865 research outputs found
Infra-Red Finite Charge Propagation
The Coulomb gauge has a long history and many uses. It is especially useful
in bound state applications. An important feature of this gauge is that the
matter fields have an infra-red finite propagator in an on-shell
renormalisation scheme. This is, however, only the case if the renormalisation
point is chosen to be the static point on the mass shell, p = (m, 0, 0, 0). In
this letter we show how to extend this key property of the Coulomb gauge to an
arbitrary relativistic renormalisation point. This is achieved through the
introduction of a new class of gauges of which the Coulomb gauge is a limiting
case. A physical explanation for this result is given.Comment: 8 pages, plain TeX, to appear in Modern Physics Letters
The factorisation of glue and mass terms in SU(N) gauge theories
In this paper we investigate the structure of the glue in Zwanziger's gauge
invariant expansion for the A^2-type mass term in Yang-Mills theory. We show
how to derive this expansion, in terms of the inverse covariant Laplacian, and
extend it to higher orders. In particular, we give an explicit expression, for
the first time, for the next to next to leading order term. We further show
that the expansion is not unique and give examples of the resulting ambiguity.Comment: 22 page
The Fermi surface and f-valence electron count of UPt3
Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data,
we arrive at a detailed picture of the Fermi surface of the heavy fermion
superconductor UPt3. Our work was partially motivated by a new proposal that
two 5f valence electrons per formula unit in UPt3 are localized by correlation
effects -- agreement with previous dHvA measurements of the Fermi surface was
invoked in its support. Comprehensive comparison with our new observations
shows that this 'partially localized' model fails to predict the existence of a
major sheet of the Fermi surface, and is therefore less compatible with
experiment than the originally proposed 'fully itinerant' model of the
electronic structure of UPt3. In support of this conclusion, we offer a more
complete analysis of the fully itinerant band structure calculation, where we
find a number of previously unrecognized extremal orbits on the Fermi surface.Comment: 23 pages, 12 figures, latex, iopart clas
A Technical Introduction to Transmission Electron Microscopy for Soft-Matter:Imaging, Possibilities, Choices, and Technical Developments
With a significant role in material sciences, physics, (soft matter) chemistry, and biology, the transmission electron microscope is one of the most widely applied structural analysis tool to date. It has the power to visualize almost everything from the micrometer to the angstrom scale. Technical developments keep opening doors to new fields of research by improving aspects such as sample preservation, detector performance, computational power, and workflow automation. For more than half a century, and continuing into the future, electron microscopy has been, and is, a cornerstone methodology in science. Herein, the technical considerations of imaging with electrons in terms of optics, technology, samples and processing, and targeted soft materials are summarized. Furthermore, recent advances and their potential for application to soft matter chemistry are highlighted
Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices
The magneto-Coulomb oscillation, the single electron repopulation induced by
external magnetic field, observed in a ferromagnetic single electron transistor
is further examined in various ferromagnetic single electron devices. In case
of double- and triple-junction devices made of Ni and Co electrodes, the single
electron repopulation always occurs from Ni to Co electrodes with increasing a
magnetic field, irrespective of the configurations of the electrodes. The
period of the magneto-Coulomb oscillation is proportional to the single
electron charging energy. All these features are consistently explained by the
mechanism that the Zeeman effect induces changes of the Fermi energy of the
ferromagnetic metal having a non-zero spin polarizations. Experimentally
determined spin polarizations are negative for both Ni and Co and the magnitude
is larger for Ni than Co as expected from band calculations.Comment: 4 pages, 3 figures, uses jpsj.sty, submitted to J. Phys. Soc. Jp
The quantitative proteomic response of Synechocystis sp. PCC6803 to phosphate acclimation.
BACKGROUND: Inorganic phosphate (Pi) is a critical nutrient for all life and is periodically limiting in marine and freshwater provinces, yet little is understood how organisms acclimate to fluctuations in Pi within their environment. To investigate whole cell adaptation, we grew Synechocystis sp. PCC6803, a model freshwater cyanobacterium, in 3%, and 0.3% inorganic phosphate (Pi) media. The cells were allowed to acclimate over 60 days, and cells were harvested for quantitative high throughput mass spectrometry-based proteomics using the iTRAQ™ labelling technology. RESULTS: In total, 120 proteins were identified, and 52 proteins were considered differentially abundant compared to the control. Alkaline phosphatase (APase) activities correlated significantly (p < 0.05) with observed relative PhoA abundances. PstS1 and PstS2 were both observed, yet PstS1 was not differentially more abundant than the control. Phycobilisome protein abundances appeared to be coordinated, and are significantly less abundant in 0.3% Pi than 3% Pi cultures. Also, the central metabolic cell function appears to have shifted towards the production of (NADPH) reducing energy and nucleotide sugars. CONCLUSIONS: This acclimation response bears strong similarity to the previously reported response to nitrogen deprivation within Synechocystis sp. PCC 6803. However, it also demonstrates some characteristics of desiccation stress, such as the regulation of fatty acids and increased abundance of rehydrin in the 3% Pi culture
One-Loop Amplitudes in Euclidean Quantum Gravity
This paper studies the linearized gravitational field in the presence of
boundaries. For this purpose, -function regularization is used to
perform the mode-by-mode evaluation of BRST-invariant Faddeev-Popov amplitudes
in the case of flat Euclidean four-space bounded by a three-sphere. On choosing
the de Donder gauge-averaging term, the resulting value is found to
agree with the space-time covariant calculation of the same amplitudes, which
relies on the recently corrected geometric formulas for the asymptotic heat
kernel in the case of mixed boundary conditions. Two sets of mixed boundary
conditions for Euclidean quantum gravity are then compared in detail. The
analysis proves that one cannot restrict the path-integral measure to
transverse-traceless perturbations. By contrast, gauge-invariant amplitudes are
only obtained on considering from the beginning all perturbative modes of the
gravitational field, jointly with ghost modes.Comment: 26 pages, plain TeX, no figure
Symmetry breaking, conformal geometry and gauge invariance
When the electroweak action is rewritten in terms of SU(2) gauge invariant
variables, the Higgs can be interpreted as a conformal metric factor. We show
that asymptotic flatness of the metric is required to avoid a Gribov problem:
without it, the new variables fail to be nonperturbatively gauge invariant. We
also clarify the relations between this approach and unitary gauge fixing, and
the existence of similar transformations in other gauge theories.Comment: 11 pages. Version 2: typos corrected, discussion of Elitzur's theorem
added. Version to appear in J.Phys.
Diversified Late Acceptance Search
The well-known Late Acceptance Hill Climbing (LAHC) search aims to overcome
the main downside of traditional Hill Climbing (HC) search, which is often
quickly trapped in a local optimum due to strictly accepting only non-worsening
moves within each iteration. In contrast, LAHC also accepts worsening moves, by
keeping a circular array of fitness values of previously visited solutions and
comparing the fitness values of candidate solutions against the least recent
element in the array. While this straightforward strategy has proven effective,
there are nevertheless situations where LAHC can unfortunately behave in a
similar manner to HC. For example, when a new local optimum is found, often the
same fitness value is stored many times in the array. To address this
shortcoming, we propose new acceptance and replacement strategies to take into
account worsening, improving, and sideways movement scenarios with the aim to
improve the diversity of values in the array. Compared to LAHC, the proposed
Diversified Late Acceptance Search approach is shown to lead to better quality
solutions that are obtained with a lower number of iterations on benchmark
Travelling Salesman Problems and Quadratic Assignment Problems
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