bluuebunny/crossref_metadata_2025 huggingface dataset:
LEARNING, THE FORWARD PREMIUM PUZZLE, AND MARKET EFFICIENCY
Authors: Chakraborty Avik
Published: May 2009

The Forward Premium Puzzle is widely considered to indicate inefficiency in the foreign exchange market. This paper proposes a resolution of the puzzle using recursive least squares learning. Risk-neutral agents learn the unknown parameters, underlying the exchange rate generation process, using constant-gain recursive least squares. Simulations using plausible model parameter values replicate the anomaly along with other observed empirical features of the forward and spot exchange rate data. Estimates of parameter values from data support the model assumptions and justify the use of constant-gain learning. The conclusion is that the puzzle is not necessarily a reflection of inefficiency.
A CORRESPONDENCE-THEORETIC APPROACH TO DYNAMIC OPTIMIZATION
Authors: Aliprantis C. D. , Camera G.
Published: May 2009

This paper introduces a method of optimization in infinite-horizon economies based on the theory of correspondences. The proposed approach allow us to study time-separable and non-time-separable dynamic economic models without resorting to fixed point theorems or transversality conditions. When our technique is applied to the standard time-separable model it provides an alternative and straightforward way to derive the common recursive formulation of these models by means of Bellman equations.
A Unique Vascular Configuration among the Efferent Branchial Arteries and Splanchnic Arteries in the Yellow Stingray,Urobatis jamaicensis
Authors: Basten Bethany L. , Sherman Robin L. , Lametschwandtner Alois , Spieler Richard E.
Published: May 2009

With light and scanning electron microscopy of vascular corrosion casts, we have observed inUrobatis jamaicensisthat the fourth epibranchial arteries do not merge completely with the dorsal aorta. Instead they form a brief anastomosis with a short vessel projecting ventrally from the dorsal aorta and maintain their integrity as separately distinct vessels. Posterior to the anastomosis, the right epibranchial becomes the celiac trunk and left epibranchial becomes the anterior mesenteric artery/posterior intestinal artery. This vascular configuration appears to be unique in elasmobranchs.
Modification of Titan's ion tail and the Kronian magnetosphere: Coupled magnetospheric simulations
Authors: Winglee R. M. , Snowden D. , Kidder A.
Published: May 2009

Three‐dimensional multifluid/multiscale modeling is used to study the coupled interaction between the Kronian magnetosphere and Titan's induced magnetosphere. The multifluid aspect of the model allows ions from the solar wind, Saturn's ionosphere, Enceladus torus, and Titan's ionosphere to be tracked separately. The multiscale aspect of the model allows simultaneous resolution of global and local processes down to 100 km near Titan. In the simulation, Titan is placed in the premidnight sector at 2100 Saturn local time. Two orientations of interplanetary magnetic field (IMF) are considered: parallel and antiparallel to Saturn's planetary field. During parallel IMF, plasma conditions near Titan are relatively stable and Titan's ion tail extends to 10 Saturn radii. The ion tail produces mass loading of the Kronian plasma disk and leads to a modification of the position of the plasma sheet. During antiparallel IMF, fingers of cold dense plasma from the inner magnetosphere propagate outward, driven by the centrifugal interchange instability. Titan's interaction with the fingers causes enhanced outflow as well as large changes in the orientation of Titan's ion tail. The plasma fingers are also disrupted by the interaction with Titan. In both IMF configurations, ions lost from Titan do not produce a complete ion torus. However, Titan's ion tail has global importance because it influences the inner boundary of the plasma sheet and has the potential to modify Kronian auroral processes when it is in this position in the Kronian magnetosphere.
Multifractal analysis of geomagnetic storm and solar flare indices and their class dependence
Authors: Yu Zu‐Guo , Anh Vo , Eastes Richard
Published: May 2009

The multifractal properties of two indices of geomagnetic activity, Dst (representative of low latitudes) and ap (representative of the global geomagnetic activity), with the solar X‐ray brightness, Xl, during the period from 1 March 1995 to 17 June 2003 are examined using multifractal detrended fluctuation analysis (MF‐DFA). The h(q) curves of Dst and ap in the MF‐DFA are similar to each other, but they are different from that of Xl, indicating that the scaling properties of Xl are different from those of Dst and ap. Hence, one should not predict the magnitude of magnetic storms directly from solar X‐ray observations. However, a strong relationship exists between the classes of the solar X‐ray irradiance (the classes being chosen to separate solar flares of class X‐M, class C, and class B or less, including no flares) in hourly measurements and the geomagnetic disturbances (large to moderate, small, or quiet) seen in Dst and ap during the active period. Each time series was converted into a symbolic sequence using three classes. The frequency, yielding the measure representations, of the substrings in the symbolic sequences then characterizes the pattern of space weather events. Using the MF‐DFA method and traditional multifractal analysis, we calculate the h(q), D(q), and τ (q) curves of the measure representations. The τ (q) curves indicate that the measure representations of these three indices are multifractal. On the basis of this three‐class clustering, we find that the h(q), D(q), and τ (q) curves of the measure representations of these three indices are similar to each other for positive values of q. Hence, a positive flare storm class dependence is reflected in the scaling exponents h(q) in the MF‐DFA and the multifractal exponents D(q) and τ (q). This finding indicates that the use of the solar flare classes could improve the prediction of the Dst classes.
On the potential of recording earthquakes for global seismic tomography by low‐cost autonomous instruments in the oceans
Authors: Simons Frederik J. , Nolet Guust , Georgief Paul , Babcock Jeff M. , Regier Lloyd A. , Davis Russ E.
Published: May 2009

