bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural stability of the cofactor binding site in Escherichia coli serine hydroxymethyltransferase – the role of evolutionarily conserved hydrophobic contacts
Authors: Florio Rita , Chiaraluce Roberta , Consalvi Valerio , Paiardini Alessandro , Catacchio Bruno , Bossa Francesco , Contestabile Roberto
Published: November 2009

According to their fold, pyridoxal 5′‐phosphate‐dependent enzymes are grouped into five superfamilies. Fold Type I easily comprises the largest and most investigated group. The enzymes of this group have very similar 3D structures. Remarkably, the location of the cofactor in the active site, between the two domains that form a single subunit, is almost identical in all members of the group. Nonetheless, Fold Type I enzymes show very little sequence identity, raising the question as to which structural features determine the common fold. An important fold determinant appears to be the presence of three evolutionarily conserved clusters of hydrophobic contacts. A previous investigation, which used Escherichia coli serine hydroxymethyltransferase, a well characterized Fold Type I member, demonstrated the involvement of one of these clusters in the stability of the quaternary structure. The present study focuses on the role of the same cluster in the stability of the cofactor binding site. The investigation was carried out by equilibrium denaturation experiments on serine hydroxymethyltransferase forms in which the hydrophobic contact area of the cluster under study was reduced by site‐directed mutagenesis. The results obtained show that the mutations clearly affected the process of pyridoxal 5′‐phosphate dissociation induced by urea, reducing the stability of the cofactor binding site. We suggest that the third cluster promotes the formation of a bridging structural region that stabilizes the overall protein structure by connecting the two domains, shaping the cofactor binding site and participating in the formation of the quaternary structure.

Structured digital abstract

MINT‐7293394, MINT‐7293405, MINT‐7293418: eSHMT (uniprotkb:P0A825) and eSHMT (uniprotkb:P0A825) bind (MI:0407) by cosedimentation in solution (MI:0028)
A MULTILEVEL ANALYSIS OF THE EFFECT OF PROMPTING SELF‐REGULATION IN TECHNOLOGY‐DELIVERED INSTRUCTION
Authors: SITZMANN TRACI , BELL BRADFORD S. , KRAIGER KURT , KANAR ADAM M.
Published: November 2009

Two studies were conducted to examine the effect of prompting self‐regulation, an intervention designed to improve learning from technology‐delivered instruction. In Study 1, trainees who were prompted to self‐regulate gradually improved their declarative and procedural knowledge over time, relative to the other conditions, whereas test scores declined over time for trainees who were not prompted to self‐regulate. In Study 2, basic performance remained stable over time and strategic performance improved over time for trainees who were prompted to self‐regulate, relative to the other conditions, whereas performance declined over time for trainees who were not prompted to self‐regulate. Trainees’ cognitive ability moderated the effect of the prompts on basic performance and task‐specific self‐efficacy moderated the effect of the prompts on strategic performance. Prompting self‐regulation resulted in stronger performance gains over time for trainees with higher ability or higher self‐efficacy. These results demonstrate prompting self‐regulation improved performance over time, relative to the other conditions, in both online, work‐related training and laboratory settings. The results are consistent with theory suggesting self‐regulation is a dynamic process that has a gradual effect on performance and highlight the importance of using a within‐subjects design in self‐regulation research.
DISENTANGLING THE MEANING OF MULTISOURCE PERFORMANCE RATING SOURCE AND DIMENSION FACTORS
Authors: HOFFMAN BRIAN J. , WOEHR DAVID J.
Published: November 2009

We extend multisource performance rating (MSPR) construct validity research by examining the pattern of relationships between factor analytically derived MSPR rating source and performance dimension factors and externally measured constructs (e.g., assessment center dimensions, personality constructs, and intelligence). The pattern of relationships among MSPR dimensions and external constructs provides modest construct validity evidence for the MSPR dimensions. In addition, MSPR source factors were differentially correlated with externally measured constructs, suggesting that MSPR source effects represent substantively meaningful source specific variance, as opposed to bias. These findings are discussed in the context of managerial skill diagnosis and the efficacy of collecting performance data from multiple sources.
Land Transitions in the Tropics: Going Beyond the Case Studies
Authors: Uriarte María , Schneider Laura , Rudel Thomas K.
Published: November 2009

Estimates of the percent of Earth's land surface that has either been transformed or degraded by human activity range between 39 and 50 percent, with agriculture accounting for the vast majority of these changes. Although much of the focus of research on land use and cover change in the tropics has been on deforestation, ongoing socioeconomic changes both locally and globally have made land transitions in the tropics extremely fluid. In addition, feedbacks between land cover change and human behavior constrain the extent and trajectories of land transitions. The sustainability of land use systems in the tropics depends on an understanding of coupled human–natural systems that can lead to general frameworks for management and prediction. The unprecedented availability of land use/cover data together with ecological data collected at large spatial scales offer exciting opportunities for advancing our understanding of socioecological systems. We rely on six studies of land transitions in the tropics to illustrate some promising approaches and pose critical questions to guide this body of research.
Litter Decomposition Within the Canopy and Forest Floor of Three Tree Species in a Tropical Lowland Rain forest, Costa Rica
Authors: Cardelús Catherine L.
Published: November 2009

