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Scientists Discover Dielectron Charging of Water Nano-droplets

Monday, July 18, 2011

Scientists have discovered fundamental steps of charging of nano-sized water droplets and unveiled the long-sought-after mechanism of hydrogen emission from irradiated water. Working together at the Georgia Institute of Technology and Tel Aviv University, scientists have discovered when the number of water molecules in a cluster exceeds 83, two excess electrons may attach to it — forming dielectrons — making it a doubly negatively charged nano droplet. Furthermore, the scientists found experimental and theoretical evidence that in droplets comprised of 105 molecules or more, the excess dielectrons participate in a water-splitting process resulting in the liberation of molecular hydrogen and formation of two solvated hydroxide anions.  The results appear in the June 30 issue of the Journal of Physical Chemistry A.

For the full article, please visit this site.

 

Summary: 

Working together at the Georgia Institute of Technology and Tel Aviv University, scientists have discovered when the number of water molecules in a cluster exceeds 83, two excess electrons may attach to it — forming dielectrons — making it a doubly negatively charged nano droplet.

Intro: 

Working together at the Georgia Institute of Technology and Tel Aviv University, scientists have discovered when the number of water molecules in a cluster exceeds 83, two excess electrons may attach to it — forming dielectrons — making it a doubly negatively charged nano droplet.

Alumni: 

Scientists Discover Dielectron Charging of Water Nano-droplets

Monday, June 27, 2011

Scientists have discovered fundamental steps of charging of
nano-sized water droplets and unveiled the long-sought-after mechanism of
hydrogen emission from irradiated water. Working together at the Georgia
Institute of Technology and Tel Aviv University, scientists have discovered
when the number of water molecules in a cluster exceeds 83, two excess
electrons may attach to it —
forming dielectrons — making it
a doubly negatively charged nano droplet. Furthermore, the scientists found
experimental and theoretical evidence that in droplets comprised of 105
molecules or more, the excess dielectrons participate in a water-splitting
process resulting in the liberation of molecular hydrogen and formation of two
solvated hydroxide anions.  The
results appear in the June 30 issue of the Journal of Physical Chemistry A.

It has been known since the early 1980s that while single
electrons may attach to small water clusters containing as few as two molecules,
only much larger clusters may attach more than single electrons. Size-selected,
multiple-electron, negatively-charged water clusters have not been observed — until now.

Understanding the nature of excess electrons in water has captured
the attention of scientists for more than half a century, and the hydrated
electrons are known to appear as important reagents in charge-induced aqueous
reactions and molecular biological processes.  Moreover, since the discovery in the early 1960s that the
exposure of water to ionizing radiation causes the emission of gaseous molecular
hydrogen, scientists have been puzzled by the mechanism underlying this
process.  After all, the bonds in
the water molecules that hold the hydrogen atoms to the oxygen atoms are very
strong. The dielectron hydrogen-evolution 
(DEHE) reaction, which produces hydrogen gas and hydroxide anions, may
play a role in radiation-induced reactions with oxidized DNA that have been
shown to underlie mutagenesis, cancer and other diseases.

“The attachment of multiple electrons
to water droplets is controlled by a fine balancing act between the forces that
bind the electrons to the polar water molecules and the strong repulsion
between the negatively charged electrons,” said Uzi Landman, Regents’ and
Institute Professor of Physics, F.E. Callaway Chair and director of the Center
for Computational Materials Science (CCMS) at Georgia Tech.

“Additionally, the binding of an
electron to the cluster disturbs the equilibrium arrangements between the
hydrogen-bonded water molecules and this too has to be counterbalanced by the
attractive binding forces.  To
calculate the pattern and strength of single and two-electron charging of
nano-size water droplets, we developed and employed first-principles quantum mechanical
molecular dynamics simulations that go well beyond any ones that have been used
in this field,” he added. 

Investigations on controlled size-selected clusters allow
explorations of intrinsic properties of finite-sized material aggregates, as
well as probing of the size-dependent evolution of materials properties from
the molecular nano-scale to the condensed phase regime.

