bluuebunny/crossref_metadata_2025 huggingface dataset:
Stent Strut Protrusion – An Uncommon Complication of Stent Placement in a Fistula
Authors: Sequeira Adrian , Artikov Shukhrat , Abreo Kenneth
Published: January 2014

Stent strut protrusion through the skin is a rare and a potentially dangerous complication from the cannulation of stents placed within arterio‐venous fistulas and grafts. Such cases are usually managed surgically. We present a case wherein strut penetration of an arterio‐venous fistula was noted at the distal (uncovered) end of a Fluency Plus® tracheo bronchial stent graft. After analyzing the various reasons why this may have happened, a nonsurgical approach was taken to preserve the access and manage strut protrusion.
Exploring aberrant bivalve shell ultrastructure and geochemistry as proxies for past sea water acidification
Authors: Hahn Sabine , Griesshaber Erika , Schmahl Wolfgang W. , Neuser Rolf D. , Ritter Ann‐Christine , Hoffmann Rene , Buhl Dieter , Niedermayr Andrea , Geske Anna , Immenhauser Adrian
Published: January 2014

Throughout much of Earth's history, marine carbonates have represented one of the most important geological archives of environmental change. Several pivotal events during the Phanerozoic, such as mass extinctions or hyperthermal events have recently been associated with ocean acidification. Nevertheless, well‐defined geological proxies for past ocean acidification events are, at best, scarce. Here, experimental work explores the response of bivalve shell ultrastructure and isotope geochemistry (δ13C, δ18O and δ26Mg) to stressful environments, in particular to sea water acidification. In this study, the common blue mussel, Mytilus edulis, was cultured (from early juvenile stages to one year of age) at four pH regimes (pHNBS 7·2 to pH 8·0). Shell growth rate and ultrastructure of mainly the calcitic portion of the shells were compared between experimental treatments. Specimens exposed to low‐pH environments show patches of disordered calcitic fibre orientation in otherwise well‐structured shells. Furthermore, the electron backscattered diffraction analyses reveal that, under acidified conditions, the c‐axis of the calcite prisms exhibits a bimodal or multi‐modal distribution pattern. Similar shell disorder patterns have been reported from mytilids kept under naturally acidified sea water conditions. In contrast, this study found no evidence that different pH regimes affect shell carbon, oxygen or magnesium isotope ratios. Based on these observations, it is proposed that: (i) stressful environments, in this case low sea water pH, predictably affect bivalve biomineralization patterns; and (ii) these findings bear potential as a novel (petrographic) proxy for ancient sea water acidification. An assessment of the applicability of these data to well‐preserved fossil shell material from selected time intervals requires additional work.
News‐Media and Terrorism: Changing Relationship, Changing Definitions
Authors: Kampf Zohar
Published: January 2014

This article discusses two aspects that are important for understanding the relationship between Western news media and terrorism: the changing representation of terrorists and terrorist attacks in the media and, with it, the changing definition of terrorism. By calling attention to evolving news media practices in times of terrorism, I argue that advanced communication technologies and the emergence of global media ecology since the 1990s has made terrorism more visible in both national and international media landscapes. One result is that the more the news media expose terrorism to global audiences via the “front door,” the more controversial the use of the terms “terrorism” and “terrorist” become in social, political, and scholarly discourses. The paper addresses the evolving journalistic practices and their consequences as documented in previous studies on media reporting of terrorism in several national contexts, mostly the UK, the United States, and Israel.
Social Stratification in Jaffna: A Survey of Recent Research on Caste
Authors: Kuganathan Prashanth
Published: January 2014

Since 1983, war has dominated the perception of Sri Lanka. This has affected scholarship on the country, such that the subjects of an overwhelming number of research proposals and publications have been on the war and the prospects and prescriptions for peace. This survey paper is an attempt to locate the system of caste in transition in the Jaffna Peninsula by reviewing recent literature written after the commencement of the war. While detailed ethnographies of caste in Jaffna may have temporarily come to a halt, caste practices have not and remain a salient part of everyday life among the Tamils in Sri Lanka. As the war ended in 2009, it is therefore important that social scientists on Sri Lanka revisit the topic of caste, that is an integral part of not just Tamil culture or society, but being Tamil itself. As the study of caste is dominated by research in India, a microanalysis of Jaffna and Sri Lanka, particularly the nuances of this system in transition due to war and militancy, could contribute to the macro‐study of caste at a sub‐continental perspective.
At the Intersection of Urban Sociology and Criminology: Fear Of Crime and the Postindustrial City
Authors: Benz Terressa A.
Published: January 2014

This essay examines the intersections between urban sociology and criminology in relation to fear of crime. I argue that there is a disconnect between theory and practice when it comes to reducing fear of crime that needs to be resolved in order for the postindustrial city to attract the new middle‐class demographic that is known for embracing and seeking out diversity. Despite the contributions made by environmental criminologists and new urbanists, the most popular explanation of fear of crime and crime reduction, offered by the field of criminology, focuses on reducing quality‐of‐life offenses and incivilities. Yet, these strategies are not known to significantly reduce fear of crime, but rather for purging the urban landscape of its diversity through exclusion.
I Just Don't Trust Them: The Development and Validation of an Assessment Instrument to Measure Trust in Science and Scientists
Authors: Nadelson Louis , Jorcyk Cheryl , Yang Dazhi , Jarratt Smith Mary , Matson Sam , Cornell Ken , Husting Virginia
Published: January 2014

