bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of contact endoscopy and frozen section histopathology in the intra-operative diagnosis of laryngeal pathology
Authors: Cikojević D , Glunčić I , Pešutić-Pisac V
Published: August 2007

Andrea et al. were the first to use contact endoscopy in the diagnosis of laryngeal disease, in 1995. This method enables in vivo microscopy of laryngeal mucosa.

In the present study, comparison of contact endoscopy with frozen section histopathology was performed in 142 patients with various diseases of the larynx. Paraffin section histopathology diagnosed 70 benign lesions, 23 precancerous lesions and 49 malignant lesions. Frozen section histopathology showed a sensitivity of 89.8 per cent, a specificity of 98.9 per cent and an accuracy of 95.7 per cent (χ2 = 1.5; p = 0.18). Frozen histopathology diagnosed 45 malignant lesions, including one false positive and five false negative results. Contact endoscopy yielded a sensitivity of 79.59 per cent, a specificity of 100 per cent and an accuracy of 92.95 per cent (χ2 = 8.1; p = 0.002). All malignant lesions diagnosed by contact endoscopy were confirmed by histopathology; contact endoscopy failed to recognise malignant lesions in 10 patients.

Contact endoscopy is preferable to frozen section histopathology as it is noninvasive, provides information on microscopic diagnosis and laryngeal lesion margins, and enables visualisation of the laryngeal mucosa microvasculature. The use of contact endoscopy along with frozen section histopathology improves diagnostic accuracy and allows for operative (or other) therapy to continue according to the results obtained.
Analysis of station locations in a road weather information system
Authors: Eriksson M , Norrman J
Published: August 2007

Many northern countries use a road weather information system (RWIS) with a network of stations to monitor winter road conditions. Present station locations were selected afterfield investigations of micro‐ and local‐climate conditions (e.g. using thermal mapping). This paper describes an approach to optimally locate and equip the stations in order to best identify conditions hazardous to road transport. This is achieved using multiple regression analysis of observed data and correlation with location meta‐data. A geographical information system (GIS) is used to develop quantitative and objective descriptions of station locations by using knowledge of local and regional climate variations. Road climate is described using a slipperiness classification, in which weather situations are classified into ten types of slipperiness from the meteorological variables collected at RWIS stations. The relationships between quantified locations and data on road slipperiness in southern Sweden during one winter are analysed. The results show that the spatial patterns for different types of slipperiness are significantly related to local parameters. The three most prevalent types are analysed in detail: snowfall on a frozen road surface, hoarfrost and low visibility, and strong formation of hoarfrost. Copyright © 2001 Royal Meteorological Society
Present weather: comparing human observations and one type of automated sensor
Authors: Merenti‐Välimäki Hanna‐Leena , Lönnqvist Jan , Laininen Pertti
Published: August 2007

Of the full set of observations carried out at weather stations, the ‘present weather’ observation is one of the most difficult to automate. Initially, elements such as rain and fog were automated. However, during the past ten years a new group of sensors, aimed at identifying the type and intensity of precipitation, has emerged. These sensors have come to be called Present Weather Sensors (PWSs). Most of the early tests and intercomparisons have been limited to liquid precipitation. Not much attention has been given to investigating the reasons for disagreement between the primary reference, the professional meteorological observer, and the automated observations. This paper presents an analysis of an intercomparison between observer and one type of PWS (Vaisala FD12P), in conditions of both liquid and frozen precipitation. An interaction model is introduced as a new and improved tool for the quality control of PWSs. Copyright © 2001 Royal Meteorological Society
A portable meteorological station plus nuclear radiation monitoring system using a BASIC‐8052 micro‐controller
Authors: Al‐Mohamad Ali , Aghabi Samer , Weiss Chafic
Published: August 2007

A portable meteorology station capable of measuring various atmospheric parameters (mainly ambient temperature, relative humidity, atmospheric pressure, wind speed and direction) was designed and built. The physical quantities were converted to electrical signals using suitable sensors. These signals were then processed and transferred to digital values to be stored in suitable memories. A nuclear radiation alarm system was also built, on the main board, to monitor the nuclear radiation releases levels. The system consists of three main parts: control board, data acquisition board and signals conditioning board. The overall system is controlled by a BASIC‐8052 micro‐controller. Copyright © 2002 Royal Meteorological Society.
Short‐term prediction of the horizontal wind vector within a wake vortex warning system
Authors: Frech Michael , Holzäpfel Frank , Gerz Thomas , Konopka Jens
Published: August 2007

A wake vortex warning system (WVWS) has been developed for Frankfurt Airport. This airport has two parallel runways which are separated by 518 m, a distance too short to operate them independently because wake vortices may be advected to the adjacent runway. The objective of the WVWS is to enable operation with reduced separation between two aircraft approaching the parallel runways during appropriate wind conditions. The WVWS applies a statistical persistence model to predict the crosswind within a 20‐minute period. One of the main problems identified in the old WVWS is discontinuity between successive forecasts. These forecast breakdowns were not acceptable to air traffic controllers. At least part of the problem was related to the fact that the forecast was solely based on the prediction of crosswind. A new method is developed on the basis of 523 days of sonic anemometer measurements at Frankfurt Airport. It is demonstrated that the prediction of the horizontal wind vector avoids these difficulties and significantly improves the system's performance. Copyright © 2002 Royal Meteorological Society.
Economic benefits of meteorological services
Authors: Freebairn John W , Zillman John W
Published: August 2007

