A Novel Function of the Triterpene Squalene in a Tritrophic System

Changes in apple leaf chemistry after infestation by leafminers and their effect on both host location and host habitat location of the generalist parasitoid Pholetesor bicolor were investigated. Chemical analysis of leaf solvent extracts from healthy and leafminer-damaged leaves revealed that herbivory increased the amount of the triterpene squalene (C₃₀H₅₀), whereas quantities of all other identified compounds were similar in both plant treatments. To assess the response of parasitoids to host location cues, contact bioassays were conducted with naïve females. Results showed that parasitoids performed a characteristic ovipositional probing more often on the mine-damaged than on the healthy leaf. This behavior was triggered by a hexane extract of the mine-damaged leaf, but not by a healthy leaf extract. A synthetic mixture of the compounds identified in the extract triggered a similar response. A mixture devoid of squalene was not active, whereas squalene alone elicited the probing behavior. To assess the use of the identified compounds in habitat location, Y-tube olfactometer experiments were conducted with naïve and experienced females. Results showed that squalene is not involved in habitat location and has no priming effect on P. bicolor. While other triterpenes are known to mediate habitat location of parasitoids, this is the first report in which a plant triterpene is shown to mediate host location of a parasitoid. The biological and ecological functions of squalene on all three trophic levels are discussed.     

UHMWPE oxidation increases matrix metalloproteinase-2 (MMP-2) release in human fibroblast

MRC-5 human fibroblast were grown polystyrene plates, UHMWPE slices and UHMWPE slices oxidized in air in oven at 120 °C for 80 h. Cell proliferation and cytotoxicity were assessed after 24, 48, and 72 h. Control cells grown on polystyrene doubled their number after 72 h while both cell population grown on UHMWPE and oxidized UHMWPE showed a reduced proliferation rate. Both UHMWPE types seem to induce a cytostatic rather than a cytotoxic effect, in fact, no difference in the LDH release were observed between the three cell populations at 24, 48, and 72 h. Gelatinase activity was assessed in cell medium at every time point using gelatin zymography. Only gelatinase B (MMP-2) activity was present in MRC-5 conditioned medium. Oxidized UHMWPE induced a strong release of MMP-2 after 72 h compared to control and UHMWPE samples. The augmented MMP-2 release in the absence of a cytotoxic phenomenon suggests a possible role for UHMWPE oxidation in the MMPs stimulation observed in the periprosthetic tissues.     

高层建筑二维流场的数值模拟

针对建筑物风场的高雷诺数特点,采用离散涡法,分析了高层建筑物的非定常分离流问题.通过引入奇异点技术摆脱了保角变换的处理过程,使离散涡法能适应于复杂形状的钝体结构.数值模拟了流场的变化特征,分析了各种攻角下,具有方形截面的高层建筑的升力系数、抗力系数和Strouhal数.计算分析表明,离散涡法具有计算速度快及精度高的特点,可以刻画出流场的流动特征,透视到流动机理,在结构风工程领域具有较好的应用价值.     

Design of CMOS checkers with improved testability of bridging and transistor stuck-on faults

This work presents a design technique for CMOS static and dynamic checkers (to be used in self-checking circuits), that allows the detection of all internal single transistor stuck-on and bridging faults causing unacceptable degradations of the circuit dynamic performance (but not logical errors). Such a technique exploits simple voltage detector circuits to make sure that the intermediate faulty voltages inevitably produced by the faults of interest are always propagated at the checker output as logic errors.With the use of our technique, the main disadvantages of static checkers, so far preventing their use in practical applications, are overcome.The method has been applied to the particular case of two-rail (static as well as dynamic) checkers and its validity has been verified by means of electrical level simulations.     

Influence of annealing on the phase composition,transmission and resistivity of SnOx thin films

Undoped and antimony-doped tin oxide films were prepared by d.c. reactive ion sputtering in an argon atmosphere with oxygen partial pressures ranging from 0 to 50%. The films were annealed in air, nitrogen and a vacuum in the temperature range 570–750 K. The influence of thermal annealing on the structural properties, electrical resistance and optical transmittance is described.     

A/B-Ratio and Transport Properties of (La0.85Sr0.15)sCoO3−δ Perovskites

The perovskites (La_0.85Sr_0.15)_0.98CoO_{3 –} and (La_0.85Sr_0.15)_1.00CoO_{3 –} have been investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical conductivity relaxation (ECR). This system was chosen in order to investigate the influence of cation vacancies on the transport properties in the materials. From ECR-measurements it is concluded that no difference in the chemical diffusion coefficient for oxide ions between the two samples can be found. The activation energy for the chemical diffusion coefficient has been found to be 107 ± 5 kJ mol^{– 1}. However, the surface exchange coefficient differs between the two samples. The Co-rich sample has a significantly higher surface exchange coefficient than the A/B-stoichiometric sample. For both samples the surface exchange coefficient was almost independent of the temperature. At all temperatures the Co-rich sample had a significantly higher electrical conductivity. The difference in electrical conductivity between the two samples diminished when going to higher temperatures. Both materials can be assigned to a single phase hexagonal perovskite. An annealed sample of (La_0.85Sr_0.15)_0.98CoO_{3 –} did however contain an unidentified secondary phase on the surface.     

Increasing usability when interacting through screen readers

The application of appropriate Web site design and evaluation methods helps to ensure more usable and accessible Web sites. While in the literature guidelines and evaluation methods for accessibility and usability are given and discussed separately, we aim at identifying the relationships between these two concepts, in particular considering usability criteria for accessible Web sites. In this work, we propose a set of such criteria targeted to improving the navigability for a specific group of disabled users, i.e., vision-impaired people. The identification of the eighteen criteria suggested herein was performed through empirical feedback, by which potential issues were identified. Subsequently, a systematic method was developed on the basis of the analysis of potential solutions, resulting in a classification of the criteria according to usability aspects. Some example applications of the proposed criteria to three existing public administration Web sites are discussed.     

Agent communication and artificial institutions

In this paper we propose an application-independent model for the definition of artificial institutions that can be used to define open multi-agent systems. Such a model of institutional reality makes us able also to define an objective and external semantics of a commitment-based Agent Communication Language (ACL). In particular we propose to regard an ACL as a set of conventions to act on a fragment of institutional reality, defined in the context of an artificial institution. Another contribution of the work presented in this paper is an operational definition of norms, a crucial component of artificial institutions. In fact in open systems interacting agents might not conform to the specifications. We regard norms as event-driven rules that when are fired by events happening in the system create or cancel a set of commitments. An interesting aspect of our proposal is that both the definition of the ACL and the definition of norms are based on the same notion of commitment. Therefore an agent capable of reasoning on commitments can reason on the semantics of communicative acts and on the system of norms.