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Over recent decades, the exploration of various allotropes of carbon at the nanoscale has attracted a significant amount of research interest. The demand for the synthesis of novel carbon-based nanostructures has resulted in the discovery of graphynes, i.e. one-atom-thick planar crystal lattice sheets of benzene rings connected by acetylene bonds. In this study, computer modelling and simulations were applied to characterise the full tensile and elastoplastic mechanical behaviour of such structures. Using a nonlinear finite element-based structural mechanics method, which is based on Morse potential functions, several parametric studies were performed, and various illustrative size-dependent diagrams were obtained, enabling the suitable and accurate design of graphyne-based material components based on key mechanical properties such as stiffness, tensile strength, and fracture strain. The four well-known types of graphyne sheets were numerically investigated: graphyne-1, also known as graphyne; graphyne-2, also known as graphdiyne; graphyne-3; and graphyne-4. The predictions of the mechanical properties of graphene were compared with other corresponding estimations to validate the research results. © 2022 Elsevier Ltd

Electromyographic peroneal reaction time measurements is a well established and reliable method of assessing the dynamic defence mechanism of the ankle joint against ankle sprains. Ankle bracing has been proved to be an effective prophylactic measure against injury since it restricts joint ROM. However, its role in improving the dynamic defence mechanism of the ankle according to the skin–brace interface application pressure, is unclear. The aim of this study was to investigate the effect of different pressures of ankle brace application in the peroneus longus reaction time. Thirty-three young, male, uninjured, physical education students were measured under three conditions: (1) without brace, (2) with brace and 30 kPa application pressure and (3) with brace and 60 kPa application pressure, as measured by a pressure sensitive sensor. Peroneal reaction time was assessed with surface electromyography, during a sudden inversion stress test on a trapdoor. The results demonstrated significant differences between the control (no brace condition) and the two brace conditions, with a significant increase of the peroneal reaction time, with increasing ankle brace application pressures, more pronounced in the 60 kPa pressure. The findings of this study show that prophylactic ankle bracing when applied tightly, seems to have a detrimental effect in the dynamic defence mechanism of the ankle joint, since it delays the peroneous longus activation onset during a simulated ankle sprain. Whether different brace application pressures introduced in this study can affect the incidence of ankle sprains remains to be examined.

Porosity is one of the defects most frequently encountered in aluminium die castings. Porosity formation causes costly scrap loss and limits the use of die-cast parts in critical high-strength applications. The amount of porosity is closely related to die casting process parameters. A considerable reduction in porosity formation can be obtained using the Taguchi approach in the die casting process. An example of the off-line technique used in the Greek die casting industry is given, with the aim of illustrating practicality and ease of use by industry engineers and managers. In the thick-walled sample casting studied, the final intensification pressure contributed 69 per cent towards the reduction in porosity. Among the other parameters considered, melt and die temperatures have a smaller effect (about 10 per cent), followed by the plunger velocities in the second and first stages which have only a slight effect on porosity formation. In addition, the expected quality improvement and the cost savings under optimum parameter settings were evaluated. The expected improvement in reduction in porosity formation was found to be 48.6 per cent, while the expected cost savings for multiple casting parts under optimum conditions was calculated to be 71.4 per cent/$1 loss before the experiment.

The use of the explicit non-linear finite element (FE) code DYNA 3D in sheet metal forming simulation is examined. A 3D FE model for the deep-drawing of cylindrical cups was constructed and the simulation results obtained using different simulation parameters, i.e. punch velocity, sheet material density, Coulomb friction coefficient at the tool–blank interfaces and type and dimensions of the FE mesh-elements, compared with experimental results regarding strain distributions (radial, circumferential and thickness through the sheet) and punch force–punch travel curves carried out on five galvanised steels and an aluminium sheet, for three different geometries of axisymmetric cup: Good agreement was obtained. The evaluation of the CPU time cost, the macroscopic deformation modes, the strain distributions of the deformed material and the process characteristics obtained for the constructed FE models, was directed towards the selection of the most efficient material and punch parameters. Finally, an attempt was made to construct rules from the above-mentioned verification, which may be used for reliable sheet metal forming simulations, using explicit finite-element codes.

