bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a four‐dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations
Authors: Sugiura Nozomi , Awaji Toshiyuki , Masuda Shuhei , Mochizuki Takashi , Toyoda Takahiro , Miyama Toru , Igarashi Hiromichi , Ishikawa Yoichi
Published: October 2008

A four‐dimensional variational (4D‐VAR) data assimilation system using a coupled ocean‐atmosphere global model has been successfully developed with the aim of better defining the dynamical states of the global climate on seasonal to interannual scales. The application of this system to state estimations of climate processes during the 1996–1998 period shows, in particular, that the representations of structures associated with several key events in the tropical Pacific and Indian Ocean sector (such as the El Niño, the Indian Ocean dipole, and the Asian summer monsoon) are significantly improved. This fact suggests that our 4D‐VAR coupled data assimilation (CDA) approach has the potential to correct the initial location of the model climate attractor on the basis of observational data. In addition, the coupling parameters that control the air‐sea exchange fluxes of mass, momentum, and heat become well adjusted. Such an initialization using the 4D‐VAR CDA approach allows us to make a roughly 1.5‐year lead time prediction of the 1997–1998 El Niño event. These results demonstrate that our 4D‐VAR CDA system has the ability to enhance forecast potential for seasonal to interannual phenomena.
A method to account for surface albedo heterogeneity in single‐column radiative transfer calculations under overcast conditions
Authors: Pirazzini Roberta , Räisänen Petri
Published: October 2008

A simple parameterization to derive the broadband effective albedo over highly reflecting surfaces under overcast conditions is presented. High spatial variability in the surface albedo affects the downwelling solar irradiance in neighboring regions via the multiple reflections of light between the surface and the cloud base. The effective albedo is defined as the albedo of a homogeneous surface that would result in the same downwelling irradiance as observed at the observation point in the presence of a heterogeneous surface. The proposed method parameterizes the effective albedo using the cloud base height and a surface albedo map as inputs. The parameterization is based on the spatial distribution of surface reflections contributing to the downwelling irradiance at the observation site, which is approximated with a gamma distribution. The parameterization was validated against reference values of effective albedo derived from three‐dimensional backward Monte Carlo and one‐dimensional DISORT radiative transfer calculations for four idealized surface albedo maps and various specifications of cloud properties. It gave values of effective albedo very close to the reference calculations, performing substantially better than any other approach tested, also when applied to the retrieval of cloud optical depth. The method can be implemented into one‐dimensional radiative transfer models or used to interpret broadband irradiance measurements in Polar coastal regions, in the marginal sea ice zones, or in patchy terrain with forests and snow‐covered fields.
First in situ investigation of a dark wind streak on Mars
Authors: Geissler P. E. , Johnson J. R. , Sullivan R. , Herkenhoff K. , Mittlefehldt D. , Fergason R. , Ming D. , Morris R. , Squyres S. , Soderblom L. , Golombek M.
Published: October 2008

Prominent low‐albedo wind streaks issue from embayments at the north end of Victoria crater in Meridiani Planum, the site of surface investigations by the Mars Exploration Rover Opportunity. Opportunity was sent to examine the darkest of these wind streaks and compare it to the adjacent soil in the brighter corridor between the streaks. Two nearby sites inside and outside of the streak were selected for visible and infrared remote sensing and for elemental abundance measurements and images of the microscopic soil morphology. The rover was next sent to study the interaction of the wind streak with an obstacle, a small rock near the source of the streak. Opportunity's observations suggest that the Victoria wind streaks are deposits of basaltic sand blown out of the crater from the dark dunes nestled below the crater rim, particularly at the base of the alcove leading up to the darkest streak. No local sources of sand have been identified within the Victoria crater wall rock, suggesting that the sand is supplied from outside the crater and is presently escaping its temporary topographic trap. This process presents a possible explanation for the serrated margin of Victoria crater through abrasion of the soft rock as trapped sands are blown out of the crater and carve alcoves under various seasonal winds. Some indication of the rate of activity of these wind streaks will be provided by continued monitoring of the erasure of the rover's tracks.
Cyclostrophic winds from the Visible and Infrared Thermal Imaging Spectrometer temperature sounding: A preliminary analysis
Authors: Piccialli A. , Titov D. V. , Grassi D. , Khatuntsev I. , Drossart P. , Piccioni G. , Migliorini A.
Published: October 2008

Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) onboard the Venus Express spacecraft has been operating since April 2006 providing new observations of the temperature structure of Venus mesosphere (60–95 km). Zonal winds in the middle atmosphere of Venus have been retrieved from VIRTIS temperature profiles using the cyclostrophic approximation. The wind field is characterized by three main features: (1) a midlatitude jet connected to the thermal feature known as the cold collar; the jet reaches a maximum speed of 80–90 ± 10 m/s near the cloud top (∼70 km altitude) at 50°S latitude; (2) a strong decrease of wind from 60°S toward the pole reaching zero velocity at ∼70°S; and (3) the decrease of the wind above the jet with increasing altitude. Local time dependence of the temperature and wind field has been analyzed. Temperatures show at cloud tops a cooling of ∼15 K during the night which propagates also on the zonal wind field. Comparison with cloud‐tracked winds from Venus Monitoring Camera images indicates a first‐order agreement.
Northern timing of deglaciation in the eastern equatorial Pacific from alkenone paleothermometry
Authors: Koutavas Athanasios , Sachs Julian P.
Published: October 2008

