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排序方式: 共有865条查询结果,搜索用时 15 毫秒
91.
Dawson K Strutwolf J Rodgers KP Herzog G Arrigan DW Quinn AJ O'Riordan A 《Analytical chemistry》2011,83(14):5535-5540
In this work, we fabricate gold nanowires with well controlled critical dimensions using a recently demonstrated facile approach termed nanoskiving. Nanowires are fabricated with lengths of several hundreds of micrometers and are easily electrically contacted using overlay electrodes. Following fabrication, nanowire device performance is assessed using both electrical and electrochemical characterization techniques. We observe low electrical resistances with typical linear Ohmic responses from fully packaged nanowire devices. Steady-state cyclic voltammograms in ferrocenemonocarboxylic acid demonstrate scan rate independence up to 1000 mV s(-1). Electrochemical responses are excellently described by classical Butler-Volmer kinetics, displaying a fast, heterogeneous electron transfer kinetics, k(0) = 2.27 ± 0.02 cm s(-1), α = 0.4 ± 0.01. Direct reduction of hydrogen peroxide is observed at nanowires across the 110 pM to 1 mM concentration range, without the need for chemical modification, demonstrating the potential of these devices for electrochemical applications. 相似文献
92.
Rebecca S. Hayden Jean‐Philippe Fortin Benjamin Harwood Balajikarthick Subramanian Kyle P. Quinn Irene Georgakoudi Alan S. Kopin David L. Kaplan 《Advanced functional materials》2014,24(4):472-479
The goals of the present study are to establish an in vitro co‐culture model of osteoblast and osteoclast function and to quantify the resulting bone remodeling. The bone is tissue engineered using well‐defined silk protein biomaterials in 2D and 3D formats in combination with human cells. Parathyroid hormone (PTH) and glucose‐dependent insulinotropic peptide (GIP) are selected because of their roles in bone remodeling for expression in tethered format on human mesenchymal stem cells (hMSCs). The cell‐modified biomaterial surfaces are reconstructed from scanning electron microscopy images into 3D models for quantitative measurement of surface characteristics. Increased calcium deposition and surface roughness are found in 3D surface models of silk protein films remodeled by co‐cultures containing tethered PTH, and decreased surface roughness is found for the films remodeled by tethered GIP co‐cultures. Increased surface roughness is not found in monocultures of hMSCs expressing tethered PTH, suggesting that osteoclast‐osteoblast interactions in the presence of PTH signaling are responsible for the increased mineralization. These data point towards the design of in vitro bone models in which osteoblast‐osteoclast interactions are mimicked for a better understanding of bone remodeling. 相似文献
93.
Mechanism of Crystallization and Implications for Charge Transport in Poly(3‐ethylhexylthiophene) Thin Films
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Duc T. Duong Victor Ho Zhengrong Shang Sonya Mollinger Stefan C.B. Mannsfeld Javier Dacuña Michael F. Toney Rachel Segalman Alberto Salleo 《Advanced functional materials》2014,24(28):4515-4521
In this work, crystallization kinetics and aggregate growth of poly(3‐ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X‐ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time‐dependent, field‐effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2–3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter‐aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics. 相似文献
94.
A Schrag Y Ben-Shlomo R Brown CD Marsden N Quinn 《Canadian Metallurgical Quarterly》1998,13(6):885-894
The authors report on clinical features and mortality rates in a group of 149 patients with apparent idiopathic parkinsonism starting before the age of 40 years. Ten had juvenile parkinsonism (JP; onset before age 21 years) and 139 had young-onset Parkinson's disease (YOPD; onset at age 21 to 40 years). Included were 60 patients originally reported 10 years ago. Fifty percent of the JP group had a positive family history of parkinsonism in a first-degree relative, and clinical presentation was heterogeneous. Mortality risk was threefold that of the normal population. In the YOPD group, the mortality risk was double that of the normal population. Poor initial response to L-dopa was a risk factor for early death. In two previously reported patients, the diagnosis had been changed to multiple system atrophy and Machado-Joseph disease. After a median disease duration of 18 years, cognitive impairment was found in only 19% of YOPD patients (13% of those younger than 60 years and 43% of those 60 years or older). Age was the most important factor for development of dementia, but female sex and positive family history of parkinsonism also had more modest predictive value. After a disease duration of 10 years or less, only 5% of patients were experiencing falls and 30% freezing, but all patients had developed L-dopa-related fluctuations and dyskinesias. The authors conclude that the mortality rate in parkinsonism starting before the age of 40 is increased in comparison to the normal population and is similar to the general Parkinson's disease population. Intellectual function and postural reflexes are usually well preserved for many years despite a long history of parkinsonism and the early and frequent occurrence of treatment complications, provided the patients remain biologically and chronologically young. 相似文献
95.
