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Sample records for blidingia minima ulvales

  1. Exploring bacteria-induced growth and morphogenesis in the green macroalga order Ulvales (Chlorophyta)

    PubMed Central

    Wichard, Thomas

    2015-01-01

    Green macroalgae, such as Ulvales, lose their typical morphology completely when grown under axenic conditions or in the absence of the appropriate microbiome. As a result, slow growing aberrant phenotypes or even callus-like morphotypes are observed in Ulvales. The cross-kingdom interactions between marine algae and microorganisms are hence not only restricted by the exchange of macronutrients, including vitamins and nutrients, but also by infochemicals such as bacterial morphogenetic compounds. The latter are a fundamental trait mediating the mutualism within the chemosphere where the organisms interact with each other via compounds in their surroundings. Approximately 60 years ago, pilot studies demonstrated that certain bacteria promote growth, whereas other bacteria induce morphogenesis; this is particularly true for the order of Ulvales. However, only slow progress was made towards the underlying mechanism due to the complexity of, for example, algal cultivation techniques, and the lack of standardized experiments in the laboratory. A breakthrough in this research was the discovery of the morphogenetic compound thallusin, which was isolated from an epiphytic bacterium and induces normal germination restoring the foliaceous morphotypes of Monostroma. Owing to the low concentration, the purification and structure elucidation of highly biologically active morphogenetic compounds are still challenging. Recently, it was found that only the combination of two specific bacteria from the Rhodobacteraceae and Flavobacteriaceae can completely recover the growth and morphogenesis of axenic Ulva mutabilis cultures forming a symbiotic tripartite community by chemical communication. This review combines literature detailing evidences of bacteria-induced morphogenesis in Ulvales. A set of standardized experimental approaches is further proposed for the preparation of axenic algal tissues, bacteria isolation, co-cultivation experiments, and the analysis of the chemosphere

  2. Energy landscapes and persistent minima

    NASA Astrophysics Data System (ADS)

    Carr, Joanne M.; Mazauric, Dorian; Cazals, Frédéric; Wales, David J.

    2016-02-01

    We consider a coarse-graining of high-dimensional potential energy landscapes based upon persistences, which correspond to lowest barrier heights to lower-energy minima. Persistences can be calculated efficiently for local minima in kinetic transition networks that are based on stationary points of the prevailing energy landscape. The networks studied here represent peptides, proteins, nucleic acids, an atomic cluster, and a glassy system. Minima with high persistence values are likely to represent some form of alternative structural morphology, which, if appreciably populated at the prevailing temperature, could compete with the global minimum (defined as infinitely persistent). Threshold values on persistences (and in some cases equilibrium occupation probabilities) have therefore been used in this work to select subsets of minima, which were then analysed to see how well they can represent features of the full network. Simplified disconnectivity graphs showing only the selected minima can convey the funnelling (including any multiple-funnel) characteristics of the corresponding full graphs. The effect of the choice of persistence threshold on the reduced disconnectivity graphs was considered for a system with a hierarchical, glassy landscape. Sets of persistent minima were also found to be useful in comparing networks for the same system sampled under different conditions, using minimum oriented spanning forests.

  3. Recent Minima of 171 Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Samolyk, G.

    2015-12-01

    This paper continues the publication of times of minima for 171 eclipsing binary stars from observations reported to the AAVSO EB section. Times of minima from observations received by the author from March 2015 thru October 2015 are presented.

  4. Recent Minima of 193 Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Samolyk, G.

    2016-06-01

    This paper continues the publication of times of minima for eclipsing binary stars from observations reported to the AAVSO Eclipsing Binary section. Times of minima from CCD observations received by the author from November 2015 through January 2016 are presented.

  5. Implications of Extended Solar Minima

    NASA Technical Reports Server (NTRS)

    Adams, Mitzi L.; Davis, J. M.

    2009-01-01

    Since the discovery of periodicity in the solar cycle, the historical record of sunspot number has been carefully examined, attempting to make predictions about the next cycle. Much emphasis has been on predicting the maximum amplitude and length of the next cycle. Because current space-based and suborbital instruments are designed to study active phenomena, there is considerable interest in estimating the length and depth of the current minimum. We have developed criteria for the definition of a minimum and applied it to the historical sunspot record starting in 1749. In doing so, we find that 1) the current minimum is not yet unusually long and 2) there is no obvious way of predicting when, using our definition, the current minimum may end. However, by grouping the data into 22- year cycles there is an interesting pattern of extended minima that recurs every fourth or fifth 22-year cycle. A preliminary comparison of this pattern with other records, suggests the possibility of a correlation between extended minima and lower levels of solar irradiance.

  6. Minima Times of Selected Eclipsing Binaries

    NASA Astrophysics Data System (ADS)

    Parimucha, S.; Dubovsky, P.; Kudak, V.; Perig, V.

    2016-05-01

    We present 221 CCD minima times of the 76 selected eclipsing binaries obtained during 2013-2016 at Observatory at Kolonica Saddle in Slovakia and Observatory of Laboratory of Space Research, Uzhhorod National University in Ukraine

  7. Finding pathways between distant local minima.

    PubMed

    Carr, Joanne M; Trygubenko, Semen A; Wales, David J

    2005-06-15

    We report a new algorithm for constructing pathways between local minima that involve a large number of intervening transition states on the potential energy surface. A significant improvement in efficiency has been achieved by changing the strategy for choosing successive pairs of local minima that serve as endpoints for the next search. We employ Dijkstra's algorithm [E. W. Dijkstra, Numer. Math. 1, 269 (1959)] to identify the "shortest" path corresponding to missing connections within an evolving database of local minima and the transition states that connect them. The metric employed to determine the shortest missing connection is a function of the minimized Euclidean distance. We present applications to the formation of buckminsterfullerene and to the folding of various biomolecules: the B1 domain of protein G, tryptophan zippers, and the villin headpiece subdomain. The corresponding pathways contain up to 163 transition states and will be used in future discrete path sampling calculations. PMID:16008483

  8. Finding pathways between distant local minima

    NASA Astrophysics Data System (ADS)

    Carr, Joanne M.; Trygubenko, Semen A.; Wales, David J.

    2005-06-01

    We report a new algorithm for constructing pathways between local minima that involve a large number of intervening transition states on the potential energy surface. A significant improvement in efficiency has been achieved by changing the strategy for choosing successive pairs of local minima that serve as endpoints for the next search. We employ Dijkstra's algorithm [E. W. Dijkstra, Numer. Math. 1, 269 (1959)] to identify the "shortest" path corresponding to missing connections within an evolving database of local minima and the transition states that connect them. The metric employed to determine the shortest missing connection is a function of the minimized Euclidean distance. We present applications to the formation of buckminsterfullerene and to the folding of various biomolecules: the B1 domain of protein G, tryptophan zippers, and the villin headpiece subdomain. The corresponding pathways contain up to 163 transition states and will be used in future discrete path sampling calculations.

  9. Occurrence of Knudsen minima in diverging microchannels

    SciTech Connect

    Hemadri, Vadiraj; Bhandarkar, Upendra; Agrawal, Amit

    2014-12-09

    Rarefied gas flow is gaining increasing importance with the emergence of Micro Electro Mechanical Systems (MEMS). Knudsen minima is one of the characteristic feature of such rarefied flows and has been observed in uniform cross section channels such as plane channel, cylindrical tube and annulus. However, data pertaining to gaseous flow in varying cross section channel is relatively sparse. Channels of varying cross section are frequently encountered in MEMS devices and are fundamental to the design of micro-scale nozzles and micro-valves. In this context, rarefied gas flow through a diverging microchannel (divergence angle – 12 degree) is studied experimentally with three different gases (argon, nitrogen and oxygen). The experiments are performed over a wide range with the mean Knudsen number varying from slip to the transitional regime (0.07 to 1.2). It is found that the effect of molecular weight of the gas on the non-dimensional mass flow rate is negligible. The Knudsen minima is experimentally observed for the first time in microchannel of non-uniform cross section.

