Efficient method for estimating the number of communities in a network

While there exist a wide range of effective methods for community detection in networks, most of them require one to know in advance how many communities one is looking for. Here we present a method for estimating the number of communities in a network using a combination of Bayesian inference with a novel prior and an efficient Monte Carlo sampling scheme. We test the method extensively on both real and computer-generated networks, showing that it performs accurately and consistently, even in cases where groups are widely varying in size or structure.Comment: 13 pages, 4 figure

Reactivity of pi-complexes of Ti, V, and Nb towards dithioacetic acid: Synthesis and structure of novel metal sulfur-containing complexes

In order to use sulfur-containing resources economically and with minimal environmental damage, it is important to understand the desulfurization processes. Hydrodesulfurization, for example, is carried out on the surface of a heterogeneous metal sulfide catalyst. Studies of simple, soluble inorganic systems provide information regarding the structure and reactivity of sulfur-containing compounds with metal complexes. Further, consistent with recent trends in materials chemistry, many model compounds warrant further study as catalyst precursors. The reactivity of low-valent organometallic sandwich pi-complexes toward dithiocarboxylic acids is described. For example, treatment of bisbenzene vanadium with CH3CSSH affords a divanadium tetrakis(dithioacetate) complex. The crystallographically determined V-V bond distance, 2.800(2), is nearly the same as the V-V bond distance in a V(mu-nu squared-S2)2V' unit in the mineral patonite (VS4)n. The stability of the V2S4 core in the dimer is demonstrated by evidence of V2S4(+) in the mass spectrum (70 eV, solid probe) of the vanadium dimer. Several other systems relevant to HDS catalysis are also discussed

Pulsating stars in the VMC survey

The VISTA survey of the Magellanic Clouds system (VMC) began observations in 2009 and since then, it has collected multi-epoch data at Ks and in addition multi-band data in Y and J for a wide range of stellar populations across the Magellanic system. Among them are pulsating variable stars: Cepheids, RR Lyrae, and asymptotic giant branch stars that represent useful tracers of the host system geometry.Comment: 8 pages, 7 figures, proceeding contribution of invited presentation at "Wide-field variability surveys: a 21st-century perspective", San Pedro de Atacama (Chile

Universality class of quantum criticality in the two-dimensional Hubbard model at intermediate temperatures (t2/U≪T≪tt^2/U\ll T\ll t)

We show that the dilute Fermi gas quantum critical universality class quantitatively describes the Mott/metal crossover of the two-dimensional Hubbard model for temperatures somewhat less than (roughly half) the tunneling but much greater than (roughly twice) the superexchange energy. We calculate the observables expected to be universal near the transition --- density and compressibility --- with numerically exact determinantal quantum Monte Carlo. We find they are universal functions of the chemical potential. Despite arising from the strongly correlated regime of the Hubbard model, these functions are given by the weakly interacting, dilute Fermi gas model. These observables and their derivatives are the only expected universal static observables of this universality class, which we also confirm by verifying there is no scaling collapse of the kinetic energy, fraction of doubly occupied sites, and nearest neighbor spin correlations. Our work resolves the universality class of the intermediate temperature Mott/metal crossover, which had alternatively been proposed to be described by more exotic theories. However, in the presence of a Zeeman magnetic field, we find that interplay of spin with itinerant charge can lead to physics beyond the dilute Fermi gas universality class.Comment: Main text: 4 pages, 2 figures (6 panels). Supplementary info.: 2 pages, 3 figures (7 panels

Foeniculum vulgare Essential Oils: Chemical Composition, Antioxidant and Antimicrobial Activities

