bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of SiC JFETs and its Application in Extreme Temperature (over 450°C) Circuit Design
Authors: Yang Jie , Fraley John , Western Bryon , Schupbach Marcelo , Lostetter Alexander B.
Published: May 2010

In order to facilitate the circuit design and simulation at extreme temperatures, APEI, Inc. fully characterized a custom-built SiC VJFET transistor at temperatures up to 525 °C and built a Spice model based on the characterization data. The temperature effects were also formulized in this Spice model to ensure its uniform applicability over the entire temperature range. Test circuits of a differential amplifier and a multivibrator were built and tested from room temperature up to 450 °C to validate the proposed SiC JFET model, which could be widely applied in Spice based circuit simulation packages.
Concentrated Chloride-Based Epitaxial Growth of 4H-SiC
Authors: Henry Anne , Leone Stefano , Andersson Sven , Kordina Olof , Janzén Erik
Published: May 2010

A chloride-based CVD process has been studied in concentrated growth conditions. A systematic study of different carrier flows and pressures has been done in order to get good quality epilayers on 8° off and on-axis substrates while using very low carrier flows. Hydrogen chloride (HCl) was added to the standard gas mixture to keep a high growth rate and to get homo-polytypic growth on on-axis substrates. The carrier flow was reduced down to one order of magnitude less than under typical growth condition. By lowering the process pressure it was possible to reduce precursor depletion along the susceptor which improved the thickness uniformity to below 2% variation (σ/mean) over a 2” diameter wafer.
Effect of Band-Edge Interface Traps and Transition Region Mobility on Transport in 4H-SiC MOSFETs
Authors: Potbhare Siddharth , Akturk Akin , Goldsman Neil , Lelis Aivars J. , Dhar Sarit , Agarwal Anant K.
Published: May 2010

We present physics based models for the occupation of interface traps and the mobility of the transition layer found in 4H-SiC MOSFETs and extract values for the same using combined numerical simulation and experimental characterization. The Si-C-O transition layer found in 4H-SiC MOS devices is electrically modeled as having a doping dependent mobility that is different from the regular bulk 4H-SiC bulk mobility. Compared to the high intrinsic bulk mobility of 4H-SiC, the transition layer intrinsic mobility was extracted to be approximately 165cm2/Vs. The occurrence of the excessive high density of interface traps near the conduction band edge led us to develop a new model for the occupation of traps lying inside the conduction band itself. Due to the conduction band trap densities being comparable to the conduction band electron states, a non-zero probability exists for their occupation, which causes the occupied trap densities to be very high in strong inversion. Detailed numerical simulations and corroboration with experiment have been performed to calibrate the models and extract physical parameter values.
Wafer-Level Hall Measurement on SiC MOSFET
Authors: Yu Liang Chun , Cheung Kin P. , Tilak Vinayak , Dunne Greg , Matocha Kevin , Campbell Jason P. , Suehle John S. , Sheng Kuang
Published: May 2010

Low channel mobility is one of the biggest challenges to commercializing SiC MOSFETs. Accurate mobility measurement is essential for understanding the mechanisms that lead to low mobility. The most widely used effective mobility measurements overestimate the inversion charge for devices that have high level of defects. Mobility measured by the Hall effect is more accurate; however the conventional Hall mobility measurement is tedious. In this work, we demonstrate a wafer-level Hall measurement technique, which is simple and convenient to implement. With this method, extensive study of the mobility degradation is possible.
Isotropic Channel Mobility in UMOSFETs on 4H-SiC C-Face with Vicinal Off-Angle
Authors: Harada Shinsuke , Ito Sachiko , Kato Makoto , Takatsuka Akio , Kojima Kazutoshi , Fukuda Kenji , Okumura Hajime
Published: May 2010

UMOSFET is theoretically suitable to decrease the on-resistance of the MOSFET. In this study, in order to determine the cell structure of the SiC UMOSFET with extremely low on-resistance, influences of the orientation of the trench and the off-angle of the wafer on the MOS properties are investigated. The channel resistance, gate I-V curves and instability of threshold voltage are superior on the {11-20} planes as compared with other planes. On the vicinal off wafer, influence of the off-angle disappears and the properties on the equivalent planes are almost the same. The obtained results indicate that the extremely low on-resistance with the high stability and high reliability is possible in the SiC UMOSFET by the hexagonal cell composed of the six {11-20} planes on the vicinal off wafer, and actually an extremely low channel resistance was demonstrated on the hexagonal UMOSFET with the six {11-20} planes on the vicinal off wafer.
Characterization of the Morphology of Si in the Modified Al-Si Alloys
Authors: Gergely Gréta , Gácsi Zoltán
Published: May 2010

One of the methods of melt-treatment of Al-Si alloys is the modification that plays a very significant role in the development of (mechanical) properties of finished product. There are a lot of well-known processes for the investigation of effectiveness of modification but an objective, exact result cannot be obtained in each case by using these methods. The method suitable for the classifi-cation of modification worked out by us was developed by integrating two methods namely the comparison by means of etalon-images and the integration of measurement of morphological pa-rameters. This method is relatively simple, does not demand lots of measurements and gives reliable results.
Effect of the High Rotating Magnetic Field (min. 30 mT) on the Unidirectionally Solidified Structure of Al7Si0.6Mg Alloy
Authors: Kovács Jenő , Rónaföldi Arnold , Roósz András
Published: May 2010

