bluuebunny/crossref_metadata_2025 huggingface dataset:
A nonlinear theory for multidimensional relativistic plasma wave wakefields
Authors: Lu W. , Huang C. , Zhou M. , Tzoufras M. , Tsung F. S. , Mori W. B. , Katsouleas T.
Published: May 2006

A nonlinear kinetic theory for multidimensional plasma wave wakes with phase velocities near the speed of light is presented. This theory is appropriate for describing plasma wakes excited in the so-called blowout regime by either electron beams or laser pulses where the plasma electrons move predominantly in the transverse direction. The theory assumes that all electrons within a blowout radius are completely expelled. These radially expelled electrons form a narrow sheath just beyond the blowout radius which is surrounded by a region which responds weakly (linearly). This assumption is reasonable when the spot size of the electron beam and laser are substantially less than the blowout radius. By using this theory one can predict the wakefield amplitudes and blowout radius in terms of the electron beam or laser beam parameters, as well as predict the nonlinear modifications to the wake’s wavelength and wave form. For the laser case, the laser spot size must also be properly matched in order for a narrow sheath to form. The requirements for forming a spherical wave form, i.e., “bubble,” are also discussed. The theory is also used to show when linear fluid theory breaks down and how this leads to a saturation of the logarithmic divergence in the linear Green’s function.
Experimental study of two-fluid effects on magnetic reconnection in a laboratory plasma with variable collisionality
Authors: Yamada Masaaki , Ren Yang , Ji Hantao , Breslau Joshua , Gerhardt Stefan , Kulsrud Russell , Kuritsyn Aleksey
Published: May 2006

This article describes the recent findings on two-fluid effects on magnetic reconnection in plasmas with variable collisionality in the magnetic reconnection experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. The MRX device has been upgraded to accommodate a variety of reconnection operation modes and high energy density experiments by increasing its capacitor bank energy and extending the discharge duration. As our experimental operation regime has moved from the collisional to the collision-free, two-fluid effects have become more evident. It is observed that the two-dimensional profile of the neutral sheet is changed significantly from the rectangular shape of the familiar Sweet-Parker type to a double wedge shape as the collisionality is reduced and the reconnection rate increases. The recent evolution of our experimental research from the magnetohydrodynamics (MHD) to the two-fluid analysis is presented to illuminate the physics of Hall MHD in a collision-free reconnection layer. In particular, a clear experimental verification of an out-of-plane quadrupole field, a characteristic signature of the Hall MHD, has been made in the MRX neutral sheet, where the sheet width is comparable to the ion skin depth. It is important to note that the Hall effect, which occurs due to two-dimensional laminar flows of electrons in the reconnection plane, is observed together with the presence of low and high frequency magnetic turbulence, which often has three-dimensional structures. These observations in MRX have striking similarities to the recent magnetospheric measurements of reconnection region, in which the quadrupole component has been detected together with magnetic fluctuations.
Charging of dust grains in a plasma with negative ions
Authors: Kim Su-Hyun , Merlino Robert L.
Published: May 2006

The effect of negative ions on the charging of dust particles in a plasma is investigated experimentally. A plasma containing a very low percentage of electrons is formed in a single-ended Q machine when SF6 is admitted into the vacuum system. The relatively cold Q machine electrons (Te≈0.2eV) readily attach to SF6 molecules to form SF6− negative ions. Calculations of the dust charge indicate that for electrons, negative ions, and positive ions of comparable temperatures, the charge (or surface potential) of the dust can be positive if the positive ion mass is smaller than the negative ion mass and if ϵ, the ratio of the electron to positive ion density, is sufficiently small. The Q machine plasma is operated with K+ positive ions (mass 39amu) and SF6− negative ions (mass 146amu), and also utilizes a rotating cylinder to dispense dust into the plasma column. Analysis of the current-voltage characteristics of a Langmuir probe in the dusty plasma shows evidence for the reduction in the (magnitude) of the negative dust charge and the transition to positively charged dust as the relative concentration of the residual electrons is reduced. Some remarks are offered concerning experiments that could become possible in a dusty plasma with positive grains.
Dual-frequency ferromagnetic resonance
Authors: Guan Y. , Bailey W. E.
Published: May 2006

We describe a new experimental technique to investigate coupling effects between different layers or modes in ferromagnetic resonance (FMR). Dual FMR frequencies are excited (2–8GHz) simultaneously and detected selectively in a broadband rf circuit using lock-in amplifier detection at separate modulation frequencies.
Hugoniot measurement of diamond under laser shock compression up to 2TPa
Authors: Nagao H. , Nakamura K. G. , Kondo K. , Ozaki N. , Takamatsu K. , Ono T. , Shiota T. , Ichinose D. , Tanaka K. A. , Wakabayashi K. , Okada K. , Yoshida M. , Nakai M. , Nagai K. , Shigemori K. , Sakaiya T. , Otani K.
Published: May 2006

