bluuebunny/crossref_metadata_2025 huggingface dataset:
Six-dimensional vibrational analysis of coupled intermolecular vibrations in a binary cluster
Authors: Jansen A. , Gerhards M.
Published: July 2004

We report on full- (six-) dimensional calculations of the intermolecular vibrations of a binary aromatic-solvent cluster. An exact Hamiltonian for this kind of interaction is modified in a general manner in order to perform calculations of molecules without symmetry. The binary cluster phenol(H2O)1 is used as a test case since its intermolecular vibrations are anharmonic and highly coupled. The formulation of the Schrödinger equation leads to a complex-valued eigenvalue problem with a dimension larger than two million, which is solved by filter diagonalization to obtain both eigenvalues and eigenvectors. With the knowledge of the eigenvectors, an interpretation of all eigenvalues is possible by a characterization with pseudoquantum numbers that are related to the widely used nomenclature of intermolecular normal motions in aromatic(solvent) clusters.
Quantum aspects of self-organized periodic chemical reactions
Authors: Mareš Jiřı́ J. , Stávek Jiřı́ , Šesták Jaroslav
Published: July 2004

It is a remarkable empirical fact, known for a long time, that in certain self-organized periodic chemical reactions, such as Liesegang’s or Belousov-Zhabotinsky’s reactions, the product of molecular weight of precipitate, precipitation length period, and speed of precipitation is of the order of universal Planck’s quantum of action h. Based on the fact that the classical and quantum diffusions are processes, which are indistinguishable in the configuration space, a quantum criterion in terms of diffusion constants has been established. This criterion enables one to find out conditions under which the quantum behavior of self-organized periodic reactions can be observed.
Electron attachment on HI and DI in a uniform supersonic flow: Thermalization of the electrons
Authors: Goulay F. , Rebrion-Rowe C. , Carles S. , Le Garrec J. L. , Rowe B. R.
Published: July 2004

In order to check the electron thermalization in the CRESU technique (Cinétique de Réaction en Ecoulement Supersonique Uniforme, e.g., “reaction kinetics in a uniform supersonic flow”), electron attachment on HI and DI has been studied in the 48–170 K range. Attachment to HI is exothermic and the reaction is expected to be fast and to proceed at a rate close to the capture limit. On the contrary, attachment to DI is slightly endothermic, and a strong positive temperature dependence of the measured rate coefficient is expected if the electrons are thermal. This dependence is not observed, and we conclude that the electrons are not in thermal equilibrium with the neutrals in the afterglow. A model, based on electron heating by superelastic collisions with the buffer gas, is proposed to explain this fact and implications for previously published results are discussed.
Plane wave packet formulation of atom-plus-diatom quantum reactive scattering
Authors: Althorpe Stuart C.
Published: July 2004

We recently interpreted several reactive scattering experiments using a plane wave packet (PWP) formulation of quantum scattering theory [see, e.g., S. C. Althorpe, F. Fernández-Alonso, B. D. Bean, J. D. Ayers, A. E. Pomerantz, R. N. Zare, and E. Wrede, Nature (London) 416, 67 (2002)]. This paper presents the first derivation of this formulation for atom-plus-diatom reactive scattering, and explains its relation to conventional time-independent reactive scattering. We generalize recent results for spherical-particle scattering [S. C. Althorpe, Phys. Rev. A 69, 042702 (2004)] to atom-rigid-rotor scattering in the space-fixed frame, atom-rigid-rotor scattering in the body-fixed frame, and finally A+BC rearrangement scattering. The reactive scattering is initiated by a plane wave packet, describing the A+BC reagents in center-of-mass scattering coordinates, and is detected by projecting onto a series of AC+B (or AB+C) plane wave “probe” packets. The plane wave packets are localized at the closest distance from the scattering center at which the interaction potential can be neglected. The time evolution of the initial plane wave packet provides a clear visualization of the scattering into space of the reaction products. The projection onto the probe packets yields the time-independent, state-to-state scattering amplitude, and hence the differential cross section. We explain how best to implement the PWP approach in a numerical computation, and illustrate this with a detailed application to the H+D2 reaction.
Comment on “Multicomponent nucleation: Thermodynamically consistent description of the nucleation work” [J. Chem. Phys. 120, 3749 (2004)]
Authors: Schmelzer Jürn W. P. , Baidakov Vladimir G.
Published: July 2004

In the above cited paper, Kashchiev extends the “thermodynamically consistent” description of nucleation work to phase formation processes in multicomponent systems. It is claimed that this approach is generally applicable widely independent on the kind of phase transformation considered. In contrast to this statement, it is shown in our Comment that Kashchiev’s approach is theoretically not well founded. It contains, in addition, a number of assumptions, which are not generally fulfilled. Because of this his method cannot give, in general, a satisfactory determination of the work of critical cluster formation in nucleation theory. An experimental example is given verifying our conclusions.
A Monte Carlo study of fluctuating polymer-grafted membranes
Authors: Laradji Mohamed
Published: July 2004

