bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of inhibition for working memory processes: ERP evidence from a short‐term storage task
Authors: Getzmann Stephan , Wascher Edmund , Schneider Daniel
Published: October 2017

Human working memory is the central unit for short‐term storage of information. In addition to the selection and adequate storage of relevant information, the suppression of irrelevant stimuli from the environment seems to be of importance for working memory processes. To learn more about the interplay of information uptake and inhibition of irrelevant information, the present study used ERP measures and a short‐term storage and retrieval task, in which pairs of either numbers or letters had to be compared. Random sequences of four stimuli (two numbers and two letters) were presented, with either the numbers or the letters being relevant for comparison. The analysis of ERPs to each of the four stimuli indicated more pronounced P2 and P3b amplitudes for relevant than irrelevant stimuli. In contrast, the N2 (reflecting inhibitory control) was only elicited by irrelevant stimuli. Moreover, the N2 amplitude of the second irrelevant stimulus was associated with behavioral performance, indicating the importance of inhibition of task‐irrelevant stimuli for working memory processes. In sum, the findings demonstrate the role of cognitive control mechanisms for protecting relevant contents in working memory against irrelevant information.
Evaluation of reproductive performance and genetic variation in bulls of the Polish White‐Backed breed
Authors: Sawicka‐Zugaj W , Chabuz W , Litwińczuk Z , Kasprzak‐Filipek K
Published: October 2017

Contents

The aim of the study was to evaluate genetic variation, reproductive performance and the degree of relationship of White‐Backed bulls entered in the breed registry and approved for breeding. The study included 32 bulls of the White‐Backed (WB) breed with an entry in the breed registry and used for breeding in the years 2003–2015. Eleven microsatellite DNA sequences (TGLA222, BM2113, TGLA53, ETH10, SPS115, TGLA126, TGLA122, INRA23, ETH3, ETH225 and BM1824) were used to analyse variation in the WB bulls. The bulls most often used for breeding were Chilon (1,073 doses), Mak (939 doses) and Jaguar (858 doses). The bulls Mak, Chilon and Jak had the greatest influence on the active population of White‐Backed cattle, with the most daughters. In the analysed population of White‐Backed bulls, a total of 79 different alleles were identified, with a mean 7.27 per locus. The analysed pool of microsatellite loci was characterized by high values for PIC, HO and HE (>0.6), and the entire population was in genetic equilibrium. The estimated level of inbreeding within the population ranged from −0.2277 (ETH225) to 0.0775 (SPS115), with a mean value of −0.0587.
Colour‐Doppler ultrasound imaging as a laparoscopy substitute to count corpora lutea in superovulated sheep
Authors: Pinto PHN , Bragança GM , Balaro MFA , Arashiro EKN , dos Santos GB , de Souza GN , Souza‐Fabjan JMG , Da Fonseca JF , Brandão FZ
Published: October 2017

Contents

This study evaluated colour‐Doppler ultrasound imaging (UI) as a substitute for laparoscopy to count the corpora lutea (CL) in superovulated sheep. Twenty‐five Santa Ines ewes were superovulated three times at 21‐day intervals. Corpora lutea were counted by colour‐Doppler UI (CLDOPPLER) 6 days after each superovulation and confirmed by laparoscopy (CLLAP) 12 hr later. The mean number of CL was similar for both techniques (2.1 ± 2.5 vs. 2.1 ± 2.7 for CLDOPPLER and CLLAP, respectively) with a significant positive correlation (r = .94; r2=.89). Colour‐Doppler UI effectively evaluated the ovarian response in superovulated ewes and efficiently identified animals that did not respond to superovulation.
DNA methylation and expression of imprinted genes are associated with the viability of different sexual cloned buffaloes
Authors: Ruan Z , Zhao X , Qin X , Luo C , Liu X , Deng Y , Zhu P , Li Z , Huang B , Shi D , Lu F
Published: October 2017

Contents

The DNA methylation of imprinted genes is an important way to regulate epigenetic reprogramming of donor cells in somatic cell nuclear transfer (SCNT). However, the effects of sexual distinction on the DNA methylation of imprinted genes in cloned animals have seldom been reported. In this study, we analysed the DNA methylation status of three imprinted genes (Xist, IGF2 and H19) from liveborn cloned buffaloes (L group, three female and three male), stillborn cloned buffaloes (S group, three female and three male) and natural reproduction buffaloes (N group, three female and three male), using bisulphite sequencing polymerase chain reaction (BS‐PCR). The expression levels of these imprinted genes were also investigated by quantitative real‐time PCR (QRT‐PCR). The DNA methylation levels of H19 were not significantly different among the groups. However, the Xist in female and IGF2 in male of the S group were found to be significantly hypomethylated in comparison with the same sexual buffaloes in L group and N group (p < .05). Furthermore, the expression levels of Xist, IGF2 and H19 in the stillborn female cloned buffaloes of S group were significantly higher than that of the female buffaloes in the L group and N group (p < .05). The expression levels of IGF2 and H19 in the stillborn male cloned buffaloes in the S group were significantly higher than that of the male buffaloes in the L group and N group (p < .05). These results indicate that Xist may be associated with the viability of female cloned buffaloes, and IGF2 may also be related to the viability of male cloned buffaloes.
Puncture and drainage of the subordinate follicles at timed artificial insemination prevents the risk of twin pregnancy in dairy cows
Authors: López‐Gatius F , Hunter RHF
Published: October 2017

