bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of the Mexican State in the Development of Chicle Extraction in Yucatán, and the Continuing Importance of Coyotaje
Authors: FORERO OSCAR A. , REDCLIFT MICHAEL R.
Published: February 2006

Most commentaries on the development of chicle (natural chewing gum) in the Yucatán Peninsula have emphasised the connections that were maintained between the chicle entrepreneurs and the companies, like William Wrigley's, which bought the raw gum for processing. The Mexican state is usually depicted as seeking to protect vulnerable forest workers from exploitation by foreign entrepreneurs and the vicissitudes of the free market. Our research, which uses archive material from Mexico City and Chetumal, interviews with former chicleros and entrepreneurs, as well as field research in Quintana Roo, suggests a slightly different interpretation. The Mexican state, far from contributing to the demise of personalistic relations (coyotaje) actually used these forms of mediation to manage and control the producers. The vulnerability of the chicleros to the full effect of market forces, their lack of physical and financial security, as well as corruption among some of the leaders of the cooperative movement, have all contributed to the continuance of coyotaje, often tacitly supported by state institutions. The article goes on to show that the need to meet demanding product and environmental standards, to achieve ‘certification’ as producers of a natural forest product, have compounded the problems of chicle producers today.
Richard Vowell's Not-So-Imperial Eyes: Travel Writing and Adventure in Nineteenth-Century Hispanic America
Authors: BROWN MATTHEW
Published: February 2006

Richard Vowell was a British mercenary who served in the Wars of Independence in Hispanic America. A study of his writings offers a new perspective from which to reconsider the influential arguments of the section of Mary Louise Pratt's Imperial Eyes: Travel Writing and Transculturation (London and New York, 1992) that deals with European travel in the region in the period. The analysis centres on the ways in which Vowell depicted Hispanic American masculinities, indigenous peoples, collective identities and the diverse groups that made up society during the wars of independence. Vowell's writings suggest that further sources might be read against the traditional canon of commercial travel literature generally used by historians for the period 1800–1850.
Cañeros and Colonos: Cane Planters in Tucumán, 1876–1895
Authors: JUAREZ-DAPPE PATRICIA
Published: February 2006

During the last quarter of the nineteenth century Tucumán's sugar industry experienced unprecedented growth. Tucumán's mills relied on their lands as well as on outside growers for the supply of the cane. By 1895 cañeros and colonos were cultivating two-thirds of the cane processed in the province. This practice resulted in the incorporation of thousands of small and medium farmers into sugar production, a rather exceptional case among Latin American sugar economies. This article sheds light on this peculiar aspect of Tucumán's sugar industry by focusing on the diversity that characterised the group of cane planters, the circumstances under which they were incorporated into cane agriculture, the tensions that materialised in sugar-growing areas, and the strategies developed by planters to settle their conflicts with mill owners.
Local Knowledge, Dynamism and the Politics of Struggle: A Case Study of the Hmong in Northern Thailand
Authors: Siriphon Aranya
Published: February 2006

The Hmong are not passive actors who wait for help from development workers and other authorities. Instead, they actively engage themselves within a process of social negotiation between unequal socio-economic and political groups, a ‘dynamic knowledge system’. Three case studies from a Hmong Thantam community are used to better understand the process of social negotiation with multiple actors within complex power relations. More importantly, their dynamic local knowledge is used as a strategy to struggle against, and reconcile with, more powerful forces; the result of this process is the ‘complexity’ which happens as a response to power

It's possible to find knowledge from any place in the world when we humans learn from one another. Throughout the generations we Hmong have learned from many diverse sources. In order to fulfil our lives, we young Hmong still learn from the whole world. Laoyeng Saehang, A headman of Thantam village, Northern Thailand, 1998.
Re-thinking the Sea in Vietnamese History: Littoral Society in the Integration of Thuâ[dot under]n-Qua[hook above]ng, Seventeenth–Eighteenth Centuries
Authors: Wheeler Charles
Published: February 2006

This article challenges conventional notions of geography in Vietnamese historiography that overlook the role of the sea as an integrative social space capable of uniting ostensibly segregated regions economically, socially and politically. Viewing history from the seashore instead of the rice field, it highlights the littoral inhabitants who connected interior agricultural and forest foragers to coasting and ocean carrier trade, and underscores the importance of the littoral as the ‘great river’ that encouraged Vietnamese political expansion and state formation along a southern trajectory.
The benefits of physical activity for health in older people – an update
Authors: Bassey E Joan
Published: February 2006

Two previous publications by the author in Reviews in Clinical Gerontology have dealt firstly with the background physiology of exercise and secondly with the benefits to health of regular exercise across a wide spectrum of diseases and disabilities in older people. This article assumes that the reader is familiar with these reviews. A useful recent report focusing on coronary heart disease, diabetes mellitus and arthritis summarizes recommended physical activities for various age groups and conditions.
Cognitive Schemata in Depressed Adolescent Girls and Their Mothers
Authors: Simmons Jane , Cooper Myra J. , Drinkwater Jonquil , Stewart Anne
Published: February 2006

