November 10, 2006

Single molecule manipulations performed

The use of scanning probe microscopy-based techniques to manipulate single molecules and deliver them in a precisely controlled manner to a specific target has been performed by a european research team. An atomic force
microscope (AFM) was used to deliver and immobilize single molecules, one at a time, on a surface. Reactive polymer molecules, attached at one end to an AFM tip, are brought into contact with a modified silicon substrate to which they become linked by a chemical reaction. When the AFM tip is pulled away from the surface, the resulting mechanical force causes the weakest bond — the one between the tip and polymer — to break. This process transfers the polymer molecule to the substrate where it can be modified by further chemical reactions.

a, Reactive polymer molecules, attached at one end to an AFM tip, are brought into contact with a substrate to which they can become linked by a chemical reaction. When the tip is pulled away from the surface, the resulting mechanical force causes the
weakest bond — the one between the tip and polymer — to break. b, During the tip–sample contact, a chemical reaction occurs between the activated esters of a
poly-N-succinimidyl acrylate chain grafted to the tip and the amino groups of the substrate to form an amide bond, which covalently links the chain to the substrate.

Gold-coated AFM tips were modified by electrografting poly-N-succinimidyl acrylate (PNSA), according to ref. 14. This electro-initiated polymerization is a convenient way to fabricate polymer brushes with a moderate grafting density and results in the direct chemisorption of the polymer onto the tip surface. Surfaces with amino functions were prepared by grafting aminopropyltrimethoxysilane to silicon substrates. The activated esters of the polymer can easily react, at room temperature, with the amino-derivatives. In an N,N-dimethylformamide (a good
solvent for PNSA) solution containing 4-dimethylaminopyridine (DMAP, a catalyst), the
functionalized AFM tip was slowly brought into contact with the surface. The chemical reaction between the PNSA activated esters and the amino groups of the
substrate forms amide bonds and covalently links polymer chains to the substrate (Fig. 1b). Upon retraction of the tip, single chains are stretched until a bond breaks. The Au(tip)–C(polymer) bond is the weakest link in the system and the most likely candidate for breaking. Upon cleavage, the polymer chain remains covalently attached to the substrate. The deposited chains are reactive and can be easily modified, subsequently, by a wide range of nucleophilic compounds.

The experiments strongly rely on the design and accurate modification of the tips. The use of a swollen brush with a low grafting density (less than one chain per 100 nm2; the compression profile shows that we are in the isolated mushrooms regime, see
Methods section) for force spectroscopy experiments prevents unspecific physisorption of a bulk three-dimensional structure onto the substrate thanks to steric repulsion and the strong adsorption of flat-lying chains (that adsorb through several attachment points) which leads to the appearance of multiple superimposed peaks in the force–distance curves. The presence of a good solvent prevents interactions within the polymer. Statistically, the bridging interactions should occur with only one isolated single polymer chain. The strategy makes the detection of the rupture of a single tip–polymer bond easy.

November 09, 2006

GPU supercomputers

Graphic chips like the Nvidia G8800 have about 520GFLOPS of performance. Some have been adapted for more general processing using the C language and are being banded together for supercomputers with 2-40 times the performance of regular CPUs.

Wired magazine talks about an array of 536 GPUs significantly outperformed some 17,485 CPUs from Linux boxes. The 536 GPUs producing 35 trillion calculations per second compared to 21 trillion calculations per second for the CPUs.

The UNC Chapel Hill Gamma Research Team under laboratory-type conditions put an Nvidia 7900 GTX GPU up against two different leading-edge optimized CPU-based implementations running on high-end, dual-3.6-GHz Intel Xeon processors or dual AMD Opteron 280 processors. The research team, which included Manocha, Naga K. Govindaraju and Scott Larsen from UNC and Jim Gray from Microsoft Research, put these systems through three fairly standard numeric-based computational algorithms, including sorting, FFT (fast Fourier transform) and matrix multiplications.

The results they recorded show that the GPU performed at anywhere from two to five times the speed of the CPU-based systems on these specific applications.

The co-lead of the Gamma group, Ming C. Lin, is leading the development of many new GPU-based technologies for physics simulation -- including collision detection, motion planning and deformable simulations -- with speeds in many cases increasing 10 to 20 times beyond previous methods.

SiCortex, a startup is also producing 5.8 teraflops for about 1-1.5 million

November 06, 2006

Higher density Superconducting Memory

Higher density superconducting memory has been designed. The concept stores data by coupling tiny ferromagnetic “dots” to electronic components called Josephson junctions – current-conducting “sandwiches” formed by a thin layer of an insulating material between two superconducting layers.

This memory concept gets around the size issue because the dimensions of the ferromagnetic dots and their distance from the Josephson junctions do not compromise the operation of the cell. The dots can be very small and very close to the junctions, and the cell will still function properly.

The group tested their concept by fabricating a memory chip out of the metal niobium (Nb). The chip consists of a pattern of several Nb Josephson junction arrays, with eight junctions per array. Each junction is coupled to a ferromagnetic dot that is 6 micrometers wide, 9 micrometers long, and 600 nanometers thick. There are many ferromagnetic materials that would work, but for this first test the group chose a nickel-iron compound commonly known as Permalloy.

