bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated photometric redshifts and SED fitting as tool for galaxy evolution studies
Authors: Kotulla Ralf
Published: February 2013

Photometric redshifts, i.e. redshifts derived by comparing an observed spectral-energy distribution (SED) to a range of empirical or theoretical SED templates, are commonly used in studies of the high-redshift Universe. Often, the next step is to use these redshifts as fixed input parameters for SED fitting to derive physical properties for each galaxy. However, this two-step approach ignores degeneracies between redshift and, e.g., stellar mass. Here I present first results using an improved approach that integrates both methods. I find that mass determinations are, on average, three times more uncertain than they seem from the common two-step approach. If not accounted for, these underestimated uncertainties can impact our ability of making meaningful comparisons between observations and simulations of galaxy evolution.
The 2massTully–Fisher Survey: Mapping the mass in the Universe
Authors: Hong T. , Staveley-Smith L. , Masters K. , Springob C. , Macri L. , Koribalski B. , Jones H. , Jarrett T.
Published: February 2013

The 2mass Tully–Fisher Survey (2mtf) aims to measure Tully–Fisher (TF) distances for all bright, inclined spirals in the 2mass Redshift Survey (2mrs) using high-quality Hi widths and 2mass photometry. Compared with previous peculiar-velocity surveys, the 2mtf survey provides more accurate width measurements and more uniform sky coverage, combining observations with the Green Bank, Arecibo, and Parkes telescopes. With this new redshift-independent distance database, we will significantly improve our understanding of the mass distribution in the local Universe.
Measuring H0 from the 6dF Galaxy Survey and future low-redshift surveys
Authors: Colless Matthew , Beutler Florian , Blake Chris
Published: February 2013

Baryon acoustic oscillations (BAO) at low redshift provide a precise and largely model-independent way to measure the Hubble constant, H0. The 6dF Galaxy Survey measurement of the BAO scale gives a value of H0 = 67 ± 3.2 km s−1 Mpc−1, achieving a 1σ precision of 5%. With improved analysis techniques, the planned wallaby (Hi) and taipan (optical) redshift surveys are predicted to measure H0 to 1–3% precision.
Accurate cosmology from gravitational-lens time delays
Authors: Suyu S. H.
Published: February 2013

The time delays between the multiple images of a strong gravitational-lens system, together with a model of the lens-mass distribution, provide a one-step determination of the time-delay distance, and thus a measure of cosmological parameters, particularly the Hubble constant, H0. I review the recent advances in measuring time-delay distances, and present the current status of cosmological constraints based on gravitational-lens time delays. In particular, I report the time-delay distance measurements of two gravitational lenses and their implication for cosmology from a recent study by Suyuet al.
Hubble constant, lensing, and time delay in Te Ve S
Authors: Tian Yong , Ko Chung-Ming , Chiu Mu-Chen
Published: February 2013

The Hubble constant can be determined from the time delay of gravitationally lensed systems. We adopt Te Ve S as the relativistic version of Modified Newtonian Dynamics to study gravitational lensing phenomena and evaluate the Hubble constant from the derived time-delay formula. We test our method on observed quasar lensing published in the literature. Three candidates are suitable for our study, HE 2149-2745, FBQ J0951+2635, and SBS 0909+532.
Gaia contribution to the low-redshift supernova population
Authors: Blagorodnova Nadejda , Walton Nicholas A. , Wyrzykowski Łukasz , Hodgkin Simon
Published: February 2013

The effectiveness of the ESA Gaia mission in obtaining a meaninful sample of supernovae (SNe) is based on three key points: detection rates, characterization capability and an extended validation phase. Focussing on the second, we present our investigations into the use of a range of classification techniques, whereby we demonstrate the ability to discriminate between various SN subtypes, based on the Gaia data (photometry and spectrophotometry) alone. In particular, we comment on the potential ability of Gaia to rapidly estimate SN redshifts and epochs. The methods presented here indicate that ground-based follow-up observations can then be more effectively targeted to the highest-priority SNe.
Planetary nebulae and determination of the bulge–disk boundary
Authors: Costa Roberto D. D. , Cavichia Oscar , Maciel Walter J.
Published: February 2013

In this paper, a sample of planetary nebulae in the Galaxy's inner-disk and bulge is used to find the galactocentric distance that optimally separates these two populations in terms of their abundances. Statistical distance scales were used to investigate the distribution of abundances across the disk–bulge interface, while a Kolmogorov–Smirnov test was used to find the distance at which the chemical properties of these regions separate optimally. The statistical analysis indicates that, on average, the inner population is characterized by lower abundances than the outer component. Additionally, for the α-element abundances, the inner population does not follow the disk's radial gradient toward the Galactic Center. Based on our results, we suggest a bulge–disk interface at 1.5 kpc, marking the transition between the bulge and the inner disk of the Galaxy as defined by the intermediate-mass population.
Recalibration of the uvbyβ photometry-based distance scale of OB-type stars using the revised Hipparcos parallaxes
Authors: Dambis A. K.
Published: February 2013

