1,852 research outputs found
Enhanced time response of 1-in. LaBr3(Ce) crystals by leading edge and constant fraction techniques
We have characterized in depth the time response of three detectors equipped
with cylindrical LaBr (Ce) crystals with dimensions of 1-in. in height
and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and
10%. Measurements were performed at Co and Na {\gamma}-ray
energies against a fast BaF reference detector. The time resolution was
optimized by the choice of the photomultiplier bias voltage and the fine tuning
of the parameters of the constant fraction discriminator, namely the
zero-crossing and the external delay. We report here on the optimal time
resolution of the three crystals. It is observed that timing properties are
influenced by the amount of Ce doping and the crystal homogeneity. For the
crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays
in addition to the Hamamatsu R9779 PMT has made it possible to improve the
LaBr(Ce) time resolution from the best literature value at 60Co photon
energies to below 100 ps.Comment: Article submitted to Nuclear Instruments and Methods in Physics
Research Section A: Accelerators, Spectrometers, Detectors and Associated
Equipmen
Bulk viscosity of the massive Gross-Neveu model
A calculation of the bulk viscosity for the massive Gross-Neveu model at zero
fermion chemical potential is presented in the large- limit. This model
resembles QCD in many important aspects: it is asymptotically free, has a
dynamically generated mass gap, and for zero bare fermion mass it is scale
invariant at the classical level (broken through the trace anomaly at the
quantum level). For our purposes, the introduction of a bare fermion mass is
necessary to break the integrability of the model, and thus to be able to study
momentum transport. The main motivation is, by decreasing the bare mass, to
analyze whether there is a correlation between the maximum in the trace anomaly
and a possible maximum in the bulk viscosity, as recently conjectured. After
numerical analysis, I find that there is no direct correlation between these
two quantities: the bulk viscosity of the model is a monotonously decreasing
function of the temperature. I also comment on the sum rule for the spectral
density in the bulk channel, as well as on implications of this analysis for
other systems.Comment: v2: 3->3 processes included, conclusions unchanged. Comments and
references added. Typos corrected. To appear in Phys. Rev.
CP violation with a dynamical Higgs
We determine the complete set of independent gauge and gauge-Higgs CP-odd
effective operators for the generic case of a dynamical Higgs, up to four
derivatives in the chiral expansion. The relation with the linear basis of
dimension six CP-odd operators is clarified. Phenomenological applications
include bounds inferred from electric dipole moment limits, and from present
and future collider data on triple gauge coupling measurements and Higgs
signals.Comment: 41 pages, 3 figures; V2: citations added, typos corrected, version
published on JHE
Ground-state configuration of neutron-rich ³⁵Al via Coulomb breakup
The ground-state configuration of ³⁵Al has been studied via Coulomb dissociation (CD) using the LAND-FRS setup (GSI, Darmstadt) at a relativistic energy of ~ 403 MeV/nucleon. The measured inclusive differential CD cross section for ³⁵Al, integrated up to 5.0 MeV relative energy between the ³³Al core and the neutron using a Pb target, is 78(13) mb. The exclusive measured CD cross section that populates various excited states of ³³Al is 29(7) mb. The differential CD cross section of ³⁵Al -> ³⁴Al + n has been interpreted in the light of a direct breakup model, and it suggests that the possible ground-state spin and parity of ³⁵Al could be, tentatively, 1/2⁺ or 3/2⁺ or 5/2⁺. The valence neutrons, in the ground state of ³⁵Al, may occupy a combination of either l = 3,0 or l = 1,2 orbitals coupled with the ³⁴Al core in the ground and isomeric state(s), respectively. This hints of a particle-hole configuration of the neutron across the magic shell gaps at N = 20,28 which suggests narrowing the magic shell gap. If the 5/2⁺ is the ground-state spin-parity of ³⁵Al as suggested in the literature, then the major ground-state configuration of ³⁵Al is a combination of ³⁴Al (g. s.; 4⁻) circle times ν_(p_(3/2)) and ³⁴Al (isomer; 1⁺) circle times ν _(d_(3/2)) states. The result from this experiment has been compared with that from a previous knockout measurement and a calculation using the SDPF-M interaction
A dynamic global model for planktonic foraminifera
International audienceSeasonal changes in the flux of planktonic foraminifera have to be understood to interpret corresponding proxy-based reconstructions. To study the seasonal cycle of planktonic foraminifera species we developed a numerical model of species concentration (PLAFOM). This model is forced with a global hydrographic dataset (e.g. temperature, mixed layer depth) and with biological information taken from an ecosystem model (e.g. "food type", zooplankton abundance) to predict monthly concentrations of the most common planktonic foraminifera species used for proxies: N. pachyderma (sinistral and dextral varieties), G. bulloides, G. ruber (white variety) and G. sacculifer. The sensitivity of each species with respect to temperature (optimal temperature and range of tolerance) is derived from sediment-trap studies. Overall, the spatial distribution patterns of most of the species are comparable to core-top data. N. pachyderma (sin.) is limited to polar regions, N. pachyderma (dex.) and G. bulloides are the most common species in high productivity zones like upwelling areas, while G. ruber and G. sacculifer are more abundant in tropical and subtropical oligotrophic waters. Modeled seasonal variation match well with sediment-trap records in most of the locations for N. pachyderma (sin), N. pachyderma (dex.) and G. bulloides. G. ruber and G. sacculifer show, in general, lower concentrations and less seasonal variability in all sites. The lower variability is reflected in the model output, but the small scale variations are not reproduced by the model in several locations. Due to the fact that the model is forced by climatological data, it can not capture interannual variations. The sensitivity experiments we carried out show that, inside the temperature tolerance range, food availability is the main parameter which controls the abundance of some species. The here presented model represents a powerful tool to explore the response of planktonic foraminifera to different boundary conditions, and to quantify the seasonal bias in foraminifera-based proxy records
