bluuebunny/crossref_metadata_2025 huggingface dataset:
Geodynamic implications for the formation of the Betic‐Rif orogen from magnetotelluric studies
Authors: Martí A. , Queralt P. , Roca E. , Ledo J. , Galindo‐Zaldívar J.
Published: January 2009

Magnetotelluric data from the central Betics mountains (Spain) have been used to determine the electrical resistivity of the crust after a three‐dimensional (3D) interpretive approach. At shallow levels (<2 km), the resulting model shows good correlation between the geoelectric structures and the geologic units. At greater depths (>3 km), the most striking and well‐resolved feature of the model is an upper‐middle crust conductive body, located at the core of the Internal Betics antiform. This approximately 14‐km‐thick body is interpreted as basic or ultrabasic rocks containing a conducting mineral phase. Its structural location above the sole thrust of the Betic orogen and beneath the Nevado‐Filábride complex confirms the presence of a major suture zone between this complex and the autochthonous Iberian plate. This suture may correspond to an ancient oceanic or transitional domain developed between Iberia and the Alboran Domain during the opening of the Tethys Ocean, partially subducted and closed during the development of the Betic orogen. The possible geodynamic scenarios for the Betics have been reconsidered, taking into account this new constraint.
Effect of relative humidity and sea level pressure on electrical conductivity of air over Indian Ocean
Authors: Pawar S. D. , Murugavel P. , Lal D. M.
Published: January 2009

The electrical conductivity measured over the Indian Ocean (15°N, 77°E to 20°S, 58°E) during the Indian Ocean Experiment (INDOEX‐1999) from 20 January to 12 March 1999 has been analyzed. The conductivity values over two oceanic regions, one with very low aerosol concentration and another with very high aerosol concentration, are studied in relation with meteorological parameters such as relative humidity and sea level pressure. The average conductivity is as low as 0.295 × 10−14 Sm−1 in the region of high aerosol concentration and it is 0.783 × 10−14 Sm−1 in the region of very low aerosol concentration. In both the regions, conductivity shows an inverse relation with relative humidity and this effect is more in the presence of high aerosol concentration. The hydrate growth of aerosol particles in high‐humidity condition may be responsible for the inverse relation between conductivity and relative humidity. Size distributions of aerosol particles measured in the same cruise during high‐humid conditions are also analyzed to show that sizes, rather than numbers, of aerosol particles increase with an increase in humidity. The relationship between conductivity and sea level pressure in these two regions is also studied and it shows good correlation in the region where the background aerosol concentration is low and no correlation in the region where aerosol concentration is high. The inverse relation between sea level pressure and electrical conductivity is attributed to the possible transportation of ultrafine particles from free troposphere, with subsiding motions associated with high pressure. The positive correlation between ultrafine particles and sea level pressure supports this idea.
Temperature and concentration feedbacks in the carbon cycle
Authors: Boer G. J. , Arora V.
Published: January 2009

Feedback processes in the carbon budget are investigated in a manner that parallels the treatment of feedback processes in the energy budget. The analysis is applied to simulations with the CCCma earth system model CanESM1 using a range of emission scenarios. For the atmosphere there is a positive “carbon‐temperature” feedback which acts to increase CO2 flux to the atmosphere as temperatures warm. There is also a negative “carbon‐concentration” feedback which acts to remove CO2 from the atmosphere via enhanced uptake of CO2 by the land and ocean as CO2 concentration increases. While the positive feedback associated with temperature change is reasonably linear and consistent as temperature increases, the feedback associated with CO2 concentration is not. The negative carbon‐concentration feedback weakens with increasing CO2 concentration thereby enhancing atmospheric CO2 and accelerating global warming. The behaviour of the inferred carbon‐concentration feedback is different for different emission scenarios implying a dependence on state variables other than CO2 concentration. The carbon‐concentration feedback behaviour inferred for a particular scenario may not, therefore, be used to infer system behaviour for other scenarios.
Role of the land‐sea thermal contrast in the interannual modulation of the North American Monsoon
Authors: Turrent Cuauhtémoc , Cavazos T.
Published: January 2009

The land‐sea thermal contrast (LSTC) that is present at the initial stage of the North American Monsoon is analyzed as a principal driving mechanism for monsoon onset interannual variability. The vertically integrated moisture flux convergence (MFC) averaged over the core monsoon during June 16–30, derived from North American Regional Reanalysis daily fields for the period 1979–2006, is proposed as an index for initial monsoon intensity. We quantify the LSTC associated to the monsoon and propose a dynamic connection between the thermal contrast and the initial monsoon intensity. It consists of a directly proportional relation between the LSTC, the surface pressure gradient along the Gulf of California, and the ensuing low level (below 850 mb) moisture transport (from the southern Gulf of California and eastern tropical Pacific) and precipitation in the core region.
Recent rainfall cycle in the Intermountain Region as a quadrature amplitude modulation from the Pacific decadal oscillation
Authors: Wang Shih‐Yu , Gillies Robert R. , Jin Jiming , Hipps Lawrence E.
Published: January 2009

