828 research outputs found
Tunnel electron-vibrational spectroscopy of adsorbed complexes on the surface of ultra-small metal nanoparticles
This work was supported by the Russian Foundation for Basic Research (the project no. 18-03-00453) and into frameworks of the state task for ICP RAS 0082-2018-0003 (the state registration number АААА-А18-118012390045-2)
Parametrization of the angular correlation and degree of linear polarization in two-photon decays of hydrogen-like ions
The two-photon decay in hydrogen-like ions is investigated within the
framework of second order perturbation theory and Dirac's relativistic
equation. Special attention is paid to the angular correlation of the emitted
photons as well as to the degree of linear polarization of one of the two
photons, if the second is just observed under given angles. Expressions for the
angular correlation and the degree of linear polarization are expanded in terms
of -polynomials, whose coefficients depend on the atomic number and
the energy sharing of the emitted photons. The effects of including higher
(electric and magnetic) multipoles upon the emitted photon pairs beyond the
electric-dipole approximation are also discussed. Calculations of the
coefficients are performed for the transitions ,
and , along the
entire hydrogen isoelectronic sequence ()
A study of nuclei of astrophysical interest in the continuum shell model
We present here the first application of realistic shell model (SM) including
coupling between many-particle (quasi-)bound states and the continuum of
one-particle scattering states to the spectroscopy of 8B and to the calculation
of astrophysical factors in the reaction 7Be(p,gamma)8B.Comment: 9 pages incl. 3 figures, LaTeX with iopart class and epsf. Invited
talk at the Int. Workshop on Physics with Radioactive Nuclear Beams, Jan.
12-17, 1998, Puri, India. Shortened version will be published in proceedings
to apear as a separate J. Phys. G volum
Deep-well ultrafast manipulation of a SQUID flux qubit
Superconducting devices based on the Josephson effect are effectively used
for the implementation of qubits and quantum gates. The manipulation of
superconducting qubits is generally performed by using microwave pulses with
frequencies from 5 to 15 GHz, obtaining a typical operating clock from 100MHz
to 1GHz. A manipulation based on simple pulses in the absence of microwaves is
also possible. In our system a magnetic flux pulse modifies the potential of a
double SQUID qubit from a symmetric double well to a single deep well
condition. By using this scheme with a Nb/AlOx/Nb system we obtained coherent
oscillations with sub-nanosecond period (tunable from 50ps to 200ps), very fast
with respect to other manipulating procedures, and with a coherence time up to
10ns, of the order of what obtained with similar devices and technologies but
using microwave manipulation. We introduce the ultrafast manipulation
presenting experimental results, new issues related to this approach (such as
the use of a feedback procedure for cancelling the effect of "slow"
fluctuations), and open perspectives, such as the possible use of RSFQ logic
for the qubit control.Comment: 9 pages, 7 figure
Surface Ozone Variability and Trends over the South African Highveld from 1990 to 2007
Surface ozone is a secondary air pollutant formed from reactions between nitrogen oxides (NOx = NO + NO2) and volatile organic compounds in the presence of sunlight. In this work we examine effects of the climate pattern known as the El Nio-Southern Oscillation (ENSO) and NOx variability on surface ozone from 1990 to 2007 over the South African Highveld, a heavily populated region in South Africa with numerous industrial facilities. Over summer and autumn (December-May) on the Highveld, El Nio, as signified by positive sea surface temperature (SST) anomalies over the central Pacific Ocean, is typically associated with drier and warmer than normal conditions favoring ozone formation. Conversely, La Nia, or negative SST anomalies over the central Pacific Ocean, is typically associated with cloudier and above normal rainfall conditions, hindering ozone production. We use a generalized regression model to identify any linear dependence that the Highveld ozone, measured at five air quality monitoring stations, may have on ENSO and NOx. Our results indicate that four out of the five stations exhibit a statistically significant sensitivity to ENSO at some point over the December-May period where El Nio amplifies ozone formation and La Nia reduces ozone formation. Three out of the five stations reveal statistically significant sensitivity to NOx variability, primarily in winter and spring. Accounting for ENSO and NOx effects throughout the study period of 18 years, two stations exhibit statistically significant negative ozone trends in spring, one station displays a statistically significant positive trend in August, and two stations show no statistically significant change in surface ozone
Dynamics of Josephson junctions and single-flux-quantum networks with superconductor-insulator-normal metal junction shunts
Within the framework of the microscopic model of tunneling, we modelled the
behavior of the Josephson junction shunted by the
Superconductor-Insulator-Normal metal (SIN) tunnel junction. We found that the
electromagnetic impedance of the SIN junction yields both the
frequency-dependent damping and dynamic reactance which leads to an increase in
the effective capacitance of the circuit. We calculated the dc I-V curves and
transient characteristics of these circuits and explained their quantitative
differences to the curves obtained within the resistively shunted junction
model. The correct operation of the basic single-flux-quanta circuits with such
SIN-shunted junctions, i.e. the Josephson transmission line and the toggle
flip-flop, have also been modelled.Comment: 8 pages incl. 7 figure
Single flux quantum circuits with damping based on dissipative transmission lines
We propose and demonstrate the functioning of a special Rapid Single Flux
Quantum (RSFQ) circuit with frequency-dependent damping. This damping is
achieved by shunting individual Josephson junctions by pieces of open-ended RC
transmission lines. Our circuit includes a toggle flip-flop cell, Josephson
transmission lines transferring single flux quantum pulses to and from this
cell, as well as DC/SFQ and SFQ/DC converters. Due to the desired
frequency-dispersion in the RC line shunts which ensures sufficiently low noise
at low frequencies, such circuits are well-suited for integrating with the
flux/phase Josephson qubit and enable its efficient control.Comment: 6 pages incl. 6 figure
A graphene electron lens
International audienceAn epitaxial layer of graphene was grown on a pre patterned 6H-SiC(0001) crystal. The graphene smoothly covers the hexagonal nano-holes in the substrate without the introduction of small angle grain boundaries or dislocations. This is achieved by an elastic deformation of the graphene by ~0.3% in accordance to its large elastic strain limit. This elastic stretching of the graphene leads to a modification of the band structure and to a local lowering of the electron group velocity of the graphene. We propose to use this effect to focus two-dimensional electrons in analogy to simple optical lenses
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