In the 1980s Landman, together
with senior research scientists in the CCMS Robert Barnett, the late Charles
Cleveland and Joshua Jortner, professor of chemistry at Tel Aviv University,
discovered that there are two ways that single excess electrons can attach to
water clusters – one in which they bind to the surface of the water droplet,
and the other where they localize in a cavity in the interior of the droplet,
as in the case of bulk water. Subsequently, Landman, Barnett and graduate
student Harri-Pekka Kaukonen reported in 1992 on theoretical investigations
concerning the attachment of two excess electrons to water clusters. They
predicted that such double charging would occur only for sufficiently large nano-droplets.
They also commented on the possible hydrogen evolution reaction. No other work
on dielectron charging of water droplets has followed since.

That is until recently, when Landman, now one of the world leaders in the area of cluster and nano
science, and Barnett teamed up with Ori Chesnovsky, professor of
chemistry, and research associate Rina Giniger at Tel
Aviv University, in a joint project aimed at understanding the process
of dielectron charging of water clusters and the mechanism of the ensuing
reaction - which has not been observed previously in experiments on water
droplets. Using large-scale, state-of-the-art
first-principles dynamic simulations, developed at the CCMS, with all valence
and excess electrons treated quantum mechanically and equipped with a newly
constructed high-resolution time-of-flight mass spectrometer, the researchers
unveiled the intricate physical processes that govern the fundamental dielectron
charging processes of microscopic water droplets and the detailed mechanism of
the water-splitting reaction induced by double charging.

The mass
spectrometric measurements, performed at Tel Aviv, revealed that singly charged
clusters were formed in the size range of six to more than a couple of hundred
water molecules. However, for clusters containing more than a critical size of
83 molecules, doubly charged clusters with two attached excess electrons were
detected for the first time. Most significantly, for clusters with 105 or more
water molecules, the mass spectra provided direct evidence for the loss of a
single hydrogen molecule from the doubly charged clusters.

The theoretical
analysis demonstrated two dominant attachment modes of dielectrons to water
clusters. The first is a surface mode (SS’), where the two repelling electrons
reside in antipodal sites on the surface of the cluster (see the two wave
functions, depicted in green and blue, in Figure 1). The second is another
attachment mode with both electrons occupying a wave function localized in a
hydration cavity in the interior of the cluster — the so-called II binding mode
(see wave function depicted in pink in Figure 2). While both dielectron
attachment modes may be found for clusters with 105 molecules and larger ones,
only the SS’ mode is stable for doubly charged smaller clusters.

“Moreover, starting
from the II, internal cavity attachment mode in a cluster comprised of 105
water molecules, our quantum dynamical simulations showed that the concerted
approach of two protons from two neighboring water molecules located on the
first shell of the internal hydration cavity, leads, in association with the
cavity-localized excess dielectron (see Figure 2), to the formation of a
hydrogen molecule. The two remnant hydroxide anions diffuse away via a sequence
of proton shuttle processes, ultimately solvating near the surface region of
the cluster, while the hydrogen molecule evaporates,” said Landman.

“What’s more, in
addition to uncovering the microscopic reaction pathway, the mechanism which we
discovered requires initial proximity of the two reacting water molecules and
the excess dielectron. This can happen only for the II internal cavity
attachment mode. Consequently, the theory predicts, in agreement with the
experiments, that the reaction would be impeded in clusters with less than 105
molecules where the II mode is energetically highly improbable. Now, that’s a
nice consistency check on the theory,” he added.

As for future plans,
Landman remarked, “While I believe that our work sets methodological and
conceptual benchmarks for studies in this area, there is a lot left to be done.
For example, while our calculated values for the excess single electron
detachment energies are found to be in quantitative agreement with
photoelectron measurements in a broad range of water cluster sizes — containing
from 15 to 105 molecules — providing a consistent interpretation of these
measurements, we would like to obtain experimental data on excess dielectron
detachment energies to compare with our predicted values,” he said.

“Additionally, we
would like to know more about the effects of preparation conditions on the
properties of multiply charged water clusters. We also need to understand the
temperature dependence of the dielectron attachment modes, the influence of
metal impurities, and possibly get data from time-resolved measurements. The understanding
that we gained in this experiment about charge-induced water splitting may
guide our research into artificial photosynthetic systems, as well as the
mechanisms of certain bio-molecular processes and perhaps some atmospheric phenomena.”

