bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential for the use of vocal individuality as a conservation research tool in two threatened Philippine hornbill species, the Visayan Hornbill and the Rufous-headed Hornbill
Authors: POLICHT RICHARD , PETRŮ MILADA , LASTIMOZA LUCIA , SUAREZ LEO
Published: January 2009

This study presents the first multivariate analysis of hornbill vocalizations and the first bioacoustic study of any Philippine hornbill species. We analyzed loud calls of two Philippine hornbill species, the Rufous-headed HornbillAceros waldeniand the Visayan HornbillPenelopides panini panini, to assess the possibility for their use in individual identification.

Our study showed that individuals of the two studied hornbill species can be identified on the basis of their loud calls, which means that these calls potentially contain information about the caller. Discriminant analysis classified 89% of individual Rufous-headed Hornbills and 90% of individual Visayan Hornbills correctly. The acoustic variables describing the most variation among individual Visayan Hornbills were spectral variables (second amplitude peak) and temporal variables (location of the maximum amplitude and call duration). The calls of individual Rufous-headed Hornbill were differentiated mainly by spectral variables (the fundamental and the first harmonic frequency, and additionally the upper quartile of the frequency range). Frequency parameters in Rufous-headed Hornbill calls were significantly lower than those in Visayan Hornbills. The use of acoustic monitoring of individuals as a non-invasive marking technique could help to monitor hornbill individual life history and to improve census data using capture-mark-recapture technique.
BRIDGING THE GAP BETWEEN GROWTH THEORY AND THE NEW ECONOMIC GEOGRAPHY: THE SPATIAL RAMSEY MODEL
Authors: Boucekkine Raouf , Camacho Carmen , Zou Benteng
Published: January 2009

We study a Ramsey problem in infinite and continuous time and space. The problem is discounted both temporally and spatially. Capital flows to locations with higher marginal return. We show that the problem amounts to optimal control of parabolic partial differential equations (PDEs). We rely on the existing related mathematical literature to derive the Pontryagin conditions. Using explicit representations of the solutions to the PDEs, we first show that the resulting dynamic system gives rise toan ill-posed problemin the sense of Hadamard. We then turn to the spatial Ramsey problem with linear utility. The obtained properties are significantly different from those of the nonspatial linear Ramsey model due to the spatial dynamics induced by capital mobility.
Planetary‐scale variability in the low‐latitude E region field‐aligned irregularities: First results from Gadanki observations
Authors: Phanikumar D. V. , Patra A. K. , Ratnam M. V. , Sripathi S.
Published: January 2009

In this paper, we present for the first time planetary‐scale wave signatures in the low‐latitude E region field‐aligned irregularities (FAI) observed during June 2004 to May 2005 using the Gadanki mesosphere‐stratosphere‐troposphere radar. We have observed a clear signature of 5–8 day variability in echo occurrence, in SNR, and also in Doppler velocity observed above 100 km. Concurrent temperature observations made using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the Thermosphere‐Ionosphere‐Mesosphere Energetic and Dynamics (TIMED) satellite have also clearly shown the presence of 5–8 day variability similar to that of FAI. The temperature variations have been characterized with zonal wave numbers of 3 and 4 and vertical wavelength of 15–20 km. These waves are found to have increasing amplitude with increasing height and phase progressing downward, suggesting that they were of lower atmospheric origin. It is emphasized that the planetary‐scale characteristics of neutral atmosphere in the FAI observations are important in understanding the vertical coupling of the low‐latitude ionosphere‐atmosphere system. These observations and the pertinent issues are discussed in the light of current understanding of the planetary‐scale role on the FAI variability.
Measurement of NOy during Campaign of Air Quality Research in Beijing 2006 (CAREBeijing‐2006): Implications for the ozone production efficiency of NOx
Authors: Chou Charles C.‐K. , Tsai Chao‐Yang , Shiu Chein‐Jung , Liu Shaw Chen , Zhu Tong
Published: January 2009

Total reactive nitrogen oxides (NOy) are among the key components in the chemistry of ozone production. In order to improve the understanding of the formation mechanisms of high‐ozone events in Beijing, China, an intensive experiment on the reactive nitrogen oxides was carried out at the observatory of Peking University during the Campaign of Air Quality Research in Beijing and surrounding areas in 2006 (CAREBeijing‐2006) campaign. In this study, analysis focusing on the data of high O3 episodes was performed to examine the relationship between the concentration of total oxidant and the composition of NOy. High levels of NO and NOy were observed in the morning rush hours, indicating the influences of fresh emissions from local traffic. However, the ratio of [NO] to [NOy] was only 11–60% in the morning, implying that there was a substantial amount of aged air pollutants remained overnight in the stagnant air mass. Significant increases in the NOz mixing ratio (= [NOy]‐[NOx]) were observed during the period from the morning toward early afternoon, consistent with the increasing oxidant level. Ozone production efficiency of NOx (OPEx), which was derived from the NOz‐Ox regression, was found to range from 3.9 to 9.7 mol/mol in Beijing. Furthermore, it was revealed that the daily [NOz] maximum was proportional to the NOx peak level in the morning, and that OPEx decreased with the increases of [NOz] in a hyperbolic form. According to the results, abatement in NOx emission would not be effective toward reducing ozone concentrations in Beijing.
Surface roughness over the northern half of the Greenland Ice Sheet from airborne laser altimetry
Authors: van der Veen C. J. , Ahn Y. , Csatho B. M. , Mosley‐Thompson E. , Krabill W. B.
Published: January 2009

