1,642 research outputs found
Multiplicative renormalizability of gluon and ghost propagators in QCD
We reformulate the coupled set of continuum equations for the renormalized
gluon and ghost propagators in QCD, such that the multiplicative
renormalizability of the solutions is manifest, independently of the specific
form of full vertices and renormalization constants. In the Landau gauge, the
equations are free of renormalization constants, and the renormalization point
dependence enters only through the renormalized coupling and the renormalized
propagator functions. The structure of the equations enables us to devise novel
truncations with solutions that are multiplicatively renormalizable and agree
with the leading order perturbative results. We show that, for infrared power
law behaved propagators, the leading infrared behavior of the gluon equation is
not solely determined by the ghost loop, as concluded in previous studies, but
that the gluon loop, the three-gluon loop, the four-gluon loop, and even
massless quarks also contribute to the infrared analysis. In our new Landau
gauge truncation, the combination of gluon and ghost loop contributions seems
to reject infrared power law solutions, but massless quark loops illustrate how
additional contributions to the gluon vacuum polarization could reinstate these
solutions. Moreover, a schematic study of the three-gluon and four-gluon loops
shows that they too need to be considered in more detail before a definite
conclusion about the existence of infrared power behaved gluon and ghost
propagators can be reached.Comment: 13 pages, 1 figure, submitted to Phys. Rev.
Ultrastructure of ostrich (Struthio camelus) spermatozoa. II. Scanning electron microscopy
The three-dimensional structure and size of ostrich sperm is unknown. In this study, the morphology and
dimensions of ostrich sperm were determined by scanning electron microscopy of semen samples obtained
from sexually mature males during the breeding season. The results indicate that sperm cells of
the ostrich are of the sauropsid type characteristic of non-passerine birds and, in general appearance, resemble
those of the chicken, turkey, guinea fowl, budgerigar and tinamou. They differ from tinamou sperm,
however, in that they do not show a small bump at the tip of the acrosome. Ostrich sperm are shorter
(69,6 μm total length) than those of the chicken, turkey and guinea fowl, but longer
than those of the budgerigar. A lack of information makes it impossible to compare the dimensions of
ostrich sperm with those of other ratites such as the rhea. In ostrich and guinea fowl, the sperm head
is proportionately longer than that of the chicken, turkey and budgerigar as determined by tail to head
ratios. Two distinct groups of ostriches could be distinguished on the basis of differences in the length
of various sperm cell components. This may reflect persistent genetic (subspecies) variations in the
domestic ostrich population.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi.
Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.Klein Karoo Landboukooperasie. University of Pretoria.mn201
Mineral exploration in the Lower Palaeozoic rocks of south-west Cumbria. Part 1, regional surveys
The results of geochemical, geological and geophysical surveys over Lower Palaeozoic rocks in the
south-western part of Cumbria are given in two reports. This report (Part 1) describes the results of a
geochemical drainage survey and an examination of mineralised sites, and relates them to information
from new geological mapping and an assessment of regional geophysical data. Part 2 contains details
of follow-up surveys in the Black Combe inlier.
The geochemical drainage survey, involving the collection and analysis of heavy mineral concentrates
and stream sediment samples from 119 sites, found substantial antimony, arsenic, barium, bismuth,
copper, iron, lead, tin, tungsten and zinc anomalies. Gold was reported for the first time from this part
of the Lake District: small amounts were noted in panned concentrates from five sites. Other minerals
identified in panned concentrates included arsenopyrite, baryte, bismutite, bismuthinite, cassiterite,
chalcopyrite, cerussite, pyrite, pyromorphite, scheelite, sphalerite, stolzite and wolfram&e.
The examination of old workings and outcrops revealed many undocumented occurrences of quartzsulphide
vein-style mineralisation. The chemical analysis of samples taken from old workings and
other occurrences confirmed field observations that locally, particularly in the Black Combe area, this
mineralisation is polymetallic with variable amounts of arsenic, gold, bismuth, copper, lead, zinc and
in a few cases antimony, barium, cobalt, nickel, tungsten and tin. Iron mineralisation occurs both as
oxide (hematite) and sulphide deposits. Mercury was present in appreciable amounts in samples from
the High Brow pyrite mine.
The distribution of panned concentrate anomalies suggests that the vein-style mineralisation is
polyphase and that individual phases may be zoned. Highest zinc anomalies occur near Torver and the
highest lead on the west side of Black Combe. Tin and tungsten are restricted largely to the central
part of Black Combe, and the most prominent arsenic and bismuth anomalies are found in the same
area. Copper anomalies are widespread over the Skiddaw Group and the Borrowdale Volcanic Group.
