bluuebunny/crossref_metadata_2025 huggingface dataset:
TWO STEPS FORWARD
Authors: Wong Janelle
Published: June 2008

In this essay, I contend that one can understand neither the development of mass action among contemporary immigrants, nor the sporadic nature of that action, without attending to the historic role of parties and community-based organizations in shaping immigrants' political mobilization. I draw connections between the mass immigrant-rights demonstrations that took place during the spring of 2006 and what we know about how immigrants' political participation in the United States is structured by (1) the declining influence of political parties, and (2) the critical function of community-based organizations. These organizations were the focus of my recent book,Democracy's Promise: Immigrants and American Civic Institutions(2006). Why haven't activists been able to sustain the momentum that brought hundreds of thousands of immigrants and their supporters out into the streets during the spring of 2006? Although they, along with the Spanish-language media, played a critical role in organizing mass demonstrations against punitive immigration legislation in early 2006, labor organizations, workers' centers, advocacy and social service organizations, ethnic voluntary associations, and religious institutions face severe constraints in terms of engaging in sustained, consistent political mobilization and, therefore, mainly achieve limited mobilization. However, voter registration data from the National Association of Latino Elected Officials suggest that the demonstrations may have spurred interest in more traditional types of political participation among immigrants and their supporters. Thus, while it is true that, for the most part, political participation does not take place overnight, there may be ways for U.S. civic institutions to speed up that process through direct mobilization and the provision of information that helps immigrants to feel more comfortable and confident taking part in the political system. Trusted community-based institutions represent a vital potential force in promoting political inclusion for immigrant newcomers who contribute to so many other aspects of American life.
Structure, institution, agency, habit, and reflexive deliberation
Authors: FLEETWOOD STEVE
Published: June 2008

The conceptual apparatus referred to generally as agency-structure or agency-institution is central to a great deal of social science, especially Institutional Economics. Despite its centrality, this apparatus has never been able to fully explain how institutions and social structures influence agents' intentions and actions. Economist, Geoff Hodgson and Sociologist, Margaret Archer have been at the forefront of endeavours to provide such an explanation. Section 1 of this paper elaborates upon Hodgson's ideas on institutional rules, habits, habituation, and the notion of reconstitutive downward causation. Section 2 elaborates upon Archer's ideas on structures, reflexive deliberation and the notion of an internal domain of mental primacy, and ends with a critical look at Archer's (brief) comments on rules and habits. The conclusion shows how a more nuanced understanding of structures, institutions, agency, habits, and deliberation, can inform research into a specific area, namely the analysis of labour markets.
Observation of particle fall velocity in cirriform cloud by VHF and millimeter‐wave Doppler radars
Authors: Yamamoto Masayuki K. , Ohno Yuichi , Horie Hiroaki , Nishi Noriyuki , Okamoto Hajime , Sato Kaori , Kumagai Hiroshi , Yamamoto Mamoru , Hashiguchi Hiroyuki , Mori Shuichi , Hashiguchi Noriko O. , Nagata Hajime , Fukao Shoichiro
Published: June 2008

In this study, it is demonstrated that a combination of VHF and millimeter‐wave Doppler radars is a key tool for observing particle fall velocity in cirriform clouds. VHF (47‐MHz) and millimeter‐wave (95‐GHz) Doppler radars observed cirriform clouds at West Sumatra, Indonesia (0.2°S, 100.32°E) from 2000 LT 14 to 0800 LT 15 November 2005. Radar reflectivity factor (Ze) observed by the 95‐GHz radar showed that echoes from cloud particles had tops around 12–14 km and bottoms around 8–10 km. Doppler velocity observed by the vertically pointed beam of the 95‐GHz radar (Vair+Z) was compared with vertical air velocity (Vair) observed by the 47‐MHz radar to confirm that Vair+Z, a sum of Vair and reflectivity‐weighted particle fall velocity (VZ), showed consistent changes with Vair and hence VZ is able to be retrieved by subtracting Vair from Vair+Z. The correlation coefficient between VZ and Ze in the middle part of clouds (10.5–12.2 km) was −0.81, which was higher than that (−0.47) in the bottom part (7.2–10.5 km). The change of VZ for Ze in the middle part was larger (Ze = −31.9 VZ − 32.2) than that in the bottom part (Ze = −90.2 VZ − 71.8). These results suggest that particle size was a dominant factor that determined Ze in the middle part. Using VZ, median volume diameter (D0) was estimated to suggest that D0 was larger than ∼70 μm in the bottom part and ranged from ∼40 μm to larger than ∼106 μm in the middle part.
Influence of sea surface temperature on soil moisture and precipitation interactions over the southwest
Authors: Mo Kingtse C.
Published: June 2008

This paper presents a hypothesis that soil moisture (SM) and precipitation (P) interactions over the Southwest depend on sea surface temperature anomalies (SSTAs). On the basis of moisture transport and geography, the Southwest can be separated into two regions. The western region (32°–36°N, 107.5°–113°W) includes Arizona and western New Mexico and the eastern region (32°–36°N, 103°–107°W) includes eastern New Mexico. For both regions, years from 1900 to 2004 are classified based on the winter to summer P evolution. When winter and the following summer P anomalies have an inverse relationship, SSTAs do not persist. The summer SSTAs have strong influence on P. Soil moisture does not play a major role in modulating P anomalies. For cases that wetness (dryness) occurs in both winter and the following summer, the SSTA forcing associated with the P regime tends to persist. Positive SM‐P feedbacks enhance P anomalies. For eastern New Mexico, there is a linear relationship between SM anomalies in spring and P anomalies in summer when SSTAs persist.
Isotope ratios of precipitation and water vapor observed in Typhoon Shanshan
Authors: Fudeyasu H. , Ichiyanagi K. , Sugimoto A. , Yoshimura K. , Ueta A. , Yamanaka M. D. , Ozawa K.
Published: June 2008

