Quantum effects in spin dynamics of one dimensional systems

We present a review of recent results concerning dynamical spin correlation functions of quantum spin chains with nearest neighbor exchange interactions. Zero and finite temperature results, as well as the influence of a magnetic field are discussed for s = 1/2, with special emphasis on quantum effects which can be observed experimentally. We also investigate the dependence on spin quantum number between extreme quantum (s = 1/2) and classical (s = ∞) systems

Heat treatment as a route to tailor the yield-damping properties in A356 alloys

A356 is a common industrial alloy due to its relatively good mechanical properties, reduced weight and capability be casted into complex structures. However, in order to display good static mechanical properties (e.g.elevated yield strength) it must be heat treated (usually T6), therefore, compromising its dynamic properties (e.g. damping ratio). This study analyses the role of such heat treatments in the overall microstructure of A356 poured in ceramic block, associating the morphology transformations with the internal mechanisms that enhance yield strength and reduce damping. It is suggested that these variables display an inverse proportionality and a linear model is determined for the design of alloys with tailored yield/damping by the use of different artificial ageing times.Supported by the project iRAIL Innovation in Railway Systems and Technologies Doctoral Programme funds and by national funds through FCT - Portuguese Foundation for Science and Technology and was developed on the aim of the Doctoral grant PD/ BD/114096/2015

Casting A356+SiCp with ultrasonically treated melts: effect reinforcement and processing in the microstructure

Low mass fractions (0.05 wt%) of SiC micro sized particles have been added to an A356 melt and dispersed by ultrasonic vibration to study their impact on the microstructural morphology of cast samples. It is shown that the ultrasonic melt treatment at 680°C can promote a homogenizeddistribution of the reinforcement while also degassing the melt and induces a moderate grain refinement. Even though SiC may act as a nucleant, its use did not induce a significant grain refinement relatively to ultrasonically treated unreinforced melts. Adding SiC microparticles, however, seems to enhance Eutectic Si modification, although it contributes to its slight coarsening at the expense of Mg2Si.publishe

Anisotropic Quantum Spin Chains

We have studied two models for anisotropic quantum spin chains. (i) XY‐chain with a field in the plane: The magnetization of the ferromagnet behaves as h1/3 for small fields, in agreement with scaling laws. The antiferromagnet shows a critical field at which the ground state is a simple Néel state and which separates power law from exponential decay of spatial correlations. (ii) Anisotropic XY‐chain: The dynamic z‐component spin correlation function can be decomposed into a spin wave and a soliton contribution. The nature of quantum soliton excitations is studied and their form compared to soliton solutions of classical equations of motion

Ceramic sonotrodes for light alloy melt treatment

Alloy melt treatment by ultrasonic vibration is a physical processing technique that has been gathering the support of the scientific community. The use of metallic sonotrodes for this purpose has been proven very efficient; however, it promotes melt inclusion by sonotrode erosion. Such an issue is being addressed by the use of ceramic sonotrodes in low-amplitude resonance. Given that these novel sonotrodes generally have complex shapes and low displacements, this study shows an innovative approach for their characterization. Based on scanning laser Doppler vibrometry, the signal processing Python-based script was used to map the overall resonant behavior of a tubular SiAlON sonotrode, and this route is able to characterize the complex shapes in low-amplitude and high-frequency radial resonance in resonant ceramic sonotrodes. Velocity time-domain profiles are shown to be dependent on the position, and even though the radial natural frequencies of ceramic sonotrodes have low amplitudes, they are proposed as an efficient tool for melt treatment. While characterizing the radial natural mode in ceramic sonotrodes, this study proves that their low-amplitude Lamb waves are responsible for the refinement of a-grains and secondary phases in light alloys.This work was supported by PTDC/EMEEME/30967/ 2017 and NORTE-0145-FEDER-030967, co-financed by the European Regional Development Fund (ERDF), through the Operational Programme for Competitive ness and Internationalization (COMPETE 2020), under Portugal 2020, and by the Fundação para a Cência e a Tecnologia – FCT I.P. national funds. Also, this work was supported by Portuguese FCT, under the reference project UIDB/04436/2020, and Stimulus of Scientific Employment Application CEECIND/03991/2017

Impact of the ultrasonic-assisted casting of an AlSi7Mg alloy on T6 heat treatment

In this work, the effect of ultrasonic vibration during solidification on the aging kinetics of an AlSi7Mg alloy is investigated. With the ultrasonic equipment coupled to the mold walls, melt treatment was performed by two approaches: (i) fully above liquidus (>635 ◦C); and (ii) in the full range between liquidus and solidus (630 ◦C→ 550 ◦C). Cast samples were then subjected to T6 heat treatment for different aging times. It is shown that indirect ultrasound treatment increases the cooling rate while active. The eutectic Si was refined and further modified when ultrasound treatment was performed in the semisolid state. Due to the significant release of solute during the decomposition of π-Al8FeMg3Si6 into fine β-Al5FeSi, this has a significant impact in the solution stage. Ultrasound treatment fully above liquidus decreased the underaging time to 50% and peak aging time to 25% without compromising strength. The results suggest aging kinetics are correlated with a higher vacancy density and solute enrichment which favors Guinier–Preston (GP) zone formation. These findings show a promising route to tailor the aging kinetics in these alloys by selectively modifying phases and cooling ratesThis work was supported by PTDC/EMEEME/30967/2017 and NORTE-0145-FEDER 030967, co-financed by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020), under Portugal 2020, and by the Fundação para a Ciência e a Tecnologia–FCT IPP national funds. Moreover, this work was supported by Portuguese FCT under the project UIDB/04436/2020 and the doctoral grants PD/BD/140094/2018 and 2020.08564.BD

