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Lindy effect - Wikipedia
The Lindy effect is a theory that the future life expectancy of some non-perishable things like a technology or an idea is proportional to their current age, so that every additional period of survival implies a longer remaining life expectancy.[1] Where the Lindy effect applies, mortality rate decreases with time. In contrast, living creatures and mechanical things follow a bathtub curve where, after "childhood", the mortality rate increases with time. Because life expectancy is probabilistically derived, a thing may become extinct before its "expected" survival. In other words, one needs to gauge both the age and "health" of the thing to determine continued survival.
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3 days ago by nhaliday
Theory of Self-Reproducing Automata - John von Neumann

Comparisons between computing machines and the nervous systems. Estimates of size for computing machines, present and near future.

Estimates for size for the human central nervous system. Excursus about the “mixed” character of living organisms. Analog and digital elements. Observations about the “mixed” character of all componentry, artificial as well as natural. Interpretation of the position to be taken with respect to these.

Evaluation of the discrepancy in size between artificial and natural automata. Interpretation of this discrepancy in terms of physical factors. Nature of the materials used.

The probability of the presence of other intellectual factors. The role of complication and the theoretical penetration that it requires.

Questions of reliability and errors reconsidered. Probability of individual errors and length of procedure. Typical lengths of procedure for computing machines and for living organisms--that is, for artificial and for natural automata. Upper limits on acceptable probability of error in individual operations. Compensation by checking and self-correcting features.

Differences of principle in the way in which errors are dealt with in artificial and in natural automata. The “single error” principle in artificial automata. Crudeness of our approach in this case, due to the lack of adequate theory. More sophisticated treatment of this problem in natural automata: The role of the autonomy of parts. Connections between this autonomy and evolution.

- 10^10 neurons in brain, 10^4 vacuum tubes in largest computer at time
- machines faster: 5 ms from neuron potential to neuron potential, 10^-3 ms for vacuum tubes
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april 2018 by nhaliday
The rate of return on everything - Marginal REVOLUTION
Here is what I learned from the paper itself:

1. Risky assets such as equities and residential real estate average about 7% gains per year in real terms.  Housing outperformed equity before WWII, vice versa after WWII.  In any case it is a puzzle that housing returns are less volatile but about at the same level as equity returns over a broader time span.
2. Equity and housing gains have a relatively low covariance.  Buy both!
3. Equity returns across countries have become increasingly correlated, housing returns not.
4. The return on real safe assets is much more volatile than you might think.
5. The equity premium is volatile too.
6. The authors find support for Piketty’s r > g, except near periods of war.  Furthermore, the gap between r and g does not seem to be correlated with the growth rate of the economy.

I found this to be one of the best and most interesting papers of the year.
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december 2017 by nhaliday
Autoignition temperature - Wikipedia
The autoignition temperature or kindling point of a substance is the lowest temperature at which it spontaneously ignites in normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure or oxygen concentration increases. It is usually applied to a combustible fuel mixture.

The time {\displaystyle t_{\text{ig}}} {\displaystyle t_{\text{ig}}} it takes for a material to reach its autoignition temperature {\displaystyle T_{\text{ig}}} {\displaystyle T_{\text{ig}}} when exposed to a heat flux {\displaystyle q''} {\displaystyle q''} is given by the following equation:
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november 2017 by nhaliday
I can throw a baseball a lot further than a ping pong ball. I cannot throw a bowling ball nearly as far as a baseball. Is there an "optimal" weight for a ball to throw it as far as possible? : answers
If there are two balls with the same size, they will have the same drag force when traveling at the same speed.
Smaller balls will have less wetted area, and therefore less drag force acting on them
A ball with more mass will decelerate less given the same amount of drag.
The human hand has difficulty holding objects that are too large or too small.
I think that a human's throw is limited by the speed of the hand at the moment of release -- the object can't move faster than your hand when it's released.
A ball with more mass will also be more difficult for a human to throw. Thier arm will rotate slower and the object will have less velocity.
As such, you want the smallest ball that a human can comfortably hold, that is heavy for its size but still light with respect to a human's perspective. Bonus points for drag reduction tech.
Golf balls are surprisingly heavy given their size, and the dimples are designed to convert a laminar boundary layer into a turbulent one. Turbulent boundary layers grip the surface better, delaying flow separation, which is likely the most significant contribution to parasitic drag.
TL; DR: probably a golf ball.
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september 2017 by nhaliday
Reynolds number - Wikipedia
The Reynolds number is the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities, in what is known as a boundary layer in the case of a bounding surface such as the interior of a pipe. A similar effect is created by the introduction of a stream of higher velocity fluid, such as the hot gases from a flame in air. This relative movement generates fluid friction, which is a factor in developing turbulent flow. Counteracting this effect is the viscosity of the fluid, which as it increases, progressively inhibits turbulence, as more kinetic energy is absorbed by a more viscous fluid. The Reynolds number quantifies the relative importance of these two types of forces for given flow conditions, and is a guide to when turbulent flow will occur in a particular situation.[6]