“You know,” he added. “We started
working on excess electrons in water clusters quite early, in the 1980s — close
to 25 years ago. If we are to make future progress in this area, it will have
to happen faster than that.”

This research was funded by the U.S. Office of Basic Energy Sciences and the Israel Science Foundation.

 

Media Contact: 

Georgia Tech Media Relations
Laura Diamond
laura.diamond@comm.gatech.edu
404-894-6016
Jason Maderer
maderer@gatech.edu
404-660-2926

Summary: 

Scientists have discovered fundamental steps of charging of nano-sized
water droplets and unveiled the long-sought-after mechanism of hydrogen
emission from irradiated water. 

Intro: 

Scientists have discovered fundamental steps of charging of nano-sized
water droplets and unveiled the long-sought-after mechanism of hydrogen
emission from irradiated water. 

Alumni: 

Professor Aims to Dispel Astrophysics Myths

Monday, June 13, 2011

Deirdre Shoemaker has become accustomed to people not believing in black holes — even one of her stepson’s teachers.     

“When he was in elementary school, my stepson came home with an English writing assignment on myths,” said the astrophysicist who is an associate professor in the School of Physics and works within the Center for Relativistic Astrophysics. “His topic choices included Big Foot, the Loch Ness monster and black holes.”

Another common misconception that Shoemaker has encountered is that black holes are giant, cosmic vacuum cleaners that will suck everything in.

“Fortunately, they’re not,” she said. “If we replaced our sun with a black hole of the same mass, Earth wouldn’t be sucked into it. However, the lack of sunlight would be a problem.”

Shoemaker has worked in her field for about 15 years, since she was a graduate student at the University of Texas at Austin. As an astrophysicist, she considers herself to be a “detective of the universe.”

“We are using clues and evidence to determine what the universe is and how and why it looks like it does to us today,” she added.

Recently, The Whistle sat down with Shoemaker to learn more about her and her time at Tech. Here’s what we learned:

How did you get to Tech?
I was an assistant professor at The Pennsylvania State University for four years before being asked to apply to Georgia Tech. I was hired as part of an effort to initiate a research and teaching group dedicated to astrophysics, which evolved into the Center for Relativistic Astrophysics.

Tell us about your research.     
I use computational techniques to solve the equations that govern how two black holes interact with each other. The byproduct of that interaction is called “gravitational radiation.” Gravitational radiation is a kind of radiation predicted by Einstein’s theory of gravity, but it has not been directly detected (we are used to electromagnetic waves like light and microwaves).   

What is your greatest challenge associated with teaching and how do you deal with it?
When I teach large introductory classes, the challenge is to maintain a persona that is respected and approachable. My personality, which is quite friendly, is a plus and a minus for this. I think it helps me be an approachable instructor and encourages students to ask questions in class, but I also have to maintain a balance in and out of the classroom. I think the balance comes from demanding that the students respect each other and me. Little things help accomplish this such as not allowing talking in the room when one person is speaking.

What are three things that are key to making learning more engaging for students?
Humor, patience and research. I think a sense of humor is essential in teaching, second only to having the patience to let students ask questions in their own time and words. These two things help create a classroom atmosphere where a student can feel comfortable. I also try to bring up relevant, current research as often as possible so students can get a feeling for why we find physics so interesting and why it is important to society.

What piece of technology could you not live without as an instructor?
The Internet, because it allows me to research how others teach material similar to my own.

What are three things everyone should do while working at Tech?
Run the annual Pi Mile 5K, slide down that crazy water slide at the Campus Recreation Center and attend a commencement ceremony.

Where is the best place to grab lunch (on or off campus), and what do you order?
I love to order soup at La Petite Café.

Tell me something unusual about yourself.
My family and I have two Great Danes — they pretty much run the household, but they are gentle dictators.

Media Contact: 

Amelia Pavlik
Communications & Marketing
404-385-4142

Summary: 

Deirdre Shoemaker has become accustomed to people not believing in black holes — even one of her stepson’s teachers.

Intro: 

Deirdre Shoemaker has become accustomed to people not believing in black holes — even one of her stepson’s teachers.

