bluuebunny/crossref_metadata_2025 huggingface dataset:
Arginine mutations within a transmembrane domain of Tar, an Escherichia coli aspartate receptor, can drive homodimer dissociation and heterodimer association in vivo
Authors: SAL-MAN Neta , SHAI Yechiel
Published: December 2004

The interactions between the TM (transmembrane) domains of many membrane proteins are important for their proper functioning. Mutations of residues into positively charged ones within TM domains were reported to be involved in many genetic diseases, possibly because these mutations affect the self- and/or hetero-assembly of the corresponding proteins. To our knowledge, despite significant progress in understanding the role of various amino acids in TM–TM interactions in vivo, the direct effect of positively charged residues on these interactions has not been studied. To address this issue, we employed the N-terminal TM domain of the aspartate receptor (Tar-1) as a dimerization model system. We expressed within the ToxR TM assembly system several Tar-1 constructs that dimerize via polar- or non-polar amino acid motifs, and mutated these by replacement with a single arginine residue. Our results have revealed that a mutation in each of the motifs significantly reduced the ability of the TMs to dimerize. Furthermore, a Tar-1 construct that contained two arginine residues was unable to correctly integrate itself into the membrane. Nevertheless, an exogenous synthetic Tar-1 peptide containing these two arginine residues was able to inhibit in vivo the marked dimerization of a mutant Tar-1 construct that contained two glutamate residues at similar positions. This indicates that hetero-assembly of TM domains can be mediated by the interaction of two oppositely charged residues, probably by formation of ion pairs. This study broadens our knowledge regarding the effect of positively charged residues on TM–TM interactions in vivo, and provides a potential therapeutic approach to inhibit uncontrolled dimerization of TM domains caused by mutations of polar amino acids.
Structural characterization of Escherichia coli sensor histidine kinase EnvZ: the periplasmic C-terminal core domain is critical for homodimerization
Authors: KHORCHID Ahmad , INOUYE Masayori , IKURA Mitsuhiko
Published: December 2004

Escherichia coli EnvZ is a membrane sensor histidine kinase that plays a pivotal role in cell adaptation to changes in extracellular osmolarity. Although the cytoplasmic histidine kinase domain of EnvZ has been extensively studied, both biochemically and structurally, little is known about the structure of its periplasmic domain, which has been implicated in the mechanism underlying its osmosensing function. In the present study, we report the biochemical and biophysical characterization of the periplasmic region of EnvZ (Ala38–Arg162). This region was found to form a dimer in solution, and to consist of two well-defined domains: an N-terminal α-helical domain and a C-terminal core domain (Glu83–Arg162) containing both α-helical and β-sheet secondary structures. Our pull-down assays and analytical ultracentrifugation analysis revealed that dimerization of the periplasmic region is highly sensitive to the presence of CHAPS, but relatively insensitive to salt concentration, thus suggesting the significance of hydrophobic interactions between the homodimeric subunits. Periplasmic homodimerization is mediated predominantly by the C-terminal core domain, while a regulatory function may be attributed mainly to the N-terminal α-helical domain, whose mutations have been shown previously to produce a high-osmolarity phenotype.
Activation of an α2A-adrenoceptor–Gαo1 fusion protein dynamically regulates the palmitoylation status of the G protein but not of the receptor
Authors: BARCLAY Elaine , O'REILLY Mark , MILLIGAN Graeme
Published: December 2004

Post-translational thio-acylation of a fusion protein between the α2A-adrenoceptor and the α subunit of the G protein Go1 is both dynamic and regulated by agonist binding. Incorporation of [3H]palmitate into the fusion protein was reduced substantially in the presence of the agonist adrenaline. This was dependent on the concentration of adrenaline and correlated with occupancy of the ligand binding site. Both the receptor and G-protein elements of the fusion construct incorporated [3H]palmitate but this occurred more rapidly for the G-protein element and regulation of acylation by the agonist occurred only for the G protein. The kinetics of de-palmitoylation of the α2A-adrenoceptor–Gαo1 fusion were accelerated markedly by agonist. Again, this reflected modulation of the G protein but not of the receptor. Agonist-induced regulation of the kinetics of thio-acylation of the G protein was abolished, however, in a mutant unable to bind guanosine 5′-[γ-[35S]thio]triphosphate ([35S]GTP[S]) in response to adrenaline. Despite the dynamic nature of the post-translational acylation and its regulation by agonist, the ability of adrenaline to activate the G protein, monitored by stimulation of the binding of [35S]GTP[S] to such fusion constructs, was unaffected by the palmitoylation potential of either the receptor or G-protein element.
Endothelial dysfunction in patients with recent myocardial infarction and hyperhomocysteinaemia: effects of vitamin supplementation
Authors: CHIA Stanley , WILSON Robert , LUDLAM Christopher A. , WEBB David J. , FLAPAN Andrew D. , NEWBY David E.
Published: December 2004