Trust in science and scientists can greatly influence consideration of scientific developments and activities. Yet, trust is a nebulous construct based on emotions, knowledge, beliefs, and relationships. As we explored the literature regarding trust in science and scientists we discovered that no instruments were available to assess the construct, and therefore, we developed one. Using a process of data collection from science faculty members and undergraduate students, field testing, expert feedback, and an iterative process of design, we developed, validated, and established the reliability of the Trust in Science and Scientist Inventory. Our 21‐item instrument has a reliability of Cronbach's alpha of .86, and we have successfully field‐tested it with a range of undergraduate college students. We discuss implications and possible applications of the instrument, and include it in the appendix.
A Comparison of TIMSS Items Using Cognitive Domains
Authors: Nixon Ryan S. , Barth Katie N.
Published: January 2014

The results of international assessments such as the Trends in International Mathematics and Science Study (TIMSS) are often reported as rankings of nations. Focusing solely on national rank can result in invalid inferences about the relative quality of educational systems that can, in turn, lead to negative consequences for teachers and students. This study seeks an alternative data analysis method that allows for improved inferences about international performance on the TIMSS. In this study, four classroom teachers categorized a sample of TIMSS items by the cognitive domains of knowing and applying using the definitions provided by the TIMSS 2011 Assessment Frameworks. Items of different cognitive domains were analyzed separately. This disaggregation allowed for more valid inferences to be made about student performance. Results showed almost no significant difference between the performance of U.S. students and the students of five other nations. Additionally, no differences were observed in U.S. students' performance on knowing items and applying items, although students from some sample nations performed significantly better on knowing items. These results suggest that policy makers, educators, and citizens should be cautious when interpreting the results of TIMSS rank tables.
Google Insights and U.S. Senate Elections: Does Search Traffic Provide a Valid Measure of Public Attention to Political Candidates?
Authors: Swearingen C. Douglas , Ripberger Joseph T.
Published: January 2014

Objective

To propose a new indicator of public attention to electoral candidates based on the relative pattern of Internet queries for opposing candidates.

Methods

To demonstrate the validity of this measure, we use ordinary least squares regression and an F‐ratio test.

Results

We find that this measure, based on Google Insights data, behaves in a manner consistent with a valid measure of public attention. Moreover, this finding holds when the measure is included in a standard model used to explain U.S. Senate election outcomes.

Conclusion

The Google Insights measure of relative public attention shows the shifts in public attention as the campaign is waged and is consistent with how we would expect to see such a measure behave. This research opens numerous avenues for research in the campaigns and elections subfield.
The Economic Crisis and Medical Care Use: Comparative Evidence from Five High‐Income Countries
Authors: Lusardi Annamaria , Schneider Daniel , Tufano Peter
Published: January 2014

Objective

We examine how the economic crisis has affected individuals’ use of routine medical care and assess the extent to which the impact varies depending on national context.

Methods

Data from a new cross‐national survey fielded in the United States, Great Britain, Canada, France, and Germany are used to estimate the effects of employment and wealth shocks and financial fragility on the use of routine care.

Results

We document reductions in individuals’ use of routine nonemergency medical care in the midst of the economic crisis. Americans reduced care more than individuals in Great Britain, Canada, France, and Germany. At the national level, reductions in care are related to the degree to which individuals must pay for it, and within countries, reductions are linked to shocks to wealth and employment and to financial fragility.

Conclusions

The economic crisis has led to reductions in the use of routine medical care, and systems of national insurance provide some protection against these effects.
Varicella zoster reactivation after hematopoietic stem cell transplant in children is strongly correlated with leukemia treatment and suppression of host T‐lymphocyte immunity
Authors: Vermont C.L. , Jol‐van der Zijde E.C.M. , Hissink Muller P. , Ball L.M. , Bredius R.G.M. , Vossen A.C. , Lankester A.C.
Published: January 2014

Background and aims

Varicella zoster virus (VZV) reactivation following hematopoietic stem cell transplantation (HSCT) may cause significant morbidity and mortality. We undertook a retrospective study to determine the frequency and risk factors associated with VZV reactivation, including underlying disease, the use of fludarabine in high‐risk leukemia chemotherapy protocols, and immune status before HSCT.

Patients and methods

We studied 163 children who underwent a first HSCT between 2002 and 2008, before introduction of routine VZV prophylaxis on our unit. VZV diagnosis was based on clinical features and supported by polymerase chain reaction on plasma and/or vesical fluid. Patient data and possible risk factors pre‐ and post HSCT were recorded and compared using a multivariate regression analysis.

Results

Within this cohort, 41 (25%) patients developed VZV reactivation during the first year after transplantation at a median of 60 days post HSCT. VZV reactivation occurred more often within the subgroup of patients with acute leukemia compared with the remainder of patients (38% vs. 15%, P < 0.01). Multivariate Cox regression analysis revealed that, besides positive VZV serology in patients pre‐HSCT (P = 0.03), acute leukemia as the indication for HSCT remained the only independent risk factor for VZV reactivation (P = 0.025, odds ratio 2.5, 95% confidence interval 1.1–5.6). This was associated with low pre‐transplant T‐cell counts, especially in the CD4+ subset. No differences were found in relation to donor type, age, or use of serotherapy.

