285 research outputs found
Time-Minimal Control of Dissipative Two-level Quantum Systems: the Generic Case
The objective of this article is to complete preliminary results concerning
the time-minimal control of dissipative two-level quantum systems whose
dynamics is governed by Lindblad equations. The extremal system is described by
a 3D-Hamiltonian depending upon three parameters. We combine geometric
techniques with numerical simulations to deduce the optimal solutions.Comment: 24 pages, 16 figures. submitted to IEEE transactions on automatic
contro
Questionnaires from the National Health Interview Survey, 1985-89
This series report includes the questions used in the National Health Interview Survey from 1980 to 1984. The report contains the basic health and demographic questionnaires and current health topic queWonnaires.By Michele M. Chyba, Division of Health Intetview Statistics, and Linda R. Washington, Division of Data Services."August 1993."Also available via the World Wide Web.Includes bibliographical references (p. 289)
Influence of shape of cutting tool on pressure conditions in workspace of mulcher with vertical axis of rotation
ArticleNowadays there is laid great insistence on work efficiency improvement. This effort
also affects the construction of mowers such as mulchers. Mulching with a vertical axis of rotation
is very energy demanding work operation mainly, due to high energy losses. These energy losses,
but also the quality of work, are influenced by the airflow and associated conditions of pressure
inside the workspace of mulcher. Airflow in the workspace ensures repetitious contact of the
truncated forage crops with the cutting edge tool and thus ensures crushing of aboveground parts
of plants. The paper deals with the influence of the cutting tool shape on the mulcher’s inside
workspace pressure conditions with the vertical axis of rotation. The influence of the trailing edge
angle and rake angle on the pressure profile in the mulcher’s workspace with dependence on the
rotor speed was examined. Measurements were performed on a laboratory single rotor mulcher
model. It was found that in the mulcher’s workspace the vacuum is formed by virtue of the rotary
movement of the cutting tools wherein the vacuum increases with rotor speed. The maximum
measured vacuum was about 2.4 kPa and from the centre of the rotor towards its circumference
almost linearly decreases. Furthermore, it was found that with decreasing trailing edge angle and
with increasing rake angle the maximum vacuum decreases. When reducing the angle of the
trailing edge from 45° to 25° led to reduction of vacuum of about 0.3 kPa (12.6%)
Semiclassical Analysis of a Detuned Ring Laser with a Saturable Absorber: New Results for the Steady States
This paper presents new results for the steady states of a detuned ring laser with a saturable absorber. We employ a semiclassical model which assumes homogeneously broadened two-level atoms. We proceed by solving the Maxwell-Bloch equations for the longitudinal dependence of the steady states of this system, and then simplify our solution by use of the uniform-field approximation. We present uniform-field results for squared electric field versus operating frequency, and for each of these versus cavity tuning and laser excitation. Various cavity linewidths and both resonant and nonresonant amplifier and absorber line-center frequencies are considered. The most notable finding is that cavity detuning breaks the degeneracies found in the steady-state solutions of the fully tuned case. This leads to the prediction that an actual system will bifurcate from the zero-intensity solution to a steady-state solution as laser excitation increases from zero, rather than to the small-amplitude pulsations found for the model with exactly resonant tuning of the cavity and the media line centers. Other phenomena suggested by the steady-state results include tuning-dependent hysteresis and bistability, and instability in both intensity and frequency due to the appearance of one or more new steady-state solutions as tuning is varied. These effects of detuning are being tested by a linearized stability analysis whose results will be reported separately
The Cosmic Coincidence as a Temporal Selection Effect Produced by the Age Distribution of Terrestrial Planets in the Universe
The energy densities of matter and the vacuum are currently observed to be of
the same order of magnitude: . The cosmological window of time during which this occurs is
relatively narrow. Thus, we are presented with the cosmological coincidence
problem: Why, just now, do these energy densities happen to be of the same
order? Here we show that this apparent coincidence can be explained as a
temporal selection effect produced by the age distribution of terrestrial
planets in the Universe. We find a large () probability that
observations made from terrestrial planets will result in finding at
least as close to as we observe today. Hence, we, and any
