Tuesday, July 20, 2010
7/20/2010 03:47:00 AM Publicado por Alquimia
Etiquetas: Materials Science
Etiquetas: Materials Science
At first, nanoshocks may seem like something to describe the millions of aftershocks of a large earthquake.
But Lawrence Livermore National Laboratory physicists are using an ultra-fast laser-based technique they dubbed “nanoshocks” for something entirely different. In fact, the “nanoshocks” have such a small spatial scale that scientists can use them to study shock behavior in tiny samples such as thin films or other systems with microscopic dimensions (a few tens of micrometers). In particular they have used the technique to shock materials under high static pressure in a diamond anvil cell (DAC).
Using a DAC, which probes the behavior of materials under ultra-high pressures (and which requires small samples), the team statically compressed a sample of argon up to 78,000 atmospheres of pressure and then further shock compressed it up to a total of 280,000 atmospheres. They analyzed the propagating shock waves using an ultra-fast interferometric technique. They achieved combinations of pressures, temperatures and time scales that are otherwise inaccessible.
In some experiments they observed a metastable argon state that may have been superheated -- a state at a pressure and temperature at which argon would normally be liquid but because of the ultra-short time scale does not have enough time to melt.
“It can be used to study fundamental physical and chemical processes as well as improve our understanding of a wide range of real-world problems ranging from detonation phenomena to the interiors of planets,” said LLNL physicist Jonathan Crowhurst, a co-author of a paper, which will appear in the July 15 edition of the Journal of Applied Physics.
The time scale is short enough to permit direct comparison with molecular dynamics simulations, which usually run for less than a nanosecond (one billionth of a second).
Shocked behavior in microscopic samples can consist of the behavior of shocked explosives before chemistry begins or the high density, low temperature states of light materials such as those that are found in giant gas planets, according to LLNL lead author Michael Armstrong.
“Essentially, this allows us to examine a very broad range of thermodynamic states, including states corresponding to planetary interiors and high density, low-temperature states that have been predicted to exhibit unobserved exotic behavior,” Armstrong said.
For decades, compression experiments have been used to determine the thermodynamic states of materials at high pressures and temperatures. The results are necessary to correctly interpret seismic data, understand planetary composition and the evolution of the early solar system, shock-wave induced chemistry and fundamental issues in condensed matter physics.
Armstrong said their technique for launching and analyzing nanoshocks was so fast they were able to see behavior in microscopic samples that is inaccessible in experiments using static or single-shock wave compression.
Lawrence Livermore National Laboratory
7/20/2010 03:46:00 AM Publicado por Alquimia
Imagine being able to drop a toothpick on the head of one particular person standing among 100,000 people in a sports stadium. It sounds impossible, yet this degree of precision at the cellular level has been demonstrated by researchers affiliated with The Johns Hopkins University Institute for NanoBioTechnology. Their study was published online in June in Nature Nanotechnology.
The team used precise electrical fields as “tweezers” to guide and place gold nanowires, each about one-two hundredth the size of a cell, on predetermined spots, each on a single cell. Molecules coating the surfaces of the nanowires then triggered a biochemical cascade of actions only in the cell where the wire touched, without affecting other cells nearby. The researchers say this technique could lead to better ways of studying individual cells or even cell parts, and eventually could produce novel methods of delivering medication.
Indeed, the techniques not relying on this new nanowire-based technology either are not very precise, leading to stimulation of multiple cells, or require complex biochemical alterations of the cells. With the new technique the researchers can, for instance, target cells that have cancer properties (higher cell division rate or abnormal morphology), while sparing their healthy neighbors.
“One of the biggest challenges in cell biology is the ability to manipulate the cell environment in as precise a way as possible,” said principal investigator Andre Levchenko, an associate professor of biomedical engineering in Johns Hopkins’ Whiting School of Engineering. In previous studies, Levchenko has used lab-on-a-chip or microfluidic devices to manipulate cell behavior. But, he said, lab-on-a-chip methods are not as precise as researchers would like them to be. “In microfluidic chips, if you alter the cell environment, it affects all the cells at the same time,” he said.
Such is not the case with the gold nanowires, which are metallic cylinders a few hundred nanometers or smaller in diameter. Just as the unsuspecting sports spectator would feel only a light touch from a toothpick being dropped on the head, the cell reacts only to the molecules released from the nanowire in one very precise place where the wire touches the cell’s surface.
With contributions from Chia-Ling Chien, a professor of physics and astronomy in the Krieger School of Arts and Sciences, and Robert Cammarata, a professor of materials science and engineering in the Whiting School, the team developed nanowires coated with a molecule called tumor necrosis factor-alpha (TNFα), a substance released by pathogen-gobbling macrophages, commonly called white blood cells. Under certain cellular conditions, the presence of TNFα triggers cells to switch on genes that help fight infection, but TNFα also is capable of blocking tumor growth and halting viral replication.
