Front Segment Research Articles

Numerical modeling and optimization of the cryosurgery operations

Numerical computation of the three dimensional problem of the freezing interface propagation during the cryosurgical impact coupled with the multi-objective optimization mechanism is used in order to improve the efficiency and safety of the cryosurgery operations performing. The heat transfer in soft tissue during the thermal exposure to low temperature is described by the Pennes bioheat model. The finite volume method combined with the control volume approximation of the heat fluxes is applied for the cryosurgery numerical modeling on the tumor tissue of a quite arbitrary shape. The flux relaxation approach is used for the stability improvement of the explicit finite difference schemes. The generalized method of effective traversals is proposed for the searching of the Pareto front segments as the multi-objective optimization problem solutions.

Crossing grain boundaries in metals by slip bands, cleavage and fatigue cracks.

The size and the character (low and large angle, special boundaries, tilt and twist boundaries, twins) of the grain boundaries (GBs) in polycrystalline materials influence their strength and their fracture toughness. Recent studies devoted to nanocrystalline (NC) materials have shown a deviation from the Hall-Petch law. Special GBs formed by Σ3 twins in face-centred cubic metals are also known to have a strong effect on the mechanical behaviour of these metals, in particular their work-hardening rate. Grain orientation influences also crack path, the fracture toughness of body-centred cubic (BCC) metals and the fatigue crack growth rate of microstructurally short cracks. This paper deals both with slip transfer at GBs and with the interactions between propagating cracks with GBs. In the analysis of slip transfer, the emphasis is placed on twin boundaries (TBs) for which the dislocation reactions during slip transfer are analysed theoretically, experimentally and using the results of atomic molecular simulations published in the literature. It is shown that in a number of situations this transfer leads to a normal motion of the TB owing to the displacement of partial dislocations along the TB. This motion can generate a de-twinning effect observed in particular in NC metals. Crack propagation across GBs is also considered. It is shown that cleavage crack path behaviour in BCC metals is largely dependent on the twist component of the GBs. A mechanism for the propagation of these twisted cracks involving a segmentation of the crack front and the existence of intergranular parts is discussed and verified for a pressure vessel steel. A similar segmentation seems to occur for short fatigue cracks although, quite surprisingly, this crossing mechanism for fatigue cracks does not seem to have been examined in very much detail in the literature. Metallurgical methods used to improve the strength of the materials, via grain boundaries, are briefly discussed.

Scaling of the appendicular skeleton of the giraffe (Giraffa camelopardalis).

Giraffes have remarkably long and slender limb bones, but it is unknown how they grow with regard to body mass, sex, and neck length. In this study, we measured the length, mediolateral (ML) diameter, craniocaudal (CC) diameter and circumference of the humerus, radius, metacarpus, femur, tibia, and metatarsus in 10 fetuses, 21 females, and 23 males of known body masses. Allometric exponents were determined and compared. We found the average bone length increased from 340 ± 50 mm at birth to 700 ± 120 mm at maturity, while average diameters increased from 30 ± 3 to 70 ± 11 mm. Fetal bones increased with positive allometry in length (relative to body mass) and in diameter (relative to body mass and length). In postnatal giraffes bone lengths and diameters increased iso- or negatively allometric relative to increases in body mass, except for the humerus CC diameter which increased with positive allometry. Humerus circumference also increased with positive allometry, that of the radius and tibia isometrically and the femur and metapodials with negative allometry. Relative to increases in bone length, both the humerus and femur widened with positive allometry. In the distal limb bones, ML diameters increased isometrically (radius, metacarpus) or positively allometric (tibia, metatarsus) while the corresponding CC widths increased with negative allometry and isometrically, respectively. Except for the humerus and femur, exponents were not significantly different between corresponding front and hind limb segments. We concluded that the patterns of bone growth in males and females are identical. In fetuses, the growth of the appendicular skeleton is faster than it is after birth which is a pattern opposite to that reported for the neck. Allometric exponents seemed unremarkable compared to the few species described previously, and pointed to the importance of neck elongation rather than leg elongation during evolution. Nevertheless, the front limb bones and especially the humerus may show adaptation to behaviors such as drinking posture.

