bluuebunny/crossref_metadata_2025 huggingface dataset:
A physics‐based correction model for homogenizing sub‐daily temperature series
Authors: Auchmann R. , Brönnimann S.
Published: August 2012

A new physics‐based technique for correcting inhomogeneities present in sub‐daily temperature records is proposed. The approach accounts for changes in the sensor‐shield characteristics that affect the energy balance dependent on ambient weather conditions (radiation, wind). An empirical model is formulated that reflects the main atmospheric processes and can be used in the correction step of a homogenization procedure. The model accounts for short‐ and long‐wave radiation fluxes (including a snow cover component for albedo calculation) of a measurement system, such as a radiation shield. One part of the flux is further modulated by ventilation. The model requires only cloud cover and wind speed for each day, but detailed site‐specific information is necessary. The final model has three free parameters, one of which is a constant offset. The three parameters can be determined, e.g., using the mean offsets for three observation times. The model is developed using the example of the change from the Wild screen to the Stevenson screen in the temperature record of Basel, Switzerland, in 1966. It is evaluated based on parallel measurements of both systems during a sub‐period at this location, which were discovered during the writing of this paper. The model can be used in the correction step of homogenization to distribute a known mean step‐size to every single measurement, thus providing a reasonable alternative correction procedure for high‐resolution historical climate series. It also constitutes an error model, which may be applied, e.g., in data assimilation approaches.
FY‐2C‐derived diurnal features of clouds in the southern contiguous China
Authors: Chen Haoming , Yu Rucong , Wu Bingyi
Published: August 2012

Hourly infrared (IR) brightness temperature (BT) derived from China's first operational geostationary meteorological satellite Feng‐Yun (FY)‐2C is analyzed over the southern contiguous China (20°N–33°N, 100°E–122°E) during 2005–2008. The main focus is to investigate the diurnal variation of clouds and compare the different features between the southwestern and southeastern China. The clouds are first divided into three categories by the cloud top temperature (CTT, derived from IR BT) according to their diurnal features in summer. The cold cloud (CC, defined as CTT lower than −30°C) occurs most frequently in the late afternoon in most regions over southern China. The frequency of the middle cloud (MC, defined as CTT between −30°C and 0°C) reaches its diurnal maxima in the early evening to the midnight. The frequency of warm cloud (WC, defined as CTT warmer than 0°C) peaks around noon. There are also distinct regional differences of the diurnal variation of summer CC and MC frequencies. The diurnal variation of CC, MC and WC frequencies also show evident seasonal changes. The late afternoon peak of CC frequency appears in almost all months, and in the cold seasons, there is also a midnight to late evening secondary peak. The MC frequency reaches its diurnal peak in the early evening in summer and in the late evening in other seasons. The diurnal amplitude of WC frequency is smaller in warmer seasons and larger in cold seasons, whereas its diurnal phase shows no evident seasonal changes.
An empirical study of the impact of human activity on long‐term temperature change in China: A perspective from energy consumption
Authors: Li Yan , Zhao Xinyi
Published: August 2012

Human activity is an important contributor to local temperature change, especially in urban areas. Energy consumption is treated here as an index of the intensity of human induced local thermal forcing. The relationship between energy consumption and temperature change is analyzed in China by Observation Minus Reanalysis (OMR) method. Temperature trends for observation, reanalysis and OMR are estimated from meteorological records and 2 m‐temperature from NCEP/NCAR Reanalysis 1 for the period 1979–2007. A spatial mapping scheme based on the spatial and temporal relationship between energy consumption and Gross Domestic Production (GDP) is developed to derive the spatial distribution of energy consumption of China in 2003. A positive relationship between energy consumption and OMR trends is found in high and mid energy consumption region. OMR trends decline with the decreasing intensity of human activity from 0.20°C/decade in high energy consumption region to 0.13°C/decade in mid energy consumption region. Forty‐four stations in high energy consumption region that are exposed to the largest human impact are selected to investigate the impact of energy consumption spatial pattern on temperature change. Results show human impact on temperature trends is highly dependent on spatial pattern of energy consumption. OMR trends decline from energy consumption center to surrounding areas (0.26 to 0.04°C/decade) and get strengthened as the spatial extent of high energy consumption area expands (0.14 to 0.25°C/decade).
Compositional investigation of the proposed chloride‐bearing materials on Mars using near‐infrared orbital data from OMEGA/MEx
Authors: Ruesch Ottaviano , Poulet François , Vincendon Mathieu , Bibring Jean‐Pierre , Carter John , Erkeling Gino , Gondet Brigitte , Hiesinger Harald , Ody Anouck , Reiss Dennis
Published: August 2012

