Waves & Packets
Mar. 9, 2013

Reconstructing the orbit of the Chelyabinsk meteoroid
A pair of Colombian scientists has made the first attempt to reconstruct the trajectory of the meteoroid (Chelby) that exploded over Chelyabinsk, Russia last month. Their analysis of the meteor's orbit, posted on arXiv, relies on an eclectic mix of data from car dashboard and stationary security cameras. First, they recorded where Chelby's light overpowered that of the Sun (the brightening point). Second, they noted Chelby's demise — the dimming of light associated with fragmentation. Videos from the city of Korkino (~35 kilometers south of Chelyabinsk) show Chelby passing through local zenith (straight up) when it exploded. Also, people found a hole in an ice-covered lake ~85 kilometers southwest of Chelyabinsk that was not there before Chelby impacted.

Taken together, this data constrained the location (height, latitude, and longitude) of Chelby at the brightening and fragmentation points as well as its average velocity. Using distance-measuring tools on Google Earth and trigonometry, they calculated the azimuth and elevation of Chelby at these two significant times. They were then able to use standard tools to calculate a range of possible orbits going back 4 years. It turns out, according to these predictions, that the Chelby meteoroid has an elliptical orbit that takes it well to the other side of Mars, before having Earth-orbit crossing trajectories. More

LHCb eyes D-meson oscillating from matter to anti-matter, evidence for charge-parity violation
American Physical Society
The LHCb Collaboration has reported in Physical Review Letters the first definitive (9.1 σ) observations of D-mesons oscillating from matter to antimatter. Combining results from other collaborations (BaBar, Belle and CDF) provided hints that D0 and anti-D0 mesons mix, i.e., share superimposed eigenstates. This new result is the first single-measurement of this phenomenon, and is well beyond the level of confidence where particle physicists call an observation a discovery. Physicists have also previously seen this kind of mixing in B-mesons (down and strange), as well as in K-mesons (kaons). "Charm mixing" phenomena are predicted by the Standard Model, and are enabled through the weak interaction. These technologically complex observations required many collisions to get good statistics, and fortuitously they could lead to more detailed studies of charge–parity (CP) violation in charm mesons. LHCb had seen an asymmetry in D0 to anti-D0 oscillations compared anti-D0 to D0 oscillations. But that observation was only with 3.5 σconfidence. So the larger data available now to LHCb will hopefully unravel this CP violation.More

Long predicted atomic collapse state observed in graphene
Lawrence Berkeley Laboratory
The extraordinary properties of graphene have allowed physicists to experimentally observe atomic collapse, a long sought after holy grail of nuclear and atomic physics. Paul Dirac first proposed that when the positive electrical charge of a super-heavy atomic nucleus surpasses a critical threshold, the resulting strong Coulomb field causes a negatively charged electron to populate a state where the electron spirals down to the nucleus and then spirals away again, emitting a positron (a positively–charged electron) in the process. This has been experimentally hard to observe because maintaining heavy nuclei is very hard to do. Reporting in Science, scientists have demonstrated how graphene allowed for the atomic collapse to occur at smaller nuclei sizes. Graphene doped with multiple calcium ion dimers exquisitely brought into close quarters by an STM tip leads to electrostatic attraction of the material's relativistic electrons. As a result the researchers were able to directly image how electrons behave around a nucleus as the nuclear charge is methodically increased from below the supercritical charge limit, where there is no atomic collapse, to above the supercritical charge limit, where atomic collapse occurs. Graphene doped in this way, with electrons collapsing in the manner, led to some very interesting electronic behavior that was interesting in its own regard. More

Hubble scientists refine age of oldest star
Hubble Site
Astronomers using the Hubble Space Telescope have refined the age estimate of the oldest known star, which brings it more in line with the calculated age of the universe. HD140283, aka, the "Methusala Star" had been estimated to be as old 14.5–16 billion years, while the entire universe is calculated to be only 13.8 billion years old — all with some uncertainty. After remeasuring the star's parallax and applying contemporary theories about the star's burn rate, chemical abundances, and internal structure, the new age estimates reduce the range of measurement uncertainty, so that the star's age overlaps with the universe's age. Other ideas about stellar fusion reactions are that leftover helium diffuses deeper into the core and so the star has less hydrogen to burn via nuclear fusion. This means it uses fuel faster and that correspondingly lowers the age. Also, the star has a higher than predicted oxygen-to-iron ratio, and this too lowers the age. HD140283 was likely born in a primeval dwarf galaxy that was gravitationally shredded and sucked in by the emerging Milky Way over 12 billion years ago. It is at the very first stages of expanding into a red giant, can be seen with binoculars as a 7th-magnitude object in the constellation Libra. This research is reported in the Astrophysical Journal. More

