Adaptive Lens Research Articles

Looking at the effects of performance-based financing through a complex adaptive systems lens

The debate on PBF is misdirected. As is too often the case in international aid financing, agencies try to prove the effectiveness of their contribution by isolating it as the main reason for success.1 In reaction, opponents will often use the same approach in an attempt to prove that another factor is actually the cause of an observed change. We argue that this endless and futile debate, often present among experts in health systems strengthening, will not contribute to improving public health in low-income countries. Rather than searching for the impossible proof of whether PBF works or not, we should instead try to learn useful lessons from experiences. We agree with Ireland et al. that the focus of PBF assessment should be on “why” and “how” the intervention works.2 Comprehensive evaluation of PBF is needed as part of complete health system reform. We think that, to respond to some of these key questions, health systems should be analysed using a complex adaptive systems lens, as others have advocated in the past.3,4 A complex adaptive system is a collection of interacting components, each of which has its own rules and responsibilities. The behaviour of this kind of system is different to the sum of the behaviour of each of its components. Examples of complex adaptive systems include the human brain, ecosystems and manufacturing businesses. Health system “behaviour” and particularly counterintuitive behaviour (unexpected changes or lack of change) can be analysed using a complex adaptive systems lens when PBF is introduced, often with a mix of other interventions such as in a context of system reform. The purpose of this analysis is not to isolate causal factors but rather to identify “macro” characteristics of the system that may explain behaviour change. Although it has often been ignored in health system evaluation, social simulation can be useful for this approach. The most frequently used technique, agent-based modelling, uses computer simulation centred on a collection of autonomous agents whose interactions are based on a set of rules. These simulations can integrate empirical data or existing knowledge or opinions.5 One of the powerful features of agent-based modelling lies in its capacity to study complex phenomena in a simple and flexible way. Indeed, this approach does not require a high level of mathematical or programming skills, making it accessible to many researchers. Furthermore, it allows for an iterative learning process that is easy to set up compared to long and costly data collection processes. While this methodological approach may not “prove” the effectiveness of an intervention, it could provide insight into the reason a health system behaves in a given way (whether it changes or remains in a steady-state) when PBF is introduced. We believe that this type of information, although maybe less appealing to the usual stakeholders in development aid debates, is much more useful in evaluating PBF.

Graphene bubbles with controllable curvature

Raised above the substrate and elastically deformed areas of graphene in the form of bubbles are found on different substrates. They come in a variety of shapes, including those which allow strong modification of the electronic properties of graphene. We show that the shape of the bubble can be controlled by an external electric field. This effect can be used to make graphene-based adaptive focus lenses.

Induced aberrations by combinative convex/concave interfaces of refractive‐index‐mismatch and capability of adaptive optics correction

AbstractAdjustable fluidic adaptive lenses have been extensively studied because of the advantage of changing the geometric shape or refractive index without any mechanical moving parts. However, the induced aberrations were rarely discussed before. We address this issue by first clarifying the aberrations experimentally due to injected fluidic volumes. Experimental results show that under the injected fluidic volume of 0.1 ml, the main aberrations come from Z1 (piston), Z2 (tip), and Z5 (defocus) and Zernike coefficients are 0.97, 0.31, and 1.31 μm, respectively. In what follows, a series of tests specifically designed to explore the convex/concave interfaces and refractive‐index‐mismatch (RIM). Furthermore, we demonstrate the capability of adaptive optics (AO) correction on aberrations induced by combinative effects of multiple layers with convex/concave interfaces and RIM. A microelectro‐mechanical system (MEMS) deformable mirror (DM) with 140 actuators was used in conjunction with Shack–Hartmann wavefront sensor to realize the experimentation. In particular, we consider the aberration introduced by interfaces of RIM between water/oil and glass. After AO correction, we can improve wavefront with root mean square (RMS) of 2.17–0.17 μm for an interface between water and glass. As for the interface between oil and glass, we are capable of improving RMS of 0.24–0.10 μm. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2610–2615, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26323

Design of polarization-insensitive multi-electrode GRIN lens with a blue-phase liquid crystal

We report the design and simulation results of an adaptive GRIN lens based on multi-electrode addressed blue phase liquid crystal. A high dielectric constant layer helps to smoothen out the horizontal electric field and reduce the operating voltage. Such a GRIN lens is insensitive to polarization while keeping parabolic phase profile as the focal length changes.