Redefining the Self: The Human Centipede and physical spectatorship

Abstract

Health Monitoring System Design of Coastal High-Piled Wharf

There is little research on health monitoring technology of coastal ports at present. Based on the characteristics of high-piled wharf in coastal ports and staying in particular environment, the mechanical properties of coastal high-piled wharf is analyzed, and the health monitoring parameters are proposed. Finally, the health monitoring system of coastal high-piled wharf is constructed. And the appropriate structural health monitoring system is designed for standardized front segment of a high-piled wharf in the Tianjin port. The monitoring parameters are proposed, and the sensors and specification parameters are provided to reach the point. The data acquisition and transmission subsystem implementation technology and related indicators are given. This can provide a reference for the long-term health monitoring system construction in coastal high-piled wharf structure.

Cholesterol-Induced Condensing and Disordering Effects on a Rigid Catanionic Bilayer: A Molecular Dynamics Study

Molecular dynamics simulation is applied to investigate the bilayer properties of a novel catanionic vesicle composed of an ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), with cholesterol. Structural properties, such as molecular organization, orientation, and conformation, were analyzed from the resulting trajectory. Simulation results showed that cholesterol could induce both condensing and disordering effects on the rigid HTMA-DS bilayer. The condensing effect of cholesterol was ascribed to the maximizing contact between cholesterol ring and the neighboring hydrocarbon chains. Thus, the inserted cholesterol ring restrained the neighboring hydrocarbon chain segments from motion and increased the order of the neighboring hydrocarbon chains. However, the presence of cholesterol would increase the distance between head groups of HTMA-DS and induce a shift of DS(-) head groups toward the inside of the bilayer. This led to the protrusion of the HTMA(+) head groups and conformational disorder in the front segments of HTMA(+) hydrocarbon chains. In addition, the cholesterol-induced void in the hydrophobic core of the HTMA-DS bilayer increased the motion freedom of the terminal segments of the hydrocarbon chains. The cholesterol-induced space in the polar region and void in the nonpolar region of the bilayer led to a conformational disorder. With high cholesterol contents, the conformational disorder effect would overwhelm the condensing effect, resulting in the apparent disordering effect on the rigid HTMA-DS bilayer.

Pyrolysis model of oil sand using thermogravimetric analysis

In this paper, the derivative thermogravimetry (DTG) curve displays an overlapping peak which consists of two subpeaks for the major oil-producing stage of Indonesian oil sand. This study was conducted to supplement the insufficiencies of the previous studies, which neglected or oversimplified the processing of the overlapping peak and did not determine the kinetic mechanism. First of all, we assume a two-component parallel reaction model to describe the mass-loss process of the major oil-producing stage (overall stage) to obtain the separated stages. Then, we present an asymmetric multi-peak fitting method, bi-Gauss, to separate the overlapping peak. Based on the results of the bi-Gauss method, the kinetic mechanism was obtained using the integral master plot method, followed by the determination of the activation energy by the integral iso-conversional non-linear (NL-INT) method. The results show that the bi-Gauss method can produce satisfactory fitting results. Moreover, the separated stages follow single mechanism; while the overall stage does not follow a single mechanism and the mechanisms of the front and back segments of the overall stage are in accordance with those of the separated stages, which prove the reliability of the two-component parallel reaction model.

Generalizing the advancing front method to composite surfaces in the context of meshing constraints topology

Being able to automatically mesh composite geometry is an important issue in the context of CAD–FEA integration. In some specific contexts of this integration, such as using virtual topology or meshing constraints topology (MCT), it is even a key requirement. In this paper, we present a new approach to automatic mesh generation over composite geometry. The proposed mesh generation approach is based on a generalization of the advancing front method (AFM) over curved surfaces. The adaptation of the AFM to composite faces (composed of multiple boundary representation (B-Rep) faces) involves the computation of complex paths along these B-Rep faces, on which progression of the advancing front is based. Each mesh segment or mesh triangle generated through this progression on composite geometry is likely to lie on multiple B-Rep faces and consequently, it is likely to be associated with a composite definition across multiple parametric spaces. Collision tests between new front segments and existing mesh elements also require specific and significant adaptations of the AFM, since a given front segment is also likely to lie on multiple B-Rep faces. This new mesh generation approach is presented in the context of MCT, which requires being able to handle composite geometry along with non-manifold boundary configurations, such as edges and vertices lying in the interior domain of B-Rep faces.