Using Monte Carlo simulations of an off-lattice model, we study the elastic properties of polymer-grafted membranes. Our results are found to be in good agreement with those predicted by the classical path approximation of the self-consistent field theory and scaling theory based on de Gennes’ blob picture. In particular, we found that when the membrane is grafted on both sides by brushes with same molecular weight N and grafting density σ, the excess bending modulus induced by the polymers scales as N3σα where α is consistent with 7/3, as predicted by the self-consistent field theory, and 5/2, as predicted by the scaling theory. When the polymers are grafted to one side of the membrane only, the membrane bends away from the polymers with a spontaneous curvature with a scaling that is consistent with both scaling and self-consistent field theories. When the thickness of the brush exceeds the membrane’s spontaneous radius of curvature, the bending modulus approaches a constant which is of the same order as the bending modulus of the bare membrane.
Binary phase behavior and aggregation of dilute methanol in supercritical carbon dioxide: A Monte Carlo simulation study
Authors: Stubbs John M. , Siepmann J. Ilja
Published: July 2004

Configurational-bias Monte Carlo simulations in the Gibbs and isobaric-isothermal ensembles using the transferable potentials for phase equilibria force field were carried out to investigate the thermophysical properties of mixtures containing supercritical carbon dioxide and methanol. The binary vapor-liquid coexistence curves were calculated at 333.15 and 353.15 K and are in excellent agreement with experimental measurements. The self-association of methanol in supercritical carbon dioxide was investigated over a range of temperatures and pressures near the mixture critical point. The temperature dependence of the equlibrium constants for the formation of hydrogen-bonded aggregates (from dimer to heptamer) allowed for the determination of the enthalpy of hydrogen bonding, ΔHHB, in supercritical carbon dioxide with values for ΔHHB of about 15 kJ mol−1 falling within the range of previously proposed values. No strong pressure dependence was observed for the formation of aggregates. Apparently the decrease of the entropic penalty and of the enthalpic benefit upon increasing pressure or solvent density mostly cancel each other’s effect on aggregate formation.
A diagrammatic formulation of the kinetic theory of fluctuations in equilibrium classical fluids. IV. The short time behavior of the memory function
Authors: Ranganathan Madhav , Andersen Hans C.
Published: July 2004

Using a recently developed diagrammatic formulation of the kinetic theory of fluctuations in liquids, we investigate the short time behavior of the memory function for density fluctuations in a classical atomic fluid. At short times, the memory function has a large contribution that is generated by the repulsive part of the interatomic potential. We introduce a small parameter that is a measure of the softness of the repulsive part of the potential. The diagrams in the memory function that contribute to lowest order in that small parameter are identified and summed to give an explicit expression for the dominant contribution to the memory function at short times. The result leads to a theory for fluids with continuous potentials that is similar to the Enskog theory for hard sphere fluids.
The Adam–Gibbs equation and the out-of-equilibrium α relaxation of glass forming systems
Authors: Goitiandia L. , Alegrı́a A.
Published: July 2004

The temperature dependence of the α-relaxation time out of equilibrium has been investigated by means of dielectric relaxation in a series of fragile glass formers including several polymers. The influence of physical aging on this behavior has also been studied. The experimental results have been quantitatively compared with the predictions of the Adam–Gibbs equation. It has been found that, whereas for small molecule glass formers the experimental values of the apparent activation energy agree quite well with the prediction of the Adam–Gibbs equation, for polymers the experimental activation energy values are systematically higher. Moreover, whereas for small molecule glass formers the experimental values of the apparent activation energy remains essentially unaffected by physical aging, for polymers a pronounced reduction of the experimental apparent activation energy is observed. These results are found to be consistent with the Adam–Gibbs equation if a significant temperature variation of the configurational entropy in the investigated temperature range would occur for nonannealed polymers, being the possible variation hardly noticeable for the small molecules. With this assumption, all the obtained results would support the validity of the Adam–Gibbs equation for describing the temperature dependence of the time scale of the α-relaxation also out of equilibrium, at least for fragile glass formers.
The chlorobenzene-argon ground state intermolecular potential energy surface
Authors: Munteanu Cristian Robert , López Cacheiro Javier , Fernández Berta , Makarewicz Jan
Published: July 2004

Using the coupled cluster singles and doubles including connected triple excitations model with the augmented correlation consistent polarized valence double ζ basis set extended with a set of 3s3p2d1f1g midbond functions, we evaluate the ground state intermolecular potential energy surface of the chlorobenzene-argon van der Waals complex. The minima of 420 cm−1 are characterized by Ar atom position vectors of the length 3.583 Å, forming an angle of 9.87° with respect to the axis perpendicular to the chlorobenzene plane. These results are compared to those obtained for similar complexes and to the experimental data available. From the potential the three-dimensional vibrational eigenfunctions and eigenvalues are calculated and the results allow to correct and complete the experimental assignment.
Absolute intensities of Raman trace scattering from bicyclo-[1.1.1]-pentane
Authors: Dawes Richard , Gough Kathleen M.
Published: July 2004

Our previous theoretical studies have identified the Raman intensity parameter for the bridgehead C–H stretch in bicyclo-[1.1.1]-pentane as the largest for any saturated hydrocarbon yet considered, while the methylene C–H parameter is predicted to be ordinary. Theoretical methods including self-consistent field, static and time dependent density functional theory, and coupled cluster, all predict a large bridgehead intensity parameter, but differ widely in the actual value. We have synthesized bicyclo-[1.1.1]-pentane and recorded the absolute intensity Raman trace scattering spectra. The recorded intensity of a resonance polyad in the C–H stretching region has been resolved and distributed onto the fundamental modes through an anharmonic resonance analysis from a computed quartic force field. The experimental internal coordinate intensity parameters have been obtained and compared with those computed. Although the static and dynamic density functional values overestimate the parameter by 10%–18%, the values predicted at the coupled-cluster level are found to be correct to within experimental error.
Reactions of C(1D) with H2 and its deuterated isotopomers, a wave packet study
Authors: Lin Shi Ying , Guo Hua
Published: July 2004