The equatorial cold tongue (ECT) of the eastern Pacific is the most dynamic ocean region in the world's tropics and sets the tempo for global climate anomalies arising from El Niño–Southern Oscillation (ENSO) events. This region's deglaciation history and relationship with north and south polar climates remains poorly understood, impeding integration of tropical Pacific ocean‐atmosphere dynamics and ENSO variability in our understanding of glacial cycles. Here we present alkenone reconstructions of sea surface temperature (SST) across the last glacial termination from five ECT cores east of the Galapagos Islands. A composite index of SST based on these demonstrates strong temporal affinity with the two‐step deglaciation of the Northern Hemisphere, composed of two distinct warming steps at the beginning of the Bölling and the end of the Younger Dryas intervals. Within dating uncertainty, warming in the ECT began in phase with the Bölling excursion, was followed by a 2–3 ka plateau, and resumed with a second pulse at the end of the Younger Dryas. On the basis of our reconstructions, about two thirds of the warming materialized at or after the end of the Younger Dryas, implying a marked delay in the region's response to deglaciation. The results challenge the prevailing paradigm that ECT deglacial history conforms to an Antarctic timing, commonly attributed to advection from the Southern Ocean through an interior oceanic link, or to synchronous response of both regions to CO2 forcing. Our results emphasize instead the role of dynamical adjustments linked to Northern Hemisphere processes, most likely transmitted through the atmosphere.
Major shifts in calcareous phytoplankton assemblages through the Eocene‐Oligocene transition of Tanzania and their implications for low‐latitude primary production
Authors: Dunkley Jones Tom , Bown Paul R. , Pearson Paul N. , Wade Bridget S. , Coxall Helen K. , Lear Caroline H.
Published: October 2008

A high‐resolution record of exceptionally well preserved calcareous nannofossil assemblages from Tanzania is marked by two key transitions closely related to the climatic events of the Eocene‐Oligocene transition (EOT). The first transition, at ∼34.0 Ma, precedes the first positive shift inδ18O and coincides with a distinct interval of very low nannofossil abundance and a cooling in sea surface temperatures (SST). The second, at ∼33.63 Ma, is immediately above the Eocene‐Oligocene boundary (EOB) and is associated with a significant drop in nannofossil diversity. Both transitions involve significant reductions in the abundance of holococcoliths and other oligotrophic taxa. These changes in calcareous phytoplankton assemblages indicate (1) a widespread and significant perturbation to the low‐latitude surface ocean closely tied to the EOB, (2) a potential role for reduced carbonate primary production at the onset of global cooling, and (3) a significant increase in nutrient availability in the low‐latitude surface ocean through the EOT.
Inflammatory caspases are critical for enhanced cell death in the target tissue of Sjögren's syndrome before disease onset
Authors: Bulosan Marievic , Pauley Kaleb M , Yo Kyumee , Chan Edward K L , Katz Joseph , Peck Ammon B , Cha Seunghee
Published: October 2008

To date, little is known about why exocrine glands are subject to immune cell infiltrations in Sjögren's syndrome (SjS). Studies with SjS‐prone C57BL/6.NOD‐Aec1Aec2 mice showed altered glandular homeostasis in the submandibular glands (SMX) at 8 weeks before disease onset and suggested the potential involvement of inflammatory caspases (caspase‐11 and ‐1). To determine whether inflammatory caspases are critical for the increased epithelial cell death before SjS‐like disease, we investigated molecular events involving caspase‐11/caspase‐1 axis. Our results revealed concurrent upregulation of caspase‐11 in macrophages, STAT‐1 activity, caspase‐1 activity and apoptotic epithelial cells in the SMX of C57BL/6.NOD‐Aec1Aec2 at 8 weeks. Caspase‐1, a critical factor for interleukin (IL)‐1β and IL‐18 secretion, resulted in an elevated level of IL‐18 in saliva. Interestingly, TUNEL‐positive cells in the SMX of C57BL/6.NOD‐Aec1Aec2 were not colocalized with caspase‐11, indicating that caspase‐11 functions in a noncell autonomous manner. Increased apoptosis of a human salivary gland (HSG) cell line occurred only in the presence of lipopolysaccharide (LPS‐) and interferon (IFN)‐γ‐stimulated human monocytic THP‐1 cells, which was reversed when caspase‐1 in THP‐1 cells was targeted by siRNA. Taken together, our study discovered that inflammatory caspases are essential in promoting a pro‐inflammatory microenvironment and influencing increased epithelial cell death in the target tissues of SjS before disease onset.
Phosphate rich organic manure as fertiliser
Authors: Sekhar DMR , Dassin Y , Momani Lutfi , Hamatteh Abu
Published: October 2008

