bluuebunny/crossref_metadata_2025 huggingface dataset:
p53 modulates homologous recombination by transcriptional regulation of the RAD51 gene
Authors: Arias‐Lopez Carmen , Lazaro‐Trueba Iciar , Kerr Peter , Lord Christopher J , Dexter Tim , Iravani Marjan , Ashworth Alan , Silva Augusto
Published: December 2005

DNA repair by homologous recombination is involved in maintaining genome stability. Previous data report that wild‐type p53 suppresses homologous recombination and physically interacts with Rad51. Here, we show the in vivo binding of wild‐type p53 to a p53 response element in the promoter of Rad51 and the downregulation of Rad51 messenger RNA and protein by wild‐type p53, favoured by DNA damage. Moreover, wild‐type p53 inhibits Rad51 foci formation in response to double‐strand breaks, whereas p53 contact mutant R280K fails to repress Rad51 mRNA and protein expression and Rad51 foci formation. We propose that transcriptional repression of Rad51 by p53 participates in regulating homologous recombination, and impaired Rad51 repression by p53 mutants may contribute to malignant transformation.
Convergence of vitamin D and retinoic acid signalling at a common hormone response element
Authors: Tavera‐Mendoza Luz , Wang Tian‐Tian , Lallemant Benjamin , Zhang Rui , Nagai Yoshihiko , Bourdeau Véronique , Ramirez‐Calderon Mario , Desbarats Julie , Mader Sylvie , White John H
Published: December 2005

Although 1,25‐dihydroxyvitamin D3 (1,25D3) and retinoic acid (RA) have distinct developmental and physiological roles, both regulate the cell cycle. We provide molecular and genomic evidence that their cognate nuclear receptors regulate common genes through everted repeat TGA(C/T)TPyN8PuG(G/T)TCA (ER8) response elements. ER8 motifs were found in the promoters of several target genes of 1,25D3 and/or RA. Notably, an element was characterized in the cyclin‐dependent kinase (CDK) inhibitor p19ink4d gene, and 1,25D3‐ or RA‐induced p19INK4D expression. P19ink4d knockdown together with depletion of p27kip1, another CDK inhibitor regulated by 1,25D3 and RA, rendered cells resistant to ligand‐induced growth arrest. Remarkably, p19INK4D‐deficient cells showed increased autophagic cell death, which was markedly enhanced by 1,25D3, but not RA, and attenuated by loss of p27KIP1. These results show a limited crosstalk between 1,25D3 and RA signalling by means of overlapping nuclear receptor DNA binding specificities, and uncover a role for p19INK4D in control of cell survival.
Miniature bioreactors for automated high‐throughput bioprocess design (HTBD): reproducibility of parallel fed‐batch cultivations with Escherichia coli
Authors: Puskeiler Robert , Kusterer Andreas , John Gernot T. , Weuster‐Botz Dirk
Published: December 2005

To verify the reproducibility of cultivations of Escherichia coli in novel millilitre‐scale bioreactors, fully automated fed‐batch cultivation was performed in seven parallel‐operated ml‐scale bioreactors with an initial volume of 10 ml/reactor. The process was automatically controlled by a liquid‐handling system responsible for glucose feeding, titration and sampling. Atline analysis (carried out externally of the reaction vessel with a short time delay) comprised automated pH and attenuance measurements. The partial pressure of oxygen (pO2) was measured online by a novel fluorimetric sensor block measuring the fluorescence lifetime of fluorophors immobilized inside the millilitre‐scale bioreactors. Within a process time of 14.6 h, the parallel cultivation yielded a dry cell weight of 36.9±0.9 g·l−1. Atline pH measurements were characterized by an S.D. of <1.1% throughout the process. Computational‐fluid‐dynamics simulation of single‐phase flow yields a mean power input of 21.9 W·l−1 at an impeller speed of 2800 rev./min corresponding to a power number (NP) of 3.7.
Hydrolysis characteristics of a β‐1,3‐d‐glucan elicitor from yeast
Authors: Huang Gang‐Liang , Zhang Hou‐Cheng , Wang Peng‐George
Published: December 2005

Fluorophore‐assisted carbohydrate electrophoresis (FACE) is a straightforward, sensitive method for determining the presence and relative abundance of individual (oligo)saccharides in a(n) (oligo)saccharide mixture. The single‐terminal aldehydes of oligoglucoside residues released by acid hydrolysis of β‐1,3‐d‐glucan from yeast were tagged with the charged fluorophore ANTS (8‐aminonaphthalene‐1,3,6‐trisulphonate), and separated with high resolution on the basis of size by PAGE. ANTS fluorescence labelling was not biased by oligoglucoside length; therefore band fluorescence intensity was directly related to the relative abundance of individual oligoglucoside moieties in a heterogeneous sample. FACE analysis revealed that the major oligoglucoside mixture released by acid hydrolysis from β‐1,3‐d‐glucan was composed of monosaccharide, disaccharide, trisaccharide, tetrasaccharide, pentasaccharide, hexasaccharide, heptasaccharide and octasaccharide, and the order of abundance from high to low was trisaccharide, monosaccharide, disaccharide, tetrasaccharide, pentasaccharide, hexasaccharide, heptasaccharide and octasaccharide respectively. In conclusion, FACE represents an accessible, sensitive and quantitative analytical tool enabling the characterization of a(n) (oligo)saccharide mixture.
Contact stimulation of prostate cancer cell migration: the role of gap junctional coupling and migration stimulated by heterotypic cell‐to‐cell contacts in determination of the metastatic phenotype of Dunning rat prostate cancer cells
Authors: Miekus Katarzyna , Czernik Marta , Sroka Jolanta , Czyz Jarosław , Madeja Zbigniew
Published: December 2005

Background information. Motile activity of tumour cells is regarded as a critical factor determining their metastatic potential. We have shown previously that contrary to the majority of normal cells, homotypic contacts between some tumour cells, among them low metastatic (AT‐2) and highly metastatic (MAT‐LyLu) rat prostate cancer cells, increase the speed of their movements. The aim of the present study was to determine the effect of heterotypic cell‐to‐cell contacts on the migration of rat prostate cancer cells differing in metastatic potential, and to correlate it with the intensity of homo‐ and heterologous gap junctional coupling.

