bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of finite difference and boundary integral solutions to three‐dimensional spontaneous rupture
Authors: Day Steven M. , Dalguer Luis A. , Lapusta Nadia , Liu Yi
Published: December 2005

The spontaneously propagating shear crack on a frictional interface has proven to be a useful idealization of a natural earthquake. The corresponding boundary value problems are nonlinear and usually require computationally intensive numerical methods for their solution. Assessing the convergence and accuracy of the numerical methods is challenging, as we lack appropriate analytical solutions for comparison. As a complement to other methods of assessment, we compare solutions obtained by two independent numerical methods, a finite difference method and a boundary integral (BI) method. The finite difference implementation, called DFM, uses a traction‐at‐split‐node formulation of the fault discontinuity. The BI implementation employs spectral representation of the stress transfer functional. The three‐dimensional (3‐D) test problem involves spontaneous rupture spreading on a planar interface governed by linear slip‐weakening friction that essentially defines a cohesive law. To get a priori understanding of the spatial resolution that would be required in this and similar problems, we review and combine some simple estimates of the cohesive zone sizes which correspond quite well to the sizes observed in simulations. We have assessed agreement between the methods in terms of the RMS differences in rupture time, final slip, and peak slip rate and related these to median and minimum measures of the cohesive zone resolution observed in the numerical solutions. The BI and DFM methods give virtually indistinguishable solutions to the 3‐D spontaneous rupture test problem when their grid spacing Δxis small enough so that the solutions adequately resolve the cohesive zone, with at least three points for BI and at least five node points for DFM. Furthermore, grid‐dependent differences in the results, for each of the two methods taken separately, decay as a power law in Δx, with the same convergence rate for each method, the calculations apparently converging to a common, grid interval invariant solution. This result provides strong evidence for the accuracy of both methods. In addition, the specific solution presented here, by virtue of being demonstrably grid‐independent and consistent between two very different numerical methods, may prove useful for testing new numerical methods for spontaneous rupture problems.
Aerosol and cloud property relationships for summertime stratiform clouds in the northeastern Atlantic from Advanced Very High Resolution Radiometer observations
Authors: Matheson Mark A. , Coakley James A. , Tahnk William R.
Published: December 2005

Advanced Very High Resolution Radiometer (AVHRR) 4‐km data collected over the northeastern Atlantic off the coast of the Iberian Peninsula for May to August 1995 were used to investigate the feasibility of empirically deriving estimates of the aerosol indirect radiative forcing. A retrieval scheme was used to derive cloud visible optical depth, droplet effective radius, cloud layer altitude, and pixel‐scale fractional cloud cover. A two‐channel aerosol retrieval scheme was used to determine aerosol optical depth in cloud‐free pixels. Mean aerosol optical depths derived from the cloud‐free pixels in 1° × 1° latitude‐longitude regions on a given satellite overpass were associated with mean cloud properties derived from the cloudy pixels in the same region for the same satellite overpass. The analysis was restricted to 1° regions that contained only single‐layered, low‐level cloud systems. Because aerosol and cloud properties are highly variable, results for the 4‐month period were composited into 5° × 5° latitude‐longitude regions and averaged to obtain reliable trends in the cloud properties as functions of aerosol burden. Consistent with expectations for the aerosol indirect effect, in some 5° regions, droplet effective radii decreased, and cloud visible optical depths increased as aerosol optical depths increased. The hypothesis that drizzle is suppressed in polluted clouds predicts that liquid water path should increase as aerosol burden increases. In three of the thirteen 5° regions studied, the liquid water path increased as aerosol optical depth increased, but in none of the regions was the increase in cloud liquid water statistically significant. In the remaining regions, cloud liquid water remained constant or even decreased with increasing aerosol optical depth. In many of the 5° regions, the retrieved aerosol optical depth increased as the percentage of cloudy pixels increased. Consistent with expectations from adiabatic cloud parcel models, droplet effective radius, cloud optical depth, and cloud liquid water path also increased as fractional cloud cover increased. The simultaneous increase in retrieved aerosol and cloud optical depths with increasing fractional cloud cover might have been due to the aerosol indirect effect, but it might also have resulted from processes that affect both the cloud and aerosol properties as cloud cover changes. The dependence on fractional cloud cover suggests that some of the trends between aerosol optical depth and the cloud properties cannot be solely attributed to the effects of the aerosols. For comparison with previous studies, the simultaneous changes in aerosol and cloud properties were used to estimate the daily average aerosol indirect forcing for overcast conditions in the summertime northeastern Atlantic. The magnitude of the indirect forcing relative to that of the direct forcing reported here is smaller than estimates reported by others.
Global anthropogenic aerosol direct forcing derived from satellite and ground‐based observations
Authors: Chung Chul Eddy , Ramanathan V. , Kim Dohyeong , Podgorny I. A.
Published: December 2005

