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

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.