Biweekly links for 08/31/2009

  • Facebook’s Religion Question Prompts Soul-Searching
    • Facebook gives people a free-form text box to describe their religion. Asking such a personal question gives some surprising answers. My favourite was probably the woman who summed up both her Catholicism and her difficulties with Catholicism by describing her religion as “Matthew 25”. “Jedi” comes in at number 10.
  • Markets marketed better « Meteuphoric
    • “What do you call a system where costs and benefits return to those who cause them? Working markets or karma, depending on whether the accounting uses money or magic.

      In popular culture karma generally has good connotations, and markets generally have bad. Reasons for unease about markets should mostly apply just as well to karma, but nobody complains…that inherent tendencies to be nice are an unfair basis for wellbeing distribution. Nor that people who have had a lot of good fortune recently might have cheated the system somehow. Nor that the divine internalizing of externalities encourages selfishness. Nor that people who are good out of desperation for fair fortune are being exploited. So why the difference?

      Perhaps mysterious forces are just more trustworthy than social institutions? Or perhaps karma seems nice because its promotion is read as ‘everyone will get what they deserve’, while markets seem nasty because their promotion is read as ‘everyone deserves what they’ve got’”

  • Astonishing video of a chimp at a magic show
  • News organisations and start-ups
    • “What would a content site look like if you started from how to make money – as print media once did – instead of taking a particular form of journalism as a given and treating how to make money from it as an afterthought?”
  • Mike Brown’s Planets: Fog! Titan! Titan Fog! (and a peer review experiment)
    • Cool for two reasons. First, Titan has fog! Second, Mike Brown seriously invites reviews of the paper, and promises to treat them as he would referee comments.
  • 25 Years Later, First Registered Domain Name Changes Hands
    • The first .com was apparently registered in 1985; it just changed hands for the first time ever.
  • Mathematics and the internet (pdf)
    • Terry Tao’s talk about how online tools are changing mathematics.

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Biweekly links for 08/28/2009

  • 25 Years Later, First Registered Domain Name Changes Hands
    • The first .com was apparently registered in 1985; it just changed hands for the first time ever.
  • Mathematics and the internet (pdf)
    • Terry Tao’s talk about how online tools are changing mathematics.
  • What We Can Learn From Craigslist
  • How XML Threatens Big Data : Dataspora Blog
    • Excellent thoughtful article on data bureaucracy and the limitations of XML.
  • The impact factor’s Matthew effect: a natural experiment in bibliometrics
    • “Using an original method for controlling the intrinsic value of papers–identical duplicate papers published in different journals with different impact factors–this paper shows that the journal in which papers are published have a strong influence on their citation rates, as duplicate papers published in high impact journals obtain, on average, twice as much citations as their identical counterparts published in journals with lower impact factors. The intrinsic value of a paper is thus not the only reason a given paper gets cited or not; there is a specific Matthew effect attached to journals and this gives to paper published there an added value over and above their intrinsic quality. “
  • The importance of failure
    • “This is a point that I don’t often hear made when people talk about failure; the moral behind a failure-related story is usually about preventing it, or dealing with the aftermath, but not about the fact that sometimes things go bad despite your best efforts, and all the careful risk management and contingency planning won’t keep you from going down in flames. This is important, because it forces every person to establish a risk threshold that they are willing to accept in every one of their life efforts. “
  • US Top All-Time Donors 1989-2008
    • Surprising list of top donors in US politics.
  • High-Speed Robot Hand
    • Incredible video of a robot which can throw a ball, pick up a grain of rice, spin a pen, and many other things, all with incredible speed.

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Biweekly links for 08/24/2009

  • Pointless babble « Stephen Fry on Twitter
    • “The clue’s in the name of the service: Twitter. It’s not called Roar, Assert, Debate or Reason, it’s called Twitter. As in the chirruping of birds. Apparently, according to Pears (the soapmakers…– certainly their “study” is froth and bubble) 40% of Twitter is “pointless babble”, (http://is.gd/2mKSg) which means of course that a full 60% of Twitter discourse is NOT pointless babble, which is disappointing. Very disappointing. I would have hoped 100% of Twitter was fully free of earnestness, usefulness and commercial intent. Why do these asinine reports jump onto a bandwagon they don’t understand and why do those reporting on them relate with such glee that a service that was never supposed in the first place to be more than gossipy tittle-tattle and proudly banal verbal doodling is “failing to deliver meaningful commercial or political content”. Bollocky bollocks to the lot of them. They can found their own “enterprise oriented” earnest microblogging service. Remind me to avoid it.”
  • Amplifying on the PCR Amplifier « Gödel’s Lost Letter and P=NP
    • Excellent explanation of how the polymerase chain reaction lets us make many copies of a DNA strand.
  • Study Hacks » How to Schedule Your Writing Like a Professional Writer

