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wave reflection

A Keerthi, A K Geim, A Janardanan, A P Rooney, A Esfandiar, S Hu, S A Dar, I V Grigorieva, S J Haigh, F C Wang, B Radha
Gas permeation through nanoscale pores is ubiquitous in nature and has an important role in many technologies1,2 . Because the pore size is typically smaller than the mean free path of gas molecules, the flow of the gas molecules is conventionally described by Knudsen theory, which assumes diffuse reflection (random-angle scattering) at confining walls3-7 . This assumption holds surprisingly well in experiments, with only a few cases of partially specular (mirror-like) reflection known5,8-11 . Here we report gas transport through ångström-scale channels with atomically flat walls12,13 and show that surface scattering can be either diffuse or specular, depending on the fine details of the atomic landscape of the surface, and that quantum effects contribute to the specularity at room temperature...
June 2018: Nature
Valeria Aparecida Costa-Hong, Henrique Cotchi Simbo Muela, Thiago Andrade Macedo, Allan Robson Kluser Sales, Luiz Aparecido Bortolotto
BACKGROUND: Evidences suggest that central hemodynamics indexes are independent predictors of future cardiovascular events and all-cause mortality. Multiple factors have been pointed to have potential influence on central aortic function: height, heart rate, left ventricular ejection duration and blood pressure level. Data related to the influence of gender and postmenopausal status on aortic waveform reflection is scarce. We aim to evaluate the impact of gender and menopause on central blood pressure of hypertensive patients...
June 19, 2018: BMC Cardiovascular Disorders
Yan Xiong, Qing Wang, Ming Duan, Jun Tan, Shenwen Fang, Jiayi Wu
An interface research method based on total internal reflection induced evanescent wave (TIR-EW) is developed to monitor the adsorption behavior of azo dye at the silica-water interface. The monitoring system is constructed by employing silica optical fiber (SOF) as both charged substrate for dye adsorption and light transmission waveguide for evanescent wave production. According to the change of evanescent wave intensity and followed by Beer's law, the methylene blue (MB) adsorption behavior can be real-time monitored at the silica-water interface...
June 19, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
D Mencarelli, B Djafari-Rouhani, Y Pennec, A Pitanti, S Zanotto, M Stocchi, L Pierantoni
In this contribution, a rigorous numerical calibration is proposed to characterize the excitation of propagating mechanical waves by interdigitated transducers (IDTs). The transition from IDT terminals to phonon waveguides is modeled by means of a general circuit representation that makes use of Scattering Matrix (SM) formalism. In particular, the three-step calibration approach called the Thru-Reflection-Line (TRL), that is a well-established technique in microwave engineering, has been successfully applied to emulate typical experimental conditions...
June 18, 2018: Scientific Reports
Noreen Goldman, Dana A Glei, Maxine Weinstein
Although there is little dispute about the impact of the US opioid epidemic on recent mortality, there is less consensus about whether trends reflect increasing despair among American adults. The issue is complicated by the absence of established scales or definitions of despair as well as a paucity of studies examining changes in psychological health, especially well-being, since the 1990s. We contribute evidence using two cross-sectional waves of the Midlife in the United States (MIDUS) study to assess changes in measures of psychological distress and well-being...
June 18, 2018: Proceedings of the National Academy of Sciences of the United States of America
Matin Amani, Chaoliang Tan, George Zhang, Chunsong Zhao, James Bullock, Xiaohui Song, Hyungjin Kim, Vivek Raj Shrestha, Yang Gao, Kenneth B Crozier, Mary Scott, Ali Javey
Two-dimensional (2D) materials, particularly black phosphorous (bP), have demonstrated themselves to be excellent candidates for high-performance infrared photodetectors and transistors. However, high-quality bP can be only obtained via mechanical exfoliation from high temperature- and high-pressure-grown bulk crystals and degrades rapidly when exposed to ambient conditions. Here, we report solution-synthesized and air-stable quasi-2D tellurium (Te) nanoflakes for short-wave infrared (SWIR) photodetectors. We perform comprehensive optical characterization via polarization-resolved transmission and reflection measurements, and report the absorbance and complex refractive index of Te crystals...
June 18, 2018: ACS Nano
Elizabeth A Mumford, Bruce G Taylor, Weiwei Liu, Peggy C Giordano
The purpose of this study was to assess the longitudinal association between adolescent dating relationship dynamics (measures of intimacy and problem dynamics), mental health, and physical and/or sexual victimization by a dating partner. Gender-stratified analyses were conducted in a sample of 261 adolescents, ages 10-18 at baseline, interviewed in three annual waves (2013-2015) of the nationally representative Survey on Teen Relationships and Intimate Violence (STRiV). Among male daters, better mental health at baseline was negatively associated with problem dynamics at follow-up, and aspects of problem dynamics at baseline predicted worse mental health at follow-up...
