bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of volcanism on the flanks of the Pacific‐Antarctic ridge between 41°30′S and 52°S
Authors: Briais Anne , Ondréas Hélène , Klingelhoefer Frauke , Dosso Laure , Hamelin Cédric , Guillou Hervé
Published: August 2009

Non–hot spot, intraplate volcanism is a common feature near the East Pacific Rise or Pacific‐Antarctic ridge. Volcanic ridges and seamount chains, tens to hundreds of kilometers long, are asymmetrically distributed about the ridge axis, with most volcanic features occurring on the Pacific plate. Their origins remain controversial. We have analyzed off‐axis volcanic ridges near the Pacific‐Antarctic ridge from bathymetry, backscatter, gravity, and geochemistry data of the Pacantarctic 2 cruise. K/Ar dating of samples dredged on these structures reveals a contrast of up to 3 Ma between the volcanoes and the underlying crust. The volcanic activity, as suggested by the strong backscatter in sonar images, appears to be limited to areas of seafloor younger than about 3 Ma. All surveyed ridges north of the Menard transform fault (TF) show recent activity close to the ridge axis and are not affected by faults. The off‐axis volcanic ridges south of the Menard TF show recent volcanic flows in their center and are affected by N‐S extension. Two different types of volcanoes can be characterized: conical, flat‐topped ones and rough, elongated ones associated with narrow, E‐W trending volcanic ridges, some of them showing strong backscattering on the EM12 imagery. From the morphology of the seamount chains and the ages of the lava samples, we infer that the magma source for the volcanic ridges is related to the feeding of the ridge axis through three‐dimensional mantle convective circulation. We suggest that a change in the relative plate motion since about 5 Ma might have induced an offset of the mantle upwelling circulation under the ridge axis so that anomalously hot mantle rises under the Pacific ridge flank. The kinematic change is also likely responsible for the tectonic deformation in the young lithosphere south of Menard TF.
The source of Saturn's periodic radio emission
Authors: Southwood David J. , Kivelson Margaret G.
Published: August 2009

This paper proposes a model of the link between the pulsing radio signals from Saturn (Saturn kilometric radiation), known to be most intense on the morningside, and the rotating magnetic (cam) field structure identified on low‐latitude orbits. On the high‐inclination orbits of the Cassini spacecraft in late 2006, large‐scale azimuthal deviations of the magnetic field, corresponding to upward field‐aligned currents, have been detected in the late morning sector. There is evidence that their intensity is modulated by the rotating cam magnetic field, the periodic field structure seen deeper inside the magnetosphere. It is proposed that the local intensification of field‐aligned currents that gives rise to the modulation of the radio signal occurs in conjunction with the passage through the morning magnetosphere of the swept‐forward sector of the perturbation field imposed beyond the shells that carry the cam currents. The morningside magnetosphere is unique as a region in which not only does the magnetopause compress rotating plasma inside the magnetosphere but also magnetic shear develops between the magnetic shells of the middle magnetosphere and an outer region of magnetic field swept back by the solar wind. The link between radio pulsing and magnetic rotation arises through the interaction of the cam currents with structures unique to this part of the magnetosphere.
The 1956 Greek tsunami recorded at Yafo, Israel, and its numerical modeling
Authors: Beisel S. , Chubarov L. , Didenkulova I. , Kit E. , Levin A. , Pelinovsky E. , Shokin Y. , Sladkevich M.
Published: August 2009

A record of a tsunami event riding on the usual tide signal was recorded by a floating‐type tidal gauge installed in the port of Yafo, Israel. The tsunami was triggered by an earthquake in the Aegean Sea on 9 July 1956. This paper presents a retrieval of tsunami waves from the record. At the first stage of the study an attempt had been undertaken to reproduce the 1956 tsunami assuming a coseismic nature of its generation source. Although these simulations resulted in tsunami waves with their amplitude close to that obtained from the record measured at Yafo, they did not contain significant spectral energy components with periods of ∼15 min as appear in the spectra of 1956 tide‐gauge records. When landslide movement, triggered by the main shock and/or by the largest aftershock, is suggested as a source of these tsunami waves, the spectra of the resulted marigram obtained in the proximity to Yafo contain harmonics with frequencies very close to those measured. This corroborates the landslide nature of the tsunamigenic source responsible for generation of higher‐frequency (relative to the tidal waves) energy components. The peak periods determined via spectral analysis of the recent tide‐gauge records (1 year and longer) in the absence of tsunami events vary from 50 to 60 min. Similar periods have been revealed in a special numerical study dealing with longwave propagation toward the coast of Israel, thus confirming that their origin is related to continental shelf resonance. These resonance periods differ significantly from those found for the 1956 tsunami.
The Challenge for AGU
Authors: Austin James A.
Published: September 2009

Our science today exists in a world of rapid economic, political, and technological change. Challenges to the importance of science in the world abound, yet science has never been more important to the future of humankind on Earth. The goal for AGU is to continue delivering quality programs and services that strengthen our international scientific community while undertaking new initiatives that will ensure that the Union remains a relevant and vibrant organization for years to come.

