bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards the development of Bacillus subtilis as a cell factory for membrane proteins and protein complexes
Authors: Zweers Jessica C , Barák Imrich , Becher Dörte , Driessen Arnold JM , Hecker Michael , Kontinen Vesa P , Saller Manfred J , Vavrová L'udmila , van Dijl Jan Maarten
Published: April 2008

Background

The Gram-positive bacterium Bacillus subtilis is an important producer of high quality industrial enzymes and a few eukaryotic proteins. Most of these proteins are secreted into the growth medium, but successful examples of cytoplasmic protein production are also known. Therefore, one may anticipate that the high protein production potential of B. subtilis can be exploited for protein complexes and membrane proteins to facilitate their functional and structural analysis. The high quality of proteins produced with B. subtilis results from the action of cellular quality control systems that efficiently remove misfolded or incompletely synthesized proteins. Paradoxically, cellular quality control systems also represent bottlenecks for the production of various heterologous proteins at significant concentrations.

Conclusion

While inactivation of quality control systems has the potential to improve protein production yields, this could be achieved at the expense of product quality. Mechanisms underlying degradation of secretory proteins are nowadays well understood and often controllable. It will therefore be a major challenge for future research to identify and modulate quality control systems of B. subtilis that limit the production of high quality protein complexes and membrane proteins, and to enhance those systems that facilitate assembly of these proteins.
Human granulocyte colony stimulating factor (hG-CSF): cloning, overexpression, purification and characterization
Authors: Vanz Ana LS , Renard Gaby , Palma Mario S , Chies Jocelei M , Dalmora Sérgio L , Basso Luiz A , Santos Diógenes S
Published: April 2008

Background

Biopharmaceutical drugs are mainly recombinant proteins produced by biotechnological tools. The patents of many biopharmaceuticals have expired, and biosimilars are thus currently being developed. Human granulocyte colony stimulating factor (hG-CSF) is a hematopoietic cytokine that acts on cells of the neutrophil lineage causing proliferation and differentiation of committed precursor cells and activation of mature neutrophils. Recombinant hG-CSF has been produced in genetically engineered Escherichia coli (Filgrastim) and successfully used to treat cancer patients suffering from chemotherapy-induced neutropenia. Filgrastim is a 175 amino acid protein, containing an extra N-terminal methionine, which is needed for expression in E. coli. Here we describe a simple and low-cost process that is amenable to scaling-up for the production and purification of homogeneous and active recombinant hG-CSF expressed in E. coli cells.

Results

Here we describe cloning of the human granulocyte colony-stimulating factor coding DNA sequence, protein expression in E. coli BL21(DE3) host cells in the absence of isopropyl-β-D-thiogalactopyranoside (IPTG) induction, efficient isolation and solubilization of inclusion bodies by a multi-step washing procedure, and a purification protocol using a single cationic exchange column. Characterization of homogeneous rhG-CSF by size exclusion and reverse phase chromatography showed similar yields to the standard. The immunoassay and N-terminal sequencing confirmed the identity of rhG-CSF. The biological activity assay, in vivo, showed an equivalent biological effect (109.4%) to the standard reference rhG-CSF. The homogeneous rhG-CSF protein yield was 3.2 mg of bioactive protein per liter of cell culture.

Conclusion

The recombinant protein expression in the absence of IPTG induction is advantageous since cost is reduced, and the protein purification protocol using a single chromatographic step should reduce cost even further for large scale production. The physicochemical, immunological and biological analyses showed that this protocol can be useful to develop therapeutic bioproducts. In summary, the combination of different experimental strategies presented here allowed an efficient and cost-effective protocol for rhG-CSF production. These data may be of interest to biopharmaceutical companies interested in developing biosimilars and healthcare community.
Protein C: a potential biomarker in severe sepsis and a possible tool for monitoring treatment with drotrecogin alfa (activated)
Authors: Shorr Andrew F , Nelson David R , Wyncoll Duncan LA , Reinhart Konrad , Brunkhorst Frank , Vail George Matthew , Janes Jonathan
Published: April 2008

Introduction

Drotrecogin alfa (activated; DrotAA) treatment, a 96-hour infusion, reduces 28-day mortality in severe sepsis to approximately 25%. The question remains whether a longer infusion or higher dose could increase rate of survival. The goal of this study was to identify a dependable, sensitive measure with which to monitor disease progression and response in patients during DrotAA treatment.

Methods

Data on severe sepsis patients included in PROWESS (placebo-controlled, double-blind, randomized study of 850 DrotAA and 840 placebo individuals) and ENHANCE (single-arm, open-label study of 2,375 DrotAA patients) studies were analyzed. In these studies, DrotAA (24 μg/kg per hour) or placebo was infused for 96 hours and patients were followed for 28 days. Data on six laboratory measures and five organ dysfunctions were systematically analyzed to identify a potential surrogate end-point for monitoring DrotAA therapy and predicting 28-day mortality at the end of therapy. To allow comparison across variables, sensitivity and specificity analyses identified cut-off values for preferred outcome, and relative risks for being above or below cut-offs were calculated, as was the 'proportion of treatment effect explained' (PTEE) to identify biomarkers that contribute to benefit from DrotAA.

