Early re-brightenings in GRB afterglows as signatures of low-to-high density boundary

The association of long gamma-ray bursts (GRBs) with star forming regions and the idea of massive stars as progenitors of GRBs are widely accepted. Because of their short lifetimes, it is very likely that massive stars are still embedded in dense molecular clouds when they give birth to GRBs. Stellar winds from GRB progenitors can create low-density bubbles with sizes and densities strongly depending on the initial ambient density. A boundary between the bubble and the dense molecular cloud must exist with the density at the boundary increasing from that of the bubble to that of the outer cloud. We have calculated the lightcurves of the afterglows in such environments with three regions: the stellar wind region, the boundary, and the molecular cloud. We show that the interaction between the cylindrical jet and the density boundary can result in a re-brightening of the afterglow occurring as early as ∼1 day after the GRB. We compare our models with the optical afterglows of GRB 970508, GRB 000301C, and GRB 030226. We find that the values of our model parameters, including the radius of the wind bubble, the densities in the bubble and in the outer molecular cloud are within typical ranges. © 2005 Elsevier B.V. All rights reserved.postprin

On the design and implementation of FIR and IIR digital filters with variable frequency characteristics

This paper studies the design and implementation of finite-impulse response (FIR) and infinite-impulse response (IIR) variable digital filters (VDFs), whose frequency characteristics can be controlled continuously by some control or tuning parameters. A least squares (LS) approach is proposed for the design of FIR VDFs by expressing the impulse response of the filter as a linear combination of basis functions. It is shown that the optimal LS solution can be obtained by solving a system of linear equations. By choosing the basis functions as piecewise polynomials, VDFs with larger tuning range than that of ordinary polynomial based approach results. The proposed VDF can be efficiently implemented using the familiar Farrow structure. Making use of the FIR VDF so obtained, an Eigensystem Realization Algorithm (ERA)-based model reduction technique is proposed to approximate the FIR VDF by a stable IIR VDF with lower system order. The advantages of the model reduction approach are: 1) it is computational simple which only requires the computation of the singular value decomposition of a Hankel matrix; 2) the IIR VDF obtained is guaranteed to be stable; and 3) the frequency response such as the phase response of the FIR prototype is well preserved. Apart from the above advantages, the proposed IIR VDF does not suffer from undesirable transient response during parameter tuning found in other approaches based on direct tuning of filter parameters. For frequency selective VDFs, about 40% of the multiplications can be saved using the IIR VDFs. The implementation of the proposed FIR VDF using sum-of-powers-of-two (SOPOT) coefficient and the multiplier block (MB) technique are also studied. Results show that about two-third of the additions in implementing the multiplication of the SOPOT coefficients can be saved using the multiplier block, which leads to significant savings in hardware complexity.link_to_subscribed_fulltex

f(R) theories

Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in Relativity, Published version, Comments are welcom

Astrocytes: biology and pathology

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions

Efficacy of preemptive analgesia for wound pain after laparoscopic operations in infertile women: A randomised, double-blind and placebo control study

Objective: To compare preemptive analgesia and preclosure analgesia in reducing wound pain after laparoscopic operation. Design: Randomised, double-blind and placebo control. Setting: University referral centre. Population: Infertile women undergoing diagnostic laparoscopy with or without additional procedures. Methods: One hundred and forty-four women were randomised to receive 10 mL of 1% lignocaine at the surgical sites before incision and 10 mL of normal saline before closure of incision (the preemptive group), saline before incision and lignocaine before closure of incision (the preclosure group) and saline at the surgical sites both before incision and closure of incision (the placebo group). Main outcome measures: Post-operative wound pain measured by linear visual analogue scale and amount of analgesic use. Results: The women in the preclosure group had significantly lower pain scores at 2, 4 and 24 hours than those in the placebo group, whereas the women in the preemptive group only showed significantly lower pain scores at 2 hours than the placebo group. The pain score at 24 hours in the preclosure group was significantly lower than that in the preemptive group. There was no significant difference in the postoperative analgesic requirement among the three groups. Conclusion: The preclosure analgesia is better than preemptive analgesia and no analgesia in reducing postoperative wound pain.link_to_subscribed_fulltex

Preclosure, but not pre-emptive, analgesia reduced wound pain more than placebo for 24 hours after laparoscopy

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Long-term results following 131I treatment for Graves' disease in Hong Kong Chinese - Discriminant factors predicting hypothyroidism

The clinical outcome of 1028 Hong Kong Chinese patients with Graves' disease treated with radioiodine therapy and followed for a mean of 9.85 ± 4.84 years (range 2-20) was analysed. Retreatment was required by 413 patients (40.2 per cent), with 134 patients (13.0 per cent) requiring more than two 131I doses. One hundred and eighty-nine patients received carbimazole after 131I until euthyroidism was achieved. The cumulative incidence of hypothyroidism at one, five, 10 and 15 years was 9.6 per cent, 31.4 per cent, 53.8 per cent and 65.8 per cent, respectively. The average incidence of hypothyroidism after the first two years was 3.3 per cent per annum. Stepwise logistic regression analysis of pretreatment variables suggested that a combination of adjunctive carbimazole therapy, absence of ophthalmopathy and longer effective half-lives of 131I were of value in predicting which patients were less likely to develop permanent hypothyroidism. However, the probability of accurately predicting permanent hypothyroidism based on the present model was only 60 per cent. We believe that no single pretreatment variable, or combination of variables, predicts long-term hypothyroidism with sufficient confidence to justify the use of a 'formula' approach for prescribing 131I therapy for Graves' disease.link_to_subscribed_fulltex