You, AGU members, have made the Union the preeminent geophysical society in the world today.
Errors caused by draft fraction in cumulus parameterization
Authors: Murata Akihiko
Published: August 2009

The assumption that the draft fraction is negligible in cumulus parameterization can be a major source of error in the parameterized tendencies of thermodynamic quantities. This study estimates the errors arising from this assumption based on an analysis of high‐resolution cloud‐resolving model output. The numerical results reveal a negative error associated with the assumption, indicating that the magnitude of the mean subgrid‐tendency of moist static energy is underestimated when the assumption is employed. The magnitude of the error is proportional to the draft fraction, and is independent of horizontal resolution. The results are confirmed by theoretical analyses, which support a linear relationship between error magnitude and draft fraction, and confirm that the error magnitude is independent of horizontal resolution. The resulting underestimates of moist static energy tendency should not be neglected in the case that the horizontal resolution is sufficiently fine to enable the frequent occurrence of large draft fractions.
On the availability of uncoated mineral dust ice nuclei in cold cloud regions
Authors: Wiacek Aldona , Peter Thomas
Published: August 2009

The ice nucleation efficiency of mineral dust decreases when it acquires coatings, e.g. through processing in liquid clouds. This study explores the availability of unprocessed mineral dust for interactions with clouds. We performed forward trajectory calculations originating near the surface of the Chinese Taklimakan desert. The initial specific humidity of each trajectory was assumed to be conserved and used to calculate the relative humidities with respect to water and ice, allowing us to estimate the formation of liquid, mixed‐phase and ice clouds downstream. Practically none of the simulated air parcels reached conditions suitable for homogeneous nucleation of ice (T ≲ −40°C) without experiencing water saturation first. Potentially the biggest impact of mineral dust is predicted to be on mixed‐phase clouds. Furthermore, most trajectories passed through ice‐saturated (but water‐subsaturated) regions where “warm” (T ≳ −40°C) ice clouds may form prior to mixed‐phase clouds.
Physical modeling of intermediate cross‐shore beach morphology: Transients and equilibrium states
Authors: Grasso F. , Michallet H. , Barthélemy E. , Certain R.
Published: August 2009

Laboratory experiments on cross‐shore beach morphodynamics are presented. A lightweight sediment (densityρs= 1.19 g cm−3) model is used in order to fulfill a Shields number and Rouse number scaling. This choice aims at correctly reproducing bed load transport as well as suspension dynamics. Terraces and barred beach profiles obtained in the experiments also present close similarities with profiles observed in the field. In order to question the concept of equilibrium beach profile, wave forcings conforming to a JONSWAP spectrum were imposed over long periods (up to more than a hundred hours). An average bottom evolution velocity is defined and used to determine when the profile reaches equilibrium. Usually, beach profiles are characterized according to the Wright and Short (1984) classification based on the Dean number Ω. This well‐known classification is investigated and refined in the intermediate range, that is, for 1 ≤ Ω < 5. For Ω close to 1, a typical reflective profile is obtained. Terraces are obtained for the Ω = 2.5 cases. For Ω ≈ 3.7, the profiles exhibit two parts: a mild dissipative offshore slope producing low reflection and a steeper beach face with slightly higher reflection. The wave dissipation, velocity skewness, and acceleration skewness are computed from the free surface elevation time series. The dissipation and wave nonlinearities patterns are similar for similar equilibrium beach profiles, that is, with the same Dean number. Dissipation peaks coincide with bottom slope transitions as higher energy dissipation occurs with milder bottom slope sections. Besides, the uniformity of volumetric wave energy dissipation seems to concern only a limited zone of beaches with a widely developed surf zone.
A Social Interactional Model of Bereavement Narrative Disclosure
Authors: Baddeley Jenna L. , Singer Jefferson A.
Published: August 2009

According to recent bereavement research, disclosing the narrative of one's loss does not per se promote emotional recovery. At the same time, social, personality, and developmental research suggests that telling personal stories is an important means of building identity and relationships throughout adulthood. Drawing on this literature, this review illustrates how bereavement narrative disclosure may be instrumental in addressing psychosocial challenges associated with bereavement (e.g., relationship formation, identity reconstruction, and meaning making). Multiple individual and social factors may affect how successful bereavement narrative disclosure is these challenges. Applying a social interactional model of memory telling, this review examines the influence of the relationship of narrator and listener, their personality characteristics, the content and structure of the narrative, the type of loss, and the time since the loss in facilitating or disrupting the putative goals of bereavement narrative disclosure. The utility of this model for clinicians working with bereaved individuals is also explored.
Prone to Bias: Development of a Bias Taxonomy from an Individual Differences Perspective
Authors: Oreg Shaul , Bayazit Mahmut
Published: August 2009

We adopt an individual-differences perspective and introduce a model that links types of biases and types of people. We propose that biases are created in the course of people's attempts to satisfy basic motivations, and that 3 such motivation categories underlie many of the biases discussed in the literature. Accordingly, our organizing framework integrates findings from previous research and classifies biases into verification biases, simplification biases, and regulation biases. Individual differences in core self-evaluations, in approach/avoidance temperament, and in cognitive ability and style help explain how biases come about and why some people are more likely than others to exhibit particular biases.
Cascades of Emotion: The Emergence of Borderline Personality Disorder from Emotional and Behavioral Dysregulation
Authors: Selby Edward A. , Joiner Thomas E.
Published: August 2009

