On a notion of partially conditionally identically distributed sequences

A notion of conditionally identically distributed (c.i.d.) sequences has been studied as a form of stochastic dependence weaker than exchangeability, but equivalent to it in the presence of stationarity. We extend such notion to families of sequences. Paralleling the extension from exchangeability to partial exchangeability in the sense of de Finetti, we propose a notion of partially c.i.d. dependence, which is shown to be equivalent to partial exchangeability for stationary processes. Partially c.i.d. families of sequences preserve attractive limit properties of partial exchangeability, and are asymptotically partially exchangeable. Moreover, we provide strong laws of large numbers and two central limit theorems. Our focus is on the asymptotic agreement of predictions and empirical means, which lies at the foundations of Bayesian statistics. Natural examples of partially c.i.d. constructions are interacting randomly reinforced processes satisfying certain conditions on the reinforcement.     

Thermoelectric behavior (PTC) of carbon black‐containing TPX/UHMWPE and TPX/XL‐UHMWPE blends

This article describes the structure and electrical performance of positive‐temperature‐coefficient/negative‐temperature‐coefficient (PTC/NTC) effects of the following three‐component blends: poly(4‐methyl pentene‐1)/ultra‐high molecular weight polyethylene/carbon black (TPX/UHMWPE/CB), poly(4‐methyl pentene‐1)/crosslinked‐ultra‐high molecular weight polyethylene/carbon black (TPX/XL‐UHMWPE/CB), and γ‐irradiated, compression‐molded plaques of these blends. CB particles are preferentially attracted to the UHMWPE and XL‐UHMWPE particles, which constitute the dispersed phase within the TPX matrix, but practically cannot or can only very slightly penetrate them because of their extremely high viscosity. Thus, CB particles initially form conductive networks on the UHMWPE phase; this is followed by distribution in the TPX matrix, electrically connecting the CB‐covered UHMWPE particles. This unusual CB distribution results in a reduced percolation threshold of all blends. A double‐PTC effect is exhibited by the XL‐UHMWPE‐containing samples. Irradiation of compression‐molded plaques improves their thermoelectric behavior by amplifying the PTC effect and reducing the NTC effect. A schematic model of the double‐PTC effect is suggested, describing the morphological changes of 70TPX/30XL‐UHMWPE/CB blends at different stages of heating with respect to their thermoelectric behavior. Irradiation of TPX/UHMWPE/CB plaques converts these systems into high‐intensity PTC materials free of the NTC effect. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1415–1428, 2001     

Light-Assisted Ullmann Coupling of Phenols and Aryl Halides: The Synergetic Effect Between Plasmonic Copper Nanoparticles and Carbon Nanotubes from Various Sources

Utilizing light and plastic wastes as resources to turn the wasted phenols and hazardous aryl halides into value added chemicals seems to be an attractive idea for alleviating the energy crisis and environmental problems. In this work, plasmonic copper nanoparticles (Cu NPs) were loaded onto carbon nanotubes (CNTs) from various sources including commercial CNTs and those derived from plastic wastes. Under visible-light irradiation, the catalyst could efficiently convert phenols and aryl halides to diaryl ethers. Similar with commercial CNTs, excellent activity is also achieved when utilizing CNTs derived from different kinds of plastic wastes as support for the system. Further investigation shows that the visible-light irradiation and light-excited plasmonic Cu NPs are necessary to inhibit the phenol degradation on CNTs and in turn promote the cross-coupling of phenol and aryl halides. Compared with metal oxides and other carbon materials, the excellent capability of CNTs to absorb light, to convert light to heat, and to adsorb both two reactants simultaneously are critical to enhance the activity of Cu NPs, achieving high yields of diaryl ethers. This study could provide a novel strategy for catalyst design and generate a more economically sustainable process.     

Aggregation of non-bonding molecules in a rapidly growing gel

The aggregation of non-bonding molecules in a rapidly growing gel is studied under three different conditions by means of Molecular Dynamics simulations. The aggregation takes place even under the unfavorable condition when the non-bonding molecules constitute only a small fraction of the total. The results also show that the morphology of the growing domains is different depending on the concentration of the non-bonding molecules. Received 30 November 1999     

可降解塑料特征分析与快速鉴别方法研究进展

塑料污染是一个重大的全球环境问题。可降解塑料替代传统塑料制品成为缓解塑料污染的重要手段,但市场中可降解塑料虚假宣传等现象频发。综述了近年来塑料分析的几种常见方法以及它们的优点和局限性,旨在为可降解塑料的特征分析和快速鉴别提供一定的理论依据和技术支持,为市场监管提供有力的帮助。随着可降解塑料的快速发展和普及,其检测分析技术需要向更快速、更准确的方向不断发展进步。     

Thermal Analysis of Some Environmentally Degradable Polymers

The thermal characteristics of a series of degradable polymers have been investigated using thermogravimetry and differential scanning calorimetry. While the results of the thermogravimetry experiments suggest that the thermal stability of the polymers should not pose any problems at the temperatures that can be expected in a commercial composting process (60°C), phase changes associated with some of the polymers investigated may cause problems in the interpretation of data from composting degradation studies. Several biodegradable polymers were observed to have melt transitions at temperatures similar to those found in a composting environment. Consequently, under the controlled composting conditions used to evaluate biodegradable polymers, degradation of a polymer may be inferred, while actually the polymer has merely undergone a phase change. This revised version was published online in July 2006 with corrections to the Cover Date.     

Microstructure and fracture mechanical properties of short fiber reinforced thermoplastic P.E.T.

Summary This report contains results of fracture mechanics tests and corresponding observations of the fracture behavior of short fiber reinforced, thermoplastic polyethylene terephthalate (P.E.T.) depending on microstructural parameters. Injection molded plaques of this composite material possess across their thickness individual layers of different fiber orientation which induce different crack propagation behavior transvers and longitudinal to the mold fill direction. The fracture toughness is higher for cracks perpendicular to the main fiber orientation and increases more general with the weight fraction of fibers. Fatigue cracks indicate the same tendency, i. e. their growth rate is lower for cracks transvers to the mold fill direction in samples with highest fiber fraction. Additional influences on fracture behavior due to differences in matrix toughness and adhesive strength of the fiber/matrix interface are discussed.The work was carried out by the author during a research study at the Center for Composite Materials, University of Delaware, Newark, Del. 19711, USA.     

热致液晶聚合物对短玻璃纤维增强聚丙烯加工性、结构与性能的改善

<正> 短切玻璃纤维增强的热塑性复合材料具有加工简便,生产周期短,可以反复加工等优点,因此得到了广泛应用。但短切玻璃纤维会给加工成型带来困难,主要在于纤维对加工设备的磨损,以及由于纤维的加入增大了熔体的粘度等。如果提高加工温度来降低粘度又会导致高聚物降解。几年前Kiss和Isayev提出用热致液晶聚合物(TLCP)的刚性棒状分子链作增强剂与被增强基体熔融共混,在加工中TLCP原位形成增强纤维,形成原位复合材料。原位复合材料中由于TLCP的流变性质,使其共混物的加工粘度