"Optimal power flow (OPF) is an important problem for power generation and it is in general non-convex. With the employment of renewable energy, it will be desirable if OPF can be solved very efficiently so its solution can be used in real time. With some special network structure, e.g. trees, the problem has been shown to have a zero duality gap and the convex dual problem yields the optimal solution. In this paper, we propose a primal and a dual algorithm to coordinate the smaller subproblems decomposed from the convexified OPF. We can arrange the subproblems to be solved sequentially and cumulatively in a central node or solved in parallel in distributed nodes. We test the algorithms on IEEE radial distribution test feeders, some random tree-structured networks, and the IEEE transmission system benchmarks. Simulation results show that the computation time can be improved dramatically with our algorithms over the centralized approach of solving the problem without decomposition, especially in tree-structured problems. The computation time grows linearly with the problem size with the cumulative approach while the distributed one can have size-independent computation time."

"Internet-scale distributed systems such as content delivery networks (CDNs) operate hundreds of thousands of servers deployed in thousands of data center locations around the globe. Since the energy costs of operating such a large IT infrastructure are a significant fraction of the total operating costs, we argue for redesigning CDNs to incorporate energy optimizations as a first-order principle. We propose techniques to turn off CDN servers during periods of low load while seeking to balance three key design goals: maximize energy reduction, minimize the impact on client-perceived service availability (SLAs), and limit the frequency of on-off server transitions to reduce wear-and-tear and its impact on hardware reliability. We propose an optimal offline algorithm and an online algorithm to extract energy savings both at the level of local load balancing within a data center and global load balancing across data centers. We evaluate our algorithms using real production workload traces from a large commercial CDN. Our results show that it is possible to reduce the energy consumption of a CDN by more than 55% while ensuring a high level of availability that meets customer SLA requirements and incurring an average of one on-off transition per server per day. Further, we show that keeping even 10% of the servers as hot spares helps absorb load spikes due to global flash crowds with little impact on availability SLAs. Finally, we show that redistributing load across proximal data centers can enhance service availability significantly, but has only a modest impact on energy savings."

"To attempt to draw a political map of the reconstituted North America is to confront these contradictions head-on. What counts as a nation? How to capture the overlapping spheres of responsibility? What about the areas all but abandoned to wilderness? Does membership confer citizen-hood?"

Going back in history, until February 2009 ATOC licensed train departure information under commercial terms to a very small number of organisations, mostly within the rail industry. Kizoom published the only smartphone app at that time, the free MyRailLite for iPhone. Then a dispute arose between ATOC and Kizoom, and ATOC withdrew Kizoom’s licence to use the train departure information. Kizoom complained to the ORR, who conducted an investigation (PDF) into whether ATOC had abused a dominant position under competition law. ORR decided that ATOC did have a dominant position in the supply of train departure information, but they “found no evidence that ATOC’s conduct in granting access to Darwin had prevented a new product from coming to market or hampered the emergence of new technology” in November 2009. When the free MyRailLite from Kizoom was taken off the market, it was immediately replaced by a £5 iPhone app from Agant which was marketed under the National Rail Enquiries brand.

"Whereas a conventional NAND gate outputs a "1" if neither of its inputs match, the output of a Bayesian NAND gate represents the odds that the two input probabilities match. This makes it possible to perform calculations that use probabilities as their input and output."

"Fatal crush conditions occur in crowds with tragic frequency. Event organisers and architects are often criticised for failing to consider the causes and implications of crush, but the reality is that the prediction and mitigation of such conditions offers a significant technical challenge. Full treatment of physical force within crowd simulations is precise but computationally expensive; the more common method of human interpretation of results is computationally "cheap" but subjective and time-consuming. In this paper we propose an alternative method for the analysis of crowd behaviour, which uses information theory to measure crowd disorder. We show how this technique may be easily incorporated into an existing simulation framework, and validate it against an historical event. Our results show that this method offers an effective and efficient route towards automatic detection of crush."

"This paper presents a complex systems overview of a power grid network. In recent years, concerns about the robustness of the power grid have grown because of several cascading outages in different parts of the world. In this paper, cascading effect has been simulated on three different networks, the IEEE 300 bus test system, the IEEE 118 bus test system, and the WSCC 179 bus equivalent model, using the DC Power Flow Model. Power Degradation has been discussed as a measure to estimate the damage to the network, in terms of load loss and node loss. A network generator has been developed to generate graphs with characteristics similar to the IEEE standard networks and the generated graphs are then … have been suggested."

"…Even though we cannot present all the algorithms in full detail, we can at least show “in princi- ple”, how a whole variety of important and practical algorithms come out from our refinement process. These include above all the (DLG) algorithm of Doligez, Leroy and Gonthier [9] – which sometimes is considered the culmination of concurrent collector development [1] – and its descendants."

"To our knowledge, the two most prominent aspects of our setting, the presence of asymmetric information and the stationarity requirement (stemming from unknown start times) have not been considered in the literature. For example, the Anderson-Weber strategy for the telephone problem is not stationary — it has a period of n − 1. It would be interesting to see what can be said about the optimal stationary strategies for this and other rendezvous problems. The interested reader is referred to [2,3] and the references therein for more information on rendezvous search games."