Hyperhomocysteinaemia is a prothrombotic condition that may cause oxidative endothelial injury and impair endogenous fibrinolysis. Vitamin supplementation enhances endothelial function in hyperhomocysteinaemic patients, but responses in patients with co-existing coronary artery disease have been variable. It is also unknown whether hyperhomocysteinaemia is associated with reduced fibrinolytic responses in patients with coronary artery disease. The study aims were to test the hypothesis that patients with recent myocardial infarction and hyperhomocysteinaemia have impaired endothelium-dependent vasomotion and fibrinolysis that is rectified by vitamin supplementation. From a cohort of 120 patients admitted with acute myocardial infarction, 18 patients were recruited from the upper (n=9) and lower (n=9) plasma homocysteine quartiles into a randomized double-blind placebo-controlled crossover trial. Following a 4-week course of placebo or folate/cyanocobalamin/pyridoxine supplements, FBF (forearm blood flow) was measured using venous occlusion plethysmography during intra-arterial substance P (4–16 pmol/min), acetylcholine (5–20 μg/min) and sodium nitroprusside (2–8 μg/min) infusions. All vasodilators caused dose-dependent increases in infused FBF (P<0.05). Patients in the upper homocysteine quartile (16.8±2.9 compared with 7.9±0.7 μmol/l; P=0.003) had reduced vasodilatation to acetylcholine (P=0.01) and substance P (P<0.05), but not sodium nitroprusside. There were no differences in substance P-induced tissue plasminogen activator release. Vitamin supplementation increased serum folate and vitamin B12 concentrations (P<0.05), but did not significantly lower homocysteine, or affect FBF or fibrinolytic responses. In patients with recent myocardial infarction, hyperhomocysteinaemia is associated with impaired endothelium-dependent vasodilatation, but no alteration in the acute fibrinolytic capacity. This endothelial vasomotor dysfunction is unaltered by vitamin supplementation.
Effect of C-reactive protein on Fcγ receptor II in cultured bovine endothelial cells
Authors: ESCRIBANO-BURGOS Marta , LÓPEZ-FARRÉ Antonio , del MAR GONZÁLEZ María , MACAYA Carlos , GARCÍA-MÉNDEZ Antonio , MATEOS-CÁCERES Petra J. , ALONSO-ORGAZ Sergio , CARRASCO Carolina , RICO Luis A. , PORRES CUBERO Juan Carlos
Published: December 2004

The major CRP (C-reactive protein) receptor on leucocytes has been identified as the low-affinity IgG receptor Fcγ receptor II (CD32). Our aim was to assess whether inflammation may modify the presence of the CD32 receptor in BAEC (bovine aortic endothelial cells). Confocal microscopy experiments showed a weak expression of the CD32 receptor in control BAEC that was slightly increased by 10 μg/ml CRP. Incubation of BAEC with TNF-α (tumour necrosis factor-α) did not modify the fluorescence signal of CD32. Addition of CRP to TNF-α-incubated BAEC enhanced the fluorescence signal of the CD32 receptors. The CD32 receptors showed a perinuclear cytoplasmic localization in BAEC. An alteration of the NO (nitric oxide)-dependent vasorelaxation has been defined as endothelial dysfunction. Endothelial dysfunction has been associated with the presence of superoxide anion and with a reduction in the expression of the eNOS (endothelial NO synthase). A concentration of CRP similar to that detected in patients with cardiovascular risk (10 μg/ml) failed to modify the generation of superoxide anion stimulated by TNF-α. Western blot experiments showed that TNF-α decreased the expression of the eNOS protein, which was partially protected by treatment with 10 μg/ml CRP. The protective effect of 10 μg/ml CRP on eNOS expression in TNF-α-incubated BAEC was prevented by an antibody against CD32 receptors. In conclusion, the present results suggest that, although CRP has been associated with inflammation, CRP may protect the expression of eNOS protein against pro-inflammatory mediators such as TNF-α.
Cardiac natriuretic peptides for cardiac health
Authors: RADEMAKER Miriam T. , RICHARDS A. Mark
Published: December 2004

The cardiac natriuretic peptides, ANP (atrial natriuretic peptide) and BNP (brain natriuretic peptide), are secreted by the heart in proportion to cardiac transmural pressures. They possess a wide range of effects in multiple tissues facilitating overall pressure/volume homoeostasis. The close relationship between plasma concentrations of these peptides and ‘cardiac load’ has led to their use as biomarkers of cardiac health with diagnostic and prognostic applications in a variety of disorders affecting the cardiovascular system. BNP and its N-terminal fragment (NT-BNP) are especially sensitive indicators of cardiac dysfunction and remodelling, and correlate strongly with severity. Given that cardiac ischaemia is also an important trigger for the release of these ventricular peptides, they may likewise play a role in the detection of coronary artery disease. Measurement of BNP/NT-BNP shows particular promise as a ‘rule out’ test for suspected cases of HF (heart failure) in both emergency care and outpatient settings, and may assist in identifying individuals with asymptomatic ventricular impairment who will benefit from therapy preventing progression to overt HF. The BNP peptides also predict subsequent haemodynamic deterioration and adverse events in cardiovascular disease, and can therefore be used to monitor those at high risk and act as a guide to optimization of treatment. The favourable biological properties of the natriuretic peptides have also led to their use as therapeutic agents.
Foldamer simulations: Novel computational methods and applications to poly-phenylacetylene oligomers
Authors: Elmer Sidney P. , Pande Vijay S.
Published: December 2004

