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Jonathon S Wright, Rong Fu, John R Worden, Sudip Chakraborty, Nicholas E Clinton, Camille Risi, Ying Sun, Lei Yin
Although it is well established that transpiration contributes much of the water for rainfall over Amazonia, it remains unclear whether transpiration helps to drive or merely responds to the seasonal cycle of rainfall. Here, we use multiple independent satellite datasets to show that rainforest transpiration enables an increase of shallow convection that moistens and destabilizes the atmosphere during the initial stages of the dry-to-wet season transition. This shallow convection moisture pump (SCMP) preconditions the atmosphere at the regional scale for a rapid increase in rain-bearing deep convection, which in turn drives moisture convergence and wet season onset 2-3 mo before the arrival of the Intertropical Convergence Zone (ITCZ)...
July 20, 2017: Proceedings of the National Academy of Sciences of the United States of America
Elder Mendoza Orbegoso, Rafael Saavedra, Daniel Marcelo, Raúl La Madrid
In the northern coastal and jungle areas of Peru, cocoa beans are dried using artisan methods, such as direct exposure to sunlight. This traditional process is time intensive, leading to a reduction in productivity and, therefore, delays in delivery times. The present study was intended to numerically characterise the thermal behaviour of three configurations of solar air heating collectors in order to determine which demonstrated the best thermal performance under several controlled operating conditions. For this purpose, a computational fluid dynamics model was developed to describe the simultaneous convective and radiative heat transfer phenomena under several operation conditions...
July 17, 2017: Journal of Environmental Management
Te-Wei Chang, Xinhao Wang, Amirreza Mahigir, Georgios Veronis, Gang Logan Liu, Manas Ranjan Gartia
Many single-molecule (SM) label-free techniques such as scanning probe microscopies (SPM) and magnetic force spectroscopies (MFS) provide high resolution surface topography information, but lack chemical information. Typical surface enhanced Raman spectroscopy (SERS) systems provide chemical information on the analytes, but lack spatial resolution. In addition, a challenge in SERS sensors is to bring analytes into the so-called "hot spots" (locations where the enhancement of electromagnetic field amplitude is larger than 10(3))...
July 20, 2017: ACS Sensors
Álvaro López-Bernal, Luca Testi, Francisco J Villalobos
Available sap flow methods are still far from being simple, cheap and reliable enough to be used beyond very specific research purposes. This study presents and tests a new single-probe heat pulse (SPHP) method for monitoring sap velocity in trees using a single-probe sensor, rather than the multi-probe arrangements used up to now. Based on the fundamental conduction-convection principles of heat transport in sapwood, convective velocity (Vh ) is estimated from the temperature increase in the heater after the application of a heat pulse (ΔT)...
July 19, 2017: New Phytologist
Scott D Augustine
Several studies have shown that the waste heat from forced-air warming (FAW) escapes near the floor and warms the contaminated air resident near the floor. The waste heat then forms into convection currents that rise up and contaminate the sterile field above the surgical table. It has been shown that a single airborne bacterium can cause a periprosthetic joint infection (PJI) following joint replacement surgery. We retrospectively compared PJI rates during a period of FAW to a period of air-free conductive fabric electric warming (CFW) at three hospitals...
June 23, 2017: Orthopedic Reviews
Swati Nagar, Richard C Korzekwa, Ken Korzekwa
Prediction of the rate and extent of drug absorption upon oral dosing needs models that capture the complexities of both the drug molecule and intestinal physiology. We report here the development of a continuous intestinal absorption model based on the convection-diffusion equation. The model includes explicit enterocyte apical membrane and intracellular lipid radial compartments along the length of the intestine. Physiologic functions along length x are built into the model, and include velocity, diffusion, surface areas, and pH of the intestine...
July 17, 2017: Molecular Pharmaceutics
Charlotte E Wainwright, Phillip M Stepanian, Don R Reynolds, Andy M Reynolds
In fine warm weather, the daytime convective atmosphere over land areas is full of small migrant insects, among them serious pests (e.g. some species of aphid), but also many beneficial species (e.g. natural enemies of pests). For many years intensive aerial trapping studies were the only way of determining the density profiles of these small insects, and for taxon-specific studies trapping is still necessary. However, if we wish to determine generic behavioural responses to air movements shown by small day-migrating insects as a whole, the combination of millimetre-wavelength 'cloud radars' and Doppler lidar now provides virtually ideal instrumentation...
