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排序方式: 共有2309条查询结果,搜索用时 46 毫秒
21.
Hermann Petra M.; Lee Arden; Hulliger Sara; Minvielle Michelle; Ma Bonita; Wildering Willem C. 《Canadian Metallurgical Quarterly》2007,121(6):1400
Age-dependent impairment in learning and memory functions occurs in many animal species, including humans. Although cell death contributes to age-related cognitive impairment in pathological forms of aging, learning and memory deficiencies develop with age even without substantial cell death. The molecular and cellular basis of this biological aging process is not well understood but seems to involve a decline in the aging brain's capacity for experience-dependent plasticity. To aid in resolving this issue, we used a simple snail appetitive classical conditioning paradigm in which the underlying molecular, cellular, and neural network functions can be directly linked to age-associated learning and memory performance (i.e., the Lymnaea stagnalis feeding system). Our results indicate that age does not affect the acquisition of appetitive memory but that retention and/or consolidation of long-term memory become progressively impaired with advancing age. The latter phenomenon correlates with declining electrophysiological excitability in key neurons controlling the feeding behavior. Together, these results present the Lymnaea feeding system as a powerful paradigm for investigations of cellular and molecular foundations of biological aging in the brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
22.
Magnetization measurements were carried out on bulk Tl2Ba2CaCu2O8 (referred to as Tl-2212) and on various site-selective substituted Tl-2212 samples. At 5K between 0 and 4.5 T, the 5 at.
% Mg-doped Tl-2212 (Tl,Mg-2212) samples displayed enhanced pinning as demonstrated by a field dependent increase of the magnetic
critical-current density Jc by 18 to 25 percent over that of pristine Tl-2212. Excess Mg (10–15 at. %), however, is deleterious. Rietveld refinement
of the x-ray diffraction pattern showed Mg on the Tl sites. Auger electron spectroscopy analysis showed part of the Mg on
grain boundaries. The flux-creep activation energies are higher for flux expulsion than for flux penetration in both Tl-2212
and Tl,Mg-2212 samples; the latter displays higher individual values. Our results demonstrate an increase in the number density
of flux lines as a result of increased density of atomic-size-structural, defects by Mg (5 at. %) doping. In the Tl2−yBa2(Ca1−zYz)Cu2O8−x(z=0–0.3; single phase; x and y represent oxygen and thallium vacancies) system also studied, the Tc decreases as z increases. At z=0.3, the sample becomes an antiferromagnetic semiconductor. 相似文献
23.
Malware-Autoren setzen zunehmend Verschleierungsmechanismen wie Komprimierung, Verschlüsselung oder sich selbst modifizierenden
Programmcode ein, welche das Auffinden der Malware durch herk?mmliche Virenerkennungsverfahren wie zum Beispiel die signaturbasierte
Suche sehr mühsam und teilweise sogar erfolglos erscheinen lassen. Ein erfolgversprechender Ansatz, um auch unbekannte Viren,
Würmer oder Trojaner zu erkennen, ist die heuristische Analyse 相似文献
24.
The immunosuppressive agent FK 506 is widely used in liver transplant patients. Neurotoxicity is a major complication of its use. We report progressive and irreversible neurologic complications occurring in a 39-year-old woman who underwent liver transplantation and was treated with FK 506. Neuropathologic examination revealed multiple vasculitic lesions. The possibility of an FK 506-mediated toxic effect on the cerebral vessels is suggested. 相似文献
25.
The effect of rapid solidification on the corrosion behaviour in aerated 0.001 M NaCl solution of Mg-Al alloys containing 9.6 to 23.4wt% AI has been investigated in comparison with chill-cast material. Polarization studies show that rapid solidification decreases corrosion current by up to two orders of magnitude corresponding to a corrosion rate of 6 to 11 mil y–1. Increasing the aluminium content in solid solution by rapid solidification gave rise to a steep increase in pitting potential between 10 and 23 wt% Al and resulted in development of an anodic plateau at 30Acm–2 attributable to magnesium depletion for the alloy surface and formation of a protective film. Chemical analysis of the electrolyte as a function of dissolution time for the rapidly solidified material indicated that initially only magnesium dissolved and that this dissolution of magnesium ceased within 2 to 5 min. The results indicate the formation of an aluminium-enriched interdiffusion zone at the surface underlying a more stable surface oxide than for ingot-processed Mg-Al-based alloys. 相似文献
26.
27.
