17,026 research outputs found
A Normal-Mode Approach to Jovian Atmospheric Dynamics
We propose a nonlinear, quasi-geostrophic, baroclinic model of Jovian atmospheric dynamics, in which vertical variations of velocity are represented by a truncated sum over a complete set of orthogonal functions obtained by a separation of variables of the linearized quasi-geostrophic potential vorticity equation. A set of equations for the time variation of the mode amplitudes in the nonlinear case is then derived. We show that for a planet with a neutrally stable, fluid interior instead of a solid lower boundary, the baroclinic mode represents motions in the interior, and is not affected by the baroclinic modes. One consequence of this is that a normal-mode model with one baroclinic mode is dynamically equivalent to a one layer model with solid lower topography. We also show that for motions in Jupiter's cloudy lower troposphere, the stratosphere behaves nearly as a rigid lid, so that the normal-mode model is applicable to Jupiter. We test the accuracy of the normal-mode model for Jupiter using two simple problem forced, vertically propagating Rossby waves, using two and three baroclinic modes and baroclinic instability, using two baroclinic modes. We find that the normal-road model provide qualitatively correct results, even with only a very limited number of vertical degrees of freedom
Comparison of CEAS and Williams-type models for spring wheat yields in North Dakota and Minnesota
The CEAS and Williams-type yield models are both based on multiple regression analysis of historical time series data at CRD level. The CEAS model develops a separate relation for each CRD; the Williams-type model pools CRD data to regional level (groups of similar CRDs). Basic variables considered in the analyses are USDA yield, monthly mean temperature, monthly precipitation, and variables derived from these. The Williams-type model also used soil texture and topographic information. Technological trend is represented in both by piecewise linear functions of year. Indicators of yield reliability obtained from a ten-year bootstrap test of each model (1970-1979) demonstrate that the models are very similar in performance in all respects. Both models are about equally objective, adequate, timely, simple, and inexpensive. Both consider scientific knowledge on a broad scale but not in detail. Neither provides a good current measure of modeled yield reliability. The CEAS model is considered very slightly preferable for AgRISTARS applications
Atmospheric transmission computer program CP
A computer program is described which allows for calculation of the effects of carbon dioxide, water vapor, methane, ozone, carbon monoxide, and nitrous oxide on earth resources remote sensing techniques. A flow chart of the program and operating instructions are provided. Comparisons are made between the atmospheric transmission obtained from laboratory and spacecraft spectrometer data and that obtained from a computer prediction using a model atmosphere and radiosonde data. Limitations of the model atmosphere are discussed. The computer program listings, input card formats, and sample runs for both radiosonde data and laboratory data are included
Flexible Invariants Through Semantic Collaboration
Modular reasoning about class invariants is challenging in the presence of
dependencies among collaborating objects that need to maintain global
consistency. This paper presents semantic collaboration: a novel methodology to
specify and reason about class invariants of sequential object-oriented
programs, which models dependencies between collaborating objects by semantic
means. Combined with a simple ownership mechanism and useful default schemes,
semantic collaboration achieves the flexibility necessary to reason about
complicated inter-object dependencies but requires limited annotation burden
when applied to standard specification patterns. The methodology is implemented
in AutoProof, our program verifier for the Eiffel programming language (but it
is applicable to any language supporting some form of representation
invariants). An evaluation on several challenge problems proposed in the
literature demonstrates that it can handle a variety of idiomatic collaboration
patterns, and is more widely applicable than the existing invariant
methodologies.Comment: 22 page
The Informal Sector In Sub-Saharan Africa: Out Of The Shadows To Foster Sustainable Employment And Equity?
