Black Hole Entropy without Brick Walls

We present evidence which confirms a suggestion by Susskind and Uglum regarding black hole entropy. Using a Pauli-Villars regulator, we find that 't Hooft's approach to evaluating black hole entropy through a statistical-mechanical counting of states for a scalar field propagating outside the event horizon yields precisely the one-loop renormalization of the standard Bekenstein-Hawking formula, S=\A/(4G). Our calculation also yields a constant contribution to the black hole entropy, a contribution associated with the one-loop renormalization of higher curvature terms in the gravitational action.Comment: 15 pages, plain LaTex minor additions including some references; version accepted for publicatio

Two investigations in quantum gravity

Two aspects of quantum field theory in curved spacetimes are discussed. First, the limits for applicability of the equivalence principle in the context of low energy effective field theories is considered. In particular, we find three classes of higher-derivative interactions for the gravitational and electromagnetic fields which produce dispersive photon propagation. One of these classes of interactions also produces birefringent propagation. This result is illustrated by calculating the energy-dependent contribution to the bending of light. In the second part, the divergences appearing in statistical black hole entropy are analysed. Using a Pauli-Villars regulator, it is shown that 't Hooft's approach to evaluating black hole entropy through a statistical-mechanical counting of states for a scalar field propagating outside the event horizon yields precisely the one-loop renormalization of the standard Bekenstein-Hawking formula, $S = { cal A}/(4G),$ where $cal A$ is the black hole area. The calculation also yields a constant contribution to the black hole entropy, which may be associated with the one-loop renormalization of certain higher curvature terms in the gravitational action. The calculation of black hole entropy is done for a Schwarzschild black hole as well as for a Reissner-Nordstrom black hole

Association Between Low-Molecular-Weight Heparin and Risk of Bleeding Among Hemodialysis Patients: A Retrospective Cohort Study

Background: Low-molecular-weight heparins (LMWH) replaced unfractionated heparin (UFH) in multiple indications. Although LMWH efficacy in hemodialysis was demonstrated through multiple studies, their safety remains controversial. The potential bioaccumulation in patients undergoing chronic hemodialysis raised the question of bleeding risk among this population. Objective: The aim of this study was to evaluate bleeding risk among patients with chronic hemodialysis receiving LMWH or UFH for the extracorporeal circuit anticoagulation. Design: We conducted a retrospective cohort study on data extracted from the Régie de l’assurance maladie du Québec (RAMQ) and Med-Echo databases from January 2007 to March 2013. Setting: Twenty-one hemodialysis centers in the province of Québec, Canada. Patients: Chronic hemodialysis patients. Measurements: Bleeding risk evaluated by proportional Cox model for time-dependent exposure using demographics, comorbidities, and drug use as covariates. Methods: Minor, major, and total bleeding events identified using International Classification of Diseases, Ninth Revision ( ICD-9 )/ International Classification of Diseases, Tenth Revision ( ICD-10 ) codes in the RAMQ and Med-Echo databases. Exposure status to LMWH or UFH was collected through surveys at the facility level. Results: We identified 5322 prevalent and incident patients with chronic hemodialysis. The incidence rate for minor, major, and total bleeding was 9.45 events/1000 patient-year (95% confidence interval [CI]: 7.61-11.03), 24.18 events/1000 patient-year (95% CI: 21.52-27.08), and 32.88 events/1000 patient-year (95% CI: 29.75-36.26), respectively. We found similar risks of minor adjusted hazard ratio (HR: 1.04; 95% CI: 0.68-1.61), major (HR: 0.83; 95% CI: 0.63-1.10), and total bleeding (HR: 0.90; 95% CI: 0.72-1.14) when comparing LMWH with UFH. Limitations: Potential misclassification of patients’ exposure status and possible underestimation of minor bleeding risk. Conclusion: LMWH was not associated with a higher minor, major, or total bleeding risk. LMWH did not increase the risk of bleeding compared with UFH for the extracorporeal circuit anticoagulation in hemodialysis. The convenience of use and predictable effect made LMWH a suitable alternative to UFH in hemodialysis

Safety of low-molecular-weight heparin compared to unfractionated heparin in hemodialysis: a systematic review and meta-analysis

Abstract Background Low molecular weight heparins (LMWH) have been extensively studied and became the treatment of choice for several indications including pulmonary embolism. While their efficacy in hemodialysis is considered similar to unfractionated heparin (UFH), their safety remains controversial mainly due to a risk of bioaccumulation in patients with renal impairment. The aim of this systematic review was to evaluate the safety of LMWH when compared to UFH for extracorporeal circuit (ECC) anticoagulation. Methods We used Pubmed, Embase, Cochrane central register of controlled trials, Trip database and NICE to retrieve relevant studies with no language restriction. We looked for controlled experimental trials comparing LMWH to UFH for ECC anticoagulation among end-stage renal disease patients undergoing chronic hemodialysis. Studies were kept if they reported at least one of the following outcomes: bleeding, lipid profile, cardiovascular events, osteoporosis or heparin-induced thrombocytopenia. Two independent reviewers conducted studies selection, quality assessment and data extraction with discrepancies solved by a third reviewer. Relative risk and 95% CI was calculated for dichotomous outcomes and mean weighted difference (MWD) with 95% CI was used to pool continuous variables. Results Seventeen studies were selected as part of the systematic. The relative risk for total bleeding was 0.76 (95% CI 0.26–2.22). The WMD calculated for total cholesterol was −28.70 mg/dl (95% CI -51.43 to −5.98), a WMD for triglycerides of −55.57 mg/dl (95% CI -94.49 to −16.66) was estimated, and finally LDL-cholesterol had a WMD of −14.88 mg/dl (95% CI -36.27 to 6.51). Conclusions LMWH showed to be at least as safe as UFH for ECC anticoagulation in chronic hemodialysis. The limited number of studies reporting on osteoporosis and HIT does not allow any conclusion for these outcomes. Larger studies are needed to evaluate properly the safety of LMWH in chronic hemodialysis

Supplementary_table_1 – Supplemental material for Association Between Low-Molecular-Weight Heparin and Risk of Bleeding Among Hemodialysis Patients: A Retrospective Cohort Study

<p>Supplemental material, Supplementary_table_1 for Association Between Low-Molecular-Weight Heparin and Risk of Bleeding Among Hemodialysis Patients: A Retrospective Cohort Study by Hind H. Lazrak, Emilie René, Naoual Elftouh and Jean-Philippe Lafrance in Canadian Journal of Kidney Health and Disease</p