AIP’s Physics News HighlightsMarch 27, 2012

TOPICS IN THIS ISSUE:1. Wind Turbines That Learn Like Humans: A control algorithm inspired by human memory may increase wind turbine efficiency while requiring less computational power than other control methods.2. Writing Graphene Circuitry with Ion “Pens”: Researchers coax graphene to grow in previously defined patterns, offering a promising new tool in the quest to develop graphene-based electronic devices. 3. The Physics of Cancer: Perspectives at the crossroads of science and medicine: The behavior of cancer cells and research into new therapies are clearly important areas in biology and medicine. The physics community, however, has much to offer in understanding this disease and may provide unique insights into innovative treatments.4. Other Content: Upcoming Conferences of Interest; Physics Today: April Articles_______________________________________________________1. Wind Turbines That Learn Like HumansDepending on the weather, wind turbines can face whispering breezes or gale-force gusts. Such variable conditions make extracting the maximum power from the turbines a tricky control problem, but a collaboration of Chinese researchers may have found a novel solution in human-inspired learning models. Most turbines are designed to produce maximum allowable power once winds reach a certain speed, called the rated speed. In winds above or below the rated speed, control systems can make changes to the turbine system, such as modifying the angle of the blades or the electromagnetic torque of the generator. These changes help keep the power efficiency high in low winds and protect the turbine from damage in high winds. Many control systems rely on complex and computationally expensive models of the turbine’s behavior, but the Chinese group decided to experiment with a different approach. The researchers developed a biologically inspired control system, described in the American Institute of Physics’ Journal of Renewable and Sustainable Energy, that used memory of past control experiences and their outcomes to generate new actions. In simulations, the controller showed initially poor results, but quickly learned how to improve, matching the performance of a more traditional control system overall. The memory-based system is attractive because of its simplicity, the researchers write, concluding that “the human-memory-based method holds great promise for enhancing the efficiency of wind power conversion.”

Article: “A Bio-inspired Approach to Enhancing Wind Power Conversion” is accepted for publication in the Journal of Renewable and Sustainable Energy.

Authors: YongDuan Song (1, 2), WenChuan Cai (2), Peng Li, (2), and YongSheng Hu (3).(1) School of Automation, Chongqing University, China(2) School of Electronic and Information Engineering, Beijing Jiaotong University, China(3) China Datang Corp. Renewable Power Co. Ltd., Beijing, China

2. Writing Graphene Circuitry with Ion “Pens”The unique electrical properties of graphene have enticed researchers to envision a future of fast integrated circuits made with the one-carbon-atom-thick sheets, but many challenges remain on the path to commercialization. Scientists from the University of Florida have recently tackled one of these challenges – how to reliably manufacture graphene on a large scale. The team has developed a promising new technique for creating graphene patterns on top of silicon carbide (SiC). SiC comprises both silicon and carbon, but at high temperatures (around 1300 degrees Celsius) silicon atoms will vaporize off the surface, leaving the carbon atoms to grow into sheets of pure graphene. Researchers had previously used this thermal decomposition technique to create large sheets of graphene, which were then etched to make the patterns required for devices. The etching process, however, can introduce defects or chemical contaminants that reduce graphene’s prized electron mobility. In contrast, the Florida team’s technique allowed the researchers to confine the growth of graphene to a defined pattern as small as 20 nanometers. The team found that implanting silicon or gold ions in SiC lowered the temperature at which graphene formed by approximately 100 degrees Celsius. The team implanted ions only where graphene layers were desired, and then heated the SiC to 1200 degrees Celcius. At this temperature the pure SiC did not form graphene, but the implanted areas did. Using this technique, the team successfully created graphene nanoribbons, thin lines of graphene with nanoscale dimensions. With further refining, the process, described in the American Institute of Physics’ journal Applied Physics Letters, may be able to encourage selective graphene growth at even lower temperatures, the researchers write.