A global estimate of the direct effects of anthropogenic aerosols on solar radiation in cloudy skies is obtained by integrating satellite and ground‐based observations with models of aerosol chemistry, transport, and radiative transfer. The models adopt global distribution of aerosol optical depths (from MODIS), clouds, water vapor, ozone, and surface albedo from various satellite climatology. Gaps and errors in satellite derived aerosol optical depths are filled and corrected by surface network (AERONET), and an aerosol chemical‐transport model (GOCART) by using statistical techniques. Using these derived aerosol properties and other related variables, we generate climatological monthly mean anthropogenic aerosol forcing for both clear and average cloudy skies. Unless otherwise stated, our estimates are for average cloudy skies, also referred to as all sky conditions. The global annual mean direct forcing is −0.35 Wm−2 (range of −0.6 to −0.1 Wm−2) at the top‐of‐the atmosphere (TOA), +3.0 Wm−2 (range of +2.7 to +3.3Wm−2) in the atmosphere, and −3.4 Wm−2 (range of −3.5 to −3.3 Wm−2) at the surface. The uncertainty of about 10–20% in the surface and atmosphere forcing translates into a six fold uncertainty in the TOA forcing because the TOA forcing is a small sum of two large terms (surface and atmosphere) of opposing signs. Given the current state of observations and modeling, it is very difficult to further reduce the uncertainty in the estimated TOA forcing. The major contributors to the uncertainty in atmospheric absorption are from the uncertainty in the vertical distribution of aerosols and the single scattering albedo of aerosols. The TOA forcing in clear skies is a factor of two different, while the surface and atmosphere forcing terms differ by only about 10–25%. Another major finding of this study is that the reduction in the surface solar radiation is a factor of 10 larger than the reduction in net solar (down minus up) radiation at TOA. The TOA forcing changes sign regionally, whereas the surface forcing is always negative. Thus caution must be exercised against relying too strongly on assessing the aerosol impacts based solely on global mean forcing. Aerosols over the NH contribute about 64% to the global surface forcing. Regionally the populated tropical regions contribute the most to the global surface forcing, with Asia the largest contributor. Roughly 49% of the total surface forcing is over the oceanic regions. Most of the previous global aerosol forcing estimate studies were conducted with a chemical transport model coupled to a general circulation model with model generated aerosols and cloudiness. Thus the present study, which adopts observed aerosol properties and observed three dimensional cloudiness, provides an independent approach for estimating the aerosol forcing.
Adaptive resolution molecular-dynamics simulation: Changing the degrees of freedom on the fly
Authors: Praprotnik Matej , Delle Site Luigi , Kremer Kurt
Published: December 2005

We present a new adaptive resolution technique for efficient particle-based multiscale molecular-dynamics simulations. The presented approach is tailor-made for molecular systems where atomistic resolution is required only in spatially localized domains whereas a lower mesoscopic level of detail is sufficient for the rest of the system. Our method allows an on-the-fly interchange between a given molecule’s atomic and coarse-grained levels of description, enabling us to reach large length and time scales while spatially retaining atomistic details of the system. The new approach is tested on a model system of a liquid of tetrahedral molecules. The simulation box is divided into two regions: one containing only atomistically resolved tetrahedral molecules, and the other containing only one-particle coarse-grained spherical molecules. The molecules can freely move between the two regions while changing their level of resolution accordingly. The hybrid and the atomistically resolved systems have the same statistical properties at the same physical conditions.
(
H
Cl
)
2
and (HF)2 in small helium clusters: Quantum solvation of hydrogen-bonded dimers
Authors: Jiang Hao , Sarsa Antonio , Murdachaew Garold , Szalewicz Krzysztof , Bačić Zlatko
Published: December 2005

We present a rigorous theoretical study of the solvation of (HCl)2 and (HF)2 by small (He4)n clusters, with n=1–14 and 30. Pairwise-additive potential-energy surfaces of Hen(HX)2 (X=Cl and F) clusters are constructed from highly accurate four-dimensional (rigid monomer) HX–HX and two-dimensional (rigid monomer) He–HX potentials and a one-dimensional He–He potential. The minimum-energy geometries of these clusters, for n=1–6 in the case of (HCl)2 and n=1–5 for (HF)2, correspond to the He atoms in a ring perpendicular to and bisecting the HX–HX axis. The quantum-mechanical ground-state energies and vibrationally averaged structures of Hen(HCl)2 (n=1–14 and 30) and Hen(HF)2 (n=1–10) clusters are calculated exactly using the diffusion Monte Carlo (DMC) method. In addition, the interchange-tunneling splittings of Hen(HCl)2 clusters with n=1–14 are determined using the fixed-node DMC approach, which was employed by us previously to calculate the tunneling splittings for Hen(HF)2 clusters, n=1–10 [A. Sarsa et al., Phys. Rev. Lett. 88, 123401 (2002)]. The vibrationally averaged structures of Hen(HX)2 clusters with n=1–6 for (HCl)2 and n=1–5 for (HF)2 have the helium density localized in an effectively one-dimensional ring, or doughnut, perpendicular to and at the midpoint of the HX–HX axis. The rigidity of the solvent ring varies with n and reaches its maximum for the cluster size at which the ring is filled, n=6 and n=5 for (HCl)2 and (HF)2, respectively. Once the equatorial ring is full, the helium density spreads along the HX–HX axis, eventually solvating the entire HX dimer. The interchange-tunneling splitting of Hen(HCl)2 clusters hardly varies at all over the cluster size range considered, n=1–14, and is virtually identical to that of the free HCl dimer. This absence of the solvent effect is in sharp contrast with our earlier results for Hen(HF)2 clusters, which show a ∼30% reduction of the tunneling splitting for n=4. A tentative explanation for this difference is proposed. The implications of our results for the interchange-tunneling dynamics of (HCl)2 in helium nanodroplets are discussed.
Structural thermodynamics of lamellar cationic lipid-DNA complex: DNA compressibility modulus
Authors: González-Amezcua O. , Hernández-Contreras M.
Published: December 2005

