1,945 research outputs found
Mixing the transition metals in transition metal carbides
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Separation dichotomy and wavefronts for a nonlinear convolution equation
This paper is concerned with a scalar nonlinear convolution equation which
appears naturally in the theory of traveling waves for monostable evolution
models. First, we prove that each bounded positive solution of the convolution
equation should either be asymptotically separated from zero or it should
converge (exponentially) to zero. This dichotomy principle is then used to
establish a general theorem guaranteeing the uniform persistence and existence
of semi-wavefront solutions to the convolution equation. Finally, we apply our
abstract results to several well-studied classes of evolution equations with
asymmetric non-local and non-monotone response. We show that, contrary to the
symmetric case, these equations can possess at the same time the stationary,
the expansion and the extinction waves.Comment: 15 pages, submitte
Pre-Training LiDAR-Based 3D Object Detectors Through Colorization
Accurate 3D object detection and understanding for self-driving cars heavily
relies on LiDAR point clouds, necessitating large amounts of labeled data to
train. In this work, we introduce an innovative pre-training approach, Grounded
Point Colorization (GPC), to bridge the gap between data and labels by teaching
the model to colorize LiDAR point clouds, equipping it with valuable semantic
cues. To tackle challenges arising from color variations and selection bias, we
incorporate color as "context" by providing ground-truth colors as hints during
colorization. Experimental results on the KITTI and Waymo datasets demonstrate
GPC's remarkable effectiveness. Even with limited labeled data, GPC
significantly improves fine-tuning performance; notably, on just 20% of the
KITTI dataset, GPC outperforms training from scratch with the entire dataset.
In sum, we introduce a fresh perspective on pre-training for 3D object
detection, aligning the objective with the model's intended role and ultimately
advancing the accuracy and efficiency of 3D object detection for autonomous
vehicles
Some investigations into non passive listening
Our knowledge of the function of the auditory nervous system is based upon a wealth of data obtained, for the most part, in anaesthetised animals. More recently, it has been generally acknowledged that factors such as attention profoundly modulate the activity of sensory systems and this can take place at many levels of processing. Imaging studies, in particular, have revealed the greater activation of auditory areas and areas outside of sensory processing areas when attending to a stimulus. We present here a brief review of the consequences of such non-passive listening and go on to describe some of the experiments we are conducting to investigate them. In imaging studies, using fMRI, we can demonstrate the activation of attention networks that are non-specific to the sensory modality as well as greater and different activation of the areas of the supra-temporal plane that includes primary and secondary auditory areas. The profuse descending connections of the auditory system seem likely to be part of the mechanisms subserving attention to sound. These are generally thought to be largely inactivated by anaesthesia. However, we have been able to demonstrate that even in an anaesthetised preparation, removing the descending control from the cortex leads to quite profound changes in the temporal patterns of activation by sounds in thalamus and inferior colliculus. Some of these effects seem to be specific to the ear of stimulation and affect interaural processing. To bridge these observations we are developing an awake behaving preparation involving freely moving animals in which it will be possible to investigate the effects of consciousness (by contrasting awake and anaesthetized), passive and active listening
Unraveling the temperature dependence of the yield strength in single-crystal tungsten using atomistically-informed crystal plasticity calculations
We use a physically-based crystal plasticity model to predict the yield
strength of body-centered cubic (bcc) tungsten single crystals subjected to
uniaxial loading. Our model captures the thermally-activated character of screw
dislocation motion and full non-Schmid effects, both of which are known to play
a critical role in bcc plasticity. The model uses atomistic calculations as the
sole source of constitutive information, with no parameter fitting of any kind
to experimental data. Our results are in excellent agreement with experimental
measurements of the yield stress as a function of temperature for a number of
loading orientations. The validated methodology is then employed to calculate
the temperature and strain-rate dependence of the yield strength for 231
crystallographic orientations within the standard stereographic triangle. We
extract the strain-rate sensitivity of W crystals at different temperatures,
and finish with the calculation of yield surfaces under biaxial loading
conditions that can be used to define effective yield criteria for engineering
design models
Nonadiabatic approach to dimerization gap and optical absorption coefficient of the Su-Schrieffer-Heeger model
An analytical nonadiabatic approach has been developed to study the
