bluuebunny/crossref_metadata_2025 huggingface dataset:
Closed-form solution of the potential flow in a contracted flume
Authors: BELAUD G. , LITRICO X.
Published: March 2008

The potential flow upstream from a contraction in a rectangular flume is analysed. In order to calculate the potential function, the flow is considered as the superposition of sinks uniformly distributed in the contraction. The effect of boundaries is taken into account by introducing virtual sinks. The calculation is performed in the complex plane and provides a closed-form solution of the complex potential function. As an illustration, the effect of contraction size and position is analysed, and the solution is compared to experimental measurements and other numerical solutions for vertical sluice gates.
Imagination and reason
Authors: Agassi Joseph
Published: March 2008

Byrne's book is intended to explain why people imagine the things they do when they create alternatives to reality. Two fruitful areas of further research are: (1) How can her approach explain dreams and daydreams? (2) What is the developmental time course of the child's understanding of reality and imagination?
Reasons to act and the mental representation of consequentialist aberrations
Authors: Bonnefon Jean-François
Published: March 2008

If imagination is guided by the same principles as rational thoughts, then we ought not to stop at the way people make inferences to get insights about the workings of imagination; we ought to consider as well the way they make rational choices. This broader approach accounts for the puzzling effect of reasons to act on the mutability of actions.
The goals of counterfactual possibilities
Authors: Legrenzi Paolo
Published: March 2008

Why do humans imagine alternatives to reality? The experiments conducted by Byrne explain the mental mechanisms we use when we do just this – that is, imagine one, or more, alternative reality. But why do we do this? The general reason is to give ourselves an explanation of the world, to tell stories; at times to console ourselves, and at times to despair. A good story is not only based on a description of what happened, but also hints at, or explains, what might have happened. Depending on our aim, we construct different kinds of counterfactuals. In all cases, however, we are faced with constraints. These constraints are specific to a given domain of beliefs and use of counterfactuals.
Thinking developmentally about counterfactual possibilities
Authors: Riggs Kevin J. , Beck Sarah R.
Published: March 2008

Byrne implies that working memory development underpins children's ability to represent counterfactuals as possibilities at 3 to 4 years of age. Recent findings suggest that (1) developments in the ability to consider alternatives to reality in children of this age are underpinned by improvements in inhibitory control, not working memory, and (2) children do not develop an understanding of counterfactuals as possibilities until mid-childhood.
When imagination is difficult: Metacognitive experiences at the fault lines of reality
Authors: Sanna Lawrence J.
Published: March 2008

Imagination and rational thought may be guided by identical principles, and Byrne's (2005) analysis expertly synthesizes a diverse literature on counterfactual thinking. Further attention should be paid to metacognitive experiences, like ease or difficulty of thought generation, which accompany the imaginative process. Only by considering metacognitive experiences along with the content of what people imagine can we fully understand imagination.
On the relation between counterfactual and causal reasoning
Authors: Spellman Barbara A. , Ndiaye Dieynaba G.
Published: March 2008

We critique the distinction Byrne makes between strong causes and enabling conditions, and its implications, on both theoretical and empirical grounds. First, we believe that the difference is psychological, not logical. Second, we disagree that there is a strict “dichotomy between the focus of counterfactual and causal thoughts.” Third, we disagree that it is easier for people to generate causes than counterfactuals.
The rational imagination and other possibilities
Authors: Byrne Ruth M. J.
Published: March 2008

In this response I discuss some of the key issues raised by the commentators on The Rational Imagination. I consider whether the imaginative creation of alternatives to reality is rational or irrational, and what happens in childhood cognition to enable a rational imagination to develop. I outline how thoughts about causality, counterfactuality, and controllability are intertwined and why some sorts of possibilities are more readily imagined than others. I conclude with a consideration of what the counterfactual imagination is for.
Verb morphology deficits in Arabic-speaking children with specific language impairment
Authors: ABDALLA FAUZIA , CRAGO MARTHA
Published: March 2008

This paper explores tense and agreement marking in the spontaneous production of verbs in Arabic-speaking children with specific language impairment (SLI) and two groups of typically developing children: one group matched for mean length of utterance, and the other group matched for age. The special characteristics of Arabic such as its rich bound morphology, intricate verb system, null subject properties, and lack of an infinitival form make it particularly valuable for determining universal versus language-specific aspects of SLI. The results indicate that the Arabic-speaking participants with SLI had obvious problems with verb morphology. They were significantly different from the two comparison groups of children on the percentage of correct use of tense and subject–verb agreement forms. Furthermore, when an error in verbal infection occurred, the substitute form was often an imperative form. The findings are examined in light of cross-linguistic research pertaining to the nature of the SLI deficit and its relationship with typical language learning.
Relations in the tautological ring derived from combinatorial classes and hyperelliptic fatgraphs
Authors: BENE ALEX JAMES
Published: March 2008

A closed formula is obtained for the integral$\int_{\Hgbs^1}\kappa_{1}\psi^{2g-2}$of tautological classes over the locus of hyperelliptic Weier points in the moduli space of curves. As a corollary, a relation between Hodge integrals is obtained.

