67 research outputs found
Height Systems and Vertical Datums: a Review in the Australian Context
This paper reviews (without equations) the various definitions of height systems and vertical geodetic datum surfaces, together with their practical realisation for users in Australia. Excluding geopotential numbers, a height system is a one-dimensional coordinate system used to express the metric distance (height) of a point from some reference surface. Its definition varies according to the reference surface chosen and the path along which the height is measured. A vertical geodetic datum is the practical realisation of a height system and its reference surface for users, nominally tied to mean sea level. In Australia, the normal-orthometric height system is used, which is embedded in the Australian Height Datum (AHD). The AHD was realised by the adjustment of ~195,000 km of spirit-levelling observations fixed to limited-term observations of mean sea level at multiple tide-gauges. The paper ends by giving some explanation of the problems with the AHD and of the differences between the AHD and the national geoid model, pointing out that it is preferable to recompute the AHD
Debye screening and Meissner effect in a two-flavor color superconductor
I compute the gluon self-energy in a color superconductor with two flavors of
massless quarks, where condensation of Cooper pairs breaks SU(3)_c to SU(2)_c.
At zero temperature, there is neither Debye screening nor a Meissner effect for
the three gluons of the unbroken SU(2)_c subgroup. The remaining five gluons
attain an electric as well as a magnetic mass. For temperatures approaching the
critical temperature for the onset of color superconductivity, or for gluon
momenta much larger than the color-superconducting gap, the self-energy assumes
the form given by the standard hard-dense loop approximation. The gluon
self-energy determines the coefficient of the kinetic term in the effective
low-energy theory for the condensate fields.Comment: 29 pages, RevTe
SolidâPhase Supports for Oligonucleotide Synthesis
This unit begins with a discussion of the advantages and disadvantages of oligonucleotide synthesis using solid supports. The physical and chemical properties of solidâphase supports are discussed in terms of their suitability for oligonucleotide synthesis. In addition, the unit outlines the properties of linkers used for transient or permanent attachment of properly protected nucleosides to the derivatized support, as well as strategies for coupling nucleosides to linkers and conditions for the release of synthetic oligonucleotides from specific supports.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143613/1/cpnc0301.pd
Ellipsoidal area mean gravity anomalies - precise computation of gravity anomaly reference fields for remove-compute-restore geoid determination
Gravity anomaly reference fields, required e.g. in remove-compute-restore (RCR) geoid computation, are obtained from global geopotential models (GGM) through harmonic synthesis. Usually, the gravity anomalies are computed as point values or area mean values in spherical approximation, or point values in ellipsoidal approximation. The present study proposes a method for computation of area mean gravity anomalies in ellipsoidal approximation ('ellipsoidal area means') by applying a simple ellipsoidal correction to area means in spherical approximation. Ellipsoidal area means offer better consistency with GGM quasi/geoid heights. The method is numerically validated with ellipsoidal area mean gravity derived from very fine grids of gravity point values in ellipsoidal approximation. Signal strengths of (i) the ellipsoidal effect (i.e., difference ellipsoidal vs. spherical approximation), (ii) the area mean effect (i.e., difference area mean vs. point gravity) and (iii) the ellipsoidal area mean effect (i.e., differences between ellipsoidal area means and point gravity in spherical approximation) are investigated in test areas in New Zealand and the Himalaya mountains. The impact of both the area mean and the ellipsoidal effect on quasigeoid heights is in the order of several centimetres. The proposed new gravity data type not only allows more accurate RCR-based geoid computation, but may also be of some value for the GGM validation using terrestrial gravity anomalies that are available as area mean values
Generalized Ward identity and gauge invariance of the color-superconducting gap
We derive a generalized Ward identity for color-superconducting quark matter
via the functional integral approach. The identity implies the gauge
independence of the color-superconducting gap parameter on the quasi-particle
mass shell to subleading order in covariant gauge.Comment: 5 pages, 1 Postscript figure, uses Revte
Diquark condensation at strong coupling
The possibility of diquark condensation at sufficiently large baryon chemical
potential and zero temperature is analyzed in QCD at strong coupling. In
agreement with other strong coupling analysis, it is found that a first order
phase transition separates a low density phase with chiral symmetry
spontaneously broken from a high density phase where chiral symmetry is
restored. In none of the phases diquark condensation takes place as an
equilibrium state, but, for any value of the chemical potential, there is a
metastable state characterized by a non-vanishing diquark condensate. The
energy difference between this metastable state and the equilibrium state
decreases with the chemical potential and is minimum in the high density phase.