We describe the development and testing of an autonomous device designed to revolutionize Earth structure determination via global seismic tomography by detecting earthquakes at teleseismic distances in the oceans. One prototype MERMAID, short for Mobile Earthquake Recording in Marine Areas by Independent Divers, was constructed and tested at sea. The instrument combines two readily available, relatively low‐cost but state‐of‐the‐art components: a Sounding Oceanographic Lagrangian Observer, or SOLO float, and an off‐the‐shelf hydrophone, with custom‐built data logging hardware. We report on the development of efficient wavelet‐based algorithms for the detection and discrimination of seismic events and analyze three time series of acoustic pressure collected at a depth of 700 m in pilot experiments conducted offshore San Diego, CA. In these tests, over 120 hours of data were gathered, and five earthquakes, of which one was teleseismic, were recorded and identified. Quantitative estimates based on these results suggest that instruments of the MERMAID type may collect up to a hundred tomographically useful teleseismic events per year. The final design will also incorporate a Global Positioning System receiver, onboard signal processing software optimized for low‐power chips, and high‐throughput satellite communication equipment for telemetered data transfer. With these improvements, we hope to realize our vision of a global array of autonomous floating sensors for whole‐earth seismic tomography.
Effect of chemistry‐aerosol‐climate coupling on predictions of future climate and future levels of tropospheric ozone and aerosols
Authors: Liao Hong , Zhang Ying , Chen Wei‐Ting , Raes Frank , Seinfeld John H.
Published: May 2009

We explore the extent to which chemistry‐aerosol‐climate coupling influences predictions of future ozone and aerosols as well as future climate using the Goddard Institute for Space Studies (GISS) general circulation model II' with on‐line simulation of tropospheric ozone‐NOx‐hydrocarbon chemistry and sulfate, nitrate, ammonium, black carbon, primary organic carbon, and secondary organic carbon aerosols. Based on IPCC scenario A2, year 2100 ozone, aerosols, and climate simulated with full chemistry‐aerosol‐climate coupling are compared with those simulated from a stepwise approach. In the stepwise method year 2100 ozone and aerosols are first simulated using present‐day climate and year 2100 emissions (denoted as simulation CHEM2100sw) and year 2100 climate is then predicted using offline monthly fields of O3 and aerosols from CHEM2100sw (denoted as simulation CLIM2100sw). The fully coupled chemistry‐aerosol‐climate simulation predicts a 15% lower global burden of O3 for year 2100 than the simulation CHEM2100sw which does not account for future changes in climate. Relative to CHEM2100sw, year 2100 column burdens of all aerosols in the fully coupled simulation exhibit reductions of 10–20 mg m−2 in DJF and up to 10 mg m−2 in JJA in mid to high latitudes in the Northern Hemisphere, reductions of up to 20 mg m−2 over the eastern United States, northeastern China, and Europe in DJF, and increases of 30–50 mg m−2 over populated and biomass burning areas in JJA. As a result, relative to year 2100 climate simulated from CLIM2100sw, full chemistry‐aerosol‐climate coupling leads to a stronger net global warming by greenhouse gases, tropospheric ozone and aerosols in year 2100, with a global and annual mean surface air temperature higher by 0.42 K. For simulation of year 2100 aerosols, we conclude that it is important to consider the positive feedback between future aerosol direct radiative forcing and future aerosol concentrations; increased aerosol concentrations lead to reductions in convection and precipitation (or wet deposition of aerosols), further increasing lower tropospheric aerosol concentrations.
Impacts of background ozone production on Houston and Dallas, Texas, air quality during the Second Texas Air Quality Study field mission
Authors: Pierce R. Bradley , Al‐Saadi Jassim , Kittaka Chieko , Schaack Todd , Lenzen Allen , Bowman Kevin , Szykman Jim , Soja Amber , Ryerson Tom , Thompson Anne M. , Bhartia Pawan , Morris Gary A.
Published: May 2009

A major objective of the 2006 Second Texas Air Quality Study (TexAQS II) focused on understanding the effects of regional processes on Houston and Dallas ozone nonattainment areas. Here we quantify the contributions of background (continental scale) ozone production on Houston and Dallas air quality during TexAQS II using ensemble Lagrangian trajectories to identify remote source regions that impact Houston and Dallas background ozone distributions. Global‐scale chemical analyses, constrained with composition measurements from instruments on the NASA Aura satellite, are used to provide estimates of background composition along ensemble back trajectories. Lagrangian averaged O3 net photochemical production (production minus loss, P‐L) rates along the back trajectories are used as a metric to classify back trajectories. Results show that the majority (6 out of 9 or 66%) of the periods of high ozone in Houston were associated with periods of enhanced background ozone production. Slightly less than 50% (7 out of 15) of the days with high ozone in the Dallas Metropolitan Statistical Area (MSA) show enhanced background ozone production. Source apportionment studies show that 5‐day Lagrangian averaged O3 P‐L in excess of 15 ppbv/d can occur during continental‐scale transport to Houston owing to NOy enhancements from emissions within the Southern Great Lakes as well as recirculation of the Houston emissions. Dallas background O3 P‐L is associated with NOy enhancements from emissions within Chicago and Houston.
Springtime tropospheric temperature over the Tibetan Plateau and evolutions of the tropical Pacific SST
Authors: Nan Sulan , Zhao Ping , Yang Song , Chen Junming
Published: May 2009

