bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission of influenza A(H1N1) 2009 pandemic viruses in Australian swine
Authors: Deng Yi‐Mo , Iannello Pina , Smith Ina , Watson James , Barr Ian G. , Daniels Peter , Komadina Naomi , Harrower Bruce , Wong Frank Y. K.
Published: February 2012

Please cite this paper as: Deng et al. (2012). Transmission of influenza A(H1N1) 2009 pandemic viruses in Australian swine. Influenza and Other Respiratory Viruses 6(3), e42–e47.

Background  Swine have receptors for both human and avian influenza viruses and are a natural host for influenza A viruses. The 2009 influenza A(H1N1) pandemic (H1N1pdm) virus that was derived from avian, human and swine influenza viruses has infected pigs in various countries.

Objectives  To investigate the relationship between the H1N1pdm viruses isolated from piggery outbreaks in Australia and human samples associated with one of the outbreaks by phylogenetic analysis, and to determine whether there was any reassortment event occurring during the human‐pig interspecies transmission.

Methods  Real‐time RT‐PCR and full genome sequencing were carried out on RNA isolated from nasal swabs and/or virus cultures. Phylogenetic analysis was performed using the Geneious package.

Results  The influenza H1N1pdm outbreaks were detected in three pig farms located in three different states in Australia. Further analysis of the Queensland outbreak led to the identification of two distinct virus strains in the pigs. Two staff working in the same piggery were also infected with the same two strains found in the pigs. Full genome sequence analysis on the viruses isolated from pigs and humans did not identify any reassortment of these H1N1pdm viruses with seasonal or avian influenza A viruses.

Conclusions  This is the first report of swine infected with influenza in Australia and marked the end of the influenza‐free era for the Australian swine industry. Although no reassortment was detected in these cases, the ability of these viruses to cross between pigs and humans highlights the importance of monitoring swine for novel influenza infections.
Review on the impact of pregnancy and obesity on influenza virus infection
Authors: Karlsson Erik A. , Marcelin Glendie , Webby Richard J. , Schultz‐Cherry Stacey
Published: February 2012

Please cite this paper as: Karlsson et al. (2012) Review on the impact of pregnancy and obesity on influenza virus infection. Influenza and Other Respiratory Viruses 6(6), 449–460.

A myriad of risk factors have been linked to an increase in the severity of the pandemic H1N1 2009 influenza A virus [A(H1N1)pdm09] including pregnancy and obesity where death rates can be elevated as compared to the general population. The goal of this review is to provide an overview of the influence of pregnancy and obesity on the reported cases of A(H1N1)pdm09 virus infection and of how the concurrent presence of these factors may have an exacerbating effect on infection outcome. Also, the hypothesized immunologic mechanisms that contribute to A(H1N1)pdm09 virus severity during pregnant or obese states are outlined. Identifying the mechanisms underlying the increased disease severity in these populations may result in improved therapeutic approaches and future pandemic preparedness.
Kallikrein 6 Regulates Early CNS Demyelination in a Viral Model of Multiple Sclerosis
Authors: Scarisbrick Isobel A. , Yoon Hyesook , Panos Michael , Larson Nadya , Blaber Sachiko I. , Blaber Michael , Rodriguez Moses
Published: February 2012

Kallikrein 6 (Klk6) is a secreted serine protease that is elevated in active multiple sclerosis lesions and patient sera. To further evaluate the involvement of Klk6 in chronic progressive demyelinating disease, we determined its expression in the brain and spinal cord of SJL mice infected with Theiler's murine encephalomyelitis virus (TMEV) and assessed the effects of Klk6‐neutralizing antibodies on disease progression. Klk6 RNA expression was elevated in the brain and spinal cord by 7 days postinfection (dpi). Thereafter, Klk6 expression persisted primarily in the spinal cord reaching a peak of fivefold over controls at mid‐chronic stages (60 dpi–120 dpi). Significant elevations in Klk6 RNA were also induced in splenocytes stimulated with viral capsid proteins in vitro and in activated human acute monocytic leukemia cells. Klk6‐neutralizing antibodies reduced TMEV‐driven brain and spinal cord pathology and delayed‐type hypersensitivity (DTH) responses when examined at early chronic time points (40 dpi). Reductions in spinal cord pathology included a decrease in activated monocytes/microglia and reductions in the loss of myelin basic protein (MBP). By 180 dpi, pathology scores no longer differed between groups. These findings point to regulatory activities for Klk6 in the development and progression of central nervous system (CNS) inflammation and demyelination that can be effectively targeted through the early chronic stages with neutralizing antibody.
Vehicle‐related flood deaths in the United States, 1995–2005
Authors: Kellar D.M.M. , Schmidlin T.W.
Published: February 2012

Vehicle‐related deaths comprise more than half of all flash flood fatalities in the United States. Using the publication Storm Data from the United States National Climatic Data Center, we found 555 vehicle‐related flood deaths that occurred in 355 flooding events during 1995–2005. Males accounted for 60% of the deaths. The difference in death rates between the sexes was small at ages 19 and younger but males died at twice the rate of females for ages 40 and older. Elevated deaths rates were found for both males and females under age 5 and over 60. Flooding events classified as flash floods accounted for most of the fatalities. Vehicle‐related flood deaths were concentrated in the Texas Hill Country, the desert Southwest, the Ohio River Valley, and eastern North Carolina.
Systematic classification of melanoma cells by phenotype‐specific gene expression mapping
Authors: Widmer Daniel S. , Cheng Phil F. , Eichhoff Ossia M. , Belloni Benedetta C. , Zipser Marie C. , Schlegel Natalie C. , Javelaud Delphine , Mauviel Alain , Dummer Reinhard , Hoek Keith S.
Published: February 2012