The calculation utilizes the homeomorphism between the moduli space of curves$\M_{g,1}$and the combinatorial moduli space$\Mc_{g,1}$, a PL-orbifold whose cells are enumerated by fatgraphs. This cell decomposition can be used to naturally construct combinatorial PL-cycles$W_a\subset\Mc_{g,1}$whose homology classes are essentially the Poin duals of the Mumford–Morita–Miller classes κa. In this paper we construct another PL-cycle$\Hgc \subset \Mc_{g,1}$representing the locus of hyperelliptic Weier points and explicitly describe the chain level intersection of this cycle withW1. Using this description of$\Hgc\cap W_1$, the duality between Witten cyclesWaand the κaclasses, and the Kontsevich--Penner method of integration, scheme of integrating ε classes, the integral$\int_{\Hgbs^1}\kappa_{1}\psi^{2g-2}$is reduced to a weighted sum over graphs and is evaluated by the enumeration of trees.
On Cheng's eigenvalue comparison theorem
Authors: BESSA G. P. , MONTENEGRO J. F.
Published: March 2008

We observe that Cheng's Eigenvalue Comparison Theorem for normal geodesic balls [4] is still valid if we impose bounds on the mean curvature of the distance spheres instead of bounds on the sectional and Ricci curvatures. In this version, there is a weak form of rigidity in case of equality of the eigenvalues. Namely, equality of the eigenvalues implies that the distance spheres of the same radius on each ball has the same mean curvature. On the other hand, we construct smooth metrics $g_{\kappa}$ on $[0,r]\times \mathbb{S}^{3}$, non-isometric to the standard metric canκ of constant sectional curvature κ, such that the geodesic balls $B_{g_{\kappa}}(r)=([0,r]\times \mathbb{S}^{3},g_{\kappa})$, $B_{{\rm can}_{\kappa}}(r)=([0,r]\times \mathbb{S}^{3},{\rm can}_{\kappa})$ have the same first eigenvalue, the same volume and the distance spheres $\partial B_{g_{\kappa}}(s)$ and$\partial B_{{\rm can}_{\kappa}}(s)$, $0<s\leq r$, have the same mean curvatures. In the end, we apply this version of Cheng's Eigenvalue Comparison Theorem to construct examples of Riemannian manifolds M with arbitrary topology with positive fundamental tone λ*(M)>0 extending Veeravalli's examples,[7]
Ridding London of smallpox: the aerial transmission debate and the evolution of a precautionary approach
Authors: MORTIMER P. P.
Published: March 2008

The efforts of the Metropolitan Asylums Board in Victorian London to isolate cases of smallpox in hospitals, and so limit its spread, set off a controversy about ‘hospital influence’, i.e. alleged escapes of the disease into the neighbourhood. When, in 1870, the Board began to gather cases of smallpox into its new intra-urban isolation hospitals, nearby householders resisted, and in 1881 their fear of aerial transmission was endorsed by a government medical inspector, W. H. Power. Not all agreed with Power, but as a result from 1885 the Board removed almost all known cases of smallpox in London to hospital ships moored in the Thames Estuary. The ships failed to provide adequate and secure accommodation, however, and so Board smallpox hospitals were erected on the adjacent Dartford marshes. After 1903, there being no more smallpox epidemics in Britain, these isolation hospitals and many similar ones outside other towns and cities were little used for their main intended purpose. Their retention for many years thereafter can be seen as an application of the precautionary principle; it bears on current contingency plans in Britain and elsewhere for dealing with serious epidemics.
Misbinding of color to form in afterimages
Authors: SHEVELL STEVEN K. , ST.CLAIR REBECCA , HONG SANG WOOK
Published: March 2008

Under dichoptic viewing conditions, rivalrous gratings that differ in both color and form can give the percept of the color from one eye in part of the form in the other eye. This study examined the afterimage following such misbinding of color to form. The first experiment established that afterimages of the misbound percept were seen. Two possible mechanisms for the misbound afterimage are (1) persisting retinal representations that are rivalrous and subsequently resolved to give misbinding, as during rivalrous viewing, and (2) a persisting response from a central neural representation of the misbound percept with the form from one eye and color from the other eye. The results support afterimage formation from a central representation of the misbound percept, not from resolution of rivalrous monocular representations.
Eel visual pigments revisited: The fate of retinal cones during metamorphosis
Authors: BOWMAKER JAMES K. , SEMO MA'AYAN , HUNT DAVID M. , JEFFERY GLEN
Published: March 2008

During their complex life history, anguilliform eels go through a major metamorphosis when developing from a fresh water yellow eel into a deep-sea silver eel. In addition to major changes in body morphology, the visual system also adapts from a fresh water teleost duplex retina with rods and cones, to a specialized deep-sea retina containing only rods. The history of the rods is well documented with an initial switch from a porphyropsin to a rhodopsin (P5232to P5011) and then a total change in gene expression with the down regulation of a “freshwater” opsin and its concomitant replacement by the expression of a typical “deep-sea” opsin (P5011to P4821). Yellow eels possess only two spectral classes of single cones, one sensitive in the green presumably expressing an RH2 opsin gene and the second sensitive in the blue expressing an SWS2 opsin gene. In immature glass eels, entering into rivers from the sea, the cones contain mixtures of rhodopsins and porphyropsins, whereas the fully freshwater yellow eels have cone pigments that are almost pure porphyropsins with peak sensitivities at about 540–545 nm and 435–440 nm, respectively. However, during the early stages of metamorphosis, the pigments switch to rhodopsins with the maximum sensitivity of the “green”-sensitive cone shifting to about 525 nm, somewhat paralleling, but preceding the change in rods. During metamorphosis, the cones are almost completely lost.
The impulse response of S-cone pathways in detection of increments and decrements
Authors: SHINOMORI KEIZO , WERNER JOHN S.
Published: March 2008

