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.

No abstract

No abstract

The beam intensity upgrade of the main ring of the Japan Proton Accelerator Research Complex (J-PARC) have been studied with simulations. The main ring delivered 30 GeV proton beams with the beam power of 500 kW at maximum to the neutrino facility in the recent operation. The number of accelerated protons was 2.61×10 14 protons per pulse (ppp). The upgrade plan aims at a beam power of 1.3 MW with reduced cycling time of 1.16 s compared to the present cycle time of 2.48 s. Upgrades of the magnet power supplies and RF system are in progress to achieve faster cycling. Furthermore, an intensity upgrade to 3.3×10 14 ppp is necessary, while keeping the beam loss under control to reduce residual radiation. The high intensity operation has been simulated with the particle tracking program SCTR, taking space charge effects into account. The simulations were performed for the present beam intensity to reproduce the present status of the beam loss and for the target beam intensity to estimate the beam loss. We studied the interaction of the beam with structure resonances as main cause of the beam loss. Possible alternative operational tunes were explored to improve beam survival.

No abstract