bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave propagation in prestretched polymer nanofibers
Authors: Wu Xiang-Fa
Published: January 2010

Wave propagation in prestretched ultrathin polymer fibers (e.g., those as-electrospun polymer nanofibers) are under the influence of prestretch, surface energy, and nonlinear elasticity. A one-dimensional nonlinear elastic model is proposed to take into account such combined influence in the wave propagation phenomenon. In the model, the polymer nanofibers are considered to behave as hyperelastic Mooney–Rivlin solid. For small dynamic disturbance, linearized wave equation is established by superimposing the dynamic displacement as linear disturbance on the prestretched equilibrium state. Explicit wave dispersion relations are obtained and relevant numerical examples are demonstrated in examining the dependency of wave phase speed upon the wave number at varying surface properties, fiber radius, and prestretch. In the limiting case of neglecting the dynamic effect, the present wave equation can yield the governing equation of surface rippling in compliant nanofibers. This governing equation is capable of predicting the initiation condition of surface rippling and the critical fiber radius, below which compliant nanofibers cannot be produced due to surface instability. Results obtained in this study are applicable as the theoretical basis of dynamic characterization of compliant nanowires/nanofibers, nanofiber device design, and nanostructural analysis.
Simulation of a toy model of cylindrical cells submitted to nonionizing electromagnetic field: Effect of membrane cell disruption
Authors: Mezeme M. Essone , Brosseau C.
Published: January 2010

At the continuum level, the dielectric response that a core-shell model of biological cells must have when they are stimulated by an electric field is investigated. For computational ease, we consider a toy model of two space dimensions modeling field simulation that describe the continuity and conservation of electric flux corresponding to the response of infinite cylinders in three space dimensions. Ab initio calculations were performed using the finite-element method described by [Salou et al., J. Appl. Phys. 105, 114702 (2009)]. In this toy model, the shell-like structure of the biological cell is perforated. The frequency and angle-dependent electric field-induced transmembrane potential (EFITP) is found to change from the nonperforated situation at low frequencies of the oscillating electric field (below the β relaxation frequency of the cell). Our modeling results illustrate complexities involved in evaluating the influence of the hole number in the membrane and their positions in the field on the EFITP. The results also point out that significant differences occur in both the modulus and phase spectra of the EFITP when a surface density of free charges is present at the outer and inner surfaces of the membrane as compared with that those predicted with no surface charge. What is so special about this heterostructure arrangement is that it produces anisotropy in the higher and lower than the β relaxation frequency of the cell regions, while the field penetration inside the cell in the lower-frequency region is very sensitive to the number of the pores into the infinitesimally thin membrane. The results are compared to Asami’s finite difference modeling of the complex permittivity spectra of spherical cell models having holes in the membrane [J. Phys. D 39, 492 (2006)].
On nonlinear multiarmed spiral waves in slowly rotating fluid systems
Authors: Li Ligang , Liao Xinhao , Chan Kit H. , Zhang Keke
Published: January 2010

Stable nonlinear equilibria of convection in the form of quasistationary, multiarmed spiral waves, up to a maximum of six spiral arms, are found in a slowly rotating fluid confined within a thin spherical shell governed by the three-dimensional Navier–Stokes equation, driven by a radial unstable temperature gradient and affected by a weak Coriolis force. It is shown that three essential ingredients are generally required for the formation of the multiarmed spirals: the influence of slow rotation, large-aspect-ratio geometry and the effect of weak nonlinearity.
Frozen natural orbitals for ionized states within equation-of-motion coupled-cluster formalism
Authors: Landau Arie , Khistyaev Kirill , Dolgikh Stanislav , Krylov Anna I.
Published: January 2010

The frozen natural orbital (FNO) approach, which has been successfully used in ground-state coupled-cluster calculations, is extended to open-shell ionized electronic states within equation-of-motion coupled-cluster (EOM-IP-CC) formalism. FNOs enable truncation of the virtual orbital space significantly reducing the computational cost with a negligible decline in accuracy. Implementation of the MP2-based FNO truncation scheme within EOM-IP-CC is presented and benchmarked using ionized states of beryllium, dihydrogen dimer, water, water dimer, nitrogen, and uracil dimer. The results show that the natural occupation threshold, i.e., percentage of the total natural occupation recovered in the truncated virtual orbital space, provides a more robust truncation criterion as compared to the fixed percentage of virtual orbitals retained. Employing 99%–99.5% natural occupation threshold, which results in the virtual space reduction by 70%–30%, yields errors below 1 kcal/mol. Moreover, the total energies exhibit linear dependence as a function of the percentage of the natural occupation retained allowing for extrapolation to the full virtual space values. The capabilities of the new method are demonstrated by the calculation of the 12 lowest vertical ionization energies (IEs) and the lowest adiabatic IE of guanine. In addition to IE calculations, we present the scans of potential energy surfaces (PESs) for ionized (H2O)2 and (H2)2. The scans demonstrate that the FNO truncation does not introduce significant nonparallelity errors and accurately describes the PESs shapes and the corresponding energy differences, e.g., dissociation energies.
Resonant field emission from two-dimensional density of state on hydrogen-terminated intrinsic diamond
Authors: Yamada Takatoshi , Shikata Shin-ichi , Nebel Christoph E.
Published: January 2010

