3,661 research outputs found
Dark Energy and the False Vacuum
In this talk, I will present highlights of a recent model of dark energy and
dark matter in which the present universe is ``trapped'' in a {\em false
vacuum} described by the potential of an axion-like scalar field (the
acceleron) which is related to a new strong interaction gauge sector,
, characterized by a scale . This
false vacuum model mimicks the scenario. In addition, there are
several additional implications such as a new mechanism for leptogenesis coming
from the decay of a ``messenger'' scalar field, as well as a new model of
``low-scale'' inflation whose inflaton is the ``radial'' partner of the
acceleron.Comment: 6 pages. To appear in the Proceedings of the 2nd International
Conference on Quantum Theories and Renormalization Group in Gravity and
Cosmology (IRGAC 2006), Barcelona, July 11-15 (2006
A new mechanism for a naturally small Dirac neutrino mass
A mechanism is proposed in which a right-handed neutrino zero mode and a
right-handed charged lepton zero mode can be localized at the same place along
an extra compact dimension while having markedly different spreads in their
wave functions: a relatively narrow one for the neutrino and a rather broad one
for the charged lepton. In their overlaps with the wave function for the
left-handed zero modes, this mechanism could produce a natural large hierarchy
in the effective Yukawa couplings in four dimensions, and hence a large
disparity in masses.Comment: 6 pages (2 with figures), twocolumn forma
Remote sensing and GIS-based analysis of cave development in the Suoimuoi Catchment (Son La - NW Vietnam)
Integration of remotely sensed imagery with ground surveys is a promising method in cave
development studies. In this research a methodology was set up in which a variety of remote
sensing and GIS techniques support cave analysis in the tropical karst area of the Suoimuoi
catchment, NW Vietnam. In order to extract the maximum information from different remotely
sensed data, the hue invariant IHS transformation was applied to integrate Landsat multispectral
channels with the high resolution Landsat 7 ETM panchromatic channel. The resulting
fused image was used, after enhancement, to visually and digitally extract lineaments.
Aerial photos evaluated the extracted lineaments. Based on lineament density indices a fracture
zone favorable for cave development is defined. The distance between caves and faults
was investigated as well as the correspondence between the cave occurrence and the fracture
zone
Superstring-Inspired E_6 Unification, Shadow Theta-Particles and Cosmology
We construct a new cosmological model considering the superstring-inspired
E_6 unification in the 4-dimensional space at the early stage of the Universe.
We develop a concept of parallel existence in Nature of the ordinary and shadow
worlds with different cosmological evolutions.Comment: 7 page
Study of cavernous underground conduits in Nam La (Northwest Vietnam) by an integrative approach
This paper presents the result of an investigation of underground conduits, which connect the swallow holes and the resurgence of a blind river in the tropical, highly karstified limestone Nam La catchment in the NW of Vietnam. The Nam La River disappears underground in several swallow holes near the outlet of the catchment. In the rainy season this results in flooding upstream of the sinkholes. A hypothesis is that the Nam La River resurges at a large cavern spring 4.5 km east of the catchment outlet. A multi-thematic study of the possible connections between the swallow holes and the resurgence was carried out to investigate the geological structure, tectonics, cave structure analysis and discharge time series. The existence of the underground conduits was also tested and proven by tracer experiments. On the basis of a lineament analysis the location of the underground conduits were predicted. A remote sensing derived lineament-length density map was used to track routes from the swallow holes to the resurgence, having the shortest length but highest lineament density. This resulted in a plan-view prediction of underground conduits that matches with the cave and fault development. The functioning of the conduits was further explained by analysing flooding records of a nearby doline, which turns out to act as a temporary storage reservoir mitigating flooding of the catchment outlet area
Exploring quantum criticality based on ultracold atoms in optical lattices
Critical behavior developed near a quantum phase transition, interesting in
its own right, offers exciting opportunities to explore the universality of
strongly-correlated systems near the ground state. Cold atoms in optical
lattices, in particular, represent a paradigmatic system, for which the quantum
phase transition between the superfluid and Mott insulator states can be
externally induced by tuning the microscopic parameters. In this paper, we
describe our approach to study quantum criticality of cesium atoms in a
two-dimensional lattice based on in situ density measurements. Our research
agenda involves testing critical scaling of thermodynamic observables and
extracting transport properties in the quantum critical regime. We present and
discuss experimental progress on both fronts. In particular, the thermodynamic
measurement suggests that the equation of state near the critical point follows
the predicted scaling law at low temperatures.Comment: 15 pages, 6 figure
Minimal SU(5) Resuscitated by Long-Lived Quarks and Leptons
The issue of gauge unification in the (non-supersymmetric) Standard Model is
reinvestigated. It is found that with just an additional fourth generation of
non-sequential and long-lived quarks and leptons, SU(3)xSU(2)xU(1) gauge
couplings converge to a common point of approximately 3.5x10^{15} GeV
(corresponding to a proton lifetime of approximately 10^{34 plus/minus 1}
years). This result is due to the non-negligible- but still perturbative-
contributions of the top and fourth generation Yukawa couplings to the gauge
two-loop beta functions, in contrast with the three generation case where such
a contribution is too small to play an important role in unification.Comment: 12 pages, 2 figure
Accurate Phase Calibration for Digital Beam-Forming in Multi-Transceiver HF Radar System
The TIGER-3 radar is being developed as an “all digital” radar with 20 integrated digital transceivers, each connected to a separate antenna. Using phased array antenna techniques, radiated power is steered towards a desired direction based on the relative phases within the array elements. This paper proposes an accurate phase measurement method to calibrate the phases of the radio output signals using Field Programmable Gate Array (FPGA) technology. The method sequentially measures the phase offset between the RF signal generated by each transceiver and a reference signal operated at the same frequency. Accordingly, the transceiver adjusts its phase in order to align to the reference phase. This results in accurately aligned phases of the RF output signals and with the further addition of appropriate phase offsets, digital beamforming (DBF) can be performed steering the beam in a desired direction. The proposed method is implemented on a Virtex-5 VFX70T device. Experimental results show that the calibration accuracy is of 0.153 degrees with 14 MHz operating frequency
Design of directional couplers for marine applications with artificial transmission lines
The article describes the design of the coupler for marine applications, on which the miniaturization of its dimensions was carried out. The description of the compact device is given. It consists of artificial transmission lines of the original form. The use of such lines for the coupler allowed to achieve good results in reducing the size. So the area of the resulting device is 72.25% less than that of a conventional device, while it has comparable characteristics. The described approach can be used for other devices requiring miniaturization and implemented on a printed circuit board. © Published under licence by IOP Publishing Ltd
Evidence of early multi-strange hadron freeze-out in high energy nuclear collisions
Recently reported transverse momentum distributions of strange hadrons
produced in Pb(158AGeV) on Pb collisions and corresponding results from the
relativistic quantum molecular dynamics (RQMD) approach are examined. We argue
that the experimental observations favor a scenario in which multi-strange
hadrons are formed and decouple from the system rather early at large energy
densities (around 1 GeV/fm). The systematics of the strange and non-strange
particle spectra indicate that the observed transverse flow develops mainly in
the late hadronic stages of these reactions.Comment: 4 pages, 4 figure
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