bluuebunny/crossref_metadata_2025 huggingface dataset:
Irreducible Brillouin conditions and contracted Schrödinger equations for n-electron systems. IV. Perturbative analysis
Authors: Kutzelnigg Werner , Mukherjee Debashis
Published: April 2004

The k-particle irreducible Brillouin conditions IBCk and the k-particle irreducible contracted Schrödinger equations ICSEk for a closed-shell state are analyzed in terms of a Møller–Plesset–type perturbation expansion. The zeroth order is Hartree–Fock. From the IBC2(1), i.e., from the two-particle IBC to first order in the perturbation parameter μ, one gets the leading correction λ2(1) to the two-particle cumulant λ2 correctly. However, in order to construct the second-order energy E2, one also needs the second-order diagonal correction γD(2) to the one-particle density matrix γ. This can be obtained: (i) from the idempotency of the n-particle density matrix, i.e., essentially from the requirement of n-representability; (ii) from the ICSE1(2); or (iii) by means of perturbation theory via a unitary transformation in Fock space. Method (ii) is very unsatisfactory, because one must first solve the ICSE3(2) to get λ3(2), which is needed in the ICSE2(2) to get λ2(2), which, in turn, is needed in the ICSE1(2) to get γ(2). Generally the (k+1)-particle approximation is needed to obtain Ek correctly. One gains something, if one replaces the standard hierarchy, in which one solves the ICSEk, ignoring λk+1 and λk+2, by a renormalized hierarchy, in which only λk+2 is ignored, and λk+1 is expressed in terms of the λp of lower particle rank via the partial trace relation for λk+2. Then the k-particle approximation is needed to obtain Ek correctly. This is still poorer than coupled-cluster theory, where the k-particle approximation yields Ek+1. We also study the possibility to use some simple necessary n-representability conditions, based on the non-negativity of γ(2) and two related matrices, in order to get estimates for γD(2) in terms of λ2(1). In general these estimates are rather weak, but they can become close to the best possible bounds in special situations characterized by a very sparse structure of λ2 in terms of a localized representation. The perturbative analysis does not encourage the use of a k-particle hierarchy based on the ICSEk (or on their reducible counterparts, the CSEk), it rather favors the approach in terms of the unitary transformation, where the k-particle approximation yields the energy correct up to E2k−1. The problems that arise are related to the unavoidable appearance of exclusion-principle violating cumulants. The good experience with perturbation theory in terms of a unitary transformation suggests that one should abandon a linearly convergent iteration scheme based on the ICSEk hierarchy, in favor of a quadratically convergent one based on successive unitary transformations.
Mixing and reaction fronts in laminar flows
Authors: Leconte M. , Martin J. , Rakotomalala N. , Salin D. , Yortsos Y. C.
Published: April 2004

Autocatalytic reaction fronts between unreacted and reacted mixtures in the absence of fluid flow propagate as solitary waves. In the presence of imposed flow, the interplay between diffusion and advection enhances the mixing, leading to Taylor hydrodynamic dispersion. We present asymptotic theories in the two limits of small and large Thiele modulus (slow and fast reaction kinetics, respectively) that incorporate flow, diffusion, and reaction. For the first case, we show that the problem can be handled to leading order by the introduction of the Taylor dispersion replacing the molecular diffusion coefficient by its Taylor counterpart. In the second case, the leading-order behavior satisfies the eikonal equation. Numerical simulations using a lattice gas model show good agreement with the theory. The Taylor model is relevant to microfluidics applications, whereas the eikonal model applies at larger length scales.
Spectroscopic consideration of the surface potential built across phthalocyanine thin films on a metal electrode
Authors: Manaka Takaaki , Li Cheng-Quan , Cheng Xiao-Man , Iwamoto Mitsumasa
Published: April 2004

The nonlinear optical properties of tert-butyl phthalocyanine copper Langmuir–Blodgett (CuttbPc LB) films and vacuum-evaporated phthalocyanine copper (CuPc) films deposited on a metal surface were investigated by second-harmonic generation (SHG) spectroscopy. At the organic/metal interface, a space charge field is formed due to the presence of excess charge injected from a metal electrode to the organic layer. Since the Pc molecule has D4h symmetry, an inversion center is present and the optical SH process is not allowed under the electric–dipole approximation. However, the space charge field at the interface directly influences the symmetric structure of the electrons in the Pc molecule. We investigated the contributions of the surface potential to the SHG using Pc LB and vacuum-evaporated films deposited on aluminum (Al) and gold (Au) metal electrodes, where a distinctive difference in the spectrum for the Pc films on the Al and Au surfaces was observed. The contribution of the surface potential was revealed based on the resonant conditions of the SH process, taking into account the electric–quadrupole transition and dc-field-induced electric–dipole transition.
Density-functional generalized-gradient and hybrid calculations of electromagnetic properties using Slater basis sets
Authors: Watson Mark A. , Handy Nicholas C. , Cohen Aron J. , Helgaker Trygve
Published: April 2004

