bluuebunny/crossref_metadata_2025 huggingface dataset:
Quadrimolecular recombination kinetics of photogenerated charge carriers in the composites of regioregular polythiophene derivatives and soluble fullerene
Authors: Tanaka Hisaaki , Yokoi Yuki , Hasegawa Naoki , Kuroda Shin-ichi , Iijima Takayuki , Sato Takao , Yamamoto Takakazu
Published: April 2010

Light-induced electron spin resonance (LESR) measurements have been performed on the composites of regioregular polythiophene derivatives and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in order to study the recombination kinetics of photogenerated charge carriers. We adopt two regioregular polymers with different side chains; head-to-tail poly(3-hexylthiophene) (RR-P3HT) and head-to-head poly(3-dodecynylthiophene-2,5-diyl) [HH-P3(C≡CDec)Th]. In both systems, two LESR signals due to positive polarons on the polymer (g∼2.002) and fullerene radical anions (g∼2.000) have been observed. Quadrimolecular recombination (QR) kinetics, previously reported for RR-P3HT/C60 composites, where two positive polarons and two radical anions recombine simultaneously, has been confirmed in both systems by the observation of Iex0.25 dependence of the LESR intensity on the excitation light intensity (Iex) and the decay curve of the LESR intensity. This process implies the formation of doubly-charged states such as bipolarons or polaron pairs on the polymer to attract two radical anions. Temperature dependence of the QR rate constant, γ, in both systems has exhibited a crossover of the transport mechanism from low temperature tunneling to high temperature hopping process, as in the case of RR-P3HT/C60 composites. In the RR-P3HT/PCBM composites, γ has exhibited marked dependencies on the PCBM concentration or annealing, which may be related to the change of the crystallinity of the phase-separated polymer and fullerene domains as well as their interface structures, affecting the carrier mobilities or the trap states at the interface. Associated change of the molecular orientation of RR-P3HT crystalline domains with the lamellar structure has been further confirmed from the anisotropic LESR signals of the cast films on the substrates, exhibiting a qualitative agreement with the reported x-ray or optical analyses. In the HH-P3(C≡CDec)Th/PCBM composite, γ has been smaller than those in the RR-P3HT/PCBM composites, reflecting the difference of local structures due to the different molecular structure. Furthermore, the hyperfine-determined LESR linewidth of the positive polaron has exhibited a smaller value than those in the RR-P3HT composite, implying the larger extension of the polaron wave function on the polymer chain, which is consistent with the highly coplanar structure of this polymer.
Global two-fluid turbulence simulations of L-H transitions and edge localized mode dynamics in the COMPASS-D tokamak
Authors: Thyagaraja A. , Valovič M. , Knight P. J.
Published: April 2010

It is shown that the transition from L-mode to H-mode regimes in tokamaks can be reproduced using a two-fluid, fully electromagnetic, plasma model when a suitable particle sink is added at the edge. Such a model is implemented in the CUTIE code [A. Thyagaraja et al., Eur. J. Mech. B/Fluids 23, 475 (2004)] and is illustrated on plasma parameters that mimic those in the COMPASS-D tokamak with electron cyclotron resonance heating [Fielding et al., Plasma Phys. Contr. Fusion 42, A191 (2000)]. In particular, it is shown that holding the heating power, current, and magnetic field constant and increasing the fuelling rate to raise the plasma density leads spontaneously to the formation of an edge transport barrier (ETB) which occurs going from low to higher density experimentally. In the following quiescent period in which the stored energy of the plasma rises linearly with time, a dynamical transition occurs in the simulation with the appearance of features resembling strong edge localized modes. The simulation qualitatively reproduces many features observed in the experiment. Its relative robustness suggests that some, at least of the observed characteristics of ETBs and L-H transitions, can be captured in the global electromagnetic turbulence model.
The effect of grain boundaries on the domain wall dynamics in Pr1−xAgxMnO3 manganites
Authors: Ahmadvand Hossein , Salamati Hadi , Kameli Parviz
Published: April 2010

We performed detailed ac susceptibility measurements on Pr1−xAgxMnO3 (x=0.15,0.20) manganites and observed unusual and interesting features, which are associated with the domain walls and the effects of grain-boundaries on their movements. It is shown that the ac field, frequency, temperature, thermal cycling, and grain coupling significantly influence the real and especially imaginary parts of the ac susceptibility. We argue that the cooperative depinning of the domain walls from the grain-boundaries accompanying with a large distance movements of the walls leads to the appearance of an anomaly at low temperatures. The anomaly is observed above a threshold ac field and depends on the intergrain coupling. The results show that in the powdered form of bulk samples, the anomaly disappears and the ac field dependence of the χ′ and χ″ suppresses. Below the anomaly temperature, significant and unusual thermal hysteresis occurs in the real and especially imaginary parts of the ac susceptibility. Thermal hysteresis depends on the thermal cycling and indicates thermally irreversible wall pinning and depinning. The susceptibility is practically frequency-independent in the temperature range of thermal hysteresis, i.e., below the anomaly. The frequency dependence of the ac susceptibility between the anomaly temperature and the transition temperature is discussed by considering the temperature dependence of the relaxation process of the domain walls.
Spontaneous formation of polyglutamine nanotubes with molecular dynamics simulations
Authors: Laghaei Rozita , Mousseau Normand
Published: April 2010

