820 research outputs found
Optical frequency waveguide and ion transmission system
Electromagnetically generated, high-dielectric tube forms a waveguide which retains the electromagnetic energy within the beam, the trapped beam establishes an optical frequency waveguide appropriate for its own conduction with minimum diffraction loss
Physical mechanism of superluminal traversal time: interference between multiple finite wave packets
The mechanism of superluminal traversal time through a potential well or
potential barrier is investigated from the viewpoint of interference between
multiple finite wave packets, due to the multiple reflections inside the well
or barrier. In the case of potential-well traveling that is classically
allowed, each of the successively transmitted constituents is delayed by a
subluminal time. When the thickness of the well is much smaller in comparision
with a characteristic length of the incident wave packet, the reshaped wave
packet in transmission maintains the profile of the incident wave packet. In
the case of potential-barrier tunneling that is classically forbidden, though
each of the successively transmitted constituents is delayed by a time that is
independent of the barrier thickness, the interference between multiple
transmitted constituents explains the barrier-thickness dependence of the
traversal time for thin barriers and its barrier-thickness independence for
thick barriers. This manifests the nature of Hartman effect.Comment: 9 pages, 3 figures, Some comments and suggestions are appreciate
Dynamic Pattern of Finite-Pulsed Beams inside One-dimensional Photonic Band Gap Materials
The dynamics of two-dimensional electromagnetic (EM) pulses through
one-dimensional photonic crystals (1DPC) has been theoretically studied.
Employing the time expectation integral over the Poynting vector as the arrival
time [Phys. Rev. Lett. 84, 2370, (2000)], we show that the superluminal
tunneling process of EM pulses is the propagation of the net forward-going
Poynting vector through the 1DPC, and the Hartman effect is due to the
saturation effect of the arrival time (smaller and smaller time accumulated) of
the net forward energy flow caused by the interference effect of the forward
and the backward field (from the interfaces of each layer) happened in the
region before the 1DPC and in the front part of the 1DPC.Comment: 18 pages, 4 figure
Effective photon-photon interaction in a two-dimensional "photon fluid"
We formulate an effective theory for the atom-mediated photon-photon
interactions in a two-dimensional ``photon fluid'' confined in a Fabry-Perot
resonator. With the atoms modelled by a collection of anharmonic Lorentz
oscillators, the effective interaction is evaluated to second order in the
coupling constant (the anharmonicity parameter). The interaction has the form
of a renormalized two-dimensional delta-function potential, with the
renormalization scale determined by the physical parameters of the system, such
as density of atoms and the detuning of the photons relative to the resonance
frequency of the atoms. For realistic values of the parameters, the
perturbation series has to be resummed, and the effective interaction becomes
independent of the ``bare'' strength of the anharmonic term. The resulting
expression for the non-linear Kerr susceptibility, is parametrically equal to
the one found earlier for a dilute gas of two-level atoms. Using our result for
the effective interaction parameter, we derive conditions for the formation of
a photon fluid, both for Rydberg atoms in a microwave cavity and for alkali
atoms in an optical cavity.Comment: 25 pages (revtex4), including 2 figure
A new class of trapped light filaments
New class light filament identified in Raman radiation of intense ruby laser bea
Signal velocity, causality, and quantum noise in superluminal light pulse propagation
We consider pulse propagation in a linear anomalously dispersive medium where
the group velocity exceeds the speed of light in vacuum (c) or even becomes
negative. A signal velocity is defined operationally based on the optical
signal-to-noise ratio, and is computed for cases appropriate to the recent
experiment where such a negative group velocity was observed. It is found that
quantum fluctuations limit the signal velocity to values less than c.Comment: 4 Journal pages, 3 figure
Dynamics and Characteristics of the Self-trapping of Intense Light Beams
Dynamics and characteristics of self-trapping of intense light beam
Culture–gene coevolution of individualism–collectivism and the serotonin transporter gene
Culture–gene coevolutionary theory posits that cultural values have evolved, are adaptive and influence the social and physical environments under which genetic selection operates. Here, we examined the association between cultural values of individualism–collectivism and allelic frequency of the serotonin transporter functional polymorphism (5-HTTLPR) as well as the role this culture–gene association may play in explaining global variability in prevalence of pathogens and affective disorders. We found evidence that collectivistic cultures were significantly more likely to comprise individuals carrying the short (S) allele of the 5-HTTLPR across 29 nations. Results further show that historical pathogen prevalence predicts cultural variability in individualism–collectivism owing to genetic selection of the S allele. Additionally, cultural values and frequency of S allele carriers negatively predict global prevalence of anxiety and mood disorder. Finally, mediation analyses further indicate that increased frequency of S allele carriers predicted decreased anxiety and mood disorder prevalence owing to increased collectivistic cultural values. Taken together, our findings suggest culture–gene coevolution between allelic frequency of 5-HTTLPR and cultural values of individualism–collectivism and support the notion that cultural values buffer genetically susceptible populations from increased prevalence of affective disorders. Implications of the current findings for understanding culture–gene coevolution of human brain and behaviour as well as how this coevolutionary process may contribute to global variation in pathogen prevalence and epidemiology of affective disorders, such as anxiety and depression, are discussed
Safety Intelligence and Legal Machine Language: Do We Need the Three Laws of Robotics?
In this chapter we will describe a legal framework for Next Generation Robots (NGRs) that has safety as its central focus. The framework is offered in response to the current lack of clarity regarding robot safety guidelines, despite the development and impending release of tens of thousands of robots into workplaces and homes around the world. We also describ
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