The rain forest canopy hosts a large percentage of the world's plant biodiversity, which is maintained, in large part, by internal nutrient cycling. This is the first study to examine the effects of site (canopy, forest floor) and tree species (Dipteryx panamensis, Lecythis ampla, Hyeronima alchorneoides) on decay rates of a common substrate andin situleaf litter in a tropical forest in Costa Rica. Decay rates were slower for both substrates within the canopy than on the forest floor. The slower rate of mass loss of the common substrate in the canopy was due to differences in microclimate between sites. Canopy litter decay rates were negatively correlated with litter lignin:P ratios, while forest floor decay rates were negatively correlated with lignin concentrations, indicating that the control of litter decay rates in the canopy is P availability while that of the forest floor is carbon quality. The slower cycling rates within the canopy are consistent with lower foliar nutrient concentrations of epiphytes compared with forest floor‐rooted plants. Litter decay rates, but not common substrate decay rates, varied among tree species. The lack of variation in common substrate decay among tree species eliminated microclimatic variation as a possible cause for differences in litter decay and points to variation in litter quality, nutrient availability and decomposer community of tree species as the causal factors. The host tree contribution to canopy nutrient cycling via litter quality and inputs may influence the quality and quantity of canopy soil resources.
Population Ecology of the Riparian Frog Eleutherodactylus cuneatus in Cuba
Authors: Fong G. Ansel , Hero Jean‐Marc , Viña Rolando , Bignotte‐Giró Irelis
Published: November 2009

A population of the poorly known riparian frog Eleutherodactylus cuneatus was studied for 1 yr along a mountain stream in eastern Cuba. We examined population structure, seasonal and daily activity, growth, and habitat use using mark‐recapture and call‐point counts. Juveniles were observed during all survey periods with a spike in March. Higher numbers of adults were present in May–July, associated with longer day length, warmer temperatures, and the onset of the rainy season. This was coincident with higher calling activity away from the stream, suggesting an increase in both reproductive and nonreproductive activity in the warmer months between May and September. The number of individuals peaked at 2000–2200 h, but high numbers of individuals were visible throughout the night. Lower activity levels were observed throughout the day. Population size estimates were 84–131 adults and 124–304 juveniles, with averages of 110 and 236 individuals, survival rates were high but capture probabilities were low for a 5‐d period in March 2004. Growth rate was negatively related to the size of recaptured individuals, although decreases in growth rate were slight. Frogs were found either in the water (49.7%), or in the banks and on the ground adjacent to the stream where most individuals were found on the ground under the cover of rocks, leaf litter, or large palm fronds. These results provide baseline knowledge of E. cuneatus population dynamics and ecology needed for a rapid detection of any decline this population may undergo in the future.
Infrared identification of 4U1323-619 revisited
Authors: Zolotukhin Ivan Yu. , Revnivtsev Mikhail G. , Shakura Nikolai I.
Published: November 2009

We re-examine the infrared counterpart of the dipping low-mass X-ray binary 4U1323-619. New X-ray data available from the XMM and Chandra observatories combined with archival infrared observations from the European Southern Observatory 3.6-m New Technology Telescope allow us to define a new possible counterpart. We present here its photometric properties and compare them with a simple analytical model of an accretion disc illuminated by a hot central corona.
Distribution of Chlorophyll‐ and Bacteriochlorophyll‐derived Photosensitizers in Human Blood Plasma
Authors: Dandler Jörg , Wilhelm Brigitte , Scheer Hugo
Published: November 2009

Chlorophylla and, in particular, bacteriochlorophyll a derivatives are promising candidates for photosensitizers in photodynamic therapy. The distribution of 21 (bacterio)chlorophyll derivatives among human blood plasma fractions was studied by iodixanol gradient ultracentrifugation and in situ absorption spectroscopy. Modifications of the natural pigments involved the central metal (Mg2+, Zn2+, Pd2+, none), the isocyclic ring (closed, open and taurinated), substituents at C‐3 (vinyl, acetyl, 1‐hydroxyethyl) and C‐173 (phytyl ester, free acid). Cellular blood components bound only a small fraction of the pigments. Distribution among low‐density lipoproteins (LDL), high‐density lipoproteins (HDL) and high‐density proteins (HDP) of the plasma was influenced as follows: (1) application in Cremophor® EL slightly altered pigment distribution by lipoprotein modification, (2) only very polar pigments with multiple hydrophilic substituents showed substantial HDP binding, (3) the presence of the esterifying alcohol at C‐173 caused enrichment in LDL, this was more pronounced with bacteriochlorophylls than with chlorophylls, (4) substituents at C‐3 had only little influence on the distribution, (5) Zn2+‐complexes were enriched in HDL compared to Mg2+ and Pd2+ complexes, indicating specific binding of the former. Equilibration of pigments among the different fractions was largely complete within 3 h.
In Vitro Photodynamic Activity of 5,15‐bis(3‐Hydroxyphenyl)porphyrin and Its Halogenated Derivatives Against Cancer Cells
Authors: Serra Arménio , Pineiro Marta , Santos Catarina Isabel , Rocha Gonsalves António Manuel d’A. , Abrantes Margarida , Laranjo Mafalda , Botelho Maria Filomena
Published: November 2009