Using a Chebyshev wave packet method, total and state-resolved reaction probabilities (J=0) were calculated for the reactions of C(1D) with various hydrogen isotopomers (H2, D2, and HD, νi=0, ji=0) on a recent ab initio potential energy surface. For all the isotopic variants, it was found that the initial state specified reaction probabilities have no energy threshold and are strongly oscillatory, indicative of the involvement of long-lived resonances in this barrierless reaction. The J=0 product vibrational and rotational distributions for all three isotopic reactions, and the CH/CD branching ratio for the C+HD reaction, show strong dependence on the collision energy, further underscoring the important role played by the resonances. The generally decaying vibrational distributions and highly excited rotational distributions, which corroborate an insertion mechanism, and the dominance of the CD+H channel in the C+HD reaction are consistent with existing experimental observations. Initial state specified integral cross sections and rate constants were estimated using a capture model. The estimated rate constants were found to be close and in the order kHD>kH2>kD2. Finally, a method to calculate branching ratio in the C+HD reaction is proposed.
Complete quantum control of the population transfer branching ratio between two degenerate target states
Authors: Gong Jiangbin , Rice Stuart A.
Published: July 2004

A five-level four-pulse phase-sensitive extended stimulated Raman adiabatic passage scheme is proposed to realize complete control of the population transfer branching ratio between two degenerate target states. The control is achieved via a three-node null eigenstate that can be correlated with an arbitrary superposition of the target states. Our results suggest that complete suppression of the yield of one of two degenerate product states, and therefore absolute selectivity in photochemistry, is achievable and predictable, even without studying the properties of the unwanted product state beforehand.
Microwave spectra and the metal-hydrogen bond lengths for the C5H5Mo(CO)3H and C5H5W(CO)3H complexes
Authors: Tanjaroon Chakree , Keck Kristen S. , Sebonia Matthew M. , Karunatilaka Chandana , Kukolich Stephen G.
Published: July 2004

The measurements of rotational spectra and metal-hydrogen bond lengths for molybdenum and tungsten hydride complexes were recently completed in our laboratory. The W-H and Mo-H bond lengths were obtained from high resolution rotational spectra of C5H5Mo(CO)3H, C5H5W(CO)3H, C5H5Mo(CO)3D, and C5H5W(CO)3D. Data for five molybdenum and four tungsten isotopomers were obtained for both the normal and deuterium-substituted species. The asymmetric-top rotational parameters A, B, C, ΔJ, and δJ were determined from the least-squares fits and these results indicate that the structures of these complexes are nearly rigid. The hydrogen bond lengths were determined for both complexes using Kraitchman analyses. The molybdenum-hydrogen bond length for the C5H5Mo(CO)3H complex is rMo-H=1.80(1) Å. The tungsten-hydrogen bond length for the C5H5W(CO)3H complex is rW-H=1.79(4) Å. Density functional theory (DFT) calculations of the structures were performed to obtain the optimized theoretical structures for C5H5Mo(CO)3H and C5H5W(CO)3H. Results obtained from the DFT calculations are in good agreement with the experimental parameters, and the Mo-H value is in good agreement with previously reported Mo-H bond lengths for similar complexes.
Kinetic isotope effect in hydrogen transfer arising from the effects of rotational excitation and occurrence of hydrogen tunneling in molecular systems
Authors: Miklavc Adolf
Published: July 2004

Hydrogen kinetic isotope effect with values of α≡ln(kH/kT)/ln(kD/kT)>3.3 which are generally ascribed to quantum tunneling of hydrogen are shown to arise in O+HCl(DCl,TCl) reactions due to the effects of rotational excitation on the distribution of encounters with the critical dividing surface. At higher rotational excitations these distributions are shifted towards the regions of the critical dividing surface with low barrier energies which can lead to a large enhancement of the barrier crossing. This effect depends strongly on the hydrogen isotope involved in the reaction and, at some temperatures, gives rise to α much larger than 3.3. It can be readily seen that the effect should arise also in condensed molecular systems, due to internal rotations or other vibrations »perpendicular« to the reaction coordinate.
Cynara cardunculus L., a potential source of inulin in the Mediterranean environment: screening of genetic variability
Authors: Raccuia S. A. , Melilli M. G.
Published: July 2004

Cynara cardunculus L. is a diploid (2n = 34) outcrossing perennial species, native to the Mediterranean basin, comprising the globe artichoke, the cultivated cardoon, and the wild cardoon. These species have potential as biomass, sugar, and oilseed crops. This paper aimed to study the genetic variability for sugar production and sugar composition in the roots of different C. cardunculus L. genotypes, in order to select those suitable for this specific purpose in the Mediterranean environment. At harvest the total biomass and root production, averaged for all genotypes, were 20.4 and 9.8 t DM/ha; they were influenced by genotype, with a CV of 37.4 and 38.5%, respectively. On average for all of the genotypes, the roots showed a total sugar content of 367 g DM/kg, with a CV of 17.1%; the main compound was inulin (85.0% of total sugars). The wild cardoon ‘SR1’ showed the highest total sugar content (470 g/kg DM). On average for all of the genotypes, the total sugar and inulin yields were 3.6 ± 0.20 and 3.0 ± 0.16 t/ha, respectively. It was possible to obtain total sugar yields higher than 4 t/ha in 6 genotypes (‘BH’, ‘VP’, ‘E438’, ‘L01’, ‘C2’, ‘P1’) of the 15 studied.
Yb(OTf)3 - TMSCl, a Novel Catalytic System in Cross-Aldol Reactions
Authors: Kagawa Natsuko , Toyota Masahiro , Ihara Masataka
Published: July 2004