Isotope ratios of precipitation and water vapor were observed during the passage of Typhoon Shanshan at Ishigaki Island, southwestern Japan, on 15–16 September 2006. Such high‐resolution isotopic observations allow for qualitative understanding of atmospheric moisture cycling; they revealed that isotope ratios of both the precipitation and water vapor decreased radially inward in the cyclone's outer region; anomalously high isotope ratios appeared in the cyclone's inner region; and d‐excess tended to decrease in the cyclone's inner region. In the cyclone's outer region, the water vapor was isotopically depleted due to the rainout effect which involves both condensation efficiency as reflected in inwardly increasing cloud thickness and isotopic exchange between falling droplets and the ambient water vapor. In contrast, water vapor in the cyclone's inner region was isotopically enriched due to weak rainout effect in conjunction with intensive isotopic recharge from the sea spray and sea surface with heavy isotope ratios. Since water vapor mainly acts as a source of precipitation, the isotope ratios of precipitation also had systematic variation. A unique circumstance is the intensity of isotopic exchange with almost saturated surface air and high winds, causing anomalously high isotope ratios and low d‐excess values in the cyclone's inner region.
A study of anthropogenic impacts of the radiation budget and the cloud field in East Asia based on model simulations with GCM
Authors: Mukai Makiko , Nakajima Teruyuki , Takemura Toshihiko
Published: June 2008

We investigated the effects of man‐made air pollutants on the climate of East Asia, focusing on eastern China where anthropogenic aerosol concentrations are rapidly increasing. The increasing emission of anthropogenic aerosols causes serious air pollution episodes and various effects on the climate in this region. It is therefore necessary to quantify the contribution of aerosols to the change in the radiation budget and the cloud field. Our purpose of this study is to evaluate the sensitivity of anthropogenic aerosols and other anthropogenic factors such as greenhouse gas (GHG) upon the radiative forcing. Then an aerosol transport model coupled to a general circulation model and an ocean mixed‐layer model was used to investigate the relationships among the anthropogenic aerosol forcing, GHG forcing, surface radiation budget, and cloud field. Our simulation results showed that copious anthropogenic aerosol loading causes significant decrease in the surface downward shortwave radiation flux (SDSWRF), which indicates that a direct effect of aerosols has the greatest influence on the surface radiation. It is found from our model simulations that low‐level clouds increase but convective clouds decrease due to reduced convective activity caused by surface cooling when anthropogenic aerosol increases, and GHG increase has an insignificant effect on SDSWRF but a significant effect on the cloud field. In other word model simulations suggested that the aerosol forcing mainly causes a reduction of SDSWRF, whereas the change in the cloud field is influenced both anthropogenic aerosol and GHG effects. Thus this work demonstrated with sensitivity experiments the importance of aerosols to cause significant climate effects in the East Asian region, though further study is needed because our study is based on results from one specific model and limited data analysis.
Analyzing the detection capability of infrasound arrays in Central Europe
Authors: Le Pichon Alexis , Vergoz Julien , Herry Pascal , Ceranna Lars
Published: June 2008

This paper demonstrates the usefulness of continuous infrasound monitoring on regional scales to advance the development of automated source location procedures, as well as provide new insights into quantitative relationships between network detection capabilities and atmospheric specification. To achieve these goals, ground truth events in regions of dense infrasound networks must be considered. The infrasound network of the International Monitoring System (IMS) of the Comprehensive Nuclear‐Test Ban Treaty Organization (CTBTO), while currently not fully established, has demonstrated its capability for locating infrasonic sources on a global scale, including meteorites and volcanic eruptions. This paper considers continuous records made by dense networks in Central Europe that are not part of the IMS. It shows the potentiality for future seismo‐acoustic monitoring system to be used for discriminating between natural and artificial acoustic sources, and confirms that most of the detected infrasound energy propagates in the ground to stratospheric waveguide.
Simulating Martian boundary layer water ice clouds and the lidar measurements for the Phoenix mission
Authors: Pathak Jagruti , Michelangeli Diane V. , Komguem Leonce , Whiteway James , Tamppari Leslie K.
Published: June 2008

Diurnal variation of ground fog and water ice cloud formation at the NASA Phoenix lander site is investigated using a one‐dimensional Mars Microphysical Model (MMM) coupled with the results from the one‐dimensional University of Helsinki atmospheric boundary layer (ABL) model. Phoenix is scheduled to reach Mars in May 2008 and land in the northern plains (65°–72°N). Observations from Mars Global Surveyor Thermal Emission Spectrometer for the proposed landing site and season Ls = 76°–125° have been used for the model initialization, both in the ABL and MMM. The diurnal variations of temperature and eddy diffusion coefficients produced by the uncoupled ABL are then applied to the MMM. Extinction and backscattering coefficients and lidar ratios are presented for the simulated dust and water ice clouds at the Phoenix location. Results of the dust and ice clouds are then used to simulate the Phoenix lidar measurements at two wavelengths, 532 and 1064 nm.
Depth selective Mössbauer spectroscopy: Analysis and simulation of 6.4 keV and 14.4 keV spectra obtained from rocks at Gusev Crater, Mars, and layered laboratory samples
Authors: Fleischer I. , Klingelhöfer G. , Schröder C. , Morris R. V. , Hahn M. , Rodionov D. , Gellert R. , de Souza P. A.
Published: June 2008