Contents

The objective of this study was to determine whether fluid drainage from the subordinate follicles by ovum pickup procedures prevents the risk of twin pregnancy without reducing the fertility of the cow. Lactating dairy cows with at least two follicles over 12 mm diameter located one on each ovary and selected from synchronized groups for fixed‐time insemination were assigned to a Control (n = 49) or Drainage (n = 49) group. The largest follicle was considered as the dominant follicle. Draining of all subordinate follicles (≥10 mm) was performed in the Drainage group. All drained follicles developed as a corpus luteum 7 days later. In the Control cows, the presence of two corpora lutea (55.1%) was lower (p = .003) than those in the Drainage cows (87.8%), whereas the incidence of twin pregnancies was 50% and 0% for the Control and Drainage groups, respectively (p < .001). Draining did not affect the pregnancy rate. These results indicate that puncture and drainage of the subordinate follicles at insemination may eliminate the risk of twin pregnancies and reduce the risk of subsequent pregnancy loss by increasing the incidence of additional corpora lutea.
Performing repentance: (in)sincerity in prodigal son drama and the Henry IVs
Authors: Horbury Ezra
Published: October 2017

The parable of the prodigal son is the most popular repentance narrative in early modern drama, yet the authenticity of these prodigals’ repentances is frequently disputed. The truly repentant prodigal and posturing sinner are functionally identical on the early modern stage, and the parable was so renowned that the prodigal's repentance and forgiveness could not only be predicted, but expected and engineered. This essay compares prodigals’ repentances across Eastward Ho, The London Prodigal, 2 If You Know Not Me You Know Nobody, and the Henry IVs. It argues that these plays exhibit discomfort with the outward display of repentance, the irrelevance of sincerity, and the viability of the parable as a repentance narrative. While some of these repentances have been discussed in isolation, their comparison allows for the examination of ambiguous repentances not as isolated incidents but a discernible trend in early modern culture, born from anxieties regarding the indistinguishability of feigned and ‘true’ performances of inward spiritual change. The authenticity of repentance, it emerges, cannot be determined, but repentance also need not be sincere to be accepted by a plays’ community. The authenticity of repentance proves not only impossible to identify, but ultimately irrelevant to these plays’ social worlds.
Risk Mapping of Groundwater‐Drawdown‐Induced Land Subsidence in Heterogeneous Soils on Large Areas
Authors: Sundell Jonas , Haaf Ezra , Norberg Tommy , Alén Claes , Karlsson Mats , Rosén Lars
Published: October 2017

Groundwater leakage into subsurface constructions can cause reduction of pore pressure and subsidence in clay deposits, even at large distances from the location of the construction. The potential cost of damage is substantial, particularly in urban areas. The large‐scale process also implies heterogeneous soil conditions that cannot be described in complete detail, which causes a need for estimating uncertainty of subsidence with probabilistic methods. In this study, the risk for subsidence is estimated by coupling two probabilistic models, a geostatistics‐based soil stratification model with a subsidence model. Statistical analyses of stratification and soil properties are inputs into the models. The results include spatially explicit probabilistic estimates of subsidence magnitude and sensitivities of included model parameters. From these, areas with significant risk for subsidence are distinguished from low‐risk areas. The efficiency and usefulness of this modeling approach as a tool for communication to stakeholders, decision support for prioritization of risk‐reducing measures, and identification of the need for further investigations and monitoring are demonstrated with a case study of a planned tunnel in Stockholm.
Is hearing impairment associated with HIV? A systematic review of data from low‐ and middle‐income countries
Authors: Ensink Robbert J. H. , Kuper Hannah
Published: October 2017

Objectives

To systematically review evidence on the prevalence and characteristics of hearing impairment among children and adults living with HIV in low‐ and middle‐income countries (LMIC).

Methods

Articles were identified up to January 2016 through searching four electronic databases. Epidemiological studies conducted in LMIC that explored the association between HIV status and hearing loss, with or without an HIV‐uninfected comparison group, were eligible for inclusion. Results were screened and assessed for eligibility, and data were extracted by two reviewers, with discussion in the case of disagreement. Findings were narratively synthesised.