We have studied theoretically the compressibility modulus B of DNA and complexation adsorption isotherms of DNA and lipids, as a function of DNA spacing dDNA and NaCl electrolyte concentration, respectively, in isoelectric states of lamellar DNA/cationic lipid (CL) self-assemblies. The electrostatic free energy derived from the Poisson-Boltzmann theory predicts partial agreement with measured B values for interhelical separations dDNA>33Å when use is made of a fit of hydration repulsion from bulk DNA hexagonal phases in solution. For lower interchain separations the prediction worsens due to the hydration interaction that overcomes the electrostatic contribution. An exact match of the system’s counterion electrochemical potentials and the coions of salt in aqueous phase leads to the electrostatic part of the free energy that renders isotherms of dDNA versus ionic strength in qualitative consistency with general trends of available experimental data of CL-DNA complexes.
Derivation of a microscopic theory of barriers and activated hopping transport in glassy liquids and suspensions
Authors: Schweizer Kenneth S.
Published: December 2005

A recently proposed microscopic activated barrier hopping theory [K. S. Schweizer and E. J. Saltzman, J. Chem. Phys. 119, 1181 (2003)] of slow single-particle dynamics in glassy liquids, suspensions, and gels is derived using nonequilibrium statistical mechanics. Fundamental elements underlying the stochastic nonlinear Langevin equation description include an inhomogeneous liquid or locally solid-state perspective, dynamic density-functional theory (DDFT), a local equilibrium closure, and a coarse-grained free-energy functional. A dynamic Gaussian approximation is not adopted which is the key for avoiding a kinetic ideal glass transition. The relevant excess free energy is of a nonequilibrium origin and is related to dynamic force correlations in the fluid. The simplicity of the approach allows external perturbations to be rather easily incorporated. Dynamic heterogeneity enters naturally via mobility fluctuations associated with the stochastic barrier-hopping process. The derivation both identifies the limitations of the theory and suggests new avenues for its systematic improvement. Comparisons with ideal mode-coupling theory, alternative DDFT approaches and a field theoretic path-integral formulation are presented.
Molecular-dynamics simulations of methane hydrate dissociation
Authors: English Niall J. , Johnson J. K. , Taylor Charles E.
Published: December 2005

Nonequilibrium molecular-dynamics simulations have been carried out at 276.65K and 68bar for the dissolution of spherical methane hydrate crystallites surrounded by a liquid phase. The liquid was composed of pure water or a water-methane mixture ranging in methane composition from 50% to 100% of the corresponding theoretical maximum for the hydrate and ranged in size from about 1600 to 2200 water molecules. Four different crystallites ranging in size from 115 to 230 water molecules were used in the two-phase systems; the nanocrystals were either empty or had a methane occupation from 80% to 100% of the theoretical maximum. The crystal-liquid systems were prepared in two distinct ways, involving constrained melting of a bulk hydrate system or implantation of the crystallite into a separate liquid phase. The breakup rates were very similar for the four different crystal sizes investigated. The method of system preparation was not found to affect the eventual dissociation rates, despite a lag time of approximately 70ps associated with relaxation of the liquid interfacial layer in the constrained melting approach. The dissolution rates were not affected substantially by methane occupation of the hydrate phase in the 80%–100% range. In contrast, empty hydrate clusters were found to break up significantly more quickly. Our simulations indicate that the diffusion of methane molecules to the surrounding liquid layer from the crystal surface appears to be the rate-controlling step in hydrate breakup. Increasing the size of the liquid phase was found to reduce the initial delay in breakup. We have compared breakup rates computed using different long-range electrostatic methods. Use of the Ewald, minimum image, and spherical cut-off techniques led to more rapid dissociation relative to the Lekner method.
Dependence of magnetization dynamics on magnetostriction in NiFe alloys
Authors: Bonin R. , Schneider M. L. , Silva T. J. , Nibarger J. P.
Published: December 2005

We present a quantitative, systematic study of the effect of magnetostriction on the dynamical properties in NiFe alloys. Both the ferromagnetic resonance frequency and the damping times are correlated to the magnetostriction. In addition, we find that the Gilbert damping parameter varies by more than 100% over the range of Ni percentage tested (61.9%–86.7%).
Analytic Coulomb matrix elements in a three-dimensional geometry
Authors: García Jaime Zaratiegui
Published: December 2005

Using a complete basis set we have obtained an analytic expression for the matrix elements of the Coulomb interaction. These matrix elements are written in a closed form. We have used the basis set of the three-dimensional isotropic quantum harmonic oscillator in order to develop our calculations, which can be useful when treating interactions in localized systems.
The scaling of forced collisionless reconnection
Authors: Sullivan Brian P. , Rogers Barrett N. , Shay M. A.
Published: December 2005

We present two-fluid simulations of forced magnetic reconnection with finite electron inertia in a collisionless two-dimensional slab geometry. Reconnection in this system is driven by a spatially localized forcing function that is added to the ion momentum equation inside the computational domain. The resulting forced reconnection process is studied as a function of the temporal and spatial structure of the forcing function, the plasma β, and strength of the out-of-plane guide magnetic field component, and the electron to ion mass ratio. Consistent with previous results found in unforced, large Δ′ systems, for sufficiently strong forcing the reconnection process is found to become Alfvénic, i.e., the inflow velocity scales roughly like some small fraction of the Alfvén speed based on the reconnecting component of the magnetic field just upstream of the dissipation region. The magnitude of this field and thus the rate of reconnection is controlled by the behavior of the forcing function. When the forcing strength is below a certain level, fast reconnection is not observed.
Simulation study of relativistic dynamics of MeV alpha particles in magnetized plasmas for explaining an experimental anomaly
Authors: Chen K. R. , Tsai T. H.
Published: December 2005

