11,189 research outputs found
Single-color two-photon spectroscopy of Rydberg states in electric fields
Rydberg states of atomic helium with principal quantum numbers ranging from
n=20 to n=100 have been prepared by non-resonance-enhanced single-color
two-photon excitation from the metastable 2 {^3}S{_1} state. Photoexcitation
was carried out using linearly and circularly polarized pulsed laser radiation.
In the case of excitation with circularly polarized radiation, Rydberg states
with azimuthal quantum number |m_{\ell}|=2 were prepared in zero electric
field, and in homogeneous electric fields oriented parallel to the propagation
axis of the laser radiation. In sufficiently strong electric fields, individual
Rydberg-Stark states were resolved spectroscopically, highlighting the
suitability of non-resonance-enhanced multiphoton excitation schemes for the
preparation of long-lived high-|m_{\ell}| hydrogenic Rydberg states for
deceleration and trapping experiments. Applications of similar schemes for
Doppler-free excitation of positronium atoms to Rydberg states are also
discussed
Evidence on the Audit Risk Model: Do Auditors Increase Audit Fees in the Presence of Internal Control Deficiencies?
The article discusses the study of determining whether audit risk model is descriptive of what occurs in the auditing practice or if the relationship between fees and internal control deficiencies (ICDs) suggest that audit enterprises exert more effort in auditing firms that impart ICDs. The study examines the internal controls over financial reporting (ICOFR), generally accepted accounting principles (GAAP), audit risk model, audit fees and sections of Sarbanes-Oxley Act. The study found out that audit fees are significantly higher for firms disclosing material weakness
Matter-wave interferometry with atoms in high Rydberg states
Matter-wave interferometry has been performed with helium atoms in high
Rydberg states. In the experiments the atoms were prepared in coherent
superpositions of Rydberg states with different electric dipole moments. Upon
the application of an inhomogeneous electric field, the different forces on
these internal state components resulted in the generation of coherent
superpositions of momentum states. Using a sequence of microwave and electric
field gradient pulses the internal Rydberg states were entangled with the
momentum states associated with the external motion of these matter waves.
Under these conditions matter-wave interference was observed by monitoring the
populations of the Rydberg states as the magnitudes and durations of the pulsed
electric field gradients were adjusted. The results of the experiments have
been compared to, and are in excellent quantitative agreement with, matter-wave
interference patterns calculated for the corresponding pulse sequences. For the
Rydberg states used, the spatial extent of the Rydberg electron wavefunction
was ~320 nm. Matter-wave interferometry with such giant atoms is of interest in
the exploration of the boundary between quantum and classical mechanics. The
results presented also open new possibilities for measurements of the
acceleration of Rydberg positronium or antihydrogen atoms in the Earth's
gravitational field.Comment: 28 pages, 10 figure
Gravitational Waves from Mesoscopic Dynamics of the Extra Dimensions
Recent models which describe our world as a brane embedded in a higher
dimensional space introduce new geometrical degrees of freedom: the shape
and/or size of the extra dimensions, and the position of the brane. These modes
can be coherently excited by symmetry breaking in the early universe even on
``mesoscopic'' scales as large as 1 mm, leading to detectable gravitational
radiation. Two sources are described: relativistic turbulence caused by a
first-order transition of a radion potential, and Kibble excitation of
Nambu-Goldstone modes of brane displacement. Characteristic scales and spectral
properties are estimated and the prospects for observation by LISA are
discussed. Extra dimensions with scale between 10 \AA and 1 mm, which enter the
3+1-D era at cosmic temperatures between 1 and 1000 TeV, produce backgrounds
with energy peaked at observed frequencies in the LISA band, between
and Hz. The background is detectable above instrument and
astrophysical foregrounds if initial metric perturbations are excited to a
fractional amplitude of or more, a likely outcome for the
Nambu-Goldstone excitations.Comment: Latex, 5 pages, plus one figure, final version to appear in Phys.