We apply several methods to probe the ensemble kinetic and structural properties of a model system of poly-phenylacetylene (pPA) oligomer folding trajectories. The kinetic methods employed included a brute force accounting of conformations, a Markovian state matrix method, and a nonlinear least squares fit to a minimalist kinetic model used to extract the folding time. Each method gave similar measures for the folding time of the 12-mer chain, calculated to be on the order of 7 ns for the complete folding of the chain from an extended conformation. Utilizing both a linear and a nonlinear scaling relationship between the viscosity and the folding time to correct for a low simulation viscosity, we obtain an upper and a lower bound for the approximate folding time within the range 70 ns<τ<350 ns. This is in agreement with the experimentally measured folding time on the order of 160 ns. The kinetic model used to fit the kinetic behavior of the ensemble of trajectories provides a framework to describe the bulk folding mechanism. We were able to identify two unique clusters of conformations that provide a structural basis to account for the appearance of a kinetic intermediate in the mechanism. We discuss the implications of these findings in the context of helix-coil theory.
The electronic states of polyfluorene copolymers with alternating donor-acceptor units
Authors: Jespersen Kim G. , Beenken Wichard J. D. , Zaushitsyn Yuri , Yartsev Arkady , Andersson Mats , Pullerits Tõnu , Sundström Villy
Published: December 2004

We calculate the electronic states of the low bandgap polyfluorene-based copolymer DiO-PFDTBT, which consists of alternating 9,9-dioctyl-9H-fluorene and 4,7-di-thiophen-2-ylbenzo[1,2,5]thiadiazole (TBT) units, and compare with the steady-state absorption, emission, and excitation spectrum. Using the semiempirical quantum-chemical (ZINDO) method we can assign the characteristic bands of the “camel-back” absorption spectrum to one charge transfer state at lower energy localized on the TBT unit, and one delocalized excitonic state at higher energy corresponding to the π-conjugated electron system. Additional “dark” charge transfer states in the gap between these bands have been revealed. Calculations are also made on the red light emitting polyfluorene-based copolymer poly(fluorene-co-benzothiadiazole) (F8BT), which contains benzo[1,2,5]thiadiazole instead of TBT. The nature of the electronic states in F8BT and DiO-PFDTBT are found to be qualitatively the same.
Dynamics of water probed with vibrational echo correlation spectroscopy
Authors: Asbury John B. , Steinel Tobias , Kwak Kyungwon , Corcelli S. A. , Lawrence C. P. , Skinner J. L. , Fayer M. D.
Published: December 2004

Vibrational echo correlation spectroscopy experiments on the OD stretch of dilute HOD in H2O are used to probe the structural dynamics of water. A method is demonstrated for combining correlation spectra taken with different infrared pulse bandwidths (pulse durations), making it possible to use data collected from many experiments in which the laser pulse properties are not identical. Accurate measurements of the OD stretch anharmonicity (162 cm−1) are presented and used in the data analysis. In addition, the recent accurate determination of the OD vibrational lifetime (1.45 ps) and the time scale for the production of vibrational relaxation induced broken hydrogen bond “photoproducts” (∼2 ps) aid in the data analysis. The data are analyzed using time dependent diagrammatic perturbation theory to obtain the frequency time correlation function (FTCF). The results are an improved FTCF compared to that obtained previously with vibrational echo correlation spectroscopy. The experimental data and the experimentally determined FTCF are compared to calculations that employ a polarizable water model (SPC-FQ) to calculate the FTCF. The SPC-FQ derived FTCF is much closer to the experimental results than previously tested nonpolarizable water models which are also presented for comparison.
An ab initio calculation of the anisotropic hyperfine coupling constants in the low-lying vibronic levels of the X 2Π electronic state of CCCH
Authors: Mladenović Milena , Perić Miljenko , Engels Bernd
Published: December 2004

The results of ab initio calculations of the vibronically averaged components of the anisotropic magnetic hyperfine tensor in the low-lying vibronic species of the X 2Π electronic state of CCCH and CCCD are reported. The electronically averaged hyperfine coupling constants for hydrogen and C13 in C12 12C 12CH, C13 12C 12CH, C12 13C 12CH, C12 12C 13CH, and C12 12C 12CD are obtained as functions of two bending vibrational modes by the density functional theory method. The vibronic wave functions are calculated with help of a variational approach which takes into account the Renner-Teller effect and spin-orbit coupling. The results of the present study help to reliably interpret the experimental data previously published and predict the yet unobserved hyperfine structure in excited vibronic states of CCCH and CCCD.
Highly entangled polymer primitive chain network simulations based on dynamic tube dilation
Authors: Yaoita Takatoshi , Isaki Takeharu , Masubuchi Yuichi , Watanabe Hiroshi , Ianniruberto Giovanni , Greco Francesco , Marrucci Giuseppe
Published: December 2004

The concept of dynamic tube dilation (DTD) is here used to formulate a new simulation scheme to obtain the linear viscoelastic response of long chains with a large number of entanglements. The new scheme is based on the primitive chain network model previously proposed by some of the authors, and successfully employed to simulate linear and nonlinear behavior of moderately entangled polymers. Scaling laws are generated by the DTD concept, and allow for prediction of the linear response of very long chains on the basis of suitable simulations performed on shorter ones, without introducing adjustable parameters. Tests of the method against existing data for linear monodisperse polyisoprene and polystyrene show good quantitative agreement.
Molecular interpretation of water structuring and destructuring effects: Hydration of alkanediols
Authors: Deshmukh Milind M. , Sastry Nandhibatla V. , Gadre Shridhar R.
Published: December 2004