In this paper we extend our density-functional theory calculations, with generalized gradient approximation and hybrid functionals, using Slater-type orbitals (STOs), to the determination of second-order molecular properties. The key to the entire methodology involves the fitting of all STO basis function products to an auxiliary STO basis, through the minimization of electron-repulsion integrals. The selected properties are (i) dipole polarizabilities, (ii) nuclear magnetic shielding constants, and (iii) nuclear spin–spin coupling constants. In all cases the one-electron integrals involving STOs were evaluated by quadrature. The implementation for (ii) involved some complexity because we used gauge-including atomic orbitals. The presence of two-electron integrals on the right-hand side of the coupled equations meant that the fitting procedure had to be implemented. For (iii) in the hybrid case, fitting procedures were again required for the exchange contributions. For each property we studied a number of small molecules. We first obtained an estimate of the basis set limit using Gaussian-type orbitals (GTOs). We then showed how it is possible to reproduce these values using a STO basis set. For (ii) a regular TZ2P quality STO basis was adequate; for (i) the addition of one set of diffuse functions (determined by Slater’s rules) gave the required accuracy; for (iii) it was necessary to add a set of 1s functions, including one very tight function, to give the desired result. In summary, we show that it is possible to predict second-order molecular properties using STO basis sets with an accuracy comparable with large GTO basis sets. We did not encounter any major difficulties with either the selection of the bases or the implementation of the procedures. Although the energy code (especially in the hybrid case) may not be competitive with a regular GTO code, for properties we find that STOs are more attractive.
Dissociative recombination of NH4+ and ND4+ ions: Storage ring experiments and ab initio molecular dynamics
Authors: Öjekull J. , Andersson P. U. , Någård M. B. , Pettersson J. B. C. , Derkatch A. M. , Neau A. , Rosén S. , Thomas R. , Larsson M. , Österdahl F. , Semaniak J. , Danared H. , Källberg A. , Ugglas M. af. , Marković N.
Published: April 2004

The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001–1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85±0.04) and NH2+2H (0.13±0.01), while the DR of ND4+ mainly results in ND3+D (0.94±0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.
Solvent reorganization energy of electron-transfer reactions in polar solvents
Authors: Matyushov Dmitry V.
Published: April 2004

A microscopic theory of solvent reorganization energy in polar molecular solvents is developed. The theory represents the solvent response as a combination of the density and polarization fluctuations of the solvent given in terms of the density and polarization structure factors. A fully analytical formulation of the theory is provided for a solute of arbitrary shape with an arbitrary distribution of charge. A good agreement between the analytical procedure and the results of Monte Carlo simulations of model systems is achieved. The reorganization energy splits into the contributions from density fluctuations and polarization fluctuations. The polarization part is dominated by longitudinal polarization response. The density part is inversely proportional to temperature. The dependence of the solvent reorganization energy on the solvent dipole moment and refractive index is discussed.
Molecular dynamics investigation of ferrous–ferric electron transfer in a hydrolyzing aqueous solution: Calculation of the pH dependence of the diabatic transfer barrier and the potential of mean force
Authors: Rustad James R. , Rosso Kevin M. , Felmy Andrew R.
Published: April 2004

We present a molecular model for ferrous–ferric electron transfer in an aqueous solution that accounts for electronic polarizability and exhibits spontaneous cation hydrolysis. An extended Lagrangian technique is introduced for carrying out calculations of electron-transfer barriers in polarizable systems. The model predicts that the diabatic barrier to electron transfer increases with increasing pH, due to stabilization of the Fe3+ by fluctuations in the number of hydroxide ions in its first coordination sphere, in much the same way as the barrier would increase with increasing dielectric constant in the Marcus theory. We have also calculated the effect of pH on the potential of mean force between two hydrolyzing ions in aqueous solution. As expected, increasing pH reduces the potential of mean force between the ferrous and ferric ions in the model system. The magnitudes of the predicted increase in diabatic transfer barrier and the predicted decrease in the potential of mean force nearly cancel each other at the canonical transfer distance of 0.55 nm. Even though hydrolysis is allowed in our calculations, the distribution of reorganization energies has only one maximum and is Gaussian to an excellent approximation, giving a harmonic free energy surface in the reorganization energy F(ΔE) with a single minimum. There is thus a surprising amount of overlap in electron-transfer reorganization energies for Fe2+–Fe(H2O)63+, Fe2+–Fe(OH)(H2O)52+, and Fe2+–Fe(OH)2(H2O)+ couples, indicating that fluctuations in hydrolysis state can be viewed on a continuum with other solvent contributions to the reorganization energy. There appears to be little justification for thinking of the transfer rate as arising from the contributions of different hydrolysis states. Electronic structure calculations indicate that Fe(H2O)62+–Fe(OH)n(H2O)6−n(3−n)+ complexes interacting through H3O2− bridges do not have large electronic couplings.
Mode-coupling study on the dynamics of hydrophobic hydration
Authors: Yamaguchi T. , Matsuoka T. , Koda S.
Published: April 2004