Field emission properties from hydrogen-terminated intrinsic diamond covered by adsorbate films are characterized as a function of surface adsorbate coverage and bulk doping with n- and p-type. The threshold of field emission from the undoped intrinsic diamond is lower than from p-type doped diamond, which is attributed to electrons arising from a two-dimensional density of state (2D-DOS) at the surface of diamond. The emission current saturates toward higher fields (“plateau”), which indicates a depletion of the 2D states. For even higher fields, the emission current rises again due to electron tunneling from the valence band. After thermal treatment of the adsorbate film to vanish surface conduction, the emission current is completely quenched since the 2D-DOS has been removed and diamond becomes fully insulating. These data are compared with p- and n-type diamonds, which show a continuous rise of emission current as a function of electric filed. Calculations based on the Fowler–Nordheim equation reveal a 2D-quantized energy level in the surface conductive layer.
Cyclotron effects on double layer ion acceleration from laser-irradiated thin foils
Authors: Sharma Anamika , Liu C. S. , Tripathi V. K.
Published: January 2010

The effect of an axial magnetic field on laser driven ion acceleration from a thin overdense plasma slab is investigated. The magnetic field modifies the refractive index of the plasma and the axial ponderomotive force. The latter compresses the electrons until the space charge field thus created offsets it. When the foil thickness is just bigger than the length at which this happens, the compressed electrons and a thin ion layer detach from the foil forming a double layer that gets accelerated by the laser radiation pressure force. The optimum thickness of laser foil, Δs, for maximum acceleration is sensitive to the polarization of the laser pulse. For right circular polarization it increases, while for left circular polarization it decreases with the magnetic field. The ion energy gain is sensitive to a02ω2∕Δsωp2 (where a0 is the laser field strength, ωp is the plasma frequency, and ω is the laser frequency) and can be tuned by varying the magnetic field.
Inverse temperature dependence of subthreshold slope in graphene nanoribbon tunneling transistors
Authors: Yoon Youngki , Salahuddin Sayeef
Published: January 2010

By performing an atomistic transport calculation, we examine the temperature dependence of the tunneling current in a graphene nanoribbon band-to-band tunneling transistor. The subthreshold swing is shown to be a nonlinear function of temperature, and in stark contrast to a conventional FET, the swing versus temperature shows a negative slope below a certain drain current. The nonlinear threshold voltage shift with temperature is also examined. A method to capture the distinguishing nonlinearity in the voltage shift with temperature and drain current is proposed.
Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal
Authors: Nagaraj Mamatha , Panarin Y. P. , Manna U. , Vij J. K. , Keith C. , Tschierske C.
Published: January 2010

We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field.
Van der Waals density functional from multipole dispersion interactions
Authors: Alves de Lima Neemias
Published: January 2010

We present a van der Waals density functional from high order multipole dispersion interactions between pairs of atoms. Calculated C2m≤16 dispersion coefficients for dimers involving alkali, alkaline-earth, and noble gas atoms show mean absolute deviations in the range of 2%–6% from highly accurate calculations. This successful test indicates that this approach can yield efficient algorithms for calculation of van der Waals forces.
Modeling of impurity effect on drift instabilities in plasmas with many ion species
Authors: Moradi S. , Tokar M. Z. , Weyssow B.
Published: January 2010

Drift microinstabilities, being the main cause of anomalous transport of charged particles and energy in fusion plasmas, can be strongly influenced by the presence of impurities. Normally a large amount of different ion species from diverse charge states and chemical elements is present. An approach, providing a possibility to take into account an arbitrary number of ion species in analysis of instabilities, is proposed and applied to study the impurity effect on unstable modes due to ion temperature gradient and trapped electrons described in a linear fluid approximation. The method is validated by comparing with the results from direct calculations in a one impurity ion case. The dependence of instability characteristics and anomalous transport coefficients on the absolute level and radial gradient of impurity density is investigated. Plasmas with several impurity ion species, including C+6, N+7, O+8, Ne+10, and Ar+18 whose density peaking factors are determined self-consistently from the impurity zero flux condition, are considered as an example of applications.
Electrically driven quantum dot-micropillar single photon source with 34% overall efficiency
Authors: Heindel T. , Schneider C. , Lermer M. , Kwon S. H. , Braun T. , Reitzenstein S. , Höfling S. , Kamp M. , Forchel A.
Published: January 2010

We report on triggered single photon emission from low mode volume electrically driven quantum dot-micropillar cavities at repetition rates of up to 220 MHz. Due to an optimized layout of the doped planar microcavity and an advanced lateral current injection scheme, highly efficient single photon sources are realized. While g(2)(0)-values as low as 0.13±0.05 and a Purcell factor of 4 are observed for a 2.0 μm diameter micropillar, single photon emission at a rate of (35±7) MHz and an overall efficiency of (34±7)% are demonstrated for a 3.0 μm device.
Diffusive reflectance for the free-space light propagation theory
Authors: Si Yuanzheng , Mao Heng , Zhang Bin , Jiang Ming
Published: January 2010

