bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal cycle as template for climate variability on astronomical timescales
Authors: Laepple Thomas , Lohmann Gerrit
Published: October 2009

We propose a new concept for insolation‐driven temperature variability on orbital timescales. It relies on the modern relationship between insolation and temperature throughout the year. The method consists of (1) estimating empirical transfer functions between daily insolation and daily temperature and (2) applying these transfer functions on the long‐term insolation to model the late Quaternary temperature evolution. On the basis of the observed insolation‐temperature relationship, different temperature response regimes across the Earth are identified. Linear relationships dominate extratropical land areas whereas in midlatitude oceans, the seasonally varying mixed layer depth renders the temperature more sensitive to summer than to winter insolation. The temperature in monsoon regions and regions of seasonal sea ice cover also shows a seasonally varying response to insolation. These transfer functions characterize the shape of the seasonal cycle in temperature and influence the temperature evolution on orbital timescales by rectifying the insolation signal. On the basis of our seasonal template model, we estimate the temperature evolution of the last 750,000 years. The model largely reproduces the Holocene temperature trends as simulated by a coupled climate model. In the frequency domain, significant temperature variability in the eccentricity and semiprecession frequency band in the tropics is found. Midlatitudes are dominated by precession, and high latitudes are dominated by obliquity. Further, it is found that the expected frequency response highly depends on the location. Our local time‐independent approach complements the global Milankovitch hypothesis (climate variations are driven by northern summer insolation) in explaining observed climate variability and potentially offers new insights in interpreting paleoclimate records.
Large changes in seasonal sea ice distribution and productivity in the Sea of Okhotsk during the deglaciations
Authors: Seki Osamu , Sakamoto Tatsuhiko , Sakai Saburo , Schouten Stefan , Hopmans Ellen C. , Sinninghe Damste Jaap S. , Pancost Richard D.
Published: October 2009

Changes in the surface environment of the central Sea of Okhotsk were reconstructed using TEX86 paleothermometry, facilitated by the BIT index, in order to investigate paleoenvironmental changes during the glacial‐interglacial cycles. The core top TEX86‐derived temperature is the same as the present‐day summer sea surface temperature (SST), suggesting that TEX86 records seasonal rather than annually averaged SSTs in this region. The TEX86 record reveals ∼3°C lower summer SST during glacial maxima than during interglacial periods and significant warming during the deglaciations (15–10 ka and 136–130 ka). This is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present‐day and its substantial retreat during the deglaciation. Timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity, suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations. The relationship could reflect an increase in the supply of fresh and warm water from the Amur River during deglaciation, which significantly impacted hydrology by facilitating sea surface stratification, which in turn promoted production of coccolithophids.
Decadal changes in ecological provinces of the Northwest Atlantic Ocean revealed by satellite observations
Authors: Devred E. , Sathyendranath S. , Platt T.
Published: October 2009

Detecting the effect of climate change on ocean ecosystems is facilitated if the data are partitioned into ecological provinces. It is recognised that the boundaries of such provinces are dynamic, raising the imperative for frequent observations. Using satellite data, we have assembled a time series of ecosystem delineation for the Northwest Atlantic Ocean over a period of ten years. For each province identified in the study area, we have compiled data on sea‐surface temperature, and on the biomass and community composition of phytoplankton. We find significant trends in these properties but they vary according to the province concerned, which emphasizes how the physical and biological changes are correlated at large scale. Comparisons between the trends computed using the average position of the provinces and the trends derived when accounting for the movements of the boundaries underline the value of the new approach.
Coherent nonlinear scattering of energetic electrons in the process of whistler mode chorus generation
Authors: Hikishima M. , Yagitani S. , Omura Y. , Nagano I.
Published: October 2009

Cyclotron resonant wave‐particle interaction of whistler mode chorus emissions drives pitch angle scatterings of a wide range of energetic electrons in the magnetosphere. We study a coherent scattering process associated with generation of the whistler mode rising chorus emissions near the geomagnetic equator in a self‐consistent electromagnetic full‐particle simulation. The simulation shows that coherent whistler mode rising chorus emissions scatter energetic electrons very effectively through formation of an electromagnetic electron hole. The nonlinear interaction induces acceleration of resonant electrons trapped by the wave and deceleration of untrapped resonant electrons. When the frequency of a rising chorus element continuously increases in time from lower frequencies to higher frequencies, the parallel resonant velocity continuously decreases toward lower‐velocity ranges resulting in significant scattering of resonant electrons. The lower limit of resonant parallel velocity is determined by the upper frequency limit of the rising chorus element. The unscattered electrons with low parallel velocities and the accelerated resonant electrons trapped by the wave result in the distribution clearly peaked at 90°. Successive generation of rising chorus elements can scatter resonant electrons in the same resonance velocity range. The repeated scatterings make the distribution much sharper at 90°, leading to formation of a pancake distribution function as observed in the inner magnetosphere.
Possible physical and thermodynamical evidence for liquid water at the Phoenix landing site
Authors: Rennó Nilton O. , Bos Brent J. , Catling David , Clark Benton C. , Drube Line , Fisher David , Goetz Walter , Hviid Stubbe F. , Keller Horst Uwe , Kok Jasper F. , Kounaves Samuel P. , Leer Kristoffer , Lemmon Mark , Madsen Morten Bo , Markiewicz Wojciech J. , Marshall John , McKay Christopher , Mehta Manish , Smith Miles , Zorzano M. P. , Smith Peter H. , Stoker Carol , Young Suzanne M. M.
Published: October 2009

