1,025 research outputs found
Development of a simplified ray path model for estimating the range and depth of vocalising marine mammals
A simplified ray path model has been developed to simulate various source, receiver geometries. The difference in the arrival time of the multi-path signals (surface and seabed reflections) were calculated and compared with those measured on recorded data obtained during sea trials. A number of assumption have been made in initial models including a constant sound velocity-depth profile and the treatment of the surface and seabed as a simple reflecting surfaces. Initial results have shown a number of examples with a reasonable correlation between estimated position of a submerged cetacean and the associated surface observations. Examples of multiple (positioning) solutions were however found, these are in the main thought to be due to imprecision in the knowledge of the hydrophone and water depth and inaccuracies in the initial timing measurements. The use of correlation techniques and stand-alone depth measurement devices is therefore proposed for future measurements and analysis using this technique. It is felt that within constraints, this technique provides valuable additional information regarding cetacean behaviour in the wild and can be used on recorded data sets to validate observer records. The addition of more complex time measurement techniques and better ray path modelling will hopefully provide a useful analysis tool in the study of cetaceans
Fast switching tunable laser sources for wavelength division multiplexing in passive optical access networks
Tunable laser structures with nanosecond switching time between wavelength channels and low-power injection locking are demonstrated on a low-cost platform. These lasers are suitable as source or slave lasers in WDM passive optical access networks
The new generation of Electronic Click Detector (ECD): the development and field trials data
The use of envelope detection methods to reduce the bandwidth of an echolocation click into the
audio-band is not a new concept. However, the increasing popularity of portable digital recorders
with excellent signal to noise performance needs such signal processing if ultrasonic transient
data needs to be captured. Similarly, this approach allows high frequency information to be
recorded onto video recorder sound tracks providing the advantage of synchronised sound with
images for behavioural studies. This paper describes the development of a new generation of
ECD with improved performance and includes cetacean echolocation data recorded using this
equipment in two independent studies
Chaotic Inflationary Universe on Brane
The chaotic inflationary model of the early universe, proposed by Linde is
explored in the brane world considering matter described by a minimally coupled
self interacting scalar field. We obtain cosmological solutions which admit
evolution of a universe either from a singularity or without a singularity. It
is found that a very weakly coupled self-interacting scalar field is necessary
for a quartic type potential in the brane world model compared to that
necessary in general relativity. In the brane world sufficient inflation may be
obtained even with an initial scalar field having value less than the Planck
scale. It is found that if the universe is kinetic energy dominated to begin
with, it transits to an inflationary stage subsequently.Comment: 13 pages, no fig., accepted in Physical Review
Flavor Symmetry for Quarks and Leptons
Present data on neutrino masses and mixing favor the highly symmetric
tribimaximal neutrino mixing matrix which suggests an underlying flavor
symmetry. A systematic study of non-abelian finite groups of order
reveals that tribimaximal mixing can be derived not only from the well known
tetrahedral flavor symmetry , but also by using the binary
tetrahedral symmetry which does not contain the
tetrahedral group as a subgroup. has the further advantage that it can
also neatly accommodate the quark masses including a heavy top quark.Comment: 12 pages latex. More typos correcte
Effects of genuine dimension-six Higgs operators
We systematically discuss the consequences of genuine dimension-six Higgs
operators. These operators are not subject to stringent constraints from
electroweak precision data. However, they can modify the couplings of the Higgs
boson to electroweak gauge bosons and, in particular, the Higgs
self-interactions. We study the sensitivity to which those couplings can be
probed at future \ee linear colliders in the sub-TeV and in the multi-TeV
range. We find that for GeV with a luminosity of 1 ab the
anomalous and couplings may be probed to about the 0.01 level, and
the anomalous coupling to about the 0.1 level.Comment: 21 pages, 17 figures; typos corrected and references adde
Effects of integrated physical exercises and gestures on preschool childrenâs foreign language vocabulary learning
