bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of an Isolated Hybrid Cooled Server With Failure Scenarios Using Warm Water Cooling
Authors: Chowdhury Uschas , Sahini Manasa , Siddarth Ashwin , Agonafer Dereje , Branton Steve
Published: October 2017

Modern day data centers are operated at high power for increased power density, maintenance, and cooling which covers almost 2 percent (70 billion kilowatt-hours) of the total energy consumption in the US. IT components and cooling system occupy the major portion of this energy consumption. Although data centers are designed to perform efficiently, cooling the high-density components is still a challenge. So, alternative methods to improve the cooling efficiency has become the drive to reduce the cooling cost. As liquid cooling is more efficient for high specific heat capacity, density, and thermal conductivity, hybrid cooling can offer the advantage of liquid cooling of high heat generating components in the traditional air-cooled servers. In this experiment, a 1U server is equipped with cold plate to cool the CPUs while the rest of the components are cooled by fans. In this study, predictive fan and pump failure analysis are performed which also helps to explore the options for redundancy and to reduce the cooling cost by improving cooling efficiency. Redundancy requires the knowledge of planned and unplanned system failures. As the main heat generating components are cooled by liquid, warm water cooling can be employed to observe the effects of raised inlet conditions in a hybrid cooled server with failure scenarios. The ASHRAE guidance class W4 for liquid cooling is chosen for our experiment to operate in a range from 25°C – 45°C. The experiments are conducted separately for the pump and fan failure scenarios. Computational load of idle, 10%, 30%, 50%, 70% and 98% are applied while powering only one pump and the miniature dry cooler fans are controlled externally to maintain constant inlet temperature of the coolant. As the rest of components such as DIMMs & PCH are cooled by air, maximum utilization for memory is applied while reducing the number fans in each case for fan failure scenario. The components temperatures and power consumption are recorded in each case for performance analysis.
Two-Phase Mini-Thermosyphon for Cooling of Datacenters: Experiments, Modeling and Simulations
Authors: Ong Chin L. , Amalfi Raffaele L. , Marcinichen Jackson B. , Lamaison Nicolas , Thome John R.
Published: October 2017

Nowadays, datacenters heat density dissipation follows an exponential increasing trend that is reaching the heat removal limits of the traditional air-cooling technology. Two-phase cooling implemented within a gravity-driven system represents a scalable and viable long-term solution for datacenter cooling in order to increase the heat density dissipation with larger energy efficiency and lower acoustic noise. The present article builds upon the 4-part set of papers presented at ITHERM 2016 for a 15-cm height thermosyphon to cool a contemporary datacenter cabinet, providing new test data over a wider range of heat fluxes and new validations of the thermal-hydrodynamics of our thermosyphon simulation code.

The thermosyphon consists of a microchannel evaporator connected via a riser and a downcomer to a liquid-cooled condenser for the cooling of a pseudo-chip to emulate an actual server. Test results demonstrated good thermal performance coupled with uniform flow distribution for the new larger range of operating test conditions. At the maximum imposed heat load of 158 W (corresponding to a heat flux of 70 W cm−2) with a water inlet coolant at 20 °C, water mass flow rate of 12 kg h−1 and thermosyphon filling ratio of 78%, the pseudo mean chip temperature was found to be 58 °C and is well below the normal thermal limits in datacenter cooling.

Finally, the in-house LTCM’s thermosyphon simulation code was validated against an expanded experimental database of about 262 data points, demonstrating very good agreement; in fact, the pseudo mean chip temperature was predicted with an error band of about 1 K.
Analysis for Evaluation of Threshold Current Density of Electromigration Damage in Taper-Shaped Metal Line
Authors: Kikuchi Hiroki , Sasagawa Kazuhiko , Fujisaki Kazuhiro
Published: October 2017

Metal lines used in integrated circuits (ICs) become narrow for raising the device performance. Due to scaling down of the ICs, current density and Joule heating are increased, which induces electromigration (EM) damage. EM is transportation phenomena of metallic atoms caused by electron wind under high current density. EM leads to hillock and void formation in the metal line, thus EM should be considered to evaluate the performances of the device safe. It is known that a value of threshold current density which is critical current density of the EM damage exists in via-connected and passivated lines. In this study, the effect of line geometry on the threshold current density is discussed in the case of taper-shaped line. The evaluation method of threshold current density is conducted based on numerical simulation technique with building-up processes of atomic density distribution in the metal line by using a governing parameter of EM damage. As the simulation results, threshold current density increased in the cases of shorter line length, lower temperature, and wider width in cathode side. Furthermore, a new parameter was proposed for simplified evaluation of the threshold current density in taper-shaped lines. The evaluation method is able to apply various line shapes and conditions and it is expected to use for confirmation of the reliability of the lines in circuit design processes.
State of the Art of Electronics Cooling for Radar Antenna Applications
Authors: Upadhya Girish , Pullins Clayton , Freitag Karl , Hall George , Marthinuss James
Published: October 2017