There is an increasing need for more rigorous and more broadly based determination of the economic value of meteorological services as an aid to decision‐making on the appropriate level of funding to be committed to their provision at the national level. This paper develops an overall framework for assessment of the economic value of meteorological services based on the recognition that most national meteorological infrastructure and services possess the non rival properties of public goods. Given this overall framework for determination of both total and marginal benefits, four main methodologies appropriate for use in valuation studies –market prices, normative or prescriptive decision‐making models, descriptive behavioural response studies and contingent valuation studies –are outlined and their strengths and limitations described. Notwithstanding the methodological limitations and the need for a much more comprehensive set of studies for the various application sectors, it is clear that the actual and potential benefits to individuals, firms, industry sectors and national economies from state‐of‐the‐art meteorological and related services are substantial and that, at this stage, they are inadequately recognised and insufficiently exploited in many countries. Copyright © 2002 Royal Meteorological Society.
Funding meteorological services
Authors: Freebairn John W , Zillman John W
Published: August 2007

Different options for funding the provision of meteorological services and for charging for the information provided are described and evaluated. The basic infrastructure and general forecasts and warnings have public good properties of non rival consumption and high costs of exclusion. For these, direct government funding and free provision to all are favoured. Value added meteorological services for use by small groups of specialised users have mixed good properties, and in some cases private good properties. In this case, setting fees at marginal incremental costs for value added services is favoured for reasons of efficiency and practicality. The other options considered include government funding with zero price, and loading user fees for a contribution to funding the public good supply costs. Copyright © 2002 Royal Meteorological Society.
The Met Office Convection Diagnosis Scheme
Authors: Hand W H
Published: August 2007

An operational system for diagnosing probability of convective development and structure from NWP model outputs over the British Isles has been developed in the Met Office. The system originated as a research and development project and so for historical reasons is now known as the Convection Diagnosis Project (CDP). The system takes account of expected model errors in temperature and humidity and allows for forcing from sub‐grid scale mechanisms on a 1‐km scale that are important for mid‐latitude convection. A NWP convection scheme is used to determine grid‐mean parameters from a range of forcings according to probability of occurrence. The grid‐mean values are then used in a simple and variable object‐oriented life‐cycle model of a convective cloud to diagnose shower structure and expected movement. Using the life‐cycle model, a range of probabilistic forecast outputs are produced four times a day from T+6 to T+36 hours ahead for individual grid squares and for larger pre‐defined regions. Case studies and rigorous objective verification, making use of an automatic method for identifying convective cloud from radar and satellite data, have shown that the CDP outputs complement the standard NWP outputs and can provide additional useful information in a forecasting environment. Copyright © 2002 Royal Meteorological Society.
DEFLATIONARY BUBBLES
Authors: BUITER WILLEM H. , SIBERT ANNE C.
Published: August 2007

In an attempt to clean up an unruly literature, we specify the necessary and sufficient conditions for household optimality in a model where money is the only financial asset and provide the relevant proofs. We use our results to analyze when deflationary bubbles can and cannot exist. Our findings are in contrast to the results in several prominent contributions to the literature. We argue for particular specifications of the no-Ponzi-game restrictions on the representative household's and the government's intertemporal budget constraints in a model with money and bonds. Using the restriction on the household we derive the necessary and sufficient conditions for household optimality. The resulting equilibrium terminal conditions are then used to demonstrate that the existence of bonds does not affect when deflationary bubbles can and cannot occur. This result differs from that in other recent works.
INAPPROPRIATE TECHNOLOGY What Is in It for the Rich?
Authors: FERNANDES ANA , KUMAR KRISHNA B.
Published: August 2007

In this paper, we investigate incentives, other than altruism, that developed countries have for improving developing country technologies. We propose a simple model of international trade between two regions, in which individuals have preferences over an inferior good and a luxury good. The poor region has a comparative advantage in the production of the inferior good. Even when costly adaptation of the technology to the poor region's characteristics is required—making the technology inappropriate for local use—there are parameter configurations for which the rich region has an incentive to incur this cost. It benefits from a terms-of-trade improvement and from greater specialization in the luxury good. Indeed, there are cases where the rich region would prefer to improve the poor region's technology for producing the inferior good rather than its own. We apply our model to the Green Revolution and provide a quantitative assessment of its welfare effects.
Origin of the southern Okinawa Trough volcanism from detailed seismic tomography
Authors: Lin Jing‐Yi , Sibuet J.‐C. , Lee Chao‐Shing , Hsu Shu‐Kun , Klingelhoefer Frauke
Published: August 2007

