bluuebunny/crossref_metadata_2025 huggingface dataset:
Searching for H2 emission from protoplanetary disks using near- and mid-infrared high-resolution spectroscopy
Authors: Carmona A. , van den Ancker M. E. , Henning Th. , Pavlyuchenkov Ya. , Dullemond C. P. , Goto M. , Fedele D. , Stecklum B. , F-.Thi W. , Bouwman J. , Waters L. B. F. M.
Published: May 2008

The mass and dynamics of protoplanetary disks are dominated by molecular hydrogen (H2). However, observationally very little is known about the H2. In this paper, we discuss two projects aimed to constrain the properties of H2 in the disk's planet forming region (R<50AU). First, we present a sensitive survey for pure-rotational H2 emission at 12.278 and 17.035 μm in a sample of nearby Herbig Ae/Be and T Tauri stars using VISIR, ESO's VLT high-resolution mid-infrared spectrograph. Second, we report on a search for H2 ro-vibrational emission at 2.1228, 2.2233 and 2.2477 μm in the classical T Tauri star LkHα 264 and the debris disk 49 Cet employing CRIRES, ESO's VLT high-resolution near-infrared spectrograph.

VISIR project: none of the sources show H2 mid-IR emission. The observed disks contain less than a few tenths of MJupiter of optically thin H2 at 150 K, and less than a few MEarth at T>300 K. % and higher T. Our non-detections are consistent with the low flux levels expected from the small amount of H2 gas in the surface layer of a Chiang and Goldreich (1997) Herbig Ae two-layer disk model. In our sources the H2 and dust in the surface layer have not significantly departed from thermal coupling (Tgas/Tdust<2) and the gas-to-dust ratio in the surface layer is very likely <1000.

CRIRES project: The H2 lines at 2.1218 μm and 2.2233 μm are detected in LkHα 264. An upper limit on the 2.2477 μm H2 line flux in LkHα 264 is derived. 49 Cet does not exhibit H2 emission in any of observed lines. There are a few MMoon of optically thin hot H2 in the inner disk (∼0.1 AU) of LkHα 264, and less than a tenth of a MMoon of hot H2 in the inner disk of 49 Cet. The shape of the 1–0 S(0) line indicates that LkHα disk is close to face-on (i<35o). The measured 1–0 S(0)/1–0 S(1) and 2–1 S(1)/1–0 S(1) line ratios in LkHα 264 indicate that the H2 is thermally excited at T<1500 K. The lack of H2 emission in the NIR spectra of 49 Cet and the absence of Hα emission suggest that the gas in the inner disk of 49 Cet has dissipated.
Astromineralogy of protoplanetary disks
Authors: Schütz O. , Meeus G. , Sterzik M. F. , Peeters E.
Published: May 2008

We review mid-infrared N-band spectra (8–13 μm) for a sample of 28 targets, obtained with the TIMMI2 camera at La Silla Observatory. The sample contains 5 FU Orionis stars, 6 Herbig Ae/Be objects, 7 T Tauri stars and 10 Vega-type main sequence objects. All targets show infrared excess, but for several the proof of circumstellar matter was lacking up to our observations. We model the N-band emission features with a mixture of silicates consisting of different grain sizes and composition, and determine the status of dust processing in these disks. While for some targets the emission spectrum resembles those of known pre-main sequence stars of evolved dust, other objects show strong isolated PAH bands but no silicate emission. For the first time we find evidence of PAH processing occurring in a T Tauri star. The Vega-type object HD 113766 exhibits highly-processed secondary generation dust, likely released by the collision of planetesimal-sized bodies. The findings of our dust analysis are set in context to previous dust studies of young stellar objects.
Origin of the dusty disks around white dwarfs
Authors: Dong R. B. , Wang Y. , Lin D. N. C. , Liu X. W.
Published: May 2008

Some circumstantial evidence for residual planetesimals is constructed based on the recent discovery of a dusty ring around a young white dwarf at the center of the Helix nebula (Suet al. 2007). This ring extends between about 35 and 150 AU from the nebula center, and have a total mass of about 0.13M⊕. In this paper we propose that this ring is the by-product of planets and planetesimals' orbital evolution during the epoch when the central star rapidly lost most of its mass. We examine the dynamical evolution of planetary systems similar to the solar system (i.e. with gas giant planets and residual planetesimals) as their host stars evolve off the main sequence. During the process, some planetesimals will be captured by the gas giants into mean motion resonances and their mutual collisions will form a dust ring similar to that observed at the center of the Helix nebula.
The effect of poloidal magnetic field on type I planetary migration
Authors: Muto Takayuki , Machida Masahiro N. , Inutsuka Shu-ichiro
Published: May 2008

We study the effect of poloidal magnetic field on type I planetary migration by linear perturbation analysis with the shearing-sheet approximation and the analytic results are compared with numerical calculation. We investigate the cases where magneto-rotational instability (MRI) does not occur: either the disk is two-dimensional, or a very strong field is exerted. We derive formulae for torque exerted on the planet for both cases. We find that two-dimensional torque is suppressed when plasma beta is less than 1 and three-dimensional modes dominate, in contrast to unmagnetized case.
Orbital determination and dynamics of resonant extrasolar planetary systems
Authors: Beaugé C. , Ferraz-Mello S. , Michtchenko T. A. , Giuppone C. A.
Published: May 2008