High heat flux from electronic devices remains a continuing challenge for cooling of electronics hardware in radar antenna applications pertaining to the defense industry. Cooling methods for such applications have varied from conduction cooling approaches for the cooling of circuit card assemblies, to advanced convection cooling using two phase flow (with pumped refrigerant) for the high heat flux devices used in transmit / receive modules. It is found that the limiting parameter in such applications is usually the heat flux from the electronic device. This paper provides an overview of the cooling techniques used for defense electronics, as well as current modeling tools and analytical methods used for thermal design during the product development phase. The role of thermal interface materials used in the material stack up for the thermal design solutions will also be touched upon. Additionally, the importance of using experimental techniques to characterize the heat transfer coefficient for the pumped refrigerant two phase flow will be discussed.
Knowledge Based Requirement Calculation for Server BGAs Temperature Cycling (TC) Qualification
Authors: Pei Min , Vujosevic Milena , Mukherjee Sibasish
Published: October 2017

In this work we present a knowledge-based qualification approach for solder joint reliability of Ball Grid Array (BGA) component used in server systems. Servers experience very few on-off power cycles during their lifetime. The primary source of BGA thermo-mechanical damage in these systems is, therefore, the temperature fluctuations during use. We employ measured server CPU die temperature during field usage and a novel physics-of-failure metric to define the requirements for qualification in temperature cycling accelerated tests. The result of this computational/empirical approach is compared against the result of the industry-standard based empirical acceleration model. The key conclusion of this work is that standard empirical acceleration models have difficulty accounting for small temperature fluctuations and lead to significant overestimation of the risks. On the other hand, the proposed computational/empirical approach provides a physically meaningful estimation of risk.
Stress-Based Design Standard for 3216 Type of Multilayer Ceramic Capacitor
Authors: Kinoshita Takahiro , Kawakami Takashi , Adachi Tadaharu , Funaki Masahiro
Published: October 2017

In this study, dynamic three points bending test by split Hopkinson pressure bar method and numerical simulations which was based on finite element method (FEM) were performed to estimate stress-based design standard for 3216 type of multilayer ceramic capacitors (MLCCs). Tool for creating the standard was suggested and linear dependence with loading rate was shown in the standard.
Experimentally Validated Computational Fluid Dynamics Model for Data Center With Active Tiles
Authors: Athavale Jayati D. , Joshi Yogendra , Yoda Minami
Published: October 2017

This paper presents an experimentally validated room-level computational fluid dynamics (CFD) model for raised-floor data center configurations employing active tiles. Active tiles are perforated floor tiles with integrated fans, which increase the local volume flowrate by redistributing the cold air supplied by the computer room air conditioning (CRAC) unit to the under-floor plenum. In a previous study [1], experiments were conducted to explore the potential of active tiles for economically and efficiently eliminating hot spots in data center. Our results indicated that active tiles, as the actuators closest to the racks, can significantly and quickly impact the local distribution of cooling resources. They could therefore be used in an appropriate control framework to rapidly mitigate hot spots, and maintain local conditions in an energy-efficient manner.

The numerical model of the data center room operates in an under-floor supply and ceiling return cooling configuration and consists of one cold aisle with 12 racks arranged on both sides and three CRAC units sited around the periphery of the room. The commercial computational fluid dynamics (CFD) software package Future Facilities 6SigmaDCX [2], which is specifically designed for data center simulation, is used to develop the model. First, a baseline model using only passive tiles was developed and experimental data were used to verify and calibrate plenum leakage for the room. Then a CFD model incorporating active tiles was developed for two configurations: (a) a single active tile and 9 passive tiles in the cold aisle; and (b) an aisle populated with 10 (i.e., all) active tiles. The active tiles are modeled as a combination of a grill, fan elements and flow blockages to closely mimic the actual active tile used in the experimental studies. The fan curve for the active tile fans is included in the model to account for changes in flow rate through the tiles in response to changes in plenum pressure.

The model with active tiles is validated by comparing the flow rate through the floor tiles, relative plenum pressure and rack inlet temperatures for selected racks with the experimental measurements. The predictions from the CFD model are found to be in good agreement with the experimental data, with an average discrepancy between the measured and computed values for total flow rate and rack inlet temperature less than 4% and 1.7 °C, respectively. These validated models were then used to simulate steady state and transient scenarios following cooling failure.

This physics-based and experimentally validated room-level model can be used to predict temperature and flow distributions in a data center using active tiles. These predictions can then be used to identify the optimal number and locations of active tiles to mitigate hot spots, without adversely affecting other parts of the data center.
Voiding Effects on the Thermal Response of Metallic Phase Change Materials Under Pulsed Power Loading
Authors: Gonzalez-Nino David , Boteler Lauren M. , Jankowski Nicholas R. , Ibitayo Dimeji , Quintero Pedro O.
Published: October 2017

Metallic phase change materials (PCMs) have been demonstrated as an excellent alternative to act as a passive cooling system for pulse power applications. The possibility of integrating metallic PCMs, directly on top of a heat source, reducing the thermal resistance between the device and the cooling solution, could result in a significant improvement in thermal management for transient applications. However, the effectiveness of this method of implementation will depend on the quality of the interface between the metallic PCM and the heat source.

