bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain in layered nanocrystals
Authors: BAE Y. , CAFLISCH R. E.
Published: October 2007

Layered nanocrystals consist of a core of one material surrounded by a shell of a second material. We present computation of the atomistic strain energy density in a layered nanocrystal, using an idealised model with a simple cubic lattice and harmonic interatomic potentials. These computations show that there is a critical size r*s for the shell thickness rs at which the energy density has a maximum. This critical size is roughly independent of the geometry and material parameters of the system. Interestingly, this critical size agrees with the shell thickness at which the quantum yield has a maximum, as observed in several systems and thus leads one to support the hypothesis that maximal quantum yield is strongly correlated with maximal elastic energy density.
The Palace Façade Motif and the Pyramid Texts as Cosmic Boundaries in Unis's Pyramid Chambers
Authors: De Trafford Aloisia
Published: October 2007

The focus of this article is the pyramid belonging to king Unis, last king of the 5th Dynasty. The striking feature of this pyramid is its ornate internal decoration with spells/utterances from the Pyramid Texts, and with the palace façade motif around the king's sarcophagus. The Pyramid Texts, one of the oldest examples of religious literature in the world, appear here for the first time. To date, research has generally focused on the language and content of the Pyramid Texts. This article looks beyond the subject matter of the Pyramid Texts to explore how these early hieroglyphic writings had additional integral symbolism embedded in their parietal format. Using a novel perspective that seeks symbolic connections across textual and non-textual elements, I argue that the Pyramid Texts and the palace façade motif, through their architectural format, represent the boundaries of the cosmos, which is itself the main theme in the Pyramid Texts.
Public Election Funding, Competition, and Candidate Gender
Authors: Werner Timothy , Mayer Kenneth R.
Published: October 2007

In 2000, Arizona and Maine implemented full public funding for state legislative elections, and Connecticut will do so in 2008. Candidates who opt to accept public funding receive grants that pay for the entire cost of their campaigns. Advocates of these so-called clean elections argue that the programs reducequid pro quocorruption, increase electoral competitiveness, and open up the process to candidates who lack access to traditional fundraising networks (Phelps 2004). Critics respond that the Maine and Arizona public funding programs have achieved nothing, save for imposing unjust burdens on candidates who refuse to participate (Basham and Zelder 2005).
Subnational Governance in Europe: Engaging Students With The Spanish Sub-state
Authors: Ortbals Candice D.
Published: October 2007

Although the study of regional and local politics has been largely conducted in the context of the United States (Loughlin 2001), in recent decades, researchers have studied sub-state transformations and multilevel governance in Europe (see, for example, Marks 1993; Bukowski et al. 2003; Weatherill 2005). In this article, I urge professors to incorporate this literature in undergraduate, comparative politics classrooms and I suggest how to do so using the case of Spain. I argue that Spain, and more generally southern Europe, provides an exciting context in which to discuss subnational themes. The article is structured in four sections. First, I explain the Comparative European Politics course in which I discuss the Spanish sub-state. The second section demonstrates Spain's comparative appeal by summarizing its State of Autonomies and situating it within the European context. The third section raises theoretical debates about democracy, subnational institutions, and the European Union. The final section offers accessible lecture examples for European politics courses.
Voting Power in Federal Systems: Spain as a Case Study
Authors: Rush Mark
Published: October 2007

Spain occupies a prominent position in the teaching of comparative politics. It is a paradigmatic example of a successful transition to and consolidation of democracy, as well as an intriguing study in constitutional development, federalism, and a host of other topics. I have found that it is particularly useful when discussing electoral systems and representation.
Join us at the 2008 Annual Meeting
Authors: Junn Jane , Keller Ed
Published: October 2007

Location and date: Boston, Aug 28–August 31, 2008

Conference theme: Categories and the Politics of Global
Inequalities

Program chairs: Jane Junn, Rutgers and Ed Keller, UCLA

Website: www.apsanet.org/2008
APSA Executive Director's Report 2007
Authors: Brintnall Michael
Published: October 2007

The APSA remains a healthy and active association—programmatically
and organizationally. We have a rich agenda of continuing programs
to support the discipline. Because our forthcoming Annual Report
will feature all of our operating programs, I will make only passing
reference in this Executive Director's report to many of these core
activities. I will focus here on some of the thinking behind how the
Association approaches to issues facing scholars and the discipline,
on some of the newest developments in our programming, and on APSA's
operating status, which remains very strong financially and
organizationally.
Climate, fire, farming and the recent vegetation history of subantarctic Campbell Island
Authors: McGlone Matt , Wilmshurst Janet , Meurk Colin
Published: October 2007

Campbell Island is a small, uninhabited peat-covered island lying in the cool southern ocean 600 km south of the New Zealand mainland. Dracophyllum scrub is the main cover from sea level to 200 m, above which tussock grassland, macrophyllous forbs and tundra dominate. Seven peat profiles from sea level to the tundra zone provide an elevational transect for pollen and charcoal records spanning the last 500 years. Scrub density was relatively low between 200 and 400 cal yrs BP, possibly due to Little Ice Age cooling, but had recovered by the time Europeans discovered the island in AD 1810. Burning and grazing during a brief farming episode (AD 1895–1931) severely reduced scrub and palatable grasses and forbs. Vegetation recovery is now well advanced following cessation of farming and the later elimination of all feral grazing animals, cats and rats. Climates were cool in the southwest Pacific during the farming period, and since AD 1970 the island has warmed by c. 0·5°C. However, there has been no upwards movement of the scrubline despite vigorous regeneration of scrub at lower altitudes. The island's cloudy, highly oceanic climate appears to offset increasing summer warmth, and scrubline is likely to rise only if clearer and less windy, as well as warmer, summers eventuate.
Separation of PEGylated α‐Lactalbumin from Unreacted Precursors and Byproducts Using Ultrafiltration
Authors: Molek Jessica R. , Zydney Andrew L.
Published: October 2007

