bluuebunny/crossref_metadata_2025 huggingface dataset:
Telltale wind indicator for the Mars Phoenix lander
Authors: Gunnlaugsson H. P. , Holstein‐Rathlou C. , Merrison J. P. , Knak Jensen S. , Lange C. F. , Larsen S. E. , Madsen M. B. , Nørnberg P. , Bechtold H. , Hald E. , Iversen J. J. , Lange P. , Lykkegaard F. , Rander F. , Lemmon M. , Renno N. , Taylor P. , Smith P.
Published: June 2008

The Telltale wind indicator is a mechanical anemometer designed to operate on the Martian surface as part of the meteorological package on the NASA Phoenix lander. It consists of a lightweight cylinder suspended by Kevlar fibers and is deflected under the action of wind. Imaging of the Telltale deflection allows the wind speed and direction to be quantified and image blur caused by its oscillations provides information about wind turbulence. The Telltale will primarily support surface operations by documenting the wind conditions to improve the efficiency of sample delivery to instruments on the lander deck. During the latter stages of the mission the Telltale investigation will focus on meteorological studies.
Heat exchanges in the heterothermic zone of a karst system: Monlesi cave, Swiss Jura Mountains
Authors: Luetscher Marc , Lismonde Baudouin , Jeannin Pierre‐Yves
Published: June 2008

Subsurface ice accumulations in temperate karst environments are assumed to be highly sensitive to external climate forcing and therefore represent a favorable setting for studying processes controlling heat exchanges in the heterothermic zone of a karst system. Air, rock, water, and ice temperatures were measured and complemented by airflow, water discharge, and cave air humidity data during a case study carried out between 2001 and 2006 at Monlesi ice cave in the Swiss Jura Mountains. The energy balance of the system could be quantified for an annual cycle, and results demonstrate that forced convection, which is controlled by the temperature difference between the cave air and the external atmosphere, is a driving force for the heat exchange between the cave and the surrounding environment. Therefore compared to the external mean annual conditions, major thermal anomalies are to be expected in the entrance zone of a cave system. Since this heterothermic zone may extend over several hundreds of meters, a better understanding of the mechanisms controlling the subsurface deposition environment represents a major prerequisite for high‐resolution paleoenvironmental reconstructions from cave deposits.
Isochron dating of sediments using luminescence of K‐feldspar grains
Authors: Li Bo , Li Sheng‐Hua , Wintle Ann G. , Zhao Hui
Published: June 2008

A new method for dating well‐bleached sediments is presented, with results for thirteen samples from China. The method uses an isochron constructed from the measurement of natural radiation doses received by potassium‐feldspar grains in a range of grain sizes using the infrared stimulated luminescence (IRSL) signal. The age of deposition of the sediment is calculated from this isochron and from the internal dose rate to the grains from40K and87Rb in the crystal lattice. This procedure appears to overcome age underestimation due to anomalous fading, a phenomenon that has precluded conventional luminescence dating of K‐feldspars and would be applicable to K‐feldspars for which the natural dose is beyond the linear dose response region. Also, since the isochron IRSL method is reliant on only the internal dose rate, it overcomes problems related to (1) changes in past dose rate due to postdepositional migration of radionuclides, (2) changes in water content as water‐lain sediments dry out, (3) spatial heterogeneity in the gamma dose rate, and (4) uncertainties in the cosmic ray dose rate during the period of sample burial.
On the definition of seasons in paleoclimate simulations with orbital forcing
Authors: Timm Oliver , Timmermann Axel , Abe‐Ouchi Ayako , Saito Fuyuki , Segawa Tomonori
Published: June 2008

Orbital forcing is a major driver of climate variability on timescales of 10,000 to 100,000 years. Changes in the orbital parameters cause variations in the length of the seasons by several days. Consequently, models using a fixed present‐day calendar result in biased paleoseasons, especially in boreal autumn when the vernal equinox is used as an anchor point. The bias is estimated for temperatures and precipitation in a transient model simulation over the last 21,000 years and an accelerated simulation over the last 129,000 years. The largest differences of up to 4 K occur over the continents in high latitudes. Precipitation estimates are mostly affected in the low latitudes. The time‐dependent bias is large enough to modify the temporal characteristics of temperature and precipitation indices. It is discussed to what extent the bias in one season is distorting comparisons between models and paleoproxies. The bias has minor implications for proxy‐model comparisons in general. However, proxies of monsoon activity should be compared with fixed angular seasons. For process studies and climate sensitivity studies the use of fixed angular seasons is imperative.
Geometrical and Taylor dispersion in a fracture with random obstacles: An experimental study with fluids of different rheologies
Authors: Boschan A. , Ippolito I. , Chertcoff R. , Auradou H. , Talon L. , Hulin J. P.
Published: June 2008