For this work, a metallic PCM (49Bi/18Pb/12Sn/21In-Bi/Pb/Sn/In for simplicity) was placed directly on top of a device that has a layer of silicon nitride on the top. The device was pulsed with powers of 40W – 160W (84W/cm2 – 338W/cm2) with a 20 ms duration. After reaching the maximum power, the device was pulsed for a second cycle, and the temperature profiles were compared. Micrographical inspections, at the interlayer between the silicon nitride and metallic PCM, were performed before and after the pulses and compared.

A maximum temperature of ≈20–25% higher was observed in the performance (at 80W) after pulse cycling. A visual inspection at the mating surfaces, between the metallic PCM and device, showed a clear difference between the contact surfaces before and after pulses. Significant voiding at the PCM interfacial layer was observed after cyclic loading which is believed to be the cause of the recorded increment in maximum temperature.
Is the Heterogeneous Microstructure of SnAgCu (SAC) Solders Going to Pose a Challenge for Heterogeneous Integration?
Authors: Jiang Qian , Deshpande Abhishek , Dasgupta Abhijit
Published: October 2017

The coarse heterogeneous microstructure of SAC alloys makes the behavior of interconnections highly sensitive to its geometric length-scale. Heterogeneous integration and the resulting increase in package complexity and miniaturization are making this scale-effect ever more important. This scale effect derives from the anisotropy of tin and the coarse multi-tiered microstructural heterogeneities in SAC solders. As a result, no two joints behave the same and every joint is unique depending on its specific microstructure. Product teams responsible for reliable heterogeneous integration have to ensure that they have adequate methods to deal with this variability.

This paper highlights the multi-tiered microstructural morphology in SAC solders due to the solidification and crystallization process. At the highest tier in the joint microstructure are individual (highly anisotropic) grains that can be 100s of microns in size. At the next lower tier the primary heterogeneity is due to individual dendrites of pro-eutectic β tin, that can have lobes as large as 10–20 microns. At the next lower tier the characteristic heterogeneity is a eutectic mix of nanoscale Ag3Sn IMC particles dispersed in a Sn matrix.

Researchers have long recognized that the grain morphology is extremely important to mechanical behavior of BGA solder joints because they are coarse-grained (i.e. there may be only a few anisotropic grains in each BGA solder joint). However, heterogeneous integration has now led to joints that are much smaller (less than 100 microns tall), thus making them of the same length-scale as individual tin dendrites within each grain. In other words, there may be just a few dendrites through the thickness of the joint. Unfortunately, very little attention has focused on SAC behavior at such a small length-scale. This study focuses on the effect of the tin-dendrite morphology on the effective behavior of SAC solder joints, using a combination of experiments and multi-tiered anisotropic models that combine dislocation nano-mechanics with composite micromechanics. The volume fraction of β-Sn dendrite within one crystal could vary from 20% to 80%, depending on the time and temperature above the liquidus temperature and the cooling rates. The effects of volume fraction and aspect ratio of Sn dendrites on the anisotropic steady-state creep rate of single crystal SAC specimen are examined. The objective of the study is to provide insights into the role that solder microstructural heterogeneity will play on package reliability in heterogeneous integration.
Prediction and Mitigation of Vertical Cracking in High-Temperature Transient Liquid Phase Sintered Joints by Thermo-Mechanical Simulation
Authors: Greve Hannes , Moeini S. Ali , McCluskey Patrick , Joshi Shailesh
Published: October 2017

Transient Liquid Phase Sintering (TLPS) is a novel high temperature attach technology. It is of particular interest for application as a die attach in power electronic systems because of its high melting temperature and high thermal conductivity. TLPS joints formed from sinter pastes are comprised of metallic particles embedded in matrices of Intermetallic Compounds (IMCs). Compared to conventional solder attach, TLPS joints contain a considerably higher percentage of brittle IMCs. This raises the concern that TLPS joints are susceptible to brittle failure. In this paper we describe and analyze the cooling-induced formation of vertical cracks as a newly detected failure mechanism unique to TLPS joints.

In a power module structure with a TLPS joint as interconnect between a power device and a Direct Bond Copper (DBC) substrate, cracks can form between the interface of the DBC and the TLPS joint when large voids are located in the proximity of the DBC. These cracks do not appear in regions with smaller voids. A method has been developed for the three-dimensional modeling of paste-based TLPS sinter joints that possess complex microstructures with heterogeneous distributions of metal particles and voids in IMC matrices. Thermo-mechanical simulations of the post-sintering cooling process have been performed and the influence of microstructure on the stress-response within the joint and at the joint interfaces have been characterized for three different material systems (Cu+Cu6Sn5, Cu+Cu3Sn, Ni+Ni3Sn4).

