Efficient generation of tunable photon pairs at 0.8 and 1.6 microm

We demonstrate efficient generation of collinearly propagating, highly nondegenerate photon pairs in a periodically poled lithium niobate cw parametric downconverter with an inferred pair generation rate of 1.4x10(7)/s/mW of pump power. Detection of an 800-nm signal photon triggers a thermoelectrically cooled 20%-efficient InGaAs avalanche photodiode for the detection of the 1600-nm conjugate idler photon. Using single-mode fibers as spatial mode filters, we obtain a signal-conditioned idler-detection probability of ~3.1%.     

An integrated model for logistics network design

In this paper we introduce a new formulation of the logistics network design problem encountered in deterministic, single-country, single-period contexts. Our formulation is flexible and integrates location and capacity choices for plants and warehouses with supplier and transportation mode selection, product range assignment and product flows. We next describe two approaches for solving the problem---a simplex-based branch-and-bound and a Benders decomposition approach. We then propose valid inequalities to strengthen the LP relaxation of the model and improve both algorithms. The computational experiments we conducted on realistic randomly generated data sets show that Benders decomposition is somewhat more advantageous on the more difficult problems. They also highlight the considerable performance improvement that the valid inequalities produce in both solution methods. Furthermore, when these constraints are incorporated in the Benders decomposition algorithm, this offers outstanding reoptimization capabilities.     

Diffusion and solubility of SO2-4 in NaCl and KCl single crystals

We describe a new and very accurate method for measuring as a function of temperature the solubility of very slightly soluble salts (≈ 10^-5) in single crystals. The method is applied to the systems NaCl, Na₂SO₄ and KCl, K₂SO₄ and to the preparation of SO^2-₄ doped KCl single crystals. The parameters for diffusion of SO^2-₄ at infinite dilution into NaCl and KCl have been measured in the intrinsic range.     

An automated system for the analysis of G protein-coupled receptor transmembrane binding pockets: alignment, receptor-based pharmacophores, and their application

G protein-coupled receptors (GPCRs) share a common architecture consisting of seven transmembrane (TM) domains. Various lines of evidence suggest that this fold provides a generic binding pocket within the TM region for hosting agonists, antagonists, and allosteric modulators. Here, a comprehensive and automated method allowing fast analysis and comparison of these putative binding pockets across the entire GPCR family is presented. The method relies on a robust alignment algorithm based on conservation indices, focusing on pharmacophore-like relationships between amino acids. Analysis of conservation patterns across the GPCR family and alignment to the rhodopsin X-ray structure allows the extraction of the amino acids lining the TM binding pocket in a so-called ligand binding pocket vector (LPV). In a second step, LPVs are translated to simple 3D receptor pharmacophore models, where each amino acid is represented by a single spherical pharmacophore feature and all atomic detail is omitted. Applications of the method include the assessment of selectivity issues, support of mutagenesis studies, and the derivation of rules for focused screening to identify chemical starting points in early drug discovery projects. Because of the coarseness of this 3D receptor pharmacophore model, however, meaningful scoring and ranking procedures of large sets of molecules are not justified. The LPV analysis of the trace amine-associated receptor family and its experimental validation is discussed as an example. The value of the 3D receptor model is demonstrated for a class C GPCR family, the metabotropic glutamate receptors.     

Embedding of the operator space OH and the logarithmic ‘little Grothendieck inequality’

We use Voiculescu’s concept of free probability to construct a completely isomorphic embedding of the operator space OH in the predual of a von Neumann algebra. We analyze the properties of this embedding and determine the operator space projection constant of OH_n:

A classification for 2-isometries of noncommutativeLp-spaces

In this paper we extend previous results of Banach, Lamperti and Yeadon on isometries ofL _p-spaces to the non-tracial case first introduced by Haagerup. Specifically, we use operator space techniques and an extrapolation argument to prove that every 2-isometryT:L _p(M) →L _p(N) between arbitrary noncommutativeL _p-spaces can always be written in the form Here π is a normal *-isomorphism fromM onto the von Neumann subalgebra π(M) ofN,w is a partial isometry inN, andE is a normal conditional expectation fromN onto π(M). As a consequence of this, any 2-isometry is automatically a complete isometry and has completely contractively complemented range. The first and second authors were partially supported by the National Science Foundation DMS-0088928 and DMS-0140067.     

Relaxation-optimized NMR spectroscopy of methylene groups in proteins and nucleic acids

A large fraction of hydrogens in proteins and nucleic acids is of the methylene type. Their detailed study, however, in terms of structure and dynamics by NMR spectroscopy is hampered by their fast relaxation properties, which give rise to low sensitivity and resolution. It is demonstrated that six different relaxation interference processes, involving 1H-13C and 1H-1H dipolar interactions and 1H and 13C chemical shift anisotropy, can be used simultaneously to mitigate these problems effectively. The approach is applicable to the majority of NMR experiments commonly used to study side chain and backbone conformation. For proteins, its efficiency is evaluated quantitatively for two samples: the third IgG-binding domain from Streptococcal Protein G and the protein calmodulin complexed with a 26-residue target peptide. Gains in both resolution and sensitivity by up to factors of 3.2 and 2.0, respectively, are observed for Gly residues at high magnetic field strengths, but even at much lower fields gains remain substantial. The resolution enhancement obtained for methylene groups makes possible a detailed analysis of spectral regions commonly considered inaccessible due to spectral crowding. For DNA, the high resolution now obtainable for C5' sites permits an H5'/H5'-based sequential NOE assignment procedure, complementary to the conventional base-H1'/H2'/H2' pathway.     

Two-photon coincident-frequency entanglement via extended phase matching

We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase-matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO4. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.