The molecular motion of water in water–hydrophobic solute mixtures was investigated by the mode-coupling theory for molecular liquids based on the interaction-site description. When the model Lennard-Jones solute was mixed with water, both the translational and reorientational motions of solvent water become slower, in harmony with various experiments and molecular dynamics simulations. We compared the mechanism of the slowing down with that of the pressure dependence of the molecular motion of neat water [T. Yamaguchi, S.-H. Chong, and F. Hirata, J. Chem. Phys. 119, 1021 (2003)]. We found that the decrease in the solvent mobility caused by the solute can essentially be elucidated by the same mechanism: That is, the fluctuation of the number density of solvent due to the cavity formation by the solute strengthens the friction on the collective polarization through the dielectric friction mechanism: We also employed the solute molecule that is the same as solvent water except for the amount of partial charges, in order to alter the strength of the solute–solvent interaction continuously. The mobility of the solvent water was reduced both by the hydrophobic and strongly hydrophilic solutes, but it was enhanced in the intermediate case. Such a behavior was discussed in connection with the concept of positive and negative hydrations.
Scaling behavior of nonisothermal phase separation
Authors: Rüllmann Max , Alig Ingo
Published: April 2004

The phase separation process in a critical mixture of polydimethylsiloxane and polyethylmethylsiloxane (PDMS/PEMS, a system with an upper critical solution temperature) was investigated by time-resolved light scattering during continuous quenches from the one-phase into the two-phase region. Continuous quenches were realized by cooling ramps with different cooling rates κ. Phase separation kinetics is studied by means of the temporal evolution of the scattering vector qm and the intensity Im at the scattering peak. The curves qm(t) for different cooling rates can be shifted onto a single mastercurve. The curves Im(t) show similar behavior. As shift factors, a characteristic length Lc and a characteristic time tc are introduced. Both characteristic quantities depend on the cooling rate through power laws: Lc∼κ−δ and tc∼κ−ρ. Scaling behavior in isothermal critical demixing is well known. There the temporal evolutions of qm and Im for different quench depths ΔT can be scaled with the correlation length ξ and the interdiffusion coefficient D, both depending on ΔT through critical power laws. We show in this paper that the cooling rate scaling in nonisothermal demixing is a consequence of the quench depth scaling in the isothermal case. The exponents δ and ρ are related to the critical exponents ν and ν* of ξ and D, respectively. The structure growth during nonisothermal demixing can be described with a semiempirical model based on the hydrodynamic coarsening mechanism well known in the isothermal case. In very late stages of nonisothermal phase separation a secondary scattering maximum appears. This is due to secondary demixing. We explain the onset of secondary demixing by a competition between interdiffusion and coarsening.
Polymer dynamics in repton model at large fields
Authors: Kolomeisky Anatoly B. , Drzewiński Andrzej
Published: April 2004

Polymer dynamics at large fields in Rubinstein–Duke repton model is investigated theoretically. Simple diagrammatic approach and analogy with asymmetric simple exclusion models are used to analyze the reptation dynamics of polymers. It is found that for polyelectrolytes the drift velocity decreases exponentially as a function of the external field with an exponent depending on polymer size and parity, while for polyampholytes the drift velocity is independent of polymer chain size. However, for polymers, consisting of charged and neutral blocks, the drift velocity approaches the constant limit which is determined by the size of the neutral block. The theoretical arguments are supported by extensive numerical calculations by means of density-matrix renormalization group techniques.
Ab initio study of the BiSe and BiTe electronic spectra: What happens with X2–X1 emission in the heavier Bi chalcogenides?
Authors: Lingott Rainer M. , Liebermann Heinz-Peter , Alekseyev Aleksey B. , Buenker Robert J.
Published: April 2004

A series of spin–orbit configuration interaction calculations has been carried out for the BiSe and BiTe molecules and analyzed in comparison with data obtained earlier for the isovalent BiO and BiS systems. An avoided crossing caused by the spin–orbit interaction between the X 2Π and A 4Π electronic states is shown to have a decisive effect on the lower-energy spectrum in each case. Irregularities in the X2 3/2 state vibrational manifold occur as a consequence of this nonadiabatic interaction, and the v vibrational number for the onset of these perturbations is found to gradually decrease in going from BiO to BiSe, in agreement with experiment. In BiTe the shape of the X2 potential curve is so altered by the avoided crossing that its minimum becomes shifted to a significantly larger distance than for the X1 state, unlike the case for BiSe or the lighter Bi chalcogenides. This characteristic appears to be the root cause for the fact that the X2 state has not yet been found experimentally in the BiTe spectrum, despite careful searches in the expected energy range. Radiative lifetimes have also been calculated for the low-lying states of both the BiSe and BiTe molecules, and these results are found to be consistent with experimental observations.
Pattern formation and fluctuation-induced transitions in protein crystallization
Authors: Nicolis Gregoire , Basios Vasileios , Nicolis Catherine
Published: April 2004

A kinetic model of protein crystallization accounting for the nucleation stage, the growth and competition of solid particles and the formation of macroscopic patterns is developed. Different versions are considered corresponding successively, to a continuous one-dimensional crystallization reactor, a coarse grained two-box model and a model describing the evolution of the space averaged values of fluid and solid material. The analysis brings out the high multiplicity of the patterns. It provides information on their stability as well as on the kinetics of transitions between different states under the influence of the fluctuations.
Resonantly enhanced two photon ionization and zero kinetic energy spectroscopy of jet-cooled 4-aminopyridine
Authors: He Yonggang , Wu Chengyin , Kong Wei
Published: April 2004

