Value at Risk

Simon Johnson discusses the Value at Risk (VAR) financial analysis technique and other issues in financial modelling in The Economics of Models

A Harvard Critique

The 'Veritas' About Harvard
Harvard has consistently admitted around 1600 undergraduates per year since 1990. The article argues that some of Harvard's wealth might be better spent by increasing undergraduate enrollment.

Fashion illustrator Kareem Iliya

Kareem Iliya, fashion illustrator, images can be found here and here.

The Hurt Locker

The Hurt Locker directed by Kathryn Bigelow is quite an intense film about an army bomb disposal unit in Iraq.

Juliette Binoche

French actress Juliette Binoche and English choreographer Akram Khan performed their dance/drama piece In-I at BAM. I saw the closing night peformance, which wound up with a spectacular finale.
She also recently published a book of her paintings "Juliette Binoche, Portraits In-Eyes". The book contains a series of side-by-side pairs of paintings inspired by each of her films. Each pair consists of a painting of the film's director and then a self portrait of herself "in character". Cool. The text is in both French and English.

William Blake at the Morgan Library

William Blake's World: "A New Heaven Is Begun" an exhibit at the Morgan Library in New York. At that link there's a nice reading of "The Tyger" and other poems by Jeremy Irons.
William's Blake's illustrations to the Book of Job can be found here. I was quite surprised by Blake's depiction of Satan: he's rather physically attractive and was not usually shown as particularly "evil looking".

Massive Violation of Bell's Inequality

Violation of Bell's inequality in Josephson phase qubits in Nature.

The measurement process plays an awkward role in quantum mechanics, because measurement forces a system to 'choose' between possible outcomes in a fundamentally unpredictable manner. Therefore, hidden classical processes have been considered as possibly predetermining measurement outcomes while preserving their statistical distributions1. However, a quantitative measure that can distinguish classically determined correlations from stronger quantum correlations exists in the form of the Bell inequalities, measurements of which provide strong experimental evidence that quantum mechanics provides a complete description2, 3, 4. Here we demonstrate the violation of a Bell inequality in a solid-state system. We use a pair of Josephson phase qubits5, 6, 7 acting as spin-1/2 particles, and show that the qubits can be entangled8, 9 and measured so as to violate the Clauser–Horne–Shimony–Holt (CHSH) version of the Bell inequality10. We measure a Bell signal of 2.0732 0.0003, exceeding the maximum amplitude of 2 for a classical system by 244 standard deviations. In the experiment, we deterministically generate the entangled state, and measure both qubits in a single-shot manner, closing the detection loophole11. Because the Bell inequality was designed to test for non-classical behaviour without assuming the applicability of quantum mechanics to the system in question, this experiment provides further strong evidence that a macroscopic electrical circuit is really a quantum system7.

Genetic Structure of India

Indian ancestry revealed in Nature.
"The mixing of two distinct lineages led to most modern-day Indians."

Ultra-Cold Microscale Optomechanical Oscillator

Demonstration of an ultracold micro-optomechanical oscillator in a cryogenic cavity

Preparing and manipulating quantum states of mechanical resonators is a highly interdisciplinary undertaking that now receives enormous interest for its far-reaching potential in fundamental and applied science. Up to now, only nanoscale mechanical devices achieved operation close to the quantum regime. We report a new micro-optomechanical resonator that is laser cooled to a level of 30 thermal quanta. This is equivalent to the best nanomechanical devices, however, with a mass more than four orders of magnitude larger (43 ng versus 1 pg) and at more than two orders of magnitude higher environment temperature (5 K versus 30 mK). Despite the large laser-added cooling factor of 4,000 and the cryogenic environment, our cooling performance is not limited by residual absorption effects. These results pave the way for the preparation of 100-um scale objects in the quantum regime. Possible applications range from quantum-limited optomechanical sensing devices to macroscopic tests of quantum physics.