The miniaturized Mössbauer spectrometer (MIMOS) II Mössbauer spectrometers on the Mars Exploration Rovers (MER) simultaneously obtained 6.4 keV and 14.4 keV Mössbauer spectra from rock and soil targets. Because photons with lower energy have a shallower penetration depth, 6.4 keV spectra contain more mineralogical information about the near‐surface region of a sample than do 14.4 keV spectra. The influence of surface layers of varying composition and thickness on Mössbauer spectra was investigated by Monte Carlo simulation and by measurement using a copy of the MER MIMOS II instrument and samples with one or two layers of known thicknesses. Thin sections of minerals or metallic Fe foil on top of a thick mineral sample were used to produce samples with thin layers of known thickness on a thick substrate. Monte Carlo simulation of MER spectra obtained on the rock Mazatzal, which displays a coating on a basaltic substrate, and other Adirondack Class rocks results in a calculated thickness of 10 μm for the Mazatzal surface layer. The 6.4 keV spectra obtained on Adirondack Class rocks, on laboratory samples, and in Monte Carlo calculations show an apparent olivine enrichment which is not related to any observable surface layer.
Phoenix surface mission operations processes
Authors: Bass Deborah S. , Talley Kevin P.
Published: June 2008

We present an overview of Phoenix Mars Scout Mission (Phoenix) surface operations process design with an emphasis on the science portion of the process. We describe the drivers and constraints on Phoenix operations and the resulting choices that the development team made to accommodate these constraints. The two most important drivers on Phoenix operations are the choice of orbiter relay only for data and the limited amount of data storage on the lander. These two combine to regulate the amount of data the spacecraft can collect, save, and transmit on any given sol. We discuss the interplay between the daily (tactical) and long‐term/multiday (strategic) processes and finish with lessons learned for future mission operations design. Integration of mostly complete engineering requirements toward the front end of the tactical process, as well as the multiday nature of science acquisition, results in particular design decisions that have not been incorporated in previous ground operations planning.
Mg/Ca–temperature proxy in benthic foraminifera: New calibrations from the Florida Straits and a hypothesis regarding Mg/Li
Authors: Bryan Sean P. , Marchitto Thomas M.
Published: June 2008

Over the past decade, the ratio of Mg to Ca in foraminiferal tests has emerged as a valuable paleotemperature proxy. However, large uncertainties remain in the relationships between benthic foraminiferal Mg/Ca and temperature. Mg/Ca was measured in benthic foraminifera from 31 high‐quality multicore tops collected in the Florida Straits, spanning a temperature range of 5.8° to 18.6°C. New calibrations are presented for Uvigerina peregrina, Planulina ariminensis, Planulina foveolata, and Hoeglundina elegans. The Mg/Ca values and temperature sensitivities vary among species, but all species exhibit a positive correlation that decreases in slope at higher temperatures. The decrease in the sensitivity of Mg/Ca to temperature may potentially be explained by Mg/Ca suppression at high carbonate ion concentrations. It is suggested that a carbonate ion influence on Mg/Ca may be adjusted for by dividing Mg/Ca by Li/Ca. The Mg/Li ratio displays stronger correlations to temperature, with up to 90% of variance explained, than Mg/Ca alone. These new calibrations are tested on several Last Glacial Maximum (LGM) samples from the Florida Straits. LGM temperatures reconstructed from Mg/Ca and Mg/Li are generally more scattered than core top measurements and may be contaminated by high‐Mg overgrowths. The potential for Mg/Ca and Mg/Li as temperature proxies warrants further testing.
Contrasts in hydrology between regions of basal deformation and sliding beneath Rutford Ice Stream, West Antarctica, mapped using radar and seismic data
Authors: Murray T. , Corr H. , Forieri A. , Smith A. M.
Published: June 2008

Spatially coincident radar and seismic data collected two weeks apart on Rutford Ice Stream were analyzed to investigate the mechanical and hydrological characteristics of the ice‐bed interface. Seismic data allow the differentiation of bed deformation from basal sliding. In radar data, sliding regions are characterised by highly variable permittivity values. We suggest these regions are characterized by small water bodies, possibly a cavity system. In contrast, deforming regions are characterised by consistent, low permittivity, which suggests intimate ice‐sediment contact without a distinct interface. However, in deforming regions we identified three bright radar features ∼50 m wide, consistent in lateral location over distances of 5–10 km up and downstream, and comprised of water less than ∼0.2 m deep. We interpret these as part of a water evacuation system, most likely canals. Our results emphasise the great potential of radar and seismic techniques in combination to infer basal conditions beneath ice streams.
Total Cerebral Blood Flow in Relation to Cognitive Function: The Rotterdam Scan Study
Authors: Poels Mariëlle MF , Ikram Mohammad Arfan , Vernooij Meike W , Krestin Gabriel P , Hofman Albert , Messen Wiro J , van der Lugt Aad , Breteler Monique MB
Published: June 2008

