bluuebunny/crossref_metadata_2025 huggingface dataset:
The “Continuously Morphing” Retail TNC During Market Entry: Interpreting Tesco's Expansion into the United States
Authors: Lowe Michelle , Wrigley Neil
Published: October 2010

abstract

One important element of recent conceptualizations of the distinctive nature and challenges of retail transnational corporations (TNCs) is a focus on the mutual transformation of both the markets entered by the retail TNCs and, reciprocally, of the organizational structures of the firms themselves. There are important similarities between this view of ongoing transnational‐operation‐induced organizational transformation of the retail TNCs and processes that strategic and organizational management scholars describe as “continuous morphing.” In this article, we provide a theoretically informed study of one of the most dynamic of the retail TNCs (Tesco plc) “morphing” its organizational structures and competencies during a high risk, but potentially transformational, market entry into the western United States. The article positions the study within the rapidly emerging literature on transnational retail and the global economy, interprets the innovative dimensions of Tesco's U.S. market entry—particularly its attempts to achieve “territorial” and “network embeddedness”—through the conceptual lens recently provided by economic geographers, and assesses ongoing transformational impacts of the entry on the firm. It adds value to the literature on retail foreign direct investment by documenting the ways in which this leading retail TNC has attempted both to reconfigure its existing capabilities and to develop the new capabilities required to support its U.S. market entry via a combination of processes that we describe as transference, splicing, and enhanced imitation.
World Development Report 2009: A Practical Economic Geography
Authors: Deichmann Uwe , Gill Indermit , Goh Chor Ching
Published: October 2010

abstract

The World Development Report 2009: Reshaping Economic Geography (WDR 2009a) was written to inform policy debates about urbanization, lagging areas, and globalization. During almost two years of consultations and dissemination, the report met with broad acceptance among government officials, development professionals, and researchers. Policymakers grappling with difficult spatial development issues have found the report's analytical framework compelling and its policy guidance useful. An exception to this generally favorable reception has been the reaction from a number of economic geographers. In this article, we respond to criticisms about the report's scope, guiding framework, and policy implications that are emphasized in the accompanying articles in this issue of Economic Geography. In conclusion, we agree with economic geographers such as Rodríguez‐Pose who call for critical engagement with the report and with the more detailed follow‐up studies that use the WDR 2009's framework. This would both improve the quality of spatial policy advice and increase the visibility of economic geographers in international development debates.
Experimental Investigation of Flow Boiling Heat Transfer Characteristics of FC-72 in Cross-Linked Microchannel Heat Sinks Using Thermochromatic Liquid Crystals
Authors: Megahed Ayman , Hassan Ibrahim , Cook Kristina
Published: October 2010

The present study investigates the effect of cross-links on flow boiling heat transfer characteristics in rectangular microchannel heat sinks, using FC-72 as the working fluid. The silicon test section consists of 45 cross-linked microchannels, measuring 16 mm in length, with a hydraulic diameter of 248 μm. The parameters investigated include mass flux, heat flux, and exit quality, ranging from 99–275 kg/m2s, 7.2–88.8 kW/m2, and 0.01–0.71, respectively. Thermochromatic liquid crystals have been used in the present study as full-field surface temperature sensors to map the temperature distribution on the heat sink surface. The flow boiling heat transfer coefficient shows a different trend in the cross-linked design relative to the straight microchannel design. The flow boiling heat transfer coefficient increases with increasing exit quality at a constant mass flux, which is caused by the domination of the nucleation boiling mechanism in the cross-link region. The predictions obtained from the existing heat transfer correlations found in the literature significantly under-estimate the present heat transfer measurements, except for the Yu et al. (2002) correlation.
Design and Fabrication of Low-Voltage Twisting-Type Thermal Actuators for Micromirrors
Authors: Kim Dong Hyun , Park Seungho , Kwon Ohmyoung , Choi Young Ki , Lee Joon Sik
Published: October 2010

A twisting-type micromirror that can be driven by two thermal bimorph actuators bending in opposite directions is designed from electro-thermo-mechanical theories and fabricated through a simple MEMS process. Each actuator consists of SiO2 and gold thin-film layers. A simplified analytical model has been built to optimize the performance of micromirrors. Operation of the actuation system agrees well with predictions from theoretical models and simulations using a commercial code.
Characteristics of Small Diffusion Flames in a Confined Space
Authors: Gan Yunhua , Yang Zeliang
Published: October 2010

With the demand of smaller scale and higher energy density power sources, Micro Energy System has received more and more concern in last few years. Flame shape is an important characteristic of laminar diffusion flames. Experiments were performed to investigate the small diffusion flames burning, liquid ethanol in quiescent, room-temperature air. Ethanol diffusion flames were stabilized on top of vertical capillary tubes. Test conditions involved burner inner diameters of 1.0 mm, and fuel mass flowrates of 1.8–2.25 ml/h. The laminar diffusion flame in a confined physical environment is considered with fuel (ethanol) admitted as a central jet and air as a co-flowing annular jet. The burner outer diameter is 2mm, and inner diameter of the tube outside the burner is 8.8mm. The extremely small ethanol flowrates were accurately controlled by a syringe pump. The flame shapes were visually observed using a high speed CCD camera. Normalized lengths of flames were correlated with Reynolds number, and Normalized widths of flames were correlated with Reynolds number and Froude number respectively. The experimental results were compared with classical theory for diffusion flames.
An Accurate and Stable Numerical Method for Solving a Micro Heat Transfer Model in a 1D N-Carrier System in Spherical Coordinates
Authors: Dai Weizhong , Tzou Da Yu
Published: October 2010

