2,041 research outputs found
An investigation of small-scale motions and the forecasting of wind profiles over short periods of time at Cape Kennedy, Florida
Small scale motions and numerical wind profiles forecasting for short periods at Cape Kenned
A comparative analysis of rawinsonde and NIMBUS 6 and TIROS N satellite profile data
Comparisons are made between rawinsonde and satellite profiles in seven areas for a wide range of surface and weather conditions. Variables considered include temperature, dewpoint temperature, thickness, precipitable water, lapse rate of temperature, stability, geopotential height, mixing ratio, wind direction, wind speed, and kinematic parameters, including vorticity and the advection of vorticity and temperature. In addition, comparisons are made in the form of cross sections and synoptic fields for selected variables. Sounding data from the NIMBUS 6 and TIROS N satellites were used. Geostrophic wind computed from smoothed geopotential heights provided large scale flow patterns that agreed well with the rawinsonde wind fields. Surface wind patterns as well as magnitudes computed by use of the log law to extrapolate wind to a height of 10 m agreed with observations. Results of this study demonstrate rather conclusively that satellite profile data can be used to determine characteristics of large scale systems but that small scale features, such as frontal zones, cannot yet be resolved
Bayesian Image Reconstruction using Deep Generative Models
Machine learning models are commonly trained end-to-end and in a supervised
setting, using paired (input, output) data. Examples include recent
super-resolution methods that train on pairs of (low-resolution,
high-resolution) images. However, these end-to-end approaches require
re-training every time there is a distribution shift in the inputs (e.g., night
images vs daylight) or relevant latent variables (e.g., camera blur or hand
motion). In this work, we leverage state-of-the-art (SOTA) generative models
(here StyleGAN2) for building powerful image priors, which enable application
of Bayes' theorem for many downstream reconstruction tasks. Our method,
Bayesian Reconstruction through Generative Models (BRGM), uses a single
pre-trained generator model to solve different image restoration tasks, i.e.,
super-resolution and in-painting, by combining it with different forward
corruption models. We keep the weights of the generator model fixed, and
reconstruct the image by estimating the Bayesian maximum a-posteriori (MAP)
estimate over the input latent vector that generated the reconstructed image.
We further use variational inference to approximate the posterior distribution
over the latent vectors, from which we sample multiple solutions. We
demonstrate BRGM on three large and diverse datasets: (i) 60,000 images from
the Flick Faces High Quality dataset (ii) 240,000 chest X-rays from MIMIC III
and (iii) a combined collection of 5 brain MRI datasets with 7,329 scans.
Across all three datasets and without any dataset-specific hyperparameter
tuning, our simple approach yields performance competitive with current
task-specific state-of-the-art methods on super-resolution and in-painting,
while being more generalisable and without requiring any training. Our source
code and pre-trained models are available online:
https://razvanmarinescu.github.io/brgm/.Comment: 27 pages, 17 figures, 5 table
Interminiband Rabi oscillations in biased semiconductor superlattices
Carrier dynamics at energy level anticrossings in biased semiconductor
superlattices, was studied in the time domain by solving the time-dependent
Schroedinger equation. The resonant nature of interminiband Rabi oscillations
has been explicitly demonstrated to arise from interference of intrawell and
Bloch oscillations. We also report a simulation of direct Rabi oscillations
across three minibands, in the high field regime, due to interaction between
three strongly coupled minibands.Comment: 13 pages, 16 figure
AN ANALYSIS OF AIR FORCE CONTRACT MANAGEMENT PERSONNEL COMPETENCY AND INTERNAL PROCESSES USING THE NATIONAL CONTRACT MANAGEMENT ASSOCIATION'S THIRD-PARTY ACCREDITED COMPETENCY STANDARD
For the last two decades, the Government Accountability Office (GAO) has listed the Department of Defense’s (DoD) contract management practices as a high-risk area. Additionally, in 2019, contract management oversight appeared as one of the DoD Inspector General’s (IG) top management challenges. DoD continues to review processes, training, and organizational assessments for effectiveness. However, the contracting workforce needs competency in both the buyer and seller roles from the contract management life cycle to be truly effective. The National Contract Management Association (NCMA) Contract Management Body of Knowledge (CMBOK) Contract Management Standard (CMS) was chosen as the competency framework for our research, as it fulfills this need. The purpose of this research is to conduct an analysis of DoD IG–reported contract management deficiencies from DoD IG inspections for the Air Force and align these deficiencies with the third-party accredited NCMA CMS competency framework. Additionally, since the Air Force contracting organizations use self-inspections as part of internal controls to prepare for DoD IG inspections, this research provides a comparative analysis between the CMS and the Air Force Contracting Self-Inspection Checklist. Finally, the research provides recommendations for training opportunities and improving the checklist, which clearly align with two of the three parts of auditability theory.Civilian, Department of the Air ForceCivilian, Department of the Air ForceCivilian, Department of the Air ForceApproved for public release. distribution is unlimite
Stability and electronic structure of the complex KPtCl structure-type hydrides
The stability and bonding of the ternary complex KPtCl structure
hydrides is discussed using first principles density functional calculations.
The cohesion is dominated by ionic contributions, but ligand field effects are
important, and are responsible for the 18-electron rule. Similarities to oxides
are discussed in terms of the electronic structure. However, phonon
calculations for SrRuH also show differences, particularly in the
polarizability of the RuH octahedra. Nevertheless, the yet to be made
compounds PbRuH and BeFeH are possible ferroelectrics. The
electronic structure and magnetic properties of the decomposition product,
FeBe are reported. Implications of the results for H storage are discussed
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