We report studies of supersonically cooled 4-aminopyridine (4-AP) using two-color resonantly enhanced multiphoton ionization (REMPI) and two-color zero kinetic energy (ZEKE) photoelectron spectroscopy. With the aid of ab initio and density functional calculations, vibrational modes of the first electronically excited state (S1) of the neutral species and those of the cation have been assigned, and the adiabatic ionization potential has been determined to be 62291±6 cm−1. The REMPI spectrum of the S1 state is dominated by ring deformation modes and the inversion mode of the amino group, while the ZEKE spectra demonstrate a strong propensity of Δv=0, where v is the vibrational quantum number of the intermediate vibronic state from S1. In addition, the ZEKE spectra obtained via different vibrational levels of the S1 state contain four common features, corresponding to the activation of four different vibrational modes of the cation. These observations are explained in terms of the structural changes from the ground state to S1 and further to the cation. The vibrational mode distributions in both the REMPI and the ZEKE spectra, the excitation energy of the S1 state, and the ionization potential of 4-AP, are remarkably similar to those of aniline, suggesting that the electronic activity is centered on the ring.
Magnetic resonance imaging of spin-polarization transfer of polarized Xe atoms dissolving into ethanol
Authors: Ishikawa Kiyoshi , Imai Hirohiko , Takagi Yoshihiro
Published: April 2004

We detect the free-induction signals of xenon atoms polarized by spin-exchange optical pumping. The temperature dependence of dissolution and spin-polarization transfer of xenon atoms to ethanol is measured by simultaneous detection of both xenon and proton signals. The polarization of proton is efficiently enhanced in the xenon-saturated solution at low magnetic fields. The large polarization and chemical shift enable us to obtain clearly the distribution image of xenon atoms near the gas–liquid and liquid–liquid boundaries. Therefore the localization of polarized xenon atoms is observed near the surface. By time-resolved magnetic resonance imaging of polarized xenon and polarization-enhanced proton, the spin dynamics is qualitatively studied for the nuclear spins interacting with each other in a dense solution.
An efficient molecular dynamics simulation method for calculating the diffusion-influenced reaction rates
Authors: Lee Jinuk , Yang Seongeun , Kim Jaemin , Lee Sangyoub
Published: April 2004

We present a molecular dynamics (MD) simulation method for calculating the diffusion-influenced reaction rates in the limit of low reactant concentrations. To calculate the reaction rate coefficient, we use MD trajectories of a nonreactive equilibrium system that are initiated with a pair of reactant molecules in reactive configuration. Hence reaction systems involving complicated reactant molecules with geometrically restricted reactivities can be treated with comparable efficiency as the simple hard-sphere reaction system. Compared to the similar MD method proposed by Van Beijeren, Dong, and Bocquet [J. Chem. Phys. 114, 6265 (2001)], the present method has a couple of advantages. First, reactions involving more general sink functions can be treated. Second, more accurate results can be obtained when the reaction probability upon collision is less than unity. As an application, we investigate the effects of nondiffusive dynamics and hydrodynamic interaction of reactants on the reaction rate.
Electron correlation effects in the adiabatic charge transfer reactions at the metal/polar liquid interface
Authors: Kuznetsov Alexander M. , Medvedev Igor G. , Sokolov Vladimir V.
Published: April 2004

New simple expressions for average number of electrons in the valence orbital of a reacting ion and the charge susceptibility are obtained that allow one to calculate adiabatic free energy surfaces (AFES) and corresponding kinetic regime diagrams (KRD) for adiabatic processes of electron transfer from the ion, located in a polar liquid, to a metal within the framework of the exactly solvable (in the limit T→0) model of the metal with the infinitely wide conduction band. This model represents one of limiting cases of the Anderson model that may be applied to s–p metals. Unlike previous studies of the adiabatic reactions in the model of the metal with the infinitely wide conduction band, the present work takes into account the electron–electron correlation effects in an exact manner. General results are illustrated with KRD which determine the regions of the physical parameters of the system corresponding to various types of electron transfer processes. AFES are calculated for some typical parameters sets. The exact AFES are compared with those calculated within the Hartree–Fock approximation. It is shown that the correlation effects are of importance and results not only in a considerable decrease of the activation free energy but also to qualitatively different shapes of AFES in some regions of the system parameters.
Theoretical studies of hyperthermal O(3P) collisions with hydrocarbon self-assembled monolayers
Authors: Troya Diego , Schatz George C.
Published: April 2004