The topic of this paper is the unidirectional solidification of ternary Al7Si0.6Mg aluminium alloy in a rotating magnetic field of 30 -150 mT and the characterisation of effect of stirring on the solidified structure. During performing the experiment-series, one of the three solidification parameters (temperature gradient, solid/liquid interface velocity and magnetic induction) was continuously changed and the other two of them was kept on a constant value. The effect of these parameters on the developed structures was analysed during the evaluation of the experimental results. Moreover, the extent of Si-macrosegregation as well as the change of the secondary dendrite arm spacing were investigated on the longitudinal and cross-sections of samples as a function of the three basic parameters.
Comparison between Simulation and Experimental Results of the Effect of RMF on Directional Solidification of Al-7wt.%Si Alloy
Authors: Budenkova Olga , Noeppel Anne , Kovács Jenő , Rónaföldi Arnold , Roósz András , Bianchi Anne Marie , Baltaretu Florin , Medina Mabel , Fautrelle Yves
Published: May 2010

A numerical investigation of directional solidification of Al-7wt.%Si alloy stirred by a rotating magnetic field is compared with experimental results. Experimental study of such process has revealed periodical macrosegregation in axial direction of the samples in the shape of a “Christmas tree”. Similar macrosegregation pattern is obtained in simulations for the two values of magnetic field. Numerical simulations have shown also that formation of the periodical structure depends not only on the external conditions but on the permeability of the mushy zone.
Shear Enhanced Heterogeneous Nucleation in AZ91D Alloy
Authors: Fan Z. , Xia M. , Wang Y. , Arumuganathar S. , Scamans Geoff M.
Published: May 2010

Intensive shearing was applied to AZ91D Mg-alloy melts at temperatures above its liquidus (600oC) by using a twin-screw mechanism. The sheared melt was then cast into a TP1 mould (Aluminium Association’s standard test mould with 3.5K/s cooling rate) for microstructural examination. Alloy melts, both with and without shearing, were also filtered using a pressurized filtration technique to collect oxides and other second phase particles. The experimental results showed a significant grain refinement of AZ91D alloy through enhancement of heterogeneous nucleation. Based on the experimental results, a multi-step heterogeneous nucleation mechanism has been proposed: (1) intensive melt shearing converts oxide films and clusters into fine and well-dispersed particles with a narrow size distribution; (2) the dispersed oxide particles act as potent sites for nucleation of Al8Mn5 intermetallic particles; (3) during the further cooling, Al8Mn5 intermetallic particles nucleate the -Mg phase, resulting in a fine and uniform microstructure. The proposed multi-step nucleation mechanism will be discussed in terms of the effect of forced wetting, particle size and particle size distribution on the enhancement of heterogeneous nucleation.
Solidification Circumstances in Case of Al-Si Cylinderhead Castings
Authors: Fegyverneki György
Published: May 2010

The requirements are getting higher and higher at the vehicle industry area first of all at cylinderhead casting. The customers would like to buy high performanced engines with low consumption.The brandnew trend in the car industry area is the „downsizing” nowdays. It means that the cylinderhead capacity is low but the accessible performance is much bigger than earlier. The problem is that the wallthickness of the cylinderheads will be less. That is the reason why the strength properties and requirements are getting stronger.
Phase Selection in Undercooled Melts of Peritectic Cu-Ge Alloys
Authors: Gao J.R. , Luo G. , Luo X.H.
Published: May 2010

Phase selection in undercooled melts of Cu-14.8Ge and Cu-18Ge compositions was investigated using the electromagnetic levitation technique in combination with substrate quenching and a drop tube. The results showed that the levitated and gas-cooled samples were all solidified into a microstructure consisting of primary -Cu plus peritectic -Cu5Ge. However, the samples quenched onto a copper substrate showed a segregation-free microstructure in the chilled zone, suggesting direct crystallization of the peritectic -Cu5Ge phase from a highly undercooled liquid. The Cu-18Ge samples quenched onto a glass substrate as well as those solidified in the drop tube also showed a segregation-free microstructure. An analysis of the nucleation kinetics revealed that the -Cu5Ge phase had a larger nucleation barrier than that of -Cu for all accessible undercoolings. It was suggested that phase selection in the undercooled Cu-Ge liquid might be controlled by transient nucleation kinetics.
Interdiffusion and Thermodynamic Forces in Binary Liquid Alloys
Authors: Griesche Axel , Zhang Bo , Horbach Jürgen , Meyer Andreas
Published: May 2010

A novel X-ray radiography method is used to measure chemical diffusion in a long-capillary in liquid Al95Ni5 at.-%. Molecular dynamics simulations provide interdiffusion coefficients and thermodynamic factors for the whole composition range in Al-Ni. The data are compared to literature data in Sb-Sn and Ag-Sn. The relation between interdiffusion coefficient and thermodynamic forces is discussed in the context of the Darken equation. In systems with common ordering tendency (Al-Ni, Sb-Sn) the thermodynamic factor is larger than one and enhances interdiffusion. In systems with common demixing tendency (Ag-Sn) the thermodynamic factor is smaller than one and reduces interdiffusion.
Investigation of the Solidified Structure of Cu-Hf-Ti Alloys
Authors: Rontó Viktória , Nagy E. , Svéda Mária , Tranta Ferenc , Hegman Norbert
Published: May 2010

