1,929 research outputs found
An algorithm for calculating the Lorentz angle in silicon detectors
Future experiments will use silicon sensors in the harsh radiation
environment of the LHC (Large Hadron Collider) and high magnetic fields. The
drift direction of the charge carriers is affected by the Lorentz force due to
the high magnetic field. Also the resulting radiation damage changes the
properties of the drift.
In this paper measurements of the Lorentz angle of electrons and holes before
and after irradiation are reviewed and compared with a simple algorithm to
compute the Lorentz angle.Comment: 13 pages, 7 figures, final version accepted by NIMA. Mainly
clarifications included and slightly shortene
Structure and electronic transport in graphene wrinkles
Wrinkling is a ubiquitous phenomenon in two-dimensional membranes. In
particular, in the large-scale growth of graphene on metallic substrates, high
densities of wrinkles are commonly observed. Despite their prevalence and
potential impact on large-scale graphene electronics, relatively little is
known about their structural morphology and electronic properties. Surveying
the graphene landscape using atomic force microscopy, we found that wrinkles
reach a certain maximum height before folding over. Calculations of the
energetics explain the morphological transition, and indicate that the tall
ripples are collapsed into narrow standing wrinkles by van der Waals forces,
analogous to large-diameter nanotubes. Quantum transport calculations show that
conductance through these collapsed wrinkle structures is limited mainly by a
density-of-states bottleneck and by interlayer tunneling across the collapsed
bilayer region. Also through systematic measurements across large numbers of
devices with wide folded wrinkles, we find a distinct anisotropy in their
electrical resistivity, consistent with our transport simulations. These
results highlight the coupling between morphology and electronic properties,
which has important practical implications for large-scale high-speed graphene
electronics.Comment: 5 figures supplemental information in separated fil
Relating 3D Geometry and Photoelectrochemical Activity of WO3-loaded n-Si Nanowires: Design Rules for Photoelectrodes
Nanostructured electrodes for photoelectrochemical (PEC) applications, such as water splitting, have rather low photocurrent density regarding their highly enlarged surface area compared to plain electrodes. This demands for further understanding of the relation between the 3D geometry and the PEC activity. To this end, we fabricate WO3/Si nanowire array photoanodes with various nanowire lengths (1.3 µm, 2.7 µm, 3.2 µm and 3.8 µm) and different WO3 thicknesses (10 nm, 30 nm and 50 nm) using wet chemical etching for nanostructuring of Si and atomic layer deposition for the deposition of WO3. It is found that by increasing the etching time, the nanowires become longer and the top surface area decreases. The photocurrent density first increases and then decreases with increasing Si etching time. This behaviour can be explained by different and opposite effects regarding absorption, geometry and materials specific properties. Particularly, the decrease of the photocurrent density can be due to: First, the longer the nanowires the heavier the recombination of the photogenerated carriers. Second, the long-time Si etching results in a loss of top part of the nanowire arrays. Because of shadowing, the WO3 located at the top part of the nanowires is more effective than that at the bottom part for the WO3/Si nanowire arrays and therefore the photocurrent is decreased. It reveals a trade-off between the top part surface area and the length of the nanowires. This study contributes to a better understand of the relation between the geometry of nanostructures and the performance of PEC electrodes.</p
Diamond thin Film Detectors for Beam Monitoring Devices
Diamonds offer radiation hard sensors, which can be used directly in primary
beams. Here we report on the use of a polycrystalline CVD diamond strip sensor
as beam monitor of heavy ion beams with up to 2.10^9 lead ions per bunch. The
strips allow for a determination of the transverse beam profile to a fraction
of the pitch of the strips, while the timing information yields the
longitudinal bunch length with a resolution of the order of a few mm.Comment: 6 pages, 7 figures, to appear in the Proceedings of the Hasselt
Diamond Workshop (Hasselt, Belgium, Feb. 2006), v4: accidentally submitted
figure, appearing at end, remove
Preferences for different nitrogen forms by co-existing plant species and soil microbes: reply
The growing awareness that plants might use a variety of nitrogen (N) forms, both organic and inorganic, has raised questions about the role of resource partitioning in plant communities. It has been proposed that coexisting plant species might be able to partition a limited N pool, thereby avoiding competition for resources, through the uptake of different chemical forms of N. In this study, we used in situ stable isotope labeling techniques to assess whether coexisting plant species of a temperate grassland (England, UK) display preferences for different chemical forms of N, including inorganic N and a range of amino acids of varying complexity. We also tested whether plants and soil microbes differ in their preference for different N forms, thereby relaxing competition for this limiting resource. We examined preferential uptake of a range of 13C15N-labeled amino acids (glycine, serine, and phenylalanine) and 15N-labeled inorganic N by coexisting grass species and soil microbes in the field. Our data show that while coexisting plant species simultaneously take up a variety of N forms, including inorganic N and amino acids, they all showed a preference for inorganic N over organic N and for simple over the more complex amino acids. Soil microbes outcompeted plants for added