Results

The search identified 638 unique references, of which 21 studies were included in the review, including 3491 people with HIV from 13 LMIC. There was lack of consistency in the definition used for hearing loss, making comparability across studies difficult. Among children with HIV, across the three studies that used a cut‐off of >15 dB in either ear, the prevalence of hearing loss ranged from 22 to 37%. Among the three studies that used >25 dB in either ear, the prevalence ranged from 32 to 39%. Among adults with HIV, for the five studies that used a threshold of >25 dB for either ear, the prevalence ranged from 10 to 43%. The prevalence of hearing impairment was significantly higher among people with HIV than in controls in eight of the ten studies that assessed this comparison. Conductive hearing loss was the most common type of hearing loss in children with HIV, while sensorineural hearing loss was more common in adults with HIV. There was a lack of evidence for an association between ART use and hearing loss, although there was some suggestion that late stage of HIV disease or low CD4 count was related to hearing loss. There were concerns about the quality of the studies included in the review.

Conclusions

The current evidence is suggestive of a high prevalence of hearing loss among people living with HIV compared to people without HIV, or to WHO estimates for the general population. More research is needed to better understand the aetiology of hearing loss in relation to HIV, and whether screening for and treatment of hearing loss can be effectively integrated into HIV treatment services needs further research.
The enclosure of “waste land”: Rethinking informality and dispossession
Authors: Inverardi‐Ferri Carlo
Published: October 2017

The paper contributes to the recent geographical debates on the connection between dispossession and informality. Existing scholarship recognises that informality is an integral part of capitalism. Arguments reinforcing the formal–informal dichotomy dominate research on processes of dispossession. Drawing on analyses of the struggle of waste recyclers in Beijing, this paper conceptualises informal activities in relation to circuits of capital. It contends that theories of dispossession need to be extended in order to analyse processes of enclosure in the informal economy. The conclusion discusses the potential of reconceptualising dispossession as a variegated process operating both outside and within the capitalist space.
Bilateral trust and trade: Evidence from China
Authors: Xing Weibo , Zhou Li‐An
Published: October 2017

By changing transaction costs, trust can be a determinant of interregional economic exchange. Based on data sets of bilateral trust and trade at provincial level in China, this study investigates the trust–trade relationship empirically. As a channel of affecting bilateral trade, bilateral trust is incorporated into gravity models. By controlling for institutional quality, labour migration and other economic indicators, the baseline results show that the bilateral trust is positively correlated with the bilateral trade significantly. The sensitivity tests using an alternative estimation of interprovincial trade in China also confirm this positive trust–trade relationship. In addition, we use an instrumental‐variable estimation to control for the endogeneity of bilateral trust, and find that the trust–trade relationship is robust. This relationship seems to reveal that improving bilateral trust can be a new channel of boosting bilateral trade.
ScvO2 changes after red‐blood‐cell transfusion for anaemia in cardiothoracic and vascular ICU patients: an observational study
Authors: Zeroual N. , Samarani G. , Gallais J. , Culas G. , Saour M. , Mourad M. , Gaudard P. , Colson P. H.
Published: October 2017

Background and Objectives

Haemoglobin threshold for transfusion has been significantly decreased, but haemoglobin plasma concentration may not be sufficient to assess the need of red‐blood‐cell (RBC) transfusion. Central venous oxygen saturation (ScvO2) is a clue of metabolic matching between O2 transport and consumption, which could help to assess when transfusion is appropriate once anaemia has been diagnosed in ICU patients.

Materials and Methods

Adult patients admitted consecutively to a cardiothoracic and vascular ICU were included in a prospective, observational and single‐centre study over a 6‐month period (September 2014 to February 2015), provided they were transfused with RBC. Patients with active bleeding or in unstable condition were excluded. Haemoglobin and ScvO2 were collected through a central venous catheter before and after transfusion. In order to identify a ScvO2 threshold, analysis of ScvO2 changes after transfusion was performed.

Results

Fifty‐three patients received 100 RBC transfusions. Haemoglobin at the time of transfusion was 7·2 g/dl [6·8–7·7], while ScvO2 was 66·9% [60–73]. A 5% increase in ScvO2 after transfusion has the best specificity and positive predictive values, with a ScvO2 threshold of 65%. After transfusion (RBC units, 2 [1‐2]), ScvO2 increased only in patients with ScvO2 ≤65%, from 58% [53–62] to 69% [64–73] (P < 0·001).