We present a dynamics study of inelastic and reactive scattering processes in collisions of hyperthermal (5 eV) O(3P) atoms with a hydrocarbon self-assembled monolayer (SAM). Molecular-dynamics simulations are carried out using a quantum mechanics/molecular mechanics (QM/MM) interaction potential that uses a high quality semiempirical Hamiltonian for the QM part and the MM3 force field for the MM part. A variety of products coming from reaction are identified, including H abstraction to generate OH, O atom addition to the SAM with subsequent elimination of H atoms, and direct C–C breakage. The C–C breakage mechanism provides a pathway for significant surface mass loss in single reactive events whereas the O addition–H elimination channel leads to surface oxidation. Reaction probabilities, product energy, and angular distributions are examined to gain insight on polymer erosion in low Earth orbit conditions and on fundamentals of inelastic and reactive hyperthermal gas–surface interactions.
A local approach to delocalized electronic systems: Semilocal evaluation of the cohesive energies of tight-binding Hamiltonians
Authors: Malrieu Jean-Paul , Robert Vincent
Published: April 2004

Starting from strongly localized N-electron functions built from either pure atomic orbitals or fully localized bond molecular orbitals, it is possible to evaluate the ground state energy of a periodic lattice ruled by a tight-binding Hamiltonian without explicitly introducing the monoelectronic crystal orbitals. The method consists of a self-consistent perturbation of the zeroth-order wave function which incorporates high order effects and offers reasonable convergence properties. Along this framework, a single variable per bond type is introduced, namely the amplitude of the charge transfer. The method leads to a set of coupled equations which can be numerically solved, if not analytically. Short-range delocalization effects under periodic conditions are explicitly taken into account and relatively accurate cohesive energies are estimated for regular homoatomic and heteroatomic one-dimensional chains as well as for honeycomb lattices. In addition, good agreement with experiment for the distortion amplitude in polyacetylene is obtained. This exploratory tool may be easily extended to more sophisticated Hamiltonians, for which the solutions are not accessible. Since our approach only introduces short-range delocalization effects, its performance questions the importance of the specifically collective delocalization effects.
Ground and valence excited states of BI: A MR-CISD+Q study
Authors: Yang Xinzheng , Lin Meirong , Zhang Baozheng
Published: April 2004

Ab initio calculations on the valence electronic states of the BI molecule have been performed by using the entirely uncontracted all-electronic aug-cc-pVQZ (for the B atom) and Sadlej-pVTZ (for the I atom) basis sets and the internally contracted multireference singles and doubles configuration interaction method with Davidson size-extensively correction and Douglas–Kroll scalar relativistic correction. The potential energy curves of all valence states and the spectroscopic constants of bound states are fitted. It is the first time that the 12 Λ–S states of BI molecule and all of the 23 Ω states generated from the former are studied in a theoretical way. Calculation results reproduce well most of the experimental data. The effects of the spin–orbit coupling and the avoided crossing rule between Ω states of the same symmetry are analyzed. The transition properties of the A 3Π0+, B 3Π1, and C 1Π1 states to the ground-state transitions are predicted, including the transition dipole moments, the Franck–Condon factors, and the radiative lifetimes. The radiative lifetime of the C 1Π1 state of BI molecule is less than 1 μs, while that of the A 3Π0+ and B 3Π1 states are the order of 1 ms.
Microscopic calculation of the energetics of charged states in amorphous polyethylene
Authors: Eilmes A. , Munn R. W.
Published: April 2004

Polarization energies are calculated for a single excess charge on a polyethylene chain in amorphous polyethylene using (i) local segment and nonlocal distributed molecular polarizabilities, (ii) material structures simulated by both general-purpose and specialist Monte Carlo software, and (iii) uniform and Gaussian distributions of charge with different extents of charge delocalization. Local and distributed response lead to results that are essentially the same except that they correspond to different mean polarizabilities. With increasing delocalization of the charge along the chain, the polarization energies shift to higher values and the width of their distribution decreases, the differences being more pronounced for the uniform distribution. The polarization energies for charges delocalized over 10–20 methylene units form a distribution some 14 eV wide centered around 1 eV, narrowing significantly for more homogeneous polymer melts. The calculations are relevant to trapping of charge in polyethylene. They also yield the microscopic variation in the potential along the polymer chain caused by the polarization energy difference, and so may provide useful inputs to theories of electronic conduction in polymer materials.
RNA interference of
achaete–scute homolog 1
in mouse prostate neuroendocrine cells reveals its gene targets and DNA binding sites
Authors: Hu Yan , Wang Ting , Stormo Gary D. , Gordon Jeffrey I.
Published: April 2004

We have previously characterized a transgenic mouse model (CR2-TAg) of metastatic prostate cancer arising in the neuroendocrine (NE) cell lineage. Biomarkers of NE differentiation in this model are expressed in conventional adenocarcinoma of the prostate with NE features. To further characterize the pathways that control NE proliferation, differentiation, and survival, we established prostate NE cancer (PNEC) cell lines from CR2-TAg prostate tumors and metastases. GeneChip analyses of cell lines harvested at different passages, and as xenografted tumors, indicated that PNECs express consistent features
ex vivo
and
in vivo
and share a remarkable degree of similarity with primary CR2-TAg prostate NE tumors. PNECs express mAsh1, a basic helix–loop–helix (bHLH) transcription factor essential for NE cell differentiation in other tissues. RNA interference knockdown of
mAsh1
, GeneChip comparisons of treated and control cell populations, and a computational analysis of down-regulated genes identified 12 transcriptional motifs enriched in the gene set. Affected genes, including
Adcy9
,
Hes6
,
Iapp1
,
Ndrg4
,
c-Myb
, and
Mesdc2
, are enriched for a palindromic E-box motif, CAGCTG, indicating that it is a physiologically relevant mAsh1 binding site. The enrichment of a c-Myb binding site and the finding that c-
Myb
is down-regulated by mAsh1 RNA interference suggest that
mAsh1
and c-
Myb
are in the same signaling pathway. Our data indicate that mAsh1 negatively regulates the cell cycle (e.g., via enhanced
Cdkn2d
,
Bub1
expression), promotes differentiation (e.g., through effects on cAMP), and enhances survival by inhibiting apoptosis. PNEC cell lines should be generally useful for genetic and/or pharmacologic studies of the regulation of NE cell proliferation, differentiation, and tumorigenesis.
Asymmetric hetero-Diels–Alder reaction catalyzed by dirhodium(II) carboxamidates
Authors: Doyle Michael P. , Valenzuela Marcela , Huang Penglin
Published: April 2004