Molecular electrostatic potential (MESP) guidelines are employed for understanding the reactivity and hydration patterns in alkanediol molecules. The deeper oxygen lone pair MESP minima indicate stronger basicity of 1,n-diols and 2,4-pentanediol (2,4-PeD) as compared to that of vicinal diols. The existence and strength of the intramolecular hydrogen bond in diols are gauged in terms of the electron density at the bond saddle points. A model named electrostatic potential for intermolecular complexation (EPIC) is used for generating the structures of hydrated complexes, which are subsequently subjected to ab initio calculations at Møller-Plesset second-order perturbation level of theory. Further, the nature of water⋯water as well as diol⋯water interactions is appraised employing many-body energy decomposition analysis. It is seen that water⋯water interactions are more favorable in vicinal diol⋯6H2O than those in 1,n-diol⋯6H2O (n=3, 4, 5,…) complexes. Exactly opposite trends are shown by diol⋯water interaction energies. Thus vicinal diols, being more effective at strengthening water⋯water network, are expected to act as water structuring agents, whereas the non-vicinal diols are expected to be water destructuring agents.
Gas-phase diatomic trications of Se23+, Te23+, and LaF3+
Authors: Franzreb K. , Hrušák J. , Alikhani M. E. , Lörinčı́k J. , Sobers R. C. , Williams P.
Published: December 2004

Three gas-phase diatomic trications Se23+, Te23+, and LaF3+ have been produced by Ar+ ion beam sputtering of Se, Te, and LaF3 surfaces, respectively. These exotic molecular ions were detected at noninteger m/z values in a magnetic sector mass spectrometer for ion flight times of ⩾13 μs that correspond to lower limits of their respective lifetimes. Se23+ and Te23+ were unambiguously identified by their characteristic isotopic abundances. Ab initio calculations of the electronic structures of Se23+, Te23+, and LaF3+ show that these molecular trications are metastable with respect to dissociation into fragment ions of Se2++Se+, Te2++Te+, and La2++F+, respectively. Their barrier heights are about 0.49, 0.29, and 0.53 eV, and the equilibrium internuclear distances (bond lengths) are about 0.23, 0.27, and 0.26 nm, respectively. The gas-phase diatomic dications Se22+ and Te22+ were also observed and unambiguously identified. They were found to be long-lived metastable molecules as well, whereas LaF2+ is thermochemically stable.
Concentration fluctuations in polymer gel investigated by neutron scattering: Static inhomogeneity in swollen gel
Authors: Koizumi Satoshi , Monkenbusch Michael , Richter Dieter , Schwahn Dietmar , Farago Bela
Published: December 2004

By using small-angle neutron scattering (SANS) and neutron spin echo (NSE), we have quantitatively investigated the static inhomogeneity in poly (N-isopropyl acrylamide) gel (PNIPA) in microscopic length scales of 0.015<q<0.16 A−1, where q is a wave number of scattered neutrons. NSE revealed that at lower q(≅0.015 A−1), the concentration fluctuations in the PNIPA gel decays more slowly as compared to the PNIPA solution without crosslinks. According to our scenario that the slower decay found for the PNIPA gel is due to the static inhomogeneity coexisting in the swollen gel, small-angle scattering S(q) obtained by SANS has been quantitatively decomposed into thermal and static scattering components, respectively, Sth(q) and Sst(q). It was further revealed that (i) the q-region where Sst(q) becomes dominant is closely related to that for the abnormal butterfly scattering under stretching, and (ii) as the temperature increases toward the temperature for volume phase transition, Sst(q) of a squared Lorentzian shape increases more drastically than Sth(q) of a Lorentzian shape. These findings were quantitatively understood in the theoretical framework by Panyukov and Rabin [Macromolecules 29, 7960 (1996)] or by Onuki [J. Phys. II. France 2, 45 (1992)], taking into account stress-fluctuation coupling under coexistence of the inherent structural heterogeneity in the real gel. We further found that the static inhomogeneity showing Sst(q) seems to relate to the necklacelike microstructure, appearing after a shallow quench into the collapsed phase.
Two-photon dissociation of the NO dimer in the region 7.1–8.2 eV: Excited states and photodissociation pathways
Authors: Dribinski V. , Potter A. B. , Fedorov I. , Reisler H.
Published: December 2004

A study of excited states of the NO dimer is carried out at 7.1–8.2 eV excitation energies. Photoexcitation is achieved by two-photon absorption at 300–345 nm followed by (NO)2 dissociation and detection of electronically excited products, mostly in n=3 Rydberg states of NO. Photoelectron imaging is used as a tool to identify product electronic states by using non-state-selective ionization. Photofragment ion imaging is used to characterize product translational energy and angular distributions. Evidence for production of NO(A 2Σ+), NO(C 2Π), and NO(D 2Σ+) Rydberg states of NO, as well as the valence NO(B 2Π) state, is obtained. On the basis of product translational energy and angular distributions, it is possible to characterize the excited state(s) accessed in this region, which must possess a significant Rydberg character.
Polymer nanodroplets forming liquid bridges in chemically structured slit pores: A computer simulation
Authors: Yaneva Jacqueline , Milchev Andrey , Binder Kurt
Published: December 2004