Results. MAT‐LyLu and AT‐2 cells moving on the surface of fibroblasts displayed significantly greater cell displacement than those moving on plastic substrata. This effect correlated with the polarization (contact guidance) and increased speed of cell movements. However, in contrast with the migration on plastic substrata, where MAT‐LyLu cells displayed considerably higher motility than AT‐2 cells, no differences between both cell lines were observed on the surface of fibroblasts. On the other hand, in contrast with AT‐2, Mat‐LyLu cells displayed extensive homologous coupling mediated by connexin43 and were able to couple with normal fibroblasts.

Conclusion. Heterotypic contacts between migrating prostatic cancer cells and normal fibroblasts can strongly stimulate their migration during invasion; however, this effect does not correlate with the gap junctional coupling between cancer cells and normal fibroblasts.
Sphingomyelins suppress the targeted disruption of lysosomes/endosomes by the photosensitizer NPe6 during photodynamic therapy
Authors: Caruso Joseph A. , Mathieu Patricia A. , Reiners John J.
Published: December 2005

Recent studies have described a biochemical pathway whereby lysosome disruption and the released proteases initiate the intrinsic apoptotic pathway. Irradiation of murine hepatoma 1c1c7 cells preloaded with the lysosomal photosensitizer NPe6 (N-aspartyl chlorin e6) caused a rapid loss of Acridine Orange staining of acidic organelles, release of cathepsin D from late endosomes/lysosomes and the activation of procaspase-3. Pretreatment of NPe6-loaded cultures with 10–50 μM 3-O-MeSM (3-O-methylsphingomyelin) caused a concentration-dependent suppression of apoptosis following irradiation. This suppression reflected a stabilization of lysosomes/endosomes, as opposed to an inhibition of the accumulation of photosensitizer in these organelles. Exogenously added sphingomyelin, at comparable concentrations, offered some protection, but less than 3-O-MeSM. Fluorescence microscopy showed that 3-O-MeSM competed with NBD-C6-sphingomyelin (6-{[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]hexanoyl} sphingosyl phosphocholine) for co-localization with LysoTracker Red in acidic organelles. Pre-treatment of 1c1c7 cultures with 3-O-MeSM also suppressed the induction of apoptosis by TNFα (tumour necrosis factor α), but offered no protection against HA14-1 [ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate], staurosporine, tunicamycin or thapsigargin. These results suggest that exogenously added 3-O-MeSM is trafficked to and stabilizes late endosomes/lysosomes against oxidant-induced damage, and further implicate a role for lysosomal proteases in the apoptotic processes initiated by TNFα and lysosomal photosensitizers.
Distinct structure and activity recoveries reveal differences in metal binding between mammalian and Escherichia coli alkaline phosphatases
Authors: Zhang Le , Buchet René , Azzar Gérard
Published: December 2005

The amino acids involved in the coordination of two Zn2+ ions and one Mg2+ ion in the active site are well conserved from EAP (Escherichia coli alkaline phosphatase) to BIAP (bovine intestinal alkaline phosphatase), whereas most of their surrounding residues are different. To verify the consequences of this heterology on their specific activities, we compared the activity and structure recoveries of the metal-free forms (apo) of EAP and of BIAP. In the present study, we found that although the sensitivities of EAP and BIAP to ions remained similar, significant differences in dimeric structure stability of apo-enzymes were observed between EAP and BIAP, as well as in the kinetics of their activity and secondary structure recoveries. After mild chelation inactive apo-EAP was monomeric under mild denaturing conditions, whereas inactive apo-BIAP remained dimeric, indicating that the monomer–monomer contact was stronger in the mammalian enzyme. Dimeric apo-EAP (0.45 μM, corresponding to 4 units/ml) recovered approx. 80% of its initial activity after 3 min incubation in an optimal recovery medium containing 5 μM Zn2+ and 5 mM Mg2+, whereas dimeric apo-BIAP (0.016 μM, corresponding to 4 units/ml) recovered 80% of its native activity after 6 h incubation in an optimal recovery medium containing 0.5 μM Zn2+ and 5 mM Mg2+. Small and different secondary structure changes were also observed during activity recoveries of apo-BIAP and apo-EAP, which were not in parallel with the activity recoveries, suggesting that distinct and subtle structural changes are required for their optimal activity recoveries.
Promiscuous interaction of SNAP-25 with all plasma membrane syntaxins in a neuroendocrine cell
Authors: Bajohrs Mark , Darios Frédéric , Peak-Chew Sew-Yeu , Davletov Bazbek
Published: December 2005

