Holographic fermions in external magnetic fields

We study the Fermi level structure of 2+1-dimensional strongly interacting electron systems in external magnetic field using the AdS/CFT correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordstrom black hole. In the probe limit the magnetic system can be reduced to the non-magnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-"strange metal" phase transition. Next we compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. For dual fermions with a large charge, many different Fermi surfaces contribute and the Hall conductivity is quantized as expected for integer Quantum Hall Effect (QHE). At strong magnetic fields, as additional Fermi surfaces open up, new plateaus typical for the fractional QHE appear. The somewhat irregular pattern in the length of fractional QHE plateaus resemble the outcomes of experiments on thin graphite in a strong magnetic field. Finally, motivated by the absence of the sign problem in holography, we suggest a lattice approach to the AdS calculations of finite density systems.Comment: 34 pages, 14 figure

Роль протеиназ крови и их ингибиторов в механизмах противовирусной защиты

Досліджено наявність трипсиноподібних протеїназ та їх інгібіторів у донорській крові людини, промислових відходах одержання гаммаглобуліну, комерційних вітчизняних препаратах (імуноглобулін, інтерферон, герпетична та туляремійна вакцини), у закордонних препаратах (протигрипозні вакцини — ''Інфлувак'', ''Ваксігрип'', ''Флюарікс'', вакцина проти гепатиту А — ''Аваксім''; препарати з крові — ''Фраксіпарин'' і ''Солкосерил''). З промислових відходів одержання гаммаглобуліну людини виділено ізоформу інгібітора трипсиноподібних протеїназ, що має захисну дію при зараженні експериментальних тварин смертельною дозою вірусу грипу A/PR/8/34 (А/Н1N1).The presence of the trypsin-like proteinases and their inhibitors in the blood of human donors, in industrial wastes of gamma-globulin, in commercial domestic preparations (immunoglobulin, interferon, vaccine for herpes and tularemia), in foreign preparations (anti-influenza vaccine — Influvac, Vaxigrір, Fluarix, vaccines for hepatitis A — Avaxim; preparations from blood — Fraxiparine, Solcoseryl) is studied. From the industrial wastes of the gamma-globulin production, an isoform of trypsin-like proteinases with protective activity at infection of experimental animals with a lethal dose of A/PR/8/34 (А/Н1N1) grippe is selected

Transport efficiency in topologically disordered networks with environmentally induced diffusion

We study transport in topologically disordered networks that are subjected to an environment that induces classical diffusion. The dynamics is phenomenologically described within the framework of the recently introduced quantum stochastic walk, allowing to study the crossover between coherent transport and purely classical diffusion. We find that the coupling to the environment removes all effects of localization and quickly leads to classical transport. Furthermore, we find that on the level of the transport efficiency, the system can be well described by reducing it to a two-node network (a dimer).Comment: 10 pages, 7 figure

Perceptions of surgical specialists in general surgery, orthopaedic surgery, urology and gynaecology on teaching endoscopic surgery in The Netherlands

BACKGROUND: Specific training in endoscopic skills and procedures has become a necessity for profession with embedded endoscopic techniques in their surgical palette. Previous research indicates endoscopic skills training to be inadequate, both from subjective (resident interviews) and objective (skills measurement) viewpoint. Surprisingly, possible shortcomings in endoscopic resident education have never been measured from the perspective of those individuals responsible for resident training, e.g. the program directors. Therefore, a nation-wide survey was conducted to inventory current endoscopic training initiatives and its possible shortcomings among all program directors of the surgical specialties in the Netherlands. METHODS: Program directors for general surgery, orthopaedic surgery, gynaecology and urology were surveyed using a validated 25-item questionnaire. RESULTS: A total of 113 program directors responded (79%). The respective response percentages were 73.6% for general surgeons, 75% for orthopaedic surgeon, 90.9% for urologists and 68.2% for gynaecologists. According to the findings, 35% of general surgeons were concerned about whether residents are properly skilled endoscopically upon completion of training. Among the respondents, 34.6% were unaware of endoscopic training initiatives. The general and orthopaedic surgeons who were aware of these initiatives estimated the number of training hours to be satisfactory, whereas the urologists and gynaecologists estimated training time to be unsatisfactory. Type and duration of endoscopic skill training appears to be heterogeneous, both within and between the specialties. Program directors all perceive virtual reality simulation to be a highly effective training method, and a multimodality training approach to be key. Respondents agree that endoscopic skills education should ideally be coordinated according to national consensus and guidelines. CONCLUSIONS: A delicate balance exists between training hours and clinical working hours during residency. Primarily, a re-allocation of available training hours, aimed at core-endoscopic basic and advanced procedures, tailored to the needs of the resident and his or her phase of training is in place. The professions need to define which basic and advanced endoscopic procedures are to be trained, by whom, and by what outcome standards. According to the majority of program directors, virtual reality (VR) training needs to be integrated in procedural endoscopic training course