Conclusion

VZV reactivation after HSCT predominates in acute leukemia patients and is associated with low T CD4+ lymphocyte counts. This finding demonstrates the impact of pre‐HSCT host immune suppression on VZV reactivation patterns after HSCT.
Clinical features and risk factors for developing varicella zoster virus dissemination following hematopoietic stem cell transplantation
Authors: Umezawa Y. , Kakihana K. , Oshikawa G. , Kobayashi T. , Doki N. , Sakamaki H. , Ohashi K.
Published: January 2014

Background

We retrospectively analyzed 80 instances of varicella zoster virus (VZV) disease in 72 patients who underwent allogeneic hematopoietic stem cell transplantation (HSCT) and examined the clinical differences between localized and disseminated disease. Risk factors for developing VZV dissemination were also evaluated.

Results

Of the 80 instances, 54 instances were localized diseases and 26 were disseminated diseases. Patient characteristics did not differ significantly between the 2 groups, except for the first‐line therapy and the duration from symptom onset to treatment. In the disseminated group, intravenous acyclovir was used as the first‐line therapy more frequently, and more time elapsed before beginning antiviral therapy compared with the localized group. In multivariate analyses, the duration from symptom onset to treatment was identified as an independent risk factor that significantly affected the development of VZV dissemination. Gender, total body irradiation, and chronic graft‐versus‐host disease, of which the latter 2 factors were reported as risk factors for the development of VZV disease after HSCT, did not affect the development of VZV dissemination.

Conclusion

Our results suggest that VZV infection or reactivation may easily progress to viremia with delayed use of antiviral agents and may result in VZV dissemination in immunocompromised patients.
Course and treatment of chronic hepatitis E virus infection in lung transplant recipients
Authors: Pischke S. , Greer M. , Hardtke S. , Bremer B. , Gisa A. , Lehmann P. , Haverich A. , Welte T. , Manns M.P. , Wedemeyer H. , Gottlieb J. ,   the Hepatitis E study group
Published: January 2014

Objective

Persistent hepatitis E virus (HEV) infections have been described in various transplant cohorts. However, the frequency and the course of HEV infection in lung transplant recipients (Lu‐Tr) are not well defined.

Methods

We retrospectively analyzed serum from 95 Lu‐Tr for HEV RNA and anti‐HEV immunoglobulin‐G (IgG) (with the MP assay). Anti‐HEV seroprevalence was compared to that of 537 healthy individuals. Prospective HEV screening was subsequently initiated in Lu‐Tr.

Results

Elevated liver enzymes were observed in 44/95 (46.3%) patients. Anti‐HEV IgG was present in 5/95 patients (5.3%), revealing a slightly higher prevalence compared to controls (2%, 11/537; P = 0.07). Chronic HEV infection with detectable viral replication was confirmed by polymerase chain reaction in 3 (3.2%) patients, all of whom demonstrated clinical and biochemical features of active liver disease (maximum alanine aminotransferase [ALTmax] 89, 215, and 270 IU/L, respectively). One patient had died from multi‐organ failure in combination with liver cirrhosis before HEV diagnosis. Two additional patients with chronic hepatitis E were identified during prospective screening (ALTmax 359 and 318 IU/L). All patients still alive commenced ribavirin therapy for 5 months, with dose adjustment (400–600 mg/day) according to renal function and hemoglobin level. Sustained resolution of HEV infection occurred in 2 patients. One patient is still under treatment, and the fourth died from graft failure considered unrelated to ribavirin therapy.

Conclusion

Chronic hepatitis E should be considered in the differential diagnosis of elevated liver enzymes, which are commonly seen in Lu‐Tr. We observed 1 case of end‐stage liver cirrhosis and death in an HEV‐infected subject, who was not treated with ribavirin. Given this potentially devastating consequence, ribavirin therapy of persistent HEV infection appears to be acceptably safe and effective in Lu‐Tr. However, larger prospective studies are warranted.
Ocular and eyelid neoplasia in birds: 15 cases (1982–2011)
Authors: Rodriguez‐Ramos Fernandez Julia , Dubielzig Richard R.
Published: January 2014

Ocular and eyelid lesions are a common finding in birds; however, avian ocular and eyelid neoplasia is seldom reported. The purpose of this study was to record clinical and pathological data from cases of avian ocular neoplasia submitted to theComparativeOcularPathologyLaboratory ofWisconsin over a 29‐year period. A total of 284 avian ocular pathology cases from 1982 to 2011 were reviewed. Out of those, 15 were diagnosed with nine different ocular tumors (5.2%). Metastatic cancer to the globe was diagnosed in seven cases. Six of the metastatic cancers were diagnosed as lymphoma and one as papillary cystic carcinoma of respiratory epithelial origin, presumably originating in the sinus. Primary tumors were diagnosed in eight cases including three tumors of epithelial origin (undifferentiated carcinoma, multicystic adenoma, and pigmented iridociliary adenoma). A teratoid medulloepithelioma and a ganglioneuroma were presumptively diagnosed. A round cell tumor and squamous cell carcinoma were detected in conjunctival samples, and a teratoma was diagnosed from an episcleral sample.
COMPUTED TOMOGRAPHY OF BALL PYTHONS (Python regius) IN CURLED RECUMBENCY
Authors: Hedley Joanna , Eatwell Kevin , Schwarz Tobias
Published: January 2014