The miscible displacement of a Newtonian or shear‐thinning fluid by another one of same rheological properties has been studied optically in a flat transparent model fracture with a random distribution of identical cylindrical obstacles on one of the walls. At the local scale, the concentration variation on individual pixels satisfies a Gaussian convection‐dispersion relation with local transit time (x, y) and dispersivity ld(x, y). The variation of ld with the Péclet number Pe shows that it results from a combination of geometrical and Taylor dispersion, respectively dominant at low and high Pe values. Using shear‐thinning solutions instead of a Newtonian fluid enhances the velocity contrasts (and therefore geometrical dispersion) and reduces Taylor dispersion. At the global scale, the front geometry is studied from the isoconcentration lines c = 0.5 (equivalent to lines of constant (x, y) value): beyond a transition travel time, their width in the direction parallel to the flow reaches a constant limit varying linearly with Log(Pe) with a slope increasing with the shear‐thinning character of the fluid. These characteristics are compared to previous observations on other model fractures with a self‐affine roughness displaying channelization effects.
Amount of CO2 emissions irreversibly leading to the total melting of Greenland
Authors: Charbit S. , Paillard D. , Ramstein G.
Published: June 2008

The long‐term response of Greenland to anthropogenic warming is of critical interest for the magnitude of the sea‐level rise and for climate‐related concerns. To explore its evolution over several millennia we use a climate‐ice sheet model forced by a range of CO2 emission scenarios, accounting for the natural removal of anthropogenic CO2 from the atmosphere. Above 3000 GtC, the melting appears irreversible, while below 2500 GtC, Greenland only experiences a partial melting followed by a re‐growth phase. Delaying emissions through sequestration slows significantly the melting, but has only a limited impact on the ultimate fate of Greenland. Its behavior is therefore mostly dependent on the cumulative CO2 emissions. This study demonstrates that the fossil fuel emissions of the next century will have dramatic consequences on sea‐level rise for several millennia.
InSAR slip rate determination on the Altyn Tagh Fault, northern Tibet, in the presence of topographically correlated atmospheric delays
Authors: Elliott J. R. , Biggs J. , Parsons B. , Wright T. J.
Published: June 2008

The interseismic strain across the Altyn Tagh Fault at 85°E has been measured using 59 interferograms from 26 ERS‐1/2 SAR acquisitions on a single track for the period 1993–2000. Using an atmospheric delay correction that scales linearly with height, we estimate the left‐lateral strike‐slip motion to be 11 ±1σ 5 mm/yr, assuming no relative vertical motion and a 15 km fault locking depth. This is in agreement with sparse GPS measurements. The atmospheric delay corrections agree well with coarse contemporaneous modelled weather data, reinforcing the importance of correcting for atmospheric delays in InSAR studies of interseismic strain accumulation, particularly in areas of high topographic relief that strongly correlate with the expected tectonic signal. We also find that, in addition to the tropospheric water vapour ‘wet’ delay, the hydrostatic ‘dry’ delay makes a significant contribution to the signal.
Influences of Typhoon Chanchu on the 2006 South China Sea summer monsoon onset
Authors: Mao Jiangyu , Wu Guoxiong
Published: June 2008

This study reveals some unique features associated with the impact of Typhoon Chanchu on the South China Sea (SCS) summer monsoon (SCSSM) onset in 2006. With Typhoon Chanchu entering the SCS in mid‐May, southwesterlies were induced over the SCS and its upstream region due to a thermally forced Rossby wave response, leading to a reversal of low‐level winds and a positive meridional temperature gradient (MTG) in the upper troposphere over the SCS. Typhoon Chanchu thus acted as an immediate trigger for the SCSSM onset, and the onset date was suggested to occur in the third pentad of May. After the typhoon landed in the coast of southern China, it still contributed to the establishment of the SCSSM due to warming the air column over the northern SCS, resulting in a persistent positive MTG with the ridge surface tilting northward.
NF3, the greenhouse gas missing from Kyoto
Authors: Prather Michael J. , Hsu Juno
Published: June 2008

Nitrogen trifluoride (NF3) can be called the missing greenhouse gas: It is a synthetic chemical produced in industrial quantities; it is not included in the Kyoto basket of greenhouse gases or in national reporting under the United Nations Framework Convention on Climate Change (UNFCCC); and there are no observations documenting its atmospheric abundance. Current publications report a long lifetime of 740 yr and a global warming potential (GWP), which in the Kyoto basket is second only to SF6. We re‐examine the atmospheric chemistry of NF3 and calculate a shorter lifetime of 550 yr, but still far beyond any societal time frames. With 2008 production equivalent to 67 million metric tons of CO2, NF3 has a potential greenhouse impact larger than that of the industrialized nations' emissions of PFCs or SF6, or even that of the world's largest coal‐fired power plants. If released, annual production would increase the lower atmospheric abundance by 0.4 ppt, and it is urgent to document NF3 emissions through atmospheric observations.
Thoughts on Grammar Intervention in AAC
Authors: Fey Marc
Published: June 2008

In this article, I propose that, for several reasons, grammar should be an early focus of communication interventions for young children using augmentative and alternative communication (AAC) systems. The basic goals for such programs should be to facilitate the child's comprehension of the language of the community, or the target language, thus leading the way to literacy, and to foster the child's use of symbol combinations that mirror the grammatical patterns of speaking children acquiring the target language, even if they cannot be fully grammatically complete. I introduce five principles that underlie most successful approaches to grammar interventions with children with specific language impairment. My initial attempts to apply these principles to interventions with children with complex communication needs indicate that they may be of considerable value to clinicians planning intervention programs. On the other hand, the challenges posed by the intellectual and physical limitations of many AAC users and their communication systems make it necessary to modify at least Principle 5 if the basic goals of intervention are to be met.
Chomsky'sMinimalist Program: A Brief Linguistic Primer
Authors: Wilson Mary Sweig
Published: June 2008

