Generation of small-scale structures in the developed turbulence

The Navier-Stokes equation for incompressible liquid is considered in the limit of infinitely large Reynolds number. It is assumed that the flow instability leads to generation of steady-state large-scale pulsations. The excitation and evolution of the small-scale turbulence is investigated. It is shown that the developed small-scale pulsations are intermittent. The maximal amplitude of the vorticity fluctuations is reached along the vortex filaments. Basing on the obtained solution, the pair correlation function in the limit $r\to 0$ is calculated. It is shown that the function obeys the Kolmogorov law $r^{2/3}$.Comment: 18 page

Comparison of REMS, NEWS, qSOFA and SIRS criteria scales for sepsis prediction in patients with diagnosis “SARS-CoV-2, virus unidentified”: a retrospective observational study

Background. Despite ample research on the coronavirus infection sequence and therapy, the incidence of adverse outcomes remains very high. Sepsis stands among the major factors greatly complicating treatment and increasing the risk of death. A timely identification of highrisk sepsis patients is a cornerstone of effective sepsis prevention.Objectives. A comparative prognostic power assessment between the quick Sequential Organ Failure Assessment (qSOFA) scale, National Early Warning Score (NEWS), Initial Prehospital Rapid Emergency Medicine Score (REMS) and the Systemic Inflammatory Response Syndrome (SIRS) criteria for sepsis detection in anaesthetic intensive care patients with a diagnosis: SARS-CoV-2, virus unidentified.Methods. A retrospective observational study included 166 patients over 18-year age with unconfirmed infection (ICD-10 code U07.2). The qSOFA, NEWS, REMS and SIRS point estimates were obtained from each patient. The patients were retrospectively divided in two cohorts by sepsis presence (Sepsis-3 criteria) to determine the express scales power in evaluating the risk of sepsis (estimated as area under ROC curve, AUROC).Results. Data on 102 patients were included in the final analysis. Fifty-eight (57%) patients were terminal, and 55 (54%) developed sepsis. The estimates are as follows: NEWS — AUROC 0.848 [95% confidence interval (CI) 0.764–0.912], sensitivity 76.36% [95% CI 63.0–86.8], specificity 82.98% [95% CI 69.2–92.4], optimal cut-off threshold >5 points; qSOFA — AUROC 0.700 [95% CI 0.602–0.787], sensitivity 76.36% [95% CI 63.0–86.8], specificity 61.70% [95% CI 46.4–75.5], optimal cut-off threshold >0 points; REMS — AUROC 0.739 [95% CI 0.643–0.821], sensitivity 69.09% [95% CI 55.2–80.9], specificity 65.96% [95% CI 50.7–79.1], optimal cut-off threshold >5 points; SIRS criteria — AUROC 0.723 [95% CI 0.626–0.807], sensitivity 98.18% [95% CI 90.3–100.0], specificity 31.91% [95% CI 19.1–47.1], optimal cut-off threshold >0 points.Conclusion. The NEWS scale revealed a good prognostic power to estimate the risk of sepsis in patients with suspected COVID-19 disease. The qSOFA, REMS scales and SIRS criteria possess a good calibration capacity, albeit insufficient resolution, which limits their prognostic value

Fully developed turbulence and the multifractal conjecture

We review the Parisi-Frisch MultiFractal formalism for Navier--Stokes turbulence with particular emphasis on the issue of statistical fluctuations of the dissipative scale. We do it for both Eulerian and Lagrangian Turbulence. We also show new results concerning the application of the formalism to the case of Shell Models for turbulence. The latter case will allow us to discuss the issue of Reynolds number dependence and the role played by vorticity and vortex filaments in real turbulent flows.Comment: Special Issue dedicated to E. Brezin and G. Paris

Initial Steps of Thermal Decomposition of Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate Crystals from Quantum Mechanics