In this communication we review some properties and applications of mean-motion resonances in extrasolar planetary systems, with particular emphasis on the 2/1 commensurability. A first part is devoted to the dynamical structure of the 2/1 resonance, including (but not restricted to) the so-called apsidal corotations. In a second part we discuss the orbital evolution of resonant systems under the effects of non-conservative forces. Special attention is given to the use of apsidal corotations as markers of largescale orbital decay, possibly due to disk-planet interactions in primordial times. Finally, we analyze the interplay between dynamical analysis and orbital fitting. Using the HD82943 planetary system as an example, we discuss: (i) up to what point present orbital fits allow us to distinguish between different resonant configurations, and (ii) in what ways may the dynamical structure of resonances be used as a complementary part of the orbital fitting process.
Stability constraints in modeling of multi-planet extrasolar systems
Authors: Goździewski Krzysztof , Migaszewski Cezary , Musieliński Arek
Published: May 2008

We present an analysis of high precision radial velocity (RV) observations of stars hosting multi-planet systems with Jovian companions. We use dynamical stability constraints and quasi-global methods of optimization. As an illustration, we present new results derived for the RV data of the Sun-like dwarfs HD 155358 and τ1 Gruis.
Extrasolar planet interactions
Authors: Barnes Rory , Greenberg Richard
Published: May 2008

The dynamical interactions of planetary systems may be a clue to their formation histories. Therefore, the distribution of these interactions provides important constraints on models of planet formation. We focus on each system's apsidal motion and proximity to dynamical instability. Although only ∼25 multiple planet systems have been discovered to date, our analyses in these terms have revealed several important features of planetary interactions. 1) Many systems interact such that they are near the boundary between stability and instability. 2) Planets tend to form such that at least one planet's eccentricity periodically drops to near zero. 3) Mean-motion resonant pairs would be unstable if not for the resonance. 4) Scattering of approximately equal mass planets is unlikely to produce the observed distribution of apsidal behavior. 5) Resonant interactions may be identified through calculating a system's proximity to instability, regardless of knowledge of angles such as mean longitude and longitude of periastron (e.g. GJ 317 b and c are probably in a 4:1 resonance). These properties of planetary systems have been identified through calculation of two parameters that describe the interaction. The apsidal interaction can be quantified by determining how close a planet is to an apsidal separatrix (a boundary between qualitatively different types of apsidal oscillations, e.g. libration or circulation of the major axes). This value can be calculated through short numerical integrations. The proximity to instability can be measured by comparing the observed orbital elements to an analytic boundary that describes a type of stability known as Hill stability. We have set up a website dedicated to presenting the most up-to-date information on dynamical interactions: http://www.lpl.arizona.edu/~rory/research/xsp/dynamics.
Secular evolution of exoplanetary systems and close encounters
Authors: Šidlichovský M. , Gerlach E.
Published: May 2008

We investigate the secular evolution of non-resonant exoplanetary systems consisting of a central star and two co-planar planets using a semi-numerical averaging method of the first order in planetary masses (in this case equivalent to “averaging by scissors” or simply dropping the fast periodic terms). The resulting Hamiltonian level curves for different exoplanetary systems were compared to those obtained by direct numerical integration. Studying the dependence of the reliability of the averaging method (as well as chaoticity of numerically integrated trajectories) upon the initial conditions, we found that the averaging methods fails even for Hill stable systems. Based on the Hill stability criterion we introduced empirically a more restrictive stability condition, that enabled us to give an estimate for the region of validity of the averaging method in the plane of initial conditions.
Habitability of super-Earths: Gliese 581c & 581d
Authors: von Bloh W. , Bounama C. , Cuntz M. , Franck S.
Published: May 2008

The unexpected diversity of exoplanets includes a growing number of super-Earth planets, i.e., exoplanets with masses smaller than 10 Earth masses. Unlike the larger exoplanets previously found, these smaller planets are more likely to have similar chemical and mineralogical composition to the Earth. We present a thermal evolution model for super-Earth planets to identify the sources and sinks of atmospheric carbon dioxide. The photosynthesis-sustaining habitable zone (pHZ) is determined by the limits of biological productivity on the planetary surface. We apply our model to calculate the habitability of the two super-Earths in the Gliese 581 system. The super-Earth Gl 581c is clearly outside the pHZ, while Gl 581d is at the outer edge of the pHZ. Therefore, it could at least harbor some primitive forms of life.
Hydrothermal deformation of granular quartz sand
Authors: Karner Stephen L. , Kronenberg Andreas K. , Chester Frederick M. , Chester Judith S. , Hajash Andrew
Published: May 2008

