Metallic and nonmetallic shine in luster: An elastic ion backscattering study

Luster is a metal glass nanocomposite layer first produced in the Middle East in early Islamic times ( 9th AD) made of metal copper or silver nanoparticles embedded in a silica-based glassy matrix. These nanoparticles are produced by ion exchange between Cu+ and Ag+ and alkaline ions from the glassy matrix and further growth in a reducing atmosphere. The most striking property of luster is its capability of reflecting light like a continuous metal layer and it was unexpectedly found to be linked to one single production parameter: the presence of lead in the glassy matrix composition. The purpose of this article is to describe the characteristics and differences of the nanoparticle layers developed on lead rich and lead free glasses. Copper luster layers obtained using the ancient recipes and methods are analyzed by means of elastic ion backscattering spectroscopy associated with other analytical techniques. The depth profile of the different elements is determined, showing that the luster layer formed in lead rich glasses is 5–6 times thinner and 3–4 times Cu richer. Therefore, the metal nanoparticles are more densely packed in the layer and this fact is related to its higher reflectivity. It is shown that lead influences the structure of the metal nanoparticle layer through the change of the precipitation kinetics

Síntesi i propietats de vidres metàl•lics massissos i materials nanocomposites basats en Fe per aplicacions com a materials magnètics tous

Estudi realitzat a partir d’una estada a l’ Institut für Komplexe Materialien, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, entre 2010 i 2011. S'ha explorat l'efecte de les condicions i influència dels elements d'aleació en la capacitat de formació de vidre, l'estructura i les propietats tèrmiques i magnètiques de vidres metàl•lics massissos i materials nanocristal•lins en base Fe. La producció d'aquests materials en forma de cintes de unes 20 micres de gruix ha estat àmpliament estudiada i s'ha vist que presenten unes propietats excel•lents com a materials magnètics tous. El propòsit general d'aquest projecte era l'obtenció de composicions òptimes amb alta capacitat de formar vidre i amb excel•lents propietats magnètiques com a materials magnètics tous combinat amb bones propietats mecàniques. El projecte prenia com a punt de partida l'aliatge [FeCoBSi]96Nb4 ja que és el que presenta millor capacitat de formar vidre i presenta una alta imantació de saturació i baix camp coercitiu. S'ha fet un estudi dels factors fonamentals que intervenen en la formació de l'estat vitri. La composició abans esmentada ha estat variada amb l'addició d'altres elements per estudiar com afecten aquests nous elements a les propietats, la formació de vidre i l'estructura dels aliatges resultants amb l'objectiu de millorar-ne les propietats magnètiques i la capacitat de formació de vidre. Entre altres s'ha usat el Zr, Mo, Y i el Gd per millorar la formació de vidre; i el Co i el Ni per millorar les propietats magnètiques a alta temperatura. S'han estudiat les relacions entre la capacitat de formació de vidre i la seva estabilitat tèrmica, la resistència a la cristal•lització i la estructura de l'aliatge resultant després del procés de solidificació. Per aquest estudi s'han determinat els mecanismes que controlen la transformació i la seva cinètica així com les fases que es formen durant el tractament tèrmic permetent la formulació de models predictius.

Correlation between the infestation level of Sitophilus zeamais Motschulsky, 1855 (Coleoptera, Curculionidae) and the quality factors of stored corn, Zea mays L. (Poaceae)

This experiment was carried out in order to evaluate the effect of Sitophilus zeamais on physical, physiological and sanitary quality of stored corn. Samples of 500 g of the hybrid OC-705, in three replicates, were conditioned in glasses covered with a screened lid, and kept in chamber at 25±2ºC, 70±5% RH and 12 h of photophase, for 150 days. The infestation levels were 0, 5, 15 and 50 adults/replicate, for the storage periods of 30, 60, 90, 120 and 150 days. The moisture content, classification, weight loss, germination and internal infestation were evaluated monthly. Significant inverse correlations were verified between the number of insects and both the germination and the weight loss; also between the internal infestation and the germination and the standard type. The presence of S. zeamais showed a positive correlation with the weight loss, what means that the internal and external infestations contribute to the reduction of physiological and physical quality of corn seeds. The mean dry matter loss was 0,36%/day, corresponding to a consumption of 0,0001%/insect/month. As the result of those damages, the product suffered reduction of the commercial grade in 30 days, with significant loss in all quality factors.

