481 research outputs found
Application of an inverse model in the community modeling effort results
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1995Inverse modeling activities in oceanography have recently been intensified, aided
by the oncoming observational data stream of WOCE and the advance of computer
power. However, interpretations of inverse model results from climatological
hydrographic data are far from simple. This thesis examines the behavior of an
inverse model in the WOCE CME (Community Modeling Effort) results where the
physics and the parameter values are known. The ultimate hypotheses to be tested
are whether the inferred circulations from a climatological hydrographic data set
(where limited time means and spatial smoothing are usually used) represent the
climatological ocean general circulations, and what the inferred "diffusion" coefficients
really are.
The inverse model is first tested in a non-eddy resolving numerical GCM
ocean. Numerical/scale analyses are used to test whether the inverse model properly
represents the GCM ocean. Experiments show how biased answers could result from
an incorrect model, and how a correct model must produce the right answers. When the inverse model is applied to the time-mean hydrographic data of
an eddy-resolving GCM ocean in the fine grid resolution of the GCM, the estimated
horizontal circulation is statistically consistent with the EGCM time means in both
patterns and values. Although the flow patterns are similar, the uncertainties for
the GCM time means and the inverse model estimates are different. The former
are very large, such that the GCM time-mean circulation has no significance in the
deep ocean. The latter are much smaller, and with them the estimated circulations
are well defined. This is consistent with the concept that ocean motions are
very energetic, while variations of tracers (temperature, salinity) are low frequency.
The inverse model succeeded in extracting the ocean general circulation from the
"climatological" hydrographic data. The estimated vertical velocities are also statistically indistinguishable from
the GCM time means. However, significant differences between the estimated "diffusion" coefficients and the EGCM eddy diffusion coefficients are found at certain
locations. These discrepancies are attributed to the differences in physics of the
inverse model and the EGCM ocean. The "diffusion" coefficients from the inversion
parameterize not only the eddy fluxes, but also (part of) the temporal variation
and biharmonic terms which are not explicitly included in the inverse model.
Given the essentially red spectrum of the ocean, it makes sense to look for
smooth solutions. Aliasing due to subsampling on a coarse grid and the effects of
spatial smoothing are addressed in the last part of this thesis. It is shown that this
aliasing could be greatly reduced by spatial smoothing. The estimated horizontal
circulation from the spatially smoothed time-mean EGCM hydrographic data with
a coarse grid resolution (2.4° longitude by 2.0° latitude) is generally consistent
with the spatially smoothed EGCM time means. Significant differences only occur
at some grid points at great depths, where the GCM circulations are very weak.
The conclusions of this study are different from some previous studies. These
discrepancies are explained in the concluding chapter.
Finally, it should be pointed out that the issue of properly representing a
GCM ocean by an inverse model is not identical to the issue of represent ing the
real ocean by the same inverse model, since the GCM ocean is not identical to the
real ocean. Numerical calculations show that both the non-eddy resolving and the
eddy-resolving GCM oceans used in this work are evolving towards a statistical
equilibrium. In the real ocean, the importance of temporal variation terms in the
property conservation equations should also be analyzed when a steady mverse
model is applied to a limited time-mean (the climatological) data set.This research was carried out under National Science Foundation grant OCE-
90-04396
Circulation and water mass balance in the Brazil Basin
Analysis of data from the Levitus (1982) atlas shows that the application of the Montgomery streamfunction to the potential density surfaces induces an error which cannot be ignored in some regions in the ocean. The error arises from the variation of the specific volume anomaly along isopycnal surfaces. By including the major part of this effect, new streamfunctions, named the pressure anomaly and mean pressure streamfunctions, are suggested for use in potential density coordinates. By including the variations of specific volume anomaly and pressure along isopycnal surfaces, the inverse model proposed by Hogg (1987) is modified for increased accuracy and then applied to the Brazil Basin to study the circulation, diffusion and water mass balances. The system of equations with constraints of positive diffusivities and oxygen consumption rates is solved by the inverse method. By using multiple tracers and controlling the scale of variation of the diffusion coefficients we are able to construct an overdetermined system whose solution is by a least-square approach. The results indicate that the circulation in the upper ocean is consistent with previous work, but that in the deep ocean differs from some previous analyses. In the NADW depth, we find a coincidence of flow with tongues of water properties. The diffusivities and diapycnal velocities seem stronger in the region near the equator than in the south, with reasonable values. Diffusion plays an important role in the water property balances. Examples show that similar property patterns may result from different processes
Deducing dynamic properties from simulated hydrographic data: Part I. Results from a non-eddy-resolving model
Inverse models are widely used in oceanography. However, their reliability remains an open question, as comparison of inverse model results with real values of ocean parameters is difficult due to insufficient knowledge of the latter. The feasibility of extracting the ocean general circulation, mixing rates, as well as air-sea heat and freshwater fluxes from hydrographic data is studied by applying an inverse model to the CME (Community Modeling Effort) results where both the physics and parameter values are known. The inverse model assumes approximate thermal wind balance and steady state conservation laws for mass, heat, and salt, assumptions satisfied by the GCM ocean although the residuals in the tracer conservation equations are comparable to the diffusion terms in the deep ocean. Effects of errors in these equations on inverse model solutions for different variables are studied in detail. A surface layer model is designed to estimate the air-sea heat and freshwater fluxes and the results are compared to their “true” values. Experiments on various parameterizations of different variables are carried out in the hope of getting some guidance in applying the inverse model to the real ocean. The inverse model estimates for horizontal circulation are relatively robust—they are consistent with the GCM ocean circulations in most of the experiments, and effects of equation errors are more pronounced in the estimates for diffusivity and air-sea fluxes. Residuals in the equations are noisy and resemble a random distribution. In such cases, the estimates for all the parameters are very close to their true values. The conclusions of this work are different from previous works, and the discrepancies are explained
