bluuebunny/crossref_metadata_2025 huggingface dataset:
Definition and Measurement of Tactical Voting: The Role of Rational Choice
Authors: FISHER STEPHEN D.
Published: September 2006

There has been substantial debate on the measurement of tactical voting in this Journal, much of which has actually been concerned with the definition of a tactical vote. For this reason it is necessary to go ‘back to basics’ to examine the notion of a tactical vote within rational choice theory and follow its implications for the measurement of tactical voting. This Note has four aims: to elucidate the formal theoretical concepts behind the notion of tactical voting; to provide a practical definition of tactical voting based on those concepts; to examine and use the implications of the theory and definition to evaluate existing measures of tactical voting; and to further appraise measures of tactical voting from general methodological considerations. This Note focuses on tactical voting in single-member simple-plurality electoral systems. The following section argues that the range of situations where it may be optimal to vote tactically is both broader and less well defined than previous authors have generally realized. This implies that both the definition, and therefore the measurement, of tactical voting rest mainly on the criteria of voting for a party other than the first choice and doing so in order to best influence who wins. The empirical section examines various approaches to the measurement of tactical voting and argues that the Heath et al. measure is a priori the most attractive available. Furthermore, detailed analysis using British Election Study (BES) data from English voters in 1987, 1992 and 1997, shows that whilst the Heath et al. measure is relatively robust, it can be usefully revised to improve consistency with the strength-of-feeling scores. A corresponding method for identifying a voter's preferred party is also presented.
Analysing Bureau-Shaping Models: Comments on Marsh, Smith and Richards
Authors: DOWDING KEITH , JAMES OLIVER
Published: September 2006

In a recent article in this Journal Marsh, Smith and Richards (MSR) note the massive recent changes in the organization of British government and the attention the bureau-shaping model has received both at a theoretical level and as an explanation of changes. They suggest that the model has breathed new life into debates about the behaviour of officials and is important in the context of the ‘Next Steps’ agency reform. They state two aims of their article: ‘First, it is a critical contribution to the literature on the bureau-shaping model’, and secondly it examines ‘the model's utility as an explanation of the changes that have occurred in British central government in the past decade’. They also use their arguments as part of an assault upon rational choice and empirical political science more generally in favour of interpretative sociology. However, in this Note, we respond to their work on the bureau-shaping model and rational choice.
Dust voids (holes) in a charge-varying complex plasma with non-isothermal trapped electrons
Authors: TRIBECHE MOULOUD , GOUGAM LEILA AIT , GRIBA SAFIA , ZERGUINI TAHA HOUSSINE
Published: September 2006

The recent analysis of dust voids (Mamun, A. A. and Shukla, P. K. 2005 J. Plasma Phys.71, 143) is extended to include self-consistent electron trapping and dust charge variation. It is found that under certain conditions the effect of dust charge variation can be quite important. In particular, it may be noted that the dust charge variation leads to an additional enlargement of the nonlinear dust voids. The effects of ion/electron temperature and trapping parameter on the properties of these nonlinear dust voids are briefly discussed. As the dust particle number density is increased, the depth, as well as the width, of the dust void decreases and the additional enlargement (due to dust charge perturbations) becomes less pronounced. Furthermore, these dust voids exhibit smaller widths than those involving isothermal electrons.
Parallel navigation for reaching a moving goal by a mobile robot
Authors: Belkhouche F. , Belkhouche B. , Rastgoufard P.
Published: September 2006

In this paper, we present a method for robot navigation toward a moving object with unknown maneuvers. Our strategy is based on the integration of the robot and the target kinematics equations with geometric rules. The tracking problem is modeled in polar coordinates using a two-dimensional system of differential equations. The control law is then derived based on this model. Our approach consists of a rendezvous course, which means that the robot reaches the moving goal without following its path. In the presence of obstacles, two navigation modes are integrated, namely the tracking and the obstacle-avoidance modes. To confirm our theoretical results, the navigation strategy is illustrated using an extensive simulation for different scenarios.
Antimicrobial susceptibility and genetic characteristics ofHaemophilus influenzaeisolated from patients with respiratory tract infections between 1987 and 2000, including β-lactamase-negative ampicillin-resistant strains
Authors: QIN L. , WATANABE H. , ASOH N. , WATANABE K. , OISHI K. , MIZOTA T. , NAGATAKE T.
Published: September 2006

The minimum inhibitory concentration (MIC) of five antibiotics and the presence of resistance genes was determined in 163Haemophilus influenzaeisolates collected over 13 years (1987–2000) in four two-yearly sampling periods from patients with respiratory tract infections. The prevalence of β-lactamase-negative ampicillin-susceptible strains was approximately 80% over the sampling period although fewer strains (65·9%) were recovered in the period 1995–1997. TEM-1 type β-lactamase-producing strains were less frequent starting at 15·6% and declining to 2·2% in the final sampling period. Low-β-lactamase-negative ampicillin-resistant (BLNAR) strains were uncommon in 1987–1989 (2·2%), peaked to 19·5% in 1995–1997, but fell back to 11·1% by 2000. Fully BLNAR strains were not detected until the last sampling period (6·7%). The MICs of ampicillin, levofloxacin, cefditoren and ceftriaxone remained stable but there was an eight-fold increase in the MIC of cefdinir over the sampling period. Pulsed-field gel electrophoresis of DNA digests showed that three representative BLNAR strains were genetically distinct and 11 DNA profiles were identified among 17 low-BLNAR strains. These data suggest that the number of genetically altered BLNAR and low-BLNAR strains are increasing in Japan.
Hepatitis C virus: laboratory surveillance in England and Wales, 1992–2004
Authors: GUNGABISSOON U. , BALOGUN M. A. , RAMSAY M. E.
Published: September 2006

