scaling exponents observed
in glassy ceramics. The critical exponents observed in homogeneous glass are
conjectured to reflect damage screening occurring for length-scales below the
size of the process zone
Las Areas Marinas Protegidas (AMPs) como Herramienta de Manejo de las PesquerÃas Demersales en la Zona Norte del Caribe Colombiano
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