Renormalization of the axial-vector current in QCD

Following the method of Ioffe and Smilga, the propagation of the baryon current in an external constant axial-vector field is considered. The close similarity of the operator-product expansion with and without an external field is shown to arise from the chiral invariance of gauge interactions in perturbation theory. Several sum rules corresponding to various invariants both for the nucleon and the hyperons are derived. The analysis of the sum rules is carried out by two independent methods, one called the ratio method and the other called the continuum method, paying special attention to the nondiagonal transitions induced by the external field between the ground state and excited states. Up to operators of dimension six, two new external-field-induced vacuum expectation values enter the calculations. Previous work determining these expectation values from PCAC (partial conservation of axial-vector current) are utilized. Our determination from the sum rules of the nucleon axial-vector renormalization constant GA, as well as the Cabibbo coupling constants in the SU3-symmetric limit (ms=0), is in reasonable accord with the experimental values. Uncertainties in the analysis are pointed out. The case of broken flavor SU3 symmetry is also considered. While in the ratio method, the results are stable for variation of the fiducial interval of the Borel mass parameter over which the left-hand side and the right-hand side of the sum rules are matched, in the continuum method the results are less stable. Another set of sum rules determines the value of the linear combination 7F-5D to be ≊0, or D/(F+D)≊(7/12). .AE

Intracellular concentrations of Ca2+ modulate the strength of signal and alter the outcomes of cytotoxic T-lymphocyte antigen-4 (CD152)-CD80/CD86 interactions in CD4(+) T lymphocytes

The costimulatory receptors CD28 and cytotoxic T-lymphocyte antigen (CTLA)-4 and their ligands, CD80 and CD86, are expressed on T lymphocytes; however, their functional roles during T cell-T cell interactions are not well known. The consequences of blocking CTLA-4-CD80/CD86 interactions on purified mouse CD4(+) T cells were studied in the context of the strength of signal (SOS). CD4(+) T cells were activated with phorbol 12-myristate 13-acetate (PMA) and different concentrations of a Ca2+ ionophore, Ionomycin (I), or a sarcoplasmic Ca2+ ATPase inhibitor, Thapsigargin (TG). Increasing concentrations of I or TG increased the amount of interleukin (IL)-2, reflecting the conversion of a low to a high SOS. During activation with PMA and low amounts of I, intracellular concentrations of calcium ([Ca2+](i)) were greatly reduced upon CTLA-4-CD80/CD86 blockade. Further experiments demonstrated that CTLA-4-CD80/CD86 interactions reduced cell cycling upon activation with PMA and high amounts of I or TG (high SOS) but the opposite occurred with PMA and low amounts of I or TG (low SOS). These results were confirmed by surface T-cell receptor (TCR)-CD3 signalling using a low SOS, for example soluble anti-CD3, or a high SOS, for example plate-bound anti-CD3. Also, CTLA-4-CD80/CD86 interactions enhanced the generation of reactive oxygen species (ROS). Studies with catalase revealed that H2O2 was required for IL-2 production and cell cycle progression during activation with a low SOS. However, the high amounts of ROS produced during activation with a high SOS reduced cell cycle progression. Taken together, these results indicate that [Ca2+](i) and ROS play important roles in the modulation of T-cell responses by CTLA-4-CD80/CD86 interactions.

Spectroscopic studies of the interactions of the pyrethroid insecticide fenvalerate with gramicidin

Fenvalerate is a pyrethroid insecticide which interacts with ionic channels. Using circular dichroism technique we have studied the interaction of fenvalerate with gramicidin, a model channel peptide which transports ions. In most organic solvents, gramicidin exists as a double helix except in trifluoroethanol where it exists as a channel forming single stranded beta(6.3) helical monomer. In model lipid membranes, under certain experimental conditions, gramicidin exists as a channel forming single stranded beta(6.3) helical dimer. Our results show that fenvalerate interacts more with the single stranded beta(6.3) helical monomer or dimer than with the double helical form of gramicidin. This was further confirmed by an increase in the rate of gramicidin mediated proton transport in liposomes by fenvalerate, using the pH sensitive fluorophore, pyranine.

