Wednesday, October 31, 2007

Magnetic Monopoles!

Magnetic Monopoles in Spin Ice
Electrically charged particles, such as the electron, are ubiquitous. By contrast, no elementary particles with a net magnetic charge have ever been observed, despite intensive and prolonged searches. We pursue an alternative strategy, namely that of realising them not as elementary but rather as emergent particles, i.e., as manifestations of the correlations present in a strongly interacting many-body system. The most prominent examples of emergent quasiparticles are the ones with fractional electric charge e/3 in quantum Hall physics. Here we show that magnetic monopoles do emerge in a class of exotic magnets known collectively as spin ice: the dipole moment of the underlying electronic degrees of freedom fractionalises into monopoles. This enables us to account for a mysterious phase transition observed experimentally in spin ice in a magnetic field, which is a liquid-gas transition of the magnetic monopoles. These monopoles can also be detected by other means, e.g., in an experiment modelled after the celebrated Stanford magnetic monopole search.

Friday, October 19, 2007

The Brightest Supernova So Far

SN 2006gy: Discovery of the most luminous supernova ever recorded, powered by the death of an extremely massive star like Eta Carinae
We report our discovery and observations of the peculiar Type IIn supernova SN2006gy in NGC1260, revealing that it reached a peak magnitude of -22, making it the most luminous supernova ever recorded. It is not yet clear what powers the total radiated energy of 1e51 erg, but we argue that any mechanism -- thermal emission, circumstellar interaction, or 56Ni decay -- requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star probably experienced an LBV eruption like the 19th century eruption of eta Carinae. Alternatively, radioactive decay of 56Ni may be a less objectionable hypothesis. That power source would imply a large Ni mass of 22 Msun, requiring that SN2006gy was a pair-instability supernova where the star's core was obliterated. SN2006gy is the first supernova for which we have good reason to suspect a pair-instability explosion. Based on a number of lines of evidence, we rule out the hypothesis that SN 2006gy was a ``Type IIa'' event. Instead, we propose that the progenitor may have been a very massive evolved object like eta Carinae that, contrary to expectations, failed to completely shed its massive hydrogen envelope before it died. Our interpretation of SN2006gy implies that the most massive stars can explode earlier than expected, during the LBV phase, preventing them from ever becoming Wolf-Rayet stars. SN2006gy also suggests that the most massive stars can create brilliant supernovae instead of dying ignominious deaths through direct collapse to a black hole.

The Quantum Measurement Problem

This preprint Can the Quantum Measurement Problem be resolved within the framework of Schroedinger Dynamics and Quantum Probability? addresses a fundamental problem in the foundations of physics. Traditionally a quantum measurement consists of two physical subsystems: a quantum subsystem (like an atom) and a classical subsystem (like a measuring instrument). The quantum subsystem is modelled using the often counterintuitive framework of quantum theory and the classical subsystem is modelled using the less startling laws of classical physics. Each subsystem in isolation evolves in a reasonably straightforward deterministic fashion, but when the two subsystems are coupled together something rather mysterious happens: a quantum measurement, which is fundamentally probabilistic in nature.

Ultimately, it's expected that the "classical" subsystem should be modelled by quantum theory as well and so too the composite of the two subsystems. After all, the classic subsystem is in term made up of constituents (like atoms) which obey the laws of quantum theory. However, it's been difficult to work out a completely quantum description of the measurement process. So much so that there has even been speculation that consciousness might be irreducibly involved.

Thursday, October 18, 2007

The Family Tree of the Placental Mammals

In PNAS Genomics, biogeography, and the diversification of placental mammals
Among the placental mammals, phylogenetic branching events have been inferred by using either nucleotide sequence data (4–11) or rare insertion/deletion patterns (12–15). Many of the results recognize four primary eutherian groups: Afrotheria, Xenarthra, Laurasiatheria, and Euarchontoglires. Afrotherians (e.g., elephants, hyraxes, manatees, aardvarks, tenrecs, and allies) are a clade of mammals that originated in Africa, and whose extant members still mostly remain on that continent with the exception of Asian elephants and sirenians such as the Florida manatee. The Xenarthra includes the sloths, armadillos, and anteaters that today are restricted to South and Central America (although some Xenarthra, such as the nine-banded armadillo, have recently dispersed to North America). The Laurasiatheria (e.g., bats, eulipotyphlans, pangolins, carnivores, perrisodactyls, and cetartiodactyls) is a diverse clade including extant lineages that originated in the ancient northern continent of Laurasia. The Euarchontoglires includes the species from five living mammalian orders (e.g., primates, treeshrews, flying lemurs, rabbits, and rodents). This last group remains the most controversial, and a number of recent studies have suggested it is not valid (4, 6, 7).

