Energy absorption by polymer crazing

During the past thirty years, a tremendous amount of research was done on the development of crazing in polymers. The phenomenon of crazing was recognized as an unusual deformation behavior associated with a process of molecular orientation in a solid to resist failure. The craze absorbs a fairly large amount of energy during the crazing process. When a craze does occur the surrounding bulk material is usually stretched to several hundred percent of its original dimension and creates a new phase. The total energy absorbed by a craze during the crazing process in creep was calculated analytically with the help of some experimental measurements. A comparison of the energy absorption by the new phase and that by the original bulk uncrazed medium is made

Estructura y propiedades térmicas de oleogeles a base de cera de abejas con diferentes tipos de aceites vegetales

Beeswax-based oleogels with different types of vegetable oil, including camellia oil (CO), soybean oil (SO), sunflower oil (SFO), or flaxseed oil (FO), were prepared and their structure and thermal properties were evaluated. The critical concentration of oleogel obtained from each of CO, SO, and SFO at 25 °C was 3% (w/w), and that from FO was 4%. Thermal measurements revealed similar thermodynamic curves for oleogels in different lipid phases. X-Ray diffraction showed orthorhombic perpendicular subcell packing and characteristic peaks of the β’ form. Furthermore, a morphology analysis of the crystals showed that they were needle shaped. Fourier transform-infrared spectra revealed that beeswax-based oleogels were formed via non-covalent bonds and may be stabilized with physical entanglements. The oleogels showed oil type-dependent oxidative abilities, but they were all stable and showed no obvious changes in peroxide value during 90 days of storage at 5 °C.Se prepararon oleogeles a base de cera de abejas con diferentes tipos de aceite vegetal, incluido el aceite de camelia (CO), de soja (SO), girasol (SFO) y linaza (FO), y se evaluaron la estructura y las propiedades térmicas. La concentración crítica de oleogel obtenida de cada uno de los aceites de CO, SO y SFO a 25 °C fue del 3% (p / p), y la del FO fue del 4%. Las medidas térmicas dieron curvas termodinámicas similares para los oleogeles en diferentes fases lipídicas. La difracción de rayos X mostró un empaquetamiento subcelular perpendicular ortorrómbico y picos característicos de la forma β’. Además, el análisis de la morfología de los cristales mostró que tenían forma de aguja. Los espectros infrarrojos de transformada de Fourier revelaron que los oleogeles basados en cera de abejas se formaron a través de enlaces no covalentes y pueden estabilizarse con enlaces físicos. Los oleogeles mostraron capacidades oxidativas dependientes del tipo de aceite, pero todos eran estables y no tuvieron cambios obvios en el valor del peróxido durante 90 días de almacenamiento a 5 °C

What factors influence UK medical students' choice of foundation school?

Background: We aimed to identify the factors influencing UK medical student applicants’ choice of foundation school. We also explored the factors that doctors currently approaching the end of their 2-year program believe should be considered. Methods: A cross-sectional study was conducted during the 2013–2014 academic year. An online questionnaire was distributed to 2092 final-year medical students from nine UK medical schools and 84 foundation year-2 (FY2) doctors from eight foundation schools. Participants were asked to rank their top 3 from a list of 12 factors that could potentially influence choice of foundation school on a 5-point Likert scale. Collated categorical data from the two groups were compared using a chi-square test with Yates correction. Results: Geographic location was overwhelmingly the most important factor for medical students and FY2 doctors with 97.2% and 98.8% in agreement, respectively. Social relationships played a pivotal role for medical student applicants. Clinical specialties within the rotations were of less importance to medical students, in comparison to location and social relationships. In contrast, FY2 doctors placed a significantly greater importance on the specialties undertaken in their 2-year training program, when compared to medical students (chi-square; p=0.0001). Conclusion: UK medical schools should make their foundation program applicants aware of the importance of choosing rotations based on specialties that will be undertaken. Individual foundation schools could provide a more favorable linked application system and greater choice and flexibility of specialties within their 2-year program, potentially making their institution more attractive to future applicants

Thermal Stress Analysis of Solar Thermochemical Reactor Using Concentrated Solar Radiation

Utilizing solar thermochemical reactor to convert exhaust gas into high-quality clean fuel by concentrated solar radiation is a valuable way to develop renewable energy. Due to the high working temperature, the issue of reactor damage occurs easily as found during the course of the experiment. In order to find out the reasons, some thermal stress simulation and analysis of solar thermochemical reactor were made in this article. The areas where thermal stress is concentrated were investigated in the contour simulation results. Based on the analysis, some suggestions for structural optimization for further research were formulated. Keywords: solar thermochemical, thermal stress, heat transfer and flow, reacto

Transient Analysis of Warm Electron Injection Programming of Double Gate SONOS Memories by means of Full Band Monte Carlo Simulation

In this paper we investigate "Warm Electron Injection" as a mechanism for NOR programming of double-gate SONOS memories through 2D full band Monte Carlo simulations. Warm electron injection is characterized by an applied VDS smaller than 3.15 V, so that electrons cannot easily accumulate a kinetic energy larger than the height of the Si/SiO2 barrier. We perform a time-dependent simulation of the program operation where the local gate current density is computed with a continuum-based method and is adiabatically separated from the 2D full Monte Carlo simulation used for obtaining the electron distribution in the phase space. In this way we are able to compute the time evolution of the charge stored in the nitride and of the threshold voltages corresponding to forward and reverse bias. We show that warm electron injection is a viable option for NOR programming in order to reduce power supply, preserve reliability and CMOS logic level compatibility. In addition, it provides a well localized charge, offering interesting perspectives for multi-level and dual bit operation, even in devices with negligible short channel effects