Precipitation in the Intermountain Region has experienced a pronounced 10–20 yr cycle during the last four decades. We present evidence of a quadrature phase coupling of these 10–20 yr cycles between the Pacific Decadal Oscillation (PDO) and the Intermountain rainfall. The PDO has been linked to precipitation anomalies in the Northwest and Southwest U.S., while the Intermountain Region remains marginal. During the transition phase of a 10–20 yr cycle in the PDO, an anomalous circulation dipole over the Gulf of Alaska is formed. This circulation dipole modulates the synoptic activity that produces rainfall in the Intermountain Region. As a result, the Intermountain rainfall cycle has repeatedly lagged the PDO cycle by a quarter phase, amounting to about 3 to 4 years. Future understanding of the 10–20 yr cycle embedded in the PDO and its quadrature phase modulation may help predict the Intermountain climate.
Clearing observed PGR in GRACE data aimed at global viscosity inversion: Weighted Mass Trends technique
Authors: Barletta V. R. , Bordoni A.
Published: January 2009

The time‐variable gravity field shows the effects of large present‐day mass variations associated with hydrological phenomena and melting ice‐sheets, resulting in a shaded Post Glacial Rebound (PGR) signal. A meaningful viscosity inversion based on a global scale comparison of GRACE data and PGR predictions is thus hard to obtain. We derive a weighted surface mass distribution in water equivalent, starting from an initial guess, which portrays the secular effects of present‐day phenomena. The gravity field it generates is then carefully removed from GRACE data, resulting in a gravity pattern where the effects of PGR are clearer and ready to be compared with the predictions. On the basis of viscoelastic stratified Earth models and different Pleistocene deglaciation models, we show that the quality of a global preliminary viscosity inversion greatly improves.
Scaling of small repeating earthquakes explained by interaction of seismic and aseismic slip in a rate and state fault model
Authors: Chen Ting , Lapusta Nadia
Published: January 2009

Because of short recurrence times and known locations, small repeating earthquakes present a rare predictable opportunity for detailed field observations. They are used to study fault creeping velocities, earthquake nucleation, stress drops, and other aspects of tectonophysics, earthquake mechanics, and seismology. An intriguing observation about repeating earthquakes is their scaling of recurrence time with seismic moment, which is significantly different from the scaling based on a simple conceptual model of circular ruptures with stress drop independent of seismic moment and no aseismic slip. Here we show that a model of repeating earthquakes based on laboratory‐derived rate and state friction laws reproduces the observed scaling. In the model, a small fault patch governed by steady state velocity‐weakening friction is surrounded by a much larger velocity‐strengthening region. Long‐term slip behavior of the fault is simulated using a methodology that fully accounts for both aseismic slip and inertial effects of occasional seismic events. The model results in repeating earthquakes with typical stress drops and sizes comparable with observations. For a fixed set of friction parameters, the observed scaling is reproduced by varying the size of the velocity‐weakening patch. In simulations, a significant part of slip on the velocity‐weakening patches is accumulated aseismically, even though the patches also produce seismic events. The proposed model supplies a laboratory‐based framework for interpreting the wealth of observations about repeating earthquakes, provides indirect evidence that rate and state friction acts on natural faults, and has important implications for possible scenarios of slip partition into seismic and aseismic parts.
Data mining for evolution of association rules for droughts and floods in India using climate inputs
Authors: Dhanya C. T. , Nagesh Kumar D.
Published: January 2009

An accurate prediction of extreme rainfall events can significantly aid in policy making and also in designing an effective risk management system. Frequent occurrences of droughts and floods in the past have severely affected the Indian economy, which depends primarily on agriculture. Data mining is a powerful new technology which helps in extracting hidden predictive information (future trends and behaviors) from large databases and thus allowing decision makers to make proactive knowledge‐driven decisions. In this study, a data‐mining algorithm making use of the concepts of minimal occurrences with constraints and time lags is used to discover association rules between extreme rainfall events and climatic indices. The algorithm considers only the extreme events as the target episodes (consequents) by separating these from the normal episodes, which are quite frequent, and finds the time‐lagged relationships with the climatic indices, which are treated as the antecedents. Association rules are generated for all the five homogenous regions of India and also for All India by making use of the data from 1960 to 1982. The analysis of the rules shows that strong relationships exist between the climatic indices chosen, i.e., Darwin sea level pressure, North Atlantic Oscillation, Nino 3.4 and sea surface temperature values, and the extreme rainfall events. Validation of the rules using data for the period 1983–2005 clearly shows that most of the rules are repeating, and for some rules, even if they are not exactly the same, the combinations of the indices mentioned in these rules are the same during validation period, with slight variations in the classes taken by the indices.
Seasonality in secular changes and interannual variability of European air temperature during the twentieth century
Authors: Zveryaev Igor I. , Gulev Sergey K.
Published: January 2009