Children around the world, no matter what their native language, follow a similar course in language acquisition from the emergence of first words to the mastery of syntax. The uniformity and rapidity of first language acquisition is possible because human infants are born with a biologically endowed innate language faculty within the brain that drives the course of language development. Although this premise was doubted 50 years ago, today biologists and linguists alike accept it. Our human language faculty orchestrates and shapes the acquisition of language. Neurotypically developing children need only the surrounding language input to acquire language. In contrast, children with receptive language delays, including many of those who are or will become augmentative and alternative communication (AAC) users, need more than exposure to language if they are to develop adult competence in their native language.
Parametric coupling of a lower hybrid pump with neutral beam driven ion cyclotron instability in a tokamak
Authors: Kumar Ashok , Tripathi V. K.
Published: June 2008

The parametric coupling of a high amplitude lower hybrid wave with the ion cyclotron instability, driven by neutral beam converted ion beam, is studied. The coupling is strong when the wave numbers of the pump and the ion cyclotron wave are perpendicular to each other; it produces lower hybrid sidebands. When the upper sideband is resonant, the growth rate of the instability is suppressed as the energy is fed into the upper sideband by the pump and the ion cyclotron wave. At different wave numbers when the lower sideband is resonant, the parametric coupling leads to the enhancement of growth rate. The effect is important when electron quiver velocity is greater than the sound speed. The study is relevant to advanced stage operations of a tokamak like ITER.
Phosphorus incorporation during Si(001):P gas-source molecular beam epitaxy: Effects on growth kinetics and surface morphology
Authors: Cho B. , Bareño J. , Foo Y. L. , Hong S. , Spila T. , Petrov I. , Greene J. E.
Published: June 2008

The effects of P doping on growth kinetics and surface morphological evolution during Si(001):P gas-source molecular beam epitaxy from Si2H6 and PH3 at temperatures Ts=500–900°C have been investigated. With increasing PH3∕Si2H6 flux ratio JP∕Si at constant Ts, we observe a decrease in the film growth rate R and an increase in the incorporated P concentration CP, both of which tend toward saturation at high flux ratios, which is accompanied by increased surface roughening and pit formation. At constant JP∕Si, R increases with increasing Ts, while CP initially increases, reaches a maximum at Ts=700°C, and then decreases at higher growth temperatures. We use in situ isotopically tagged D2 temperature programed desorption (TPD) to follow changes in film surface composition and dangling bond density θdb as a function of JP∕Si and Ts. Measurements are carried out on both as-deposited Si(001):P layers and P-adsorbed Si(001) surfaces revealing β1 and β2 peaks due to D2 desorption from Si monohydride and dihydride species, respectively, as well as the formation of a third peak β3 corresponding to D2 desorption from mixed SiP dimers. Dissociative PH3 adsorption on Si(001) results in a decrease in θdb and an initial increase in P surface coverage θP with increasing Ts. Saturation θP values reach a maximum of ∼1 ML at Ts=550°C, and decrease with Ts>600°C due to the onset of P2 desorption. Comparison of θP(Ts) results obtained during film growth with postdeposition CP(Ts) results reveals the presence of strong P surface segregation. From measurements of θP versus CP in Si(001):P layers grown as a function of Ts, we obtain a P segregation enthalpy ΔHs=−0.86eV. By using the combined set of results, we develop a predictive model for CP versus Ts and, JP∕Si incorporating the dependence of the PH3 reactive sticking probability SPH3 on θP, which provides an excellent fit to the experimental data.
Longitudinally excited N2 lasers without high-voltage switches
Authors: Uno Kazuyuki , Nakamura Kenshi , Goto Tatsumi , Jitsuno Takahisa
Published: June 2008

We have developed novel excitation circuits without high-voltage switches for two longitudinally excited N2 lasers (wavelength: 337nm). One uses a single tube without a trigger and the other uses a tandem tube with a trigger. In both systems, the discharge tube acts as a switch. In the single-tube system, the laser output energy was 125.8μJ and the efficiency was 0.16% at 18Torr (2.4kPa) when a slow-rising voltage pulse of −28kV was applied (rise time: 21.3μs). In the tandem-tube system, the laser output energy was 259.4μJ and the efficiency was 0.11% at 18Torr when a slow-rising voltage pulse of −48kV was applied (rise time: 27μs).
Enhanced electromechanical response of nonpercolating polymer-nanoparticle composite films
Authors: Mainwaring David , Murugaraj Pandiyan , Mora-Huertas Nelson , Sethupathi Kanikrishnan
Published: June 2008

We have prepared semiconducting carbon nanoparticle polyimide composite thin film with spatially distributed localized energy states exhibiting three-dimensional variable range hopping electron transport. Applied strain (compression or extensional) introduces proportional variations in the spacing between these energy states, as demonstrated in the linear variation of measured electrical resistance. The electromechanical sensitivity is the same in both deformation modes due to this underlying operating mechanism, enabling quantitative measurement of torsional deformations also. Electrical responses across all deformation modes remained in phase with applied strain indicating negligible hysteresis and an ability to operate over a wide strain ranges up to 40 000 microstrains.
Gigantic magneto-optical effects induced by (Fe∕Co)-cosubstitution in titania nanosheets
Authors: Osada Minoru , Itose Masayuki , Ebina Yasuo , Ono Kanta , Ueda Shigenori , Kobayashi Keisuke , Sasaki Takayoshi
Published: June 2008