Study on absorption location of four components from Naoxintong capsule

To study the absorption characteristics of four components from Naoxintong capsule in intestines. In vitro everted gut sac method was adopted for preparing the intestinal absorption solution of Naoxintong capsule. UPLC was used to detect the content of chemical components in different intestinal segments, and comparing the results with the absorption of chemical components of Naoxintong capsule in each intestinal segment. The time-accumulative absorption curve was drawn to observe the changes in the accumulative absorption concentration with time. Four ingredients of Naoxintong capsule can be detected in intestinal absorption solution, they are ferulic acid, paeoniflorin, salvianolic acid B and hydroxysafflor yellow A. Specifically, the accumulative absorption concentrations of ferulic acid, salvianolic acid B and paeoniflorin in ileum and rear jejunum segments were higher than that in front and middle jejunum segments; the absorption of ferulic acid, paeoniflorin, salvianolic acid B and hydroxysafflor yellow A did not reach saturated conditions in 3 hours. Ferulic acid, paeoniflorin, salvianolic acid B and hydroxysafflor yellow A are absorbed in the whole intestine. Ferulic acid, paeoniflorin and salvianolic acid B may be absorbed in specific segments.

Modeling three‐dimensional hydraulic fracture propagation using virtual multidimensional internal bonds

SUMMARYPropagation of fractures, especially those emanating from wellbores and closed natural fractures, often involves Mode I and Mode II, and at times Mode III, posing significant challenges to its numerical simulation. When an embedded inclined fracture is subjected to compression, the fracture edge is constrained by the surrounding materials so that its true propagation pattern cannot be simulated by 2D models. In this article, a virtual multidimensional internal bond (VMIB) model is presented to simulate three‐dimensional (3D) fracture propagation. The VMIB model bridges the processes of macro fracture and micro bond rupture. The macro 3D constitutive relation in VMIB is derived from the 1D bond in the micro scale and is implemented in a 3D finite element method. To represent the contact and friction between fracture surfaces, a 3D element partition method is employed. The model is applied to simulate fracture propagation and coalescence in typical laboratory experiments and is used to analyze the propagation of an embedded fracture. Simulation results for single and multiple fractures illustrate 3D features of the tensile and compressive fracture propagation, especially the propagation of a Mode III fracture. The results match well with the experimental observation, suggesting that the presented method can capture the main features of 3D fracture propagation and coalescence. Moreover, by developing an algorithm for applying pressure on the fracture surfaces, propagation of a natural fracture is also simulated. The result illustrates an interesting and important phenomenon of Mode III fracture propagation, namely the fracture front segmentation. Copyright © 2012 John Wiley & Sons, Ltd.

Crack front penetration in transgranular cleavage cracking in an iron-silicon alloy

Based on the analysis of the crack trapping effect of cleavage ridges and penetration of crack front segments in an iron-silicon alloy, the distance between break-through points along a high-angle grain boundary is investigated. If the break-through points are close to each other, the crack trapping effect is dominant; otherwise, the grain boundary separation in break-through windows governs the front transmission process. The relationship between the overall grain boundary fracture resistance and the break-through-point distance is quite complex. The minimum grain boundary resistance is achieved when the break-through points are about 2–3 µm apart, which is also influenced by the grain boundary shear strength, the crystallographic toughness and orientation, as well as the crack front profile.