The objective of the Phoenix mission is to determine if Mars' polar region can support life. Since liquid water is a basic ingredient for life, as we know it, an important goal of the mission is to determine if liquid water exists at the landing site. It is believed that a layer of Martian soil preserves ice by forming a barrier against high temperatures and sublimation, but that exposed ice sublimates without the formation of the liquid phase. Here we show possible independent physical and thermodynamical evidence that besides ice, liquid saline water exists in areas disturbed by the Phoenix Lander. Moreover, we show that the thermodynamics of freeze‐thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures on the Phoenix landing site on Mars' Arctic. Thus, we hypothesize that liquid saline water might occur where ground ice exists near the Martian surface. The ideas and results presented in this article provide significant new insights into the behavior of water on Mars.
Sublacustrine depositional fans in southwest Melas Chasma
Authors: Metz Joannah M. , Grotzinger John P. , Mohrig David , Milliken Ralph , Prather Bradford , Pirmez Carlos , McEwen Alfred S. , Weitz Catherine M.
Published: October 2009

Two depositional fan complexes have been identified on the floor of southwest Melas Chasma. The western fan complex is located near the center of an enclosed basin in southwest Melas Chasma and is composed of multiple lobes with dendritic finger‐like terminations. These fans are very flat and have a morphology unlike any other fan that has been previously identified on Mars. On the basis of the morphologic similarity of the western fan complex to the Mississippi submarine fan complex, we suggest that it may be a deep subaqueous fan depositional system. There are numerous channels on the surface of the western fan complex, and measurements of channel length, width, and sinuosity are consistent with channels observed on terrestrial submarine fans. The eastern Melas depositional fans are less well preserved and may be of deltaic or sublacustrine origin. Recognition of the fans supports earlier suggestions for the presence of a former lake in Melas Chasma and indicates that a significant body of water was present and stable at the surface of Mars for at least 102 to 104 years.
High‐frequency field‐deployable isotope analyzer for hydrological applications
Authors: Berman Elena S. F. , Gupta Manish , Gabrielli Chris , Garland Tina , McDonnell Jeffrey J.
Published: October 2009

A high‐frequency, field‐deployable liquid water isotope analyzer was developed that is capable of quantifying δ18O and δ2H to better than ±0.17 and ±0.32‰, respectively, on over 90 samples/d. The instrument was deployed for 4 contiguous weeks in the H. J. Andrews Experimental Forest Long‐term Ecological Research site in western Oregon, where it was used for real‐time measurement of the isotope ratios of precipitation and stream water during three large storm events. We were able to document fine‐scale changes in rainfall composition and damping effects in the stream channel continuously through these periods. We also performed a rain‐on‐snow experiment where we sampled leachate from a melting snow core continuously at 2 min intervals for 5 h. These data show remarkable fine‐scale patterns of internal rain‐snow mixing, patterns that would not have been detected without such high‐frequency sampling. These two preliminary applications show proof of concept of the new field analyzer, a device that will ultimately provide hydrologists with insight into water flow dynamics with unprecedented frequency over long time scales.
The hepatitis C virus and its hepatic environment: a toxic but finely tuned partnership
Authors: Perrault Marie , Pécheur Eve-Isabelle
Published: October 2009

Twenty years after its discovery, HCV (hepatitis C virus) still infects 170 million people worldwide and cannot be properly treated due to the lack of efficient medication. Its life cycle must be better understood to develop targeted pharmacological arsenals. HCV is an enveloped virus bearing two surface glycoproteins, E1 and E2. It only infects humans through blood transmission, and hepatocytes are its only target cells. Hepatic trabeculae are formed by hepatocyte rows surrounded by sinusoid capillaries, irrigating hepatic cells. Hepatocytes are polarized and have basolateral and apical poles, separated by tight junctions in contact with blood and bile respectively. In blood, HCV remains in contact with lipoproteins. It then navigates through hepatic microenvironment and extracellular matrix, composed of glycosaminoglycans and proteins. HCV then encounters the hepatocyte basolateral membrane, where it interacts with its entry factors: the low-density lipoprotein receptor, CD81 tetraspanin, and the high-density lipoprotein (scavenger) receptor SR-BI (scavenger receptor BI). How these molecules interact with HCV remains unclear; however, a tentative sequence of events has been proposed. Two essential factors of HCV entry are the tight junction proteins claudin-1 and occludin. Cell polarity therefore seems to be a key for HCV entry. This raises several exciting questions on the HCV internalization pathway. Clathrin-dependent endocytosis is probably the route of HCV transport to intracellular compartments, and the ultimate step of its entry is fusion, which probably takes place within endosomes. The mechanisms of HCV membrane fusion are still unclear, notably the nature of the fusion proteins is unknown and the contribution of HCV-associated lipoproteins to this event is currently under investigation.
Think the impossible: β-blockers for treating asthma
Authors: J. LIPWORTH Brian , A. WILLIAMSON Peter
Published: October 2009