Surface roughness, defined as the standard deviation of small‐scale elevation fluctuations from the linear trend over 0.5 km, can be estimated from high‐resolution airborne laser altimetry. Here we present results for the northern half of the Greenland Ice Sheet using laser data collected in May 1995. Roughness is smallest in the central region straddling the ice divide, increases in amplitude toward the coast, and appears to be correlated with slope of the ice surface. For most of the study region surface roughness is 8 cm or less (<2.5 cm water equivalent). In smaller regions associated with fast flow, larger values are found. Comparison of the size of small‐scale topographic disturbances with the spatial noise estimated from five closely spaced ice cores drilled in northwest Greenland shows good agreement. Similar correspondence was found earlier using nine ice cores from the Summit region. These results indicate that the airborne laser altimeter provides an efficient platform for characterizing the statistical nature of the snow surface over large areas of the polar ice sheets.
Assessment of second‐order ionosphere error in GPS range observables using Arecibo incoherent scatter radar measurements
Authors: Morton Yu T. , Zhou Qihou , van Graas Frank
Published: January 2009

The second‐order ionosphere error in GPS range measurements is determined by the electron densities and the geomagnetic field projection onto the GPS signal propagation direction along the GPS signal propagation path. It can be a delay or an advancement error. This paper presents the second‐order error analysis based on an extensive collection of electron density profiles measured by the Arecibo incoherent scatter radar and geomagnetic field vectors generated using the International Geomagnetic Reference Field model. The results indicate that the 56–500 km altitude range contributes a maximum of −1.1 cm for GPS L1 signals arriving from the zenith at Arecibo. For signals coming from the north and south at 10 degree elevation angles, the maximum errors are 0.9 cm and −3.4 cm, respectively. The maximum of the mean values of the second‐order error computed using the entire data set are −0.55 cm, 0.48 cm, and −1.74 cm for a signal arriving from the zenith, from the north at 10 degrees elevation, and from the south at 10 degrees elevation, respectively. The paper also discusses the diurnal patterns and geomagnetic activity dependency of the second‐order error. Finally, the International Reference Ionosphere model is used to obtain an upper bound estimation of error contributions from the 500–2000 km altitude range.
The Ornstein–Zernike equation and critical phenomena in fluids
Authors: Martynov G. A.
Published: January 2009

It is shown that there are two classes of closure equations for the Ornstein–Zernike (OZ) equation: the analytical equations B=B(an) type of hyper-netted-chain approximation, Percus-Yevick approximation etc., and the nonanalytical equation B=B(non), where B(nan)=B(RG)+B(cr); B(RG) is the regular (analytical) component of the bridge functional, and B(cr) is the critical (nonanalytical) component of B(nan). The closure equation B(an) defines coordinates of a critical point and other individual features of critical phenomena, and B(nan) defines known relations between critical exponents. It is shown that a necessary condition for the existence of a nonanalytical solution of the OZ equation is the equality 5−η=δ(1+η), where η and δ are critical exponents, the values of which can change in a narrow interval. It is shown that the transition from analytical solution to nonanalytical solution is accompanied by a step of derivative of pressure. On the phase diagram of fluids the boundaries dividing the area of existence of analytical and nonanalytical solutions are indicated.
Positronium formation as a three-body reaction. II. The second-order nuclear amplitudes
Authors: Shojaei F. , Ghanbari-Adivi E. , Brunger M. J. , Bolorizadeh M. A.
Published: January 2009

We derive an exact analytic form for the second-order nuclear amplitudes, under the Faddeev three-body approach, which is applicable to the nonrelativistic high energy impact interaction where positronium is formed in the collision of a positron with an atom.
Three dimensional silicon photonic crystals fabricated by two photon phase mask lithography
Authors: Shir D. , Nelson E. C. , Chen Y. C. , Brzezinski A. , Liao H. , Braun P. V. , Wiltzius P. , Bogart K. H. A. , Rogers J. A.
Published: January 2009

We describe the fabrication of silicon three dimensional photonic crystals using polymer templates defined by a single step, two-photon exposure through a layer of photopolymer with relief molded on its surface. The resulting crystals exhibit high structural quality over large areas, displaying geometries consistent with calculation. Spectroscopic measurements of transmission and reflection through the silicon and polymer structures reveal excellent optical properties, approaching properties predicted by simulations that assume ideal layouts.
Angular distribution of Auger electrons from fixed-in-space and rotating C 1s→2π photoexcited CO: Theory
Authors: Fink R. F. , Piancastelli M. N. , Grum-Grzhimailo A. N. , Ueda K.
Published: January 2009

