NNadir
NNadir's JournalA few minutes after the Germans...John Abercrombie.
Hot Cracks and Addressing Questions in the Origin of Life.
I spent part of my day yesterday reading about cracks in two ways, first in thinking about fracture toughness in silicon nitride, a cool material, which is not the subject of this post, and then about the effect of heat flowing through a crack to cause the polymerization of nucleotides into nucleic acids, which is the subject of this post.
I described my renewed interest in this topic here: Open source paper on "Defining Life."
Over the weekend, I found myself thinking about the anti-entropy that life is, and went poking around in the library.
Here's a cool paper I found on exactly that subject, the difficult case or the origin of nucleic acids, since many people postulate that life arose from an "RNA world:" Heat flux across an open pore enables the continuous replication and selection of oligonucleotides towards increasing length (Moritz Kreysing, Lorenz Keil, Simon Lanzmich and Dieter Braun, Nature Chemistry volume 7, pages 203208 (2015))
Entropy is discussed in the introduction:
It has been known since Spiegelmans experiments in the late 1960s11 that, even if humans assist with the assembly of an extracellular evolution system, genetic information from long nucleic acids is quickly lost. This is because shorter nucleic acids are replicated with faster kinetics and outcompete longer sequences. If mutations in the replication process can change the sequence length, the result is an evolutionary race towards ever shorter sequences.
In the experiments described here we present a counterexample. We demonstrate that heat dissipation across an open rock pore, a common setting on the early Earth12 (Fig. 1b), provides a promising non-equilibrium habitat for the autonomous feeding, replication and positive length selection of genetic polymers...
...Here we extend the concept to the geologically realistic case of an open pore with a slow flow passing through it. We find continuous, localized replication of DNA together with an inherent nonlinear selection for long strands. With an added mutation process, the shown system bodes well for an autonomous Darwinian evolution based on chemical replicators with a built-in selection for increasing the sequence length. The complex interplay of thermal and fluid dynamic effects, which leads to a length-selective replication (Fig. 1c, (1)(4)), is introduced in a stepwise manner.
The caption:
The authors take dilute short DNA fragments and drive the through a crack which has a temperature gradient on either end, the direction of flow being from hot to cold.
Here's a schematic picture from the paper:
A convective flow cycles the growing nucleic acid chain, and the overall flow determines the size of the DNA that exits from the system, and the heat provides the energy required for sequence replication:
The famous PCR technique, albeit a process using a thermally stable enzyme as a catalyst, also relies on heat for replication - the authors do some PCR work in their experiments.
However in this case, the enzyme is omitted, and the reaction takes place via cycling through thermal gradients.
Another picture:
The caption:
Another figure shows the effect of flow rate on strand length:
Finally "size selection habitats" are shown:
The caption:
The authors write:
...and in their conclusion state:
In another paper, not cited here that I encountered this weekend, John D. Sutherland, who has done very exciting work demonstrating a potential path for sugar containing phosphorylated sugars to arise out of simple molecules, used a Churchillian phrase to discuss where we are with explaining the generation of life from prebiotic very simple molecules, saying that the science of the prebiotic generation of life has reached "the end of the beginning."
Fascinating stuff, I think.
I hope you're having a pleasant week thus far.
Open source paper on "Defining Life."
As I age and more and more come face to face with the inevitably of dying, I wonder more and more, having experienced the real beauty of being alive, of whence life came to be.
I have always wanted to read Schroedinger's famous book, "What is Life?" but probably will never find the time.
Nevertheless, I resolved to spend some time reading this review article, Prebiotic Systems Chemistry: New Perspectives for the Origins of Life (Kepa Ruiz-Mirazo, Carlos Briones, and Andrés de la Escosura*§ Chem. Rev., 2014, 114 (1), pp 285366), when, not far in, I came across the following text:
However, we do not aim to discuss here in detail the issue of defining life: the reader is referred to a special issue of the journal Origins of Life and Evolution of Biospheres,9 or to a comprehensive anthology of articles on this subject.10
When I see references I'd like to pick up, I always email them to myself for my library time, and I usually send the reference as a link to the paper when possible so I can use my library time efficiently.
But when I generated the link to reference 9, I found that it opened at home, and thus is open sourced.
