bluuebunny/crossref_metadata_2025 huggingface dataset:
Protein modification by advanced Maillard adducts can be modulated by dietary polyunsaturated fatty acids
Authors: Portero-Otin M. , Bellmunt M.J. , Requena J.R. , Pamplona R.
Published: December 2008

Advanced Maillard adducts, such as N∊-(carboxymethyl)lysine and N∊-(carboxyethyl)lysine, can be formed efficiently in vitro from both peroxidation of polyunsaturated fatty acids and glycolysis intermediates. In an attempt to differentiate the in vivo influence of the two pathways in these modifications, Wistar rats were chronically fed with specially designed diets rich in saturated or unsaturated fats. The degree of fatty acid unsaturation of all analysed organs (liver, kidney, brain) was altered by these dietary stresses. Protein glycoxidative and lipoxidative modifications were measured by GC/MS. In accordance with fatty acid profiles, concentrations of N∊-(malondialdehyde)lysine in these tissues were significantly increased in animals fed the unsaturated fat diet. In contrast, N∊-(carboxymethyl)lysine and N∊-(carboxyethyl)lysine concentrations were strongly dependent on the tissue analysed; although the unsaturated fat diet increased their levels significantly in brain, levels were unchanged in kidney and decreased in liver. These later results could be interpreted on the basis that polyunsaturated fatty acids decrease the expression of several glycolytic enzymes in liver. Globally, these data suggest that tissue-specific metabolic characteristics play a key role in the degree of cellular protein modification by Maillard reactions, e.g. by modulation of the concentration of glycolysis intermediates or via specific defensive systems in these organs.
Quantitative screening of protein biomarkers of early glycation, advanced glycation, oxidation and nitrosation in cellular and extracellular proteins by tandem mass spectrometry multiple reaction monitoring
Authors: Ahmed N. , Thornalley P.J.
Published: December 2008

Glycation of proteins forms fructosamines and AGEs (advanced glycation end products). Oxidative and nitrosative stress leads to the formation of oxidative and nitrosative modifications. The modified amino acid residues formed in these processes are biomarkers of protein damage: some are risk markers and some may be risk factors for disease development. We developed a method for the concurrent quantitative measurement of 16 biomarkers indicative of protein glycation, oxidation and nitrosation damage using LC-MS/MS (LC with tandem MS detection). Underivatized analytes were detected free in physiological fluids and in enzymatic hydrolysates of cellular and extracellular proteins. Hydroimidazolones were the most important glycation biomarkers, and methionine sulphoxide was the most important oxidative biomarker quantitatively; 3-nitrotyrosine was the biomarker of nitrosation. Quantitative screening showed high levels of AGEs in cellular protein and moderate levels in protein of blood plasma. Levels of 3-nitrotyrosine were typically 100-fold lower than this. The major glycation adducts in blood plasma had high renal clearances in normal healthy human subjects, whereas methionine sulphoxide and 3-nitrotyrosine had low renal clearances due to further metabolism. Physiological AGEs in blood plasma were eliminated from the circulation in the kidney and not in the liver. LC-MS/MS peptide mapping was also used to locate the protein biomarkers. These studies reveal that advanced glycation is a significant modification of cellular and extracellular protein. The enzymatic defences against glycation, antioxidants and proteasomal protein degradation inside cells are probable factors regulating biomarker levels of cellular protein.
Reactive oxygen species in oncogenic transformation
Authors: Behrend L. , Henderson G. , Zwacka R.M.
Published: December 2008

Ever since ROS (reactive oxygen species) were shown to meet the criteria of true signalling molecules, such as regulated production and a specific biological function, many efforts have been made to understand the precise role of ROS. The function of ROS in pathological mechanisms is taking a more and more central role in various fields of biomedical research, including neurobiology, cardiology and cancer. An elevated oxidative status has been found in many types of cancer cells, and the introduction of chemical and enzymological antioxidants can inhibit tumour cell proliferation, pointing to a critical role of ROS in mediating loss of growth control. The present review describes ROS-regulated mechanisms that are associated with cancer and tumour invasiveness. The cellular processes that are linked to these ROS functions are mitogenic signalling and cell motility, while ROS have also been implicated in apoptosis and cellular senescence, two mechanisms regarded as being anti-tumorigenic. This ‘two-faced’ character of free radicals will be discussed and placed in the context of the physiological conditions of the tumour cell, the different molecular backgrounds, and the specific ROS. More detailed understanding of the signalling pathways regulated by ROS in tumour cells will open up new prospects for chemo- or gene-therapeutic interventions.
Rapid S-nitrosothiol metabolism by platelets and megakaryocytes
Authors: Shah C.M. , Locke I.C. , Chowdrey H.S. , Gordge M.P.
Published: December 2008

