258 research outputs found
Evidence of Plasmonic Induced Photocatalytic Hydrogen Production on Pd/TiO2 Upon Deposition on Thin Films of Gold
H2-production from renewables using sunlight is probably the holy grail of modern science and technology. Among the many approaches for increasing reaction rates, by increasing light absorption, plasmonic materials are often invoked. Yet, most plasmonic metals on semiconductors are also good for Schottky barrier formation. In this work, we are presenting evidences of de-coupling the plasmonic from Schottky effects on photoreaction. To conduct this we have systematically changed the under-layer gold film thickness and associated particle size. On top of the thin film layer, we have deposited the exact amount of a prototypical Schottky-based photo-catalyst (Pd/TiO2). We found up to 4 times increase in the H2-production rate at a critical Au film thickness (8 nm-thick). Below this thickness, the plasmonic response is not too strong while above it, the PR decays in favor of the Drude absorption mode. The reaction requires the presence of both UV (to excite the semiconductor) and visible light (to excite Au particles) in order to obtain high hydrogen production, 800 µmol/gCatal.min (probably the highest direct hydrogen (not current) production rate reported on a performing catalyst). The enhancement origin is quantitatively traced to its computed electric field strength (EFS). Adding a dielectric (SiO2) in between the Au thin layer and the catalyst exponentially decreased the reaction rate and EFS, with increasing its thickness. This work indicates the possibility of making an active and stable photo-catalyst from fundamental concepts yet further progress on the structural (technological) front is needed to make a practical catalyst
Bioefficacy of Plant Extracts to Control Cercospora Leaf Spot of Mungbean (Vigna radiata)
The experiment was conducted at Bangladesh Agricultural Research Institute farm, Joydebpur, Gazipur during March to July 2007 to evaluate the bioefficacy of some plant extracts in controlling Cercospora leaf spot of mungbean. Six indigenous plant species i.e. Neem leaves extract (1:4 w/v), Garlic cloves extract (1:5 w/v), Biskatali leaves extract (1:4 w/v), Alamanda leaves extract (1:6 w/v), Arjun leaves extract (1:4 w/v) and Debdaru leaves extract (1:5 w/v) were used in this experiment. The experiment was laid out in RCBD with seven treatments and four replications. Data on disease incidence, severity, yield contributing characters and yield of mungbean were recorded. Naturally, infection of the disease was considered in this experiment. The lowest disease incidence (7.33%) at 60 DAS was found in T1. Lowest and similar disease severity (PDI= 4.55) was found in T2 and T3 at the same DAS. Neem extract treated plots gave better response in yield (1.26 t ha-1) and all the yield contributing parameters like inflorescences plant-1 (13.45), tallest plant (51.44 cm), the maximum number of pods plant-1 (26.81), length of pod (8.56 cm), number of seeds pod-1 (12.64) and 1000 seeds weight (27.33 g) followed by T2 and T3. The highest disease incidence (26.50%) and disease index (13.65%) were recorded in treatment T7 at 60 DAS. Yield and all yield contributing factors were lowest in same treatment. The results of the experiment suggested that the use of neem leaves extracts are effective for minimizing Cercospora leaf spot incidence, severity and increasing yield of mungbean. Int. J. Agril. Res. Innov. & Tech. 3 (1): 60-65, June, 2013 DOI: http://dx.doi.org/10.3329/ijarit.v3i1.1609
Probing the Superfluid to Mott Insulator Transition at the Single Atom Level
Quantum gases in optical lattices offer an opportunity to experimentally
realize and explore condensed matter models in a clean, tunable system. We
investigate the Bose-Hubbard model on a microscopic level using single
atom-single lattice site imaging; our technique enables space- and
time-resolved characterization of the number statistics across the
superfluid-Mott insulator quantum phase transition. Site-resolved probing of
fluctuations provides us with a sensitive local thermometer, allows us to
identify microscopic heterostructures of low entropy Mott domains, and enables
us to measure local quantum dynamics, revealing surprisingly fast transition
timescales. Our results may serve as a benchmark for theoretical studies of
quantum dynamics, and may guide the engineering of low entropy phases in a
lattice
Hyperechogenic renal parenchyma in potential live related kidney donors: Does it justify exclusion?
The aim of this work is to asses theimportance of ultrasonic grade I echogenicity inpotential kidney donors in the absence of urinaryabnormality and with perfect renal function.Thirty four living related kidney donors with thisabnormality were included, age range between 23-48years. Ten matched healthy donors were studied ascontrols.All cases were thoroughly investigated includingmeasuring GFR by isotopic scan and estimation ofrenal reserve by dopamine and aminoacid infusion.Renal biopsy was done for 17 cases of theechogenicity group and 8 controls. Our resultsshowed that the renal reserve was comparable in bothgroups. Glomerular changes were found in 41% ofapparently normal donors and only one case ofcontrols.Conclusion: Grade I echogenicity may be sign ofunrecognised kidney disease. Renal biopsy ismandatory when such related donors are the onlyavailable
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Photon-Assisted Tunneling in a Biased Strongly Correlated Bose Gas
We study the impact of coherently generated lattice photons on an atomic Mott insulator subjected to a uniform force. Analogous to an array of tunnel-coupled and biased quantum dots, we observe sharp, interaction-shifted photon-assisted tunneling resonances corresponding to tunneling one and two lattice sites either with or against the force and resolve multiorbital shifts of these resonances. By driving a Landau-Zener sweep across such a resonance, we realize a quantum phase transition between a paramagnet and an antiferromagnet and observe quench dynamics when the system is tuned to the critical point. Direct extensions will produce gauge fields and site-resolved spin flips, for topological physics and quantum computing.Physic
Quantum Simulation of Antiferromagnetic Spin Chains in an Optical Lattice
Understanding exotic forms of magnetism in quantum mechanical systems is a
central goal of modern condensed matter physics, with implications from high
temperature superconductors to spintronic devices. Simulating magnetic
materials in the vicinity of a quantum phase transition is computationally
intractable on classical computers due to the extreme complexity arising from
quantum entanglement between the constituent magnetic spins. Here we employ a
degenerate Bose gas confined in an optical lattice to simulate a chain of
interacting quantum Ising spins as they undergo a phase transition. Strong spin
interactions are achieved through a site-occupation to pseudo-spin mapping. As
we vary an applied field, quantum fluctuations drive a phase transition from a
paramagnetic phase into an antiferromagnetic phase. In the paramagnetic phase
the interaction between the spins is overwhelmed by the applied field which
aligns the spins. In the antiferromagnetic phase the interaction dominates and
produces staggered magnetic ordering. Magnetic domain formation is observed
through both in-situ site-resolved imaging and noise correlation measurements.
