Control of multistability

Multiple attractors can be found in many nonlinear dynamical system with multistability. Recently, experimental attractors with two stable saddle-foci were reported to find in a non-ideal active voltage-controlled memristor based Chua's circuit. In this paper we focus on the multiple attractors found in the proposed memristive Chua's circuit. Concretely, by numerical simulations of mathematical model, hardware circuit experiments and PSIM circuit simulations, multiple attractors with different initial states are revealed and with the dimensionless system equations, complex dynamics with different initial conditions are further discussed. Theoretical derivation results indicate that the normalized memristive Chua's system has two stable nonzero saddle-foci in globally adjusting normalized parameter region and exhibits the unusual and striking dynamical behavior of multiple attractors with multistability.

Multiple attractors in a non-ideal active voltage-controlled memristor based Chua's circuit

Wide field-of-view (FOV) and high-resolution imaging requires microscopy modalities to have large space-bandwidth products. Lensfree on-chip microscopy decouples resolution from FOV and can achieve a space-bandwidth product greater than one billion under unit magnification using state-of-the-art opto-electronic sensor chips and pixel super-resolution techniques. However, using vertical illumination, the effective numerical aperture (NA) that can be achieved with an on-chip microscope is limited by a poor signal-to-noise ratio (SNR) at high spatial frequencies and imaging artifacts that arise as a result of the relatively narrow acceptance angles of the sensor's pixels. Here, we report, for the first time, a synthetic aperture-based on-chip microscope in which the illumination angle is scanned across the surface of a dome to increase the effective NA of the reconstructed lensfree image to 1.4, achieving e.g., ∼250-nm resolution at 700-nm wavelength under unit magnification. This synthetic aperture approach not only represents the largest NA achieved to date using an on-chip microscope but also enables color imaging of connected tissue samples, such as pathology slides, by achieving robust phase recovery without the need for multi-height scanning or any prior information about the sample. To validate the effectiveness of this synthetic aperture-based, partially coherent, holographic on-chip microscope, we have successfully imaged color-stained cancer tissue slides as well as unstained Papanicolaou smears across a very large FOV of 20.5 mm2. This compact on-chip microscope based on a synthetic aperture approach could be useful for various applications in medicine, physical sciences and engineering that demand high-resolution wide-field imaging. An on-chip microscope that offers both a high-resolution and a wide field of view looks set to benefit the biological and physical sciences. The lensfree imaging device, developed by researchers at the University of California at Los Angeles, CA, USA, makes use a synthetic aperture approach to provide a very large effective numerical aperture of 1.4 over a field of view of >20 mm2; this is a much larger numerical aperture than previous lensfree approaches had realized (<0.9). Consequently, very high spatial resolution (for example, 250 nm at a wavelength of 700 nm) was achieved. By illuminating samples with light of three different wavelengths (470 nm, 532 nm and 632 nm), the researchers also obtained lens-free color images of samples such as breast cancer tissue.

/pdf/synthetic-aperture-based-on-chip-microscopy-384rgdqqkz.pdf

Synthetic aperture-based on-chip microscopy

Pixel-size limitation of lensfree on-chip microscopy can be circumvented by utilizing pixel-super-resolution techniques to synthesize a smaller effective pixel, improving the resolution. Here we report that by using the two-dimensional pixel-function of an image sensor-array as an input to lensfree image reconstruction, pixel-super-resolution can improve the numerical aperture of the reconstructed image by ~3 fold compared to a raw lensfree image. This improvement was confirmed using two different sensor-arrays that significantly vary in their pixel-sizes, circuit architectures and digital/optical readout mechanisms, empirically pointing to roughly the same space-bandwidth improvement factor regardless of the sensor-array employed in our set-up. Furthermore, such a pixel-count increase also renders our on-chip microscope into a Giga-pixel imager, where an effective pixel count of ~1.6–2.5 billion can be obtained with different sensors. Finally, using an ultra-violet light-emitting-diode, this platform resolves 225 nm grating lines and can be useful for wide-field on-chip imaging of nano-scale objects, e.g., multi-walled-carbon-nanotubes.

/pdf/increased-space-bandwidth-product-in-pixel-super-resolved-1lgjxuk1zb.pdf

Increased space-bandwidth product in pixel super-resolved lensfree on-chip microscopy

Lab-on-a-chip systems have been rapidly emerging to pave the way toward ultra-compact, efficient, mass producible and cost-effective biomedical research and diagnostic tools. Although such microfluidic and microelectromechanical systems have achieved high levels of integration, and are capable of performing various important tasks on the same chip, such as cell culturing, sorting and staining, they still rely on conventional microscopes for their imaging needs. Recently, several alternative on-chip optical imaging techniques have been introduced, which have the potential to substitute conventional microscopes for various lab-on-a-chip applications. Here we present a critical review of these recently emerging on-chip biomedical imaging modalities, including contact shadow imaging, lens-free holographic microscopy, fluorescent on-chip microscopy and lens-free optical tomography.

On-Chip Biomedical Imaging

A major issue so far for digital holography is the low spatial resolution generally achieved. The numerical aperture is limited by the area of currently available detectors, such as CCD sensors, which is significantly lower than that of a holographic plate. This is an even more severe constraint when IR sensors such as microbolometers are taken into account. In order to increase the numerical aperture of such systems, we developed an automatic technique which is capable of recording several holograms and of stitching them together, obtaining a digital hologram with a synthetic but larger numerical aperture. In this way we show that more detail can be resolved and a wider parallax angle can be achieved. The method is demonstrated for visible as well IR digital holography, recording and displaying large size objects.

An automatic method for assembling a large synthetic aperture digital hologram

We study, both numerically and experimentally, the synchronization of uncoupled excitable systems due to a common noise. We consider two identical FitzHugh–Nagumo systems, which display both spiking and non-spiking behaviours in chaotic or periodic regimes. An electronic circuit provides a laboratory implementation of these dynamics. Synchronization is tested with both white and coloured noise, showing that coloured noise is more effective in inducing synchronization of the systems. We also study the effects on the synchronization of parameter mismatch and of the presence of intrinsic (not common) noise, and we conclude that the best performance of coloured noise is robust under these distortions.

https://iopscience.iop.org/article/10.1088/1367-2630/12/5/053040/pdf

Synchronization of uncoupled excitable systems induced by white and coloured noise

Digital Holography (DH) in the infrared (IR) range presents some peculiar aspects compared with the more common DH in the visible range. The current major drawback is due to the size of the pixel pitch of presently available thermal cameras, which is rather large compared to what would be optimal, and what is possible with analog films. However, since the ${\hbox{CO}}_{2}$ laser wavelength is 15 times longer than average visible wavelength, a much higher stability, a wider view angle, and shorter acquisition distances are achievable, allowing easier acquisition of large object holograms.

Reliability of 3D Imaging by Digital Holography at Long IR Wavelength

A circular holographic display that consists of phase-only spatial light modulators is used to reconstruct images in visible light from digital holograms recorded under infrared (10.6 μm) illumination. The reconstruction yields a holographic digital video display of a three-dimensional ghostlike image of an object floating in space where observers can move and rotate around it.

/pdf/visible-reconstruction-by-a-circular-holographic-display-2xrdxnrh86.pdf

A. Geltrude

Papers

An automatic method for assembling a large synthetic aperture digital hologram

Synchronization of uncoupled excitable systems induced by white and coloured noise

Reliability of 3D Imaging by Digital Holography at Long IR Wavelength

Visible reconstruction by a circular holographic display from digital holograms recorded under infrared illumination

Feedback control of bursting and multistability in chaotic systems