10,224 research outputs found
Polarized Proton Pionic Capture in Deuterium as a Probe of 3N Dynamics
The proton analyzing power Ay in pion production reaction pd --> pi0 3He has
been calculated including one- and two-body meson production mechanisms with a
proper treatment of the three-nucleon dynamics and an accurate solution of the
3N bound-state problem for phenomenological two-nucleon potentials. In the
region around the Delta resonance, the structure of the analyzing power can be
understood once interference effects among amplitudes describing intermediate
Delta N formation in different orbital states are considered along with the
additional interference with the S-wave pion production amplitudes. Then, the
inclusion of three-nucleon dynamics in the initial state produces the structure
of the analyzing power that has been observed experimentally.Comment: 9 pages, 5 figure
Energy Requirement of Control: Comments on Szilard's Engine and Maxwell's Demon
In mathematical physical analyses of Szilard's engine and Maxwell's demon, a
general assumption (explicit or implicit) is that one can neglect the energy
needed for relocating the piston in Szilard's engine and for driving the trap
door in Maxwell's demon. If this basic assumption is wrong, then the
conclusions of a vast literature on the implications of the Second Law of
Thermodynamics and of Landauer's erasure theorem are incorrect too. Our
analyses of the fundamental information physical aspects of various type of
control within Szilard's engine and Maxwell's demon indicate that the entropy
production due to the necessary generation of information yield much greater
energy dissipation than the energy Szilard's engine is able to produce even if
all sources of dissipation in the rest of these demons (due to measurement,
decision, memory, etc) are neglected.Comment: New, simpler and more fundamental approach utilizing the physical
meaning of control-information and the related entropy production. Criticism
of recent experiments adde
Tunneling mechanism of light transmission through metallic films
A mechanism of light transmission through metallic films is proposed,
assisted by tunnelling between resonating buried dielectric inclusions. This is
illustrated by arrays of Si spheres embedded in Ag. Strong transmission peaks
are observed near the Mie resonances of the spheres. The interaction among
various planes of spheres and interference effects between these resonances and
the surface plasmons of Ag lead to mixing and splitting of the resonances.
Transmission is proved to be limited only by absorption. For small spheres, the
effective dielectric constant can be tuned to values close to unity and a
method is proposed to turn the resulting materials invisible.Comment: 4 papges, 5 figure
Radial rotating antenna-feed system
System incorporating two or more radial feed assemblies tracks and communicates with multiple moving transmitters, receivers, or transponders. System utilizes a fixed parabolic reflector or other beam-forming device such as a lens or spherical reflector
Perfect imaging with positive refraction in three dimensions
Maxwell's fish eye has been known to be a perfect lens within the validity
range of ray optics since 1854. Solving Maxwell's equations we show that the
fish-eye lens in three dimensions has unlimited resolution for electromagnetic
waves
Reversible viscosity and Navier--Stokes fluids
Exploring the possibility of describing a fluid flow via a time-reversible
equation and its relevance for the fluctuations statistics in stationary
turbulent (or laminar) incompressible Navier-Stokes flows.Comment: 7 pages 6 figures, v2: replaced Fig.6 and few changes. Last version:
appendix cut shorter, because of a computational erro
Theory of hopping conduction in arrays of doped semiconductor nanocrystals
The resistivity of a dense crystalline array of semiconductor nanocrystals
(NCs) depends in a sensitive way on the level of doping as well as on the NC
size and spacing. The choice of these parameters determines whether electron
conduction through the array will be characterized by activated
nearest-neighbor hopping or variable-range hopping (VRH). Thus far, no general
theory exists to explain how these different behaviors arise at different
doping levels and for different types of NCs. In this paper we examine a simple
theoretical model of an array of doped semiconductor NCs that can explain the
transition from activated transport to VRH. We show that in sufficiently small
NCs, the fluctuations in donor number from one NC to another provide sufficient
disorder to produce charging of some NCs, as electrons are driven to vacate
higher shells of the quantum confinement energy spectrum. This
confinement-driven charging produces a disordered Coulomb landscape throughout
the array and leads to VRH at low temperature. We use a simple computer
simulation to identify different regimes of conduction in the space of
temperature, doping level, and NC diameter. We also discuss the implications of
our results for large NCs with external impurity charges and for NCs that are
gated electrochemically.Comment: 14 pages, 10 figures; extra schematic figures added; revised
introductio
- …