Hugoniot data of diamond was obtained using laser-driven shock waves in the terapascal range of 0.5–2TPa. Strong shock waves were generated by direct irradiation of a 2.5ns laser pulse on an Al driver plate. The shock wave velocities in diamond and Al were determined from optical measurements. Particle velocities and pressures were obtained using an impedance matching method and known Al Hugoniot. The obtained Hugoniot data of diamond does not show a marked difference from the extrapolations of the Pavlovskii Hugoniot data in the TPa range within experimental errors.
Lewis-Base Adducts of Lead(II) Compounds. IX. Synthetic and Structural Studies of Some 1:1 Adducts of 'cyclam' and Its Hexamethylated Derivative 'tet-b' With Lead(II) Oxoanion Salts
Authors: Harrowfield JM , Miyamae H , Shand TM , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1 : 1 adducts of (1,4,8,11-tetraazacyclotetradecane) ('cyclam') with lead(II) perchlorate and (7R*,14R*)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane ('tet -b') with lead(II) nitrate, perchlorate and acetate ('ac'). [( cyclam ) Pb (ClO4)2] is orthorhombic, Pb21a, a 16.024(7), b 13.595(4), c 8.6810(5) Ǻ, Z = 4 f.u .; R was 0.055 for No 1318 independent 'observed' (I > 3σ(I)) reflections. [( tet -b) Pb (NO3)2]2 is monoclinic. P 21/a, a 16.15(2), b 14.550(6), c 19.775(2) Ǻ, β
90.86(5)°, Z = 4 dimers ; R 0.074 for No 3184. [( tet -b) Pb (ClO4)2]2.H2O is monoclinic, P 21/c, a 13.663(9), b 9.031(3). c 20.61(1) Ǻ, β 100.40(3)°, Z = 4 f.u .; R 0.044 for No 2857. [( tet -b) Pb (ac)2].2H2O is triclinic, Pī , a 13.138(5), b 10.924(4), c 10.518(3) Ǻ, α 115.48(3), β 91.95(2), γ 102.38(2)°, Z = 2 f.u .; R 0.031 for No 6485. In all complexes, the macrocycle-N4 ligand occupies one 'side' of the coordination sphere of the lead atom, with anionic oxygens opposed; the cyclam/perchlorate complex is, like the nitrate, mononuclear with seven-coordinate (N4)PbO3 with a bidentate O,O'- and a unidentate O- perchlorate . In the tet-b acetate, the anionic oxygen atoms are surprisingly sparse, comprising simply a bidentate acetate in a mononuclear (N4)PbO2 environment with the other (lattice) acetate bonded to the macrocycle axial NH hydrogens . The nitrate and perchlorate complexes involve bridging anions: in the nitrate. a central centrosymmetric PbO2Pb array is found, the lead atoms being bridged by one oxygen of a bidentate nitrate, the other nitrate being unidentate and the coordination sphere (N4)PbO4: in the perchlorate , again a centrosymmetric dimer is found, the lead atoms being linked by O,O'-bridging perchlorates (again with (N4)PbO2
coordination environments), the complex being essentially [( tet -b) Pb (OClO2O)2Pb( tet -b)](ClO4)2H2O. The structure of [cyclamH4]4+ (NO3-)4.2H2O is also recorded [triclinic, Pī , a 8.626(2), b 8.549(1), c 8.400(2) Ǻ, α 80.60(2), β 76.62(2), γ 65.06(1)°, Z = 1; R 0.044 for No 1539], together with that of the diprotonated hexamethyl derivative [tet-bH2]2+(ClO4-)2.CH3OH [monoclinic, P21/c, a 11.296(3), b 8.834(8), c 26.22(1) Ǻ, β 99.05(3)°, Z = 4 f.u .; R 0.063 for No 2583].
Lewis-Base Adducts of Lead (II) Compounds. XI. Synthetic and Structural Studies of Some 1:1 Adducts of 2,2'-Bipyridine and 1,10-Phenanthroline With Lead(II) Oxoanion Salts
Authors: Harrowfield JM , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1 : 1 adducts of 1,10-phenanthroline ('phen') with lead(II) nitrate (as a monohydrate; the structure of the isomorphous 2,2'-bipyridine (' bpy ') analogue is also recorded) and of its lead(II) acetate ('ac') analogue (as a dihydrate ). [( bpy ) Pb (NO3)2](∞|∞).H2O is monoclinic, P 21/c; a 7.244(9), b 9.872(2), c 20.395(5) Ǻ, β 109.08(7)°, Z = 4 f.u ., R being 0.048 for No = 3447 independent 'observed' (I > 3σ(I)) reflections. [( phen ) Pb (NO3)2](∞|∞).H2O has a 7.168(2), b 9.972(1), c 21.069(3) Ǻ, β 99.47(1)°, R 0.034 for No 3596. [( phen ) Pb (ac)2]2.4H2O is triclinic, Pī , a 13.932(3), b 12.904(4), c 12.716(5) Ǻ, α 62.37(2), β 71.16(2), γ 60.55(2)°, Z = 2 ( dimers ); R was 0.029 for No 5457. The nitrates are one-dimensional polymers along b, successive lead atoms being linked by one oxygen of one of the nitrate groups, each of the other oxygen atoms completing a chelate to either side; the lead environment is completed as N2PbO7 by the other nitrate (as a chelate ), the bidentate base, and the water molecule. In the acetate which is a centrosymmetric dimer (manifested in two distinct independent dimers ) the two lead atoms are linked by bridging oxygen atoms derived from pairs of chelating acetate moieties about each lead atom. The coordination sphere of each lead atom is completed by the bidentate aromatic base. The two dimers differ significantly in parallel comparison of their geometrical descriptors.
Lewis-Base Adducts of Lead(II) Compounds. XII. Synthetic, Spectroscopic and Structural Studies of Some 1:1 Adducts of Lead(II) (Pseudo-)Halides With Aromatic Bidentate Ligands
Authors: Bowmaker GA , Harrowfield JM , Miyamae H , Shand TM , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for some 1 : 1 adducts of lead(II) (pseudo-)halides with 1,10-phenanthroline (' phen ') and 2,2'-bipyridine (' bpy '). [( phen )PbX2](∞|∞), X = Cl , Br, I, have been refined in a common monoclinic C2/c setting, a ≈ 16.2, b ≈ 10.6, c ≈ 8.25 Ǻ, β 105°, Z = 4 f.u .; (conventional R on |F| 0.034, 0.046, 0.043 for No = 1694, 1626, 1387 independent, 'observed' (I > 3σ(I)) reflections respectively); [( bpy )PbI2](∞|∞) is isomorphous with similar cell dimensions (R 0.035 for No 1263), but, in its chloride counterpart, the symmetry is degraded to P21/c, a 15.336(5), b 9.476(5), c 8.191(3) Ǻ, β 92.81(3)�, Z = 4 (R 0.041 for No 2849). In the C2/c model the lead atoms are disposed on crystallographic 2 axes, as also are the associated N,N′- bidentate ligands, with the six-coordinate (cis-N2) Pb (μ-X)4 environments linked in an infinite …(μ-X)2Pb(μ-X)2Pb… one-dimensional polymeric chain by bridging halogen atoms. A somewhat similar, albeit more complex, array is found in [( bpy ) Pb (SCN)2](∞|∞), monoclinic, C2/c, a 17.655(6), b 12.027(3), c 6.794(1) Ǻ, β 107.03(2)°, Z = 4 (R 0.028 for No 1064), isomorphous with its previously studied phen analogue, in which a web of bridging SCN units is found. Stacks of successive strands up b have interleaving arrays of ligands and (pseudo-)halide atoms. The far-infrared spectrum of [( phen )PbCl2] shows four strong, broad bands at 152, 144, 116 and 96 cm-1 which are assigned as vPb-Cl. The corresponding bands in the bromo and iodo complexes are shifted to below 100 cm-1, revealing sharper bands at about 120 and 150 cm-1 which are assigned to vPb -N modes. The low wavenumbers of the vPb-X bands are indicative of weak Pb-X bonding. The far-infrared spectrum of the previously reported [( phen ) Pb (NCS)2] complex is similar to that of the chloro complex, consistent with its similarity in structure.
