The texture of clouds

Using a precise definition of clustering, it is shown that in two tropical cumulus clouds, droplets appear to be bunched over distances ranging from at least a kilometer or more down to several centimeters. A statistical framework is proposed for quantifying clustering in terms of a Poisson probability mixture. While these observations require further substantiation in many different clouds, droplet clustering may play a role in diverse phenomena from the coalescence growth of raindrops to the scattering of radiation by clouds

Low- and high-frequency noise from coherent two-level systems

Recent experiments indicate a connection between the low- and high-frequency noise affecting superconducting quantum systems. We explore the possibilities that both noises can be produced by one ensemble of microscopic modes, made up, e.g., by sufficiently coherent two-level systems (TLS). This implies a relation between the noise power in different frequency domains, which depends on the distribution of the parameters of the TLSs. We show that a distribution, natural for tunneling TLSs, with a log-uniform distribution in the tunnel splitting and linear distribution in the bias, accounts for experimental observations.Comment: minor corrections, references adde

Dynamic scaling approach to study time series fluctuations

We propose a new approach for properly analyzing stochastic time series by mapping the dynamics of time series fluctuations onto a suitable nonequilibrium surface-growth problem. In this framework, the fluctuation sampling time interval plays the role of time variable, whereas the physical time is treated as the analog of spatial variable. In this way we found that the fluctuations of many real-world time series satisfy the analog of the Family-Viscek dynamic scaling ansatz. This finding permits to use the powerful tools of kinetic roughening theory to classify, model, and forecast the fluctuations of real-world time series.Comment: 25 pages, 7 figures, 1 tabl

Volatiles as a link between planetary interiors and the environment

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 163-179).Volatiles derived from planetary interiors influence magma evolution and environmental processes. Over appropriate timescales, Earth's mantle, crust, ocean, and atmosphere constitute coupled systems. The apparently synchronous Siberian Traps eruption and end-Permian mass extinction offer an ideal test case to study the interactions between magmatism and climate. In this thesis, I use experimental petrology, numerical modeling, geochemical measurements, and field observations to investigate the petrologic sources, eruptive transfer, and climatic effects of volatiles released during emplacement of the Siberian large igneous province. In an extreme variation on terrestrial volatile cycling, I also explore the erosional history of Titan as recorded in valley networks carved by rivers of liquid hydrocarbons.by Benjamin A. Black.Ph.D

Morphology of fluvial networks on Titan: Evidence for structural control

Although Titan’s surface shows clear evidence of erosional modification, such as fluvial incision, evidence for tectonism has been less apparent. On Earth, fluvial networks with strongly preferred orientations are often associated with structural features, such as faults or joints, that influence flow or erodibility. We delineated and classified the morphologies of fluvial drainages on Titan and discovered evidence of structural control. Fluvial networks were delineated both on synthetic aperture radar (SAR) images covering ∼40% of Titan from the Cassini Titan Radar Mapper up through T71 and on visible light images of the Huygens landing site collected by the Descent Imager/Spectral Radiometer (DISR). The delineated networks were assigned to one of three morphologic classes—dendritic, parallel or rectangular—using a quantitative terrestrial drainage pattern classification algorithm modified for use with Titan data. We validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations, and confirmed that only a small fraction of the networks are falsely identified as structurally controlled. As a second validation, we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular. Application of this modified algorithm to our Titan networks results in a classification of rectangular for one-half of the SAR and DISR networks. A review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages. Based on the similar brittle response of rock and cryogenic ice to stress, we infer that structures formed under tension are the most likely cause of the rectangular Titan networks delineated here. The distribution of these rectangular networks suggests that tensional stresses on Titan may have been widespread.United States. National Aeronautics and Space Administration (NASA Cassini Data Analysis Program Grant NNX08BA81G

