bluuebunny/crossref_metadata_2025 huggingface dataset:
Examining Intercity Rail Passenger Station Access Patterns
Authors: Sperry Benjamin R. , Warner Jeffery E.
Published: July 2013

Travel on intercity passenger rail is growing in popularity across the U.S. Amtrak, the nation’s intercity passenger rail operator, reported a steady growth in ridership over the last decade; for the 12-month period ending in September 2011, Amtrak carried more than 30 million passengers, a first in the company’s 40-year history. This growth has resulted in widespread interest in developing new intercity passenger rail services or improving existing services with new station facilities and other investments. An issue of interest to the rail planning and policy community revolves around station access patterns, and there are many questions that remain unanswered on this subject. For this paper, these questions include: What is the mode share for passenger trips to and from the rail station? How far do passengers travel to access rail services? Has the market area for intercity passenger rail expanded with increasing ridership, or has the market area remained unchanged during this recent period of growth?

Using data obtained from on-board surveys of existing Amtrak passengers in Michigan and Wisconsin, USA, this paper examines the evolving nature of rail passenger station access patterns over the last decade. Specifically, patterns in the overall station access trip mode split, the passengers’ self-reported travel time to and from the rail station, and the spatial distribution of passenger home residential zip codes relative to the rail station are analyzed. Analysis shows that 50 percent of rail passengers reside between 8 and 20 miles from a rail station, depending on the route, and that the market area for selected routes has expanded in recent years. Rail planners can use the findings from this paper to develop new station facility designs or to correct issues that may be present at existing stations. The findings of this paper can also be used to guide the deployment of marketing and promotion of rail services to residents within the “catchment area” of a station.
Impact of Passenger Trains in Double Track Networks
Authors: Sogin Samuel L. , Barkan Christopher P. L. , Lai Yung-Cheng , Saat Mohd Rapik
Published: July 2013

North American freight railroads are expected to experience increasing capacity constraints across their networks. To help plan for this increased traffic, railroads use simulation software to analyze the benefits of capacity expansion projects. Simultaneous operation of heterogeneous traffic further increases delay relative to additional homogenous traffic. Additional passenger trains can cause more delays to freight trains than additional freight trains. Rail Traffic Controller (RTC) was used to run simulations with varying mixes of unit freight and passenger trains operating at various speeds on a double track configuration. Basic assumptions on the relative difference in priority between train types lead to drastically different results on the impact of adding higher priority trains. This assumption dictates whether the track in the opposing direction should be used for overtake maneuvers. Also, higher speed differentials between train types can result in higher delays as faster trains catch up to slower trains more quickly. These analyses will help planners improve their understanding of the tradeoff in capacity due to operation of different types of trains at different priorities and speeds.
Railroad Tie Responses to Directly Applied Rail Seat Loading in Ballasted Tracks: A Computational Study
Authors: Yu Hailing , Jeong David
Published: July 2013

This paper describes work in-progress that applies the finite element (FE) method in predicting the responses of individual railroad crossties to rail seat pressure loading in a ballasted track. Both wood and prestressed concrete crossties are examined. The concrete tie is modeled as a heterogeneous medium with prestressing wires or strands embedded in a concrete matrix. The constitutive relations employed in the models are: elasticity followed by damaged plasticity for the concrete material, linear elastic bond-slip relations with potential initiation and evolution of damage to the bond for the steel-concrete interfaces, orthotropic elasticity followed by failure dictated by orthotropic stress criteria for the wood ties, extended Drucker-Prager plasticity for the granular and frictional ballast material, and elastic half space for the subgrade. The corresponding material parameters are obtained from the open literature.

Under a simplified pressure load uniformly distributed over the rail seat area, the FE method predicts tensile cracking at the tie base below the rail seats of a concrete tie and compressive failure in the rail seats of a wood tie. The rail seat force-displacement relations are obtained from the simulations. The resultant rail seat forces at which tie failures occur are compared for concrete and wood ties.

The FE method appears to be a promising tool for studying the railroad tie behavior under rail seat loading conditions in a ballasted track. Experimental data will be sought to calibrate the material parameters and verify the modeling approach. Additional track components, particularly rails, rail pads and fasteners, will be incorporated in future modeling efforts. This detailed modeling approach may help to shed light on the rail seat deterioration failure mechanisms observed in some concrete ties.
Design Factors Effecting Capacity of Rail and Transit Systems
Authors: Thurston David F.
Published: July 2013

The overall impact on system “capacity” is typically described in terms of train control design. There are several other key factors that determine the ultimate system capacity of a rail line. Among the most influential of these are: vehicle type and configuration, stations and platform design and configuration, and overall civil alignment. In the analysis of the maximum capacity delivered from the train control system, all of these require optimization of design to achieve the highest throughput, and have a direct influenced by train control design as well. This paper describes how fully optimized design of non train control issues and factors have an impact on signal system design and have a consequence that is permanent once constructed.
Comparison of Interior Crashworthiness Observed in Passenger Train Accidents and 8G Dynamic Seat Sled Tests
Authors: Severson Kristine , Tyrell David
Published: July 2013

The Office of Research and Development of the Federal Railroad Administration conducts engineering research to address protection of passengers and crew during train accidents. This research includes accident investigations and dynamic seat testing to assess occupant injury during simulated accident conditions.