Using monthly mean data from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCAR) reanalysis and HadISST SST data sets, we investigate the relationship between springtime tropospheric temperature over the Tibetan Plateau and sea surface temperature (SST) over the equatorial Pacific and the associated physical processes. When the Tibetan temperature is low (high) in spring, positive (negative) SST anomalies appear over the tropical central‐eastern Pacific in spring and summer. The relationship is explained by the Asian‐Pacific Oscillation (APO) and the ocean‐atmosphere interaction over the tropical Pacific. In the context of the APO, a lower spring Tibetan tropospheric temperature is associated with a higher tropospheric temperature over the subtropical North Pacific, which is accompanied by a weaker subtropical high over the eastern North Pacific. Accordingly, large‐scale westerly anomalies appear in the lower troposphere of the equatorial central‐eastern Pacific, resulting in an increase in SST over the equatorial central‐eastern Pacific. Numerical simulations with both an ocean‐atmosphere coupled model (the NCAR Community Climate System Model version 3) and an atmospheric model with a prescribed SST scheme (the NCAR Community Atmospheric Model version 3) demonstrate the impacts of the spring Tibetan thermal condition on the tropospheric temperature and atmospheric circulation over the Asian‐Pacific sector and then on the SST over the equatorial eastern Pacific, better explaining the physical processes of the observed Tibetan temperature–Pacific SST relationship.
Diminished mercury emission from waters with duckweed cover
Authors: Wollenberg Jennifer L. , Peters Stephen C.
Published: May 2009

Duckweeds (Lemnaceae) are a widely distributed type of floating vegetation in freshwater systems. Under suitable conditions, duckweeds form a dense vegetative mat on the water surface, which reduces light penetration into the water column and limits gas exchange at the water‐air interface by decreasing the area of open water surface. Experiments were conducted to determine whether duckweed decreases mercury emission by limiting gas diffusion across the water‐air interface and attenuating light, or, conversely, enhances emission via transpiration of mercury vapor. Microcosm flux chamber experiments indicate that duckweed decreases mercury emission from the water surface compared to open water controls. Fluxes under duckweed were 17–67% lower than in controls, with lower fluxes occurring at higher percent cover. The decrease in mercury emission suggests that duckweed may limit emission through one of several mechanisms, including limited gas transport across the air‐water interface, decreased photoreactions due to light attenuation, and plant‐mercury interactions. The results of this experiment were applied to a model lake system to illustrate the magnitude of potential effects on mercury cycling. The mercury retained in the lake as a result of hindered emission may increase bioaccumulation potential in lakes with duckweed cover.
Canadian High Arctic Ionospheric Network (CHAIN)
Authors: Jayachandran P. T. , Langley R. B. , MacDougall J. W. , Mushini S. C. , Pokhotelov D. , Hamza A. M. , Mann I. R. , Milling D. K. , Kale Z. C. , Chadwick R. , Kelly T. , Danskin D. W. , Carrano C. S.
Published: May 2009

Polar cap ionospheric measurements are important for the complete understanding of the various processes in the solar wind‐magnetosphere‐ionosphere system as well as for space weather applications. Currently, the polar cap region is lacking high temporal and spatial resolution ionospheric measurements because of the orbit limitations of space‐based measurements and the sparse network providing ground‐based measurements. Canada has a unique advantage in remedying this shortcoming because it has the most accessible landmass in the high Arctic regions, and the Canadian High Arctic Ionospheric Network (CHAIN) is designed to take advantage of Canadian geographic vantage points for a better understanding of the Sun‐Earth system. CHAIN is a distributed array of ground‐based radio instruments in the Canadian high Arctic. The instrument components of CHAIN are 10 high data rate Global Positioning System ionospheric scintillation and total electron content monitors and six Canadian Advanced Digital Ionosondes. Most of these instruments have been sited within the polar cap region except for two GPS reference stations at lower latitudes. This paper briefly overviews the scientific capabilities, instrument components, and deployment status of CHAIN. This paper also reports a GPS signal scintillation episode associated with a magnetospheric impulse event. More details of the CHAIN project and data can be found at http://chain.physics.unb.ca/chain.
Regionalization of transit time estimates in montane catchments by integrating landscape controls
Authors: Hrachowitz M. , Soulsby C. , Tetzlaff D. , Dawson J. J. C. , Malcolm I. A.
Published: May 2009