Results

Protein C was the only variable that correlated with outcome across all analyses. Using placebo data, a baseline protein C under 40% was established as a useful predictor of outcome (odds ratio 2.12). Similar odds ratios were associated with cut-off values of other biomarkers, but the treatment benefit associated with DrotAA was significantly greater below the cut-off than above the cut-off only for protein C (relative risk for 28-day mortality 0.66 versus 0.88; P = 0.04). Protein C was the only end-of-infusion biomarker that potentially explained at least 50% of the benefit from DrotAA (PTEE 57.2%). The PTEE was 41% for cardiovascular Sequential Organ Failure Assessment score and for d-dimer. At the end of infusion (day 4), protein C categories (≤40%, 41% to 80%, and > 80%) remained significantly related to mortality, regardless of treatment assignment.

Conclusion

Based on systematic analyses of 11 variables measured in severe sepsis clinical trials, protein C was the only variable consistently correlated with both DrotAA treatment effect and survival. Further study is needed to determine whether longer infusions or higher doses of DrotAA would achieve the goal of normalizing protein C in more patients with severe sepsis.
Antiviral NK cell responses in HIV infection: II. viral strategies for evasion and lessons for immunotherapy and vaccination
Authors: Iannello Alexandre , Debbeche Olfa , Samarani Suzanne , Ahmad Ali
Published: April 2008

As is the case in other viral infections, humans respond to HIV infection by activating their NK cells. However, the virus uses several strategies to neutralize and evade the host’s NK cell responses. Consequently, it is not surprising that NK cell functions become compromised in HIV-infected individuals in early stages of the infection. The compromised NK cell functions also adversely affect several aspects of the host’s antiviral adaptive immune responses. Researchers have made significant progress in understanding how HIV counters NK cell responses of the host. This knowledge has opened new avenues for immunotherapy and vaccination against this infection. In the first part of this review article, we gave an overview of our current knowledge of NK cell biology and discussed how the genes encoding NK cell receptors and their ligands determine innate genetic resistance/susceptibilty of humans against HIV infections and AIDS. In this second part, we discuss NK cell responses, viral strategies to counter these responses, and finally, their implications for anti-HIV immunotherapy and vaccination.
CD44 mobilization in allogeneic dendritic cell–T cell immunological synapse plays a key role in T cell activation
Authors: Hegde Venkatesh L , Singh Narendra P , Nagarkatti Prakash S , Nagarkatti Mitzi
Published: April 2008

CD44 is involved in several biological processes owing to its dual role as a cell adhesion and signaling molecule. In an allogeneic dendritic cell (DC)–T cell interaction model, we show here that CD44 gets clustered at the contact between T cells with mature but not immature DCs. Also, CD44 colocalized with lipid rafts at the immunological synapse (IS). Using DCs or T cells derived from CD44-deficient mice, we observed that the presence of CD44 on DCs and T cells is important for the formation of DC–T cell tight conjugates. However, deficiency of CD44 on DCs but not T cells affected the functional IS, as indicated by decreased phosphotyrosine and protein kinase C-θ enrichment at the synapse. Also, CD44-deficient DCs induced significantly decreased proliferation as well as IL-2 and IFN-γ production from allogeneic T cells. The polarization of CD44 at the synapse was also noted in an antigen (OVA)-specific, syngeneic DC–T cell interaction using OVA-specific T cells derived from OT-II mice. It was believed that large molecules such as CD44 were excluded from the IS. Results presented here show for the first time that CD44 is recruited to the IS during allogeneic DC and T cell interactions and plays an important role in subsequent T cell activation.
Oxidative Stress Stimulates Testicular Orphan Receptor 4 through Forkhead Transcription Factor Forkhead Box O3a
Authors: Li Gonghui , Lee Yi-Fen , Liu Su , Cai Yi , Xie Shaozhen , Liu Ning-Chun , Bao Bo-Ying , Chen Zhaodian , Chang Chawnshang
Published: April 2008

Early studies reveal that testicular orphan nuclear receptor 4 (TR4) modulates signaling pathways that control various cell functions. However, how TR4 activity is regulated without the involvement of specific ligand(s) remains unclear. Here we identify a daf-16 family protein-binding element (DBE; 5′-TGTTTAC-3′) in the TR4 promoter that can be recognized by the forkhead transcriptional factor FOXO3a, a key stress-responsive factor, through which TR4 gene expression is activated. The interaction between DBE and FOXO3a was confirmed using EMSA and chromatin immunoprecipitation assays. Activation of FOXO3a by oxidative stress and phosphatidylinositol 3-kinase inhibitor induced TR4 expression; in contrast, suppression of FOXO3a by small interfering RNA can reduce oxidative stress-induced TR4 expression. The biological consequence of the FOXO3a-induced TR4 by oxidative stress is to protect against stress-induced cell death in which cells with reduced FOXO3a are less resistant to oxidative stress, and addition of functional TR4 can increase stress resistance. These results suggest that this new identified oxidative stress-FOXO3a-TR4 pathway is a fundamentally important mechanism regulating stress resistance and cell survival.
Epithelial Sodium Channel Is a Key Mediator of Growth Hormone-Induced Sodium Retention in Acromegaly
Authors: Kamenicky Peter , Viengchareun Say , Blanchard Anne , Meduri Geri , Zizzari Philippe , Imbert-Teboul Martine , Doucet Alain , Chanson Philippe , Lombès Marc
Published: April 2008

