1,153 research outputs found
Restoration of missing lines in grip patterns for biometrics authentication on a smart gun
The Secure Grip project1 aims to develop a grip-pattern recognition system, as part of a smart gun. Its target users are the police officers. The current authentication algorithm is based on a likelihood-ratio classifier. The grip pattern is acquired by sensors on the grip of the gun. Since in practice various factors can result in missing lines in a grip pattern, restoration of these missing
lines will be useful and practical. We present a restoration algorithm based on null-space error minimization. The simulation results of the restoration and authentication experiments show that this restoration algorithm effectively restores grip patterns,
and is, therefore, capable of improving the system’s authentication performance when missing lines are present
Food Quality in Producer-Grazer Models: A Generalized Analysis
Stoichiometric constraints play a role in the dynamics of natural
populations, but are not explicitly considered in most mathematical models.
Recent theoretical works suggest that these constraints can have a significant
impact and should not be neglected. However, it is not yet resolved how
stoichiometry should be integrated in population dynamical models, as different
modeling approaches are found to yield qualitatively different results. Here we
investigate a unifying framework that reveals the differences and commonalities
between previously proposed models for producer-grazer systems. Our analysis
reveals that stoichiometric constraints affect the dynamics mainly by
increasing the intraspecific competition between producers and by introducing a
variable biomass conversion efficiency. The intraspecific competition has a
strongly stabilizing effect on the system, whereas the variable conversion
efficiency resulting from a variable food quality is the main determinant for
the nature of the instability once destabilization occurs. Only if the food
quality is high an oscillatory instability, as in the classical paradox of
enrichment, can occur. While the generalized model reveals that the generic
insights remain valid in a large class of models, we show that other details
such as the specific sequence of bifurcations encountered in enrichment
scenarios can depend sensitively on assumptions made in modeling stoichiometric
constraints.Comment: Online appendixes include
The power of syllabi: Faculty roles in ePortfolio
A study of faculty views about General Education requirements, paired with a review of faculty syllabi, revealed concerns about communication of General Education goals to students. Syllabi reviewed were those meeting the natural sciences General Education requirement. Students demonstrate natural science competency with work from various science courses, deposited in an electronic portfolio. Electronic portfolios are evaluated systematically as part of the university General Education assessment plan. We explore possible reasons for gaps in faculty communication about the natural science competency requirement, including issues such as institution type and faculty desire for autonomy. Factors which contribute to creation of successful syllabi are also reviewed, and we discuss how these factors could be employed to better communicate General Education requirements to students
Continuation of connecting orbits in 3D-ODEs: (I) Point-to-cycle connections
We propose new methods for the numerical continuation of point-to-cycle
connecting orbits in 3-dimensional autonomous ODE's using projection boundary
conditions. In our approach, the projection boundary conditions near the cycle
are formulated using an eigenfunction of the associated adjoint variational
equation, avoiding costly and numerically unstable computations of the
monodromy matrix. The equations for the eigenfunction are included in the
defining boundary-value problem, allowing a straightforward implementation in
AUTO, in which only the standard features of the software are employed.