Asthma was originally thought to be associated with an intrinsic defect in β2ADR (β2-adrenoceptor) function, tipping the balance towards parasympathetic bronchoconstriction. Hence β-blocking drugs (such as β2ADR antagonists and inverse agonists) may cause acute bronchoconstriction which, in turn, may be attenuated by anti-cholinergic agents. Although β2-agonists are highly effective for the acute relief of bronchoconstriction, their chronic use is accompanied by an adaptive reduction in β2ADR numbers and associated desensitization of response, resulting in increased exacerbations and rare cases of death. The hypothesis examined in the present article is that, while single dosing with a β-blocker may cause acute bronchoconstriction, chronic dosing may afford putative beneficial effects including attenuated airway hyper-responsiveness.
Positioning the Institutional Perspective in Information Systems Research
Authors: Mignerat Muriel , Rivard Suzanne
Published: October 2009

In recent years, a number of studies have adopted institutional theory as a perspective for examining Information Systems (IS)/Information Technology (IT)-related phenomena such as IT innovation, IS development and implementation, and IT adoption and use. The objective of this paper is to take stock of how institutional theory is being used in IS research. To this end, it first proposes a conceptual framework to encapsulate the main concepts of institutional theory. Second, it synthesizes the findings of 53 articles that adopted an institutional perspective to study IS/IT phenomena. Finally, it identifies conceptual and methodological issues that researchers need to address when adopting an institutional perspective.
Design and development of an automated flow injection instrument for the determination of arsenic species in natural waters
Authors: Hanrahan Grady , Fan Tina K. , Kantor Melanie , Clark Keith , Cardenas Steven , Guillaume Darrell W. , Khachikian Crist S.
Published: October 2009

The design and development of an automated flow injection instrument for the determination of arsenite [As(III)] and arsenate [As(V)] in natural waters is described. The instrument incorporates solenoid activated self-priming micropumps and electronic switching valves for controlling the fluidics of the system and a miniature charge-coupled device spectrometer operating in a graphical programming environment. The limits of detection were found to be 0.79 and 0.98 μM for As(III) and As(V), respectively, with linear range of 1–50 μM. Spiked ultrapure water samples were analyzed and recoveries were found to be 97%–101% for As(III) and 95%–99% for As(V), respectively. Future directions in terms of automation, optimization, and field deployment are discussed.
Surface orientation dependence of interface properties of GeO2/Ge metal-oxide-semiconductor structures fabricated by thermal oxidation
Authors: Sasada Takashi , Nakakita Yosuke , Takenaka Mitsuru , Takagi Shinichi
Published: October 2009

We have fabricated GeO2/Ge interfaces on (100), (110), and (111) orientation substrates by direct thermal oxidation. The x-ray photoelectron spectroscopy analyses suggest that the Ge oxides are composed of GeO2 and have almost the same interfacial structure, independent of the surface orientations. The gate current conduction mechanism through the GeO2/Ge metal-oxide-semiconductor structure is dominated by Fowler–Nordheim tunneling. In addition, the barrier height between Ge and GeO2 is evaluated to be 1.2–1.4 eV. In interface trap density (Dit) measurement by using the low temperature conductance method, the amount of Dit in the conduction band side is also almost the same, while Dit in the valence band side is lowest for the (111) surface. Minimum detectable Dit is lower than 1×1011 eV−1 cm2 for all the orientations. These surface orientation dependences of the GeO2/Ge interface properties are quite different from those of the SiO2/Si interface.
High mobility amorphous zinc oxynitride semiconductor material for thin film transistors
Authors: Ye Yan , Lim Rodney , White John M.
Published: October 2009

Zinc oxynitride semiconductor material is produced through a reactive sputtering process in which competition between reactions responsible for the growth of hexagonal zinc oxide (ZnO) and for the growth of cubic zinc nitride (Zn3N2) is promoted. In contrast to processes in which the reaction for either the oxide or the nitride is dominant, the multireaction process yields a substantially amorphous or a highly disordered nanocrystalline film with higher Hall mobility, 47 cm2 V−1 s−1 for the as-deposited film produced at 50 °C and 110 cm2 V−1 s−1 after annealing at 400 °C. In addition, it has been observed that the Hall mobility of the material increases as the carrier concentration decreases in a carrier concentration range where a multicomponent metal oxide semiconductor, indium–gallium–zinc oxide, follows the opposite trend. This indicates that the carrier transports in the single-metal compound and the multimetal compound are probably dominated by different mechanisms. Film stability and thin film transistor performance of the material have also been tested, and results are presented herein.
Relaxor ferroelectric and magnetic properties of Ba6CoNb9O30 ceramics with tungsten bronze structure
Authors: Liu P. P. , Zhu X. L. , Chen X. M.
Published: October 2009