Cerebral hypoperfusion has been associated with worse cognitive function. We investigated the association between cerebral blood flow and cognition and whether this association is independent of brain volume. In 892 participants, aged 60 to 91 years, of the population-based Rotterdam Scan study, we measured total cerebral blood flow (tCBF) and brain volume using magnetic resonance imaging. Lower tCBF was associated with worse information-processing speed, executive function, and global cognition. However, after correcting tCBF for brain volume, these associations disappeared. The association between tCBF and cognition may be mediated or confounded by brain atrophy. Future studies on tCBF should take into account brain atrophy.
Cerebral Mitochondrial Metabolism in Early Parkinson's Disease
Authors: Powers William J , Videen Tom O , Markham Joanne , Black Kevin J , Golchin Nima , Perlmutter Joel S
Published: June 2008

Abnormal cerebral energy metabolism owing to dysfunction of mitochondrial electron transport has been implicated in the pathogenesis of Parkinson's disease (PD). However, in vivo data of mitochondrial dysfunction have been inconsistent. We directly investigated mitochondrial oxidative metabolism in vivo in 12 patients with early, never-medicated PD and 12 age-matched normal controls by combined measurements of the cerebral metabolic rate of oxygen (CMRO2) and the cerebral metabolic rate of glucose (CMRglc) with positron emission tomography. The primary analysis showed a statistically significant 24% increase in bihemispheric CMRO2 and no change in CMRO2/CMRglc. These findings are inconsistent with a defect in mitochondrial oxidative phosphorylation owing to reduced activity of the mitochondrial electron transport system (ETS). Because PD symptoms were already manifest, deficient energy production owing to a reduced activity of the mitochondrial ETS cannot be a primary mechanism of neuronal death in early PD. Alternatively, this general increase in CMRO2 could be due not to an increased metabolic demand but to an uncoupling of ATP production from oxidation in the terminal stage of oxidative phosphorylation. Whether this is the case in early PD and whether it is important in the pathogenesis of PD will require further study.
Role of CX3CR1 (Fractalkine Receptor) in Brain Damage and Inflammation Induced by Focal Cerebral Ischemia in Mouse
Authors: Dénes Ádám , Ferenczi Szilamér , Halász József , Környei Zsuzsanna , Kovács Krisztina J
Published: June 2008

CX3CR1 (fractalkine receptor) is important for sustaining normal microglial activity in the brain. Lack of CX3CR1 reportedly results in neurotoxic microglial phenotype in disease models. The objective of this study was to test the hypothesis that the absence of CX3CR1 worsens the outcome in cerebral ischemia. We observed significantly smaller (56%) infarcts and blood—brain barrier damage in CX3CR1-deficient (CX3CR1−/−) animals compared with CX3CR1 +/− and wild-type mice after transient occlusion of the middle cerebral artery (MCAo). Functional recovery of CX3CR1−/−animals was enhanced, while less number of apoptotic cells and infiltrating leukocytes were found in the ipsilateral hemisphere. Expression of IL-1β mRNA, protein, and interleukin (IL)-1Ra and tumor necrosis factor (TNF)-α mRNAs was lower in CX3CR1−/− mice, whereas no difference was observed in the number of IL-1β-expressing microglia or plasma IL-1β concentration. We observed early IL-1β expression in astrocytes in vivo after MCAo and after oxygen—glucose deprivation in vitro, which might contribute to the ischemic damage. Our findings indicate that lack of CX3CR1 does not result in microglial neurotoxicity after MCAo, but rather significantly reduces ischemic damage and inflammation. Reduced IL-1β and TNFα expression as well as decreased leukocyte infiltration might be involved in the development of smaller infarcts in CX3CR1−/− animals.
Dinucleotide polyphosphates contribute to purinergic signalling via inhibition of adenylate kinase activity
Authors: Yegutkin Gennady G. , Jankowski Joachim , Jalkanen Sirpa , Günthner Thomas , Zidek Walter , Jankowski Vera
Published: June 2008

Dinucleoside polyphosphates are well described as direct vasoconstrictors and as mediators with strong proliferative properties, however, less is known about their effects on nucleotide-converting pathways. Therefore, the present study investigates the effects of Ap4A (diadenosine tetraphosphate), Up4A (uridine adenosine tetraphosphate) and Ap5A (diadenosine pentaphosphate) and the non-selective P2 antagonist suramin on human serum and endothelial nucleotide-converting enzymes. Human serum and HUVECs (human umbilical vein endothelial cells) were pretreated with various concentrations of dinucleotide polyphosphates and suramin. Adenylate kinase and NDP kinase activities were then quantified radiochemically by TLC analysis of the ATP-induced conversion of [3H]AMP and [3H]ADP into [3H]ADP/ATP and [3H]ATP respectively. Endothelial NTPDase (nucleoside triphosphate diphosphohydrolase) activity was additionally determined using [3H]ADP and [3H]ATP as preferred substrates. Dinucleoside polyphosphates and suramin have an inhibitory effect on the serum adenylate kinase [pIC50 values (−log IC50): Ap4A, 4.67±0.03; Up4A, 3.70±0.10; Ap5A, 6.31±0.03; suramin, 3.74±0.07], as well as on endothelial adenylate kinase (pIC50 values: Ap4A, 4.17±0.07; Up4A, 2.94±0.02; Ap5A, 5.97±0.04; suramin, 4.23±0.07), but no significant effects on serum NDP kinase, emphasizing the selectivity of these inhibitors. Furthermore, Ap4A, Up4A, Ap5A and suramin progressively inhibited the rates of [3H]ADP (pIC50 values: Ap4A, 3.38±0.09; Up4A, 2.78±0.06; Ap5A, 4.42±0.11; suramin, 4.10±0.07) and [3H]ATP (pIC50 values: Ap4A, 3.06±0.06; Ap5A, 3.05±0.12; suramin, 4.14±0.05) hydrolyses by cultured HUVECs. Up4A has no significant effect on the endothelial NTPDase activity. Although the half-lives for Ap4A, Up4A and Ap5A in serum are comparable with the incubation times of the assays used in the present study, secondary effects of the dinucleotide metabolites are not prominent for these inhibitory effects, since the concentration of metabolites formed are relatively insignificant compared with the 800 μmol/l ATP added as a phosphate donor in the adenylate kinase and NDP kinase assays. This comparative competitive study suggests that Ap4A and Ap5A contribute to the purinergic responses via inhibition of adenylate-kinase-mediated conversion of endogenous ADP, whereas Up4A most likely mediates its vasoregulatory effects via direct binding-mediated mechanisms.
Basic Principles of Language Intervention for Children Who Use AAC
Authors: Loncke Filip
Published: June 2008

