bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular simulation studies of the structure of phosphorylcholine self-assembled monolayers
Authors: Zheng Jie , He Yi , Chen Shengfu , Li Lingyan , Bernards Matthew T. , Jiang Shaoyi
Published: November 2006

We report a study of the structure of phosphorylcholine self-assembled monolayers (PC-SAMs) on Au(111) surfaces using both molecular mechanics (MM) and molecular dynamics (MD) simulation techniques. The lattice structure (i.e., packing densities and patterns) of the PC chains was determined first, by examining the packing energies of different structures by MM simulations in an implicit solvent. The chain orientation (i.e., antiparallel and parallel arrangements of the PC head groups) was then evaluated. The initial azimuthal angles of the PC chains were also adjusted to ensure that the optimal lattice structure was found. Finally, the two most probable lattice structures were solvated with explicit water molecules and their energies were compared after 1.5ns of MD simulations to verify the optimal structures obtained from MM. We found that the optimal lattice structure of the PC-SAM corresponds to a √7×√7 R19° lattice structure (i.e., surface coverage of 50.4Å2∕molecule) with a parallel arrangement of the head groups. The corresponding thickness of the optimal PC-SAM is 13.4Å which is in agreement with that from experiments. The head groups of the PC chains are aligned on the surface in such a way that their dipole components are minimized. The P→N vector of the head groups forms an angle of 82° with respect to the surface normal. The tilt direction of molecular chains was observed to be towards their next nearest neighbor.
Coherent polyatomic dynamics studied by femtosecond time-resolved photoelectron spectroscopy: Dissociation of vibrationally excited CS2 in the 6s and 4d Rydberg states
Authors: Knappenberger Kenneth L. , Lerch Eliza-Beth W. , Wen Patrick , Leone Stephen R.
Published: November 2006

The dissociation dynamics of the 6s and 4d Rydberg states of carbon disulfide (CS2*) are studied by time-resolved photoelectron spectroscopy. The CS2 is excited by two photons of 267nm (pump) to the 6s and 4d Rydberg states and probed by ionization with either 800 or 400nm. The experiments can distinguish and successfully track the time dynamics of both spin [1∕2] (upper) and [3∕2] (lower) cores of the excited Rydberg states, which are split by 60meV, by measuring the outgoing electron kinetic energies. Multiple mode vibrational wave packets are created within the Rydberg states and observed through recurrence interferences in the final ion state. Fourier transformation of the temporal response directly reveals the coherent population of several electronic states and vibrational modes. The composition of the wave packet is varied experimentally by tuning the excitation frequency to particular resonances between 264 and 270nm. The work presented here shows that the decay time of the spin components exhibits sensitivity to the electronic and vibrational states accessed in the pump step. Population of the bending mode results in an excited state lifetime of as little as 530fs, as compared to a several picosecond lifetime observed for the electronic origin bands. Experiments that probe the neutral state dynamics with 400nm reveal a possible vibrationally mediated evolution of the wave packet to a different Franck-Condon window as a consequence of Renner-Teller splitting. Upon bending, symmetry lowering from D∞h to C2v enables ionization to the CS2+ (BΠu2) final state. The dissociation dynamics observed are highly mode specific, as revealed by the frequency and temporal domain analysis of the photoelectron spectra.
Modes and the alpha-gamma transition in rf capacitive discharges in N2O at different rf frequencies
Authors: Lisovskiy V. , Booth J.-P. , Landry K. , Douai D. , Cassagne V. , Yegorenkov V.
Published: November 2006

This paper reports current-voltage characteristics and pressure-voltage transition curves from the weak-current α-mode to the strong-current γ-mode for rf capacitive discharges in N2O at frequencies of 2MHz, 13.56MHz, and 27.12MHz. At 2MHz the rf discharge is mostly resistive whereas at 13.56MHz and 27.12MHz it is mostly capacitive. The weak-current α-mode was found to exist only above a certain minimum gas pressure for all frequencies studied. N. Yatsenko [Sov. Phys. Tech. Phys. 26, 678 (1981)] previously proposed that the α−γ transition corresponds to breakdown of the sheaths. However, we show that this is the case only for sufficiently high gas pressures. At lower pressure there is a smooth transition from the weak-current α-mode to a strong-current γ-mode, in which the sheaths produce fast electrons but the sheath has not undergone breakdown.
Turbulent transport of alpha particles in reactor plasmas
Authors: Estrada-Mila C. , Candy J. , Waltz R. E.
Published: November 2006

A systematic study of the behavior of energetic ions in reactor plasmas is presented. Using self-consistent gyrokinetic simulations, in concert with an analytic asymptotic theory, it is found that alpha particles can interact significantly with core ion-temperature-gradient turbulence. Specifically, the per-particle flux of energetic alphas is comparable to the per-particle flux of thermal species (deuterium or helium ash). This finding opposes the conventional wisdom that energetic ions, because of their large gyroradii, do not interact with the turbulence. For the parameters studied, a turbulent modification of the alpha-particle density profile appears to be stronger than turbulent modification of the alpha-particle pressure profile. Crude estimates indicate that the alpha density modification, which is directly proportional to the core turbulence intensity, could be in the range of 15% at midradius in a reactor. The corresponding modification of the alpha-particle pressure profile is predicted to be smaller (in the 1% range).
Spray impact: Rim transverse instability initiating fingering and splash, and description of a secondary spray
Authors: Roisman Ilia V. , Horvat Kristijan , Tropea Cam
Published: November 2006

