1,452 research outputs found
Unraveling the Nature of Charge Excitations in LaCuO with Momentum-Resolved Cu -edge Resonant Inelastic X-ray Scattering
Results of model calculations using exact diagonalization reveal the orbital
character of states associated with different Raman loss peaks in Cu -edge
resonant inelastic X-ray scattering (RIXS) from LaCuO. The model
includes electronic orbitals necessary to highlight non-local Zhang-Rice
singlet, charge transfer and - excitations, as well as states with apical
oxygen 2 character. The dispersion of these excitations is discussed with
prospects for resonant final state wave-function mapping. A good agreement with
experiments emphasizes the substantial multi-orbital character of RIXS profiles
in the energy transfer range 1-6 eV.Comment: Original: 4.5 pages. Replaced: 4 pages and 4 figures with updated
content and reference
Astrochemical models of interstellar ices: History matters
Ice is ubiquitous in the interstellar medium. We model the formation of the
main constituents of interstellar ices, including H2O, CO2 , CO, and CH3 OH. We
strive to understand what physical or chemical parameters influence the final
composition of the ice and how they benchmark to what has already been
observed, with the aim of applying these models to the preparation and analysis
of JWST observations. We used the Nautilus gas-grain model, which computes the
gas and ice composition as a function of time for a set of physical conditions,
starting from an initial gas phase composition. All important processes
(gas-phase reactions, gas-grain interactions, and grain surface processes) are
included and solved with the rate equation approximation. We first ran an
astrochemical code for fixed conditions of temperature and density mapped in
the cold core L429-C to benchmark the chemistry. One key parameter was revealed
to be the dust temperature. When the dust temperature is higher than 12 K, CO2
will form efficiently at the expense of H2O, while at temperatures below 12 K,
it will not form. Whatever hypothesis we assumed for the chemistry (within
realistic conditions), the static simulations failed to reproduce the observed
trends of interstellar ices in our target core. In a second step, we simulated
the chemical evolution of parcels of gas undergoing different physical and
chemical situations throughout the molecular cloud evolution and starting a few
1e7 yr prior to the core formation (dynamical simulations). Our dynamical
simulations satisfactorily reproduce the main trends already observed for
interstellar ices. Moreover, we predict that the apparent constant ratio of
CO2/H2O observed to date is probably not true for regions of low AV , and that
the history of the evolution of clouds plays an essential role, even prior to
their formation.Comment: Accepted for publication in A&
Nuclear break-up of 11Be
The break-up of 11Be was studied at 41AMeV using a secondary beam of 11Be
from the GANIL facility on a 48Ti target by measuring correlations between the
10Be core, the emitted neutrons and gamma rays. The nuclear break-up leading to
the emission of a neutron at large angle in the laboratory frame is identified
with the towing mode through its characteristic n-fragment correlation. The
experimental spectra are compared with a model where the time dependent
Schrodinger equation (TDSE) is solved for the neutron initially in the 11 Be. A
good agreement is found between experiment and theory for the shapes of neutron
experimental energies and angular distributions. The spectroscopic factor of
the 2s orbital is tentatively extracted to be 0.46+-0.15. The neutron emission
from the 1p and 1d orbitals is also studied
Drift Observations and Mitigation in LCLS-II RF
The LCLS-II RF system physically spans ~700m and has strict requirements --
on the order of 20 fs -- on the phase stability of the accelerating RF fields
in its SRF linac. While each LLRF rack is crudely temperature-stabilized, the
weather inside the service building as a whole is usually compared to a tin
shack in the California sun. A phase-averaging reference line is the primary
system deployed in support of the phase stability goals. There are other,
secondary subsystems (SEL phase offset, and determination of cavity detuning)
that are also sensitive to RF phase drift. We present measurements of phase
shifts observed in the overall RF system, and how diagnostics are able to sense
and correct for them during beam operations.Comment: Talk presented at LLRF Workshop 2023 (LLRF2023, arXiv: 2310.03199
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Impact of particles on the Planck HFI detectors: Ground-based measurements and physical interpretation
The Planck High Frequency Instrument (HFI) surveyed the sky continuously from
August 2009 to January 2012. Its noise and sensitivity performance were
excellent, but the rate of cosmic ray impacts on the HFI detectors was
unexpectedly high. Furthermore, collisions of cosmic rays with the focal plane
produced transient signals in the data (glitches) with a wide range of
characteristics. A study of cosmic ray impacts on the HFI detector modules has
been undertaken to categorize and characterize the glitches, to correct the HFI
time-ordered data, and understand the residual effects on Planck maps and data
products. This paper presents an evaluation of the physical origins of glitches
observed by the HFI detectors. In order to better understand the glitches
observed by HFI in flight, several ground-based experiments were conducted with
flight-spare HFI bolometer modules. The experiments were conducted between 2010
and 2013 with HFI test bolometers in different configurations using varying
particles and impact energies. The bolometer modules were exposed to 23 MeV
protons from the Orsay IPN TANDEM accelerator, and to Am and Cm
-particle and Fe radioactive X-ray sources. The calibration data
from the HFI ground-based preflight tests were used to further characterize the
glitches and compare glitch rates with statistical expectations under
laboratory conditions. Test results provide strong evidence that the dominant
family of glitches observed in flight are due to cosmic ray absorption by the
silicon die substrate on which the HFI detectors reside. Glitch energy is
propagated to the thermistor by ballistic phonons, while there is also a
thermal diffusion contribution. The implications of these results for future
satellite missions, especially those in the far-infrared to sub-millimetre and
millimetre regions of the electromagnetic spectrum, are discussed.Comment: 11 pages, 13 figure
Comparison of the diagnostic accuracy of three current guidelines for the evaluation of asymptomatic pancreatic cystic neoplasms.