RSNOs (S-nitrosothiols) regulate platelet and megakaryocyte function, and may act in vivo as a nitric oxide reservoir. There is a discrepancy between the spontaneous rate of NO release from different RSNO compounds and their pharmacological effects, implying that target cells may mediate biological activity either by metabolism of RSNOs or by displaying cell surface receptors. In the present study, we sought evidence for rapid cell-mediated metabolism of RSNOs. Exposure of platelets to GSNO (S-nitrosoglutathione) for as little as 5 s inhibited thrombin-induced platelet aggregation by >95%; however, AlbSNO (S-nitrosoalbumin) was much less effective over these short time periods. Incubation of 1 μM GSNO or AlbSNO with platelets and megakaryocytes resulted in a 25–34% loss of RSNO recoverable from the supernatant (P<0.02) within 30 s. This rapid cell-mediated RSNO decay did not progress further over 5 min, and could not be accounted for by release of free NO. The γ-glutamyl transpeptidase inhibitor acivicin (100 μM) partially decreased GSNO decay, whereas the membrane-impermeable thiol-blocking agent 5,5´-dithiobis-(2-nitrobenzoic acid) (100 μM) completely blocked cell-mediated GSNO decay and partially blocked AlbSNO decay. Our results highlight differences between high- and low-molecular-mass RSNOs with regard to their rapid metabolism/uptake and subsequent cellular responses, and indicate a critical role for extracellular thiols in RSNO metabolism by platelets and megakaryocytes.
Interpreting correlations in metabolomic networks
Authors: Steuer R. , Kurths J. , Fiehn O. , Weckwerth W.
Published: December 2008

Correlations, as observed between the concentrations of metabolites in a biological sample, may be used to gain additional information about the physiological state of a given tissue. In this mini-review, we discuss the integration of these observed correlations into metabolomic networks and their relationships with the underlying biochemical pathways.
Integrating functional genomics data
Authors: Kemmeren P. , Holstege F.C.P.
Published: December 2008

Functional annotation of fully sequenced genomes is still a major issue. High-throughput data sets could be used to provide more and better functional annotations. However differences in data quality need to be taken into account. For this purpose these high-throughput data sets need to be integrated so that the data quality can be assessed, hypotheses can be prioritized and existing annotations can be improved and extended.
Fatigue damage characterization using surface acoustic wave nonlinearity in aluminum alloy AA7175-T7351
Authors: Jaya Rao V. V. S. , Kannan Elankumaran , Prakash Raghu V. , Balasubramaniam Krishnan
Published: December 2008

Nonlinear ultrasonic (NLU) harmonic generation system was used to characterize the fatigue damage in a flat hour-glass, high strength Al–Cu–Zn–Mg alloy, AA7175-T7351 specimens. Experiments were carried out to introduce controlled levels of fatigue damage under constant amplitude loading to determine the NLU response using surface acoustic wave (or Rayleigh mode) at regular intervals of fatigue life. The NLU parameter (A2/A12) plotted as a function of percentage of fatigue life shows two peaks for all the samples tested, independent of the amplitude of fatigue loading. The first peak appeared between 40%–50% of fatigue life and the second peak between 80%–90% of fatigue life. Among the two flat surfaces of the specimen, a higher nonlinearity response was observed on the surface which had the first crack initiation. The appearance of two peaks in the nonlinear response during fatigue damage progression is explained based on the dislocation dynamics and dislocation-crack interaction present in the specimens during the fatigue process.
A mean field model for spin glasses based on a 2-level perceptron
Authors: Talagrand Michel
Published: December 2008

We introduce a mean field model for spin glasses that is obtained by “iterating” the definition of the perceptron model of [SG] and we prove the validity of the replica-symmetric solution under a condition of the type “high temperature.” The replica-symmetric equations involve six different parameters. This model illustrates, on one hand, that we now have efficient tools to deal with such systems, and on the other hand, that it is probably unreasonable to hope for abstract theorems independent of the specific type of the system.
Quantum dots in strained layers—preventing relaxation through the precipitate hardening effect
Authors: Beanland R. , David J. P. R. , Sanchez A. M.
Published: December 2008

The internal strain in epitaxial layers due to lattice misfit has long been recognized as a limiting factor in the design of semiconductor structures. In strained layer structures above a critical thickness hc, this strain is relaxed by the introduction of misfit dislocations. Here, we show that the interaction between the strain fields of a self-assembled quantum dot and a dislocation can lead to a threading dislocation being trapped, or pinned, by the quantum dot. The strength of this interaction is always larger than the force exerted on the dislocation by a surrounding layer with lower misfit strain. This gives a significant increase in the critical thickness for relaxation hc(QD). In layers between hc and hc(QD), threading dislocations can at best move only small distances, effectively preventing relaxation. Furthermore it is not possible to destabilize such a layer by the deposition of strained layers above it. The classical critical thickness condition thus does not apply to these structures, and they can be produced with essentially no limits to thickness before relaxation occurs. This may be expected to have significant technological consequences and allow a much wider range of structures to be produced than is possible using current strained layer design rules.
Influence of doping profiles on coherent acoustic phonon detection and generation in semiconductors
Authors: Hudert F. , Bartels A. , Dekorsy T. , Köhler K.
Published: December 2008

The doping profile in different n-doped GaAs homoepitaxial structures grown by molecular beam epitaxy is investigated in the time domain by employing a laser based picosecond ultrasound technique in a contactless and noninvasive way. Experiments based on asynchronous optical sampling employ two femtosecond lasers, which allow us to detect changes in the optical reflectivity over a 1 ns time delay with a signal-to-noise ratio of 107 and 100 fs time resolution in <1 min of acquisition time. We show that the doping profile with doping densities of the order of 1018 cm−3 can be detected with picosecond ultrasound, although there is no difference in the acoustic properties of the doped and undoped region. The detection mechanism is based on a different sensitivity function for a coherent strain pulse in the doped and undoped regions. These results are corroborated by experiments at room temperature and 10 K.
Extrapolation to the complete-basis-set limit and the implications of avoided crossings: The X Σ1g+, B Δ1g, and B′ Σ1g+ states of C2
Authors: Varandas A. J. C.
Published: December 2008

