546 research outputs found
Impact of co-adsorbed oxygen on crotonaldehyde adsorption over gold nanoclusters : a computational study
Crotonaldehyde (2-butenal) adsorption over gold sub-nanometer particles, and the influence of co-adsorbed oxygen, has been systematically investigated by computational methods. Using density functional theory, the adsorption energetics of crotonaldehyde on bare and oxidised gold clusters (Au13, d = 0.8 nm) were determined as a function of oxygen coverage and coordination geometry. At low oxygen coverage, sites are available for which crotonaldehyde adsorption is enhanced relative to bare Au clusters by 10 kJ molâ1. At higher oxygen coverage, crotonaldehyde is forced to adsorb in close proximity to oxygen weakening adsorption by up to 60 kJ molâ1 relative to bare Au. Bonding geometries, density of states plots and Bader analysis, are used to elucidate crotonaldehyde bonding to gold nanoparticles in terms of partial electron transfer from Au to crotonaldehyde, and note that donation to gold from crotonaldehyde also becomes significant following metal oxidation. At high oxygen coverage we find that all molecular adsorption sites have a neighbouring, destabilising, oxygen adatom so that despite enhanced donation, crotonaldehyde adsorption is always weakened by steric interactions. For a larger cluster (Au38, d = 1.1 nm) crotonaldehyde adsorption is destabilized in this way even at a low oxygen coverage. These findings provide a quantitative framework to underpin the experimentally observed influence of oxygen on the selective oxidation of crotyl alcohol to crotonaldehyde over gold and goldâpalladium alloys
Impact of co-adsorbed oxygen on crotonaldehyde adsorption over gold nanoclusters : a computational study
Crotonaldehyde (2-butenal) adsorption over gold sub-nanometer particles, and the influence of co-adsorbed oxygen, has been systematically investigated by computational methods. Using density functional theory, the adsorption energetics of crotonaldehyde on bare and oxidised gold clusters (Au13, d = 0.8 nm) were determined as a function of oxygen coverage and coordination geometry. At low oxygen coverage, sites are available for which crotonaldehyde adsorption is enhanced relative to bare Au clusters by 10 kJ molâ1. At higher oxygen coverage, crotonaldehyde is forced to adsorb in close proximity to oxygen weakening adsorption by up to 60 kJ molâ1 relative to bare Au. Bonding geometries, density of states plots and Bader analysis, are used to elucidate crotonaldehyde bonding to gold nanoparticles in terms of partial electron transfer from Au to crotonaldehyde, and note that donation to gold from crotonaldehyde also becomes significant following metal oxidation. At high oxygen coverage we find that all molecular adsorption sites have a neighbouring, destabilising, oxygen adatom so that despite enhanced donation, crotonaldehyde adsorption is always weakened by steric interactions. For a larger cluster (Au38, d = 1.1 nm) crotonaldehyde adsorption is destabilized in this way even at a low oxygen coverage. These findings provide a quantitative framework to underpin the experimentally observed influence of oxygen on the selective oxidation of crotyl alcohol to crotonaldehyde over gold and goldâpalladium alloys
Coupling a quantum dot, fermionic leads and a microwave cavity on-chip
We demonstrate a hybrid architecture consisting of a quantum dot circuit
coupled to a single mode of the electromagnetic field. We use single wall
carbon nanotube based circuits inserted in superconducting microwave cavities.
By probing the nanotube-dot using a dispersive read-out in the Coulomb blockade
and the Kondo regime, we determine an electron-photon coupling strength which
should enable circuit QED experiments with more complex quantum dot circuits.Comment: 4 pages, 4 figure
A report on the nonlinear squeezed states and their non-classical properties of a generalized isotonic oscillator
We construct nonlinear squeezed states of a generalized isotonic oscillator
potential. We demonstrate the non-existence of dual counterpart of nonlinear
squeezed states in this system. We investigate statistical properties exhibited
by the squeezed states, in particular Mandel's parameter, second-order
correlation function, photon number distributions and parameter in
detail. We also examine the quadrature and amplitude-squared squeezing effects.
