Modeling low energy sputtering of hexagonal boron nitride by xenon ions

The sputtering of hexagonal boron nitride due to low energy xenon ion bombardments occurs in various applications including fabrication of cubic boron nitride and erosion of Hall thruster channel walls. At low ion energies, accurate experimental characterization of sputter yields increases in difficulty due to the low yields involved. A molecular dynamics model is employed to simulate the sputtering process and to calculate sputter yields for ion energies ranging from 10 eV to 350 eV. The results are compared to experimental data and a semi-empirical expression developed by Bohdansky is found to adequately describe the simulation data. Surface temperature effects are also investigated, and the sputter yield at 850 K is approximately twice that at 423 K.Comment: 19 pages, 8 figure

Optical Mass Gauging System for Measuring Liquid Levels in a Reduced Gravity Environment

A compact and rugged fiber-coupled liquid volume sensor designed for flight on a sounding rocket platform is presented. The sensor consists of a Mach-Zehnder interferometer capable of measuring the amount of liquid contained in a tank under any gravitational conditions, including a microgravity environment, by detecting small changes in the index of refraction of the gas contained within a sensing region. By monitoring changes in the interference fringe pattern as the system undergoes a small compression provided by a piston, the ullage volume of a tank can be directly measured allowing for a determination of the liquid volume. To demonstrate the technique, data are acquired using two tanks containing different volumes of liquid, which are representative of the levels of liquid in a tank at different time periods during a mission. The two tanks are independently exposed to the measurement apparatus, allowing for a determination of the liquid level in each. In a controlled, laboratory test of the unit, the system demonstrated a capability of measuring a liquid level in an individual tank of 10.53 mL with a 2% error. The overall random uncertainty for the flight system is higher than that one test, at +/- 1.5 mL

Analytical and discrete solutions for the incipient motion of ellipsoidal sediment particles