Schemata (and other cognitions) were investigated in depressed adolescent girls and their mothers and were compared to those in a control group. Links between adolescent and maternal cognitions were also examined. There were 14 girls and mothers in the clinical group and 15 in the control group. The depressed adolescents had higher total scores on a measure of schemata than the control adolescents, and higher scores on several of its sub-scales. They also scored more highly on two other measures of cognition (dysfunctional attitudes and negative automatic thoughts). The mothers of the depressed adolescents were more depressed than mothers of control adolescents. However, the two groups of mothers did not differ on the measures of cognition, including schemata. Depression and schemata in adolescents were related to these variables in their mothers but only in the depressed group. Possible explanations for the findings, including the nature of the link between mood and cognition in the groups studied, are considered. Implications for cognitive theory and therapy in depressed adolescents are briefly discussed.
The Relation Between Onset, Offset, and Duration Perception as Examined by Psychophysical Data and Event-Related Brain Potentials
Authors: Bendixen Alexandra , Grimm Sabine , Schröger Erich
Published: February 2006

Abstract: By means of behavioral data and electrophysiological recordings, we investigated the relation between the subjective duration of stimuli in the millisecond range and the moments of their perceived onset and offset. In three consecutive tasks, subjects (1) judged the duration of auditory stimuli and performed simple reaction time tasks to (2) onset and (3) offset of the same tones. All stimuli were presented with variable response-stimulus-intervals (RSI). To a certain extent, this manipulation was shown to affect onset, offset, and duration perception in a similar way. However, more profound analyses revealed dissociations between the tasks. Consequently, there seems to be no simple relation between perceived duration and the moments of onset and offset perception, but duration judgments seem to be based on more complex processes.
Attentive Perception Can Diminish Vagal Inhibition
Authors: Rynkiewicz Andrzej
Published: February 2006

A systematic decrease in heart rate when anticipating an important stimulus or when preparing to react is called anticipatory bradycardia. Numerous studies have shown that the initiation of motor activity prompts the termination of anticipatory bradycardia in reaction time tasks. However, in experiments with procedures based on more complex reactions, the termination of anticipatory bradycardia is delayed until later cardiac cycles. This unexpected effect may be attributed to perceptual processes that are engaged in the feedback mechanism essential for effectiveness in prolonged and complex motor reactions. The experiment presented in this article was carried out to verify the hypothesis that the initiation of a motor reaction, when processed simultaneously with sustained attentive perception, does not evoke acceleration of heart rate. The experimental task was a simulated shooting at a moving target. The procedure in the experimental group induced participants to attentively observe events before and after the required reaction, whereas in the control group, attentive perception of task events after the reaction was not possible. The expected pattern of heart-rate changes appeared in the experimental group. During the initial block of trials, the initiation of the motor reaction did not evoke immediate termination of anticipatory bradycardia. During later trials in the experimental group and during all trials in the control group, heart-rate changes were completely typical - heart rate increased after the motor reaction began. The results show that attentive perception engaged immediately after the initiation of motor activity can affect the pattern of phasic heart-rate changes observed during typical reaction time tasks. Additionally, the difference between the patterns characteristic of the initial and later trials suggests possible competition between the neuronal influences that modulate heart rate.
Dynamics of thermochemical plumes: 1. Plume formation and entrainment of a dense layer
Authors: Lin Shu‐Chuan , van Keken Peter E.
Published: February 2006

Density variations due to changes in bulk chemistry in the lowermost mantle play an important role in the dynamics and chemistry of plumes. In this study we perform a series of high‐resolution numerical experiments in an axisymmetric spherical shell to systematically investigate the formation of plumes from a thermochemical boundary layer and the entrainment of the dense material by plumes. In particular, we investigate the effects of the temperature dependence of viscosity, the chemical density contrast, and thickness of the compositionally distinct layer. Our results show that all three factors influence the nature of plume formation and entrainment of dense material. The complexity of the evolution of the plumes and of the entrainment process increases profoundly with increasing viscosity contrast. The entrainment commonly becomes a transient process for models with variable viscosity. It is generally stronger in the isoviscous models, but the development of plumes is easier in the models with variable viscosity, which is mainly determined by the mechanical coupling between the dense material and the surrounding mantle. Our model results indicate that the compositionally distinct region in D″ can survive in the Earth's history if the intrinsic density contrast of the compositionally distinct layer is greater than about 2%. We also present a series of benchmark tests for thermochemical convection problems in an axisymmetric spherical shell. Our tests indicate that high‐resolution models are necessary for the thermochemical convection systems in which strongly temperature‐dependent viscosity is considered.
Quantifying the impact of future land‐use changes against increases in GHG concentrations
Authors: Voldoire A.
Published: February 2006