5,15‐Diarylporphyrins (1‐5) with hydroxyl groups and halogens as substituents were prepared by condensation between unsubstituted dipyrromethane and halogenated m‐hydroxybenzaldehydes. Photophysical properties show that the nonhalogenated porphyrin 1 has higher fluorescence yield but lower singlet oxygen formation quantum yield than the halogenated derivatives due to the heavy atom effect. The in vitro activity of these derivatives was tested against WiDr colorectal adenocarcinoma and A375 melanoma cancer cells. All porphyrins present a much higher phototoxicity than Photofrin® with IC50 values lower than the 50 nm level for WiDr cells and 25 nm level for A375 cancer cells. The most photoactive compound is the nonhalogenated porphyrin 1 which also presents the highest uptake. Halogenated derivatives present much lower uptakes than 1. However, their photoactivity is similar to compound 1 showing that their intrinsic photoactivity (ISP) is very high. Iodinated compound 4 presents the highest ISP. The greater ability of these porphyrins to destroy cancer cells could be related to their photophysical and photochemical properties.
Increased UV‐B Radiation Affects the Viability, Reactive Oxygen Species Accumulation and Antioxidant Enzyme Activities in Maize (Zea mays L.) Pollen
Authors: Wang Shiwen , Xie Beitao , Yin Lina , Duan Liusheng , Li Zhaohu , Egrinya Eneji A. , Tsuji Wataru , Tsunekawa Atsushi
Published: November 2009

The increase in UV‐B radiation reaching the earth’s surface has prompted extensive studies on the effects of UV‐B on plants. However, most of these studies have not addressed the close characteristics related to future survival of plant populations. The purpose of this study was to investigate the effects of UV‐B radiation on reactive oxygen species (ROS) accumulation and antioxidant defense system in relation to germination, tube length and viability of maize pollen. Our results indicate that increased UV‐B radiation decreased the pollen germination rate and tube length in vitro and also its fertilization ability in the field. Production of O2•− and H2O2 increased by UV‐B radiation treatment, and their continuous accumulation resulted in lipid peroxidization. The activities of superoxide dismutase, catalase, peroxidase and DPPH‐radical scavenging were decreased by increased UV‐B radiation. The increased ROS and lipid peroxidization, and decreased activities of the antioxidants may be attributed to the effects of UV‐B radiation on pollen germination, tube growth and fertilization ability.
Macular changes detected by Fourier‐domain optical coherence tomography in patients with hypotony without clinical maculopathy
Authors: Lima Verônica C. , Prata Tiago S. , Castro Dinorah P. E. , Castro Leonardo C. , De Moraes Carlos G. V. , Mattox Cynthia , Rosen Richard B. , Liebmann Jeffrey M. , Ritch Robert
Published: November 2009

Purpose:  To investigate macular changes in eyes with postoperative hypotony without clinical maculopathy using high‐resolution Fourier‐domain optical coherence tomography (FD‐OCT).

Methods:  Fourteen eyes of 12 patients with postoperative intraocular pressure (IOP) ≤ 6 mmHg for at least 4 weeks but with no detectable clinical features associated with hypotony maculopathy were imaged by FD‐OCT prospectively. Images were analysed by two retina specialists masked to clinical findings.

Results:  Most patients were female (83%) and myopic (75%) with a mean age of 65 ± 17 [standard deviation (SD)] years (range 2–86 years). Mean central corneal thickness was 519 ± 34 μm [95% confidence interval (CI) 502–537] and mean IOP before surgery was 20 ± 8 mmHg (95% CI 15–24). During the period of hypotony (mean 15 ± 6 weeks), the average mean IOP was 4 ± 1 mmHg (95% CI 3–5). Abnormal FD‐OCT findings (retinal folds and/or intraretinal fluid) were present in eight eyes. These patients had a higher rate of visual symptoms (75% versus 17%), visual acuity loss (≥ 2 lines; 63% versus 17%) and increased mean foveal thickness (250 ± 26 versus 210 ± 12 μm; p < 0.01, Mann–Whitney U‐test) compared with those with normal FD‐OCT.

Conclusion:  FD‐OCT identified subclinical macular abnormalities in over half of the eyes with postoperative hypotony. These findings were accompanied by visual disturbances and central macular thickening. FD‐OCT can be an important diagnostic tool for this disorder when clinical features are absent.
DECHLORINATION BY ULTRAVIOLET RADIATION: A SUITABLE ALTERNATIVE TO ACTIVATED CARBON IN DIALYSIS WATER SYSTEMS?
Authors: James Ray
Published: November 2009

Chlorine‐based products are widely used in the water supply industry, and the potential for adverse effects in the haemodialysis setting is well documented. To date, the most commonly used method of chlorine removal has been granular activated carbon filters. An increasingly popular method of dechlorination is the use of high intensity, broad‐spectrum UV systems to reduce both free chlorine and combined chlorine compounds (chloramines) into easily removed by‐products.

