bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Thermal and Energy Analysis of a Hybrid Cooling Data Center With Rear Door Heat Exchangers
Authors: Gao Tianyi , Samadiani Emad , Sammakia Bahgat , Schmidt Roger
Published: January 2014

Data centers consume a considerable amount of energy which is estimated to be about 2 percent of the total electrical energy consumed in the US, and their power consumption continues to increase every year. It is also estimated that roughly 30–40 percent of the total energy used in a data center is due to the thermal management systems. So, there is a strong need for better cooling methods which could improve the cooling capacity and also reduce energy consumption for high density data centers. In this regard, liquid cooling systems have been utilized to deal with demanding cooling and energy efficiency requirements in high density data centers. In this paper, a hybrid cooling system in data centers is investigated. In addition to traditional raised floor, cold aisle-hot aisle configuration, a liquid-air hybrid cooling system consisting of rear door heat exchangers attached to the back of racks is considered. The room is analyzed numerically using two CFD based simulation approaches for modeling rear door heat exchangers that are introduced in this study. The presented model is used in the second section of the paper to compare the hybrid cooling system with traditional air cooling systems. Several case studies are taken into account including the power increases in the racks and CRAC unit failure scenarios. A comparison is made between the hybrid cooling room and a purely air cooled room based on the rack inlet temperatures. Also in this study, total energy consumption by the cooling equipment in both air-cooled and hybrid data centers are modeled and compared with each other for different scenarios. The results show that under some circumstances the hybrid cooling could be an alternative to meet the ASHRAE recommended inlet air temperatures, while at the same time it reduces the cooling energy consumption in high density data centers.
Characterization of Crack Growth in BGA Under Drop Impact
Authors: Nguyen Quang , Park Seungbae , Nguyen Tung
Published: January 2014

This paper presents the characterization of the crack growth rate of Sn-4.0wt.%Ag-0.5wt.%Cu (SAC405) solder joints under drop impact. Several actual ChipArray® BGA (CTBGA) packages were cross-sectioned, polished and used as the test vehicles. The ball drop tests were performed using a specially-designed tester. The drop impact from the drop ball induces bending in the PCB, which damages the solder joints. The crack lengths in the solder joints were measured after every five drops using microscope imaging. Crack growth rates were calculated from the test results. Insight into the crack growth rate in solder joints under drop impact is provided. The direct cyclic approach for low-cycle fatigue analysis in ABAQUS was used to simulate the crack growth in the solder joints.
Evaluation of Strength in Joints of Silicon and Sapphire Coating Silicon
Authors: Koguchi Hideo , Kimura Naoki
Published: January 2014

Recent electronic device packaging, for instance, Chip size package (CSP) has a bonded structure of IC chip and polymers, and delamination occurs frequently at the interface between IC and a resin. Furthermore, thermal stresses which are caused by a temperature variation in the bonding process of CSP and heat cycles for environment temperature will influence on the strength of interface. In the present paper, the delamination test for specimens with different bonding areas and geometries is carried out to investigate the strength of multi-layered joints. In particular, a silicon wafer is joined with a silicon-on-sapphire (SOS) plate by a resin. The SOS is composed of silicon film, SiO2 film and sapphire plate. The thicknesses of silicon film, SiO2 film and sapphire plate are 0.45μm, 0.2μm, 600μm, respectively. The joining strength in silicon, resin and SOS joints with triangular and rectangular bonding area is investigated. The triangular and rectangular shape bonding areas are 3mm2 and 12mm2, respectively. The bonded specimens are prepared under different cooling rate. Load is applied to the specimen so as to delaminate at the interfaces of SiO2 film and sapphire. From the delamination test, it is found that residual thermal stress and the geometry of bonding area affect the strength of interface. In the case of the triangular area specimen, delamination occurs at the interface between SiO2 film and sapphire plate in the silicon-resin-SOS specimen. The nominal stress for delamination is about 1.99MPa. In the case of rectangular bonding area specimen, delamination occurs at the interface between SiO2 film and sapphire plate in the silicon-resin-SOS specimen. Nominal stress for delamination is about 2.23MPa. From a comparison of the strength of joint for rapid and slow cooling conditions, it is found that the residual stress reduces the strength of joint.
Fabrication of Anodic Aluminum Oxide Template and Cu Nanowire Surface Fastener
Authors: Teshima Hiromasa , Kojima Kohei , Ju Yang
Published: January 2014

There is an urgent need in surface mount technology (SMT) for a nontoxic, reusable and low temperature bonding technique which can afford good mechanical support as well as electrical contact. Meanwhile in the nanotechnology, many excellent and unique structure-related properties such as the high mechanical strength, the high conductivity and the adhesion ability of gecko feet have been studied. Our lab proposes a new patterned structure of Au nanowire array named nanowire surface fastener (NSF), which cold bonding for surface mount technology can be realized at room temperature. Then various methods have been developed to fabricate nanowire, such as arc discharge, catalytic CVD growth and template synthesis, and so on. Among these methods, the template method has been widely used for preparing one-dimensional nanostructures such as metals, semiconductors, polymers, and other materials by electrochemical, electroless deposition or sol-gel technique. Especially anodic aluminum oxide template assisted way has attached considerable attention due to its unique structure properties, such as controllable pore diameter, extremely narrow pore size distribution with high densities, high aspect ratios, and ideally cylindrical pore shape.

