8,957 research outputs found
Research on digital transducer principles. Volume 7 - Dielectric properties of thin polymer films, 1 July 1967 - 30 June 1968
Dielectric properties of thin films of polymerized oil-metal-silicon structure
Electronic bandstructure and optical gain of lattice matched III-V dilute nitride bismide quantum wells for 1.55 m optical communication systems
Dilute nitride bismide GaNBiAs is a potential semiconductor alloy for near-
and mid-infrared applications, particularly in 1.55 m optical
communication systems. Incorporating dilute amounts of Bismuth (Bi) into GaAs
reduces the effective bandgap rapidly, while significantly increasing the
spin-orbit-splitting energy. Additional incorporation of dilute amounts of
Nitrogen (N) helps to attain lattice matching with GaAs, while providing a
route for flexible bandgap tuning. Here we present a study of the electronic
bandstructure and optical gain of the lattice matched
GaNBiAs/GaAs quaternary alloy quantum well (QW) based on the
16-band kp model. We have taken into consideration the interactions
between the N and Bi impurity states with the host material based on the band
anticrossing (BAC) and valence band anticrossing (VBAC) model. The optical gain
calculation is based on the density matrix theory. We have considered different
lattice matched GaNBiAs QW cases and studied their energy dispersion curves,
optical gain spectrum, maximum optical gain and differential gain; and compared
their performances based on these factors. The thickness and composition of
these QWs were varied in order to keep the emission peak fixed at 1.55 m.
The well thickness has an effect on the spectral width of the gain curves. On
the other hand, a variation in the injection carrier density has different
effects on the maximum gain and differential gain of QWs of varying
thicknesses. Among the cases studied, we found that the 6.3 nm thick
GaNBiAs lattice matched QW was most suited for 1.55
m (0.8 eV) GaAs-based photonic applications.Comment: Accepted in AIP Journal of Applied Physic
Electronic and optical properties of quantum wells embedded in wrinkled nanomembranes
The authors theoretically investigate quantum confinement and transition
energies in quantum wells (QWs) asymmetrically positioned in wrinkled
nanomembranes. Calculations reveal that the wrinkle profile induces both blue-
and redshifts depending on the lateral position of the QW probed. Relevant
radiative transistions include the ground state of the electron (hole) and
excited states of the hole (electron). Energy shifts as well as stretchability
of the structure are studied as a function of wrinkle amplitude and period.
Large tunable bandwidths of up to 70 nm are predicted for highly asymmetric
wrinkled QWs.Comment: 3 pages, 4 figures. The following article has been submitted to
Applied Physics Letters. After it is published, it will be found at
http://apl.aip.or
Non-thermal nuclear magnetic resonance quantum computing using hyperpolarized Xenon
Current experiments in liquid-state nuclear magnetic resonance quantum
computing are limited by low initial polarization. To address this problem, we
have investigated the use of optical pumping techniques to enhance the
polarization of a 2-qubit NMR quantum computer (13C and 1H in 13CHCl3). To
efficiently use the increased polarization, we have generalized the procedure
for effective pure state preparation. With this new, more flexible scheme, an
effective pure state was prepared with polarization-enhancement of a factor of
10 compared to the thermal state. An implementation of Grover's quantum search
algorithm was demonstrated using this new technique.Comment: 4 pages, 3 figures. Submitted for publicatio
First passage times and asymmetry of DNA translocation
Motivated by experiments in which single-stranded DNA with a short hairpin
loop at one end undergoes unforced diffusion through a narrow pore, we study
the first passage times for a particle, executing one-dimensional brownian
motion in an asymmetric sawtooth potential, to exit one of the boundaries. We
consider the first passage times for the case of classical diffusion,
characterized by a mean-square displacement of the form , and for the case of anomalous diffusion or subdiffusion, characterized by a
mean-square displacement of the form with
. In the context of classical diffusion, we obtain an expression
for the mean first passage time and show that this quantity changes when the
direction of the sawtooth is reversed or, equivalently, when the reflecting and
absorbing boundaries are exchanged. We discuss at which numbers of `teeth'
(or number of DNA nucleotides) and at which heights of the sawtooth potential
this difference becomes significant. For large , it is well known that the
mean first passage time scales as . In the context of subdiffusion, the
mean first passage time does not exist. Therefore we obtain instead the
distribution of first passage times in the limit of long times. We show that
the prefactor in the power relation for this distribution is simply the
expression for the mean first passage time in classical diffusion. We also
describe a hypothetical experiment to calculate the average of the first
passage times for a fraction of passage events that each end within some time
. We show that this average first passage time scales as in
subdiffusion.Comment: 10 pages, 4 figures We incorporated reviewers' suggestions from
Physical Review E. We reformulated a few paragraphs in the introduction and
further clarified the issue of the (a)symmetry of passage times. In the
results section, we re-expressed the results in a form that manifest the
important features. We also added a few references concerning anomalous
diffusion. The look (but not the content) of figure 1 was also change
Bounds on Decoherence and Error
When a confined system interacts with its walls (treated quantum
mechanically), there is an intertwining of degrees of freedom. We show that
this need not lead to entanglement, hence decoherence. It will generally lead
to error. The wave function optimization required to avoid decoherence is also
examined.Comment: 10 pages, plain TeX, no figure
Cryogenic-coolant He4-superconductor dynamic and static interactions
A composite superconducting material (NbTi-Cu) was evaluated with emphasis on post quench solid cooling interaction regimes. The quasi-steady runs confirm the existence of a thermodynamic limiting thickness for insulating coatings. Two distinctly different post quench regimes of coated composites are shown to relate to the limiting thickness. Only one regime,, from quench onset to the peak value, revealed favorable coolant states, in particular in He2. Transient recovery shows favorable recovery times from this post quench regime (not drastically different from bare conductors) for both single coated specimens and a coated conductor bundle
- …