There is growing evidence that the metastatic spread of melanoma is driven not by a linear increase in tumorigenic aggressiveness, but rather by switching back and forth between two different phenotypes of metastatic potential. In vitro these phenotypes are respectively defined by the characteristics of strong proliferation/weak invasiveness and weak proliferation/strong invasiveness. Melanoma cell phenotype is tightly linked to gene expression. Taking advantage of this, we have developed a gene expression–based tool for predicting phenotype called Heuristic Online Phenotype Prediction. We demonstrate the predictive utility of this tool by comparing phenotype‐specific signatures with measurements of characteristics of melanoma phenotype‐specific biology in different melanoma cell lines and short‐term cultures. We further show that 86% of 536 tested melanoma lines and short‐term cultures are significantly associated with the phenotypes we describe. These findings reinforce the concept that a two‐state system, as described by the phenotype switching model, underlies melanoma progression.
Association of Wild Bird Density and Farm Management Factors with the Prevalence of E. coli O157 in Dairy Herds in Ohio (2007–2009)
Authors: Cernicchiaro N. , Pearl D. L. , McEwen S. A. , Harpster L. , Homan H. J. , Linz G. M. , LeJeune J. T.
Published: February 2012

Our objective was to determine the role that European starlings (Sturnus vulgaris) play in the epidemiology of Escherichia coli O157:H7 in dairy cattle. We visited 150 dairy farms in Ohio twice during summer and fall months from 2007 to 2009. Fresh faecal pats from 30 lactating cows were collected during each visit. Information on farm management and environmental variables was gathered through a questionnaire administered to the farm owner. The number of starlings observed on the farm was also recorded. Approximately 1% of dairy cattle and 24% of farms were positive for E. coli O157. Risk factors associated with the presence of E. coli O157 in faecal pats included contact between adult cattle and calves, types or number of ventilation and manure management systems and number of birds per milking cow.
Effects of interferon therapy on development of hepatocellular carcinoma in patients with hepatitis C‐related cirrhosis: A meta‐analysis of randomized controlled trials
Authors: Qu Li‐Shuai , Chen Hong , Kuai Xiao‐Ling , Xu Zheng‐Fu , Jin Fei , Zhou Guo‐Xiong
Published: February 2012

Aim:  The role of interferon (IFN) therapy on prevention of hepatocellular carcinoma (HCC) in patients with hepatitis C virus (HCV)‐related cirrhosis remains controversial. This meta‐analysis aimed to determine whether IFN therapy reduced the incidence of HCC in HCV‐related cirrhotic patients.

Methods:  We performed a meta‐analysis including eight randomized controlled trials (RCT) (a total of 1505 patients) to assess the effect of IFN therapy on prevention of HCC in patients with HCV‐related cirrhosis. The pooled odds ratios (OR) were calculated using a random or fixed effects model.

Results:  Our results showed that IFN therapy significantly decreased the overall HCC incidence in HCV‐related cirrhotic patients (OR, 0.29; 95% confidence interval [CI], 0.10–0.80; P = 0.02). HCC risk in patients who failed to achieve sustained virological response (SVR) in the initial IFN‐based treatment was also reduced by maintenance IFN therapy (OR, 0.54; 95% CI, 0.32–0.90; P = 0.02). Subgroup analysis indicated that IFN therapy decreased HCC incidence in HCV‐related cirrhotic patients during long‐term follow up (>48 months) evidently (OR, 0.25; 95% CI, 0.09–0.67; P = 0.006). However, subgroup analysis of four RCT with short‐term follow up (≤48 months) did not demonstrate the significant difference in HCC incidence between IFN‐treated cirrhotic patients and controls (OR, 0.78; 95% CI, 0.39–1.55; P = 0.48).

Conclusion:  The present study suggested that IFN therapy could efficiently reduce HCC development in patients with HCV‐related cirrhosis; this effect was more evident in the subgroup of patients with long‐term follow up (>48 months). Patients who received maintenance IFN therapy had a lower risk of HCC than controls.
Bronchomalacia in Dogs with Myxomatous Mitral Valve Degeneration
Authors: Singh M.K. , Johnson L.R. , Kittleson M.D. , Pollard R.E.
Published: February 2012

Background

Cough in the geriatric small breed dog with myxomatous mitral valve degeneration (MMVD), a large left atrium, and absence of heart failure often is attributed to compression of the left mainstem bronchus by the left atrium. Studies investigating this syndrome are lacking in dogs.

Hypothesis

Airway collapse is independent of left atrial enlargement.

Animals

A total of 16 dogs presenting with chronic cough in the absence of congestive heart failure. Group 1 dogs (n = 10) had moderate‐to‐severe left atrial enlargement based on an echocardiographically calculated left atrial:aortic surface area [LA:Ao(a)] > 6. Group 2 dogs (n = 6) had no to mild left atrial enlargement [LA:Ao(a) ≤ 6].