It's 244 pages on the question of "What is life," updated from Shroedinger, 85 years ago.
If you're interested, here it is:
Defining Life: Conference Proceedings.
Perhaps I don't know what life it, other than whatever it, it is extraordinarily beautiful, even with the pain, and very much worth living.
Have a great weekend!
My kid is in France learning how to become a Brazilian, calling soccer "football" and complaining...
...about the "dirty tactics" the Swiss used against Brazil in the World Cup.
He shares his office in the lab with four Brazilians, who he says, speak a language that sort of is to Spanish what German is to English.
The Brazilians, he says, are "just like Americans."
After work, his new friends invite him to play "football."
Some day, he says, he'd like to spend time learning Portuguese.
Should I be concerned?
Scaling Graphene.
There's a lot being written about graphene these days. Graphene, for those who don't know, is a carbon allotrope that has the carbons bonded an a series of almost infinite series of fused hexagonal aromatic rings that make it planar. The neat thing about this allotrope is that it is exactly one atom thick. If it's thinker than one atom, it's graphite, most commonly experience by most people as pencil lead.
There are thousands of pictures on the internet. Here's an electron micrograph, out of the Los Alamos National Laboratory, of the stuff with resolution on an atomic scale:
Source Page of the Image.
Graphene is proposed to have many uses and if I actually read all the papers I've seen in which it appears in the title, I'd be able to discuss some of them intelligently, but frankly, I skip over a lot of these papers, quite possibly all of them in fact because I'm too interested in other stuff. Mostly I've just mused to myself about the stuff, particularly its oxide, which I imagined might be functionalized as an interesting carbon capture material, but well, there's lots and lots and lots of those. The problem is not discovering new carbon capture materials; the problem is utilizing them without creating carbon dioxide waste dumps that don't exist and, were they to exist, would be unacceptably dangerous to future generations, not that we care about future generations.
When my son was touring Materials Science Departments at various universities in both "informational" sessions and in "accepted students" forums the word graphene came up a lot. At one such session, we were introduced to a professor who was described as having developed a way to prepare "kg quantities" of graphene, and I meekly raised my hand and asked, "What does a 'kilogram of graphene actually mean?" If I was as rude as I sometimes am around here, I might have asked the question as "Isn't a kilogram of stacked graphene just graphite?"
But I wasn't. I didn't want to screw things up for my kid if he decided to go there. (He didn't.)
At another university, during an informational session for students who might apply, a graduate student, who was writing his thesis at the time, took an interest in my son and decided to give us a full tour of the department. Somehow I used (or muttered) the word "graphene" during the tour and he, a somewhat jaded guy with a decidedly sarcastic edge - my kind of guy - said, "Well, I'm sure it would be useful if they knew how to make it in useful quantities, but they don't."
My son did apply there, by the way, was accepted there, and is, in fact, going there, a wonderful university.
To my surprise I suddenly find myself interested in graphene though because of a recent lecture on a subject about which I know nothing but about which I am interested in finding about more, as I discussed last night in a post in this space: Topological Semimetals.
The paper I linked in that post has the following remark:
The prototype of a DSM is graphene. The perfect DSM has the same electronic structure of graphene; i.e., it should consist of two sets of linearly dispersed bands that cross each other at a single point. Ideally, no other states should interfere at the Fermi level.
Graphene is a "perfect DSM," a "perfect Dirac Semimetal."
And today in my library hour, what should happen but that I was to come across a paper that reports an approach to scaling up graphene.
The paper is here: Exfoliation of Graphite into Graphene by a RotorStator in Supercritical CO2: Experiment and Simulation (Zhao et al, Ind. Eng. Chem. Res., 2018, 57 (24), pp 82208229)
I have been and am very interested in supercritical CO2, by the way. "Supercritical" refers to a substance that is neither a liquid nor a gas but exists in a state that has properties of both and can only exist above certain temperatures and pressures called respectively the "critical temperature" and, of course, "the critical pressure." The critical temperature of carbon dioxide is only a little above room temperature, which makes it a readily accessible material.
