Busca por excesso no infravermelho médio em estrelas evoluídas com fotometria WISE e 2MASS

Debris discs are commonly detected orbiting main-sequence stars, but little is known regarding their fate as stars evolve along subgiant and giant stages. Jones (2008) has found strong evidence on the presence of mid-IR excess in G and K stars of luminosity class III, using photometric data from the Two-Micron All-Sky Survey (2MASS) and GLIMPSE catalogues. While the origin of these excesses remains uncertain, it is plausible that they arise from debris discs around these stars. The present study brings an unprecedent survey in the search for mid-IR excess among single and binary F, G and K-type evolved stars of luminosity classes IV, III, II and Ib. For this study, we use WISE and 2MASS photometric data for a sample of 3000 evolved stars, complete up to visual magnitude of 6.5. As major results, we found that the frequency of evolved stars showing mid-IR WISE excess increases from the luminosity classes IV and III to luminosity classes II and Ib. In addition, there is no clear difference between the presence of IR excess in binary and single stars for all the analyzed luminosity classes.

Busca por excesso no infravermelho médio em estrelas evoluídas com fotometria WISE e 2MASS

Debris discs are commonly detected orbiting main-sequence stars, but little is known regarding their fate as stars evolve along subgiant and giant stages. Jones (2008) has found strong evidence on the presence of mid-IR excess in G and K stars of luminosity class III, using photometric data from the Two-Micron All-Sky Survey (2MASS) and GLIMPSE catalogues. While the origin of these excesses remains uncertain, it is plausible that they arise from debris discs around these stars. The present study brings an unprecedent survey in the search for mid-IR excess among single and binary F, G and K-type evolved stars of luminosity classes IV, III, II and Ib. For this study, we use WISE and 2MASS photometric data for a sample of 3000 evolved stars, complete up to visual magnitude of 6.5. As major results, we found that the frequency of evolved stars showing mid-IR WISE excess increases from the luminosity classes IV and III to luminosity classes II and Ib. In addition, there is no clear difference between the presence of IR excess in binary and single stars for all the analyzed luminosity classes.

Universal critical behavior of the two-dimensional Ising spin glass

We use finite size scaling to study Ising spin glasses in two spatial dimensions. The issue of universality is addressed by comparing discrete and continuous probability distributions for the quenched random couplings. The sophisticated temperature dependency of the scaling fields is identified as the major obstacle that has impeded a complete analysis. Once temperature is relinquished in favor of the correlation length as the basic variable, we obtain a reliable estimation of the anomalous dimension and of the thermal critical exponent. Universality among binary and Gaussian couplings is confirmed to a high numerical accuracy.

The fastest unbound star in our Galaxy ejected by a thermonuclear supernova

Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy. Several acceleration mechanisms have been discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we present a spectroscopic and kinematic analysis of US 708. Traveling with a velocity of ∼1200 kilometers per second, it is the fastest unbound star in our Galaxy. In reconstructing its trajectory, the Galactic center becomes very unlikely as an origin, which is hardly consistent with the most favored ejection mechanism for the other HVSs. Furthermore, we detected that US 708 is a fast rotator. According to our binary evolution model, it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova.

The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries

Context: The initial distribution of spin rates of massive stars is a fingerprint of their elusive formation process. It also sets a key initial condition for stellar evolution and is thus an important ingredient in stellar population synthesis. So far, most studies have focused on single stars. Most O stars are, however, found in multiple systems. 

Aims: By establishing the spin-rate distribution of a sizeable sample of O-type spectroscopic binaries and by comparing the distributions of binary subpopulations with one another and with that of presumed-single stars in the same region, we aim to constrain the initial spin distribution of O stars in binaries, and to identify signatures of the physical mechanisms that affect the evolution of the spin rates of massive stars. 

Methods: We use ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS) to establish the projected equatorial rotational velocities (ν_esini) for components of 114 spectroscopic binaries in 30 Doradus. The ν_esini values are derived from the full width at half maximum (FWHM) of a set of spectral lines, using a FWHM vs. ν_esini calibration that we derive based on previous line analysis methods applied to single O-type stars in the VFTS sample. 

Results: The overall ν_esini distribution of the primary stars resembles that of single O-type stars in the VFTS, featuring a low-velocity peak (at ν_esini<200 kms^-1) and a shoulder at intermediate velocities (200 <ν_esini<300 kms^-1). The distributions of binaries and single stars, however, differ in two ways. First, the main peak at ν_esini ~ 100kms^-1 is broader and slightly shifted towards higher spin rates in the binary distribution than that of the presumed-single stars. This shift is mostly due to short-period binaries (P_orb~<10 d). Second, the ν_esini distribution of primaries lacks a significant population of stars spinning faster than 300 kms^-1, while such a population is clearly present in the single-star sample. The ν_esini distribution of binaries with amplitudes of radial velocity variation in the range of 20 to 200 kms^-1 (mostly binaries with P_orb ~ 10-1000 d and/or with q<0.5) is similar to that of single O stars below ν_esini_~<170kms^-1. 