Magneto-optical Faraday effect has been investigated for 3d-transition-metal-substituted titania nanosheets Ti1−xMxO2 (M=Fe,Co). In Ti0.8Co0.2O2 and Ti0.6Fe0.4O2 nanosheets, a strong magneto-optical response (∼104deg∕cm) appeared near the absorption edge at 260nm. We find that tailoring magneto-optical properties could be achieved by (Fe∕Co) cosubstitution and an optimally doped Ti0.75Fe0.1Co0.15O2 nanosheet exhibits a gigantic magneto-optical response (∼105deg∕cm) over the wide wavelength region (400–750nm). By analyzing electronic structures from first-principle calculations, we have clarified that the d-d transitions are responsible for the gigantic signal in (Fe∕Co)-cosubstituted nanosheets.
Modeling the effect of SiO2 additions and cooling rate on the electrical behavior of donor-acceptor codoped positive temperature coefficient thermistors
Authors: Zubair M. A. , Leach C.
Published: June 2008

The resistivity-temperature [ρ(T)] characteristics of two series of (Ba,Ca)TiO3 based positive temperature coefficient (PTC) of resistance thermistors, prepared with different levels of SiO2 addition and cooling rates, have been analyzed in the context of the double Schottky barrier model. A significant improvement in fit, compared to earlier studies, was achieved between the modeled and experimental ρ(T) behavior over the full temperature range of the PTC transition through the incorporation of experimentally obtained permittivity data, coupled with an optimized acceptor energy spread (0.40±0.05eV). The permittivity below the Curie temperature (TC) increased slowly when either the SiO2 content or cooling rate was increased, but above TC the permittivities were almost unaffected. The bulk resistivity and average grain size were affected only slightly by increases in SiO2 addition or cooling rate, but the gradient of the ρ(T) curve and peak resistivity gradually decreased due to a reduction in surface state density from 1.1×1014to5.9×1013cm−2 at an acceptor energy depth of 1.57–1.60eV. A reduction in room temperature resistivity with increasing SiO2 content and cooling rate was consistent with a concomitant reduction in the ratio of residual surface charge unit density to permittivity.
Generation of low-frequency electrostatic and electromagnetic waves as nonlinear consequences of beam–plasma interactions
Authors: Umeda Takayuki
Published: June 2008

Nonlinear evolution of the electron two-stream instability in a current-carrying plasma is examined by using a two-dimensional electromagnetic particle-in-cell simulation. Formation of electron phase-space holes is observed as an early nonlinear consequence of electron–beam–plasma interactions. Lower-hybrid waves, electrostatic, and electromagnetic whistler mode waves are also excited by different mechanisms during the ensuing nonlinear wave–particle interactions. It is shown by the present computer simulation with a large simulation domain and a long simulation time that these low-frequency waves can disturb the electrostatic equilibrium of electron phase-space holes, suggesting that the lifetime of electron phase-space holes sometimes becomes shorter in a current-carrying plasma.
Effect of plasma profile on ion acceleration in the interaction of a short laser pulse with a thin overdense target
Authors: Kwon Duck-Hee , Rhee Yong-Joo , Lee Sungman , Cha Hyungki
Published: June 2008

Energetic ion generation from the interaction of a short laser pulse with a thin overdense plasma accompanied by a preplasma and a rear side plasma gradient is investigated by particle-in-cell simulations. The dynamics of ion acceleration depending on the maximum density of the preplasma in front of the overdense plasma slab with a smooth density gradient at the rear side are presented and discussed by comparing a sharp rear side boundary case.
Streaming potential and electroviscous effects in periodical pressure-driven microchannel flow
Authors: Gong Lei , Wu Jiankang , Wang Lei , Cao Kan
Published: June 2008

An analytical solution for pressure-driven periodical electrokinetic flows in a two-dimensional uniform microchannel is presented based on the Poisson–Boltzmann equation for electrical double layer and the Navier–Stokes equations for incompressible viscous fluid. The analytical results indicate that the periodical streaming potential strongly depends on the periodical Reynolds number (Re=ωh2∕ν) which is a function of the frequency, the channel size, and the kinetic viscosity of fluids. For Re<1, the streaming potential behaves similarly to that of steady flow, whereas it decreases rapidly with Re as Re>1. In addition, the electroviscous force affects greatly both the periodical flow and streaming potential, particularly when the nondimensional electrokinetic diameter κh is small. The electroviscous force has been found to depend on three factors: first, the electroviscous parameter, which is defined as the ratio of the maximum electroviscous force to the pressure gradient; second, the distribution parameter describing the distribution of the electroviscous force over the cross section of the microchannel; third, the coupling coefficient, which is a function of both the periodical Reynolds number and electroviscous parameter, determining both the amplitude attenuation and phase offset of the electroviscous force.
Evaluation of a deep-water wave breaking criterion
Authors: Tian Zhigang , Perlin Marc , Choi Wooyoung
Published: June 2008