Magmatism associated with subducting plate edges or slab tears has been suggested in the southern Okinawa Trough. The cross back‐arc volcanic trail, which consists of a cluster of about 70 seamounts, is located above a Ryukyu slab tear lying along the 123.3°E meridian. In November 2003, more than 3300 earthquakes recorded in this area by 15 ocean bottom seismometers and surrounding land stations during a period of 12 days were used to determine the three‐dimensional Vp and Vs velocity structures and Vp/Vs ratios. A mantle inflow characterized by low Vp and Vs and high Vp/Vs passing through the slab tear is imaged. The fluid and/or melt component is rising obliquely from the slab tear in the directions of the cross back‐arc volcanic trail, the northern slope of the southern Okinawa Trough and to north of Iriomote Island. The asthenospheric intake is also imaged by an inclined chip‐like high Vp/Vs and low Vp and Vs body dipping northerly, which might be linked to the slab retreat. West of the slab tear, most of the earthquakes are located around low Vp and Vs and high Vp/Vs bodies, which suggests that the seismicity is related to magmatic and/or fluid activities. East of it, earthquakes are concentrated in an area characterized by high Vp and Vs velocities and low Vp/Vs, suggesting that the magma chamber is absent beneath the axial part of the trough and that normal faulting is the main factor controlling the seismicity.
Putting it all together: Exhumation histories from a formal combination of heat flow and a suite of thermochronometers
Authors: d'Alessio M. A. , Williams C. F.
Published: August 2007

A suite of new techniques in thermochronometry allow analysis of the thermal history of a sample over a broad range of temperature sensitivities. New analysis tools must be developed that fully and formally integrate these techniques, allowing a single geologic interpretation of the rate and timing of exhumation and burial events consistent with all data. We integrate a thermal model of burial and exhumation, (U‐Th)/He age modeling, and fission track age and length modeling. We then use a genetic algorithm to efficiently explore possible time‐exhumation histories of a vertical sample profile (such as a borehole), simultaneously solving for exhumation and burial rates as well as changes in background heat flow. We formally combine all data in a rigorous statistical fashion. By parameterizing the model in terms of exhumation rather than time‐temperature paths (as traditionally done in fission track modeling), we can ensure that exhumation histories result in a sedimentary basin whose thickness is consistent with the observed basin, a physically based constraint that eliminates otherwise acceptable thermal histories. We apply the technique to heat flow and thermochronometry data from the 2.1‐km‐deep San Andreas Fault Observatory at Depth pilot hole near the San Andreas fault, California. We find that the site experienced <1 km of exhumation or burial since the onset of San Andreas fault activity ∼30 Ma.
Sublimation and ice condensation in hyperarid soils: Modeling results using field data from Victoria Valley, Antarctica
Authors: Hagedorn Birgit , Sletten Ronald S. , Hallet Bernard
Published: August 2007

Most soils of the Dry Valleys of Antarctica are ice‐cemented within a few decimeters of the ground surface despite the hyperarid conditions. This fact brings into question current sublimation models since they indicate that water vapor in soils is being lost at rates that would rid them of ice to at least several meters in less than a few thousand years, and yet most ice‐rich soils in the Dry Valleys are much older. In this paper, we explore mechanisms that slow or may reverse ice loss from the soil to the atmosphere and incorporate them into a sublimation model that uses high‐resolution climate and soil temperature data from 2002 to 2005 in Victoria Valley, where the surface is ∼10 ka old and the soil is ice‐cemented 0.22 m below the surface. According to this model, ice currently sublimates 0.22 mm a−1, which corresponds to a descent of the ice cement boundary of ∼1.2 mm a−1. Water vapor condenses in the upper dry soil during the winter but is lost completely to the atmosphere during the austral summer. Some water vapor diffuses downward into the frozen soil, condensing at rates of 0.02–0.09 mm a−1. Snow cover in the summer temporarily reverses the vapor transport and reduces the annual ice loss. Hence while snow slows long‐term sublimation, the dearth of data on the duration and timing of snow cover prevent us from quantifying this effect and from assessing the potential of snowmelt to offset water loss from the soil.
Early Holocene paleoseismic history at the Pakarae locality, eastern North Island, New Zealand, inferred from transgressive marine sequence architecture
Authors: Wilson Kate , Berryman Kelvin , Cochran Ursula , Little Tim
Published: August 2007

Early Holocene transgressive marine deposits infilling the Pakarae River paleovalley are used to extend the paleoseismic history of the Pakarae River locality, East Coast, North Island, New Zealand, back in time prior to eustatic sea level stabilization at ∼7 calibrated (cal) ka B.P. Paleoenvironmental evolution of the Pakarae River paleovalley from 7 to 10 cal ka B.P is reconstructed using sedimentology and biostratigraphy. Two estuarine units display sudden vertical transitions to floodplain sediments implying significant marine regressions and estuary abandonment. These regressions are attributed to coseismic coastal uplift events at ∼9000 and ∼8500 cal years B.P. A third uplift between 8500 and ∼7350 cal years B.P. is inferred from a significant difference between the amount of sediment preserved and the predicted sediment thickness according to the eustatic sea level curve. This study demonstrates the utility of the analysis of transgressive deposits and their paleoenvironmental characteristics for neotectonic investigations on active coasts.
Evolution of mixing state of black carbon in polluted air from Tokyo
Authors: Shiraiwa M. , Kondo Y. , Moteki N. , Takegawa N. , Miyazaki Y. , Blake D. R.
Published: August 2007