As my wont lately in this space when discussing scientific papers, I'll do some brief excerpts and invite you to look at the pictures, since whenever I decide whether or not to actually read a paper upon which I stumble (as opposed to a paper that I've sought for some reason), that's what I do, look at the pictures.
From the intro:
...The purpose of this work is to investigate the exfoliation mechanism of a rotor−stator mixer in supercritical CO2 by a combination of the experiment and CFD simulation and to make the optimal design of the rotor−stator mixer in terms of exfoliation efficiency for the potential industrial application.
CFD is computational fluid dynamics if you didn't know.
Now some pictures...
Here's a schematic of things they evaluate by computer simulation:
The caption:
Rotor design and (low, if higher than usual where graphene is concerned) yields:
The caption:
A little discussion of the mathematical physics of the situation:
2.2.1. Eulerian−Eulerian Two-Fluid Equations. Different phases were treated as interpenetration continuum. The conservation equations were solved simultaneously for each phase in the Eulerian framework. Then, the continuity equations for phase n (n = l for the liquid phase, s for the solid phase) can be expressed by
...
Some more cool math:
2.2.1. Eulerian−Eulerian Two-Fluid Equations. Different phases were treated as interpenetration continuum. The conservation equations were solved simultaneously for each phase in the Eulerian framework. Then, the continuity equations for phase n (n = l for the liquid phase, s for the solid phase) can be expressed by
At the same time, a granular temperature was introduced into the model:
...
Some simulation results:
The caption:
More simulation showing vessels and rotors:
The caption:
Figure 6. Stator and the contours of velocity and volume fraction in multiwall stator at 3000 rpm (A). The lateral view and the vertical view of the multiwall stator, (B) horizontal, and (C) perpendicular fluid flow pattern induced by multiwall stator; the graphite of volume fraction in (D) eighttooth stator and (E) multiwall stator.
Then they set about making themselves some graphene. It, along with graphene by other processes is pictured here:
The caption:
NMP is N-methylpyrollidine. I've used it, I'm still alive but know nothing of its toxicology. If it turns out to be toxic, we can use it to make solar cells, whereupon it will be declared "green," no matter what it's effect on living things.
Some more electron micrographs:
The caption:
Nevertheless the yields are not spectacular enough to make industrial application straight forward, although if it turns out that graphene solar cells are "great" we can bet the planetary atmosphere on the expectation that they'll be available "by 2050" when I - happily for many people who don't find me amusing - will be dead.
The caption:
Some concluding remarks:
Love that percent talk!
Interesting, I think, although I think that graduate student had a point.
I hope your Friday will be pleasant and productive.
Chemical Principles of Topological Semimetals
In the midst of the White House generated horror of the last days, I had the guilty pleasure of attending my favorite kind of lecture: A lecture that was not only on a subject about which I know nothing, but on a subject about which I never even heard, topological semimetals.
One of my goals in life is to feel as often as is possible like I'm the dumbest person in the room, and I definitely succeeded in this case.
The lecture was given by Dr. Leslie M. Schoop, the newest faculty member of the Princeton University Department of Chemistry.
I immediately went home after the lecture and began to look into the topic and was pleased to see that I recently downloaded (but clearly didn't read) a review article written by Dr. Schoop and her colleagues.
The article, from which the total of this post is taken is here: Chemical Principles of Topological Semimetals (Leslie M. Schoop,*, Florian Pielnhofer, and Bettina V. Lotsch, Chem. Mater., 2018, 30 (10), pp 31553176)
It's a relatively new, if rapidly expanding field, so I guess I can be excused for knowing nothing at all about it, but it apparently involves some novel particle physics apparently predicted by the mathematical physicist Hermann Weyl during the scientifically transcendent 20th century.
Since it involves the structure of matter, I plan to share this with my son when he returns from Europe, I believe he'll find it cool.
Much of the topic remains over my head, but I thought it might be interesting to post brief excerpts of the paper along with some of the beautiful graphics from it.
The practical application, should it ever develop, would be computers so fast as to revolutionize computation as much as the original digital computer did in the 20th century, the elusive quantum computer: At least this is what Dr. Shoop claimed.
The caption:
The intro continues:
...
The review then discusses the remarkable properties of graphene which Dr. Schoop remarked with some amusement can be made by peeling a single layer of carbon atoms off of graphite with masking tape.
