Wannier-based calculation of the orbital magnetization in crystals

We present a first-principles scheme that allows the orbital magnetization of a magnetic crystal to be evaluated accurately and efficiently even in the presence of complex Fermi surfaces. Starting from an initial electronic-structure calculation with a coarse ab initio k-point mesh, maximally localized Wannier functions are constructed and used to interpolate the necessary k-space quantities on a fine mesh, in parallel to a previously-developed formalism for the anomalous Hall conductivity [X.Wang, J. Yates, I. Souza, and D. Vanderbilt, Phys. Rev. B 74, 195118 (2006)]. We formulate our new approach in a manifestly gauge-invariant manner, expressing the orbital magnetization in terms of traces over matrices in Wannier space. Since only a few (e.g., of the order of 20) Wannier functions are typically needed to describe the occupied and partially occupied bands, these Wannier matrices are small, which makes the interpolation itself very efficient. The method has been used to calculate the orbital magnetization of bcc Fe, hcp Co, and fcc Ni. Unlike an approximate calculation based on integrating orbital currents inside atomic spheres, our results nicely reproduce the experimentally measured ordering of the orbital magnetization in these three materials.Comment: 13 pages, 3 figures, 4 table

Long-Term Fish Assemblage Dynamics of the Alvarado Lagoon Estuary, Veracruz, Mexico

The fish assemblages of Alvarado Lagoon Estuary (a complex of coastal lagoons in the state of Veracruz, Mexico) have been surveyed intermittently by different researchers over the last 40 years. Assessing longterm trends in fish assemblage composition for this ecosystem is problematic due to differences in sampling efforts among the survey periods (1966–1968, 1987–1988, 1989, 1989–1990, 1990–1991 and 2000–2001) and by the inherent ecological variability of estuaries. To overcome these data limitations and better understand fish assemblage change over time, we used robust, simulation-based analyses to compare collections from the different surveys. The 107 fish species collected from the Alvarado Lagoon Estuary in these surveys represent 4 ecological guilds: marine stenohaline, marine euryhaline, estuarine, and freshwater fishes. The occurrence frequency of fish species representing each guild did not change significantly among the survey periods: the chi-square deviation statistic ( 2 = 8.53) was not significantly larger than the average value for 1000 simulated matrices ( 2 = 138.64; P = 1.00). A non-metric multidimensional scaling (MDS) based on Bray-Curtis similarities of fish species presenceabsence data showed that the 1966–1968 survey period was the least similar to the other survey periods. For the 1966–1968 survey, the range of Bray-Curtis inter-survey similarities was 40.4–58.6 (n = 5). By comparison, the remaining range of inter-survey similarities was 61.5–81.7 (n = 10). Average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+), two sample size-independent measures of diversity, were calculated for all survey periods. Although Δ+ and Λ+ for all survey periods were within the simulated 95% confidence limits for expected values, these values for the 2000–2001 survey period were less than the average Δ+ and Λ+ values for the entire species pool. This suggests that the fish assemblage collected during the latest survey reflects a loss of both widespread higher taxa (reduced Δ+) and that the higher taxa lost are those with only a few representative species in the assemblage (reduced Λ+). These assemblage data show that fish assemblages of Alvarado Lagoon Estuary have not experienced significant changes over 40 years, but differences among the earliest (1966–1968), the latest (2000–2001), and the remaining survey periods indicate a recent decline in diversity

On the analytical approximation to the GLAP evolution at small x and moderate Q^2

Comparing the numerically evaluated solution to the leading order GLAP equations with its analytical small-x approximation we have found that in the domain covered by a large fraction of the HERA data the analytic approximation has to be augmented by the formally non-leading term which has been usually neglected. The corrected formula fits the data much better and provides a natural explanation of some of the deviations from the $\sigma$ scaling observed in the HERA kinematical range.Comment: LaTeX, 13 pages including 6 figures, figure 5 replaced, to appear in Phys. Lett.

