21世纪的加速老化测试

研究了老化试验科学在21世纪的状况,以及取得最新突破性成果之前的漫长征程。介绍了一个全新的突破性的ASTM测试方法的诞生。     

The Influence of Section Size and Base Sulphur Content on the Structure of Compacted Vermicular Graphite Cast Iron Produced by the Inmold Process

Abstract

The paper discusses the effect of certain variables involved in the production of compacted graphite cast iron by the Inmold Process,? using a 5% Mg-FeSi alloy, such as sulphur content of the base iron, copper content and section size. Experimental results show that acceptable compacted graphite irons can be produced in castings with section sizes ranging from 12.5 to 50 mm. The required residual Mg was a function of the base sulphur as follows: 0.013–0.021 % Mg for a base sulphur of 0.0083–0.0092% and 0.019–0.024% Mg for a base sulphur of 0.017–0.019%. When the base sulphur was 0.025–0.030%, it was impossible to produce compacted graphite microstructures. As expected, copper additions increased the amount of pearlite in the microstructure. For example, a 0.42% Cu content resulted in microstructures containing more than 50% pearlite in sections of 12.5 and 25 mm.     

Modelling tempering behaviour of dark chocolates from varying particle size distribution and fat content using response surface methodology

Central Composite Rotatable Design (CCRD) for K = 2 was used to study the combined effects of multi-stage heat exchangers for Stages 1 (14–30 °C) and 2 (12–28 °C) coolant temperatures at constant Stage 3 coolant and holding temperatures during tempering of dark chocolates using laboratory-scale mini-temperer. Quantitative data on chocolate temper index (slope) were obtained for products with varying particle size distribution (PSD) (D₉₀ of 18, 25, 35 and 50 μm) and fat (30% and 35%) content. Regression models generated using stepwise regression analyses were used to plot response surface curves, to study the tempering behaviour of products. The results showed that both Stage 1 and Stage 2 coolant temperatures had significant linear and quadratic effects on the crystallization behaviour causing wide variations in chocolate temper index during tempering of products with variable PSD and fat content. Differences in fat content exerted the greatest variability in temperature settings of the different zones for attaining well-tempered products. At 35% fat content, changes in PSD caused only slight and insignificant effect on tempering behaviour. No unique set of conditions was found to achieve good temper in dark chocolate with a specified tempering unit. Thus, different combinations of temperatures could be employed between the multi-stage heat exchangers to induce nucleation and growth of stable fat crystal polymorphs during tempering. Variations in tempering outcomes of the dark chocolates were dependent more on the fat content than PSD.

Industrial relevance

Tempering consists of shearing chocolate mass at controlled temperatures to promote cocoa butter crystallization in a stable polymorphic form. During industrial processing, multi-stage heat exchangers are used to control temperature adjustments to promote formation of appropriate stable polymorphic crystals to obtain products with good snap, colour, contraction, gloss and shelf life characteristics. The process employs varying time–temperature throughputs of the multi-stage units making it difficult to obtain standard tempering conditions for products with variable particle sizes and fat content, thus prolonging equipment standardization periods with consequential effects on processing times and product quality characteristics. Modelling the tempering behaviour of dark chocolates from varying PSD and fat content would enhance our knowledge and understanding on the optimal temperature conditions for obtaining good tempered products during industrial manufacture, with significance for reducing processing (tempering) times and assurances in quality and shelf characteristics.     

LOWER SILURIAN "HOT SHALES" IN JORDAN: A NEW DEPOSITIONAL MODEL

Data are presented from the Batra Formation (also known as the Mudawwara Shale Formation) of a core from well BG‐14 in the Batna el Ghoul area, southern Jordan, which enable a new depositional model to be proposed for the middle Rhuddanian (lower Llandovery, Silurian) “hot shale” which may be applicable to other Arabian and North African “hot shales” of similar stratigraphical age. This “hot shale” probably results from rapid early burial of organic carbon associated with a minor regression during which anoxic bottom conditions were maintained for most, but not all, of the time. Evidence for regression comes from (1) increased sediment grain size within the “hot shale” by comparison with underlying shales; (2) palynological changes including a decrease in acritarch species diversity; an increase in the relative abundance of sphaeromorphs, veryhachiids with three processes and acritarchs with short, simple processes; and a decrease in the relative abundance of acanthomorphs; (3) a positive δ¹³C_org excursion (other Late Ordovician and Silurian positive δ¹³C_org excursions occur during regressions); and (4) very brief intervals of oxygenation (associated with sediment influx) reflected in the preservation of graptolites as three‐dimensional pyrite internal moulds, rather than as flattened periderm. The minor regression reflects a eustatic sea‐level fall, evidence for which has recently been presented from several regions, including Arctic Canada, Bohemia and Scotland. The BG‐14 “hot shale” is shown to be thicker than estimated in previous studies. Previous TOC measurements from the upper part of the “hot shale” were affected by the weathering of overlying strata in the BG‐14 core. ICP‐MS measurements show that uranium content is high in these weathered levels, extending the stratigraphical extent of the “hot shale” interval into the middle Rhuddanian. Depositional models such as that presented here rely on a robust biostratigraphical framework; in the Ordovician and Silurian of Arabia and North Africa, this can be provided by graptolites and chitinozoans.     