Physical Properties of Very Powerful FRII Radio Galaxies

We estimate ages and physical properties of powerful radio galaxies. An analysis of new multi-wavelength VLA observations of eleven very powerful classical double (FRIIb) radio galaxies with redshifts between 0.4 and 1.3 is presented. We estimate ages and velocities for each side of each source. The eleven new sources are combined with previously studied samples and the characteristics of the full sample of 31 sources are studied; the full sample includes sources with redshifts between 0.056 and 1.79, and core-hot spot sizes of about 30 to 400 kpc. The velocities are independent of core-hotspot separation, suggesting the rate of growth of a given source is roughly constant over the source lifetime. We combine the rate of growth, width, and pressure of a source to study the beam power, lifetime, energy, and ambient gas density using standard methods previously applied to smaller samples. Typical beam powers are in the range from 1E44 to 1E46 erg/s; we show that this quantity is insensitive to assumptions regarding minimum energy conditions. The beam powers are independent of core-hotspot separation suggesting that the beam power of a given source is roughly constant over the source lifetime. Typical total source lifetimes are found to be about a few E6 to E7 years, and typical total outflow energies (E/c^2) are found to be about 5(E5 - E6) solar masses. Ambient gas densities are found to decrease with increasing core-hotspot distance, but have no redshift dependence. Overall, the results obtained with the sample of 31 sources studied here are consistent with those obtained earlier with smaller samples.Comment: Astronomy and Astrophysics, accepte

Teachers' classroom feedback: still trying to get it right

This article examines feedback traditionally given by teachers in schools. Such feedback tends to focus on children's acquisition and retrieval of externally prescribed knowledge which is then assessed against mandated tests. It suggests that, from a sociocultural learning perspective, feedback directed towards such objectives may limit children's social development. In this article, I draw on observation and interview data gathered from a group of 27 9- to 10-year olds in a UK primary school. These data illustrate the children's perceived need to conform to, rather than negotiate, the teacher's feedback comments. They highlight the children's sense that the teacher's feedback relates to school learning but not to their own interests. The article also includes alternative examples of feedback which draw on children's own inquiries and which relate to the social contexts within which, and for whom, they act. It concludes by suggesting that instead of looking for the right answer to the question of what makes teachers' feedback effective in our current classrooms, a more productive question might be how a negotiation can be opened up among teachers and learners themselves, about how teachers' feedback could support children's learning most appropriately

The amyloid-β1-42-oligomer interacting peptide D-AIP possesses favorable biostability, pharmacokinetics, and brain region distribution.

We have previously developed a unique 8-amino acid Aβ42 oligomer-Interacting Peptide (AIP) as a novel anti-amyloid strategy for the treatment of Alzheimer's disease. Our lead candidate has successfully progressed from test tubes (i.e., in vitro characterization of protease-resistant D-AIP) to transgenic flies (i.e., in vivo rescue of human Aβ42-mediated toxicity via D-AIP-supplemented food). In the present study, we examined D-AIP in terms of its stability in multiple biological matrices (i.e., ex-vivo mouse plasma, whole blood, and liver S9 fractions) using MALDI mass spectrometry, pharmacokinetics using a rapid and sensitive LC-MS method, and blood brain barrier (BBB) penetrance in WT C57LB/6 mice. D-AIP was found to be relatively stable over 3 h at 37 °C in all matrices tested. Finally, label-free MALDI imaging showed that orally administered D-AIP can readily penetrate the intact BBB in both male and female WT mice. Based upon the favorable stability, pharmacokinetics, and BBB penetration outcomes for orally administered D-AIP in WT mice, we then examined the effect of D-AIP on amyloid "seeding" in vitro (i.e., freshly monomerized versus preaggregated Aβ42). Complementary biophysical assays (ThT, TEM, and MALDI-TOF MS) showed that D-AIP can directly interact with synthetic Aβ42 aggregates to disrupt primary and/or secondary seeding events. Taken together, the unique mechanistic and desired therapeutic potential of our lead D-AIP candidate warrants further investigation, that is, testing of D-AIP efficacy on the altered amyloid/tau pathology in transgenic mouse models of Alzheimer's disease

Radiative transfer and the energy equation in SPH simulations of star formation

We introduce and test a new and highly efficient method for treating the thermal and radiative effects influencing the energy equation in SPH simulations of star formation. The method uses the density, temperature and gravitational potential of each particle to estimate a mean optical depth, which then regulates the particle's heating and cooling. The method captures -- at minimal computational cost -- the effects of (i) the rotational and vibrational degrees of freedom of H2, H2 dissociation, H0 ionisation, (ii) opacity changes due to ice mantle melting, sublimation of dust, molecular lines, H-, bound-free and free-free processes and electron scattering; (iv) external irradiation; and (v) thermal inertia. The new algorithm reproduces the results of previous authors and/or known analytic solutions. The computational cost is comparable to a standard SPH simulation with a simple barotropic equation of state. The method is easy to implement, can be applied to both particle- and grid-based codes, and handles optical depths 0<tau<10^{11}.Comment: Submitted to A&A, recommended for publicatio