Conclusion

In anaemic patients, RBC transfusion induced a significant increase in ScvO2, provided it was low before transfusion. A 65% cut‐off value of ScvO2 before transfusion showed good specificity and good positive predictive value for a 5% increase after transfusion.
Investigation of Physics Teacher Candidates’ Cognitive Structures about “Electric Field”: A Free Word Association Test Study
Authors: Türkkan Ercan
Published: October 2017

The aim of this study is to investigate the cognitive structures of physics teacher candidates about “electric field”. Phenomenographic research method, one of the qualitative research patterns, was used in the study. The data of the study was collected from 91 physics teacher candidates who had taken General Physics II course at Education Faculty of a university in Anatolia. The stimulus word, “electric field” has been presented to teacher candidates through Free Word Association Test (FWAT). The totally 43 responses obtained from FWAT were presented as frequency tables. The responses were divided into 13 categories by the - content analysis. A concept network which reveals cognitive structure of physics teacher candidates about “electric field” was created considering frequencies and categories. According to results of the study, the highest frequency values related with "electric field" which stimulus of physics teacher candidates were power, charge, vector/vectoral quantity, current, magnet, etc. and the categories with the highest frequency of response words were figured out as electrical force, electric charge, magnetic field and magnitude of electric field, etc.
Toward Investigation of External Oil Flow From a Journal Bearing in an Epicyclic Gearbox
Authors: Berthold Martin , Morvan Hervé , Young Colin , Jefferson-Loveday Richard
Published: October 2017

High loads and bearing life requirements make journal bearings the preferred choice for use in high-power, planetary gearboxes in jet engines. With the planet gears rotating about their own axis and orbiting around the sun gear, centrifugal forces generated by both motions interact with each other and create complex kinematic conditions. This paper presents a literature and state-of-the-art knowledge review to identify existing work performed on cases similar to external journal bearing oil flow. In order to numerically investigate external journal bearing oil flow, an approach to decompose an actual journal bearing into simplified models is proposed. Preliminary modeling considerations are discussed. The findings and conclusions are used to create a three-dimensional (3D), two-component computational fluid dynamics (CFD) sector model with rotationally periodic boundaries of the most simplistic approximation of an actual journal bearing: a nonorbiting representation, rotating about its own axis, with a circumferentially constant, i.e., concentric, lubricating gap. In order to track the phase interface between the oil and the air, the volume of fluid (VoF) method is used. External journal bearing oil flow is simulated with a number of different mesh densities. Two different operating temperatures, representing low and high viscosity oil, are used to assess the effect on the external flow field behavior. In order to achieve the future objective of creating a design tool for routine use, key areas are identified in which further progress is required.
Role of a Liquid Accumulator in a Passive Two-Phase Liquid Cooling System for Electronics: Experimental Analysis
Authors: Lamaison Nicolas , Amalfi Raffaele L. , Marcinichen Jackson B. , Thome John R. , Salamon Todd
Published: October 2017

Gravity-driven two-phase liquid cooling systems using flow boiling within micro-scale evaporators are becoming a game-changing solution for electronics cooling. The optimization of the system’s filling ratio can however become a challenging problem for a system operating over a wide range of cooling capacities and temperature ranges. The benefits of a liquid accumulator to overcome this difficulty are evaluated in the present paper.

An experimental thermosyphon cooling system was built to cool multiple electronic components up to a power dissipation of 1800 W. A double-ended cylinder with a volume of 150 cm3 is evaluated as the liquid accumulator for two different system volumes (associated to two different condensers).

Results demonstrated that the liquid accumulator provided robust thermal performance as a function of filling ratio for the entire range of heat loads tested. In addition, the present liquid accumulator was more effective for a small volume system, 599 cm3, than for a large volume system, 1169 cm3, in which the relative size of the liquid accumulator increased from 12.8 % to 25% of the total system’s volume.
Piezoresistive Silicon Stress Sensor As a Tool to Monitor Health of an Electronic System
Authors: Palczynska Alicja , Prisacaru Alexandru , Gromala Przemyslaw , Han Bongtae , Mayer Dirk , Melz Tobias
Published: October 2017

This paper presents a failure mode detection methodology using a piezoresistive silicon based stress sensor. Data from experiment is used to validate algorithms developed for detection. Dedicated test vehicles are designed and fabricated, where the process parameters and materials are carefully selected to produce delamination between molding compound and PCB after fabrication. The test vehicles are then subjected to thermal cycling of −40°C to 125°C to grow the delamination area. After every 150 cycles, the samples are examined using Scanning Acoustic Microscopy (SAM), and the results are correlated with stress sensor signal. It is demonstrated that the propagation of the delamination area can be detected using the stress sensor. Collected data is also used to examine the applicability of statistical pattern recognition algorithms for detecting the failure. The algorithms considered in the study include Mahalanobis Distance (MD) and Singular Value Decomposition (SVD), which do not require a prior knowledge about failures and are just searching for deviation from norm in the data. The results from the analysis indicate that both techniques are suitable to stress sensor measurements, and thus are capable of detecting failure during reliability testing.
The Performance Enhancement of a Heat Pipe for Power Electronics Cooling With a Partially Applied Hybrid Wick
Authors: Boo Joon Hong , Kim Hyun Gon , Han Chang Woo
Published: October 2017