Based on the free-space light propagation theory, the noncontact measurement technique for optical tomography provides high quality data sets by using charge coupled device camera for light detection. The free-space theory was originally formulated for a single object but did not take into account the reflection among object surfaces. However, complex geometries of small animals can induce multiple light reflections on surfaces. A major issue is how to model the surface reflectance to work with the free-space light propagation theory. In this letter, we utilize the Monte Carlo simulation technique to evaluate the performance of the free-space theory with multiple light reflections. Two types of surface reflectance have been simulated, including the specular or diffuse reflectance, respectively. It is found that for tissuelike objects the diffusive reflectance works the best with the free-space theory and a discrepancy occurs when the surface exhibits specular reflectance.
Efficient heterojunction solar cells on p-type crystal silicon wafers
Authors: Wang Qi , Page M. R. , Iwaniczko E. , Xu Yueqin , Roybal L. , Bauer R. , To B. , Yuan H.-C. , Duda A. , Hasoon F. , Yan Y. F. , Levi D. , Meier D. , Branz Howard M. , Wang T. H.
Published: January 2010

Efficient crystalline silicon heterojunction solar cells are fabricated on p-type wafers using amorphous silicon emitter and back contact layers. The independently confirmed AM1.5 conversion efficiencies are 19.3% on a float-zone wafer and 18.8% on a Czochralski wafer; conversion efficiencies show no significant light-induced degradation. The best open-circuit voltage is above 700 mV. Surface cleaning and passivation play important roles in heterojunction solar cell performance.
Communications: The structure of Rh8+ in the gas phase
Authors: Harding D. J. , Walsh T. R. , Hamilton S. M. , Hopkins W. S. , Mackenzie S. R. , Gruene P. , Haertelt M. , Meijer G. , Fielicke A.
Published: January 2010

The geometric structure of the Rh8+ cation is investigated using a combination of far-infrared multiple photon dissociation spectroscopy and density functional theory (DFT) calculations. The energetic ordering of the different structural motifs is found to depend sensitively on the choice of pure or hybrid exchange functionals. Comparison of experimental and calculated spectra suggests the cluster to have a close-packed, bicapped octahedral structure, in contrast to recent predictions of a cubic structure for the neutral cluster. Our findings demonstrate the importance of including some exact exchange contributions in the DFT calculations, via hybrid functionals, when applied to rhodium clusters, and cast doubt on the application of pure functionals for late transition metal clusters in general.
The glass transition and relaxation behavior of bulk water and a possible relation to confined water
Authors: Swenson Jan , Teixeira José
Published: January 2010

Due to the widespread importance of water and the difficulty to study it in the so-called no man’s land between 150 and 235 K, deeply supercooled bulk water is currently heavily debated. It speculates about its properties from extrapolations of experimental data on bulk water above 235 K and below 150 K, computer simulations, and experiments on confined water for which the finite size effects may prevent crystallization in the no man’s land. However, it is far from obvious how experimental data on bulk water should be extrapolated to the temperature range of the no man’s land or how relevant results from computer simulations and studies of confined water are for bulk water. In this paper the structural and dynamical properties of supercooled bulk water are tried to be understood from experimental results on confined water and comparisons with bulk water. We propose that a similar crossover from a high temperature α-relaxation to a low temperature β-relaxation occurs also for bulk water but at a higher temperature than for confined water due to the larger average number of hydrogen bonds between the water molecules in bulk water. In the case of bulk water the crossover is expected to occur around the critical temperature Ts≈228 K when the buildup of an icelike tetrahedral network structure is completed. The proposed interpretation is the simplest one that is able to explain many of the peculiar properties of supercooled water.
Optimal modeling of atomic fluctuations in protein crystal structures for weak crystal contact interactions
Authors: Hafner Jeffrey , Zheng Wenjun
Published: January 2010

The accurate modeling of protein dynamics in crystalline states holds keys to the understanding of protein dynamics relevant to functions. In this study, we used coarse-grained elastic network models (ENMs) to explore the atomic fluctuations of a protein structure that interacts with its crystalline environment, and evaluated the modeling results using the anisotropic displacement parameters (ADPs) obtained from x-ray crystallography. To ensure the robustness of modeling results, we used three ENM schemes for assigning force constant combined with three boundary conditions for treating the crystalline environment. To explore the role of crystal contact interactions in the modeling of ADPs, we varied the strength of interactions between a protein structure and its environment. For a list of 83 high-resolution crystal structures, we found that the optimal modeling of ADPs, as assessed by a variety of metrics, is achieved for weak protein-environment interactions (compared to the interactions within a protein structure). As a result, the ADPs are dominated by contributions from rigid-body motions of the entire protein structure, and the internal protein dynamics is only weakly perturbed by crystal packing. Our finding of weak crystal contact interactions is also corroborated by the calculations of residue-residue contact energy within a protein structure and between protein molecules using a statistical potential.
Performance and applicability of a dc refrigerator powered by the photovoltaics
Authors: Zhang P. , Liu Q. S. , Wang R. Z.
Published: January 2010

