Effect of the Composition of Hybrid Sands on the Change in Thermal Expansion

In the foundry industry, silica sands are the most commonly used type of sands for the production of sand foundry moulds using various types of binders. Their greatest disadvantage is their significant volume changes at elevated temperatures, which are associated with the formation of many foundry defects from stress, such as veining, and thus have a direct influence on the final quality of the casting. In the case of non-silica sands and synthetic sands, the volume stability is more pronounced, but this is accompanied by a higher purchase price. Therefore, a combination of silica sand and synthetic sand CERABEADS is considered in order to influence and reduce the thermal expansion. The hybrid mixtures of sands, and their most suitable ratios, were evaluated in detail using sieve analysis, log W and cumulative curve of granularity. It was found that the addition of 50% CERABEADS achieves a 32.2% reduction in dilatation but may increase the risk of higher stresses. The measurements showed a significant effect of the granulometric composition of the sand on the resulting thermal expansion, where the choice of grain size and sorting can achieve a significant reduction in dilatation with a small addition of CERABEADS.     

Numerical approximations for an age-structured model of a population dispersing in a spatially heterogeneous environment.

As ecological information on life history and habitat characteristics has become more sophisticated, models have become more realistic, and simulation methodology has become more important. The numerical analysis of simulation models, especially those of complex structured ecological systems, is generally lacking. The numerical analysis techniques developed here are to help form a systematic basis for a simulation theory for physiologically structured, individual-based population models in a spatially heterogeneous habitat. The major thrust of this paper is to develop and analyse a finite-difference-finite-element numerical approximation scheme for a mathematical model of an age-structured population dispersing in a bounded spatial environment in Rn. The numerical scheme applies a characteristic finite-difference discretization for the time-age domain and a finite-element discretization with numerical integral modifications for the spatial domain. The scheme not only provides optimal error estimates from the numerical analysis perspective but also produces biologically reasonable approximate solutions in that the solutions remain non-negative. The existence and boundedness of the non-negative approximate solution are shown, and the optimal error estimate is proved.     

Application of the hypo-osmotic swelling test to spermatozoa prepared by swim-up and discontinuous Percoll separation

The quality of spermatozoa prepared by washing and swim-up or by discontinuous Percoll centrifugation, was compared by applying the hypo-osmotic swelling (HOS) test to semen samples from 116 men of infertile couples. The HOS test performed on 95 normal semen samples showed that the percentage of swollen spermatozoa separated by both techniques was significantly higher than in the initial ejaculate ( p <0.001). The percentage of HOS-positive spermatozoa separated by the Percoll gradient technique was significantly higher than that separated by the swim-up technique ( p <0.001). On the contrary, in 21 abnormal semen samples, there was no significant difference in the percentage of spermatozoa which were positive in the HOS test between the Percoll gradient and the swim-up technique ( p =0.44). It is suggested that the Percoll gradient technique appears to be preferable to the swim-up technique when semen parameters are normal, but there is no significant difference between these two techniques in abnormal semen.     

Failure of Impulse Propagation in a Mathematically Simulated Ischemic Border Zone: Influence of Direction of Propagation and Cell-to-Cell Electrical Coupling

Propagation in a Modeled Ischemic Border Zone. Introduction: It is suggested that heterogeneous extracellular potassium concentration, cell-to-cell coupling, and geometric nonuniformities of the ischemic border zone contribute to the incidence of unidirectional block and subsequent development of lethal ventricular arrhythmias.
Method and Results: A discrete electrical network was used to model a single cardiac fiber with a [K⁺]_e gradient characteristic of an ischemic border zone. Directional differences in propagation were evaluated by creating discrete regions with increased gap junctional resistance within the [K⁺]_e gradient. Furthermore, the effect of homogeneity/heterogeneity of cell length on impulse propagation through the [K⁺]_e gradient in the presence of increased gap junctional resistance was evaluated. The results indicate that failure of impulse propagation occurs at the junction between partially uncoupled and normally coupled cells. Furthermore, propagation failure was more likely to occur as the impulse propagated from a region of high [K⁺]_e to low [K⁺]_e. Heterogeneity in cell length contributes to the variability in the occurrence of unidirectional and bidirectional block.
Conclusions: The onset of cellular uncoupling in an ischemic border zone may interact with the inherent [K⁺]_e gradient leading to unidirectional conduction block. This mechanism may be important for the generation of reentrant arrhythmias at the ischemic border zone.     

Laser Scanner Observations of Heterogeneous Conduction Patterns in Rabbit Epicardium Induced by Cellular Uncoupling with Heptanol

Heptanol Disrupts Epicardial Conduction. This study examines how severely reduced intercellular electrical coupling affects the pattern of activation of left ventricular rahhit epicardium. Five thin (< 1-mm thick) flaps of < 60 mm² were stained in vitro with potentiometric dye WW781. A helium-neon laser beam was scanned over 63 spots on each flap, and the voltage-dependent fluorescence intensity from each spot was used to construct maps of the activation resulting from pacing at a single site. Introducing heptanol (1.75 mM) produced lines of conduction hlock in four of the five preparations after times ranging from 7 to 71 minutes; at varying intervals during this time, activation patterns were obtained. Fiber orientation was later determined from histologic sections. Heptanol changed the relatively uniform conduction seen under control conditions to heterogeneous patterns having regions of slowed conduction and lines of partial and complete block oriented predominantly parallel to the fiber direction (i.e., transverse propagation was blocked). The two partial blocks, which did not extend across the entire tissue, caused the activation wave to pivot around one end of the block line. The subsequent retrograde activation of the line's distal side was consequently delayed. Two points on opposite sides of these hlocks, separated by < 1 mm, had activation times differing by as much as 89 msec rather than a normal 3–5 msec. Thus, sufficient uncoupling can alter conduction pathways on the scale of a few millimeters. The resulting dispersion in activation times at closely spaced points may predispose poorly-coupled cardiac tissue to development of reentrant arrhythmias. (J Cardiovasc Electrophysiol. Voi. I, pp, 426–436. October 1990)     

消化道肿瘤切除后一层缝合术的临床应用

目的：探讨消化道切除后，吻合口采用一层缝合法吻合的可行性。方法：对121例消化道肿瘤切除后，采用吻合口一层缝合法行消化道重建术的病历资料进行回顾分析。结果：本组均治愈，无手术死亡病例，无出血及吻合口漏，术后随访1—12个月，未发现吻合狭窄。结论：消化道肿瘤切除后，吻合口采用一层缝合法，操作简便省时，安全可靠，可广泛用于胃肠道吻合重建。     

In smokers, swim-up and discontinuous gradient centrifugation recover spermatozoa with equally lower amounts of DNA damage than spermatozoa obtained from neat semen

We compared the abilities of two commonly used semen preparation techniques to decrease the amount of benzo(a)pyrene-diol-epoxide (BPDE)-DNA adducts in the spermatozoa of ten smokers. Semen processing by swim-up or discontinuous gradient centrifugation recovered spermatozoa showing an equally significantly lower amount of BPDE-DNA adducts than in unprepared spermatozoa from neat semen.     

改良皮肤入路间断埋线重睑成形术

目的:探讨间断埋线重睑探讨成形术的手术方法和术后效果。方法:通过改进皮肤入路间断埋线法的结膜出针点,使缝针穿透睑板和结膜,确保上睑皮肤与睑板牢固联结。结果:本组50例受术者(95侧重睑),经1～24个月随访,重睑线流畅自然,无线结外露或松脱现象。结论:该法术后重睑线牢固不易消失,操作简便可行,手术损伤小,术后恢复快。