links for 2010-​​06-​​29

links for 2010-​​06-​​28

links for 2010-​​06-​​27

  • “But here’s the won­der­ful rev­e­la­tion. If you’re a well-​​adjusted per­son, once you’ve dis­carded the unhealthy fic­ti­tious rela­tion­ship with a phan­tasm, you can look around and notice all those other peo­ple who are like­wise alone, and you’ll real­ize that we’re all alone together. And that means you aren’t alone at all — you’re among friends. That’s the next step in human progress, is get­ting away from the notion of min­ions liv­ing under a trail boss, and onwards to work­ing as a coop­er­a­tive com­mu­nity, with no gods and no mas­ters, only autonomous agents free to think and act.”

links for 2010-​​06-​​25

  • “We con­sider the prob­lem of doing fast and reli­able esti­ma­tion of the num­ber of non-​​zero entries in a sparse boolean matrix prod­uct. This prob­lem has appli­ca­tions in data­bases and com­puter alge­bra. Let n denote the total num­ber of non-​​zero entries in the input matri­ces. We show how to com­pute a 1 +- epsilon approx­i­ma­tion (with small prob­a­bil­ity of error) in expected time O(n) for any epsilon > 4/\sqrt[4]{n}. The pre­vi­ously best esti­ma­tion algo­rithm, due to Cohen (JCSS 1997), uses time O(n/epsilon^2). We also present a vari­ant using O(sort(n)) I/​Os in expec­ta­tion in the cache-​​oblivious model. In con­trast to these results, the cur­rently best algo­rithms for com­put­ing a sparse boolean matrix prod­uct use time omega(n^{4/3}) (resp. omega(n^{4/3}/B) I/​Os), even if the result matrix has only z=O(n) nonzero entries.…”
  • “Spa­tially con­fined rigid mem­branes reor­ga­nize their mor­phol­ogy in response to the imposed con­straints. A crum­pled elas­tic sheet presents a com­plex pat­tern of ran­dom folds focus­ing the defor­ma­tion energy while com­press­ing a mem­brane rest­ing on a soft foun­da­tion cre­ates a reg­u­lar pat­tern of sinu­soidal wrin­kles with a broad dis­tri­b­u­tion of energy. … The phys­i­cal model, exhibit­ing an anal­ogy with para­met­ric res­o­nance in non­lin­ear oscil­la­tor, is a new the­o­ret­i­cal toolkit to under­stand the mor­phol­ogy of var­i­ous con­fined sys­tems, such as coated mate­ri­als or liv­ing tis­sues, e.g., wrin­kled skin, inter­nal struc­ture of lungs, inter­nal elas­tica of an artery, brain con­vo­lu­tions or for­ma­tion of fin­ger­prints. More­over, it opens the way to new kind of micro­fab­ri­ca­tion design of mul­ti­peri­odic or chaotic (ape­ri­odic) sur­face topog­ra­phy via self-​​organization.”

links for 2010-​​06-​​24