4,017 research outputs found
Ni-dispersed fullerenes: Hydrogen storage and desorption properties
Our study shows that the H2 storage media using Ni-dispersed fullerenes could be viable alternatives to reversible hydrogen storage. It is demonstrated that a single Ni coated on the fullerene surface can store up to three H2 molecules. Consequently, at high Ni coverage, Ni-dispersed fullerenes are considered to be the novel hydrogen storage media capable of storing ~6.8 wt % H2, thus exceeding the Department of Energy target (6.5 wt %) for automobile applications. Moreover, the H2 desorption activation barrier of 11.8 kcal/mol H2 is ideal for many practical hydrogen storage applications
Resonant Raman of OH/OD vibrations and photoluminescence studies in LiTaO3 thin film
Resonant Raman spectra (RRS) of O-H and O-D vibration and libration modes,
their combinations and higher harmonics have been observed in LiTaO3
polycrystalline thin films. RRS peaks are superimposed on photoluminescence
(PL) spectrum. Monochromatic light from a xenon lamp is used as excitation
source. PL spectrum shows two broad peaks, first near the band gap in UV
(4.4-4.8eV) and another in the sub band gap region (< 4.0 eV). Band gap PL
along with RRS peaks are reported for the first time. Photoluminescence
excitation spectrum (PLE) shows a peak at 4.8 eV. Peak positions and full width
at half maximum (FWHM) of RRS peaks depend upon the excitation energy.
Dispersions of the fundamental and the third harmonic of the stretching mode of
O-H with excitation energy are about 800 cm-1/eV and 2000 cm-1/eV respectively.
This dispersion is much higher than reported in any other material.Comment: 20 page
Miocene deep water agglutinated foraminifera from Viosca Knoll, offshore Louisiana (Gulf of Mexico)
An exploration well from the Gulf of Mexico, Amoco Viosca Knoll-915, has been studied in order
to document the Neogene foraminiferal assemblages. Ditch cuttings samples from the Amoco
V.K. 915 well yielded diverse assemblages of agglutinated and calcareous benthic foraminifera
over a stratigraphic interval of 2940 m. Three species associations can be identified in the studied
interval; the stratigraphical location of these associations is evident when total agglutinated
species abundance for each sampling interval is plotted. In this study we use a combination of
morphotype habitat preference and test functional morphology to interpret depositional
environments. The associations indicate a change from a well-ventilated water column, to the
development of a strong oxygen minimum zone characterised by alveolar foraminifera. The
species composition of the lowermost association indicates a depositional environment dominated
by fine-grained overbank fines and channel levee deposits, in agreement with sedimentological
data. Colour plates of key agglutinates species are presented, created using digital image
manipulation techniques (Palaeovision Technique, NHM)
The Kondo Effect in Non-Equilibrium Quantum Dots: Perturbative Renormalization Group
While the properties of the Kondo model in equilibrium are very well
understood, much less is known for Kondo systems out of equilibrium. We study
the properties of a quantum dot in the Kondo regime, when a large bias voltage
V and/or a large magnetic field B is applied. Using the perturbative
renormalization group generalized to stationary nonequilibrium situations, we
calculate renormalized couplings, keeping their important energy dependence. We
show that in a magnetic field the spin occupation of the quantum dot is
non-thermal, being controlled by V and B in a complex way to be calculated by
solving a quantum Boltzmann equation. We find that the well-known suppression
of the Kondo effect at finite V>>T_K (Kondo temperature) is caused by inelastic
dephasing processes induced by the current through the dot. We calculate the
corresponding decoherence rate, which serves to cut off the RG flow usually
well inside the perturbative regime (with possible exceptions). As a
consequence, the differential conductance, the local magnetization, the spin
relaxation rates and the local spectral function may be calculated for large
V,B >> T_K in a controlled way.Comment: 9 pages, invited paper for a special edition of JPSJ "Kondo Effect --
40 Years after the Discovery", some typos correcte
Estimating the cost of generic quantum pre-image attacks on SHA-2 and SHA-3
We investigate the cost of Grover's quantum search algorithm when used in the
context of pre-image attacks on the SHA-2 and SHA-3 families of hash functions.
Our cost model assumes that the attack is run on a surface code based
fault-tolerant quantum computer. Our estimates rely on a time-area metric that
costs the number of logical qubits times the depth of the circuit in units of
surface code cycles. As a surface code cycle involves a significant classical
processing stage, our cost estimates allow for crude, but direct, comparisons
of classical and quantum algorithms.
We exhibit a circuit for a pre-image attack on SHA-256 that is approximately
surface code cycles deep and requires approximately
logical qubits. This yields an overall cost of
logical-qubit-cycles. Likewise we exhibit a SHA3-256 circuit that is
approximately surface code cycles deep and requires approximately
logical qubits for a total cost of, again,
logical-qubit-cycles. Both attacks require on the order of queries in
a quantum black-box model, hence our results suggest that executing these
attacks may be as much as billion times more expensive than one would
expect from the simple query analysis.Comment: Same as the published version to appear in the Selected Areas of
Cryptography (SAC) 2016. Comments are welcome
Ultrasound instrumentation for the 7 inch Mach seven tunnel
The use of an Apple II+ microcomputer to collect data during the operation of the 7 inch Mach Seven Tunnel is discussed. A method by which the contamination of liquid oxygen is monitored with sound speed techniques is investigated. The electrical equivalent of a transducer bonded to a high pressure fill plug is studied. The three areas are briefly explained and data gathered for each area are presented
On steady-state currents through nano-devices: a scattering-states numerical renormalization group approach to open quantum systems
We propose a numerical renormalization group (NRG) approach to steady-state
currents through nano-devices. A discretization of the scattering-states
continuum ensures the correct boundary condition for an open quantum system. We
introduce two degenerate Wilson chains for current carrying left and
right-moving electrons reflecting time-reversal symmetry in the absence of a
finite bias . We employ the time-dependent NRG to evolve the known
steady-state density operator for a non-interacting junction into the density
operator of the fully interacting nano-device at finite bias. We calculate the
temperature dependent current as function of and applied external magnetic
field using a recently developed algorithm for non-equilibrium spectral
functions.Comment: 4 pages, 6 figure
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