3,609 research outputs found
Hydrostatic equilibrium and stellar structure in f(R)-gravity
We investigate the hydrostatic equilibrium of stellar structure by taking
into account the modi- fied La\'e-Emden equation coming out from f(R)-gravity.
Such an equation is obtained in metric approach by considering the Newtonian
limit of f(R)-gravity, which gives rise to a modified Poisson equation, and
then introducing a relation between pressure and density with polytropic index
n. The modified equation results an integro-differential equation, which, in
the limit f(R) \rightarrow R, becomes the standard La\'e-Emden equation. We
find the radial profiles of gravitational potential by solving for some values
of n. The comparison of solutions with those coming from General Relativity
shows that they are compatible and physically relevant.Comment: 9 pages, 1 figur
Sudden hearing loss as an early detector of multiple sclerosis: a systematic review
To evaluate whether Sudden Sensorineural Hearing Loss (S-SNHL) may be an early symptom of Multiple Sclerosis (MS). A systematic review was conducted using the following keywords: "Multiple sclerosis, hearing loss, sudden hearing loss, vertigo, tinnitus, magnetic resonance imaging, otoacoustic emission, auditory brainstem responses, white matter lesions, sensorineural hearing loss, symptoms of MS and otolaryngology, nerve disease and MS". Only the articles that included results of at least one auditory test and MRI were considered. We evaluated the prevalence of SNHL in patients with MS, the presence of different forms of SNHL (S-SNHL and Progressive SNHL (P-SNHL)) and their correlation with the stage of MS, the results of electrophysiological tests, and the location (if any) of MS lesions as detected by white matter hyperintensities in the MRI. We reviewed a total of 47 articles, which included 29 case reports, 6 prospective studies, 6 cohort studies, 4 case-control studies, and 2 retrospective studies. 25% of patients suffered from SNHL. S-SNHL typically occurred in the early stage of the disease (92% of patients) and was the only presenting symptom in 43% of female subjects. Instead, P-SNHL occurred in the late stage of MS (88% of patients). Auditory Brainstem Responses (ABR) were abnormal in all MS patients with S-SNHL. When S-SNHL appeared during the early stage of the disease, MS lesions were found in the brain in 60% of patients and in the Internal Auditory Canal in 40% of patients. ABR remained abnormal after recovery. S-SNHL can be an early manifestation of MS and should always be considered in the differential diagnosis of this condition, especially in women. The pathophysiology can be explained by the involvement of microglia attacking the central and/or peripheral auditory pathways as indicated by WMHs
Scanning and data extraction from crop collecting mission documents
Poster presented at TDWG 2009, Montpellier (France). 9 - 13 Nov 2009
Underwater acoustic channel properties in the Gulf of Naples and their effects on digital data transmission
In this paper we studied the physical properties of the Gulf of Naples (Southern Italy) for its use as a commu-
nication channel for the acoustic transmission of digital data acquired by seismic instruments on the seafloor to
a moored buoy. The acoustic link will be assured by high frequency acoustic modems operating with a central
frequency of 100 kHz and a band pass of 10 kHz. The main operational requirements of data transmission con-
cern the near horizontal acoustic link, the maximum depth of the sea being about 300 m and the planned hori-
zontal distance between seismic instruments and buoy 2 km. This study constructs the signal-to-noise ratio maps
to understand the limits beyond which the clarity of the transmission is no longer considered reliable. Using ray-
theory, we compute the amplitudes of a transmitted signal at a grid of 21×12 receivers to calculate the transmis-
sion loss at each receiver. The signal-to-noise ratio is finally computed for each receiver knowing also the trans-
mitter source level and the acoustic noise level in the Gulf of Naples. The results show that the multipath effects
predominate over the effects produced by the sound velocity gradient in the sea in the summer period. In the case
of omnidirectional transmitters with a Source Level (SL) of 165 dB and a baud rate of 2.4 kbit/s, the results al-
so show that distances of 1400-1600 m can be reached throughout the year for transmitter-receiver connections
below 50 m depth in the underwater acoustic channel
The Newtonian Limit of F(R) gravity
A general analytic procedure is developed to deal with the Newtonian limit of
gravity. A discussion comparing the Newtonian and the post-Newtonian