Between 1992 and 2004, a total of 49 819 confirmed hepatitis C infections have been reported to the Health Protection Agency (HPA) by laboratories in England and Wales; the annual number of reports increased from 241 in 1991 to 8149 in 2004. Most reports with a known risk factor were in injecting drug users (87%, 12 438/14 221), but 71% (35 598/49 819) of the total had no reported identified risk. The age-sex distribution of the latter cases was similar to that in injecting drug users. Using names to assign ethnicity, individuals with South Asian names had an older age distribution and a different risk factor profile from non-South Asians. Using published age-specific prevalence data from 1996, it was estimated that around 281 764 cases of hepatitis C infection exist in England and Wales, and that only 17% of these cases have been reported to the HPA. Surveillance reports continue to provide important information regarding trends in hepatitis C infection in specific risk groups.
Single‐crystal elasticity and sound velocities of (Mg0.94Fe0.06)O ferropericlase to 20 GPa
Authors: Jackson Jennifer M. , Sinogeikin Stanislav V. , Jacobsen Steven D. , Reichmann Hans J. , Mackwell Stephen J. , Bass Jay D.
Published: September 2006

The single‐crystal elastic properties of high‐spin (Mg0.94Fe0.06)O ferropericlase were measured by Brillouin spectroscopy on a sample compressed to 20 GPa with diamond anvil cells using methanol‐ethanol‐water as a pressure‐transmitting medium. At room pressure, the adiabatic bulk (K0S) and shear (μ0S) moduli are K0S = 163 ± 3 GPa and μ0S = 121 ± 2 GPa, in excellent agreement with ultrasonic results from the same bulk sample (Jacobsen et al., 2002). A fit to all our high‐pressure Brillouin data using a third‐order finite‐strain equation of state yields the following pressure derivatives of the adiabatic bulk and shear moduli: K′0S = 3.9 ± 0.2 and μ′0S = 2.1 ± 0.1. Within the uncertainties, we find that K0S and K′0S of (Mg0.94Fe0.06)O are unchanged from MgO. However, μ0S and μ′0S of (Mg0.94Fe0.06)O are reduced by 8% and 11%, respectively. The aggregate compressional (VP) and shear (VS) wave velocities are reduced by 4% and 6%, respectively, as compared to MgO. The pressure dependence of the single‐crystal elastic moduli and aggregate sound velocities is linear within the investigated pressure range. The elastic anisotropy of (Mg0.94Fe0.06)O is about 10% greater than that of MgO at ambient conditions. At the highest pressure obtained here, the elastic anisotropy of (Mg0.94Fe0.06)O is close to zero. On the basis of our measurements and earlier ultrasonic measurements, we find that the pressure derivatives of shear moduli obtained at room pressure for low iron concentrations (<20 mol% FeO) of high‐spin ferropericlase are inconsistent with those inferred from the lower mantle PREM model.
Atmospheric mercury emissions from substrates and fumaroles associated with three hydrothermal systems in the western United States
Authors: Engle Mark A. , Gustin Mae Sexauer , Goff Fraser , Counce Dale A. , Janik Cathy J. , Bergfeld Deborah , Rytuba James J.
Published: September 2006

This paper quantifies atmospheric mercury (Hg) emissions from substrates and fumaroles associated with three hydrothermal systems: Lassen Volcanic Center, California (LVC); Yellowstone Caldera, Wyoming (YC); and Dixie Valley, Nevada (DV). Substrate Hg fluxes were measured using field chamber methods at thermal and nonthermal sites. The highest Hg fluxes (up to 541 ng m−2 h−1) were measured at thermal active areas. Fluxes from altered and unaltered nonthermal sites were <10 ng m−2 h−1 and were comparable to those measured in natural low‐Hg background regions for YC and DV, and at LVC they were slightly elevated. Similarly, reactive gaseous mercury concentrations were higher in thermal active areas. Using a Geographic Information System framework for scaling, estimated area‐average Hg emissions from substrates were 0.9–3.8 ng m−2 h−1 at LVC, 0.8–2.8 ng m−2 h−1 at YC, and 0.4–0.5 ng m−2 h−1 at DV. At LVC, nonthermal areas were the primary substrate source of atmospheric Hg (>98%). At YC, substrate Hg emissions were dominated (50 to 90%) by acidically altered thermal areas. Substrate emissions at DV were low and primarily from nonthermal areas (66% to 75%). Fumarole emissions at LVC (91–146 kg yr−1) and YC (0.18–1.6 kg yr−1 for Mud Volcano) were estimated by applying Hg:H2O and Hg:CO2 ratios in hydrothermal gas samples to H2O and CO2 emissions. Applying total area‐average emissions from substrates and thermal features at LVC, YC, and DV to similar systems across the conterminous United States, yearly atmospheric Hg emissions from active hydrothermal systems are projected to be 1.3–2.1 Mg.
Response of water vapor and clouds to El Niño warming in three National Center for Atmospheric Research atmospheric models
Authors: Zhang Tao , Sun De‐Zheng
Published: September 2006