Observation of strong coupling between a micromechanical resonator and an optical cavity field

Achieving coherent quantum control over massive mechanical resonators is a current research goal. Nano- and micromechanical devices can be coupled to a variety of systems, for example to single electrons by electrostatic or magnetic coupling, and to photons by radiation pressure or optical dipole forces. So far, all such experiments have operated in a regime of weak coupling, in which reversible energy exchange between the mechanical device and its coupled partner is suppressed by fast decoherence of the individual systems to their local environments. Controlled quantum experiments are in principle not possible in such a regime, but instead require strong coupling. So far, this has been demonstrated only between microscopic quantum systems, such as atoms and photons (in the context of cavity quantum electrodynamics) or solid state qubits and photons. Strong coupling is an essential requirement for the preparation of mechanical quantum states, such as squeezed or entangled states, and also for using mechanical resonators in the context of quantum information processing, for example, as quantum transducers. Here we report the observation of optomechanical normal mode splitting, which provides unambiguous evidence for strong coupling of cavity photons to a mechanical resonator. This paves the way towards full quantum optical control of nano- and micromechanical devices.

Nature 460, 724-727 (2009)
DOI: 10.1038/nature08171

Cool Airship Video

The Lockheed P-791.

Gravity Insulators??

I noticed this stone a long time ago on the Tufts campus. A couple of older ladies with pronounced Irish accents read it and pronounced it "a lovely idea", haha.
I wondered at the time how such an outlandish monument ended up at a reputable university. Well Wikipedia Knows All: Gravity Research Foundation

Supersymmetry and Division Algebras

There's a surprising connection between supersymmetry , a hot topic in theoretical physics, and division algebras: the real, complex, quaternion and octonion number systems. Supersymmetry only works in 3,4,6 and 10 space time dimensions. That's because there's a cute little trick which allows us to represent an n+2 dimensional spacetime vector using one number from a division algebra and two additional real numbers. There are only four division algebras - which just happen to have 1,2,4 and 8 dimensions. John Baez Explains It All To You here.

Equal Temperament: Music Meets Mathematics

Generalized continued fractions and equal temperament
It would be nice if we could divide an octave into equal notes and then be able to have an interval close to a perfect fifth (which raises the frequency by 3/2). That's how equal temperament works: it divides an octave into twelve equal notes and then it turns out that an interval of seven notes is close to a perfect fifth. That's actually why this particular scale was chosen and a reason it has been so successful.

Antigravity

Antigravitation

We discuss why there are no negative gravitational sources in General Relativity and show that it is possible to extend the classical theory such that repulsive gravitational interaction occurs.

Interesting, but as the author points out in a previous preprint which provides more details of the theory: A Bi-Metric Theory with Exchange Symmetry "As this example shows, the bi-metric model is not causal ..."

A Previous Yale Murder, Still Unsolved

Murder Most Yale a 1999 article in Vanity Fair about the murder of Suzanne Jovin a talented and beautiful Yale student - one of her professors was a suspect.

Fractal Cosmology

Fractal Cosmology is a theory of cosmology which models the universe as fractal: the universe is similar to itself at different scales.
Robert L. Oldershaw has published a series of papers in which he conjectures that certain types of stars are may be similiar to ... atoms of corresponding elements.
I would be very surprised if this turned out to be a fruitful approach, but it's a cool concept nonetheless.

Mandelbrot set: an example of a fractal - click for more info, more images

Inconstant Moon

Inconstant Moon is an episode of the Outer Limits American television show. It's based the short story (also titled Inconstant Moon) by Larry Niven. Many of Niven's stories have a basis in science fact, including this one.

Mike Murphy's reaction to the show was something like this "Absolute maximum horror: the world is ending so let's get married - then the world doesn’t end."

Optical Levitation

Cavity optomechanics using an optically levitated nanosphere

Recently, remarkable advances have been made in coupling a number of high-Q modes of nano-mechanical systems to high-finesse optical cavities, with the goal of reaching regimes where quantum behavior can be observed and leveraged toward new applications. To reach this regime, the coupling between these systems and their thermal environments must be minimized. Here we propose a novel approach to this problem, in which optically levitating a nano-mechanical system can greatly reduce its thermal contact, while simultaneously eliminating dissipation arising from clamping. Through the long coherence times allowed, this approach potentially opens the door to ground-state cooling and coherent manipulation of a single mesoscopic mechanical system or entanglement generation between spatially separate systems, even in room temperature environments. As an example, we show that these goals should be achievable when the mechanical mode consists of the center-of-mass motion of a levitated nanosphere.

