2,055 research outputs found
A Minimum Effort Control Approach to Guided Munition Path Planning
An advance in the development of smart munitions entails autonomously modifying target selection during flight to maximize the value of the target being destroyed. Target identification and classification provides a basis for target value, which is used in conjunction with multi-target tracks to determine an optimal aim point for the munition. A unique guidance law can be constructed that exploits attribute and kinematic data from an onboard video sensor. This thesis develops an innovative path planning algorithm that provides an obstacle avoidance function while navigating the munition toward the highest value target. The foundation of this path planning method is found in the principles of minimum effort control optimization. Results demonstrate the ability of the path planning algorithm to determine a path for the munition to follow which is both stable and feasible
On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films
The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces
Non-adiabatic spin torque investigated using thermally activated magnetic domain wall dynamics
Using transmission electron microscopy, we investigate the thermally
activated motion of domain walls (DWs) between two positions in permalloy
(Ni80Fe20) nanowires at room temperature. We show that this purely thermal
motion is well described by an Arrhenius law, allowing for a description of the
DW as a quasi-particle in a 1D potential landscape. By injecting small
currents, the potential is modified, allowing for the determination of the
non-adiabatic spin torque: the non-adiabatic coefficient is 0.010 +/- 0.004 for
a transverse DW and 0.073 +/- 0.026 for a vortex DW. The larger value is
attributed to the higher magnetization gradients present
Data analysis of gravitational-wave signals from spinning neutron stars. V. A narrow-band all-sky search
We present theory and algorithms to perform an all-sky coherent search for
periodic signals of gravitational waves in narrow-band data of a detector. Our
search is based on a statistic, commonly called the -statistic,
derived from the maximum-likelihood principle in Paper I of this series. We
briefly review the response of a ground-based detector to the
gravitational-wave signal from a rotating neuron star and the derivation of the
-statistic. We present several algorithms to calculate efficiently
this statistic. In particular our algorithms are such that one can take
advantage of the speed of fast Fourier transform (FFT) in calculation of the
-statistic. We construct a grid in the parameter space such that
the nodes of the grid coincide with the Fourier frequencies. We present
interpolation methods that approximately convert the two integrals in the
-statistic into Fourier transforms so that the FFT algorithm can
be applied in their evaluation. We have implemented our methods and algorithms
into computer codes and we present results of the Monte Carlo simulations
performed to test these codes.Comment: REVTeX, 20 pages, 8 figure
Cell-free prediction of protein expression costs for growing cells
Translating heterologous proteins places significant burden on host cells, consuming expression resources leading to slower cell growth and productivity. Yet predicting the cost of protein production for any given gene is a major challenge, as multiple processes and factors combine to determine translation efficiency. To enable prediction of the cost of gene expression in bacteria, we describe here a standard cell-free lysate assay that provides a relative measure of resource consumption when a protein coding sequence is expressed. These lysate measurements can then be used with a computational model of translation to predict the in vivo burden placed on growing E. coli cells for a variety of proteins of different functions and lengths. Using this approach, we can predict the burden of expressing multigene operons of different designs and differentiate between the fraction of burden related to gene expression compared to action of a metabolic pathway
Energy-level quantization in YBa2Cu3O7-x phase-slip nanowires
Significant progress has been made in the development of superconducting
quantum circuits, however new quantum devices that have longer decoherence
times at higher temperatures are urgently required for quantum technologies.
Superconducting nanowires with quantum phase slips are promising candidates for
use in novel devices that operate on quantum principles. Here, we demonstrate
ultra-thin YBa2Cu3O7-x nanowires with phase-slip dynamics and study their
switching-current statistics at temperatures below 20 K. We apply theoretical
models that were developed for Josephson junctions and show that our results
provide strong evidence for energy-level quantization in the nanowires. The
crossover temperature to the quantum regime is 12-13 K, while the lifetime in
the excited state exceeds 20 ms at 5.4 K. Both values are at least one order of
magnitude higher than those in conventional Josephson junctions based on
low-temperature superconductors. We also show how the absorption of a single
photon changes the phase-slip and quantum state of a nanowire, which is
important for the development of single-photon detectors with high operating
temperature and superior temporal resolution. Our findings pave the way for a
new class of superconducting nanowire devices for quantum sensing and
computing
X-Ray Emitting Ejecta of Supernova Remnant N132D
The brightest supernova remnant in the Magellanic Clouds, N132D, belongs to
the rare class of oxygen-rich remnants, about a dozen objects that show optical
emission from pure heavy-element ejecta. They originate in explosions of
massive stars that produce large amounts of O, although only a tiny fraction of
that O is found to emit at optical wavelengths. We report the detection of
substantial amounts of O at X-ray wavelengths in a recent 100 ks Chandra ACIS
observation of N132D. A comparison between subarcsecond-resolution Chandra and
Hubble images reveals a good match between clumpy X-ray and optically emitting
ejecta on large (but not small) scales. Ejecta spectra are dominated by strong
lines of He- and H-like O; they exhibit substantial spatial variations
partially caused by patchy absorption within the LMC. Because optical ejecta
are concentrated in a 5 pc radius elliptical expanding shell, the detected
ejecta X-ray emission also originates in this shell.Comment: 5 pages, 6 figures, ApJ Letters, in pres
- …