The response of water vapor and clouds to El Niño warming over the tropical Pacific in the most recent three versions of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM2, T42 CAM3, and T85 CAM3) is quantified and compared to observations. It is found that all three models have a stronger response in the greenhouse effect of water vapor than that indicated in Earth Radiation Budget Experiment (ERBE) observations. The overestimate is most severe in the T85 CAM3 (up to 36%). Compared with National Centers for Environmental Prediction (NCEP) reanalysis, all three models have an excessive response of atmospheric moisture content in the upper troposphere, suggesting a cause for the excessive response in the greenhouse effect of water vapor. The response in the greenhouse effect of clouds (the longwave forcing of clouds) in two of the models (CAM2 and T42 CAM3) is significantly weaker than that indicated in ERBE observations, but it is comparable to the observed in the T85 CAM3. The improvement in the T85 CAM3 in simulating the response in the greenhouse effect is helped by a stronger response in the middle level clouds in the model (compared to CAM2 and T42 CAM3). In contrast to the strong negative response in the shortwave forcing seen in the ERBE observations, the response of the shortwave forcing of clouds in the CAM2 and the T42 CAM3 is weak and even has a sign opposite to observations when it is averaged over the entire region of surface warming. The simulation of the response of the shortwave forcing in the T85 CAM3 is considerably improved, though the negative response over the equatorial Pacific is still not strong enough compared to ERBE observations. The stronger negative response in the shortwave forcing in the T85 CAM3 is apparently linked to a stronger response in the middle level cloud cover. All three models fail to simulate the observed pattern of the response in the low cloud cover over the central and eastern Pacific, resulting in deficiency in the response of the shortwave cloud forcing in that region. The deficiency in the low cloud cover response suggests that the low cloud cover scheme has room for improvement.
Modeling the provenance of the Apollo 16 regolith
Authors: Petro N. E. , Pieters C. M.
Published: September 2006

The regolith at the Apollo 16 landing site, the only Apollo landing site in the central lunar highlands, contains material derived from a number of sources. A model that accounts for the introduction of basin ejecta and mixing of the megaregolith is used to estimate the abundance of basin material in the Apollo 16 regolith. Megaregolith mixing model estimates of the abundance of primary ejecta from the Imbrium, Serenitatis, and Nectaris basins are found to be present in roughly equal (8–10%) proportions. Additionally, the presence of mare‐derived material in the Apollo 16 regolith suggests that a significant component of the regolith (15–23%) is derived from lateral transport. There are inherent difficulties in directly comparing model results with ground truth at Apollo 16. Results suggest shallower mixing during ejecta emplacement than predicted by Oberbeck et al. (1975).
Stellar occultations observed by SPICAM on Mars Express
Authors: Quémerais Eric , Bertaux Jean‐Loup , Korablev Oleg , Dimarellis Emmanuel , Cot Charles , Sandel Bill R. , Fussen Didier
Published: September 2006

Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) is the first instrument orbiting a planet other than Earth that is dedicated to the technique of stellar occultation. During the first year of operation on board Mars Express, SPICAM observed more than 500 star occultations, yielding vertical profiles of CO2, ozone, and dust/clouds/aerosols. We review the principles of a star occultation in the absorptive regime, emphasizing two advantages of this method: an absolute value is obtained from a relative measurement without the need for an absolute calibration of the instrument, and the altitude of the measurement is accurately known because it depends only on the position of the spacecraft and not on the pointing of the instrument. We describe a general algorithm used for all occultations. First, we derive from the raw data the transmission of the atmosphere as a function of wavelength, T(λ, z), taking account of instrument‐specific factors. Then a spectral inversion retrieves the slant densities (local densities integrated along the line of sight) of all absorbing species for each measurement of the transmission T(λ, z) during the occultation. Finally, a vertical inversion retrieves the vertical distribution of the local densities from the series of the slant density measurements. This vertical inversion includes a new scheme of Tikhonov regularization. This paper will serve as a reference for the SPICAM Mars Express data which will be systematically made available to the public in the PDS‐like archive managed by ESA.
Fire detection and monitoring using MSG Spinning Enhanced Visible and Infrared Imager (SEVIRI) data
Authors: Calle A. , Casanova J. L. , Romo A.
Published: September 2006

Detection and parameterization of forest fires is a task traditionally performed by polar‐orbiting sensors, mainly advanced very high resolution radiometer (AVHRR) advanced along track scanning radiometer (AATSR), bispectral infrared detection (BIRD), and Moderate Resolution Imaging Spectroradiometer (MODIS). However, their time resolution is a problem to operate in real time. New geostationary sensors have proven their capacity for Earth observation. GOES, MSG, and MTSAT are already operative with time resolutions below 30 min. The international community feels that a real‐time global observation network may become a reality, which is the aim of the Global Observations of Forest Cover and Land Cover Dynamics (GOFC/GOLD) FIRE Mapping and Monitoring program, focusing internationally on decision‐making concerning research into global change. This paper shows the operation in real time by the MSG SEVIRI sensor over the Iberian Peninsula. For fire detection, a temporal gradient of temperature 3.9 μm is used, which is more efficient at eliminating incoming false alarms from solar reflection. Capacity to detect hot forest fires below 0.3 ha in Mediterranean latitudes has been analyzed along with the conditions in which it is possible to apply the MODIS methodology to establish the fire radiative energy (FRE) by means of experimental relation. We found that in this case, fire size can introduce maximum differences of 40% in FRE for small‐scale fires. The capacity of this sensor is shown in different cases that have greatly impacted Spain and Portugal because of the loss of human life.
Low‐temperature first‐order reversal curve (FORC) diagrams for synthetic and natural samples
Authors: Carvallo Claire , Muxworthy Adrian
Published: September 2006