Expansion of polyglutamine (polyQ) beyond the pathogenic threshold (35–40 Gln) is associated with several neurodegenerative diseases including Huntington’s disease, several forms of spinocerebellar ataxias and spinobulbar muscular atrophy. To determine the structure of polyglutamine aggregates we perform replica-exchange molecular dynamics simulations coupled with the optimized potential for effective peptide forcefield. Using a range of temperatures from 250 to 700 K, we study the aggregation kinetics of the polyglutamine monomer and dimer with chain lengths from 30 to 50 residues. All monomers show a similar structural change at the same temperature from α-helical structure to random coil, without indication of any significant β-strand. For dimers, by contrast, starting from random structures, we observe spontaneous formation of antiparallel β-sheets and triangular and circular β-helical structures for polyglutamine with 40 residues in a 400 ns 50 temperature replica-exchange molecular dynamics simulation (total integrated time 20 μs). This ∼32 Å diameter structure reorganizes further into a tight antiparallel double-stranded ∼22 Å nanotube with 22 residues per turn close to Perutz’ model for amyloid fibers as water-filled nanotubes. This diversity of structures suggests the existence of polymorphism for polyglutamine with possibly different pathways leading to the formation of toxic oligomers and to fibrils.
Nonlinear oscillations in a cold dissipative plasma
Authors: Verma Prabal Singh , Soni J. K. , Sengupta S. , Kaw P. K.
Published: April 2010

Recently, it has been shown that when viscosity and resistivity is included in the cold plasma model, nonlinear plasma oscillations exhibit a new nonlinear effect in the form of splitting of density peak [Infeld et al., Phys. Rev. Lett. 102, 145005 (2009)]. Infeld et al. have analytically derived this result for a specific model of viscosity as 4/3νe=ν[n0/ne(x,t)]. In a realistic case however, electron viscosity has a relatively weak dependence on density through Coulomb logarithm. In this work, first Infeld’s result is numerically extended for the more realistic case where electron viscosity is chosen to be independent of density and second an alternative electron dissipative mechanism is studied by substituting viscosity with hyperviscosity. In both cases, results are found to be qualitatively similar to Infeld et al.
Vibrational absorption spectra calculated from vibrational configuration interaction response theory using the Lanczos method
Authors: Seidler Peter , Hansen Mikkel Bo , Győrffy Werner , Toffoli Daniele , Christiansen Ove
Published: April 2010

The Lanczos method is used to efficiently obtain the linear vibrational response function for all frequencies in an arbitrary interval. The complex part of the response function gives the absorption spectrum which can subsequently be analyzed. The method provides a way to obtain global information on the absorption spectrum without explicitly converging all vibrational eigenstates of the system. The tridiagonal Lanczos matrix used to obtain the response functions needs only be constructed once for each operator. Example calculations on cyclopropene and uracil are presented.
The multiscale coarse-graining method. V. Isothermal-isobaric ensemble
Authors: Das Avisek , Andersen Hans C.
Published: April 2010

The multiscale coarse-graining (MS-CG) method is a method for determining the effective potential energy function for a coarse-grained (CG) model of a system using the data obtained from molecular dynamics simulation of the corresponding atomically detailed model. The MS-CG method, as originally formulated for systems at constant volume, has previously been given a rigorous statistical mechanical basis for the canonical ensemble. Here, we propose and test a version of the MS-CG method suitable for the isothermal-isobaric ensemble. The method shows how to construct an effective potential energy function for a CG system that generates the correct volume fluctuations as well as correct distribution functions in the configuration space of the CG sites. The formulation of the method requires introduction of an explicitly volume dependent term in the potential energy function of the CG system. The theory is applicable to simulations with isotropic volume fluctuations and cases where both the atomistic and CG models do not have any intramolecular constraints, but it is straightforward to extend the theory to more general cases. The present theory deals with systems that have short ranged interactions. (The extension to Coulombic forces using Ewald methods requires additional considerations.) We test the theory for constant pressure MS-CG simulations of a simple model of a solution. We show that both the volume dependent and the coordinate dependent parts of the potential are transferable to larger systems than the one used to obtain these potentials.
Reactions of molybdenum and tungsten atoms with nitrous oxide in excess argon: A combined matrix infrared spectroscopic and theoretical study
Authors: Jiang Ling , Xu Qiang
Published: April 2010

Reactions of laser-ablated Mo and W atoms with the N2O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. In the reaction of the N2O molecule with the Mo atom, the absorptions at 1960.3 and 934.4 cm−1 are assigned to the N–N and Mo–O stretching vibrations of the OMoNN complex, respectively. An analogous OWNN complex has also been observed in the W+N2O reaction. Infrared spectroscopy also provides evidence for the formation of the OW(NN)2 complexes. Density functional theory calculations have been performed on the products. Overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Furthermore, a plausible reaction mechanism for the formation of these products has been proposed.
Quantum effects of hydrogen atoms on the dynamical rearrangement of hydrogen-bond networks in liquid water
Authors: Hyeon-Deuk Kim , Ando Koji
Published: April 2010