Mean transit time (MTT) is being increasingly used as a metric of hydrological function in intercatchment comparisons. Estimating MTT usually involves relating the temporally varying input concentration of a conservative tracer to the signal in the stream using various transfer functions as transit time distributions (TTDs). Most studies have been confined to data collection periods of 1–2 years at single sites, often limiting the transferability of the findings as such short periods usually only capture a narrow range of climatic variability within a spatially restricted area. In this study, we use longer‐term (up to 17 years) weekly input‐output relationships of Cl−to estimate MTTs using a range of TTD models in 20 headwater catchments (ranging from <1 to 35 km2) in seven geomorphologically and climatically distinct parts of the Scottish Highlands. The MTTs obtained from a Gamma distribution model were the best identified and ranged from about 50 to 1700 days for individual catchments. The MTTs, in conjunction with GIS analysis of landscape characteristics and climatic indices, allowed the development of a robust multiple‐regression model to establish the relative importance of different landscape and climate controls on MTTs. The best model combines the prediction variables percent responsive soil cover, drainage density, precipitation intensity, and topographic wetness index and yieldsR2adj= 0.88. Cross validation shows small absolute error, suggesting that the model can be used to estimate MTTs in ungauged headwater catchments throughout the Scottish Highlands and potentially in similar regions where comparable information is available.
Gondwana breakup and plate kinematics: Business as usual
Authors: Eagles Graeme , Vaughan Alan P. M.
Published: May 2009

A tectonic model of the Weddell Sea is built by composing a simple circuit with optimized rotations describing the growth of the South Atlantic and SW Indian oceans. The model independently and accurately reproduces the consensus elements of the Weddell Sea's spreading record and continental margins, and offers solutions to remaining controversies there. At their present resolutions, plate kinematic data from the South Atlantic and SW Indian oceans and Weddell Sea rule against the proposed, but controversial, independent movements of small plates during Gondwana breakup that have been attributed to the presence or impact of a mantle plume. Hence, although supercontinent breakup here was accompanied by extraordinary excess volcanism, there is no indication from plate kinematics that the causes of that volcanism provided a unique driving mechanism for it.
Thermal phase curves observed in Saturn's main rings by Cassini‐CIRS: Detection of an opposition effect?
Authors: Altobelli N. , Spilker L. , Pilorz S. , Leyrat C. , Eddgington S. , Wallis B. , Flandes A.
Published: May 2009

We report on thermal phase curve measurements of Saturn's main rings by the CIRS infrared spectrometer on‐board the CASSINI spacecraft. The extensive data set acquired by Cassini since its insertion in orbit around Saturn provides for the first time spatially resolved temperature measurements over broad phase angle ranges and for different solar elevations. Each of these curves exhibit a nonlinear variation in temperature with phase angle, with pronounced surges at medium to low phase angles that we interpret as an opposition effect in thermal infrared. The transition from a relatively flat linear regime to an exponential behavior in the A and B rings occurs at phase angles of 30° to 40° and is significantly broader in the C ring and Cassini Division. Analytical description of the phase curves is provided to serve as basis for future modeling work. The role played by mutual shadowing as possible origin of the broad thermal surge in thicker ring regions is emphasized. In turn, regolith properties might be inferred from the thermal phase curves in the optically thin ring regions.
Solution structure of the Mesorhizobium loti K1 channel cyclic nucleotide‐binding domain in complex with cAMP
Authors: Schünke Sven , Stoldt Matthias , Novak Kerstin , Kaupp U Benjamin , Willbold Dieter
Published: May 2009

Cyclic nucleotide‐sensitive ion channels, known as HCN and CNG channels, are crucial in neuronal excitability and signal transduction of sensory cells. HCN and CNG channels are activated by binding of cyclic nucleotides to their intracellular cyclic nucleotide‐binding domain (CNBD). However, the mechanism by which the binding of cyclic nucleotides opens these channels is not well understood. Here, we report the solution structure of the isolated CNBD of a cyclic nucleotide‐sensitive K+ channel from Mesorhizobium loti. The protein consists of a wide anti‐parallel β‐roll topped by a helical bundle comprising five α‐helices and a short 310‐helix. In contrast to the dimeric arrangement (‘dimer‐of‐dimers’) in the crystal structure, the solution structure clearly shows a monomeric fold. The monomeric structure of the CNBD supports the hypothesis that the CNBDs transmit the binding signal to the channel pore independently of each other.
An Interdisciplinary Treatment Approach for Soldiers With TBI/PTSD: Issues and Outcomes
Authors: Schneider Sandra L. , Haack Lisa , Owens Jenny , Herrington Dominique P. , Zelek Anita
Published: May 2009

Purpose: While the co-morbidity of symptoms associated with traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) in the injured military population is currently being discussed and researched, those of us in the rehabilitation fields need to be ready now to serve this complex population. We are challenged to provide the best services with limited research and evidence-based practices to guide us. This article presents an interdisciplinary approach to treatment for soldiers with TBI.

Method: We compare and contrast the blast-induced brain injury acquired in the military population, designated as the “signature injury of this war,” to “typical” TBI populations.