Theories of borderline personality disorder (BPD) have often considered it a disorder involving both emotional and behavioral dysregulation ( Linehan, 1993 ), yet the connection between these phenomena has been elusive. The following paper proposes the Emotional Cascade Model, a model that attempts to establish a clear relationship between emotional dysregulation and the wide array of dysregulated behaviors found in BPD. In this model, subsequent to an emotional stimulus, ruminative processes result in a positive feedback loop that increases emotional intensity, and this emotional intensity leads to ensuing behavioral dysregulation. These behaviors then provide negative feedback, in the form of distraction, which induces temporary reduction of negative emotion and thus relief. The model is presented in a framework in which BPD is considered an emergent phenomenon ( Lewin, 1992 ), in which the disorder arises from the total interactions of a network containing emotional cascades and other important factors. The model is then evaluated in light of various theories and therapeutic traditions, including both cognitive–behavioral and psychodynamic, indicating that it is a model that may transcend traditional theoretical and therapeutic doctrines.
“Why did You Hurt Me?” Victim's Interpersonal Betrayal Attribution and Trust Implications
Authors: Chan MeowLan Evelyn
Published: August 2009

In this paper, I propose an attribution-based typology of betrayal. Specifically, incidental betrayal occurs when the trustee (perpetrator) violates the pivotal trust expectations of the trustor (victim) in the course of pursuing other goals; intentional betrayal occurs when the goal of the perpetrator is to violate the critical trust expectations of the victim in order to cause harm to him or her. Incidental betrayal is further categorized into egoistic betrayal and ideological betrayal, whereas intentional betrayal is further categorized into personalistic betrayal and reciprocal betrayal. In addition, I explicate how these various types of betrayal differentially affect the victim's perception of the perpetrator's trustworthiness.
The Undisordered Personality: Normative Assumptions Underlying Personality Disorder Diagnoses
Authors: Leising Daniel , Rogers Katherine , Ostner Julia
Published: August 2009

Clinical diagnoses are impossible without referring to normative assumptions about what is desirable functioning. In this paper, the authors explicate the implicit normative assumptions that seem to have guided the formulation of the Diagnostic and Statistical Manual of Mental Disorders ( DSM–IV) personality disorder (PD) criteria. Then the authors discuss various conceptual reference frames in which such assumptions may be grounded: (1) a given diagnostician's personal value system, (2) the expectations of the culture in which a person currently lives, (3) the expectations of the culture in which a person was raised, (4) models of “natural” personality functioning that are rooted in evolution theory, and (5) the presence of distress and/or impairment. In accordance with Wakefield (1992a , 2006 ), the authors argue that PD diagnoses necessarily involve both an evolutionary and a cultural component. If PDs were defined completely in cultural terms, investigating their biological underpinnings would be nonsensical. In addition, the values of any specific culture should not be given too much weight, because cultural expectations may themselves be harmful. Future editions of DSM should define personality pathology in less culture-relative terms, and address the inevitable issue of values more explicitly.
Purpose in Life as a System that Creates and Sustains Health and Well-Being: An Integrative, Testable Theory
Authors: McKnight Patrick E. , Kashdan Todd B.
Published: August 2009

Purpose—a cognitive process that defines life goals and provides personal meaning—may help explain disparate empirical social science findings. Devoting effort and making progress toward life goals provides a significant, renewable source of engagement and meaning. Purpose offers a testable, causal system that synthesizes outcomes including life expectancy, satisfaction, and mental and physical health. These outcomes may be explained best by considering the motivation of the individual—a motivation that comes from having a purpose. We provide a detailed definition with specific hypotheses derived from a synthesis of relevant findings from social, behavioral, biological, and cognitive literatures. To illustrate the uniqueness of the purpose model, we compared purpose with competing contemporary models that offer similar predictions. Addressing the structural features unique to purpose opens opportunities to build upon existing causal models of “how and why” health and well-being develop and change over time.
Seeds banks of desert annuals in an aridity gradient in the southern Atacama Desert
Authors: Sotomayor Diego , Gutiérrez Julio
Published: August 2009

*Background/Question/Methods*

Annual plant communities are important components of the biodiversity found in the coastal southern Atacama Desert in Chile. Moreover, they are an important economic resource for the human communities living in that area. These plant communities develop, after heavy rainfall episodes, a phenomenon locally known as the “blooming of the desert”. Although the minimum rainfall thresholds for these plants to emerge are relatively well known, little is known about their seed banks, its composition, dynamics and variation across the latitudinal aridity gradient from south to north. This system is interesting to study species coexistence, as well as, to look for exotic plants invasion, since previous studies have shown that exotic annual plants decreases in importance northwards. We hypothesize that, as a result of the gradient, we should find more seeds of annuals in the southern part because of the increase of exotic species. The lowest diversity will be found in the northern limit, while the highest in the middle part of the gradient, coincident with a natural protected area, and less influence of exotics. In terms of seed size and viability, we should find larger and more viable seeds in the southern limit of the gradient, probably contrasting with smaller and more dormant seeds to the north. To test these hypotheses we selected 8 sites along the gradient and collected soil samples after seed set in December 2008 for seed bank determination.