The one-center approach for molecular Auger decay is applied to predict the angular distribution of Auger electrons from rotating and fixed-in-space molecules. For that purpose, phase shifts between the Auger decay amplitudes have been incorporated in the atomic model. The approach is applied to the resonant Auger decay of the photoexcited C 1s→2π resonance in carbon monoxide. It is discussed how the symmetry of the final ionic state is related to features in the angular distributions and a parametrization for the molecular frame Auger electron angular distribution is suggested. The angular distribution of Auger electrons after partial orientation of the molecule by the σ→π-excitation process is also calculated and compared to available experimental and theoretical data. The results of the one-center approach are at least of the same quality as the available theoretical data even though the latter stem from a much more sophisticated method. As the one-center approximation can be applied with low computational demand even to extended systems, the present approach opens a way to describe the angular distribution of Auger electrons in a wide variety of applications.
The peculiar phase structure of random graph bisection
Authors: Percus Allon G. , Istrate Gabriel , Gonçalves Bruno , Sumi Robert Z. , Boettcher Stefan
Published: January 2009

The mincut graph bisection problem involves partitioning the n vertices of a graph into disjoint subsets, each containing exactly n/2 vertices, while minimizing the number of “cut” edges with an endpoint in each subset. When considered over sparse random graphs, the phase structure of the graph bisection problem displays not only certain familiar properties but also some surprises. It is known that when the mean degree is below the critical value of 2 log 2, the cutsize is zero with high probability. We study how the minimum cutsize increases with mean degree above this critical threshold, finding a new analytical upper bound that improves considerably upon previous bounds. Combined with recent results on expander graphs, our bound suggests the unusual scenario that random graph bisection is replica symmetric up to and beyond the critical threshold, with a replica symmetry breaking transition possibly taking place above the threshold. An intriguing algorithmic consequence is that although the problem is NP-hard, we can conceivably find near-optimal cutsizes (whose ratio to the optimal value approaches 1 asymptotically) in polynomial time for typical instances near the phase transition.
Theoretical study of noble-gas containing metal halides
Authors: Mou Chun-Hao , Witek Henryk A.
Published: January 2009

Equilibrium structures, energetic stability, and vibrational frequencies of noble-gas containing metal halides, MNgX and NgMX (Ng=Ar,Kr,Xe; M=Cu,Ag,Au; X=F,Cl,Br) have been studied computationally using coupled cluster, density functional, and perturbation techniques. The NgMX species have been found to be stable with the Ng–M bond dissociation energy of 2–22kcal∕mol. Our calculations indicate that the argon-containing MNgX compounds are unstable or very weakly bound. For most of the krypton- and xenon-containing species, well-defined (MNg)δ+Xδ− equilibrium structures have been located. Large MNgX→Ng+MX reorganization barriers for some of the MNgX molecules (e.g., AuXeF and AuXeCl) indicate their considerable kinetic stability. The presented results suggest that direct observation of the most stable of the MNgX molecules might be possible in experiment.
Amorphous SnO2–SiO2 thin films with reticular porous morphology for lithium-ion batteries
Authors: Zhang J. , Chen L. B. , Li C. C. , Wang T. H.
Published: January 2009

Amorphous SnO2–SiO2 thin films with reticular porous morphology were fabricated by electrostatic spray deposition method for lithium-ion batteries. An initial discharge capacity of the SnO2–SiO2 electrodes with 15% of SiO2 was about 1271 mA h/g, and the reversible capacity stayed in the range of 869–501 mA h/g during the successive 100 cycles, but only 1141 and 694–174 mA h/g for the pure SnO2 electrodes. The high capacity was attributed to the addition of SiO2, which facilitated the formation of the Li–Sn alloy. The improved cycle performance was due to reticular porous structure, which accommodated the volume change during cycling.
High efficiency blue phosphorescent organic light emitting diodes using a simple device structure
Authors: Jeon Soon Ok , Yook Kyoung Soo , Joo Chul Woong , Lee Jun Yeob
Published: January 2009

High efficiency blue phosphorescent organic light emitting diodes have been developed by using a simple device structure. A derivative of spirobifluorene based phosphine oxide was used both as a host and an electron transport layer with an exciton blocking function. A maximum quantum efficiency of 19.2% and a current efficiency of 37.2cd∕A were obtained by using a simple device structure without a hole blocking layer.
Spin-free intermediate Hamiltonian Fock space coupled-cluster theory with full inclusion of triple excitations for restricted Hartree Fock based triplet states
Authors: Musial Monika , Bartlett Rodney J.
Published: January 2009

The recently reported inclusion of the connected triples into the intermediate Hamiltonian realization of the Fock space coupled-cluster (IH-FS-CC) theory [M. Musial and R. J. Bartlett, J. Chem. Phys. 129, 044101 (2008)] is extended to produce the triplet states. This is done entirely in spatial orbitals on the basis of the double occupancy in the restricted Hartree Fock reference function. New equations for the triplet state amplitudes expressed in terms of the Goldstone diagrams are derived and implemented. Several applications show the usefulness of the IH-FS-CC scheme to describe the triplet states with the computational gains inherent to a spin-free implementation.
Methane dissociation and methyl diffusion on PdO{100}
Authors: Blanco-Rey M. , Jenkins S. J.
Published: January 2009

