3,292 research outputs found
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Progress Toward Replacing Animals in Toxicity Testing for Cosmetics
In the 1980’s, animal rights activists successfully motivated the cosmetic industry to begin researching alternatives to animal tests. The European Union has taken action to stimulate development and validation of alternatives to animal testing through the Sixth and Seventh Amendments to the Cosmetics Directive. In this paper, I will briefly describe the history of the search for alternatives to animal testing for cosmetics. I will then discuss the progress that has been made toward developing and validating replacement alternatives in the eleven toxicological safety testing areas; alternatives are needed in all eleven areas in order for animal tests to be totally replaced
The Variational Homoencoder: Learning to learn high capacity generative models from few examples
Hierarchical Bayesian methods can unify many related tasks (e.g. k-shot
classification, conditional and unconditional generation) as inference within a
single generative model. However, when this generative model is expressed as a
powerful neural network such as a PixelCNN, we show that existing learning
techniques typically fail to effectively use latent variables. To address this,
we develop a modification of the Variational Autoencoder in which encoded
observations are decoded to new elements from the same class. This technique,
which we call a Variational Homoencoder (VHE), produces a hierarchical latent
variable model which better utilises latent variables. We use the VHE framework
to learn a hierarchical PixelCNN on the Omniglot dataset, which outperforms all
existing models on test set likelihood and achieves strong performance on
one-shot generation and classification tasks. We additionally validate the VHE
on natural images from the YouTube Faces database. Finally, we develop
extensions of the model that apply to richer dataset structures such as
factorial and hierarchical categories.Comment: UAI 2018 oral presentatio
Rotator and extender ferroelectrics: Importance of the shear coefficient to the piezoelectric properties of domain-engineered crystals and ceramics
The importance of a high shear coefficient d15 (or d24) to the piezoelectric
properties of domain-engineered and polycrystalline ferroelectrics is
discussed. The extent of polarization rotation, as a mechanism of piezoelectric
response, is directly correlated to the shear coefficient. The terms "rotator"
and "extender" are introduced to distinguish the contrasting behaviors of
crystals such as 4mm BaTiO3 and PbTiO3. In "rotator" ferroelectrics, where d15
is high relative to the longitudinal coefficient d33, polarization rotation is
the dominant mechanism of piezoelectric response; the maximum longitudinal
piezoelectric response is found away from the polar axis. In "extender"
ferroelectrics, d15 is low and the collinear effect dominates; the maximum
piezoelectric response is found along the polar axis. A variety of 3m, mm2 and
4mm ferroelectrics, with various crystal structures based on oxygen octahedra,
are classified in this way. It is shown that the largest piezoelectric
anisotropies d15/d33 are always found in 3m crystals; this is a result of the
intrinsic electrostrictive anisotropy of the constituent oxygen octahedra.
Finally, for a given symmetry, the piezoelectric anisotropy increases close to
ferroelectric-ferroelectric phase transitions; this includes morphotropic phase
boundaries and temperature induced polymorphic transitions.Comment: accepted in J. Appl. Phy
Spatio-temporal vortex beams and angular momentum
We present a space-time generalization of the known spatial (monochromatic)
wave vortex beams carrying intrinsic orbital angular momentum (OAM) along the
propagation direction. Generic spatio-temporal vortex beams are polychromatic
and can carry intrinsic OAM at an arbitrary angle to the mean momentum.
Applying either (i) a transverse wave-vector shift or (ii) a Lorentz boost to a
monochromatic Bessel beam, we construct a family of either (i) time-diffracting
or (ii) non-diffracting spatio-temporal Bessel beams, which are exact solutions
of the Klein-Gordon wave equations. The proposed spatio-temporal OAM states are
able to describe either photon or electron vortex states (both relativistic and
nonrelativistic), and can find applications in particle collisions, optics of
moving media, quantum communications, and astrophysics.Comment: 9 pages, 6 figures, to appear in Phys. Rev.
