196 research outputs found
High spectral resolution Fabry-Perot interferometer measurements of comet Halley at H-alpha and 6300 A
A 40.6 cm Newtonian telescope has been interfaced to the Fabry-Perot interferometer at the Arecibo Observatory to make high spectral resolution measurements of Comet Halley emissions at 6562.72 A (H-alpha) and 6300.3 A (OI). In March 1986 the H-alpha surface brightness for a 5'.9 field of view centered on the comet nucleus decreased from 39+/-7.8 rayleighs on 12 March to 16+/-3.8 rayleighs on 23 March. The atomic hydrogen production rate on 12 March 1986 was 1.62+/-0.5 x 1030 s-1, and on 23 March 1986 it was 6.76+/-2.3 x 1029 s-1. Using spectral resolution of 0.196 A, we found the atomic hydrogen outflow velocity to be approximately 7.9+/-1.0 km s-1. In general, the H-alpha spectra are highly structured, and indicative of a multiple component atomic hydrogen velocity distribution. An isotropic outflow of atomic hydrogen at various velocities is not adequate to explain the spectra measured at H-alpha. The 6300.3 A emission of O(1D) had a surface brightness of 81+/-16 rayleighs on 15 March 1986, and 95+/-11 rayleighs on 17 March 1986. After adjustment for atmospheric extinction, the implied O(1D) production rate on 15 March is 6.44+/-3.0 x 1028 s-1, and the production rate on 17 March is 5.66+/-2.7 x 1028 s-1. These spectra included a feature at 6300.8 A that we attribute to NH2. The brightness of this emission feature was 37+/-11 rayleighs on 15 March.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25881/1/0000444.pd
Finite time singularities in a class of hydrodynamic models
Models of inviscid incompressible fluid are considered, with the kinetic
energy (i.e., the Lagrangian functional) taking the form in 3D Fourier representation, where
is a constant, . Unlike the case (the usual Eulerian
hydrodynamics), a finite value of results in a finite energy for a
singular, frozen-in vortex filament. This property allows us to study the
dynamics of such filaments without the necessity of a regularization procedure
for short length scales. The linear analysis of small symmetrical deviations
from a stationary solution is performed for a pair of anti-parallel vortex
filaments and an analog of the Crow instability is found at small wave-numbers.
A local approximate Hamiltonian is obtained for the nonlinear long-scale
dynamics of this system. Self-similar solutions of the corresponding equations
are found analytically. They describe the formation of a finite time
singularity, with all length scales decreasing like ,
where is the singularity time.Comment: LaTeX, 17 pages, 3 eps figures. This version is close to the journal
pape
Resolving Curvature Singularities in Holomorphic Gravity
We formulate holomorphic theory of gravity and study how the holomorphy
symmetry alters the two most important singular solutions of general
relativity: black holes and cosmology. We show that typical observers (freely)
falling into a holomorphic black hole do not encounter a curvature singularity.
Likewise, typical observers do not experience Big Bang singularity. Unlike
Hermitian gravity \cite{MantzHermitianGravity}, Holomorphic gravity does not
respect the reciprocity symmetry and thus it is mainly a toy model for a
gravity theory formulated on complex space-times. Yet it is a model that
deserves a closer investigation since in many aspects it resembles Hermitian
gravity and yet calculations are simpler. We have indications that holomorphic
gravity reduces to the laws of general relativity correctly at large distance
scales.Comment: 14 pages, 7 figure
On the construction of a geometric invariant measuring the deviation from Kerr data
This article contains a detailed and rigorous proof of the construction of a
geometric invariant for initial data sets for the Einstein vacuum field
equations. This geometric invariant vanishes if and only if the initial data
set corresponds to data for the Kerr spacetime, and thus, it characterises this
type of data. The construction presented is valid for boosted and non-boosted
initial data sets which are, in a sense, asymptotically Schwarzschildean. As a
preliminary step to the construction of the geometric invariant, an analysis of
a characterisation of the Kerr spacetime in terms of Killing spinors is carried
out. A space spinor split of the (spacetime) Killing spinor equation is
performed, to obtain a set of three conditions ensuring the existence of a
Killing spinor of the development of the initial data set. In order to
construct the geometric invariant, we introduce the notion of approximate
Killing spinors. These spinors are symmetric valence 2 spinors intrinsic to the
initial hypersurface and satisfy a certain second order elliptic equation
---the approximate Killing spinor equation. This equation arises as the
Euler-Lagrange equation of a non-negative integral functional. This functional
constitutes part of our geometric invariant ---however, the whole functional
does not come from a variational principle. The asymptotic behaviour of
solutions to the approximate Killing spinor equation is studied and an
existence theorem is presented.Comment: 36 pages. Updated references. Technical details correcte
Detection of freeze injury in oranges using magnetic resonance imaging under motion conditions
Magnetic resonance imaging (MRI) is applied for on-line inspection of fruits. The aim of this work is to address the applicability of MRI for freeze injury detection in oranges directly on a distribution chain. Undamaged and damaged oranges are conveyed at 50 and 100 mm/s by a specially designed conveyor within a 4.7 T spectrometer obtaining fast low-angle shot images. An automatic segmentation algorithm is proposed that allows the discrimination between undamaged and damaged orange