The well arranged porous anodic aluminum oxide membrane is fabricated from aluminum film by two steps zM oxalic acid electrolytes. The anodic aluminum oxide membrane was investigated for features such as pore size, interpore distance, and thickness by 40 V. It is important for fabrication of porous anodic aluminum oxide template to find out elimination of the barrier layer of oxide and the pore extending rate by 0.5 M phosphoric acid. Morphologies of surface of aluminum film between anodization process and the anodic aluminum oxide barrier layer was researched by using atomic force microscope and scanning electron microscope. Results showed that the anodic aluminum oxide having the same diameter of the pore and the well arranged pore array without branching channel was obtained. The diameter of the pore before the pore extending treatment is 42 nm and the diameter of the pore after the pore extending treatment for 30 minutes is 86 nm. It was found that the diameter of the pore increased per 15 nm by the pore extending treatment for 10 minutes. We fabricated the through-hole anodic aluminum oxide template and made Cu nanowire by the template of our own making. By using Cu nanowire, we try to produce nanowire surface fastener and evaluate its properties.
Enhancing Heat Transfer in a Cold Plate, Inserts vs. Nanofluids: Application to IT Servers
Authors: Mammeri Amrid , Bakir Farid , Kouidri Smaine , Coutancier Lionel , Bonnin Jean-Christophe
Published: January 2014

This work is a comparative experimental study of two ways of heat transfer intensification inside the cold plate of an Indirect Liquid Cooled IT Server. The first way is classical, as surface extension or heat transfer coefficient enhancement by adding fins, turbulators, or surface roughness modification. The second is more recent, it is about using nanofluids. For comparison purpose, we have defined three criteria: thermal performance, hydraulic performance, and efficiency. According to those parameters, classical methods have shown better performances comparatively to nanofluids.
Data Center Trends Toward Higher Ambient Inlet Temperatures and the Impact on Server Performance
Authors: Vallury Aparna , Matteson Jason
Published: January 2014

With the extension of the 2011 ASHRAE Thermal Design Guidelines to incorporate a broader Class A3 and A4 specification, the server industry is trying to adapt to the changing landscape of industry best practices and initiatives, and adopt the new ASHRAE Class A3 and A4 environments. In order to accommodate the high ambient inlet conditions while meeting the IT efficiency initiatives in the industry, certain design considerations must occur and it becomes very important to understand the implication of adhering to Class A3 and A4 environments on the performance of the servers.

This paper describes a study that was conducted to understand the impact on performance of different servers under various workloads and inlet ambient conditions specifically adhering to class A3 specification only. The results from the study are presented in this paper which shows that no performance impact was observed in a 35°C environment, and bounded by 2% running worst case applications at 40°C and 0% when running lighter loads.
Maximizing Data Center Energy Efficiency by Utilizing New Thermal Management and Acoustic Control Methodology
Authors: Matteson Jason A. , Vallury Aparna , Medlin Billy
Published: January 2014

Today’s server designs continue to package more electronics consuming higher levels of power in smaller and smaller spaces which increases the demand on the cooling subsystem within a server. These trends continue to drive the total cooling power and airflow demands up, resulting in increased acoustics. Due to the imposed high cooling requirements, data centers are frequently limited by the amount of flow that the raised floor environments are capable of providing. Server cooling demands are outpacing the data center airflow capabilities, resulting in energy inefficient scenarios as well as increasingly high acoustics levels.

Given these concerns, there is a dire need for new thermal management techniques. This paper describes a new technique that offers more advanced yet simplified user controls, which provide the end user the ability to minimize acoustic signature and cooling energy spent, while maximizing the server performance.
Reliability of Bonded Interfaces for Automotive Power Electronics
Authors: DeVoto Douglas , Paret Paul , Narumanchi Sreekant , Mihalic Mark
Published: January 2014

In automotive power electronics packages, conventional thermal interface materials such as greases, gels, and phase change materials pose bottlenecks to heat removal and are also associated with reliability concerns. There is an industry trend towards high thermal performance bonded interfaces. However, due to coefficient of thermal expansion mismatches between materials/layers and resultant thermomechanical stresses, adhesive and cohesive fractures could occur, posing a problem from a reliability standpoint. These defects manifest themselves in increased thermal resistance in the package.