SNAP-25 (25 kDa synaptosome-associated protein) is found in cells that release neurotransmitters and hormones, and plays a central role in the fusion of secretory vesicles with the plasma membrane. SNAP-25 has been shown to interact specifically with syntaxin 1, a 35 kDa membrane protein, to mediate the fusion process. Here, we investigated whether other known syntaxin isoforms found at the plasma membrane can serve as binding partners for SNAP-25 in vivo. In our analysis, we employed rat phaeochromocytoma PC12 cells that are often used as a model of neuronal functions. We now show that these cells contain large amounts of SNAP-25, which interacts not only with syntaxin 1, but also with ubiquitous syntaxins 2, 3 and 4. The plasma membrane syntaxins appear to occupy complementary domains at the plasma membrane. In defined reactions, the ubiquitous plasma membrane syntaxin isoforms, when in binary complexes with SNAP-25, readily bound vesicular synaptobrevin to form SDS-resistant SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) complexes implicated in membrane fusion. However, vesicular synaptotagmin and cytosolic complexin, both implicated in the fusion process, exhibited differential ability to interact with the SNARE complexes formed by syntaxins 1–4, suggesting that the plasma membrane syntaxins may mediate vesicle fusion events with different properties.
The G0/G1 switch gene 2 is a novel PPAR target gene
Authors: Zandbergen Fokko , Mandard Stéphane , Escher Pascal , Tan Nguan Soon , Patsouris David , Jatkoe Tim , Rojas-Caro Sandra , Madore Steve , Wahli Walter , Tafuri Sherrie , Müller Michael , Kersten Sander
Published: December 2005

PPARs (peroxisome-proliferator-activated receptors) α, β/δ and γ are a group of transcription factors that are involved in numerous processes, including lipid metabolism and adipogenesis. By comparing liver mRNAs of wild-type and PPARα-null mice using microarrays, a novel putative target gene of PPARα, G0S2 (G0/G1 switch gene 2), was identified. Hepatic expression of G0S2 was up-regulated by fasting and by the PPARα agonist Wy14643 in a PPARα-dependent manner. Surprisingly, the G0S2 mRNA level was highest in brown and white adipose tissue and was greatly up-regulated during mouse 3T3-L1 and human SGBS (Simpson–Golabi–Behmel syndrome) adipogenesis. Transactivation, gel shift and chromatin immunoprecipitation assays indicated that G0S2 is a direct PPARγ and probable PPARα target gene with a functional PPRE (PPAR-responsive element) in its promoter. Up-regulation of G0S2 mRNA seemed to be specific for adipogenesis, and was not observed during osteogenesis or myogenesis. In 3T3-L1 fibroblasts, expression of G0S2 was associated with growth arrest, which is required for 3T3-L1 adipogenesis. Together, these data indicate that G0S2 is a novel target gene of PPARs that may be involved in adipocyte differentiation.
Evolution of the acyl-CoA binding protein (ACBP)
Authors: Burton Mark , Rose Timothy M. , Færgeman Nils J. , Knudsen Jens
Published: December 2005

Acyl-CoA-binding protein (ACBP) is a 10 kDa protein that binds C12–C22 acyl-CoA esters with high affinity. In vitro and in vivo experiments suggest that it is involved in multiple cellular tasks including modulation of fatty acid biosynthesis, enzyme regulation, regulation of the intracellular acyl-CoA pool size, donation of acyl-CoA esters for β-oxidation, vesicular trafficking, complex lipid synthesis and gene regulation. In the present study, we delineate the evolutionary history of ACBP to get a complete picture of its evolution and distribution among species. ACBP homologues were identified in all four eukaryotic kingdoms, Animalia, Plantae, Fungi and Protista, and eleven eubacterial species. ACBP homologues were not detected in any other known bacterial species, or in archaea. Nearly all of the ACBP-containing bacteria are pathogenic to plants or animals, suggesting that an ACBP gene could have been acquired from a eukaryotic host by horizontal gene transfer. Many bacterial, fungal and higher eukaryotic species only harbour a single ACBP homologue. However, a number of species, ranging from protozoa to vertebrates, have evolved two to six lineage-specific paralogues through gene duplication and/or retrotransposition events. The ACBP protein is highly conserved across phylums, and the majority of ACBP genes are subjected to strong purifying selection. Experimental evidence indicates that the function of ACBP has been conserved from yeast to humans and that the multiple lineage-specific paralogues have evolved altered functions. The appearance of ACBP very early on in evolution points towards a fundamental role of ACBP in acyl-CoA metabolism, including ceramide synthesis and in signalling.
Recombinant prion protein does not possess SOD-1 activity
Authors: Jones Samantha , Batchelor Mark , Bhelt Daljit , Clarke Anthony R. , Collinge John , Jackson Graham S.
Published: December 2005

A considerable body of evidence now shows that PrP (prion protein) binds metal ions with high affinity and it has been claimed that the binding of copper (II) ions to PrP confers SOD (superoxide dismutase) activity. In turn, it has been suggested that PrP is a synaptic dismutase and that loss of this function, as a result of the conversion of PrPC into PrPSc, results in pathology and hence morbidity associated with prion disease. However, contrary to previous reports, in the present study we have found that PrP exhibits no detectable dismutase activity above baseline levels measured for copper (II) ions in water when assayed using a reliable procedure with a detection limit of at least 2 units of activity/mg of protein. This was true when the assay was performed with either PrP refolded from a denatured state in the presence of copper, as in previous studies, or native PrP loaded with copper. Thus if PrP has any role in oxidative stress, it must be indirect as a regulator of protective cellular responses.
Bacterial enzymes that can deglycate glucose- and fructose-modified lysine
Authors: Monnier Vincent M.
Published: December 2005