The Human Visual System is Tuned for Animals

From this PNAS article: Category-specific attention for animals reflects ancestral priorities, not expertise
Visual attention mechanisms are known to select information to process based on current goals, personal relevance, and lower-level features. Here we present evidence that human visual attention also includes a high-level category-specialized system that monitors animals in an ongoing manner. Exposed to alternations between complex natural scenes and duplicates with a single change (a change-detection paradigm), subjects are substantially faster and more accurate at detecting changes in animals relative to changes in all tested categories of inanimate objects, even vehicles, which they have been trained for years to monitor for sudden life-or-death changes in trajectory. This animate monitoring bias could not be accounted for by differences in lower-level visual characteristics, how interesting the target objects were, experience, or expertise, implicating mechanisms that evolved to direct attention differentially to objects by virtue of their membership in ancestrally important categories, regardless of their current utility.

Where do Supernovas Come From?

In the preprint Constraining the Type Ia Supernova Progenitor: The Search for Hydrogen in Nebular Spectra the investigator looks for hydrogen emissions that are expected by theories of supernova formation. This signal has not been detected to date.

Wednesday, October 17, 2007

The "Mean King's" Problem

Quantum theory makes many very peculiar predictions and worse, they have always been confirmed by experiment. First of all, quantum theory often gives only a probability for an outcome. Einstein disliked this, hence his comment "God does not play dice with the Universe".
A further odd situation is a mutually complementary set of measurements. In a two state quantum system (also known as spin 1/2), there are exactly two possible outcomes for any measurement. Depending on the state of the system and the measurement chosen, quantum theory assigns a probability to each outcome. If a measurement is performed on a system and the actual outcome is noted, the new state of the system is determined - there's no addition influence from the original state. Two measurements X and Y are complementary when the probabilities of the two possible outcomes of Y performed immediately after X, are equally likely. In this case, performing X first completely randomizes Y's outcomes. The definition of a mutually complementary set of measurements is: each pair of measurements is complementary. As it turns out, in quantum theory for a two state system, we may have a set of three mutually complementary measurements, but no more.

The preprint The "mean king's problem" with continuous variables explains the "mean king's" problem:
In its original version [1] (and as
retold in the whimsical setting of Refs. [2, 3]), a physicist,
Alice, is challenged by a mean king to precisely ascer-
tain the outcome of an ideal measurement that the king
performs of a spin-1/2 observable randomly chosen from
the mutually complementary set {ˆσx, ˆσy, ˆσz}.

So first Alice gets access to the system (she can perform measurements and observe the outcome), then without Alice being present the King gets to choose and perform one of the three complementary measurements and notes the outcome. Alice returns and may perform additional measurements on the system. Finally the King reveals which measurement he performed and Alice must predict the outcome.

How can Alice possibily do such a thing? As it turns out, it's crucial that Alice uses an auxillary quantum system. She performs her measurements not just on the King's system, but on a composite system which includes her auxillary. She seperates the original system and her auxillary while the King is doing his thing but recomposes them when she gets her second shot.

Monday, October 15, 2007

Cosmic Microwave Background Anomalies

Probing the Origin of the Large-angle CMB Anomalies
There has been mounting evidence that the large-angle cosmic microwave background (CMB) anisotropy has anomalies roughly at 3 sigma level.


How far over the edge of the table can we reach by stacking n identical, homogeneous, frictionless blocks of length 1? A classical solution achieves an overhang asymptotic to 1/2 ln n. This solution is widely believed to be optimal. We show, however, that it is exponentially far from optimality by constructing simple n-block stacks that achieve an overhang of cn^1/3, for some constant c>0.

With the restriction that only one block can be on top of another, the classical solution is optimal. However with multiple blocks on top of each the solution can be improved significantly.