The evolution of the mixing state of black carbon aerosol (BC) was investigated using a single‐particle soot photometer (SP2) in polluted air transported from Tokyo. Ground‐based measurements of aerosols and trace gases were conducted at a suburban site (Kisai) 50 km north of Tokyo during July–August 2004. The ratio of 2‐pentyl nitrate (2‐PeONO2) to n‐pentane (n‐C5H12) was used to derive the photochemical age. According to the SP2 measurement, the number fraction of thickly coated BC (Shell/Corel Ratio > ca. 2) with a core diameter of 180 nm increased at the rate of 1.9% h−1, as the photochemical clock proceeded under land‐sea breeze circulation. Positive matrix factorization was applied to investigate the time‐dependent contributions of different coating materials using the mass concentrations of sulfate, nitrate, and organics measured using an aerosol mass spectrometer. The main coating materials found in this study were sulfate and organics.
Tropical vertical temperature trends: A real discrepancy?
Authors: Thorne P. W. , Parker D. E. , Santer B. D. , McCarthy M. P. , Sexton D. M. H. , Webb M. J. , Murphy J. M. , Collins M. , Titchner H. A. , Jones G. S.
Published: August 2007

We examine the sensitivity of modeled and observed tropical tropospheric temperature trend amplification (the ratio of T2LT “lower troposphere” to surface changes) to several sources of uncertainty. Model behaviour is robust across a large perturbed physics ensemble of HadCM3, yielding a smaller amplification range (1.44 ± 0.06) than a previous multi‐model ensemble (1.41 ± 0.24). The uncertainty of inter‐satellite calibration implied by available MSU T2 (mid‐troposphere) estimates (σ = 0.035K) is much greater than that required to adequately resolve the trend (σ < 0.01K), or the amplification behaviour (implied amplification range ±0.95). Trend amplification uncertainty in both models and observations decreases as the timescale increases. Depending upon choice of dataset and time period, uncertainty in trend amplification estimates over 21 years lies between ±1.5 and ±0.2.
Dynamically driven mantle flow and shear wave splitting asymmetry across the EPR, MELT area
Authors: Conder James A.
Published: August 2007

The southern East Pacific Rise exhibits profound asymmetries in its geophysical character, implying asymmetric melting and flow patterns beneath the plate boundary with inflow from the Pacific superswell region. Shear wave splitting is 0.5–1 seconds larger on the Pacific plate than the Nazca plate. As seismic anisotropy is a measure of mantle strain history, the shear wave splitting signature provides an important constraint on mantle flow patterns. Finite‐element models of mantle flow using rheology that accounts for both dislocation and diffusion creep, coupled with calculations of mineral texturing and subsequent shear wave splitting predictions, show that either a model of dynamically driven flow or a passive thermal anomaly model can provide a reasonable fit to the observed asymmetric shear wave splitting. Dynamic flow produces a thicker anisotropic layer beneath the Pacific plate, while extending the melting region westward, simultaneously explaining shear wave splitting observations and the inferred asymmetric melt production.
Topography, exhumation pathway, age uncertainties, and the interpretation of thermochronometer data
Authors: Huntington Katharine W. , Ehlers Todd A. , Hodges Kip V. , Whipp David M.
Published: August 2007

The relationship between thermochronometer age and structural elevation is commonly used to infer long‐term exhumation histories. Previous studies suggest that inferred exhumation rates from the conventional (one‐dimensional, 1‐D) age‐elevation approach are sensitive to topography and variations in exhumation rate and pathway. Here we evaluate the magnitude of these effects by (1) using a 3‐D thermal‐kinematic model of the central Nepalese Himalaya to predict age‐elevation profiles for multiple thermochronometers as a function of exhumation rate and pathway (vertical, oblique, or thrust fault), and (2) calculating the probability that the true exhumation rate will be recovered from an age‐elevation profile for sample uncertainties of different magnitudes. Results suggest that profiles oriented orthogonal to long‐wavelength topography and the direction of lateral transport are relatively insensitive to their influence. For profiles oriented parallel to the transport direction, horizontal transport during exhumation partly counteracts topographic effects. The difference between model imposed and 1‐D exhumation rates from the slope of a best fit line through an age‐elevation plot is greatest when rocks are exhumed vertically and low‐temperature thermochronometers are used. The magnitude of error in 1‐D exhumation rate estimates varies dramatically as a function of sample uncertainty, particularly when exhumation is rapid. The nature of this variation can be used to design sampling strategies for which 1‐D interpretations of age‐elevation gradients are likely to be within error of the true exhumation rate. Alternatively, if sample uncertainties can be reduced, studies that combine thermal modeling with age‐elevation data can potentially provide important constraints on thermal and kinematic fields at depth.
Noninvasive Study of Neurovascular Coupling during Graded Neuronal Suppression
Authors: Zhang Nanyin , Liu Zhongming , He Bin , Chen Wei
Published: August 2007