Impulse response functions (IRFs) were obtained from two-pulse detection thresholds using isoluminant stimuli that produced increments or decrements in S-cone excitation. The pulses were chromatically modulated at constant luminance (based on 18 Hz heterochromatic flicker photometry). Chromatic stimuli were presented as a Gaussian patch (±1 SD = 2.3°) in one of four quadrants around a central fixation cross on a CRT screen. Each of the two pulses (6.67 ms) was separated by an inter-stimulus interval (ISI) from 20 to 360 ms. Chromaticity of the pulses was changed from the equal-energy white of the background to a bluish or yellowish color along individually determined tritan lines (based on color matching under strong S-cone adaptation from a 420 nm background superimposed in Maxwellian view). Chromatic detection thresholds were determined by a four-alternative forced-choice method with staircases for each ISI interleaved in each session. Measurements were repeated in at least four sessions for each observer. IRFs were calculated by varying four parameters of an exponentially-damped sinewave. Both S-cone increment and decrement IRFs are characterized by a single excitatory phase and a much longer time course compared with IRFs derived for luminance modulation using the same apparatus and observers. S-cone increment IRFs are faster than S-cone decrement IRFs; the time to peak amplitude of S-cone increment and decrement IRFs is 50–70 and 100–120 ms, respectively. These results were used to derive the temporal contrast sensitivity for human observers of putative ON- and OFF-channels carrying signals from S-cones.
Cross-language mediated priming: Effects of context and lexical relationship
Authors: SCHWARTZ ANA I. , ARÊAS DA LUZ FONTES ANA B.
Published: March 2008

We examined how linguistic context influences the nature of bilingual lexical activation. We hypothesized that in single-word context, form-related words would receive the strongest activation while, in sentence context, semantically related words would receive the strongest activation. Spanish–English bilinguals performed a semantic verification task on English target words preceded by a prime. On critical trials, the prime and target words were paired based either on a form-mediated relationship through the native language (L1), [e.g., bark (barco): BOAT] (Experiment 1) or on a semantically-mediated relationship [e.g., boat (barco): BARK] (Experiment 2). The prime word was presented either in isolation or after a sentence context. In Experiment 1 interference was observed in the single word condition only. In Experiment 2 interference was observed in both single-word and sentence contexts. The findings demonstrate that the context in which words are embedded has an impact on the type of lexical competitors that become active.
Words that second language learners are likely to hear, read, and use
Authors: DAVIDSON DOUGLAS J. , INDEFREY PETER , GULLBERG MARIANNE
Published: March 2008

In the present study, we explore whether multiple data sources may be more effective than single sources at predicting the words that language learners are likely to know. Second language researchers have hypothesized that there is a relationship between word frequency and the likelihood that words will be encountered or used by second language learners, but it is not yet clear how this relationship should be effectively measured. An analysis of word frequency measures showed that spoken language frequency alone may predict the occurrence of words in learner textbooks, but that multiple corpora as well as textbook status can improve predictions of learner usage.
Experimental approach to measuring functional food consumption for risk factor surveillance
Authors: Beer-Borst Sigrid , Costanza Michael C , Morabia Alfredo
Published: March 2008

Objective

To develop and integrate the assessment of functional foods (FuF; manufactured foods with altered composition carrying a health claim) consumption into an existing risk factor surveillance system.

Design

FuF market research followed by an experimental FuF intake study incorporated into an ongoing community-based survey. Concurrent completion of a self-administered semi-quantitative FFQ and a self-administered, qualitative FuF frequency questionnaire (FuFFQ) followed by a face-to-face control step using FuF photographs and combined food group-based data analyses.

Setting

‘Bus Santé’ risk factor surveillance programme, Geneva/Switzerland.

Subjects

Population-based random sample of 639 residents (52 % women, aged 35–74 years) surveyed from September 2003 to April 2004.

Results

Local Geneva/French neighbourhood market research identified 148 FuF in five major FuF food groups which were compiled into a functional ingredient database. Prior to the face-to-face verification, 210 (33 %) individuals categorized themselves as FuF consumers, 429 (67 %) as non-consumers. The control step revealed that 70 % of the 639 participants were already familiar with the FuF concept, and thus were correctly self-categorized as FuF consumers or non-consumers. For the remaining 30 % of participants the true FuF consumption status was established, resulting in a final number of 285 FuF consumers (45 %; 12 % net increase) and 354 (55 %) non-consumers.

