Approximation for the mean value performance of locking algorithms for distributed database systems: a partitioned database

Concurrent access to databases must be synchronized for correct execution of transactions and preservation of data consistency. This is usually achieved through use of concurrency control algorithms, amongst which locking algorithms are the most popular both in the literature and in practice. Several analytic methods have been developed for predicting the performance of centralized database systems employing locking algorithms for concurrency control, but very few exist for distributed database systems.This paper proposes a method to approximate the mean value of various performance parameters in distributed database systems using locking for concurrency control. The main contribution of this approach is its ability to model the interaction between resource and data contention and the resulting effect on system performance. System performance is evaluated at a point where the interaction between these two factors is in equilibrium (stable state) and both the data and resource contention equations are simultaneously satisfied.The model involves the solution of a set of simultaneous polynomial equations whose order is dependent on several problem parameters such as the number of nodes and number of locks requested per transaction. These equations are solved by an iterative procedure to evaluate approximate values of relative throughput, utilization of servers and transaction response time. The small computational requirements of the analytical model permit sensitivity analysis on network parameters, and can thus be effectively used by system designers to evaluate choices of communication line speeds, processor capacity, database sizes, etc.The analytic approximations have been extensively verified against simulations for networks with up to 20 nodes. The input traffic was varied from light loads (about 5% utilization of the channels and processors) to heavy loads (about 65% utilization of the processors and channels). The discrepancies between the analytic approximation and the simulation were quite small (2–8%).This work was done while the authors were at Drexel University, Philadelphia.     

Prediction and correlations of some delayed neutron precursor yields for certain actinide nuclides

In this paper some predictions about some delayed neutron precursor yields are presented. The predictions are applied for certain actinides with some special interest in the nuclear energy field. The predictions are based on correlations which might be related to the cluster structure of the nucleus.     

Spatial information transmission using axial temporal coherence coding

We present an approach that can be used for transmission of information through space-limited systems or for superresolution. The spatial information is coded with different axial temporal coherence by interfering every spatial region in the input with the same region, but with a certain known delay in the longitudinal axis. Every spatial region has different delay. After mixing all of the spatial information, it is transmitted through the space-limited system. At the detection the information is passed through a similar interference setup containing certain axial delay. By temporally scanning along the longitudinal axis, each time a different spatial region that was coded with the corresponding axial delay is reconstructed. To allow coding of different spatial regions with different and small axial delays, we use a thermal light source that has very short coherence length. We include experimental validation of the presented approach.     

Coating Platinum Nanoparticles with Methyl Radicals: Effects on Properties and Catalytic Implications

It was recently reported that the reaction of methyl radicals with Pt⁰ nanoparticles (NPs), prepared by the reduction of Pt(SO₄)₂ with NaBH₄, is fast and yields as the major product stable (Pt⁰‐NPs)?(CH₃)_n and as side products, in low yields, C₂H₆, C₂H₄, and some oligomers. We decided to study the effect of this coating on the properties of the Pt⁰‐NPs. The results show that the coating can cover up to 75 % of the surface Pt⁰ atoms. The rate constant of the reaction, k( ^. CH₃+Pt⁰‐NPs), decreases with the increase in the surface coverage, leading to competing reaction paths in the solution, which gradually become dominant, affecting the composition of the products. The methyl coating also affects the zeta potential, the UV spectra, and the electrocatalytic reduction of water in the presence of the NPs. Thus, the results suggest that binding alkyl radicals to Pt⁰ surfaces might poison the NPs catalytic activity. When the Pt⁰‐NPs are prepared by the reduction of a different precursor salt, PtCl₆^2?, nearly no C₂H₄ and oligomers are formed and the methyl coating covers a larger percentage of the surface Pt⁰ atoms. The difference is attributed to the morphology of the Pt⁰‐NPs: those prepared from Pt(SO₄)₂ are twinned nanocrystals, whereas those prepared from PtCl₆^2? consist mostly of single crystals. Thus, the results indicate that the side products, or most of them at least, are formed on the twinned Pt⁰ nanocrystal edges created between (111) facets. In addition, the results show that Pt⁰‐NPs react very differently compared with other noble metals, for example, Au⁰ and Ag⁰; this difference is attributed in part to the difference in the bond strength, (M⁰‐NP)?CH₃, and should be considered in heterogeneous catalytic processes involving alkyl radicals as intermediates.     