Dihydroxylammonium 5,5?-bistetrazole-1,1?-diolate (TKX-50) is a recently synthesized energetic material (EM) with most promising performance, including high energy content, high density, low sensitivity, and low toxicity. TKX-50 forms an ionic crystal in which the unit cell contains two bistetrazole dianions {c-((NO)N3C)-[c-(CN3(NO)], formal charge of ?2} and four hydroxylammonium (NH3OH)+ cations (formal charge of +1). We report here quantum mechanics (QM)-based reaction studies to determine the atomistic reaction mechanisms for the initial decompositions of this system. First we carried out molecular dynamics simulations on the periodic TKX-50 crystal using forces from density functional based tight binding calculations (DFTB-MD), which finds that the chemistry is initiated by proton transfer from the cation to the dianion. Continuous heating of this periodic system leads eventually to dissociation of the protonated or diprotonated bistetrazole to release N2 and N2O. To refine the mechanisms observed in the periodic DFTB-MD, we carried out finite cluster quantum mechanics studies (B3LYP) for the unimolecular decomposition of the bistetrazole. We find that for the bistetrazole dianion, the reaction barrier for release of N2 is 45.1 kcal/mol, while release of N2O is 72.2 kcal/mol. However, transferring one proton to the bistetrazole dianion decreases the reaction barriers to 37.2 kcal/mol for N2 release and 59.5 kcal/mol for N2O release. Thus, we predict that the initial decompositions in TKX-50 lead to N2 release, which in turn provides the energy to drive further decompositions. On the basis of this mechanism, we suggest changes to make the system less sensitive while retaining the large energy release. This may help improve the synthesis strategy of developing high nitrogen explosives with further improved performance

Nuclear Interaction Gamma-Ray Lines from the Galactic Center Region

Aims. The accretion of stars onto the central supermassive black hole at the center of the Milky Way is predicted to generate large fluxes of subrelativistic ions in the Galactic center region. We analyze the intensity, shape and spatial distribution of de-excitation gamma-ray lines produced by nuclear interactions of these energetic particles with the ambient medium. Methods. We first estimate the amount and mean kinetic energy of particles released from the central black hole during star disruption. We then calculate from a kinetic equation the energy and spatial distributions of these particles in the Galactic center region. These particle distributions are then used to derive the characteristics of the main nuclear interaction gamma-ray lines. Results. Because the time period of star capture by the supermassive black hole is expected to be shorter than the lifetime of the ejected fast particles against Coulomb losses, the gamma-ray emission is predicted to be stationary. We find that the nuclear de-excitation lines should be emitted from a region of maximum 5$^\circ$ angular radius. The total gamma-ray line flux below 8 MeV is calculated to be $\approx10^{-4}$ photons cm$^{-2}$ s$^{-1}$. The most promising lines for detection are those at 4.44 and $\sim$6.2 MeV, with a predicted flux in each line of $\approx$$10^{-5}$ photons cm$^{-2}$ s$^{-1}$. Unfortunately, it is unlikely that this emission can be detected with the INTEGRAL observatory. But the predicted line intensities appear to be within reach of future gamma-ray space instruments. A future detection of de-excitation gamma-ray lines from the Galactic center region would provide unique information on the high-energy processes induced by the central supermassive black hole and the physical conditions of the emitting region.Comment: 7 pages, 5 figures, accepted for publication in A&

Small-scale clumps in the galactic halo and dark matter annihilation

Production of small-scale DM clumps is studied in the standard cosmological scenario with an inflation-produced primeval fluctuation spectrum. Special attention is given to three following problems: (i) The mass spectrum of small-scale clumps with $M \lesssim 10^3 M_{\odot}$ is calculated with tidal destruction of the clumps taken into account within the hierarchical model of clump structure. Only 0.1 - 0.5% of small clumps survive the stage of tidal destruction in each logarithmic mass interval $\Delta\ln M\sim1$. (ii) The mass distribution of clumps has a cutoff at $M_{\rm min}$ due to diffusion of DM particles out of a fluctuation and free streaming at later stage. $M_{\rm min}$ is a model dependent quantity. In the case the neutralino, considered as a pure bino, is a DM particle, $M_{\rm min} \sim 10^{-8} M_{\odot}$. (iii) The evolution of density profile in a DM clump does not result in the singularity because of formation of the core under influence of tidal interaction. The radius of the core is $R_c \sim 0.1 R$, where $R$ is radius of the clump. The applications for annihilation of DM particles in the Galactic halo are studied. The number density of clumps as a function of their mass, radius and distance to the Galactic center is presented. The enhancement of annihilation signal due to clumpiness, valid for arbitrary DM particles, is calculated. In spite of small survival probability, the annihilation signal in most cases is dominated by clumps. For observationally preferable value of index or primeval fluctuation spectrum $n_p \approx 1$, the enhancement of annihilation signal is described by factor 2 - 5 for different density profiles in a clump.Comment: inor changes in text and 2 references adde