The CH4→CH3+H dissociation on the defect-free Pd–2O terminated PdO{100} surface is investigated by first principles calculations. CH3 chemisorbs preferentially at O sites, where the adsorption is 0.68 eV more stable than at Pd sites. Analysis of the electronic structure of adsorption geometries reveals that the enhanced stability is due to the strongly covalent character of the bonding between surface O and CH3. However, transition state searches suggest that the Pd atom is the most likely active site for CH4 dissociation. An alternative route toward the most stable chemisorbed state is proposed that involves diffusion of CH3 on the surface.
Atomic and molecular adsorption on RhMn alloy surface: A first principles study
Authors: Ma Xiufang , Deng Huiqiu , Yang Ming-Mei , Li Wei-Xue
Published: January 2009

Density functional theory calculations have been employed to study the effects of alloy on energetics and preferential adsorption sites of atomic (H, C, N, O, S), molecular (N2, NO, CO), and radical (CH3, OH) adsorption on RhMn(111) alloy surface, and underlying electronic and structural reasons have been mapped out. We find that though Mn is energetically favorable to stay in the subsurface region, the RhMn surface alloy may be developed via the segregation induced by strong interaction between oxygen-containing species and Mn. Independent of adsorbates (not including O and OH), the interactions between these species and Rh atoms are preferential, and enhanced in general due to the ligand effects induced by Mn nearby. In contrast, oxygen-containing species (atomic oxygen and hydroxyl) prefer to coordinate with Mn atom due to the significant hybridization between oxygen and Mn, a manifestation of the ensemble effects. The order of the binding energies on RhMn alloy surface from the least to the most strongly bound is N2<CH3<CO<NO<H<OH<O<N<S<C, which is also found on Rh(111) surface, due to the distinct reactivity of these species overwhelming the ligand/ensemble effects present in surface alloy. The implication of the modification of the adsorption energy, site preferences, and their relative stability on RhMn alloy surface, on the syngas (CO+H2) selective conversion, are discussed.
Stability diagram for the forced Kuramoto model
Authors: Childs Lauren M. , Strogatz Steven H.
Published: January 2009

We analyze the periodically forced Kuramoto model. This system consists of an infinite population of phase oscillators with random intrinsic frequencies, global sinusoidal coupling, and external sinusoidal forcing. It represents an idealization of many phenomena in physics, chemistry, and biology in which mutual synchronization competes with forced synchronization. In other words, the oscillators in the population try to synchronize with one another while also trying to lock onto an external drive. Previous work on the forced Kuramoto model uncovered two main types of attractors, called forced entrainment and mutual entrainment, but the details of the bifurcations between them were unclear. Here we present a complete bifurcation analysis of the model for a special case in which the infinite-dimensional dynamics collapse to a two-dimensional system. Exact results are obtained for the locations of Hopf, saddle-node, and Takens–Bogdanov bifurcations. The resulting stability diagram bears a striking resemblance to that for the weakly nonlinear forced van der Pol oscillator.
Synchronization of chaotic systems with uncertain chaotic parameters by linear coupling and pragmatical adaptive tracking
Authors: Ge Zheng-Ming , Yang Cheng-Hsiung
Published: January 2009

We study the synchronization of general chaotic systems which satisfy the Lipschitz condition only, with uncertain chaotic parameters by linear coupling and pragmatical adaptive tracking. The uncertain parameters of a system vary with time due to aging, environment, and disturbances. A sufficient condition is given for the asymptotical stability of common zero solution of error dynamics and parameter update dynamics by the Ge–Yu–Chen pragmatical asymptotical stability theorem based on equal probability assumption. Numerical results are studied for a Lorenz system and a quantum cellular neural network oscillator to show the effectiveness of the proposed synchronization strategy.
Implosion dynamics and K-shell x-ray generation in large diameter stainless steel wire array Z pinches with various nesting configurations
Authors: Jones Brent , Coverdale Christine A. , Deeney Christopher , Sinars Daniel B. , Waisman Eduardo M. , Cuneo Michael E. , Ampleford David J. , LePell P. David , Cochrane Kyle R. , Thornhill J. Ward , Apruzese J. P. , Dasgupta Arati , Whitney Kenneth G. , Clark Robert W. , Chittenden Jeremy P.
Published: January 2009

Nested stainless steel wire array variations were investigated on the 20MA Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)]. In order to reach experimentally observed electron temperatures near 3.8keV and excite the K shell, these ∼6.7keV photon energy x-ray sources must be of large initial diameter (45–80mm) which poses a concern for magnetic Rayleigh–Taylor instability growth. We discuss the implosion dynamics in these large diameter wire arrays, including an analysis of the ablation phase indicating that the prefill material is snowplowed at large radius. Nested array configurations with various mass and radius ratios are compared for instability mitigation and K-shell scaling. Degradation of the K-shell x-ray power and yield was observed for shots that did not have simultaneous implosion of the outer and inner wire arrays. Shots that were designed per this constraint exhibited K-shell yield scaling consistent with the model of J. W. Thornhill et al. [IEEE Trans. Plasma Sci. 34, 2377 (2006)] which had been benchmarked to single array results. This lends confidence to K-shell yield predictions using this model for future shots on the refurbished Z machine. Initial results employing a triple nested wire array to stabilize the large diameter implosion are also reported.
Description of nonspecific DNA-protein interaction and facilitated diffusion with a dynamical model
Authors: Florescu Ana-Maria , Joyeux Marc
Published: January 2009