The impact on atmospheric climate of future land‐use changes relative to the increase in greenhouse gas (GHG) concentrations is assessed in time‐slice simulations with the ARPEGE‐Climat atmospheric general circulation model (AGCM). Future land cover maps are provided by the IMAGE2.2 integrated model, developed by RIVM. We show that the relative impact of vegetation change to GHG concentration increase is of the order of 10% for a B2 scenario, and can reach 30% over localized tropical regions.
EOS MLS observations of ozone loss in the 2004–2005 Arctic winter
Authors: Manney G. L. , Santee M. L. , Froidevaux L. , Hoppel K. , Livesey N. J. , Waters J. W.
Published: February 2006

Earth Observing System Microwave Limb Sounder O3 and N2O are used to examine transport and chemical O3 loss in the unusually cold 2004–2005 Arctic winter. The vortex was dynamically active, with episodic mixing events throughout the winter; descent was the dominant transport process only through late January. Before the onset of lower stratospheric chemical loss, O3 was higher near the vortex edge than in the vortex core, causing different effects of mixing depending on the vortex region and time, either masking or mimicking chemical loss. O3 loss ceased by 10 March because of an early final warming. Rough estimates suggest maximum vortex‐averaged O3 loss of 1.2–1.5 ppmv between 450 and 500 K, with up to ∼2 ppmv loss in the outer vortex near 500 K. Despite record cold, chemical O3 loss was less in 2004–2005 than in previous cold Arctic winters.
Data derived continuous time model for the Dst dynamics
Authors: Zhu D. , Billings S. A. , Balikhin M. , Wing S. , Coca D.
Published: February 2006

Understanding space weather and forecasting geomagnetic storms are the most important applications of solar‐terrestrial physics. Geomagnetic storms are complex sequences of physical processes, which include both microprocesses, (e.g., magnetic reconnection) and macroprocesses (relaxation of the ring current around the Earth, which is the main contributor to the geomagnetic storms). To derive a mathematical description of the magnetospheric dynamics from first principles the models of all processes involved should be conjugated into a global model. This goal will ultimately be accomplished. However the present level of understanding means that this will not happen in the foreseeable future. An alternative approach used here is based on system identification. A physically interpretable continuous time model capturing the magnetospheric dynamics has been identified directly from measurements of the solar wind and geomagnetic Dst index. It is shown that such a model can provide reliable forecasts of geomagnetic disturbances.
Wind‐driven zonal jets in the South Pacific Ocean
Authors: Kessler William S. , Gourdeau Lionel
Published: February 2006

Zonal jets west of the large islands of the South Pacific Ocean are predicted by theory, commonly seen in ocean models with sufficiently high resolution, and are beginning to be observed. These jets are often taken to reflect the blocking effect of the islands in the South Equatorial Current through “Island Rule” dynamics. Here it is shown that quasi‐permanent structures of the basin‐wide wind field imply the existence of jets formed independently of the islands. Evidence for the existence of the wind‐driven jets is found in climatological geostrophic currents. The hydrographic structures that produce the jets occur well below the thermocline.
Magnetic signatures of equatorial spread F as observed by the CHAMP satellite
Authors: Stolle C. , Lühr H. , Rother M. , Balasis G.
Published: February 2006

Magnetic observations on board the CHAMP satellite are used for the first comprehensive study of magnetic signatures of the postsunset equatorial spread F (ESF) events. This is derived from a continuous database covering the years 2001–2004. On the basis of an extended survey, the global distribution of magnetic signatures is derived. We find a distinct seasonal/longitudinal variation of the occurrence rate of magnetic signatures that is consistent with that obtained from previous satellite observations of plasma depletions. The latitudinal distribution of the ESF magnetic signatures from CHAMP is symmetrical about the dip equator. It can be approximated by two Gaussian curves peaking at ±9.5° magnetic latitude, both exhibiting an 1σ‐width of 4.5°. We further find a close relation between the occurrence frequency and the solar EUV flux. The global average of the occurrence rate is linearly proportional to solar activity attaining ∼0.1% times the F10.7 value. The response of the ESF magnetic signatures to geomagnetic activity is also investigated. However, only a weak relation between the signature occurrence rate and the Kp index is found. Using high‐resolution magnetic field measurements of the ESF structures, we are able to identify very small spatial scales of spread F of only few tens of meters. The vector magnetic field observations provide experimental evidence of the electromagnetic characteristics of ESF, valuable for testing model predictions. Finally, we discuss the effect of the ESF phenomenon on magnetic field modeling efforts based on satellite data.
FAST observations of the solar illumination dependence of downgoing auroral electron beams: Relationship to electron energy flux
Authors: Cattell C. , Dombeck J. , Carlson C. , McFadden J.
Published: February 2006