The objective of this research is to investigate and improve the thermal performance and reliability of emerging bonded interface materials for power electronics packaging applications. We present results for thermal performance and reliability of bonded interfaces based on thermoplastic (polyamide) adhesive, with embedded near-vertical aligned carbon fibers, as well as sintered silver material. The results for these two materials are compared to conventional lead-based (Sn63Pb37) bonded interfaces. These materials were bonded between 50.8-mm × 50.8-mm cross-sectional footprint silicon nitride substrates and copper base plate samples. Samples of the substrate/base plate bonded assembly underwent thermal cycling from −40°C to 150°C according to Joint Electron Devices Engineering Council standard Number 22-A104D for up to 2,000 cycles. The dwell time of the cycle was 10 minutes and the ramp rate was 5°C/minute. Damage was monitored every 100 cycles by acoustic microscopy as an indicator of an increase in thermal resistance of the interface layer. The acoustic microscopic images of the bonded interfaces after 2,000 thermal cycles showed that thermoplastics with embedded carbon fibers performed quite well with no defects, whereas interface delamination occurred in the case of sintered silver material. Both these materials showed a superior bond quality as compared to the lead-based solder interface even after 1,000 thermal cycles.
Correlation Between Behaviors of the Vapor Bubbles and the Characteristics of the Heat Transfer Over the Heated Surface on MEB
Authors: Saiki Takahito , Osawa Tomohiko , Ueno Ichiro , Hong Chungpyo
Published: January 2014

A series of experiments on subcooled pool boiling on a plate and on a thin wire are carried out. We focus on the condensation and collapse processes of vapor bubbles generated on the heated surface. We find the different patterns of the vapor bubble behaviors resulting in the emission of the microbubbles around the heated plate and the thin wire by employing high-speed observation with frame rate up to 150,000 frame per second (fps). From the experimental results, we provide a physical explanation on the correlation between the behavior of the vapor bubble at a high heat flux and the heat transfer characteristics. We propose this simple core-periphery model as a qualitative model for understanding the generation of the MEB.
Heat Transfer in Nanoelectronics by Quantum Mechanics
Authors: Prevenslik Thomas
Published: January 2014

Today, the transient Fourier heat conduction equation is not considered valid for the derivation of temperatures from the dissipation of Joule heat in nanoelectronics because the dimension of the circuit element is comparable to the mean free path of phonon energy carriers. Instead, the Boltzmann transport equation (BTE) for ballistic transport based on the scattering of phonons within the element is thought to govern heat transfer. However, phonons respond at acoustic frequencies in times on the order of 10–100 ps, and therefore the BTE would not have meaning if the Joule heat is conserved by a faster mechanism.

Unlike phonons with response times limited by acoustic frequencies, heat transfer in nanoelectronics based on QED induced heat transfer conserves Joule heat in times < 1 fs by the creation of EM radiation at optical frequencies. QED stands for quantum electrodynamics. In effect, QED heat transfer negates thermal conduction in nanoelectronics because Joule heat is conserved well before phonons respond.

QED induced heat transfer finds basis in Planck’s QM given by the Einstein-Hopf relation in terms of temperature and EM confinement of the atom as a harmonic oscillator. QM stands for quantum mechanics and EM for electromagnetic. Like the Fourier equation, the BTE is based on classical physics allowing the atom in nanoelectronic circuit elements to have finite heat capacity, thereby conserving Joule heat by an increase in temperature. QM differs by requiring the heat capacity of the atom to vanish. Conservation of Joule heat therefore proceeds by QED inducing the creation of excitons (hole and electron pairs) inside the circuit element by the frequency up-conversion of Joule heat to the element’s TIR confinement frequency. TIR stands for total internal reflection. Under the electric field across the element, the excitons separate to produce a positive space charge of holes that reduce the electrical resistance or upon recombination are lost by the emission of EM radiation to the surroundings.

TIR confinement of EM radiation is the natural consequence of the high surface to volume ratio of the nanoelectronic circuit elements that concentrates Joule heat almost entirely in their surface, the surfaces coinciding with the TIR mode shape of the QED radiation. TIR confinement is not permanent, present only during the absorption of Joule heat.

Charge creation aside, QM requires nanoelectronics circuit elements to remain at ambient temperature while dissipating Joule heat by QED radiation to the surroundings. Hot spots do not occur provided the RI of the circuit element is greater than the substrate or surroundings. RI stands for refractive index.

In this paper, QED radiation is illustrated with memristors, PC-RAM devices, and 1/ f noise in nanowires, the latter of interest as the advantage of QM in avoiding hot spots in nanoelectronics may be offset by the noise from the holes created in the circuit elements by QED induced radiation.
Advanced Natural Convection Cooling Designs for LED Bulb Systems
Authors: Petroski James
Published: January 2014