Master alloys with different compositions of the Cu-Hf-Ti alloy system were prepared by arc-melting. The pieces were then cast into a wedge- and rod – shaped Cu mould by centrifugal casting. The different mould shapes generated various cooling conditions and produced various microstructures in the samples. Moreover due to the wedge shape, the change of the microstructure can be observed within the samples. The wedge samples became amorphous in 1-1.5 mm thickness, and dendritic structure formed in the thicker parts. The change in the microstructure in the rod samples along the radius can be studied as well. The solidified phases were also investigated by X-ray diffraction and SEM-EDAX.
Effect of Healing Temperature on Crack-Healing of Al2O3 Toughened by SiC Particles
Authors: Shi Chun Yan , Guo Ying Kui , Zhao Shu Jin , Song Chun Mei
Published: May 2010

Al2O3 Toughened by SiC particles was hot-press sintered. Cracks of ~300μm in diameter were introduced in the surfaces of specimens, which then healed at 1000°C, 1200°C, 1300°C, 1400°C, and individually for 2h, 4h, 6h and 8h. Effect of healing temperature on bending strength, healing mechanism were systematically investigated, the results show that the best bending strength recovered at room temperature was 583.61MPa obtained at 1300°C for 4h, which was the same value as perfect specimens. The recovery of bending strength contributes to three kinds of mechanisms. When specimens were healed individually at 1000°C, 1200°C, 1300°C for 2h, adsorption mechanism and proliferation mechanism were as the dominant healing mechanisms; when healed at 1400°C for 2h, oxidation reaction mechanism was the important healing mechanism. Also, the length of surface cracks is shorter as healing temperature increasing.
Degradation Behavior of MgB2 Powders in Different Medium Environment
Authors: Zhu Hao , Wang Shu Mao , Li Zhi Nian , Liu Xiao Peng , Jiang Li Jun
Published: May 2010

High purity MgB2 powders were synthesized by solid sintering reaction. The degradation behavior of MgB2 powders in deionized water was investigated. XRD and SEM analysis indicate that the changes of MgB2 are a function of time. XRD patterns show that the lattice constants are increasing with the time, and MgB2 samples mostly contain amorphous phase after water treated. The decomposition reaction equation was obtained based on the IR and mass spectrum results. The changes of MgB2 exposed to the 10%HCl, 10%H2SO4, 10%NaOH, 1%HCl, 1%H2SO4 and 1%NaOH (mole concentration) were also studied. The variation of phase composition and morphology indicate that the small amount of MgB2 has decomposed on some extent. The results show that acid can catalyze the decomposition of MgB2 but inversely alkali inhibits the decomposition. The decomposition reaction is limited in water, acid and alkali for less than 1h, and it could be said that the stability of MgB2 is better under such conditions.
Variation of the Reversed Austenite Amount with the Tempering Temperature in a Fe-13%Cr-4%Ni-Mo Martensitic Stainless Steel
Authors: Song Yuan Yuan , Li Xiu Yan , Yin Fu Xing , Ping De Hai , Rong Li Jian , Li Yi Yi
Published: May 2010

Tempering temperature dependence of the amount of the reversed austenite in the range of 570 oC to 680 oC was investigated by means of X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) in a low carbon Fe-13%Cr-4%Ni-Mo (wt.%) martensitic stainless steel. It was found that the reversed austenite began to form at the tempered temperature slightly above the As temperature. As the tempered temperature increased, the amount of the reversed austenite changed little in the temperature range of 580-595 oC. Then, the amount of the reversed austenite increased sharply with the increased tempered temperature. When the tempered temperature increased to about 620 oC, the amount of the reversed austenite exhibited a peak. Afterward, it decreased quickly at the elevated tempered temperature. The microstructural evolvement of the reversed austenite at different tempering temperature was also observed by TEM.
Effect of Ti Content on Hydrogen Storage Properties of Amorphous MgNi Alloy
Authors: Gao Shan , Wang Jing Feng , Ding Pei Dao , Pan Fu Sheng , Tang Ai Tao
Published: May 2010

Cycle capacities of Amorphous Mg-Ni alloys declined so fast therefore they can’t be used practically. In this paper，the influence of adding Ti on the discharge capacity and cycle stability of the alloys were investigated. Amorphous Mg1-xTixNi (x=0, 0.1, 0.2, 0.3) alloy powder was prepared successfully by mechanical alloying (MA). X-ray diffraction (XRD) results show that MgNi alloy formed completely amorphous phase after ball milling with 15h. But for Mg1-xTixNi (x=0.1, 0.2, 0.3) alloy, it took 23h. It can be concluded that Ti partial substituting Mg would decrease the amorphous phase forming ability of Mg-Ni based alloy. Compared with amorphous MgNi alloy, the maximal discharge capacities of Mg1-xTixNi (x=0.1, 0.2, 0.3) alloy were decreased slightly, but the cycle stabilities were significantly enhanced. Mg0.9Ti0.1Ni alloy showed the largest discharge capacity and the best cycle stability.
The Study of Interfacial Reactions and Mechanics Properties for Die Casting (Al63Cu25Fe12)p /AZ91 Composites
Authors: Li Xiao Ping , Xu Zhou , Yu Yun
Published: May 2010