N after 50 hours, but in the long term (33 days) the proportion of added 15N contained in the plant pool increased for all N forms except for phenylalanine, while the proportion in the microbial biomass declined relative to the first harvest. These findings suggest that in the longer term plants become more effective competitors for added 15N. This might be due to microbial turnover releasing 15N back into the plant–soil system or to the mineralization and subsequent plant uptake of 15N transferred initially to the organic matter pool. We found no evidence that soil microbes preferentially utilize any of the N forms added, despite previous studies showing that microbial preferences for N forms vary over time. Our data suggest that coexisting plants can outcompete microbes for a variety of N forms, but that such plant species show similar preferences for inorganic over organic N
ALD-grown two-dimensional TiSx metal contacts for MoS2 field-effect transistors
Metal contacts to MoS2 field-effect transistors (FETs) play a determinant role in the device electrical characteristics and need to be chosen carefully. Because of the Schottky barrier (SB) and the Fermi level pinning (FLP) effects that occur at the contact/MoS2 interface, MoS2 FETs often suffer from high contact resistance (Rc). One way to overcome this issue is to replace the conventional 3D bulk metal contacts with 2D counterparts. Herein, we investigate 2D metallic TiSx (x ∼ 1.8) as top contacts for MoS2 FETs. We employ atomic layer deposition (ALD) for the synthesis of both the MoS2 channels as well as the TiSx contacts and assess the electrical performance of the fabricated devices. Various thicknesses of TiSx are grown on MoS2, and the resultant devices are electrically compared to the ones with the conventional Ti metal contacts. Our findings show that the replacement of 5 nm Ti bulk contacts with only ∼1.2 nm of 2D TiSx is beneficial in improving the overall device metrics. With such ultrathin TiSx contacts, the ON-state current (ION) triples and increases to ∼35 μA μm−1. Rc also reduces by a factor of four and reaches ∼5 MΩ μm. Such performance enhancements were observed despite the SB formed at the TiSx/MoS2 interface is believed to be higher than the SB formed at the Ti/MoS2 interface. These device metric improvements could therefore be mainly associated with an increased level of electrostatic doping in MoS2, as a result of using 2D TiSx for contacting the 2D MoS2. Our findings are also well supported by TCAD device simulations.<br/
Effects of Motivational Prompts on Motivation, Effort, and Performance on a Low-Stakes Standardized Test
Increased demands for accountability have placed an emphasis on assessment of student learning outcomes. At the post-secondary level, many of the assessments are considered low-stakes, as student performance is linked to few, if any, individual consequences. Given the prevalence of low-stakes assessment of student learning, research that investigates the relationship between student motivation, effort, and performance on low-stakes tests is warranted as these tests are increasingly being used to make judgments about the quality of student learning. This quasi-experimental study was conducted at a public mid-sized university with 87 undergraduate students enrolled in four 100-level general education courses. The researchers examined the effects of motivational prompts on student motivation, effort, and performance on a low-stakes test. Results indicated that motivational condition had a significant effect on students\u27 performance as measured by total mean scores on a low-stakes standardized test. Students in the personal motivational condition outperformed students in the other conditions. However, motivational prompts were not found to affect students\u27 critical thinking subscores or self-reported effort and importance scores
Assessing the potential of co-composting rose waste as a sustainable waste management strategy:Nutrient availability and disease control
The current limited usage of rose waste makes rose cultivation far from a sustainable circular industry. Unfavorable properties of horticultural waste such as the high lignin content of stems and high polyphenol levels in both flowers and leaves makes it difficult to re-use. These traits hamper an effective composting process and so far little studies have focused on optimizing this process. The aim of this study was to investigate the potential of (co-)composting rose waste with other on-farm available green wastes (tomato and kalanchoe) or mature rose compost to obtain an improved compost with high fertilizing capacity. In a small-scale composting system the evolution of five mixtures was closely monitored in terms of their physico-chemical parameters. The in-vitro disease suppressive capacity of mature rose compost was assessed. All mixtures resulted in stable and mature compost after six months showing industry standard suitable macro- and micro-nutrient concentrations. The matured compost showed a C/N below 10, a strong decrease in polyphenols of ≥70% and a good fertilizing capacity with an increase in cation exchange capacity since the start of ≥100%. These results demonstrate that the ligneous character of rose waste is not preventing an effective composting process. However, an increased duration of the maturation phase might be favored for optimal results. The addition of mature compost accelerated the composting process as shown by significantly increases in OM degradation rates. For the first time a high disease suppressive capacity against several common rose pathogens was shown for mature rose compost. Overall, this study showed the potential of (co-)composting rose waste as sustainable waste management strategy to further improve the circular economy waste-based objectives of the horticultural sector.</p
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