4,306 research outputs found
Robust seismic velocity change estimation using ambient noise recordings
We consider the problem of seismic velocity change estimation using ambient
noise recordings. Motivated by [23] we study how the velocity change estimation
is affected by seasonal fluctuations in the noise sources. More precisely, we
consider a numerical model and introduce spatio-temporal seasonal fluctuations
in the noise sources. We show that indeed, as pointed out in [23], the
stretching method is affected by these fluctuations and produces misleading
apparent velocity variations which reduce dramatically the signal to noise
ratio of the method. We also show that these apparent velocity variations can
be eliminated by an adequate normalization of the cross-correlation functions.
Theoretically we expect our approach to work as long as the seasonal
fluctuations in the noise sources are uniform, an assumption which holds for
closely located seismic stations. We illustrate with numerical simulations and
real measurements that the proposed normalization significantly improves the
accuracy of the velocity change estimation
Braess's Paradox in Wireless Networks: The Danger of Improved Technology
When comparing new wireless technologies, it is common to consider the effect
that they have on the capacity of the network (defined as the maximum number of
simultaneously satisfiable links). For example, it has been shown that giving
receivers the ability to do interference cancellation, or allowing transmitters
to use power control, never decreases the capacity and can in certain cases
increase it by , where is the
ratio of the longest link length to the smallest transmitter-receiver distance
and is the maximum transmission power. But there is no reason to
expect the optimal capacity to be realized in practice, particularly since
maximizing the capacity is known to be NP-hard. In reality, we would expect
links to behave as self-interested agents, and thus when introducing a new
technology it makes more sense to compare the values reached at game-theoretic
equilibria than the optimum values.
In this paper we initiate this line of work by comparing various notions of
equilibria (particularly Nash equilibria and no-regret behavior) when using a
supposedly "better" technology. We show a version of Braess's Paradox for all
of them: in certain networks, upgrading technology can actually make the
equilibria \emph{worse}, despite an increase in the capacity. We construct
instances where this decrease is a constant factor for power control,
interference cancellation, and improvements in the SINR threshold (),
and is when power control is combined with interference
cancellation. However, we show that these examples are basically tight: the
decrease is at most O(1) for power control, interference cancellation, and
improved , and is at most when power control is
combined with interference cancellation
Sex-Dependent Changes in miRNA Expression in the Bed Nucleus of the Stria Terminalis Following Stress
Anxiety disorders disproportionately affect women compared to men, which may arise from sex differences in stress responses. MiRNAs are small non-coding RNAs known to regulate gene expression through actions on mRNAs. MiRNAs are regulated, in part, by factors such as stress and gonadal sex, and they have been implicated in the pathophysiology of multiple psychiatric disorders. Here, we assessed putative sex differences in miRNA expression in the bed nucleus of the stria terminalis (BNST) â a sexually dimorphic brain region implicated in anxiety â of adult male and female rats that had been exposed to social isolation (SI) stress throughout adolescence. To assess the translational utility of our results, we assessed if childhood trauma in humans resulted in changes in blood miRNA expression that are similar to those observed in rats. Male and female Sprague-Dawley rats underwent SI during adolescence or remained group housed (GH) and were tested for anxiety-like behavior in the elevated plus maze as adults. Small RNA sequencing was performed on tissue extracted from the BNST. Furthermore, we re-analyzed an already available small RNA sequencing data set from the Grady Trauma Project (GTP) from men and women to identify circulating miRNAs that are associated with childhood trauma exposure. Our results indicated that there were greater anxiogenic-like effects and changes in BNST miRNA expression in SI versus GH females compared to SI versus GH males. In addition, we found nine miRNAs that were regulated in both the BNST from SI compared to GH rats and in blood samples from humans exposed to childhood trauma. These studies emphasize the utility of rodent models in studying neurobiological mechanisms underlying psychiatric disorders and suggest that rodent models could be used to identify novel sex-specific pharmacotherapies for anxiety disorders
Formation and growth of atmospheric nanoparticles in the eastern Mediterranean: results from long-term measurements and process simulations
Atmospheric new particle formation (NPF) is a common phenomenon all over
the world. In this study we present the longest time series of NPF records in
the eastern Mediterranean region by analyzing 10 years of aerosol number size
distribution data obtained with a mobility particle sizer. The measurements
were performed at the Finokalia environmental research station on Crete,
Greece, during the period June 2008âJune 2018. We found that NPF took place
on 27 % of the available days, undefined days were 23 % and non-event
days 50 %. NPF is more frequent in April and May probably due to the
terrestrial biogenic activity and is less frequent in August. Throughout the
period under study, nucleation was observed also during the night. Nucleation
mode particles had the highest concentration in winter and early spring,
mainly because of the minimum sinks, and their average contribution to the
total particle number concentration was 8 %. Nucleation mode particle
concentrations were low outside periods of active NPF and growth, so there
are hardly any other local sources of sub-25 nm particles. Additional
atmospheric ion size distribution data simultaneously collected for more than
2 years were also analyzed. Classification of NPF events based on ion
spectrometer measurements differed from the corresponding classification
based on a mobility spectrometer, possibly indicating a different
representation of local and regional NPF events between these two measurement
data sets. We used the MALTE-Box model
for simulating a case study of NPF in the eastern Mediterranean region.
Monoterpenes contributing to NPF can explain a large fraction of the observed
NPF events according to our model simulations. However the adjusted
parameterization resulting from our sensitivity tests was significantly
different from the initial one that had been determined for the boreal
environment.</p
Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic Calorimeter
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2010 IOPEnsuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered
Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up
Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
Combined search for the quarks of a sequential fourth generation
Results are presented from a search for a fourth generation of quarks
produced singly or in pairs in a data set corresponding to an integrated
luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in
2011. A novel strategy has been developed for a combined search for quarks of
the up and down type in decay channels with at least one isolated muon or
electron. Limits on the mass of the fourth-generation quarks and the relevant
Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a
simple extension of the standard model with a sequential fourth generation of
fermions. The existence of mass-degenerate fourth-generation quarks with masses
below 685 GeV is excluded at 95% confidence level for minimal off-diagonal
mixing between the third- and the fourth-generation quarks. With a mass
difference of 25 GeV between the quark masses, the obtained limit on the masses
of the fourth-generation quarks shifts by about +/- 20 GeV. These results
significantly reduce the allowed parameter space for a fourth generation of
fermions.Comment: Replaced with published version. Added journal reference and DO
- âŚ