Quantifying loopy network architectures

Biology presents many examples of planar distribution and structural networks having dense sets of closed loops. An archetype of this form of network organization is the vasculature of dicotyledonous leaves, which showcases a hierarchically-nested architecture containing closed loops at many different levels. Although a number of methods have been proposed to measure aspects of the structure of such networks, a robust metric to quantify their hierarchical organization is still lacking. We present an algorithmic framework, the hierarchical loop decomposition, that allows mapping loopy networks to binary trees, preserving in the connectivity of the trees the architecture of the original graph. We apply this framework to investigate computer generated graphs, such as artificial models and optimal distribution networks, as well as natural graphs extracted from digitized images of dicotyledonous leaves and vasculature of rat cerebral neocortex. We calculate various metrics based on the Asymmetry, the cumulative size distribution and the Strahler bifurcation ratios of the corresponding trees and discuss the relationship of these quantities to the architectural organization of the original graphs. This algorithmic framework decouples the geometric information (exact location of edges and nodes) from the metric topology (connectivity and edge weight) and it ultimately allows us to perform a quantitative statistical comparison between predictions of theoretical models and naturally occurring loopy graphs.Comment: 17 pages, 8 figures. During preparation of this manuscript the authors became aware of the work of Mileyko at al., concurrently submitted for publicatio

A high-pressure hydrogen time projection chamber for the MuCap experiment

The MuCap experiment at the Paul Scherrer Institute performed a high-precision measurement of the rate of the basic electroweak process of nuclear muon capture by the proton, $\mu^- + p \rightarrow n + \nu_\mu$. The experimental approach was based on the use of a time projection chamber (TPC) that operated in pure hydrogen gas at a pressure of 10 bar and functioned as an active muon stopping target. The TPC detected the tracks of individual muon arrivals in three dimensions, while the trajectories of outgoing decay (Michel) electrons were measured by two surrounding wire chambers and a plastic scintillation hodoscope. The muon and electron detectors together enabled a precise measurement of the $\mu p$ atom's lifetime, from which the nuclear muon capture rate was deduced. The TPC was also used to monitor the purity of the hydrogen gas by detecting the nuclear recoils that follow muon capture by elemental impurities. This paper describes the TPC design and performance in detail.Comment: 15 pages, 13 figures, to be submitted to Eur. Phys. J. A; clarified section 3.1.2 and made minor stylistic corrections for Eur. Phys. J. A requirement

On the study of catalytic membrane reactor for water detritiation: Membrane characterization.

Tritium waste recycling is a real economic and ecological issue. Generally under the non-valuable Q2Oform (Q = H, D or T), waste can be converted into fuel Q2for a fusion machine (e.g. JET, ITER) by isotopeexchange reaction Q2O + H2= H2O + Q2. Such a reaction is carried out over Ni-based catalyst bed packed ina thin wall hydrogen permselective membrane tube. This catalytic membrane reactor can achieve higherconversion ratios than conventional fixed bed reactors by selective removal of reaction product Q2bythe membrane according to Le Chatelier’s Law. This paper presents some preliminary permeation tests performed on a catalytic membrane reactor.Permeabilities of pure hydrogen and deuterium as well as those of binary mixtures of hydrogen, deu-terium and nitrogen have been estimated by measuring permeation fluxes at temperatures ranging from573 to 673 K, and pressure differences up to 1.5 bar. Pure component global fluxes were linked to perme-ation coefficient by means of Sieverts’ law. The thin membrane (150 �m), made of Pd–Ag alloy (23 wt.%Ag),showed good permeability and infinite selectivity toward protium and deuterium. Lower permeabilityvalues were obtained with mixtures containing non permeable gases highlighting the existence of gasphase resistance. The sensitivity of this concentration polarization phenomenon to the composition andthe flow rate of the inlet was evaluated and fitted by a two-dimensional model

A taxonomic revision of Camptocerus Dejean (Coleoptera: Curculionidae: Scolytinae)