A combination of Yb(OTf)3 and TMSCl influenced the outcome of cross-aldol reactions of cycloalkanones and benzaldehyde. Interestingly, reaction of cycloheptanone and cyclooctanone with aldehydes under the Yb(OTf)3–TMSCl reagent system provides 3-(2-oxocycloalkyl)-3-phenylpropanals in conjunction with the corresponding aldol products.
Asymmetric Synthesis of ( - )-Swainsonine
Authors: Lindsay Karl B. , Pyne Stephen G.
Published: July 2004

This paper describes a new synthesis of (–)-swainsonine via the ring-closing metathesis reaction of a substituted 3-allyl-4-vinyloxazolindin-2-one and subsequent diastereoselective syn-dihydroxylation of the resulting pyrrolo- [1,2-c]oxazol-3-one.
Integrating Structural and Functional Genomics
Authors: Parsons Lisa , Liu Fang , Yeh Deok Cheon , Sari Nese , Orban John
Published: July 2004

Structural genomics has provided many three-dimensional structures of proteins with unknown or poorly defined function where analysis of the fold suggests a possible binding site for small molecules. An approximate function may be evident from the structure but, most often, the specific target ligand remains unknown. This is a widespread observation in structural genomics programs and demonstrates the limits of structure-based approaches to determining function. Methods to identify the natural target ligands for such proteins, and therefore bridge structural and functional genomics studies, are discussed.
Understanding Metal-Free Catalytic Hydrogenation: A Systematic Theoretical Study of the Hydrogenation of Ethene
Authors: Chan Bun , Radom Leo
Published: July 2004

Metal-free catalytic hydrogenation of ethene has been examined using high-level [G3(MP2)-RAD] ab initio molecular orbital theory. The dependence of the catalytic activity on the nature of the catalyst Z–X–H has been explored. We find that the catalytic activity is generally greater as Z–X–H becomes more acidic, both for first- and second-row atoms X. Molecules in which X is a second-row atom generally lead to more effective catalysis than the corresponding first-row analogues. The proton affinity at X of Z–X–H also contributes significantly to the catalysis in some cases (e.g. amines).
Efficient Synthesis of an Enantiopure Thiasteroid by a Double Heck Reaction
Authors: Tietze Lutz F. , Lücke Lars P. , Major Felix , Müller Peter
Published: July 2004

The thiaestrane 7 was synthesized by two sequential Heck reactions starting from the thiophene derivatives 8a–8c, which contain a (Z)-halogenovinyl group, and the enantiopure hydrindene 2a. The first intermolecular Pd-catalyzed reaction leads to 11a and 11b in a highly regio- and diastereoselective manner. A subsequent intramolecular Heck reaction catalyzed by the palladacycle 4 then gave the thiasteroid 7 with an unusual cis-junction of the rings B and C.
A Chemoenzymatic Synthesis of the cis-Decalin Core Associated with the Novel Anti-Mitotic Agent Phomopsidin: Some Observations Concerning a High-Pressure-Promoted Diels–Alder Cycloaddition Reaction of (1S,2R)-3-Methyl-cis-1,2-dihydrocatechol and the Anionic Oxy–Cope Rearrangement of Compounds Derived from the Adduct
Authors: Banwell Martin G. , Edwards Alison J. , McLeod Malcolm D. , Stewart Scott G.
Published: July 2004

The enantiomerically pure and enzymatically derived cis-1,2-dihydrocatechol 2 engages in a diastereofacially selective Diels–Alder cycloaddition reaction with commercially available lactone 3 at 19 kbar to afford adduct 4, which is readily elaborated to the diene-ol 13. Treatment of this last compound with KH/18[crown]-6 resulted in successive anionic oxy-Cope and 1,2-Wittig rearrangements to afford acyloin 14 embodying the cis-decalin core associated with the natural product phomopsidin (1). Compound 16 also engages in an anionic oxy-Cope rearrangement reaction to give, depending on the molar equivalents of base used, either the cis-decalin 17 or the hexahydroindene 18. The structure of compound 18 has been established by single-crystal X-ray diffraction analysis.
Two Approaches to the Synthesis of the Macrodiolide Colletotriene
Authors: Muñoz Dulce M. , Passey Stephen C. , Simpson Thomas J. , Willis Christine L. , Campbell John B. , Rosser Richard
Published: July 2004

The first total syntheses of the 14-membered ring macrodilactone colletotriene are described. Starting from ethyl (R)-3-hydroxybutanoate, two synthetic strategies are compared which will enable the incorporation of deuterium at non-exchangeable sites for biosynthetic studies.
Some Synthetic Approaches to Glutamate AMPA Receptor Agonists Based on Isoxazolones
Authors: Cox Matthew , Jahangiri Saba , Perkins Michael V. , Prager Rolf H.
Published: July 2004