A series of experiments was conducted to investigate the performance characteristics of a heat pipe with a hybrid wick that combined grooves and a wire screen. The heat pipe in this study was designed primarily for the cooling of high-density power electronic elements such as IGBTs, and it had tiny triangular grooves along its entire length. The container was a copper tube which had an outer diameter of 19 mm and length of 0.8 m, and the working fluid was water. To lower the thermal resistance against increased thermal loads, a higher performance was desired for the heat pipe, without changing the external dimensions. A fine mesh wire screen was partially applied to the evaporator to enhance the heat transfer performance. The hybrid wick heat pipe was tested and analyzed from the viewpoints of thermal resistance, effective thermal conductance, and operating temperature. For a 1.6 kW effective thermal load, as a typical result, the heat pipe with the hybrid wick exhibited a 70 % decrease in thermal resistance compared to that with a groove wick only. The paper includes results for various thermal loads and fluid charges. The results herein can be utilized in applications that require an intensive enhancement in heat pipe performance.
Effects of Build-Up Material Properties on Warpage Dispersion of Organic Substrates Caused by Manufacturing Variations
Authors: Okamoto Keishi , Kohara Sayuri , Mori Hiroyuki
Published: October 2017

In large-die (20mm and above) flip-chip packaging applications such as high-end processors, the organic substrates have been widely used. In most cases, they are double-sided multi-layer printed wiring boards. The substrates mainly consist of glass-reinforced rigid core, build-up film resin layers and copper trace patterns. During chip attaching process, the substrates are warped due mainly to the unbalance in copper loading ratio of the build-up layers between the front and the back of the core layer. A common practice for minimizing the warpage of a substrate is to balance its copper loading as much as possible at its design stage. However, the thickness of each build-up layer and trace pattern can shift from its designed value due to fluctuation in process conditions during manufacturing. Consequently, the substrate warpage becomes larger than the minimized value, since the copper loading is no longer balanced. One of the possible solutions for this challenge is to minimize the errors in manufacturing process. Another solution is to make the substrates more resilient to the manufacturing variations. The latter can be performed at the design stage. The substrates can be made resilient by minimizing the warpage deviation when the thickness of the build-up layer and trace pattern are varied.

In this paper, we have found that the warpage dispersion can be reduced by the build-up material properties which are the key components in balancing the front and back build-up layers. To study the effect of the build-up material properties, we performed dispersion analyses using the multilayered beam model. The analyses results showed a minimum in warpage dispersion when the coefficient of thermal expansion (CTE) of build-up materials is varied at a fixed Young’s modulus. They also show that the warpage dispersion decreases with decreasing Young’s modulus of build-up materials.

The analyses are also done by Monte Carlo simulation with finite element analyses (FEA) so that the analyses can be applied to more complex substrates made for actual packages. The results of Monte Carlo simulations were consistent with those of obtained by the multilayered beam model. The values in build-up material for minimizing the warpage dispersion are in realistic range. In summary, we showed that the organic substrates can be made resilient to manufacturing variations by choosing build-up materials with appropriate material properties which minimize the warpage dispersion.
Numerical Performance Characterization of an Innovative Micro-Scale Electrohydrodynamic Conduction Pumping Device
Authors: Talmor Michal , Yagoobi Jamal
Published: October 2017

As technological advances lead to miniaturization of high power electronics, the concentration of heat generating components per area increases to the point of requiring innovative, integrated cooling solutions to maintain operational temperatures. Traditional coolant pumps have many moving parts, making them susceptible to mechanical failure and requiring periodic maintenance. Such devices are too complex to be miniaturized and embedded in small scale systems. Electrohydrodynamic (EHD) conduction pumps offer an alternative way of generating fluid flow in small scales for use in modern thermal control systems for high power electronics, both for terrestrial and aerospace applications. In EHD conduction, the interaction between an applied electrical field and the dissociation of electrolyte species in a dielectric fluid generates an accumulation of space charge near the electrodes, known as heterocharge layers. These layers apply electric body forces in the fluid, resulting in a flow in the desired direction based on the pump characteristics. EHD conduction pumps work with dielectric fluids and have simple, flexible designs with no moving parts. These pumps have very low power consumption, operate reliably for longer periods than mechanical pumps, and have the ability to operate in microgravity. EHD conduction pumps have been previously proven effective for heat transfer enhancement in multiple size scales, but were only studied in a flush ring or flush flat electrode configurations at the micro-scale. This study provides the pressure and flow rate generation performance characterization for a micro-scale pump with perforated electrodes, designed to be manufactured and assembled using innovative techniques, and incorporated into an evaporator embedded in an electronic cooling system. The performance of the pump is numerically simulated based on the fully coupled equations of the EHD conduction model, showcasing the distinctive heterocharge layer structure and subsequent force generation unique to this innovative design.
Thermal Metamaterials for Heat Flow Control in Electronics
Authors: Dede Ercan M. , Zhou Feng , Schmalenberg Paul , Nomura Tsuyoshi
Published: October 2017

