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

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

One-dimensional metal-organic framework photonic crystals used as platforms for vapor sorption.

We present the fabrication of one-dimensional photonic crystals (Bragg stacks) based on a microporous metal–organic framework material and mesoporous titanium dioxide. The Bragg stack heterostructures were obtained using two complementary synthesis approaches utilizing the bottom-up assembly of heterogeneous, i.e. two-component photonic crystal multilayer structures. Zeolitic imidazolate framework ZIF-8 and mesoporous titanium dioxide were chosen as functional components with different refractive indices. While ZIF-8 is intended to impart molecular selectivity, mesoporous TiO2 is used to ensure high refractive index contrast and to guarantee molecular diffusion within the Bragg stack. The combination of micro- and mesoporosity within one scaffold endows the 1D-MOF PC with characteristic adsorption properties upon exposure to various organic vapors. In this context, the sorption behavior of the photonic material was studied as a function of partial pressure of organic vapors. The results show that the multilayered photonic heterostructures are sensitive and selective towards a series of chemically similar solvent vapors. It is thus anticipated that the concept of multilayer heterogeneous photonic structures will provide a versatile platform for future selective, label-free optical sensors

TiO2/Cu2O all-oxide heterojunction solar cells produced by spray pyrolysis

n/