Methods

Dogs were prospectively evaluated.CBC, biochemistry, urinalysis, cervical and thoracic radiographs, fluoroscopy, echocardiography, and bronchoscopy were performed. Bronchoscopic abnormalities were compared between groups using Fisher's Exact Test.P < .05 was considered significant.

Results

Fluoroscopy identified airway collapse in both groups. Bronchoscopic evidence of airway collapse >50% was observed in multiple bronchi with no difference between groups. All dogs had inflammation on airway cytology with respiratory infection in 1 dog in group 2. Left atrial size was interpreted radiographically as enlarged in 9 of 10 group 1 dog and in 2 of 6 group 2 dogs.VHSwas above normal in both groups of dogs regardless of echocardiographic evidence of cardiomegaly.

Conclusions

Results failed to identify an association between left atrial enlargement and airway collapse in dogs withMMVD, but did suggest that airway inflammation is common in dogs with airway collapse.
Assessment of a point‐of‐care test for measurement of blood triglyceride levels for rapid detection of equid hypertriglyceridaemia
Authors: Williams A. , Peachey L. E. , Christley R. M.
Published: February 2012

This project investigated the clinical value of a human whole blood point‐of‐care (POC) triglyceride (TG) measurement device to determine equid blood TG concentrations. Equid plasma TG measurements were determined in a commercial laboratory and also using whole blood and plasma on the POC device from equid patients with TG concentrations from within the normal range to severely hypertriglyceridaemic. Results were compared between methods using the Bland‐Altman method for validation. Seventy‐four samples were collected: 35 from inappetent or starved equid patients (considered ‘at‐risk’ of developing hypertriglyceridaemia) and 39 from equids eating with a normal appetite. The POC device readable range is 0.8–6.86 mmol/l; high readings were diluted and measurements repeated and calculated. Inappetent/starved patients had a higher risk of developing raised plasma triglycerides (OR 16.8, 95% CI 4.8–58.4, P<0.0001) than the appetent ones with 34% (12/35) having mildly increased TG and 31% (11/35) having moderately to severely increased TG concentrations. In comparison, there were no severely hypertriglyceridaemic patients, one moderately increased and 3/39 (8%) mildly elevated TG patients in the appetent group. In the readable range, using whole blood, the POC device had excellent agreement with the laboratory (mean difference ‐0.59). However, accuracy varied with TG concentration and the POC instrument overestimated TG values, particularly when TG values were above the POC device's range. For a given value in the readable range of the POC device, multiplication of the POC value by a factor of 0.77 (whole blood) and 0.72 (plasma) provides an estimation of the laboratory TG value. Whole blood TG readings below the POC instrument's range were reliably low. The POC device reliably predicted TG values in a clinical setting. Use of this device provides rapid, easy to perform, reliable assessment of blood TG concentration in equids at risk of developing hypertriglyceridaemia.
Comparison of ultrasound‐guided vs. ‘blind’ techniques for intra‐synovial injections of the shoulder area in horses: Scapulohumeral joint, bicipital and infraspinatus bursae
Authors: Schneeweiss W. , Puggioni A. , David F.
Published: February 2012

Reasons for performing study:Diagnosis and treatment of pathologies involving synovial structures in the shoulder region are technically difficult. Ultrasound‐guided (UG) injection techniques have been shown to be highly accurate, safe and reliable for various structures in human and equine patients.

Objectives:To develop easy‐to‐use and reliable UG injection techniques for the infraspinatus bursa (IB), bicipital bursa (BB) and scapulohumeral joint (SHJ) and to compare them with conventional ‘blind’ methods.

Methods:Eight pairs of equine shoulders were positioned on a computed‐tomography (CT) table with left and right shoulders randomly assigned to Operator A (UG) and Operator B (‘blind’). Contrast medium mixed with methylene blue was injected into the target structures. Time and number of attempts for correct needle placement and ease of injection were recorded. A CT scan of each shoulder was performed after every injection to evaluate the location of contrast material. Once injections and CT scans were completed, anatomic dissections were conducted. Statistical analysis was used to compare UG and ‘blind’ techniques with significance set at P<0.05.

Results:Intra‐synovial injections using UG techniques were successful in all 24 synovial structures compared with 14/24 with conventional methods. The median number and range of needle repositioning to obtain accurate needle placement was 1 (1–2) for UG and 2 (1–4) for the ‘blind’ techniques. The median time and range required for accurate needle placement was 75.5 s (32–210 s) for UG and 43.5 s (11–140) for ‘blind’ technique. In 31% of all attempts, ease of injection was not indicative of successful intra‐synovial administration.

Conclusions:Ultrasound‐guided injections of IB, BB and SHJ proved to be highly reliable and more accurate than conventional ‘blind’ techniques.