We propose a dynamical model for nonspecific DNA-protein interaction, which is based on the “bead-spring” model previously developed by other groups, and investigate its properties using Brownian dynamics simulations. We show that the model successfully reproduces some of the observed properties of real systems and predictions of kinetic models. For example, sampling of the DNA sequence by the protein proceeds via a succession of three-dimensional motion in the solvent, one-dimensional sliding along the sequence, short hops between neighboring sites, and intersegmental transfers. Moreover, facilitated diffusion takes place in a certain range of values of the protein effective charge, that is, the combination of one-dimensional sliding and three-dimensional motion leads to faster DNA sampling than pure three-dimensional motion. At last, the number of base pairs visited during a sliding event is comparable to the values deduced from single-molecule experiments. We also point out and discuss some discrepancies between the predictions of this model and some recent experimental results as well as some hypotheses and predictions of kinetic models.
Molecular information processing in nonequilibrium copolymerizations
Authors: Andrieux David , Gaspard Pierre
Published: January 2009

We consider general fluctuating copolymerization processes, with or without underlying templates. We study the spatial ordering resulting from the nonequilibrium conditions as well as the information transmitted between the template and the synthesized copolymer. Information transmission turns out to be optimal in the infinite-dissipation limit when no correlations between the monomers are present. By contrast, we show that optimized regimes of information generation may exist when template and correlations effects interact.
Amide I Raman optical activity of polypeptides: Fragment approximation
Authors: Choi Jun-Ho , Cho Minhaeng
Published: January 2009

Vibrational optical activity (VOA) is an important property used to determine the absolute configuration of a chiral molecule in condensed phases. In particular, vibrational circular dichroism and Raman optical activity (ROA) are two representative VOA measurement techniques that have been extensively used to study structures and dynamics of biomolecules. Recently, the amide I vibrational circular dichroism of polypeptides was theoretically described by using fragment approximation methods, which are based on the assumption that amide I VOA can be described as a linear combination of those of constituent fragment peptide units. Here, we develop a fragment approximation theory applicable to numerical simulations of Raman and Raman optical activity spectra for the amide I vibrations in polypeptides. For an alanine dipeptide and pentapeptide analogs, we carried out density functional theory calculations of polarizability, magnetic dipole-, and electric quadrupole-ROA tensors. Numerically simulated spectra using the fragment approximation are directly compared to density functional theory results. Furthermore, the simulated ROA spectra of alanine-based right-handed α-helix and polyproline II polypeptides are directly compared to the previously reported experimental results. The agreements were found to be excellent, which suggests that the fragment approximation method developed for the numerical simulation of ROA spectrum of polypeptide in solution is valid and useful.
Experimental investigations of compressible vortex loops
Authors: Zare-Behtash H. , Kontis K. , Gongora-Orozco N.
Published: January 2009

The present study involves the shock wave and consequent vortex loop generated when a shock tube with various nozzle geometries is employed. It aims to provide quantitative and qualitative insight into the physics of these compressible phenomena. The geometries included two elliptic nozzles with minor to major axis ratios of 0.4 and 0.6, a 15 mm circular nozzle and a 30×30 mm2 square nozzle. The experiments were performed for driver gas (air) pressures of 4, 8 and 12 bars. Schlieren, shadowgraphy, and particle image velocimetry techniques were employed to visualize and quantify the induced flow field.
An experimental study of the airside flow structure during natural convection
Authors: Bukhari Syed J. K. , Siddiqui Kamran
Published: January 2009

We report on an experimental study conducted to investigate the airside flow structure above an evaporative water surface during natural convection. Two-dimensional airside velocity fields were measured using particle image velocimetry for three different surface heat flux conditions. Detailed analysis of the turbulent velocity fields shows a complex flow structure due the local interactions of fluid motions in vertical, horizontal, and normal directions. The trends of turbulent intensity profiles on airside and waterside are found to be similar. However, the airside turbulent intensities are approximately 20 times stronger than that on the waterside. The spectral analysis of the turbulent velocities showed the existence of two distinct power law regimes. In low wavenumber range, the buoyancy subrange is observed with a slope of −3 whereas, in high wavenumber range, the inertial subrange with the classical slope of −5/3 is observed. The results also indicate that the airside turbulent velocity fields control the local evaporation rate, which in turn influences the water surface temperature field and the waterside velocity field.
Confined drop motion in viscoelastic two-phase systems
Authors: You Ruobo , Haj-Hariri Hossein , Borhan Ali
Published: January 2009

In this study, we numerically examine the buoyancy-driven, axisymmetric motion of drops through vertical cylindrical capillaries. Combinations of Newtonian and viscoelastic drop and suspending fluid phases are considered. The effects of confinement, material properties, and rheological properties of the two phases on drop mobility and deformation are examined. Four dimensionless parameters (Reynolds number, capillary number, Deborah number, and the drop-to-tube size ratio) play critical roles in determining the drop motion. In general, a Newtonian drop immersed in a viscoelastic fluid experiences an extending trailing edge, while a viscoelastic drop in a Newtonian fluid develops an indentation around the rear stagnation point. Under certain conditions, a cusped drop appears due to fluid viscoelasticity that triggers shape instability.
A comparative analysis of deep level emission in ZnO layers deposited by various methods
Authors: Ahn Cheol Hyoun , Kim Young Yi , Kim Dong Chan , Mohanta Sanjay Kumar , Cho Hyung Koun
Published: January 2009