July 14, 2017: Scientific Reports
Philippe Angot, Benoît Goyeau, J Alberto Ochoa-Tapia
We develop asymptotic modeling for two- or three-dimensional viscous fluid flow and convective transfer at the interface between a fluid and a porous layer. The asymptotic model is based on the fact that the thickness d of the interfacial transition region Ω_{fp} of the one-domain representation is very small compared to the macroscopic length scale L. The analysis leads to an equivalent two-domain representation where transport phenomena in the transition layer of the one-domain approach are represented by algebraic jump boundary conditions at a fictive dividing interface Σ between the homogeneous fluid and porous regions...
June 2017: Physical Review. E
Ehab S Selima, Xiaohua Yao, Abdul-Majid Wazwaz
In this research, the surface waves of a horizontal fluid layer open to air under gravity field and vertical temperature gradient effects are studied. The governing equations of this model are reformulated and converted to a nonlinear evolution equation, the perturbed Korteweg-de Vries (pKdV) equation. We investigate the latter equation, which includes dispersion, diffusion, and instability effects, in order to examine the evolution of long surface waves in a convective fluid. Dispersion relation of the pKdV equation and its properties are discussed...
June 2017: Physical Review. E
Raphaël Poryles, Germán Varas, Valérie Vidal
We investigate experimentally the influence of a fixed obstacle on gas rising in a dense suspension. Air is injected at a constant flow rate by a single nozzle at the bottom center of a Hele-Shaw cell. Without obstacles, previous works have shown that a fluidized zone is formed with a parabolic shape, with a central air channel and two granular convection rolls on its sides. Here, we quantify the influence of the obstacle's shape, size, and height on the location and dynamics of the central air channel. Different regimes are reported: the air channel can simply deviate (stable), or it can switch sides over time (unstable), leading to two signatures not only above the obstacle, but sometimes also below it...
June 2017: Physical Review. E
T Nagayama, J E Bailey, G P Loisel, G A Rochau, J J MacFarlane, I E Golovkin
Iron opacity calculations presently disagree with measurements at an electron temperature of ∼180-195 eV and an electron density of (2-4)×10^{22}cm^{-3}, conditions similar to those at the base of the solar convection zone. The measurements use x rays to volumetrically heat a thin iron sample that is tamped with low-Z materials. The opacity is inferred from spectrally resolved x-ray transmission measurements. Plasma self-emission, tamper attenuation, and temporal and spatial gradients can all potentially cause systematic errors in the measured opacity spectra...
June 2017: Physical Review. E
Ian Tobasco, Charles R Doering
We consider wall-to-wall transport of a passive tracer by divergence-free velocity vector fields u. Given an enstrophy budget ⟨|∇u|^{2}⟩≤Pe^{2} we construct steady two-dimensional flows that transport at rates Nu(u)≳Pe^{2/3}/(logPe)^{4/3} in the large enstrophy limit. Combined with the known upper bound Nu(u)≲Pe^{2/3} for any such enstrophy-constrained flow, we conclude that maximally transporting flows satisfy Nu∼Pe^{2/3} up to possible logarithmic corrections. Combined with known transport bounds in the context of Rayleigh-Bénard convection, this establishes that while suitable flows approaching the "ultimate" heat transport scaling Nu∼Ra^{1/2} exist, they are not always realizable as buoyancy-driven flows...
June 30, 2017: Physical Review Letters
Fei Ye, Wentao Tang, Fengxian Xie, Maoshu Yin, Jinjin He, Yanbo Wang, Han Chen, Yinghuai Qiang, Xudong Yang, Liyuan Han
Large-scale high-quality perovskite thin films are crucial to produce high-performance perovskite solar cells. However, for perovskite films fabricated by solvent-rich processes, film uniformity can be prevented by convection during thermal evaporation of the solvent. Here, a scalable low-temperature soft-cover deposition (LT-SCD) method is presented, where the thermal convection-induced defects in perovskite films are eliminated through a strategy of surface tension relaxation. Compact, homogeneous, and convection-induced-defects-free perovskite films are obtained on an area of 12 cm(2) , which enables a power conversion efficiency (PCE) of 15...
