500 research outputs found
Spectral analysis of the Elatina varve series
The Elatina formation in South America, which provides a rich fossil record of presumptive solar activity in the late Precambrian, is of great potential significance for the physics of the sun because it contains luminae grouped in cycles of about 12, an appearance suggestive of the solar cycle. Here, the laminae are treated as varves laid down yearly and modulated in thickness in accordance with the late Precambrian sunspot activity for the year of deposition. The purpose is to present a simple structure, or intrinsic spectrum, that will be uncovered by appropriate data analysis
Harmonic analysis of irradiation asymmetry for cylindrical implosions driven by high-frequency rotating ion beams
Cylindrical implosions driven by intense heavy ions beams should be
instrumental in a near future to study High Energy Density Matter. By rotating
the beam by means of a high frequency wobbler, it should be possible to deposit
energy in the outer layers of a cylinder, compressing the material deposited in
its core. The beam temporal profile should however generate an inevitable
irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI)
during the implosion phase. In this paper, we compute the Fourier components of
the target irradiation in order to make the junction with previous works on RTI
performed in this setting. Implementing a 1D and 2D beam models, we find these
components can be expressed exactly in terms of the Fourier transform of the
temporal beam profile. If is the beam duration and its rotation
frequency, "magic products" can be identified which cancel the first
harmonic of the deposited density, resulting in an improved irradiation
symmetry.Comment: 19 pages, 8 figures, to appear in PR
Trapped Resonant Fermions above Superfluid Transition Temperature
We investigate trapped resonant fermions with unequal populations within the
local density approximation above the superfluid transition temperature. By
tuning the attractive interaction between fermions via Feshbach resonance, the
system evolves from weakly interacting fermi gas to strongly interacting fermi
gas, and finally becomes bose-fermi mixture. The density profiles of fermions
are examined and compared with experiments. We also point out the simple
relationships between the local density, the axial density, and the gas
pressure within the local density approximation.Comment: 9 pages, 4 figure
Tomographic RF Spectroscopy of a Trapped Fermi Gas at Unitarity
We present spatially resolved radio-frequency spectroscopy of a trapped Fermi
gas with resonant interactions and observe a spectral gap at low temperatures.
The spatial distribution of the spectral response of the trapped gas is
obtained using in situ phase-contrast imaging and 3D image reconstruction. At
the lowest temperature, the homogeneous rf spectrum shows an asymmetric
excitation line shape with a peak at 0.48(4) with respect to the
free atomic line, where is the local Fermi energy
Measurements of Surface Diffusivity and Coarsening During Pulsed Laser Deposition
Pulsed Laser Deposition (PLD) of homoepitaxial SrTiO3 was studied with
in-situ x-ray specular reflectivity and surface diffuse x-ray scattering.
Unlike prior reflectivity-based studies, these measurements access both the
time- and the length-scales of the evolution of the surface morphology during
growth. In particular, we show that this technique allows direct measurements
of the diffusivity for both inter- and intra-layer transport. Our results
explicitly limit the possible role of island break-up, demonstrate the key
roles played by nucleation and coarsening in PLD, and place an upper bound on
the Ehrlich-Schwoebel (ES) barrier for downhill diffusion
Green's function of a finite chain and the discrete Fourier transform
A new expression for the Green's function of a finite one-dimensional lattice
with nearest neighbor interaction is derived via discrete Fourier transform.
Solution of the Heisenberg spin chain with periodic and open boundary
conditions is considered as an example. Comparison to Bethe ansatz clarifies
the relation between the two approaches.Comment: preprint of the paper published in Int. J. Modern Physics B Vol. 20,
No. 5 (2006) 593-60
Tomographic approach to resolving the distribution of LISA Galactic binaries
The space based gravitational wave detector LISA is expected to observe a
large population of Galactic white dwarf binaries whose collective signal is
likely to dominate instrumental noise at observational frequencies in the range
10^{-4} to 10^{-3} Hz. The motion of LISA modulates the signal of each binary
in both frequency and amplitude, the exact modulation depending on the source
direction and frequency. Starting with the observed response of one LISA
interferometer and assuming only doppler modulation due to the orbital motion
of LISA, we show how the distribution of the entire binary population in
frequency and sky position can be reconstructed using a tomographic approach.
The method is linear and the reconstruction of a delta function distribution,
corresponding to an isolated binary, yields a point spread function (psf). An
arbitrary distribution and its reconstruction are related via smoothing with
this psf. Exploratory results are reported demonstrating the recovery of binary
sources, in the presence of white Gaussian noise.Comment: 13 Pages and 9 figures high resolution figures can be obtains from
http://www.phys.utb.edu/~rajesh/lisa_tomography.pd
Polarization imaging in ferroelectric polymer thin film capacitors by pyroelectric scanning microscopy
A Pyroelectric Scanning Microscopy system, which uses laser-induced thermal modulation for mapping the pyroelectric response, has been used to image a bipolar domain pattern in a ferroelectric polymer thin film capacitor. This system has achieved a resolution of 660±28 nm by using a violet laser and high f-number microscope objective to reduce the optical spot size, and by operating at high modulation frequencies to reduce the thermal diffusion length. The results agree well with a thermal model implemented numerically using finite element analysis
Joule expansion of a pure many-body state
We derive the Joule expansion of an isolated perfect gas from the principles
of quantum mechanics. Contrary to most studies of irreversible processes which
consider composite systems, the gas many-body Hilbert space cannot be
factorised into Hilbert spaces corresponding to interesting and ignored degrees
of freedom. Moreover, the expansion of the gas into the entire accessible
volume is obtained for pure states. Still, the number particle density is
characterised by a chemical potential and a temperature. We discuss the special
case of a boson gas below the Bose condensation temperature
Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas
We have observed phase separation between the superfluid and the normal
component in a strongly interacting Fermi gas with imbalanced spin populations.
The in situ distribution of the density difference between two trapped spin
components is obtained using phase-contrast imaging and 3D image
reconstruction. A shell structure is clearly identified where the superfluid
region of equal densities is surrounded by a normal gas of unequal densities.
The phase transition induces a dramatic change in the density profiles as
excess fermions are expelled from the superfluid.Comment: 5 pages, 7 figure
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