Augmented versus Virtual Reality Laparoscopic Simulation: What Is the Difference?: A Comparison of the ProMIS Augmented Reality Laparoscopic Simulator versus LapSim Virtual Reality Laparoscopic Simulator

BACKGROUND: Virtual reality (VR) is an emerging new modality for laparoscopic skills training; however, most simulators lack realistic haptic feedback. Augmented reality (AR) is a new laparoscopic simulation system offering a combination of physical objects and VR simulation. Laparoscopic instruments are used within an hybrid mannequin on tissue or objects while using video tracking. This study was designed to assess the difference in realism, haptic feedback, and didactic value between AR and VR laparoscopic simulation. METHODS: The ProMIS AR and LapSim VR simulators were used in this study. The participants performed a basic skills task and a suturing task on both simulators, after which they filled out a questionnaire about their demographics and their opinion of both simulators scored on a 5-point Likert scale. The participants were allotted to 3 groups depending on their experience: experts, intermediates and novices. Significant differences were calculated with the paired t-test. RESULTS: There was general consensus in all groups that the ProMIS AR laparoscopic simulator is more realistic than the LapSim VR laparoscopic simulator in both the basic skills task (mean 4.22 resp. 2.18, P <0.000) as well as the suturing task (mean 4.15 resp. 1.85, P <0.000). The ProMIS is regarded as having better haptic feedback (mean 3.92 resp. 1.92, P <0.000) and as being more useful for training surgical residents (mean 4.51 resp. 2.94, P <0.000). CONCLUSIONS: In comparison with the VR simulator, the AR laparoscopic simulator was regarded by all participants as a better simulator for laparoscopic skills training on all tested feature

Virtual reality training for endoscopic surgery: voluntary or obligatory?

INTRODUCTION: Virtual reality (VR) simulators have been developed to train basic endoscopic surgical skills outside of the operating room. An important issue is how to create optimal conditions for integration of these types of simulators into the surgical training curriculum. The willingness of surgical residents to train these skills on a voluntary basis was surveyed. METHODS: Twenty-one surgical residents were given unrestricted access to a VR simulator for a period of four months. After this period, a competitive element was introduced to enhance individual training time spent on the simulator. The overall end-scores for individual residents were announced periodically to the full surgical department, and the winner was awarded a prize. RESULTS: In the first four months of study, only two of the 21 residents (10%) trained on the simulator, for a total time span of 163 minutes. After introducing the competitive element the number of trainees increased to seven residents (33%). The amount of training time spent on the simulator increased to 738 minutes. CONCLUSIONS: Free unlimited access to a VR simulator for training basic endoscopic skills, without any form of obligation or assessment, did not motivate surgical residents to use the simulator. Introducing a competitive element for enhancing training time had only a marginal effect. The acquisition of expensive devices to train basic psychomotor skills for endoscopic surgery is probably only effective when it is an integrated and mandatory part of the surgical curriculu

Методические основы оценки качества обслуживания в туристическом бизнесе

Проблема определения качества обслуживания в туристическом бизнесе является актуальной, т.к. туристическая деятельность является приоритетным направлением развития в АР Крым. Рассмотрена методика определения качества обслуживания туристов с учетом специфики функционирования туристской сферы.Проблема визначення якості обслуговування у туристичному бізнесі є актуальною, тому що туристична діяльність є пріоритетним напрямком розвитку в АР Крим. Розглянута методика визначення якості обслуговування туристів з умовою специфіки функціонування туристичної сфери.The problem of quality service in the tourist's business is very actuality, because the tourist's activity is the priority directions of development in the Crimea. Given the method of definition of the quality service in the tourist's business with registration of specific tourism sphere

Distributed versus massed training: efficiency of training psychomotor skills

Virtual reality simulators have shown to be valid and useful tools for training psychomotor skills for endoscopic surgery. Discussion arises how to integrate these simulators into the surgical training curriculum. Distributed training is referred to as short training periods, with rest periods in between. Massed training is training in continuous and longer training blocks. This study investigates the difference between distributed and massed training on the initial development and retention of psychomotor skills on a virtual reality simulator. Four groups of eight medical students lacking any experience in endoscopic training were created. Two groups trained in a distributed fashion, one group trained in a massed fashion and the last group not at all (control group). All performed a post-test immediately after finishing their training schedule. Two months after this test a second post- test was performed. The one-way analysis of variance (ANOVA) with Post-Hoc test Tukey-Bonferoni was used to determine differences in mean scores between the four groups, whereas a pvalue ≤0.05 was considered to be statistically significant. Distributed training resulted in higher scores and a better retention of relevant psychomotor skills. Distributed as well as massed training resulted in better scores and retention of skills than no training at all. Our study clearly shows that distributed training yields better results in psychomotor endoscopic skills. Therefore, in order to train as efficient as possible, training programs should be (re)-programmed accordingly