The dependence of the occurrence frequency of downgoing auroral electron beams on solar illumination, as a function of energy flux, has been examined utilizing data from the FAST satellite. Solar illumination has almost no effect on the occurrence frequency of electron beams with energy flux less than or equal to a few erg/cm2s; however, the ratio of the occurrence frequency in darkness to that in sunlight increases with the energy flux carried by the beam. For an energy flux >5 ergs/cm2s, the ratio is ∼2 to 2.5, consistent with the results of Newell et al. (1996b). The characteristic energy of dayside beams is less than that on the nightside by a factor of ∼2. Both on the dayside and nightside, the characteristic energy of the electron beams increases with the energy flux carried by the beam and the energy is somewhat dependent on solar illumination, ∼50% (20%) higher in darkness for dusk (morning) beams. Although there are fewer very intense aurora in sunlight, the very intense aurora that occur have characteristic energies comparable to those in darkness. These results are consistent with a density and scale height dependent mechanism for parallel potential drops in the auroral acceleration region.
Evolution of equatorial ionospheric bubbles during a large auroral electrojet index increase in the recovery phase of a magnetic storm
Authors: Keskinen M. J. , Ossakow S. L. , Fejer B. G. , Emmert John
Published: February 2006

We present a model and observations of the evolution of equatorial ionospheric bubbles during a large auroral electrojet (AE) index increase in the recovery phase of a geomagnetic storm. Using a three‐dimensional time‐dependent numerical simulation model, we find, for the 19–21 October 1998 storm, that the equatorial bubble evolution is different during storm time as compared to quiet time conditions. We have found that the storm time vertical drift in conjunction with reduced off‐equatorial E region shorting is the primary mechanism that distinguishes the large AE increase recovery phase storm time evolution from the quiet time case. Comparison of the simulation model with ground‐based storm time radar observations is made.
Apportionment of black carbon in the South Shetland Islands, Antarctic Peninsula
Authors: Pereira Enio Bueno , Evangelista Heitor , Pereira Kely Cristine Dalia , Cavalcanti Iracema F. A. , Setzer Alberto W.
Published: February 2006

Simultaneous time series measurements of black carbon (BC), aerosol particle number (ANC), radon, and SEM‐EDS analysis for total carbon were collected at the Brazilian Antarctic station Ferraz, northwest of the Antarctic Peninsula (62°05′S, 58°23.5′W) for the years of 1993, 1997, and 1998. A new data screening technique was applied in an effort to distinguish long‐range from local contaminations of BC. Analyses of data revealed a small increase in BC concentration during winter‐to‐spring seasons. The mean annual BC concentration of 8.3 ng m−3 was consistent with global model estimates for this region. The intermittent coupling mechanism between the regional circulation of the low‐level jets and the passages of the frontal systems explained the transport of BC from areas of burning biomass in Brazil to the northern Antarctic Peninsula. Principal component analysis applied to BC, Radon, ANC, and meteorological data presented significant factor loadings linking BC with 222Rn and with wind velocity corroborating with this hypothesis.
Correlation between a negative group velocity and a slanted stop band in two‐dimensionally periodic structures
Authors: Hwang R. B.
Published: February 2006

In this paper, we employed the rigorous mode‐matching method to carry out the calculation for the scattering characteristics of a two‐dimensionally periodic structure made up of metallic rectangular cylinders. From the scattering characteristics, the interesting phenomenon of an anomalous dispersion was observed to possess negative group velocities. In order to understand the underlying physics involved, we begin with the investigation of the band structure associated with the corresponding structure of infinite extent; thereby, the band structures are classified into two types: vertical stop band that is mainly due to the effect of periodicity in a single direction and slanted stop band that is due to the combined effects of periodicities in two directions. Notably, the negative group velocity (delay) within the slanted stop band of a two‐dimensional periodic structure was directly related to the experimentally measurable scattering characteristics of the finite structure.
Quantifying the protein core flexibility through analysis of cavity formation
Authors: Pereira Brian , Jain Sandeep , Garde Shekhar
Published: February 2006

We present an extensive analysis of cavity statistics in the interior of three different proteins, in liquid n-hexane, and in water performed using molecular-dynamics simulations. The heterogeneity of packing density over atomic length scales in different parts of proteins is evident in the wide range of values observed for the average cavity size, the probability of cavity formation, and the corresponding free energy of hard-sphere insertion. More interestingly, however, the distribution of cavity sizes observed at various points in the protein interior is surprisingly homogeneous in width. That width is significantly smaller than that measured for similar distributions in liquid n-hexane or water, indicating that protein interior is much less flexible than liquid hexane. The width of the cavity size distribution correlates well with the experimental isothermal compressibility data for liquids and proteins. An analysis of cavity statistics thus provides an efficient method to quantify local properties, such as packing, stiffness, or compressibility in heterogeneous condensed media.
New four-dimensional solutions of the Jacobi equations for Poisson structures
Authors: Hernández-Bermejo Benito
Published: February 2006

A four-dimensional family of skew-symmetric solutions of the Jacobi equations for Poisson structures is characterized. As a consequence, previously known types of Poisson structures found in a diversity of physical situations appear to be obtainable as particular cases of new family of solutions. Additionally, it is possible to apply constructive methods for the explicit determination of fundamental properties of those solutions, such as their Casimir invariants, symplectic structure and the algorithm for the reduction to the Darboux canonical form, which have been reported only for a limited sample of known finite-dimensional Poisson structures. Moreover, the results developed are valid globally in phase space, thus ameliorating the usual scope of Darboux theorem which is of local nature.
Grain-boundary free energy via thermodynamic integration
Authors: Lusk Mark T. , Fellinger Michael R. , Beale Paul D.
Published: February 2006