The absolute visual and infrared magnitudes of moderately evolved OB-type stars are directly calibrated as a function of Stroemgren four-color and Hβ photometric indices using the trigonometric parallaxes from the new reduction of Hipparcos data. The resulting calibrations have an average accuracy of ~ 0.4 mag and, when applied to members of young open clusters, yield distances that are fairly consistent with those determined using the MV–(B − V) zero-age main-sequence fitting procedure.
Maximum-likelihood fitting of the 6dFGS peculiar velocities
Authors: Magoulas Christina , Springob Christopher , Colless Matthew , Jones D. Heath , Campbell Lachlan , Lucey John , Mould Jeremy
Published: February 2013

We develop a robust Bayesian model to derive peculiar velocities and Fundamental Plane (FP) distances for a subsample of 9000 galaxies from the 6dF Galaxy Survey (6dFGS). These galaxies form the basis of 6dFGSv, the largest and most uniform galaxy peculiar-velocity sample to date. We perform a Bayesian analysis of the data set as a whole, determining cosmological parameters from the peculiar-velocity field (e.g., fitting β and the bulk flow), by comparing to the field predicted from the redshift survey and assuming that the galaxy distribution traces the matter distribution.
3D motions of 6.7 GHz methanol masers and effects of the Galactic bar
Authors: Matsumoto Naoko , Honma Mareki ,   the VERA collaboration
Published: February 2013

To search for kinematic evidence of the existence of the Galactic bar, we observed 10 methanol maser sources at the near end of the bar with VERA (VLBI Exploration of Radio Astrometry). From these observations, we obtained absolute proper motions of eight sources based on the phase-referencing technique. We compared the motions with the predictions of three simple models in a 3D plane. This comparison showed that a non-flat circular rotation model and a dynamical model including a bar potential reproduce the observed data better than a flat rotation model. In addition, the bar model suggests that the inclination angle of the Galactic bar is around 35°, which is consistent with previous studies.
Using L dwarfs with distances to test models
Authors: Wang Youfen , Jones H. R. A. , Smart R. L. , Shao Z.
Published: February 2013

We test two contemporary low-mass atmospheric models using three L dwarfs with distances and published spectra. We find that the two models do not predict the same trends for temperature, gravity and metallicity in absorption lines. We find that one model appears to better reflect the temperature, but this sample is too small to investigate the other parameters in depth.
The scientific goal of the Japanese small astrometric satellite, Small-JASMINE
Authors: Yano Taihei , Gouda Naoteru , Kobayashi Yukiyasu , Tsujimoto Takuji , Niwa Yoshito , Yamada Yoshiyuki
Published: February 2013

Small-JASMINE is a small Japanese astrometric satellite, developed mainly at the National Astronomical Observatory of Japan. The target launch date of Small-JASMINE is around 2017. The satellite will be equipped with a telescope with an aperture size of 30 cm and a focal length of approximately 3.9 m. The operational wavelength will be centered on the infrared Hw band, between 1.1 and 1.7 μm, using a HgCdTe detector with 4k × 4k pixels. This will enable us to observe the central regions of our Galaxy and clarify the dynamical structure of the bulge region. A restricted region of the Galactic bulge will be observed using a frame-linking method, which is different from the approach taken by both Hipparcos and Gaia, both developed at ESA. The target accuracy of the annual parallax and proper motion is approximately 10 μas and 10 μas yr−1, respectively, in the central region of the survey area of 0.3 × 0.3 deg2. The target accuracy of the annual parallax, ~ 50 μas, and that of the proper motion, ~ 50 μas yr−1, will be obtained within a region of 2 × 2 deg2. The observing region covers a field of approximately 3 × 3 deg2. The mission is required to continue for around three years to obtain reliable measurements. In the winter season, the angular distance between the Sun and the Galactic bulge region is small. Accordingly, we may have the chance to observe different regions which contain scientifically interesting targets, such as Cygnus X-1. If we are successful in observing the object over the course of a few weeks, the orbital elements of the star accompanying Cygnus X-1 can be resolved by Small-JASMINE.
Trends in health and health inequalities among major states of India: assessing progress through convergence models
Authors: Goli Srinivas , Arokiasamy Perianayagam
Published: February 2013

Convergence in health and health inequalities reflects not only a sense of equity, but also provides a critical assessment tool for monitoring the health progress of differently placed individuals. This study examines convergence hypothesis for health and health inequalities across major Indian states, using both standard and cutting-edge convergence metrics. The findings lend support to the convergence in average health status among the states and the socioeconomic group of India, examined through select health indicators. However, results also suggest a setback in convergence in decline of health inequalities in recent times, particularly in life expectancy at birth, child immunization and underweight. Evidence signals that from the late 1990s, convergence in decline of health inequalities are replaced by emerging divergence. This paper contributes to health policy and planning by identifying areas where, India needs to work to achieve efficiency with equity in health status across geographical divisions and social groups.
Der Zusammenhang zwischen Sucht und Schlaf: Grundlagen der Schlafregulation
Authors: Unbehaun Thomas , Jähne Andreas , Riemann Dieter
Published: February 2013