First‐order reversal curve (FORC) diagrams were measured on a variety of synthetic and natural (submarine basalts and potsherds) samples, as well as for a mixture, between room temperature and 10 K. Measuring FORC diagrams allowed us to examine the behavior of the coercivity field and interaction field distributions with decreasing temperature. Generally, as the temperature is decreased, FORC contours were observed to expand in all directions, e.g., the maximum coercivity peak migrates toward a higher coercivity. For synthetic magnetite samples, there were abrupt changes in the FORC distribution at the Verwey transition (120 K), while in the more complex natural magnetite samples the FORC distribution gradually progressed with temperature. As the temperature decreased, FORC diagrams were found to display different domain state characteristics. For example, samples with dominant superparamagnetic signals became single‐domain (SD)‐like, a SD‐like sample stayed SD‐like, and a PSD‐like sample became more SD‐like. In addition to these general features, we also observed some more specialized features. First, in both synthetic and natural magnetite samples, a secondary higher‐coercivity peak is occasionally present below the Verwey transition, which we suggest is a twinning contribution. Second, the coercivity increases by a factor 15 between 300 K and 20 K in some of the seamount samples. Third, the effect of field cooling/zero‐field cooling on FORC diagrams is negligible, with the hysteresis parameters HC and HCR displaying a greater dependency. Finally, it is shown that in mixtures of magnetite and hematite, the hematite contribution disappears on cooling below the Morin transition, leaving a strong, well‐defined magnetite signal.
On the use of calibrated relative paleointensity records to improve millennial‐scale geomagnetic field models
Authors: Korte M. , Constable C. G.
Published: September 2006

Current millennial‐scale time‐varying global geomagnetic field models suffer from a lack of intensity data compared to directional data, because only thermoremanently magnetized material can provide absolute information about the past field strength. The number of archeomagnetic artifacts that can provide such data diminishes rapidly prior to 3000 B.C. Sediment cores provide time series of declination and inclination and of variations of magnetization: the latter can reflect relative geomagnetic field variations if suitably normalized. We propose a calibration technique based on predictions from global models and use the CALS7K.2 model to calibrate relative paleointensity records from 22 globally distributed locations and assess whether they reflect actual field variations. All except a few contain useful information for 0 to 7 ka and could be used to improve the existing models. Using synthetic data from a numerical dynamo simulation, we show that with the existing directional data the distribution of intensity data has an important influence on model quality. Intensity data from a broad range of latitudes seem particularly important. This study opens the possibility of extending global time‐varying geomagnetic field models further back in time than the current 7 kyr interval.
Will Greenland melting halt the thermohaline circulation?
Authors: Jungclaus J. H. , Haak H. , Esch M. , Roeckner E. , Marotzke J.
Published: September 2006

Climate projections for the 21st century indicate a gradual decrease of the Atlantic Meridional Overturning Circulation (AMOC). The weakening could be accelerated substantially by meltwater input from the Greenland Ice Sheet (GIS). Here we repeat recent experiments conducted for the Intergovernmental Panel of Climate Change, providing an idealized additional source of freshwater along Greenland's coast. For conservative and high melting estimates, the AMOC reduction is 35% and 42%, respectively, compared to a weakening of 30% for the original A1B scenario. Even for the high meltwater estimate the AMOC recovers in the 22nd century. The impact of the additional fresh water is limited to further enhancing the static stability in the Irminger and Labrador Seas, whereas the backbone of the overturning is maintained by the overflows across the Greenland‐Scotland Ridge. Our results suggest that abrupt climate change initiated by GIS melting is not a realistic scenario for the 21st century.
On the stability of a geodetic no‐net‐rotation frame and its implication for the International Terrestrial Reference Frame
Authors: Kreemer Corné , Lavallée David A. , Blewitt Geoffrey , Holt William E.
Published: September 2006

One of the important implications of a no‐net‐rotation (NNR) model of the Earth's horizontal surface velocity is that it is used as a constraint in the definition of the International Terrestrial Reference Frame (ITRF). We present here our most recent estimates of an NNR model (GSRM‐NNR‐2) that uses over 5700 geodetic station velocities. We test the sensitivity of our model by varying data input and model assumptions. The difference between our various models is maximally 0.6 mm yr−1, but can be larger if we use only a geographically limited core velocity data set, or if a significant bias in frame origin translation rate exists. Although plate boundary zones should not be considered as being part of rigid plates (Kreemer and Holt, 2001), the details of the velocity field within the plate boundaries have an insignificant effect on the NNR frame. The difference between the various NNR models that we test is small compared to the difference between our NNR models and ITRF2000, which can be up to 3.1 mm yr−1. We conclude that the ITRF2000 does not satisfy the NNR condition when considering an NNR model that is based on the actual present‐day velocity of the entire Earth's surface, instead of NNR‐NUVEL‐1A.
Tomomorphometry of the Somma‐Vesuvius volcano (Italy)
Authors: Ventura Guido , Vilardo Giuseppe
Published: September 2006

