Mesoporous matrices for quantum computation with improved response through redundance

We present a solid state implementation of quantum computation, which improves previously proposed optically driven schemes. Our proposal is based on vertical arrays of quantum dots embedded in a mesoporous material which can be fabricated with present technology. The redundant encoding typical of the chosen hardware protects the computation against gate errors and the effects of measurement induced noise. The system parameters required for quantum computation applications are calculated for II-VI and III-V materials and found to be within the experimental range. The proposed hardware may help minimize errors due to polydispersity of dot sizes, which is at present one of the main problems in relation to quantum dot-based quantum computation. (c) 2007 American Institute of Physics

Applying an accurate spherical model to gamma-ray burst afterglow observations

We present results of model fits to afterglow data sets of GRB970508, GRB980703 and GRB070125, characterized by long and broadband coverage. The model assumes synchrotron radiation (including self-absorption) from a spherical adiabatic blast wave and consists of analytic flux prescriptions based on numerical results. For the first time it combines the accuracy of hydrodynamic simulations through different stages of the outflow dynamics with the flexibility of simple heuristic formulas. The prescriptions are especially geared towards accurate description of the dynamical transition of the outflow from relativistic to Newtonian velocities in an arbitrary power-law density environment. We show that the spherical model can accurately describe the data only in the case of GRB970508, for which we find a circumburst medium density consistent with a stellar wind. We investigate in detail the implied spectra and physical parameters of that burst. For the microphysics we show evidence for equipartition between the fraction of energy density carried by relativistic electrons and magnetic field. We also find that for the blast wave to be adiabatic, the fraction of electrons accelerated at the shock has to be smaller than 1. We present best-fit parameters for the afterglows of all three bursts, including uncertainties in the parameters of GRB970508, and compare the inferred values to those obtained by different authors

Preparation of Carbon Aerogels from Polymer-Cross-Linked Xerogel Powders Without Supercritical Fluid Drying and their Application in Highly Selective CO2Adsorption

Carbon aerogels are well-known materials for their high porosity and high surface areas. They are typically made from pyrolysis of carbonizable polymeric aerogels. Here, we report an alternative route to monolithic carbon aerogels starting from xerogel powders. Use of powders speeds up solvent exchanges along sol-gel processing, and xerogelling bypasses the supercritical fluid drying step that is needed for making polymeric aerogels. Overall, this alternative route results in time, energy, and materials efficiency in the fabrication of carbon aerogels. Specifically, polymer-cross-linked silica xerogel powders were prepared via free-radical surface-initiated polymerization of acrylonitrile (AN) on a suspension of silica particles derived from tetramethylorthosilicate (TMOS) surface modified with 3-aminopropyltriethoxysilane (APTES)-derived initiator. Alternatively, cross-linked silica xerogel powders were prepared with a carbonizable polyurea (PUA) derived from the reaction of an aromatic triisocyanate (tris(4-isocyanatophenyl)methane) with -OH, -NH2, and adsorbed water on the surface of a TMOS/APTES-derived silica suspension. Wet-gel powders by either method were dried under vacuum at 50 °C to xerogel powders, which were compressed into discs. In turn, these discs were carbonized and then they were treated with HF to remove silica and with CO2 to create microporosity. The resulting monolithic carbon aerogels had porosities up to 83% v/v, Brunauer-Emmett-Teller (BET) surface areas up to 1934 m2 g-1, and could uptake up to 9.15 mmol g-1 of CO2 at 273 K, with high selectivity over H2, N2, and CH4

