Asymptotic Behavior of Ext functors for modules of finite complete intersection dimension

Let $R$ be a local ring, and let $M$ and $N$ be finitely generated $R$-modules such that $M$ has finite complete intersection dimension. In this paper we define and study, under certain conditions, a pairing using the modules \Ext_R^i(M,N) which generalizes Buchweitz's notion of the Herbrand diference. We exploit this pairing to examine the number of consecutive vanishing of \Ext_R^i(M,N) needed to ensure that \Ext_R^i(M,N)=0 for all $i\gg 0$. Our results recover and improve on most of the known bounds in the literature, especially when $R$ has dimension at most two

Dimers on the Triangular Kagome Lattice

We derive exact results for close-packed dimers on the triangular kagome lattice (TKL), formed by inserting triangles into the triangles of the kagome lattice. Because the TKL is a non-bipartite lattice, dimer-dimer correlations are short-ranged, so that the ground state at the Rokhsar-Kivelson (RK) point of the corresponding quantum dimer model on the same lattice is a short-ranged spin liquid. Using the Pfaffian method, we derive an exact form for the free energy, and we find that the entropy is 1/3 ln2 per site, regardless of the weights of the bonds. The occupation probability of every bond is 1/4 in the case of equal weights on every bond. Similar to the case of lattices formed by corner-sharing triangles (such as the kagome and squagome lattices), we find that the dimer-dimer correlation function is identically zero beyond a certain (short) distance. We find in addition that monomers are deconfined on the TKL, indicating that there is a short-ranged spin liquid phase at the RK point. We also find exact results for the ground state energy of the classical Heisenberg model. The ground state can be ferromagnetic, ferrimagnetic, locally coplanar, or locally canted, depending on the couplings. From the dimer model and the classical spin model, we derive upper bounds on the ground state energy of the quantum Heisenberg model on the TKL.Comment: 9 pages, 7 figures, http://www.physics.purdue.edu/~dyao

Thermoelectric properties of Higher Manganese Silicides

This work aims to cover a variety of aspects relating to the Higher Manganese Silicide (HMS) system, e.g. composites, substitutions, synthesis methods, and structural evolutions. The composites made of HMS-based compounds and nano-inclusions have been prepared via two different procedures, i.e. (i) solid state reaction, manually mixing, and hot pressing, or (ii) soft ball milling and reactive spark plasma sintering. The later approach has proved its effectiveness in preparing the multi-walled carbon nanotube (MWCNT)/HMS-based material composites mainly containing the HMS phases with a homogeneous distribution of MWCNTs. It was demonstrated that a fine distribution of the nano-inclusions played a crucial role in reducing thermal conductivity through enhancing phonon scattering in HMS-based materials, resulting in an improvement by about 20% for the maximum efficiency for the MWCNT/HMS-based material composite with 1.0 wt.-% MWCNTs. The substitution of molybdenum, tungsten, or silver at the Mn sites, and of germanium or aluminium at the Si sites has been studied for the HMS-based materials. The best thermoelectric efficiency among different Ge contents was achieved for the phase mixture of the non-stoichiometric composition MnSi1.75Ge0.02, which was then chosen to be the base material for further substitutions. No crucial modification of the electrical properties of the base material was observed, but large decreases of lattice thermal conductivity were achieved because of enhanced phonon scattering, with the highest reduction up to 25% for molybdenum substitution. The maximum figure of merit, ZT, value was approximately 0.40 for the material with 2 at.-% molybdenum substitution at the Mn sites. The maximum ZT values ranging from 0.31 to 0.42 have been achieved for various compositions prepared by mechanical alloying, mechanical milling and heat treating in conventional furnace, as well as by solid state reaction, which could possibly be improved by completely eliminating the side products. Subsequently, a simple and effective process was used to synthesize undoped HMS, involving ball milling in n-hexane under soft conditions to obtain homogeneous mixtures of constituting elements, and subsequent spark plasma sintering for a direct solid state reaction. The obtained fine particles after the milling process in n-hexane helped to improve the reaction rate later on, resulting in pure HMS materials. As a consequence, the maximum thermoelectric figure of merit obtained was 0.55 at 850 K, a high value for undoped HMS. Moreover, single crystals of HMS have been prepared using chemical vapor transport with very low yield, but their poor qualities resulted in low resolution in single crystal XRD. HMS-based materials including the ones with different Si/Mn atomic ratios and various dopants, e.g. Ge, Al, Cr, and Mo, have been prepared for the investigation of structural evolution upon heating up from room temperature to high temperature. The average structural formula at room temperature and its temperature dependence were strongly impacted by the phase compositions of the starting materials as well as the nature of dopants. Physical property measurements on the MnSi1.75 compound revealed that a correlation between the thermoelectric properties and the average structural formula of bulk HMS-based materials could be expected