  10. Cloud supersaturations from CCN spectra Hoppel minima

    NASA Astrophysics Data System (ADS)

    Hudson, James G.; Noble, Stephen; Tabor, Samantha

    2015-04-01

    High-resolution cloud condensation nucleus (CCN) spectral measurements in two aircraft field projects, Marine Stratus/Stratocumulus Experiment (MASE) and Ice in Clouds Experiment-Tropical (ICE-T), often showed bimodality that had previously been observed in submicrometer aerosol size distributions obtained by differential mobility analyzers. However, a great deal of spectral shape variability from very bimodal to very monomodal was observed in close proximity. Cloud supersaturation (S) estimates based on critical S, Sc, at minimal CCN concentrations between two modes (Hoppel minima) were ascertained for 63% of 325 measured spectra. These cloud S were lower than effective S (Seff) determined by comparing ambient CCN spectra with nearby cloud droplet concentrations (Nc). Averages for the polluted MASE stratus were 0.15 and 0.23% and for the cumulus clouds of ICE-T 0.44 and 1.03%. This cloud S disagreement between the two methods might in part be due to the fact that Hoppel minima include the effects of cloud processing, which push CCN spectra toward lower S. Furthermore, there is less cloud processing by the smaller cloud droplets, which might be related to smaller droplets evaporating more readily. Significantly lower concentrations within the more bimodal spectra compared with the monomodal spectra indicated active physical processes: Brownian capture of interstitial CCN and droplet coalescence. Chemical cloud processing also contributed to bimodality, especially in MASE.

  11. Global ozone minima in the historical record

    NASA Technical Reports Server (NTRS)

    Rood, Richard B.

    1986-01-01

    The magnitude and structure of the global total ozone minimum between 1958 and 1962 is similar to that observed between 1979 and 1983. Analysis of the single station data that exhibit the most pronounced minima suggest that the spatial structure of the global minimum is different from the currently observed reduction. Very low north polar values were observed, but there is no indication of anomalously low ozone in Antarctica. The temporal relationship to the sun spot cycle is similar in both time periods. Rather than solar terrestrial interaction, however, a more likely explanation of the early 1960's reduction is normal climatology caused by a persistent period of planetary wave activity. Such a natural explanation may also be appropriate for the current depletion.

  12. Relationships between bond dissociation energies, electron density minima and electrostatic potential minima

    NASA Astrophysics Data System (ADS)

    Wiener, John J. M.; Murray, Jane S.; Grice, M. Edward; Politzer, Peter

    The experimental dissociation energies of a group of homonuclear diatomic molecules are found to correlate with computed electron densities pho(r) and electrostatic potentials V (r) at the bond midpoints, supporting an earlier prediction based on density functional arguments (N. H. March, P. M. Kozlowski and F. Perrot 1990, J. molec. Struct. Theochem, 209, 433). The relationships are generalized to 45 molecules of various types, focusing upon the minima of pho(r) and V (r) along internuclear axes. Dissociation energies are shown to be related distinctly more closely to the minimum values of V (r) than to those of pho(r). This complements previous findings for negative monatomic ions as well as the recent observation that the V (r) minima provide the more realistic boundary points between bonded atoms (relative to literature values of covalent radii), and thus further establishes the significance of electrostatic potential axial minima with respect to covalent bonding. In the present work, all calculations were carried out by a density functional procedure (Becke exchange, Lee, Yang and Parr correlation, 6-31G** basis sets).

  13. Ecology of common salvinia, Salvinia minima, in southern Florida

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The floating macrophyte, Salvinia minima, grows in a variety of freshwater habitats in Florida. We conducted a 39-month study at four sites in southern Florida to elucidate the abiotic and biotic factors that influenced the density, nutritional profile, and size of S. minima. These factors include...

  14. 14 CFR 121.625 - Alternate Airport weather minima.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false Alternate Airport weather minima. 121.625... Alternate Airport weather minima. Except as provided in § 121.624 for ETOPS Alternate Airports, no person may list an airport as an alternate in the dispatch or flight release unless the appropriate...

  15. 14 CFR 121.625 - Alternate Airport weather minima.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false Alternate Airport weather minima. 121.625... Alternate Airport weather minima. Except as provided in § 121.624 for ETOPS Alternate Airports, no person may list an airport as an alternate in the dispatch or flight release unless the appropriate...

  16. 14 CFR 121.625 - Alternate Airport weather minima.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false Alternate Airport weather minima. 121.625... Alternate Airport weather minima. Except as provided in § 121.624 for ETOPS Alternate Airports, no person may list an airport as an alternate in the dispatch or flight release unless the appropriate...

  17. 14 CFR 121.625 - Alternate Airport weather minima.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false Alternate Airport weather minima. 121.625... Alternate Airport weather minima. Except as provided in § 121.624 for ETOPS Alternate Airports, no person may list an airport as an alternate in the dispatch or flight release unless the appropriate...

  18. 14 CFR 121.625 - Alternate Airport weather minima.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Alternate Airport weather minima. 121.625... Alternate Airport weather minima. Except as provided in § 121.624 for ETOPS Alternate Airports, no person may list an airport as an alternate in the dispatch or flight release unless the appropriate...

  19. Aquasols: on the role of secondary minima.

    PubMed

    Hahn, Melinda W; Abadzic, Dean; O'Melia, Charles R

    2004-11-15

    Experiments are presented that test the hypothesis of deposition into and reentrainment from secondary minima during flow through porous media. The release of deposited particles following a decrease in ionic strength is inconsistent with deposition in the primary minimum of either simple DLVO interaction energy curves (which suggest that deposition is irreversible) or Born-DLVO interaction energy curves (which create a finite primary minimum that deepens with decreasing ionic strength). The observed release of particles is, on the other hand, consistent with deposition in the secondary minimum because this energy minimum decreases and can disappear with decreasing ionic strength. The implications for colloid transport of a reversible deposition process in the secondary minimum are very different from those of a process involving irreversible deposition in the primary minimum. First, particles that are continually captured and released will travel much farther in the subsurface than might be expected if the classic irreversible filtration model is applied. Second, and perhaps more significantly, deposition in the secondary well can increase with increasing particle size. Although particle transport by convective diffusion increases as particle size decreases, particle "attachment" in secondary minima decreases with decreasing particle size. Thus, smaller particles (those with diameters in the order of a few tens of nanometers) would be more effective in the facilitated transport of highly sorbing contaminants such as hydrophobic organic molecules, metals, and radionuclides. Other contaminants are themselves particles, such as viruses (tens of nanometers in diameter) and bacteria (near 1 microm in diameter). Due to this difference in size, viruses could be transported over much larger distances than bacteria. Third, the transport of colloids and, hence, the transport of contaminants associated with them, depends on the Hamaker constant of the particle

  20. CCD Times of Minima of Selected Eclipsing Binaries

    NASA Astrophysics Data System (ADS)

    Zejda, Miloslav

    2004-12-01

    682 CCD minima observations of 259 eclipsing binaries made mainly by author are presented. The observed stars were chosen mainly from catalogue BRKA of observing programme of BRNO-Variable Star Section of CAS.

  1. GRAND MINIMA AND NORTH-SOUTH ASYMMETRY OF SOLAR ACTIVITY

    SciTech Connect

    Olemskoy, S. V.; Kitchatinov, L. L.

    2013-11-01

    A solar-type dynamo model in a spherical shell is developed with allowance for random dependence of the poloidal field generation mechanism on time and latitude. The model shows repeatable epochs of a strongly decreased amplitude of magnetic cycles similar to the Maunder minimum of solar activity. Random dependence of dynamo parameters on latitude breaks the equatorial symmetry of generated fields. The model shows the correlation of the occurrence of grand minima with deviations in the dynamo field from dipolar parity. An increased north-south asymmetry of magnetic activity can, therefore, be an indicator of transitions to grand minima. Qualitative interpretation of this correlation is suggested. Statistics of grand minima in the model are close to the Poisson random process, indicating that the onset of a grand minimum is statistically independent of preceding minima.