By demonstrating a route to quantum magnetism in an optical lattice, this work
should facilitate further investigations of magnetic models using ultracold
atoms, improving our understanding of real magnetic materials.Comment: 12 pages, 9 figure
Topological Schr\"odinger cats: Non-local quantum superpositions of topological defects
Topological defects (such as monopoles, vortex lines, or domain walls) mark
locations where disparate choices of a broken symmetry vacuum elsewhere in the
system lead to irreconcilable differences. They are energetically costly (the
energy density in their core reaches that of the prior symmetric vacuum) but
topologically stable (the whole manifold would have to be rearranged to get rid
of the defect). We show how, in a paradigmatic model of a quantum phase
transition, a topological defect can be put in a non-local superposition, so
that - in a region large compared to the size of its core - the order parameter
of the system is "undecided" by being in a quantum superposition of conflicting
choices of the broken symmetry. We demonstrate how to exhibit such a
"Schr\"odinger kink" by devising a version of a double-slit experiment suitable
for topological defects. Coherence detectable in such experiments will be
suppressed as a consequence of interaction with the environment. We analyze
environment-induced decoherence and discuss its role in symmetry breaking.Comment: 7 pages, 4 figure
Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems
Quantum simulators are controllable quantum systems that can reproduce the
dynamics of the system of interest, which are unfeasible for classical
computers. Recent developments in quantum technology enable the precise control
of individual quantum particles as required for studying complex quantum
systems. Particularly, quantum simulators capable of simulating frustrated
Heisenberg spin systems provide platforms for understanding exotic matter such
as high-temperature superconductors. Here we report the analog quantum
simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type
interactions among four spin-1/2 particles . Depending on the interaction
strength, frustration within the system emerges such that the ground state
evolves from a localized to a resonating valence-bond state. This spin-1/2
tetramer is created using the polarization states of four photons. The
single-particle addressability and tunable measurement-induced interactions
provide us insights into entanglement dynamics among individual particles. We
directly extract ground-state energies and pair-wise quantum correlations to
observe the monogamy of entanglement
Microscopic observation of magnon bound states and their dynamics
More than eighty years ago, H. Bethe pointed out the existence of bound
states of elementary spin waves in one-dimensional quantum magnets. To date,
identifying signatures of such magnon bound states has remained a subject of
intense theoretical research while their detection has proved challenging for
experiments. Ultracold atoms offer an ideal setting to reveal such bound states
by tracking the spin dynamics after a local quantum quench with single-spin and
single-site resolution. Here we report on the direct observation of two-magnon
bound states using in-situ correlation measurements in a one-dimensional
Heisenberg spin chain realized with ultracold bosonic atoms in an optical
lattice. We observe the quantum walk of free and bound magnon states through
time-resolved measurements of the two spin impurities. The increased effective
mass of the compound magnon state results in slower spin dynamics as compared
to single magnon excitations. In our measurements, we also determine the decay
time of bound magnons, which is most likely limited by scattering on thermal
fluctuations in the system. Our results open a new pathway for studying
fundamental properties of quantum magnets and, more generally, properties of
interacting impurities in quantum many-body systems.Comment: 8 pages, 7 figure
Orbital excitation blockade and algorithmic cooling in quantum gases
Interaction blockade occurs when strong interactions in a confined few-body
system prevent a particle from occupying an otherwise accessible quantum state.
Blockade phenomena reveal the underlying granular nature of quantum systems and
allow the detection and manipulation of the constituent particles, whether they
are electrons, spins, atoms, or photons. The diverse applications range from
single-electron transistors based on electronic Coulomb blockade to quantum
logic gates in Rydberg atoms. We have observed a new kind of interaction
blockade in transferring ultracold atoms between orbitals in an optical
lattice. In this system, atoms on the same lattice site undergo coherent
collisions described by a contact interaction whose strength depends strongly
on the orbital wavefunctions of the atoms. We induce coherent orbital
excitations by modulating the lattice depth and observe a staircase-type
excitation behavior as we cross the interaction-split resonances by tuning the
modulation frequency. As an application of orbital excitation blockade (OEB),
we demonstrate a novel algorithmic route for cooling quantum gases. Our
realization of algorithmic cooling utilizes a sequence of reversible OEB-based
quantum operations that isolate the entropy in one part of the system, followed
by an irreversible step that removes the entropy from the gas. This work opens
the door to cooling quantum gases down to ultralow entropies, with implications
for developing a microscopic understanding of strongly correlated electron
systems that can be simulated in optical lattices. In addition, the close
analogy between OEB and dipole blockade in Rydberg atoms provides a roadmap for
the implementation of two-qubit gates in a quantum computing architecture with
natural scalability.Comment: 6 pages, 4 figure
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