Your Hippocampus Remembers More than You Do

Remembering Without Knowing It
In a memory task in which the subject was shown a photograph and then later asked to pick out that photo among several others, the subject's hippocampus activated when they were seeing the correct photo, even when they ended up choosing the wrong one!

Cosmology Review

Cosmology at a Crossroads

A fundamental question in cosmology is, "How did the universe begin?" The two pivotal ideas of inflation and cold dark matter (CDM), combined with extensive observational results, including the unpredicted accelerated expansion of the universe, underpin a new standard model of cosmology

Neanderthals were more Carnivorous than early modern Humans

Isotopic evidence for the diets of European Neanderthals and early modern humans
Neanderthals mainly fed on big-game, while early modern humans had a more varied diet, sometimes including lots of fish.

Genetics of the Human Expansion Out of Africa

Explaining worldwide patterns of human genetic variation using a coalescent-based serial founder model of migration outward from Africa
It seems that modern humans may have expanded out of Africa without mixing much with the descendants of earlier waves of migration.

Larvae and Adults are Hybrids??

Caterpillars evolved from onychophorans by hybridogenesis

I reject the Darwinian assumption that larvae and their adults evolved from a single common ancestor. Rather I posit that, in animals that metamorphose, the basic types of larvae originated as adults of different lineages, i.e., larvae were transferred when, through hybridization, their genomes were acquired by distantly related animals. “Caterpillars,” the name for eruciforms with thoracic and abdominal legs, are larvae of lepidopterans, hymenopterans, and mecopterans (scorpionflies). Grubs and maggots, including the larvae of beetles, bees, and flies, evolved from caterpillars by loss of legs. Caterpillar larval organs are dismantled and reconstructed in the pupal phase. Such indirect developmental patterns (metamorphoses) did not originate solely by accumulation of random mutations followed by natural selection; rather they are fully consistent with my concept of evolution by hybridogenesis. Members of the phylum Onychophora (velvet worms) are proposed as the evolutionary source of caterpillars and their grub or maggot descendants. I present a molecular biological research proposal to test my thesis. By my hypothesis 2 recognizable sets of genes are detectable in the genomes of all insects with caterpillar grub- or maggot-like larvae: (i) onychophoran genes that code for proteins determining larval morphology/physiology and (ii) sequentially expressed insect genes that code for adult proteins. The genomes of insects and other animals that, by contrast, entirely lack larvae comprise recognizable sets of genes from single animal common ancestors.

I would be surprised if this were true, but it's an interesting and novel hypothesis.

Sanction Threats reduce Reciprocity

Neural responses to sanction threats in two-party economic exchange

Sanctions are used ubiquitously to enforce obedience to social norms. However, recent field studies and laboratory experiments have demonstrated that cooperation is sometimes reduced when incentives meant to promote prosocial decisions are added to the environment. Although various explanations for this effect have been suggested, the neural foundations of the effect have not been fully explored. Using a modified trust game, we found that trustees reciprocate relatively less when facing sanction threats, and that the presence of sanctions significantly reduces trustee's brain activities involved in social reward valuation [in the ventromedial prefrontal cortex (VMPFC), lateral orbitofrontal cortex, and amygdala] while it simultaneously increases brain activities in the parietal cortex, which has been implicated in rational decision making. Moreover, we found that neural activity in a trustee's VMPFC area predicts her future level of cooperation under both sanction and no-sanction conditions, and that this predictive activity can be dynamically modulated by the presence of a sanction threat.

Jumping Robot

Video: Precision Urban Hopper leaps over fences, makes enemies cringe

Yow.

Palindromes on the Y Chromosome

New Clues to Sex Anomalies in How Y Chromosomes Are Copied
Most chromosomes come in pairs, which helps in detecting and repairing errors when DNA is copied. However, there's only one copy of the Y chromosome (found only in males) but many of its genes occur in palindromes (sequences which read the same forward and backward e.g. Madam Im Adam). When the Y chromosome is copied, the palindromic regions are folded over, so they can be compared for errors.