Anesthesia and tube restraint methods are often required for computed tomography (CT) of snakes due to their natural tendency to curl up. However, these restraint methods may cause animal stress. The aim of this study was to determine whether the CT appearance of the lungs differs for ball pythons in a curled position vs. tube restraint. Whole body CT was performed on ten clinically healthy ball pythons, first in curled and then in straight positions restrained in a tube. Curved multiplanar reformatted (MPR) lung images from curled position scans were compared with standard MPR lung images from straight position scans. Lung attenuation and thickness were measured at three locations for each scan. Time for positioning and scanning was 12 ± 5 min shorter for curled snakes compared to tube restraint. Lung parenchyma thickness and attenuation declined from cranial to caudal on both straight and curled position images. Mean lung parenchyma thickness was greater in curled images at locations 1 (P = 0.048) and 3 (P = 0.044). Mean lung parenchyma thickness decreased between location 1 and 2 by 86–87% (straight: curled) and between location 1 and 3 by 51‐50% (straight: curled). Mean lung attenuation at location 1 was significantly greater on curled position images than tube restraint images (P = 0.043). Findings indicated that CT evaluation of the lungs is feasible for ball pythons positioned in curled recumbency if curved MPR is available. However, lung parenchyma thickness and attenuation in some locations may vary from those acquired using tube restraint.
EVALUATION OF THE WARP‐TURBO SPIN ECHO SEQUENCE FOR 3 TESLA MAGNETIC RESONANCE IMAGING OF STIFLE JOINTS IN DOGS WITH STAINLESS STEEL TIBIAL PLATEAU LEVELING OSTEOTOMY IMPLANTS
Authors: Simpler Renee E. , Kerwin Sharon C. , Eichelberger Bunita M. , Wall Corey R. , Thompson James A. , Padua Abraham , Purdy David , Griffin John F.
Published: January 2014

Susceptibility artifacts caused by ferromagnetic implants compromise magnetic resonance imaging (MRI) of the canine stifle after tibial plateau leveling osteotomy (TPLO) procedures. The WARP‐turbo spin echo sequence is being developed to mitigate artifacts and utilizes slice encoding for metal artifact reduction. The aim of the current study was to evaluate the WARP‐turbo spin echo sequence for imaging post TPLO canine stifle joints. Proton density weighted images of 19 canine cadaver limbs were made post TPLO using a 3 Tesla MRI scanner. Susceptibility artifact sizes were recorded and compared for WARP vs. conventional turbo spin echo sequences. Three evaluators graded depiction quality for the tibial tuberosity, medial and lateral menisci, tibial osteotomy, and caudal cruciate ligament as sufficient or insufficient to make a diagnosis. Artifacts were subjectively smaller and local structures were better depicted in WARP‐turbo spin echo images. Signal void area was also reduced by 75% (sagittal) and 49% (dorsal) in WARP vs. conventional turbo spin echo images. Evaluators were significantly more likely to grade local anatomy depiction as adequate for making a diagnosis in WARP‐turbo spin echo images in the sagittal but not dorsal plane. The proportion of image sets with anatomic structure depiction graded adequate to make a diagnosis ranged from 28 to 68% in sagittal WARP‐turbo spin echo images compared to 0–19% in turbo spin echo images. Findings indicated that the WARP‐turbo spin echo sequence reduces the severity of susceptibility artifacts in canine stifle joints post TPLO. However, variable depiction of local anatomy warrants further refinement of the technique.
Applications of Cold Plate Units With Micro-Channel for Cooling Electronics
Authors: Mashiko Koichi , Mochizuki Masataka , Goto Kazuhiko , Takahashi Makoto , Matsuda Masahiro , Horiuchi Yasuhiro , Nguyen Tien
Published: January 2014

Until recently, effective cooling solutions with high performance were required especially in data-centers and super computers because of the huge and ever-increasing power consumption in these applications. Water cooling systems have been considered for use in the cooling of large scale data-centers and super computers.

For the cooling of super computer CPUs, a water cooling system using advanced cold plate technology is reconsidered. The thermal resistance of a cold plate for cooling the CPU is required to dissipate 80 to 100W of heat at 0.05 K/W. Also, in this application, the cold plate is required to be mechanically reliable in withstanding a cooling water pressure of 1MPa. We adopted a micro-channel structure as a heat transfer surface of this cold plate and developed a new brazing method so that the tips of the micro-channel fins are bonded to the inside of cover plate of the cold plate. In collaboration with a customer in charge of the design, we completed the water cooling unit consisting of cold plates, pipes and coupler manifold, assembled by brazing.

Finally, the high volume products were manufactured with reliability inspection (pressure test and helium leakage test) and used to effectively cool the CPUs of an advanced super computer, which was awarded the fastest super computer record.