This study examined the origin of visible luminescence from ZnO layers deposited on p-Si substrates by various growth methods using temperature dependent photoluminescence measurements. The deep level emissions of ZnO layers are found to be strongly dependent on the growth conditions and growth methods used. For the samples grown by sputtering, the visible emission consisted of violet, green, and orange-red regions, which corresponded to zinc interstitial (Zni), oxygen vacancy (VO), and oxygen interstitial (Oi) defect levels, respectively. In contrast, the deep level emissions of metal organic chemical vapor deposition grown samples consisted of blue and green emissions and blue and orange-red emissions at low and high oxygen flow rates, respectively. The ZnO nanorods synthesized by thermal evaporation showed a dominant deep level emission at the green region, which is associated with oxygen vacancies (VO).
Role of spall in microstructure evolution during laser-shock-driven rapid undercooling and resolidification
Authors: Colvin Jeffrey D. , Jankowski Alan F. , Kumar Mukul , MoberlyChan Warren J. , Reed Bryan W. , Paisley Dennis L. , Tierney Thomas E.
Published: January 2009

We previously reported [Colvin et al., J. Appl. Phys. 101, 084906 (2007)] on the microstructure morphology of pure Bi metal subjected to rapid laser-shock-driven melting and subsequent resolidification upon release of pressure, where the estimated effective undercooling rates were of the order of 109–1010 K/s. More recently, we repeated these experiments, but with a Bi/Zn alloy (Zn atomic fraction of 2%–4%) instead of elemental Bi and with a change in target design to suppress spall in the Bi/Zn samples. We observed a similar microstructure morphology in the two sets of experiments, with initially columnar grains recrystallizing to larger equiaxed grains. The Bi samples, however, exhibited micron-scale dendrites on the spall surfaces, whereas there were no dendritic structures anywhere in the nonspalled Bi/Zn, even down to the nanometer scale as observed by transmission electron microscopy. We present the simulations and the interferometry data that show that the samples in the two sets of experiments followed nearly identical hydrodynamic and thermodynamic paths apart from the presence of (probably partially liquid) spall in pure Bi. Simulations also show that the spall occurs right at the moving phase front and, hence, the spall itself cuts off the principal direction for latent heat dissipation across the phase boundary. We suggest that it is the liquid spall itself that creates the conditions for dendrite formation.
Dynamic polarizability, Cauchy moments, and the optical absorption spectrum of liquid water: A sequential molecular dynamics/quantum mechanical approach
Authors: Mata Ricardo A. , Cabral Benedito J. Costa , Millot Claude , Coutinho Kaline , Canuto Sylvio
Published: January 2009

The dynamic polarizability and optical absorption spectrum of liquid water in the 6–15 eV energy range are investigated by a sequential molecular dynamics (MD)/quantum mechanical approach. The MD simulations are based on a polarizable model for liquid water. Calculation of electronic properties relies on time-dependent density functional and equation-of-motion coupled-cluster theories. Results for the dynamic polarizability, Cauchy moments, S(−2), S(−4), S(−6), and dielectric properties of liquid water are reported. The theoretical predictions for the optical absorption spectrum of liquid water are in good agreement with experimental information.
On the nonlinear stress-strain behavior of nematic elastomers – materials of two coupled preferred directions
Authors: Menzel Andreas M. , Pleiner Harald , Brand Helmut R.
Published: January 2009

We present a nonlinear macroscopic model in which nematic side-chain liquid single crystal elastomers are understood as materials that show two preferred directions. One of the two directions is connected to the director of the liquid crystalline phase and the other one becomes anchored in the polymer network during the procedure of synthesis. The specific properties of the materials arise from the coupling between these two preferred directions. We take into account this coupling via the variables of relative rotations between the two directions. For this purpose, we have extended the variables of relative rotations to the nonlinear regime. In addition, we generalize the concept in such a way that it can also be used for the description of other systems coupling two preferred directions. In order to test our picture, we compare its predictions to the experimental observations on nematic monodomain elastomers. As a result, we find that our model describes the nonlinear strain-induced director reorientation and the related plateaulike behavior in the stress-strain relation, which are characteristic of these materials. In addition, our model avoids the unphysical notion of a vanishing or small linear elastic shear modulus. Finally, we demonstrate that ordinary nonlinear elastic behavior of the materials, i.e., not connected to any reorientation of the director field, also plays an important role in the appearance of the stress-strain curves and must be taken into account.
The temperature-pressure-volume equation of state of platinum
Authors: Matsui Masanori , Ito Eiji , Katsura Tomoo , Yamazaki Daisuke , Yoshino Takashi , Yokoyama Ayako , Funakoshi Ken-ichi
Published: January 2009

