Chemorheological changes in crosslinked epoxy resins subjected to large strains

Chemorheological changes in epoxy resins subjected to large strains while heated were observed earlier, but the subject was not treated quantitatively. This paper describes the investigation of an epoxy resin—Epon 826, of known chemical, structure, crosslinked with two different amines. By means of a simple calibrated apparatus, the epoxide samples were subjected to large strains in a non-oxidizing atmosphere and in air. They were heated to different temperatures for various times; the results were compared with data obtained from unstrained samples kept in otherwise the same conditions. The results show a linear-logarithmic relation between the torsion modulus, G₍₁₀₎ and the time of applied strain at a certain temperature and also a linear relation between G₍₁₀₎, and 1/T°K, both above T₍₁₀₎. The results obtained in swelling experiments support the data from 10 sec torsional modulus vs temperature measurements. An increase in the amount of solubles and in M_c is observed on extending the time of heating. A clear difference in properties between the strained and unstrained samples, kept in otherwise the sane conditions, is observed and the contribution of the applied strain to chemorheology has been shown. Both systems of crosslinked Epon 826 showed the same general behavior, although the specific data were different.     

Implicit leadership theory as a determinant of the factor structure underlying supervisory behavior scales.

Examined implicit leadership theory (preconceptions about the patterning of leadership variables) in 235 college students. Ss completed the Survey of Organizations questionnnaire on a fictitious "Plant X" about which they were given little information. Factor analysis, performed on the items purported to measure 4 leadership factors, resulted in the conceptualized factor structure. Since no information was given regarding supervisory behavior in Plant X, the factor structure was attributed to an implicit leadership theory. Factor analysis on subsamples indicated the factor structure could not be attributed to either experience in organizations or previous instruction in management. It is suggested that responses to questionnaires regarding organizational variables may be contaminated by implicit theory and that multitrait-multimethod procedures may be required to validate questionnaires. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An equivalent pressure source for the heart

A technique is described for the representation of the left ventricle as a one-port source characterized by a generator pressure and an internal impedance. The Fourier components of the pressure and impedance are determined from phasor analysis performed on recorded time-domain functions of pressure and flow under two conditions of loading. One condition is the quiescent state corresponding to normal operation of the circulatory system, and the other is obtained by use of a phase-shift balloon pump situated in the descending thoracic aorta. The use of the balloon pump for determining source parameters is novel. The Fourier components of pressure and impedance are determined for the first five harmonics of the quiescent pulse rate. Heart failure is simulated by ligation of all branches of the anterior descending coronary artery. The source parameters have been found to vary considerably between normal and failing hearts. Valve impedance and the impedance at the root of the aorta were also measured. The generator time-domain pressure waveforms were determined from the Fourier components. Effects of long duration pumping, upon the source parameters were found. The ratio of the calculated magnitudes of internal to external or load impedance indicates the possibility of considering the heart as a pressure source.     

General Analytical Framework for Design of Flexible Reinforced Earth Structures

Current design methods divide reinforced earth structures into walls and slopes by using an arbitrary face inclination of 70° as the boundary. The required maximum strength of reinforcement computed for reinforced walls are significantly higher than that computed for reinforced slopes even if the inclination is practically the same. Presented is a general analytical framework for design of flexible reinforced earth structures regardless of the slope face inclination. In fact, the framework is consistent for any structural geometry and any applicable slope stability analysis although, for demonstration purposes, the simple Culmann formulation is utilized for simple geometry with zero batter. Using an adequate slope stability formulation, the required tensile resistance of reinforcement for a given layout is calculated so as to produce the same prescribed factor of safety anywhere within the reinforced zone. That is, using the design shear strength of the soil, the required reinforcement resistance along each layer is computed to fully mobilize this shear strength for all possible slip surfaces. That is, a baseline solution is produced for an ideal long-term strength of reinforcement at any location. Consequently, the required strength of the connection between each reinforcement layer and the facing unit can also be determined. This connection strength, however, assumes small facing units with negligibly small shear and moment resistance. Parametric study is conducted to demonstrate the reasonableness of the presented framework. It is shown that the required tensile resistance and connection strength depend on factors such as: reinforcement length; intermediate reinforcement; percent coverage; and quality of fill. When compared with the current AASHTO design for walls, the required maximum long-term strength of the reinforcement as well as the required connection strength in the proposed approach are substantially smaller.     