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Biweekly links for 08/21/2009

  • Avatar
    • First trailer for the new James Cameron film.
  • Public Library of Science announces new initiative for sharing influenza research
    • “PLoS is launching PLoS Currents (Beta) — a new and experimental website for the rapid communication of research results and ideas. In response to the recent worldwide H1N1 influenza outbreak, the first PLoS Currents research theme is influenza.

      PLoS Currents: Influenza, which we are launching today, is built on three key components: a small expert research community that PLoS is working with to run the website; Google Knol with new features that allow content to be gathered together in collections after being vetted by expert moderators; and a new, independent database at the National Center for Biotechnology Information (NCBI) called Rapid Research Notes, where research targeted for rapid communication, such as the content in PLoS Currents: Influenza will be freely and permanently accessible. To ensure that researchers are properly credited for their work, PLoS Currents content will also be given a unique identifier by the NCBI so that it is citable.”

  • Nicholas Carr’s Blog: Close down the schools!
  • Cosma Shalizi’s course on Data Mining
    • Lecture notes included. I wish I’d looked at these earlier – the bits I’ve read are very informative.
  • LogiLogi: Philosophy beyond the paper
    • Thoughtful and stimulating discussion of how philosophy might benefit from the introduction of new online tools.
  • Science magazine and JoVE announce scientific-video partnership
    • “Science, the journal of scientific research, news, and commentary published by The American Association for the Advancement of Science (AAAS), and JoVE, the scientific video journal, announced that they have entered into a partnership for joint production and publication of scientific videos online. The purpose of the partnership is to enhance scientific articles published in Science through video demonstrations of experimental techniques.

      Under the partnership, which is currently in its pilot phase, Science will select papers suitable for the video enhancement, and will identify author groups willing to help shape the video demonstrations. JoVE will then work with the authors to create the actual demonstrations, using the company’s platform for geographically distributed video-production. According to Stewart Wills, Online Editor at Science, direct, in-article video demonstrations should increase the value of Science research to its main audience, working scientists and students. “

  • The definitive, two-part answer to “is data journalism?” | Holovaty.com
    • “It’s a hot topic among journalists right now: Is data journalism? Is it journalism to publish a raw database? Here, at last, is the definitive, two-part answer:

      1. Who cares?

      2. I hope my competitors waste their time arguing about this as long as possible.”

  • Sharing with Google Groups
    • Potentially rather handy: you can share stuff on Google with entire groups: “As more and more businesses and organizations “go Google,” we find that many of the features we develop based on feedback from large enterprises end up benefiting all of our users. We recently rolled out improvements to the way Google Groups interacts with several of our applications. Now, sharing calendars, sites and documents with multiple people is easy — instead of adding people one at a time, you can simply share with an entire Google Group.”
  • Official Google Research Blog: On the predictability of Search Trends
    • “As we see that many of the search trends are predictable, we are introducing today a new forecasting feature in Insights for Search, along with a new version of the product. The forecasting feature is applied to queries which are identified as predictable (see, for instance, basketball or the trends in the Automotive category) and then shown as an extrapolation of the historical trends and search patterns.”

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Bertrand’s postulate

This post is motivated by the ongoing Polymath Project “finding primes”, an open source mathematics project whose aim (roughly speaking) is to find an efficient algorithm to deterministically generate a prime number of at least [tex]k[/tex] digits. The post isn’t a contribution to the ongoing research discussion, but rather describes background material I wanted to understand better: a proof of a mathematical theorem known as Bertrand’s Postulate, a simple result from the 19th century about how frequently prime numbers occur. It’s being cross-posted to the Polymath wiki. The post requires some familiarity with elementary number theory.

Despite its name, Bertrand’s postulate is a theorem, not an example of what we’d ordinarily call a postulate in mathematics. Here’s what it says:

Theorem (Bertrand’s Postulate): For every integer [tex]n \geq 2[/tex], there is a prime [tex]p[/tex] satisfying [tex]n < p < 2n[/tex].