The uniform singlet- and triplet-pair extrapolation scheme and its generalized variant are utilized to describe bond breaking of the C2 molecule in the ground electronic state, as well as in two other excited states of the same spin symmetry by extrapolating multireference configuration interaction energies calculated with the correlation consistent basis sets of Dunning to the complete-basis set limit. It is shown that the correlation energy changes drastically (with a symmetric sigmoidal-type shape) near the geometry (R∼1.6 Å) where the two lowest Σ1g+ adiabatic states show the avoided crossing. The implications of such a feature on extrapolating the dynamical correlation are then analyzed, and the attributes of the extrapolated ground electronic state shown to be in excellent agreement with the most recent experimental data available in the literature.
The autocorrelation functions of a fluid of molecules interacting through steep attractive potentials
Authors: Rickayzen G. , Heyes D. M.
Published: December 2008

In a previous paper [G. Rickayzen and D. M. Heyes, J. Chem. Phys. 126, 234503 (2007)] we investigated by theory and molecular dynamics (MD) simulation the force and velocity autocorrelation functions of a fluid of molecules interacting through steeply varying potentials of the form ϕ(r)=4ε[z2(r)−z(r)], where z(r)=(σ∕r)n, ε and σ set the energy and length scale of the interaction, respectively, and n is an adjustable exponent (n=72 and 144 were considered in that work). Discrepancies between the theory and simulation were found except at the shortest times for some of the state points. In order to identify the origin(s) of these discrepancies, we have investigated here another fluid, in which the particles interact via the Morse potential in which z(r)=exp(−κ(r−σ)∕σ), where κ is now the “steepness” parameter. The parameter κ is the analog of n, and this potential form is used in order to compare with previous results and establish better the origin of the differences between theory and simulation. It is shown in a further development of the theory that the actual form of the potential in the steep and short-ranged attractive limit is immaterial, and there exists a law of corresponding states for such potentials. This conclusion is confirmed by the MD simulations with the two potential forms for κ=n=144. The difference between the theory and simulation correlation functions increases with density, and it is concluded that these differences probably originate in many-body effects in time, which are absent in the theory. For packing fractions below about 0.2 the agreement between the theory and MD simulation force and velocity autocorrelation functions is nevertheless very good at all accessible times.
Effect of initial plasma density on laser induced ion acceleration
Authors: Holkundkar Amol R. , Gupta N. K.
Published: December 2008

The effect of initial plasma density on the energetics of the laser accelerated ions is studied using one dimensional particle in cell simulations. It is observed that the initial plasma density plays an important role in the generation of high energy particles. In the case of a spatially constant initial density, there exists an optimum value for the maximum ion acceleration. Similarly for the case of a density ramp, an optimum value of ramp length exists for the maximum ion acceleration. At a laser intensity of 5×1020 W/cm2, a maximum energy of about 1 GeV is seen with an optimum initial density ramp.
Secondary shock wave in laser-material interaction
Authors: Gacek Sobieslaw , Wang Xinwei
Published: December 2008

In this work, the effects of shock driven process of the laser-ablated argon plume in a background gas environment are explored via molecular dynamics simulations. The primary shock wave propagation and its influence on the backward motion of the target material are delineated. It is observed that the strong pressure gradient inside the main shock wave overcomes the forward momentum of the plume and some compressed gas, leading to backward movement and redeposition on the target surface. Reflection of the backward moving gas on the target surface results in the secondary shock wave. Detailed investigation of the secondary shock wave phenomenon is provided, which gives, for the first time, an insight into formation and evolution of the internal gaseous shock at the atomistic level.
Nature of the pressure-induced collapse of an ice clathrate by dielectric spectroscopy
Authors: Andersson Ove , Johari G. P.
Published: December 2008

Collapse of an ice clathrate of type II structure containing tetrahydrofuran as guest molecules has been studied at different pressures by dielectric spectroscopy. The sample was pressurized to 1.3 GPa at 130 K and the resulting collapsed state was pressure cycled. The dielectric relaxation time increases at a progressively rapid rate during pressurizing and then decreases slowly on depressurizing, but the dielectric relaxation time does not reach the value of the original state. With increase in pressure, the limiting high frequency permittivity due to orientation of H2O molecules first increases by about 5% until 0.75 GPa and then decreases slightly until 1 GPa, and finally it increases until ∼1.2 GPa. The decrease is attributed to the loss of contribution from the reorientational motion of tetrahydrofuran molecules and the increase to densification as the structure mechanically collapses completely in the 1–1.25 GPa range. The relaxation time of the collapsed state is comparable with that of the high-density amorph formed on pressure collapse of ice.
Dielectric nonlinearity in a compositionally graded lead zirconate titanate structure
Authors: Khodorov A. , Rodrigues S. A. S. , Pereira M. , Gomes M. J. M.
Published: December 2008