Deglycating enzymes, i.e. enzymes that reverse the initial stage of the Maillard reaction between glucose and primary amines, are known to occur in mammalian, fungal and other eukaryotic and prokaryotic cells. In this issue of Biochemical Journal, Wiame et al. now report the existence of bacterial enzymes and an operon that control the metabolism and deglycation of glucoselysine 6-phosphate, i.e. the phosphorylated condensation product of fructose and ϵ-aminolysine. The discovery has broad implications for bacterial metabolism and possibly for the repair of protein damage by fructose.
Haematopoietic stem cells and repair of the ischaemic heart
Authors: Balsam Leora B. , Robbins Robert C.
Published: December 2005

HSCs (haematopoietic stem cells) are multipotent stem cells that give rise to all cells of the blood cell lineage. In recent years, it has been proposed that bone marrow serves as a reservoir for cardiomyogenic precursors and that, following cardiac injury, these stem cells circulate to the site of injury where they contribute to myocardial repair and regeneration. This concept of stem cell plasticity has been controversial and, in fact, several key studies on the cardiomyogenic potential of HSCs have not been reproducible in the hands of independent investigators. Despite this controversy, the clinical community has pushed forward with clinical trials of bone marrow transplantation for the treatment of ischaemic heart disease. The following review summarizes the mechanistic underpinnings of bone marrow transplantation into ischaemic myocardium, focusing on the basic science that forms the foundation of this field, and highlights the controversies and new avenues for research that have emerged. It also describes the current state of the art in clinical trials of bone marrow transplantation for heart failure.
Adenoviral delivery of the β2-adrenoceptor gene in sepsis: a subcutaneous approach in rat for kidney protection
Authors: Nakamura Akio , Imaizumi Akira , Niimi Ryo , Yanagawa Yukishige , Kohsaka Takao , Johns Edward J.
Published: December 2005

Successful gene therapy requires gene delivery that is efficient, has an optimal route of administration and has biosafety. The aims of the present study were to evaluate the safety and applicability of the subcutaneous delivery route for adenoviral transgenes containing the human β2-adrenoceptor (adeno-β2-AR) and to investigate whether this approach prevented renal dysfunction in a rat model of endotoxaemic shock induced by LPS (lipopolysaccharide). Subcutaneous administration of adeno-β2-AR (a total of 1010 viral particles) significantly increased β-AR density in the kidney, lung and liver, but was without effect on physiological and plasma biochemical parameters. Moreover, this dose of virus did not cause any of the potential toxic responses of viral administration, such as inflammation and tissue TNF (tumour necrosis factor)-α expression. Although the LPS challenge caused a decrease in glomerular filtration rate, fractional excretion of sodium and renal β-AR density in all groups, the reduction in renal function was significantly less in the rats given adeno-β2-AR compared with non-treated rats. Thus, although further evaluation will be required, this initial study demonstrated that the subcutaneous injection of adeno-β2-AR was efficient, comparatively non-pathogenic and potentially therapeutic to deal with acute renal failure associated with sepsis.
Varying the heart rate response to dynamic exercise in pacemaker-dependent subjects: effects on cardiac output and cerebral blood velocity
Authors: Bogert Lysander W. J. , Erol-Yilmaz Ayten , Tukkie Raymond , Van Lieshout Johannes J.
Published: December 2005

Cerebral blood flow increases upon the transition from rest to moderate exercise, but becomes affected when the ability to raise CO (cardiac output) is limited. HR (heart rate) is considered to contribute significantly to the increase in CO in the early stages of dynamic exercise. The aim of the present study was to test whether manipulation of the HR response in patients dependent on permanent rate-responsive ventricular pacing contributes to the increase in CO, MCA Vmean [mean MCA (middle cerebral artery) velocity] and work capacity during exercise. The effect of setting the pacemaker to DSS (‘default’ sensor setting) compared with OSS (‘optimized’ sensor setting) on blood pressure, CO, SV (stroke volume) and MCA Vmean was evaluated during ergometry cycling. From rest to exercise at 75 W, the rise in HR in OSS [from 73 (65–87) to 116 (73–152) beats/min; P<0.05] compared with DSS [70 (60–76) to 97 (67–117) beats/min; P<0.05] was larger. There was an increase in SV during exercise with DSS, but not with OSS, such that, at all workloads, SVs were greater during DSS than OSS. The slope of the HR–CO relationship was larger with DSS than OSS (P<0.05). From rest to exercise, MCA Vsys (systolic MCA velocity) increased in OSS and DSS, and MCA Vdias (diastolic MCA velocity) was reduced with DSS. No changes were observed in MCA Vmean. Manipulation of the pacemaker setting had no effect on the maximal workload [133 (100–225) W in OSS compared with 129 (75–200) W in DSS]. The results indicate that, in pacemaker-dependent subjects with complete heart block and preserved myocardial function, enhancing the HR response to exercise neither augments CO by a proportional offset of the exercise-induced increase in SV nor improves cerebral perfusion.
13C- and 2H-labelled glucose compared for minimal model estimates of glucose metabolism in man
Authors: Bluck Leslie J. C. , Clapperton Allan T. , Coward W. Andy
Published: December 2005