Bertrand’s postulate is relevant to the finding primes problem because it guarantees the existence of a [tex]k[/tex]-digit prime for any [tex]k[/tex]. Brute force search thus yields a [tex]k[/tex]-digit prime after about [tex]O(10^k)[/tex] steps; this can be considered the “trivial bound” for the problem.

Bertrand’s postulate was apparently first proved by Chebyshev. For large [tex]n[/tex], the claim follows as a consequence of the prime number theorem. We will give an elementary proof due to Erdos.

Our strategy is to analyse the prime factorization of the binomial coefficient [tex]{2n \choose n}[/tex]. What we’ll discover is that for primes [tex]p \leq n[/tex], the corresponding prime power in the prime factorization of [tex]{2n \choose n}[/tex] is never very big. In fact, we can guarantee that those powers are quite small – much smaller than what one might a priori believe could be the case. What we’ll find as a consequence is that when we take the product of all the prime powers for [tex]p \leq n[/tex], the product can’t possibly be as big as [tex]{2n \choose n}[/tex]. And that means that there must be primes in the range [tex]n < p < 2n[/tex] which appear in the prime factorization of [tex]{2n \choose n}[/tex]. Rather than prove Bertrand's postulate directly, we'll first prove two results of independent interest. The first is a bound on the product of all primes less than [tex]n[/tex], due to Chebyshev. Lemma (Chebyshev bound): For integers [tex]n \geq 2[/tex], [tex]\prod_{p \leq n} p \leq 4^n[/tex], where the product is over all primes [tex]p[/tex] less than or equal to [tex]n[/tex].

The Chebyshev bound tells us that primes can’t occur too frequently (for example, with constant density) in the positive integers, for if they did, the product of primes on the left would rise much faster than [tex]4^n[/tex]. Although it’s not needed for a proof of Bertrand’s postulate, insight can be gained by expressing this idea in a simple quantitative way. Observe that if [tex]\pi(n)[/tex] is the number of primes less than or equal to [tex]n[/tex], then [tex]\pi(n)! \leq \prod_{p \leq n} p[/tex], simply because the [tex]k[/tex]th prime must be at least [tex]k[/tex]. Combining this observation with Chebyshev’s bound gives [tex]\pi(n)! \leq 4^n[/tex]. Taking logarithms of both sides, and applying Stirling’s approximation, we see that up to constant factors and small corrections, we have [tex]\pi(n) \ln \pi(n) \leq n[/tex]. This, in turn, implies that, up to constant factors and small corrections, [tex]\pi(n) \leq n \ln \ln n / \ln n[/tex]. Roughly speaking, the prime numbers are at most logarithmically dense in the positive integers. In fact, the prime number theorem tells us that [tex]\pi(n) \approx n / \ln n[/tex], as [tex]n[/tex] becomes large.

Proof of Chebyshev’s bound: We will induct on [tex]n[/tex]. The case when [tex]n=2[/tex] is obviously true. Furthermore, if we assume the result when [tex]n[/tex] is odd, it follows immediately for [tex]n+1[/tex], since the left-hand side is not affected by incrementing [tex]n[/tex]. So we assume the result is true up to some even number, [tex]n = 2m[/tex], and try to prove the result for [tex]2m+1[/tex]. What we’ll aim to show is that:

[tex] (*) \prod_{m+1 < p \leq 2m+1} p \leq 4^m [/tex] If we can prove this, then multiplying by the inequality [tex]\prod_{p \leq m+1} p \leq 4^{m+1}[/tex] (which is true by the inductive hypothesis) will give us the desired result. To prove (*), note that every prime [tex]p[/tex] satisfying [tex]m+1 < p \leq 2m+1[/tex] must divide [tex]{2m+1 \choose m}[/tex], since [tex]p[/tex] appears in the numerator, but not the denominator. Furthermore, the uniqueness of prime factorization means that the product of all such primes must also divide [tex]{2m+1 \choose m}[/tex], and so we have [tex] \prod_{m+1 < p \leq 2m+1} p \leq {2m+1 \choose m}. [/tex] The proof is completed by noting that [tex]{2m+1 \choose m}[/tex] appears twice in the binomial expansion of [tex](1+1)^{2m+1}[/tex], and thus [tex]{2m+1 \choose m} \leq 4^m[/tex]. QED