A novel Mg-based composites (Al63Cu25Fe12)p /AZ91 was prepared by pressure die casting protected by CO2/SF6 condition. The–200mesh quasicrystalline powders were poured into the molten AZ91Mg alloy and then rapidly stirred for 30 min in 720°C. The phases and phase transformation in the process of heat treatment for Al63Cu25Fe12 powder, and the reaction between matrix metal AZ91 and Al63Cu25Fe12 particle has been investigated using Scanning Electron microscopy (SEM) and Energy spectrum diffraction analysis technology（EDAX）. It is shown that i-phase decomposed in process of stir and the Cu atoms diffuse from powders into the matrix and combine with Mg and Al in the matrix, which produces metallic-compound dispersing along the grain boundary. The Mg atoms diffuse into the powders and substitute the Cu atom sites. After heated with solution and ageing, composites of (Al63Cu25Fe12)p /AZ91 is different from magnesium alloy, they need less time to get the ageing hardness peak. The mechanics properties of composites have been improved outstandingly by hot-extruded and treatment of solution and ageing, the tensile strength σb is from 189.54MPa up to 359.38MPa. However, because of their brittleness, the plasticity of composites decreased.
An Electrochemical Method for the Preparation of Al-Mg Master Alloys from MgO
Authors: Cao Da Li , Wang Ji Kun , Guo Si Chen , Fang Qin Hong , Shi Zhong Ning
Published: May 2010

The electrochemical formation of Al-Mg master alloys were investigated in NaCl-MgF2-MgO melt at 850°C. The results revealed that cell voltage was nearly constant during electrolysis process, Mg content in Al-Mg master alloys increased with increasing of electrolysis time when Mg content was less 7.03mass%, Mg content in Al-Mg master alloys can be up to 7.03mass% for 4h electrolysis. The results of XRD indicated that phase structure of the Al-7.03Mg mass% alloy existed single phase α-Al, MgCl2 and NaMgF3 in electrolyte were observed after electrolysis. And the formation mechanism of Al-Mg master alloy was discussed as well.
Study on Tensile Fractured Surfaces and Toughening Mechanism of Ti/Ti-Al Micro-Laminate Sheet
Authors: Ma Li , Hu Zhao Hui
Published: May 2010

Large-sized Ti/Ti-Al micro laminated thin sheet with thickness of 0.12mm was prepared by high-power electron beam physical vapor deposition technology, and then tensile tests of specimen after hot-pressing densification were carried out at room and high temperature, and tensile specimen was examined the fractured surfaces by SEM and OM. It was found that the tensile specimen under room temperature presents a compound quasi-cleavage and intergranular fracture, and a certain plastic deformation of Ti toughening layer was detected during fracture process. Tensile fractured surfaces under high temperature present the feature of compound dimple models and quasi-cleavage, furthermore, the size and the quantity of dimple exhibited an enhancing trend with test temperature increased. Results show that the cracks will stagger along the inter-laminar interface or the layer due to which micro-laminate expresses a good characteristic of delayed fracture. The toughening mechanisms are that the crack deflection and micro-bridge connection caused by the toughening layers increases crack propagation resistance.
Study on Growth of Carbon Nanotubes by Using Modified Bentonite as Catalyst
Authors: Zheng Ju Gong , Chen Quan Shui , Liu Xiao Dong , Yang Ting
Published: May 2010

Titanate modified bentonite could catalyze methane into synthesis carbon nanotubes at high temperature by thermal chemical vapor deposition. The element iron contained in bentonite acts as the catalytic metal of nanotubes. A conclusion was drawn that the quality and quantity of carbon nanotubes were best and largest respectively at 800 °C. If the temperature is higher than 900 °C,the quality of nanotubes would be bad. The catalytic capacity of modified bentonite would disappear below 700 °C. The catalyst is cheaper, and the treatment process of the catalyst is simpler than traditional metal catalyst , which may accelerate industrial synthesis of carbon nanotubes.
Effect of High-Dispersed Nano-ZnO on the Properties of Vulcanized Natural Rubber
Authors: Li Ling , Liu Lan
Published: May 2010

High-dispersed nano-ZnO were used for alternating ordinary ZnO in the vulcanization process of nature rubber. The properties of vulcanized natural rubber including the mechanical properties and anti-aging properties were investigated in this paper. The results showed that high-dispersed nano-ZnO made natural rubber the scorched time longer, the degrees of cross-linking higher and anti-aging properties remarkably stronger, compared with 99.5 % of ordinary ZnO under the same vulcanization conditions. Specially, when 0.8 dosages of high-dispersed nano-ZnO being used, the mechanical properties and anti-aging ability of natural rubber were best and better than that of 5 dosages of 99.5 % of ordinary ZnO in traditional formula. The reasons may be that high-dispersed nano-ZnO were completely resolved in rubber and can fully be contacted with the double bond of rubber molecules and the surface of sulfur so that they increased the efficiency of rubber vulcanization to improve the properties of natural rubber.
Immune Complex-Mediated Enhancement of Secondary Antibody Responses
Authors: Goins Chelsey L. , Chappell Craig P. , Shashidharamurthy Rangaiah , Selvaraj Periasamy , Jacob Joshy
Published: May 2010

Immunologic memory is a hallmark of the vertebrate immune system. The first antigenic exposure leads to a slow and modest immune response, whereas repeated exposure, even many years later, leads to a rapid and exaggerated response that is two to three orders of magnitude greater than the primary. In the case of humoral immunity, the increased efficacy of recall responses is due to the production of amplified levels of Ag-specific Ab, as well as the accelerated kinetics of their production. Current thinking suggests that this is due to selective activation of long-lived, Ag-specific memory B cells. A downside of restricting secondary responses solely to memory cells is that the repertoire of the memory B cell pool remains static while pathogens continue to evolve. In this study, we propose that during secondary responses, naive Ag-specific B cells participate alongside memory cells. We show that immune complexes formed in vivo between the Ag and pre-existing Abs from the primary response activate these naive B cells, inducing them to respond with accelerated kinetics and increased magnitude. Thus, the continued recruitment of new B cell clones after each antigenic exposure enables the immune system to stay abreast of rapidly changing pathogens.
A Role for IL-1 Receptor-Associated Kinase-M in Prostaglandin E2-Induced Immunosuppression Post-Bone Marrow Transplantation
Authors: Hubbard Leah L. N. , Ballinger Megan N. , Thomas Peedikayil E. , Wilke Carol A. , Standiford Theodore J. , Kobayashi Koichi S. , Flavell Richard A. , Moore Bethany B.
Published: May 2010

