Tachyon Tunnelling in D-brane-anti-D-brane

Using the tachyon DBI action proposal for the effective theory of non-coincident D$_p$-brane-anti-D$_p$-brane system, we study the decay of this system in the tachyon channel. We assume that the branes separation is held fixed, i.e. no throat formation, and then find the bounce solution which describe the decay of the system from false to the true vacuum of the tachyon potential. We shall show that due to the non-standard form of the kinetic term in the effective action, the thin wall approximation for calculating the bubble nucleation rate gives a result which is independent of the branes separation. This unusual result might indicate that the true decay of this metastable system should be via a solution that represents a throat formation as well as the tachyon tunneling.Comment: 15 pages, 4 figures, Latex file, minor changes, reference adde

Resistive and magnetized accretion flows with convection

We considered the effects of convection on the radiatively inefficient accretion flows (RIAF) in the presence of resistivity and toroidal magnetic field. We discussed the effects of convection on transports of angular momentum and energy. We established two cases for the resistive and magnetized RIAFs with convection: assuming the convection parameter as a free parameter and using mixing-length theory to calculate convection parameter. A self-similar method was used to solve the integrated equations that govern the behavior of the presented model. The solutions showed that the accretion and rotational velocities decrease by adding the convection parameter, while the sound speed increases. Moreover, by using mixing-length theory to calculate convection parameter, we found that the convection can be important in RIAFs with magnetic field and resistivity.Comment: 7 pages, 3 figures, accepted by Ap&S

Development of a local dose-response relationship for osteoradionecrosis within the mandible

Purpose: Osteoradionecrosis (ORN) of the mandible is a severe complication following radiotherapy of the head and neck, but not all regions of the mandible may be equally at risk. Therefore our goal was to explore a local dose response relationship for subregions of the mandible. Materials and methods: All oropharyngeal cancer patients treated at our hospital between 2009 and 2016 were reviewed. Follow-up was cut-off at 3 years. For patients that developed ORN, the ORN volume was delineated on the planning CT. Each mandible was divided into 16 volumes of interest (VOIs) based on the location of the dental elements and the presence of ORN in each was scored. Generalized estimating equations were used to build a model for the probability of developing ORN in an element VOI. Results: Of the 219 included patients, 22 developed ORN in 89 element VOIs. Mean dose to the element VOI (odds ratio (OR) = 1.05 per Gy, 95% confidence interval (CI): (1.04,1.07)), pre-radiotherapy extractions of an element ipsilateral to element of interest (OR = 2.81, 95% CI: (1.12,7.05)), and smoking at start of radiotherapy (OR = 3.37, 95% CI: (1.29,8.78)) were significantly associated with an increased probability of ORN in the VOI. Conclusion: The developed dose-response model indicates that the probability of ORN varies within the mandible and strongly depends on the local dose, the location of extractions, and smoking.</p

Stirring Strongly Coupled Plasma

We determine the energy it takes to move a test quark along a circle of radius L with angular frequency w through the strongly coupled plasma of N=4 supersymmetric Yang-Mills (SYM) theory. We find that for most values of L and w the energy deposited by stirring the plasma in this way is governed either by the drag force acting on a test quark moving through the plasma in a straight line with speed v=Lw or by the energy radiated by a quark in circular motion in the absence of any plasma, whichever is larger. There is a continuous crossover from the drag-dominated regime to the radiation-dominated regime. In the crossover regime we find evidence for significant destructive interference between energy loss due to drag and that due to radiation as if in vacuum. The rotating quark thus serves as a model system in which the relative strength of, and interplay between, two different mechanisms of parton energy loss is accessible via a controlled classical gravity calculation. We close by speculating on the implications of our results for a quark that is moving through the plasma in a straight line while decelerating, although in this case the classical calculation breaks down at the same value of the deceleration at which the radiation-dominated regime sets in.Comment: 27 pages LaTex, 5 figure

Self-similar solutions of viscous and resistive ADAFs with thermal conduction

We have studied the effects of thermal conduction on the structure of viscous and resistive advection-dominated accretion flows (ADAFs). The importance of thermal conduction on hot accretion flow is confirmed by observations of hot gas that surrounds Sgr A$^*$ and a few other nearby galactic nuclei. In this research, thermal conduction is studied by a saturated form of it, as is appropriated for weakly-collisional systems. It is assumed the viscosity and the magnetic diffusivity are due to turbulence and dissipation in the flow. The viscosity also is due to angular momentum transport. Here, the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and $\alpha$-prescription is used for them. The govern equations on system have been solved by the steady self-similar method. The solutions show the radial velocity is highly subsonic and the rotational velocity behaves sub-Keplerian. The rotational velocity for a specific value of the thermal conduction coefficient becomes zero. This amount of conductivity strongly depends on magnetic pressure fraction, magnetic Prandtl number, and viscosity parameter. Comparison of energy transport by thermal conduction with the other energy mechanisms implies that thermal conduction can be a significant energy mechanism in resistive and magnetized ADAFs. This property is confirmed by non-ideal magnetohydrodynamics (MHD) simulations.Comment: 8 pages, 5 figures, accepted by Ap&S