The Simple Art of Murder

The Simple Art of Murder by Raymond Chandler (1950). An essay on the art and practice of the murder mystery.
See also The Simple Art of Murder a 1995 book review by Joyce Carol Oates about Raymond Chandler and an overview and critique of genre fiction.

The Origin of Farming in Europe: Cultural Diffusion or Migration?

Ancient DNA Says Europe's First Farmers Came From Afar

Dogs and Infants make similiar errors, wolves don't

Like Infant, Like Dog
"The infants apparently believed believed adult instruction more than they believe their own eyes." Dogs behaved similarly.
Dogs: Kids in Fur Coats?

Erasing Fear Memories

Erasing Fear Memories
Memories of stressful events can be extinguished in young animals but are resistent to complete erasure in adults. New research hints at the neurobiological basis for these observations.

Photosystem genes in viruses

Photosystems at the double
Marine cyanobacteria viruses contain genes for both photosystems used in host photosynthesis.

Nano storage scheme which doesn't wear out

Nanotechnology: A gentle jackhammer

A futuristic method of data storage depends on the 'write–read' action of a multitude of tiny silicon tips. The concept of dynamic superlubricity offers a way to avoid the wear that would otherwise cripple them.

The History of Oxygen

Early Earth: Oxygen for heavy-metal fans

Chromium isotopes provide an eyebrow-raising history of oxygenation of Earth's atmosphere. Not least, it seems that oxygen might have all but disappeared half a billion years after its initial rise.

Sex Determination in Birds

Sex determination: Birds do it with a Z gene

The gene that determines sex in birds has eluded scientists for a decade. Now this all-important locus is revealed as a gene on the Z chromosome known for its proclivity for determining sex in all kinds of animals.

In mammals, males have XY chromosome pairs and females are XX, so the Y chromosome determines maleness and sex. In particular the SRY gene found on the Y chromosome determines testis.
In birds it's the other way around: males have ZZ chromosome pairs and females are ZW. However in birds the key gene is again for maleness and it resides on the Z chromosome.

London Brick Lane Walls

Skateboard Park London

Sundial in Westminster London

Sundial at Saint Maragret's Church Westminster London. Also the correction curve to get civil time.

Arcadia by Tom Stoppard

Last night I saw Arcadia a play by Tom Stoppard in London. Ed Stoppard, the playwright's son, performs. The play discusses chaos theory, fractals, the second law of thermodyamics, romance versus rationality, poetry and academic rivalries - all in the format of a drawing room comedy.
I also saw the 1995 New York production directed by Trevor Nunn at Lincoln Center, which was absolutely brilliant.

The poet Lord Byron is a constant but never seen presence in the play which quotes the following lines from one of his poems:

She walks in beauty, like the night
Of cloudless climes and starry skies,
And all that's best of dark and bright
Meets in her aspect and her eyes;
Thus mellow'd to that tender light
Which Heaven to gaudy day denies

Paris Street Poster ...

Medusa Heads at Carnavalet Museum Paris

Medusa Heads at Carnavalet Museum Paris:

Sundial Hotel de Sully Paris

Sundial Hôtel de Sully Paris:



The doorway on the right opens onto the Place des Vosges


see also Solar-Powered Timekeeping in Paris an article in the New York Times about the sundials of Paris.

Life is Beautiful

Paris store front:

Le Boudoir et sa Philosophie

I'm in Paris today: a shop in 3e. Click on picture for larger image.

Self Enforcing Protocols

Self Enforcing Protocols at Schneier on Security.

Here’s a self-enforcing protocol for determining property tax: the homeowner decides the value of the property and calculates the resultant tax, and the government can either accept the tax or buy the home for that price. Sounds unrealistic, but the Greek government implemented exactly that system for the taxation of antiquities. It was the easiest way to motivate people to accurately report the value of antiquities.

String Theory: 25 Years after the Revolution

Here's a post from Peter Woit's Not Even Wrong Blog 25 Years On ... summarizing the disappointing state of string theory research.

Krakow Jewish Quarter: Words on the Street

Click on Photos for Larger Image

Weird Flash Effect

I was taking a tour of a salt mine near Krakow Poland. I was using a Nikon D200 camera and a Nikon SB800 flash triggered remotely. The first shot came out rather strangely and at first I didn't know why. I happened to take a second shot (8 seconds later) which came out more or less normally.