Acromegalic patients present with volume expansion and arterial hypertension, but the renal sites and molecular mechanisms of direct antinatriuretic action of GH remain unclear. Here, we show that acromegalic GC rats, which are chronically exposed to very high levels of GH, exhibited a decrease of furosemide-induced natriuresis and an increase of amiloride-stimulated natriuresis compared with controls. Enhanced Na+,K+-ATPase activity and altered proteolytic maturation of epithelial sodium channel (ENaC) subunits in the cortical collecting ducts (CCDs) of GC rats provided additional evidence for an increased sodium reabsorption in the late distal nephron under chronic GH excess. In vitro experiments on KC3AC1 cells, a murine CCD cell model, revealed the expression of functional GH receptors and IGF-I receptors coupled to activation of Janus kinase 2/signal transducer and activator of transcription 5, ERK, and AKT signaling pathways. That GH directly controls sodium reabsorption in CCD cells is supported by: 1) stimulation of transepithelial sodium transport inhibited by GH receptor antagonist pegvisomant; 2) induction of α-ENaC mRNA expression; and 3) identification of signal transducer and activator of transcription 5 binding to a response element located in the α-ENaC promoter, indicative of the transcriptional regulation of α-ENaC by GH. Our findings provide the first evidence that GH, in concert with IGF-I, stimulates ENaC-mediated sodium transport in the late distal nephron, accounting for the pathogenesis of sodium retention in acromegaly.
Developmental Dependence on NurRE and EboxNeuro for Expression of Pituitary Proopiomelanocortin
Authors: Lavoie Pierre-Luc , Budry Lionel , Balsalobre Aurélio , Drouin Jacques
Published: April 2008

Cell-specific expression of the pituitary proopiomelanocortin (POMC) gene depends on the combinatorial action of a large number of DNA-binding transcription factors (TFs). These include general and cell-restricted factors, as well as factors that act as effectors of signaling pathways. We have previously defined in the distal POMC promoter a composite regulatory element that contains targets for basic helix-loop-helix TFs conferring cell specificity and for NGFI-B orphan nuclear receptors that are responsive to CRH signaling and to glucocorticoid negative feedback. These factors act on neighboring regulatory elements, the EboxNeuro and NurRE, respectively. Currently, the EboxNeuro is thought to be the target of NeuroD1 during fetal development, but this factor may not account for activity in the adult pituitary; it is also unknown whether the NurRE and NGFI-B-related factors are active before establishment of the hypothalamic-pituitary portal system. In order to assess the importance of these regulatory elements and their cognate TFs throughout pituitary organogenesis and in the adult, we have assessed the activity of mutant POMC promoters in transgenic mice throughout development. These experiments indicate that the EboxNeuro and cognate basic helix-loop-helix factors are required throughout development and in the adult gland, beyond expression of NeuroD1. Similarly, the data reveal sustained importance of the NurRE and its cognate factors throughout pituitary development. These data contrast the sustained dependence throughout development on the same regulatory elements with the highly dynamic patterns of TF expression and the modulation of their activity in response to signaling pathways.
Ultrafast dynamic reflectivity of vanadium pentoxide
Authors: Taft Gregory J. , Newby Matthew T. , Hrebik Joel J. , Onellion Marshall , George Thomas F. , Szentesi Dániel , Szatmári Sándor , Nánai László
Published: April 2008

The ultrafast dynamic reflectivity of vanadium pentoxide is measured using 40 fs pulses from a self-mode-locked Ti:sapphire laser. The laser pulses excite acoustic vibrations at wave numbers of 145 and 103 cm−1. The amplitudes of the induced oscillations depend strongly on the orientation between the linear polarization of the laser pulses and the crystal axes, with the largest oscillations observed for an orientation of 45°. The higher-frequency oscillation is induced immediately upon arrival of the laser pulse, while the lower-frequency oscillation appears a few picoseconds later. The oscillations persist for approximately 10 ps after the arrival of the pulse. The oscillations are attributed to transverse acoustic modes propagating along the a-axis of the crystal.
Corrosion resistance of ZrO2–Zr-coated biodegradable surgical magnesium alloy
Authors: Xin Yunchang , Liu Chenglong , Zhang Wenjun , Huo Kaifu , Tang Guoyi , Tian Xiubo , Chu Paul K.
Published: April 2008

Magnesium alloys are potential biodegradable biomaterials in hard tissue implants. However, the fast degradation rate in the biological environment has hampered widespread applications. We propose to use a ZrO2 coating in conjunction with a Zr transition layer to improve the corrosion resistance of AZ91 magnesium alloy. X-ray photoelectron spectroscopy discloses that the coating is composed of ZrO2. The Vickers hardness measurement demonstrates that the surface hardness of the alloy is significantly enhanced. The electrochemical behavior of the coated sample is systematically evaluated by means of potentiodynamic polarization, open-circuit potential evolution, and electrochemical impedance spectroscopy. The electrochemical results indicate that the corrosion resistance of the coated alloy is enhanced significantly, and the electrode-controlled processes in a coated alloy–solution system are discussed.
Interfacial characteristics and mechanical properties of a modified Nb-containing Zr-based bulk metallic glass composite reinforced with W fiber
Authors: Wang M.L. , Hui X. , Chen G.L.
Published: April 2008

Tungsten (W) fiber reinforced Zr47Ti13Cu11Ni10Be16Nb3 bulk metallic glass composite has been prepared by melt infiltration casting. Interfacial characteristics of the composite were analyzed by sessile drop technique, x-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe x-ray microanalysis (EPMA), and nanoindenter. Results indicate that Zr47Ti13Cu11Ni10Be16Nb3 melt wets the W substrate, and the interfacial bond composed of a diffusion–dissolution layer between Zr47Ti13Cu11Ni10Be16Nb3 matrix and W fiber is in good condition. Due to these excellent interfacial characteristics, the mechanical properties of the composite are considerably enhanced with increasing volume fraction of W fiber. It was found that the compressive strength of 70% volume fraction of W fiber composite is 2.6 GPa, which is 58% higher than the value exhibited by the unreinforced matrix. At the same time, the reinforced matrix exhibits 13% plastic deformation when tested under quasi-static compression conditions. Instead of shear mode seen for the unreinforced matrix, the failure mode of the 70% volume fraction W fiber composite is mainly caused by fiber splitting and buckling. Also, the W fiber hinders localized shear bands from propagating and gives rise to multiple shear bands, which results in the enhancement of the compressive strength and plastic deformation.
Isothermal oxidation of bulk Zr2Al3C4 at 500 to 1000 °C in air
Authors: He L.F. , Lin Z.J. , Bao Y.W. , Li M.S. , Wang J.Y. , Zhou Y.C.
Published: April 2008