Isotropic and triaxial compression experiments were performed on porous aggregates of St Peter quartz sand to explore the influence of temperature (to 225°C). During isotropic stressing, samples loaded at elevated temperature exhibit the same sigmoidal stress‐strain curves and non‐linear acoustic emission rates as have previously been observed from room temperature studies on sands, sandstones, and soils. However, results from our hydrothermal experiments show that the critical effective pressure (P*) associated with the onset of significant pore collapse and pervasive cataclastic flow is lower at increased temperature. Samples subjected to triaxial loading at elevated temperature show yield behavior resembling that observed from room temperature studies on granular rocks and soils. When considered in terms of distortional and mean stresses, the yield strength data for a given temperature define an elliptical envelope consistent with critical state and CAP models from soil mechanics. For the conditions we tested, triaxial yield data at low effective pressure are essentially temperature‐insensitive whereas yield levels at high effective pressure are lowered as a function of elevated temperature. We interpret our yield data in a manner consistent with Arrhenius behavior expected for thermally assisted subcritical crack growth. Taken together, our results indicate that increased stresses and temperatures associated with subsurface burial will significantly alter the yield strength of deforming granular media in systematic and predictable ways.
Low reservoir ages for the surface ocean from mid‐Holocene Florida corals
Authors: Druffel Ellen R. M. , Robinson Laura F. , Griffin Sheila , Halley Robert B. , Southon John R. , Adkins Jess F.
Published: May 2008

The 14C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th‐dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ18O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ14C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.
The cannabinoid receptor‐1 antagonist rimonabant inhibits platelet activation and reduces pro‐inflammatory chemokines and leukocytes in Zucker rats
Authors: Schäfer A , Pfrang J , Neumüller J , Fiedler S , Ertl G , Bauersachs J
Published: May 2008

Background and purpose:

We investigated the effect of rimonabant on inflammation and enhanced platelet reactivity in type 2 diabetic Zucker rats, an experimental model of impaired glucose tolerance and the metabolic syndrome.

Experimental approach:

Rimonabant (10 mg kg−1 by gavage) was fed for 2 weeks to 3‐month‐old male obese Zucker rats as an impaired glucose tolerance model and for 10 weeks to 6‐month‐old male obese Zucker rats as a model of the metabolic syndrome. RANTES (Regulated upon Activation, Normal T cell Expressed, and Secreted) and MCP‐1 (monocyte chemotactic protein‐1) serum levels were determined by ELISA. Leukocyte populations were quantitatively assessed using a veterinary differential blood cell counter. Platelet activation was assessed by flow‐cytometry, platelet aggregation, and adhesion of isolated platelets to immobilized fibrinogen.

Key results:

RANTES and MCP‐1 serum levels were increased in obese vs lean Zucker rats and significantly reduced by long‐term treatment with rimonabant, which slowed weight gain in rats with the metabolic syndrome. Neutrophils and monocytes were significantly increased in young and old obese vs lean Zucker rats and lowered by rimonabant. Platelet‐bound fibrinogen was significantly enhanced in obese vs lean Zucker rats of both age, and was reduced by rimonabant. Platelets from obese rats were more sensitive to thrombin‐induced aggregation and adhesion to fibrinogen, which were both attenuated by rimonabant therapy.

Conclusions and implications:

We demonstrate positive modulation of circulating neutrophil and monocyte numbers, reduced platelet activation and lower RANTES and MCP‐1 levels by rimonabant in Zucker rats. This may potentially contribute to a reduction of cardiovascular risk.

British Journal of Pharmacology (2008) 154, 1047–1054; doi:fn1; published online 12 May 2008
Characterization of heat‐labile uracil‐DNA glycosylase from Psychrobacter sp. HJ147 and its application to the polymerase chain reaction
Authors: Lee Mi Sun , Kim Gun A. , Seo Moo Seok , Lee Jung‐Hyun , Kwon Suk‐Tae
Published: May 2008

The gene encoding Psp HJ147 UDG (Psychrobacter sp. HJ147 uracil‐DNA glycosylase) was cloned and sequenced. The gene consists of 735 bp for coding a protein with 244 amino acid residues. The deduced amino acid sequence of Psp HJ147 UDG showed a high similarity to that of Psychrobacter articus, Psychrobacter cryohalolentis K5 and Psychrobacter sp. PRwf‐1. The PCR‐amplified Psp HJ147 UDG gene was expressed under the control of the T7lac promoter on pTYB1 in Escherichia coli BL21(DE3). The expressed enzyme was purified with IMPACT™‐CN (intein‐mediated purification with an affinity chitin‐binding tag) system. The optimum pH and temperature of the purified enzyme were 7.0–7.5 and 20–25 °C respectively. The optimum NaCl and KCl concentrations for the activity of the purified enzyme ranged from 50 to75 mM. The half‐life of the enzyme at 50 °C was approx. 45 s. These heat‐labile characteristics enabled Psp HJ147 UDG to control carry‐over contamination in direct PCR without loss of the PCR product. Psp HJ147 UDG's contaminant control in both direct PCR and indirect PCR exhibited superiority over the UDG of the marine psychrophilic bacterium strain BMTU 3346 and that of E. coli.
Regulation of diacylglycerol production and protein kinase C stimulation during sperm‐ and PLCζ‐mediated mouse egg activation
Authors: Yu Yuansong , Halet Guillaume , Lai F. Anthony , Swann Karl
Published: May 2008

Background information. At fertilization in mammalian eggs, the sperm induces a series of Ca2+ oscillations via the production of inositol 1,4,5‐trisphosphate. Increased inositol 1,4,5‐trisphosphate production appears to be triggered by a sperm‐derived PLCζ (phospholipase C‐ζ) that enters the egg after gamete fusion. The specific phosphatidylinositol 4,5‐bisphosphate hydrolytic activity of PLCζ implies that DAG (diacylglycerol) production, and hence PKC (protein kinase C) stimulation, also occurs during mammalian egg fertilization. Fertilization‐mediated increase in PKC activity has been demonstrated; however, its precise role is unclear.