*Results/Conclusions*

According to our hypothesis we found more seeds in the southern part of the gradient. The northern seed banks (Rodillo and Cisne) are characterized by their low number of seeds and low species richness, according with their more extreme aridity. The central and southern seed banks have more than two times higher number and species richness than the northern ones. Southern seed banks (Lagunillas, Romeral and Punta Choros) contain more exotics’ seeds; meanwhile central seed banks (Pajonales, Carrizal Bajo and Los Bronces) have less seeds, and less exotics’ seeds. These results suggest that the increased seed number in the southern portion of the gradient could be due to an increased number of exotic species, rather than an increased diversity of native annuals. More viable and larger seeds were found in the southern sites, meanwhile, smaller seeds were found to the north indicating the use of a cautious opportunism strategy by these species. This is the first report on seed banks composition of this Atacama Desert area.
Enhancing Jatropha Productivity by Canopy Management
Authors: Reddy Chalapathy , Naole Vishal
Published: September 2009

Jatropha seed and oil yield is function of planting material used, growing conditions, plant architecture development and maintenance. Jatropha is hardy plant; thrives well in arid and semi arid regions with an average rainfall ranging from 500 to 1200 mm. It has been planted in varied soil types, marginal and waste lands; where in utilization of in situ resources by agronomic practices and development and management of canopy by pruning are very crucial for harvesting higher seed for biodiesel production. Building ideal canopy by pruning during first growing season is very important. Pruning is done during winter season when plants are in dormant condition.
Elevated CO2 and O3 Effects on Fine-Root Life Span in Ponderosa Pine
Authors: Phillips Donald , Johnson Mark , Tingey David , Storm Marjorie
Published: September 2009

Atmospheric carbon dioxide (CO2) and ozone (O3) concentrations are rising, which may have opposing effects on tree C balance and allocation to fine roots. More information is needed on interactive CO2 and O3 effects on roots, particularly fine-root life span, a critical demographic parameter and determinant of soil C and N pools and cycling rates. We conducted a study in which ponderosa pine (Pinus ponderosa) seedlings were exposed to two levels of CO2 and O3 in sun-lit controlled-environment terracosms for three years. Minirhizotrons were used to monitor individual fine roots in three soil horizons every 28 days. Proportional hazards regression was used to analyze effects of CO2, O3, diameter, depth, and season of root initiation on fine-root survivorship. More fine roots were produced in the elevated CO2 treatment than in ambient CO2. Median life spans varied from 140-448 days depending on the season of root initiation. Elevated CO2, increasing root diameter, and increasing root depth all significantly increased fine-root survivorship and median life span. Life span was slightly, but not significantly, lower in elevated O3, and increased O3 did not reduce the effect of elevated CO2. These results indicate the potential for elevated CO2 to increase the number of fine roots and their residence time in the soil, which is also affected by root diameter, root depth, and phenology.
One-dimensional quaternion homogeneous polynomial differential equations
Authors: Gasull Armengol , Llibre Jaume , Zhang Xiang
Published: August 2009

In this paper we study the dynamics of real four-dimensional polynomial differential equations of the forms q̇=aqkq¯m or q̇=qkaqm, where q,a are quaternions, q¯ is the conjugate of q, and k and m are non-negative integers. In many parts of the work the quaternion structure is used along the proofs.
Influence of an external magnetic field on forced turbulence in a swirling flow of liquid metal
Authors: Gallet Basile , Berhanu Michael , Mordant Nicolas
Published: August 2009

We report an experimental investigation on the influence of an external magnetic field on forced three-dimensional turbulence of liquid gallium in a closed vessel. We observe an exponential damping of the turbulent velocity fluctuations as a function of the interaction parameter N (ratio of Lorentz force over inertial terms of the Navier–Stokes equation). The flow structures develop some anisotropy but do not become bidimensional. From a dynamical viewpoint, the damping first occurs homogeneously over the whole spectrum of frequencies. For larger values of N, a very strong additional damping occurs at the highest frequencies. However, the injected mechanical power remains independent of the applied magnetic field. The simultaneous measurement of induced magnetic field and electrical potential differences shows a very weak correlation between magnetic field and velocity fluctuations. The observed reduction in the fluctuations is in agreement with a previously proposed mechanism for the saturation of turbulent dynamos and with the order of magnitude of the Von Kármán sodium dynamo magnetic field.
Near field millimeter wave microscopy with conical Teflon probes
Authors: Weiss Manoja D. , Zadler Brian , Schafer Scott , Scales John
Published: August 2009

