2,526 research outputs found
Carrier-envelope phase dependence in single-cycle laser pulse propagation with the inclusion of counter-rotating terms
We focus on the propagation properties of a single-cycle laser pulse through
a two-level medium by numerically solving the full-wave Maxwell-Bloch
equations. The counter-rotating terms in the spontaneous emission damping are
included such that the equations of motion are slightly different from the
conventional Bloch equations. The counter-rotating terms can considerably
suppress the broadening of the pulse envelope and the decrease of the group
velocity rooted from dispersion. Furthermore, for incident single-cycle pulses
with envelope area 4, the time-delay of the generated soliton pulse from
the main pulse depends crucially on the carrier-envelope phase of the incident
pulse. This can be utilized to determine the carrier-envelope phase of the
single-cycle laser pulse.Comment: 6 pages, 5 figure
Student experiences of virtual reality - a case study in learning special relativity
We present a study of student learning through the use of virtual reality. A
software package is used to introduce concepts of special relativity to
students in a game-like environment where users experience the effects of
travelling at near light speeds. From this new perspective, space and time are
significantly different to that experienced in everyday life. The study
explores how students have worked with this environment and how these students
have used this experience in their study of special relativity. A mixed method
approach has been taken to evaluate the outcomes of separate implementations of
the package at two universities. Students found the simulation to be a positive
learning experience and described the subject area as being less abstract after
its use. Also, students were more capable of correctly answering concept
questions relating to special relativity, and a small but measurable
improvement was observed in the final exam
Optimal Depth, Very Small Size Circuits for Symmetrical Functions in AC0
AbstractIt is well known which symmetric Boolean functions can be computed by constant depth, polynomial size, unbounded fan-in circuits, i.e., which are contained in the complexity class AC0. This result is sharpened. Symmetric Boolean functions in AC0 can be computed by unbounded fan-in circuits with the following properties. If the optimal depth of AC0-circuits is d, the depth is at most d + 2, the number of wires is almost linear, namely n logO(1)n, and the number of gates is subpolynomial (but superpolylogarithmic), namely 2O(logδn) for some δ < 1
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Vertebrate Hosts as Islands: Dynamics of Selection, Immigration, Loss, Persistence, and Potential Function of Bacteria on Salamander Skin.
Skin bacterial communities can protect amphibians from a fungal pathogen; however, little is known about how these communities are maintained. We used a neutral model of community ecology to identify bacteria that are maintained on salamanders by selection or by dispersal from a bacterial reservoir (soil) and ecological drift. We found that 75% (9/12) of bacteria that were consistent with positive selection, <1% of bacteria that were consistent with random dispersal and none of the bacteria that were consistent under negative selection had a 97% or greater match to antifungal isolates. Additionally we performed an experiment where salamanders were either provided or denied a bacterial reservoir and estimated immigration and loss (emigration and local extinction) rates of bacteria on salamanders in both treatments. Loss was strongly related to bacterial richness, suggesting competition is important for structuring the community. Bacteria closely related to antifungal isolates were more likely to persist on salamanders with or without a bacterial reservoir, suggesting they had a competitive advantage. Furthermore, over-represented and under-represented operational taxonomic units (OTUs) had similar persistence on salamanders when a bacterial reservoir was present. However, under-represented OTUs were less likely to persist in the absence of a bacterial reservoir, suggesting that the over-represented and under-represented bacteria were selected against or for on salamanders through time. Our findings from the neutral model, migration and persistence analyses show that bacteria that exhibit a high similarity to antifungal isolates persist on salamanders, which likely protect hosts against pathogens and improve fitness. This research is one of the first to apply ecological theory to investigate assembly of host associated-bacterial communities, which can provide insights for probiotic bioaugmentation as a conservation strategy against disease
Magnetic metamaterials at telecommunication and visible frequencies
Arrays of gold split-rings with 50-nm minimum feature size and with an LC
resonance at 200-THz frequency (1500-nm wavelength) are fabricated. For normal
incidence conditions, they exhibit a pronounced fundamental magnetic mode,
arising from a coupling via the electric component of the incident light. For
oblique incidence, a coupling via the magnetic component is demonstrated as
well. Moreover, we identify a novel higher-order magnetic resonance at around
370 THz (800-nm wavelength) that evolves out of the Mie resonance for oblique
incidence. Comparison with theory delivers good agreement and also shows that
the structures allow for a negative magnetic permeability.Comment: 4 pages, 3 figure
Novedades sobre el poblamiento antiguo en la parte navarra de la Val d’Onsella
El presente trabajo recoge un análisis basado en arqueología espacial llevado a cabo en el Valle del río Onsella, en el límite entre Navarra y Aragón. Se establecen las pautas de ocupación del territorio desde la Segunda Edad del Hierro hasta la tardoantigüedad, prestando especial atención al periodo romano, que marca un momento de profunda transformación y fuerte dinamismo. El espacio se configura en torno al enclave de carácter urbano de Fi- llera/Campo Real (Sos del Rey Católico, Zaragoza) y en menor medida en torno al posible vicus de Cementerio de Gordún (Gordún, Zaragoza).The present comunication summarizes an spatial archaeology analysis executed on the Onsella’s valley, placed betwen Navarra and Aragón.Guidelines are established on the occupation of the territory from the Second Iron Age to the Late Antiquity, with particular attention to the Roman period, being a remarkable time of deep transformation and strong dynamism. The space set around an urban site of Fillera/Campo Real and less on the possible vicus ofCementerio de Gordún
Verifying proofs in constant depth
In this paper we initiate the study of proof systems where verification of proofs proceeds by NC circuits. We investigate the question which languages admit proof systems in this very restricted model. Formulated alternatively, we ask which languages can be enumerated by NC functions. Our results show that the answer to this problem is not determined by the complexity of the language. On the one hand, we construct NC proof systems for a variety of languages ranging from regular to NP-complete. On the other hand, we show by combinatorial methods that even easy regular languages such as Exact-OR do not admit NC proof systems. We also present a general construction of proof systems for regular languages with strongly connected NFA's
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