Several approaches to the synthesis of derivatives of the antifungal antibiotic TAN-950A, which is also an agonist of glutamate at hippocampal neurons, are reported. Additions of isoxazolon-4-yl anions to methyleneoxazolidinones were not useful because addition occurred predominantly through N-2. Similarly addition of the isoxazolon-4-yl radicals to model Michael acceptors occurred predominantly through N-2. Racemic analogues of TAN-950A were prepared by reaction of isoxazolone Mannich bases with acetylaminomalonate or addition of β-ketoester anions to dehydroalanines. The best approach to enantiomerically pure analogues was by acylation of pyroglutamates, followed by reaction with hydroxylamine.
Unexpected Formation of the Arcyriacyanin System by Condensation of a 3-Bromo-4-(indol-3-yl)maleimide with (2-Nitrophenyl)acetates
Authors: Mayer Guido , Hinze Claudia , Polborn Kurt , Steglich Wolfgang
Published: July 2004

The reaction of an N-protected 3-bromo-4-(indol-3-yl)maleimide with methyl (2-nitrophenyl)acetates in the presence of base affords condensed cycloheptatriene derivatives which can be transformed into arcyriacyanin-type alkaloids. The unusual reaction sequence implies a heptatrienyl–cycloheptadienyl anion rearrangement followed by a 1,5-sigmatropic shift to yield the thermodynamically more stable cycloheptatriene derivative.
Concerning the Proposed Structure of (+)-Laurobtusol: Spectral Discrepancies with Synthetic, Racemic Stereoisomers
Authors: Blanchfield Joanne T. , Chow Sharon , Bernhardt Paul V. , Kennard Colin H. L. , Kitching William
Published: July 2004

Laurobtusol, a minor metabolite from Laurencia obtusa, had been assigned constitution 1 and relative stereochemistry, 2. However, several stereoisomers of this novel, cyclopropane-containing system 1 have now been synthesized and spectral correspondence between the synthesized isomers and laurobtusol is lacking.
Management of photoperiod to control caprine reproduction in the subtropics
Authors: Delgadillo José Alberto , Fitz-Rodríguez Gonzalo , Duarte Gerardo , Véliz Francisco Gerardo , Carrillo Evaristo , Flores José Alfredo , Vielma Jesús , Hernandez Horacio , Malpaux Benoît
Published: July 2004

Reproductive seasonality is observed in some breeds originating from or adapted to subtropical latitudes. In ‘photoperiodic flexible breeds’, such as Australian cashmere goats, the annual breeding season can be manipulated through nutrition, whereas in ‘photoperiodic rigid breeds’, such as Creole goats from subtropical Mexico, sexual activity can be controlled by altering the photoperiod. In males from the latter breed, artificial long days, whether or not accompanied by the administration of melatonin, stimulate sexual activity during the non-breeding season. These treated males are able to induce the sexual activity of anoestrous females through the male effect under intensive or extensive conditions. Photoperiodic treatments and the male effect can be easily integrated into different breeding management systems in subtropical latitudes.
New treatments associated with timed artificial insemination in small ruminants
Authors: Menchaca Alejo , Rubianes Edgardo
Published: July 2004

Timed artificial insemination (TAI) is a very important tool in production systems, as it has a direct impact on cost-efficiency by reducing labour resulting from oestrus detection. However, to make TAI commercially feasible, hormonal treatments need to assure acceptable pregnancy rates and be economically viable. Recent advances in the knowledge of ovarian physiology (e.g. determination of follicular waves, sensitivity of the early corpus luteum) in small ruminants allowed the development of new treatments focused on an efficient estimation and synchronisation of the time of ovulation of the females of a treated flock/herd. In this review we summarise new information and concepts in the hormonal control of the life span of the corpus luteum, as well as methods to manipulate follicular growth in small ruminants. Additionally, we elaborate on recent studies concerning the use of TAI associated with short progestogen treatment in goats and the newly developed Synchrovine™ protocol (two doses of prostaglandin F2α given seven days apart) in sheep.
Overview of the response of anoestrous ewes to the ram effect
Authors: Ungerfeld R. , Forsberg M. , Rubianes E.
Published: July 2004

The present review summarises knowledge of the reproductive response of anoestrous ewes to the introduction of rams – in other words, the ram effect. The ovarian and endocrine response, the factors that determine whether ewes will respond or not (associated with both the stimulus and the receptivity of the ewes) and some aspects of practical management are discussed. Information on the use of the ram effect to stimulate post-partum, prepubertal and cyclic ewes is also given. New insights are provided on ovarian response patterns, including recently collected information on luteal responses. The existence of delayed ovulation (5–7 days after the introduction of the rams) followed by luteal phases of normal or short length, luteal cysts and luteinised follicles is reported after scanning the ovaries with ultrasound. Endocrine parameters for depth of anoestrus, such as LH pulsatility and FSH concentrations, and how the concentrations of these hormones should be considered are discussed. Particular attention is paid to the observation of spontaneous, higher LH pulsatility and higher FSH concentrations in anoestrous ewes that respond to rams with luteal phases than in those that fail to respond. The use of progestogen priming and single progestogen administration and the possible advantages for synchronisation of oestrus are also discussed. Other factors that should be considered before the ram effect is applied, such as the strength of the stimulus and some practical considerations, are also included.
Leukocyte adhesion during hypoxia is mediated by HIF-1-dependent induction of β2integrin gene expression
Authors: Kong Tianqing , Eltzschig Holger K. , Karhausen Jorn , Colgan Sean P. , Shelley C. Simon
Published: July 2004

