61,699 research outputs found
Evolution of Resource Competition between Mutually Dependent Digital Organisms
We study the emergence and dynamics of competing strains of digital organisms in a world with two depletable resources. Consumption of one resource produces the other resource as a by-product, and vice versa. As a consequence, two types of mutually dependent organisms emerge that each prey on the waste product of the other. In the absence of mutations, that is, in a purely ecological setting, the abundances of the two types of organisms display a wide range of different types of oscillations, from regular
oscillations with large amplitude to irregular oscillations with amplitudes ranging from small to large. In this regime,
time-averaged abundance levels seem to be controlled by the
relative fitness of the organisms in the absence of resources. Under mutational pressure, on the other hand, populations evolve that seem to avoid the oscillations of intermediate to large amplitudes. In this case, the relative fitness of the organisms in the presence of resources plays an important role in the time-averaged abundance levels as well
Broadband power amplifier tube: Klystron tube 5K70SK-WBT and step tuner VA-1470S
The design concept, the fabrication, and the acceptance testing of a wide band Klystron tube and remotely controlled step tuner for channel selection are discussed. The equipment was developed for the modification of an existing 20 KW Power Amplifier System which was provided to the contractor as GFE. The replacement Klystron covers a total frequency range of 2025 to 2120 MHz and is tuneable to six (6) each channel with a band width of 22 MHz or greater per channel. A 5 MHz overlap is provided between channels. Channels are selected at the control panel located in the front of the Klystron magnet or from one of three remote control stations connected in parallel with the step tuner. Included in this final report are the results of acceptance tests conducted at the vendor's plant and of the integrated system tests
Fracture toughness and fatigue-crack propagation in a Zr–Ti–Ni–Cu–Be bulk metallic glass
The recent development of metallic alloy systems which can be processed with an amorphous structure over large dimensions, specifically to form metallic glasses at low cooling rates (similar to 10 K/s), has permitted novel measurements of important mechanical properties. These include, for example, fatigue-crack growth and fracture toughness behavior, representing the conditions governing the subcritical and critical propagation of cracks in these structures. In the present study, bulk plates of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy, machined into 7 mm wide, 38 mm thick compact-tension specimens and fatigue precracked following standard procedures, revealed fracture toughnesses in the fully amorphous structure of K(lc)similar to 55 MPa root m, i.e., comparable with that of a high-strength steel or aluminum ahoy. However, partial and full crystallization, e.g., following thermal exposure at 633 K or more, was found to result in a drastic reduction in fracture toughness to similar to 1 MPa root m, i.e., comparable with silica glass. The fully amorphous alloy was also found to be susceptible to fatigue-crack growth under cyclic loading, with growth-rate properties comparable to that of ductile crystalline metallic alloys, such as high-strength steels or aluminum alloys; no such fatigue was seen in the partially or fully crystallized alloys which behaved like very brittle ceramics. Possible micromechanical mechanisms for such behavior are discussed
Velocity correlations in dense granular flows
Velocity fluctuations of grains flowing down a rough inclined plane are
experimentally studied. The grains at the free surface exhibit fluctuating
motions, which are correlated over few grains diameters. The characteristic
correlation length is shown to depend on the inclination of the plane and not
on the thickness of the flowing layer. This result strongly supports the idea
that dense granular flows are controlled by a characteristic length larger than
the particle diameter
Adiabatic self-tuning in a silicon microdisk optical resonator
We demonstrate a method for adiabatically self-tuning a silicon microdisk resonator. This mechanism is not only able to sensitively probe the fast nonlinear cavity dynamics, but also provides various optical functionalities like pulse compression, shaping, and tunable time delay
A proposal for highly tunable optical parametric oscillation in silicon micro-resonators
We propose a novel scheme for continuous-wave pumped optical parametric oscillation (OPO) inside silicon micro-resonators. The proposed scheme not only requires a relative low lasing threshold, but also exhibits extremely broad tunability extending from the telecom band to mid infrared
New dynamical scaling universality for quantum networks across adiabatic quantum phase transitions
We reveal universal dynamical scaling behavior across adiabatic quantum phase
transitions (QPTs) in networks ranging from traditional spatial systems (Ising
model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our
findings, which lie beyond traditional critical exponent analysis and adiabatic
perturbation approximations, are applicable even where excitations have not yet
stabilized and hence provide a time-resolved understanding of QPTs encompassing
a wide range of adiabatic regimes. We show explicitly that even though two
systems may traditionally belong to the same universality class, they can have
very different adiabatic evolutions. This implies more stringent conditions
need to be imposed than at present, both for quantum simulations where one
system is used to simulate the other, and for adiabatic quantum computing
schemes.Comment: 5 pages, 3 figures, plus supplementary material (6 pages, 1 figure
Large dynamic light-matter entanglement from driving neither too fast nor too slow
A significant problem facing next-generation quantum technologies is how to
generate and manipulate macroscopic entanglement in light and matter systems.
Here we report a new regime of dynamical light-matter behavior in which a
giant, system-wide entanglement is generated by varying the light-matter
coupling at \emph{intermediate} velocities. This enhancement is far larger and
broader-ranged than that occurring near the quantum phase transition of the
same model under adiabatic conditions. By appropriate choices of the coupling
within this intermediate regime, the enhanced entanglement can be made to
spread system-wide or to reside in each subsystem separately.Comment: 7 pages, 7 figure
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