A tomomorphometric analysis of the Somma‐Vesuvius topography is presented. This consists in extracting horizontal cross sections at different altitudes, and in determining some morphometric parameters: radius of the circle with a surface area equal to the cross section, circularity, ratio between the major and minor axis of the best fitting ellipse, orientation α of the ellipse major axis, and the x‐y centroid. The Somma includes three portions: the apron zone, the flanks, and the summit caldera boundary. Between 225 m and 525 m, α is 50°–60°. Between 600 m and 775 m, α is 130°–135°. These are the preferred strike of the eruptive fissures affecting the northwestern Somma flanks, the faults affecting the whole edifice, the nodal planes from local earthquakes. The Somma activity developed along a NE‐SW structural discontinuity, whereas the post‐caldera activity concentrated along a NW‐SE striking structure. Somma activity migrates from SE to NW.
Depletion of perennial sea ice in the East Arctic Ocean
Authors: Nghiem S. V. , Chao Y. , Neumann G. , Li P. , Perovich D. K. , Street T. , Clemente‐Colón P.
Published: September 2006

The extent of perennial sea ice in the East Arctic Ocean (0–180°E) decreased by nearly one half with an abrupt reduction of 0.95 × 106 km2, while the West Arctic Ocean (0–180°W) had a slight gain of 0.23 × 106 km2 between 2004 and 2005, as observed by satellite scatterometer data during November–December. The net decrease in the total perennial ice extent is 0.72 × 106 km2, about the size of Texas. Perennial ice in the East Arctic Ocean continued to be depleted with an areal reduction of 70% from October 2005 to April 2006. With the East Arctic Ocean dominated by seasonal sea ice, a strong summer melt may open a vast ice‐free region with a possible record minimum ice extent largely confined to the West Arctic Ocean. Simultaneous scatterometer measurements of sea ice and winds will be crucial for sea ice monitoring and forecasts.
Reduction in Himalayan snow accumulation and weakening of the trade winds over the Pacific since the 1840s
Authors: Zhao Hongxu , Moore G. W. K.
Published: September 2006

In 1884, Blanford suggested that summer rainfall over Northwest India was anti‐correlated with snow cover during the preceding winter and spring in the western Himalaya. Walker elaborated on this suggestion in his seminal work on predictors of the Indian summer monsoon, a body of work that forms the basis of our understanding of how Eurasia influences this monsoonal circulation. Recently, a number of studies have questioned the existence of this relationship or have proposed a more complex coupling between Eurasian snow cover, including the Himalaya, and the Indian summer monsoon. Here, we present a 196‐year record of snow accumulation from a Himalayan ice core that contains a decreasing trend in accumulation that began in the 1840s. Indian summer monsoon rainfall shows no evidence of such a trend and we argue that this reduction in snow accumulation is associated with a long‐term weakening of the trade winds over the Pacific Ocean
Dielectric charge measurements in capacitive microelectromechanical switches
Authors: Molinero D. , Comulada R. , Castañer L.
Published: September 2006

Measurements of transient currents from the discharge of microelectromechanical capacitive switches after charging the dielectric with an ion gun are reported. It is shown that both the charge sign and the charge amount can be independently measured and that the values can be related to the pull-in shift as measured from C-V characteristics. Several capacitive switches of different sizes were fabricated and subjected to charging and discharging experiments. The analysis of the transients shows that several time constants are governing the charge dynamics, one of them is related to the resistivity-permittivity product of the dielectric.
A detailed quantum mechanical and quasiclassical trajectory study on the dynamics of the H++H2→H2+H+ exchange reaction
Authors: González-Lezana Tomás , Roncero Octavio , Honvault Pascal , Launay Jean-Michel , Bulut Niyazi , Javier Aoiz F. , Bañares Luis
Published: September 2006

The H++H2 exchange reaction has been studied theoretically by means of a different variety of methods as an exact time independent quantum mechanical, approximate quantum wave packet, statistical quantum, and quasiclassical trajectory approaches. Total and state-to-state reaction probabilities in terms of the collision energy for different values of the total angular momentum obtained with these methods are compared. The dynamics of the reaction is extensively studied at the collision energy of Ecoll=0.44eV. Integral and differential cross sections and opacity functions at this collision energy have been calculated. In particular, the fairly good description of the exact quantum results provided by the statistical quantum method suggests that the dynamics of the process is governed by an insertion mechanism with the formation of a long-lived collision complex.
Coherent control of collision processes: Penning versus associative ionization
Authors: Arango Carlos A. , Shapiro Moshe , Brumer Paul
Published: September 2006

Coherent control theory is applied to the control of Ne*(3s,P23)+Ar(S01) collisions and computations are shown that display extensive control over these processes. Indeed we demonstrate that it is possible to essentially turn on and off the cross sections for both the Penning and associative ionization processes. This facility arises from the interference between matter waves induced by creating a linear superposition of the degenerate M={−2,−1,0,1,2} Zeeman sublevels of the Ne*(3s,P23) target atom. The computations, conducted at collision energies in the 1–8kcal∕mole range, are based on combining, within the “rotating atom approximation,” empirically derived and ab initio ionization widths.
Graded-base InGaN∕GaN heterojunction bipolar light-emitting transistors
Authors: Chu-Kung B. F. , Feng M. , Walter G. , Holonyak N. , Chung T. , Ryou J.-H. , Limb J. , Yoo D. , Shen S.-C. , Dupuis R. D. , Keogh D. , Asbeck P. M.
Published: September 2006