Electrochemical synthesis of mesoporous gold films toward mesospace-stimulated optical properties

Mesoporous gold (Au) films with tunable pores are expected to provide fascinating optical properties stimulated by the mesospaces, but they have not been realized yet because of the difficulty of controlling the Au crystal growth. Here, we report a reliable soft-templating method to fabricate mesoporous Au films using stable micelles of diblock copolymers, with electrochemical deposition advantageous for precise control of Au crystal growth. Strong field enhancement takes place around the center of the uniform mesopores as well as on the walls between the pores, leading to the enhanced light scattering as well as surface-enhanced Raman scattering (SERS), which is understandable, for example, from Babinet principles applied for the reverse system of nanoparticle ensembles. © 2015 Macmillan Publishers Limited. All rights reserved

Les effets du développement sur les politiques d’adoption des enfants : les cas de la Corée du Sud et du Vietnam

Le séisme dévastateur et meurtrier subi par Haïti en janvier 2010 a porté une nouvelle fois et brutalement sur le devant de la scène médiatique mondialisée la question de l’adoption d’enfants victimes du sous-développement : Est-ce une bonne réponse aux malheurs d’un pays pauvre ? Peut-elle régler les problèmes posés par l’enfance dans les pays du Tiers-monde ? Ne doit-on pas encadrer davantage l’adoption Internationale [André-Trevennec, 2008] Et chacun de prendre position pour ou contre l’adoption internationale, d’ériger en règle générale ou en loi commune tel ou tel cas de son entourage. Le regard de l’historien, s’appuyant sur des sources identifiées et une démarche construite permet de prendre du recul, de mettre en perspective les événements présents et passés [Denéchère, 2011]

Quasinormal modes for asymptotic safe black holes

Under the hypothesis of asymptotic safety of gravity, the static, spherically symmetric black hole solutions in the infrared limit are corrected by non-perturbative effects. Specifically, the metric is modified by the running of gravitational couplings. In this work, we investigate the effects of this correction to the quasinormal modes (QNMs) of a test scalar field propagating in this kind of black hole background analytically and numerically. It is found that although the quasi-period frequencies and the damping of oscillations are respectively enhanced and weakened by the quantum correction term, the stability of the black hole remains.Comment: 11 pages, 1 figures, accepted for publication in CQG. arXiv admin note: text overlap with arXiv:1007.131

Synthesis and characterization of hybrid organic-inorganic materials based on sulphonated polyamideimide and silica

The preparation of hybrid organic–inorganic membrane materials based on a sulphonated polyamideimide resin and silica filler has been studied. The method allows the sol–gel process to proceed in the presence of a high molecular weight polyamideimide, resulting in well dispersed silica nanoparticles (<50 nm) within the polymer matrix with chemical bonding between the organic and inorganic phases. Tetraethoxysilane (TEOS) was used as the silica precursor and the organosilicate networks were bonded to the polymer matrix via a coupling agent aminopropyltriethoxysilane (APTrEOS). The structure and properties of these hybrid materials were characterized via a range of techniques including FTIR, TGA, DSC, SEM and contact angle analysis. It was found that the compatibility between organic and inorganic phases has been greatly enhanced by the incorporation of APTrEOS. The thermal stability and hydrophilic properties of hybrid materials have also been significantly improved