We consider the generalized micro heat transfer model in a 1D microsphere with N-carriers and Neumann boundary condition in spherical coordinates, which can be applied to describe non-equilibrium heating in biological cells. An accurate and unconditionally stable Crank-Nicholson type of scheme is presented for solving the generalized model, where a new second-order accurate numerical scheme for the Neumann boundary condition is developed so that the overall truncation error is second-order. The present scheme is then tested by a numerical example. Results show that the numerical solution is much more accurate than that obtained based on the Crank-Nicholson scheme with the conventional method for the Neumann boundary condition. Furthermore, the convergence rate of the present scheme is about 1.8 with respect to the spatial variable, while the convergence rate of the Crank-Nicholson scheme with the conventional method for the Neumann boundary condition is only 1.0 with respect to the spatial variable.
Two-Way Coupling Model for Fractal-Like Agglomerate-Laden Multiphase Flow
Authors: Yu Mingzhou , Lin Jianzhong , Zhang Kai , Zhang Gaohui
Published: October 2010

The disturbing of ultrafine particles on carrying phase is usually ignored in studies on dilute ultrafine particle systems. In a dense fractal-like agglomerate system, however, the effect of particle phase on carrier phase should be considered due to its unique heat and mass transfer while the corresponding mathematical model for this problem has not been established. By taking the agglomerate-laden suspension as a single pseudo fluid, we propose a two-way coupling model in which the developed governing equations for suspension and particle general dynamic equation (PGDE) for particle coagulation and breakage due to turbulence are simultaneously solved. The Taylor-expansion moment method has been applied to solve fractal-like aggregate process and dilute gas-to-particle conversion, and in this study it is further extended to close the PGDE equation by invoking fractal theory. The newly coupling model is not limited in dilute particle system, and thus it is expected to play important roles in studying dense fractal-like agglomerate synthesis or other particulate industrial applications.
Improving Micro Combustor Stability With External Heating
Authors: Zhou Zhijun , Wang Yang , Yang Weijuan , Zhou Junhu , Liu Jianzhong , Wang Zhihua , Cen Kefa
Published: October 2010

Heat loss is the key factor to micro combustor stability. In this experiment, a quartz-glass micro combustor with inner diameter of 2 mm is tested with wind sweeping over its surface. The wind temperature is adjusted from 4 to 728 °C to control the combustor heat loss. According to the experimental results, the combustor stability increases with the wind temperature. Take 0.2 L/min as an example, the equivalence ratio at stability limit is 0.652–3.96 with 4 °C wind, and extends to 0.540–12.0 with 107 °C wind. Computational fluid dynamic simulation reveals that hotter wind intensifies the reaction, thus reaction temperature and OH concentration increase accordingly. Moreover, hotter wind enhances the heat recirculation, which causes shift upstream of flame. Increasing flow rates also inhibits extinction. But the quenching mode transforms from extinction to blowout, while the flow rate exceeds about 0.28 L/min. In the rich cases, hot wind with higher temperature aggravates blowout, which is opposite to the lean cases. According to the experimental phenomenon, the reaction region locates close to the inlet in the rich cases, where the flow velocity increases dramatically. Therefore, the imbalance between flow velocity and burning velocity causes blowout.
A Numerical Investigation on Micro Particle Dynamics Near an Evaporating Meniscus
Authors: Pan Zhenhai , Wang Hao
Published: October 2010

Clarifying the particle dynamics near an evaporating meniscus in microfluidics makes great sense in many biological and chemical processes such as analyte enrichment, particle detection and cell position control. In the present work, a numerical model is developed to describe the mass transport and particle dynamics near an evaporating meniscus sustained at the outlet of a micro PDMS tube. The micro flow field is simulated in Computational Fluid Dynamics (CFD) approach. Both the evaporation at the liquid-air interface and the vapor diffusion in air are considered. The convection near meniscus caused by the evaporation and Marangoni effect at interface is presented. Discrete Element Method (DEM) is introduced and coupled to CFD to study the particle dynamics in liquid affected by the convection, the gravity and the buoyancy.
Using an Evaporating Meniscus to Trap Cells in a Microfluidic Chip: Design and Modeling
Authors: Pan Zhenhai , Wang Hao
Published: October 2010

A microfluidic device based on Marangoni effect on a volatile meniscus is proposed for cell enrichment and collection. The device consists of a main channel in which cells are flowing with the mainstream, and an open-outlet channel which is connected with the main channel. A meniscus is sustained in the opening channel and keeps evaporating since the outlet is open to the atmosphere. Marangoni vortexes are generated near the meniscus due to the non-uniform evaporation on the meniscus. The vortexes influence the flow field and cell dynamics in the main channel, which can be used to trap the cells. A comprehensive numerical simulation is adopted in present work to reveal how the heat and mass transport going on in such a system. The evaporation and vapor diffusion at the liquid-air interface, and the vapor diffusion in air are considered. The convections due to the evaporation and Marangoni effect are simulated.
Impacts of Nanoscale Features on Infrared Radiative Properties of Metallic Slit Arrays
Authors: Chen Y.-B. , Chen J.-S. , Hsu P.-F.
Published: October 2010