Over the past twenty years or so, there has been a debate that basically asks “…whether the informal sector should really be seen as a marginalized, ‘survival’ sector, which mops up excess or entrenched workers, or as a vibrant, entrepreneurial part of the economy which can stimulate economic growth and job creation.” (African Union 2008). This paper argues the latter. Further, this paper argues that employment in the informal sector is no longer a journey, but has become the destination of many. If the aim is to create jobs and reduce poverty, the informal sector must be included in the debate. Indeed, this paper recommends that the debate about the advantages of formal sector vs. the informal sector needs to end. Governments need to unequivocally recognize and admit the importance of the informal sector and finds ways to encourage its growth. They also need, at the same time, to decide how to strengthen the formal sector and extend benefits to those in the informal sector, while removing barriers to the formal sector to allow more to participate. Specifically, there are at least five major areas where changes need to be made: 1) Establish an enabling environment and supportive regulatory framework, 2) Provide access to appropriate training, 3) Improve basic facilities and amenities and infrastructure, 4) Increase ability to obtain property title and access to credit, and 5) Improve national databases and establish uniform standards
Comment on "Regge Trajectories for All Flavors"
We show that Regge trajectories for all flavors suggested recently by
Filipponi et al. cannot combine both meson spectroscopy and additivity of
intercepts. Other defects of these trajectories are also discussed.Comment: 2 pages, LaTe
Constraints for quantum logic arising from conservation laws and field fluctuations
We explore the connections between the constraints on the precision of
quantum logical operations that arise from a conservation law, and those
arising from quantum field fluctuations. We show that the conservation-law
based constraints apply in a number of situations of experimental interest,
such as Raman excitations, and atoms in free space interacting with the
multimode vacuum. We also show that for these systems, and for states with a
sufficiently large photon number, the conservation-law based constraint
represents an ultimate limit closely related to the fluctuations in the quantum
field phase.Comment: To appear in J. Opt. B: Quantum Semiclass. Opt., special issue on
quantum contro
Large-uncertainty intelligent states for angular momentum and angle
The equality in the uncertainty principle for linear momentum and position is
obtained for states which also minimize the uncertainty product. However, in
the uncertainty relation for angular momentum and angular position both sides
of the inequality are state dependent and therefore the intelligent states,
which satisfy the equality, do not necessarily give a minimum for the
uncertainty product. In this paper, we highlight the difference between
intelligent states and minimum uncertainty states by investigating a class of
intelligent states which obey the equality in the angular uncertainty relation
while having an arbitrarily large uncertainty product. To develop an
understanding for the uncertainties of angle and angular momentum for the
large-uncertainty intelligent states we compare exact solutions with analytical
approximations in two limiting cases.Comment: 20 pages, 9 figures, submitted to J. Opt. B special issue in
connection with ICSSUR 2005 conferenc
Non-Markovian dynamics of a nanomechanical resonator measured by a quantum point contact
We study the dynamics of a nanomechanical resonator (NMR) subject to a
measurement by a low transparency quantum point contact (QPC) or tunnel
junction in the non-Markovian domain. We derive the non-Markovian
number-resolved (conditional) and unconditional master equations valid to
second order in the tunneling Hamiltonian without making the rotating-wave
approximation and the Markovian approximation, generally made for systems in
quantum optics. Our non-Markovian master equation reduces, in appropriate
limits, to various Markovian versions of master equations in the literature. We
find considerable difference in dynamics between the non-Markovian cases and
its Markovian counterparts. We also calculate the time-dependent transport
current through the QPC which contains information about the measured NMR
system. We find an extra transient current term proportional to the expectation
value of the symmetrized product of the position and momentum operators of the
NMR. This extra current term, with a coefficient coming from the combination of
the imaginary parts of the QPC reservoir correlation functions, has a
substantial contribution to the total transient current in the non-Markovian
case, but was generally ignored in the studies of the same problem in the
literature. Considering the contribution of this extra term, we show that a
significantly qualitative and quantitative difference in the total transient
current between the non-Markovian and the Markovian wide-band-limit cases can
be observed. Thus, it may serve as a witness or signature of the non-Markovian
features in the coupled NMR-QPC system.Comment: Accepted for publication in Physical Review B (20 pages, 13 figures
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