Homotopy methods to find connecting orbits are discussed in general and
illustrated with several examples, including the Lorenz equations. Complete
AUTO demos, which can be easily adapted to any autonomous 3-dimensional ODE
system, are freely available.Comment: 18 pages, 10 figure
IF impedance and mixer gain of NbN hot electron bolometers
The intermediate frequency (IF) characteristics, the frequency dependent IF impedance, and the mixer conversion gain of a small area hot electron bolometer (HEB) have been measured and modeled. The device used is a twin slot antenna coupled NbN HEB mixer with a bridge area of 1×0.15 µm^2, and a critical temperature of 8.3 K. In the experiment the local oscillator frequency was 1.300 THz, and the (IF) 0.05–10 GHz. We find that the measured data can be described in a self-consistent manner with a thin film model presented by Nebosis et al. [Proceedings of the Seventh International Symposium on Space Terahertz Technology, Charlottesville, VA, 1996 (unpublished), pp. 601–613], that is based on the two temperature electron-phonon heat balance equations of Perrin-Vanneste [J. Phys. (Paris) 48, 1311 (1987)]. From these results the thermal time constant, governing the gain bandwidth of HEB mixers, is observed to be a function of the electron-phonon scattering time, phonon escape time, and the electron temperature. From the developed theory the maximum predicted gain bandwidth for a NbN HEB is found to be 5.5–6 GHz. In contrast, the gain bandwidth of the device under discussion was measured to be ~2.3 GHz which, consistent with the outlined theory, is attributed to a somewhat low critical temperature and nonoptimal film thickness (6 nm)
Smith-Purcell Radiation from Low-Energy Electrons
Recent advances in the fabrication of nanostructures and nanoscale features
in metasurfaces offer a new prospect for generating visible, light emission
from low energy electrons. In this paper, we present the experimental
observation of visible light emission from low-energy free electrons
interacting with nanoscale periodic surfaces through the Smith-Purcell (SP)
effect. SP radiation is emitted when electrons pass in close proximity over a
periodic structure, inducing collective charge motion or dipole excitations
near the surface, thereby giving rise to electromagnetic radiation. We
demonstrate a controlled emission of SP light from nanoscale gold gratings with
periodicity as small as 50 nm, enabling the observation of visible SP radiation
by low energy electrons (1.5 to 6 keV), an order of magnitude lower than
previously reported. We study the emission wavelength and intensity dependence
on the grating pitch and electron energy, showing agreement between experiment
and theory. Further reduction of structure periodicity should enable the
production of SP-based devices that operate with even slower electrons that
allow an even smaller footprint and facilitate the investigation of quantum
effects for light generation in nanoscale devices. A tunable light source
integrated in an electron microscope would enable the development of novel
electron-optical correlated spectroscopic techniques, with additional
applications ranging from biological imaging to solid-state lighting.Comment: 16 pages, 4 figure
Direct Visualization of Laser-Driven Focusing Shock Waves
Cylindrically or spherically focusing shock waves have been of keen interest
for the past several decades. In addition to fundamental study of materials
under extreme conditions, cavitation, and sonoluminescence, focusing shock
waves enable myriad applications including hypervelocity launchers, synthesis
of new materials, production of high-temperature and high-density plasma
fields, and a variety of medical therapies. Applications in controlled
thermonuclear fusion and in the study of the conditions reached in laser fusion
are also of current interest. Here we report on a method for direct real-time
visualization and measurement of laser-driven shock generation, propagation,
and 2D focusing in a sample. The 2D focusing of the shock front is the
consequence of spatial shaping of the laser shock generation pulse into a ring
pattern. A substantial increase of the pressure at the convergence of the
acoustic shock front is observed experimentally and simulated numerically.
Single-shot acquisitions using a streak camera reveal that at the convergence
of the shock wave in liquid water the supersonic speed reaches Mach 6,
corresponding to the multiple gigapascal pressure range 30 GPa
OBSERVATIONS ON PHOTICALLY EVOKED OCCIPITAL AND VERTEX WAVES DURING SLEEP IN MAN *
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75014/1/j.1749-6632.1964.tb26756.x.pd
Single-bubble and multi-bubble cavitation in water triggered by laser-driven focusing shock waves
In this study a single laser pulse spatially shaped into a ring is focused
into a thin water layer, creating an annular cavitation bubble and cylindrical
shock waves: an outer shock that diverges away from the excitation laser ring
and an inner shock that focuses towards the center. A few nanoseconds after the
converging shock reaches the focus and diverges away from the center, a single
bubble nucleates at the center. The inner diverging shock then reaches the
surface of the annular laser-induced bubble and reflects at the boundary,
initiating nucleation of a tertiary bubble cloud. In the present experiments,
we have performed time-resolved imaging of shock propagation and bubble wall
motion. Our experimental observations of single-bubble cavitation and collapse
and appearance of ring-shaped bubble clouds are consistent with our numerical
simulations that solve a one dimensional Euler equation in cylindrical
coordinates. The numerical results agree qualitatively with the experimental
observations of the appearance and growth of bubble clouds at the smallest
laser excitation rings. Our technique of shock-driven bubble cavitation opens
novel perspectives for the investigation of shock-induced single-bubble or
multi-bubble cavitation phenomena in thin liquids
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