The farmer as a landscape steward: Comparing local understandings of landscape stewardship, landscape values, and land management actions

We develop a landscape stewardship classification which distinguishes between farmers’ understanding of landscape stewardship, their landscape values, and land management actions. Forty semi-structured interviews were conducted with smallholder (5 acres), medium-holders (5-100 acres), and large- holders (100 acres) in South-West Devon, UK. Thematic analysis revealed four types of stewardship understandings: (1) an environmental frame which emphasized the farmers’ role in conserving or restoring wildlife; (2) a primary production frame which emphasized the farmers’ role in taking care of primary production assets; (3) a holistic frame focusing on farmers’ role as a conservationist, primary producer, and manager of a range of landscape values, and; (4) an instrumental frame focusing on the financial benefits associated with compliance with agri-environmental schemes. We compare the landscape values and land management actions that emerged across stewardship types, and discuss the global implications of the landscape stewardship classification for the engagement of farmers in landscape management

On the MBM12 Young Association

I present a comprehensive study of the MBM12 young association (MBM12A). By combining infrared (IR) photometry from the Two-Micron All-Sky Survey (2MASS) survey with new optical imaging and spectroscopy, I have performed a census of the MBM12A membership that is complete to 0.03 Msun (H~15) for a 1.75deg X 1.4deg field encompassing the MBM12 cloud. I find five new members with masses of 0.1-0.4 Msun and a few additional candidates that have not been observed spectroscopically. From an analysis of optical and IR photometry for stars in the direction of MBM12, I identify M dwarfs in the foreground and background of the cloud. By comparing the magnitudes of these stars to those of local field dwarfs, I arrive at a distance modulus 7.2+/-0.5 (275 pc) to the MBM12 cloud; it is not the nearest molecular cloud and is not inside the local bubble of hot ionized gas as had been implied by previous distance estimates of 50-100 pc. I have also used Li strengths and H-R diagrams to constrain the absolute and relative ages of MBM12A and other young populations; these data indicate ages of 2 +3/-1 Myr for MBM12A and 10 Myr for the TW Hya and Eta Cha associations. MBM12A may be a slightly evolved version of the aggregates of young stars within the Taurus dark clouds (~1 Myr) near the age of the IC 348 cluster (~2 Myr).Comment: to be published in The Astrophysical Journal, 41 pages, 14 figures, also found at http://cfa-www.harvard.edu/sfgroup/preprints.htm

String and string-inspired phenomenology

In these lectures I review the progress made over the last few years in the subject of string and string-inspired phenomenology. I take a practical approach, thereby concentrating more on explicit examples rather than on formal developments. Topics covered include: introduction to string theory, the free-fermionic formulation and its general features, generic conformal field theory properties, $SU(5)\times U(1)$ GUT and string model-building, supersymmetry breaking, the bottom-up approach to string-inspired models, radiative electroweak symmetry breaking, the determination of the allowed parameter space of supergravity models and the experimental constraints on this class of models, and prospects for direct and indirect tests of string-inspired models. (Lectures delivered at the XXII ITEP International Winter School of Physics, Moscow, Russia, February 22 -- March 2, 1994)Comment: CTP-TAMU-17/94, 39 pages (latex), 27 figures (not included). Figures are available via anonymous ftp from hplaa02.cern.ch (/pub/lopez) as one uuencoded file (MoscowFigs.uu, 1.31MB

Investigating Sources of Variability and Error in Simulations of Carbon Dioxide in an Urban Region

Greenhouse gas (GHG) emissions estimation methods that use atmospheric trace gas observations, including inverse modeling techniques, perform better when carbon dioxide (CO2) fluxes are more accurately transported and dispersed in the atmosphere by a numerical model. In urban areas, transport and dispersion is particularly difficult to simulate using current mesoscale meteorological models due, in part, to added complexity from surface heterogeneity and fine spatial/temporal scales. It is generally assumed that the errors in GHG estimation methods in urban areas are dominated by errors in transport and dispersion. Other significant errors include, but are not limited to, those from assumed emissions magnitude and spatial distribution. To assess the predictability of simulated trace gas mole fractions in urban observing systems using a numerical weather prediction model, we employ an Eulerian model that combines traditional meteorological variables with multiple passive tracers of atmospheric CO2 from anthropogenic inventories and a biospheric model. The predictability of the Eulerian model is assessed by comparing simulated atmospheric CO2 mole fractions to observations from four in situ tower sites (three urban and one rural) in the Washington DC/Baltimore, MD area for February 2016. Four different gridded fossil fuel emissions inventories along with a biospheric flux model are used to create an ensemble of simulated atmospheric CO2 observations within the model. These ensembles help to evaluate whether the modeled observations are impacted more by the underlying emissions or transport. The spread of modeled observations using the four emission fields indicates the model's ability to distinguish between the different inventories under various meteorological conditions. Overall, the Eulerian model performs well; simulated and observed average CO2 mole fractions agree within 1% when averaged at the three urban sites across the month. However, there can be differences greater than 10% at any given hour, which are attributed to complex meteorological conditions rather than differences in the inventories themselves. On average, the mean absolute error of the simulated compared to actual observations is generally twice as large as the standard deviation of the modeled mole fractions across the four emission inventories. This result supports the assumption, in urban domains, that the predicted mole fraction error relative to observations is dominated by errors in model meteorology rather than errors in the underlying fluxes in winter months. As such, minimizing errors associated with atmospheric transport and dispersion may help improve the performance of GHG estimation models more so than improving flux priors in the winter months. We also find that the errors associated with atmospheric transport in urban domains are not restricted to certain times of day. This suggests that atmospheric inversions should use CO2 observations that have been filtered using meteorological observations rather than assuming that meteorological modeling is most accurate at certain times of day (such as using only mid-afternoon observations)