In this study, the neurovascular coupling relationship was noninvasively studied in the human visual cortex. Graded neuronal/hemodynamic suppression conditions were generated using a paired-stimulus paradigm. Visual evoked potential was measured to quantify neuronal activity. Hemodynamic activities were measured and quantified by perfusion and blood oxygenation level-dependent changes. All quantification was normalized to the same activation condition induced by a single stimulus paradigm within each experimental session. This experiment design eliminated the confounding factors such as anesthesia and inconsistent neurovascular coupling patterns within and/or among tasks. The results reveal that (i) there is a tight neurovascular coupling at graded neuronal suppression conditions; (ii) the neurovascular coupling relationship contains a subtle, but significant, nonlinear component; and (iii) the linear model, nevertheless, is still a good approximation reflecting the neurovascular coupling relationship. This study extends the range of the neurovascular coupling relationship from graded neuronal excitation conditions to graded neuronal suppression conditions.
An analysis of the effects of environmental factors on conidial dispersal of Uncinula necator (grape powdery mildew) in vineyards
Authors: Willocquet L. , Clerjeau M.
Published: August 2007

Aerial spore concentration of Uncinula necator (the causal agent of grape powdery mildew), weather data and cropping practices were monitored during two consecutive seasons in two vineyards of the Bordeaux area. During days with no rain, spore dispersal was mainly diurnal and showed variations that followed the same pattern as that of wind speed, and a reverse pattern to that of relative humidity. Light falls of rain, of approximately 2 mm, coincided with increased spore densities in the air. Pesticide sprays using high pressure equipment generated high wind speeds at the canopy level. This may trigger high spore dispersal. High conidial stocks were produced under spontaneous conditions in the canopy. These stocks were released only under particular events, such as heavy rains, or pesticide applications with high pressure sprayers. Other cropping practices causing leaf shaking, such as pruning, may enhance spore dispersal. Over the observation period, the onset of spore dispersal was observed during a period with no rain following a rainy period, suggesting the detrimental effect of rains on epidemic onset. Epidemiological and disease management implications are discussed.
Influence of microwave irradiation on the current inducing phase-slip processes in wide tin films
Authors: Dmitriev V. M. , Zolochevskii I. V.
Published: August 2007

The temperature dependences of the microwave-enhanced maximum current ImP(T) at which a resistive vortex state exists in wide and thin tin films are investigated experimentally and analyzed. It is shown that the experimentally obtained temperature dependences of the current ImP(T) are well approximated by formulas analogous to that for the equilibrium case of the Aslamazov–Lempitskiĭ theory but with the critical temperature Tc replaced by an enhanced critical temperature TcP, and this is valid for the whole temperature region of existence of the wide-film regime. It is found that with increasing frequency of the irradiation the absolute value of ImP(T) increases, and the temperature region of enhancement of ImP(T) is broadened to lower temperatures.
Effect of single-ion anisotropy on the phase states of 2D non-Heisenberg ferromagnets
Authors: Fridman Yu. A. , Matyunin D. A. , Klevets F. N.
Published: August 2007

The phase states and elementary excitation spectra of an anisotropic 2D non-Heisenberg ferromagnet are investigated. It is shown that easy-axis single-ion anisotropy has a strong effect on the formation of the quadrupole phase and on the appearance of the canted phase. The conditions for phase transitions with respect to the material constants and the magnetic field are determined. The phase diagrams of the system are constructed.
Non-nuclear attractor of electron density as a manifestation of the solvated electron
Authors: Timerghazin Qadir K. , Peslherbe Gilles H.
Published: August 2007

Two or more polar molecules can trap an excess electron either in a dipole-bound fashion where it is located outside of the cluster (dipole-bound electron) or inside the cluster (solvated electron). The topology of the electron density in dipole-bound and solvated-electron clusters has been examined for the paradigm (HF)3− cluster. As spatial confinement of the excess electron increases, a non-nuclear maximum (or attractor) of the electron density eventually forms, which suggests that the solvated electron can be described as a topological atom with its own set of physicochemical properties.
Effects of coverage on the structures, energetics, and electronics of oxygen adsorption on RuO2(110)
Authors: Wang Hangyao , Schneider William F.
Published: August 2007

Plane-wave supercell DFT calculations within the PW91 generalized gradient approximation are used to examine the influence of oxygen coverage on the structure, energetics, and electronics of the RuO2(110) surface. Filling of Obr and Ocus sites is exothermic with respect to molecular O2 at all coverages and causes changes in local Ru electronic structure consistent with the changing metal coordination. By fitting the surface energies of a large number of surface configurations to a two-body interaction model, an O atom is calculated to be bound by 2.55eV within a filled Obr row and by 0.98eV along an otherwise vacant Ocus row. Lateral interactions modify these binding energies by up to 20%. Ocus–Ocus interactions are repulsive and diminish binding energy with increasing Ocus filling. Due to the favorable relief of local strain, Obr–Obr interactions are attractive and favor filling of neighbor br sites. These interaction effects are relatively modest in absolute magnitude but are large enough to influence the ability of the RuO2(110) surface to promote oxidation of relatively weak reductants, such as NO and C2H4.
O
O
C
O
+
cation. II. Its role during the atmospheric ion-molecule reactions
Authors: Ndome H. , Alcaraz C. , Hochlaf M.
Published: August 2007