An experimental and numerical study is presented to investigate the breaking criterion of Song and Banner [J. Phys. Oceanogr. 32, 2541 (2002)] who suggested a threshold range of (1.4±0.1)×10−3 for a predictive wave breaking parameter, measuring the rate of change in the local energy maximum and the local wave number, to differentiate between wave trains that lead to breaking and those that do not. To examine the breaking criterion experimentally, four separate wave groups of progressive surface gravity waves with slowly decreasing frequency are generated mechanically in a two-dimensional wave tank. Surface elevations as a function of time are measured using capacitance wave probes; surface elevations as a function of space prior to and during breaking are obtained by recording subregions with an imaging system and combining the measurements from repeated experiments. In addition, nonlinear numerical solutions for the surface elevation profiles for the four wave groups are obtained by solving a set of nonlinear evolution equations using a pseudospectral method and are compared to experiments and linear predictions. It is found that the breaking criterion of Song and Banner is sensitive to the choice of the local wave number, but that a particular local wave number based on the local wave geometry distinguishes wave groups leading to breaking from wave groups that do not break. It is shown that the lead time between the parameter exceeding the threshold and incipient wave breaking increases as wave breaking intensifies. The total energy loss is related strongly to this parameter immediately prior to breaking.
Analytical solution of electro-osmotic flow in a semicircular microchannel
Authors: Wang Chang-Yi , Liu Ying-Hong , Chang Chien C.
Published: June 2008

The electro-osmotic flow through a microchannel with a semicircular cross section is studied under the Debye–Huckel approximation. Analytical series solutions are found for two basic cases. The solutions for the two basic cases considered can be superposed to yield solutions for any combination of constant zeta potentials on the flat or curved wall boundaries. Moreover, in the limit of a thin electric double layer (small Debye length compared to the nominal dimension), a method of solution is shown for variable zeta potentials by using the Smoluchowski slip approximation.
Path instability of rising spheroidal air bubbles: A shape-controlled process
Authors: Zenit Roberto , Magnaudet Jacques
Published: June 2008

The conditions for which the paths of freely rising bubbles become oscillatory are studied experimentally using silicone oils with viscosities ranging from 0.5 to 9.4 times that of water. Since these fluids are nonpolar, as opposed to water, the gas-liquid interfaces remain clean without the need of an ultrapure environment. We find the Reynolds number at incipient transition to vary from 70 to 470, for decreasing liquid viscosity. Correspondingly, the bubble aspect ratio remains almost constant, ranging only from 2.36 to 2.0 for the same set of conditions. Hence, we argue that the dominant parameter to trigger the instability is the bubble shape and not the Reynolds number. Since vorticity generated at the bubble surface is almost independent of the Reynolds number and mostly depends on the bubble aspect ratio in the parameter range covered by our experiments, present results strongly support the view that path instability is a direct consequence of the wake instability that occurs when this surface vorticity exceeds a certain threshold.
Ab initio investigation of interfacial layer formation in the Mo∕Si boundary for extreme ultraviolet lithography
Authors: Kang In-Yong , Chung Yong-Chae
Published: June 2008

The energetics and the electronic structure of the Si∕Mo(110) surface were investigated using the density functional theory calculations in an attempt to clarify the initial stage of silicide layer formation. The energy barriers for the migration of Si adatom to an adjacent hollow site passing the bridge site were calculated to be 0.64eV [Mo (110)] and 0.74eV [Si-substituted Mo (110)]. In order to analyze the bonding nature between Si adatom and Mo (110) surface, layer density of states and total valence electron density were obtained. It can be reasonably inferred that Mo 4d states mainly contributed to the bonding between Mo and Si and, consequently, four Mo–Si covalent bonds were formed around the Si atom at the hollow site.
On the nonaxisymmetric instability of round liquid jets
Authors: Ruo An-Cheng , Chang Min-Hsing , Chen Falin
Published: June 2008

A fully temporal linear stability analysis for round liquid jets is accomplished in this study. Three-dimensional disturbances are considered and a detailed parametric investigation is performed. The results indicate that only the nonaxisymmetric mode with azimuthal wavenumber m=1 may prevail over the axisymmetric mode and appear to dominate the maximum growth rate. The domain in which the nonaxisymmetric modes may start to grow is also clarified. A comparison with experimental observations in the literature is also presented. The results provide a complete understanding of the stability characteristics of round liquid jets.
Influence of Nd:Zn codoping in near-stoichiometric lithium niobate
Authors: Babu Reddy J. N. , Ganesh Kamath K. , Vanishri S. , Bhat H. L. , Elizabeth Suja
Published: June 2008

