173,572 research outputs found

    The standard model and parity conservation

    Get PDF
    On the basis of previous work on chiral gauged fermions on a lattice, we discuss the lattice-regularization of the standard model by introducing two Weyl fields interacting with quarks and leptons. These interactions form massive bound states to gauge-invariantly decouple doublers at high energies and these bound states dissolve into their constituents at low energies. No any hard spontaneous symmetry breakings occur at the lattice scale \pi/a. As a consequence, the gauge symmetries of the standard model are realized by both massive vectorlike spectra at high energies and massless chiral spectra at low energies. Such a scenario is consistent with the gauge-anomaly cancelation, flavor-singlet anomaly and Witten's anomaly. These studies predict that the parity symmetry must be restored at high energies.Comment: 4 pages, latex and espcrc2.sty, Lattice2000 and to appear in Nucl. Phys. (Suppl.)

    Computerized Analysis of Magnetic Resonance Images to Study Cerebral Anatomy in Developing Neonates

    Get PDF
    The study of cerebral anatomy in developing neonates is of great importance for the understanding of brain development during the early period of life. This dissertation therefore focuses on three challenges in the modelling of cerebral anatomy in neonates during brain development. The methods that have been developed all use Magnetic Resonance Images (MRI) as source data. To facilitate study of vascular development in the neonatal period, a set of image analysis algorithms are developed to automatically extract and model cerebral vessel trees. The whole process consists of cerebral vessel tracking from automatically placed seed points, vessel tree generation, and vasculature registration and matching. These algorithms have been tested on clinical Time-of- Flight (TOF) MR angiographic datasets. To facilitate study of the neonatal cortex a complete cerebral cortex segmentation and reconstruction pipeline has been developed. Segmentation of the neonatal cortex is not effectively done by existing algorithms designed for the adult brain because the contrast between grey and white matter is reversed. This causes pixels containing tissue mixtures to be incorrectly labelled by conventional methods. The neonatal cortical segmentation method that has been developed is based on a novel expectation-maximization (EM) method with explicit correction for mislabelled partial volume voxels. Based on the resulting cortical segmentation, an implicit surface evolution technique is adopted for the reconstruction of the cortex in neonates. The performance of the method is investigated by performing a detailed landmark study. To facilitate study of cortical development, a cortical surface registration algorithm for aligning the cortical surface is developed. The method first inflates extracted cortical surfaces and then performs a non-rigid surface registration using free-form deformations (FFDs) to remove residual alignment. Validation experiments using data labelled by an expert observer demonstrate that the method can capture local changes and follow the growth of specific sulcus

    Do high-energy neutrinos travel faster than photons in a discrete space-time?

    Get PDF
    The recent OPERA measurement of high-energy neutrino velocity, once independently verified, implies new physics in the neutrino sector. We revisit the theoretical inconsistency of the fundamental high-energy cutoff attributing to quantum gravity with the parity-violating gauge symmetry of local quantum field theory describing neutrinos. This inconsistency suggests high-dimension operators of neutrino interactions. Based on these studies, we try to view the OPERA result, high-energy neutrino oscillations and indicate to observe the restoration of parity conservation by measuring the asymmetry of high-energy neutrinos colliding with left- and right-handed polarized electrons.Comment: revised version to appear in Phys. Lett. B. 13 pages and 2 figure

    Observation of the antimatter helium-4 nucleus at RHIC

    Full text link
    We present the observation of the \Heebar nucleus, the heaviest antinucleus observed to date. In total, 18 \Heebar counts were detected at the STAR experiment at RHIC in 109^{9} recorded Au+Au collisions at beam energies of sNN\sqrt{s_{NN}} = 200 GeV and 62 GeV. The background has been estimated, and the misidentification probability is found to be lower than 1011^{-11}.Comment: 4 pages, 3 figures, to appear as proceedings of QM2011 conference at Annecy, Franc

    Contextualised problem-based approach for teaching undergraduate database module

    Get PDF
    In this paper, a new approach has been used in teaching the second year undergraduate database module. The approach is a combination of contextualisation, problem-based approach, group work and continuous formative assessment. The contextualisation ensures the visibility of teaching/learning activities so that students are aware of the values of activities and how they can fit into a big picture. Problem-based approach gives the students tasks/problems to solve before the relevant lecture takes place, hence can better develop effective reasoning processes, independently learning skills and improve motivation and engagement. Group work is regularly used due to the diversity of student backgrounds and level of prior knowledge of certain topics. By having group work, students can learn from each other and easily clarify confusions among themselves before approaching the lecturer. This gives the lecture more time focusing on common issues. Formative assessment has also been used to support teaching/learning activities and to reinforce their understanding. The work in this paper has been evaluated via an end-of-year online module survey. The results show good effectiveness of the new approach, although there are still spaces for improvement

    On the F.Smarandache LCM function SL(n)

    Get PDF
    For any positive integer n, the famous F.Smarandache LCM function SL(n) is de¯ned as the smallest positive integer k