Energetic stability of absorbed H in Pd and Pt nanoparticles in a more realistic environment

Absorbed hydrogen can dramatically increase hydrogenation activity of Pd nanoparticles and was predicted to do so also for Pt. This calls for investigations of the energetic stability of absorbed H in Pd and Pt using nanoparticle models as realistic as possible, i.e., (i) sufficiently large, (ii) supported, and (iii) precovered by hydrogen. Herein, hydrogen absorption is studied in MgO(100)-supported 1.6 nm large Pd and Pt nanoparticles with surfaces saturated by hydrogen. The effect of surface H on the stability of absorbed H is found to be significant and to exceed the effect of the support. H absorption is calculated to be endothermic in Pt, energy neutral in Pd(111) and bare Pd nanoparticles, and exothermic in H-covered Pd nanoparticles. Hence, we identify the abundance of surface H and the nanostructuring of Pd as prerequisites for facile absorption of hydrogen in Pd and for the concomitantly altered catalytic activity

Hyperfine quenching of the metastable 3P0,2^3P_{0,2} states in divalent atoms

Hyperfine quenching rates of the lowest-energy metastable $^3P_0$ and $^3P_2$ states of Mg, Ca, Sr, and Yb atoms are computed. The calculations are carried out using ab initio relativistic many-body methods. The computed lifetimes may be useful for designing novel ultra-precise optical clocks and trapping experiments with the $3P_2$ fermionic isotopes. The resulting natural widths of the $^3P_0 -> ^1S_0$ clock transition are 0.44 mHz for $^{25}$Mg, 2.2 mHz for $^{43}$Ca, 7.6 mHz for $^{87}$Sr, 43.5 mHz for $^{171}$Yb, and 38.5 mHz for $^{173}$Yb. Compared to the bosonic isotopes, the lifetime of the $3P_2$ states in fermionic isotopes is noticeably shortened by the hyperfine quenching but still remains long enough for trapping experiments.Comment: 10 pages, 1 figure, submitted to Phys. Rev.

Lagrangian formalism and Noether-type theorems for second-order delay ODEs

The Lagrangian formalism for variational problem for second-order delay ordinary differential equations (DODEs) is developed. The Noether-type operator identities and theorems for DODEs of second order are presented. Algebraic construction of integrals for DODEs based on symmetries are demonstrated by examples

One-dimensional MHD flows with cylindrical symmetry: Lie symmetries and conservation laws

A recent paper considered symmetries and conservation laws of the plane one-dimensional flows for magnetohydrodynamics in the mass Lagrangian coordinates. This paper analyses the one-dimensional magnetohydrodynamics flows with cylindrical symmetry in the mass Lagrangian coordinates. The medium is assumed inviscid and thermally non-conducting. It is modeled by a polytropic gas. Symmetries and conservation laws are found. The cases of finite and infinite electric conductivity need to be analyzed separately. For finite electric conductivity $\sigma (\rho,p)$ we perform Lie group classification, which identifies $\sigma (\rho,p)$ cases with additional symmetries. The conservation laws are found by direct computation. For cases with infinite electric conductivity variational formulations of the equations are considered. Lie group classifications are obtained with the entropy treated as an arbitrary element. A variational formulation allows to use the Noether theorem for computation of conservation laws. The conservation laws obtained for the variational equations are also presented in the original (physical) variables

Ранние особенности кровообращения у больных с неблагоприятным исходом абдоминального сепсиса (предварительное сообщение)