The isothermal oxidation behavior of Zr2Al3C4 in the temperature range of 500 to 1000 °C for 20 h in air has been investigated. The oxidation kinetics follow a parabolic law at 600 to 800 °C and a linear law at higher temperatures. The activation energy is determined to be 167.4 and 201.2 kJ/mol at parabolic and linear stages, respectively. The oxide scales have a monolayer structure, which is a mixture of ZrO2 and Al2O3. As indicated by x-ray diffraction and Raman spectra, the scales formed at 500 to 700 °C are amorphous, and at higher temperatures are α-Al2O3 and t-ZrO2 nanocrystallites. The nonselective oxidation of Zr2Al3C4 can be attributed to the strong coupling between Al3C2 units and ZrC blocks in its structure, and the close oxygen affinity of Zr and Al.
Grain boundary strengthening in copper/niobium multilayered foils and fine-grained niobium
Authors: Lewis A.C. , Eberl C. , Hemker K.J. , Weihs T.P.
Published: April 2008

Uniaxial tensile tests were performed on Cu/Nb multilayered foils to investigate yield strength and grain boundary strengthening in the layered foils at room temperature and in fine-grained Nb at 600 °C. At room temperature, yielding in Cu/Nb multilayered foils is controlled by deformation in both layers, and grain boundary strengthening is observed with a Hall–Petch slope (kRT) of 198 ± 56 MPa·μm1/2 at a strain rate of 10−4 s−1. At 600 °C, yielding in Cu/Nb multilayered foils is controlled by deformation in just the Nb layers. Hall–Petch strengthening is observed over a range of strain rates, but the Hall–Petch slope decreases from 197 ± 71 MPa·μm1/2 for a strain rate of 10−4 s−1 to only 25 ± 40 MPa·μm1/2 for a strain rate of 10−6 s−1. The significant drop in the Hall–Petch slope for Nb with decreasing strain rate indicates a change in the controlling deformation mechanism from dislocation glide to dislocation creep.
Carbon nanostructures formed on mesoporous silica by catalytic chemical vapor deposition of ethene
Authors: Zhang Lingxia , Shi Jianlin , Li Jiangtian , Hua Zile , Ruan Meiling
Published: April 2008

Three different strategies, wet impregnation, in situ reduction, and grafting with silane coupling agents, have been used to introduce CoNi nanoparticles with different existing forms into mesoporous silica. These composites were used as catalysts to grow nanostructured carbons by catalytic chemical vapor deposition using ethene. Carbon nanotubes (CNTs) with different inner diameters can grow out of mesoporous silica particles incorporated with CoNi nanoclusters. Many fewer CNTs could be found in the pore channels of the sample prepared by using silane coupling agents than in those of the sample synthesized via wet impregnation. No CNTs formed in the pore channels of the sample prepared by in situ reduction. After the removal of silica, different carbon nanostructures have been obtained in the pore channels. Ordered graphite carbon mesostructure was obtained from the sample prepared by in situ reduction. Highly dispersed metal catalysts inside mesopore channels are favorable for the formation of graphite carbons with ordered mesostructures.
Grain growth and texture development in lithium fluoride thin films
Authors: Kim Hakkwan , King Alexander H.
Published: April 2008

We have studied grain-growth and texture development in polycrystalline lithium fluoride thin films using dark-field transmission electron microscopy. We demonstrate that we can isolate the size distribution of 〈111〉 surface normal grains from the overall size distribution, based on simple and plausible assumptions about the texture. The {111} texture formation and surface morphology were also observed by x-ray diffraction and atomic force microscopy, respectively. The grain-size distributions become clearly bimodal as the annealing time increases, and we deduce that the short-time size distributions are also a sum of two overlapping peaks. The smaller grain-size peak in the distribution corresponds to the {111}-oriented grains, which do not grow significantly, while all other grains increase in size with annealing time. A novel feature of the LiF films is that the {111} texture component strengthens with annealing, despite the absence of growth for these grains, through the continued nucleation of new grains.
Preparation of MgB2 powder for ex situ tape with high Jc-B performance
Authors: Nakane Takayuki , Kumakura Hiroaki
Published: April 2008

The relationship between the preparation conditions of MgB2 powder and the performance of the critical current density (Jc) of an applied magnetic field (B) of the final ex situ tape produced from it was investigated. The pelletizing pressure of the precursor is crucially important for improving the Jc-B performance of ex situ tape. The higher the pressure, the greater the resulting Jc of the ex situ MgB2 tape. We have shown that the pelletizing pressure used for the precursor mixture during the powder preparation process affects the phases formed in the MgB2. On the other hand, the heating time used is effective in changing the slope of the Jc-B curve of the final tape. This is thought to be due to a change in the crystallinity of the prepared MgB2 powder. The experimental data gathered here will become the basis for investigating the establishment of a guideline for preparing the starting powder used for the manufacture of ex situ MgB2 tape.
Effects of microstructure on the formation, shape, and motion of voids during electromigration in passivated copper interconnects
Authors: Choi Z-S. , Mönig R. , Thompson C.V.
Published: April 2008