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure was studied as a function of frequency and amplitude of measuring field. The nonlinear behavior was observed above “threshold” value Et of electric field strength giving rise to field-dependent dielectric properties. Just above Et the nonlinearity was well fitted by the empirical Rayleigh relations. The values of Rayleigh coefficients were observed to be different from those of homogenous PZT films. The analysis of the nonlinearity allows us to suggest higher density of domain walls and/or their better mobility in graded structure.
Raman spectroscopy study of ammonia borane at high pressure
Authors: Lin Yu , Mao Wendy L. , Drozd Vadym , Chen Jiuhua , Daemen Luke L.
Published: December 2008

Ammonia borane, NH3BH3, has attracted significant interest as a promising candidate material for hydrogen storage. The effect of pressure on the bonding in NH3BH3 was investigated using Raman spectroscopy to over 20 GPa in a diamond anvil cell, and two new transitions were observed at approximately 5 and 12 GPa. Vibrational frequencies for the modes of the NH3 proton donor group exhibited negative pressure dependence, which is consistent with the behavior of conventional hydrogen bonds, while the vibrational frequencies of the BH3 proton acceptor group showed positive pressure dependence. The observed behavior of these stretching modes supports the presence of dihydrogen bonding at high pressure. In addition, the BH3 and NH3 bending modes showed an increase in spectral complexity with increasing pressure together with a discontinuity in dν/dP which suggests rotational disorder in this molecule. These results may provide guidance for understanding and developing improved hydrogen storage materials.
Modeling heat generation in a submicrometric n+−n−n+ silicon diode
Authors: Muscato Orazio , Di Stefano Vincenza
Published: December 2008

In this paper a hydrodynamic model for electron and phonon transport in silicon semiconductors has been formulated on the basis of the maximum entropy principle to describe off-equilibrium phenomena in submicron devices. One dimensional steady-state simulations of a n+−n−n+ silicon diode have been carried out.
Sheath criterion and Sagdeev potential for both electronegative and electropositive plasmas
Authors: Alterkop B.
Published: December 2008

The sheath criterion was considered for electronegative as well as electropositive plasma in contact with a material boundary that is either more negative than the plasma space potential or more positive than the space potential. A fluid model accounted for the inertia and pressures of all the plasma components and the Sagdeev potential in the whole sheath without any power series expansion were used. The criterion was specified for several special cases of both electronegative and electropositive plasmas. In the cases, a cold ion critical velocity at the sheath entrance was greater by a factor of 1.585 for qϕ>0 than that for qϕ<0, where q is the ion charge and ϕ is the electrical potential in the sheath. In the case of a plasma with Boltzmann electrons and positive ions and a cold ion beam, this conclusion is true only for q<0 and ϕ<0.
Relative optically stimulated luminescence and thermoluminescence efficiencies of Al2O3:C dosimeters to heavy charged particles with energies relevant to space and radiotherapy dosimetry
Authors: Sawakuchi G. O. , Yukihara E. G. , McKeever S. W. S. , Benton E. R. , Gaza R. , Uchihori Y. , Yasuda N. , Kitamura H.
Published: December 2008

This article presents a comprehensive characterization of the thermoluminescence (TL) and optically stimulated luminescence (OSL) relative luminescence efficiencies of carbon-doped aluminum (Al2O3:C) for heavy charged particles (HCPs) with atomic numbers ranging from 1 (proton) to 54 (xenon) and energies ranging from 7 to 1000 MeV/u, and investigates the dependence of the Al2O3:C response on experimental conditions. Relative luminescence efficiency values are presented for 19 primary charge/energy combinations, plus 31 additional charge/energy combinations obtained by introducing absorbers in the primary beam. Our results show that for energies of hundreds of MeV/u the data can be described by a single curve of relative luminescence efficiency versus linear energy transfer (LET). This information is needed to compensate for the reduced OSL efficiency to high-LET particles in such applications as space dosimetry. For lower energies, the relative luminescence efficiency as function of LET cannot be described by a single curve; instead, it separates into different components corresponding to different particles. We also present data on the low-LET dose response of Al2O3:C, measured under the same experimental conditions in which the relative luminescence efficiencies to HCPs were obtained, providing information relevant to future theoretical investigations of HCP energy deposition and luminescence production in Al2O3:C.
Diffusion properties of Ga in Si1−xGex alloys
Authors: Riihimäki I. , Virtanen A. , Kettunen H. , Pusa P. , Räisänen J.
Published: December 2008

Diffusion of Ga in relaxed intrinsic Si1−xGex layers has been determined at 907 °C within the whole composition range. Based on current results and available systematic diffusion data for Si, Ge, and Si1−xGex alloys, it is suggested that Ga diffusion is interstitialcy mediated in Si rich materials and vacancy mediated in Ge rich materials. The results indicate that the dominating diffusion mechanism change takes place at x∼0.6.
Change of InAs/GaAs quantum dot shape and composition during capping
Authors: Eisele H. , Lenz A. , Heitz R. , Timm R. , Dähne M. , Temko Y. , Suzuki T. , Jacobi K.
Published: December 2008

