1,383 research outputs found
Electromagnetic Form Factors of Charged and Neutral Kaons
The charged and neutral kaon form factors are calculated as a
phenomenological application of the QCD Dyson-Schwinger equations. The results
are compared with the pion form factor calculated in the same framework and
yield \mbox{} on
\mbox{~GeV}; and a neutral kaon form factor that is similar in
form and magnitude to the neutron charge form factor. These results are
sensitive to the difference between the kaon and pion Bethe-Salpeter amplitude
and the - and -quark propagation characteristics.Comment: 11 Pages, 2 figures, REVTEX, uses epsfig. No chang
Nucleon form factors and a nonpointlike diquark
Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for
the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the
relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and
the quark are confined. A good description of the data requires a nonpointlike
diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite,
nonpointlike nature of the diquark is crucial. It provides for diquark-breakup
terms that are of greater importance than the diquark photon absorption
contribution.Comment: 5 pages, REVTEX, epsfig, 3 figure
Nucleation and Growth of Insulin Fibrils in Bulk Solution and at Hydrophobic Polystyrene Surfaces
AbstractA technique was developed for studying the nucleation and growth of fibrillar protein aggregates. Fourier transform infrared and attenuated total reflection spectroscopy were used to measure changes in the intermolecular ÎČ-sheet content of bovine pancreatic insulin in bulk solution and on model polystyrene (PS) surfaces at pH 1. The kinetics of ÎČ-sheet formation were shown to evolve in two stages. Combined Fourier transform infrared, dynamic light scattering, atomic force microscopy, and thioflavin-T fluorescence measurements confirmed that the first stage in the kinetics was related to the formation of nonfibrillar aggregates that have a radius of 13±1nm. The second stage was found to be associated with the growth of insulin fibrils. The ÎČ-sheet kinetics in this second stage were used to determine the nucleation and growth rates of fibrils over a range of temperatures between 60°C and 80°C. The nucleation and growth rates were shown to display Arrhenius kinetics, and the associated energy barriers were extracted for fibrils formed in bulk solution and at PS surfaces. These experiments showed that fibrils are nucleated more quickly in the presence of hydrophobic PS surfaces but that the corresponding fibril growth rates decrease. These observations are interpreted in terms of the differences in the attempt frequencies and energy barriers associated with the nucleation and growth of fibrils. They are also discussed in the context of differences in protein concentration, mobility, and conformational and colloidal stability that exist between insulin molecules in bulk solution and those that are localized at hydrophobic PS interfaces
Correlated GNSS and temperature measurements at 10-minute intervals on the Severn Suspension Bridge
Global Navigation Satellite System (GNSS) data were gathered on the 998-m-long Severn Suspension Bridge main span. The antennas were located on the tops of the four support towers, as well as five locations on the suspension cables; data were gathered at rates of 10 and 20 Hz. In addition, air and steel temperatures were gathered every 10 min. The GNSS data were processed in an On The Fly manner relative to a reference receiver located on a fixed position adjacent to the Bridge, and the resulting dataset was compared to the air and steel temperature data measurements, and correlations reported. Moving average filters that eliminate short-term movements due to wind loading and traffic loading were applied to the GNSS data, resulting in the longer-term deflections due to temperature changes every 10 min. The temperature over the 3 days varied by up to 10 °C, and movements of the order of decimetres were seen. Clear numerical correlations between the changes in temperature and the changes in height are presented when analysed at these 10-min intervals, suggesting that temperature compensation in structural health monitoring systems could be readily applied, resulting in a sustainable structure
Diquarks: condensation without bound states
We employ a bispinor gap equation to study superfluidity at nonzero chemical
potential: mu .neq. 0, in two- and three-colour QCD. The two-colour theory,
QC2D, is an excellent exemplar: the order of truncation of the quark-quark
scattering kernel: K, has no qualitative impact, which allows a straightforward
elucidation of the effects of mu when the coupling is strong. In rainbow-ladder
truncation, diquark bound states appear in the spectrum of the three-colour
theory, a defect that is eliminated by an improvement of K. The corrected gap
equation describes a superfluid phase that is semi-quantitatively similar to
that obtained using the rainbow truncation. A model study suggests that the
width of the superfluid gap and the transition point in QC2D provide reliable
quantitative estimates of those quantities in QCD.Comment: 7 pages, 3 figures, REVTEX, epsfi
Selected nucleon form factors and a composite scalar diquark
A covariant, composite scalar diquark, Fadde'ev amplitude model for the
nucleon is used to calculate pseudoscalar, isoscalar- and isovector-vector,
axial-vector and scalar nucleon form factors. The last yields the nucleon
sigma-term and on-shell sigma-nucleon coupling. The calculated form factors are
soft, and the couplings are generally in good agreement with experiment and