Rapid advancement of modern electronics has pushed the limits of traditional thermal management techniques. Novel approaches to the manipulation of the flow of heat in electronic systems have potential to open new design spaces. Here, the field of thermal metamaterials as it applies to electronics is briefly reviewed. Recent research and development of thermal meta-material systems with anisotropic thermal conductivity for the manipulation of heat flow in ultra-thin composites is explained. An explanation of fundamental experimental studies on heat flow control using standard printed circuit board technology follows. From this, basic building blocks for heat flux cloaking, focusing, and reversal are reviewed, and their extension to a variety of electronics applications is emphasized. While device temperature control, thermal energy harvesting, and electro-thermal circuit design are the primary focus, some discussion on the extension of thermal-guiding structures to device-scale applications is provided. In total, a holistic view is offered of the myriad of possible applications of thermal metamaterials to heat flow control in future electronics.
Electrothermal Analysis of the Field-Plated AlGaN/GaN HEMTs With SiO2 Passivation
Authors: Kara Dogacan , Donmezer Akgun F. Nazli
Published: October 2017

AlGaN/GaN high electron mobility transistors (HEMTs) are widely used in high frequency and power applications of the space and military industries due to their high RF power densities. When operated in full capacity, reliability of GaN HEMTs drop significantly due to device degradation, electron collapse phenomena, and concentrated heating effects. Although significant research has been done to investigate the effects of passivation, field-plates on the device degradation and the electron collapse separately, combined electrothermal analysis of the field-plates and the SiO2 passivation on GaN HEMTs has not been performed from the perspective of device reliability. For this purpose, electrothermal simulations of the field-plated and non-field-plated devices with different SiO2 passivation thicknesses are performed using Sentaurus TCAD to obtain the electrical field distribution and Joule heating caused temperature distribution in operating devices. Using these results, electrical and thermal effects of the field-plates on the devices with different SiO2 passivation thicknesses are analyzed to obtain the most effective and reliable operating conditions.
Estimation of Effective Thermal and Mechanical Properties of Particulate Thermal Interface Materials (TIMs) by a Random Network Model
Authors: Vaitheeswaran Pavan Kumar , Subbarayan Ganesh
Published: October 2017

Particulate thermal interface materials (TIMs) are commonly used to transport heat from chip to heat sink. While high thermal conductance is achieved by large volume loadings of highly conducting particles in a compliant matrix, small volume loadings of stiff particles will ensure reduced thermal stresses in the brittle silicon device. Developing numerical models to estimate effective thermal and mechanical properties of TIM systems would help optimize TIM performance with respect to these conflicting requirements. Classical models, often based on single particle solutions or regular arrangement of particles, are insufficient as real-life TIM systems contain a distriubtion of particles at high volume fractions, where classical models are invalid. In our earlier work, a computationally efficient random network model was developed to estimate the effective thermal conductivity of TIM systems [1,2]. This model is extended in this paper to estimate the effective elastic modulus of TIMs. Realistic microstructures are simulated and analyzed using the proposed method. Factors affecting the modulus (volume fraction and particle size distribution) are also studied.
Lead-Free Alternatives for Interconnects in High-Temperature Electronics
Authors: Mallampati Sandeep , Yin Liang , Shaddock David , Schoeller Harry , Cho Junghyun
Published: October 2017

Predominant high melting point solders for high temperature and harsh environment electronics (operating temperatures from 200 to 250°C) are Pb-based systems, which are being subjected to RoHS regulations because of their toxic nature. In this study, high bismuth (Bi) alloy compositions with Bi-XSb-10Cu (X from 10 wt.% to 20 wt.%) were designed and developed to evaluate their potential as high-temperature, Pb-free replacements. Reflow processes were developed to make die-attach samples made out of the cast Bi alloys. In particular, die-attach joints made out of Bi-15Sb-10Cu alloy exhibited an average shear strength of 24 MPa, which is comparable to that of commercially available high Pb solders. These alloy compositions also retained original shear strength even after thermal shock between −55°C and +200°C and high temperature storage at 200°C. Brittle interfacial fracture sometimes occurred along the interfacial NiSb layer formed between Bi(Sb) matrix and Ni metallized surface. In addition, heat dissipation capabilities, using flash diffusivity, were measured on the die-attach assembly, compared to the corresponding bulk alloys. The thermal conductivity of all the Bi-Sb alloys was higher than that of pure Bi. By creating high volume fraction of precipitates in a die-attach joint microstructure, it was feasible to further increase thermal conductivity of this joint to 24 W/m·K, which is three times higher than that of pure Bi (8 W/m·K). Bi-15Sb-10Cu alloy has so far shown the most promising performance as a die-attach material for high temperature applications (operated over 200°C). Hence, this alloy was further studied to evaluate its potential for plastic deformation. Bi-15Sb-10Cu alloy has shown limited plastic deformation in room temperature tensile testing, in which premature fracture occurred via the cracks propagated on the (111) cleavage planes of rhombohedral crystal structure of the Bi(Sb) matrix. The same alloy has, however, shown up to 7% plastic strain under tension when tested at 175°C. The cleavage planes, which became oriented at smaller angles to the tensile stress, contributed to improved plasticity in the high temperature test.
Silica Nanoparticle Formation by Using Droplet-Based Microreactor
Authors: Nikdoost Arsalan , Ozkan Alican , Kelestemur Yusuf , Demir Hilmi Volkan , Erdem E. Yegan
Published: October 2017