'Magnetogenetics' probes the inner space of a cell
Ars Technica
Cells usually form specialized internal structures in response to signals from their environment. Nerve cells, for example, receive signals from elsewhere in the body, which direct where their axons grow. And as they grow, scientists have observed protein globules forming in discrete parts of the cell. In the usual case these local structures are mediated through some biochemical coupling to mechanical, electrical, or chemical stimuli. To study the impact of these structures, scientists have had to use genetic manipulations to either knock-out or amplify the expression of the proteins that make up the structure. In a Nature Nanotechnology paper, a team of biophysicists describes a new way to manipulate cell morphology with a magnetic tip. They decorated proteins known to regulate cell morphology with magnetic nanobeads and fluorescent tags. As a result they were able to manipulate the organization of the intracellular protein architecture, and thus the morphology of the cell, by a controllable external magnetic field. This is not only a new tool for the lab, but may also lead to better understanding of how magnetic fields impact normal physiology. More

Dark matter may explain Fermi bubbles
Daily Galaxy
In 2011 astrophysicists working with NASA's Fermi Gamma-Ray Space Telescope found so-called Fermi bubbles at the center of the Milky Way galaxy. They show up as lobes of gamma radiation both above and below the center of our galaxy. Their supposed sources are the black hole thought to be at the center of the galaxy and stellar explosions. The lobes also contain a massive outflow of charged particles. Yet the amount of particles observed is more than what the two supposed sources can explain. A paper recently posted on arXiv suggests that the Fermi bubbles may be partly due to annihilating collisions between dark matter particles. Dark matter is the theoretical substance devised to explain the gravitational pull on objects that cannot be explained by the amount of matter that we can see. Astrophysicists have theorized that dark matter annihilations result in tau leptons and gamma ray emissions. More

Physicists crack science of ice formation
Cornell University
By observing the kinetics of ice formation as well as the minimum nucleation cluster size required for crystal formation, physicists at Cornell University have determined the mechanism of ice formation and how solutes increase melting points. In supercooled pure water, ice forms in about 1 microsecond. That time gets multiplied by 10 for every incremental increase in solute concentration. In a 50 percent glycerol-water solution, for example, ice formation can take almost a minute. In a Physical Review Letters paper, the researchers explain that it takes approximate 50 water molecules to form a nucleation site for solid ice formation. Increasing the concentration of solutes reduces the space available for a volume free of the solute molecules that is also on the order of that required for nucleation. With implications ranging from climate change to biomedical cryopreservation , the researchers derived the exponential dependence of water freezing on solute concentration, and were able to quantitatively replicate data for eight different solutes, ranging from salt to sugar to alcohol. More

The future of ion traps
Joint Quantum Institute
An invited paper in Science speculates on using ion trap technology as a scalable option for quantum information processing. Trapped atomic ions are a promising architecture that satisfies many of the critical requirements for constructing a quantum computer. Quantum computers depend upon qubits , a basic unit of quantum information in which a system (say of atomic ions) is in a superposition of two states at the same time. In current computers, information exists in bits that are either in one state or another state. In quantum computers the information will be in qubits, which means that the information is in multiple states at the same time and operations can be performed in all of them. A system with n qubits can perform 2n calculations at once! Qubits (trapped ions) must be stably maintained for long enough periods to perform calculations. In ion traps, qubit states can be both stably maintained and precisely manipulated by lasers and microwaves. Ion traps themselves were invented more than a half-century ago, but researchers have implemented new technologies in order to store large ion crystals and shuttle ions around as quantum computing operations are executed. More

Scientist discover a natural topological insulator
American Chemical Society
Scientists have found a natural mineral called Kawazulite with the general chemical composition Bi2(Te,Se)2(Se,S) in a Czech gold mine that has the property of being a topological insulator, i.e., conducts electricity on its surface, while acting as an insulator inside. Reporting in the ACS journal Nano Letters, the researchers determined that their exact sample had the stoichiometric composition (Bi2.12Sb0.06)Te2(Se0.14S0.32). Raman spectroscopy as well as electron microscopy and diffraction were used to confirm the molecular structure, while angle-resolved photoelectron spectroscopy and magnetoresistance measurements were used to reveal that the electrical conductivity was due to two decoupled surface channels. Heretofore topological insulators studied by experimental physicists have been synthetics compounds. This is likely only the first of many natural minerals that have exhibited this property. Prospective candidates for further study include the members of the Tetradymite and Aleksite group which together comprise more than 20 compounds. More

Pan-STARRS finds a 'lost' supernova
Harvard-Smithsonian Center for Astrophysics
Using the Pan-STARRS telescope, astronomers have spotted a rare Type Ibn supernova (PS1-12sk) in an elliptical galaxy. This is only the sixth such example of this type of supernova found out of thousands of supernovae found. They are almost never seen in elliptical galaxies where star formation has nearly ceased. Instead they are found in spiral galaxies where star formation is happening all the time. Astronomers surmise that this particular galaxy has star forming activity that is presently hidden from view, or that PS1-12sk resulted from the collision of two white dwarfs, one of which was helium-rich. A paper describing this discovery has been submitted to the Astrophysical Journal.More