Near-stoichiometric lithium niobate (SLN) crystals doped with up to 1.6mol% Zn and codoped with various Nd concentrations in the melt (0.2, 0.5, 0.9, and 1.5mol%) (Nd:Zn:SLN) are grown from 58.6mol% Li2O using conventional Czochralski technique. Crystals are pulled at the rate of 0.35mm∕h with seed rotation at 9rpm. Concentrations of Zn and Nd in the crystal are varied by adding appropriate amounts of ZnO and Nd2O3 to the starting composition. Unit cell parameters of the grown crystals are calculated by Rietveld refinement method using FULLPROFF software. Domain structure studies are carried out by chemical etching followed by microscopic examination. Dielectric studies reveal the existence of piezoelectric resonance at high frequencies. Enhancement in dielectric constant and tanδ in Nd doped samples has been attributed to the space charge polarization. Nd doped samples exhibit reduction in the relative permittivity after oxygen annealing. Transmission spectra of Nd:Zn:SLN crystals in the UV region exhibit blueshift in the cutoff wavelength. In Mid Infrared (MIR) region crystals doped with 1.6mol% Zn have shift in the OH absorption peak from 2873to2833nm. Judd–Ofelt analysis carried out on the absorption spectra of codoped crystal yields the lifetime of 104μs for the metastable state F3∕24. The branching ratio for the electronic transition from F3∕24 to I11∕24 is high compared to that for F3∕24 to I13∕24, indicating a higher emission cross section for the former transition. Laser damage threshold evaluated using 532nm, 5ns pulsed neodymium doped yttrium aluminum garnet laser, shows an increase by two orders of magnitude for crystals doped with 1.6mol% Zn. Photorefractive damage threshold for these crystals shows an enhancement of four orders of magnitude due to increase in the photoconductivity.
Theoretical simulations of the tip-induced configuration changes of the 4,4′-diacetyl-p-terphenyl molecule chemisorbed on Si(001)
Authors: Mamatkulov M. , Stauffer L. , Sonnet Ph. , Mayne A. J. , Comtet G. , Dujardin G.
Published: June 2008

We have investigated from a theoretical point of view modifications of the 4,4′-diacetyl-p-terphenyl molecule chemisorbed on Si(001) induced by the scanning tunneling microscope (STM). In previous experiments, these modifications were observed to occur preferentially at the end of the molecule after a +4.0V voltage pulse and at the center after a +4.5V voltage pulse. In the framework of ab initio simulations, we have realized a systematic energetic study of the dissociative chemisorption of one, two, or three phenyl rings of the substituted p-terphenyl molecule. Charge densities were then calculated for the investigated configurations and compared to the STM topographies. Before manipulation with the STM tip, the substituted p-terphenyl molecule is preferentially adsorbed without phenyl ring dissociation, allowing a partial rotation of the central phenyl ring. Our results show that the STM induced modifications observed at the end of the molecule might originate from the dissociation of two phenyl rings (one central and one external ring), while the modifications occurring at the central part of the molecule can be interpreted as a dissociation of the two external rings.
Structure and energetics of equiatomic K–Cs and Rb–Cs binary clusters
Authors: Hristova Elisaveta , Grigoryan Valeri G. , Springborg Michael
Published: June 2008

The basin-hopping algorithm combined with the Gupta many-body potential is used to study the structural and energetic properties of (KCs)n and (RbCs)n bimetallic clusters with N=2n up to 50 atoms. Each binary structure is compared to those of the pure clusters of the same size. For the cluster size N=28 and for the size range of N=34–50, the introduction of K and Rb atoms in the Cs alkali metal cluster results in new ground state structures different from those of the pure elements. In the size range N⩾38 the binary and pure clusters show not only structural differences, but they also display different magic numbers. Most of the magic Rb–Cs and K–Cs clusters possess highly symmetric structures. They belong to a family of pIh structures, where a fivefold pancake is a dominant structural motif. Such geometries have not been reported for alkali binary clusters so far, but have been found for series of binary transition metal clusters with large size mismatch. Moreover, tendency to phase separation (shell-like segregation) is predicted for both K–Cs and Rb–Cs clusters with up to 1000 atoms. Our finding of a surface segregation in Rb–Cs clusters is different from that of theoretical and experimental studies on bulk Rb–Cs alloys where phase separation does not occur.
Study of the H+O2 reaction by means of quantum mechanical and statistical approaches: The dynamics on two different potential energy surfaces
Authors: Bargueño Pedro , González-Lezana Tomás , Larrégaray Pascal , Bonnet Laurent , Rayez Jean-Claude , Hankel Marlies , Smith Sean C. , Meijer Anthony J. H. M.
Published: June 2008

The possible existence of a complex-forming pathway for the H+O2 reaction has been investigated by means of both quantum mechanical and statistical techniques. Reaction probabilities, integral cross sections, and differential cross sections have been obtained with a statistical quantum method and the mean potential phase space theory. The statistical predictions are compared to exact results calculated by means of time dependent wave packet methods and a previously reported time independent exact quantum mechanical approach using the double many-body expansion (DMBE IV) potential energy surface (PES) [Pastrana et al., J. Phys. Chem. 94, 8073 (1990)] and the recently developed surface (denoted XXZLG) by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. The statistical approaches are found to reproduce only some of the exact total reaction probabilities for low total angular momenta obtained with the DMBE IV PES and some of the cross sections calculated at energy values close to the reaction threshold for the XXZLG surface. Serious discrepancies with the exact integral cross sections at higher energy put into question the possible statistical nature of the title reaction. However, at a collision energy of 1.6eV, statistical rotationally resolved cross sections managed to reproduce the experimental cross sections for the H+O2(v=0,j=1)→OH(v′=1,j′)+O process reasonably well.
Role of attractive methane-water interactions in the potential of mean force between methane molecules in water
Authors: Asthagiri D. , Merchant Safir , Pratt Lawrence R.
Published: June 2008