Using a coarse-grained bead–spring model of flexible polymer chains, the structure of a polymeric nanodroplet adsorbed on a chemically decorated flat wall is investigated by means of molecular dynamics simulation. We consider sessile drops on a lyophilic (attractive for the monomers) region of circular shape with radius RD while the remaining part of the substrate is lyophobic. The variation of the droplet shape, including its contact angle, with RD is studied, and the density profiles across these droplets also are obtained. In addition, the interaction of droplets adsorbed on two walls forming a slit pore with two lyophilic circular regions just opposite of one another is investigated, paying attention to the formation of a liquid bridge between both walls. A central result of our study is the measurement of the force between the two substrate walls at varying wall separation as well as the kinetics of droplet merging. Our results are compared to various phenomenological theories developed for liquid droplets of mesoscopic rather than nanoscopic size.
Low-resistivity and transparent indium-oxide-doped ZnO ohmic contact to p-type GaN
Authors: Lim Jae-Hong , Hwang Dae-Kue , Kim Hyun-Sik , Oh Jin-Yong , Yang Jin-Ho , Navamathavan R. , Park Seong-Ju
Published: December 2004

We report on the indium-oxide-doped ZnO (IZO) transparent ohmic contact to the p-GaN. The IZO transparent ohmic contact layer was deposited on p-GaN by e-beam evaporation. The transmittance of an IZO film with a thickness of 250nm was 84%–92% for the light in the wavelength range of 400 and 600nm. In addition, the IZO contact film yielded a low specific contact resistance of 3.4×10−4Ωcm2 on p-GaN when annealed at 600°C for 5min under a nitrogen ambient. Auger electron spectroscopy and x-ray photoemission spectroscopy analyses of the IZO and p-GaN interface indicated that Ga atoms had out-diffused and an InN phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. The light output power of a light-emitting diode (LED) with an IZO ohmic contact layer was increased by 34% at 83mW of electrical input power compared to that of a LED with a Ni∕Au ohmic contact layer.
Coupling-mediated ghost resonance in mutually injected lasers
Authors: Buldú Javier M. , González C. M. , Trull J. , Torrent M. C. , García-Ojalvo J.
Published: December 2004

We experimentally and numerically study the phenomenon of ghost resonance in coupled nonlinear systems. Two mutually injected semiconductor lasers are externally perturbed in their pump currents by two respective periodic signals of different frequencies f1 and f2. For small amplitudes of the external modulations, the two laser intensities display synchronized optical pulses, in the form of dropout events occurring at irregular times. By adjusting the amplitude and frequencies of the driving signals, the system exhibits a ghost resonance in the dropout appearance at a frequency fr not present in the distributed inputs.
Cavitation in flow through a micro-orifice inside a silicon microchannel
Authors: Mishra Chandan , Peles Yoav
Published: December 2004

Hydrodynamic cavitation in flows through a micro-orifice entrenched in a microchannel has been detected and experimentally investigated. Microfabrication techniques have been employed to design and develop a microfluidic device containing an 11.5μm wide micro-orifice inside a 100.2μm wide and 101.3μm deep microchannel. The flow of de-ionized water through the micro-orifice reveals the presence of multifarious cavitating flow regimes. This investigation divulges both similarities and differences between cavitation in micro-orifices and cavitation in their macroscale counterparts. The low incipient cavitation number obtained from the current experiments suggests a dominant size scale effect. Choking cavitation is observed to be independent of any pressure or velocity scale effects. However, choking is significantly influenced by the small stream nuclei residence time at such scales. Flow rate choking leads to the establishment of a stationary cavity. Large flow and cavitation hysteresis have been detected at the microscale leading to very high desinent cavitation numbers. The rapid transition from incipient bubbles to choking cavitation and subsequent supercavitation suggests the presence of radically different flow patterns at the microscale. Supercavitation results in a thick cavity, which extends throughout the microchannel, and is encompassed by the liquid. Cavitation at the microscale is expected to considerably influence the design of innovative high-speed microfluidic systems.
The origin of signal-to-noise ratio improvements in laminated recording media
Authors: Margulies D. T. , Schabes M. E. , Supper N. , Do H. , Berger A. , Moser A. , Rice P. M. , Arnett P. , Madison M. , Lengsfield B. , Rosen H. , Fullerton Eric E.
Published: December 2004

We report an experimental and theoretical study of laminated recording media made of two CoPtCrB magnetic layers separated by a Ru spacer layer. We find that a 4Å Ru spacer layer is sufficient to decorrelate the noise of the magnetic transitions in the two layers, thus producing improved media signal-to-noise ratios. This result is surprising given that the layers remain structurally correlated due to their epitaxial growth, and therefore the noise in the layers would be expected to be correlated as well. Experiments suggest that the reduced transition noise is produced by a slight shift between the transition locations in the layers. This shift is on the order of the grain size and allows the transitions to sample a different microstructure causing the noise associated with the transitions to be uncorrelated.
Vibrational relaxation of the H2O bending mode in liquid water
Authors: Larsen Olaf F. A. , Woutersen Sander
Published: December 2004

We have studied the vibrational relaxation of the H2O bending mode in an H2O:HDO:D2O isotopic mixture using infrared pump–probe spectroscopy. The transient spectrum and its delay dependence reveal an anharmonic shift of 55±10 cm−1 for the H2O bending mode, and a value of 400±30 fs for its vibrational lifetime.
Interface states in cycled hot electron injection program∕hot hole erase silicon–oxide-nitride–oxide–silicon memories
Authors: Daniel Ramiz , Shaham-Diamand Yossi , Roizin Yakov
Published: December 2004