A "normal" photo of a tableaux illustrating work at the salt mine.
Apparently the explanation is this: I might have accidently twisted the zoom ring while I was taking the first photo.

St. Mary's Basilica, Krakow, Poland

St. Mary's Basilica, Krakow, Poland is gorgeous and naturally by-and-large rather solemn.
However this particular bird figure seemed to me to be just a little bit funky and out of place. Is it really supposed to be the Polish Eagle?

Krakow Sundial

This is a nodus-based sundial on the wall of St. Mary's Basilica in Krakow Poland. It was taken on August 12th - this type of sundial is supposed to indicate the date as well as the time. The astrological signs are depicted on the sundial, the shadow seems to fall within Leo (July 23 to August 23) but I'm not sure which part of the shadow is supposed to indicate the exact date, etc. Click on the picture to see a larger version.

The Meeting of Minds

Click on a picture for a slightly larger and (hopefully) more humorous view.









While I was shooting these I overheard a tourist ask her boyfriend "Why does he keep taking the same picture over and over again?"

Lidia in Warsaw

Lidia Berger and some of her wonderful friends have been introducing me to Warsaw the past few days. Click on a picture for a slightly larger view.

Quantum Measurement Processes

The Measurement Process in Local Quantum Theory and the EPR Paradox

We describe in a qualitative way a possible picture of the Measurement Process in Quantum Mechanics, which takes into account: 1. the finite and non zero time duration T of the interaction between the observed system and the *microscopic part* of the measurement apparatus; 2. the finite space size R of that apparatus; 3. the fact that the *macroscopic part* of the measurement apparatus, having the role of amplifying the effect of that interaction to a macroscopic scale, is composed by a very large but finite number N of particles.
The conventional picture of the measurement, as an instantaneous action turning a pure state into a mixture, arises only in the limit where N tends to infinity, T tends to zero, R tends to infinity.
The limit where N tends to infinity has been often discussed as the origin of decoherence. We argue here that, as a consequence of the Principle of Locality, before those three limits are taken, no long range entanglement between the values of observables which are spacelike separated far away can be detected (although entangled states for such observables are well known to exist in local theories, simple examples are given in an Appendix). In order to detect correlations, one of the observers has to wait until he enters the future causal shadow of the region employed by the apparatus of the other. Accordingly, in this picture of the measurement process there would be no Einstein Podolski Rosen Paradox. (Similar views had been proposed already [6], [22]). A careful comparison with the growing experimental results of the recent decades might settle the question

The EPR Paradox is one of the most spectacular and disturbing consequences of Quantum theory and Special Relativity. But maybe if we really pay close attention to the microscopic details of the quantum measurement process, the paradox will disappear. This paper doesn't completely resolve these issues, but it does point out some of the idealizations of standard quantum theory that may be contributing to the EPR paradox.

Quantum Gravity

Quantum Gravity: Motivations and Alternatives

The mutual conceptual incompatibility between GR and QM/QFT is generally seen as the most essential motivation for the development of a theory of Quantum Gravity (QG). It leads to the insight that, if gravity is a fundamental interaction and QM is universally valid, the gravitational field will have to be quantized, not at least because of the inconsistency of semi-classical theories of gravity. If this means to quantize GR, its identification of the gravitational field with the spacetime metric has to be taken into account. And the resulting quantum theory has to be background-independent. This can not be achieved by means of quantum field theoretical procedures. More sophisticated strategies have to be applied. One of the basic requirements for such a quantization strategy is that the resulting quantum theory has GR as a classical limit. - However, should gravity not be a fundamental, but an residual, emergent interaction, it could very well be an intrinsically classical phenomenon. Should QM be nonetheless universally valid, we had to assume a quantum substrate from which gravity would result as an emergent classical phenomenon. And there would be no conflict with the arguments against semi-classical theories, because there would be no gravity at all on the substrate level. The gravitational field would not have any quantum properties, and a quantization of GR would not lead to any fundamental theory. The objective of a theory of 'QG' would instead be the identification of the quantum substrate from which gravity results. - The paper tries to give an overview over the main options for theory construction in the field of QG. Because of the still unclear status of gravity and spacetime, it pleads for the necessity of a plurality of conceptually different approaches to QG.