Using plan-view and cross-sectional scanning tunneling microscopy, the shape and composition of InAs/GaAs quantum dots are investigated before and after capping by GaAs. During capping, the original pyramidally shaped quantum dots become truncated, resulting in a flat (001) top facet and steeper side facets. The InAs quantum dots are found to be intermixed at their top with GaAs due to material rearrangement. Since the bottom interface of quantum dots and wetting layer is always sharp, this intermixing occurs during capping and not during quantum dot growth. Considering strain energies, a model for the capping is presented.
Impact response of titanium from the ambient temperature to 1000 °C
Authors: Zaretsky E. B.
Published: December 2008

The yield and spall strengths of polycrystalline high purity (99.99%) and commercial (grade 2) titanium were studied in a series of planar impact experiments with the initial sample temperature ranging from 20 to 1000 °C. In a separate series of impact experiments, the temperature dependence of the longitudinal speed of sound in pure Ti was measured making use of the reverberation of the stress pulse generated in the 3 mm Ti sample by an aluminum impactor. In all the experiments, the velocity of the sample free surface was continuously monitored by VISAR. The stress-strain diagrams of the two kinds of samples were derived from the free surface velocity profiles using the simple wave approximation. Analysis of these diagrams made allowed revealing the sequence of the dislocation-based processes governing the plastic flow in the two materials, from the ambient to some 100 °C above the hcp-bcc transformation temperature. On the basis of the spall data obtained from impact experiments with pure titanium, the limits of existence of nonequilibrium titanium phases were outlined.
Crystal structure and dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 complex perovskite at microwave frequencies
Authors: Hu Mingzhe , Gu Haoshuang , Chu Xiangcheng , Qian Jun , Xia Zhiguo
Published: December 2008

The crystal structure and microwave dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 (0≤x≤1.0) solid solutions incorporated with 1 wt % CuO were investigated. Pure perovskite phases were formed in the whole composition range, and the crystal space group and unit cell volume of the perovskites were analyzed based on x-ray diffraction patterns. The configuration of octahedral tilting and the B-site ordering phase transition between x=0.9 and 1.0 were unambiguously assigned, respectively, to the corresponding superlattice diffractions. Moreover, the two important fingerprints A1g mode and F2g mode in Raman spectra, associated with the evolution of short range ordering and long range ordering of B-site cations, respectively, were further investigated by employing the full width at half-maximum and their Raman shifts to determine the degree of B-site ordering and the crystal bond strength in the perovskites. The microwave dielectric constants, quality factors, and temperature coefficients of resonant frequency of the solid solutions were elaborately investigated and correlated with their crystal structures. The microscopic structure-related thermal parameters in the solid solution were calculated using the Claussius–Mossotti equation to determine the original contributors in the temperature coefficients. Temperature compensated τf value ceramics could be obtained in the range of 0.3<x<0.5. When sintered at 1400 °C for 2.5 h, a dielectric constant εr of 39.9, a quality factor product of 12 600 GHz, and a τf of −25.3 ppm/°C microwave dielectric ceramic were obtained in 0.5Ca0.61Nd0.26TiO3+0.5Nd(Mg1/2Ti1/2)O3+1 wt % CuO composition.
Phase diagrams and electrical properties of (Bi1/2Na1/2)TiO3-based solid solutions
Authors: Hiruma Yuji , Nagata Hajime , Takenaka Tadashi
Published: December 2008

In this study, we demonstrated the relationship between the phase diagrams and the electrical properties of (Bi1/2Na1/2)TiO3 (BNT)-based solid solutions. In this study, (1−x)(Bi1/2Na1/2)TiO3–xNaNbO3 and (1−x)(Bi1/2Na1/2)TiO3–xKNbO3 (abbreviated to BNT-NN100x and BNT-KN100x) ceramics were prepared by a conventional ceramic fabrication process, and (1−x)(Bi1/2Na1/2)TiO3–x(Bi1/2K1/2)TiO3 (abbreviated to BNKT100x) ceramic was prepared for comparison. We revealed the phase transition temperatures, such as the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant, from the temperature dependence of dielectric properties using poled and unpoled specimens. As a result, it was shown that the BNT-based solid solutions form three types of phase diagrams. In addition, we clarified the relationship between the phase diagrams and the electrical properties of BNT-NN100x, BNT-KN100x, and BNKT100x. The piezoelectric properties were markedly enhanced when TR-T shifted to a lower temperature, and a large piezoelectric constant d33 of 168 pC/N was obtained at the morphotropic phase boundary (MPB) between the ferroelectric rhombohedral and ferroelectric tetragonal phases for BNKT100x. Although the piezoelectric properties almost disappeared when Td shifted to room temperature, the field-induced strain S and the normalized strain d33∗ (=Smax/Emax) abruptly increased to 0.22% and 259 pm/V, respectively, for BNT-NN100x. In particular, a very large reversible strain of S=0.40 with d33∗=498 pm/V was obtained at the MPB between the ferroelectric rhombohedral and ferroelectric relaxor with pseudocubic (tetragonal) phases for BNT-KN100x. This very large reversible strain was clarified to be due to non-180° (71° and 109°) domain switching of the field-induced ferroelectric rhombohedral phase.
An alternative approach to understand the photoluminescence and the photoluminescence peak shift with excitation in porous silicon
Authors: Pradeep J. Anto , Agarwal Pratima
Published: December 2008

