Turbidity breaks the diffraction barrier

LB13391

“Turbidity” caused by multiple scattering is normally considered detrimental to optical imaging. For example, translucent media such as biological tissues and a ground glass make an object underneath invisible. In our study, we developed a method of extracting the original image information from the multiple scattering. This enabled us to see through the turbid media. More importantly, we made a counter-intuitive finding that optical turbidity, rather than being a hindrance to imaging, can in fact dramatically improve both the spatial resolution and the field of view of the target images. In essence, our method turns a turbid medium into a unique and unconventional lens. We believe that this will lead to great important applications in deep-tissue biological imaging and super-resolution imaging.

Figure caption:

Live cell imaging under a rat skin tissue. (a) the image of a microglia cell hidden under a skin tissue. (b) reconstructed image from (a).

A trick for visual stabilization in a hovering bird

EBJ1059

- Using fundamental mechanics principles, we interpret the complicated phenomenon of visual stabilization in a flying bird. For birds, mechanisms of visual stabilization are of great significance because blurred vision resulting from vigorous body vibrations caused by wing flapping could seriously jeopardize their survival. Most relevant studies have attributed the bird’s vision stabilization to their nervous and musculoskeletal systems that sense and reduce the vibrations. In our study, however, we found that a flapping passerine exploits a trick to fix the eyes: the production of a lift force exerted posterior to the center of mass of the bird’s body. This trick concurrently results in rotational and translational displacements of the bird's body. Such a complicated body motion does not deteriorate the stability of the eye; instead, the eye remains stabilized because the displacement caused by body translation becomes an offset due to the displacement caused by body rotation. This trick for visual stabilization can offer bio-inspired guidance for engineers to enhance the visual stability of surveillance cameras incorporated in micro aerial vehicles.

Cancer Cells as Fractals: possible new way of cancer diagnostics

LB12649


- Here it was shown that the surface of human cervical epithelial cells demonstrates substantially different fractal behavior when the cell becomes cancerous. Fractals are "self-similar" irregular shapes that repeat their pattern when zoomed in or out. These complex disorderly patterns are typically formed under far-from-equilibrium conditions, or emerge from chaos. Examples of fractal shape range from the large-scale structure of the Universe to the shape of trees and snowflakes. This paper demonstrated that the surface of human cancer cells could be treated as fractal. Analyzing the adhesion images of individual cells obtained with atomic force microscopy, it was found that cancer cells demonstrate a simple fractal behavior, whereas normal cells could only be approximated at best as multifractal. This leads to an unusually high accuracy in identification of cancer at the single cell level. Although some difference in the surface of cancer cell was expected, the observed unambiguous divergence of the fractal behavior was a surprise. This may shed light on the nature of cancer from a new physics prospective. Furthermore, it can be used for early detection of cervical cancer with accuracy surpassing the existing methods.

St. Elmo’s fire helps emerging organic electronics

LD13757

- For centuries, sailors observed St. Elmo’s fire on ship masts before a storm: this intriguing phenomenon visualizes strong increase of the electric field at sharp conducting edges. Here we find that a remarkably similar effect appears in organic electronic devices at micro-scales, and it may be controlled to improve the device performance.

Everyday electronics is expected to be revolutionized by the introduction of organic polymer semiconductors, which are new “green” materials with unique properties and low cost. These soft polymers can be transformed in-situ from an insulating to highly conducting state via electrochemical doping. When voltage is applied, doping zones spread in the polymers in a manner similar to flame fronts. However, electrochemical doping is rather slow, which represents a serious obstacle for many technical applications. In this paper we obtain a new fundamental effect, doping front instability, which speeds up the process considerably. We find that small humps at a doping front produce local increase of the electric field, similar to St. Elmo’s fire, which, in turn, leads to further growth of the humps. As a result, the front becomes strongly corrugated and moves much faster. This new effect exhibits deep similarities to the speed-up of corrugated flames in car engines and in powerful star explosions, Supernovae.

At the Edge: Why Drops Spread

LA13026


- The spreading of a liquid drop on a solid surface is a simple everyday phenomenon, yet much of the process is complex and remains under investigation. Hydrodynamic analysis of the spreading leads to a non-physical singularity at the contact line, or the triple point where air, solid, and liquid meet. In 1919, Sir William Bates Hardy discovered that the edge of a spreading drop emits a microscopically thin layer of fluid, invisible to the naked eye. The existence of this "precursor film" relieves the singularity issue. In the mid-1980s, Pierre-Gilles de Gennes and coworkers developed a theoretical model for the precursor film, considering intermolecular forces close to the contact line. Since then, physicists have striven to capture experimental evidence of its behavior and characteristics. However, due to the film's nano-scale features, it has been a challenge to overcome the limitations of many detection techniques. Researchers have recently measured the dynamic evolution of the precursor film using fluorescence microscopy. This work is the first to provide experimental support for the theory governing the precursor film's behavior with respect to time and space.