APS Physics News Ticker

Tuesday, November 19, 2013

Market Turbulence is Like Fluid Turbulence

From the authors of manuscript XE10048E, to be published in Phys. Rev. E:

The physics of complexity helps one understand turbulent
financial markets.

Symmetry is loved by physicists because it makes the description of
our world simple and harmonious. This work shows that ideas inspired
by physics could also simplify the complex world of finance.
The historical changes in the price of financial assets present
similarities with variations in turbulent fluids. In spite of the
erratic, unpredictable character of these variations, in both cases
symmetry allows one to infer, from the knowledge of a distribution at
one time, the same distribution at other times.
Inspired by theoretical methods which led to the understanding of
this scaling symmetry in physics, we show that scaling alone can be
used as a guide for the construction of a model of asset price evolution.
Besides allowing one to evaluate financial risk or to price derivatives
on the basis of past market records, the novel description reproduces
key features of price histories in finance. In particular, it allows
one to discriminate between the past and future. There is an "arrow of
time".

Contact:
Matteo Rini
631 591 4224 (office)
646 288 5441 (cell)
mrini@aps.org

Wednesday, November 13, 2013

Riding an electron wave into the future of microchip fabrication

Computer simulation explores how intense plasma waves generate suprathermal electrons, which are critical to microchip fabrication



		A plasma wave can give rise to a population of suprathermal electrons.

Advanced plasma-based etching is a key enabler of Moore's Law that observes that the number of transistors on integrated circuits doubles nearly every two years. It is the plasma's ability to reproduce fine patterns on silicon that makes this scaling possible and has made plasma sources ubiquitous in microchip manufacturing.

A groundbreaking fabrication technique, based on what is called a DC-augmented capacitively coupled plasma source, affords chip makers unprecedented control of the plasma. This process enables DC-electrode borne electron beams to reach and harden the surface of the mask that is used for printing the microchip circuits.

More importantly, the presence of the beam creates a population of suprathermal electrons in the plasma, producing the plasma chemistry that is necessary to protect the mask. The energy of these electrons is greater than simple thermal heating could produce—hence the name "suprathermal." But how the beam electrons transform themselves into this suprathermal population has been a puzzle.

Now a computer simulation developed at the U.S. Department of Energy's Princeton

Plasma Physics Laboratory in collaboration with the University of Alberta has shed light on this transformation. The simulation reveals that the initial DC-electrode borne beam generates intense plasma waves that move through the plasma like ripples in water. And it is this beam-plasma instability that leads to the generation of the crucial suprathermal electrons.

Understanding the role these instabilities play provides a first step toward still-greater control of the plasma-surface interactions, and toward further increasing the number of transistors on integrated circuits. Insights from both numerical simulations and experiments related to beam-plasma instabilities thus portend the development of new plasma sources and the increasingly advanced chips that they fabricate.

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Abstracts:
TO6.00005 Collisionless acceleration of plasma electrons by intense electron beam
Session: Low Temperature Plasma Science, Engineering and Technology
9:30 AM–11:06 AM, Thursday, November 14, 2013

Contact:
James Riordon
riordon@aps.org
301-209-3238

Tuesday, November 12, 2013

APS Physics Tip Sheet – Nov 12, 2013

In this issue: Color Darkening in Historical Paintings, Thickening When Stirred, How the Oldest Fossils Were Formed and More

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Color Darkening in Historical Paintings

X-ray studies of medieval murals explain why red pigments in historical paintings have degraded over time.

For over two millennia vermilion (mercury sulfide) has been the painter’s finest red. But in many old paintings the pigment has discolored to a drab brownish black. The reason for the change has been controversial, but a team of researchers from Belgium, Italy and France now claims to have figured out the cause of such degradation. The authors applied X-ray techniques to examine the composition of a discolored vermilion paint layer from a medieval mural in a Catalan monastery. Guided by simulations, they suggest the pigment darkens via a sequence of light-initiated chemical reactions that involve the formation of metallic mercury. The finding clarifies the connection between degradation and environmental conditions and may lead to better ways of protecting paintings through the proper choice of lighting and humidity conditions.

* Fabiana Da Pieve (contact author) et al, “Casting light on the darkening of colors in historical paintings”, Physical Review Letters (expected publication date: Nov 15)

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Thickening When Stirred

Researchers have developed a new model able to predict the behavior of fluids that thicken when stirred.

Certain liquid suspensions like cornstarch in water respond differently than normal liquids to shear: they thicken when they are stirred, becoming solid-like. The phenomenon may be detrimental in industrial applications (e.g. the processing of ink or slurries) but could also be exploited to engineer liquid body armors. Now a research team in New York has developed a numerical model that, for the first time, can accurately describe and predict the shear-thickening transition. The development is based on the recognition of the key role played by friction between particles suspended in the liquid.

