10,458 research outputs found

    Coordinated NanoSIMS and TEM Analysis of a Large 26Mg-Rich AGB Silicate from the Meteorite Hills 00426 CR2 Chondrite

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    Silicates are one of the most abundant presolar phases around evolved stars, in the inter-stellar medium (ISM), and in our Solar System. These grains afford the opportunity for O, Si, Mg, Fe, and Ca isotopic analyses to constrain stellar nucleosynthetic and mixing processes, and Galactic chemical evolution (GCE). While Mg and Fe isotopic studies have been successfully conducted on presolar silicates, isotopic analyses beyond O and Si are often hampered by the small grain sizes (average ~250 nm). This also makes coordinated mineral and chemical characterization challenging. These studies provide insight into the dust condensation conditions as well as subsequent alteration in the ISM and/or the Solar System. TEM studies of presolar silicates have shown that they are much more mineralogically and chemically diverse than other presolar phases [1 and references therein]. Large (>500nm) presolar silicate grains are rare, but they allow for detailed isotopic, mineral, and chemical characterization. We identified a large presolar silicate grain in the MET 00426 CR2 chondrite and report the O, Si, Mg, and Fe isotopic compositions and TEM study of this grain

    Mathematical models for the synthesis and optimization of spiral bevel gear tooth surfaces

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    The geometry of spiral bevel gears and to their rational design are studied. The nonconjugate tooth surfaces of spiral bevel gears are, in theory, replaced (or approximated) by conjugated tooth surfaces. These surfaces can be generated by two conical surfaces, and by a conical surface and a revolution. Although these conjugated tooth surfaces are simpler than the actual ones, the determination of their principal curvatures and directions is still a complicated problem. Therefore, a new approach, to the solution of these is proposed. Direct relationships between the principal curvatures and directions of the tool surface and those of the generated gear surface are obtained. With the aid of these analytical tools, the Hertzian contact problem for conjugate tooth surfaces can be solved. These results are useful in determining compressive load capacity and surface fatigue life of spiral bevel gears. A general theory of kinematical errors exerted by manufacturing and assembly errors is developed. This theory is used to determine the analytical relationship between gear misalignments and kinematical errors. This is important to the study of noise and vibration in geared systems

    An Efficient Data Aggregation Algorithm for Cluster-based Sensor Network

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    Data aggregation in wireless sensor networks eliminates redundancy to improve bandwidth utilization and energy-efficiency of sensor nodes. One node, called the cluster leader, collects data from surrounding nodes and then sends the summarized information to upstream nodes. In this paper, we propose an algorithm to select a cluster leader that will perform data aggregation in a partially connected sensor network. The algorithm reduces the traffic flow inside the network by adaptively selecting the shortest route for packet routing to the cluster leader. We also describe a simulation framework for functional analysis of WSN applications taking our proposed algorithm as an exampl

    Adjusting the frequency of mammography screening on the basis of genetic risk: Attitudes among women in the UK.

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    Purpose To explore public attitudes towards modifying frequency of mammography screening based on genetic risk. Methods Home-based interviews were carried out with a population-based sample of 942 women aged 18ā€“74 years in the UK. Demographic characteristics and perceived breast cancer (BC) risk were examined as predictors of support for risk-stratified BC screening and of the acceptability of raised or lowered screening frequency based on genetic risk, using multivariate logistic regression. Results Over two-thirds of respondents (65.8%) supported the idea of varying screening frequency on the basis of genetic risk. The majority (85.4%) were willing to have more frequent breast screening if they were found to be at higher risk, but fewer (58.8%) were willing to have less frequent screening if at lower risk (t (956) = 15.6, p < 0.001). Ethnic minority status was associated with less acceptability of more frequent screening (OR = 0.40, 95% CI = 0.21ā€“0.74), but there were no other significant demographic correlates. Higher perceived risk of BC was associated with greater acceptability of more frequent screening (OR = 1.71, 95%CI = 1.27ā€“2.30). Conclusion Women were positive about adjusting the frequency of mammography screening in line with personal genetic risk, but it will be important to develop effective communication materials to minimise resistance to reducing screening frequency for those at lower genetic risk