Chiral dirhodium(II) carboxamidates are highly efficient catalysts for reactions between a variety of aldehydes and activated dienes. Catalyst loadings as low at 0.01 mol % have been realized with enantioselectivities up to 97%. Kinetic investigations reveal a pronounced electronic influence on the rate of the hetero-Diels–Alder reaction with a Hammett ρ value of +1.9 (versus σ+). Inhibition of the catalyst by reactant aldehyde is apparent, but reactions show first-order dependence on aldehyde and diene, and there is a variable dependence on catalyst.
Distinct cell types control lymphoid subset development by means of IL-15 and IL-15 receptor α expression
Authors: Schluns Kimberly S. , Nowak Elizabeth C. , Cabrera-Hernandez Arturo , Puddington Lynn , Lefrançois Leo , Aguila Hector L.
Published: April 2004

IL-15 and the IL-15 receptor (IL-15R)α chain are essential for normal development of naive CD8 T cells, intestinal intraepithelial lymphocytes (IEL), and natural killer (NK)/NK/T cells. However, whether IL-15Rα expression by these subsets is necessary for their production and which cell type needs to produce IL-15 to drive development are unknown. We analyzed the requirements for IL-15 and IL-15Rα expression by bone marrow-derived or parenchymal cells for mediating lymphocyte subset development. Naive CD8 T cell development required IL-15Rα expression by both bone marrow-derived and parenchymal cells, whereas memory-phenotype CD8 T cells required IL-15Rα expression only by hematopoietic cells. In contrast and surprisingly, the development of IEL subsets, particularly CD8ααThy1–Vγ5+T cell antigen receptor γδ and the CD8αα Thy1–T cell antigen receptor αβ IEL populations, depended completely on parenchymal cell expression of IL-15Rα and IL-15 but not IL-15Rβ. In the case of NK and NK/T cell generation and maturation, expression of IL-15 and IL-15Rα by both parenchymal and hematopoietic cells was important, although the latter played the greatest role. These results demonstrated dichotomous mechanisms by which IL-15 regulated lymphoid development, interacting with distinct cell types depending on the developmental pathway.
Designed angiopoietin-1 variant, COMP-Ang1, protects against radiation-induced endothelial cell apoptosis
Authors: Cho Chung-Hyun , Kammerer Richard A. , Lee Hyuek Jong , Yasunaga Kunio , Kim Kyung-Tae , Choi Han-Ho , Kim Won , Kim Sung Hyun , Park Sung Kwang , Lee Gyun Min , Koh Gou Young
Published: April 2004

Radiation therapy is a widely used cancer treatment, but it causes side effects even when localized radiotherapy is used. Extensive apoptosis of microvascular endothelial cells of the lamina propria is the primary lesion initiating intestinal radiation damage after abdominal radiation therapy. Many
in vitro
studies suggest that angiopoietin-1 (Ang1) has potential therapeutic applications in enhancing endothelial cell survival. For
in vivo
use, we developed a soluble, stable, and potent Ang1 variant, COMP-Ang1. COMP-Ang1 is more potent than native Ang1 in phosphorylating the Tie2 receptor in lung endothelial cells
in vivo
. Interestingly, COMP-Ang1 administered i.v. was mainly localized to microvascular endothelial cells of the intestinal villi and lung but not to microvascular endothelial cells of the liver. In irradiated mice, i.v. COMP-Ang1 protected against radiation-induced apoptosis in microcapillary endothelial cells of the intestinal villi and prolonged survival. Thus, COMP-Ang1 could be used as a therapeutic protein for specific protection against endothelial cell injury.
Acetylcholinesterase/paraoxonase genotype and expression predict anxiety scores in Health, Risk Factors, Exercise Training, and Genetics study
Authors: Sklan Ella H. , Lowenthal Alexander , Korner Mira , Ritov Ya'acov , Landers Daniel M. , Rankinen Tuomo , Bouchard Claude , Leon Arthur S. , Rice Treva , Rao D. C. , Wilmore Jack H. , Skinner James S. , Soreq Hermona
Published: April 2004