The maximum principal stress within the assembly was found to be a poor indicator for prediction of vertical crack formation. In contrast, stress levels at the interface between the TLPS joint and the power substrate metallization are good indicators for this failure mechanism. Small voids lead to higher joint maximum principal stresses, but large voids induce higher interfacial stresses, which explain why the vertical cracking failure was only observed in joints with large voids.
Preliminary Results on the Fabrication of Interconnect Structures Using Microscale Selective Laser Sintering
Authors: Roy Nilabh , Dibua Obehi , Foong Chee Seng , Cullinan Michael
Published: October 2017

The ability to create 3D ICs can significantly increase transistor packing density, reduce chip area and power dissipation leading to possibilities of large-scale on-chip integration of different systems. A promising process for this application is the microscale additive manufacturing (AM) of 3D interconnect structures and capability of writing 3D metal structures with feature sizes of approximately 1 μm on a variety of substrates. Current microscale AM techniques are limited in their capabilities to produce 3D conductive interconnect structures. This paper presents the design and development of a new micro AM technique — microscale selective laser sintering (μ-SLS) — which overcomes many of the limitations of other micro AM processes to achieve true micron sized, electrically conductive features on a variety of substrates.

This paper will present preliminary results from set of sintering experiments on copper (Cu) nanoparticle (NP) ink using the continuous wave (CW) laser to be employed in the μ-SLS system which will be compared to Cu NP sintering results produced with other laser sources such as nanosecond (ns) & femtosecond (fs) lasers. This study is important to estimate the optimum working range of fluence/irradiance to be used in the μ-SLS setup depending upon the laser employed. In general, it provides an experimental estimate of the sintering fluence/irradiance range of Cu NPs depending upon the type of laser used and compares their sintering quality based on morphology of sintered spots.
Failure Analysis of Direct Liquid Cooling System in Data Centers
Authors: Alkharabsheh Sami , Ramakrishnan Bharath , Sammakia Bahgat
Published: October 2017

In this paper, the impact of direct liquid cooling (DLC) system failure on the IT equipment is studied experimentally. The main factors that are anticipated to affect the IT equipment response during failure are the CPU utilization, coolant set point temperature (SPT) and the server type. These factors are varied experimentally and the IT equipment response is studied in terms of chip temperature and power, CPU utilization and total server power. It was found that failure of the cooling system is hazardous and can lead to data center shutdown in less than a minute. Additionally, the CPU frequency throttling mechanism was found to be vital to understand the change in chip temperature, power, and utilization. Other mechanisms associated with high temperatures were also observed such as the leakage power and the fans speed change. Finally, possible remedies are proposed to reduce the probability and the consequences of the cooling system failure.
Application Driven Reliability Research of Next Generation for Automotive Electronics: Challenges and Approaches
Authors: Rzepka Sven , Otto Alexander , Vogel Dietmar , Dudek Rainer
Published: October 2017

The revolutionary changes in automotive industry towards fully connected automated electrical vehicles necessitates developments in automotive electronics at unprecedented speed. Signal, control, and power electronics will heterogeneously be integrated at minimum space with sensors and actuators to form highly compact and ultra-smart systems for functions like traction, lighting, energy management, computation, and communication. Most of these systems will be highly safety relevant with the requirements in system availability exceeding today’s already high automotive standards. Other than the human drivers of today, passengers in the automated car do not pay constant attention to the driving actions of the vehicle. Hence, reliability research is massively challenged by the new automotive applications. Guaranteeing the specified lifetime at statistical average is no longer sufficient. Assuring that no failure of an individual safety relevant part occurs unexpectedly, becomes most important. The paper surveys the priority actions underway to cope with the tremendous challenges. It highlights practical examples in all three directions of reliability research. i) Experimental reliability tests and physical analyses: New and highly efficient accelerated stress tests are able to cover the complex and multi-fold loading situation in the field. New analytics techniques can identify the typical failure modes and their physical root causes. ii) Virtual techniques: Schemes of validated simulations allow capturing the physics of failure proactively in the design for reliability process. iii) Prognostics health management (PHM): A new concept is introduced for adding a minimum of PHM features at the various levels of automotive electronics to provide functional safety as required for autonomous vehicles. This way, the new generation of reliability methods will continuously provide estimates of the remaining useful life (RUL) for each relevant part under the actual use conditions to allow triggering maintenance in time.
Inverse Conduction Heat Transfer and Kriging Interpolation Applied to Temperature Sensor Location in Microchips
Authors: Gonzalez Cuadrado D. , Marconnet A. , Paniagua G.
Published: October 2017