Omitting the dry period between lactations does not reduce subsequent milk production in goats

Four goats were studied from the end of their second lactation. One mammary gland of each goat was dried off just prior to the start of the third gestation, whilst the other gland was milked throughout gestation, with no dry period. At the end of gestation the continuously milked gland was significantly smaller than the gland that had been allowed a dry period. However, this difference did not persist beyond parturition and there was no significant difference between the milk yields of the two glands in the next lactation, although the continuously milked gland tended to have the higher yield. At 18 weeks of lactation, mammary parenchyma weight and secretory cell number were significantly greater in the continuously milked gland, but mammary enzyme activities did not differ between the two glands.     

Demonstration of a non-steroidal,non-inhibin factor in the ovine corpus luteum of pregnancy that reduces pituitary responsiveness to GnRH-induced LH secretion in vitro

The decline in pulsatile LH secretion and pituitary responsiveness to GnRH as pregnancy advances may be due to non-steroidal factors secreted by the ovine corpus luteum of pregnancy. Corpora lutea from ten ewes on days 70-80 of gestation were homogenized, charcoal-treated and, together with charcoal-treated follicular fluid from superovulated women, were subjected to inhibin immunoaffinity chromatography, reducing dimeric inhibin A and B by >90% and abolishing inhibin bioactivity. These preparations were investigated using cultures of rat pituitary cells. GnRH-induced LH and FSH secretion in vitro was reduced by ovine corpus luteum extract and human follicular fluid by 47+/-5% and 42+/-5% of control LH and by 37+/-5% and 50+/-10% of control FSH, respectively (P<0.001). Extracts prepared from corpora lutea and placentae that were collected on days 50, 90 and 120 of pregnancy (five ewes per stage of pregnancy) showed increased GnRH-induced LH-suppressing bioactivity, particularly in the case of the placental extracts, with a threefold increase in activity. When partially purified by pseudochromatofocusing, GnRH-induced LH-suppressing bioactivity in extracts of ovine corpora lutea was identified at pH 5.40 and 5.77. Although these values are similar to published gonadotrophin surge-attenuating factor (GnSAF) bioactivity pI values, a GnSAF-blocking antiserum had no consistent effect on ovine corpus luteum extract GnRH-induced LH-suppressing bioactivity. It was concluded that the ovine corpus luteum of pregnancy contains a non-steroidal, non-inhibin factor, probably not GnSAF, that has the ability to reduce pituitary responsiveness to GnRH in vitro.     

Physical characteristics of pig fat and their relation to fatty acid composition

One hundred and five samples of pig backfat were assessed for appearance (colour and translucency) and hardness. The fatty acid profile of a selected subset of 50 samples was determined. Increased yellow colour was associated with increased linoleic and α-linolenic acid percentages. Increased translucency and fat softness were associated with decreased percentages of palmitic and stearic and oleic acid and a concurrent increase in the proportions of linoleic and α-linolenic acid. Oleic acid was found to be the single highest component (33.0-45.4%) and linoleic to show the greatest variation in range (9.8-28.4%).     

MQBV: multicast quality of service swarm bee routing for vehicular ad hoc networks

Vehicular ad hoc networks (VANETs) are witnessing in recent years a rapid development for road transmissions and are considered as one of the most important types of next generation networks, in which drivers can have access anywhere and anytime to information. However, vehicles have to deal with many challenges such as the links failures due to their frequent mobility as well as limited degrees of freedom in their mobility patterns. In this paper, we propose a new quality of service multicast and multipath routing protocol for VANETs, based on the paradigm of bee's communication, called multicast quality of service swarm bee routing for VANETs (MQBV). The MQBV finds and maintains robust routes between the source node and all multicast group members. Therefore, the average end‐to‐end delay and the normalized overhead load should be reduced, while at the same time increasing the average bandwidth and the packet delivery ratio. Extensive simulation results were obtained using ns‐2 simulator in a realistic VANET settings and demonstrated the efficiency of the proposed protocol. Copyright © 2013 John Wiley & Sons, Ltd.     

Reset noise reduction in capacitive sensors

Reset noise sets a fundamental detection limit on capacitive sensors. Many sensing circuits depend on accumulating charge on a capacitor as the sensing method. Reset noise is the noise that occurs when the capacitor is reset prior to the charge accumulation cycle. Therefore, it is important to understand the factors which determine reset noise, and how this noise may be mitigated. The purpose of this paper is to show how capacitive reset noise can be reduced during the reset cycle. We present and analyze three circuits that implement the basic methods for directly reducing capacitive reset noise. In addition, we present a time-domain technique for analyzing the time-varying statistics of these circuits. This technique makes use of Ito/spl circ/ calculus to obtain solutions to the time-varying stochastic differential equations. Theoretical noise calculations and Monte Carlo simulation results are presented for each technique. We show that theory and simulation yield similar results. Finally, we show in the examples that reset noise may be reduced by a factor of 20 or more. We also refer to implemented sensor arrays which achieve these results.     

Spectral engineering of terahertz quantum cascade lasers using focused ion beam etched photonic lattices

Focused ion beam etching has been used to introduce one-dimensional photonic lattices, of periods 9.11, 9.24, 9.44 /spl mu/m, between the cleaved facets of three 4.44 THz Fabry-Perot quantum cascade lasers. Singlemode lasing has been achieved at precisely defined wavelengths of 67.59, 68.48, 70.00 /spl mu/m, respectively.