In the present study, we have investigated the use of 1-[13C]glucose and GC/combustion/isotope-ratio MS as an alternative to 6,6-[2H2]glucose and GC/MS in the determination of parameters of glucose metabolism using the IVGTT (intravenous glucose tolerance test) interpreted by labelled (hot) minimal models. The study has been done in four populations, normoglycaemics (subdivided into lean and obese individuals), subjects with impaired glucose tolerance and those with diabetes mellitus. Although the use of carbon label may in some circumstances be compromised by substrate recycling, our hypothesis was that this would not be an issue under the condition of suppression of hepatic glucose production during the short timescale of an IVGTT. In all four groups, we found that the methodology employing the carbon label gave equivalent results to those obtained using the conventional deuterated material, but the sensitivity of the measurement technique in the new approach was sufficient to allow an approx. 15-fold reduction in the quantity of isotope administered. In addition to the clear cost advantages, this represents a significant scientific advance in that true tracer status is more nearly attained in these measurements with near-physiological tracee loads.
Phase behavior of a blend of polymer-tethered nanoparticles with diblock copolymers
Authors: Reister Ellen , Fredrickson Glenn H.
Published: December 2005

Using the self-consistent field theory (SCFT), we investigate the phase behavior of a mixture of diblock copolymers and nanoparticles with monodisperse polymer chains tethered to their surfaces. We assume the size of the nanoparticles to be much smaller than that of the attached polymer chains and therefore model the particles with their grafted polymer “shell” as star polymers. The polymer chains attached to the particles are of the same species as one of the blocks of the symmetric diblock copolymer. Of primary interest is how to tune the shell of the particle by changing both the length and number of tethered polymers in order to achieve higher loading of nanoparticles within an ordered structure without macrophase separation occurring. We find that the phase behavior of the system is very sensitive to the size of the particle including its tethered shell. The region of microphase separation is increased upon decreasing the star polymer size, which may be achieved by shortening and/or removing tethered polymer chains. To explore the possible structures in these systems we employ SCFT simulations that provide insight into the arrangement of the different species in these complex composites.
Nematic-isotropic interfaces under shear: A molecular-dynamics simulation
Authors: Germano Guido , Schmid Friederike
Published: December 2005

We present a large-scale molecular-dynamics study of nematic-paranematic interfaces under shear. We use a model of soft repulsive ellipsoidal particles with well-known equilibrium properties, and consider interfaces which are oriented normal to the direction of the shear gradient (common stress case). The director at the interface is oriented parallel to the interface (planar). A fixed average shear rate is imposed with moving periodic boundary conditions, and the heat is dissipated with a profile-unbiased thermostat. First, we study the properties of the interface at one particular shear rate in detail. The local interfacial profiles and the capillary wave fluctuations of the interfaces are calculated and compared with those of the corresponding equilibrium interface. Under shear, the interfacial width broadens and the capillary wave amplitudes at large wavelengths increase. The strain is distributed inhomogeneously in the system (shear banding), the local shear rate in the nematic region being distinctly higher than in the paranematic region. Surprisingly, we also observe (symmetry-breaking) flow in the vorticity direction, with opposite direction in the nematic and the paranematic state. Finally, we investigate the stability of the interface for other shear rates and construct a nonequilibrium phase diagram.
New isoreticular metal-organic framework materials for high hydrogen storage capacity
Authors: Sagara Tatsuhiko , Ortony Julia , Ganz Eric
Published: December 2005

We propose new isoreticular metal-organic framework (IRMOF) materials to increase the hydrogen storage capacity at room temperature. Based on the potential-energy surface of hydrogen molecules on IRMOF linkers and the interaction energy between hydrogen molecules, we estimate the saturation value of hydrogen sorption capacity at room temperature. We discuss design criteria and propose new IRMOF materials that have high gravimetric and volumetric hydrogen storage densities. These new IRMOF materials may have gravimetric storage density up to 6.5wt% and volumetric storage density up to 40kgH2∕m3 at room temperature.
B -site doping effect on ferroelectric property of bismuth titanate ceramic
Authors: Li Wei , Gu Jun , Song Chunhua , Su Dong , Zhu Jinsong
Published: December 2005

It is well known that doping can greatly affect the ferroelectric properties of Bi4Ti3O12: however, the mechanisms of the doping effect, especially doping at the B site, are not well understood. The effect of B-site doping with different ion sizes and valences on the remanent polarization and fatigue endurance was investigated to clarify the mechanism of B-site doping. The experimental results indicated that both the radius of doping ion and the concentration of oxygen vacancies have no certain relation with the enhancement of remanent polarization. However, oxygen vacancies play an important role in fatigue endurance in doped Bi4Ti3O12. The effect of B-site doping is briefly discussed.
Swelling of SiC under helium implantation
Authors: Leclerc S. , Declémy A. , Beaufort M. F. , Tromas C. , Barbot J. F.
Published: December 2005

Single crystals 4H-SiC were implanted with 50 keV helium ions at temperatures up to 600 °C and fluences in the range 1×1016–1×1017cm−2. The helium implantation-induced swelling was studied through the measurement of the step height. The different contributions of swelling were determined by combining simulations of x-ray diffraction curves and transmission electron microscopy observations. At room temperature, amorphization occurs between 1 and 2×1016cm−2, inducing the decrease in density of about 15%. For high-temperature implants, amorphization does not occur. The strain profiles show saturation in the near-surface region, indicating that a threshold concentration of defects is reached. All the additional point defects created during the implantation have been supposed to annihilate. In the region of high-energy deposition density, the value of strain increases with fluence up to values larger than 6%. The elastic contribution to swelling has been obtained by integration of the strain profile determined by x-ray diffraction simulations. Then, the contribution of helium bubbles to the step height is found to be linear with the fluence: 0.8nm∕1016He∕cm2.
Orientational self-assembled field-effect transistors based on a single-walled carbon nanotube
Authors: Li Xianglong , Liu Yunqi , Shi Dachuan , Sun Yanming , Yu Gui , Zhu Daoben , Liu Hongmin , Liu Xinyu , Wu Dexin
Published: December 2005