The movement to LED lighting systems worldwide is accelerating quickly as energy savings and reduction in hazardous materials increase in importance. Government regulations and rapidly lowering prices help to further this trend. Today’s strong drive is to replace light bulbs of common outputs (60W, 75W and 100W) without resorting to Compact Fluorescent (CFL) bulbs containing mercury while maintaining the standard industry bulb size and shape referred to as A19. For many bulb designs, this A19 size and shape restriction forces a small heat sink which is barely capable of dissipating heat for 60W equivalent LED bulbs with natural convection for today’s LED efficacies. 75W and 100W equivalent bulbs require larger sizes, some method of forced cooling, or some unusual liquid cooling system; generally none of these approaches are desirable for light bulbs from a consumer point of view. Thus, there is interest in developing natural convection cooled A19 light bulb designs for LEDs that cool far more effectively than today’s current designs. Current A19 size heat sink designs typically have thermal resistances of 5–7°C/W. This paper presents designs utilizing the effects of chimney cooling, well developed for other fields that reduce heat sink resistances by significant amounts while meeting all other requirements for bulb system design. Numerical studies and test data show performance of 3–4°C/W for various orientations including methods for keeping the chimney partially active in horizontal orientations. Significant parameters are also studied with effects upon performance. The simulations are in good agreement with the experimental data. Such chimney-based designs are shown to enable 75W and 100W equivalent LED light bulb designs critical for faster penetration of LED systems into general lighting applications.
Anticipatory Thermoelectric Cooling of a Transient Germanium Hotspot
Authors: Manno Michael , Wang Peng , Bar-Cohen Avram
Published: January 2014

On-chip kW-level hotspots have become a significant factor in the thermal design of modern electronic packages. Thermoelectric cooling has been shown to be capable of suppressing such hotspots, but it is not yet clear how to best deploy embedded thermoelectric microcoolers for notional hot spot scenarios. This paper will present the results of recent work on thermoelectric “self cooling” of transient hotspots. A 3-D multi-physics numerical model is used to simulate the spatial and temporal temperature variations associated with a dynamic hotspot on a germanium substrate, for which the hotspot heat flux varies over time. The temporal interaction between the hotspot and the thermoelectric microcooler for specified hotspot duty cycle, hotspot heat flux profile, and thermoelectric cooler current profile will be examined. Due to the spatial separation between the cooler and the hotspot, the results suggest that anticipatory cooling, with a prescribed current profile, is a critical factor in the efficient removal of a transient hotspot.
Modified Model for Improved Flow Regime Prediction in Internally-Grooved Tubes
Authors: Sharar Darin J. , Jankowski Nicholas R. , Bar-Cohen Avram
Published: January 2014

The absence of phenomenological insights and accurate flow regime models makes it difficult to predict the improved effectiveness of internally-grooved tubes for two-phase heat transfer. A re-interpretation of available data and flow regime maps is used to suggest that performance improvement is a result of early transition to Annular flow. A modified flow regime map, with a newly-developed Stratified-Wavy to Annular transition criteria for internally-grooved tubes, is shown to increase regime prediction accuracy by 27% relative to the traditional, smooth tube flow regime prediction.
Effect of Cold Aisle Containment Leakage on Flow Rates and Temperatures in a Data Center
Authors: Alkharabsheh Sami A. , Shrivastava Saurabh K. , Sammakia Bahgat G.
Published: January 2014

Many modern data centers utilize containment systems as a practical and inexpensive thermal management solution. In this paper we investigate the effect of various containment leakage ratios on the flow rates and the temperatures in a representative data center. The modular data center is an actual contained cold aisle system in an experimental laboratory. The numerical model is validated using experimental measurements presented in a previous study for uncontained and contained cold aisle data center configurations [1]. The model takes into account the fan curves in the CRAC and IT-equipment.

A commercial CFD code is used to conduct this study. The k-ε model and the Boussinesq approximation are used to model the turbulent airflow and the buoyancy effect, respectively. An approximate overall leakage model in the cold aisle is used in this study rather than a detailed model where the simulated leakage sources include floor tiles, containment surfaces, and racks. Several parametric studies are conducted by varying the leakage ratios ranging between 0% (perfectly sealed containment system) to 100% (uncontained cold aisle). The results are used to investigate the effect of leakage ratios on the flow rates of the CRAC unit and the IT-equipment. Ultimately the effect on the inlet temperatures is also investigated. Leakage in containment system is found to have a critical effect on the containment systems performance. A threshold leakage ratio is found after which the containment system does not have benefits over the conventional uncontained cold aisle system. This approach can be used to characterize the leakage in contained systems.
Benefit of Cold Aisle Containment During Cooling Failure
Authors: Shrivastava Saurabh K. , Ibrahim Mahmoud
Published: January 2014

During a cooling equipment failure, temperatures within a data center can rise to the threshold limits of IT equipment very quickly. Data center operators want to know: how much ride-through time do I have? Does cold aisle containment increase or decrease the ride-through time? This study presents thermal transient data for tests conducted at a data center lab. The results reveal an interesting phenomenon that puts cold aisle containment at an advantage over the standard open hot aisle/cold aisle configuration.
Effects of Moisture Exposure on the Mechanical Behavior of Polymer Encapsulants in Microelectronic Packaging
Authors: Chhanda Nusrat J. , Suhling Jeffrey C. , Lall Pradeep
Published: January 2014

