4,329 research outputs found
Strategic Alliances In Public Accounting Firms
The decade of the 1990s saw the emergence of the concept of the strategic alliance and its significant growth in both numbers and diversity of alliance areas as well as its impact on business performance in terms of new service or product introductions and/or increases in revenue, profit, volume or market share. Public accounting (CPA) firms have participated in such alliances especially during times of staffing shortages and seasonal peak periods, but their participation has not been well reported in the literature. This study examines the state of strategic alliances in public accounting firms. The topic is particularly relevant now in light of the greater responsibilities placed on management since the passage of the Sarbanes-Oxley Act, and the issuance recently of two Statements of Financial Accounting Standards (SFAS No. 157 in 2006 and SFAS No. 159 in 2007) which give companies the option to report certain financial assets and liabilities at fair value. These additional responsibilities may include the restructuring and restatement of financial reports to more accurately reflect the financial position and results of operations of a business. This has resulted in a greater demand for accounting services which some CPA firms were not able to provide. The findings reveal that participation in strategic alliances enables accounting firms to pool their resources, increase revenues, build a larger knowledge support system to serve a wider clientele, and compete with larger firms both nationally and on a global basis
The baryon fraction of LambdaCDM haloes
We investigate the baryon fraction in dark matter haloes formed in
non-radiative gas-dynamical simulations of the LambdaCDM cosmogony. By
combining a realisation of the Millennium Simulation (Springel et al.) with a
simulation of a smaller volume focussing on dwarf haloes, our study spans five
decades in halo mass, from 10^10 Msun/h to 10^15 Msun/h. We find that the
baryon fraction within the halo virial radius is typically 90% of the cosmic
mean, with an rms scatter of 6%, independently of redshift and of halo mass
down to the smallest resolved haloes. Our results show that, contrary to the
proposal of Mo et al. (2005), pre-virialisation gravitational heating is unable
to prevent the collapse of gas within galactic and proto-galactic haloes, and
confirm the need for non-gravitational feedback in order to reduce the
efficiency of gas cooling and star formation in dwarf galaxy haloes.
Simulations including a simple photoheating model (where a gas temperature
floor of T_{floor} = 2x10^4 K is imposed from z=11) confirm earlier suggestions
that photoheating can only prevent the collapse of baryons in systems with
virial temperatures T_{200} < ~2.2 T_{floor} ~ 4.4x10^4 K (corresponding to a
virial mass of M_{200} ~ 10^10 Msun/h and a circular velocity of V_{200} ~ 35
km/s). Photoheating may thus help regulate the formation of dwarf spheroidals
and other galaxies at the extreme faint-end of the luminosity function, but it
cannot, on its own, reconcile the abundance of sub-L* galaxies with the vast
number of dwarf haloes expected in the LambdaCDM cosmogony. The lack of
evolution or mass dependence seen in the baryon fraction augurs well for X-ray
cluster studies that assume a universal and non-evolving baryon fraction to
place constraints on cosmological parameters.Comment: 9 pages, 5 figures (Figs 1. and 2 reduced in quality), 1 table,
submitted to MNRAS. Version with high-resolution figures can be obtained from
http://star-www.dur.ac.uk/~rcrain/baryonfractions
The theory of quantum levitators
We develop a unified theory for clocks and gravimeters using the
interferences of multiple atomic waves put in levitation by traveling light
pulses. Inspired by optical methods, we exhibit a propagation invariant, which
enables to derive analytically the wave function of the sample scattering on
the light pulse sequence. A complete characterization of the device sensitivity
with respect to frequency or to acceleration measurements is obtained. These
results agree with previous numerical simulations and confirm the conjecture of
sensitivity improvement through multiple atomic wave interferences. A realistic
experimental implementation for such clock architecture is discussed.Comment: 11 pages, 6 Figures. Minor typos corrected. Final versio
Growth of a dynamical correlation length in an aging superspin glass
We report on zero field cooled magnetization relaxation experiments on a
concen- trated frozen ferrofluid exhibiting a low temperature superspin glass
transition. With a method initially developed for spin glasses, we investigate
the field dependence of the relaxations that take place after different aging
