5,805 research outputs found
Role of contractile prostaglandins and Rho-kinase in growth factor-induced airway smooth muscle contraction
Background: In addition to their proliferative and differentiating effects, several growth factors are capable of inducing a sustained airway smooth muscle (ASM) contraction. These contractile effects were previously found to be dependent on Rho-kinase and have also been associated with the production of eicosanoids. However, the precise mechanisms underlying growth factor-induced contraction are still unknown. In this study we investigated the role of contractile prostaglandins and Rho-kinase in growth factor-induced ASM contraction.Methods: Growth factor-induced contractions of guinea pig open-ring tracheal preparations were studied by isometric tension measurements. The contribution of Rho-kinase, mitogen-activated protein kinase ( MAPK) and cyclooxygenase ( COX) to these reponses was established, using the inhibitors Y-27632 ( 1 mu M), U-0126 ( 3 mu M) and indomethacin ( 3 mu M), respectively. The Rho-kinase dependency of contractions induced by exogenously applied prostaglandin F-2 alpha (PGF(2 alpha)) and prostaglandin E-2 (PGE(2)) was also studied. In addition, the effects of the selective FP-receptor antagonist AL-8810 (10 mu M) and the selective EP1-antagonist AH-6809 (10 mu M) on growth factor-induced contractions were investigated, both in intact and epithelium-denuded preparations. Growth factor-induced PGF(2 alpha)- and PGE(2)-release in the absence and presence of Y-27632, U-0126 and indomethacin, was assessed by an ELISA-assay.Results: Epidermal growth factor (EGF)- and platelet-derived growth factor ( PDGF)- induced contractions of guinea pig tracheal smooth muscle preparations were dependent on Rho-kinase, MAPK and COX. Interestingly, growth factor-induced PGF(2 alpha)- and PGE(2)-release from tracheal rings was significantly reduced by U-0126 and indomethacin, but not by Y-27632. Also, PGF2a- and PGE(2)-induced ASM contractions were largely dependent on Rho-kinase, in contrast to other contractile agonists like histamine. The FP-receptor antagonist AL-8810 ( 10 mu M) significantly reduced ( approximately 50 %) and the EP1-antagonist AH-6809 ( 10 mu M) abrogated growth factor-induced contractions, similarly in intact and epithelium-denuded preparations.Conclusion: The results indicate that growth factors induce ASM contraction through contractile prostaglandins - not derived from the epithelium - which in turn rely on Rho-kinase for their contractile effects.</p
Single crystal growth and physical properties of the layered arsenide BaRh_2As_2
Single crystals of BaRh_2As_2 have been synthesized from a Pb flux. We
present the room temperature crystal structure, single crystal x-ray
diffraction measurements as a function of temperature T, anisotropic magnetic
susceptibility \chi versus T, electrical resistivity in the ab-plane \rho
versus T, Hall coefficient versus T and magnetic field H, and heat capacity C
versus T measurements on the crystals. The single crystal structure
determination confirms that BaRh_2As_2 forms in the tetragonal ThCr_2Si_2 type
structure (space group I4/mmm) with lattice parameters a = b = 4.0564(6)\AA and
c = 12.797(4) \AA. Band structure calculations show that BaRh_2As_2 should be
metallic with a small density of states at the Fermi energy N(E_ F) = 3.49
states/eV f.u. (where f.u. \equiv formula unit) for both spin directions.
\rho(T) data in the ab-plane confirm that the material is indeed metallic with
a residual resistivity \rho(2K) = 29 \mu \Omega cm, and with a residual
resistivity ratio \rho(310K)/\rho(2K) = 5.3. The observed \chi(T) is small
(\sim 10^{-5} cm^3/mol) and weakly anisotropic with \chi_{ab}/\chi_ c \approx
2. The C(T) data indicate a small density of states at the Fermi energy with
the low temperature Sommerfeld coefficient \gamma = 4.7(9) mJ/mol K^2. There
are no indications of superconductivity, spin density wave, or structural
transitions between 2K and 300K. We compare the calculated density of states
versus energy of BaRh_2As_2 with that of BaFe_2As_2.Comment: Accepted for publication in Phys. Rev.
The Physical Projector and Topological Quantum Field Theories: U(1) Chern-Simons Theory in 2+1 Dimensions
The recently proposed physical projector approach to the quantisation of
gauge invariant systems is applied to the U(1) Chern-Simons theory in 2+1
dimensions as one of the simplest examples of a topological quantum field
theory. The physical projector is explicitely demonstrated to be capable of
effecting the required projection from the initially infinite number of degrees
of freedom to the finite set of gauge invariant physical states whose
properties are determined by the topology of the underlying manifold.Comment: 24 pages, no figures, plain LaTeX file; one more reference added.
Final version to appear in Jour. Phys.
