37 research outputs found
Prostorna raspodjela 40K i 232Th u recentnim sedimentima estuarija rijeke Krke
Spatial radionuclides distribution was studied in recent estuarine sediments in the Krka River Estuary. Sediment samples were analyzed for 40K and 232Th by gamma-spectrometry. Activities of 40K were found in the range of 18–457 Bq kg–1 and activities of 232Th in range of 1.9–29.4 Bq kg–1. Distribution of 232Th activities follows that of 40K, with correlation coefficients higher than 0.97 in all analyzed samples from the Krka River estuary. Spatial distribution of natural radionuclides (40K and 232Th) in recent estuarine and marine sedimentation area can be a useful tool for recognizing the possible input of terrigenous material, as well as for fast locating of the area where such material is predominantly settled.U radu je proučavana prostorna raspodjela radionuklida u recentnim sedimentima estuarija rijeke Krke. Uzorci sedimenta analizirani su tijekom protekle dvije godine i aktivnost 40K i 232Th određena je gamaspektrometrijski. Izmjerene aktivnosti za 40K bile su između 18–457 Bq kg–1, a za 232Th izme|u 1.9–29.4 Bq kg–1. Raspodjela aktivnosti 232Th prati raspodjelu aktivnosti 40K, i njihov korelacijski faktor vi{i je od 0,97 u svim analiziranim uzorcima. Prostorna raspodjela prirodnih radionuklida (40K i 232Th) u recentnim estuarijskim i morskim sedimentima pod značajnim je utjecajem unosa terigenog materijala i može biti koristan ključ za prepoznavanje mogućeg izvora materijala kao i boljeg određivanja mjesta najvećeg taloženja tog materijala
Toric multifocal and extended range of vision intraocular lenses in correction of astigmatism and presbyopia
Influence of Passive Smoking on Basic Anthropometric Characteristics and Respiratory Function in Young Athletes
The primary objective of this study is to investigate the maintenance difference in basic anthropometric characteristics
and to outline the dynamics of respiratory function change in youngsters athletes exposed to passive smoking (PS)
and athletes not exposed to passive smoking in their families (NPS). High and weight were determined as basis anthropometric
characteristics. Measured parameters for respiratory function were vital capacity (VC), forced expiratory
volume in the first second (FEV1), maximum expiratory flow (PEF), forced expiratory flow at 50% forced vital capacity
(MEF 50) and forced expiratory flow at 25% forced vital capacity (MEF 25). Significant statistical differences in separate
spirometric variable were found in three variables (FEV1, MEF50, and MEF25) for group older youngsters. Analysis of
variance showed statistical differences between athletes unexposed to passive smoking (NPS) and athletes exposed to passive
smoking (PS) in even four spirometric variables (VC, FEV1, MEF50 and MEF25)
Emergence of superconductivity in the cuprates via a universal percolation process
A pivotal step toward understanding unconventional superconductors would be
to decipher how superconductivity emerges from the unusual normal state upon
cooling. In the cuprates, traces of superconducting pairing appear above the
macroscopic transition temperature , yet extensive investigation has led
to disparate conclusions. The main difficulty has been the separation of
superconducting contributions from complex normal state behaviour. Here we
avoid this problem by measuring the nonlinear conductivity, an observable that
is zero in the normal state. We uncover for several representative cuprates
that the nonlinear conductivity vanishes exponentially above , both with
temperature and magnetic field, and exhibits temperature-scaling characterized
by a nearly universal scale . Attempts to model the response with the
frequently evoked Ginzburg-Landau theory are unsuccessful. Instead, our
findings are captured by a simple percolation model that can also explain other
properties of the cuprates. We thus resolve a long-standing conundrum by
showing that the emergence of superconductivity in the cuprates is dominated by
their inherent inhomogeneity
Percolative nature of the dc paraconductivity in the cuprate superconductors
We present an investigation of the planar direct-current (dc)
paraconductivity of the model cuprate material HgBaCuO in the
underdoped part of the phase diagram. The simple quadratic
temperature-dependence of the Fermi-liquid normal-state resistivity enables us
to extract the paraconductivity above the macroscopic with great