Fragestellung: Drogen greifen als psychotrope Substanzen in aktivierende oder hemmende Systeme des zentralen Nervensystems ein und können somit Einfluss auf die Schlafregulation nehmen. Gegenstand dieser Arbeit ist die Darstellung des Einflusses verschiedener Substanzen auf den Schlaf. Einleitend soll ein Überblick über wichtige Schlafcharakteristika und Schlafregulationsmechanismen gegeben werden. Ergebnisse: Schlaf wird anhand charakteristischer elektroenzephalographischer Merkmale in einzelne Stadien eingeteilt, die in bestimmter Weise während der Nacht durchlaufen werden. Bei der Schlafregulation werden Mechanismen der Wachheit, der Schlafinduktion und des Wechsels zwischen REM- und non-REM-Schlaf unterschieden. Für die Regulation ist ein Netzwerk spezialisierter Kerngebiete des Gehirns verantwortlich, in dem das Aufsteigende retikuläre aktivierende System, Raphe-Kerne, Locus coeruleus, ventrolaterale präoptische Nucleus, der tuberomammilläre Nucleus und die laterodorsalen und pedunculopontinen tegmentalen Nuclei beteiligt sind. Die Interaktion dieser Kerngebiete wird durch Neurotransmitter wie Acetylcholin, Noradrenalin, Serotonin, Dopamin, GABA, Histamin, Orexin und Adenosin vermittelt. Die Regulation unterliegt einerseits der wechselseitigen Inhibition der Zentren wie auch circadianen Taktgebern. Schlussfolgerung: Externe Einflussnahme auf die Interaktion dieser Neurotransmitter führt zu Veränderungen der Schlafarchitektur und könnte den Ansatzpunkt verschiedener schlafstörender oder -fördernder Substanzen darstellen.
Suchtbezogene Gesundheitsversorgung von Inhaftierten in Deutschland – eine Bestandsaufnahme
Authors: Jakob Lisa , Stöver Heino , Pfeiffer-Gerschel Tim
Published: February 2013

Ziel: Die vorliegende Übersichtsarbeit geht der Frage nach, wie viele Suchtmittelabhängige sich in deutschen Haftanstalten befinden und welche Angebote im Bereich der suchtbezogenen Gesundheitsversorgung von Inhaftierten in Deutschland existieren. Ergebnisse: Der Anteil intravenös konsumierender Drogenabhängiger in deutschen Gefängnissen wird auf etwa 30 % (Männer) und über 50 % (Frauen) geschätzt, der Anteil Alkoholabhängiger auf ca. 38 % und der Anteil aktueller und täglicher Raucher auf 79 % der Gefangenen. Unter dem siebten Titel des Strafvollzugsgesetzes (Gesundheitsversorgung) werden keine gesonderten Vorgaben für den Umgang mit dieser Klientel gemacht. Das Fehlen verbindlicher bundesweiter Richtlinien zur suchtbezogenen Gesundheitsversorgung in Haft führt zu Unterschieden in der Art und Verfügbarkeit von Therapieangeboten zwischen den Bundesländern. Schlussfolgerungen: Obwohl die Raten Suchtmittel konsumierender Inhaftierter um ein Vielfaches über denen der Allgemeinbevölkerung liegen und ein umfassendes intramurales Behandlungsangebot erfordern, existieren trotz Äquivalenzprinzip deutliche Unterschiede zwischen intra- und extramuraler Behandlung Suchtmittel konsumierender oder abhängiger Personen.
Emotion Display Norms in Virtual Teams
Authors: Glikson Ella , Erez Miriam
Published: February 2013

Norms for displaying emotions influence how individuals express their feelings and interpret the emotional expressions of others. Prior research found cross-cultural variation of emotion display norms, but primarily examined face-to-face communication and culturally homogeneous contexts. This study examined perceived emotion display norms for virtual teams, using a sample of 167 MBA students from five countries, who rated the appropriateness of virtually displaying positive and negative emotions for culturally homogeneous and multicultural teams. Results indicate that display norms call for greater expression of positive emotions and suppression of negative emotions in multicultural versus culturally homogeneous teams; national identity influences norms for culturally homogeneous but not multicultural teams, and the strength of norms in multicultural teams is higher among participants with high versus low global identity.
Healable Polymer Systems
Authors:   Royal Society of Chemistry
Published: February 2013

Polymers are used in many everyday technologies and their degradation due to environmental exposure has lead to great interest in materials which can heal and repair themselves. In order to design new self healing polymers it's important to understand the fundamental healing mechanisms behind the material. Healable Polymer Systems will outline the key concepts and mechanisms underpinning the design and processing of healable polymers, and indicate potential directions for progress in the future development and applications of these fascinating and potentially valuable materials.

The book covers the different techniques developed successfully to date for both autonomous healable materials (those which do not require an external stimulus to promote healing) and rehealable or remendable materials (those which only recover their original physical properties if a specific stimulus is applied). These include the encapsulated-monomer approach, reversible covalent bond formation, irreversible covalent bond formation and supramolecular self-assembly providing detailed insights into their chemistry.

