Suppression of hysteresis in absorption of hydrogen by a Pd-Au alloy

Published by the American Physical Society. Hydrogen absorption by Pd exhibits hysteresis loops (provided the temperature is not too high) and represents one of the classical examples of first-order phase transitions in metals. Experiments indicate that addition of even a small amount of Au is able to suppress hysteresis. From this perspective, we analyze the energetics of hydrogen in a Pd-Au alloy by using extensive density-functional-theory (DFT) calculations. The dependence of the hydrogen binding energy on the number (n) of Au atoms forming an adsorption site is found to be appreciably nonlinear. With the DFT input for statistical calculations, we reproduce special features of the hydrogen absorption isotherms and explain the rapid decrease of the corresponding critical temperature with increasing Au fraction. The key factor here is that the phase transition is related primarily to absorption in sites formed only by Pd. With increasing Au amount, the fraction of such sites rapidly decreases, the distance between H atoms located there becomes on average larger, the interaction between them becomes weaker, and accordingly the driving force for the phase transition decreases. It is of interest that all these effects can be illustrated by taking only the configurations with n≤2 into account. This means that in the context under consideration the fine details of the dependence of the hydrogen binding energy on n are in fact not too important

Development of a Study on the Vitkimological Prevention of Offenses During the Years of Independence

In the article, the development of victimological prevention of crimes by the internal affairs bodies is divided into separate stages, the features of each stage are briefly disclosed. Especially at the 5th stage, reflecting the years of independence, during this period the formation and development of scientific and theoretical views and important changes in this area were reflected. This approach is based on the scientific, theoretical and historical necessity of victimological crime prevention

Partial or complete suppression of hysteresis in hydride formation in binary alloys of Pd with other metals

At temperatures below 600 K, the isotherms of hydrogen absorption by Pd exhibit hysteresis loops related to the first-order phase transition or, more specifically, to separation of a diluted phase and hydride. According to the experiments, addition of even small amount of the second metal, e.g. Au or Ta, can appreciably suppress hysteresis. This interesting effect is important in various applications, e.g., in the context of fabrication of efficient hydrogen sensors. To clarify its physical background, we present statistical calculations of the hydrogen absorption isotherms for a series of binary alloys of Pd with Mg, Cu, Ag, Ta, Pt, or Au by using the values of the H-metal interaction provided by the density functional theory (DFT). Aiming at the situations with small amount (≤15%) of the second metal, the metal atoms in an alloy are considered to be located at random or with short-range correlations. In the random alloy approximation, appreciable suppression of hysteresis is predicted for all the additives under consideration except Cu. Concerning the correlations, we show that the tendency of metals to mixing (as, e.g., predicted for the Pd–Au or Pd–Ta alloy) is in favour of additional suppression of hysteresis whereas the tendency to segregation (as, e.g., predicted for the Pd-Ag alloy) makes the hysteresis loops wider. For Au and Ta, our findings are in good agreement with available experimental data

Uzbekistan 's foreign policy for the implementation of our national interests

Today, the term "New Uzbekistan" is accepted in the international arena not only as a new concept, but also as a real social phenomenon. Such achievements and results, which are the result of the enormous legal opportunities created by our Constitution, certainly give us great pride and honor. It should be noted that the Constitution is an encyclopedic document that defines the independence of our people, the peaceful and peaceful life, the restoration of our national values, history and culture, as well as the guarantees of human rights and freedoms. At the same time, our Constitution is the sum of our national interests, which embodies the development of our country, ensuring the welfare and security of our people, strengthening our sovereignty, our country's activity as an equal subject in international relations. In addition, radical changes and large-scale reforms in all spheres of state and public life, including the strengthening of the rule of law and human rights, the development of an economy based on free market relations and the priority of private property, cooperation with far and near abroad. Our Constitution serves as an important basis for the establishment of mutually beneficial relations