The study of language acquisition and processing and the practice of augmentative and alternative communication (AAC) intervention have a mutual beneficial impact. Each of the three major approaches in explaining language acquisition (rationalistic, empiricist, and functionalist) provides interesting perspectives in understanding the uniqueness of language acquisition through AAC. When looking at language processing, studies of AAC use can provide information on the multimodality and internal multimodal representational networks.

The study of the main language components (phonology, morphology and syntax, lexicon) in AAC users raises interesting questions concerning (a) the effect of the use of a speech-generating device on an internal phonology, (b) the relation between morphological and syntactic rules and communicative effectiveness, and (c) the effect of the use of communication boards and devices on lexical development and lexical growth.

AAC practice is a potential source of data that can lead to more effective intervention as well as to a better understanding of language processes in general.
Language Acquisition Theory and AAC Intervention
Authors: Sutton Ann
Published: June 2008

This article presents a reflection on the relationship between language acquisition theories and augmentative and alternative (AAC) intervention, particularly related to grammar. Aspects of the language-learning situation for children needing AAC and of production of language using an AAC system that may pose challenges for acquisition of grammar are discussed. The implications for AAC intervention that can be drawn from several language acquisition theories are explored. It is suggested that establishing clearer or more overt links between theories and intervention is important in order to make underlying assumptions more explicit and to be aware of the theoretical underpinnings of AAC intervention.
Grammatical Morpheme Intervention Issues for Students Who Use AAC
Authors: Binger Cathy
Published: June 2008

Many children who use AAC experience difficulties with acquiring grammar. At the 9th Annual Conference of ASHA's Special Interest Division 12, Augmentative and Alternative Communication, Binger presented recent research results from an intervention program designed to facilitate the bound morpheme acquisition of three school-aged children who used augmentative and alternative communication (AAC). Results indicated that the children quickly began to use the bound morphemes that were taught; however, the morphemes were not maintained until a contrastive approach to intervention was introduced. After the research results were presented, the conference participants discussed a wide variety of issues relating to grammar acquisition for children who use AAC. Some of the main topics of discussion included the following: provision of supports for grammar comprehension and expression, intervention techniques to support grammatical morpheme acquisition, and issues relating to AAC device use when teaching grammatical morpheme use.
Turbulent transport of beam ions
Authors: Dannert T. , Günter S. , Hauff T. , Jenko F. , Lapillonne X. , Lauber P.
Published: June 2008

The radial redistribution of energetic ions by background turbulence is investigated by means of linear and nonlinear gyrokinetic simulations with the GENE code [T. Dannert and F. Jenko, Phys. Plasmas 12, 072309 (2005)]. The fast particles are described by an asymmetric and anisotropic Maxwellian distribution function, and they are treated as passive tracers. It is found that there can be a significant fast ion diffusivity for particle energies up to about 10 times the thermal energy, with details depending on the properties of the magnetic geometry and of the microinstabilities driving the turbulence. This finding provides a possible explanation of experimental results concerning the efficiency of neutral beam current drive reported recently from ASDEX Upgrade [S. Günter et al., Nucl. Fusion 47, 920 (2007)].
Nonconventional morphologies in two-length scale block copolymer systems beyond the weak segregation theory
Authors: Kriksin Yury A. , Erukhimovich Igor Ya. , Khalatur Pavel G. , Smirnova Yuliya G. , ten Brinke Gerrit
Published: June 2008