Potential relevance:Ultrasound‐guided injection techniques may be of great help for equine practitioners in the diagnosis and treatment of pathologies involving synovial structures in the shoulder region. Further work is needed to confirm these results in clinical cases.
Using the Tukey–Kramer omnibus test in the Hayter–Fisher procedure
Authors: Richter Scott J. , McCann Melinda H.
Published: February 2012

Using Tukey–Kramer versus the ANOVA F‐test as the omnibus test of the Hayter–Fisher procedure for comparing all pairs of normally distributed means, when sample sizes are unequal, is investigated. Simulation results suggest that using Tukey–Kramer leads to as much or more any‐pairs power compared to using the F‐test for certain patterns of mean differences, and equivalent per‐pair and all‐pairs power for all cases. Furthermore, using Tukey–Kramer results in a consonant test procedure, where there cannot be disagreement between the results of the omnibus test and the subsequent pairwise tests. The results suggest that when sample sizes are unequal, Tukey–Kramer may be preferred over the F‐test as the omnibus test for the Hayter–Fisher procedure.
Transient Free Convection Flow Past an Infinite Moving Vertical Cylinder in a Stably Stratified Fluid
Authors: Deka R. K. , Paul A.
Published: February 2012

This paper presents an analytical treatment for the unsteady one-dimensional natural convective flow past an infinite moving vertical cylinder in the presence of thermal stratification. Exact solutions of the dimensionless unsteady coupled linear governing equations are obtained, in terms of Bessel functions by the Laplace transform technique, for the tractable case of unit Prandtl number. Numerical computations for velocity, temperature, skin-friction, and Nusselt number are made for various set of physical parameters and presented in graphs. Due to the presence of thermal stratification, the fluid velocity and temperature approach steady state, whereas the corresponding flow in an unstratified fluid does not. The steady state is attained at smaller times as the stratification increases. Furthermore, in the presence of stratification, the skin-friction and Nusselt number approaches fixed value as time progresses, while for unstratified fluid, there is a gradual decrease as time increases.
Energy Modeling of Air-Cooled Data Centers: Part I—The Optimization of Enclosed Aisle Configurations
Authors: Demetriou Dustin W. , Khalifa H. Ezzat
Published: February 2012

The work presented in this paper describes a simplified thermodynamic model that can be used for exploring optimization possibilities in air-cooled data centers. The model is used to parametrically evaluate the total energy consumption of the data center cooling infrastructure for data centers that utilize aisle containment. The analysis highlights the importance of reducing the total power required for moving the air within the CRACs, the plenum, and the servers, rather than focusing primarily or exclusively on reducing the refrigeration system’s power consumption and shows the benefits of bypass recirculation in enclosed aisle configurations. The analysis shows a potential for as much as a 57% savings in cooling infrastructure energy consumption by utilizing an optimized enclosed aisle configuration with bypass recirculation, instead of a traditional enclosed aisle, where all the data center exhaust is forced to flow through the computer room air conditioners (CRACs), for racks with a modest temperature rise (∼10°C). However, for racks with larger temperature rise (> ∼20°C), the saving are less than 5%. Furthermore, for servers whose fan speed (flow rate) varies as a function of inlet temperature, the analysis shows that the optimum operating regime for enclosed aisle data centers falls within a very narrow band and that power reductions are possible by lowering the uniform server inlet temperature in the enclosed aisle from 27°C to 22°C. However, the optimum CRAC exit temperature over the 22-to-27°C range of enclosed cold aisle temperature falls between ∼16 and 20°C because a significant reduction in the power consumption is possible through the use of bypass recirculation. Without bypass recirculation, the power consumption for a server inlet temperature of 22°C enclosed aisle case with a server temperature rise of 10°C would be a whopping 43% higher than with bypass recirculation. It is worth noting that, without bypass recirculation maintaining the enclosed cold aisle at 22°C instead of 27°C would reduce power consumption by 48%. It is also shown that enclosing the aisles together with bypass recirculation (when beneficial) also reduces the dependence of the optimum cooling power on server temperature rise.
Energy Modeling of Air-Cooled Data Centers: Part II—The Effect of Recirculation on the Energy Optimization of Open-Aisle, Air-Cooled Data Centers
Authors: Demetriou Dustin W. , Khalifa H. Ezzat
Published: February 2012

The work presented in this paper describes a simplified thermodynamic model that can be used for exploring optimization possibilities in air-cooled data centers. The model has been used to identify optimal, energy-efficient designs, operating scenarios, and operating parameters such as flow rates and air supply temperature. The model is used to parametrically evaluate the total energy consumption of the data center cooling infrastructure, by considering changes in the server temperature rise. The results of this parametric analysis highlight the important features that need to be considered when optimizing the operation of air-cooled data centers, especially the trade-off between low air supply temperature and increased air flow rate. The analysis is used to elucidate the deleterious effect of temperature non-uniformity at the inlet of the racks on the data center cooling infrastructure power consumption. A recirculation non-uniformity metric, θ, is introduced, which is the ratio of the maximum recirculation of any server to the average recirculation of all servers. The analysis of open-aisle data centers shows that as the recirculation non-uniformity at the inlet of the racks increases, optimal operation tends toward lower recirculation and higher power consumption; stressing the importance of providing as uniform conditions to the racks as possible. Cooling infrastructure energy savings greater than 40% are possible for a data center with uniform recirculation (θ = 0) compared to a data center with a typical recirculation non-uniformity (θ = 4). It is also revealed that servers with a modest temperature rise (∼10°C) have a wider latitude for cooling optimization than those with a high temperature rise (≥20°C).
Modeling of Fan Failures in Networking Enclosures
Authors: Narasimhan Susheela , Shankaran Gokul
Published: February 2012

