Local field effect as a function of pulse duration

In this note we give semiclassical consideration of the role of pulse duration in observation of local field effects in the regime of optical switching. We show that the main parameter governing local field influence is the ratio of peak Rabi frequency corresponding to medium inversion and Lorentz frequency of the medium. To obtain significant local field effect, this parameter should be near unity that is valid only for long enough pulses. We also discuss the role of relaxation and pulse shape in this processes.Comment: 4 pages, 3 figure

Non-resonant terahertz field enhancement in periodically arranged nanoslits

We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength k of the impinging radiation. Two regimes of operation are found. First, when the grating period, frequency-independent enhancement is observed, accompanied by a very high transmission approaching unity. With high accuracy, this enhancement equals the ratio of P to the slit width w. Second, when the grating period approaches the THz wavelength but before entering the Raleigh-Wood anomaly, the field enhancement in nanoslit stays close to that in a single isolated slit, i.e., the well-known inversefrequency dependence. Both regimes are non-resonant and thus extremely broadband. The results are obtained by the microscopic Drude-Lorentz model taking into account retardation processes in the metal film and validated by the finite difference frequency domain method. We expect sensor and modulation applications of the predicted giant broadband field enhancement

Влияние плотности фотонных состояний на сдвиг Лэмба в плазме

A possible effect of the low photon density of states in plasma on the Lamb shift is analysed. It is found that because of a significant contribution of high-energy virtual photons to the Lamb shift, its modification in plasma does not exceed 1 % with respect to vacuum even at electron concentrations as high as 1022 cm–3. This behavior results from an asymptotic tendency of plasma properties to vacuum ones at an unlimited frequency growth.Исследовано возможное влияние пониженной плотности фотонных состояний в плазме на сдвиг Лэмба и установлено, что вследствие значительного вклада в сдвиг Лэмба высокоэнергетических виртуальных фотонов даже при концентрациях электронов порядка 1022 см–3 относительное изменение сдвига Лэмба в плазме в сравнении с вакуумом не превышает 1 %. Такое поведение сдвига Лэмба в плазме обусловлено асимптотическим приближением свойств плазмы к свойствам вакуума при неограниченном увеличении частоты фотонов

Время туннелирования электромагнитного излучения сквозь слой идеальной плазмы

In this paper, we derived the relation for the phase time of electromagnetic radiation tunneling through an ideal plasma layer in a dielectric for frequencies ω below the plasma frequency ωp in the limit of low transparency of the layer. Within the framework of the model under consideration, the tunneling time is found to be independent of the layer thickness and determined only by the ω and  ωp values. For lower frequencies the tunneling time tends to the limit defined by the inverse plasma frequency which allows us to treat the tunneling process in this case as a ‘splash’ of a plasma layer as a whole entity to form the transmitted radiation. Since the transmittance of the plasma layer is very low, the result obtained does not allow us to speak about superluminal energy transfer.Получено соотношение для фазового времени туннелирования электромагнитного излучения для слоя идеальной плазмы в диэлектрике для частот ω ниже плазменной частоты ωp в пределе низкой прозрачности слоя. Установлено, что в рамках рассматриваемой модели время туннелирования не зависит от толщины плазменного слоя и задается только значениями частот ω и ωp. С понижением частоты излучения время туннелирования стремится к пределу, определяемому обратной плазменной частотой, что позволяет в этом случае интерпретировать процесс туннелирования как своеобразный всплеск плазменного слоя как целого, в результате которого и формируется прошедшее излучение. Поскольку коэффициент пропускания плазменного слоя весьма низок, полученный результат не позволяет говорить о сверхсветовом переносе энергии.

Risk of sudden cardiac death in strength training

Physical activity is a generally accepted means of primary and secondary prevention of cardiovascular diseases, but in some cases, it can be a risk factor for cardiovascular events, including sudden cardiac death (SCD). Most studies analyze the relationship of cardiovascular events with the volume and general directions of exercise. Besides, a significant part of the guidelines and studies are devoted to the effects of aerobic exercise, while the importance of anaerobic exercise remains controversial. The review analyzes works devoted to the influence of strength training, such as weightlifting, bodybuilding, powerlifting, etc., on the cardiovascular system, as well as their relationship with SCD and other cardiovascular events. The design and contingent of the analyzed papers did not allow them to be systematized correctly. Therefore, the review is largely analytical in nature

Improvement of cardiovascular risk assessment using machine learning methods

The increase in the prevalence of cardiovascular diseases (CVDs) specifies the importance of their prediction, the need for accurate risk stratification, preventive and treatment interventions. Large medical databases and technologies for their processing in the form of machine learning algorithms that have appeared in recent years have the potential to improve predictive accuracy and personalize treatment approaches to CVDs. The review examines the application of machine learning in predicting and identifying cardiovascular events. The role of this technology both in the calculation of total cardiovascular risk and in the prediction of individual diseases and events is discussed. We compared the predictive accuracy of current risk scores and various machine learning algorithms. The conditions for using machine learning and developing personalized tactics for managing patients with CVDs are analyzed

Timing Constraints of In Vivo Gag Mutations during Primary HIV-1 Subtype C Infection

