The co-location of innovation and production in clusters

ABSTRACT

This paper quantifies the extent of co-location of innovation and production for industry clusters with varying knowledge intensity. If input-output, knowledge, and skill linkages are interdependent and geographically bounded, then we would expect innovation and production to be co-located in regional clusters. However, theory predicts that the degree of agglomeration benefits associated with co-location may vary across economic activities with different knowledge intensity. Using data from the U.S. Cluster Mapping Project, I develop measures of the co-location of innovation and production for 27 industry clusters, examining patterns across regions and over time (1998–2015) in the United States. I find that there is a significant co-location of innovation and production for many clusters, especially for those with higher knowledge intensity. This paper focuses on the Information Technology and Analytical Instruments cluster and the Automotive cluster to illustrate the co-location measures and the micro-geography of innovation and production.     

Evolution of the electronic structure and properties of neutral and charged aluminum arsenide clusters: A comprehensive analysis

The B3LYP-DFT/6-311+G(d) method has been used to optimize the geometries of (AlAs)_n neutrals and charged ions in the size range of n = 1–15. Frequency analyses are performed at the B3LYP/6-31G(d) level to check whether the optimized structures are transition states or true minima on the potential energy surfaces of corresponding clusters. The total energies of these clusters are then used to study the evolution of their binding energy, relative stability, and electronic properties as a function of size. The geometries are found to undergo a structural change from two-dimensional to three-dimensional when the cluster contains 6 atoms. The medium size clusters (n = 6–15) display the hollow globular conformers with large surface effect, which may cause the bulk limit still far from my computed results. The geometrical changes are companied by corresponding changes in the nearest-neighbor distances and coordination numbers. For medium size clusters (n = 6–15), both ionization potential and electron affinity have the tendency of decrease when the number of AlAs units in the cluster increases. Some magic clusters in neutral, cationic, and anionic form compared to its neighboring clusters are argued according to the calculated results of the second energy difference and electronic properties.     

Nonlinear dynamics of rectangular plates: investigation of modal interaction in free and forced vibrations

Nonlinear vibrations of thin rectangular plates are considered, using the von kármán equations in order to take into account the effect of geometric nonlinearities. Solutions are derived through an expansion over the linear eigenmodes of the system for both the transverse displacement and the Airy stress function, resulting in a series of coupled oscillators with cubic nonlinearities, where the coupling coefficients are functions of the linear eigenmodes. A general strategy for the calculation of these coefficients is outlined, and the particular case of a simply supported plate with movable edges is thoroughly investigated. To this extent, a numerical method based on a new series expansion is derived to compute the Airy stress function modes, for which an analytical solution is not available. It is shown that this strategy allows the calculation of the nonlinear coupling coefficients with arbitrary precision, and several numerical examples are provided. Symmetry properties are derived to speed up the calculation process and to allow a substantial reduction in memory requirements. Finally, analysis by continuation allows an investigation of the nonlinear dynamics of the first two modes both in the free and forced regimes. Modal interactions through internal resonances are highlighted, and their activation in the forced case is discussed, allowing to compare the nonlinear normal modes (NNMs) of the undamped system with the observable periodic orbits of the forced and damped structure.     

Monte Carlo and molecular dynamics simulation of argon clusters andn-alkanes in the confined regions of zeolites

Geometry and energy of argon clusters confined in zeolite NaCaA are compared with those of free clusters. Results indicate the possible existence of magic numbers among the confined clusters. Spectra obtained from instantaneous normal mode analysis of free and confined clusters give a larger percentage of imaginary frequencies for the latter indicating that the confined cluster atoms populate the saddle points of the potential energy surface significantly. The variation of the percentage of imaginary frequencies with temperature during melting is akin to the variation of other properties. It is shown that confined clusters might exhibit inverse surface melting, unlike medium-to-large-sized free clusters that exhibit surface melting. Configurational-bias Monte Carlo (CBMC) simulations ofn-alkanes in zeolites Y and A are reported. CBMC method gives reliable estimates of the properties relating to the conformation of molecules. Changes in the conformational properties ofn-butane and other longern-alkanes such asn-hexane andn-heptane when they are confined in different zeolites are presented. The changes in the conformational properties ofn-butane andn-hexane with temperature and concentration is discussed. In general, in zeolite Y as well as A, there is significant enhancement of thegauche population as compared to the pure unconfined fluid. Contribution No. 1260 from the Solid State and Structural Chemistry Unit     

Development of sustained-release tablets containing sodium valproate: in vitro and in vivo correlation

We have developed a 200 mg and 400 mg sustained-release sodium valproate tablet that allows effective blood concentration of the active drug with once-a-day dosing. The controlled dissolution or sustained release of the drug was attained by a membrane-controlled system. A single-coating system did not adequately control the dissolution rate, and therefore double-coated tablets were prepared and a human pharmacokinetic study was conducted. With the 200 mg VPA-Na tablets, the nonfasting C_max was only 20% higher than the fasting C_max. An in vitro dissolution test was conducted to predict the effects of food on drug dissolution after administration of this tablet. A relatively good correlation was observed between the absorption profiles and the dissolution profiles of the drug.