In a Test Fusion Tokamak Reactor [R. J. Hawryluk et al., Phys. Plasmas 5, 1577 (1998)] experiment, the measured energy spectrum of the deeply trapped alpha particles is found to be 1MeV too broad to be explained by classical collisions and the peak energy similarly off by 450keV. The relativistic effect is proposed as an explanation. Here, we report high-resolution Monte Carlo (MC) and particle-in-cell (PIC) simulation studies in detail, under the assumption of a uniform magnetic field, for the identification of the cause of the observed anomaly. The 3.5MeV alpha particles produced by thermonuclear fusion reaction are broadened due to Doppler effect. The relativistic alpha particle dynamics are followed with the PIC code. The relativistic ion cyclotron instability grows to saturation on a time scale (10−5s) much shorter than the experimental time scale of 0.1s. The MC code is then used to follow, in real time, the collisional slowing down of the gyrobroadened alphas, including the effect of the time delay in diagnostic pellet releasing and flight. Relativistic gyrobroadening is shown to be crucial in shaping the birth and slowed-down spectra. The resultant alpha particle energy spectrum fits well with that of the measurement, with a reduced chi square of unity.
A computational investigation of copper-doped germanium and germanium clusters by the density-functional theory
Authors: Wang Jin , Han Ju-Guang
Published: December 2005

The geometries, stabilities, and electronic properties of Gen and CuGen (n=2–13) clusters have been systematically investigated by using density-functional approach. According to optimized CuGen geometries, growth patterns of Cu-capped Gen or Cu-substituted Gen+1 clusters for the small- or middle-sized CuGen clusters as well as growth patterns of Cu-concaved Gen or Ge-capped CuGen−1 clusters for the large-sized CuGen clusters are apparently dominant. The average atomic binding energies and fragmentation energies are calculated and discussed; particularly, the relative stabilities of CuGe10 and Ge10 are the strongest among all different sized CuGen and Gen clusters, respectively. These findings are in good agreement with the available experimental results on CoGe10− and Ge10 clusters. Consequently, unlike some transition metal (TM)Si12, the hexagonal prism CuGe12 is only low-lying structure; however, the basketlike structure is located as the lowest-energy structure. Different from some TM-doped silicon clusters, charge always transfers from copper to germanium atoms in all different sized clusters. Furthermore, the calculated highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gaps are obviously decreased when Cu is doped into the Gen clusters, together with the decrease of HOMO-LUMO gaps, as the size of clusters increases. Additionally, the contribution of the doped Cu atom to bond properties and polarizabilities of the Gen clusters is also discussed.
Liquid-bridge mediated droplet switch: A tristable capillary system
Authors: Bhandar Anand S. , Steen Paul H.
Published: December 2005

The double-droplet switch is the simplest example of a system of capillary surfaces (liquid/gas interfaces at small scales) that demonstrates bistability. A liquid bridge placed between the droplets allows the nonlinear response to be mediated by a pressure po maintained outside the bridge. Response diagrams that give droplet volumes versus po are constructed through computations. The combination of the nonlinear pV responses of the bridge and the droplet switch reveals regions with markedly different behaviors depending on the control parameters. The response diagrams show regions with high sensitivity to po, behavior dominated by the double-droplet response, and also regions with low sensitivity to po, where the bridge response dominates. Stability is determined following the Poincaré approach with illustration using nonequilibrium energy contours (“landscapes”). The computations predict regions of hysteresis with three stable equilibria. When imperfections arising from contact-circle movement at the boundaries are included, five simultaneously stable equilibria and double hysteresis loops are predicted.
Thinning out clusters while conserving stoichiometry of labeling
Authors: Moertelmaier Manuel , Brameshuber Mario , Linimeier Mario , Schütz Gerhard J. , Stockinger Hannes
Published: December 2005

Here we present a method for the stoichiometric analysis of molecular aggregates in the cellular plasma membrane, based on single molecule fluorescence microscopy. We use selective photobleaching to erase all active fluorophores within a small region of the membrane, while conserving the stoichiometry of labeling in the remaining part of the membrane. At the onset of repopulation due to Brownian motion, single diffraction limited spots of individual aggregates can be resolved and quantified. We demonstrate the proof of principle of this method by quantifying the dye load of fluorescently labeled immunoglobulins diffusing in a supported lipid bilayer.
cis-1,2-Dihydrocatechols in Chemical Synthesis: First Synthesis of L-Ascorbic Acid (Vitamin C) from a Non-Carbohydrate Source
Authors: Banwell Martin G. , Blakey Simon , Harfoot Gwion , Longmore Robert W.
Published: December 2005

The cis-1,2-dihydrocatechol (2), which is obtained in
enantiopure form by microbial oxidation of chlorobenzene, has been converted,
via 3,5-O-benzylidene-L-gulono-1,4-lactone (8), into
L-ascorbic acid (1).
Studies in the Cycloproparene Series: Formation of a New Dimer of 1H-Cyclopropa[b]naphthalene
Authors: Halton Brian , Jones Carissa S. , Northcote Peter T. , Boese Roland
Published: December 2005

1-(Trimethylsilyl)-1H-cyclopropa[b]naphthalene
(10) and its 1-methyl derivative (11) have been isolated as pure compounds
from use of a lipophilic size exclusion gel. Acylation of the
1H-cyclopropa[b]naphthalenyl
anion (2) is effected with N,N -dimethyl-benzamide
and -acetamide to give (5) and (6), respectively. Analogous reactions with the
1-(trimethylsilyl)-1H-cyclopropa[b]naphthalenyl
anion (9) do not yield the
1-acyl-1-(trimethylsilyl)-1H-cyclopropa[b]naphthalenes
(12) and (13); instead the novel 6-methyl-
7H-dibenzo[b,g]fluorene
(15) results from attempted acetylation. Compound (15), a formal dimer of
1H-cyclopropa[b]naphthalene
(1), is formed also from anion (9) both in toluene and from addition of
hydrocarbon (1); its structure is assigned from spectroscopic data and
confirmed by single-crystal X-ray analysis.
Energetics of Intramolecular Bonds in 1H-1,2,4-Triazole and 1H-Benzotriazole
Authors: Sabbah Raphaël , Perez Laurence
Published: December 2005

