Acceleration of ultra-thin electron layer. Analytical treatment compared with 1D-PIC simulation

In this paper, we apply an analytical model [V.V. Kulagin et al., Phys. Plasmas 14,113101 (2007)] to describe the acceleration of an ultra-thin electron layer by a schematic single-cycle laser pulse and compare with one-dimensional particle-in-cell (1D-PIC) simulations. This is in the context of creating a relativistic mirror for coherent backscattering and supplements two related papers in this EPJD volume. The model is shown to reproduce the 1D-PIC results almost quantitatively for the short time of a few laser periods sufficient for the backscattering of ultra-short probe pulses.Comment: 4 pages, 4 figures, submitted to the special issue "Fundamental Physics with Ultra-High Fields" in The European Physical Journal

The reflectivity of relativistic ultra-thin electron layers

The coherent reflectivity of a dense, relativistic, ultra-thin electron layer is derived analytically for an obliquely incident probe beam. Results are obtained by two-fold Lorentz transformation. For the analytical treatment, a plane uniform electron layer is considered. All electrons move with uniform velocity under an angle to the normal direction of the plane; such electron motion corresponds to laser acceleration by direct action of the laser fields, as it is described in a companion paper. Electron density is chosen high enough to ensure that many electrons reside in a volume \lambda_R^3, where \lambda_R is the wavelength of the reflected light in the rest frame of the layer. Under these conditions, the probe light is back-scattered coherently and is directed close to the layer normal rather than the direction of electron velocity. An important consequence is that the Doppler shift is governed by \gamma_x=(1-(V_x/c)^2)^{-1/2} derived from the electron velocity component V_x in normal direction rather than the full \gamma-factor of the layer electrons.Comment: 7 pages, 4 figures, submitted to the special issue "Fundamental Physics with Ultra-High Fields" in The European Physical Journal

Epidemiology and impact of colonization by multidrug-resistant Gram-negative bacteria on bloodstream infections in early phase of allogeneic hematopoietic stem cell transplantation

Objective. To study epidemiology and impact of colonization by multidrug-resistant Gram-negative bacteria (MDRGNB) on bloodstream infections (BSI) during allogeneic hematopoietic stem cell transplantation (allo-HSCT). Materials and Methods. The retrospective study included 288 patients received the first allo-HSCT between 2018 and 2019. The median age was 32 (18–66) years, male – 53% (n = 152). The majority of patients had acute leukemia – 62% (n = 178) and received transplant from matched unrelated – 42% (n = 120) or haploidentical donor – 26% (n = 75). Relapse of underlying disease at the moment of all-HSCT was registered in 23% (n = 66) of patients. Results. Colonization of non-sterile sites before allo-HSCT by at least one MDRGNB was detected in 28% (n = 64). In most cases resistance is due to extended spectrum beta-lactamases (ESBL) – 86% (n = 55), while carbapenemases in combination with ESBL were detected in 14% (n = 9) of patients. After allo-HSCT the colonization was significantly higher than before transplantation (n = 161, 56%, p = 0.001), mainly due to carbapenemase- and ESBL-producing bacteria – 73% (n = 118) (p = 0.001). BSI in the early period after transplantation developed in 26% (n = 76), and in 56% (n = 43) was caused by MDRGNB. The etiology of BSI included K. pneumoniae – 51% in mostly cases. The etiology of BSI was the same bacteria that colonized non-sterile sites 2 weeks before the detection bacteria in bloodstream in 69% (n = 30) patients. Colonization by MDRGNB was associated with the development of BSI (p < 0.0001). The 100-day overall survival (OS) after all-HSCT was significantly lower in patients with colonization of non-sterile sites by MDRGNB compared with patients without colonization (60.6% vs 88.2%, p = 0.001). Conclusions. Colonization of MDRGNB after allo-HSCT reached 56%. K. pneumoniae was predominant etiology in both colonization and bloodstream infections. Colonization by MDRGNB was associated with the development of BSI and decreased OS after allo-HSCT

Assessment of the effectiveness of determining the duration of HIV infection by analysis of viral genetic variability

The objective. Assessment of the sensitivity and specificity of a method of calculating variable positions in HIV genome for detection of the duration of infection in a cohort of HIV-infected population of Russia. Patients and methods. The effectiveness of the method based on detection of HIV heterogenicity was assessed on 119 plasma specimens of HIV-infected patients with the known date of infection. The average duration of infection was 15 months, and the median - 8 months. In the studied sample, specimens of patients infected less than one year before amounted to 68% (81 of 119). The cohort consisted of 55 women (46%) and 64 men (54%). At the moment of blood testing for studying viral genome the patients' age varied from 0 to 79 years, the mean age was 31 years, median - 31 years. Results. As has been calculated for 119 examined specimens, the linear dependence between the duration of infection and the degree of variability of the sequence can be described by the formula y = 0.0012∗X + 0.0021 (R2 = 0.52). This equation permitted to calculate the variability threshold of 0.33%, which determined the duration of HIV infection as 12 months. Based on the obtained data, we calculated the sensitivity and specificity of the molecular method of detecting recent infection, which were 79.01 and 63.16%, respectively (comparable with previously published data). The duration of infection was calculated for each patient, then it was compared with the duration based on epidemiological data: for 42% of specimens the error in determining the duration of infection was less than 1 years, and for 92% of specimens - less than 3 years. Conclusion. This method might be successfully used in practice to assess the quality of screening programmes of detecting HIV infection performed in various regions and for various risk groups. Also, it might be used to confirm the presence of a recent (less than 1 year) infection

Phase error estimation of a hydro-acoustic signal with swept carrier in conditions of multipath propagation

Представлены результаты математического моделирования сигнала с непрерывной разверткой несущей в додетекторной точке приемника. Показана возможность оценки доплеровских смещений на основе cравнения измеренного и оценочного значения (модели) сигнала. Продемонстрировано убывающее влияние задержанного (несинхронного) луча при увеличении его избыточной задержки распространения на точность оценки фазы сигнала.Розглядаються результати математичного моделювання сигналу з безперервною розгорткою несучої в додетекторній точці приймальника. Доведена можливість оцінки коефіцієнта Допплера на основі порівняння виміряного і оціночного значення (моделі) сигналу. Продемонстровано зменшення впливу затриманих (несинхронних) променів при зростанні надлишкової затримки розповсюдження сигналу на похибку оцінки фази сигналу.There are considered the results of numerical modelling of a signal with swept carrier in the receiver predetection point in conditions of multipath propagation. The possibility of Doppler coefficient estimation is proven on the base of comparison of signal measured and expected values. There is demonstrated the influence reduction of delayed (non-synchronous) multipath with increase of excess delay on the phase error estimation