1,620 research outputs found
Covariant Gauge Fixing for Super IIA D-branes
For the kappa-symmetric super IIA D-brane action by the canonical approach we
construct an equivalent effective action which is characterized by an auxiliary
scalar field. By analyzing the canonical equations of motion for the
kappa-symmetry-gauge-fixed action we find a suitable conformal-like covariant
gauge fixing of reparametrization symmetry to obtain a simplified effective
action where the non-linear square root structure is removed. We discuss how
the two effective actions are connected.Comment: 9 pages, LaTeX2e, no figures, one reference adde
Silicon Sensors implemented on p-type substrates for high radiation resistance applications
Silicon based micropattern detectors are essential elements of modern high
energy physics experiments. Cost effectiveness and high radiation resistance
are two important requirements for technologies to be used in inner tracking
devices. Processes based on p-type substrates have very strong appeal for these
applications. Recent results and prototype efforts under way are reviewed.Comment: 7 pages, 2 figures; invited paper at Vertex 2006, Perugia, Italy,
september 200
T-duality and Generalized Kahler Geometry
We use newly discovered N = (2, 2) vector multiplets to clarify T-dualities
for generalized Kahler geometries. Following the usual procedure, we gauge
isometries of nonlinear sigma-models and introduce Lagrange multipliers that
constrain the field-strengths of the gauge fields to vanish. Integrating out
the Lagrange multipliers leads to the original action, whereas integrating out
the vector multiplets gives the dual action. The description is given both in N
= (2, 2) and N = (1, 1) superspace.Comment: 14 pages; published version: some conventions improved, minor
clarification
Radiation Induced Point and Cluster-Related Defects with Strong Impact to Damage Properties of Silicon Detectors
This work focuses on the investigation of radiation induced defects
responsible for the degradation of silicon detectors. Comparative studies of
the defects induced by irradiation with 60Co- rays, 6 and 15 MeV electrons, 23
GeV protons and 1 MeV equivalent reactor neutrons revealed the existence of
point defects and cluster related centers having a strong impact on damage
properties of Si diodes. The detailed relation between the microscopic reasons
as based on defect analysis and their macroscopic consequences for detector
performance are presented. In particular, it is shown that the changes in the
Si device properties after exposure to high levels of 60Co- doses can be
completely understood by the formation of two point defects, both depending
strongly on the Oxygen concentration in the silicon bulk. Specific for hadron
irradiation are the annealing effects which decrease resp. increase the
originally observed damage effects as seen by the changes of the depletion
voltage. A group of three cluster related defects, revealed as deep hole traps,
proved to be responsible specifically for the reverse annealing. Their
formation is not affected by the Oxygen content or Si growth procedure
suggesting that they are complexes of multi-vacancies located inside extended
disordered regions.Comment: 14 pages, 15 figure
Stable nitrogen-cycling capacity in relation to fertilization and intercropping in a sub-boreal grassland
Grasslands are important in sub-boreal climate agricultural systems and are managed with various combinations of N fertilization and plant species. Ammonia-oxidizing and denitrifying microorganisms are key players in determining the fate of nitrogen (N) and thereby also the yield in grassland systems and their impact on gaseous N losses and leaching. We established a three-year field study in southern Finland with fertilizer treatment as a main-plot factor, including organic and synthetic fertilizers and plant species and mixtures thereof as the sub-plot factor. We quantified six genes encoding key N-cycling enzymes by quantitative PCR to determine the abundance of the communities involved in N-transformation processes and also included previously published data on crop yield, soil properties and the overall bacterial community composition. With the exception of ammonia oxidizing bacteria (AOB), which were primarily affected by fertilization, the abundances of all other N-cycling communities changed over time with either an increase or decrease from summer to autumn. Differences in gene abundances between plant species treatments and in fertilizer by plant species interactions were detected mainly in the beginning of the cropping season during the first year. The nirS-type denitrifiers and nosZII nitrous oxide reducers responded more to changes in soil properties than their functional counterpart nirK and nosZI communities. Using structural equation modeling, we show that the overall microbial community composition and diversity played an important role in mediating the management effects on crop yield, genetic potential for N retention and N2O sink capacity. However, a trade-off between the genetic potential for N retention and N2O sink capacity was detected, indicating the challenges in managing grasslands in a sustainable way.Peer reviewe