Due to the gradual depletion and excessive consumption of fossil fuels and the resulting environmental problems, increasing attention has been paid to the utilization of the renewable energy sources such as solar energy, etc. The development and performance investigation of a photovoltaic-powered refrigerator is presented in the paper. The field performance test results show that the refrigerator can work well in Shanghai area and the lowest temperature in the freezer can reach near −15 °C and the power consumption is also reasonable. Furthermore, the energy flow of the system and applicability of it to different climatic regions have been analyzed and discussed. It can be concluded that the performance of the refrigerator is very stable and it can serve for perishable food storage, vaccine, and drug depositing at low temperatures in the remote area and it can even be used as the electrical appliance in “zero-energy” building.
Characteristic length scales governing plasticity/brittleness of bulk metallic glasses at ambient temperature
Authors: Yang Y. , Ye J. C. , Lu J. , Liaw P. K. , Liu C. T.
Published: January 2010

In this letter, we propose a unified theory for the size-dependent plasticity of bulk metallic glasses (BMGs) at room temperature. Based on the principle of energy balance and the shear-banding kinetics, two characteristic length scales are derived. One is a sample-geometry dependent variable related to the elastic energy released to drive shear-band propagation and the other is a material-dependent constant related to the internal resistance to brittle fracture. It is shown that this unified theory is effective in explaining many unusual deformation and fracture behaviors of BMGs.
Nanoscale domain growth dynamics of ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) thin films
Authors: Kim Yunseok , Kim Wooyoung , Choi Hyunwoo , Hong Seungbum , Ko Hyungsoo , Lee Heechul , No Kwangsoo
Published: January 2010

Nanoscale domain growth dynamics of ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) thin films were investigated by piezoresponse force microscopy. A 90 nm thick ferroelectric polymer thin films were fabricated on Au substrate by spin-coating method. The domain size of nanoscale dot pattern was linearly proportional to logarithmic value of the pulse width. However there was a significant asymmetry in nucleation and lateral domain growth depending on the voltage polarity, which implies the existence of the preferred polarization states. The obtained activation field indicates the nucleation-limited domain switching behaviors of ferroelectric polymer thin films.
Spin-orbit ab initio investigation of photolysis of o-, m-, and p-iodotoluene
Authors: Liu Ya-Jun , Tian Yan-Cong , Fang Wei-Hai
Published: January 2010

The multistate second order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space state interaction (MS-CASPT2/CASSI-SO) was employed to calculate the potential energy curves for the ground and low-lying excited states of o-, m-, and p-iodotoluene along the assumed photolysis reaction coordinates. The mechanism and channels leading to products I(P23/2) and I∗(P23/2) for o-, m-, and p-iodotoluene photolysis at 266 and 304 nm were elucidated with the computed potential energy curves and the surface crossing points. The effects of methyl substituent and heavy atom on the photodissociation mechanism were discussed by the comparison to related alkyl and aryl halides.
Quantum gate operations using midinfrared binary shaped pulses on the rovibrational states of carbon monoxide
Authors: Zaari Ryan R. , Brown Alex
Published: January 2010

Frequency domain shaped binary laser pulses were optimized to perform 2 qubit quantum gate operations in C12O16. The qubit rovibrational state representation was chosen so that all gate operations consisted of one-photon transitions. The amplitude and phase varied binary pulses were determined using a genetic algorithm optimization routine. Binary pulses have two possible amplitudes, 0 or 1, and two phases, 0 or π, for each frequency component of the pulse. Binary pulses are the simplest to shape experimentally and provide a minimum fidelity limit for amplitude and phase shaped pulses. With the current choice of qubit representation and using optimized binary pulses, fidelities of 0.80 and as high as 0.97 were achieved for the controlled-NOT and alternative controlled-NOT quantum gates. This indicates that with a judicious choice of qubits, most of the required control can be obtained with a binary pulse. Limited control was observed for 2 qubit NOT and Hadamard gates due to the need to control multiple excitations. The current choice of qubit representation produces pulses with decreased energies and superior fidelities when compared with rovibrational qubit representations consisting of two-photon transitions. The choice of input pulse energy is important and applying pulses of increased energy does not necessarily lead to a better fidelity.
Granulated Carbon Nanotubes as the Catalyst Support for Pt for the Hydrogenation of Nitrobenzene
Authors: Jin Shao , Qian Weizhong , Liu Yi , Wei Fei , Wang Dezeng , Zhang Jinchang
Published: January 2010

Granulated Pt/carbon nanotubes (CNTs) were found to have a much better catalytic activity in the liquid phase hydrogenation of nitrobenzene than Pt/activated carbon (AC). The granulated CNTs had much larger pores than the AC particles, which gave a faster mass transfer rate of H2 that helped produce aniline with high selectivity.
2-(1H-2-Benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylnickel Complexes: Synthesis, Characterization, and Ethylene Oligomerization
Authors: Xiao Liwei , Zhang Min , Gao Rong , Cao Xiaoping , Sun Wen-Hua
Published: January 2010