A gridded terrestrial monthly surface air temperature (AT) data set for 1901–2000 from the Climatic Research Unit (CRU), University of East Anglia, is used to investigate seasonality in the long‐term AT variability over Europe. Prominent seasonal differences are detected in all considered characteristics of AT variability. Significant warming trends over western and southern Europe are found during summer and fall. In winter, the largest positive trends are observed mostly in southern Europe, whereas during spring, they are detected over Scandinavia and northeastern European Russia. The spatial‐seasonal differentiation of warming trends implies that, in different parts of Europe, different seasons play the role as major contributor to the warming trend. The first empirical orthogonal functions (EOF) modes of winter, spring, and fall AT over Europe are associated with the North Atlantic Oscillation (NAO) and explain about 50% of AT variability. For the summer season, the second EOF mode (explaining only 15% of AT variance) might be associated with the summer NAO but has a very different (compared to other seasons) spatial pattern and principal components. The second EOF mode of the winter AT might be linked to the East Atlantic/West Russia (EAWR) teleconnection pattern. Analysis of running correlations between the principal components of the leading EOF modes of AT and the NAO index has revealed nonstationarity of the links between European AT and the NAO and evident seasonality in their long‐term changes. Subsequent singular value decomposition analysis performed for the climatic periods of strong/weak links to the NAO revealed considerable interdecadal changes both in the strength and the structure of the links between European AT and regional atmospheric circulation.
No “Student Members”—Only Student Fees
Authors: Spilhaus Fred
Published: January 2009

AGU has three classes of individual membership: Members, Fellows, and Honorary Fellows. As you can see, “students” is not a membership class. For almost 50 years, members of AGU who are students have enjoyed much reduced dues and special rates for most AGU publications, meetings, and other services and activities. Throughout those years, AGU has tried to create a welcoming environment for students.

Like many members who are now leaders in our community, I joined AGU as a graduate student. We benefited from our generous seniors as we joined the scientific fray at our early meetings and battled our way for recognition. I trust that we have shown the same support for the next generation and that this tradition continues to prosper.
Overestimation of the field-effect mobility via transconductance measurements and the origin of the output/transfer characteristic discrepancy in organic field-effect transistors
Authors: Reese Colin , Bao Zhenan
Published: January 2009

Paramount to the rational design of electronic materials is the accurate characterization of their intrinsic properties. In particular, many applications of conducting and semiconducting soft materials have been driven by the development of materials with high, bias-stable field-effect mobility. Here, we demonstrate the effect of parasitic resistance and bias-dependent mobility on device electrical characteristics. Specifically, we analyze two of the most commonly employed test algorithms—the output and transfer curves—via a closed-form analysis. The analysis exhibits characteristics endemic to those published in literature, such as effective mobilities with maxima with respect to gate voltage that may lead to overstatements of mobility by manyfold. Furthermore, analysis reveals that common overestimation relative to intrinsic and output-estimated mobilities is caused solely by gate-bias-dependent mobility, and parasitic resistance can only lead to an underestimation of the effective mobility. We introduce a method for accurate mobility estimation and a dimensionless variable for evaluating the importance of contact resistance.
Critical-current density analysis of force and stability in maglev systems
Authors: Sanchez Alvaro , Del-Valle Nuria , Navau Carles , Chen Du-Xing
Published: January 2009

The levitation force and stability in a superconductor-magnet system with maglev geometry are studied as function of the critical-current density of the superconductor, from a realistic model based on minimizing the magnetic energy. Results show that although the force is an increasing function of the critical-current density Jc, an overhigh Jc may result in instability. Therefore, the optimum critical-current density in the superconductor for a given levitation system should be an intermediate value which depends on the system dimensions and the magnetic field of the magnet.
Rotationally resolved photoelectron spectroscopic study of the Jahn–Teller effect in allene
Authors: Schulenburg A. M. , Merkt F.
Published: January 2009

The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of allene (C3H4) and perdeuterated allene have been recorded from the first adiabatic ionization energy up to 2200 cm−1 of internal energy in the cations at a resolution sufficient to observe the full rotational structure. The intensity distributions in the spectra are dominated by vibrational progressions in the torsional mode, which were analyzed in the realm of a two-dimensional model of the E⊗(b1⊕b2) Jahn–Teller effect in the allene cation [C. Woywod and W. Domcke, Chem. Phys. 162, 349 (1992)]. Whereas the rotational structure of the transitions to the lowest torsional levels (00 and 41) are regular and can be qualitatively analyzed in terms of a simple orbital ionization model, the rotational structure of the spectra of the 42 and 43 levels are strongly perturbed. The photoelectron spectrum of C3H4 also reveals several weak vibrational bands in the immediate vicinity of these levels that are indicative of (ro)vibronic perturbations. A slight broadening of the transitions to the 41 levels compared to that of the vibronic ground state and the increase of the number of sharp features in the rotational structure of the spectrum of the 42 level point at the importance of large-amplitude motions not considered in previous treatments of the Jahn–Teller effect in the allene cation.
Solid-solid transition of the size-polydisperse hard sphere system
Authors: Yang Mingcheng , Ma Hongru
Published: January 2009

The solid-solid coexistence of a polydisperse hard sphere system is studied by using the Monte Carlo simulation. The results show that for large enough polydispersity the solid-solid coexistence state is more stable than the single-phase solid. The two coexisting solids have different composition distributions but the same crystal structure. Moreover, there is evidence that the solid-solid transition terminates in a critical point as in the case of the fluid-fluid transition.
The growth process of first water layer and crystalline ice on the Rh(111) surface
Authors: Beniya Atsushi , Sakaguchi Yuji , Narushima Tetsuya , Mukai Kozo , Yamashita Yoshiyuki , Yoshimoto Shinya , Yoshinobu Jun
Published: January 2009