Horse Dung and Telescopes

I'm reading The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science by Richard Holmes. It's about science and culture in the late eighteenth and early nineteen century - mostly British. I just finished the section about William Herschel, the German/English discoverer of the planet Uranus. He was an innovative telescope maker and he employed horse dung to make the moulds which he used to cast the metal mirrors for his telescopes. The book says that horse dung was used for this purpose until the early twentieth century. Herschel was also a professional musician and that's how he made his living until he became famous for discovering the planet.

Distribution of Stars at the Center of the Galaxy

High angular resolution integral-field spectroscopy of the Galaxy's nuclear cluster: a missing stellar cusp?
The distribution of stars near the center of the galaxy isn't what is expected from a model of a supermassive black hole.

Ward Cunningham Interview

Here's a really nice interview with computer programmer Ward Cunningham the originator of the term "Wiki" as in Wikipedia.

The baryonic Tully-Fisher relation

The baryonic Tully-Fisher relation and its implication for dark matter halos

The baryonic Tully-Fisher relation (BTF) is a fundamental relation between baryonic mass and maximum rotation velocity. It can be used to estimate distances, as well as to constrain the properties of dark matter and its relation with the visible matter. In this paper, we explore if extremely low-mass dwarf galaxies follow the same BTF relation as high-mass galaxies. We quantify the scatter in the BTF relation and use this to constrain the allowed elongations of dark matter halo potentials. We obtained HI synthesis data of 11 dwarf galaxies and derive several independent estimates for the maximum rotation velocity. Constructing a BTF relation using data from the literature for the high-mass end, and galaxies with detected rotation from our sample for the low-mass end results in a BTF with a scatter of 0.33 mag. This scatter constrains the ellipticities of the potentials in the plane of the disks of the galaxies to an upper limit of 0-0.06 indicating that dwarf galaxies are at most only mildly tri-axial. Our results indicate that the BTF relation is a fundamental relation which all rotationally dominated galaxies seem to follow.

Honesty - Will or Grace?

Patterns of neural activity associated with honest and dishonest moral decisions

What makes people behave honestly when confronted with opportunities for dishonest gain? Research on the interplay between controlled and automatic processes in decision making suggests 2 hypotheses: According to the “Will” hypothesis, honesty results from the active resistance of temptation, comparable to the controlled cognitive processes that enable the delay of reward. According to the “Grace” hypothesis, honesty results from the absence of temptation, consistent with research emphasizing the determination of behavior by the presence or absence of automatic processes. To test these hypotheses, we examined neural activity in individuals confronted with opportunities for dishonest gain. Subjects undergoing functional magnetic resonance imaging (fMRI) gained money by accurately predicting the outcomes of computerized coin-flips. In some trials, subjects recorded their predictions in advance. In other trials, subjects were rewarded based on self-reported accuracy, allowing them to gain money dishonestly by lying about the accuracy of their predictions. Many subjects behaved dishonestly, as indicated by improbable levels of “accuracy.” Our findings support the Grace hypothesis. Individuals who behaved honestly exhibited no additional control-related activity (or other kind of activity) when choosing to behave honestly, as compared with a control condition in which there was no opportunity for dishonest gain. In contrast, individuals who behaved dishonestly exhibited increased activity in control-related regions of prefrontal cortex, both when choosing to behave dishonestly and on occasions when they refrained from dishonesty. Levels of activity in these regions correlated with the frequency of dishonesty in individuals.

Some people were always honest and they showed no special brain activity, other people were sometimes dishonest and they did display increased brain activity. This doesn't really seem surprising. Which isn't to say that this experiment is trivial, far from it - it's fascinating. It would be interesting to see if there are unusual people who can perform dishonestly without registering any special brain activity. Presumably these people would be naturally good spys, poker players, etc.
See the web page of the Moral Cognition Lab at Harvard.
There's a discussion of the paper at this blog post: Angels and Demons.