UV radiation has been successfully used in the pharmaceutical and food industries to destroy free chlorine and/or chloramines present in water, and kill all known spoilage microorganisms including bacteria, viruses, yeasts and moulds (and their spores). This nonchemical method can offer significant advantages and benefits compared to conventional dechlorination technologies currently employed in dialysis water systems.

Whilst UV treatment at 254 nm wavelength has been routinely used for disinfection purposes in dialysis water systems, this paper considers whether UV radiation can be used as an alternative to more traditional methods of chlorine removal.
Increased Ca2+ leak and spatiotemporal coherence of Ca2+ release in cardiomyocytes during β‐adrenergic stimulation
Authors: Ogrodnik Jakob , Niggli Ernst
Published: November 2009

β‐Adrenergic receptor (β‐AR) stimulation of cardiac muscle has been proposed to enhance Ca2+ release from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs). However, the anticipated increase in RyR Ca2+ sensitivity has proven difficult to study in intact cardiomyocytes, due to accompanying alterations in SR Ca2+ content, inward Ca2+ current (ICa) and diastolic cytosolic Ca2+ concentration ([Ca2+]i). Here, we studied whole‐cell Ca2+ release and spontaneous Ca2+ leak (Ca2+ sparks) in guinea‐pig ventricular myocytes with confocal Ca2+ imaging before and during β‐AR stimulation by isoproterenol (Iso), but under otherwise nearly identical experimental conditions. The extent of SR Ca2+ loading was controlled under whole‐cell voltage‐clamp conditions. UV flash‐induced uncaging of Ca2+ from DM‐nitrophen was employed as an invariant trigger for whole‐cell Ca2+ release. At matched SR Ca2+ content, we found that Iso enhanced the spatiotemporal coherence of whole‐cell Ca2+ release, evident from spatially intercorrelated release and accelerated release kinetics that resulted in moderately (∼20%) increased release amplitude. This may arise from higher RyR Ca2+ sensitivity, and was also reflected in spontaneous SR Ca2+ leak. At comparable SR Ca2+ content and cytosolic [Ca2+]i, we observed a ∼4‐fold increase in Ca2+ spark frequency in Iso that also appeared in quiescent cells within 2 min without increased SR Ca2+ content. This was likely to have been mediated by Ca2+/calmodulin‐dependent protein kinase (CaMKII), rather than cAMP dependent protein kinase (PKA). We conclude that Iso increases the propensity of RyRs to open, both in response to rapid elevations of [Ca2+]i and at diastolic [Ca2+]i. While this could be beneficial in enhancing and synchronizing systolic whole‐cell SR Ca2+ release, the same behaviour could also be proarrhythmogenic during diastole.
On the Generalized Frequency Response Functions of Volterra Systems
Authors: Jing Xingjian , Lang Ziqiang
Published: November 2009

The generalized frequency response function (GFRF) for Volterra systems described by the nonlinear autoregressive with exogenous input model is determined by a new mapping function based on its parametric characteristic. The nth-order GFRF can now be directly determined in terms of the first order GFRF, which represents the linear component of the system, and model parameters, which define system nonlinearities. Some new properties of the GFRFs are therefore developed. These results can analytically reveal the linear and nonlinear effects on system frequency response functions, and also demonstrate the relationship between convergence of system Volterra series expansion and model parameters.
Nanoscale Friction Dynamic Modeling
Authors: Landolsi Fakhreddine , Ghorbel Fathi H. , Lou Jun , Lu Hao , Sun Yuekai
Published: November 2009

Friction and system models are fundamentally coupled. In fact, the success of models in predicting experimental results depends highly on the modeling of friction. This is true at the atomic scale where the nanoscale friction depends on a large set of parameters. This paper presents a novel nanoscale friction model based on the bristle interpretation of single asperity contact. This interpretation is adopted after a review of dynamic friction models representing stick-slip motion in macrotribology literature. The proposed model uses state variables and introduces a generalized bristle deflection. Jumping mechanisms are implemented in order to take into account the instantaneous jumps observed during 2D stick-slip phenomena. The model is dynamic and Lipchitz, which makes it suitable for future control implementation. Friction force microscope scans of a muscovite mica sample were conducted in order to determine numerical values of the different model parameters. The simulated and experimental results are then compared in order to show the efficacy of the proposed model.
Thermal Stress Analysis of SMT PQFP Packages and Interconnections
Authors: Lau J. H.
Published: November 2009

An elasto-plastic analysis of the thermal stresses and strains in a surface mounted plastic-quad-flat-pack (PQFP) assembly by using a 3-D finite element method is presented in this paper. Detailed stress and strain distributions and whole-field displacements of the assembly are also provided for a better understanding of its mechanical behavior during thermal cycling. It was found that the stresses and strains in the PQFP solder joint are smaller than those in the plastic-leaded-chip-carrier (PLCC) solder joint. The results presented herein should be useful in the design for reliability of this class of surface mount assemblies.
An Interfacing Software Package for Thermal Analysis: Application to Microelectronics
Authors: Hadim A. , Chang A. T. , Chu A. , Yskamp A.
Published: November 2009