New or newly available online from Eric Drexler

Newly available online pdf, for Eric Drexlers 1995 perspective on the Ultimate limits of fabrication

A 2006 article for a primer on productive nanosystems

Eric Drexler's site has some more links. One of the links to a pdf on fundamental issues in design and modeling of Integrated nanosystems is having errors. It may get fixed when you try it.

Desalinization four times better with new membrane with nanoscale structure

Researchers at the UCLA Henry Samueli School of Engineering and Applied Science today announced they have developed a new reverse osmosis (RO) membrane that promises to reduce the cost of seawater desalination and wastewater reclamation.

Initial tests suggest new nanoscale membranes with embedded nanoparticles have up to twice the productivity -- or consume 50 percent less energy -- reducing the total expense of desalinated water by as much as 25 percent. The water-loving nanoparticles embedded in hte UCLA membrane repel organics and bacteria, which tend to clog up conventional membranes over time. They also repel salt and other impurities.

New ways to detect nuclear material

US nuclear power company Westinghouse Electric has been developing a clever new way to spot nuclear contraband.

Many US ports already X-ray ship containers to see if they contain hidden nuclear material. But X-ray machines may fail to spot hidden uranium or plutonium if it is hidden behind lead shielding.

So Westinghouse Electric proposes generating a powerful controlled beam of neutrons by propelling deuterons into tritium. These will then cut through lead shielding and excite any fissile material, creating an "echo" of neutrons caused by a "fast fission" effect.

The echoes only last a microsecond or so and are quickly damped out, so there is no risk of a triggering a chain reaction. But they can be detected by a silicon carbide semiconductor sensor, which is switched on and off in between the trigger pulses. The sensor then gives instant and unambiguous warning of hidden nuclear cargo."

Speculation: It seems that if one did remotely detect a bunch of material in an enemy country then a prolonged and higher volume of neutrons could trigger a chain reaction. A way to blow up fissile material remotely.

New nuclear arms races are officially on

From the UK Times Online, what people have long suspected appears to be pretty much official. We have a race to nuclear arms in the middle east. Yesterday’s disclosure that Algeria, Egypt, Morocco, Saudi Arabia and smaller states such as Tunisia and the UAE want to acquire nuclear technology.

New techniques pave way for carbon nanotubes in electronic devices

Many of the desired applications of carbon nanotubes require the ability to attach them to electrically conductive surfaces, but we have only been successful in creating high-resistance interfaces between nanotubes and substrates. Now a team from Rensselaer Polytechnic Institute reports two new techniques, each following a different approach, for placing carbon nanotube patterns on metal surfaces of just about any shape and size.

First is "floating catalyst chemical vapor deposition". They heat a carbon-rich compound at extremely high temperatures until the material vaporizes. As the system cools, carbon deposits directly on the metal surface in the form of nanotube arrays. For this experiment, the team used surfaces made from Inconel, a nickel-based "super alloy" with good electrical conductivity. Until now this technique has only been used to grow nanotubes on substrates that are poor conductors of electricity.

There are many potential advantages to growing carbon nanotubes directly on metals with this simple, single-step process, according to Talapatra. Nanotubes attach to the surface with much greater strength; excellent electrical contact is established between the two materials; and nanotubes can be grown on surfaces of almost any shape and size, from curved sheets to long metal rods.

Second, the team developed a procedure that mimics the way photographs are printed from a film negative. They first grow patterns of carbon nanotubes on silicon surfaces using chemical vapor deposition, and then the nanotubes are transferred to metal surfaces that are coated with solder -- a metal alloy that is melted to join metallic surfaces together. The nanotubes stick in the solder, maintaining their original arrangement on the new surface. And since solder has a low melting point, the process takes place at low temperature.

The researchers also demonstrated that the chemical vapor deposition procedure can be used to make nanotube electrodes for "super capacitors" -- devices that have unusually high energy densities when compared to common capacitors, which are used to store energy in electrical circuits. These are of particular interest in automotive applications for hybrid vehicles and as supplementary storage for battery electric vehicles, according to the researchers.

November 05, 2006

Fast Wireless in South Korea

From the BBC, the future of communication is happening in South Korea first High Speed Downlink Packet Access (HSDPA) piggybacks on the 3G cellular networks, but HDSPA gives speeds which are about three to four times faster than regular 3G. Seoul is just starting to roll out Wibro, which stands for wireless broadband. Koreans cannot actually use Wibro on their phones because no-one has figured out how to cram in the bulky and power-hungry Wibro chipsets, and make what is essentially a data service work alongside voice calls.

DMB - Digital Multimedia Broadcasting - is now being watched by over a million Koreans since its launch last year. DMB lets you watch several dozen channels of TV content on your phone.

4G networks are in trials and demonstrations. They provie 100 megabit stream of data whilst moving at 60 kph and 1 gigabit while stationary.

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