New Technical Information

Now available online:

Design and Analysis of a Molecular Tool for Carbon Transfer in Mechanosynthesis [PDF]
By Damian G. Allis and K. Eric Drexler

Mechanosynthesis exploits mechanical positioning to direct reactive moieties to specific reactive sites on target structures. This mechanism of control contrasts with that of conventional synthesis techniques, in which solution-phase diffusion produces undirected molecular encounters. Despite this lack of direct positional control, diffusion-based synthesis techniques can achieve considerable site specificity by seeking reaction sequences in which each distinct reactive site, at each step, differs from the rest in its reactivity.

This strategy for structural control becomes more difficult as structures grow larger and more complex, due to the proliferation of similar reactive sites. Mechanosynthetic techniques, in contrast, can perform different synthetic operations on target sites of similar reactivity that are distinguished solely by their structural position.This means of control is essentially independent of product scale and complexity and can be quite reliable.

Diffusion-based synthesis techniques have been under development for more than a century and have achieved striking results. Mechanosynthetic techniques are rudimentary today, but their further development promises to greatly expand the scale, diversity, and complexity of products made by structurally precise molecular synthesis.

Mechanosynthesis of a target class of graphene-, nanotube-, and diamond-like structures will require molecular tools capable of transferring carbon moieties to structures that have binding energies in the range of 1.105 to 1.181 aJ per atom (159 to 170 kcal mol^−1). Desirable properties for tools include exoergic transfer of moieties to these structures; good geometrical exposure of moieties; and structural, electronic, and positional stability.

This paper [PDF] introduces a novel carbon-transfer tool design (named "DC10c"), the first predicted to exhibit these properties in combination.

Also available online:

Kinematic Self-Replicating Machines

Robert A. Freitas Jr. and Ralph C. Merkle co-authored the most comprehensive review ever published about self-replicating machine systems, specifically kinematic self-replicating machines: systems in which actual physical objects, not mere patterns of information, undertake their own replication.

Kinematic Self-Replicating Machines (KSRM) was published in hardback in late 2004. The book is still available in print, but KSRM is now freely accessible online as well.

With 200+ illustrations and 3200+ literature references, KSRM describes all proposed and experimentally realized self-replicating systems that were publicly known as of 2004, ranging from nanoscale to macroscale systems. The book extensively describes the historical development of the field. It presents for the first time a detailed 137-dimensional map of the entire kinematic replicator design space to assist future engineering efforts. KSRM has been cited in two articles appearing in Nature this year (Zykov et al, Nature 435, 163 [12 May 2005] and Griffith et al, Nature 437, 636 [29 September 2005]) and appears well on its way to becoming the classic reference in this field.

Tags: nanotechnology nanotech nano science technology ethics weblog blog

Comments

[Hal]

I'm glad to see KSRM referenced here. With its emphasis on the traditional self-replicating assembler concept, KSRM is decidedly old-school in its approach to nanotech. Apparently these boys haven't gotten with the program of politically-correct nanotech, where microscopic self-replicating assemblers are either impossible or so unnecessary that no sane person would ever even think of pursuing them.

Freitas and Merkle unashamedly present their concept for a molecular assembler in http://www.molecularassembler.com/KSRM/4.11.3.1.htm. Able to self-replicate and less than 2 cubic microns in size, it is far removed from the desktop nanofactory which CRN and Foresight are pushing. Attempts by these organizations to rewrite history and pretend that assemblers were just an embarrassing and minor side road on the highway to mature nanotech are directly contradicted by the importance that Freitas and Merkle place on the concept.

The authors directly address the "too dangerous" argument in http://www.molecularassembler.com/KSRM/6.3.1.htm. Their design is based on a broadcast architecture and requires a custom environment, preventing any kind of gray goo scenario. Perhaps their strongest argument for going forward with assembler development, despite the dangers, is that other groups are likely to pursue it irrespective of the dangers.

I have been annoyed and frustrated by the attempts of the MM "establishment" to sweep the assembler concept under the rug for political reasons. I welcome F&M's work which will hopefully restore this important design to the central role it deserves. Drexler's assemblers were not a mistake and not a sideline. If they can be built, they will be. They are too useful and have too many capabilities to ignore.

[Tom Craver]

F&M's free-floating, broadcast-instruction , "brick extrusion" architecture seems best at producing large quantities of identical tiny objects. That isn't sufficient for constructing macroscale objects. For that, there must be a second stage - a molefactory, or perhaps "foglets" that arrange themselves into objects.

Also, if one's objective is security, self-replicating molebots might be limited to ultra-high security plants, with the rest of the world's economy using fixed function atomically precise assemblers, and assemblers limited to moleblock precision. I'm not advocating this as a long term solution - it leaves a bit too much control in centralized hands for my taste - but it might be a good compromise approach to limiting the problems created by the rapid onset of moletechnology.

[Chris Phoenix, CRN]

Hal:

The only problem is the use of the word "assembler" to mean two different things. Drexler's original meaning (1986/Engines) was a system with an onboard computer and navigation system. And when thinking about gray goo, he was thinking of designs derivative from biology.

The "assembler" described in KSRM has no onboard computer, no navigation capability, and is utterly non-biological.

In other words, the Merkle/Freitas design is not a Drexler assembler by any stretch of the imagination.

We have had this conversation before. You already know the information I'm providing here. So are you just trolling?

Chris