337 research outputs found
Covariant gauge-natural conservation laws
When a gauge-natural invariant variational principle is assigned, to
determine {\em canonical} covariant conservation laws, the vertical part of
gauge-natural lifts of infinitesimal principal automorphisms -- defining
infinitesimal variations of sections of gauge-natural bundles -- must satisfy
generalized Jacobi equations for the gauge-natural invariant Lagrangian. {\em
Vice versa} all vertical parts of gauge-natural lifts of infinitesimal
principal automorphisms which are in the kernel of generalized Jacobi morphisms
are generators of canonical covariant currents and superpotentials. In
particular, only a few gauge-natural lifts can be considered as {\em canonical}
generators of covariant gauge-natural physical charges.Comment: 16 pages; presented at XXXVI Symposium on Math. Phys., Torun
09/06-12/06/04; the last paragraph of Section 3 has been reformulated, in
particular a mistake in the equation governing the vertical part of
gauge-natural lifts with respect to prolongations of principal connections
(appearing e.g. in the vertical superpotential) has been correcte
Molecular simulations of the ribosome and associated translation factors
The ribosome is a macromolecular complex which is responsible for protein synthesis in all living cells according to their transcribed genetic information. Using X-ray crystallography and, more recently, cryo-electron microscopy (cryo-EM), the structure of the ribosome was resolved at atomic resolution in many functional and conformational states. Molecular dynamics simulations have added information on dynamics and energetics to the available structural information, thereby have bridged the gap to the kinetics obtained from single-molecule and bulk experiments. Here, we review recent computational studies that brought notable insights into ribosomal structure and function
Binary self-similar one-dimensional quasilattices: Mutual local-derivability classification and substitution rules
Self-similar binary one-dimensional (1D) quasilattices (QLs) are classified
into mutual local-derivability (MLD) classes. It is shown that the MLD
classification is closely related to the number-theoretical classification of
parameters which specify the self-similar binary 1D QLs. An algorithm to derive
an explicit substitution rule, which prescribes the transformation of a QL into
another QL in the same MLD class, is presented. An explicit inflation rule,
which prescribes the transformation of the self-similar 1D QL into itself, is
obtained as a composition of the explicit substitution rules. Symmetric
substitution rules and symmetric inflation rules are extensively discussed.Comment: 24 pages, 4 figures, submitted to PR
Concurrent Design of Railway Vehicles by Simulation Model Reuse
This paper describes a concurrent design approach to railway vehicle design. Current railway vehicles use many different concepts that are combined into the final design concept. The design support for such systems is based on reusing components from previous design cases. The key part of the railway vehicle design concept is its simulation model. Therefore the support is based on support for reuse of previous simulation models. The simulation models of different railway component concepts are stored using the methodology from the EU CLOCKWORK project. The new concept usually combines stored components
Research on influence of cyclic degradation process on changes of structural adhesive bonds mechanical properties
ArticleThe paper deals with an influence of a cyclic degradation process on changes of a shear
tensile strength of single lap-shear adhesive bonds and their elongation according to ÄŚSN EN
ISO 9142. Five one-component structural adhesives used in a construction of car body works
were used within the research. The degradation of adhesive bonds is a significant factor which
influences a quality and a service life of adhesive bonds exposed to environment. A main
requirement in production companies is not only reaching satisfactory initial mechanical
properties but namely ensuring a reliability and a safety of adhesive bonds during their usage.
These reasons show a great importance of adhesive bonds tests either directly in the operating
environment or by a simulation of operating conditions in laboratories. The degradation process
of adhesive bonds worsens mechanical properties of not only the bond itself but also of the bonded
material. This process is progressing and it is usually permanent and irreversible. It is a change
of mechanical and physical properties which can endanger a safety and a reliability of parts,
prospectively of the whole equipment. It can leads up to a complete failure of its function in the
extreme case. A temperature, a moisture, a direct contact with water and chemicals or an
atmospheric corrosion belong among the most serious degradation agents. It is important to take
into regard time of the processes influence at the same time which can act either independently
or concurrently when their effects grow stronger.