dimerization gap and the optical absorption coefficient of the
Su-Schrieffer-Heeger model where the electrons interact with dispersive quantum
phonons. By investigating quantitatively the effects of quantum phonon
fluctuations on the gap order and the optical responses in this system, we show
that the dimerization gap is much more reduced by the quantum lattice
fluctuations than the optical absorption coefficient is. The calculated optical
absorption coefficient and the density of states do not have the
inverse-square-root singularity, but have a peak above the gap edge and there
exist a significant tail below the peak. The peak of optical absorption
spectrum is not directly corresponding to the dimerized gap. Our results of the
optical absorption coefficient agree well with those of the experiments in both
the shape and the peak position of the optical absorption spectrum.Comment: 14 pages, 7 figures. to be published in PR
Detection of heat shock protein 70 in choroidal neovascular membranes secondary to age related macular degeneration
<p>Abstract</p> <p>Background</p> <p>Heat shock proteins are acute phase proteins that are upregulated in inflammation or following thermal stress. We analyzed the presence of the heat shock protein 70 (Hsp 70) in choroidal neovascular (CNV) membranes secondary to AMD after treatment with verteporphin photodynamic therapy (PDT) or transpupillary thermo therapy (TTT) to determine whether treatment correlated with the presence of Hsp70.</p> <p>Results</p> <p>CNV membranes were removed by pars plana vitrectomy (ppV) and subretinal extraction. The membranes were analysed by light microscopy and the presence of Hsp 70 was examined using histochemistry. HeLa Cells served as controls.</p> <p>Of the 14 membranes analysed 11 were Hsp70 positive and 3 negative. In the no pre-treatment group of 8 membranes 6 were Hsp70 positive and 2 negative; in the PTD group all 4 membranes were positive and in the TTT group 1 membrane was positive and 1 membrane was negative for Hsp70.</p> <p>Conclusion</p> <p>Hsp70 is present in the most CNV membranes secondary to AMD. Pre-treatment of the membrane with PTD or TTT does not appear to influence the expression of Hsp70.</p
Demonstration of all-or-none loss of imprinting in mRNA expression in single cells
Loss of imprinting (LOI) is the reactivation of the silenced allele of an imprinted gene, leading to perturbation of monoallelic expression. We tested the hypothesis that LOI of PLAGL1, a representative maternally imprinted gene, occurs through an all-or-none process leading to a mixture of fully imprinted and nonimprinted cells. Herein using a quantitative RT-PCR-based experimental approach, we measured LOI at the single cell level in human trophoblasts and demonstrated a broad distribution of LOI among cells exhibiting LOI, with the mean centered at ∼100% LOI. There was a significant (P < 0.01) increase in expression after 2 days of 5-aza-2′-deoxycytidine (AZA) treatment and a significant (P < 0.01) increase in LOI after both 1 and 2 days of AZA treatment, while the distribution remained broad and centered at ∼100% LOI. We propose a transcriptional pulsing model to show that the broadness of the distribution reflects the stochastic nature of expression between the two alleles in each cell. The mean of the distribution of LOI in the cells is consistent with our hypothesis that LOI occurs by an all-or-none process. All-or-none LOI could lead to a second distinct cell population that may have a selective advantage, leading to variation of LOI in normal tissues, such as the placenta, or in neoplastic cells
A search for steep spectrum radio relics and halos with the GMRT
Context: Diffuse radio emission, in the form of radio halos and relics,
traces regions in clusters with shocks or turbulence, probably produced by
cluster mergers. Some models of diffuse radio emission in clusters indicate
that virtually all clusters should contain diffuse radio sources with a steep
spectrum. External accretion shocks associated with filamentary structures of
galaxies could also accelerate electrons to relativistic energies and hence
produce diffuse synchrotron emitting regions. Here we report on Giant Metrewave
Radio Telescope (GMRT) observations of a sample of steep spectrum sources from
the 74 MHz VLSS survey. These sources are diffuse and not associated with
nearby galaxies.
Aims: The main aim of the observations is to search for diffuse radio
emission associated with galaxy clusters or the cosmic web.
Methods: We carried out GMRT 610 MHz continuum observations of unidentified
diffuse steep spectrum sources.
Results: We have constructed a sample of diffuse steep spectrum sources,
selected from the 74 MHz VLSS survey. We identified eight diffuse radio sources
probably all located in clusters. We found five radio relics, one cluster with
a giant radio halo and a radio relic, and one radio mini-halo. By complementing
our observations with measurements from the literature we find correlations
between the physical size of relics and the spectral index, in the sense that
smaller relics have steeper spectra. Furthermore, larger relics are mostly
located in the outskirts of clusters while smaller relics are located closer to
the cluster center.Comment: 20 pages, 26 figures, accepted for publication in A&A on October 7,
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