11,509 research outputs found
The whistler nozzle phenomenon
The whistler nozzle is a simple device which can induce jet self-excitations of controllable amplitudes and frequencies and appears highly promising for many applications involving turbulent transport, combustion and aerodynamic noise. The characteristics of this curious phenomenon are documented for different values of the controlling parameters and attempts to explain the phenomenon. It is shown that the whistler excitation results from the coupling of two independent resonance mechanisms: shear-layer tone resulting from the impingement of the pipe-exit shear layer on the collar lip, and organ-pipe resonance of the pipe-nozzle. The crucial role of the shear-layer tone in driving the organ-pipe resonance is proven by reproducing the event in pipe-ring and pipe-hole configurations in the absence of the collar. It is also shown that this phenomenon is the strongest when the self-excitation frequency matches the preferred mode of the jet
ARPES studies of cuprate Fermiology: superconductivity, pseudogap, and quasiparticle dynamics
We present angle-resolved photoemission spectroscopy (ARPES) studies of the
cuprate high-temperature superconductors which elucidate the relation between
superconductivity and the pseudogap and highlight low-energy quasiparticle
dynamics in the superconducting state. Our experiments suggest that the
pseudogap and superconducting gap represent distinct states, which coexist
below T. Studies on Bi-2212 demonstrate that the near-nodal and
near-antinodal regions behave differently as a function of temperature and
doping, implying that different orders dominate in different momentum-space
regions. However, the ubiquity of sharp quasiparticles all around the Fermi
surface in Bi-2212 indicates that superconductivity extends into the
momentum-space region dominated by the pseudogap, revealing subtlety in this
dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals
particle-hole asymmetry and anomalous spectral broadening, which may constrain
the explanation for the pseudogap. Recognizing that electron-boson coupling is
an important aspect of cuprate physics, we close with a discussion of the
multiple 'kinks' in the nodal dispersion. Understanding these may be important
to establishing which excitations are important to superconductivity.Comment: To appear in a focus issue on 'Fermiology of Cuprates' in New Journal
of Physic
Hyperforin: A lead for antidepressants
Depression is a complex but treatable disorder if diagnosed appropriately. However, despite the advances in the understanding of the molecular basis of this disorder and the vast range of medication, psychotherapy and electroconvulsive therapy, very safe and effective drug to treat this disease is still being sought. Several studies suggest that St.John’s wort (Hypericum perforatum L.) has phloroglucinol derivative, hyperforin, exhibiting antidepressant activity. This bioactive component can be exploited to create a major shift in the safer treatment of
depression.
Keywords: Hypericum perforatum L., St. John's wort, Antidepressant, Hyperfori
Hidden itinerant-spin phase in heavily-overdoped La2-xSrxCuO4 revealed by dilute Fe doping: A combined neutron scattering and angle-resolved photoemission study
We demonstrated experimentally a direct way to probe a hidden propensity to
the formation of spin density wave (SDW) in a non-magnetic metal with strong
Fermi surface nesting. Substituting Fe for a tiny amount of Cu (1%) induced an
incommensurate magnetic order below 20 K in heavily-overdoped La2-xSrxCuO4
(LSCO). Elastic neutron scattering suggested that this order cannot be ascribed
to the localized spins on Cu or doped Fe. Angle-resolved photoemission
spectroscopy (ARPES), combined with numerical calculations, revealed a strong
Fermi surface nesting inherent in the pristine LSCO that likely drives this
order. The heavily-overdoped Fe-doped LSCO thus represents the first plausible
example of the long-sought "itinerant-spin extreme" of cuprates, where the
spins of itinerant doped holes define the magnetic ordering ground state. This
finding complements the current picture of cuprate spin physics that highlights
the predominant role of localized spins at lower dopings. The demonstrated set
of methods could potentially apply to studying hidden density-wave
instabilities of other "nested" materials on the verge of density wave
ordering.Comment: Abstract and discussion revised; to appear in Phys. Rev. Let
Bandwidth and Electron Correlation-Tuned Superconductivity in RbFe(SeS)
We present a systematic angle-resolved photoemission spectroscopy study of
the substitution-dependence of the electronic structure of
RbFe(SeS) (z = 0, 0.5, 1), where
superconductivity is continuously suppressed into a metallic phase. Going from
the non-superconducting RbFe(SeS) to
superconducting RbFeSe, we observe little change of the Fermi
surface topology, but a reduction of the overall bandwidth by a factor of 2 as
well as an increase of the orbital-dependent renormalization in the
orbital. Hence for these heavily electron-doped iron chalcogenides, we have
identified electron correlation as explicitly manifested in the quasiparticle
bandwidth to be the important tuning parameter for superconductivity, and that
moderate correlation is essential to achieving high
New Development of Anodic Electro-catalyst for Chlor-alkali Industry
Anodic electro catalysts are developed by using a titanium substrate coated with different compositions of mixed oxides, as it follows: ruthenium-titanium mixed oxides; ruthenium-titanium-tin mixed oxides; and ruthenium-titanium-iridium mixed oxides. The performance of electro catalysts was further evaluated by measuring coating thickness, studying coating morphology with microscope, identifying the presence of RuO2, TiO2, IrO2 and SnO2 in coating film, analyzing shape of individual crystal by XRD, performing accelerated life test and current efficiency test of the selected anode. The coating composition of 15% RuO2, 15% IrO2 and 70% TiO2 exhibited premium properties among the studied anodes
CLIMATE CHANGE IMPACT ON MOUNTAIN BIODIVERSITY: A SPECIAL REFERENCE TO GILGIT-BALTISTAN OF PAKISTAN
Climate Change is not a stationary phenomenon; it moves from time to time, it represents a major threat to mountainous biodiversity and to ecosystem integrity. The present study is an attempt to identify the current knowledge gap and the effects of climate change on mountainous biodiversity, a special reference to the Gilgit-Baltistan is briefly reviewed. Measuring the impact of climate change on mountain biodiversity is quite challenging, because climate change interacts with every phenomenon of ecosystem. The scale of this change is so large and very adverse so strongly connected to ecosystem services, and all communities who use natural resources. This study aims to provide the evidences on the basis of previous literature, in particular context to mountain biodiversity of Gilgit-Baltistan (GB). Mountains of Gilgit-Baltistan have most fragile ecosystem and are more vulnerable to climate change. These mountains host variety of wild fauna and flora, with many endangered species of the world. There are still many gaps in our knowledge of literature we studied because very little research has been conducted in Gilgit-Baltistan about climate change particular to biodiversity. Recommendations are made for increased research efforts in future this including jointly monitoring programs, climate change models and ecological research. Understanding the impact of climate change particular to biodiversity of GB is very important for sustainable management of these natural resources. The Government organizations, NGOs and the research agencies must fill the knowledge gap, so that it will help them for policy making, which will be based on scientific findings and research based
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