Exposure to too much TNFα, however, causes an organism to go into a potentially lethal state called septic shock, Levchenko said. Fortunately, TNFα stays put once it is released from the wire to the cell surface, and because the effect of TNFα is localized, the tiny bit delivered by the wire is enough to trigger the desired cellular response. Much the same thing happens when TNFα is excreted by a white blood cell.
Additionally, the coating of TNFα gives the nanowire a negative charge, making the wire easier to maneuver via the two perpendicular electrical fields of the “tweezer” device, a technique developed by Donglei Fan as part of her Johns Hopkins doctoral research in materials science and engineering. “The electric tweezers were initially developed to assemble, transport and rotate nanowires in solution,” Cammarata said. “Donglei then showed how to use the tweezers to produce patterned nanowire arrays as well as construct nanomotors and nano-oscillators. This new work with Dr. Levchenko’s group demonstrates just how extremely versatile a technique it is.”
To test the system, the team cultured cervical cancer cells in a dish. Then, using electrical fields perpendicular to one another, they were able to zap the nanowires into a pre-set spot and plop them down in a precise location. “In this way, we can predetermine the path that the wires will travel and deliver a molecular payload to a single cell among many, and even to a specific part of the cell,” Levchenko said.
During the course of this study, the team also established that the desired effect generated by the nanowire-delivered TNFα was similar to that experienced by a cell in a living organism.
The team members envision many possibilities for this method of subcellular molecule delivery. “For example, there are many other ways to trigger the release of the molecule from the wires: photo release, chemical release, temperature release. Furthermore, one could attach many molecules to the nanowires at the same time,” Levchenko said. He added that the nanowires can be made much smaller, but said that for this study the wires were made large enough to see with optical microscopy.
Ultimately, Levchenko sees the nanowires becoming a useful tool for basic research. “With these wires, we are trying to mimic the way that cells talk to each other,” he said. “They could be a wonderful tool that could be used in fundamental or applied research.” Drug delivery applications could be much further off. However, Levchenko said, “If the wires retain their negative charge, electrical fields could be used to manipulate and maneuver their position in the living tissue.”
(Photo: Will Kirk/HomewoodPhoto.jhu.edu)
Johns Hopkins University
7/20/2010 03:46:00 AM Publicado por Alquimia
An exploration to the bottom of the sea has uncovered a new species which scientists believe could be one of the missing evolutionary links between backboned and invertebrate animals.
The team – made up of experts from 16 nations and including scientists from Newcastle University – has just returned from a six-week research trip aboard the RRS James Cook.
Among the finds were a possible 10 new species as well as rare marine animals such as the deep-sea enteropneust acorn worms – a creature which has no eyes, no obvious sense organs or brain but has a defined head end, tail end and the primitive body plan of back-boned animals.
The expedition was the final leg of MAR-ECO - an international research programme set up to enhance our understanding of the occurrence, distribution and ecology of animals along the Mid-Atlantic Ridge between Iceland and the Azores.
The University of Aberdeen is leading the UK contribution to the project which includes Newcastle University and the National Oceanography Centre in Southampton.
Newcastle University's Dr Ben Wigham has been working on the project for the past four years, studying the biology of animals living on the ridge.
“We are interested in how these animals are feeding in areas of the deep-sea where food is often scarce,” he said.
“The differences we see in the diversity of species and numbers of individuals may well be related to how they are able to process and share out a rather common but meagre food supply. We certainly see indications that there are differences between the north and south regions of the ridge.”
During more than 300 hours of diving to depths of 3,600m using 'Isis' - the UK’s deepest diving remotely-operated vehicle (ROV) - the team surveyed flat plains, cliff faces and slopes of the giant mountain range that divides the Atlantic Ocean into two halves, east and west.
Professor Monty Priede, Director of the University of Aberdeen’s Oceanlab, said: “We were surprised at how different the animals were on either side of the ridge which is just tens of miles apart.
“In the north-east, sea urchins were dominant on the flat plains and the cliffs were colourful and rich with sponges, corals and other life. In the north-west, the cliffs were dull grey bare rock with much less life."
Professor Priede said the expedition had "revolutionised our thinking about deep-sea life in the Atlantic Ocean".
"It shows that we cannot just study what lives around the edges of the ocean and ignore the vast array of animals living on the slopes and valleys in the middle," he said.
“Using new technology and precise navigation we can access these regions and discover things we never suspected existed.”
(Photo: Newcastle U.)