Inflammatory responses are associated with significant changes in tissue metabolism. In particular, metabolic shifts during inflammation can result in significant tissue hypoxia, with resultant induction of hypoxia-responsive genes. Given this association, we hypothesized that leukocyte functional responses are influenced by hypoxia. Initial experiments revealed that exposure of the promonocytic cell line U937 to hypoxia resulted in increased adhesion to activated endothelia. Such increases were transcription-dependent and were blocked by antibodies directed against β2, but not β1, integrins. Analysis of β2integrin mRNA and protein in U937 cells revealed a 5- to 6-fold increase with hypoxia. Extension of this analysis to hypoxic human whole blood revealed prominent induction of β2integrin mRNA and proteinex vivo. Furthermore, murine β2integrin mRNA was found to be significantly induced during hypoxiain vivo. Subsequent studies identified a binding site for hypoxia-inducible factor 1 (HIF-1) in the CD18 gene. This gene encodes the subunit common to all four known types of β2integrin heterodimer. HIF-1 binding was demonstratedin vivo, and mutational analysis of the HIF-1 site within the CD18 promoter resulted in a loss of hypoxia inducibility. Taken together, these results demonstrate that hypoxia induces leukocyte β2integrin expression and function by transcriptional mechanisms dependent upon HIF-1.
Biophysical constraints on the origin of leaves inferred from the fossil record
Authors: Osborne C. P. , Beerling D. J. , Lomax B. H. , Chaloner W. G.
Published: July 2004

The molecular tool kit for producing flat-bladed photosynthetic structures evolved in marine and terrestrial plants during the middle Paleozoic, but it took a further 20 million years before leaves suddenly spread throughout land floras. This delay has long been difficult to explain, given the apparent advantage of leaves for photosynthetic primary production. Theory and experiments predict that exceptionally high atmospheric CO
2
levels in the middle Paleozoic delayed the origin of leaves by restricting stomatal development. This would have limited evaporative cooling, leading to lethal overheating of leaves absorbing large quantities of solar energy. Here we test the central prediction of this argument with a morphometric analysis of 300 plant fossils from major European collections. We show a 25-fold enlargement of leaf blades in two phylogenetically independent clades as atmospheric CO
2
levels fell during the late Paleozoic. Furthermore, preliminary data suggest that the first abrupt increase in leaf size was accompanied by an 8-fold rise in stomatal density. These evolutionary patterns support the relaxation of biophysical constraints on leaf area predicted by theory and point to a significant role for CO
2
in plant evolution.
The evolution of H5N1 influenza viruses in ducks in southern China
Authors: Chen H. , Deng G. , Li Z. , Tian G. , Li Y. , Jiao P. , Zhang L. , Liu Z. , Webster R. G. , Yu K.
Published: July 2004

The pathogenicity of avian H5N1 influenza viruses to mammals has been evolving since the mid-1980s. Here, we demonstrate that H5N1 influenza viruses, isolated from apparently healthy domestic ducks in mainland China from 1999 through 2002, were becoming progressively more pathogenic for mammals, and we present a hypothesis explaining the mechanism of this evolutionary direction. Twenty-one viruses isolated from apparently healthy ducks in southern China from 1999 through 2002 were confirmed to be H5N1 subtype influenza A viruses. These isolates are antigenically similar to A/Goose/Guangdong/1/96 (H5N1) virus, which was the source of the 1997 Hong Kong “bird flu” hemagglutinin gene, and all are highly pathogenic in chickens. The viruses form four pathotypes on the basis of their replication and lethality in mice. There is a clear temporal pattern in the progressively increasing pathogenicity of these isolates in the mammalian model. Five of six H5N1 isolates tested replicated in inoculated ducks and were shed from trachea or cloaca, but none caused disease signs or death. Phylogenetic analysis of the full genome indicated that most of the viruses are reassortants containing the A/Goose/Guangdong/1/96-like hemagglutinin gene and the other genes from unknown Eurasian avian influenza viruses. This study is a characterization of the H5N1 avian influenza viruses recently circulating in ducks in mainland China. Our findings suggest that immediate action is needed to prevent the transmission of highly pathogenic avian influenza viruses from the apparently healthy ducks into chickens or mammalian hosts.
Engagement of B7 on effector T cells by regulatory T cells prevents autoimmune disease
Authors: Paust Silke , Lu Linrong , McCarty Nami , Cantor Harvey
Published: July 2004

Although there is considerable evidence that a subpopulation of regulatory CD4+CD25+T cells can suppress the response of autoreactive T cells, the underlying molecular mechanism is not understood. We find that transmission of a suppressive signal by CD4CD25+regulatory cells requires engagement of the B7 molecule expressed on target T cells. The response of T cells from B7-deficient mice is resistant to suppressionin vitro, and these cells provoke a lethal wasting disease in lymphopenic mice despite the presence of regulatory T cells. Susceptibility of B7-deficient cells to suppression is restored by lentiviral-based expression of full-length, but not truncated, B7 lacking a transmembrane/cytoplasmic domain. Because expression of these B7 truncation mutants restores CD28-dependent costimulatory activity, these findings that indicate B7-based transmission of suppressive activity suggest new approaches to modifying autoimmune responses.
Inhibition of fatty acid synthase (FAS) suppressesHER2/neu(erbB-2) oncogene overexpression in cancer cells
Authors: Menendez Javier A. , Vellon Luciano , Mehmi Inderjit , Oza Bharvi P. , Ropero Santiago , Colomer Ramon , Lupu Ruth
Published: July 2004