We demonstrate 260 GHz (λ=1.15 mm) near field imaging using a conical Teflon probe whose tip protrudes through an aperture in a tapered aluminum holder. The imaging system is based on a quasioptical millimeter wave vector network analyzer. We present a variety of different imaging examples of dielectrics and metals, in both reflection and transmission modes, as well as an analysis of interesting diffraction and scattering effects observed in some of the images. The probe has an approximate tip diameter of 0.17 mm and an aperture size of about 1 mm. We observe horizontal resolution ranging from 0.2–0.5 mm depending on the sample being imaged.
Scratching properties of nickel-iron thin film and silicon using atomic force microscopy
Authors: Tseng Ampere A. , Shirakashi Jun-ichi , Nishimura Shinya , Miyashita Kazuya , Notargiacomo Andrea
Published: August 2009

Atomic force microscopy (AFM) is well known for its ability for nanopatterning many different materials. The patterning technique using an AFM tip as a scratch tool, known as scratch nanolithography, is used to study the scratch characteristics of 80% Permalloy thin film and silicon, with the emphasis on establishing their scratchability or the nanoscale machinability. The effects of the scratch parameters, including the applied tip force, scratch speed, and number of scratches, on the size of the scratched geometry were specifically evaluated. The primary factors that measure the scratchability were then identified and the governing material properties for scratchability were evaluated. To demonstrate its versatility, the scratching technique was applied to fabricate a NiFe-based nanoconstriction, which is used for many ferromagnetic devices. All results indicated that NiFe thin film has much better scratchability than that of Si and the scratched groove geometry can be accurately correlated with and precisely controlled by the tip normal force.
Spatial control in the heterogeneous nucleation of water
Authors: Varanasi Kripa K. , Hsu Ming , Bhate Nitin , Yang Wensha , Deng Tao
Published: August 2009

Heterogeneous nucleation of water plays an important role in a wide range of natural and industrial processes. Though heterogeneous nucleation of water is ubiquitous and an everyday experience, spatial control of this important phenomenon is extremely difficult. Here we show for the first time that spatial control in the heterogeneous nucleation of water can be achieved by manipulating the local nucleation energy barrier and nucleation rate via the modification of the local intrinsic wettability of a surface. Such ability to control water nucleation could address the condensation-related limitations of superhydrophobic surfaces and has implications for efficiency enhancements in energy and desalination systems.
Enlarged near-field optical imaging
Authors: Lérondel G. , Sinno A. , Chassagne L. , Blaize S. , Ruaux P. , Bruyant A. , Topçu S. , Royer P. , Alayli Y.
Published: August 2009

Millimeter scale near-field optical microscopy is here reported. It is demonstrated in the near infrared by observing light propagating in an integrated glass waveguide. Enlarged near-field imaging was made possible thanks to the use of a homemade interferometric translation stage with nanometric scale repeatabilities combined with a commercial atomic force microscope. An integrated optical component was used as a representative example of multiscale components requiring large scale highly resolved optical mapping. By imaging stationary waves on a millimeter long range followed by Fourier analysis, an uncertainty of a few 10−4 on the waveguide modes effective index was obtained. While improving the optogeometrical parameter retrieval precision, millimeter scans make the technique sensitive to properties such as birefringence.
Clustering of passive impurities in magnetohydrodynamic turbulence
Authors: Homann H. , Bec J. , Fichtner H. , Grauer R.
Published: August 2009

The transport of heavy, neutral, or charged pointlike particles by three-dimensional incompressible, resistive magnetohydrodynamic turbulence is investigated by means of high-resolution numerical simulations. The spatial distribution of such impurities is observed to display strong deviations from homogeneity, both at dissipative and inertial range scales. Neutral particles tend to cluster in the vicinity of coherent vortex sheets due to their viscous drag with the flow, leading to the simultaneous presence of very concentrated and almost empty regions. The signature of clustering is different for charged particles because they are influenced both by the drag and the Lorentz forces. The regions of spatial inhomogeneities change due to attractive and repulsive vortex sheets. While small charges increase clustering, larger charges have a reverse effect.
Supertetrahedra and superalgebras
Authors: Sergeev Sergey M.
Published: August 2009

In this paper we give a detailed classification scheme for three-dimensional quantum zero curvature representation and tetrahedron equations. This scheme includes both even and odd parity components; the resulting algebras of observables are either Bose q-oscillators or Fermi oscillators. Three-dimensional R-matrices intertwining variously oriented tensor products of Bose and Fermi oscillators and satisfying tetrahedron and supertetrahedron equations are derived. The 3d→2d compactification reproduces Uq(gl̂(n∣m)) superalgebras and their representation theory.
Time-resolved x-ray diffraction study of laser-induced shock and acoustic waves in single crystalline silicon
Authors: Liss K.-D. , d’Almeida T. , Kaiser M. , Hock R. , Magerl A. , Eloy J. F.
Published: August 2009