Results and conclusions: We share what we have learned by serving this population and present each discipline's assessments, treatment strategies, outcome measures, and suggestions for navigating the military “mindset” of the soldiers being served.
Effects of defect permittivity on resonant frequency and mode shape in the three-dimensional woodpile photonic crystal
Authors: Stieler Daniel , Barsic Anthony , Tuttle Gary , Li Ming , Ho Kai-Ming
Published: May 2009

Tuning the resonant frequency of a 1uc defect across the bandgap of a three-dimensional woodpile photonic crystal (PC) was achieved by altering the defect’s permittivity. Experiments were performed at microwave frequencies and calculations were made using the transfer-scattering matrix method. Defect permittivity was varied by using solid materials of different permittivities or by constructing structures smaller than a lattice constant from the the PC lattice materials. These small structures, which will be referred to as “sublattice defects,” produce an effective permittivity between their two materials’ permittivities. Changes in mode shape with resonant frequency and permittivity were also examined.
Analysis of individual magnetic particle motion near a chip surface
Authors: van Ommering Kim , Lamers Carolien C. H. , Nieuwenhuis Jeroen H. , van IJzendoorn Leo J. , Prins Menno W. J.
Published: May 2009

We describe an analysis of the dynamics of individual superparamagnetic micro- and nanoparticles in order to quantify their magnetic properties and mobility near a chip surface. The particles are attracted to the chip surface by integrated microscopic current wires. We show that it is possible to accurately analyze particles with a diameter of about 1 μm by the magnetophoretic movement between current wires because of the very high field gradients. This reveals distinct differences in volume susceptibilities of particles with the same outer diameter. Smaller particles are characterized using the technique of confined Brownian motion analysis. By capturing 300 nm particles on a current wire with surface barriers or a focused shape, the magnetization of the particles can be measured with an accuracy better than 10%.
Fracture in electrophoretically deposited CdSe nanocrystal films
Authors: Jia Shengguo , Banerjee Sarbajit , Lee Dongyun , Bevk Joze , Kysar Jeffrey W. , Herman Irving P.
Published: May 2009

We have studied the fracture, strain, and stress of electrophoretically deposited (EPD) films of CdSe nanocrystals as a function of the film thickness, nanocrystal size, and drying method. Fracture results from the film stress that develops with the loss of residual solvent after EPD when the film exceeds a threshold thickness that increases with nanocrystal core diameter from ∼300 to 1200 nm for core diameters from 2.3 to 5.0 nm, respectively. A hierarchical pattern of wider first generation and then narrower higher-generation cracks is observed after drying and this generational crack formation and a preferred direction for film drying are observed in real time. Delamination is seen to initiate from wider cracks, mostly between the bulk of the film and a very thin layer of nanocrystals strongly bound to the Au-coated silicon substrate. Estimates of the film toughness are made for channel cracking and delamination.
A multiple phase demodulation method for high resolution of the laser scanner
Authors: Yoon Heesun , Yeom Woosub , Kang Seonggu , Hong Jinpyo , Park Kyihwan
Published: May 2009

To have higher resolution of distance in the laser scanner using the phase demodulation method, signal should be modulated with a high frequency. In the signal processing of modulation and demodulation, it is inevitable to amplify the signals. However, it is not easy to amplify the high frequency since the amplifying gain is restricted by the frequency bandwidth. It is advantageous to demodulate using an intermediate frequency in which high gain amplification as well as less contaminated signal is obtained. Analytical and experimental results are presented to show how the intermediate frequency demodulation method works and how good performance is obtained in the time and frequency domains.
Structural, electronic, and vibrational properties of high-density amorphous silicon: A first-principles molecular-dynamics study
Authors: Morishita Tetsuya
Published: May 2009

We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be ∼5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).
Multicolor upconversion and color tunability in Tm3+/Ho3+/Yb3+ doped opaque aluminum tellurite ceramics
Authors: Sun L. X. , Gong H. , Chen B. J. , Lin H. , Pun E. Y. B.
Published: May 2009

Rare earth doped opaque aluminum tellurite ceramics exhibiting multicolor upconversion and color tunability have been synthesized and characterized. The multicolor fluorescence comprises of green, red, and blue upconversion emissions from Ho3+ and Tm3+ ions. By varying the intensity ratios between the upconversion emission bands, the fluorescence color can be tuned from multicolor to white color by changing the infrared wavelength pump power. The fluorescence color tunability in Ho3+/Tm3+/Yb3+ triply doped aluminum tellurite ceramics will lead to new applications in the field of multicolor fluorescence technology.
Comparison of output power of InGaN laser diodes for different Al compositions in the AlGaN n-cladding layer
Authors: Ryu H. Y. , Ha K. H. , Son J. K. , Paek H. S. , Sung Y. J. , Kim K. S. , Kim H. K. , Park Y. , Lee S. N. , Nam O. H.
Published: May 2009

The output power of InGaN multiple-quantum-well laser diodes (LDs) emitting at 405 nm wavelength is compared for several Al composition in the AlGaN n-cladding layer. The Al composition has been varied from 2% to 6% to study the effect of n-cladding refractive index on threshold current and slope efficiency of the LDs. As the Al composition in the AlGaN n-cladding layer increases, both threshold current and slope efficiency decrease. This behavior can be explained by the change in optical field distribution with refractive index of the AlGaN n-cladding layer. It is found that the Al composition of ≤4% would be advantageous for achieving more than 100 mW output power and high level of catastrophic optical damage.
Nature of ferroelectricity in nonperovskite semiconductors like ZnO:Li
Authors: Glinchuk M. D. , Kirichenko E. V. , Stephanovich V. A. , Zaulychny B. Y.
Published: May 2009

