6,331 research outputs found
DPTC -- an FPGA-based trace compression
Recording of flash-ADC traces is challenging from both the transmission
bandwidth and storage cost perspectives. This paper presents a
configuration-free lossless compression algorithm which addresses both
limitations, by compressing the data on-the-fly in the controlling
field-programmable gate array (FPGA). Thus the difference predicted trace
compression (DPTC) can easily be used directly in front-end electronics. The
method first computes the differences between consecutive samples in the
traces, thereby concentrating the most probable values around zero. The values
are then stored as groups of four, with only the necessary least-significant
bits in a variable-length code, packed in a stream of 32-bit words. To evaluate
the efficiency, the storage cost of compressed traces is modeled as a baseline
cost including the ADC noise, and a cost for pulses that depends on their
amplitude and width. The free parameters and the validity of the model are
determined by comparing it with the results of compressing a large set of
artificial traces with varying characteristics. The compression method was also
applied to actual data from different types of detectors, thereby demonstrating
its general applicability. The compression efficiency is found to be comparable
to popular general-purpose compression methods, while available for FPGA
implementation using limited resources. A typical storage cost is around 4 to 5
bits per sample. Code for the FPGA implementation in VHDL and for the CPU
decompression routine in C of DPTC are available as open source software, both
operating at multi-100 Msamples/s speeds.Comment: 9 pages, 7 figure
Effect of Compton Scattering on the Electron Beam Dynamics at the ATF Damping Ring
Compton scattering provides one of the most promising scheme to obtain
polarized positrons for the next generation of -- colliders.
Moreover it is an attractive method to produce monochromatic high energy
polarized gammas for nuclear applications and X-rays for compact light sources.
In this framework a four-mirror Fabry-P\'erot cavity has been installed at the
Accelerator Test Facility (ATF - KEK, Tsukuba, Japan) and is used to produce an
intense flux of polarized gamma rays by Compton scattering
\cite{ipac-mightylaser}. For electrons at the ATF energy (1.28 GeV) Compton
scattering may result in a shorter lifetime due to the limited bucket
acceptance. We have implemented the effect of Compton scattering on a 2D
tracking code with a Monte-Carlo method. This code has been used to study the
longitudinal dynamics of the electron beam at the ATF damping ring, in
particular the evolution of the energy spread and the bunch length under
Compton scattering. The results obtained are presented and discussed. Possible
methods to observe the effect of Compton scattering on the ATF beam are
proposed
Telemedicine-enabled accelerated discharge of patients hospitalized with COVID-19 to isolation in repurposed hotel rooms.
No abstract availabl
Are braneworlds born isotropic?
It has recently been suggested that an isotropic singularity may be a generic
feature of brane cosmologies, even in the inhomogeneous case. Using the
covariant and gauge-invariant approach we present a detailed analysis of linear
perturbations of the isotropic model which is a past attractor in
the phase space of homogeneous Bianchi models on the brane. We find that for
matter with an equation of state parameter , the dimensionless
variables representing generic anisotropic and inhomogeneous perturbations
decay as , showing that the model is asymptotically stable
in the past. We conclude that brane universes are born with isotropy naturally
built-in, contrary to standard cosmology. The observed large-scale homogeneity
and isotropy of the universe can therefore be explained as a consequence of the
initial conditions if the brane-world paradigm represents a description of the
very early universe.Comment: Changed to match published versio
ISW effect in Unified Dark Matter Scalar Field Cosmologies: an analytical approach
We perform an analytical study of the Integrated Sachs-Wolfe (ISW) effect
within the framework of Unified Dark Matter models based on a scalar field
which aim at a unified description of dark energy and dark matter. Computing
the temperature power spectrum of the Cosmic Microwave Background anisotropies
we are able to isolate those contributions that can potentially lead to strong
deviations from the usual ISW effect occurring in a CDM universe. This
helps to highlight the crucial role played by the sound speed in the Unified
Dark Matter models. Our treatment is completely general in that all the results
depend only on the speed of sound of the dark component and thus it can be
applied to a variety of unified models, including those which are not described
by a scalar field but relies on a single dark fluid.Comment: 15 pages, LateX file; one comment after Eq.(36) and formula (44)
added in order to underline procedure and main results. Accepted for
publication in JCAP; some typos correcte
Length Measurement of High-brightness Electron Beam thanks to the 3-Phase Method
