3,188 research outputs found
Covariant formulation of non-Abelian gauge theories without anticommuting variables
A manifestly Lorentz invariant effective action for Yang-Mills theory
depending only on commuting fields is constructed. This action posesses a
bosonic symmetry, which plays a role analogous to the BRST symmetry in the
standard formalism.Comment: 8 pages, Late
Detecting energy dependent neutron capture distributions in a liquid scintillator
A novel technique is being developed to estimate the effective dose of a neutron field based on the distribution of neutron captures in a scintillator. Using Monte Carlo techniques, a number of monoenergetic neutron source energies and locations were modelled and their neutron capture response was recorded. Using back propagation Artificial Neural Networks (ANN) the energy and incident direction of the neutron field was predicted from the distribution of neutron captures within a 6Li-loaded liquid scintillator. Using this proposed technique, the effective dose of 252Cf, 241AmBe and 241AmLi neutron fields was estimated to within 30% for four perpendicular angles in the horizontal plane. Initial theoretical investigations show that this technique holds some promise for real-time estimation of the effective dose of a neutron field
A novel approach to neutron dosimetry
Purpose:
Having been overlooked for many years, research is now starting to take into account the directional distribution of neutron workplace fields. Existing neutron dosimetry instrumentation does not account for this directional distribution, resulting in conservative estimates of dose in neutron workplace fields (by around a factor of 2, although this is heavily dependent on the type of field). This conservatism could influence epidemiological studies on the health effects of radiation exposure. This paper reports on the development of an instrument which can estimate the effective dose of a neutron field, accounting for both the direction and the energy distribution.
Methods:
A 6Li-loaded scintillator was used to perform neutron assays at a number of locations in a 20 × 20 × 17.5 cm3 water phantom. The variation in thermal and fast neutron response to different energies and field directions was exploited. The modeled response of the instrument to various neutron fields was used to train an artificial neural network (ANN) to learn the effective dose and ambient dose equivalent of these fields. All experimental data published in this work were measured at the National Physical Laboratory (UK).
Results:
Experimental results were obtained for a number of radionuclide source based neutron fields to test the performance of the system. The results of experimental neutron assays at 25 locations in a water phantom were fed into the trained ANN. A correlation between neutron counting rates in the phantom and neutron fluence rates was experimentally found to provide dose rate estimates. A radionuclide source behind shadow cone was used to create a more complex field in terms of energy and direction. For all fields, the resulting estimates of effective dose rate were within 45% or better of their calculated values, regardless of energy distribution or direction for measurement times greater than 25 min.
Conclusions:
This work presents a novel, real-time, approach to workplace neutron dosimetry. It is believed that in the research presented in this paper, for the first time, a single instrument has been able to estimate effective dose
QCD effective action with dressing functions - consistency checks in the perturbative regime
In a previous paper, we presented solution to the Slavnov--Taylor identity
for the QCD effective action, and argued that the action terms containing
(anti)ghost fields are unique. These terms have the same form as those in the
classical action, but the gluon and (anti)ghost effective fields are convoluted
with gluon and ghost dressing functions G_A and G_c, the latter containing
perturbative and nonperturbative effects (but not including the soliton-like
vacuum effects). In the present work we show how the perturbative QCD (pQCD)
can be incorporated into the framework of this action, and we present explicit
one-loop pQCD expressions for G_A and G_c. We then go on to check the
consistency of the obtained results by considering an antighost
Dyson--Schwinger equation (DSE). By solving the relations that result from the
Legendre transformation leading to the effective action, we obtain the
effective fields as power expansions of sources. We check explicitly that the
aforementioned one-loop functions G_A and G_c fulfil the antighost DSE at the
linear source level. We further explicitly check that these one-loop G_A and
G_c have the regularization-scale and momentum dependence consistent with the
antighost DSE at the quadratic source level. These checks suggest that the the
effective action with dressing functions represents a consistent framework for
treating QCD, at least at the one-loop level.Comment: 17 pages, revtex4; dimensional regularization used instead of
Pauli-Villars, the check of identity in the linear-in-sources Dyson-Schwinger
equation now includes the finite part; conclusions unchanged; to appear in
Phys.Rev.