Several hundred occurrences of chloride‐bearing salt deposits have been proposed in terrains within the southern highlands of Mars on the basis ofThermal Emission Imaging System and Thermal Emission Spectrometerinfrared observations. The spectral identification of chloride salts by remote sensing is challenging because they are transparent over much of the thermal infrared portion of the spectrum. Further ambiguity arises from the diverse geologic settings in which the putative chloride‐bearing materials are found. In order to better constrain the composition of these unique compositional units, we perform a global survey of these materials in the Near‐Infrared (NIR) domain with theObservatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité(OMEGA) imaging spectrometer. The spectral signatures of the deposits are consistent with – although not specific of – chlorides. We do not observe olivine to be associated with the deposits, which confirms that sulfides are an unlikely alternative candidate. Our systematic search reveals the global lack of association with hydrated minerals (phyllosilicates, sulfates, hydrated silica) except for a few deposits (noteworthy in northwestern Terra Sirenum) where a small fraction of chloride material overlaps Fe/Mg‐rich clay‐bearing terrains. Even in these locations, the morphology and crosscutting relationships of the deposits suggest two separate episodes of mineralization, first phyllosilicates then chlorides, followed by subsequent formation of sulfates. Our study shows that local groundwater upwelling seems to be the most frequent source for the water involved in the formation of chloride, rather than surface runoff.
Response of eastern tropical Atlantic central waters to Atlantic meridional overturning circulation changes during the Last Glacial Maximum and Heinrich Stadial 1
Authors: Huang Enqing , Mulitza Stefan , Paul André , Groeneveld Jeroen , Steinke Stephan , Schulz Michael
Published: August 2012

Benthic foraminiferal δ18O and Mg/Ca of sediment cores off tropical NW Africa are used to study the properties of Atlantic central waters during the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1). We combined our core top data with published results to develop a new Mg/Ca‐temperature calibration forPlanulina ariminensis, which shows a Mg/Ca‐temperature sensitivity of 0.19 mmol/mol per °C. Estimates of the LGM and HS1 thermocline temperatures are comparable to the present‐day values between 200 and 400 m water depth, but were 1.2–1.5°C warmer at 550–570 m depth. The HS1 thermocline waters (200–570 m depth) did not show any warming relative to the LGM. This is in contrast to previous climate model studies, which concluded that tropical Atlantic thermocline waters warmed significantly when Atlantic meridional overturning circulation was reduced. However, our results suggest that thermocline temperatures of the northeastern tropical Atlantic show no pronounced sensitivity to changes in the thermohaline circulation during glacial periods. In contrast, we find a significant increase in thermocline‐water salinity during the LGM (200–550 m depth) and HS1 (200–400 m depth) with respect to the present‐day, which we relate to changes in the wind‐driven circulation. We infer that the LGM thermocline (200–550 m depth) and the HS1 upper thermocline (200–400 m depth) in the northeastern tropical Atlantic was ventilated by surface waters from the North Atlantic rather than the southern‐sourced waters. This suggests that the frontal zone between the modern South Atlantic and North Atlantic Central Waters was probably shifted southward during the LGM and HS1.
Drivers of change in estuarine‐coastal ecosystems: Discoveries from four decades of study in San Francisco Bay
Authors: Cloern James E. , Jassby Alan D.
Published: August 2012

Poised at the interface of rivers, ocean, atmosphere and dense human settlement, estuaries are driven by a large array of natural and anthropogenic forces. San Francisco Bay exemplifies the fast‐paced change occurring in many of the world's estuaries, bays, and inland seas in response to these diverse forces. We use observations from this particularly well‐studied estuary to illustrate responses to six drivers that are common agents of change where land and sea meet: water consumption and diversion, human modification of sediment supply, introduction of nonnative species, sewage input, environmental policy, and climate shifts. In San Francisco Bay, responses to these drivers include, respectively, shifts in the timing and extent of freshwater inflow and salinity intrusion, decreasing turbidity, restructuring of plankton communities, nutrient enrichment, elimination of hypoxia and reduced metal contamination of biota, and food web changes that decrease resistance of the estuary to nutrient pollution. Detection of these changes and discovery of their causes through environmental monitoring have been essential for establishing and measuring outcomes of environmental policies that aim to maintain high water quality and sustain services provided by estuarine‐coastal ecosystems. The many time scales of variability and the multiplicity of interacting drivers place heavy demands on estuarine monitoring programs, but the San Francisco Bay case study illustrates why the imperative for monitoring has never been greater.
New Frontiers in Surgical and Medical Management of Voice
Authors: Dailey Seth H.
Published: August 2012

Rapid technological innovation, a growing interest in voice care, and evolving scientific discovery have helped catalyze rapid advances in the surgical care of voice patients. In this article, I will review new and emerging technologies in voice management from the perspective of the otolaryngologist. Advances include improved methods for visualizing the larynx, newer light applications that hold promise for early stage detection and monitoring of epithelial disease, and office-based methods for performing biopsies and physiological testing. In addition, I will review newer treatment options such as lasers, vocal fold injectables, and minimally invasive techniques for manipulating the arytenoid. Finally, I will present new frontiers in research for patients with lamina propria disease. Speech-language pathologists must be aware of new technologies as they emerge to assure the best possible care of voice patients.
Plädoyer für NIDCAP in Deutschland
Authors: Rist Stephanie
Published: August 2012

Intensivmedizinische Maßnahmen haben einen enormen Einfluss auf das Verhalten und die
Entwicklung Frühgeborener. Um ihnen trotz der belastenden Eingriffe eine optimale
Entwicklung zu ermöglichen, benötigen sie eine besondere, individuelle Betreuung. NIDCAP,
ein Pflegekonzept für Frühgeborene, fördert gezielt die Hirnentwicklung und somit
das kognitive Outcome.
On a singular incompressible porous media equation
Authors: Friedlander Susan , Gancedo Francisco , Sun Weiran , Vicol Vlad
Published: August 2012