Sunday, October 14, 2007

Reason and the Passions

"Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them"
David Hume

Childhood Origins of Adult Resistance to Science

Childhood Origins of Adult Resistance to Science in Science Magazine.
Resistance to certain scientific ideas derives in large part from assumptions and biases that can be demonstrated experimentally in young children and that may persist into adulthood. In particular, both adults and children resist acquiring scientific information that clashes with common-sense intuitions about the physical and psychological domains. Additionally, when learning information from other people, both adults and children are sensitive to the trustworthiness of the source of that information. Resistance to science, then, is particularly exaggerated in societies where nonscientific ideologies have the advantages of being both grounded in common sense and transmitted by trustworthy sources.

Friday, October 12, 2007

Accelerated Expansion

Astrophysics preprint Chasing Lambda
Recent astronomical observations of SNIa, CMB, as well as BAO in the Sloan Digital Sky Survey suggest that the current Universe has entered a stage of an accelerated expansion with the redshift transition at about z=0.5. While the simplest candidates for explanation of this fact is cosmological constant/vacuum energy there exist a serious problem of coincidence. In the theoretical cosmology we can find many possible approaches alleviating this problem by applying new physics or other conception of dark energy. We consider state of art candidates for the description of accelerating Universe in the framework of the Bayesian model selection. We point out advantages as well as troubles of this approach. We find that the combination of four data bases gives a stringent posterior probability of the LambdaCDM model which is 74%. This fact is a quantitative exemplification of a turmoil in modern cosmology over the Lambda problem.

Wednesday, October 10, 2007

Ultra Compact Dwarf Galaxies

In the astrophysics preprint UCDs - more massive than allowed?, Ultra Compact Dwarf Galaxies (UCD) found in Galaxy Clusters are observed to have a very high mass to light ratio. One possible explanation is an extraordinarily dense concentration of Dark Matter.

Tuesday, October 09, 2007

Chimpanzees are insensitive to fairness

Chimpanzees Are Rational Maximizers in an Ultimatum Game in Science Magazine.
Traditional models of economic decision-making assume that people are self-interested rational maximizers. Empirical research has demonstrated, however, that people will take into account the interests of others and are sensitive to norms of cooperation and fairness. In one of the most robust tests of this finding, the ultimatum game, individuals will reject a proposed division of a monetary windfall, at a cost to themselves, if they perceive it as unfair. Here we show that in an ultimatum game, humans' closest living relatives, chimpanzees (Pan troglodytes), are rational maximizers and are not sensitive to fairness. These results support the hypothesis that other-regarding preferences and aversion to inequitable outcomes, which play key roles in human social organization, distinguish us from our closest living relatives.

Gould's Belt

Many of the bright stars in the spectacular constellations Orion and Scorpio are a part of Gould's Belt a nearby ring of stars - the cause of which is still unknown.

Cosmic Reionization

In the Big Bang model of cosmology, early in the history of the universe it was too hot for neutral hydrogen gas, all the electrons were stripped from the nucleus (usually a proton), and the hydrogen gas filling the universe was ionized. As the universe expanded, the temperature cooled enough for neutral hydrogen, and the electrons became bound to protons. At some point stars began to form and the ultraviolet radiation the stars radiated was sufficient to ionize hydrogen gas once again - cosmic reionization. In this preprint Testing Reionization with Gamma Ray Burst Absorption Spectra the era of reionization is studied by looking for very ancient gamma ray bursts, the most energetic events known in the universe.

Communication with Gravitational Waves?

Generation and detection of gravitational waves at microwave frequencies by means of a superconducting two-body system
In engineering, it could open up the possibility of intercontinental communications by means of microwave-frequency gravitational waves directly through the interior of the Earth, which is transparent to such waves. This would eliminate the need of communications satellites, and would allow an economical means of communication with people deep underground or underwater in submarines in the oceans. Such a new direction of gravitational-wave engineering could aptly be called “gravity radio”

Chilling Account of the "Storm Worm"

Gathering 'Storm' Superworm Poses Grave Threat to PC Nets by Bruce Schneier. See also his blog: Schneier on Security for interesting information on security and privacy.