  2. O-C Gateway, a Collection of Minima Timings

    NASA Astrophysics Data System (ADS)

    Paschke, A.; Brat, L.

    2006-02-01

    The huge world-wide database of minima timings maintained by A. Paschke is presented. There is described another similar databases and their availability. The O-C Gateway is freely available at http://var.astro.cz/ocgate and users can plot O-C diagrams and extract the source data (list of minima timings). The web based application was created by L. Brat.

  3. The Earth's climate at minima of Centennial Gleissberg Cycles

    NASA Astrophysics Data System (ADS)

    Ruzmaikin, Alexander; Feynman, Joan

    2015-10-01

    The recent extended, deep minimum of solar variability and the extended minima in the 19th and 20th centuries (1810-1830 and 1900-1920) are consistent with minima of the Centennial Gleissberg Cycle (CGC), a 90-100 year variation of the amplitude of the 11-year sunspot cycle observed on the Sun and at the Earth. The Earth's climate response to these prolonged low solar radiation inputs involves heat transfer to the deep ocean causing a time lag longer than a decade. The spatial pattern of the climate response, which allows distinguishing the CGC forcing from other climate forcings, is dominated by the Pacific North American pattern (PNA). The CGC minima, sometimes coincidently in combination with volcanic forcing, are associated with severe weather extremes. Thus the 19th century CGC minimum, coexisted with volcanic eruptions, led to especially cold conditions in United States, Canada and Western Europe.

  4. Fullerene valence photoemission time delay near ionization cavity minima

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, Maia; Anstine, Dylan; Dixit, Gopal; Madjet, Mohamed; Chakraborty, Himadri

    2015-05-01

    We investigate photoemission quantum phases and associated Wigner-Smith time delays for HOMO and HOMO-1 electrons of a C60 molecule using time-dependent local density approximation (TDLDA). The interference oscillations in C60 valence emissions produce series of minima whose energy separation depends on the molecular size. We show that the quantum phase associated with these minima exhibits rapid variations due to electron correlations, causing rich structures in the photoemission time delay. Besides fullerenes, the detection of photoemission minima in metal clusters suggests a possible universality of the phenomenon in cluster systems, or even quantum dots, that confine finite-sized electron gas. The work predicts a new research direction to apply attosecond metrology, such as RABITT, in the world of nanosystems. This work was supported by the U.S. National Science Foundation.

  5. Chemopreventive Agents from Physalis minima Function as Michael Reaction Acceptors

    PubMed Central

    Men, Ruizhi; Li, Ning; Ding, Chihong; Tang, Yingzhan; Xing, Yachao; Ding, Wanjing; Ma, Zhongjun

    2016-01-01

    Background: The fruits of some varieties of genus Physalis have been used as delicious fruits and functional food in the Northeast of China. Materials and Methods: To reveal the functional material basis, we performed bioactivity-guided phytochemical research and chemopreventive effect assay of the constituents from Physalis minima. Results: It was demonstrated that the ethyl acetate extract of P. minima L. (EEPM) had potential quinone reductase (QR) inducing activity with induction ratio (IR, QR induction activity) value of 1.47 ± 0.24, and glutathione binding property as potential Michael reaction acceptors (with an α, β-unsaturated ketone moiety). Furthermore, bioactivity-guided phytochemical research led eight compounds (1–8), which were elucidated as 3-isopropyl-5-acetoxycyclohexene-2-one-1 (1), isophysalin B (2), physalin G (3), physalin D (4), physalin I (5), physordinose B (6), stigmasterol-3-O-β-D-glucopyranoside (7) and 5α-6β-dihydroxyphysalin R (8) on the basis of nuclear magnetic resonance spectroscopy analyses and HRESIMS. Then, isophysalin B (2) and physordinose B (6) showed significant QR inducing activity with IR value of 2.80 ± 0.19 and 2.38 ± 0.46, respectively. SUMMARY An ultra-performance liquid chromatographic method with glutathione as the substrate was used to detect the Michael reaction acceptors in extracts of Physalis minima (EPM)We investigated the chemical constituents of EPM guided by biological activity methodIsophysalin B (1) and physordinose B (6) showed strong quinone reductase inducing activity with induction ratio values of 2.80 ± 0.19 and 2.38 ± 0.46This study generated useful information for consumers and many encourage researchers to utilize edible fruits from Physalis as a source of phytochemicals Abbreviations used: EPM: Extracts of Physalis minima, EEPM: Ethyl acetate extract of Physalis minima L., GSH: Glutathione, MRAs: Michael reaction acceptors, QR: Quinone reductase. PMID:27279713

  6. Historical records of solar grand minima: a review

    NASA Astrophysics Data System (ADS)

    Vaquero, José M.

    2012-07-01

    Knowing solar activity during the past centuries is of great interest for many purposes. Historical documents can help us to know about the behaviour of the Sun during the last centuries. The observation of aurorae and naked-eye sunspots provides us with continuous information through the last few centuries that can be used to improve our knowledge of the long-term solar activity including solar Grand Minima. We have more or less detailed information on only one Grand minimum (the Maunder minimum in the second half of 17th century), which serves as an archetype for Grand minima in general. Telescopic sunspot records and measurements of solar diameter during Maunder minimum are available. In this contribution, I review some recent progress on these issues.

  7. Differences Between the Current Solar Minimum and Earlier Minima

    NASA Astrophysics Data System (ADS)

    Basu, S.; Broomhall, A.-M.; Chaplin, W. J.; Elsworth, Y.; Fletcher, S.; New, R.

    2010-06-01

    The Birmingham Solar-Oscillations Network (BiSON) has collected helioseismic data over three solar cycles. We use these data to determine how the internal properties of the Sun during this minimum differ from the previous two minima. The Cycle 24 data show oscillatory differences with respect to the other two sets, indicating relatively localized changes in the solar interior. Analysis of MDI data from Cycle 23 and Cycle 24 also show significant signs of differences.

  8. Grand minima of solar activity and sociodynamics of culture

    NASA Astrophysics Data System (ADS)

    Vladimirsky, B. M.

    2012-12-01

    Indices of creative productivity introduced by C. Murrey were used to verify S. Ertel's conclusion about a global increase in creative productivity during the prolonged minimum of solar activity in 1640-1710. It was found that these indices for mathematicians, philosophers, and scientists increase in the Maunder era by factor of 1.6 in comparison with intervals of the same length before and after the minimum. A similar effect was obtained for mathematicians and philosophers for five earlier equitype minima in total (an increase by a factor of 1.9). The regularity that is revealed is confirmed by the fact that the most important achievements of high-ranking mathematicians and philosophers during the whole time period (2300 years) considered in this study fall on epochs of reduced levels of solar activity. The rise in the probability of the generation of rational ideas during grand minima is reflected also in the fact that they precede the appearance of written language and farming. Ultra-low-frequency electromagnetic fields appear to serve as a physical agent stimulating the activity of the brain's left hemisphere during the epochs of minima.

  9. Observations of Hoppel Minima in CCN Spectra in Oklahoma

    NASA Astrophysics Data System (ADS)

    Tabor, Samantha S.