3D effects of turning corner on stability of geosynthetic-reinforced soil structures

Current design procedures of Geosynthetic-Reinforced Soil Structures (GRSS's) are for walls/slopes with long straight alignments. When two GRSS segments intersect, an abrupt change in the alignment forms a turning corner. Experience indicate potential instability problems occurring at corners. The purpose of this study is to explore the effects of turning corner on the stability of reinforced slopes. Three-dimensional (3D) slope stability analysis, based on limit equilibrium, resulted in the maximum tensile force of reinforcement. Parametric studies required numerous computations considering various geometrical parameters and material properties. The computed results produced efficient practical format of stability charts. For long-term stability of reinforced slopes with turning corner, the influences of pore water pressure and seismic loading are also considered. Turning corner can improve the stability of reinforced slopes by virtue of inclusion of end effects. However, localized increase of pore water pressure or directional seismic amplification may decrease locally thus stability requiring strength of reinforcement larger than in two-dimensional (2D) plane-strain. While using 2D analysis for non-localized conditions may require stronger reinforcement, it also requires shorter reinforcement than in 3D analysis; i.e., 2D analysis may be unconservative in terms of reinforcement length.     

Reduction of the incidence of postharvest quality losses,and future prospects

Both quantitative and qualitative food losses of extremely variable magnitude occur during all harvest and postharvest stages, from harvesting, through handling, storage, processing and marketing, to final delivery to the consumer. The latest values published indicated that industrialized and developing countries dispose of roughly similar quantities of food. Whereas in developed countries the losses occur at the retailer and consumer stages, in the developing countries the losses occur during the production, harvest, postharvest and processing phases, because of poor infrastructure, low levels of technology, and low investment in food production systems. Quality cannot be improved after harvest, only maintained; therefore it is important to harvest fruits, vegetables and flowers at the proper stage and size and at peak quality. Preharvest production practices and factors such as cultivation practices, water supply, type of soil, environmental temperature and mechanical damage may seriously affect postharvest quality and result in the rejection or downgrading of produce at the point of sale. In addition, after harvest, improper temperature and humidity management as well as packaging and handling may have adverse effects on storage life and quality. Thus, integration of treatment methods calls for specific differential combinations of treatments for each product in each country.     

亚麻酸处理对苹果果实愈伤的促进作用及相关机理

目的：研究亚麻酸（linolenic acid,LA）对苹果果实采后愈伤的影响,探讨相关生化机理。方法：用1 mmol/L LA浸泡处理模拟损伤的‘富士’苹果果实,以含微量乙醇的无菌水处理为对照,通过测定苹果病情指数和质量损失率评价LA的愈伤效果,并分析果实伤口处苯丙烷代谢关键酶活力及代谢产物含量,以及H2O2含量和过氧化物酶活力。结果：与对照组相比,LA处理降低了愈伤期间损伤果实的质量损失率和损伤接种果实的病情指数;此外,LA处理提高了果实伤口处4 种苯丙烷代谢关键酶（苯丙氨酸解氨酶、肉桂酸-4-羟化酶、4-香豆酰辅酶A连接酶和肉桂醇脱氢酶）的活力,增加了4 种酚酸（芥子酸、阿魏酸、肉桂酸和咖啡酸）、3 种木质素单体（松柏醇、肉桂醇和芥子醇）以及总酚、类黄酮和木质素的含量;处理果实伤口处的H2O2含量和过氧化物酶活力也明显提高。结论：LA可通过激活苯丙烷代谢、提高H2O2含量和过氧化物酶活性来促进苹果果实愈伤。     

