bluuebunny/crossref_metadata_2025 huggingface dataset:
Gcn5- and Elp3-induced histone H3 acetylation regulates hsp70 gene transcription in yeast
Authors: Han Qiuju , Lu Jun , Duan Jizhou , Su Dongmei , Hou Xiaozhe , Li Fen , Wang Xiuli , Huang Baiqu
Published: January 2008

The purpose of this study was to elucidate the mechanisms by which histone acetylation participates in transcriptional regulation of hsp70 (heat-shock protein 70) genes SSA3 and SSA4 in yeast. Our results indicated that histone acetylation was required for the transcriptional activation of SSA3 and SSA4. The HATs (histone acetyltransferases) Gcn5 (general control non-derepressible 5) and Elp3 (elongation protein 3) modulated hsp70 gene transcription by affecting the acetylation status of histone H3. Although the two HATs possessed overlapping function regarding the acetylation of histone H3, they affected hsp70 gene transcription in different ways. The recruitment of Gcn5 was Swi/Snf-dependent and was required for HSF (heat-shock factor) binding and affected RNAPII (RNA polymerase II) recruitment, whereas Elp3 exerted its roles mainly through affecting RNAPII elongation. These results provide insights into the effects of Gcn5 and Elp3 in hsp70 gene transcription and underscore the importance of histone acetylation for transcriptional initiation and elongation in hsp genes.
Nucleosomes represent a physical barrier for cleavage activity of DNA topoisomerase I in vivo
Authors: Di Felice Francesca , Chiani Francesco , Camilloni Giorgio
Published: January 2008

DNA topoisomerase I together with the other cellular DNA topoisomerases releases the torsional stress from DNA caused by processes such as replication, transcription and recombination. Despite the well-defined knowledge of its mechanism of action, DNA topoisomerase I in vivo activity has been only partially characterized. In fact the basic question concerning the capability of the enzyme to cleave and rejoin DNA wrapped around a histone octamer remains still unanswered. By studying both in vivo and in vitro the cleavage activity of DNA topoisomerase I in the presence of camptothecin on a repeated trinucleotide sequence, (TTA)35, lying in chromosome XIII of Saccharomyces cerevisiae, we can conclude that nucleosomes represent a physical barrier for the enzyme activity.
Effect of methylglyoxal modification on stress-induced aggregation of client proteins and their chaperoning by human αA-crystallin
Authors: Biswas Ashis , Wang Benlian , Miyagi Masaru , Nagaraj Ram H.
Published: January 2008

α-Crystallin prevents protein aggregation under various stress conditions through its chaperone-like properties. Previously, we demonstrated that MGO (methylglyoxal) modification of αA-crystallin enhances its chaperone function and thus may affect transparency of the lens. During aging of the lens, not only αA-crystallin, but its client proteins are also likely to be modified by MGO. We have investigated the role of MGO modification of four model client proteins (insulin, α-lactalbumin, alcohol dehydrogenase and γ-crystallin) in their aggregation and structure and the ability of human αA-crystallin to chaperone them. We found that MGO modification (10–1000 μM) decreased the chemical aggregation of insulin and α-lactalbumin and thermal aggregation of alcohol dehydrogenase and γ-crystallin. Surface hydrophobicity in MGO-modified proteins decreased slightly relative to unmodified proteins. HPLC and MS analyses revealed argpyrimidine and hydroimidazolone in MGO-modified client proteins. The degree of chaperoning by αA-crystallin towards MGO-modified and unmodified client proteins was similar. Co-modification of client proteins and αA-crystallin by MGO completely inhibited stress-induced aggregation of client proteins. Our results indicate that minor modifications of client proteins and αA-crystallin by MGO might prevent protein aggregation and thus help maintain transparency of the aging lens.
Roles for TAB1 in regulating the IL-1-dependent phosphorylation of the TAB3 regulatory subunit and activity of the TAK1 complex
Authors: Mendoza Heidi , Campbell David G. , Burness Kerry , Hastie James , Ronkina Natalia , Shim Jae-Hyuck , Arthur J. Simon C. , Davis Roger J. , Gaestel Matthias , Johnson Gary L. , Ghosh Sankar , Cohen Philip
Published: January 2008