Classifying fronts in data from a VHF wind-profiling radar

Many fronts over the UK do not fit the traditional conceptual model of a single maximum of vertical shear of the horizontal wind sloped over the cold air. A 2-year climatology of 296 cold, warm, and occluded fronts from a mesosphere–stratosphere–troposphere radar near Aberystwyth, Wales, reveals that 74% of warm fronts were associated with multiple linear bands representing maxima of vertical wind shear, radar return signal power, or both. In contrast, 51% of cold fronts lacked any such maxima. Similarly, the warm frontal segments of occluded fronts exhibited more banding than the cold frontal segments. Copyright © 2011 Royal Meteorological Society

Ocular manifestation in canine leishmaniasis

This paper presents a case of ocular changes in leishmaniasis in a dog brought in for examination because of visible changes in the eyes. An ocular manifestation in leishmaniasis can be bilateral or unilateral. Changes most often occur on the conjunctive and the front segment of the eye, the cornea and iris. From 70 to 80% of dogs diseased with leishmaniasis exhibit frontal uveitis, and dry eye, keratoconjunctivitis sicca, is also a frequent finding. Based on the clinical picture and the positive immunochromatographic rapid test it was established that the dog was diseased with leishmaniasis.

Criterion for initiation of cracks under mixed-mode I + III loading

The initiation of crack growth under a combination of opening and anti-plane shearing mode loading is considered in this paper. It is shown that such cracks do not grow through a continuous evolution of the crack surface. Rather, an abrupt fragmentation or segmentation of the crack front is generated. Through experimental observations and a theoretical model, we postulate a relationship between the scale of the fragmentation and the mode mix.

The Conception of the Segmented Kinetic Energy Penetrators for Tank Guns

In this paper we present possibilities of increasing the depth of penetration through a steel plate by using segmented kinetic energy penetrators. Conclusions about the possibilities of increasing the penetration depth were formulated based on the critical review of the literature, simulations, and firing test results. A new concept called “forced segmented penetration,” where applied penetrator is composed of two tungsten alloy pieces connected by a screwed steel muff, is presented in this paper. The axial deformation of the connecting muff during the penetration process results in a decrease in the distance between tungsten segments. For this reason the rear segment can hit the front segment to give it some additional kinetic energy, enhancing the penetration depth. Such type of segmented penetration phenomena was not presented earlier. The numerical analyses of the segmented penetrator of the new design are presented in this paper.

One-photon annihilation of an electron-positron pair in the field of pulsed circularly polarized light wave

The one-photon annihilation of an electron-positron pair in the pulsed light field is investigated theoretically. The pulsed laser field is described by the plane circularly polarized electromagnetic wave with the envelope function. The analytical expressions for an amplitude and probability of the studied process are derived. The conditions for an observation of the one-photon annihilation the pulsed light field are ascertained. It is demonstrated, that the region of numerical values of the initial particles parameters within which the one-photon annihilation in the pulsed light field may be possibly realized is significantly broader in comparison with the monochromatic wave case. Within the observation domain the probability of one-photon annihilation process in the pulsed light field essentially exceeds the correspondent one the external field absence, except the points with the strong suppression of the probability which is the result of an interference of the amplitude’s parts; the last ones correspond to the contributions of the front and posterior segments of the pulse.

Coarticulation effects of Korean sibilant /s/ before a high front segment

This paper investigates acoustic characteristics of Korean /s/ before a high front segment and argues that Korean /s/ shows acoustic characteristics of a palatalized segment due to the coarticulation with the following high front segments. In Experiment, it is shown that the first 30 msec of /s/ before /i, ye, ya/ shows spectral peaks around 4 kHz whereas /s/ before open vowels like /e, a/ shows peaks around 6 kHz. We suggest that this is due to the tongue body position at the palatal area placed at the beginning of /s/ when it is followed by /i/ or /y/. Center of gravity frequency, and band energy difference also show differences of Korean /s/ in different contexts. Based on the results of this experiment, we argue that Korean /s/ is modified from its beginning due to the coarticulation with the following segments if articulators of /s/ are compatible with those of the following segments. Interestingly, this paper also shows that in case /s/ is followed by /yu/ or /yo/, its spectral shape shows significant differences from /s/ followed by /ya/ or /ye/. It raises the question that in Korean the domain of coarituclation may be larger than the target and its immediately surrounding segment.

