30 July 2010

Friday Musings

First, Mumford & Son's "Little Lion Man" is amazing.  Listen.  Purchase.  Bonus points for accidentally starting two or more copies and noticing it sounds excellent in a round.  Found it on thesixtyone.com, which is a great source for day-to-day working music and occasionally emits gems like this one.

Second, the Richtmyer-Meshkov setup I've been mucking with for two days is working. In it, a shock wave interacts with a perturbed, constant pressure interface between two different densities (details). Courtesy of gnuplot and gifsicle, here's an animated gif showing density evolution for a problem that's periodic in y and reflective at both x boundaries (click to view animation, 3.2M):

Just a roll up?
The reflective condition at the left boundary causes a re-reshock, which isn't usually what folks are interested in for these problems.  I'm not entirely sure how to enforce a strict inflow condition for compressible simulations like these-- presumably such an inflow condition would eat the outgoing characteristics and stop the re-reshock seen here.

23 July 2010

Glam Shot

Today at LLNL I was involved in some photos for a story on the summer students at ISCR:

Daniel from Ghana, Hilary from Dallas, and me
The screen images are from the 2D WENO-based code I've been revising to investigate RANS modeling of Rayleigh-Taylor instabilities with Dr. Oleg Schilling. As a bit of nerd sniping, I made sure Trac, VIM's NERD tree, and some Mathematica reproducing classic results from Roe's JCP 1981 paper were clearly visible.

Unrelated, today I also had a couple of beers with Ondřej Čertík of sympy and theoretical physics fame. Unbelievably swell guy— easily one of the smartest one or two people with whom I've ever shared a brew.

Update: Entertainingly, in the related story the lab released, the caption shows me as a "Livermore scientist".

20 July 2010

Burst traffic smoothing for SIP processing elements

I received another patent grant from my IBM days. This time its United States Patent 7,742,417:

Mechanisms for burst traffic smoothing for Session Initiation Protocol (SIP) processing elements are provided. A dispatch queue management engine determines whether a received packet is a TCP or UDP packet. If the packet is a TCP packet, the packet is automatically added to the dispatch queue. If the packet is a UDP packet, a value for a drop function f is generated and a random or pseudo-random number r is generated. If r has a predetermined relationship to f, then the UDP packet is added to the dispatch queue, otherwise the UDP packet is discarded. The value for f is based on the current dispatch queue load, the network quality, the retransmission rate, and the allowable drop rate. Thus, the determination as to whether to drop UDP packets or not is configurable by an administrator and also adaptable to the current network and dispatch queue conditions.

The idea for this patent came from dealing with overflowing UDP buffers during a SIP-enabled Java application server stress test. We observed that garbage collection events would pause the application server and cause a backlog of SIP retransmissions over UDP to grow. The invention is a way to selectively toss out UDP packets during such a retransmission burst in a way that would allow the application server to catch up again while maintaining a probabilistically high QoS.

15 July 2010

Wireless tunes on the bike

I'm quite stoked about combining three new toys:
  1. BlueAnt's F4 Interphone Bluetooth helmet communication system
  2. Sony's TMR-BT8IP Bluetooth iPod transmitter
  3. HJC's IS-16 helmet
I've tried out the first two (to Kids of the K Hole no less, an excellent escapist riding anthem) and am supremely impressed.  It'll be nice to not be tethered to the tankbag by a huge, flaky PS/2 cable a la my klunkotronic Chatterbox GMRS X1.

I can't speak to mounting the Interphone's helmet speakers since the new HJC hasn't arrived yet, but the mounting hardware BlueAnt provided looks solid.  Also no verdict yet on the intercom functionality, but the full duplex sound should be a welcome improvement compared to the GMRS X1 (unless Pauly abuses said duplex connection by singing along to decidedly non-escapist anthems).

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