There is considerable clinical interest in the use of “second‐generation” therapeutic proteins produced by conjugation of the native protein with various polymers including poly(ethylene glycol) (PEG). One of the challenges in the production of polymer‐protein conjugates is the need to remove residual polymer, native (unreacted) protein, and any reaction byproducts from the final therapeutic formulation. The overall objective of this study was to evaluate the possibility of using ultrafiltration for the purification of a model PEGylated protein. Sieving data were obtained using PEGylated α‐lactalbumin, the native protein, and the poly(ethylene glycol) over a range of pH, ionic strength, and filtrate flux using both neutral and charge‐modified composite regenerated cellulose membranes. Purification of the PEGylated protein was achieved using a two‐stage diafiltration process. The first stage used a neutral membrane to remove the unreacted protein and any small reaction byproducts while retaining the large PEGylated product. The second stage used a negatively charged membrane to remove the neutral poly(ethylene glycol) while retaining the PEGylated α‐lactalbumin as a result of strong electrostatic interactions. These results clearly demonstrate the potential of using membrane‐based separations for the purification of second‐generation therapeutic proteins.
Je mehr der Patient weiß, desto besser seine Position? Über die Grenzen der Wissensvermittlung von Fachleuten an Patienten
Authors: Langewitz
Published: October 2007

Empowerment als Informationsvermittlung entspricht den Wünschen, die Patienten und Patientinnen artikulieren. Gerade wenn es um lebensentscheidende Fakten geht, sind Ärztinnen und Ärzte aufgefordert, aufrichtig und vollständig Informationen zu vermitteln. Dies kann allerdings nicht in einem unbegrenzten Übermitteln von Fakten bestehen, sondern muss sich an den jeweils aktuellen Informationsbedürfnissen und an dem jeweils vorhandenen Auffassungsvermögen der Patientin orientieren. Bei dieser Gratwanderung helfen bestimmte kommunikative Techniken, deren mächtigster Gegenspieler die mangelnde Flexibilität einer Ärztin ist, die starr und unbeirrbar einem einmal festgelegten Skript folgt, ohne auf die Reaktionen ihrer Patienten zu achten.
Plantarer Pruritus nach Vietnamaufenthalt
Authors: Tanneberger  , Fehr  , Nuesch
Published: October 2007

Ein 33-jähriger Patient stellt sich wegen Pruritus an der rechten Fusssohle vor. Drei Wochen zuvor watete er in Süd-Vietnam barfuss durch einen Fluss. In der klinischen Untersuchung finden sich an der rechten Fusssohle gerötete, ca. 1–2 mm breite, linienförmige Hautveränderungen. Auf Grund der Anamnese und des klinischen Befundes wird die Diagnose einer Larva migrans gestellt. Nach Einleitung einer Albendazolbehandlung ist der Patient beschwerdefrei.
Recent observations of seasonal variability of the Mediterranean outflow in the Strait of Gibraltar
Authors: García Lafuente J. , Sánchez Román A. , Díaz del Río G. , Sannino G. , Sánchez Garrido J. C.
Published: October 2007

Recent observations of the outflowing Mediterranean water collected near the bottom in key points of the Strait of Gibraltar show the existence of a seasonal cycle with warmer and lighter waters leaving the Mediterranean Sea in winter and cooler and denser waters in spring early summer. The amplitude of the signal is around 5 10−2 °C for potential temperature and 1.5 10−2 for potential density, salinity hardly showing seasonal fluctuations. The outflow also shows a seasonal cycle with maximum volume transport in April, in coincidence with the minimum of the signal of potential temperature. A simple analysis of the composition of the outflow in terms of the main water masses of the western Mediterranean basin and its comparison with climate indicators suggests that the seasonal cycle follows the annual process of the Western Mediterranean Deep Water formation that replenish the deep portion of the basin by the end of winter and rises the level of the deep water reservoir, facilitating the suction of cooler and denser water from the Mediterranean over the sills of the Strait. From this time onwards, the data show a smooth warming that would be explained by the progressive fall of the level of the Western Mediterranean Deep Water as it is drained out the Mediterranean, which would leave warmer water available for suction. The process is asymmetric in the sense that the transition from high to low temperature is completed in a short period while the progressive warming spans a longer period.
Effect of state of compensation on the relaxation of crustal plateaus on Venus
Authors: Nunes Daniel Cahn , Phillips Roger J.
Published: October 2007