The protein kinase TAK1 (transforming growth factor-β-activated kinase 1), which has been implicated in the activation of MAPK (mitogen-activated protein kinase) cascades and the production of inflammatory mediators by LPS (lipopolysaccharide), IL-1 (interleukin 1) and TNF (tumour necrosis factor), comprises the catalytic subunit complexed to the regulatory subunits, termed TAB (TAK1-binding subunit) 1 and either TAB2 or TAB3. We have previously identified a feedback-control mechanism by which p38α MAPK down-regulates TAK1 and showed that p38α MAPK phosphorylates TAB1 at Ser423 and Thr431. In the present study, we identified two IL-1-stimulated phosphorylation sites on TAB2 (Ser372 and Ser524) and three on TAB3 (Ser60, Thr404 and Ser506) in human IL-1R cells [HEK-293 (human embryonic kidney) cells that stably express the IL-1 receptor] and MEFs (mouse embryonic fibroblasts). Ser372 and Ser524 of TAB2 are not phosphorylated by pathways dependent on p38α/β MAPKs, ERK1/2 (extracellular-signal-regulated kinase 1/2) and JNK1/2 (c-Jun N-terminal kinase 1/2). In contrast, Ser60 and Thr404 of TAB3 appear to be phosphorylated directly by p38α MAPK, whereas Ser506 is phosphorylated by MAPKAP-K2/MAPKAP-K3 (MAPK-activated protein kinase 2 and 3), which are protein kinases activated by p38α MAPK. Studies using TAB1−/− MEFs indicate important roles for TAB1 in recruiting p38α MAPK to the TAK1 complex for the phosphorylation of TAB3 at Ser60 and Thr404 and in inhibiting the dephosphorylation of TAB3 at Ser506. TAB1 is also required to induce TAK1 catalytic activity, since neither IL-1 nor TNFα was able to stimulate detectable TAK1 activity in TAB1−/− MEFs. Surprisingly, the IL-1 and TNFα-stimulated activation of MAPK cascades and IκB (inhibitor of nuclear factor κB) kinases were similar in TAB1−/−, MEKK3−/− [MAPK/ERK (extracellular-signal-regulated kinase) kinase kinase 3] and wild-type MEFs, suggesting that another MAP3K (MAPK kinase kinase) may mediate the IL-1/TNFα-induced activation of these signalling pathways in TAB1−/− and MEKK3−/− MEFs.
Hepatic selenoprotein P (SePP) expression restores selenium transport and prevents infertility and motor-incoordination in Sepp-knockout mice
Authors: Renko Kostja , Werner Margarethe , Renner-Müller Ingrid , Cooper Trevor G. , Yeung Ching Hei , Hollenbach Birgit , Scharpf Marcus , Köhrle Josef , Schomburg Lutz , Schweizer Ulrich
Published: January 2008

SePP (selenoprotein P) is central for selenium transport and distribution. Targeted inactivation of the Sepp gene in mice leads to reduced selenium content in plasma, kidney, testis and brain. Accordingly, activities of selenoenzymes are reduced in Sepp−/− organs. Male Sepp−/− mice are infertile. Unlike selenium deficiency, Sepp deficiency leads to neurological impairment with ataxia and seizures. Hepatocyte-specific inactivation of selenoprotein biosynthesis reduces plasma and kidney selenium levels similarly to Sepp−/− mice, but does not result in neurological impairment, suggesting a physiological role of locally expressed SePP in the brain. In an attempt to define the role of liver-derived circulating SePP in contrast with locally expressed SePP, we generated Sepp−/− mice with transgenic expression of human SePP under control of a hepatocyte-specific transthyretin promoter. Secreted human SePP was immunologically detectable in serum from SEPP1-transgenic mice. Selenium content and selenoenzyme activities in serum, kidney, testis and brain of Sepp−/−;SEPP1 (SEPP1-transgenic Sepp−/−) mice were increased compared with Sepp−/− controls. When a selenium-adequate diet (0.16-0.2 mg/kg of body weight) was fed to the mice, liver-specific expression of SEPP1 rescued the neurological defects of Sepp−/− mice and rendered Sepp−/− males fertile. When fed on a low-selenium diet (0.06 mg/kg of body weight), Sepp−/−;SEPP1 mice survived 4 weeks longer than Sepp−/− mice, but ultimately developed the neurodegenerative phenotype. These results indicate that plasma SePP derived from hepatocytes is the main transport form of selenium supporting the kidney, testis and brain. Nevertheless, local Sepp expression is required to maintain selenium content in selenium-privileged tissues such as brain and testis during dietary selenium restriction.
Anandamide inhibits IL-12p40 production by acting on the promoter repressor element GA-12: possible involvement of the COX-2 metabolite prostamide E2
Authors: Correa Fernando , Docagne Fabian , Clemente Diego , Mestre Leyre , Becker Christoph , Guaza Carmen
Published: January 2008

The eCB [endoCB (cannabinoid)] system is being considered as a novel therapeutic target for immune disorders. Cytokines of the IL-12 (interleukin-12) family have essential functions in cell-mediated immunity. In the present study, we have addressed the mechanisms of action of the eCB AEA (anandamide) on the regulation of IL-12p40 in activated microglia/macrophages. We demonstrated that AEA can inhibit the expression of p35, p19 and p40 subunits, which form the biologically-active cytokines IL-12 and IL-23 in microglia stimulated with LPS (lipopolysaccharide)/IFNγ (interferon γ). Additionally, we have provided evidence that AEA reduces the transcriptional activity of the IL-12p40 gene in LPS- and IFNγ-co-activated cells, and this is independent of CB or vanilloid receptor activation. Site-directed mutageneis of the different elements of the p40 promoter showed that AEA regulates IL-12p40 expression by acting on the repressor site GA-12 (GATA sequence in IL-12 promoter). Prostamide E2 (prostaglandin E2 ethanolamide), a product considered to be a putative metabolite of AEA by COX-2 (cyclo-oxygenase 2) oxygenation, was also able to inhibit the activity of the IL-12p40 promoter by acting at the repressor site. The effects of AEA and prostamide E2 on p40 transcription were partially reversed by an antagonist of EP2 (prostanoid receptor-type 2), suggesting the possibility that prostamide E2 may contribute to the effects of AEA on IL-12p40 gene regulation. Accordingly, the inhibition of COX-2 by NS-398 partially reversed the inhibitory effects of AEA on IL-12 p40. Overall, our findings provide new mechanistic insights into the activities of AEA in immune-related disorders, which may be relevant for the clinical management of such diseases.
Preventing restenosis after angioplasty: a multistage approach
Authors: Zargham Ramin
Published: January 2008