Charge pumping measurements were performed to characterize the interface between silicon and bottom oxide in silicon–oxide-nitride–oxide–silicon memory transistors, where information is stored as charges in nitride at the edges of the channel. The charge pumping signal was found to strongly increase with the number of performed program∕erase cycles, thus indicating the creation of traps with a density on the order of 1012cm−2 (after 100 000 cycles). To estimate the length of the degraded region, the charge pumping signal dependence on the drain voltage was compared with the simulated drain depletion length using TSUPREM∕Medici software. The damaged length calculated from the metallurgical junction is about 200Å at the beginning of the endurance test and increases to 500Å after 100 000 cycles.
Atomic-scale analysis of hydrogen-terminated Si(110) surfaces after wet cleaning
Authors: Arima Kenta , Katoh Jun , Endo Katsuyoshi
Published: December 2004

Atomically resolved scanning tunneling microscopy observations are performed on hydrogen-terminated Si(110) surfaces after wet cleaning. When a Si(110) wafer is dipped into dilute HF-containing solution, the surface is constructed by piling small terraces and steps. When the sample is consequently rinsed with ultrapure water, some characteristic features such as a zig–zag chain inside a terrace, a single row at step edges and an isolated zig–zag chain on a terrace are clearly observed, and their atomic arrangements are determined. Excessive rinsing, however, creates the ridge-shaped structure of nanometer height, which is explained by anisotropic etching by OH− ions in water.
Diffraction by an optical fractal grating
Authors: Hou Bo , Xu Gu , Wen Weijia , Wong George K. L.
Published: December 2004

We report experimental and theoretical studies of Fraunhofer diffraction pattern of a 15-level H-fractal grating. The diffraction pattern was found to exhibit self-similarity. In particular, the diffracted light was found to be more intense at higher spatial frequencies than at lower frequencies, in stark contrast to the diffraction patterns of wire gratings and grid gratings. Using Fourier transform theory, we show that this unusual behavior comes from the structural coherence of the H-fractal, which makes it favorable to use higher-order diffraction spectra for larger dispersion. In addition, the fractal dimension of the grating is shown analytically and experimentally to be two.
Observation of self-sputtering in energetic condensation of metal ions
Authors: Anders André
Published: December 2004

The condensation of energetic metal ions on a surface may cause self-sputtering even in the absence of substrate bias. Charge-state-averaged self-sputtering yields were determined for both zirconium and gold ions generated by a cathodic vacuum arc. Films were deposited on differently biased substrates exposed to streaming Zr and Au vacuum arc plasma. The self-sputtering yields for both metals were estimated to be about 0.05 in the absence of bias, and exceeding 0.5 when bias reached −50V. These surprisingly high values can be reconciled with binary collision theory and molecular dynamics calculations taking the high kinetic and potential energy of vacuum arc ions into account.
Charge and spin distribution in ferromagnetic Mn-doped InGaAs∕GaAs multilayers
Authors: Sipahi G. M. , Rodrigues S. C. P. , Scolfaro L. M. R. , da Cunha Lima I. C.
Published: December 2004

The search for materials tailored for spintronic devices led recently to the study of III–V diluted magnetic semiconductors (DMS). These materials are found to be closer to room-temperature ferromagnetism than their II–VI counterparts. Following this pathway, heterostructures based on III–V DMS were found to have higher Curie temperature. In this work, we propose geometrical arrangements that maximize spin separation combining strained and DMS III–V layers.
Organic solar cells protected by very thick naphthalene tetracarboxylic anhydride films
Authors: Suemori Kouji , Miyata Takahiro , Yokoyama Masaaki , Hiramoto Masahiro
Published: December 2004

The insertion of very thick naphthalene tetracarboxylic anhydride films under vacuum-deposited metal electrodes effectively protected pn-heterojunction organic solar cells from shorting-out electrically. Fill-factors of 0.56 and conversion efficiencies (corrected for absorbed light) of 3.07% were observed. The present technique would be a powerful tool for the fabrication of large area organic solar cells.
Epitaxial thin film growth of Ca2RuO4+δ by pulsed laser deposition
Authors: Wang X. , Xin Y. , Stampe P. A. , Kennedy R. J. , Zheng J. P.
Published: December 2004

Epitaxial Ca2RuO4+δ thin films have been grown on (001) LaAlO3 substrate by pulsed laser deposition. X-ray diffraction and transmission electron microscopy studies show that the films are single crystal with good structural quality. The films are determined to have quasitetragonal structure with a=5.352(8)Å, c=12.20(9)Å and epitaxially grown on the substrate with in-plane tensile strains. C plane of the film is parallel to the substrate surface and its ⟨100⟩ is along ⟨110⟩ of the pseudocubic LaAlO3 cell. Resistivity versus temperature measurement reveals that the thin film has metallic-like behavior with low resistivity (<0.002Ωcm) and no metal-to-insulator transition between 2 and 300 K, different from its bulk material property.
Drive current enhancement in p-type metal–oxide–semiconductor field-effect transistors under shear uniaxial stress
Authors: Shifren L. , Wang X. , Matagne P. , Obradovic B. , Auth C. , Cea S. , Ghani T. , He J. , Hoffman T. , Kotlyar R. , Ma Z. , Mistry K. , Nagisetty R. , Shaheed R. , Stettler M. , Weber C. , Giles M. D.
Published: December 2004