Building on Nunes et al. (2004), which examined the end‐member case of viscous relaxation of fully compensated crustal plateaus on Venus, we now investigate viscous relaxation for the other end‐member case of uncompensated topography. The approach consists of modeling viscous flow in a crust‐mantle system by means of analytic and finite element methods. Differential stresses produced by uncompensated plateau topography concentrate beneath the entire domain of the plateau and extend deep into the mantle. Loss of topography occurs via fast subsidence due to isostatic adjustment, and a slower lateral flow due to spreading of the thickened crust. Rims arise from the isostatic adjustment, and rim dimensions depend on the thickness of the competent layer, controlled by the thermal state of the system. Rim dimensions after 1 Myr are ∼1 km high and ∼300 km wide for a surface temperature of 740 K and thermal gradient of <10 K/km, and ∼600 m high and ∼100 km wide for hotter crustal conditions. Although models predict the marginal circumferential (hoop) folding observed at crustal plateaus, they do not account for the large radial grabens also observed. Adding a subcrustal zone of time‐dependent buoyancy causes a delay in the isostatic adjustment. During this period of delay, viscous flow in a relatively hot crust leads to a reduction in rim amplitude once isostatic adjustment takes place. Only cooler conditions in this model can reproduce the wide and high rims observed at crustal plateaus on Venus. Consequently, phase transitions in the lower crust may produce sufficiently large variations in buoyancy to affect the surface topography and are more compatible with a cooler thermal state, but they cannot explain the thickened crust or the interpretation of gravity data showing current isostatic support. Lateral variation in heat flow (and thickness of the competent layer) may help address the latter and needs to be explored through both lithospheric and mantle convection models.
Interferometric seismic imaging of crustal structure using scattered teleseismic waves
Authors: Abe Susumu , Kurashimo Eiji , Sato Hiroshi , Hirata Naoshi , Iwasaki Takaya , Kawanaka Taku
Published: October 2007

The deployment of a dense seismic array of portable broadband stations has presented a number of imaging opportunities using scattered teleseismic waves. Interferometric seismic imaging (ISI) of surface‐related multiple reflections extracted from cross‐correlations of teleseismic waves among pairs of receiver stations was investigated for possible applications and compared to receiver function(RF) method. Synthetic seismograms simulated by the elastic pseudospectral method for a simple 2‐D crustal model demonstrate the potential imaging capabilities of ISI for the Moho structure with high spatial resolution. ISI has also been applied to teleseismic data from dense‐array experiments conducted at the Northern Fossa Magna Basin in central Japan. The results indicate that the Moho phase, with positive polarity at a depth of 38–40 km in the ISI profile, is consistent with the lower crustal structure estimated by RF imaging.
Rapid reduction of Arctic perennial sea ice
Authors: Nghiem S. V. , Rigor I. G. , Perovich D. K. , Clemente‐Colón P. , Weatherly J. W. , Neumann G.
Published: October 2007

The extent of Arctic perennial sea ice, the year‐round ice cover, was significantly reduced between March 2005 and March 2007 by 1.08 × 106 km2, a 23% loss from 4.69 × 106 km2 to 3.61 × 106 km2, as observed by the QuikSCAT/SeaWinds satellite scatterometer (QSCAT). Moreover, the buoy‐based Drift‐Age Model (DM) provided long‐term trends in Arctic sea‐ice age since the 1950s. Perennial‐ice extent loss in March within the DM domain was noticeable after the 1960s, and the loss became more rapid in the 2000s when QSCAT observations were available to verify the model results. QSCAT data also revealed mechanisms contributing to the perennial‐ice extent loss: ice compression toward the western Arctic, ice loading into the Transpolar Drift (TD) together with an acceleration of the TD carrying excessive ice out of Fram Strait, and ice export to Baffin Bay. Dynamic and thermodynamic effects appear to be combining to expedite the loss of perennial sea ice.
Uncertainty in the sensitivity of Arctic sea ice to global warming in a perturbed parameter climate model ensemble
Authors: Ridley Jeff , Lowe Jason , Brierley Chris , Harris Glen
Published: October 2007

The retreat of Arctic sea ice is a very likely consequence of climate change and part of a key feedback process, which can accelerate global warming. The uncertainty in predictions in the rate of sea ice retreat requires quantification and ultimately reduction via observational constraints. Here we analyse a climate model ensemble with perturbations to parameters in the atmosphere model. We find a large range of the sensitivity of Arctic sea‐ice retreat to global temperature change, from 11 to 18% per °C. This is placed in the context of the uncertainty obtained by alternative model ensembles. Reasons for the different sensitivities are explored and we find that differences in the amount of ocean and atmospheric heat transported from low to high latitudes dominates over local radiative contributions to the heat budget. Furthermore, we find no significant relationship between the uncertainty in sea ice response to climate change and climate sensitivity.
Aerosol physical properties and Radiative forcing at the outflow region from the Indo‐Gangetic plains during typical clear and hazy periods of wintertime
Authors: Niranjan K. , Sreekanth V. , Madhavan B. L. , Krishna Moorthy K.
Published: October 2007