Certain types of rock phosphates of sedimentary origin are applied to acidic soils as fertilizer directly. Recent research in India showed that high grade rock phosphate in fine size when used as a mix with organic manure works as efficiently as di-ammonium phosphate (DAP) in alkaline soils. The rock phosphate from Jhamarkotra, India (sedimentary origin), Egypt (sedimentary origin) and South Africa (volcanic origin) showed good agronomic efficiency when used as Phosphate Rich Organic Manure (PROM). Further PROM shows equal residual effect. The results of efficiency of PROM made using two grades (+ 24% P2O5 and 34% P2O5) of rock phosphate mineral from Jordan show that low grade rock phosphate slimes are as effective as high grade phosphate concentrate when used in PROM. Also PROM is very effective even in the saline soils where DAP completely fails.
Activation of the small GTPase Rac1 by a specific guanine‐nucleotide‐exchange factor suffices to induce glucose uptake into skeletal‐muscle cells
Authors: Ueda Shuji , Kataoka Tohru , Satoh Takaya
Published: October 2008

Background information. Insulin‐stimulated glucose uptake into skeletal muscle is crucial for glucose homoeostasis, and depends on the recruitment of GLUT4 (glucose transporter 4) to the plasma membrane. Mechanisms underlying insulin‐dependent GLUT4 translocation, particularly the role of Rho family GTPases, remain controversial.

Results. In the present study, we show that constitutively active Rac1, but not other Rho family GTPases tested, induced GLUT4 translocation in the absence of insulin, suggesting that Rac1 activation is sufficient for GLUT4 translocation in muscle cells. Rac1 activation occurred in dorsal membrane ruffles of insulin‐stimulated cells as revealed by a novel method to visualize activated Rac1 in situ. We further identified FLJ00068 as a GEF (guanine‐nucleotide‐exchange factor) responsible for this Rac1 activation. Indeed, constitutively active FLJ00068 caused Rac1 activation in dorsal membrane ruffles and GLUT4 translocation without insulin stimulation. Down‐regulation of Rac1 or FLJ00068 by RNA interference, on the other hand, abrogated insulin‐induced GLUT4 translocation. Basal, but not insulin‐stimulated, activity of the serine/threonine kinase Akt was required for the induction of GLUT4 translocation by constitutively active Rac1 or FLJ00068.

Conclusion. Collectively, Rac1 activation specifically in membrane ruffles by the GEF FLJ00068 is sufficient for insulin induction of glucose uptake into skeletal‐muscle cells.
Repulsive guidance molecule A (RGM A) and its receptor neogenin during neural and neural crest cell development of Xenopus laevis
Authors: Gessert Susanne , Maurus Daniel , Kühl Michael
Published: October 2008

Background information. RGM A (repulsive guidance molecule A) is a GPI (glycosylphosphatidylinositol)‐anchored glycoprotein which has repulsive properties on axons due to the interaction with its receptor neogenin. In addition, RGM A has been demonstrated to function as a BMP (bone morphogenetic protein) co‐receptor.

Results. In the present study, we provide the first analysis of early RGM A and neogenin expression and function in Xenopus laevis neural development. Tissue‐specific RGM A expression starts at stage 12.5 in the anterior neural plate. Loss‐of‐function analyses suggest a function of RGM A and neogenin in regulating anterior neural marker genes, as well as eye development and neural crest cell migration. Furthermore, overexpression of RGM A leads to ectopic expression of neural crest cell marker genes.

Conclusions. These data indicate that RGM A and neogenin have important functions during early neural development, in addition to their role during axonal guidance and synapse formation.
Atypical sialylated N-glycan structures are attached to neuronal voltage-gated potassium channels
Authors: Cartwright Tara A. , Schwalbe Ruth A.
Published: October 2008

Mammalian brains contain relatively high amounts of common and uncommon sialylated N-glycan structures. Sialic acid linkages were identified for voltage-gated potassium channels, Kv3.1, 3.3, 3.4, 1.1, 1.2 and 1.4, by evaluating their electrophoretic migration patterns in adult rat brain membranes digested with various glycosidases. Additionally, their electrophoretic migration patterns were compared with those of NCAM (neural cell adhesion molecule), transferrin and the Kv3.1 protein heterologously expressed in B35 neuroblastoma cells. Metabolic labelling of the carbohydrates combined with glycosidase digestion reactions were utilized to show that the N-glycan of recombinant Kv3.1 protein was capped with an oligo/poly-sialyl unit. All three brain Kv3 glycoproteins, like NCAM, were terminated with α2,3-linked sialyl residues, as well as atypical α2,8-linked sialyl residues. Additionally, at least one of their antennae was terminated with an oligo/poly-sialyl unit, similar to recombinant Kv3.1 and NCAM. In contrast, brain Kv1 glycoproteins consisted of sialyl residues with α2,8-linkage, as well as sialyl residues linked to internal carbohydrate residues of the carbohydrate chains of the N-glycans. This type of linkage was also supported for Kv3 glycoproteins. To date, such a sialyl linkage has only been identified in gangliosides, not N-linked glycoproteins. We conclude that all six Kv channels (voltage-gated K+ channels) contribute to the α2,8-linked sialylated N-glycan pool in mammalian brain and furthermore that their N-glycan structures contain branched sialyl residues. Identification of these novel and unique sialylated N-glycan structures implicate a connection between potassium channel activity and atypical sialylated N-glycans in modulating and fine-tuning the excitable properties of neurons in the nervous system.
Theory analysis of wavelength dependence of laser-induced phase explosion of silicon
Authors: Lu Quanming , Mao Samuel S. , Mao Xianglei , Russo Richard E.
Published: October 2008