In a previous publication by Lusk and Beale [Phys. Rev. E 69, 026117 (2004)], fluctuating cell (FC) theory was used to estimate the free energy of symmetric tilt grain boundaries in an assembly of nearly hard disks. The FC method is much faster than the more traditional thermodynamic integration, but the accuracy of the algorithm has not been assessed in association with persistent defect structures. This motivated the present work wherein the FC free energies are compared directly with the data obtained via thermodynamic integration from an Einstein crystal to an assembly of hard disks. This comparison is made over the range of possible misorientations for symmetric tilt boundaries and indicates that the FC method gives quantitatively accurate estimates for grain-boundary free energy. We also demsonstrate that the FC approximation is quantitatively accurate at determining the free-energy contribution of each particle whether in the bulk or the grain boundary. The FC calculation is about two orders of magnitude faster than a full thermodynamic integration. This approach may offer a numerically efficient means of estimating the free energy of persistent defect structures to greater accuracy than is afforded by the quasiharmonic and local harmonic approximations.
High-resolution studies of tropolone in the S and S1 electronic states: Isotope driven dynamics in the zero-point energy levels
Authors: Keske John C. , Lin Wei , Pringle Wallace C. , Novick Stewart E. , Blake Thomas A. , Plusquellic David F.
Published: February 2006

Rotationally resolved microwave (MW) and ultraviolet (UV) spectra of jet-cooled tropolone have been obtained in S0 and S1 electronic states using Fourier-transform microwave and UV-laser/molecular-beam spectrometers. In the ground electronic state, the MW spectra of all heavy-atom isotopomers including one O18 and four C13 isotopomers were observed in natural abundance. The OD isotopomer was obtained from isotopically enriched samples. The two lowest tunneling states of each isotopomer except O18 have been assigned. The observed inversion splitting for the OD isotopomer is 1523.227(5) MHz. For the asymmetric C13 structures, the magnitudes of tunneling-rotation interactions are found to diminish with decreasing distance between the heavy atom and the tunneling proton. In the limit of closest approach, the 0+ state of O18 was well fitted to an asymmetric rotor Hamiltonian, reflecting significant changes in the tautomerization dynamics. Comparisons of the substituted atom coordinates with theoretical predictions at the MP2/aug-cc-pVTZ level of theory suggest the localized 0+ and 0− wave functions of the heavier isotopes favor the C–OH and C=O forms of tropolone, respectively. The only exception occurs for the C13-OH and C13=O structures which correlate to the 0− and 0+ states, respectively. These preferences reflect kinetic isotope effects as quantitatively verified by the calculated zero-point energy differences between members of the asymmetric atom pairs. From rotationally resolved data of the 0+←0+ and 0−←0− bands in S1, line-shape fits have yielded Lorentzian linewidths that differ by 12.2(16) MHz over the 19.88(4)cm−1 interval in S1. The fluorescence decay rates together with previously reported quantum yield data give nonradiative decay rates of 7.7(5)×108 and 8.5(5)×108s−1 for the 0+ and 0− levels of the S1 state of tropolone.
Estimation of electronic coupling in π-stacked donor-bridge-acceptor systems: Correction of the two-state model
Authors: Voityuk Alexander A.
Published: February 2006

Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of Vda because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a π stack, where donor and acceptor are separated by a bridging unit, can be obtained as Ṽda=(E2−E1)μ12∕Rda+(2E3−E1−E2)2μ13μ23∕Rda2, where E1, E2, and E3 are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, μij is the transition dipole moments between the states i and j, and Rda is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.
Structure of penetrable-rod fluids: Exact properties and comparison between Monte Carlo simulations and two analytic theories
Authors: Malijevský Alexandr , Santos Andrés
Published: February 2006

Bounded potentials are good models to represent the effective two-body interaction in some colloidal systems, such as the dilute solutions of polymer chains in good solvents. The simplest bounded potential is that of penetrable spheres, which takes a positive finite value if the two spheres are overlapped, being 0 otherwise. Even in the one-dimensional case, the penetrable-rod model is far from trivial, since interactions are not restricted to nearest neighbors and so its exact solution is not known. In this paper the structural properties of one-dimensional penetrable rods are studied. We first derive the exact correlation functions of the penetrable-rod fluids to second order in density at any temperature, as well as in the high-temperature and zero-temperature limits at any density. It is seen that, in contrast to what is generally believed, the Percus-Yevick equation does not yield the exact cavity function in the hard-rod limit. Next, two simple analytic theories are constructed: a high-temperature approximation based on the exact asymptotic behavior in the limit T→∞ and a low-temperature approximation inspired by the exact result in the opposite limit T→0. Finally, we perform Monte Carlo simulations for a wide range of temperatures and densities to assess the validity of both theories. It is found that they complement each other quite well, exhibiting a good agreement with the simulation data within their respective domains of applicability and becoming practically equivalent on the borderline of those domains. A comparison with numerical solutions of the Percus-Yevick and the hypernetted-chain approximations is also carried out. Finally, a perspective on the extension of our two heuristic theories to the more realistic three-dimensional case is provided.
Enhanced conductivity in graphene layers and at their edges
Authors: Banerjee S. , Sardar M. , Gayathri N. , Tyagi A. K. , Raj Baldev
Published: February 2006