Asymptomatic pancreatic cysts are a common clinical problem but only a minority of these cases progress to cancer. Our aim was to compare the accuracy to detect malignancy of the 2015 American Gastroenterological Association (AGA), the 2012 International Consensus/Fukuoka (Fukuoka guidelines [FG]), and the 2010 American College of Radiology (ACR) guidelines.We conducted a retrospective study at 3 referral centers for all patients who underwent resection for an asymptomatic pancreatic cyst between January 2008 and December 2013. We compared the accuracy of 3 guidelines in predicting high-grade dysplasia (HGD) or cancer in resected cysts. We performed logistic regression analyses to examine the association between cyst features and risk of HGD or cancer.A total of 269 patients met inclusion criteria. A total of 228 (84.8%) had a benign diagnosis or low-grade dysplasia on surgical pathology, and 41 patients (15.2%) had either HGD (nâ=â14) or invasive cancer (nâ=â27). Of the 41 patients with HGD or cancer on resection, only 3 patients would have met the AGA guideline\u27s indications for resection based on the preoperative cyst characteristics, whereas 30/41 patients would have met the FG criteria for resection and 22/41 patients met the ACR criteria. The sensitivity, specificity, positive predictive value, negative predictive value of HGD, and/or cancer of the AGA guidelines were 7.3%, 88.2%, 10%, and 84.1%, compared to 73.2%, 45.6%, 19.5%, and 90.4% for the FG and 53.7%, 61%, 19.8%, and 88% for the ACR guidelines. In multivariable analysis, cyst size \u3e3âcm, compared to â€3âcm, (odds ratio [OR]â=â2.08, 95% confidence interval [CI]â=â1.11, 4.2) and each year increase in age (ORâ=â1.07, 95% CIâ=â1.03, 1.11) were positively associated with risk of HGD or cancer on resection.In patients with asymptomatic branch duct-intraductal papillary mucinous neoplasms or mucinous cystic neoplasms who underwent resection, the prevalence rate of HGD or cancer was 15.2%. Using the 2015 AGA criteria for resection would have missed 92.6% of patients with HGD or cancer. The more inclusive FG and ACR had a higher sensitivity for HGD or cancer but lower specificity. Given the current deficiencies of these guidelines, it will be important to determine the acceptable rate of false-positives in order to prevent a single true-positive
Assessment of right ventricular function at rest and during exercise by echocardiography in patients with pulmonary hypertension
Fast-neutron induced background in LaBr3:Ce detectors
The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce
crystal to incident neutrons has been measured in the energy range En = 2-12
MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6
MeV with pulsed proton beams. Using the time-of-flight information between
target and detector, energy spectra of the LaBr3:Ce detector resulting from
fast neutron interactions have been obtained at 4 different neutron energies.
Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured
in a nearby Ge detector at the lowest proton beam energy. In addition, we
obtained data for neutron irradiation of a large-volume high-purity Ge detector
and of a NE-213 liquid scintillator detector, both serving as monitor detectors
in the experiment. Monte-Carlo type simulations for neutron interactions in the
liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and
compared with measured data. Good agreement being obtained with the data, we
present the results of simulations to predict the response of LaBr3:Ce
detectors for a range of crystal sizes to neutron irradiation in the energy
range En = 0.5-10 MeVComment: 28 pages, 10 figures, 4 Table
Cross sections relevant to gamma-ray line emission in solar flares:He-induced reactions on O nuclei
Gamma-ray production cross sections have been measured for gamma-ray lines
copiously emitted in the He bombardment of O nuclei: the 937, 1042
and 1081 keV lines of F and the 1887 keV line of Ne. Four Ge
detectors with BGO shielding for Compton suppression were used to measure the
angular distributions of the gamma-rays. The excitation functions have been
obtained for He bombarding energies from 3.7 to 36 MeV. Total cross
sections are tabulated for calculations relevant to gamma-ray astronomy. The
importance of these lines as diagnosis for the presence and properties of
accelerated He in solar flares is discussed in light of the measured cross
sections.Comment: Phys. Rev. C68 (2003) 0258XX, in pres
Age effect on the prediction of risk of prolonged length hospital stay in older patients visiting the emergency department: results from a large prospective geriatric cohort study.
With the rapid growth of elderly patients visiting the Emergency Department (ED), it is expected that there will be even more hospitalisations following ED visits in the future. The aim of this study was to examine the age effect on the performance criteria of the 10-item brief geriatric assessment (BGA) for the prolonged length of hospital stay (LHS) using artificial neural networks (ANNs) analysis.
Based on an observational prospective cohort study, 1117 older patients (i.e., aged â„â65Â years) ED users were admitted to acute care wards in a University Hospital (France) were recruited. The 10-items of BGA were recorded during the ED visit and prior to discharge to acute care wards. The top third of LHS (i.e., â„â13Â days) defined the prolonged LHS. Analysis was successively performed on participants categorized in 4 age groups: aged â„â70, â„â75, â„â80 andââ„Â 85Â years. Performance criteria of 10-item BGA for the prolonged LHS were sensitivity, specificity, positive predictive value [PPV], negative predictive value [NPV], likelihood ratios [LR], area under receiver operating characteristic curve [AUROC]). The ANNs analysis method was conducted using the modified multilayer perceptron (MLP).
Values of criteria performance were high (sensitivity>â89%, specificityâ„â96%, PPVâ>â87%, NPVâ>â96%, LR+â>â22; LR-ââ€â0.1 and AUROC>â93), regardless of the age group.
Age effect on the performance criteria of the 10-item BGA for the prediction of prolonged LHS using MLP was minimal with a good balance between criteria, suggesting that this tool may be used as a screening as well as a predictive tool for prolonged LHS
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