bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermohydraulic Characteristics of Fluid Flow in a Zig-Zag Square Microchannel
Authors: Mathew B. , John T. J. , Hegab H.
Published: March 2011

This paper deals with understanding the thermohydraulic characteristics of one type of zig-zag square microchannel. Studies are done to understand the individual effect of geometric parameters like hydraulic diameter, orientation angle and connector length for Reynolds number between 100 and 400. The hydraulic diameter is varied between 100 μm and 300 μm with increment of 100 μm. Studies are carried out for orientation angle of 10°, 20° and 30°. The connector length of the study conducted in this paper is varied from 200 μm to 400 μm to 600 μm. The results are presented in terms of enhancement of Nusselt number and Poiseuille number over that in straight square microchannels. With increase in hydraulic diameter the enhancement in Nusselt number and Poiseuille number increased at a specific Reynolds number. Similarly with increase in the orientation angle the enhancement in these two thermohydraulic characteristics is observed for a specific Reynolds number. With increase in connector length both Nusselt number and Poiseuille number increased over that in straight channels of the same hydraulic diameter for a particular Reynolds number. Enhancement in Nusselt number and Poiseuille number is observed with increase in Reynolds number for all zig-zag microchannels. For the three fold increase in each of the geometric parameters the smallest enhancement is observed with increase in connector length. The greatest enhancement in thermohydraulic characteristics is observed with change in orientation between the arm and the connector.
Parametric Study of a Transient Liquid Flow in a Microchannel of Square Cross-Section
Authors: Ngoma Guyh Dituba , Sadiki Amsini
Published: March 2011

Time-dependent laminar liquid flow and thermal characteristics in a square cross-section microchannel were numerically investigated using computational fluid dynamics code. In the numerical model developed the upper and bottom microchannel substrate properties, Joule heating caused by applying electric potential, pressure driven flow, electroosmosis, heat transfer coefficients on the microchannel bottom wall and variations in the liquid thermophysical properties were all taken into account. Liquid flow velocity distribution and temperature fields were calculated by solving both Navier-Stokes and energy equations, and electric field distribution was determined based on their electric potential. The results obtained demonstrate the impact that applied potential, pressure difference, heat transfer coefficient and microchannel dimensions have on liquid flow and thermal behaviors in a square microchannel. Finally, the results with the model developed were then compared with those of a liquid having constant thermophysical properties.
Multi Layer Micro Pin-Fins Heat Sinks for Better Performance
Authors: John T. J. , Mathew B. , Hegab H.
Published: March 2011

This study numerically investigates the feasibility and advantages of using a multilayer pin-fin heat sink to increase the overall performance of the heat sink. For the purpose of determining overall performance of the pin-fin heat sink a figure of merit (FOM) term is introduced in this paper, which constituted of both the thermal resistance and the pumping power of the heat sink. Higher the FOM of a heat sink better is its overall performance. A computational fluid dynamics software CoventorWARE™ is used for the analysis of micro heat sink performance. A small portion of the entire heat sink is modeled in this study assuming repeatability towards both sides for the ease of analysis. The developed models consist of two sections, the substrate (silicon) and the fluid (water at 278K). A uniform heat flux is applied to the base of the heat sink. A single layer micro pin-fin heat sinks with same dimensions as of the multi layer heat sink was also modeled for the comparison purpose. Temperature distribution at five different locations from the inlet to the outlet section is also analyzed to study the temperature distribution over the heat sink. Circular pin-fins were used in both the multilayer and single layer micro heat sinks. Feasibility of using micro channels as the second layer was also investigated in this paper and it proved to have advantages over using pin-fin structures on both layers. A geometric optimization based on the substrate thickness of the second layer of the double layer heat sink showed that the substrate thickness of the second layer doesn’t have any effect on the overall thermal resistance of the heat sink.
IR Thermography and High Speed Imaging of Cerium Nitrate Precursor Droplets Heated by Monochromatic Irradiation
Authors: Saha Abhishek , Tijerino Erick , Kumar Ranganathan , Basu Saptarshi
Published: March 2011

An experimental setup using radiative heating has been used to understand the thermophysical phenomena and chemical transformations inside acoustically levitated cerium nitrate precursor droplets. IR imaging in conjunction with high speed imaging shows presence of four distinct phases of heating. The droplet initially undergoes pure vaporization followed by surface precipitation. This results in a gelatinous phase due to precipitation of cerium nitrate which eventually goes though chemical transformation and forms a porous precipitate. Transmission Electron Microscopy (TEM) of the final precipitate revealed the presence of trapped gases in the form of bubbles. TEM also showed the presence of nano-ceria crystalline structures at 70°C. The current study also looks into the effect of different heating power on the process. At higher power each phase is sustained for smaller duration and higher maximum temperature. At all laser power, TEM showed the formation of nanoceria. In addition, the porosity of the final precipitate increased with power.
Nozzle Effects in Thermal Wind Tunnels
Authors: Wang Zhu , Han Jaehoon , Alajbegovic Ales
Published: March 2011