We fabricate single-walled carbon nanotube field-effect transistors (SWNT FETs) with a simple, low-cost, high-efficiency, and solution-based orientational self-assembly method. The SWNT was first functionalized with thiol groups, then suspended in an N,N-dimethylformamide solution, and finally self-assembled on predefined gold contact pads by an orientational N2 blow. A relatively high mobility of 9.2×102cm2∕Vs and an on∕off ratio greater than 105 at a bias voltage of −1V have been achieved as a result of directly covalent interaction between end-thiolated SWNT and gold contacts, which favors the fabrication of SWNT FETs as compared to the SWNT FETs bearing the similar geometry but relies on random deposition. Therefore, this orientational self-assembly approach should be a valuable tool in the mass fabrication of high-performance SWNT FETs and SWNT-based molecular-scale electronic devices.
Interface structure and perpendicular exchange bias in (Co∕Pt)n∕FeMn multilayers
Authors: Ji Xiaosong , Ju Honglyoul , McCready David E. , Krishnan Kannan M.
Published: December 2005

We have performed a critical experimental evaluation of the dependence of both perpendicular magnetic anisotropy and exchange bias on the structure of the ferromagnet (FM)/nonferromagnet and FM/antiferromagnet interfaces of (Co∕Pt)n and (Co∕Pt)n∕FeMn multilayers. The growth of these heterostructures by ion-beam sputtering was optimized and the characteristics of their interfaces were systematically controlled by varying the ion-beam energy from 250 to 1500 eV. Calculated effective anisotropy constants and exchange bias fields from hysteresis loops were correlated with both structural roughness and the degree of interdiffusion measured by x-ray reflectivity. Whilst the physical roughness remained unchanged, the degree of interdiffusion was found to increase with higher ion-beam energy—concurrently the magnetic anisotropy changed from perpendicular to in plane—leading directly to a decrease in exchange bias and coercivity.
Local strain and potential distribution induced by single dislocations in GaN
Authors: Gmeinwieser N. , Gottfriedsen P. , Schwarz U. T. , Wegscheider W. , Clos R. , Krtschil A. , Krost A. , Weimar A. , Brüderl G. , Lell A. , Härle V.
Published: December 2005

The presence of a threading edge dislocation terminated at the surface of GaN bulk substrates causes a dipole-like strain state ranging over a several micrometer square area. The local strain state is derived from microphotoluminescence mappings of the near-band-edge spectrum and is quantitatively reproduced by a three-dimensional elastic deformation model approach. These results are compared with the local electrical potential distortion due to the core charge and attracted defects as analyzed by scanning surface-potential microscopy. In contrast to the local strain, the potential profile does not show a dipole-like behavior and decreases laterally faster.
Phase formation and magnetocaloric effect in rapidly quenched La(Fe1−xCox)11.4Si1.6
Authors: Liu X. B , Liu X. D , Altounian Z.
Published: December 2005

The effect of Co content on the phase formation, structure, and magnetocaloric effect of rapidly quenched La(Fe1−xCox)11.4Si1.6 with x=0 to 0.12 were investigated by x-ray diffractometry and magnetic measurements. Rietveld analyses indicate that with increasing Co content, the amount of the 1:13 phase increases from about 22 to 62 wt. % in the rapidly quenched alloys. A very short time annealing (1273K∕20min) of the as-quenched alloy is sufficient for the formation of a single phase 1:13 structure. The peak value of the magnetic entropy change is 20.5,11.8,9.9J∕kgK for the annealed rapidly quenched compounds with x=0, 0.04, and 0.08, respectively. Increasing Co content drives the order of magnetic transition, near TC, from first order to second order and eliminates the occurrence of the field-induced magnetic transition above TC, which is responsible for the decrease in the magnetocaloric effect.
Simulation study on the correlation between morphology and electrical breakdown in polyethylene
Authors: Wu Kai , Okamoto Tatsuki , Suzuoki Yasuo
Published: December 2005

On the basis of the percolation model for electrical breakdown, a theoretical approach was proposed to investigate the correlation between morphology and breakdown strength. By introducing the void sites in the percolation model, it is indicated that tiny nanovoids (below several nm) acting as deep traps lead to a slight increase of breakdown strength, but large nanovoids and sub-microvoids cause an obvious reduction of the breakdown strength and may play an important role in determining it. Moreover, the morphology change was expressed by the aggregation pattern and the orientation of voids. Monte Carlo simulation also confirmed that the breakdown strength changes with the void shape and size distribution, and can be improved by orientation.
Experimental and theoretical characterization of a lithium niobate photonic crystal
Authors: Roussey Matthieu , Bernal Maria-Pilar , Courjal Nadège , Baida Fadi I.
Published: December 2005

