Molecular dynamics study of cluster structure and properties of rotational waves in solid nanostructures

The paper reports a molecular dynamics analysis of rotary properties of a transformational wave generated due to compressive influence. Studies are performed in the time interval prior to the onset of elastic precursor reflection from the free boundary. It is shown that the leading front of a rotary wave coincides with the transformational wave front. The rotary wave velocity for copper is determined, being equal to 1300 m/s. The values of angular moment projections onto the coordinate axes in a plane perpendicular to wave propagation are found to be symmetrical, and their total sum equals zero

Molecular dynamics study of cluster structure and properties of rotational waves in solid nanostructures

The paper reports a molecular dynamics analysis of rotary properties of a transformational wave generated due to compressive influence. Studies are performed in the time interval prior to the onset of elastic precursor reflection from the free boundary. It is shown that the leading front of a rotary wave coincides with the transformational wave front. The rotary wave velocity for copper is determined, being equal to 1300 m/s. The values of angular moment projections onto the coordinate axes in a plane perpendicular to wave propagation are found to be symmetrical, and their total sum equals zero

Deformation Behavior under Static and Cyclic Tension of Polymer Grafts without and after Modification by RGD Peptides

The structure, mechanical properties, and deformation behavior under static and cyclic tension of biofunctionalized biodegradable vascular grafts based on polyhydroxybutyrate/valerate and polycaprolactone were studied. It is shown that the modification gives rise to an almost twofold decrease of the elongation at break as well as the ultimate strength. It is shown that under cyclic loading the modification of grafts results in decreasing cyclic durability by more than twice. In doing so, the level of deforming stress decreases to a much lesser extent and is practically inferior to that for unmodified material. The analysis of principal strain [epsilon]1 and [epsilon]2 component distribution patterns in grafts of both types is carried out while the reason for the observed changes is discussed

Lamb wave ultrasonic evaluation of welded AA2024 specimens at tensile static and fatigue testing

The paper deals with the investigation of Lamb waves ultrasonic testing technique applied for evaluation of different stress-strain and damaged state of aluminum specimens at static and fatigue loading in order to develop a Structural Health Monitoring (SHM) approach. The experimental results of tensile testing of AA2024T3 specimens with welded joints are presented. Piezoelectric transducers used as actuators and sensors were adhesively bonded to the specimen's surface using two component epoxy. The set of static and cyclic tensile tests with two frequencies of acoustic testing (50 kHz and 335 kHz) were performed. The recorded signals were processed to calculate the maximum envelope in order to evaluate the changes of the stress-strain state of the specimen and its microstructure during static tension. The registered data are analyzed and discussed in terms of signal attenuation due to the formation of fatigue defects during cyclic loading. Understanding the relations between acoustic signal features and fatigue damages will provide us the ability to determine the damage state of the structure and its residual lifetime in order to design a robust SHM system

Dislocation structure and deformation hardening alloy fcc single crystals at the mesolevel

The article presents the evaluation results of impacts of various strengthening mechanisms to flow stress. Such evaluations were made on the basis of the measured parameters of the dislocation substructure formed in monocrystals of [001]-Ni3Fe alloy deformed by compression within the stage II. It was found that the main impact to deformation resistance in the alloys with net substructure is made by the mechanism of dislocation impediment, which is caused by contact interaction between moving dislocations and forest dislocations

Dislocation structure and deformation hardening alloy fcc single crystals at the mesolevel

The article presents the evaluation results of impacts of various strengthening mechanisms to flow stress. Such evaluations were made on the basis of the measured parameters of the dislocation substructure formed in monocrystals of [001]-Ni3Fe alloy deformed by compression within the stage II. It was found that the main impact to deformation resistance in the alloys with net substructure is made by the mechanism of dislocation impediment, which is caused by contact interaction between moving dislocations and forest dislocations

Assessment of gastrointestinal dysfunction in selection of an effective method of nutritional support in patients with acute pancreatitis.

Potential mortality in acute pancreatitis (AP) is 5%. Patients with AP represent II type of intestinal insufficiency, which occurs on the background of dyspeptic syndrome and increased intra-abdominal pressure (IAP). IAP is a differentiated indicator. With the increase of IAP more than 10 mmHg, intra-abdominal hypertension (IAH) arises. Increasing IAP to this level is considered as safe. Monitoring of IAP level allows to achieve better clinical results. Totally 47 patients with acute pancreatitis were examined. Depending on the function of the gastrointestinal tract and the selected type of starting nutritional support (NS), they were divided into 2 groups. The first group consisted of IAH patients of I degree and dyspeptic syndrome who underwent parenteral nutrition (PN) with 3-component compounds begun on the 2nd day of disease and after restoration of gastrointestinal tract function a late enteral feeding (LEF) was performed. In the second group, patients with AP were initially diagnosed with elevated IAP at a safe level and dyspeptic syndrome. They were prescribed early enteral nutrition (EEN) with specialized blends from the 2nd day of disease. In 2 days a significant reduction in pain syndrome with the persistence of dyspeptic syndrome and intestinal insufficiency (II) was recorded. In patients with intra-abdominal hypertension, total parenteral nutrition is the effective method of nutritional support, against which, after 5 days manifestations of dyspeptic syndrome and IAP indices decrease to a safe level. Therefore in-time detection of high level of intra-abdominal pressure in patients with acute pancreatitis can help to choose a more rational method of nutritional support

Experimental investigation of high-energy photon splitting in atomic fields

The new data analysis of the experiment, where the photon splitting in the atomic fields has been observed for the first time, is presented. This experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, the statistics of $1.6\cdot 10^9$ photons incident on the BGO target was collected. About 400 candidates to the photon splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the cross section calculated exactly in an atomic field. The predictions obtained in the Born approximation significantly differ from the experimental results.Comment: 11 pages, 6 figures, LaTe

Dynamic fragmentation of Al-W granular rings with different mesostructures

The support of this project was provided by the Office of Naval research Multidisciplinary University Research Initiative Award N00014-07-1-0740, Program Manager Dr. Clifford D. Bedford