19,513 research outputs found
Frequency response of electrochemical cells
Impedance concepts can be applied to the analysis of battery electrodes, yielding information about the structure of the electrode and the processes occurring in the electrode. Structural parameters such as the specific area (surface area per gram of electrode) can be estimated. Electrode variables such as surface overpotential, ohmic losses, and diffusion limitations may be studied. Nickel and cadmium electrodes were studied by measuring the ac impedance as a function of frequency, and the specific areas that were determined were well within the range of specific areas determined from BET measurements. Impedance spectra were measured for the nickel and cadmium electrodes, and for a 20 A-hr NiCd battery as functions of the state of charge. More work is needed to determine the feasibility of using frequency response as a nondestructive testing technique for batteries
Neural-inspired sensors enable sparse, efficient classification of spatiotemporal data
Sparse sensor placement is a central challenge in the efficient
characterization of complex systems when the cost of acquiring and processing
data is high. Leading sparse sensing methods typically exploit either spatial
or temporal correlations, but rarely both. This work introduces a new sparse
sensor optimization that is designed to leverage the rich spatiotemporal
coherence exhibited by many systems. Our approach is inspired by the remarkable
performance of flying insects, which use a few embedded strain-sensitive
neurons to achieve rapid and robust flight control despite large gust
disturbances. Specifically, we draw on nature to identify targeted
neural-inspired sensors on a flapping wing to detect body rotation. This task
is particularly challenging as the rotational twisting mode is three
orders-of-magnitude smaller than the flapping modes. We show that nonlinear
filtering in time, built to mimic strain-sensitive neurons, is essential to
detect rotation, whereas instantaneous measurements fail. Optimized sparse
sensor placement results in efficient classification with approximately ten
sensors, achieving the same accuracy and noise robustness as full measurements
consisting of hundreds of sensors. Sparse sensing with neural inspired encoding
establishes a new paradigm in hyper-efficient, embodied sensing of
spatiotemporal data and sheds light on principles of biological sensing for
agile flight control.Comment: 21 pages, 19 figure
Structure factor of interacting one-dimensional helical systems
We calculate the dynamical structure factor S(q, {\omega}) of a weakly
interacting helical edge state in the presence of a magnetic field B. The
latter opens a gap of width 2B in the single-particle spectrum, which becomes
strongly nonlinear near the Dirac point. For chemical potentials |{\mu}| > B,
the system then behaves as a nonlinear helical Luttinger liquid, and a
mobile-impurity analysis reveals interaction-dependent power-law singularities
in S(q,{\omega}). For |{\mu}| < B, the low-energy excitations are gapped, and
we determine S(q,{\omega}) by using an analogy to exciton physics.Comment: 5 pages, 3 figure
ANALYSIS OF RECENT OPTIONS FOR CHANGES IN U.S. DAIRY POLICY
Agricultural and Food Policy,
Studying the Nature of Dark Energy with Galaxy Clusters
We report on the status of our effort to constrain the nature of dark energy
through the evolution of the cluster mass function. Chandra temperature
profiles for 31 clusters from a local cluster sample are shown. The X-ray
appearance of the proto supermassive binary black hole at the center of the
cluster Abell 400 is described. Preliminary weak lensing results obtained with
Megacam@MMT for a redshift z=0.5 cluster from a distant cluster sample are
given.Comment: 5 pages, to appear in: Aschenbach, B., Burwitz, V., Hasinger, G.,
Leibundgut, B. (eds.), Relativistic Astrophysics and Cosmology - Einstein's
Legacy. ESO Astrophysics Symposia, Springer Verlag, Berlin, German
The sciences in America, circa 1880
For many years American science in the late 19th century was regarded as an intellectual backwater. This view derived from the assumption that the health of American science at the time was equivalent to the condition of pure science, especially pure physics. However, a closer look reveals that there was considerable vitality in American scientific research, especially in the earth and life sciences. This vitality is explainable in part by the natural scientific resources of the American continent but also in part by the energy given science from religious impulses, social reformism, and practicality. Furthermore, contrary to recent assumptions, the federal government was a significant patron of American science. The portrait of American science circa 1880 advanced in this article suggests that the nation's scientific enterprise was characterized by pluralism of institutional support and motive and that such pluralism has historically been the normal mode
Dustbuster: a compact impact-ionization time-of-flight mass spectrometer for in situ analysis of cosmic dust
We report on the design and testing of a compact impact-ionization time-of-flight mass spectrometer for analysis of cosmic dust, suitable for use on deep space missions. The instrument, Dustbuster, incorporates a large target area with a reflectron, simultaneously optimizing mass resolution, particle detection, and ion collection. Dust particles hit the 65-cm2 target plate and are partially ionized by the impact. The resulting ions, with broad energy and angular distributions, are accelerated through a modified reflectron, focusing ions of specific m/z in space and time to produce high-resolution mass spectra. The cylindrically symmetric instrument is 10 cm in diameter and 20 cm in length, considerably smaller than previous in situ dust analyzers, and can be easily scaled as needed for specific mission requirements. Laser desorption ionization of metal and mineral samples embedded in the impact plate simulated particle impacts for evaluations of instrument performance. Mass resolution in these experiments ranged from 60–180, permitting resolution of isotopes. The mass spectrometer can be combined with other instrument components to determine dust particle trajectories and sizes
Quantification of the Individual Characterstics of the Human Dentition: Methodology
This study provides a method for comparing six individual human dentition characteristics using the standard measuring tool in Adobe Photoshop CS2 as compared to measuring individual characteristics with an automated software program under development at Marquette University, which has been adapted for bitemark analysis. The algorithm identifies color-specific pixels and automatically calculates the measurements
Estimating the weak-lensing rotation signal in radio cosmic shear surveys
Weak lensing has become an increasingly important tool in cosmology and the
use of galaxy shapes to measure cosmic shear has become routine. The
weak-lensing distortion tensor contains two other effects in addition to the
two components of shear: the convergence and rotation. The rotation mode is not
measurable using the standard cosmic shear estimators based on galaxy shapes,
as there is no information on the original shapes of the images before they
were lensed. Due to this, no estimator has been proposed for the rotation mode
in cosmological weak-lensing surveys, and the rotation mode has never been
constrained. Here, we derive an estimator for this quantity, which is based on
the use of radio polarisation measurements of the intrinsic position angles of
galaxies. The rotation mode can be sourced by physics beyond CDM, and
also offers the chance to perform consistency checks of CDM and of
weak-lensing surveys themselves. We present simulations of this estimator and
show that, for the pedagogical example of cosmic string spectra, this estimator
could detect a signal that is consistent with the constraints from Planck. We
examine the connection between the rotation mode and the shear -modes and
thus how this estimator could help control systematics in future radio
weak-lensing surveys
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