27,863 research outputs found
Blind Normalization of Speech From Different Channels
We show how to construct a channel-independent representation of speech that
has propagated through a noisy reverberant channel. This is done by blindly
rescaling the cepstral time series by a non-linear function, with the form of
this scale function being determined by previously encountered cepstra from
that channel. The rescaled form of the time series is an invariant property of
it in the following sense: it is unaffected if the time series is transformed
by any time-independent invertible distortion. Because a linear channel with
stationary noise and impulse response transforms cepstra in this way, the new
technique can be used to remove the channel dependence of a cepstral time
series. In experiments, the method achieved greater channel-independence than
cepstral mean normalization, and it was comparable to the combination of
cepstral mean normalization and spectral subtraction, despite the fact that no
measurements of channel noise or reverberations were required (unlike spectral
subtraction).Comment: 25 pages, 7 figure
Which User Interaction for Cross-Language Information Retrieval? Design Issues and Reflections
A novel and complex form of information access is cross-language information retrieval: searching for texts written in foreign languages based on native language queries. Although the underlying technology for achieving such a search is relatively well understood, the appropriate interface design is not. This paper presents three user evaluations undertaken during the iterative design of Clarity, a cross-language retrieval system for rare languages, and shows how the user interaction design evolved depending on the results of usability tests. The first test was instrumental to identify weaknesses in both functionalities and interface; the second was run to determine if query translation should be shown or not; the final was a global assessment and focussed on user satisfaction criteria. Lessons were learned at every stage of the process leading to a much more informed view of what a cross-language retrieval system should offer to users
Resonant enhanced multiphoton ionization studies of atomic oxygen
In resonant enhanced multiphoton ionization (REMPI), an atom absorbs several photons making a transition to a resonant intermediate state and subsequently ionizing out of it. With currently available tunable narrow-band lasers, the extreme sensitivity of REMPI to the specific arrangement of levels can be used to selectively probe minute amounts of a single species (atom) in a host of background material. Determination of the number density of atoms from the observed REMPI signal requires a knowledge of the multiphoton ionization cross sections. The REMPI of atomic oxygen was investigated through various excitation schemes that are feasible with available light sources. Using quantum defect theory (QDT) to estimate the various atomic parameters, the REMPI dynamics in atomic oxygen were studied incorporating the effects of saturation and a.c. Stark shifts. Results are presented for REMPI probabilities for excitation through various 2p(3) (4S sup o) np(3)P and 2p(3) (4S sup o) nf(3)F levels
High performance dash on warning air mobile, missile system
An aircraft-missile system which performs a high acceleration takeoff followed by a supersonic dash to a 'safe' distance from the launch site is presented. Topics considered are: (1) technological feasibility to the dash on warning concept; (2) aircraft and boost trajectory requirements; and (3) partial cost estimates for a fleet of aircraft which provide 200 missiles on airborne alert. Various aircraft boost propulsion systems were studied such as an unstaged cryogenic rocket, an unstaged storable liquid, and a solid rocket staged system. Various wing planforms were also studied. Vehicle gross weights are given. The results indicate that the dash on warning concept will meet expected performance criteria, and can be implemented using existing technology, such as all-aluminum aircraft and existing high-bypass-ratio turbofan engines
Diboson Physics in ATLAS
At the LHC, the diboson states (W,W) (Z,Z), (W,Z), (W,) and (Z,) arise primarly through quark-quark interactions and to a lesser extent from gluon-gluon fusion. Diboson production cross sections are determined, in part, by the Standard Model triple-gauge-boson couplings and the strength of anomalous triple gauge couplings. We report on the studies of expected ATLAS measurements of diboson production cross sections with leptonic and photon final states. Such potential measurements can probe anomolous triple gauge boson couplings and are sensitive to physics beyond the Standard Model
Dependence of effective spectrum width of synchrotron radiation on particle energy
For an exact quantitative description of spectral properties in the theory of
synchrotron radiation, the concept of effective spectral width is introduced.
In the classical theory, numeric calculations of effective spectral width
(using an effective width not exceeding 100 harmonics) for polarization
components of synchrotron radiation are carried out. The dependence of the
effective spectral width and initial harmonic on the energy of a radiating
particle is established
Effective spectrum width of the synchrotron radiation
For an exact quantitative description of spectral properties of synchrotron
radiation (SR), the concept of effective width of the spectrum is introduced.
In the most interesting case, which corresponds to the ultrarelativistic limit
of SR, the effective width of the spectrum is calculated for the polarization
components, and new physically important quantitative information on the
structure of spectral distributions is obtained. For the first time, the
spectral distribution for the circular polarization component of the SR for the
upper half-space is obtained within classical theory
Dynamical study of the empty Bianchi type I model in generalised scalar-tensor theory
A dynamical study of the generalised scalar-tensor theory in the empty
Bianchi type I model is made. We use a method from which we derive the sign of
the first and second derivatives of the metric functions and examine three
different theories that can all tend towards relativistic behaviours at late
time. We determine conditions so that the dynamic be in expansion and
decelerated at late time.Comment: 18 pages, 3 figures, to appear in General Relativity and Gravitatio
Hydromagnetic and gravitomagnetic crust-core coupling in a precessing neutron star
We consider two types of mechanical coupling between the crust and the core
of a precessing neutron star. First, we find that a hydromagnetic (MHD)
coupling between the crust and the core strongly modifies the star's
precessional modes when ; here is the
Alfven crossing timescale, and and are the star's spin and
precession periods, respectively. We argue that in a precessing pulsar PSR
B1828-11 the restoring MHD stress prevents a free wobble of the crust relative
to the non-precessing core. Instead, the crust and the proton-electron plasma
in the core must precess in unison, and their combined ellipticity determines
the period of precession. Link has recently shown that the neutron superfluid
vortices in the core of PSR B1828-11 cannot be pinned to the plasma; he has
also argued that this lack of pinning is expected if the proton Fermi liquid in
the core is type-I superconductor. In this case, the neutron superfluid is
dynamically decoupled from the precessing motion. The pulsar's precession
decays due to the mutual friction between the neutron superfluid and the plasma
in the core. The decay is expected to occur over tens to hundreds of precession
periods and may be measurable over a human lifetime. Such a measurement would
provide information about the strong n-p interaction in the neutron-star core.
Second, we consider the effect of gravitomagnetic coupling between the neutron
superfluid in the core and the rest of the star and show that this coupling
changes the rate of precession by about 10%. The general formalism developed in
this paper may be useful for other applications.Comment: 6 page
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