Results. We investigated PLCζ‐ and fertilization‐mediated generation of DAG in mouse eggs by monitoring plasma‐membrane translocation of a fluorescent DAG‐specific reporter. Consistent plasma‐membrane DAG formation at fertilization, or after injection of physiological concentrations of PLCζ, was barely detectable. However, when PLCζ is overexpressed in eggs, significant plasma‐membrane DAG production occurs in concert with a series of unexpected secondary high‐frequency Ca2+ oscillations. We show that these secondary Ca2+ oscillations can be mimicked in a variety of situations by the stimulation of PKC and that they can be prevented by PKC inhibition. The way PKC leads to secondary Ca2+ oscillations appears to involve Ca2+ influx and the loading of thapsigargin‐sensitive Ca2+ stores.

Conclusions. Our results suggest that overproduction of DAG in PLCζ‐injected eggs can lead to PKC‐mediated Ca2+ influx and subsequent overloading of Ca2+ stores. These results suggest that DAG generation in the plasma membrane of fertilizing mouse eggs is minimized since it can perturb egg Ca2+ homoeostasis via excessive Ca2+ influx.
Hypovolaemia after glucose/insulin infusions in volunteers
Authors: Berndtson Dan , Olsson Joel , Hahn Robert G.
Published: May 2008

High-dose intravenous infusion of 5% glucose promotes rebound hypoglycaemia and hypovolaemia in healthy volunteers. To study whether such effects occur in response to glucose/insulin, 12 healthy firemen (mean age, 39 years) received three infusions over 1–2 h that contained 20 ml of 2.5% glucose/kg of body weight, 5 ml of 10% glucose/kg of body weight with 0.05 unit of rapid-acting insulin/kg of body weight, and 4 ml of 50% glucose/kg of body weight with 1 unit of insulin/kg of body weight. The plasma glucose concentration and plasma dilution were compared at 5–10 min intervals over 4 h. Regardless of the amount of administered fluid and whether insulin was given, the plasma glucose concentration decreased to hypoglycaemic levels within 30 min of the infusion ending. The plasma dilution closely mirrored plasma glucose and became negative by approx. 5%, which indicates a reduction in the plasma volume. These alterations were only partially restored during the follow-up period. A linear relationship between plasma glucose and plasma dilution was most apparent when the infused glucose had been dissolved in only a small amount of fluid. For the strongest glucose/insulin solution, this linear relationship had a correlation coefficient of 0.77 (n=386, P<0.0001). The findings of the present study indicate that a redistribution of water due to the osmotic strength of the glucose is the chief mechanism accounting for the hypovolaemia. It is concluded that infusions of 2.5%, 10% and 50% glucose, with and without insulin, in well-trained men were consistently followed by long-standing hypoglycaemia and also by hypovolaemia, which averaged 5%. These results emphasize the relationship between metabolism and fluid balance.
Hybrid spacer for high-efficiency white organic light-emitting diodes
Authors: Seo Ji Hoon , Park Il Houng , Kim Gu Young , Lee Kum Hee , Kim Min Kyu , Yoon Seung Soo , Kim Young Kwan
Published: May 2008

High-efficient white organic light-emitting diodes (WOLEDs) were fabricated by using the following three different emitting materials: 4″-(2,2-diphenylvinyl)-1-[4-(N,N-diphenylamino)-styryl]-terphenyl for blue emission, fac-tris(2-phenypyridine) iridium(III) for green emission, and bis(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) for red emission. For higher efficiency, a hybrid spacer (HS) was inserted between each emissive layer (blue-red, red-green, and green-blue emissive layers). It was found that the WOLEDs using HS showed maximum power efficiency of 28.69lm∕W, maximum external quantum efficiency of 13.1%, and Commission Internationale de I’Eclairage coordinates (CIEx,y) of (x=0.37,y=0.37).
Subcritical to supercritical mixing
Authors: Segal C. , Polikhov S. A.
Published: May 2008

Liquid jet injection into a quiescent gaseous environment has been experimentally and analytically studied covering subcritical to supercritical conditions. The focus was placed on the influence that the surrounding gas pressure and temperature have on the jet breakup. Under subcritical conditions, the surrounding gas inertia and surface tension forces controlled this process with ligament formation from which the material broke off and the drops, later, formed. Decreasing surface tension influenced the jet surface behavior under transcritical conditions: Ligament formation was significantly reduced under these conditions with only occasional drop formation. Further increasing the pressure and temperature led to supercritical breakup modes. This manifested through a smoothening of the liquid-gas interface. Ligament formation was not observed under supercritical conditions; this indicated that surface tension did not play any role in the supercritical jet breakup. The experimental technique, using planar laser induced fluorescence, revealed important core jet structures previously undetected. A linear jet stability analysis was, then, performed to gain physical insight into the jet breakup mechanisms. The results showed good correlation with experimental results under subcritical mixing but failed to predict the transcritical and supercritical regimes.
Interchain coupling effects on dynamics of photoexcitations in conjugated polymers
Authors: Meng Y. , Di B. , Liu X. J. , An Z. , Wu C. Q.
Published: May 2008