Initial Decomposition Reactions of Bicyclo-HMX [BCHMX or cis

We investigated the initial chemical reactions of BCHMX [cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole] with the following procedure. First we used density functional theory molecular dynamics simulations (DFT-MD) on the periodic crystal to discover the initial reaction steps. This allowed us to determine the most important reactions through DFT-MD simulations at high temperatures. Then we started with the midpoint of the reaction (unimolecular or bimolecular) from the DFT-MD and carried out higher quality finite cluster DFT calculations to locate the true transition state of the reaction, followed by calculations along the reaction path to determine the initial and final states. We find that for the noncompressed BCHMX the nitro-aci isomerization reaction occurs earlier than the NO2-releasing reaction, while for compressed BCHMX intermolecular hydrogen-transfer and bimolecular NO2-releasing reactions occur earlier than the nitrous acid (HONO)-releasing reaction. At high pressures, the initial reaction involves intermolecular hydrogen transfer rather than intramolecular hydrogen transfer, and the intermolecular hydrogen transfer decreases the reaction barrier for release of NO2 by ∼7 kcal/mol. Thus, the HONO-releasing reaction takes place more easily in compressed BCHMX. We find that this reaction barrier is 10 kcal/mol lower than the unimolecular NO2 release and ∼3 kcal/mol lower than the bimolecular NO2 release. This rationalizes the origin of the higher sensitivity of BCHMX compared to RDX (1,3,5-trinitrohexahydro-1,3,5-triazine) and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine). We suggest changes in BCHMX that might help decrease the sensitivity by avoiding the intermolecular hydrogen-transfer and HONO-releasing reaction

Inhibition of Hotspot Formation in Polymer Bonded Explosives Using an Interface Matching Low Density Polymer Coating at the Polymer–Explosive Interface

In order to elucidate how shocks in heterogeneous materials affect decomposition and reactive processes, we used the ReaxFF reactive force field in reactive molecules dynamics (RMD) simulations of the effects of strong shocks (2.5 and 3.5 km/s) on a prototype polymer bonded explosive (PBX) consisting of cyclotrimethylene trinitramine (RDX) bonded to hydroxyl-terminated polybutadiene (HTPB). We showed earlier that shock propagation from the high density RDX to the low density polymer (RDX ? Poly) across a nonplanar periodic interface (sawtooth) leads to a hotspot at the initial asperity but no additional hotspot at the second asperity. This hotspot arises from shear along the interface induced by relaxation of the stress at the asperity. We now report the case for shock propagation from the low density polymer to the high density RDX (Poly ? RDX) where we find a hotspot at the initial asperity and a second more dramatic hotspot at the second asperity. This second hotspot is enhanced due to shock wave convergence from shock wave interaction with nonplanar interfaces. We consider that this second hotspot is likely the source of the detonation in realistic PBX systems. We showed how these hotspots depend on the density mismatch between the RDX and polymer and found that decreasing the density by a factor of 2 dramatically reduces the hotspot. These results suggest that to make PBX less sensitive for propellants and explosives, the binder should be designed to provide low density at the asperity in contact with the RDX. Based on these simulations, we propose a new design for an insensitive PBX in which a low density polymer coating is deposited between the RDX and the usual polymer binder. To test this idea, we simulated shock wave propagation from two opposite directions (RDX ? Poly and Poly ? RDX) through the interface matched PBX (IM-PBX) material containing a 3 nm coating of low density (0.48 g/cm3) polymer. These simulations showed that this IM-PBX design dramatically suppresses hotspot formation

Гендерное сравнение непосредственных и среднесрочных результатов операции Озаки: анализ Propensity Score Matching