The impact of labor unionization on CSR reporting

Purpose Corporate social responsibility (CSR) reporting has been theorized as a key communication device and an integral part of a broader stakeholder integration management strategy. This paper aims to examine the relationship between CSR disclosures and organized labor, an important internal stakeholder, whose institutional role in dynamically advancing employee interests creates opportunities and challenges for strategic management and firm sustainability. Design/methodology/approach By using a sample of 2,526 US firm-year observations for the period 2002–2015, the authors demonstrate that managers in unionized contexts are more likely to issue CSR reports than managers in firms, where labor is not organized. Findings The authors demonstrate that managers in unionized contexts are more likely to issue CSR reports than managers in firms where labor is not organized. Considering stakeholder theory, they argue that, in unionized contexts, managers more intensively resort to CSR disclosures to form an alignment of interests, develop collaborative bonds with unions and smoothen relationships with external financial stakeholders. This effect is more prominent in areas where corporate spatial clustering and the prevailing political ideology facilitate the role of unions. Research limitations/implications First, the data refer to USA, which may limit the generalization of the results. Hence, researchers could use cross-country datasets to overcome this limitation. Second, it would be important to know what benefits are enjoyed by the unionized companies that issue CSR reports. Third, they acknowledge that there is useful qualitative information they do not analyze. This analysis could potentially relate specific CSR information to unions’ needs and demands. Further, there are alternative channels through which companies disclose relevant information such as 10-K filings, annual reports, firm websites, media, public announcements, etc. These are not captured by the data. Practical implications Managers could benefit from the empirical analysis, which suggests that through the initiation of CSR reports a dialogue with unions is greatly facilitated. Managers should consider that CSR reports reduce information asymmetries and may attract the interest of investors. Unionists should be aware that CSR reports constitute an opportunity to identify mutual interests and align goals. Business analysts, investors and shareholders should be aware that standalone CSR reports are used by managers to reduce information asymmetries and disparities with unions and to communicate an investment-friendly context. So, market participants should factor such policies by unionized firms into their investment analyses. Social implications The authors offer implications for managers, labor unionists and market participants. Originality/value This paper examines the relationship between CSR disclosures and organized labor, an important internal stakeholder, whose institutional role in dynamically advancing employee interests creates opportunities and challenges for strategic management and firm sustainability

The impact of religiosity and corruption on CSR reporting: The case of U.S. banks

In this paper, we provide insights into CSR disclosure strategies by bringing to the fore the important role played by contextual factors. We examine the impact of religiosity upon the instigation of voluntary CSR disclosures and the way that corruption, a trans-systemic contextual feature, moderates this relationship. We draw upon social norm and institutional theories to illuminate the mechanisms through which contextual elements give rise to management disclosure strategies. Our investigation focuses on the U.S. context, where religiosity is of increasing importance and concentrates on the U.S. banking industry, whose impacts and ramifications are global. We demonstrate that the probability of a bank issuing a standalone CSR report is positively associated with the level of adherence to religious norms, a relationship which weakens in regions characterized by high levels of corruption. The implications of our findings are important for analysts and other market participants

Polybenzodiazine Aerogels: All-Nitrogen Analogues of Polybenzoxazines Synthesis, Characterization, and High-Yield Conversion to Nanoporous Carbons

Tetrahydroquinazoline (THQ) was designed as an all-nitrogen analogue of main-stream benzoxazine monomers. THQ solutions in DMF gelled at 100 °C via HCl-catalyzed ring-opening polymerization to polybenzodiazine (PBDAZ) wet gels, which were dried in an autoclave with supercritical fluid CO2 to aerogels. These as-prepared PBDAZ-100 aerogels undergo ring-fusion aromatization at 240 °C under O2. This oxidized form is referred to as PBDAZ-240. Chemical identification of PBDAZ-100 and PBDAZ-240 relied on consideration of all nine possible polymerization pathways, in combination with elemental analysis, infrared and solid-state 13C NMR spectroscopy, and 15N NMR spectroscopy of aerogels from the selectively 15N-enriched THQ monomer. Fully oxidized PBDAZ-240 aerogels were carbonized at 800 °C under Ar to carbon aerogels with 61% w/w yield and with retention of the nanomorphology of the parent PBDAZ-100 aerogels. Direct pyrolysis of PBDAZ-100 at 800 °C, i.e., without prior oxidation, resulted in only 40% w/w yield and complete loss of the fine nanostructure. The evolution of PBDAZ-240 aerogels along pyrolysis toward carbonization was monitored using progressively higher pyrolysis temperatures from 300 to 800 °C under Ar. Aerogels received at 600 and 800 °C (referred to as PBDAZ-600 and PBDAZ-800, respectively) had relatively high surface areas (432 and 346 m2 g-1, respectively), a significant portion of which (79% in both materials) was assigned to micropores. The new polymer aerogels, together with polybenzoxazine aerogels, comprise a suitable basis set for comparing N-rich versus O-rich porous carbons as adsorbers

Using Catalysis To Control The Morphology And Stiffness Of Shape Memory Poly(isocyanurate-urethane) (PIR-PUR) Aerogels