Written by leading experts, the book provides polymer scientists with a compact and readily accessible source of reference for healable polymer systems.
Encapsulation-Based Self-Healing Polymers and Composites
Authors: Keller Michael W.
Published: February 2013

One of the most established areas in the field of healable polymeric materials is encapsulation-based healing agents. This chapter provides a comprehensive review of the range of chemical approaches to generating encapsulated healing agents; these systems are embedded into a host matrix, often in combination with catalysts or additional reagents. When the host matrix is subjected to damage, the embedded capsules are fractured, leading to release of the healing agents via capillary action; when in contact with the other reagents, this leads to polymerization in the damaged zones, thus regaining the physical integrity of the host matrix. This chapter describes the synthesis, characterization and applications of encapsulation-based healing agents.
Thermodynamics of Self-Healing in Polymeric Materials
Authors: Yang Ying , Urban Marek W.
Published: February 2013

Inspired by biological systems, the self-healing of polymers represents an array of events involving conformational and configurational changes of macromolecular segments, associated with covalent, supramolecular or coordination bond reformations and usually induced by external stimuli. This chapter discusses recent advances in self-healing of thermoplastic and thermosetting polymers in the context of physico-chemical events responsible for repair processes. The first part focuses on thermodynamic considerations of self-healing and the role of entropic and enthalpic contributions to the Gibbs free energy during self-healing events. The proposed recoupling self-healing lattice model allows an estimate of the contributions of configurational changes, as well as chemical reactions occurring during self-healing, to the Gibbs free energy. As chains undergo transitions from non-equilibrium to equilibrium Gaussian states during self-healing, the magnitude of entropic and enthalpic contributions undergoes dynamic changes that lead to equilibrium at which Gibbs free energy reaches the minimum. The second part reviews recent advances in chemical reactions that involve remolding of thermoplastic and thermosetting polymers by reforming covalent bonding, coordination and supramolecular chemistries. Although the field of self-healing materials is still in its early stages, the combination of multi-faceted reactions offers significant promises in the development of new self-healing thermoplastic and thermosetting polymers.
Role of the CYP4A/20-HETE pathway in vascular dysfunction of the Dahl salt-sensitive rat
Authors: Lukaszewicz Kathleen M. , Lombard Julian H.
Published: February 2013

20-HETE (20-hydroxyeicosatetraenoic acid), a vasoconstrictor metabolite of arachidonic acid formed through the action of CYP4A (cytochrome P450-4A) in vascular smooth muscle cells, has been implicated in the development of hypertension and vascular dysfunction. There have been a number of reports in human subjects demonstrating an association between elevated urinary excretion of 20-HETE and hypertension, as well as increased 20-HETE production and vascular dysfunction. The Dahl SS (salt-sensitive) rat is a genetic model of salt-sensitive hypertension that exhibits vascular dysfunction, even when maintained on a normal-salt diet and before the development of hypertension. This mini-review highlights our current research on the role of CYP4A and 20-HETE in the vascular dysfunction of the Dahl SS rat. In our studies, the SS rat is compared with the consomic SS-5BN rat, having chromosome 5 from the salt-resistant Brown Norway rat (carrying all CYP4A genes) introgressed on to the SS genetic background. Our laboratory has demonstrated restoration of normal vascular function in the SS rat with inhibition of the CYP4A/20-HETE pathway, suggesting a direct role for this pathway in the vascular dysfunction in this animal model. Our studies have also shown that the SS rat has an up-regulated CYP4A/20-HETE pathway within their cerebral vasculature compared with the SS-5BN consomic rat, which causes endothelial dysfunction through the production of ROS (reactive oxygen species). Our data shows that ROS influences the expression of the CYP4A/20-HETE pathway in the SS rat in a feed-forward mechanism whereby elevated ROS stimulates production of 20-HETE. The presence of this vicious cycle offers a possible explanation for the spiralling effects of elevated 20-HETE on the development of vascular dysfunction in this animal model.
Improved algorithm for detecting zero‐quantised discrete cosine transform coefficients in H.264/AVC (revised version)
Authors: Wang Li‐Li , Siu Wan‐Chi
Published: February 2013

In this study, an efficient approach for detecting zero‐quantised discrete cosine transform (DCT) coefficients for video coding is developed. Compared with conventional detection methods of zero‐quantised DCT coefficients used in H.264/AVC, the proposed algorithm has two major features. First, a new classification of patterns for DCT, quantisation, inverse quantisation and inverse discrete cosine transform processes is proposed. By taking a zigzag scanning order into the classification, the quantised DCT coefficients can be coded efficiently. Second, the thresholds for detecting zero‐quantised DCT coefficients are determined by combining the Gaussian distribution with a theoretical analysis of the DCT and quantisation in H.264/AVC. Experimental results show that the proposed algorithm achieves an average timesaving of more than 40% compared with the algorithm in reference software JM12.2 of H.264/AVC. When compared with other algorithms in the literature, it also gives the best performance in terms of both rate‐distortion and time saving.
Whitening central projection descriptor for affine‐invariant shape description
Authors: Lan Rushi , Yang Jianwei , Jiang Yong , Fyfe Colin , Song Zhan
Published: February 2013