Finally, we derive expression for the -parameterized quasi-probability
distribution function of these states. All these information about the system
are new to the literature.Comment: Accepted for publication in J. Phys. A: Math. Theo
Ultrasensitive Photoresponse of Graphene Quantum Dot in the Coulomb Blockade Regime to THz Radiation
Graphene quantum dots (GQDs) have recently attracted considerable attention,
with appealing properties for terahertz (THz) technology. This includes the
demonstration of large thermal bolometric effects in GQDs when illuminated by
THz radiation. However, the interaction of THz photons with GQDs in the Coulomb
blockade regime - single electron transport regime - remains unexplored. Here,
we demonstrate the ultrasensitive photoresponse to THz radiation (from <0.1 to
10 THz) of a hBN-encapsulated GQD in the Coulomb blockade regime at low
temperature (170 mK). We show that THz radiation of 10 pW provides a
photocurrent response in the nanoampere range, resulting from a renormalization
of the chemical potential of the GQD of 0.15 meV. We attribute this
photoresponse to an interfacial photogating effect. Furthermore, our analysis
reveals the absence of thermal effects, opening new directions in the study of
coherent quantum effects at THz frequencies in GQDs
Circuit Quantum Electrodynamics with a Spin Qubit
Circuit quantum electrodynamics allows spatially separated superconducting
qubits to interact via a "quantum bus", enabling two-qubit entanglement and the
implementation of simple quantum algorithms. We combine the circuit quantum
electrodynamics architecture with spin qubits by coupling an InAs nanowire
double quantum dot to a superconducting cavity. We drive single spin rotations
using electric dipole spin resonance and demonstrate that photons trapped in
the cavity are sensitive to single spin dynamics. The hybrid quantum system
allows measurements of the spin lifetime and the observation of coherent spin
rotations. Our results demonstrate that a spin-cavity coupling strength of 1
MHz is feasible.Comment: Related papers at http://pettagroup.princeton.edu
Long-Term Functionality of Rural Water Services in Developing Countries: A System Dynamics Approach to Understanding the Dynamic Interaction of Causal Factors
Research has shown that sustainability of rural water infrastructure in developing countries is largely affected by the dynamic and systemic interactions of technical, social, financial, institutional, and environmental factors that can lead to premature water system failure. This research employs systems dynamic modeling, which uses feedback mechanisms to understand how these factors interact dynamically to influence long-term rural water system functionality. To do this, the research first identified and aggregated key factors from literature, then asked water sector experts to indicate the polarity and strength between factors through Delphi and cross impact survey questionnaires, and finally used system dynamics modeling to identify and prioritize feedback mechanisms. The resulting model identified 101 feedback mechanisms that were dominated primarily by three and four-factor loops that contained some combination of the factors: Water System Functionality, Community, Financial, Government, Management, and Technology. These feedback mechanisms were then scored and prioritized, with the most dominant feedback mechanism identified as Water System Functionality â Community â Finance â Management. This research offers insight into the dynamic interaction of factors impacting sustainability of rural water infrastructure through the identification of these feedback mechanisms and makes a compelling case for future research to longitudinally investigate the interaction of these factors in various contexts
One hundred second bit-flip time in a two-photon dissipative oscillator
Current implementations of quantum bits (qubits) continue to undergo too many
errors to be scaled into useful quantum machines. An emerging strategy is to
encode quantum information in the two meta-stable pointer states of an
oscillator exchanging pairs of photons with its environment, a mechanism shown
to provide stability without inducing decoherence. Adding photons in these
states increases their separation, and macroscopic bit-flip times are expected
even for a handful of photons, a range suitable to implement a qubit. However,
previous experimental realizations have saturated in the millisecond range. In
this work, we aim for the maximum bit-flip time we could achieve in a
two-photon dissipative oscillator. To this end, we design a Josephson circuit
in a regime that circumvents all suspected dynamical instabilities, and employ
a minimally invasive fluorescence detection tool, at the cost of a two-photon
exchange rate dominated by single-photon loss. We attain bit-flip times of the
order of 100 seconds for states pinned by two-photon dissipation and containing
about 40 photons. This experiment lays a solid foundation from which the
two-photon exchange rate can be gradually increased, thus gaining access to the
preparation and measurement of quantum superposition states, and pursuing the
route towards a logical qubit with built-in bit-flip protection
An exploration of the use of simple statistics to measure consensus and stability in Delphi studies
<p>Abstract</p> <p>Background</p> <p>The criteria for stopping Delphi studies are often subjective. This study aimed to examine whether consensus and stability in the Delphi process can be ascertained by descriptive evaluation of trends in participants' views.</p> <p>Methods</p> <p>A three round email-based Delphi required participants (n = 12) to verify their level of agreement with 8 statements, write comments on each if they considered it necessary and rank the statements for importance. Each statement was analysed quantitatively by the percentage of agreement ratings, importance rankings and the amount of comments made for each statement, and qualitatively using thematic analysis. Importance rankings between rounds were compared by calculating Kappa values to observe trends in how the process impacts on subject's views.</p> <p>Results</p> <p>Evolution of consensus was shown by increase in agreement percentages, convergence of range with standard deviations of importance ratings, and a decrease in the number of comments made. Stability was demonstrated by a trend of increasing Kappa values.</p> <p>Conclusion</p> <p>Following the original use of Delphi in social sciences, Delphi is suggested to be an effective way to gain and measure group consensus in healthcare. However, the proposed analytical process should be followed to ensure maximum validity of results in Delphi methodology for improved evidence of consensual decision-making.</p
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