Observations from selected accident investigations are compared with dynamic seat test results, based on the requirements in the Standard for Passenger Seats in Passenger Rail Cars, APTA-SS-C&S-99-016 [1], referred to simply as the Seat Standard. The Seat Standard requires sled testing of rail passenger seats to demonstrate that seats provide a minimum level of crashworthiness in the event of an accident.

The interior crashworthiness comparisons between accidents and seat tests are based on the deceleration time history (crash pulse), damage to seats and/or tables, injury type and severity, and occupant kinematics. These comparisons have been made to assess the degree to which current test practice produces injury measurements and interior fixture damage that are consistent with the injuries and equipment damage observed in accidents. When test results and accident observations do not compare well, revisions to the prescribed test conditions may be warranted.

The following three accidents have been selected for comparison in this paper. They were selected from accident investigations in which the Volpe National Transportation Systems Center participated, the amount of relevant data collected during the investigation, and the dynamic seat test data that was available for comparison of the specific type of seats or tables involved in the accidents. The accidents represent a range of accident speeds, type of equipment, and collision severity:

- passenger train to freight train collision with a closing speed of 80 mph in Chatsworth, California, on September 12, 2008 [2];

- passenger train to freight train collision with a closing speed of 33 mph in Chicago, Illinois, on November 30, 2007 [3, 4];

- passenger train to freight car collision with a closing speed of 23 mph in Canton, Massachusetts, on March 25, 2008.

A companion paper provides detail on the structural crashworthiness of the cars in the same three accidents, and describes the computer models that were developed to estimate the crash pulse, or acceleration-time history, for each rail car in the accidents [5].
Track Performance Modeling Under Mixed Traffic
Authors: Huang Hai
Published: July 2013

The majority US high speed trains are sharing the same track network with freight trains, which will bring different load patterns i.e. different peak loads, speeds, and loading sequence and durations to the current track infrastructure. The change in loading characteristics especially when train is moving at so called “Critical Speeds” may however cause unfavorable track performances, for instance increase in track settlement (both in ballast and the subgrade soil). Effort has been taken in this research to investigate the impact of different load patterns on the track settlement accumulation. A fully coupled dynamic track model consists of a vehicle, rail-tie-ballast “Sandwich” upper structure, and a finite 3D soil substructure model is developed and utilized to obtain the loading pulses and pulse combinations introduced by different traffic patterns. A Discrete Element Modeling approach is then employed to simulate the ballast settlement under those realistic loading pulses and pulse combinations. Results and conclusions will be highlighted and recommendations will be made in the end.
Formal Methods Verification and Validation (V&V) for Legacy Systems
Authors: Georgiadis Sofia K.
Published: July 2013

For over a decade, the benefits of Formal Methods software system development techniques have been realized in safety critical applications in a variety of industries, such as aerospace, aviation, and of course rail-transit. Many of these Formal Methods techniques have focused on the development of new systems. In new system development, Formal Methods provide assurance of error-free specification, design, and software code implementation, often via automated code generators. Legacy systems have been largely excluded from the Formal Methods field, due to a perception that their use would entail costly re-engineering, require specialized knowledge, and would necessitate a large learning curve.

However, Formal Methods may be used for Verification and Validation (V&V) of legacy systems without the costly risk factors enumerated above. A description of the methodologies used is provided, including a description of how the process is tailored to new acquisitions and deployments of legacy systems. The modeling was fully integrated in the rail property and contractor development processes. As each design phase progressed, the formal methods process provided an increased level of confidence with regard to safety assurance and the correctness of the system design. This was achieved by generating formal proofs for each safety critical function, and by refining these formal proofs into progressively lower-level elements. These proofs then provided criteria for design reviews, code reviews, and test scenarios. The benefits of obtaining formal, that is, mathematical, formula-based, proofs of system design and consistency is indisputable. The criteria for evaluation are objective and thorough. One need not rely on the adequacy of peer reviews and manually generated test cases. Formal Methods V&V is therefore a cost-effective process that provides proof of correctness early in the system development life-cycle.
Spot Cooling Using Electrowetting-Controlled Thin Film Heat Transfer
Authors: Cheng Jiangtao , Chen Chung-Lung
Published: July 2013

