1,217 research outputs found
Different Melting Behavior in Pentane and Heptane Monolayers on Graphite; Molecular Dynamics Simulations
Molecular dynamics simulations are utilized to study the melting transition
in pentane (C5H12) and heptane (C7H16), physisorbed onto the basal plane of
graphite at near-monolayer coverages. Through use of the newest, optimized
version of the anisotropic united-atom model (AUA4) to simulate both systems at
two separate coverages, this study provides evidence that the melting
transition for pentane and heptane monolayers are significantly different.
Specifically, this study proposes a very rapid transition from the solid
crystalline rectangular-centered (RC) phase to a fluid phase in pentane
monolayers, whereas heptane monolayers exhibit a slower transition that
involves a more gradual loss of RC order in the solid-fluid phase transition.
Through a study of the melting behavior, encompassing variations where the
formation of gauche defects in the alkyl chains are eliminated, this study
proposes that this gradual melting behavior for heptane monolayers is a result
of less orientational mobility of the heptane molecules in the solid RC phase,
as compared to the pentane molecules. This idea is supported through a study of
a nonane monolayer, which gives the gradual melting signature that heptane
monolayers also seem to indicate. The results of this work are compared to
previous experiment over pentane and heptane monolayers, and are found to be in
good agreement
A mechanism for unipolar resistance switching in oxide non-volatile memory devices
Building on a recently introduced model for non-volatile resistive switching,
we propose a mechanism for unipolar resistance switching in
metal-insulator-metal sandwich structures. The commutation from the high to low
resistance state and back can be achieved with successive voltage sweeps of the
same polarity. Electronic correlation effects at the metal-insulator interface
are found to play a key role to produce a resistive commutation effect in
qualitative agreement with recent experimental reports on binary transition
metal oxide based sandwich structures.Comment: 4 pages, 2 figure
Calcium dependence of exo- and endocytotic coupling at a glutamatergic synapse.
SummaryThe mechanism coupling exocytosis and endocytosis remains to be elucidated at central synapses. Here, we show that the mechanism linking these two processes is dependent on microdomain-[Ca2+]i similar to that which triggers exocytosis, as well as the exocytotic protein synaptobrevin/VAMP. Furthermore, block of endocytosis has a limited, retrograde action on exocytosis, delaying recruitment of release-ready vesicles and enhancing short-term depression. This effect sets in so rapidly that it cannot be explained by the nonavailability of recycled vesicles. Rather, we postulate that perturbation of a step linking exocytosis and endocytosis temporarily prevents new vesicles from docking at specialized sites for exocytosis
Inhibition of Casein Kinase 2 Modulates XBP1-GRP78 Arm of Unfolded Protein Responses in Cultured Glial Cells
Stress signals cause abnormal proteins to accumulate in the endoplasmic reticulum (ER). Such stress is known as ER stress, which has been suggested to be involved in neurodegenerative diseases, diabetes, obesity and cancer. ER stress activates the unfolded protein response (UPR) to reduce levels of abnormal proteins by inducing the production of chaperon proteins such as GRP78, and to attenuate translation through the phosphorylation of eIF2α. However, excessive stress leads to apoptosis by generating transcription factors such as CHOP. Casein kinase 2 (CK2) is a serine/threonine kinase involved in regulating neoplasia, cell survival and viral infections. In the present study, we investigated a possible linkage between CK2 and ER stress using mouse primary cultured glial cells. 4,5,6,7-tetrabromobenzotriazole (TBB), a CK2-specific inhibitor, attenuated ER stress-induced XBP-1 splicing and subsequent induction of GRP78 expression, but was ineffective against ER stress-induced eIF2α phosphorylation and CHOP expression. Similar results were obtained when endogenous CK2 expression was knocked-down by siRNA. Immunohistochemical analysis suggested that CK2 was present at the ER. These results indicate CK2 to be linked with UPR and to resist ER stress by activating the XBP-1-GRP78 arm of UPR
Fingerprinting Soft Materials: A Framework for Characterizing Nonlinear Viscoelasticity
We introduce a comprehensive scheme to physically quantify both viscous and
elastic rheological nonlinearities simultaneously, using an imposed large
amplitude oscillatory shear (LAOS) strain. The new framework naturally lends a
physical interpretation to commonly reported Fourier coefficients of the
nonlinear stress response. Additionally, we address the ambiguities inherent in
the standard definitions of viscoelastic moduli when extended into the
nonlinear regime, and define new measures which reveal behavior that is
obscured by conventional techniques.Comment: 10 pages, 3 figures, full-page double-space preprint forma
Synthesis and properties of radiopaque polymer hydrogels: polyion complexes of copolymers of acrylamide derivatives having triiodophenyl and carboxyl groups and p-styrene sulfonate and polyallylamine
In order to pursue a possibility of application of radiopaque polymer hydrogels to vascular embolization, studies were done on synthesis of iodine-containing copolyanions and properties of their hydrogels with polycation via formation of polyion complexes. Acrylamide derivatives having triiodophenyl and carboxyl groups were synthesized and copolymerized with sodium styrene sulfonate at various molar ratios of initiator to monomer and temperatures. Hydrogels were prepared by mixing aqueous solutions of the obtained radiopaque copolyanions and polyallylamine. Embolization was examined by injection of these hydrogels into vein of a removed porcine kidney as a preliminary test for transcatheter arterial embolization (TAE) for hepatocellular carcinoma. It was found that the hydrogels prepared from the copolycation obtained under particular conditions give high X-ray contrasts of the vein and remained there, though copolycations with low molecular weights had a tendency to drain through the capillaries to the peripheral tissues. It is therefore concluded that the hydrogels examined in the present study are promising for vascular embolization
Relapsed and/or Refractory Mantle Cell Lymphoma: What Role for Temsirolimus?
Mantle Cell Lymphoma (MCL) is associated with a dismal prognosis. Recently, along with the improved understanding of the pathophysiology of this disease, new first line regimens have been established and in addition novel treatment options have entered the clinical arena. In consequence, prognosis of the disease has fortunately improved. We here focus on the rationale, current clinical knowledge and future concepts of Temsirolimus, an inhibitor of mTOR, in the treatment of MCL. At this time this drug has been shown to be effective as single agent for relapsed disease and early combination data show promising results. In addition, with a brief outline of other treatment options, we aim to guide at which place in the current treatment algorithms Temsirolimus can be integrated into the treatment of MCL patients
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