bluuebunny/crossref_metadata_2025 huggingface dataset:
Three years of Atmospheric Infrared Sounder radiometric calibration validation using sea surface temperatures
Authors: Aumann H. H. , Broberg Steve , Elliott Denis , Gaiser Steve , Gregorich Dave
Published: August 2006

This paper evaluates the absolute accuracy and stability of the radiometric calibration of the Atmospheric Infrared Sounder (AIRS) by analyzing the difference between the brightness temperatures measured at 2616 cm−1 and those calculated at the top of the atmosphere (TOA), using the Real‐Time Global Sea Surface Temperature (RTGSST) for cloud‐free night tropical oceans between ±30° latitude. The TOA correction is based on radiative transfer. The analysis of the first 3 years of AIRS radiances verifies the absolute calibration at 2616 cm−1 to better than 200 mK, with better than 16 mK/yr stability. The AIRS radiometric calibration uses an internal full aperture wedge blackbody with the National Institute of Standards and Technology (NIST) traceable prelaunch calibration coefficients. The calibration coefficients have been unchanged since launch. The analysis uses very tight cloud filtering, which selects about 7000 cloud‐free tropical ocean spectra per day, about 0.5% of the data. The absolute accuracy and stability of the radiometry demonstrated at 2616 cm−1 are direct consequences of the implementation of AIRS as a thermally controlled, cooled grating‐array spectrometer and meticulous attention to details. Comparable radiometric performance is inferred from the AIRS design for all 2378 channels. AIRS performance sets the benchmark for what can be achieved with a state‐of‐the‐art hyperspectral radiometer from polar orbit and what is expected from future hyperspectral sounders. AIRS was launched into a 705 km altitude polar orbit on NASA's Earth Observation System (EOS) Aqua spacecraft on 4 May 2002. AIRS covers the 3.7–15.4 micron region of the thermal infrared spectrum with a spectral resolution of ν/Δν = 1200 and has returned 3.7 million spectra of the upwelling radiance each day since the start of routine data gathering in September 2002.
Initial results of a global circuit model with variable stratospheric and tropospheric aerosols
Authors: Tinsley Brian A. , Zhou Limin
Published: August 2006

A new model of the global circuit has been constructed that treats more realistically than previous models the external influences due to varying charged particle fluxes from space, the internal variability due to the transport of radon by atmospheric dynamics, and the varying aerosol populations. An approximate treatment of the effects of explosive volcanic eruptions, that introduce SO2 and H2O into the stratosphere, involves the creation of ultrafine aerosol particles in the downward branch of the Brewer‐Dobson circulation from sulfuric acid aerosol particles vaporized in the upward branch. A large increase in stratospheric column resistance occurs at high latitudes, but for much of the time this column resistance is reduced by stratospheric ionizing radiation due to relativistic electron precipitation. Here we present results for the variability of the global circuit due to the variations of the aerosol populations in the stratosphere and troposphere, the variability of the cosmic ray flux, and the geographical and seasonal variability of the near‐surface radioactivity. We discuss inferred changes in the circuit parameters associated with climate change, on interannual to Milankovich timescales.
Characterization of zonal winds in the stratosphere of Titan with UVES: 2. Observations coordinated with the Huygens Probe entry
Authors: Luz D. , Civeit T. , Courtin R. , Lebreton J.‐P. , Gautier D. , Witasse O. , Kaufer A. , Ferri F. , Lara L. , Livengood T. , Kostiuk T.
Published: August 2006

The Huygens Probe has successfully entered Titan's atmosphere and landed on its surface on 14 January 2005. With the aim of characterizing the zonal wind flow in Titan's stratosphere close to the time of entry, coordinated observations were carried out at the Very Large Telescope on the nights of 7, 12, 14, and 15 January. As in our previous investigation (Luz et al., 2005), we used the UVES instrument, mounted on the Kueyen‐UT2 telescope, simultaneously achieving high spectral resolving power and high spatial resolution. The field has been derotated in order to align the 0.3‐arcsec aperture perpendicularly to Titan's rotation axis. In this configuration, spatial information in the east‐west direction is preserved in a set of spectra in the direction perpendicular to dispersion. We present measurements of zonal winds obtained with the technique of absolute accelerometry. The observations were made in the wavelength range 4200–6200 Å, probing between 115 and 280 km, with peak contributions at 200 and 170 km for the lower and upper parts of the domain. We detect prograde zonal winds with lower limits 46 and 53 ms−1 at these altitudes. These values are close to our previous measurements.
Peculiar geometry of northern Luzon, Philippines: Implications for regional tectonics of new gravity and paleomagnetic data
Authors: Milsom John , Ali Jason R. , Queano Karlo L.
Published: August 2006