In this paper, normal spray impact onto a rigid wall, leading to the formation of secondary spray, is considered. The mechanism of splash is explained by the bending instability of a rim bounding a free liquid sheet. The linear stability analysis of the rim is performed in the framework of the long-wave, quasi-one-dimensional approach. The rim instability is caused by the moment of forces associated with the inertia of the liquid entering the rim. Next, two components of the drop velocity and their diameter, as well as various flux density vectors (number, volume, mass fluxes) and tensors (momentum flux), are measured using a phase Doppler instrument. It is shown that the viscous length scale of drop impact can be used in describing the splash threshold, diameter of secondary droplets, and their velocity. Consequently, a closed semi-empirical model for the secondary spray has been proposed and validated using a numerical simulation of spray transport based on an Euler-Lagrange approach.
Efficient cooling in supersonic jet expansions of supercritical fluids: CO and CO2
Authors: Christen Wolfgang , Rademann Klaus , Even Uzi
Published: November 2006

Pulsed, supersonic beams of pure carbon monoxide and carbon dioxide at stagnation conditions above their critical point have been investigated by time-of-flight measurements as a function of pressure and temperature. Although both molecules form clusters readily in adiabatic expansions, surprisingly large speed ratios (above 100) indicative of very low translational temperatures (below 0.1K) have been achieved. In particular, the supersonic expansion of CO2 at stagnation temperatures slightly above the phase transition to the supercritical state results in unprecedented cold beams. This efficient cooling is attributed to the large values of the heat capacity ratio of supercritical fluids in close vicinity of their critical point.
Random lasing from dye-gold nanoparticles in polymer films: Enhanced gain at the surface-plasmon-resonance wavelength
Authors: Popov O. , Zilbershtein A. , Davidov D.
Published: November 2006

The authors report on gold nanoparticle enhancement of the gain in dyes/nanoparticles/polymer film for random lasers. Importantly, they demonstrate a lower threshold for lasing and a stronger output intensity, which depend on the nanoparticle (NP) size. By calculating the “NP scattering resonance” using Mie theory and the measured surface-plasmon resonance, we can qualitatively explain the results, suggesting that the random lasing properties are dominated by an enhanced photon scattering mechanism induced by the surface plasmons.
Effective molecular polarizabilities and crystal refractive indices estimated from x-ray diffraction data
Authors: Whitten Andrew E. , Jayatilaka Dylan , Spackman Mark A.
Published: November 2006

Although it was proposed some time ago that (hyper)polarizabilities might be estimated from the results of x-ray charge density refinements, early results were unconvincing. In this work we show that the one particle density obtained from the usual multipole refinement model does not contain sufficient information to determine these response properties and instead pursue the “constrained wave function” approach of fitting to x-ray structure factors. Simplified sum-over-states expressions are derived for determining the dipole polarizability from these wave functions, and these clearly show that the earlier work ignored important two-electron expectation values for the dipole polarizability, and two- and three-electron terms for β, etc. Correction factors for the simplified sum-over-states polarizability tensors from the constrained wave function are obtained by calibration against coupled Hartree-Fock ab initio results to yield in-crystal effective polarizability tensors. Results obtained for benzene, urea, and 2-methyl-4-nitroaniline demonstrate that the effective molecular polarizabilities clearly include the effects of intermolecular interactions and electron correlation, especially for urea where the effects on the polarizability are known to be quite large. We also carefully consider the way in which the linear bulk susceptibility, χ(1), and refractive indices are determined from the x-ray fitted polarizabilities, employing three models based on a rigorous treatment of the local field. Incorrect results are obtained for the sort of molecules that are of interest in nonlinear optical applications if the molecules are approximated by single point dipoles. In contrast, the use of Lorentz-factor tensors averaged over several sites yields excellent results, with refractive indices obtained using this model in remarkably good agreement with optical measurements extrapolated to zero frequency.
Relationship between dust acoustic waves in two and three dimensions
Authors: Piel A. , Goree J.
Published: November 2006

Low frequency electrostatic waves are investigated for a monolayer suspension of dust particles that are shielded by an ambient plasma of three-dimensional extension. The dispersion of the resulting dust acoustic surface waves is compared with dust acoustic waves in three dimensions and with lattice modes in two dimensions. It is found that the wave dispersion is determined by shielding of electric fields by electrons and ions on either side of the dust monolayer; this differs from previously studied cases of charged sheets in a vacuum. The phase velocity of these surface waves suggests the definition of a proper dust plasma frequency for monolayer systems.
Size-dependent surface CO stretching frequency investigations on nanodiamond particles
Authors: Tu J.-S. , Perevedentseva E. , Chung P.-H. , Cheng C.-L.
Published: November 2006

In this work, the spectroscopic properties of surface functionalized nanodiamond particles are investigated via Fourier transform infrared spectroscopy. The functionalization of the nanodiamond surface was achieved chemically using strong acid treatment method. The size dependent CO stretching frequency (between 1680 and 1820cm−1) are studied for particle diameter sizes from the 5to500nm range. The surface CO stretching frequencies at ∼1820cm−1, for large particle size (500nm), down shifted to 1725cm−1 (5nm) with decreasing particle sizes. We attributed the shift as a result of hydrogen bond formation between the COOH groups in the carboxylated nanodiamond surfaces. Particle size was characterized with dynamic light scattering method and surface morphology of the particles was investigated with scanning electron microscopy. The influence of pH value on CO stretching frequency is also analyzed. This finding affords useful information for the studying of surface functionalized nanodiamonds with implications for their interaction with biomolecules.
On parameter estimation of chaotic systems via symbolic time-series analysis
Authors: Piccardi Carlo
Published: November 2006