For the charge transfer and vibrational and electronic deexcitations between O2∕O2++CO+∕CO, O∕O++CO2+∕CO2, and C∕C++O3+∕O3, multistep reaction pathways are discussed in light of the theoretical data of this and previous paper together with close comparison with the experimental observations. Our calculations show that these pathways involve both the long range and molecular region ranges of the potential energy surfaces of the electronic states of the stable isomers of OOCO+ and mostly those of the weakly bound charge transfer complex OOCO+. The couplings between these electronic states such as vibronic, Renner-Teller, Jahn-Teller, and spin orbit are viewed to play crucial roles here. Moreover, the initial orientation of the reactants, in the entrance channels, strongly influences the reaction mechanisms undertaken. We propose for the first time a mechanism for the widely experimentally studied spin-forbidden exothermic O+(Su4)+CO2(XΣg+1)→O2+(XΠg2)+CO(XΣ+1) reaction where the O turns around the OCO molecule.
Experimental and theoretical study of the pyrrole cluster photochemistry: Closing the πσ* dissociation pathway by complexation
Authors: Poterya Viktoriya , Profant Václav , Fárník Michal , Slavíček Petr , Buck Udo
Published: August 2007

Photolysis of size selected pyrrole clusters has been investigated and compared to the photolysis of an isolated pyrrole molecule. Experimentally, size distributions of different mean cluster sizes (n¯=3 and n¯⪢5) have been prepared in supersonic expansions and the clusters were photolyzed at 243 and 193nm. The kinetic energy distributions of the H photofragments have been measured. The distributions exhibit a bimodal character with fast and slow H-fragment peaks similar to the spectra of the bare molecule. However, with increasing cluster size the slow component gains intensity with respect to the fast one. A similar effect is observed with increasing the excitation energy from 243to193nm. Theoretical calculations at the CASSCF/CASPT2 level have been performed for bare and complexed pyrroles (pyrrole is complexed with an argon atom and with another pyrrole unit). Combination of theoretical and experimental approaches leads to the conclusion that the direct dissociative pathway along the πσ* potential energy surface in the N–H stretch coordinate is closed by the presence of the solvent molecule. This pathway is an important channel leading to the fast H atoms in the dissociation of the bare molecule. The solvent molecule influences significantly the electronic structure in the Rydberg-type πσ* state while it has little influence on the valence states. The slow channel is mostly populated by the out-of-plane deformation mode which is also not influenced by solvation. We have also studied other possible reaction channels in pyrrole clusters (hydrogen transfer, dimerization). The present study shows that more insight into the bulk behavior of biologically relevant molecules can be gained from cluster studies.
Theoretical study on the sound absorption of electrolytic solutions. II. Assignments of relaxations
Authors: Yamaguchi T. , Matsuoka T. , Koda S.
Published: August 2007

The theory on the ultrasonic absorption spectrum of electrolytic solutions recently proposed by us is applied to the model system that resembles to the aqueous solution of MgSO4. The charges on ions are reduced to ±1.5e in order to obtain the equilibrium structure by the integral equation theory. The theory reproduces the existence of two relaxations around 100kHz and 1GHz. The physical origin of the relaxation is analyzed based on the theoretical expression. The slower relaxation is shown to originate in the formation of contact ion pair, in harmony with the conventional assignment. The amplitude of this relaxation agrees with the experimental one fairly well. The absorption cross section is a weakly increasing function of the concentration of the salt in theory, whereas it depends little on the concentration in experiment, which is ascribed to the weaker association of the pair in the theory. The deviation from the Debye relaxation is found for the faster process, and the concentration dependence is small. The analysis shows that this relaxation stems from the coupling between the pressure and the long-range concentration fluctuation, and the concentration independence and the non-Debye relaxation are explained based on the theoretical analysis. In particular, the theory demonstrates that this process has the t−3∕2 tail in the time domain, which is confirmed by numerical calculation. The deviation of the theoretical relaxation amplitude from the experimental one is elucidated in terms of the theoretical expression of the coefficient.
Interlayer water molecules in vanadium pentoxide hydrate. IX. Anisotropic translational diffusion leading to anisotropic ac conductivity
Authors: Kittaka Shigeharu , Yamaguchi Toshio , Bellissent-Funel Marie-Claire
Published: August 2007

The anisotropy of the dynamic properties of interlayer water molecules along the a and b axes of vanadium pentoxide hydrate, orthorhombic V2O5∙nH2O, was studied using quasielastic neutron scattering (QENS) in relation to the anisotropy of the ac conductivity. The QENS spectra were analyzed using a stretched exponential function and a Lorentzian function. Both methods showed that the double-layer water molecules along the b axis are more mobile than those along the a axis. The difference in mobility between the two axes is more pronounced using a Lorentzian function analysis. These facts suggest that the diffusion coefficient of water molecules along the b axis is larger than that along the a axis, which is closely related to the ac conductivity originating from proton hopping. The anisotropy of the dynamic motion of water molecules can be attributed to the shorter b-axis length (b=3.60Å), with respect to the longer and less regular repetition of the atomic arrangements along the a axis (42.34Å).
Temperature dependence of negative ion lifetimes
Authors: Cannon M. , Liu Y. , Suess L. , Dunning F. B. , Steill J. D. , Compton R. N.
Published: August 2007