There have been many different models proposed for the luminescence in porous silicon (PS), yet it is believed that the quantum confinement effect persists at the absorption. However, from our investigation on both constant and pulsed electrochemically etched silicon (PS), the absence of quantum confinement effect at the absorption has been identified from the close correspondence of photoluminescence excitation (PLE) spectra of PS to the simulated absorption spectrum of an ultrathin silicon film with the bulk optical constants. In the simulation of absorption spectrum, the spectral dependence of reflectivity of the solid, which had been omitted in the traditional analysis of PLE, is considered. Further, although nanocrystallites of silicon are present in the PS matrix, the absence of quantum confinement is explained on the basis of structural characteristics of PS. Following that, many common observations in the luminescence of PS are attributed to the surface states. The blueshift of the PL peak with the increase in excitation energy is explained with the idea of quasithermal equilibrium and the probability of occupation of the carriers at the surface states.
p
-type doping in organic light emitting diodes based on fluorinated C60
Authors: Yu Young-Jun , Solomeshch Olga , Chechik Helena , Goryunkov A. A. , Tuktarov R. F. , Choi Dong Hoon , Jin Jung-Il , Eichen Yoav , Tessler Nir
Published: December 2008

We report on hybrid organic light emitting diodes based on spin coated PVK (poly(vinylcarbazole))/poly-TPD (poly(triphenyldiamine)) formulation electron blocking and conjugated peptide emitter layers while the hole blocking, BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), layer is vacuum sublimed. The device structure is realized through the use of fluorinated C60 as a p-dopant in a cross-linked hole transporting formulation. The lowering of the turn-on voltage is demonstrated using a conjugated peptide as the emitter layer. We suggest that fluorinated C60s could play a major role as tunable dopants in organic electronics.
Highly confined mode above the light line in a two-dimensional photonic crystal slab
Authors: Xu Tao , Wheeler Mark S. , Nair Selvakumar V. , Ruda H. E. , Mojahedi Mohammad , Aitchison J. Stewart
Published: December 2008

We found that certain modes above the light line can satisfy total internal reflection in a two-dimensional photonic crystal slab, resulting in negligible vertical leakage. A heterogeneous cavity utilizing such a mode was designed and constructed for the microwave spectrum. Numerical calculations show the mode has a quality factor (Q) of 6×105 neglecting the material loss and 7600 including it. The measured Q (9000), resonance frequency, and mode pattern agreed well with the calculation. The mode has more than 50% of electric field energy in void space and is promising to have stronger interaction with materials introduced there.
Peculiar effect of mechanical stress on polarization stability in micrometer-scale ferroelectric capacitors
Authors: Gruverman A. , Cross J. S. , Oates W. S.
Published: December 2008

Piezoresponse force microscopy (PFM) has been used to study the polarization stability in micrometer size Pb(Zr,Ti)O3 capacitors. It is shown that the top electrode thickness has a profound effect on the equilibrium polarization state of poled capacitors triggering spontaneous polarization backswitching in the absence of an applied electric field and leading to the formation of an abnormal domain pattern. PFM examination of poled capacitors with thick (250 nm) top electrodes reveals domain patterns with the central regions always oriented in the direction opposite to the applied field. It is suggested that the driving force behind the observed effect is a transient response to the residual shear stress created by the top electrode in the poled capacitors during field-induced polarization switching. The proposed mechanism is quantified using finite element ferroelectric phase field modeling. The observed effect provides valuable insight into the polarization retention behavior in micrometer size ferroelectric capacitors.
Large electric-field-induced strain in Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 solid solution single crystals
Authors: Izumi Makoto , Yamamoto Katsuya , Suzuki Muneyasu , Noguchi Yuji , Miyayama Masaru
Published: December 2008

Single crystals of ferroelectric (1−x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3 (BKT) solid solution with rhombohedral structure were grown by flux method in the composition range of 0<x<0.14. The polarization hysteresis, electric-field-induced strain, and temperature dependence of dielectric permittivity were investigated along the [100]cubic direction. Although small substitution of BKT suppressed the remanent polarization from 38 μC/cm2 at x=0 to about 15 μC/cm2 at x>0.02, piezoelectric strain constant (d33) was enhanced with increasing x up to 297 pm/V at x=0.14.
Gold work function reduction by 2.2eV with an air-stable molecular donor layer
Authors: Bröker B. , Blum R.-P. , Frisch J. , Vollmer A. , Hofmann O. T. , Rieger R. , Müllen K. , Rabe J. P. , Zojer E. , Koch N.
Published: December 2008

Ultraviolet photoelectron spectroscopy was used to investigate neutral methyl viologen (1,1′-dimethyl-1H,1′H-[4,4′]bipyridinylidene, MV0) deposited on Au(111). As a result of molecule-to-metal electron transfer, the work function of Au(111) was decreased from 5.50to3.30eV. The energy levels of electron transport layers deposited on top of modified Au surfaces were shifted to higher binding energies compared to layers on pristine Au, and the electron injection barrier was reduced by 0.80eV for tris(8-hydroxyquinoline)aluminum (Alq3) and by 0.65eV for C60. The air-stable donor MV0 can thus be used to facilitate electron injection into organic semiconductors even from high work function metals.
Lithium salt doped conjugated polymers as electron transporting materials for highly efficient blue polymer light-emitting diodes
Authors: Huang Fei , Shih Ping-I , Liu Michelle S. , Shu Ching-Fong , Jen Alex K.-Y.
Published: December 2008