Dielectric characteristics of Ba6CoNb9O30 tetragonal tungsten bronze ceramics have been evaluated over a broad temperature and frequency range. A broad dielectric peak with strong frequency dispersion is observed at 140–225 K, which well follows the Vogel–Fulcher relationship and indicates the relaxor ferroelectric nature in the present ceramics. The P-E hysteresis loops varying with temperature are consistent with this dielectric relaxation process and provide the further evidence on the relaxor ferroelectric nature. The nonlinear magnetic hysteresis curve is observed in Ba6CoNb9O30 ceramics at 5 K, indicating the soft magnetic behavior which is related to the tetragonal tungsten bronze crystal structure containing magnetic ions of Co3+.
CH spectroscopy for carbon chemical erosion analysis in high density low temperature hydrogen plasma
Authors: Westerhout J. , Lopes Cardozo N. J. , Rapp J. , van Rooij G. J.
Published: October 2009

The CH A−X molecular band is measured upon seeding the hydrogen plasma in the linear plasma generator Pilot-PSI [electron temperature Te=0.1–2.5 eV and electron density ne=(0.5–5)×1020 m−3] with methane. Calculated inverse photon efficiencies for these conditions range from 3 up to >106 due to a steeply decreasing electron excitation cross section. The experiments contradict the calculations and show a constant effective inverse photon efficiency of ∼100 for Te<1 eV. The discrepancy is explained as the CH A level is populated through dissociative recombination of the molecular ions formed by charge exchange. Collisional de-excitation is observed for ne>5×1020 m−3 and 0.1 eV<Te<1 eV. These results form a framework for in situ carbon erosion measurements in future fusion reactors such as ITER.
Actual temperatures of growing surfaces of III-nitride-based materials depending on substrates and forced convection conditions in metal organic chemical vapor deposition
Authors: Choi Suk , Kim Hee Jin , Ryou Jae-Hyun , Dupuis Russell D.
Published: October 2009

We have investigated the differences in the actual surface temperature of various substrates for the growth of III-nitride materials and the influence of this difference in the characteristics of the resulting epitaxial films. From calculations using the finite element method, high-thermal conductivity substrates have significantly higher surface temperature than substrates with low thermal conductivity in typical growth conditions of metal organic chemical vapor deposition. Also, the hydrodynamics of various growth parameters and the chamber condition play a significant role in establishing the actual surface temperature. The thickness of the substrate is found to be another important factor on the temperature of the surface. High resolution x-ray diffraction analysis of AlGaN epitaxial layers grown on bulk AlN substrates and sapphire substrates with different thicknesses supports our theoretical calculations, showing that the Al compositional discrepancy originated from the differences in the surface temperature during growth.
A kilowatt pulsed 94 GHz electron paramagnetic resonance spectrometer with high concentration sensitivity, high instantaneous bandwidth, and low dead time
Authors: Cruickshank Paul A. S. , Bolton David R. , Robertson Duncan A. , Hunter Robert I. , Wylde Richard J. , Smith Graham M.
Published: October 2009

We describe a quasioptical 94 GHz kW pulsed electron paramagnetic resonance spectrometer featuring π/2 pulses as short as 5 ns and an instantaneous bandwidth of 1 GHz in nonresonant sample holders operating in induction mode and at low temperatures. Low power pulses can be as short as 200 ps and kilowatt pulses as short as 1.5 ns with timing resolution of a few hundred picoseconds. Phase and frequency can be changed on nanosecond time scales and complex high power pulse sequences can be run at repetition rates up to 80 kHz with low dead time. We demonstrate that the combination of high power pulses at high frequencies and nonresonant cavities can offer excellent concentration sensitivity for orientation selective pulsed electron double resonance (double electron-electron resonance), where we demonstrate measurements at 1 μM concentration levels.
Total transmission of electrons in semiconductor heterostructures at oblique incidence
Authors: Hinkey Robert T. , Yang Rui Q.
Published: October 2009

An alternative method to resonant tunneling for obtaining total transmission in semiconductor heterostructures is investigated. This nonresonant total transmission has been shown to be difficult to achieve for electrons at normal incidence. However, if the momentum of the electron is altered so that the component in the direction parallel to the material interface is nonzero, the transmission properties of the electron change, and the potential for total transmission is more promising. In the single-band approximation, for incident electron energies above the crossing points of the dispersion curves of the two materials, there exists an angle between the direction of the electron’s momentum and the material interface at which total transmission is achieved. The experimental demonstration of nonresonant total transmission could potentially open the door to a number of applications. In particular, its potential for the measurement of small band offsets between two materials in a heterostructure and in electronic applications is discussed.
Correlation between structure and rheology of a model colloidal glass
Authors: Di Cola E. , Moussaïd A. , Sztucki M. , Narayanan T. , Zaccarelli E.
Published: October 2009