    Aerosols are one of the most fundamental keys to understanding the future state of the climate. Aerosols impact the radiation budget of the Earth in numerous ways and are poorly understood. Some aerosols can act as cloud condensation nuclei (CCN) and can significantly change the properties of clouds; this is known as the Indirect Aerosol Effect (IAE) and it remains the largest climate change uncertainty. Most studies concerning CCN and the impacts of the CCN distributions occur over the ocean, leaving questions about the processing occurring over the continents. Eleven days of measurements from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site were taken from an Aerosol Intensive Operational Period (IOP) during May 2003. A ground based CCN spectrometer and differential mobility analyzer (DMA) were deployed to study the distributions of the CCN spectra and dry aerosol size distributions. 268 measurement periods were sorted by their spectral shapes by using two rating systems. Case studies of the characteristics of the spectra observed during specific times of day or particular meteorological conditions were created and it was shown that meteorological conditions have a significant impact on the shapes of the CCN distributions. Back trajectories were also analyzed and shown to have an even larger impact on the observations of the Hoppel Minima, a minima located between the processed and unprocessed CCN modes. Using vertical velocity and back trajectories along with numerous meteorological measurements it can be shown that cloud processing is not only occurring over the continent but transport of the cloud processed air to the surface is also occurring. The Hoppel Minima during this Oklahoma project had a mean critical supersaturation (Sc) of 0.68%.

  10. B.R.N.O. Contributions #38 Times of minima

    NASA Astrophysics Data System (ADS)

    Hoňková, K.; Juryšek, J.; Lehký, M.; Šmelcer, L.; Trnka, J.; Mašek, M.; Urbaník, M.; Auer, R.; Vrašták, M.; Kučáková, H.; Ruocco, N.; Magris, M.; Polák, J.; Brát, L.; Audejean, M.; Banfi, M.; Moudrá, M.; Lomoz, F.; Přibík, V.; Dřevěný, R.; Scaggiante, F.; Kocián, R.; Cagaš, P.; Poddaný, S.; Zíbar, M.; Jacobsen, J.; Marek, P.; Colazo, C.; Zardin, D.; Sobotka, P.; Starzomski, J.; Hladík, B.; Vincenzi, M.; Skarka, M.; Walter, F.; Chapman, A.; Díaz, N. D.; Aceti, P.; Singh, P.; Kalista, L.; Kamenec, M.; Zejda, M.; Marchi, F.; Bílek, R.; Guzzo, P.; Corfini, G.; Onderková, K.; Hečko, A.; Mina, F.; Vítek, M.; Barsa, R.; Quinones, C.; Taormina, M.; Melia, R.; Schneiter, M.; Scavuzzo, A.; Marcionni, N.; Ehrenberger, R.; Tapia, L.; Fasseta, G.; Suarez, N.; Scaggiante, D.; Artusi, E.; Garcia, R.; Grnja, J.; Fišer, A.; Hynek, T.; Vilášek, M.; Rozehnal, J.; Kalisch, T.; Lang, K.; Gorková, S.; Novysedlák, R.; Salvaggio, F.; Smyčka, T.; Spurný, M.; Wikander, T.; Mravik, J.; Šuchaň, J.; Čaloud, J.

    2013-12-01

    This paper presents observations of eclipsing binaries acquired by members and cooperating observers of the Variable Star and Exoplanet Section of Czech Astronomical Society (B.R.N.O. observing project). Paper contains 3417 times of minima for 969 objects. It was obtained by 80 observers during 2011 ± 2013 period. Some neglected southern eclipsing binaries and newly discovered stars by the observers of project B.R.N.O. are included in the list. New accurate ephemerides have been found for 447 binary systems. Time of primary minimum of long period variable eps Aur is presented as well.

  11. Estimation procedures for the GEV distribution for the minima

    NASA Astrophysics Data System (ADS)

    Raynal-Villasenor, Jose A.; Raynal-Gutierrez, M. Elena

    2014-11-01

    The biased and unbiased moments (MOM1 and MOM2), maximum likelihood (ML), sextiles (SEX1 and SEX2) and probability weighted moments (PWM) methods for the estimation the parameters and quantiles of the General Extreme Value (GEV) Distribution for the minima were analyzed and compared by using data generation techniques of the type of distribution sampling experiments. Considering bias, variance and mean square error criteria of estimates of parameters and quantiles, it is concluded that in general for the values of the shape parameter considered: -0.1, -0.3, and -0.5 and 0.1, 0.3 and 0.5, the sample sizes analyzed: 9 ⩽ N ⩽ 99 and non-exceedance probabilities: 0.01 ⩽ Π(x) ⩽ 0.10, the ML method performed better than the other five. However, for sample sizes bigger than 49, most of the methods, with the exception of SEX1, produced similar results. As a general conclusion of the study reported here, it can be stated that the ML method resulted to be better to the other five when estimating the parameters and quantiles of the GEV distribution for the minima, for the cases analyzed in this study.

  12. Symmetry-protected local minima in infinite DMRG

    NASA Astrophysics Data System (ADS)

    Pfeifer, Robert N. C.

    2015-11-01

    The infinite density matrix renormalization group (iDMRG) algorithm is a highly successful numerical algorithm for the study of low-dimensional quantum systems, and is also frequently used to initialize the more popular finite DMRG algorithm. Implementations of both finite and infinite DMRG frequently incorporate support for the protection and exploitation of symmetries of the Hamiltonian. In common with other variational tensor network algorithms, convergence of iDMRG to the ground state is not guaranteed, with the risk that the algorithm may become stuck in a local minimum. In this paper, I demonstrate the existence of a particularly harmful class of physically irrelevant local minima affecting both iDMRG and to a lesser extent also infinite time-evolving block decimation (iTEBD), for which the ground state is compatible with the protected symmetries of the Hamiltonian but cannot be reached using the conventional iDMRG or iTEBD algorithms. I describe a modified iDMRG algorithm which evades these local minima, and which also admits a natural interpretation on topologically ordered systems with a boundary.

  13. Viscosity minima in binary mixtures of ionic liquids + molecular solvents.

    PubMed

    Tariq, M; Shimizu, K; Esperança, J M S S; Canongia Lopes, J N; Rebelo, L P N

    2015-05-28

    The viscosity (η) of four binary mixtures (ionic liquids plus molecular solvents, ILs+MSs) was measured in the 283.15 < T/K < 363.15 temperature range. Different IL/MS combinations were selected in such a way that the corresponding η(T) functions exhibit crossover temperatures at which both pure components present identical viscosity values. Consequently, most of the obtained mixture isotherms, η(x), exhibit clear viscosity minima in the studied T-x range. The results are interpreted using auxiliary molecular dynamics (MD) simulation data in order to correlate the observed η(T,x) trends with the interactions in each mixture, including the balance between electrostatic forces and hydrogen bonding. PMID:25933136

  14. SOLAR ROTATION EFFECTS ON THE HELIOSHEATH FLOW NEAR SOLAR MINIMA

    SciTech Connect

    Borovikov, Sergey N.; Pogorelov, Nikolai V.; Ebert, Robert W.

    2012-05-01

    The interaction between fast and slow solar wind (SW) due to the Sun's rotation creates corotating interaction regions (CIRs), which further interact with each other creating complex plasma structures at large heliospheric distances. We investigate the global influence of CIRs on the SW flow in the inner heliosheath between the heliospheric termination shock (TS) and the heliopause. The stream interaction model takes into account the major global effects due to slow-fast stream interaction near solar minima. The fast and slow wind parameters are derived from the Ulysses observations. We investigate the penetration of corotating structures through the TS and their further propagation through the heliosheath. It is shown that the heliosheath flow structure may experience substantial modifications, including local decreases in the radial velocity component observed by Voyager 1.

  15. Effect of correlations between minima on a complex energy landscape

    NASA Astrophysics Data System (ADS)

    Pusuluri, Sai Teja; Lang, Alex H.; Mehta, Pankaj; Castillo, Horacio E.

    We recently modeled cellular interconvertion dynamics by using an epigenetic landscape model inspired by neural network models. Given an arbitrary set of patterns, the model can be used to construct an energy landscape in which those patterns are the global minima. We study the possible stable states and metastable states of the landscapes thus constructed. We consider three different cases: i) choosing the patterns to be random and independently distributed ii) choosing a set of patterns directly derived from the experimental cellular transcription factor expression data for a representative set of cell types in an organism and iii) choosing randomly generated trees of hierarchically correlated patterns, inspired by biology. For each of the three cases, we study the energy landscapes. In particular we study the basins of attraction of both the stable states and the metastable states, we compute the configurational entropy as a function of energy, and we demonstrate how those results depend on the correlations between the patterns.

