bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal controls on the exchange of carbon and water in an Amazonian rain forest
Authors: Hutyra Lucy R. , Munger J. William , Saleska Scott R. , Gottlieb Elaine , Daube Bruce C. , Dunn Allison L. , Amaral Daniel F. , de Camargo Plinio B. , Wofsy Steven C.
Published: July 2007

The long‐term resilience of Amazonian forests to climate changes and the fate of their large stores of organic carbon depend on the ecosystem response to climate and weather. This study presents 4 years of eddy covariance data for CO2 and water fluxes in an evergreen, old‐growth tropical rain forest examining the forest's response to seasonal variations and to short‐term weather anomalies. Photosynthetic efficiency declined late in the wet season, before appreciable leaf litter fall, and increased after new leaf production midway through the dry season. Rates of evapotranspiration were inelastic and did not depend on dry season precipitation. However, ecosystem respiration was inhibited by moisture limitations on heterotrophic respiration during the dry season. The annual carbon balance for this ecosystem was very close to neutral, with mean net loss of 890 ± 220 kg C ha−1 yr−1, and a range of −221 ± 453 (C uptake) to +2677 ± 488 (C loss) kg C ha−1 yr−1 over 4 years. The trend from large net carbon release in 2002 towards net carbon uptake in 2005 implies recovery from prior disturbance. The annual carbon balance was sensitive to weather anomalies, particularly the timing of the dry‐to‐wet season transition, reflecting modulation of light inputs and respiration processes. Canopy carbon uptake rates were largely controlled by phenology and light with virtually no indication of seasonal water limitation during the 5‐month dry season, indicating ample supplies of plant‐available‐water and ecosystem adaptation for maximum light utilization.
Significance of pelagic aerobic methane oxidation in the methane and carbon budget of a tropical reservoir
Authors: Guérin Frédéric , Abril Gwenaël
Published: July 2007

The Petit Saut Reservoir (French Guiana), flooded in 1994, has an anoxic and methane‐rich (>400 μmol.L−1) hypolimnion and an oxycline located at around 5 meters depth. Waters passing through the turbines are enriched in CH4, which partly degasses downstream of the dam. Aerobic methane oxidation rates were measured in the waters of the reservoir epilimnion and, in river waters downstream of the dam, during the wet and dry seasons. A unique first order relationship between methane concentration (CCH4) and aerobic methane oxidation rates (CH4‐ox) was found for the reservoir and the river downstream of the dam (CH4‐ox = 0.11 ± 0.01 CCH4 + 1.18 ± 0.74) giving a specific CH4 oxidation rate of 0.11 ± 0.01 h−1. In the reservoir, depth‐integrated methane oxidation rates were calculated from oxidation rates and the distributions of CH4 and oxygen and ranged between 11 ± 6 and 310 ± 132 mmol.m−2.d−1, consistent with the turbulent vertical flux from the hypolimnion (38–321 mmol.m−2.d−1) and almost two orders of magnitude higher than the atmospheric fluxes (0.3 ± 0.2–1.9 ± 1.2 mmol.m−2.d−1). The average integrated methane oxidation rate in the epilimnion given by these two independent methods is 100 ± 80 mmol.m−2.d−1. Downstream of the dam, about 40% of the methane entering the river was oxidized (77 ± 40 mmol.m−2.d−1) and 50% was emitted to the atmosphere (98 ± 28 mmol.m−2.d−1). Our results show that total pelagic oxidation (67 ± 64 Gg C‐CH4.y−1) reduce atmospheric emissions by more than 85% for the whole lake‐river system and that this process is responsible for more than 25% of total CO2 emissions from the whole reservoir‐river system.
Sea surface temperature records in the northern South China Sea from mid‐Holocene coral Sr/Ca ratios
Authors: Wei Gangjian , Deng Wenfeng , Yu Kefu , Li Xian‐hua , Sun Weidong , Zhao Jian‐xin
Published: July 2007

Three mid‐Holocene sea surface temperature (SST) records spanning more than 30 years were reconstructed for the northern South China Sea using Sr/Ca ratios in Porites corals. The results indicate warmer than present climates between circa 6100 yr B.P. and circa 6500 yr B.P. with the mid‐Holocene average minimum monthly winter SSTs, the average maximum monthly summer SSTs, and the average annual SSTs being about 0.5°–1.4°C, 0°–2.0°C, and 0.2°–1.5°C higher, respectively, than they were during 1970–1994. Summer SSTs decrease from circa 6500 yr B.P. to circa 6100 yr B.P. with a minimum centered at circa 6300 yr B.P. The higher average summer SSTs are consistent with a stronger summer monsoon during the mid‐Holocene, and the decreasing trend indicates a secular decrease of summer monsoon strength, which reflects the change in summer insolation in the Northern Hemisphere. El Niño–Southern Oscillation (ENSO) cycles were apparent in both the mid‐Holocene coral and modern instrumental records. However, the ENSO variability in the mid‐Holocene SSTs was weaker than that in the modern record, and the SST record with the highest summer temperatures from circa 6460 yr B.P. to 6496 yr B.P. shows no robust ENSO cycle. This agrees with other studies that indicate that stronger summer monsoon circulation may have been associated with suppressed ENSO variability during the mid‐Holocene.
Nitrate reduction, sulfate reduction, and sedimentary iron isotope evolution during the Cenomanian‐Turonian oceanic anoxic event
Authors: Jenkyns Hugh C. , Matthews Alan , Tsikos Harilaos , Erel Yigal
Published: July 2007