Waste Wood Processing Technologies Review

Summary: Four biomass conversion technologies were reviewed and assessed for potential use to convert the forest waste wood (biomass) in the Gisborne area. These conversion technologies include combustion, gasification, pyrolysis and torrefaction. The assessment is based on the maturity and complexity of the technology, products and applications, production costs and the environmental impact. The biomass combustion process is a mature technology and can produce heat or combined heat and power (CHP). Heat generation requires local users who can be wood processors or district heating. Power generated can be sent to the grid. Although biomass contains low contents of sulphur and nitrogen, emissions from the flue gas still need to be carefully monitored. Biomass gasification is a proven technology operating at 700 to 1200C, although 700-900C is most common. Both demonstration and commercial biomass gasification plants are available in the world. This technology produces a gas mixture, termed producer gas, with H2, CO, CO2 and CH4 being the major components. The producer gas is expected to contain a significant amount of N2 if air is used as the gasification agent. On the other hand, the producer gas also contains tar and gaseous contaminants, which need to be removed before the producer gas is further used. The cleaned producer gas can be used for power generation using a gas turbine or gas engine. In addition, the producer gas can be further processed for gaseous fuel (synthetic natural gas, hydrogen) or liquid fuel. In this case, the overall process is complex and capital investment is significantly increased. Biomass pyrolysis is also a proven technology operating at 400-650C with demonstration and commercial plants available around the world. In general, biomass can produce products in liquid (bio-oil), gas (non-condensable) and solid (bio-char). The target product in most cases is the liquid bio-oil, which is further processed for liquid fuel. In this case, sophisticated upgrading is needed due to the complex composition of the bio-oil. Torrefaction is a relatively simple process in which the wood is heated in the absence of oxygen to remove volatiles; thus, only solid char is produced at a yield of 85% or higher. The solid char can be used to substitute coal in combustion or co-firing. Recently, solid char has been applied in ironmaking to replace coal-derived coke. Based on the assessment of technology maturity, products and market demand, production costs and environmental impacts for the four conversion technologies, biomass torrefaction stands out as a preferred technology to process the forest waste wood to solid char

Superconducting and normal-state interlayer-exchange-coupling in La0.67_{0.67}Sr0.33_{0.33}MnO3{3}-YBa2_{2}Cu3_{3}O7−La_{7}-La_{0.67}SrSr_{0.33}MnO MnO{3}$ epitaxial trilayers

The issue of interlayer exchange coupling in magnetic multilayers with superconducting (SC) spacer is addressed in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) - YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) - La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) epitaxial trilayers through resistivity, ac-susceptibility and magnetization measurements. The ferromagnetic (FM) LSMO layers possessing in-plane magnetization suppress the critical temperature (T$_{c})$ of the c-axis oriented YBCO thin film spacer. The superconducting order, however, survives even in very thin layers (thickness d$_{Y} \sim$ 50 {\AA}, $\sim$ 4 unit cells) at T $<$ 25 K. A predominantly antiferromagnetic (AF) exchange coupling between the moments of the LSMO layers at fields $<$ 200 Oe is seen in the normal as well as the superconducting states of the YBCO spacer. The exchange energy J$_{1}$ ($\sim$ 0.08 erg/cm$^{2}$ at 150 K for d$_{Y}$ = 75 {\AA}) grows on cooling down to T$_{c}$, followed by truncation of this growth on entering the superconducting state. The coupling energy J$_{1}$ at a fixed temperature drops exponentially with the thickness of the YBCO layer. The temperature and d$_{Y}$ dependencies of this primarily non-oscillatory J$_{1}$ are consistent with the coupling theories for systems in which transport is controlled by tunneling. The truncation of the monotonic T dependence of J$_{1}$ below T$_{c}$ suggests inhibition of single electron tunneling across the CuO$_{2}$ planes as the in-plane gap parameter acquires a non-zero value.Comment: Accepted for publication in Phys. Rev.

Doping dependence of phonon and quasiparticle heat transport of pure and Dy-doped Bi_2Sr_2CaCu_2O_{8+\delta} single crystals

The temperature and magnetic-field (H) dependences of thermal conductivity (\kappa) of Bi_2Sr_2CaCu_2O_{8+\delta} (Bi2212) are systematically measured for a broad doping range by using both pure Bi2212 single crystals with tuned oxygen contents and Bi_2Sr_2Ca_{1-x}Dy_xCu_2O_{8+\delta} (Dy-Bi2212) single crystals with different Dy contents x. In the underdoped samples, the quasiparticle (QP) peak below T_c is strongly suppressed, indicating strong QP scattering by impurities or oxygen defects, whereas the phonon conductivity is enhanced in moderately Dy-doped samples and a phonon peak at 10 K is observed for the first time in Bi2212 system, which means Dy^{3+} ions not only introduce the impurities or point defects but also stabilize the crystal lattice. The subkelvin data show that the QP heat conductivity gradually decreases upon lowering the hole doping level. The magnetic-field dependence of \kappa at temperature above 5 K is mainly due to the QP scattering off vortices. While the underdoped pure Bi2212 show very weak field dependence of \kappa, the Dy-doped samples present an additional "dip"-like term of \kappa(H) at low field, which is discussed to be related to the phonon scattering by free spins of Dy^{3+} ions. For non-superconducting Dy-Bi2212 samples with x \simeq 0.50, an interesting "plateau" feature shows up in the low-T \kappa(H) isotherms with characteristic field at 1 -- 2 T, for which we discuss the possible revlevance of magnon excitations.Comment: 11 pages, 11 figures, accepted for publication in Phys. Rev.