This paper deals with a thermodynamic study of
1H-1,2,4-triazole and
1H-benzotriazole (general formula
C2H3N3 and
C6H5N3
respectively). Investigations were performed by combustion calorimetry of
small amounts of substance (a few milligrams), sublimation calorimetry,
differential thermal analysis and heat capacity measurements. The experimental
combustion, sublimation and fusion enthalpies of the two compounds were
determined as well as their triple point temperatures and are as follows:

From these results, experimental resonance energies have been obtained and
compared with theoretical values. The experimental atomization enthalpy of
1H-1,2,4-triazole is compatible with the calculated
value. In the case of 1H-benzotriazole, it was possible
to determine from this thermodynamic quantity a value of 298·4 kJ
mol-1 for the N=N bond enthalpy.
The crystal structures of six polybromo carvones
Authors: Smith Graham , Venzke Brian N. , Bott Raymond C. , Carman Raymond M. , Kennard Colin H. L.
Published: December 2005

The crystal structures of six polybromo carvones have been determined by
single-crystal X-ray diffraction. These are the three previously reported
isomeric tetrabromo carvones,
(1S,3S,4R,8R)-1,3,8,9-tetrabromo-p-menthan-2-
one (4),
(1S,3S,4R,8S)-1,3,8,9-tetrabromo-p-menthan-2-one
(5) and
(1R,3S,4R,8R)-1,3,8,9-tetrabromo-p-menthan-2-one
(12), two tribromo derivatives,
(1S,4R,8R)-1,8,9-tribromo-p-menthan-2-one
(10) and
(1S,4R,8S)-1,8,9-tribromo-p-menthan-2-one
(11) [all derived from (R)-carvone (1)],
together with a pentabromo derivative,
(1S,3S,4R,6R,8R)-1,3,6,8,9-pentabromo-p-menthan-2-one
(7) [derived from (S)-carvone
ent-(1)]. In all examples, the stereochemistry
agrees with that predicted from the synthetic pathway, while with one
[the
(1R,3S,4R,8R)-tetrabromide
(12)] a distorted twist-chair conformation is found.
Corrigendum to: A New Catalyst for the Reductive Elimination of Acylated Glycosyl Bromides to Form Glycals
Authors: Stick R. V. , Stubbs K. A. , Tilbrook D. M. G. , Watts A. G.
Published: December 2005

Ethylene-N,N-bis(salicylideneiminato)oxovanadium(IV) {VO(salen)} has been developed as a useful catalyst for the reductive elimination of acylated glycosyl bromides to form glycals, both in the pyranose and furanose series, using zinc/ammonium chloride/methanol or zinc/acetic acid/acetonitrile.
Structural Systematics of Rare Earth Complexes. XVI (‘Maximally’) Hydrated Rare Earth(III) Bromides
Authors: Semenova Lioubov I. , Junk Peter C. , Skelton Brian W. , White Allan H.
Published: December 2005

Room-temperature single-crystal X-ray structure determinations carried out on
rare earth bromides crystallized from water at room temperature define three
series of hydrates LnBr3.nH2O. For
Ln = La, Ce, a heptahydrate phase (n = 7)
is defined, triclinic P 1, a ≈
8·6, b ≈ 9·4, c
≈ 8·3 Å, α ≈ 108, β ≈ 99, γ ≈ 72°,
isomorphous with the array described for the ‘early’ (Ln =
La-Pr) rare earth chlorides, being binuclear
[(H2O)7Ln(-Br)2Ln(OH2)7]
Br4, Z = 1 dimer;
conventional R on
|F| were 0·051, 0·042 for
2323, 3451 independent ‘observed’ (I >
3σ(I)) diffractometer reflections respectively.
For Ln = Pr(-)Dy, a hexahydrate phase is defined, monoclinic
P 2/n, a
≈ 10·0, b ≈ 6·8,
c ≈ 8·2 Å, β ≈ 93·5°,
Z = 2 f.u., isomorphous with the array defined
for the heavier (Ln = Nd, Lu, Y) rare earth chlorides, being
[(H2O)6LnBr2]
Br, with R 0·029, 0·034 for
No 1590, 1388 respectively. For Ln
= Ho(-)Lu, Y, an octahydrate is defined for the first time, monoclinic
P 21/n,
a ≈ 8·1, b ≈
16·0, c ≈ 10·1 Å,
b ≈ 94·0°, Z
= 4 f.u., a new array of the form
[Ln(OH2)8]
Br3 emerging, with R 0·061,
0·048, 0·042 for No
1191, 2402, 1674 respectively, the metal environment being square
antiprismatic.
Structural Systematics of Rare Earth Complexes. XVII Hydrated 1 : 1 Adducts of 2,2′:6′,2″-Terpyridine with the Lanthanoid(III) Bromides and Some Binuclear Hydroxy-Bridged Dimers
Authors: Semenova Lioubov I. , White Allan H.
Published: December 2005