A rod of single crystalline silicon has been subjected to high-power nanosecond laser pulses inducing ultrasonic and shock waves traveling into the bulk of the material. Stroboscopic time-resolved high-energy x-ray diffraction measurements were carried out in situ to probe for strain states in the bulk of the sample. First, a supersonic shock front is observed which moves faster than the longitudinal acoustic phonons. Following the shock front, a much slower bunch of waves travels along the crystal. The x-ray diffraction records obtained in different configurations reflect a strong dependence of the wave propagation on the sample geometry. These results offer an experimental approach for the investigation of coherent phonons, structural phase transformations, plastic deformations induced during shock peening, and for the development of x-ray free-electron-laser optics.
Shielding of external magnetic perturbations by torque in rotating tokamak plasmas
Authors: Park Jong-Kyu , Boozer Allen H. , Menard Jonathan E. , Gerhardt Stefan P. , Sabbagh Steve A.
Published: August 2009

The imposition of a nonaxisymmetric magnetic perturbation on a rotating tokamak plasma requires energy and toroidal torque. Fundamental electrodynamics implies that the torque is essentially limited and must be consistent with the external response of a plasma equilibrium f⃗=j⃗×B⃗. Here magnetic measurements on National Spherical Torus Experiment device are used to derive the energy and the torque, and these empirical evaluations are compared with theoretical calculations based on perturbed scalar pressure equilibria f⃗=∇⃗p coupled with the theory of nonambipolar transport. The measurement and the theory are consistent within acceptable uncertainties, but can be largely inconsistent when the torque is comparable to the energy. This is expected since the currents associated with the torque are ignored in scalar pressure equilibria, but these currents tend to shield the perturbation.
Strain relaxation in epitaxial Pt films on (001) SrTiO3
Authors: Son Junwoo , Cagnon Joël , Stemmer Susanne
Published: August 2009

The relationship between strain relaxation and microstructure evolution of epitaxial, (001)-oriented Pt thin films on (001) SrTiO3 substrates is investigated as a function of Pt film thickness. X-ray diffraction shows that the Pt films gradually relax after film coalescence with increasing film thickness. The Pt film surfaces exhibit a cross-hatched surface pattern that increases in amplitude and density with film thickness and is due to progressive relaxation of the lattice mismatch strain by twinning. The potential of these Pt films as bottom electrodes for functional perovskite films is discussed.
Solar collector basics
Authors: Richter John L.
Published: August 2009

This is a guide for solar collector use. Section II shows the effective number of sunlit hours per day at the solstices and equinox captured by several solar collector types: stationary flat, sun tracking flat, east-west parabolic and two-trough concentrators and a north-south, sun tracking, two-trough concentrator. Section III introduces the sun direction from the circular orbit earth; it is accurate enough for most applications. Section IV develops atmospheric attenuation of sunlight. Section V puts it all together for the calculated results presented in Sec. II.
Catalyst proximity effects on the growth rate of Si nanowires
Authors: Boles S. T. , Fitzgerald E. A. , Thompson C. V. , Ho C. K. F. , Pey K. L.
Published: August 2009

Si nanowires grown by the vapor-liquid-solid (VLS) mechanism were fabricated using Au-catalyst nanoparticles and silane (SiH4) gas on Si substrates. Au was deposited on the substrate surface both by electron-beam evaporation and Au-colloid deposition. Both kinking defects and vertical nanowire epitaxy on Si ⟨111⟩ substrates were found to be directly related to SiH4 flow rate. A correlation between Au-colloid dilution and the nanowire growth rate was also observed, with the growth rate increasing with increasing concentrations of Au-catalyst particles on the wafer surface. Systematic experiments relating the nanowire growth rate to the proximity of nearest-neighbor Au particles and Au reservoirs were carried out, and the results were found to be in good agreement with a SiH4 reaction model, which associates decomposition to form SiH2 with higher nanowire growth rates. Implications toward the realization of VLS-grown single nanowire transistors are discussed.
Effect of uniaxial stress on ferroelectric behavior of (Bi1/2Na1/2)TiO3-based lead-free piezoelectric ceramics
Authors: Tan X. , Aulbach E. , Jo W. , Granzow T. , Kling J. , Marsilius M. , Kleebe H.-J. , Rödel J.
Published: August 2009

Prior studies have shown that a field-induced ferroelectricity in ceramics with general chemical formula (1−x−y)(Bi1/2Na1/2)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 and a very low remanent strain can produce very large piezoelectric strains. Here we show that both the longitudinal and transverse strains gradually change with applied electric fields even during the transition from the nonferroelectric to the ferroelectric state, in contrast to known Pb-containing antiferroelectrics. Hence, the volume change and, in turn, the phase transition can be affected using uniaxial compressive stresses, and the effect on ferroelectricity can thus be assessed. It is found that the 0.94(Bi1/2Na1/2)TiO3–0.05BaTiO3–0.01(K0.5Na0.5)NbO3 ceramic (largely ferroelectric), with a rhombohedral R3c symmetry, displays large ferroelectric domains, significant ferroelastic deformation, and large remanent electrical polarizations even at a 250 MPa compressive stress. In comparison, the 0.91(Bi1/2Na1/2)TiO3–0.07BaTiO3–0.02(K0.5Na0.5)NbO3 ceramic (largely nonferroelectric) possesses characteristics of a relaxor ferroelectric ceramic, including a pseudocubic structure, limited ferroelastic deformation, and low remanent polarization. The results are discussed with respect of the proposed antiferroelectric nature of the nonferroelectric state.
Current oscillations in a wide graphene sheet
Authors: Dragoman M. , Dragoman D. , Deligiorgis G. , Konstantinidis G. , Neculoiu D. , Cismaru A. , Plana R.
Published: August 2009