Organic carbon‐rich shales from localities in England, Italy, and Morocco, which formed during the Cenomanian‐Turonian oceanic anoxic event (OAE), have been examined for their total organic carbon (TOC) values together with their carbon, nitrogen, and iron isotope ratios. Carbon isotope stratigraphy (δ13Corg and δ13Ccarb) allows accurate recognition of the strata that record the oceanic anoxic event, in some cases allowing characterization of isotopic species before, during, and after the OAE. Within the black shales formed during the OAE, relatively heavy nitrogen isotope ratios, which correlate positively with TOC, suggest nitrate reduction (leading ultimately to denitrification and/or anaerobic ammonium oxidation). Black shales deposited before the onset of the OAE in Italy have unusually low bulk δ57Fe values, unlike those found in the black shale (Livello Bonarelli) deposited during the oceanic anoxic event itself: These latter conform to the Phanerozoic norm for organic‐rich sediments. Pyrite formation in the pre‐OAE black shales has apparently taken place via dissimilatory iron reduction (DIR), within the sediment, a suboxic process that causes an approximately −2‰ fractionation between a lithogenic Fe(III)oxide source and Fe(II)aq. In contrast, bacterial sulfate reduction (BSR), at least partly in the water column, characterized the OAE itself and was accompanied by only minor iron isotope fractionation. This change in the manner of pyrite formation is reflected in a decrease in the average pyrite framboid diameter from ∼10 to ∼7 μm. The gradual, albeit irregular increase in Fe isotope values during the OAE, as recorded in the Italian section, is taken to demonstrate limited isotopic evolution of the dissolved iron pool, consequent upon ongoing water column precipitation of pyrite under euxinic conditions. Given that evidence exists for both nitrate and sulfate reduction during the OAE, it is evident that redox conditions in the water column were highly variable, in both time and space.
Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard‐Oeschger oscillations caused by variations of North Atlantic Deep Water subduction
Authors: Schmittner Andreas , Galbraith Eric D. , Hostetler Steven W. , Pedersen Thomas F. , Zhang Rong
Published: July 2007

Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial‐scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature oscillations. Yet the mechanism of this teleconnection between the remote ocean basins remains elusive. Here we present model simulations of the oxygen and nitrogen cycles that explain how changes in deepwater subduction in the North Atlantic can cause large and synchronous variations of oxygen minimum zones throughout the Northern Hemisphere of the Indian and Pacific oceans, consistent with the paleoclimate records. Cold periods in the North Atlantic are associated with reduced nutrient delivery to the upper Indo‐Pacific oceans, thereby decreasing productivity. Reduced export production diminishes subsurface respiration of organic matter leading to higher oxygen concentrations and less denitrification. This effect of reduced oxygen consumption dominates at low latitudes. At high latitudes in the Southern Ocean and North Pacific, increased mixed layer depths and steepening of isopycnals improve ocean ventilation and oxygen supply to the subsurface. Atmospheric teleconnections through changes in wind‐driven ocean circulation modify this basin‐scale pattern regionally. These results suggest that changes in the Atlantic Ocean circulation, similar to those projected by climate models to possibly occur in the centuries to come because of anthropogenic climate warming, can have large effects on marine ecosystems and biogeochemical cycles even in remote areas.
A time‐frequency method for detecting VHF underdense meteor signals
Authors: Kang Chunmei , Palo Scott E.
Published: July 2007

Underdense meteor echoes observed using very high frequency (VHF) radar can be accurately modeled as a single complex damped sinusoid in additive white Gaussian noise. The normalized damping coefficient is expected to be between 0 and 0.3 for a VHF meteor return based on the modeled ambipolar diffusion rates near 90 km and a radar operating between 30 and 50 MHz. Current meteor echo detection routines operate either in the frequency domain, where it is difficult to detect highly damped signals, or in the time domain, where it is difficult to detect narrow band signals. An added difficulty is that typical approaches require a priori knowledge of the noise variance which can bias the performance of these estimators. In this paper, a time‐frequency waveform detector is proposed to address these problems. By normalizing the signal power and power spectral density in the time and frequency domains, respectively, a detector that is invariant to the noise variance can be implemented. The characteristics of a damped sinusoid in the time and frequency domains are exploited to construct the detector. The threshold for the proposed detector is only a function of of the time series length, and is stable with respect to a range of damping coefficients and noise levels. The time‐frequency waveform detector exhibits superior performance to the conventional energy or power detectors when the signal of interest is highly damped or the noise variance is unknown. A derivation of the time‐frequency waveform detector, comparison with the energy and power detectors and numerical results demonstrating the effectiveness of this detector are presented.
Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering
Authors: Trenberth Kevin E. , Dai Aiguo
Published: July 2007