Conclusions

The developed self-administered, brief, qualitative food group-based FuF frequency check list in combination with an FFQ and a photo-assisted control step provides a flexible assessment tool for measuring FuF consumption in the context of a specific fluctuating FuF market and may be applicable to other population settings and times.
Exceptionalism, politics and liberty: a response to Professor Tushnet from the Antipodes
Authors: Lynch Andrew
Published: March 2008

In this comment, the author takes issue with Professor Tushnet’s favourable stance on the protection which political controls can afford human rights relative to legal ones. Writing in a jurisdiction with no formal legal instrument of human rights enables the author to speak with experience of the operation of political controls in a ‘pristine parliamentary environment’. The author outlines the ineffectiveness in the Australian experience of counter-terrorism since September 11 of many of the mechanisms which Tushnet has suggested impose constraints upon the diminishment of liberties. The comment concludes that the essential condition for the enhancement of political controls is the presence of legal ones.
On the sheet‐like nature of 150 km (F1) radar echoes
Authors: Tsunoda Roland T. , Ecklund Warner L.
Published: March 2008

The so‐called 150 km (or F1) echoes are shown to arise from field‐aligned irregularities (FAI) that are embedded in a sheet‐like region. Using a 49.92 MHz radar on Christmas Island, which has an antenna beam directed toward geographic east at a zenith angle of 29.5°, high‐resolution Doppler‐velocity variations within the radar scattering volume are used to infer that the sheet‐like region could have both tilt and curvature. This finding is used to infer that plasma density (N) must be enhanced within the sheet‐like region, and that FAI could be generated by an interchange instability, driven by a vertical electric field or a zonal neutral wind that acts on the horizontal component of the gradient in N. How tilted sheet‐like structures could form in the F1 region is discussed.
Cluster observations of collisionless Hall reconnection at high‐latitude magnetopause
Authors: Zhang H. , Zong Q.‐G. , Fritz T. A. , Fu S. Y. , Schaefer S. , Glassmeier K. H. , Daly P. W. , Rème H. , Balogh A.
Published: March 2008

The first in situ observation of collisionless Hall reconnection in the high‐latitude region when the interplanetary magnetic field (IMF) By dominates is reported in this paper. On 23 March 2002, Cluster crossed the magnetopause current sheet when it traveled outbound in the Northern Hemisphere. The interface between the cusp and the magnetosheath is clearly associated with sharp transitions of the magnetic field and plasma moments. These variations suggest that the interface is a clear current sheet with a thickness of 218 km. Energetic electrons, protons, helium, and oxygen ions were observed and their intensity peaked at this current sheet. During that time period, the IMF Bz is around zero and the IMF By component dominates. The geometry of the magnetic field preferred By reconnection. The bipolar signature in the magnetic field observed by Cluster is consistent with Hall effects in the reconnection process. Characteristics of three By reconnection events are presented in this paper.
Reconstruction of the Talkeetna intraoceanic arc of Alaska through thermobarometry
Authors: Hacker Bradley R. , Mehl Luc , Kelemen Peter B. , Rioux Matthew , Behn Mark D. , Luffi Peter
Published: March 2008

The Talkeetna arc is one of two intraoceanic arcs where much of the section from the upper mantle through the volcanic carapace is well exposed. We reconstruct the vertical section of the Talkeetna arc by determining the (re)crystallization pressures at various structural levels. The thermobarometry shows that the tonalites and quartz diorites intruded at ∼5–9 km into a volcanic section estimated from stratigraphy to be 7 km thick. The shallowest, Tazlina and Barnette, gabbros crystallized at ∼17–24 km; the Klanelneechena Klippe crystallized at ∼24–26 km; and the base of the arc crystallized at ∼35 km depth. The arc had a volcanic:plutonic ratio of ∼1:3–1:4. However, many or most of the felsic plutonic rocks may represent crystallized liquids rather than cumulates so that the liquid:cumulate ratio might be 1:2 or larger. The current 5‐ to 7‐km structural thickness of the plutonic section of the arc is ∼15–30% of the original 23‐ to 28‐km thickness. The bulk composition of the original Talkeetna arc section was ∼51–58 wt % SiO2.
The role of adiabaticity in the aerosol first indirect effect
Authors: Kim Byung‐Gon , Miller Mark A. , Schwartz Stephen E. , Liu Yangang , Min Qilong
Published: March 2008

Aerosol indirect effects are the most uncertain of the climate forcing mechanisms that have operated through the industrial period. Several studies have demonstrated modifications of cloud properties due to aerosols and corresponding changes in shortwave and longwave radiative fluxes under specific cloud conditions, but some recent studies have indicated that cloud dynamical processes such as entrainment‐mixing may be the primary modulator of cloud optical properties in certain situations. For example, day‐to‐day variations of the cloud drop effective radius (re) determined from the ground‐based remote sensing at the Southern Great Plains were found to be weakly associated with the variations in aerosol loading as characterized by its light‐scattering coefficient at the surface, implying that other processes were impacting the cloud radiative properties. To study these other impacts, we extend a previous study to investigate the role of changes in liquid water path (LWP) and re in single layer stratiform clouds that are induced by entrainment‐mixing processes and their effects on cloud radiative properties. We quantify the degree of entrainment‐mixing in terms of the adiabaticity defined as the ratio of the observed cloud liquid water path to the corresponding adiabatic value. The cloud optical depth is, as expected, governed primarily by LWP, but that adiabaticity is the next most influential factor. In contrast, re is found to be equally sensitive to adiabaticity and LWP. In adiabatic clouds the aerosol first indirect effect is clearly observed and related to independent measures of aerosol loading. In sub‐adiabatic clouds the aerosol first indirect effect is not readily observed; this may in some circumstances be due to interference from heterogeneous mixing processes that change the droplet number density in a manner that attenuates the effect.
A vertical profile of PM10 dust concentrations measured during a regional dust event identified by MODIS Terra, western Queensland, Australia
Authors: McGowan Hamish A. , Clark Andrew
Published: March 2008