Aim: to study characteristics of the central hemodynamics (CHD) in patients with severe abdominal sepsis with different outcomes of the disease.Materials and Methods. 18 patients with abdominal sepsis, aged 50.2±3, with the APACHE II and SOFA severity scoring of 13.7±0.8 and 8.4±0.5, respectively, were enrolled in the retrospective study. The CHD was studied using the transpulmonary thermodilution. The following groups were identified: Group 1 (deceased, n=9) and Group 2 (survivors, n=9). The groups did not differ (P>0.05) in age, sex, and the severity of the condition at admission to the ICU. The significance of differences was assessed using the t-test and the chi-squared test. The prognostic value of the parameters was studied using the ROC analysis.Results. On Day 1, the intergroup differences included the average blood pressure (BPav) (85.3±3.3 and 101.6±4.6 mmHg, respectively (P<0.05)) and the cardiac power index (CPI) (306±22 and 429.9±48.9 W/m2, respectively) (Р<0.05). The intergroup difference in the CPI and the global ejection fraction (GEF) persisted on Day 3: 22.3±2.3 and 29.3±1.5%, respectively (P<0.05); there was no other difference. The intergroup difference in the GEF remained on Day 5. On Day 7, the CHD parameters demonstrated no intergroup difference. The SOFA severity scoring in Group 1 patients became greater than that in Group 2 starting from Day 5. According to ROC analysis, BPav (95 mmHg, sensitivity: 88.9%, specificity: 88.9%), CPI (373 W/m2, sensitivity: 88.9%, specificity: 77.8%), and GEF (26.1%, sensitivity: 66.7%, specificity: 77,8%) were the most important predictors of the lethal outcome on Days 1—3 (areas under ROC curves: 0.765—0.840; P<0.05). On days 5—7, the SOFA scoring >7 (sensitivity: 88.9%, specificity: 88.9%) was the most important predictor of the lethal outcome (areas under ROC curves: 0.957—0.994; P<0.05).Conclusion: during the first five days of the intensive treatment of severe sepsis in patients with unfavorable prognosis, a moderate decrease in the cardiac power index and overall cardiac systolic function was registered. The prognostic significance of such parameters as CPI and GEF may become obvious within the first 3 days of the intensive treatment.Цель исследования: изучить особенности центральной гемодинамики (ЦГД) у больных тяжелым абдоминальным сепсисом при различных исходах заболевания.Материалы и методы. В ретроспективное исследование включили 18 больных абдоминальным сепсисом в возрасте 50,2±3 лет с тяжестью состояния по шкале APACHE II 13,7±0,8 балла, SOFA — 8,4±0,5 балла. ЦГД изучали с помощью транспульмональной термодилюции. Выделили группы больных: 1-я (умершие, n=9) и 2-я (выжившие , n=9). Группы не различались (p>0,05) по возрасту, половому составу и тяжести состояния больных при поступлении в отделение реаниматологии. Достоверность отличий оценивали по критерию t-критерию Стьюдента и критерию Хи-квадрат. Прогностическую значимость показателей изучали с помощью ROC-анализа.Результаты. В 1-е сутки межгрупповые отличия выявлены в уровне среднего артериального давления (АДср.) — 85,3±3,3 и 101,6±4,6 мм рт. ст. (р<0,05) и индекса мощности сердца (ИМС) — 306±22 и 429,9±48,9 Вт/м2 (р<0,05). На 3-и сутки сохранялись межгрупповые отличия значений ИМС, проявлялись отличия величины глобальной фракции изгнания сердца (ГФИС) — 22,3±2,3 и 29,3±1,5% (р<0,05); других отличий не было. На 5-е сутки сохранялось межгрупповое отличие значений ГФИС. На 7-е сутки показатели ЦГД не имели межгрупповых отличий. Тяжесть состояния по SOFA у больных 1-й группы становилась больше, чем во 2-й, начиная с 5-х суток. По данным ROC-анализа в 1-3-и сутки наиболее значимыми предикторами летального исхода (площади под ROC-кривыми 0,765—0,840; p<0,05) явились АДср. (95 мм рт. ст., чувствительность 88,9%, специфичность 88,9%), ИМС (373 Вт/м2, чувствительность 88,9%, специфичность 77,8%) и ГФИС (26,1%, чувствительность 66,7%, специфичность 77,8%). На 5—7-е сутки наиболее значимым предиктором летальности (площади под ROC-кривой 0,957—0,994; p<0,05) становилась тяжесть состояния по шкале SOFA >7 баллов (чувствительность 88,9%, специфичность 88,9%).Заключение: в течение первых 5-и суток интенсивного лечения тяжелого сепсиса у больных с неблагоприятным прогнозом заболевания отмечено умеренное снижение показателей мощности и общей систолической функции сердца. Прогностическая значимость таких показателей, как ИМС и ГФИС, может проявляться в первые трое суток интенсивного лечения