Room-temperature single-crystal X-ray structural characterizations are
recorded for hydrated lan- thanoid(III)
bromide/2,2′:6′,2″-terpyridine (tpy) (1 : 1) complexes,
showing all to be ionic and of the form
[(tpy)Ln(OH2)x]Br3.yH2O,
where x and y are 6 and 1 for the
isomorphous series Ln = La(-)Er (and intermediate members, by
presumption), and 5 and various values for Ln = Tm, Yb, Lu. Crystals of
[(tpy)Ln(OH2)6]Br3.H2O
are monoclinic, P
21/c, a
≈ 8·5, b ≈ 18, c ≈
16·3 Å, β ≈ 108°, Z = 4;
for Ln = La, Er, conventional R values on
|F| were 0·048, 0·080 for
No 4027, 1347
‘observed’ (I >
3σ(I)) diffractometer reflections respectively.
The complex
[(tpy)Tm(OH2)5]Br3.H2O
is monoclinic, P
21/c, a
8·506(4), b 17·376(1),
c 15·951(6) Å, β 106·87(3)°,
Z = 4, (quasi-)isomorphous with the Ln =
La-Er array, R 0·065 for
No 2067.
[(tpy)Yb(OH2)5]Br3.4H2O
is triclinic, P 1, a
11·902(2), b 11·639(3),
c 9·831(2) Å, α 98·92(2),
β 106·84(2), γ 92·42(2)°, Z
= 2, R 0·062 for
No 3422, while
[(tpy)Lu(OH2)5]Br3.H2O
is monoclinic, P 21/n,
a 13·635(8), b
9·022(5), c 19·03(1) Å, β
99·02(5)°, Z = 4,
R 0·043 for
No 3139. Despite a common
N3LnO5 coordination sphere in the
last three compounds, subtle differences are found in stereochemistry; in the
N3LnO6 array, one of the outer
water molecules becomes progressively detached as the lanthanoid radius
contracts. Some tendency is found toward the end of the lanthanoid series
toward the formation of di(hydroxy-bridged) neutral dimers,
Ln(OH)Br2/tpy/H2O(1 : 1 :
8)(×2),
[(tpy)(H2O)3Ln(µ-OH)2Ln(OH2)3(tpy)]Br4.10H2O,
monoclinic, C 2/c,
a ≈ 19·5, b ≈
14·5, c ≈ 17·1 Å, β ≈
92°, Z = 4 dimers, thus far defined by full
determinations for the extrema Lu = Er, Lu (and Y),
R 0·055, 0·043, (0·047) for
No 3141, 4591, (2991)
respectively; the dimer is disposed about a crystallographic
2 -axis. An Ln = Dy example, seemingly
isomorphous, has also been characterized by cell determination.
1,6-Epithio- and 1,6-Episeleno-β-D-glucopyranose: Useful Adjuncts in the Synthesis of 6-Deoxy-β-D-glucopyranosides
Authors: Stick Robert V. , Tilbrook D. Matthew G. , Williams Spencer J.
Published: December 2005

Derivatives of 1,6-dideoxy-1,6-epithio- and
1,6-dideoxy-1,6-episeleno-β-D-glucopyranose have
been shown to be effective glycosyl donors toward carbohydrate alcohols under
the agency of N-
iodosuccinimide/trifluoromethanesulfonic acid. Reduction of the
intermediate disulfides and diselenides affords
6-deoxy-β-D-glucopyranosides. The synthesis of a
range of such 6′-deoxy disaccharide derivatives is
reported.
The Synthesis and X-Ray Crystal Structure of Phenylalanine-Based N-Benzyloxysuccinimides
Authors: Abell Andrew D. , Oldham Mark D. , Moore Michael M. , Robinson Ward T.
Published: December 2005

X-Ray crystal structures of the N-benzyloxysuccinimide
(8) and its unprotected amino analogue (6) have been determined to reveal the
conformation of the cycle and the constituent phenylalanine. An improved
synthesis of
C-benzyl-N-benzyloxysuccinimide
(12), a simple, but nevertheless important member of this class of
peptidomimetic, is also presented.
High-Temperature Rearrangements of 2-Acylisoxazol-5(2H)-ones and Related Oxazoles.
Authors: Clark Adrian D. , Ha Uyen T. , Prager Rolf H. , Smith Jason A.
Published: December 2005

2-Acyl-3-arylisoxazol-5(2H)-ones give
2-alkyl(aryl)-4-aryloxazoles in good yields at 540°C under flash vacuum
pyrolysis conditions, but at higher temperatures the expected oxazoles are
accompanied by increasing amounts of isomeric 2,5-disubstituted oxazoles, as
well as anilides and decomposition products of the 2,4-disubstituted oxazole.
The rearrangement mechanisms have been studied by the use of
13C labelled substrates and
p-substituted 3-arylisoxazolones. The 2,5-disubstituted
oxazoles are considered to arise from 1H-azirines, and
the anilides from the nitrone ketene isomer of the acylisoxazolone.
Titanium Amino Alcohol Complexes from α-Titanic Acid: X-Ray Crystal Structure of Titanium Bis[2,2´-(methylimino)diethanolate]
Authors: Kemmitt Tim , Al-Salim Najeh I. , Gainsford Graeme J. , Henderson William
Published: December 2005

A method for producing amino alcohol complexes of titanium from hydrated
titania (α-titanic acid) is described. Thus hydrated titania was
completely converted into triethanolamine and diethanolamine complexes during
reaction at 120°C for 6 h. This represents a synthetic method for titanium
sol–gel precursors which are free from chlorine-containing impurities.
Products were characterized with assistance from 1 H and
13 C nuclear magnetic resonance spectroscopy, and
electrospray mass spectrometry. A single-crystal X-ray structure of titanium
bis[2,2´- (methyl-imino)ethanolate], tetragonal, space group
P4 – 2 1
c, is presented. The titanium centre is coordinated by
an N2O4 donor set which can be
most closely described as a bifacially capped tetrahedral geometry.
Professor Sev Sternhell
Authors: Field Les
Published: December 2005