Arterial reconstruction procedures, including balloon angioplasty, stenting and coronary artery bypass, are used to restore blood flow in atherosclerotic arteries. Restenosis of these arteries has remained a major limitation of the application of these procedures, especially in the case of balloon angioplasty. Post-angioplasty restenosis results from two major processes: neointimal formation and constrictive remodelling. Neointimal formation is initiated by arterial injury with a resultant loss of contractile phenotype in tunica media, leading to VSMC [vascular SM (smooth muscle) cell] migration from the tunica media to the intima. Migrated VSMCs contribute to the intimal thickening by the excessive synthesis of ECM (extracellular matrix) and proliferation. However, increased neointimal mass is not solely responsible for luminal narrowing. Inward constrictive remodelling is also considered as a major cause of delayed failure of angioplasty. At later stages after angioplasty, the increase in contractile forces leads to lumen narrowing. Recent studies show that SM contractile proteins are re-expressed in the neointima, concomitant with late lumen loss. Therefore one important question is whether the restoration of contractile phenotype, which can suppress VSMC migration, is favourable or detrimental. In this review, the importance of viewing restenosis as a multistage process is discussed. Different stages of restenosis occur in a sequential manner and are related to each other, but in each stage a different strategy should be taken into consideration to reduce restenosis. Defining the role of each process not only reshapes the current concept, but also helps us to target restenosis with more efficacy.
Prevalence and predictors of cardiac hypertrophy and dysfunction in patients with Type 2 diabetes
Authors: Srivastava Piyush M. , Calafiore Paul , Macisaac Richard J. , Patel Sheila K. , Thomas Merlin C. , Jerums George , Burrell Louise M.
Published: January 2008

The aim of the present study was to determine the prevalence and predictors of an abnormal echocardiogram in patients with Type 2 diabetes. Cardiac function and structure were rigorously assessed by comprehensive transthoracic echocardiographic techniques in 229 patients with Type 2 diabetes. Cardiovascular risk factors and diabetic complications were assessed, and predictors of an abnormal echocardiogram were identified using multivariate logistic regression analysis. An abnormal echocardiogram was present in 166 patients (72%). LVH (left ventricular hypertrophy) occurred in 116 patients (51%), and cardiac dysfunction was found in 146 patients (64%), of whom 109 had diastolic dysfunction alone and 37 had systolic±diastolic dysfunction. Independent predictors of an abnormal echocardiogram were obesity, age, the number of antihypertensive drugs used (all P<0.001) and creatinine clearance (P<0.05). The risk of an abnormal echocardiogram increased by 9% for each year over 50 years of age {OR (odds ratio), 1.09 [95% CI (confidence interval), 1.04–1.15]}, 3-fold if obesity was present [BMI (body mass index) >30; OR, 4.2 (95% CI, 1.9–9.0)] and by 80% for each antihypertensive agent used [OR, 1.8 (95% CI, 1.3–2.4) per agent]. In conclusion, an abnormal cardiac echocardiogram is common in patients with Type 2 diabetes. Importantly, although cardiac abnormalities can be predicted by traditional risk factors, such as age, obesity and renal function, the absence of micro- or macro-vascular complications does not predict a normal echocardiogram. We suggest that an echocardiogram identifies those with Type 2 diabetes at increased cardiovascular risk due to occult LVH and diastolic dysfunction, and this information may lead to more aggressive management of known risk factors in the clinic.
Nobel Physics Prize Goes to Charpak for Inventing Particle Detectors
Authors: Schwarzschild Bertram
Published: January 2008

The 1992 Nobel Prize in Physics has gone to a virtuoso instrument maker. The Royal Swedish Academy of Sciences awarded the prize to Georges Charpak of France “for his inventionand development of particle detectors, in particular the multiwire proportional chamber.”
Decision Approaching on CERN's Proposed Large Hadron Collider
Authors: Schwarzschild Bertram
Published: January 2008

The Large Hadron Collider is Europe's answer to the Superconducting Super Collider. The final decision to build the LHC must come from the CERN Council, the governing body that represents the European laboratory's 17 member states. That decision is likely to be made at the Council's meeting in December. In the meantime, the LHC project is moving forward on several fronts.
Tunnel Boring Begins at Superconducting Super Collider
Authors: Schwarzschild Bertram
Published: January 2008

The first of the Superconducting Super Collider's 60-foot-wide tunnel-access shafts opens down into a cavernous magnet-transfer area 236 feet below the sod of Ellis County, Texas. Some eight thousand 50-foot-long superconducting bending magnets will eventually be lowered down such access shafts, arrayed around the 54- mile-circumference underground SSC ring. Just after this picture was taken at the end of December, the first of the SSC's 250-ton “inchworm” tunnel borers was lowered down the shaft in segments to begin the actual boring of the 14-foot-high SSC tunnel.
In Old and New Experiments, the 17-KeV Neutrino Goes Away
Authors: Schwarzschild Bertram
Published: January 2008

For more than a decade now, experiments in high-energy physics have yielded very few real surprises. Far from being a reproach to the experimenters, this state of affairs is a testament to the encompassing success of the standard model of the elementary particles that took its definitive shape in the 1970s. In the early 1980s the heavy vector bosons, W± and Z0, that mediate the weak interactions were found just about where they were expected, and the millions of Z0s created since then have confirmed the predictions of the standard model in spectacular detail.
Three-Dimensional Optical Molasses Binds a New Type of Crystal
Authors: Collins Graham P.
Published: January 2008