Results of a campaign mode measurements of column integrated aerosol optical depths, near surface mass concentrations and LIDAR profiles during winter 2004 at Kharagpur located at the vent of the out flow region from the Indo‐Gangetic plains are presented with a view to characterize the atmospheric aerosol radiative forcing during hazy and clear sky conditions. The multispectral optical depths, surface mass concentrations and black carbon are high, while a decrease in Angstrom exponent value was observed during the hazy sky days. During hazy conditions, the LIDAR profiles show a decrease in the mixed layer height leading to confinement and subsidence of aerosols. Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model along with Optical Properties of Aerosols and Clouds (OPAC) are used to perform composite aerosol forcing estimation, incorporating LIDAR derived mixed layer heights. A considerable decrease in estimated single scattering albedo has been observed during hazy sky days. The atmospheric absorption during hazy sky days increased by 75% compared to clear days. Negative forcing was observed both at the top of the atmosphere and at the surface. The forcing estimates of the present study are compared with the similar studies over other locations in the Indo‐Gangetic plains during the campaign period.
Families Travelling with a Disabled Member: Analysing the Potential of an Emerging Niche Market Segment
Authors: Huh Chang , Singh A.J.
Published: October 2007

The 2000 Census of Population indicated that 50 million Americans, or 19.3 per cent of the US population, were people with disabilities and covered under the Americans with Disabilities Act. It is estimated that the number of families with a member with a disability will grow significantly. Although people with disabilities and their families have sufficient discretionary income and time to take pleasure trips, tourism and hospitality marketers and practitioners to date generally have not much considered this group to be a focal market segment. The objective of the study was to determine whether families with a member with a disability should be considered a viable niche market by tourism and hospitality industry. Two secondary data sets from US Census reports and a six-state longitudinal travel market survey were used to evaluate the viability of this group as a market segment according to Kotler's criteria for market segmentation. Substantiality, differentiability and actionability were identified as the three most important criteria to determine that this segment is a viable niche tourism market. The findings indicate that this market can possibly be attracted through discount deals and reached through auto club publications and specially designed web pages. The marketing implications of this study are discussed.
Ecological Orientation of Tourists: An Empirical Investigation
Authors: Uriely Natan , Reichel Arie , Shani Amir
Published: October 2007

This study presents a tourist ecological orientation (TEO) construct based on the responses of participants who were asked to state the importance of various ecological features of planned tourist sites. The higher the TEO score, the more sensitive the person's attitudes toward the ecological requirements and responsibilities of tourist sites. A principal component factor analysis reveals two alternative dimensions of the TEO concept: ‘destination oriented’ and ‘visitor oriented’. The higher score that was given to the latter dimension supports the argument that successful implementation of ecological values at tourist sites requires a strong orientation towards consumer needs in addition to an ideological commitment to the environment. In addition, differences in ecological orientation patterns and structure were analysed along age and nationality.
Spectrally resolved microprobe cathodoluminescence of intergrowth Bi5−xLaxTiNbWO15 ferroelectrics
Authors: Ge Wanyin , Zhu Wenliang , Higashino Masayuki , Li Yongxiang , Yi Zhiguo , Pezzotti Giuseppe
Published: October 2007

Spectrally resolved cathodoluminescence measurements of Bi5−xLaxTiNbWO15 (x=0–1.50) ceramics at room temperature showed three distinct luminescence bands located at about 380, 502, and 660nm, respectively, which were tentatively assigned to F+ center, oxygen vacancy-related defect and octahedron structure-related luminescence center, respectively. These assignments could be made in light of electron irradiation experiments with different exposure times. Bands related to oxygen vacancies were clearly enhanced by lanthanum doping, indicating that charge compensation occurred by the substitution of Bi for La3+ in perovskitelike structured intergrowth ferroelectrics. We observed that, for contents of La3+ x>0.75, La3+ ions entered the [Bi2O2]2+ layer according to a doping mechanism which is briefly discussed in this letter.
Local electrostatics algorithm for classical molecular dynamics simulations
Authors: Rottler Jörg
Published: October 2007

An implementation of a local, linear scaling algorithm for computing electrostatic interactions in molecular dynamics simulations that was recently proposed [J. Rottler and A. C. Maggs, Phys. Rev. Lett. 93, 170201 (2004)] is presented. Coulombic forces are mediated by a propagating electric field that obeys Gauss’s law. A detailed description of the numerical implementation is presented, and the accuracy is calibrated by comparing the electrostatic force to that obtained from a standard Ewald summation. A parallelized implementation exhibits excellent scaling behavior on a contemporary low latency compute cluster, and therefore becomes an interesting alternative to existing algorithms for computing electrostatics in large-scale molecular dynamics. The approach opens new possibilities for the study of physical situations that are difficult or impossible to treat with standard reciprocal space methods, in particular nonperiodic boundary conditions and spatially heterogeneous dielectric environments in implicit solvent models.
Resonant two-photon ionization and ab initio conformational analysis of haloethyl benzenes (PhCH2CH2X,X=Cl,F)
Authors: Martin Danielle E. , Robertson Evan G. , Morrison Richard J. S. , Dobney Bruce
Published: October 2007