  16. The cosmic radiation in the heliosphere at successive solar minima

    NASA Technical Reports Server (NTRS)

    Mcdonald, Frank B.; Moraal, Harm; Reinecke, J. P. L.; Lal, Nand; Mcguire, Robert E.

    1992-01-01

    Cosmic ray observations at 1 AU are compared for the last three solar minimum periods along with the 1977/1989 and 1987 Pioneer 10 and Voyager 1 and 2 data from the outer heliosphere. There is good agreement between the 1965 and 1987 Galactic cosmic ray H and He spectra at 1 AU. Significant and complex differences are found between the 1977/1978 and 1987 measurements of the Galactic and anomalous cosmic ray components at 1 and 15 AU. In the outer heliosphere there are negative latitudinal gradients that reach their maximum magnitude when the inclination of the outer heliosphere current sheet is at a minimum. The radial gradients decrease with heliocentric distance as about 1/r exp 0.7 and do not differ significantly at the successive solar minima. The measured radial and latitudinal gradients are used to estimate the particle transport parameters in the outer heliosphere. Using the local interstellar He spectrum of Webber et al. (1987), it is estimated that the modulation boundary is of the order of 160 AU.

  17. Competition between Salvinia minima and Spirodela polyrhiza mediated by nutrient levels and herbivory.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We investigated the effects of initial biomass, nutrients, herbivory, and competition with Spirodela polyrhiza on Salvinia minima biomass and density. Salvinia minima populations were subjected to two levels of herbivory from the weevil Cyrtobagous salviniae and various levels of competition from S...

  18. Anti lipid peroxidation activity of Piper trioicum Roxb. and Physalis minima L. extracts.

    PubMed

    Dinakaran, Sathis Kumar; Saraswathi, Narasimha Raju; Nalini, Venkata Rama Rao; Srisudharson; Bodanapu, Venkat Ram Reddy; Avasarala, Harani; Banji, David

    2011-07-01

    Attempt has been made to evaluate free radical scavenging activity of ethanolic extract of Piper trioicum Roxb. and Physalis minima L. individually. In this study goat liver has been used as lipid source. This in vitro evaluation was done by measuring the malondialdehyde (MDA) of tissue homogenates. The results suggest that the ethanolic extract of the Piper trioicum Roxb. and Physalis minima L. has the ability to suppress the lipid peroxidation and it was also found that Piper trioicum Roxb. extract has more activity than Physalis minima L. extract. PMID:21715277

  19. Erratum: "B.R.N.O. Contributions #38 Times of minima of eclipsing binary" (OEJV #160, [2013])

    NASA Astrophysics Data System (ADS)

    Honková, K.; Juryšek, J.; Lehký, M.; Šmelcer, L.; Trnka, J.; Mašek, M.; Urbaník, M.; Auer, R.; Vrašták, M.; Kučáková, H.; Ruocco, N.; Magris, M.; Polák, J.; Brát, L.; Audejean, M.; Banfi, M.; Moudrá, M.; Lomoz, F.; Přibík, V.; Dřevěný, R.; Scaggiante, F.; Kocián, R.; Cagaš, P.; Poddaný, S.; Zíbar, M.; Jacobsen, J.; Marek, P.; Colazo, C.; Zardin, D.; Sobotka, P.; Starzomski, J.; Hladík, B.; Vincenzi, M.; Skarka, M.; Walter, F.; Chapman, A.; Díaz, N. D.; Aceti, P.; Singh, P.; Kalista, L.; Kamenec, M.; Zejda, M.; Marchi, F.; Bílek, R.; Guzzo, P.; Corfini, G.; Onderková, K.; Hečko, A.; Mina, F.; Vítek, M.; Barsa, R.; Quinones, C.; Taormina, M.; Melia, R.; Schneiter, M.; Scavuzzo, A.; Marcionni, N.; Ehrenberger, R.; Tapia, L.; Fasseta, G.; Suarez, N.; Scaggiante, D.; Artusi, E.; Garcia, R.; Grnja, J.; Fišer, A.; Hynek, T.; Vilášek, M.; Rozehnal, J.; Kalisch, T.; Lang, K.; Gorková, S.; Novysedlák, R.; Salvaggio, F.; Smyčka, T.; Spurný, M.; Wikander, T.; Mravik, J.; Šuchań, J.; Čaloud, J.

    2014-08-01

    Due to an errors in calculated heliocentric corrections, there are 404 wrong HJD minima timings (with larger Difference than Min error; see header of the Table) in "B.R.N.O. Contributions #38 Times of minima of eclipsing binary" paper. The correct minima timings are presented hereafter.

  20. Minima in generalized oscillator strengths for initially excited hydrogen-like atoms

    NASA Technical Reports Server (NTRS)

    Matsuzawa, M.; Omidvar, K.; Inokuti, M.

    1976-01-01

    Generalized oscillator strengths for transitions from an initially excited state of a hydrogenic atom to final states (either discrete or continuum) have complicated structures, including minima and shoulders, as functions of the momentum transfer. Extensive calculations carried out in the present work have revealed certain systematics of these structures. Some implications of the minima to the energy dependence of the inner-shell ionization cross section of heavy atoms by proton impact are discussed.

  1. Grand Minima of Solar Activity and the Mean-Field Dynamo

    NASA Astrophysics Data System (ADS)

    Usoskin, I. G.; Sokoloff, D.; Moss, D.

    2009-02-01

    We demonstrate that a simple solar dynamo model, in the form of a Parker migratory dynamo with random fluctuations of the dynamo governing parameters and algebraic saturation of dynamo action, can at least qualitatively reproduce all the basic features of solar Grand Minima as they are known from direct and indirect data. In particular, the model successfully reproduces such features as an abrupt transition into a Grand Minimum and the subsequent gradual recovery of solar activity, as well as mixed-parity butterfly diagrams during the epoch of the Grand Minimum. The model predicts that the cycle survives in some form during a Grand Minimum, as well as the relative stability of the cycle inside and outside of a Grand Minimum. The long-term statistics of simulated Grand Minima appears compatible with the phenomenology of the Grand Minima inferred from the cosmogenic isotope data. We demonstrate that such ability to reproduce the Grand Minima phenomenology is not a general feature of the dynamo models but requires some specific assumption, such as random fluctuations in dynamo governing parameters. In general, we conclude that a relatively simple and straightforward model is able to reproduce the Grand Minima phenomenology remarkably well, in principle providing us with a possibility of studying the physical nature of Grand Minima.

  2. Coupled factors influencing detachment of nano- and micro-sized particles from primary minima.

    PubMed

    Shen, Chongyang; Lazouskaya, Volha; Jin, Yan; Li, Baoguo; Ma, Zhiqiang; Zheng, Wenjuan; Huang, Yuanfang

    2012-06-01

    This study examined the detachments of nano- and micro-sized colloids from primary minima in the presence of cation exchange by laboratory column experiments. Colloids were initially deposited in columns packed with glass beads at 0.2 M CaCl(2) in the primary minima of Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies. Then, the columns were flushed with NaCl solutions with different ionic strengths (i.e., 0.001, 0.01, 0.1 and 0.2 M). Detachments were observed at all ionic strengths and were particularly significant for the nanoparticle. The detachments increased with increasing electrolyte concentration for the nanoparticle whereas increased from 0.001 M to 0.01 M and decreased with further increasing electrolyte concentration for the micro-sized colloid. The observations were attributed to coupled influence of cation exchange, short-range repulsion, surface roughness, surface charge heterogeneity, and deposition in the secondary minima. The detachments of colloids from primary minima challenge the common belief that colloid interaction in primary minimum is irreversible and resistant to disturbance in solution ionic strength and composition. Although the significance of surface roughness, surface charge heterogeneity, and secondary minima on colloid deposition has been widely recognized, our study implies that they also play important roles in colloid detachment. Whereas colloid detachment is frequently associated with decrease of ionic strength, our results show that increase of ionic strength can also cause detachment due to influence of cation exchange. PMID:22575872

  3. Long-Term Changes in Sunspot Activity, Occurrence of Grand Minima, and Their Future Tendencies

    NASA Astrophysics Data System (ADS)

    Mordvinov, A. V.; Kramynin, A. P.

