Varaprasad B.S.D.Ch.S.,Japan National Institute of Materials Science |
Takahashi Y.K.,Japan National Institute of Materials Science |
Ajan A.,Western Digital |
Hono K.,Japan National Institute of Materials Science
Journal of Applied Physics | Year: 2013
We have explored a new electrically conductive underlayer material to grow (001) textured L10-FePt films on glass substrates for potential application in ultrahigh density magnetic recording media. We found (Mg 0.2Ti0.8)O (MTO) polycrystalline film grows with a strong (001) texture on Cr buffer layer, which induces strong (001) texture of L1 0-FePt polycrystalline and granular films. Strong perpendicular anisotropy of 3.8 × 107 erg/cm3 and coercivity of 15 kOe of a FePt-C film has been demonstrated using the MTO underlayer on glass substrates. © 2013 AIP Publishing LLC.
Huang C.,University of Tennessee at Knoxville |
Li F.,University of Tennessee at Knoxville |
Jin Z.,Western Digital
IEEE Transactions on Industrial Electronics | Year: 2015
Under the global trend of renewable energy development, various advanced techniques such as forecasting algorithm, intelligent computation, and optimal control are expected to make the complex and uncertain renewable energy system stable and profitable in the near future. This paper presents a new control strategy for large-scale wind energy conversion systems to achieve a balance between power output maximization and operating cost minimization. First, an intelligent maximum power point tracking (IMPPT) algorithm is proposed such that short-term wind speed prediction, wind turbine dynamics, and MPPT are collectively considered to improve system efficiency. Second, in view of a spatial and temporal distribution of wind speed disturbances, a box uncertainty set is embedded in the forecast wind speed, which is likely more realistic for practicing engineers. Then, the IMPPT and box uncertainties are applied to the wind energy conversion system (WECS) control strategy, which is formulated as a min-max optimization problem and efficiently solved with semi-definite programming (SDP). Finally, a comparison with the conventional MPPT control method demonstrates that the proposed approach can obtain higher efficiency, which validates this paper. © 1982-2012 IEEE.
News Article | December 1, 2015
Sometimes technology companies don't even bother to protect users' data, while others give it a shot, but fail miserably. VTech, a Hong-Kong based company that makes internet connected toys, falls into the latter. On Monday, Motherboard revealed that the same hacker who had obtained the personal data of 5 million parents and over 200,000 children from VTech had also managed to get hold of potentially tens of thousands of photos of children, taken by the company's devices and stored on its servers. Now, a researcher has found that the Android app used by parents to communicate with their child playing with a VTech product employs weak cryptography to protect its users' data and photos. “At the weekend I reversed the Vtech kidconnect app and found this. Not surprised at the latest developments at all,” tweeted the well-known pseudonymous researcher slipstream/RoL on Monday. Slipstream/RoL examined the Android version of the app, which is “for the parents' devices,” he told Motherboard in an online chat. The first mistake is how the app handles photos taken by the device. The app creates an MD5 hash of the KidConnect username, in uppercase, and a constant value. According to slipstream/RoL's screenshots, this constant is either “vtech” or “vtechvtech” every time. MD5 is a hashing algorithm: a method for storing data in a more secure form, or checking that files haven’t been tampered with. But MD5 is notoriously weak, and using the company's own name as a variable in that process likely makes the result easier to crack. “The uppercase KidConnect username is part of the filenames of the encrypted images!” slipstream/RoL pointed out. Motherboard confirmed this to be the case with images sourced from the VTech hacker. Slipstream/RoL found another problem for media such as photos or audio recordings—which the VTech hacker also managed to get hold of—that was embedded in the chats between VTech app users, he said. To encrypt that data, the app combines the current time with a pseudorandom number generator: a “cryptographically insecure method,” slipstream/RoL added. This is similar to a problem uncovered in certain models of Western Digital encrypted hard drives. “Weaker random number generators are more likely to produce duplicates (for example, after 65,000 images),” Scott Arciszewski, chief development officer for Paragon Initiative Enterprises, a cybersecurity company, told Motherboard in a Twitter message. Overall, even after a pretty catastrophic hack, things are just looking worse for VTech. “Let's see, it uses bad encryption, it passes the hash to login, it got pwned. Yeah, not looking great,” slipstream/RoL said.