Jessica A. Schroeder 《Journal of Materials Science》1988,23(9):3073-3082
The cohesive, mode I (tensile cleavage) fracture energy (or fracture toughness), G
Ic, of bulk tapered double cantilevered beam (TDCB) samples of a series of three epoxy thermoset networks was determined using a linear elastic fracture mechanics (LEFM) analysis. Networks of different crosslink density were obtained by mixing various amounts of an aromatic epoxy novolac and an aliphatic epoxy and crosslinking with an imidazole catalyst. Brittle, stick-slip fracture was observed for all formulations, with G
Ic increasing as the amount of aliphatic epoxy increased. However, fracture surface morphologies exhibited evidence of increasing plastic deformation as G
Ic increased. In the investigation of structure-property relationships for this series of thermoset networks, G
Ic was found to be inversely related to both network crosslink density and glass transition temperature (T
g). It was also found that the room temperature frequency of the glassy state transition (-transition) increased as fracture toughness increased. 相似文献
28.
Maria Immaculata Arifin Samia Hannaoui Sheng Chun Chang Simrika Thapa Hermann M. Schatzl Sabine Gilch 《International journal of molecular sciences》2021,22(5)
Chronic wasting disease (CWD) is a prion disease found in both free-ranging and farmed cervids. Susceptibility of these animals to CWD is governed by various exogenous and endogenous factors. Past studies have demonstrated that polymorphisms within the prion protein (PrP) sequence itself affect an animal’s susceptibility to CWD. PrP polymorphisms can modulate CWD pathogenesis in two ways: the ability of the endogenous prion protein (PrPC) to convert into infectious prions (PrPSc) or it can give rise to novel prion strains. In vivo studies in susceptible cervids, complemented by studies in transgenic mice expressing the corresponding cervid PrP sequence, show that each polymorphism has distinct effects on both PrPC and PrPSc. It is not entirely clear how these polymorphisms are responsible for these effects, but in vitro studies suggest they play a role in modifying PrP epitopes crucial for PrPC to PrPSc conversion and determining PrPC stability. PrP polymorphisms are unique to one or two cervid species and most confer a certain degree of reduced susceptibility to CWD. However, to date, there are no reports of polymorphic cervid PrP alleles providing absolute resistance to CWD. Studies on polymorphisms have focused on those found in CWD-endemic areas, with the hope that understanding the role of an animal’s genetics in CWD can help to predict, contain, or prevent transmission of CWD. 相似文献
29.
本文对FMS50系统结构进行了介绍,着重阐述了该系统的多种物流模式.并分析了其通信控制系统的构成。 相似文献
30.
Anna Kutschenko Selma Staege Karen Grütz Hannes Glaß Norman Kalmbach Thomas Gschwendtberger Lisa M. Henkel Johanne Heine Anne Grünewald Andreas Hermann Philip Seibler Florian Wegner 《International journal of molecular sciences》2021,22(7)
Myoclonus-dystonia (DYT-SGCE, formerly DYT11) is characterized by alcohol-sensitive, myoclonic-like appearance of fast dystonic movements. It is caused by mutations in the SGCE gene encoding ε-sarcoglycan leading to a dysfunction of this transmembrane protein, alterations in the cerebello-thalamic pathway and impaired striatal plasticity. To elucidate underlying pathogenic mechanisms, we investigated induced pluripotent stem cell (iPSC)-derived striatal medium spiny neurons (MSNs) from two myoclonus-dystonia patients carrying a heterozygous mutation in the SGCE gene (c.298T>G and c.304C>T with protein changes W100G and R102X) in comparison to two matched healthy control lines. Calcium imaging showed significantly elevated basal intracellular Ca2+ content and lower frequency of spontaneous Ca2+ signals in SGCE MSNs. Blocking of voltage-gated Ca2+ channels by verapamil was less efficient in suppressing KCl-induced Ca2+ peaks of SGCE MSNs. Ca2+ amplitudes upon glycine and acetylcholine applications were increased in SGCE MSNs, but not after GABA or glutamate applications. Expression of voltage-gated Ca2+ channels and most ionotropic receptor subunits was not altered. SGCE MSNs showed significantly reduced GABAergic synaptic density. Whole-cell patch-clamp recordings displayed elevated amplitudes of miniature postsynaptic currents and action potentials in SGCE MSNs. Our data contribute to a better understanding of the pathophysiology and the development of novel therapeutic strategies for myoclonus-dystonia. 相似文献