Modeling of fan failures in networking chassis is a challenging task. There is not enough data or literature available to accurately model fan failures. This paper embarks on a study consisting of both modeling and experimental cases to investigate how to accurately model fan failures. The study will include CFD simulations in different ways to model fan failures and also real life experimental measurements to verify the simulation concepts. Recommendations will then be made about the exact and accurate ways of modeling fan failures. Normally the fans have been modeled as a two dimensional entity. The fan curve measured by the vendor is used in the fan during modeling. The problem that arises with this kind of a fan modeling especially during fan failures is that the three dimensional effect of the rotor and stator blades of the fan is not taken into account. In reality, the fan blades provide a big obstruction to the flow reversal that happens due to pressure imbalance during fan failures. In this paper, we start with modeling a single fan in an AMCA wind tunnel. The complete rotor and stator geometry of the fan is modeled. We run a MRF (Multiple Reference Frame) model to generate the fan curve for the fan and compare it with the experimental fan curve. After we validate the fan curve in an AMCA model for a single fan, the paper discusses three different sets of temperature and flow data: i. Temperature and flow data in a real system with four fans modeled with two dimensional fans. ii. Temperature and flow data in a real system with four fans modeled with MRF fans (full 3 dimensional rotor and stator blade geometry). iii. Experimental comparisons with the simulated data Conclusions will be drawn based on this modeling and experimental data about accurate ways of modeling fans during fan failures in real systems.
An Experimental Study of Heat Transfer Characteristics in Miniature Loop Heat Pipes With Rectangular Shaped Evaporator
Authors: Lin Z. R. , Lee Z. Y. , Zhang L. W. , Wang S. F. , Merrikh A. A. , Refai-Ahmed G.
Published: February 2012

Loop heat pipe (LHP) is a highly efficient cooling device. It has gained great attention in the electronics cooling industry due to its superior heat transport capability — that is, its ability to carry heat over long distances. For this article, a miniature flat loop heat pipe (MFLHP) with rectangular-shaped evaporator was developed. The LHP’s evaporator was combined with the compensation chamber. MFLHPs with different diameters and lengths for the connecting pipeline were selected for a series of experimental studies on their heat transfer characteristics. In these experiments, pure water was used as the working fluid. The studies showed that the heat transport capability of a MFLHP with 4 mm diameter was better than that a MFLHP with 3 mm diameter. At a low thermal resistance of 0.04°C /W (at 200W), an optimal length for the connecting pipeline for a particular MFLHP with 4 mm diameter was identified. Finally, a heat sink attached to a MFLHP was developed for cooling a graphics processing unit (GPU), the thermal design power (TDP) of which was 200 W. The results showed the GPU heat sink with MFLHP had good performance and satisfied GPU cooling requirements. Compared to the conventional heat pipe solutions, only one MFLHP was able to cope with high power dissipation, offering the potential to make a lighter heat sink.
Heat Transfer Characteristics of Aluminum Plate Pulsating Heat Pipes
Authors: Lin Z. R. , Lee Z. Y. , Zhang L. W. , Wang S. F. , Merrikh A. A. , Refai-Ahmed G.
Published: February 2012

Heat transfer characteristics of an aluminum plate pulsating heat pipe (PHPs) were investigated experimentally. Sizes, consisting of parallel and square channels as well as different cross-sections and different number of turns were considered. Acetone was used as working fluid. The characterization had been done for various heating mode orientations, cooling conditions, and internal structures via flow visualization and thermal performance tests. The flow visualization showed that the aluminum plate PHPs can maintain the heat transfer characteristics of the liquid and the vapor slug as well as the conventional tubular PHPs. The trend of flow pattern changed from the intermittent oscillation to unidirectional circulation. It was also observed that the PHPs’ thermal performance improved as heating power increased. The gravity greatly influenced the thermal performance of plate PHPs. Increasing the cooling temperature decreased the thermal resistance of the plate PHPs. Increasing the number of turns and the area of channel cross-section improved the heat transport capability of plate PHPs for some specific scenarios. A heat sink with a plate PHP was developed for comparing with the pure metal and conventional heat pipe solutions. The result showed that the plate PHPs solution performed well, and had the potential to replace previous solutions in some cases.
A Novel Precision Die Attach Technique for Opto-Electronics Packaging
Authors: Bhagavatula V. , Chaparala S. , Himmelreich J.
Published: February 2012

Semiconductor Laser diodes that emit visible light have various interesting applications such as sensing, high density optical storage and projection displays. In any opto-electronic package, the laser diode chips are typically attached or soldered to metal or ceramic substrates that have good thermal conductivity and are well-matched in coefficient of thermal expansion using solder. Some applications require a critical alignment of the front facet of the laser diode to the front edge of the substrate onto which the laser diode chip is attached to. Depending on the application, the alignment precision could be varying from 20 μm to being as stringent as 0.5 to 1 μm. In many of these applications, the cost of packaging is also a very important factor. In such applications, it is essential to develop a laser diode chip bonding process that can meet such stringent die alignments along with a low cost manufacturing process. Therefore, the objective of this research work is to provide a low cost alternative solution for die attach process that can guarantee alignment precision of 0.5 to 1 microns and can be easily adapted to high volume manufacturing. The novel technique proposed in this work uses primarily gravity force for the facet alignments between the two components. In this passive-gravity assisted precision (P-GAP) assembly process, the laser diode (LD) chip is placed on the substrate using a traditional pick and place machine and later the substrate and the chip are tilted such that the chip slides on the substrate due to the gravity and touches a mechanical stop in-front of them. This does not involve any active alignment. In addition, we have provided few ideas to improve the sliding when gravity is used. This technique has been implemented on several samples and the feasibility of achieving the alignment precision to within a micron was demonstrated.
Dynamic Reduced Order Thermal Modeling of Data Center Air Temperatures
Authors: Ghosh Rajat , Joshi Yogendra
Published: February 2012