Presented is an investigation of the wind-tunnel nozzle effects on the thermal performance within passenger vehicle underhood area. The Lattice-Boltzmann Equation (LBE) based flow solver is coupled with the system tool to solve for airflow and temperature distribution around the passenger vehicle in the wind tunnel. Several simulations with different nozzle sizes were performed. The simulation results are compared with airflow, temperature, and heat exchangers heat rejection measurements in the thermal wind tunnel. Good agreement is observed confirming that nozzle geometry dominates the airflow around the vehicle. The results show that different nozzle sizes can produce flows that have almost the same macroscopic characteristics while at the same time have subtle differences that can be very important for the vehicle design.
Numerical Study of Solutal and Thermal Instabilities in Mini-Channels for Membrane-Less Applications
Authors: Iorio C. S. , Perfetti C. , Galand Q. , Van Vaerenbergh S.
Published: March 2011

Many industrial processes make extensive use of membranes to separate fluxes while allowing some of the constituent species to diffuse into each other. In recent years, high production and maintenance costs induced by fouling, poisoning and clogging of the membrane pores due to impurities have create conditions to study alternative way of making liquid and/or gaseous streams interact and diffuse without the presence of a physical barrier. One of the possibilities is offered by the essentially laminar character of the flow in microfluidic devices that allows two or more different fluid streams to merge without mixing in a large range of experimental and industrial conditions. In this work, we will study, numerically, the case of two streams of different composition merging in a micro-channel. The upper and lower sides of the micro-channel are heated differentially and the inlet velocity of the streams is set independently in the range 0–1m/s. Simulations are carried out in 2D and 3D while fluids are chosen by considering their industrial importance and application. The main results are that the stability of the streams is very sensitive to the inlet conditions and that it is possible to modulate the mixing layer thickness by acting on thermal gradients, geometrical constraints and slip flow conditions.
Modeling of Newtonian Fluids in Annular Geometries With Inner Pipe Rotation
Authors: Sorgun Mehmet , Schubert Jerome J. , Aydin Ismail , Ozbayoglu M. Evren
Published: March 2011

Flow in annular geometries, i.e., flow through the gap between two cylindrical pipes, occurs in many different engineering professions, such as petroleum engineering, chemical engineering, mechanical engineering, food engineering, etc. Analysis of the flow characteristics through annular geometries is more challenging when compared with circular pipes, not only due to the uneven stress distribution on the walls but also due to secondary flows and tangential velocity components, especially when the inner pipe is rotated. In this paper, a mathematical model for predicting flow characteristics of Newtonian fluids in concentric horizontal annulus with drill pipe rotation is proposed. A numerical solution including pipe rotation is developed for calculating frictional pressure loss in concentric annuli for laminar and turbulent regimes. Navier-Stokes equations for turbulent conditions are numerically solved using the finite differences technique to obtain velocity profiles and frictional pressure losses. To verify the proposed model, estimated frictional pressure losses are compared with experimental data which were available in the literature and gathered at Middle East Technical University, Petroleum & Natural Gas Engineering Flow Loop (METU-PETE Flow Loop) as well as Computational Fluid Dynamics (CFD) software. The proposed model predicts frictional pressure losses with an error less than ± 10% in most cases, more accurately than the CFD software models depending on the flow conditions. Also, pipe rotation effects on frictional pressure loss and tangential velocity is investigated using CFD simulations for concentric and fully eccentric annulus. It has been observed that pipe rotation has no noticeable effects on frictional pressure loss for concentric annuli, but it significantly increases frictional pressure losses in an eccentric annulus, especially at low flow rates. For concentric annulus, pipe rotation improves the tangential velocity component, which does not depend on axial velocity. It is also noticed that, as the pipe rotation and axial velocity are increased, tangential velocity drastically increases for an eccentric annulus. The proposed model and the critical analysis conducted on velocity components and stress distributions make it possible to understand the concept of hydro transport and hole cleaning in field applications.
Modeling Drug Eluting Stents for Coronary Artery Bifurcation Considering Non-Newtonian Effects
Authors: Zarandi Marjan Molavi , Mongrain Rosaire , Bertrand Olivier F.
Published: March 2011

Drug Eluting Stents (DES) are commonly used for the treatment of stenotic arteries. Restenosis can be treated by delivering anti-thrombotic and anti-proliferative drugs to the arterial wall. The main mechanism of the drug eluting stent is to allow diffusion of the drug from the coating on the stent, into the arterial wall over a prolonged period of time. Investigation of blood flow hemodynamics and shear stress are of great importance in understanding the transport of drugs through the circulatory systems and predicting the performance of drug eluting stents. While drug eluting stent effectively reduces restenosis rate, the conventional drug eluting stent should be optimized to be used in the bifurcation stenting. Various flow patterns due to specific designs of drug eluting stent influence drug delivery. Numerical simulation techniques are appropriate approaches to study such phenomena which can be used to optimize the design of drug eluting stents for bifurcations. In this paper, the complexity of drug eluting stent function in the bifurcation is presented by employing computational fluid dynamics analysis for various stent strut designs. Drug transportation through the lumen and determination of local drug concentrations in arterial wall is carried out for both Newtonian and non-Newtonian flow conditions. It is, to the author’s best knowledge, the first investigation of drug dispersion in arterial bifurcation considering the effects of both the blood rheological properties and stent strut design.
Computational Methodology for Integrated CFD-CSD Simulations of Fluid-Structure Interaction Problems
Authors: Lee Jinmo , You Donghyun
Published: March 2011