A series of tridentate N,N,N-nickel complexes bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines was synthesized and characterized by elemental and IR spectroscopic analysis. The molecular structures of representative complexes were determined by single-crystal diffraction, and these were found to have a six-coordinate distorted octahedral geometry around the Ni centre. On treatment with Et2AlCl, all nickel complexes exhibited good catalytic activities up to 106 g mol–1(Ni) h–1 for ethylene oligomerization with major dimerization. The steric and electronic effects on catalytic activities of metal complexes as well as the influence of various reaction parameters were carefully investigated.
Organometallic Gold(I) Acetylide/Polyoxometalate Hybrid Langmuir-Blodgett Films: Preparation, Characterization, and Photoelectric Properties
Authors: Liu Li , Liu Qian , Chen Ming , Li Ming-Jian , Xu Li-Ping , Liu Shi-Zhong , Du Zu-Liang , Wong Wai-Yeung
Published: January 2010

A new series of organometallic/inorganic hybrid Langmuir-Blodgett (LB) films containing an organometallic gold(i) aryleneethynylene metal complex (OMA) as the π-conjugated organometallic molecule and a polyoxometalate (POM, POM = H3BW12O40, H6As2W18O62, or H6P2Mo18O62) of the Keggin and Dawson structure as the inorganic composite, were prepared and characterized by π–A isotherms, UV-vis absorption spectra, photoluminescence spectra, atomic force microscopy imaging, scanning tunnelling microscopy, and surface photovoltage spectroscopy. Our experimental results indicate that stable, well defined and well organized Langmuir and LB films are formed in pure water and polyoxometalate subphases. There is a quenching effect in the luminescence of the gold(i) complex when it is made into the LB films. The OMA/POM hybrid LB films display strong photovoltage effect in the UV-vis region. The photovoltage response of OMA/H6As2W18O62 can be as high as 3338 μV. OMA/POM monolayer films show good electrical conductivity, and the tunnelling current for a OMA/H3BW12O40 monolayer film amounts to 50 to approximately –100 nA when the voltage is set at ±9 V.
Synthesis and Electrochemical Studies of Nickel β-Diketonate Complexes Incorporating Asymmetric Diimine Ligands
Authors: Harding Phimphaka , Harding David J. , Soponrat Nitisastr , Tinpun Kittiya , Samuadnuan Sirirat , Adams Harry
Published: January 2010

The reaction of ppaX {(4-X-phenyl)-pyridin-2-ylmethylene-amine; X = H, Me, Et, OMe, F, Cl, Br, and I} with [Ni(β-diketonate)2(H2O)2] {β-diketonate = 1,3-diphenylpropanedionate (dbm), 2,2,6,6-tetramethyl-3,5-heptadionate (tmhd), or hexafluoroacetylacetonate (hfac)} yields a series of nickel complexes. X-ray crystallography reveals octahedral coordinated nickel centres with a cis arrangement of the β-diketonate ligands. The β-diketonate ligands adopt ‘planar’ or ‘bent’ coordination modes, whereas the aryl ring of the ppaX ligand is twisted with respect to the pyridylimine unit. The electrochemical behaviour of the complexes reveals quasi-reversible or irreversible one-electron oxidation to Ni(iii) in the case of the [Ni(tmhd)2(ppaX)] and [Ni(dbm)2(ppaX)] complexes, respectively. The peak potential for oxidation is dependent on the type of β-diketonate ligand but essentially independent of the substituent, X, on the ppaX ligand. The [Ni(β-diketonate)2(ppaX)] complexes (X = F, Cl, Br, and I) also undergo ligand based reduction.
A Study of the Metabolome of Ricinus communis for Forensic Applications
Authors: Ovenden Simon P. B. , Gordon Benjamin R. , Bagas Christina K. , Muir Bob , Rochfort Simone , Bourne David J.
Published: January 2010

Investigations were undertaken to ascertain the appropriateness of studying the metabolome of Ricinus communis for cultivar and provenance determination. Seeds from 14 R. communis specimens (a total of 56 seeds) collected from the east coast of Australia were analyzed by high pressure liquid chromatography with UV detection (HPLC-UV), liquid chromatography–mass spectrometry (LC-MS), and 1H NMR spectroscopy. The collected data were then analyzed using principle component analysis (PCA). For HPLC-UV analysis, six R. communis specimens were unambiguously identified by PCA as belonging to separate classes relating to specimen. LC-MS data allowed unique ions to be identified for four specimens. Conversely 10 specimens were unambiguously segregated in the PCA of the 1H NMR data. The ratio of ricinine 1 to demethylricinine analogues 2 and 3 was found to be important for specimen determination. These combined analyses suggested that a combination of HPLC-UV and 1H NMR in conjunction with PCA could allow for specimen differentiation.
Conjoint Analysis of Kinetic and Equilibrium Data for Mechanistic Elucidation in Polynuclear Complexation Reactions, Exemplified by Metal(II) Helicate Complex Formation
Authors: Clifford Sarah E. , Lawrance Geoffrey A. , Neuhold Yorck-Michael , Maeder Marcel
Published: January 2010