The microstructure and rheological properties of a model colloidal system was probed in the vicinity of the glass transition by small-angle and ultra small-angle x-ray scattering, dynamic light scattering (DLS) and bulk rheology. The volume fraction of the particles was deduced by modeling the structure factor and the absolute scattered intensity in a self-consistent way. The glass transition (ϕG) was identified from the frequency dependence of the shear moduli in the linear regime. The experimentally observed behavior was then compared with the viscoelastic properties derived from mode-coupling theory (MCT) using the experimental structure factor as input to the theory. The ensemble-averaged intermediate scattering functions from DLS measurements were also compared with those calculated from the MCT and reasonable agreement was obtained.
A study of the performance of an ion shutter for drift tubes in atmospheric pressure ion mobility spectrometry: Computer models and experimental findings
Authors: Tadjimukhamedov Fatkhulla K. , Puton Jaroslaw , Stone John A. , Eiceman Gary A.
Published: October 2009

Ion mobility spectra are initiated when ions, derived from a sample, are pulsed or injected through ion shutters into a drift region. The effect on signal intensity from electric fields arising from the shutter grids (Es) and a superimposed electric field of the drift tube (Ed) was determined experimentally and simulated computationally for ion motion at ambient pressure. The combination of these two fields influenced shutter performance in three ways: (1) intensity of an ion peak was suppressed by increased current in the baseline due to continuous leakage of ions into the drift region from insufficient Es to block ion motion when needed, at a given value of Ed; (2) the ion shutter provided maximum peak intensity with some optimal ratio of Es/Ed when ions were fully blocked except using the injection time; (c) the signal intensity was reduced when the blocking voltage of the ion shutter exceeded this optimal Es/Ed ratio from ion depletion at the shutter grids. The optimal ratio from the computer models was equal to 1.50, whereas a value of 2.50 was obtained from the experimental findings. This difference was attributed to nonideal geometry with the grids of the shutter and the conducting elements in the drift tube establishing both Es and Ed. As both the experimental and modeling results demonstrated, a mobility dependence of ion yield from the ionization source was found to cause a mobility dependent ion signal at the collector electrode.
A method for correlating in vivo prostate magnetic resonance imaging and histopathology using individualized magnetic resonance -based molds
Authors: Shah Vijay , Pohida Thomas , Turkbey Baris , Mani Haresh , Merino Maria , Pinto Peter A. , Choyke Peter , Bernardo Marcelino
Published: October 2009

A method for the design and rapid manufacture of a patient specific tissue slicing device based on in vivo images in order to facilitate the process of correlating the images with histopathology is presented. The method is applied to radical prostatectomy specimens where the customized mold is designed using magnetic resonance (MR) images of each patient obtained prior to surgery. In this case, the mold holds the prostate in place while a knife with a single blade or multiple blades is inserted in slots which are positioned to obtain tissue blocks corresponding to the slices in the MR images. The resulting histological specimens demonstrate good anatomical correlation with the MR images.
Quantum dot energy levels and spectrum for different geometries
Authors: Tablero C.
Published: October 2009

The dispersion in the dot size, shape, and composition leads to a difficult comparison with experimental spectroscopy and transport data even if the growth conditions are similar. In this work, an extensive analysis of the influence of the dot size and shape on the electron and hole energy states and on transition energies is carried out using a unified model of the semiconductor band structure. In this study we obtain the electron energy spectra for three-dimensional small InAs∕GaAs quantum dots of several different truncated shapes described in the literature: tetrahedral, pyramidal with base of different geometry, etc. Also, in order to give an idea of the flexibility of the method, the icosahedral geometry is analyzed. The combination of theoretical results using a unified model for all the geometries with structural techniques will allow a more precise analysis of experimental samples.
Magnetic bubbles in FePd thin films near saturation
Authors: Jourdan Thomas , Masseboeuf Aurélien , Lançon Frédéric , Bayle-Guillemaud Pascale , Marty Alain
Published: October 2009

The structure of domain walls delimiting magnetic bubbles in L10 FePd thin layers is described on the basis of Lorentz transmission electron microscopy (LTEM) and multiscale magnetic simulations. Images obtained by high resolution LTEM show the existence of magnetization reversal areas inside domain walls, called vertical Bloch lines (VBLs). Combining these observations and multiscale simulations on various geometries, we can identify the structure of these VBLs, notably the presence or not of magnetic singularities.
Simulation study of the magnetized sheath of a dusty plasma
Authors: Foroutan G. , Mehdipour H. , Zahed H.
Published: October 2009

Numerical solutions of stationary multifluid equations are used to study the formation and properties of the magnetized sheath near the boundary of a dusty plasma. The impacts of the strength of the magnetic field, the dust and plasma number densities, and the electron temperature on the sheath structure and spatial distributions of various quantities are investigated. It is shown that for a given angle of incidence of the magnetic field, there is a threshold magnetic field intensity above which some kind of large regular inhomogeneities develop on the spatial profile of the dust particles. The sheath thickness, the electron and ion number densities, and the absolute dust charge are strongly affected by the variation in the dust number density. The sheath demonstrates a nonlinear dependence on the electron temperature; as the electron temperature rises, the sheath first is broadened and the absolute wall potential decreases but then at higher temperatures the sheath becomes narrower and the absolute wall potential increases.
Bonding in boranes and their interaction with molecular hydrogen at extreme conditions
Authors: Wang Shibing , Mao Wendy L. , Autrey Tom
Published: October 2009