Monday, October 08, 2007

How to Grow a Silicon Crystal

It's not easy!
Czochralski Crystal Growth Method from the BBC.

Czochralski Crystal Growth Process tells more about why it is difficult.

Britney's Guide to Semiconductor Physics

Britney's Guide to Semiconductor Physics
It is a little known fact, that Ms Spears is an expert in semiconductor physics. Not content with just singing and acting, in the following pages, she will guide you in the fundamentals of the vital laser components that have made it possible to hear her super music in a digital format.

Vanadium Dioxide is Fast

Timing nature’s fastest optical shutter
It's nature's fastest quick-change artist: In less than the time it takes a beam of light to travel a tenth of a millimeter, vanadium dioxide can switch from a transparent to a reflective, mirror-like state.
How this material (VO2) can turn from a transparent insulator into a reflective metal so rapidly has physicists scratching their heads, but a collaboration among researchers at Vanderbilt, Oak Ridge National Laboratory and Lawrence Berkeley National Laboratory has clocked the transfiguration at one-tenth of a trillionth of a second.

Thursday, October 04, 2007

More on the Pioneer Anomaly

Here's the abstract from a new preprint: Physics Engineering in the Study of the Pioneer Anomaly
The Pioneer 10/11 spacecraft yielded the most precise navigation in deep space to date. However, their radio-metric tracking data received from the distances between 20--70 astronomical units from the Sun has consistently indicated the presence of a small, anomalous, Doppler frequency drift. The drift is a blue frequency shift that can be interpreted as a sunward acceleration of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2 for each particular spacecraft. This signal has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained.
Recently new Pioneer 10 and 11 radio-metric Doppler and flight telemetry data became available. The newly available Doppler data set is significantly enlarged when compared to the data used in previous investigations and is expected to be the primary source for the investigation of the anomaly. In addition, the flight telemetry files, original project documentation, and newly developed software tools are now used to reconstruct the engineering history of both spacecraft. With the help of this information, a thermal model of the Pioneer vehicles is being developed to study possible contribution of thermal recoil force acting on the two spacecraft. The ultimate goal of these physics engineering efforts is to evaluate the effect of on-board systems on the spacecrafts' trajectories.

Here's a previous post on the Pioneer Anomaly.

30 Rock

I haven't actually watched this show, but it's having a season premier this week. As I understand it, Alec Baldwin does a good job playing Jack, a crazy network executive in the show. There's a review in the New York Times Sophomore Jitters and Seinfeld Vision :
Jack has decided to increase advertising revenues by digitally inserting Mr. Seinfeld into NBC shows like “Law & Order” and “Deal or No Deal.” Jack calls his computer-generated fakery “SeinfeldVision.” The counterfeited comedian shows up at Rockefeller Center to complain, and that’s when the show goes a little wobbly: Mr. Seinfeld is strangely ill at ease playing himself, making his self-impersonation unpersuasive.

Tina Fey is the creator of the show and also appears in it. In real life she has a family and a very busy schedule - here's a quote from a recent interview:
"At home,” she added, “I cry” — about, among other things, not being home enough.

Wednesday, October 03, 2007

A census of nearby galaxies

In Mining the Local Volume 550 galaxies have been found within 10 million parsecs. A surprising observation was that there seems to be an absence of dark matter outside of the galaxy groups - if I understood the paper correctly. The preprint had some nice graphics too!

The Ant Nebula

The gorgeous Ant Nebula image from the .Hubble Space Telescope

Surprisingly Evolved Galaxies in the Early Universe

This astrophysics preprint describes A Population of Massive and Evolved Galaxies at z>=5, when the universe was less than a billion years old, which "... seems surpising at first sight". z is the redshift which according to the standard Big Bang models of cosmology is related to the age of the galaxy.
The galaxies found in this study are remarkable in that they contain a large stellar mass, have small physical sizes and that their main epoch of star formation occured at z >= 10. Galaxies with similar properties have, however, also been found by others.

Here's another preprint Morphologies of Two Massive Old Galaxies at z ~ 2.5 which says
Considerable observational evidence has built up over
the past few years that a substantial fraction of the mas-
sive galaxies around us today were already massive at
very early epochs.