Accurate determination of the spatiotemporal properties of dust plumes and their dust concentrations is essential for calibration of satellite products and the initialization and validation of numerical models that simulate the physical properties and affects of dust events. In this paper, we present a 500 m vertical profile of PM10 dust concentrations measured during a regional dust event in western Queensland, Australia. PM10 dust concentrations within the haze were found to be >20 times background ambient values and decreased with height following an exponential function. We apply an over‐land algorithm to MODIS Terra satellite images of the dust haze to enhance its visual appearance against the bright land surface and define its size. In conjunction with the measured attenuation of dust concentrations with height we calculate the PM10 dust load of the plume to be ∼60% of that which would have been calculated assuming a constant dust concentration up to the dust ceiling height. Results extend previous findings from tower‐based studies made close to the surface and confirm that atmospheric dust concentrations decrease rapidly with increasing height, thereby enabling more accurate calculation of atmospheric dust loads during synoptic‐scale dust outbreaks.
Investigations of the law‐of‐the‐wall over sparse roughness elements
Authors: King James , Nickling William G. , Gillies John A.
Published: March 2008

This paper examines the application of the law‐of‐the‐wall or gradient method for calculating the shear velocity, roughness length, and displacement height over three increasing roughness densities replicated with three different sized cubes within a recirculating wind tunnel. We compare these aerodynamic parameter estimates with estimates of the same parameters derived from other established methods: Reynolds stress analysis and the outer‐layer velocity‐defect law. By using more than one roughness height for the same roughness density (λ), dependencies of these parameters on roughness element height were also evaluated. Using the vertical wind speed logarithmic profile layer (determined graphically), resulted in shear velocity estimates that are greater by more than a factor of two than those determined using hot‐film anemometry. The law‐of‐the‐wall method provided a good estimate of the roughness length when applied to only that portion of the wind speed profile identified by Reynolds stress measurements to be within the constant stress layer; however, the shear velocity was overestimated by an average of 43% compared with that measured directly by hot‐film anemometry. The best prediction of both of the roughness length and shear velocity, compared to estimates using Reynolds stress analysis, was obtained using the outer‐layer velocity‐defect law. We advocate that the velocity‐defect law method be used in wind tunnel testing for calculating the shear velocity and roughness length from velocity profiles over sparsely spaced roughness elements, or when flow is highly heterogeneous, instead of the law‐of‐the‐wall.
A shift in heavy and clay mineral provenance indicates a middle Miocene onset of a perennial sea ice cover in the Arctic Ocean
Authors: Krylov Alexey A. , Andreeva Irina A. , Vogt Christoph , Backman Jan , Krupskaya Viktoria V. , Grikurov Garrik E. , Moran Kathryn , Shoji Hitoshi
Published: March 2008

During the Arctic Coring Expedition (ACEX), a 428‐m‐thick sequence of Upper Cretaceous to Quaternary sediments was penetrated. The mineralogical composition of the upper 300 m of this sequence is presented here for the first time. Heavy and clay mineral associations indicate a major and consistent shift in provenance, from the Barents‐Kara–western Laptev Sea region, characterized by presence of common clinopyroxene, to the eastern Laptev‐East Siberian seas in the upper part of the section, characterized by common hornblende (amphibole). Sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the ACEX drill site, if considering modern sea ice trajectories and velocities. This shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the Arctic Ocean, which occurred at about 13 Ma, thus suggesting a coeval freeze in the Arctic and Antarctic regions.
Intrinsic vulnerability assessment in karst areas: A numerical modeling approach
Authors: Butscher Christoph , Huggenberger Peter
Published: March 2008

The main objective of this study was to quantify the intrinsic vulnerability of karst springs by numerical modeling. A global approach is used, modeling the discharge of a karst spring. This approach includes the hydrological dynamics of karst systems and is applicable to complex karst settings, where structural and hydraulic characteristics cannot be spatially resolved with sufficient accuracy. A basis model and four extended versions were set up to determine the individual characteristics of the present karst system and to include different flow processes that could affect the vulnerability of the system. All these model setups consider, besides recharge (soil and epikarst system), the conduit and the diffuse flow system as the main characteristics of the karst aquifer. The extended setups additionally account for surface runoff, an intermediate flow system, exchange flow between the conduit and the diffuse system and seasonal variation in the water storage capacity of the recharge system. Potential use of the calibrated models to quantify the intrinsic vulnerability of karst springs is discussed on the basis of (1) the temporally changing contributions of the conduit and diffuse flow systems to spring discharge, and (2) modeled breakthrough curves resulting from a standardized contaminant input into the karst system. The modeling approach complements vulnerability mapping methods by addressing temporal and quantitative aspects of vulnerability.
Regulation of nif gene expression and the energetics of N2 fixation over the diel cycle in a hot spring microbial mat
Authors: Steunou Anne-Soisig , Jensen Sheila I , Brecht Eric , Becraft Eric D , Bateson Mary M , Kilian Oliver , Bhaya Devaki , Ward David M , Peters John W , Grossman Arthur R , Kühl Michael
Published: March 2008