The S1←S0 transitions of the gaseous (2-fluoroethyl)-benzene (FEB) and (2-chloroethyl)-benzene (CEB) have been investigated using a combination of two-color resonant two-photon ionization and UV-UV hole burning spectroscopy. Both anti and gauche conformers have been identified on the basis of rotational band contour analysis supported by ab initio calculations on the ground and electronically excited states. The gauche origin band of FEB at 37673cm−1 is redshifted 50cm−1 relative to the corresponding anti origin, while CEB origin bands overlap at 37646cm−1. Relative conformational stability and populations in the jet have been estimated for both molecules, based on the intensity ratio of S1←S0 band origin transitions. These are compared with a range of related molecules with the structural motif PhCH2CH2X (X=CH3,CH2CH3,NH2,OH,COOH,CCH,CN). Theory and experimental results for FEB and CEB show repulsive interactions between the halogen substituents and the π cloud of the phenyl rings destabilizing the gauche conformers, but the preference for the anti conformers is relatively modest. The gauche conformer origins show very different hybrid character: FEB is largely b type, while CEB is an a∕c hybrid in keeping with theoretically computed TM “rotations” (θelec) of −7° and −56°, respectively. This difference is attributed largely to rotation of the side chain in opposite directions about the C1Cα bond. Spectra of FEB(H2O) and CEB(H2O) single water clusters show evidence of an anti conformation in the host molecule.
Warm-fluid equilibrium theory of a thermal charged-particle beam in a periodic solenoidal focusing field
Authors: Samokhvalova Ksenia R. , Zhou Jing , Chen Chiping
Published: October 2007

A warm-fluid equilibrium theory is presented which describes a new thermal equilibrium of a rotating charged-particle beam in a periodic solenoidal focusing field. Warm-fluid equations are solved in the paraxial approximation. The rms beam envelope, the density and flow velocity profiles, and the self-consistent Poisson equations are derived. Density profiles are calculated numerically for high-intensity and low-intensity beams. Temperature effects in such beams are investigated. Radial confinement of the beam is discussed.
Role of scaling limits in the rigorous analysis of Bose-Einstein condensation
Authors: Michelangeli Alessandro
Published: October 2007

In the context of the rigorous analysis of Bose-Einstein condensation, recent achievements have been obtained in the form of asymptotic results when some appropriate scaling is performed in the Hamiltonian, and the limit of infinite number of particles is taken. In particular, two modified thermodynamic limits of infinite dilution turned out to provide an insight in this analysis, the so-called Gross-Pitaevskiĭ limit and the related Thomas-Fermi limit. Here such scalings are discussed with respect to their physical and mathematical motivations and to the currently known results obtained within this framework.
Improving ion irradiated high Tc Josephson junctions by annealing: The role of vacancy-interstitial annihilation
Authors: Sirena M. , Matzen S. , Bergeal N. , Lesueur J. , Faini G. , Bernard R. , Briatico J. , Crété D. G.
Published: October 2007

The authors have studied the annealing effect in the transport properties of high Tc Josephson junctions (JJs) made by ion irradiation. Low temperature annealing (80°C) increases the JJ coupling temperature (TJ) and the IcRn product, where Ic is the critical current and Rn the normal resistance. They have found that the spread in JJ characteristics can be reduced by sufficient long annealing times, increasing the reproducibility of ion irradiated Josephson junctions. The characteristic annealing time and the evolution of the spread in the JJ characteristics can be explained by a vacancy-interstitial annihilation process rather than by an oxygen diffusion one.
Self-controlled signal branch by the use of a nonlinear liquid crystal cell
Authors: Saito Mitsunori , Takeda Ryosuke , Yoshimura Kazuhiro , Okamoto Ryota , Yamada Itsunari
Published: October 2007

A nonlinear input-output characteristic was observed when neodymium doped yttrium aluminum garnet laser passed through a silicon cell containing a twisted-nematic liquid crystal. The laser beam excited free carriers in the silicon plate, which triggered electrical reorientation of the liquid crystal. Consequently, the polarization direction of the laser beam changed, and the output beam passing through a polarizer became weaker as the input power increased. This function was utilized for self-branching of an optical pulse train.
Stability of polymeric thin film transistors for x-ray imaging applications
Authors: Newman Christopher R. , Sirringhaus Henning , Blakesley James C. , Speller Robert
Published: October 2007

The effects of x-ray irradiation on the electrical performance of organic thin film transistors (OTFTs) have been examined up to equivalent lifetime doses for medical digital x-ray imaging backplanes. Transistor performance metrics have been assessed before and after exposures up to 500Gy for bottom-gate, bottom-contact OTFTs of p-channel polytriarylamine and polyfluorene semiconductors. There is no discernible degradation in device performance for either material and no indication of the creation of additional trap states. In situ measurements indicate that x-ray exposure tends to reverse undesirable shifts in the threshold voltage due to prolonged atmospheric exposure and bias stress.
Processing control of phase separation, cation ordering, and the dielectric properties of Ba3(Co0.6Zn0.4)Nb2O9
Authors: Mallinson P. M. , Rosseinsky M. J. , Ibberson R. M. , Price T. , Iddles D. M.
Published: October 2007

The dielectric and crystallographic properties of the ceramic Ba3(Co0.6Zn0.4)Nb2O9 have been investigated in relation to the processing schedule. Regimes incorporating slow cooling or a lower-temperature annealing stage are found to enhance the dielectric properties with the unloaded quality factor value increasing up to Qu=24300 at 3.21GHz, as compared with Qu=14425 at 3.21GHz using the standard schedule, while high relative permittivity εr=34 is retained. High-resolution neutron powder diffraction studies reveal the materials to be biphasic assemblages of trigonal perovskites which exhibit varying degrees of cation order. The higher Q samples are found to contain the highest proportion of the fully cation-ordered phase.
High-temperature conduction behaviors of HfO2/TaN-based metal-insulator-metal capacitors
Authors: Pan Shaohui , Ding Shi-Jin , Huang Yue , Huang Yu-Jian , Zhang David Wei , Wang Li-Kang , Liu Ran
Published: October 2007