Polymer encapsulants exhibit evolving properties that change significantly with environmental exposures such as moisture uptake, isothermal aging and thermal cycling. In this study, the effects of moisture adsorption on the stress-strain behavior of a polymer encapsulant were evaluated experimentally. The uniaxial test specimens were exposed in an adjustable thermal and humidity chamber to combined hygrothermal exposures at 85 °C/85% RH for various durations. After moisture preconditioning, a microscale tension-torsion testing machine was used to evaluate the complete stress-strain behavior of the material at several temperatures. It was found that moisture exposure caused plasticization and strongly reduced the mechanical properties of the encapsulant including the initial elastic modulus and ultimate tensile stress. Reversibility tests were also conducted to evaluate whether the degradations in the mechanical properties were recoverable. Upon fully redrying, the polymer was found to recover most but not all of its original mechanical properties. As revealed by FTIR, some of the adsorbed water had been hydrolyzed in the organic structure of the epoxy-based adhesive, causing permanent changes to the mechanical behavior.
A Methodology for High Cycle Fatigue Characterization of Lead-Free Interconnects Under Simultaneous Harsh Environments of High Temperature and Vibration
Authors: Lall Pradeep , Limaye Geeta
Published: January 2014

Current trends in the automotive industry warrant a variety of electronics for improved control, safety, efficiency and entertainment. Many of these electronic systems like engine control units, variable valve sensor, crankshaft-camshaft sensors are located under-hood. Electronics installed in under-hood applications are subjected simultaneously to mechanical vibrations and thermal loads. Typical failure modes caused by vibration induced high cycle fatigue include solder fatigue, copper trace or lead fracture. The solder interconnects accrue damage much faster when vibrated at elevated temperatures. Industry migration to lead-free solders has resulted in a proliferation of a wide variety of solder alloy compositions. Presently, the literature on mechanical behavior of lead-free alloys under simultaneous harsh environment of high-temperature vibration is sparse. In this paper, the reduction in stiffness of the PCB with temperature has been demonstrated by measuring the shift in natural frequencies. The test vehicle consisting of a variety of lead-free SAC305 daisy chain components including BGA, QFP, SOP and TSOPs has been tested to failure by subjecting it to two elevated temperatures and harmonic vibrations at the corresponding first natural frequency. The test matrix includes three test temperatures of 25C, 75C and 125C and simple harmonic vibration amplitude of 10G which are values typical in automotive testing. PCB deflection has been shown to increase with increase in temperature. The full field strain has been extracted using high speed cameras operating at 100,000 fps in conjunction with digital image correlation. Material properties of the PCB at test temperatures have been measured using tensile tests and dynamic mechanical analysis. FE simulation using global-local finite element models is thus correlated with the system characteristics such as modal shapes, natural frequencies and displacement amplitudes for every temperature. The solder level stresses have been extracted from the sub-models. Stress amplitude versus cycles to failure curves are obtained at all the three test temperatures. A comparison of failure modes for different surface mount packages at elevated test temperatures and vibration has been presented in this study.
Liquid Cooled High Power Aerospace Electronics Fluid Channel Layout Design Strategy Based on Analytical Calculation
Authors: Wang Frank Fan
Published: January 2014

This article is about the application of liquid cooling in high power aerospace electronics. This article discusses liquid cooled cold plate fluid channel layout design strategy based on hand or analytical calculations before the three dimensional thermal model is constructed. Everybody knows how to perform thermal analysis using CFD software; however, CFD software cannot generate three dimension models automatically. Thermal engineers still need to design preliminary models to analyze. CFD software cannot solve the problems for the designer. Computers cannot substitute the human in design. In the end, it is the thermal engineer’s education, experience, knowledge, strategic thinking, and know-how that determine the outcome of the design. To simplify the task, sections of the cooling channel are suggested to be designed individually to meet the cooling needs of each individual component that segment of the fluid channel is cooling. The sections of the fluid channel routed directly underneath the heat dissipating components can be connected in parallel or in series. This article will discuss the pros and cons of both design approaches. Pressure drops versus heat transfer are the tradeoffs of the fluid layout design. An example of the analytical pressure drop calculation is provided. This article also provides guidance on calculating the flow rate of each of the cooling sections and the strategy of determining the linear velocity of the liquid. In the discussion, a brief trade study of machined or casted cold plate versus tube-in-plate cold plate design is presented. Positioning of the cold plate to control the internal ambient temperature is also briefly discussed.
Fabrication of Heat Pipes on an Acrylic Resin Board
Authors: Koito Yasushi , Maehara Hiroyuki , Tomimura Toshio
Published: January 2014

As a first step to develop an electronic wiring board in which micro or miniature heat pipes are internally fabricated, the experimental and analytical studies are performed on a wickless gravity-assisted heat pipe, namely thermosyphon, fabricated on a surface of an acrylic resin board. This proposal aims at performing a phase-change heat transfer inside an electronic wiring board having a low thermal conductivity. In experiments, the evaporator section of the heat pipe is heated by a heater while the condenser section is water-cooled by a heat sink. Water is used as a working fluid. Changing a heat input and a liquid volume ratio inside the heat pipe, the temperature distribution is measured by thermocouples and then compared to the case where the working fluid is not charged. Moreover, the simple model of the heat pipe is made based on a thermal resistance network, and the analysis is performed on a phase-change heat transfer and a conductive heat transfer inside the resin board having the heat pipe. The effective thermal conductivity of the heat pipe is evaluated. Although this study is an initial stage, the operational and the heat transfer characteristics of the resin board having the heat pipe are confirmed.
Room-Level Transient CFD Modeling of Rack Shutdown
Authors: Erden Hamza Salih , Khalifa H. Ezzat , Schmidt Roger R.
Published: January 2014