Fatty acid synthase (FAS) activity is a potential therapeutic target to treat cancer and obesity. Here, we have identified a molecular link between FAS andHER2(erbB-2) oncogene, a marker for poor prognosis that is overexpressed in 30% of breast and ovarian cancers. Pharmacological FAS inhibitors cerulenin and C75 were found to suppress p185HER2oncoprotein expression and tyrosine-kinase activity in breast and ovarianHER2overexpressors. Similarly, p185HER2expression was dramatically down-regulated when FAS gene expression was silenced by using the highly sequence-specific mechanism of RNA interference (RNAi). Pharmacological and RNAi-mediated silencing of FAS specifically down-regulatedHER2mRNA and, concomitantly, caused a prominent up-regulation of PEA3, a transcriptional repressor ofHER2. A cytoplasmic redistribution of p185HER2was associated with marked morphological changes of FAS RNAi-transfected cells, whereas chemical inhibitors of FAS promoted a striking nuclear accumulation of p185HER2. The simultaneous targeting of FAS andHER2by chemical FAS inhibitors and the humanized antibody directed against p185HER2trastuzumab, respectively, was synergistically cytotoxic towardHER2overexpressors. Similarly, concurrent RNAi-mediated silencing of FAS andHER2genes synergistically stimulated apoptotic cell death inHER2overexpressors. p185HER2was synergistically down-regulated after simultaneous inhibition of FAS andHER2by either pharmacological inhibitors or small interfering RNA. These findings provide evidence of an active role of FAS in cancer evolution by specifically regulating oncogenic proteins closely related to malignant transformation, strongly suggesting thatHER2oncogene may act as the key molecular sensor of energy imbalance after the perturbation of tumor-associated FAS hyperactivity in cancer cells.
The schooling of children of immigrants: Contextual effects on the educational attainment of the second generation
Authors: Portes Alejandro , Hao Lingxin
Published: July 2004

We supplement earlier published findings on the academic achievement of the immigrant second generation with an analysis of school contextual effects based on the same large data set used by the best-known prior analyses, the Children of Immigrants Longitudinal Study. A hierarchical model of contextual and individual-level effects on academic achievement and school attrition reveals patterns that reproduce those found in national student surveys but also others that are unique to the second generation. Among the latter are the resilient negative effect of length of U.S. residence on achievement across school contexts and the fact that strong effects of national origin on grades are attenuated in schools with high proportions of coethnics. Mexican-origin students display significant disadvantages in achievement and retention that are generally compounded, not alleviated, by the schools that they attend. A theoretical explanation of this pattern is advanced, and its practical implications are discussed.
Cre-lox-regulated conditional RNA interference from transgenes
Authors: Ventura Andrea , Meissner Alexander , Dillon Christopher P. , McManus Michael , Sharp Phillip A. , Van Parijs Luk , Jaenisch Rudolf , Jacks Tyler
Published: July 2004

We have generated two lentiviral vectors for conditional, Cre-lox-regulated, RNA interference. One vector allows for conditional activation, whereas the other permits conditional inactivation of short hairpin RNA (shRNA) expression. The former is based on a strategy in which the mouse U6 promoter has been modified by including a hybrid between a LoxP site and a TATA box. The ability to efficiently control shRNA expression by using these vectors was shown in cell-based experiments by knocking down p53, nucleophosmin and DNA methyltransferase 1. We also demonstrate the usefulness of this approach to achieve conditional, tissue-specific RNA interference in Cre-expressing transgenic mice. Combined with the growing array of Cre expression strategies, these vectors allow spatial and temporal control of shRNA expression
in vivo
and should facilitate functional genetic analysis in mammals.
Anthocyanin metabolites in human urine and serum
Authors: Kay Colin D. , Mazza G. , Holub Bruce J. , Wang Jian
Published: July 2004

In the present study we investigated the metabolic conversion of cyanidin glycosides in human subjects using solid-phase extraction, HPLC–diode array detector, MS, GC, and enzymic techniques. Volunteers consumed approximately 20 g chokeberry extract containing 1·3 g cyanidin 3-glycosides (899 mg cyanidin 3-galactoside, 321 mg cyanidin 3-arabinoside, 51 mg cyanidin 3-xyloside and 50 mg cyanidin 3-glucoside). Blood samples were drawn at 0, 0·5, 1, and 2 h post-consumption of the extract. Urine samples were also collected at 0, 4–5, and 22–24 h. We have confirmed that human subjects have the capacity to metabolise cyanidin 3-glycosides, as we observed at least ten individual anthocyanin metabolites in the urine and serum. Average concentrations of anthocyanins and anthocyanin metabolites in the urine reached levels of 17·9 (range 14·9–20·9) μmol/l within 5 h post-consumption and persisted in 24 h urine samples at levels of 12·1 (range 11·1–13·0) nmol/l. In addition, average total levels of anthocyanins and anthocyanin metabolites detected in the serum were observed at 591·7 (range 197·3–986·1) nmol/l within 2 h post-consumption. Cyanidin 3-galactoside accounted for 55·4 % (9·9 (range 7·2–12·6) μmol/l) and 66·0 % (390·6 (range 119·4–661·9) nmol/l) of the detected anthocyanins in the urine and serum samples, respectively. The metabolites were identified as glucuronide conjugates, as well as methylated and oxidised derivatives of cyanidin 3-galactoside and cyanidin glucuronide. Conjugation probably affects the biological activity of anthocyanins and these metabolic products are likely in part responsible for the reported health benefits associated with the consumption of anthocyanins.
Diagnosis and duration of sickness absence as predictors for disability pension: Results from a three-year, multi-register based* and prospective study
Authors: Gjesdal Sturla , Bratberg Espen
Published: July 2004