The order-disorder and order-order transitions (ODT and OOT) in the linear multiblock copolymers with two-length scale architecture AfmN(BN∕2AN∕2)nB(1−f)mN are studied under intermediate cooling below the ODT critical point where a nonconventional sequence of the OOTs was predicted previously [Smirnova et al., J. Chem. Phys. 124, 054907 (2006)] within the weak segregation theory (WST). To describe the ordered morphologies appearing in block copolymers (BCs) under cooling, we use the pseudospectral version of the self-consistent field theory (SCFT) with some modifications providing a good convergence speed and a high precision of the solution due to using the Ng iterations [J. Chem. Phys. 61, 2680 (1974)] and a reasonable choice of the predefined symmetries of the computation cell as well as initial guess for the iterations. The WST predicted sequence of the phase transitions is found to hold if the tails of the BCs under consideration are symmetric enough (∣0.5−f∣⩽0.05); the quantitative agreement between the WST and SCFT phase diagrams is reasonable in a narrow (both in f and χ̃=χN) region close to the critical point, though. For ∣0.5−f∣>0.05, a large region of the face-centered cubic phase stability is found (up to our knowledge, first within the SCFT framework) inside of the body-centered cubic phase stability region. Occurrence of the two-dimensional and three-dimensional phases with the micelles formed, unlike the conventional diblock copolymers, by the longer (rather than shorter) tails, and its relationship to the BC architecture is first described in detail. The calculated spectra of the ordered phases show that nonmonotonous temperature dependence of the secondary peak scattering intensities accompanied by their vanishing and reappearance is rather a rule than exception.
Surface tank treading: Propulsion of Purcell’s toroidal swimmer
Authors: Leshansky A. M. , Kenneth O.
Published: June 2008

In this work we address the “smoking ring” propulsion technique, originally proposed by Purcell [Am. J. Phys. 45, 3 (1977)] for self-locomotion at low Reynolds numbers. We first consider self-locomotion of a doughnut-shaped swimmer powered by surface rotation. Different modes of surface motion are assumed and propulsion velocity and swimming efficiency are determined. The swimmer is propelled against the direction of its outer surface motion, the inner surface having very little effect. The simplest swimming mode corresponding to constant angular velocity can achieve propulsion speeds of up to 66% of the surface tank-treading velocity and swimming efficiency of up to 13%. Higher efficiency is possible for more complicated modes powered by nonuniform twirling of extensible surface. A practical design of a necklace-shaped swimmer motivated by Purcell’s idea is proposed and demonstrated numerically. Finally, the explicit solution is found for the two-dimensional swimmer composed of two counter-rotating disks, using complex variable techniques.
Core molecule dependence of energy migration in phenylacetylene nanostar dendrimers: Ab initio molecular orbital–configuration interaction based quantum master equation study
Authors: Kishi Ryohei , Minami Takuya , Fukui Hitoshi , Takahashi Hideaki , Nakano Masayoshi
Published: June 2008

The core molecule dependence of energy (exciton) migration in phenylacetylene nanostar dendrimers is investigated using the ab initio molecular orbital (MO)–configuration interaction based quantum master equation approach. We examine three kinds of core molecular species, i.e., benzene, anthracene, and pentacene, with different highest occupied MO–lowest unoccupied MO (HOMO-LUMO) gaps, which lead to different orbital interactions between the dendron parts and the core molecule. The nanostars bearing anthracene and pentacene cores are characterized by multistep exciton states with spatially well-segmented distributions: The exciton distributions of high-lying exciton states are spatially localized well in the periphery region, whereas those of low-lying exciton states are done in the core region. On the other hand, for the nanostar bearing benzene core, which also has multistep exciton states, the spatial exciton distributions of low-lying exciton states are delocalized over the dendron and the core regions. It is found that the former nanostars exhibit nearly complete exciton migration from the periphery to the core molecule in contrast to the latter one, in which significant exciton distribution remains in the dendron parts attached to the core after the exciton relaxation, although all these dendrimers exhibit fast exciton relaxation from the initially populated states. It is predicted from the analysis based on the MO correlation diagrams and the relative relaxation factor that the complete exciton migration to the core occurs not only when the HOMO-LUMO gap of the core molecule is nearly equal to that of the dendron parts attached to the core (anthracene case) but also when fairly smaller than that (pentacene case), whereas the complete migration is not achieved when the HOMO-LUMO gap of the core is larger than that of the dendron parts (benzene case). These results suggest that the fast and complete exciton migration of real dendrimers could be realized by adjusting the HOMO-LUMO gap of the core molecule to be smaller than that of dendron parts, although there exist more complicated relaxation processes as compared to simple dendritic aggregate models studied so far.
Effect of the intrinsic width on the piezoelectric force microscopy of a single ferroelectric domain wall
Authors: Morozovska Anna N. , Eliseev Eugene A. , Svechnikov George S. , Gopalan Venkatraman , Kalinin Sergei V.
Published: June 2008

Intrinsic domain wall width is a fundamental parameter that reflects bulk ferroelectric properties and governs the performance of ferroelectric memory devices. We present closed-form analytical expressions for vertical and lateral piezoelectric force microscopy (PFM) profiles of a single ferroelectric domain wall for the conical and disk models of the tip, beyond point charge and sphere approximations. The analysis takes into account the finite intrinsic width of the domain wall and dielectric anisotropy of the material. These analytical expressions provide insight into the mechanisms of PFM image formation and can be used for a quantitative analysis of the PFM domain wall profiles. The PFM profile of a realistic domain wall is shown to be the convolution of its intrinsic profile and the resolution function of PFM.
Comment on “Oblique axisymmetric stagnation flows in magnetohydrodynamics” [Phys. Fluids 19, 114106 (2007)]
Authors: Thess André
Published: June 2008

It is shown that the model used in the paper “Oblique axisymmetric stagnation flows in magnetohydrodynamics” [Amaouche et al. Phys. Fluids 19, 114106 (2007)] is incomplete since the electric potential has been neglected. The results of the work should therefore be considered as qualitative until the analysis has been repeated using the correct set of equations.
Schwinger–Dyson operators as invariant vector fields on a matrix model analog of the group of loops
Authors: Krishnaswami Govind S.
Published: June 2008