An adaptive MR‐compatible lens and objective

AbstractThis work presents an MR‐compatible adaptive liquid lens, designed to form part of an in‐bore optical imaging system. The lens is integrated into a wide‐angle objective, which is suitable for use with a camera mounted above the head coil to monitor subject head motion. Compatibility tests indicate that focusing of the lens is unaffected by the static, gradient, or radio frequency (RF) fields of the scanner. Field mapping shows that no B0 field distortions are visible with the system mounted 55 mm above a water‐filled phantom. The total increase in RF noise observed on a 1.5‐T system when using the lens and lighting setup is less than 2%, and this is mostly attributable to the lighting. This work was originally motivated by head tracking for prospective motion correction; however, the lens may have other applications whenever high‐quality optical images are required in the MR environment and motion of the object makes a fixed lens unsuitable. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 39B: 141–148, 2011

Russia’s Perfect Firestorm: Climate Adaptation Lessons from the Summer of 2010

Record-high temperatures, drought, and ensuing wildfires devastated Central Russia in the summer of 2010. But even before the temperatures and smog peaked, many started wondering about a possible connection between the natural disaster and climate change. In this paper I view Russia’s response to the 2010 fires (prevention and suppression) through the lens of climate adaptation. Namely, I examine the damage from the fires, as well as how the causes of the fires connect to climate change. Additionally, I review Russia’s response to the forest fires and analyze the legal and policy framework that served as the foundation for the response. Finally, after summarizing the results of my inquiry, I examine the Russian government’s policy response to the 2010 fires with a particular focus on amendments to the Forestry Code and the new Federal Law, “On Volunteer Firefighting Force.”

Variable aperture stop based on the design of a single chamber silicone membrane lens with integrated actuation

In this Letter we report on the fabrication and testing of an extremely thin variable aperture stop based on the design of a single chamber adaptive membrane lens with integrated actuation. The aperture consists of a ring-shaped piezoelectric bending actuator with an elastic silicone membrane in the center. The formed cavity is filled with a nontransparent fluid and sealed with a glass platelet. In a voltage range up to 80 V, an opening of the aperture of 4.55 mm in diameter is obtained. The transmission in comparison to a standard mechanical aperture stop is maximum 6% lower.

Adaptive lenticular lens array using a hybrid liquid crystal–carbon nanotube nanophotonic device

We present a switchable liquid crystal cylindrical lens array fabricated with a combination of a sparse electrode array of multiwall carbon nanotubes (MWCNTs) grown upon a silicon substrate, and a second glass substrate featuring an in-plane switching (IPS) electrode structure. A cylindrical shape of an electric field profile was produced between the MWCNT substrate and the IPS substrate. This cylindrical shape was controlled by the application of an external electric field. The average focal lengths at different voltages were calculated. This adaptive lenticular lens array can be used in autostereoscopic displays.

Coupled economic-ecological systems with slow and fast dynamics — Modelling and analysis method

The purpose of this article is to contribute to the exploration of non-convex dynamics in coupled human-nature systems. We study welfare issues associated with the management of a human-nature complex adaptive system with a threshold and a stochastic driver. We exemplify with a specific system where we link changes in the number and diversity of birds to the abundance of a pest (insects) that causes damages to goods and services valuable to human beings. We present a method that simplifies the analysis and helps us discuss different management models that combine direct and indirect controls of the pest. This allows us to show that 1) the choice of control method depends in a highly non-linear way on biodiversity characteristics and 2) the socially optimal outcome may not be reachable using price instruments. Hence the price vs. quantity debate needs to be revisited using a complex adaptive system lens.

Adaptive mechanical-wetting lens actuated by ferrofluids

We report an adaptive mechanical-wetting lens actuated by ferrofluids. The ferrofluids works like a piston to pump liquids in and out from the lens chamber, which in turn reshapes the lens curvature and changes the focal length. Both positive and negative lenses are demonstrated experimentally. The ferrofluid-actuated mechanical-wetting lens exhibits some attractive features, such as high resolution, fast response time, low power consumption, simple structure and electronic control, weak gravity effect, and low cost. Its potential applications in medical imaging, surveillance, and commercial electronics are foreseeable.

