5,933 research outputs found
Ion-water clusters, bulk medium effects, and ion hydration
Thermochemistry of gas-phase ion-water clusters together with estimates of
the hydration free energy of the clusters and the water ligands are used to
calculate the hydration free energy of the ion. Often the hydration
calculations use a continuum model of the solvent. The primitive quasichemical
approximation to the quasichemical theory provides a transparent framework to
anchor such efforts. Here we evaluate the approximations inherent in the
primitive quasichemical approach and elucidate the different roles of the bulk
medium. We find that the bulk medium can stabilize configurations of the
cluster that are usually not observed in the gas phase, while also
simultaneously lowering the excess chemical potential of the ion. This effect
is more pronounced for soft ions. Since the coordination number that minimizes
the excess chemical potential of the ion is identified as the optimal or most
probable coordination number, for such soft ions, the optimum cluster size and
the hydration thermodynamics obtained without account of the bulk medium on the
ion-water clustering reaction can be different from those observed in
simulations of the aqueous ion. The ideas presented in this work are expected
to be relevant to experimental studies that translate thermochemistry of
ion-water clusters to the thermodynamics of the hydrated ion and to evolving
theoretical approaches that combine high-level calculations on clusters with
coarse-grained models of the medium
Molecular packing and chemical association in liquid water simulated using ab initio hybrid Monte Carlo and different exchange-correlation functionals
In the free energy of hydration of a solute, the chemical contribution is
given by the free energy required to expel water molecules from the
coordination sphere and the packing contribution is given by the free energy
required to create the solute-free coordination sphere (the observation volume)
in bulk water. With the SPC/E water model as a reference, we examine the
chemical and packing contributions in the free energy of water simulated using
different electron density functionals. The density is fixed at a value
corresponding to that for SPC/E water at a pressure of 1 bar. The chemical
contribution shows that water simulated at 300 K with BLYP is somewhat more
tightly bound than water simulated at 300 K with the revPBE functional or at
350 K with the BLYP and BLYP-D functionals. The packing contribution for
various radii of the observation volume is studied. In the size range where the
distribution of water molecules in the observation volume is expected to be
Gaussian, the packing contribution is expected to scale with the volume of the
observation sphere. Water simulated at 300 K with the revPBE and at 350 K with
BLYP-D or BLYP conforms to this expectation, but the results suggest an earlier
onset of system size effects in the BLYP 350 K and revPBE 300 K systems than
that observed for either BLYP-D 350 K or SPC/E. The implication of this
observation for constant pressure simulations is indicated. For water simulated
at 300 K with BLYP, in the size range where Gaussian distribution of occupation
is expected, we instead find non-Gaussian behavior, and the packing
contribution scales with surface area of the observation volume, suggesting the
presence of heterogeneities in the system
Micromegas TPC studies at high magnetic fields using the charge dispersion signal
The International Linear Collider (ILC) Time Projection Chamber (TPC)
transverse space-point resolution goal is 100 microns for all tracks including
stiff 90 degree tracks with the full 2 meter drift. A Micro Pattern Gas
Detector (MPGD) readout TPC can achieve the target resolution with existing
techniques using 1 mm or narrower pads at the expense of increased detector
cost and complexity. The new MPGD readout technique of charge dispersion can
achieve good resolution without resorting to narrow pads. This has been
demonstrated previously for 2 mm x 6 mm pads with GEMs and Micromegas in cosmic
ray tests and in a KEK beam test in a 1 Tesla magnet. We have recently tested a
Micromegas-TPC using the charge dispersion readout concept in a high field
super-conducting magnet at DESY. The measured Micromegas gain was found to be
constant within 0.5% for magnetic fields up to 5 Tesla. With the strong
suppression of transverse diffusion at high magnetic fields, we measure a flat
50 micron resolution at 5 Tesla over the full 15 cm drift length of our
prototype TPC.Comment: 7 pages, 3 figure
Rate Determining Factors in Protein Model Structures
Previous research has shown a strong correlation of protein folding rates to
the native state geometry, yet a complete explanation for this dependence is
still lacking. Here we study the rate-geometry relationship with a simple
statistical physics model, and focus on two classes of model geometries,
representing ideal parallel and antiparallel structures. We find that the
logarithm of the rate shows an almost perfect linear correlation with the
"absolute contact order", but the slope depends on the particular class
considered. We discuss these findings in the light of experimental results.Comment: 4 pages, 2 figure
Power in the Multinational Corporation in Industry Equilibrium
Recent theories of the multinational corporation introduce the property rights model of the firm and examine whether to integrate our outsource firm activities locally or to a foreign country. This paper focus instead on the internal organization of the multinational corporation by examining the power allocation between headquarters and subsidiaries. We provide a framework to analyse the interaction between the decision to serve the local market by exporting or FDI, market acces and the optimal mode of organization of the multinational corporation. We find that subsidiary managers are given most autonomy in their decision how to run the firm at intermediate levels of local competition. We then provide comparative statics for changes in fixed FDI entry costs and trade costs, information technology, the number of local competitors, and in the size of the local market
Accurate estimations of circumstellar and interstellar lines of quadruply ionized vanadium using the coupled cluster approach
Accurate {\it ab initio} calculations have been carried out to study the
valence electron removal energies and oscillator strengths of astrophysically
important electromagnetic transitions of quadruply ionized vanadium, .
