157 research outputs found
Thermal shock resistance of ceramic fibre composites characterized by non-destructive methods
Alumina based ceramic fibres and alumina based ceramic were used to produce composite material. Behaviour of composite ceramics after thermal shock treatments was investigated. Thermal shock of the samples was evaluated using water quench test. Surface deterioration level of samples was monitored by image analysis before and after a number of quenching cycles. Ultrasonic measurements were done on samples after quench tests. Dynamic Young modulus of elasticity and strength degradation were calculated using measured values of ultrasonic velocities. Strengths deterioration was calculated using the non-destructive measurements and correlated to degradation of surface area and number of quenches. The addition of small amount of ceramic fibres improves the strengths and diminishes the loss of mechanical properties of samples during thermal shock experiments
A new epigean false scorpion: Roncus sumadijae n. sp. (Neobisiidae, Pseudoscorpiones) from the Balkan Peninsula (Western Serbia)
A new endemic epigean species from the village of Adžina Livada, nr. Kragujevac, Mts. GlediÄke Planine, western Serbia, is erected, described and thoroughly illustrated. Its main morphometric characters and important diagnostic features are analyzed and compared to the two closest congeners, Roncus ivanjicae B. ÄurÄiÄ, and R. golijae B. ÄurÄiÄ from western Serbia, respectively
Supplementary data for the article: VukoviÄ, G.; AniÄiÄ UroÅ”eviÄ, M.; Å krivanj, S.; MiliÄeviÄ, T.; DimitrijeviÄ, D.; TomaÅ”eviÄ, M.; PopoviÄ, A. Moss Bag Biomonitoring of Airborne Toxic Element Decrease on a Small Scale: A Street Study in Belgrade, Serbia. Sci. Total Environ. 2016, 542, 394ā403. https://doi.org/10.1016/j.scitotenv.2015.10.091
Supplementary material for: [https://doi.org/10.1016/j.scitotenv.2015.10.091]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2002
Prospective of the LDI MS to characterization the corrosion products of silver-copper alloys on an example of the Ag-Cu-X (X- Zn, Pd, In) system
This work presents the perspective of applying the laser desorption/ionization mass spectrometry (LDI MS) for characterization the anode film of the Ag60Cu26Zn14, Ag58.5Cu31.5Pd10, and Ag63Cu27In10 alloys (at high concentrations of chloride ions in solutions). The reference LDI mass spectra of anode films of pure Ag and Cu have been used for the identification of product corrosion. Knowing the clusters detected in the reference spectra lead to the facilitating identification of the LDI mass spectrum of the sample and reduces the analysis time. The LDI MS analysis of these alloys revealed that the predominant corrosion product are AgCl (from AgnCln+1ā/+, nĀ =Ā 1ā3), and CuCl (from āsuperhalogenā CumClnā clusters, mĀ =Ā 1ā2, nĀ =Ā 2ā6); it also revealed Cu2(OH)3Cl (from Cu2(OH)(H2O)2+) and Cu2O (from Cu(H2O)+, Cu2O doped with chlorine). These results are in accordance with the X-ray diffraction and Raman analysis. The LDI MS spectra of alloys contain the additional peaks formed due to the mutual influences of different metals in the alloys (AgCuCl3ā (AgCl-CuCl2ā), AgCu2Cl4ā (AgCl-CuCl-CuCl2ā), and Ag2CuCl4ā (AgCl-AgCl-CuClā), which is consistent with the identified corrosion products. It should be noted that the LDI MS suggest the presence of CuCl2, which can be interpreted as the corrosion products retained in the porous films of alloys, and not detected by the other methods due to a small amount. The future theoretical and experimental studies of metal clusters, significant for metallurgy, can contribute that the LDI MS is becoming a powerful analytical tool for characterization the metal surfaces
Twist Deformations of the Supersymmetric Quantum Mechanics
The N-extended Supersymmetric Quantum Mechanics is deformed via an abelian
twist which preserves the super-Hopf algebra structure of its Universal
Enveloping Superalgebra. Two constructions are possible. For even N one can
identify the 1D N-extended superalgebra with the fermionic Heisenberg algebra.
Alternatively, supersymmetry generators can be realized as operators belonging
to the Universal Enveloping Superalgebra of one bosonic and several fermionic
oscillators. The deformed system is described in terms of twisted operators
satisfying twist-deformed (anti)commutators. The main differences between an
abelian twist defined in terms of fermionic operators and an abelian twist
defined in terms of bosonic operators are discussed.Comment: 18 pages; two references adde
Collisional kinetics of non-uniform electric field, low-pressure, direct-current discharges in H
A model of the collisional kinetics of energetic hydrogen atoms, molecules,
and ions in pure H discharges is used to predict H emission
profiles and spatial distributions of emission from the cathode regions of
low-pressure, weakly-ionized discharges for comparison with a wide variety of
experiments. Positive and negative ion energy distributions are also predicted.