Radiative properties (absorptance, reflectance, and transmittance) of deep slits with five nanoscale slit profile variations at the transverse magnetic wave incidence are numerically investigated in this work by employing the rigorous coupled-wave analysis. For slits with attached features, their radiative properties can be much different due to the modified cavity geometry and dangled structures, even at wavelengths between 3 and 15 μm. The shifts of cavity resonance excitation result in higher transmittance through narrower slits at specific wavelengths and resonance modes are confirmed with the electromagnetic fields. Opposite roles possibly played by features in increasing or decreasing absorptance are determined by the feature position and demonstrated by Poynting vectors. Correlations among all properties of a representative slit array, the angle of incidence, and the slit density are also comprehensively studied.
Separation of Nanocolloids by Taylor Cone Harmonics
Authors: Cheng Xinguang , Senapati Satyajyoti , Chang Hsueh-Chia
Published: October 2010

The conducting Taylor cone can activate specified harmonics of Laplace equation near the cone and can generate field maxima at multiple discrete polar angles. As the nanocolloids are ejected out from the cone tip, the difference of dominating forces in axial and transverse direction defines size-dependent initial angle before the colloids are trapped by the field maxima of the harmonics at the closest polar angle. This size-dependent selection of harmonics governs the different size colloids to travel along different trajectories and form separated deposition in the downstream of the electrospray. This electrospray-based separation of nanocolloids is successfully used to detect DNA hybridization. A family of cone shape is generated by changing voltage in a finite range. Variation of Taylor cone angle changes the harmonics and the trajectory of colloid is found to shift to a larger polar angle under higher voltage.
Thermal Conductivity of Carbon Nanotubes With Stone-Wales Defects
Authors: Li Wei , Feng Yanhui , Peng Jia , Zhang Xinxin
Published: October 2010

Thermal conductivity of (5,5) and (3,3) carbon nanotubes with Stone-Wales (SW) defects is investigated by molecular dynamics simulation. Non-equilibrium molecular dynamics method is employed and the reactive empirical bond order potential is chosen. In the simulation, the temperature difference is given by applying the Berendsen thermostat model to each end of carbon nanotubes (CNTs). The thermal conductivity is calculated by Fourier’s equation. Different from linear temperature distribution along the tube for perfect CNTs without defects, there is temperature jump at defects for CNTs with a SW defect. The defect acts as additional phonon scattering centers and result in a local higher temperature gradient, which leads to a higher resistance to heat flow across the defect and thus a reduction in the thermal conductivity of the tube. The rotation angle of a SW defect barely influences the thermal conductivity of the tube. Probably, the thermal conductivity of CNTs with SW defects is more sensitive to the defect concentration than the defect distribution.
Experimental Study on Steam Condensation in Horizontal Microchannels
Authors: Ma Xuehu , Fan Xiaoguang , Lan Zhong , Hao Tingting , Song Tianyi
Published: October 2010

Experiment was conducted to study steam condensation in horizontal microchannel etched on silicon wafer and bonded by a Pyrex glass plate from the top. The trapezoidal microchannel had a top width of 7943.11μm and depth of 81.77μm with hydraulic diameter of 161.49μm. The experiments were performed at different steam mass fluxes ranged from 128 kg m−2 s−1 to 320 kg m−2 s−1, while the inlet temperature of cooling water was fixed at 30°C or 50°C. Characteristics of condensation heat transfer and pressure drop in microchannels were measured and discussed. The temperature of Pyrex glass and local steam quality were also tested. It is found that the heat transfer flux, heat transfer coefficient and pressure drop depend greatly on steam mass flux and cooling water temperature.
Generalized Adiabatic Two-Phase Pressure Drop Correlation in Evaporative Micro/Mini-Channels
Authors: Li Wei , Wu Zan
Published: October 2010

This paper presents an adiabatic two-phase pressure drop correlation using quality, the reduced pressure, Bond number, Froude number and Weber number covering wide range of channel dimensions, working fluids and operational conditions. With the channel diameter less than 3.25mm, existing adiabatic two-phase pressure drop database and correlations are reviewed. However, none of the existing correlations can predict the data sets precisely. Theoretically, there are four forces related to two-phase flow in channels: body forces, inertia, viscous and surface tension. The basic reason for the difference between conventional channel and micro-channel is the relative significance of the four forces. Thus, Bo (body forces/surface tension), Fr (inertia forces/gravitational forces) and We (inertia forces/surface tension) were included in the new correlation. Viscous force is considered in the reduced pressure term. The new correlation predicts the existing data sets accurately. Furthermore, Bond number could be used as a criterion to classify a flow path as a micro-channel or conventional channel.
Study on the Heat Source and Heat Sink for Micro Thermoelectric Generator Device
Authors: Song Ruiyin , Wang Xiancheng
Published: October 2010