other determinations. Elements in the dressed-quark-axial-vector vertex that
are not constrained by the Ward-Takahashi identity contribute ~20% to the
magnitude of g_A. The calculation of the nucleon sigma-term elucidates the only
unambiguous means of extrapolating meson-nucleon couplings off the meson
mass-shell.Comment: 12 pages, REVTEX, 5 figures, epsfi
Strategies towards robust interpretations of in situ zircon LuâHf isotope analyses
The combination of UâPb and LuâHf compositions measured in zircon crystals is a remarkably powerful isotopic couplet that provides measures on both the timing of mineral growth and the radiogenic enrichment of the source from which the zircon grew. The UâPb age documents the timing of zircon crystallization/recrystallization and Hf isotopes inform on the degree to which the host melt was derived from a radiogenic reservoir (e.g. depleted mantle) versus an unradiogenic reservoir (e.g. ancient continental crust), or some mixture of these sources. The ease of generating large quantities of zircon UâPb and LuâHf data has been in large part facilitated by instrument advances. However, the dramatic increase in time constrained zircon LuâHf analyses in the Earth science community has brought to the fore the importance of careful data collection and reduction workflows, onto which robust geological interpretations may be based. In this work, we discuss the fundamentals of LuâHf isotopes in zircon, which then allows us to provide a robust, accessible, methodology for the assessment of data quality. Additionally, we discuss some novel techniques for: data visualization â that facilitates better transparency of data interpretation; integration of geographic information â that may reveal spatial trends where temporal trends were only apparent before; and some novel statistical evaluation tools â that may provide more rigorous inter- and intra-sample comparisons
Strong Decays of Light Vector Mesons
The vector meson strong decays rho-->pi pi, phi-->KK, and K^star-->pi K are
studied within a covariant approach based on the ladder-rainbow truncation of
the QCD Dyson--Schwinger equation for the quark propagator and the
Bethe--Salpeter equation for the mesons. The model preserves the one-loop
behavior of QCD in the ultraviolet, has two infrared parameters, and implements
quark confinement and dynamical chiral symmetry breaking. The 3-point decay
amplitudes are described in impulse approximation. The Bethe--Salpeter study
motivates a method for estimating the masses for heavier mesons within this
model without continuing the propagators into the complex plane. We test the
accuracy via the rho, phi and K^{star} masses and then produce estimates of the
model results for the a_1 and b_1 masses as well as the mass of the proposed
exotic vector pi_1(1400).Comment: Submitted for publication; 10x2-column pages, REVTEX 4, 3 .eps files
making 3fig
Fibroblast migration and collagen deposition during dermal wound healing: mathematical modelling and clinical implications,
The extent to which collagen alignment occurs during dermal wound healing determines the severity of scar tissue formation. We have modelled this using a multiscale approach, in which extracellular materials, for example collagen and fibrin, are modelled as continua, while fibroblasts are considered as discrete units. Within this model framework, we have explored the effects that different parameters have on the alignment process, and we have used the model to investigate how manipulation of transforming growth factor-ÎČ levels can reduce scar tissue formation. We briefly review this body of work, then extend the modelling framework to investigate the role played by leucocyte signalling in wound repair. To this end, fibroblast migration and collagen deposition within both the wound region and healthy peripheral tissue are considered. Trajectories of individual fibroblasts are determined as they migrate towards the wound region under the combined influence of collagen/fibrin alignment and gradients in a paracrine chemoattractant produced by leucocytes. The effects of a number of different physiological and cellular parameters upon the collagen alignment and repair integrity are assessed. These parameters include fibroblast concentration, cellular speed, fibroblast sensitivity to chemoattractant concentration and chemoattractant diffusion coefficient. Our results show that chemoattractant gradients lead to increased collagen alignment at the interface between the wound and the healthy tissue. Results show that there is a trade-off between wound integrity and the degree of scarring. The former is found to be optimized under conditions of a large chemoattractant diffusion coefficient, while the latter can be minimized when repair takes place in the presence of a competitive inhibitor to chemoattractants
Constructing the fermion-boson vertex in QED3
We derive perturbative constraints on the transverse part of the
fermion-boson vertex in massive QED3 through its one loop evaluation in an
arbitrary covariant gauge. Written in a particular form, these constraints
naturally lead us to the first non-perturbative construction of the vertex,
which is in complete agreement with its one loop expansion in all momentum
regimes. Without affecting its one-loop perturbative properties, we also
construct an effective vertex in such a way that the unknown functions defining
it have no dependence on the angle between the incoming and outgoing fermion
momenta. Such a vertex should be useful for the numerical study of dynamical
chiral symmetry breaking, leading to more reliable results.Comment: 13 pages, 2 figure
- âŠ