    2010-06-01

    Long-term changes in the magnetic activity of the Sun were studied in terms of the empirical mode decomposition that revealed their essential modes. The occurrence of grand minima was also studied in their relation to long-term changes in sunspot activity throughout the past 11 000 yr. Characteristic timescales of long-term changes in solar activity manifest themselves in the occurrence of grand minima. A quantitative criterion has been defined to identify epochs of grand minima. This criterion reveals the important role of secular and bicentennial activity variations in the occurrence of grand minima and relates their amplitudes with the current activity level, which is variable on a millennial timescale. We have revealed specific patterns in the magnetic activity between successive grand minima which tend to recur approximately every 2300 yr but occasionally alternate with irregular changes. Such intermittent activity behavior indicates low dimensional chaos in the solar dynamo due to the interplay of its dominant modes. The analysis showed that in order to forecast activity level in forthcoming cycles, one should take into account long-term changes in sunspot activity on a ≈2300-yr timescale. The regularities revealed suggest solar activity to decrease in the foreseeable future.

  4. Fast-Flowering Mini-Maize: Seed to Seed in 60 Days.

    PubMed

    McCaw, Morgan E; Wallace, Jason G; Albert, Patrice S; Buckler, Edward S; Birchler, James A

    2016-09-01

    Two lines of Zea mays were developed as a short-generation model for maize. The Fast-Flowering Mini-Maize (FFMM) lines A and B are robust inbred lines with a significantly shorter generation time, much smaller stature, and better greenhouse adaptation than traditional maize varieties. Five generations a year are typical. FFMM is the result of a modified double-cross hybrid between four fast-flowering lines: Neuffer's Early ACR (full color), Alexander's Early Early Synthetic, Tom Thumb Popcorn, and Gaspe Flint, followed by selection for early flowering and desirable morphology throughout an 11-generation selfing regime. Lines A and B were derived from different progeny of the initial hybrid, and crosses between Mini-Maize A and B exhibit heterosis. The ancestry of each genomic region of Mini-Maize A and B was inferred from the four founder populations using genotyping by sequencing. Other genetic and genomic tools for these lines include karyotypes for both lines A and B, kernel genetic markers y1 (white endosperm) and R1-scm2 (purple endosperm and embryo) introgressed into Mini-Maize A, and ∼24× whole-genome resequencing data for Mini-Maize A. PMID:27440866

  5. Influence of multiple orbital effect on shifts of minima in harmonic spectra

    NASA Astrophysics Data System (ADS)

    Wu, Yan; Li, Chaorong; Gong, Cheng; Yu, Yongli; Gong, Shangqing

    2014-09-01

    Using the Lewenstein model combined with the molecular Ammosov-Delone-Krainov ionization theory, laser induced harmonics generated from aligned N2 molecules are calculated. We focus attention on shifts in minima of the harmonic spectra due to interference between harmonics generated from different molecular orbitals (MOs). When harmonic spectra generated from different MOs are of the same intensity (i.e., the “cross” region of the harmonic spectra), interference is most pronounced. We find that contributions to the harmonic spectrum from different MOs respond differently to the change of the laser intensity. This difference in response results in two phenomena. On the one hand, by changing the laser intensity, harmonics generated from an individual MO may become more or less prominent, thus, structure-induced minima can appear. On the other hand, when the laser intensity increases, the “cross” region shifts, and multiple-orbital-interference-induced minima appear at different energies.

  6. Time spans between price maxima and price minima in stock markets

    NASA Astrophysics Data System (ADS)

    Zou, Yongjie; Li, Honggang

    2014-02-01

    We empirically investigate the distribution of time spans between price maxima and price minima in international stock markets, where a time span is defined as the time interval between a local price minimum and a local price maximum, and local price extrema are identified by a method introduced by Preis and Stanley (Preis et al. (2011), Preis (2011), Preis and Stanley (2011, 2010), Preis (2010), Preis and Stanley (2010), Stanley et al. (2010), Preis and Stanley (2009)). The empirical results show that both the tail distributions of time spans from local price maxima to local price minima and the tail distributions of time spans from local price minima to local price maxima yield an exponential distribution. In addition, price rise/fall asymmetry is observed by comparing the values of the exponents of the distribution curves. These results are robust across eight representative stock markets.

  7. Evaluation of Docking Target Functions by the Comprehensive Investigation of Protein-Ligand Energy Minima

    PubMed Central

    Oferkin, Igor V.; Katkova, Ekaterina V.; Sulimov, Alexey V.; Kutov, Danil C.; Sobolev, Sergey I.; Voevodin, Vladimir V.; Sulimov, Vladimir B.

    2015-01-01

    The adequate choice of the docking target function impacts the accuracy of the ligand positioning as well as the accuracy of the protein-ligand binding energy calculation. To evaluate a docking target function we compared positions of its minima with the experimentally known pose of the ligand in the protein active site. We evaluated five docking target functions based on either the MMFF94 force field or the PM7 quantum-chemical method with or without implicit solvent models: PCM, COSMO, and SGB. Each function was tested on the same set of 16 protein-ligand complexes. For exhaustive low-energy minima search the novel MPI parallelized docking program FLM and large supercomputer resources were used. Protein-ligand binding energies calculated using low-energy minima were compared with experimental values. It was demonstrated that the docking target function on the base of the MMFF94 force field in vacuo can be used for discovery of native or near native ligand positions by finding the low-energy local minima spectrum of the target function. The importance of solute-solvent interaction for the correct ligand positioning is demonstrated. It is shown that docking accuracy can be improved by replacement of the MMFF94 force field by the new semiempirical quantum-chemical PM7 method. PMID:26693223

  8. A combined method for determining reaction paths, minima, and transition state geometries

    NASA Astrophysics Data System (ADS)

    Ayala, Philippe Y.; Schlegel, H. Bernhard

    1997-07-01

    Mapping out a reaction mechanism involves optimizing the reactants and products, finding the transition state and following the reaction path connecting them. Transition states can be difficult to locate and reaction paths can be expensive to follow. We describe an efficient algorithm for determining the transition state, minima and reaction path in a single procedure. Starting with an approximate path represented by N points, the path is iteratively relaxed until one of the N points reached the transition state, the end points optimize to minima and the remaining points converged to a second order approximation of the steepest descent path. The method appears to be more reliable than conventional transition state optimization algorithms, and requires only energies and gradients, but not second derivative calculations. The procedure is illustrated by application to a number of model reactions. In most cases, the reaction mechanism can be described well using 5 to 7 points to represent the transition state, the minima and the path. The computational cost of relaxing the path is less than or comparable to the cost of standard techniques for finding the transition state and the minima, determining the transition vector and following the reaction path on both sides of the transition state.

  9. Biological control of common salvinia (Salvinia minima) in Louisiana using Cyrtobagous salviniae (Coleoptera: curculionidae)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Common salvinia, Salvinia minima Baker, is an aquatic invasive fern that obstructs waterways and impacts water quality throughout the southeastern United States. In an effort to establish populations for classical biological control, the weevil, Cyrtobagous salviniae Calder and Sands, was released a...

  10. Release and evaluation of Cyrtobagous salviniae on common salvinia minima in southern Louisiana

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Common salvinia (Salvinia minima) is one of the most widespread, non-native invasive species at the Barataria Preserve of Jean Lafitte National Historical Park and Preserve in southern Louisiana and currently infests more than 3,600 ha and 48 km of navigable waterways. A proven biological control a...