Nitrogen fixation, a prokaryotic, O2-inhibited process that reduces N2 gas to biomass, is of paramount importance in biogeochemical cycling of nitrogen. We analyzed the levels of nif transcripts of Synechococcus ecotypes, NifH subunit and nitrogenase activity over the diel cycle in the microbial mat of an alkaline hot spring in Yellowstone National Park. The results showed a rise in nif transcripts in the evening, with a subsequent decline over the course of the night. In contrast, immunological data demonstrated that the level of the NifH polypeptide remained stable during the night, and only declined when the mat became oxic in the morning. Nitrogenase activity was low throughout the night; however, it exhibited two peaks, a small one in the evening and a large one in the early morning, when light began to stimulate cyanobacterial photosynthetic activity, but O2 consumption by respiration still exceeded the rate of O2 evolution. Once the irradiance increased to the point at which the mat became oxic, the nitrogenase activity was strongly inhibited. Transcripts for proteins associated with energy-producing metabolisms in the cell also followed diel patterns, with fermentation-related transcripts accumulating at night, photosynthesis- and respiration-related transcripts accumulating during the day and late afternoon, respectively. These results are discussed with respect to the energetics and regulation of N2 fixation in hot spring mats and factors that can markedly influence the extent of N2 fixation over the diel cycle.
Phase transitions and magnetoresistance in Ni50Mn50−xInx Heusler alloys
Authors: Pathak Arjun Kumar , Gautam Bhoj Raj , Dubenko Igor , Khan Mahmud , Stadler Shane , Ali Naushad
Published: March 2008

The phase transitions and magnetoresistance in polycrystalline ferromagnetic Ni50Mn50−xInx (15⩽x⩽16.2) Heusler alloys were studied through ac susceptibility, magnetization, thermal expansion, and resistivity measurements in the temperature interval of 5–400K. The temperatures of the martensitic transformations were found to be strongly dependent on In concentration and on the strength of the applied external magnetic field. We observed large magnetoresistance (MR) Δρ∕ρo≈−80% for x=16 at T≈125K and Δρ∕ρo≈−56% for x=15 at T≈309K for ΔH=5T. In addition to large MR, the Ni50Mn50−xInx system exhibits ferromagnetic shape-memory effect and a large magnetic entropy change. Hence this system has potential to be a multifunctional applied material.
Experimental and theoretical investigation of electron attachment to SF5Cl
Authors: Van Doren Jane M. , Miller Thomas M. , Viggiano Albert A. , Španěl Patrik , Smith David , Bopp Joseph C. , Troe Jürgen
Published: March 2008

Thermal electron attachment to SF5Cl has been studied with the flowing afterglow Langmuir probe technique. The rate coefficient is moderate, 4.8(±1.2)×10−8cm3s−1, and invariant with temperature over the temperature range of 300–550K. The reaction is dissociative, forming mainly SF5−+Cl. Minor yields of Cl− and FCl− were also found. The yields of the minor channels increase slightly with temperature. Statistical unimolecular rate modeling is employed to elucidate the character of the dissociation pathways and to support the assumption that the dissociations involve the formation of metastable anionic SF5Cl−.
Synthesis and magnetic properties of the ThMoB4-type modification of ErAlB4
Authors: Mori T. , Cardoso–Gil R. , Leithe–Jasper A. , Schnelle W. , Borrmann H. , Grin Yu.
Published: March 2008

β - Er Al B 4 with the ThMoB4-type crystal structure, which is a polytype to the YCrB4-type α-crystal structure, was synthesized, and the magnetic properties and specific heat were investigated. Recent developments in the REAlB4 compounds, where RE denotes rare earth, have attracted interest due to the heavy fermion behavior observed for β-YbAlB4 and the multiple anomalies manifesting below the Néel temperatures in α-TmAlB4 attributed to be due to intrinsic building defects. Multiple antiferromagnetic transitions were found for β-ErAlB4 at TN1≈18K and TN2=4.3K. The absence of low temperature anomalies in the magnetic properties and specific heat of β-ErAlB4 below the Néel temperatures indicates that the generation of intrinsic building defects is not a general phenomenon for compounds with the YCrB4 and ThMoB4-type crystal structures but is rather due to a special circumstance of TmAlB4 having close energies in the structure formation.
Interchange-tunneling splitting in HCl dimer in helium nanodroplets
Authors: Skvortsov Dmitry , Sliter Russell , Choi Myong Yong , Vilesov Andrey F.
Published: March 2008

Midinfrared spectra of HCl dimers have been obtained in helium nanodroplets. The interchange-tunneling (IT) splitting in the vibrationally excited state of the bonded H–Cl stretching band (ν2) in (HCl35–HCl37) dimers was measured to be 2.7±0.2cm−1, as compared to 3.7cm−1 in free dimer. From the splitting, the strength of the IT coupling in liquid helium of 0.85±0.15cm−1 was obtained, which is about a factor of 2 smaller than in the free dimer. The results are compared with the previous spectroscopic study of (HF)2 in He droplets as well as the theoretical study of (HF)2 and (HCl)2 dimers in small He clusters.
The influences of particle number on hot spots in strongly coupled metal nanoparticles chain
Authors: Wang Z. B. , Luk’yanchuk B. S. , Guo W. , Edwardson S. P. , Whitehead D. J. , Li L. , Liu Z. , Watkins K. G.
Published: March 2008