We report an electrowetting-controlled cooling system with site-specific treatments on the heat source (evaporator or hot spot) surfaces. Electrowetting-on-dielectric (EWOD) has great potential in thermal management because EWOD-driven droplet transport has unique characteristics of prompt response, low power consumption and programmable paths without the need for any mechanical moving parts. Prompt and fast droplet transport is necessary for adaptive and active cooling of high heat flux targets. Using a multi-channel DC/AC control system, we carried out sequenced activation of AC voltages on coplanar electrodes and transmitted a droplet to the spot target along a programmable path. With high positioning accuracy at the chip level, we have successfully transmitted a water droplet of 15 μL at speeds as high as ∼10 cm/s. We further improved electrowetting cooling performance by coating a fine copper screen on the cooling targets. The capillarity associated with the copper screen facilitates the delivered droplets automatically spreading and clinging to the target surfaces. As a result, heat transfer is in the more efficient form of filmwise evaporation at the evaporator sites. To maintain a thin film with proper thickness on the hot spots, we implemented EWOD-assisted droplet splitting and merging to precisely control the droplet volume to avoid fluid flooding (accumulation) on the hot spot surfaces. Our investigation indicates that thin-film evaporation is a high-efficiency heat transfer mechanism on a hydrophilized hot spot surface. Based on EWOD technique with surface treatments, the superheat on a hot spot of 4mm × 4mm was maintained well below 30°C even when the heat flux reached as high as 80W/cm2. The closed loop of this novel thermal management system can potentially function as a wickless vapor chamber or heat pipe with enhanced heat dissipation capabilities.
Numerical Study on Near-Wall Natural Convection Over a Microscale Heating Wire
Authors: Zhou Leping , Zhang Yunfang , Yang Lijun , Du Xiaoze , Yoda Minami , Peterson G. P.
Published: July 2013

The study of the natural convection over a very small heat sources is important in the analysis of heat transfer problems in the electronics industry. However, the characteristics of the spatial distribution of the velocity in the near wall region, which is crucial to the mechanisms of heat transfer process in natural convection around a microscale object, is not well understood. In this investigation, the microscale natural convection in the near wall region of a platinum micro heat source was investigated numerically, using FLUENT, a commercially available computational fluid dynamics (CFD) software, and compared with corresponding experimental results. The influence of the nanoparticles on the natural convection was observed using the single-phase or two-phase models available in FLUENT. The temperature and velocity fields were obtained, with which the Brownian diffusion coefficient was deduced. The results indicate that the temperature gradient induced Brownian diffusion and thermophoresis in the near wall region plays an important role in the microscale natural convection in the water/nanoparticle mixture investigated and are in good agreement with the results from a corresponding experimental investigation.
Thermal Transport in Graphene Supported on Copper
Authors: Chen Liang , Kumar Satish
Published: July 2013

The present study investigates the thermal transport in suspended graphene and graphene supported on copper substrate using equilibrium molecular dynamics simulations, Green-Kubo method and relaxation time approximation (RTA) approach. The thermal coupling between graphene and copper substrate was investigated by varying the interaction strength between the carbon atoms and Cu atoms at the interface. The contribution of different phonon modes to the thermal conductivity of suspended and supported graphene was analyzed in order to elucidate the graphene-substrate thermal interactions. The thermal conductivity of graphene decreases with the increasing strength of the interfacial interaction. The analysis shows that the interactions with copper substrate can reduce the thermal conductivity by up to 44%. The decrease of thermal conductivity is primarily due to the suppression of contribution from out-of-plane acoustic (ZA) phonons in the large wave vector region.
Surface Plasmon Resonance Shifts of a Dispersion of Core-Shell Nanoparticles for Efficient Solar Absorption
Authors: Lv Wei , Otanicar Todd P. , Phelan Patrick E. , Dai Lenore , Taylor Robert A. , Swaminathan Rajasekaran
Published: July 2013

Nanoparticles are known to offer a variety of benefits for thermal transport, and of particular relevance here are the vast changes to the radiative properties due to the large extinction cross section at the corresponding surface plasmon resonance wavelength [1, 2]. Recent papers have indicated that dielectric core metallic shell nanoparticles yielded a plasmon resonance tunable from ultraviolet to infrared by changing the ratio of core radius to the total radius [3–6]. We are interested in developing a dispersion of core-shell multifunctional nanoparticles capable of dynamically changing their volume ratio and thus their spectral radiative properties. This work addresses the plasmon resonance tuning ranges for different metallic shell nanoparticles, and explores the solar-weighted efficiencies of corresponding core-shell nanoparticle dispersions. Through our electrostatic model, we achieve a shift in the plasmon resonance peak from a wavelength of about 500 nm to around 1500 nm for Au-coated silica core nanoparticles. Using core-shell nanoparticles dispersions, we show that it is possible to create efficient spectral solar absorption fluids. We also demonstrate that it is possible to design materials for applications which require variable spectral absorption or scattering.
Thermal Conductivity Behavior of Yttria Nanofluids
Authors: Masharqa Salim J. S. , Tesfai Waka , Singh Pawan K. , Chiesa Matteo , Shatilla Youssef
Published: July 2013