Recent attention has been given to metal–oxide–semiconductor field-effect transistor (MOSFET) device designs that utilize stress to achieve performance gain in both n-type MOSFETs (NMOS) and p-type MOSFETs (PMOS). The physics behind NMOS gain is better understood than that of PMOS gain, which has received less attention. In this letter, we describe the warping phenomena which is responsible for the gain seen in [110] uniaxially stressed PMOS devices on [100] orientated wafers. We also demonstrate that shear uniaxial stress in PMOS is better suited to MOSFET applications than biaxial stress as it is able to maintain gain at high vertical and lateral fields.
Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)
Authors: Slobodskyy T. , Rüster C. , Fiederling R. , Keller D. , Gould C. , Ossau W. , Schmidt G. , Molenkamp L. W.
Published: December 2004

We have investigated the growth by molecular-beam epitaxy of the II–VI diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates. The growth start has been optimized by using low-temperature epitaxy. Surface properties were assessed by Nomarski and scanning electron microscopy. Optical properties of (Zn,Mn)Se have been studied by photoluminescence and a giant Zeeman splitting of up to 30meV has been observed. Our observations indicate a high crystalline quality of the epitaxial films.
Giant Zeeman effect of excitons in a hybrid nanostructure of diluted magnetic semiconductor quantum well sandwiched in Co wires
Authors: Sakuma M. , Hyomi K. , Souma I. , Murayama A. , Oka Y.
Published: December 2004

Giant Zeeman effects of excitons in a hybrid nanostructure of diluted magnetic semiconductor (DMS) quantum well (QW) with ferromagnetic Co have been demonstrated, where the DMS-QW wire with the width of 200 nm is sandwiched in the Co wires and magnetic fields nearly perpendicular to the well plane can efficiently be applied from the Co wires to all of the DMS QW. The spectral shape of excitonic photoluminescence and the field dependence show clearly that the microscopic perpendicular fields generated from the Co wires induce the giant Zeeman shifts of excitons in the DMS QW.
Abrupt change in the structure of self-assembled monolayers upon metal evaporation
Authors: Tai Y. , Shaporenko A. , Eck W. , Grunze M. , Zharnikov M.
Published: December 2004

We have studied the interaction of vapor-deposited nickel with thiol-terminated self-assembled monolayers (SAMs) of oligophenylthiolates on Au, which can be considered as model systems for molecular electronics. Instead of usually observed disordering of the molecular layer, a drastic decrease in molecular tilt was observed at the initial stage of the deposition. This was attributed to the formation of Ni-thiol complexes at the SAM–ambient interface. The reorientation resulted in the appearance of transient channels for the metal diffusion into the SAM and to the SAM–substrate interface.
Dynamic force microscopy at high cantilever resonance frequencies using heterodyne optical beam deflection method
Authors: Fukuma Takeshi , Kimura Kenjiro , Kobayashi Kei , Matsushige Kazumi , Yamada Hirofumi
Published: December 2004

We have developed a dynamic force microscope (DFM) with a wideband cantilever deflection sensor using heterodyne optical beam deflection (HOBD) method. The bandwidth of HOBD method is limited only by the maximum frequency for laser power modulation, which can be as high as gigahertz order. This technique allows us to use high cantilever resonance frequencies for improving the sensitivity and time response of DFM. In this letter, basic principle and experimental setup of HOBD method are described. Deflection measurement of a cantilever vibration at about 7MHz is demonstrated. Using this cantilever, DFM imaging with a relatively fast scanning speed is performed.
The evolution of electroluminescence in Ge quantum-dot diodes with the fold number
Authors: Peng Y. H. , Hsu Chih-Hsiung , Kuan C. H. , Liu C. W. , Chen P. S. , Tsai M.-J. , Suen Y. W.
Published: December 2004

The electroluminescence of the light-emitting diodes with five-, ten and 30-fold p-type Ge quantum dots grown on n+ Si substrates is studied. The enhanced integral electroluminescence intensity and blueshift of the 30-fold one at high temperature (>200K) act contrary to those in five- and ten-fold ones. It is attributed to the emission in the higher-fold quantum dots enabled by the injected electrons diffusing the farther at the higher temperature. Transmission electron microscopy shows that the size of the Ge quantum dots and the Si component in them, both increase with increasing the fold number. Due to the strain-induced intermixing at the high-fold quantum dots, those dots hence have large band gap and result in the intensity increment and blueshift at the high temperature.
Telomere length regulation during cloning, embryogenesis and ageing
Authors: Schaetzlein S. , Rudolph K. L.
Published: December 2004

