41 research outputs found
Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling
Nonstationary pump-probe interaction between short laser pulses propagating
in a resonant optically dense coherent medium is considered. A special
attention is paid to the case, where the density of two-level particles is high
enough that a considerable part of the energy of relatively weak external
laser-fields can be coherently absorbed and reemitted by the medium. Thus, the
field of medium reaction plays a key role in the interaction processes, which
leads to the collective behavior of an atomic ensemble in the strongly coupled
light-matter system. Such behavior results in the fast excitation interchanges
between the field and a medium in the form of the optical ringing, which is
analogous to polariton beating in the solid-state optics. This collective
oscillating response, which can be treated as successive beats between light
wave-packets of different group velocities, is shown to significantly affect
propagation and amplification of the probe field under its nonlinear
interaction with a nearly copropagating pump pulse. Depending on the probe-pump
time delay, the probe transmission spectra show the appearance of either
specific doublet or coherent dip. The widths of these features are determined
by the density-dependent field-matter coupling coefficient and increase during
the propagation. Besides that, the widths of the coherent features, which
appear close to the resonance in the broadband probe-spectrum, exceed the
absorption-line width, since, under the strong-coupling regime, the frequency
of the optical ringing exceeds the rate of incoherent relaxation. Contrary to
the stationary strong-field effects, the density- and coordinate-dependent
transmission spectra of the probe manifest the importance of the collective
oscillations and cannot be obtained in the framework of the single-atom model.Comment: 10 pages, 8 figures, to be published in Phys. Rev.
Reliability-Focused Scheduling with (m, k)-firm Deadlines over Wireless Channels - A Reinforcement-Learning Approach
In wireless radio applications, the quality of an underlying wireless channel
is important, however, we know of a few applications that can tolerate some
losses. As an example, real-time applications like streaming voice or video
do permit packet loss and still retain a bearable service. With respect to
quality of service requirement, we embrace one concise method to distinguish
between the allowed and forbidden loss patterns. This method is known as
the (m; k)- rm deadlines; at least m out of k consecutive packets have to
be successfully delivered to their destination. We consider a point to multi-
point network with a known population of wireless communication terminals
and with one base station periodically polling all terminals. Given limited
network resources, a recovery from data losses in such arrangement might
be very challenging under high error rates and with large number of nodes.
In this thesis, we consider policies that improve quality of multiple periodic
streams by retransmission of failed packets. The base scheduler decides which
streams to serve with respect to the primary goal of minimizing violation
of the stream's deadline. We introduce an algorithm from Reinforcement
Learning theory and compare its performance to a few baseline scheduling
policies with static channels and channels with time-varying characteristics.
We found that although the Learning scheme introduces good performance
it doesn't outperform a baseline technique which is based on immediate slot
allocation decisions with respect to packet error rate of each stream
Relayer-Enabled Retransmission Scheduling in 802.15.4e LLDNâExploring a Reinforcement Learning Approach
We consider the scheduling of retransmissions in the low-latency deterministic network (LLDN) extension to the IEEE 802.15.4 standard. We propose a number of retransmission schemes with varying degrees of required changes to the LLDN specification. In particular, we propose a retransmission scheme that uses cooperative relayers and where the best relayer for a source node is learned using a reinforcement-learning method. The method allows for adapting relayer selections in the face of time-varying channels. Our results show that the relayer-based methods achieve a much better reliability over the other methods, both over static (but unknown) and over time-varying channels
Relayer-Enabled Retransmission Scheduling in 802.15.4e LLDN -- Exploring a Reinforcement Learning Approach
We consider the scheduling of retransmissions in the low-latency deterministic network
(LLDN) extension to the IEEE 802.15.4 standard. We propose a number of retransmission schemes
with varying degrees of required changes to the LLDN specification. In particular, we propose
a retransmission scheme that uses cooperative relayers and where the best relayer for a source
node is learned using a reinforcement-learning method. The method allows for adapting relayer
selections in the face of time-varying channels. Our results show that the relayer-based methods
achieve a much better reliability over the other methods, both over static (but unknown) and over
time-varying channels
FOUR WAVE MIXING OBSERVATION OF A SATELLITE IN THE Na-Xe NON-IMPACT COLLISIONAL LINESHAPE
Modulation of Actin-Myosin Interaction by N-terminal Unique Domain of Myorod of Molluscan Catch Muscle
Multistep orthophosphate release tunes actomyosin energy transduction
Release of the ATP hydrolysis product orthophosphate (Pi) from the myosin active site is central in force generation but is poorly understood. Here, Moretto et al. present evidence for multistep Pi-release reconciling apparently contradictory results. Muscle contraction and a range of critical cellular functions rely on force-producing interactions between myosin motors and actin filaments, powered by turnover of adenosine triphosphate (ATP). The relationship between release of the ATP hydrolysis product ortophosphate (Pi) from the myosin active site and the force-generating structural change, the power-stroke, remains enigmatic despite its central role in energy transduction. Here, we present a model with multistep Pi-release that unifies current conflicting views while also revealing additional complexities of potential functional importance. The model is based on our evidence from kinetics, molecular modelling and single molecule fluorescence studies of Pi binding outside the active site. It is also consistent with high-speed atomic force microscopy movies of single myosin II molecules without Pi at the active site, showing consecutive snapshots of pre- and post-power stroke conformations. In addition to revealing critical features of energy transduction by actomyosin, the results suggest enzymatic mechanisms of potentially general relevance