Quantum effects such as zero-point energy and delocalization of wave packets (WPs) representing water hydrogen atoms are essential to understand anomalous energetics and dynamics in water. Since quantum calculations of many-body dynamics are highly complicated, no one has yet directly viewed the quantum WP dynamics of hydrogen atoms in liquid water. Our semiquantum molecular dynamics simulation made it possible to observe the hydrogen WP dynamics in liquid water. We demonstrate that the microscopic WP dynamics are closely correlated with and actually play key roles in the dynamical rearrangement in the hydrogen-bond network (HBN) of bulk water. We found the quantum effects of hydrogen atoms on liquid water dynamics such as the rearrangement of HBN and the concomitant fluctuation and relaxation. Our results provide new physical insights on HBN dynamics in water whose significance is not limited to pure liquid dynamics but also a greater understanding of chemical and biological reactions in liquid water.
Infrared study on hydrogen chloride complexed with allene
Authors: Chevalier Michele , Broquier Michel , Brenner Valerie
Published: April 2010

The first rotationally resolved observation of the infrared (IR) spectrum of the molecular complex C3H4–HCl in gas phase is reported. New IR spectra have been recorded at high resolution by means of a slit jet. Rotational constants and vibrational frequencies have been obtained from these spectra. These data are presented and compared with high level ab initio calculations (CCSD(T)/cc-pVTZ). The results obtained in this study are compared with those on acetylene and ethene-HCl complexes. We observe a broadening of the lines interpreted as a decrease of the lifetime of the excited vibrational state with the size of the partner of complexation and also a correlation between the vibrational shift of the H–Cl stretching mode and the proton affinity of the acceptor molecule.
Structures of Aln, its anions and cations up to n=34: A theoretical investigation
Authors: Drebov Nedko , Ahlrichs Reinhart
Published: April 2010

A systematic density functional study has been performed for neutral and singly charged clusters of aluminum with up to 34 atoms. A thorough search for global minimum structures has been carried out for Aln employing genetic algorithm and basin-hopping procedures. For Aln this confirms results of previous investigations up to n=22; new global minima have been located for n=23–31, 33. Structures for singly charged cations and anions have been obtained by reoptimization of the pool of 40 low-energy structures of the neutral clusters. The global minima of charged and neutral clusters are always low-spin states with the possible exception of a triplet state of Al28, which is isoenergetic with a singlet. The cluster structures are mostly quite irregular and do not resemble fractions of the fcc bulk phase. High symmetries are found only for the global minimum of Al23 and the triplet state of Al28.
Recrystallization of picosecond laser-melted ZnO nanoparticles in a liquid: A molecular dynamics study
Authors: Hu Ming , Poulikakos Dimos , Grigoropoulos Costas P. , Pan Heng
Published: April 2010

We employ molecular dynamics simulation to investigate the rapid melting and subsequent cooling process of zinc oxide (ZnO) nanoparticles in liquid tetradecane upon picosecond laser heating. The coalescence of two neighboring melted nanoparticles into a larger particle and the recrystallization of the latter upon cooling were studied. Severe undercooling and distinct recalescence occurs and the structure of the nanoparticle transforms from its initial hexagonal wurtzite structure to a face-centered cubic structure after recrystallization. By analyzing the heating/cooling process, we demonstrated that the particle size has a large impact on the interfacial thermal conductance between the nanoparticle and the surrounding liquid, as well as on the solidification initiation and solidification completion temperatures. We also investigated the thermal behavior of the surrounding liquid layer at the neighborhood of the particle surface. Boiling of the liquid layer was found in the case of extremely high heat fluxes.
Crystallization and high temperature shape memory behavior of sputter-deposited NiMnCoIn thin films
Authors: Rios S. , Karaman I. , Zhang X.
Published: April 2010

Amorphous Ni50Mn38Co6In6 films of 20 μm in thickness are fabricated using dc magnetron sputtering technique. Ex situ annealing studies demonstrate the crystallization at elevated temperature, and the retention of L10 martensite at room temperature. In situ annealing inside a transmission electron microscope reveals the crystallization process as well as the transformation to B2 austenite at elevated temperatures. Differential scanning calorimetry studies show the crystallization activation energy of ∼239 kJ/mol, a reversible martensitic phase transformation temperature of ∼350 °C, and a hysteresis of ∼75 °C.
Quantum cascade detectors for very long wave infrared detection
Authors: Buffaz A. , Carras M. , Doyennette L. , Nedelcu A. , Marcadet X. , Berger V.
Published: April 2010

A high responsivity GaAs/AlGaAs quantum cascade detector is demonstrated at a wavelength of 15 μm. The quantum design is optimized for negative bias operation, so that the capture of photoexcited electrons back to the fundamental level is minimized. The detectivity of the detector presented here reaches 1.1×1012 Jones at 25 K for an applied bias of −0.6 V.
Mechanically flexible thin film transistors and logic gates on plastic substrates by use of single-crystal silicon wires from bulk wafers
Authors: Lee Seoung-Ki , Jang Houk , Hasan Musarrat , Koo Jae Bon , Ahn Jong-Hyun
Published: April 2010