Many important electron correlations are considered to all-orders using the
relativistic coupled-cluster theory. Calculated ionization potentials and fine
structure splittings are compared with the experimental values, wherever
available. To our knowledge, oscillator strengths of electric dipole
transitions are predicted for the first time for most of the transitions. The
transitions span in the range of ultraviolet, visible and near infrared regions
and are important for astrophysical observations.Comment: Submitted in Astrophysical
Phycoremediation of Dairy Wastewater by Microalgae for elimination of organic pollution load
The present study aims to demonstrate the potential of microalgae Chlorococcum humicola for treatment of dairy industry effluent and reduction of its pollution load with the cultivation of microalgae in the same effluent. Dairy industry wastewater supplies the required nutrients for the growth of C. humicola and its growth was comparatively higher in 50 % dairy industry effluent as compare to Bold basal growth medium. Optimization of growth parameters of algae showed that growth of C. humicola was favoured by alkaline pH and optimum growth was observed at pH 8, whereas acidic pH does not favour the growth of selected algae. The exponential growth phase of C. humicola was achieved between 3-7 days, at 20˚C temperature, a further increase in temperature decreases the algal growth. The results for the effect of different concentration of dairy wastewater (0, 10, 25, 50, 75 and 100 %) on biochemical content (protein, chlorophyll a, carbohydrate) of C. humicola revealed that 50 % wastewater concentration was more efficient for enhancement of biochemical content of microalgae as compare to control. The result further showed considerable reduction in the organic pollution load of dairy wastewater as biological oxygen demand (BOD) and chemical oxygen demand (COD) reduced to 72 and 78 % respectively, after 15 days of treatment with C. humicola. The results also showed a reduction in the nutrient concentration of dairy wastewater such as nitrate, phosphate and sulphate by 92, 43, 62 % respectively, after 10 days of treatment and 96, 67 and 78 % respectively, after 15 days of microalgal treatment as compared to control (without microalgae). These findings suggested that dairy industry wastewater was a good nutrient supplement and can be directly used for mass cultivation of C. humicola without requiring additional nutrient supplements and also the microalgae C. humicola has a great potential for the treatment of dairy industry wastewate
Corporate Hierarchies and the Size of Nations: Theory and Evidence
Corporate organization varies within a country and across countries with country size. The paper starts by establishing some facts about corporate organization based on unique data of 660 Austrian and German corporations. The larger country (Germany) has larger firms with flatter more decentral corporate hierarchies compared to the smaller country (Austria). Firms in the larger country change their organization less fast than firms in the smaller country. Over time firms have been introducing less hierarchical organizations by delegating power to lower levels of the corporation. We develop a theory which explains these facts and which links these features to the trade environment that countries and firms face. We introduce firms with internal hierarchies in a Krugman (1980) model of trade. We show that international trade and the toughness of competition in international markets induce a power struggle in firms which eventually leads to decentralized corporate hierarchies. We offer econometric evidence which is consistent with the models predictions
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