VA Tyurin YY Tyurina PJ Quinn NF Schor R Balachandran BW Day VE Kagan 《Canadian Metallurgical Quarterly》1998,60(2):270-281
Incubation of mock-transfected PC12 rat pheochromocytoma cells (PC12) for 2 h with increasing concentrations of glutamate caused progressive loss of viability (e.g., 67% with 15 mM glutamate). In contrast, the viability of bcl-2-transfected cells (PC12/bcl-2) was unaffected by glutamate. Neither PC12 nor PC12/bcl-2 cells showed a significant incidence of apoptosis in response to glutamate. Conventional phospholipid analysis by high-performance TLC and phosphorous determination showed no significant changes in the phospholipid composition of either cell line incubated with =15 mM glutamate. Phospholipid peroxidation was quantified in the cells using our newly developed method based on fluorescence-HPLC analysis of metabolically incorporated oxidation-sensitive and fluorescent fatty acid, cis-parinaric acid. Unlike previous studies that measured total phospholipid oxidation, this novel technology permitted quantitation of oxidative stress in different classes of labeled phospholipids (the amount of labeled phospholipids in the cells did not exceed 1% of total phospholipids). Significant peroxidation of phosphatidylcholine and phosphatidylethanolamine occurred in PC12 cells treated with >5 mM glutamate. The peroxyl radical initiator 2,2'-azobis(2,4-dimethylvaleronitrile) caused a pronounced loss of all major phospholipid classes in PC12 cells, but no loss of cell viability. No phospholipid peroxidation was detected in PC12/bcl-2 cells incubated with =15 mM glutamate or with 2, 2'-azobis(2,4-dimethylvaleronitrile). These results directly demonstrate that peroxidation of membrane phospholipids is not responsible for the cytotoxicity of glutamate in PC12 cells. Total cellular thiol, protein thiol and GSH reserves were quantified by a previously described electron paramagnetic resonance spectrometric method. Total thiols were ca. 1.5-fold greater in PC12/bcl-2 than in PC12 cells. Glutamate (=5 mM) caused a progressive and equally significant decrease in total thiols and GSH in both PC12 and PC12/bcl-2 cells. High glutamate concentrations caused oxidation of protein sulfhydryls in PC12 cells, but not in PC12/bcl-2 cells. The results suggest that the changes in cellular milieu caused by bcl-2 gene transfection protect PC12 cells from the toxic effects of glutamate in a manner consistent with prevention of protein sulfhydryl oxidation. 相似文献
96.
97.
Determination of Stress Concentration Factors for Holes in Cylinders Using Thermoelastic Stress Analysis 总被引:1,自引:0,他引:1
Thermoelastic stress analysis is used to obtain the stress concentration factors (SCFs) from a variety of circular holes in cylinders. The cylinders are loaded in uniaxial tension, uniaxial compression and a combination of bending and compression. Firstly, radial holes are investigated and the results from the thermoelastic data obtained by the SPATE equipment are compared with previous experimental and numerical work. SCFs are then obtained from offset, oblique and offset–oblique holes using the Deltatherm system. The effect of hole obliquity and direction of applied load relative to the hole geometry are discussed in detail. Finally, the results from the cylinders are compared with predictions of the SCFs in cylinders from a previous study of oblique holes in flat plates. 相似文献
98.
S Gilman PA Low N Quinn A Albanese Y Ben-Shlomo CJ Fowler H Kaufmann T Klockgether AE Lang PL Lantos I Litvan CJ Mathias E Oliver D Robertson I Schatz GK Wenning 《Canadian Metallurgical Quarterly》1998,74(2-3):189-192
We report the results of a consensus conference on the diagnosis of multiple system atrophy (MSA). We describe the clinical features of the disease, which include four domains: autonomic failure/urinary dysfunction, parkinsonism and cerebellar ataxia, and corticospinal dysfunction. We set criteria to define the relative importance of these features. The diagnosis of possible MSA requires one criterion plus two features from separate other domains. The diagnosis of probable MSA requires the criterion for autonomic failure/urinary dysfunction plus poorly levodopa responsive parkinsonism or cerebellar ataxia. The diagnosis of definite MSA requires pathological confirmation. 相似文献
99.
ML Doherty ML Monaghan HF Bassett PJ Quinn WC Davis 《Canadian Metallurgical Quarterly》1996,49(4):307-320
Nine M. bovis-infected cattle on a diet deficient in both protein and energy for 133 days lost approximately 17% of their original body weight. However, dietary restriction did not result in any significant reduction in skin sensitivity to PPD, in vitro production of IFN-gamma or lymphocyte blastogenesis. The number of circulating BoCD4+ cells and B cells were similar in both the malnourished and the control cattle. However, significantly lower numbers (P < 0.01) of circulating BoCD2+ cells, BoCD8+ cells, WC1+ gamma delta T cells and ACT2+ cells were found in the malnourished cattle. With the exception of inorganic phosphate, the changes in plasma biochemical parameters were unremarkable. 相似文献
100.