From that reason the adhesive bonds were exposed to the cyclic degradation process according
to the standard ÄŚSN EN ISO 9142. Subsequently, the adhesive bonds mechanical properties were
tested on universal testing machine and by means of SEM analysis (TESCAN MIRA 3).
Results of mechanical tests proved a fall of the shear tensile strength of single lap-shear adhesive
bonds after 42 cycles of the degradation process of 12.8 to 21.7%. The bond strength fall was
gradual and it showed a linear trend at some adhesives. Other adhesives showed a significant fall
after the exposition to the degradation process after which the strength fall stabilized
Vortices in simulations of solar surface convection
We report on the occurrence of small-scale vortices in simulations of the
convective solar surface. Using an eigenanalysis of the velocity gradient
tensor, we find the subset of high vorticity regions in which the plasma is
swirling. The swirling regions form an unsteady, tangled network of filaments
in the turbulent downflow lanes. Near-surface vertical vortices are underdense
and cause a local depression of the optical surface. They are potentially
observable as bright points in the dark intergranular lanes. Vortex features
typically exist for a few minutes, during which they are moved and twisted by
the motion of the ambient plasma. The bigger vortices found in the simulations
are possibly, but not necessarily, related to observations of granular-scale
spiraling pathlines in "cork animations" or feature tracking.Comment: 11 pages, 13 figures, accepted for publication in A&A, complementary
movies at http://www.mps.mpg.de/homes/moll/strudel/papermovies
DYNAMIC STRAY CURRENT MEASURING METHODS IN URBAN AREAS
In areas where urban tracks are used as public transportation,
dynamic stray currents cause high maintenance costs for the tracks and
metal structures near the tracks. Stray currents caused by rail vehicles
depend on many factors (traffic density, vehicle speed, acceleration and
deceleration, soil and track moisture), so it is very difficult to get a clear picture
of the harmfulness of the stray current based on the results of a single field
measurement. However, there are several measurement methods that can
be used to determine the presence of stray currents and predict appropriate
track maintenance actions. Some of these methods are described in this article,
namely the use of stray current mapper, measurement of rail potential and rail current, measurement at the stray current collection system, and the use of nondestructive sensors. In track construction, measuring the electrical potential
between rail and ground is one of the most common methods of detecting the
damaging influence of stray current
Lagrangian reductive structures on gauge-natural bundles
A reductive structure is associated here with Lagrangian canonically defined
conserved quantities on gauge-natural bundles. Parametrized transformations
defined by the gauge-natural lift of infinitesimal principal automorphisms
induce a variational sequence such that the generalized Jacobi morphism is
naturally self-adjoint. As a consequence, its kernel defines a reductive split
structure on the relevant underlying principal bundle.Comment: 11 pages, remarks and comments added, this version published in ROM
Trace and antitrace maps for aperiodic sequences, their extensions and applications
We study aperiodic systems based on substitution rules by means of a
transfer-matrix approach. In addition to the well-known trace map, we
investigate the so-called `antitrace' map, which is the corresponding map for
the difference of the off-diagonal elements of the 2x2 transfer matrix. The
antitrace maps are obtained for various binary, ternary and quaternary
aperiodic sequences, such as the Fibonacci, Thue-Morse, period-doubling,
Rudin-Shapiro sequences, and certain generalizations. For arbitrary
substitution rules, we show that not only trace maps, but also antitrace maps
exist. The dimension of the our antitrace map is r(r+1)/2, where r denotes the
number of basic letters in the aperiodic sequence. Analogous maps for specific
matrix elements of the transfer matrix can also be constructed, but the maps
for the off-diagonal elements and for the difference of the diagonal elements
coincide with the antitrace map. Thus, from the trace and antitrace map, we can
determine any physical quantity related to the global transfer matrix of the
system. As examples, we employ these dynamical maps to compute the transmission
coefficients for optical multilayers, harmonic chains, and electronic systems.Comment: 13 pages, REVTeX, now also includes applications to electronic
systems, some references adde
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