This paper considers a family of active scalar equations with transport velocities which are more singular by a derivative of order β than the active scalar. We prove that the equations with 0 < β ⩽ 2 are Lipschitz ill-posed for regular initial data. On the contrary, when 0 < β < 1 we show local well-posedness for patch-type weak solutions.
Shell trajectory measurements from direct-drive implosion experiments
Authors: Michel D. T. , Sorce C. , Epstein R. , Whiting N. , Igumenshchev I. V. , Jungquist R. , Froula D. H.
Published: August 2012

A technique to measure the shell trajectory in direct-drive inertial confinement fusion implosions is presented. The x-ray self emission of the target is measured with an x-ray framing camera. Optimized filtering limits the x-ray emission from the corona plasma, isolating a sharp intensity gradient very near the ablation surface. This enables one to measure the radius of the imploding shell with an accuracy better than 1 μm and to determine a 200-ps average velocity to better than 2%.
Neutron activation diagnostics at the National Ignition Facility (invited)
Authors: Bleuel D. L. , Yeamans C. B. , Bernstein L. A. , Bionta R. M. , Caggiano J. A. , Casey D. T. , Cooper G. W. , Drury O. B. , Frenje J. A. , Hagmann C. A. , Hatarik R. , Knauer J. P. , Johnson M. Gatu , Knittel K. M. , Leeper R. J. , McNaney J. M. , Moran M. , Ruiz C. L. , Schneider D. H. G.
Published: August 2012

Neutron yields are measured at the National Ignition Facility (NIF) by an extensive suite of neutron activation diagnostics. Neutrons interact with materials whose reaction cross sections threshold just below the fusion neutron production energy, providing an accurate measure of primary unscattered neutrons without contribution from lower-energy scattered neutrons. Indium samples are mounted on diagnostic instrument manipulators in the NIF target chamber, 25–50 cm from the source, to measure 2.45 MeV deuterium-deuterium fusion neutrons through the 115In(n,n’)115m In reaction. Outside the chamber, zirconium and copper are used to measure 14 MeV deuterium-tritium fusion neutrons via 90Zr(n,2n), 63Cu(n,2n), and 65Cu(n,2n) reactions. An array of 16 zirconium samples are located on port covers around the chamber to measure relative yield anisotropies, providing a global map of fuel areal density variation. Neutron yields are routinely measured with activation to an accuracy of 7% and are in excellent agreement both with each other and with neutron time-of-flight and magnetic recoil spectrometer measurements. Relative areal density anisotropies can be measured to a precision of less than 3%. These measurements reveal apparent bulk fuel velocities as high as 200 km/s in addition to large areal density variations between the pole and equator of the compressed fuel.
Density fluctuation measurements using beam emission spectroscopy on Heliotron J
Authors: Kobayashi S. , Kado S. , Oishi T. , Ohshima S. , Kagawa T. , Nagae Y. , Yamamoto S. , Mizuuchi T. , Nagasaki K. , Okada H. , Minami T. , Estrada T. , Murakami S. , Lee H. Y. , Minami T. , Harada T. , Nakamura Y. , Konoshima S. , Toushi K. , Sano F.
Published: August 2012

This paper describes the measurement of the density fluctuation using beam emission spectroscopy in Heliotron J, having the non-symmetrical helical-magnetic-axis configuration. In order to optimize the sightlines, the numerical calculations are carried out to estimate the spatial resolution and the observation location. When a tangential neutral beam is used as diagnostic one, suitable sightlines from the newly installed diagnostic port are selected whose spatial resolution Δρ is less than ±0.07 over the entire plasma region. Modification of the interference filter and the detection systems enables us to measure the radial profile of the density fluctuation. Each of the three coherent modes due to the fast-ion-driven magnetohydrodynamic instabilities has different radial structure of the density fluctuation.
On the determination of absolute vibrational excitation probabilities in molecule-surface scattering: Case study of NO on Au(111)
Authors: Cooper Russell , Li Zhisheng , Golibrzuch Kai , Bartels Christof , Rahinov Igor , Auerbach Daniel J. , Wodtke Alec M.
Published: August 2012

We describe a method to obtain absolute vibrational excitation probabilities of molecules scattering from a surface based on measurements of the rotational state, scattering angle, and temporal distributions of the scattered molecules and apply this method to the vibrational excitation of NO scattering from Au(111). We report the absolute excitation probabilities to the v = 1 and v = 2 vibrational states, rotational excitation distributions, and final scattering angle distributions for a wide range of incidence energies and surface temperatures. In addition to demonstrating the methodology for obtaining absolute scattering probabilities, these results provide an excellent benchmark for theoretical calculations of molecule-surface scattering.
Location of the Lee-Yang zeros and absence of phase transitions in some Ising spin systems
Authors: Lebowitz Joel L. , Ruelle David , Speer Eugene R.
Published: August 2012