The adsorption states and growth process of the first layer and multilayer of water (D2O) on Rh(111) above 135K were investigated using infrared reflection absorption spectroscopy (IRAS), temperature programed desorption, spot-profile-analysis low-energy electron diffraction, and scanning tunneling microscopy (STM). At the initial stage, water molecules form commensurate (√3×√3)R30° islands, whose size is limited for several hexagonal units; the average diameter is ∼2.5nm. This two-dimensional (2D) island includes D-down species, and free OD species exist at the island edge. With increasing coverage, the D-up species starts to appear in IRAS. At higher coverages, the 2D islands are connected in STM images. By the titration of Xe adsorption we estimated that the D-down domain occupies about 55% on Rh(111) at the saturation coverage. Further adsorption of water molecules forms three-dimensional ice crystallites on the first water layer; thus, the growth mode of crystalline water layers on Rh(111) is a Stranski–Krastanov type. We have found that an ice crystallite starts to grow on D-down domains and the D-down species do not reorient upon the formation of a crystalline ice.
Non-Condon nature of fluctuating bridges on nonadiabatic electron transfer: Analytical interpretation
Authors: Zhao Yi , Liang WanZhen
Published: January 2009

Rigorous expressions for the calculation of nonadiabatic electron transfer rates are presented in closed forms for donor-acceptor systems incorporated fluctuating bridges and their non-Condon electronic couplings. In high temperature limit, they show a similar property to the Marcus formula. However, the Marcus parabolic with respect to the driving force is shifted for the exponential coupling while it becomes an overlap of several Gaussian functions for the linear coupling. Furthermore, the effective couplings are exponentially and linearly dependent on temperature and the squared frequencies of bridge modes for the exponential and linear couplings, respectively.
Linear aggregation beyond isodesmic symmetry
Authors: Henderson J. R.
Published: January 2009

Exactly solvable models of linear aggregation have been known since Ising’s seminal one-dimensional model. This model is defined by a unique nearest-neighbor bond strength that is independent of the length of the cluster; known as isodesmic symmetry. Linear aggregation in real systems has often been associated with broken isodesmic symmetry. Here we show that important examples can be mapped to a class of one-dimensional models that are also exactly solvable.
Effect of mixed grain sizes on thermoelectric performance of Bi2Te3 compound
Authors: Zhao Li-Dong , Zhang Bo-Ping , Liu Wei-Shu , Li Jing-Feng
Published: January 2009

Coarse (about 1 μm) and fine (about 100 nm) Bi2Te3 particles were synthesized by mechanical alloying for different times, respectively. Their mixtures at different ratios were consolidated by spark plasma sintering to produce nano-/microstructured composites with the same chemical compositions. The Seebeck coefficient was significantly enhanced by addition of fine particles through the potential barrier scattering. The electrical resistivity increased rapidly when the weight fraction of fine particles exceeded about 60%, probably due to an effect similar to percolation phenomenon. However, the thermal conductivity was reduced almost linearly with increasing fraction of fine particles. Because of the combined effects of the potential barrier scattering, nonlinear change in electrical property and linear change in thermal transport property, a peak value of dimensionless figure of merit (ZT) was achieved for the sample containing 60% fine particles. This study demonstrated the possibility to enhance ZT value by introducing nonuniform microstructures even without changing chemical compositions.
Metal-insulator transition in n-3C-SiC epitaxial films
Authors: Lebedev A. A. , Abramov P. L. , Agrinskaya N. V. , Kozub V. I. , Lebedev S. P. , Oganesyan G. A. , Tregubova A. S. , Shamshur D. V. , Skvortsova M. O.
Published: January 2009

The paper reports a study of galvanomagnetic properties of n-3C-SiC/n-6H-SiC heterostructures at liquid-helium temperatures. 3C-SiC epitaxial layers were grown by sublimation epitaxy in a vacuum on the (0001)C face of 6H-SiC substrates produced by the Lely method and 4H-SiC substrates grown by modified Lely method. The x-ray topography demonstrated the high quality structure of the epitaxial layers and the absence of any transition regions between 3C-SiC epitaxial layer and substrate. The low-temperature conductivity and magnetoresistance of the films have been studied as functions of their doping level and structural quality. It was found that the metal-insulator transition occurs in the n-3C-SiC layer at concentrations Nd−Na≤3×1017 cm−3.
Al substituted Ba-hexaferrite single-crystal films for millimeter-wave devices
Authors: Ustinov A. B. , Tatarenko A. S. , Srinivasan G. , Balbashov A. M.
Published: January 2009

Microwave and magnetic properties of single-crystal aluminum substituted barium hexaferrites BaAlxFe12−xO19 with Al substitution level x from 0 to 2 are reported. The single crystals were grown by the floating zone melting method. Films in the form of 100 μm thick, 1 mm wide, and 2 mm long resonators were used for ferromagnetic resonance (FMR) measurements in the frequency domain over 40–110 GHz for applied magnetic fields of 0–10 kOe. Based on these measurements, the hexaferrite parameters are determined. With increasing x from 0 to 2, the uniaxial magnetocrystalline anisotropy field increases from 17.88 to 33.68 kOe, while reasonable values of full FMR linewidth (35 Oe at 47 GHz and 140 Oe at 108 GHz) are maintained. These parameters ensure the potential for use of the ferrites in millimeter-wave devices.
Size-dependent thermal diffusivity of multilayered thin films deposited on substrates characterized by transient grating technique
Authors: Ju Heng-yi , Zhang Shu-yi , Li Zhe , Shui Xiu-ji , Kuo Pao-kuang
Published: January 2009