[EN] This work introduces analytical and numerical approaches to compute the incipient motion of ellipsoidal sediment particles. Initiation of motion of spherical particles is dominated by rolling mode. However, solutions for initiation of motion for non-spherical grains have to incorporate rolling, sliding, and mixed modes. The proposed approaches include a wide variety of shapes and inclinations that represent realistic configurations of sediment bed layers. The numerical procedure is based on the discrete element method, simulating the micro-mechanics of the sediment as an aggregate of rigid ellipsoids interacting by contact. The numerical solution covers a range of incipient movements that cannot be covered by the analytical approach. Hence, some trapped modes observed in analytical calculations are complemented by the numerical computation of threshold stresses. The main results are organized as novel extended Shields diagrams for non-spherical grains, where non-dimensional critical shear stress is represented in terms of friction Reynolds number.This work was supported by the Ministerio de Ciencia e Innovación Grant [#BIA-2012-32918 and #BIA-2015-64994-P (MINECO/FEDER)].Bravo, R.; Ortiz, P.; Pérez-Aparicio, JL. (2018). Analytical and discrete solutions for the incipient motion of ellipsoidal sediment particles. Journal of Hydraulic Research. 56(1):29-43. https://doi.org/10.1080/00221686.2017.1289263S2943561Belytschko, T., & Neal, M. O. (1991). Contact-impact by the pinball algorithm with penalty and Lagrangian methods. International Journal for Numerical Methods in Engineering, 31(3), 547-572. doi:10.1002/nme.1620310309Bravo, R., Ortiz, P., & Pérez-Aparicio, J. L. (2014). Incipient sediment transport for non-cohesive landforms by the discrete element method (DEM). Applied Mathematical Modelling, 38(4), 1326-1337. doi:10.1016/j.apm.2013.08.010Bravo, R., Pérez-Aparicio, J. L., & Gómez-Hernández, J. J. (2015). Numerical sedimentation particle-size analysis using the Discrete Element Method. Advances in Water Resources, 86, 58-72. doi:10.1016/j.advwatres.2015.09.024Bravo, R., Pérez-Aparicio, J. L., & Laursen, T. A. (2012). An energy consistent frictional dissipating algorithm for particle contact problems. International Journal for Numerical Methods in Engineering, 92(9), 753-781. doi:10.1002/nme.4346Buffington, J. M., & Montgomery, D. R. (1997). A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bedded rivers. Water Resources Research, 33(8), 1993-2029. doi:10.1029/96wr03190Cheng, N.-S., & Chiew, Y.-M. (1999). Incipient sediment motion with upward seepage. Journal of Hydraulic Research, 37(5), 665-681. doi:10.1080/00221689909498522Chiew, Y.-M., & Parker, G. (1994). Incipient sediment motion on non-horizontal slopes. Journal of Hydraulic Research, 32(5), 649-660. doi:10.1080/00221689409498706Derksen, J. J. (2015). Simulations of granular bed erosion due to a mildly turbulent shear flow. Journal of Hydraulic Research, 53(5), 622-632. doi:10.1080/00221686.2015.1077354Dey, S. (1999). Sediment threshold. Applied Mathematical Modelling, 23(5), 399-417. doi:10.1016/s0307-904x(98)10081-1Dey, S. (2003). Threshold of sediment motion on combined transverse and longitudinal sloping beds. Journal of Hydraulic Research, 41(4), 405-415. doi:10.1080/00221680309499985Dey, S., Sarker, H. K. D., & Debnath, K. (1999). Sediment Threshold under Stream Flow on Horizontal and Sloping Beds. Journal of Engineering Mechanics, 125(5), 545-553. doi:10.1061/(asce)0733-9399(1999)125:5(545)Hölzer, A., & Sommerfeld, M. (2008). New simple correlation formula for the drag coefficient of non-spherical particles. Powder Technology, 184(3), 361-365. doi:10.1016/j.powtec.2007.08.021James, C. S. (1990). Prediction of entrainment conditions for nonuniform, noncohesive sediments. Journal of Hydraulic Research, 28(1), 25-41. doi:10.1080/00221689009499145Ji, C., Munjiza, A., Avital, E., Ma, J., & Williams, J. J. R. (2013). Direct numerical simulation of sediment entrainment in turbulent channel flow. Physics of Fluids, 25(5), 056601. doi:10.1063/1.4807075Klamkin, M. S. (1971). Elementary Approximations to the Area of N-Dimensional Ellipsoids. The American Mathematical Monthly, 78(3), 280. doi:10.2307/2317530Mandø, M., & Rosendahl, L. (2010). On the motion of non-spherical particles at high Reynolds number. Powder Technology, 202(1-3), 1-13. doi:10.1016/j.powtec.2010.05.001MILLER, M. C., McCAVE, I. N., & KOMAR, P. D. (1977). Threshold of sediment motion under unidirectional currents. Sedimentology, 24(4), 507-527. doi:10.1111/j.1365-3091.1977.tb00136.xWan Mohtar, W. H. M., & Munro, R. J. (2013). Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence. Physics of Fluids, 25(1), 015103. doi:10.1063/1.4774341Ortiz, P., & Smolarkiewicz, P. K. (2006). Numerical simulation of sand dune evolution in severe winds. International Journal for Numerical Methods in Fluids, 50(10), 1229-1246. doi:10.1002/fld.1138Ortiz, P., & Smolarkiewicz, P. K. (2009). Coupling the dynamics of boundary layers and evolutionary dunes. Physical Review E, 79(4). doi:10.1103/physreve.79.041307Van Rijn, L. C. (1984). Sediment Transport, Part I: Bed Load Transport. Journal of Hydraulic Engineering, 110(10), 1431-1456. doi:10.1061/(asce)0733-9429(1984)110:10(1431)Shi, G.-H., & Goodman, R. E. (1985). Two dimensional discontinuous deformation analysis. International Journal for Numerical and Analytical Methods in Geomechanics, 9(6), 541-556. doi:10.1002/nag.1610090604Shields, A. (1936). Application of similarity principles and turbulence research to bed-load movement (Tech. Rep.). Lab. for Hydraulic Water Resources.Wellmann, C., Lillie, C., & Wriggers, P. (2008). A contact detection algorithm for superellipsoids based on the common‐normal concept. Engineering Computations, 25(5), 432-442. doi:10.1108/02644400810881374Wiberg, P. L., & Smith, J. D. (1985). A theoretical model for saltating grains in water. Journal of Geophysical Research, 90(C4), 7341. doi:10.1029/jc090ic04p0734

Associations with photoreceptor thickness measures in the UK Biobank.