Background: Aiming to answer the broad question “When does mutation occur?” this study examined the time of appearance, dominance, and completeness of in vivo Gag mutations in primary HIV-1 subtype C infection. Methods: A primary HIV-1C infection cohort comprised of 8 acutely and 34 recently infected subjects were followed frequently up to 500 days post-seroconversion (p/s). Gag mutations were analyzed by employing single-genome amplification and direct sequencing. Gag mutations were determined in relation to the estimated time of seroconversion. Time of appearance, dominance, and completeness was compared for different types of in vivo Gag mutations. Results: Reverse mutations to the wild type appeared at a median (IQR) of 62 (44;139) days p/s, while escape mutations from the wild type appeared at 234 (169;326) days p/s (p<0.001). Within the subset of mutations that became dominant, reverse and escape mutations appeared at 54 (30;78) days p/s and 104 (47;198) days p/s, respectively (p<0.001). Among the mutations that reached completeness, reverse and escape mutations appeared at 54 (30;78) days p/s and 90 (44;196) days p/s, respectively (p = 0.006). Time of dominance for reverse mutations to and escape mutations from the wild type was 58 (44;105) days p/s and 219 (90;326) days p/s, respectively (p<0.001). Time of completeness for reverse and escape mutations was 152 (100;176) days p/s and 243 (101;370) days p/s, respectively (p = 0.001). Fitting a Cox proportional hazards model with frailties confirmed a significantly earlier time of appearance (hazard ratio (HR): 2.6; 95% CI: 2.3–3.0), dominance (4.8 (3.4–6.8)), and completeness (3.6 (2.3–5.5)) of reverse mutations to the wild type Gag than escape mutations from the wild type. Some complex mutational pathways in Gag included sequential series of reversions and escapes. Conclusions: The study identified the timing of different types of in vivo Gag mutations in primary HIV-1 subtype C infection in relation to the estimated time of seroconversion. Overall, the in vivo reverse mutations to the wild type occurred significantly earlier than escape mutations from the wild type. This shorter time to incidence of reverse mutations remained in the subsets of in vivo Gag mutations that reached dominance or completeness

Single-centre experience of allogeneic haemopoietic stem cell transplant in paediatric patients in Cape Town, South Africa

Background. Allogeneic haemopoietic stem cell transplant (Allo-HSCT) is a specialised and costly intervention, associated with significant morbidity and mortality. It is used to treat a broad range of paediatric conditions. South Africa (SA) is an upper middle-income country with limitations on healthcare spending. The role of paediatric Allo-HSCT in this setting is reviewed.Objectives. To review paediatric patients who underwent Allo-HSCT at the Groote Schuur Hospital/University of Cape Town Private Academic Hospital transplant unit in Cape Town, South Africa, and received post-transplant care at Red Cross War Memorial Children’s Hospital, over the period January 2006 - December 2014 in respect of indications for the transplant, donor sources, conditioning regimens, treatment-related morbidity and overall survival (OS).Methods. A retrospective analysis of patient records was performed and a database was created in Microsoft Access. Descriptive analyses of relevant demographic, clinical and laboratory data were performed. Summary statistics of demographic and clinical parameters were derived with Excel. OS was calculated from the date of transplant to the date of an event (death) or last follow-up using the Kaplan-Meier method in Statistica.Results. A total of 48 children received Allo-HSCT: 24 for haematological malignancies, 20 for non-oncological haematological conditions, 3 for immune disorders and 1 for adrenoleukodystrophy. There were 28 boys (median age 7.5 years) and 20 girls (8.5 years). There were 31 sibling matched peripheral-blood stem cell (PBSC) transplants and 1 maternal haploidentical PBSC transplant. Stem cells were mobilised from bone marrow into peripheral blood by administering granulocyte-colony stimulating factor to donors. PBSCs were harvested by apheresis. Eight patients received 10/10 HLA-matched grafts from unrelated donors. Six were PBSC grafts and 2 were bone marrow grafts. Three of the unrelated PBSC grafts were from SA donors. Eight transplants used umbilical cord blood from international registries. OS for patients with non-oncological disorders was 91.3% (median follow-up 3.9 years), while that for oncology patients was 56.8% (1.9 years). Two of the survivors developed chronic graft-versus-host disease.Conclusions. OS for non-oncological conditions was excellent, while outcomes for oncological disorders were on par with those in high-income settings. Transplantation offers many patients the opportunity for long-term survival and has been shown to be both feasible and rewarding in a less well-resourced environment servicing an economically diverse population

Действие хелатирующих агентов на предстательную железу у крыс

It was shown in experiments on rats, that dithizone induced zinc deficiency in prostate cells. Three phase type of fluctuations of cytochemically detected zinc concentration was observed in the cells: phase of primary decrease, phase of temporary partial restoration and the phase of secondary decrease. Sodium diethyldithiocarbamate unlike to dithizone didn’t induce damage of cells and secondary decrease zinc content in its.В эксперименте на крысах показано, что дитизон вызывает развитие дефицита цинка в клетках предстательной железы. Наблюдается трехфазный тип колебаний концентрации цитохимически определяемого цинка в клетках: фаза первичного снижения, фаза временного частичного восстановления, фаза вторичного снижения. Диэтилдитиокарбамат натрия в отличие от дитизона не вызывает повреждений клеток и вторичного дефицита в них цинка

Emission spectra and intrinsic optical bistability in a two-level medium

Scattering of resonant radiation in a dense two-level medium is studied theoretically with account for local field effects and renormalization of the resonance frequency. Intrinsic optical bistability is viewed as switching between different spectral patterns of fluorescent light controlled by the incident field strength. Response spectra are calculated analytically for the entire hysteresis loop of atomic excitation. The equations to describe the non-linear interaction of an atomic ensemble with light are derived from the Bogolubov-Born-Green-Kirkwood-Yvon hierarchy for reduced single particle density matrices of atoms and quantized field modes and their correlation operators. The spectral power of scattered light with separated coherent and incoherent constituents is obtained straightforwardly within the hierarchy. The formula obtained for emission spectra can be used to distinguish between possible mechanisms suggested to produce intrinsic bistability.Comment: 18 pages, 5 figure