A novel descriptor, referred to as the whitening central projection predictor (WCPD), is developed for affine‐invariant shape description. The proposed descriptor is based on central projection transform (CPT) and whitening transform (WT). Dislike contour‐based or region‐based approaches, an object is first converted to a closed curve by CPT, which is called the general curve (GC). The derived GC not only keeps the affine transform information, but also is very robust to noise. Then WT is performed to the GC with the purpose that the affine transformation is simplified to a rotation only. Finally, Fourier descriptors are employed to remove the rotation, and WCPD is obtained. One advantage of using WCPD for affine‐invariant description lies in that it is applicable to objects consisting of several components. Furthermore, the approach used on the GC is contour‐based, and is of small computational complexity. Several experiments have been conducted to evaluate the performance of the proposed method. Experimental results show that the proposed method has a powerful discrimination ability, and is more robust to noise.
Fast and reliable iris segmentation algorithm
Authors: Radman Abduljalil , Jumari Kasmiran , Zainal Nasharuddin
Published: February 2013

Design a fast and reliable iris segmentation algorithm for less constrained iris images is essential to build a robust iris recognition system. Daugman's integrodifferential operator (IDO) is one of powerful iris segmentation mechanisms, but in contrast consumes a large portion of the computational time for localising the rough position of the iris centre and eyelid boundaries. To address this problem, a fast iris segmentation algorithm is proposed. First, the circular Gabor filter is adopted to find the rough position of the pupil centre. Second, the iris and pupil circles are localised using the IDO taken into account that the real centres of the iris and pupil are in the small area around the rough position of the pupil centre. Third, the upper and lower eyelid boundaries are extracted using the live‐wire technique. Experimental results demonstrate that the proposed iris segmentation algorithm significantly minimises the required time to segment the iris without affecting the segmentation accuracy. Moreover, the comparison results with state‐of‐the‐art iris segmentation algorithms show the superiority of the proposed algorithm in terms of segmentation accuracy and recognition performance. The challenging UBIRIS.v1 iris image database is utilised to evaluate the performance of the proposed algorithm.
Is there a relationship between peak‐signal‐to‐noise ratio and structural similarity index measure?
Authors: Horé Alain , Ziou Djemel
Published: February 2013

In this study, the authors analyse two well‐known image quality metrics, peak‐signal‐to‐noise ratio (PSNR) as well as structural similarity index measure (SSIM), and the authors derive an analytical relationship between them which works for some kinds of common image degradations such as Gaussian blur, additive Gaussian noise, Jpeg and Jpeg2000 compressions. The analytical relationship brings more clarity on the interpretation of PSNR and SSIM values, explains some differences found between these quality measures in the literature and confirms some experimental observations regarding these measures. A series of tests realised on images from the Kodak database give a better understanding of the performance of SSIM and PSNR in assessing image quality.
String-like cooperative motion in homogeneous melting
Authors: Zhang Hao , Khalkhali Mohammad , Liu Qingxia , Douglas Jack F.
Published: February 2013

Despite the fundamental nature and practical importance of melting, there is still no generally accepted theory of this ubiquitous phenomenon. Even the earliest simulations of melting of hard discs by Alder and Wainwright indicated the active role of collective atomic motion in melting and here we utilize molecular dynamics simulation to determine whether these correlated motions are similar to those found in recent studies of glass-forming (GF) liquids and other condensed, strongly interacting, particle systems. We indeed find string-like collective atomic motion in our simulations of “superheated” Ni crystals, but other observations indicate significant differences from GF liquids. For example, we observe neither stretched exponential structural relaxation, nor any decoupling phenomenon, while we do find a boson peak, findings that have strong implications for understanding the physical origin of these universal properties of GF liquids. Our simulations also provide a novel view of “homogeneous” melting in which a small concentration of interstitial defects exerts a powerful effect on the crystal stability through their initiation and propagation of collective atomic motion. These relatively rare point defects are found to propagate down the strings like solitons, driving the collective motion. Crystal integrity remains preserved when the permutational atomic motions take the form of ring-like atomic exchanges, but a topological transition occurs at higher temperatures where the rings open to form linear chains similar in geometrical form and length distribution to the strings of GF liquids. The local symmetry breaking effect of the open strings apparently destabilizes the local lattice structure and precipitates crystal melting. The crystal defects are thus not static entities under dynamic conditions, such as elevated temperatures or material loading, but rather are active agents exhibiting a rich nonlinear dynamics that is not addressed in conventional “static” defect melting models.
Static triplet correlations in glass-forming liquids: A molecular dynamics study
Authors: Coslovich Daniele
Published: February 2013

We present a numerical evaluation of the three-point static correlations functions of the Kob-Andersen Lennard-Jones binary mixture and of its purely repulsive, Weeks-Chandler-Andersen variant. In the glassy regime, the two models possess a similar pair structure, yet their dynamics differ markedly. The static triplet correlation functions S(3) indicate that the local ordering is more pronounced in the Lennard-Jones model, an observation consistent with its slower dynamics. A comparison of the direct triplet correlation functions c(3) reveals that these structural differences are due, to a good extent, to an amplification of the small discrepancies observed at the pair level. We demonstrate the existence of a broad, positive peak at small wave-vectors and angles in c(3). In this portion of k-space, slight, systematic differences between the models are observed, revealing “genuine” three-body contributions to the triplet structure. The possible role of the low-k features of c(3) and the implications of our results for dynamic theories of the glass transition are discussed.
Static replica approach to critical correlations in glassy systems
Authors: Franz Silvio , Jacquin Hugo , Parisi Giorgio , Urbani Pierfrancesco , Zamponi Francesco
Published: February 2013