Math, physics and maple syrup
Society for Industrial and Applied Mathematics
Waves and Packets is normally delivered on Saturday mornings, when our readers may be enjoying it with pancakes, waffles, or French toast with maple syrup. Research reported in the SIAM Journal of Applied Mathematics will increase your reading enjoyment as well as your understanding of how that syrup made it out of that tree. Maple trees covert CO2, water and sunlight into starch, which is stored in the tree's vascular tissue as sap and converted into sugar. The "physical" model of sap exudation attributes the mechanism entirely to pressure and volume changes that result from passive, physical effects in the tree’s vascular tissue: expansion and contraction of gas as well as freezing and thawing of sap, which occur in response to temperature changes. The mathematical model is a system of differential-algebraic equations that describes the multiphase gas-liquid-ice environment and incorporates the dynamics and effects of thawing sap, dissolving gas bubbles and an osmotic pressure gradient between vessels and fibers in the tree’s non-living vascular tissue. Numerical simulations indicate that gas bubbles build up pressure and allow for the sap to be tapped from the tree. Other than for maintaining gas bubbles osmosis is not an essential process to maintain the pressure differential for material flow.More

Increase your options for graduate or REU program admissions
The NSBP GradApps and REUApps services are open to all students and allows them to upload all the elements of an admissions application, including academic and work history, transcripts, letters of recommendation and a personal statement. Graduate and REU programs can subscribe to these databases to increase the programs' applicant pool, while at the same time allowing students can put their credentials in front of more programs than to which they would otherwise apply. More

Physicists and astronomers encouraged to participate in Congressional Visits Day, March 12-13
Science-Engineering-Technology Working Group
The Congressional Visits Day is a two-day annual event that brings scientists, engineers, researchers, educators and technology executives to Washington, D.C., to raise visibility and support for science, engineering and technology. Uniquely multi-sector and multi-disciplinary, the CVD is coordinated by coalitions of companies, professional societies, including American Astronomical Society, the American Physical Society and the National Society of Black Physicists, as well as several educational institutions. During the event the Science-Engineering-Technology Working Group bestows the George E. Brown, Jr. Award for S-E-T Leadership upon Members of Congress who have been especially effective in S&T advocacy and leadership. CVD participants are encouraged visit their Representative in the House and their two Senators so that they can hear about the importance of S&T directly from one of their constituents. The event is open to all who believe that science and technology comprise the cornerstone of our Nation's future. If you cannot make it to Washington DC for the event, you can still write to your Senators and Representative to urge them to prioritize investment in science and technology, as well as to take action on several other important policy matters.More

National Society of Black Physicists jobs board postings
Schuler Postdoctoral Fellowship
Postdoctoral Fellowship — Stanford Molecular Imaging Scholars Program
Physics Academic Coordinator I/Lecturer
Summer Undergraduate Researcher
REU summer program on complex materials
REU Student
National Radio Astronomy Observatory Research Experience for Undergraduates
Postdoctoral Research Associate PositionsMore

Pan-STARRS finds a 'lost' supernova
Harvard-Smithsonian Center for Astrophysics
Using the Pan-STARRS telescope, astronomers have spotted a rare Type Ibn supernova (PS1-12sk) in an elliptical galaxy. This is only the sixth such example of this type of supernova found out of thousands of supernovae found. They are almost never seen in elliptical galaxies where star formation has nearly ceased. Instead they are found in spiral galaxies where star formation is happening all the time. More

Astronomers capture image of planet formation for the first time
European Southern Observatory
Research on planet formation has mostly involved theoretical models and computer simulations. According to the most accepted theory of planet formation, giant planets grow by capturing some of the gas and dust that remains after the formation of a star. Astronomers using ESO's Very Large Telescope in Chile have obtained what is likely the first direct observation of a forming planet still embedded in a thick disc of gas and dust. More

Spin rate of black hole definitely measured by NuStar and XMM-Newton
Astronomers using two X-ray space observatories, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency's XMM-Newton, have teamed up to measure definitively, for the first time, the spin rate of a black hole. They determined that the supermassive black hole at the center of the galaxy NGC 1365 is spinning almost as fast as Einstein's theory of gravity will allow. The spin rate of a black hole tells a lot about how it formed. Fast spinning black holes formed quickly, while slower ones formed more slowly. More

Latest research from European Journal of Physics
IOP Publishing
Thévenin equivalents for inhomogeneous ladder networks of generators

An experiment to evaluate the thermal performance of an oil-heating copper spiral coil

Deflection and potential energy of linear and nonlinear springs: approximate expressions in terms of generalized coordinates

Build-up of interference patterns with single electrons

A simple method for synthesizing and producing guitar sounds


Latest research from Physical Review Letters Special Topics: Physics Education
American Physical Society
Student difficulties measuring distances in terms of wavelength: Lack of basic skills or failure to transfer?

Categorization of first-year university students’ interpretations of numerical linear distance-time graphs

Problem-solving rubrics revisited: Attending to the blending of informal conceptual and formal mathematical reasoning

Does using a visual-representation tool foster students’ ability to identify forces and construct free-body diagrams?

New approach to analyzing physics problems: A Taxonomy of Introductory Physics Problems