Research suggests that integrating human movement into a cognitive learning task can be effective for learning due to its cognitive and physiological effects. In this study, the learning effects of enacting words through whole-body movements (i.e., physical exercise) and part-body movements (i.e., gestures) were investigated in a foreign language vocabulary task. Participants were 111 preschool children of 15 childcare centers, who were randomly assigned to one of four conditions. Participants had to learn 14 Italian words in a 4-week teaching program. They were tested on their memory for the words during, directly after, and 6 weeks after the program. In the integrated physical exercise condition, children enacted the actions indicated by the words to be learned in physical exercises. In the non-integrated physical exercise condition children performed physical exercises at the same intensity, but unrelated to the learning task. In the gesturing condition, children enacted the actions indicated by the words to be learned by gesturing while remaining seated. In the conventional condition, children verbally repeated the words while remaining seated. Results confirmed the main hypothesis, indicating that children in the integrated physical exercise condition achieved the highest learning outcomes. Implications of integrated physical exercise programs for preschool childrenâs cognition and health are discussed
Cell-free protein synthesis as a tool to study RXFP3- Relaxin-3 protein interactions
With the discovery of the relaxin family peptide receptors there is interest in obtaining a clearer understanding of the structure of these proteins and the molecular mechanism of receptor-ligand interaction. As G-protein coupled receptors, obtaining milligram quantities for structural investigations is hampered by the inherent instability of these integral membrane proteins. In the current context, understanding of GPCR structural biology has increased dramatically with crystal structures of several inactive and now active forms solved. In addition, the first nuclear magnetic resonance structure of a GPCR was obtained which is of crucial importance to studying these receptors in a more âbiologically relevantâ setting. However despite this expansion in the field, most structures have been solved on modified systems so as to increase stability and are not necessarily representative of the native receptors. In relation to the relaxin family peptide receptors, we chose to investigate relaxin-family peptide receptor-3 expressed by cellfree protein synthesis. In contrast to in-vivo expression, cell-free was capable of producing large amounts of native receptor which makes it amenable to demanding structural studies
Tachyonic Inflation in a Warped String Background
We analyze observational constraints on the parameter space of tachyonic
inflation with a Gaussian potential and discuss some predictions of this
scenario. As was shown by Kofman and Linde, it is extremely problematic to
achieve the required range of parameters in conventional string
compactifications. We investigate if the situation can be improved in more
general compactifications with a warped metric and varying dilaton. The
simplest examples are the warped throat geometries that arise in the vicinity
of of a large number of space-filling D-branes. We find that the parameter
range for inflation can be accommodated in the background of D6-branes wrapping
a three-cycle in type IIA. We comment on the requirements that have to be met
in order to realize this scenario in an explicit string compactification.Comment: Latex, JHEP class, 20 pages, 4 figures. v2: references added, small
error in section 7 corrected, published versio
Hamiltonian 2-forms in Kahler geometry, III Extremal metrics and stability
This paper concerns the explicit construction of extremal Kaehler metrics on
total spaces of projective bundles, which have been studied in many places. We
present a unified approach, motivated by the theory of hamiltonian 2-forms (as
introduced and studied in previous papers in the series) but this paper is
largely independent of that theory.
We obtain a characterization, on a large family of projective bundles, of
those `admissible' Kaehler classes (i.e., the ones compatible with the bundle
structure in a way we make precise) which contain an extremal Kaehler metric.
In many cases, such as on geometrically ruled surfaces, every Kaehler class is
admissible. In particular, our results complete the classification of extremal
Kaehler metrics on geometrically ruled surfaces, answering several
long-standing questions.
We also find that our characterization agrees with a notion of K-stability
for admissible Kaehler classes. Our examples and nonexistence results therefore
provide a fertile testing ground for the rapidly developing theory of stability
for projective varieties, and we discuss some of the ramifications. In
particular we obtain examples of projective varieties which are destabilized by
a non-algebraic degeneration.Comment: 40 pages, sequel to math.DG/0401320 and math.DG/0202280, but largely
self-contained; partially replaces and extends math.DG/050151
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