Statistics - Levy Laws and 1/f noise

A unified and universal explanation for Lévy laws and 1/f noises

Lévy laws and 1/f noises are shown to emerge uniquely and universally from a general model of systems which superimpose the transmissions of many independent stochastic signals. The signals are considered to follow, statistically, a common—yet arbitrary—generic signal pattern which may be either stationary or dissipative. Each signal is considered to have its own random transmission amplitude and frequency. We characterize the amplitude-frequency randomizations which render the system output's stationary law and power-spectrum universal—i.e., independent of the underlying generic signal pattern. The classes of universal stationary laws and power spectra are shown to coincide, respectively, with the classes of Lévy laws and 1/f noises—thus providing a unified and universal explanation for the ubiquity of these classes of “anomalous statistics” in various fields of science and engineering.

Cosmic Impact at the Younger Dryas Boundary

Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (≈12,900 ± 100 cal BP or 10,900 ± 100 14C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to ≈12,950 ± 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event ...

Helitrons

Structure-based discovery and description of plant and animal Helitrons

Helitrons are recently discovered eukaryotic transposons that are predicted to amplify by a rolling-circle mechanism. They are present in most plant and animal species investigated, but were previously overlooked partly because they lack terminal repeats and do not create target site duplications.

Plant genomes: Massive changes of the maize genome are caused by Helitrons

Helitrons are eukaryotic transposable elements recognized only recently by computer analysis of repetitive DNA sequences of Arabidopsis, rice and Caenorhabditis elegans (Kapitonov and Jurka, 2001). Helitrons are quite large (>10 kbp) but unlike virtually all other classes of transposable elements, Helitrons lack terminal repeats and do not duplicate host sequences during the insertion process. They insert within the host dinucleotide, AT.

Living Fossils?

Nine exceptional radiations plus high turnover explain species diversity in jawed vertebrates

The other main deviations from our constant-rate model are the prototypical ‘‘living fossil’’ lineages, old lineages with few extant species (17, 18). In our study, 3 living fossil lineages are notable for both their low rate of speciation and extremely low rates of extinction. These groups stand out in stark contrast to the rest of the vertebrate tree, which is characterized by high rates of both speciation and extinction (Fig. 2). This highlights one of the key challenges presented by living fossils to molecular based studies of extant diversity: although young species-rich groups can be explained by a transient increase in net diversification rates for a relatively short period, older species-poor groups require negligible rates of both speciation and extinction over tremendously long periods of time to explain their persistence. We note that all 3 slowly evolving lineages were historically more diverse than they are today.

Why are these groups called "living fossils"? They diverged a long time ago and they have few surviving species. Why does that lead anyone to believe that the modern organisms are similiar to ancient ones?

Sirtuins - enzymes which regulate lifespan?

Recent progress in the biology and physiology of sirtuins

The sirtuins are a highly conserved family of NAD+-dependent enzymes that regulate lifespan in lower organisms. Recently, the mammalian sirtuins have been connected to an ever widening circle of activities that encompass cellular stress resistance, genomic stability, tumorigenesis and energy metabolism. Here we review the recent progress in sirtuin biology, the role these proteins have in various age-related diseases and the tantalizing notion that the activity of this family of enzymes somehow regulates how long we live.

Electricity from Kites

Wind power: High hopes in Nature.

A vast supply of energy is racing around the planet far above the surface. Erik Vance meets the engineers trying to bring the power of high-altitude wind down to earth.

Helical Dirac fermions

A tunable topological insulator in the spin helical Dirac transport regime

Helical Dirac fermions—charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum—are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics

First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy

Electron systems that possess light-like dispersion relations or the conical Dirac spectrum, such as graphene and bismuth, have recently been shown to harbor unusual collective states in high magnetic fields. Such states are possible because their light-like electrons come in spin pairs that are chiral,which means that their direction of propagation is tied to a quantity called pseudospin that describes their location in the crystal lattice. An emerging direction in quantum materials research is the manipulation of atomic spin-orbit coupling to simulate the effect of a spin dependent magnetic field,in attempt to realize novel spin phases of matter. This effect has been proposed to realize systems consisting of unpaired Dirac cones that are helical, meaning their direction of propagation is tied to the electron spin itself, which are forbidden to exist in graphene or bismuth.