Within an extended Su–Schrieffer–Heeger model including interchain interactions and the extended Hubbard model, the dynamical relaxation of photoexcitations in two coupled conjugated polymer chains is investigated by using a nonadiabatic evolution method. Initially, one of the two chains is photoexcited and the other chain is in the dimerized ground state. Due to the interchain interactions, the electron and/or the hole can be transferred from one chain to the other chain. For weak interchain coupling, the dynamical evolution of the lattice on the photoexcited chain is similar to that found in an isolate single chain case. With interchain interactions increasing, the amplitude of the distortions on the photoexcited chain decreases, and simultaneously, that on the other chain gradually increases. Until stronger interchain coupling, the deformations of the two chains have almost the same amplitude. Besides intrachain polaron-excitons and intrachain oppositely charged polaron pairs as found in single chain case, interchain polaron-excitons and interchain separated charged polaron pairs are obtained. The results show that the yield of interchain products increases and that of intrachain products decreases with interchain coupling increasing. Totally, the yield of charged polarons (including intrachain oppositely charged polaron pairs and interchain oppositely charged polaron pairs) is about 25%, in good agreement with results from experiments.
Poloidal motion of trapped particle orbits in real-space coordinates
Authors: Nemov V. V. , Kasilov S. V. , Kernbichler W. , Leitold G. O.
Published: May 2008

The bounce averaged poloidal drift velocity of trapped particles in stellarators is an important quantity in the framework of optimization of stellarators because it allows us to analyze the possibility for closure of contours of the second adiabatic invariant and therefore for improvement of α-particle confinement in such a device. Here, a method is presented to compute such a drift velocity directly in real space coordinates through integration along magnetic field lines. This has the advantage that one is not limited to the usage of magnetic coordinates and can use the magnetic field produced by coil currents and more importantly also results of three-dimensional magnetohydrodynamic finite beta equilibrium codes, such as PIES [A. H. Reiman and H. S. Greenside, J. Comput. Phys. 75, 423 (1988)] and HINT [Y. Suzuki et al., Nucl. Fusion 46, L19 (2006)].
Interface-resolved direct numerical simulation of vertical particulate channel flow in the turbulent regime
Authors: Uhlmann Markus
Published: May 2008

We have conducted a direct numerical simulation study of dilute turbulent particulate flow in a vertical plane channel by considering thousands of finite-size rigid particles with resolved phase interfaces. The particle diameter corresponds to approximately 11 wall units and their terminal Reynolds number is set to 136. The fluid flow with a bulk Reynolds number of 2700 is directed upward, which maintains the particles suspended on average. Two density ratios were simulated, differing by a factor of 4.5. The corresponding Stokes numbers of the two flow cases were O(10) in the near-wall region and O(1) in the outer flow. We have observed the formation of large-scale elongated streaklike structures with streamwise dimensions of the order of eight channel half-widths and cross-stream dimensions of the order of one half-width. At the same time, we have found no evidence of significant formation of particle clusters, which suggests that the large structures are due to an intrinsic instability of the flow, which is triggered by the presence of the particles. It was found that the mean fluid velocity profile tends toward a concave shape, and the turbulence intensity and the normal stress anisotropy are strongly increased. The effect of varying the Stokes number while maintaining the buoyancy, particle size, and volume fraction constant was relatively weak.
Correlation between luminescent properties and local coordination environment for erbium dopant in yttrium oxide nanotubes
Authors: Mao Yuanbing , Bargar John , Toney Michael , Chang Jane P.
Published: May 2008

The local dopant coordination environment and its effect on the photoluminescent (PL) spectral features of erbium-doped yttrium oxide nanotubes (NTs) were probed by synchrotron-based x-ray diffraction (XRD), x-ray absorption near-edge spectroscopy (XANES), and extended x-ray absorption fine structure (EXAFS). XRD, XANES, and EXAFS data demonstrate that single phase solid solutions of Y(2−x)ErxO3 were formed at 0≤x<0.4 and 1.2<x≤2, and the valence state of Er ions in the Y2O3 NTs is +3. The x-ray spectroscopic data clearly show that the erbium dopants largely reside in two types of sites in the Y2O3 host material, both of which possess a well-defined intermediate-range structure, and that the doping of erbium into Y2O3 does not cause a loss in intermediate-range order and crystallinity in the Er3+:Y2O3 NTs. This well-defined distribution of erbium doping inside the Y2O3 matrix correlates well with the observed sharp and well-resolved PL behavior of these Er3+:Y2O3 NTs at around 1.535 μm.
Impact of feature-size dependent etching on the optical properties of photonic crystal devices
Authors: Berrier A. , Ferrini R. , Talneau A. , Houdré R. , Anand S.
Published: May 2008

Feature size dependence in Ar/Cl2 chemically assisted ion beam etching of InP-based photonic crystals (PhCs) and its influence on the optical properties of PhC devices operating in the band gap are investigated. The analysis of the measured quality factors, the determined mirror reflectivities, and losses of one-dimensional Fabry–Pérot cavities clearly demonstrates the importance of feature-size dependent etching. The optical properties show a dramatic improvement up to a hole depth of about 3.5 μm that is primarily due to a significant reduction in extrinsic losses. However, beyond this hole depth, the improvement is at a lower rate, which suggests that extrinsic losses, although present, are not dominant.
The effect of wafer curvature on x-ray rocking curves from gallium nitride films
Authors: Moram M. A. , Vickers M. E. , Kappers M. J. , Humphreys C. J.
Published: May 2008

