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Topics - Md. Khalid Hasan

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EEE / Speeding swarms of sensor robots
« on: May 10, 2018, 01:07:00 PM »

Concerns about the spread of radiation from damaged Japanese nuclear reactors — even as scientists are still trying to assess the consequences of the year-old Deepwater Horizon oil spill — have provided a painful reminder of just how important environmental monitoring can be. But collecting data on large expanses of land and sea can require massive deployments of resources.

At the Institute of Electrical and Electronics Engineers’ International Conference on Robotics and Automation in May, MIT researchers will present a new algorithm enabling sensor-laden robots to focus on the parts of their environments that change most frequently, without losing track of the regions that change more slowly. At the same conference, they’ll present a second paper describing a test run of the algorithm on underwater sensors that researchers at the University of Southern California (USC) are using to study algae blooms.

The work of Daniela Rus, a professor of computer science and electrical engineering, and postdocs Mac Schwager and Stephen Smith (now an assistant professor at the University of Waterloo in Ontario), the algorithm is designed for robots that will be monitoring an environment for long periods of time, tracing the same routes over and over. It assumes that the data of interest — temperature, the concentration of chemicals, the presence of organisms — fluctuate at different rates in different parts of the environment. In ocean regions with strong currents, for instance, chemical concentrations might change more rapidly than they do in more sheltered areas.

Floor it

In its current version, the algorithm assumes that researchers already have a mathematical model of the rates at which conditions change in different parts of the environment. The algorithm simply determines how the robots should adjust their velocities as they trace their routes. For instance, given particular rates of change along a route, would it make more sense to make one pass in an hour, slowing down considerably in areas of frequent change, or to make four or five passes, collecting less detailed data but taking more regular samples?

“From a practical point of view, it seems like an easy problem,” says Calin Belta, an assistant professor of mechanical engineering, systems engineering and bioinformatics at Boston University, who was not involved in the research. But it turns out to be a monstrously complex calculation. “It’s very hard to come up with a mathematical proof that you can really optimize the acquired knowledge,” he adds.

The MIT researchers draw an analogy with dust accumulating on a floor — dust that’s cleared whenever a sensor passes nearby. Because environmental change occurs at different rates in different areas, the dust piles up unevenly. The researchers were able to show that, with their algorithm, the height of the piles of dust would never exceed some limit: Only so much change could occur in any area before the sensor would measure it.

Ups and downs

Although the MIT researchers’ algorithm is designed to control robots’ velocity, the first robots on which it was tested don’t actually have velocity controllers. USC researchers have been studying harmful algae blooms using commercial robotic sensors designed by the Massachusetts company Webb Research. Because the sensors are intended to monitor ocean environments for weeks on end, they have to use power very sparingly, so they have no moving parts. Each sensor is shaped like an airplane, with an inflatable bladder on its nose. When the bladder fills, the sensor rises to the surface of the ocean; as the bladder empties, the sensor glides downward.

The more rapidly the bladder fills and empties, the steeper the sensor’s trajectory up and down, and the longer it takes to traverse a given distance — so it’s possible to concentrate the sensor’s attention in a particular location. Working with colleagues in the USC computer science department, the MIT team developed an interface that allows ocean researchers to specify regions of interest by drawing polygons around them on a digital map and indicating their priority with a numerical rating. The new algorithm then determines a trajectory for the sensor that will maximize the amount of data it collects in high-priority regions, without neglecting lower-priority regions.

At the moment, the algorithm depends on either some antecedent estimate of rates of change for an environment or researchers’ prioritization of regions. But in principle, a robotic sensor should be able to deduce rates of change from its own measurements, and the MIT researchers are currently working to modify the algorithm so that it can revise its own computations in light of new evidence. “That’s going to be a hard problem as well,” Belta says. “But they have the right background, and they’re strong, so I think they might be able to do it.”

The researchers also envision that the algorithm could prove useful for fleets of robots performing tasks other than environmental monitoring, such as tending produce, or — in a more literal application of the vacuuming-dust metaphor — cleaning up environmental hazards, such as oil leaking from underwater wells.

EEE / Why Your GPS Receiver Isn’t Bigger Than a Breadbox
« on: May 09, 2018, 11:16:22 AM »
As I drive through the vineyard-covered hills of San Luis Obispo, Calif., the tiny Global Positioning System receiver in my phone works with Google Maps to alert me to upcoming turns. The app reassures me that I’ll arrive at my destination on time, in spite of a short delay for construction.

How different this trip would have been in the pre-GPS era, when the obscured road sign at one intersection would likely have sent me off track. I have a weak sense of direction, and getting lost—or worrying about getting lost—was a stressful part of my life for a long time.

This GPS-guided journey is taking me to Bradford W. Parkinson, the person who made GPS technology—a tool we now take for granted—come together. Parkinson is being awarded the 2018 IEEE Medal of Honor for leading the development of GPS and pushing its early applications.

Power systems are going through a paradigm change from centralized generation to distributed generation and further on to smart grids. More and more renewable-energy sources, electric vehicles, energy storage systems, and so forth are being connected to power systems through power electronic converters. Moreover, the majority of loads are expected to connect to the grid through power electronic converters as well. This article shows that these converters, either on the supply side or on the load side, can all be controlled to behave like virtual synchronous machines (VSMs) and possess the dynamics of synchronous machines, providing a unified interface for smart grid integration. Synchroconverter technology and its developments are the focus of this article because the mathematical model of synchronous machines is embedded in the controller of synchronverters to provide close imitation.