In this letter, we investigate the feasibility of tunable lithium niobate (LiNbO3) photonic crystals. The optical response through a LiNbO3 photonic structure is theoretically determined in order to obtain a photonic band gap with optimal tunability. We show by means of a finite difference time domain simulation that the optimal lattice parameters can provide a Δλ=7nm shift in the photonic band gap for a Δn=0.01 variation of the refractive index with an extinction ratio of −22.5dB. The fabrication process and the optical characterization of these novel photonic crystal structures are also reported. The extinction ratio of the measured photonic band gap is lower than −12dB.
Three-dimensional gravity-capillary solitary waves in water of finite depth and related problems
Authors: Părău E. I. , Vanden-Broeck J.-M. , Cooker M. J.
Published: December 2005

Numerical solutions for three-dimensional gravity capillary waves in water of finite depth are presented. The full Euler equations are used and the waves are calculated by a boundary integral equation method. The findings generalize previous results of Părău, Vanden-Broeck, and Cooker [J. Fluid Mech. 536, 99 (2005)] in water of infinite depth. It is found that there are both lumps that bifurcate from linear sinusoidal waves and other fully localized solitary waves which exist for large values of the Bond number. These findings are consistent with rigorous analytical results and asymptotic calculations. The relation between the solitary waves and free surface flows generated by moving disturbances is also explored.
Electrorheological-fluid-based microvalves
Authors: Niu Xize , Wen Weijia , Lee Yi-Kuen
Published: December 2005

We present the successful design and fabrication of push-and-pull microvalves that use a giant electrorheological (GER) fluid. Our multilayer microvalves, including the GER fluid control channel, the electrode, the flow channel, and the flexible membrane, are fabricated with polydimethylsioxane-based materials by soft lithography techniques. The GER effect is able to provide high-pressure changes in GER control channel so as to fully close and open an associated flow channel. The fast response time of the GER fluid and the push-and-pull valve design adopted assure fast switching time of the valve less than 10ms and sound reliability. This GER-fluid-based microvalve has other advantages of easy fabrication and biocompatibility and is suitable for most microfluidic applications.
Monte Carlo simulations of imprint behavior in ferroelectrics
Authors: Schorn Peter J. , Böttger Ulrich , Waser Rainer
Published: December 2005

In this letter, Monte Carlo simulation methods were used to investigate the influence of the defect orientation and concentration on the hysteresis loop in ferroelectric thin films. The hysteresis loops were calculated by an existing Monte Carlo model. For a certain type of defect orientation, the simulations revealed an asymmetric hysteresis loop behavior, similar to hysteresis curves recorded by imprint measurements. Though these results may not directly offer a new explanation for the imprint mechanism in ferroelectric thin films, they still provide insight information about the often observed phenomenon of imprinted hysteresis loops of as-prepared thin-film capacitors.
Contributions to the homogeneous plastic flow of in situ metallic glass matrix composites
Authors: Fu X. L. , Li Y. , Schuh C. A.
Published: December 2005

The homogeneous deformation of Zr-based bulk metallic glass composites is studied near the glass transition temperature, at various levels of reinforcement volume fraction. Through examination of the constitutive response, it is seen that the presence of in situ reinforcements increases the flow resistance of the glass dramatically. This strengthening effect is shown to arise from two separate contributions: load transfer from the amorphous matrix to the reinforcements, and changes to the glass composition and structure upon in situ precipitation of reinforcements.
Characterization of growth and crystallization processes in CoFeB∕MgO∕CoFeB magnetic tunnel junction structure by reflective high-energy electron diffraction
Authors: Yuasa Shinji , Suzuki Yoshishige , Katayama Toshikazu , Ando Koji
Published: December 2005

We performed reflective high-energy electron diffraction observations to investigate the growth and crystallization processes of Co60Fe20B20∕MgO∕Co60Fe20B20 magnetic tunnel junction structures. A MgO layer grown on an amorphous CoFeB layer has an amorphous structure up to the MgO thickness (tMgO) of 4 monoatomic layers (ML) and begins to crystallize with (001) preferred orientation when tMgO⩾5ML. By annealing, an amorphous CoFeB layer grown on MgO(001) crystallizes in a body-centered-cubic structure with (001) orientation because MgO(001) acts as a template to crystallize CoFeB. The results give important information for understanding the mechanism of giant tunneling magnetoresistance effect in CoFeB∕MgO∕CoFeB MTJs.
Simulation of hybrid ZnO∕AlGaN single-heterostructure light-emitting diode
Authors: Bulashevich Kirill A. , Evstratov Igor Yu. , Nabokov Vladislav N. , Karpov Sergey Yu.
Published: December 2005

Using simulations, we have examined specific features of a hybrid n-ZnO∕p-AlGaN light-emitting diode (LED) operation, originated from a type-II band alignment and a negative polarization charge at the ZnO∕AlGaN interface. These factors are found to improve the carrier confinement near the interface and to affect significantly the light emission spectra and internal quantum efficiency of the LED. The theoretical predictions are compared with available observations.
Growth and characterization of CaCu2Mn5O12 thin films deposited on CaCu3Ti4O12-buffered LaAlO3 substrates
Authors: Autier-Laurent S. , Mercey B. , Simon Ch.
Published: December 2005

Thin films of perovskitelike CaCu2Mn5O12 have been grown by pulsed laser deposition. These films are ferromagnetic with a Curie temperature (TC) of 292 K which is very close to that expected for the bulk material (TC=310K). Increasing the oxygen pressure during cooling does not markedly affect the out-of-plane lattice parameter (c) or TC of the films, but enhances the magnetization at low temperature. Transport properties of films exhibit metallic behavior in the temperature range of 10–360 K. The most important difference between these films and the bulk material was observed in their magnetotransport characteristics. The magnetoresistance effect is important at low temperatures for the bulk material, while for the thin films, this effect is large (−8%) close to TC, as expected for a regular ferromagnetic material.
Density of defect states of aluminum nitride grown on silicon and silicon carbide substrates at room temperature
Authors: Ligatchev V. , Rusli  , Pan Zhao
Published: December 2005