We discuss the slow relaxation phenomenon in glassy systems by means of replicas by constructing a static field theory approach to the problem. At the mean field level we study how criticality in the four point correlation functions arises because of the presence of soft modes and we derive an effective replica field theory for these critical fluctuations. By using this at the Gaussian level we obtain many physical quantities: the correlation length, the exponent parameter that controls the mode-coupling dynamical exponents for the two-point correlation functions, and the prefactor of the critical part of the four point correlation functions. Moreover, we perform a one-loop computation in order to identify the region in which the mean field Gaussian approximation is valid. The result is a Ginzburg criterion for the glass transition. We define and compute in this way a proper Ginzburg number. Finally, we present numerical values of all these quantities obtained from the hypernetted chain approximation for the replicated liquid theory.
Mechanical spectra of glass-forming liquids. II. Gigahertz-frequency longitudinal and shear acoustic dynamics in glycerol and DC704 studied by time-domain Brillouin scattering
Authors: Klieber Christoph , Hecksher Tina , Pezeril Thomas , Torchinsky Darius H. , Dyre Jeppe C. , Nelson Keith A.
Published: February 2013

This paper presents and discusses the temperature and frequency dependence of the longitudinal and shear viscoelastic response at MHz and GHz frequencies of the intermediate glass former glycerol and the fragile glass former tetramethyl-tetraphenyl-trisiloxane (DC704). Measurements were performed using the recently developed time-domain Brillouin scattering technique, in which acoustic waves are generated optically, propagated through nm thin liquid layers of different thicknesses, and detected optically after transmission into a transparent detection substrate. This allows for a determination of the frequency dependence of the speed of sound and the sound-wave attenuation. When the data are converted into mechanical moduli, a linear relationship between longitudinal and shear acoustic moduli is revealed, which is consistent with the generalized Cauchy relation. In glycerol, the temperature dependence of the shear acoustic relaxation time agrees well with literature data for dielectric measurements. In DC704, combining the new data with data from measurements obtained previously by piezo-ceramic transducers yields figures showing the longitudinal and shear sound velocities at frequencies from mHz to GHz over an extended range of temperatures. The shoving model's prediction for the relaxation time's temperature dependence is fairly well obeyed for both liquids as demonstrated from a plot with no adjustable parameters. Finally, we show that for both liquids the instantaneous shear modulus follows an exponential temperature dependence to a good approximation, as predicted by Granato's interstitialcy model.
The relationship of dynamical heterogeneity to the Adam-Gibbs and random first-order transition theories of glass formation
Authors: Starr Francis W. , Douglas Jack F. , Sastry Srikanth
Published: February 2013

We carefully examine common measures of dynamical heterogeneity for a model polymer melt and test how these scales compare with those hypothesized by the Adam and Gibbs (AG) and random first-order transition (RFOT) theories of relaxation in glass-forming liquids. To this end, we first analyze clusters of highly mobile particles, the string-like collective motion of these mobile particles, and clusters of relative low mobility. We show that the time scale of the high-mobility clusters and strings is associated with a diffusive time scale, while the low-mobility particles' time scale relates to a structural relaxation time. The difference of the characteristic times for the high- and low-mobility particles naturally explains the well-known decoupling of diffusion and structural relaxation time scales. Despite the inherent difference of dynamics between high- and low-mobility particles, we find a high degree of similarity in the geometrical structure of these particle clusters. In particular, we show that the fractal dimensions of these clusters are consistent with those of swollen branched polymers or branched polymers with screened excluded-volume interactions, corresponding to lattice animals and percolation clusters, respectively. In contrast, the fractal dimension of the strings crosses over from that of self-avoiding walks for small strings, to simple random walks for longer, more strongly interacting, strings, corresponding to flexible polymers with screened excluded-volume interactions. We examine the appropriateness of identifying the size scales of either mobile particle clusters or strings with the size of cooperatively rearranging regions (CRR) in the AG and RFOT theories. We find that the string size appears to be the most consistent measure of CRR for both the AG and RFOT models. Identifying strings or clusters with the “mosaic” length of the RFOT model relaxes the conventional assumption that the “entropic droplets” are compact. We also confirm the validity of the entropy formulation of the AG theory, constraining the exponent values of the RFOT theory. This constraint, together with the analysis of size scales, enables us to estimate the characteristic exponents of RFOT.
Note: Design of a dose-controlled phototherapy system based on hyperspectral studies
Authors: Ugarte M. F. , Chávarri L. , Briz S.
Published: February 2013

Phototherapy consists in applying radiation on a part of the human body in order to treat an illness. A radiation dose is established for each treatment. In order to apply the correct dose a treatment time is set. However, in this work we have carried out some hyperspectral imaging studies that conclude that the radiation sources and the absorption properties of each patient can change. Therefore, the same treatment time does not ensure that the patient receive the appropriate dose. Thus, an optimized therapy system must measure the radiation emitted by the source and absorbed by the patient on real time to calculate the optimal dose at which the treatment is effective. In this work, we have developed and designed a custom system to measure the effectiveness of a radiative therapy treatment to adapt the appropriate dose for a specific patient in real time.
EXAFS Debye-Waller factors issued from Car-Parrinello molecular dynamics: Application to the fit of oxaliplatin and derivatives
Authors: Provost K. , Beret E. C. , Muller D. Bouvet , Michalowicz A. , Marcos E. Sánchez
Published: February 2013