In this paper the effect of nanoparticle concentration and temperature on the thermal conductivity of Yttria-Ethylene glycol nanofluid has been investigated. In addition, the effect of aging on the viscosity and the thermal conductivity of these nanofluids also have been studied. The nanofluids were prepared by two-step method, and particle size distributions were characterized using acoustic spectroscopy. It was found that the thermal conductivity of Yttria nanofluids increases beyond the classical Hamilton-Crosser model. Moreover, the enhancement in the thermal conductivity of this nanofluid showed high temperature dependence behavior. For instance at 3.0% by volume particles loading, the thermal conductivity enhancement increased from 16.6% at 26 °C to 27.0% at 59 °C, making these nanofluids attractive and effective for cooling systems that operates at high temperatures. Finally, time dependent viscosity and thermal conductivity measurements showed stable behavior for 16 days of study demonstrating the good stability of these nanofluids.
Feasibility Assessment of the Integration of Microfluidics and NEPCM for Cooling Microelectronics Systems
Authors: Tigner Julaunica , Floyd-Smith Tamara
Published: July 2013

The growing demand for microelectronic systems to be smaller and faster has increased the energy released by these devices in the form of heat. Microelectronic systems such as laptop computers and hand held devices are not exempted from these demands. The primary traditional technologies currently used to remove heat generated in these devices are fins and fans. In this study, traditional methods were compared to more novel methods like cooling using forced convection in microfluidic channels and stagnant nanoparticle enhanced phase change materials (NEPCM). For this study, the difference between the surface temperature of a simulated microelectronic system without any cooling and with a particular cooling method was compared for several cooling scenarios. Higher ΔT values indicate more effective cooling. The average ΔT values for fans, fins, NEPCM and microchannels with water were 2°C, 5°C, 3°C and 4°C respectively. These results suggest that, separately, microchannel cooling and NEPCM are promising methods for managing heat in microelectronic systems.

Even more interesting than NEPCM or microchannel cooling alone is the potential cooling that can be achieved by combining the two methods to achieve multimode cooling first by the phase change of the NEPCM and then by circulating the nanofluid (melted NEPCM) through microchannels. A feasibility assessment, however, reveals that the combination of the two methods is not equal to the sum of the parts due to the viscosity and associated pumping power requirements for the melted phase change material. Nonetheless, the combination of the method still holds promise as a competitive alternative to existing thermal management solutions.
Impact of Contact Resistances on Electrical and Thermal Transport in Carbon Nanotube Network Transistors
Authors: Gupta Man Prakash , Estrada David , Pop Eric , Kumar Satish
Published: July 2013

The breakdown mechanism of carbon nanotube (CNT) networks is explored using a coupled electro-thermal model, which simulates both electrical and thermal transport in CNT network thin film transistors (CN-TFTs). The numerical results are validated against experimental observations on CN-TFTs with similar device geometry, network statistics, and thermal environment. We find the numerical predictions are in good agreement with experimental measurements of power and temperature of CN-TFT devices. Comparing the simulation results with experiments, we observe that the CNT-substrate thermal conductance per unit length is ∼0.1 Wm−1 K−1. This value represents high contact thermal resistance, but is very close to experimental estimations. The thermal profile and breakdown behavior of the CNT network is observed to be more sensitive to CNT-substrate interfacial thermal conductance compared to that of the CNT-CNT interface. The effect of CNT network density on breakdown behavior is also analyzed for relatively low densities of the network. The peak power dissipation in CN-TFTs before breakdown increases with network density, and this peak power is reached at the same source-to-drain bias (VSD) for all considered densities. The breakdown patterns in CN-TFTs of all considered densities are also observed to have similar characteristics.
Thermal Conductivity of Carbon Nanotube Aerogels With Different Filling Gases
Authors: Schiffres Scott N. , Kim Kyu Hun , Oh Youngseok , Islam Mohammad F. , Malen Jonathan A.
Published: July 2013

We report on measurements of thermal conductivity in single-walled carbon nanotube (SWCNT) aerogels in vacuum, and as infiltrated by different gases. The remarkable thermal, mechanical and electrical properties of single CNTs have led to great interest in bulk carbon nanotube materials, including the CNT aerogels. Carbon nanotube aerogels are light-weight (7–8kg/m3) and porous, which means that heat will be conducted in parallel through the SWCNT matrix and the filling gas. The overall thermal conductivity of the aerogel was measured with helium, and argon filling gases, using a modified 3ω method designed to interrogate low thermal effusivity materials. Measurements of thermal conductivity at vacuum are 0.023 W/m-K and at atmospheric pressure infiltrated SWCNT aerogels have thermal conductivities in helium of 0.19 W/m-K and in argon of 0.039 W/m-K. Our vacuum measurement suggests that transport within the aerogel is limited by the thermal interface resistance between SWCNTs, rather than by phonon transport within the SWCNT itself. We have also extracted the mean distance traveled by gas molecules between collisions with SWCNT aerogel by fitting the gas contribution to thermal conductivity using a kinetic theory based model.
Electrothermal Modeling and Design Strategies for Multibit Phase Change Memory
Authors: Li Zijian , Jeyasingh Rakesh G. D. , Lee Jaeho , Asheghi Mehdi , Wong H.-S. Philip , Goodson Kenneth E.
Published: July 2013

