String Method for the Study of Rare Events

We present a new and efficient method for computing the transition pathways, free energy barriers, and transition rates in complex systems with relatively smooth energy landscapes. The method proceeds by evolving strings, i.e. smooth curves with intrinsic parametrization whose dynamics takes them to the most probable transition path between two metastable regions in the configuration space. Free energy barriers and transition rates can then be determined by standard umbrella sampling technique around the string. Applications to Lennard-Jones cluster rearrangement and thermally induced switching of a magnetic film are presented.Comment: 4 pages, 4 figure

A Doubly Nudged Elastic Band Method for Finding Transition States

A modification of the nudged elastic band (NEB) method is presented that enables stable optimisations to be run using both the limited-memory quasi-Newton (L-BFGS) and slow-response quenched velocity Verlet (SQVV) minimisers. The performance of this new `doubly nudged' DNEB method is analysed in conjunction with both minimisers and compared with previous NEB formulations. We find that the fastest DNEB approach (DNEB/L-BFGS) can be quicker by up to two orders of magnitude. Applications to permutational rearrangements of the seven-atom Lennard-Jones cluster (LJ7) and highly cooperative rearrangements of LJ38 and LJ75 are presented. We also outline an updated algorithm for constructing complicated multi-step pathways using successive DNEB runs.Comment: 13 pages, 8 figures, 2 table

Highly site-specific H2 adsorption on vicinal Si(001) surfaces

Experimental and theoretical results for the dissociative adsorption of H_2 on vicinal Si(001) surfaces are presented. Using optical second-harmonic generation, sticking probabilities at the step sites are found to exceed those on the terraces by up to six orders of magnitude. Density functional theory calculations indicate the presence of direct adsorption pathways for monohydride formation but with a dramatically lowered barrier for step adsorption due to an efficient rehybridization of dangling orbitals.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Lett. (1998). Other related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Microscopic theory of quadrupolar ordering in TmTe

We have calculated the crystal electric field of TmTe (T>T_Q) and have obtained that the ground state of a Tm 4f hole is the $\Gamma_7$ doublet in agreement with Mossbauer experiments. We study the quadrupole interactions arising from quantum transitions of 4f holes of Tm. An effective attraction is found at the L point of the Brillouin zone, $\vec{q}_L$. Assuming that the quadrupolar condensation involves a single arm of $\vec{q}_L$ we show that there are two variants for quadrupole ordering which are described by the space groups C2/c and C2/m. The Landau free energy is derived in mean-field theory. The phase transition is of second order. The corresponding quadrupole order parameters are combinations of $T_{2g}$ and $E_g$ components. The obtained domain structure is in agreement with observations from neutron diffraction studies for TmTe. Calculated lattice distortions are found to be different for the two variants of quadrupole ordering. We suggest to measure lattice displacements in order to discriminate between those two structures.Comment: 10 pages, 2 figures, 5 tables; accepted by PR

Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand

The synthesis, lanthanide complexation, and solvent ex- traction of actinide(III) and lanthanide(III) radiotracers from nitric acid solutions by a phenanthroline-derived quadridentate bis-triazine ligand are described. The ligand separates Am(III) and Cm(III) from the lanthanides with remarkably high efficiency, high selectivity, and fast extraction kinetics compared to its 2,2'-bipyridine counterpart. Structures of the 1:2 bis-complexes of the ligand with Eu(III) and Yb(III) were elucidated by X-ray crystallography and force field calculations, respec-tively. The Eu(III) bis-complex is the first 1:2 bis-complex of a quadridentate bis-triazine ligand to be characterized by crystallography. The faster rates of extraction were verified by kinetics measurements using the rotating membrane cell technique in several diluents. The improved kinetics of metal ion extraction are related to the higher surface activity of the ligand at the phase interface. The improvement in the ligand's properties on replacing the bipyridine unit with a phenanthroline unit far exceeds what was anticipated based on ligand design alone

Изучение взаимосвязи между тяжестью течения алкогольной кардиомиопатии и уровнем потребления алкоголя у самцов и самок крыс на модели «бытового пьянства»