Researchers in Germany and France have bound neutral atoms in regular two- and three-dimensional lattices induced by the interference patterns of several laser beams. The work builds on the techniques of magnetooptical trapping and sub-Doppler laser cooling and on previous work in which atoms were bound in onedimensional standing waves of light. The fields of light in these techniques are called optical molasses, because atoms within them experience viscous forces, which cool the atoms to temperatures on the order of microkelvins. In the new, “crystalline” molasses, the standing waves produce a stable, regular array of potential wells—a microscopic “egg carton”— and the atoms become localized at the bottoms of the wells.
Experiments Find Relatively Long-Lived Isotope of Element 106
Authors: Levi Barbara G.
Published: January 2008

There's more to research on heavy elements than simply producing them. Recent experiments continue to explore their properties. In a welcome collaborative effort, researchers from the Joint Institute for Nuclear Research in Dubna, Russia, and from the Lawrence Livermore National Laboratory announced at the Actinides ‘93 Conference in Santa Fe, New Mexico, in September that they had produced an isotope of element 106 that emits an alpha particle with a particularly low energy within a decay time between 10 and 30 sec. That's long compared with the lifetimes of microseconds to milliseconds that are more typical of the elements at the upper end of the periodic table.
COBE Measures Anisotropy in Cosmic Microwave Background Radiation
Authors: Levi Barbara Goss
Published: January 2008

Proponents of the standard inflationary model of cosmology breathed a collective sigh of relief when members of the scientific team of NASA's Cosmic Background Explorer described their measurements of the microwave radiation anisotropy at the APS spring meeting. The COBE satellite had provided the data necessary to keep the theories alive. To explain the observation of such structures as galaxies, galactic clusters and the enormous agglomeration of galaxies called the “Great Wall,” those models required some indication that the very early universe contained density fluctuations from which such structures might grow. But the cosmic background radiation, which should reflect any deviations from a uniform density at those formative times, had appeared remarkably homogeneous in its spatial distribution. (See PHYSICS TODAY, June 1990, page 20.)
Gallex Data Can't Quite Lay the Solar Neutrino Problem to Rest
Authors: Schwarzschild Bertram
Published: January 2008

16 July issue of Physics Letters brings us the eagerly awaited report of the first results from the Gallex solar neutrino experiment. The Gallex detector, with its 30 tons of gallium, sits in a laboratory underneath the Gran Sasso d'ltalia, a 2900-meter peak in the Apennines northeast of Rome. The suspense was heightened last fall when the SAGE collaboration, which operates the only other gallium detector, reported that it had seen no clear evidence of any solar neutrinos in its first seven months of running. The name Soviet-American Gallium Experiment may now seem out of date, but the experiment, located under a mountain in the Caucasus, goes on. SAGE is now operating with 57 tons of gallium.
What's the Shape of Things to Come in Semiconductor Lasers?
Authors: Levi Barbara Goss
Published: January 2008

The semiconductor industry has thrived on its ability to miniaturize electrical components so that an increasingly large number can be crammed on a single chip. If optoelectronic or even purely optical circuits are to play a competing role, components such as lasers may have to become as small and as cheaply manufactured as today's transistors. The current generation of semiconductor lasers are typically several hundred microns long, and their manufacture require special steps to cleave the wafer at each end to create mirrors. Micron-sized vertical-cavity lasers, millions of which can be etched on a single chip, are on the threshold of commercial production.
Resonant x-ray scattering from self-assembled InP∕GaAs(001) islands: Understanding the chemical structure of quaternary quantum dots
Authors: Coelho L. N. , Magalhães-Paniago R. , Malachias A. , Zelcovit J. G. , Cotta M. A.
Published: January 2008

Lattice parameter profiles and the chemical structure of InP self-assembled islands grown on GaAs(001) were determined with x-ray resonant scattering. By accessing four different photon energies, near x-ray absorption edges of two of the atomic species present on the samples, composition maps of all four atomic constituents of these islands were obtained. This experiment was performed for samples grown at two different temperatures and the effect of temperature was associated to Ga-interdiffusion and strain relief in the dots.
Molecular origin of the hydrophobic effect: Analysis using the angle-dependent integral equation theory
Authors: Kinoshita Masahiro
Published: January 2008

The molecular origin of the hydrophobic effect is investigated using the angle-dependent integral equation theory combined with the multipolar water model. The thermodynamic quantities of solvation (excess quantities) of a nonpolar solute are decomposed into the translational and orientational contributions. The translational contributions are substantially larger with the result that the temperature dependence of the solute solubility, for example, can well be reproduced by a model simple fluid where the particles interact through strongly attractive potential such as water and the particle size is as small as that of water. The thermodynamic quantities of solvation for carbon tetrachloride, whose molecular size is ∼1.9 times larger than that of water, are roughly an order of magnitude smaller than those for water and extremely insensitive to the strength of solvent-solvent attractive interaction and the temperature. The orientational contributions to the solvation energy and entropy are further decomposed into the solute-water pair correlation terms and the solute-water-water triplet and higher-order correlation terms. It is argued that the formation of highly ordered structure arising from the enhanced hydrogen bonding does not occur in the vicinity of the solute. Our proposition is that the hydrophobic effect is ascribed to the interplay of the exceptionally small molecular size and the strongly attractive interaction of water, and not necessarily to its hydrogen-bonding properties.
Controlling bistability in microelectromechanical resonators
Authors: Chen Qingfei , Huang Liang , Lai Ying-Cheng
Published: January 2008