  11. Multiple local minima in radiotherapy optimization problems with dose-volume constraints.

    PubMed

    Deasy, J O

    1997-07-01

    The cause of multiple local minima in beam weight optimization problems subject to dose-volume constraints is analyzed. Three objective functions were considered: (a) maximization of tumor control probability (TCP), (b) maximization of the minimum target dose, and (c) minimization of the mean-squared-deviation of the target dose from the prescription dose. It is shown that: (a) TCP models generally result in strongly quasiconvex objective functions; (b) maximization of the minimum target dose results in a strongly quasiconvex objective function; and (c) minimizing the root-mean-square dose deviation results in a convex objective function. Dose-volume constraints are considered such that, for each region at risk (RAR), the volume of tissue whose dose exceeds a certain tolerance dose (DTol) is kept equal to or below a given fractional level (VTol). If all RARs lack a "volume effect" (i.e., VTol = 0 for all RARs) then there is a single local minimum. But if volume effects are present, then the feasible space is possibly nonconvex and therefore possibly leads to multiple local minima. These conclusions hold for all three objective functions. Hence, possible local minima come not from the nonlinear nature of the objective functions considered, but from the "either this volume or that volume but not both" nature of the volume effect. These observations imply that optimization algorithms for dose-volume constraint types of problems should have effective strategies for dealing with multiple local minima. PMID:9243478

  12. Checklist of insects associated with Salvinia minima (Baker) in Louisiana, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    his study presents a list of adult insects (excluding Diptera and Lepidoptera) collected from an infestation of an invasive aquatic weed, common salvinia (Salvinia minima Baker), in southern Louisiana, USA. Insects were sampled from May – November of 2009 and 2010 using floating pitfall traps. A to...

  13. Influence of shape resonances on minima in cross sections for photoionization of excited atoms

    SciTech Connect

    Felfli, Z.; Manson, S.T. Department of Astronomy, Georgia State University, Atlanta, Georgia 30303 )

    1990-02-01

    A relationship between the location of Cooper minima and the difference between the quantum defect of the initial state and the threshold phase shift (in units of {pi}) of the final state in excited photoionization has been suggested earlier (Phys. Rev. Lett. 48, 473 (1982)). The existence of a shape resonance in the final state is shown to modify this relationship.

  14. Spontaneous Detachment of Colloids from Primary Energy Minima by Brownian Diffusion

    PubMed Central

    Wang, Zhan; Jin, Yan; Shen, Chongyang; Li, Tiantian; Huang, Yuanfang; Li, Baoguo

    2016-01-01

    The Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profile has been frequently used to interpret the mechanisms controlling colloid attachment/detachment and aggregation/disaggregation behavior. This study highlighted a type of energy profile that is characterized by a shallow primary energy well (i.e., comparable to the average kinetic energy of a colloid) at a small separation distance and a monotonic decrease of interaction energy with separation distance beyond the primary energy well. This energy profile is present due to variations of height, curvature, and density of discrete physical heterogeneities on collector surfaces. The energy profile indicates that colloids can be spontaneously detached from the shallow primary energy well by Brownian diffusion. The spontaneous detachment from primary minima was unambiguously confirmed by conducting laboratory column transport experiments involving flow interruptions for two model colloids (polystyrene latex microspheres) and engineered nanoparticles (fullerene C60 aggregates). Whereas the spontaneous detachment has been frequently attributed to attachment in secondary minima in the literature, our study indicates that the detached colloids could be initially attached at primary minima. Our study further suggests that the spontaneous disaggregation from primary minima is more significant than spontaneous detachment because the primary minimum depth between colloid themselves is lower than that between a colloid and a collector surface. PMID:26784446

  15. Third Minima in Thorium and Uranium Isotopes in a Self-Consistent Theory

    SciTech Connect

    McDonnell, J. D.

    2013-01-01

    Background: Well-developed third minima, corresponding to strongly elongated and reflection-asymmetric shapes associated with dimolecular configurations, have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential-energy surfaces in the third minimum region.

    Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular (cluster) states. We study the isentropic potential-energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects.

    Methods: We use the finite-temperature superfluid nuclear density functional theory. We consider two Skyrme energy density functionals: a traditional functional SkM and a recent functional UNEDF1 optimized for fission studies.

    Results: We predict very shallow or no third minima in the potential-energy surfaces of 232Th and 232U. In the lighter Th and U isotopes with N = 136 and 138, the third minima are better developed. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly magic 132Sn and a lighter deformed Zr or Mo fragment. The potential-energy surfaces for 228,232Th and 232U at several excitation energies are presented. We also study isotopic chains to demonstrate the evolution of the depth of the third minimum with neutron number.

    Conclusions: We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr andMo isotopes around N = 58.We demonstrate that the depth of

  16. Third minima in thorium and uranium isotopes in a self-consistent theory

    NASA Astrophysics Data System (ADS)

    McDonnell, J. D.; Nazarewicz, W.; Sheikh, J. A.

    2013-05-01

    Background: Well-developed third minima, corresponding to strongly elongated and reflection-asymmetric shapes associated with dimolecular configurations, have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential-energy surfaces in the third minimum region.Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular (cluster) states. We study the isentropic potential-energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects.Methods: We use the finite-temperature superfluid nuclear density functional theory. We consider two Skyrme energy density functionals: a traditional functional SkM* and a recent functional UNEDF1 optimized for fission studies.Results: We predict very shallow or no third minima in the potential-energy surfaces of 232Th and 232U. In the lighter Th and U isotopes with N=136 and 138, the third minima are better developed. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly magic 132Sn and a lighter deformed Zr or Mo fragment. The potential-energy surfaces for 228,232Th and 232U at several excitation energies are presented. We also study isotopic chains to demonstrate the evolution of the depth of the third minimum with neutron number.Conclusions: We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr and Mo isotopes around N=58. We demonstrate that the depth of the third minimum

  17. Dust around young stars. Observations of the polarization of UX Ori in deep minima

    SciTech Connect

    Voshchinnikov, N.V.; Grinin, V.P.; Kiselev, N.N.; Minikulov, N.K.

    1988-09-01

    Photometric and polarimetric monitoring observations of UX Ori begun in 1986 in the Crimea and Bolivia have resulted in the observation of two deep minima of the brightness during which a growth of the linear polarization (to approx. =7%) was observed, together with a tendency for the circular polarization to increase (up to approx. =1%). Analysis of the observational data shows that the main source of the polarized radiation in the deep minima is the emission of the star scattered by grains of circumstellar dust. On the basis of Mie's theory for a polydisperse graphite-silicate mixtures of particles the optical properties of ellipsoidal dust envelopes have been calculated and a model of the Algol-like minimum constructed.

  18. The 2p photoionization of ground-state sodium in the vicinity of Cooper minima

    NASA Astrophysics Data System (ADS)

    Liu, Xiaobin; Shi, Yinglong; Dong, Chenzhong

    2016-07-01

    The photoionization processes of ground-state sodium have been investigated with the multiconfiguration Dirac–Fock method. The results are in good or at least reasonable agreement with available experimental and theoretical data. In the energy region near the threshold, the cross sections show non-monotonic changes because of Cooper minima, which due to the sign changes of dominant dipole matrix elements and are very sensitive to electron correlations. As the energy increases continuously, the radial wave functions of the photoelectrons will move towards the nucleus. The values of the cross sections, and hence the Cooper minima, mainly depend on the relative positions of the one-electron radial wave functions of the initial bound electrons 2{p}1/{2,3/2} and the continuum photoelectrons.

  19. The solar wind during current and past solar minima and maxima

    NASA Astrophysics Data System (ADS)

    Zerbo, J.-L.; Richardson, J. D.