In situ scanning electron microscope observations have been performed on passivated damascene Cu interconnect segments of different widths during accelerated electromigration tests. In some cases, voids form and grow at the cathode. However, an alternative failure mode is also observed, during which voids form distant from the cathode end of the interconnect segment and drift toward the cathode, where they eventually lead to failure. The number of observations of this failure mode increased with increasing linewidth. During void motion, the shape and the velocity of the drifting voids varied significantly. Postmortem electron backscattered diffraction (EBSD) analysis was performed after in situ testing, and a correlation of EBSD data with the in situ observations reveals that locations at which voids form, their shape evolution, and their motion all strongly depend on the locations of grain boundaries and the crystallographic orientations of neighboring grains.
The influence of Nb and Zr on glass-formation ability in the ternary Fe–Nb–B and Fe–Zr–B and quaternary Fe–(Nb,Zr)–B alloy systems
Authors: Yao J.H. , Yang H. , Zhang J. , Wang J.Q. , Li Y.
Published: April 2008

Glass-forming ability (GFA) in relation to microstructure evolution in the ternary Fe–Nb–B and Fe–Zr–B and quaternary Fe–(Nb,Zr)–B systems was systematically studied in a three-dimensional composition space. Through navigating, it was revealed that alloys with the optimum glass-forming ability (GFA) are coupled with composition regions surrounded by competing crystalline phases. Alloys Fe71Nb6B23, Fe77Zr4B19, and Fe71(Nb0.8Zr0.2)6B23 were illustrated to be the best glass formers in the ternary Fe–Nb–B and Fe–Zr–B systems and the quaternary Fe–(Nb,Zr)–B system, respectively, with a critical size for amorphous formation up to 2 mm. They were compared with the theoretical predictions on the basis of an efficient dense-packing model, and good agreements were obtained.
The most powerful tool for the structural analysis of tungsten suboxide nanowires: Raman spectroscopy
Authors: Lu Dong Yu , Chen Jian , Deng Shao Zhi , Xu Ning Sheng , Zhang Wei Hong
Published: April 2008

Crystalline tungsten suboxide nanowires were grown on silicon substrates by thermal evaporation of tungsten powder in a flow of argon gas without any catalyst. With different growth temperatures, two kinds of tungsten suboxide nanowires (W18O49 and W20O58) were obtained. The structures, morphologies, and compositions of these two nanowires were characterized by scanning electron microscopy (SEM), electron probe microanalyzer (EPMA), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and Raman techniques. The results show that XRD and TEM are not good characterization techniques for identifying W18O49 and W20O58 nanowires; however, Raman spectroscopy (RS) is a powerful tool to distinguish the difference between them. This is due to the notable molecular bond contributing to the vibrational frequency.
The evolution of grain-boundary cracking evaluated through in situ tensile-creep testing of Udimet alloy 188
Authors: Boehlert C.J. , Longanbach S.C. , Nowell M. , Wright S.
Published: April 2008

In situ scanning electron microscopy was performed during elevated-temperature (⩽760 °C) tensile-creep deformation of a face-centered-cubic cobalt-based Udimet 188 alloy to characterize the deformation evolution and, in particular, the grain boundary-cracking evolution. In situ electron backscatter diffraction observations combined with in situ secondary electron imaging indicated that general high-angle grain boundaries were more susceptible to cracking than low-angle grain boundaries and coincident site-lattice boundaries. The extent of general high-angle grain-boundary cracking increased with increasing creep time. Grain-boundary cracking was also observed throughout subsurface locations as observed for postdeformed samples. The electron backscattered diffraction orientation mapping performed during in situ tensile-creep deformation proved to be a powerful means for characterizing the surface deformation evolution and in particular for quantifying the types of grain boundaries that preferentially cracked.
Improved critical current densities in MgB2 tapes fabricated through an ex situ process using powders treated in various chemical solutions
Authors: Fujii H. , Togano K. , Ozawa K.
Published: April 2008

We have studied grain coupling and critical current density (Jc) in ex situ processed Fe-sheathed MgB2 tapes fabricated by a powder-in-tube (PIT) technique, using MgB2 powder soaked in various chemical solutions. The grain coupling and the Jc are strongly influenced by the chemical solutions. Compared with the chemical treatment in a benzene solution of benzoic acid, the use of a cyclohexane solution of benzoic acid doubles the Jc value. Cyclohexane is less stable and hence effectively removed from the surface of MgB2 grains, bringing about the improved coupling of grains and the Jc enhancement.
Poisson’s ratio and fragility of bulk metallic glasses
Authors: Na J.H. , Park E.S. , Kim Y.C. , Fleury E. , Kim W.T. , Kim D.H.
Published: April 2008