For a microelectromechanical (MEM) resonator, the combination of mechanical nonlinearity and electrical driving force can lead to bistability. In such a case, the system exhibits two coexisting stable oscillatory states (attractors): one with low and another with high energy. Under the influence of noise, with high probability the system can be perturbed into the low-energy state. We propose a robust control scheme to place the system in the high-energy state. Our idea is not to pull the system out of the bistable regime but instead to take advantage of the nonlinear dynamics to achieve high-energy output. In particular, our control scheme consists of two steps: bifurcation control that temporarily drives the system to a regime with only one attractor, one that is the continuation of the high-energy attractor in the bistable regime; and ramping parameter control that restores the bistability while maintaining the system in the high-energy attractor. We derive an analytic theory to guide the control, provide numerical examples, and suggest a practical method to realize the control experimentally. Our result may find potential usage in devices based on MEM resonators where high output energy is desired.
Electrostatic solitary structures in dusty plasmas with nonthermal and superthermal electrons
Authors: Aoutou Kamel , Tribeche Mouloud , Zerguini Taha Houssine
Published: January 2008

A theoretical model is presented to show the existence, formation, and possible realization of arbitrary amplitude solitary potentials in a dusty plasma with both nonthermal and superthermal electrons. A physically meaningful κ-like electron distribution function is outlined. It is shown that due to electron superthermality, the present dusty plasma model can support subsonic as well as supersonic electrostatic solitary waves involving cusped potential humps. Interestingly, one finds that the effect of increasing the spectral index κ is to reduce and restrict the domain of allowable dust Mach numbers. An increase of the nonthermal parameter α would lead to a shift of this domain and a drastic restriction of the spectral index regime in which compressive and rarefactive solitons can coexist. Our results may provide an explanation for the strong spiky waveforms observed in auroral electric fields measurements by Viking and Fast.
The importance of an external circuit in a particle-in-cell/Monte Carlo collisions model for a direct current planar magnetron
Authors: Bultinck E. , Kolev I. , Bogaerts A. , Depla D.
Published: January 2008

In modeling direct current (dc) discharges, such as dc magnetrons, a current-limiting device is often neglected. In this study, it is shown that an external circuit consisting of a voltage source and a resistor is inevitable in calculating the correct cathode current. Avoiding the external circuit can cause the current to converge (if at all) to a wrong volt-ampere regime. The importance of this external circuit is studied by comparing the results with those of a model without current-limiting device. For this purpose, a 2d3v particle-in-cell/Monte Carlo collisions model was applied to calculate discharge characteristics, such as cathode potential and current, particle fluxes and densities, and potential distribution in the plasma. It is shown that the calculated cathode current is several orders of magnitude lower when an external circuit is omitted, leading to lower charged particle fluxes and densities, and a wider plasma sheath. Also, it was shown, that only simulations with external circuit can bring the cathode current into a certain plasma regime, which has its own typical properties. In this work, the normal and abnormal regimes were studied.
Coherent heterodyne time-domain spectrometry covering the entire “terahertz gap”
Authors: Karpowicz Nicholas , Dai Jianming , Lu Xiaofei , Chen Yunqing , Yamaguchi Masashi , Zhao Hongwei , Zhang X.-C. , Zhang Liangliang , Zhang Cunlin , Price-Gallagher Matthew , Fletcher Clark , Mamer Orval , Lesimple Alain , Johnson Keith
Published: January 2008

Terahertz waves, electromagnetic radiation in the spectral region commonly defined between 0.3 and 10THz, allow innovative sensing and imaging techniques that can provide spectroscopic information unavailable at other wavelengths. However, simultaneously intense, broadband, and coherent spectroscopic measurement remains challenging. We report spectrometry using gases ionized by femtosecond pulses to generate and sense broadband terahertz pulses. Using a coherent heterodyne technique, the measurements span the “terahertz gap” with ⩾10% of the maximum signal from 0.3to10THz. This spectrometer, using a recycled optical probe beam and coherent detection, offers a high field strength and time-resolved measurement.
Instability of a vertical chemical front: Effect of viscosity and density varying with concentration
Authors: Swernath Subramanian , Pushpavanam S.
Published: January 2008

In this work we analyze the behavior of a chemical front in a vertical porous medium. A homogeneous autocatalytic reaction occurs in the liquid phase. The column is filled with a chemical species and the reaction is initiated at one end of the vertical column by instantaneously adding the product. The reaction occurs at the interface of the products and the reactants. This causes the reaction front to move down (up) when the product is added to the top (bottom). The front or interface demarcates the domain into two regions: one rich in the reactants and the other rich in products. In this work chemohydrodynamic instabilities are studied, when the density and viscosity of the reactants and products are different and concentration dependent. The dependency of these properties on concentration is explicitly considered. We assume the process to be isothermal and other properties such as diffusivity and permeability to be constant. A traveling wave of chemical concentration is generated in the upward direction (when the products are introduced at the bottom) as the product reacts at the interface. The stability of the interface is determined by the viscosity and density of the two fluids. A shooting method in combination with a Runge–Kutta fourth-order scheme is used for generating the base state of the traveling front. Here, the conditions at which an interfacial instability induced by the density gradients is stabilized due to the viscosity dependence on concentration are determined. Linear stability predictions are determined by inducing perturbations on the traveling wave base state and analyzing their evolution. The effect of various parameters on the stability of the flow was calculated and compared with the nonlinear simulations. The nonlinear problem is modeled using the stream-function, vorticity equations. These equations are solved using a second-order finite difference scheme in space and first-order forward difference scheme in time. The instability predicted from the linear stability analysis is validated with nonlinear simulations.
Field emission from Mo2C coated carbon nanosheets
Authors: Bagge-Hansen M. , Outlaw R. A. , Miraldo P. , Zhu M. Y. , Hou K. , Theodore N. D. , Zhao X. , Manos D. M.
Published: January 2008