In understanding of the hot spot phenomenon in single-molecule surface enhanced Raman scattering (SM-SERS), the electromagnetic field within the gaps of dimers (i.e., two particle systems) has attracted much interest as it provides significant field amplification over single isolated nanoparticles. In addition to the existing understanding of the dimer systems, we show in this paper that field enhancement within the gaps of a particle chain could maximize at a particle number N>2, due to the near-field coupled plasmon resonance of the chain. This particle number effect was theoretically observed for the gold (Au) nanoparticles chain but not for the silver (Ag) chain. We attribute the reason to the different behaviors of the dissipative damping of gold and silver in the visible wavelength range. The reported effect can be utilized to design effective gold substrate for SM-SERS applications.
Wave-pinned filaments of scroll waves
Authors: Bánsági Tamás , Meyer Kevin J. , Steinbock Oliver
Published: March 2008

Scroll waves are three-dimensional excitation patterns that rotate around one-dimensional space curves. Typically these filaments are closed loops or end at the system boundary. However, in excitable media with anomalous dispersion, filaments can be pinned to the wake of traveling wave pulses. This pinning is studied in experiments with the 1,4-cyclohexanedione Belousov–Zhabotinsky reaction and a three-variable reaction-diffusion model. We show that wave-pinned filaments are related to the coexistence of rotating and translating wave defects in two dimensions. Filament pinning causes a continuous expansion of the total filament length. It can be ended by annihilating the pinning pulse in a frontal wave collision. Following such an annihilation, the filament connects itself to the system boundary. Its postannihilation shape that is initially the exposed rim of the scroll wave unwinds continuously over numerous rotation periods.
Depth profiling of magnetic properties of surface-modified materials by model-assisted multi-frequency analysis of Barkhausen effect signals
Authors: Lo Chester C. H.
Published: March 2008

This paper presents model-assisted analysis of Barkhausen effect (BE) signals with an aim of evaluating surface-modified materials whose magnetic properties vary with depth. The approach is based on an extended BE model which describes the signal power spectrum. In the extended model, the local pinning field fluctuation and correlation length parameters, which characterize domain wall motion and hence the generation of BE signals, are related to the domain wall pinning strength that varies with depth as described in terms of a parametrized function. The BE signals measured over a broad frequency range from oxidized Ni97Al3 and carburized steel samples were analyzed using multiple frequency passbands to extract signals generated at different depths. Depth profiles of the pinning field fluctuation and correlation length were determined by obtaining the best fit of the modeled signal power to the experimental data for all frequency bands. The inverted profiles show changes at depths which agree with the oxidization depths of the Ni97Al3 samples and the case depths of the carburized steel samples.
A pulse-compression-ring circuit for high-efficiency electric propulsion
Authors: Owens Thomas L.
Published: March 2008

A highly efficient, highly reliable pulsed-power system has been developed for use in high power, repetitively pulsed inductive plasma thrusters. The pulsed inductive thruster ejects plasma propellant at a high velocity using a Lorentz force developed through inductive coupling to the plasma. Having greatly increased propellant-utilization efficiency compared to chemical rockets, this type of electric propulsion system may one day propel spacecraft on long-duration deep-space missions. High system reliability and electrical efficiency are extremely important for these extended missions. In the prototype pulsed-power system described here, exceptional reliability is achieved using a pulse-compression circuit driven by both active solid-state switching and passive magnetic switching. High efficiency is achieved using a novel ring architecture that recovers unused energy in a pulse-compression system with minimal circuit loss after each impulse. As an added benefit, voltage reversal is eliminated in the ring topology, resulting in long lifetimes for energy-storage capacitors. System tests were performed using an adjustable inductive load at a voltage level of 3.3kV, a peak current of 20kA, and a current switching rate of 15kA∕μs.
Resonant spin transport through lateral ferromagnet-quantum dot-ferromagnet sandwich device
Authors: Chen W. , Jalil M. B. A. , Tan S. G.
Published: March 2008

The spin transport was investigated in a system composed of a quantum dot sandwiched between two ferromagnetic metal contacts (FM-QD-FM) based on the Keldysh nonequilibrium Green’s function formalism. The calculated spin current shows sharp resonant peaks in the intradot state εd, with energy separation given by the Coulomb interaction energy. The relative magnitude of the spin current peaks is strongly influenced by QD’s occupation number, which can be tuned by changing the lead-dot coupling energy. It was found that the spin-split chemical potential Δμ due to spin accumulation in the leads has a relatively smaller effect on the spin current than the leads’ polarization ratio p. Interestingly, under condition of spin-antisymmetric electrochemical potentials μσα in the leads, the magnitude of the spin current reduces with increasing p, and that a pure spin current occurs only when p=0.
Thermal stability dependence on the stacking order and thickness ratio of the CoPt–TiO2∕CoCrPt–SiO2 stacked media
Authors: Park S. H. , Lee T. D. , Kong S. H. , Yoon S. Y. , Lee H. S. , Kim H. J. , Oh H. S.
Published: March 2008

