817 research outputs found
Age Problem in Lemaitre-Tolman-Bondi Void Models
As is well known, one can explain the current cosmic acceleration by
considering an inhomogeneous and/or anisotropic universe (which violates the
cosmological principle), without invoking dark energy or modified gravity. The
well-known one of this kind of models is the so-called
Lema\^{\i}tre-Tolman-Bondi (LTB) void model, in which the universe is
spherically symmetric and radially inhomogeneous, and we are living in a
locally underdense void centered nearby our location. In the present work, we
test various LTB void models with some old high redshift objects (OHROs).
Obviously, the universe cannot be younger than its constituents. We find that
an unusually large (characterizing the size of the void) is required to
accommodate these OHROs in LTB void models. There is a serious tension between
this unusually large and the much smaller inferred from other
observations (e.g. SNIa, CMB and so on). However, if we instead consider the
lowest limit 1.7\,Gyr for the quasar APM 08279+5255 at redshift , this
tension could be greatly alleviated.Comment: 17 pages, 9 figures, revtex4; v2: discussions added, Phys. Lett. B in
press; v3: published versio
Numerical Strategies of Computing the Luminosity Distance
We propose two efficient numerical methods of evaluating the luminosity
distance in the spatially flat {\Lambda}CDM universe. The first method is based
on the Carlson symmetric form of elliptic integrals, which is highly accurate
and can replace numerical quadratures. The second method, using a modified
version of Hermite interpolation, is less accurate but involves only basic
numerical operations and can be easily implemented. We compare our methods with
other numerical approximation schemes and explore their respective features and
limitations. Possible extensions of these methods to other cosmological models
are also discussed.Comment: 4 pages, 2 figures. v2: A minor error in the last equation has been
corrected (conclusions are not affected). v3: Accepted by MNRA
New Generalizations of Cosmography Inspired by the Pade Approximant
The current accelerated expansion of the universe has been one of the most
important fields in physics and astronomy since 1998. Many cosmological models
have been proposed in the literature to explain this mysterious phenomenon.
Since the nature and cause of the cosmic acceleration are still unknown,
model-independent approaches to study the evolution of the universe are
welcome. One of the powerful model-independent approaches is the so-called
cosmography. It only relies on the cosmological principle, without postulating
any underlying theoretical model. However, there are several shortcomings in
the usual cosmography. For instance, it is plagued with the problem of
divergence (or an unacceptably large error), and it fails to predict the future
evolution of the universe. In the present work, we try to overcome or at least
alleviate these problems, and we propose two new generalizations of cosmography
inspired by the Pad\'e approximant. One is to directly parameterize the
luminosity distance based on the Pad\'e approximant, while the other is to
generalize cosmography with respect to a so-called -shift
, which is also inspired by the Pad\'e approximant.
Then, we confront them with the observational data with the help of the Markov
chain Monte Carlo (MCMC) code emcee, and find that they work fairly well.Comment: 16 pages, 3 tables, 5 figures, revtex4; v2: discussions added, Eur.