Esotropie précoce: résultats à long terme d'une série de 82 cas opérés par myopexie rétro-équatoriale et recul simultané des deux muscles droits médiaux avant l'âge de 24 mois [Early-onset esotropia operated before the age of 24 months: long-term results of Cüpper's retropexy combined with simultaneous recession of both medial recti]

BACKGROUND: When and how to operate an early-onset esotropia (onset before 6 months of age) is still controversial. We conducted a retrospective study of such patients operated before the age of 24 months. PATIENTS AND METHODS: 82 patients were operated by one surgeon (GK) and followed by the same team. At 5 years post-operation, evaluation criteria included the residual angle of deviation, visual acuity (Birkhäuser Nr 505, 5 m) and binocularity (Lang stereotest I, Bagolini glasses). RESULTS: At 5 years, the residual angle was excellent (0 degrees to + 5 degrees ) in 67 % good, (>+5 degrees to +10 degrees or 0 to -5 degrees ) in 23 %, and poor (>+10 degrees or <-5 degrees ) in 10 %. During the 5 years of follow-up the rate of reoperation was 9.7 %. Isoacuity was obtained in 62 %, slight amblyopia (2 lines of interocular difference) was present in 32 %, and average amblyopia (> 3 lines of interocular difference) was noted in 6 %. Simultaneous perception was present in 53 %, whereas one eye was suppressed or results were undetermined in 47 %. No patient demonstrated stereoscopy using the Lang's stereotest I. CONCLUSION: The results from our study demonstrate that early surgery of early-onset esotropia has a favourable outcome on both visual acuity and the residual angle of strabismus. Simultaneous perception was achieved in 53 %. These figures are comparable to the results of the ELISSS multicentric study.

Finite-size scaling analysis of the avalanches in the three-dimensional Gaussian random-field Ising model with metastable dynamics

A numerical study is presented of the third-dimensional Gaussian random-field Ising model at T=0 driven by an external field. Standard synchronous relaxation dynamics is employed to obtain the magnetization versus field hysteresis loops. The focus is on the analysis of the number and size distribution of the magnetization avalanches. They are classified as being nonspanning, one-dimensional-spanning, two-dimensional-spanning, or three-dimensional-spanning depending on whether or not they span the whole lattice in different space directions. Moreover, finite-size scaling analysis enables identification of two different types of nonspanning avalanches (critical and noncritical) and two different types of three-dimensional-spanning avalanches (critical and subcritical), whose numbers increase with L as a power law with different exponents. We conclude by giving a scenario for avalanche behavior in the thermodynamic limit.

The Gibbs free energy of formation of a glass alloy

A simple expression for the Gibbs free energy of formation of a pure component or a eutectic alloy glass, relative to the stable crystalline phase (or phases) at the same temperature is deduced by use of thermodynamic arguments. The expression obtained is supposed to apply to both monocomponent and multicomponent liquid alloys that might become glasses from the supercooled liquid state, irrespective of the critical cooling rate needed to avoid crystallization.

Slow Dynamics of Ising Models with Energy Barriers

Using Monte Carlo simulations we study the dynamics of three-dimensional Ising models with nearest-, next-nearest-, and four-spin (plaquette) interactions. During coarsening, such models develop growing energy barriers, which leads to very slow dynamics at low temperature. As already reported, the model with only the plaquette interaction exhibits some of the features characteristic of ordinary glasses: strong metastability of the supercooled liquid, a weak increase of the characteristic length under cooling, stretched-exponential relaxation, and aging. The addition of two-spin interactions, in general, destroys such behavior: the liquid phase loses metastability and the slow-dynamics regime terminates well below the melting transition, which is presumably related with a certain corner-rounding transition. However, for a particular choice of interaction constants, when the ground state is strongly degenerate, our simulations suggest that the slow-dynamics regime extends up to the melting transition. The analysis of these models leads us to the conjecture that in the four-spin Ising model domain walls lose their tension at the glassy transition and that they are basically tensionless in the glassy phase.