X Rays from Nanotubes

Nanotubes sharpen X-ray vision

Mini X-ray tubes could revolutionize radiotherapy — and airport baggage scanners.

Is the Toucan's Bill primarily a Heat Exchanger?

Heat Exchange from the Toucan Bill Reveals a Controllable Vascular Thermal Radiator

The toco toucan (Ramphastos toco), the largest member of the toucan family, possesses the largest beak relative to body size of all birds. This exaggerated feature has received various interpretations, from serving as a sexual ornament to being a refined adaptation for feeding. However, it is also a significant surface area for heat exchange. Here we show the remarkable capacity of the toco toucan to regulate heat distribution by modifying blood flow, using the bill as a transient thermal radiator. Our results indicate that the toucan's bill is, relative to its size, one of the largest thermal windows in the animal kingdom, rivaling elephants’ ears in its ability to radiate body heat.

Polarized Signalling in Animals

Many animals create striking visual effects not with pigments but with intricately structured materials. See how some scarab beetles produce their colorful appearence in Evolutionary Photonics with a Twist.

Pathological Science

Pathological Science is when investigators trick themselves into believing false results. There was a classic talk PATHOLOGICAL SCIENCE given by Irving Langmuir in 1953.

Did the Immune System Originate with a Virus?

The immune system has the incredible ability to create a vast number of very specific antibodies. In Immune System: Success Owed to a Virus? the author conjectures that the recombination process which generates so much variety may have originated with a virus.

Rare Venomous Mammal

The Solenodon is a very rare and strange little mammal, it is the only mammal that injects venom through its teeth like snakes. See Saving a Venomous Ghost in Science. The are kind of cute too, see Venomous mammal caught on camera.

Phonon Lasers

Phonon laser action in a tunable, two-level photonic molecule

The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around 50 $\mu$W. The device features a continuously tunable, gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed as a Brillouin process, the system accesses a regime in which the phonon plays what has traditionally been the role of the Stokes wave. For this reason, it should also be possible to controllably switch between phonon and photon laser regimes. Cooling of the mechanical mode is also possible.

Nuclear Astrophysics

Massive stars as thermonuclear reactors and their explosions following core collapse

Nuclear reactions transform atomic nuclei inside stars. This is the process of stellar nucleosynthesis. The basic concepts of determining nuclear reaction rates inside stars are reviewed. How stars manage to burn their fuel so slowly most of the time are also considered. Stellar thermonuclear reactions involving protons in hydrostatic burning are discussed first. Then I discuss triple alpha reactions in the helium burning stage. Carbon and oxygen survive in red giant stars because of the nuclear structure of oxygen and neon. Further nuclear burning of carbon, neon, oxygen and silicon in quiescent conditions are discussed next. In the subsequent core-collapse phase, neutronization due to electron capture from the top of the Fermi sea in a degenerate core takes place. The expected signal of neutrinos from a nearby supernova is calculated. The supernova often explodes inside a dense circumstellar medium, which is established due to the progenitor star losing its outermost envelope in a stellar wind or mass transfer in a binary system. The nature of the circumstellar medium and the ejecta of the supernova and their dynamics are revealed by observations in the optical, IR, radio, and X-ray bands, and I discuss some of these observations and their interpretations.

Musical Numerology

Why the Kirnberger Kernel Is So Small discusses some interesting numerical coincidences in the most commonly used musical scale.

Open Problems in HadronPhysics

Confinement & Chiral Symmetry Breaking: The fundamental problems of hadron physics

Some of the difficulties arising when one tries to understand confinement as well as dynamical and anomalous chiral symmetry breaking are reviewed. Criteria to be fulfilled by a successful and complete picture of these phenomena are presented, and a few of the suggested explanations are listed.

Whale Sharks

I went swimming with whale sharks near Cancun, Mexico with Manuel Lazcano. We saw over a hundred whale sharks feeding together right on the surface. The hydrodynamics of swimming with the whale sharks was quite interesting. It was almost effortless to stay next to the whale sharks when swimming in a certain spot, over the pectorial fin. Otherwise, they were travelling fast enough that it required a lot of work to keep up.
Alas neither of the photos below (by Carlos Requena) show me in the "sweet spot".