There are two main ideas in our proof of Chebyshev’s bound, and it’s worth pausing to appreciate them. The first idea is that there should be a relationship between products of primes and factorials, e.g.,

[tex] \prod_{m+1 < p \leq 2m+1} p \leq {2m+1 \choose m}. [/tex] The second is that there should be a relationship between combinatorial coefficients like [tex]{2m+1 \choose m}[/tex] and exponentials with fixed bases, e.g., [tex]{2m+1 \choose m} \leq 4^m[/tex]. Once these two ideas are firmly in mind, the proof of the Chebyshev bound is obvious. The second lemma used in our proof of Bertrand's postulate is a useful fact about the prime factorization of [tex]{2n \choose n}[/tex], telling us that [tex]{2n \choose n}[/tex] has a rather special prime factorization which only involves low powers. After the main statement of the lemma we will single out two special cases where the proof can be used to make statements that are a little stronger than the main statement. These cases are included explicitly only because they are useful later. Note that although they complicate the statement of the lemma somewhat, they are trivial consequences of the proof of the main statement in the lemma. Lemma: Let [tex]p[/tex] be a prime, and define [tex]r(p,n)[/tex] to be the largest number such that [tex]p^{r(p,n)}[/tex] divides [tex]{2n \choose n}[/tex]. Then [tex]p^{r(p,n)} \leq 2n[/tex]. There are two special cases where we can make stronger statements: (1) if [tex]p > \sqrt{2n}[/tex], then [tex]r(p,n)[/tex] is [tex]1[/tex] or [tex]0[/tex]; (2) if [tex]2n/3 < p \leq n[/tex], then [tex]r(p,n) = 0[/tex].

This lemma contains the essential insight underlying Bertrand’s postulate, and that we explained earlier: because we can guarantee that the prime powers are low, [tex]{2n \choose n}[/tex] must have many prime factors. A careful accounting using the Chebyshev bound will show that we simply don’t have enough if one of those prime factors isn’t in the range [tex]n < p < 2n[/tex]. Proof: To prove the lemma, first note that the prime power of [tex]p[/tex] in the factorization of [tex]n![/tex] is given by [tex]\sum_{j=1}^{\infty} \lfloor n / p^j \rfloor[/tex]. As a result, [tex]r(p,n) = \sum_{j=1}^\infty ( \lfloor 2n / p^j \rfloor – 2 \lfloor n / p^j \rfloor)[/tex]. All terms in this sum are either [tex]0[/tex] or [tex]1[/tex], depending on whether [tex]\lfloor 2n/p^j \rfloor[/tex] is even or odd, and they are always [tex]0[/tex] when [tex]j > \log_p (2n)[/tex], whence [tex]r(p,n) \leq \log_p (2n)[/tex], which gives the main result.

In the special case of (1), [tex]p > \sqrt{2n}[/tex], simply observe that all but the first term in the sum vanishes, and so [tex]r(p,n) = \lfloor 2n/ p \rfloor – 2 \lfloor n/p \rfloor[/tex], which is either [tex]0[/tex] or [tex]1[/tex], according to whether [tex]\lfloor 2n/p \rfloor[/tex] is even or odd.

In the special case of (2), [tex]2n/3 < p \leq n[/tex], observe again that all but the first term in the sum vanishes, and so [tex]r(p,n) = \lfloor 2n/p \rfloor - 2 \lfloor n/p \rfloor[/tex]. But for any such value of [tex]p[/tex] we see that [tex]\lfloor 2n/p \rfloor[/tex] is equal to [tex]2[/tex], which is even, and so [tex]r(p,n) = 0[/tex]. QED

The proof of Bertrand’s postulate is now straightforward.