observers in the Universe who have evolved on terrestrial planets, should not
be surprised to find . This result is
relatively robust if the time it takes an observer to evolve on a terrestrial
planet is less than Gyr.Comment: Submitted to Ap
Semiclassical Analysis of a Detuned Ring Laser with a Saturable Absorber: New Results for the Steady States
This paper presents new results for the steady states of a detuned ring laser with a saturable absorber. We employ a semiclassical model which assumes homogeneously broadened two-level atoms. We proceed by solving the Maxwell-Bloch equations for the longitudinal dependence of the steady states of this system, and then simplify our solution by use of the uniform-field approximation. We present uniform-field results for squared electric field versus operating frequency, and for each of these versus cavity tuning and laser excitation. Various cavity linewidths and both resonant and nonresonant amplifier and absorber line-center frequencies are considered. The most notable finding is that cavity detuning breaks the degeneracies found in the steady-state solutions of the fully tuned case. This leads to the prediction that an actual system will bifurcate from the zero-intensity solution to a steady-state solution as laser excitation increases from zero, rather than to the small-amplitude pulsations found for the model with exactly resonant tuning of the cavity and the media line centers. Other phenomena suggested by the steady-state results include tuning-dependent hysteresis and bistability, and instability in both intensity and frequency due to the appearance of one or more new steady-state solutions as tuning is varied. These effects of detuning are being tested by a linearized stability analysis whose results will be reported separately
Secular evolution of a satellite by tidal effect. Application to Triton
Some of the satellites in the Solar System, including the Moon, appear to
have been captured from heliocentric orbits at some point in their past, and
then have evolved to the present configurations. The exact process of how this
trapping occurred is unknown, but the dissociation of a planetesimal binary in
the gravitational field of the planet, gas drag, or a massive collision seem to
be the best candidates. However, all these mechanisms leave the satellites in
elliptical orbits that need to be damped to the present almost circular ones.
Here we give a complete description of the secular tidal evolution of a
satellite just after entering a bounding state with the planet. In particular,
we take into account the spin evolution of the satellite, which has often been
assumed synchronous in previous studies. We apply our model to Triton and
successfully explain some geophysical properties of this satellite, as well as
the main dynamical features observed for the Neptunian system.Comment: 4 pages, 1 figur
Air flow conditions in workspace of mulcher
ArticleCurrently, there has been a great effort on increasing the efficiency of agricultural
machinery. The energy demands of mulching with the
vertical
axis of rotation
depends
on the
amount
of pr
ocessed material per unit of time, its properties and efficiency of material processing.
Another
important
factor that is affecting the overall energy demands is the energy losses, which
can be even higher than energy, required
for
the processing of materi
al.
The efficiency
of the
material processing and the energy losses
are influenced
to a large extent by the air flow inside
the mulcher workspace, which
is created
by the movement of working tools. The air flow ensures
the repeated contact of the processed
material with the working tools, affects the energy losses
and the quality of work. The contribution deals with the air flow conditions inside the workspace
of mulcher with the
vertical
axis of rotation. The velocity of the
air flow
was measured
my
means
of LDA (Laser Doppler Anemometry) method in three planes above the surface (180, 100 and
20
mm
) and
in
two directions (peripheral and radial). The laboratory model of one mulcher rotor
from mulcher MZ 6000 made by BEDNAR Ltd. company
was used
for the measu
rement. From
the
results
it is evident that the maximum values of peripheral velocity of the air flow reach
approx. 50% of the velocity of the tools. In the radial
plane
an air vortex is created between 20
and 100
mm
planes above the surface around the tip
of the blade
Hamiltonian dynamics and constrained variational calculus: continuous and discrete settings
The aim of this paper is to study the relationship between Hamiltonian
dynamics and constrained variational calculus. We describe both using the
notion of Lagrangian submanifolds of convenient symplectic manifolds and using
the so-called Tulczyjew's triples. The results are also extended to the case of
discrete dynamics and nonholonomic mechanics. Interesting applications to
geometrical integration of Hamiltonian systems are obtained.Comment: 33 page
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