Energy loss in a strongly coupled anisotropic plasma

We study the energy loss of a rotating infinitely massive quark moving, at constant velocity, through an anisotropic strongly-coupled N=4 plasma from holography. It is shown that, similar to the isotropic plasma, the energy loss of the rotating quark is due to either the drag force or radiation with a continuous crossover from drag-dominated regime to the radiation dominated regime. We find that the anisotropy has a significant effect on the energy loss of the heavy quark, specially in the crossover regime. We argue that the energy loss due to radiation in anisotropic media is less than the isotropic case. Interestingly this is similar to analogous calculations for the energy loss in weakly coupled anisotropic plasma.Comment: 26+1 pages, 10 figures, typos fixe

Use of data-mining to support real-world cost analyses: An example using HER2-positive breast cancer in Iran

INTRODUCTION: Patient registries play an important role in obtaining real-world evidence of the cost-effectiveness of treatments. However, their implementation is costly and sometimes infeasible in many middle-income countries (MICs). We explored the combination of data-mining and a large claims database to estimate the direct healthcare costs of HER2-positive breast cancer (BC) treatment in Iran and the fraction of total costs from trastuzumab use.METHOD: We performed a retrospective analysis of claims data from the Iran Social Security Organization, a health insurer which covers approximately 50%(~40 million) of the Iranian population, in the period of 21/03/2011-20/03/2014. A data-mining algorithm using R software and validated using patient dossiers in the Cancer Research Center identified 1295 patients and divided them into the three main HER2-positive breast cancer stages (early, loco-regional and advanced). A payer perspective was used to calculate the absolute and relative direc

Factors Affecting the Reluctance to Pursue Teaching as a Career from the Perspective of Students in the Sultanate of Oman: A mixed-approach Investigation

هدفت الدراسة الحالية إلى الكشف عن العوامل المؤثرة في عزوف الطلبة عن مهنة التدريس بسلطنة عمان. استخدمت الدراسة المنهج المختلط، حيث تم جمع البيانات الكمية من خلال مقياس العوامل المؤثرة على اختيار مهنة التدريس بعد تعريبه وتكييفه لمجتمع الدراسة المكون من طلبة الصفوف 10-12 (ن= 3455)، أما البيانات النوعية فقد تم جمعها من خلال مجموعات النقاش البؤرية مع طلبة هذه الصفوف (ن= 253). أشارت النتائج إلى أن العوامل المؤثرة في عزوف الطلبة عن مهنة التدريس تمحورت حول: صعوبة المهنة، وقلة حوافزها المادية، وتدني المكانة الاجتماعية لها مقارنة بالمهن الأخرى، بينما بينت نتائج مجموعات النقاش البؤرية وجود آراء إيجابية وسلبية للمهنة، ووجود تحديات أبرزها: صعوبة التعامل مع عدد كبير من الطلبة، وتوقف ترقيات المعلمين، وتعيين المعلمين بعيدا عن أماكن إقامتهم. كما بين أغلبية طلبة المدارس من الجنسين بأنه ليس لديهم الرغبة والاتجاه الإيجابي لاختيار التدريس كمهنة المستقبل. كما أشارت نتائج الدراسة المتعلقة بالفروق بين الجنسين إلى وجود فروق دالة إحصائيا لصالح الذكور في العزوف عن مهنة التدريس

An epoxide intermediate in glycosidase catalysis

Retaining glycoside hydrolases cleave their substrates through stereochemical retention at the anomeric position. Typically, this involves two-step mechanisms using either an enzymatic nucleophile via a covalent glycosyl enzyme intermediate or neighboring-group participation by a substrate-borne 2-acetamido neighboring group via an oxazoline intermediate; no enzymatic mechanism with participation of the sugar 2-hydroxyl has been reported. Here, we detail structural, computational, and kinetic evidence for neighboring-group participation by a mannose 2-hydroxyl in glycoside hydrolase family 99 endo-α-1,2-mannanases. We present a series of crystallographic snapshots of key species along the reaction coordinate: a Michaelis complex with a tetrasaccharide substrate; complexes with intermediate mimics, a sugar-shaped cyclitol β-1,2-aziridine and β-1,2-epoxide; and a product complex. The 1,2-epoxide intermediate mimic displayed hydrolytic and transfer reactivity analogous to that expected for the 1,2-anhydro sugar intermediate supporting its catalytic equivalence. Quantum mechanics/molecular mechanics modeling of the reaction coordinate predicted a reaction pathway through a 1,2-anhydro sugar via a transition state in an unusual flattened, envelope (E 3) conformation. Kinetic isotope effects (k cat/K M) for anomeric-2H and anomeric-13C support an oxocarbenium ion-like transition state, and that for C2-18O (1.052 ± 0.006) directly implicates nucleophilic participation by the C2-hydroxyl. Collectively, these data substantiate this unprecedented and long-imagined enzymatic mechanism