IRP Focus: Imaging, Sensing & Networked Systems: Research Projects
Enabling Wireless Communications without Infrastructure
Sekhar Tatikonda, Dept. of Electrical Eng., Dept. of Statistics, Dept. of Comp. Sci.
In the modern world of wireless communications, a dynamic network is one where parameters change due to the mobility and traffic variations among users, and an ad hoc network is one in which devices organize themselves to create a wireless communication network. Dynamic ad hoc networks are highly useful in situations such as emergency rescue settings, military communications, sensor networks, and personal networking where only a lightweight infrastructure is possible, control of the network is not centralized, and there is a need for rapid deployment.
The engineering challenges to creating such networks, however, are numerous. The Tatikonda electrical engineering lab is working to optimize dynamic wireless ad hoc networks for more widespread use in situations where users’ parameters are constantly changing—where nodes are moving and the type of transmission, data or voice, is variable.
Simple algorithms exist for scheduling time and assigning frequencies for a small number of users, but Tatikonda and team are tackling what is known as the graph coloring problem. With different colors corresponding to different frequencies, they assign colors to each node so that there is no contention when there are many thousands of users. The Yale electrical engineers test their work in the field in collaboration with robotics engineers at the University of Texas, Austin, using fleets of all-terrain, semi-autonomous robots.
Their goal is to develop algorithms that are scalable, efficient, robust to changes, and local in order to accommodate many users without exhausting the available number of frequencies and without requiring communication across the entire network. Ideally, Tatikonda’s color graphing solution will enable each node in an ad hoc network to look only at its neighbors and determine what frequency is available.
In the News:
Is This Frequency Available? The Next Generation of Communication Networks
Interpreting and Quantifying Images with Computers
Hemant Tagare, Yale School of Medicine, Dept. of Biomedical Eng., Dept. of Electrical Eng.; Frederick Sigworth, Yale School of Medicine, Dept. of Biomedical Eng.; Hongwei Wang, Dept. of MB&B
Teaching a computer to understand and interpret an image is a difficult problem that engineers have long been trying to solve with sophisticated mathematics and computational power. The problem becomes especially challenging when the image is noisy, out of focus, or contains confusing extraneous information.
Hemant Tagare’s lab is developing algorithms that process biological or medical images to filter out the noise, detect weak signals, and quantify their geometric content. One example is the lab's new effort in creating three-dimensional protein structure from two-dimensional electron microscopy images of the protein. Electron microscopy protein images can be as unclear as the view through a window in a heavy rainstorm, but Tagare’s team takes noisy images of the protein from a variety of angles and processes them to recreate the protein's 3D structure.
In collaboration with Yale professors Frederick Sigworth and Hongwei Wang, the Tagare team is trying to create 3D models that capture the flexible structure of the Dicer protein. Dicer is known for its ability to chop up viral RNA that enters a cell. Modeling its structure could help explain how it does this, and perhaps enable scientists to manipulate or mimic that mechanism in other proteins. What sets Tagare’s efforts apart from engineers elsewhere who are trying to model Dicer is the interdisciplinary approach that relies on close collaboration among biophysicists, biochemists, and image processing experts.
Application of Systems Engineering To Human Motor Control
Kumpati Narendra, Dept. of Electrical Eng.
Controlling the human body is a formidable task. It takes the newborn baby countless experiments with its limbs to acquire motor control skills needed to ambulate. Most people take for granted the ability to control movement, unless of course they are afflicted with a movement disorder.
Since 2006, Kumpati Narendra has been collaborating with Peter Reeves (formerly a graduate student at Yale, now at Michigan State University) to apply systems engineering and control theory to the study of human motor control. For the past six years, they have been investigating the effects of control impairments on common conditions such as back pain; more recently they have initiated a study of Parkinson’s Disease (PD).
Research on Back Pain: Interest in controlling human movement has had a long and distinguished history. For instance, Giovanni Alfonso Borelli applied mechanistic theory in the 17th century to predict how much effort was required by muscles in the spine to support the body and external loads. Others developed more sophisticated models of the spine to predict loading on the spine and related it to risk of injury. However, it wasn’t until fairly recently that researchers started to investigate how a motor control error, an unintentional mistake in muscle recruitment, could lead to injury under relatively nominal loads.
