311 research outputs found
A low-voltage retarding-field Mott polarimeter for photocathode characterization
Nuclear physics experiments at Thomas Jefferson National Accelerator
Facility's CEBAF rely on high polarization electron beams. We describe a
recently commissioned system for prequalifying and studying photocathodes for
CEBAF with a load-locked, low-voltage polarized electron source coupled to a
compact retarding-field Mott polarimeter. The polarimeter uses simplified
electrode structures and operates from 5 to 30 kV. The effective Sherman
function for this device has been calibrated by comparison with the CEBAF 5 MeV
Mott polarimeter. For elastic scattering from a thick gold target at 20 keV,
the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV,
defined as the detected count rate divided by the incident particle current, is
5.4(2) x 10-4, yielding a figure-of-merit, or analyzing power squared times
efficiency, of 1.0(1) x 10-5. The operating parameters of this new polarimeter
design are compared to previously published data for other compact Mott
polarimeters of the retarding-field type.Comment: 9 figure
Implementing a small media intervention to increase colorectal cancer screening in primary care clinics
Colorectal cancer (CRC) is one of the most common cancers in the USA. In 2017, an estimated 135,420 people were diagnosed with CRC and 50,260 people died from CRC. Several screening modalities are recommended by the United States Preventive Services Task Force (USPSTF), including annual stool tests that are usually completed at home and under-used compared with colonoscopy despite stated patient preferences for an alternative to colonoscopy. The Community Preventive Services Task Force recommends use of small media interventions (SMIs) to increase CRC screening and calls for a greater understanding of its independent impact on screening participation. This study tested whether a SMI increased the likelihood of participant return of a USPSTF recommended Fecal Immunochemical Test (FIT). In total, 804 individuals participated in a two-group, prospective randomized controlled trial. Descriptive statistics with chi-square tests compared differences in participant characteristics and return rates. Multivariable log-binomial modeling estimated combined effects of patient characteristics with FIT return rates. No differences in return rates were observed overall or by participant characteristics other than the year of enrollment. A multivariable model controlling for all covariates, found gender, insurance type, and regular place for healthcare to be significantly associated with return rates. Receipt of the SMI did not independently increase overall return rates but it may have improved the ease of completing the FIT by some participants, particularly women, those with insurance, and those with a regular place for healthcare
Perioperative complications among head and neck surgery patients with COVID-19
Background: Patients undergoing surgery for head and neck cancer (HNC) have potentially high perioperative complication rates. Recent studies indicate that preoperative COVID-19 infection poses increased risk for postoperative complications in other fields. However, to date, there has not been data showing the effect of COVID-19 on complication rates for HNC. Here, a large database was employed to assess if perioperative COVID-19 increased the risk of perioperative complications among those undergoing HNC surgery. Methods: A retrospective investigation was conducted using a multi-institutional research database. Subjects who underwent HNC surgery from January 2020 to September 2022 were identified using the International Classification of Diseases and Current Procedure Terminology codes. Thirty-day surgical and medical complications were assessed for those diagnosed with COVID-19 infection from 7 days before or after surgery compared to those who were COVID-19 negative. Cohorts were propensity scores matched by age, sex, and race. Results: Perioperative COVID-19 was present in n = 208 and absent in n = 15 158 subjects that underwent HNC surgery. For unmatched analyses, there was a statistically significant increased risk in the 30-day postoperative period in COVID-19-positive patients for the following surgical complications: surgical site fistula, free tissue transfer (FTT) complication, FTT failure, and death. Additionally, there was a statistically significant increased risk in the 30-day postoperative period in COVID-19-positive patients for the following medical complications: ventilator support, pneumonia, vasopressor, acute renal failure, and myocardial infarction. Conclusion: This large, retrospective populational study suggests HNC patients are at increased risk for death and several perioperative complications. This investigation is the first to address this clinical question
Probing the Environment with Galaxy Dynamics
I present various projects to study the halo dynamics of elliptical galaxies.
This allows one to study the outer mass and orbital distributions of
ellipticals in different environments, and the inner distributions of groups
and clusters themselves.Comment: 5 pages, 2 figs, to appear in Proc. ESO Workshop, Groups of Galaxies
in the Nearby Universe (5-9 Dec 2005), eds. I. Saviane, V. Ivanov & J.
Borissova (Springer-Verlag
Dispersive properties of quasi-phase-matched optical parametric amplifiers
The dispersive properties of non-degenerate optical parametric amplification
in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary
grating profile are theoretically investigated in the no-pump-depletion limit.
The spectral group delay curve of the amplifier is shown to be univocally
determined by its spectral power gain curve through a Hilbert transform. Such a
constraint has important implications on the propagation of spectrally-narrow
optical pulses through the amplifier. In particular, it is shown that anomalous
transit times, corresponding to superluminal or even negative group velocities,
are possible near local minima of the spectral gain curve. A possible
experimental observation of such effects using a QPM Lithium-Niobate crystal is
suggested.Comment: submitted for publicatio
Multi-method approach shows stock structure in Loligo forbesii squid
Knowledge of stock structure is a priority for effective assessment of commercially-fished cephalopods. Loligo forbesii squid are thought to migrate inshore for breeding and offshore for feeding and long-range movements are implied from past studies showing genetic homogeneity in the entire neritic population. Only offshore populations (Faroe and Rockall Bank) were considered distinct. The present study applied mitchondrial and microsatellite markers (nine loci) to samples from Rockall Bank, north Scotland, North Sea, various shelf locations in Ireland, English Channel, northern Bay of Biscay, north Spain, and Bay of Cadiz. No statistically significant genetic sub-structure was found, although some non-significant trends involving Rockall were seen using microsatellite markers. Differences in L. forbesii statolith shape were apparent at a subset of locations, with most locations showing pairwise differences and statoliths from north Ireland being highly distinct. This suggests that (i) statolith shape is highly sensitive to local conditions and (ii) L. forbesii forms distinguishable groups (based on shape statistics), maintaining these groups over sufficiently long periods for local conditions to affect the shape of the statolith. Overall evidence suggests that L. forbesii forms separable (ecological) groups over short timescales with a semi-isolated breeding group at Rockall whose distinctiveness varies over time.Postprin
Cephalopods of the European Shelf and their associated oceanographic parameters based on occurrence in standardized demersal fishing trawls
A review of recent studies on the life history and ecology of European cephalopods with emphasis on species with the greatest commercial fishery and culture potential.
With the depletion of many commercial fish stocks and an increasing demand for marine protein for human
consumption, cephalopods have become more important as a fishery resource. In EU waters, cephalopod stocks
are not routinely assessed and exploitation of these species by large-scale fisheries is largely unregulated. For
sustainable exploitation, adequate assessment and scientifically-supported management strategies are needed.
However, there is still a lack of data on stock status and inadequate knowledge of the life history and ecology of
these species. The present review examined more than 200 scientific articles, on life history and ecology of
European cephalopods, published since 2013. It describes recent contributions to knowledge in the context of
previously identified research priorities, along with recent advances towards sustainable fishing and aquaculture.
It also identifies outstanding knowledge gaps. While some priority areas, such as the development of the species
identification guides and evaluation of climate change impacts on cephalopods, have seen significant advances,
other challenges remain for the future. These include monitoring of the life history traits and fishery status for the
main commercially exploited species in the area, implementation of improved species identification methods
during scientific surveys and fisheries monitoring, development of tools to identify stock units, and the study of
the environmental and anthropogenic impacts on the stocks of cephalopods inhabiting European waters.S
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
- …