* Ryohei Seto (contact author), R Mari, JF Morris, MM Denn, “Discontinuous shear thickening of frictional hard-sphere suspensions”, Physical Review Letters (expected publication date: Nov 18)

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How the Oldest Fossils Were Formed

The analysis of billion-year-old sedimentary rocks provides information on some of the earliest microorganisms on Earth.

Stromatolites are 3.5-billion-year-old sedimentary rocks that are regarded as the fossilized deposits of ancient biological layers. These formations may thus carry information on the oldest life forms on Earth. A team of researchers from MIT and the University of Johannesburg, in South Africa, has developed a model that explains the growth of conical stromatolites, the most simply structured forms of the fossils. They grow as ions of calcium or silica diffuse thorough a biofilm and precipitate as minerals around cells, causing them to fossilize. Over many generations, these structures can grow into meter-sized structures with conical symmetry. The model allowed the authors to estimate some of the properties of the microbial mats that led to the fossils we see today.

* Alexander P Petroff (contact author), NJ Beukes, DH Rothman, T Bosak, “Biofilm growth and fossil form”, Physical Review X (expected publication date: Nov 13)

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Bring a 50,000-degree Plasma into Your Living Room

An online open-user experiment puts users in control of a real physics laboratory.

DENVER, CO— With the rise of online open course platforms such as Khan Academy, MIT
OpenCourseWare and iTunes U, it has never been easier to teach yourself everything
from American history to semiconductor manufacturing. These courses enable students to
advance at their own pace while accessing the limitless resources available on the internet
for supplemental material.

But there’s a glaring exception to this cornucopia of courseware: Online physics classes
that enable students to interact with a real physical experiment. While excellent online
sites like Phet Interactive Simulations have developed virtual labs that simulate
laboratory environments, there is no substitute for actual live experiments.

At the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), we’ve
developed software for an experiment that can be observed and controlled from anywhere
in the world.

The user can operate the experiment with a set of controls, shown on the left side of the
screen, and watch the effect on the apparatus at PPPL using the web stream video, shown
on the right. This “Remote Glow Discharge Experiment (RGDX)” consists of three main
components:

• A live-streaming video that constantly observes an experimental apparatus housed
at PPPL.
• A set of online controls.
• Information that explains what the user observes and controls, plus more in-depth
resources that explore plasma and its uses.

The RGDX consists of a hollow glass tube with air held under vacuum. Supplying a
voltage of up to 2000V generates a glow discharge within. The user has control of the
pressure inside the tube, the voltage supplied to the plasma and of the strength of an
electromagnet surrounding the tube. Users are guided through steps that gradually
increase their level of engagement and introduce them to new physical concepts and
topics. If the user is interested in the physics behind the voltages, pressures and magnets,
further explanations are given for each topic.

Audiences for the RGDX can range from someone simply interested in controlling a
physical apparatus from afar, to an undergraduate or graduate student who wants to study
phenomena such as instabilities in plasma or the physics behind plasma breakdown
voltages. The RGDX can be used as a novel experimental component of either an online
or in-class physics course, and the software can be adapted to a wide array of experiments
in other fields of physics and, potentially, to experiments in other sciences as well.

Abstracts:
JP8.00006 Remote control of a DC discharge experiment
Session JP8: Poster Session IV: Education and Outreach, MHD, Alpha
Heating & Computational Methods
2:00 PM–5:00 PM, Tuesday, November 12, 2013
Room: Plaza ABC

Contact:
James Riordon
riordon@aps.org
301-209-3238

Wednesday, November 6, 2013

How To Get Women to Pursue Physics Careers

Of five common approaches to encouraging women to pursue physics careers, only discussing the reasons women don't enter the field appears to be effective.

Phys. Rev. ST Physics Ed. Research 9, 020115

There are many hypotheses regarding factors that may encourage female students to pursue careers in the physical sciences. Using multivariate matching methods on national data drawn from the Persistence Research in Science and Engineering (PRiSE) project (n=7505), we test the following five commonly held beliefs regarding what factors might impact females’ physical science career interest: (i) having a single-sex physics class, (ii) having a female physics teacher, (iii) having female scientist guest speakers in physics class, (iv) discussing the work of female scientists in physics class, and (v) discussing the underrepresentation of women in physics class. The effect of these experiences on physical science career interest is compared for female students who are matched on several factors, including prior science interests, prior mathematics interests, grades in science, grades in mathematics, and years of enrollment in high school physics. No significant effects are found for single-sex classes, female teachers, female scientist guest speakers, and discussing the work of female scientists. However, discussions about women’s underrepresentation have a significant positive effect.