The Neotropical ambrosia beetle genus Camptocerus Dejean was revised. Monophyly of the genus was tested using 66 morphological characters in a cladistic analysis. Camptocerus was recovered as monophyletic and 31 species were recognized. Six new synonyms were discovered: C. auricomus Blandford 1896 (= C. striatulus Hagedorn 1905), C. inoblitus (Schedl) 1939 (= C. morio (Schedl) 1952), C. niger (Fabricius) 1801 (= C. tectus Eggers 1943), C. opacicollis (Eggers) 1929 (= C. infidelis Wood 1969; = C. uniseriatus Schedl 1972), C. suturalis (Fabricius) 1801 (= C. cinctus Chapuis 1869). Two species were removed from synonymy: C. charpentierae Schedl and C. hirtipennis Schedl. Twelve new species of Camptocerus were described: C. coccoformus (Brazil, Ecuador), C. distinctus (Ecuador), C. doleae (Ecuador), C. igniculus (Brazil), C. mallopterus (Ecuador), C. noel (widely distributed across Amazonia), C. petrovi (Ecuador), C. pilifrons (Ecuador), C. pseudoangustior (widely distributed across Amazonia), C. satyrus (Brazil), C. unicornus (Brazil) and C. zucca (Ecuador). Lectotypes are here designated for the following species: Camptocerus auricomus Blandford, Camptocerus squammiger Chapuis, Hylesinus gibbus Fabricius, Hylesinus suturalis Fabricius, Hylesinus fasciatus Fabricius. A key, diagnosis, distribution, host records and images were provided for each species

Muon Catalyzed Fusion in 3 K Solid Deuterium

Muon catalyzed fusion in deuterium has traditionally been studied in gaseous and liquid targets. The TRIUMF solid-hydrogen-layer target system has been used to study the fusion reaction rates in the solid phase of D_2 at a target temperature of 3 K. Products of two distinct branches of the reaction were observed; neutrons by a liquid organic scintillator, and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state of $\mu d$ and the hyperfine transition rate have been measured: $\tilde{\lambda}_(3/2)=2.71(7)_{stat.}(32)_{syst.} \mu/s$, and $\tilde{\lambda}_{(3/2)(1/2)} =34.2(8)_{stat.}(1)_{syst.} \mu /s$. The molecular formation rate is consistent with other recent measurements, but not with the theory for isolated molecules. The discrepancy may be due to incomplete thermalization, an effect which was investigated by Monte Carlo calculations. Information on branching ratio parameters for the s and p wave d+d nuclear interaction has been extracted.Comment: 19 pages, 11 figures, submitted to PRA Feb 20, 199

Muon Capture on the Proton and Deuteron

By measuring the lifetime of the negative muon in pure protium (hydrogen-1), the MuCap experiment determines the rate of muon capture on the proton, from which the proton's pseudoscalar coupling g_p may be inferred. A precision of 15% for g_p has been published; this is a step along the way to a goal of 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD's chiral symmetry. Meanwhile, the MuSun experiment is in its final design stage; it will measure the rate of muon capture on the deuteron using a similar technique. This process can be related through pionless effective field theory and chiral perturbation theory to other two-nucleon reactions of astrophysical interest, including proton-proton fusion and deuteron breakup.Comment: Submitted to the proceedings of the 2007 Advanced Studies Institute on Symmetries and Spin (SPIN-Praha-2007

New method for highly accurate calculations of the photodetachment cross-sections of the negatively charged hydrogen ions

New approach to highly accurate calculations of the photodetachment cross-sections of the negatively charged hydrogen ions is developed. This effective, fast and numerically stable method is based on the use of the Rayleigh's formula for the spherical Bessel functions. Photodetachment cross-sections of the negatively charged hydrogen ion(s) ${}^{\infty}$H$^{-}$, ${}^{1}$H$^{-}$ (protium), ${}^{2}$H$^{-}$ (deuterium D$^{-}$) and ${}^{3}$H$^{-}$ (tritium T$^{-}$) are determined with the use of highly accurate, truly correlated, variational wave functions constructed for these ions. Our method allows one to investigate the problem of photodetachment of the negatively charged hydrogen ions completely, i.e. without any limitation by numerical values of the photo-electron momentum $p_e$