Servers have time constants on the order of several minutes, which is significantly longer than many other time constants observed in data centers. When server thermal masses are not negligible, transient scenarios cannot be modeled appropriately with the steady state boundary conditions. By using the time constant and thermal masses of the servers, transient server air exit temperature can be calculated by solving unsteady heat balance equations for the server and air stream. This paper presents a room-level CFD case study of rack shutdown in which transient server exit air temperature are introduced via user defined functions. The results include verification of simulation results with the experimental data taken in a 3-rack test cell.
A Capacitance-Based Technique for Characterization of Dielectric Interfaces Using a Grid of Electrode Junctions
Authors: Taylor Stephen H. , Garimella Suresh V.
Published: January 2014

A sensor for detecting imperfections in the distribution of a dielectric thermal interface is proposed. The sensor can detect imperfections such as voids, cracks, and interface gap changes on the millimeter scale. A rake of long, parallel electrodes is imbedded flush into each opposing substrate face of a narrow gap interface, and exposed to the gap formed between the two surfaces. Electrodes are oriented such that their lengthwise dimension in one substrate runs perpendicular to the other. Capacitance measurements taken at each crossing point (junction) allow for characterization of the region, and subsequently, detection of voids present or changes in gap size. The electric field associated with each electrode junction is numerically simulated and analyzed. Design criteria for the electrode junctions that localize the electric fields are presented. The electrode configuration employed gives rise to a non-trivial network of interacting capacitances. Due to these interactions, the actual capacitance at any given junction cannot be measured directly; instead, the measurement represents an equivalent capacitance resulting from this network. A generalized solution for analyzing the circuit network is presented. An experimental test unit is described, and experimental data are presented for measurements from a typical electrode junction. The results agree with predictions from the network model for cases that meet the design criteria for electric field localization; when the localization criteria are not met, the measurements deviate from the model predictions as expected.
Method for Assessment of Prolonged and Intermittent Storage on Reliability of Leadfree Electronics Using Leading Indicators
Authors: Lall Pradeep , Mirza Kazi , Harsha Mahendra , Suhling Jeff , Goebel Kai
Published: January 2014

Electronic systems may be subjected to prolonged and intermittent periods of storage prior to deployment or usage. Prior studies have shown that leadfree solder interconnects show measurable degradation in the mechanical properties even after brief exposures to high temperature. In this paper, a method has been developed for the determining equivalent storage time to produce identical damage at a different temperature. Electronics subjected to accelerated tests often have a well-defined thermal profile for a specified period of time. Quantification of the thermal profile in field deployed electronics may be often difficult because of variance in the environment conditions and usage profile. There is need for tools and techniques to quantify damage in deployed systems in absence of macro-indicators of damage without knowledge of prior stress history. Approach for mapping damage in leadfree second-level interconnects under between thermal conditions is new. High reliability applications such as avionics and missile systems may be often exposed to long periods of storage prior to deployment. Effect of storage at different temperature conditions can be mapped using the presented approach. A framework has been developed to investigate the system state and estimate the remaining useful life of solder ball subjected to a variety of isothermal aging conditions including 60°C, 75°C and 125°C for periods of time between 1-week and 4-week. Data on damage precursors has been collected and analyzed to derive physics based damage mapping relationships for aging. Mathematical relationships have been derived for the damage mapping to various thermal storage environments to facilitate determining appropriate time-temperature combination to reach a particular level of damage state. Activation energy for the leading indicators of failure is also computed. Specific damage proxies examined include the phase-growth indicator and the intermetallic thickness. The viability of the approach has been demonstrated for leadfree test assemblies subjected to multiple thermal aging at 60° C, 75°C and 125°C. Damage mapping relationships are derived from data based on the two separate leading indicators.
Influences of Specimen Size and Annealing Temperature on Mechanical Reliability of FIB-Fabricated Si Nanowires for NEMS
Authors: Fujii Tatsuya , Sudoh Koichi , Inoue Shozo , Namazu Takahiro
Published: January 2014

This paper describes the effects of specimen size, focused ion beam (FIB) induced damage, and annealing on the mechanical properties of sub-100nm-sized silicon (Si) nanowires (NWs) that were evaluated by means of uniaxial tensile testing. Si NWs were made from silicon-on-nothing membranes that were produced by deep reactive ion etching trench fabrication and ultra-high vacuum (UHV) annealing. FIB system’s probe manipulation and film deposition functions were used to fabricate Si NWs and to directly bond them onto the sample stage of a tensile test device. The mean Young’s modulus and the mean strength of FIB-damaged NWs were 131.0 GPa and 5.6 GPa, respectively. After 700°C and 1000°C annealing in UHV, the mean Young’s modulus was increased to 168.1 GPa and 169.4 GPa, respectively, due to recrystallization by annealing. However, the mean strength was decreased to 4.1 GPa and 4.0 GPa, respectively. These experimental facts imply that the crystallinity of NWs improved, but the morphology was degraded. The surface degradation was probably related to gallium ion implantation into NWs surface during FIB fabrication.
Soil-Pipeline Interaction Modeling and Assessment in Unstable Slopes
Authors: Pereira Mauricio , Contreras Maria Fernanda , Vergara Carlos
Published: January 2014