A software package called: INterfacing Software for Thermal ANalysis (INSTAN) is developed to interface finite element general purpose programs with finite-difference thermal network analyzers for detailed analysis of complex thermal problems. The finite element mesh is used to generate the thermal network representation of the problem. INSTAN performs automatically the thermal network calculations and generates a complete input file for the thermal analysis program. The INSTAN software package is a powerful modeling tool which uses the preprocessing and postprocessing features available in a finite element program. It has also the flexibility and heat transfer calculation capabilities of a finite-difference program. It can handle problems with three-dimensional irregular geometries, time and temperature dependent properties, and anisotropic materials. The software possesses enhanced capabilities that make it suitable for thermal analysis of microelectronic equipment.
Slow Crack Growth in Glasses and Ceramics Under Residual and Applied Stresses
Authors: Erdogan F.
Published: November 2009

The problem of slow crack growth under residual stresses and externally applied loads in plates is considered. Even though the technique developed to treat the problem is quite general, in the solution given it is assumed that the plate contains a surface crack and the residual stresses are compressive near and at the surfaces and tensile in the interior. The crack would start growing subcritically when the stress intensity factor exceeds a threshold value. Initially the crack faces near the plate surface would remain closed. A crack-contact problem would, therefore, have to be solved to calculate the stress intensity factor. Depending on the relative magnitudes of the residual and applied stresses and the threshold and critical stress intensity factors, the subcritically growing crack would either be arrested or become unstable. The problem is solved and examples showing the time to crack arrest or failure are discussed.
Chemically Driven Deformation of Polymers
Authors: Hui C.-Y. , Wu K.-C. , Lasky Ronald C. , Kramer Edward J.
Published: November 2009

Chemically driven deformation of polymer glasses is important in a variety of electronic packaging applications ranging from stripping of photoresists to diffusion of processing liquids into printed circuit boards. The swelling of such glasses by small molecules requires the deformation of polymer chains, a deformation that can be modelled as driven by an osmotic pressure. Equations governing the rate of this process are developed and the predictions are compared with the results of experiments in which the volume fraction φ of iodohexane (IOH) sorbed at the surface of polystyrene is measured as a function of exposure time. Once a critical φ is reached, a diffusion front develops and moves into the polymer at a constant velocity. The velocity V of this front can be predicted quantitatively from V=D(φm)a′(φm)a(φm)∂φ∂tφm where D is the diffusion coefficient of the IOH in the glass, a, and a′ are the activity of IOH and its derivative with respect to φ and the subscript m signifies that the quantities are evaluated at the volume fraction of the maximum osmotic pressure ahead of the front. The φ(t) and V predicted by a pressure dependent viscous swelling model for ∂φ/∂t are in good agreement with the experimental results at low IOH activities.
Finite Element Predictions of Free Convection Heat Transfer Coefficients of Simulated Electronic Circuit Boards
Authors: Rajakumar C. , Johnson D.
Published: November 2009

A numerical simulation of the buoyancy-induced flow around microelectronic components mounted on a circuit board has been performed using the finite element method. The circuit board is modeled by a vertical plate on which rectangular strip heating surfaces are mounted. Computations have been performed in two-dimensional plane applying a simplifying assumption that the circuit board and the strip heating surfaces are infinitely long. The Navier-Stokes, the flow continuity and the energy equations for laminar flow have been considered in the finite element discretizations. Results of the computations are presented in the form of temperature contour plots and velocity vector plots in the flow field. The convection heat transfer coefficients at the surface of the microelectronic components are presented as a function of their height. The convection coefficients computed have been compared with experimental correlations of free convection heat transfer found in the literature.
A Transient Technique to Measure the Temperature Coefficient of Resistance for Thin Film Resistors
Authors: Sammakia Bahgat , Vadala Phillip , Homa Thomas
Published: November 2009

The temperature coefficient of resistance (TCR) is defined as: TCR=(R2−R1)R1×1(t2−t1) where R2 and R1 are the resistances measured at temperatures t1 and t2, respectively. The conventional TCR measurement method consists of measuring resistance at room temperature, then heating the resistor to a known higher temperature, then measuring the resistance again. This technique is very accurate and repeatable, however it is slow and cumbersome because it takes a moderate amount of time for the sample to reach steady state in an oven before the resistance can be measured. The present study proposes a new transient technique for measuring TCR. Thin film resistors are heated by passing a constant electric current through them. At an arbitrarily set time, the resistor temperature is estimated from the known transient conduction solution for a uniform flux surface imbedded in a semi-infinite medium. Measurements of the resistance at that time, along with the resistance at the initial (usually room) temperature will now permit the calculation of TCR. The method was found to be very fast, repeatable, and in good agreement with the conventional technique.
Observations on the Mechanisms of Fatigue in Eutectic Pb-Sn Solder Joints
Authors: Tribula D. , Grivas D. , Frear D. R. , Morris J. W.
Published: November 2009