Symbolic time-series analysis is used for estimating the parameters of chaotic systems. It is assumed that a “target model” (i.e., a discrete- or continuous-time description of the data-generating mechanism) is available, but with unknown parameters. A time series, i.e., a noisy, finite sequence of a measured (output) variable, is given. The proposed method first prescribes to symbolize the time series, i.e., to transform it into a sequence of symbols, from which the statistics of symbols are readily derived. Then, a symbolic model (in the form of a Markov chain) is derived from the data. It allows one to predict, in a probabilistic fashion, the time evolution of the symbol sequence. The unknown parameters are derived by matching either the statistics of symbols, or the symbolic prediction derived from data, with those generated by the (parametrized) target model. Three examples of application (the Henon map, a population model, and the Duffing system) prove that satisfactory results can be obtained even with short time series.
Delay-coordinates embeddings as a data mining tool for denoising speech signals
Authors: Napoletani D. , Struppa D. C. , Sauer T. , Berenstein C. A. , Walnut D.
Published: November 2006

In this paper, we utilize techniques from the theory of nonlinear dynamical systems to define a notion of embedding estimators. More specifically, we use delay-coordinates embeddings of sets of coefficients of the measured signal (in some chosen frame) as a data mining tool to separate structures that are likely to be generated by signals belonging to some predetermined data set. We implement the embedding estimator in a windowed Fourier frame, and we apply it to speech signals heavily corrupted by white noise. Our experimental work suggests that, after training on the data sets of interest, these estimators perform well for a variety of white noise processes and noise intensity levels.
Accumulation of electric-field-stabilized geminate polaron pairs in an organic semiconductor to attain high excitation density under low intensity pumping
Authors: Giebink N. C. , Forrest S. R.
Published: November 2006

The recombination dynamics of geminate polaron pair (PP) states are investigated by monitoring electric-field-induced delayed fluorescence in thin films consisting of the green laser dye, Coumarin-6 (C6) doped at 1wt% into 4,4′-bis(N-carbazolyl)biphenyl. We find that the PP decay follows τ−m (with m∼0.1), where τ is the time that the PPs are held in the field. This sublinear decay suggests the possibility for accumulation of PPs over time that can then be reconverted into excitons upon field removal. We demonstrate the generation of short (∼50ns full width at half maximum) bursts of C6 fluorescence with peak intensities >20 times the steady-state fluorescence intensity (corresponding to a C6 singlet exciton density NS>4×1015cm3) when pumped continuously by a low intensity (<1W∕cm2) laser in the presence of a pulsed electric field.
Nitride-based light-emitting diodes with p-AlInGaN surface layers prepared at various temperatures
Authors: Kuo C. H. , Kuo C. W. , Chen C. M. , Pong B. J. , Chi G. C.
Published: November 2006

The authors have prepared bulk p-AlInGaN layers and light-emitting diodes (LEDs) with p-AlInGaN surface layers by metal organic chemical vapor deposition. They found that the surfaces of the LEDs with p-AlInGaN layers are rough with high density of hexagonal pits. They also found that the pit width and the pit density depend on the growth temperature of the p-AlInGaN layer. Furthermore, it is found that a 62% enhancement in output intensity can be achieved from the LED with an 820°C p-AlInGaN cap layer without increasing the LED operation voltage.
Eddy current generation enhancement using ferrite for electromagnetic acoustic transduction
Authors: Dixon S. , Jian X.
Published: November 2006

Eddy currents are generated in an electrically conducting surface as a step in electromagnetic acoustic transduction (EAT). In eddy current testing, wire coils are often wound onto a ferrite core to increase the generated eddy current. With EAT, increased coil inductance is unacceptable as it leads to a reduction in the amplitude of a given frequency of eddy current from a limited voltage source, particularly where the current arises from capacitor discharge. The authors present a method for EAT where ferrite is used to increase the eddy current amplitude without significantly increasing coil inductance or changing the frequency content of the eddy current.
Very short wavelength (λ=3.1–3.3μm) quantum cascade lasers
Authors: Devenson J. , Barate D. , Cathabard O. , Teissier R. , Baranov A. N.
Published: November 2006

Quantum cascade lasers emitting at wavelengths as short as 3.1–3.3μm are reported. Such high intersubband emission energies (up to 400meV) have been obtained thanks to the high conduction band offset of the InAs∕AlSb material system. The structures, grown by molecular beam epitaxy on InAs substrates, are based on the bound-to-continuum design and use a low loss plasmon enhanced waveguide consisting of n+-InAs cladding layers with InAs∕AlSb superlattice spacers surrounding the active zone. The lasers exhibit threshold current densities close to 3kA∕cm2 at 83K and operate in pulsed mode up to 240K.
In situ experimental study of a near-field lens at visible frequencies
Authors: Webb-Wood G. , Ghoshal A. , Kik P. G.
Published: November 2006

Frequency dependent near-field scanning optical microscopy (NSOM) measurements of plasmon-mediated near-field focusing using a 50nm thick Au film are presented. In these studies the tip aperture of a NSOM probe acts as a localized light source, while the near-field image formed by the metal lens is detected in situ using nanoscale scatterers placed in the image plane. By scanning the relative position of object and probe, the near-field image generated by the lens is resolved. NSOM scans performed at different illumination frequencies reveal an optimum near-field image quality at frequencies close to the surface plasmon resonance frequency.
Monte Carlo simulation of the effects of adsorption on interparticle forces
Authors: Lane JE , Spurling TH
Published: November 2006

