4,083 research outputs found

    Magnetic quantum phase transition of cold atoms in an optical lattice

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    We propose a scheme to investigate the magnetic phase transition of cold atoms confined in an optical lattice. We also demonstrate how to get coupled two-leg spin ladders which display a phase transition from a spin liquid to magnetic ordered state in two-dimensional optical lattice. An experimental protocol is further designed for observing this phenomenon. © 2007 The American Physical Society.published_or_final_versio

    Highly heterogeneous Late Mesozoic lithospheric mantle beneath the North China Craton: evidence from Sr–Nd–Pb isotopic systematics of mafic igneous rocks

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    The lithospheric mantle beneath the North China Craton changed dramatically in its geophysical and geochemical characteristics from Palaeozoic to Cenozoic times. This study uses samples of Mesozoic basalts and mafic intrusions from the North China Craton to investigate the nature of this mantle in Mesozoic times. Sr-Nd-Pb isotopic data demonstrate that the Late Mesozoic lithospheric mantle was extremely heterogeneous. In the central craton or the Luzhong region, it is slightly Sr-Nd isotopically enriched, beneath the Taihangshan region it has an EMI character (87Sr/86Sri = 0.7050-0.7066; εNd = -17--10), and beneath the Luxi-Jiaodong region, it possesses EM2-like characteristics (87Sr/86Sri up to 0.7114). Compositional variation with time is also apparent in the Mesozoic lithospheric mantle. Our data suggest that the old lithospheric mantle was modified during Mesozoic times by a silicic melt, where beneath the Luxi-Jiaodong region it was severely modified, but in the Luzhong and Taihangshan regions the effects were much less marked. The silicic melt may have been the product of partial melting of crustal materials brought into the mantle by the subducted slab during the formation of circum-cratonic orogenic belts. This Mesozoic mantle did not survive for a long time, and was replaced by a Cenozoic mantle with depleted geochemical characteristics. © 2004 Cambridge University Press.published_or_final_versio

    Hyperoxia resensitizes chemoresistant human glioblastoma cells to temozolomide

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    Temozolomide (TMZ) is standard chemotherapy for glioblastoma multiforme (GBM). Intratumoral hypoxia is common in GBM and may be associated with the development of TMZ resistance. Oxygen therapy has previously been reported to potentiate the effect of chemotherapy in cancer. In this study, we investigated whether hyperoxia can enhance the TMZ-induced cytotoxicity of human GBM cells, and whether and how it would resensitize TMZ-resistant GBM cells to TMZ. TMZ-sensitive human GBM cells (D54-S and U87-S) were treated with TMZ to develop isogenic subclones of TMZ-resistant cells (D54-R and U87-R). All cell lines were then exposed to different oxygen levels (1, 21, 40, or 80 %), with or without concomitant TMZ treatment, before assessment of cell cytotoxicity and morphology. Cell death and survival pathways elicited by TMZ and/or hyperoxia were elucidated by western blotting. Our results showed that TMZ sensitivity of both chemo-sensitive and resistant cells was enhanced significantly under hyperoxia. At the cell line-specific optimum oxygen concentration (D54-R, 80 %; U87-R, 40 %), resistant cells had the same response to TMZ as the parent chemosensitive cells under normoxia via the caspase-dependent pathway. Both TMZ and hyperoxia were associated with increased phosphorylation of ERK p44/42 MAPK (Erk1/2), but to a lesser extent in D54-R cells, suggesting that Erk1/2 activity may be involved in regulation of hyperoxia and TMZ-mediated cell death. Overall, hyperoxia enhanced TMZ toxicity in GBM cells by induction of apoptosis, possibly via MAPK-related pathways. Induced hyperoxia is a potentially promising approach for treatment of TMZ-resistant GBM.published_or_final_versio

    MicroRNA-210 and endoplasmic reticulum chaperones in the regulation of chemoresistance in glioblastoma

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    Glioblastoma multiforme (GBM) is the commonest primary brain tumour in adults characterized by relentless recurrence due to resistance towards the standard chemotherapeutic agent temozolomide (TMZ). Prolyl 4-hydroxylase, beta polypeptide (P4HB), an endoplasmic reticulum (ER) chaperone, is known to be upregulated in TMZ-resistant GBM cells. MicroRNAs (miRNAs) are non-protein-coding transcripts that may play important roles in GBM chemoresistance. We surmised that miRNA dysregulations may contribute to P4HB upregulation, hence chemoresistance.We found that miRNA-210 (miR-210) was P4HB-targeting and was highly downregulated in TMZ-resistant GBM cells. Forced overexpression of miR-210 led to P4HB downregulation and a reduction in TMZ-resistance. A reciprocal relationship between their expressions was also verified in clinical glioma specimens. Our study is the first to demonstrate a potential link between miR-210 and ER chaperone in determining chemosensitivity in GBM. The findings have important translational implications in suggesting new directions of future studies.published_or_final_versio

    Shape memory characteristics of woven glass fibre fabric reinforced epoxy composite in flexure