Alumni: 

Flower-Like Defects May Help Graphene Respond to Stress

Friday, June 10, 2011

Graphene has amazing mechanical properties, including high strength that could one day be useful in lightweight, robust structures. However the material does have flaws.  Researchers at Georgia Tech and the National Institute of Standards and Technology (NIST) have described a family of seven potential defect structures that may appear in sheets of graphene and imaged examples of the lowest-energy defect in the family.  According to a NIST researcher, the fabrication process plays a big role in creating the defects.  “As the graphene forms under high heat, sections of the lattice can come loose and rotate," he said. "As the graphene cools, these rotated sections link back up with the lattice, but in an irregular way. It's almost as if patches of the graphene were cut out with scissors, turned clockwise, and made to fit back into the same place. Only it really doesn't fit, which is why we get these flowers.” Georgia Tech Physics Professor Phil First noted that “…even with these defects, graphene is still spectacularly strong.” Professor First hopes the team can continue studying the defects, both to learn whether their formation can be controlled and to clarify the role of defects in the material's mechanical properties.  Read the article about this research in Physical Review B 83, 195425 (2011).

Summary: 

Researchers at Georgia Tech and the National Institute of Standards and Technology (NIST) have described a family of seven potential defect structures that may appear in sheets of graphene and imaged examples of the lowest-energy defect in the family.

Intro: 

Researchers at Georgia Tech and the National Institute of Standards and Technology (NIST) have described a family of seven potential defect structures that may appear in sheets of graphene and imaged examples of the lowest-energy defect in the family.

Alumni: 

Astrophysicists Use X-ray Fingerprints to Study Massive Black Holes

Tuesday, June 7, 2011

By studying the X-rays emitted when superheated gases plunge into distant and massive black holes, astrophysicists at the Georgia Institute of Technology have provided an important test of a long-standing theory that describes the extreme physics occurring when matter spirals into these massive objects.

Matter falling into black holes emits tremendous amounts of energy which can escape as visible light, ultraviolet light and X-rays. This energy can also drive outflows of gas and dust far from the black hole, affecting the growth and evolution of galaxies containing the black holes. Understanding the complex processes that occur in these active galactic nuclei is vital to theories describing the formation of galaxies such as the Milky Way, and is therefore the subject of intense research.

For the full article, go here.

Summary: 

By studying the X-rays emitted when superheated gases plunge into distant and massive black holes, astrophysicists at the Georgia Institute of Technology have provided an important test of a long-standing theory that describes the extreme physics occurring when matter spirals into these massive objects.

Intro: 

By studying the X-rays emitted when superheated gases plunge into distant and massive black holes, astrophysicists at the Georgia Institute of Technology have provided an important test of a long-standing theory that describes the extreme physics occurring when matter spirals into these massive objects.

Alumni: 

Physical Biology Highlights of 2010

Wednesday, May 11, 2011

The Highlights of 2010 is a special collection of papers that represent the breadth and excellence of the work published in the Physical Biology last year. The articles were selected for their presentation of outstanding new research, received the highest praise from our international referees, and had the highest numbers of downloads in 2010.  Adjunct Professor of Physics Joshua Weitz’s paper:  Quantifying enzymatic lysis: estimating the combined effects of chemistry, physiology, and physics was one of these highlighted articles.

 

As we are aware, the number of microbial pathogens resistant to antibiotics increases as the rate of discovery and approval of new antibiotic therapeutics decreases. Characterization of lytic enzymes using techniques based on synthetic substrates is often difficult because lytic enzymes bind to the complex superstructure of intact cell walls. Dr. Weitz and his group present a new standard for the analysis of lytic enzymes based on turbidity assays which allow scientists to probe the dynamics of lysis without preparing a synthetic substrate. The challenge in the analysis of these assays is to infer the microscopic details of lysis from macroscopic turbidity data. They proposed a model of enzymatic lysis that integrated the chemistry responsible for bond cleavage with the physical mechanisms leading to cell wall failure. Then they presented a solution to an inverse problem where they estimated reaction rate constants and the heterogeneous susceptibility to lysis among target cells. The ability to estimate reaction rate constants for lytic enzymes will facilitate their biochemical characterization and the development of antimicrobial therapeutics.