A Monte Carlo simulation
study of the force between two adsorbing walls is described. The adsorbate is in equilibrium with either a bulk gas or a
liquid phase. The force is correlated with the adsorption, singlet and radial
distribution functions, all of which vary with the distance of separation of
the walls, when this is of the order of a few atomic diameters. When the bulk
phase is a gas, a new type of surface transition occurs in which the distance
of wall separation is one of the determining degrees of freedom.
The preparation, aquation kinetics and activation volumes of trans-chloro-and trans-bromo-azido(meso-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)cobalt(III) perchlorate
Authors: Lawrance GA , Suvachittanont S
Published: November 2006

The macrocyclic complexes
trans-[Co(dtcd)(N3)X]ClO4 (dtcd = meso-5,12-
dimethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene; X = Cl-
or Br-) have been prepared and characterized. Halide aquation in 0.1 M HNO3 at 25�C proceeds at rates
of 4.6 × 10-4 s-1, ΔH‡ 77(�2) kJ mol-1,
ΔS?-51(�6) J K-1 mol-1 (X = Cl-)
and 10.2x10-4 s-1, ΔH‡ 80(�3) kJ mol-1,
ΔS‡ -34(�10) J K-1 mol-1 (X = Br-). The
pressure dependence of the aquation rate at elevated
pressures yields ΔV‡ +8.3(�0.5) cm3 mol-1 (X = Cl-) and ΔV‡ +5.3(�0.7) cm3 mol-1
(X = Br-). While the observed positive ΔV‡ values are
consistent with a dissociative mechanism they differ
markedly from reported negative ΔV‡ values for acid hydrolysis of [Co(NH3)5X]2+
ions.
Colouring matters of Australian plants. XXII. Ventilagone: crystal structure and an approach to synthesis
Authors: Cooke RG , Liu A , Raston CL , White AH
Published: November 2006

The crystal structure of
the title compound, a naturally occurring tricyclic quinone, C16H16O5,
has been found to be (1R*,3S*)-7,10- dihydroxy-1,3,8-trimethyl-3,4,6,9-tetrahydro-1H-naphtho[2,3-c]-pyran-
6,9-dione by single-crystal X-ray diffraction methods at 295(1) K and refined
by least squares to a residual of 0.033 for 1143 'observed' reflections.
Crystals are monoclinic, P21, a 8.346(8), b 16.79(2), c
4.911(5)Ǻ, β 101.17(8)°, Z 2. The molecule is shown to have the cis
configuration. As an approach to the synthesis of the pigment the model compound
5-chloro-8-methoxy-1,3-dimethylisochroman has been prepared and the two racemic
forms have been separated and characterized.
The Synthesis of 5-Oxo-2,5-dihydrofuran-2-ylideneacetic Acids
Authors: Massy-Westropp R , Price M
Published: November 2006

The 5-oxo-2,5-dihydrofuran-2-ylideneacetic
acids (2a), (3a), (9a), (10a), (11a), (12a) and (13a) have been synthesized by
a procedure which allows the unambiguous assignment of the stereochemistry about
the double bond in each isomer. The method, of general application, enables the
acids to be prepared from the corresponding t-butyl esters with acid without
isomerization about the double bond. The t-butyl esters are available from the
Wittig reaction between anhydrides and t- butoxy-carbonylmethylenetriphenylphosphorane.Where
mainly one isomer is produced in the Wittig reaction, isomerization to an
easily separable mixture of the esters can be achieved. Aspects of the isomerization
of enol-lactone esters (e.g. (2b)) are described.
Oxidation of bisphenols. II. Some compounds related to galvinoxyl
Authors: Colegate SM , Hewgill FR
Published: November 2006

The oxidation of a series
of 4,4'-alkylidenebis(2,6-di-t-butylphenols) having increasing substitution of
the central methylene carbon by alkyl groups is examined. In the
monosubstituted compounds the stability of the monophenoxy radical increases
with increase in the size of the substituent, while the stability of the galvinoxyl type radical decreases. β-Coupled products
are only obtained from the ethylidene bisphenol, a result that can be
correlated with e.s.r. hyperfine splitting constants. With increasing mono- or di-substitution bisspiroperoxides become the preferred
oxidation products. The e.s.r. spectrum of an ethylenebisgalvinoxyl
biradical is described.
Conversion of (+)-(R)-Limonene into (+)-(1S,4R)-p-mentha-2,8-dien-1-ol, an intermediate in the synthesis of tetrahydrocannabinoids
Authors: Rickards RW , Watson WP
Published: November 2006

(+)-(1S,4R)-p-Mentha-2,8-dien-1-ol
(3), an important intermediate in the synthesis of (-)-Δ9-trans-6a,10a-tetrahydrocannabinol
(1) and other tetrahydrocannabinoids, is conveniently prepared from
(+)-(R)-limonene (5) by rearrangement of its (1S,2R)-1,2-epoxide (7). Similar
rearrangement of the diastereoisomeric (1R,2S)-1,2-epoxide (6) yields (+)-(2S,4R)-p-mentha-1(7),8-dien-2-ol
(12), a major constituent of gingergrass oil.
Synthesis of haptens related to (Z)- and (E)-clomiphene
Authors: Johnson DW , Phillipou G , Seaborn CJ
Published: November 2006

Syntheses of (Z)- and
(E)-3-[4-(2-chloro-1,2- diphenylvinyl)phenoxy]propanoic acids (12) and (11),potential
haptens for the individual quantitation of the Z and of the E isomers of
clomiphene,2-[4-(2-chloro-1,2-diphenylvinyl)phenoxy]-N,N- diethylethanamine (2)
and (1), by radioimmunoassay, are described.
Death model for tussock perennial grasses: thresholds for grazing-induced mortality of mulga Mitchell grass (Thyridolepis mitchelliana)
Authors: Hacker Ronald B. , Hodgkinson Kenneth C. , Melville Gavin J. , Bean Judith , Clipperton Stephen P.
Published: November 2006

