5,994 research outputs found
Geologic considerations in underground coal mining system design
Geologic characteristics of coal resources which may impact new extraction technologies are identified and described to aid system designers and planners in their task of designing advanced coal extraction systems for the central Appalachian region. These geologic conditions are then organized into a matrix identified as the baseline mine concept. A sample region, eastern Kentucy is analyzed using both the developed baseline mine concept and the traditional geologic investigative approach
Variational electric fields at low latitudes and their relation to spread F and plasma irregularities
Recordings from OGO 6 show that electric field irregularities are frequently present between + or - 35 deg geomagnetic latitude in the 2000 - 0600 local time sector. The signatures are very clear, and are easily distinguished from the normal AC background noise, and whistler and emission activity. The spectral appearance of the fields makes it meaningful to distinguish between 3 different types of irregularities: strong irregularities, weak irregularities, and weak irregularities with a rising spectrum. Strong irregularities seem most likely to occur in regions where gradients in ionization are present. Changes in plasma composition, resulting in an increase in the mean ion mass, are also often observed in the irregularity regions. Comparison with ground based ionosondes indicates a connection between strong irregularities and low latitude spread F. A good correlation is also present between strong fields and small scale fluctuations in ionization, delta N/N 1 percent. From the data it appears as if a gradient driven instability is the most likely source of the strong irregularities
Adaptive gain and filtering circuit for a sound reproduction system
Adaptive compressive gain and level dependent spectral shaping circuitry for a hearing aid include a microphone to produce an input signal and a plurality of channels connected to a common circuit output. Each channel has a preset frequency response. Each channel includes a filter with a preset frequency response to receive the input signal and to produce a filtered signal, a channel amplifier to amplify the filtered signal to produce a channel output signal, a threshold register to establish a channel threshold level, and a gain circuit. The gain circuit increases the gain of the channel amplifier when the channel output signal falls below the channel threshold level and decreases the gain of the channel amplifier when the channel output signal rises above the channel threshold level. A transducer produces sound in response to the signal passed by the common circuit output
Adaptive noise reduction circuit for a sound reproduction system
A noise reduction circuit for a hearing aid having an adaptive filter for producing a signal which estimates the noise components present in an input signal. The circuit includes a second filter for receiving the noise-estimating signal and modifying it as a function of a user's preference or as a function of an expected noise environment. The circuit also includes a gain control for adjusting the magnitude of the modified noise-estimating signal, thereby allowing for the adjustment of the magnitude of the circuit response. The circuit also includes a signal combiner for combining the input signal with the adjusted noise-estimating signal to produce a noise reduced output signal
Prisoner's Dilemma cellular automata revisited: evolution of cooperation under environmental pressure
We propose an extension of the evolutionary Prisoner's Dilemma cellular
automata, introduced by Nowak and May \cite{nm92}, in which the pressure of the
environment is taken into account. This is implemented by requiring that
individuals need to collect a minimum score , representing
indispensable resources (nutrients, energy, money, etc.) to prosper in this
environment. So the agents, instead of evolving just by adopting the behaviour
of the most successful neighbour (who got ), also take into account if
is above or below the threshold . If an
individual has a probability of adopting the opposite behaviour from the one
used by its most successful neighbour. This modification allows the evolution
of cooperation for payoffs for which defection was the rule (as it happens, for
example, when the sucker's payoff is much worse than the punishment for mutual
defection). We also analyse a more sophisticated version of this model in which
the selective rule is supplemented with a "win-stay, lose-shift" criterion. The
cluster structure is analyzed and, for this more complex version we found
power-law scaling for a restricted region in the parameter space.Comment: 15 pages, 8 figures; added figures and revised tex
Electronic filters, hearing aids and methods
An electronic filter for an electroacoustic system. The system has a microphone for generating an electrical output from external sounds and an electrically driven transducer for emitting sound. Some of the sound emitted by the transducer returns to the microphone means to add a feedback contribution to its electical output. The electronic filter includes a first circuit for electronic processing of the electrical output of the microphone to produce a filtered signal. An adaptive filter, interconnected with the first circuit, performs electronic processing of the filtered signal to produce an adaptive output to the first circuit to substantially offset the feedback contribution in the electrical output of the microphone, and the adaptive filter includes means for adapting only in response to polarities of signals supplied to and from the first circuit. Other electronic filters for hearing aids, public address systems and other electroacoustic systems, as well as such systems, and methods of operating them are also disclosed
Random Topologies and the emergence of cooperation: the role of short-cuts
We study in detail the role of short-cuts in promoting the emergence of
cooperation in a network of agents playing the Prisoner's Dilemma Game (PDG).