The max power per mass/volume of micro (mini) thermoelectric is related not only to the internal efficiency of thermoelectric generator but also to heat source and heat sink of the device. In this paper, high caloric value liquid fuel and high energy store PCM fuels were used as heat source while low phase transition temperature PCM as heat sink, and thermoelectric device was designed for test. Furthermore, the analysis of related data was conducted by experiments, and the merit and status in quo of using Radioisotope in thermoelectric device was analyzed, which shows that it is useful to make thermoelectric device from mini to micro. The experimental results show that adding heat sink is helpful to reduce the volume and improve the output power of the device.
Measurement of Effective Thermal Conductivity of CNT-Nanofluids by Transient Short-Wire Method
Authors: Kohno Masamichi , Kimura Koichi , Moroe Shogo , Takata Yasuyuki , Woodfield Peter L. , Fujii Motoo
Published: October 2010

Thermal conductivity and thermal diffusivity of CNT-nanofluids and Al2O3-nanofulids were measured by the transient short-hot-wire method. The uncertainty of their measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. Three different shapes of Al2O3 particles were prepared for Al2O3–water nanofluids. For the thermal conductivity of Al2O3-water nanofluids, there are differences in the enhancement of thermal conductivity for differences in particle shapes. Hardly any enhancement of thermal conductivity was observed for SWCNT-water nanofluids because the volume fraction of SWCNT was extremely low. However, we consider by increasing the volume fraction of SWCNTs, it will be possible to enhance the thermal conductivity.
The Experimental Research and Numerical Simulation on Thermal Properties of Molten Salt at Melting Point
Authors: Liang Yannan , Zhou Jiemin , Yang Ying , Wu Ye , He Yanyan
Published: October 2010

The use of phase-change materials for latent heat storage is a new type of environmentally-friendly energy-saving technologies. Molten salts, one kind of phase-change materials, which have high latent heats, and whose phase transition temperatures match the high temperatures of heat engines, are the most widely used high-temperature phase-change heat storage materials. However, the heat transfer at solid/liquid phase interface belongs to Micro/Nanoscale Heat transfer, lots of the thermal properties of molten salt at melting point is difficult to test. In this investigation, based on the theory that the thermal conductivity can be determined by measuring the speed of the propagation of the solid/liquid phase interface during phase change, a set of system is developed to investigate the thermal conductivity of molten salts at liquid/solid phase transformation point. Meanwhile, mathematical calculation is applied to intuitively simulate the melting and solidifying process in the phase change chamber, by which the error could be analyzed and partly corrected and the result precision could also be increased. And a series of verification experiments have been performed to estimate the precision and the applicability of the measuring system to evaluate the feasibility of the method and measuring system. This research will pave the way to the follow-on research on heat storage at high temperature in industry.
An Investigation for the Usability of K-K Equations for Nano Porous Membranes
Authors: Lu Junfeng , Chu Yang , Lu Wen-Qiang
Published: October 2010

As physical model used to interpret the fluid behavior when it passes through a semi-permeable membrane, Kedem-Ketchalsky’s (K-K) equations [1, 2] were successfully used in a bunch of filtration processes. However, because they were developed and dedicated to normal ultra- and micro-filtration systems, their limitations were obviously observed in some sort of nano-filtration processes that the pore size of the filtration membrane is only several nanometers. This paper analyzed the feasible utilization scopes of K-K equations. And two methods, Molecular Dynamics (MD) method and Computational Fluid Dynamics (CFD) method, used respectively to analyze nano- and ultra-filtration processes are introduced in this paper.
Study on the Evolution of Nanofluid Droplet Heated on Horizontal Substrate
Authors: Guo Yali , Shen Shengqiang , Li Weizhong , Bennacer R.
Published: October 2010

Based on the moment space, the lattice Boltzmann method is applied to simulate the evolution of nanofluid droplet on a heated substrate. The results show that the evolution of nanofluid droplet experiences pinning, depinning stage and in the end ring stain is obviously found because of the nanoparticles’ strong pinning. The simulation results are compared with the experimental investigations of reference, and good agreements are obtained.
Mass Flow Rate Measurements in Microchannels
Authors: Graur Irina A. , Perrier Pierre , Me´olans J. G.
Published: October 2010

Mass flow rate measurements in a single silicon micro channel were carried out for various gases in isothermal steady flows. The results obtained from hydrodynamic to near free molecular regime by using a powerful experimental platform, allowed us to deduce interesting information, notably about the reflection/accommodation process at the wall. In the 0 – 0.3 Knudsen range, a continuum analytic approach was derived from NS equations, associated to first or second order slip boundary conditions. Identifying the experimental mass flow rate curves to the theoretical ones the tangential momentum accommodation coefficient (TMAC) of various gases was extracted. Over all the Knudsen range [0 – 50] the experimental results were compared with theoretical values calculated from the kinetic approaches: using variable accommodation coefficient values as fitting parameter, the theoretical curves were fitted to the experimental ones. Whatever the Knudsen range and whatever the theoretical approach, the TMAC values are found decreasing when the molecular weights of the gas increase (as long as the different gases are compared using the same approach). Moreover, the values of the various accommodation coefficients are rather close one to other but sufficiently smaller than unity to conclude that the full accommodation modelling is not satisfactory to describe the gas/wall interaction.
Silicon Nanowire Conductance in the Ballistic Regime: Models and Simulation
Authors: Lacroix David , Joulain Karl , Muller Jerome , Parent Gilles
Published: October 2010

