Electro-microinjection of fish eggs with an immobile capillary electrode

Microinjection with ultra-fine glass capillaries is widely used to introduce cryoprotective agents and other foreign molecules into animal cells, oocytes, and embryos. The fragility of glass capillaries makes difficult the microinjection of fish eggs and embryos, which are usually protected by a hard outer shell, called the chorion. In this study, we introduce a new electromechanical approach, based on the electropiercing of fish eggs with a stationary needle electrode. The electropiercing setup consists of two asymmetric electrodes, including a μm-scaled nickel needle placed opposite to a mm-scaled planar counter-electrode. A fish egg is immersed in low-conductivity solution and positioned between the electrodes. Upon application of a short electric pulse of sufficient field strength, the chorion is electroporated and the egg is attracted to the needle electrode by positive dielectrophoresis. As a result, the hard chorion and the subjacent yolk membrane are impaled by the sharp electrode tip, thus providing direct access to the egg yolk plasma. Our experiments on early-stage medaka fish embryos showed the applicability of electro-microinjection to fish eggs measuring about 1 mm in diameter. We optimized the electropiercing of medaka eggs with respect to the field strength, pulse duration, and conductivity of bathing medium. We microscopically examined the injection of dye solution into egg yolk and the impact of electropiercing on embryos'' viability and development. We also analyzed the mechanisms of electropiercing in comparison with the conventional mechanical microinjection. The new electropiercing method has a high potential for automation, e.g., via integration into microfluidic devices, which would allow a large-scale microinjection of fish eggs for a variety of applications in basic research and aquaculture.     

Blockbusters and market expansion: evidence from the motion picture industry

Like other cultural industries, the theatrical film industry is subject to the ‘blockbuster effect’, where popular products often dominate their competition by orders of magnitude over relatively short-run time horizons. This paper investigates this particular feature of the industry and the implication for overall market size. Using simple regression analysis, a positive relationship between (product-level) market concentration and market size is established using weekly box office revenue data from the US motion picture industry. This empirical evidence supports a simple theoretical model of heterogeneous consumers who selectively participate in the market.     

Effects of differently polarized microwave radiation on the microscopic structure of the nuclei in human fibroblasts

To investigate the influence of microwave radiation on the human fibroblast nuclei, the effects of three variants of electromagnetic wave polarization, linear and left-handed and right-handed elliptically polarized, were examined. Experimental conditions were: frequency (f) 36.65 GHz, power density (P) at the surface of exposed object 1, 10, 30, and 100 μW/cm², exposure time 10 s. Human fibroblasts growing in a monolayer on a cover slide were exposed to microwave electromagnetic radiation. The layer of medium that covered cells during microwave exposure was about 1 mm thick. Cells were stained immediately after irradiation by 2% (w/v) orcein solution in 45% (w/v) acetic acid. Experiments were made at room temperature (25 °C), and control cell samples were processed in the same conditions. We assessed heterochromatin granule quantity (HGQ) at 600× magnification. Microwave irradiation at the intensity of 1 μW/cm² produced no effect, and irradiation at the intensities of 10 and 100 μW/cm² induced an increase in HGQ. More intense irradiation induced more chromatin condensation. The right-handed elliptically polarized radiation revealed more biological activity than the left-handed polarized one.     

The Development of Attention to Objects and Scenes: From Object-Biased to Unbiased

Selective attention is the ability to focus on goal-relevant information while filtering out irrelevant information. This work examined the development of selective attention to natural scenes and objects with a rapid serial visual presentation paradigm. Children (N = 69, ages 4–6 years) and adults (N = 80) were asked to attend to either objects or scenes, while ignoring the other type of stimulus. A multinomial processing tree model was used to decompose selective attention into focusing and filtering components. The results suggest that attention is object-biased in children, due to difficulty filtering attention to goal-irrelevant objects, whereas attention in adults is relatively unbiased. The findings suggest important developmental asymmetries in selective attention to scenes and objects.     

Single landmark feedback-based time optimal navigation for a differential drive robot

In this paper, we propose a feedback-based control approach to execute the time optimal motion trajectories for a differential drive robot. These trajectories are composed of straight lines and rotations in place. We show that the evolution of the position of a single landmark over time, in a local reference frame, makes it possible to track a prescribed time-optimal robot’s trajectory, based on feedback of the landmark’s position. We also show that the closed-loop system is an exponentially stable one with a nonvanishing perturbation, and that globally uniformly ultimately boundedness of the tracking errors can be achieved. The two main results of this work are: 1) Our approach leverages visual servo control type of methods with tools from optimal control for executing time-optimal trajectories in the state space based on feedback information. 2) The approach is able to work with the minimum number of landmarks–only one–this represents a necessary and sufficientcondition for landmark-based navigation. Experiments in a physical robot, a nonholonomic differential drive system equipped with an omnidirectional laser sensor, are shown, which validate the proposed theoretical modelling.