216 research outputs found
Charge storage mechanism in nanoporous carbons and its consequence for electrical double layer capacitors
Electrochemical capacitors, also known as supercapacitors, are energy storage devices that fill the gap between batteries and dielectric capacitors. Thanks to their unique
features, they have a key role to play in energy storage and harvesting, acting as a complement to or even a replacement of batteries which has already been achieved in
various applications. One of the challenges in the supercapacitor area is to increase their energy density. Some recent discoveries regarding ion adsorption in microporous carbon exhibiting pores in the nanometre range can help in designing the next generation of high-energy-density supercapacitors
Current-perpendicular-to-plane giant magnetoresistance of a spin valve using Co2MnSi Heusler alloy electrodes
We report the current-perpendicular-to-plane giant magnetoresistance of a
spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A
multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a
MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown
on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after
annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu
spacer layer despite the large lattice mismatch between Cu and CMS. The highest
MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room temperature and 6
K, respectively. The high spin polarization of the epitaxial CMS layers is the
most likely origin of the high MR ratio.Comment: 14 pages, 3 figures, presented at the 53rd Annual Conference on
Magnetism and Magnetic Materials, to be published in J. Appl. Phy
In-gap state and effect of light illumination in CuIrS probed by photoemission spectroscopy
We have studied disorder-induced in-gap states and effect of light
illumination in the insulating phase of spinel-type CuIrS using
ultra-violet photoemission spectroscopy (UPS). The Ir/Ir
charge-ordered gap appears below the metal-insulator transition temperature.
However, in the insulating phase, in-gap spectral features with are
observed in UPS just below the Fermi level (), corresponding to the
variable range hopping transport observed in resistivity. The spectral weight
at is not increased by light illumination, indicating that the
Ir-Ir dimer is very robust although the long-range octamer order
would be destructed by the photo-excitation. Present results suggest that the
Ir-Ir bipolaronic hopping and disorder effects are responsible
for the conductivity of CuIrS.Comment: 14 pages, 5 figure
Novel electronic states close to Mott transition in low-dimensional and frustrated systems
Recent studies demonstrated that there may appear different novel states in
correlated systems close to localized-itinerant crossover. Especially
favourable conditions for that are met in low-dimensional and in frustrated
systems. In this paper I discuss on concrete examples some of such novel
states. In particular, for some spinels and triangular systems there appears a
"partial Mott transition", in which first some finite clusters (dimers, trimes,
tetramers, heptamers) go over to the itinerant regime, and the real bulk Mott
transition occurs only later. Also some other specific possibilities in this
crossover regime are shortly discussed, such as spin-Peierls-Peierls transition
in TiOCl, spontaneous charge disproportionation in some cases, etc.Comment: To be published in Journal of Physics - Condensed Matter, conference
serie
Phase diagram and upper critical field of homogenously disordered epitaxial 3-dimensional NbN films
We report the evolution of superconducting properties with disorder, in
3-dimensional homogeneously disordered epitaxial NbN thin films. The effective
disorder in NbN is controlled from moderately clean limit down to Anderson
metal-insulator transition by changing the deposition conditions. We propose a
phase diagram for NbN in temperature-disorder plane. With increasing disorder
we observe that as kFl-->1 the superconducting transition temperature (Tc) and
minimum conductivity (sigma_0) go to zero. The phase diagram shows that in
homogeneously disordered 3-D NbN films, the metal-insulator transition and the
superconductor-insulator transition occur at a single quantum critical point at
kFl~1.Comment: To appear in Journal of Superconductivity and Novel Magnetism
(ICSM2010 proceedings
Seasonal Migration of Sika Deer in the Oku-Chichibu Mountains, Central Japan
Movements and seasonal home ranges of 6 GPS collared sika deer were investigated at the Oku-Chichibu Mountains, central Honshu, from April 2009 to March 2010. All deer migrated between discrete summer and winter home ranges. The linear migration distance ranged from 2.5 to 31.9 km. Mean elevation during the summer and the winter ranged from 980 to 1,782 m, and from 1,204 to 1,723 m, respectively. Two deer were upward migrants and 4 deer were downward migrants. Taking into consideration of the relatively small snow accumulation in the summer home range, the possibility of autumn migration to avoid deep snow is low. The percentage of steep slope in the winter home range was higher than that in the summer. Bamboo grass was not found in the summer home range, but was predominant in the winter home range. Road density decreased in the winter home range compared to the summer. Only 2 out of 6 deer stayed mainly in the wildlife protection area during the winter. Our results indicate that the autumn migration was affected by winter forage and human disturbance, thereby assured the survival of the deer during winter.ArticleMAMMAL STUDY. 37(2):127-137 (2012)journal articl
