Exploration of the effect of surface roughness on heat transfer in microscale liquid flow

As technology provides smaller devices with greater heat dissipation needs, microfludic systems become essential. The scale of device architecture causes concerns to arise that were previously not an issue. The results of manufacturing processes, such as roughness structures on machined surfaces, now play a significant role in transport phenomena. This study takes an analytical and experimental approach to understanding the fundamental heat transfer process in rectangular channels with artificially roughened walls. Steady, incompressible, fully developed liquid flow is modeled with lubrication theory to develop an expression for the fully developed Nusselt number. The heat transfer performance of the small aspect ratio rectangular channels with two wall heating under the H2 boundary condition is experimentally investigated. A constant wall heat flux is applied at opposing long walls. Four different structured roughness geometries are investigated along with smooth channels as the heated walls. In total, hydraulic diameters ranged from Dh=183 µm to Dh = 1698 µm and were tested over a Reynolds number range of 45 to 600. The pitch to height ratio of the sinusoidal roughness surfaces covered the ranged of 2.6 to 10.6. The resulting relative roughness was 2.17% to 16.53%. Fully developed Nusselt was found to lie below classic theory. Sinusoidal roughness geometries were found not to provide heat transfer enhancement over smooth channel walls

Liquid Cell Electron Microscopy With the Nanoaquarium: Radiation and Electrochemistry

The advent of the electron microscope has fostered major advances in a broad spectrum of disciplines. The required vacuum environment of standard electron microscopy, however, precludes imaging of systems containing high vapor pressure liquids. The recent development of liquid cells like the Penn nanoaquarium overcomes this limitation, enabling imaging of temporally evolving processes in liquids with nanoscale resolution at video frame rates. We used Liquid Cell Electron Microscopy to investigate the morphological evolution of the electrode-electrolyte interface during electroplating, the onset of diffusive instabilities in electrodeposits, beam-mediated nucleation, growth, and dissolution of metallic nanoparticles, the nucleation and growth of nanobubbles, and the fundamentals of the electron-water interactions (Radiation Chemistry). The control of interfacial morphology in electrochemical processes is essential for applications ranging from nanomanufacturing to battery technologies. Critical questions still remain in understanding the transition between various growth regimes, particularly the onset of diffusion-limited growth. We present quantitative observations at previously unexplored length and time scales that clarify the evolution of the metal-electrolyte interface during deposition. The interface evolution during initial stages of galvanostatic Cu deposition on Pt from an acidic electrolyte is consistent with kinetic roughening theory, while at later times the behavior is consistent with diffusion limited growth physics. To control morphology, we demonstrate rapid pulse plating without entering the diffusion-limited regime, and study the effects of the inorganic additive Pb on the growth habit. The irradiating electrons used for imaging, however, affect the chemistry of the suspending medium. The electron beam\u27s interaction with the water solvent produces molecular and radical products such as hydrogen, oxygen, and hydrated (solvated) electrons. A detailed understanding of the interactions between the electrons and the irradiated medium is necessary to correctly interpret experiments, minimize artifacts, and take advantage of the irradiation as a tool. We predict the composition of water subjected to electron irradiation under conditions relevant to liquid cell electron microscopy. We interpret experimental data, such as beam-induced colloid aggregation and observations of crystallization and etching of metallic particles as functions of dose rate. Our predictive model is useful for designing experiments that minimize unwanted solution chemistry effects, extend liquid cell microscopy to new applications, take advantage of beam effects for nanomanufacturing such as the patterning of nanostructures, and properly interpreting experimental observations

A Comprehensive Analysis of Io's Atmosphere and Torus

This final report describes the results of our NASA/Planetary Atmospheres program studying the atmosphere of Jupiter's moon Io and the plasma torus which it creates. Io is the most volcanically active body in the solar system, and it is embedded deep within the strongest magnetosphere of any planet. This combination of circumstances leads to a host of scientifically compelling phenomena, including (1) an atmosphere out of proportion with such a small object, (2) a correspondingly large atmospheric escape rate, (3) a ring of dense plasma locked in a feedback loop with the atmosphere, and (4) a host of Io-induced emissions from radio bursts to UV auroral spots on Jupiter. This proposal seeks to continue our investigation into the physics connecting these phenomena, with emphasis on Io's atmosphere and plasma torus. The physical processes are clearly of interest for Io, and also other places in the solar system where they are important but not so readily observable