Following immune reconstitution, hematopoietic stem cell transplant patients often display reduced immune function and are especially susceptible to lung infections. In a mouse model of syngeneic bone marrow transplantation (BMT), we previously reported that PGE2 is overproduced in lungs of BMT mice, significantly impairing host defense against Pseudomonas aeruginosa. This impairment in host defense post-BMT is also marked by diminished alveolar macrophage (AM) phagocytosis, bacterial killing, and production of TNF-α and cysteinyl leukotrienes. However, a mechanism by which overproduction of PGE2 suppresses pulmonary host defense post-BMT is unknown. As IL-1R–associated kinase (IRAK)-M is a known inhibitor of MyD88-dependent IL-1R/TLR signaling and macrophage function, we sought to determine whether IRAK-M is involved in PGE2-induced immunosuppression post-BMT. We found that IRAK-M expression is elevated 3.5-fold in BMT AMs relative to control AMs, and this is related to AM overproduction of PGE2. Furthermore, genetic ablation of IRAK-M in the bone marrow of BMT mice restores host defense against P. aeruginosa. Despite AM overproduction of PGE2 and elevated E prostanoid 2 receptor expression, AM phagocytosis, killing, and production of cysteinyl leukotrienes and TNF-α are restored in the absence of IRAK-M post-BMT. Also, treatment with PGE2 does not inhibit AM phagocytosis in the absence of IRAK-M. These data suggest that the absence of IRAK-M in the hematopoietic compartment post-BMT enhances pulmonary host defense and mitigates AM sensitivity to the inhibitory effects of PGE2. Therefore, strategies to limit IRAK-M elevation post-BMT may be efficacious in reducing patient susceptibility to infection.
Hemoglobin Transforms Anti-Inflammatory Salmonella typhi Virulence Polysaccharide into a TLR-2 Agonist
Authors: Garg Rohini , Qadri Ayub
Published: May 2010

Vi capsular polysaccharide is a major virulence determinant of the human typhoid- causing pathogen Salmonella typhi; it is absent in nontyphoidal Salmonella serovars. We show in this study that through its specific interaction with the membrane recognition complex containing the prohibitin family of molecules, Vi can inhibit the production of inflammatory cytokines from mononuclear phagocytes stimulated with Salmonella flagellin. Remarkably, Vi lost this anti-inflammatory capability and switched to a proinflammatory state when cell stimulations were performed in the presence of serum. The serum-transformed proinflammatory form of Vi induced secretion of cytokines from monocytes by specifically engaging TLR-2/TLR-1. The molecule responsible for bringing about this conversion of Vi from an anti-inflammatory to a proinflammatory form was serum-derived hemoglobin. Derivatives of Vi incapable of interacting with hemoglobin did not switch to a proinflammatory state in vitro or in vivo. These findings provide compelling evidence for a role of hemoglobin in transforming the anti-inflammatory S. typhi virulence polysaccharide into an immune activator.
Superior Antitumor Response Induced by Large Stress Protein Chaperoned Protein Antigen Compared with Peptide Antigen
Authors: Wang Xiang-Yang , Sun Xiaolei , Chen Xing , Facciponte John , Repasky Elizabeth A. , Kane John , Subjeck John R.
Published: May 2010

Our previous studies have demonstrated that the natural chaperone complexes of full-length tumor protein Ags (e.g., gp100) and large stress proteins (e.g., hsp110 and grp170) with exceptional Ag-holding capabilities augment potent tumor protective immunity. In this study, we assess the peptide-interacting property of these large chaperones and, for the first time, compare the immunogenicity of the recombinant chaperone vaccines targeting two forms of Ags (protein versus peptide). Both hsp110 and grp170 readily formed complexes with antigenic peptides under physiologic conditions, and the peptide association could be further stimulated by heat shock. The large chaperones displayed similar but distinct peptide-binding features compared with hsp70 and grp94/gp96. Immunization with hsp110- or grp170-tyrosinase–related protein 2 (TRP2175–192) peptide complexes effectively primed CD8+ T cells reactive with TRP2-derived, MHC class I-restricted epitope. However, the tumor protective effect elicited by the TRP2175–192 peptide vaccine was much weaker than that achieved by full-length TRP2 protein Ag chaperoned by grp170. Furthermore, immunization with combined chaperone vaccines directed against two melanoma protein Ags (i.e., gp100 and TRP2) significantly improved overall anti-tumor efficacy when compared with either of the single Ag vaccine. Lastly, treatment of tumor-bearing mice with these dual Ag-targeted chaperone complexes resulted in an immune activation involving epitope spreading, which was associated with a strong growth inhibition of the established tumors. Our results suggest that high m.w. chaperones are superior to conventional chaperones as a vaccine platform to deliver large protein Ags, and provide a rationale for translating this recombinant chaperoning-based vaccine to future clinical investigation.
Lack of Original Antigenic Sin in Recall CD8+ T Cell Responses
Authors: Zehn Dietmar , Turner Michael J. , Lefrançois Leo , Bevan Michael J.
Published: May 2010