We show that in nontypical ferroelectric substances (having nonperovskite crystalline structure and hence no soft phonon mode) such as ZnO:Li, Be, Mg, the ferroelectricity might appear due to indirect interaction of dipoles, formed by Li, Be, or Mg off-center impurities, via free charge carriers. Our estimations show that the typical semiconducting concentration of the carriers like 1017 cm−3 suffices for effect to occur. We have also shown that the properties of impurity-generated ferroelectricity depend on the difference in the ionic radii of the impurity and host lattice ion as well as on their concentrations. Namely, the growing amount of Li and Be promotes ferroelectricity, while the same for Mg inhibits it. Our calculations of spontaneous polarization and ferroelectric phase transition temperature in the above nontypical ferroelectrics as the functions of concentrations of impurity dipoles and carriers capture well the main peculiarities of all available experimental data.
Activation energy of heterojunction diode currents in the limit of interface recombination
Authors: Scheer R.
Published: May 2009

In this paper, we treat diode currents caused by Shockley–Read–Hall recombination at the interface of pn heterojunctions. We are interested in the activation energy of the saturation current. To this end, we discriminate the cases of ΔEc,v≤0 and ΔEc,v>0, where ΔEc,v is the band offset in the minority carrier band of the small band gap heteropartner, as well as the case of Fermi level pinning. Using analytical considerations, we find that the activation energy of the saturation current equals the band gap of the small band gap heteropartner for ΔEc,v>0 but equals the interface band gap for ΔEc,v≤0. In the case of Fermi level pinning, the value of the potential barrier of the small band gap minority carrier equals the activation energy. These findings serve to discriminate different cases of interface recombination and to give information about the heterojunction energy band diagram.
Enhanced photoluminescence caused by localized excitons observed in MgZnO alloy
Authors: Zhu H. , Shan C. X. , Li B. H. , Zhang Z. Z. , Zhang J. Y. , Yao B. , Shen D. Z. , Fan X. W.
Published: May 2009

Temperature-dependent photoluminescence of MgZnO alloy film has been studied, and it is found that the emission intensity increases significantly at a certain temperature range and then decreases when increasing temperature further. The anomalous increase is resulted from the localized excitons in MgZnO alloy, as revealed by the enhanced second-order longitudinal optical phonon in the Raman spectrum of the MgZnO film. A schematic model was suggested to depict the carrier transportation process in the MgZnO film considering the existence of localized exciton states. The results reported in this paper indicate that localized excitons in MgZnO alloy can result in greatly enhanced emission efficiency, which is eagerly wanted for the application of ZnO-based materials in high-efficiency light-emitting devices.
Semiconductor-based superlens for subwavelength resolution below the diffraction limit at extreme ultraviolet frequencies
Authors: Vincenti M. A. , D’Orazio A. , Cappeddu M. G. , Akozbek Neset , Bloemer M. J. , Scalora M.
Published: May 2009

We theoretically demonstrate negative refraction and subwavelength resolution below the diffraction limit in the UV and extreme UV ranges using semiconductors. The metal-like response of typical semiconductors such as GaAs or GaP makes it possible to achieve negative refraction and superguiding in resonant semiconductor/dielectric multilayer stacks, similar to what has been demonstrated in metallodielectric photonic band gap structures. The exploitation of this basic property in semiconductors raises the possibility of yet-untapped applications in the UV and soft x-ray ranges.
Photoinduced conductivity in tin dioxide thin films
Authors: Muraoka Y. , Takubo N. , Hiroi Z.
Published: May 2009

The effects of ultraviolet light irradiation on the conducting properties of SnO2−x thin films grown epitaxially on TiO2 or Al2O3 single-crystal substrates are studied at room temperature. A large increase in conductivity by two to four orders of magnitude is observed with light irradiation in an inert atmosphere and remains after the light is removed. The high-conducting state reverts to the original low-conducting state by exposing it to oxygen gas. These reversible phenomena are ascribed to the desorption and adsorption of negatively charged oxygen species at the grain boundaries, which critically change the mobility of electron carriers already present inside grains by changing the potential barrier height at the grain boundary. The UV light irradiation provides us with an easy and useful route to achieve a high-conducting state even at low carrier density in transparent conducting oxides and also to draw an invisible conducting wire or a specific pattern on an insulating film.
Coherency of su(1,1)-Barut–Girardello type and entanglement for spherical harmonics
Authors: Fakhri H. , Dehghani A.
Published: May 2009

Barut–Girardello coherent states corresponding to the (l−m)- and (l+m)-integer discrete irreducible representations of su(1,1) Lie algebra are calculated by the spherical harmonics Ylm(θ,ϕ). Their explicit compact forms and also, to realize the resolution of the identity, their corresponding positive definite measures on the complex plane are obtained in terms of the known functions. It is also shown that coherent states of both positive and negative representations separately lead us to construct new representation bases for su(1,1) Lie algebra. Then, it is shown that the su(1,1)-Barut–Girardello coherent states corresponding to two particles containing the spatial parity symmetries of a bipartite quantum system can be entangled in ten different ways.
Comparison of kinetic and thermodynamic parameters of single crystal pentaerythritol tetranitrate using atomic force microscopy and thermogravimetric analysis: Implications on coarsening mechanisms
Authors: Burnham Alan K. , Qiu S. R. , Pitchimani Rajasekar , Weeks Brandon L.
Published: May 2009