Due to their length, oil and gas pipelines usually face different geotechnical problems along their routes (fast or slow, shallow or deep landslides) that impact the pipe integrity. In the current state of practice, this problems are analyzed considering the system as a beam on elastic foundation (Winkler type models), in which the loads on the pipe (e.g. internal pipe pressure and geostatic loads) are studied independently. A more realistic description of the soil-pipe interaction phenomenon that allows the prediction and explanation of the pipe failures found in the practice requires more advanced methodologies, involving the constitutive behavior of soil and pipe and the combined effect of different types of loads. In order to assess in a better way the soil-pipe interaction problem in landslides, this paper presents a 3D numerical model of the system, including the combined effect of different loads (such as landslide loads, geostatic loads and pipe internal pressure). The results obtained with the model were validated against real field measures in the OCENSA pipeline system and are expressed as soil displacement versus pipe strain relations. These relations are being used successfully in the evaluation of the behavior of the pipeline in unstable slopes, resulting in an important tool in the OCENSA pipeline integrity program.
A Proposed Geotechnical Risks Management Plan for Pipeline Integrity
Authors: Oliveira Hudson Régis
Published: January 2014

Linear works, such as highways, power lines, gas and oil pipelines among others, as well as other types of engineering works can be threaten by natural hazards, such as landslides, floods, erosions, earthquakes, hurricanes, seaquakes and others, which could lead to great environmental impacts, very high sum of money lost and even deaths.

Aiming to reduce geological and geotechnical risks, preventive or corrective actions can be executed from the design phase to the operational and maintenance stages in pipelines. In this last phase, an integrity management plan of these facilities can be adopted, with the purpose of mitigating residual risks that had not been covered on the design and construction phases.

One of the alternatives to implement an integrity management of gas pipelines is found in the code “Managing System Integrity of Gas Pipelines” – ASME B31.8S (2005). However, this code has some limitations in actions concerning to prevention, identification and correction of geological and geotechnical problems.

This paper presents information about geotechnical risks in transmission pipelines and tools applied in identification, prevention and correction of geotechnical problems in pipelines, as well as, others with potential to be applied in pipelines.

A basic pipeline integrity management plan focused in geotechnical risks is proposed in the paper, transcribed as a contribution to ASME B31.8S Code. This plan is composed by actions: from identification, prevention, evaluation and analysis to correction of geotechnical instabilities in pipelines. The plan is composed by a flowchart with all actions selected for the geotechnical risk care. The plan was developed based on directions set in ASME B31.8S Code, together with Brazilian, Italian and Canadian experiences.
Thin films of carbon nanotubes via ultrasonic spraying of suspensions in N-methyl-2-pyrrolidone and N-cyclohexyl-2-pyrrolidone
Authors: Willey Anthony D. , Holt Josh M. , Larsen Brian A. , Blackburn Jeffrey L. , Liddiard Steven , Abbott Jonathan , Coffin Mallorie , Vanfleet Richard R. , Davis Robert C.
Published: January 2014

Described is a method for ultrasonically spraying thin films of carbon nanotubes that have been suspended in organic solvents. Nanotubes were sonicated in N-methyl-2-pyrrolidone or N-cyclohexyl-2-pyrrolidone (CHP) and then sprayed onto a heated substrate using an ultrasonic spray nozzle. The solvent was quickly evaporated, leaving a thin film of randomly oriented nanotubes. Unlike other methods of spraying nanotube films, this does not require removal of surfactant after spraying and is compatible with creating films of functionalized nanotubes. Film thickness was controlled by the spray time and films were sprayed with thicknesses between 10 and 500 nm. Single-walled, multiwalled, and functionalized multiwalled nanotubes were sprayed. Transparent conducting thin films prepared by spraying single-walled carbon nanotubes dispersed in CHP demonstrated similar sheet resistance (for a given optical transmittance) as those prepared by spraying aqueous polymer-based dispersions that required postdeposition polymer removal.
CrNx films prepared using feedback-controlled high power impulse magnetron sputter deposition
Authors: Wu Wan-Yu , Hsiao Bo-Hung , Chen Pin-Hung , Chen Wei-Chih , Ho Chun-Ta , Chang Chi-Lung
Published: January 2014