Carbon nanosheets have recently evolved into useful edge emitters with high emission current densities, low threshold electric fields, and long lifetimes. In addition to further improvement in these characteristics, good stability and repeatability are also essential for these materials to be suitable for high vacuum applications such as microwave tubes and flat panel displays. Since the work function of graphite, carbon nanotubes, and amorphous carbon is relatively high, 4.6–4.8eV, selective thin film coatings may offer significant advantages. Carbides are a good film choice for their corrosive resistance, chemical stability, and substantially lower work function. Approximately 3 ML (monolayer) (∼1nm) of molybdenum were deposited on carbon nanosheets by physical vapor deposition and the carbide (Mo2C) formed by heating to >200°C at 1×10−8Torr. The carbide stoichiometry was confirmed in situ by the characteristic Auger triple peak at 272eV. A stoichiometric Mo2C calibration sample was used to acquire the Auger electron spectroscopy asymmetric ratio of 0.7 and this was used to determine the carbide growth as a function of temperature (from room temperature to 1000°C). Field emission currents of up to 400μA were compared with uncoated CNS at a given electric field. The Mo2C∕CNS cathodes were shown to have greater than a factor of 100 increase in current and greater than 2V∕μm decrease in threshold. The Fowler-Nordheim plots were exceptionally linear and quite repeatable (correlation coefficient R2=0.999+). Using the slope and vertical intercept, an emission area for the 0.07cm2 Mo2C∕CNS dot sample was determined to be ∼3×10−9cm2 and the field enhancement factor was found to be β∼530.
Micromagnetic simulation of the magnetic spectrum of ferromagnetic nanowire
Authors: Liu Ronglin , Wang Jianbo , Liu Qingfang , Wang Haixin , Jiang Changjun
Published: January 2008

The dynamic susceptibilities of permalloylike nanowires (20×500×20nm3) have been investigated using the three-dimensional object oriented micromagnetic framework (OOMMF) code. The investigated systems show two resonant peaks associated with a “bulk” and an “edge” mode, which are attributed to the local effective field relevant to the local magnetic moments. A local analysis for ferromagnetic resonance calculation has been developed. It handles the local magnetic moments at the edge and the middle of the nanowire, respectively. The resonant frequencies of the edge mode are directly proportional to Ms or A under the same fundamental length scale, i.e., the exchange length.
Gamma-ray irradiated polymer optical waveguides
Authors: Lai Cheng-Chih , Wei Tso-Yun , Chang Chin-Yu , Wang Way-Seen , Wei Yuan-Yaw
Published: January 2008

Optical waveguides fabricated by gamma-ray irradiation on polymer through a gold mask are presented. The gamma-ray induced index change is found almost linearly dependent on the dose of the irradiation. And the measured propagation losses are low enough for practical application. Due to the high penetrability of gamma ray, uniform refractive index change in depth can be easily achieved. Moreover, due to large-area printing, the uniformity of waveguide made by gamma-ray irradiation is much better than that by e-beam direct writing.
Interface studies of ZnO nanowire transistors using low-frequency noise and temperature-dependent I-V measurements
Authors: Ju Sanghyun , Kim Sunkook , Mohammadi Saeed , Janes David B. , Ha Young-Geun , Facchetti Antonio , Marks Tobin J.
Published: January 2008

Single ZnO nanowire (NW) transistors fabricated with self-assembled nanodielectric (SAND) and SiO2 gate insulators were characterized by low-frequency noise and variable temperature current-voltage (I-V) measurements. According to the gate dependence of the noise amplitude, the extracted Hooge’s constants (αH) are ∼3.3×10−2 for SAND-based devices and ∼3.5×10−1 for SiO2-based devices. Temperature-dependent I-V studies show that the hysteresis of the transfer curves and the threshold voltage shifts of SAND-based devices are significantly smaller than those of SiO2-based devices. These results demonstrate the improved SAND/ZnO NW interface quality (lower interface-trap states and defects) in comparison to those fabricated with SiO2.
Electrical behavior of zinc oxide layers grown by low temperature atomic layer deposition
Authors: Huby N. , Ferrari S. , Guziewicz E. , Godlewski M. , Osinniy V.
Published: January 2008

We report on the electrical properties of thin film transistors based on zinc oxide (ZnO) layers grown by low temperature (100–170°C) atomic layer deposition. As evidenced through Hall effect measurements, a drastic decrease of the carrier concentration occurred for ZnO films grown at 100°C. Time of flight–secondary ions mass spectroscopy analysis revealed that this decrease is associated with an increase of the hydroxide groups in the ZnO layer which suppressed oxygen vacancy formation. Transistors fabricated from ZnO films grown at 100°C exhibit a high Ion∕Ioff ratio (∼107) and an encouraging intrinsic channel mobility (∼1cm2∕Vs).
Thermomagnetic history dependence of magnetocaloric effect in Ni50Mn34In16
Authors: Chattopadhyay M. K. , Sharma V. K. , Roy S. B.
Published: January 2008