June 17, 2018: Journal of Research on Adolescence: the Official Journal of the Society for Research on Adolescence
D Veysset, U Gutiérrez-Hernández, L Dresselhaus-Cooper, F De Colle, S Kooi, K A Nelson, P A Quinto-Su, T Pezeril
In this study a single laser pulse spatially shaped into a ring is focused into a thin water layer, creating an annular cavitation bubble and cylindrical shock waves: an outer shock that diverges away from the excitation laser ring and an inner shock that focuses towards the center. A few nanoseconds after the converging shock reaches the focus and diverges away from the center, a single bubble nucleates at the center. The inner diverging shock then reaches the surface of the annular laser-induced bubble and reflects at the boundary, initiating nucleation of a tertiary bubble cloud...
May 2018: Physical Review. E
Xiutao Lou, Chen Chen, Yabo Feng, Yongkang Dong
We present a novel method based on optical frequency-modulated continuous-wave interferometry that can realize simultaneous measurement of gas absorption spectra and optical path lengths (OPLs) in the widely used multipass cells (MPCs). This method involves a Fourier transform (FT) and an inverse FT, by which the gas absorption spectrum and the OPL are retrieved in frequency and time domains, respectively. Various OPLs are achieved by retrieving gas absorption spectra associated with different reflection positions in the MPC...
June 15, 2018: Optics Letters
L De Angelis, L Kuipers
Vortices, phase singularities, and topological defects of any kind often reflect information that is crucial for understanding physical systems in which such entities arise. With near-field experiments supported by numerical calculations, we determine the fluctuations of the topological charge for phase singularities in isotropic random waves as a function of the size R of the observation window. We demonstrate that for two-dimensional fields such fluctuations increase with a superlinear scaling law, consistent with a R log R behavior...
June 15, 2018: Optics Letters
Jun Cao, Fenghua Qi, Senlin Yan, Lifa Zhang
There is growing interest in designing waveguide couplers with low reflections. Using impedance-tunable transformation optics, we propose a coordinate transformation technique in the design of compact three-dimensional waveguide couplers. To transmit electromagnetic waves between two coaxial waveguides with different inner and outer radii in the microwave range, a suitable impedance function is derived to reduce the impedance mismatch at the boundary, which make the fabrication process being simplified due to the reduced set of transformation media(dielectric response materials only)...
June 14, 2018: Scientific Reports
Yin Zhang, Junming Zhao, Jie Cao, Bo Mao
In this work, we propose a metamaterial absorber at microwave frequencies with significant sensitivity and non-destructive sensing capability for grain samples. This absorber is composed of cross-resonators periodically arranged on an ultrathin substrate, a sensing layer filled with grain samples, and a metal ground. The cross-resonator array is fabricated using the printed circuit board process on an FR-4 board. The performance of the proposed metamaterial is demonstrated with both full-wave simulation and measurement results, and the working mechanism is revealed through multi-reflection interference theory...
June 12, 2018: Sensors
Anowarul Habib, Sanat Wagle, Adit Decharat, Frank Melandsø
High-frequency unfocused polymer array transducers are developed using an adhesive-free layer-by-layer assembly method. The current paper focuses on experimental and numerical methods for measuring the acoustic performance of these types of array transducers. Two different types of numerical approaches were used to simulate the transducer performance, including a finite element method (FEM) study of the transducer response done in COMSOL 5.2a Multiphysics, and modeling of the excited ultrasonic pressure fields using the open source software k-Wave 1...
June 12, 2018: Sensors
Thomas C Gent, Mojtaba Bandarabadi, Carolina Gutierrez Herrera, Antoine R Adamantidis
Slow waves (0.5-4 Hz) predominate in the cortical electroencephalogram during non-rapid eye movement (NREM) sleep in mammals. They reflect the synchronization of large neuronal ensembles alternating between active (UP) and quiescent (Down) states and propagating along the neocortex. The thalamic contribution to cortical UP states and sleep modulation remains unclear. Here we show that spontaneous firing of centromedial thalamus (CMT) neurons in mice is phase-advanced to global cortical UP states and NREM-wake transitions...