Lewis-Base Adducts of Lead(II) Compounds. XIII. Synthetic, Structural and Theoretical Studies of Some 2:1 Adducts of 1,10-Phenanthroline With Lead(II) Oxoanion Salts
Authors: Bytheway I , Engelhardt LM , Harrowfield JM , Kepert DL , Miyamae H , Patrick JM , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 2 : 1 adducts of the N,N′- bidentate aromatic base 1,10-phenanthroline (' phen ') with lead(II) nitrate and perchlorate . [( phen )2Pb(NO3)2] is monoclinic, P21/n, a 18.104(4), b 7.733(2), c 16.688(3) Ǻ, β 98.17(2)′, Z = 4, R being 0.036 for No = 3381 independent 'observed' reflections, while [( phen )2Pb(ClO4)2] is triclinic, Pī , a 13.134(4), b 12.342(4), c 7.771(3) Ǻ, α 94.34(3), β 101.49(3), γ 93.91(2)′, Z = 2, R being 0.056 for No 3473. The two systems are mononuclear with eight-coordinate PbN4O4 coordination environments incorporating a pair of O,O'- bidentate anions. Stereochemical calculations, based on valence shell electron pair repulsion (VSEPR) theory, have been performed for coordination complexes of the general type [M( bidentate A)n( bidentate B)4-n] (n = 1 or 2) and for several types of lead(II) complex thought to contain sterically active lone pairs of electrons. Expected deviations from ideal stereochemistry have been successfully predicted and for many of the complexes studied there is good agreement between the observed and calculated stereochemistry. In the particular case of these lead(II)/ phen complexes it appears to be necessary to invoke steric interactions of the a-hydrogen atoms in addition to a sterically active lone pair.
Lewis-Base Adducts of Lead(II) Compounds. XVI. Synthetic and Structural Studies of Some Adducts of 2-Aminomethylpyridine With Lead(II) Compounds
Authors: Harrowfield JM , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 2:1 adducts of 2-aminomethylpyridine ('amp') with lead(II) nitrate and thiocyanate . [(amp)2Pb(NO3)2]2 is triclinic, Pī, a 11.616(4), b 11.145(6), c 7.341(3) Ǻ, α 83.87(4), β 89.17(3), γ 64.12(3)°, Z = 1 dimer ; R was 0.043 for No 3529 independent 'observed' (I > 3σ(I)) reflections. [(amp)2Pb(SCN)2]2 is also triclinic, Pī , a 12.121(9), b 9.301(14), c 8.615(8) Ǻ, α 70.11(10), β 84.00(7), γ 79.38(10)°, Z = 1 dimer (R 0.033 for No 3467). Both complexes are centrosymmetric dimers ; the coordination environment is made up in each case of a pair of N,N°-bidentate bases, one terminally bound anion (O,O°-chelating nitrate or S-bonded thiocyanate ) and bridging anions. In the case of the thiocyanates, these bridge end-on, so that the lead(II) environment is seven-coordinate PbN5S2; in the nitrate, the anion chelates through two of its oxygen atoms, bridging via the third, so that the lead(II) environment is nine-coordinate PbN4O5. A 'problem structure', [(amp)2Pb(ClO4)2], monoclinic, C2/c (?), a 14.528(3), b 8.203(3), c 15.495(6) Ǻ, β 91.14(3)°, Z = 4 f.u ., R 0.044 for No 1775, is also recorded, the crystal seemingly a disordered aggregate of [(N, N′-amp)2Pb(OClO3)2] moieties.
Lewis-Base Adducts of Lead(II) Compounds. XVII. Synthetic and Structural Studies of Some 1:1 Adducts of 2,2':6,2'-Terpyridine With Lead(II) Salts
Authors: Engelhardt LM , Harrowfield JM , Miyamae H , Patrick JM , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1:1 adducts of 2,2':6',2"-terpyridine (' tpy ') with the lead(II) oxoanion salts perchlorate, nitrate and nitrite, ( tpy ) Pb ( oxoanion )2. All structures are monoclinic, C2/c, Z = 4, with approximate ranges a from 9 to 11 Ǻ, b from 16 to 20 Ǻ, c from 9.8 to 13.8 Ǻ, β from 113 to 130° and V from 1650 to 1850 Ǻ3. In all cases the lead(II) atoms are disposed on crystallographic 2 axes which also pass through the axis of the central tpy ring; a pair of symmetry related oxoanions link successive lead atoms in a one-dimensional polymeric chain parallel to the ac cell diagonal, one pair of oxygen atoms functioning as an O,O'-bidentate with another oxygen (replaced by the nitrogen in the nitrite) bridging to the adjacent lead atom; the third anionic oxygen atom in the nitrate is replaced by a water molecule in the nitrite, which thus becomes a monohydrate. Residuals were 0.030, 0.034 and 0.040 for 2122, 1564 and 2059 independent 'observed' (I > 3σ(I)) reflections respectively. Also recorded are the syntheses and room-temperature single-crystal X-ray structure determinations for 1:1 aducts of 2,2':6',2"-terpyridine with lead(II) chloride, bromide and iodide, the chloride and bromide being hydrated. ( tpy )PbCl2.H2O is monoclinic, P 21/c, a 8.938(1), b 15,210(7), c 13.414(3) Ǻ, β 115.17(1)°, Z = 4 f.u .; R was 0.036 for No = 3346 independent, 'observed' reflections. The complex is centrosymmetric, binuclear [( tpy ) (H2O)( Cl ) Pb (μ- Cl )2Pb( Cl )(OH2)( tpy )], with the two lead atoms linked by bridging chlorine atoms; the lead atoms are seven-coordinate N3,O,ClPb(μ- Cl )2. The bromide ( tpy )PbBr2.2/3H2O, triclinic, Pī, a 12.360(6), b 12.452(4), c 18.372(6) Ǻ, α 108.31(3), β 109.44(3), γ 90.56(3)°, Z = 6 f.u ., R being 0.046 for No 7282, is in fact trinuclear [Pb3Br6( tpy )6].2H2O, a novel and elegant oligomer with quasi-2 symmetry in which a central lead atom (on the quasi-2 axis) is seven-coordinated [( tpy ) Pb (μ-Br)4] with the associated bromides bridging to a pair of peripheral lead atoms, also seven coordinated, [( tpy )(Br) Pb (μ-Br)3]. Unsolvated ( tpy )PbI2, triclinic, Pī , a 10.834(3), b 9.023(3), c 8.906(2) Ǻ, α 80.34(2), β 89.40(2), γ 79.78(2)°, Z = 2 f.u ., R 0.031 for No 2347 is, like the chloride, centrosymmetric binuclear, [( tpy )(I) Pb (μ-I)2Pb(I)( tpy )], but with the lead(II) now six-coordinate N3(I) Pb (μ-I)2. In both chloride and iodide, the tpy plane is approximately normal to the Pb ... Pb line with the water molecule of the chloride approximately trans to the central tpy nitrogen; in the iodide that site is occupied by the terminal halide.
Lewis-Base Adducts of Lead(II) Compounds. XX. Synthesis and Structure of the 1:1 Adduct of Pyridine With Lead(II) Thiocyanate
Authors: Harrowfield JM , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