Water cooling technology provides effective high capacity cooling in compact space limits, and has been widely used in applications like fiber laser machines and others. This paper describes the development of cold plate with micro-channels and its applications.
Heat Transfer due to the Impingement of an Axisymmetric Synthetic Jet Emanating From a Circular Orifice: A Numerical Investigation of a Canonical Geometry
Authors: Ebrahim M. , Silva L. , Ortega A.
Published: January 2014

Synthetic jets are produced by periodically injecting and ejecting fluid from an orifice. The mass flow rate is conserved in such a jet but net momentum flux is created due to the difference in the fluid dynamics at the orifice between the ejection and suction parts of each cycle. When pointed towards a heated surface, the synthetic jet can be used for cooling using the well-known advantages of jet impingement. In the present work, we have created a “canonical” jet in order to investigate the flow and heat transfer of a purely periodic synthetic jet which is not influenced by the manner in which it is generated. As such the “canonical” jet and the resulting heat transfer, can be considered to be dependent solely on the driving suction/ejection mechanisms at the orifice and thus can be examined independently of the actuator. The unsteady Navier-Stokes equations and the convection-diffusion equation were solved using a fully unsteady, laminar, three-dimensional axisymmetric finite volume approach in order to capture the complex time-dependent flow field created by different frequencies. The influence of jet-to-surface distance, Reynolds number, and driving frequency on heat transfer were investigated. Both stagnation and averaged Nusselt numbers were observed to be less dependent on frequency. Heat transfer was found to be higher at high Re numbers and low jet-to-surface distance. Results were compared with the steady continuous jet, experimental data of previous studies and the canonical slot synthetic jet at the same Reynolds number. A circular jet was found to be less efficient in removing heat over the heated wall than a slot synthetic jet.
Novel Immersion Cooling Technique for a 3D Chip Stack
Authors: Sinha Ashish , Kota Krishna , Hidalgo Pablo , Joshi Yogendra , Glezer Ari
Published: January 2014

An experimental investigation of a scheme for cooling electronics packaged in a 3D stack arrangement will be presented in this paper. The scheme utilizes immersion cooling of the stacked electronics in an enclosure filled with a dielectric fluid. Convection and conduction within the dielectric fluid drive heat from the 3D stack to the walls of the enclosure from where a ‘synthetic jet /fan air-cooled heat sink’ ultimately dissipates heat to the ambient. Four layers of thick film heaters embedded in FR-4 sheets, each attached to thin copper plates (innovatively stacked in a pyramidal arrangement for conducting heat laterally to the dielectric fluid and simultaneously promoting natural convection in the fluid), were used to simulate a 3D stack of electronics. For a comparative study, several runs were carried out, where the enclosure was filled with dielectric fluid (FC-770), FC-770 in combination with copper wool (with a goal of enhancing heat transfer in FC-770), and water. For a 40 W total power input to the stack, it was observed that the thermal resistance for heat dissipation to ambient from the four heaters varied from 1.67 K/W to 1.96 K/W with FC-770, 1.47 K/W to 1.87 K/W with FC-770 combined with copper wool, and 1.06 K/W to 1.50 K/W with water. The proposed cooling solution is passive and scalable, and is demonstrated to be practicable and effective in cooling 3D stacked electronics.
A Statistical Approach to Real-Time Updating and Automatic Scheduling of Physical Models
Authors: Jiang Huijing , Deng Xinwei , Lopez Vanessa , Hamann Hendrik
Published: January 2014

Energy consumption of data center has increased dramatically due to the massive computing demands driven from every sector of the economy. Hence, data center energy management has become very important for operating data centers within environmental standards while achieving low energy cost. In order to advance the understanding of thermal management in data centers, relevant environmental information such as temperature, humidity and air quality are gathered through a network of real-time sensors or simulated via sophisticated physical models (e.g. computational fluid dynamics models). However, sensor readings of environmental parameters are collected only at sparse locations and thus cannot provide a detailed map of temperature distribution for the entire data center. While the physics models yield high resolution temperature maps, it is often not feasible, due to computational complexity of these models, to run them in real-time, which is ideally required for optimum data center operation and management. In this work, we propose a novel statistical modeling approach to updating physical model outputs in real-time and providing automatic scheduling for re-computing physical model outputs. The proposed method dynamically corrects the discrepancy between a steady-state output of the physical model and real-time thermal sensor data. We show that the proposed method can provide valuable information for data center energy management such as real-time high-resolution thermal maps. Moreover, it can efficiently detect systematic changes in a data center thermal environment, and automatically schedule physical models to be re-executed whenever significant changes are detected.
Thermal Transport Phenomenon in Circular Pipe Flow Using Different Nanofluids
Authors: Torii Shuichi
Published: January 2014

The aim of the present study is to investigate the thermal fluid flow transport phenomenon of nanofluids in the heated horizontal circular tube. Consideration is given to the effects of volume fraction of the nanoparticle on the laminar heat transfer and thermal properties. Alumina (Al2O3) and oxide copper (CuO) are employed here as nanoparticles. It is found from the study that (1) the viscosity ratio of nanofluids increases in accordance with an increase of the volume fraction of the nanoparticles, (2) the nanofluids have substantially higher value of Nusselt number than the same liquids without nanoparticles and the Nusselt number of nanofluids increase with an increase of the Reynolds number, and (3) the dispersibility of particle in the nanofluid becomes worse slightly with an increase of the volume fraction of the nanoparticles.
Improved Zonal Model for Data Center Analysis
Authors: Song Zhihang , Murray Bruce T. , Sammakia Bahgat
Published: January 2014