High-temperature (∼90–150 °C) conduction mechanisms of metal-insulator-metal (MIM) capacitors with atomic-layer-deposited HfO2 dielectric are studied. In the low field range, the Schottky emission current is dominant, and the deduced dielectric constant is close to the static one of HfO2. In the high field range, the resulting leakage current complies with the Poole-Frenkel (PF) emission, which is demonstrated by the fact that the extracted dielectric constant equals the optical frequency one (i.e., square of refractive index) of HfO2. The underlying mechanisms are discussed based on carrier velocities under different electric fields. Further, the deduced Schottky barrier height is ∼0.251–0.274 eV in the low field range, which relates to the contributions from high density traps in the HfO2 film and the nonideal TaN/HfO2 interface, etc. The extracted trap potential well depth for the PF effect is ∼1.11–1.37 eV in the high field range.
Formation of cesium peroxide and cesium superoxide on InP photocathode activated by cesium and oxygen
Authors: Sun Yun , Liu Zhi , Pianetta Piero , Lee Dong-Ick
Published: October 2007

Activation of p-type III-V semiconductors with cesium and oxygen has been widely used to prepare negative electron affinity (NEA) photocathodes. However, the nature of the chemical species on the surface after the activation is not well understood. In this study, InP NEA photocathodes activated with cesium and oxygen are studied using synchrotron radiation photoelectron spectroscopy, also called photoemission. Based on the O 1s core level as well as the valence band spectra, Cs peroxide and Cs superoxide are identified on the InP surface. Transformation from Cs peroxide to Cs superoxide is observed after the activation, and is probably the major reason for the decay of the quantum yield of the photocathode. The oxidation of the InP substrate is also observed with elapse of time, adding to the decay of the quantum yield.
Structural, electrical, magnetic, and electronic structure studies of PrFe1−xNixO3 (x⩽0.5)
Authors: Kumar Ravi , Choudhary R. J. , Ikram M. , Shukla D. K. , Mollah S. , Thakur P. , Chae K. H. , Angadi Basavaraj , Choi W. K.
Published: October 2007

We report the x-ray absorption studies on O K, Fe L3,2, Ni L3,2, and Pr M5,4 edges in PrFe1−xNixO3 along with their structural, electrical transport, and magnetization characterizations. All the samples are in single phase having orthorhombic structure with space group Pnma for x⩽0.4. Ni doping at Fe site brings the system in the conducting regime, resistivity decreases from GΩcmto260mΩcm at room temperature, and the magnetic ordering is stabilized. The temperature dependent resistivity follows the semiconducting behavior and fits well with Greaves’ variable range hopping model. The gap parameter is reduced from 2to0.118eV. The materials are in weak ferromagnetic state and magnetization is gradually decreasing with the enhancement of Ni substitution, whereas magnetic anisotropy is reduced substantially. A new feature about 2.0eV lower than the pre-edge of PrFeO3 in O K edge is observed with Ni substitution at Fe site due to the 3d contraction effect and is growing with the increase of Ni substitution. From 2p edges (L3,2 edges) of Fe and Ni, it is confirmed that both are in trivalent state and Ni is in mixed spin state with 3d7 (t2g5,eg2 and t2g6,eg1) configuration in ground state. The trivalent state of Pr is confirmed by x-ray absorption spectroscopy of Pr at M5,4 edges. These observations have been explained on the basis of charge carrier doping in PrFeO3 with the Ni substitution. The disorder induced localization is found to control the conductivity and magnetism in the present materials. The controlled doping of carriers in semiconducting regime and ferromagnetism propose these materials as a promising candidate for the spintronic applications.
Low temperature electrical transport properties of B-doped ZnO films
Authors: Liu X. D. , Jiang E. Y. , Li Z. Q.
Published: October 2007

Low temperature electrical transport properties of boron-doped zinc oxide thin films prepared by metal-organic chemical vapor deposition technique were investigated. The temperature coefficient of resistivities is negative at low temperatures and becomes positive at relatively high temperatures. The magnetic field dependence of resistivity was measured at different temperatures from 2to30K. The samples exhibit negative magnetoresistivity at all measuring temperatures and the absolute values of the negative magnetoresistivities systematically increase with decreasing temperature at a given magnetic field. Weak-localization effect and two-band model were used to analyze the experimental results. Least-squares fits showed that the data can be well described by the theory. The inelastic scattering time is proportional to T−3∕2, suggesting that the electron-electron scattering is the dominant coherent backscattering breaker.
Spectra of Husimi cacti: Exact results and applications
Authors: Galiceanu Mircea , Blumen Alexander
Published: October 2007

Starting from exact relations for finite Husimi cacti we determine their complete spectra to very high accuracy. The Husimi cacti are dual structures to the dendrimers but, distinct from these, contain loops. Our solution makes use of a judicious analysis of the normal modes. Although close to those of dendrimers, the spectra of Husimi cacti differ. From the wealth of applications for measurable quantities which depend only on the spectra, we display for Husimi cacti the behavior of the fluorescence depolarization under quasiresonant Förster energy transfer.
Soft particle model for block copolymers
Authors: Eurich F. , Karatchentsev A. , Baschnagel J. , Dieterich W. , Maass P.
Published: October 2007