The synthesis and room-temperature single-crystal X-ray structure determination are recorded for a 1:1 adduct of lead(II) thiocyanate with pyridine (' py '). [( py ) Pb (SCN)2](∞|∞) is triclinic, Pī , a 10.544(1), b 7.3729(7), c 6.705(2) Ǻ, α 103.91(2), β 95.99(2), γ 100.51(1)°, Z = 2 f.u .; R was 0.041 for 3226 'observed' (I > 3σ(I)) reflections. The structure is a two-dimensional polymer in the be plane with eight-coordinate ( py -N)PbN3S4 linked by the familiar four- membered Pb2S2 and eight-membered Pb2(NCS)2 motifs by way of bridging thiocyanate groups; one of the latter, unusually, has a bifurcating bridging nitrogen atom leading to the introduction of Pb2N2 motifs. The structure of the parent lead(II) thiocyanate is also discussed.
Conductance of a biomolecular wire
Authors: Visoly-Fisher Iris , Daie Kayvon , Terazono Yuichi , Herrero Christian , Fungo Fernando , Otero Luis , Durantini Edgardo , Silber Juana J. , Sereno Leonides , Gust Devens , Moore Thomas A. , Moore Ana L. , Lindsay Stuart M.
Published: May 2006

Carotenoids (Car) act as “wires” that discharge unwanted electrons in the reaction center of higher plants. One step in this “side-path” electron conduction is thought to be mediated by Car oxidation. We have carried out direct measurements of the conductance of single-Car molecules under potential control in a membrane-mimicking environment, and we found that when Car are oxidized conductance is enhanced and the electronic decay constant (β) is decreased. However, the neutral molecule may already be conductive enough to account for observed electron transfer rates.
Phosphatidylinositol 3-kinase mediates activation of ATM by high NaCl and by ionizing radiation: Role in osmoprotective transcriptional regulation
Authors: Irarrazabal Carlos E. , Burg Maurice B. , Ward Stephen G. , Ferraris Joan D.
Published: May 2006