The northern termination of the Philippine archipelago is remarkably abrupt. The distinctive, almost rectangular, shape of northern Luzon is a consequence of the almost simultaneous disappearance near 18°N of the Central Cordillera, the much narrower Sierra Madre, and the broad floodplain of the Cagayan River. The floodplain is underlain by a deep sedimentary basin that is closed off just inland of the coast by an ENE‐WSW structural high known as the Sicalao Ridge. Gravity surveys show that the ridge has steep flanks that are almost certainly defined by faulting. In the same region, there is also a dramatic change in the Luzon Arc, which is the volcanic expression of subduction of the South China Sea. The volcanic centers in the Central Cordillera (the North Luzon Segment of the arc) are all now inactive, but further north eruptions are frequent on the small eastern islands of the Bashi Segment. The differences between the North Luzon and Bashi segments suggest that they had very different geological histories until the late Neogene, but the evolution of northern Luzon is so poorly understood that it is not even known on which plate it originated. New paleomagnetic data and the existence of the Sicalao Ridge provide important constraints on reconstructions and, when combined with geological data, favor the possibility that in the Paleogene the Central Cordillera and Sierra Madre were combined as parts of an arc at the southern margin of the Philippine Sea. The Sicalao Ridge can be interpreted as a rift margin feature created during the detachment of Luzon from continental Sundaland.
Steady‐state properties and statistical distribution of atmospheric dust devils
Authors: Kurgansky Michael V.
Published: August 2006

A steady Rankine‐like vortex model of a dust devil is reported, which takes into account the sunlight absorption by airborne dust particles and the diabatic heating of a rotating dust column. For the maximum swirl velocity being a few times larger than the mean updraft velocity, the model admits significant simplifications allowing for its complete analytical treatment. The competitive effects of (i) the surface heat fluxes and (ii) the suspended‐dust‐caused diabatic heating on the vortex constitution (strength, height and shape) are examined. The second factor is found to be more influential for the strongest vortices. A reference exponential distribution of dust devils over their radius (visible diameter), which was introduced based on general arguments of mathematical information theory, is shown to fit satisfactory well the observational data on dust devils in Arizona and southern California and, in a preliminary way, on Mars.
Argo profiling floats document Subantarctic Mode Water formation west of Drake Passage
Authors: Schneider Wolfgang , Bravo Luis
Published: August 2006

Subantarctic Mode Water (SAMW), the precursor of Antarctic Intermediate Water, which occupies the 600 to 1100 m layer of the water column in the oceans of the southern hemisphere, is formed in the southern oceans north of the Polar Frontal Zone (56°–60°S), where saltier upper deep water is upwelled close to the surface. The surface layer there, in contrast, is determined by fresher water which occupies about the upper 100 m of the water column during austral summer. Surface cooling during austral winter initiate vertical convection which supposedly homogenizes several hundreds of meters of the upper water column, hereby transforming saltier upper deep water to lighter SAMW by incorporating fresh Subantarctic Surface Water. Here we show the formation process of SAMW west of Drake Passage as documented by autonomous profiling floats. Vertical convection exceeds 500 m during September and October but only south of 56°S.
Evidence in support of the climate change–Atlantic hurricane hypothesis
Authors: Elsner James B.
Published: August 2006

The power of Atlantic tropical cyclones is rising rather dramatically and the increase is correlated with an increase in the late summer/early fall sea surface temperature over the North Atlantic. A debate concerns the nature of these increases with some studies attributing them to a natural climate fluctuation, known as the Atlantic Multidecadal Oscillation (AMO), and others suggesting climate change related to anthropogenic increases in radiative forcing from greenhouse‐gases. Here tests for causality using the global mean near‐surface air temperature (GT) and Atlantic sea surface temperature (SST) records during the Atlantic hurricane season are applied. Results show that GT is useful in predicting Atlantic SST, but not the other way around. Thus GT “causes” SST providing additional evidence in support of the climate change hypothesis. Results have serious implications for life and property throughout the Caribbean, Mexico, and portions of the United States.
Forming chainlike filaments of magnetic colloids: The role of the relative strength of isotropic and anisotropic particle interactions
Authors: Martínez Pedrero F. , Tirado Miranda M. , Schmitt A. , Callejas Fernández J.
Published: August 2006

The influence of the interplay between anisotropic magnetic and isotropic electrostatic interactions on the aggregation behavior of aqueous suspensions of electric double layered magnetic particles was studied. Therefore, the particles were aggregated under the action of an external magnetic field and in the presence of different amounts of an indifferent 1:1 electrolyte. After removing the field, linear aggregates remained in the sample. Static light scattering and electron micrographs confirmed the chainlike cluster morphology. Dynamic light scattering was used for monitoring the average diffusion coefficient of these magnetic filaments. A theoretical model that allows the experimental mean diffusion coefficient to be related to the average chain length was successfully employed. The results show that, at fixed exposure time and field strength, the average filament size is proportional to the amount of electrolyte added. The light scattering data and transmission electron microscopy micrographs prove that permanent chains coexist with a relatively large fraction of individual particles when no or little electrolyte was added to the samples. A plausible explanation for this “selective aggregation” phenomenon could be given in terms of surface charge heterogeneities. The chain growth was found to follow a power law with a similar exponent for all the electrolyte concentrations studied. Scaling theories were employed for estimating the ratio of particles taking part in the aggregation process.
Toeplitz algebras and spectral results for the one-dimensional Heisenberg model
Authors: Damak Mondher , Măntoiu Marius , Tiedra de Aldecoa Rafael
Published: August 2006

We determine the structure of the spectrum and obtain nonpropagation estimates for a class of Toeplitz operators acting on a subset of the lattice ZN. This class contains the Hamiltonian of the one-dimensional Heisenberg model.
Direct imaging of repulsive and attractive colloidal glasses
Authors: Kaufman Laura J. , Weitz David A.
Published: August 2006