Highly efficient blue polymer light-emitting diodes (PLEDs) are fabricated using a conjugated polymer, poly[9,9-bis(2-(2-(2-diethanol-amino-ethoxy) ethoxy) ethyl) fluorene-alt-4, 4′-phenylether] as an electron transporting layer (ETL). It was found that the performance of these blue-emitting devices could be greatly improved if the ETL was doped with LiF or Li2CO3 salts. A bis[(4,6-di-fluorophenyl)-pyridinato-N, C2] (picolinate) Ir(III) (FIrpic) complex based blue phosphorescent PLED exhibited a maximum luminance efficiency of 20.3 cd/A with a luminance of 1600 cd/m2 at the current density of 7.9 mA/cm2 and drive voltage of 8.0 V.
Study of trap generation in the Sc2O3/La2O3/SiOx gate dielectric stack by scanning tunneling microscopy
Authors: Ang D. S. , Ong Y. C. , O’Shea S. J. , Pey K. L. , Kakushima K. , Iwai H.
Published: December 2008

Through scanning tunneling microscopy, the rate of electrical stress induced trap generation in the vicinity of the tip/high-κ interface of the Sc2O3/La2O3/SiOx gate stack is observed to be much higher than that at the SiOx/Si interface, implying that the former is more susceptible to electrical stress induced wear out. This polarity dependence is discussed in the context of current trap generation models and is shown to be best explained by anode hot-hole effect induced by inherently lower surface plasmon threshold energy at the metal/high-κ interface and a higher hole trapping rate in the relatively thick high-κ.
Design of midinfrared photodetectors enhanced by resonant cavities with subwavelength metallic gratings
Authors: Hu Xinhua , Li Ming , Ye Zhuo , Leung Wai Y. , Ho Kai-Ming , Lin Shawn-Yu
Published: December 2008

We propose a metallic Fabry–Pérot cavity with a Au grating and a Au film acting as two reflectors to enhance the field and absorption in the active detector region, leading to better performance of quantum-dot-based photodetectors at a wavelength of 10 μm. One- and two-dimensional Au gratings are applied to achieve enhancement for polarized and unpolarized light, respectively. With optimizing grating parameters, the absorption can be enhanced by about 20 times in the active detector region compared to conventional photodetectors without the Au reflectors.
Causes of incorrect carrier-type identification in van der Pauw–Hall measurements
Authors: Bierwagen Oliver , Ive Tommy , Van de Walle Chris G. , Speck James S.
Published: December 2008

The impact of macroscopic sample inhomogeneity and contact placement on the measured carrier type and concentration in the widely used van der Pauw–Hall method is investigated using finite-element analysis of the electrostatics. A variety of likely macroscopic inhomogeneities in mobility or carrier concentration across a square-shaped sample are considered. Inhomogeneities in mobilities do not affect the measured carrier type and concentration, as long as the carrier concentration remains homogeneous. Inhomogeneities in carrier concentrations can result in an incorrect assignment of the carrier type. However, when contacts are placed at the sample corners and not inside the sample area, the correct carrier type is recovered. Our calculations provide an explanation for recent measurements on ZnO [Ohgaki et al., J. Mater. Res. 23, 2293 (2008)]. Guidelines for avoiding incorrect interpretation of van der Pauw–Hall measurements are provided.
Structural origins for the product specificity of SET domain protein methyltransferases
Authors: Couture Jean-François , Dirk Lynnette M. A. , Brunzelle Joseph S. , Houtz Robert L. , Trievel Raymond C.
Published: December 2008

SET domain protein lysine methyltransferases (PKMTs) regulate transcription and other cellular functions through site-specific methylation of histones and other substrates. PKMTs catalyze the formation of monomethylated, dimethylated, or trimethylated products, establishing an additional hierarchy with respect to methyllysine recognition in signaling. Biochemical studies of PKMTs have identified a conserved position within their active sites, the Phe/Tyr switch, that governs their respective product specificities. To elucidate the mechanism underlying this switch, we have characterized a Phe/Tyr switch mutant of the histone H4 Lys-20 (H4K20) methyltransferase SET8, which alters its specificity from a monomethyltransferase to a dimethyltransferase. The crystal structures of the SET8 Y334F mutant bound to histone H4 peptides bearing unmodified, monomethyl, and dimethyl Lys-20 reveal that the phenylalanine substitution attenuates hydrogen bonding to a structurally conserved water molecule adjacent to the Phe/Tyr switch, facilitating its dissociation. The additional space generated by the solvent's dissociation enables the monomethyllysyl side chain to adopt a conformation that is catalytically competent for dimethylation and furnishes sufficient volume to accommodate the dimethyl ε-ammonium product. Collectively, these results indicate that the Phe/Tyr switch regulates product specificity through altering the affinity of an active-site water molecule whose dissociation is required for lysine multiple methylation.
Antagonism of E2F-1 regulated Bnip3 transcription by NF-κB is essential for basal cell survival
Authors: Shaw James , Yurkova Natalia , Zhang Tong , Gang Hongying , Aguilar Floribeth , Weidman Danielle , Scramstad Carly , Weisman Harvey , Kirshenbaum Lorrie A.
Published: December 2008