EEE / Wide-Bandgap Power Devices: Adoption Gathers Momentum
« on: May 09, 2018, 11:12:45 AM »
As power electronics continues to extend into renewable energy markets, smart grids, smart homes, transportation electrification, electric and hybrid electric vehicles (EV/HEVs), and other emerging industrial and medical applications, more designers are attracted to the wide-bandgap (WBG) power devices, e.g., silicon carbide (SiC) and gallium nitride (GaN). In the past few years, engineers have spent time understanding the virtues of these emerging power devices and their drawbacks, e.g., reliability, cost, and availability. Today, many analysts believe that engineers are transitioning from education mode to implementation mode. According to research firm Yole D?veloppement's technology and market analyst Hong Lin, "We are gradually going from the customer awareness and education stage to the customer trial and adoption stage. And this is especially true for SiC transistors."

The diverse collection of capacitor types has not changed much over recent years, but applications certainly have. In this article, we look at how capacitors are used in power electronics and compare the available technologies. Film capacitors are showing their advantages in upcoming applications such as electric vehicles, alternative energy power conversion, and inverters in drives. However, aluminum (Al) electrolytics are still important when energy storage density is the main requirement.

Faculty Sections / Control of Power Converters in AC Microgrids
« on: May 09, 2018, 11:03:11 AM »
The enabling of ac microgrids in distribution networks allows delivering distributed power and providing grid support services during regular operation of the grid, as well as powering isolated islands in case of faults and contingencies, thus increasing the performance and reliability of the electrical system. The high penetration of distributed generators, linked to the grid through highly controllable power processors based on power electronics, together with the incorporation of electrical energy storage systems, communication technologies, and controllable loads, opens new horizons to the effective expansion of microgrid applications integrated into electrical power systems. This paper carries out an overview about microgrid structures and control techniques at different hierarchical levels. At the power converter level, a detailed analysis of the main operation modes and control structures for power converters belonging to microgrids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations. This analysis is extended as well toward the hierarchical control scheme of microgrids, which, based on the primary, secondary, and tertiary control layer division, is devoted to minimize the operation cost, coordinating support services, meanwhile maximizing the reliability and the controllability of microgrids. Finally, the main grid services that microgrids can offer to the main network, as well as the future trends in the development of their operation and control for the next future, are presented and discussed.

EEE / DC Motor, How it works?
« on: April 20, 2017, 04:36:14 PM »

A world of millimeter-wave networks, laid out by computer, crisscrossing cities and into the stratosphere, where cell phone towers can be easily replaced by tethered autonomous copters—that’s the telecommunications infrastructure of the future. So says Facebook’s Yael Maguire, head of the company’s Connectivity Lab.

Speaking at Facebook’s F8 developer conference in San Jose today, Maguire said that Facebook is aiming to bring down the cost of connecting by an order of magnitude, working to develop the building blocks of more flexible and extensible networks.

A big part of that strategy, he said, is millimeter wave communications. Near term, he says, are millimeter wave networks connecting cities, a simpler route to high capacity communications than extending fiber optic networks to every building.  The company’s project here is called Terragraph; it is, Maguire said, “designed to be consumer level in pricing and deployed by mobile operators.”

Facebook’s real secret sauce in city-level millimeter wave communications, Maguire explained, is its use of computer vision and artificial intelligence to analyze a city and determine possible paths for communications. It has also, he said, developed new technology for rerouting these networks when communications are interrupted, and is currently testing this technology in San Jose.

Further out are Facebook’s efforts to use its Aquila aircraft in the stratosphere to allow long-distance communications. In recent tests, Facebook engineers clocked 36 Gbps of data transfer over 13 km using a stationary millimeter-wave link and 16 Gbps of data transfer from the ground to a Cessna aircraft; the Cessna acted as a stand-in for the futuristic Aquila. Maguire admitted it could take 10 years before this communications technology becomes practical. (Facebook also achievedand 80 Gbps using an optical link to the Cessna.)

Nearer term for connectivity in rural areas, he said, is reducing the cell-phone tower to what Maguire calls its absolute essence: the Tether-tenna. He described this as a cable tethered to ground-based power and fiber optic networks, held up by an autonomous ultralight helicopter. There are a few things to work out, he said, “it’s a high voltage system, it has to survive high winds and lightning.” In tests, he reported, the Tether-tenna has run for 24 hours; the company expects to extend that to months.

Maguire also said the company is particularly interested in using its technology to create instant infrastructure for use in a crisis; long term, Aquila will be able to be fill that niche, but he sees Tether-tenna as also being useful—and just a few years away from implementation.

EEE / EarthDay2017
« on: April 20, 2017, 03:55:11 PM »
No planet is better studied than the one we actually live on.
#NASA's fleet of 18 Earth science missions in space, supported by aircraft, ships and ground observations, measure aspects of the environment that touch the lives of every person around the world. They study everything from the air we breathe, to rain and snow that provide water for agriculture and communities, to natural disasters such as droughts and floods, to the oceans, which cover 70 percent of Earth’s surface and provide food for many people around the world.
Satellites and instruments on the International Space Station (#ISS) circle the whole globe, seeing both where people live and those remote parts of deserts, mountains and the vast oceans that are difficult if not impossible to visit. With instruments in space, scientists can get data for the whole globe in detail that they can't get anywhere else. This visualization shows the NASA fleet in 2017, from low Earth orbit all the way out to the DSCOVR satellite taking in the million-mile view. #EarthDay #EarthDay2017

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