High NaCl causes DNA double-strand breaks and activates the transcription factor, TonEBP/OREBP, resulting in increased transcription of several protective genes, including those involved in accumulation of compatible organic osmolytes. Several kinases are known to contribute to signaling activation of TonEBP/OREBP, including ATM, which is a member of the phosphatidylinositol 3-kinase (PI3K)-like kinase family and is activated by DNA double-strand breaks. The purpose of the present studies was to investigate a possible role of PI3K Class IA (PI3K-IA). We found that high NaCl increases PI3K-IA lipid kinase activity. Inhibiting PI3K-IA either by expressing a dominant negative of its regulatory subunit, p85, or by small interfering RNA-mediated knockdown of its catalytic subunit, p110α, reduces high NaCl-induced increases in TonEBP/OREBP transcriptional activity and transactivation, but not nuclear translocation of TonEBP/OREBP, or increases in its abundance. Further, suppression of PI3K-IA inhibits the activation of ATM that is caused by either ionizing radiation or high NaCl. High NaCl-induced increase in TonEBP/OREBP activity is reduced equally by inhibition of ATM or PI3K-IA, and the effects are not additive. The conclusions are as follows: (i) PI3K-IA activity is necessary for both high NaCl- and ionizing radiation-induced activation of ATM and (ii) high NaCl activates PI3K-IA, which, in turn, contributes to full activation of TonEBP/OREBP via ATM.
Capillary Hemodynamics and Oxygen Pressures in the Aging Microcirculation
Authors: POOLE DAVID C. , BEHNKE BRAD J. , MUSCH TIMOTHY I.
Published: May 2006

Healthy aging acts to redistribute blood flow (Q̇) and thus O2 delivery (Q̇O2) among and within the exercising muscles such that Q̇O2 to highly oxidative muscle fibers may be compromised. Within the microcirculation of old muscles capillary hemodynamics are altered and the matching of Q̇O2 to oxidative requirements (V̇O2) is impaired such that at exercise onset the microvascular O2 pressure falls below that seen in their younger counterparts. This is important because the microvascular O2 pressure denotes the sole driving force for blood‐myocyte O2 transfer and any compromise may slow V̇O2 kinetics and reduce exercise tolerance. This review considers the microcirculatory evidence for a reduced perfusive (Q̇O2) and diffusive O2 flux within aged muscle and highlights the pressing need for intravital microscopy studies of the muscle microcirculation during exercise.
α‐Adrenergic Control of Skeletal Muscle Circulation at Rest and During Exercise in Aging Humans
Authors: DINENNO FRANK A. , JOYNER MICHAEL J.
Published: May 2006

Aging is associated with many changes in autonomic nervous system function that often lead to impairments in the normal ability to respond to physiological stressors commonly encountered in daily life. In addition, many of these chronic age‐related changes in autonomic‐circulatory function can potentially predispose the older adult to elevated risk for acute and chronic cardiovascular complications. One of the most pronounced and repeatable findings with respect to changes in the autonomic nervous system with human aging is the progressive increase in basal muscle sympathetic nerve activity (MSNA) directed to skeletal muscle vascular beds. Although the mechanism(s) underlying this sustained age‐associated increase in MSNA are not completely understood, several changes in sympathetic α‐adrenergic function occur with age. In this review, the authors discuss how aging affects (1) α‐adrenergic control of skeletal muscle vascular tone under resting conditions and the differences that exist in this control of the upper and lower limbs (forearm vs leg circulation); (2) vasoconstrictor responsiveness to endogenous norepinephrine release, as well as the specific responsiveness of postjunctional α1‐ and α2‐adrenergic receptors; and (3) sympathetic α‐adrenergic control of muscle blood flow and vascular tone during exercise in humans. Further, they discuss how these changes in sympathetic α‐adrenergic control of skeletal muscle blood vessels have important physiological and clinical implications for the aging human.
Vasodilation and Vascular Control in Contracting Muscle of the Aging Human
Authors: PROCTOR DAVID N. , PARKER BETH A.
Published: May 2006

There is accumulating evidence in humans that the control of blood flow to dynamically contracting skeletal muscle is altered with normal aging. Despite some inconsistencies in the literature, most healthy older subject groups studied to date (∼55–75 years) exhibited attenuated leg blood flow responses to moderate intensity leg exercise in comparison to younger (∼20–30 years) controls. In most cases, older subjects also have higher arterial perfusion pressures at rest and at any submaximal workload than their younger counterparts, suggesting a heightened level of vasoconstriction in the legs that could result from structural and/or functional alterations within the arterial vasculature. The influence of age on vasodilator responsiveness in the contracting limbs of humans remains an open question, with reports of blunted, similar, and augmented increases in local vascular conductance during graded exercise in older vs. younger adults. Recent results from the authors' laboratory suggest that the ability of vascular smooth muscle in the legs to dilate in response to physiological and pharmacological stimuli is relatively well preserved with advancing age in men; however, a sex difference may exist in that older estrogen‐deficient women exhibit blunted leg vasodilator responses compared to younger women. Potential mechanisms underlying altered vascular control within the resistance vasculature of contracting muscles of older men and women remain to be determined, but could include (1) fewer, smaller, and/or stiffer vessels, (2) impaired endothelium‐dependent vasodilation, (3) augmented sympathetic vasoconstriction, (4) alterations in metabolic or myogenic control, and (5) reduced effectiveness of the skeletal muscle pump. Systematic research involving both humans and animal models will be necessary to fully elucidate the mechanisms underlying compromised muscle blood flow in old age.
Aging‐Induced Adaptations of Microvascular Reactivity
Authors: MULLER‐DELP JUDY M.
Published: May 2006