times. We extract the typical number of correlated spins involved in the aging
dynamics. This brings important insights into the dynamical correlation length
and its time growth. Our results, consistent with expressions obtained for spin
glasses, extend the generality of these behaviours to the class of superspin
glasses. Since the typical flipping time is much larger for superspins than for
atomic spins, our experiments probe a time regime much closer to that of
numerical simulations
Precision atomic gravimeter based on Bragg diffraction
We present a precision gravimeter based on coherent Bragg diffraction of
freely falling cold atoms. Traditionally, atomic gravimeters have used
stimulated Raman transitions to separate clouds in momentum space by driving
transitions between two internal atomic states. Bragg interferometers utilize
only a single internal state, and can therefore be less susceptible to
environmental perturbations. Here we show that atoms extracted from a
magneto-optical trap using an accelerating optical lattice are a suitable
source for a Bragg atom interferometer, allowing efficient beamsplitting and
subsequent separation of momentum states for detection. Despite the inherently
multi-state nature of atom diffraction, we are able to build a Mach-Zehnder
interferometer using Bragg scattering which achieves a sensitivity to the
gravitational acceleration of with an
integration time of 1000s. The device can also be converted to a gravity
gradiometer by a simple modification of the light pulse sequence.Comment: 13 pages, 11 figure
Mosquitoes and malaria transmission in irrigated rice-fields in the Benoue valley of northern Cameroon
International audienc
Light-shift tomography in an optical-dipole trap for neutral atoms
We report on light-shift tomography of a cloud of 87 Rb atoms in a
far-detuned optical-dipole trap at 1565 nm. Our method is based on standard
absorption imaging, but takes advantage of the strong light-shift of the
excited state of the imaging transition, which is due to a quasi-resonance of
the trapping laser with a higher excited level. We use this method to (i) map
the equipotentials of a crossed optical-dipole trap, and (ii) study the
thermalisation of an atomic cloud by following the evolution of the
potential-energy of atoms during the free-evaporation process
Transport regimes of cold gases in a two-dimensional anisotropic disorder
We numerically study the dynamics of cold atoms in a two-dimensional
disordered potential. We consider an anisotropic speckle potential and focus on
the classical regime, which is relevant to some recent experiments. First, we
study the behavior of particles with a fixed energy and identify different
transport regimes. For low energy, the particles are classically localized due
to the absence of a percolating cluster. For high energy, the particles undergo
normal diffusion and we show that the diffusion constants scale algebraically
with the particle energy, with an anisotropy factor which significantly differs
from that of the disordered potential. For intermediate energy, we find a
transient sub-diffusive regime, which is relevant to the time scale of typical
experiments. Second, we study the behavior of a cold-atomic gas with an
arbitrary energy distribution, using the above results as a groundwork. We show
that the density profile of the atomic cloud in the diffusion regime is
strongly peaked and, in particular, that it is not Gaussian. Its behavior at
large distances allows us to extract the energy-dependent diffusion constants
from experimental density distributions. For a thermal cloud released into the
disordered potential, we show that our numerical predictions are in agreement
with experimental findings. Not only does this work give insights to recent
experimental results, but it may also serve interpretation of future
experiments searching for deviation from classical diffusion and traces of
Anderson localization.Comment: 19 pages, 16 figure
Anderson localization in Bose-Einstein condensates
The understanding of disordered quantum systems is still far from being
complete, despite many decades of research on a variety of physical systems. In
this review we discuss how Bose-Einstein condensates of ultracold atoms in
disordered potentials have opened a new window for studying fundamental
phenomena related to disorder. In particular, we point our attention to recent
experimental studies on Anderson localization and on the interplay of disorder
and weak interactions. These realize a very promising starting point for a
deeper understanding of the complex behaviour of interacting, disordered
systems.Comment: 15 pages review, to appear in Reports on Progress in Physic
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