Electromagnetic liquid pistons for capillarity-based pumping

The small scales associated with lab-on-a-chip technologies lend themselves well to capillarity-dominated phenomena. We demonstrate a new capillarity-dominated system where two adjoining ferrofluid droplets can behave as an electronically-controlled oscillator or switch by an appropriate balance of magnetic, capillary, and inertial forces. Their oscillatory motion can be exploited to displace a surrounding liquid (akin to an axial piston pump), forming electromagnetic "liquid pistons." Such ferrofluid pistons can pump a precise volume of liquid via finely tunable amplitudes (cf. pump stroke) or resonant frequencies (cf. pump speed) with no solid moving parts for long-term operation without wear in a small device. Furthermore, the rapid propagation of electromagnetic fields and the favorable scaling of capillary forces with size permit micron sized devices with very fast operating speeds (∼kHz). The pumping dynamics and performance of these liquid pistons is explored, with experimental measurements showing good agreement with a spherical cap model. While these liquid pistons may find numerous applications in micro- and mesoscale fluidic devices (e.g., remotely activated drug delivery), here we demonstrate the use of these liquid pistons in capillarity-dominated systems for chip-level, fast-acting adaptive liquid lenses with nearly perfect spherical interfaces.

A novel adaptive mechanical-wetting lens for visible and near infrared imaging

We demonstrate an adaptive mechanical-wetting lens with a concentric reservoir to reduce image aberrations and overcome the gravity effect. This lens adopts liquid pressure to change the interface between two immiscible liquids which, in turn, changes the focal length of the resultant liquid lens. Good optical performance, high resolution, and a wide dynamic range of both positive and negative optical power are achieved. Since no PDMS is employed, such lenses can extend their working range to infrared region by choosing proper liquids.

Low aberrations symmetrical adaptive modal liquid crystal lens with short focal lengths

We describe the design, fabrication, and characterization of modal liquid crystal lenses (MLCLs) with a symmetrical electrode structure using a resistive composite polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). We achieved MLCLs with shorter focal lengths (up to 1cm), shorter apertures (1 to 5mm), and lower aberrations compared to other MLCLs. We demonstrate a very uniform conductivity distribution in the PEDOT-PSS layers over a wide resistivity range (100kOmega/sq-10MOmega/sq) combined with a symmetrical electrode structure, enabling us to manufacture MLCLs with short f-numbers, large depths of focus, and low aberrations.

Moving Beyond Fidelity Expectations: Rethinking Curriculum Reform for Controversial Topics in Post-Communist Settings

This study explores the implementation of a Holocaust curriculum, designed for Latvian schools through the method of curriculum deliberation, five years after its enactment. By exploring the complexity of implementation, the study provides a generative knowledge base for curriculum proposals, symposia, and other initiatives that seek to disrupt reticence on silenced controversial histories in post-communist and post-authoritarian states. The findings reveal the promises and challenges of implementation through a mutual adaptation lens, including the forces of student interest, academic freedom, institutional support, teacher training, and the structure and organization of curriculum. Similar to other post-communist and post-authoritarian states, Latvia faces a number of challenges, including the legacy of communism, the Ministry of Education's prescribed curriculum, few opportunities to address controversies, and limited instructional time.

Characterisation of Adaptive Fluidic Silicone-Membrane Lenses

We compare the performance and optical quality of two types of adaptive fluidic silicone-membrane lenses. The membranes feature either a homogeneous thickness, or they are shaped resulting in an inhomogeneous cross-section. The lens systems incorporate a piezoelectric actuator which is operated in a regime of ±40 V. The shaped membrane lenses show lower wave front errors than the planar ones, down to 24 nm. The pumping actuator indicates a maximum pump volume of 1159 nl at an inner piezo radius of 2.75 mm for the smallest supporting ring configuration. The full system with a planar membrane achieves a larger refractive power ranging from +19 to -14 dpt. It also shows a shorter full scale response time ( tplanar = 23.9 ms) compared to the shaped membrane ( tshaped = 35.4 ms).