Coherent anti-Stokes Raman scattering microscopy is performed on glassy systems of poly(methylmethacrylate) colloidal particles in density- and refractive-index-matched solvents. Samples are prepared with varying amounts of linear polystyrene, which induces a depletion driven attraction between the nearly hard-sphere particles. Images collected over several hours confirm the existence of a reentrant glass transition. The images also reveal that the dynamics of repulsive and attractive glasses are qualitatively different. Colloidal particles in repulsive glasses exhibit cage rattling and escape, while those in attractive glasses are nearly static while caged but exhibit large displacements upon (infrequent) cage escape.
Activation energy for hydrogen abstraction from methane over Li-doped MgO: A density functional theory study
Authors: Zobel Nico , Behrendt Frank
Published: August 2006

Hydrogen abstraction from methane over Li-doped MgO is studied by means of density functional theory. The generalized synchronous transit method is applied to determine the transition state of the reaction. This method allows a transition state search that is more comprehensive compared with previous studies. The convergence of the calculated activation barrier with respect to cutoff energy, k-point mesh, vacuum layer thickness, and number of ionic layers in the crystal slab is examined. The activation barrier is calculated to be 0.745±0.01eV (71.9±1.0kJ∕mol).
Cross sections for electron trapping by DNA and its component subunits I: Condensed tetrahydrofuran deposited on Kr
Authors: Park Yeun Soo , Cho Hyuck , Parenteau Luc , Bass Andrew D. , Sanche Léon
Published: August 2006

We report cross sections for electron capture processes occurring in condensed tetrahydrofuran (THF) for incident electron energies in the range of 0–9eV. The charge trapping cross section for 6–9eV electrons is very small, and an upper limit of 4×10−19cm2 is estimated from our results. This latter is thus also an upper bound for the cross section for dissociative electron attachment process that is known to occur at these energies for condensed THF. At energies close to zero eV electron trapping proceeds via intermolecular stabilization. The cross section for this process is strongly dependent on the quantity of deposited THF. Since THF may model the furyl ring found in deoxyribose, these measurements indicate that this ring likely plays little role in either initiating or enhancing strand break damage via the attachment of the low energy secondary electrons produced when DNA is exposed to ionizing radiation.
Efficient and precise solvation free energies via alchemical adiabatic molecular dynamics
Authors: Abrams Jerry B. , Rosso Lula , Tuckerman Mark E.
Published: August 2006

A new molecular dynamics method for calculating free energies associated with transformations of the thermodynamic state or chemical composition of a system (also known as alchemical transformations) is presented. The new method extends the adiabatic dynamics approach recently introduced by Rosso et al. [J. Chem. Phys. 116, 4389 (2002)] and is based on the use of an additional degree of freedom, λ, that is used as a switching parameter between the potential energy functions that characterize the two states. In the new method, the coupling parameter λ is introduced as a fictitious dynamical variable in the Hamiltonian, and a system of switching functions is employed that leads to a barrier in the λ free energy profile between the relevant thermodynamic end points. The presence of such a barrier, therefore, enhances sampling in the end point (λ=0 and λ=1) regions which are most important for computing relevant free energy differences. In order to ensure efficient barrier crossing, a high temperature Tλ is assigned to λ and a fictitious mass mλ is introduced as a means of creating an adiabatic separation between λ and the rest of the system. Under these conditions, it is shown that the λ free energy profile can be directly computed from the adiabatic probability distribution function of λ without any postprocessing or unbiasing of the output data. The new method is illustrated on two model problems and in the calculation of the solvation free energy of amino acid side-chain analogs in TIP3P water. Comparisons to previous work using thermodynamic integration and free energy perturbation show that the new λ adiabatic free energy dynamics method results in very precise free energy calculations using significantly shorter trajectories.
Darwin and mass-velocity relativistic corrections in non-Born-Oppenheimer variational calculations
Authors: Kedziera Dariusz , Stanke Monika , Bubin Sergiy , Barysz Maria , Adamowicz Ludwik
Published: August 2006

The Pauli approach to account for the mass-velocity and Darwin relativistic corrections has been applied to the formalism for quantum mechanical molecular calculations that does not assume the Born-Oppenheimer (BO) approximation regarding separability of the electronic and nuclear motions in molecular systems. The corrections are determined using the first order perturbation theory and are derived for the non-BO wave function of a diatomic system expressed in terms of explicitly correlated Gaussian functions with premultipliers in the form of even powers of the internuclear distance. As a numerical example we used calculations of the transition energies for pure vibrational states of the HD+ ion.
Optical constants and thermo-optic coefficients of nanocrystalline diamond films at 30–500°C
Authors: Hu Z. G. , Hess P.
Published: August 2006

The refractive index and absorption index of nanocrystalline diamond (NCD) films were investigated using spectroscopic ellipsometry between 30 and 500°C. Due to their high transparency the experimental spectra could be well fitted in the subgap region using a single-oscillator model with a four-phase layered structure. The single-oscillator model yields a small optical absorption in the band gap region. The temperature dependence of dispersion of the refractive index over the photon energy range of 1.15–4.75eV was determined. Based on the Bose-Einstein model, a thermo-optic coefficient of (1∕n)(∂n∕∂T)=6.5×10−6K−1 at 300K was obtained for the NCD film in the near-infrared region.
Fluorescence correlation spectroscopy analysis of segmental dynamics in actin filaments
Authors: Bernheim-Groswasser Anne , Shusterman Roman , Krichevsky Oleg
Published: August 2006