We report on measurements and modeling of a new physical effect in graphene, which consists of oscillations in the current-voltage characteristic measured between wide contacts patterned across a graphene flake. The origin of this effect is the carrier transport dependence on the two spatial components of the wave vector, dependence that becomes evident for wide contacts and affects the transmission of ballistic electrons, similar to the case of non-normal incidence.
Electron spin resonance of defect-rich vanadium oxide nanotubes
Authors: Won Lee Kyu , Kweon Hyocheon , Lee Cheol Eui
Published: August 2009

We have studied defect-rich vanadium oxide nanotubes, with reduced V4+ concentration, by means of x-ray diffraction, infrared spectroscopy, x-ray photoemission spectroscopy, and electron spin resonance (ESR) measurements. In particular, prominent anomalies at 320 and 370 K attributed to structural phase transitions were manifest in the ESR measurements. The ESR spin susceptibility exhibited a singlet-triplet transition of the spin dimers and an antiferromagnetic exchange coupling. In the high-temperature region above 370 K, where the two distinct ESR lines merged, an activation energy of the fast hopping polaron motion, 0.48 eV, was obtained.
On the breakup of fluid rivulets
Authors: Diez Javier A. , González Alejandro G. , Kondic Lou
Published: August 2009

We study the stability of rivulets on horizontal substrates. The implemented model includes the effects of capillarity, fluid-solid interaction, and gravity if appropriate, within the framework of the lubrication approximation. We find that the results compare favorably with those in literature, in the regime where previous analyses are valid. By isolating the effect of van der Waals interactions for nanoscale rivulets, and of gravity for macrosize rivulets, we are able to analyze the influence of these forces on the stability. We discuss in detail the scaling of the emerging wavelengths (distance between drops formed after the breakup process) with the rivulet cross-sectional area. Perhaps surprisingly, we uncover close connection between this scaling and the one for the breakup of a free-space fluid jet (Rayleigh–Plateau instability). Finally, we consider rivulets of finite length and find that the finite size effects are considerably different from the ones obtained previously for semi-infinite fluid films.
Bottom reconstruction in thin-film flow over topography: Steady solution and linear stability
Authors: Heining C. , Aksel N.
Published: August 2009

We consider viscous gravity-driven films flowing over undulated substrates. Instead of the widely studied direct problem of finding the free surface for a given bottom topography, we focus on the inverse problem: Given a specific free surface shape, we seek the corresponding bottom topography which causes this free surface profile. As an asymptotic approach for thin films and moderate Reynolds numbers, we apply the weighted-residual integral boundary-layer method which enables us to derive a set of two evolution equations for the film thickness and the flow rate. We prescribe the free surface as a monofrequent periodic function and discuss the influence of inertia, film thickness, and surface tension on the shape of the corresponding substrate. For small free surface undulations, we can solve the bottom contour analytically and study its parametric dependence. The analytical results are then validated with numerical simulations. Furthermore, we consider the stability of the corresponding direct problem, which reveals that the bottom topography is stabilizing or destabilizing, depending on surface tension.
Interrogating vertically oriented carbon nanofibers with nanomanipulation for nanoelectromechanical switching applications
Authors: Kaul Anupama B. , Khan Abdur R. , Bagge Leif , Megerian Krikor G. , LeDuc Henry G. , Epp Larry
Published: August 2009

We have demonstrated electrostatic switching in vertically oriented carbon nanofibers synthesized on refractory metallic nitride substrates, where pull-in voltages Vpi ranged from 10 to 40 V. A nanoprobe was used as the actuating electrode inside a scanning-electron microscope and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical Vpi and results were compared to experiment. Nanomanipulation tests also revealed tubes synthesized directly on Si by dc plasma-enhanced chemical-vapor deposition with ammonia and acetylene were electrically unsuitable for dc nanoelectromechanical switching applications.
Temporal optimization of neutron generation from the exploding deuterated methane jet of clusters subjected to an intense laser pulse
Authors: Lu Haiyang , Liu Jiansheng , Wang Cheng , Wang Wentao , Zhou Zili , Deng Aihua , Xia Changquan , Xu Yi , Leng Yuxin , Ni Guoquan , Li Ruxin , Xu Zhizhan
Published: August 2009