Highlights. A retrospective analysis of the patients’ data after Ozaki operation in four Russian Medical Centers was carried out. A comparative gender assessment of the immediate and medium-term results of Ozaki operation was performed.Aim. Gender assessment of Ozaki operation immediate and mid-term results in patients with aortic valve (AV) pathology.Methods. A retrospective multicenter study enrolled 251 patients (135 women, median age 66 (60–70) years old) who underwent Ozaki operation (2017–2020) was carried out in four centers in Russia. After propensity score matching, 92 patients were selected (mean age 65.8±10.8 years old). Two groups were formed in the gender structure: 46 females (average age 67.8±6.3 years old), 46 males (average age 63.8±15.4 years old). The main cause of AV dysfunction was severe aortic stenosis – in 86 (93.5%) cases. Chronic heart failure of III–IV functional class according to NYHA was observed in 26 (28.3%) patients. A bicuspid AV was in 24 cases (26.1%). The primary endpoint was hospital mortality. Postoperative complications and mid-term results (three-year overall survival and freedom from reoperation on AV) were assessed as secondary endpoints; the median follow-up period was 23 (18–33) months.Results. There was no statistically significant difference between the groups in the duration of surgery (275 minutes for females and 285 minutes for males, p = 0.4), cardiopulmonary bypass (98 minutes for females and 115 minutes for males, p = 0.3), aortic clamping (80 minutes for females and 93 minutes for males, p = 0.7). Hospital mortality among the studied patients did not differ: in the female group – 2.2% (1 case) and 0 in the male one, p = 0.9. There were no significant differences in postoperative complications: sepsis (2.2% in women and 0 in men, p = 0.9), superficial wound infection (8.7% in women and 6.5% in men, p = 0.9). Acute kidney injury, stroke, pacemaker implantation, resternotomy for bleeding were not observed in any patient. Three-year overall survival was 91.8% in females and 91.6% in males, p = 0.8; three-year freedom from reoperation – 94.4% for females and 100% for males, p = 0.1.Conclusion. Ozaki operation is equally reproducible with the same hospital mortality, postoperative complications, and medium-term outcomes in both females and males.Основные положения. Проведен ретроспективный анализ данных больных, перенесших операцию Озаки в четырех медицинских центрах России. • Выполнена сравнительная гендерная оценка непосредственных и среднесрочных результатов операции Озаки.Цель. Гендерная оценка непосредственных и среднесрочных результатов операции Озаки у пациентов с патологией аортального клапана (АК).Материалы и методы. Проведено ретроспективное многоцентровое исследование 251 больного (135 женщин, медиана возраста 66 (60–70) лет), которым выполнена операция Озаки (2017–2020 гг.) в четырех медицинских центрах России. После псевдорандомизации (propensity score matching) отобраны 92 пациента (средний возраст 65,8±10,8 года). В зависимости от гендерной принадлежности сформированы две группы: 46 женщин (средний возраст 67,8±6,3 года), 46 мужчин (средний возраст 63,8±15,4 года). Основной причиной дисфункции АК был тяжелый аортальный стеноз – 86 (93,5%) случаев. Хроническая сердечная недостаточность III–IV функционального класса по NYHA отмечена у 26 (28,3%) больных. В 24 случаях (26,1%) АК был двустворчатый. Первичной конечной точкой являлась госпитальная летальность. В качестве вторичных конечных точек оценивали послеоперационные осложнения и среднесрочные результаты (трехлетняя общая выживаемость и свобода от реоперации на АК), медиана периода наблюдения составила 23 (18–33) мес.Результаты. Не получено статистически значимой разницы между группами по длительности операции (275 мин у женщин и 285 мин у мужчин, p = 0,4), искусственного кровообращения (98 и 115 мин, p = 0,3), пережатия аорты (80 и 93 мин соответственно, p = 0,7). Госпитальная летальность среди исследуемых больных не различалась: в женской группе – 1 случай (2,2%), в мужской – 0, p = 0,9. По послеоперационным осложнениям значимых различий не зарегистрировано: сепсис (2,2% у женщин и 0 у мужчин, p = 0,9), раневая поверхностная инфекция (8,7 и 6,5% соответственно, p = 0,9). Острого повреждения почек, инсульта, имплантации постоянного электрокардиостимулятора, рестернотомии по поводу кровотечения не выявлено ни у одного пациента. Трехлетняя общая выживаемость составила 91,8% у женщин и 91,6% у мужчин, p = 0,8; трехлетняя свобода от реоперации – 94,4 и 100% соответственно, p = 0,1.Заключение Операция Озаки воспроизводима у мужчин и женщин с одинаковыми госпитальной летальностью, послеоперационными осложнениями и среднесрочными результатами.