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Lower Mobility (lower + mobility)
Selected AbstractsVariable Temperature Mobility Analysis of n-Channel, p-Channel, and Ambipolar Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Joseph A. Letizia Abstract The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5,,,-bis(perfluorophenacyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (1, n-channel), 5,5,,,-bis(perfluorohexyl carbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5,,,-bis(hexylcarbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (4, ambipolar), 5,5,,,-bis-(phenacyl)-2,2,: 5,,2,:5,,2,,,-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N -(2-octyldodecyl)-2,2,-bithiophene-3,3,-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (µeff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1,3 of 21, 22, and 30,meV, respectively. Higher EA values of 40,70,meV are exhibited by 4,7 -derived FETs having lower mobilities (µeff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and µeff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits EA,=,27,meV, the p-channel regime exhibits significantly more trapping with EA,=,250,meV. Interestingly, calculated free carrier mobilities (µ0) are in the range of ,0.2,0.8,cm2,V,1 s,1 in this materials set, largely independent of µeff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (VT) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature µeff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature µeff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set. [source] Host plants and butterfly biology.ECOLOGICAL ENTOMOLOGY, Issue 1 2004Do host-plant strategies drive butterfly status? Abstract., 1.,To determine whether rarity and decline is linked to organism ecology, associations have been examined between butterfly larval host-plant competitive, stress-tolerant, ruderal (C-S-R) strategies and butterfly biology. 2.,Associations have been sought between mean C-S-R scores for larval host plants with butterfly life history, morphology and physiology variables, resource use, population attributes, geography, and conservation status. Comparisons are carried out across species and controlled for phylogenetic patterning. 3.,Butterfly biology is linked to host-plant strategies. An increasing tendency of a butterfly's host plants to a particular strategy biases that butterfly species to functionally linked life-history attributes and resource breadth and type. In turn, population attributes and geography are significantly and substantially affected by host choice and the strategies of these host plants. 4.,The greatest contrast is between butterfly species whose host plants are labelled C and R strategists and those whose host plants are labelled S strategists. Increasingly high host-plant C and R strategy scores bias butterflies to rapid development, short early stages, multivoltinism, long flight periods, early seasonal emergence, higher mobility, polyphagy, wide resource availability and biotope occupancy, open, areally expansive, patchy population structures, denser distributions, wider geographical ranges, resistance to range retractions as well as to increasing rarity in the face of environmental changes. Increasing host-plant S strategy scores have reversed tendencies, biasing those butterfly species to extended development times, fewer broods, short flight periods, smaller wing expanse and lower mobility, monophagy, restricted resource exploitation and biotope occupancy, closed, areally limited populations with typical metapopulation structures, sparse distributions, and limited geographical ranges, range retractions, and increased rarity. 5.,Species with S strategy host plants are species vulnerable to current environmental changes and species of conservation concern. [source] Charge density profiling of circulating human low-density lipoprotein particles by capillary zone electrophoresisELECTROPHORESIS, Issue 17 2004Mine-Yine Liu Abstract Capillary zone electrophoresis (CZE) has been utilized to profile the low-density (LDL) particles in human blood serum in this study. A 5 mM sodium phosphate buffer, pH 7.40, was chosen as the most suitable CE buffer and an extensive ultrafiltration (UF) procedure was applied to purify the LDL sample. Two LDL particle species, LDL with lower mobility and LDL, with higher mobility were observed. The electropherograms were highly reproducible with good precision of effective mobilities, corrected peak areas (CPAs) and CPA ratio of LDL,/LDL. LDL particles shown on the electropherogram were also characterized by several procedures. The applications of Sigma HDL cholesterol reagent and CE on-line 2-propanol precipitation indicated that the two particle species shown in the electropherogram belong to LDL. The LDL particles