Recycling of the Curve Planning in Gat Technology (Auto Cad) Program

In construction engineering, a curve with a given radius must be perfectly planned. Nowadays, given the development of GAT technologies, their electronic processing further increases the accuracy of the result. Designed with this in mind, this program improves the engineer's workflow and reduces the time of work performed

Advancements in arthroscopic treatment of ankle pathology: insights from our clinical experience

Ankle and foot injuries are prevalent musculoskeletal pathologies, comprising a significant portion of cases reported in both foreign and Russian literature. Arthroscopic examinations have emerged as a high-level medical technology, offering minimally invasive interventions with excellent diagnostic capabilities for joint injuries and diseases. This study aimed to enhance the diagnosis of ankle joint pathology by employing a combination of advanced research methods, including X-ray, MRI, MSCT, and arthroscopy. The article discusses the diagnostic capabilities of each method, highlighting their specific contributions to identifying various ankle joint conditions such as fractures, osteoarthritis, soft tissue injuries, and chronic instability. The study conducted arthroscopic interventions on 16 patients, focusing on therapeutic measures such as microfracturing, chondroplasty, osteophyte removal, impingement syndrome treatment, and ligament reconstruction. The postoperative outcomes were evaluated using a modified scale for assessing ankle joint function, showing a significant improvement in functional capabilities and pain reduction. The article concludes that arthroscopic intervention in the ankle joint is a technologically advanced, minimally invasive procedure that enables early rehabilitation initiation, reduces hospital stays, and accelerates patient recovery compared to open interventions

Force fields for divalent cations based on single-ion and ion-pair properties

We develop force field parameters for the divalent cations Mg2+, Ca2+, Sr2+, and Ba2+ for molecular dynamics simulations with the simple point charge- extended (SPC/E) water model. We follow an approach introduced recently for the optimization of monovalent ions, based on the simultaneous optimization of single ion and ion-pair properties.We consider the solvation free energy of the divalent cations as the relevant single-ion property. As a probe for ion- pair properties we compute the activity derivatives of the salt solutions. The optimization of the ionic force fields is done in two consecutive steps. First, the cation solvation free energy is determined as a function of the Lennard-Jones (LJ) parameters. The peak in the ion-water radial distribution function (RDF) is used as a check of the structural properties of the ions. Second, the activity derivatives of the electrolytes MgY2, CaY2 , BaY2, SrY2 are determined through Kirkwood-Buff solution theory, where Y = Cl−, Br−, I−. The activity derivatives are determined for the restricted set of LJ parameters which reproduce the exact solvation free energy of the divalent cations. The optimal ion parameters are those that match the experimental activity data and therefore simultaneously reproduce single-ion and ion-pair thermodynamic properties. For Ca2+, Ba2+, and Sr2+ such LJ parameters exist. On the other hand, for Mg2+ the experimental activity derivatives can only be reproduced if we generalize the combination rule for the anion-cation LJ interaction and rescale the effective cation-anion LJ radius, which is a modification that leaves the cation solvation free energy invariant. The divalent cation force fields are transferable within acceptable accuracy, meaning the same cation force field is valid for all halide ions Cl−, Br−, I− tested in this study

Optimization of classical nonpolarizable force fields for OH− and H3O+

We optimize force fields for H3O+ and OH− that reproduce the experimental solvation free energies and the activities of H3O+ Cl− and Na+ OH− solutions up to concentrations of 1.5 mol/l. The force fields are optimized with respect to the partial charge on the hydrogen atoms and the Lennard-Jones parameters of the oxygen atoms. Remarkably, the partial charge on the hydrogen atom of the optimized H3O+ force field is 0.8 ± 0.1|e|—significantly higher than the value typically used for nonpolarizable water models and H3O+ force fields. In contrast, the optimal partial charge on the hydrogen atom of OH− turns out to be zero. Standard combination rules can be used for H3O+ Cl− solutions, while for Na+ OH− solutions, we need to significantly increase the effective anion- cation Lennard-Jones radius. While highlighting the importance of intramolecular electrostatics, our results show that it is possible to generate thermodynamically consistent force fields without using atomic polarizability