countercurrent #heat-exchangers called recuperators are commonly used to recover 70-80% of the exhaust heat to preheat incoming air and fuel in metallurgical furnaces, heat engines including microturbines, and also in #Gelbart’s uniflow #steam-engine. #mecheng
I wonder if #Braess’s Paradox is applicable to negative-#stiffness #metamaterials? Braess’s original formulation was, "an extension of the road network may cause a redistribution of the traffic that results in longer individual running times”, but I’m pretty sure I’ve seen this in the form of a mobile that hangs higher after you cut a thread in it.
A #paper on a numerically-simulated analog of the #Braess paradox in mesoscopic (? quantum-phase-coherent?) #semiconductor networks: “adding a third branch can paradoxically induce transport inefficiency that manifests itself in a sizable conductance drop of the network.” This is less interesting now that I understand Cohen & Horowitz 1991.
A #video of a mechanical demonstration of #Braess’s paradox using the #stiffness of springs.
a #paper on mechanical and electrical analogs of #Braess’s paradox, using zeners in the electrical case. Has a clear explanation of the mechanical version of the system; it depends only on the nonlinear stress-strain behavior of buckling string. (String! Not springs!) The fixed maximum length of the string corresponds to the fixed maximum voltage of the zener. On p.700 (the second page) there’s a diagram showing something like a negative-#stiffness region in this network! Also explains that nonlinearity is necessary to produce this effect, and gives a hydraulic analogue as well.
this #paper about muscle myosin folding mentions “negative #stiffness at the point where all cross-bridges collectively flip... Similar mechanical behavior has been recently artificially engineered in #metamaterials by drawing on the #Braess paradox ... the mean-field type coupling in such materials is achieved via parallel connections with multiple shared links.” The references given are Cohen & Horowitz 1991 (the paper with the springs and strings) and Nicolaou and Motter 2012 in “Nat Mater”, which I guess is “Mechanical metamaterials with negative compressibility transitions” in Nature Materials.
#Abstract of “Mechanical #metamaterials with negative compressibility transitions” (i.e. negative #stiffness, although they contrast it in figure 1). This is Nicolaou and Motter 2012.
Another #abstract from Nature Materials on negative-compressibility or negative-#stiffness #metamaterials.
some PowerPoint slides showing, among other things, a sheet full of round holes (“holey sheet”) exhibiting negative #stiffness on p.63. Apparently this is from “Mullin et al, PRL 99, 2007.”
about “negative linear compressibility” (#NLC) which I think may be the same as negative #stiffness; the remarkable thing in this case is that they’re reporting it in zinc dicyanoaurate, not a metamaterial.
This is the actual Nicolaou and Motter 2012 paper on negative-#stiffness #metamaterials. They allude to giant-stiffness metamaterials in one of their references.
Jaglinski, Kochmann, Stone, and Lakes 2007. A giant-#stiffness metamaterial of 10% barium titanate particles dispersed in a tin matrix with a Young's modulus of several TPa, greater than that of diamond at 1TPa, and more than an order of magnitude greater than that of the components (100 and 50 GPa); but only within a critical temperature range of about 58–59°. “The constraint [of the expansion of the inclusions by the matrix] stabilizes the negative bulk modulus (inverse compressibility) of the inclusions. This negative modulus arises from stored elastic energy in the inclusions, in contrast to periodic composite #metamaterials that exhibit negative refraction by inertial resonant effects.” Also note that this doesn’t help with shear (e.g. torsion) stiffness, and that their materials decayed after thermal (and load?) cycling, though they suggest that using a stronger matrix would help.
Dennis Kochmann’s #metamaterials lab at #Caltech, which participated in the work on giant-#stiffness barium-titanate/tin composite. (Did Sofia work in his lab? She was analyzing perovskite behavior under stress when I met her.) Huge list of publications on giant-stiffness materials.
interesting stuff about waves propagating through strongly nonlinear #metamaterials (with negative #stiffness, actually very similar to the negative-stiffness structures being sold now to isolate turntables).
This “micro” “MEMS” gas #turbine runs at 500krpm on, obviously, an #air-bearing (they achieved a record speed of 1.2Mrpm), with a 20mm rotor (in a total 100mm×110mm casing) producing 1kW. The turbine itself is die-sink-EDM-machined conductive ceramic (composite #silicon-nitride and titanium nitride) to withstand the 1200 K gas; supposedly 20% overall efficiency with the 74.5%-efficient recuperator. This seems like overkill on the efficiency front for mobile-power uses (cellphones, laptops, drones), where the big issue is that batteries have an #energy-density of about 500kJ/kg, while hydrocarbons are at almost 50MJ/kg, so any efficiency over about 1% would be a victory condition for microturbines over batteries.
Newton’s Principia Mathematica #ebook in Latin.
Using #Coq #formalmethods to do a proof of a sort program.
2003 overview of millimeter-scale #turbines.
the #TCE range of different common #materials; e.g. fused silica is 0.55ppm/°, invar is 1.3, #silicon-nitride is 3.2, titanium is 9.5, copper is 16.7, polymers are 50–200, and silicone is 30–300.
a radio-controlled #flight-simulator included with the PicoLisp #Lisp interpreter. Doesn’t use OpenGL for #3D. PicoLisp's interpeter is 296 kB statically linked.
Another programming-language #benchmarks page like the Shootout.
much of the #security model of Urbit is explained here, along with the czar/duke/earl/king/pawn #neoreactionary hierarchy embedded into it.
Nick #Szabo writing on the #archaeology of #money and how it relates to seals, rituals, and I suppose implicitly #Bitcoin, though he wrote it in 2002.
“[T]he maternal aunts and grandmothers of homosexual probands were significantly more fecund compared with the maternal aunts and maternal grandmothers of the heterosexual probands. Moreover, due to the selective increase in maternal female fecundity, the total female fecundity was significantly higher in homosexual than heterosexual probands, thus compensating for the reduced fecundity of homosexuals. Altogether, these data support an X-linked multi-locus sexually antagonistic hypothesis rather than an autosomal multi-locus overdominance hypothesis” #gaygene #fecundity #natural-selection #lgbt
Raph Levien has put his 1989 #paper about Io, a programming language consisting entirely of syntactic sugar for explicit CPS, on the web!
“Growing a Compiler”, on a language and #virtual-machine called GEM, with the first version of the compiler written in Matlab. #compilers
Martin v. Löwis got #Unicode #UTF-8B implemented in Python 3! Or something very much like it. Unfortunately, it’s not the default.
How to learn #type-theory for #formal-methods.
“Practical Foundations for Programming Languages”, an #introduction #ebook to #type-theory for #formal-methods. 2012 to 2014.