Near-eutectic Pb-Sn solders are widely used for joints in electrical devices. These are liable to failure by thermal fatigue during operation of the device. Since the thermal fatigue load is often in shear, mechanisms of thermal fatigue in shear are of particular interest. Recent research has shown that the thermal fatigue of eutectic solders in shear is preceded by the formation of bands of coarsened material in the eutectic microstructure, which concentrate the deformation and cause the nucleation of fatigue cracks. Such coarsened bands are also observed in isothermal fatigue and unidirectional creep in shear. Since creep experiments are relatively simple to conduct and analyze, these have been used to study the formation and growth of coarsened bands. The mechanism includes three steps: the formation of inhomogeneous shear bands, the onset of recrystallization in the shear band to create a planar region of coarsened material, and the propagation of the coarsened band by progressive recrystallization at its tip. The results are applied to thermal fatigue and some of their implications are discussed.
Ceramic Materials for Electronic Packaging
Authors: Rabinovich E. M.
Published: November 2009

The paper reviews ceramic materials that are used or can be used in electronic packaging. Main attention is given in relatively new packaging materials such as highly thermal conductive AlN and SiC (BeO-doped) or low-firing cordierite and spodumene glass-ceramics. Application of sol-gel processes in preparation of ceramic powders is discussed.
Calculated Interfacial Stresses in Elongated Bimaterial Plates Subjected to Bending
Authors: Suhir E.
Published: November 2009

In this analysis we suggest a simple engineering method for the evaluation of the interfacial stresses in elongated bimaterial plates subjected to bending. The taken approach enables one to satisfy the boundary conditions at the plate’s ends within the framework of the elementary beam, or long-and-narrow plate, theory. The analysis is carried out in application to bending on a circular mandrel, which is regarded by many reliability engineers as a suitable test vehicle for the evaluation of the mechanical performance of the attachment material in adhesively bonded and soldered assemblies in electronic packaging.
Designing Electronic Products to Withstand the Distribution Environment
Authors: Peache R. , Privitera D. , Gasper J. , Heasty D.
Published: November 2009

During the past few years product mechanical shock fragility analysis has become an accepted part of the product design cycle at Wang Laboratories, Inc. This analysis is used to insure that the product has sufficient strength to work in the user environment without problem, and to survive the shipping environment from Wang to the customer without requiring excessively expensive shipping packaging. In some cases it is possible to make relatively inexpensive changes in the product which increase the mechanical shock resistance of that product. The cost of these changes is weighed against the cost of the amount of cushioning and related recurring costs needed in the shipping package to provide protection for the lower shock level the unmodified product is capable of withstanding. If the cost of product modification is lower than the cost of the increased package materials, freight and storage (increased cube), the modification is made to the product. A brief background of shock testing products is given, with particular attention to the use of ASTM D 3332. This process is presented as a specific case study on a recently developed CRT monitor.
Solder Fillet Height Criteria for Surface Mounted Chip Components
Authors: Rafanelli A. J.
Published: November 2009

An evaluation has been performed to determine the effects of solder joint fillet height variations of blue tantalum chip capacitors (CWR06) when exposed to thermal shock. Capacitors were soldered to ceramic multilayer interconnect boards (MIBs) used on U.S. Navy Format D standard electronic modules (SEM). Three fillet heights were tested; 100 percent of the capacitor height, 50 percent of the capacitor height, and a minimum amount to wet the bottom edges and face of the components. Results showed that components with 50 percent and minimum wetting solder disclosed no detrimental conditions whereas those with the 100 percent fillet height showed cracks in the MIB material during and at the end of 125 cycles of thermal shock. Accordingly, it is concluded that the maximum desired solder joint fillet height for chip capacitors mounted on ceramic substrates is fifty percent (50 percent) of the component height. This conclusion agrees with research on ceramic chip components mounted on organic substrates in which the desirable condition is to have low solder volumes.
The Military Specifications for Hybrid Microelectronics and How They Influence Future Hybrid Technology
Authors: Spears W. J.
Published: November 2009

Introduced almost five years ago and first implemented on 29 November 1985, MIL-STD-1772 has had a profound impact upon the military hybrid microelectronics industry. Through their efforts to qualify their facilities to MIL-STD-1772, a growing number of hybrid manufacturers have proven their understanding of and their compliance to the applicable portions of MIL-M-38510 and MIL-STD-883. This has led to a wholesale raising of the “Quality Consciousness” in the hybrid microelectronics industry and it has fostered a higher degree of customer confidence in the hybrid facilities which have qualified. Four years since its implementation, it can be stated that MIL-STD-1772 has accomplished its purpose of assuring the highest level of reliability possible in the products of qualified hybrid manufacturers. This paper is not only a survey of how this has been accomplished, but it also discusses the effects that the MIL-Specs continue to have upon the design and manufacture of military hybrid microelectronics.
Can Power Cycling Life of Solder Joint Interconnections be Assessed on the Basis of Temperature Cycling Tests?
Authors: Suhir E.
Published: November 2009

We discuss how temperature cycling test conditions could be modified to be used for a tentative evaluation of the fatigue life of solder joint interconnections in surface mounted devices subjected to power cycling.
A New Approach for Erosion Prediction Due To Fly Ash
Authors: Kotwal R. , Tabakoff W.
Published: November 2009