Tuesday, October 02, 2007

the Jailing of Black America

Chilling statistics from the New York Times article: Jena, O. J. and the Jailing of Black America by ORLANDO PATTERSON of Harvard University.
America has more than two million citizens behind bars, the highest absolute and per capita rate of incarceration in the world. Black Americans, a mere 13 percent of the population, constitute half of this country’s prisoners. A tenth of all black men between ages 20 and 35 are in jail or prison; blacks are incarcerated at over eight times the white rate.

The effect on black communities is catastrophic: one in three male African-Americans in their 30s now has a prison record, as do nearly two-thirds of all black male high school dropouts.
The rate at which blacks commit homicides is seven times that of whites.

Something is very wrong - obviously. See Prof. Patterson's article for his perhaps surprising views.

I don't think that word means what you think it means

“Today, a megayacht is indispensable,” said Olivier Milliex, head of yacht finance at the Dutch bank ING. “It’s not like 15 years ago, when a yacht was a luxury item.”
[emphasis added]

from The New York Times: For the Yachting Class, the Latest Amenity Can Take Flight

Boston Molasses Disaster

The Boston Molasses Disaster of 1919 has to be one of the most bizzare calamities ever.

"A large molasses tank burst and a wave of molasses rushed through the streets at an estimated 35 mph (56 km/h), killing 21 and injuring 150. The event has entered local folklore, and residents claim that on hot summer days the area still smells of molasses."

Though I used to live less than a mile away and still live fairly nearby, I don't ever remember hearing of this event.

Great Storm of 1953

Speaking of winter weather, The Great Storm of 1953 in the North Sea was one of the great weather catastrophes in recent history. While 1,835 lost their lives in Holland, a much great calamity was narrowly avoided - from Wikipedia:

The Schielandse Hoge Zeedijk dyke along the river Hollandse IJssel was all that protected three million people in the provinces of South and Noord Holland from flooding. A section of this dyke, known as the Groenendijk, was not reinforced with stone revetments. The waterlevel was just below the crest and the seaside slope was weak. Volunteers worked to reinforce this stretch. Neverthelesss, the Groenendijk collapsed under the pressure around 5:30 am on 1 February. The seawater moved into the deep polder. In desperation, the mayor of Nieuwerkerk commandeered the river ship de Twee Gebroeders (The Two Brothers) and ordered the owner to plug the hole in the dike by navigating the ship into it. Fearing that the ship might break through and dive into the polder, captain Arie Evegroen took a row boat with him. The mayor's plan turned out to be successful, as the ship lodged itself firmly into the dike, saving many lives.

The North Atlantic Oscillation

For the past five years I've spent several weeks each winter with the Humpback Whales of the Silver Bank in the Dominican Republic. I'm planning to go again this year. Naturalist Tom Conlin of Aquatic Adventures leads expeditions that give us the opportunity to observe these magnificent animals and their fascinating behaviour.

Being moored 80 miles offshore on the Silver Bank, I've taken a keen interest in the weather. In the winter of 2005 (February/March) in particular, I noticed a seemingly relentless series of "cold fronts" which brought high winds, rain and cooler weather from the north. Typically the wind on the Silver Bank (which is north of the Dominican Republic and south of the Turks and Caicos) blows from the east at 10-15 knots and brings pleasant warm temperatures in the 80's farenheight. The cold fronts would bring higher winds (20-30 knots), cooler temperatures and rain, often in a series of very localized squalls.

The North Atlantic Oscillation seems to be a major factor in the winter weather for a vast region including the Silver Bank: see the maps on this NAO page at Columbia University. It appears that when the NAO index is negative, the easternly winds reaching the Silver Bank will be weaker. The page also says the the Eastern U.S. experiences more cold air outbreaks. The Silver Bank cold fronts seemed to originate from cold systems in the U.S. which then moved south (my interpretation from looking at the satellite weather maps available on the boats).

So the question is: was the NAO index actually particularly negative in the winter of 2005? And of course, what are is prospect for the upcoming winter of 2008?

And the answer is ...

Apparently the NAO index was dropping rapidly in the winter of 2005, it was in transition from a fairly high index to a fairly low one. Here's a graphic I found at NOAA.

NOAA graphic

The next step would be to find actual weather data for the region as opposed to relying on my subjective recollections.