The introduction of alkyl,ester, carboxylate,amino, hydroxyl,and phosphate functional groups to the surface of polyethylene

The surface of polyethylene was derivatized with ester, carboxylate, amino, hydroxyl, and phosphate functional groups. α, ω bifunctional alkanes, containing on one end a primary amine, were coupled to oxidized polyethylene through an amide linkage. Polyethylene was first oxidized with chromic acid, the carboxylate groups were converted to the acyl chloride with phosphorus pentachloride, and then reacted with a primary amine to give the covalently bound amide. The copposing ends of the bifunctional alkanes were the methyl, tertiary amine, ester, and hydroxyl groups. The ester was converted to the carboxylate by acid cleavage and the hydroxyl group converted to the phosphate by treatment first with phosphorus oxychloride and then aqueous base. Attenuated total reflection FTIR, XPS, and pH-dependent contact angle wetting were used to characterize the surfaces. The FTIR data were used to confirm the formation of the amide and to detect an undesired carboxylate/ammonium ion complex formed in the presence of trace amounts of water. XPS data were used to confirm expected changes in elemental composition and to provide quantitative estimates of the yields. Oxidation of the polyethylene introduced 5 × 10¹⁴ carboxylate groups/cm² in the 25 Å XPS sampling depth. Of these, up to 98% could be converted to the amide. The advancing contact angle data confirmed the acid/base behavior of the functional groups.     

Contact areas in the thumb carpometacarpal joint

The thumb carpometacarpal joint is a common site of osteoarthritis. It has been hypothesized that peaks of localized stress on the dorsoradial or volar-ulnar regions, or both, of the articular surfaces of the trapezium and metacarpal lead to erosion of cartilage and may be responsible for the progression of the disease. The objective of this study was to determine the contact areas in this joint under the functional position of lateral (key) pinch and in the extremes of range of motion of the joint. These contact areas were assessed relative to the observed sites of cartilage thinning. Eight hands from cadavers of women and five from cadavers of men were tested in vitro with the thumb under a 25 N load in the lateral pinch position, and under small muscle loads (0-5 N) with the thumb in flexion, extension, abduction, adduction, and neutral positions. Contact areas of articular surfaces of the thumb carpometacarpal joint were determined for these positions using a stereophotogrammetric technique. The lateral pinch position produced contact areas predominantly on the central, volar, and volar-ulnar regions of the trapezium and the metacarpal. In three specimens, contact areas were distinctly separated between the dorsoradial and volar-ulnar regions, and in one specimen, from a man, contact occurred exclusively on the dorsoradial region of the trapezium. Using stereophotogrammetry, maps of cartilage thickness also were determined for a subset of nine specimens. The volar-ulnar, ulnar, and dorsoradial regions of the trapezium were the most common sites of thin cartilage, and these may be sites of cartilage wear.(ABSTRACT TRUNCATED AT 250 WORDS)     

Word-fragment cuing: The lexical search hypothesis.

In four experiments we evaluated aspects of the hypothesis that word-fragment completion depends on the results of lexical but not semantic search. Experiment 1 showed that the number of meaningful associates linked to a studied word does not affect its recovery when the test cue consists of letters and spaces for missing letters. Experiments 2 and 3 showed retroactive interference effects in fragment completion when words in a second list were lexically related to words in a first list but not when the words in the second list were meaningfully related. Experiment 4 indicated that for studied words, instructions to search at the word level facilitated completion performance and that instructions to generate letters to fill missing spaces had no effect. Other findings indicate that completion was affected by the number of words lexically related to the fragment and by the number of letters missing from the fragment. In general, experimental manipulations that focused on lexical characteristics were effective, and those that focused on semantic characteristics were ineffective. The findings support the conclusion that word fragments engender a lexical search process that does not depend on retrieving encoded meaning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Effect of Polymer Optoelectronic Properties on the Performance of Multilayer Hybrid Polymer/TiO2 Solar Cells

We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO₂ and a conjugated polymer. Three different poly(2‐methoxy‐5‐(2′‐ethylhexoxy)‐1,4‐phenylenevinylene) (MEH‐PPV)‐based polymers and a fluorene–bithiophene copolymer are compared. We use photoluminescence quenching, time‐of‐flight mobility measurements, and optical spectroscopy to characterize the exciton‐transport, charge‐transport, and light‐harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic‐device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO₂/polymer devices as a function of the fabrication route and device design. Including a dip‐coating step before spin‐coating the polymer leads to excellent polymer penetration into highly structured TiO₂ networks, as was confirmed through transient optical measurements of the photoinduced charge‐transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip‐coated and PEDOT:PSS layers produced a short‐circuit current density of about 1 mA cm^–2, a fill factor of 0.50, and an open‐circuit voltage of 0.86 V under simulated AM 1.5 illumination (100 mW cm^–2, 1 sun). The corresponding power conversion efficiency under 1 sun was ≥ 0.4 %.     