We consider a class of Ising spin systems on a set Λ of sites. The sites are grouped into units with the property that each site belongs to either one or two units, and the total internal energy of the system is the sum of the energies of the individual units, which in turn depend only on the number of up spins in the unit. We show that under suitable conditions on these interactions none of the |Λ| Lee-Yang zeros in the complex z = e2βh plane, where β is the inverse temperature and h the uniform magnetic field, touch the positive real axis, at least for large values of β. In some cases one obtains, in an appropriately taken β↗ ∞ limit, a gas of hard objects on a set Λ′; the fugacity for the limiting system is a rescaling of z and the Lee-Yang zeros of the new partition function also avoid the positive real axis. For certain forms of the energies of the individual units the Lee-Yang zeros of both the finite- and zero-temperature systems lie on the negative real axis for all β. One zero-temperature limit of this type, for example, is a monomer-dimer system; our results thus generalize, to finite β, a well-known result of Heilmann and Lieb that the Lee-Yang zeros of monomer-dimer systems are real and negative.
Introducing minimum Fisher regularisation tomography to AXUV and soft x-ray diagnostic systems of the COMPASS tokamak
Authors: Mlynar J. , Imrisek M. , Weinzettl V. , Odstrcil M. , Havlicek J. , Janky F. , Alper B. , Murari A. ,   JET-EFDA Contributors
Published: August 2012

The contribution focuses on plasma tomography via the minimum Fisher regularisation (MFR) algorithm applied on data from the recently commissioned tomographic diagnostics on the COMPASS tokamak. The MFR expertise is based on previous applications at Joint European Torus (JET), as exemplified in a new case study of the plasma position analyses based on JET soft x-ray (SXR) tomographic reconstruction. Subsequent application of the MFR algorithm on COMPASS data from cameras with absolute extreme ultraviolet (AXUV) photodiodes disclosed a peaked radiating region near the limiter. Moreover, its time evolution indicates transient plasma edge cooling following a radial plasma shift. In the SXR data, MFR demonstrated that a high resolution plasma positioning independent of the magnetic diagnostics would be possible provided that a proper calibration of the cameras on an x-ray source is undertaken.
Stereo correlated dynamics in the energy transfer process of aligned N2 (A 3Σu+) + oriented NO (X 2Π, Ω = 1/2) → NO (A 2Σ+) + N2 (X 1Σg+)
Authors: Ohoyama H. , Maruyama S.
Published: August 2012

Steric effect for the NO (A 2Σ+) formation in the aligned N2 (A 3Σu+) + oriented NO (X 2Π, Ω = 1/2) reaction has been observed as a function of the mutual orientational configurations between the two molecular reactants in the collision frame. Multidimensional molecular steric opacity function has been determined. A significant NO (X 2Π) alignment dependence is recognized in contrast with little dependence on NO (X 2Π) orientation. The NO alignment selectivity turns out to depend on the N2 (A 3Σu+) alignment: The axial configuration of NO (X 2Π) is favorable for the axial and sideways configurations of N2 (A 3Σu+), while the sideways configuration of NO (X 2Π) is favorable for the oblique configuration of N2 (A 3Σu+) at an orientation angle of ${\rm \theta }_{{\rm v}_{\rm R} }$θvR ∼ 45°. with respect to the relative velocity (vR).
General solution to the electric double layer with discrete interfacial charges
Authors: Vangaveti S. , Travesset A.
Published: August 2012

We provide extensive molecular dynamics simulations of counterion and coion distributions near an impenetrable plane with fixed discrete charges. The numerical results are described by an explicit solution that distinguishes the plasma (\documentclass[12pt]{minimal}\begin{document}$\sqrt{A_c}/\sigma > 3$\end{document}Ac/σ>3) and the binding regime (\documentclass[12pt]{minimal}\begin{document}$\sqrt{A_c}/\sigma <3$\end{document}Ac/σ<3) where σ is the ion diameter and Ac = |e/ν| (ν is the surface charge density). In the plasma regime, the solution consists of a product of two functions that can be computed from simpler models and reveals that the effects of the discreteness of the charge extends over large distances from the plane. The solution in the binding regime consists of a Stern layer of width σ and a diffuse layer, but contrary to standard approaches, the strong correlations between ions within the Stern layer and the diffuse layer require a description in terms of a “displaced” diffuse layer. The solution is found to describe electrolytes of any valence at all concentrations investigated (up to 0.4M) and includes the case of additional specific interactions such as van der Waals attraction and other generalizations. We discuss some open questions.
Cavity ring-down spectroscopy with an automated control feedback system for investigating nitrate radical surface chemistry reactions
Authors: Flemmer Michael M. , Ham Jason E.
Published: August 2012

Nitrate radical (NO3•) surface chemistry of indoor environments has not been well studied due to the difficulty in generating and maintaining NO3• at low concentrations for long term exposures. This article presents the Surface Chemistry Reactant Air Delivery and Experiment System (SCRADES), a novel feedback controlled system developed to deliver nitrate radicals at specified concentrations (50–500 ppt, ±30 ppt) and flow rates (500–2000 ml min−1) to a variety of indoor surfaces to initiate reaction chemistry for periods of up to 72 h. The system uses a cavity ring-down spectrometer (CRDS), with a detection limit of 1.7 ppt, to measure the concentration of NO3• supplied to a 24 l experiment chamber. Nitrate radicals are introduced via thermal decomposition of N2O5 and diluted with clean dry air until the desired concentration is achieved. Additionally, this article addresses details concerning NO3• loss through the system, consistency of the NO3• concentration delivered, and stability of the CRDS cavity over long exposure durations (72 h).
Para-conductivity and critical regime of (Tl1−xCx)Ba2Ca3Cu4O12−δ superconductors
Authors: Khan Nawazish A. , Ahmad Shakil
Published: August 2012