This letter presents a method to fabricate single-crystal silicon wires from (100) wafer and print them onto thin plastic substrates for high-performance, mechanically flexible, thin-film transistors by dry transfer printing. Electrical measurements indicate excellent performance, with a per ribbon mobility of 580 cm2/V s, subthreshold voltage of 100 mV/dec and on/off ratios >107. The inverter shows good performance and voltage gains of ∼2.5 at 3 V supply voltage. In addition, these devices revealed stable performance at bending configuration, an important feature essential for flexible electronic systems.
Brownian motion induced dynamic near-field interaction between quantum dots and plasmonic nanoparticles in aqueous medium
Authors: Xu Lina , Lee Bong Jae , Hanson Willard L. , Han Bumsoo
Published: April 2010

Metal-enhanced fluorescence has been studied over the past three decades in order to improve fluorescence sensing and imaging techniques in microfluidics and medical diagnostics. However, most of previous studies were performed while precisely maintaining the distance between fluorophore and plasmonic nanoparticles. In the present study, we investigate the enhanced fluorescence from quantum dots (QDs) that are mixed with plasmonic nanoparticles, such as gold nanoshell (GNS), in the aqueous medium without confining the interparticle distance. Although the near-field interaction could not occur based on the estimated interparticle distance according to particle concentrations, the experimental results indicate that the QD fluorescence can be greatly enhanced. A Monte Carlo simulation revealed that there exists considerable probability that QDs can reach the near-field region of GNS due to the thermally induced Brownian motion.
Delay of the excited state lasing of 1310 nm InAs/GaAs quantum dot lasers by facet coating
Authors: Cao Yu-Lian , Yang Tao , Xu Peng-Fei , Ji Hai-Ming , Gu Yong-Xian , Wang Xiao-Dong , Wang Qing , Ma Wen-Quan , Chen Liang-Hui
Published: April 2010

In this letter, we present a facet coating design to delay the excited state (ES) lasing for 1310 nm InAs/GaAs quantum dot lasers. The key point of our design is to ensure that the mirror loss of ES is larger than that of the ground state by decreasing the reflectivity of the ES. In the facet coating design, the central wavelength is at 1480 nm, and the high- and low-index materials are Ta2O5 and SiO2, respectively. Compared with the traditional Si/SiO2 facet coating with a central wavelength of 1310 nm, we have found that with the optimal design the turning temperature of the ES lasing has been delayed from 90 to 100 °C for the laser diodes with cavity length of 1.2 mm. Furthermore, the characteristic temperature (T0) of the laser diodes is also improved.
Kernel Densities and Mixed Functionality in a Multicentred Urban Region
Authors: Adolphson Marcus
Published: April 2010

Interurban-level focus during the last decade has shifted from the compact city towards a polycentric urban framework. The ability to define consistent urban structures and also link them with sustainability goals has been hindered by inconsistent evaluation methods for density and mixed functionality in a polycentric framework. The aim of this research is to test and combine various methods from these perspectives in order to define more reliable and consistent descriptions of urban structures. The methods used are spatial-density modelling using kernel convolution, a polycentric density estimation, and methods depicting mixed functionality and the association between density and mixed functionality. The empirical findings relate to planning goals at both national and international level. The study region is the municipality of Strängnäs, within the Stockholm City Region since 1997. Results from the analysis reveal urban development towards further segregated land use and sprawl, as well as a decreasing link with a polycentric urban scheme. The methods developed for depicting urban form could be useful tools in the planning process and may reinforce the possibility for analysing links between urban form and sustainability aspects. This improved knowledge in turn could contribute towards formulating future planning principles.
Factors Explaining the Regulatory Activity of the Spanish Autonomous Communities (1989–2001)
Authors: López-Laborda Julio , Vallés-Giménez Jaime
Published: April 2010

The aim of this paper is to explain the regulatory activity of the Autonomous Communities (Spanish regional governments) between 1989 and 2001, employing the methodological framework provided by the economic theory of regulation. To this end, a ‘model of regulatory demand’ and a ‘model of regulatory supply’ are specified and estimated for the seventeen Autonomous Communities over this period. The results of these estimations show that for the fields of institutional and economic regulation the behaviour of the Autonomous Communities between 1989 and 2001 may be explained by a complementary set of supply and demand factors: financial, political, and institutional factors on the supply side, and the heterogeneity of preferences and the role of interest groups on the demand side. However, with respect to total regulation and social regulation, supply factors outweigh demand factors in the explanation of regional regulatory production.
Organising Intergovernmental Relations: Insights from Cultural Theory
Authors: Entwistle Tom
Published: April 2010

That England has a hierarchical relationship between central and local government is a staple of postwar constitutional commentary. By using cultural theory's five modes of organisation—namely, hierarchies, markets, networks, autonomism, and fatalism—to analyse 109 interviews conducted with politicians and managers in nine local authorities I question the adequacy of this characterisation. While many of those interviewed did indeed describe the operation of a very hierarchical system, others pointed to the excesses of network and market forms of organisation. Others, still, seemed to think that local authorities enjoyed altogether too much autonomy in certain areas.
Coupling and cooperativity in voltage activation of a limited-state BK channel gating in saturating Ca2+
Authors: Shelley Christopher , Niu Xiaowei , Geng Yanyan , Magleby Karl L.
Published: April 2010