Pressure induced Superconductor-Insulator transition in the spinel compound CuRh2S4
We performed resistivity measurements in CuRhS under
quasi-hydrostatic pressure of up to 8.0 GPa, and found a pressure induced
superconductor-insulator (SI) transition. Initially, with increasing pressure,
the superconducting transition temperature increases from 4.7 K at
ambient pressure to 6.4 K at 4.0 GPa, but decreases at higher pressures. With
further compression, superconductivity in CuRhS disappears abruptly
at a critical pressure between 5.0 and 5.6 GPa, when it becomes an
insulator.Comment: 4 pages, 4 figure
Electronic structure of CuV2S4
The results of ab initio band-structure calculations and measurements of x-ray-emission valence spectra (XES) (Cu Lα, V Kβ5, V Lα, S Kβ1,3, S L2,3) and X-ray-photoelectron valence-band and core-level spectra (XPS) of CuV2S4 thiospinel are presented. It is found that a peak in valence-conduction bands close to the Fermi level is formed by V 3d states, which provide the metallic properties of CuV2S4. The valence band is formed by Cu 3d, V 3d, V 4p, and S 3p states. Examination of the XES and XPS results and the calculated charge-density maps and densities of states indicates that the valences of both Cu and V are similar to those of their elemental solids. Calculations show a strong electron-phonon coupling in CuV2S4 and the prospect of superconducting behavior has not been confirmed
Tuning of Electrical and Optical Properties of Highly Conducting and Transparent Ta-Doped TiO2 Polycrystalline Films
We present a detailed study on polycrystalline transparent conducting Ta-doped TiO2 films, obtained by room temperature pulsed laser deposition followed by an annealing treatment at 550°C in vacuum. The effect of Ta as a dopant element and of different synthesis conditions are explored in order to assess the relationship between material structure and functional properties, i.e. electrical conductivity and optical transparency. We show that for the doped samples it is possible to achieve low resistivity (of the order of 5×10-4 Ωcm) coupled with transmittance values exceeding 80% in the visible range, showing the potential of polycrystalline Ta:TiO2 for application as a transparent electrode in novel photovoltaic devices. The presence of trends in the structural (crystalline domain size, anatase cell parameters), electrical (resistivity, charge carrier density and mobility) and optical (transmittance, optical band gap, effective mass) properties as a function of the oxygen background pressures and laser fluence used during the deposition process and of the annealing atmosphere is discussed, and points towards a complex defect chemistry ruling the material behavior. The large mobility values obtained in this work for Ta:TiO2 polycrystalline films (up to 13 cm2V-1s-1) could represent a definitive advantage with respect to the more studied Nb-doped TiO2
Phytotoxic Effects of (±)-Catechin In vitro, in Soil, and in the Field
BACKGROUND: Exploring the residence time of allelochemicals released by plants into different soils, episodic exposure of plants to allelochemicals, and the effects of allelochemicals in the field has the potential to improve our understanding of interactions among plants. METHODOLOGY/PRINCIPAL FINDINGS: We conducted experiments in India and the USA to understand the dynamics of soil concentrations and phytotoxicity of (+/-)-catechin, an allelopathic compound exuded from the roots of Centaurea maculosa, to other plants in vitro and in soil. Experiments with single and pulsed applications into soil were conducted in the field. Experimental application of (+/-)-catechin to soils always resulted in concentrations that were far lower than the amounts added but within the range of reported natural soil concentrations. Pulses replenished (+/-)-catechin levels in soils, but consistently at concentrations much lower than were applied, and even pulsed concentrations declined rapidly. Different natural soils varied substantially in the retention of (+/-)-catechin after application but consistent rapid decreases in concentrations over time suggested that applied experimental concentrations may overestimate concentrations necessary for phytotoxicity by over an order of magnitude. (+/-)-Catechin was not phytotoxic to Bambusa arundinacea in natural Indian soil in a single pulse, but soil concentrations at the time of planting seeds were either undetectable or very low. However, a single dose of (+/-)-catechin suppressed the growth of bamboo in sand, in soil mixed with organic matter, and Koeleria macrantha in soils from Montana and Romania, and in field applications at 40 microg l(-1). Multiple pulses of (+/-)-catechin were inhibitory at very low concentrations in Indian soil. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that (+/-)-catechin is highly dynamic in natural soils, but is phytotoxic well below natural concentrations measured in some soils and applied at low concentrations in the field. However, there is substantial conditionality in the effects of the allelochemical
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