An experimental investigation on the interaction of an ultraintense femtosecond laser pulse at the intensity of 2×1017 W/cm2 (60 fs, 120 mJ at 800 nm) with clusters in a supersonic jet of deuterated methane gas has shown the generation of energetic deuterons and nuclear fusion events. The deuteron density and the average size of the clusters in the gas jet, as well as the fusion neutron yields under different backing pressures were measured simultaneously as a function of the time delays of the laser pulses with respect to the puffing of the gas jet. The results demonstrate that during the development of the gas jet expanding through a conical nozzle, the clusters grew up with time, and the average size of the clusters reached the maximum when the molecular density in the jet started to drop. The fusion neutron yields were found to increase with the larger average cluster size and the higher deuteron density, in accordance with the theoretical prediction. Experimental data indicate the existence of a ∼1 ms steady region in which the fusion neutron yields have reached the maximum of 2.0×105 per shot at the backing pressure of 74 bars. Consequently, an efficiency of 1.6×106 neutrons per joule of incident laser energy was realized.
Design of a variable temperature scanning force microscope
Authors: Nazaretski E. , Graham K. S. , Thompson J. D. , Wright J. A. , Pelekhov D. V. , Hammel P. C. , Movshovich R.
Published: August 2009

We have developed the variable temperature scanning force microscope capable of performing both magnetic resonance force microscopy (MRFM) and magnetic force microscopy (MFM) measurements in the temperature range between 5 and 300 K. Modular design, large scanning area, and interferometric detection of the cantilever deflection make it a sensitive, easy to operate, and reliable instrument suitable for studies of the dynamic and static magnetization in various systems. We have verified the performance of the microscope by imaging vortices in a Nb thin film in the MFM mode of operation. MRFM spectra in a diphenyl-picryl-hydrazyl film were recorded to evaluate the MRFM mode of operation.
Wideband digital frequency detector with subtraction-based phase comparator for frequency modulation atomic force microscopy
Authors: Mitani Yuji , Kubo Mamoru , Muramoto Ken-ichiro , Fukuma Takeshi
Published: August 2009

We have developed a wideband digital frequency detector for high-speed frequency modulation atomic force microscopy (FM-AFM). We used a subtraction-based phase comparator (PC) in a phase-locked loop circuit instead of a commonly used multiplication-based PC, which has enhanced the detection bandwidth to 100 kHz. The quantitative analysis of the noise performance revealed that the internal noise from the developed detector is small enough to provide the theoretically limited noise performance in FM-AFM experiments in liquid. FM-AFM imaging of mica in liquid was performed with the developed detector, showing its stability and applicability to true atomic-resolution imaging in liquid.
Friction on the microscale
Authors: Paul K. B. , Malkinski L.
Published: August 2009

A new method is presented for measurements of friction of microsized particles on surfaces. Specifically in this work, the particles are alumina with diameters between ≈1 and 50 μm and the surfaces are InP, Si, and Cr. Friction is analyzed, its components are determined, and the friction coefficients are estimated from the experimental results. The technique and the specific instrument allow measurements of coefficients of friction for spherical particles with radii as small as 1 μm. For smaller sizes, the instrument needs to be modified by using a more powerful power supply, actuator with extended frequency and amplitude ranges, cooling of the actuator and the power supply, and the related mechanical modifications of the sample holder.
Selective subsurface absorption of hydrogen in palladium using laser distillation
Authors: Tremblay Jean Christophe , Saalfrank Peter
Published: August 2009

A theoretical model for the selective subsurface absorption of atomic hydrogen in a Pd(111) surface by infrared (IR) laser pulses is presented. The dynamics of the adsorbate is studied within the reduced density matrix approach. Energy and phase relaxation of the hydrogen atom are treated using the semigroup formalism. The vibrational excitation leading to subsurface absorption is performed using rationally designed pulses as well as IR laser pulses optimized on-the-fly. It is shown that dissipation can be used as a tool to transfer population to an otherwise inaccessible state via a mechanism known as “laser distillation.” We demonstrate that when the reaction path is generalized from a reduced one-dimensional to full three-dimensional treatment of the system, the laser control strategy can prove very different.
A comprehensive study of the phase diagram of KxNa1−xNbO3
Authors: Baker D. W. , Thomas P. A. , Zhang N. , Glazer A. M.
Published: August 2009

The phase diagram of lead-free piezoelectric KxNa1−xNbO3 has been studied, with particular focus on the proposed morphotropic phase boundaries, by powder and single crystal x-ray diffraction. The tilt system and cation displacement has been mapped out as a function of temperature and composition, highlighting changes in the oxygen octahedra at x=0.2 and x=0.4 at room temperature. The orthorhombic to monoclinic boundary at x=0.5 has been investigated, with a subtle change in the structure observed. The conclusion is that KxNa1−xNbO3 does not display a morphotropic phase boundary comparable with that in lead zirconate titanate, and that the most significant structural change as a function of composition occurs at x=0.2 because of the change of the tilt system.
Resistivity noise in crystalline magnetic nanowires and its implications to domain formation and kinetics
Authors: Singh Amrita , Chowdhury Debtosh , Ghosh Arindam
Published: August 2009

We have investigated the time-dependent fluctuations in electrical resistance, or noise, in high-quality crystalline magnetic nanowires within nanoporous templates. The noise increases exponentially with increasing temperature and magnetic field, and has been analyzed in terms of domain wall depinning within the Neel–Brown framework. The frequency-dependence of noise also indicates a crossover from nondiffusive kinetics to long-range diffusion at higher temperatures, as well as a strong collective depinning, which need to be considered when implementing these nanowires in magnetoelectronic devices.