Voltage-dependent gating mechanisms of large conductance Ca2+ and voltage-activated (BK) channels were investigated using two-dimensional maximum likelihood analysis of single-channel open and closed intervals. To obtain sufficient data at negative as well as positive voltages, single-channel currents were recorded at saturating Ca2+ from BK channels mutated to remove the RCK1 Ca2+ and Mg2+ sensors. The saturating Ca2+ acting on the Ca2+ bowl sensors of the resulting BKB channels increased channel activity while driving the gating into a reduced number of states, simplifying the model. Five highly constrained idealized gating mechanisms based on extensions of the Monod-Wyman-Changeux model for allosteric proteins were examined. A 10-state model without coupling between the voltage sensors and the opening/closing transitions partially described the voltage dependence of Po but not the single-channel kinetics. With allowed coupling, the model gave improved descriptions of Po and approximated the single-channel kinetics; each activated voltage sensor increased the opening rate approximately an additional 23-fold while having little effect on the closing rate. Allowing cooperativity among voltage sensors further improved the description of the data: each activated voltage sensor increased the activation rate of the remaining voltage sensors approximately fourfold, with little effect on the deactivation rate. The coupling factor was decreased in models with cooperativity from ∼23 to ∼18. Whether the apparent cooperativity among voltage sensors arises from imposing highly idealized models or from actual cooperativity will require additional studies to resolve. For both cooperative and noncooperative models, allowing transitions to five additional brief (flicker) closed states further improved the description of the data. These observations show that the voltage-dependent single-channel kinetics of BKB channels can be approximated by highly idealized allosteric models in which voltage sensor movement increases Po mainly through an increase in channel opening rates, with limited effects on closing rates.
Cyclic AMP potentiates Ca2+-dependent exocytosis in pancreatic duct epithelial cells
Authors: Jung Seung-Ryoung , Hille Bertil , Nguyen Toan D. , Koh Duk-Su
Published: April 2010

Exocytosis is evoked by intracellular signals, including Ca2+ and protein kinases. We determined how such signals interact to promote exocytosis in exocrine pancreatic duct epithelial cells (PDECs). Exocytosis, detected using carbon-fiber microamperometry, was stimulated by [Ca2+]i increases induced either through Ca2+ influx using ionomycin or by activation of P2Y2 or protease-activated receptor 2 receptors. In each case, the exocytosis was strongly potentiated when cyclic AMP (cAMP) was elevated either by activating adenylyl cyclase with forskolin or by activating the endogenous vasoactive intestinal peptide receptor. This potentiation was completely inhibited by H-89 and partially blocked by Rp-8-Br-cAMPS, inhibitors of protein kinase A. Optical monitoring of fluorescently labeled secretory granules showed slow migration toward the plasma membrane during Ca2+ elevations. Neither this Ca2+-dependent granule movement nor the number of granules found near the plasma membrane were detectably changed by raising cAMP, suggesting that cAMP potentiates Ca2+-dependent exocytosis at a later stage. A kinetic model was made of the exocytosis stimulated by UTP, trypsin, and Ca2+ ionophores with and without cAMP increase. In the model, without a cAMP rise, receptor activation stimulates exocytosis both by Ca2+ elevation and by the action of another messenger(s). With cAMP elevation the docking/priming step for secretory granules was accelerated, augmenting the releasable granule pool size, and the Ca2+ sensitivity of the final fusion step was increased, augmenting the rate of exocytosis. Presumably both cAMP actions require cAMP-dependent phosphorylation of target proteins. cAMP-dependent potentiation of Ca2+-induced exocytosis has physiological implications for mucin secretion and, possibly, for membrane protein insertion in the pancreatic duct. In addition, mechanisms underlying this potentiation of slow exocytosis may also exist in other cell systems.
Allosteric mechanism of Ca2+ activation and H+-inhibited gating of the MthK K+ channel
Authors: Pau Victor P.T. , Abarca-Heidemann Karin , Rothberg Brad S.
Published: April 2010

MthK is a Ca2+-gated K+ channel whose activity is inhibited by cytoplasmic H+. To determine possible mechanisms underlying the channel’s proton sensitivity and the relation between H+ inhibition and Ca2+-dependent gating, we recorded current through MthK channels incorporated into planar lipid bilayers. Each bilayer recording was obtained at up to six different [Ca2+] (ranging from nominally 0 to 30 mM) at a given [H+], in which the solutions bathing the cytoplasmic side of the channels were changed via a perfusion system to ensure complete solution exchanges. We observed a steep relation between [Ca2+] and open probability (Po), with a mean Hill coefficient (nH) of 9.9 ± 0.9. Neither the maximal Po (0.93 ± 0.005) nor nH changed significantly as a function of [H+] over pH ranging from 6.5 to 9.0. In addition, MthK channel activation in the nominal absence of Ca2+ was not H+ sensitive over pH ranging from 7.3 to 9.0. However, increasing [H+] raised the EC50 for Ca2+ activation by ∼4.7-fold per tenfold increase in [H+], displaying a linear relation between log(EC50) and log([H+]) (i.e., pH) over pH ranging from 6.5 to 9.0. Collectively, these results suggest that H+ binding does not directly modulate either the channel’s closed–open equilibrium or the allosteric coupling between Ca2+ binding and channel opening. We can account for the Ca2+ activation and proton sensitivity of MthK gating quantitatively by assuming that Ca2+ allosterically activates MthK, whereas H+ opposes activation by destabilizing the binding of Ca2+.
Glycine311, a determinant of paxilline block in BK channels: a novel bend in the BK S6 helix
Authors: Zhou Yu , Tang Qiong-Yao , Xia Xiao-Ming , Lingle Christopher J.
Published: April 2010