We developed a Proper Orthogonal Decomposition (POD) based dynamic reduced order model that can predict transient temperature field in an air-cooled data center. A typical data center is modeled as a turbulent convective thermal system with multiple length scales. A representative case study is presented to validate the developed methodology. The model is observed to be capable of predicting the transient air temperature field accurately and rapidly. Comparing with the computational fluid mechanics/heat transfer (CFD/HT) based model, it is revealed that our model is 100x faster without compromising solution accuracy. The developed modeling framework is potentially useful for designing a control system that can regulate flow parameters in a transient data center.
Energy Conversion Efficiency of Synthetic Jets
Authors: Li Ri , Sharma Rajdeep , Arik Mehmet
Published: February 2012

Synthetic jets are driven by a periodic electrical signal to generate pulsated airflow that can provide cooling to a hot surface. The working principle of synthetic jets involves conversion of electrical energy into mechanical and fluid energy. Piezoelectric actuators, comprising of a thin metal substrate bonded to a piezoelectric disk are induced to undergo vibration motion in bending mode by an AC sine-wave voltage with zero bias. Synthetic jets, which consist of two piezoelectric actuators separated by a compliant ring at the outer periphery of the actuators, undergo a bellow-like action due to the periodic motion of the actuators, thereby ingesting air and pushing air at high velocities through the orifice. In this paper, we seek to understand and quantify the efficiency of synthetic jets with a view towards optimizing their design. In this study, energy efficiency of synthetic jet is defined based on thermodynamics principles. Analytical equations for calculating consumed electric power and airflow power are derived. Using the derived equations, energy efficiency of synthetic jets is experimentally investigated. Air velocity at the jet orifice is measured using constant temperature hotwire anemometry. Voltage signal and resultant current waveform are recorded to calculate electric power. In order to understand the structural behavior, laser vibrometer is used to measure the center out-of-plane deflection of the piezoelectric synthetic jet. Electrical power input is varied by changing signal frequency and voltage amplitude. Synthetic jets with two different orifice sizes are tested, and the efficiency of energy conversion is determined. The effects of jet design and operation conditions on energy efficiency are discussed.
Study on High Reliability of Lead-Free Solder Joint on Metal Substrate
Authors: Takagi Kanji , Wakabayashi Masaki , Inoue Junichi , Yu Qiang , Akutsu Takahiro
Published: February 2012

This paper proposes the high reliable design method for lead-free solder joint on metal substrate on chip component. First, the crack propagation analysis method for estimating rupture life of solder joint was constructed. And then, the effect of material properties of insulating layer on metal substrate and solder joint shape for rupture life of solder joint was evaluated using crack propagation analysis. As the result, the relation between young’s modulus of insulating layer and rupture life was indicated quantitatively. Also, the relation of filet length for rupture life of solder joint was evaluated. Secondary, evaluation method of heat dissipation for metal substrate was proposed. Because thermal conductivity of insulating layer affects temperature rise of heating device. And, the relation between thermal conductivity of insulating layer and temperature rise of heating device was indicated.
On the Lateral Motion of Bubbles Generated From Re-Entrant Cavities Located on Asymmetrically Structured Surfaces
Authors: Thiagarajan Naveenan , Kapsenberg Florian , Narayanan Vinod , Bhavnani Sushil H. , Ellis Charles
Published: February 2012

This paper describes a novel concept of lateral motion of bubbles in pool boiling, which has the potential to be translated into a liquid propulsion system when used in a closed loop. The lateral motion of bubbles is achieved due to nucleation from cavities on an asymmetric saw-tooth profile created on a silicon surface. The surface modification involves etching a 3D sawtooth structure with a nominal angle of approximately 24° using gray-scale lithography. The downstream slope of each sawtooth structure features re-entrant cavity structures that act as controlled nucleation sites. The angle of the surface thus obtained causes a net imbalance of forces acting in concert on the flow field around the bubbles departing from the surface. The first part of the paper discusses the steps involved in fabricating such a heat sink with a saw-tooth structure augmented by re-entrant cavities. This is followed by description of the experimental facility used for studying the feasibility of the concept. High-speed photography in conjunction with bubble tracking is used to determine the bubble velocities. Results for a subcooled condition show substantial axial bubble velocities on the order of up to 68.5 cm/s near the cavities and a far-field velocity of up to 4 cm/s.
Minimization of the Local Residual Stress in 3D Flip Chip Structures by Optimizing the Mechanical Properties of Electroplated Materials and the Alignment Structure of TSVs and Fine Bumps
Authors: Nakahira Kohta , Tago Hironori , Endo Fumiaki , Suzuki Ken , Miura Hideo
Published: February 2012

