3,511 research outputs found
Cross sections of proton-induced reactions on 152Gd, 155Gd and 159Tb with emphasis on the production of selected Tb radionuclides
Cross sections are presented for various Dy, Tb and Gd radionuclides produced in the proton bombardment
of 159Tb as well as for the reactions 152Gd(p,4n)149Tb and 155Gd(p,4n)152Tb up to 66 MeV. The
experimental excitation functions are compared with theoretical predictions by means of the geometrydependent
hybrid (GDH) model as implemented in the code ALICE/ASH, as well as with values from the
TENDL-2012 library and previous literature experimental data, where available. Physical yields have been
derived for the production of some of the medically important radioterbiums, namely 149Tb (radionuclide
therapy), 152Tb (PET) and 155Tb (SPECT). The indirect production of high-purity 155Tb via the decay of
its precursor 155Dy is reported. The possibility of a large-scale production facility based on a commercial
70 MeV cyclotron is also discussed
Winning strategies in congested traffic
One-directional traffic on two-lanes is modeled in the framework of a
spring-block type model. A fraction of the cars are allowed to change
lanes, following simple dynamical rules, while the other cars keep their
initial lane. The advance of cars, starting from equivalent positions and
following the two driving strategies is studied and compared. As a function of
the parameter the winning probability and the average gain in the
advancement for the lane-changing strategy is computed. An interesting
phase-transition like behavior is revealed and conclusions are drawn regarding
the conditions when the lane changing strategy is the better option for the
drivers.Comment: 5 pages, 5 figure
Ab-initio elastic tensor of cubic TiAlN alloy: the dependence of the elastic constants on the size and shape of the supercell model
In this study we discuss the performance of approximate SQS supercell models
in describing the cubic elastic properties of B1 (rocksalt)
TiAlN alloy by using a symmetry based projection technique. We
show on the example of TiAlN alloy, that this projection
technique can be used to align the differently shaped and sized SQS structures
for a comparison in modeling elasticity. Moreover, we focus to accurately
determine the cubic elastic constants and Zener's type elastic anisotropy of
TiAlN. Our best supercell model, that captures accurately both
the randomness and cubic elastic symmetry, results in GPa,
GPa and GPa with 3% of error and for Zener's
elastic anisotropy with 6% of error. In addition, we establish the general
importance of selecting proper approximate SQS supercells with symmetry
arguments to reliably model elasticity of alloys. In general, we suggest the
calculation of nine elastic tensor elements - , , ,
, , , , and , to evaluate and
analyze the performance of SQS supercells in predicting elasticity of cubic
alloys via projecting out the closest cubic approximate of the elastic tensor.
The here described methodology is general enough to be applied in discussing
elasticity of substitutional alloys with any symmetry and at arbitrary
composition.Comment: Submitted to Physical Review
Effects of chemical treatments on infestation of Alternaria spp. and Fusarium spp. in correlation with technological wheat quality
In this study, the time of infestation by fungi from genus Alternaria spp. and Fusarium spp. was investigated in different stages of wheat maturity (milk, waxy, and technological maturity); the effects of different fungicides on the yield, technological properties, and content of mycotoxin DON were studied also. The results showed that Alternaria spp. attacked spike and kernel in f lowering and end-f lowering stage, as it was already known for Fusarium species. Fungicide treatment increases the yield up to 20%, test weight by 3.7%, and thousand-kernel weight up to 19.1%. High content of mycotoxin DON, above tolerable limits, was detected only in the treatment with fungicide Caramba and in untreated control
Diszlokáció rendszerek statisztikus tulajdonságainak vizsgálata = Investigation of the statistical properties of dislocation ensembles