The thermal diffusivities of bilayered thin films with nanoscaled thickness deposited on substrates are characterized by nanosecond transient grating method. Based on the transient grating experiment, two-dimensional thermal diffusivity model and eigenfunction expansion method are used to calculate the thermal fields in the trilayered structures. By fitting the theoretical calculations to the experimental data of a series of trilayered structures Al/ZnO/Si with different thicknesses of ZnO films, the thermal diffusivities of the Al and ZnO films can be evaluated simultaneously. The results show that the thermal diffusivities of the ZnO films are size dependent and increase with thickness of the films.
Free carrier dynamics of InN nanorods investigated by time-resolved terahertz spectroscopy
Authors: Ahn H. , Chuang C.-H. , Ku Y.-P. , Pan C.-L.
Published: January 2009

Ultrafast time-resolved terahertz spectroscopy is employed to investigate the carrier dynamics of indium nitride (InN) nanorod arrays and an epitaxial film. Transient differential transmission of terahertz wave shows that hot carrier cooling and defect-related nonradiative recombination are the common carrier relaxation processes for InN film and nanorods. However, the electrons confined in the narrow structure of nanorods are significantly affected by the carrier diffusion process near the surface, which causes the abnormally long relaxation time for nanorods.
Mechanical characterization of magnetic nanowire–polydimethylsiloxane composites
Authors: Keshoju K. , Sun L.
Published: January 2009

One-dimensional magnetic nanowires have been introduced into polydimethylsiloxane (PDMS) to form polymer based nanocomposites. In contrast to the conventional nanofillers such as carbon nanotubes, carbon nanofibers, nanoparticles, and layer-structured materials, these well-defined anisotropic metallic nanowires are highly conductive and have much weaker van der Waals interactions. Moreover, composition modulation can be introduced along the wire axis to achieve multifunctionalities. Incorporation of magnetic segment(s) to the nanowire makes it possible to use external magnetic field to manipulate the distribution and alignment of nanowires when they are suspended in liquids. To characterize the mechanical responses of the nanowire-elastomer composite, an approach using microscale rulers has been developed to improve the resolution of strain measurement. Mechanical strengthening effects in PDMS composites with randomly and aligned nickel nanowires have been investigated.
Annealing of ion irradiated high TC Josephson junctions studied by numerical simulations
Authors: Sirena M. , Matzen S. , Bergeal N. , Lesueur J. , Faini G. , Bernard R. , Briatico J. , Crété D. G.
Published: January 2009

Recently, annealing of ion irradiated high Tc Josephson iunctions (JJs) has been studied experimentally in the perspective of improving their reproducibility. Here we present numerical simulations based on random walk and Monte Carlo calculations of the evolution of JJ characteristics such as the transition temperature Tc′ and its spread ΔTc′, and compare them with experimental results on junctions irradiated with 100 and 150 keV oxygen ions, and annealed at low temperatures (below 80 °C). We have successfully used a vacancy-interstitial annihilation mechanism to describe the evolution of the Tc′ and the homogeneity of a JJ array, analyzing the evolution of the defects density mean value and its distribution width. The annealing first increases the spread in Tc′ for short annealing times due to the stochastic nature of the process, but then tends to reduce it for longer times, which is interesting for technological applications.
Formation of planar defects over GeSi islands in Si capping layer grown at low temperature
Authors: Lin J. H. , Wu Y. Q. , Cui J. , Fan Y. L. , Yang X. J. , Jiang Z. M. , Chen Y. , Zou J.
Published: January 2009

Coherently strained GeSi/Si(001) islands were overgrown with a Si capping layer of different thicknesses at temperature 300 °C. The structures of the islands and the Si capping layer were investigated by high resolution transmission electron microscopy. The shapes of the embedded islands were well preserved, whereas planar defects were observed exactly over the islands in the capping layers. The strain energy in regions over the islands accumulated with increasing thickness of the Si capping layer, resulting in the formation of the planar defects. By means of a two-step deposition in which 20-nm-thick Si capping layer was first deposited at a low temperature of 300 °C followed by 70-nm-thick Si capping layer deposition at a high temperature of 640 °C, the defect-free Si capping layer with flat surface can be obtained.
Three-dimensional theory of the Smith–Purcell free-electron laser with side walls
Authors: Andrews H. L. , Jarvis J. D. , Brau C. A.
Published: January 2009

We present an analytic theory for the operation of a Smith–Purcell free-electron laser with side walls that includes the effects of transverse diffraction in the optical beam. We allow the width of the electron beam and the width of the grating to vary independently and require the walls to be high compared to the wavelength of the evanescent wave. The results show that the side walls change the empty-grating dispersion relation in important ways. When the separation of the walls is not too large, it is sufficient to consider only the lowest-order transverse mode of the grating. In this case, we obtain excellent agreement with numerical simulations and experimental results.
Mechanical wave propagation in carbon nanotubes driven by an oscillating tip actuator
Authors: Chen Min , Zang Ji , Xiao Dingquan , Liu Feng
Published: January 2009