Estimates for heritability and consumer-validation of a penetrometer method for phenotyping softness of cooked cassava roots
Although breeders have made significant progress in the genetic
improvement of cassava ( Manihot esculenta Crantz) for agronomic
traits, lack of information on heritability and limited testing of
high-throughput phenotyping methods are major limitations to improving
root quality traits, such as softness after cooking, which rank high
among Ugandan consumers. The objectives of this study were to determine
heritability for softness of cooked cassava roots, and quantify the
relationship between penetrometer and consumer testing methods for
phenotyping softness of cassava roots. Softness defined as the maximum
force (N) needed to penetrate cooked root samples using a penetrometer,
was evaluated at four cooking time intervals: 15, 30, 45, and 60 min on
268 cassava genotypes. Estimates of broad-sense heritability
(repeatability) ranged from 0.17 to 0.37, with the highest value
observed at 45 min of cooking time interval. In the second study
involving 135 cassava consumers from Kibaale district in Uganda,
penetrometer measurements of cooked roots from six cassava varieties
were found to be in strong agreement (r2 = 0.91; P-value = 0.003) with
ordinal scores of root softness from consumer testing. These results
suggest that: (a) softness of cooked cassava roots is a trait amenable
for evaluation and selection; and (b) a penetrometer can readily be
used for assessment of cooked root softness. These findings form the
basis for operationalising the routine assessment of root softness in
cassava breeding trials, an output that will enhance ongoing efforts to
breed for desired end-user root quality traits.Les s\ue9lectionneurs ont fait des progr\ue8s consid\ue9rables
dans l\u2019am\ue9lioration g\ue9n\ue9tique des caract\ue8res
agronomiques du manioc ( Manihot esculenta Crantz). Cependant un
manque de m\ue9thodes de ph\ue9notypage haut-d\ue9bit
adapt\ue9es aux caract\ue8res de qualit\ue9s tel que la
fermet\ue9 de la racine apr\ue8s cuisson, essentiel pour les
consommateurs Ougandais. Cette \ue9tude ambitionne a) de determiner
l\u2019h\ue9ritabilit\ue9 de la fermete de racine cuite b) de
quantifier la relation entre l \ue9valuation de la fermet\ue9 de
racine cuite au p\ue9n\ue9trom\ue8tre et un panel consommateurs.
Cette \ue9valuation a \ue9t\ue9 realisee a quatre intervals de
temps: 15, 30, 45 et 60 minutes sur 268 genotypes de manioc. Pour
d\ue9finir l\u2019h\ue9ritabilit\ue9 de la fermet\ue9 de la
racine, celle ci a \ue9t\ue9 d\ue9finie par la force maximum (N)
n\ue9cessaire pour p\ue9n\ue9trer des \ue9chantillons de
racines incluant diff\ue8rent temps de cuisson (15, 30, 45, and 60
min) a l\u2019aide d\u2019un p\ue9n\ue9trom\ue8tre.
L\u2019h\ue9ritabilit\ue9 au sens large (ou
r\ue9p\ue9tabilit\ue9) observ\ue9e varie de 0.17 a 0.37, la
valeur la plus \ue9lev\ue9 \ue9tant observ\ue9e pour un temps
de cuisson de 45 minutes. Dans une seconde \ue9tude impliquant 135
consommateurs du district de Kibaale (Ouest de l\u2019Ouganda), les
mesures au p\ue9n\ue9trom\ue8tre de racines cuites de six
vari\ue9t\ue9s ont confirm\ue9es la forte correlation (r2 = 0.91;
P-value = 0.003) avec les valeurs ordinales de fermet\ue9 de racine
du panel consommateur. Les r\ue9sultats de cette \ue9tude indiquent
que cette m\ue9thodologie de ph\ue9notypage est a) utile pour
l\u2019 \ue9valuation de la fermet\ue9 sur des racines cuites en
selection et b) d\ue9montre que l\u2019usage du
p\ue9n\ue9trom\ue8tre est efficace pour celle ci. Ces
r\ue9sultats offrent aux s\ue9lectionneurs une methode d\u2019
\ue9valuation de routine de la qualite de racine pour les essais
experimentaux. Ceux ci contribueront aux efforts actuels pour
l\u2019am\ue9lioration des caract\ue8res qualit\ue9s chers aux
consommateurs
On formation of a locally self-similar collapse in the incompressible Euler equations
The paper addresses the question of existence of a locally self-similar
blow-up for the incompressible Euler equations. Several exclusion results are
proved based on the -condition for velocity or vorticity and for a range
of scaling exponents. In particular, in dimensions if in self-similar
variables and u \sim \frac{1}{t^{\a/(1+\a)}}, then the blow-up
does not occur provided \a >N/2 or -1<\a\leq N/p. This includes the
case natural for the Navier-Stokes equations. For \a = N/2 we exclude
profiles with an asymptotic power bounds of the form |y|^{-N-1+\d} \lesssim
|u(y)| \lesssim |y|^{1-\d}. Homogeneous near infinity solutions are eliminated
as well except when homogeneity is scaling invariant.Comment: A revised version with improved notation, proofs, etc. 19 page
Motion of influential players can support cooperation in Prisoner's Dilemma
We study a spatial Prisoner's dilemma game with two types (A and B) of
players located on a square lattice. Players following either cooperator or
defector strategies play Prisoner's Dilemma games with their 24 nearest
neighbors. The players are allowed to adopt one of their neighbor's strategy
with a probability dependent on the payoff difference and type of the given
neighbor. Players A and B have different efficiency in the transfer of their
own strategy therefore the strategy adoption probability is reduced by a
multiplicative factor (w < 1) from the players of type B. We report that the
motion of the influential payers (type A) can improve remarkably the
maintenance of cooperation even for their low densities.Comment: 7 pages, 7 figure
Perfil hematológico de cabras Saanen e mestiças (1/2 Saanen e 1/2 Anglo-nubiana) criadas em clima tropical do Ceará
- …