Diving behaviour of whale sharks in relation to a predictable food pulse

We present diving data for four whale sharks in relation to a predictable food pulse (reef fish spawn) and an analysis of the longest continuous fine-resolution diving record for a planktivorous shark. Fine-resolution pressure data from a recovered pop-up archival satellite tag deployed for 206 days on a whale shark were analysed using the fast Fourier Transform method for frequency domain analysis of time-series. The results demonstrated that a free-ranging whale shark displays ultradian, diel and circa-lunar rhythmicity of diving behaviour. Whale sharks dive to over 979.5 m and can tolerate a temperature range of 26.4 degrees C. The whale sharks made primarily diurnal deep dives and remained in relatively shallow waters at night. Whale shark diving patterns are influenced by a seasonally predictable food source, with shallower dives made during fish spawning periods

Unusual light spectra from a two-level atom in squeezed vacuum

We investigate the interaction of an atom with a multi-channel squeezed vacuum. It turns out that the light coming out in a particular channel can have anomalous spectral properties, among them asymmetry of the spectrum, absence of the central peak as well as central hole burning for particular parameters. As an example plane-wave squeezing is considered. In this case the above phenomena can occur for the light spectra in certain directions. In the total spectrum these phenomena are washed out.Comment: 16 pages, LaTeX, 3 figures (included via epsf

When resources collide: Towards a theory of coincidence in information spaces

This paper is an attempt to lay out foundations for a general theory of coincidence in information spaces such as the World Wide Web, expanding on existing work on bursty structures in document streams and information cascades. We elaborate on the hypothesis that every resource that is published in an information space, enters a temporary interaction with another resource once a unique explicit or implicit reference between the two is found. This thought is motivated by Erwin Shroedingers notion of entanglement between quantum systems. We present a generic information cascade model that exploits only the temporal order of information sharing activities, combined with inherent properties of the shared information resources. The approach was applied to data from the world's largest online citizen science platform Zooniverse and we report about findings of this case study

Electromagnetic and corpuscular emission from the solar flare of 1991 June 15: Continuous acceleraton of relativistic particles

Data on X-,γ-ray, optical and radio emission from the 1991 June 15 solar flare are considered. We have calculated the spectrum of protons that producesγ-rays during the gradual phase of the flare. The primary proton spectrum can be described as a Bessel-function-type up to 0.8 GeV and a power law with the spectral index ≈3 from 0.8 up to 10 GeV or above. We have also analyzed data on energetic particles near the Earth. Their spectrum differed from that of primary protons producingγ-ray line emission. In the gradual phase of the flare additional pulses of energy release occurred and the time profiles of cm-radio emission andγ-rays in the 0.8–10 MeV energy band and above 50 MeV coincided. A continuous and simultaneous stochastic acceleration of the protons and relativistic electrons at the gradual phase of the flare is considered as a natural explanation of the data

Imaging stress and magnetism at high pressures using a nanoscale quantum sensor

Pressure alters the physical, chemical and electronic properties of matter. The development of the diamond anvil cell (DAC) enables tabletop experiments to investigate a diverse landscape of high-pressure phenomena ranging from the properties of planetary interiors to transitions between quantum mechanical phases. In this work, we introduce and utilize a novel nanoscale sensing platform, which integrates nitrogen-vacancy (NV) color centers directly into the culet (tip) of diamond anvils. We demonstrate the versatility of this platform by performing diffraction-limited imaging (~600 nm) of both stress fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from 25-340 K. For the former, we quantify all six (normal and shear) stress components with accuracy $<0.01$ GPa, offering unique new capabilities for characterizing the strength and effective viscosity of solids and fluids under pressure. For the latter, we demonstrate vector magnetic field imaging with dipole accuracy $<10^{-11}$ emu, enabling us to measure the pressure-driven $\alpha\leftrightarrow\epsilon$ phase transition in iron as well as the complex pressure-temperature phase diagram of gadolinium. In addition to DC vector magnetometry, we highlight a complementary NV-sensing modality using T1 noise spectroscopy; crucially, this demonstrates our ability to characterize phase transitions even in the absence of static magnetic signatures. By integrating an atomic-scale sensor directly into DACs, our platform enables the in situ imaging of elastic, electric and magnetic phenomena at high pressures.Comment: 18 + 50 pages, 4 + 19 figure

The Power of General Relativity

We study the cosmological and weak-field properties of theories of gravity derived by extending general relativity by means of a Lagrangian proportional to $R^{1+\delta}$. This scale-free extension reduces to general relativity when $\delta \to 0$. In order to constrain generalisations of general relativity of this power class we analyse the behaviour of the perfect-fluid Friedmann universes and isolate the physically relevant models of zero curvature. A stable matter-dominated period of evolution requires $\delta >0$ or $\delta <-1/4$. The stable attractors of the evolution are found. By considering the synthesis of light elements (helium-4, deuterium and lithium-7) we obtain the bound $-0.017<\delta <0.0012.$ We evaluate the effect on the power spectrum of clustering via the shift in the epoch of matter-radiation equality. The horizon size at matter--radiation equality will be shifted by $\sim 1$ for a value of $\delta \sim 0.0005.$ We study the stable extensions of the Schwarzschild solution in these theories and calculate the timelike and null geodesics. No significant bounds arise from null geodesic effects but the perihelion precession observations lead to the strong bound $\delta =2.7\pm 4.5\times 10^{-19}$ assuming that Mercury follows a timelike geodesic. The combination of these observational constraints leads to the overall bound $0\leq \delta <7.2\times 10^{-19}$ on theories of this type.Comment: 26 pages and 5 figures. Published versio

Spitzer Mid-Infrared Photometry of 500 - 750 K Brown Dwarfs

Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] photometry, is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature (T_eff) drops from 800 K to 400 K, the fraction of flux emitted beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] a very sensitive temperature indicator, and it can be combined with a gravity- and metallicity-sensitive color like H-K to constrain all three of these fundamental properties, which in turn gives us mass and age for these slowly cooling objects. Determination of mid-infrared color trends also allows better exploitation of the WISE mission by the community. We use new Spitzer Cycle 6 IRAC photometry, together with published data, to present trends of color with type for L0 to T10 dwarfs. We also use the atmospheric and evolutionary models of Saumon & Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and T_eff ~ 500 K to 750 K.Comment: To be published in the on-line version of the Proceedings of Cool Stars 16 (ASP Conference Series). This is an updated version of Leggett et al. 2010 ApJ 710 1627; a photometry compilation is available at http://www.gemini.edu/staff/slegget