We investigated the relationship between grazing intensity and death of mulga Mitchell grass [Thyridolepis mitchelliana (Nees) S.T. Blake] plants in semi-arid wooded grasslands of eastern Australia. The study (from July 1993 to March 1997) involved factorial combinations of intensity and duration of sheep grazing before rest from grazing. Grazing intensity varied considerably among plants within the small plots and logit analysis of the binary responses of individual plants (a plant was judged to be alive or not) was used to establish the relationships between grazing history and death. Average residual (shoot) biomass over a moving window of 10–12 months was a good predictor of either general plant death or death during summer drought. Death over summer increased as average residual biomass dropped below 70%, and increased rapidly when the average fell below 50%. Variables based on residual shoot biomass generally provided better predictors of death than variables based on foliar height. However, as a predictor of death over summer, current foliar height was as good as average residual shoot biomass over the extended period. Summer death increased rapidly as foliar height fell below 10 cm. Environmental conditions were much less important than grazing in determining death rates, indicating that grazing management can have important benefits in maintaining productive grasslands even in more or less ‘normal’ seasons.
Sphingosine-1-phosphate lyase potentiates apoptosis via p53- and p38-dependent pathways and is down-regulated in colon cancer
Authors: Oskouian Babak , Sooriyakumaran Prathap , Borowsky Alexander D. , Crans Angelina , Dillard-Telm Lisa , Tam Yuen Yee , Bandhuvula Padmavathi , Saba Julie D.
Published: November 2006

Sphingolipid metabolites such as sphingosine-1-phosphate (S1P) and ceramide modulate apoptosis during development and in response to stress. In general, ceramide promotes apoptosis, whereas S1P stimulates cell proliferation and protects against apoptosis. S1P is irreversibly degraded by the enzyme S1P lyase (SPL). In this study, we show a crucial role for SPL in mediating cellular responses to stress. SPL expression in HEK293 cells potentiated apoptosis in response to stressful stimuli including DNA damage. This effect seemed to be independent of ceramide generation but required SPL enzymatic activity and the actions of p38 MAP kinase, p53, p53-inducible death domain protein (PIDD), and caspase-2 as shown by molecular and chemical inhibition of each of these targets. Further, SPL expression led to constitutive activation of p38. Endogenous SPL expression was induced by DNA damage in WT cells, whereas SPL knockdown diminished apoptotic responses. Importantly, SPL expression was significantly down-regulated in human colon cancer tissues in comparison with normal adjacent tissues, as determined by quantitative real-time PCR (Q-PCR) and immunohistochemical analysis. Down-regulation of S1P phosphatases was also observed, suggesting that colon cancer cells manifest a block in S1P catabolism. In addition, SPL expression and activity were down-regulated in adenomatous lesions of the
Min
mouse model of intestinal tumorigenesis. Taken together, these results indicate that endogenous SPL may play a physiological role in stress-induced apoptosis and provide an example of altered SPL expression in a human tumor. Our findings suggest that genetic or epigenetic changes affecting intestinal S1P metabolism may correlate with and potentially contribute to carcinogenesis.
Redefining the concept of reactive astrocytes as cells that remain within their unique domains upon reaction to injury
Authors: Wilhelmsson Ulrika , Bushong Eric A. , Price Diana L. , Smarr Benjamin L. , Phung Van , Terada Masako , Ellisman Mark H. , Pekny Milos
Published: November 2006

Reactive astrocytes in neurotrauma, stroke, or neurodegeneration are thought to undergo cellular hypertrophy, based on their morphological appearance revealed by immunohistochemical detection of glial fibrillary acidic protein, vimentin, or nestin, all of them forming intermediate filaments, a part of the cytoskeleton. Here, we used a recently established dye-filling method to reveal the full three-dimensional shape of astrocytes assessing the morphology of reactive astrocytes in two neurotrauma models. Both in the denervated hippocampal region and the lesioned cerebral cortex, reactive astrocytes increased the thickness of their main cellular processes but did not extend to occupy a greater volume of tissue than nonreactive astrocytes. Despite this hypertrophy of glial fibrillary acidic protein-containing cellular processes, interdigitation between adjacent hippocampal astrocytes remained minimal. This work helps to redefine the century-old concept of hypertrophy of reactive astrocytes.
On the feasibility of N
2
fixation via a single-site Fe
I
/Fe
IV
cycle: Spectroscopic studies of Fe
I
(N
2
)Fe
I
, Fe
IV
N, and related species
Authors: Hendrich Michael P. , Gunderson William , Behan Rachel K. , Green Michael T. , Mehn Mark P. , Betley Theodore A. , Lu Connie C. , Peters Jonas C.
Published: November 2006