Phys. J. C in press; v3: published versio
A new species of Polycelis (Platyhelminthes, Tricladida, Planariidae) from China
In this paper, a new species of Polycelis of the family
Planariidae from China is described. Mature individuals have
80–140 eyespots; the testes are well-developed and most of
them occupy the entire dorso-ventral space; the penis is a
long cone with well-developed musculature; the boundary
between the penis bulb and penis papilla is vague and the
bulbar cavity is not observed; the bursal canal is surrounded
by a well-developed coat of circular muscles, and a thin
layer of longitudinal muscles. The karyotype shows a diploid
complement of 38 chromosomes, with the formula 2n = 38 = 24m
+ 14sm
Polycystic ovary syndrome in patients with epilepsy: A study in 102 Chinese women
AbstractPurposeThe incidence of polycystic ovary syndrome (PCOS) increases in women with epilepsy (WWE), which appears to vary with ethnicity. This study was conducted to determine the incidence and risk factors of PCOS in Chinese WWE.MethodsThe study was carried out in 102 of 139 Chinese WWE at reproductive ages, with 32 receiving valproic acid (VPA), 40 receiving other antiepileptic drugs (AEDs), and 30 without AEDs therapy. PCOS was defined as having 2 or more of the following components: polycystic ovaries, hyperandrogenism, and amenorrhoea or oligomenorrhoea (a/oligomenorrhoea).ResultsOne or more isolated components of PCOS were found in 56 (54.9%) patients, with 29 (28.4%) having polycystic ovaries, 20 (19.6%) with a/oligomenorrhea, 7 (6.9%) with hyperandrogenism, and 13 (12.7%) with defined PCOS. Their average age at the start of seizure was 13.8±6.5years, younger than that of patients without these disorders (16.9±8.6years, p<0.05). VPA therapy increased the incidence of PCOS (11/32, 34.4%), in addition to increased blood levels of testosterone and luteinizing hormone (LH) as well as LH to FSH (follicle-stimulating hormone) ratio. No significant relationship was found between the incidence of PCOS and the type, duration, or frequency of seizures in these WWE.ConclusionThere is an increased incidence of PCOS in Chinese WWE at reproductive ages, by more than 2 times of that in the general population. Risk factors include seizures starting at a young age and VPA therapy
Improved Feature Distillation via Projector Ensemble
In knowledge distillation, previous feature distillation methods mainly focus
on the design of loss functions and the selection of the distilled layers,
while the effect of the feature projector between the student and the teacher
remains under-explored. In this paper, we first discuss a plausible mechanism
of the projector with empirical evidence and then propose a new feature
distillation method based on a projector ensemble for further performance
improvement. We observe that the student network benefits from a projector even
if the feature dimensions of the student and the teacher are the same. Training
a student backbone without a projector can be considered as a multi-task
learning process, namely achieving discriminative feature extraction for
classification and feature matching between the student and the teacher for
distillation at the same time. We hypothesize and empirically verify that
without a projector, the student network tends to overfit the teacher's feature
distributions despite having different architecture and weights initialization.
This leads to degradation on the quality of the student's deep features that
are eventually used in classification. Adding a projector, on the other hand,
disentangles the two learning tasks and helps the student network to focus
better on the main feature extraction task while still being able to utilize
teacher features as a guidance through the projector. Motivated by the positive
effect of the projector in feature distillation, we propose an ensemble of
projectors to further improve the quality of student features. Experimental
results on different datasets with a series of teacher-student pairs illustrate
the effectiveness of the proposed method
Quantum Earth Mover's Distance: A New Approach to Learning Quantum Data
Quantifying how far the output of a learning algorithm is from its target is
an essential task in machine learning. However, in quantum settings, the loss
landscapes of commonly used distance metrics often produce undesirable outcomes
such as poor local minima and exponentially decaying gradients. As a new
approach, we consider here the quantum earth mover's (EM) or Wasserstein-1
distance, recently proposed in [De Palma et al., arXiv:2009.04469] as a quantum
analog to the classical EM distance. We show that the quantum EM distance
possesses unique properties, not found in other commonly used quantum distance
metrics, that make quantum learning more stable and efficient. We propose a
quantum Wasserstein generative adversarial network (qWGAN) which takes
advantage of the quantum EM distance and provides an efficient means of
performing learning on quantum data. Our qWGAN requires resources polynomial in
the number of qubits, and our numerical experiments demonstrate that it is
capable of learning a diverse set of quantum data
(E)-N′-(3,4-Dimethoxybenzylidene)-2,4-dihydroxybenzohydrazide methanol solvate
The title compound, C16H16N2O5·CH3OH, was obtained from a condensation reaction of 3,4-dimethoxybenzaldehyde and 2,4-dihydroxybenzohydrazide. The non-H atoms of the Schiff base molecule are approximately coplanar (r.m.s. deviation = 0.043 Å) and the dihedral angle between the two benzene rings is 1.6 (1)°. The molecule adopts an E configuration with respect to the C=N double bond. An intramolecular O—H⋯O hydrogen bond is observed. The Schiff base and methanol molecules are linked into a two-dimensional network parallel to (10) by intermolecular N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds
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