Significant thermal gradients and hotspots is a major safety and operational issue in microprocessors, hence accurate real-time monitoring hot spots is a critical need. This thermal monitoring is typically performed using temperature sensors embedded in the chip or processor board. The location of the temperature sensors is primarily determined by the sensor space claim rather than the ideal location for thermal management. This manuscript presents an optimization methodology to determine the most beneficial locations for the temperature sensors inside of the microprocessors, based input from high resolution surface infrared thermography combined with inverse heat transfer solvers to predict hot spot locations. Specifically, the infrared image is used to obtain the temperature map over the processor surface, and subsequently delivers the input to a 3D inverse heat conduction methodology, used to determine the temperature field within the processor. In this paper, simulated thermal maps are utilized to assess the accuracy of the method. The inverse methodology is based in a function specification method combined with a sequential regularization in order to increase accuracy in the results. Together with a number of sensors, the temperature field within the processor is then used to determine the optimal location of the temperature sensors using a genetic algorithm optimization combined with a Kriging interpolation. This combination of methodologies was validated against the Finite Element Analysis of a chip incorporating heaters and temperature sensors. An uncertainty analysis of the inverse methodology and the Kriging interpolation was performed separately to assess the reliability of the procedure.
Optimization of Graphite Composite Latent Heat Storage Systems
Authors: Mallow Anne , Gluesenkamp Kyle , Abdelaziz Omar , Graham Samuel
Published: October 2017

The energy density and power density are critical properties of thermal energy storage systems. Use of a phase change material as the storage medium provides high energy density due to the ability to store energy as latent heat during the phase transition; however, the power density is limited by the low thermal conductivity. Insertion of a highly conductive graphite foam within the material can increase the rate of thermal response of the phase change material. As the graphite bulk density increases, the thermal conductivity increases, but the composite latent heat decreases due to displacement of the phase change material. This introduces a trade-off between energy density and power density of the composite.

In this work, a validated numerical model is used to study the trade-off between energy density and power density with respect to graphite bulk density under various imposed heat fluxes. Comparisons are made based on the melting time, junction temperature between the composite and the heat source, and the volumetric energy density. To simplify the complicated relationship between composite thermophysical properties and charging response, two non-dimensional numbers are used. The Fourier number provides a comparison between the heat storage and heat diffusion by considering the thermal conductivity, latent heat, sensible heat, density, melting time, and volume. A dimensionless temperature compares the junction temperature (temperature between the heat source and the composite) when the sample is fully melted to the melt onset temperature. These non-dimensional numbers can assist in the design of latent heat storage systems where some parameters are fixed (such as heat flux, junction temperature, mass, operating time, or required energy storage) and others must be determined by the design (such as required thermal conductivity or height).
Effects of Sustained Exposure to Temperature and Humidity on the Reliability and Performance of MEMS Microphone
Authors: Lall Pradeep , Abrol Amrit , Locker David
Published: October 2017

MEMS microphones are extensively used in many applications that require reliability, small size, and high sound quality. For harsh environment reliability data MEMS microphones need to be monitored under conditions mimicking their areas of applications. MEMS microphones have an opening/sound port in order to interact with the environment, therefore cannot be sealed completely since the sensing mechanism requires interaction between sound waves and the sensing element. Little to no information exists on reliability data for MEMS microphones under low/high temperature operating life and temperature humidity bias condition. Our work is primarily focused on providing harsh environmental reliability data which can be useful to MEMS designers and engineers. In this paper the test vehicles with MEMS Microphones have been tested under three different harsh environmental conditions: high temperature operating life (HTOL) at 125°C at 3.3V, low temperature storage (LTS) at −35°C and temperature humidity 85°C/85%RH at 3.3V. The main motive of this study is to document the incremental shift and degradation in output parameters namely distortion, frequency response, power supply rejection capability of IC, frequency vs pressure characteristics and analog output voltage of the MEMS microphone. The survivability of MEMS microphone, ADMP401, has been demonstrated as a function of change in the output parameters. Failure analysis has been conducted on the microphone samples to study failure modes and sites using analytical methods such as SEM, EDS and X-ray.
Reliability Analysis of Ultra-Low-K Large-Die Package and Wire Bond Chip Package on Varying Structural Parameter Under Thermal Loading
Authors: Rahangdale Unique , Rajmane Pavan , Misrak Abel , Agonafer Dereje
Published: October 2017

The reliability assessment of package assembly is important to predict the performance of any microelectronic devices. Formation of fatigue cracks at the interface between the solder joint and component is the common failure occur in widely used microelectronic devices. Lead-free solders and advanced silicon process nodes with ultra-low-k (ULK) dielectrics flip chip package are used and are facing significant reliability challenges. The ultra-low-k materials improve performance by reducing parasitic capacitance and crosstalk between adjacent metal lines. [2] With low modulus, lower fracture toughness, higher coefficient of thermal expansion (CTE) and poorer adhesion of ultra-low-k material, when it is compared to the common dielectric materials, it becomes a major concern to analyze thermomechanical failures. From our past study, it has been concluded that solder joint reliability (SJR) of the small package depends on the copper content in the printed circuit boards (PCB). Also, the wire bond large PBGA packages are a cost-effective package with a substantial number of solder balls. The substrate and PCB have its impact on the solder ball, the mismatch in CTE of different components cause solder failure. In this paper, critical attention has been given to the copper content present in the PCB of different thicknesses and how PCB thickness is related to SJR. The structure of package plays a vital role in deciding reliability of package, as the different structure can shift stress point or distribute stresses to one or more components. The substrate or PCB stack-up or composition can strongly affect the package life. Many parameters need to be studied and package to substrate ratio is one of its which is discussed in this work. Material characterization of PCB with different thickness has been done. Thermal Mechanical Analyzer (TMA) is leveraged to measure temperature-dependent CTE, Dynamic Mechanical Analyzer (DMA) and Universal testing machine are used for measuring Elastic modulus and Poisson’s ratio. Further, a package assembly for the PCB of different thickness has been a model using ANSYS Workbench 18.0.
Design Analysis and Performance Evaluation of a Data Center With Indirect Evaporative Cooling
Authors: Tavakkoli Fatemeh , Ebrahimi Siavash , Sun Xiaogang , Cui Yan , Heydari Ali
Published: October 2017