Edge states and topological orders in the spin liquid phases of star lattice

A group of novel materials can be mapped to the star lattice, which exhibits some novel physical properties. We give the bulk-edge correspondence theory of the star lattice and study the edge states and their topological orders in different spin liquid phases. The bulk and edge-state energy structures and Chern number depend on the spin liquid phases and hopping parameters because the local spontaneous magnetic flux in the spin liquid phase breaks the time reversal and space inversion symmetries. We give the characteristics of bulk and edge energy structures and their corresponding Chern numbers in the uniform, nematic and chiral spin liquids. In particular, we obtain analytically the phase diagram of the topological orders for the chiral spin liquid states SL[\phi,\phi,-2\phi], where \phi is the magnetic flux in two triangles and a dodecagon in the unit cell. Moreover, we find the topological invariance for the spin liquid phases, SL[\phi_{1},\phi_{2},-(\phi_{1}+\phi_{2})] and SL[\phi_{2},\phi_{1},-(\phi_{1}+\phi_{2})]. The results reveal the relationship between the energy-band and edge-state structures and their topological orders of the star lattice.Comment: 7 pages, 8 figures, 1 tabl

XXZ and Ising Spins on the Triangular Kagome Lattice

The recently fabricated two-dimensional magnetic materials Cu9X2(cpa)6.xH2O (cpa=2-carboxypentonic acid; X=F,Cl,Br) have copper sites which form a triangular kagome lattice (TKL), formed by introducing small triangles (``a-trimers'') inside of each kagome triangle (``b-trimer''). We show that in the limit where spins residing on b-trimers have Ising character, quantum fluctuations of XXZ spins residing on the a-trimers can be exactly accounted for in the absence of applied field. This is accomplished through a mapping to the kagome Ising model, for which exact analytic solutions exist. We derive the complete finite temperature phase diagram for this XXZ-Ising model, including the residual zero temperature entropies of the seven ground state phases. Whereas the disordered (spin liquid) ground state of the pure Ising TKL model has macroscopic residual entropy ln72=4.2767... per unit cell, the introduction of transverse(quantum) couplings between neighboring $a$-spins reduces this entropy to 2.5258... per unit cell. In the presence of applied magnetic field, we map the TKL XXZ-Ising model to the kagome Ising model with three-spin interactions, and derive the ground state phase diagram. A small (or even infinitesimal) field leads to a new phase that corresponds to a non-intersecting loop gas on the kagome lattice, with entropy 1.4053... per unit cell and a mean magnetization for the b-spins of 0.12(1) per site. In addition, we find that for moderate applied field, there is a critical spin liquid phase which maps to close-packed dimers on the honeycomb lattice, which survives even when the a-spins are in the Heisenberg limit.Comment: 12 pages, 12 figure

Effects of air pollution on the nervous system and its possible role in neurodevelopmental and neurodegenerative disorders

Recent extensive evidence indicates that air pollution, in addition to causing respiratory and cardiovascular diseases, may also negatively affect the brain and contribute to central nervous system diseases. Air pollution is comprised of ambient particulate matter (PM) of different sizes, gases, organic compounds, and metals. An important contributor to PM is represented by traffic-related air pollution, mostly ascribed to diesel exhaust (DE). Epidemiological and animal studies have shown that exposure to air pollution may be associated with multiple adverse effects on the central nervous system. In addition to a variety of behavioral abnormalities, the most prominent effects caused by air pollution are oxidative stress and neuro-inflammation, which are seen in both humans and animals, and are supported by in vitro studies. Among factors which can affect neurotoxic outcomes, age is considered most relevant. Human and animal studies suggest that air pollution may cause developmental neurotoxicity, and may contribute to the etiology of neurodevelopmental disorders, including autism spectrum disorder. In addition, air pollution exposure has been associated with increased expression of markers of neurodegenerative disease pathologies, such as alpha-synuclein or beta-amyloid, and may thus contribute to the etiopathogenesis of neurodegenerative diseases, particularly Alzheimer's disease and Parkinson's disease