We have observed that the conductivity of graphene sheets is higher whenever they are loosely bound to the underlying bulk graphite. We also observe that certain edges of the graphene layers show sharp rise in current when biased, indicating enhanced electronic density of states spatially localized near those edges. In certain edges, we do not observe this phenomenon. These two observations, i.e., enhancement of conductivity of loosely bound layers and sharp rise in current at the edges are discussed with possible reasons and invoking recent theoretical predictions.
Nonlinear damping of zonal modes in anisotropic weakly collisional trapped electron mode turbulence
Authors: Gatto R. , Terry P. W. , Baver D. A.
Published: February 2006

Comprehensive spectral analysis of a fluid model for trapped electron mode (TEM) turbulence reveals that marginally stable zonal modes at infinitesimal amplitude become robustly damped at finite amplitude. Zonal-mode structure, anisotropy, excitation, and wave number spectra are shown to result from interaction of the zero-frequency drift wave with the density advection nonlinearity. Heuristic dimensional balances, closure theory, and simulations manifest the primacy of the interaction, and yield energy transfer rates, fluctuation levels, spectra and finite-amplitude-induced dissipation. Strong sensitivity to the zero-frequency wave induces a marked spectral energy-transfer anisotropy that preferentially drives zonal modes relative to nonzonal modes. Zonal-mode excitation is accompanied by the nonlinear excitation of a spectrum of damped eigenmodes. The mixing of unstable TEM eigenmodes with the damped spectrum subjects zonal modes to finite-amplitude-induced damping. The combination of anisotropic transfer to zonal wave numbers and their nonlinear damping is shown to make this the dominant saturation mechanism for TEM turbulence.
Spectroscopy of the ground and low-lying excited states of ThO+
Authors: Goncharov Vasiliy , Heaven Michael C.
Published: February 2006

The ThO+ cation is of interest as it is a useful prototype for experimental and theoretical studies of bonding in a simple actinide compound. Formally the ground state of ThO+ has the configuration Th3+(7s)O2−, where there is a single unpaired electron associated with a closed-shell Th4+-ion core. The first tier of excited states above the XΣ+2 ground state is expected to be 1Δ2, 1Π2, and 2Σ+2 derived from the Th3+(6d)O2− configuration. Spectroscopic observations of ThO+ using the pulsed field ionization–zero kinetic-energy photoelectron technique are reported here. Rotationally resolved spectra were recorded for the XΣ+2, 1Δ2, and 1Π2 states. Extensive vibrational progressions were observed. Surprisingly, it was found that ionization of ThO decreases the dissociation energy, while increasing the vibrational frequency and decreasing the bond length. Accurate values for the ionization energies of ThO [53253.8(2)cm−1] and Th [50868.71(8)cm−1] were determined as part of this investigation.
Radially resolved measurements of plasma rotation and flow-velocity shear in the Maryland Centrifugal Experiment
Authors: Ghosh J. , Elton R. C. , Griem H. R. , Case A. , DeSilva A. W. , Ellis R. F. , Hassam A. , Lunsford R. , Teodorescu C.
Published: February 2006

In diagnosing the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et al., Phys. of Plasmas 8, 2057 (2001)], earlier spectroscopic measurements of averaged plasma rotation velocities have been upgraded to include radial distributions, using a five-channel fiber-optic collection system. Detailed information from each view is now possible with an 8-times increase in spectral resolution, by using a 2m spectrograph and a 2400lines∕mm grating. Inversion of the integrated chordal radiation into a radial dependence of local emissions is performed by two methods: (a) an iterative simulation beginning with assumed emissions in five axially concentric cylindrical zones followed by summation along the five viewing chords, and (b) inversion of a combination of dual Abel-type matrices. The radial profiles of the absolute velocities derived cover a range from 20to70km∕s for both C+ and C++ impurity ions. Previous apparent differences in velocities between ions from a single chordal observation are now explained by the measured radial dependence of velocities and relative emissions. An important result is the first direct and quantitative measurement on MCX of a radial shear in rotational flow velocity as large as 9×105s−1, 9 times a threshold of 1×105s−1 for magnetohydrodynamic stability. Stark-broadened hydrogen Balmer-series spectral lines provide both a value for electron density of Ne=(8.5±1.5)1014cm−3 and supporting data for radial particle distributions.
Global visibility of naked singularities
Authors: Giambò Roberto
Published: February 2006