On the basis of a Gaussian quasichemical model of hydration, a model of non-van der Waals character, we explore the role of attractive methane-water interactions in the hydration of methane and in the potential of mean force between two methane molecules in water. We find that the hydration of methane is dominated by packing and a mean-field energetic contribution. Contributions beyond the mean-field term are unimportant in the hydration phenomena for a hydrophobic solute such as methane. Attractive solute-water interactions make a net repulsive contribution to these pair potentials of mean force. With no conditioning, the observed distributions of binding energies are super-Gaussian and can be effectively modeled by a Gumbel (extreme value) distribution. This further supports the view that the characteristic form of the unconditioned distribution in the high-ε tail is due to energetic interactions with a small number of molecules. Generalized extreme value distributions also effectively model the results with minimal conditioning, but in those cases the distributions are sufficiently narrow that the details of their shape are not significant.
Quantum initial condition sampling for linearized density matrix dynamics: Vibrational pure dephasing of iodine in krypton matrices
Authors: Ma Z. , Coker D. F.
Published: June 2008

This paper reviews the linearized path integral approach for computing time dependent properties of systems that can be approximated using a mixed quantum-classical description. This approach is applied to studying vibrational pure dephasing of ground state molecular iodine in a rare gas matrix. The Feynman–Kleinert optimized harmonic approximation for the full system density operator is used to sample initial conditions for the bath degrees of freedom. This extremely efficient approach is compared to alternative initial condition sampling techniques at low temperatures where classical initial condition sampling yields dephasing rates that are nearly an order of magnitude too slow compared to quantum initial condition sampling and experimental results.
Construction of the free energy landscape of biomolecules via dihedral angle principal component analysis
Authors: Altis Alexandros , Otten Moritz , Nguyen Phuong H. , Hegger Rainer , Stock Gerhard
Published: June 2008

A systematic approach to construct a low-dimensional free energy landscape from a classical molecular dynamics (MD) simulation is presented. The approach is based on the recently proposed dihedral angle principal component analysis (dPCA), which avoids artifacts due to the mixing of internal and overall motions in Cartesian coordinates and circumvents problems associated with the circularity of angular variables. Requiring that the energy landscape reproduces the correct number, energy, and location of the system’s metastable states and barriers, the dimensionality of the free energy landscape (i.e., the number of essential components) is obtained. This dimensionality can be determined from the distribution and autocorrelation of the principal components. By performing an 800 ns MD simulation of the folding of hepta-alanine in explicit water and using geometric and kinetic clustering techniques, it is shown that a five-dimensional dPCA energy landscape is a suitable and accurate representation of the full-dimensional landscape. In the second step, the dPCA energy landscape can be employed (e.g., in a Langevin simulation) to facilitate a detailed investigation of biomolecular dynamics in low dimensions. Finally, several ways to visualize the multidimensional energy landscape are discussed.
Real time monitoring of pentacene growth on SiO2 from a supersonic source
Authors: Hong S. , Amassian A. , Woll A. R. , Bhargava S. , Ferguson J. D. , Malliaras G. G. , Brock J. D. , Engstrom J. R.
Published: June 2008

Thin film growth of pentacene on SiO2 using a supersonic source has been investigated with in situ real time synchrotron x-ray scattering and ex situ atomic force microscopy, focusing on the effects of incident kinetic energy Ei and growth rate GR on the evolution of surface roughness and the crystalline structure of the thin films. For the conditions examined here, Ei=2.5–7.2eV and GR=0.0015–0.2MLs−1, the thin film phase is always observed. We find that while the effect of Ei on interlayer transport is minimal, at high growth rates, slightly smoother films are observed.
Relaxorlike dielectric behavior and weak ferromagnetism in YFeO3 ceramics
Authors: Ma Y. , Chen X. M. , Lin Y. Q.
Published: June 2008

Dielectric characteristics of YFeO3 antiferromagnetic ceramics were evaluated over broad temperature and frequency ranges. Two dielectric relaxations were observed at low and high temperatures, respectively, and a dielectric constant step was detected between them. The low temperature dielectric relaxation was an intrinsic thermally activated process following the Arrhenius law with the activation energy very close to that for electronic ferroelectrics, while the high temperature dielectric relaxation was related to the point defect since it could be significantly suppressed by O2 annealing. M-H hysteresis loop was detected at room temperature, and this indicated the weak ferromagnetism in YFeO3 ceramics.
A Mach–Zehnder interferometer for the detection and noninvasive optical amplification of polarization rotation
Authors: LaForge Joshua M. , Steeves Geoffrey M.
Published: June 2008

We present the theory and design of a Mach–Zehnder interferometer with orthogonally polarized arms that passively, noninvasively, optically amplifies polarization rotation in one arm of the interferometer. Theoretical analysis of the electric fields in the two arms is used to compare the significance of device optimizations. Design of the beam alignment, beam recombination, noise isolation, and active stabilization to enable reliable measurements are thoroughly discussed. Finally, we review a comparison between the interferometer with an optical gain factor of ∼4.5 and the optical bridge (OB) technique for polarization rotation detection that shows the interferometer offers better performance than the OB.
Interface phase and tuning of polarization in metal-ferroelectric junctions: A theoretical study
Authors: Núñez Matías , Buongiorno Nardelli M.
Published: June 2008

