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Articles by X. Xu
Total Records ( 6 ) for X. Xu
  J.R. Fernandez , C.J. Mertens , D. Bilitza , X. Xu , J.M. Russell III and M.G. Mlynczak
  We present a new technique for improving ionospheric models of nighttime E-region electron densities under geomagnetic storm conditions using TIMED/SABER measurements of broadband 4.3 μm limb radiance. The response of E-region electron densities to geomagnetic activity is characterized by SABER-derived NO+(v) 4.3 μm Volume Emission Rates (VER). A storm-time E-region electron density correction factor is defined as the ratio of storm-enhanced NO+(v) VER to a quiet-time climatological average NO+(v) VER, which will be fit to a geomagnetic activity index in a future work. The purpose of this paper is to demonstrate the feasibility of our technique in two ways. One, we compare storm-to-quiet ratios of SABER-derived NO+(v) VER with storm-to-quiet ratios of electron densities measured by Incoherent Scatter Radar. Two, we demonstrate that NO+(v) VER can be parameterized by widely available geomagnetic activity indices. The storm-time correction derived from NO+(v) VER is applicable at high-latitudes.
  H Wang , A Zhao , L Chen , X Zhong , J Liao , M Gao , M Cai , D. H Lee , J Li , D Chowdhury , Y. g Yang , G. P Pfeifer , Y Yen and X. Xu

Human Rap1-interacting protein 1 (RIF1) contributes to the ataxia telangiectasia, mutated-mediated DNA damage response against the dexterous effect of DNA lesions and plays a critical role in the S-phase checkpoint. However, the molecular mechanisms by which human RIF1 conquers DNA aberrations remain largely unknown. We here showed that inhibition of RIF1 expression by small interfering RNA led to defective homologous recombination-mediated DNA double-strand break repair and sensitized cancer cells to camptothecin or staurosporine treatment. RIF1 underwent caspase-dependent cleavage upon apoptosis. We further found that RIF1 was highly expressed in human breast tumors, and its expression status was positively correlated with differentiation degrees of invasive ductal carcinoma of the breast. Our results suggest that RIF1 encodes an anti-apoptotic factor required for DNA repair and is a potential target for cancer treatment.

  H. Yang , Y. Wei , X. Gao , X. Xu , L. Fan , J. He , Y. Hu , X. Liu , X. Chen , Z. Yang and C. Zhang
  Aims  To determine the incidence of gestational diabetes mellitus (GDM) in China and to further identify population specific risk factors for GDM.

Methods  Following a universal GDM screening recommendation, 16 286 pregnant women who underwent a 50-g glucose challenge test from 18 cities in China were followed up through pregnancy. GDM was confirmed by oral glucose tolerance test according to American Diabetes Association criteria.

Results  The incidence of GDM was 4.3%. Previously reported risk factors for GDM, including advanced maternal age, pre-pregnancy obesity and family history of diabetes, were strongly associated with an elevated GDM risk. Moreover, after the adjustment for the above-mentioned risk factors, a history of recurrent vulvovaginal candidiasis, residency in south China and a history of spontaneous abortion were significantly associated with an increased GDM risk; adjusted odds ratio (OR) [95% confidence interval (95% CI)] were 1.97 (1.39, 2.80), 1.84 (1.59-2.13), and 1.46 (1.12, 1.91), respectively.

Conclusions  In this large study of GDM in Chinese women, advanced maternal age, pre-pregnancy overweight or obesity and family history of diabetes were confirmed to be risk factors. In addition, a history of recurrent vulvovaginal candidiasis or spontaneous abortion and residency in south China appeared to be novel risk factors in this population.