The correlation among apparent global plasticity, Poisson’s ratio, and fragility in monolithic bulk metallic glass (BMG) alloys has been investigated in the present study. The shear and bulk moduli in monolithic Cu-based BMG alloys have been measured by resonant ultrasound spectroscopy (RUS) and ultrasonic technique. The Cu43Zr43Al7Ag7 BMG alloy showing a large apparent global plasticity (∼8%) exhibits a high Poisson’s ratio when compared with that of Cu43Zr43Al7Be7 BMG alloy. In addition, the fragility of Cu-based BMG alloys can be obtained by differential scanning calorimetry (DSC). The fragility index m of Cu43Zr43Al7Ag7 BMG alloy is slightly larger than that of Cu43Zr43Al7Be7 BMG alloy. The correlation between Poisson’s ratio and fragility in BMG alloys can be presented by a simple relation of m − 17 = 14 (B∞/G∞ − 1). Poisson’s ratio and fragility might be regarded as an important parameter that controls global plasticity of glass-forming alloys.
Unusual magnetic properties of Mn-doped ThO2 nanoparticles
Authors: Bhide M.K. , Kadam R.M. , Tyagi A.K. , Muthe K.P. , Salunke H.G. , Gupta S.K. , Vinu A. , Asthana A. , Godbole S.V.
Published: April 2008

We report the synthesis of Th1–xMnxO2 (x = 0, 0.001, 0.002, 0.004, and 0.01 wt%) nanoparticles by the urea combustion method using thorium nitrate gel followed by heat treatment at a higher temperature (T). The obtained Th1–xMnxO2 nanocrystals were characterized by x-ray diffraction (XRD), direct-current magnetization (M) measurements and electron paramagnetic resonance (EPR). XRD analysis revealed that Th1–xMnxO2 crystallizes in the cubic structure (Fm3m). M measurements showed ferromagnetic ordering at room temperature for Th0.99Mn0.01O2 samples annealed at 775 K. An intense and broad ferromagnetic resonance (FMR) having linewidth of ∼1200 G, was observed at relatively lower fields in the EPR spectra of Th0.99Mn0.01O2 samples annealed at 775 K, indicating the presence of a ferromagnetic phase at room temperature. EPR measurements were used to estimate the number of spins involved in the ferromagnetic ordering. Out of the total Mn present in Th0.99Mn0.01O2 samples, about 25% of the Mn2+ ions were found to be responsible for the ferromagnetic ordering. In addition to the FMR signal, a weak hyperfine sextet was observed at g = 2.0048 (55Mn, I = 5/2), which corresponds to the −1/2 ↔ +1/2 transition of Mn2+ ions, suggesting its presence at thorium sites (uncoupled spins). X-ray photoelectron spectra indicated that the manganese ions exist mainly as Mn2+, Mn3+, and Mn4+. The room-temperature ferromagnetism may be attributed to the coupling between these Mn2+ ions at thorium sites in ThO2 rather than due to the formation of any metastable secondary phases.
Load transfer in bovine plexiform bone determined by synchrotron x-ray diffraction
Authors: Akhtar R. , Daymond M.R. , Almer J.D. , Mummery P.M.
Published: April 2008

High-energy synchrotron x-ray diffraction (XRD) has been used to quantify load transfer in bovine plexiform bone. By using both wide-angle and small-angle XRD, strains in the mineral as well as the collagen phase of bone were measured as a function of applied compressive stress. We suggest that a greater proportion of the load is borne by the more mineralized woven bone than the lamellar bone as the applied stress increases. With a further increase in stress, load is shed back to the lamellar regions until macroscopic failure occurs. The reported data fit well with reported mechanisms of microdamage accumulation in bovine plexiform bone.
Giant pop-ins in nanoindented silicon and germanium caused by lateral cracking
Authors: Oliver D.J. , Lawn B.R. , Cook R.F. , Reitsma M.G. , Bradby J.E. , Williams J.S. , Munroe P.
Published: April 2008

Giant “pop-in” displacements are observed in crystalline silicon and germanium during high-load nanoindentation with a spherical diamond tip. These events are consistent with material removal triggered by lateral cracking during loading, which poses a hazard to microelectromechanical systems (MEMS) operation. We examine the scaling of the pop-in displacements as a function of peak indentation load and demonstrate a correlation with the depth of the plastic contact zone. We argue that giant pop-ins may occur in a broad range of highly brittle materials.
Creep characteristics of alumina, nickel aluminate spinel, zirconia composites
Authors: Dillon R. Peter , Kim Dong-Kyu , Trujillo Joy E. , Kriven Waltraud M. , Mecartney Martha L.
Published: April 2008

Fine grained, three-phase ceramic composites that exhibit favorable toughness, hardness, and high room-temperature strength were evaluated for high-temperature mechanical stability. A 50vol%Al2O3–25vol%NiAl2O4–25vol%3 mol%yttria-stabilized tetragonal zirconia polycrystal (3Y–TZP) and a 33vol%Al2O3–33vol%NiAl2O4–33vol%3Y-TZP composite were compression creep tested at temperatures between 1350 and 1450 °C under constant stresses of 20–45 MPa. The three-phase microstructure effectively limited grain growth (average d0 = 1.3 μm, average df = 1.6 μm after 65% true strain). True strain rates were 10−4 to 10−6 s−1 with stress exponents n = 1.7 to 1.8 and a grain-size exponent p = 1.3. A method for compensating for grain growth is presented using stress jump tests. The apparent activation energy for high-temperature deformation for 50vol%Al2O3–25vol%NiAl2O4–25vol%3Y–TZP was found to be 373 kJ/mol-K.
Reversible multilevel resistance switching of Ag–La0.7Ca0.3MnO3–Pt heterostructures
Authors: Shang Dashan , Chen Lidong , Wang Qun , Wu Zihua , Zhang Wenqing , Li Xiaomin
Published: April 2008