A large array of anhydrous metal ions were tested as catalysts in the preparation of shape memory poly(isocyanurate-urethane) (PIR-PUR) aerogels from the reaction of 1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur N3300A: a well-known isocyanurate-based aliphatic triisocyanate) and triethylene glycol (TEG) in anhydrous acetonitrile. The reaction yielded wet gels that were dried into aerogels in an autoclave with supercritical fluid CO2. The catalytic activity was mostly identified among CH3CN-soluble salts (mainly chlorides) of third-row d-block elements from iron to zinc, group 13 elements from aluminum to thallium, as well as cadmium, bismuth, and tin. Tin (119Sn) NMR indicated that the metal ion complexes with TEG, followed by reaction with the isocyanate. By using a fixed monomer concentration (20% w/w) and varying only the chemical identity and concentration of the catalysts, it was possible to demonstrate that the micromorphology of the resulting aerogels depended only on the gelation time. That is, for equal gelation times, the morphology was approximately the same, irrespective of the catalyst. For short gelation times (around 5 min or less), the aerogel frameworks were bicontinuous, changing to small spheroids at around 20 min and to large microspheres for gelation times around 75 min or more. Having obtained control over micromorphology, leaving other material properties such as density and porosity practically unaffected, it was possible to demonstrate that the bicontinuous structures of PIR-PUR aerogels can be up to 4 times stiffer and up to 2 times better thermal conductors than structures consisting of microspheres. This finding was attributed to the different widths of the neck zones between particles, noting that in bicontinuous morphologies, the neck diameters were almost equal to the particle diameters

Effect of Processing Conditions on Chemical Makeup of Di-isocyanate Crosslinked Silica Aerogels

Sol-gel derived silica aerogels are attractive candidates for many unique thermal, optical, catalytic, and chemical applications1 because of their low density and high mesoporosity. However, their inherent fragility has restricted their use to, for example, insulation in extreme temperature environments such as Mars. We have previously reported crosslinking the mesoporous silica structure of an aerogel with di-isocyanates reacted with silanols on the surface,2,3 or epoxies reacting with an amine decorated silica surface.4 Either approach has been shown to significantly increase the strength of the aerogel with only a small effect on density or porosity. Thus, these hybrid materials may be enabling for future space exploration missions as well as advanced aeropropulsion systems which demand lighter weight, robust, dual purpose materials for insulation, radiation protection and/or structural elements of habitats, rovers, astronaut suits and cryotanks. Utilizing amine-decorated silica particles to react with di-isocyanate oligomers analogous to the epoxies will produce polyurea crosslinks, in addition to carbamates produced from reaction with silanols on the surface as shown in Scheme 1. Since it is suggested in the literature that polyureas are mechanically more robust in general than are polyurethanes5, this approach might result in yet stronger materials. Herein, we have examined the effects of four processing parameters for producing this type of polymer crosslinked aerogel on properties of the resulting monoliths. Concentration of total silane (total APTES plus TMOS in a 1 to 3 v/v ratio) from 7 to 30% by volume in acetonitrile (CH3CN) and the amount of water (7 to 25% by volume) used to catalyze gellation should determine the density of the underlying silica. The number of washes (from 0 to 4) to remove water and by-products of gellation, and concentration of diisocyanate crosslinker (7 to 34% by weight in CH3CN) used for soaking the silica gels should determine the amount/length of polymer forming the crosslinks. A statistical experimental design methodology was employed to reduce the number of experiments and to allow computation of empirical models describing the relationship between the variables and the measured responses. In all, 30 different runs using different combinations of the four variables plus 5 repeats were utilized to produce a total of 35 separate crosslinked aerogels. These were evaluated by NMR, microscopy, surface analysis, mechanical testing and skeletal and bulk density. Herein, we will focus on the results of CP-MAS NMR, giving insight to the amount of polymer crosslink present in the monoliths and relate this to microstructure

Surface modified aerogel monoliths

This invention comprises reinforced aerogel monoliths such as silica aerogels having a polymer coating on its outer geometric surface boundary, and to the method of preparing said aerogel monoliths. The polymer coatings on the aerogel monoliths are derived from polymer precursors selected from the group consisting of isocyanates as a precursor, precursors of epoxies, and precursors of polyimides. The coated aerogel monoliths can be modified further by encapsulating the aerogel with the polymer precursor reinforced with fibers such as carbon or glass fibers to obtain mechanically reinforced composite encapsulated aerogel monoliths