ISBN 978-3-95450-132-8International audienceThe goal of 3-phase method is to determine the length of an electron beam without dedicated diagnostics by varying the measurement conditions of its energy spread, through a change in the RF phase of an accelerating structure. The originality here comes from the fact that it is applied on high-brightness electron beams of few MeV generated by RF photo-injectors. It allows testing the accuracy of 3-phase method, since the length to reconstruct is known as being that of the laser pulse generating the beam. It requires establishing the longitudinal transfer matrix of a RF photo-injector, which is difficult since the electron velocity vary from 0 to relativistic during its path*. The 3-phase method in RF photo-injector has been simulated by ASTRA and PARMELA codes, validating the principle of the method. First measurement has been done on PHIL accelerator at LAL, showing a good agreement with the expected length. I will then show results obtained at PITZ with a standing wave booster and a comparison with those coming from a Cerenkov detector. Finally, measurements at higher energy performed on the SOLEIL LINAC with travelling wave accelerating structures will be exposed
TG/FT-IR: An Analysis of the Conditions Affecting the Combined TG/Spectral Response
The results of TG/FT-IR measurements performed on hydrated beta-cyclodextrin at different heating rates and with different carrier gas fluxes are reported. It is shown that the shape of the spectral curve and the its degree of matching with the DTG curves depend on both the TG heating rate and the carrier gas flow rate
On average properties of inhomogeneous fluids in general relativity II: perfect fluid cosmologies
For general relativistic spacetimes filled with an irrotational perfect fluid
a generalized form of Friedmann's equations governing the expansion factor of
spatially averaged portions of inhomogeneous cosmologies is derived. The
averaging problem for scalar quantities is condensed into the problem of
finding an `effective equation of state' including kinematical as well as
dynamical `backreaction' terms that measure the departure from a standard FLRW
cosmology. Applications of the averaged models are outlined including
radiation-dominated and scalar field cosmologies (inflationary and
dilaton/string cosmologies). In particular, the averaged equations show that
the averaged scalar curvature must generically change in the course of
structure formation, that an averaged inhomogeneous radiation cosmos does not
follow the evolution of the standard homogeneous-isotropic model, and that an
averaged inhomogeneous perfect fluid features kinematical `backreaction' terms
that, in some cases, act like a free scalar field source. The free scalar field
(dilaton) itself, modelled by a `stiff' fluid, is singled out as a special
inhomogeneous case where the averaged equations assume a simple form.Comment: TeX 21 pages, matches published version: G.R.G., in pres
Cross-cultural variation and fMRI lie-detection
As decidedly underscored by a recent editorial in Nature Neuroscience (2010), many experiments
in cognitive neuroscience have been carried out with a sample that is not representative of the general human
population, as the subjects are usually university students in psychology. The underlying assumption of this
practice is that the workings of the brain do not vary much even when subjects come from different cultural
groups. Recent research by Henrich et al. (2010) shows that this assumption is unwarranted. On several
basic features of perception and cognition, Western university students turn out to be outliers relative to the
general human population, so that data based on them should be interpreted with caution. In particular, this
situation seems to provide an argument for questioning the conformity of functional Magnetic Resonance
Imaging (fMRI) lie-detection to Federal Rule of Evidence 702 and Daubert. Deception is a social
phenomenon and it is related to mental functions, such as theory of mind, for which cross-cultural variability
at the neural level has been detected. Furthermore, culture is a multi-dimensional variable whose effects are
diverse. Thus, the use of fMRI lie-detection in legal contexts may hinder the ascertainment of truth if the
experimental results are not shown to be conserved in different cultures. Cross-cultural variability in
neural activation patterns is just a facet of the broader issue of external and ecological validity for
neuroscientific experiments on the detection of deception; nonetheless, fMRI lie- detection is unlikely
to meet the Daubert standards if cross-cultural variation is not controlled by appropriate experiments
Locally extracting scalar, vector and tensor modes in cosmological perturbation theory
Cosmological perturbation theory relies on the decomposition of perturbations
into so-called scalar, vector and tensor modes. This decomposition is non-local
and depends on unknowable boundary conditions. The non-locality is particularly
important at second- and higher-order because perturbative modes are sourced by
products of lower-oder modes, which must be integrated over all space in order
to isolate each mode. However, given a trace-free rank-2 tensor, a locally
defined scalar mode may be trivially derived by taking two divergences, which
knocks out the vector and tensor degrees of freedom. A similar local
differential operation will return a pure vector mode. This means that scalar
and vector degrees of freedom have local descriptions. The corresponding local
extraction of the tensor mode is unknown however. We give it here. The
operators we define are useful for defining gauge-invariant quantities at
second-order. We perform much of our analysis using an index-free
`vector-calculus' approach which makes manipulating tensor equations
considerably simpler.Comment: 13 pages. Final version to appear in CQ
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