Article: “Drawing graphene nanoribbons on SiC by ion implantation” is published in Applied Physics Letters.

Authors: S. Tongay (1, 2), M. Lemaitre (1), J. Fridmann (3), A.F. Hebard (2), B.P. Gila (1), and B.R. Appleton (1).(1) Department of Material Science and Engineering, University of Florida(2) Department of Physics, University of Florida(3) Raith USA Inc., Ronkonkoma, New York

3. The Physics of Cancer: Perspectives at the crossroads of science and medicineThe American Institute of Physics’ journal AIP Advances features a special section that examines the behavior of tumors from a physical science perspective. The goal is to enable new ideas, grounded in the physical and mathematical sciences, to flow to the cancer research community. The main themes for the special section came from a workshop held in June 2011 at Princeton Physical Sciences Oncology Center.Researchers create cellular automation model to study complex tumor-host role in cancer

Cancer remains a medical mystery – despite all of the research efforts devoted to understanding and controlling it. The most sought-after tumor model is one that would be able to formulate theoretical and computational tools to predict cancer progression and propose individual treatment strategies. To better understand the role complex tumor-host interactions play in tumor growth, Princeton University researchers developed a cellular automation model for tumor growth in heterogeneous microenvironments. They then used this same model to investigate the effects of pressure on the growth of a solid tumor in a confined heterogeneous environment, such as a brain cancer growing in the cranium, and discovered that pressure accumulated during tumor growth can lead to a wide spectrum of growth dynamics and morphologies for both noninvasive and invasive tumors. Depending on the magnitude of the pressure and the physical properties of the host environment, the types of tumor patterns that emerge range from strongly malignant tumors characterized by finger-like protrusions at the tumor surface to those in which fingering growth is diminished. These results should have important applications for cancer diagnosis, prognosis, and therapy.

Article: “Diversity of dynamics and morphologies of invasive solid tumors” is published in AIP Advances.

Authors: Yang Jiao (1) and Salvatore Torquato (1,2,3,4,5).(1) Physical Science in Oncology Center, Princeton University, N.J.(2) Department of Chemistry, Princeton University, N.J.(3) Department of Physics, Princeton University, N.J.(4) Princeton Center for Theoretical Science, Princeton University, N.J.(5) Program in Applied and Computational Mathematics, Princeton University, N.J.

Photoacoustics technique detects small number of cancer cellsResearchers have developed multiple techniques and procedures to detect cancer cells during the earliest stages of the disease or after treatment. But one of the major limitations of these technologies is their inability to detect the presence of only a few cancer cells. Now, a research collaboration between the University of Missouri-Columbia and Mexico’s Universidad de Guanajuato shows that pulsed photoacoustic techniques, which combine the high optical contrast of optical tomography with the high resolution of ultrasound, can do just that, in vitro. Most cancer cells are naturally elusive, so they used a photoacoustic enhancer to detect them. New developments are necessary, the researchers say, to be able to properly use photoacoustic techniques to recognize different cancer cell types inside the human body or in blood or tissue samples.

Article: “An experimental and theoretical approach to the study of the photoacoustic signal produced by cancer cells” is published in AIP Advances.

Authors: Rafael Pérez Solano (1), Francisco I. Ramirez-Perez (1), Jorge A. Castorena-Gonzalez (2), Edgar Alvarado Anell (3), Gerardo Gutiérrez-Juárez (1), and Luis Polo-Parada (4, 5).(1) División de Ciencias e Ingenierías-Campus León, Universidad de Guanajuato, México(2) Department of Bioengineering, University of Missouri-Columbia(3) Facultad de Ingeniería en Computación y Electrónica, Universidad De La Salle, México(4) Department of Medical Pharmacology and Physiology, University of Missouri-Columbia(5) Dalton Cardiovascular Research Center, University of Missouri-Columbia