Proof of Bertrand’s postulate: For a contradiction, suppose there are no primes satisfying [tex]n < p < 2n[/tex]. In light of case (2) of the last lemma, we can assume that all the prime factors in [tex]{2n \choose n}[/tex] satisfy [tex]p \leq 2n/3[/tex]. We split the prime factorizing of [tex]{2n \choose n}[/tex] up into the cases where [tex]p \leq \sqrt{2n}[/tex] and where [tex]\sqrt{2n} < p \leq 2n/3[/tex]. Applying the last lemma we obtain: [tex] {2n \choose n} \leq \prod_{p \leq \sqrt{2n}} (2n) \prod_{\sqrt{2n} < p \leq 2n/3} p [/tex] We can bound the first product by noting that there are no more than [tex]\sqrt{2n}[/tex] primes of size at most [tex]\sqrt{2n}[/tex], and bound the second product using Chebyshev's bound: [tex] {2n \choose n} \leq (2n)^{\sqrt 2n} 4^{2n/3}. [/tex] Observing that [tex]{2n \choose n}[/tex] is the largest of the [tex]2n+1[/tex] terms in the binomial expansion of [tex](1+1)^{2n}=4^n[/tex], we see that [tex] \frac{4^n}{2n+1} \leq {2n \choose n} [/tex] Combinining the last two inequalities and rearranging a little gives [tex] 4^{n/3} \leq (2n+1)(2n)^{\sqrt 2n}. [/tex] The left-hand side rises much faster than the right, and so this inequality can only be true over some finite set of [tex]n[/tex]. It should be straightforward to convince yourself that it fails for [tex]n > 2048[/tex], for example, and thus we must have [tex]n \leq 2048[/tex]. In fact, we can do quite a bit better than [tex]n \leq 2048[/tex] with a bit more work, but the bound suffices for our purposes. What we have now shown is that our initial assumption – no prime in the range [tex]n < p < 2n[/tex] - can only possibly hold when [tex]n \leq 2048[/tex]. But it's easily seen that the assumption is also false in that range, just by considering the sequence of primes [tex]2,3,5,7,13,23,43,83,163,317,631,1259[/tex], and [tex]2503[/tex]. Each prime in the sequence is less than twice its predecessor, and so there must be a prime between [tex]n[/tex] and [tex]2n[/tex] for any [tex]n \leq 2048[/tex]. QED

Published
Categorized as Polymath

Biweekly links for 08/17/2009

  • Project Chanology – Wikipedia, the free encyclopedia
    • Excellent Wikipedia article on the confrontations between Anonymous and the Church of Scientology.
  • rehash.nl
    • Archive of materials (including video) from the series of hacker conferences in the Netherlands.
  • Measuring Distances in Google Maps
    • How to measure distances along customized routes in Google Maps.
  • DebugAdvisor: A Recommender System for Debugging – Microsoft Research
    • “In large software development projects, when a programmer is assigned a bug to fix, she typically spends a lot of time searching (in an ad-hoc manner) for instances from the past where similar bugs have been debugged, analyzed and resolved. Systematic search tools that allow the programmer to express the context of the current bug, and search through diverse data repositories associated with large projects can greatly improve the productivity of debugging. This paper presents the design, implementation and experience from such a search tool called DebugAdvisor.

      The context of a bug includes all the information a programmer has about the bug, including natural language text, textual rendering of core dumps, debugger output etc.

      Our key insight is to allow the programmer to collate this entire context as a query to search for related information. Thus, DebugAdvisor allows the programmer to search using a fat query, which could be kilobytes of structured and unstructured data…”

  • Happiness and unhappiness in east and west: Themes…[Emotion. 2009] – PubMed Result
    • Why studies which ask people to self-assess “happiness” on some scale are of dubious utility (what do they measure?): “Cultural folk models of happiness and unhappiness are likely to have important bearings on social cognition and social behavior… the authors systematically analyzed American and Japanese participants’ spontaneously produced descriptions of the two emotions and observed… that whereas Americans associated positive hedonic experience of happiness with personal achievement, Japanese associated it with social harmony. Furthermore, Japanese were more likely than Americans to mention both social disruption and transcendental reappraisal as features of happiness… descriptions of unhappiness included various culture-specific coping actions: Whereas Americans focused on externalizing behavior (e.g., anger and aggression), Japanese highlighted transcendental reappraisal and self-improvement. Implications for research on culture and emotion are discussed.”
  • Genesis 1 – LOLCat Bible Translation Project
    • “Boreded Ceiling Cat makinkgz Urf n stuffs

      1 Oh hai. In teh beginnin Ceiling Cat maded teh skiez An da Urfs, but he did not eated dem.

      2 Da Urfs no had shapez An haded dark face, An Ceiling Cat rode invisible bike over teh waterz.

      3 At start, no has lyte. An Ceiling Cat sayz, i can haz lite? An lite wuz.4 An Ceiling Cat sawed teh lite, to seez stuffs, An splitted teh lite from dark but taht wuz ok cuz kittehs can see in teh dark An not tripz over nethin.5 An Ceiling Cat sayed light Day An dark no Day. It were FURST!!!1”

  • Scylla and Charybdis
    • “Institutions need both fixed representations and novel representations to remain organized and retain people’s attention. Interpretive traditions, where the interpretand is fixed, face a special challenge in this regard. That they are able to resolve it successfully, most of the time, is a testament to the immense skill of our species as information managers.”
  • Thinking about Mario, Pompeii and the internet – confused of calcutta
  • co5TARS
    • Fun and informative way of visualizing the careers of actors, directors, etc.