X-ray nanofocusing by kinoform lenses: A comparative study using different modeling approaches

We conduct a comparative study on various kinoform lenses (KLs) for x-ray nanofocusing by using the geometrical theory, the dynamical diffraction theory, and the beam propagation method. This study shows that the geometrical theory becomes invalid to describe the performance of a KL for nanofocusing. The strong edge diffraction effect from individual lens element, which distorts the desired wave field, leads to a reduction in the effective numerical aperture and imposes a limit on how small a focus a KL can achieve. Because this effect is associated with a finite thickness of a lens, larger lens thickness depicts a stronger distortion. We find that a short KL where all lens elements are folded back to a single plane shows an illumination preference: if the illuminating geometry is in favor of the Bragg diffraction for a focusing order, its performance is enhanced and vice versa. We also find that a short KL usually outperforms its long version where all lens elements do not lie in a single plane because the short one suffers less the wave field distortion due to the edge diffraction. Simulation results suggest that for a long KL, an adaptive lens design is needed to correct the wave field distortion in order to achieve a better performance.

Chapter 4 - Adaptive Lens

Publisher Summary Adaptive or varifocal lenses with variable focusing powers have attracted much attention because of their wide applications in vision care, consumer electronics such as digital cameras, aberration correction, optical interconnects, and three-dimensional biomedical imaging. The focal power of an optical system is usually changed by nonlinear movement of lenses with spherical or cylindrical powers along the optical axis and such a system consists of several lens components. A lot of efforts have been devoted to the research in adaptive lens. Recent advances in this field have been reviewed in this chapter. For liquid crystal lens, refractive and diffractive LC lenses based on discrete electrodes, hole-patterned electrodes, modal control electrode, hybrid alignment, and polymer/LC materials have been discussed in detail. For liquid lenses, lenses based on mechanic pressure, electrowetting effect, dielectric effect, and hydrogel and thermal effect have been reviewed. Examples of applications in vision care, aberration compensation, zoom lens, and optical tweezers have been discussed.

Nanoimprint lithography for optic fluidics with phase gratings for environmental monitoring application

Optic fluidic devices, which combine optical elements such as adaptive optical lenses or diffraction gratings into micro-fluidic devices, are now becoming increasingly important for environmental monitoring, medical diagnostics and chemical detection. In this paper, we present a novel and simple micro/nanofabrication process for SU-8 based optic fluidics structures with phase gratings on the bottom of the micro-channel using our silicon grating templates. The refraction index difference between the fluid and the SU-8 gratings generates a modulation in the phase of the light passing through the device. Our method of fabricating optic fluidic device is promising to be economic in fabrication, high throughput in production and have potential applications for sensing.

Adaptive liquid lens actuated by photo-polymer

An adaptive liquid lens actuated by a photo-polymer is demonstrated. The lens cell consists of a top glass substrate and a bottom plastic slab with two holes: reservoir hole and lens hole, which are sealed with elastic membranes. A photo-sensitive polymer is attached to the membrane of the reservoir hole. Under blue light irradiation, the polymer is bent which exerts a pressure to regulate the curvature of the membrane on the lens hole and then change the focal length of the plano-convex lens. The focal length is tunable from infinity to 21.2 mm in seconds. Non-mechanical driving, easy integration with other optical components and compact system are the key features of this lens.

Optical characterization of adaptive fluidic silicone-membrane lenses

We present an extended optical characterization of an adaptive microfluidic silicone-membrane lens at a wavelength of 633 nm, respectively 660 nm. Two different membrane variations; one with a homogeneous membrane thickness, and one with a shaped cross section, have been realized. This paper includes the theoretical predictions of the optical performance via FEM simulation and ray tracing, and a subsequent orientation dependent experimental analysis of the lens quality which is measured with an MTF setup and a Mach-Zehnder interferometer. The influence of the fabrication process on the optical performance is also characterized by the membrane deformation in the non-deflected state. The lens with the homogeneous membrane of 5 mm in diameter and an aperture of 2.5 mm indicates an almost orientation independent image quality of 117 linepairs/mm at a contrast of 50%. The shaped membrane lenses show a minimum wave front error of WFE(RMS) = 24 nm, and the lenses with a planar membrane of WFE(RMS) = 31 nm at an aperture of 2.125 mm.