The essential oils from Foeniculum vulgare commercial aerial parts and fruits were isolated by hydrodistillation, with different distillation times (30 min, I h, 2 h and 3 h), and analyzed by GC and GC-MS. The antioxidant ability was estimated using four distinct methods. Antibacterial activity was determined by the agar diffusion method. Remarkable differences, and worrying from the quality and safety point of view, were detected in the essential oils. trans-Anethole (31-36%), alpha-pinene (14-20%) and limonene (11-13%) were the main components of the essentials oil isolated from F. vulgare dried aerial parts, whereas methyl chavicol (= estragole) (79-88%) was dominant in the fruit oils. With the DPPH method the plant oils showed better antioxidant activity than the fruits oils. With the TBARS method and at higher concentrations, fennel essential oils showed a pro-oxidant activity. None of the oils showed a hydroxyl radical scavenging capacity >50%, but they showed an ability to inhibit 5-lipoxygenase. The essential oils showed a very low antimicrobial activity. In general, the essential oils isolated during 2 h were as effective, from the biological activity point of view, as those isolated during 3 h.info:eu-repo/semantics/publishedVersio

Different intra- and inter-molecular hydrogen-bonding patterns in (3S,4aS,8aS)-2-[(2R,3S)-3-(2,5-X2-benzamido)-2-(2,5-X2-benzo-yloxy)-4-phenyl-butyl]-N-tert-butyldeca-hydro-iso-quinoline-3-carboxamides (X = H or Cl) : compounds with moderate aspartyl protease inhibition activity

We thank the EPSRC National Crystallography Service (University of Southampton) for the X-ray data collections.Peer reviewedPublisher PD

Optimal focusing for maximal collection of entangled narrow-band photon pairs into single-mode fibers

We present a theoretical and experimental investigation of the emission characteristics and the flux of photon pairs generated by spontaneous parametric downconversion in quasi-phase matched bulk crystals for the use in quantum communication sources. We show that, by careful design, one can attain well defined modes close to the fundamental mode of optical fibers and obtain high coupling efficiencies also for bulk crystals, these being more easily aligned than crystal waveguides. We distinguish between singles coupling, conditional coincidence, and pair coupling, and show how each of these parameters can be maximized by varying the focusing of the pump mode and the fiber-matched modes using standard optical elements. Specifically we analyze a periodically poled KTP-crystal pumped by a 532 nm laser creating photon pairs at 810 nm and 1550 nm. Numerical calculations lead to coupling efficiencies above 94% at optimal focusing, which is found by the geometrical relation L/z_R to be ~ 1 to 2 for the pump mode and ~ 2 to 3 for the fiber-modes, where L is the crystal length and z_R is the Rayleigh-range of the mode-profile. These results are independent on L. By showing that the single-mode bandwidth decreases as 1/L, we can therefore design the source to produce and couple narrow bandwidth photon pairs well into the fibers. Smaller bandwidth means both less chromatic dispersion for long propagation distances in fibers, and that telecom Bragg gratings can be utilized to compensate for broadened photon packets--a vital problem for time-multiplexed qubits. Longer crystals also yield an increase in fiber photon flux proportional to sqrt{L}, and so, assuming correct focusing, we can only see advantages using long crystals.Comment: 19 pages, 15 figures, ReVTeX4, minor revisio

d-Wave Superfluidity in Optical Lattices of Ultracold Polar Molecules

Recent work on ultracold polar molecules, governed by a generalization of the t-J Hamiltonian, suggests that molecules may be better suited than atoms for studying d-wave superfluidity due to stronger interactions and larger tunability of the system. We compute the phase diagram for polar molecules in a checkerboard lattice consisting of weakly coupled square plaquettes. In the simplest experimentally realizable case where there is only tunneling and an XX-type spin-spin interaction, we identify the parameter regime where d-wave superfluidity occurs. We also find that the inclusion of a density-density interaction destroys the superfluid phase and that the inclusion of a spin-density or an Ising-type spin-spin interaction can enhance the superfluid phase. We also propose schemes for experimentally realizing the perturbative calculations exhibiting enhanced d-wave superfluidity.Comment: 22 pages, 12 figures; v2: revised discussion