228 research outputs found
Completeness Rules for Spin Observables in Pseudoscalar Meson Photoproduction
The number and type of measurements needed to ascertain the amplitudes for
pseudoscalar meson photoproduction are analyzed in this paper. It is found that
8 carefully selected measurements can determine the four transversity
amplitudes without discrete ambiguities. That number of measurements is one
less than previously believed. We approach this problem in two distinct ways:
(1) solving for the amplitude magnitudes and phases directly; and (2) using a
bilinear helicity product formulation to map an algebra of measurements over to
the well-known algebra of the Gamma matrices. It is shown that the
latter method leads to an alternate proof that 8 carefully chosen experiments
suffice for determining the transversity amplitudes completely. In addition,
Fierz transformations of the Gamma matrices are used to develop useful linear
and nonlinear relationships between the spin observables. These relationships
not only help in finding complete sets of experiments, but also yield important
constraints between the 16 observables for this reaction.Comment: 32 pages, no figures, LaTeX/REVTeX, submitted to Phys. Rev. C, typos
correcte
Coupled-channel study of gamma p --> K+ Lambda
A coupled-channel (CC) approach has been developed to investigate kaon
photoproduction on the nucleon. In addition to direct K+ Lambda production, our
CC approach accounts for strangeness production including K+ Lambda final state
interactions with both pi0 p and pi+ n intermediate states. Calculations for
the gamma p --> K+ Lambda reaction have been performed, and compared with the
recent data from SAPHIR, with emphasis on the CC effects. We show that the CC
effects are significant at the level of inducing 20% changes on total cross
sections; thereby, demonstrating the need to include pi N channels to correctly
describe the gamma p --> K+ Lambda reaction.Comment: 12 pages, 6 eps figures, uses elsart.cls, submitted to Phys.Lett.B;
v2: added paragraph in section
Spin Information from Vector-Meson Decay in Photoproduction
For the photoproduction of vector mesons, all single and double spin
observables involving vector meson two-body decays are defined consistently in
the center of mass. These definitions yield a procedure for
extracting physically meaningful single and double spin observables that are
subject to known rules concerning their angle and energy evolution. As part of
this analysis, we show that measuring the two-meson decay of a photoproduced
or does not determine the vector meson's vector polarization, but
only its tensor polarization. The vector meson decay into lepton pairs is also
insensitive to the vector meson's vector polarization, unless one measures the
spin of one of the leptons. Similar results are found for all double spin
observables which involve observation of vector meson decay. To access the
vector meson's vector polarization, one therefore needs to either measure the
spin of the decay leptons, make an analysis of the background interference
effects or relate the vector meson's vector polarization to other accessible
spin observables.Comment: 22 pages, 3 figure
Roles of Reactive Oxygen Species in Anticancer Therapy with Salvia miltiorrhiza Bunge
Cancer is a leading cause of death worldwide. We aim to provide a systematic review about the roles of reactive oxygen species (ROS) in anticancer therapy with Salvia miltiorrhiza Bunge (Danshen). Danshen, including its lipophilic and hydrophilic constituents, is potentially beneficial for treating various cancers. The mechanisms of ROS-related anticancer effects of Danshen vary depending on the specific type of cancer cells involved. Danshen may enhance TNF-α-induced apoptosis, upregulate caspase-3, caspase-8, caspase-9, endoplasmic reticulum stress, P21, P53, Bax/Bcl-2, DR5, and AMP-activated protein kinase, or activate the p38/JNK, mitogen-activated protein kinase, and FasL signaling pathways. Conversely, Danshen may downregulate human telomerase reverse transcriptase mRNA, telomerase, survivin, vascular endothelial growth factor/vascular endothelial growth factor receptor 2, CD31, NF-ÎșB, Erk1/2, matrix metalloproteinases, microtubule assembly, and receptor tyrosine kinases including epidermal growth factor receptors, HER2, and P-glycoprotein and inhibit the PI3K/Akt/mTOR or estrogen receptor signaling pathways. Therefore, Danshen may inhibit cancer cells proliferation through antioxidation on tumor initiation and induce apoptosis or autophagy through ROS generation on tumor progression, tumor promotion, and tumor metastasis. Based on the available evidence regarding its anticancer properties, this review provides new insights for further anticancer research or clinical trials with Danshen