The simulation of stretch forming using the explicit non-linear FE-Code DYNA 3D is reported. FE models concerning forming-limit diagrams and the physical modelling of the process from a macroscopic point of view have been constructed, the theoretical results obtained being compared with the results of experiments carried out on the stretching of four coated sheet steels. For these materials, modelled as isotropic elastic-plastic work-hardening, good agreement between modelling and experiment has been obtained, indicating, therefore, that the proposed FE model predicts FLDs satisfactorily.

In the last decades, the outstanding role of Thyroid gland in regulating both physiological and pathological operation of cardiovascular system has been acknowledged worldwide. Three main domains of Thyroid function, that is to say, euthyroidism -hyperthyroidism-hypothyroidism, have a direct impact on cardiac response through a variety of mechanisms. Cellular pathways mediate in cardiac contractility, cardiac output, cardiac rhythm, arterial blood pressure and peripheral vessel resistance. Particular biochemical algorithms exist not only between Thyroid hormones’ serum concentration and thyroid gland but also between the hormones’ serum level and heart muscle genes. These biochemical pathways primarily regulate the appropriate secretion of levothyroxine (T4) and triiodothyronine(T3) via Thyroid- Stimulating-Hormone(TSH) pituitary system, and secondly adjust the cardiac function. In this study, a mathematic model has been developed describing significant aspects of positive or negative feedback mechanisms of THYRO-CARDIAC (THY-CAR) system along with potential applications of novel up-to-date patents in this area of research.

The simulation of the deep-drawing of square cups using the explicit non-linear finite-element (FE) Code DYNA 3D is reported. FE models concerning punch-force and physical modelling of the process from a macroscopic point of view were constructed. The theoretical results obtained are compared with the results of experiments carried out on four coated steel sheets. For these materials, modelled as elasto-plastic work-hardened materials, a good agreement between modelling and experiments was obtained. The proposed FE model predicts satisfactory the load curves and the material flow and it is efficient for sheet-metal forming analysis.

The explicit FE code DYNA 3D was used to simulate precision forging at elevated temperatures (warm- and hot-working conditions) of two axisymmetric preforms, namely a conical shell and bevel gear preform. For simple and quick calculations the coupled thermomechanical process was simulated as an isothermal mechanical process for a particular temperature distribution of the steel preform. The metal flow, preform profiles, forging loads, stress and strain distributions in the workpiece and the tooling are well predicted by this technique. The upper-bound elemental technique (UBET), a kinematic admissible upper-bound approach, was also employed for quick engineering-approximation prediction of the forging loads and metal flow for the axisymmetric preform. The results obtained from the two simulating techniques are in good agreement for the forging loads, up to a particular degree of deformation, whilst the material flow is well predicted by the FEM but is only approximated when UBET is employed.

The implicit FE code MARC has been used to simulate the precision forging of a bevel gear. The true coupled thermomechanical forming conditions have been adopted to describe the metal flow during the process and the results obtained have been validated by extensive experimental work. An attempt has been made also to use a time-consuming explicit FE code, DYNA 3D; however, limitations were apparent in simulating the total procedure due to structural restrictions of this code. A CAD/CAM/CAE system able to successfully analyse such a precision forging operation is on hand.