Using first principles calculations, we have studied how the control of the interface structure in metal-ferroelectric junctions can be used to tune the polarization of the ferroelectric film. Using a Pt∕BaTiO3∕Pt as a prototypical system, we show that the polarization of the oxide can be tuned by the introduction of an interface layer of a different metal and that this interface effect varies with the thickness of the ferroelectric film. These results can be easily interpreted in terms of the local electronic structure of the interface and provide a phenomenological criterion for choosing the metal intralayer in order to obtain the desired polarization.
Residual and fracture strains of Bi2223 filaments and their relation to critical current under applied bending and tensile strains in Bi2223∕Ag∕Ag alloy composite superconductor
Authors: Ochiai S. , Shin J. K. , Iwamoto S. , Okuda H. , Oh S. S. , Ha D. W. , Sato M.
Published: June 2008

Mechanical and electromagnetic stresses are exerted on Bi2223∕Ag∕Ag alloy superconducting composite tapes during fabrication∕winding and operation, which cause reduction in critical current when the Bi2223 filaments are damaged. In the damage process, the thermally induced residual strain and fracture strain of the Bi2223 filaments play a dominant role. The aim of the present work was to propose a comprehensive method for estimation of these strain values and a quantitative description method of the relation of critical current to the applied bending∕tensile strain, and to examine the accuracy of the method in comparison with the experimental results. The residual strain of Bi2223 filaments in the composite tape was measured by the x-ray diffraction method. The measured residual strain value was used for analysis of the load-strain curve, from which the intrinsic fracture strain of filaments was estimated. The relation of critical current to applied bending∕tensile strain was predicted by the proposed calculation procedure, in which the estimated strain values were input. The predicted critical current-applied strain relation agreed well with the experimental results, suggesting that the present method is a useful tool for prediction∕description of tensile∕bending applied strain dependence of critical current of multifilamentary-type conductors.
High-linearity analog-to-digital acquisition board for photon-timing applications
Authors: Resnati D. , Rech I. , Geraci A.
Published: June 2008

Nowadays a wide range of scientific applications require the detection of very weak and fast luminescence signals in the time domain. Single molecule spectroscopy, diffuse optical tomography, time-resolved emission spectra are only a few examples among them. Advanced time-correlated single photon counting, that relies on multidetector and multidimensional acquisition, reveals itself as a powerful technique to gather deeper insight into various photochemical and biological processes. In this paper we present a high-speed, high-linearity A/D acquisition board that is designed as a building block for a compact, low-cost, multidetector acquisition system for photon-timing experiments. The prototype has been experimentally tested and the results fully comply the goal design specifications.
Quantitative measurement of indentation hardness and modulus of compliant materials by atomic force microscopy
Authors: Passeri D. , Bettucci A. , Biagioni A. , Rossi M. , Alippi A. , Lucci M. , Davoli I. , Berezina S.
Published: June 2008

An atomic force microscopy (AFM) based technique is proposed for the characterization of both indentation modulus and hardness of compliant materials. A standard AFM tip is used as an indenter to record force versus indentation curves analogous to those obtained in standard indentation tests. In order to overcome the lack of information about the apex geometry, the proposed technique requires calibration using a set of reference samples whose mechanical properties have been previously characterized by means of an independent technique, such as standard indentation. Due to the selected reference samples, the technique has been demonstrated to allow reliable measurements of indentation modulus and hardness in the range of 0.3–4.0GPa and 15–250MPa, respectively.
Surface plasmon on aluminum concentric rings arranged in a long-range periodic structure
Authors: Chang Yi-Tsung , Tzuang Dah-Ching , Wu Yi-Ting , Chan Chi-Feng , Ye Yi-Han , Hung Ting-Hsiang , Chen Yu-Fan , Lee Si-Chen
Published: June 2008

The enhanced optical transmission through the annular aluminum metal with different number of concentric rings arranged in a long-range periodic structure on the silicon substrate is investigated. The measured transmission spectra demonstrate that the surface plasmon modes depend sensitively on the structural parameters of the metallic rings. The degenerate (1,0), (1,1), and (2,1) Al∕Si surface plasmon modes are determined by the long periodicity of the structure. The localized modes in cavities with different length can be observed in this structure as well. These phenomena suggest that both surface plasmons and localized cavity modes are excited within super unit cell.
Enhanced magnetic behavior in carbon encapsulated nickel nanotubules through a linear polymer template
Authors: Singh Vidyadhar , Ram S. , Ranot M. , Park Je-Geun , Srinivas V.
Published: June 2008

Carbon encapsulated Ni nanotubules, synthesized by a simple chemical method with linear polymer templates, reveal a high saturation magnetization (Ms) close to bulk fcc-Ni value, with larger coercivity 140Oe at 300K. An improvement in basic ferromagnetic character is reflected in the remanent magnetization (Mr), which is enhanced to be Mr∕Ms∼0.3, intrinsic of strongly ferromagnetic pseudosingle domains. The TEM images consist of fcc-Ni of ∼350nm long cylindrical tubules with an average 20nm diameter. The sample has two Raman bands of 1350cm−1 (D-band) and 1590cm−1 (G-band) characterizing the presence of a graphitic carbon (disordered).