Combined kinetic and equilibrium studies of the complexation of the ligand N,N′-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide with copper(ii) and nickel(ii), examined conjointly employing advanced chemometric methods, provides elucidation of speciation and formation pathways in solution for complexes such as M2L2 and M2L3 helicates, respectively.
Mechanistic details of a protein–protein association pathway revealed by paramagnetic relaxation enhancement titration measurements
Authors: Fawzi Nicolas L. , Doucleff Michaeleen , Suh Jeong-Yong , Clore G. Marius
Published: January 2010

Protein–protein association generally proceeds via the intermediary of a transient, lowly populated, encounter complex ensemble. The mechanism whereby the interacting molecules in this ensemble locate their final stereospecific structure is poorly understood. Further, a fundamental question is whether the encounter complex ensemble is an effectively homogeneous population of nonspecific complexes or whether it comprises a set of distinct structural and thermodynamic states. Here we use intermolecular paramagnetic relaxation enhancement (PRE), a technique that is exquisitely sensitive to lowly populated states in the fast exchange regime, to characterize the mechanistic details of the transient encounter complex interactions between the N-terminal domain of Enzyme I (EIN) and the histidine-containing phosphocarrier protein (HPr), two major bacterial signaling proteins. Experiments were conducted at an ionic strength of 150 mM NaCl to eliminate any spurious nonspecific associations not relevant under physiological conditions. By monitoring the dependence of the intermolecular transverse PRE (Γ
2
) rates measured on
15
N-labeled EIN on the concentration of paramagnetically labeled HPr, two distinct types of encounter complex configurations along the association pathway are identified and dissected. The first class, which is in equilibrium with and sterically occluded by the specific complex, probably involves rigid body rotations and small translations near or at the active site. In contrast, the second class of encounter complex configurations can coexist with the specific complex to form a ternary complex ensemble, which may help EIN compete with other HPr binding partners in vivo by increasing the effective local concentration of HPr even when the active site of EIN is occupied.
Observations of aminium salts in atmospheric nanoparticles and possible climatic implications
Authors: Smith James N. , Barsanti Kelley C. , Friedli Hans R. , Ehn Mikael , Kulmala Markku , Collins Donald R. , Scheckman Jacob H. , Williams Brent J. , McMurry Peter H.
Published: January 2010

We present laboratory studies and field observations that explore the role of aminium salt formation in atmospheric nanoparticle growth. These measurements were performed using the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) and Ultrafine Hygroscopicity Tandem Differential Mobility Analyzers. Laboratory measurements of alkylammonium—carboxylate salt nanoparticles show that these particles exhibit lower volatilities and only slightly lower hygroscopicities than ammonium sulfate nanoparticles. TDCIMS measurements of these aminium salts showed that the protonated amines underwent minimal decomposition during analysis, with detection sensitivities comparable to those of organic and inorganic deprotonated acids. TDCIMS observations made of a new particle formation event in an urban site in Tecamac, Mexico, clearly indicate the presence of protonated amines in 8–10 nm diameter particles accounting for about 47% of detected positive ions; 13 nm particles were hygroscopic with an average 90% RH growth factor of 1.42. Observations of a new particle formation event in a remote forested site in Hyytiälä, Finland, show the presence of aminium ions with deprotonated organic acids; 23% of the detected positive ions during this event are attributed to aminium salts while 10 nm particles had an average 90% RH growth factor of 1.27. Similar TDCIMS observations during events in Atlanta and in the vicinity of Boulder, Colorado, show that aminium salts accounted for 10–35% of detected positive ions. We conclude that aminium salts contribute significantly to nanoparticle growth and must be accounted for in models to accurately predict the impact of new particle formation on climate.
Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect
Authors: Swann Abigail L. , Fung Inez Y. , Levis Samuel , Bonan Gordon B. , Doney Scott C.
Published: January 2010

Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is up to 1.5 times larger than the forcing due to albedo change from the forest. Furthermore, the greenhouse warming by additional water vapor melts sea-ice and triggers a positive feedback through changes in ocean albedo and evaporation. Land surface albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration of water vapor and feedbacks from the ocean and sea-ice.
On Force in Cartesian Physics
Authors: Manchak John Byron
Published: January 2010

There does not seem to be a consistent way to ground the concept of “force” in Cartesian first principles. In this article, I first review the literature on the subject. Then, I offer an alternative interpretation of force—one that seems to be coherent and consistent with Descartes’ project. Not only does the new position avoid the problems of previous interpretations, but it does so in such a way as to support and justify those previous interpretations.
Defending Evo-Devo: A Response to Hoekstra and Coyne
Authors: Craig Lindsay R.
Published: January 2010

The study of evolutionary developmental biology (“evo-devo”) has recently experienced a dramatic surge in popularity among researchers and theorists concerned with evolution. However, some biologists and philosophers remain skeptical of the claims of evo-devo. This paper discusses and responds to the recent high profile criticisms of evo-devo presented by biologists Hopi E. Hoekstra and Jerry A. Coyne. I argue that their objections are unconvincing. Indeed, empirical research supports the main tenets of evo-devo, including the claim that morphological evolution is the result of cis-regulatory change and the distinction that evo-devo draws between morphological and physiological traits.
Technology and Goodman's Paradox
Authors: Nordin Ingemar
Published: January 2010