Thermal stability of the present CoCrPt–SiO2 media becomes a more critical issue as recording density steadily increases. In the present study, thermal stability of the stacked media composed of high Ku CoPt–TiO2 and normal Ku CoCrPt–SiO2 was studied by changing stacking order and thickness of each layer while keeping a constant total thickness. When the CoPt–TiO2 layer was placed under the CoCrPt–SiO2 layer, negative nucleation field and coercivity increased much more than those of the reverse stacking case. Thermal stability of the CoPt–TiO2 bottom group was superior to that of the CoCrPt–SiO2 bottom group when measured by a spin stand.
Properties of Ga1−xMnxAs with high x (>0.1)
Authors: Chiba D. , Yu K. M. , Walukiewicz W. , Nishitani Y. , Matsukura F. , Ohno H.
Published: March 2008

We have investigated the magnetic and the crystalline properties of a set of Ga1−xMnxAs layers with high nominal Mn compositions (x=0.101–0.198). Magnetization measurements and combined channeling Rutherford backscattering (c-RBS) and particle induced x-ray emission (c-PIXE) measurements have been performed to determine the effective Mn composition xeff and the fraction of Mn atoms at various lattice sites. Here, xeff determined from magnetization measurements, which increases with increasing x, is consistent with the results determined from c-RBS-PIXE measurements.
Validity of thermal activation volume estimated by using Wohlfarth’s equation in perpendicular recording hard disk media
Authors: Igarashi Masukazu , Akagi Fumiko , Sugita Yutaka
Published: March 2008

The physical volume of thermal switching unit, the activation volume for perpendicular recording media, has been investigated using the Wohlfarth equation based on micromagnetic simulation. It was found that the activation volume obtained from the Wohlfarth equation Vac-Wohlfarth exhibits significant field dependence, which is very different from direct observation of thermal switching process. This shows that Vac-Wohlfarth is invalid for perpendicular recording media. The reason for that was interpreted in terms of the narrow dispersion of the energy barrier for thermal switching, originating from the high degree of easy axes orientation along the direction perpendicular to the film plane.
Tip-enhanced Raman scattering of p-thiocresol molecules on individual gold nanoparticles
Authors: Chen Jianing , Yang Weisheng , Dick Kimberly , Deppert Knut , Xu H. Q. , Samuelson Lars , Xu Hongxing
Published: March 2008

We present a study of tip-enhanced Raman scattering on Au aerosol nanoparticles deposited on gold films. Under the tunneling current state, the Au tip and the Au aerosol nanoparticle form a narrow cavity, where large electromagnetic field enhancements are created to enhance Raman scattering enormously. Colorless p-thiocresol molecules are used as probe molecules. The estimated Raman enhancement is about nine orders of magnitude for the tip/particle configuration.
The impact of thermal annealing and adhesion film thickness on the resistivity and the agglomeration behavior of titanium/platinum thin films
Authors: Schmid Ulrich
Published: March 2008

In this study, the influence of postdeposition annealings (PDA) up to temperatures of TPDA=900 °C on the room-temperature resistivity of e-beam evaporated titanium/platinum (Ti/Pt) bilayers on Si/SiO2 substrates is investigated. The thickness of the adhesion promoter is fixed to df,Ti=15 nm. In contrast, the Pt layer is varied between df,Pt=23 and 90 nm. In the “as deposited” state, an effective mean-free path for the electrons of 18 nm is extracted from the thickness-dependent electrical measurements, in reasonable agreement with theoretical predictions. Up to TPDA=450 °C, the dependence between the reciprocal platinum film thickness and the corresponding resistivity is linear, as expected from the size effect. At TPDA=450 °C, the resistivity is substantially increased independent of Pt film thickness. Due to an enhanced diffusion of titanium into the top layer the conductivity decreases preferentially at samples with df,Ti=15 nm compared to those with a lower adhesion promoter thickness of 5 or 10 nm. Above this annealing range, this effect is more pronounced, especially at a low platinum film thickness. In addition, thermal grooving effects occur which are more facilitated at higher TPDA levels and larger values for df,Ti. Upon annealing at TPDA≥1000 °C, the onset of a capillary-driven agglomeration process is detected. When applying a thicker adhesion promoter, a higher annealing level and/or a larger duration at TPDA is requested to complete the agglomeration process.
Irreversible volume growth in polymer-bonded powder systems: Effects of crystalline anisotropy, particle size distribution, and binder strength
Authors: Maiti Amitesh , Gee Richard H. , Hoffman D. Mark , Fried Laurence E.
Published: March 2008

Pressed-powdered crystallites of intrinsically anisotropic materials have been shown to undergo irreversible volume expansion when subjected to repeated cycles of heating and cooling. In a previous letter publication [R. H. Gee et al., Appl. Phys. Lett. 70, 254105 (2007)], we developed a coarse-grained (micron-scale) interaction Hamiltonian for such a system and quantitatively reproduced experimentally observed irreversible growth through explicit molecular dynamics simulations. In this paper, we report (1) recent experiments with a high-density fluoropolymer binder that significantly lowers irreversible growth, (2) identification of a critical interaction parameter of our model that has a strong correlation with binder properties, (3) sensitivity of irreversible growth to the details of particle size and alignment distribution, and (4) a physical picture of irreversible growth in terms of particle displacements.