A newly constructed zonal model based on the velocity propagation method (VPM) was developed as a thermal analysis tool for data centers. A viscous loss model is included, to better account for airflow momentum instead of using the basic power law method (PLM). The zonal model is implemented in the equation-based and object-oriented environment SPARK. A CFD model for a single cold aisle server room configuration was built and analyzed using the commercial software FloTHERM. Cold aisle containment was studied. Results from the zonal model, including both the plenum flow field and rack inlet temperature distributions were compared with those from the CFD package. Good agreement (within 10% average relative error) was obtained between the zonal model predictions and the CFD results. A primary goal of the study is to develop an effective real-time thermal analysis tool based on the zonal approach.
Steady and Transient Heat Transfer Analysis of the Microprocessor System Using One-Dimensional Thermal Network
Authors: Nishi Koji , Hatakeyama Tomoyuki , Ishizuka Masaru
Published: January 2014

This paper introduces and discusses one-dimensional thermal network for microprocessor silicon die temperature prediction both under steady and transient states. Firstly, one-dimensional thermal network with average temperature nodes is constructed with the thermal spreading resistance and the thermal local resistance. Secondly, characteristics of thermal resistances under steady state are discussed. By conducting three-dimensional heat conduction simulation, thermal resistance values are evaluated for the case with different cooling solutions and different heat distributions at silicon die bottom of microprocessor. Thirdly, thermal resistance behavior of introduced thermal network during transient state is explored for further understanding of temperature transition of the microprocessor silicon die. Since the thermal spreading resistance takes relatively large value and changes its value drastically, this paper investigates transient behavior of thermal spreading resistance from TIM (Thermal Interface Material) to heat sink base as an example.
Effects of Non-Uniform Heating on Two-Phase Flow Through Microchannels
Authors: Ritchey Susan N. , Weibel Justin A. , Garimella Suresh V.
Published: January 2014

As size, weight, and performance demands drive electronics packages to become increasingly thinner and more compact, volume restrictions prevent the use of large intermediate heat spreaders to mitigate heat generation non-uniformities. Instead, these non-uniform heat flux profiles are imposed directly on the ultimate heat sink, either due to chip-scale variations or the desire to cool multiple discrete devices. A better understanding of the impacts of non-uniform heating on two-phase flow characteristics and thermal performance limits for microchannel heat sinks is needed to address these thermal packaging trends. An experimental investigation is performed to explore flow boiling phenomena in a microchannel heat sink with point hotspots, as well as non-uniform streamwise and transverse heating conditions across the entire heat sink area. The investigation is conducted using a silicon microchannel heat sink with a 5 × 5 array of individually controllable heaters attached to a 12.7 mm × 12.7 mm square base. The channels are 240 μm wide, 370 μm deep, and separated by 110 μm wide fins. The working fluid is FC-77, flowing at a mass flux of approximately 890 kg/m2s. High-speed visualizations of the flow are recorded to observe the local flow regimes. It is found that even though the substrate thickness beneath the microchannels is very small (200 μm), significant lateral conduction occurs and must be accounted for in the calculation of the local heat flux imposed. For non-uniform heat input profiles, with peak heat fluxes along the central streamwise and transverse directions, it is found that the local flow regimes, heat transfer coefficients, and wall temperatures deviate significantly from a uniformly heated case. These trends are assessed as a function of an increase in the relative magnitude of the nonuniformity between the peak and background heat fluxes.
Fundamental Research on Via Processing by Using Short Pulse Laser in SiC
Authors: Iwatani Naoki , Doan Hong Duc , Fushinobu Kazuyoshi
Published: January 2014

Laser drilling of silicon carbide (SiC) wafer in air (dry ablation) and underwater by using ns pulsed infrared (1064 nm) Nd: YAG laser is investigated. In order to suggest optimal parameters of via processing in SiC wafer, the effects of pulse number, laser fluence, water film thickness, and focus position are evaluated. As compared with dry ablation vias, decreasing etching rate, increasing via diameter, and generation of cracks in high-energy regime are observed in liquid-assisted processing. However, it is found that it can create vias without debris, HAZ, cracks. Also, optimal parameter set for infrared pulse laser processing under water is found to be the laser fluence of less than 10 J/cm2 and water thickness of 1mm.
Unsteady Thermo-Structural Simulation of Nano-Bridge Resonators
Authors: Maghsoudi Elham , Martin Michael James
Published: January 2014