The tremorogenic fungal metabolite, paxilline, is widely used as a potent and relatively specific blocker of Ca2+- and voltage-activated Slo1 (or BK) K+ channels. The pH-regulated Slo3 K+ channel, a Slo1 homologue, is resistant to blockade by paxilline. Taking advantage of the marked differences in paxilline sensitivity and the homology between subunits, we have examined the paxilline sensitivity of a set of chimeric Slo1/Slo3 subunits. Paxilline sensitivity is associated with elements of the S5–P loop–S6 module of the Slo1 channel. Replacement of the Slo1 S5 segment or the second half of the P loop results in modest changes in paxilline sensitivity. Replacing the Slo1 S6 segment with the Slo3 sequence abolishes paxilline sensitivity. An increase in paxilline affinity and changes in block kinetics also result from replacing the first part of the Slo1 P loop, the so-called turret, with Slo3 sequence. The Slo1 and Slo3 S6 segments differ at 10 residues. Slo1-G311S was found to markedly reduce paxilline block. In constructs with a Slo3 S6 segment, S300G restored paxilline block, but most effectively when paired with a Slo1 P loop. Other S6 residues differing between Slo1 and Slo3 had little influence on paxilline block. The involvement of Slo1 G311 in paxilline sensitivity suggests that paxilline may occupy a position within the central cavity or access its blocking position through the central cavity. To explain the differences in paxilline sensitivity between Slo1 and Slo3, we propose that the G311/S300 position in Slo1 and Slo3 underlies a structural difference between subunits in the bend of S6, which influences the occupancy by paxilline.
Ability of Healthcare Workers to Recall Previous Receipt of Tetanus-Containing Vaccination
Authors: Fontanilla Jose-Mario , Kirkland Kathryn B. , Cotter J. Gavin , Talbot Elizabeth A.
Published: April 2010

Vaccination of healthcare workers (HCWs) is an important strategy in the control and prevention of hospital outbreaks. The decision to vaccinate is often based on self-report of vaccination status. Self-report of previous receipt of tetanus-diphtheria or tetanus toxin vaccination was validated using an electronic medical record. Results showed that HCWs' self-report is reliable during a vaccination campaign.
Age-structure-dependent recruitment: a meta-analysis applied to Northeast Atlantic fish stocks
Authors: Brunel Thomas
Published: April 2010

Brunel, T. 2010. Age-structure-dependent recruitment: a meta-analysis applied to Northeast Atlantic fish stocks. – ICES Journal of Marine Science, 67: 1921–1930. Exploitation alters the age structure of fish stocks. Several stock-specific studies have suggested that changes in the age structure might have consequences for subsequent recruitment, but the evidence is not universal. To investigate how common such effects are among 39 Northeast Atlantic fish stocks, relationships were tested between age structure (spawner mean age, age diversity, and proportion of recruit spawners) and recruitment (number of recruits, sensitivity to environment, and recruitment variability). Significant correlations in the expected direction were observed for a few stocks, but not for the majority; significant correlations in the opposite direction were also found. Meta-analyses combining the stock-level tests revealed that none of the effects were significant overall. However, effects were significant for some species (cod, haddock, and plaice) and indices. The low variability in the age structure might explain the absence of significant effects for individual stocks. Other reasons could be the absence of a biological basis (reproductive characteristics not dependent on age) or the stronger influence of environmental variability than of age structure on recruitment.
Lessons learned from stock collapse and recovery of North Sea herring: a review
Authors: Dickey-Collas Mark , Nash Richard D. M. , Brunel Thomas , van Damme Cindy J. G. , Marshall C. Tara , Payne Mark R. , Corten Ad , Geffen Audrey J. , Peck Myron A. , Hatfield Emma M. C. , Hintzen Niels T. , Enberg Katja , Kell Laurence T. , Simmonds E. John
Published: April 2010