This paper deals with phonon heat transport in silicon nanowires. A review of various techniques that can be used to assess thermal conductance of such nanodevices is presented and a peculiar attention is paid to the case of the Landauer Formalism that can describe extremely thin wires. Several models for normal modes of silicon nanowire determination are considered, among them elastic wave theory has been used to determine the normal mode number. Besides, transmission and reflection of phonon at the interface between two nanostructures is discussed. Calculations and comparisons of thermal conductance of a 20 nm silicon nanowire between bulk thermal reservoirs are thus discussed.
Atomistic Modeling of Conduction and Transport Processes in Micro-Porous Electrodes Containing Nafion Electrolytes
Authors: Zhou Xiangyang
Published: October 2010

Atomistic modeling and/or experimental methods were conducted to study transport processes in the porous electrodes of polymer electrolyte fuel cells (PEFCs) and of mediator enhanced polymer electrolyte supercapacitors (MEPESCs). The simulations show that vibrations of the Pt nanocrystallines on rhe carbon supports significantly impacts diffusion in the Nafion electrolyte clusters between the carbon supports and enhances the diffusivity of hydrogen, oxygen, methanol, water, and hydronium up to 8 times the nominal value. Charging the carbon support alters the diffusivities. It was visualized that charging of Pt nanocrystallines resulted in disintegration of the Pt catalysts leading to a reduction in catalytic activity of the catalyst layer. Re-precipitation and re-crystallization of the Pt under a full discharging condition can also be visualized using the molecular dynamics (MD) modeling method. MD simulations also indicate that the mobility of the iodine mediators is at least 10 times greater than other small ions in the Nafion electrolyte. The degradation of the MEPESC is dominated by the crossover of I− ions but not I2 in Nafion.
Numerical Study on Mixing of Two Fluids With Modified Tesla Structure
Authors: Hossain Shakhawat , Ansari Mubashshir Ahmad , Husain Afzal , Kim Kwang-Yong
Published: October 2010

In this study, a parametric investigation on mixing of two fluids in a modified Tesla microchannel, has been preformed. Modified Tesla micromixer applies both flow separation and vortices string principles to enhance the mixing. The fluid stream splits into two sub-streams and one of them mixes with the other again at the exit of the Tesla unit. Analyses of mixing and flow field have been carried out for a wide range of Reynolds number from 0.05 to 40. Mixing performance and pressure drop characteristics with two geometrical parameters, i.e, ratio of the diffuser gap to channel width (h/w) and ratio of the curved gap to the channel width (s/w), have been analyzed at six different Reynolds numbers. The vortical structure of the flow has been analyzed to explain mixing performance. The sensitivity analysis reveals that mixing is more sensitive s/w, than the h/w.
Experimental Study on Thermal Hydraulic Characteristics of Steam Condensation in Capillary Glass Tubes
Authors: Iiyama Koji , Kaneko Akiko , Abe Yutaka , Suzuki Yutaka
Published: October 2010

At present, a microchannel heat exchanger is requested to achieve high efficiency in small size energy equipments. In order to clarify the heat transfer mechanism in a microchannel heat exchanger, knowledge on the thermal hydraulic characteristics of condensation flow in the channels is essential. However, study on the thermal hydraulic characteristics of condensation flow in a microchannel is hardly conducted except visualization of flow patterns. Objectives of the present study are to estimate the heat transfer performance of the present device and to observe the condensation behavior of vapor flow to clarify the thermal hydraulic characteristics of condensation flow in a capillary tube. As the results, it is confirmed that the microchannel heat exchanger realizes heat exchange of 7 kW when phase changes. In a single capillary glass tube as a simulated unit microchannel, the annular flow, the injection flow and the bubbly flow in a capillary tube are observed. According to the comparison of the present device and the glass tube experiment, it is suggested that the flow structure in the microchannel heat exchanger is almost same as that in the glass capillary tube.
A Cryptographic System Utilizing the Reflectance From Periodic Nanostructures
Authors: Chen Y.-B. , Chen J.-S. , Hsu P.-f.
Published: October 2010

Both advances in nanoscale fabrication and in-depth understanding to physical mechanisms tailoring radiative properties paved the way for a cryptographic system utilizing periodic nanostructures and their optical responses. Here we numerically demonstrated working principles and capabilities of the system with a representative nanostructure and its specular reflectance. The ciphertext was a binary surface-relief silver grating and a series of numbers, which contained the information of the sender’s signature and plaintext. Though principles were universal to everyone using the system, messages kept their security because keys could much vary among each communication and different keys were employed for encryption/decryption. The system thus guaranteed the confidentiality and authentication of a message while high-density information could be hidden and delivered with a tiny or even a virtual structure. This work also presented strategies enhancing the safety of the proposed cryptographic system.
Control of Near-Field Emitted by Micro and Nanostructured Materials
Authors: Ben-Abdallah Philippe , Joulain Karl , Drevillon Je´re´mie , Domingues Gilberto
Published: October 2010