Barium anomalies indicate that baryte mineralisation is weak and localised, occurring principally
within the Black Combe area and close to the Windermere Supergroup basal unconformity. Iron
oxides from host rocks and hematite mineralisation are responsible for local enrichments of iron,
antimony, arsenic and molybdenum in panned concentrates
A piezoelectric microvalve for compact high frequency high differential pressure micropumping systems
A piezoelectrically driven hydraulic amplification microvalve for use in compact high-performance hydraulic pumping systems was designed, fabricated, and experimentally characterized. High-frequency, high-force actuation capabilities were enabled through the incorporation of bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. Large valve stroke at the microscale was achieved with an hydraulic amplification mechanism that amplified (40/spl times/-50/spl times/) the limited stroke of the piezoelectric material into a significantly larger motion of a micromachined valve membrane with attached valve cap. These design features enabled the valve to meet simultaneously a set of high frequency (/spl ges/1 kHz), high pressure(/spl ges/300 kPa), and large stroke (20-30 /spl mu/m) requirements not previously satisfied by other hydraulic flow regulation microvalves. This paper details the design, modeling, fabrication, assembly, and experimental characterization of this valve device. Fabrication challenges are detailed
The relativistic influence on the dielectric behaviour of a plasma near cyclotron resonance
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
Nonperturbative Renormalization and the QCD Vacuum
We present a self consistent approach to Coulomb gauge Hamiltonian QCD which
allows one to relate single gluon spectral properties to the long range
behavior of the confining interaction. Nonperturbative renormalization is
discussed. The numerical results are in good agreement with phenomenological
and lattice forms of the static potential.Comment: 23 pages in RevTex, 4 postscript figure
Multiplicative renormalizability and quark propagator
The renormalized Dyson-Schwinger equation for the quark propagator is
studied, in Landau gauge, in a novel truncation which preserves multiplicative
renormalizability. The renormalization constants are formally eliminated from
the integral equations, and the running coupling explicitly enters the kernels
of the new equations. To construct a truncation which preserves multiplicative
renormalizability, and reproduces the correct leading order perturbative
behavior, non-trivial cancellations involving the full quark-gluon vertex are
assumed in the quark self-energy loop. A model for the running coupling is
introduced, with infrared fixed point in agreement with previous
Dyson-Schwinger studies of the gauge sector, and with correct logarithmic tail.
Dynamical chiral symmetry breaking is investigated, and the generated quark
mass is of the order of the extension of the infrared plateau of the coupling,
and about three times larger than in the Abelian approximation, which violates
multiplicative renormalizability. The generated scale is of the right size for
hadronic phenomenology, without requiring an infrared enhancement of the
running coupling.Comment: 17 pages; minor corrections, comparison to lattice results added;
accepted for publication in Phys. Rev.
The views of five participating undergraduate students of the Student Associates Scheme in England
This paper reports findings from a study which explored undergraduate perceptions of the Student Associates Scheme in England (SAS). The scheme was established by the Training and Development Agency for Schools in an attempt to increase the number of graduates entering the teaching profession, particularly in shortage subjects such as the physical sciences and mathematics. The scheme places undergraduate students on short-term placements in secondary schools throughout England to provide them with experiences that may encourage them to consider teaching as a career option. Findings show that the SAS school placements were a positive experience for the students participating in this study. However, a question emerged as to whether or not the scheme is targeting students who have yet to decide upon teaching as a career or just reinforcing the existing aspirations of students who have already decided to teach. As the scheme is attempting to increase the number of teachers entering the profession this question has important implications for this study and further work which will focus on undergraduates who think that their career ambitions would not be fulfilled by teaching
Renormalization and Chiral Symmetry Breaking in Quenched QED in Arbitrary Covariant Gauge
We extend a previous Landau-gauge study of subtractive renormalization of the
fermion propagator Dyson-Schwinger equation (DSE) in strong-coupling, quenched
QED_4 to arbitrary covariant gauges. We use the fermion-photon proper vertex
proposed by Curtis and Pennington with an additional correction term included
to compensate for the small gauge-dependence induced by the ultraviolet
regulator. We discuss the chiral limit and the onset of dynamical chiral
symmetry breaking in the presence of nonperturbative renormalization. We
extract the critical coupling in several different gauges and find evidence of
a small residual gauge-dependence in this quantity.Comment: REVTEX 3.0, 27 pages including 14 Extended Postscript files
comprising 9 figures. Replacement: discussion of chiral limit corrected, and
some minor typographical errors fixed. To appear in Phys. Rev.
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