Dickey-Collas, M., Nash, R. D. M., Brunel, T., van Damme, C. J. G., Marshall, C. T., Payne, M. R., Corten, A., Geffen, A. J., Peck, M. A., Hatfield, E. M. C., Hintzen, N. T., Enberg, K., Kell, L. T., and Simmonds, E. J. 2010. Lessons learned from stock collapse and recovery of North Sea herring: a review. – ICES Journal of Marine Science, 67: 1875–1886. The collapse and recovery of North Sea herring in the latter half of the 20th century had both ecological and economic consequences. We review the effect of the collapse and investigate whether the increased understanding about the biology, ecology, and stock dynamics gained in the past three decades can aid management to prevent further collapses and improve projections of recovery. Recruitment adds the most uncertainty to estimates of future yield and the potential to reach biomass reference points within a specified time-frame. Stock–recruitment relationships must be viewed as being fluid and dependent on ecosystem change. Likewise, predation mortality changes over time. Management aimed at maximum sustainable yield (MSY) fishing mortality targets implies interannual variation in TACs, and variability in supply is therefore unavoidable. Harvest control rules, when adhered to, aid management greatly. We advocate that well-founded science can substantially contribute to management through improved confidence and increased transparency. At present, we cannot predict the effects of collapse or recovery of a single stock on the ecosystem as a whole. Moreover, as managers try to reconcile commitments to single-species MSY targets with the ecosystem-based approach, they must consider the appropriate management objectives for the North Sea ecosystem as a whole.
An ecological study of two shallow, equatorial lakes: Lake Mburo and Lake Kachera, Uganda
Authors: Nyakoojo Clement , Byarujali Stephen M.
Published: April 2010

Lake Mburo and Lake Kachera are shallow, eutrophic lakes in mid‐western Uganda. Lake Mburo recorded higher values of Secchi and eutrophic depths and lower extinction coefficient (k) values. The lakes showed a ‘red shift’ phenomenon in maximum light transmission. The average values of electrical conductivity in Lake Mburo and Lake Kachera were 136 and 244 μS cm−1, respectively. The pH values indicated high photosynthetic activity. Dissolved oxygen concentration averaged 6.9 and 7.8 mg l−1 in Lake Mburo and Lake Kachera, respectively. The lakes had high total nitrogen (TN) : total phosphorus (TP) ratios averaging 200 and 280 in Lake Mburo and Lake Kachera, respectively. The lakes are dominated by cyanobacterial blooms that reduce light penetration to less than 1 m. Lake Mburo had a lower algal biomass than Lake Kachera. Chlorophyll a concentrations correlated positively (r = 0.73, P < 0.05) with the extinction coefficient in Lake Mburo but not in Lake Kachera. The correlations between chlorophyll a and TN and TP were also high. Both lakes recorded high primary productivity, Lake Mburo showing higher values. The study highlighted the need to investigate the organism–community interrelationships in the two water bodies.
Contact urticaria to cosmetic and industrial dyes
Authors: Davari P. , Maibach H. I.
Published: April 2010

Contact urticaria (CU) defines the weal-and-flare reaction that occurs after external cutaneous contact with a causative agent. These reactions often cause discomfort for patients, affect their quality of life, and in severe cases may be life-threatening. Some dyes are known to be urticariogens. Many people have daily exposure to these urticariogens, because of the widespread use of dyes, for example in textiles, cosmetics and foods. We reviewed industrial and cosmetic dyes such as hair dyes, basic blue 99 dye, patent blue dyes, henna, red dyes, curcumin and reactive dyes, which can potentially cause CU. Overall, the reported cases of CU lacked appropriate controls. Hair-dye constituents such as preservatives and intensifiers may play an important role as causative agents of CU. We recommend appropriate protection guidelines to reduce the incidence of CU in high-risk groups such as hairdressers, dye-factory workers or workers in dye-related industries.
Arboreal substrates influence foraging in tropical ants
Authors: CLAY NATALIE A. , BAUER MONICA , SOLIS MANUEL , YANOVIAK STEPHEN P.
Published: April 2010

1. Physically complex substrates impart significant costs on cursorial central‐place foragers in terms of time spent outside the nest and total distance travelled. Ants foraging in trees navigate varied surfaces to access patchy resources, thus providing an appropriate model system for examining interactions between foraging efficiency and substrates.

2. We expected that the speed of recruitment, body size distribution and species richness of foraging arboreal ants would differ predictably among common substrate types occurring on tropical tree trunks. We measured changes in ant abundance and species composition over time at baits placed on bare tree bark, moss‐covered bark, and vine‐like vegetation appressed to bark. We also measured average body size and body size frequency on the three substrate types. Ants discovered baits sooner and accumulated at baits relatively faster when using vine substrates as the primary foraging trail. Average body size was smaller on vine substrates than on bark. Experimental removal of vine and moss substrates nullified these differences. Contrary to our predictions, species richness and body size distributions did not differ among the three substrate types, due in part to the frequent presence of a few common ground‐nesting species at baits on bare bark.