The effects of high pressure and temperature on the bonding in ammonia borane (AB), NH3BH3 and decaborane (DB), B10H14 and their interactions with molecular hydrogen (H2) were investigated using Raman spectroscopy in a diamond anvil cell. At 0.7 GPa, AB becomes amorphous between 120 and 127 °C, indicating a positive Clapeyron slope. Heated to 140 °C, AB begins to undergo decomposition to polyaminoborane. The amorphous and decomposed AB does not recrystallize back to AB during slow cooling to room temperature or upon application of high pressure up to 3 GPa, underscoring the challenge of rehydrogenation of decomposed AB. The molecular Raman modes broaden in the reacted phase, and the NH3 modes show no pressure dependence. DB was studied at room temperature up to 11 GPa. The observed frequency dependence with pressure (dν/dP) and mode Grüneisen parameters varied for different spectral groups, and a new transition was identified at approximately 3 GPa. In both DB and heated AB, we found that they could store additional H2 with the application of pressure. We estimate that we can store approximately 3 wt % H2 in heated AB at 3 GPa and 1 wt % H2 in DB at 4.5 GPa.
Three-dimensional electronic spectroscopy of excitons in GaAs quantum wells
Authors: Turner Daniel B. , Stone Katherine W. , Gundogdu Kenan , Nelson Keith A.
Published: October 2009

We demonstrate three-dimensional (3D) electronic Fourier transform spectroscopy of GaAs quantum wells using four fully phase-coherent, noncollinear optical fields. Since the full complex signal field is measured as a function of all three time intervals, nearly every peak in the resulting 3D spectral solid arises from a distinguishable sequence of transitions represented by a single Feynman pathway. We use the 3D spectral peaks to separate two pathways involving weakly bound mixed biexcitons generated in different time orders. In the process, we reveal a peak that was previously obscured by a correlated but unbound exciton pair coherence. We also demonstrate a calibration procedure for the carrier frequency which yields biexciton binding energy values with high accuracy.
Magnetic domain wall pinning by a curved conduit
Authors: Lewis E. R. , Petit D. , Thevenard L. , Jausovec A. V. , O’Brien L. , Read D. E. , Cowburn R. P.
Published: October 2009

The pinning of a magnetic domain wall in a curved Permalloy (NiFe) nanostrip is experimentally studied. We examine the dependence of the pinning on both the radius of curvature of the bend and the chirality of the transverse domain wall. We find that bends act as potential wells or potential barriers depending on the chirality of the domain wall; the pinning field in both cases increases with decreasing radius of curvature. Micromagnetic simulations are consistent with the experimental results and show that both exchange and demagnetizing energies play an important role.
Epitaxial-strain effect on charge/orbital order in Pr0.5Ca0.5MnO3 films
Authors: Okuyama D. , Nakamura M. , Wakabayashi Y. , Itoh H. , Kumai R. , Yamada H. , Taguchi Y. , Arima T. , Kawasaki M. , Tokura Y.
Published: October 2009

Effect of growth orientation on charge- and orbital-ordering (CO-OO) phenomena has been studied for Pr0.5Ca0.5MnO3 epitaxial thin films fabricated on (LaAlO3)0.3–(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates by means of resistivity, synchrotron x-ray diffraction, and polarized optical microscopy measurements. CO-OO transition is observed around 220 K for a film grown on an LSAT (011) substrate [(011) film], similarly to a bulk sample, while a film grown on a (001) plane of LSAT [(001) film] shows much higher transition temperature around 300 K. The domain size of OO is approximately three times as large in the (011) film as in the (001) film. These results demonstrate that various properties of CO-OO phenomena can be controlled with the growth orientation via the epitaxial strain from the substrate.
Diffusion and clustering of Au adatoms on H-terminated Si(111)-(1×1): A first principles study
Authors: Lee Soo-Hwan , Hwang Gyeong S.
Published: October 2009

We have examined the diffusion and agglomeration of Au adatoms on the H-terminated Si(111)-(1×1) surface using periodic slab density functional theory calculations. We find that a single Au atom favorably resides atop a surface Si atom by breaking an original ≡Si–H bond while the H atom is bonded to the Au atom in the vertical direction, leading to the ≡Si–Au–H state. Starting from the most favorable on-top (T) site, a Au adatom is predicted to undergo diffusion by moving in and out of the T site without disrupting surface Si–H bonds. The predicted overall activation energy for the Au diffusion is 0.5 eV. Our calculations show that Au agglomeration leads to libration of H atoms from the Au/Si interface, while the H atoms are weakly bound to Au clusters and subsequently undergo associative H2 desorption with no significant barrier. Based on charge density analysis we also discuss bonding mechanisms for Au on H-terminated Si(111)-(1×1). Our findings are as a whole consistent with experimental results available in literature.
Dimension of ring polymers in bulk studied by Monte-Carlo simulation and self-consistent theory
Authors: Suzuki Jiro , Takano Atsushi , Deguchi Tetsuo , Matsushita Yushu
Published: October 2009