The problem of global warming arises from the buildup of greenhouse gases such as carbon dioxide from burning of fossil fuels and other human activities that change the composition of the atmosphere and alter outgoing longwave radiation (OLR). One geoengineering solution being proposed is to reduce the incoming sunshine by emulating a volcanic eruption. In between the incoming solar radiation and the OLR is the entire weather and climate system and the hydrological cycle. The precipitation and streamflow records from 1950 to 2004 are examined for the effects of volcanic eruptions from El Chichón in March 1982 and Pinatubo in June 1991, taking into account changes from El Niño‐Southern Oscillation. Following the eruption of Mount Pinatubo in June 1991 there was a substantial decrease in precipitation over land and a record decrease in runoff and river discharge into the ocean from October 1991–September 1992. The results suggest that major adverse effects, including drought, could arise from geoengineering solutions.
Targeting toll‐like receptors for drug development: a summary of commercial approaches
Authors: Gearing Andrew J H
Published: July 2007

Toll‐like receptors (TLRs) play a fundamental role in recognizing infectious and noxious agents as well as products of tissue damage. They are capable of initiating both protective and damaging inflammatory and immune responses. Several biotechnology and pharmaceutical companies have programmes to develop new drugs that are either: agonists of TLRs to enhance immune responses against tumours and infectious agents, or to correct allergic responses; or antagonists designed to reduce inflammation due to infection or autoimmune disease. This article reviews the commercial approaches being undertaken to develop new TLR drugs.
Influence of Visual Information on the Intelligibility of Dysarthric Speech
Authors: Keintz Connie K. , Bunton Kate , Hoit Jeannette D.
Published: July 2007

Purpose

To examine the influence of visual information on speech intelligibility for a group of speakers with dysarthria associated with Parkinson’s disease.

Method

Eight speakers with Parkinson’s disease and dysarthria were recorded while they read sentences. Speakers performed a concurrent manual task to facilitate typical speech production. Twenty listeners (10 experienced and 10 inexperienced) transcribed sentences while watching and listening to videotapes of the speakers (auditory-visual mode) and while only listening to the speakers (auditory-only mode).

Results

Significant main effects were found for both presentation mode and speaker. Auditory-visual scores were significantly higher than auditory-only scores for the 3 speakers with the lowest intelligibility scores. No significant difference was found between the 2 listener groups.

Conclusions

The findings suggest that clinicians should consider both auditory-visual and auditory-only intelligibility measures in speakers with Parkinson’s disease to determine the most effective strategies aimed at evaluation and treatment of speech intelligibility decrements.
Speech-Language Pathologists' Assessment Practices for Children With Suspected Speech Sound Disorders: Results of a National Survey
Authors: Skahan Sarah M. , Watson Maggie , Lof Gregory L.
Published: July 2007

Purpose

This study examined assessment procedures used by speech-language pathologists (SLPs) when assessing children suspected of having speech sound disorders (SSD). This national survey also determined the information participants obtained from clients' speech samples, evaluation of non-native English speakers, and time spent on assessment.

Method

One thousand surveys were mailed to a randomly selected group of SLPs, self-identified as having worked with children with SSD. A total of 333 (33%) surveys were returned.

Results

The assessment tasks most frequently used included administering a commercial test, estimating intelligibility, assessing stimulability, and conducting a hearing screening. The amount of time dedicated to assessment activities (e.g., administering formal tests, contacting parents) varied across participants and was significantly related to years of experience but not caseload size. Most participants reported using informal assessment procedures, or English-only standardized tests, when evaluating non-native English speakers.

Conclusions

Most participants provided assessments that met federal guidelines to qualify children for special education services; however, additional assessment may be needed to create comprehensive treatment plans for their clients. These results provide a unique perspective on the assessment of children suspected of having SSD and should be helpful to SLPs as they examine their own assessment practices.
Phonological Processing and Reading in Children With Speech Sound Disorders
Authors: Rvachew Susan
Published: July 2007

Purpose

To examine the relationship between phonological processing skills prior to kindergarten entry and reading skills at the end of 1st grade, in children with speech sound disorders (SSD).

Method

The participants were 17 children with SSD and poor phonological processing skills (SSD-low PP), 16 children with SSD and good phonological processing skills (SSD-high PP), and 35 children with typical speech who were first assessed during their prekindergarten year using measures of phonological processing (i.e., speech perception, rime awareness, and onset awareness tests), speech production, receptive and expressive language, and phonological awareness skills. This assessment was repeated when the children were completing 1st grade. The Test of Word Reading Efficiency was also conducted at that time. First-grade sight word and nonword reading performance was compared across these groups.

Results

At the end of 1st grade, the SSD-low PP group achieved significantly lower nonword decoding scores than the SSD-high PP and typical speech groups. The 2 SSD groups demonstrated similarly good receptive language skills and similarly poor articulation skills at that time, however. No between-group differences in sight word reading were observed. All but 1 child (in the SSD-low PP group) obtained reading scores that were within normal limits.

