Thermal characterization of n‐alkyl maleate‐styrene‐allyl propionate terpolymers

Thermal characterization of maleic anhydride‐styrene‐allyl propionate (MA‐St‐AP) terpolymer and its ester derivatives named as n‐alkyl maleate and shown as nPr MA‐St‐AP, nBu MA‐St‐AP, nPn MA‐St‐AP, and nBz MA‐St‐AP was carried out. The thermal characterization was performed using thermal analysis techniques such as TGA, DTA, DSC, and TMA. Different results were observed between the original terpolymer and its ester derivatives. Thermal stabilities of the terpolymer and its ester derivatives were compared by using various measurements plotted as TGA, DTA, DSC, and TMA curves. The increase in the alcohols' carbon numbers added to the original terpolymer results in ester derivatives with different thermal stability behavior. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 600–604, 2007     

A survey on bacteria isolated as hydrogen sulfide-producers from marine fish

Aim of the work was to identify sulfide-producers isolated from tuna and swordfish and to evaluate some physiological characteristics, particularly those that could be related to spoiling potential.16S rDNA sequencing revealed Shewanella baltica as the main species, followed by Serratia spp. and other Shewanella species, while RAPD- and rep-PCR analyses indicated the presence of several biotypes. Shewanella baltica and Shewanella putrefaciens showed rapid growth at 4 and 8 °C, production of TMA and H₂S, amino acids decarboxylation and proteolytic activity also at refrigeration temperatures, therefore being potentially able to modify texture and sensory characteristics of finfish. Extracellular DNAse activity and growth in presence of high salt concentrations can provide a competitive advantage in unfavourable environments.Our data provide new insights into specific metabolic features of Shewanella spp., rarely studied before, such as extracellular DNAse activity and amino acid decarboxylating activity. Moreover, our results highlight the clear necessity of more specific media and research methods to count H₂S-producing bacteria.     

大口径非球面系统的共基准加工与检验

针对大口径离轴非球面系统加工与装调的难点,提出了非球面光学系统共基准加工与检测的方法,对该方法的基本原理和实现过程进行了分析和研究。当光学系统的主镜和第三镜面形的RMS值优于λ/10(λ=632.8nm)时,对主镜和第三镜进行共基准装调和测试,并进行背板一体化装嵌,然后利用离子束对其进行一体化共基准加工。结合工程实例,对一大口径非球面系统口径为724mm×247mm的非球面主镜和口径为632mm×205mm的第三镜进行了共基准加工与检测,最终利用离子束共基准一体化精抛光得到主镜和第三镜面形的RMS值分别为0.019λ和0.017λ,满足光学成像。     

The Marginal Density of a TMA(1) Process

This note reconsiders the marginal density of a threshold moving average process and proposes a simple yet effective numerical algorithm to implement that by solving an associated integral equation. This algorithm can also be applied to calculate stationary probability density or distribution functions of a few other types of nonlinear stationary stochastic processes numerically.     

离轴三反空间相机的焦距测量

离轴三反光学系统的焦距是空间相机的重要指标之一,离轴三反空间相机在完成光学系统装调及光学镜头装配后需要进行焦距测量。通过对两种经典的焦距测量方法即放大率法和测角法进行对比分析,选用测角法作为焦距的测量方法,同时对用于同轴光学系统的焦距测量公式增加离轴角修正量使其适用于离轴三反光学系统,并以某离轴三反空间相机为例论述焦距测量方法及步骤。由修正后的焦距计算公式计算出相机的焦距为8 010mm,证实了该测量方法的可行性。     

离轴三反空间相机与卫星平台的优化连接方式

对于与卫星平台卧式安装的长焦距离轴三反空间相机,由于地面与在轨状态环境条件不同引起平台接口与相机产生温度差,导致相机视轴漂移影响成像质量。为解决此问题,提出了将柔性连接座、刚性连接座和可解锁连接座配合应用的优化连接方式,实现了相机与平台在轨状态3点静定柔性连接,并在运载阶段利用可解锁连接座提高相机基频。利用有限元方法对优化连接方式进行验证,平台接口温度降低15℃引起次镜角度变化为9.62(安装位置跨距1.2 m),满足光学设计要求;同时运载阶段相机在X、Y、Z三方向频率响应基频分别为120 Hz、120 Hz、110 Hz,与全刚性连接情况相比无明显降低。利用试验工装模拟平台进行温度变化替代试验,平台在温度提高15 ℃情况下,试验结果与仿真结果相符,且次镜转角实测值与仿真结果最大误差为9%。试验结果说明优化连接方式解决了卫星平台与相机在轨状态温度差引起的视轴漂移的问题,提高了相机的在轨环境适应性。     

大视场、大口径双波段红外非制冷光学系统

军事和安全应用都需要利用红外探测技术来进行目标跟踪和搜索.由于红外或热成像系统探测的目标辐射能量低,因此需要光学系统具有强的集光能力;另外,用凝视方式可以获取大场景红外图像以去除传统的机械扫描装置,这要求红外光学系统具有足够大的视场.该工作研究的光学系统视场大于60×3.5度,F数F/1~F/2.5.采用了离轴三反射镜光学系统,系统结构简单,成像质量达到衍射极限.     

Biochemical,microbiological and sensory changes in shrimp (Panaeus aztecus) dipped in different solutions using face‐centred central composite design

Biochemical, microbiological and sensory changes during shelf‐life at ?1 °C were determined in shrimp (Panaeus aztecus) previously dipped in ascorbic acid, citric acid, potassium sorbate and 4‐hexyl resorcinol solutions using face‐centred central composite design. Microbiological count, trimethylamine and hypoxantine production were measured. The lowest level of the total psychrotrophic bacteria, hypoxantine and trimethylamine were found in samples dipped in all containing chemicals solutions comparing to control treatment. Sensory studies showed that treatment A (ascorbic acid 4.50, citric acid 0.12, potassium sorbate 18.60 and 4‐hexyl resorcinol 0.25, all g L^?1) and B (ascorbic acid 4.37, citric acid 1.26, potassium sorbate 7.03 and 4‐hexyl resorcinol 0.25, all g L^?1) did not alter the typical sensory features of shrimp and were effective at delaying the bitter off‐flavour formation for 26 days. This study constitutes a promising alternative to extent shelf‐life of shrimp kept at ?1 °C without freezing.     

Thermo-mechanical properties and microstructural considerations of MDI isocyanate-based bituminous foams

Stable bituminous foams have been obtained by using a 35/50 penetration grade bitumen and a reactive prepolymer (MDI-PPG) synthesized by the reaction of polymeric 4,4′-diphenylmethane diisocyanate (MDI) with a low molecular weight polypropylene glycol (PPG). In a first step, MDI-PPG and bitumen were allowed to react for up to 7 days. Foams were then obtained by adding an excess of water. The results obtained point out important changes in the material colloidal structure, as a consequence of the reactions between the –NCO groups and bitumen most polar fractions. Modification led to bituminous foams with low density and improved in-service properties (higher elasticity and resistance to deformation at high in-service temperatures, reduced thermal susceptibility and better flexibility at low temperatures), demonstrating their adequacy to be used in building applications. Properties were enhanced by subjecting the material to longer periods of curing prior to promote foaming.