A pályázat célkitűzéseinek megfelelően diszlokációk kollektív tulajdonságait vizsgáltuk mint elméletileg mind kísérletileg. Analitikus számításokkal és numerikus szimulációval vizsgáltuk a diszlokációk következtében kialakuló belső feszültségeloszlás tulajdonságait. Megállapítottuk, hogy az eloszlás központi része Lorentz eloszlású, míg a lecsengő tartományban a feszültség köbével fordítottan arányos. Továbbá kimutattuk, hogy a külső feszültség hatására egy a feszültség 4. hatványával leeső aszimmetrikus tag jelenik meg. Megmutattuk, hogy egy 2D diszlokációrendszer relaxációja során a különböző fizikai mennyiségek az idő hatványfüggvényeként csengenek le. Kimutattuk, hogy a diszlokáció climb bekapcsolása jól definiált cellaszerkezet kialakulásához vezet.. A korábban mikroszkopikus meggondolásokkal kidolgozott diszlokáció kontinuum elméletet sikerült egy variációs elvből származtatni. Ez lehetővé tette az elmélet általánosítását többszörös csúszásra ill. oldott atomok hatásának beépítését is. Az elmélet segítségével részletesen megvizsgáltuk egy extra hozzáadott diszlokáció terének árnyékolását a többi diszlokáció átrendeződése következtében (Debye screening) . A kísérleti munka során nanoindentációval Cu egykristályokon meghatároztuk a mikrokeménység relatív fluktuációját. Az irodalomban először megállapítottuk, hogy a diszlokációsűrűséghez hasonlóan ez is az alkalmazott feszültség függvényében egy éles maximumot mutat. | According to the proposal the collective properties of dislocations were investigated both by theoretical and experimental methods. The properties of the internal stress distribution generated by dislocations were investigated by analytical calculations and computer simulations. It was found that the central part of the distribution is Loretzian while its tail decays with the invers cube of the stress. If external stress is applied the distribution becomes asymmetric. The antisymmetric part decaying with the invers fourth power of the stress. Numerical studies show that during the relaxation of the dislocation ensemble the different macroscopic quantities decay with some power of the time. Beside this, it is obtained that the dislocation climb leads to the the formation of cell structure. The continuum theory of dislocations derived earlier from microscopic considerations was reformulated into a phase field theory. This allowed us to extend the theory to multiple slip and study the influence of solute atoms. With this framework the Debye screening of the stress field of an extra dislocation was analysed in details . The relative fluctuation of microhardness (RFM) was determined by nanoindentation performed on deformed Cu single crystals. It was found that like the fluctuation of the dislocation density the RFM alo exhibits a sharp maximum as a function of applied stress
Submicron plasticity: yield stress, dislocation avalanches, and velocity distribution
The existence of a well defined yield stress, where a macroscopic piece of
crystal begins to plastically flow, has been one of the basic observations of
materials science. In contrast to macroscopic samples, in micro- and
nanocrystals the strain accumulates in distinct, unpredictable bursts, which
makes controlled plastic forming rather difficult. Here we study by simulation,
in two and three dimensions, plastic deformation of submicron objects under
increasing stress. We show that, while the stress-strain relation of individual
samples exhibits jumps, its average and mean deviation still specify a
well-defined critical stress, which we identify with the jamming-flowing
transition. The statistical background of this phenomenon is analyzed through
the velocity distribution of short dislocation segments, revealing a universal
cubic decay and an appearance of a shoulder due to dislocation avalanches. Our
results can help to understand the jamming-flowing transition exhibited by a
series of various physical systems.Comment: 5 page
Out-of-equilibrium critical dynamics at surfaces: Cluster dissolution and non-algebraic correlations
We study nonequilibrium dynamical properties at a free surface after the
system is quenched from the high-temperature phase into the critical point. We
show that if the spatial surface correlations decay sufficiently rapidly the
surface magnetization and/or the surface manifold autocorrelations has a
qualitatively different universal short time behavior than the same quantities
in the bulk. At a free surface cluster dissolution may take place instead of
domain growth yielding stationary dynamical correlations that decay in a
stretched exponential form. This phenomenon takes place in the
three-dimensional Ising model and should be observable in real ferromagnets.Comment: 4 pages, 4 figure
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