The caption:
Some remarks on graphene as a prototype of the "Dirac Semimetal"
Dirac Semimetals
The prototype of a DSM is graphene. The perfect DSM has the same electronic structure of graphene; i.e., it should consist of two sets of linearly dispersed bands that cross each other at a single point. Ideally, no other states should interfere at the Fermi level. Note that in a DSM, the bands that cross are spin degenerate, meaning that we would call them two-fold degenerate, and thus the Dirac point is four-fold degenerate. When discussing degeneracies within this Review, we will always refer to spin orbitals. In any crystal that is inversion symmetric and non-magnetic (i.e., time reversal symmetry is present), all bands will always be two-fold degenerate. Time reversal symmetry (T-symmetry) means that a systems properties do not change if a clock runs backward. A requirement for T-symmetry is that electrons at momentum points k and −k have opposite spin, which means that the spin has to rotate with k around the Fermi surface since backscattering between k and −k is forbidden. Introducing a perturbation, e.g., an external magnetic field, lifts the spin degeneracy and violates T-symmetry.
The caption:
"SOC" is spin orbit coupling.
Weyl Semimetals:
The difference between a DSM and a WSM is that, in the latter, the crossing point is only two-fold degenerate.(28,93,94) This is because in WSMs the bands are spin split; thus each band is only singly degenerate. If a spin-up band and a spin-down band cross, this results in a Weyl monopole, meaning that there is a chirality assigned to this crossing. Since there cannot be a net chirality in the crystals, Weyl cones always come in pairs. The resulting Weyl Fermions are chiral in nature and thus will behave physically different from regular Fermions. One example of this manifestation is the chiral anomaly, which we will discuss in the Properties and Applications of TSMs section below. Here, we will focus on the requirements necessary to realize a WSM.
In order to have spin split bands, we cannot have inversion (I) and time-reversal (T) symmetry at the same time, since the combination of these two symmetries will always force all bands to be doubly degenerate. In I asymmetric, i.e., non-centrosymmetric crystals, this degeneracy can be lifted with the help of SOC; this is the so-called Dresselhaus effect.(95)
The caption:
Figures for a 3D Dirac Semimetal, trisodium bismuthide, a Zintl salt (at least I knew about Zintl salts for the lecture):
The caption:
A Weyl Semimetal:
The caption:
A "Non-symmorphic Topological Semimetal: "
The caption:
And now, to generate some interest in saving the world after Elon Musk is done saving the world, a possible application, the ever popular solar hydrogen:
Well, at least the degeneracy here doesn't involve that awful excuse for a human being in the White House.
A little interesting if still obscure, at least to me, science is a great way to escape. It's a pleasure to be the dumbest guy in the room, really a pleasure.
I wish you a pleasant day tomorrow.
The greatest car ever, the car that saved all life on earth, spontaneously ignites.
Tesla spontaneously catches fire with no crashIt's green. It's solar. It's wind turbiney. It's the savior of the common man. We need this car more than life itself. The entire US budget should be devoted to its worship.
People Get Ready.
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" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen>2017 Establishes a New Record for Coal and For So Called "Renewables."
The data comes from the BP Statistical Report, which is generally more current than the WEO (published each November) but perhaps not as accurate.
I've downloaded all the data from the BP Report nonetheless, and am going through it. It's an interesting read, showing that things are every bit as bad as I've come to believe, maybe even worse, particularly since energy and environmental issues are filled with so much wishful thinking, outright delusion, and denial on both ends of the political spectrum, this in a world where the center is disappearing.
Other big "winners," besides so called "renewables" and coal were oil and gas, and oh, yes, carbon dioxide emissions.
Carbon Brief: BP Global Data Shows Record Highs for Coal Power
There's a certain amount of "percent talk" here about so called "renewable energy," which is tightly linked to the use of dangerous fossil fuels.
The so called "renewable energy" industry remains what it has always been, trivial, outside of "percent talk" compared to dangerous fossil fuels, and is clearly incompetent to stop their growth.
Oh my God! I was there last evening. This is terrible at a beautiful community event.
My son had a painting on display there.
This is horrible, particularly because "Mothers against gun" had a display there.
Screw the NRA.
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