Wavelength dependence of laser ablation of silicon was investigated with nanosecond ultraviolet, visible, and infrared laser pulses in the irradiance range from 3×1010 to 1×1012 W/cm2. For 266 and 532 nm laser pulses, the depth of laser-produced crater shows a dramatic increase at a laser irradiance threshold of approximately 2×1010 and 4×1011 W/cm2 respectively, above which, large micron-sized particulates were observed to eject from the target about 300–400 ns after the laser pulse. In contrast, for 1064 nm pulse, this dramatic increase was not observed. The underlying mechanism for the observed threshold phenomenon is presented in this study, which can be attributed to the thermal diffusion and subsequent explosive boiling after the completion of the interaction between the nanosecond laser pulse and silicon. Based on our delayed phase explosive model, the ablation depths were calculated for different wavelengths and compared to experimental results. Plasma shielding during laser irradiation was included in the model, which plays a key role to the coupling of laser energy to the irradiated material.
Electronic spectroscopy of the Au(6p)–Kr complex
Authors: Plowright Richard J. , Watkins Mark J. , Gardner Adrian M. , Wright Timothy G. , Breckenridge W. H. , Wallimann Franz , Leutwyler Samuel
Published: October 2008

We report electronic absorption spectra, recorded using one- and two-color resonance-enhanced multiphoton ionization spectroscopy, of the Au–Kr complex. The transition is localized on the gold atom, and corresponds to a 6p←6s atomic excitation; we observe transitions to the DΠ1∕22 and DΠ3∕22 spin-orbit states. In addition, we report the results of ab initio calculations, which consider electronic states arising from the 6S2, 5D2, and 6P2 atomic energy levels of Au. Further, we also report an accurate value for the dissociation energy of the ground state of Au–Kr, based on basis set extrapolated RCCSD(T) calculations. The experimental results are discussed in the light of the theoretical ones.
Radiochemical tracers as a mix diagnostic for the ignition double-shell capsule
Authors: Colvin Jeffrey , Cerjan Charles , Hoffman Robert , Stoyer Mark , Amendt Peter
Published: October 2008

One of the most important challenges confronting laser-driven capsule implosion experiments will be a quantitative evaluation of the implosion dynamics. Since these experiments will encounter extreme conditions of pressure and temperature, establishing robust, sensitive diagnostics will be difficult. Radiochemical signatures provide insight into material mixing and laser drive asymmetry and complement x-ray and other nuclear diagnostics, since the relevant nuclear reactions sample core implosion conditions directly. Simulations of an ignition double shell target indicate that several experimentally accessible isomeric ratios will be suitable monitors of mix.
Can convection induced by heating delay a thermal explosion?
Authors: Al-Aseeri M. , Guo W. , Johns L. E. , Narayanan R.
Published: October 2008

A thermal explosion is said to occur in a region if heat generated steadily therein cannot be conducted to its boundaries. Our interest is in the effect of natural convection on the conditions for thermal explosion. It is surprising that adding a second mechanism for heat loss lowers the steady rate of heat generation and, therefore, that natural convection appears to do little to change the point of explosion. This is due to the fact that the flow, by lowering the heat generation, is self-weakening.
Using the isotropic periodic sum method to calculate long-range interactions of heterogeneous systems
Authors: Wu Xiongwu , Brooks Bernard R.
Published: October 2008

Isotropic periodic sum (IPS) is a method for the calculation of long-range interactions in molecular simulation based on the homogeneity of simulation systems. Three IPS models, 3D IPS, 2D IPS, and 1D IPS have been developed for three common types of homogeneous systems. Based on the fact that 3D IPS can well describe the long-range interactions of a heterogeneous system if a local region larger than the homogeneity scale is used, this work presents a method based on 3D IPS to calculate long-range interactions for all kinds of simulation systems, including homogeneous, heterogeneous, and finite systems. Unlike the original 3D IPS method that uses a local region defined by the cutoff distance, this method uses a local region larger than that defined by the cutoff distance to reach the homogeneity scale. To efficiently calculate interactions within such a large local region, this method split long-range interactions into two parts, a cutoff part and a long-range part. The cutoff part is calculated by summing over atom pairs within a cutoff range (about 10Å), and the long-range part is calculated using the discrete fast Fourier transform (DFFT) technique. This method is applied to electrostatic and van der Waals interactions for both periodic and non-periodic systems. Example simulations demonstrate that this method can accurately and efficiently calculate long-range interactions for molecular simulation.
Effect of ferroelastic twin walls on local polarization switching: Phase-field modeling
Authors: Choudhury S. , Zhang J. X. , Li Y. L. , Chen L. Q. , Jia Q. X. , Kalinin S. V.
Published: October 2008

Local polarization switching in epitaxial ferroelectric thin films in the presence of ferroelastic domain walls was studied using phase-field approach. The nucleation bias profile across a twin wall was analyzed, and the localization of preferential nucleation sites was established. This analysis was further extended to a realistic domain structure with multiple twin boundaries. It was observed that the local nucleation voltage required for a 180° domain switching is closely related to the number of such local defects.
Properties of a solid state device with mobile dopants: Analytic analysis for the thin film device
Authors: Gil Y. , Umurhan O. M. , Riess I.
Published: October 2008