Voice Conversion Based on Cross-Domain Features Using Variational Auto Encoders
An effective approach to non-parallel voice conversion (VC) is to utilize
deep neural networks (DNNs), specifically variational auto encoders (VAEs), to
model the latent structure of speech in an unsupervised manner. A previous
study has confirmed the ef- fectiveness of VAE using the STRAIGHT spectra for
VC. How- ever, VAE using other types of spectral features such as mel- cepstral
coefficients (MCCs), which are related to human per- ception and have been
widely used in VC, have not been prop- erly investigated. Instead of using one
specific type of spectral feature, it is expected that VAE may benefit from
using multi- ple types of spectral features simultaneously, thereby improving
the capability of VAE for VC. To this end, we propose a novel VAE framework
(called cross-domain VAE, CDVAE) for VC. Specifically, the proposed framework
utilizes both STRAIGHT spectra and MCCs by explicitly regularizing multiple
objectives in order to constrain the behavior of the learned encoder and de-
coder. Experimental results demonstrate that the proposed CD- VAE framework
outperforms the conventional VAE framework in terms of subjective tests.Comment: Accepted to ISCSLP 201
Consistent Right-Invariant Fixed-Lag Smoother with Application to Visual Inertial SLAM
State estimation problems without absolute position measurements routinely
arise in navigation of unmanned aerial vehicles, autonomous ground vehicles,
etc., whose proper operation relies on accurate state estimates and reliable
covariances. Unaware of absolute positions, these problems have immanent
unobservable directions. Traditional causal estimators, however, usually gain
spurious information on the unobservable directions, leading to over-confident
covariance inconsistent with actual estimator errors. The consistency problem
of fixed-lag smoothers (FLSs) has only been attacked by the first estimate
Jacobian (FEJ) technique because of the complexity to analyze their
observability property. But the FEJ has several drawbacks hampering its wide
adoption. To ensure the consistency of a FLS, this paper introduces the right
invariant error formulation into the FLS framework. To our knowledge, we are
the first to analyze the observability of a FLS with the right invariant error.
Our main contributions are twofold. As the first novelty, to bypass the
complexity of analysis with the classic observability matrix, we show that
observability analysis of FLSs can be done equivalently on the linearized
system. Second, we prove that the inconsistency issue in the traditional FLS
can be elegantly solved by the right invariant error formulation without
artificially correcting Jacobians. By applying the proposed FLS to the
monocular visual inertial simultaneous localization and mapping (SLAM) problem,
we confirm that the method consistently estimates covariance similarly to a
batch smoother in simulation and that our method achieved comparable accuracy
as traditional FLSs on real data.Comment: 13 pages, 4 figures, AAAI 2021 Conferenc
Input Estimation Algorithms for Reentry Vehicle Trajectory Estimation
Fast and accurate estimation of trajectory is important in tracking and intercepting reentry vehicles. Validating model is a real challenge associated with the qverall trajectory estimation problem. Input estimation technique provides a’solution to this challenge. Two input estimation algorithms were introduced based on different assumptions about the input applied to the model. This investigation presents approaches consisting of an extended Kahnan filter and two input estimation algorithms to identify the reentry vehicle trajectory in its terminal phase using data from a single radar source. Numerical simulations with data generated from two models demonstrate superior capabilities as measured by accuracy compared to the extended Kalman filter. Evaluation using real flight data provides the consistent results. The comparison between two input estimation algorithms is also presented. The trajectory estimation approaches based on two algorithms are effective in solving the reentry vehicle tracking problem
Phase structure in the baryon density-dependent quark mass model
The properties of phase diagram of strange quark matter in equilibrium with
hadronic matter at finite temperature are studied, where the quark phase and
hadron phase are treated by baryon density-dependent quark mass model and
hadron resonance gas model with hard core repulsion factor, respectively. Our
results indicate that the strangeness fraction fs, perturbation parameter C,
and confinement parameter D have strong influence on the properties of phase
diagram and the formation of strangelets, where a large fs, small C and D favor
the formation of strangelets. Consider the isentropic expansion process, we
found that the initial entropy per baryon is about 5, which gives a large
probability for the formation of strangelets. Furthermore, as the strangeness
fraction fs and one gluon-exchange interaction strength C decrease and
confinement parameter D increases, the reheating effect becomes more
significant, reducing the possibility of forming strangelets. The new phase
diagram could support a massive compact star with the maximum mass exceeding
twice the solar mass and have a significant impact on the mass-radius
relationship for hybrid stars
Dense Polarized Positrons from Laser-Irradiated Foil Targets in the QED Regime
Dense positrons are shown to be effectively generated from laser-solid
interactions in the strong-field quantum electrodynamics (QED) regime. Whether
these positrons are polarized has not yet been reported, limiting their
potential applications. Here, by QED particle-in-cell simulations including
electron-positron spin and photon polarization effects, we investigate a
typical laser-solid setup that an ultraintense linearly polarized laser
irradiates a foil target with m-scale-length preplasma. We find that once
the positron yield becomes appreciable with the laser intensity exceeding
, the positrons are obviously polarized. The polarized
positrons can acquire polarization degree and nC charge with a
flux of . The polarization relies on the deflected
angles and can reach 60\% at some angles and energies. The angularly-dependent
polarization is attributed to the asymmetrical laser fields positrons undergo
in the skin layer of overdense plasma, where the radiative spin-flip and
radiation reaction play significant roles. The positron polarization is robust
and could generally appear in future 100-PW-class laser-solid experiments for
various applications.Comment: 6 pages, 5 figures, with Supplemental Materia
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