Spectral-domain OCT (SD-OCT) provides high resolution images enabling identification of individual retinal layers. We included 32,923 participants aged 40-69 years old from UK Biobank. Questionnaires, physical examination, and eye examination including SD-OCT imaging were performed. SD OCT measured photoreceptor layer thickness includes photoreceptor layer thickness: inner nuclear layer-retinal pigment epithelium (INL-RPE) and the specific sublayers of the photoreceptor: inner nuclear layer-external limiting membrane (INL-ELM); external limiting membrane-inner segment outer segment (ELM-ISOS); and inner segment outer segment-retinal pigment epithelium (ISOS-RPE). In multivariate regression models, the total average INL-RPE was observed to be thinner in older aged, females, Black ethnicity, smokers, participants with higher systolic blood pressure, more negative refractive error, lower IOPcc and lower corneal hysteresis. The overall INL-ELM, ELM-ISOS and ISOS-RPE thickness was significantly associated with sex and race. Total average of INL-ELM thickness was additionally associated with age and refractive error, while ELM-ISOS was additionally associated with age, smoking status, SBP and refractive error; and ISOS-RPE was additionally associated with smoking status, IOPcc and corneal hysteresis. Hence, we found novel associations of ethnicity, smoking, systolic blood pressure, refraction, IOPcc and corneal hysteresis with photoreceptor thickness

Derived coisotropic structures I: affine case

We define and study coisotropic structures on morphisms of commutative dg algebras in the context of shifted Poisson geometry, i.e. $P_n$-algebras. Roughly speaking, a coisotropic morphism is given by a $P_{n+1}$-algebra acting on a $P_n$-algebra. One of our main results is an identification of the space of such coisotropic structures with the space of Maurer--Cartan elements in a certain dg Lie algebra of relative polyvector fields. To achieve this goal, we construct a cofibrant replacement of the operad controlling coisotropic morphisms by analogy with the Swiss-cheese operad which can be of independent interest. Finally, we show that morphisms of shifted Poisson algebras are identified with coisotropic structures on their graph.Comment: 49 pages. v2: many proofs rewritten and the paper is split into two part

Assessment of Methods Used in 1D Models for Computing Bed-Load Transport in a Large River: The Danube River in Slovakia

Comprehensive measurements of bedload sediment transport through a section of the Danube River, located approximately 70km downstream from Bratislava, Slovakia, are used to assess the accuracy of bedload formulae implemented in 1D modelling. Depending on water discharge and water level, significant variations in the distribution of bedload across the section were observed. It appeared that, whatever the water discharge, the bed shear stress tau is always close to the estimated critical bed shear stress for the initiation of sediment transport . The discussion focusses on the methods used in 1D models for estimating bedload transport. Though usually done, the evaluation of bedload transport using the mean cross-sectional bed shear stress yields unsatisfactory results. It is necessary to use an additional model to distribute the bed shear stress across the section and calculate bedload locally. Bedload predictors also need to be accurate for tau close to tau. From that point of view, bedload formulae based on an exponential decrease of bedload transport close to tau appear to be more appropriate than models based on excess bed shear stress. A discussion on the bedload formula capability to reproduce grain sorting is also provided

Estimating Exposome Score for Schizophrenia Using Predictive Modeling Approach in Two Independent Samples: The Results From the EUGEI Study

Exposures constitute a dense network of the environment: exposome. Here, we argue for embracing the exposome paradigm to investigate the sum of nongenetic "risk" and show how predictive modeling approaches can be used to construct an exposome score (ES; an aggregated score of exposures) for schizophrenia. The training dataset consisted of patients with schizophrenia and controls, whereas the independent validation dataset consisted of patients, their unaffected siblings, and controls. Binary exposures were cannabis use, hearing impairment, winter birth, bullying, and emotional, physical, and sexual abuse along with physical and emotional neglect. We applied logistic regression (LR), Gaussian Naive Bayes (GNB), the least absolute shrinkage and selection operator (LASSO), and Ridge penalized classification models to the training dataset. ESs, the sum of weighted exposures based on coefficients from each model, were calculated in the validation dataset. In addition, we estimated ES based on meta-analyses and a simple sum score of exposures. Accuracy, sensitivity, specificity, area under the receiver operating characteristic, and Nagelkerke's R2 were compared. The ESMeta-analyses performed the worst, whereas the sum score and the ESGNB were worse than the ESLR that performed similar to the ESLASSO and ESRIDGE. The ESLR distinguished patients from controls (odds ratio [OR] = 1.94, P < .001), patients from siblings (OR = 1.58, P < .001), and siblings from controls (OR = 1.21, P = .001). An increase in ESLR was associated with a gradient increase of schizophrenia risk. In reference to the remaining fractions, the ESLR at top 30%, 20%, and 10% of the control distribution yielded ORs of 3.72, 3.74, and 4.77, respectively. Our findings demonstrate that predictive modeling approaches can be harnessed to evaluate the exposome