A newly developed computational methodology for high-fidelity prediction of fluid and structure dynamics and their unsteady interaction is presented. The present methodology combines an immersed-boundary method, which is capable of simulating flow over non-grid-conforming complex moving bodies and a structural dynamics solver, which is based on a finite-element method and is capable of predicting time-accurate dynamics of deforming solid structures. The pressure and velocity of fluid and geometric information of submerged structures are time-accurately coupled through an integration algorithm. The capability of the present computational fluid dynamics (CFD)–computational structure dynamics (CSD) coupling technique is assessed in a number of validation simulations.
Bileaflet Prosthetic Heart Valve Disease: Numerical Approach Using 3-D Fluid-Structure Interaction Model With Realistic Aortic Root
Authors: Smadi Othman , Hassan Ibrahim , Pibarot Philippe , Kadem Lyes
Published: March 2011

Surgical replacement, in the incidence of severely diseased heart valve, is vital in order to restore the normal heart function. Every year around 280,000 valve replacements occur around the world, half of them are bileaflet mechanical heart valves (BMHVs). Despite the remarkable improvement in valve design resulting in minimizing prosthetic valve complications (thromboembolic events or pannus formation), these complications are still possible with BMHV Implantation. As a consequence, an obstruction in one or both MHV leaflets could happen and threaten the patient life. In the present study, an obstructed bileaflet MHV with different percentages of malfunction was simulated assuming 3-D fluid structure interaction (FSI) adapting k-w turbulence as a robust model for the transitional flow using 2.5 million elements and creating a realistic aortic root model with three sinuses. Velocity contours for different percentages of malfunction were compared mainly at B-datum plane and the perpendicular plane to the B-Datum. Also, the development of coherent structures was investigated. Clinically, the maximum pressure gradients were estimated by mimicking the Echo Doppler assumptions (using the simplified Bernoulli equation).
Modeling and Analysis of Low Voltage Electro-Osmotic Micropump
Authors: Ozhikandathil Jayan , Packirisamy Muthukumaran , Stiharu Ion
Published: March 2011

Scaling down the biochemical analytical system has been an important topic of research recently. Minimizing the energy requirement for the microfluidic transportation is essential for the realization of a Lab-on-a-chip (LOC) that can perform the Point-of-Care Testing (POCT). In this work, modeling and analysis of a low voltage Electro-osmotic (EO) micropump applicable for the Bio-Microfluidic systems using COMSOL Multiphysics software package is presented. In the previously reported low voltage EO micropump (3), position of electrodes makes the fabrication process a tedious task. Here, we investigate the effects of placing the electrodes tangential to the microchannel since such designs can be easily fabricated using PDMS/glass fabrication process, and also comparing the effect of different electrode configurations on the pump performance. In addition, the effects of geometrical parameters of micropump on volumetric flow rate and velocity profiles are investigated.
An Investigation Into the Non-Uniformity of Density in Nanofluids
Authors: Shelton John , Pyrtle Frank
Published: March 2011

This study uses molecular dynamics simulations to investigate the affects of platinum nanoparticle lognormal size distribution and agglomeration on the local density of the surrounding xenon base fluid. Over the range of platinum nanoparticle diameters (25–150 nm), the radial distribution function showed an increase in the local fluid density. This increase in local density is shown to be caused by the formation of liquid layers that surround the nanoparticle. Liquid layer formation is found to be highly dependent on the cross-correlation between the platinum and xenon atoms. The local density is shown to increase with smaller nanoparticle diameter and aggregation reduces this change in density. Since aggregation is a dynamic phenomenon, the density becomes both spatially and temporally dependent. This space-time dependency of nanofluid density is compared to the linear mixing models normally applied to nanofluid systems.
New Correlation for Two-Phase Flow in 90 Degree Horizontal Elbows
Authors: Sanchez-Silva Florencio , Carvajal-Mariscal Ignacio , Tolentino-Eslava Rene
Published: March 2011

The comparison of experimental data and results obtained from four global models — homogeneous, Dukler, Martinelli and Chisholm, used to evaluate the two-phase flow pressure drop in circular 90° horizontal elbows — is presented in this paper. An experimental investigation was carried out using three galvanized steel 90° horizontal elbows (E1, E2, E3) with internal diameters of 26.5, 41.2 and 52.5 mm, and curvature radii of 194.0, 264.0 and 326.6 mm, respectively. According to the experimental results, the model proposed by Chisholm best fitted them, presenting for each elbow an average error of E1 = 18.27%, E2 = 28.40% and E3 = 42.10%. Based on experimental results two correlations were developed. The first one is the classical Chisholm model modified to obtain better results in a wider range of conditions; it was adjusted by a dimensionless relationship which is a function of the homogeneous volumetric fraction and the Dean number. As a result, the predictions using modified Chisholm model were improved presenting an average error of 8.66%. The second developed correlation is based on the entire two-phase mass flow taken as liquid and adjusted by the homogeneous volumetric fraction ratio. The results show that this last correlation is easier and accurate than the adjusted Chisholm model, presenting an average error of 7.75%. Therefore, this correlation is recommended for two-phase pressure drop evaluation in horizontal elbows.
Reynolds Stress Anisotropy in Rotating Homogeneous Decay
Authors: Koppula Karuna , Be´nard Andre´ , Petty Charles
Published: March 2011