We adapt fluorescence correlation spectroscopy (FCS) formalism to the studies of the dynamics of semiflexible polymers and derive expressions relating FCS correlation function to the longitudinal and transverse mean-square displacements of polymer segments. The obtained relations do not depend on any specific model of polymer dynamics. We use the derived expressions to measure the dynamics of actin filaments in two experimental situations: filaments labeled at distinct positions and homogeneously labeled filaments. Both approaches give consistent results and allow to measure the temporal dependence of the segmental mean-square displacement over almost five decades in time, from ∼40μsto∼2s. These noninvasive measurements allow for a detailed quantitative comparison of the experimental data to the current theories of semiflexible polymer dynamics. Good quantitative agreement is found between the experimental results and theories explicitly accounting for the hydrodynamic interactions between polymer segments.
Ordering transition and demixing of a binary mixture of thick and thin rodlike molecules in the presence of an external field
Authors: Dobra Szabolcs , Szalai István , Varga Szabolcs
Published: August 2006

The effect of an external field (electric/magnetic) on the phase behavior of the binary mixture of very long thick and thin rodlike particles is studied. Both the thick and thin particles possess positive but different susceptibility anisotropics (Δα). The difference in the extent of interaction between the external field and the two species is varied by means of a coupling parameter (l=Δαthick∕Δαthin). Isotropic-nematic phase transition and demixing phase transitions taking place both in the isotropic and nematic phases are examined as a function of field strength on the level of the second virial theory of Onsager in the range of 0<l<1. The approximate sixth order Legendre polynomial expansion method is used to represent the excluded volume interaction between the rodlike particles. It is found that the isotropic phase becomes weakly nematic (paranematic) in the presence of external field and the field orients both components in the direction of the field even if the field does not have direct interaction with the thick component (l=0). Analytical expressions are derived for the external field induced order parameters and birefringence. The increasing field destabilizes both types of demixing transitions (isotropic-isotropic and nematic-nematic) and the paranematic-nematic phase transition. Moreover it induces closed loop immiscibility, and upper and lower critical points terminating the paranematic-nematic phase coexistence may occur for low values of the coupling parameter. It is interesting that while the phase boundaries of the paranematic-paranematic demixing and the paranematic-nematic transitions are very sensitive to the value of the coupling parameter at low pressures, the paranematic-nematic and nematic-nematic phase boundaries are practically independent of the coupling parameter at high pressures.
Diamagnetic expansions for perfect quantum gases
Authors: Briet Philippe , Cornean Horia D. , Louis Delphine
Published: August 2006

In this work we study the diamagnetic properties of a perfect quantum gas in the presence of a constant magnetic field of intensity B. We investigate the Gibbs semigroup associated with the one particle operator at finite volume, and study its Taylor series with respect to the field parameter ω≔eB∕c in different topologies. This allows us to prove the existence of the thermodynamic limit for the pressure and for all its derivatives with respect to ω (the so-called generalized susceptibilities).
Photoabsorption spectra of Ti8C12 metallocarbohedrynes: Theoretical spectroscopy within time-dependent density functional theory
Authors: Martinez J. I. , Castro A. , Rubio A. , Alonso J. A.
Published: August 2006

The photoabsorption spectra of several of the most stable isomers of the Ti8C12 metallocarbohedryne are calculated using time-dependent density functional theory. Several ground-state magnitudes have been also calculated, such as cohesive energies, electronic gaps between the highest occupied and lowest unoccupied molecular orbitals, and static polarizabilities. Since significant differences are found among the photoabsorption spectra of the different isomers in the low energy region (0–5eV), we propose the comparison of experimental and the calculated absorption spectra as a tool to elucidate the isomers that appear to form in the experiments. Between 10 and 13eV all the spectra show a region of high absorption that we identify as due to collective electronic excitations. The existence of this prominent feature explains the occurrence of delayed ionization and delayed ion emission phenomena observed in previous experiments.
Organic light-emitting diodes having exclusive near-infrared electrophosphorescence
Authors: Williams Evan L. , Li Jian , Jabbour Ghassan E.
Published: August 2006

Near-infrared (NIR) emission is demonstrated from phosphorescent organic light-emitting diodes containing blends of polymeric host and heavy metal complex, iridium(III) bis(1-pyrenyl-isoquinolinato-N,C′) acetylacetonate. The devices exhibit exclusive NIR emission with a peak value at 720nm. Forward light output exceeds 100μW∕cm2, and the external quantum efficiency is nearly 0.1%. These values are shown to increase upon using a hole blocking layer in the device architecture.
What really enhances the adsorption of polymers onto chemically nonuniform surfaces: Surface randomness or its heterogeneity?
Authors: Chervanyov A. I. , Heinrich G.
Published: August 2006