The electric-pulse–induced resistance switching of the Ag–La0.7Ca03MnO3(LCMO)–Pt heterostructures was studied. The multilevel resistance switching (MLRS), in which several resistance states can be obtained, was observed in the switching from high to low resistance state (HRS → LRS) by applying electric pulse with various pulse voltages. The threshold pulse voltages of MLRS are related to the initial resistance values as well as the switching directions. On the other hand, the resistance switching behavior from low to high resistance states (LRS → HRS) shows unobvious MLRS. According to the resistance switching behavior in serial and parallel modes, MLRS was explained by the parallel effect of multifilament forming/rupture in the Ag–LCMO interface layer. The present results suggest a possible application of Ag–LCMO–Pt heterostructures as multilevel memory devices.
Damage tolerance andR-curve behavior of Al2O3–ZrO2–Nb multiphase composites with synergistic toughening mechanism
Authors: Gutiérrez-González C.F. , Bartolomé J.F.
Published: April 2008

In the present work, the damage tolerance andR-curve behavior of alumina–zirconia–niobium multiphase composites were studied by the indentation strength method. A matrix of yttria-stabilized zirconia (3Y–TZP) strengthened with particles of Al2O3(ATZ) and an alumina matrix strengthened with particles of 3Y-TZP (ZTA) were prepared by hot press of commercial powders, containing Nb metal particles as reinforcing phase. The crack growth behavior was analyzed, and it was found that stress-induced transformation toughening of ZrO2and bridging of the Nb inclusions were the two main factors that can shield an advancing crack and exert crack closure stresses on the crack wake. Moreover, on the basis of quantitative toughening analysis, it is argued that a synergistic effect originated from the interaction between the toughening mechanisms of Nb grains and zirconia, takes place in the alumina–zirconia–Nb multiphase composites. This showed that the combined toughening effect was bigger than the sum of the individual toughening effects when either reinforcement acted alone.
Microstructures, surface areas, and oxygen absorption of Ti and Ti–Zr–V films grown using glancing-angle sputtering
Authors: Li Chien-Cheng , Huang Jow-Lay , Lin Ran-Jin , Lin Hong-Ping , Lii Ding-Fwu , Liu Chuan-Pu
Published: April 2008

Highly porous Ti and TiZrV getter film coatings have been successfully grown on (100) silicon substrates using the glancing-angle direct-current magnetron sputtering method. The evolution of the microstructures of the Ti and the TiZrV films strongly depends on the sputtering flux rate, surface diffusion rate, nucleation rate, compositions, and self-shadowing geometry of the nuclei on the sputtering flux. The larger the glancing angle, the higher the porosity and specific surface area of the Ti and TiZrV films. The weight-gain results strongly depend on several factors, such as specific surface area, the surface structure of the getter film, the diffusion rate of O in the getter film, the reactivity of Ti, Zr, and V on O, and the order of the stabilities of Ti, Zr, and V oxides on the film’s surface. Porous Ti film absorbs oxygen better than porous TiZrV film does due to its higher surface area and the high diffusion rate of O in Ti films.
Regulation of Self-Renewal and Pluripotency by Sox2 in Human Embryonic Stem Cells
Authors: Fong Helen , Hohenstein Kristi A. , Donovan Peter J.
Published: April 2008

Human embryonic stem (hES) cells, derived from blastocysts, are capable of unlimited self-renewal and differentiation into all cell lineages of the body. Because of their pluripotent nature, hES cells are valuable tools for understanding human development and advancing the field of regenerative medicine. However, one key to harnessing the therapeutic power of hES cells for biomedical applications begins with determining how these cells maintain their pluripotent and undifferentiated state. Studies in mice have implicated three factors in regulating pluripotency in embryonic stem cells, Oct4, Nanog, and Sox2. However, significant differences in growth regulation between mouse embryonic stem and hES cells have been identified, suggesting a need to determine when and how factors work in hES cells. To date, the transcription factors Oct4 and Nanog have been identified as critical regulators of stem cell fate by functional studies in hES cells. To determine the role of Sox2 in maintaining hES cell pluripotency and self-renewal, we used RNA interference to specifically knock down Sox2 gene expression. Reduction of Sox2 expression in hES cells results in loss of the undifferentiated stem cell state, as indicated by a change in cell morphology, altered stem cell marker expression, and increased expression of trophectoderm markers. In addition, knockdown of Sox2 results in reduced expression of several key stem cell factors, including Oct4 and Nanog, linking these three factors together in a pluripotent regulatory network.

Disclosure of potential conflicts of interest is found at the end of this article.
Concise Review: Adult Multipotent Stromal Cells and Cancer: Risk or Benefit?
Authors: Lazennec Gwendal , Jorgensen Christian
Published: April 2008

This review focuses on the interaction between multipotent stromal cells (MSCs) and carcinoma and the possible use of MSCs in cell-based anticancer therapies. MSCs are present in multiple tissues and are defined as cells displaying the ability to differentiate in multiple lineages, including chondrocytes, osteoblasts, and adipocytes. Recent evidence also suggests that they could play a role in the progression of carcinogenesis and that MSCs could migrate toward primary tumors and metastatic sites. It is possible that MSCs could also be involved in the early stages of carcinogenesis through spontaneous transformation. In addition, it is thought that MSCs can modulate tumor growth and metastasis, although this issue remains controversial and not well understood. The immunosuppressive properties and proangiogenic properties of MSCs account, at least in part, for their effects on cancer development. On the other hand, cancer cells also have the ability to enhance MSC migration. This complex dialog between MSCs and cancer cells is certainly critical for the outcome of tumor development. Interestingly, several studies have shown that MSCs engineered to express antitumor factors could be an innovative choice as a cell-mediated gene therapy to counteract tumor growth. More evidence will be needed to understand how MSCs positively or negatively modulate carcinogenesis and to evaluate the safety of MSC use in cell-mediated gene strategies.

