147 research outputs found
Shoulder posture and median nerve sliding
Background: Patients with upper limb pain often have a slumped sitting position and poorshoulder posture. Pain could be due to poor posture causing mechanical changes (stretch; localpressure) that in turn affect the function of major limb nerves (e.g. median nerve). This studyexamines (1) whether the individual components of slumped sitting (forward head position, trunkflexion and shoulder protraction) cause median nerve stretch and (2) whether shoulderprotraction restricts normal nerve movements.Methods: Longitudinal nerve movement was measured using frame-by-frame cross-correlationanalysis from high frequency ultrasound images during individual components of slumped sitting.The effects of protraction on nerve movement through the shoulder region were investigated byexamining nerve movement in the arm in response to contralateral neck side flexion.Results: Neither moving the head forward or trunk flexion caused significant movement of themedian nerve. In contrast, 4.3 mm of movement, adding 0.7% strain, occurred in the forearm duringshoulder protraction. A delay in movement at the start of protraction and straightening of thenerve trunk provided evidence of unloading with the shoulder flexed and elbow extended and thescapulothoracic joint in neutral. There was a 60% reduction in nerve movement in the arm duringcontralateral neck side flexion when the shoulder was protracted compared to scapulothoracicneutral.Conclusion: Slumped sitting is unlikely to increase nerve strain sufficient to cause changes tonerve function. However, shoulder protraction may place the median nerve at risk of injury, sincenerve movement is reduced through the shoulder region when the shoulder is protracted andother joints are moved. Both altered nerve dynamics in response to moving other joints and localchanges to blood supply may adversely affect nerve function and increase the risk of developingupper quadrant pain
QCD sum rules and chiral logarithms
Standard QCD sum-rule analyses of the nucleon mass give results that are
inconsistent with chiral perturbation theory due to an overly simple continuum
ansatz on the phenomenological side of the sum rule. We show that a careful
treatment of the continuum, including - states and other states with
virtual pions, resolves the inconsistency associated with chiral logs.Comment: 10 pages, no figure
Redundance of -isobar Parameters in Effective Field Theories
It is shown that the off-shell parameters in the interaction Lagrangian of
pions, nucleons, and -isobars are redundant in the framework of
effective field theories. Our results also suggest the necessity of including
the as an explicit dynamical degree of freedom.Comment: 11 pages, RevTex, no figures, a minor error corrected, to appear in
PL
QCD Sum Rule Calculation of Twist-3 Contributions to Polarized Nucleon Structure Functions
Using the framework of QCD sum rules we predict the twist-3 contribution to
the second moment of the polarized nucleon structure function . As the
relevant local operator depends explicitely on the gluon field, we employ a
recently studied interpolating nucleon current which contains three quark field
and one gluon field operator. Despite the fact that our calculation is based on
the analysis of a completely different correlation function, our estimates are
consitent with those of Balitsky, Braun and Kolesnichenko who used a
three-quark current.Comment: 16pp. , 2 figures (uuencoded eps-files), LateX. Some misprints
corrected, results unchange
Comparison of Chiral Perturbation Theory and QCD Sum Rule Results for Pseudoscalar Isoscalar-Isovector Mixing
The forms of the neutral, non-strange pseudoscalar propagator matrix and
mixed axial current correlator, \lngle0|T(A_\mu^3 A_\nu^8)|0\rangle, are
discussed at next-to-leading (one-loop) order in chiral perturbation theory,
and the results compared to those obtained using QCD sum rules. This comparison
provides a check of the truncations employed in the sum rule treatment of the
current correlator. Values for the slope of the correlator with in the
two approaches are found to differ by more than an order of magnitude and the
source of this discrepancy is shown to be the incorrect chiral behavior of the
sum rule result.Comment: 14 pages, uses REVTEX Entire manuscript available as a ps file at
http://www.physics.adelaide.edu.au/theory/home.html . Also available via
anonymous ftp at ftp://adelphi.adelaide.edu.au/pub/theory/ADP-95-2.T169.ps To
appear in Physics Letters
Meson-baryon sigma terms in QCD Sum Rules
We evaluate the pion-nucleon and the pion-Delta sigma terms by employing the
method of quantum chromodynamics (QCD) sum rules. The obtained value of the
pion-nucleon sigma term is compatible with the larger values already
anticipated by the recent calculations. It is also found that the pion-Delta
sigma term is as large as the pion-nucleon sigma term.Comment: 14 pages, 2 figures; extended discussion and added references;
version to be published in Phys. Lett.
Newly established human retinoblastoma cell lines exhibit an "immortalized" but not an invasive phenotype in vitro
Retinoblastoma (RB), an intraocular childhood tumor occurring in a hereditary (mostly bilateral) or non-hereditary (unilateral) form, is associated with the inactivation of both alleles of a putative tumor suppressor gene (RB-I) located on chromosome 13q14. Both the process of RB development and the biological characteristics of RB cells are as yet poorly understood. We have established 7 new RBL lines (RBL13, RBL14, RBL18 and RBL30, derived from unilateral RB; and RBL7, RBL15 and RBL20, derived from bilateral RB). Southern blot analyses of restriction fragment length polymorphisms in DNA samples from 6 cell lines revealed loss of constitutional heterozygosity at one or several polymorphic locion chromosome 13 in 4 cases. Gross deletions involving the RB-1 locus and amplification of the N-myc gene were not detected in any of the RBL lines. The phenotypic properties of the RBL lines were analyzed in comparison with cells from the original RB tumors, with 4 RB lines established by others (RB383, RB355, RB247C3 and Y79) and with the adenovirus-EIA-transformed human retinoblast line HER-Xhol-CC2. It was found that RB tumors consist of phenotypically heterogeneous cell subpopulations with varying nutrient requirements and differentiation potential in vitro. All cell lines showed the typical characteristics of established (immortalized) cells. In some cases, cells from original RB tumors or cell lines were able to form colonies when cell aggregates of 2-10 cells were suspended in semi-solid agar medium; however, anchorage-independent colonies never developed from single cells. Cell lines RBL13, RBL18, RB247C3, RB355, RB383 and Y79 were tested for invasion into embryonic chick heart fragments in vitro and found to be non-invasive. None of the RBL or RB lines were tumorigenic in nu/nu (T-) mice. Y79 cells (propagated in culture for many years) exhibited properties distinctly different from those of the other cell lines, and thus cannot be considered phenotypically representative of RB cells
Four-Quark Condensates in Nucleon QCD Sum Rules
The in-medium behavior of the nucleon spectral density including
self-energies is revisited within the framework of QCD sum rules. Special
emphasis is given to the density dependence of four-quark condensates. A
complete catalog of four-quark condensates is presented and relations among
them are derived. Generic differences of such four-quark condensates occurring
in QCD sum rules for light baryons and light vector mesons are discussed.Comment: Version accepted for publication: corrected typos, minor changes
based on referee comments included, reference adde
- …