Role of polarization in probing anomalous gauge interactions of the Higgs boson

We explore the use of polarized e(+)/e(-) beams and/or the information on final state decay lepton polarizations in probing the interaction of the Higgs boson with a pair of vector bosons. A model independent analysis of the process e(+)e(-) -> f (f) over barH, where f is any light fermion, is carried out through the construction of observables having identical properties under the discrete symmetry transformations as different individual anomalous interactions. This allows us to probe an individual anomalous term independent of the others. We find that initial state beam polarization can significantly improve the sensitivity to CP-odd couplings of the Z boson with the Higgs boson (ZZH). Moreover, an ability to isolate events with a particular tau helicity, with even 40% efficiency, can improve sensitivities to certain ZZH couplings by as much as a factor of 3. In addition, the contamination from the ZZH vertex contributions present in the measurement of the trilinear Higgs-W (WWH) couplings can be reduced to a great extent by employing polarized beams. The effects of initial state radiation and beamstrahlung, which can be relevant for higher values of the beam energy are also included in the analysis.

Relativistic particle models with separable interactions

We present relativistic, classical particle models that possess Poincaré invariance, invariant world lines, particle interaction, and separability.

Structure and interactions of aspirin-like drugs

A pre-requisite for the elucidation of the mechanism of action of aspirin-like drugs, which are believed to exert their pharmacological effects through the inhibition of prostaglandin biosynthesis, is an understanding of their molecular geometry, the non-covalent interactions they are likely to be involved in, and the geometrical and the electronic consequences of such interactions. This has been sought to be achieved through the x-ray analysis of these drug molecules and their crystalline complexes with other suitable molecules. The results obtained from such studies have been discussed in terms of specific typical examples. For instance, antipyrine can form metal and hydrogen-bonded complexes; phenylbutazone can form ionic complexes with basic molecules. Complex formation is accompanied by characteristic changes in the molecular geometry and the electronic structure in both the cases. The results obtained so far appear to indicate that the important common invariant structural features of the fenamates, deduced from crystal structures, are retained even when complexation takes place.

Structural studies of analgesics and their interactions .10. A hydrated 1-1 complex between niflumic acid and ethanolamine, c13h8f3n2o-2.c2h8no+.h2o.

Mr= 361.3, triclinic, P1, a = 6-239 (2), b=11.280(2), c=12-451(2)A, a=101.2 (1), B= 92.3 (1), 7=99.9(1)°, V=844.123 A3, Z=2, Dx= 1.42, D m = 1.42 (1) Mg m -3, n(Cu Ka) = 1.5418 ,A., g = 1-102 mm -1, F(000) = 376, T= 293 K. Final R = 0.064 for 2150 observed reflections. The niflumic acid anions consist essentially of three planar groupings, namely, two six-membered rings and a carboxylate group attached to one of them. The invariant common structural features observed in the crystal structures of fenamates, namely, the coplanarity of the carboxyl group and the six-membered ring bearing it, and the internal hydrogen bond between the carboxyl group and the imino N atom that bridges the two sixmembered rings, are retained in the complex. The amino N atom is gauche with respect to the terminal hydroxyl group in the ethanolamine cation. The complexation between the two molecules is achieved through ionic and hydrogen-bonded interactions involving the carboxylate group in niflumic acid.

Base-base interactions in nucleic acids containing A-T base pairs: Structure of poly[d(A-T)]

The Watson-Crick type of base pairing is considered to be mandatory for the formation of duplex DNA. However, conformational calculations carried out in our laboratory, have shown that some combinations of backbone torsion angles and sugar pucker lead to duplexes with Hoogsteen type of base pairing also. Here we present the results of energy calculations performed on A-T containing doublet sequences in the D-form with both Hoogsteen and Watson-Crick type of base pairing and the 3 viable models for the A-T containing polynucleotide duplex poly[d(A-T)].