Disclosure of potential conflicts of interest is found at the end of this article.
Assessment of Stromal-Derived Inducing Activity in the Generation of Dopaminergic Neurons from Human Embryonic Stem Cells
Authors: Vazin Tandis , Chen Jia , Lee Chun-Ting , Amable Rose , Freed William J.
Published: April 2008

Producing dopaminergic (DA) neurons is a major goal of human embryonic stem cell (hESC) research. DA neurons can be differentiated from hESC by coculture with the mouse PA6 stromal cell line; this differentiation-inducing effect is termed stromal-derived inducing activity (SDIA). The molecular and biochemical nature of SDIA is, however, unknown. Various studies have suggested that SDIA involves either a fixation-resistant component located on the PA6 cell surface or factors secreted into the medium by PA6 cells. To address this question, hESC were cocultured with PA6 cells for 12 days and then further differentiated with sonic hedgehog homolog, fibroblast growth factor-8, and glial cell line-derived neurotrophic factor. After 18 days, 34% of cells were tyrosine hydroxylase (TH)+. When PA6 cells were fixed or irradiated, the number of TH+ cells was decreased by threefold, whereas mitomycin-c treatment of feeder cells decreased the number of TH+ cells by 32%. The neural-inducing effect of PA6 cells, as monitored by β-III-tubulin expression, was minimally affected by mitomycin-c treatment or fixation but was decreased 50% by irradiation. Medium conditioned by PA6 cells was ineffective in differentiating TH+ cells when used alone. Conditioned medium combined with heparin and/or fixed PA6 cells produced TH+ cell differentiation, although less effectively than PA6 cell coculture. Thus, PA6 cell surface activity is required for neural differentiation of hESC, but secreted factors are required for the specific DA neuron-inducing effect.

Disclosure of potential conflicts of interest is found at the end of this article.
Neuropeptide Y Promotes Neurogenesis in Murine Subventricular Zone
Authors: Agasse Fabienne , Bernardino Liliana , Kristiansen Heidi , Christiansen Søren H. , Ferreira Raquel , Silva Bruno , Grade Sofia , Woldbye David P.D. , Malva João O.
Published: April 2008

Stem cells of the subventricular zone (SVZ) represent a reliable source of neurons for cell replacement. Neuropeptide Y (NPY) promotes neurogenesis in the hippocampal subgranular layer and the olfactory epithelium and may be useful for the stimulation of SVZ dynamic in brain repair purposes. We describe that NPY promotes SVZ neurogenesis. NPY (1 μM) treatments increased proliferation at 48 hours and neuronal differentiation at 7 days in SVZ cell cultures. NPY proneurogenic properties are mediated via the Y1 receptor. Accordingly, Y1 receptor is a major active NPY receptor in the mouse SVZ, as shown by functional autoradiography. Moreover, short exposure to NPY increased immunoreactivity for the phosphorylated form of extracellular signal-regulated kinase 1/2 in the nucleus, compatible with a trigger for proliferation, whereas 6 hours of treatment amplified the phosphorylated form of c-Jun-NH2-terminal kinase signal in growing axons, consistent with axonogenesis. NPY, as a promoter of SVZ neurogenesis, is a crucial factor for future development of cell-based brain therapy.

Disclosure of potential conflicts of interest is found at the end of this article.
The influence of traumatic acid on the growth and metabolite content of the green alga Chlorella vulgaris Beijerinck
Authors: Pietryczuk Anna , Piotrowska Alicja , Czerpak Romuald
Published: April 2008

The effect of exogenous traumatic acid, (2E)-dodecene-1,12-dioic acid (TA), at concentrations of 10-6 - 10-3 M on the growth and development of the unicellular green alga Chlorella vulgaris was examined over 7 days. TA plays an important role in algal growth and development. Treatment with 10-5 M TA resulted in the greatest increase in cell numbers, by 77%, chlorophyll a content, by 126%, chlorophyll b, by 45%, total carotenoids, by 65%, monosaccharides, by 111%, and water-soluble proteins, by 37%, in relation to the control. After three days of treatment with 10-5 M TA cultures were analysed by SDS-PAGE, which showed the presence of new polypeptides with molecular weights 13-103 kDa.
Resuscitation of Seventeen-year Stressed Salmonella typhimurium
Authors: Amel Dhiaf , Amina Bakhrouf
Published: April 2008

Salmonella enterica serovar typhimurium was stressed by incubation in seawater microcosms for seventeen years. The microcosms were prepared in such a way as to allow progressive evaporation of the water. Despite being introduced into the sterile seawater at very high concentrations, the Salmonella rapidly declined to levels undetectable by plate counts on nutrient agar. After two years of starvation, about half of the seawater volume had evaporated from each microcosm, and salt crystals appeared. Inoculation of the salty suspension did not result in any culturable strains in selective and non-selective media. However, incubation of samples in nutrient-rich broth, without supplemental growth factors, allowed resuscitation of stressed cells, yielding colonies that remained viable for extended periods of time. After three years the total volume of water had evaporated from each microcosm, and only salt crystals remained. These microcosms were then incubated at room temperature for seventeen years. Resuscitation of VBNC Salmonella from the salt crystals was conducted in vitro and in vivo; recovery occurring after incubation in both nutrient broth and in mice. Recovery occurred in the Salmonella administered orally into the mice, but not in those administered by intra-peritoneal injection. The identity of initial, stressed and revived strains was confirmed by DGGE analysis and sequencing of 16S RNA gene fragments.