Electrothermal transport and crystallization dynamics govern the speed and reliability of multibit phase change memory (PCM). This work develops a transient simulation code incorporating the nanoscale electrical, thermal, and crystalline growth models to investigate various cell structures and programming strategies. The simulation evaluates the multibit performances of two standard PCM structures, the “mushroom” cell and the “confined pillar” cell, with feature sizes smaller than 40nm. This paper implements the simulation code to explore a more compact and reliable architecture, the stacked vertical cell, for precise control of the Joule heating and the intermediate resistance states. For an electrode area of 10nm × 20nm, very low programming current of 60μA – 90μA generates sufficient heating power to amorphize the phase change elements sequentially, resulting four distinct resistance levels for multibit applications.
A Study of On-Chip Aqueous Two Phase System Formation and its Applications
Authors: Wijethunga Pavithra A. L. , Moon Hyejin
Published: July 2013

Although there are several reports demonstrating the use of aqueous two-phase systems (ATPS) for biological sample separation in miniaturized devices, they only used ATPS prepared in macro scale by following the conventional way. Formation of ATPS in a confined micro scale environment and their characteristics has not been studied yet. While ATPS formation in macro scale is supported by vigorous mixing and gravitational force to form two phases, both mixing capability and gravitational force aid are insignificant in micro scale. Hence, in this study, we investigated the formation of ATPS under these inferior conditions of micro scale. An electrowetting on a dielectric (EWOD) digital microfluidic chip was used as the confined miniaturized environment. In an EWOD device, micro/nano scale droplets are manipulated on an array of electrodes by sequential application of voltages to the electrodes. The common polyethylene glycol (PEG) and dextran (DEX) polymer/polymer ATPS was used as the model system. Nanoliter volume droplets of the two pure polymer solutions were brought into contact, mixed, and successfully formed ATPS on an EWOD chip. Furthermore, it was possible to separate the two phases into two droplets, demonstrating the promising capability of on-chip biological sample separations effectively by integrating formation of ATPS and separation process using ATPS in a single chip. This study also compares the characteristics of ATPS generated in microfluidic chip with that generated in conventional macro scale. The effect of mixing performance on the ATPS formation is studied experimentally.
Measurement of Near Field Radiation Between a Microsphere and an Infinite Plane With Improved Optical Beam
Authors: Gu Ning , Sasihithlu Karthik , Narayanaswamy Arvind
Published: July 2013

Classical theory of thermal radiation can be used to describe radiative transfer between two objects when the characteristic length scales, such as linear dimensions of the objects and inter-object separation, are much longer than the characteristic thermal wave length given by Wien’s displacement law. In situations where the separation is comparable or smaller than the characteristic wave length, near field effects need to be taken into account. Near field radiative transfer can be enhanced by several orders of magnitude if the materials of the objects support surface phonon polaritons. Although near field radiation between two parallel surfaces have been well studied theoretically, the difficulties in probing radiative transfer between parallel surfaces with nanoscale gaps have prevented meaningful experimental validation. In recent years several experiments have measured near field radiation beyond blackbody limitation between a microsphere and a substrate. In those experiments employing optical beam deflection technique, the sphere has to be placed near the edge of the substrate in order to prevent unintentional chopping of the laser beam by the edge of the substrate. The actual measurements are performed between a sphere and a semi-infinite plane instead of an infinite plane. We report here an improved optical beam deflection system to measure the near field radiative heat transfer between a sphere and a substrate. With the new setup, the sphere can be placed sufficiently far away from the substrate edge, rendering it a better approximation of a sphere and an infinite plane. The experimental results and the numerical prediction using modified proximity approximation will be discussed.
Marangoni Asymmetrical Instability in a T-Junction Microchannel With an Open Outlet
Authors: Pan Zhenhai , Wang Hao
Published: July 2013

The Marangoni convections in microchannels are of interest in various applications such as heat transfer, material and microfluidics. In this paper, the Marangoni asymmetrical instability at a T-junction in a microchannel is investigated. The T-junction is formed by a main channel which water going through and a side channel which is open to the ambient. A convex meniscus is formed in side channel near the T-junction, evaporating/volatizing into the ambient. The consumption of water due to the evaporation is compensated by the supply from the main channel. It is found that for weak evaporations, the evaporation-induced Marangoni convections are symmetrical. However, when the evaporation reaches a critical intensity, the symmetrical Marangoni convection becomes unstable and evolves into an asymmetrical one, with one single vortex under the meniscus. More interestingly, the vortex creates a steady convection through the main channel from its one end to the other, just like a pump. The pumping flow rate is found linearly correlated with the Marangoni number at the T-junction.
A First-Principles Method of Determining Van Der Waals Forces in a Dissipative Media
Authors: Zheng Yi , Narayanaswamy Arvind
Published: July 2013