3. Our results collectively indicate that linear substrates facilitate access of foraging ants to patchy resources. Ant use of vine‐like substrates appears to be opportunistic; vine use is not confined to certain species nor constrained by body size.
Negative priming effect on mineralization in a soil free of vegetation for 80 years
Authors: Guenet B. , Leloup J. , Raynaud X. , Bardoux G. , Abbadie L.
Published: April 2010

The priming effect (PE) is a complex process corresponding to a modification of mineralization rates of soil organic matter (SOM) following inputs of fresh organic matter (FOM). The priming effect can be either positive or negative (i.e. an acceleration or retardation of SOM decomposition) and is controlled by several factors such as microbial community composition, SOM chemical structure and nutrient availability. The first objective of our experiment was to study negative or positive PE of stabilized SOM. The second was to identify the role of FOM decomposers in the PE of stabilized SOM. We incubated, for 39 days, a fallow soil free of vegetation for 80 years amended with 13C‐cellulose and inoculated with a FOM‐decomposing community. The soil contained stabilized SOM. The PE of the stable organic matter was always negative and tended to be more negative when the FOM‐decomposing community was added. This suggests that for this particular soil, SOM mineralization was not limited by energy. Moreover, as the inoculation of a FOM‐decomposing community led to a more negative PE, we assume that the FOM‐decomposing community facilitated the access of FOM to the indigenous bare soil community.
Net mineralization of N at deeper soil depths as a potential mechanism for sustained forest production under elevated [CO2]
Authors: IVERSEN C. M. , HOOKER T. D. , CLASSEN A. T. , NORBY R. J.
Published: April 2010

Elevated atmospheric carbon dioxide concentrations [CO2] is projected to increase forest production, which could increase ecosystem carbon (C) storage. This study contributes to our broad goal of understanding the causes and consequences of increased fine‐root production and mortality under elevated [CO2] by examining potential gross nitrogen (N) cycling rates throughout the soil profile. Our study was conducted in a CO2‐enriched sweetgum (Liquidambar styraciflua L.) plantation in Oak Ridge, TN, USA. We used 15N isotope pool dilution methodology to measure potential gross N cycling rates in laboratory incubations of soil from four depth increments to 60 cm. Our objectives were twofold: (1) to determine whether N is available for root acquisition in deeper soil and (2) to determine whether elevated [CO2], which has increased inputs of labile C resulting from greater fine‐root mortality at depth, has altered N cycling rates. Although gross N fluxes declined with soil depth, we found that N is potentially available for roots to access, especially below 15 cm depth where rates of microbial consumption of mineral N were reduced relative to production. Overall, up to 60% of potential gross N mineralization and 100% of potential net N mineralization occurred below 15 cm depth at this site. This finding was supported by in situ measurements from ion‐exchange resins, where total inorganic N availability at 55 cm depth was equal to or greater than N availability at 15 cm depth. While it is likely that trees grown under elevated [CO2] are accessing a larger pool of inorganic N by mining deeper soil, we found no effect of elevated [CO2] on potential gross or net N cycling rates. Thus, increased root exploration of the soil volume under elevated [CO2] may be more important than changes in potential gross N cycling rates in sustaining forest responses to rising atmospheric CO2.
Histone and ribosomal RNA repetitive gene clusters of the boll weevil are linked in a tandem array
Authors: Roehrdanz R. , Heilmann L. , Senechal P. , Sears S. , Evenson P.
Published: April 2010

Histones are the major protein component of chromatin structure. The histone family is made up of a quintet of proteins, four core histones (H2A, H2B, H3 & H4) and the linker histones (H1). Spacers are found between the coding regions. Among insects this quintet of genes is usually clustered and the clusters are tandemly repeated. Ribosomal DNA contains a cluster of the rRNA sequences 18S, 5.8S and 28S. The rRNA genes are separated by the spacers ITS1, ITS2 and IGS. This cluster is also tandemly repeated. We found that the ribosomal RNA repeat unit of at least two species of Anthonomine weevils,Anthonomus grandisandAnthonomus texanus(Coleoptera: Curculionidae), is interspersed with a block containing the histone gene quintet. The histone genes are situated between the rRNA 18S and 28S genes in what is known as the intergenic spacer region (IGS). The complete reiteratedAnthonomus grandishistone‐ribosomal sequence is 16 248 bp.
Beyond taxonomy: a review of macroinvertebrate trait‐based community descriptors as tools for freshwater biomonitoring
Authors: Menezes Salomé , Baird Donald J. , Soares Amadeu M. V. M.
Published: April 2010

1. Species traits have been frequently used in ecological studies in an attempt to develop a general ecological framework linking biological communities to habitat pressures. The trait approach offers a mechanistic alternative to traditional taxonomy‐based descriptors. This review focuses on research employing traits as biomonitoring tools for freshwater ecosystems, although the lessons learned have wider application in the assessment of other ecosystem types.

2. We review the support from ecological theory to employ species traits for biomonitoring purposes (e.g. the habitat templet concept, landscape filtering hypothesis), and the subsequent studies that test the hypotheses arising from these theories, and apply this knowledge under real freshwater biomonitoring scenarios. We also include studies that deal with more specific issues such as trait trade‐offs and trait syndromes.

3. We highlight the functional trait approach as one of the most promising tools emerging for biomonitoring freshwater ecosystems. Several technical issues are addressed and solutions are proposed. We discuss the need for: a broader unified trait biomonitoring tool; a more accurate understanding of the natural variation of community patterns of trait expression; approaches to diminish the effects of trait trade‐offs and trait syndromes; additional life history and ecological requirement studies; and the detection of specific impacts under multiple stressor scenarios.

4. Synthesis and applications. This review provides biologists with the conceptual underpinning for the use of species traits as community descriptors and for freshwater biomonitoring and management. We expect that the functional trait approach will ultimately improve communication to managers and legislators of the importance of protecting freshwater ecosystem functions.