June 11, 2018: Nature Neuroscience
Stella Y Sun, Jason T Kaelber, Muyuan Chen, Xiaoduo Dong, Yasaman Nematbakhsh, Jian Shi, Matthew Dougherty, Chwee Teck Lim, Michael F Schmid, Wah Chiu, Cynthia Y He
In the unicellular parasite Trypanosoma brucei, the causative agent of human African sleeping sickness, complex swimming behavior is driven by a flagellum laterally attached to the long and slender cell body. Using microfluidic assays, we demonstrated that T. brucei can penetrate through an orifice smaller than its maximum diameter. Efficient motility and penetration depend on active flagellar beating. To understand how active beating of the flagellum affects the cell body, we genetically engineered T. brucei to produce anucleate cytoplasts (zoids and minis) with different flagellar attachment configurations and different swimming behaviors...
June 11, 2018: Proceedings of the National Academy of Sciences of the United States of America
Huihui Liu, Yajing Li, Mengwei Yuan, Genban Sun, Huifeng Li, Shulan Ma, Qingliang Liao, Yue Zhang
The electrospinning and annealing methods is applied to prepare cobalt nanoparticles decorated in N-doped carbon nanofibers (Co/N-C NFs) with solid and macroporous structures. In detail, the nanocomposites are synthesized by carbonization of as-electrospun polyacrylonitrile (PAN)/cobalt acetylacetonate nanofibers in an argon atmosphere. The solid Co/N-C NFs has lengths up to dozens of microns with the average diameter of ca. 500 nm and possess abundant cobalt nanoparticles on both the surface and within the fibers, and the cobalt nanoparticles size is about 20 nm...
June 11, 2018: ACS Applied Materials & Interfaces
Magdalena A Lazarewicz, Dorota Wlodarczyk, Joanna Chylinska, Mariusz Jaworski, Marta Rzadkiewicz, Miroslawa Adamus, GØrill Haugan, Monica Lillefjell, Geir A Espnes
AIMS: Patients' attitude towards treatment and health (ATH) is crucial for compliance at all stages of treatment. This study examined the psychometric properties of the developed PRACTA Attitude Towards Treatment and Health questionnaire, designed to measure ATH as perceived by seniors (PRACTA-ATH) and doctors (PRACTA-ATH-D) in primary health care. METHODS: The data were collected in two waves of the Polish-Norwegian PRACTA project. Exploratory factor analyses (EFAs) were conducted on wave 1 data from senior patients ( n = 3392) and their general practitioners ( n = 491)...
June 1, 2018: Scandinavian Journal of Public Health
Alys R Clark, Joanna L James, Gordon N Stevenson, Sally L Collins
INTRODUCTION: Uterine artery (UtA) Doppler indices are one of the most commonly employed screening tests for pre-eclampsia worldwide. Abnormal indices appear to result from increased uterine vascular resistance, but anatomical complexity and lack of appropriate animal models mean that little is known about the relative contribution of each of the components of the uterine vasculature to the overall UtA Doppler waveform. Previous computational models suggested that trophoblast-mediated spiral artery remodeling has a dominant effect on the UtA Doppler waveform...
June 2018: Placenta
Jung-Hwan Oh, Jieun Kim, Hyeongrae Lee, Yeonjune Kang, Il-Kwon Oh
Innovative sound absorbers, the design of which is based on carbon nanotubes and graphene derivatives, could be used to make more efficient sound absorbing materials, because of their excellent intrinsic mechanical and chemical properties. However, controlling the directional alignments of low-dimensional carbon nanomaterials, such as restacking, alignment, and dispersion, has been a challenging problem when developing sound absorbing forms. Herein, we present the directionally antagonistic graphene oxide-polyurethane hybrid aerogel we developed as a sound absorber, the physical properties of which differ according to the alignment of the microscopic graphene oxide sheets...
June 8, 2018: ACS Applied Materials & Interfaces
Karen E Charlton, Lisa J Ware, Jeannine Baumgartner, Marike Cockeran, Aletta E Schutte, Nirmala Naidoo, Paul Kowal
The iodine status of populations is conventionally assessed using spot urinary samples to obtain a median urinary iodine concentration (UIC) value, which is assessed against standard reference cut-offs. The assumption that spot UIC reflects daily iodine intake may be flawed because of high day-to-day variability and variable urinary volume outputs. This study aimed to compare iodine status in a sample of South African adults when determined by different approaches using a spot urine sample (median UIC (MUIC), predicted 24 h urinary iodine excretion (PrUIE) using different prediction equations) against measured 24 h urinary iodine excretion (mUIE)...
June 7, 2018: Nutrients
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