Towards dimension expanders over finite fields

In this paper we study the problem of explicitly constructing a dimension expander raised by [3]: Let \mathbbFⁿ \mathbb{F}^n be the n dimensional linear space over the field \mathbbF\mathbb{F}. Find a small (ideally constant) set of linear transformations from \mathbbFⁿ \mathbb{F}^n to itself {A _i } _i∈I such that for every linear subspace V ⊂ \mathbbFⁿ \mathbb{F}^n of dimension dim(V)<n/2 we have

Enantiotopic discrimination in the deuterium NMR spectrum of solutes with S4 symmetry in chiral liquid crystals

Enantiotopic discrimination in the NMR spectra of prochiral rigid solutes in chiral liquid crystals (CLC), by the ordering mechanism, is limited to molecules possessing one of the four, so called, "allowed" symmetries, D(2d), C(2v), C(s), and S(4). So far, such spectral discrimination was demonstrated only for solutes possessing one of the first three symmetries. In this work, we present deuterium NMR measurements on a rigid S(4) compound dissolved in a chiral nematic solvent and demonstrate, for the first time, enantiotopic discrimination in such symmetry. The measurements were performed on the isotopically normal icosane derivative (1) and on its isotopomer (1-d(8)), specifically deuterated in its four core methylene groups. As a CLC solvent, a lyotropic mesophase, consisting of a solution of poly-γ-benzyl-L-glutamate (PBLG) in pyridine, was employed. For comparison with a corresponding achiral liquid crystal (ALC) solvent, a solution of a racemic mixture of poly-γ-benzylglutamate (PBG) of similar composition in the same co-solvent was used. The spectra were recorded at 92.1 MHz using the 2D Q-COSY Fz sequence with proton decoupling. In the CLC solvents they exhibited clear discrimination due to different enantiotopic sites, with components displaced symmetrically, at frequencies below and above those in the corresponding ALC, as expected for discrimination by ordering. Two procedures were employed for correlating the enantiotopic sites in the CLC spectra. For 1-d(8) the dipolar cross-peaks in a 2D (2)H-(2)H COSY-90 experiment provided identification of signals belonging to the same methylene (and hence the same enantiotopic) groups. For 1 the correlation was achieved using a least-square-deviation fitting of the experimental quadrupole splittings with respect to those expected from the molecular geometry. These results, with appropriate symmetry considerations were used to determine the symmetric (S(zz)) and antisymmetric (S(xy) and S(xx)-S(yy)) components of the Saupe ordering matrix. Interpretation of the NMR spectra of prochiral solutes in CLC suffers from the ambiguity in identifying the signals with specific enantiotopic groups. For this reason only the relative (but not the absolute) signs of the antisymmetric elements of the ordering matrix can be determined. For the S(4) group this leads to sign ambiguity in the rhombic term in the diagonalized ordering matrix. Similar (but not identical) ambiguities occur for solutes belonging to the other allowed groups. In a concluding section of the paper, the ambiguities in the antisymmetric order parameters for the various allowed groups are compared and their physical meaning are discussed.     

Electronic structures of Group 9 metallocorroles with axial ammines

The electronic structures of metallocorroles (tpfc)M(NH(3))(2) and (tfc)M(NH(3))(2) (tpfc is the trianion of 5,10,15-(tris)pentafluorophenylcorrole, tfc is the trianion of 5,10,15-trifluorocorrole, and M = Co, Rh, Ir) have been computed using first principles quantum mechanics [B3LYP flavor of Density Functional Theory (DFT) with Poisson-Boltzmann continuum solvation]. The geometry was optimized for both the neutral systems (formal M(III) oxidation state) and the one-electron oxidized systems (formally M(IV)). As expected, the M(III) systems have a closed shell d(6) configuration; for all three metals, the one-electron oxidation was calculated to occur from a ligand-based orbital (highest occupied molecular orbital (HOMO) of B(1) symmetry). The ground state of the formal M(IV) system has M(III)-Cπ character, indicating that the metal remains d(6), with the hole in the corrole π system. As a result the calculated M(IV/III) reduction potentials are quite similar (0.64, 0.67, and 0.56 V vs SCE for M = Ir, Rh and Co, respectively), whereas the differences would have been large for purely metal-based oxidations. Vertically excited states with substantial metal character are well separated from the ground state in one-electron-oxidized cobalt (0.27 eV) and rhodium (0.24 eV) corroles, but become closer in energy in the iridium (0.15 eV) analogues. The exact splittings depend on the chosen functional and basis set combination and vary by ~0.1 eV.