We studied equilibrium conformations of ring polymers in melt over the wide range of segment number N of up to 4096 with Monte-Carlo simulation and obtained N dependence of radius of gyration of chains Rg. The simulation model used is bond fluctuation model (BFM), where polymer segments bear excluded volume; however, the excluded volume effect vanishes at N→∞, and linear polymer can be regarded as an ideal chain. Simulation for ring polymers in melt was performed, and the ν value in the relationship Rg∝Nν is decreased gradually with increasing N, and finally it reaches the limiting value, 1/3, in the range of N≥1536, i.e., Rg∝N1/3. We confirmed that the simulation result is consistent with that of the self-consistent theory including the topological effect and the osmotic pressure of ring polymers. Moreover, the averaged chain conformation of ring polymers in equilibrium state was given in the BFM. In small N region, the segment density of each molecule near the center of mass of the molecule is decreased with increasing N. In large N region the decrease is suppressed, and the density is found to be kept constant without showing N dependence. This means that ring polymer molecules do not segregate from the other molecules even if ring polymers in melt have the relationship ν=1/3. Considerably smaller dimensions of ring polymers at high molecular weight are due to their inherent nature of having no chain ends, and hence they have less-entangled conformations.
Gas-phase reaction between calcium monocation and fluoromethane: Analysis of the potential energy hypersurface and kinetics calculations
Authors: Varela-Álvarez Adrián , Rayón V. M. , Redondo P. , Barrientos C. , Sordo José A.
Published: October 2009

The gas-phase reaction between calcium monocation and fluoromethane: Ca++CH3F→CaF++CH3 was theoretically analyzed. The potential energy hypersurface was explored by using density functional theory methodology with different functionals and Pople’s, Dunning’s, Ahlrichs’, and Stuttgart–Dresden basis sets. Kinetics calculations (energy and total angular momentum resolved microcanonical variational/conventional theory) were accomplished. The theoretically predicted range for the global kinetic rate constant values at 295 K (7.2×10−11–5.9×10−10 cm3 molecule−1 s−1) agrees reasonably well with the experimental value at the same temperature [(2.6±0.8)×10−10 cm3 molecule−1 s−1]. Explicit consideration of a two transition state model, where the formation of a weakly bounded prereactive complex is preceded by an outer transition state (entrance channel) and followed by an inner transition state connecting with a second intermediate that finally leads to products, is mandatory. Experimental observations on the correlation, or lack of correlation, between reaction rate constants and second ionization energies of the metal might well be rationalized in terms of this two transition state model.
Enhancing the retention properties of ZnO memory transistor by modifying the channel/ferroelectric polymer interface
Authors: Park C. H. , Lee Gyubaek , Lee Kwang H. , Im Seongil , Lee Byoung H. , Sung Myung M.
Published: October 2009

We report on the fabrication of ZnO nonvolatile memory thin-film transistors (NVM-TFTs) with thin poly(vinylidene fluoride/trifluoroethylene) [P(VDF-TrFE)] ferroelectric layer. Our NVM-TFT operates on glass substrates under low voltage write-erase (WR-ER) pulse of ±20 V with a maximum field effect mobility of ∼1 cm2/V s, maximum memory window of ∼20 V, and WR-ER current ratio of 4×102. When the NVM-TFT has a modified channel/ferroelectric interface with an inserted thin Al2O3 buffer layer, our device shows long retention time of more than 104 s, which is much enhanced compared to that of the other device without the buffer. The dynamic response of our devices with or without the buffer was clear enough to distinguish the WR and ER states as performed with 300 ms pulse.
High spatial resolution single multiwalled carbon nanotube electrode for stimulation, recording, and whole cell voltage clamping of electrically active cells
Authors: de Asis Edward D. , Leung Joseph , Wood Sally , Nguyen Cattien V.
Published: October 2009

We report the stimulation, recording, and voltage clamp of muscle fibers using a 30 nm diameter single multiwalled carbon nanotube electrode (sMWNT electrode) tip. Because of the lower access resistance, the sMWNT electrode conducts extracellular and intracellular stimulation more efficiently compared to glass micropipettes. The sMWNT electrode records field potentials and action potentials and performs whole cell voltage clamping of single fibers.
Tm 3 + -doped ion-exchanged aluminum germanate glass waveguide for S-band amplification
Authors: Yang D. L. , Pun E. Y.B. , Lin H.
Published: October 2009

K + – Na + ion-exchanged channel waveguide amplifiers have been fabricated in Tm3+-doped acid-resistant aluminum germanate glasses. The optical and relative gains of a 3.15-cm-long waveguide channel were achieved to be 4.05 and 2.29 dB at 1.482 μm wavelength under 110 mW 793 nm laser excitation, respectively. After compensating the propagation loss, an internal gain of 1.50 dB and a remarkable gain coefficient of 0.48 dB/cm were obtained, which reveals a definite S-band signal amplification in the low phonon energy glass waveguide. As an expectation, UV-radiation-sensitive glass waveguide should promote the developments of gain-flatten S-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact multifunctional integrated optical devices.
Large contrast enhancement of graphene monolayers by angle detection
Authors: Yu V. , Hilke M.
Published: October 2009