Progress in synthesis technologies of micro and nanocomposite materials has opened the way to the control of electromagnetic field these media spontaneously emit in their surrounding. If numerous nanostructured materials [1–3] have been designed during the last decade to control both spectrally and directionally the far (propagative) field that they radiate in their surrounding, very few attention has been paid so far to the control of non-radiative field which exponentially decreases from their surface. However, such control is very important to improve the performance of numerous near-field technologies such as the plasmon assisted nanophotolitography [4], the near-field spectroscopy [5] and to develop new energy conversion technologies such as the near-field thermophotovoltai¨c energy conversion [6]. The near field properties of micro and nanostructured materials are closely conditioned by the presence, hybridization and coupling of localized modes within the structure. These modes come from the presence of collective oscillations of free electrons in metallic compounds or from the vibrations of partial charges carried out by atoms in polar materials. In this paper we present an approach we have recently developed [7] to design micro and nanolayered thermal sources with a tailored near-field emission spectrum and we briefly discuss the basic physical mechanisms involved in these modifications of field.
Analysis of Laminar Heat Transfer on Super-Hydrophobic Surface With Slip Velocity
Authors: Sun Wei , Zhou Yuhong , Fan Xinxin , Liu Tianqing
Published: October 2010

It is still in suspense for the effects of slip velocity and structural parameters on the heat transfer on a super-hydrophobic surface. It is thus necessary to study it in both theory and experiments. In this paper, the convective heat transfer with constant heat flux condition inside a circular microchannel was investigated. The velocity and temperature profiles when slip velocity exists were derived firstly, and then the heat transfer coefficient and Nusselt number were obtained. Furthermore, an effective conduction model for the super-hydrophobic surface with different structural parameters was proposed and the thermal resistance of the surface with trapped air was calculated. Finally, the effective heat transfer coefficient of super-hydrophobic surface was found with the integration of heat transfer coefficient and surface thermal resistance. The calculation results show that 1) the slip of fluid on a super-hydrophobic surface makes the temperature profile inside the channel more uniform, and the heat transfer coefficient or Nusselt number increased, 1.8 times higher maximally under constant heat flux condition; 2) the thermal resistance of super-hydrophobic surface increases with trapped air volume; 3) the effective heat transfer coefficient on super-hydrophobic surface declines seriously with trapped air volume, especially with the trapped air area; 4) there exists a critical thickness for the trapped air on a super-hydrophobic surface with given surface structural parameters, under which the effective heat transfer coefficient is not less than that on normal surfaces without slip. Therefore, it is necessary to consider the structural parameters of super-hydrophobic surfaces, such as rib height and distance between ribs, so that the heat transfer on the super-hydrophobic surface will not be impacted by the trapped air.
Miniaturized Pulse Compressor of Deep-Etched Gratings
Authors: Jia Wei , Zhou Changhe , Feng Jijun
Published: October 2010

In this paper we propose a miniaturized pulse compressor which can be used to compensate the group velocity dispersion (GVD) that is produced from a commercial femtosecond laser cavity. The compressor is composed of two identical high efficient deep-etched transmittive gratings. Compared with prism pairs, high efficient deep-etched transmittive grating pairs will have the advantages of small size and light weight. With optimized groove depth and duty cycle, 98% diffraction efficiency of the −1 transmittive order can be achieved at wavelength of 800 nm under Littrow condition. The deep-etched gratings are fabricated in fused silica by inductively coupled plasma (ICP) etching technology. With a pair of the fabricated gratings, the input positively-chirped femtosecond pulses of 73.9 fs are nicely compressed into the nearly-Fourier-transform-limited pulses of 43.2 fs. The miniaturized deep-etched-grating-based pulse compressor should be highly interesting for practical applications.
Flow and Convective Heat Transfer Characteristics of Nanofluids With Various Shapes of Alumina Nanoparticles
Authors: Hwang Kyo Sik , Ha Hyo Jun , Lee Seung Hyun , Kim Hyun Jin , Jang Seok Pil , Lim Hyung Mi , Choi Stephen U. S.
Published: October 2010

This paper is to investigate flow and convective heat transfer characteristics of nanofluids with various shapes of Al2O3 nanoparticles flowing through a uniformly heated circular tube under fully developed laminar flow regime. For the purpose, Al2O3 nanofluids of 0.3 Vol.% with sphere, rod, platelet, blade and brick shapes are manufactured by a two-step method. Zeta potential as well as TEM image is experimentally obtained to examine suspension and dispersion characteristics of Al2O3 nanofluids with various shapes. To investigate flow characteristics, the pressure drop of Al2O3 nanofluids with various shapes are measured. In order to investigate convective heat transfer characteristics, the effective thermal conductivities of Al2O3 nanofluids with various shapes, the temperature distribution at the tube surface and the mean temperature of nanofluids at the inlet are measured, respectively. Based on the experimental results, the convective heat transfer coefficient of Al2O3 nanofluids with various shapes is compared with that of pure water and the thermal conductivity of Al2O3 nanofluids with various shapes. Thus, the effect of nanoparticles shape on the flow and convective heat transfer characteristics flowing through a uniformly heated circular tube under fully developed laminar flow regime is experimentally investigated.
Molecular Dynamics Simulations of Relaxation and Heat Conduction in One-Dimensional FPU β Lattice
Authors: Hou Quan-Wen , Cao Bing-Yang , Guo Zeng-Yuan
Published: October 2010

