4,230 research outputs found
Electronic Cooling via Interlayer Coulomb Coupling in Multilayer Epitaxial Graphene
In van der Waals bonded or rotationally disordered multilayer stacks of
two-dimensional (2D) materials, the electronic states remain tightly confined
within individual 2D layers. As a result, electron-phonon interactions occur
primarily within layers and interlayer electrical conductivities are low. In
addition, strong covalent in-plane intralayer bonding combined with weak van
der Waals interlayer bonding results in weak phonon-mediated thermal coupling
between the layers. We demonstrate here, however, that Coulomb interactions
between electrons in different layers of multilayer epitaxial graphene provide
an important mechanism for interlayer thermal transport even though all
electronic states are strongly confined within individual 2D layers. This
effect is manifested in the relaxation dynamics of hot carriers in ultrafast
time-resolved terahertz spectroscopy. We develop a theory of interlayer Coulomb
coupling containing no free parameters that accounts for the experimentally
observed trends in hot-carrier dynamics as temperature and the number of layers
is varied.Comment: 54 pages, 15 figures, uses documentclass{achemso}, M.T.M. and J.R.T.
contributed equally to this wor
Referral for coronary artery revascularization procedures after diagnostic coronary angiography: Evidence for gender bias?
AbstractObjectives. We sought to determine whether there is a gender bias in the selection of patients for coronary revascularization once the severity of the underlying coronary artery disease has been established with angiography.Background. It has been suggested that women with coronary artery disease are less likely to be referred for coronary angiography and coronary artery bypass surgery than men. Whether such a referral bias for revascularization procedures, including coronary angioplasty, is present once angiography has been performed is not clear.Methods. We retrospectively analyzed 22,795 patients with suspected coronary artery disease who underwent coronary angiography between 1981 and 1991 and compared the numbers of women and men who underwent either coronary artery bypass surgery or coronary angioplasty within 30 days of coronary angiography.Results. Angiography revealed significant (one-vessel or more) disease in 15,455 patients (52% of women, 76% of men). Despite worse symptoms, women had less extensive coronary disease than men as judged by the number of vessels diseased. Women were also more likely to have other co-morbid diseases. An equal proportion of women (54%) and men underwent revascularization procedures. After adjustment for baseline differences and age, differences in the two individual revascularization strategies were very small: More women tended to have coronary angioplasty ([absolute difference ± 1 SD] + 3.3 ± 0.7%, p < 0.0001), but fewer had coronary artery bypass surgery than men (−2.5 ± 0.8%, p = 0.003). When the two revascularization strategies were considered together, there was no significant gender difference in overall adjusted use of revascularization (+0.8 ± 0.9%, p = 0.41).Conclusions. Once diagnostic coronary angiography had been performed, no major differences in the overall utilization of revascularization procedures were noted for women compared with men
Boundary Layer Transition Flight Experiment Overview and In-Situ Measurements
In support of the Boundary Layer Transition Flight Experiment (BLTFE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for the flights of STS-119 and STS-128. Additional instrumentation was also installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLTFE Project, including the project history, organizations involved, and motivations for the flight experiment. Significant efforts were made to place the protuberance at an appropriate location on the Orbiter and to design the protuberance to withstand the expected environments. Efforts were also extended to understand the as-fabricated shape of the protuberance and the thermal protection system tile configuration surrounding the protuberance. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that predictions for boundary layer transition onset time closely match the flight data, while predicted temperatures were significantly higher than observed flight temperatures
The VLTI / PIONIER near-infrared interferometric survey of southern T Tauri stars. I. First results
Context : The properties of the inner disks of bright Herbig AeBe stars have
been studied with near infrared (NIR) interferometry and high resolution
spectroscopy. The continuum and a few molecular gas species have been studied
close to the central star; however, sensitivity problems limit direct
information about the inner disks of the fainter T Tauri stars.
Aims : Our aim is to measure some of the properties of the inner regions of
disks surrounding southern T Tauri stars.
Methods : We performed a survey with the PIONIER recombiner instrument at
H-band of 21 T Tauri stars. The baselines used ranged from 11 m to 129 m,
corresponding to a maximum resolution of 3mas (0.45 au at 150 pc).
Results : Thirteen disks are resolved well and the visibility curves are
fully sampled as a function of baseline in the range 45-130 m for these 13
objects. A simple qualitative examination of visibility profiles allows us to
identify a rapid drop-off in the visibilities at short baselines in 8 resolved
disks. This is indicative of a significant contribution from an extended
contribution of light from the disk. We demonstrate that this component is
compatible with scattered light, providing strong support to a prediction made
by Pinte et al. (2008). The amplitude of the drop-off and the amount of dust
thermal emission changes from source to source suggesting that each disk is
different. A by-product of the survey is the identification of a new
milli-arcsec separation binary: WW Cha. Spectroscopic and interferometric data
of AK Sco have also been fitted with a binary and disk model.