In the real world, mice and men are not immunologically naive, having been exposed to numerous antigenic challenges. Prior infections sometimes negatively impact the response to a subsequent infection. This can occur in serial infections with pathogens sharing cross-reactive Ags. At the T cell level it has been proposed that preformed memory T cells, which cross-react with low avidity to epitopes presented in subsequent infections, dampen the response of high-avidity T cells. We investigated this with a series of related MHC class-I restricted Ags expressed by bacterial and viral pathogens. In all cases, we find that high-avidity CD8+ T cell precursors, either naive or memory, massively expand in secondary cross-reactive infections to dominate the response over low-avidity memory T cells. This holds true even when >10% of the CD8+ T cell compartment consists of memory T cells that cross-react weakly with the rechallenge ligand. Occasionally, memory cells generated by low-avidity stimulation in a primary infection recognize a cross-reactive epitope with high avidity and contribute positively to the response to a second infection. Taken together, our data show that the phenomenon of original antigenic sin does not occur in all heterologous infections.
Cutting Edge: A Thymocyte-Thymic Epithelial Cell Cross-Talk Dynamically Regulates Intrathymic IL-7 Expression In Vivo
Authors: Alves Nuno L. , Huntington Nicholas D. , Mention Jean-Jacques , Richard-Le Goff Odile , Di Santo James P.
Published: May 2010

Thymic epithelial cells (TECs) are the predominant intrathymic source of the essential thymopoietin IL-7. Whether thymocyte-TEC interactions have a role in the regulation of IL-7 expression is not known. By exploiting IL-7 reporter mice in which yellow fluorescent protein expression identifies TECs expressing high levels of IL-7 (Il7+ TECs), we show that Il7+ TECs segregate from emerging medullary TECs during thymic organogenesis. Although Il7+ TECs normally diminish with age, we found that Il7+ TECs are markedly retained in alymphoid Rag2−/−Il2rg−/− IL-7 reporter mice that manifest a profound thymopoietic arrest. Transfer of Tcra−/− or wild-type (but not Rag2−/−) hematopoietic progenitors to alymphoid IL-7 reporter recipients normalizes the frequency of Il7+ TECs and re-establishes cortical TEC/medullary TEC segregation. Although thymocyte-derived signals are often considered stimulatory for TEC maturation, our findings identify a negative feedback mechanism in which signals derived from TCRβ-selected thymocytes modulate TEC-dependent IL-7 expression.
Fulminant Giant Cell Myocarditis and Cardiogenic Shock: An Unusual Presentation of Malignant Thymoma
Authors: Koul Deepak , Kanwar Manreet , Jefic Dane , Kolluru Anuradha , Singh Tejwant , Dhar Sunil , Kumar Preetham , Cohen Gerald
Published: May 2010

Malignant thymoma is rarely associated with giant cell myocarditis. We present a case study that illustrates this association and cardiogenic shock with underlying tamponade. The dramatic presentation of this scenario has not been previously described.
Transcriptomic Signatures of Alterations in a Myoblast Cell Line Infected with Four Distinct Strains of Trypanosoma cruzi
Authors: Adesse Daniel , Iacobas Dumitru A. , Iacobas Sanda , Garzoni Luciana R. , Meirelles Maria de Nazareth , Tanowitz Herbert B. , Spray David C.
Published: May 2010

We examined the extent to which different Trypanosoma cruzi strains induce transcriptomic changes in cultured L6E9 myoblasts 72 hours after infection with Brazil (TC I), Y (TC II), CL (TC II), and Tulahuen (TC II) strains. Expression of 6,289 distinct, fully annotated unigenes was quantified with 27,000 rat oligonucleotide arrays in each of the four replicas of all control and infected RNA samples. Considering changes greater than 1.5-fold and P values < 0.05, the Tulahuen strain was the most disruptive to host transcriptome (17% significantly altered genes), whereas the Y strain altered only 6% of the genes. The significantly altered genes in the infected cells were largely different among the strains, and only 21 genes were similarly changed by all four strains. However, myoblasts infected with different strains showed proportional overall gene-expression alterations. These results indicate that infection with different parasite strains modulates similar but not identical pathways in the host cells.
Detection of Trypanosoma cruzi and T. rangeli Infections from Rhodnius pallescens Bugs by Loop-Mediated Isothermal Amplification (LAMP)
Authors: Thekisoe Oriel M. M. , Rodriguez Carol V. , Rivas Francisco , Coronel-Servian Andrea M. , Fukumoto Shinya , Sugimoto Chihiro , Kawazu Shin-Ichiro , Inoue Noboru
Published: May 2010

We have developed two loop-mediated isothermal amplification (LAMP) assays for specific detection of Trypanosoma cruzi and Trypanosoma rangeli based on the 18S ribosomal RNA (rRNA) and the small nucleolar RNA (snoRNA) genes, respectively. The detection limit of the assays is 100 fg and 1 pg for T. cruzi and T. rangeli, respectively, with reactions conducted in 60 minutes. The two LAMP assays were used in detection of T. cruzi and T. rangeli infections in comparison with polymerase chain reaction (PCR) for DNA samples extracted from Rhodnius pallescens bugs collected from palm trees in Panama. Out of a total of 52 DNA samples from R. pallescens bugs 17 (33%) and 14 (27%) were T. cruzi-positive by LAMP and PCR, respectively, while, 7 (13%) and 4 (8%) were T. rangeli-positive by LAMP and PCR, respectively. Further evaluation of these LAMP assays is needed, especially with specimens collected from human patients as well as blood kept for transfusion purposes.
Clinical and Laboratory Features That Differentiate Dengue from Other Febrile Illnesses in an Endemic Area—Puerto Rico, 2007–2008
Authors: Gregory Christopher J. , Santiago Luis Manuel , Argüello D. Fermin , Hunsperger Elizabeth , Tomashek Kay M.
Published: May 2010