A soft particle model for diblock (AB) copolymer melts is proposed. Each molecule is mapped onto two soft spheres built by Gaussian A- and B-monomer distributions. An approximate analytical expression for the joint distribution function for the distance between both spheres and their radii of gyration is derived, which determines the entropic contribution to the intramolecular free energy. Adding a mean-field expression for the intermolecular interactions, we obtain the total free energy of the system. Based on this free energy, Monte Carlo simulations are carried out to study the kinetics of microphase ordering in the bulk and its effect on molecular diffusion. This is followed by an analysis of thin films, with emphasis on pattern transfer from walls with a periodic structure. It is shown that the level of coarse graining in the soft particle model is suitable to describe structural and kinetic properties of copolymers on mesoscopic scales.
On the limitations of adiabatic population transfer between molecular electronic states induced by intense femtosecond laser pulses
Authors: Gräfe S. , Kiefer W. , Engel V.
Published: October 2007

The possibility to perform a stimulated Raman adiabatic passage process in molecules on the ultrafast time scale is investigated theoretically. Motivated by recent experiments, the ∣B⟩←∣X⟩ electronic transitions in molecular iodine are studied as a prototype example with the goal to selectively induce a population transfer employing two intense and time-delayed ultrashort laser pulses and different coupling schemes. For the purpose of interpretation, the coupled multilevel vibronic problem is reduced to a quasi-three-level system by averaging over the vibrational degree of freedom. It is shown that the vibrational dynamics becomes essential at high field intensities. Considering a 2-dimensional parameter space (intensity and delay time of the femtosecond laser pulses), a strong-field control landscape is constructed.
Atomistic simulation of discotic liquid crystals: Transition from isotropic to columnar phase example
Authors: Cristinziano Pier Luigi , Lelj Francesco
Published: October 2007

Molecular dynamics simulations at atomistic level have been performed on a metal-porphyrazine complex. Starting from an isotropic state, the system was cooled until transition from isotropic to columnar phase was observed; no nematic phase was encountered. Many tools were utilized to follow the system evolution: order parameter, g(r), g‖(r‖), gc(r‖), g⊥(r⊥), g2(r), also density and energy changes. Very long runs were required to get reliable results, times greater than 40ns of simulation. The structure of columnar phase was analyzed and the organization of molecules in the columns was investigated, along with the role of conformation of side chains. We found that in columnar phase the molecules are tilted versus the column axis and the conformation of side chains changes during the phase transition to allow this kind of organization; moreover the direction of columns axes is different from that of the director.
Efficient Kα x-ray source from submillijoule femtosecond laser pulses operated at kilohertz repetition rate
Authors: Serbanescu C. G. , Chakera J. A. , Fedosejevs R.
Published: October 2007

We report an efficient CuKα x-ray source produced by focusing submillijoule, 120fs Ti:sapphire laser pulses on a solid copper target to a spot diameter of few microns. The experimental results show strong emission of Kα x-rays from solid targets from microplasmas created by p-polarized 0.2–0.3mJ laser pulses at 1kHz repetition rate. We have demonstrated Kα x-ray point source emission rates of 6.7×109photons∕s into 2π sr at 1kHz repetition rate. The source has an x-ray conversion efficiency into CuKα line emission of 3.2×10−5. The source has a measured size of ∼8μm. Such a high repetition rate Kα x-ray source can be very useful for time resolved x-ray diffraction and radiographic applications.
Holographic inscription of helical wavefronts in a liquid crystal polarization grating
Authors: Choi Hyunhee , Woo J. H. , Wu J. W. , Kim Dong-Wook , Lim Tong-Kun , Song Seok Ho
Published: October 2007

A space-varying polarization hologram (PH) grating is fabricated in a nematic liquid crystal (LC) cell with azo-side-chain polymer alignment layers. The polarization-sensitive photoisomerization property of azo-side-chain polymer is utilized to inscribe the PH in a LC cell. Both transmission and reflection holographic configurations are adopted in fabrication. The transmission PH made by the circular orthogonal polarizations exhibits the polarization-controlled Laguerre-Gaussian beam generation, while the reflection PH made by the linear orthogonal polarizations generates a variety of Laguerre-Gaussian beam, though not polarization controlled.
Stretchable helical gold conductor on silicone rubber microwire
Authors: Béfahy S. , Yunus S. , Pardoen T. , Bertrand P. , Troosters M.
Published: October 2007

Compliant and stretchable three-dimensional golden tracks are produced by metallization of silicone wires maintained under twisting and stretching constraints. Upon release, the metallic track deforms to a helix presenting a wavy and cracked surface. Wavelet and crack orientations are function of three parameters: the wire radius, the number of imposed rotations divided by the length of the cylinder, and the stretching in its axis direction. Electrical conductivity at rest and under stretching can be optimized by finding the prestraining conditions that provide the best trade off between the maximum amount of surface buckling and a limited amount of cracks.
Superconducting quantum interference device setup for magnetoelectric measurements
Authors: Borisov P. , Hochstrat A. , Shvartsman V. V. , Kleemann W.
Published: October 2007