Antisymmetric tensor coupling and conformal invariance in sigma models corresponding to gauged WZNW theories
String backgrounds associated with gauged WZNW models generically
depend on or . The exact expressions for the corresponding
metric G_{\m\n}, antisymmetric tensor B_{\m\n}, and dilaton can be
obtained by eliminating the gauge field from the local part of the
effective action of the gauged WZNW model. We show that there exists a
manifestly gauge-invariant prescription for the derivation of the antisymmetric
tensor coupling. When the subgroup is one-dimensional and is simple the
antisymmetric tensor is given by the semiclassical (-independent)
expression. We consider in detail the simplest non-trivial example with
non-trivial B_{\m\n} -- the D=3 sigma model corresponding to the gauged WZNW theory (`charged black string') and show that the exact
expressions for G_{\m\n}, B_{\m\n} and solve the Weyl invariance
conditions in the two-loop approximation. Similar conclusion is reached for the
closely related chiral gauged WZNW model. We find that there exists
a scheme in which the semiclassical background is also a solution of the
two-loop conformal invariance equations (but the tachyon equation takes a
non-canonical form). We discuss in detail the role of field redefinitions
(scheme dependence) in establishing a correspondence between the sigma model
and conformal field theory results.Comment: 55 pages, harvmac, CERN-TH.6969/93, THU-93/25, Imperial/TP/92-93/59.
(Another prescription for extracting the exact antisymmetric tensor is
described leading to a purely semiclassical expression for it
Pion electroproduction, PCAC, chiral Ward identities, and the axial form factor revisited
We re-investigate Adler's PCAC relation in the presence of an external
electromagnetic field within the framework of QCD coupled to external fields.
We discuss pion electroproduction within a tree-level approximation to chiral
perturbation theory and explicitly verify a chiral Ward identity referred to as
the Adler-Gilman relation. We critically examine soft-momentum techniques and
point out how inadmissable approximations may lead to results incompatible with
chiral symmetry. As a result we confirm that threshold pion electroproduction
is indeed a tool to obtain information on the axial form factor of the nucleon.Comment: 33 pages, RevTex, 9 figure
PHASES High Precision Differential Astrometry of delta Equulei
delta Equulei is among the most well-studied nearby binary star systems.
Results of its observation have been applied to a wide range of fundamental
studies of binary systems and stellar astrophysics. It is widely used to
calibrate and constrain theoretical models of the physics of stars. We report
27 high precision differential astrometry measurements of delta Equulei from
the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES).
The median size of the minor axes of the uncertainty ellipses for these
measurements is 26 micro-arcseconds. These data are combined with previously
published radial velocity data and other previously published differential
astrometry measurements using other techniques to produce a combined model for
the system orbit. The distance to the system is determined to within a
twentieth of a parsec and the component masses are determined at the level of a
percent. The constraints on masses and distance are limited by the precisions
of the radial velocity data; we outline plans improve this deficiency and
discuss the outlook for further study of this binary.Comment: Accepted by AJ. Complete versions of tables 2-7 now available at
http://stuff.mit.edu/~matthew1/deltaEquTables/ (removed from astroph server
Conformal Orbifold Partition Functions from Topologically Massive Gauge Theory
We continue the development of the topological membrane approach to open and
unoriented string theories. We study orbifolds of topologically massive gauge
theory defined on the geometry , where is a generic
compact Riemann surface. The orbifold operations are constructed by gauging the
discrete symmetries of the bulk three-dimensional field theory. Multi-loop
bosonic string vacuum amplitudes are thereby computed as bulk correlation
functions of the gauge theory. It is shown that the three-dimensional
correlators naturally reproduce twisted and untwisted sectors in the case of
closed worldsheet orbifolds, and Neumann and Dirichlet boundary conditions in
the case of open ones. The bulk wavefunctions are used to explicitly construct
the characters of the underlying extended Kac-Moody group for arbitrary genus.
The correlators for both the original theory and its orbifolds give the
expected modular invariant statistical sums over the characters.Comment: 47 pages LaTeX, 3 figures, uses amsfonts and epsfig; v2: Typos
corrected, reference added, clarifying comments on modular invariance
inserted; v3: Further comments on modular invariance added; to be published
in JHE
Field transformations and simple models illustrating the impossibility of measuring off-shell effects
In the context of simple models illustrating field transformations in
Lagrangian field theories we discuss the impossibility of measuring off-shell
effects in nucleon-nucleon bremsstrahlung, Compton scattering, and related
processes. To that end we introduce a simple phenomenological Lagrangian
describing nucleon-nucleon bremsstrahlung and perform an appropriate change of
variables leading to different off-shell behavior in the nucleon-nucleon
amplitude as well as the photon-nucleon vertex. As a result we obtain a class
of equivalent Lagrangians, generating identical S-matrix elements, of which the
original Lagrangian is but one representative. We make use of this property in
order to show that what appears as an off-shell effect in an S-matrix element
for one Lagrangian may originate in a contact term from an equivalent
Lagrangian. By explicit calculation we demonstrate for the case of
nucleon-nucleon bremsstrahlung as well as nucleon Compton scattering the
equivalence of observables from which we conclude that off-shell effects cannot
in any unambiguous way be extracted from an S-matrix element. Finally, we also
discuss some implications of introducing off-shell effects on a
phenomenological basis, resulting from the requirement that the description of
one process be consistent with that of other processes described by the same
Lagrangian.Comment: 19 pages, Latex, using RevTe
- …