Current-voltage relations, electric field, and charge distribution profiles are calculated for a device in which the dopants are mobile. The thin film limit is discussed. The model solved is restricted to: (a) mobile holes and acceptors, (b) steady state, and (c) metal electrodes which block the ionic current. The solution is expressed as a series expansion in the small parameter δ=L/λD, where L is the sample thickness and λD is a Debye length. The second order of the series expansion is found to vanish, thus the corrections to the leading order appear only in the third term. The approximated analytic solution agrees with numerical results from a previous publication up to the quite high value of δ=1. The leading order in the I-V relations and in the hole distribution is independent of the acceptor motion. This implies that for thin devices of this form any motion of the dopants may be neglected and that dopants need not be limited only to those which exhibit low diffusion constants. Rectification is observed as long as asymmetry is introduced by two different contact potentials. This holds whether the contacts lead to depletion or accumulation.
Bragg scattering of x-rays in multiwalled carbon nanotubes
Authors: Ong S. Y. , Childs P. A. , Herbert D. C. , O’Neill A. G.
Published: October 2008

In the past few years it has been shown theoretically that carbon nanotubes coated with various materials have the potential to act as waveguides at x-ray frequencies. At these frequencies the angle of incidence relative to the axis of the nanotube is a few milliradians, creating significant challenges for the experimental confirmation of mode formation. Recent developments in the growth of multiwalled carbon nanotubes with WS2 walls suggest that they have the potential to act as Bragg fibers at x-ray frequencies. In this paper we use the scattering matrix method to study mode formation in multiwalled carbon nanotubes coated with gold. It is found that they are capable of acting as Bragg fibers but the wall thickness and the number of bilayers must be increased in order to obtain mode confinement.
Light emission properties and mechanism of low-temperature prepared amorphous SiNX films. I. Room-temperature band tail states photoluminescence
Authors: Wang M. , Xie M. , Ferraioli L. , Yuan Z. , Li D. , Yang D. , Pavesi L.
Published: October 2008

A room-temperature photoluminescence (PL) study of amorphous nonstoichiometric silicon nitride (SiNX) films prepared under low temperature is reported. PL peak position can be tuned from 1.90 to 2.90 eV by adjusting the film composition. The luminescence lifetime is within the nanosecond range. The dependence of the PL lifetime on the emission energy suggests that band tail states are involved in the thermalization and recombination of photon-generated carriers. This is further supported by the correlation between the optical band gap, the PL peak energy, and the width of the PL spectrum. We propose that optical transitions among band tail states are the main light emission mechanisms.
Intramolecular vibrational energy relaxation in nitrous acid (HONO)
Authors: Botan Virgiliu , Hamm Peter
Published: October 2008

Intramolecular vibrational energy relaxation (IVR) in nitrous acid (HONO) is studied with the help of ultrafast two-color pump-probe spectroscopy. In a previous paper [V. Botan et al., J. Chem. Phys. 124, 234511 (2006)], it has been observed that trans-HONO cools through a cascade of overtones of one specific mode after pumping the OH stretch vibration. We had suggested that this cooling mode is the ONO bend vibration. Furthermore, molecules that have initially been excited by the OH stretch vibration of cis-HONO and then underwent isomerization follow the same relaxation pathway. In the present study, we extend the investigation of IVR of cis- and trans-HONO to the N=O stretch and HON bend spectral regions, finding further evidence that the bottleneck of trans cooling is indeed the ONO bend vibration. In combination with information on the anharmonic coupling constants of different modes, the energy relaxation dynamics preceding this cooling cascade can also be followed in unprecedented detail.
Application of the string method to the study of critical nuclei in capillary condensation
Authors: Qiu Chunyin , Qian Tiezheng , Ren Weiqing
Published: October 2008

We adopt a continuum description for liquid-vapor phase transition in the framework of mean-field theory and use the string method to numerically investigate the critical nuclei for capillary condensation in a slit pore. This numerical approach allows us to determine the critical nuclei corresponding to saddle points of the grand potential function in which the chemical potential is given in the beginning. The string method locates the minimal energy path (MEP), which is the most probable transition pathway connecting two metastable/stable states in configuration space. From the MEP, the saddle point is determined and the corresponding energy barrier also obtained (for grand potential). Moreover, the MEP shows how the new phase (liquid) grows out of the old phase (vapor) along the most probable transition pathway, from the birth of a critical nucleus to its consequent expansion. Our calculations run from partial wetting to complete wetting with a variable strength of attractive wall potential. In the latter case, the string method presents a unified way for computing the critical nuclei, from film formation at solid surface to bulk condensation via liquid bridge. The present application of the string method to the numerical study of capillary condensation shows the great power of this method in evaluating the critical nuclei in various liquid-vapor phase transitions.
Nonperturbative ab initio calculations in strong magnetic fields using London orbitals
Authors: Tellgren Erik I. , Soncini Alessandro , Helgaker Trygve
Published: October 2008