The electronic properties of an unusually redox-rich iron system, [PhBP
R
3
]Fe

N
x
(where [PhBP
R
3
] is [PhB(CH
2
PR
2
)
3
]
−
), are explored by Mössbauer, EPR, magnetization, and density-functional methods to gain a detailed picture regarding their oxidation states and electronic structures. The complexes of primary interest in this article are the two terminal iron(IV) nitride species, [PhBP

i
Pr

3
]Fe

N (3a) and [PhBP
CH2Cy
3
]Fe

N (3b), and the formally diiron(I) bridged-Fe(μ-N
2
)Fe species, {[PhBP

i
Pr

3
]Fe}
2
(μ-N
2
) (
4
). Complex 4 is chemically related to 3a via a spontaneous nitride coupling reaction. The diamagnetic iron(IV) nitrides 3a and 3b exhibit unique electronic environments that are reflected in their unusual Mössbauer parameters, including quadrupole-splitting values of 6.01(1) mm/s and isomer shift values of −0.34(1) mm/s. The data for 4 suggest that this complex can be described by a weak ferromagnetic interaction (
J
/
D
< 1) between two iron(I) centers. For comparison, four other relevant complexes also are characterized: a diamagnetic iron(IV) trihydride [PhBP

i
Pr

3
]Fe(H)
3
(PMe
3
) (
5
), an
S
= 3/2 iron(I) phosphine adduct [PhBP

i
Pr

3
]FePMe
3
(6), and the
S
= 2 iron(II) precursors to 3a, [PhBP

i
Pr

3
]Fe

Cl and [PhBP

i
Pr

3
]Fe-2,3:5,6-dibenzo-7-aza bicyclo[2.2.1]hepta-2,5-diene (dbabh). The electronic properties of these respective complexes also have been explored by density-functional methods to help corroborate our spectral assignments and to probe their electronic structures further.
Specific SNARE complex binding mode of the Sec1/Munc-18 protein, Sec1p
Authors: Togneri John , Cheng Yi-Shan , Munson Mary , Hughson Frederick M. , Carr Chavela M.
Published: November 2006

The Sec1/Munc-18 (SM) family of proteins is required for vesicle fusion in eukaryotic cells and has been linked to the membrane-fusion proteins known as soluble
N
-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). SM proteins may activate the target-membrane SNARE, syntaxin, for assembly into the fusogenic SNARE complex. In support of an activation role, SM proteins bind directly to their cognate syntaxins. An exception is the yeast Sec1p, which does not bind the yeast plasma-membrane syntaxin, Sso1p. This exception could be explained if the SM interaction motif were blocked by the highly stable closed conformation of Sso1p. We tested the possibility of a latent binding motif using
sso1
mutants in yeast and reconstituted the Sec1p binding specificity observed
in vivo
with purified proteins
in vitro
. Our results indicate there is no latent binding motif in Sso1p. Instead, Sec1p binds specifically to the ternary SNARE complex, with no detectable binding to the binary t-SNARE complex or any of the three individual SNAREs in their uncomplexed forms. We propose that vesicle fusion requires a specific interaction between the SM protein and the ternary SNARE complex.
Bacterial metapopulations in nanofabricated landscapes
Authors: Keymer Juan E. , Galajda Peter , Muldoon Cecilia , Park Sungsu , Austin Robert H.
Published: November 2006

We have constructed a linear array of coupled, microscale patches of habitat. When bacteria are inoculated into this habitat landscape, a metapopulation emerges. Local bacterial populations in each patch coexist and weakly couple with neighbor populations in nearby patches. These spatially distributed bacterial populations interact through local extinction and colonization processes. We have further built heterogeneous habitat landscapes to study the adaptive dynamics of the bacterial metapopulations. By patterning habitat differences across the landscape, our device physically implements an adaptive landscape. In landscapes with higher niche diversity, we observe rapid adaptation to large-scale, low-quality (high-stress) areas. Our results illustrate the potential lying at the interface between nanoscale biophysics and landscape evolutionary ecology.
Correlation between β cell mass and glycemic control in type 1 diabetic recipients of islet cell graft
Authors: Keymeulen Bart , Gillard Pieter , Mathieu Chantal , Movahedi Babak , Maleux Geert , Delvaux Georges , Ysebaert Dirk , Roep Bart , Vandemeulebroucke Evy , Marichal Miriam , In 't Veld Peter , Bogdani Marika , Hendrieckx Christel , Gorus Frans , Ling Zhidong , van Rood Jon , Pipeleers Daniel
Published: November 2006

Islet grafts can induce insulin independence in type 1 diabetic patients, but their function is variable with only 10% insulin indepence after 5 years. We investigated whether cultured grafts with defined β cell number help standardize metabolic outcome. Nonuremic C-peptide-negative patients received an intraportal graft with 0.5–5.0 × 10
6
β cells per kilogram of body weight (kgBW) under antithymocyte globulin and mycophenolate mofetil plus tacrolimus. Metabolic outcome at posttransplant (PT) month 2 was used to decide on a second graft under maintenance mycophenolate mofetil/tacrolimus. Graft function was defined by C-peptide >0.5 ng/ml and reduced insulin needs, metabolic control by reductions in HbA
1c
, glycemia coefficient of variation, and hypoglycemia. At PT month 2, graft function was present in 16 of 17 recipients of >2 × 10
6
β cells per kgBW versus 0 of 5 with lower number. The nine patients with C-peptide >1 ng/ml and glycemia coefficient of variation of <25% did not receive a second graft; five of them were insulin-independent until PT month 12. The 12 others received a second implant; it achieved insulin-independence at PT month 12 when the first and second graft contained >2 × 10
6
β cells per kgBW. Of the 20 recipients of at least one graft with >2 × 10
6
β cells per kgBW, 17 maintained graft function and metabolic control up to PT month 12. At PT month 12, β cell function in insulin-independent patients ranged around 25% of age-matched control values. Thus, 1-year metabolic control can be reproducibly achieved and standardized by cultured islet cell grafts with defined β cell number.
Recent fear is resistant to extinction
Authors: Maren Stephen , Chang Chun-hui
Published: November 2006

