143,098 research outputs found
Measurement of surface potential decay of corona-charged polymer films using the pulsed electroacoustic method
In this paper, the pulsed electroacoustic (PEA) technique that allows the determination of space charge in a dielectric material has been used to monitor the electrical potential decay of corona-charged polyethylene films of different thicknesses. To prevent possible disturbance on the surface charge during the PEA measurements, two thin polyethylene films were placed on both sides of the corona-charged sample. Charge profiles measured at different times were used to calculate the potential across the sample. The obtained potential decay was compared with the potential measured using the conventional method. A good agreement has been obtained. More importantly, the charge profile obtained using the PEA technique indicates that bipolar charge injection has taken place
Spatiotemporal Patterns and Predictability of Cyberattacks
Y.C.L. was supported by Air Force Office of Scientific Research (AFOSR) under grant no. FA9550-10-1-0083 and Army Research Office (ARO) under grant no. W911NF-14-1-0504. S.X. was supported by Army Research Office (ARO) under grant no. W911NF-13-1-0141. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
Differential space-time block-coded OFDMA for frequency-selective fading channels
Combining differential Alamouti space-time block code (DASTBC) with orthogonal frequency-division multiple access (OFDMA), this paper introduces a multiuser/multirate transmission scheme, which allows full-rate and full-diversity noncoherent communications using two transmit antennas over frequency-selective fading channels. Compared with the existing differential space-time coded OFDM designs, our scheme imposes 10 restrictions on signal constellations, and thus can improve the spectral efficiency by exploiting efficient modulation techniques such as QAM, APSK etc. The main principles of our design are s follows: OFDMA eliminates multiuser interference, and converts multiuser environments to single-user ones; Space-time coding achieves performance improvement by exploiting space diversity available with multiple antennas, no matter whether channel state information is known to the receiver. System performance is evaluated both analytically and with simulations
Repeating head-on collisions in an optical trap and the evaluation of spin-dependent interactions among neutral particles
A dynamic process of repeating collisions of a pair of trapped neutral
particles with weak spin-dependent interaction is designed and studied. Related
theoretical derivation and numerical calculation have been performed to study
the inherent coordinate-spin and momentum-spin correlation. Due to the
repeating collisions the effect of the weak interaction can be accumulated and
enlarged, and therefore can be eventually detected. Numerical results suggest
that the Cr-Cr interaction, which has not yet been completely clear, could be
thereby determined. The design can be in general used to determine various
interactions among neutral atoms and molecules, in particular for the
determination of very weak forces.Comment: 15 pages, 7 figure
A Two-Step Etching Method to Fabricate Nanopores in Silicon
A cost effectively method to fabricate nanopores in silicon by only using the
conventional wet-etching technique is developed in this research. The main
concept of the proposed method is a two-step etching process, including a
premier double-sided wet etching and a succeeding track-etching. A special
fixture is designed to hold the pre-etched silicon wafer inside it such that
the track-etching can be effectively carried out. An electrochemical system is
employed to detect and record the ion diffusion current once the pre-etched
cavities are etched into a through nanopore. Experimental results indicate that
the proposed method can cost effectively fabricate nanopores in silicon.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
High-Order-Mode Soliton Structures in Two-Dimensional Lattices with Defocusing Nonlinearity
While fundamental-mode discrete solitons have been demonstrated with both
self-focusing and defocusing nonlinearity, high-order-mode localized states in
waveguide lattices have been studied thus far only for the self-focusing case.
In this paper, the existence and stability regimes of dipole, quadrupole and
vortex soliton structures in two-dimensional lattices induced with a defocusing
nonlinearity are examined by the theoretical and numerical analysis of a
generic envelope nonlinear lattice model. In particular, we find that the
stability of such high-order-mode solitons is quite different from that with
self-focusing nonlinearity. As a simple example, a dipole (``twisted'') mode
soliton which may be stable in the focusing case becomes unstable in the
defocusing regime. Our results may be relevant to other two-dimensional
defocusing periodic nonlinear systems such as Bose-Einstein condensates with a
positive scattering length trapped in optical lattices.Comment: 14 pages, 10 figure
- ā¦