The authors report radiative recombination from a graded-base InGaN∕GaN heterojunction bipolar transistor (HBT) grown by metal-organic chemical vapor deposition on sapphire. For a device with a 40×40μm2 emitter area, a differential dc current gain of 15 is measured from the common-emitter current-voltage characteristics, with the HBT breakdown voltage BVCEO>65V. The heterojunction bipolar light-emitting transistor exhibits a base-region recombination radiation peak in the visible spectral range with a dominant peak at λ=385nm (blue emission).
Electrical properties of ferromagnetic semiconducting single-walled carbon nanotubes
Authors: Li Y. F. , Hatakeyama R. , Kaneko T. , Izumida T. , Okada T. , Kato T.
Published: September 2006

Electrical properties of single-walled carbon nanotubes (SWCNTs) filled with Fe are studied by fabricating them as the channels of field-effect transistor devices. The synthesis of Fe-filled SWCNTs is realized by using ferrocene as the starting material. Our results reveal that ferrocene-filled SWCNTs show the interesting ambipolar behavior. In contrast, Fe-filled SWCNTs can exhibit high performance unipolar n-type semiconducting characteristics, suggesting the possibility of creating ferromagnetic semiconducting SWCNTs. Moreover, Coulomb blockade oscillations are significantly observed on Fe-filled SWCNTs, which indicates that they exhibit excellent single-electron transistor characteristics at low temperatures.
Two-step behavior of initial oxidation at HfO2∕Si interface
Authors: Miyata Noriyuki
Published: September 2006

In situ x-ray photoelectron spectroscopy revealed that initial Si oxidation at the HfO2∕Si(001) interface in O2 proceeds in a two-step manner with an initial slow stage followed by a fast one. This transition in the oxidation process is most likely caused by crystallization of the HfO2 film. The first stage at 400–600°C exhibited postdeposition annealing conditions suitable for suppressing the interfacial Si oxide in a monolayer region.
Effect of uniaxial stress on solid phase epitaxy in patterned Si wafers
Authors: Rudawski N. G. , Siebein K. N. , Jones K. S.
Published: September 2006

The effect of uniaxial stress on solid phase epitaxy in patterned {001} Si wafers after ion implantation and annealing was investigated. It was found that mask edge defect formation was suppressed when tensile stresses greater than 100MPa were applied along the ⟨110⟩ direction. The application of compressive stress retarded ⟨001⟩ regrowth up to ∼6% and enhanced ⟨110⟩ regrowth up to ∼6%, while tensile stress enhanced ⟨001⟩ regrowth up to ∼60% and retarded ⟨110⟩ regrowth up to ∼40%. A stress-dependent regrowth velocity model qualitatively agrees with the observed trends in the ratio of ⟨001⟩ and ⟨110⟩ regrowth velocities.
Electron density and temperature measurement method by using emission spectroscopy in atmospheric pressure nonequilibrium nitrogen plasmas
Authors: Kim Ji Hun , Choi Yoon Ho , Hwang Y. S.
Published: September 2006

A novel spectroscopic method is proposed for the measurement of electron density and temperature in atmospheric pressure dielectric barrier discharges using nitrogen gas. Simplified collisional-radiative models for the electronic and the vibrational states yield two separate continuity equations as a function of the electron density and the temperature with the coefficients expressed in terms of rotational temperature, vibrational temperature, and emission intensity ratio between the first positive system and the second positive system of nitrogen molecules. The electron density and the temperature in nonequilibrium atmospheric pressure plasmas can be determined by solving the continuity equations with the coefficients estimated from the spectroscopic measurements. It was confirmed by applying to a high power dielectric barrier discharge, where the measured plasma parameters were in good agreement with the estimation by using the electron conductivity of the discharge.
Negative refraction and plano-concave lens focusing in one-dimensional photonic crystals
Authors: Vodo P. , Lu W. T. , Huang Y. , Sridhar S.
Published: September 2006

Negative refraction is demonstrated in one-dimensional (1D) dielectric photonic crystals (PCs) at microwave frequencies. Focusing by plano-concave lens made of 1D PCs due to negative refraction is also demonstrated. The frequency-dependent negative refractive indices, calculated from the experimental data, match very well with those determined from band structure calculations. The easy fabrication of one-dimensional photonic crystals may open the door for future applications.
Structural and magnetic properties of manganese and phosphorus codoped ZnO films on (0001) sapphire substrates
Authors: Wan Q.
Published: September 2006

ZnO films doped with manganese (Mn) and phosphorus (P) are grown on (0001) sapphire substrates by pulsed laser deposition at different temperatures and oxygen pressures. The structural and magnetic properties of the codoped ZnO films are carefully investigated. Experimental results demonstrate that p-type conduction is necessary for the observation of ferromagnetism in Mn+P codoped ZnO films at room temperature. A distinct aging effect is observed, which is likely due to the instability of p-type conduction of Mn+P codoped ZnO films.
On the essential constants in Riemannian geometries
Authors: Papadopoulos G. O.
Published: September 2006