Contact:
James Riordon
riordon@aps.org
301-209-3238

APS Physics Tip Sheet – Nov 5, 2013

In this issue: Measuring Slow Blood Flow, Cities Fragment Under Traffic Burden, An Electron Bucket Brigade, Chaos in a Transient World, Building a SQUID with Bose-Einstein Condensates, and More

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Measuring Slow Blood Flow

A new laser-based scheme allows the visualization of blood flowing at very small speeds.

The measurement of blood flow in human tissues is important for the diagnosis and assessment of many diseases. Current ultrasound techniques use the Doppler shift of the sound waves’ frequency to measure the motion of blood cells. But the effect is undetectable for blood moving slower than about ten millimeters per second. Now, researchers in the US have demonstrated an ultrasound-based technique that can measure speeds as low as a quarter of a millimeter per second. The scheme uses laser pulses to track the sound waves generated by locally heating the blood with ultrasound. The method may find use in biomedical applications ranging from functional brain imaging to the detection of cancer and atherosclerotic plagues

* Lidai Wang (contact author) et al, “Ultrasonically encoded photoacoustic flowgraphy in biological tissue”, Physical Review Letters (expected publication date: Nov 12)

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Cities Fragment Under Traffic Burden

Traffic congestion may be the root cause for why cities become more decentralized as they grow.

Most modern cities tend to develop several centers around which inhabitants organize their lives. A new model proposed by French researchers suggests that the transition from a monocentric to a polycentric structure is driven by traffic congestion. The authors find that the formation of multiple activity centers results from an instability due to the tension between the desire for better-paid jobs and the dread of long commutes. The model provides quantitative predictions that might help urban planners prepare for city growth.

* Rémi Louf (contact author), M Barthelemy, “Modeling the polycentric transition of cities”, Physical Review Letters (expected publication date: Nov 6)

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An Electron Bucket Brigade

Arrays of nanopillars could harvest energy from ambient vibrations with high efficiency.

Inside piezoelectric shoes or bounce backpack dynamos, certain electromechanical devices convert the energy harvested from ambient motion into electricity. An important limit to their efficiency is posed by the fact that such harvesters can only absorb a narrow spectrum of frequencies from the input motion. A team of researchers from South Korea, Germany, Spain and the US has demonstrated a new scheme based on nanometer-sized vertical rods that wave back and forth in response to motion, thereby generating an electric current. Since the mechanism works over a broad range of frequencies, these nanorod shuttles may improve the efficiency of energy harvesting by several orders of magnitude.

* C Kim, Marta Prada (contact author), G Platero, RH Blick, “Realizing broadbands of strong nonlinear coupling in nanoelectromechanical electron shuttles”, Physical Review Letters (expected publication date: Nov 5)

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Chaos in a Transient World

A new model suggests chaotic behavior could emerge even in systems in which all motion dies out due to the effects of dissipation

Chaotic systems exhibit a number of characteristic signatures, such as the butterfly effect (a pronounced sensitivity to initial conditions that makes long-term predictions impossible). Such behavior has always been studied in systems that perpetually evolve: they either don’t lose energy or they are constantly subject to external forces. But what would happen in a dissipative system without any energy input, in which all motion eventually dies out? A new study by researchers in the US and Hungary shows that the hallmarks of chaos could also be observed in these systems. The results imply that processes like the evolution of chemical reactions toward equilibrium or the coalescence of binary stars as they lose energy to gravitational waves could be chaotic – and thus far less predictable than expected.

* Adilson E Motter (contact author), M Gruiz, G Károlyi, T Tél, “Doubly Transient Chaos: The Generic Form of Chaos in Autonomous Dissipative Systems”, Physical Review Letters (expected publication date: Nov 7)

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Building a SQUID with Bose-Einstein Condensates

SQUIDs (superconducting quantum interference devices) are the basis of today’s most sensitive magnetometers. A research team at the Los Alamos National Lab has now built an analog of a SQUID made of a Bose-Einstein-condensed atomic gas. Since in this atomic SQUID rotation plays the same role as the magnetic field in a SQUID magnetometer, the device has potential as an ultrasensitive rotation sensor.

* C Ryu, PW Blackburn, AA Blinova, MG Boshier (contact author), “Experimental realization of Josephson junctions for an Atom SQUID”, Physical Review Letters (expected publication date: Nov 11)

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Wednesday, October 30, 2013

Most Invisibility Cloak Schemes Would Make Objects More Visible, Not Less

"Making an object invisible to red light, for instance, may actually make it bright blue, increasing its overall visibility."