Aim: A study was undertaken to identify predictors for the transition from long-term sickness absence into disability pension with special emphasis on routinely collected medical information (e.g. diagnoses on sickness certificates) and the duration of sickness-absence spells. Methods: The study used a 10% random sample of the Norwegian population of working age (the KIRUT database). Individuals below 60 years of age, with spells of long-term sickness absence starting in 1990 - 91, where the medical diagnoses on the sickness certificates were known, were identified. This group (4,432 men and 5,645 women) was followed up for three years after the end of sickness absence with regard to disability pension and working status. Results: In logistic regression the following predictors significantly increased the risk of obtaining disability pension during the first three years after the long-term sickness spell: age, part-time employment, and duration of absence >197 days. Higher education and having children <11 years significantly decreased the risk. Having the medical diagnoses ``mental problems'' and diseases in the nervous system, respiratory system, and circulatory systems indicated high risk (compared with musculoskeletal disease). The diagnostic groups ``pregnancy-related disease'' and ``injuries'' implied low risk for disability pension. In separate regressions for both genders the ``protective effect'' of having small children remained only for women. High risk for sickness absence caused by ``mental problems'' reached significance only for men. Conclusions and implications: Several risk factors for transition from long-term sickness absence into disability pension were identified. The finding that spells of sickness absence with duration up to seven months did not imply increased risk of disability during the first three years may have implications for interventions aimed at long-term sickness absentees.
Bacterial Inhibition of Phosphatidylcholine Synthesis Triggers Apoptosis in the Brain
Authors: Zweigner Janine , Jackowski Suzanne , Smith Shannon H. , van der Merwe Marie , Weber Joerg R. , Tuomanen Elaine I.
Published: July 2004

Streptococcus pneumoniae is the most common cause of bacterial meningitis of high mortality and morbidity. Neurological sequelae include paralysis, mental retardation, and learning disorders. In humans, neurons of the hippocampus undergo apoptosis as a result of meningitis. Phosphatidylcholine (PtdCho) is an essential component of mammalian cell membranes and PtdCho deficiency, either due to chemicals or altered nutrition, leads to apoptosis, especially in hippocampal neurons. We show that apoptosis of a variety of brain cells after pneumococcal infection arises from inhibition of PtdCho biosynthesis, the first such activity described for a bacterium. Apoptosis inhibitors did not prevent the bacterial-dependent inhibition of PtdCho biosynthesis. Supplementation with exogenous lyso-phosphatidylcholine prevents cell death and treatment of mice with cytidine diphosphocholine attenuates hippocampal damage during meningitis, even after the onset of infection. We conclude that bacterial inhibition of PtdCho biosynthesis activates an apoptotic cascade that is a causative event in pathogenesis and amenable to therapeutic intervention.
Essential Role of Lung Plasmacytoid Dendritic Cells in Preventing Asthmatic Reactions to Harmless Inhaled Antigen
Authors: de Heer Hendrik Jan , Hammad Hamida , Soullié Thomas , Hijdra Daniëlle , Vos Nanda , Willart Monique A.M. , Hoogsteden Henk C. , Lambrecht Bart N.
Published: July 2004

Tolerance is the usual outcome of inhalation of harmless antigen, yet T helper (Th) type 2 cell sensitization to inhaled allergens induced by dendritic cells (DCs) is common in atopic asthma. Here, we show that both myeloid (m) and plasmacytoid (p) DCs take up inhaled antigen in the lung and present it in an immunogenic or tolerogenic form to draining node T cells. Strikingly, depletion of pDCs during inhalation of normally inert antigen led to immunoglobulin E sensitization, airway eosinophilia, goblet cell hyperplasia, and Th2 cell cytokine production, cardinal features of asthma. Furthermore, adoptive transfer of pDCs before sensitization prevented disease in a mouse asthma model. On a functional level, pDCs did not induce T cell division but suppressed the generation of effector T cells induced by mDCs. These studies show that pDCs provide intrinsic protection against inflammatory responses to harmless antigen. Therapies exploiting pDC function might be clinically effective in preventing the development of asthma.
Inactivation of c-Cbl Reverses Neonatal Lethality and T Cell Developmental Arrest of SLP-76–deficient Mice
Authors: Chiang Y. Jeffrey , Sommers Connie L. , Jordan Martha S. , Gu Hua , Samelson Lawrence E. , Koretzky Gary A. , Hodes Richard J.
Published: July 2004

c-Cbl is an adaptor protein that negatively regulates signal transduction events involved in thymic-positive selection. To further characterize the function of c-Cbl in T cell development, we analyzed the effect of c-Cbl inactivation in mice deficient in the scaffolding molecule SLP-76. SLP-76–deficient mice show a high frequency of neonatal lethality; and in surviving mice, T cell development is blocked at the DN3 stage. Inactivation of c-cbl completely reversed the neonatal lethality seen in SLP-76–deficient mice and partially reversed the T cell development arrest in these mice. SLP-76−/− Cbl−/− mice exhibited marked expansion of polarized T helper type (Th)1 and Th2 cell peripheral CD4+ T cells, lymphoid infiltrates of parenchymal organs, and premature death. This rescue of T cell development is T cell receptor dependent because it does not occur in recombination activating gene 2−/− SLP-76−/− Cbl−/− triple knockout mice. Analysis of the signal transduction properties of SLP-76−/− Cbl−/− T cells reveals a novel SLP-76– and linker for activation of T cells–independent pathway of extracellular signal–regulated kinase activation, which is normally down-regulated by c-Cbl.