Dengue infection can be challenging to diagnose early in the course of infection before severe manifestations develop, but early diagnosis can improve patient outcomes and promote timely public health interventions. We developed age-based predictive models generated from 2 years of data from an enhanced dengue surveillance system in Puerto Rico. These models were internally validated and were able to differentiate dengue infection from other acute febrile illnesses with moderate accuracy. The accuracy of the models was greater than either the current World Health Organization case definition for dengue fever or a proposed modification to this definition, while requiring the collection of fewer data. In young children, thrombocytopenia and the absence of cough were associated with dengue infection; for adults, rash, leucopenia, and the absence of sore throat were associated with dengue infection; in all age groups, retro-orbital pain was associated with dengue infection.
Serologic and Molecular Studies of Leptospira and Leptospirosis among Rats in the Philippines
Authors: Villanueva Sharon Y. A. M. , Ezoe Hirokazu , Baterna Rubelia A. , Yanagihara Yasutake , Muto Maki , Koizumi Nobuo , Fukui Takashi , Okamoto Yoshihiro , Masuzawa Toshiyuki , Cavinta Lolita L. , Gloriani Nina G. , Yoshida Shin-ichi
Published: May 2010

Rats are known to be the most important reservoirs and transmission sources of leptospirosis. However, the status of leptospirosis in the Philippines regarding reservoirs and transmission remains unknown. A survey was conducted in Metro Manila and Laguna that analyzed samples obtained from 106 rats. Using the microscopic agglutination test, we found that 92% of rat serum samples were positive for anti-Leptospira antibodies; the most common infecting serovars were Manilae, Hebdomadis, and Losbanos. On the basis of pulsed-field gel electrophoresis and gyrase B gene sequence analyses, four groups of rat kidney isolates were found: L. interrogans serovar Manilae, serovar Losbanos, and serogroup Grippotyphosa, and L. borgpetersenii serogroup Javanica. Most isolates were lethal after experimental infection of golden Syrian hamsters. Results showed that these four Leptospira serovars and serogroups are circulating among rats, and that these animals may be one of the possible transmission sources of leptospirosis in the Philippines.
Methods and Baseline Results of a Repeated Cross-Sectional Survey to Assess the Public Health Impact of Antiretroviral Therapy in Lusaka, Zambia
Authors: Giganti Mark J. , Levy Jens W. , Banda Yolan , Kusanthan Thankian , Sinkala Moses , Stringer Jeffrey S. A. , Chi Benjamin H.
Published: May 2010

Although the individual-level impact of antiretroviral therapy (ART) is well documented, there are few available data describing the public health impact of services for persons infected with human immunodeficiency virus in resource-constrained settings. We describe the methods and baseline results of a household survey that assessed the population-level impact of the national program for HIV care in Zambia and treatment in the city of Lusaka. The survey was timed with the staggered expansion of services and repeated cross-sectional surveys planned for pre-implementation and post-implementation comparisons made by community. In the initial survey round, which was performed during the early phases of the program (November–December 2004), 18,110 persons were enumerated from 3,600 households surveyed. Respondents were asked questions designed to evaluate community-level mortality and respondent knowledge and attitudes towards HIV. These findings will serve as a reliable reference in the future analysis of the population-level impact of this HIV treatment and care program in Zambia.
Testing the Honeywell Durafet® for seawater pH applications
Authors: Martz Todd R. , Connery James G. , Johnson Kenneth S.
Published: May 2010

We report on the first seawater tests at 1 atm of the Honeywell Durafet® pH sensor, a commercially available ion sensitive field effect transistor (ISFET). Performance of this sensor was evaluated in a number of different situations including a temperature‐controlled calibration vessel, the MBARI test tank, shipboard underway mapping, and a surface mooring. Many of these tests included a secondary reference electrode in addition to the internal reference supplied with the stock Durafet sensor. We present a theoretical overview of sensor response using both types of reference electrode. The Durafet sensor operates with a short term precision of ± 0.0005 pH over periods of several hours and exhibits stability of better than 0.005 pH over periods of weeks to months. Our tests indicate that the Durafet pH sensor operates at a level of performance satisfactory for many types of biogeochemical studies at low pressure.
Combined biogeophysical and biogeochemical effects of large-scale forest cover changes in the MPI earth system model
Authors: Bathiany S. , Claussen M. , Brovkin V. , Raddatz T. , Gayler V.
Published: May 2010

Abstract. Afforestation and reforestation have become popular instruments of climate mitigation policy, as forests are known to store large quantities of carbon. However, they also modify the fluxes of energy, water and momentum at the land surface. Previous studies have shown that these biogeophysical effects can counteract the carbon drawdown and, in boreal latitudes, even overcompensate it due to large albedo differences between forest canopy and snow. This study investigates the role forest cover plays for global climate by conducting deforestation and afforestation experiments with the earth system model of the Max Planck Institute for Meteorology (MPI-ESM). Complete deforestation of the tropics (18.75° S–15° N) exerts a global warming of 0.4 °C due to an increase in CO2 concentration by initially 60 ppm and a decrease in evapotranspiration in the deforested areas. In the northern latitudes (45° N–90° N), complete deforestation exerts a global cooling of 0.25 °C after 100 years, while afforestation leads to an equally large warming, despite the counteracting changes in CO2 concentration. Earlier model studies are qualitatively confirmed by these findings. As the response of temperature as well as terrestrial carbon pools is not of equal sign at every land cell, considering forests as cooling in the tropics and warming in high latitudes seems to be true only for the spatial mean, but not on a local scale.
Quantification of DOC concentrations in relation with soil properties of soils in tundra and taiga of Northern European Russia
Authors: Oosterwoud M. R. , Temminghoff E. J. M. , van der Zee S. E. A. T. M.
Published: May 2010