Dynamical coupled-channel model of kaon-hyperon interactions
The pi N --> KY and KY --> KY reactions are studied using a dynamical
coupled-channel model of meson-baryon interactions at energies where the baryon
resonances are strongly excited. The channels included are: pi N, K \Lambda,
and K\Sigma. The resonances considered are: N^* [S_{11}(1650), P_{11}(1710),
P_{13}(1720),D_{13}(1700)]; \Delta^* [S_{31}(1900), P_{31}(1910),
P_{33}(1920)]; \Lambda ^* [S_{01}(1670), P_{01}(1810)] \Sigma^* [P_{11}(1660),
D_{13}(1670)]; and K^*(892). The basic non-resonant \pi N --> KY and KY --> KY
transition potentials are derived from effective Lagrangians using a unitary
transformation method. The dynamical coupled-channel equations are simplified
by parametrizing the pi N -->pi N amplitudes in terms of empirical pi N
partial-wave amplitudes and a phenomenological off-shell function. Two models
have been constructed. Model A is built by fixing all coupling constants and
resonance parameters using SU(3) symmetry, the Particle Data Group values, and
results from a constituent quark model. Model B is obtained by allowing most of
the parameters to vary around the values of model A in fitting the data. Good
fits to the available data for pi^- p to K^0 \Lambda, K^0 \Sigma^0 have been
achieved. The investigated kinematics region in the center-of-mass frame goes
from threshold to 2.5 GeV. The constructed models can be imbedded into
associated dynamical coupled-channel studies of kaon photo- and
electro-production reactions.Comment: 35 pages, 11 Figure
Knowing who to know in Knowledge Sharing Communities: A Social Network Analysis Approach
Information stored in online communities consist not only knowledge contents, but also the information of knowledge providers and searchersâ connective relationships, and network structures. Online Communities provide effective platforms for interaction and play pivotal roles in making provision for the basis of analysis as all the ask-response paired relationships are automatically recorded. This paper demonstrates how to apply social network analysis to analyze the interaction data for generating the ârole informationâ of the knowledge searchers and providers. Integrating concepts of uncertainty in knowledge searching and sociometric used in social network analysis, we develop a mechanism for role matching in knowledge search for each questions posed. Roles identified in this approach including central, network entrepreneur (e.g. spanning structural holes), neighboring mediate (e.g. knowledge gate keeper), and resource competitor (e.g. structural equivalent players). The result is demonstrated and visualized in a web-based community platform and tested in a real-world programmer forum-based community
Unitary model for the reaction and the magnetic dipole moment of the
Radiative pion photoproduction in the resonance region is
studied with the aim to access the magnetic dipole moment. We
present a unitary model of the () reactions, where the rescattering is included in an on-shell
approximation. In this model, the low energy theorem which couples the process in the limit of a soft final photon to the process is exactly satisfied. We study the sensitivity of the
process at higher values of the final photon
energy to the magnetic dipole moment. We compare our results
with existing data and give predictions for forthcoming measurements of angular
and energy distributions. It is found that the photon asymmetry and a helicity
cross section are particularly sensitive to the magnetic dipole
moment.Comment: 23 pages, 18 figure
Threshold production in nucleon-nucleon collisions
We analyze production in nucleon-nucleon collisions near threshold
in the framework of a general model independent formalism, which can be applied
to any reaction , where , , or . Such
reactions show large isotopic effects: a large difference for - and
-collisions, which is due to the different spin structure of the
corresponding matrix elements. The analysis of the spin structure and of the
polarization observables is based on symmetry properties of the strong
interaction. Using existing experimental data on the different decays of
meson, we suggest a model for , based on
channel -exchanges. We predict polarization phenomena for the
-reaction and the ratio of cross sections for and
-collisions. For the processes we apply two
different approaches: vector meson exchange and local four-particle
interaction. In both cases we find larger -production in
-collisions, with respect to -collisions.Comment: 17 pages, 6 figure
- âŠ