 

2011 Phys. Biol. 8 202010

Summary: 

Adjunct Professor of Physics Joshua Weitz’s paper: Quantifying enzymatic lysis: estimating the combined effects of chemistry, physiology, and physics was one of these highlighted articles.

Intro: 

Adjunct Professor of Physics Joshua Weitz’s paper: Quantifying enzymatic lysis: estimating the combined effects of chemistry, physiology, and physics was one of these highlighted articles.

Alumni: 

Heads Up, Robots: A Tiltable Head Could Improve the Ability of Undulating Robots to Navigate Disaster Debris

Tuesday, May 10, 2011

Georgia Tech School of Physics assistant professor Daniel Goldman and his team were able to show that by tilting this undulating robot’s head up and down slightly, they could control the robot’s vertical motion as it traveled forward within a granular medium. The robot is built with seven connected segments, powered by servo motors, packed in a latex sock and wrapped in a spandex swimsuit.  Full article here.

Summary: 

Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and “swim” through granular material.

Intro: 

Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and “swim” through granular material.

Alumni: 

A Tiltable Head Could Improve Robot Navigation of Disaster Debris

Monday, May 9, 2011

Search and rescue missions have followed each of the devastating earthquakes that hit Haiti, New Zealand and Japan during the past 18 months. Machines able to navigate through complex dirt and rubble environments could have helped rescuers after these natural disasters, but building such machines is challenging.

Researchers at the Georgia Institute of Technology recently built a robot that can penetrate and "swim" through granular material. In a new study, they show that varying the shape or adjusting the inclination of the robot's head affects the robot's movement in complex environments.

"We discovered that by changing the shape of the sand-swimming robot's head or by tilting its head up and down slightly, we could control the robot's vertical motion as it swam forward within a granular medium,” said Daniel Goldman, an assistant professor in the Georgia Tech School of Physics.

Results of the study will be presented on May 10 at the 2011 IEEE International Conference on Robotics and Automation in Shanghai. Funding for this research was provided by the Burroughs Wellcome Fund, National Science Foundation and Army Research Laboratory.

The study was conducted by Goldman, bioengineering doctoral graduate Ryan Maladen, physics graduate student Yang Ding and physics undergraduate student Andrew Masse, all from Georgia Tech, and Northwestern University mechanical engineering adjunct professor Paul Umbanhowar.

"The biological inspiration for our sand-swimming robot is the sandfish lizard, which inhabits the Sahara desert in Africa and rapidly buries into and swims within sand," explained Goldman. "We were intrigued by the sandfish lizard's wedge-shaped head that forms an angle of 140 degrees with the horizontal plane, and we thought its head might be responsible for or be contributing to the animal's ability to maneuver in complex environments."

For their experiments, the researchers attached a wedge-shaped block of wood to the head of their robot, which was built with seven connected segments, powered by servo motors, packed in a latex sock and wrapped in a spandex swimsuit. The doorstop-shaped head -- which resembled the sandfish's head -- had a fixed lower length of approximately 4 inches, height of 2 inches and a tapered snout. The researchers examined whether the robot's vertical motion could be controlled simply by varying the inclination of the robot's head.

Before each experimental run in a test chamber filled with quarter-inch-diameter plastic spheres, the researchers submerged the robot a couple inches into the granular medium and leveled the surface. Then they tracked the robot's position until it reached the end of the container or swam to the surface.

The researchers investigated the vertical movement of the robot when its head was placed at five different degrees of inclination. They found that when the sandfish-inspired head with a leading edge that formed an angle of 155 degrees with the horizontal plane was set flat, negative lift force was generated and the robot moved downward into the media. As the tip of the head was raised from zero to 7 degrees relative to the horizontal, the lift force increased until it became zero. At inclines above 7 degrees, the robot rose out of the medium.

"The ability to control the vertical position of the robot by modulating its head inclination opens up avenues for further research into developing robots more capable of maneuvering in complex environments, like debris-filled areas produced by an earthquake or landslide," noted Goldman.

The robotics results matched the research team's findings from physics experiments and computational models designed to explore how head shape affects lift in granular media.

"While the lift forces of objects in air, such as airplanes, are well understood, our investigations into the lift forces of objects in granular media are some of the first ever," added Goldman.