With increasing interest in the burning of coal in industrial gas turbines, there is also concern for the precise determination of the erosive effects on the turbine components. Series of experiments were conducted to determine the effects of fly ash constituents, particle size, particle velocity, angle of attack and target temperature on the erosion of iron and nickel base alloys. Based on the experimental results, a semi-empirical equation has been obtained for the prediction of the erosion losses. This equation provides a new technique for predicting the metal erosion due to the fly ash produced by the conventional burning of coal.
On the Pressure Losses Due to the Tip Clearance of Centrifugal Blowers
Authors: Ishida M. , Senoo Y.
Published: November 2009

The pressure distribution along the shroud is measured for three types of centrifugal impeller at seven different values of tip clearance each. The change of input power due to a change of tip clearance is related to the effective blockage at the impeller tip. Since the change of input power is little for the test cases, the variation of local pressure gradient along the shroud is mostly attributed to the change of local pressure loss. The local pressure loss is related to the local tip clearance ratio and to the local pressure gradient based on the deceleration of relative velocity in the impeller. Since the local pressure gradient is largest near the throat of the impeller, for many impellers the clearance ratio at the throat is used as the representative value. The tip clearance loss is related to the clearance ratio and the pressure rise based on the deceleration of relative velocity in the impeller. A good correlation is observed in all cases at various flow rate.
Vorticity Modeling of Blade Wakes behind Isolated Annular Blade-Rows: Induced Disturbances in Swirling Flows
Authors: Tan C. S.
Published: November 2009

A general analysis is proposed for studying the fluid-mechanical behavior of blade wakes from an annular blade-row in highly swirling flow. The coupling between the centrifugal force and the vorticity, which is inherent to highly swirling flows, can significantly modify the wake behavior from that in a two-dimensional situation. In steady flow, theoretical considerations show that a blade wake consists primarily of two distinct types of vorticity: (1) trailing vorticity shed from the blade due to a spanwise variation in blade circulation; and (2) vorticity associated with defects in stagnation pressure (or rotary stagnation in relative coordinate system). Three types of disturbances can be identified in the resulting three-dimensional disturbance field: (1) the exponentially decaying type (potential, irrotational), (2) the purely convected type (rotational), and (3) the nonconvected type (both rotational and irrotational parts). Type (3) arises because of the interaction of centrifugal and Coriolis forces with (1) and (2). It is found that near the blade row the nonconvected disturbances grow linearly in magnitude with the axial distance. However, although those nonconvected disturbances associated with the trailing vorticity (also called Beltrami vorticity) persist for moderate distances downstream, they eventually decay inversely with the axial distance, irrespective of the types of swirl distribution. In contrast, those parts of nonconvected disturbances which are induced by the vorticity caused by (rotary) stagnation pressure defects persist indefinitely downstream for any type of swirl other than free-vortex. In the limit of free-vortex swirl, all disturbances decay at least inversely with the axial distance downstream.
The Effect of Aerodynamic Phase Lag on the Twin Vibration Mode Model of Aeroengine Fan Flutter
Authors: Ford R. A. J.
Published: November 2009

An earlier paper analyzed aeroengine fan flutter in terms of twin orthogonal vibration modes in the fan. This paper extends the analysis by incorporating variable aerodynamic phase lags between a blade motion and the resulting aerodynamic forces. The extended analysis predicts two independent kinds of flutter. If the total damping within each mode is negative, each mode develops a self-sustaining vibration at its own natural frequency. This was not predicted by the earlier twin mode analysis. Even when the damping in each mode is positive an interaction between the modes can cause flutter under some conditions. This behavior is basically of the form described in the earlier paper, but there are significant detailed changes when variable aerodynamic phase lags are introduced.
Preliminary Design Analysis of a Catalytic Ceramic Structure in a Turbine Combustor
Authors: Hung W. S. Y. , Dickson W. H. , DeCorso S. M.
Published: November 2009

Analysis and design of a catalytic ceramic element and its support structure in a turbine combustor for low emission application have been performed. Preliminary analysis including a survey of literature has helped identify certain design considerations and conceptual designs of the catalytic ceramic element. A thermo-mechanical analysis of the major components in these conceptual designs has been performed for both steady-state and transient (shut-down) situations. Consequently, an arrangement to build a viable catalytic ceramic combustor element has been identified which is expected to perform its mechanical functions.
Calculations of Three-Dimensional, Viscous Flow and Wake Development in a Centrifugal Impeller
Authors: Moore J. , Moore J. G.
Published: November 2009

A partially-parabolic calculation procedure is used to calculate flow in a centrifugal impeller. This general-geometry, cascade-flow method is an extension of a duct-flow calculation procedure. The three-dimensional pressure field within the impeller is obtained by first performing a three-dimensional inviscid flow calculation and then adding a viscosity model and a viscous-wall boundary condition to allow calculation of the three-dimensional viscous flow. Wake flow, resulting from boundary layer accumulation in an adverse reduced-pressure gradient, causes blockage of the impeller passage and results in significant modifications of the pressure field. Calculated wake development and pressure distributions are compared with measurements.
Techniques for Aerodynamic and Turbulence Measurements in Turbomachinery Rotors
Authors: Lakshminarayana B.
Published: November 2009