For a class of large-N multimatrix models, we identify a group G that plays the same role as the group of loops on space-time does for Yang–Mills theory. G is the spectrum of a commutative shuffle-deconcatenation Hopf algebra that we associate with correlations. G is the exponential of the free Lie algebra. The generating series of correlations is a function on G and satisfies quadratic equations in convolution. These factorized Schwinger–Dyson or loop equations involve a collection of Schwinger–Dyson operators, which are shown to be right-invariant vector fields on G, one for each linearly independent primitive of the Hopf algebra. A large class of formal matrix models satisfying these properties are identified, including as special cases, the zero momentum limits of the Gaussian, Chern–Simons, and Yang–Mills field theories. Moreover, the Schwinger–Dyson operators of the continuum Yang–Mills action are shown to be right-invariant derivations of the shuffle-deconcatenation Hopf algebra generated by sources labeled by position and polarization.
Robust reproducible large-area molecular rectifier junctions
Authors: Che Hui-Juan , Chia Perq-Jon , Chua Lay-Lay , Sivaramakrishnan Sankaran , Tang Jie-Cong , Wee Andrew T. S. , Chan Hardy S. O. , Ho Peter K. H.
Published: June 2008

Stable rectifying molecular junctions have been obtained by sandwiching self-assembled monolayer films containing “push-pull” donor-π-acceptor (D-π-A) moieties between Au and poly(3,4-ethylenedioxythiophene) electrodes. These D-π-A moieties possess moderate molecular dipoles, but assemble into films with nearly zero dipole moment due to adoption of high average tilt angles. Nevertheless reproducible and well-behaved rectifications (ratio up to 3.3) in the expected polarity were obtained. At low biases, the current-voltage characteristics follow Simmon’s tunneling theory with reasonable barrier heights and an effective tunnel mass of ∼0.5me. This suggests that asymmetric tunneling, and not carrier injection, is the origin of the rectification.
Rototranslational sum rules for electromagnetic hypershielding at the nuclei and related atomic Cartesian derivatives of the optical rotatory power
Authors: Liégeois Vincent , Champagne Benoît , Lazzeretti Paolo
Published: June 2008

Two molecular properties, the nuclear electromagnetic hypershielding (ψγ,αβ′I) and the gradient of the electric dipole–magnetic dipole polarizability (∇IγGαβ′), have been calculated using the time-dependent Hartree–Fock method. Provided the Hellmann–Feynman theorem is satisfied, these quantities are equivalent and are related through the ∇IγGαβ′=eZIψγ,αβ′I relation, where ZI is the atomic number of atom I and e the magnitude of the electron charge. In such a case, the determination of the nuclear electromagnetic hypershielding presents the computational advantage over the evaluation of the gradient of Gαβ′ of requiring only the knowledge of nine mixed second-order derivatives of the density matrix with respect to both electric and magnetic fields (Dα,β(−ω,ω)) instead of the 3N (N is the number of atoms) derivatives of the density matrix with respect to the Cartesian coordinates (DIγ). It is shown here for the H2O2 molecule that very large basis sets such as the aug-cc-pVQZ or the R12 basis are required to satisfy the Hellmann–Feynman theorem. These basis set requirements have been substantiated by considering the corresponding rototranslational sum rules. The origin dependence of the rototranslational sum rules for the gradient of Gαβ′ has then been theoretically described and verified for the H2O2 molecule.
Implementations of Nosé–Hoover and Nosé–Poincaré thermostats in mesoscopic dynamic simulations with the united-residue model of a polypeptide chain
Authors: Kleinerman Dana S. , Czaplewski Cezary , Liwo Adam , Scheraga Harold A.
Published: June 2008

Molecular dynamics (MD) simulations generate a canonical ensemble only when integration of the equations of motion is coupled to a thermostat. Three extended phase space thermostats, one version of Nosé–Hoover and two versions of Nosé–Poincaré, are compared with each other and with the Berendsen thermostat and Langevin stochastic dynamics. Implementation of extended phase space thermostats was first tested on a model Lennard-Jones fluid system; subsequently, they were implemented with our physics-based protein united-residue (UNRES) force field MD. The thermostats were also implemented and tested for the multiple-time-step reversible reference system propagator (RESPA). The velocity and temperature distributions were analyzed to confirm that the proper canonical distribution is generated by each simulation. The value of the artificial mass constant, Q, of the thermostat has a large influence on the distribution of the temperatures sampled during UNRES simulations (the velocity distributions were affected only slightly). The numerical stabilities of all three algorithms were compared with each other and with that of microcanonical MD. Both Nosé–Poincaré thermostats, which are symplectic, were not very stable for both the Lennard-Jones fluid and UNRES MD simulations started from nonequilibrated structures which implies major changes of the potential energy throughout a trajectory. Even though the Nosé–Hoover thermostat does not have a canonical symplectic structure, it is the most stable algorithm for UNRES MD simulations. For UNRES with RESPA, the “extended system inside-reference system propagator algorithm” of the RESPA implementation of the Nosé–Hoover thermostat was the only stable algorithm, and enabled us to increase the integration time step.
Inversion-type indium phosphide metal-oxide-semiconductor field-effect transistors with equivalent oxide thickness of 12Å using stacked HfAlOx∕HfO2 gate dielectric
Authors: Zhao Han , Shahrjerdi Davood , Zhu Feng , Kim Hyoung-Sub , OK Injo , Zhang Manghong , Yum Jung Hwan , Banerjee Sanjay K. , Lee Jack C.
Published: June 2008