Anxiety involves complex, incompletely understood interactions of genomic, environmental, and experience-derived factors, and is currently being measured by psychological criteria. Here, we report previously nonperceived interrelationships between expression variations and nucleotide polymorphisms of the chromosome 7q21–22 acetylcholinesterase-paraoxonase 1 (ACHE-PON1) locus with the trait- and state-anxiety measures of 461 healthy subjects from the Health, Risk Factors, Exercise Training, and Genetics Family Study. The AChE protein controls the termination of the stress-enhanced acetylcholine signaling, whereas the PON protein displays peroxidase-like activity, thus protecting blood proteins from oxidative stress damages. Serum AChE and PON enzyme activities were both found to be affected by demographic parameters, and showed inverse, reciprocal associations with anxiety measures. Moreover, the transient scores of state anxiety and the susceptibility score of trait anxiety both appeared to be linked to enzyme activities. This finding supported the notion of corresponding gene expression relationships. Parallel polymorphisms in theACHEandPON1genes displayed apparent associations with both trait- and state-anxiety scores. Our findings indicate that a significant source of anxiety feelings involves inherited and acquired parameters of acetylcholine regulation that can be readily quantified, which can help explaining part of the human variance for state and trait anxiety.
Asymmetric autocatalysis: Novel structures, novel mechanism?
Authors: Gridnev Ilya D. , Brown John M.
Published: April 2004

The amplifying asymmetric autocatalysis discovered by Soai and coworkers in 1995 does not fit easily into the extensively investigated framework of organozinc alkylation of aldehydes. In that case the catalyst is a monomeric Zn chelate that functions as both Lewis acid and Lewis base, permitting the simultaneous coordination of both dialkylzinc reagent and aldehyde reactant. By contrast, the Soai reactants are rigid γ-aminoaldehydes that cannot function as mononuclear chelates. Structural and computational evidence for a binuclear resting state is presented, and the energetics of mono-, di-, tri-, and tetrameric species accessible to the reacting system have been computed.
Human rights and ethnic attitudes in Spain: The role of cognitive, social status, and individual difference factors
Authors: Dunbar Edward , Blanco Amalio , Sullaway Megan , Horcajo Javier
Published: April 2004

Cognitive, individual differences, and intergroup contact factors were examined in the formation of attitudes about human rights and ethnic bias in two studies conducted in Spain. A 7‐item scale measuring knowledge about human rights laws in Spain and the European Union was used in both studies. Participants were university students enrolled at the Universidad Autónoma de Madrid. In study one, participant (n= 127) knowledge about human rights laws, intergroup contact, Right Wing Authoritarianism (RWA), and Gough's Prejudice/Tolerance (Pr/To) scale were examined in relationship to bias towards Gitanos. Findings revealed that knowledge about human rights and social status variables (gender and age) were not significant predictors of Gitano bias, whereas Pr/To, RWA, and contact were all (R2= .28) significant predictors of bias against Gitanos. Findings provided cross‐cultural replication (Dunbar & Simonova, in press) of the relationship of Pr/To and RWA to Gitano bias. In study two, participant (n= 100) knowledge and feelings (measured on a three‐item semantic differential scale) about human rights laws, Pr/To, and RWA were examined in relation to strategies influencing peer attitudes about human rights on the Raven Social Influence Inventory (RSII) scale. Findings indicated that knowledge about human rights laws were correlated (r= .47,p< .001) with positive feelings about these laws. Results of a hierarchical regression analysis, controlling for knowledge about human rights laws and participants' social status, found that the Prejudice/Tolerance scale and feelings about human rights were related with both hard (R2= .11) and soft (R2= .08) social influence strategies influencing peer human rights attitudes on the RSII. Men and higher‐scoring participants on Pr/To both employed more hard social influence strategies. Findings indicate that while knowledge of human rights laws is unrelated to ethnic bias, more accurate knowledge is correlated to more positive feelings about laws meant to protect the rights of ethnic minorities.
Filial belief and parent—child conflict
Authors: Yeh Kuang‐Hui , Bedford Olwen
Published: April 2004

This study examines the relation between filial belief and the frequency, origins, and solutions to parent‐child conflict using an indigenous Chinese perspective. The Dual Filial Piety model is employed to categorize the four types of filial belief: nonfilial, authoritarian, reciprocal, and absolute. Questionnaires were completed by 773 junior and senior high school students from around Taiwan for the study. Results provided support for the indigenous Chinese notion that a child's filial beliefs relate to the level of parent‐child conflict. The results go beyond this common conception to highlight that filial beliefs may have a particular role in decreasing self‐centred but not inappropriate conflict between parents and children, and that reciprocal filial beliefs may have a more important role in decreasing conflict than authoritarian filial beliefs. Clear differences were identified in the reported origins of conflict (Demands Conflict with Desire. Unreasonable Behaviour, Demand Exceeds Ability, Role Conflict, Interparental Dispute. Immoral Demands) and solutions to conflict (self‐sacrifice, compromise, refraining, ego‐centred, escape) among the four filial types. Parent demands conflicting with the child's desire was the greatest source of conflict for each of the four filial types. Nonfilial types reported significantly more conflict than absolute types for four of the six origins of conflict examined. Low incidence of conflict may explain why the filial types did not differ for the remaining two origins. Overall, the four filial types reported self‐sacrifice as their least used solution to parent‐child conflict, and nonfilials reported significantly less use of this solution than the other three filial types. Absolutes and reciprocals reported significantly more use of refraining than the other two filial types. Results of this study provide the first empirical support for the Dual Filial Piety model and constitute a foundation for continued indigenous research on parent‐child relations in Chinese culture. It is expected that an indigenous theory of parent‐child relations incorporating the Dual Filial Piety model can eventually be integrated into a global psychology.
Conceptualization in the pigeon: What do we know?
Authors: Khallad Yacoub
Published: April 2004