The transcription factor E2F-1 drives proliferation and death, but the mechanisms that differentially regulate these divergent actions are poorly understood. The hypoxia-inducible death factor Bnip3 is an E2F-1 target gene and integral component of the intrinsic mitochondrial death pathway. The mechanisms that govern Bnip3 gene activity remain cryptic. Herein we show that the transcription factor NF-κB provides a molecular switch that determines whether E2F-1 signals proliferation or death under physiological conditions. We show under basal nonapoptotic conditions that NF-κB constitutively occupies and transcriptionally silences Bnip3 gene transcription by competing with E2F-1 for Bnip3 promoter binding. Conversely, in the absence of NF-κB, or during hypoxia when NF-κB abundance is reduced, basal Bnip3 gene transcription is activated by the unrestricted binding of E2F-1 to the Bnip3 promoter. Genetic knock-down of E2F-1 or retinoblastoma gene product over-expression in cardiac and human pancreatic cancer cells deficient for NF-κB signaling abrogated basal and hypoxia-inducible Bnip3 transcription. The survival kinase PI3K/Akt inhibited Bnip3 expression levels in cells in a manner dependent upon NF-κB activation. Hence, by way of example, we show that the transcriptional inhibition of E2F-1-dependent Bnip3 expression by NF-κB highlights a survival pathway that overrides the E2F-1 tumor suppressor program. Our data may explain more fundamentally how cells, by selectively inhibiting E2F-1-dependent death gene transcription, avert apoptosis down-stream of the retinoblastoma/E2F-1 cell cycle pathway.
IRF4 is essential for IL-21-mediated induction, amplification, and stabilization of the Th17 phenotype
Authors: Huber Magdalena , Brüstle Anne , Reinhard Katharina , Guralnik Anna , Walter Gina , Mahiny Azita , von Löw Eberhard , Lohoff Michael
Published: December 2008

Differentiation of murine T-helper (Th) 17 cells is induced by antigenic stimulation and the sequential action of the cytokines IL-6, IL-21, and IL-23, along with TGFβ. Current dogma proposes that IL-6 induces IL-21, which, in a STAT3-dependent manner, amplifies its own transcription, contributes to IL-17 production, and, moreover, promotes the expression of the IL-23 receptor. This, in turn, prepares cells for IL-23-mediated stabilization of the Th17 phenotype. Here we demonstrate that these effects of IL-21 on Th17 differentiation are completely dependent on IFN regulatory factor 4 (IRF4). After culturing in the presence of IL-21 plus TGFβ, IRF4-deficient (
Irf4
−/−
) Th cells showed a profound intrinsic defect in IL-17 production and in the autocrine IL-21 loop. Likewise, the levels of IL-23 receptor and the lineage-specific orphan nuclear receptors RORα and RORγt were diminished, whereas the T regulatory (Treg) transcription factor forkhead box P3 (Foxp3) was strongly up-regulated, consistent with the reciprocal relationship between Th17 and Treg development. Despite this loss of IL-21 functions, IL-21-induced STAT3 activation was unimpaired and induced normal
Socs3
expression. Forced expression of Foxp3 in WT cells inhibited IL-21-mediated IL-17 production, suggesting that the increase in Foxp3 contributes to the
Irf4
−/−
phenotype. Additionally, the low levels of RORα and RORγt are also partially responsible, because simultaneous overexpression of both proteins restored IL-17 production in
Irf4
−/−
cells to some extent. These data highlight IRF4 as a decisive factor during the IL-21-mediated steps of Th17 development by influencing the balance of Foxp3, RORα, and RORγt.
miR-519 reduces cell proliferation by lowering RNA-binding protein HuR levels
Authors: Abdelmohsen Kotb , Srikantan Subramanya , Kuwano Yuki , Gorospe Myriam
Published: December 2008

Gene expression is potently regulated through the action of RNA-binding proteins (RBPs) and microRNAs (miRNAs). Here, we present evidence of a miRNA regulating an RBP. The RBP HuR can stabilize and modulate the translation of numerous target mRNAs involved in cell proliferation, but little is known about the mechanisms that regulate HuR abundance. We identified two putative sites of miR-519 interaction on the HuR mRNA, one in its coding region (CR), one in its 3′-untranslated region (UTR). In several human carcinoma cell lines tested, HeLa (cervical), HCT116 and RKO (colon), and A2780 (ovarian), overexpression of a miR-519 precursor [(Pre)miR-519] reduced HuR abundance, while inhibiting miR-519 by using an antisense RNA [(AS)miR-519] elevated HuR levels. The influence of miR-519 was recapitulated using heterologous reporter constructs that revealed a greater repressive effect on the HuR CR than the HuR 3′-UTR target sequences. miR-519 did not alter HuR mRNA abundance, but reduced HuR biosynthesis, as determined by measuring nascent HuR translation and HuR mRNA association with polysomes. Modulation of miR-519 leading to altered HuR levels in turn affected the levels of proteins encoded by HuR target mRNAs. In keeping with HuR's proliferative influence, (AS)miR-519 significantly increased cell number and [
3
H]-thymidine incorporation, while (Pre)miR-519 reduced these parameters. Importantly, the growth-promoting effects of (AS)miR-519 required the presence of HuR, because downregulation of HuR by RNAi dramatically suppressed its proliferative action. In sum, miR-519 represses HuR translation, in turn reducing HuR-regulated gene expression and cell division.