Control of blood flow to skeletal muscle depends on the vasomotor tone present in the resistance vasculature. Although muscle blood flow has been shown to decline with advancing age, our knowledge of how alterations of reactivity of the resistance vasculature contribute to reduced delivery or altered distribution of blood in the aged is limited. Recent work has demonstrated that age alters the reactivity of resistance arteries and arterioles from skeletal muscle, and that impairment of both vasodilator and vasoconstrictor responses occurs with advancing age. The alterations in cellular mechanisms that contribute to age‐related impairment of vasoreactive responses encompass both the vascular endothelium and smooth muscle, and differ in muscles of varying function and fiber type. Current research suggests that some degree of age‐induced endothelial dysfunction occurs in resistance arteries and arterioles from most skeletal muscle; however, the severity of endothelial impairment appears greater in resistance arteries and arterioles from highly oxidative locomotory muscles. Age‐related impairment of vasoconstrictor responses to metabolites and endogenous constrictor agents has also been documented. These age‐related reductions in vasoreactivity that occur in the skeletal muscle resistance vasculature may contribute to inadequate delivery or distribution of blood flow during exercise and ultimately be a factor in loss of exercise capacity that occurs with advancing age.
Challenges and strategies for Chinese university journals
Authors: Shuhua Wang , Hengjun Wang
Published: May 2006

Both the shift from a planned economy to a market economy system and the advent of the information era pose great challenges to Chinese university journals. The strategy of the Chinese government is to improve the system of university journals by encouraging mergers and partnerships with the aim of reducing the number of titles while improving their overall quality. The specific case of a geosciences journal demonstrates that Chinese university journals do have the ability to meet the challenges they face.
The International Consortium for the Advancement of Academic Publication — an idea whose time has come (finally!)
Authors: Sosteric Michael
Published: May 2006

The scholarly communication process is undergoing change and evolution. New initiatives and new approaches have been emerging for some time. This article outlines one Canadian initiative. The International Consortium for the Advancement of Academic Publication (ICAAP) provides a unique and low‐cost publication alternative for those seeking to move outside the commercial mainstream of scholarly journal publication. A brief history of ICAAP and an account of its theoretical and political rationale are provided
After the goldrush — the golden age of reference linking
Authors: Rapple Charlie
Published: May 2006

Reference linking is emerging as a key differentiator in the evaluation of online content. However, many publishers find themselves unfamiliar with the buzzwords, unsure of the technologies and overwhelmed by the concepts involved. This article provides a simple overview of the evolution of linking technology, reviews the current situation and suggests some requirements for continued development. The practical benefits to various groups within the information community, along with their potential responsiblities, are addressed.
The Red Jacket UTB: a model for co‐operative textbook publishing
Authors: Hühn Volker , Huter Michael
Published: May 2006

UTB is a joint paperback imprint of a number of medium‐sized German publishers. Its working is described, together with its financial arrangements.
Comparing print and online readership: matching perception to reality across media
Authors: Anderson Kent R.
Published: May 2006

Comparing the print and online readership is possible, and these comparisons can have dramatic effects on editorial and publishing perceptions. This article outlines the technique used at The New England Journal of Medicine, and discusses some of the ramifications.
Scoping the STM publishing market
Authors: Worlock Kate
Published: May 2006

An account is given of the EPS Market Monitor research programme in respect of scientific, technical and medical (STM) publishing. Its initial key findings are summarized.
IEE professional magazines and networks
Authors: Jackson Paul
Published: May 2006

The Institution of Electrical Engineers (IEE) has changed its approach to member publications over a two‐year period with an increased focus on understanding the needs of its broad membership and structuring its portfolio of magazines and websites to meet members' needs and complement the organization's research publications. The process of market research and product development is outlined in this article and the resulting combination of online and print products described. The products have been well received by IEE members and the wider community and have been recognized within the publishing industry with important awards in the business‐to‐business and not‐for‐profit sectors.
Building preservation functionality in a digital archive: the National Library of The Netherlands
Authors: Bellekom Chris
Published: May 2006

An increasing volume of information exists only in digital form. It can be scanned material; material actually created as digital publications; or material created as part of the day‐to‐day business of an organization. In The Netherlands, initiatives such as the ‘Memory of The Netherlands’ have emerged, creating a demand for good‐quality digital materials to support them. Many other digitization initiatives are constantly being announced. The digital form offers many advantages but presents challenges in respect of preservation and of changes in platforms and software.
A male sexually dimorphic trait provides antimicrobials to eggs in blenny fish
Authors: Giacomello Eva , Marchini Daniela , Rasotto Maria B
Published: May 2006

Predation and microbial infections are the major causes of natural mortality for early life stages of oviparous species. The parental traits reducing the effects of predation are rather well described, whereas antimicrobial mechanisms enhancing offspring survival are largely unexplored. In this paper, we report that a male sexually dimorphic trait, the anal glands, of the redlip blenny (
Ophioblennius atlanticus atlanticus
) and the peacock blenny (
Salaria pavo
), two fish species with paternal egg care, produce a mucus enriched with antimicrobial substances. Histological and histochemical analyses showed that the anal glands of these species are characterized by the massive presence of mucus-secreting cells. Anal gland extracts, from both the hydrophilic and the hydrophobic protein fraction, exhibited a lysozyme-like activity. Field observations demonstrated that redlip blenny males, while performing egg care, rub the anal region over the nest internal surface, probably facilitating the transfer of mucus to eggs. These results strongly indicate that this sexually dimorphic trait is involved in egg defence against microbial infections.
The emerging amphibian pathogen
Batrachochytrium dendrobatidis
globally infects introduced populations of the North American bullfrog,
Rana catesbeiana
Authors: Garner Trenton W.J , Perkins Matthew W , Govindarajulu Purnima , Seglie Daniele , Walker Susan , Cunningham Andrew A , Fisher Matthew C
Published: May 2006