The phonon relaxation and heat conduction of the Femi-Pasta-Ulam β lattice are studied via molecular dynamics simulations. The phonon relaxation rate is calculated from the energy autocorrelation function for different modes at various temperatures through equilibrium molecular dynamics simulations. The relaxation rate as a function of wave vector k is estimated to be proportional to k1.688, which leads to a N0.41 divergence of the thermal conductivity in the framework of Green-Kubo relation. This result is in agreement with that obtained by non-equilibrium molecular dynamics simulations which estimate the length dependence exponent of thermal conductivity as 0.415. Our results confirm the N2/5 divergence in one-dimensional FPU β lattice. The effect of the heat flux on the thermal conductivity is also studied by imposing large temperature differences on the two ends of the lattice in non-equilibrium molecular dynamics simulations. The results indicate that the thermal conductivity is insensitive to the heat flux under our simulation conditions, and the linear response theory is widely applicable.
Thermal Conductivity Enhancement of Binary Nanoemulsion(O/S) for Absorption Application
Authors: Sul Hea Youn , Cho Changhwan , Jung Jung-Yeul , Kang Yong Tae
Published: October 2010

Binary nanoemulsions, oil-droplet suspensions in binary solution (H2O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration cycles. This paper studies the formation and stability of n-decane in H2O/LiBr nanoemulsions produced by using polyoxyethylene lauryl ether and polyoxyethylene sorbitan monolaurate as surfactant. To stabilize the nanoemulsions in a strong electrolyte, polymeric stabilizer (gum Arabic) is used as a steric stabilizer. The droplet size and the thermal conductivity of binary nanoemulsions are measured by the dynamic light scattering method and the transient hot-wire method, respectively. It is found that the effective thermal conductivity of binary nanoemulsions (1.0 vol % of n-decane in 30 wt % H2O/LiBr) enhances up to 3.59% with the average droplet size of 44.3 nm. The stability has more significant effect on the thermal conductivity enhancement than the initial drop size.
Numerical Modeling of the Conjugate Heat Transfer Problem for Annular Laminar Film Condensation in Microchannels
Authors: Nebuloni Stefano , Thome John R.
Published: October 2010

This paper presents numerical simulations of annular laminar film condensation heat transfer in micro-channels of different internal shapes. The model, which is based on a finite volume formulation of the Navier-Stokes and energy equations for the liquid phase only, importantly accounts for the effects of axial and peripheral wall conduction and non-uniform heat flux not included in other models so far in the literature. The contributions of the surface tension, axial shear stresses and gravitational forces are included. This model has so far been validated versus various benchmark cases and versus experimental data available in literature, predicting microchannel heat transfer data with an average error of 20% or better. It is well-known that the thinning of the condensate film induced by surface tension due to gravity forces and shape of the surface, also known as the ‘Grigorig’ effect, has a strong consequence on the local heat transfer coefficient in condensation. Thus, the present model accounts for these effects on the heat transfer and pressure drop for a wide variety of geometrical shapes, sizes, wall materials and working fluid properties. In this paper, the conjugate heat transfer problem arising from the coupling between the thin film fluid dynamics, the heat transfer in the condensing fluid and the heat conduction in the channel wall has been studied. In particular, the work has focused on three external channel wall boundary conditions: a uniform wall temperature, a non uniform wall heat flux and single-phase convective cooling is presented. As the scale of the problem is reduced, i.e. when moving from mini to micro channels, the results shows that the axial conduction effects can become very important in the prediction of the wall temperature profile and the magnitude of the heat transfer coefficient and its distribution along the channel.
Determination of Loss Coefficients for Micro-Flow Devices: A Method Based on the Second Law Analysis (SLA)
Authors: Zhang H.-C. , Schmandt B. , Herwig H.
Published: October 2010

The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has only been applied to fully turbulent flows it is extended here to also cover the laminar flow regime. Specific numbers of K can be determined by integration of the entropy production field (second law analysis). This general approach is discussed and illustrated with the specific example of a conical diffusor.
Modeling Infrared Radiative Properties of Heavily Doped Silicon Complex Gratings With Geometric Modifications
Authors: Wang Ai-Hua , Hsu Pei-feng , Chen Yu-Bin , Liu Lin-Hua
Published: October 2010

Based on the prior work by authors, radiative properties of modified complex gratings with nanoscale features are studied. The purpose of this work is to demonstrate, even preliminary, the possibility of using complex gratings and nanoscale surface features to modify far field radiative properties. A finite-difference time-domain numerical scheme was used to model the infrared radiative properties of heavily doped silicon simple and complex gratings. The solutions were validated with those of rigorous coupled-wave analysis method. By properly choosing the carrier concentration and geometry, silicon complex gratings exhibit a broadband absorptance peak resulting from the excitation of surface plasmon polaritons. Meanwhile, the absorptance of four modified complex gratings with attached features has been numerically investigated for the impacts of the attached structures. Firstly, though absorptance spectra of gratings almost remain unchanged, their locations shift towards longer wavelengths. Secondly, the spectral absorptance peak of two modified complex gratings is wider than that of gratings without attached features due to the cavity resonance excitation. Thirdly, the spectral absorptance of complex gratings with square features in three sizes was compared and shows that the peak wavelength shifts toward longer wavelengths with enlarged feature size.
Plasma Lithography for Probing Cell Mechanoregulation
Authors: Junkin Michael , Wong Pak Kin
Published: October 2010