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Biweekly links for 08/14/2009

  • ongoing · Blog & Tweet
    • Tim Bray: “Because whenever you see a vendor owning a communications medium, that’s part of the problem, not part of the solution. Even if the vendor is as lovable as Twitter; and I do love ’em. So I’m going to route around the breakage, and you might want to think about doing the same.”
  • Motivic stuff
    • Another interesting new mathematical blog, this one focusing on cohomology, homotopy theory, and arithmetic geometry.
  • Augmented Social Cognition: More details of changing editor resistance in Wikipedia
    • Data showing that new editors are much more likely to have their edits reverted. Claims that this shows Wikipedia is become more resistant to new ideas. The obvious objection is that maybe all it shows is that the contributions of new editors aren’t very good compared to established editors. Stil, lots of interesting data.
  • Augmented Social Cognition: The slowing growth of Wikipedia: some data, models, and explanations
    • Wikipedia’s growth rate has essentially plateaued.
  • David Byrne: So, How Does It Work on the Bus?
    • Excellent article from David Byrne about being a rock star on tour. A few little tidbits: they place at least 4 shows a week to make ends meet, so there’s not a lot of time to stick around; the tour used to be viewed as a loss leader to sell albums (no more!); they usually depart just 90 minutes after show ends; and much more.
  • A Comparison of Open Source Search Engines « zooie’s blog
  • Benchmarking Amazon EC2 for High-Performance Scientific Computing
    • Interesting, though many others factors will often need to be compared in practice. Abstract: “How effective are commercial cloud computers for high-performance scientific computing compared to currently available alternatives? I aim to answer a specific instance of this question by examining the performance of Amazon EC2 for high-performance scientific applications. I used macro and micro benchmarks to study the performance of a cluster composed of EC2 high-CPU compute nodes and compared this against the performance of a cluster composed of equivalent processors available to the open scientific research community. My results show a significant performance gap in the examined clusters that system builders, computational scientists, and commercial cloud computing vendors need to be aware of.”

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Biweekly links for 08/10/2009

  • Bad science: Hit and myth: curse of the ghostwriters
    • Excellent article explaining mechanisms by which incorrect science can be amplified and become widely accepted: “Using the interlocking web of citations you can see how this happened. A small number of review papers funnelled large amounts of traffic through the network. These acted like a lens, collecting and focusing citations on the papers supporting the hypothesis.”
  • Citing papers that you’ve never read — or that were never written « IREvalEtAl
    • “The Most Influential Paper Gerard Salton Never Wrote, an article by David Dubin tracing the history of the vector space model as applied to the field of information retrieval. In this article, Dubin points out that a highly cited paper, “A Vector Space Model for Information Retrieval”, published by Gerard Salton in 1975 in the Journal of the American Society for Information Science, does not in fact exist…Nevertheless, the non-existent article is cited 215 times according to Google Scholar.”
  • Decca Aitkenhead meets Clive James | The Guardian
    • Clive James on writing: “Thomas Mann, he said – and this is great, this is writing – he said a writer is someone for whom writing is harder than it is for other people.

      That line is perfect in every way. Not only is it perfectly written, but it’s absolutely true.

      The only thing I’ve got better at as the years have gone by is I’ve grown more resigned to the fact that it comes hard. You realise that hesitation and frustration and waiting are part of the process, and you don’t panic. I get a lot better at not panicking. I get up every morning early if it’s a writing day and I will do nothing else but write that day. But the secret is not to panic if it doesn’t come.”