We have synthesized (Tl1−yCy)Ba2Ca3Cu4O12−δ (Tl1−yCy-1234) (y = 0, 0.25, 0.5, and 0.75) samples at normal pressure and studied the role of carbon doping on the intrinsic superconductivity parameters via excess conductivity analysis (FIC) of resistivity data. The FIC analysis in the transition region is carried out by using Ginzburg-Landau equations, whereas beyond the critical regimes, we have employed Lawrence and Doniach (LD) and Maki-Thompson models. Through such analyses, it is observed that the values of Bc(0), Bc1(0), and Jc(0) are marginally decreased whereas vF, τφ, ξc(0), J (interlayer-coupling parameter), and width of three dimensional regimes are increased with carbon doping in (Tl1−yCy)Ba2Ca3Cu4O12−δ (Tl1−yCy-1234) (y = 0, 0.25, 0.5, and 0.75) samples. Since the absolute values of vF, τφ, and ξc(0) crucially depend on the coherence length of the carriers, which in turn depends on the density of the carriers. Increase in the values of these parameters strongly suggests that the numbers of the carriers get homogenized in the inner and outer CuO2 planes, which suppress the pseudo-gap in the final compound. The suppression in the pseudo-gap can be witnessed in the form of an increase in the width of 3D LD regime with the doping of carbon in the final compound.
FTIR investigation of the O–H···Xe interaction in simple carboxylic acids in solid xenon
Authors: Ildiz Gulce Ogruc , Nunes Cláudio M. , Kuş Nihal , Fausto Rui
Published: August 2012

The O–H stretching region of the infrared spectra of a series of carboxylic acids in Xe matrices was investigated as a function of temperature. Upon increasing the temperature, the νO–H band site-components undergo reversible frequency blue-shifts, which are larger for the lowest-frequency components. This unprecedented observation indicates both that different types of O–H···Xe specific interactions occur, depending on different trapping sites, and the prevalence of stronger interactions of this type for molecules trapped in sites corresponding to lower frequency νO–H band site-components. These results are in agreement with previous investigations pointing to an increased stabilization and larger νO–H frequency red-shifts in carboxylic acid/Xe complexes bearing a specific H-bond like O–H···Xe interaction. O–H···Xe interaction energies were obtained theoretically and also estimated from the spectroscopic data. Changes in the interaction energies upon temperature variation were also evaluated.
Investigation of dissociative electron attachment to 2′-deoxycytidine-3′-monophosphate using DFT method and time dependent wave packet approach
Authors: Bhowmick Somnath , B Renjith , Mishra Manoj K. , Sarma Manabendra
Published: August 2012

Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2′-deoxycytidine-3′-monophosphate [3′-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.15 eV) where the LEE transfers from π* to σ* resonance state which resembles a SN2 type mechanism. In addition, for the first time, an indication of quantum mechanical tunneling in strand breaking is seen from the highest anionic bound vibrational state (χ5), which may have a substantial role during DNA damage.
Extension of the measurable temperature range of the LHD Thomson scattering system
Authors: Yamada I. , Narihara K. , Funaba H. , Yasuhara R. , Hayashi H. , Kohmoto T.
Published: August 2012

The large helical device Thomson scattering system was designed for the target electron temperature (Te) range, Te = 50 eV–10 keV. Above 10 keV, the experimental error becomes rapidly worse. In order to obtain reliable Te data in the temperature range above 10 keV, we are planning to extend the measurable Te range by following two methods. First we have installed one more wavelength channel that observes shorter wavelength region in polychromators. Next applying forward scattering configuration is another candidate. We estimate the data quality when the two methods are used. Both of the two methods are expected to improve Te data quality at Te ≥ 10 keV.
Photoelectron spectroscopy and the electronic structure of the uranyl tetrachloride dianion: UO2Cl42−
Authors: Dau Phuong Diem , Su Jing , Liu Hong-Tao , Huang Dao-Ling , Li Jun , Wang Lai-Sheng
Published: August 2012

The uranyl tetrachloride dianion (UO2Cl42−) is observed in the gas phase using electrospray ionization and investigated by photoelectron spectroscopy and relativistic quantum chemical calculations. Photoelectron spectra of UO2Cl42− are obtained at various photon energies and congested spectral features are observed. The free UO2Cl42− dianion is found to be highly stable with an adiabatic electron binding energy of 2.40 eV. Ab initio calculations are carried out and used to interpret the photoelectron spectra and elucidate the electronic structure of UO2Cl42−. The calculations show that the frontier molecular orbitals in UO2Cl42− are dominated by the ligand Cl 3p orbitals, while the U–O bonding orbitals are much more stable. The electronic structure of UO2Cl42− is compared with that of the recently reported UO2F42− [P. D. Dau, J. Su, H. T. Liu, J. B. Liu, D. L. Huang, J. Li, and L. S. Wang, Chem. Sci. 3 1137 (2012)]. The electron binding energy of UO2Cl42− is found to be 1.3 eV greater than that of UO2F42−. The differences in the electronic stability and electronic structure between UO2Cl42− and UO2F42− are discussed.
Nonlinear dimensionality reduction for nonadiabatic dynamics: The influence of conical intersection topography on population transfer rates
Authors: Virshup Aaron M. , Chen Jiahao , Martínez Todd J.
Published: August 2012

