1,008 research outputs found
Study of leakage currents in pCVD diamonds as function of the magnetic field
pCVD diamond sensors are regularly used as beam loss monitors in accelerators
by measuring the ionization of the lost particles. In the past these beam loss
monitors showed sudden increases in the dark leakage current without beam
losses and these erratic leakage currents were found to decrease, if magnetic
fields were present. Here we report on a systematic study of leakage currents
inside a magnetic field. The decrease of erratic currents in a magnetic field
was confirmed. On the contrary, diamonds without erratic currents showed an
increase of the leakage current in a magnetic field perpendicular to the
electric field for fields up to 0.6T, for higher fields it decreases. A
preliminary model is introduced to explain the observations.Comment: 6 pages, 16 figures, poster at Hasselt Diamond Workshop, Mar 2009,
accepted version for publicatio
Nanoparticle characterization: What to measure?
What to measure? is a key question in nanoscience, and it is not straightforward to address as different physicochemical properties define a nanoparticle sample. Most prominent among these properties are size, shape, surface charge, and porosity. Today researchers have an unprecedented variety of measurement techniques at their disposal to assign precise numerical values to those parameters. However, methods based on different physical principles probe different aspects, not only of the particles themselves, but also of their preparation history and their environment at the time of measurement. Understanding these connections can be of great value for interpreting characterization results and ultimately controlling the nanoparticle structure–function relationship. Here, the current techniques that enable the precise measurement of these fundamental nanoparticle properties are presented and their practical advantages and disadvantages are discussed. Some recommendations of how the physicochemical parameters of nanoparticles should be investigated and how to fully characterize these properties in different environments according to the intended nanoparticle use are proposed. The intention is to improve comparability of nanoparticle properties and performance to ensure the successful transfer of scientific knowledge to industrial real‐world applications
Helium irradiation effects in polycrystalline Si, silica, and single crystal Si
Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change
Unlocking Spatial Comprehension in Text-to-Image Diffusion Models
We propose CompFuser, an image generation pipeline that enhances spatial
comprehension and attribute assignment in text-to-image generative models. Our
pipeline enables the interpretation of instructions defining spatial
relationships between objects in a scene, such as `An image of a gray cat on
the left of an orange dog', and generate corresponding images. This is
especially important in order to provide more control to the user. CompFuser
overcomes the limitation of existing text-to-image diffusion models by decoding
the generation of multiple objects into iterative steps: first generating a
single object and then editing the image by placing additional objects in their
designated positions. To create training data for spatial comprehension and
attribute assignment we introduce a synthetic data generation process, that
leverages a frozen large language model and a frozen layout-based diffusion
model for object placement. We compare our approach to strong baselines and
show that our model outperforms state-of-the-art image generation models in
spatial comprehension and attribute assignment, despite being 3x to 5x smaller
in parameters
Spin flip from dark to bright states in InP quantum dots
We report measurements of the time for spin flip from dark (non-light
emitting) exciton states in quantum dots to bright (light emitting) exciton
states in InP quantum dots. Dark excitons are created by two-photon excitation
by an ultrafast laser. The time for spin flip between dark and bright states is
found to be approximately 200 ps, independent of density and temperature below
70 K. This is much shorter than observed in other quantum dot systems. The rate
of decay of the luminescence intensity, approximately 300 ps, is not simply
equal to the radiative decay rate from the bright states, because the rate of
decay is limited by the rate of conversion from dark excitons into bright
excitons. The dependence of the luminescence decay time on the spin flip time
is a general effect that applies to many experiments.Comment: 3 figure
The effect of excess atomic volume on He bubble formation at fcc-bcc interfaces