Goodman's paradox gives rise to a cluster of problems, problems that are in need of different answers. I will discuss some variants of the grue hypothesis applied to the technological context. One conclusion in this paper is that there is room for rational decisions, and that solutions to the paradoxes in technology can be found in the practical choice situation.
Visual Representations in Science
Authors: Goodwin William
Published: January 2010

This paper evaluates a general argument for the conclusion that visual representations in science must play the role of truth bearers if they are to figure as legitimate contributors to scientific arguments and explanations. The argument is found to be unsound. An alternative approach to assessing the role of visual representations in science is exemplified by an examination of the role of structural formulas in organic chemistry. Structural formulas are found not to play the role of truth bearers; nonetheless, they contribute to the arguments and explanations of organic chemistry. An early success of conformational analysis is presented in order to illustrate the role of structural formulas in the discourse of organic chemistry.
Essay Review: Physical Relativity and Understanding Space-Time
Authors: Huggett Nick
Published: January 2010

The two books discussed here make important contributions to our understanding of the role of spacetime concepts in physical theories and how that understanding has changed during the evolution of physics. Both emphasize what can be called a ‘dynamical’ account, according to which geometric structures should be understood in terms of their roles in the laws governing matter and force. I explore how the books contribute to such a project; while generally sympathetic, I offer criticisms of some historical claims concerning Newton, and argue that the dynamical account does not undercut ontological issues as the books claim.
Optimizing Empirical Antimicrobial Therapy for Infection due to Gram-Negative Pathogens in the Intensive Care Unit: Utility of a Combination Antibiogram
Authors: Christoff Jennifer , Tolentino Jocelyn , Mawdsley Emily , Matushek Scott , Pitrak David , Weber Stephen G.
Published: January 2010

Objective.

To determine whether the use of dual antimicrobial therapy based on the results of a combination antibiotic susceptibility report (antibiogram) increases the likelihood of selecting adequate empirical coverage in critically ill patients with infection due to potentially resistant gram-negative pathogens.

Design.

Retrospective data analysis.

Setting.

Urban academic medical center.

Methods.

An analysis of culture results and susceptibility data from intensive care unit patients determined by the clinical microbiology laboratory was performed. The proportion of 5 common gram-negative pathogens susceptible to monotherapy with 1 of 3 antipseudomonal antibiotics (piperacillin-tazobactam, ceftazidime, or imipenem) was compared with the proportion susceptible to each of these 3 “backbone” agents plus 1 of 4 additional antimicrobial agents used in combination.

Results.

More than 5,000 clinical isolates were examined. When all isolates recovered during the entire study period were included, the addition of any of the second antibiotics studied to each of the 3 backbone agents significantly increased the likelihood of covering the causative pathogen (P<.01 for each). The benefit of combination therapy was variable when results for each of the 5 organisms were examined individually. When temporal trends in susceptibility were examined, the decrease in the proportion of organisms susceptible to monotherapy was statistically significant for both imipenem and ceftazidime (P<.01).

Conclusions.

Reporting antibiotic susceptibility data in the form of a combination antibiogram may be useful to clinicians who are considering empirical antimicrobial therapy in the intensive care unit.
Comment on “Towards a precautionary approach to managing Canada's commercial harp seal hunt” by Leaper et al.
Authors: Hammill Michael O. , Stenson Garry B.
Published: January 2010

Hammill, M. O., and Stenson, G. B. 2010. Comment on “Towards a precautionary approach to managing Canada's commercial harp seal hunt” by Leaper et al. – ICES Journal of Marine Science, 67: 321–322. The Objective-Based Fisheries Management used by Canada to manage the Northwest Atlantic seal hunt conforms to United Nations and Canadian Government precautionary approach frameworks in its structure and industry involvement. Managers and industry use clearly identified thresholds and harvest control rules to adjust quotas to respect the management framework. Although simulation testing is needed to evaluate management model performance under additional sources of uncertainty, this approach has successfully maintained the harp seal population at or near the highest level ever seen, during a period of intensive hunting.
A Nylon Membrane Bag Assay for Determination of the Effect of Chemicals on Soilborne Plant Pathogens in Soil
Authors: Lin Youjian , He Zhenli , Rosskopf Erin N. , Conn Kenneth L. , Powell Charles A. , Lazarovits George
Published: January 2010

