566 research outputs found
Measuring the notched compressive strength of composite laminates: Specimen size effects
Large fibre reinforced composite structures can give much lower strengths than small test specimens, so a proper understanding of scaling is vital for their safe and efficient use. Small size (scale) specimens are commonly tested to justify allowable stresses, but could be dangerous if results are extrapolated without accounting for scaling effects. On the other hand large factors are sometimes applied to compensate for uncertainties, resulting in overweight designs. The most important variables of scaling effects on the strength of composites with open holes have been identified from experimental tests as notch size, ply and laminate thickness. In this study, these have been scaled both independently and simultaneously over a large range of combinations. The specimens are fabricated from commercially available (Hexcel Composites Ltd.) carbon/epoxy pre-impregnated tapes 0.125 mm thick (IM7/8552). The material is laid up by hand in unidirectional [04]ns with n = 2, 3, 4, and 8 (i.e., 2, 3, 4 and 8 mm thick) and multidirectional laminates; two generic quasi-isotropic lay-ups, one fabricated with blocked plies [45n/90n/−45n/0n]s and the other with distributed layers [45/90/−45/0]ns with n = 2, 4 and 8 are examined. It is shown that the critical failure mechanism in these laminates is in the form of fibre microbuckling or kinking. The unnotched compressive strength in unidirectional specimens thicker than 2 mm is found to be limited by the stress concentration developed at the end tabs and manufacturing induced defects in the form of ply waviness, fibre misalignment and voids rather than specimen size (scaling). In the open hole specimens, for both lay-ups, the strength reduction observed is due to hole size effect rather than specimen thickness or volume increase. The open hole (notched) compressive strength results obtained compare favourably to predictions by a linear softening cohesive zone fracture model developed in earlier work by the second author
An attractive nucleon-nucleon spin-orbit force from skyrmions with dilatons
Within the skyrmion approach for the nucleon-nucleon force, difficulties have
been experienced in obtaining an isoscalar attractive spin-orbit potential, in
parallel to the problems of finding attraction in the isoscalar central
potential. We here study the spin-orbit force using a skyrmion with four- and
six-derivative stabilizing terms in the lagrangian as well as with the crucial
addition of a dilaton. With these features present the spin-orbit force proves
to be attractive as does the central potential. In the absence of the dilaton,
attraction can also be found for the spin-orbit potential but only at the
expense of a greatly over-emphasized term with six derivatives and a continuing
absence of attraction in the central potential.Comment: 8 pages plus 5 figures in uuencoded tar-compressed for
The deformation of the interacting nucleon in the Skyrme model
Changes in the nucleon shape are investigated by letting the nucleon deform
under the strong interactions with another nucleon. The parameters of the axial
deformations are obtained by minimizing the static energy of the two nucleon
system at each internucleon distance . It is shown that the intrinsic
quadrupole moment of the interacting proton, , is about at
distances near fm.Comment: 11 pages, uudecode, gzip, tar, latex, 3 eps figures, accepted for the
publication by Phys.Lett.
Analysis of Chiral Mean-Field Models for Nuclei
An analysis of nuclear properties based on a relativistic energy functional
containing Dirac nucleons and classical scalar and vector meson fields is
discussed. Density functional theory implies that this energy functional can
include many-body effects that go beyond the simple Hartree approximation.
Using basic ideas from effective field theory, a systematic truncation scheme
is developed for the energy functional, which is based on an expansion in
powers of the meson fields and their gradients.
Chiral models are analyzed by considering specific lagrangians that realize
the spontaneously broken chiral symmetry of QCD in different ways and by
studying them at the Hartree level. Models that include a light scalar meson
playing a dual role as the chiral partner of the pion and the mediator of the
intermediate-range nucleon-nucleon interaction, and which include a
"Mexican-hat" potential, fail to reproduce basic ground-state properties of
nuclei. In contrast, chiral models with a nonlinear realization of the symmetry
are shown to contain the full flexibility inherent in the general energy
functional and can therefore successfully describe nuclei.Comment: 47 pages, REVTeX 3.0 with epsf.sty, plus 12 figures in separate
uuencoded compressed postscript fil
Radio Observations of the Hubble Deep Field South region: I. Survey Description and Initial Results
This paper is the first of a series describing the results of the Australia
Telescope Hubble Deep Field South (ATHDFS) radio survey. The survey was
conducted at four wavelengths - 20, 11, 6, and 3 cm, over a 4-year period, and
achieves an rms sensitivity of about 10 microJy at each wavelength. We describe
the observations and data reduction processes, and present data on radio
sources close to the centre of the HDF-S. We discuss in detail the properties
of a subset of these sources. The sources include both starburst galaxies and
galaxies powered by an active galactic nucleus, and range in redshift from 0.1
to 2.2. Some of them are characterised by unusually high radio-to-optical
luminosities, presumably caused by dust extinction.Comment: Accepted by AJ. 32 pages, 4 tables, 3 figures. PDF with
full-resolution figures is on
http://www.atnf.csiro.au/people/rnorris/N197.pd
Isoscalar NN spin-orbit potential from a Skyrme model with scalar mesons
As a first step toward circumventing the difficulty to obtain an attractive
isospin-independent NN spin-orbit force from Skyrme-type models involving only
pions, we investigate an improved Skyrme Lagrangian that incorporates the
scalar-isoscalar meson \epsilon which can be viewed as the cause behind the
enhancement of the -wave. We find that at large distances, the main
contribution to the spin-orbit potential comes from the scalar Lagrangian and
it is found to be attractive. We briefly discuss how to pursue this work to
finally obtain a medium-range attractive interaction.Comment: 10 pages (revtex) + 2 figures; use \psfig command. Minor changes in
the text and some discussion added in the last section. To be published in Z.
Phys.
A Distinct Gene Module for Dysfunction Uncoupled from Activation in Tumor-Infiltrating T Cells
Reversing the dysfunctional T cell state that arises in cancer and chronic viral infections is the focus of therapeutic interventions; however, current therapies are effective in only some patients and some tumor types. To gain a deeper molecular understanding of the dysfunctional T cell state, we analyzed population and single-cell RNA profiles of CD8+tumor-infiltrating lymphocytes (TILs) and used genetic perturbations to identify a distinct gene module for T cell dysfunction that can be uncoupled from T cell activation. This distinct dysfunction module is downstream of intracellular metallothioneins that regulate zinc metabolism and can be identified at single-cell resolution. We further identify Gata-3, a zinc-finger transcription factor in the dysfunctional module, as a regulator of dysfunction, and we use CRISPR-Cas9 genome editing to show that it drives a dysfunctional phenotype in CD8+TILs. Our results open novel avenues for targeting dysfunctional T cell states while leaving activation programs intact
The kinetic energy and and the geometric structure in the sector of the Skyrme model: A study using the Atiyah-Manton Ansatz
We study the construction of the collective-coordinate manifold in the baryon
number two sector of the Skyrme model. To that end we use techniques of
adiabatic large amplitude collective motion, which treat potential and kinetic
energy on an equal footing. In this paper the starting point is the Ansatz
proposed by Atiyah and Manton (Phys.~Lett.~{\bf 438B}, 222 (1989)), which
allows a study of the dynamics using a finite and small number of variables.
From these variables we choose a subset of collective ones. We then study the
behavior of inertial parameters along parts of the collective manifold, and
study the dynamical parts of the interaction.Comment: FAU-T3-94/1, 42 pages. 21 postscript figures can be included in the
text using epsf.sty. Postscript file of complete manuscript avalailabe as
ftp://theorie3.physik.uni-erlangen.de/pub/publications/NRWAMSk.ps.g
- …