Digital karyotyping reveals probable target genes at 7q21.3 locus in hepatocellular carcinoma

<p>Abstract</p> <p>Background</p> <p>Hepatocellular carcinoma (HCC) is a worldwide malignant liver tumor with high incidence in China. Subchromosomal amplifications and deletions accounted for major genomic alterations occurred in HCC. Digital karyotyping was an effective method for analyzing genome-wide chromosomal aberrations at high resolution.</p> <p>Methods</p> <p>A digital karyotyping library of HCC was constructed and 454 Genome Sequencer FLX System (Roche) was applied in large scale sequencing of the library. Digital Karyotyping Data Viewer software was used to analyze genomic amplifications and deletions. Genomic amplifications of genes detected by digital karyotyping were examined by real-time quantitative PCR. The mRNA expression level of these genes in tumorous and paired nontumorous tissues was also detected by real-time quantitative RT-PCR.</p> <p>Results</p> <p>A total of 821,252 genomic tags were obtained from the digital karyotyping library of HCC, with 529,162 tags (64%) mapped to unique loci of human genome. Multiple subchromosomal amplifications and deletions were detected through analyzing the digital karyotyping data, among which the amplification of 7q21.3 drew our special attention. Validation of genes harbored within amplicons at 7q21.3 locus revealed that genomic amplification of SGCE, PEG10, DYNC1I1 and SLC25A13 occurred in 11 (21%), 11 (21%), 11 (21%) and 23 (44%) of the 52 HCC samples respectively. Furthermore, the mRNA expression level of SGCE, PEG10 and DYNC1I1 were significantly up-regulated in tumorous liver tissues compared with corresponding nontumorous counterparts.</p> <p>Conclusions</p> <p>Our results indicated that subchromosomal region of 7q21.3 was amplified in HCC, and SGCE, PEG10 and DYNC1I1 were probable protooncogenes located within the 7q21.3 locus.</p

The impact of non-equilibrium flow on the structure of turbulence over river dunes

This piece of research expands our description of how rivers flow over dunes on a river bed. Most of the scientific communities' research to date has used unnaturally steady conditions to measure how water moves over dunes. Yet these flow conditions are not strictly true to the variety of conditions nature produces, most importantly during floods. This research is the first detailed description of a wide range of flow states over dunes, and changes our present understanding of the structure of flow over dunes in rivers. Consequently, the scientific community will be able to use this new information to better model and simulate how rivers work, how they flood, and how they transport sediment towards the worlds deltas

Distributed Stochastic Power Control in Ad-hoc Networks: A Nonconvex Case

Utility-based power allocation in wireless ad-hoc networks is inherently nonconvex because of the global coupling induced by the co-channel interference. To tackle this challenge, we first show that the globally optimal point lies on the boundary of the feasible region, which is utilized as a basis to transform the utility maximization problem into an equivalent max-min problem with more structure. By using extended duality theory, penalty multipliers are introduced for penalizing the constraint violations, and the minimum weighted utility maximization problem is then decomposed into subproblems for individual users to devise a distributed stochastic power control algorithm, where each user stochastically adjusts its target utility to improve the total utility by simulated annealing. The proposed distributed power control algorithm can guarantee global optimality at the cost of slow convergence due to simulated annealing involved in the global optimization. The geometric cooling scheme and suitable penalty parameters are used to improve the convergence rate. Next, by integrating the stochastic power control approach with the back-pressure algorithm, we develop a joint scheduling and power allocation policy to stabilize the queueing systems. Finally, we generalize the above distributed power control algorithms to multicast communications, and show their global optimality for multicast traffic.Comment: Contains 12 pages, 10 figures, and 2 tables; work submitted to IEEE Transactions on Mobile Computin