Resistance to cleavage cracking and subsequent shearing of high-angle grain boundary

In a previous experimental study, it was observed that the break-through process of a cleavage front across a high-angle grain boundary can be highly nonuniform. While the central part of the boundary can be cleaved quite smoothly, the rest parts must be sheared apart. In this paper, the trapping effect of grain boundary shearing is analyzed in considerable detail. Before the shearing is completed, the crack flanks are locally pinned together and a bridging stress must be provided. The bridging stress has a negative contribution to the local stress intensity at the cleavage front segment that penetrates across the grain boundary, and thus the crack growth driving force must be increased. A closed-form equation is derived to relate the overall fracture resistance to the fracture mode through an energy analysis.

Associação entre medidas lineares e angulares de equinos da raça Mangalarga Marchador

Foram analisadas 12 medidas de comprimento dos ossos, duas medidas de altura, duas medidas de perímetro e 11 medidas de ângulos articulares) de 169 equinos da raça Mangalarga Marchador, de ambos os sexos (82% de fêmeas), com idades entre 35 e 269 meses, de 11 criatórios do Estado de Minas Gerais e cinco de São Paulo. Os efeitos de estado e criatório de origem, tipo de criação (baia ou pasto), idade e sexo sobre essas características foram avaliados pelo método dos quadrados mínimos, e as associações entre as características foram quantificadas por meio da correlação de resíduos. Os modelos justificaram pouco da variação observada, com coeficientes de determinação variando de 0,09 a 0,48 para as medidas lineares e de 0,11 a 0,44 para as medidas angulares. Estado e criatório de origem, sexo, idade e tipo de criação foram importantes fontes de variação, respectivamente para 13 (48,1%), 12 (44,4%), seis (22,2%), quatro (14,8%) e três (11,1%) das 27 características avaliadas. As correlações de resíduo entre as características indicaram que a escolha de animais com úmero de maior comprimento está associada a animais com membros torácicos e pélvicos mais longos e que a escolha de animais a partir do tamanho dos membros acarretará concomitante incremento na altura da cernelha e na garupa e do perímetro da canela e torácico. Ainda, a escolha dos animais considerando as medidas dos ângulos metacarpofalangeano e dedo torácico com a horizontal refletirá positivamente na altura da cernelha e da garupa.

Prototyping studies for the Blanket Shield Module of the ITER ECH Upper Port Plug

A team of European associations is planning to procure ECH launcher turnkey systems for MHD control in the ITER plasma. ECH launchers will be installed to four ports on the upper level of the ITER vacuum vessel (VV). The structural system of the launchers accommodates the mm-wave components, cooling devices and elements for nuclear shielding. Its main components are the Blanket Shield Module (BSM), including the plasma facing First Wall Panel (FWP) and the port plug mainframe. A removable flange connection between the BSM and the main frame provides access to the internals. Appropriate remote handling capability is also taken as a design requirement. The BSM with the flange connection will be exposed to substantial nuclear heat loads. The manufacturing of machined components requires complex shaping with small tolerances and good quality of the surfaces due to operation under vacuum conditions. For the BSM and the front segment of the main frame a rigid double wall structure with meandering rectangular cooling channels was designed and analysed to meet these requirements. To investigate industrial manufacturing routes, a typical single-piece sample was machined and the manufacturing process was evaluated. Further two prototypes of a characteristic section of the BSM were manufactured, using two different fabrication techniques. These are (a) Hot Isostatic Pressing (HIP), which combines the sintering of metal powder inside of welded capsules and diffusion welding of solid parts and (b) brazing of bent and machined individual parts. The prototypes are under study at the Launcher Handling Test facility (LHT) at FZK, which offers a water circuit to provide coolant with adjustable parameters, simulating different ITER operating conditions. Extensive test series were performed to validate underlying analysis related to homogenous temperature distribution, tolerable pressure drop within the cooling paths and removal of applied heat loads.