The full width at half maximum (FWHM) of x-ray rocking curves is often used as a measure of the crystalline quality of thin films. In this paper, the effects of wafer curvature on the x-ray rocking curves (ω-scans) obtained from a 2in. 0001-oriented sapphire wafer and an epitaxial 0001-oriented GaN film grown on such a wafer are discussed. Beam height reduction can limit curvature-related effects for symmetric and asymmetric reflections; these effects are generally significant for low dislocation density GaN films. Due to the shape of the area illuminated by the x-ray beam in the skew symmetric geometry, beam width reduction is instead appropriate, but this still gives an underestimate of ω-FWHM values obtained with an open detector and an overestimate of ω-FWHM values obtained with an analyzer. Therefore, skew symmetric ω-FWHM values from curved samples are often unreliable. Additionally, Williamson–Hall analysis using ω-scans is rendered unreliable in the presence of significant curvature. Variations in ω-FWHM values for different experimental configurations are attributed to nonspherical wafer curvature, changes in illuminated area for each reflection, and changes in sampled volume at each step in the ω-scan. Although this paper focuses on GaN films, the results are applicable to a wide range of other materials exhibiting wafer curvature.
Terahertz Gunn-like oscillations in InGaAs/InAlAs planar diodes
Authors: Pérez S. , González T. , Pardo D. , Mateos J.
Published: May 2008

A microscopic analysis of self-generated terahertz current oscillations that take place in planar InAlAs/InGaAs slot diodes operating under dc bias is presented. An ensemble Monte Carlo simulation is used for the calculations. The onset of the oscillations is thresholdlike, for drain-source voltages surpassing 0.6 V. The Gunn-like mechanisms and the modulation of the injection of electrons into the recess-to-drain region, which alternatively takes place in the Γ or L valley, are found at the origin of the phenomenon. Terahertz frequencies are reached because of the presence of ultrafast Γ electrons in the region of interest. Extremely high velocities are achieved by (i) the effect of the recess, which focuses the electric field and launches very fast electrons into the drain region, and (ii) the influence of degeneracy, which significantly reduces the rate of scattering mechanisms and enhances the electron mobility in the channel.
Infrared absorption line shapes in the classical limit: A comparison of the classical dipole and fluctuating frequency approximations
Authors: Schmidt J. R. , Corcelli S. A.
Published: May 2008

Infrared spectroscopy is a versatile technique for probing the structure and dynamics of condensed-phase systems. Simulating infrared absorption spectra with molecular dynamics (MD) offers a powerful means to establish a molecular-level interpretation of experimental results, as well as a basis for the parametrization of more accurate simulation force-fields. Two distinct methods for the calculation of infrared absorption line shapes of high-frequency (ℏω∕kBT⪢1) vibrational probes from MD simulations are examined: The classical dipole approximation (CDA) and the fluctuating frequency approximation (FFA). Although these two formalisms result in expressions for the infrared absorption line shape that appear very different, both approximations are shown to yield identical results for the infrared line shape of a harmonic system in the condensed-phase. The equivalence of the FFA and CDA is also demonstrated in the case where the transition dipole of the oscillator fluctuates in response to the environment (i.e., where the Condon approximation has been relaxed). Finally we examine the effects of solute anharmonicity and demonstrate that the CDA and FFA are not equivalent in general, and the magnitude of the deviations increases with anharmonicity. We conclude that the calculation of infrared absorption line shapes via the CDA is a promising alternative to the FFA approach in cases where it may be difficult or undesirable to employ the latter, particularly when the effects of anharmonicity are small.
Tests of Monte Carlo perturbation theory for the free energy of liquid copper
Authors: Greeff C. W.
Published: May 2008

Monte Carlo perturbation theory, in which terms in the thermodynamic perturbation series are evaluated by Monte Carlo averaging, has potentially large advantages in efficiency for calculating free energies of liquids from ab initio potential surfaces. In order to test the accuracy of perturbation theory for liquid metals, a series of calculations has been done on liquid copper, modeled by an embedded atom potential. A simple 1∕r12 pair potential is used as the reference system. The free energy is calculated to third order in perturbation theory, and the results are compared to an exact formula. It is found that for optimal reference potential parameters, second order perturbation theory is essentially exact. Second and third order theories give accurate results for significantly nonoptimal reference parameters. The relation between perturbation theory and reweighting is discussed, and an approximate formula is derived that shows an exponential dependence of the efficiency of reweighting on the second order free energy correction. Finally, techniques for application to ab initio potentials are discussed. It is shown that with samples of 100 configurations, it is possible to obtain accuracy and precision at the level of ∼1meV∕atom.
The relation between shock-state particle velocity and free surface velocity: A molecular dynamics study on single crystal Cu and silica glass
Authors: Luo Sheng-Nian , Han Li-Bo , Xie Yun , An Qi , Zheng Lianqing , Xia Kaiwen
Published: May 2008