Conical intersections play a critical role in the nonadiabatic relaxation of excited electronic states. However, there are an infinite number of these intersections and it is difficult to predict which are actually relevant. Furthermore, traditional descriptors such as intrinsic reaction coordinates and steepest descent paths often fail to adequately characterize excited state reactions due to their highly nonequilibrium nature. To address these deficiencies in the characterization of excited state mechanisms, we apply a nonlinear dimensionality reduction scheme (diffusion mapping) to generate reaction coordinates directly from ab initio multiple spawning dynamics calculations. As illustrated with various examples of photoisomerization dynamics, excited state reaction pathways can be derived directly from simulation data without any a priori specification of relevant coordinates. Furthermore, diffusion maps also reveal the influence of intersection topography on the efficiency of electronic population transfer, providing further evidence that peaked intersections promote nonadiabatic transitions more effectively than sloped intersections. Our results demonstrate the usefulness of nonlinear dimensionality reduction techniques as powerful tools for elucidating reaction mechanisms beyond the statistical description of processes on ground state potential energy surfaces.
Relativistic plasmas in uniform magnetic fields. I. General off-axis coupling methods
Authors: Tautz R. C. , Lerche I.
Published: August 2012

The dispersion relation for relativistic plasmas in a uniform magnetic field is analyzed for general particle velocity distribution functions. Without any prior assumptions, the conductivity tensor is evaluated. Special emphasis is placed on mode coupling and oblique propagating modes. Several limiting cases are considered such as (i) weak isotropic contribution; (ii) small coupling; (iii) parallel mode propagation. The general method therefore allows for the evaluation of approximate solutions. Furthermore, it is shown how and under which conditions the well-known classic longitudinal and transverse dispersion relations for parallel wave propagation can be recovered.
A novel method for modeling the neutron time of flight detector response in current mode to inertial confinement fusion experiments (invited)
Authors: Nelson A. J. , Ruiz C. L. , Cooper G. W. , Chandler G. A. , Fehl D. L. , Hahn K. D. , Leeper R. J. , Smelser R. , Torres J. A.
Published: August 2012

A novel method for modeling the neutron time of flight (nTOF) detector response in current mode for inertial confinement fusion experiments has been applied to the on-axis nTOF detectors located in the basement of the Z-Facility. It will be shown that this method can identify sources of neutron scattering, and is useful for predicting detector responses in future experimental configurations, and for identifying potential sources of neutron scattering when experimental set-ups change. This method can also provide insight on how much broadening neutron scattering contributes to the primary signals, which is then subtracted from them. Detector time responses are deconvolved from the signals, allowing a transformation from dN/dt to dN/dE, extracting neutron spectra at each detector location; these spectra are proportional to the absolute yield.
Electron wavepacket dynamics in highly quasi-degenerate coupled electronic states: A theory for chemistry where the notion of adiabatic potential energy surface loses the sense
Authors: Yonehara Takehiro , Takatsuka Kazuo
Published: August 2012

We develop a theory and the method of its application for chemical dynamics in systems, in which the adiabatic potential energy hyper-surfaces (PES) are densely quasi-degenerate to each other in a wide range of molecular geometry. Such adiabatic electronic states tend to couple each other through strong nonadiabatic interactions. Technically, therefore, it is often extremely hard to accurately single out the individual PES in those systems. Moreover, due to the mutual nonadiabatic couplings that may spread wide in space and due to the energy-time uncertainty relation, the notion of the isolated and well-defined potential energy surface should lose the sense. On the other hand, such dense electronic states should offer a very interesting molecular field in which chemical reactions to proceed in characteristic manners. However, to treat these systems, the standard theoretical framework of chemical reaction dynamics, which starts from the Born-Oppenheimer approximation and ends up with quantum nuclear wavepacket dynamics, is not very useful. We here explore this problem with our developed nonadiabatic electron wavepacket theory, which we call the phase-space averaging and natural branching (PSANB) method [T. Yonehara and K. Takatsuka, J. Chem. Phys. 129, 134109 (2008)]10.1063/1.2987302, or branching-path representation, in which the packets are propagated in time along the non-Born-Oppenheimer branching paths. In this paper, after outlining the basic theory, we examine using a one-dimensional model how well the PSANB method works with such densely quasi-degenerate nonadiabatic systems. To do so, we compare the performance of PSANB with the full quantum mechanical results and those given by the fewest switches surface hopping (FSSH) method, which is known to be one of the most reliable and flexible methods to date. It turns out that the PSANB electron wavepacket approach actually yields very good results with far fewer initial sampling paths. Then we apply the electron wavepacket dynamics in path-branching representation and the so-called semiclassical Ehrenfest theory to a hydrogen molecule embedded in twelve membered boron cluster (B12) in excited states, which are densely quasi-degenerate due to the vacancy in 2p orbitals of boron atom [1s22s22p1]. Bond dissociation of the hydrogen molecule quickly takes place in the cluster and the resultant hydrogen atoms are squeezed out to the surface of the cluster. We further study collision dynamics between H2 and B12, which also gives interesting phenomena. The present study suggests an interesting functionality of the boron clusters.
CO oxidation on Ir(111) surfaces under large non-Gaussian noise
Authors: Cisternas Jaime , Wehner Stefan , Descalzi Orazio
Published: August 2012