  • Total Recall
    • Blog for the book “Total Recall”, a book about lifelogging, by Gordon Bell and Jim Gemmell. Many interesting tidbits about what you can do with a record of your life.
  • MyLifeBits – Microsoft Research
    • Gordon Bell’s remarkable MyLifeBits project: “MylifeBits is a lifetime store of everything. It is the fulfillment of Vannevar Bush’s 1945 Memex vision including full-text search, text & audio annotations, and hyperlinks…. a lifetime’s worth of articles, books, cards, CDs, letters, memos, papers, photos, pictures, presentations, home movies, videotaped lectures, and voice recordings and stored them digitally. He is now paperless, and is beginning to capture phone calls, IM transcripts, television, and radio.”
  • Three Rivers Institute » Approaching a Minimum Viable Product
    • I’ve been guilty of this: Kent Beck: “By far the dominant reason for not releasing sooner was a reluctance to trade the dream of success for the reality of feedback.” Interesting to think about what this means in the context of open science.
  • MediaFile » Why I believe in the link economy
    • From Chris Ahearn, President, Media at Thomson Reuters: “Blaming the new leaders or aggregators for disrupting the business of the old leaders, or saber-rattling and threatening to sue are not business strategies – they are personal therapy sessions. Go ask a music executive how well it works… If you are doing something that you would object to if others did it to you – stop. If you don’t want search engines linking to you, insert code to ban them. I believe in the link economy. Please feel free to link to our stories — it adds value to all producers of content… I don’t believe you could or should charge others for simply linking to your content. Appropriate excerpting and referencing are not only acceptable, but encouraged. If someone wants to create a business on the back of others’ original content, the parties should have a business relationship that benefits both.”
  • Scan This Book! – New York Times
    • Kevin Kelly on book digitization. I was particularly interested to see that Kelly takes very seriously both the idea that: (1) it will be near-impossible to maintain current business models built around copyright; and (2) we may end up with a lot less creative work going on as a result. Many people take (1) seriously, and many people take (2) seriously; relatively few people really do both.

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Polymath4

The Polymath4 Project is now underway, with the first formal post here.

The basic problem is very simple and appealing: it’s to find a deterministic algorithm which will quickly generate a prime of at least some given length, ideally in time polynomial in that length. There are fast algorithms which will generate such a prime with high probability – cryptography algorithms like RSA wouldn’t work if that weren’t true. But there’s no known deterministic algorithm.

I’m going to miss the first week of the project – I’ll be camping in a field in the Netherlands, surrounded by 1000+ hackers. But I’m looking forward to catching up when I come back.

On a related note, John Baez asks what mathematicians need to know about blogs.

Biweekly links for 08/07/2009

  • The Tragedy of the Coffee Shop
    • Nice article about the history of coffee shops as “third places”, inbetween home and work.
  • List of cities by time of continuous habitation – Wikipedia, the free encyclopedia
    • A remarkable list. Why do some cities die, and others live on? Jericho and Damscus have existed for roughly 10,000 years. As a child I lived briefly in a former goldmining town, whose 1880 population was more than 10,000, but which had dropped to about 200. Many cities initially thrive because they have access to some scarcity (a mine, a beautiful beach, a river); later they thrive because of network effects (you go to the mining town because all the mining companies are already there); presumably what happens is that some exogeneous event (collapse of some market, or depletion of a resource) destroys the value of the networks there.
  • Cory Doctorow: Metacrap
    • Cory Doctorow on the semantic web: “If everyone would subscribe to such a system and create good metadata for the purposes of describing their goods, services and information, it would be a trivial matter to search the Internet for highly qualified, context-sensitive results: a fan could find all the downloadable music in a given genre, a manufacturer could efficiently discover suppliers, travelers could easily choose a hotel room for an upcoming trip.

      A world of exhaustive, reliable metadata would be a utopia. It’s also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. “

  • Edifying Editing (pdf)
    • Stimulating and very well written article about editing an academic journal, by Preston McAfee.
  • Wandering Gaia
    • Excellent blog from a science writer who quit her job to go “travelling the world meeting the people, plants and animals that make up our unique living planet.”
  • IREvalEtAl: William Webber’s research blog
    • Blog of information retrieval researcher William Webber.
  • TotallySynthetic.com » Blog Archive » NaH as an Oxidant – Liveblogging!
    • Liveblogging a chemistry experiment to refute a paper: “an intriguing paper has been published in JACS by Xinbo Wang, Bo Zhang and David Zhigang Wang. In this, they suggest it is possible to oxidise benzylic alcohols to the corresponding ketones using sodium hydride (amongst other chemistry). Given that sodium hydride is, well, a hydride – this is quite something. Does it work? Hard to say without giving it a go, so I am.”

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