A self-consistent field (SCF) London-orbital computational scheme to perform gauge-origin independent nonperturbative calculations for molecules in strong magnetic fields is presented. The crucial difference in the proposed approach with respect to common-origin finite-field SCF implementations consists in the evaluation of molecular integrals over the field-dependent molecular basis functions, which is tantamount to computing molecular integrals in a hybrid Gaussian and plane-wave basis set. The implementation of a McMurchie–Davidson scheme for the calculation of the molecular integrals over London orbitals is discussed, and preliminary applications of the newly developed code to the calculation of fourth-rank hypermagnetizabilities for a set of small molecules, benzene, and cyclobutadiene are presented. The nonperturbative approach is particularly useful for studying the highly nonlinear response of paramagnetic closed-shell systems such as boron monohydride, or the π-electron response of cyclobutadiene.
Electromagnetic dynamics of magnetized accretion disks with strong collisional coupling of neutrals with ions and dust grains
Authors: Nekrasov A. K.
Published: October 2008

The electromagnetic dynamics of multicomponent collisional magnetized accretion disks is considered. The sufficiently ionized regions of the disk are explored where there is the strong collisional coupling of neutrals with ions and dust grains simultaneously. The stationary state is investigated in detail and the azimuthal and radial velocities of species are found. It is obtained that due to collisions, neutrals, dust grains, and electrons drift inward and ions drift outward. The general solutions for the perturbed velocities of species with collisional and thermal effects are derived. The effect of perturbation of collisional frequencies due to the density perturbations of charged species and neutrals is taken into account. It is shown that the dust grains can be involved in the fast electromagnetic perturbations induced by ions and electrons via the strong collisions with neutrals having the strong collisional coupling with ions. The dispersion relations for axisymmetric perturbations are derived and unstable solutions due to different background velocities of species are found. The growth rates of the considered streaming instabilities can be much larger than the Keplerian frequency.
Dynamical parameter identification from a scalar time series
Authors: Yu Dongchuan , Liu Fang
Published: October 2008

If a drive system with unknown parameters represents “reality” and the response system a “computational model,” the unidirectional coupling can be used to change model parameters, as well as the model state, such that both systems synchronize with each other and model parameters coincide with their true values of “reality.” Such a parameter identification method is called adaptive synchronization (also autosynchronization) method and is widely used in the literature. Because one usually cannot find proper parameter update rules by exploiting information obtained from only a scalar time series, parameter identification with adaptive synchronization from a scalar time series is not well understood and still remains challenging until now. In this paper we introduce a novel adaptive synchronization approach with an effective guidance parameter to update rule design. This method includes three steps: (i) finding some proper control signals such that the “computational model” synchronizes with the “real” system if no parameter mismatch exists (that is, both systems have identical parameters); (ii) designing parameter update rules in terms of a necessary condition for ensuring local synchronization; and (iii) determining the value for each parameter update rate for ensuring the local stability of autosynchronization manifold according to the conditional Lyapunov exponents method. The reliability of the suggested technique is illustrated with the Lorenz system and a unified chaotic model.
High-pressure x-ray diffraction and Raman spectra study of indium oxide
Authors: Liu D. , Lei W. W. , Zou B. , Yu S. D. , Hao J. , Wang K. , Liu B. B. , Cui Q. L. , Zou G. T.
Published: October 2008

High-pressure synchrotron radiation x-ray diffraction and Raman spectroscopy measurements of indium oxide (In2O3) were carried out at room temperature up to 27.8 and 26.2 GPa, respectively. A pressure-induced phase transition from cubic-phase (Ia3¯) was observed at a pressure above 12.8–15.3 GPa, which disagrees with earlier theoretical prediction (3.8 GPa). According to the x-ray diffraction experimental data, the high-pressure phase is isostructural with hexagonal corundum-type structure (R3¯c symmetry). However, broad peaks observed in Raman spectra suggest that the high-pressure structure is disordered. The volume change from cubic phase to corundum phase is about 4% and the axial ratio c/a in the corundum phase decreases with increasing pressure.
Physics of collisionless reconnection in a stressed X-point collapse
Authors: Tsiklauri D. , Haruki T.
Published: October 2008

Recently, magnetic reconnection during collisionless, stressed, X-point collapse was studied using kinetic, 2.5-dimensional, fully electromagnetic, relativistic particle-in-cell numerical code [D. Tsiklauri and T. Haruki, Phys. Plasmas 14, 112905 (2007)]. Here we finalize the investigation of this topic by addressing key outstanding physical questions: (i) Which term in the generalized Ohm’s law is responsible for the generation of the reconnection electric field? (ii) How does the time evolution of the reconnected flux vary with the ion-electron mass ratio? (iii) What is the exact energy budget of the reconnection process; i.e., in which proportion initial (mostly magnetic) energy is converted into other forms of energy? (iv) Are there any anisotropies in the velocity distribution of the accelerated particles? The following points have been established. (i) A reconnection electric field is generated by the electron pressure tensor off-diagonal terms, resembling to the case of tearing unstable Harris current sheet studied by the GEM reconnection challenge. (ii) For mi∕me⪢1, the time evolution of the reconnected flux is independent of ion-electron mass ratio. In addition, in the case of mi∕me=1, we show that reconnection proceeds slowly as the Hall term is zero; when mi∕me⪢1 (i.e., the Hall term is nonzero) reconnection is fast and we conjecture that this is due to magnetic field being frozen into electron fluid, which moves significantly faster than ion fluid. (iii) Within one Alfvén time, somewhat less than half (∼40%) of the initial total (roughly magnetic) energy is converted into the kinetic energy of electrons, and somewhat more than half (∼60%) into kinetic energy of ions (similar to solar flare observations). (iv) In the strongly stressed X-point case, in about one Alfvén time, a full isotropy in all three spatial directions of the velocity distribution is seen for superthermal electrons (also commensurate with solar flare observations).
A widely tunable laser frequency offset lock with digital counting
Authors: Hughes Joshua , Fertig Chad
Published: October 2008