This paper describes a method for the synthesis of silica nanoparticles that can be later used for coating of quantum dots inside a microfluidic reactor. Here, a droplet-based system is used where two reagents were mixed inside the droplets to obtain silica. Particles in the size range of 25±2.7 nm were obtained with comparable size distribution to controlled batch-wise synthesis methods. This method is suitable to be used later to coat CdSe nanoparticles inside the microreactor.
Thermo-Optic Tuning Efficiency of Micro Ring Resonators on Low Thermal Resistance Silicon Photonics Substrates
Authors: Lei Shenghui , Shen Alexandre , Enright Ryan
Published: October 2017

Silicon photonics has emerged as a scalable technology platform for future optotelectronic communication systems. However, the current use of SiO2-based silicon-on-insulator (SOI) substrates presents a thermal challenge to integrated active photonic components such as lasers and semiconductor optical amplifiers due to the poor thermal properties of the buried SiO2 optical cladding layer beneath these devices. To improve the thermal performance of these devices, it has been suggested that SiO2 be replaced with aluminum nitride (AlN); a dielectric with suitable optical properties to function as an effective optical cladding that, in its crystalline state, demonstrates a high thermal conductivity (∼100× larger than SiO2 in current SOI substrates).

On the other hand, the tuning efficiencies of thermally-controlled optical resonators and phase adjusters, crucial components for widely tunable lasers and modulators, are directly proportional to the thermal resistance of these devices. Therefore, the low thermal conductivity buried SiO2 layer in the SOI substrate is beneficial. Moreover, to further improve the thermal performance of these devices air trenches have been used to further thermally isolate these devices, resulting in up to ∼10× increase in tuning efficiency.

Here, we model the impact of changing the buried insulator on a SOI substrate from SiO2 to high quality AlN on the thermal performance of a MRR. We map out the thermal performance of the MRR over a wide range of under-etch levels using a thermo-electrical model that incorporates a pseudo-etching approach. The pseudo-etching model is based on the diffusion equation and distinguishes the regions where substrate material is removed during device fabrication. The simulations reveal the extent to which air trenches defined by a simple etch pattern around the MRR device can increase the thermal resistance of the device.

We find a critical under-etch below which no benefit is found in terms of the MRR tuning efficiency. Above this critical under-etch, the tuning efficiency increases exponentially. For the SiO2-based MRR, the thermal resistance increases by ∼7.7× between the un-etched state up to the most extreme etch state. In the unetched state, the thermal resistance of the AlN-based MRR is only ∼4% of the SiO2-based MRR. At the extreme level of under-etch, the thermal resistance of the AlN-based MRR is still only ∼60% of the un-etched SiO2-based MRR. Our results suggest the need for a more complex MRR thermal isolation strategy to significantly improve tuning efficiencies if an AlN-based SOI substrate is used.
Numerical and Experimental Determination of Temperature Distribution in 3D Stacked Power Devices
Authors: Morgan Adam , Choobineh Leila , Fresne David , Hopkins Douglas C.
Published: October 2017

During the last few decades, the microelectronics packaging industry has moved into the 2.5D to 3D space for increased density, functionality, and speed. Similar concepts and ideas for developing 2.5D to 3D power electronics packaging are desired to achieve even greater efficiency and power density over conventional power electronics packaging methods. Wide-band gap (WBG) semiconductors, such as SiC and GaN, have accelerated the ability to shrink the volumetric size and weight of these power conversion systems, and thus improve overall power density metrics, due to their inherent high frequency, high temperature, and high voltage capabilities. WBG power semiconductor devices, with these attributes, thus make themselves excellent candidates for more aggressive packaging, compared to Si-derived packaging, in order to not only take full advantage of the WBG device ratings, but also to achieve high power densities of the overall power conversion systems. Already different/multiple power semiconductor devices are being combined by processing them together on the same die to boost electrical performance and increase power density. It can be assumed that further levels of integration will be sought after for the next levels of packaging to enable similar gains, especially with the advent of double side solderable die. The 3D stacking of die, components, and substrates creates the question of how well will each of these perform in close proximity to each other. This work focuses on the numerical simulation and experimental measurements to predict the temperature distribution of power converters built in a stacked fashion. Thermal models of a stacked power electronic switching unit — a silicon controlled rectifier and anti-parallel diode — are modeled under the assumption of equally sized die. Temperature field maps are generated for 20W to 250W of power dissipations across the power semiconductor die. Thermal models are then compared with matching experimental setups to observe the effect of switching unit placement attached to a given substrate on the die junction temperatures for various scenarios of thermal crosstalk. Results from this work are expected to aid in the development 2.5D to 3D power electronic packaging by predicting thermal performance of stacked, ultra-dense, WBG device -based packages.
Design and Development of Biometric Sensor Wearable Band Using Flexible Electronics
Authors: Lall Pradeep , Zhang Hao , Lall Rahul
Published: October 2017