Conclusion

Weaknesses in phonological processing were stable for the SSD-low PP subgroup over a 2-year period.
Women in Turkish Political Thought: Between Tradition and Modernity
Authors: Coşar Simten
Published: July 2007

This article aims at revealing the patriarchal pattern that has dominated Turkish political thought in the 20th century. I analyse the construction of woman's identity in the writings of three prominent thinkers of the early-republican era (1923–1945); namely, Ahmet Aǧaoǧlu, Peyami Safa and Zekeriya Sertel. The thinkers are deliberately chosen since each represents challenging political dispositions vis-à-vis the others. Ahmet Aǧaoǧlu is a liberal-nationalist, Peyami Safa is a well-known conservative thinker and Zekeriya Sertel is a leftist. However, despite the differences between and/or opposing foundations of their approaches all the three thinkers agree that there is a universally valid woman nature, attested by women's reproductive function, and approach the ‘woman issue’ on the basis of this assumption. The thinkers also argue that participation of women in public sphere inevitably results in their masculinization. Moreover, they distinguish between femininity and womanhood and offer their ideal models of womanhood. Although one can trace differences among the models, all converge on the concept of ‘nation's motherhood’ as the most significant feature of ideal womanhood. The main argument of the article is that women's subordination in the Turkish context is reinforced by the wide acceptance of these assumptions, and is further reproduced by the exclusion of the construction of gender typologies in the studies on Turkish political thought for a considerably long time.
The Gender Politics of Political Violence: Women Armed Activists in ETA
Authors: Hamilton Carrie
Published: July 2007

This article aims to contribute to the developing area of feminist scholarship on women and political violence, through a study of women in one of Europe's oldest illegal armed movements, the radical Basque nationalist organization ETA. By tracing the changing patterns of women's participation in ETA over the past four decades, the article highlights the historical factors that help explain the choice of a small number of Basque women to participate directly in political violence, and shows how these factors have differed from those for men. While the gender politics of radical nationalism are intricately linked to cross-cultural associations of militarism with certain forms of masculinity, the article also stresses the importance of understanding women's activism in ETA in the context of the organization's characteristic as an ethnic nationalist movement, as well as the wider historical circumstances of the movement's development, including the modernization of Spanish and Basque society over the past four decades. Although comparisons with women in other armed movements are possible, such historical specificities undermine any attempt to construct a universal theory of women and ‘terrorism’, such as Robin Morgan's ‘couple terrorism’ thesis. Finally, the article examines the changing representations of female ETA activists in the Spanish and Basque media. Although women ETA activists are now regarded as ‘normal’, popular representations continue to link women's armed activism with deviant sexuality and the transgression of their natural destiny as mothers. The different treatment of women is evident as well in claims of sexual torture made by some detainees. The article concludes that although the participation of women in political violence poses disquieting questions for the largely anti-militarist women's movement, case studies of women in armed organizations, as well as their place in the wider practices of conflict, are an important contribution both to feminist debates about violence and to wider studies of political violence.
The Science of Rape: (Mis)Constructions of Women's Trauma in Evolutionary Theory
Authors: Zeedyk Suzanne
Published: July 2007

The social sciences are witnessing renewed enthusiasm for sociobiological accounts of human behaviour. Feminist theory has, understandably, tended to engage cautiously with biological reasoning, because women have often been poorly served by the politics of such research. It is important, though, that feminists continue to contribute to this literature, in order to challenge problematic discourses that may emerge. The present paper seeks to analyse a domain of sociobiology that has been the focus of recent controversy: an evolutionary explanation of rape. Particular attention is given to the way in which women's traumatic experience of rape is constructed within this framework. It is argued that women's psychological pain is contorted, via the strategies of (a) diminishing women's pain and (b) ignoring their experience altogether. The operation of these two strategies is illuminated, and their practical consequences in the domains of legal reform and the depoliticization of science are evaluated.
Beautiful Dead Bodies: Gender, Migration and Representation in Anti-Trafficking Campaigns
Authors: Andrijasevic Rutvica
Published: July 2007

This essay addresses the link between sex trafficking and European citizesnhip by examining several anti-trafficking campaigns launched in post-socialist Europe. In illustrating which techniques are used in the production of images, it points to the highly symbolic and stereotypical constructions of femininity (victims) and masculinity (criminals) of eastern European nationals. A close analysis of female bodies dispayed in the campaigns indicates that the use of victimizing images goes hand in hand with the erotization of women's bodies. Wounded and dead women's bodies are read as attempts to stabilize the current political and social transformations in Europe by capturing women within the highly immobile boundaries of the sign ‘Woman’. The essay suggests that the representation of violence is thus violent itself since it confirms the stereotypes about eastern European women, equates the feminine with the passive object, severs the body from its materiality and from the historical context in which trafficking occurs, and finally confines women within the highly disabling symbolic register of ‘Woman’ as to maintain an imaginary social order in Europe.
The Biggest Computer Programme in the World Ever! How's it Going?
Authors: Brennan Sean
Published: July 2007

Early in 2004, the British Government announced the award of eight enormous IT contracts with a combined value of more than £6 billion. The companies selected would introduce new IT systems and processes to Europe's largest public sector organisation, the National Health Service (NHS) in England. The contracts were due to run for 7 years, until December 2010. At the end of June this year, the contracts will be exactly halfway through. But all is not well with the National Programme for IT (NPfIT), and both the programme and the agency NHS Connecting for Health (NHS CfH) set up to deliver the programme, have received considerable, and sustained criticism from many sources since their inception. Is this criticism justified or are some critics simply jumping onto a bandwagon? This paper attempts to provide an unbiased (if such a thing is possible) commentary on the programme so far.
On the thermodynamic stability of hydrogen clathrate hydrates
Authors: Katsumasa Keisuke , Koga Kenichiro , Tanaka Hideki
Published: July 2007