Using Game Theory to Understand the Physics of Cancer PropagationIn search of a different perspective on the physics of cancer, Princeton University and University of California, San Francisco researchers teamed up to use game theory to look for simplicity within the complexity of the dynamics of cooperator and cheater cells under metabolic stress conditions and high spatial heterogeneity. In the context of cancer, cooperator cells obey the general rules of communal survival, while cheater cells do not. The ultimate goal of this research was to gain an understanding of the dynamics of cancer tumor evolution under stress. Since cancer can be likened to a community of bacteria, the researchers zeroed in on a simple bacterial model to examine the progression of resistance to drugs under high competition and stress conditions. Among their key findings: they discovered emergent cooperative outcomes between the two cell types after modifying their game theory framework to account for heterogeneous stress patterns.

Article: “Physics of cancer propagation: A game theory perspective” is published in AIP Advances.

Authors: R Chris Cleveland (1), David Liao (2), and Robert Austin (1).(1) Department of Physics, Princeton University, N.J.(2) Department of Pathology, University of California, San Francisco

Androgen SuppressionAndrogen suppression – the inhibition of testosterone and other male hormones – is a routine therapy for prostate cancer. Unfortunately, it can dramatically reduce the quality of patients’ sex lives and, more importantly, lead to cancer recurrence in a more deadly androgen-independent form. A new paper combining mathematical modeling with clinical data validates a different approach: cycling patients on and off treatment. Such intermittent androgen suppression alleviates most unwanted side effects and postpones the development of resistance to treatment. With the model, the authors say, clinicians can predict the maximum length of treatment for a given patient before they become resistant, leading to more effective therapy.

Article: “A clinical data validated mathematical model of prostate cancer growth under intermittent androgen suppression therapy” is published in AIP Advances.

Authors: Travis Portz (1), Yang Kuang (2), and John D. Nagy (3).(1) School of Computing and Informatics, Arizona State University(2) School of Mathematical and Statistical Sciences, Arizona State University(3) Department of Biology, Scottsdale Community College, Ariz.

Quantum Effects and CancerThe theory of quantum metabolism is the idea that quantum processes, such as entanglement, influence the metabolism of cells. This idea offers scientists a new explanation for the metabolic changes that cause healthy cells to transform into cancerous ones. The metamorphosis gives cancerous cells the ability to outcompete healthy cells for space and nutrients, causing the disease to spread. Understanding the quantum metabolic underpinnings of the transformation could potentially lead to new types of treatment to stop cancer growth, researchers argue.

Article: “Implications of quantum metabolism and natural selection for the origin of cancer cells and tumor progression” is published in AIP Advances.

Authors: Paul Davies (1), Lloyd A. Demetrius (2,3), and Jack A. Tuszynski(4).(1) Beyond Center for Fundamental Concepts in Science, Arizona State University(2) Department of Organismic and Evolutionary Biology, Harvard University, Mass.(3) Max Planck Institute for Molecular Genetics, Germany(4) Department of Oncology, University of Alberta, Canada _____________________________________________________Upcoming Conferences of Interest• The Optical Society’s Conference on Lasers and Electro-Optics (CLEO) will be held May 6 – 11, 2012, in San Jose, Calif.http://www.cleoconference.org/• The Acoustical Society of America’s 163rd meeting will be held May 13 – 18, 2012, in Hong Kong, China.http://acousticalsociety.org/• The American Astronomical Society’s 220th meeting will be held June 10 – 14, 2012, in Anchorage, Alaska.http://aas.org/meetings/aas220

Physics Today: April Articleshttp://www.physicstoday.org1. Networks in motion: Networks that govern communication, growth, herd behavior, and other key processes in nature and society are becoming increasingly amenable to modeling, forecast, and control.2. Precious fossils of the infant universe: The ancient, metal-poor stars at the outskirts of the Milky Way provide a window on the conditions that governed the universe shortly after the Big Bang.3. Solar eruptive events: It’s long been known that the Sun plays host to the most energetic explosions in the solar system. But key insights into how they work have only recently become available.

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