Intoduction: The aim of the study was to investigate whether chaotic phenomena (chaos theory) affects the process of Gene Expression. Methods: Modeling the genes X, Y and Z-which encode a certain protein P-a set of three first order differential equations has been developed and studied in phase-space (x,y,z). Results: The elementary equilibrium points in three dimensional phase portrait analysis, include attractors, saddles and repellors. Conclusions: Attractors indicate a stable equilibrium point which attenuates the production of the protein P, while the saddles and particularly the repellors correspond to an unstable dynamic system, which promotes either the production of a P-flaw protein or totally inhibits gene expression. Among other mechanisms-e.g. patents for gene treatment (US2007000515344) and modulation(US20040014083A1)-chaotic phenomena also seem to regulate in a particular way the DNA encoding, that calls for further theoretical and experimental research(e.g. cardiovascular disease, oncology). © 2011 Bentham Science Publishers Ltd.

Crashworthiness analysis has become an integral part of the automotive design cycle. Since oblique impacts and vehicle rollover are common vehicle accidents, further studies investigating frame collapse due to bending loading are needed. The main focus of this paper is to study both experimentally and theoretically the effect of shear on collapse characteristics during the bending of cylindrical tubes. Theoretical and experimental results were found to be in good agreement.

The crumpling mechanisms of thin-walled octagonal steel tubes subjected to axial static compression and their efficiency as energy absorbing components under impact conditions are investigated and compared with the equivalent circular and square tubes of same material. Both inextensional and extensible collapse mechanisms are theoretically analysed. Theoretically predicted values based on the deformation modes encountered, as well as experimentally obtained ones, are compared and found to be in good agreement.

The present paper reports on the bending of thin-walled fibre-reinforced composite circular tubes under certain end-clamping conditions, simulating the oblique collision of structural elements of impacted vehicles. The fracture mechanism of the crushed composite tubes is quite different from that of metallic components loaded under the same conditions. Energy absorption in the present case is achieved by material fragmentation; i.e., the mechanism of fracture dominates the phenomenon, rather than plastic deformation. The effect of clamping conditions on the energy absorbing efficiency of the shell is also examined.

Objective: To study the impact of pressure drop (PD) which was developed along experimental stenoses on Pulse Wave Velocity (PWV). Methods: Eight, healthy, Landrace pigs were subjected to thoracotomy. In the upper segment of descending thoracic aorta a circumferential symmetric constriction 5 mm in length, was imposed and stabilized so that a pressure drop of 0 (DP-0, control group) 10 (DP-10), 20 (DP-20) and 30 mmHg (DP-30) could be created. respectively. Via catheterization of the vessel with pressure tip catheters, PD could be monitored. Pulse Wave Velocity (PWV) was measured via simultaneous recordings of Electrocardiogram and Doppler pressure waveforms which were received from right carotid and femoral artery. Then the recordings were fed to a computer for analytical estimation of PWV on several occasions: PWV-DP-0=8.27 +/- 0.12 m/sec, PWV-DP-10=8.68 +/- 0.13 m/sec, PWV-DP-20=9.19 +/- 0.13 m/sec and PWV-DP-30=9.51+/-0.14. Results: Significant increase in PWV estimated for all pressure drops compared to the control group. Thus, PWV-DP-0 vs. PWV-DP-10 or PWV-DP-20 or PWV-DP-30 were found to be statistical different (p

Objective: We assessed the radial distribution of elasticity in healthy porcine thoracic aorta. Methods: Cylindrical aortic specimens (n=24) were tested in a uniaxial tension device so that their Stiffness Modulus (SM) could be determined. The specimens were divided into three groups: Group A, radial stretching at zero degrees; Group B, radial stretching at forty five degrees; and Group C, radial stretching at ninety degrees. Results: Stress-Strain analysis showed that (SM-A) vs. (SM-B) and (SM-A vs. SM-C) and (SM-B vs. SM-C) were not statistically different for all strain levels (e=0.5, 1, 1.5, 2.3). Conclusions: In vitro, the radial expansion of aortic tissue appears to be uniform.Thus, diminished elastic properties of the aorta in cases of atheromatosis, would appear in these radial directions where the tissue is atheromatic. So, a useful site prediction could be made for future development of vessel abnormalities (i.e. aneurysm rupture) and the necessary vascular prosthesis might be applied more effectively. © 2007 Bentham Science Publishers Ltd.