The cage occupancy of hydrogen clathrate hydrate has been examined by grand canonical Monte Carlo (GCMC) simulations for wide ranges of temperature and pressure. The simulations are carried out with a fixed number of water molecules and a fixed chemical potential of the guest species so that hydrogen molecules can be created or annihilated in the clathrate. Two types of the GCMC simulations are performed; in one the volume of the clathrate is fixed and in the other it is allowed to adjust itself under a preset pressure so as to take account of compression by a hydrostatic pressure and expansion due to multiple cage occupancy. It is found that the smaller cage in structure II is practically incapable of accommodating more than a single guest molecule even at pressures as high as 500 MPa, which agrees with the recent experimental investigations. The larger cage is found to encapsulate at most 4 hydrogen molecules, but its occupancy is dependent significantly on the pressure of hydrogen.
Theory of femtosecond coherent anti-Stokes Raman scattering spectroscopy of gas-phase transitions
Authors: Lucht Robert P. , Kinnius Paul J. , Roy Sukesh , Gord James R.
Published: July 2007

A theoretical analysis of coherent anti-Stokes Raman scattering (CARS) spectroscopy of gas-phase resonances using femtosecond lasers is performed. The time-dependent density matrix equations for the femtosecond CARS process are formulated and manipulated into a form suitable for solution by direct numerical integration (DNI). The temporal shapes of the pump, Stokes, and probe laser pulses are specified as an input to the DNI calculations. It is assumed that the laser pulse shapes are 70fs Gaussians and that the pulses are Fourier-transform limited. A single excited electronic level is defined as an effective intermediate level in the Raman process, and transition strengths are adjusted to match the experimental Raman polarizability. The excitation of the Raman coherence is investigated for different Q-branch rotational transitions in the fundamental 2330cm−1 band of diatomic nitrogen, assuming that the pump and Stokes pulses are temporally overlapped. The excitation process is shown to be virtually identical for transitions ranging from Q(2) to Q(20). The excitation of the Raman coherences is also very efficient; for laser irradiances of 5×1017W∕m2, corresponding approximately to a 100μJ, 70fs pulse focused to 50μm, approximately 10% of the population of the ground Raman level is pumped to the excited Raman level during the impulsive pump-Stokes excitation, and the magnitude of the induced Raman coherence reaches 40% of its maximum possible value. The theoretical results are compared with the results of experiments where the femtosecond CARS signal is recorded as a function of probe delay with respect to the impulsive pump-Stokes excitation.
Structure of higher spin gauge interactions
Authors: Bengtsson Anders K. H.
Published: July 2007

In a previous paper, higher spin gauge field theory was formulated in an abstract way, essentially only keeping enough machinery to discuss gauge invariance of an action. The approach could be thought of as providing an interface (or syntax) toward an implementation (or semantics) yet to be constructed. The structure then revealed turned out to be that of a strongly homotopy Lie algebra. In the present paper, the framework will be connected to more conventional field theoretic concepts. The Fock complex vertex operator implementation of the interactions in the BRST-BV formulation of the theory will be elaborated. The relation between the vertex order expansion and homological perturbation theory will be clarified. A formal nonobstruction argument is reviewed. The syntactically derived sh-Lie algebra structure is semantically mapped to the Fock complex implementation, and it is shown that the equations governing the higher order vertices are reproduced. Global symmetries and subsidiary conditions are discussed and as a result the tracelessness constraints are discarded. Thus, all equations needed to compute the vertices to any order are collected. The framework is general enough to encompass all possible interaction terms. Finally, the abstract framework itself will be strengthened by showing that it can be naturally phrased in terms of category theory.
Pair correlation functions and a free energy functional for the nematic phase
Authors: Mishra Pankaj , Singh Swarn Lata , Ram Jokhan , Singh Yashwant
Published: July 2007

In this paper we have presented the calculation of pair correlation functions in a nematic phase for a model of spherical particles with the long-range anisotropic interaction from the mean spherical approximation (MSA) and the Percus-Yevick (PY) integral equation theories. The results found from the MSA theory have been compared with those found analytically by Holovko and Sokolovska [J. Mol. Liq. 82, 161 (1999)]. A free energy functional which involves both the symmetry conserving and symmetry broken parts of the direct pair correlation function has been used to study the properties of the nematic phase. We have also examined the possibility of constructing a free energy functional with the direct pair correlation function which includes only the principal order parameter of the ordered phase and found that the resulting functional gives results that are in good agreement with the original functional. The isotropic-nematic transition has been located using the grand thermodynamic potential. The PY theory has been found to give a nematic phase with pair correlation function harmonic coefficients having all the desired features. In a nematic phase the harmonic coefficient of the total pair correlation function h(x1,x2) connected with the correlations of the director transverse fluctuations should develop a long-range tail. This feature has been found in both the MSA and PY theories.
Upconversion as a discriminating tool in site-selective spectroscopy of the praseodymium ion in Y3Al5O12
Authors: Özen G. , Forte O. , Di Bartolo B. , Collins J. M.
Published: July 2007

We exploit the upconversion process, utilizing it as a sensitive tool in site-selective spectroscopy of rare earth ion-doped solids. In the Y3Al5O12:Pr3+ praseodymium-doped yttrium aluminum garnet (YAG:Pr) crystals the Pr ions are situated in sites having slightly different environments. Under pulsed excitation into the D21 level, the upconverted emission from the P03 level of each Pr subsystem exhibits its unique, and easily identifiable, response to pulsed excitation, simplifying the process of selectively exciting ions in different sites. Using this technique, we have been able to identify three different sites in a sample of YAG with Pr concentration of 0.5%. We present the physical reasons for the sensitivity of this technique as an example of a useful approach to distinguish among atomic systems residing in slightly dissimilar environments.
Noise correlation-induced splitting of Kramers’ escape rate from a metastable state
Authors: Ghosh Pulak Kumar , Bag Bidhan Chandra , Ray Deb Shankar
Published: July 2007

