Probing the Structure of the Pomeron

We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark--pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron.We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of the pomeron to quarks is viable for a harder quark--pomeron form factor, as is a model based on the leading-twist operator contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for the determination of the partonic structure of the pomeron

XMM-Newton Spectra of Intermediate-Mass Black Hole Candidates: Application of a Monte-Carlo Simulated Model

We present a systematic spectral analysis of six ultraluminous X-ray sources (NGC1313 X-1/X-2, IC342 X-1, HoIX X-1, NGC5408 X-1 and NGC3628 X-1) observed with XMM-Newton Observatory. These extra-nuclear X-ray sources in nearby late-type galaxies have been considered as intermediate-mass black hole candidates. We have performed Monte-Carlo simulations of Comptonized multi-color black-body accretion disks. This unified and self-consistent spectral model assumes a spherically symmetric, thermal corona around each disk and accounts for the radiation transfer in the Comptonization. We find that the model provides satisfactory fits to the XMM-Newton spectra of thesources. The characteristic temperatures of the accretion disks (T_in), for example, are in the range of ~ 0.05-0.3 keV, consistent with the intermediate-mass black hole interpretation. We find that the black hole mass is typically about a few times 10^3 M_\odot and has an accretion rate ~ 10^{-6} - 10^{-5} M_\odot yr^{-1}. For the spectra considered here, we find that the commonly used multi-color black-body accretion disk model with an additive power law component, though not physical, provides a good mathematical approximation to the Monte-Carlo simulated model. However, the latter model provides additional constraints on the properties of the accretion systems, such as the disk inclination angles and corona optical depths.Comment: 23 pages, 4 figures, 5 tables. ApJ accepted, July 2004 issu

Demographic characteristics of exploited tropical lutjanids: a comparative analysis

Demographic parameters from seven exploited coral reef lutjanid species were compared as a case study of the implications of intrafamily variation in life histories for multispecies harvest management. Modal lengths varied by 4 cm among four species (Lutjanus fulviflamma, L. vitta, L. carponotatus, L. adetii), which were at least 6 cm smaller than the modal lengths of the largest species (L. gibbus, Symphorus nematophorus, Aprion virescens). Modal ages, indicating ages of full selection to fishing gear, were 10 years or less for all species, but maximum ages ranged from 12 (L. gibbus) to 36 years (S. nematophorus). Each species had a unique growth pattern, with differences in length-at-age and mean asymptotic fork length (L∞), but smaller species generally grew fast during the first 1–2 years of life and larger species grew more slowly over a longer period. Total mortality rates varied among species; L. gibbus had the highest mortality and L. fulviflamma, the lowest mortality. The variability in life history strategies of these tropical lutjanids makes generalizations about lutjanid life histories difficult, but the fact that all seven had characteristics that would make them particularly vulnerable to fishing indicates that harvest of tropical lutjanids should be managed with caution

A Multi-Core Numerical Framework for Characterizing Flow in Oil Reservoirs

Presented at the SCS Spring Simulation Multi-Conference – SpringSim 2011, April 4-7, 2011 – Boston, USA Awarded Best Paper in the 19th High Performance Computing Symposium and Best Overall Paper at SpringSim 2011.This paper presents a numerical framework that enables scalable, parallel execution of engineering simulations on multi-core, shared memory architectures. Distribution of the simulations is done by selective hash-tabling of the model domain which spatially decomposes it into a number of orthogonal computational tasks. These tasks, the size of which is critical to optimal cache blocking and consequently performance, are then distributed for execution to multiple threads using the previously presented task management algorithm, H-Dispatch. Two numerical methods, smoothed particle hydrodynamics (SPH) and the lattice Boltzmann method (LBM), are discussed in the present work, although the framework is general enough to be used with any explicit time integration scheme. The implementation of both SPH and the LBM within the parallel framework is outlined, and the performance of each is presented in terms of speed-up and efficiency. On the 24-core server used in this research, near linear scalability was achieved for both numerical methods with utilization efficiencies up to 95%. To close, the framework is employed to simulate fluid flow in a porous rock specimen, which is of broad geophysical significance, particularly in enhanced oil recovery

Virtual Delivery of Stress Management and Resiliency Training (SMART) During the COVID-19 Pandemic to Hematology/Oncology Fellows: A Pilot Study

