January 3, 2013
Physics News Highlights of the American Institute of Physics (AIP) contains summaries of interesting research from the AIP journals, notices of upcoming meetings, and other information from the AIP Member Societies. Copies of papers are available to journalists upon request.
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TOPICS IN THIS ISSUE:
1. Sorting Sterm Cells
When an embryonic stem cell is in the first stage of its development it has the potential to grow into any type of cell in the body, a state scientists call undifferentiated. A team of researchers from Scotland has now demonstrated a way to easily distinguish undifferentiated embryonic stem cells from later-stage stem cells whose fate is sealed. The results are published in the American Institute of Physics’ (AIP) journal Biomicrofluidics. The researchers used an electric field to pull stem cells through a fluid in a process called dielectrophoresis. They varied the frequency of the voltage used to generate the electric field and studied how the cells moved, a response that was affected by the cell’s electrical properties. The researchers found that differentiated stem cells could store a significantly greater charge on their outer membranes, a characteristic that might be used to effectively identify and separate them from undifferentiated cells. The researchers write that the wrinkling, folding, and thinning of a cell’s membrane as it differentiates may explain why the later-stage cells can store more charge. The sorting method may prove useful in separating cells for biomedical research or ultimately for treatments of diseases such as Parkinson’s.
2. Power Spintronics: Producing AC Voltages By Manipulating Magnetic Fields
Scientists are putting a new spin on their approach to generating electrical current by harnessing a recently identified electromotive force known as spinmotive force, which is related to the field of spintronics that addresses such challenges as improving data storage in computers. Now, a novel application of spintronics is the highly efficient and direct conversion of magnetic energy to electric voltage by using magnetic nanostructures and manipulating the dynamics of magnetization. According to a report published in the American Institute of Physics’ (AIP) journal Applied Physics Letters, this conversion could be the foundation for future development of spin-based power electronics, a field the authors call "power spintronics.” Their newly published results of an experimental model suggest that a power spintronics-based device may one day be a promising approach to obtaining alternating current (AC) voltages from direct current (DC) magnetic fields. The researchers demonstrated for the first time the feasibility of a device that generates a voltage based on manipulating an effective magnetic field within a nanowire that arises from width modulation. Technically such a field is not a true magnetic field, but it can be viewed as such. The team tested a one-dimensional model. It showed that DC magnetic field characteristics such as magnitude, and design parameters such as wire width, can be used to control, or "tune," the frequency and amplitude of AC current. Importantly, their results showed that a variable frequency ranging from megahertz to gigahertz can be achieved. Control and range in tuning ability are highly desirable management features in generating current. The team’s results suggest that applying their spintronics approach may one day meet a variety of commercial energy demands due to control and scalability.
3. Liquid Jets and Bouncing Balls Combine for Surprising Results
A new study published in the American Institute of Physics’ (AIP) journal Physics of Fluids reveals that the normal rebounding of a ball changes when it is partially filled with a liquid. Unlike an empty sphere or a solid rubber ball, which both rebound in a classical and well-understood fashion, a fluid-filled ball has its second bounce remarkably cut short. A team of researchers from Brigham Young University in Provo, Utah, uncovered this phenomenon when they investigated what would happen if a sphere were partially filled with a liquid and how that would affect the way it bounces. To their surprise, they discovered that on the first bounce the sphere behaved rather predictably, but on the second bounce it produced more of a thud than a bounce. The reason for the stalled second bounce is that a large portion of the energy of the ball-liquid system is transferred from a falling mass into a liquid jet, dampening the rebound force. This form of passive dampening was produced when two separate masses (sphere and liquid) that once behaved as one were suddenly separated, or decoupled. As revealed in high-speed images, this decoupling didn't occur until the second bounce because the surface of the liquid first had to be perturbed by the initial bounce. The researchers hope to apply these insights to engineer better methods of mitigating violent motions, ranging from improved sport helmet designs to removing some of the force associated with waves slamming into boats. Further research will also help answer additional questions about the scale of the phenomenon, as well as how other types of fluids (such as non-Newtonian fluids) might react under the same circumstances.
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Entries are requested for the American Institute of Physics’ 2013 Science Communication Awards, which recognize effective science communication, both in print and new media, that improves the general public's appreciation of physics, astronomy, and allied science fields.
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