Global visibility of naked singularities is analyzed here for a class of spherically symmetric spacetimes, extending previous studies—limited to inhomogeneous dust cloud collapse—to more physical valid situations in which pressures are non-vanishing. Existence of nonradial geodesics escaping from the singularity is shown, and the observability of the singularity from far-away observers is discussed.
Electrically controllable laser based on cholesteric liquid crystal with negative dielectric anisotropy
Authors: Lin Tsung-Hsien , Jau Hung-Chang , Chen Ching-Hsu , Chen Yi-Jan , Wei Tai-Huei , Chen Chen-Wei , Fuh Andy Y.-G.
Published: February 2006

This work examines a planar cholesteric liquid crystal (CLC) cell with a negative dielectric anisotropy, doped with laser dye, as an electrically tunable one-dimensional photonic crystal laser device. The lasing wavelength is demonstrated to be tunable by applying a voltage. Additionally, lasing can be switched on and off changing the frequency of the applied voltage. Wavelength tuning caused by the shift of the reflection band of CLC is attributed to the electrohydrodynamical effect in the negative dielectric cell.
Role of stable eigenmodes in saturated local plasma turbulence
Authors: Terry P. W. , Baver D. A. , Gupta Sangeeta
Published: February 2006

The excitation of stable eigenmodes in unstable plasma turbulence, previously documented in collisionless trapped electron mode turbulence, is shown to be a generic behavior of local (quasihomogeneous) systems. A condition is derived to indicate when such excited eigenmodes achieve a sufficient level in saturation to affect the turbulence, and produce changes in saturation levels, instability drive, and transport. The condition is shown to be consistent with the results of collisionless and dissipative trapped electron turbulence, and is further illustrated by an entirely different model describing simple ion turbulence driven by the ion temperature gradient. The condition suggests that all eigenmodes of the ion model affect saturation, but none dominates. This is consistent with the results of simulations, which show nonlinear modifications to eigenmode structure, growth rate, and transport that occur intermittently in time, despite fixed driving gradients.
Multiple separation of self-running drops by pinching a three-phase contact line
Authors: Mo Gary C. H. , Kwok Daniel Y.
Published: February 2006

We produced multiple minute self-running drops from an original drop without external input power by pinching a three-phase contact line. By branching into surface energy barriers, the drop is forced to separate while translating on a flat surface. A symmetry in the drop front wetted perimeter conduces to equal division of the drop. Our experiments suggest that at least seven divisions (128 drops) can be conducted sequentially to give equal final volumes of approximately 4nl. A division of carrier liquid volume by 1∕27 is expected to enable multiple analysis on many separate stations. This is the only drop separation method at present that does not require external power input.
GaN light-emitting diodes with Archimedean lattice photonic crystals
Authors: David Aurélien , Fujii Tetsuo , Matioli Elison , Sharma Rajat , Nakamura Shuji , DenBaars Steven P. , Weisbuch Claude , Benisty Henri
Published: February 2006

We study GaN-based light emitting diodes incorporating an omnidirectional photonic crystal with Archimedean lattice. Photonic bands are observed over several Brillouin zones, revealing reciprocal space symmetries and evidencing the omnidirectionality of the photonic crystal. Intensities of the diffracted bands are found to agree with the Fourier transform of the crystal lattice, and confirm its Archimedean nature.
Hole-mobility limit of amorphous silicon solar cells
Authors: Liang Jianjun , Schiff E. A. , Guha S. , Yan Baojie , Yang J.
Published: February 2006

We present temperature-dependent measurements and modeling for a thickness series of hydrogenated amorphous silicon nip solar cells. The comparison indicates that the maximum power density (PMAX) from the as-deposited cells has achieved the hole-mobility limit established by valence bandtail trapping, and PMAX is thus not significantly limited by intrinsic-layer dangling bonds or by the doped layers and interfaces. Measurements of the temperature-dependent properties of light-soaked cells show that the properties of as-deposited and light-soaked cells converge below 250 K; a model perturbing the valence band tail traps with a density of dangling bonds accounts adequately for the convergence effect.
Monte Carlo simulations of the adsorption of CO2 on the MgO(100) surface
Authors: Daub Christopher D. , Patey G. N. , Jack D. B. , Sallabi A. K.
Published: February 2006

The adsorption of CO2 gas on the MgO (100) crystal surface is investigated using grand canonical Monte Carlo simulations. This allows us to obtain adsorption isotherms that can be compared with experiment, as well as to explore the possible formation of monolayers of different densities. Our model calculations agree reasonably well with the available experimental results. We find a “low-density” adsorbed monolayer where each CO2 molecule is bound to two Mg2+ ions on the MgO substrate. We also observe the formation of monolayers of higher density, where some of the CO2 molecules have rotated and tilted to expose additional binding sites. Low-temperature simulations of both the low- and high-density monolayers reveal that these states are very close in energy, with binding energies of approximately 7kcal∕mol at T=5K. The high-density monolayer given by our model has a density that is significantly less than the reported experimental value. We discuss this discrepancy and offer suggestions for resolving it.
Plain superconducting films as magnetic field tunable two-dimensional rectifiers
Authors: Pryadun V. V. , Sierra J. , Aliev F. G. , Golubovic D. S. , Moshchalkov V. V.
Published: February 2006