The year is 2015 and yet the promise of the “personal cloud” has failed me. There are tons of drag and drop and syncing “backup services” but nowhere that’s my slice of the puffy white stuff. Enter the 80 employees and impressive pedigree of Palo Alto based Upthere. Google Drive, Dropbox, Apple’s iCloud, Box, IDrive, Hightail, Microsoft OneDrive, SugarSync: These are some of the better known services to keep your stuff in one place in the cloud. Some tout themselves as having strengths in file-syncing, some push online backup as a reason for using them. I have files in every single one of these places. Why is that? They’re all great in their own ways and they all suck in their own ways. I use Dropbox, and even Slack now, to share files with colleagues. I use Google Drive for document editing. Google Photos for photo and video. iCloud backs up my iPhone, iPad and camera roll on both (which also go to Google Photos). OneDrive has some product shots that I may or may not ever use. Box has my videos from Vegas in 2007 and some random photos. Dropbox has about 10,000 of my photos …a backup of Flickr in case it ever died and and the downloads folder from my last four jobs. SugarSync has the documents folder of my laptop from two jobs ago. And Hightail has a few MP3s from a computer that was in my dad’s basement. If you asked me where my personal slice of the cloud was, I’d say “everywhere.” A Palo Alto based company coming out of “stealth” today, Upthere, aims to fix that. The company has been working in secret since 2011 and I sat down with its more notable leaders this week to find out what they’ve been working on, their mission and values and their upcoming beta testing. Upthere carries such notable investors as KPCB, Google Ventures, Elevation Partners, Floodgate, NTT DOCOMO Ventures and Western Digital. More on Western Digital in a bit. The company isn’t disclosing the size or number of rounds it has raised, but given the firms on the list…it’s not pennies. Upthere was founded by Bertrand Serlet, Roger Bodamer and Alex Kushnir in 2011. Let’s start with Serlet, Upthere’s founder and board director. He was SVP of Software Engineering at Apple after coming over with its acquisition of Steve Jobs’ NeXT in 1996. At the former, he led OS X through Snow Leopard and helped get iOS going. As someone who is a major contributor to personal computing, his view of Upthere through the lens of his work at Apple is quite fascinating: And there you have the core of Upthere. Caring for data. Upthere’s co-founder and CEO, Roger Bodamer, has a history of heavy interest in solving data computation and storage challenges in distributed networks, most notably at Oracle. He went on to become a GM at MongoDB and worked at Apple for a spell. I asked Upthere board member John Doerr of KPCB why he decided to take the long-game investment plunge of building a brand new infrastructure in the cloud for consumers (something that sounds so geeky typing, I know my Mom will be like “what?” Give it a bit, Mom; you’ll understand hopefully). He said the engineering-heavy company’s founding team impressed him. “Their history, but also the hybrid natures of their DNA. Oracle, Mongo, Apple, and Google,” he said. “Their ambition was to reimagine and look at every phase of cloud computing, from the motherboards to the metal and silicon.” “We’d like the word ‘backup’ to vanish from the dictionary,” Bodamer told me as we discussed dragging and dropping files and syncing them in folders on various services. Why isn’t what we have good enough? Bodamer continued: “We built a consumer cloud from the ground up. We questioned everything, literally. We experimented a lot. We want the cloud to be the primary place for your data.” The idea is that no matter what device you’re carrying around or using, be it a laptop, phone, tablet, phablet or desktop, you should have direct-write access to the cloud at all times. The cloud should be your hard drive, not your device. Chris Bourdon, Upthere’s VP of Product, went a bit deeper when I poked about why syncing isn’t good enough and why huge storage capabilities on devices might not even be necessary: Jargon-free? The cloud can crunch a crapload of data and serve it up to your iPhone in a pretty way without being a burden on said iPhone. Why should a device slow down because it’s trying to figure out what you’re searching for, how to display it to you, etc. Upthere will be your storage, allowing your devices to do what they do best…gather stuff. The ground-up approach includes the entire stack. Hardware to software. The company has designed its own servers down to the bend of the metal and the motherboards used. Its strategic investment from Western Digital is also coming in handy since, well, they’re using a lot of physical storage that you’ll luckily never have to see or deal with. Upthere is storage with APIs and a framework that will allow the company, as well as other developers eventually through an API, build secure and scalable consumer applications quickly. The syncing technology that the team, and developers everywhere, have familiarity with is POSIX. It’s been around since the