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    Shape memory characteristics of a woven glass fibre (GF) fabric reinforced epoxy composite (reinforcement content: 38 vol.%) were assessed in three point bending mode in a dynamic-mechanical analysis device and compared to those of the parent epoxy resin (EP). From unconstrained tests the shape fixity and recovery ratios and the recovery rate, whereas from constrained tests the recovery stress were determined. The shape fixity and recovery rate decreased due to the GF reinforcement which had, however, no effect on the shape recovery. Major benefit of the woven GF fabric was that the recovery stress could be enhanced by two orders of magnitude in comparison to the neat EP. GF reinforcement was accompanied with a substantial decrease in the failure-free flexural deformability of the composite specimen

    Microwave assisted heterogeneous catalysis: effects of varying oxygen concentrations on the oxidative coupling of methane

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    The oxidative coupling of methane was investigated over alumina supported La2O3/CeO2 catalysts under microwave dielectric heating conditions at different oxygen concentrations. It was observed that, at a given temperature using microwave heating, selectivities for both ethane and ethylene were notably higher when oxygen was absent than that in oxygen/methane mixtures. The differences were attributed to the localised heating of microwave radiation resulting in temperature inhomogeneity in the catalyst bed. A simplified model was used to estimate the temperature inhomogeneity; the temperature at the centre of the catalyst bed was 85 °C greater than that at the periphery when the catalyst was heated by microwaves in a gas mixture with an oxygen concentration of 12.5% (v/v), and the temperature difference was estimated to be 168 °C in the absence of oxygen

    Quantum anti-Zeno effect without wave function reduction

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    We study the measurement-induced enhancement of the spontaneous decay (called quantum anti-Zeno effect) for a two-level subsystem, where measurements are treated as couplings between the excited state and an auxiliary state rather than the von Neumann's wave function reduction. The photon radiated in a fast decay of the atom, from the auxiliary state to the excited state, triggers a quasi-measurement, as opposed to a projection measurement. Our use of the term "quasi-measurement" refers to a "coupling-based measurement". Such frequent quasi-measurements result in an exponential decay of the survival probability of atomic initial state with a photon emission following each quasi-measurement. Our calculations show that the effective decay rate is of the same form as the one based on projection measurements. What is more important, the survival probability of the atomic initial state which is obtained by tracing over all the photon states is equivalent to the survival probability of the atomic initial state with a photon emission following each quasi-measurement to the order under consideration. That is because the contributions from those states with photon number less than the number of quasi-measurements originate from higher-order processes.Comment: 7 pages, 3 figure

    Latent atrophy factors related to phenotypical variants of posterior cortical atrophy

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    OBJECTIVE: To determine whether atrophy relates to phenotypical variants of posterior cortical atrophy (PCA) recently proposed in clinical criteria; dorsal, ventral, dominant-parietal and caudal, we assessed associations between latent atrophy factors and cognition. METHODS: We employed a data-driven Bayesian modelling framework based on latent Dirichlet allocation to identify latent atrophy factors in a multi-center cohort of 119 individuals with PCA (age:64±7, 38% male, MMSE:21±5, 71% amyloid-β-positive, 29% amyloid-β status unknown). The model uses standardized gray matter density images as input (adjusted for age, sex, intracranial volume, field-strength and whole-brain gray matter volume) and provides voxelwise probabilistic maps for a predetermined number of atrophy factors, allowing every individual to express each factor to a degree without a-priori classification. Individual factor expressions were correlated to four PCA-specific cognitive domains (object-perception, space-perception, non-visual/parietal functions and primary visual processing) using general linear models. RESULTS: The model revealed four distinct yet partially overlapping atrophy factors; right-dorsal, right-ventral, left-ventral, and limbic. We found that object-perception and primary visual processing were associated with atrophy that predominantly reflects the right-ventral factor. Furthermore, space-perception was associated with atrophy that predominantly represents the right-dorsal and right-ventral factors. However, individual participant profiles revealed that the vast majority expressed multiple atrophy factors and had mixed clinical profiles with impairments across multiple domains, rather than displaying a discrete clinical-radiological phenotype. CONCLUSION: Our results indicate that particular brain-behavior networks are vulnerable in PCA, but most individuals display a constellation of affected brain-regions and symptoms, indicating that classification into four mutually exclusive variants is unlikely to be clinically useful

    Pauli's Principle in Probe Microscopy

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    Exceptionally clear images of intramolecular structure can be attained in dynamic force microscopy through the combination of a passivated tip apex and operation in what has become known as the "Pauli exclusion regime" of the tip-sample interaction. We discuss, from an experimentalist's perspective, a number of aspects of the exclusion principle which underpin this ability to achieve submolecular resolution. Our particular focus is on the origins, history, and interpretation of Pauli's principle in the context of interatomic and intermolecular interactions.Comment: This is a chapter from "Imaging and Manipulation of Adsorbates using Dynamic Force Microscopy", a book which is part of the "Advances in Atom and Single Molecule Machines" series published by Springer [http://www.springer.com/series/10425]. To be published late 201