accuracy. The paraconductivity exhibits unusual exponential temperature
dependence, with a characteristic temperature scale that is distinct from
. In the entire temperature range where it is discernable, the
paraconductivity is quantitatively explained by a simple superconducting
percolation model, which implies that underlying gap disorder dominates the
emergence of superconductivity
Transport Properties of YbCu4.4 Giant-unit-cell Metallic Compound
The experimental results of the transport properties: electrical resistivity, ρ, thermopower, S, and thermal conductivity, κ, of a polycrystalline sample of YbCu4.4, in the temperature range 2 to 300 K, are presented. In contrast to the divalent YbCu2 compound, YbCu4.4 has transport properties typical of an intermediate valence compound: relatively high electrical resistivity and large thermoelectric power. The electrical resistivity ρ(T) exhibits a typical Kondo lattice systems’ behaviour, with a room temperature value of ρr.t. ≈ 60 μΩ cm, while thermoelectric power S(T) is negative in the whole investigated temperature range. S(T) shows a distinct temperature dependence, which is attributed to the Kondo interaction. The room temperature, r.t., value of the thermal conductivity is κr.t. ≈ 20 W/mK. The pronounced maximum in κ(T) at low temperatures, which is frequently found in simple nonmagnetic and rather pure samples, is absent. The thermal conductivity decreases monotonically in a whole temperature range with a change in the slope around 50 K. The absence of a maximum in κ(T) could be related to the larger contribution of residual scattering processes and to the considerably weak coupling of electrons with phonons. The results are compared to the reported transport properties of similar Ce-Cu and Yb-Cu Kondo systems.</p
Demonstrating the model nature of the high-temperature superconductor HgBaCuO
The compound HgBaCuO (Hg1201) exhibits a simple tetragonal
crystal structure and the highest superconducting transition temperature
(T) among all single Cu-O layer cuprates, with T = 97 K (onset) at
optimal doping. Due to a lack of sizable single crystals, experimental work on
this very attractive system has been significantly limited. Thanks to a recent
breakthrough in crystal growth, such crystals have now become available. Here,
we demonstrate that it is possible to identify suitable heat treatment
conditions to systematically and uniformly tune the hole concentration of
Hg1201 crystals over a wide range, from very underdoped (T = 47 K, hole
concentration p ~ 0.08) to overdoped (T = 64 K, p ~ 0.22). We then present
quantitative magnetic susceptibility and DC charge transport results that
reveal the very high-quality nature of the studied crystals. Using XPS on
cleaved samples, we furthermore demonstrate that it is possible to obtain large
surfaces of good quality. These characterization measurements demonstrate that
Hg1201 should be viewed as a model high-temperature superconductor, and they
provide the foundation for extensive future experimental work.Comment: 15 pages, 6 Figure
Optical conductivity of cuprates in a new light
Understanding the physical properties of unconventional superconductors as
well as of other correlated materials presents a formidable challenge. Their
unusual evolution with doping, frequency, and temperature, has frequently led
to non-Fermi-liquid (non-FL) interpretations. Optical conductivity is a major
challenge in this context. Here, the optical spectra of two archetypal
cuprates, underdoped HgBaCuO and optimally-doped
BiSrCaCuO, are interpreted based on the standard Fermi
liquid (FL) paradigm. At both dopings, perfect frequency-temperature FL scaling
is found to be modified by the presence of a second, gapped electronic
subsystem. This non-FL component emerges as a well-defined mid-infrared
spectral feature after the FL contribution -- determined independently by
transport -- is subtracted. Temperature, frequency and doping evolution of the
MIR feature identifies a gapped rather than dissipative response. In contrast,
the dissipative response is found to be relevant for pnictides and ruthenates.
Such an unbiased FL/non-FL separation is extended across the cuprate phase
diagram, providing a natural explanation why the superfluid density is
attenuated on the overdoped side. Thus, we obtain a unified interpretation of
optical responses and transport measurements in all analyzed physical regimes
and all analyzed compounds.Comment: 43 pages, 13 figure