"We consider scheduling weighted packets in a capacity-bounded buffer. In this model, there is a buffer with a limited capacity B such that at any time, the buffer cannot accommodate more than B packets. Packets arrive over time. Each packet has a non-negative real value. Packets do not expire and they leave the buffer only because either we send them or we drop them. The packets that have left the buffer will not be reconsidered for delivery any more. In each time step, at most one packet in the buffer can be sent. The order in which the packets are sent should comply with the order of their arriving time. The objective is to maximize the total value of the packets sent in an online manner.…"

"Write performance in Cassandra is excellent. The internals are specifically geared towards a heavy-write system. It writes to a memory table and a serial commit log, and every so often the memory table is flushed to disk in what the Big Table paper describes as a sorted strings table, often called an SSTable — an immutable data structure. There is a lot more happening behind the scenes, but the performance characteristics are clear: there is nothing slow in the write path. The Cassandra wiki page on Architecture Internals provides more details."

"These are provocative ideas. Very analogous to the ideas found in the ping hub discussions and the peer to peer discussions. It would be fun to try and build a heuristic prefeching/pushing privacy respecting http proxy server swarm along these lines. No doubt somebody already has."

"Over the past year, VNL, based in Haryana, India, has reengineered the traditional technology of the dominant cellular standard, called GSM, in order to create base stations that only require between 50 and 150 watts of power, supplied by a solar-charged battery. The components can be assembled and booted up by two people and mounted on a rooftop in six hours."

"Email is still the easiest way to collaborate with a group of people.
We built tgethr in response to the increasingly complex world of online collaboration. Why set up a project management site or an entire social network when all you need is to correspond by email more efficiently?"

"You, Randall Stephenson, and your lazy stupid company — you are the problem. You are what’s wrong with this country."

"The MPAA has successfully shut down an entire town's municipal WiFi because a single user was found to be downloading a copyrighted movie. Rather than being embarrassed by this gross example of collective punishment (a practice outlawed in the Geneva conventions) against Coshocton, OH, the MPAA's spokeslizard took the opportunity to cry poor (even though the studios are bringing in record box-office and aftermarket receipts)."

"It is true. You are. Go try it now. That is an order. I can wait for you to come back and finish reading this post. I could end the post now, but I suppose I’ll go on and tell you a bit about my experience with Heroku yesterday."

[R tools for financial time-series analysis, among other things]

"Open source, if we view it through a different lens, is really more about a distributed methodology for software development. The burden of creation is widely distributed across a massive community with more-or-less equal access to tools and systems. In this context, the role of the legal tool is more akin to an enzyme. It was an essential piece of a puzzle, but it was not the only piece. In fact, without the rest of the infrastructure (connectivity, tools, and people) the legal tool on its own would not have led us to GNU/Linux."

"High-speed rail doesn’t simply proceed from point A to point B; it has the potential to energize the cities and towns where it stops in between. The normal practice is to locate intermediate stations in populated areas roughly 50 miles apart. In Europe, high-speed railroads have generated the most growth in provincial cities, as once remote districts benefit from their newfound closeness to hubs such as Paris and Berlin. In a century that will demand more compact, energy-efficient development, high-speed rail has the potential to establish a new superstructure for growth."

"System disruption leverages network structure and dynamics to turn small attacks into large events. Selection of the best point to attack is based on an analysis of the network's design and flows. The term to describe this point is: the systempunkt. Essentially, the systempunkt is the point in the network, that if attacked, will yield the maximal possible impact."

"For a while i was interested to see how many of the rails developers i know, use macs. After talking about this urge of mine with the awesome @hakunin we have decided to collect a bunch of our colleagues desktop portraits. almost everyone is on a mac (duh!).

Foolishly, i forgot to notate some of the pictures people sent me with the name of the developer, so if you recognize yours and want to link the image/title to somewhere, lemme know."

"rssCloud is meant to carry more frequent traffic and more content than the original RSS and Atom. It maintains an XML format (making it relatively verbose for SMS, although Winer tries to separate out the rich, enhanced data). Perhaps because of the increased traffic it would cause, it's less decentralized than RSS, storing updates in Amazon S2."

Consider replacing "oil" with "auto".

"But with any energy boom eventually comes the energy bust. Here are some photos I took showing what a community looks like if its economy is disproportionately based on oil and the oil companies leave. I’m not a particularly good photographer, so these aren’t artistically impressive, but they capture what the area looks like now."

"The recent disruption marked the final blowup in a year-long game of chicken played by Sprint Nextel and Cogent and brought to light an uncomfortable reality: The Internet is held together by collection of secret contracts struck between private companies, free from government oversight and regulation."

"This decision has confirmed what was already obvious from a plain reading of the statutes, that Minnesota cities can use their bonding authority for deploying the essential infrastructure of the next century."

Porous concrete

"...overtime is any time when you wish you weren't at the office"

Big damned batteries

Big damned batteries