Telomeres are nucleoprotein complexes at the end of eukaryotic chromosomes with an essential role in chromosome capping. Owing to the end-replication problem of DNA polymerase, telomeres shorten during each cell division. When telomeres become critically short, they loose their capping function, which in turn induces a DNA damage-like response. This mechanism inhibits cell proliferation at the senescence stage and there is evidence that it limits the regenerative capacity of tissues and organs during chronic diseases and ageing. The holoenzyme telomerase synthesises telomeric DNA de novo, but, in humans, it is active only during embryogenesis, in immature germ cells and in a subset of stem/progenitor cells during postnatal life. Telomere length can be maintained or increased by telomerase, a process that appears to be regulated by a variety of telomere-binding proteins that control telomerase recruitment and activity at the telomeres. During embryogenesis, telomerase is strongly activated at the morula/blastocyst transition. At this transition, telomeres are significantly elongated in murine and bovine embryos. Early embryonic telomere elongation is telomerase dependent and leads to a rejuvenation of telomeres in cloned bovine embryos. Understanding of the molecular mechanisms underlying this early embryonic telomere elongation programme is of great interest for medical research in the fields of regeneration, cell therapies and therapeutic cloning.
Potential and limitations of bovine-specific arrays for the analysis of mRNA levels in early development: preliminary analysis using a bovine embryonic array
Authors: Sirard Marc-André , Dufort Isabelle , Vallée Maud , Massicotte Lyne , Gravel Catherine , Reghenas Hélène , Watson Andrew J. , King W. Allan , Robert Claude
Published: December 2004

New insights into the early development of large mammals are becoming available through the measurement of differential mRNA levels in oocytes and preimplantation embryos. These advances in knowledge are rapidly picking up in pace, mainly owing to the advantages brought by new molecular biology approaches being developed. The possibility of amplifying the starting material and therefore making measurements in single embryo units is now feasible. With these tools, the evaluation of variations in gene expression patterns during the preimplantation period or the impact of culture on mRNA levels is now possible. However, it is important to keep in mind that these methods still have limitations associated with sample preparation or the use of the appropriate controls. Even proper methods of analysis are very important to achieve the full benefit of the application of these tools. The present paper describes some of the potential, as well as limitations, of mRNA level analysis in early embryos, especially for microarray analysis. We have generated a bovine cDNA array (>2000 clones) that contains expressed sequence tags (ESTs) collected from various preimplantation development stages. Using this chip, we have initiated the characterisation of global mRNA level patterns of several key developmental stages from the immature oocyte to the blastocyst stage. As expected, the hybridisation results indicate very different expression profiles involving hundreds of genes when comparing oocyte and blastocyst samples to a reference mRNA sample made from a pool of ESTs from pooled somatic tissues. Although this array is still in its preliminary stage and the EST bank has not been processed to contain only unigenes, it is already a very useful tool for discovering candidate genes that may play important roles during early embryonic life.
1 LONG TERM HEALTH AND BEHAVIOR OF ICSI PRODUCED MICE
Authors: Fernandez-Gonzalez R. , Moreira P. , Bilbao A. , Ramirez M.A. , Perez-Crespo M. , Pintado B. , Rodriguez de Fonseca F. , Gutierrez-Adan A.
Published: December 2004

Intracytoplasmic sperm injection (ICSI) is a relatively new treatment for human male-related infertility (1992) and for the production of transgenic animals (1995). However, ICSI bypasses many natural biological processes such as sperm maturation, interaction within the female genital tract, sperm capacitation, interaction with oocyte vestments, and sperm membrane fusion with the oocyte. With the widespread use of this technology, its potential adverse outcomes need to be ascertained. It is theoretically possible that ICSI may cause specific problems through injury to the sperm or egg or injection of damaged or defective sperm. Here, we determined if ICSI has a long-term effect on mouse growth, behavior, and health. Female CD1 mice were superovulated and oocytes were injected with frozen-thawed spermatozoa (without cryoprotector or chelating agent) obtained from CD1 mice epididymes (Moreira et al. 2004 Biol. Reprod. 71, in press). Embryos were cultured 24 h in KSOM, and 2-cell embryos were transferred into CD1 females. Fifty-six mice (36 males and 20 females) produced by ICSI and 41 control mice (18 males and 23 females) obtained from in vivo-fertilized mice were analyzed. On week 20, animals were submitted to the following behavior tests: locomotor activity (open field), exploratory/anxiety behavior (elevated plus maze, open field), and spatial memory (free-choice exploration paradigm in Y maze). Comparison between groups was made using analysis of variance followed by least significant difference post hoc test. Postnatal weight gain of female mice produced by ICSI was heavier than for their control counterparts from 10 weeks on (P < 0.01). Males produced by ICSI showed more anxiety and lower locomotion in the p-maze and the Y-maze tests (P < 0.05), but no significant differences were found in the open-field test. Also, no differences were found in spatial memory or in the habituation pattern. Anatomopathological analysis of animals at 16 months of age showed some large organs (heart, lung, and liver; P < 0.01) and an increase in pathologies (15% of animals produced by ICSI presented some solid tumors in lung, dermis of back, or neck). Loss of imprinting is one of the most common epigenetic changes associated with the development of a wide variety of tumours. An association between some imprinting disorders, rare tumors, and ICSI has recently been reported in humans (Wittermer et al. 2004 Med. Sci. 20, 352). We are now analyzing the epigenetic modifications that may be induced by our ICSI protocol and whether the sperm DNA fragmentation that may take place during sperm freezing before the ICSI procedure might not only affect postnatal development, growth, and physiology, but also increase the risk of tumors in adult animals. Our data suggest that our ICSI method produces mice with sex-dimorphic alterations in aberrant growth and anxiety, as well as with a higher probability of developing a solid tumor.