late 60s, early 70s and was designed for file systems that were a few megabytes. Not the gigs that we’re moving around these days. By building a filesystem that directly writes to the cloud, the company is taking advantage of the fact that our devices are pretty much always connected to the Internet. Think about the last time you were connection-free. Maybe it was a flight without Wi-Fi. But even that is becoming less common these days. Bourdon tells me that Upthere’s plan is to completely bypass local storage and go directly to the cloud: “By doing this we have a single unified placed for your things, and it grows to accommodate. It’s accessible from any device anywhere, and it’s better at sharing your things.” Bourdon went on to show me two apps that demonstrate the stack. Both will be made available over the next few weeks on Mac OS, iOS and Android. Both have been operating under the code name of Zephyr. The first is a “Home” of sorts, where you can view your stored files. This includes photos, videos, music (including imports from iTunes) and documents. It’s super fast to search through, since the team explains that it took a non-hardcoded approach to displaying files, it’s all search-query based and Upthere’s servers are doing all of the hard work. Founder Bertrand Serlet decided that folders and hierarchy are a thing of the past. Mind you, this is coming from the person who helped design the folders and hierarchy you’re possibly using right now. The second app, Camera, does exactly what you think it would do. Take photos. But those photos are never stored on your device, not even for a second. The second you snap one, it’s in the cloud. The app also lets you set up shared cameras, which are basically groups of people who have the app or not and can access your photos. You can choose which camera you’re using, but you could accidentally share a photo with mom that you didn’t intend to if you aren’t careful. And there’s no going back because, well, the writing and sharing is that fast. I watched the notifications ping pong around the room and was frightened. On the sharing side, this does offer a less filtered view of what you’re experiencing — much more intimate than what you’d share on Instagram or Twitter. The key to these two apps is that they’re built on Upthere’s 4-year-in-the-making stack that’s lightning-fast and secure. Doerr even told me that the team scrapped what it was doing a few times and went back to the drawing board. As an investor, that takes some patience to hear. He didn’t flinch, he tells me. “They’re on a mission to do something really important in a high quality way,” and that’s coming from the man who has backed the likes of Jeff Bezos, Larry Page and Sergey Brin at a very early stage. If you peel away all of the new technology that’s been built, the apps built on top of it and the hopes of more being built by developers, it all comes down to trust. The companies that I name at the top of this post, for one reason or another, I trust with my data. However, some of them haven’t followed through and let me do anything new or cool with it. My files are just…there. The company unveiled a bit of a mission statement today on its site, along with a sign-up link to be invited to their beta: This thorough and measured approach, which some outsiders could see as slow (and fairly, given the fast-paced nature of Silicon Valley innovation), is what Upthere and its investors are betting on. The proof’s in the pudding now once people start using it. To get all of my files into Upthere, it’s going to be a gradual process. Not only technically, for me, since my stuff is everywhere, but as I get to know their products and learn how they act to support its customers, I’m going to be a little cautious of going “all in.” I mean, I haven’t anywhere else yet. Somebody has to be “the one,” right?
Huang C.,University of Tennessee at Knoxville |
Li F.,University of Tennessee at Knoxville |
Ding T.,University of Tennessee at Knoxville |
Ding T.,Tsinghua University |
And 2 more authors.
IEEE Transactions on Sustainable Energy | Year: 2015
An efficient control strategy of a wind energy conversion system (WECS) plays a crucial role in wind power utilization. In this paper, a novel multivariable control strategy for a variable-speed variable-pitch WECS is proposed. It is designed for the complete operating regions of a wind turbine, including both of the partial load region and the full load region, with the objectives of maximizing energy capture, smoothing power output, alleviating drive train transient loads, and reducing pitch actuator activities. In particular, this paper considers the wind speed disturbance as norm-bounded, instead of deterministic or chance constraints in the widely used quadratic control methods such as linear quadratic Gaussian control and model predictive control. Moreover, the WECS control with the norm-bounded disturbance is formulated as a second-order cone programming (SOCP) problem that has not been previously employed for wind power control. Finally, simulation results are provided to demonstrate the validity of the proposed method. © 2010-2012 IEEE.