Objective: To study the vibration adaptation of the aortic wall, after experimentally-induced stenosis in pig descending thoracic aorta. Methods: A 5 mm length, circumferential, rigid, symmetric constriction was created surgically, in eight healthy pigs, producing approximately a 15-20 mmHg pressure drop. Pressure Tip Catheters were used to monitor the pressure drop. Blood flow waveforms were recorded via a Bi-Directional Doppler Flow-meter at pre-A and post-B stenotic areas. Measurements were carried out before, 10 min after and 90 days after the creation of stenosis. The oscillating force acting on the aorta at regions A and B was approximated with the help of blood pressure waveforms. Euthanasia was performed after 90 days and the descending thoracic aorta removed. Eight sham-operated pigs were used as controls. Results: Pressure waveforms were recorded at both A and B sites and maintained until euthanasia. Also, vibration analysis proved that the oscillation frequency of the applied force at A and B regions was greater than that of the control tissues (p

On of the most typical forming processes used for the production of long, straight semi-finished products in the form of various section geometries is extrusion. Hot extrusion is a thermo-mechanical process whish involves complicated interactions between process parameters, tooling and deforming material /1,2/. In the present paper, FEM simulation is performed in the aluminum extrusion using circular dies with different geometries in order to extract quantitative simulating results regarding various forming parameters. Most specifically the parameters that are investigated are the die design-geometry, the process parameters (i.e. ram speed, container temperature, billet temperature) and the product quality (i.e. extruded shape, surface condition). The finite element modeling is based on 3D simulation tools using the DEFORM 3D software /3–5/. The used work piece is the aluminum AA6061 in cylindrical form with a diameter of 14 mm. The used material for the extrusion die is the hot work steel AISI H13. The geometry of the die is circular with a variation in die angle. The container and the billet temperature will vary from 450 to 550 degrees, and the mandrel (ram) speed will be at the range of 2 mm/sec. On the basis of simulating results such as pressure distribution on the extrusion die, effective stresses on the billet and product quality, new and improve die geometry will be introduced. Although the simulation problem is an axisymmetric one the authors decide to proceed with 3D FEM simulation in order to examine and verify the 3D simulating results. This paper is the first part of a further research project in which more complicated die geometries will be used as simulating and experimental specimens. In addition to simulating results, experimental results will be presented in the next few months.Copyright © 2006 by ASME

Electromyographic peroneal reaction time measurements is a well established and reliable method of assessing the dynamic defence mechanism of the ankle joint against ankle sprains. Ankle bracing has been proved to be an effective prophylactic measure against injury since it restricts joint ROM. However, its role in improving the dynamic defence mechanism of the ankle according to the skin-brace interface application pressure, is unclear. The aim of this study was to investigate the effect of different pressures of ankle brace application in the peroneus longus reaction time. Thirty-three young, male, uninjured, physical education students were measured under three conditions: (1) without brace, (2) with brace and 30 kPa application pressure and (3) with brace and 60 kPa application pressure, as measured by a pressure sensitive sensor. Peroneal reaction time was assessed with surface electromyography, during a sudden inversion stress test on a trapdoor. The results demonstrated significant differences between the control (no brace condition) and the two brace conditions, with a significant increase of the peroneal reaction time, with increasing ankle brace application pressures, more pronounced in the 60 kPa pressure. The findings of this study show that prophylactic ankle bracing when applied tightly, seems to have a detrimental effect in the dynamic defence mechanism of the ankle joint, since it delays the peroneous longus activation onset during a simulated ankle sprain. Whether different brace application pressures introduced in this study can affect the incidence of ankle sprains remains to be examined. © 2005 Elsevier Ltd. All rights reserved.