A commercial superconducting quantum interference device (SQUID) setup (MPMS 5S from Quantum Design), equipped with a magnetic ac susceptibility option, is modified for measurements of the linear magnetoelectric (ME) effect, i.e., of the magnetic moment induced by an applied external electric field in a ME sample. Test measurements on a Cr2O3 (111) single crystal are in excellent agreement with previously reported data of its ME susceptibility. The main advantages of the proposed setup are the improved precision due to the high sensitivity of the SQUID magnetometer in combination with the lock-in technique and a relatively simple experimental realization.
Optimally accurate thermal-wave cavity photopyroelectric measurements of pressure-dependent thermophysical properties of air: Theory and experiments
Authors: Kwan Chi-Hang , Matvienko Anna , Mandelis Andreas
Published: October 2007

An experimental technique for the measurement of thermal properties of air at low pressures using a photopyroelectric (PPE) thermal-wave cavity (TWC) was developed. In addition, two theoretical approaches, a conventional one-dimensional thermal-wave model and a three-dimensional theory based on the Hankel integral, were applied to interpret the thermal-wave field in the thermal-wave cavity. The importance of radiation heat transfer mechanisms in a TWC was also investigated. Radiation components were added to the purely conductive model by linearizing the radiation heat transfer component at the cavity boundary. The experimental results indicate that the three-dimensional model is necessary to describe the PPE signal, especially at low frequencies where thermal diffusion length is large and sideways propagation of the thermal-wave field becomes significant. Radiation is found to be the dominant contributor of the PPE signal at high frequencies and large cavity lengths, where heat conduction across the TWC length is relatively weak. The three-dimensional theory and the Downhill Simplex algorithm were used to fit the experimental data and extract the thermal diffusivity of air and the heat transfer coefficient in a wide range of pressures from 760to2.6Torr. It was shown that judicious adjustments of cavity length and computational best fits to frequency-scanned data using three-dimensional photopyroelectric theory lead to optimally accurate value measurements of thermal diffusivity and heat transfer coefficient at various pressures.
Entropy encoding, Hilbert space, and Karhunen-Loève transforms
Authors: Jorgensen Palle E. T. , Song Myung-Sin
Published: October 2007

By introducing Hilbert space and operators, we show how probabilities, approximations, and entropy encoding from signal and image processing allow precise formulas and quantitative estimates. Our main results yield orthogonal bases which optimize distinct measures of data encoding.
Control of bonding and epitaxy at copper/sapphire interface
Authors: Oh Sang Ho , Scheu Christina , Wagner Thomas , Rühle Manfred
Published: October 2007

The nature of bonding evolving at a metal/oxide interface depends strongly on the termination of oxide surface stabilized in the bonding environment. Specific surface treatments in ultrahigh vacuum allow control of the termination of sapphire (α-Al2O3) (0001) surface varying from hydroxyl-terminated to aluminum-terminated to oxygen-terminated surfaces. With this capability, the interfacial bonding forming between epitaxial Cu films and sapphire (0001) substrates can be tailored. Transmission electron microscopy studies reveal that the interatomic interaction at the interface plays a decisive role in determining wetting, orientation relationship, and thermal behavior of Cu thin films.
Spin noise spectroscopy in semiconductors
Authors: Römer M. , Hübner J. , Oestreich M.
Published: October 2007

Spin noise spectroscopy in semiconductors is an optical method that allows nearly perturbation free measurements of the spin dynamics of electrons in thermal equilibrium. The article explains the basic principles of spin noise spectroscopy and introduces an optimized experimental setup which promotes spin noise spectroscopy to an extraordinary sensitive tool. Exemplary measurements on n-doped bulk GaAs yield the temperature dependence of the electron spin relaxation time and the electron Landé g factor and reveal a dependence of the spin relaxation time on the laser probe wavelength. The magnitude and wavelength dependence of the measured spin noise signal compares well to basic calculations.
Natural focusing of x rays from ferroelectric lithium niobate wafers
Authors: Durbin Stephen , Jach Terrence , Kim Sungwon , Gopalan Venkatraman
Published: October 2007

The interaction of waves with inhomogeneous media leads to the natural focusing of light, the channelling of waves into stable caustics. We have extended natural focusing to x rays, observing caustics in topographs of ferroelectric lithium niobate. Voltage across domains of reversed polarity induces perturbations to the local crystal planes, producing dramatic variations in the images. Ray tracing shows a “catastrophic” discontinuity, causing bright focal lines. Analysis reveals details of boundary strains and local ferroelectric properties. Controlled focusing could be extended to designed domain patterns to probe microstructural properties, and also to a type of voltage-controlled ferroelectric optics for x rays.
Discovery of Bragg confined hybrid modes with high Q factor in a hollow dielectric resonator
Authors: le Floch Jean-Michel , Tobar Michael E. , Mouneyrac David , Cros Dominique , Krupka Jerzy
Published: October 2007

The authors report on observation of Bragg confined mode in a hollow cylindrical dielectric cavity. A resonance was observed at 13.4GHz with an unloaded Q factor of order 2×105, which is more than a factor of 6 above the dielectric loss limit. Previously, such modes have only been realized from pure transverse electric modes with no azimuthal variations and only the Eϕ component. From rigorous numeric simulations, it is shown that the mode is a hybrid mode with nonzero azimuthal variations and with dominant Er and Eϕ electric field components and Hz magnetic field component.