    Gathering experience in trust-based interactions

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    As advances in mobile and embedded technologies coupled with progress in adhoc networking fuel the shift towards ubiquitous computing systems it is becoming increasingly clear that security is a major concern. While this is true of all computing paradigms, the characteristics of ubiquitous systems amplify this concern by promoting spontaneous interaction between diverse heterogeneous entities across administrative boundaries [5]. Entities cannot therefore rely on a specific control authority and will have no global view of the state of the system. To facilitate collaboration with unfamiliar counterparts therefore requires that an entity takes a proactive approach to self-protection. We conjecture that trust management is the best way to provide support for such self-protection measures

    Engineered valley-orbit splittings in quantum confined nanostructures in silicon

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    An important challenge in silicon quantum electronics in the few electron regime is the potentially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding the "valley-orbit" (VO) gap is essential for silicon qubits, as a large VO gap prevents leakage of the qubit states into a higher dimensional Hilbert space. The VO gap varies considerably depending on quantum confinement, and can be engineered by external electric fields. In this work we investigate VO splitting experimentally and theoretically in a range of confinement regimes. We report measurements of the VO splitting in silicon quantum dot and donor devices through excited state transport spectroscopy. These results are underpinned by large-scale atomistic tight-binding calculations involving over 1 million atoms to compute VO splittings as functions of electric fields, donor depths, and surface disorder. The results provide a comprehensive picture of the range of VO splittings that can be achieved through quantum engineering.Comment: 4 pages, 4 figure

    Berudu Anura di Sungai Kedurang, Bengkulu Selatan dan Pusat Pendidikan Konservasi Alam Bodogol, Jawa Barat

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    This paper aims is to identify and to describe morphological characteristic of tadpoles in Kedurang River, South Bengkulu and Cisuren River, PPKA Bodogol. Visual Encounter Survey along the river method was used to collect the sample of tadpoles. Three species were found in both rivers, namely Bufo melanostictus, Limnonectes sp. and Rhacophorus sp

    Lifetime enhanced transport in silicon due to spin and valley blockade

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    We report the observation of Lifetime Enhanced Transport (LET) based on perpendicular valleys in silicon by transport spectroscopy measurements of a two-electron system in a silicon transistor. The LET is manifested as a peculiar current step in the stability diagram due to a forbidden transition between an excited state and any of the lower energy states due perpendicular valley (and spin) configurations, offering an additional current path. By employing a detailed temperature dependence study in combination with a rate equation model, we estimate the lifetime of this particular state to exceed 48 ns. The two-electron spin-valley configurations of all relevant confined quantum states in our device were obtained by a large-scale atomistic tight-binding simulation. The LET acts as a signature of the complicated valley physics in silicon; a feature that becomes increasingly important in silicon quantum devices.Comment: 4 pages, 4 figures. (The current version (v3) is the result of splitting up the previous version (v2), and has been completely rewritten

    Digital contact tracing technology in the COVID-19 pandemic: a systematic review

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    Introduction: The COVID-19 pandemic prompted public health teams across the world to emphasize case identification, contact tracing, and isolation in outbreak management strategies. Contact tracing was advanced by global access to mobile phones to develop and implement digital contact tracing (DCT) technology with the objective of increasing the rate of contact tracing while reducing the resources required. Purpose: This study aimed to describe the DCT technology used during the COVID-19 pandemic across the world, and to identify differences and similarities between characteristics and uses. Methods: This review followed the PRISMA (2020) guidelines for systematic reviews. Literature searches were conducted using Embase, MEDLINE, and PubMed and were restricted to English studies published between 2019 to 2023. Studies were excluded if they did not report findings for DCT during COVID-19, did not provide data for technology characteristics or outcomes, or were a study design listed for exclusion. Results: Sixty one studies were included in the review producing results for 147 digital contact tracing technologies across 83 countries. The majority of digital contact tracing (DCT) technologies are government-owned (75.6%), primarily developed for COVID-19 tracing (96.4%). Bluetooth is the most favored technology (70%) used in their development, followed by GPS (30%) and QR codes (22%). Applications are the preferred platform (90.9%), with a few using applets (6.3%) and wearable devices (1.4%). Only 2 DCT technologies have achieved over 100 million downloads or uses (3.1%). Most DCTs fall into the 1ā€“9.99 million downloads range (27.7%) and 10,000ā€“99,999 downloads (20%). The majority of DCTs are voluntarily used by the population (63.6%), while 27.3% are mandated for use. Conclusions: Digital contact tracing technologies were developed and implemented globally as a strategy in emergency outbreak management to reduce the spread of disease. This review describes the use of DCT across the world by identifying key features and characteristics that will serve as a lesson learned for improvement of existing DCT technologies for other emergency response outbreak management
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