We present InP metal-oxide-semiconductor capacitors (MOSCAPs) and metal-oxide-semiconductor field-effect transistors (MOSFETs) with stacked HfAlOx∕HfO2 gate dielectric deposited by atomic layer deposition. Compared with single HfO2, the use of stacked HfAlOx∕HfO2 results in better interface quality with InP substrate, as illustrated by smaller frequency dispersion and lower leakage current density. The equivalent oxide thickness of MOSCAPs with 10Å HfAlOx∕25Å HfO2 stacked gate dielectric is 12Å. The MOSFETs with this gate dielectric achieve two times higher transconductance than those with single 35Å HfO2. They also exhibit drive current of 60mA∕mm and subthreshold swing of 83mV/decade for 5μm gate length.
Differential scattering of cold molecules in superimposed electric and magnetic fields
Authors: Tscherbul T. V.
Published: June 2008

We present a detailed theoretical study of differential cross sections for inelastic collisions of Σ2 molecules in the presence of superimposed electric and magnetic fields. Using rigorous quantum dynamical calculations, we show that the angular dependence of cross sections for Zeeman relaxation in collisions of CaD molecules with He atoms at low temperatures can be significantly modified by electric fields of less than 100kV∕cm. Our results suggest that the differential scattering cross sections are more sensitive to the electric field than the averaged integral cross sections. We show that the integral cross sections corresponding to a fixed orientation of the incoming collision flux may exhibit interference effects induced by electric fields.
Mesoscale model parameters from molecular cluster calculations
Authors: Akkermans Reinier L. C.
Published: June 2008

We present an efficient, systematic, and universal method to estimate the interaction parameters used in mesoscale simulation methods such as dissipative particle dynamics and self-consistent field methods from molecular cluster calculations. The method is based on a generalized Flory–Huggins model in which molecules, or fragments thereof, are in contact with their van der Waals surface. We sample the density of states of molecular clusters in the space spanned by the coarse-grained degrees of freedom. From here, we calculate the sum over states and free energy of the cluster at a temperature of interest by histogram reweighting. The method allows to calculate the energy and entropy contributions to the cluster free energy explicitly. For two components, we then obtain the excess free energy of mixing and the Flory–Huggins χ-parameter, and their energetic and entropic contributions. We present two applications of the method: a simple liquid mixture of hexane and nitrobenzene, and a series of polymer blends. In the case of hexane/nitrobenzene, we compare to alternative simulation methods; here we find that the energy of mixing alone is too high to explain the critical point. By including the excess entropy of mixing, however, the predicted phase behavior is in reasonable agreement with experiment. The tendency of calculations based on average energy alone to overestimate the χ-parameter is also apparent in the polymer blend calculations.
Enhanced field emission from hexagonal rhodium nanostructures
Authors: Sathe Bhaskar R. , Kakade Bhalchandra A. , Mulla Imtiaz S. , Pillai Vijayamohanan K. , Late Dattatray J. , More Mahendra A. , Joag Dilip S.
Published: June 2008

Shape selective synthesis of nanostructured Rh hexagons has been demonstrated with the help of a modified chemical vapor deposition using rhodium acetate. An ultralow threshold field of 0.72V∕μm is observed to generate a field emission current density of 4×10−3μA∕cm2. The high enhancement factor (9325) indicates that the origin of electron emission is from nanostructured features. The smaller size of emitting area, excellent current density, and stability over a period of more than 3h are promising characteristics for the development of electron sources.
Dipole-bound CH3CN− ions: Temperature dependence of ion production rates and lifetimes
Authors: Cannon M. , Liu Y. , Suess L. , Dunning F. B.
Published: June 2008

The formation of long-lived (τ≲10μs) dipole-bound CH3CN− ions through electron transfer in K(14p)∕CH3CN collisions is investigated as a function of target temperature. The rate for their formation is observed to decrease steadily with increasing target temperature. The results are consistent with earlier suggestions that only target molecules in the ground vibrational state and low-lying rotational states can form long-lived dipole-bound anions. For CH3CN, the data indicate that creation of long-lived ions requires that the target molecules be in states with rotational quantum numbers j≲20. The measurements further demonstrate that the lifetime of the longest-lived (τ≳50μs) ions is limited by blackbody-radiation-induced photodetachment.
High efficiency n-type Si solar cells on Al2O3-passivated boron emitters
Authors: Benick Jan , Hoex Bram , van de Sanden M. C. M. , Kessels W. M. M. , Schultz Oliver , Glunz Stefan W.
Published: June 2008

In order to utilize the full potential of solar cells fabricated on n-type silicon, it is necessary to achieve an excellent passivation on B-doped emitters. Experimental studies on test structures and theoretical considerations have shown that a negatively charged dielectric layer would be ideally suited for this purpose. Thus, in this work the negative-charge dielectric Al2O3 was applied as surface passivation layer on high-efficiency n-type silicon solar cells. With this front surface passivation layer, a confirmed conversion efficiency of 23.2% was achieved. For the open-circuit voltage Voc of 703.6mV, the upper limit for the emitter saturation current density J0e, including the metalized area, has been evaluated to be 29fA∕cm2. This clearly shows that an excellent passivation of highly doped p-type c-Si can be obtained at the device level by applying Al2O3.