For the physics experiments, the researchers dragged wedge-shaped blocks through a granular medium. Blocks with leading edges that formed angles with the horizontal plane of less than 90 degrees resembled upside-down doorstops, the block with a leading edge equal to 90 degrees was a square, and blocks with leading edges greater than 90 degrees resembled regular doorstops.

They found that blocks with leading edges that formed angles with the horizontal plane less than 80 degrees generated positive lift forces and wedges with leading edges greater than 120 degrees created negative lift. With leading edges between 80 and 120 degrees, the wedges did not generate vertical forces in the positive or negative direction.

Using a numerical simulation of object drag and building on the group’s previous studies of lift and drag on flat plates in granular media, the researchers were able to describe the mechanism of force generation in detail.

"When the leading edge of the robot head was less than 90 degrees, the robot's head experienced a lift force as it moved forward, which resulted in a torque imbalance that caused the robot to pitch and rise to the surface," explained Goldman.

Since this study, the researchers have attached a wedge-shaped head on the robot that can be dynamically modulated to specific angles. With this improvement, the researchers found that the direction of movement of the robot is sensitive to slight changes in orientation of the head, further validating the results from their physics experiments and computational models.

Being able to precisely control the tilt of the head will allow the researchers to implement different strategies of head movement during burial and determine the best way to wiggle deep into sand. The researchers also plan to test the robot's ability to maneuver through material similar to the debris found after natural disasters and plan to examine whether the sandfish lizard adjusts its head inclination to ensure a straight motion as it dives into the sand.

This material is based on research sponsored by the Burroughs Wellcome Fund, the National Science Foundation (NSF) under Award Number PHY-0749991, and the Army Research Laboratory (ARL) under Cooperative Agreement Number W911NF-08-2-0004. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of NSF, ARL or the U.S. government.

Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 314
Atlanta, Georgia 30308 USA

Media Relations Contacts: Abby Robinson (abby@innovate.gatech.edu; 404-385-3364) or John Toon (jtoon@gatech.edu; 404-894-6986)

Writer: Abby Robinson

Media Contact: 

Abby Robinson
Research News and Publications
Contact Abby Robinson
404-385-3364

Summary: 

Researchers built a robot that can penetrate and "swim" through granular material. In this study, they show that by varying the shape of the robot's head or by tilting it up or down, they can control the robot's vertical movement in complex environments.

Intro: 

Researchers built a robot that can penetrate and "swim" through granular material. In this study, they show that by varying the shape of the robot's head or by tilting it up or down, they can control the robot's vertical movement in complex environments.

Alumni: 

"Post-Shuttle Age: The Future of NASA": A Blended Research @ the Library panel discussion

Friday, April 29, 2011

Panelists David Ballantyne, Assistant Professor in the School of Physics and the Center for Relativistic Astrophysics (CRA); Ashley Korzun, graduate student in the Daniel Guggenheim School of Aerospace Engineering; John Krige, Kranzberg Professor in the School of History, Technology and Society; and David Spencer, Professor in the School of Aerospace Engineering and Director of the Center for Space Systems. discussed the future of NASA after the end of the space shuttle program, touching on topics such as the future of payload delivery, the exploration of Mars, the commercialization of space, funding issues and much more.

To view the presentation, please go to http://smartech.gatech.edu/handle/1853/38548.

Summary: 

"Post-Shuttle Age: The Future of NASA": A Blended Research @ the Library panel discussion

Intro: 

"Post-Shuttle Age: The Future of NASA": A Blended Research @ the Library panel discussion

Alumni: 

Swimming in the Sahara

Monday, April 25, 2011

The sandfish, a type of desert lizard, can vanish into a sandy substrate in a blink of an eye. Approaches that draw on mathematics, physics, and engineering provide complementary insights into how the animal achieves this feat.  In a paper in the Journal of the Royal Society Interface, graduate student Ryan Maladen, Assistant Professor Dan Goldman, and their colleagues describe how they have used a refinement of their resistive force theory to show that a sand-swimming lizard moves forward about as fast as it can. Their model will allow biologists and engineers to explore loco¬motion in granular solids with unprecedented ease and speed. (Nature, 472:177, April 14, 2011)

Summary: 

Swimming in the Sahara

Intro: 

Swimming in the Sahara

Alumni: 

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