Stochastic resonance in electrical circuits—II: Nonconventional stochastic resonance.

Stochastic resonance (SR), in which a periodic signal in a nonlinear system can be amplified by added noise, is discussed. The application of circuit modeling techniques to the conventional form of SR, which occurs in static bistable potentials, was considered in a companion paper. Here, the investigation of nonconventional forms of SR in part using similar electronic techniques is described. In the small-signal limit, the results are well described in terms of linear response theory. Some other phenomena of topical interest, closely related to SR, are also treate

Stochastic resonance in electrical circuits—I: Conventional stochastic resonance.

Stochastic resonance (SR), a phenomenon in which a periodic signal in a nonlinear system can be amplified by added noise, is introduced and discussed. Techniques for investigating SR using electronic circuits are described in practical terms. The physical nature of SR, and the explanation of weak-noise SR as a linear response phenomenon, are considered. Conventional SR, for systems characterized by static bistable potentials, is described together with examples of the data obtainable from the circuit models used to test the theory

Changing the Magnetic Configurations of Nanoclusters Atom-by-Atom

The Korringa-Kohn-Rostoker Green (KKR) function method for non-collinear magnetic structures was applied on Mn and Cr ad-clusters deposited on the Ni(111) surface. By considering various dimers, trimers and tetramers, a large amount of collinear and non-collinear magnetic structures is obtained. Typically all compact clusters have very small total moments, while the more open structures exhibit sizeable total moments, which is a result of the complex frustration mechanism in these systems. Thus, as the motion of a single adatom changes the cluster structure from compact to open and vice versa, this can be considered as a magnetic switch, which via the local exchange field of the adatom allows to switch the cluster moment on and off, and which might be useful for future nanosize information storage.Comment: 7 page

Noise-enhanced heterodyning

A new form of heterodyning is reported, related to stochastic resonance, in which a heterodyne signal can be enhanced by adding noise

Nonconventional stochastic resonance.

It is argued, on the basis of linear response theory (LRT), that new types of stochastic resonance (SR) are to be anticipated in diverse systems, quite different from the one most commonly studied to date, which has a static double-well potential and is driven by a net force equal to the sum of periodic and stochastic terms. On this basis, three new nonconventional forms of SR are predicted, sought, found, and investigated both theoretically and by analogue electronic experiment: (a) in monostable systems; (b) in bistable systems with periodically modulated noise; and (c) in a system with coexisting periodic attractors. In each case, it is shown that LRT can provide a good quantitative description of the experimental results for sufficiently weak driving fields. It is concluded that SR is a much more general phenomenon than has hitherto been appreciated

Development and validation of a cost-effective and sensitive bioanalytical HPLC-UV method for determination of lopinavir in rat and human plasma

© 2020 The Authors. Biomedical Chromatography published by John Wiley & Sons Ltd A simple, sensitive and cost-effective HPLC-UV bioanalytical method for determination of lopinavir (LPV) in rat and human plasma was developed and validated. The plasma sample preparation procedure includes a combination of protein precipitation using cold acetonitrile and liquid–liquid extraction with n-hexane–ethyl acetate (7:3, v/v). A good chromatographic separation was achieved with a Phenomenex Gemini column (C18, 150 mm × 2.0 mm, 5 μm) at 40°C with gradient elution, at 211 nm. Calibration curves were linear in the range 10–10,000 ng/mL, with a lower limit of quantification of 10 ng/mL using 100 μL of plasma. The accuracy and precision in all validation experiments were within the criteria range set by the guidelines of the Food and Drug Administration. This method was successfully applied to a preliminary pharmacokinetic study in rats following an intravenous bolus administration of LPV. Moreover, the method was subsequently fully validated for human plasma, allowing its use in therapeutic drug monitoring (TDM). In conclusion, this novel, simple and cost-efficient bioanalytical method for determination of LPV is useful for pharmacokinetic and drug delivery studies in rats, as well as TDM in human patients

Switching Time Statistics for Driven Neuron Models: Analytic Expressions versus Numerics

Analytical expressions are put forward to investigate the forced spiking activity of abstract neuron models such as the driven leaky integrate-and-fire (LIF) model. The method is valid in a wide parameter regime beyond the restraining limits of weak driving (linear response) and/or weak noise. The novel approximation is based on a discrete state Markovian modeling of the full dynamics with time-dependent rates. The scheme yields very good agreement with numerical Langevin and Fokker-Planck simulations of the full non-stationary dynamics for both, the first-passage time statistics and the interspike interval (residence time) distributions.Comment: 4 pages, 4 figures, RevTeX4 used, final versio

NFIRAOS adaptive optics for the Thirty Meter Telescope

NFIRAOS (Narrow-Field InfraRed Adaptive Optics System) will be the first-light multi-conjugate adaptive optics system for the Thirty Meter Telescope (TMT). NFIRAOS houses all of its opto-mechanical sub-systems within an optics enclosure cooled to precisely -30°C in order to improve sensitivity in the near-infrared. It supports up to three client science instruments, including the first-light InfraRed Imaging Spectrograph (IRIS). Powering NFIRAOS is a Real Time Controller that will process the signals from six laser wavefront sensors, one natural guide star pyramid WFS, up to three low-order on-instrument WFS and up to four guide windows on the client instrument’s science detector in order to correct for atmospheric turbulence, windshake, optical errors and plate-scale distortion. NFIRAOS is currently preparing for its final design review in late June 2018 at NRC Herzberg in Victoria, British Columbia in partnership with Canadian industry and TMT