Bubble and Pattern Formation in Liquid Induced by an Electron Beam

Liquid cell electron microscopy has emerged as a powerful technique for in situ studies of nanoscale processes in liquids. An accurate understanding of the interactions between the electron beam and the liquid medium is essential to account for, suppress, and exploit beam effects. We quantify the interactions of high energy electrons with water, finding that radiolysis plays an important role, while heating is typically insignificant. For typical imaging conditions, we find that radiolysis products such as hydrogen and hydrated electrons achieve equilibrium concentrations within seconds. At sufficiently high dose-rate, the gaseous products form bubbles. We image bubble nucleation, growth, and migration. We develop a simplified reaction-diffusion model for the temporally and spatially varying concentrations of radiolysis species and predict the conditions for bubble formation by . We discuss the conditions under which hydrated electrons cause precipitation of cations from solution, and show that the electron beam can be used to “write” structures directly, such as nanowires and other complex patterns, without the need for a mask

Ni(salen): Development of a two-week introduction to synthesis and characterization in general chemistry

As introductions to organic and inorganic synthesis, safe and expedient preparations of salen (N,N′- ethylenebis(salicylimine)) and its nickel complex have been developed for execution in the General 19 Chemistry II laboratory. Preparation and isolation can be completed in no more than 45 minutes. Prepared compounds are then analyzed by an assortment of characterization methods: melting point determination, mass spectrometry, IR spectroscopy, UV-vis spectrophotometry and 13C NMR spectroscopy. These lab exercises are meant to serve as soft introductions for methods and instrumentation that will be utilized more heavily in the subsequent chemistry courses. Students are given basic training in analyzing data for each method to begin learning their utility for identifying product presence and purity. Simulated and modeled spectra are also used as accompaniment to experimental data to aid in analysis and interpretation training

Stress-Dependent Opioid And Adrenergic Modulation Of Newly Retrieved Fear Memory

Recent studies on the effect of stress on modulation of fear memory in our laboratory have uncovered endogenous opioid and adrenergic based modulation systems, working in concert, that limit the strengthening or weakening of newly acquired fear memory during consolidation under conditions of mild or intense stress, respectively. The present study sought to determine if similar stress-dependent modulation, mediated by endogenous opioid and adrenergic systems, occurs during reconsolidation of newly retrieved fear memory. Rats underwent contextual fear conditioning followed 24 h later by reactivation of fear memory; a retention test was administered the next day. Stress was manipulated by varying duration of recall of fear memory during reactivation. In the first experiment, vehicle or the opioid-receptor blocker naloxone was administered immediately after varied durations (30 or 120 s) of reactivation. The results indicate that (1) reactivation, in the absence of drug, has a marked effect on freezing behavior-as duration of reactivation increases from 30 to 120 s, freezing behavior and presumably fear-induced stress increases and (2) naloxone, administered immediately after 30 s (mild stress) or 120 s (intense stress) of reactivation, enhances or impairs retention, respectively, the next day. In the second experiment, naloxone and the g-adrenergic blocker propranolol were administered either separately or in combination immediately after 120 s (intense stress) reactivation. The results indicate that separate administration of propranolol and naloxone impairs retention, while the combined administration fails to do so. Taken together the results of the two experiments are consistent with a protective mechanism, mediated by endogenous opioid and adrenergic systems working in concert, that limits enhancement and impairment of newly retrieved fear memory during reactivation in a stress-dependent manner. (C) 2013 Elsevier Inc. All rights reserved

Mean Spectral Energy Distributions and Bolometric Corrections for Luminous Quasars

We explore the mid-infrared (mid-IR) through ultraviolet (UV) spectral energy distributions (SEDs) of 119,652 luminous broad-lined quasars with 0.064<z<5.46 using mid-IR data from Spitzer and WISE, near-infrared data from Two Micron All Sky Survey and UKIDSS, optical data from Sloan Digital Sky Survey, and UV data from Galaxy Evolution Explorer. The mean SED requires a bolometric correction (relative to 2500A) of BC=2.75+-0.40 using the integrated light from 1um-2keV, and we further explore the range of bolometric corrections exhibited by individual objects. In addition, we investigate the dependence of the mean SED on various parameters, particularly the UV luminosity for quasars with 0.5<z<3 and the properties of the UV emission lines for quasars with z>1.6; the latter is a possible indicator of the strength of the accretion disk wind, which is expected to be SED dependent. Luminosity-dependent mean SEDs show that, relative to the high-luminosity SED, low-luminosity SEDs exhibit a harder (bluer) far-UV spectral slope, a redder optical continuum, and less hot dust. Mean SEDs constructed instead as a function of UV emission line properties reveal changes that are consistent with known Principal Component Analysis (PCA) trends. A potentially important contribution to the bolometric correction is the unseen extream-UV (EUV) continuum. Our work suggests that lower-luminosity quasars and/or quasars with disk-dominated broad emission lines may require an extra continuum component in the EUV that is not present (or much weaker) in high-luminosity quasars with strong accretion disk winds. As such, we consider four possible models and explore the resulting bolometric corrections. Understanding these various SED-dependent effects will be important for accurate determination of quasar accretion rates.Comment: 19 pages, 18 figure