Add caption

Phys. Rev. X 3, 041005 (2013): From ancient times, humanity has been fascinated by the concept of invisibility, and recently, scientists have moved a step closer to bringing this idea to reality by exploiting engineered artificial materials, or metamaterials. Several recent studies have indeed shown that a properly tailored metamaterial cover can, in principle, render an object invisible when illuminated by an electromagnetic wave oscillating at the specific frequency of interest. Yet, experimental realizations and theoretical investigations have consistently shown that reducing the visibility of an object with a passive cloak in a specific window of the electromagnetic spectrum is generally accompanied by a drastic increase of its visibility in other frequency ranges. Making an object invisible to red light, for instance, may actually make it bright blue, increasing its overall visibility.

In this paper, we quantitatively assess the potentials and limitations of passive cloaks in terms of overall visibility, integrated over the entire frequency spectrum. Quite surprisingly, our results show that any linear, causal, and passive invisibility cloak, without special superconducting features, is deemed to increase the scattering and visibility of the original uncloaked object, when integrated over all frequencies. This result confirms that the most popular cloaking devices actually scatter more, not less, when considered over a sufficiently broad frequency range, allowing easy detection using, e.g., pulsed excitation.

Our general theorem holds a relevant exception if specific covers with a strong static diamagnetism are considered, and, based on this principle, we propose a technique to reduce the global scattering, as well as the local response around a frequency of interest, using diamagnetic and superconducting thin cloaking layers. More generally, our results provide a quantitative measure to compare the overall performance of different cloaking devices and generally assess their detectability. These findings may open important research directions in the quest for invisibility, not only in the electromagnetic domain but also for acoustic, mechanical, and matter waves.

Contact:
James Riordon
riordon@aps.org
301-209-3238

Tuesday, October 29, 2013

APS Physics Tip Sheet – Oct 29, 2013

In this issue: Planet Search Finds No Dark-Matter Black Holes, Secure Quantum Commitment, A Single-Atom Switch, and More

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Planet Search Finds No Dark-Matter Black Holes

(Image credit: NASA/Kepler mission/Wendy Stenzel)

Using data from a planet-hunting mission, scientists place new limits on a supposed population of moon-sized black holes that could act as dark matter in our galaxy

According to recent theoretical studies, small, primordial black holes (PBHs) formed during the universe’s early expansion could be responsible for the gravitational effects attributed to dark matter. A team of researchers from the US and Taiwan has searched for PBHs using observations by Kepler - a NASA satellite designed to look for Earth-like planets orbiting other stars. Over 4 years, Kepler monitored ~150,000 stars in the Milky Way. If a primordial black hole passed in front of one of these stars, the star would become temporarily brighter due to the hole’s gravitational lensing. The analysis revealed no black-hole lensing events, ruling out the possibility that primordial black holes could account for a major fraction of the dark matter that is known to exist in our galaxy.

* Kim Griest (contact author), AM Cieplak, and MJ Lehner, “New limits on primordial black-hole dark matter from an analysis of Kepler source microlensing data”, Physical Review Letters (expected publication date: Oct 31)

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Secure Quantum Commitment

Researchers have demonstrated a secure quantum commitment scheme - a cryptographic protocol that allows one to commit to a chosen value, while keeping it secret until the value is revealed.

Secure commitment schemes could find use in bidding or voting systems, in which no one should learn anyone else's intent before an appointed time. Inspired by the success of quantum cryptography techniques like Quantum Key Distribution, researchers have turned to quantum mechanics to develop inherently secure commitment protocols. Some theoretical work seemed to demonstrate that a secure quantum commitment scheme was impossible, but according to a 2012 proposal, a solution could be found if relativistic effects were present. Now, a group of researchers from Switzerland, Singapore, the UK and Canada has experimentally realized this proposal. In an optical fiber link between Geneva and Singapore, the team showed that a committed bit could be kept secret for up to 15 milliseconds - a time that may be sufficient for high-speed applications such as stock trading.

* T Lunghi, Felix Bussières (contact author) et al, “Experimental bit commitment based on quantum communication and special relativity”, Physical Review Letters (expected publication date: Nov 1)

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A Single-Atom Switch

A research team at the Vienna Center for Quantum Science and Technology has demonstrated an optical switch made of a single rubidium atom placed in a microscopic cavity. Controlled by the atom position, the switch can be used to reroute optical signals from an optical fiber to different output fiber ports.

* D O’Shea, C Junge, J Volz, Arno Rauschenbeutel (contact author), “Fiber-optical switch controlled by a single atom”, Physical Review Letters (expected publication date: Nov 4)

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