Rev. Let
A new multi-gas constrained model of trace gas non-homogeneous transport in firn: evaluation and behaviour at eleven polar sites
Insoluble trace gases are trapped in polar ice at the firn-ice transition, at approximately 50 to 100 m below the surface, depending primarily on the site temperature and snow accumulation. Models of trace gas transport in polar firn are used to relate firn air and ice core records of trace gases to their atmospheric history. We propose a new model based on the following contributions. First, the firn air transport model is revised in a poromechanics framework with emphasis on the non-homogeneous properties and the treatment of gravitational settling. We then derive a nonlinear least square multi-gas optimisation scheme to calculate the effective firn diffusivity (automatic diffusivity tuning). The improvements gained by the multi-gas approach are investigated (up to ten gases for a single site are included in the optimisation process). We apply the model to four Arctic (Devon Island, NEEM, North GRIP, Summit) and seven Antarctic (DE08, Berkner Island, Siple Dome, Dronning Maud Land, South Pole, Dome C, Vostok) sites and calculate their respective depth-dependent diffusivity profiles. Among these different sites, a relationship is inferred between the snow accumulation rate and an increasing thickness of the lock-in zone defined from the isotopic composition of molecular nitrogen in firn air (denoted d15N). It is associated with a reduced diffusivity value and an increased ratio of advective to diffusive flux in deep firn, which is particularly important at high accumulation rate sites. This has implications for the understanding of d15N of N2 records in ice cores, in relation with past variations of the snow accumulation rate. As the snow accumulation rate is clearly a primary control on the thickness of the lock-in zone, our new approach that allows for the estimation of the lock-in zone width as a function of accumulation may lead to a better constraint on the age difference between the ice and entrapped gases
On the use of blow up to study regularizations of singularities of piecewise smooth dynamical systems in
In this paper we use the blow up method of Dumortier and Roussarie
\cite{dumortier_1991,dumortier_1993,dumortier_1996}, in the formulation due to
Krupa and Szmolyan \cite{krupa_extending_2001}, to study the regularization of
singularities of piecewise smooth dynamical systems
\cite{filippov1988differential} in . Using the regularization
method of Sotomayor and Teixeira \cite{Sotomayor96}, first we demonstrate the
power of our approach by considering the case of a fold line. We quickly
recover a main result of Bonet and Seara \cite{reves_regularization_2014} in a
simple manner. Then, for the two-fold singularity, we show that the regularized
system only fully retains the features of the singular canards in the piecewise
smooth system in the cases when the sliding region does not include a full
sector of singular canards. In particular, we show that every locally unique
primary singular canard persists the regularizing perturbation. For the case of
a sector of primary singular canards, we show that the regularized system
contains a canard, provided a certain non-resonance condition holds. Finally,
we provide numerical evidence for the existence of secondary canards near
resonance.Comment: To appear in SIAM Journal of Applied Dynamical System
The Impact of Atmospheric Fluctuations on Degree-scale Imaging of the Cosmic Microwave Background
Fluctuations in the brightness of the Earth's atmosphere originating from
water vapor are an important source of noise for ground-based instruments
attempting to measure anisotropy in the Cosmic Microwave Background. This paper
presents a model for the atmospheric fluctuations and derives simple
expressions to predict the contribution of the atmosphere to experimental
measurements. Data from the South Pole and from the Atacama Desert in Chile,
two of the driest places on Earth, are used to assess the level of fluctuations
at each site.Comment: 29 pages, 7 figures, 1 table, appears in The Astrophysical Journa
Internal Control Disclosures, Monitoring, and the Cost of Debt
We test the relationship between the change in a firm\u27s cost of debt and the disclosure of a material weakness in an initial Section 404 report. We find that, on average, a firm\u27s credit spread on its publicly traded debt marginally increases if it discloses a material weakness. We also examine the impact of monitoring by credit rating agencies and/or banks on this result and find that the result is more pronounced for firms that are not monitored. Additional analysis indicates that the effect of bank monitoring appears to be the primary driver of these monitoring results. This finding is consistent with the argument that banks are effective delegated monitors for the debt market. The results of this study suggest the need for future research, particularly to test the differential effects of monitoring on the cost of debt compared to the cost of equity
Optical integral field spectroscopy of intermediate redshift infrared bright galaxies
The extreme infrared (IR) luminosity of local luminous and ultra-luminous IR
galaxies (U/LIRGs; 11 12,
respectively) is mainly powered by star-formation processes triggered by
mergers or interactions. While U/LIRGs are rare locally, at z > 1, they become
more common, they dominate the star-formation rate (SFR) density, and a
fraction of them are found to be normal disk galaxies. Therefore, there must be
an evolution of the mechanism triggering these intense starbursts with
redshift. To investigate this evolution, we present new optical SWIFT integral
field spectroscopic H{\alpha}+[NII] observations of a sample of 9
intermediate-z (0.2 < z < 0.4) U/LIRG systems selected from Herschel 250{\mu}m
observations. The main results are the following: (a) the ratios between the
velocity dispersion and the rotation curve amplitude indicate that 10-25% (1-2
out of 8) might be compatible with being isolated disks while the remaining
objects are interacting/merging systems; (b) the ratio between un-obscured and
obscured SFR traced by H{\alpha} and LIR, respectively, is similar in both
local and these intermediate-z U/LIRGs; and (c) the ratio between 250{\mu}m and
the total IR luminosities of these intermediate-z U/LIRGs is higher than that
of local U/LIRGs with the same LIR . This indicates a reduced dust temperature
in these intermediate-z U/LIRGs. This, together with their already measured
enhanced molecular gas content, suggests that the interstellar medium
conditions are different in our sample of intermediate-z galaxies when compared
to local U/LIRGs.Comment: Accepted for publication in MNRA
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