Lifshitz theory of van der Waals (vdW) force and energy is strictly valid when the location at which the stress tensor is calculated is in vacuum. Generalization of Lifshitz theory to the case when the stress tensor is to be calculated in a dissipative material, as opposed to vacuum, is a surprisingly difficult undertaking because there is no expression for the electromagnetic stress tensor in dissipative materials. Here, we derive the expression for vdW force in planar dissipative media by calculating the Maxwell stress tensor in a fictious layer of vacuum, that is eventually made to vanish, introduced in the structure, without employing the complicated quantum field theoretic method proposed by Dzyaloshinskii, Lifshitz, and Pitaevskii. Even though this work has proven to be a corroboration of Dzyaloshinskii et al., it has thrown new light on our understanding of vdW forces and suggests that it should be possible to achieve the similar result for objects with arbitrary shapes.
Ultrasensitive Bimaterial Cantilevers Optimized for Nanowire Heat Conduction Measurement
Authors: Canetta Carlo , Gu Ning , Narayanaswamy Arvind
Published: July 2013

We have developed a microcantilever-based technique for measurement of heat conduction through individual nanowires. We fabricated silicon nitride cantilevers with nominal dimensions of length 100 μm, width 2–6 μm, and thickness 130 nm. Cantilever chips are designed with multiple cantilevers spaced at varying distances. With a reflective aluminum coating of optimized thickness, these bimaterial cantilevers can be used as ultrasensitive thermal sensors capable of measuring very small heat flux through a nanostructure fixed between two cantilevers. The ultrasensitive bimaterial cantilevers designed in this work are not limited to heat conduction measurements, but will also be useful for measuring near-field radiative heat transfer between a sphere, attached to the tip of the cantilever, and a flat plate.
Analysis of USP Laser Induced Ablation Threshold in Transparent Aqueous Tissue
Authors: Jiao Jian , Guo Zhixiong
Published: July 2013

The ultrashort pulsed (USP) laser induced plasma-mediated ablation in transparent media is modeled and studied in this work. We propose that a certain number of free electrons are required to trigger the avalanche ionization for the first time. Based on this assumption, the ablation process is postulated as two separate processes — the multiphoton and avalanche ionizations. For USP laser induced ablation in the transparent corneal epithelium at 800 nm, the critical seed free-electron density and the time to initialize the avalanche ionization for pulse widths from picoseconds down to the femtoseconds range are calculated. It is found that the critical seed free-electron density decreases as the pulse width increases, obeying a tp−5.65 rule. Moreover, this model is also extended to the estimation of crater sizes in USP laser ablation of polydimethylsiloxane (PDMS). The crater sizes ablated in a PDMS by a 900 fs pulsed laser at wavelength 1552 nm are modeled using the present model, and the results match with the existing experimental measurements.
Thermo-Fluid Model for High Thermal Conductivity Thermal Ground Planes
Authors: Ababneh Mohammed T. , Gerner Frank M. , Chamarthy Pramod , de Bock Peter , Chauhan Shakti , Deng Tao
Published: July 2013

The thermal ground plane (TGP) is an advanced planar heat pipe designed for cooling microelectronics in high gravitational fields. A thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). Viscous laminar flow pressure losses are predicted to determine the maximum heat load when the capillary limit is reached. This paper shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that the thermo-fluid model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP. The wick porosity plays an important effect on maximum heat transport capability. A large adverse gravitational field strongly decreases the maximum heat transport capability of the TGP. Axial effective thermal conductivity is mostly unaffected by the gravitational field. The maximum length of the TGP before reaching the capillary limit is inversely proportional to input power.
Pressure Drop During Condensation in Microchannels
Authors: Wang H. S. , Rose J. W.
Published: July 2013

The paper examines the special case of annular laminar flow pressure drop, or more precisely pressure gradient, during condensation in microchannels. This is the only flow regime permitting wholly theoretical solution without having recourse to experimental data. Solutions are obtained and comparisons made with empirical formulae for void fraction (needed to calculate the momentum pressure gradient) when obtaining the friction pressure gradient from experimentally measured or “total” pressure gradient. To date calculations and comparisons are restricted to one fluid (R134a), one channel section and one flow condition. For the case considered it is found that earlier approximate models for estimating void fraction agree quite well with the theoretical annular flow solutions. There is, however, significant difference between momentum pressure gradients obtained from approximate models used in the earlier investigations and that given by the theoretical annular flow solution which is (numerically) higher than all of them. The annular flow solution indicates that the momentum pressure gradient is not small in comparison with the friction pressure gradient. The friction pressure gradient in the annular flow case is appreciably smaller than given by the earlier correlations.
Critical Review of the Novel Applications and Uses of Nanofluids
Authors: Taylor Robert , Coulombe Sylvain , Otanicar Todd , Phelan Patrick , Gunawan Andrey , Lv Wei , Rosengarten Gary , Prasher Ravi , Tyagi Himanshu
Published: July 2013