Fragile-glass behavior of a short-range p-spin model

We propose a short-range generalization of the p-spin interaction spin-glass model. The model is well suited to test the idea that an entropy collapse is at the bottom line of the dynamical singularity encountered in structural glasses. The model is studied in three dimensions through Monte Carlo simulations, which put in evidence fragile glass behavior with stretched exponential relaxation and super-Arrhenius behavior of the relaxation time. Our data are in favor of a Vogel-Fulcher behavior of the relaxation time, related to an entropy collapse at the Kauzmann temperature. We, however, encounter difficulties analogous to those found in experimental systems when extrapolating thermodynamical data at low temperatures. We study the spin-glass susceptibility, investigating the behavior of the correlation length in the system. We find that the increase of the relaxation time is accompanied by a very slow growth of the correlation length. We discuss the scaling properties of off-equilibrium dynamics in the glassy regime, finding qualitative agreement with the mean-field theory.

Erasing the glassy state in magnetic fine particles

BaFe10.4Co0.8Ti0.8O19 magnetic fine particles exhibit most of the features attributed to glassy behavior, e.g., irreversibility in the hysteresis loops and in the zero-field-cooling and field-cooling curves extends up to very high fields, and aging and magnetic training phenomena occur. However, the multivalley energy structure of the glassy state can be strongly modified by a field-cooling process at a moderate field. Slow relaxation experiments demonstrate that the intrinsic energy barriers of the individual particles dominate the behavior of the system at high cooling fields, while the energy states corresponding to collective glassy behavior play the dominant role at low cooling fields.

Reply to "Comment on 'Erasing glassy state in magnetic fine particles'"

The Comment affirms that no phase transition occurs in spin-glass systems with an applied magnetic field. However, only according to the droplet model is this result expected. Other models do not predict this result and, consequently, it is under current discussion. In addition, we show how the experimental results obtained in our system correspond to a cluster glass rather than to a true spin glass.

Squared interaction matrix Sherrington-Kirkpatrick model for a spin glass

The mean-field theory of a spin glass with a specific form of nearest- and next-nearest-neighbor interactions is investigated. Depending on the sign of the interaction matrix chosen we find either the continuous replica symmetry breaking seen in the Sherrington-Kirkpartick model or a one-step solution similar to that found in structural glasses. Our results are confirmed by numerical simulations and the link between the type of spin-glass behavior and the density of eigenvalues of the interaction matrix is discussed.

Donor site morbidity of the posterior conchal region.

BACKGROUND: The perichondral cutaneous graft (PCCG) from the posterior conchal region is an elegant solution for the coverage of facial defects with particular stability requirements. The donor defect can easily be covered with a transposition flap from the postauricular region. Although this region is a common donor site for skin grafts and has an important supporting function for glasses or hearing aids, little is known about long-term morbidity after graft harvest. OBJECTIVE: To assess the morbidity of the posterior concha and the postauricular region in terms of pain, scar formation, and patient satisfaction. MATERIALS AND METHODS: A retrospective study of 16 patients who had a PCCG harvested from the posterior concha. RESULTS: Two patients presented with a postoperative wound dehiscence on the postauricular region and one with a keloid scar on the posterior concha. One case of transitory hyperesthesia and pain when sleeping on the operated site was observed. None had complaints related to wearing glasses or hearing aids. CONCLUSION: Donor site morbidity of the postauricular and posterior conchal region is minimal and associated with high patient satisfaction, excellent aesthetic results, and emotional detachment from the hidden donor site.

General method to determine replica symmetry breaking transitions

We introduce a new parameter to investigate replica symmetry breaking transitions using finite-size scaling methods. Based on exact equalities initially derived by F. Guerra this parameter is a direct check of the self-averaging character of the spin-glass order parameter. This new parameter can be used to study models with time reversal symmetry but its greatest interest lies in models where this symmetry is absent. We apply the method to long-range and short-range Ising spin-glasses with and without a magnetic field as well as short-range multispin interaction spin-glasses.

Glassiness in a model without energy barriers

We propose a microscopic model without energy barriers in order to explain some generic features observed in structural glasses. The statics can be exactly solved while the dynamics has been clarified using Monte Carlo calculations. Although the model has no thermodynamic transition, it captures some of the essential features of real glasses, i.e., extremely slow relaxation, time dependent hysteresis effects, anomalous increase of the relaxation time, and aging. This suggests that the effect of entropy barriers can be an important ingredient to account for the behavior observed in real glasses.