Conclusions: Our results are compatible with the assumption that binary components formed with the same spin distribution as single stars, and that this distribution contains few or no fast-spinning stars. The higher average spin rate of stars in short-period binaries may either be explained by spin-up through tides in such tight binary systems, or by spin-down of a fraction of the presumed-single stars and long-period binaries through magnetic braking (or by a combination of both mechanisms). Most primaries and secondaries of SB2 systems with P_orb~<10 d appear to have similar rotational velocities. This is in agreement with tidal locking in close binaries where the components have similar radii. The lack of very rapidly spinning stars among binary systems supports the idea that most stars with ν_esini_~> 300kms^-1 in the single-star sample are actually spun-up post-binary interaction products. Finally, the overall similarities (low-velocity peak and intermediate-velocity shoulder) of the spin distribution of binary and single stars argue for a massive star formation process in which the initial spin is set independently of whether stars are formed as single stars or as components of a binary system.

User Behavioral Modeling of Web-based Systems for Continuous User Authentication

Authentication plays an important role in how we interact with computers, mobile devices, the web, etc. The idea of authentication is to uniquely identify a user before granting access to system privileges. For example, in recent years more corporate information and applications have been accessible via the Internet and Intranet. Many employees are working from remote locations and need access to secure corporate files. During this time, it is possible for malicious or unauthorized users to gain access to the system. For this reason, it is logical to have some mechanism in place to detect whether the logged-in user is the same user in control of the user's session. Therefore, highly secure authentication methods must be used. We posit that each of us is unique in our use of computer systems. It is this uniqueness that is leveraged to "continuously authenticate users" while they use web software. To monitor user behavior, n-gram models are used to capture user interactions with web-based software. This statistical language model essentially captures sequences and sub-sequences of user actions, their orderings, and temporal relationships that make them unique by providing a model of how each user typically behaves. Users are then continuously monitored during software operations. Large deviations from "normal behavior" can possibly indicate malicious or unintended behavior. This approach is implemented in a system called Intruder Detector (ID) that models user actions as embodied in web logs generated in response to a user's actions. User identification through web logs is cost-effective and non-intrusive. We perform experiments on a large fielded system with web logs of approximately 4000 users. For these experiments, we use two classification techniques; binary and multi-class classification. We evaluate model-specific differences of user behavior based on coarse-grain (i.e., role) and fine-grain (i.e., individual) analysis. A specific set of metrics are used to provide valuable insight into how each model performs. Intruder Detector achieves accurate results when identifying legitimate users and user types. This tool is also able to detect outliers in role-based user behavior with optimal performance. In addition to web applications, this continuous monitoring technique can be used with other user-based systems such as mobile devices and the analysis of network traffic.

Correlation and prediction of mixing thermodynamic properties of ester-containing systems Ester+alkane and ester+ester binary systems and the ternary dodecane+ethyl pentonoate+ethyl ethanoate

[EN]Excess thermodynamic properties VE m and HE m, have been measured for the ternary mixture dodecane + ethyl pentanoate + ethyl ethanoate and for the corresponding binaries dodecane + ethyl pentanoate, dodecane + ethyl ethanoate, ethyl pentanoate + ethyl ethanoate at 298.15 K. All mixtures show endothermic and expansive effects. Experimental results are correlated with a suitable equation whose final form for the excess ternary quantity ME contains the particular contributions of the three binaries (i–j) and a last term corresponding to the ternary, all of them obtained considering fourth-order interactions.

Thermodynamic and topological instability approaches for forecasting glass-forming ability in the ternary Al-Ni-Y system

A thermodynamic approach to predict bulk glass-forming compositions in binary metallic systems was recently proposed. In this approach. the parameter gamma* = Delta H-amor/(Delta H-inter - Delta H-amor) indicates the glass-forming ability (GFA) from the standpoint of the driving force to form different competing phases, and Delta H-amor and Delta H-inter are the enthalpies for-lass and intermetallic formation, respectively. Good glass-forming compositions should have a large negative enthalpy for glass formation and a very small difference for intermetallic formation, thus making the glassy phase easily reachable even under low cooling rates. The gamma* parameter showed a good correlation with GFA experimental data in the Ni-Nb binary system. In this work, a simple extension of the gamma* parameter is applied in the ternary Al-Ni-Y system. The calculated gamma* isocontours in the ternary diagram are compared with experimental results of glass formation in that system. Despite sonic misfitting, the best glass formers are found quite close to the highest gamma* values, leading to the conclusion that this thermodynamic approach can lie extended to ternary systems, serving as a useful tool for the development of new glass-forming compositions. Finally the thermodynamic approach is compared with the topological instability criteria used to predict the thermal behavior of glassy Al alloys. (C) 2007 Elsevier B. V. All rights reserved.

