1,156 research outputs found
The Corralitos Observatory program for the detection of lunar transient phenomena
This is a final report on the establishment, observing procedures, and observational results of a survey program for the detection of lunar transient phenomena (LTP's) by electro-optical image conversion means. For survey, a unique detection system with an image orthicon was used as the primary element in conjunction with a 24-in. f/20 Cassegrainian telescope. Observations in three spectral ranges, with 6,466 man-hours of observing, were actually performed during the period from October 27, 1965, to April 26, 1972. Within this entire period, no color or feature change within the detection capabilities of the instrumentation was observed, either independently or in follow up of amateur LTP reports, with the exception of one general bluing and several localized bluings (probably ascribable to the effects of the terrestrial atmosphere) that were observed solely by the Corralitos system. A table is presented indicating amateur and professional reports of LTP's and the results of efforts to confirm these reports through the Corralitos system
Nonlinear Schroedinger equation with two symmetric point interactions in one dimension
We consider a time-dependent one-dimensional nonlinear Schroedinger equation
with a symmetric potential double well represented by two delta interactions.
Among our results we give an explicit formula for the integral kernel of the
unitary semigroup associated with the linear part of the Hamiltonian. Then we
establish the corresponding Strichartz-type estimate and we prove local
existence and uniqueness of the solution to the original nonlinear problem
Stem Cells in the Nervous System
Given their capacity to regenerate cells lost through injury or disease, stem cells offer new vistas into possible treatments for degenerative diseases and their underlying causes. As such, stem cell biology is emerging as a driving force behind many studies in regenerative medicine. This review focuses on the current understanding of the applications of stem cells in treating ailments of the human brain, with an emphasis on neurodegenerative diseases. Two types of neural stem cells are discussed: endogenous neural stem cells residing within the adult brain and pluripotent stem cells capable of forming neural cells in culture. Endogenous neural stem cells give rise to neurons throughout life, but they are restricted to specialized regions in the brain. Elucidating the molecular mechanisms regulating these cells is key in determining their therapeutic potential as well as finding mechanisms to activate dormant stem cells outside these specialized microdomains. In parallel, patient-derived stem cells can be used to generate neural cells in culture, providing new tools for disease modeling, drug testing, and cell-based therapies. Turning these technologies into viable treatments will require the integration of basic science with clinical skills in rehabilitation
On the lowest eigenvalue of Laplace operators with mixed boundary conditions
In this paper we consider a Robin-type Laplace operator on bounded domains.
We study the dependence of its lowest eigenvalue on the boundary conditions and
its asymptotic behavior in shrinking and expanding domains. For convex domains
we establish two-sided estimates on the lowest eigenvalues in terms of the
inradius and of the boundary conditions
A terrain-based parameterization for the effect of wind-induced snow transport in Alpine terrain
Global modelling of the early Martian climate under a denser CO2 atmosphere: Water cycle and ice evolution
We discuss 3D global simulations of the early Martian climate that we have
performed assuming a faint young Sun and denser CO2 atmosphere. We include a
self-consistent representation of the water cycle, with atmosphere-surface
interactions, atmospheric transport, and the radiative effects of CO2 and H2O
gas and clouds taken into account. We find that for atmospheric pressures
greater than a fraction of a bar, the adiabatic cooling effect causes
temperatures in the southern highland valley network regions to fall
significantly below the global average. Long-term climate evolution simulations
indicate that in these circumstances, water ice is transported to the highlands
from low-lying regions for a wide range of orbital obliquities, regardless of
the extent of the Tharsis bulge. In addition, an extended water ice cap forms
on the southern pole, approximately corresponding to the location of the
Noachian/Hesperian era Dorsa Argentea Formation. Even for a multiple-bar CO2
atmosphere, conditions are too cold to allow long-term surface liquid water.
Limited melting occurs on warm summer days in some locations, but only for
surface albedo and thermal inertia conditions that may be unrealistic for water
ice. Nonetheless, meteorite impacts and volcanism could potentially cause
intense episodic melting under such conditions. Because ice migration to higher
altitudes is a robust mechanism for recharging highland water sources after
such events, we suggest that this globally sub-zero, `icy highlands' scenario
for the late Noachian climate may be sufficient to explain most of the fluvial
geology without the need to invoke additional long-term warming mechanisms or
an early warm, wet Mars.Comment: Minor revisions to text, one new table, figs. 1,3 11 and 18 redon
Fast Approximate Spoken Term Detection from Sequence of Phonemes
We investigate the detection of spoken terms in conversational speech using phoneme recognition with the objective of achieving smaller index size as well as faster search speed. Speech is processed and indexed as a sequence of one best phoneme sequence. We propose the use of a probabilistic pronunciation model for the search term to compensate for the errors in the recognition of phonemes. This model is derived using the pronunciation of the word and the phoneme confusion matrix. Experiments are performed on the conversational telephone speech database distributed by NIST for the 2006 spoken term detection. We achieve about 1500 times smaller index size and 14 times faster search speed compared to the state-of-the-art system using phoneme lattice at the cost of relatively lower detection performance
Analysis of Confusion Matrix to Combine Evidence for Phoneme Recognition
In this work we analyze and combine evidences from different classifiers for phoneme recognition using information from the confusion matrices. Speech signals are processed to extract the Perceptual Linear Prediction (PLP) and Multi-RASTA (MRASTA) features. Neural network classifiers with different architectures are built using these features. The classifiers are analyzed using their confusion matrices. The motivation behind this analysis is to come up with some objective measures which indicate the complementary nature of information in each of the classifiers. These measures are useful for combining a subset of classifiers. The classifiers can be combined using different combination schemes like product, sum, minimum and maximum rules. The significance of the objective measures is demonstrated in terms the results of combination. Classifiers selected through the proposed objective measures seem to provide the best performance
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