The malaria parasite cyclic GMP-dependent protein kinase plays a central role in blood-stage schizogony
A role for the Plasmodium falciparum cyclic GMP (cGMP)-dependent protein kinase (PfPKG) in gametogenesis in the malaria parasite was elucidated previously. In the present study we examined the role of PfPKG in the asexual blood-stage of the parasite life cycle, the stage that causes malaria pathology. A specific PKG inhibitor (compound 1, a trisubstituted pyrrole) prevented the progression of P. falciparum schizonts through to ring stages in erythrocyte invasion assays. Addition of compound 1 to ring-stage parasites allowed normal development up to 30 h postinvasion, and segmented schizonts were able to form. However, synchronized schizonts treated with compound 1 for ≥6 h became large and dysmorphic and were unable to rupture or liberate merozoites. To conclusively demonstrate that the effect of compound 1 on schizogony was due to its selective action on PfPKG, we utilized genetically manipulated P. falciparum parasites expressing a compound 1-insensitive PfPKG. The mutant parasites were able to complete schizogony in the presence of compound 1 but not in the presence of the broad-spectrum protein kinase inhibitor staurosporine. This shows that PfPKG is the primary target of compound 1 during schizogony and provides direct evidence of a role for PfPKG in this process. Discovery of essential roles for the P. falciparum PKG in both asexual and sexual development demonstrates that cGMP signaling is a key regulator of both of these crucial life cycle phases and defines this molecule as an exciting potential drug target for both therapeutic and transmission blocking action against malaria
An approach to solve Slavnov-Taylor identities in nonsupersymmetric non-Abelian gauge theories
We present a way to solve Slavnov--Taylor identities in a general
nonsupersymmetric theory. The solution can be parametrized by a limited number
of functions of spacetime coordinates, so that all the effective fields are
dressed by these functions via integral convolution. The solution restricts the
ghost part of the effective action and gives predictions for the physical part
of the effective action.Comment: revised version, section 3 is enlarged, 24 pages, Latex2e, no
figures, version accepted by Phys. Rev.
Hierarchy of massive gauge fields
An explicitely gauge invariant polynomial action for massive gauge fields is
proposed. For different values of parameters it describes massive Yang-Mills
field, the Higgs-Kibble model, the model with spontaneously broken symmetry and
two scalar mesons.Comment: 8 pages, no figure
Voltage security evaluation based on perturbation method
This is the post-print version of the final paper published in International Journal of Electrical Power & Energy Systems. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2009 Elsevier B.V.This paper proposes a new algorithm for estimating voltage security margin. The algorithm is based on the perturbation method and has significant computational efficiency. The proposed algorithm can be used for on-line voltage security evaluation. It has been validated using IEEE-14, IEEE-30 and IEEE-57 bus systems. Results from the tests show higher efficiency and smaller error margins compared to continuation power flow (CPF) method.
Voltage collapse is a serious threat to the security of stressed power systems; therefore, voltage security (VS) has become a major challenge for management of power systems. The motivation for this research is a direct consequence of the deregulation of electricity industries and markets worldwide
Transformed-FNV:Wave forces on a vertical cylinder — A free-surface formulation
Existing force models for a vertical surface-piercing cylinder require water depth integration from the seabed to the free surface to determine the total inline force. However, acquiring the full wave kinematics profiles beneath the water surface presents a significant computational task. We revisit the finite water depth version of the well-known FNV theory (Kristiansen and Faltinsen, 2017) and propose a transformed version that expresses the total force solely in terms of the fully nonlinear wave properties at the free surface. This novel Transformed-FNV (T-FNV) formulation treats the Morison inertia term exactly and approximates the remaining two convective-derivative type terms with an assumption of slowly varying kinetic energy type terms. We evaluate the accuracy of this transformation against the original formulation, using wave kinematics obtained from fully nonlinear numerical simulations. Two T-FNV formulations are proposed with different input properties required. The first formulation uses the fully nonlinear wave kinematic properties at the free surface, whereas a fully approximated T-FNV formulation requires only the nonlinear free-surface elevation time history measured or calculated at the position of the column but in its absence. Both T-FNV formulations demonstrate good accuracy for wave forces for both deep and shallow-water cases against the original FNV model. The new T-FNV formulations also show the increased role of higher harmonics in the predicted force time histories when compared to those in the free-surface displacement, and the importance of using accurate higher order harmonic wave profiles in nonlinear force calculations
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