With the rapid growth of data centers worldwide and the global shift towards energy sustainability, deploying new cooling technologies has an utmost importance. Conventional cooling systems such as chilled water system, usually have high capital costs and relatively low energy efficiency, leading to a high PUE and TCO values. Indirect evaporative cooling is a promising technology, which offers air cooling with high efficiency, hygiene air quality, and lower total cost. This paper details the design of a proof-of-concept data center with indirect evaporative cooling, which will be eventually deployed at megawatt-scale Baidu datacenters. BIN data analysis and CFD simulation are performed to optimize the physical design and operating conditions. CFD analysis of the data center room is established to optimize rack placement, air flow management, and cold aisle hot aisle configuration. A comprehensive TCO analysis is established, which shows a total savings of 9% using IDEC technology compared to chilled water system for cooling. In addition, TCO analysis indicates small to negligible effect of air supply temperature. Hence, air supply to the cold aisle is set to 27 °C to improve cooling performance. Finally, ROI sensitivity analysis is performed to measure the sensitivity of ROI on power usage effectiveness of the IDEC unit.
Edge Computing and Contextual Information for the Internet of Things Sensors
Authors: Turlapati Lavanya , Hinds Nigel , Nair Dhruv , Klein Levente J.
Published: October 2017

Interpreting sensor data requires knowledge of sensor placement and the contextual environment surrounding the sensor. For a single sensor measurement, it is easy to document the context usually by visual observation. However, for millions of sensors reporting data back to a server, the contextual information needs to be automatically extracted from either data analysis or leveraging complimentary data sources. Data layers that overlap spatially or temporally with sensor locations, can be used to extract the context and validate the measurement. The second challenge is to minimize the amount of sensor data transmitted through the internet while preserving signal information content. Here we demonstrate two methods for communication bandwidth reduction: computation at the edge and compressed sensing. We validate the above methods on wind and chemical sensor data to: (1) eliminate redundant measurement from wind sensors and (2) extract peak value of a chemical sensor measuring a methane plume. We present a general cloud based framework to validate sensor data based on statistical and physical modeling and contextual data extracted from geospatial data.
Challenges in 3D Printing of High Conductivity Copper
Authors: El-Wardany Tahany , She Ying , Jagdale Vijay , Garofano Jacquelynn K. , Liou Joe , Schmidt Wayde
Published: October 2017

With recent advancements in additive manufacturing (AM) technology, it is possible to deposit copper conductive paths and insulation layers of an electric machine in a selective controlled manner. AM of copper enables higher fill factors that improves the internal thermal conduction in the stator core of the electric machine (induction motor), which will enhance its efficiency and power density. This will reduce the motor size and weight and make it more suitable for aerospace and electric vehicle applications, while reducing / eliminating the rare-earth dependency. The objective of this paper is to present the challenges associated with AM of copper coils having 1×1mm cross section and complex features that are used in producing ultra-high efficiency induction motor for traction applications. The paper also proposes different approaches that were used by the authors in attempts to overcome those challenges.
Interfacial Delamination and Fracture Properties of Potting Compounds and PCB/Epoxy Interfaces Under Flexure Loading After Exposure to Multiple Cure Temperatures
Authors: Lall Pradeep , Dornala Kalyan , Suhling Jeff , Deep John
Published: October 2017

Electronics components operating under extreme thermo-mechanical stresses are often protected with conformal coating and potting encapsulation to isolate the thermal and vibration shock loads. Development of predictive models for high-g shock survivability of electronics requires the measurement of the interface properties of the potting compounds with the printed circuit board materials. There is scarcity of interface fracture properties of porting compounds with printed circuit board materials. Potting and encapsulation resins are commonly two-part systems which when mixed together form a solid, fully cured material, with no by-products. The cured potting materials are prone to interfacial delamination under dynamic shock loading which in turn potentially cause failures in the package interconnects. The study of interfacial fracture resistance in PCB/epoxy potting systems under dynamic shock loading is important in mitigating the risk of system failure in mission critical applications. In this paper three types of epoxy potting compounds were used as an encapsulation on PCB samples. The potting compounds were selected on the basis of their ultimate elongation under quasi-static loading. Potting compound, A is stiffer material with 5% of ultimate elongation before failure. Potting compound, B is a moderately stiff material with 12% ultimate elongation. Finally potting compound C is a softer material with 90% ultimate elongation before failure. The fracture properties and interfacial crack delamination of the PCB/epoxy interface was determined using three-point bend loading with a pre-crack in the epoxy near the interface. The fracture toughness and crack initiation of the three epoxy systems was compared with the cure schedule and temperature. Fracture modeling was performed with crack tip elements in ABAQUS finite element models to determine the crack initiation and interfacial stresses. A comparison of the fracture properties and the performance of epoxy system resistance to delamination was shown through the three-point bend tests. The finite element model results were correlated with the experimental findings.
Theory and numerical simulation for a design of broadband constant beam pattern transducer
Authors: Huang Dehua
Published: October 2017