A large inverse magnetocaloric effect has been reported to be associated with the austenite to martensite phase transition in Ni50Mn34In16. It is shown here that the magnitude of the observed magnetocaloric effect as well as effective refrigerant capacity depend significantly on the thermo-magnetic history of the sample.
Noncontact atomic force microscopy study of ligand-coated Au55 clusters
Authors: Radu G. , Mautes D. , Hartmann U.
Published: January 2008

Thin films of ligand-stabilized Au55 clusters deposited on Au (111)-oriented thin films have been investigated by noncontact atomic force microscopy and spectroscopy. The properties of the clusters with a diameter of about 2nm have been investigated by force spectroscopy performed above individual clusters. The interaction force and dissipated energy were deduced from the obtained data. The conservative component of the interaction between tip and individual Au55 cluster is given by an interplay between the interactions of the tip apex with the ligand shell and with the gold core. In contrast, only the ligand shell contributes to the dissipative interaction.
Comment on “Method to analyze electromechanical stability of dielectric elastomers” [Appl. Phys. Lett. 91, 061921 (2007)]
Authors: Norris Andrew N.
Published: January 2008

The model of Zhao and Suo can be readily generalized to predict the critical breakdown electric field Ec of elastomers with arbitrary elastic strain energy function. An explicit expression for Ec is presented for elastomeric thin films under biaxial strain and comparisons are made with experimental data using a two term Ogden rubber elasticity model. Simplified results for uniaxial and for equibiaxial stress provide further insight into the electromechanical stability model.
Experimental study of the minimum metal gate thickness required to fix the effective work function in metal-oxide-semiconductor capacitors
Authors: Fillot F. , Maîtrejean S. , Matko I. , Chenevier B.
Published: January 2008

We have investigated the dependence of the effective work function (EWF) of a poly-p+∕TiN∕SiO2∕Si capacitor as a function of the TiN layer thickness. By using a pulsing chemical vapor deposition process, the nitride layer was demonstrated to be continuous from 2.2nm. It was also shown that the EWF of capacitors, made with TiN layer thickness ranging between 2.2 and 7.1nm, is independent of the thickness and similar to that of bulk TiN. Our study indicates that the EWF of the entire gate electrode stack is determined by the first metallic monolayers (<2.2nm) in contact with the gate dielectric.
A Sn-based metal substrate technology for the fabrication of vertical-structured GaN-based light-emitting diodes
Authors: Kuo Hon-Yi , Wang Shui-Jinn , Wang Pei-Ren , Uang Kai-Ming , Chen Tron-Min , Kuan Hon
Published: January 2008

Through the use of tin (Sn) based solder balls and patterned laser lift-off technique, a metal substrate technology was proposed for the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs). Advantages including reserving the merits of metallic substrate and simplifying the fabrication processes of vertical-structured GaN-based LEDs were demonstrated. As compared to conventional sapphire substrate GaN-based LEDs, the fabricated VM-LEDs with an emission area of 620×620μm2 show an increase in light output power about 145.36% at 350mA with a significant decrease in forward voltage from 4.51to3.46V.
High-efficiency hole extraction/electron-blocking layer to replace poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) in bulk-heterojunction polymer solar cells
Authors: Hains Alexander W. , Marks Tobin J.
Published: January 2008

An anode interfacial layer is reported for bulk-heterojunction (BHJ) polymer solar cells to replace the commonly used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). A poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB)+4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi2) blend is crosslinked, forming robust ∼10nm thick films covalently bound to indium tin oxide, which transport holes while blocking misdirected electrons. The thermal stability and photovoltaic performance metrics of TFB:TPDSi2-modified BHJ cells are significantly greater than those of cells fabricated in parallel with PEDOT:PSS or with no interfacial layer. For a poly[2-methoxy-5-(3′,7′-dimethyloctyloxyl]-1,4-phenylene vinylene: methanofullerene[6 6]-phenyl C61-butyric acid methyl ester cell, Voc=0.89V, Jsc=4.62mA∕cm2, FF=54.4%, and ηp=2.23%.
Optoacoustic tomography utilizing focused transducers: The resolution study
Authors: Khokhlova T. D. , Pelivanov I. M. , Karabutov A. A.
Published: January 2008

The goal of this work was to investigate numerically the dependence of the resolution and the imaging window size, provided by a cylindrically focused wideband piezoelectric detector in optoacoustic tomography, on the detector dimensions and frequency bandwidth. Analytical expressions found by O’Neil for a continuous spherically focused ultrasonic radiator were found to fit the numerical data accurately to within a constant factor. The range of application and limitations of these expressions were investigated.
Progress toward Ignition and Burn Propagation in Inertial Confinement Fusion
Authors: Lindl John D. , McCrory Robert L. , Campbell E. Michael
Published: January 2008

For the past four decades, scientists throughout the world have pursued the dream of controlled thermonuclear fusion. The attraction of this goal is the enormous energy that is potentially available in fusion fuels and the view of fusion as a safe, clean energy source. The fusion reaction with the highest cross section uses the deuterium and tritium isotopes of hydrogen, and D-T would be the fuel of choice for the first generation of fusion reactors. (See the article by J. Geoffrey Cordey, Robert J. Goldston and Ronald R. Parker, January, page 22.)
Wannier-Stark Ladders and Bloch Oscillations in Superlattices
Authors: Mendez Emilio E. , Bastard Gérald
Published: January 2008

