8,246 research outputs found
Spin oscillations of the normal polarized Fermi gas at Unitarity
Using density functional theory in a time dependent approach we determine the
frequencies of the compressional modes of the normal phase of a Fermi gas at
unitarity as a function of its polarization. Our energy functional accounts for
the typical elastic deformations exhibited by Landau theory of Fermi liquids.
The comparison with the available experiments is biased by important
collisional effects affecting both the {\it in phase} and the {\it out of
phase} oscillations even at the lowest temperatures. New experiments in the
collisionless regime would provide a crucial test of the applicability of
Landau theory to the dynamics of these strongly interacting normal Fermi gases.Comment: 5 pages, 1 figur
Can Inflation solve the Hierarchy Problem?
Inflation with tunneling from a false to a true vacuum becomes viable in the
presence of a scalar field that slows down the initial de Sitter phase. As a
by-product this field also sets dynamically the value of the Newton constant
observed today. This can be very large if the tunneling rate (which is
exponentially sensitive to the barrier) is small enough. Therefore along with
Inflation we also provide a natural dynamical explanation for why gravity is so
weak today. Moreover we predict a spectrum of gravity waves peaked at around
0.1 mHz, that will be detectable by the planned space inteferometer LISA.
Finally we discuss interesting predictions on cosmological scalar and tensor
fluctuations in the light the WMAP 3-year data.Comment: 7 pages. Replaced version with comparison with WMAP 3-year dat
Optimal generation of entanglement under local control
We study the optimal generation of entanglement between two qubits subject to
local unitary control. With the only assumptions of linear control and unitary
dynamics, by means of a numerical protocol based on the variational approach
(Pontryagin's Minimum Principle), we evaluate the optimal control strategy
leading to the maximal achievable entanglement in an arbitrary interaction
time, taking into account the energy cost associated to the controls. In our
model we can arbitrarily choose the relative weight between a large
entanglement and a small energy cost.Comment: 4 page
Experimental analysis of multistatic multiband radar signatures of wind turbines
This study presents the analysis of recent experimental data acquired using two radar systems at S-band and X-band to measure simultaneous monostatic and bistatic signatures of operational wind turbines near Shrivenham, UK. Bistatic and multistatic radars are a potential approach to mitigate the adverse effects of wind farm clutter on the performance of radar systems, which is a well-known problem for air traffic control and air defence radar. This analysis compares the simultaneous monostatic and bistatic micro-Doppler signatures of two operational turbines and investigates the key differences at bistatic angles up to 23°. The variations of the signature with different polarisations, namely vertical transmitted and vertical received and horizontal transmitted and horizontal received, are also discussed
Modelling of quantum information processing with Ehrenfest guided tra jectories: a case study
We apply a numerical method based on multi-configurational Ehrenfest tra
jectories, and demonstrate converged results for the Choi fidelity of an
entangling quantum gate between two two-level systems interacting through a set
of bosonic modes. We consider both spin-boson and rotating wave Hamiltonians,
for various numbers of mediating modes (from 1 to 100), and extend our
treatment to include finite temperatures. Our results apply to two-level
impurities interacting with the same band of a photonic crystal, or to two
distant ions interacting with the same set of motional degrees of freedom.Comment: 12 pages, figures aplent
Quantile contours and allometric modelling for risk classification of abnormal ratios with an application to asymmetric growth-restriction in preterm infants
We develop an approach to risk classification based on quantile contours and
allometric modelling of multivariate anthropometric measurements. We propose
the definition of allometric direction tangent to the directional quantile
envelope, which divides ratios of measurements into half-spaces. This in turn
provides an operational definition of directional quantile that can be used as
cutoff for risk assessment. We show the application of the proposed approach
using a large dataset from the Vermont Oxford Network containing observations
of birthweight (BW) and head circumference (HC) for more than 150,000 preterm
infants. Our analysis suggests that disproportionately growth-restricted
infants with a larger HC-to-BW ratio are at increased mortality risk as
compared to proportionately growth-restricted infants. The role of maternal
hypertension is also investigated.Comment: 31 pages, 3 figures, 8 table
Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3
Tungsten trioxide is a versatile material with widespread applications
ranging from electrochromic and optoelectronic devices to water splitting and
catalysis of chemical reactions. For technological applications, thin films of
WO3 are particularly appealing, taking advantage from high surface-to-volume
ratio and tunable physical properties. However, the growth of stoichiometric,
crystalline thin films is challenging because the deposition conditions are
very sensitive to the formation of oxygen vacancies. In this work, we show how
background oxygen pressure during pulsed laser deposition can be used to tune
the structural and electronic properties of WO3 thin films. By performing X-ray
diffraction and low-temperature transport measurements, we find changes in WO3
lattice volume up to 10%, concomitantly with an insulator-to-metal transition
as a function of increased level of electron doping. We use advanced ab initio
calculations to describe in detail the properties of the oxygen vacancy defect
states, and their evolution in terms of excess charge concentration. Our
results depict an intriguing scenario where structural, electronic, optical,
and transport properties of WO3 single-crystal thin films can all be purposely
tuned by a suited control of oxygen vacancies formation during growth
Understanding the Nature of Accounts Using Comprehensive Tools to Understand Financial Statements
Accounting is an integral part of the financial and economic activity of economic entities, regardless of the type of activity and industry in which the enterprise operates. This paper summarizes the arguments and counterarguments in the scientific discussion regarding the nature of accounts in accounting practice. The
purpose of the study is to deepen the analysis of European financial accounting practices, in particular in
the context of the use of methodological support for the classification of the nature of accounts
Spin fluctuations, susceptibility and the dipole oscillation of a nearly ferromagnetic Fermi gas
We discuss the spin fluctuations and the role played by the magnetic
susceptibility in an atomic Fermi gas interacting with positive scattering
length. Both thermal and quantum fluctuations are considered. Using a sum rule
approach and recent {\it ab initio} Monte Carlo results for the magnetic
susceptibility of uniform matter we provide explicit predictions for the
frequency of the spin dipole oscillation of a gas trapped by a harmonic
potential and discuss the deviations from the behaviour of an ideal gas when
the system approaches the ferromagnetic transition. The role of the Landau's
parameters in the characterization of the magnetic properties is also
discussed.Comment: 5 pages, 2 figure
- …