Nanofluids — one simple product of the emerging world nanotechnology — where nanoparticles (nominally 1–100 nm in size) are mixed with conventional base fluids (water, oils, glycols, etc.). Nanofluids have seen enormous growth in popularity since they were proposed by Choi in 1995 [1]. In the year 2010 alone there were nearly 500 research articles where the term nanofluid was used in the title, showing rapid growth from 2000 (12) and 2005 (78). Much of the first decade of nanofluid research was focused on measuring and modeling fundamental thermophysical properties of nanofluids (thermal conductivity, density, viscosity, convection coefficients). Recent research, however, has started to highlight how nanofluids might perform in a wide variety of other applications. These applications range from their use in nanomedicine [2] to their use as solar energy harvesting media [3]. By analyzing the available body of research to date, this article presents trends of where nanofluid research is headed and suggests which applications may benefit the most from employing nanofluids. Overall, this review summarizes the novel applications and uses of nanofluids while setting the stage for future nanofluid use in industry.
Effect of Oxide Film on Bi-Directional Reflection Properties of Two-Dimensional Random Rough Surface of Silicon
Authors: Qiu J. , Liu L. H. , Hsu P.-f.
Published: July 2013

The bidirectional reflectance distribution function (BRDF) describes spatial distribution of light scattered from rough surfaces and can be used to calculate other radiative properties. There have been many researches focus on the BRDF of rough surface structures. A number of approximate techniques such as perturbation theory, the Kirchhoff approximation, and geometric optics approximation (GOA) are widely used due to the complexity of the electromagnetic theory. However, these approximate techniques neglect some phenomenon such as surface plasmon polaritons (SPP), the diffraction effect, cavity resonance etc., which can be efficiently studied by the finite-difference time-domain (FDTD) method. As the increasing improvement of the computational science, it is feasible to simulate the radiative properties of complex surface structures by electromagnetic theory. Silicon tends to oxidize naturally, which hence changes the radiative properties of the rough surface structure. The focus of this study is on the effect of oxide films on BRDF of two-dimensional randomly rough surface of silicon using the FDTD method. The BRDF of different surface roughness of silicon substrate coated with oxide film has been investigated. The results show that, the BRDF of the rough surface of silicon will be affected by the RMS roughness (σ) and correlation length (τ). The energy of the reflection peaks increase as the roughness decreases (σ), when the correlation length (τ) remains the same. And the energy of the reflection peaks decrease as the correlation length decreases, when the roughness remains the same. The calculation domain and time increase as the rate of στ/λ increases. Moreover, when the rough surface of silicon covered with oxide film, the reflection peak will be weakened obviously, which is mainly due to that the absorbing oxide film.
Fluctuation Hydrodynamics, Thermophoresis of Nanoparticles and Heat Transfer in Nanofluids
Authors: Dmitriev Alexandr S.
Published: July 2013

In this paper we studied in the framework of two-fluid hydrodynamics with fluctuations the behavior of nanoparticles in the liquid with temperature gradient [1, 2]. It is shown that the acoustic long-wave fluctuations are not damped in liquids (long-wavelength phonons) and leads to an additional force acting on the nanoparticles, as well as lead to the emergence of a new force of thermophoresis [3], which is proportional to the temperature in three second degree. It is also shown that such a thermophoresis force arising under the two-fluid hydrodynamics, can lead to instability of an ensemble of nanoparticles in the presence of a temperature gradient. The last effect leads to the possible merger of the nanoparticles in the form of elongated clusters. The appearance of such clusters on the one hand, leads to an increase in effective thermal conductivity of nanofluids, and secondly, appearing elongated clusters contribute to the propagation of long-wavelength phonons along of such clusters. In fact, this new type of heat transfer in nanofluids, which must be considered in addition to the Brownian motion of nanoparticles.
An In-Plane Nanofluidic Nanoplasmonics-Based Platform for Biodetection
Authors: Wei Jianjun , Song Hongjun , Singhal Sameer , Kofke Matthew , Mendis Madu , Waldeck David
Published: July 2013

This paper reports a new nanofluidic plasmonics-based sensing platform which can be readily integrated with microfluidics devices, and potentially enable an in-parallel transmission surface plasmon resonance (SPR), lab-on-chip sensing technology. The technology overcomes the current SPR size limitations through a combination of nanofluidics and nanoplasmonics in a rationally designed in-plane nanoslit array capable of concurrent plasmonic sensing and confined-flow for analyte delivery. This work is leveraged on our previous work of using nanoslit metal films for SPR sensing [1, 2], and the in-plane nanofluidic nanoplasmonic platform is different from recently reported nanohole-based nanofluidic plasmonics sensors [3, 4]. The work presented here includes an integrated device with nanofluidic nanoplasmonic arrays interfacing with microfluidic channels, and preliminary findings, from both theoretical and experimental fronts, of the device for bio-sensing.
The Effects of Van Der Waals Bonding Strength on the In-Plane Lattice Thermal Conductivities of Multilayer Thin Films
Authors: Chen Weiyu , Ni Zhonghua , Yang Juekuan , Zhang Yan , Li Deyu , Chen Yunfei
Published: July 2013