A correlation between two noise processes driving the thermally activated particles in a symmetric triple-well potential may cause a symmetry breaking and a difference in relative stability of the two side wells with respect to the middle one. This leads to an asymmetric localization of population and splitting of Kramers’ rate of escape from the middle well, ensuring a preferential distribution of the products in the course of a parallel reaction.
On the properties of a primitive semiclassical surface hopping propagator for nonadiabatic quantum dynamics
Authors: Wu Yinghua , Herman Michael F.
Published: July 2007

A previously developed nonadiabatic semiclassical surface hopping propagator [M. F. Herman J. Chem. Phys. 103, 8081 (1995)] is further studied. The propagator has been shown to satisfy the time-dependent Schrödinger equation (TDSE) through order ℏ, and the O(ℏ2) terms are treated as small errors, consistent with standard semiclassical analysis. Energy is conserved at each hopping point and the change in momentum accompanying each hop is parallel to the direction of the nonadiabatic coupling vector resulting in both transmission and reflection types of hops. Quantum mechanical analysis and numerical calculations presented in this paper show that the ℏ2 terms involving the interstate coupling functions have significant effects on the quantum transition probabilities. Motivated by these data, the ℏ2 terms are analyzed for the nonadiabatic semiclassical propagator. It is shown that the propagator can satisfy the TDSE for multidimensional systems by including another type of nonclassical trajectories that reflect on the same surfaces. This ℏ2 analysis gives three conditions for these three types of trajectories so that their coefficients are uniquely determined. Besides the nonadiabatic semiclassical propagator, a numerically useful quantum propagator in the adiabatic representation is developed to describe nonadiabatic transitions.
Theory of polaron resonance in quantum dots and quantum-dot molecules
Authors: Hung K.-M.
Published: July 2007

This work presents the theory of exciton coupling to photons and longitudinal optical (LO) phonons in quantum dots (QDs) and quantum-dot molecules (QDMs). Resonant-round trips of the exciton between the ground (bright) and excited (dark or bright) states, mediated by the LO phonon, alter the decay time and yield the Rabi oscillation. The initial distributions of the population in the ground and the excited states dominate the oscillating amplitude and frequency. This property provides a detectable signature to the information that is stored in a qubit that is made from QD or QDM, over a wide range of temperatures T. The results herein explain the anomaly of T-dependent decay in self-assembled InGaAs/GaAs QDMs, which has recently been experimentally identified.
Relaxation dynamics of Ag4Te3O8 glass nanocomposites embedded with Ag2S nanoparticles
Authors: Dutta D. , Ghosh A.
Published: July 2007

Stable β-Ag2S nanocrystals were dispersed in the Ag4Te3O8 glass network. These β-Ag2S nanocrystals modified the tellurite network by rupturing the Te–O–Te linkages in the tellurite matrix. This structural modification was found to be different from that of the AgI doped silver tellurite glasses. The presence of β-Ag2S nanoparticles was confirmed from the transmission electron micrographs. The structural modification was observed in the Fourier transform infrared spectra of the composites. Electrical properties for these composites were investigated in the temperature range of 125–303K and in the frequency range of 10Hz–2MHz and were compared with those of the AgI doped silver tellurite glass system to shed some light on the influence of Ag2S nanoparticles on the ionic conduction and relaxation in the silver tellurite nanocomposites. The ionic relaxation in this system was also investigated using the electrical modulus formalism. Formation of nanocrystal in this nanocomposite system left some signature on the frequency exponent, crossover frequency, and the relaxation frequency, which became clear when compared with those of the silver tellurite glasses.
Mesoscale scanning probe tips with subnanometer rms roughness
Authors: Xu Dewei , Liechti Kenneth M. , Ravi-Chandar K.
Published: July 2007

Surface smoothness of probe tips is critical for applications, such as measuring surface tension of various liquids, oscillatory hydration forces, and interfacial shear strengths from friction experiments. In this study we establish conditions for fabricating tips with smooth surfaces by controlling the electrochemical polishing process throughout the tip evolution rather than following the current practice of producing tips by the drop-off method. Polishing is conducted under a constant voltage, with the wire immersed below the nominal air/electrolyte interface by no more than one-half of the wire diameter and stopping the etching at different current levels. This process provides a tip radius range of approximately 100nmto5μm for a tungsten wire with a 0.2mm diameter. Alternatively, the wire can be placed above the nominal air/electrolyte interface but within the meniscus until the current drops to zero. In this case, the tip radii range from 5to50μm. In both cases, atomic force microscopy scans of these tips show that the surface rms roughness is about 0.3nm.
Role of the solvent in the dynamical transitions of proteins: The case of the lysozyme-water system
Authors: Mallamace Francesco , Chen Sow-Hsin , Broccio Matteo , Corsaro Carmelo , Crupi Vincenza , Majolino Domenico , Venuti Valentina , Baglioni Piero , Fratini Emiliano , Vannucci Chiara , Stanley H. Eugene
Published: July 2007