In some individuals, fearful experiences (e.g., combat) yield persistent and debilitating psychological disturbances, including posttraumatic stress disorder (PTSD). Early intervention (e.g., debriefing) after psychological trauma is widely practiced and argued to be an effective strategy for limiting subsequent psychopathology, although there has been considerable debate on this point. Here we show in an animal model of traumatic fear that early intervention shortly after an aversive experience yields poor long-term fear reduction. Extinction trials administered minutes after aversive fear conditioning in rats suppressed fear acutely, but fear suppression was not maintained the next day. In contrast, delivering extinction trials 1 day after fear conditioning produced an enduring suppression of fear memory. We further show that the recent experience of an aversive event, not the timing of the extinction intervention
per se
, inhibits the development of long-term fear extinction. These results reveal that the level of fear present at the time of intervention is a critical factor in the efficacy of extinction. Importantly, our work suggests that early intervention may not yield optimal outcomes in reducing posttraumatic stress, particularly after severe trauma.
Introduction of oncogenes into mammary glands
in vivo
with an avian retroviral vector initiates and promotes carcinogenesis in mouse models
Authors: Du Zhijun , Podsypanina Katrina , Huang Shixia , McGrath Amanda , Toneff Michael J. , Bogoslovskaia Ekaterina , Zhang Xiaomei , Moraes Ricardo C. , Fluck Michele , Allred D. Craig , Lewis Michael T. , Varmus Harold E. , Li Yi
Published: November 2006

We have adapted the avian leukosis virus RCAS (replication-competent avian sarcoma-leukosis virus LTR splice acceptor)-mediated somatic gene transfer technique to introduce oncogenes into mammary cells in mice transgenic for the avian subgroup A receptor gene,
tva
, under control of the mouse mammary tumor virus (MMTV) promoter. Intraductal instillation of an RCAS vector carrying the polyoma middle T antigen (PyMT) gene (RCAS-
PyMT
) induced multiple, oligoclonal tumors within 3 weeks in infected mammary glands of MMTV-
tva
transgenic mice. The rapid appearance of these tumors from a relatively small pool of infected cells (estimated to be ≈2 × 10
3
cells per gland by infection with RCAS carrying a GFP gene; RCAS-
GFP
) was accompanied by a high fraction of cells positive for Ki67, Cyclin D1, and c-Myc, implying strong proliferation competence. Furthermore, the tumors displayed greater cellular heterogeneity than did tumors arising in MMTV-
PyMT
mice, suggesting that RCAS-
PyMT
transforms a relatively immature cell type. Infection of mice transgenic for both MMTV-
Wnt-1
and MMTV-
tva
with RCAS virus carrying an activated
Neu
oncogene dramatically enhanced tumor formation over what is observed in uninfected bitransgenic animals. We conclude that infection of mammary glands with retrovirus vectors is an efficient means to screen candidate oncogenes for their capacity to initiate or promote mammary carcinogenesis in the mouse.
Carbamylated erythropoietin ameliorates the metabolic stress induced
in vivo
by severe chronic hypoxia
Authors: Fantacci Monica , Bianciardi Paola , Caretti Anna , Coleman Thomas R. , Cerami Anthony , Brines Michael , Samaja Michele
Published: November 2006

Ischemia and chronic hypoxia (CH) trigger a variety of adverse effects arising from metabolic stress that injures cells. In response to reduced O
2
, hypoxia-inducible factor 1α (HIF-1α) activates erythropoietin (Epo) as well as many other target genes that counteract the effects of O
2
deficiency. Epo produced by the kidney stimulates erythrocyte production, leading to decreased HIF-1α production by improved tissue O
2
delivery. However, Epo is produced by many other tissues, and it is currently unclear to what extent, if any, locally produced Epo modulates HIF-1α expression. Derivatives of Epo that possess tissue-protective activities but do not stimulate erythropoiesis [e.g., carbamylated Epo (CEpo)] are useful tools with which to determine whether exogenous Epo modulates HIF-1α in the absence of changes in hemoglobin concentration. We compared the effects of CH (6.5% O
2
for 10 days) with or without CEpo administered by daily s.c. injection (10 μg/kg of body weight). CEpo administration did not alter the survival rate, weight loss, or increased hemoglobin concentration associated with CH. Therefore, CEpo does not directly suppress HIF-mediated erythropoiesis. CEpo does, however, prevent CH-induced neuronal increases of HIF-1α and Epo receptor-associated immunoreactivity (a measure of stress) while reducing the apoptotic index. In contrast, the myocardium did not exhibit increased HIF-1α expression during CH, although CEpo did reduce the apoptotic index. These observations therefore demonstrate that CEpo administration reduces the metabolic stress caused by severe CH, resulting in improved cellular survival independent of erythrocyte production.
Immunoabsorbent nanoparticles based on a tobamovirus displaying protein A
Authors: Werner Stefan , Marillonnet Sylvestre , Hause Gerd , Klimyuk Victor , Gleba Yuri
Published: November 2006

Earlier attempts to express peptides longer than 20 aa on the surface of tobamoviruses such as tobacco mosaic virus have failed. Surprisingly, we found that a functional fragment of protein A (133 aa) can be displayed on the surface of a tobamovirus as a C-terminal fusion to the coat protein via a 15-aa linker. The macromolecular nature of these nanoparticles allowed the design of a simple protocol for purification of mAbs with a recovery yield of 50% and >90% product purity. The extremely dense packing of protein A on the nanoparticles (>2,100 copies per viral particle) results in an immunoadsorbent with a binding capacity of 2 g mAb per g. This characteristic, combined with the high level of expression of the nanoparticles (>3 g adsorbent per kg of leaf biomass), provides a very inexpensive self-assembling matrix that could meet the criteria for a single-use industrial immunoadsorbent for antibody purification.
NSAIDs and scavenging birds: potential impacts beyond Asia's critically endangered vultures
Authors: Cuthbert Richard , Parry-Jones Jemima , Green Rhys E , Pain Deborah J
Published: November 2006