Re = ρuL/μ

(inertial forces)/(viscous forces)
= (mass)(acceleration) / (dynamic viscosity)(velocity/distance)(area)
= (ρL^3)(v/t) / μ(v/L)L^2
= Re

NB: viscous force/area ~ μ du/dy is definition of viscosity
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september 2017 by nhaliday
Europa, Enceladus, Moon Miranda | West Hunter
A lot of ice moons seem to have interior oceans, warmed by tidal flexing and possibly radioactivity.  But they’re lousy candidates for life, because you need free energy; and there’s very little in the interior oceans of such system.

It is possible that NASA is institutionally poor at pointing this out.
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september 2017 by nhaliday
diffusion - Surviving under water in air bubble - Physics Stack Exchange
I get d≈400md≈400m.

It's interesting to note that this is independent of pressure: I've neglected pressure dependence of DD and human resilience to carbon dioxide, and the maximum safe concentration of carbon dioxide is independent of pressure, just derived from measurements at STP.

Finally, a bubble this large will probably rapidly break up due to buoyancy and Plateau-Rayleigh instabilities.
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august 2017 by nhaliday
Historically significant lunar eclipses - Wikipedia
On 30 June 1503, Christopher Columbus beached his two last caravels and was stranded in Jamaica. The indigenous people of the island welcomed Columbus and his crew and fed them, but Columbus' sailors cheated and stole from the natives. After six months, the natives halted the food supply.[8]

Columbus had on board an almanac authored by Regiomontanus of astronomical tables covering the years 1475–1506; upon consulting the book, he noticed the date and the time of an upcoming lunar eclipse. He was able to use this information to his advantage. He requested a meeting for that day with the Cacique, the leader, and told him that his god was angry with the local people's treatment of Columbus and his men. Columbus said his god would provide a clear sign of his displeasure by making the rising full Moon appear "inflamed with wrath".

The lunar eclipse and the red moon appeared on schedule, and the indigenous people were impressed and frightened. The son of Columbus, Ferdinand, wrote that the people:

“ with great howling and lamentation came running from every direction to the ships laden with provisions, praying to the Admiral to intercede with his god on their behalf... ”
Columbus timed the eclipse with his hourglass, and shortly before the totality ended after 48 minutes, he told the frightened indigenous people that they were going to be forgiven.[8] When the moon started to reappear from the shadow of the Earth, he told them that his god had pardoned them.[9]
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august 2017 by nhaliday
rotational dynamics - Why do non-rigid bodies try to increase their moment of inertia? - Physics Stack Exchange
This happens to isolated rotating system that is not a rigid body.

Inside such a body (for example, steel chain in free fall) the parts move relatively to each other and there is internal friction that dissipates kinetic energy of the system, while angular momentum is conserved. The dissipation goes on until the parts stop moving with respect to each other, so body rotates as a rigid body, even if it is not rigid by constitution.

The rotating state of the body that has the lowest kinetic energy for given angular momentum is that in which the body has the greatest moment of inertia (with respect to center of mass). For example, a long chain thrown into free fall will twist and turn until it is all straight and rotating as rigid body.


If LL is constant (net torque of external forces acting on the system is zero) and the constitution and initial conditions allow it, the system's dissipation will work to diminish energy until it has the minimum value, which happens for maximum IaIa possible.
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august 2017 by nhaliday
Introduction to Scaling Laws

Galileo’s Discovery of Scaling Laws:
Days 1 and 2 of Two New Sciences

An example of such an insight is “the surface of a small solid is comparatively greater than that of a large one” because the surface goes like the square of a linear dimension, but the volume goes like the cube.5 Thus as one scales down macroscopic objects, forces on their surfaces like viscous drag become relatively more important, and bulk forces like weight become relatively less important. Galileo uses this idea on the First Day in the context of resistance in free fall, as an explanation for why similar objects of different size do not fall exactly together, but the smaller one lags behind.
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august 2017 by nhaliday

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