In this article we consider the CO oxidation on Ir(111) surfaces under large external noise with large autocorrelation imposed on the composition of the feed gas, both in experiments and in theory. We report new experimental results that show how the fluctuations force the reaction rate to jump between two well defined states. The statistics of the reaction rate depend on those of the external noise, and neither of them have a Gaussian distribution, and thus they cannot be modeled by white or colored noise. A continuous-time discrete-state Markov process is proposed as a suitable model for the observed phenomena. The model captures the main features of the observed fluctuations and can be modified to accommodate other surface reactions and other systems under non-Gaussian external noise.
A one-dimensional model with water-like anomalies and two phase transitions
Authors: Heckmann Lotta , Drossel Barbara
Published: August 2012

We investigate a one-dimensional model that shows several properties of water. The model combines the long-range attraction of the van der Waals model with the nearest-neighbor interaction potential by Ben-Naim, which is a step potential that includes a hard core and a potential well. Starting from the analytical expression for the partition function, we determine numerically the Gibbs energy and other thermodynamic quantities. The model shows two phase transitions, which can be interpreted as the liquid-gas transition and a transition between a high-density and a low-density liquid. At zero temperature, the low-density liquid goes into the crystalline phase. Furthermore, we find several anomalies that are considered characteristic for water. We explore a wide range of pressure and temperature values and the dependence of the results on the depth and width of the potential well.
Free vibrations of a spherical drop constrained at an azimuth
Authors: Ramalingam Santhosh , Ramkrishna Doraiswami , Basaran Osman A.
Published: August 2012

Two droplets coupled through a liquid filled (a) hole in a plate or (b) tube is referred to as a double droplet system (DDS) or a capillary switch. Such capillary systems are gaining increasing attention due to their utility in applications. A particularly exciting application is one where a DDS is employed as a liquid lens, one flavor of which entails using a DDS as a variable focus lens by keeping it under sustained oscillations at its natural frequencies. The natural modes of oscillation of a DDS are determined analytically here in the limit in which the plate thickness (or tube length) is vanishingly small and when the effect of gravity is negligible compared to that of surface tension. In this limit, a DDS at rest reduces to two spherical caps that are pinned to and coupled along a common circular ring of contact of negligible thickness. Here, the caps are taken to be complementary pieces of a sphere so that the equilibrium state of the system is a sphere that is constrained by a ring of negligible thickness at an azimuthal angle with respect to the center of the sphere. Both the constrained drop and the fluid exterior to it are taken to be inviscid fluids undergoing irrotational flow. Similar to the linear oscillations of a free drop first studied by Rayleigh, the analytical formulation of the linear oscillations of the constrained drop results in a linear operator eigenvalue problem but with one additional boundary condition, i.e., that which accounts for zero shape perturbation along the circle of contact. Exploiting properties of linear operators, an implicit expression is obtained for the frequency of each mode of oscillation, a feat that appears not to have been accomplished to date in any problem involving oscillations of constrained drops. An extension of a method based on Green's functions that was developed to analyze the linear oscillations of a drop in contact with a spherical bowl [M. Strani and F. Sabetta, “Free-vibrations of a drop in partial contact with a solid support,” J. Fluid Mech. 141, 233–247 (1984)]10.1017/S0022112084000811 is also employed to verify the aforementioned results. Results obtained from these two approaches are then compared to those reported by Bostwick and Steen [“Capillary oscillations of a constrained liquid drop,” Phys. Fluids 21, 032108 (2009)]10.1063/1.3103344. Careful examination of flow fields within drops reveals that by pinning a drop, it should be possible to selectively excite just a portion of a drop's surface.
Dynamical hysteresis in a self-oscillating polymer gel
Authors: Das Debojyoti , Das Moupriya , Ray Deb Shankar
Published: August 2012

An ionic polymer gel may undergo rhythmical swelling-deswelling kinetics induced by chemical oscillation. We demonstrate that the gel admits of dynamical hysteresis, which is manifested in the non-vanishing area of the response function—concentration (of reaction substrate) hysteresis loop, the response function being the integrated probability of residence of the polymer in any one of the swelled or deswelled states. The loop area depends on temperature and exhibits a turnover as a function of the strength of thermal noise—a phenomenon reminiscent of stochastic resonance. The numerical simulations agree well with our proposed analytical scheme.
Using enveloping distribution sampling to compute the free enthalpy difference between right- and left-handed helices of a β-peptide in solution
Authors: Lin Zhixiong , Timmerscheidt Tobias A. , van Gunsteren Wilfred F.
Published: August 2012