This study provides a thermo-structural simulation to investigate the behavior of nano-bridge resonators. A three-dimensional doubly clamped bridge with a length of 10 microns, a width of 1 micron and a thickness of 300 nm vibrating in the air is simulated. A free molecular heat transfer model is used to define the heat transfer coefficient and the damping coefficient. A Finite Difference method is used to solve the transient heat transfer equation coupled with the dynamic structural equation at each time step. The study is performed for silicon. The results show the steady state amplitude variations and vibration amplitude variations by the total heat amplitude correspond to a linear system. The results also show that increasing the total heat amplitude has more significant effects on increasing the vibration amplitude rather than the steady state amplitude by a factor of 1.2. The steady state amplitude and vibration amplitude variation by the surrounding gas pressure is investigated over a range of pressures from 1 kPa to 500 kPa for a total heat amplitude of 5000 MW/m2 (50 mW). The steady state amplitude and the vibration amplitude decrease by increasing the pressure due to an increase in the damping coefficient and the heat transfer coefficient. The rate of decrease is significantly higher for the vibration amplitude. This is due to the combination of increasing heat transfer coefficient, and increased damping, as the pressure increases.
Thermal Performance of a Silicon-Based Multiple Micro-Jet Impingement Heat Sink
Authors: Husain Afzal , Kim Jun-Hee , Kim Kwang-Yong
Published: January 2014

The present study investigates thermal performance of a silicon-based multiple micro-jet impingement heat sink for thermal management of electronics. Three-dimensional numerical analysis was performed for steady incompressible laminar flow and conjugate heat transfer through a finite volume solver. A moderate heat flux, 100 W/cm2, is applied at the one end of the silicon substrate, while at the other end jet impingement system is designed. The jet plate is consisted of many jet holes whereas computational domain was simplified by utilizing symmetric boundary conditions across a lateral pitch as well as a central plane in x-direction. The effect of design parameters, namely, jet diameter and jet pitch has been analyzed at constant jet Reynolds numbers under laminar flow conditions on the performance of the heat sink. In view of the low pumping powers available from the micro-pumping devices, low flow rates are applied for the analysis. The cross-flow effects of the spent-flow are investigated for finding out optimum design parameters of the heat sink. The temperature distribution is discussed for number of jets, jet diameter and jet-to-jet spacing across the flow direction. While a moderate thermal resistance of the heat sink was obtained under laminar flow conditions, high performance can be achieved for turbulent flow conditions at the expense of excessive pressure drop which would be investigated in future studies.
Optimization Algorithms for Energy-Efficient Data Centers
Authors: Hamann Hendrik F.
Published: January 2014

Real-time optimization algorithms for managing energy efficiency in data centers have been developed and implemented. For example, for a given cooling configuration (which is being measured and modeled in real-time using IBM’s Measurement and Management Technologies) an optimization algorithm allows identifying the optimum placement of new servers (or workloads) or alternatively where to remove servers (or workload) for different constraints. Another optimization algorithm optimizes performance of the data center without creating hotspots. The optimization algorithms use a physical model in junction with linear programming as well as linear least square methods.
Investigation on the Multiple Jet Impingement Heat Transfer Using Al2O3-Water Nanofluid
Authors: Senkal Caner , Torii Shuichi
Published: January 2014

In recent years, increasing demands for high performance electronic devices give rise to a necessity to remove enormous amount of heat fluxes from small areas. Uniform temperature distribution and sufficient heat transfer dissipation are crucial issues for proper operation of electronic components. To cope up with thermal management of high heat dissipation devices, an efficient cooling method is required. Jet impingement cooling is one of those promising candidates which can handle heat dissipation in an effective way due to its superior heat transfer rates. In this paper, Al2O3 nanofluid heat transfer characteristics are investigated experimentally. Particle diameter of 31nm Al2O3 is taken into consideration in experiments. Impingement surface (surface area:780mm2) were made from oxygen-free copper to simulate high heat flux dissipating electronic component.

The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid.. Nanofluids with particle volume fractions up to 4% can provide significant heat transfer enhancement, on the other hand, it has been found that high volume fractions (higher then 6%), is not appropriate for heat transfer enhancement under the free jet array configuration. Within the range of parameters considered in this study, experimental results indicated that maximum heat transfer coefficient can be obtained for the intermediate jet to heated target distance (around five times of jet diameter) and closely spaced jets (S/D = 3) for the particle volume fraction 2%. Closely spaced jets are particularly suitable for the electronics cooling applications with regards to provide temperature uniformity on the heated surface.
Fracture Behaviors of Simulated Sn-Ag-Cu Solder Microbumps: Effects of Joint Scale and Aging
Authors: Huang Z. , Dutta I. , Subbarayan G. S.
Published: January 2014

Solder microbumps are widely applied in 3D packages using fine-pitch Cu-pillar or Through Silicon Via (TSV) technologies. Due to the small scale of these joints, the volumetric proportion of intermetallic compounds (IMCs) formed in these joints is typically very high. This renders microbump-joints much more brittle compared to traditional solder joints (flip-chip or BGA). In particular, the reliability of microbumps during a drop, which corresponds to a mixed-mode high strain rate fracture test, is of substantial concern because of the brittleness of these joints. This study reports on the fracture mechanics and mechanisms of simulated microbumps, which have similar thicknesses and IMC contents as actual microbumps, but are laterally scaled up to constitute valid fracture mechanics samples. Compact mixed mode (CMM) specimens with adhesive solder joints (Sn-3.0%Ag-0.5%Cu) between massive Cu substrates were utilized to measure the fracture properties. The fracture behavior was characterized as a function of joint thickness and proportion of IMC, the latter being controlled by adjusting the dwell time and aging time. It was found that the fracture toughness GC decreased monotonically with joint thickness (hJoint) due to increased triaxial constraint imposed by the substrates. With aging, the proportion of IMC thickness relative to the joint thickness (2hIMC/hJoint) increased, as did hJoint. This resulted in lower GC values. The associated mechanisms of fracture that led to these effects are discussed.
Measured-Temperature Interpolation and Visualization for Data Centers
Authors: Zhang Xuanhang (Simon) , Healey Christopher M. , Sheffer Zachary R. , VanGilder James W.
Published: January 2014