We introduce a model whose topology interpolates between the one-dimensional
euclidean lattice (a ring) and the complete graph by changing the value of one
parameter (the probability p to add a link between two nodes not already
connected in the euclidean configuration). We show that there is a region of
values of p in which cooperation is largely enhanced, whilst for smaller values
of p only a few cooperators are present in the final state, and for p
\rightarrow 1- cooperation is totally suppressed. We present analytical
arguments that provide a very plausible interpretation of the simulation
results, thus unveiling the mechanism by which short-cuts contribute to promote
(or suppress) cooperation
Proton lifetime bounds from chirally symmetric lattice QCD
We present results for the matrix elements relevant for proton decay in Grand
Unified Theories (GUTs). The calculation is performed at a fixed lattice
spacing a^{-1}=1.73(3) GeV using 2+1 flavors of domain wall fermions on
lattices of size 16^3\times32 and 24^3\times64 with a fifth dimension of length
16. We use the indirect method which relies on an effective field theory
description of proton decay, where we need to estimate the low energy
constants, \alpha = -0.0112(25) GeV^3 and \beta = 0.0120(26) GeV^3. We relate
these low energy constants to the proton decay matrix elements using leading
order chiral perturbation theory. These can then be combined with experimental
bounds on the proton lifetime to bound parameters of individual GUTs.Comment: 17 pages, 9 Figure
2018 NASA Green Propulsion Technology Development Roadmap
The NASA Green Propulsion Working Group (GPWG) was tasked by the NASA Chemical Propulsion Subcapabilities Management (CPSM) with the development of this NASA Green Propulsion Technologies Development Roadmap, herein referred to as the Green Propulsion Roadmap, or simply the Roadmap, to provide guidance to NASA through the CPSM on green propulsion technology development. Other agencies or commercial partners may refer to this roadmap as well. It is envisioned that the synthesis of various Center-based activities and knowledge repositories will result in a cumulative knowledge gain, and will provide capabilities beyond the sum contribution of individual Centers. Ultimately, a well-defined roadmap of technology investment path, the enhanced coordination and alignment of activities among NASA Centers and other Federal Agencies, and a well-supported green propulsion community will facilitate the path towards the broader infusion of green propulsion technologies for science and human exploration missions, as well as a deeper understanding of the fundamental behaviors and characteristics of these systems that is on par with other historically used monopropellant propulsion systems, such as hydrazine
Selection of noise level in strategy adoption for spatial social dilemmas
We studied spatial Prisoner's Dilemma and Stag Hunt games where both the
strategy distribution and the players' individual noise level could evolve to
reach higher individual payoff. Players are located on the sites of different
two-dimensional lattices and gain their payoff from games with their neighbors
by choosing unconditional cooperation or defection. The way of strategy
adoption can be characterized by a single (temperature-like) parameter
describing how strongly adoptions depend on the payoff-difference. If we start
the system from a random strategy distribution with many different player
specific parameters, the simultaneous evolution of strategies and
parameters drives the system to a final stationary state where only one
value remains. In the coexistence phase of cooperator and defector strategies
the surviving parameter is in good agreement with the noise level that
ensures the highest cooperation level if uniform is supposed for all
players. In this paper we give a thorough overview about the properties of this
evolutionary process.Comment: 10 two-column pages, 10 figures; accepted for publication in Physical
Review
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