Recently, the method of enveloping distribution sampling (EDS) to efficiently obtain free enthalpy differences between different molecular systems from a single simulation has been generalized to compute free enthalpy differences between different conformations of a system [Z. X. Lin, H. Y. Liu, S. Riniker, and W. F. van Gunsteren, J. Chem. Theory Comput. 7, 3884 (2011)]10.1021/ct200623b. However, the efficiency of EDS in this case is hampered if the parts of the conformational space relevant to the two end states or conformations are far apart and the conformational diffusion from one state to the other is slow. This leads to slow convergence of the EDS parameter values and free enthalpy differences. In the present work, we apply the EDS methodology to a challenging case, i.e., to calculate the free enthalpy difference between a right-handed 2.710/12-helix and a left-handed 314-helix of a hexa-β-peptide in solution from a single simulation. No transition between the two helices was detected in a standard EDS parameter update simulation, thus enhanced sampling techniques had to be applied, which included adiabatic decoupling (AD) of solute and solvent motions in combination with increasing the solute temperature, and lowering the shear viscosity of the solvent. AD was found to be unsuitable to enhance the sampling of the solute conformations in the EDS parameter update simulations. Lowering the solvent shear viscosity turned out to be useful during EDS parameter update simulations, i.e., it did speed up the conformational diffusion of the solute, more transitions between the two helices were observed. This came at the cost of more CPU time spent due to the shorter time step needed for simulations with the lower solvent shear viscosity. Using an improved EDS parameter update scheme, parameter convergence was five-fold enhanced. The resulting free enthalpy difference between the two helices calculated from EDS agrees well with the result obtained through direct counting from a long MD simulation, while the EDS technique significantly enhances the sampling of both helices over non-helical conformations.
Design and development of a novel nuclear magnetic resonance detection for the gas phase ions by magnetic resonance acceleration technique
Authors: Fuke K. , Tona M. , Fujihara A. , Sakurai M. , Ishikawa H.
Published: August 2012

Nuclear magnetic resonance (NMR) technique is a well-established powerful tool to study the physical and chemical properties of a wide range of materials. However, presently, NMR applications are essentially limited to materials in the condensed phase. Although magnetic resonance was originally demonstrated in gas phase molecular beam experiments, no application to gas phase molecular ions has yet been demonstrated. Here, we present a novel principle of NMR detection for gas phase ions based on a “magnetic resonance acceleration” technique and describe the design and construction of an apparatus which we are developing. We also present an experimental technique and some results on the formation and manipulation of cold ion packets in a strong magnetic field, which are the key innovations to detect NMR signal using the present method. We expect this novel method to lead new realm for the study of mass-selected gas-phase ions with interesting applications in both fundamental and applied sciences.
Photodissociation dynamics of benzyl alcohol at 193 nm
Authors: Dyakov Yuri A. , Hsu Wen Hsin , Ni Chi-Kung , Tsai Wan-Chen , Hu Wei-Ping
Published: August 2012

Photodissociation dynamics of benzyl alcohol, C6H5CH2OH and C6H5CD2OH, in a molecular beam was investigated at 193 nm using multimass ion imaging techniques. Four dissociation channels were observed, including OH elimination and H2O elimination from the ground electronic state, H atom elimination (from OH functional group), and CH2OH elimination from the triplet state. The dissociation rate on the ground state was found to be 7.7 × 106 s−1. Comparison to the potential energy surfaces from ab initio calculations, dissociation rate, and branching ratio from Rice–Ramsperger–Kassel–Marcus calculations were made.
On the mechanisms of energy transfer between quantum well and quantum dashes
Authors: Sęk G. , Kudrawiec R. , Podemski P. , Misiewicz J. , Somers A. , Höfling S. , Reithmaier J. P. , Kamp M. , Forchel A.
Published: August 2012

We investigate energy transfer mechanisms from a quantum well (QW) to quantum dashes (QDashes) separated by a few nanometer thick barrier in InAs/InGaAs/InGaAlAs/InP material system. We show that at sufficiently low temperatures excitons, which are non-resonantly photogenerated in the QW and then transferred to the ground state via phonon relaxation, can be retrieved by QDashes. The excess of the transferred energy, defined by the energy difference between the QW and QDash exciton states, can be dissipated via interaction with LO phonons if the respective energy matching is satisfied. This kind of exciton injection from QW to QDashes is a process insensitive to the energy level structure of the individual exciton components, i.e., electrons and holes. It is shown that within the single particle picture, the electron energy in QDashes is higher by more than 50 meV compared to the corresponding QW energy, which prevents the electron transfer from quantum well to the dashes. We show experimentally that despite this unfavorable energy difference for single carriers whole QW excitons are efficiently transferred to QDashes and recombine there radiatively.
Laser induced thermal-wave fields in multi-layered spherical solids based on Green function method
Authors: Zhang Jie , Xie Guangxi , Wang Chinhua , Mandelis Andreas
Published: August 2012

In this paper, we establish a Green-function based theoretical model for evaluating solid multi-layered spherical samples which are illuminated by a frequency modulated incident beam. The specific Green function for the multi-layered spherical structure is derived and an analytical expression for the thermal-wave field in such a spherical sample is presented. The characteristics of the thermal-wave field with respect to the thermophysical, geometrical, and measurement parameters are presented. Unlike the quadruple method, the Green function method is capable of evaluating thermal-wave fields at any point of multi-layered structures with arbitrary intensity distributions of incident laser beams. Furthermore, experimental validation is also presented in the form of experimental results with steel spheres of various diameters.