The autodetachment lifetimes of SF6−* and C6F6−* ions formed by charge transfer in K(np)∕SF6, C6F6 collisions are measured as a function of target temperature over the range of ∼300–600K with the aid of time-of-flight techniques and a Penning ion trap. At room temperature only formation of long-lived SF6−* ions with lifetimes τ≳1ms is seen. As the temperature is increased the lifetime of these long-lived ions is reduced, some having lifetimes as short as ∼0.4ms. The appearance of a short-lived, τ≲10μs, SF6−* signal is also observed. Rydberg electron transfer to room temperature C6F6 leads predominantly to formation of short-lived, τ≲10μs, C6F6−* ions, although a small number of longer-lived anions with lifetimes of ∼50–100μs is also evident. This signal disappears as the temperature is raised and the lifetime of the short-lived ions decreases dramatically. The measured lifetimes are compared to those predicted using quasiequilibrium theory and updated values of the input parameters, including calculated vibrational frequencies for the anions. For C6F6, the calculated anion lifetimes are in good agreement with those measured experimentally. While similarly good agreement is obtained for SF6 at room temperature, the predicted temperature dependence of the lifetime is very different to that observed. This suggests that the excitation energy is not completely randomized in the anion and the measurements point to formation of at least two quasi-independent groups of anion states that have very different lifetimes. The present results are compared to those of earlier work.
Three-dimensional evolution of vortical structures and associated flow bifurcations in the wake of two side-by-side square cylinders
Authors: Sau Amalendu , Hsu Tai-Wen , Ou Shan-Hwei
Published: August 2007

In this paper, we focus on the three-dimensional growth of the vortical structures behind two square cylinders when placed in a side-by-side arrangement and examine different possible modes of flow bifurcation along their spanwise extended corelines. For this, unsteady three-dimensional flow simulations are conducted with five different values of gap/diameter ratios (g*), namely, 2.1, 1.7, 0.7, 0.5, and 0.2, that cover important known phases, i.e., coshedding (g*=2.1 and 1.7), asymmetric (g*=0.7 and 0.5), and single-body type (g*=0.2) of wake evolution. In order to exploit flow physics within the transition range, the Reynolds number of the flow is taken as 100. Notably, for all the investigated cases, parallel vortex shedding has been observed behind the two cylinders. However, with the decrease of gap ratio g*, the downstream flow gradually lost stability and the corelines of the shedded vortices appeared in a wavy fashion. While for g*=2.1 and 1.7, the simulated streamwise flows exhibit antiphase and in-phase synchronization of the wake, respectively, there is also observed a notable difference in the structural growth of corresponding spanwise flows. For the antiphase flow (at g*=2.1) the downstream wake evolved through a symmetry-breaking mode-I Hopf bifurcation along various spanwise extended vortex corelines. However, the presence of an additional mode-II Hopf bifurcation was detected in the wake of an in-phase flow (at g*=1.7). The development of a number of local pressure maxima over different spanwise extended vortex corelines, and the gradual decrease of pressure along their left and right, respectively, are noted to be responsible for initiating such flow bifurcations. In the biased (asymmetric) regime, with g*=0.7 and 0.5, the flow behind the cylinders showed visible signs of growing instability and there occurred significant spanwise pressure fluctuations, which in turn inflicted large three dimensionality into the downstream wake and local velocity irregularities. The corresponding wake evolution patterns are thereby noted to exhibit predominantly unsteady and transitional features. In this biased flow regime, the gap flow flip-flopped randomly and became deflected alternately towards the top and bottom cylinders. On the one hand, clear dominance of both mode-I and mode-II flow bifurcations was observed with both of these initially locked biased flows. However, due to increased flow asymmetry the spanwise length scales of such bifurcations changed significantly. On the other hand, for the single-body regime flow with g*=0.2, the occurrence of only mode-I bifurcation was detected in the wake of the cylinders.
Photodissociation of S atom containing amino acid chromophores
Authors: Lin Ming-Fu , Dyakov Yuri A. , Lee Yuan T. , Lin S. H. , Mebel Alexander M. , Ni Chi-Kung
Published: August 2007

Photodissociation of 3-(methylthio)propylamine and cysteamine, the chromophores of S atom containing amino acid methionine and cysteine, respectively, was studied separately in a molecular beam at 193nm using multimass ion imaging techniques. Four dissociation channels were observed for 3-(methylthio)propylamine, including (1) CH3SCH2CH2CH2NH2→CH3SCH2CH2CH2NH+H, (2) CH3SCH2CH2CH2NH2→CH3+SCH2CH2CH2NH2, (3) CH3SCH2CH2CH2NH2→CH3S+CH2CH2CH2NH2, and (4) CH3SCH2CH2CH2NH2→CH3SCH2+CH2CH2NH2. Two dissociation channels were observed from cysteamine, including (5) HSCH2CH2NH2→HS+CH2CH2NH2 and (6) HSCH2CH2NH2→HSCH2+CH2NH2. The photofragment translational energy distributions suggest that reaction (1) and parts of the reactions (2), (3), and (5) occur on the repulsive excited states. However, reaction (4) and (6) occur only after the internal conversion to the electronic ground state. Since the dissociation from an excited state with a repulsive potential energy surface is very fast, it would not be quenched completely even in the condensed phase. Our results indicate that reactions following dissociation may play an important role in the UV photochemistry of S atom containing amino acid chromophores in the condensed phase. A comparison with the potential energy surface from ab initio calculations and branching ratios from RRKM calculations was made.
Chemiluminescent reaction of Ba(P3) with N2O at hyperthermal collision energies: Rotational alignment of the BaO(AΣ+1) product
Authors: Rossa Maximiliano , Rinaldi Carlos A. , Ferrero Juan C.
Published: August 2007