In rotating homogeneous decay, the prolate quadratic form associated with the normalized Reynolds (NR-) stress is elongated by a coupling between velocity fluctuations and the Coriolis acceleration. This paper shows that this well-known turbulence phenomenon is consistent with an algebraic anisotropic prestress (APS-) closure for the NR-stress that unifies the study of turbulent flows in rotating and non-rotating frames-of-reference. The APS-closure is a non-negative mapping of the NR-stress into itself and is, thereby, universally realizable for all turbulent flows.
Tube Banks Heat Transfer Enhancement Using Conical Fins
Authors: Carvajal-Mariscal Ignacio , Sanchez-Silva Florencio , Polupan Georgiy
Published: March 2011

In this work the heat transfer and pressure drop experimental results obtained in a two step finned tube bank with conical fins are presented. The tube bank had an equilateral triangle array composed of nine finned tubes with conical fins inclined 45 degrees in respect with the tube axis. The heat exchange external area of a single tube is approximately 0.07 m2. All necessary thermal parameters, inlet/outlet temperatures, mass flows, for the heat balance in the tube bank were determined for different air velocities, Re = 3400–18400, and one constant thermal charge provided by a hot water flow with a temperature of 80 °C. As a result, the correlations for the heat transfer and pressure drop calculation were obtained. The experimental results were compared against the analytical results for a tube bank with annular fins with the same heat exchange area. It was found that the proposed tube bank using finned tubes with conical fins shows an increment of heat transfer up to 58%.
Improving the Electrokinetic Properties of PDMS With Surface Treatments
Authors: Almutairi Zeyad , Ren Carolyn , Simon Leonardo
Published: March 2011

PDMS (Polydimethylsiloxane) is widely used as a microfluidic chip material for various applications due to its desirable properties [1, 2]. However PDMS has several drawbacks that limit its utilization in a number of microfluidic applications [1–4]. Properties such as the hydrophobic nature, sample absorption, and low electrokinetic properties (low zeta potential) are some issues that must be considered before using PDMS for numerous applications [3]. In many PDMS based chips electroosmotic pumping is used for fluid flow and sample transport along the microchannel networks. Simplicity of implementation in microfluidic chips, fast response time, and the plug-like velocity profile are the major advantages of electroosmotic flow compared to other fluid pumping techniques [2]. This type of flow utilizes the formation of electric double layer (EDL) in microchannels and the movement of ions under an applied external electric field. Thus, the surface properties of the channel material and liquid properties (ionic concentration, pH, and viscosity) play major roles in electroosmotic pumping for different solutions in microchannels.
On the Representation of Numerical Solutions Using Taylor Series Approximation
Authors: Elizalde-Blancas Francisco , Celik Ismail B.
Published: March 2011

In this study, the representation of discretization error using Taylor series in finite difference solutions is investigated as well as the behavior of the exact solutions to the finite difference equations as a function of the grid size and grid refinement factor. The results are compared to the classical Richardson Extrapolation method whereby the numerical solution (or the error) is explicitly expressed as a Taylor series expansion. The exact finite difference solutions are used to demonstrate that oscillatory convergence is a common occurrence. The expansion of the numerical solutions in Taylor series is based on the exact finite difference solutions that are obtained using different discretization schemes. It is shown that in some cases the numerical solution exhibited a singular behavior which can not be remedied easily. Some exact finite difference solutions also exhibited oscillatory behavior which was not due to the use of mixed order terms as is usually believed by the Computational Fluid Dynamics community. Moreover, representation of the numerical solution using Taylor series is not always satisfactory even in case of relatively simple one-dimensional problems.
Numerical Simulation of Gas-Liquid Two-Phase Flows on Wetted Walls
Authors: Iso Yoshiyuki , Chen Xi
Published: March 2011

Gas-liquid two-phase flows on the wall like liquid film flows, which are the so-called wetted wall flows, are observed in many industrial processes such as absorption, desorption, distillation and others. For the optimum design of packed columns widely used in those kind of processes, the accurate predictions of the details on the wetted wall flow behavior in packing elements are important, especially in order to enhance the mass transfer between the gas and liquid and to prevent flooding and channeling of the liquid flow. The present study focused on the effects of the change of liquid flow rate and the wall surface texture treatments on the characteristics of wetted wall flows which have the drastic flow transition between the film flow and rivulet flow. In this paper, the three-dimensional gas-liquid two-phase flow simulation by using the volume of fluid (VOF) model is applied into wetted wall flows. Firstly, as one of new interesting findings in this paper, present results showed that the hysteresis of the flow transition between the film flow and rivulet flow arose against the increasing or decreasing stages of the liquid flow rate. It was supposed that this transition phenomenon depends on the history of flow pattern as the change of curvature of interphase surface which leads to the surface tension. Additionally, the applicability and accuracy of the present numerical simulation were validated by using the existing experimental and theoretical studies with smooth wall surface. Secondary, referring to the texture geometry used in an industrial packing element, the present simulations showed that surface texture treatments added on the wall can improve the prevention of liquid channeling and can increase the wetted area.
Pneumatically Actuated Diaphragm Single Chamber Micropump
Authors: Ho Son H. , Rahman Muhammad M. , Katkoori Srinivas , Talukder Ashit
Published: March 2011