In the present work the problem of distinguishing between essential and spurious (i.e., absorbable) constants contained in a metric tensor field in a Riemannian geometry is considered. The contribution of the study is the presentation of a sufficient and necessary criterion, in terms of a covariant statement, which enables one to determine whether a constant is essential or not. It turns out that the problem of characterization is reduced to that of solving a system of partial differential equations of the first order. In any case, the metric tensor field is assumed to be smooth with respect to the constant to be tested. It should be stressed that the entire analysis is purely of local character.
Bias-current dependence of anticorrelation polarization dynamics in vertical-cavity surface-emitting lasers with long external cavity
Authors: Hong Yanhua , Paul Jon , Spencer Paul S. , Shore K. Alan
Published: September 2006

The bias-current dependence of anticorrelation polarization dynamics in vertical-cavity surface-emitting lasers with long external cavity has been studied experimentally. With fixed optical feedback strength, the minimum cross-correlation coefficient exhibits exponential decay with the bias current. Strong anticorrelation is obtained at frequencies lower than 1GHz for all bias currents. Near the relaxation oscillation frequency good correlation is found at higher bias current but poor correlation is found at lower bias currents.
Bias polarity dependent data retention of resistive random access memory consisting of binary transition metal oxide
Authors: Kinoshita K. , Tamura T. , Aoki M. , Sugiyama Y. , Tanaka H.
Published: September 2006

The authors investigated the data retention properties of NiOy resistors exposed to sputtered particles and found that they depended on the bias polarity used to program the data. Only the data in the high resistance state programmed by applying positive bias to the top electrode were easily damaged. This suggests that the “reset” process can take place when the anodic side of the conductive filaments, which were formed during the “forming” process, is insulated. In addition, the data retention test for thermal stress suggests that the reset process can take place thermally.
Magnetic domain wall serial-in parallel-out shift register
Authors: Allwood D. A. , Xiong Gang , Cowburn R. P.
Published: September 2006

We demonstrate a three-terminal magnetic nanowire logic junction that combines logical NOT and signal fan-out operations. The behavior and performance of the three-terminal device are similar to those of previous two-terminal NOT gates. However, the third terminal provides an additional, noninverted output. We have demonstrated the versatility that this brings by integrating a chain of the three-terminal hybrid elements with other nanowire logic elements to create a serial-in parallel-out shift register.
Intermolecular potentials of the methane dimer calculated with Møller-Plesset perturbation theory and density functional theory
Authors: Li Arvin Huang-Te , Chao Sheng D.
Published: September 2006

We have calculated the intermolecular interaction potentials of the methane dimer at the minimum-energy D3d conformation using the Hartree-Fock (HF) self-consistent theory, the correlation-corrected second-order Møller-Plesset (MP2) perturbation theory, and the density functional theory (DFT) with the Perdew-Wang (PW91) functional as the exchange or the correlation part. The HF calculations yield unbound potentials largely due to the exchange-repulsion interaction. In the MP2 calculations, the basis set effects on the repulsion exponent, the equilibrium bond length, the binding energy, and the asymptotic behavior of the calculated intermolecular potentials have been thoroughly studied. We have employed basis sets from the Slater-type orbitals fitted with Gaussian functions (STO-nG) (n=3–6) [Quantum Theory of Molecular and Solids: The Self-Consistent Field for Molecular and Solids (McGraw-Hill, New York, 1974), Vol. 4], Pople’s medium size basis sets of Krishnan et al. [J. Chem. Phys. 72, 650 (1980)] [up to 6-311++G(3df,3pd)] to Dunning’s correlation consistent basis sets [J. Chem. Phys. 90, 1007 (1989)] (cc-pVXZ and aug-cc-pVXZ) (X=D, T, and Q). With increasing basis size, the repulsion exponent and the equilibrium bond length converge at the 6-31G** basis set and the 6-311++G(2d,2p) basis set, respectively, while a large basis set (aug-cc-pVTZ) is required to converge the binding energy at a chemical accuracy (∼0.01kcal∕mol). Up to the largest basis set used, the asymptotic dispersion coefficient has not converged to the destined C6 value from molecular polarizability calculations. The slow convergence could indicate the inefficacy of using the MP2 calculations with Gaussian-type functions to model the asymptotic behavior. Both the basis set superposition error (BSSE) corrected and uncorrected results are presented to emphasize the importance of including such corrections. Only the BSSE corrected results systematically converge to the destined potential curve with increasing basis size. The DFT calculations generate a wide range of interaction patterns, from purely unbound to strongly bound, underestimating or overestimating the binding energy. The binding energy calculated using the PW91PW91 functional and the equilibrium bond length calculated using the PW91VP86 functional are close to the MP2 results at the basis set limit.
A new quantum method for electrostatic solvation energy of protein
Authors: Mei Ye , Ji Changge , Zhang John Z. H.
Published: September 2006

