On gravitational wave-Cherenkov radiation from photons when passing through diffused dark matters

Analogy to Cherenkov radiation, when a particle moves faster than the propagation velocity of gravitational wave in matter ($v>c_{\rm{g}}$), we expect gravitational wave-Cherenkov radiation (GWCR). In the situation that a photon travels across diffuse dark matters, the GWCR condition is always satisfied, photon will thence loss its energy all the path. This effect is long been ignored in the practice of astrophysics and cosmology, without justification with serious calculation. We study this effect for the first time, and shows that this energy loss time of the photon is far longer than the Hubble time, therefore justify the practice of ignoring this effect in astrophysics context.Comment: 3 pages; We add a citation to Caves (1980) to the original journal version, after kindly reminde

Neurodegeneration induced by general anaesthetics in the developing brain: Mechanism and prevention

In the early development of brain, there is an important period called the synaptogenesis period (also known as the brain growth-spurt period) which occurs in different mammalian species at different times relative to birth. In rodents, it begins a day or two before birth and ends 2 weeks after birth, whereas in humans it starts at the beginning of the third trimester and ends several years after birth. This is a critical period during neural development as neurons are establishing communications with their environment and other neurons to ensure that they develop and function appropriately; disruption at this stage by toxic agents including anaesthetic agents may compromise the normal neuronal development of the central nervous system. During the course of my PhD study, I found that inhalational agents isoflurane (ISO) alone or in combination with nitrous oxide (N2O) caused a wide spread neurodegeneration in the brain including the cingulated cortex, hippocampus, substantia nigra and basal forebrain in postnatal day 7 Sprague-Dawley rat pups. In those brain regions, the cells involved included glutamatergic, GABAergic and dopaminergic neurons. However, the cholinergic neurons in the basal forebrain were spared from anaesthesia-induced neuroapoptosis. My studies also showed that the neurodegeneration was not only confined to the higher centres, but was also observed in the spinal cord. These data indicated that the anaesthetics studied acted at molecular level and induced neuronal apoptosis by activating the intrinsic apoptotic pathway. It has been well documented that preconditioning with hypoxia or other interventions including pharmacological agents can protect against subsequent brain injury induced by hypoxia/ischemia. However, my data showed that hypoxic preconditioning exacerbated N2O+ISO-induced neonatal neurodegeneration, while xenon preconditioning protected against anaesthetics-induced neuroapoptosis and subsequent neurocognitve impairment. Most studies in this field including my own study described above are more relevant to the clinical situation where neonates are managed in the critical care unit, i.e. in the absence of surgery. For this reason, I implemented another experimental setting to mimic the clinical situation in the operating room where neonates receiving anaesthetic drugs are also subjected to nociceptive surgical stimuli. Therefore, in another experiment, rat pups in addition to receiving anaesthetic drugs were also subjected to standardised nociceptive stimuli. The results suggested that nociceptive stimuli enhanced neuronal apoptosis induced by anaesthetic drugs in the brain and the spinal cord and consequently impaired neurological function. Were the data reported in my thesis to be extrapolated to the clinical setting, it would have very important implications for the clinical management of paediatric population receiving general anaesthesia

Analysis of association studies and inference of haplotypic phase using hidden Markov models

In this thesis I focus on the development and application of hidden Markov model (HMM) to solve problems in statistical genetics. Our method, based on a HMM, models the joint haplotype structure in the samples, where the parameters in the model are estimated by the Baum-Welch EM algorithm. Also, the model does not require pre-defined blocks or a sliding window scheme to define haplotype boundaries. Thus our method is computationally efficient and applicable for either the whole genome sequence or the candidate gene sequence. The first application of this model is for disease association testing using inferred ancestral haplotypes. We employed a HMM to cluster haplotypes into groups of predicted common ancestral haplotypes from diploid genotypes. The results from simulation studies show that our method greatly outperforms single-SNP analyses and has greater power than a haplotype-based method, CLADHC, in most simulation scenarios. The second application is for inferring haplotypic phase and to predict missing genotypes in polyploid organisms. Using a simulation study we demonstrate that the method provides accurate estimates of haplotypic phase and missing genotypes for diploids, triploids and tetraploids. The third application is for joint CNV/SNP haplotype and missing data inference. The results are very encouraging for this application. With the increasing availability of genotype data in both diploid and polyploid organisms, we believe that our programs can facilitate the investigation of genetic variations in genome-wide scale studies

A new approach to the GeV flare of PSR B1259-63/LS2883

PSR B1259-63/LS2883 is a binary system composed of a pulsar and a Be star. The Be star has an equatorial circumstellar disk (CD). The {\it Fermi} satellite discovered unexpected gamma-ray flares around 30 days after the last two periastron passages. The origin of the flares remain puzzling. In this work, we explore the possibility that, the GeV flares are consequences of inverse Compton-scattering of soft photons by the pulsar wind. The soft photons are from an accretion disk around the pulsar, which is composed by the matter from CD captured by the pulsar's gravity at disk-crossing before the periastron. At the other disk-crossing after the periastron, the density of the CD is not high enough so that accretion is prevented by the pulsar wind shock. This model can reproduce the observed SEDs and light curves satisfactorily.Comment: 14 pages, 8 figures, 1 table. Accepted for publication in Ap

Probing the properties of the pulsar wind via studying the dispersive effects in the pulses from the pulsar companion in a double neutron-star binary system

The velocity and density distribution of $e^\pm$ in the pulsar wind are crucial distinction among magnetosphere models, and contains key parameters determining the high energy emission of pulsar binaries. In this work, a direct method is proposed, which might probe the properties of the wind from one pulsar in a double-pulsar binary. When the radio signals from the first-formed pulsar travel through the relativistic $e^\pm$ flow in the pulsar wind from the younger companion, the components of different radio frequencies will be dispersed. It will introduce an additional frequency-dependent time-of-arrival delay of pulses, which is function of the orbital phase. In this paper, we formulate the above-mentioned dispersive delay with the properties of the pulsar wind. As examples, we apply the formula to the double pulsar system PSR J0737-3039A/B and the pulsar-neutron star binary PSR B1913+16. For PSR J0737-3039A/B, the time delay in 300\,MHz is $\lesssim10\mu$s near the superior-conjunction, under the optimal pulsar wind parameters, which is $\sim$ half of the current timing accuracy. For PSR B1913+16, with the assumption that the neutron star companion has a typical spin down luminosity of $10^{33}$\,ergs/s, the time delay is as large as $10\sim20\mu$s in 300\,MHz. The best timing precision of this pulsar is $\sim5\mu$s in 1400\,MHz. Therefore, it is possible that we can find this signal in archival data. Otherwise, we can set an upper-limit on the spin down luminosity. Similar analysis can be apply to other eleven known pulsar-neutron star binariesComment: 6 pages, 6 figures, accepted for publication in MNRA