We theoretically perform a comparative analysis of the adsorption of polymers onto the regularly and randomly nonuniform surfaces. By developing and making use of the self-consistent perturbation expansion we calculate the surface excesses of the polymers adsorbed on the random and periodically patterned surfaces. In both cases the enhancement of the polymer adsorption is indicated, as compared to the adsorption onto the homogeneous surface that has the same average affinity for polymers. Moreover, the results obtained for the randomly nonuniform and periodically patterned adsorbing surfaces show striking quantitative similarity, when compared at the same characteristic sizes of inhomogeneities of these surfaces. This finding leads to the conclusion that the adsorption ability of the nonuniform surface primarily depends on the characteristic size of the surface inhomogeneity, rather than on the spatial distribution of the inhomogeneities on this surface. In all cases, the calculated total surface excess is found to be a decaying function of the ratio of the radius of gyration of polymers to the characteristic size of the surface inhomogeneity. The effect of the excluded volume is found to reduce the polymer adsorption.
Bulk and surface oxygen vacancy formation and diffusion in single crystals, ultrathin films, and metal grown oxide structures
Authors: Carrasco J. , Lopez N. , Illas F. , Freund H.-J.
Published: August 2006

The neutral oxygen vacancy (OV) energy formation for bulk, subsurface sites at different depths from the surface and various surface sites has been estimated for single crystals, unsupported ultrathin films of MgO, CaO, and BaO, and MgO ultrathin films supported on Ag(001). From the calculated energy barriers for diffusion through the surface and from the surface to the bulk it is found that diffusion is a hindered event, especially for MgO. Nevertheless, diffusion from the terrace to step edges is largely favored while diffusion through terrace sites is less likely and surface to bulk has a very low probability. It is argued that this explains recent scanning tunneling microscopy images for MgO thin films supported on Ag(001) showing OV populating preferentially the step edge sites.
Wurtzite NiO: A potential half-metal for wide gap semiconductors
Authors: Wu R. Q. , Peng G. W. , Liu L. , Feng Y. P.
Published: August 2006

Calculations based on spin density functional theory (DFT), with and without on-site Coulomb and exchange term (U-J), were performed to study the structural and electronic properties of wurtzite NiO (w-NiO). A small hole pocket in the majority spin was found at the Γ point in the band structure calculated with pure DFT. However, when a moderate value of U-J was included, it became half-metallic. With U-J=7.0eV, w-NiO remains half-metallic when its lattice constant a is compressed to match that of SiC (3.09Å) or stretched to match that of ZnO (3.28Å), suggesting that w-NiO is a promising half-metallic electrode for these technologically important wide gap semiconductors in spintronic applications.
Abel inversion of a holographic interferogram for determination of the density profile of a sheared-flow Z pinch
Authors: Jackson S. L. , Shumlak U.
Published: August 2006

A holographic interferometer is used to determine the radial electron number density profile of a sheared-flow Z pinch. Chord-integrated density information is recorded during a plasma pulse using the expanded beam of a pulsed ruby laser and holographic techniques. An Interactive Data Language (IDL) computer routine that requires only minimal user interaction is used to measure the resulting fringe shift in the reconstructed interferogram. This chord-integrated density information is inverted using an Abel inversion to determine the radial electron density profile. The density profiles obtained show a radially symmetric plasma column with an electron density of 1016–1017cm−3 above the background plasma density. Holographic measurements are made at different times on separate plasma pulses to track the evolution of the density profile over time. These measurements are corroborated by time-dependent measurements made using a He–Ne interferometer.
Signal analysis and characterization of experimental setup for the transient thermoreflectance technique
Authors: Stevens Robert J. , Smith Andrew N. , Norris Pamela M.
Published: August 2006

The transient thermoreflectance (TTR) technique is a powerful optical pump-probe technique often used to measure thermal properties and monitor ultrafast processes. The technique has been used to measure a range of properties including the thermal conductivities of thin films and electron-phonon coupling factors to mention a few. TTR measurements are sensitive to residual heating and misalignment, which can lead to erroneous analysis of TTR data. To minimize these errors, we have developed a simple phase correction technique to reduce errors associated with residual heating and other background noise. Besides its simple implementation, the technique also requires no previous knowledge of the transient reflectance response. The technique is verified with simulated experimental data. The importance of proper alignment of the pump and probe beams over the entire range of pump-probe time delays of interest is discussed, along with a means of quantifying error associated with misalignment.
Novel capacitor discharging system
Authors: Qi Xiaoguang , Boggs Steven
Published: August 2006

A relatively simple high voltage discharge system has been designed for capacitor pulse discharge with peak current around 1.5kA with a time to peak in the microsecond range. The circuit is novel in that all low voltage electronics are powered from the high voltage supply, and the system operates as a relaxation oscillator. The system can be used to study the degradation of the capacitors as a result of pulse discharge.
Photoacoustic methodology to measure thermal and optical properties of dye solutions
Authors: Balderas-López J. A.
Published: August 2006

The analytical solution for the one-dimensional heat diffusion problem for a two layer system, in the Beer-Lambert model for light absorption, is shown to be useful for the implementation of a novel photoacoustic methodology, in the rear configuration, for the measurement of thermal and optical properties of dye solutions. The photoacoustic signal as a function of the sample’s thickness is used for this goal. This methodology was tested by measuring the optical absorption coefficient (at 650nm) and the thermal diffusivity for a solution of methylene blue in distilled water at various concentrations.
Coarse-grained V representability
Authors: Lammert Paul E.
Published: August 2006