Synthesis and characterization of ternary hybrid material based on poly-o-methoxyaniline and poly(ethylene oxide) in mesostructured V(2)O(5)

New hybrid composites based on mesostructured V(2)O(5) containing intercalated poly(ethylene oxide), poly-o-methoxyaniline and poly(ethylene oxide)/poly-o-methoxyaniline were prepared. The results suggest that the polymers were intercalated into the layers of the mesostructured V(2)O(5). Electrochemical studies showed that the presence of both polymers in the mesostructured V(2)O(5) (ternary hybrid) leads to an increase in total charge and stability after several cycles compared with binary hybrid composites. This fact makes this material a potential component as cathode for lithium ion intercalation and further, a promising candidate for applications in batteries.

Development of Performance Properties of Ternary Mixtures: Field Demonstrations and Project Summary, TPF-5(117), 2012

Supplementary cementitious materials (SCM) have become common parts of modern concrete practice. The blending of two or three cementitious materials to optimize durability, strength, or economics provides owners, engineers, materials suppliers, and contractors with substantial advantages over mixtures containing only portland cement. However, these advances in concrete technology and engineering have not always been adequately captured in specifications for concrete. Users need specific guidance to assist them in defining the performance requirements for a concrete application and the selection of optimal proportions of the cementitious materials needed to produce the required durable concrete. The fact that blended cements are currently available in many regions increases options for mixtures and thus can complicate the selection process. Both Portland and blended cements have already been optimized by the manufacturer to provide specific properties (such as setting time, shrinkage, and strength gain). The addition of SCMs (as binary, ternary, or even more complex mixtures) can alter these properties, and therefore has the potential to impact the overall performance and applications of concrete. This report is the final of a series of publications describing a project aimed at addressing effective use of ternary systems. The work was conducted in several stages and individual reports have been published at the end of each stage.

Acid base characteristics of binary oxides of Zr with Ce and La

The surface acidity and basicity of binary oxides of Zr with Ce and La are determined using a series of Hammet indicators and Ho,,max values are reported. The generation of new acid sites habe been ascribed to the charge imbalance of M1-O-M2 bonds, where M1 and M2 are metal atoms. Both Bronsted and Lewis acid sites contribute to the acidity of the oxides

Solubility and release modulation effect of sulfamerazine ternary complexes with cyclodextrins and meglumine

This study investigated the effect on solubility and release of ternary complexes of sulfamerazine (SMR) with beta-(beta CD), methyl-(M beta CD) and hydroxypropyl-P-cyclodextrin (HP beta CD) using meglumine (MEG) as the ternary component. The combination of MEG with M beta CD resulted the best approach, with an increased effect (29-fold) of the aqueous solubility of SMR. The mode of inclusion was supported by 2D NMR, which indicated that real ternary complexes were formed between SMR, MEG and M beta CD or HP beta CD. Solid state analysis was performed using Fourier-transform infrared spectroscopy (FT IR), differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD), which demonstrated that different interactions occurred among SMR, MEG and M beta CD or HP beta CD in the ternary lyophilized systems. The ternary complexes with beta CD and M beta CD produced an additional retention effect on the release of SMR compared to the corresponding binary complexes, implying that they were clearly superior in terms of solubility and release modulation. (C) 2014 Elsevier B.V. All rights reserved.

Mixing properties of ester-containing solutions: a study on the ternary (methyl alkanoate (pentanoate and methanoate)+methanol and the corresponding binaries. New contributions to the (ester+ester) interactions

[EN]This work studies the volumetric (VE m) and energetic (HE m) properties resulting from the mixing processes of binary systems and the corresponding ternary of two methyl esters (methanoate and pentanoate) with methanol. The three binaries produce net endothermic mixing effects, with important energetic interactions, with maximum values of HE m ffi 400 J mol 1 , for the (ester + ester) system. This produces expansive effects VE m > 0, but the binaries of the (methyl esters + methanol) give rise to contractions VE m < 0, due to the formation of molecular aggregates.

Constitution and Specific Gravity of the Ternary Mattes Cu2S-FeS-PbS.

The constitution of the ternary mattes CU2S-FeS-PbS has never been completely investigated. Fulton and Goodner 1) have investigated the binary mattes CU2S-FeS, CU2S-PbS, PbSFeS and have shown that the three binaries show eutectics. There has been no attempt however to draw the complete ternary diagram. The following work is intended to be a contribution toward the completion of this diagram by first of all pointing out those mattes which separate on melting into two layers, and second by determining the specific gravities of mattes of different compositions.

Correlation of the liquid–liquid equilibrium data for specific ternary systems with one or two partially miscible binary subsystems

This paper presents the results of a liquid–liquid equilibrium data correlation for 11 ternary systems which have not been previously fitted using the NRTL model or, when they have, the results presented in the literature are inconsistent with the experimental behavior of the system. These ternary systems include mixtures with one or two partially miscible pairs. During the correlation process, new restrictions were imposed on the values for the NRTL binary parameters to ensure correct prediction of the total or partial miscibility for the binary pairs involved. In addition, topological concepts related to the Gibbs stability test have been applied in order to validate the results in the whole range of compositions.