… very influential, not only directly through his work, but also
indirectly because of the graduates that he has inspired …
An Alternative Synthesis of N-Acetyl-4-deoxyneuraminic Acid
Authors: Ooi Hua Chee , Marcuccio Sebastian M. , Jackson W. Roy
Published: December 2005

A synthesis of N-acetyl-4-deoxyneuraminic acid (11) from
N-acetylneuraminic acid (1) via the corresponding
unsaturated derivative (4) is described. This synthesis of the important
N-acetylneuraminic acid aldolase (EC 4.1.3.3) inhibitor
overcomes several difficulties associated with two previously published
syntheses.
Key features of the regional producer network for enabling social learning
Authors: Andrew J.
Published: December 2005

This paper outlines a form of research and extension that involves producers, researchers, program administrators, facilitators and others with an interest in on-farm, natural resource management and production improvement. Drawing predominantly from a review of the Sustainable Grazing Systems (SGS) regional producer network involving 88 interviews with producers, managers and scientists and in-depth studies of 4 SGS regional producer committees, findings advocate the establishment of arrangements where producers are in control of research and development to maximise learning and on-ground change. The justification for this need is based on the principle that major change will not occur unless the theories of those people whose practices are most affected by research and development outcomes are dominant in the research and development approach itself. In this way, research and development responds to the context in which change is to take place. Additionally, the SGS regional producer network provided a broad framework that enabled producers and other people to come together and actively learn from each other in a non-threatening environment. This approach provided a learning environment that was essentially directed by and for producers.
North-east Victoria SGS National Experiment site: water and nutrient losses from grazing systems on contrasting soil types and levels of inputs
Authors: Ridley A. M. , Christy B. P. , White R. E. , McLean T. , Green R.
Published: December 2005

Water and nutrient losses, pasture and animal production were measured for a prime lamb enterprise at Maindample (rainfall 750 mm/year) and a wool enterprise at Ruffy (rainfall 671 mm/year) in north-east Victoria from 1998 to 2000. Each site comprised 3 paddock-scale treatments: control, unsown pasture receiving about 5�kg�phosphorus (P)/ha.year; medium input, sown pasture (about 10 kg P/ha.year); and high input, sown pasture (≥22 kg P/ha.year). Sown pastures were based on phalaris (Phalaris aquatica L.) at Maindample and cocksfoot (Dactylis glomerata L.) at Ruffy, and sheep were set stocked. Pastures at Maindample created a larger soil water deficit (commonly about 120 mm) compared with Ruffy (about 70 mm) in summer. Maximum soil water deficit at Maindample occurred under the high input pasture and was about 30 mm greater than the medium or control treatments. Phalaris content ranged between about 200 and 1300 kg DM/ha, between 10 and 70% of total composition (commonly about 20%). In contrast, at Ruffy the control, which had 20–40% native grasses (Austrodanthonia and Microlaena) achieved the greatest soil water deficit, about 25 mm greater than for sown pastures. Cocksfoot persisted poorly at the acid soil at Ruffy. Small differences in green leaf area over summer (about 200 kg DM/ha) between treatments could generate the soil water deficit differences over the summer.The most striking result was the markedly different pathways of water loss between surface losses and deep drainage at the 2 sites, which was of greater consequence than the effect of pasture type. At Maindample, on average, 166 mm of water was lost annually (22% of rainfall) with 110 mm of this as surface runoff. At Ruffy, annual water loss was 128 mm (19% of rainfall) with 110 mm of this total water loss estimated as loss through deep drainage.Phosphorus losses were low in all treatments (≤1 kg P/ha.year), and nitrate-N (NO3-N) losses (7–12 kg N/ha.year) were comparable with previous work. Concentrations of P in water were highest from the high treatments at both sites, averaging 0.91 and 0.83 mg P/L in surface runoff from Maindample high and Ruffy high treatments, respectively. Average soil water NO3-N concentrations ranged from 3 to 26 mg N/L. Both P and N concentrations were higher than acceptable for aquatic health.Environmental risks in terms of water and nutrient losses could be either higher or lower for sown than unsown pastures, depending upon soil type, botanical stability, persistence and the soil water extracting ability of the pasture. Results indicated that better environmental outcomes could be achieved if soil types were targeted for particular land uses. High management skills are needed if grazing enterprises are to be both profitable and have lower off-site impacts.
Utilization of oaten hay by cattle: effects of milling and urea supplementation
Authors: Yates NG , Moir RJ
Published: December 2005

Oaten hay in either long or milled form, with or without a continuous intra-ruminal infusion of urea at the rate of 160 g/d, was offered ad libitum to four rumen fistulated steers in a 4 x 4 Latin square design experiment. Milling increased dry matter intake from 49.2 to 65.4 g/kg LW0 75.d (P< 0.001) and decreased mean retention time from 66.7 to 54.2 h (P< 0.001). Rates of cellulose digestion and dry matter digestibilities were similar for long and milled hay. Urea increased dry matter intake (from 49.0 to 65.6 g/kg LW0 75.d; P< 0.001), dry matter digestibility (from 58.1 to 65.3%; P< 0.01) cellulose digestibility (from 48.5 to 63.1%; P< 0.01) and the rate of cellulose digestion (P< 0.001), and decreased mean retention time from 65.3 to 55.6 h ( P < 0.01). Digestible dry matter intakes increased 29% with milling and 52% with urea and the effects were additive. Urea increased digestible cellulose intake to a greater extent with milled hay (91 %) than with long hay (64%). Digestible dry matter intake was closely related to liveweight change. When urea was given liveweight gain was higher for milled hay than for long hay (0.69 vs 0.11 kg/head.d) and without urea liveweight loss was less for milled hay than for long hay (-0.07 vs -0.45 kg/head.d). Nitrogen digestibility and balance were significantly higher when urea was given. Total volatile fatty acid concentrations were significantly higher and rumen pH significantly lower with urea compared with no urea and with milled hay compared with long hay. Urea increased rumen-ammonia concentration from 1.65 to 19.68 mg1100 ml (P< 0.001) and total free bacterial concentration (P < 0.05). The results demonstrate significant and additive benefits from the administration of urea to hay containing 0.8% nitrogen and from milling through a screen size of 7.6 mm.
Effects of systemic fungicidal seed dressings on the incidence of Phytophthora megasperma, nodulation, and nitrogen fixation in two soybean cultivars
Authors: Diatloff A , Irwin JAG , Rose JL
Published: December 2005