Cirugía radiodirigida de Osteoma Osteoide: nota clínica
Se presenta el caso de una paciente joven con clínica y pruebas de imagen compatibles con osteoma
osteoide en la tibia, que es tratada mediante cirugía-exéresis de la lesión dirigida por radiolocalización tras
la realización de una gammagrafía ósea. La radiología peroperatoria y, posteriormente, el estudio patológico
definitivo confirman la lesión. Se describe las características y ventajas de la localización radioguiada en este
tipo de lesiones.We present the case of a young patient with clinical and testing compatible with osteoid osteoma
image in the tibia, which is treated by surgery-resection of the lesion led by radiolocation after performing a
bone scan. The intraoperative radiology and the definitive pathological study confirmed the injury. Features and
advantages of the radioguided location in these injuries are described
Disentangling a dynamical Higgs
The pattern of deviations from Standard Model predictions and couplings is
different for theories of new physics based on a non-linear realization of the
gauge symmetry breaking and those assuming a linear
realization. We clarify this issue in a model-independent way via its effective
Lagrangian formulation in the presence of a light Higgs particle, up to first
order in the expansions: dimension-six operators for the linear expansion and
four derivatives for the non-linear one. Complete sets of pure gauge and
gauge-Higgs operators are considered, implementing the renormalization
procedure and deriving the Feynman rules for the non-linear expansion. We
establish the theoretical relation and the differences in physics impact
between the two expansions. Promising discriminating signals include the
decorrelation in the non-linear case of signals correlated in the linear one:
some pure gauge versus gauge-Higgs couplings and also between couplings with
the same number of Higgs legs. Furthermore, anomalous signals expected at first
order in the non-linear realization may appear only at higher orders of the
linear one, and vice versa. We analyze in detail the impact of both type of
discriminating signals on LHC physics.Comment: Version published in JHE
Characteristic study, its identification and self-tuned approach to control hydro-power plants
The water time constant and mechanical time constant greatly influences the power and speed oscillations of hydro-turbine-generator unit. This paper discusses the turbine power transients in response to different nature and changes in the gate position. The work presented here analyses the characteristics of hydraulic system with an emphasis on changes in the above time constants. The simulation study is based on mathematical first-, second-, third- and fourth-order transfer function models. The study is further extended to identify discrete time-domain models and their characteristic representation without noise and with noise content of 10 & 20 dB signal-to-noise ratio (SNR). The use of self-tuned control approach in minimising the speed deviation under plant parameter changes and disturbances is also discussed
Atomistic simulations of magnetoelastic effects on sound velocity
In this work, we leverage atomistic spin-lattice simulations to examine how
magnetic interactions impact the propagation of sound waves through a
ferromagnetic material. To achieve this, we characterize the sound wave
velocity in BCC iron, a prototypical ferromagnetic material, using three
different approaches that are based on the oscillations of kinetic energy,
finite-displacement derived forces, and corrections to the elastic constants,
respectively. Successfully applying these methods within the spin-lattice
framework, we find good agreement with the Simon effect including high order
terms. In analogy to experiments, morphic coefficients associated with the
transverse and longitudinal waves propagating along the [001] direction are
extracted from fits to the fractional change in velocity data. The present
efforts represent an advancement in magnetoelastic modelling capabilities which
can expedite the design of future magneto-acoustic devices
Finding answers in lipid profile in COVID-19 patients
Introduction: A small percentage of patients will develop a severe form of COVID-19 caused by SARS-CoV-2 infection. Thus, it is important to predict the potential outcomes identifying early markers of poor prognosis. In this context, we evaluated the association of SARS-CoV-2 infection with lipid abnormalities and their role in prognosis. Methods: Single-center, retrospective, observational study of COVID-19 patients admitted from March to October 2020. Clinical and laboratory data, comorbidities, and treatments for COVID-19 were evaluated. Main outcomes including intensive care unit (ICU) admission and mortality were analyzed with a multivariable Cox proportional hazards regression model. Results: We selected 1489 from a total of 2038 consecutive patients with confirmed COVID-19, who had a complete lipid profile before ICU admission. During the follow-up performed in 1109 patients, we observed a decrease in T-c, HDL-c, and LDL-c in 28.6%, 42.9%, and 30.4% of patients, respectively, and an increase in TG in 76.8%. The decrease of both T-c and HDL- c was correlated with a decrease in albumin levels (r = 0.39 and r = 0.37, respectively). Kaplan–Meier survival curves found an increased ICU admission in patients with lower T-c (HR 0.55, CI 0.36–0.86), HDL-c (HR 0.61, CI 0.45–0.84), and LDL-c (HR 0.85, CI 0.74–0.97). Higher values of T-c (HR 0.45, CI 0.36–0.57), HDL-c (HR 0.66, CI 0.54–0.81), and LDL-c (HR 0.86, CI 0.78–0.94) showed a protective effect on mortality. Conclusions: Abnormalities in lipid profile are a frequent complication of SARS-CoV-2 infection and might be related to morbidity and mortalityThis work was supported by the following grants: Proyectos
de Investigación en Salud (FIS) PI16-02091 and PI19-00584 (funded
by Instituto de Salud Carlos III), TIRONET2-CM, B2017/BMD-3724
(funded by Comunidad de Madrid) and cofinanced by FEDER funds to
M.M
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