The unsolved problem of determining which densities are ground state densities of an interacting electron system in some external potential is important to the foundations of density functional theory. A coarse-grained version of this ensemble V-representability problem is shown to be thoroughly tractable. Averaging the density of an interacting electron system over the cells of a regular partition of space produces a coarse-grained density. It is proved that every strictly positive coarse-grained density is coarse-grained ensemble V representable: there is a unique potential, constant over each cell of the partition, which has a ground state with the prescribed coarse-grained density. For a system confined to a box, the (coarse-grained) Lieb [Int. J. Quantum Chem. 24, 243 (1983)] functional is also shown to be Gâteaux differentiable. All results extend to open systems.
A near linear-scaling smooth local coupled cluster algorithm for electronic structure
Authors: Subotnik Joseph E. , Sodt Alex , Head-Gordon Martin
Published: August 2006

We demonstrate near linear scaling of a new algorithm for computing smooth local coupled-cluster singles-doubles (LCCSD) correlation energies of quantum mechanical systems. The theory behind our approach has been described previously, [J. Subotnik and M. Head-Gordon, J. Chem. Phys. 123, 064108 (2005)], and requires appropriately multiplying standard iterative amplitude equations by a bump function, creating local amplitude equations (which are smooth according to the implicit function theorem). Here, we provide an example that this theory works in practice: we show that our algorithm leads to smooth potential energy surfaces and yields large computational savings. As an example, we apply our LCCSD approach to measure the post-MP2 correction to the energetic gap between two different alanine tetrapeptide conformations.
The 5f2→5f16d1 absorption spectrum of Cs2GeF6:U4+ crystals: A quantum chemical and experimental study
Authors: Ordejón Belén , Karbowiak Miroslaw , Seijo Luis , Barandiarán Zoila
Published: August 2006

Single crystals of U4+-doped Cs2GeF6 with 1% U4+ concentration have been obtained by the modified Bridgman-Stockbarger method in spite of the large difference in ionic radii between Ge4+ and U4+ in octahedral coordination. Their UV absorption spectrum has been recorded at 7K, between 190 and 350nm; it consists of a first broad and intense band peaking at about 38000cm−1 followed by a number of broad bands of lower intensity from 39000to45000cm−1. None of the bands observed shows appreciable fine vibronic structure, so that the energies of experimental electronic origins cannot be deduced and the assignment of the experimental spectrum using empirical methods based on crystal field theory cannot be attempted. Alternatively, the profile of the absorption spectrum has been obtained theoretically using the U–F bond lengths and totally symmetric vibrational frequencies of the ground 5f2−1A1g and 5f16d(t2g)1−iT1u excited states, their energy differences, and their corresponding electric dipole transition moments calculated using the relativistic ab initio model potential embedded cluster method. The calculations suggest that the observed bands are associated with the lowest five 5f2−1A1g→5f16d(t2g)1−iT1u (i=1–5) dipole allowed electronic origins and their vibrational progressions. In particular, the first broad and intense band peaking at about 38000cm−1 can be safely assigned to the 0-0 and 0-1 members of the a1g progression of the 5f2−1A1g→5f16d(t2g)1−1T1u electronic origin. The electronic structure of all the states with main configurational character 5f16d(t2g)1 has been calculated as well. The results show that the lowest crystal level of this manifold is 5f16d(t2g)1−1Eu and lies about 6200cm−1 above the 5f2 level closest in energy, which amounts to some 11 vibrational quanta. This large energy gap could result in low nonradiative decay and efficient UV emission, which suggest the interest of investigating further this new material as a potential UV solid state laser.
Links between polydomain phases in electric-field-cooled (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 single crystals
Authors: Topolov V. Yu.
Published: August 2006

This letter is devoted to the analysis of interconnections between non-180° domain structures of ferroelectric phases in 0.70Pb(Mg1∕3Nb2∕3)O3–0.30PbTiO3 and 0.65Pb(Mg1∕3Nb2∕3)O3–0.35PbTiO3 single crystals cooled in the electric field E‖[001] or E‖[110]. Diagrams are proposed for the description of interfaces between the polydomain phases at various volume fractions of some domain types. Examples of the elastic matching of the polydomain phases along zero net strain planes are also considered.
Effect of magnetic field in electron-impact ion sources and simulation of electron trajectories
Authors: Park Chang J. , Ahn Jong R.
Published: August 2006

Effect of magnetic field has been studied for the electron-impact ion sources coupled with a quadrupole mass spectrometer. Computer simulation of electron trajectories showed better collimation and more helical rotations under stronger magnetic field, suggesting enhanced ionization efficiency. However, the magnetic field showed different effect on the mass spectrometer signals for different types of ion sources. For the cross beam ion source, where ion beam direction is perpendicular to the magnetic field, the mass spectrometer signals decreased when the magnetic field strength was higher than 20G. For the axial ion source, where both the electron beam and ion beam are on the same axis of the magnetic field, the mass spectrometer signals increased almost linearly with the applied magnetic field intensity. The axial ion source with a magnet intensity of 800G showed about five times improvement in mass spectrometer sensitivity compared with the cross beam ion source.
Focused ion beam milling monitored by an additional electrode
Authors: Kunstmann T. , Utzat D. , Schlarb A. , Mazarov P. , Wucher A. , Möller R.
Published: August 2006