Pentaerythritol tetranitrate (PETN) is a secondary energetic material generally used in initiators for industrial and government applications. Changes in the morphology and surface area of aging powders have been observed during aging, which can modify the initiability and performance. Here work is presented using two different techniques to determine kinetic and thermodynamic parameters of single crystal PETN. Atomic force microscopy is used for low-temperature analysis, while thermogravimetric analysis is used at higher temperatures. A mechanism is proposed to expand the understanding of coarsening observed in real world PETN.
High coercivity in nanocrystalline Nd25Fe40Co20Al10B5 prepared by out-of-equilibrium techniques
Authors: Ky V. H. , Bessais L. , Djéga-Mariadassou C. , Phuc N. X.
Published: May 2009

Nd 25 Fe 40 Co 20 Al 10 B 5 was prepared by high-energy milling and melt-spinning techniques. The as-milled and as-quenched samples were subsequently annealed in a temperature range from 400to1100°C for 20min. For the annealed samples, x-ray diffraction combined with high-resolution transmission microscopy show the presence of ferromagnetic Nd2(Fe,Co,Al)14B crystallites coexisting with antiferromagnetic Nd6(Fe,Co,Al)14 ones, among an amorphous matrix. After annealing, coercivities of about 22 and 25kOe can be reached with the high-energy milled and melt-spun samples, respectively, while the Curie temperature of both samples reaches 660K.
Electronic and magnetic properties of graphene absorbed with S atom: A first-principles study
Authors: Zhou Y. G. , Zu X. T. , Gao F. , Xiao H. Y. , Lv H. F.
Published: May 2009

Stable configuration, electronic structures, and magnetic behaviors for S adsorption on graphene have been investigated by first-principles calculations. It is found that the adsorption site of S on graphene is coverage dependent. As the increase in coverage from 0 to 0.5 ML, the preferred site is changed from bridge to hollow site. For the adsorption of S at bridge site, no magnetic moment is detected, and the adsorption is characterized by strong hybridization between the S 2s state and graphene σ states. For the adsorption of S at hollow site, a magnetic moment of 1.98μB was induced. In this case, the hybridization occurs between S 2p states and graphene π states. Furthermore, from the investigation of the surface potential energy curve, we find that graphene is a suitable candidate for the S storage.
Thermal buckling of double-walled carbon nanotubes
Authors: Hsu Jung-Chang , Lee Haw-Long , Chang Win-Jin
Published: May 2009

The thermal buckling of an armchair double-walled carbon nanotube (DWCNT), which is subjected to axial compression due to temperature rise, is derived and analyzed based on Timoshenko beam model, including transverse shear deformation and rotary inertia. According to the analysis, the effect of van der Waals force between the nanotubes on the critical buckling temperature of mode 1 of armchair DWCNT is significant, especially for smaller diameter nanotubes. The van der Waals force makes the DWCNT stiffer and increases the buckling temperature. In addition, the effect of shear deformation and rotary inertia on the buckling temperature is more obvious for the higher-order modes. The critical buckling temperature ratio of a Timoshenko beam to a Euler beam for the armchair DWCNT significantly decreases with increasing the diameter and mode number. Therefore, for the higher-order modes, the Timoshenko beam model is able to predict the critical buckling temperature of larger diameter DWCNT.
Electromechanical characterization of Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals as a function of crystallographic orientation and temperature
Authors: Zhang Shujun , Luo Jun , Hackenberger Wesley , Sherlock Nevin P. , Meyer Richard J. , Shrout Thomas R.
Published: May 2009

Relaxor based Pb(In0.5Nb0.5)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary single crystals (PIN-PMN-PT) were reported to have broader temperature usage range (TR-T) and comparable piezoelectric properties to Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) crystals. In this work, the orientation dependent dielectric, piezoelectric and electromechanical properties for PIN-PMN-PT crystals were investigated along ⟨001⟩ and ⟨110⟩ directions. The electromechanical couplings k33 and k32 for ⟨110⟩ poled crystals were found to be 0.91 and 0.91, respectively, with piezoelectric coefficients d33 and d32 on the order of 925 and −1420 pC/N. Of particular significance was the mechanical quality factor Q33 for ⟨110⟩ oriented crystals, which was found to be ≥500, much higher than the Q values of ⟨001⟩ oriented relaxor-PT crystals (Q∼70–200). The temperature dependence of the piezoelectric properties exhibited good temperature stability up to their ferroelectric phase transition TR-T∼125 °C, indicating ⟨001⟩ and ⟨110⟩ oriented PIN-PMN-PT are promising materials for transducer applications, with the latter for high power resonant devices where low loss (high Q) was required.
Magnetism of hexagonal closed-packed Ni nanowires from ab initio calculations
Authors: Cheng Zhida , Zhu Jing , Tang Zheng
Published: May 2009

Hexagonal closed-packed (hcp) nickel has only been discovered in nanostructures. In this work, systematic ab initio calculations have been applied to study nickel nanowires with hexagonal close-packed structure in diameters of up to 2.2 nm. For all comparable nickel nanowires in our calculations, the hcp nanowire with [0001] axial direction is energetically favored against fcc nanowire with [111] axial direction. In hcp nickel nanowires, ferromagnetism is found existing at ground state and surface atoms of the nanowires are found having larger magnetic moments than core atoms have.
Modulational instability and exact solutions for a three-component system of vector nonlinear Schrödinger equations
Authors: Yomba Emmanuel , Sell George R.
Published: May 2009