We demonstrate a hybrid analog+digital electronic lock to stabilize a dynamically tunable rf offset between two lasers. Our method features an 80 MHz capture range, ±7 GHz tuning range, frequency agility of 1 MHz/μs, and low (<30 ppm) drift in the absolute optical frequency difference after ∼1000 s. With this scheme, multiple slave lasers can easily be referenced to one stable master laser, while each remains rapidly and accurately tunable over the wide frequency ranges encountered in typical laser cooling and trapping experiments.
Mode confinement in photonic quasicrystal point-defect cavities for particle accelerators
Authors: Di Gennaro E. , Savo S. , Andreone A. , Galdi V. , Castaldi G. , Pierro V. , Masullo M. Rosaria
Published: October 2008

In this letter, we present a study of the confinement properties of point-defect resonators in finite-size photonic-bandgap structures composed of aperiodic arrangements of dielectric rods, with special emphasis on their use for the design of cavities for particle accelerators. Specifically, for representative geometries, we study the properties of the fundamental mode (as a function of the filling fraction, structure size, and losses) via two-dimensional and three-dimensional full-wave numerical simulations, as well as microwave measurements at room temperature. Results indicate that for reduced-size structures, aperiodic geometries exhibit superior confinement properties by comparison with periodic ones.
Fabrication and characterization of ultrafast carbon nanotube saturable absorbers for solid-state laser mode locking near 1μm
Authors: Yim Jong Hyuk , Cho Won Bae , Lee Soonil , Ahn Yeong Hwan , Kim Kihong , Lim Hanjo , Steinmeyer Günter , Petrov Valentin , Griebner Uwe , Rotermund Fabian
Published: October 2008

Transmitting and reflecting ultrafast saturable absorbers based on single-walled carbon nanotubes are developed that are applicable for stable mode locking of bulk solid-state lasers operating near 1μm. For fabrication of these saturable absorbers, relatively simple spin coating and spray methods are employed. Parameters important for stable mode locking, such as transient nonlinear absorption, saturation fluence, and recovery time, are investigated by nonlinear transmission and time-resolved pump-probe measurements near 1μm. Typical modulation depths and recovery times amount to ∼0.21%–0.25% and <1ps, respectively.
Tunable transmission and harmonic generation in nonlinear metamaterials
Authors: Shadrivov Ilya V. , Kozyrev Alexander B. , van der Weide Daniel W. , Kivshar Yuri S.
Published: October 2008

We study the properties of a tunable nonlinear metamaterial operating at microwave frequencies. We fabricate the nonlinear metamaterial composed of double split-ring resonators and wires where a varactor diode is introduced into each resonator so that the magnetic resonance can be tuned dynamically by varying the input power. We show that at higher powers the transmission of the metamaterial becomes power dependent, and we demonstrate experimentally power-dependent transmission properties and selective generation of higher harmonics.
Low temperature plasma diagnostics with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry
Authors: Wang Jing , Li Yuyang , Tian Zhenyu , Zhang Taichang , Qi Fei , Tao Xiaoping
Published: October 2008

Plasma-based technology is of great importance for a range of industrial applications. However, due to the complexity of gas-phase and surface chemical reactions, the underlying plasma chemistry is still poorly understood, leading to a growing demand for experimental setups on plasma diagnostics. In this paper, we report an apparatus that combines tunable synchrotron vacuum ultraviolet (VUV) photoionization with molecular-beam mass spectrometry for detecting ionic and neutral species formed in the processes of plasma discharge. The products including reactive intermediates such as enols can be identified unambiguously with the measurements of photoionization mass spectrometry (PIMS) and photoionization efficiency spectra. The tunable VUV PIMS has been proven as an ideal and sensitive tool for a comprehensive understanding of plasma chemistry.
Kerr and free carrier ultrafast all-optical switching of GaAs/AlAs nanostructures near the three photon edge of GaAs
Authors: Hartsuiker Alex , Harding Philip J. , Nowicki-Bringuier Yoanna-Reine , Gérard Jean-Michel , Vos Willem L.
Published: October 2008

We performed nondegenerate pump-probe experiments on a GaAs/AlAs photonic cavity structure. We switched the photonic properties using the optical Kerr effect and free carriers excited by three photon absorption. The structure was probed at 1150–1640 nm, in the telecom spectral range below the stop gap. In the measurements we observe surprisingly large nondegenerate electronic Kerr coefficients over a broad wavelength range. We also extracted the three photon absorption coefficient for GaAs at three wavelengths in the near infrared. We conclude that the electronic Kerr effect is so large that the resonance of a moderate Q (Q>1000) photonic cavity could be successfully switched instantaneous.
Study of the strata formation during the explosion of a wire in vacuum
Authors: Rousskikh A. G. , Oreshkin V. I. , Chaikovsky S. A. , Labetskaya N. A. , Shishlov A. V. , Beilis I. I. , Baksht R. B.
Published: October 2008