We present an idea to control the progress during focused ion beam milling of cantilevers. Since the monitoring options given by the focused ion beam machine did not satisfy our needs for complete control of the milling process, we decided to measure the current behind the target. A simple current to voltage converter and the electric setup are presented in this Note.
A photonic band-gap resonator to facilitate GHz-frequency conductivity experiments in pulsed magnetic fields
Authors: McDonald R. D. , Singleton J. , Goddard P. A. , Harrison N. , Mielke C. H.
Published: August 2006

We describe instrumentation designed to perform millimeter-wave conductivity measurements in pulsed high magnetic fields at low temperatures. The main component of this system is an entirely nonmetallic microwave resonator. The resonator utilizes periodic dielectric arrays (photonic band-gap structures) to confine the radiation, such that the resonant modes have a high Q factor, and the system possesses sufficient sensitivity to measure small samples within the duration of a magnet pulse. As well as measuring the sample conductivity to probe orbital physics in metallic systems, this technique can detect the sample permittivity and permeability allowing measurement of spin physics in insulating systems. We demonstrate the system performance in pulsed magnetic fields with both electron paramagnetic resonance experiments and conductivity measurements of correlated electron systems.
Ultrasonic interferometric sensor for rheological changes of fluids
Authors: Balasubramaniam Krishnan , Sethuraman S.
Published: August 2006

An ultrasonic interferometric sensor has been introduced for the measurement of subtle changes in the physical properties of fluids such as density, viscosity, and bulk modulus. Tone burst ultrasonic waves are generated using a single peizocrystal bonded in between two solid delay line media of slightly different lengths. One side is in contact with a reference fluid (with known properties) and the other with a fluid whose properties are to be measured. The ultrasonic waves reflect from the two solid-fluid boundaries and are received back by the peizocrystal where the interference effects are measured. The longitudinal waves were used to measure the longitudinal impedance, while shear waves were used to measure the shear impedance. Glycerin-water mixtures were used as the test material. A simple plane wave model was shown to provide satisfactory comparison with experiments. Various parameters that influence the measurement were studied.
Development of a parallel local oxidation nanolithography instrument
Authors: Martinez Javier , Losilla Nuria S. , Biscarini Fabio , Schmidt Georg , Borzenko Tanja , Molenkamp Laurens W. , Garcia Ricardo
Published: August 2006

We have developed an instrument to perform local oxidation nanofabrication processes in parallel. The instrument has three major components, the stamp holder, the sample base, and the supporting frame. The sample base is actuated by three precision screws that enable motion in the three orthogonal directions. Sample base and stamp holder are enclosed and sealed inside a chamber with two inlets to introduce different gases. The chamber is supported by a rigid frame. We show the parallel patterning of silicon oxide features on silicon surfaces by the application of a bias voltage between the sample and the stamp when they are in contact. Arrays of parallel lines separated by 100nm have been patterned over cm2 regions in one minute.
Erasure of photoconductivity by magnetic field in oxygen-deficient La2∕3Sr1∕3MnO3−δ thin films
Authors: Sheng Z. G. , Sun Y. P. , Dai J. M. , Zhu X. B. , Song W. H.
Published: August 2006

Both transient and persistent photoconductivities (abbreviated to TPC and PPC, respectively) are observed in oxygen-deficient La2∕3Sr1∕3MnO3−δ thin films at low temperatures. The magnitudes of TPC and PPC are 7.6% and 6.08%, respectively, with light density of 4.35mW∕cm2 at 50K. Moreover, a small magnetic field can erase most of PPC effect sharply. The proportion of PPC erased by magnetic field achieves 73% in magnetic field of 0.001T and 97.5% in 0.5T. Electrons trapped by oxygen vacancies are released by the magnetic field and recombine with holes are suggested to be the origin for depression of PPC effect.
Pinning of size-selected Pd nanoclusters on graphite
Authors: Gibilisco S. , Di Vece M. , Palomba S. , Faraci G. , Palmer R. E.
Published: August 2006

The production of stable cluster arrays on smooth surfaces has several potential technological applications. We report a study of the pinning of size-selected palladium nanoclusters on the graphite surface. The clusters formed during gas aggregation in vacuum are projected with sufficient kinetic energy to create a defect in the graphite surface. The energy necessary to create such an immobilizing defect is investigated as a function of the palladium cluster size. The palladium pinning energy is found to deviate from the simple binary collision model as appropriate to previously reported silver and gold results. This finding is in agreement with the deviation of nickel clusters and points to the influence of the interatomic cluster bonding on the mechanics of the collision.
Molecular dynamics simulations of self-organized polyicosahedral Si nanowire
Authors: Nishio Kengo , Morishita Tetsuya , Shinoda Wataru , Mikami Masuhiro
Published: August 2006