Conduction electrons in real crystalline solids behave very much like electrons in free space, moving in straight lines between collisions when subject to an electric field. But in an ideal (although cold) world, free from scattering by impurities, imperfections and thermal vibrations of the lattice, how would conduction electrons behave? That question, answered in principle long ago in light of the then newly developed quantum mechanics, was purely academic until recently.
The XXIV Physics Olympiad Examinations
Authors: French Anthony P.
Published: January 2008

In July of this year, at the College of William and Mary in Williamsburg, Virginia, the United States hosted for the first time the International Physics Olympiad, an annual competition open to pre-college students from all over the world. (See the article by Barbara Goss Levi in PHYSICS TODAY, September, page 40, and the accompanying box by Arthur Eisenkraft.) The olympiad is a major cultural and social event, lasting a full week. The examination itself occupies only two half-days of that time; it is, however, the raison d'être underlying the whole occasion, and the creation of an appropriate test is a considerable challenge, as well as a very interesting experience.
Solid-State Physics at Microkelvin Temperatures: Is Anything Left to Learn?
Authors: Pobell Frank
Published: January 2008

Temperature is the most important parameter that one can vary in the laboratory to change the properties of matter so as to get a better understanding of its behavior. Heike Kamerlingh Onnes's liquefaction of helium-4 in 1908 made the low-kelvin-temperature range accessible. Subsequent discoveries in low-temperature physics included verification of essential predictions of quantum mechanics and statistical physics—for example, the temperature dependence of the specific heat of insulators and of metals. the introduction of the He3-He4 dilution refrigerator in the late 1960s extended condensed matter physics into the millikelvin temperature range. Once again the opening of a new temperature range allowed many fundamental discoveries, particularly in condensed matter physics—heavy-fermion superconductivity and the quantum Hall effect, for example.
The Birth of the Nuclear Age
Authors: Wattenberg Albert
Published: January 2008

Fifty years ago last month Enrico Fermi demonstrated that a self-sustaining nuclear chain reaction could be produced and controlled. It was a quantitative experiment, and it was Fermi who decided upon all the cautious steps to be followed and all the measurements to be made.
Special Issue: Physical Review Centenary—From Basic Research to High Technology
Authors: Adair Robert K. , Henley Ernest M.
Published: January 2008

Edward Nichols and Ernest Merritt began the physical review at Cornell University in 1893. Any new journal incurs a financial risk; Cornell assumed that risk.
The Introductory University Physics Project
Authors: Rigden John S. , Holcomb Donald F. , DiStefano Rosanne
Published: January 2008

The last period of extensive curriculum reform in physics occurred about 30 years ago. The objectives of that earlier effort were sweeping. The high school physics course was an early target, and the Physical Science Study Committee was created to effect its reform. The Commission on College Physics, formed in June 1960, had as its objective the revitalization of the entire undergraduate physics curriculum. In the wake of this period of reform a new genre of introductory textbooks, modeled on the successful textbook authored by David Halliday and Robert Resnick, became standard. These texts followed the more mathematical emphasis favored after World War II but gave more attention to worked-out examples and other pedagogical elements as well as more substantial exercises and problems than was characteristic of their predecessors
The Physics Job Market: Bleak for Young Physicists
Authors: Kirby Kate , Czujko Roman
Published: January 2008

During the past several years, many developments on both a national and global scale have greatly altered the job market for scientists and engineers in the US. The end of the cold war has meant deepening cuts in the Defense Department's research programs and at nuclear weapons facilities funded by the Department of Energy. The recession has been unexpectedly persistent, and many large corporations have eliminated tens of thousands of jobs. Pressures on state and Federal budgets combined with the continued decline in the number of Americans who are of traditional college age (18–24 years old) have affected state and private colleges and universities. Geopolitical changes, especially the turmoil in the former Soviet and East Bloc countries, have prompted a significant number of senior scientists from those countries to look for positions elsewhere—in particular the US. These changes are sending shock waves through all sectors of the physics work force and adversely affecting the availability of jobs for physicists.
Artificial Atoms
Authors: Kastner Marc A.
Published: January 2008

The wizardry of modern semiconductor technology makes it possible to fabricate particles of metal or “pools” of electrons in a semiconductor that are only a few hundred angstroms in size. Electrons in these structures can display astounding behavior. Such structures, coupled to electrical leads through tunnel junctions, have been given various names: single-electron transistors, quantum dots, zero-dimensional electron gases and Coulomb islands. In my own mind, however, I regard all of these as artificial atoms—atoms whose effective nuclear charge is controlled by metallic electrodes. Like natural atoms, these small electronic sytems contain a discrete number of electrons and have a discrete spectrum of energy levels. Artificial atoms, however, have a unique and spectacular property: The current through such an atom or the capacitance between its leads can vary by many orders of magnitude when its charge is changed by a single electron. Why this is so, and how we can use this property to measure the level spectrum of an artificial atom, is the subject of this article.
Visiometrics, Juxtaposition and Modeling
Authors: Zabusky Norman J. , Silver Deborah , Pelz Richard ,   Vizgroup
Published: January 2008

With the advent of massively parallel computers, the evolution of nonlinear dynamical systems such as fluids and plasmas is being investigated in three dimensions at increasingly high resolutions. Today a typical physical volume is represented by 1003 grid points, and we may expect the resolution to increase to 10003 by the end of the decade.