High-temperature and high-pressure equations of state (EOSs) of Pt have been developed using measured shock compression data up to 290 GPa and volume thermal expansion data between 100 and nearly 2000 K and 0 GPa. The lattice thermal pressures at high temperatures have been estimated based on the Mie–Grüneisen relation with the Debye thermal model and the Vinet isothermal EOS. The contribution of electronic thermal pressure at high temperatures has also been included here. The optimized EOS parameters of Pt are K0T=273 GPa, K0T′=5.20, γ0=2.70, and q=1.10 with Θ0=230 K, where the subscript 0 refers to the ambient conditions. The temperature-pressure-volume (T-P-V) data of Pt have also been measured up to 1600 K and 42 GPa, using synchrotron powder x-ray diffraction experiments combined with a Kawai-type multianvil high pressure apparatus and sintered diamond anvils. We find that the newly developed T-P-V EOS of Pt is fully consistent with not only the shock compression data up to 290 GPa and volume thermal expansion data up to near 2000 K, but also the present measured synchrotron T-P-V data and recently measured T-P-V data of Pt up to 1900 K and 80 GPa. Thus we find that there is no need to include a volume dependence of q over a wide pressure range up to more than 300 GPa. The present EOS has been developed without any pressure scale. Such excellent consistency between the EOS and experimental values over wide temperature and pressure ranges shows that the present EOS can be used as a reliable primary pressure standard for static experiments up to 300 GPa and 3000 K.
On the spectrum of fluctuations of a liquid surface: From the molecular scale to the macroscopic scale
Authors: Blokhuis Edgar M.
Published: January 2009

We show that to account for the full spectrum of surface fluctuations from low scattering vector qd⪡1 (classical capillary wave theory) to high qd≳1 (bulklike fluctuations), one must take account of the interface’s bending rigidity at intermediate scattering vector qd≲1, where d is the molecular diameter. A molecular model is presented to describe the bending correction to the capillary wave model for short-ranged and long-ranged interactions between molecules. We find that the bending rigidity is negative when the Gibbs equimolar surface is used to define the location of the fluctuating interface and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations of a phase-separated colloid-polymer system.
A statistical-mechanical analysis on the hypermobile water around a large solute with high surface charge density
Authors: Kinoshita Masahiro , Suzuki Makoto
Published: January 2009

In connection with the experimental observation that the hypermobile water is induced around F-actin, we calculate physically insightful components of the rotational entropy of hydration of a solute using the angle-dependent integral equation theory combined with the multipolar model for water. It is shown that when a sufficiently large nonpolar solute is inserted into water, the rotational freedom (RF) of water molecules near the solute is significantly restricted due to the water structuring. When the solute has a moderate surface charge density (SCD), in the region adjacent to the solute and in the region within which the solute-water surface separations are close to the molecular diameter of water, the RF of water molecules becomes considerably higher than in the bulk. As the SCD increases, these regions shift slightly more outside with further enhancement of the RF. For sufficiently high SCD, the water molecules in contact with the solute turn largely restrained. It is shown that the appearance of water molecules with anomalously high RF is the most remarkable for a very large solute with high SCD. We argue that the theoretical results are in qualitatively good accord with the experimental observations for the rotational mobility of water molecules near nonpolar side chains of amino acids and F-actin with the domains which are rich in negative charges.
Effect of laser self-defocusing on third harmonic generation in a tunnel ionizing gas
Authors: Verma Updesh , Sharma A. K.
Published: January 2009

A paraxial theory of third harmonic generation by a finite spot size laser in a tunnel ionizing gas is developed. The laser, with intensity close to tunnel ionization threshold, creates plasma whose density rises in a stepwise manner in every half wave period, giving a strong second harmonic component in electron density. The density beats with the oscillatory velocity at the fundamental to produce a nonlinear current, driving the third harmonic. The region of harmonic generation is localized near the laser axis. Further, the strong radial nonuniformity, created in electron density by the ionization process, causes defocusing of the laser, limiting the efficiency of harmonic generation.
Pressure-energy correlations and thermodynamic scaling in viscous Lennard-Jones liquids
Authors: Coslovich D. , Roland C. M.
Published: January 2009

We use molecular dynamics simulation results on viscous binary Lennard-Jones mixtures to examine the correlation between the potential energy and the virial. In accord with a recent proposal [U. R. Pedersen et al., Phys. Rev. Lett. 100, 015701 (2008)], the fluctuations in the two quantities are found to be strongly correlated, exhibiting a proportionality constant, Γ, numerically equal to one-third the slope of an inverse power law approximation to the intermolecular potential function. The correlation is stronger at higher densities, where interatomic separations are in the range where the inverse power law approximation is more accurate. These same liquids conform to thermodynamic scaling of their dynamics, with the scaling exponent equal to Γ. Thus, the properties of strong correlation between energy and pressure and thermodynamic scaling both reflect the ability of an inverse power law representation of the potential to capture interesting features of the dynamics of dense, highly viscous liquids.
Charge on a weak polyelectrolyte
Authors: Wang Shengqin , Granick Steve , Zhao Jiang
Published: January 2009