Batrachochytrium dendrobatidis
is the chytridiomycete fungus which has been implicated in global amphibian declines and numerous species extinctions. Here, we show that introduced North American bullfrogs (
Rana catesbeiana
) consistently carry this emerging pathogenic fungus. We detected infections by this fungus on introduced bullfrogs from seven of eight countries using both PCR and microscopic techniques. Only native bullfrogs from eastern Canada and introduced bullfrogs from Japan showed no sign of infection. The bullfrog is the most commonly farmed amphibian, and escapes and subsequent establishment of feral populations regularly occur. These factors taken together with our study suggest that the global threat of
B. dendrobatidis
disease transmission posed by bullfrogs is significant.
Adaptive importance sampling for risk analysis of complex infrastructure systems
Authors: Dawson Richard , Hall Jim
Published: May 2006

Complex civil infrastructure systems are typically exposed to random loadings and have a large number of possible failure modes, which often exhibit spatially and temporally variable consequences. Monte Carlo (level III) reliability methods are attractive because of their flexibility and robustness, yet computational expense may be prohibitive, in which case variance reduction methods are required. In the importance sampling methodology presented here, the joint probability distribution of the loading variables is sampled according to the contribution that a given region in the joint space makes to risk, rather than according to probability of failure, which is the conventional importance sampling criterion in structural reliability analysis. Results from simulations are used to intermittently update the importance sampling density function based on the evaluations of the (initially unknown) risk function. The methodology is demonstrated on a propped cantilever beam system and then on a real coastal dike infrastructure system in the UK. The case study demonstrates that risk can be a complex function of loadings, the resistance and interactions of system components and the spatially variable damage associated with different modes of system failure. The methodology is applicable in general to Monte Carlo risk analysis of systems, but it is likely to be most beneficial where consequences of failure are a nonlinear function of load and where system simulation requires significant computational resources.
Sham nepotism as a result of intrinsic differences in brood viability in ants
Authors: Holzer Barbara , Kümmerli Rolf , Keller Laurent , Chapuisat Michel
Published: May 2006

In animal societies, cooperation for the common wealth and latent conflicts due to the selfish interests of individuals are in delicate balance. In many ant species, colonies contain multiple breeders and workers interact with nestmates of varying degrees of relatedness. Therefore, workers could increase their inclusive fitness by preferentially caring for their closest relatives, yet evidence for nepotism in insect societies remains scarce and controversial. We experimentally demonstrate that workers of the antFormica exsectado not discriminate between highly related and unrelated brood, but that brood viability differs between queens. We further show that differences in brood viability are sufficient to explain a relatedness pattern that has previously been interpreted as evidence for nepotism. Hence, our findings support the view that nepotism remains elusive in social insects and emphasize the need for further controlled experiments.
Harvesting can increase severity of wildlife disease epidemics
Authors: Choisy Marc , Rohani Pejman
Published: May 2006

Theoretical studies of wildlife population dynamics have proved insightful for sustainable management, where the principal aim is to maximize short-term yield, without risking population extinction. Surprisingly, infectious diseases have not been accounted for in harvest models, which is a major oversight because the consequences of parasites for host population dynamics are well-established. Here, we present a simple general model for a host species subject to density dependent reproduction and seasonal demography. We assume this host species is subject to infection by a strongly immunizing, directly transmitted pathogen. In this context, we show that the interaction between density dependent effects and harvesting can substantially increase both disease prevalence and the absolute number of infectious individuals. This effect clearly increases the risk of cross-species disease transmission into domestic and livestock populations. In addition, if the disease is associated with a risk of mortality, then the synergistic interaction between hunting and disease-induced death can increase the probability of host population extinction.
The origin, current diversity and future conservation of the modern lion (
Panthera leo
)
Authors: Barnett Ross , Yamaguchi Nobuyuki , Barnes Ian , Cooper Alan
Published: May 2006

Understanding the phylogeographic processes affecting endangered species is crucial both to interpreting their evolutionary history and to the establishment of conservation strategies. Lions provide a key opportunity to explore such processes; however, a lack of genetic diversity and shortage of suitable samples has until now hindered such investigation. We used mitochondrial control region DNA (mtDNA) sequences to investigate the phylogeographic history of modern lions, using samples from across their entire range. We find the sub-Saharan African lions are basal among modern lions, supporting a single African origin model of modern lion evolution, equivalent to the ‘recent African origin’ model of modern human evolution. We also find the greatest variety of mtDNA haplotypes in the centre of Africa, which may be due to the distribution of physical barriers and continental-scale habitat changes caused by Pleistocene glacial oscillations. Our results suggest that the modern lion may currently consist of three geographic populations on the basis of their recent evolutionary history: North African–Asian, southern African and middle African. Future conservation strategies should take these evolutionary subdivisions into consideration.
Insect odour perception: recognition of odour components by flower foraging moths
Authors: Cunningham John Paul , Moore Chris J , Zalucki Myron P , Cribb Bronwen W
Published: May 2006