Background. Earlier, on the translational model of alcoholic cardiomyopathy (ACMP) developed by us in outbred white rats, which reproduces the main clinical diagnostic signs of this disease, it was shown that in rats of both sexes under conditions of constant 24/7 alcoholization for 24 weeks, AСMP is formed.This study purpose is a comparative assessment of the features of the ACM formation in male and female rats depending on the level of ethanol consumption in model experiments simulating "domestic drunkenness" with periodic alcoholization 24/2 for 24 weeks.Materials and methods. Experiments were performed on outbred white rats randomized into 4 groups: group 1 — control male rats (n=18), group 2 — control female rats (n = 18), group 3 — alcoholized male rats (n = 39) and group 4 — alcoholized female rats (n = 19). Control animals received a normal diet and free access to water. Animals of the 3rd and 4th groups weekly, for 24 weeks, from Friday 22.00 to Monday 8.00, received a 10 % ethanol solution as the only source of liquid with unlimited access to standard food, and the usual diet on the remaining days.Results. In animals of both sexes, after 24 weeks from the consumption start of the ethanol solution, ACM is formed, as evidenced by an increase in the end-systolic and end-diastolic sizes of the left ventricle of the heart (p = 0.0001) and a decrease in its ejection fraction (p = 0.0001), while the degree of pathological myocardial remodeling is more pronounced in females. According to cluster analysis, by the consumption of ethanol (CET), animals of both sexes are divided into 3 subgroups: low, medium and high CET, however, in males, the subgroup with an average CET prevails — 56 %, and in females with a high CET — 47 % (p = 0.0286), the low CET subgroup is minimal (16 %). At the same time, if in males in all subgroups, starting from the 8th week of alcoholization, CET dynamically decreases, then how in females in subgroups with medium and high CET, starting from the 16th week, it increases. It was found that the degree of left ventricular remodeling in females with high and moderate CET was almost 2 times higher than in males (p < 0.05).Conclusion. In model experiments imitating “domestic drunkenness”, it was shown that in females the intensity of the left ventricle heart remodeling is significantly higher than in males, which, apparently, is determined by the identified gender-dependent multidirectional trends in the formation of alcoholic behavior characterized by dynamic growth. consumption of ethanol in female rats as the duration of alcoholization increases.Введение. Ранее на разработанной нами трансляционной модели алкогольной кардиомиопатии (АКМП) у беспородных белых крыс, воспроизводящей основные клинико-диагностические признаки этого заболевания, показано, что у крыс обоего пола в условиях постоянной 24/7 алкоголизации в течение 24 недель формируется АКМП.Цель настоящего исследования — сравнительная оценка особенностей формирования АКМП у самцов и самок крыс в зависимости от уровня потребления этанола в модельных экспериментах, имитирующих «бытовое пьянство», при периодической алкоголизации 24/2 в течение 24 недель.Материалы и методы. Эксперименты выполнены на беспородных белых крысах, рандомизированных на 4 группы: 1-я группа — контрольные крысы-самцы (n = 18), 2-я группа — контрольные крысы-самки (n = 18), 3-я группа — алкоголизированные крысы-самцы (n = 39) и 4-я группа — алкоголизированные крысы-самки (n = 19). Контрольные животные получали обычный рацион питания и свободный доступ к воде. Животные 3-й и 4-й групп еженедельно, в течение 24 недель, с 22:00 пятницы по 8:00 понедельника в качестве единственного источника жидкости получали 10 % раствор этанола при неограниченном доступе к стандартному корму, а в остальные дни обычный рацион.Результаты. У животных обоего пола через 24 недели от начала потребления раствора этанола формируется АКМП, о чем свидетельствует увеличение конечно-систолического и конечно-диастолического размеров левого желудочка сердца (p = 0,0001) и снижение его фракции выброса (p = 0,0001), при этом степень патологического ремоделирования миокарда более выражена у самок. Согласно кластерному анализу, по потреблению этанола (ПЭ) животные обоего пола подразделяются на 3 подгруппы: низкое, среднее и высокое ПЭ, однако у самцов превалирует подгруппа со средним ПЭ — 56 %, а у самок с высоким ПЭ — 47 % (р = 0,0286), подгруппа с низким ПЭ минимальна (16 %). При этом, если у самцов во всех подгруппах, начиная с 8-й недели алкоголизации, ПЭ динамически снижается, то у самок в подгруппах со средним и высоким ПЭ оно, начиная с 16-й недели, возрастает. Установлено, что степень ремоделирования левого желудочка сердца у самок с высоким и средним ПЭ почти в 2 раза выше, чем у самцов (p < 0,05).Заключение. В модельных экспериментах, имитирующих «бытовое пьянство», показано, что у самок интенсивность ремоделирования левого желудочка сердца значимо больше, чем у самцов, что, по-видимому, определяется выявленными зависимыми от пола разнонаправленными тенденциями в формировании алкогольного поведения, характеризующегося динамическим ростом потребления этанола у самок крыс по мере нарастания сроков алкоголизации