The growing demand for data center facilities has made intelligently managed data center operations necessary. For temperature measurement and thermal management, a common practice is to install a limited number of temperature sensors evenly distributed throughout the room. However, data center operators rarely fully equip facilities with temperature sensors due to their cost, complexity, and maintenance requirements, creating vacancies in the data center temperature and cooling picture. The local nature of sensor data can also be misinterpreted and misused. Without novel methods to interpret and visualize temperatures obtained by prediction or measurement, data center operators cannot easily identify urgent local cooling issues or quickly examine the temperature at other location. This paper presents methods to predict a full three-dimensional temperature field in data centers from a limited number of measurement points. Several different statistical interpolating schemes are discussed. We also validate the interpolated temperature fields against benchmark data from Computation Fluid Dynamics (CFD) and show good agreement.
Development of Plate Heat Pipes for the Thermal Management of Power Electronics
Authors: Abe Yoshiyuki , Nakajima Akira , Maeda Yoshihiko , Shimose Makoto
Published: January 2014

Plate heat pipes, 4.0mm × 40mm × 375mm, of maximum heat transfer capability, Qmax, of the order of hundred W have been developed for the thermal management in power electronic devices such as IGBT (Insulated Gate Bipolar Transistor), MOSFET (Metal Oxide Semiconductor Field Effect Transistor), et al. The thermal performance in both horizontal and vertical orientations were experimentally evaluated, and outstanding thermal performance of Qmax up to 600W in the vertical orientation and thermal resistance as low as 0.01K/W were confirmed. In addition to the heat pipes, thermosyphons of the same dimensions as the plate heat pipes were also fabricated and tested as a comparison. The plate heat pipes were then applied to the thermal management systems for a CPU in a 1-U server and for SiC power JFET, and stable and satisfactory cooling performance of the heat pipes for the electronics devices was demonstrated.
Analysis and Characterization of Thermal Expansion-Matched Wick-Based Multi-Chip Passive Heat Spreaders in Static and Dynamic Environments
Authors: Altman David H. , Gupta Anurag , Dubrowski Thomas E. , Sharar Darin J. , Jankowski Nicholas R. , North Mark T.
Published: January 2014

Ensuring adequate spreading of heat dissipated by high power density devices is a critical part of many electronics packaging designs. In many cases, passive wick-based heat spreaders can offer improved heat spreading performance relative to solid conductor alternatives. However, concerns related to performance degradation in high-inertial force environments frequently limit their use to static or near-static applications. In this work we investigate the performance of low coefficient of thermal expansion (CTE) wick-based heat spreaders cooling multiple high heat flux devices in static and high-g environments. Two high-power devices are simulated using custom-manufactured resistor-thermometer chips, enabling dissipation of die average heat fluxes in excess of 150W/cm2. Comparative thermal performance is evaluated for wick-based heat spreaders and solid CuMo heat spreaders of equivalent CTE affixed with interface materials typical of those used when attaching a low CTE package to a high CTE cold plate (e.g., Al or Cu). Thermal performance is characterized as a function of heat input during exposure to increasing g-forces applied using a custom-built centrifuge. Experimental observations are interpreted through detailed modeling of fluid flow patterns within the wick structure of the passive heat spreader. Results from these experiments demonstrate that properly designed wick-based heat spreaders have utility in both static and dynamic environments, exhibiting effective conductivities in excess of that obtainable with competitive low-expansion composites.
Relationships Between Supply Flow Rate of Small Cooling Fans and Pressure Drop Characteristics in Electronic Enclosure
Authors: Fukue Takashi , Hatakeyama Tomoyuki , Ishizuka Masaru , Hirose Koichi , Koizumi Katsuhiro
Published: January 2014

This study describes a prediction method of a supply flow rate of axial cooling fans mounted in high-density packaging electronic equipment. The performance of an air-cooling fan is defined by its P – Q (pressure difference – flow rate) curve. Generally the operating point of a fan, which is the operating pressure and the flow rate in equipment, is the point of intersection of a P – Q curve and a flow resistance curve. Recently, some researchers reported that catalogue P – Q curves have not necessarily been able to predict a correct supply flow rate in thermal design of high-density packaging equipment. Our study aims to improve prediction accuracy of the supply flow rate. In this report, a relationship between the P – Q curve and a pressure drop characteristic in a fan-mounted enclosure was investigated. A test enclosure which includes an obstruction was mounted in front of a test fan and the supply flow rate of the fan was measured while changing the obstruction. Additionally the flow resistance curves in the test enclosure were measured and the relationship among the supply flow rate, the P – Q curve and the flow resistance curve was investigated. It is found that the correct supply flow rate can be obtained by using the flow resistance from the enclosure inlet through the fan outlet and the revised P – Q curve which is made compensation for the pressure drop at the inlet and the outlet of the fan.