A feedback-controlled high power impulse magnetron sputter deposition system was used to deposit CrNx thin films in a reactive mode. The plasma emission intensity of Cr at 358 nm was monitored and the amount of the reactive gas of N2 was precisely controlled to have a stable emission intensity during the deposition process. By controlling the N2 input, giving different Cr 358 nm (neutral state) emission intensities, various CrNx thin films were obtained at a fixed duty cycle of 4.5% under a stable reactive mode. The characteristics and the mechanical properties of the obtained films were also investigated. The results show that a Cr emission intensity at 40% relative intensity between pure metal deposition (100%) and fully poisoned deposition (0%) has the highest hardness and the elastic modulus of 29 and 357 GPa, respectively. Besides, the lowest friction coefficient, lowest corrosion rate, and highest corrosion resistance were also observed.
Population Pharmacokinetic Assessment of the Effect of Food on Piperaquine Bioavailability in Patients with Uncomplicated Malaria
Authors: Tarning Joel , Lindegardh Niklas , Lwin Khin Maung , Annerberg Anna , Kiricharoen Lily , Ashley Elizabeth , White Nicholas J. , Nosten François , Day Nicholas P. J.
Published: January 2014

Previously published literature reports various impacts of food on the oral bioavailability of piperaquine. The aim of this study was to use a population modeling approach to investigate the impact of concomitant intake of a small amount of food on piperaquine pharmacokinetics. This was an open, randomized comparison of piperaquine pharmacokinetics when administered as a fixed oral formulation once daily for 3 days with (
n
= 15) and without (
n
= 15) concomitant food to patients with uncomplicated
Plasmodium falciparum
malaria in Thailand. Nonlinear mixed-effects modeling was used to characterize the pharmacokinetics of piperaquine and the influence of concomitant food intake. A modified Monte Carlo mapped power approach was applied to evaluate the relationship between statistical power and various degrees of covariate effect sizes of the given study design. Piperaquine population pharmacokinetics were described well in fasting and fed patients by a three-compartment distribution model with flexible absorption. The final model showed a 25% increase in relative bioavailability per dose occasion during recovery from malaria but demonstrated no clinical impact of concomitant intake of a low-fat meal. Body weight and age were both significant covariates in the final model. The novel power approach concluded that the study was adequately powered to detect a food effect of at least 35%. This modified Monte Carlo mapped power approach may be a useful tool for evaluating the power to detect true covariate effects in mixed-effects modeling and a given study design. A small amount of food does not affect piperaquine absorption significantly in acute malaria.
Detection of New Bunyavirus RNA by Reverse Transcription–Loop-Mediated Isothermal Amplification
Authors: Huang Xue-Yong , Hu Xiao-Ning , Ma Hong , Du Yan-Hua , Ma Hong-Xia , Kang Kai , You Ai-Guo , Wang Hai-Feng , Zhang Li , Chen Hao-Min , Dumler J. Stephen , Xu Bian-Li
Published: January 2014

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging and epidemic infectious disease in central and northeast China. It is caused by New Bunyavirus and carries an average 12% case fatality rate. Early and rapid detection is critical for prevention and control of New Bunyavirus infection, since no vaccine or antiviral drugs are currently available, and prevention requires careful attention to control of the suspected tick vector. In this study, a simple and sensitive reverse transcription–loop-mediated isothermal amplification (RT-LAMP) assay was developed for rapid detection of New Bunyavirus. The detection limit of the RT-LAMP assay was approximately 10
3
50% tissue culture infective doses/ml of New Bunyavirus in culture supernatants, and no cross-reactive amplification of other viruses known to cause similar clinical manifestations was observed. The assay was further evaluated using 138 specimens from clinically suspected SFTS and 40 laboratory-proven hantavirus infection with fever and renal syndrome patients, and the assay exhibited 97% agreement compared to real-time RT-PCR and conventional RT-PCR. Using real-time RT-PCR as the diagnostic gold standard, RT-LAMP was 99% sensitive and 100% specific. The RT-LAMP assay could become a useful alternative in clinical diagnosis of SFTS caused by New Bunyavirus, especially in resource-limited hospitals or rural clinics of China.
Non-traumatic, bilateral subcapital femoral fractures postpartum
Authors: Yassin Anhar , Jawad Issrah , Coomber Ross , Gonzalez-Castro Aurora
Published: January 2014

A 28-year-old Romanian woman, presented 2 weeks postnatally with pain in her left hip. Plain radiography suggested a left intracapsular, subcapital hip fracture. A CT scan of the pelvis showed diffuse osteopaenia with bilateral subcapital fractures of both femurs. From this imaging and subsequent investigation, a diagnosis of transient osteoporosis of pregnancy was made. The patient was treated with a closed reduction and cannulated screw fixation. Rehabilitative treatment, vitamin D, calcium and bisphosphonate therapy were initiated. She remains under close follow-up from orthopaedic, rheumatological and endocrine teams. Multiple opportunities were missed to identify the source of the patient's pain and inability to weight bear. Early detection and management of this condition is crucial because of the associated morbidity, including debilitating pain, reduced mobility, fractures and avascular necrosis. Cessation of breastfeeding, adequate pain relief, early use of bisphosphonates and rehabilitative treatment are essential.