The results indicate that there is attraction in the quark-quark sector also at
strong coupling, and that the attraction is more effective at high baryon
density, but for infinite coupling it is not enough to produce diquark
condensation. It is argued that the absence of diquark condensation is not a
peculiarity of the strong coupling limit, but persists at sufficiently large
finite couplings.Comment: 10 pages, 2 figures. An important discussion concerning the extension
of the results to finite couplings adde
Instanton Effects in QCD at High Baryon Density
We study instanton effects in QCD at very high baryon density. In this regime
instantons are suppressed by a large power of , where
is the QCD scale parameter and is the baryon chemical
potential. Instantons are nevertheless important because they contribute to
several physical observables that vanish to all orders in perturbative QCD. We
study, in particular, the chiral condensate and its contribution to the masses of Goldstone bosons in the CFL phase of QCD
with flavors. We find that at densities , where
is the density of nuclear matter, the result is dominated by large
instantons and subject to considerable uncertainties. We suggest that these
uncertainties can be addressed using lattice calculations of the instanton
density and the pseudoscalar diquark mass in QCD with two colors. We study the
topological susceptibility and Witten-Veneziano type mass relations in both
and QCD.Comment: 27 pages, 8 figures, minor revision
Thermal fluctuations of gauge fields and first order phase transitions in color superconductivity
We study the effects of thermal fluctuations of gluons and the diquark
pairing field on the superconducting-to-normal state phase transition in a
three-flavor color superconductor, using the Ginzburg-Landau free energy. At
high baryon densities, where the system is a type I superconductor, gluonic
fluctuations, which dominate over diquark fluctuations, induce a cubic term in
the Ginzburg-Landau free energy, as well as large corrections to quadratic and
quartic terms of the order parameter. The cubic term leads to a relatively
strong first order transition, in contrast with the very weak first order
transitions in metallic type I superconductors. The strength of the first order
transition decreases with increasing baryon density. In addition gluonic
fluctuations lower the critical temperature of the first order transition. We
derive explicit formulas for the critical temperature and the discontinuity of
the order parameter at the critical point. The validity of the first order
transition obtained in the one-loop approximation is also examined by
estimating the size of the critical region.Comment: 12 pages, 4 figures, final version published in Phys. Rev.
Low Energy Theory for 2 flavors at High Density QCD
We construct the effective Lagrangian describing the low energy excitations
for Quantum Chromodynamics with two flavors at high density. The non-linear
realization framework is employed to properly construct the low energy
effective theory. The light degrees of freedom, as required by 't Hooft anomaly
conditions, contain massless fermions which we properly include in the
effective Lagrangian. We also provide a discussion of the linearly realized
Lagrangian.Comment: 17 pages, RevTeX format, references added. To appear in Phys. Rev.
Error sources and data limitations for the prediction ofsurface gravity: a case study using benchmarks
Gravity-based heights require gravity values at levelled benchmarks (BMs), whichsometimes have to be predicted from surrounding observations. We use EGM2008 andthe Australian National Gravity Database (ANGD) as examples of model and terrestrialobserved data respectively to predict gravity at Australian national levelling network(ANLN) BMs. The aim is to quantify errors that may propagate into the predicted BMgravity values and then into gravimetric height corrections (HCs). Our results indicatethat an approximate ±1 arc-minute horizontal position error of the BMs causesmaximum errors in EGM2008 BM gravity of ~ 22 mGal (~55 mm in the HC at ~2200 melevation) and ~18 mGal for ANGD BM gravity because the values are not computed atthe true location of the BM. We use RTM (residual terrain modelling) techniques toshow that ~50% of EGM2008 BM gravity error in a moderately mountainous regioncan be accounted for by signal omission. Non-representative sampling of ANGDgravity in this region may cause errors of up to 50 mGals (~120 mm for the Helmertorthometric correction at ~2200 m elevation). For modelled gravity at BMs to beviable, levelling networks need horizontal BM positions accurate to a few metres, whileRTM techniques can be used to reduce signal omission error. Unrepresentative gravitysampling in mountains can be remedied by denser and more representative re-surveys,and/or gravity can be forward modelled into regions of sparser gravity
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