AI-driven web API testing

Testing of web APIs is nowadays more critical than ever before, as they are the current standard for software integration. A bug in an organization’s web API could have a huge impact both in ternally (services relying on that API) and externally (third-party applications and end users). Most existing tools and testing ap proaches require writing tests or instrumenting the system under test (SUT). The main aim of this dissertation is to take web API testing to an unprecedented level of automation and thoroughness. To this end, we plan to apply artificial intelligence (AI) techniques for the autonomous detection of software failures. Specifically, the idea is to develop intelligent programs (we call them “bots”) ca pable of generating hundreds, thousands or even millions of test inputs and to evaluate whether the test outputs are correct based on: 1) patterns learned from previous executions of the SUT; and 2) knowledge gained from analyzing thousands of similar programs. Evaluation results of our initial prototype are promising, with bugs being automatically detected in some real-world APIs.Ministerio de Economía y Competitividad BELI (TIN2015-70560-R)Ministerio de Ciencia, Innovación y Universidades RTI2018-101204-B-C21 (HORATIO)Ministerio de Educación, Cultura y Deporte FPU17/0407

Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068

We present sub-arcsecond 7.5$-$13 $\mu$m imaging- and spectro-polarimetric observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio CANARIAS. At all wavelengths, we find: (1) A 90 $\times$ 60 pc extended polarized feature in the northern ionization cone, with a uniform $\sim$44$^{\circ}$ polarization angle. Its polarization arises from dust and gas emission in the ionization cone, heated by the active nucleus and jet, and further extinguished by aligned dust grains in the host galaxy. The polarization spectrum of the jet-molecular cloud interaction at $\sim$24 pc from the core is highly polarized, and does not show a silicate feature, suggesting that the dust grains are different from those in the interstellar medium. (2) A southern polarized feature at $\sim$9.6 pc from the core. Its polarization arises from a dust emission component extinguished by a large concentration of dust in the galaxy disc. We cannot distinguish between dust emission from magnetically aligned dust grains directly heated by the jet close to the core, and aligned dust grains in the dusty obscuring material surrounding the central engine. Silicate-like grains reproduce the polarized dust emission in this feature, suggesting different dust compositions in both ionization cones. (3) An upper limit of polarization degree of 0.3 per cent in the core. Based on our polarization model, the expected polarization of the obscuring dusty material is $\lesssim$0.1 per cent in the 8$-$13 $\mu$m wavelength range. This low polarization may be arising from the passage of radiation through aligned dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA

The first steps of iodine gas-to-particle conversion as seen in the lab: constraints on the role of iodine oxides and oxyacids

