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排序方式: 共有979条查询结果,搜索用时 46 毫秒
51.
Wande Zhang Pranav Soman Kyle Meggs Xin Qu Shaochen Chen 《Advanced functional materials》2013,23(25):3226-3232
Cells sense and respond to mechanical forces, regardless of whether the source is from a normal tissue matrix, an adjacent cell or a synthetic substrate. In recent years, cell response to surface rigidity has been extensively studied by modulating the elastic modulus of poly(ethylene glycol) (PEG)‐based hydrogels. In the context of biomaterials, Poisson's ratio, another fundamental material property parameter has not been explored, primarily because of challenges involved in tuning the Poisson's ratio in biological scaffolds. Two‐photon polymerization is used to fabricate suspended web structures that exhibit positive and negative Poisson's ratio (NPR), based on analytical models. NPR webs demonstrate biaxial expansion/compression behavior, as one or multiple cells apply local forces and move the structures. Unusual cell division on NPR structures is also demonstrated. This methodology can be used to tune the Poisson's ratio of several photocurable biomaterials and could have potential implications in the field of mechanobiology. 相似文献
52.
53.
Kyle Kai-Hung Yu Karthikeyan S. M. Pillai Praveen R. Nalla Oliver Chyan 《Journal of Applied Electrochemistry》2010,40(1):143-149
On-chip microscopic corrosion, originating from contact of dissimilar metals, can cause serious reliability issues for integrated circuits and microelectromechanical devices. A new micropattern corrosion screening method combined with Tafel plots were employed to study Cu bimetallic corrosion in acid and base solutions relevant to the chemical–mechanical planarization process. The results demonstrated that Cu corrosion on Ru is much more severe compared to Cu corrosion on Ta substrates. Tafel plots confirm the nobility trend of Ru > Cu > Ta. The micropattern corrosion study shows the Cu bimetallic corrosion depends on specific chemicals and bimetallic contacts. Strong complexing ligands like NH3 combined with energetically favorable Cu/Ru bimetallic contact promote faster Cu corrosion under alkaline conditions (9 ≤ pH ≤ 11.4). Micropattern corrosion screening was shown to be useful in identifying the metastable surface layer during Cu corrosion and determining the optimal benzotriazole concentration for Cu corrosion inhibition. 相似文献
54.
David J. Comer Donald T. Comer Craig S. Petrie 《International Journal of Electronics》2013,100(8):491-502
This work demonstrates the utility of the composite cascode stage by considering its use (1) as a high-gain amplifying stage; (2) as a high-impedance load for an amplifying stage; and (3) as a low-impedance, high-frequency summing circuit. A simulation of the summing circuit using 0.18?µm channel lengths leads to a rise time of less than 30?ps and good linearity. When used as a high-gain amplifier, both devices of the active cascode stage must be biased into the active region. In the summing circuit, one device is biased into the triode region whereas the second device must operate in the active region. Guidelines for achieving proper bias with a single bias source are provided in this work. 相似文献
55.
Kyle M. Allen Nick Auyeung Nima Rahmatian James F. Klausner Eric N. Coker 《JOM Journal of the Minerals, Metals and Materials Society》2013,65(12):1682-1693
The kinetics of 10 wt.% cobalt ferrite (CoFe2O4) in 8 mol.% yttria-stabilized zirconia, synthesized via the co-precipitation method and formed into a porous structure, are investigated in support of simulating the performance of a solar thermochemical reactor. Kinetic parameters for the thermal reduction (T-R) of CoFe2O4 at temperatures of 1325–1500°C were investigated by thermogravimetry. A nonlinear best fit of a uniform conversion model was used to determine kinetic parameters from experimental data. In the temperature range of 1375–1450°C, the activation energy and preexponential term were found to be 386 ± 13 kJ mol?1 and 8.8 × 109 ± 2.0 × 108 min?1, respectively, while increasing at higher temperatures. Simultaneous thermogravimetric analysis and differential scanning calorimetry studies showed an increase in the reaction rate of T-R upon the onset of melting (1440°C). Oxidation studies of the material using CO2 yield an activation energy and preexponential term of 52.1 ± 6.8 kJ mol?1 and 2.86 ± 0.2 min?1, respectively, which is in good agreement with past work. The reaction order for CO2 was determined to be 0.750 ± 0.08. The reaction kinetics for oxidation using CO2 were best described by a 3-D diffusion Jander model. 相似文献
56.