Density of defect states of aluminum nitride (AlN) films deposited by rf magnetron sputtering on ⟨100⟩-oriented silicon (Si) and 4H-silicon carbide (4H-SiC) have been investigated using the deep-level-transient-spectroscopy technique. The films were grown at room temperature with varying nitrogen flow from 4 to 20 sccm and a constant argon flow of 10 sccm. In general the defect densities of AlN are lower when grown on 4H-SiC substrates than on Si substrates. The observed defect levels are identified as donor-like triplet of nitrogen vacancy and DX-like centers. Defects located at 0.35–0.42 eV below the conduction band, attributed to dangling bonds of nitrogen atoms, are seen in samples grown with higher nitrogen flow rate. Shallow level defects, observed at approximately 0.1 eV below the conduction band, can be attributed to the recently discovered prismatic staking fault in the AlN atomic structure.
BMP signaling stimulates cellular differentiation at multiple steps during cartilage development
Authors: Kobayashi Tatsuya , Lyons Karen M. , McMahon Andrew P. , Kronenberg Henry M.
Published: December 2005

Bone morphogenetic proteins (BMPs) play important roles at multiple stages of endochondral bone formation. However, the roles of BMP signaling in chondrocytes
in vivo
are still contentious. In the present study, we overexpressed a constitutively active BMP receptor 1A (
caBmpr1a
) in chondrocytes by using two systems:
caBmpr1a
was directly driven by a rat type II collagen promoter in a conventional transgenic system and indirectly driven in a
UAS-Gal4
binary system.
CaBmpr1a
expression caused shortening of the columnar layer of proliferating chondrocytes and up-regulation of maturation markers, suggesting acceleration of differentiation of proliferating chondrocytes toward hypertrophic chondrocytes. In addition to the acceleration of chondrocyte differentiation, conventional transgenic mice showed widening of cartilage elements and morphological alteration of perichondrial cells, possibly due to stimulation of differentiation of prechondrogenic cells. Moreover, bigenic expression of
caBmpr1a
rescued the differentiation defect of prechondrogenic cells in
Bmpr1b
-null phalanges. This finding indicates that BMP signaling is necessary for phalangeal prechondrogenic cells to differentiate into chondrocytes and that signaling of BMP receptor 1B in this context is replaceable by that of a constitutively active BMP receptor 1A. These results suggest that BMP signaling in prechondrogenic cells and in growth plate chondrocytes stimulates their chondrocytic differentiation and maturation toward hypertrophy, respectively.
Sex ratio bias, male aggression, and population collapse in lizards
Authors: Le Galliard Jean-François , Fitze Patrick S. , Ferrière Régis , Clobert Jean
Published: December 2005

The adult sex ratio (ASR) is a key parameter of the demography of human and other animal populations, yet the causes of variation in ASR, how individuals respond to this variation, and how their response feeds back into population dynamics remain poorly understood. A prevalent hypothesis is that ASR is regulated by intrasexual competition, which would cause more mortality or emigration in the sex of increasing frequency. Our experimental manipulation of populations of the common lizard (
Lacerta vivipara
) shows the opposite effect. Male mortality and emigration are not higher under male-biased ASR. Rather, an excess of adult males begets aggression toward adult females, whose survival and fecundity drop, along with their emigration rate. The ensuing prediction that adult male skew should be amplified and total population size should decline is supported by long-term data. Numerical projections show that this amplifying effect causes a major risk of population extinction. In general, such an “evolutionary trap” toward extinction threatens populations in which there is a substantial mating cost for females, and environmental changes or management practices skew the ASR toward males.
Exercise and Neurotransmission: A Window to the Future?
Authors: Meeusen Romain , Piacentini M
Published: December 2005

Peripheral physiological adaptations to exercise have been the subject of several studies. To adjust to the disturbance in resting homeostasis induced by the exercise stimulus, a number of regulatory systems are called upon to return the body to a new level of homeostasis. In contrast with our knowledge about the peripheral adaptations to exercise, studies relating exercise to brain neurotransmitter levels are scarce. It is of interest to examine the effect of acute and chronic exercise on neurotransmitter release, since movement initiation and control of locomotion have been shown to be related to striatal neurotransmitter function. One of the possible therapeutic modalities in movement and mental disorders is exercise therapy. But also chronic adaptations to training and disturbances caused by overtraining might be reflected in brain functioning. Physical exercise influences the central dopaminergic, noradrenergic, and serotonergic systems. A number of studies have examined brain noradrenaline (NA), serotonin (5‐hydroxytryptamine, or 5‐HT), and dopamine (DA) with exercise. Although there are great discrepancies in experimental protocols, the results indicate that there is evidence in favor of changes in synthesis and metabolism of monoamines during exercise. In previous studies, we used the microdialysis technique to monitor the release of neurotransmitters in different brain nuclei during exercise. We have shown that DA, NA, and 5‐HT release is increased during exercise. We also showed that acute exercise and/or exercise training influences extracellular DA, NA, GLU, and GABA levels. Taken together this could indicate that chronic disturbance of homeostasis could also influence transmitter release and that this paradigm could serve as a tool to explore the central effects of overtraining.