The chemiluminescent reaction Ba(6s6pP3)+N2O was studied at an average collision energy of 1.56eV in a beam-gas arrangement. Ba(P3) was produced by laser ablation of barium, which resulted in a broad collision energy distribution extending up to ∼5.7eV. A series of experiments was made to extract the Ba(P3) contribution to chemiluminescence from that corresponding to Ba 6s2 S01 and 6s5d D3, which are the other two most populated states in the atomic beam. The fully dispersed polarized chemiluminescence spectra at 400–600nm from the title reaction were recorded and assigned to a BaO molecule excited in the AΣ+1 level. In addition, the average and wavelength-resolved degrees of polarization associated to the parallel BaO(AΣ+1→XΣ+1) emission are reported. The analysis of the average polarization degree show that the BaO(AΣ+1) product is significantly aligned, suggesting that the reaction mechanism is predominantly direct. The product rotational alignment was found to depend markedly on the emission wavelength, which revealed a negative correlation with the BaO(AΣ+1) product vibrational state. On the basis of experimental and theoretical investigations on the reactions of N2O with both the S01, D3, and P11 states of Ba and the lighter group 2 atoms, it is suggested that the Ba(P3) reaction involves a charge transfer at relatively short reagent separations and that restricted collision geometries at the highest velocity components of the broad distribution are necessary to rationalize the data.
State-to-state reaction probabilities for the H+O2(v,j)→O+OH(v′,j′) reaction on three potential energy surfaces
Authors: Hankel Marlies , Smith Sean C. , Meijer Anthony J. H. M.
Published: August 2007

We report state-to-state and total reaction probabilities for J=0 and total reaction probabilities for J=2 and 4 for the title reaction, both for ground-state and initially rovibrationally excited reactants. The results for three different potential energy surfaces are compared and contrasted. The potential energy surfaces employed are the DMBE IV surface by Pastrana et al. [J. Phys. Chem. 94, 8073 (1990)], the surface by Troe and Ushakov (TU) [J. Chem. Phys. 115, 3621 (2001)], and the new XXZLG ab initio surface by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. Our results show that the total reaction probabilities from both the TU and XXZLG surfaces are much smaller in magnitude for collision energies above 1.2eV compared to the DMBE IV surface. The three surfaces also show different behavior with regards to the effect of initial state excitation. The reactivity is increased on the XXZLG and the TU surfaces and decreased on the DMBE IV surface. Vibrational and rotational product state distributions for the XXZLG and the DMBE IV surface show different behaviors for both types of distributions. Our results show that for energies above 1.25eV the dynamics on the DMBE IV surface are not statistical. However, there is also evidence that the dynamics on the XXZLG surface are not purely statistical for energies above the onset of the first excited product vibrational state v′=1. The magnitude of the total reaction probability is decreased for J>0 for the DMBE IV and the XXZLG surfaces for ground-state reactants. However, for initially rovibrationally excited reactants, the total reaction probability does not decrease as expected for both surfaces. As a result the total cross section averaged over all Boltzmann accessible rotational states may well be larger than the cross section reported in the literature for j=1.
Multitone large-signal analysis of superconducting transition-edge sensors for astronomy
Authors: Rostem K. , Withington S. , Goldie D. J.
Published: August 2007

A simple transition-edge sensor (TES) is governed by two coupled, nonlinear equations, which when solved give the behavior of the device given the initial conditions. The two equations describe the full electrical and thermal characteristics of the device and the way in which the device interacts with the external electrical and thermal circuits. To date these coupled nonlinear equations have been solved analytically in the small-signal limit, by linearizing the equations about some operating point. The resulting coupled linear equations contain a wealth of interesting physics, and form the principal tool by which all detectors are currently designed and modeled. In this article we describe a numerical technique for solving the coupled nonlinear equations rigorously, without any assumptions about the magnitudes of the various signals and parameters that determine the behavior of a device. The technique is based on a harmonic balance algorithm that searches, in the frequency domain, for voltage, current, and temperature wave forms that are consistent with the solid-state physics of the device. Indeed, both the small and large signal limits can be simulated, and the full harmonic content of the system retrieved. In this article, we will outline the principal features of the algorithm, and show various results such as I−V curves, saturation when signal power is modulated, impedance response when the bias current is modulated and signal power kept constant, and pulsed signal power analysis that shows the dynamics of a device. Numerous extensions of this fundamental technique are now possible including multitone nonharmonic analysis, large-signal impedance calculation, modeling of complicated thermal circuits, noise models, and frequency-domain multiplexing. We believe that our algorithm will become the principle technique for analyzing the large-signal behavior of all TES detectors and on that basis we are developing computer aided design software.