Two cultivars of soybeans, Davis and Ross, resistant and susceptible to Phytophthora root rot, respectively, were grown in a field trial where there was a moderately high level of Phytophthora megasperma f. sp. glycinea. The efficacy of metalaxyl and Dowco 444 as fungicidal seed dressings, their interaction with host resistance and the effect of plant health on nodulation and nitrogen fixing activity (acetylene reduction) were assessed. The cultivar Davis showed a relatively high level of field resistance in the absence of fungicidal protection; this was manifest in increased emergence and a lower incidence of disease in the surviving plants. In contrast cv. Ross had virtually no field resistance. In both cultivars, disease incidence was lower where fungicides were used. Metalaxyl was more effective than Dowco 444 on cv. Ross but not on cv. Davis. This suggests that the better performance of Dowco 444 on Davis was through an enhancement of existing resistance mechanisms of the host. Nitrogen fixing activity was generally higher in Davis than in Ross with a positive correlation between nitrogen fixing activity and nodule number. Disease incidence was negatively correlated with nitrogen fixing activity indicating the dependence of nitrogen fixation on root health. Neither fungicides suppressed nitrogen fixing activity at the rates used.
Neural activity in speech-sensitive auditory cortex during silence
Authors: Hunter M. D. , Eickhoff S. B. , Miller T. W. R. , Farrow T. F. D. , Wilkinson I. D. , Woodruff P. W. R.
Published: December 2005

That auditory hallucinations are voices heard in the absence of external stimuli implies the existence of endogenous neural activity within the auditory cortex responsible for their perception. Further, auditory hallucinations occur across a range of healthy and disease states that include reduced arousal, hypnosis, drug intoxication, delirium, and psychosis. This suggests that, even in health, the auditory cortex has a propensity to spontaneously “activate” during silence. Here we report the findings of a functional MRI study, designed to examine baseline activity in speech-sensitive auditory regions. During silence, we show that functionally defined speech-sensitive auditory cortex is characterized by intermittent episodes of significantly increased activity in a large proportion (in some cases >30%) of its volume. Bilateral increases in activity are associated with foci of spontaneous activation in the left primary and association auditory cortices and anterior cingulate cortex. We suggest that, within auditory regions, endogenous activity is modulated by anterior cingulate cortex, resulting in spontaneous activation during silence. Hence, an aspect of the brain's “default mode” resembles a (preprepared) substrate for the development of auditory hallucinations. These observations may help explain why such hallucinations are ubiquitous.
The
Bacillus subtilis
spore coat provides “eat resistance” during phagocytic predation by the protozoan
Tetrahymena thermophila
Authors: Klobutcher Lawrence A. , Ragkousi Katerina , Setlow Peter
Published: December 2005

Bacillus
spores are highly resistant to many environmental stresses, owing in part to the presence of multiple “extracellular” layers. Although the role of some of these extracellular layers in resistance to particular stresses is known, the function of one of the outermost layers, the spore coat, is not completely understood. This study sought to determine whether the spore coat plays a role in resistance to predation by the ciliated protozoan
Tetrahymena
, which uses phagocytosis to ingest and degrade other microorganisms. Wild-type dormant spores of
Bacillus subtilis
were efficiently ingested by the protozoan
Tetrahymena thermophila
but were neither digested nor killed. However, spores with various coat defects were killed and digested, leaving only an outer shell termed a rind, and supporting the growth of
Tetrahymena
. A similar rind was generated when coat-defective spores were treated with lysozyme alone. The sensitivity of spores with different coat defects to predation by
T. thermophila
paralleled the spores' sensitivities to lysozyme. Spore killing by
T. thermophila
was by means of lytic enzymes within the protozoal phagosome, not by initial spore germination followed by killing. These findings suggest that a major function of the coat of spores of
Bacillus
species is to protect spores against predation. We also found that indigestible rinds were generated even from spores in which cross-linking of coat proteins was greatly reduced, implying the existence of a coat structure that is highly resistant to degradative enzymes.
V600E B-Raf requires the Hsp90 chaperone for stability and is degraded in response to Hsp90 inhibitors
Authors: Grbovic O. M. , Basso A. D. , Sawai A. , Ye Q. , Friedlander P. , Solit D. , Rosen N.
Published: December 2005

The Raf family includes three members, of which B-Raf is frequently mutated in melanoma and other tumors. We show that Raf-1 and A-Raf require Hsp90 for stability, whereas B-Raf does not. In contrast, mutated, activated B-Raf binds to an Hsp90–cdc37 complex, which is required for its stability and function. Exposure of melanoma cells and tumors to the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin results in the degradation of mutant B-Raf, inhibition of mitogen-activated protein kinase activation and cell proliferation, induction of apoptosis, and antitumor activity. These data suggest that activated mutated B-Raf proteins are incompetent for folding in the absence of Hsp90, thus suggesting that the chaperone is required for the clonal evolution of melanomas and other tumors that depend on this mutation. Hsp90 inhibition represents a therapeutic strategy for the treatment of melanoma.