1,177 research outputs found
Phase Transitions of Repulsive Two-Component Fermi Gases in Two Dimensions
We predict the phase separations of two-dimensional Fermi gases with
repulsive contact-type interactions between two spin components. Using
density-potential functional theory with systematic semiclassical
approximations, we address the long-standing problem of itinerant
ferromagnetism in realistic settings. We reveal a universal transition from the
paramagnetic state at small repulsive interactions towards ferromagnetic
density profiles at large interaction strengths, with intricate particle-number
dependent phases in between. Building on quantum Monte Carlo results for
uniform systems, we benchmark our simulations against Hartree-Fock calculations
for a small number of trapped fermions. We thereby demonstrate that our
employed corrections to the mean-field interaction energy and especially to the
Thomas-Fermi kinetic energy functional are necessary for reliably predicting
properties of trapped mesoscopic Fermi gases. The density patterns of the
ground state survive at low finite temperatures and confirm the Stoner-type
polarization behavior across a universal interaction parameter, albeit with
substantial quantitative differences that originate in the trapping potential
and the quantum-corrected kinetic energy. We also uncover a zoo of metastable
configurations that are energetically comparable to the ground-state density
profiles and are thus likely to be observed in experiments. We argue that our
density-functional approach can be easily applied to interacting
multi-component Fermi gases in general.Comment: 23 pages, 8 figure
CMBR Constraint on a Modified Chaplygin Gas Model
In this paper, a modified Chaplygin gas model of unifying dark energy and
dark matter with exotic equation of state
which can also explain the recent accelerated expansion of the universe is
investigated by the means of constraining the location of the peak of the CMBR
spectrum. We find that the result of CMBR measurements does not exclude the
nonzero value of parameter , but allows it in the range .Comment: 4 pages, 3 figure
Square or not Square--That’s the Question!
Background: Most heavy metals from industrial catalysts are harmful to human body; however, to function normally, the human body does need traces of essential metal cofactors. Histidine is one of the nine essential amino acids to the human body, and cobalt(II) ion is cost effective and is known to be less toxic to the body. Methods: This project investigates the binding reactions between the cobalt(II) ion and histidine amino acids. Due to unsuccessful attempts to crystalize Cobalt(II)-Histidine complex in the lab, the quantum mechanics modeling package, G09, was employed to provide the binding mode and interaction between the metal and histidine complex. Geometric parameters were attained in order to predict the crystal structure the complex. Results: The data confirms that complexes between cobalt ions and deprotonated histidine will only settle into a square planar geometry, regardless of the initial geometry. However, with neutral histidine, the complex is not in square planar formation at all. Instead, the five-member ring formed among cobalt and histidine’s N- and C-terminus forms an angle, where N-Co-N is almost linear (167.5°). Conclusion: Different reaction conditions will yield either tetrahedral and square planar geometry at the metal center, which will influence the band gap. Such influence can then be used to create a tunable and broadspectrum solar panel materials
Strong Interplay between Stripe Spin Fluctuations, Nematicity and Superconductivity in FeSe
Elucidating the microscopic origin of nematic order in iron-based
superconducting materials is important because the interactions that drive
nematic order may also mediate the Cooper pairing. Nematic order breaks
fourfold rotational symmetry in the iron plane, which is believed to be driven
by either orbital or spin degrees of freedom. However, as the nematic phase
often develops at a temperature just above or coincides with a stripe magnetic
phase transition, experimentally determining the dominant driving force of
nematic order is difficult. Here, we use neutron scattering to study
structurally the simplest iron-based superconductor FeSe, which displays a
nematic (orthorhombic) phase transition at K, but does not order
antiferromagnetically. Our data reveal substantial stripe spin fluctuations,
which are coupled with orthorhombicity and are enhanced abruptly on cooling to
below . Moreover, a sharp spin resonance develops in the superconducting
state, whose energy (~4 meV) is consistent with an electron boson coupling mode
revealed by scanning tunneling spectroscopy, thereby suggesting a spin
fluctuation-mediated sign-changing pairing symmetry. By normalizing the dynamic
susceptibility into absolute units, we show that the magnetic spectral weight
in FeSe is comparable to that of the iron arsenides. Our findings support
recent theoretical proposals that both nematicity and superconductivity are
driven by spin fluctuations.Comment: 19 pages, 8 figure
The effects of nail rigidity on fracture healing in rats with osteoporosis
Background and purpose Stress shielding from rigid internal fixation may lead to refracture after removal of the osteosynthesis material. We investigated the effect of a low-rigidity (Ti-24Nb-4Zr-7.9Sn) intramedullary nail regarding stress shielding and bone healing of osteoporotic fractures in the rat
Symbolic Dynamics Analysis of the Lorenz Equations
Recent progress of symbolic dynamics of one- and especially two-dimensional
maps has enabled us to construct symbolic dynamics for systems of ordinary
differential equations (ODEs). Numerical study under the guidance of symbolic
dynamics is capable to yield global results on chaotic and periodic regimes in
systems of dissipative ODEs which cannot be obtained neither by purely
analytical means nor by numerical work alone. By constructing symbolic dynamics
of 1D and 2D maps from the Poincare sections all unstable periodic orbits up to
a given length at a fixed parameter set may be located and all stable periodic
orbits up to a given length may be found in a wide parameter range. This
knowledge, in turn, tells much about the nature of the chaotic limits. Applied
to the Lorenz equations, this approach has led to a nomenclature, i.e.,
absolute periods and symbolic names, of stable and unstable periodic orbits for
an autonomous system. Symmetry breakings and restorations as well as
coexistence of different regimes are also analyzed by using symbolic dynamics.Comment: 35 pages, LaTeX, 13 Postscript figures, uses psfig.tex. The revision
concerns a bug at the end of hlzfig12.ps which prevented the printing of the
whole .ps file from page 2
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