Odours emitted by flowers are complex blends of volatile compounds. These odours are learnt by flower-visiting insect species, improving their recognition of rewarding flowers and thus foraging efficiency. We investigated the flexibility of floral odour learning by testing whether adult moths recognize single compounds common to flowers on which they forage. Dual choice preference tests onHelicoverpa armigeramoths allowed free flying moths to forage on one of three flower species;Argyranthemum frutescens(federation daisy),Cajanus cajan(pigeonpea) orNicotiana tabacum(tobacco). Results showed that, (i) a benzenoid (phenylacetaldehyde) and a monoterpene (linalool) were subsequently recognized after visits to flowers that emitted these volatile constituents, (ii) in a preference test, other monoterpenes in the flowers' odour did not affect the moths' ability to recognize the monoterpene linalool and (iii) relative preferences for two volatiles changed after foraging experience on a single flower species that emitted both volatiles. The importance of using free flying insects and real flowers to understand the mechanisms involved in floral odour learning in nature are discussed in the context of our findings.
Dynamics of recurrent viral infection
Authors: Yao W , Hertel L , Wahl L.M
Published: May 2006

In chronic viral infection, low levels of viral replication and infectious particle production are maintained over long periods, punctuated by brief bursts of high viral production and release. We apply well-established principles of modelling virus dynamics to the study of chronic viral infection, demonstrating that a model which incorporates the distinct contributions of cytotoxic T lymphocytes (CTLs) and antibodies exhibits long periods of quiescence followed by brief bursts of viral production. This suggests that for recurrent viral infections, no special mechanism or exogenous trigger is necessary to provoke an episode of reactivation; rather, the system may naturally cycle through recurrent episodes at intervals which can be many years long. We also find that exogenous factors which cause small fluctuations in the natural course of the infection can trigger a recurrent episode. Our model predicts that longer periods between recurrences are associated with more severe viral episodes. Four factors move the system towards less frequent, more severe episodes: decreased viral infectivity, decreased CTL efficacy, decreased memory T cell response and increased antibody efficacy.
Aggregation, defence and warning signals: the evolutionary relationship
Authors: Ruxton Graeme D , Sherratt Thomas N
Published: May 2006

In a seminal contribution, Fisher argued how distastefulness could incrementally evolve in a prey species that was distributed in family groups. Many defended prey species occur in aggregations, but did aggregation facilitate the evolution of defence as Fisher proposed or did the possession of a defence allow individuals to enjoy the benefits of group living? Contemporary theory suggests that it can work both ways: pre-existing defences can make the evolution of gregariousness easier, but gregariousness can also aid the evolution of defence and warning signals. Unfortunately, the key phylogenetic analyses to elucidate the ordering of events have been hampered by the relative rarity of gregarious species, which in itself indicates that aggregation is not a pre-requisite for defence. Like the underlying theory, experimental studies have not given a definitive answer to the relative timing of the evolution of defence and aggregation, except to demonstrate that both orderings are possible. Conspicuous signals are unlikely to have evolved in the absence of a defence and aggregated undefended prey are likely to be vulnerable to predation in the absence of satiation effects. It therefore seems most likely that defence generally preceded the evolution of both aggregation and signalling, but alternative routes may well be possible.
Herbivory: effects on plant abundance, distribution and population growth
Authors: Maron John L , Crone Elizabeth
Published: May 2006

Plants are attacked by many different consumers. A critical question is how often, and under what conditions, common reductions in growth, fecundity or even survival that occur due to herbivory translate to meaningful impacts on abundance, distribution or dynamics of plant populations. Here, we review population-level studies of the effects of consumers on plant dynamics and evaluate: (i) whether particular consumers have predictably more or less influence on plant abundance, (ii) whether particular plant life-history types are predictably more vulnerable to herbivory at the population level, (iii) whether the strength of plant–consumer interactions shifts predictably across environmental gradients and (iv) the role of consumers in influencing plant distributional limits. Existing studies demonstrate numerous examples of consumers limiting local plant abundance and distribution. We found larger effects of consumers on grassland than woodland forbs, stronger effects of herbivory in areas with high versus low disturbance, but no systematic or unambiguous differences in the impact of consumers based on plant life-history or herbivore feeding mode. However, our ability to evaluate these and other patterns is limited by the small (but growing) number of studies in this area. As an impetus for further study, we review strengths and challenges of population-level studies, such as interpreting net impacts of consumers in the presence of density dependence and seed bank dynamics.
The environment and evolution of the West Antarctic ice sheet: setting the stage
Authors: Bindschadler Robert
Published: May 2006

The West Antarctic ice sheet is the last ice sheet of the type cradled in a warm, marine geologic basin. Its perimeter stretches into the surrounding seas allowing warmer ocean waters to reach the undersides of its floating ice shelves and its relatively low surface elevation permits snow-carrying storms to extend well into its interior. This special environment has given rise to theories of impending collapse and for the past quarter-century has challenged researchers who seek a quantitative prediction of its future behaviour and the corresponding effect on sea level. Observations confirm changes on a variety of time scales from the quaternary to less than a minute. The dynamics of the ice sheet involve the complex interaction of ice that is warm at its base and cold along the margins of ice streams; subglacial till that is composed of a combination of marine sediment and eroded sedimentary rocks; and water that moves primarily between the ice and bed, but whose flow direction can differ from the direction of ice motion. The pressure of the water system is often sufficient to float the ice sheet locally and small changes in the amount of water in the till can cause it to rapidly switch from very weak to very stiff.