We study the dynamics of hydration water in the protein lysozyme in the temperature range 180K<T<360K using Fourier-transform-infrared and nuclear magnetic resonance (NMR) spectroscopies. By analyzing the thermal evolution of spectra of the OH-stretching vibration modes and the NMR self-diffusion (DS) and spin-lattice relaxation time (T1), we demonstrate the existence of two dynamical transitions in the protein hydration water. Below the first transition, at about 220K, the hydration water displays an unambiguous fragile-to-strong dynamic crossover, resulting in the loss of the protein conformational flexibility. Above the second transition, at about 346K, where the protein unfolds, the dynamics of the hydration water appears to be dominated by the non-hydrogen-bonded fraction of water molecules.
AlN air-bridge photonic crystal nanocavities demonstrating high quality factor
Authors: Arita M. , Ishida S. , Kako S. , Iwamoto S. , Arakawa Y.
Published: July 2007

The authors report an achievement of high quality AlN ultraviolet photonic crystal nanocavities. Convex AlN air-bridge structures with embedded GaN quantum dots have been formed by utilizing photoelectrochemical etching of 6H-SiC substrates. Room-temperature microscopic photoluminescence measurements reveal the high quality of the nanocavities. For the lowest-order cavity mode of a 150-nm-period nanocavity with seven missing holes, the highest Q factor (>2400) ever reported in nitride-based photonic crystals has been obtained.
Highly sensitive ZnO nanowire ethanol sensor with Pd adsorption
Authors: Hsueh Ting-Jen , Chang Shoou-Jinn , Hsu Cheng-Liang , Lin Yan-Ru , Chen I.-Cherng
Published: July 2007

The authors report the growth of high-density single crystalline ZnO nanowires on patterned ZnO:Ga∕SiO2∕Si templates, Pd adsorption on nanowire surfaces, and the fabrication of ZnO nanowire-based ethanol gas sensors. With Pd adsorption, it was found that measured sensitivities of the ethanol gas sensors increased from 18.5% to 44.5% at 170°C and increased from 36.0% to 61.5% at 230°C.
Observation of femtojoule optical bistability involving Fano resonances in high-Q∕Vm silicon photonic crystal nanocavities
Authors: Yang Xiaodong , Husko Chad , Wong Chee Wei , Yu Mingbin , Kwong Dim-Lee
Published: July 2007

The authors observe experimentally optical bistability enhanced through Fano interferences in high-Q localized silicon photonic crystal resonances (Q∼30000 and modal volume ∼0.98 cubic wavelengths). This phenomenon is analyzed through nonlinear coupled-mode formalism, including the interplay of χ(3) effects such as two-photon absorption and related free-carrier dynamics, and optical Kerr as well as thermal effects and linear losses. Experimental and theoretical results demonstrate Fano resonance based bistable states with switching thresholds of 185μW and 4.5fJ internally stored cavity energy (∼540fJ consumed energy) in silicon for scalable optical buffering and logic.
Electric-pulse-induced resistive switching effect enhanced by a ferroelectric buffer on the Pr0.7Ca0.3MnO3 thin film
Authors: Xing Z. W. , Wu N. J. , Ignatiev A.
Published: July 2007

An enhanced electric-pulse-induced resistance (EPIR) switching effect is observed in the Ag∕Pb0.7Zr0.3TiO3∕Pr0.7Ca0.3MnO3∕YBa2Cu3O7 (Ag/PZT/PCMO/YBCO) structures. Compared with the Ag/PCMO/YBCO devices, the insertion of the PZT buffer into the Ag/PCMO interface is found to greatly increase the EPIR ratio and significantly decrease the threshold pulse voltage necessary to switching the resistive device decrease. They are attributed to the resistive change of the depletion region at the Ag/PCMO interface including the PZT buffer, in which ferroelectric polarizations play a crucial role in the enhanced EPIR switching effect.
Molecular simulation of adsorption and diffusion of chlorinated alkenes in ZSM-5 zeolites
Authors: Göktug Ahunbay M.
Published: July 2007

In this work, adsorption and diffusion of trichloroethylene (TCE) and tetrachloroethylene (PCE) in ZSM-5-type zeolites were studied using molecular simulation methods. Grand canonical Monte Carlo technique was to calculate adsorption isotherms and heats of vaporization of TCE and PCE in zeolite. The results demonstrated that the Pnma-P212121 symmetry transition of the zeolite framework has no significant effect on the TCE adsorption capacity of the silicalite, but it causes an increase of the PCE adsorption capacity. Simulations using a silicalite framework with Pnma symmetry showed that the adsorption capacity of the silicalite was limited to five molecules per unit cell. However, when a framework with P212121 symmetry was used in the simulations, the capacity reached to eight molecules per unit cell, which is the actual adsorption capacity. To calculate intracrystalline diffusion coefficients of these compounds, molecular dynamics simulations were performed at different temperatures and loadings. The results show that the zeolite symmetry has a significant impact on diffusion coefficients of the sorbate molecules.
Ultraviolet electro-optic amplitude modulation in β-BaB2O4 waveguides
Authors: Degl’Innocenti R. , Majkic A. , Vorburger P. , Poberaj G. , Günter P. , Döbeli M.
Published: July 2007