Longitudinal and transversal permanent electric fields generated by an ac current through superconducting Pb and Nb thin strips have been studied as the function of the drive frequency (103<f<108Hz), temperature, and magnetic field. At low frequencies (f<104Hz) and below the critical temperature, the superconducting strips behave as one-dimensional rectifiers, whereas for higher drive frequencies (f>105Hz) the rectification becomes two dimensional. The rectification strongly depends on the magnetic field, temperature and ac drive. The unusual dc electric field topology generated by the ac current in the superconducting strips can be explained by a local rectification due the oppositely directed asymmetric edge (Bean-Livingston type) barriers.
Nonlocal electron electrodynamics in high-frequency capacitive discharges
Authors: Kim H. C. , Park G. Y. , Lee J. K.
Published: February 2006

Several nonlocal electron behaviors in low-pressure high-frequency capacitive discharges were found through particle-in-cell/Monte Carlo simulations. First, a negative power deposition region becomes wider as the rf frequency decreases. Second, in the spatial profile of the amplitude of the rf electric field, a nonmonotonic structure appears at the bulk-sheath boundary along with an abrupt change in the phase of the rf electric field. Third, in the spatial profile of the amplitude of the rf electron current, the second peak appears in the bulk.
Tunable and augmented plasmon resonances of Au∕SiO2∕Au nanodisks
Authors: Su K. H. , Wei Q. H. , Zhang X.
Published: February 2006

The plasmon resonance of Au∕SiO2 multilayered nanodisks was studied using light scattering spectroscopy and numerical calculations. Compared to single layered Au nanodisks, multilayered nanodisks exhibit several distinctive properties including significantly enhanced plasmon resonances and tunable resonance wavelengths which can be tailored to desired values by simply varying dielectric layer thickness while the particle diameter is kept constant. Numerical calculations show that slicing one metal layer into metal multilayers leads to higher scattering intensity and more “hot spots,” or regions of strong field enhancement. This tunable and augmented plasmon resonance holds a great potential in the applications of surface-enhanced Raman scattering (SERS).
Laser-induced shockwave propagation from ablation in a cavity
Authors: Zeng Xianzhong , Mao Xianglei , Mao Samuel S. , Wen Sy-Bor , Greif Ralph , Russo Richard E.
Published: February 2006

The propagation of laser-induced shockwaves from ablation inside of cavities was determined from time-resolved shadowgraph images. The temperature and electron number density of the laser-induced plasma was determined from spectroscopic measurements. These properties were compared to those for laser ablation on the flat surface under the same energy and background gas condition. A theoretical model was proposed to determine the amount of energy and vaporized mass stored in the vapor plume based on these measurements.
Thermally excited fluctuations as a pure electron plasma temperature diagnostic
Authors: Shiga N. , Anderegg F. , Dubin D. H. E. , Driscoll C. F. , Gould R. W.
Published: February 2006

Thermally excited charge fluctuations in pure electron plasma columns provide a diagnostic for the plasma temperature over a range of 0.05<kBT<10eV. Three different nonperturbative methods have been developed to determine the plasma temperature. The first method fits the near-Lorentzian spectrum of thermal fluctuations near a single weakly damped mode. This method works well where the modes are weakly damped, i.e., when λD∕Rp<0.3. The second method utilizes the emission spectrum over a broad frequency range encompassing several modes and the nonresonant fluctuations between modes. This method works for long columns with λD∕Rp>0.2, so that Landau damping is dominant and well modeled by theory. The third method compares the total (frequency-integrated) number δN of fluctuating image charges on the wall antenna to a simple thermodynamic calculation. This method works when λD∕Rp>0.2.
Sheath structure for cylindrical probe in low-pressure electronegative discharges
Authors: Chung T. H.
Published: February 2006

A theoretical model for collisionless and weakly collisional plasmas with cold positive ions is developed for the presheath and sheath that surround a cylindrical probe immersed in electronegative discharges. The model is solved numerically, and the spatial distributions of the normalized potential, the normalized density, and the normalized velocity and flux of positive ions are calculated for a low-pressure electronegative discharge as a function of the ratio of the negative ion density to the electron density and the ratio of the electron temperature to the negative ion temperature. As the ratio of the Debye length to the ionization length increases, it is found that the sheath width decreases, the velocity of the positive ion gets smaller, and the positive ion flux to the probe decreases. As the electronegativity increases, the sheath width decreases.
Molecular geometry and polarizability of small cadmium selenide clusters from all-electron ab initio and Density Functional Theory calculations
Authors: Karamanis Panaghiotis , Maroulis George , Pouchan Claude
Published: February 2006

We have calculated molecular geometries and electric polarizabilities for small cadmium selenide clusters. Our calculations were performed with conventional ab initio and density functional theory methods and Gaussian-type basis sets especially designed for (CdSe)n. We find that the dipole polarizability per atom converges rapidly to the bulk value.