Magnetic vortices in thin films can encode information in the perpendicular magnetization pointing up or down relative to the vortex core. These binary states could be useful for non-volatile data storage devices such as RAM memories, but the switching between them must be fast and energy-efficient. However, despite many efforts switching is still slow and requires very large currents. Pac-man disks, whose shape resembles the retro arcade game, seem to be a promising approach and Yoshinobu Nakatani and co-workers from the University of Electro-Communications now show a more efficient way of controlling switching in these devices ("Control of magnetic vortex core switching in a Pac-man disk using a single current pulse"). To better understand the mechanisms and the best switching conditions in the Pac-man disks, Nakatani's team used micro-magnetic simulations to investigate vortex core switching driven by an in-plane nanosecond current pulse. The simulations uncovered several interesting features. They found that the notch - Pac-man's mouth - plays the double role of annihilating and nucleating the vortex core. The kinetic field induced by the core motion gives the direction of nucleation. 
Prof. Nakatani team performed micro-magnetic simulations and took snapshots of the Pac-man disk (diameter = 200 nm, thickness = 40 nm) at different times (t = 0∼2.0 ns) .The rainbow images indicating the direction of the in-plane magnetization component, whereas the grayscale images show the out-of-plane magnetization (white,up; black,down). The vortex core switches from upward to downward. These results suggest that "by utilizing both the core switching at the notch edge and the direction of the core motion, the core polarity can be uniquely controlled by adjusting the direction of the current pulse". In this way the current density could be reduced by 75% compared with that of a circular disk of the same diameter and thickness. The insights provided by Nakatani's team could lead to an improved design of vortex core memory cells.
Prof. Nakatani team performed micro-magnetic simulations and took snapshots of the Pac-man disk (diameter = 200 nm, thickness = 40 nm) at different times (t = 0∼2.0 ns) .The rainbow images indicating the direction of the in-plane magnetization component, whereas the grayscale images show the out-of-plane magnetization (white,up; black,down). The vortex core switches from upward to downward. These results suggest that "by utilizing both the core switching at the notch edge and the direction of the core motion, the core polarity can be uniquely controlled by adjusting the direction of the current pulse". In this way the current density could be reduced by 75% compared with that of a circular disk of the same diameter and thickness. The insights provided by Nakatani's team could lead to an improved design of vortex core memory cells.
Composite photonic crystal cavity formed by combining an optical nanofiber and a nanofabricated grating. The PL intensity spectra of single quantum dots show strong enhancement at the cavity resonance demonstrating the cavity QED effect. "We have been working with our industrial partner Ishihara Sangyo Inc. to develop equipment for producing tapered nanofibers," explains Hakuta. "The resulting 400 nm diameter tapered fibers have 99% light transmission." A critical technology is to pick up single quantum dots from colloidal solution and deposit it on the nanofiber. This is accomplished using a computer controlled pico-liter liquid dispenser combined with an inverted microscope and precision translation stages. Photon counting experiments show the realization of single quantum dot deposition with spatial accuracy better than 3µm, and importantly, the maximum photon channelling efficiency is measured to be 22.0% as predicted from the theory. Furthermore, Hakuta and colleagues have developed a novel method to enhance this photon channelling efficiency by incorporating cavity structures. They are developing two methods. "On one hand, we can produce photonic crystal nanofibers with an array of thousands of highly ordered nano-craters using femto second lasers" explains Hakuta. "We were surprised to find highly periodic craters produced on the shadow sides of the nanofibers. Promptly we understood, it is due to the lensing effect of the nanofiber itself. On the other hand we are developing composite nanofiber cavities with external nano-grating structures". Using these composite nanofiber cavities they have demonstrated cavity QED with single quantum dots. This research has the potential of being a new paradigm in cavity QED, and forms the basis for quantum internet and other applications. Furthermore, femto-second laser fabricated photonic crystal nanofiber cavities coupled with cold atoms can realize various manipulation methods of single photons which offer the basic tools for the next generation of internet communications. References R. R. Yalla, M. Sadgrove, K. P. Nayak, and K. Hakuta. "Cavity quantum electrodynamics on a nanofiber using a composite photonic crystal cavity," . 113, 143601 (2014). K. P. Nayak, P. Zhang, and K. Hakuta, "Optical nanofiber based photonic crystal cavity," 39, 232 (2014). M. Sadgrove, R. R. Yalla, K. P. Nayak, and K. Hakuta. "Photonic crystal nanofiber using an external grating," 38, 2542 (2013). K. P. Nayak and K. Hakuta, "Photonic crystal formation on optical nanofibers using femtosecond laser ablation technique," 21, 2480 (2013). R. R. Yalla, Fam Le Kien, M. Morinaga, and K. Hakuta, "Efficient channeling of fluorescence photons from single quantum dots into guided modes of optical nanofiber," 109, 063602 (2012). R. R. Yalla, K. P. Nayak, and K. Hakuta, "Fluorescence photon measurements from single quantum dots on an optical nanofiber," 20, 2932 (2012).
Illinois professor Kyekyoon “Kevin” Kim, graduate student Elizabeth Joachim and research scientist Hyungsoo Choi developed tiny gelatin nanoparticles that can carry medication to the brain, which could lead to longer treatment windows for stroke patients. The researchers found that gelatin nanoparticles could be laced with medications for delivery to the brain, and that they could extend the treatment window for when a drug could be effective. Gelatin is biocompatible, biodegradable, and classified as “Generally Recognized as Safe” by the Food and Drug Administration. Once administered, the gelatin nanoparticles target damaged brain tissue thanks to an abundance of gelatin-munching enzymes produced in injured regions. The tiny gelatin particles have a huge benefit: They can be administered nasally, a noninvasive and direct route to the brain. This allows the drug to bypass the blood-brain barrier, a biological fence that prevents the vast majority of drugs from entering the brain through the bloodstream. “Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of most neurological disorders,” said Choi. “However, if drug substances can be transferred along the olfactory nerve cells, they can bypass the blood-brain barrier and enter the brain directly.” To test gelatin nanoparticles as a drug-delivery system, the researchers used the drug osteopontin (OPN), which in rats can help to reduce inflammation and prevent brain cell death if administered immediately after a stroke. “It is crucial to treat ischemic strokes within three hours to improve the chances of recovery. However, a significant number of stroke victims don’t get to the hospital in time for the treatment,” Kim said. By lacing gelatin nanoparticles with OPN, the researchers found that they could extend the treatment window in rats, so much so that treating a rat with nanoparticles six hours after a stroke showed the same efficacy rate as giving them OPN alone after one hour – 70 percent recovery of dead volume in the brain. The researchers hope the gelatin nanoparticles, administered through the nasal cavity, can help deliver other drugs to more effectively treat a variety of brain injuries and neurological diseases. “Gelatin nanoparticles are a delivery vehicle that could be used to deliver many therapeutics to the brain,” Choi said. “They will be most effective in delivering drugs that cannot cross the blood-brain barrier. In addition, they can be used for drugs of high toxicity or a short half-life.“