The theory and numerical simulations for the constant beam pattern (CBP) broadband transducer design are introduced. For a large spherical transducer, if the normal direction radial velocity distribution on the surface of the sphere transducer is a single Legendre polynomial, the far field angular beam pattern shows the same Legendre polynomial distribution due to a spherical Hankel function asymptotic approximation. Arbitrary radial velocity shading functions, including the equal sidelobe classic Dolph-Chebyshev shading, can be expanded by the Legendre series per Sturm-Liouville theory, such that the converging acoustic beam pattern displays the same angular shape as the original shading function itself for the broadband CBP transducer.
Enterococcus faecalis Responds to Individual Exogenous Fatty Acids Independently of Their Degree of Saturation or Chain Length
Authors: Saito Holly E. , Harp John R. , Fozo Elizabeth M.
Published: October 2017

Enterococcus faecalis
is a commensal of the human gastrointestinal tract that can persist in the external environment and is a leading cause of hospital-acquired infections. Given its diverse habitats, the organism has developed numerous strategies to survive a multitude of environmental conditions. Previous studies have demonstrated that
E. faecalis
will incorporate fatty acids from bile and serum into its membrane, resulting in an induced tolerance to membrane-damaging agents. To discern whether all fatty acids induce membrane stress protection, we examined how
E. faecalis
responded to individually supplied fatty acids.
E. faecalis
readily incorporated fatty acids 14 to 18 carbons in length into its membrane but poorly incorporated fatty acids shorter or longer than this length. Supplementation with saturated fatty acids tended to increase generation time and lead to altered cellular morphology in most cases. Further, exogenously supplied saturated fatty acids did not induce tolerance to the membrane-damaging antibiotic daptomycin. Supplementation with unsaturated fatty acids produced variable growth effects, with some impacting generation time and morphology. Exogenously supplied unsaturated fatty acids that are normally produced by
E. faecalis
and those that are found in bile or serum could restore growth in the presence of a fatty acid biosynthetic inhibitor. However, only the eukaryote-derived fatty acids oleic acid and linoleic acid provided protection from daptomycin. Thus, exogenous fatty acids do not lead to a common physiological effect on
E. faecalis
. The organism responds uniquely to each, and only host-derived fatty acids induce membrane protection.

IMPORTANCE
Enterococcus faecalis
is a commonly acquired hospital infectious agent with resistance to many antibiotics, including those that target its cellular membrane. We previously demonstrated that
E. faecalis
will incorporate fatty acids found in human fluids, like serum, into its cellular membrane, thereby altering its membrane composition. In turn, the organism is better able to survive membrane-damaging agents, including the antibiotic daptomycin. We examined fatty acids commonly found in serum and those normally produced by
E. faecalis
to determine which fatty acids can induce protection from membrane damage. Supplementation with individual fatty acids produced a myriad of different effects on cellular growth, morphology, and stress response. However, only host-derived unsaturated fatty acids provided stress protection. Future studies are aimed at understanding how these specific fatty acids induce protection from membrane damage.
Influence of
cis
Element Arrangement on Promoter Strength in Trichoderma reesei
Authors: Kiesenhofer Daniel P. , Mach Robert L. , Mach-Aigner Astrid R.
Published: October 2017

Trichoderma reesei
can produce up to 100 g/liter of extracellular proteins. The major and industrially relevant products are cellobiohydrolase I (CBHI) and the hemicellulase XYNI. The genes encoding both enzymes are transcriptionally activated by the regulatory protein Xyr1. The first 850 nucleotides of the
cbh1
promoter contain 14 Xyr1-binding sites (XBS), and 8 XBS are present in the
xyn1
promoter. Some of these XBS are arranged in tandem and others as inverted repeats. One such
cis
element, an inverted repeat, plays a crucial role in the inducibility of the
xyn1
promoter. We investigated the impact of the properties of such
cis
elements by shuffling them by insertion, exchange, deletion, and rearrangement of
cis
elements in both the
cbh1
and
xyn1
promoter. A promoter-reporter assay using the
Aspergillus niger
goxA
gene allowed us to measure changes in the promoter strength and inducibility. Most strikingly, we found that an inverted repeat of XBS causes an important increase in
cbh1
promoter strength and allows induction by xylan or wheat straw. Furthermore, evidence is provided that the distances of
cis
elements to the transcription start site have important influence on promoter activity. Our results suggest that the arrangement and distances of
cis
elements have large impacts on the strength of the
cbh1
promoter, whereas the sheer number of XBS has only secondary importance. Ultimately, the biotechnologically important
cbh1
promoter can be improved by
cis
element rearrangement.