Conclusions : Visibility data are reproduced well when thermal emission and
scattering form dust are fully considered. The inner radii measured are
consistent with the expected dust sublimation radii. Modelling of AK Sco
suggests a likely coplanarity between the disk and the binary's orbital planeComment: 19 pages, 11 figure
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The structure of blocks with a Klein four defect group
We prove Erdmann’s conjecture [16] stating that every block with a Klein four defect group has a simple module with trivial source, and deduce from this that Puig’s finiteness conjecture holds for source algebras of blocks with a Klein four defect group. The proof uses the classification of finite simple groups
Dilepton-tagged jets in relativistic nucleus-nucleus collisions: A case study
We study the A+B -> l+ l- + jet +X process in nucleus-nucleus collisions at
relativistic energies. The dilepton as well as the jet will pass through the
matter produced in such collisions. The recoiling dilepton will carry
information about the kinematical features of the jet, and will thus prove to
be a very effective tool in isolating in-medium effects such as energy-loss and
fragmentation function modifications. We estimate the contributions due to
correlated charm and bottom decay and we identify a window where they are small
as compared to pairs from the NLO Drell-Yan process.Comment: 7 pages, 9 figures Two figures modified, references adde
Initiation of a critical pathway for pancreaticoduodenectomy at an academic institution -- the first step in multi-disciplinary team building
Objective: This study was designed to identify quantifiable parameters to track performance improvements brought about by the implementation of a critical pathway for complex alimentary tract surgery.
Background: Pancreaticoduodenectomy (PD) is a complex general surgical procedure performed in varying numbers at many academic institutions. Originally associated with significant perioperative morbidity and mortality, multiple studies have now shown that this operation can be performed quite safely at high volume institutions that develop a particular expertise. Critical pathways are one of the key tools used to achieve consistently excellent outcomes as these institutions. It remains to be determined if implementation of a critical pathway at an academic institution with prior moderate experience with PD will result in performance gains and improved outcomes.
Methods: Between January 1, 2004 and October 15, 2006 135 patients underwent PD, 44 before the implementation of a critical pathway on October 15, 2005, and 91 after. Perioperative and postoperative parameters were analyzed retrospectively to identify those that could be used to track performance improvement and outcomes. Key aspects of the pathway include spending the night of surgery in the intensive care unit with careful attention to fluid balance, early mobilization on post-operative day one, aggressive early removal of encumbrances such as nasogastric tubes and urinary catheters, early post-operative feeding, and targeting discharge for postoperative day 6 or 7.
Results: The pre- and post-pathway implementation groups were not statistically different with regards to age, sex, race, or pathology (malignant versus benign). Perioperative mortality, operative blood loss, and number of transfused units of packed red blood cells were also similar. As compared to the pre-pathway group, the post-pathway group had a significantly shorter postoperative length of stay (13 versus 7 days, P ≤ 0.0001), operative time (435 ± 14 minutes versus 379 ± 12 minutes, P ≤ 0.0001), and in room non-operative time (95 ± 4 minutes versus 76 ± 2 minutes, P ≤ 0.0001). Total hospital charges were significantly reduced from 32,490 versus 4883 (P ≤ 0.0001) after pathway implementation. Postoperative complication rates remained constant (44% pre-pathway versus 37% after, P = NS). Readmission rates were not negatively affected by the reduction in length of stay, with a 7% readmission rate prior to implementation and a 7.7% rate after implementation.
Conclusion: Implementation of a critical pathway for a complex procedure can be demonstrated to improve short-term outcomes at an academic institution. This improvement can be quantified and tracked and has implications for better utilization of resources (greater OR and hospital bed availability) and overall cost containment. With a very conservative estimate of 75 pancreaticoduodenectomies per year by this group, this translates to a savings of 450 hospital days and over $8,550,000 in hospital charges on an annual basis. As we enter the pay for performance era, institutions will be required to generate such data in order to retain patient volumes, attract new patients, and receive incentive payments for high quality services rendered
Reduction of the Three Dimensional Schrodinger Equation for Multilayered Films
In this paper, we present a method for reducing the three dimensional
Schrodinger equation to study confined metallic states, such as quantum well
states, in a multilayer film geometry. While discussing some approximations
that are employed when dealing with the three dimensionality of the problem, we
derive a one dimensional equation suitable for studying such states using an
envelope function approach. Some applications to the Cu/Co multilayer system
with regard to spin tunneling/rotations and angle resolved photoemission are
discussed.Comment: 14 pages, 1 figur
Evaluating 'Prefer not to say' Around Sensitive Disclosures
As people's offline and online lives become increasingly entwined, the sensitivity of personal information disclosed online is increasing. Disclosures often occur through structured disclosure fields (e.g., drop-down lists). Prior research suggests these fields may limit privacy, with non-disclosing users being presumed to be hiding undesirable information. We investigated this around HIV status disclosure in online dating apps used by men who have sex with men. Our online study asked participants (N=183) to rate profiles where HIV status was either disclosed or undisclosed. We tested three designs for displaying undisclosed fields. Visibility of undisclosed fields had a significant effect on the way profiles were rated, and other profile information (e.g., ethnicity) could affect inferences that develop around undisclosed information. Our research highlights complexities around designing for non-disclosure and questions the voluntary nature of these fields. Further work is outlined to ensure disclosure control is appropriately implemented around online sensitive information disclosures
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