&amp;lt;p&amp;gt;The photooxidation of gas phase iodine-bearing molecules emitted by marine biota leads to intense particle nucleation events in the coastal and polar marine boundary layer&amp;lt;sup&amp;gt;1-3&amp;lt;/sup&amp;gt;. The ubiquity of iodine in the marine atmospheric environment&amp;lt;sup&amp;gt;4-7&amp;lt;/sup&amp;gt; has suggested that this may be a previously unrecognized global source of new aerosol particles&amp;lt;sup&amp;gt;8&amp;lt;/sup&amp;gt;. Atmospheric modeling is required in order to evaluate the importance of this process, but a substantial lack of understanding of the gas-to-particle conversion mechanism is hindering this effort, especially regarding the gas phase chemistry of the nucleating molecules (iodine oxides&amp;lt;sup&amp;gt;9&amp;lt;/sup&amp;gt;&amp;lt;sup&amp;gt;,&amp;lt;/sup&amp;gt;&amp;lt;sup&amp;gt;10&amp;lt;/sup&amp;gt; and/or oxyacids&amp;lt;sup&amp;gt;7&amp;lt;/sup&amp;gt;) and the formation kinetics of molecular clusters. To address this problem, we have conducted new flow tube laboratory experiments where pulsed laser photolysis or continuous broad-band photolysis of I&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;/O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; mixtures&amp;amp;#160; in air are used to generate iodine radicals in the presence of atmospherically representative mixing ratios of water vapor. The molecular reactants and the resulting molecular products are detected by time-resolved VUV laser photo-ionization time-of-flight mass spectrometry. High-level quantum chemistry and master equation calculations and gas kinetics modelling are used to analyse the experimental data. In this presentation we discuss our results and their implications for the interpretation of field meassurements and for the implementatiion of an iodine oxide particle formation mechanism in atmospheric models.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;References:&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;1. Hoffmann, T., O'Dowd, C. D. &amp;amp; Seinfeld, J. H. Iodine oxide homogeneous nucleation: An explanation for coastal new particle production. Geophys. Res. Lett. &amp;lt;strong&amp;gt;28&amp;lt;/strong&amp;gt;, 1949-1952 (2001).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;2. McFiggans, G. et al. Direct evidence for coastal iodine particles from Laminaria macroalgae - linkage to emissions of molecular iodine. Atmos. Chem. Phys. &amp;lt;strong&amp;gt;4&amp;lt;/strong&amp;gt;, 701-713 (2004).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;3. O'Dowd, C. D. et al. Marine aerosol formation from biogenic iodine emissions. Nature &amp;lt;strong&amp;gt;417&amp;lt;/strong&amp;gt;, 632-636 (2002).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;4. Prados-Roman, C. et al. Iodine oxide in the global marine boundary layer. Atmos. Chem. Phys. &amp;lt;strong&amp;gt;15&amp;lt;/strong&amp;gt;, 583-593, doi:10.5194/acp-15-583-2015 (2015).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;5. Sch&amp;amp;#246;nhardt, A. et al. Simultaneous satellite observations of IO and BrO over Antarctica. Atmos. Chem. Phys. &amp;lt;strong&amp;gt;12&amp;lt;/strong&amp;gt;, 6565-6580, doi:10.5194/acp-12-6565-2012 (2012).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;6. Mahajan, A. S. et al. Concurrent observations of atomic iodine, molecular iodine and ultrafine particles in a coastal environment. Atmos. Chem. Phys. &amp;lt;strong&amp;gt;10&amp;lt;/strong&amp;gt;, 27227-27253 (2010).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;7. Sipil&amp;amp;#228;, M. et al. Molecular-scale evidence of aerosol particle formation via sequential addition of HIO3. Nature &amp;lt;strong&amp;gt;537&amp;lt;/strong&amp;gt;, 532-534, doi:10.1038/nature19314 (2016).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;8. Saiz-Lopez, A. et al. Atmospheric Chemistry of Iodine. Chem. Rev. &amp;lt;strong&amp;gt;112&amp;lt;/strong&amp;gt;, 1773&amp;amp;#8211;1804, doi:DOI: 10.1021/cr200029u (2012).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;9. G&amp;amp;#243;mez Mart&amp;amp;#237;n, J. C. et al. On the mechanism of iodine oxide particle formation. Phys. Chem. Chem. Phys. &amp;lt;strong&amp;gt;15&amp;lt;/strong&amp;gt;, 15612-15622, doi:10.1039/c3cp51217g (2013).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;10. Saunders, R. W., Mahajan, A. S., G&amp;amp;#243;mez Mart&amp;amp;#237;n, J. C., Kumar, R. &amp;amp; Plane, J. M. C. Studies of the Formation and Growth of Aerosol from Molecular Iodine Precursor. Z. Phys. Chem. &amp;lt;strong&amp;gt;224&amp;lt;/strong&amp;gt;, 1095-1117 (2010).&amp;lt;/p&amp;gt; </jats:p