Photographs from Space by Karen L. Nyberg

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Amazing photographs from astronaut and engineer Karen L. Nyberg on Twitter during ISS-Expeditionen 36/37: The astronauts and engineers in space have internet: NASA Extends the World Wide Web Out Into Space. BTW, Karen L. Nyberg also posted a photo of a dinosaur in space.

Electronic Mathematical Journals

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Below journals, loosely related to topics in Numerical Analysis, offer unencumbered full text: Electronic Transactions on Numerical Analysis Applied Mathematics E-Notes (no longer active) The Electronic Journal of Linear Algebra arXiv Unfortunately, Numerische Mathematik, BIT, SIAM Journal on…

Re-installing Grub when MS Windows Destroyed It

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I have now done it a couple of times, but always have to look it up. Here are the steps to re-install Grub from a live Ubuntu CD, when you have Windows and Linux on your hard disk. You must be root, or run these commands with sudo. Change /dev/sdaXY accordingly. mount /dev/sda2 /mnt mount…

Gil Kalai on Zhang's Breakthrough in Number Theory

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Below I copy some paragraphs from a recent article in Polymath 8 – a Success! | Combinatorics and more by Gil Kalai on Zhang’s breakthrough regarding prime numbers: Twin primes are two primes $p$ and $p+2$. The ancient twin prime conjecture asserts that there are infinitely many twin primes.…

My Blog Statistics by Country

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Except notably Russia and Africa this blog has been visited by quite a number of countries. I am surprised. Also see Statistics of this Blog: Top Views by Country.

dotScale 2013 MySQL Talk

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Very interesting talk on the scaling challenge at WordPress.com given by Barry Abrahamson, CTO of WordPress. Some key points: 500 million database tables 3 data centers in USA 400.000 shards moved per day storage on SSD ~10% of total infrastructure costs are related to backups ~500 GB / shard 50…

WordPress/Automattic: Monthly Unique Visits and Employees

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Below table is from work-with-us (data as of 22-Sep-2013): One of these things is not like the other. Company NameMonthly Uniques…

Georg Hager's Blog: Intel vs. GCC for the OpenMP vector triad: Barrier shootout!

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Georg Hager's Blog posted an illustrative article on icc versus g++ performance w.r.t. OpenMP. Dr. Georg Hager is one of the authors of Introduction to High Performance Computing for Scientists and Engineers. Measurement of double precision, dimension(N) :: a,b,c,d ! initialization etc. omitted s =…

Graphs with JpGraph by Asial

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JpGraph is a library of PHP code to draw a variety of graphs: line+bar+pie charts radar+polar+contour graphs bar+QR codes Gantt charts a couple of other chart types Here are two examples: JpGraph is a free product by Asial if used in a non-commercial context. Installation is quite easy on…

Line Integral of a Vector Field

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Inspired by a discussion with my son regarding movement of a point-charge between two other charges I revisited the definition of the line integral. Wikipedia offers an excellent visualization of the definition of the line integral for a vector field. See animated graphic below: This is something…

Torricelli's Trumpet: Infinite Surface Area but Finite Volume

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Just read on Torricelli's trumpet in Wikipedia. This states that there is a body having infinite surface but finite volume! That sounds contradictory at first. Function in question is $$ y = 1 / x $$ from $x=1$ to $a$. Volume is $$ V = \pi \int_1^a \left({1\over x^2}\right)\,dx =…

The Attraction of Curves – Brian Koberlein

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Brian Koberlein wrote a very good introductory article on curvature of space and time in the vicinity of gravity: see The Attraction of Curves – Brian Koberlein.

Dramatic Faster Sorting in Linux Using Nsort

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Last year I used a drop-in replacement for the ordinary Linux sort command called nsort from Ordinal Technology. Ordinal's nsort is free but not open-source. One thing is clear, however, it is very fast. nsort was written by Chris Nyberg. The motivation for looking for a faster sort was as follows.…

Harddisk Drive Speed in MB/s

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Below picture is from Read Throughput Average in Tom's Hardware.

Proportion of Papers on hgpu.org

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hgpu.org contains links to reviews, tutorials, research papers, program packages concerning various aspects of graphics and non-graphics (general purpose computing) using of GPU and related parallel architectures (FPGA, Cell processors etc.). The majority is on NVidia, see picture below.

India is now the third largest Smartphone market in the world - Android Authority

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An article in Android Authority from 26-Jun-2013, India is now the third largest Smartphone market in the world, states that: There are 14 major carriers listed for India, including two state owned providers. None have over 180 million subscribers. The smartphone market in India is expanding at…

Inhibit Annoying Message of the Day in Ubuntu

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I find the motd annoying when you log in to a Ubuntu server machine. To get rid of this I do the following as root: cd /etc/update-motd.d mkdir klmDisabled mv ??-* klmDisabled Unfortunately, whenever the packages update-manager-core, landscape-common, base-files, update-notifier-common change,…

WordPress.com News and Numbers: The August 2013 Hot List

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As already posted last month, there are around 4 billion pageviews per month. This makes 1.4 pageviews per millisecond on the average. Each pageview incurs hundred of lines of PHP code executed, a couple of MySQL queries and updates.

China Built 600 Dams per Year Since 1950

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According Los Angeles Times (dead link) China built 600 dams per year on average. This trend will continue. According Wikipedia, or Jie Cai's Master Thesis (dead link), China has the largest potential for hydropower in the world and currently ranks first in hydroelectric generating capacity with…

Newer GPUGRID Tasks Keep GPU Really Hot

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Recent GPUGRID tasks, like I60R2-NATHAN_KIDKIXc22 or 27x0-SANTI_RAP74wtCUBIC really keep my NVidia GTX 560 hot, i.e., as warm as 70° Celsius or higher. Fri Sep 6 17:16:38 2013 +------------------------------------------------------+ | NVIDIA-SMI 5.325.15 Driver…