DN Maiorov ER Wilton E Badoer D Petrie GA Head SC Malpas 《Canadian Metallurgical Quarterly》1999,815(2):227-236
OBJECT: This study is a retrospective analysis of clinical data obtained in 28 patients affected by obstructive hydrocephalus who presented with signs of midbrain dysfunction during episodes of shunt malfunction. METHODS: All patients presented with an upward gaze palsy, sometimes associated with other signs of oculomotor dysfunction. In seven cases the ocular signs remained isolated and resolved rapidly after shunt revision. In 21 cases the ocular signs were variably associated with other clinical manifestations such as pyramidal and extrapyramidal deficits, memory disturbances, mutism, or alterations in consciousness. Resolution of these symptoms after shunt revision was usually slow. In four cases a transient paradoxical aggravation was observed at the time of shunt revision. In 11 cases ventriculocistemostomy allowed resolution of the symptoms and withdrawal of the shunt. Simultaneous supratentorial and infratentorial intracranial pressure recordings performed in seven of the patients showed a pressure gradient between the supratentorial and infratentorial compartments, with a higher supratentorial pressure before shunt revision. Inversion of this pressure gradient was observed after shunt revision and resolution of the gradient was observed in one case after third ventriculostomy. In six recent cases, a focal midbrain hyperintensity was evidenced on T2-weighted magnetic resonance imaging sequences at the time of shunt malfunction. This rapidly resolved after the patient underwent third ventriculostomy. CONCLUSIONS: It is probable that in obstructive hydrocephalus, at the time of shunt malfunction, the development of a transtentorial pressure gradient could initially induce a functional impairment of the upper midbrain, inducing upward gaze palsy. The persistence of the gradient could lead to a global dysfunction of the upper midbrain. Third ventriculostomy contributes to equalization of cerebrospinal fluid pressure across the tentorium by restoring free communication between the infratentorial and supratentorial compartments, resulting in resolution of the patient's clinical symptoms. 相似文献
57.
Cyclic Lateral Load Behavior of a Pile Cap and Backfill 总被引:1,自引:0,他引:1
A series of static cyclic lateral load tests were performed on a full-scale 4×3 pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap 5.18×3.05?m in plan and 1.12?m in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the second and subsequent cycles. The concave up shape continued to degrade with additional cycles past the second and typically became relatively constant after five to seven cycles. A gap formed between the backfill soil and the pile cap, which contributed to the load-deflection degradation. Crack patterns and sliding surfaces were consistent with that predicted by the log spiral theory. The results from this study indicate that passive resistance contributes considerably to the lateral resistance. However, with cyclic loading the passive force degrades significantly for deflections greater than 0.5% of the pile cap height. 相似文献
58.
David Cohen Peter Jeavons Christopher Jefferson Karen E. Petrie Barbara M. Smith 《Constraints》2006,11(2-3):115-137
We review the many different definitions of symmetry for constraint satisfaction problems (CSPs) that have appeared in the
literature, and show that a symmetry can be defined in two fundamentally different ways: as an operation preserving the solutions
of a CSP instance, or else as an operation preserving the constraints. We refer to these as solution symmetries and constraint symmetries. We define a constraint symmetry more precisely as an automorphism of a hypergraph associated with a CSP instance, the microstructure
complement. We show that the solution symmetries of a CSP instance can also be obtained as the automorphisms of a related
hypergraph, the k-ary nogood hypergraph and give examples to show that some instances have many more solution symmetries than constraint symmetries. Finally, we
discuss the practical implications of these different notions of symmetry. 相似文献
59.
Lysine metabolism by the mammary gland of lactating goats at two stages of lactation 总被引:1,自引:0,他引:1
An arteriovenous kinetics technique was used to monitor mammary gland lysine and protein metabolism in goats (n = 4) at two stages of lactation (80 +/- 17 vs. 233 +/- 14 DIM) in response to an i.v. infusion of lysine (Lys) plus methionine (Met). At each stage of lactation [2-15N] and [1-13C; 6,6-2H2] Lys kinetics were performed on the last day of 5-d i.v. infusion of saline followed by Lys (370 mg/h) plus Met (84 mg/h, LM). Milk and protein yields and dry matter intake were higher in early than in late lactation, but LM infusion did not affect these variables. Regardless of stage of lactation, the absolute and fractional oxidation rates of Lys by the mammary gland increased in response to LM infusion. When corrected for Lys oxidation, net uptake of Lys by the gland was less than milk protein Lys secretion. However, correction for the contribution of peptides (15.8%) to Lys uptake brought net Lys uptake close into balance with milk Lys secretion. The present data suggests that when Lys is in excess of requirements, the mammary gland appears to dispose of the extra supply via the oxidative mechanism. 相似文献
60.
The homeobox gene Otx2 is a mouse cognate of the Drosophila orthodenticle gene, which is required for development of the brain, rostral to rhombomere three. We have investigated the mechanisms involved in this neural function and specifically the requirement for Otx2 in the visceral endoderm and the neuroectoderm using chimeric analysis in mice and explant recombination assay. Analyses of chimeric embryos composed of more than 90% of Otx2-/- ES cells identified an essential function for Otx2 in the visceral endoderm for induction of the forebrain and midbrain. The chimeric studies also demonstrated that an anterior neural plate can form without expressing Otx2. However, in the absence of Otx2, expression of important regulatory genes, such as Hesx1/Rpx, Six3, Pax2, Wnt1 and En, fail to be initiated or maintained in the neural plate. Using explant-recombination assay, we could further demonstrate that Otx2 is required in the neuroectodem for expression of En. Altogether, these results demonstrate that Otx2 is first required in the visceral endoderm for the induction, and subsequently in the neuroectoderm for the specification of forebrain and midbrain territories. 相似文献