We investigate the mechanical wave propagation in single-walled carbon nanotubes (SWNTs) induced by two oscillating tips, using molecular dynamics simulations. We found a mandatory correlation condition between the tip oscillation frequency and magnitude in order to generate a quasi-steady-state standing wave with a characteristic wavelength and frequency changing with the tube radius, but independent of tip conditions. Our findings suggest the possibility of using SWNTs as nanopumping systems for potential applications of fluid transport and drug delivery.
Temperature variation in liquid infiltration and defiltration in a MCM41
Authors: Han Aijie , Lu Weiyi , Punyamurtula Venkata K. , Kim Taewan , Qiao Yu
Published: January 2009

In a calometric measurement of infiltration and defiltration of pressurized liquid in a hydrophobic MCM41, it is observed that in nanopores the energy change between solid and liquid phases is dependent on the direction of liquid motion: liquid infiltration is exothermic and liquid defiltration is endothermic. The sorption curves and the temperature variation are insensitive to the loading rate. The magnitude of temperature decrease in defiltration is smaller than the temperature increase in infiltration, fitting well with the hysteresis of the sorption curve. These phenomena can be attributed to the confinement effect of nanopore walls and the thermally/mechanically aided surface diffusion of liquid molecules.
Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route
Authors: Rout S. K. , Sinha E. , Hussian A. , Lee J. S. , Ahn C. W. , Kim I. W. , Woo S. I.
Published: January 2009

A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy=0.02 eV and freezing temperature=362 °C. All these measurements confirmed its relaxorlike phase transition.
Improved extended Hamiltonian and search for local symmetries
Authors: Deriglazov A. A.
Published: January 2009

We analyze a structure of the singular Lagrangian L with first and second class constraints of an arbitrary stage. We show that there exist an equivalent Lagrangian (called the extended Lagrangian L̃) that generates all the original constraints on second stage of the Dirac–Bergmann procedure. The extended Lagrangian is obtained in closed form through the initial one. The formalism implies an extension of the original configuration space by auxiliary variables. Some of them are identified with gauge fields supplying local symmetries of L̃. As an application of the formalism, we found closed expression for the gauge generators of L̃ through the first class constraints. It turns out to be much more easy task as those for L. All the first class constraints of L turn out to be the gauge symmetry generators of L̃. By this way, local symmetries of L with higher order derivatives of the local parameters decompose into a sum of the gauge symmetries of L̃.
Low-temperature and high magnetic field dynamic scanning capacitance microscope
Authors: Baumgartner A. , Suddards M. E. , Mellor C. J.
Published: January 2009

We demonstrate a dynamic scanning capacitance microscope (DSCM) that operates at large bandwidths, cryogenic temperatures, and high magnetic fields. The setup is based on a noncontact atomic force microscope (AFM) with a quartz tuning fork sensor for the nonoptical excitation and readout in topography, force, and dissipation measurements. The metallic AFM tip forms part of a rf resonator with a transmission characteristics modulated by the sample properties and the tip-sample capacitance. The tip motion gives rise to a modulation of the capacitance at the frequency of the AFM sensor and its harmonics, which can be recorded simultaneously with the AFM data. We use an intuitive model to describe and analyze the resonator transmission and show that for most experimental conditions it is proportional to the complex tip-sample conductance, which depends on both the tip-sample capacitance and the sample resistivity. We demonstrate the performance of the DSCM on metal disks buried under a polymer layer and we discuss images recorded on a two-dimensional electron gas in the quantum Hall effect regime, i.e. at cryogenic temperatures and in high magnetic fields, where we directly image the formation of compressible stripes at the physical edge of the sample.
Influence of the electron cyclotron resonance plasma confinement on reducing the bremsstrahlung production of an electron cyclotron resonance ion source with metal-dielectric structures
Authors: Schachter L. , Stiebing K. E. , Dobrescu S.
Published: January 2009

The influence of metal-dielectric (MD) layers (MD structures) inserted into the plasma chamber of an electron cyclotron resonance ion source (ECRIS) onto the production of electron bremsstrahlung radiation has been studied in a series of dedicated experiments at the 14 GHz ECRIS of the Institut für Kernphysik der Universität Frankfurt. The IKF-ECRIS was equipped with a MD liner, covering the inner walls of the plasma chamber, and a MD electrode, covering the plasma-facing side of the extraction electrode. On the basis of similar extracted currents of highly charged ions, significantly reduced yields of bremsstrahlung radiation for the “MD source” as compared to the standard (stainless steel) source have been measured and can be explained by the significantly better plasma confinement in a MD source as compared to an “all stainless steel” ECRIS.
Piezoelectric properties and stabilities of CuO-modified Ba(Ti,Zr)O3 ceramics
Authors: Zheng P. , Zhang J. L. , Shao S. F. , Tan Y. Q. , Wang C. L.
Published: January 2009