A non-equilibrium molecular dynamics (NEMD) simulation model is established to investigate the impact of vdW strength on thermal transport along the in-plane direction in argon bi-layer films (BLFs) and silicon BLFs. Simulation results indicate that higher strength leads to a higher in-plane thermal conductivity. However, interface roughness also increases with the continuous increase of the van der Waals (vdW) strength and leads to the reduction of thermal conductivities. The bonding strength does play an important role in manipulating thermal conductivity of multilayer thin films.
Non-Equilibrium Molecular Dynamics Simulation on Thick Dependence Thermal Conductivities of Semiconductors
Authors: Li Calvin H.
Published: July 2013

With the rapidly increasing demand for efficient, small, light, low cost, and reliable electronic devices, the nano-scale thermal transport properties of semiconductors has become a prominent focus of research. Molecular dynamic simulation has emerged as a powerful compliment to experiment and is beginning to play a crucial role in tailored material properties for improved thermal management of electronic devices.

The thermal conductivity of semiconductor has been investigated using the Stillinger-Weber (SW) and the Modified Embedded Atom Method (MEAM) potential model, the dependence of temperature, system size, and simulation time has been investigated.

We find this MEAM model to quantitatively reproduce bulk thermal conductivity predictions using the linear extrapolation method comparable to previous literature using the well studied Stillenger-Weber (SW) potential.
Heat Conduction and Interface Thermal Resistance in Liquid Argon Filled Silver and Graphite Nanochannels
Authors: Barisik Murat , Shi Ziyuan , Beskok Ali
Published: July 2013

Heat conduction between two parallel solid walls separated by liquid argon is investigated using three-dimensional molecular dynamics (MD) simulations. Liquid argon molecules confined in silver and graphite nano-channels are examined separately. Heat flux and temperature distribution within the nano-channels are calculated by maintaining a fixed temperature difference between the two solid surfaces. Temperature profiles are linear sufficiently away from the walls, and heat transfer in liquid argon obeys the Fourier law. Temperature jump due to the interface thermal resistance (i.e., Kapitza length) is characterized as a function of the wall temperature. MD results enabled development of a phenomenological model for the Kapitza length, which is utilized as the coefficient of a Navier-type temperature jump boundary condition using continuum heat conduction equation. Analytical solution of this model results in successful predictions of temperature distribution in liquid-argon confined in silver and graphite nano-channels as thin as 7 nm and 3.57 nm, respectively.
Size Dependent Orientation of Knudsen Force
Authors: Zhu Taishan , Ye Wenjing , Zhang Jun
Published: July 2013

Knudsen force acting on a heated microbeam adjacent to a cold substrate in a rarefied gas is a mechanical force created by unbalanced thermal gradients. The measured force has its direction pointing towards the side with a lower thermal gradient and its magnitude vanishes in both continuum and free-molecule limits. In our previous study, negative Knudsen forces were discovered at the high Knudsen regime before diminishing in the free-molecule limit. Such a phenomenon was however not observed in the experiment. In this paper, the existence of such a negative Knudsen force is further confirmed using both numerical simulation and theoretical analysis. The asymptotic order of the Knudsen force near the collisionless limit is analyzed and the analytical expression of its leading term is provided, from which approaches for the enhancement of negative Knudsen forces are proposed.
Modeling and Numerical Simulations of Vapor-Liquid Flow and Heat Transfer Within Microchannel Heat Sinks
Authors: Xin Chengyun , Wang Jianhua , Xie Jianheng , Song Yuee
Published: July 2013

Microchannel heat sinks have demonstrated the ability to dissipate large amounts of heat flux. This ability can be strongly enhanced by phase change of a liquid coolant. This paper numerically simulates the processes of liquid coolant flow, heat absorption and phase change within a microchannel, which is heated at one side by given heat fluxes. The two-phase flow model widely used in the investigations on heat and mass transfer within porous media is firstly introduced into microchannnel heat sinks by this paper. Experiential equations of the heat transfer coefficients in single phase and boiling region within microchannels are employed to calculate the convective heat exchange between solid wall and flowing fluid by an iterative process. The numerical results of pressure and temperature distributions obtained at different conditions are exhibited and analyzed. The results indicated that the trends predicted by this approach agree well with the previous references. Therefore the modeling is validated in some sense. At the same time, two phenomena, countercurrent flow in two-phase region and special pressure variations near the transition point, are exhibited.