Fluorescence measurements with single-molecule sensitivity are used to measure the hydrodynamic size and local pH of a weak polyelectrolyte, poly-2-vinyl pyridine end labeled with pH-sensitive dye, the polyelectrolyte having concentration so low (nanomolars) that molecular properties are resolvable only from fluorescence experiments and cannot be accessed by light scattering. We find that the local pH near the dye, inferred from its brightness, is consistently three orders of magnitude higher than the bulk pH. Upon varying the bulk pH, we measure the collapse point at which hydrophobic attraction overwhelms electrostatic repulsion between charged elements along the chain, and conclude that adding monovalent salt shifts this coil-to-globule collapse to higher pH than in the absence of salt. The influence of salt appears to shift the ionization equilibrium of this weak polyelectrolyte in the direction of the chain possessing enhanced electric charge at a given pH. Phenomenologically, this is opposite to the case for strong polyelectrolytes, although the mechanism differs.
Lattice parameters, deviations from Vegard’s rule, and E2 phonons in InAlN
Authors: Darakchieva V. , Xie M.-Y. , Tasnádi F. , Abrikosov I. A. , Hultman L. , Monemar B. , Kamimura J. , Kishino K.
Published: January 2009

The lattice parameters of InxAl1−xN in the whole compositional range are studied using first-principle calculations. Deviations from Vegard’s rule are obtained via the bowing parameters, δa=0.0412±0.0039Å and δc=−0.060±0.010Å, which largely differ from previously reported values. Implications of the observed deviations from Vegard’s rule on the In content extracted from x-ray diffraction are discussed. We also combine these results with x-ray diffraction and Raman scattering studies on InxAl1−xN nanocolumns with 0.627⩽x⩽1 and determine the E2 phonon frequencies versus In composition in the scarcely studied In-rich compositional range.
Polydimethylsiloxane microfluidic chip with integrated microheater and thermal sensor
Authors: Wu Jinbo , Cao Wenbin , Wen Weijia , Chang Donald Choy , Sheng Ping
Published: January 2009

A microheater and a thermal sensor were fabricated inside elastomeric polydimethylsiloxane microchannels by injecting silver paint (or other conductive materials) into the channels. With a high-precision control scheme, microheaters can be used for rapid heating, with precise temperature control and uniform thermal distribution. Using such a microheater and feedback system, a polymerase chain reaction experiment was carried out whereas the DNA was successfully amplified in 25cycles, with 1minpercycle.
Tunability of notch angles in quantum cascade microlasers with highly deformed spiral resonators
Authors: Qu Dongxia , Cendejas Richard , Liu Zhijun , Gmachl Claire , Towner Fred
Published: January 2009

We study the mode spectra and lasing thresholds of spiral-shaped quantum cascade lasers with a deformation in the range of 10%–45% with respect to the radius and with various notch angles. We observe that the initial lasing wavelength and the threshold of a laser are correlated with each other, and they can be jointly tuned by both the deformation coefficient and notch angle. The dependence of the cavity loss on the deformation coefficient is analyzed via the measured lasing thresholds and frequency dependent gain coefficients. Moreover, we achieve single mode emission by tuning the notch angle and deformation coefficients.
Direct measurement of oxygen incorporation into thin film oxides at room temperature upon ultraviolet photon irradiation
Authors: Tsuchiya Masaru , Shutthanandan Vaithiyalingam , Engelhard Mark H. , Ramanathan Shriram
Published: January 2009

Minute changes in oxygen concentration in complex oxides even of the order of ∼0.001% can significantly influence functional properties ranging from the onset of superconductivity to colossal dielectric constant and ferroic response. We report on direct experimental measurement of enhanced oxygen incorporation into ultrathin oxide films at room temperature under gentle UV photon exposure. Oxygen concentration changes in nanoscale yttria doped zirconia (YDZ) films grown on Ge substrate were quantified using the O16(d,p)O17 nuclear reaction. The oxygen concentration was consistently ∼3% larger in UV irradiated YDZ films compared to as-grown YDZ films. Possible incorporation mechanisms are discussed.
Pt redistribution during Ni(Pt) silicide formation
Authors: Demeulemeester J. , Smeets D. , Van Bockstael C. , Detavernier C. , Comrie C. M. , Barradas N. P. , Vieira A. , Vantomme A.
Published: January 2009

We report on a real-time Rutherford backscattering spectrometry study of the erratic redistribution of Pt during Ni silicide formation in a solid phase reaction. The inhomogeneous Pt redistribution in Ni(Pt)Si films is a consequence of the low solubility of Pt in Ni2Si compared to NiSi and the limited mobility of Pt in NiSi. Pt further acts as a diffusion barrier and resides in the Ni2Si grain boundaries, significantly slowing down the Ni2Si and NiSi growth kinetics. Moreover, the observed incorporation of a large amount of Pt in the NiSi seeds indicates that Pt plays a major role in selecting the crystallographic orientation of these seeds and thus in the texture of the resulting Ni1−xPtxSi film.
Diagnostics of ballistic electrons in a dc/rf hybrid capacitively coupled discharge
Authors: Xu Lin , Chen Lee , Funk Merritt , Ranjan Alok , Hummel Mike , Bravenec Ron , Sundararajan Radha , Economou Demetre J. , Donnelly Vincent M.
Published: January 2009

The energy distribution of ballistic electrons in a dc/rf hybrid parallel-plate capacitively coupled plasma reactor was measured. Ballistic electrons originated as secondaries produced by ion and electron bombardment of the electrodes. The energy distribution of ballistic electrons peaked at the value of the negative bias applied to the dc electrode. As that bias became more negative, the ballistic electron current on the rf substrate electrode increased dramatically. The ion current on the dc electrode also increased.