1,602 research outputs found
Thermal Conductivity, Thermopower, and Figure of Merit of La_{1-x}Sr_xCoO_3
We present a study of the thermal conductivity k and the thermopower S of
single crystals of La_{1-x}Sr_xCoO_3 with 0<= x <= 0.3. For all Sr
concentrations La_{1-x}Sr_xCoO_3 has rather low k values, whereas S strongly
changes as a function of x. We discuss the influence of the temperature- and
the doping-induced spin-state transitions of the Co ions on both, S and k. From
S, k, and the electrical resistivity rho we derive the thermoelectric figure of
merit Z=S^2/(k*rho). For intermediate Sr concentrations we find notably large
values of Z indicating that Co-based materials could be promising candidates
for thermoelectric cooling.Comment: 7 pages, 5 figures included, submitted to Phys. Rev.
Spin-State Transition and Metal-Insulator Transition in LaEuCoO}
We present a study of the structure, the electric resistivity, the magnetic
susceptibility, and the thermal expansion of LaEuCoO. LaCoO
shows a temperature-induced spin-state transition around 100 K and a
metal-insulator transition around 500 K. Partial substitution of La by
the smaller Eu causes chemical pressure and leads to a drastic increase
of the spin gap from about 190 K in LaCoO to about 2000 K in EuCoO, so
that the spin-state transition is shifted to much higher temperatures. A
combined analysis of thermal expansion and susceptibility gives evidence that
the spin-state transition has to be attributed to a population of an
intermediate-spin state with orbital order for and without orbital
order for larger . In contrast to the spin-state transition, the
metal-insulator transition is shifted only moderately to higher temperatures
with increasing Eu content, showing that the metal-insulator transition occurs
independently from the spin-state distribution of the Co ions. Around
the metal-insulator transition the magnetic susceptibility shows a similar
increase for all and approaches a doping-independent value around 1000 K
indicating that well above the metal-insulator transition the same spin state
is approached for all .Comment: 10 pages, 6 figure
МЕТОДИКА ПРОВЕДЕННЯ ІСТОРИКО-КРАЄЗНАВЧИХ ЕКСПЕДИЦІЙ НА ПІВДНІ УКРАЇНИ ІНСТИТУТОМ ЕТНОГРАФІЇ АН СРСР у 50-60-ті рр. ХХ ст.
Український народ у своїй історії має великий досвід духовного життя, бо з покоління в покоління передає набуті навички, що стали невід’ємною части-ною нашої національності. Але з кожним роком наше покоління, на жаль, втра-чає зв’язок з попередніми поколіннями. Тому, щоб зберегти традиції, націона-льні особливості, в різні часи різноманітні інститути, товариства, окремі дослі-дники намагались створити найоптимальнішу методику організації та прове-дення історико-краєзнавчих експедицій
Worldwide evidence of a unimodal relationship between productivity and plant species richness
The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity
The spin state transition in LaCoO; revising a revision
Using soft x-ray absorption spectroscopy and magnetic circular dichroism at
the Co- edge we reveal that the spin state transition in LaCoO
can be well described by a low-spin ground state and a triply-degenerate
high-spin first excited state. From the temperature dependence of the spectral
lineshapes we find that LaCoO at finite temperatures is an inhomogeneous
mixed-spin-state system. Crucial is that the magnetic circular dichroism signal
in the paramagnetic state carries a large orbital momentum. This directly shows
that the currently accepted low-/intermediate-spin picture is at variance.
Parameters derived from these spectroscopies fully explain existing magnetic
susceptibility, electron spin resonance and inelastic neutron data
Evaluation of Cathode Gas Composition and Temperature Influences on Alkaline Anion Exchange Membrane Fuel Cell (AAEMFC) Performance
The effects of different temperatures (55, 65, 75 and 85 °C) and cathode gas compositions (O2, synthetic air, air and 90% synthetic air+10% CO2) on alkaline anion exchange membrane fuel cell (AAEMFC) were evaluated. Membrane electrode assemblies (MEA) were fabricated using commercial anion exchange membrane (AEM) in OH- form and Pt catalyst. Polarization curves and voltage responses during constant current were performed in order to describe the influences of temperature and gas composition on the AAEMFC performance. The experimental results showed that the fuel cell performance increases with elevating temperatures for all applied gas compositions. Highest power density of 34.7 mW cm-2 was achieved for pure O2 as cathode feed. A decrease to 20.3 mW cm-2 was observed when cathode gas composition was changed to synthetic air due to reduction of the O2 partial pressure. The presence of CO2 in atmospheric air applied to the cathode stream caused a further drop of the maximum power density to 15.2 mW cm-2 driven by neutralization of OH- ions with CO2
Bound -> free and bound -> bound multichannel emission spectra from selectively excited Rydberg states in the ZnAr and CdAr van der Waals complexes
Multichannel dispersed emission spectra recorded upon a selective excitation
of Rydberg electronic energy states in the ZnAr and CdAr van der Waals (vdW)
complexes are analysed as a proof-of-concept of the future experimental
approach. Simulations of the emission spectra are based on ab-initio calculated
interatomic potentials and transition dipole moments (TDMs). Experimental
set-up that is under construction along with the experimental procedure are
discussed
Disentangling the processes driving plant assemblages in mountain grasslands across spatial scales and environmental gradients
1. Habitat filtering and limiting similarity are well-documented ecological assembly processes that hierarchically filter species across spatial scales, from a regional pool to local assemblages. However, information on the effects of fine-scale spatial partitioning of species, working as an additional mechanism of coexistence, on community patterns, is much scarcer.
2. In this study, we quantified the importance of fine-scale spatial partitioning, relative to habitat filtering and limiting similarity, in structuring grassland communities in the western Swiss Alps. To do so, 298 vegetation plots (2 m × 2 m ) each with five nested subplots (20 cm × 20 cm) were used for trait based assembly tests (i.e. comparisons with several alternative null expectations), examining the observed plot and subplot level α-diversity (indicating habitat filtering and limiting similarity) and the between-subplot β-diversity of traits (indicating fine-scale spatial partitioning). We further assessed variations in the detected signatures of these assembly processes along a set of environmental gradients.
3. We found habitat filtering to be the dominating assembly process at the plot level with diminished effect at the subplot level, while limiting similarity prevailed at the subplot level with weaker average effect at the plot level. Plot-level limiting similarity was positively correlated with fine-scale partitioning suggesting that the trait divergence may result from a combination of competitive exclusion between functionally similar species and environmental micro-heterogeneities. Overall, signatures of assembly processes only marginally changed along environmental gradients but the observed trends were more prominent at the plot than at the subplot scale.
Synthesis: Our study emphasises the importance of considering multiple assembly processes and traits simultaneously across spatial scales and environmental gradients to understand the complex drivers of plant community composition
Looking at Vector Space and Language Models for IR using Density Matrices
In this work, we conduct a joint analysis of both Vector Space and Language
Models for IR using the mathematical framework of Quantum Theory. We shed light
on how both models allocate the space of density matrices. A density matrix is
shown to be a general representational tool capable of leveraging capabilities
of both VSM and LM representations thus paving the way for a new generation of
retrieval models. We analyze the possible implications suggested by our
findings.Comment: In Proceedings of Quantum Interaction 201
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