true love

As I eagerly await the return of my muse, I stumbled upon this at xkcd via pithy prof anon:

solid state audio

Attached is the PCB schematic for an audio amp based around national’s overture series. I designed and built this to suit a B&O beogram purchased when I had v. little coinage. The pad layout was created under circad, on a little old laptap running windmills 95. I was at a conference in Monterrey CA at the time (2004), and the bucolic scenery was too much to resist; I mostly sat on the beach drinking it all in, knocking this design together. There was a neat record shop which appeared to be the last bastion of the counterculture popular in Monterrey during the sixties. I picked up several LP’s including rare garage rock and was regaled by the owner’s tales of hearing Dylan back in the day.

I sampled out the 56W overture model from national; if you’re not familiar with this, engineers etc can get free samples from manufacturers, try it sometime. I also included a phono stage based around the LM833, to perform the RIAA equalization. This is of course necessary since the freq response of LP playback is not flat, so as to counteract deleterious mechanical issues. You could of course forgo this stage for a rather weird aural experience.

All you need to know is contained in the National tech note on the LM833 and overture, including supporting discrete components. I also include in the circuit a mixer/balance IC and notch filter for 50Hz. Thankfully I didn’t need to utilize the latter, the hum left when I eliminated all the ground loops; don’t forget to tie the ground of your LP to the amp & connect voltages to the right rails. The speaker(s) I built from pine to suit, which has a lower resonance than a hardwood like oak and to my mind the sound is richer, more mellow. The speakers (bose) and cross overs were bought online from allelectronics.com for pennies.

In the works 2009 is a tube amp…

main board PCB art

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Weezer blue album

Makes me miss 1994

concrete counter

We’re nearing the end of an almost total restoration of our ~1860 house. It’s gigantic with many beautiful details but some aspects needed severe TLC, including the kitchen. We tore back ~100 years worth of previous alterations to expose bricks, uncovering large windows which had been boarded up(!). In order to work in some modern industrial design features whilst working with the rustic nature of the room, we struck upon using concrete for a large center island, referring to Cheng’s book for inspiration.

I decided to experiment a little, straying from the designs within the book, largely due to the weight issue. For instance a 2″ by 7′x3′ slab suitable for the island would be something like 600lbs and given the nature of the old joists, I didn’t fancing loading the floor to that degree. So for my design, I settled on a 2.5″x 2.5″ overhang, and used a blank to remove some of the volume; the majority of the counter is 1.5″ thick. I used quickrete mix with fibreglass in the hopes of reducing the threat of cracking given the thin slab.

Pictured is some of the detail of the mould, including water run off, fashioned from tin sheet and lumber, filled with car body filler. I made the corners by heating acrylic in a conventional oven on 250F for 5-10 mins and dropped them in the sink corners to capture the shape before cooling. Along the underside of the mold are 3″ strips of pine, ripped up on the table saw and screwed and glued edgewise to the mould back to keep it true. I used threaded re-bar with coupling nuts within the overhang for extra support, given that there is some cantilever action at the (unsupported) eatery end of the island. The sink is undermounted, for an undulating surface finish… more photos of the kitchen in ..er.. ‘photos’

MQMAS sim paper in press

Abstract: The majority of nuclei available for study in solid state Nuclear Magnetic Resonance have half-integer spin I > 1/2, with corresponding electric quadrupole moment. As such, they may couple with a surrounding electric field gradient. This effect introduces anisotropic line broadening to spectra, arising from distinct chemical species within polycrystalline solids. In Multiple Quantum Magic Angle Spinning (MQMAS) experiments, a second frequency dimension is created, devoid of quadrupolar anisotropy. As a result, the center of gravity of peaks in the high resolution dimension are functions of isotropic quadrupole and chemical shifts alone. However, for complex materials, these parameters take on a stochastic nature due in turn to structural and chemical disorder. Lineshapes may still overlap in the isotropic dimension, complicating the task of assignment and interpretation. A distributed computational approach is presented here which permits simulation of the MQMAS spectrum, generated by random variates from model distributions of isotropic chemical and quadrupole shifts. Owing to the non-convex nature of the least squared cost function between experimental and simulated spectra, simulated annealing is used to optimize the simulation parameters. In this manner, local chemical environments for disordered materials may be characterized, and via a re-sampling approach, error estimates for parameters produced.

Key words: Nuclear Magnetic Resonance, Multiple Quantum Magic Angle Spinning, OpenMP, Sobol sequence, quasi-random numbers, simulated annealing, distribution functions, quadrupole interaction.

A touch of Frost

Sure it’s cliché, but the hint of spring and coming close to finishing postdoc brings to mind Frost’s “The road not taken”:

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TWO roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;

Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,

And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.

emergence via connectedness

Cellular Automata have proved fertile research for at least 50 years, providing models for everything ranging from crystal growth to fluid dynamics. Discrete rules are applied at each time step to evolve a particular cellular state; ordered patterns emerge from random initial configurations. The example given here using the connected components labeling (CCL) algorithm demonstrates how topology also can give rise to order from randomness.

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CCL in OCTAVE:

lab=1; freq=1; x=0; y=0;
% main loop(s)

for i=2:c-1
for j=2:d-1

if ( a(i,j)!=0 & label(i,j)==0)

x=i;
y=j;

label(i,j)=lab;
while (x!=1) & (y!=1) & (x!=c) & (y!=d)

[mm,x,nn,y]=pop_s(x,y);

if (a(mm-1,nn-1)==1 && label(mm-1,nn-1)==0 )

[x,y]=push_s(mm-1,x,nn-1,y);
label(mm-1,nn-1)=lab;
freq(lab)++;
end

if (a(mm-1,nn)==1 && label(mm-1,nn)==0)

[x,y]=push_s(mm-1,x,nn,y);
label(mm-1,nn)=lab;
freq(lab)++;
end

if (a(mm-1,nn+1)==1 && label(mm-1,nn+1)==0)

[x,y]=push_s(mm-1,x,nn+1,y);
label(mm-1,nn+1)=lab;
freq(lab)++;
end

if (a(mm,nn-1)==1 && label(mm,nn-1)==0)

[x,y]=push_s(mm,x,nn-1,y);
label(mm,nn-1)=lab;
freq(lab)++;
end

if (a(mm,nn+1)==1 && label(mm,nn+1)==0)

[x,y]=push_s(mm,x,nn+1,y);
label(mm,nn+1)=lab;
freq(lab)++;
end

if (a(mm+1,nn-1)==1 && label(mm+1,nn-1)==0)

[x,y]=push_s(mm+1,x,nn-1,y);
label(mm+1,nn-1)=lab;
freq(lab)++;
end

if (a(mm+1,nn)==1 && label(mm+1,nn)==0)

[x,y]=push_s(mm+1,x,nn,y);
label(mm+1,nn)=lab;
freq(lab)++;
end

if (a(mm+1,nn+1)==1 && label(mm+1,nn+1)==0)

[x,y]=push_s(mm+1,x,nn+1,y);
label(mm+1,nn+1)=lab;
freq(lab)++;
end

end %endwhile

lab++;
freq=[freq, 1];

end %endif

end
end