limit of these models is proposed in order to point out the differences between
the two approaches. We calculate the post-Newtonian parameters of such theories
without any redefinition of the degrees of freedom, in particular, without
adopting some scalar fields and without any change from Jordan to Einstein
frame. Considering the Taylor expansion of a generic theory, it is
possible to obtain general solutions in term of the metric coefficients up to
the third order of approximation. In particular, the solution relative to the
component gives a gravitational potential always corrected with
respect to the Newtonian one of the linear theory . Furthermore, we
show that the Birkhoff theorem is not a general result for -gravity since
time-dependent evolution for spherically symmetric solutions can be achieved
depending on the order of perturbations. Finally, we discuss the
post-Minkowskian limit and the emergence of massive gravitational wave
solutions.Comment: 16 page
Underwater acoustic channel properties in the Gulf of Naples and their effects on digital data transmission
In this paper we studied the physical properties of the Gulf of Naples (Southern Italy) for its use as a commu-
nication channel for the acoustic transmission of digital data acquired by seismic instruments on the seafloor to
a moored buoy. The acoustic link will be assured by high frequency acoustic modems operating with a central
frequency of 100 kHz and a band pass of 10 kHz. The main operational requirements of data transmission con-
cern the near horizontal acoustic link, the maximum depth of the sea being about 300 m and the planned hori-
zontal distance between seismic instruments and buoy 2 km. This study constructs the signal-to-noise ratio maps
to understand the limits beyond which the clarity of the transmission is no longer considered reliable. Using ray-
theory, we compute the amplitudes of a transmitted signal at a grid of 21×12 receivers to calculate the transmis-
sion loss at each receiver. The signal-to-noise ratio is finally computed for each receiver knowing also the trans-
mitter source level and the acoustic noise level in the Gulf of Naples. The results show that the multipath effects
predominate over the effects produced by the sound velocity gradient in the sea in the summer period. In the case
of omnidirectional transmitters with a Source Level (SL) of 165 dB and a baud rate of 2.4 kbit/s, the results al-
so show that distances of 1400-1600 m can be reached throughout the year for transmitter-receiver connections
below 50 m depth in the underwater acoustic channel
Enhancing CFD predictions in shape design problems by model and parameter space reduction
In this work we present an advanced computational pipeline for the approximation and prediction of the lift coefficient of a parametrized airfoil profile. The non-intrusive reduced order method is based on dynamic mode decomposition (DMD) and it is coupled with dynamic active subspaces (DyAS) to enhance the future state prediction of the target function and reduce the parameter space dimensionality. The pipeline is based on high-fidelity simulations carried out by the application of finite volume method for turbulent flows, and automatic mesh morphing through radial basis functions interpolation technique. The proposed pipeline is able to save 1/3 of the overall computational resources thanks to the application of DMD. Moreover exploiting DyAS and performing the regression on a lower dimensional space results in the reduction of the relative error in the approximation of the time-varying lift coefficient by a factor 2 with respect to using only the DMD
Enhancing CFD predictions in shape design problems by model and parameter space reduction
In this work we present an advanced computational pipeline for the
approximation and prediction of the lift coefficient of a parametrized airfoil
profile. The non-intrusive reduced order method is based on dynamic mode
decomposition (DMD) and it is coupled with dynamic active subspaces (DyAS) to
enhance the future state prediction of the target function and reduce the
parameter space dimensionality. The pipeline is based on high-fidelity
simulations carried out by the application of finite volume method for
turbulent flows, and automatic mesh morphing through radial basis functions
interpolation technique. The proposed pipeline is able to save 1/3 of the
overall computational resources thanks to the application of DMD. Moreover
exploiting DyAS and performing the regression on a lower dimensional space
results in the reduction of the relative error in the approximation of the
time-varying lift coefficient by a factor 2 with respect to using only the DMD
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