Due to the orthorhombic-tetragonal polymorphic phase transition near room temperature, undesirable large temperature dependence of piezoelectric properties is observed over common usage temperature range in BaTiO3 ceramics with high d33 values. Whereas shifting the phase transition temperature upward by partially substituting Ti with Zr is effective in reducing the piezoelectric temperature dependence, serious long-term degradation occurs. However, it is found that this could be overcome by incorporating a small amount of CuO additive. CuO-modified Ba(Ti0.9625Zr0.0375)O3 ceramics possess excellent piezoelectric properties of d33=300 pC/N, kp=0.493, and k33=0.651 with tan δ=0.011, and its kp remains larger than 0.40 in the broad temperature range from −43 to 73 °C and is almost constant between −25 and 55 °C. The results indicate that CuO-modified Ba(Ti,Zr)O3 ceramics are a promising low-cost lead-free material for practical applications.
Spectral collocation-based numerical simulations of cylindrical ac-electro-osmotic flows for bioconcentration purposes and experimental validations
Authors: Tanguy L. , Salomon S. , Nicu L.
Published: January 2009

Electro-osmotic flows are used to actuate the surrounding fluid and bring particles in the solution at the proximity of a biosensor surface. This phenomenon allows the local increase in particle number and should decrease the biosensor’s response time. To predict concentration rate and efficiency, we compute the electric field and the flow velocity above the electrodes. Spectral collocation is used to solve the electrical and fluidic governing equations of the phenomenon. Theoretical results are proposed and experimental measurements are compared with the calculations.
A microfluidic Coulter counting device for metal wear detection in lubrication oil
Authors: Murali Srinidhi , Jagtiani Ashish V. , Xia Xingao , Carletta Joan , Zhe Jiang
Published: January 2009

We present the design, fabrication, and testing of a microfluidic device for metal wear detection in lubrication oils. The detection is based on the capacitance Coulter counting principle, that is, on the change in a microchannel’s capacitance caused by the presence of a metal particle in the microchannel. The testing of the microfluidic device using 10–25 μm aluminum particles has demonstrated the feasibility for detection and counting of microscale metal particles in low-conductive lubrication oils. This microfluidic device is promising for online oil debris detection by the use of multiple detection microfluidic channels.
Influence of a transient hexagonal phase on the microstructure and morphological stability of NiSi films
Authors: Van Bockstael C. , De Keyser K. , Van Meirhaeghe R. L. , Detavernier C. , Jordan-Sweet J. L. , Lavoie C.
Published: January 2009

The morphological stability of NiSi is investigated when 40% of Si is mixed into an as deposited 10 nm Ni film. When annealing at 3 °C/s, scanning electron microscopy images and in situ sheet-resistance measurements show that NiSi agglomeration is delayed by more than 100 °C. In situ x-ray diffraction reveals that NiSi grows from an unusual transient hexagonal θ-nickel-silicide phase. The significant improvement of the NiSi film’s morphological stability can be related to its microstructure, with large grains and a strong texture. This peculiar microstructure is compared to the microstructure of the θ-nickel-silicide precursor by electron backscattering diffraction and pole figures.
Spin injection studies into GaAs quantum wells in the presence of confined electrons
Authors: Yasar M. , Mallory R. , Petrou A. , Hanbicki A. T. , Kioseoglou G. , Li C. H. , van’t Erve O. M. J. , Jonker B. T.
Published: January 2009

We compare the electroluminescence spectra (spectral composition and polarization characteristics) of two types of Fe-based AlGaAs/GaAs n-i-p spin light emitting diodes (spin LEDs). In type A spin LEDs the GaAs quantum well (QW) does not contain any confined carriers, while in type B LEDs the GaAs QW is occupied by confined electrons generated by excess n-type doping in the AlGaAs(n) barrier. Type B LEDs show a significantly smaller circular polarization at the e1h1 feature than type A devices. Other differences include the presence of the e1ℓ1 exciton as well as excitonic phonon replicas in type B LEDs. Possible mechanisms for these differences are discussed.
Vacuum Rabi splitting with a single quantum dot embedded in a H1 photonic crystal nanocavity
Authors: Ota Yasutomo , Shirane Masayuki , Nomura Masahiro , Kumagai Naoto , Ishida Satomi , Iwamoto Satoshi , Yorozu Shinichi , Arakawa Yasuhiko
Published: January 2009

We report here the first observation of vacuum Rabi splitting in a single quantum dot (QD) embedded in a H1 photonic crystal nanocavity by photoluminescence measurement. The QD emission was tuned into a cavity mode by controlling the temperature. At the resonance condition, clear anticrossing with a Rabi splitting of ∼124 μeV was observed, where the cavity mode possesses the smallest mode volume V∼0.43(λ/n)3 among strongly coupled QD-cavity systems reported to date.
Delicate selective single particle handling with a float-sink scheme
Authors: Xu Lin , Ng Tuck Wah , Neild Adrian
Published: January 2009

Selective single particle handling with high degrees of controllability, precision, and delicateness is sought after for operations such as sorting, isolation, and placement. Here, we describe and demonstrate an approach that operates based on a droplet dispensed directly above a selected particle floating on the liquid surface to cause it to sink. The mode of sinking appears to be based on the detachment of the particle from the liquid interface with an applied force. This method offers the desired attributes of particle handling and is amenable to the incorporation of automation to speedily accomplish the selective handling of multiple particles.
Surface area of lipid membranes regulates the DNA-binding capacity of cationic liposomes
Authors: Marchini Cristina , Montani Maura , Amici Augusto , Pozzi Daniela , Caminiti Ruggero , Caracciolo Giulio
Published: January 2009