  Q. Huang , Y.L. Li , X. Xu , Y. Huang , Z.W. Cui , D.Y. Yu and W.F. Li
  The aim of this study is to investigate the effects of Bacillus subtilis BS02 on viability and immune responses of RAW 264.7 cells. RAW 264.7 cells were stimulated with and without B. subtilis spores for 12 h in the treatment group and the control group, respectively. Cytotoxic effect of B. subtilis BS02 on macrophages was measured by cell viability and LDH cytotoxicity assay. Immune responses of macrophage elicited by B. subtilis BS02 were analyzed by measuring the activities of Acid Phosphatase (ACP) and Lactate Dehydrogenase (LDH), the production of Nitric Oxide (NO) and inducible Nitric Oxide Synthase (iNOS) and the secretion of inflammatory cytokines. The results showed that after 12 h incubation, B. subtilis BS02 spores had no influence on viability of RAW 264.7 cells; ACP and LDH activities, the production of NO and iNOS, the levels of inflammatory cytokines [Tumor Necrosis Factor-alpha (TNF-α), Interferon-gamma (IFN-γ), Interleukin-1 beta (IL-1β), IL-6, IL-8, IL-10 and IL-12] were significantly higher than that in the control group (p<0.01). These results indicate that B. subtilis BS02 is not only safe for RAW 264.7 cells but also can activate macrophage immune function.
  Thomas W. McDowell , R. G. Dong , X. Xu , D. E. Welcome and C. Warren
  In the interest of providing more effective evaluations of impact wrench vibration exposures and the development of improved methods for measuring vibration emissions produced by these tools, this study focused on three variables: acceleration measured at the tool surface, vibration exposure duration per test trial, and the amount of torque required to unseat the nuts following a test trial. For this evaluation, six experienced male impact wrench operators used three samples each of five impact wrench models (four pneumatic models and one battery-powered model) in a simulated work task. The test setup and procedures were based on those provided by an International Organization for Standardization (ISO) Technical Committee overseeing the revision of ISO 8662-7. The work task involved the seating of 10 nuts onto 10 bolts mounted on steel plates. The results indicate that acceleration magnitudes vary not only by tool type but also by individual tools within a type. Thus, evaluators are cautioned against drawing conclusions based on small numbers of tools and/or tool operators. Appropriate sample sizes are suggested. It was further noted that evaluators could draw different conclusions if tool assessments are based on ISO-weighted acceleration as opposed to unweighted acceleration. As expected, vibration exposure durations varied by tool type and by test subject; duration means varied more for study participants than they did for tool types. For the 12 pneumatic tools evaluated in this study, torque varied directly with tool handle acceleration. Therefore, in order to reduce vibration exposure, tools should be selected and adjusted so that they produce no more than the needed torque for the task at hand.
  R. Yang , T. Xia , G. Xu , Z. Li , Z. Ying and X. Xu
  Our study sought to investigate the immune response of cytotoxic T lymphocytes to human cytomegalovirus (HCMV) in kidney transplant recipients with virus reactivation. Nine kidney transplant recipients with serum HCMV immunoglobulin G and HLA-A*0201 genotype displayed HCMV pp65 antigenemia and were compared with 29 control recipients who were free of antigenemia. The frequency of total HCMV-specific cytotoxic T cells was determined using HLA-A2-NLVPMVATV-pentamer staining. The frequency of HCMV specific interferon (INF)-γ secreting CD8+ T cells was determined using intracellular INF-γ staining after NLVPMVATV pulsing in vitro. The proportion of IFN-γ secreting pentamer-stained CD8+ T cells was calculated, representing the capacity for INF-γ secretion among HCMV-specific CD8+ T cells. We observed that the frequency of HCMV-specific pentamer-stained CD8+ T cells and HCMV-specific IFN-γ secreting CD8+ T cells both remained unchanged, yet the proportion of IFN-γ secreting CD8+ T cells showed a significant difference between the 2 groups (39.2% ± 17.2% vs 20.0% ± 13.3% respectively; P = .004), reflecting impaired IFN-γ secreting capacity of HCMV-specific CD8+ T cells among kidney transplant recipients displaying antigenemia, which may be a crucial reason for HCMV reactivation in immunosuppressed patients.
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