The formation of strata during fast electrical explosions of aluminum wires at current densities of (1–1.4)×108 A/cm2 has been studied experimentally. To observe the strata, the soft x radiation generated at the hot point of an x-pinch was used. It has been revealed that strata are formed before the voltage collapse, that is, at the stage of heating of the wire metal. Two wire explosion modes were realized: with and without cutoff of the current carried by the exploding wire. Analysis of the experimental results shows that the stratification is most probably due to the thermal instability that develops as a consequence of the increase in metal resistivity with temperature.
High angle annular dark field and electron energy loss spectroscopy study on the substitution and distribution of cobalt in ZnO by multilayer growth
Authors: Chen Shu-Fang , Liu Chuan-Pu , Hsu H. S. , Huang J. C. A.
Published: October 2008

Co-doped ZnO films were synthesized by ion beam sputtering using multilayer (ZnO/Co) growth. Both the distribution and the chemical states of Co in ZnO can be well controlled by varying the ratio of the nominal layer thickness of ZnO to Co. Transmission electron microscopy indicated that all of the as-deposited Zn1−x(Co)xO films were polycrystalline with a (0002) preferred orientation. The local microstructures and chemical states were identified by Z-contrast imaging and electron energy loss spectroscopy. In ZnO (1.5 nm)/Co (0.1 nm), homogeneous Co-doped ZnO was observed to have been formed through interdiffusion. However, decreasing or increasing the thickness of ZnO leads to the formation of Co clusters in the ZnO matrix or Zn1−x(Co)xO multilayers, respectively. For ZnO thickness≧1.5 nm, Co is substituted for Zn, and its valence state is 2+. All Co-doped ZnO films show room-temperature ferromagnetic behavior, which appears to depend strongly on the Co distribution.
Suppressed bimodal size distribution of InAs quantum dots grown with an As2 source using molecular beam epitaxy
Authors: Sugaya Takeyoshi , Amano Takeru , Komori Kazuhiro
Published: October 2008

We demonstrate the suppressed bimodal size distribution of InAs quantum dots (QDs) grown with an As2 source using molecular beam epitaxy. QDs grown with an As2 source have single mode photoluminescence (PL) spectra, whereas QDs grown with an As4 source have bimodal spectra. The PL intensities of QDs grown with an As2 source are higher than those grown with an As4 source. The density of QDs grown with an As2 source decreases at high As pressure, whereas the density of As4 grown QDs increases with As pressure. These results indicate that the surface migration of In atoms is enhanced at a higher As2 pressure, resulting in improved optical properties. The enhanced surface migration is thought to be due to the stable As–As dimer structures under an As2 source.
Quantum confinement effect of ZnO nanocrystallites embedded in In2O3 films
Authors: Stoehr M. , Juillaguet S. , Marshall M. , Wen J. G.
Published: October 2008

High quality In2O3 films are grown by chemical vapor transport and condensation using high purity commercial In2O3 and ZnO powders as starting materials, under an Ar/O2 gas mixture. The cubic structure of the In2O3 films is determined by x-ray diffraction and Raman spectroscopy. At 300 K, the photoluminescence (PL) results from In2O3 films display only an intense deep level emission line centered at 1.968 eV, similar to that obtained from the commercial In2O3 powder. In the UV range, 5 K PL measurements of the films reveal sharp lines which are not observed on the 5 K PL spectrum from commercial In2O3 powder. The dominating peak at 3.3672 eV, as well as energy differences of 72 meV between lines are characteristic of ZnO and correspond to a neutral donor bound exciton (D0X) emission and the energy of the LO phonon in ZnO, respectively. In comparison to the D0X line position from ZnO nanostructures, this D0X line displays a blueshift of 8 meV which is well explained by a quantum confinement of ZnO nanocrystallites in In2O3. Low temperature PL measurements reveal ZnO nanocrystallites embedded in In2O3 film, which are not observed by either x-ray diffraction and Raman spectroscopy.
Stray field of a Landau magnetization pattern
Authors: Breitenstein Lena , Lendecke Peter , Bohlens Stellan , Meier Guido , Merkt Ulrich
Published: October 2008

We present experiments and micromagnetic simulations on Hall micromagnetometry of magnetic vortices. The magnetization reversal in a 2×2 μm2 Permalloy square of 20 nm thickness is investigated at liquid helium temperatures. Nucleation, displacement, and annihilation of the vortex state in an external magnetic field are observed by detecting its stray field. The findings are corroborated by images taken with a magnetic-force microscope at room temperature. The experimental data are compared to micromagnetic simulations.
Growth-interruption-induced low-density InAs quantum dots on GaAs
Authors: Li L. H. , Chauvin N. , Patriarche G. , Alloing B. , Fiore A.
Published: October 2008

We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/μm2) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 μm emission at 4 K.
The calculation of the bilinear Boltzmann operator for gas mixtures
Authors: Ao Ji-jun , Wang Achilaltu
Published: October 2008

The formula of the bilinear Boltzmann integral operator of gas mixtures is obtained. With the use of Bobylev’s transform it can be carried out much easier and an extended formula of more general validity is obtained. The formula can give the eigenvalues and the eigenfunctions of the bilinear Boltzmann integral operator of a gas mixture, which is essential to the solution of the Boltzmann equation.