Limiting behaviour of Fréchet means in the space of phylogenetic trees
As demonstrated in our previous work on T4, the space of phylogenetic trees with four leaves, the topological structure of the space plays an important role in the non-classical limiting behaviour of the sample Fréchet means in T4. Nevertheless, the techniques used in that paper cannot be adapted to analyse Fréchet means in the space Tm of phylogenetic trees with m(⩾5)m(⩾5) leaves. To investigate the latter, this paper first studies the log map of Tm. Then, in terms of a modified version of this map, we characterise Fréchet means in Tm that lie in top-dimensional or co-dimension one strata. We derive the limiting distributions for the corresponding sample Fréchet means, generalising our previous results. In particular, the results show that, although they are related to the Gaussian distribution, the forms taken by the limiting distributions depend on the co-dimensions of the strata in which the Fréchet means lie
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American power and identities in the age of Obama
Although the election of Barack Obama to the US presidency represents a landmark event in the history of that country, questions remain over its broader political significance. What is the likelihood of Obama's foreign and national security policies differing fundamentally from those of the Bush administrations Does Obama's election signal a post-racial phase in American national life What are the factors that suggest opportunities to change and expand American identities as opposed to those that limit Obama's sphere of action This article introduces the special issue and suggests that although Obama's room for manoeuvre is limited by legacies inherited from the Bush administration, Obama's own appointments to high office as well as other actions, despite the availability of alternative courses, indicate that he is not the transformational president he claimed to be. American identities, therefore, are deeply embedded and remain heavily imbued with racial, religious and imperial features
Millisecond accuracy video display using OpenGL under Linux
To measure people’s reaction times to the nearest millisecond, it is necessary to know exactly when
a stimulus is displayed. This article describes how to display stimuli with millisecond accuracy on a
normal CRT monitor, using a PC running Linux. A simple C program is presented to illustrate how this
may be done within X Windows using the OpenGL rendering system. A test of this system is reported
that demonstrates that stimuli may be consistently displayed with millisecond accuracy. An algorithm
is presented that allows the exact time of stimulus presentation to be deduced, even if there are relatively
large errors in measuring the display time
Abrupt grain boundary melting in ice
The effect of impurities on the grain boundary melting of ice is investigated
through an extension of Derjaguin-Landau-Verwey-Overbeek theory, in which we
include retarded potential effects in a calculation of the full frequency
dependent van der Waals and Coulombic interactions within a grain boundary. At
high dopant concentrations the classical solutal effect dominates the melting
behavior. However, depending on the amount of impurity and the surface charge
density, as temperature decreases, the attractive tail of the dispersion force
interaction begins to compete effectively with the repulsive screened Coulomb
interaction. This leads to a film-thickness/temperature curve that changes
depending on the relative strengths of these interactions and exhibits a
decrease in the film thickness with increasing impurity level. More striking is
the fact that at very large film thicknesses, the repulsive Coulomb interaction
can be effectively screened leading to an abrupt reduction to zero film
thickness.Comment: 8 pages, 1 figur
Probing Cold Dark Matter Cusps by Gravitational Lensing
I elaborate on my prediction that an indirect detection of cold dark matter
(CDM) may be possible by observing the gravitational lensing effects of the CDM
cusp caustics at cosmological distances. Cusps in the distribution of CDM are
plentiful once density perturbations enter the nonlinear regime of structure
formation. Caustic ring model of galactic halo formation provides a well
defined density profile and geometry near the cusps of the caustic rings. I
calculate the gravitational lensing effects of the cusps in this model. As a
pointlike background source passes behind a cusp of a cosmological foreground
halo, the magnification in its image may be detected by present instruments.
Depending on the strength of detected effect and the time scale of brightness
change, it may even be possible to discriminate between the CDM candidates:
axions and weakly interacting massive particles.Comment: Invited Contribution to the IJMPD Special Issue on Dark Matter and
Dark Energy edited by D. Ahluwalia-Khalilova and D. Grumiller. To appear in
Int. J. Mod. Phys. D Special December 2006 issu
A compilation, classification, and comparison of lists of spontaneous speaking vocabulary of children in kindergarten, Grade I, Grade II, and Grade III
Thesis (Ed.M.)--Boston UniversityLanguage development has been studied for many years.
The beginning vocabularies are easy to count ana record.
As tne child grows and moves about, his speaking vocabulary
increases very rapidly. Some estimates suggest
that a minimum speaking vocabulary at six years would include
three thousand words.
New words have come into children's speaking vocabularies
as a result of modern technology since World War II.
Lists of spontaneous vocabulary furnish material for teachers
and text book writers. The purpose of this study is
to analyze two lists recorded in 1954 and 1955.
An attempt has been made to classify the new list.
The lists were compared with three existing lists, Rinsland,
International Kindergarten Union and Gates
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