July 14, 2017: Advanced Materials
Ryan M Evans, David A Edwards
Scientists measure rate constants associated with biochemical reactions in an optical biosensor-an instrument in which ligand molecules are convected through a flow cell over a surface to which receptors are immobilized. We quantify transport effects on such reactions by modeling the associated convection-diffusion equation with a reaction boundary condition. In experimental situations, the full PDE model reduces to a set of unwieldy integrodifferential equations (IDEs). Employing common physical assumptions, we may reduce the system to an ODE model, which is more useful in practice, and which can be easily adapted to the inverse problem of finding rate constants...
July 13, 2017: Journal of Mathematical Biology
A Strugarek, P Beaudoin, P Charbonneau, A S Brun, J-D do Nascimento
The magnetic fields of solar-type stars are observed to cycle over decadal periods-11 years in the case of the Sun. The fields originate in the turbulent convective layers of stars and have a complex dependency upon stellar rotation rate. We have performed a set of turbulent global simulations that exhibit magnetic cycles varying systematically with stellar rotation and luminosity. We find that the magnetic cycle period is inversely proportional to the Rossby number, which quantifies the influence of rotation on turbulent convection...
July 14, 2017: Science
Reza Amiri Chayjan, Mosayeb Fealekari
BACKGROUND: In recent years, infrared drying has gained popularity as an alternative drying method for a va- riety of agricultural products. The use of infrared radiation technology in drying agricultural products has several advantages. These may include decreased drying time, high energy efficiency, high-quality finished products and uniform temperature in the product. With intermittent infrared and convection heating of a thick porous material, the drying time can be reduced compared to convection alone, while keeping good food quality and high energy efficiency...
April 2017: Acta Scientiarum Polonorum. Technologia Alimentaria
Kanav Khosla, Yiru Wang, Mary Hagedorn, Zhenpeng Qin, John Bischof
Zebrafish embryos can attain a stable cryogenic state by microinjection of cryoprotectants followed by rapid cooling, but the massive size of the embryo has consistently led to failure during the convective warming process. Here we address this zebrafish cryopreservation problem by using gold nanorods (GNRs) to assist in the warming process. Specifically, we microinjected the cryoprotectant propylene glycol into zebrafish embryos along with GNRs, and the samples were cooled at a rate of 90 000 °C/min in liquid nitrogen...
July 13, 2017: ACS Nano
Ziyang Lu, Amgad Rezk, Fernando Jativa, Leslie Yeo, Xuehua Zhang
Toroidal microstructures of nanocolloidal assemblies promise important applications ranging from sensing, catalysis, drug delivery, and separation. In this work, we will first investigate the rich dissolution dynamics of a droplet comprising a nanoparticle suspension in a binary solution, and then show that the dissolution dynamics can be a potential approach to assembling a wide range of colloids with microtoroids. As the sessile droplet dissolves in the binary solution of miscible and immiscible solvents, two simultaneous effects are observed: if the dissolution rate is sufficiently high under large concentrations of the cosolvent in the surrounding solution, a strong plume emanates from the droplet pole as a consequence of a body force (i...
July 12, 2017: Nanoscale
Junsuk Kim, Inhee Cho, Hyomin Lee, Sung Jae Kim
Ion concentration polarization (ICP) is a fundamental electrokinetic process that occurs near a perm-selective membrane under dc bias. Overall process highly depends on the current transportation mechanisms such as electro-convection, surface conduction and diffusioosmosis and the fundamental characteristics can be significantly altered by external parameters, once the permselectivity was fixed. In this work, a new ICP device with a bifurcated current path as for the enhancement of the surface conduction was fabricated using a polymeric nanoporous material...
July 11, 2017: Scientific Reports
Lan Cuo, Yongxin Zhang
The Tibetan Plateau and the surrounding (TPS) with its vast land mass and high elevation affects regional climate and weather. The TPS is also the headwater of 9 major Asian rivers that provide fresh water for 1.65 billion people and many ecosystems, with wet season (May-September) precipitation being the critical component of the fresh water. Using station observations, ERA-Interim and MERRA2 reanalysis, we find that wet season precipitation displays vertical gradients (i.e., changes with elevation) that vary within the region on the TPS...
July 11, 2017: Scientific Reports
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