The authors report on the realization of an electro-optical amplitude modulator based on β-BaB2O4 (BBO) waveguide operating in the ultraviolet wavelength range down to 257nm. The ridge waveguides are produced by He+ implantation, photolithography masking, and plasma etching. Electrodes are deposited by the standard lift-off technique. A minimum half-wave voltage times modulator length Vπ×1 of 43Vcm has been demonstrated at 257nm in a 6.5-mm-long modulator. Because of BBO’s broad transparency range (190–3500nm), such device could be employed in the deep ultraviolet with Vπ×1 estimated to reach 24Vcm at 200nm.
Nonlinear optical properties of thiol-capped CdTe quantum dots in nonresonant region
Authors: Pan Lingyun , Tamai Naoto , Kamada Kenji , Deki Shigehito
Published: July 2007

Size-dependent χ(3) of water-soluble thiol-capped CdTe quantum dots (QDs) in nonresonant region has been examined by Z-scan and degenerate four-wave mixing experiments. Two-photon absorption cross section as high as 104GM was observed for 4.9nm sized CdTe QDs. Both imaginary and real parts of χ(3) were found to increase with QD size. Compared with the bulk CdTe semiconductor, 30 times enhancement of nonlinear figures of merit defined by ReχQD(3)∕ImχQD(3) was found for 3.1nm CdTe QDs in nonresonant excitation.
All-optical format conversion using a periodically poled lithium niobate waveguide and a reflective semiconductor optical amplifier
Authors: Wang Jian , Sun Junqiang , Sun Qizhen , Wang Dalin , Zhou Minjuan , Zhang Xinliang , Huang Dexiu , Fejer M. M.
Published: July 2007

In the present letter, the authors report on the realization of all-optical format conversion by using the cascaded sum- and difference-frequency generation in a periodically poled lithium niobate waveguide and the active mode locking in a reflective-semiconductor-optical-amplifier-based fiber ring laser. Tunable format conversions from nonreturn-to-zero pseudorandom binary sequence (PRBS) signal to return-to-zero PRBS idler at 10 and 20Gbit∕s are observed in the experiment.
Influence of lateral electric fields on multiexcitonic transitions and fine structure of single quantum dots
Authors: Vogel M. M. , Ulrich S. M. , Hafenbrak R. , Michler P. , Wang L. , Rastelli A. , Schmidt O. G.
Published: July 2007

The quantum-confined Stark effect of excitonic states in self-assembled (In,Ga)As∕GaAs quantum dots was studied by microphotoluminescence spectroscopy. A similar Stark-shift behavior for excitons, biexcitons, and a charged state was observed. Investigations suggest the absence of a permanent dipole moment in the lateral quantum dot plane. Values of the polarizability could be derived for all the investigated states. Furthermore, high-resolution Fabry-Pérot interferometry was applied to resolve the excitonic fine structure splitting and to investigate the influence of a lateral electric field. For a single dot, the splitting could be tuned to zero, thus affording the possibility to create electrically controlled entangled photon pairs.
Correlation of edge roughness to nucleation field and nucleation field distribution in patterned Permalloy elements
Authors: Lau J. W. , McMichael R. D. , Schofield M. A. , Zhu Y.
Published: July 2007

The effects of edge roughness on vortex nucleation field and its distribution are measured in Permalloy nanostructured arrays. Teardrop-shaped elements, 250 nm wide and 30 nm thick, were fabricated using electron beam lithography and lift-off. Roughness variations were created by varying the electron dose during patterning, and measured by analysis of in-focus transmission electron microscopy (TEM) images. In situ measurements of the vortex nucleation fields and the nucleation field distributions of the dose arrays were performed with Lorentz mode TEM. In combining the measurements of edge roughness with measurements of nucleation field and its distribution, we show that edge roughness increases the probability for vortex nucleation and thus permits vortices to nucleate at larger applied fields, but at the same time, edge roughness broadens the nucleation-field distribution in magnetic nanostructured arrays.
Heating rate effects in the transient nucleation problem
Authors: Shneidman Vitaly A.
Published: July 2007

The matched asymptotic (singular perturbation) treatment of the nucleation equation [V. A. Shneidman, Sov. Phys. Tech. Phys. 32, 76 (1987); 33, 1338 (1988)] is modified to include finite heating rate effects, which follow the isothermal transient stage. Despite the complicated mathematical structure of the discrete Becker-Döring equation, the obtained analytical solution is shown to be accurate numerically. The described situation is typical for two-step annealing crystallization studies and can lead to reinterpretation of some of the classical experiments.
Chemical bath deposition of CdS quantum dots onto mesoscopic TiO2 films for application in quantum-dot-sensitized solar cells
Authors: Chang Chi-Hsiu , Lee Yuh-Lang
Published: July 2007

Alcohol, instead of water, was used as a solvent in a chemical bath deposition process for the in situ synthesis of CdS quantum dots onto mesoporous TiO2 films. Due to low surface tension, the alcohol solutions have high wettability and superior penetration ability on the mesoscopic TiO2 film, leading to a well-covered CdS on the surface of mesopores. The CdS-sensitized TiO2 electrode prepared using the alcohol system not only has a higher incorporated amount of CdS but also greatly inhibits the recombination of injected electrons. The efficiency of a CdS quantum-dots-sensitized solar cell prepared using the present method is as high as 1.84% under the illumination of one sun (AM1.5, 100mW∕cm2).