To elaborate on this work, Reeves and Narendra examined, in a series of papers, how the central nervous system maintains stability of the spine, and suggested how different types of control impairments may be responsible for back pain.
N. P. Reeves, K. S. Narendra, and J. Cholewicki, “Spine Stability: The six blind men and the elephant.” Clinical Biomechanics, vol. 22, pp. 266-274, 2007.
N. Reeves, J. Cholewicki, and K. S. Narendra, “Effects of reflex delays on postural control during unstable seated balance.” Journal of Biomechanics, vol. 42, pp. 164-170, 2009.
N. P. Reeves, K. S. Narendra, and J. Cholewicki, “Spine Stability: lessons from balancing a stick.” Clinical Biomechanics, vol. 26, pp. 325-330, May 2011.
Research on Parkinson’s Disease
Jean Martin Charcot, father of neurology, coined the term Parkinson’s Disease, after a London doctor, James Parkinson, who wrote a paper entitled “An Essay on the Shaking Palsy” in 1817. However, it was only after Sherrington’s work on the nervous system was well established that PD was related to malfunctions within motor circuits.
At present PD is considered as a set of neurodegenerative conditions affecting humans. While no single cause is known to be responsible, it is attributed to the composite result of defects or changes in a number of benign biological processes. Narendra and Reeves believe (following the significant work done at the Hamilton Institute in Maynooth, Ireland), that a systems approach can be a most effective one for the study of PD. They are investigating systematically the effects of small changes in different cellular and metabolic subsystems on motor control. They also believe that the same models can be used to propose corrective actions that may be best suited for an individual.
An alternative form of treatment for PD is through external electrical stimulation. In the 1990s, experiments were described which showed spectacular results using such an approach. Stimulation of the subthalamic nucleus was shown to dramatically reduce Parkinson’s Disease symptoms and restore normal motor function. Since that time, this form of stimulation has evolved into a second form of treating PD. Recently, Narendra and Reeves have also initiated research on the effect of external stimulation on electro-chemical signals in biological systems.
Investigating Atomic Precision at the Oxide Interface
Eric I. Altman, Dept. of ChE & EnvE; Sohrab Ismail-Beigi, Dept. of Applied Physics, Dept. of Physics
For many materials scientists, what goes on at the interface between two different materials is where the excitement is. Long gone are the days when electronics developers glued materials together by hand. Today’s materials are sandwiched together with atomic-scale precision – an advancement that has led to the control of exotic solid-state phenomena, such as magnetism and superconductivity at the nanoscale and a promise of applications that will have broad-sweeping impact on the technologies of our time.
The Atomic Scale Design, Control, and Characterization of Oxide Structures Interdisciplinary Research Group at the Center for Research on Innovative Structures and Phenomena (CRISP), led by Yale Professor of Chemical and Environmental Engineering Eric Altman and Associate Professor of Applied Physics Sohrab Ismail-Beigi is investigating the novel chemical, electronic, and magnetic properties that emerge at interfaces between oxides. The group’s work revolves around crystalline oxides –common compounds that can exhibit nearly every possible effect seen in solid-state physics.
Oxide materials range from the very common, such as sand, to esoteric materials that include high temperature superconductors and materials that change from insulators to metals when placed near magnets. Because of their lattice structure, crystalline oxides of different chemical composition can be stacked together, allowing for atomic-scale sandwiching of a variety of materials. What goes on at the interface between materials is of great interest and sometimes surprising, as was the case when researchers found superconducting properties could be displayed between two insulating materials. It can take years to design and grow materials with atomic precision, but CRISP has some of the top “growers” in the field, a team of theorists, and four oxide molecular beam epitaxy (MBE) machines—the sophisticated vacuum systems that grow materials a single atomic layer at a time– as well as state-of-the-art characterization tools uniquely suited to determining the positions and identities of all of the atoms at the interface and their chemical bonding.
The group’s research focuses on designing new materials with unique physical properties; creating new computing, communication, and sensing devices enabled by the novel properties of oxide interfaces; and understanding and manipulating the interactions between electrons that give rise to the novel properties.
In the news:
The Center for Research on Interface Structures and Phenomena
At the Oxide Interface: Where Experimentalists Play