One of the main pitfalls in EXAFS fitting is correlation among parameters, which can lead to unreliable fits. The use of theoretical Debye-Waller factors (DWs) is a promising way to reduce the number of fitted parameters. When working with molecular dynamics, it is not only possible to evaluate DWs from the statistical distributions issued from the trajectory but also to estimate the distribution anharmonicity, and to compute simulated average EXAFS spectra that can be fitted as experimental ones, in order to assess the ability of EXAFS fitting to recover information on DWs, as well as other structural and spectroscopical parameters. The case studied is oxaliplatin, a third generation anticancer drug. The structural information and the simulated average spectra were derived from a Car-Parrinello molecular dynamics (CP-MD) trajectory of a compound closely related to oxaliplatin. We present the DWs issued from this simulation and their use, by taking their theoretical absolute values (no DW fitted) or their ratios (one DW fitted). In this second approach, the fit of oxaliplatin experimental spectra leads to DWs values very close to the theoretical ones. This shows that the CP-MD trajectory provides a good representation of the distance distributions for oxaliplatin. Transferability of oxaliplatin DWs, for all relevant single and multiple scattering paths, to closely related compounds is proven for the case of bis(oxalato)platinum(II) and bis(ethylene diamine)platinum(II).
A stable method to model the acoustic response of multilayered structures
Authors: Dazel O. , Groby J.-P. , Brouard B. , Potel C.
Published: February 2013

A general approach to determine the acoustic reflection and transmission coefficients of multilayered panels is proposed in this paper. Contrary to the Transfer Matrix Method (TMM), this method does not become unstable for high frequencies or large layer thicknesses. This method is shown to be as general as the TMM and mathematically equivalent. Its principle is to consider a so called Information Vector which contains all the information necessary to deduce the State Vector through a Translation Matrix. The Information Vector is of reduced length compared to that of the State Vector and can be propagated in any layer without involving exponentially growing terms. In addition, this method enables the coupling between any type of physical media as far as proper boundary relations can be written. Moreover, the method does not lead to an enlargement of the systems’ size in the case of interfaces between media of different physical type. Finally, this method can be easily implemented in numerical codes. The method is validated on three cases classically encountered in acoustic problems. However, it is general enough to model any type of multilayered problems in any field of applied physics.
Homogeneous bubble nucleation in water at negative pressure: A Voronoi polyhedra analysis
Authors: Abascal Jose L. F. , Gonzalez Miguel A. , Aragones Juan L. , Valeriani C.
Published: February 2013

We investigate vapor bubble nucleation in metastable TIP4P/2005 water at negative pressure via the Mean First Passage Time (MFPT) technique using the volume of the largest bubble as a local order parameter. We identify the bubbles in the system by means of a Voronoi-based analysis of the molecular dynamics trajectories. By comparing the features of the tessellation of liquid water at ambient conditions to those of the same system with an empty cavity we are able to discriminate vapor (or interfacial) molecules from the bulk ones. This information is used to follow the time evolution of the largest bubble until the system cavitates at 280 K above and below the spinodal line. At the pressure above the spinodal line, the MFPT curve shows the expected shape for a moderately metastable liquid from which we estimate the bubble nucleation rate and the size of the critical cluster. The nucleation rate estimated using Classical Nucleation Theory turns out to be about 8 order of magnitude lower than the one we compute by means of MFPT. The behavior at the pressure below the spinodal line, where the liquid is thermodynamically unstable, is remarkably different, the MFPT curve being a monotonous function without any inflection point.
The impact of deformable interfaces and Poiseuille flow on the thermocapillary instability of three immiscible phases confined in a channel
Authors: Alvarez Nicolas J. , Uguz A. Kerem
Published: February 2013

The majority of studies considering thermocapillary convection in multilayer systems assume the interface is rigid (non-deformable) and the fluids are stationary. Motivated by the potential of using thermally generated convection patterns in moving droplets for mixing, this paper re-examines the Marangoni-Bénard instability for a three-layer system with deformable interfaces undergoing Poiseuille flow. Taking into account the deformability of the interface reveals new physics. Linear stability analysis shows that at small wave numbers a deformable interface is of the orders of magnitude less stable than a non-deformable interface. At large wave numbers, both a rigid and a deformable interface have the same stability. Furthermore, a base planar Poiseuille flow affects the linear stability of the system and the type of instability when the interface is allowed to deform. Flow stabilizes an already unstable system and works to destabilize a stable system. Lastly, the dependence of the linear stability of the system on viscosity ratio, depth ratio, and Prandtl number, Pr, experimentally adjustable parameters, is discussed. Whereas Pr has little effect on the stability of the system, we show that a small viscosity ratio and a large depth ratio are advantageous in making the system unstable.
High pressure-induced phase transitions in CdS up to 1 Mbar
Authors: Li Yanchun , Zhang Xiaona , Li Hui , Li Xiaodong , Lin Chuanlong , Xiao Wangsheng , Liu Jing
Published: February 2013