Veterinary treatment of livestock with diclofenac, a non-steroidal anti-inflammatory drug (NSAID), has caused catastrophic declines of
Gyps
vultures in Asia. This has highlighted a lack of knowledge on the potential impacts of NSAIDs on scavenging birds. Surveys of veterinarians and zoos document the outcomes of the treatment of over 870 scavenging birds from 79 species. As well as diclofenac, carprofen and flunixin were associated with mortality, with deaths observed in 13 and 30% of cases, respectively. Mortality was also found following treatment with ibuprofen and phenylbutazone. NSAID toxicity was reported for raptors, storks, cranes and owls, suggesting that the potential conservation impact of NSAIDs may extend beyond
Gyps
vultures and could be significant for New World vultures. In contrast, there were no reported mortalities for the NSAID meloxicam, which was administered to over 700 birds from 60 species. The relative safety of meloxicam supports other studies indicating the suitability of this NSAID to replace diclofenac in Asia.
Are clonal T‐cell large granular lymphocytes to blame for unexplained haematological abnormalities?
Authors: Sabnani Indu , Tsang Patricia
Published: November 2006

Abnormalities diagnosed on routine blood work, such as mild neutropenia, anaemia, thrombocytopenia and relative lymphocytosis, often have obscure aetiologies. A series of 30 patients were evaluated for various unexplained haematological abnormalities between 1997 and 2005, and found to have circulating monoclonal T‐cell large granular lymphocytes (T‐LGL). These patients fit the diagnosis of T‐cell clonopathy of unknown significance (TCUS), which may represent a clinical spectrum of clonal T‐LGL proliferation. Our patients were characterised by a complete absence of severe neutropenia (<0·5 × 109/l), absence of recurrent neutropenic infection (0%), negative rheumatoid serology (0%) and a low incidence of constitutional symptoms (20%). This overall asymptomatic clinical presentation appeared to be different from other previously reported series of TCUS or T‐LGL leukaemia who typically had symptomatology and required treatment. Our series of 30 patients represented the benign end of the spectrum of clonal T‐LGL proliferation, and might reflect diagnosis at earlier stages of the condition relative to other reported series. TCUS may be a heterogeneous and under‐diagnosed condition. This study further broadens our understanding of the clinical and laboratory manifestations of indolent clonal T‐cell proliferation, and raises our awareness of this condition. We suggest that TCUS should be considered in the diagnostic evaluation of unexplained haematological problems.
Decreased anticoagulant response to tissue factor pathway inhibitor type 1 in plasmas from patients with lupus anticoagulants
Authors: Liestøl Sigurd , Sandset Per Morten , Jacobsen Eva Marie , Mowinckel Marie‐Christine , Wisløff Finn
Published: November 2006

Inhibition of tissue factor pathway inhibitor type 1 (TFPI) is one of the mechanisms by which lupus anticoagulants (LA) may upregulate tissue factor (TF) activity. We wanted to examine whether purified immunoglobulin G (IgG) from patients with LA may interfere with the ability of TFPI to inhibit ex vivo TF‐induced thrombin generation. The endogenous thrombin potential (ETP) in pooled normal plasma (PNP) supplemented with IgG from either patients with LA or controls was determined in the absence or presence of recombinant TFPI (rTFPI). In the presence of a heparin neutraliser, the ETP was also determined in plasmas from patients with LA and controls before and after heparin injection in order to quantify the anticoagulant effect of heparin‐releasable TFPI in vivo. Compared with IgG from controls (n = 14), IgG from patients with LA (n = 28) induced a wide range of enhancing or inhibitory effects on the ETP in PNP. The response to rTFPI in PNP with IgG from patients with LA correlated inversely with thrombin generation (rs = 0·637, P = 0·0003). Correspondingly, the relative inhibition of ETP in postheparin plasmas was smaller for patients (n = 11) than for controls (n = 9) (32% vs. 68%, P = 0·007). Our findings support the hypothesis that TFPI anticoagulant activity is inhibited in some patients with LA.
Microstructural analysis of iron aluminide formed by self‐propagating high‐temperature synthesis mechanism in aluminium matrix composite
Authors: OLSZÓWKA‐MYALSKA ANITA , MAZIARZ WOJCIECH
Published: November 2006

An aluminium matrix composite with iron aluminide formed in situ as a result of self‐propagated high‐temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle‐like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self‐propagating high‐temperature synthesis consisted only of the Al3Fe phase.
Evolution of rapidly solidified NiAlCu(B) alloy microstructure
Authors: CZEPPE TOMASZ , OCHIN PATRICK
Published: November 2006

This study concerned phase transformations observed after rapid solidification and annealing at 500, 700 and 800 °C in 56.3 Ni‐39.9 Al‐3.8 Cu‐0.06 B (E1) and 59.8 Ni‐36.0 Al‐4.3 Cu‐0.06 B (E2) alloys (composition in at.%). Injection casting led to a homogeneous structure of very small, one‐phase grains (2–4 µm in size). In both alloys, the phase observed at room temperature was martensite of L10 structure. The process of the formation of the Ni5Al3 phase by atomic reordering proceeded at 285–394 °C in the case of E1 alloy and 450–550 °C in the case of E2 alloy. Further decomposition into NiAl (β) and Ni3Al (γ′) phases, the microstructure and crystallography of the phases depended on the path of transformations, proceeding in the investigated case through the transformation of martensite crystallographic variants. This preserved precise crystallographic orientation between the subsequent phases, very stable plate‐like morphology and very small β + γ′ grains after annealing at 800 °C.