The objective of this paper is to review the techniques employed for the measurement of flow in turbomachinery rotors. Only nonoptical techniques are included. Measurement of the following properties are covered: three-dimensional mean velocity, turbulence intensity and Reynolds stresses, static and stagnation pressures, and blade surface measurement. Both the conventional as well as the hot-wire/film techniques, including both the rotating- and the stationary-probe measurements, are reviewed. A brief description of various rotating-probe traverse mechanisms and rotor flow data transmission systems in use is also included.
Spanwise Mixing in Multistage Axial Flow Compressors: Part II—Throughflow Calculations Including Mixing
Authors: Gallimore S. J.
Published: November 2009

The important influence of spanwise mixing on the flow through multistage axial compressors has been investigated by incorporating the effect into an axisymmetric streamline curvature throughflow program. The mixing was modeled as a turbulent diffusion process based on the experimental observations reported in Part I of this paper, which showed that this was the dominant physical mechanism. The inclusion of the mixing was found to be crucial in accurately predicting spanwise variations of exit total temperature in multistage machines. The effect of mixing on loss distributions inferred from measurements was found to be significant so that upstream loss sources could only be determined from downstream distributions when the effect of mixing was included.
Laminar and Transitional Boundary Layer Structures in Accelerating Flow With Heat Transfer
Authors: Rued K. , Wittig S.
Published: November 2009

The accurate prediction of heat transfer coefficients on cooled gas turbine blades requires consideration of various influence parameters. The present study continues previous work with special efforts to determine the separate effects of each of several parameters important in turbine flow. Heat transfer and boundary layer measurements were performed along a cooled flat plate with various freestream turbulence levels (Tu = 1.6−11 percent), pressure gradients (k = 0−6 × 10−6), and cooling intensities (Tw/T∞ = 1.0−0.53). Whereas the majority of previously available results were obtained from adiabatic or only slightly heated surfaces, the present study is directed mainly toward application on highly cooled surfaces as found in gas turbine engines.
Systematic Study of Film Cooling With a Three-Dimensional Calculation Procedure
Authors: Demuren A. O. , Rodi W. , Scho¨nung B.
Published: November 2009

The present paper describes three-dimensional calculations of film cooling by injection from a single row of holes. A systematic study of the influence of different parameters on the cooling effectiveness has been carried out. Twenty-seven test cases have been calculated, varying the injection angle (α = 10/45/90 deg), the relative spacing (s/D = 1.5/3/5) and the blowing rate (M = 0.5/1/2) for the same mainstream conditions. The governing three-dimensional equations are solved by a finite volume method. The turbulent stresses and heat fluxes are obtained from a k–ε model modified to account for nonisotropic eddy viscosities and diffusivities. Examples of predicted velocity and temperature distributions are presented and compared with available experimental data. For all the test cases, the laterally averaged cooling effectiveness is given. On the whole, the agreement with experiments is fairly good, even though there are discrepancies about details in some of the cases. The influence of the individual parameters on the film cooling effectiveness is predicted correctly in all cases. This influence is discussed in some detail and the parameter combination with the best overall cooling performance is identified.
Flat-Plate Film Cooling With Steam Injection Through One Row and Two Rows of Inclined Holes
Authors: Han J. C. , Mehendale A. B.
Published: November 2009

Experiments have been performed to investigate the film-cooling characteristics with steam injection through one row (7 tubes) and two rows (13 tubes) of holes, inclined at an angle of 35 deg, over a flat plate. The spacing between the holes as well as the distance between the rows is 2 1/2 hole diameters. Data have been obtained for both steam and air film-cooling effectiveness at different axial and lateral locations downstream of the injection holes. The blowing rate M varied from 0.2 to 1.5. In the case of one-row injection, the results show that the film-cooling effectiveness with steam injection is about 50 to 100 percent higher than that with air injection at downstream locations, depending upon the blowing rate; however, the increase in film-cooling effectiveness is reduced near the injection hole region at high blowing rates. In the case of two-row injection, the laterally averaged film cooling effectiveness η can be correlated with the two-dimensional film-cooling parameter ξ. The η with steam injection is about 80 to 100 percent higher than that with air injection at low blowing rates and/or at downstream locations (ξ ≥ 15). However, the increase in η with steam injection is reduced near the injection hole region and/or at high blowing rates (ξ ≤ 15).
The Development of a Second Generation of Controlled Diffusion Airfoils for Multistage Compressors
Authors: Behlke R. F.
Published: November 2009

The evolution of Controlled Diffusion Airfoils is traced from inception of the theoretical design model to demonstration of significant performance gains at engine operating conditions in a multistage compressor rig. The proven aerodynamic benefits and versatility of first-generation Controlled Diffusion Airfoil blade elements are extended to the endwall flow region using an Integrated Core/Endwall Vortex design model to produce a new full-span optimized second-generation Controlled Diffusion design. Highlighted are the essential roles of extensive cascade, low-speed, large-scale, and high Mach number compressor rig testing in developing and substantiating the second-generation Controlled Diffusion technology resulting in a 1.5 percent increase in efficiency and 30 percent increase in surge-free operation relative to first-generation Controlled Diffusion Airfoils.