Optically active gossypol as a circular dichroism probe of interactions with serum albumins

The (+)-enantiomer of the polyphenolic binaphthyl gossypol, has been shown to be a useful CD probe of interactions with human and bovine serum albumin. (+)-Gossypol binds to albumin with same affinity as recemic (±)-gossypol, as shown by fluorescence quenching, and also displaces bilirubin from its albumin binding site. The CD characteristics of bound gossypol are different in the case of the two proteins.

Stabilization of the Alleged 'Bishomoaromatic' Bicyclo[3.2.l]octa-2,6-dienyl Anion by Counterion Interactions and by Hyperconjugation

Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution.

Gluon-field contribution in QCD sum rules for the magnetic moments of the nucleons

The Wilson coefficient corresponding to the gluon-field strength GμνGμν is evaluated for the nucleon current correlation function in the presence of a static external electromagnetic field, using a regulator mass Λ to separate the high-momentum part of the Feynman diagrams. The magnetic-moment sum rules are analyzed by two different methods and the sensitivity of the results to variations in Λ are discussed.

Effect of inter-edge Coulomb interactions on transport through a point contact in nu=5/2 quantum Hall state

We study transport across a point contact separating two line junctions in a nu = 5/2 quantum Hall system. We analyze the effect of inter-edge Coulomb interactions between the chiral bosonic edge modes of the half-filled Landau level (assuming a Pfaffian wave function for the half-filled state) and of the two fully filled Landau levels. In the presence of inter-edge Coulomb interactions between all the six edges participating in the line junction, we show that the stable fixed point corresponds to a point contact that is neither fully opaque nor fully transparent. Remarkably, this fixed point represents a situation where the half-filled level is fully transmitting, while the two filled levels are completely backscattered; hence the fixed point Hall conductance is given by G(H) = 1/2e(2)/h. We predict the non-universal temperature power laws by which the system approaches the stable fixed point from the two unstable fixed points corresponding to the fully connected case (G(H) = 5/2e(2)/h) and the fully disconnected case (G(H) = 0).

Non-bonded interactions in 2,2,4,4-tetramethyl-1,3-cyclobutanedithione and 2,2,4,4-tetramethyl-3-thio-1,3-cyclobutanedione

Electronic absorption and emission spectra as well as He(I) photoelectron spectra of 2,2,4,4-tetramethyl-,3-cyclobutanedithione and 2,2,4,4-tetramethyl-1-3-thio-1,3-cyclobutanedione have been interpreted on the basis of molecular orbital calculations. The results show that the non-bonded orbital of the dithione is split owing to through-bond interaction, the magnitude of splitting being 0.4 eV. The π* orbital of the dithione appears to be split by about 0.2 eV. Electronic absorption spectra show evidence for the existence of four n—π* transitions, arising out of the splitting of the orbitals referred to above, just as in the case of 2,2,4,4-tetramethyl-1,3-cyclobutanedione. Electronic and photoelectron spectra of the thio-dione show evidence for weak interaction between the C=S and C&.zdbnd;O groups, probably via π* orbitals. Infrared spectra of both the dithione and the thio-dione are consistent with the planar cyclobutane ring; the ring-puckering frequency responsible for non-bonded interactions is around 67 cm−1 in both the dithione and the thio-dione, the value not being very different from that in the dione. The 1,3-transannular distance is also similar in the three molecules.

Electron-electron interactions in polyacetylene

Experimental evidence for strong electron-electron interactions in polyacetylene is presented. These include (i) observation of a dipole forbidden state below the optical gap, (ii) observation of negative spin densities at sites at which noninteracting models predict zero spin density (iii) vanishing optical gap, in the infinite chain limit, in the closely related symmetrical linear cyanine dyes. To correctly explain these features it is necessary to solve correlated model Hamiltonians. Using diagrammatic valence bond method model exact solutions of correlated models of finite-size systems can be obtained and various physical properties of the low-lying states can be computed. These properties, when extrapolated to the infinite chain limit explain many of the experimental features observed in polyacetylene.