Stable nitrogen-cycling capacity in relation to fertilization and intercropping in a sub-boreal grassland
Grasslands are important in sub-boreal climate agricultural systems and are managed with various combinations of N fertilization and plant species. Ammonia-oxidizing and denitrifying microorganisms are key players in determining the fate of nitrogen (N) and thereby also the yield in grassland systems and their impact on gaseous N losses and leaching. We established a three-year field study in southern Finland with fertilizer treatment as a main-plot factor, including organic and synthetic fertilizers and plant species and mixtures thereof as the sub-plot factor. We quantified six genes encoding key N-cycling enzymes by quantitative PCR to determine the abundance of the communities involved in N-transformation processes and also included previously published data on crop yield, soil properties and the overall bacterial community composition. With the exception of ammonia oxidizing bacteria (AOB), which were primarily affected by fertilization, the abundances of all other N-cycling communities changed over time with either an increase or decrease from summer to autumn. Differences in gene abundances between plant species treatments and in fertilizer by plant species interactions were detected mainly in the beginning of the cropping season during the first year. The nirS-type denitrifiers and nosZII nitrous oxide reducers responded more to changes in soil properties than their functional counterpart nirK and nosZI communities. Using structural equation modeling, we show that the overall microbial community composition and diversity played an important role in mediating the management effects on crop yield, genetic potential for N retention and N2O sink capacity. However, a trade-off between the genetic potential for N retention and N2O sink capacity was detected, indicating the challenges in managing grasslands in a sustainable way.Peer reviewe
AV-Courant algebroids and generalized CR structures
We construct a generalization of Courant algebroids which are classified by
the third cohomology group , where is a Lie Algebroid, and is
an -module. We see that both Courant algebroids and
structures are examples of them. Finally we introduce generalized CR structures
on a manifold, which are a generalization of generalized complex structures,
and show that every CR structure and contact structure is an example of a
generalized CR structure.Comment: 18 page
Geometric Actions for D-Branes and M-Branes
New forms of Born-Infeld, D-brane and M theory five-brane actions are found
which are quadratic in the abelian field strength. The gauge fields couple both
to a background or induced metric and a new auxiliary metric, whose elimination
reproduces the non-polynomial Born-Infeld action. This is similar to the
introduction of an auxiliary metric to simplify the Nambu-Goto string action.
This simplifies the quantisation and dualisation of the gauge fields.Comment: LaTeX, 9 pages, no figures. Minor corrections; version to appear in
Physics Letters
Three-dimensional topologically gauged N=6 ABJM type theories
In this paper we construct the conformal supergravity in three
dimensions from a set of Chern-Simons-like terms one for each of the graviton,
gravitino, and R-symmetry gauge field and then couple this theory to the
superconformal ABJM theory. In a first step part of the coupled
Lagrangian for this topologically gauged ABJM theory is derived by demanding
that all terms of third and second order in covariant derivatives cancel in the
supersymmtry variation of the Lagrangian. To achieve this the transformation
rules of the two separate sectors must be augmented by new terms. In a second
step we analyze all terms in that are of first order in covariant
derivatives. The cancelation of these terms require additional terms in the
transformation rules as well as a number of new terms in the Lagrangian. As a
final step we check that all remaining terms in which are bilinear
in fermions cancel which means that the presented Lagrangian and transformation
rules constitute the complete answer. In particular we find in the last step
new terms in the scalar potential containing either one or no structure
constant. The non-derivative higher fermion terms in that have not
yet been completely analyzed are briefly discussed.Comment: 26 pages, v.2 minor corrections, comment on relation to chiral
gravity added
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