Abstract. Potential mobilization and transport of Dissolved Organic Carbon (DOC) in subarctic river basins towards the oceans is enormous, because 23–48% of the worlds Soil Organic Carbon (SOC) is stored in northern regions. As climate changes, the amount and composition of DOC exported from these basins are expected to change. The transfer of organic carbon between soils and rivers results in fractionation of organic carbon compounds. The aim of this research is to determine the DOC concentrations, its fractions, i.e. humic (HA), fulvic (FA), and hydrophilic (HY) acids, and soil characteristics that influence the DOC sorptive properties of different soil types within a tundra and taiga catchment of Northern European Russia. DOC in taiga and tundra soil profiles (soil solution) consisted only of HY and FA, where HY became more abundant with increasing depth. Adsorption of DOC on mineral phases is the key geochemical process for release and removal of DOC from potentially soluble carbon pool. We found that adsorbed organic carbon may desorb easily and can release DOC quickly, without being dependent on mineralization and degradation. Although Extractable Organic Carbon (EOC) comprise only a small part of SOC, it is a significant buffering pool for DOC. We found that about 80–90% of released EOC was previously adsorbed. Fractionation of EOC is also influenced by the fact that predominantly HA and FA adsorbed to soil and therefore also are the main compounds released when desorbed. Flowpaths vary between taiga and tundra and through seasons, which likely affects DOC concentration found in streams. As climate changes, also flowpaths of water through soils may change, especially in tundra caused by thawing soils. Therefore, adsorptive properties of thawing soils exert a major control on DOC leaching to rivers. To better understand the process of DOC ad- and de-sorption in soils, process based soil chemical modelling, which could bring more insight in solution speciation, mineral solubility, and adsorption reactions, is appropriate.
Spectral approach to seawater intrusion in heterogeneous coastal aquifers
Authors: Chang C.-M. , Yeh H.-D.
Published: May 2010

Abstract. This work presents a two-dimensional horizontal plane model of seawater intrusion into a heterogeneous coastal unconfined aquifer under the spatially random recharge condition from a stochastic point of view. The stochastic response of the coastal unconfined aquifer is attributed to uncertainties related to the heterogeneity of aquifer properties and spatial variability of the recharge. Based on the sharp-interface assumption, analytical expressions for the variances of the seawater-freshwater interface elevation and specific discharge in the longitudinal and transverse directions are developed using the perturbation approximation and spectral Fourier-Stieltjes nonstationary representations. We focus on the study of the impact of the heterogeneity of aquifer properties and recharge on these results.
Multifunctional Mesoporous Silica Material Used for Detection and Adsorption of Cu2+ in Aqueous Solution and Biological Applications in vitro and in vivo
Authors: Meng Qingtao , Zhang Xiaolin , He Cheng , He Guangjie , Zhou Peng , Duan Chunying
Published: May 2010

An inorganic–organic silica material (SBA–P2), prepared by immobilization of the 1,8‐naphthalimide‐based receptor P2 within the channels of the mesoporous silica material SBA‐15, is characterized by transmission electron microscopy and several spectroscopic methods. SBA–P2 features a high affinity Cu2+‐specific fluorescence response in aqueous solution with a detection limit for Cu2+ of ca. 0.65 ppb (10 × 10−9 M) under optimized conditions. It can extract Cu2+ from the solution with only trace amounts remaining. Through isolating of the toxic ions within the mesopores of the silica, SBA–P2 has the potential to work as a toxicide for Cu2+ in living systems. The fluorogenical responses are reversible and do not vary over a broad (4.0 to 9.0) pH range suitable for application under physiological conditions. The fluorescence responses of Cu2+ in vitro (human breast cancer cells) and in vivo (five‐day‐old zebrafish) demonstrate the possibility of further application in biology.
Brief communication: Identification reassessment of the isolated tooth Krapina D58 through occlusal fingerprint analysis
Authors: Fiorenza Luca , Benazzi Stefano , Tausch Jeremy , Kullmer Ottmar , Schrenk Friedemann
Published: May 2010

High variability in the dentition of Homo can create uncertainties in the correct identification of isolated teeth. For instance, standard tooth identification criteria cannot determine with absolute certainty if an isolated tooth is a second or third maxillary molar. In this contribution, using occlusal fingerprint analysis, we reassess the identification of Krapina D58 (Homo neanderthalensis), which is catalogued as a third maxillary molar. We have hypothesized that the presence/absence of the distal occlusal wear facets can be used to differentiate second from third maxillary molars. The results obtained confirm our hypothesis, showing a significant difference between second and third maxillary molars. In particular we note the complete absence of Facets 7 and 10 in all third molars included in this analysis. The presence of these facets in Krapina D58 eliminates the possibility that it is a third maxillary molar. Consequently it should be reclassified as a second molar. Although this method is limited by the degree of dental wear (i.e., unworn teeth cannot be analyzed) and to individual molars in full occlusion, it can be used for tooth identification when other common criteria are not sufficient to discriminate between second and third maxillary molars. Am J Phys Anthropol 143:306–312, 2010. © 2010 Wiley‐Liss, Inc.