The pressure-induced structural transformations of CdS have been investigated using synchrotron x-ray diffraction in a diamond anvil cell up to 104 GPa and the density functional theory calculations. The x-ray diffraction experiments show that CdS is stable with the wurtzite-type structure at ambient conditions. The wurtzite-type phase transforms to NaCl-type structure at 3 GPa, which is followed by a second phase transition at 52.3 GPa. In the diffraction patterns, the peak-splitting is observed, indicating that the high-pressure phase appearing at 52.3 GPa is the Pmmn structure, rather than the Cmcm phase reported earlier. With increasing pressure, the lattice parameter a of the Pmmn phase increases abnormally, contrary to decrease of b and c axes. Our calculations reveal that the abnormal change of the a-axis could be related to the pressure-induced crystal structural change. The bulk modulus (B0), is 64.3(9) GPa for wurzite-type phase, 105(2) GPa for NaCl-type phase, and 54(4) GPa for the Pmmn phase, respectively.
Separated topologies—A method for relative binding free energy calculations using orientational restraints
Authors: Rocklin Gabriel J. , Mobley David L. , Dill Ken A.
Published: February 2013

Orientational restraints can improve the efficiency of alchemical free energy calculations, but they are not typically applied in relative binding calculations, which compute the affinity difference been two ligands. Here, we describe a new “separated topologies” method, which computes relative binding free energies using orientational restraints and which has several advantages over existing methods. While standard approaches maintain the initial and final ligand in a shared orientation, the separated topologies approach allows the initial and final ligands to have distinct orientations. This avoids a slowly converging reorientation step in the calculation. The separated topologies approach can also be applied to determine the relative free energies of multiple orientations of the same ligand. We illustrate the approach by calculating the relative binding free energies of two compounds to an engineered site in Cytochrome C Peroxidase.
Multidimensional master equation and its Monte-Carlo simulation
Authors: Pang Juan , Bai Zhan-Wu , Bao Jing-Dong
Published: February 2013

We derive an integral form of multidimensional master equation for a Markovian process, in which the transition function is obtained in terms of a set of discrete Langevin equations. The solution of master equation, namely, the probability density function is calculated by using the Monte-Carlo composite sampling method. In comparison with the usual Langevin-trajectory simulation, the present approach decreases effectively coarse-grained error. We apply the master equation to investigate time-dependent barrier escape rate of a particle from a two-dimensional metastable potential and show the advantage of this approach in the calculations of quantities that depend on the probability density function.
Method of extreme surfaces for optimizing geometry of acousto-optic interactions in crystalline materials: Example of LiNbO3 crystals
Authors: Buryy О. А. , Andrushchak А. S. , Kushnir O. S. , Ubizskii S. B. , Vynnyk D. М. , Yurkevych O. V. , Larchenko A. V. , Chaban K. O. , Gotra O. Z. , Kityk A. V.
Published: February 2013

We suggest a method for optimizing geometry of acousto-optic (AO) interactions in anisotropic crystalline materials. Within the framework of this method, one gets global maximums of AO figure of merit M2 and their spatial orientations, proceeding from so-called “extreme” indicative surfaces, which are obtained after finding such an acoustic wave propagation direction that maximizes the M2 parameter for each propagation direction of the incident electromagnetic wave. The method improves earlier indicative surface-based techniques in several aspects, particularly in properly accounting for the momentum conservation condition for the AO diffraction, and yields a higher accuracy in assessing spatial anisotropy of the AO effect. We have constructed the extreme surfaces of LiNbO3 crystals for all possible cases, including those of isotropic/anisotropic AO diffractions and longitudinal/transverse acoustic waves. The anisotropy of the AO figure of merit for LiNbO3 is analyzed for the acoustic frequencies 0.01–2.0 GHz and the light wavelengths 405–1444 nm. The absolute M2 maximums refer to ‘indirect crystal cuts' and are equal to 26.3 × 10−15 s3/kg at 2 GHz and 405 nm, and 15.4 × 10−15 s3/kg at 0.4 GHz and 1444 nm.
Film drainage of viscous liquid on top of bare bubble: Influence of the Bond number
Authors: Kočárková Helena , Rouyer Florence , Pigeonneau Franck
Published: February 2013

We present experimental results of film drainage on top of gas bubbles pushed by gravity towards the free surface of highly viscous Newtonian liquid with a uniform interface tension. The temporal evolution of the thickness of the film between a single bubble and the air/liquid interface is investigated via interference method. Experiments under various physical conditions (range of viscosities and surface tension of the liquid, and bubble sizes) evidence the influence of the deformation of the thin film on the thinning rate and confirm the slow down of film drainage with Bond number as previously reported by numerical work of Pigeonneau and Sellier [Phys. Fluids 23, 092102 (2011)]10.1063/1.3629815. Considering the liquid flow in the cap squeezed by buoyancy force of the bubble, we provide an approximation of thinning rate as a function of Bond number that agrees with experimental and numerical data. Qualitatively, the smaller the area of the thin film compare to the surface of the bubble, the faster the drainage.