扩展青霉侵染对苹果果实膜磷脂代谢的影响

目的：研究扩展青霉侵染对苹果果实膜透性及膜磷脂代谢的影响。方法：以‘元帅’苹果为试材,测定扩展青霉损伤接种果实病健交界处组织的细胞膜透率、膜磷脂代谢关键酶活力以及相关底物和产物含量的变化。结果：扩展青霉侵染早期（2 d前）果实病斑直径无明显变化,侵染后期（2 d后）果实病斑直径和细胞膜透率明显增大。侵染期间,果实的磷脂酶A2、磷脂酶C和磷脂酶D活力,以及磷脂酸含量持续升高,磷脂酰胆碱和磷脂酰肌醇含量逐渐降低;磷脂酰胆碱、磷脂酰肌醇和磷脂酸与对照组的显著差异出现在侵染后期。此外,侵染早期果实的不饱和脂肪酸含量迅速升高,第2天时油酸、亚油酸和亚麻酸含量分别高出对照组31.58%、55.57%和43.67%;侵染后期果实的饱和脂肪酸含量快速升高,第6天时的棕榈酸和硬脂酸含量分别高出对照组49.46%和43.39%。侵染果实的脂肪酸不饱和度早期高于对照组,后期低于对照组。相关性分析表明,侵染果实细胞膜透率与磷脂酶A2、磷脂酶C和磷脂酶D活力,以及磷脂酸、棕榈酸和硬脂酸含量呈极显著正相关,但与磷脂酰胆碱和磷脂酰肌醇含量呈极显著负相关。结论：扩展青霉侵染激活了果实的磷脂酶,促进了膜磷脂的降解和脂肪酸的释放,破坏了细胞膜的完整性。侵染早期不饱和脂肪酸的迅速释放可能与果实抗性相关。     

Hydrogels from silk fibroin metastable solution: Formation and characterization from a biomaterial perspective

Silk fibroin (SF) hydrogels were obtained from the dialysis of a SF metastable solution. Temperature and calcium concentration in SF solution/hydrogel were measured, as critical variables for SF gelation phenomenon. Gelation time of SF solution was increased by decreasing the dialysis temperature, whereas the residual calcium concentration was higher when higher dialysis temperatures were applied. Hydrogels obtained at 20 °C were characterized after freeze-drying. SEM micrographs showed porous structures, of ca. 20 μm (in cross-sectional area) and 5 μm (on surface). XRD indicated the presence of a β-sheet structure that is formed during SF gelation. In hydrogel formation, SF molecules in solution are dehydrated and interact by intra and intermolecular hydrogen bonds, forming a stable hydrogel. DSC measurements showed the decomposition peak for SF at 290 °C, characteristic of SF β-sheet structure, which is in accordance with the XRD results and demonstrate its high thermal resistance. SF hydrogels were found not to be toxic to cells using in vitro cytotoxicity tests. Results indicate that silk fibroin hydrogels hold promise for use in the biomaterial field.     

Tumor necrosis factor-related apoptosis inducing ligand expression and activity in hen granulosa cells

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) represents one of several cytokine members of the tumor necrosis factor superfamily reported to initiate apoptosis in a wide range of transformed, but not most normal, cell types. The present studies were conducted to evaluate the potential for TRAIL to promote apoptotic cell death in differentiated granulosa cells collected from hen preovulatory follicles. While mRNA encoding critical components (including TRAIL) required for a functional extrinsic cell death pathway are expressed in granulosa cells, TRAIL treatment by itself fails to induce either caspase-3 activity or a decrease in cell viability. On the other hand, preculture of cells with the conventional chemotherapeutic, cisplatin, or the 20S proteosome inhibitor, Z-LLF-CHO, sensitizes granulosa cells to TRAIL as evidenced by enhanced caspase-3 activity after 4 h of culture and loss of cell viability after 24 h when compared with either cisplatin or Z-LLF-CHO treatment alone. Moreover, the sensitizing effect of Z-LLF-CHO on TRAIL-induced loss of cell viability is prevented by the selective caspase-8 inhibitor, Z-IETD-FMK. Interestingly, TRAIL mRNA expression is elevated both in prehierarchal follicles undergoing spontaneous atresia and in prehierarchal follicles induced to undergo atresia for 6 h in vitro. In summary, the data demonstrate the presence of a functional TRAIL signaling pathway in hen granulosa cells, and are consistent with the possibility that TRAIL signaling may directly or indirectly participate in the process of follicle atresia in vivo.