We investigate the ratio Rrp of the free surface velocity to the shock-state particle velocity during shock wave loading with molecular dynamics simulations on two representative solids, single crystal Cu, and silica glass. The free surface velocity is obtained as a function of the particle velocity behind the shock front (or shock stress) for loading on Cu along ⟨100⟩, ⟨110⟩, and ⟨111⟩, and on the isotropic glass. Rrp≥1 for Cu and Rrp<1 for silica glass, and it increases with shock strength; the simulations agree well with the experimental results. For supported shock loading of silica glass at 30–90 GPa, the SiIV–SiVI transition occurs upon shock, inducing substantial densification and thus small Rrp (0.65–0.78). For single crystal Cu, Rrp deviates from 1 near the Hugoniot elastic limit and reaches ∼1.2 at 355 GPa for ⟨100⟩ shock. Rrp is anisotropic, e.g., it is about 1.02, 1.08, and 1.06 for shock loading to about 80 GPa along ⟨100⟩, ⟨110⟩, and ⟨111⟩, respectively. Such an anisotropy is mostly due to that in the degree of stress relaxation at low pressures and that in solid state disordering at high pressures. These results suggest that Rrp is materials dependent and the assumption of Rrp=1 is only valid in a limited stress range. Caution should be exercised when interpreting the free surface velocity measurements as regards the shock states.
Magnetic-field-enhanced synthesis of single-wall carbon nanotubes in arc discharge
Authors: Keidar Michael , Levchenko Igor , Arbel Tamir , Alexander Myriam , Waas Anthony M. , Ostrikov Kostya Ken
Published: May 2008

The ability to control the properties of single-wall nanotubes (SWNTs) produced in the arc discharge is important for many practical applications. Our experiments suggest that the length of SWNTs significantly increases (up to 4000 nm), along with the purity of the carbon deposit, when the magnetic field is applied to arc discharge. Scanning electron microscopy and transmission electron microscopy analyses have demonstrated that the carbon deposit produced in the magnetic-field-enhanced arc mainly consists of the isolated and bunched SWNTs. A model of a carbon nanotube interaction and growth in the thermal plasma was developed, which considers several important effects such as anode ablation that supplies the carbon plasma in an anodic arc discharge technique, and the momentum, charge, and energy transfer processes between nanotube and plasma. It is shown that the nanotube charge with respect to the plasma as well as nanotube length depend on plasma density and electric field in the interelectrode gap. For instance, nanotube charge changes from negative to positive value with an electron density decrease. The numerical simulations based on the Monte Carlo technique were performed, which explain an increase in the nanotubes produced in the magnetic-field-enhanced arc discharge.
Domain dynamics in piezoresponse force spectroscopy: Quantitative deconvolution and hysteresis loop fine structure
Authors: Bdikin Igor K. , Kholkin Andrei L. , Morozovska Anna N. , Svechnikov Sergei V. , Kim Seung-Hyun , Kalinin Sergei V.
Published: May 2008

Domain dynamics in the piezoresponse force spectroscopy (PFS) experiment is studied using the combination of local hysteresis loop acquisition with simultaneous domain imaging. The analytical theory for PFS signal from domain of arbitrary cross section and length is developed for the analysis of experimental data on Pb(Zr,Ti)O3 films. The results suggest formation of oblate domain at early stage of the nucleation and growth, consistent with efficient screening of depolarization field. The fine structure of the hysteresis loop is shown to be related to the observed jumps in domain geometry during domain wall propagation (nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.
Silicon depletion layer actuators
Authors: Ransley J. H. T. , Aziz A. , Durkan C. , Seshia A. A.
Published: May 2008

The uncompensated donor or acceptor atoms present within the depletion layer of a diode can be employed in an electrostatic actuator, which utilizes the force between opposing charges on either side of the semiconductor junction. We describe the theory of this actuator and demonstrate its application for the case of a diode on the top surface of a silicon cantilever. The Schottky diodes fabricated on the top surface of cantilevers were used to drive them into resonance. As the actuator driving voltages are varied, the amplitude of vibration of the cantilevers changes, which is in agreement with the theoretical predictions.
Resonant optical excitation of longitudinal-optical phonons and intermixing in InAs∕AlAs single quantum dots
Authors: Sarkar D. , van der Meulen H. P. , Calleja J. M. , Meyer J. M. , Haug R. J. , Pierz K.
Published: May 2008

Excitations of a single InAs∕AlAs self-assembled quantum dot were investigated by photoluminescence excitation spectroscopy. Resonant absorption by longitudinal-optical (LO) phonons of the quantum dot and the barriers is observed. In particular, a resonance at 41meV is attributed to the AlAs-like mode of InAlAs with low Al content. Our results represent a direct optical measure of the intermixing (estimated below 10%) in a single quantum dot. They also demonstrate that all LO phonons of this mixed quantum dot system couple to the exciton states.
Strong Fano resonance of oxygen-hydrogen bonds on oblique angle deposited Mg nanoblades
Authors: Hlaing Oo W. M. , McCluskey M. D. , He Y. P. , Zhao Y. P.
Published: May 2008