This article reviews studies on conceptual behaviour in the pigeon that have been conducted over the past four decades. These studies reveal a variety of definitions and procedures employed in the assessment of this behaviour, a reflection of its multifaceted nature. Overall, pigeons have been found capable of categorizing a wide variety of static and moving natural and artificial stimuli. They have also demonstrated learning of abstract or relational concepts, even though such concepts seem to be more challenging. More recently, pigeons have also been shown to be capable of conceptualization as reflected in the ability to form functional or contingency classes (Lea, 1984), and some preliminary findings point to the possibility that pigeons can exhibit the more demanding equivalence classes (Sidman, 1990) that manifest themselves in the formal properties of reflexivity, symmetry, and transitivity emerging from conditional discriminations, when adequate procedures are employed. Available evidence now seems to suggest that functional and equivalence classes are closely related, but more work is needed to specify the nature of this relationship. At this point, it seems safe to conclude that language may not be necessary for conceptualization, including equivalence learning. Taken together, the findings of this review reveal learning abilities in the pigeon far beyond simple discrimination or categorization, although it is not yet well understood how this learning is achieved. Memorization of individual stimuli, featural analysis, and formation of prototypes have all been suggested as strategies utilized by pigeons in perceptual categorization tasks, while abstraction has been posited in explaining pigeons' relational concept learning. The reinforcement contingency has more recently been offered as a possible mechanism underlying equivalence learning. More broadly, the review illustrates how a hybrid of psychological and biological approaches can be employed in animal experimentation to tackle complex questions and enhance our understanding of behaviour and cognition.
Differential growth rates of the cerebellum and posterior fossa assessed by post mortem magnetic resonance imaging of the fetus: implications for the pathogenesis of the chiari 2 deformity
Authors: Griffiths P. D. , Wilkinson I. D. , Variend S. , Jones A. , Paley M. N. J. , Whitby E.
Published: April 2004

Purpose: To evaluate post mortem magnetic resonance imaging of the fetus to provide data on the rate of growth of the cerebellum, bony posterior fossa, supratentorial bony compartment and cerebrum.

Material and Methods: Twenty fetuses subsequently shown to have normal brain and spines on autopsy were studied using MRI post mortem. MRI from 20 normal pediatric brain examinations in children aged 6 years or younger were studied for comparison. Post mortem MRI was performed using a high‐resolution fast spin echo technique providing T2 weighted images. The area of the cerebellar vermis, posterior fossa, supratentorial skull cavity and cerebral hemispheres was measured in the sagittal plane in all cases. These measurements were compared over the age ranges studied.

Results: We have shown that there are differences in the rate of growth and the apparent commencement of growth between the structures under study. The cerebellum appeared to start its significant growth at 16.5 weeks with a rate of 16 mm2/week throughout pregnancy, while the cerebral hemisphere appeared to commence significant growth at 13 weeks at a rate of 184 mm2/week throughout pregnancy. This is in contrast to the bony posterior fossa, whose growth paralleled the supratentorial bony compartment at all ages studied.

Conclusion: We interpret our findings as showing relatively late commencement of cerebellar growth compared to the cerebral hemispheres, whereas the growth of the bony posterior fossa appears to be in advance and independent of cerebellar growth. Our results support the hypothesis that posterior fossa development depends on raised hydrostatic pressure in the CSF containing structures of the posterior fossa. When this mechanism fails, as in some cases of myelomeningocoele, a small posterior fossa is formed which characterizes the Chiari 2 malformation.
Dermoid tumor with involvement of the frontal lobes
Authors: Sener R. N. , Mechl M. , Prokes B. , Valek V. A.
Published: April 2004

Intraparenchymal location of a dermoid tumor is extremely rare, and there are only four reports in the literature. This article presents a patient with a dermoid tumor with trilobulated components; an extra‐axial component in the basal frontal/ethmoidal region, and two intra‐axial components located in each frontal lobe. In addition, two small fat‐density lesions anterior to the component in the left frontal lobe were present, probably due to partial intraparenchymal rupture of the tumor. The pathogenesis of intra‐axial locations is still controversial, and this article proposes that in at least some cases intraparenchymal rupture of dermoids can cause intra‐axial dermoids.
Book review
Authors: Rossitti Sandro
Published: April 2004

Magnetic Resonance Imaging in Stroke. Edited by S. Davis, M. Fisher and S. Warach. Cambridge University Press, Cambridge 2003. ISBN 0-521-80683-6. Hardback. 280 pages. Price GBP 80.00.