A new nylon membrane bag (NMB) assay was developed for studies to determine the effect of chemicals added to soil on survival of soilborne plant pathogens. The rapid and effective assay can be used to study organisms for which there are no selective media or for which a selective medium is expensive or difficult to prepare. This assay consists of placing pathogens inside a bag made of small-pore (0.22-μm) nylon filtration membrane, which is placed in soil and later retrieved to determine survival of the pathogens on nonselective media. Chemicals but not other microorganisms can enter the bag from the soil. Using this assay, Streptomyces scabies, Fusarium oxysporum f. sp. lycopersici race 3, and Ralstonia solanacearum were successfully recovered from soil after 72 h as demonstrated by growth on a semiselective Streptomyces medium (S. scabies) or nonselective potato dextrose agar medium (F. oxysporum f. sp. lycopersici race 3 and R. solanacearum) with minimal microbial contamination. Addition of acetic acid (200 mM) to soil killed 100% of S. scabies. SPK (a mixture of organic chemicals) at a concentration of 1,500 mg kg–1 of soil killed 83.3% of F. oxysporum f. sp. lycopersici race 3 culture plugs, 100% of F. oxysporum f. sp. lycopersici race 3 spores, and 97.2% of R. solanacearum cells. SPK at 1,000 mg kg–1 of soil killed 50% of F. oxysporum f. sp. lycopersici race 3 culture plugs, 68.2% of F. oxysporum f. sp. lycopersici race 3 spores, and 12% of R. solanacearum. Benlate (500 to 1,500 mg kg–1 of soil) did not kill the culture plugs of F. oxysporum f. sp. lycopersici race 3 but reduced the growth rate of F. oxysporum f. sp. lycopersici race 3. Benlate (500, 1,000, and 1,500 mg kg–1 of soil) reduced F. oxysporum f. sp. lycopersici race 3 spore germination by 39.4, 49.3, and 50.4%, respectively. Streptomycin sulfate (1,500, 800, 400, and 200 mg kg–1 of soil) caused 75.3, 21, 11.9, and 0.9% mortality, respectively, of R. solanacearum.
Two Mutations in β-Tubulin 2 Gene Associated with Thiophanate-Methyl Resistance in Colletotrichum cereale Isolates from Creeping Bentgrass in Mississippi and Alabama
Authors: Young Joseph R. , Tomaso-Peterson Maria , de la Cerda Karla , Wong Francis P.
Published: January 2010

Turfgrass anthracnose, caused by Colletotrichum cereale (≡C. graminicola), has become a common disease of creeping bentgrass putting greens during the summer in Mississippi and Alabama over the last 15 years. Thiophanate-methyl is a single-site mode-of-action fungicide applied to control C. cereale. In vitro bioassays were performed to evaluate the sensitivity of 103 isolates to thiophanate-methyl concentrations ranging from 0.039 to 10 μg/ml. Eighty-three isolates were collected from creeping bentgrass in Mississippi and Alabama that had been exposed to thiophanate-methyl. An additional 20 isolates were included from nonexposed turfgrasses. Radial colony growth in amended media was relative to nonamended media for all in vitro bioassays. With thiophanate-methyl at 10 μg/ml, relative growth of exposed isolates ranged from 77.5 to 130.7% with a mean of 99.3% compared with nonexposed, baseline isolates that ranged from 0.0 to 48.7% with a mean of 20.4%. A representative sample of thiophanate-methyl-exposed and nonexposed isolates was used to determine the mechanism of resistance by comparing amino acid sequences of the β-tubulin 2 protein. All of the thiophanate-methyl-exposed isolates that were sequenced had a point mutation resulting in substitutions from glutamic acid to alanine at position 198 or from phenylalanine to tyrosine at position 200 of the β-tubulin 2 protein. These amino acid substitutions in C. cereale isolates from Mississippi and Alabama appear to confer resistance to thiophanate-methyl and differ from those reported previously for this pathogen.
Evaluation of Onion Cultivars for Resistance to Enterobacter cloacae in Storage
Authors: Schroeder B. K. , Waters T. D. , du Toit L. J.
Published: January 2010

Sixty-nine storage onion (Allium cepa) cultivars (seven white, five red, and 57 yellow cultivars) were evaluated in the Washington State University Onion Cultivar Trials in the semiarid Columbia Basin of central Washington in 2007–08 and/or 2008–09. Each cultivar was inoculated with Enterobacter cloacae, cured, stored under commercial storage conditions, and evaluated for bacterial storage rot symptoms approximately 4.5 months after storage. Noninoculated bulbs of each cultivar served as a control treatment in each experiment. In addition, bulbs injected with water served as a second control treatment in the 2008–09 experiment. Inoculation of onion bulbs with E. cloacae resulted in significantly higher incidence and severity of Enterobacter bulb decay compared to noninoculated bulbs and bulbs injected with sterile water. For bulbs inoculated with E. cloacae, mean severity of bacterial storage rot per cultivar ranged from 5 to 19% of the cross-section evaluated for each onion bulb in 2007–08 and from 9 to 29% in 2008–09. For noninoculated bulbs, mean severity ranged from 0 to 1% in 2007–08 and 0 to 3% in 2008–09. For bulbs injected with water in the 2008–09 experiment, severity of bulb rot ranged from 0 to 10% per cultivar, with four cultivars (OLYX05-26, RE-E, Redwing, and Talon) displaying bulb rot ratings significantly greater than 0%. For the 33 cultivars included in both experiments, a significant correlation in bulb rot severity ratings was detected for the 2007–08 versus 2008–09 experiments (r = 0.43 at P = 0.013). Redwing, Red Bull, T-433, Centerstone, and Salsa had low severity ratings in both experiments; whereas Montero, OLYS05N5, Caveat, and Granero had severe bulb rot ratings in both experiments. The results demonstrate that it should be possible to select for increased resistance to Enterobacter bulb decay in storage onion cultivars.