were found to associate with the buoyant LDL fraction and the LDL, particles associate with the dense LDL fraction. This study utilizes CZE for the profiling of LDL isoforms and provides a new analytical method for the resolution of LDL subspecies. It demonstrates a high-mobility LDL particle which circulates in healthy subjects and diminishes in atherosclerotic patients. Diminution of the high-mobility LDL subspecies may be linked to minimal formation of arterial plaque in atherosclerotic patients. [source] Effects of throughfall and litterfall manipulation on concentrations of methylmercury and mercury in forest-floor percolatesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2007Maria Hojdová Abstract The forest floor was shown to be an effective sink of atmospherically deposited methylmercury (MeHg) but less for total mercury (Hgtotal). We studied factors controlling the difference in dynamics of MeHg and Hgtotal in the forest floor by doubling the throughfall input and manipulating aboveground litter inputs (litter removal and doubling litter addition) in the snow-free period in a Norway spruce forest in NE Bavaria, Germany, for 14 weeks. The MeHg concentrations in the forest-floor percolates were not affected by any of the manipulation and ranged between 0.03 (Oa horizon) and 0.11 (Oi horizon) ng Hg L,1. The Hgtotal concentrations were largest in the Oa horizon (24 ng Hg L,1) and increased under double litterfall (statistically significant in the Oi horizon). Similarly, concentrations of dissolved organic C (DOC) increased after doubling of litterfall. The concentrations of Hgtotal and DOC correlated significantly in forest-floor percolates from all plots. However, we did not find any effect of DOC on MeHg concentrations. The difference in the coupling of Hgtotal and MeHg to DOC might be one reason for the differences in the mobility of Hg species in forest floors with a lower mobility of MeHg not controlled by DOC. [source] Acute lethal and behavioral sublethal responses of two stored-product psocids to surface insecticidesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 12 2008Raul Narciso C Guedes Abstract BACKGROUND: The psocids Liposcelis bostrychophila Badonnel and L. entomophila (Enderlein) (Liposcelididae) are emerging pests of stored products. Although their behavior, particularly their high mobility, may contribute to the reported relatively low efficacy of insecticides against them, studies to investigate this have not been conducted. The present study aimed to assess the label rate efficacy of three commercial insecticides (,-cyfluthrin, chlorfenapyr and pyrethrins) applied on concrete surfaces against L. bostrychophila and L. entomophila, and also their sublethal effect on the mobility of these species. RESULTS: The synthetic insecticides ,-cyfluthrin and chlorfenapyr showed high short-term efficacy (LT95,15 h) against both psocid species, unlike the natural pyrethrins (LT95 , 4 days). Liposcelis bostrychophila was slightly more tolerant (,1.2×) than L. entomophila to all three insecticides. Behavioral assays with fully sprayed and half-sprayed concrete arenas indicated that the insecticides reduced the mobility of both species. Pyrethrins seem to elicit weak repellence in L. bostrychophila. CONCLUSION: ,-Cyfluthrin and chlorfenapyr were effective against both psocid species, but not pyrethrins. The mobility of both species does not seem to play a major role in the differential selectivity observed, but the lower mobility of L. bostrychophila may be a contributing factor to its higher insecticide tolerance. Published in 2008 by John Wiley & Sons, Ltd. [source] Paths of Effects of Early Childhood Intervention on Educational Attainment and Delinquency: A Confirmatory Analysis of the Chicago Child-Parent CentersCHILD DEVELOPMENT, Issue 5 2004Arthur J. Reynolds This study investigated the contributions of 5 mechanisms to the effects of preschool participation in the Child-Parent Centers for 1,404 low-income children in the Chicago Longitudinal Study. Based on a matched-group design, preschool participation was associated with significantly higher rates of educational attainment and lower rates of juvenile arrest. LISREL analysis revealed that the primary mediators of effects for both outcomes were attendance in high-quality elementary schools and lower mobility (school support hypothesis), literacy skills in kindergarten and avoidance of grade retention (cognitive advantage hypothesis), and parent involvement in school and avoidance of child maltreatment (family support hypothesis). The model accounted for 58% and 79% of the preschool links with school completion and juvenile arrest, respectively. The maintenance early intervention effects are influenced by many alterable factors. [source] | ||||||||||