Since the thickness of the stacked silicon chips in 3D integration has been thinned to less than 100 μm, the local thermal deformation of the chips has increased drastically because of the decrease of the flexural rigidity of the thinned chips. The clear periodic thermal deformation and thus, the thermal residual stress distribution appears in the stacked chips due to the periodic alignment of metallic bumps, and they deteriorate the reliability of products. In this paper, the dominant structural factors of the local residual stress in a silicon chip are discussed quantitatively based on the results of a three-dimensional finite element analysis and the measurement of the local residual stress in a chip using stress sensor chips. The piezoresistive strain gauges were embedded in the sensor chips. The length of each gauge was 2 μm, and an unit cell consisted of 4 gauges with different crystallographic directions. This alignment of strain gauges enables to measure the tensor component of three-dimensional stress fields separately. Test flip chip substrates were made by silicon chip on which the area-arrayed tin/copper bumps were electroplated. The width of a bump was fixed at 200 μm, and the bump pitch was varied from 400 μm to 1000 μm. The thickness of the copper layer was about 40 μm and that of tin layer was about 10 μm. This tin layer was used for the rigid joint formation by alloying with copper interconnection formed on a stress sensing chip. The measured amplitude of the residual stress increased from about 30 MPa to 250 MPa depending on the combination of materials such as bump, underfill, and interconnections. It was confirmed that both the material constant of underfill and the alignment structure of fine bumps are the dominant factors of the local deformation and stress of a silicon chip mounted on area-arrayed metallic bumps. It was also confirmed experimentally that both the hound’s-tooth alignment between a TSV (Through Silicon Via) and a bump and control of mechanical properties of electroplated copper thin films used for the TSV and bump is indispensable in order to minimize the packaging-induced stress in the three-dimensionally mounted chips. This test chip is very effective for evaluating the packaging-process induced stress in 3D stacked chips quantitatively.
Reduced Rack Exhaust Temperature Gradient via Variable Chassis Flow Rate
Authors: Dang Thong , Serreli Carine , Khalifa H. Ezzat , Schmidt Roger R. , Iyengar Madhusudan
Published: February 2012

An effective method of reducing the temperature gradient in data centers (or “hot” and “cold” spots) is to minimize the maximum temperature at the rack exit plane. For a given rack’s heat load, one way to achieve this is to vary the chassis flow rate in such a way that the rack exit temperature gradient is small. In this paper, a simple algorithm based on the energy equation is developed to set the chassis flow rate such that the exit rack temperature is uniform. When compared to a constant chassis flow rate algorithm, the proposed method is demonstrated through CFD simulations to achieve significant reduction in maximum chassis inlet temperature for the same CRAH flow rate.
Effect of Micro Structure on Fatigue Characteristics of Lead Free Solder Joints
Authors: Akutsu Takahiro , Yu Qiang
Published: February 2012

This paper presents the influence of the micro structure on the crack propagation in lead free solder joint. The author’s group have studied the Manson-Coffin’s law for lead free solder joint by using the isothermal fatigue test and FEM analytical approaches to establish the practicable evaluation of thermal fatigue life of solder joints, for example, for the Sn-Cu-Ni solder, because this solder is attracted from the aspect of the decrease of solder leach in the flow process and material cost. However, even if the same loading is given to the solder joints of BGA test piece, there was a large dispersion in the fatigue life. Even though the effect of the shape difference has been considered, the range of the dispersion could not been explained sufficiently. In the study, the fatigue crack propagation modes in the solder joints were investigated, and an internal fatigue crack mode and an interfacial fatigue crack mode were confirmed. And the tendency of a shorter on fatigue life in the interfacial fatigue mode was confirmed. To clarify the mechanism of these fatigue crack modes, the crystal grain size in the solder joints was investigated before the fatigue test and also after the test. Furthermore, the verification of the mechanism using FEM models considering the crystal grain size was carried out. First of all, each element in FEM models matching to the average crystal grain size was made. Second, the inelastic strain ranges in each FEM models were studied. As a result, it was shown that the influence of the crude density of the crystal grain to the fatigue crack progress can be evaluated. In addition, the micro structure of the solder joint of large-scale electronic devices is observed, and FEM model was made based on the observation result. As a result, it was shown that the influence of the directionality with the crystal grain to the fatigue crack progress can be evaluated.
Joule Heat Welding of Thin Metallic Wires and Thermoelectric Effects Around Dissimilar Metal Weld
Authors: Tohmyoh Hironori , Tanaka Tomochika , Fujimori Masato , Saka Masumi
Published: February 2012

Fine thermoelectric elements were fabricated on an electrode chip where the tips of the Pt and W thin wires having the diameter of 5 μm were welded together by Joule heat welding. Firstly, the dissimilar metal weld was contacted to thin wire heater and the voltage appeared in the circuit due to Seebeck effect was measured. Current was supplied to the one of the thermoelectric element and the temperature at the Pt/W weld was measured by the other element. It was found that the temperature at dissimilar metal weld depended on the direction of current and Peltier effect was successfully observed.
Effect of the Organic Acid Surface Modification on Bond Strength of Tin and Copper
Authors: Koyama Shinji , Aoki Yukinari , Shohji Ikuo
Published: February 2012