The analysis of a single chamber micropump with a diaphragm driven by a pulse train of external pressure and two passive check valves at inlet and outlet is performed. The model for the micropump is developed based on the fundamentals of fluid mechanics and theory of plates with quasi-static approximation. The simulation results are compared with existing experimental data. They are in good agreement on flow rate and in reasonable agreement on backpressure for low driving frequency up to 3 Hz. It is found that the flow rate increases as the driving frequency increases or the backpressure decreases. The results also predict that a duty cycle of 50% results in the highest flow rate at the same frequency and actuating pressure. Also, a higher actuating pressure yields a higher flow rate. The model presented here can effectively assist the design process of micropumps since the model is directly related to the basic design parameters such as geometric dimensions and material properties.
The BEPU Challenge in Current Licensing of Nuclear Reactors
Authors: D’Auria F. , Petruzzi A. , Muellner N. , Mazzantini O.
Published: March 2011

Within the licensing process of the Atucha II PHWR (Pressurized Heavy Water Reactor) the BEPU (Best Estimate Plus Uncertainty) approach has been selected for issuing of the Chapter 15 on FSAR (Final Safety Analysis Report). The key steps of the entire process are basically two: a) the selection of PIE (Postulated Initiating Events) and, b) the analysis by best estimate models supported by uncertainty evaluation. The key elements of the approach are: 1) availability of qualified computational tools including suitable uncertainty method; 2) demonstration of quality; 3) acceptability and endorsement by the licensing authority. The effort of issuing Chapter 15 is terminated at the time of issuing of the present paper and the safety margins available for the operation of the concerned NPP (Nuclear Power Plant) have been quantified.
Uncertainties in Predictions by Thermal-Hydraulic Codes: Approaches and Results
Authors: Petruzzi A. , D’Auria F.
Published: March 2011

The present paper deals with the description of the salient features of three independent approaches for estimating uncertainties associated with predictions of complex system codes. The 1st approach is the “standard” one and the most used at the industrial level: it is based upon the selection of input uncertain parameters, on assigning related ranges of variations and, possibly, PDF (Probability Density Functions) and on performing a suitable number of code runs to get the combined effect of variation on the results. In the 2nd approach the uncertainty derives from the comparison between relevant measured data and results of corresponding code calculations. The 3rd approach is based upon a sensitivity analysis procedure and uses the experimental data to characterize the ranges of variation of ‘all’ input parameters. Selected results from the application of the 2nd approach are outlined.
BEPU Methodologies and Plant Technical Specifications
Authors: Mendiza´bal R. , Pelayo F.
Published: March 2011

The Technical Specifications (TS) of a nuclear power plant define the conditions for a safe normal operation. With such an objective, the TS set limits on operational parameters of the plant and give surveillance requirements for the observation of such bounds. The values of TS limits are obtained from the safety analyses of the plant. In fact, the traditional conservative methodologies of deterministic safety analysis (DSA) have been profusely used in this task. Nevertheless, in recent years realistic (also termed BEPU) methodologies have started to replace the conservative ones. This new methodologies use realistic models and assumptions and implement techniques for performing uncertainty analysis of their results. Many of them are statistical, with a probabilistic representation of uncertainty, and based on the random sampling of uncertain inputs and uncertainty propagation to the outputs. In this paper the relation between BEPU safety analyses and TS is analyzed. The authors have a deep regulatory experience in the evaluation and licensing of DSA methodologies. Safety analyses are aimed at showing that the real operation of the plant is safe, but they have a stronger goal: to prove that the allowed operation of the plant is safe. BEPU methodologies are not fitted for the estimation of TS bounds. They rather are used to prove the coherence of the safety analysis with the preestablished TS. Procedures for proving such coherence, with different degree of strictness, are discussed in the case of Monte Carlo-based methodologies.
Flow Investigation in a Disk Micropump
Authors: Lisibach Andre´ , Casartelli Ernesto , Schmid Noah
Published: March 2011

The flow field in a disk micropump is investigated using CFD. The results are validated with experimental data, showing good agreement. Flow field details are presented for different pump parameters. In order to better understand the influence of the pump geometry and fluid properties on the pump performance, an analytical model for the pump head has been derived. Since the pumping mechanism is mainly due to viscous forces, a typical turbomachinery approach, which is based on the effect of centrifugal forces, is not appropriate. The proposed analytical model, which is general and can also be used for scale up purposes, shows that the non-dimensional results of CFD and measurements matches very well.
Optical measurements of single CdTe self-assembled quantum dots grown on ZnTe/GaSb
Authors: Pimpinella R. E. , Mintairov A. M. , Liu X. , Kosel T. H. , Merz J. L. , Furdyna J. K. , Dobrowolska M.
Published: March 2011