A novel polyicosahedral nanowire is spontaneously formed in a series of annealing molecular dynamics simulations of liquid Si inside a nanopore of 1.36nm in diameter. The polyicosahedral Si nanowire is stable even in a vacuum up to about 77% of the melting temperature of bulk Si. Our structural energy calculations reveal that the polyicosahedral nanowire is energetically advantageous over the pentagonal one for a wire whose diameter is less than 6.02nm, though the latter has been recently proposed as the lowest energy wire. These results suggest the possibility of the formation of a new stable polyicosahedral Si nanowire.
In situ chemical and structural investigations of the oxidation of Ge(001) substrates by atomic oxygen
Authors: Molle Alessandro , Bhuiyan Md. Nurul Kabir , Tallarida Grazia , Fanciulli Marco
Published: August 2006

The exposure of Ge(001) substrates to atomic oxygen was studied in situ to establish the stability of the germanium oxide. After preparing chemically clean and atomically flat Ge(001) surfaces, the Ge samples were exposed to atomic oxygen in a wide temperature range from room temperature to 400°C. The chemical composition of the so-formed oxides was studied by means of x-ray photoelectron spectroscopy, while the structure was observed by reflection high energy electron diffraction. At low substrate temperatures the atomic oxygen is efficiently chemisorbed and suboxides coexist with the dioxide, which in turn is remarkably promoted in the high temperature range.
Electrorheological fluid-actuated microfluidic pump
Authors: Liu Liyu , Chen Xiaoqing , Niu Xize , Wen Weijia , Sheng Ping
Published: August 2006

The authors report the design and implementation of an electrorheological (ER) fluid-actuated microfluidic pump, with programmable digital control. Our microfluidic pump has a multilayered structure fabricated on polydimethylsiloxane by soft-lithographic technique. The ER microfluidic pump exhibits good performance at high pumping frequencies and uniform liquid flow characteristics. It can be easily integrated with other microfluidic components. The programmable control also gives the device flexibility in its operations.
Selective surface treatment of micro printing pin and its performance
Authors: Tsai Jane Gin Fai , Chen Zugen , Nelson Stanley F. , Kim Chang-Jin
Published: August 2006

Biological microarray construction relies on the sequential deposition of liquid samples, typically by contact or ink-jet printing. One drawback of contact printing is excessive solution pickup on the pin’s outer surface, resulting in inefficiency. The authors combated this problem with a simple method that treats pin surfaces selectively so the outer surface becomes hydrophobic while the inner surface remains hydrophilic. Silicon-micromachined pins were utilized to evaluate the effect. The results demonstrated elimination of preprinting, greater droplet size consistency (e.g., 42±5μm vs 63±13μm), and more spots (∼800 vs ∼300) printed per loading. Consequently, an average spot diameter, between 30 and 100μm, can be controlled, depending on the pin design.
Understanding of hydrogel network formation and its application in the architecture of significantly enhanced hydrogel
Authors: Xiong J. Y. , Liu X. Y. , Li J. L. , Narayanan J. , Wang R. Y.
Published: August 2006

An understanding of the physical hydrogel network formation has been obtained by dynamic rheological experiments. The evidence shows that the network formation turns out to be a nucleation-controlled process. It was found that there exists a critical temperature Tc; fiber branching is greatly enhanced when the network formation is performed in the regime of T<Tc (T, the final setting temperature). This finding enables the authors to build significantly enhanced gel networks. So far G′ (elastic modulus) of the hydrogel network has been enhanced by 187% while the formation period can be greatly shortened to only 1∕20 of the previous process.
Ferroelectric and piezoelectric behaviors of individual single crystalline BaTiO3 nanowire under direct axial electric biasing
Authors: Wang Zhaoyu , Suryavanshi Abhijit P. , Yu Min-Feng
Published: August 2006

A method, which is especially useful for the study of ferroelectric nanowire with piezoresponse force microscopy (PFM), was developed. In this method electric bias is directly applied on the axial direction of nanowire. The axial poling and switching of single crystalline BaTiO3 nanowire were realized, and hysteresis loop and shear piezoresponse were acquired with PFM operated in lateral mode. The study demonstrated the ferroelectric nature of the nanowire and the need of a significantly higher poling electric field to reach polarization saturation in nanowire than that in bulk BaTiO3 crystal.
Fabrication of iron silicide nanowires from nanowire templates
Authors: Yamamoto Keiichi , Kohno Hideo , Takeda Seiji , Ichikawa Satoshi
Published: August 2006

The authors demonstrate that Fe silicide nanowires can be fabricated from vapor-liquid-solid grown Si nanowire templates. By heating simple Si nanowires with Fe, Fe infuses into Si nanowires through a surface oxide layer and Si nanowires are converted to α-FeSi2 or ε-FeSi partially. Furthermore, when Au catalyst forms Au∕Si heterostructured nanowires, heating with Fe results in the formation of β-FeSi2.
Self-assembled growth of ordered GaAs nanostructures
Authors: Ohtake Akihiro , Koguchi Nobuyuki
Published: August 2006

The authors have fabricated an ordered array of GaAs nanoislands using the network of misfit dislocations at the InAs∕GaAs(111)A interface. Ga nanoislands are preferably formed at compressively strained regions between buried dislocations. GaAs nanoislands fabricated by supplying As4 flux to the Ga islands also show a high degree of ordering, while simultaneous deposition of Ga and As results in random nucleation of GaAs nanoislands.