Flexible electronics have a myriad of potential applications in fields such as healthcare, soldier situational awareness, soldier rehabilitation, sports performance, and textile manufacturing among other areas. The primary benefits that flexible electronics provide to both the producers and consumers are their light weight, low power consumption, efficiency, low cost of production, flexibility, and scalability. In comparison to rigid electronics, these systems would be subjected to a greater amount of mechanical and thermal stress in real-time due to their ability to be flexed, rolled, folded, and stretched. Environmental conditions such as bending, mechanical shock, water immersion, sweat, UV radiation, and temperature exposure could degrade the performance of these embedded electronic systems. At this time, there is a lack of suitable test standards and reliability data about flexible electronics manufacturing, assembly, and real-time use. In this paper, a fully flexible medical electronics system was built in full dimension to study the assembly and operation-related failure mechanisms of flexible and wearable electronics. The fabricated flexible electronics system measures pulse and muscle activity, and then transmits this data to a paired mobile device. The pulse rate was measured using an LED and a photo diode, while an electromyography (EMG) sensor was used to measure muscle activity. After collecting the data, the microcontroller sends it to a Bluetooth module, which can in turn transmit this information to a paired mobile device. Through experimentation with the fabricated flexible electronics device, unexpected degradation and quality issues were observed. In flexible PCBs, the space between the IC lead could not be isolated by the solder mask because of its large feature size and as a result, increases the risk of shortage between IC leads when subjected to mechanical stress. In addition, during the assembly process, high reflow temperature was found to subject a huge thermal stress on the connections between the solder pad and copper trace. Proper support of the solder pad should be designed to compensate the thermal stress during the reflow process, and prevent the copper joint on top of the board from being damaged. A set of guidelines for flexible medical electronics and an implementable reliability test standard can, therefore, be established for medical device manufacturers based on these reliability assessments.
Development of Packaging and Modular Control of Thermoelectric Clothes Dryer, With Performance Evaluation
Authors: Patel Viral K. , Gluesenkamp Kyle R.
Published: October 2017

This paper provides an overview of a thermoelectric heat pump clothes dryer which was developed with the aim of reducing the significant primary energy consumption attributed to residential electric clothes drying in the United States (623 TBtu/yr). The use of thermoelectric modules in place of the conventional electric resistance heater resulted in a 40% reduction in the energy consumption of the system, compared to the minimum energy efficiency standard. This was achieved for the first time for a standard test load of 8.45 lb, using a clothes dryer prototype with a thermoelectric heat pump module as the sole heating mechanism. The current experimental prototype was developed after extensive modeling, system design and control optimization, and experimental system-level evaluation of control parameters. The demonstration of improved energy consumption has laid the foundation for future development of this technology.
Thermomechanical Reliability Challenges and Goals and Design for Reliability Methodologies for Electric Vehicle Systems
Authors: Huitink David
Published: October 2017

With the anticipated growth in the electric vehicle market, advances in power electronics used in electric drivetrain, battery charging systems, etc. are delivering higher power densities, and with them, associated thermal challenges for operation in relatively closed vehicular systems. As such, the framework of reliability qualifications of electronic devices need to be reconsidered as system needs have moved beyond typical consumer electronic device needs, such as laptops or entertainment devices, where safe operation and longevity is essential to electric vehicle market viability. This work provides an overview of the reliability challenges associated with the operating environments and characteristics of power inverters in electric vehicles, particularly with respect to thermomechanical stresses. When considering the acceleration models presumed by the AEC Q100 specification for automotive electronics qualification, it is shown that inconsistencies in acceleration model form result in lack of clarity of how grades are chosen for different vehicle applications. Furthermore, the differences in vehicle drive cycles among user types show that service vehicles may have the most challenge to reliable operation, particularly in cold weather climates.

As an alternative metric for determining reliability in cyclic stresses, a novel test methodology for correlating solder fatigue life (and other thermomechanical failure modes) is proposed. The mechanical test for electronic packages is capable to disentangle the effects of temperature and design from the thermal cycling reliability such that the fundamental physics of failure can be extracted in a systematic fashion, and thereby develop better physics-based reliability acceleration models. Moreover, this novel approach enables the determination of independent stress to failure metrics that can translate risk across design and operating conditions for different system layouts without the need for multiple qualification tests.