The CdTe quantum dots (QDs) grown on a ZnTe epilayer deposited directly on a GaSb substrate are studied by transmission electron microscopy (TEM) and near-field scanning optical microscopy. High resolution TEM images show CdTe QD of planoconvex shape. Near-field photoluminescence (NPL) in an applied magnetic field is used to measure the Zeeman splitting and diamagnetic shift of single CdTe QDs. Finally, time resolved NPL measurements suggest that the higher energy lines in the CdTe QD NPL spectra correspond to exciton transitions occurring in larger CdTe QDs and have shorter exciton lifetimes.
Increased pattern transfer fidelity of ZEP 520A during reactive ion etching through chemical modifications by additional dosing of the electron beam resist
Authors: Czaplewski David A. , Ocola Leonidas E.
Published: March 2011

This article describes a postdevelopment, additional electron exposure to enhance the etch selectivity and improve pattern transfer fidelity of an electron beam resist, ZEP 520A, through chemical changes of the resist. After the critical features were patterned and developed, the resist was exposed at 5 kV accelerating voltage to a second dose of electrons ranging from 300 to 300 000 μC/cm2. The etch rate of the resist decreased by approximately 25% in a CHF3 and O2 plasma. More critically, the fidelity of the pattern transfer was improved. Infrared and Raman spectroscopies were used to characterize the resist before and after electron beam exposure for doses up to 3000 μC/cm2. The carbonyl bonding in the polymer showed significant changes after electron beam exposure that can be associated with improvement in the etch performance of this resist.
Harnessing Students' Interest in Physics with Their Own Video Games
Authors: Like Christopher
Published: March 2011

Many physics teachers assign projects where students are asked to measure real-world motion. One purpose of this student-centered activity is to cultivate the relevance of physics in their lives. Typical project topics may include measuring the speed of a student's fastball and calculating how much reaction time batters are given. Another student may find the trajectory of her dive off the blocks at the pool and its effect on race time. Leaving the experimental design to the student's imagination allows for a variety of proposals ranging from stopwatches to highly technical video analysis. The past few years have shown an increase in students' eagerness to tackle the physics behind the motion of virtual characters and phenomena in their own video games. This paper puts forth a method of analyzing the physics behind bringing the games students are playing for enjoyment into the physics classroom.
Inexpensive Instruments for a Sound Unit
Authors: Brazzle Bob
Published: March 2011

My unit on sound and waves is embedded within a long-term project in which my high school students construct a musical instrument out of common materials. The unit culminates with a performance assessment: students play the first four measures of “Somewhere Over the Rainbow”—chosen because of the octave interval of the first two notes—in the key of C, and write a short paper describing the theory underlying their instrument. My students have done this project for the past three years, and it continues to evolve. This year I added new instructional materials that I developed using a freeware program called Audacity.1 This software is very intuitive, and my students used it to develop their musical instruments. In this paper I will describe some of the inexpensive instructional materials in my sound unit, and how they fit with my learning goals.
A Mechanical Analogue of the Refracting Telescope
Authors: Vannoni Maurizio , Molesini Giuseppe , Sordini Andrea , Straulino Samuele
Published: March 2011

The recent celebration of the discoveries made by Galileo four centuries ago has attracted new attention to the refracting telescope and to its use as an instrument for the observation of the night sky.1 This has offered the opportunity for addressing in the classroom the basic principles explaining the operation of the telescope. When doing so, a key concept that is faced is magnification. In geometrical optics, the treatment of magnification is generally given in terms of light rays and first-order (Gaussian or paraxial) ray tracing. Computer programs are available with which the light path through the lenses and the whole telescope can be simulated.
Engineering Design Modules as Physics Teaching Tools
Authors: Oliver Douglas L. , Kane Jackie
Published: March 2011

Pre-engineering is increasingly being taught as a high school subject. This development presents challenges as well as opportunities for the physics education community. If pre-engineering is taught as a separate class, it may divert resources and students from traditional physics classes. However, design modules can be used as physics teaching tools that can seamlessly integrate technology, engineering, and math into high school physics using a variety of teaching styles. This paper discusses a rationale for using design modules as tools for teaching physics. As an illustration, an example of an engineering design module is presented. This example module is appropriate for an algebra-based physics class that covers Ohm's law.
Response to Comment on “Global Convergence in the Temperature Sensitivity of Respiration at Ecosystem Level”
Authors: Mahecha Miguel D. , Reichstein Markus , Carvalhais Nuno , Lasslop Gitta , Lange Holger , Seneviratne Sonia I. , Vargas Rodrigo , Ammann Christof , Arain M. Altaf , Cescatti Alessandro , Janssens Ivan A. , Migliavacca Mirco , Montagnani Leonardo , Richardson Andrew D.
Published: March 2011