Mechanical and physical cues in the cellular microenvironment are important factors in the regulation of cellular activities, such as proliferation, apoptosis, differentiation, migration and adhesion. For instance, cells are known to respond dynamically to different topographical cues and biophysical structures, such as surface roughness, fiber diameters, and micro/nano scale patterns. Nevertheless, little is known about the fundamental physical mechanisms that govern the cell-substrate interactions and their roles in the regulation of physiological processes. This presents a major hurdle toward the realization of nanoengineered medicine. Herein, we report a plasma lithography technique to elucidate the influences of biophysical cues on different cellular activities. The plasma lithography technique selectively functionalizes polymeric and other biologically relevant surfaces, such as PDMS, glass and polystyrene, at scales ranging from millimeters to hundreds of nanometers. We applied this method to cellular patterning and examined the response of human mammary gland epithelial cells and mouse embryo fibroblasts to patterns of hydrophobic and hydrophilic areas towards the elucidation of the mechanoregulation of cellular processes. The technique enables us to systematically investigate the essential role of physical cues on cell migration, proliferation, and morphology. Collectively, these activities are not only fundamental in cell biology but also essential to the creation of novel tissue engineering constructs and medical implants. This study will shed light on how cells interact with their microenvironment as well as demonstrate a means to exercise control over cellular processes for future nanoengineered medical applications.
Entrainment of DNA and Charged Nano-Particles Using AC Electrospray
Authors: Wang Shau-Chun , Chen Hsiao-Ping , Chang Hsueh-Chia
Published: October 2010

We examine our earlier finding that AC electrospray cone can preferentially entrain and concentrate low-mobility ions generated at the cone tip [Chetwani, Maheshwari and Chang, Phys Rev Lett., 101, 204501 (2008)]. Instead of tip ionization, we scrutinize entrainment effects on dispersed ionic species in the spray solution. Fluorescence images of ejected ionic species, including anionic oxide ions, organic dyes, charged nano-particles, and stained DNA from AC electrospray cone generated with a 4–5 kV source. Negatively charged species such as anionic dyes concentrate at the tip of AC spray cone before ejection. Cationic dyes are more homogeneously distributed in the cone during ejection. Larger particles with negative charges, including fluorescence dye-tagged nano-particles (about 50 nm) and dye-stained DNA, have similar spatio-temporal evolutions of anioic dyes within the cone before ejection. These observations extend our previous entrainment and concentration effect to AC spray without ionization. The images will be correlated with tandem Mass Spectrometry and will be used to selectively gate either cationic (protein) or anionic polymers (DNA).
Microfluidic Solvent Extraction of Copper for Mineral Processing
Authors: Zhou Jingfang , Priest Craig , Sedev Rossen , Ralston John , Aota Arata , Mawatari Kazuma , Kitamori Takehiko
Published: October 2010

Solvent extraction of copper has been explored in a microfluidic chip (μSX). The transfer efficiency and rate of phase separation in μSX were compared to that achieved using conventional methods (bulk dispersion) both with and without fine silica particles present. Using the microfluidic approach, transfer efficiency was comparable to that achieved in conventional extraction. Phase separation is slow or totally arrested in bulk extraction, while instantaneous phase separation was achieved in μSX, even at high particle concentrations.
Dielectrophoretic Manipulation of Polystyrene Micro Particles in Microfluidic Systems
Authors: Zhang C. , Khoshmanesh K. , Kayani A. A. , Tovar-Lopez F. J. , Wlodarski W. , Mitchell A. , Kalantar-zadeh K.
Published: October 2010

In this work, DEP platforms with funnelled and micro-tip electrode patterns were fabricated, and integrated with polydimethylsiloxane (PDMS) microchannel blocks. The DEP platforms were employed to manipulate polystyrene particles of 1 and 3 μm. The response of the system was characterised in a wide range of signal magnitudes (1–30 V peak-to-peak) and frequencies (100 kHz to 200 MHz), as well as the liquid flow rates (1 to 10 μL/min). Calculations were also carried out to analyse the DEP spectra of polystyrene particles when suspended in the medium (deionised water) to determine the optimum operating frequency of the DEP systems. Both experimental results and theoretical calculations indicated that polystyrene particles can experience positive and negative DEP forces within certain frequency ranges of the applied electric field, and the crossover frequency (where the DEP force is zero) of the system strongly depends on the conductivities of the particles. Additionally, larger particles experience stronger DEP forces and can be more efficiently concentrated at or repelled along the electrodes. The concentration performance of the DEP systems were evaluated by measuring the thickness of particle streams at different flow rates. Finally, the ability of funnelled and micro-tip electrodes to trap the particles was compared.