180 research outputs found
Detection problems of vortical structures
Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Main conceptual problems faced in detection of vortical structures are dealt with and discussed on the background of a brief review of existing vortex-identification schemes.mp201
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
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
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
Systematic analytical characterization of new psychoactive substances: A case study
AbstractNew psychoactive substances (NPS) are synthesized compounds that are not usually covered by European and/or international laws. With a slight alteration in the chemical structure of existing illegal substances registered in the European Union (EU), these NPS circumvent existing controls and are thus referred to as “legal highs”. They are becoming increasingly available and can easily be purchased through both the internet and other means (smart shops). Thus, it is essential that the identification of NPS keeps up with this rapidly evolving market.In this case study, the Belgian Customs authorities apprehended a parcel, originating from China, containing two samples, declared as being “white pigments”. For routine identification, the Belgian Customs Laboratory first analysed both samples by gas-chromatography mass-spectrometry and Fourier-Transform Infrared spectroscopy. The information obtained by these techniques is essential and can give an indication of the chemical structure of an unknown substance but not the complete identification of its structure. To bridge this gap, scientific and technical support is ensured by the Joint Research Centre (JRC) to the European Commission Directorate General for Taxation and Customs Unions (DG TAXUD) and the Customs Laboratory European Network (CLEN) through an Administrative Arrangement for fast recognition of NPS and identification of unknown chemicals. The samples were sent to the JRC for a complete characterization using advanced techniques and chemoinformatic tools.The aim of this study was also to encourage the development of a science-based policy driven approach on NPS.These samples were fully characterized and identified as 5F-AMB and PX-3 using 1H and 13C nuclear magnetic resonance (NMR), high-resolution tandem mass-spectrometry (HR-MS/MS) and Raman spectroscopy. A chemoinformatic platform was used to manage, unify analytical data from multiple techniques and instruments, and combine it with chemical and structural information
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
Morita base change in Hopf-cyclic (co)homology
In this paper, we establish the invariance of cyclic (co)homology of left
Hopf algebroids under the change of Morita equivalent base algebras. The
classical result on Morita invariance for cyclic homology of associative
algebras appears as a special example of this theory. In our main application
we consider the Morita equivalence between the algebra of complex-valued smooth
functions on the classical 2-torus and the coordinate algebra of the
noncommutative 2-torus with rational parameter. We then construct a Morita base
change left Hopf algebroid over this noncommutative 2-torus and show that its
cyclic (co)homology can be computed by means of the homology of the Lie
algebroid of vector fields on the classical 2-torus.Comment: Final version to appear in Lett. Math. Phy
New Cases of Universality Theorem for Gravitational Theories
The "Universality Theorem" for gravity shows that f(R) theories (in their
metric-affine formulation) in vacuum are dynamically equivalent to vacuum
Einstein equations with suitable cosmological constants. This holds true for a
generic (i.e. except sporadic degenerate cases) analytic function f(R) and
standard gravity without cosmological constant is reproduced if f is the
identity function (i.e. f(R)=R). The theorem is here extended introducing in
dimension 4 a 1-parameter family of invariants R' inspired by the
Barbero-Immirzi formulation of GR (which in the Euclidean sector includes also
selfdual formulation). It will be proven that f(R') theories so defined are
dynamically equivalent to the corresponding metric-affine f(R) theory. In
particular for the function f(R)=R the standard equivalence between GR and
Holst Lagrangian is obtained.Comment: 10 pages, few typos correcte
Remarks on Conserved Quantities and Entropy of BTZ Black Hole Solutions. Part I: the General Setting
The BTZ stationary black hole solution is considered and its mass and angular
momentum are calculated by means of Noether theorem. In particular, relative
conserved quantities with respect to a suitably fixed background are discussed.
Entropy is then computed in a geometric and macroscopic framework, so that it
satisfies the first principle of thermodynamics. In order to compare this more
general framework to the prescription by Wald et al. we construct the maximal
extension of the BTZ horizon by means of Kruskal-like coordinates. A discussion
about the different features of the two methods for computing entropy is
finally developed.Comment: PlainTEX, 16 pages. Revised version 1.
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