We estimated the sensitivity of terrestrial ecosystem respiration to air temperature across 60 FLUXNET sites by minimizing the effect of seasonally confounding factors. Graf
et al
. now offer a theoretical perspective for an extension of our methodology. However, their critique does not change our main findings and, given the currently available observational techniques, may even impede a comparison across ecosystems.
A Planar Rhombic Charge-Separated Tetrasilacyclobutadiene
Authors: Suzuki Katsunori , Matsuo Tsukasa , Hashizume Daisuke , Fueno Hiroyuki , Tanaka Kazuyoshi , Tamao Kohei
Published: March 2011

A stable silicon analog of a reactive, antiaromatic hydrocarbon has been synthesized and characterized.
Neutrophils Activate Plasmacytoid Dendritic Cells by Releasing Self-DNA–Peptide Complexes in Systemic Lupus Erythematosus
Authors: Lande Roberto , Ganguly Dipyaman , Facchinetti Valeria , Frasca Loredana , Conrad Curdin , Gregorio Josh , Meller Stephan , Chamilos Georgios , Sebasigari Rosalie , Riccieri Valeria , Bassett Roland , Amuro Hideki , Fukuhara Shirou , Ito Tomoki , Liu Yong-Jun , Gilliet Michel
Published: March 2011

In systemic lupus erythematosus, neutrophils release peptide/self-DNA complexes that trigger plasmacytoid dendritic cell activation and autoantibody formation.
Bones Break the News on Reproduction
Authors: Cheng Mickie H.
Published: March 2011

Osteocalcin produced by bone regulates testosterone production and male fertility.
Innate Immune Evasion Mediated by the Ambystoma tigrinum Virus Eukaryotic Translation Initiation Factor 2α Homologue
Authors: Jancovich James K. , Jacobs Bertram L.
Published: March 2011

Ranaviruses (family
Iridoviridae
, genus
Ranavirus
) are large, double-stranded DNA (dsDNA) viruses whose replication is restricted to ectothermic vertebrates. Many highly pathogenic members of the genus
Ranavirus
encode a homologue of the eukaryotic translation initiation factor 2α (eIF2α). Data in a heterologous vaccinia virus system suggest that the
Ambystoma tigrinum
virus (ATV) eIF2α homologue (vIF2αH; open reading frame [ORF] 57R) is involved in evading the host innate immune response by degrading the interferon-inducible, dsRNA-activated protein kinase, PKR. To test this hypothesis directly, the ATV vIF2αH gene (ORF 57R) was deleted by homologous recombination, and a selectable marker was inserted in its place. The ATVΔ57R virus has a small plaque phenotype and is 8-fold more sensitive to interferon than wild-type ATV (wtATV). Infection of fish cells with the ATVΔ57R virus leads to eIF2α phosphorylation, in contrast to infection with wtATV, which actively inhibits eIF2α phosphorylation. The inability of ATVΔ57R to prevent phosphorylation of eIF2α correlates with degradation of fish PKZ, an interferon-inducible enzyme that is closely related to mammalian PKR. In addition, salamanders infected with ATVΔ57R displayed an increased time to death compared to that of wtATV-infected salamanders. Therefore, in a biologically relevant system, the ATV vIF2αH gene acts as an innate immune evasion factor, thereby enhancing virus pathogenesis.
Human Papillomavirus Type 16 E5 Protein Induces Expression of Beta Interferon through Interferon Regulatory Factor 1 in Human Keratinocytes
Authors: Muto Valentina , Stellacci Emilia , Lamberti Angelo Giuseppe , Perrotti Edvige , Carrabba Aurora , Matera Giovanni , Sgarbanti Marco , Battistini Angela , Liberto Maria Carla , Focà Alfredo
Published: March 2011

Crucial steps in high-risk human papillomavirus (HR-HPV)-related carcinogenesis are the integration of HR-HPV into the host genome and loss of viral episomes. The mechanisms that promote cervical neoplastic progression are, however, not clearly understood. During HR-HPV infection, the HPV E5 protein is expressed in precancerous stages but not after viral integration. Given that it has been reported that loss of HPV16 episomes and cervical tumor progression are associated with increased expression of antiviral genes that are inducible by type I interferon (IFN), we asked whether E5, expressed in early phases of cervical carcinogenesis, affects IFN-β signaling. We show that the HPV type 16 (HPV16) E5 protein expression
per se
stimulates IFN-β expression. This stimulation is specifically mediated by the induction of interferon regulatory factor 1 (IRF-1) which, in turn, induces transcriptional activation of IRF-1-targeted interferon-stimulated genes (ISGs) as double-stranded RNA-dependent protein kinase R (PKR) and caspase 8. Our data show a new and unexpected role for HR-HPV E5 protein and indicate that HPV16 E5 may contribute to the mechanisms responsible for cervical carcinogenesis in part via stimulation of IFN-β and an IFN signature, with IRF-1 playing a pivotal role. HPV16 E5 and IRF-1 may thus serve as potential therapeutic targets in HPV-associated premalignant lesions.
Role of the Herpes Simplex Virus 1 Us3 Kinase Phosphorylation Site and Endocytosis Motifs in the Intracellular Transport and Neurovirulence of Envelope Glycoprotein B
Authors: Imai Takahiko , Arii Jun , Minowa Atsuko , Kakimoto Aya , Koyanagi Naoto , Kato Akihisa , Kawaguchi Yasushi
Published: March 2011