The modulational instability (MI) of the three-component system of vector nonlinear Schrödinger equations is investigated. It is found that there are a number of possibilities for the MI regions due to the generalized nonlinear dispersion relation, which relates the frequency and the wave number of modulating perturbations. Some classes of exact traveling wave solutions are obtained. Under some special parameter values, some representative wave structures are graphically displayed. These solutions are obtained by the use of F-expansion method.
A Monte Carlo study of crowding effects on the self-assembly of amphiphilic molecules
Authors: Zheng Fengxian , Chen Guangjin , Zhang Xianren , Wang Wenchuan
Published: May 2009

In this work, lattice Monte Carlo was used to study the effects of crowding on the self-assembly of surfactants. Simulation results show that crowding strongly shifts the critical micelle concentration (CMC) of surfactants from the bulk value. Two effects originated from crowding are found to govern the CMC shift: one is the depletion effect by crowding agents and the other is the available volume for micelle formation. The depletion effects inevitably result in the enrichment of surfactants in crowding-free regions and cause the decrease in CMC. On the other hand, the appearance of crowding agents decreases the available volume for micelle formation, which reduces the conformational entropy and impedes the micelle formation. Three factors, including the radius of crowding agents, the arrangement of crowding agents, and the volume fraction of crowding agents, are considered in this work to study the crowding effects. The trends of CMC shifts are interpreted from the competition between the depletion effects and the available volume for micelle formation.
A comprehensive gyrokinetic description of global electrostatic microinstabilities in a tokamak
Authors: Chowdhury J. , Ganesh R. , Brunner S. , Vaclavik J. , Villard L. , Angelino P.
Published: May 2009

It is believed that low frequency microinstabilities such as ion temperature gradient (ITG) driven modes and trapped electron modes (TEMs) are largely responsible for the experimentally observed anomalous transport via the ion and electron channels in a tokamak. In the present work, a comprehensive global linear gyrokinetic model incorporating fully kinetic (trapped and passing) electrons and ions, actual ion to electron mass ratio, radial coupling, and profile variation is used to investigate the ITG driven modes and pure TEMs. These modes are found to exhibit multiscale structures in the presence of nonadiabatic passing electrons. The multiscale structure is related to the large nonadiabaticity of electrons in the vicinity of mode rational magnetic surfaces and leads to reduced mixing length estimates of transport compared to those obtained from adiabatic electron models.
Competing A-site and B-site driven ferroelectric instabilities in the (1−x)PbTiO3-(x)BiAlO3 system
Authors: Kalyani Ajay Kumar , Garg Rohini , Ranjan Rajeev
Published: May 2009

The system (1−x)PbTiO3-(x)BiAlO3 has been investigated with regard to its solid solubility, crystal structure, microstructure, and ferroelectric transition. The unit cell volume and the tetragonality exhibit anomalous behavior near x=0.10. The Curie point (TC) of PbTiO3 was however found to be nearly unchanged. The study seems to suggest that the decrease in the stability of the ferroelectric state due to dilution of the Ti-sublattice by smaller sized Al+3 ions is compensated by the increase in the ferroelectric stability by the Bi+3 ions.
Interfacial electronic structures of C60 molecules on a K-doped CuPc surface
Authors: Cheng Chiu-Ping , Chen Wen-Yen , Wei Ching-Hsuan , Pi Tun-Wen
Published: May 2009

The evolution of interfacial electronic structures of C60 on a K-doped CuPc surface is studied via synchrotron-radiation photoemission spectroscopy. Layer-by-layer growth has been identified. As the heterointerface formed, the K diffuses into the C60 overlayer, and transfers negative charge into the lowest unoccupied molecular orbital (LUMO) of C60, resulting in a significant interfacial dipole potential. With K doping, increased photon absorption, due to the existence of gap states, and an enhanced energy-level difference between the LUMO of C60 and the highest occupied molecular orbital of CuPc could possibly improve the efficiency of organic photovoltaic devices.
Energy barriers at interfaces between (100) InxGa1−xAs (≤x≤0.53) and atomic-layer deposited Al2O3 and HfO2
Authors: Afanas’ev V. V. , Stesmans A. , Brammertz G. , Delabie A. , Sionke S. , O’Mahony A. , Povey I. M. , Pemble M. E. , O’Connor E. , Hurley P. K. , Newcomb S. B.
Published: May 2009

The electron energy band alignment at interfaces of InxGa1−xAs (0≤x≤0.53) with atomic-layer deposited insulators Al2O3 and HfO2 is characterized using internal photoemission and photoconductivity experiments. The energy of the InxGa1−xAs valence band top is found to be only marginally influenced by the semiconductor composition. This result suggests that the known bandgap narrowing from 1.42 to 0.75 eV when the In content increases from 0 to 0.53 occurs mostly through downshift of the semiconductor conduction band bottom. It finds support from both electron and hole photoemission data. Similarly to the GaAs case, electron states originating from the interfacial oxidation of InxGa1−xAs lead to reduction in the electron barrier at the semiconductor/oxide interface.