Objective: To carry out research into the possible changes of the spectral content of pressure pulse wave after the creation of an experimentally induced stenosis in the pig descending thoracic aorta. Methods: Eight healthy, normotensive Landrace pigs were subjected to thoracotomy under sterile conditions. At the upper segment of the descending thoracic aorta, a 5-mm-long circumferential symmetric constriction was imposed and stabilized; hence, a 15–20 mm Hg pressure gradient was established. Pressure tip catheters were used in order to monitor the pressure gradient. Blood flow disturbances were recorded through a bidirectional Doppler flow meter at pre- and poststenotic areas (A and B, respectively). Measurements were carried out before, 10 min after, and 90 days after the creation of the stenosis. The recorded waveforms were analyzed mathematically by using Fourier Transform, in order to determine their spectral component. Eight sham-operated pigs were used as controls. Results: Fourier Transform analysis showed a significant increase (P

To investigate the alterations of mechanical properties in pre- (A) and post- (B) stenotic aortic regions after an experimentally induced stenosis in the descending thoracic aorta.Eight healthy, normalipemic and normotensive Landrace pigs were subjected to thoracotomy under sterile conditions. In the upper segment of the descending thoracic aorta a circumferential symmetric constriction 5 mm in length was imposed and stabilized; thus, a 15-20 mm Hg pressure gradient was established. The pressure gradient was verified via catheterization of the vessel with pressure tip catheters. Pre- and poststenotic hemodynamic disturbances were recorded by the use of a bidirectional Doppler flowmeter. Pressure and flow measurements were carried out before, 10 min after, and 90 days after the creation of the stenosis. Euthanasia was performed after 90 days, and the descending thoracic aorta removed. In the A and B regions serial sections of aorta (5 mm in length) create appropriate aortic "rings," to test in a uniaxial tension device, in order to determine the mechanical properties of the vessel. Histological analysis was performed, so as to estimate the content (%) of collagen and elastin fibers within the aortic wall. Eight sham-operated pigs were used as controls.Reverse blood flow was recorded at both the A and B sites, and was maintained until euthanasia. Reverse flow in the poststenotic region B was greater than that in the prestenotic region. Mechanical analysis showed that the aortic wall in A and B regions became stiffer particularly at high strains (P0.05). Histological analysis indicated that the percentage of elastin fibers remained almost the same in both regions while the percentage of collagen fibers increased considerably, especially in the B region (P0.05).A nonhemodynamically significant experimental stenosis located at the level of the descending thoracic aorta induced reverse blood flow before and after the stenosis. The higher the reverse flow, the more collagen fibers were produced and the stiffer the aortic wall. Since hypercholesterolemia can be ruled out as a hardening factor in the present study, disturbed flow seems to be an independent factor which activates fibroblasts to overproduce collagen and to eventually reduce the aorta's compliance.

Objective: To carry out research into the possible changes of the spectral content of pressure pulse wave after the creation of an experimentally induced stenosis in the pig descending thoracic aorta. Methods: Eight healthy, normotensive Landrace pigs were subjected to thoracotomy under sterile conditions. At the upper segment of the descending thoracic aorta, a 5-mm-long circumferential symmetric constriction was imposed and stabilized; hence, a 15-20 mm Hg pressure gradient was established. Pressure tip catheters were used in order to monitor the pressure gradient. Blood flow disturbances were recorded through a bidirectional Doppler flow meter at pre- and poststenotic areas (A and B, respectively). Measurements were carried out before, 10 min after, and 90 days after the creation of the stenosis. The recorded waveforms were analyzed mathematically by using Fourier Transform, in order to determine their spectral component. Eight sham-operated pigs were used as controls. Results: Fourier Transform analysis showed a significant increase (P < 0.05) of spectral content in A and B areas. Also, the "relative" harmonic amplitudes in nonstenotic subjects were higher than in stenotic animals (P < 0.05). Conclusions: A minor experimental constriction located at the level of the descending thoracic aorta increased the spectral content of the pressure pulse wave, indicating that spectral analysis may detect slight flow disturbances before developing remarkable signs of an impaired circulation system.