The influence of precipitation hardening on the damping capacity in Al–Si–Mg cast components at different strain amplitudes

An A356 alloy is a classic casting light alloy, which is able to be processed into complex geometrical shapes with tailored static and dynamic mechanical properties. As a promising material to reduce fuel and energy consumption in future vehicle designs, there is an interest in understanding the impact of heat treatments on the damping capacity of this alloy. The Granato–Lücke theory is used to detail the forced vibration response in gravity cast A356. It is shown that a solution treatment enhances damping capacity in lower stress states (i.e., strain-independent regime) due to the increase in weak pinning length. However, in high-stress states (i.e., strain-dependent regime), peak-aged (T6) samples display higher damping capacity. This is proposed to be originated by releasing dislocations from weak pinning points, which start bowing in the precipitates that act as strong pinning points. Based on these results, it is shown for the first time that the selection of heat treatments to optimize damping in forced vibration is highly dependent on the expected stress–strain state and must be considered in the design of cast components.This research was funded by PTDC/EMEEME/30967/2017 and NORTE-0145-FEDER-030967, co-financed by the European Regional Development Fund (ERDF) through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020), under Portugal 2020, and by the Fundação para a Ciência e a Tecnologia—FCT I.P. national funds. Additionally, this work was supported by the Portuguese FCT, under the reference project UIDB/04436/2020. This work also acknowledges the financial support of the Portuguese Science Foundation for Science and Technology (FCT) under the projects UIDB/EMS/00481/2020 (TEMA) and CENTRO-01-0145-FEDER-022083 (Centro2020, PORTUGAL 2020, European Regional Development Fund). This work was financially supported by project PRIDOP (POCI-01-0247-FEDER-040271), co-financed by the European Community Fund FEDER through POCI—Programa Operacional Competitividade e Internacionalização

Mobile communications of the needy and poor: Affordability indicators, European data, social tariffs

This section summarizes the data and information collected across Europe and beyond, inside the COST 605 Action (2008-2011), and can be relevant for separate analysis, research and regulations about the mobile communications costs of poor and needy groups. Miscellaneous social and macro-economic data on the needy and their mobile communications usage in five European countries are presented. It also contains the specification of a new indicator whereby the affordability of mobile communications for poor and needy can be established, and the corresponding results for 7 countries in 2006 and 2010. The indicator is the "poor's purchasing power parity (PPP) in wireless minutes per month", based on reported data collected on the distribution amongst poor and needy groups in Georgia and France. An Appendix gives some data sources for the countries where data were collected

Effect of grain and secondary phase morphologies in the mechanical and damping behavior of Al7075 alloys

The present study evaluates the role of the microstructure in the static and dynamic mechanical behavior of as-cast Al7075 alloy promoted by ultrasonic treatment (US) during solidification. The characterization of samples revealed that US treatment promoted grain and intermetallics refinement, changed the shape of the intermetallic phases (equilibrium phases of soluble M and/or T (Al, Cu, Mg, Zn) and their insoluble Al-Cu-Fe compounds) and lead to their uniform distribution along the grain boundaries. Consequently, the mechanical properties and damping capacity above critical strain values were enhanced by comparison with values obtained for castings produced without US vibration. This results suggest that the grain and secondary phases refinement by US can be a promising solution to process materials to obtain high damping and high strength characteristics.This research was supported by FEDER/COMPETE funds and by national funds through FCT - Portuguese Foundation for Science and Technology and was developed on the aim of the research Post-Doctoral grant SFRH/BPD/76680/2011. Also, this work has been supported by the FCT in the scope of the project: UID/EEA/04436/2013.info:eu-repo/semantics/publishedVersio

Identification of transitional disks in Chamaeleon with Herschel

Transitional disks are circumstellar disks with inner holes that in some cases are produced by planets and/or substellar companions in these systems. For this reason, these disks are extremely important for the study of planetary system formation. The Herschel Space Observatory provides an unique opportunity for studying the outer regions of protoplanetary disks. In this work we update previous knowledge on the transitional disks in the Chamaeleon I and II regions with data from the Herschel Gould Belt Survey. We propose a new method for transitional disk classification based on the WISE 12 micron-PACS 70 micron color, together with inspection of the Herschel images. We applied this method to the population of Class II sources in the Chamaeleon region and studied the spectral energy distributions of the transitional disks in the sample. We also built the median spectral energy distribution of Class II objects in these regions for comparison with transitional disks. The proposed method allows a clear separation of the known transitional disks from the Class II sources. We find 6 transitional disks, all previously known, and identify 5 objects previously thought to be transitional as possibly non-transitional. We find higher fluxes at the PACS wavelengths in the sample of transitional disks than those of Class II objects. We show the Herschel 70 micron band to be an efficient tool for transitional disk identification. The sensitivity and spatial resolution of Herschel reveals a significant contamination level among the previously identified transitional disk candidates for the two regions, which calls for a revision of previous samples of transitional disks in other regions. The systematic excess found at the PACS bands could be a result of the mechanism that produces the transitional phase, or an indication of different evolutionary paths for transitional disks and Class II sources.Comment: Accepted for publication in A&A: 11 March 2013 11 pages, 15 figure