Exfoliated graphene monolayers are identified by optical inspection. In order to improve the monolayer detection, we investigate the angle dependence of the optical contrast of graphene on a 90 nm SiO2/Si substrate. We observe a significant enhancement of the visibility of graphene by changing the polarization and the angle of optical incidence. This method can be used to detect graphene on arbitrary substrates such as GaAs/AlAs based materials, which have a much cleaner surface.
Concurrent droplet charging and sorting by electrostatic actuation
Authors: Ahn Byungwook , Lee Kangsun , Louge Romain , Oh Kwang W.
Published: October 2009

This paper presents a droplet-based microfluidic device for concurrent droplet charging and sorting by electrostatic actuation. Water-in-oil droplets can be charged on generation by synchronized electrostatic actuation. Then, simultaneously, the precharged droplets can be electrostatically steered into any designated laminar streamline, thus they can be sorted into one of multiple sorting channels one by one in a controlled fashion. In this paper, we studied the size dependence of the water droplets under various relative flow rates of water and oil. We demonstrated the concurrent charging and sorting of up to 600 droplets/s by synchronized electrostatic actuation. Finally, we investigated optimized voltages for stable droplet charging and sorting. This is an essential enabling technology for fast, robust, and multiplexed sorting of microdroplets, and for the droplet-based microfluidic systems.
Level of cottonseed meal but not frequency of feeding regulates whole-body protein synthesis and growth of sheep fed a roughage diet
Authors: Kahn L. P. , Rao Somu B. N. , Nolan J. V.
Published: October 2009

An incomplete factorial experiment was conducted to determine the effect of level and frequency of feeding of a protein-rich supplement on the growth and whole-body protein metabolism of young sheep fed a medium quality roughage diet. Cottonseed meal (CSM) was used as the protein supplement and provided at 0, 0.2 or 0.4% liveweight per day at a frequency of 1 or 3 times each week and chopped oaten (0.95) and lucerne (0.05) hay was the roughage. Growth rate more than doubled (P < 0.01) following provision of CSM but there was no advantage of feeding CSM at the highest level. Frequency of feeding CSM did not alter growth rate. Intake of hay was little affected by CSM and as a consequence the food conversion ratio declined (P < 0.01) favourably from 22 : 1 (nil CSM) to 9 : 1 as a result of supplementation. The rate of whole-body protein synthesis increased (P < 0.01) in response to the highest level of CSM with no apparent change in protein degradation, underpinning an increase (P < 0.01) in protein retention. These results highlight the role of protein supplements for promoting growth of young sheep on roughage diets and indicate that these supplements need to be provided only once a week.
Efficient Synthesis of Dendritic Architectures by One-Pot Double Click Reactions
Authors: Xiong Xing Quan
Published: October 2009

Dendritic macromolecules with 8 and 16 hydroxy end-groups on the periphery have been synthesized using double click reactions (Cu-catalyzed azide/alkyne click chemistry, i.e., CuAAC and Diels–Alder [4 + 2] cycloaddition reactions) with a one-pot technique. The structure of the dendrimers was characterized by 1H and 13C NMR spectroscopy, and matrix-assisted laser desorpton–ionization time-of-flight mass spectrometry. The purity was determined by size exclusion chromatography.
Elucidating Photochemical Pathways of Tyrosine Oxidation in an Engineered Bacterioferritin 'Reaction Centre'
Authors: Hingorani Kastoori , Conlan Brendon , Hillier Warwick , Wydrzynski Tom
Published: October 2009

Photosystem II (PSII) is the chlorophyll/protein complex in green plants that catalyzes the oxidation of water to molecular oxygen. We have utilized bacterioferritin (BFR), an iron storage protein found in Escherichia coli, as a protein scaffold to build in PSII cofactors in a simpler in vitro model system. Previously, we have shown that the native heme in BFR can be replaced with the chlorophyll analog zinc-chlorin (ZnCe6) and that the intrinsic di-iron site can bind two manganese ions. Upon flash excitation of the ZnCe6 modified BFR, not only is the dinuclear manganese complex oxidized but also a tyrosine residue. There are seven tyrosine residues in each BFR monomeric subunit. We mutated the three tyrosine residues within electron tunnelling distance of the ZnCe6. Here we present evidence based on electron paramagnetic resonance and fluorescence spectroscopy that one is not oxidized while the other two seem to be oxidized in parallel. Localization of this photoactive tyrosine is the first step in creating a linear electron flow in BFR like in PSII.
Synthesis of MUC1 Peptide and Glycopeptide Dendrimers
Authors: Chun Candy K. Y. , Payne Richard J.
Published: October 2009

Several dendrimers possessing multiple copies of peptides and glycopeptides belonging to the MUC1 eicosapeptide tandem repeat sequence have been prepared. Fmoc-strategy solid-phase peptide synthesis was used to construct the peptides and glycopeptides, which were conjugated to suitably functionalized dendrimer cores using the copper-catalyzed azide-alkyne cycloaddition reaction to produce multivalent peptide and glycopeptide dendrimers.