arXiv subjects

Bernard Leong

Publications and source records attributed to Bernard Leong.

6 recordsLinked to original sources

arXiv2010

The robustness of the galaxy distribution function to effects of merging and evolution

We examine the evolution of the spatial counts-in-cells distribution of galaxies and show that the form of the galaxy distribution function does not change significantly as galaxies merge and evolve. In particular, bound merging pairs follow a similar distribution to that of individual galaxies. From the adiabatic expansion of the universe we show how clustering, expansion and galaxy mergers affect the clustering parameter b. We also predict the evolution of b with respect to redshift.

astro-ph.CO↗

arXiv2004

A Machine Learning Strategy to Identity Exonic Splice Enhancers in Human Protein-coding Sequence

Background: Exonic splice enhancers are sequences embedded within exons which promote and regulate the splicing of the transcript in which they are located. A class of exonic splice enhancers are the SR proteins, which are thought to mediate interactions between splicing factors bound to the 5' and 3' splice sites. Method and results: We present a novel strategy for analysing protein-coding sequence by first randomizing the codons used at each position within the coding sequence, then applying a motif-based machine learning algorithm to compare the true and randomized sequences. This strategy identified a collection of motifs which can successfully discriminate between real and randomized coding sequence, including -- but not restricted to -- several previously reported splice enhancer elements. As well as successfully distinguishing coding exons from randomized sequences, we show that our model is able to recognize non-coding exons. Conclusions: Our strategy succeeded in detecting signals in coding exons which seem to be orthogonal to the sequences' primary function of coding for proteins. We believe that many of the motifs detected here may represent binding sites for previously unrecognized proteins which influence RNA splicing. We hope that this development will lead to improved knowledge of exonic splice enhancers, and new developments in the field of computational gene prediction.

q-bio.GN↗

arXiv2004

Gravitational Binding, Virialization and the Peculiar Velocity Distribution of the Galaxies

We examine the peculiar velocity distribution function of galaxies in cosmological many-body gravitational clustering. Our statistical mechanical approach derives a previous basic assumption and generalizes earlier results to galaxies with haloes. Comparison with the observed peculiar velocity distributions indicates that individual massive galaxies are usually surrounded by their own haloes, rather than being embedded in common haloes. We then derive the density of energy states, giving the probability that a randomly chosen configuration of N galaxies in space is bound and virialized. Gravitational clustering is very efficient. The results agree well with the observed probabilities for finding nearby groups containing N galaxies. A consequence is that our local relatively low mass group is quite typical, and the observed small departures from the local Hubble flow beyond our group are highly probable.

astro-ph↗

arXiv2003

Spin-Torsion, Braneworlds and Changing Symmetry in the Universe

In this thesis, we explore three phenomenological alternatives to the current paradigm of the standard inflationary big bang scenario. The three alternative themes are spin torsion (or Einstein-Cartan-Kibble-Sciama) theories, extra dimensions (braneworld cosmology) and changing global symmetry. In the spin torsion theories, we found new cosmological solutions with a cosmological constant as alternative to the standard scalar field driven inflationary scenario and we conclude that these toy models do not exhibit an inflationary phase. In the theme of extra dimensions, we discuss the dynamics of linearized scalar and tensor perturbations in an almost Friedmann-Robertson-Walker braneworld cosmology of Randall-Sundrum type II using the 1+3 covariant approach. We derive a complete set of frame-independent equations for the total matter variables, and a partial set of equations for the non-local variables, which arise from the projection of the Weyl tensor in the bulk. The latter equations are incomplete since there is no propagation equation for the non-local anisotropic stress. In the simplest approximation, we show the braneworld imprint as a correction to the power spectra for standard temperature and polarization anisotropies and similarly show that the tensor anisotropies are also insensitive to the high energy effects. Finally in the theme of changing global symmetry, we constructed a bounded isothermal solution embedded in an expanding Einstein de Sitter universe and showed that there is a possible phase transition in the far future.

gr-qc↗

arXiv2002

Braneworld Tensor Anisotropies in the CMB

Cosmic microwave background (CMB) observations provide in principle a high-precision test of models which are motivated by M theory. We set out the framework of a program to compute the tensor anisotropies in the CMB that are generated in braneworld models. In the simplest approximation, we show the braneworld imprint as a correction to the power spectra for standard temperature and polarization anisotropies.

astro-ph↗

arXiv2002

(1+3) Covariant Dynamics of Scalar Perturbations in Braneworlds

We discuss the dynamics of linear, scalar perturbations in an almost Friedmann-Robertson-Walker braneworld cosmology of Randall-Sundrum type II using the 1+3 covariant approach. We derive a complete set of frame-independent equations for the total matter variables, and a partial set of equations for the non-local variables which arise from the projection of the Weyl tensor in the bulk. The latter equations are incomplete since there is no propagation equation for the non-local anisotropic stress. We supplement the equations for the total matter variables with equations for the independent constituents in a cold dark matter cosmology, and provide solutions in the high and low-energy radiation-dominated phase under the assumption that the non-local anisotropic stress vanishes. These solutions reveal the existence of new modes arising from the two additional non-local degrees of freedom. Our solutions should prove useful in setting up initial conditions for numerical codes aimed at exploring the effect of braneworld corrections on the cosmic microwave background (CMB) power spectrum. As a first step in this direction, we derive the covariant form of the line of sight solution for the CMB temperature anisotropies in braneworld cosmologies, and discuss possible mechanisms by which braneworld effects may remain in the low-energy universe.

gr-qc↗