Сравнительное изучение кардиопротекторного действия триметазидина и фабомотизола гидрохлорида у крыс со сформировавшейся алкогольной кардиомиопатией в условиях продолжающегося потребления этанола

In the previousLy deveLoped transLation modeL of aLcohoLic cardiomyopathy in white nonLinear rats was studied the cardioprotective effects of trimetazidine and fabomotizoLe hydrochLoride that were injected daiLy during the 25th - 28th weeks of continued consumption of 10% ethanoL It is shown that trimetazidine (30 mg/kg/day i.p.) and fabomotizoLe hydrochLoride (15 mg/kg / day i.p/) in the above conditions, significantLy reduced the remodeLing of the Left and right ventricLes of the heart and increased the heart contractiLe function.На разработанной ранее трансляционной модели алкогольной кардимиопатии у белых беспородных крыс изучали кардиопротекторные эффекты триметазидина и фабомотизола гидрохлорида, вводимых ежедневно в период 25-28-й недель продолжающегося потребления 10% этилового спирта. Показано, что триметазидин (30 мг/кг/сут, в/б) и фабомотизола гидрохлорид (15 мг/кг/сут, в/б) в указанных выше условиях статистически значимо уменьшали ремоделирование левого и правого желудочков сердца и увеличивали сократительную функцию сердца

Intra- site 4f-5d electronic correlations in the quadrupolar model of the gamma-alpha phase transition in Ce

As a possible mechanism of the $\gamma-\alpha$ phase transition in pristine cerium a change of the electronic density from a disordered state with symmetry Fm-3m to an ordered state Pa-3 has been proposed. Here we include on-site and inter- site electron correlations involving one localized 4f-electron and one conduction 5d-electron per atom. The model is used to calculate the crystal field of $\gamma$-Ce and the temperature evolution of the mean-field of $\alpha$-Ce. The formalism can be applied to crystals where quadrupolar ordering involves several electrons on the same site.Comment: 12 pages, 2 figures, 4 tables, submitted to Phys. Rev.

Pharmacologic Inhibition of the TGF-β Type I Receptor Kinase Has Anabolic and Anti-Catabolic Effects on Bone

During development, growth factors and hormones cooperate to establish the unique sizes, shapes and material properties of individual bones. Among these, TGF-β has been shown to developmentally regulate bone mass and bone matrix properties. However, the mechanisms that control postnatal skeletal integrity in a dynamic biological and mechanical environment are distinct from those that regulate bone development. In addition, despite advances in understanding the roles of TGF-β signaling in osteoblasts and osteoclasts, the net effects of altered postnatal TGF-β signaling on bone remain unclear. To examine the role of TGF-β in the maintenance of the postnatal skeleton, we evaluated the effects of pharmacological inhibition of the TGF-β type I receptor (TβRI) kinase on bone mass, architecture and material properties. Inhibition of TβRI function increased bone mass and multiple aspects of bone quality, including trabecular bone architecture and macro-mechanical behavior of vertebral bone. TβRI inhibitors achieved these effects by increasing osteoblast differentiation and bone formation, while reducing osteoclast differentiation and bone resorption. Furthermore, they induced the expression of Runx2 and EphB4, which promote osteoblast differentiation, and ephrinB2, which antagonizes osteoclast differentiation. Through these anabolic and anti-catabolic effects, TβRI inhibitors coordinate changes in multiple bone parameters, including bone mass, architecture, matrix mineral concentration and material properties, that collectively increase bone fracture resistance. Therefore, TβRI inhibitors may be effective in treating conditions of skeletal fragility