The model developed for spatially uniform electric fields and current densities
less than A/m is extended to non-uniform electric fields, current
densities of A/m, and electric field to gas density ratios MTd at 0.002 to 5 Torr pressure. (1 Td = V m and 1 Torr =
133 Pa) The observed far-wing Doppler broadening and spatial distribution of
the H emission is consistent with reactions among H, H,
H, and H ions, fast H atoms, and fast H molecules, and with
reflection, excitation, and attachment to fast H atoms at surfaces. The
H excitation and H formation occur principally by collisions of
fast H, fast H, and H with H. Simplifications include using a
one-dimensional geometry, a multi-beam transport model, and the average
cathode-fall electric field. The H emission is linear with current
density over eight orders of magnitude. The calculated ion energy distributions
agree satisfactorily with experiment for H and H, but are only in
qualitative agreement for H and H. The experiments successfully modeled
range from short-gap, parallel-plane glow discharges to beam-like,
electrostatic-confinement discharges.Comment: Submitted to Plasmas Sources Science and Technology 8/18/201
Profiling of microorganism-binding serum antibody specificities in professional athletes
The goal of this work was to elucidate similarities between microorganisms from the perspective of the humoral immune system reactivity in professional athletes. The reactivity of serum IgG of 14 young, individuals was analyzed to 23 selected microorganisms as antigens by use of the in house ELISA. Serum IgM and IgA reactivity was also analyzed and a control group of sex and age matched individuals was used for comparison. The obtained absorbance levels were used as a string of values to correlate the reactivity to different microorganisms. IgM was found to be the most cross reactive antibody class, Pearsonās r = 0.7ā0.92, for very distant bacterial species such as Lactobacillus and E. coli.High correlation in IgG levels was found for Gammaproteobacteria and LPS (from E. coli) (r = 0.77 for LPS vs. P. aeruginosa to r = 0.98 for LPS vs. E.coli), whereas this correlation was lower in the control group (r = 0.49 for LPS vs. P. aeruginosa to r = 0.66 for LPS vs. E.coli). The correlation was also analyzed between total IgG and IgG subclasses specific for the same microorganism, and IgG2 was identified as the main subclass recognising different microorganisms, as well as recognising LPS. Upon correlation of IgG with IgA for the same microorganism absence of or negative correlation was found between bacteria-specific IgA and IgG in case of Lactobacillus and Staphylococcusgeni, whereas correlation was absent or positive for Candida albicans, Enterococcusfaecalis,Streptococcus species tested in professional athletes. Opposite results were obtained for the control group. Outlined here is a simple experimental procedure and data analysis which yields functional significance and which can be used for determining the similarities between microorganisms from the aspect of the humoral immune system, for determining the main IgG subclass involved in an immune response as well as for the analysis of different target populations
Dynamical noncommutativity and Noether theorem in twisted phi^*4 theory
A \star-product is defined via a set of commuting vector fields X_a = e_a^\mu
(x) \partial_\mu, and used in a phi^*4 theory coupled to the e_a^\mu (x)
fields. The \star-product is dynamical, and the vacuum solution phi =0, e_a^\mu
(x)=delta_a^\mu reproduces the usual Moyal product. The action is invariant
under rigid translations and Lorentz rotations, and the conserved
energy-momentum and angular momentum tensors are explicitly derived.Comment: 15 pages LaTeX, minor typos, added reference
Noncommutative Differential Forms on the kappa-deformed Space
We construct a differential algebra of forms on the kappa-deformed space. For
a given realization of the noncommutative coordinates as formal power series in
the Weyl algebra we find an infinite family of one-forms and nilpotent exterior
derivatives. We derive explicit expressions for the exterior derivative and
one-forms in covariant and noncovariant realizations. We also introduce
higher-order forms and show that the exterior derivative satisfies the graded
Leibniz rule. The differential forms are generally not graded-commutative, but
they satisfy the graded Jacobi identity. We also consider the star-product of
classical differential forms. The star-product is well-defined if the
commutator between the noncommutative coordinates and one-forms is closed in
the space of one-forms alone. In addition, we show that in certain realizations
the exterior derivative acting on the star-product satisfies the undeformed
Leibniz rule.Comment: to appear in J. Phys. A: Math. Theo
N=1/2 Deformations of Chiral Superspaces from New Quantum Poincare and Euclidean Superalgebras
We present a large class of supersymmetric classical r-matrices, describing
the supertwist deformations of Poincare and Euclidean superalgebras. We
consider in detail new family of four supertwists of N=1 Poincare superalgebra
and provide as well their Euclidean counterpart. The proposed supertwists are
better adjusted to the description of deformed D=4 Euclidean supersymmetries
with independent left-chiral and right-chiral supercharges. They lead to new
quantum superspaces, obtained by the superextension of twist deformations of
spacetime providing Lie-algebraic noncommutativity of space-time coordinates.
In the Hopf-algebraic Euclidean SUSY framework the considered supertwist
deformations provide an alternative to the N=1/2 SUSY Seiberg's star product
deformation scheme.Comment: 17 pages, LaTeX, new (re-worked) revised and extended versio
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