We have applied electrophoresis on agarose gels to investigate the DNA-binding capacity of cationic liposomes made of cationic DC-cholesterol and neutral dioleoylphosphatidylethanolamine as a function of membrane charge density and cationic lipid/DNA charge ratio. While each cationic liposome formulation exhibits a distinctive DNA-protection ability, here we show that such a capacity is universally regulated by surface area of lipid membranes available for binding in an aspecific manner. The relevance of DNA protection for gene transfection is also discussed.
Genetics in conservation and wildlife management: a revolution since Caughley
Authors: Sarre Stephen D. , Georges Arthur
Published: January 2009

In his 1994 review of conservation biology, Graeme Caughley questioned the central role for genetics in that discipline. His central theme was that there was no known case of genetic malfunction leading to the extinction of a population or species, and that driving forces such as overkill, habitat fragmentation and introduced predators as well as environmental and demographic stochasticity of small populations should be considered ahead of genetics in the debate about extinction prevention. At the time, only indirect and theoretical evidence existed for genetic contributions to the declines of wildlife and most of the debate revolved around the impact of genetic variation on fitness and long-term persistence. In addition, the application of DNA technologies to the study of wildlife was in its infancy. Though this was not Caughley’s intention, many within wildlife management took his criticisms of genetic aspects of species decline as the cue to dismiss this branch of science as of minor relevance to conservation biology. Since Caughley’s critique, there has been a revolution in genetic technologies for non-model organisms with the arrival of highly informative hypervariable DNA markers. Perhaps even more importantly, developments in DNA and gene technologies have provided the opportunity to study fundamental life-history traits such as disease resistance in more direct ways than previously possible. In concert with these tools, conservation geneticists have risen to Caughley’s challenge and demonstrated unambiguously a clear role for genetic analysis in conservation biology. Despite these impressive advances, there remains an important gap between the genetic approaches available and their uptake by managers. Bridging this gap will greatly increase the capacity of wildlife managers to generate the data necessary for sound management.
The nature of the TRAP–Anti-TRAP complex
Authors: Watanabe Masahiro , Heddle Jonathan G. , Kikuchi Kenichi , Unzai Satoru , Akashi Satoko , Park Sam-Yong , Tame Jeremy R. H.
Published: January 2009

Tryptophan biosynthesis is subject to exquisite control in species of
Bacillus
and has become one of the best-studied model systems in gene regulation. The protein TRAP (
trp
RNA-binding attenuation protein) predominantly forms a ring-shaped 11-mer, which binds cognate RNA in the presence of tryptophan to suppress expression of the
trp
operon. TRAP is itself regulated by the protein Anti-TRAP, which binds to TRAP and prevents RNA binding. To date, the nature of this interaction has proved elusive. Here, we describe mass spectrometry and analytical centrifugation studies of the complex, and 2 crystal structures of the TRAP–Anti-TRAP complex. These crystal structures, both refined to 3.2-Å resolution, show that Anti-TRAP binds to TRAP as a trimer, sterically blocking RNA binding. Mass spectrometry shows that 11-mer TRAP may bind up to 5 AT trimers, and an artificial 12-mer TRAP may bind 6. Both forms of TRAP make the same interactions with Anti-TRAP. Crystallization of wild-type TRAP with Anti-TRAP selectively pulls the 12-mer TRAP form out of solution, so the crystal structure of wild-type TRAP–Anti-TRAP complex reflects a minor species from a mixed population.
Gfi-1 represses
CDKN2B
encoding p15
INK4B
through interaction with Miz-1
Authors: Basu Suchitra , Liu Qingquan , Qiu Yaling , Dong Fan
Published: January 2009

Gfi-1 is a nuclear zinc finger (ZF) transcriptional repressor that plays an important role in hematopoiesis and inner ear development, and has been implicated in lymphomagenesis. Gfi-1 represses transcription by directly binding to the consensus DNA sequence in the promoters of its target genes. We report here an alternative mechanism by which Gfi-1 represses
CDKN2B
encoding p15
INK4B
. Gfi-1 does not directly bind to
CDKN2B
, but interacts with Miz-1 and, via Miz-1, is recruited to the core promoter of
CDKN2B
. Miz-1 is a POZ-ZF transcription factor that has been shown to mediate transcriptional repression by c-Myc. Like c-Myc, upon recruitment to the
CDKN2B
promoter, Gfi-1 represses transcriptional activation of
CDKN2B
by Miz-1 and in response to TGFβ. Consistent with its role in repressing
CDKN2B
transcription, knockdown of Gfi-1 in human leukemic cells or deficiency of Gfi-1 in mouse bone marrow cells results in augmented expression of p15
INK4B
. Notably, Gfi-1 and c-Myc are both recruited to the
CDKN2B
core promoter and act in collaboration to repress
CDKN2B
. Our data reveal a mechanism of transcriptional repression by Gfi-1 and may have important implications for understanding the roles of Gfi-1 in normal development and tumorigenesis.