IMPORTANCE
In the present study, we demonstrate that the arrangement of
cis
elements has a major impact on promoter strength and inducibility. We discovered an influence on promoter activity by the distances of
cis
elements to the transcription start site. Furthermore, we found that the configuration of
cis
elements has a greater effect on promoter strength than does the sheer number of transactivator binding sites present in the promoter. Altogether, the arrangement of
cis
elements is an important factor that should not be overlooked when enhancement of gene expression is desired.
Fate of Salmonella enterica and Enterohemorrhagic Escherichia coli Cells Artificially Internalized into Vegetable Seeds during Germination
Authors: Liu Da , Cui Yue , Walcott Ronald , Chen Jinru
Published: October 2017

Vegetable seeds contaminated with bacterial pathogens have been linked to fresh-produce-associated outbreaks of gastrointestinal infections. This study was undertaken to observe the physiological behavior of
Salmonella enterica
and enterohemorrhagic
Escherichia coli
(EHEC) cells artificially internalized into vegetable seeds during the germination process. Surface-decontaminated seeds of alfalfa, fenugreek, lettuce, and tomato were vacuum-infiltrated with four individual strains of
Salmonella
or EHEC. Contaminated seeds were germinated at 25°C for 9 days, and different sprout/seedling tissues were microbiologically analyzed every other day. The internalization of
Salmonella
and EHEC cells into vegetable seeds was confirmed by the absence of pathogens in seed-rinsing water and the presence of pathogens in seed homogenates after postinternalization seed surface decontamination. Results show that 317 (62%) and 343 (67%) of the 512 collected sprout/seedling tissue samples were positive for
Salmonella
and EHEC, respectively. The average
Salmonella
populations were significantly larger (
P
< 0.05) than the EHEC populations. Significantly larger
Salmonella
populations were recovered from the cotyledon and seed coat tissues, followed by the root tissues, but the mean EHEC populations from all sampled tissue sections were statistically similar, except in pregerminated seeds. Three
Salmonella
and two EHEC strains had significantly larger cell populations on sprout/seedling tissues than other strains used in the study.
Salmonella
and EHEC populations from fenugreek and alfalfa tissues were significantly larger than those from tomato and lettuce tissues. The study showed the fate of internalized human pathogens on germinating vegetable seeds and sprout/seedling tissues and emphasized the importance of using pathogen-free seeds for sprout production.

IMPORTANCE
The internalization of microorganisms into vegetable seeds could occur naturally and represents a possible pathway of vegetable seed contamination by human pathogens. The present study investigated the ability of two important bacterial pathogens,
Salmonella
and enterohemorrhagic
Escherichia coli
(EHEC), when artificially internalized into vegetable seeds, to grow and disseminate along vegetable sprouts/seedlings during germination. The data from the study revealed that the pathogen cells artificially internalized into vegetable seeds caused the contamination of different tissues of sprouts/seedlings and that pathogen growth on germinating seeds is bacterial species and vegetable seed-type dependent. These results further stress the necessity of using pathogen-free vegetable seeds for edible sprout production.
Draft Genome Sequence of the Wood-Degrading Ascomycete
Kretzschmaria deusta
DSM 104547
Authors: Büttner Enrico , Gebauer Anna Maria , Hofrichter Martin , Liers Christiane , Kellner Harald
Published: October 2017

We report here the draft genome of
Kretzschmaria
(
Ustulina
)
deusta
, an ascomycetous fungus that colonizes and substantially degrades hardwood and can infest living broad-leaved trees. The genome was assembled into 858 contigs, with a total size of 46.5 Mb, and 11,074 protein-coding genes were predicted.
Draft Genome Assembly of a
Wolbachia
Endosymbiont of
Plutella australiana
Authors: Ward Christopher M. , Baxter Simon W.
Published: October 2017

Wolbachia
spp. are endosymbiotic bacteria that infect around 50% of arthropods and cause a broad range of effects, including manipulating host reproduction. Here, we present the annotated draft genome assembly of
Wolbachia
strain wAus, which infects
Plutella australiana
, a cryptic ally of the major
Brassica
pest
Plutella xylostella
(diamondback moth).
Complete Genome Sequence of the Circulatory Foot-and-Mouth Disease Virus Serotype Asia1 in Bangladesh
Authors: Ali M. Rahmat , Alam A. S. M. Rubayet Ul , Amin M. Al , Ullah Huzzat , Siddique Mohammad Anwar , Momtaz Samina , Sultana Munawar , Hossain M. Anwar
Published: October 2017

The complete genome sequence of foot-and-mouth disease virus (FMDV) serotype Asia1 isolated from Bangladesh is reported here. Genome analysis revealed amino acid substitutions in the VP1 antigenic region and deletions in both the 5′ and 3′ untranslated regions (UTRs) compared to the genome of the existing vaccine strain (GenBank accession no. AY304994).