4,707 research outputs found

    Astrophysical constraints on the proton-to-electron mass ratio with FAST

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    That the laws of physics are the same at all times and places throughout the Universe is one of the basic assumptions of physics. Astronomical observations provide the only means to test this basic assumption on cosmological time and distance scales. The possibility of variations in the dimensionless physical constant {\mu} - the proton-to-electron mass ratio, can be tested by comparing astronomical measurements of the rest frequency of certain spectral lines at radio wavelengths with laboratory determinations. Different types of molecular transitions have different dependencies on {\mu} and so observations of two or more spectral lines towards the same astronomical source can be used to test whether there is any evidence for either temporal or spatial changes in the physical fundamental constants. {\mu} will change if the relative strength of the strong nuclear force compared to the electromagnetic force varies. Theoretical studies have shown that the rotational transitions of some molecules which have transitions in the frequency range that will be covered by FAST (e.g., CH3OH, OH and CH) are sensitive to changes in {\mu}. A number of studies looking for possible variations in {\mu} have been undertaken with existing telescopes, however, the greater sensitivity of FAST means it will open new opportunities to significantly improve upon measurements made to date. In this paper, we discuss which molecular transitions and sources (both in the Galaxy and external galaxies) are likely targets for providing improved constraints on {\mu} with FAST

    Becoming Taiwanese: Self-perception1 Of The New Taiwanese Immigrant Females

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    Southeast Asian and Chinese women have been marrying Taiwanese men since the 1980s. Nonetheless, cross-border marriages were not common until the 1990s, when the ″Go-South Policy″ was implemented. Unfortunately, these cross-border marriages have become commoditised. In addition, misperceptions broadcasted by the mass media have stigmatised these self-titled Taiwan new immigrant females (or TNIFs). This ethnographic research explores the self-perceptions of a particular group of TNIFs who have moved to Taiwan from urban regions in their homeland. Participant observation and in-depth interviews were employed to gather data, and these two sources of data were triangulated between one another. Research results indicate that many people came to Taiwan seeking a better life and not necessarily for economic reasons. However, their experiences in Taiwan have been largely unpleasant. Nevertheless, by working together with other TNIFs and Taiwanese people, they have come to call Taiwan their "home"

    Pyridine Hydrogen Iodide as an Ether Cleaving Agent in Coal Chemistry

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    Reactions of several phenyl ethers and an ester with pyridine hydrogen iodide were examined under various conditions as model studies for the recently reported molecular weight reduction of a fraction of Illinois No. 6 coal by hydrogen iodide in pyridine at 50°. No ether or ester cleavage was observed at 60-80° in pyridine, acetonitrile, ethanol or the absence of solvent. Sealed tube reactions at 210° resulted in cleavage to phenol plus various hydrocarbon and alkyl halide products. Pyridine and benzyl phenyl ether at 210° produced no cleavage in the absence of hydrogen iodide. Syntheses of crystalline pyridine hydrogen iodide and pyridine hydrogen bisulfate as well as cyclohexyl phenyl ether are described

    Regression Analysis of Recurrent Gap Times with Time-Dependent Covariates

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    Individual subjects may experience recurrent events of same type over a relatively long period of time in a longitudinal study. Researchers are often interested in the distributional pattern of gaps between the successive recurrent events and their association with certain concomitant covariates as well. In this article, their probability structure is investigated in presence of censoring. According to the identified structure, we introduce the proportional reverse-time hazards models that allow arbitrary baseline function for every individual in the study, when the time-dependent covariates effect is of main interest. Appropriate inference procedures are proposed and studied to estimate the parameters of interest in the models. The proposed methodology is demonstrated with the Monte-Carlo simulations and applied to a well-known Denmark schizophrenia cohort study data set

    Semiparametric Regression Analysis on Longitudinal Pattern of Recurrent Gap Times

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    In longitudinal studies, individual subjects may experience recurrent events of the same type over a relatively long period of time. The longitudinal pattern of the gaps between the successive recurrent events is often of great research interest. In this article, the probability structure of the recurrent gap times is first explored in the presence of censoring. According to the discovered structure, we introduce the proportional reverse-time hazards models with unspecified baseline functions to accommodate heterogeneous individual underlying distributions, when the ongitudinal pattern parameter is of main interest. Inference procedures are proposed and studied by way of proper riskset construction. The proposed methodology is demonstrated by Monte-Carlo simulations and an application to the well-known Denmark schizophrenia cohort study data se

    Detection of Progressive Deterioration in Early Onset Schizophrenia with a New Statistical Method

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    Much controversy exists over whether the course of schizophrenia, as defined by the lengths of repeated community tenures, is progressively ameliorating or deteriorating. This article employs a new statistical method proposed by Wang and Chen (2000) to analyze the Denmark registry data in Eaton, et al (1992). The new statistical method correctly handles the bias caused by induced informative censoring, which is an interaction of the heterogeneity of schizophrenia patients and long-term follow-up. The analysis shows a progressive deterioration pattern in terms of community tenures for the full registry cohort, rather than a progressive amelioration pattern as reported for a selected sub-cohort in Eaton, et al (1992). When adjusted for the long-term chronicity of calendar time, no significant progressive pattern was found for the full cohort

    Additive Hazards Models with Latent Treatment Effectiveness Lag Time

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    In many clinical trials to evaluate treatment efficacy, it is believed that there may exist latent treatment effectiveness lag times after which medical procedure or chemical compound would be in full effect. In this article, semiparametric regression models are proposed and studied to estimate the treatment effect accounting for such latent lag times. The new models take advantage of the invariance property of the additive hazards model in marginalizing over random effects, so parameters in the models are easy to be estimated and interpreted, while the flexibility without specifying baseline hazard function is kept. Monte Carlo simulation studies demonstrate the appropriateness of the proposed semiparametric estimation procedure. Data collected in the actual randomized clinical trial, which evaluates the effectiveness of biodegradable carmustine polymers for treatment of recurrent brain tumors, are analyzed
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