A new method that incorporates the conductorlike polarizable continuum model (CPCM) with the recently developed molecular fractionation with conjugate caps (MFCC) approach is developed for ab initio calculation of electrostatic solvation energy of protein. The application of the MFCC method makes it practical to apply CPCM to calculate electrostatic solvation energy of protein or other macromolecules in solution. In this MFCC-CPCM method, calculation of protein solvation is divided into calculations of individual solvation energies of fragments (residues) embedded in a common cavity defined with respect to the entire protein. Besides computational efficiency, the current approach also provides additional information about contribution to protein solvation from specific fragments. Numerical studies are carried out to calculate solvation energies for a variety of peptides including α helices and β sheets. Excellent agreement between the MFCC-CPCM result and those from the standard full system CPCM calculation is obtained. Finally, the MFCC-CPCM calculation is applied to several real proteins and the results are compared to classical molecular mechanics Poisson-Boltzmann (MM/PB) and quantum Divid-and-Conque Poisson-Boltzmann (D&C-PB) calculations. Large wave function distortion energy (solute polarization energy) is obtained from the quantum calculation which is missing in the classical calculation. The present study demonstrates that the MFCC-CPCM method is readily applicable to studying solvation of proteins.
Surface plasmon polariton mediated photoluminescence from excitons in silicon nanocrystals
Authors: Takeda Eiji , Nakamura Toshihiro , Fujii Minoru , Miura Satoru , Hayashi Shinji
Published: September 2006

Surface plasmon polaritons (SPPs) of a metal film can efficiently be excited when a light emitter is placed nearby. The excited SPPs are converted to photons by compensating for the momentum mismatch. The authors study SPP-mediated emission from excitons in Si nanocrystals (Si-nc’s) by placing an organic grating on a thin Au film placed near Si-nc’s. The dispersion relation is obtained from angle-resolved photoluminescence measurements, and all the observed modes are well explained by model calculation. The results indicate that excitons in Si-nc’s can efficiently excite SPPs in thin metal films and directed photoluminescence can be realized.
Long range surface plasmon fluorescence spectroscopy
Authors: Kasry Amal , Knoll Wolfgang
Published: September 2006

Surface plasmon modes, resonantly excited at the two sides of an ultrathin (noble) metal layer in contact with two (nearly) identical dielectric media interact via the overlap of their electromagnetic fields resulting in two new coupled modes, i.e., a short range and a long range surface plasmon (LRSP), respectively. The authors demonstrate that both the enhanced optical field of the LRSP wave at the metal/dielectric interface as well as its increased (evanescent) penetration depth reaching farther into the analyte solution can be used for significant enhancements when using LRSP optics in a fluorescence spectroscopic mode of operation. They demonstrate this for the detection of fluorescence intensities from chromophore labeled proteins bound to the sensor surface matrix.
Study of hole concentration of 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′ diamine doped with tungsten oxide by admittance spectroscopy
Authors: Hsieh Ming-Ta , Chang Chan-Ching , Chen Jenn-Fang , Chen Chin H.
Published: September 2006

The effect of tungsten oxide (WO3) incorporation into 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′ diamine (NPB) layer is investigated in NPB-tris(8-hydroxyquinoline)aluminium heterojunction organic light-emitting diodes. The admittance spectroscopy studies show that increasing the WO3 volume percentage from 0% to 16% can increase the hole concentration of the NBP layer from 1.97×1014to1.90×1017cm−3 and decrease the activation energy of the resistance of the NPB layer from 0.354to0.176eV. Thus, this incorporation reduces the Ohmic loss and increases the band bending in the NBP layer near the interface, resulting in an improved hole injection via tunneling through a narrow depletion region.
Local structure of luminescent InGaN alloys
Authors: Kachkanov V. , O’Donnell K. P. , Martin R. W. , Mosselmans J. F. W. , Pereira S.
Published: September 2006

Comparative Ga and In K-edge extended x-ray absorption fine structure studies provide the first direct evidence of an inequality of mean In–Ga and Ga–In next-nearest neighbor separations in InGaN alloys. The degree of inequality increases with decreasing InN fraction x in the range accessible to extended x-ray absorption fine structure analysis of alloys (0.9<x<0.1). Its concurrence with an increase of luminescence efficiency in this composition range suggests that the breakdown of In∕Ga randomness in InGaN is correlated with efficient radiative recombination in blue-green light emitting devices.
Hydration and contact ion pairing of Ca2+ with Cl− in supercritical aqueous solution
Authors: Fulton John L. , Chen Yongsheng , Heald Steve M. , Balasubramanian Mahalingam
Published: September 2006

X-ray absorption fine structure (XAFS) spectroscopy was used to measure the first-shell structure about Ca2+ in high-temperature aqueous solution. XAFS spectra were acquired at the Ca K edge at temperatures up to 400°C and pressures up to 350bars. For the system at 400°C, both Ca (4038.5eV) and Cl (2822.4eV) K-edge data were acquired and a global model was used to fit the two independent sets of XAFS data. Measurements were made at the bending magnet beamline (sector 20) at the Advanced Photon Source, Argonne. Above 250°C, a significant number of Ca2+–Cl− direct contact ion pairs form in agreement with existing thermodynamic data for this system. For a 1m CaCl2 solution at 400°C, the mean coordination structure about Ca2+ contains 3.2±0.6 water molecules at an average Ca–O distance of 2.356±0.026Å and 1.8±0.7 Cl− at a Ca–Cl distance of 2.677±0.007Å. An evaluation of the Ca and Cl preedge and near-edge (x-ray absorption structure) spectra provided further confirmation of the change in the Ca2+ first-shell structure and symmetry. Overall these measurements provide a structural basis for understanding solvation of Ca2+ in hydrothermal systems. These results also provide important new insights into the structural aspects of Ca2+ ion pairing that are the basis of many biological processes under ambient conditions.