Atomistic modeling shows that Cu–Nb and Cu–V interfaces contain high excess atomic volume due to constitutional vacancy concentrations of ∼ 5 at. % and ∼ 0.8 at. %., respectively. This finding is supported by experiments demonstrating that an approximately fivefold higher He concentration is required to observe He bubbles via through-focus transmission electron microscopy at Cu–Nb interfaces than in Cu–V interfaces. Interfaces with structures tailored to minimize precipitation and growth of He bubbles may be used to design damage-resistant composites for fusion reactors.United States. Dept. of Energy. Office of Basic Energy Sciences (award 2008LANL1026
Influence of oxidation on the high-temperature mechanical properties of zirconia/nickel cermets
The influence of an oxidizing atmosphere on the high-temperature plasticity of zirconia/nickel cermets has been studied by conducting creep tests in air. The resulting microstructure has been characterized by scanning, conventional and high-resolution electron microscopy. Despite the large microstructural changes, the composites do not exhibit mechanical degradation.Ministerio de Ciencia y Tecnología MAT2000-1117, MAT2003-04199-C02-02Max-Planck-Gesellschaft (Germany) PMT-CT-2000-0005
Microstructural characteristics of TZP/Ni cermets plastically deformed at high temperature
The microstructure of 3 mol% Y2O3-stabilized tetragonal ZrO2/Ni (TZP/Ni) composites has been investigated for nickel concentrations of 20, 30 and 40 vol.% before and after creep tests conducted in argon atmosphere at 1250 °C under stresses between 9 and 14 MPa. The microstructures have been characterized using scanning, conventional and high-resolution transmission and analytical electron microscopy. Two types of microstructure were found depending on the presence/absence of percolation in the metal phase. The deformation process strongly affects the percolation threshold due to the elongation of metallic grains and subsequently formation of aggregates. TEM and HRTEM studies in as-received and deformed cermets show the lack of dislocation activity and the absence of secondary phases in both zirconia/zirconia and zirconia/nickel interfaces and triple junctions.Ministerio de Educación y Ciencia MAT2000-1117, MAT2003-04199-CO2-0
The Chloroplast RNA Binding Protein CP31A Has a Preference for mRNAs Encoding the Subunits of the Chloroplast NAD(P)H Dehydrogenase Complex and Is Required for Their Accumulation
Chloroplast RNA processing requires a large number of nuclear-encoded RNA binding proteins (RBPs) that are imported post-translationally into the organelle. Most of these RBPs are highly specific for one or few target RNAs. By contrast, members of the chloroplast ribonucleoprotein family (cpRNPs) have a wider RNA target range. We here present a quantitative analysis of RNA targets of the cpRNP CP31A using digestion-optimized RNA co-immunoprecipitation with deep sequencing (DO-RIP-seq). This identifies the mRNAs coding for subunits of the chloroplast NAD(P)H dehydrogenase (NDH) complex as main targets for CP31A. We demonstrate using whole-genome gene expression analysis and targeted RNA gel blot hybridization that the ndh mRNAs are all down-regulated in cp31a mutants. This diminishes the activity of the NDH complex. Our findings demonstrate how a chloroplast RNA binding protein can combine functionally related RNAs into one post-transcriptional operon.Peer Reviewe
The sex-specific factor SOA controls dosage compensation in <i>Anopheles</i> mosquitos
The Anopheles mosquito is one of thousands of species in which sex differences play a central role in their biology, as only females need a blood meal in order to produce eggs. Sex differentiation is regulated by sex chromosomes, but their presence creates a dosage imbalance between males (XY) and females (XX). Dosage compensation (DC) can re-equilibrate the expression of sex-chromosomal genes, but because DC mechanisms have only been fully characterized in a few model organisms, key questions about its evolutionary diversity and functional necessity remain unresolved 1. Here we report the discovery of a previously uncharacterized gene (SOA, for sex chromosome activation) as a master regulator of DC in the malaria mosquito Anopheles gambiae. Sex-specific alternative splicing prevents functional SOA protein expression in females. The male isoform encodes a DNA-binding protein that binds the promoters of active X chromosomal genes. Expressing male SOA is sufficient to induce DC in female cells. Male mosquitoes lacking SOA or female mosquitos ectopically expressing the male isoform exhibit X chromosome misregulation, which is compatible with viability but causes developmental delay. Thus, our molecular analysis of the first DC master regulator in a non-model organism elucidates the evolutionary steps leading to the establishment of a chromosome-specific fine-tuning mechanism
- …