Herpes simplex virus 1 (HSV-1) Us3 protein kinase phosphorylates threonine at position 887 (Thr-887) in the cytoplasmic tail of envelope glycoprotein B (gB) in infected cells. This phosphorylation downregulates cell surface expression of gB and plays a role in viral pathogenesis in the mouse herpes stromal keratitis model. In the present study, we demonstrated that Us3 phosphorylation of gB Thr-887 upregulated the accumulation of endocytosed gB from the surfaces of infected cells. We also showed that two motifs in the cytoplasmic tail of gB, tyrosine at position 889 (Tyr-889) and dileucines at positions 871 and 872, were required for efficient downregulation of gB cell surface expression and upregulation of accumulation of endocytosed gB in infected cells. A systematic analysis of mutations in these three sequences in gB suggested that the expression of gB on the surfaces of infected cells was downregulated in part by the increase in the accumulation of endocytosed gB, which was coordinately and tightly regulated by the three gB trafficking signals. Tyr-889 appeared to be of predominant importance in regulating the intracellular transport of gB and was linked to HSV-1 neurovirulence in mice following intracerebral infection. These observations support the hypothesis that HSV-1 evolved the three gB sequences for proper regulation of gB intracellular transport and that this regulation plays a critical role in diverse aspects of HSV-1 pathogenesis.
ZITTERBEWEGUNG IS NOT AN OBSERVABLE
Authors: O'CONNELL R. F.
Published: March 2011

It has recently been claimed that Zitterbewegung has been observed. However, we argue that it is not an observable and that the authors' observations must be reinterpreted.
ENTANGLEMENT IN THE ANISOTROPIC KONDO NECKLACE MODEL
Authors: MENDOZA-ARENAS J. J. , FRANCO R. , SILVA-VALENCIA J.
Published: March 2011

We study the entanglement in the one-dimensional Kondo necklace model with exact diagonalization, calculating the concurrence as a function of the Kondo coupling J and an anisotropy η in the interaction between conduction spins, and we review some results previously obtained in the limiting cases η = 0 and 1. We observe that as J increases, localized and conduction spins get more entangled, while neighboring conduction spins diminish their concurrence; localized spins require a minimum concurrence between conduction spins to be entangled. The anisotropy η diminishes the entanglement for neighboring spins when it increases, driving the system to the Ising limit η = 1 where conduction spins are not entangled. We observe that the concurrence does not give information about the quantum phase transition in the anisotropic Kondo necklace model (between a Kondo singlet and an antiferromagnetic state), but calculating the von Neumann block entropy with the density matrix renormalization group in a chain of 100 sites for the Ising limit indicates that this quantity is useful for locating the quantum critical point.
OPTICAL PROPERTIES AND KINETIC ROUGHENING INFLUENCE ON DISPERSIVE CASIMIR AND VAN DER WAALS FORCES
Authors: PALASANTZAS G. , SVETOVOY V. B. , VAN ZWOL P. J.
Published: March 2011

Casimir and van der Waals dispersive forces between real material surfaces can be strongly influenced by surface roughness and the frequency dependent dielectric functions of the interacting materials. The Lifshitz theory allows calculations of these forces between two flat plates if the frequency dependent dielectric function is known. Even in this case in order to compare different measurements of the Casimir force the accuracy must be higher than the force uncertainty arising as a result of the variation in the measured dielectric functions for a given material. Therefore, when we are dealing with dispersive forces between real materials, precise characterization of the particular interacting samples is critical. For this reason the effects of optical properties and surface roughness on dispersive forces will be first discussed in this review paper. Finally, we will compare research results among various research groups, at relatively large surface separations where roughness plays insignificant role, in order to show the level of consensus that has developed in this field in the recent years.
LEAKAGE POWER REDUCTION OF ASYNCHRONOUS PIPELINES
Authors: GHAVAMI BEHNAM , PEDRAM HOSSEIN , SALARPOUR AREZOO
Published: March 2011

With CMOS technology scaling, leakage power is expected to become a significant portion of the total power. A dual-threshold CMOS circuit, which has both high and low threshold transistors in a single chip, can be used to deal with the leakage problem in high performance applications. This paper presents dual-threshold voltage technique for reducing leakage power dissipation of Quasi Delay Insensitive asynchronous pipelines while still maintaining high performance of these circuits. We exploited the Dependency Graph model to produce a formal performance analysis. In order to reduce leakage power an efficient algorithm for selecting and assigning high threshold voltage to templates of a pipeline is proposed. Results obtained indicate that our proposed technique can achieve on average 40% savings for leakage power, while there is no performance penalty.
ON THE TRANSFORMATION OF GROUNDED INDUCTORS TO FLOATING INDUCTORS USING OFA AND FCCII
Authors: SOLIMAN AHMED M.
Published: March 2011

It is well known that a floating inductor circuit is realized from a grounded inductor circuit by replacing the operational amplifier by a floating operational transconductance amplifier. This idea is extended to transform current conveyor grounded inductors to floating inductors by replacing the current conveyor by the recently introduced floating current conveyor. Several examples are considered and simulation results are given to support the theory. Although the paper is partially a review in nature it includes several new realizations of floating inductors.