413,345 research outputs found

### Self-tuning of cosmological constant and exit from inflation

I review the recent 5D self-tuning solutions of the cosmological constant
problem, and try to unify two cosmological constant problems within the
framework of the self-tuning solutions. One problem, the large cosmological
constant needed for inflation, is interpreted by starting with the parameters
allowing only the dS vacuum, and the vanishing cosmological constant at a true
vacuum is realized by changing parameters by exit from inflation at the brane
such that the self-tuning solution is allowed.Comment: Latex file of 8 pages, including 2 figures. Talk presented at
COSPA-03, Taipei, Taiwan, Nov. 13-15, 200

### Optimal circular flight of multiple UAVs for target tracking in urban areas

This work is an extension of our previous result in which a novel single-target tracking
algorithm for fixed-wing UAVs (Unmanned Air Vehicles) was proposed. Our previous
algorithm firstly finds the centre of a circular flight path, rc, over the interested ground
target which maximises the total chance of keeping the target inside the camera field of view
of UAVs, , while the UAVs fly along the circular path. All the UAVs keep their maximum
allowed altitude and fly along the same circle centred at rc with the possible minimum turn
radius of UAVs. As discussed in [1,4], these circular flights are highly recommended for
various target tracking applications especially in urban areas, as for each UAV the
maximum altitude flight ensures the maximum visibility and the minimum radius turn
keeps the minimum distance to the target at the maximum altitude.
Assuming a known probability distribution for the target location, one can quantify ,
which is incurred by the travel of a single UAV along an arbitrary circle, using line-of-sight
vectors. From this observation, (the centre of) an optimal circle among numerous feasible
ones can be obtained by a gradient-based search combined with random sampling, as
suggested in [1]. This optimal circle is then used by the other UAVs jointly tracking the
same target. As the introduction of multiple UAVs may minimise further, the optimal
spacing between the UAVs can be naturally considered. In [1], a typical line search method
is suggested for this optimal spacing problem. However, as one can easily expect, the
computational complexity of this search method may undesirably increase as the number of
UAVs increases.
The present work suggests a remedy for this seemingly complex optimal spacing problem.
Instead of depending on time-consuming search techniques, we develop the following
algorithm, which is computationally much more efficient. Firstly, We calculate the
distribution (x), where x is an element of , which is the chance of capturing the target by
one camera along . Secondly, based on the distribution function, (x), find separation
angles between UAVs such that the target can be always tracked by at least one UAV with a
guaranteed probabilistic measure. Here, the guaranteed probabilistic measure is chosen by
taking into account practical constraints, e.g. required tracking accuracy and UAVs'
minimum and maximum speeds. Our proposed spacing scheme and its guaranteed
performance are demonstrated via numerical simulations

### New q-Euler numbers and polynomials associated with p-adic q-integrals

In this paper we study q-Euler numbers and polynomials by using p-adic
q-fermionic integrals on Z_p. The methods to study q-Euler numbers and
polynomials in this paper are new.Comment: 13 page

### Pulsar Velocity with Three-Neutrino Oscillations in Non-adiabatic Processes

We have studied the position dependence of neutrino energy on the
Kusenko-Segr\`{e} mechanism as an explanation of the proper motion of pulsars.
The mechanism is also examined in three-generation mixing of neutrinos and in a
non-adiabatic case. The position dependence of neutrino energy requires the
higher value of magnetic field such as $B\sim 3\times 10^{15}$ Gauss in order
to explain the observed proper motion of pulsars. It is shown that possible
non-adiabatic processes decrease the neutrino momentum asymmetry, whereas an
excess of electron neutrino flux over other flavor neutrino fluxes increases
the neutrino momentum asymmetry. It is also shown that a general treatment with
all three neutrinos does not modify the result of the two generation treatment
if the standard neutrino mass hierarchy is assumed.Comment: 8 pages, REVTEX, no figure

### Modulation of the Curie Temperature in Ferromagnetic/Ferroelectric Hybrid Double Quantum Wells

We propose a ferromagnetic/ferroelectric hybrid double quantum well
structure, and present an investigation of the Curie temperature (Tc)
modulation in this quantum structure. The combined effects of applied electric
fields and spontaneous electric polarization are considered for a system that
consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well.
We calculate the change in the envelope functions of carriers at the lowest
energy sub-band, resulting from applied electric fields and switching the
dipole polarization. By reversing the depolarizing field, we can achieve two
different ferromagnetic transition temperatures of the ferromagnetic quantum
well in a fixed applied electric field. The Curie temperature strongly depends
on the position of the Mn \delta-doped layer and the polarization strength of
the ferroelectric well.Comment: 9 pages, 5 figures, to be published in Phys. Rev. B (2006) minor
revision: One of the line types is changed in Fig.

### The EnTrak system : supporting energy action planning via the Internet

Recent energy policy is designed to foster better energy efficiency and assist with the deployment of clean energy systems, especially those derived from renewable energy sources. To attain the envisaged targets will require action at all levels and effective collaboration between disparate groups (e.g. policy makers, developers, local authorities, energy managers, building designers, consumers etc) impacting on energy and environment. To support such actions and collaborations, an Internet-enabled energy information system called 'EnTrak' was developed. The aim was to provide decision-makers with information on energy demands, supplies and impacts by sector, time, fuel type and so on, in support of energy action plan formulation and enactment. This paper describes the system structure and capabilities of the EnTrak system

### 20 K superconductivity in heavily electron doped surface layer of FeSe bulk crystal

A superconducting transition temperature Tc as high as 100 K was recently
discovered in 1 monolayer (1ML) FeSe grown on SrTiO3 (STO). The discovery
immediately ignited efforts to identify the mechanism for the dramatically
enhanced Tc from its bulk value of 7 K. Currently, there are two main views on
the origin of the enhanced Tc; in the first view, the enhancement comes from an
interfacial effect while in the other it is from excess electrons with strong
correlation strength. The issue is controversial and there are evidences that
support each view. Finding the origin of the Tc enhancement could be the key to
achieving even higher Tc and to identifying the microscopic mechanism for the
superconductivity in iron-based materials. Here, we report the observation of
20 K superconductivity in the electron doped surface layer of FeSe. The
electronic state of the surface layer possesses all the key spectroscopic
aspects of the 1ML FeSe on STO. Without any interface effect, the surface layer
state is found to have a moderate Tc of 20 K with a smaller gap opening of 4
meV. Our results clearly show that excess electrons with strong correlation
strength alone cannot induce the maximum Tc, which in turn strongly suggests
need for an interfacial effect to reach the enhanced Tc found in 1ML FeSe/STO.Comment: 5 pages, 4 figure

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