Transient Green’s Tensor for a Layered Solid Half-Space With Different Interface Conditions

Pulsed ultrasonic techniques can be and have been used to examine the interface conditions of a bonded structure. To provide a theoretical basis for such testing techniques we model the structure as a layer on top of a half-space, both of different elastic properties, with various interface bonding conditions. The exact dynamic Green’s tensor for such a structure is explicitly derived from the three-dimensional equations of motion. The final solution is a series. Each term of the series corresponds to a successive arrival of a “generalized ray” and each is a definite line integral along a fixed path which can be easily computed numerically. Willis’ method is used in the derivation. A new scheme of automatic generation of the arrivals and ray paths using combinatorial analysis, along with the summation of the corresponding products of reflection coefficients is presented. A FORTRAN code is developed for computation of the Green’s tensor when both the source and the detector are located on the top surface. The Green’s tensor is then used to simulate displacements due to pulsed ultrasonic point sources of known time waveform. Results show that the interface bonding conditions have a great influence on the transient displacements. For example, when the interface bonding conditions vary, some of the first few head waves and regular reflected rays change polarities and amplitudes. This phenomenon can be used to infer the quality of the interface bond of materials in ultrasonic nondestructive evaluation. In addition the results are useful in the study of acoustic microscopy probes, coatings, and geo-exploration.     

论网络升级方式与光纤选择的关系

在重点说明影响传输光纤设计的主要问题的同时，简要介绍了各种升级方式所面临的主要技术挑战，并详细说明这些挑战对传输光纤提出的技术要求。     

No increased mortality in later life for cohorts born during famine

Nutrition early in life may influence adult mortality. The fetal-origins hypothesis suggests that nourishment before birth and during the individual's infancy programs the development of risk factors for several important diseases of middle and old age. The present study was designed to evaluate the impact of extreme nutritional deprivation in utero and during infancy and early childhood on mortality in later life. The authors analyzed the survival of the cohorts born in Finland during the severe 1866-1868 famine and during the 5 years immediately preceding and 5 years immediately following the famine. The study included 331,932 individuals born prior to the famine, 161,744 born during the famine, and 323,321 born after the famine. The authors assessed survival by cohorts from birth to age 17 years and from age 17 to 40, 60, and 80 years, as well as average length of life after age 80 years. Survival from birth to age 17 years was significantly lower in cohorts born before and during the famine than in the cohorts born after the famine (males, 0.566 vs. 0.671, a difference of 0.105 (95% confidence interval (CI) 0.102-0.108); females, 0.593 vs. 0.692, a difference of 0.099 (95% CI 0.096-0.102)). At subsequent ages, including old age, mortality was practically identical in the famine-born cohorts and in the five cohorts born before and after the crisis. For both males and females, survival from 17 to 80 years and mean remaining lifetime at age 80 years were very similar across the 13 cohorts studied. These findings suggest that, although cohorts subjected to prolonged and extreme nutritional deprivation in utero and during infancy and early childhood suffer an immediate rise in mortality, after the crisis has passed, they carry no aftereffects that influence their survival in later life.     

The morphology of rigid-rod polymers and molecular composites resulting from coagulation processing

The effects of processing conditions on the morphology of molecular composite films are examined by optical and electron microscopy. During coagulation processing from solutions in methanesulfonic acid (MSA), rigid-rod polymer, such as poly(p-phenylenebenzobisoxazole) (PBO), phase separates into undesirable aggregates. The coagulant and the method of its introduction have been found to exert a strong impact on the final film morphology. A quench of a PBO solution in MSA into a water bath results in a three dimensional interconnected network of PBO, while a slower introduction of water results in a more amorphous material. A computer simulation program of the coagulation process has been developed to better understand the different structures emerging from coagulation processing of molecular composites. The simulation results are in qualitative agreement with the experimental observations.