Magnesium hydroxide [Mg(OH)2] thin layers were formed by a chemical reaction between Mg nanoblades and water. Infrared (IR) spectroscopy showed a OH bond-stretching vibrational mode at 3699cm−1. The assignment was verified by reactions with heavy water, producing OD bonds with the expected isotopic frequency shift. An asymmetric Fano line shape was observed for the OH layer on metallic Mg, while a symmetric Lorentzian (or Bright–Wigner) profile was observed for the OH layer on insulating MgH2. The results indicate that the OH layer on the Mg nanoblades is so thin that the vibrational mode couples to the free-electron continuum of Mg metal.
Hydrostatic pressure effect on archetypal Sm0.52Sr0.48MnO3 single crystal
Authors: Mydeen K. , Sarkar P. , Mandal P. , Murugeswari A. , Jin C. Q. , Arumugam S.
Published: May 2008

The effect of hydrostatic pressure (P) on the c-axis electrical resistivity (ρc) and ferromagnetic (FM) transition temperature (TC) of Sm0.52Sr0.48MnO3 single crystal has been investigated. At P=0, the strong hysteretic nature of metal-insulator transition (MIT) and the abrupt decrease of ρc by several orders just below TC suggest that the FM transition is discontinuous in nature. The application of pressure strongly decreases ρc, shifts MIT to higher temperature at the rate of 19K∕GPa, and suppresses the hysteresis width. The nature of the FM phase transition would change from discontinuous to continuous at around P=2.5GPa.
Representations of the Schrödinger–Virasoro algebras
Authors: Li Junbo , Su Yucai
Published: May 2008

In this paper, it is proved that an irreducible weight module with finite-dimensional weight spaces over the Schrödinger–Virasoro algebras is a highest∕lowest weight module or a uniformly bounded module. Furthermore, indecomposable modules of the intermediate series over these algebras are completely determined.
Electrical detection of the mechanical resonances in AlN-actuated microbridges for mass sensing applications
Authors: González-Castilla S. , Olivares J. , Clement M. , Iborra E. , Sangrador J. , Malo J. , Izpura J. I.
Published: May 2008

We report the fabrication and frequency characterization of mechanical resonators piezoelectrically actuated with aluminum nitride films. The resonators consist of a freestanding unimorph structure made up of a metal/AlN/metal piezoelectric stack and a Si3N4 supporting layer. We show that the electrical impedance of the one-port device can be used to assess the vibrational behavior of the resonators, provided that the modes do not exhibit specific symmetries, for which the impedance variations cancel. Frequency shifts arise when loading the resonators with small masses. As gravimetric sensors, the microbridges exhibit mass sensitivities of 0.18fg∕Hz for vibrational modes around 2MHz.
Photoinduced electron transfer in C60 encapsulated single-walled carbon nanotube
Authors: Li Y. F. , Kaneko T. , Hatakeyama R.
Published: May 2008

The transport properties of field-effect transistors based on C60 fullerene peapods have been investigated and our findings indicate that the transport characteristics of single-walled carbon nanotubes (SWNTs) are highly sensitive to the encapsulated fullerenes due to the charge-transfer effect. Under light illumination, the photoinduced electron transfer characteristics are found in C60 peapods, which is different from those observed for empty SWNTs. The response characteristic of peapod devices to light is reflected in a shift of threshold voltage toward negative values, indicating an electron-doping process. After removing light the photoresponse is fully recoverable, indicating complete restoration of transferred electrons.
Deposited debris characteristics and its reduction of a laser-produced plasma extreme ultraviolet source using a colloidal tin dioxide jet target
Authors: Kaku Masanori , Suetake Sumihiro , Senba Yusuke , Kubodera Shoichi , Katto Masahito , Higashiguchi Takeshi
Published: May 2008

Debris characteristics and their reduction have been investigated for a laser-produced plasma extreme ultraviolet source by using a colloidal jet target containing tin dioxide nanoparticles. The amounts of deposited debris on a witness plate were determined by total laser energy irradiated onto a target. In situ low-temperature (100°C) heating of a plate was effective to reduce the amounts of deposited debris, since colloidal debris was easily vaporized by the heat.
Tuning the band structures of single walled silicon carbide nanotubes with uniaxial strain: A first principles study
Authors: Wang Zhiguo , Zu Xiaotao , Xiao Haiyan , Gao Fei , Weber William J.
Published: May 2008

Electronic band structures of single-walled silicon carbide nanotubes are studied under uniaxial strain using first principles calculations. The band structure can be tuned by mechanical strain in a wide energy range. The band gap decreases with uniaxial tensile strain, but initially increases with uniaxial compressive strain and then decreases with further increases in compressive strain. These results may provide a way to tune the electronic structures of silicon carbide nanotubes, which may have promising applications in building nanodevices.
Irreversible redshift of transmission spectrum of gold nanoparticles doped in liquid crystals
Authors: Hsu Li-Hsuan , Lo Kuang-Yao , Huang Shih-An , Huang Chi-Yen , Yang Chung-Sung
Published: May 2008

The absorption peak of gold (Au) nanoparticles doped in liquid crystal (ANDLC) is controllable by applying an external applied voltage before aggregation occurs. Au nanoparticles aggregate when the dielectrophoresis force, which is induced by the gradient of the square of the electric filed close to the sides of the host liquid crystal cell, overcomes the viscosity between Au nanoparticles and the LCs. This result leads to the irreversible redshift. A controllable filter with unpolarized light enables an ANDLC cell under the threshold voltage to prevent the aggregation effect.