The effect of citric-acid surface modification on the bond strength of the solid-state bonded interface of tin and copper has been investigated by SEM observation of the interfacial microstructures and fractured surfaces. Citric-acid surface modification was carried out in a vacuum chamber at a bonding temperature of 383–473 K and a bonding pressure of 7 MPa (bonding time: 1800 s). The citric-acid surface modification decreased bonding temperature by 70 K at which bonded joints could be obtained and bond strength comparable with the base metal was achieved.
Investigation of Effect of Wiring Patterns on In-Plane Thermal Conductivity of Printed Circuit Boards
Authors: Nakano Yuta , Hatakeyama Tomoyuki , Ishizuka Masaru , Nakagawa Shinji , Hirokawa Masataka , Tomimura Toshio
Published: February 2012

This paper describes a measurement method for the in-plane thermal conductivity of Printed Circuit Boards (PCBs). We designed two types of PCBs with several wiring patterns on their surfaces. This means copper amount on the PCBs is different. We measured their effective thermal conductivity in thickness direction to investigate the effects of the wiring patterns on the in-plane thermal conductivity of the PCBs. One is normal PCBs and the other is about 18 times larger PCBs than the normal PCBs. The experimental results showed that the thermal conductivity of normal PCBs was not dependent on the wiring patterns. On the other hand, the thermal conductivity of larger PCBs increased with increasing amount of copper wire due to the heat diffusion in in-plane direction by copper wires. We concluded that the effect of the wiring patterns on the in-plane thermal conductivity can be observed with our measurement method. We also performed Computational Fluid Dynamics (CFD) analyses and clarified the correlation between amount of copper wire and in-plane thermal conductivity of the PCBs.
Electromigration in Copper-Core Solder Ball Joints During Thermal Cycle Tests
Authors: Fujiwara Shinichi , Chiwata Nobuhiko , Fujiyoshi Masaru , Wakano Motoki , Tanie Hisashi
Published: February 2012

Electromigration current densities in Cu and Al lines on a silicon die exceed 1.0 × 106 A/cm2. However, solder joints can only withstand electromigration current densities below about 1.0 × 104 A/cm2. Thus, electromigration in solder joints will become a problem in semiconductor packages in the near future. Previous studies demonstrated that Cu-core solder balls increased the electromigration lifetime and led to better current stability at temperatures below 423K. This is because electrons flow through the Cu cores, reducing the current density on the cathode side, which is where electromigration occurs. In the present study, we forcused on the reliability of solder joints in a combined environment by examining the effect of thermal cycle tests on the current in a new test sample. A new test sample for the evaluation of joining reliability by using Cu-core solder balls in a combined enbironment was made. In initial tests, this test sample exhibited similar results to those observed in previous studies. Cu-core solder balls subjected to cyclic testing at 233/398K and a current density of 1.0 × 104 A/cm2 exhibited lower reliabilities than when there was no current. Examination of cross-sections of the solder balls after reliability testing revealed that the combined environment accelerated growth of intermetallic compounds and cracks in the joining region. In a combined environment, Cu-core balls were converted into intermetallic compounds on the anode side. This phenomenon is thought to occur due to the different electrical resistivities of Cu-Sn intermetallic compounds.
Cold Aisle Air Distribution in a Raised Floor Data Center With Heterogeneous Opposing Orientation Racks
Authors: Kumar Pramod , Joshi Yogendra , Patterson Michael K. , Steinbrecher Robin , Mena Marissa
Published: February 2012

In this paper we experimentally investigate the air flow distribution at the inlets of two opposing racks in a cold aisle. The racks have non uniform heat load and air flow requirements creating a heterogeneous data center environment. The Computer Room Air Conditioning (CRAC) unit fan speed is set to meet the air requirement of the high heat density rack. The effect of perforated tile air velocity on air distribution to both the racks is studied using particle image velocimetry (PIV) technique. PIV images are recorded at various rack heights corresponding to the locations of the servers in the rack. The PIV images recorded at various locations are stitched to construct a complete rack inlet air flow map. Three cases of rack air flow distributions are studied by varying the server work load and perforated tile flow rate. A significant change in the air distribution pattern is observed for the three cases investigated.
A Data Center Environmental Advisory System
Authors: Hoover Christopher , Kumari Niru , Felix Carlos , Bash Cullen
Published: February 2012

We present Avatar, a data center environmental advisory system for raised floor data centers. Using limited information such as inlet and reference temperatures for IT equipment and basic floor plan geometry, Avatar produces recommendation to adjust the operation of computer room air conditioners (CRACs) and the configuration of vent tiles in a data center so as to reducing excess provisioning of cooling and to remove hot spots. Avatar reduces operating expenses by cooling the same load with less energy. Avatar reduces capital expenses by recovering stranded cooling capacity that would otherwise have to be replaced.
On the Need for Energy Efficiency Metrics That Span Integrated IT-Facility Infrastructures
Authors: Shah Amip J. , Bash Cullen E. , Kumari Niru , Cader Tahir , Breen Thomas J. , Walsh Ed J. , Punch Jeff
Published: February 2012

Infrastructure efficiency metrics, such as Power Usage Effectiveness (PUE) and Data Center Infrastructure Efficiency (DCiE), have gained much traction within the industry for evaluating data center energy efficiency. Gradually, however, as the lines between traditional IT systems in the data center and the facility infrastructure supporting the data center get blurred, adaptations to the usage of infrastructure efficiency metrics will be required. This paper presents three cases where holistic data center energy efficiency does not necessarily track infrastructure efficiency, implicitly emphasizing the need for new metrics that address the IT-facility infrastructure in holistic fashion.