Introduction: Medical trainees experience a high degree of stress that predisposes them to burnout. This pilot study tested a scalable approach to deliver a validated resilience program (Stress Management and Resiliency Training (SMART)) among Hematology/Oncology fellows at an academic medical center. Methods: This was a mixed-methods, prospective, single-arm clinical trial involving Hematology/Oncology fellows at Mayo Clinic in Rochester, MN, USA. Four one-hour training sessions were conducted virtually with 26 fellows. Stress, burnout, and emotional resilience were measured at baseline, three months, and six months post-intervention using the Perceived Stress Scale (PSS-10), Maslach Burnout Inventory (MBI-HSS), and Connor-Davidson Resilience Scale (CD-RISC2). Changes in mean scores were assessed using paired t-tests. Feasibility and acceptability data were obtained during a virtual focus group. Results: Statistically significant improvements in mean stress (p = 0.004) and professional achievement (p \u3c 0.001) were seen at three months post-intervention. At six months post-intervention, mean stress (p \u3c 0.001) and professional achievement (p = 0.032) continued to improve, while improvements in emotional exhaustion (p = 0.001) and depersonalization (p \u3c 0.001) also became significant. Focus group participants found the program beneficial and reported improved stress and work performance as a result of participation. Conclusion: Virtual implementation of the SMART program is feasible and resulted in improvements in stress and burnout. Focus group participants found the training beneficial, reporting lower stress and improved work performance

Investigation of discrepancies in satellite rainfall estimates over Ethiopia

Tropical Applications of Meteorology Using Satellite and Ground-Based Observations (TAMSAT) rainfall estimates are used extensively across Africa for operational rainfall monitoring and food security applications; thus, regional evaluations of TAMSAT are essential to ensure its reliability. This study assesses the performance of TAMSAT rainfall estimates, along with the African Rainfall Climatology (ARC), version 2; the Tropical Rainfall Measuring Mission (TRMM) 3B42 product; and the Climate Prediction Center morphing technique (CMORPH), against a dense rain gauge network over a mountainous region of Ethiopia. Overall, TAMSAT exhibits good skill in detecting rainy events but underestimates rainfall amount, while ARC underestimates both rainfall amount and rainy event frequency. Meanwhile, TRMM consistently performs best in detecting rainy events and capturing the mean rainfall and seasonal variability, while CMORPH tends to overdetect rainy events. Moreover, the mean difference in daily rainfall between the products and rain gauges shows increasing underestimation with increasing elevation. However, the distribution in satellite–gauge differences demon- strates that although 75% of retrievals underestimate rainfall, up to 25% overestimate rainfall over all eleva- tions. Case studies using high-resolution simulations suggest underestimation in the satellite algorithms is likely due to shallow convection with warm cloud-top temperatures in addition to beam-filling effects in microwave- based retrievals from localized convective cells. The overestimation by IR-based algorithms is attributed to nonraining cirrus with cold cloud-top temperatures. These results stress the importance of understanding re- gional precipitation systems causing uncertainties in satellite rainfall estimates with a view toward using this knowledge to improve rainfall algorithms

90-Day all-cause mortality can be predicted following a total knee replacement:an international, network study to develop and validate a prediction model

Purpose: The purpose of this study was to develop and validate a prediction model for 90-day mortality following a total knee replacement (TKR). TKR is a safe and cost-effective surgical procedure for treating severe knee osteoarthritis (OA). Although complications following surgery are rare, prediction tools could help identify high-risk patients who could be targeted with preventative interventions. The aim was to develop and validate a simple model to help inform treatment choices. Methods: A mortality prediction model for knee OA patients following TKR was developed and externally validated using a US claims database and a UK general practice database. The target population consisted of patients undergoing a primary TKR for knee OA, aged ≥ 40 years and registered for ≥ 1 year before surgery. LASSO logistic regression models were developed for post-operative (90-day) mortality. A second mortality model was developed with a reduced feature set to increase interpretability and usability. Results: A total of 193,615 patients were included, with 40,950 in The Health Improvement Network (THIN) database and 152,665 in Optum. The full model predicting 90-day mortality yielded AUROC of 0.78 when trained in OPTUM and 0.70 when externally validated on THIN. The 12 variable model achieved internal AUROC of 0.77 and external AUROC of 0.71 in THIN. Conclusions: A simple prediction model based on sex, age, and 10 comorbidities that can identify patients at high risk of short-term mortality following TKR was developed that demonstrated good, robust performance. The 12-feature mortality model is easily implemented and the performance suggests it could be used to inform evidence based shared decision-making prior to surgery and targeting prophylaxis for those at high risk. Level of evidence: III.</p

Illusions of gunk

The possibility of gunk has been used to argue against mereological nihilism. This paper explores two responses on the part of the microphysical mereological nihilist: (1) the contingency defence, which maintains that nihilism is true of the actual world; but that at other worlds, composition occurs; (2) the impossibility defence, which maintains that nihilism is necessary true, and so gunk worlds are impossible. The former is argued to be ultimately unstable; the latter faces the explanatorily burden of explaining the illusion that gunk is possible. It is argued that we can discharge this burden by focussing on the contingency of the microphysicalist aspect of microphysical mereological nihilism. The upshot is that gunk-based arguments against microphysical mereological nihilism can be resisted