    2015-12-01

    This paper presents solar wind data from the last five solar cycles. We review solar wind parameters over the four solar minima and five maxima for which spacecraft data are available and show the recovery from the last very weak minimum to the current solar maximum. The solar wind magnetic field, speed, and density have remained anomalously low in this time period. However, the distributions of these parameters about the (lower than normal) average are similar to those from previous solar minima and maxima. This result suggests that the acceleration mechanism for the recent weak solar wind is probably not significantly different from earlier solar cycles. The He++/H+ ratio variation with solar cycle continues to be a function of speed, but the most recent solar minimum has significantly lower ratios than in the previous solar cycle.

  20. Cooper minima and Young-type interferences in the photoionization of H{sub 2}{sup +}

    SciTech Connect

    Della Picca, R.; Fainstein, P. D.; Dubois, A.

    2011-09-15

    We present a detailed study of the partial and total cross sections for photon-induced electron emission from H{sub 2}{sup +}. By comparing the results employing exact and approximate, bounded and continuum wave functions, for one- and two-center basis functions, we find the origin and position of the Cooper-like minima in the partial cross sections and their relationship with the Young-type interference pattern.

  1. Theoretical analysis of the single-particle states in the secondary minima of fissioning nuclei

    NASA Astrophysics Data System (ADS)

    Dudek, J.; Nazarewicz, W.; Faessler, A.

    1984-01-01

    The structure of the single-particle levels in the secondary minima of fissioning nuclei is analysed with the help of the deformed Woods-Saxon potential. The parametrisation of the spin-orbit part of the potential at large elongations is analysed in detail. A set of parameters is found which reproduces simultaneously results of the g-factor measurements for 239mPu, 237mpu and 239mAm, the data on single-particle resonances in the secondary minima of 231Th, 233Th, and which also gives rise to a significant energy gap at the neutron magic number N0 = 146 ( ΔE~ 1.3 MeV). The structure of the single-particle states around N0 = 146 is analysed and the results are compared with the existing experimental information. The total enegy surfaces are recalculated with the new-found parametrisation of the potential; an overall improvement of the barrier characteristics is found. Decoupling parameters and g-factors are tabulated for deformations corresponding to the secondary minima.

  2. Scale-estimation of quantum coherent energy transport in multiple-minima systems

    PubMed Central

    Farrow, Tristan; Vedral, Vlatko

    2014-01-01

    A generic and intuitive model for coherent energy transport in multiple minima systems coupled to a quantum mechanical bath is shown. Using a simple spin-boson system, we illustrate how a generic donor-acceptor system can be brought into resonance using a narrow band of vibrational modes, such that the transfer efficiency of an electron-hole pair (exciton) is made arbitrarily high. Coherent transport phenomena in nature are of renewed interest since the discovery that a photon captured by the light-harvesting complex (LHC) in photosynthetic organisms can be conveyed to a chemical reaction centre with near-perfect efficiency. Classical explanations of the transfer use stochastic diffusion to model the hopping motion of a photo-excited exciton. This accounts inadequately for the speed and efficiency of the energy transfer measured in a series of recent landmark experiments. Taking a quantum mechanical perspective can help capture the salient features of the efficient part of that transfer. To show the versatility of the model, we extend it to a multiple minima system comprising seven-sites, reminiscent of the widely studied Fenna-Matthews-Olson (FMO) light-harvesting complex. We show that an idealised transport model for multiple minima coupled to a narrow-band phonon can transport energy with arbitrarily high efficiency. PMID:24980547

  3. Minima of the fluctuations of the order parameter of global seismicity

    SciTech Connect

    Sarlis, N. V. Christopoulos, S.-R. G.; Skordas, E. S.

    2015-06-15

    It has been recently shown [N. V. Sarlis, Phys. Rev. E 84, 022101 (2011) and N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012)] that earthquakes of magnitude M greater or equal to 7 are globally correlated. Such correlations were identified by studying the variance κ{sub 1} of natural time which has been proposed as an order parameter for seismicity. Here, we study the fluctuations of this order parameter using the Global Centroid Moment Tensor catalog for a magnitude threshold M{sub thres} = 5.0 and focus on its behavior before major earthquakes. Natural time analysis reveals that distinct minima of the fluctuations of the order parameter of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than 8.4. This phenomenon corroborates the recent finding [N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013)] that similar minima of the seismicity order parameter fluctuations had preceded all major shallow earthquakes in Japan. Moreover, on the basis of these minima a statistically significant binary prediction method for earthquakes of magnitude larger than 8.4 with hit rate 100% and false alarm rate 6.67% is suggested.

  4. Dynamics of driven transitions between minima of a complex energy landscapes

    NASA Astrophysics Data System (ADS)

    Pusuluri, Sai Teja; Lang, Alex H.; Mehta, Pankaj; Castillo, Horacio E.

    We recently modeled cellular interconvertion dynamics by using an epigenetic landscape model inspired by neural network models. Given an arbitrary set of patterns, the model can be used to construct an energy landscape in which those patterns are the global minima. Here we study the transitions between stable states of the landscapes thus constructed, under the effect of an external driving force. We consider three different cases: i) choosing the patterns to be random and independendently distributed ii) choosing a set of patterns directly derived from the experimental cellular transcription factor expression data for a representative set of cell types in an organism and iii) choosing randomly generated trees of hierarchically correlated patterns, inspired by biology. For each of the three cases, we study the stability of the global minima against thermal fluctuations and external driving forces, and the dynamics of the driven transitions away from global minima. We compare the results obtained in the three cases defined above, and in particular we explore to what degree the correlations between patterns affect the transition dynamics.

  5. Grand solar minima and maxima deduced from 10Be and 14C: magnetic dynamo configuration and polarity reversal

    NASA Astrophysics Data System (ADS)

    Inceoglu, F.; Simoniello, R.; Knudsen, M. F.; Karoff, C.; Olsen, J.; Turck-Chiéze, S.; Jacobsen, B. H.

    2015-05-01

    Aims: This study aims to improve our understanding of the occurrence and origin of grand solar maxima and minima. Methods: We first investigate the statistics of peaks and dips simultaneously occurring in the solar modulation potentials reconstructed using the Greenland Ice Core Project (GRIP) 10Be and IntCal13 14C records for the overlapping time period spanning between ~1650 AD to 6600 BC. Based on the distribution of these events, we propose a method to identify grand minima and maxima periods. By using waiting time distribution analysis, we investigate the nature of grand minima and maxima periods identified based on the criteria as well as the variance and significance of the Hale cycle during these kinds of events throughout the Holocene epoch. Results: Analysis of grand minima and maxima events occurring simultaneously in the solar modulation potentials, reconstructed based on the 14C and the 10Be records, shows that the majority of events characterized by periods of moderate activity levels tend to last less than 50 years: grand maxima periods do not last longer than 100 years, while grand minima can persist slightly longer. The power and the variance of the 22-year Hale cycle increases during grand maxima and decreases during grand minima, compared to periods characterized by moderate activity levels. Conclusions: We present the first reconstruction of the occurrence of grand solar maxima and minima during the Holocene based on simultaneous changes in records of past solar variability derived from tree-ring 14C and ice-core 10Be, respectively. This robust determination of the occurrence of grand solar minima and maxima periods will enable systematic investigations of the influence of grand solar minima and maxima episodes on Earth's climate.

  6. Polar and equatorial coronal hole winds at solar minima: From the heliosphere to the inner corona

    SciTech Connect

    Zhao, L.; Landi, E.

    2014-02-01

    Fast solar wind can be accelerated from at least two different sources: polar coronal holes and equatorial coronal holes. Little is known about the relationship between the wind coming from these two different latitudes and whether these two subcategories of fast wind evolve in the same way during the solar cycle. Nineteen years of Ulysses observations, from 1990 to 2009, combined with ACE observations from 1998 to the present provide us with in situ measurements of solar wind properties that span two entire solar cycles. These missions provide an ideal data set to study the properties and evolution of the fast solar wind originating from equatorial and polar holes. In this work, we focus on these two types of fast solar wind during the minima between solar cycles 22 and 23 and 23 and 24. We use data from SWICS, SWOOPS, and VHM/FGM on board Ulysses and SWICS, SWEPAM, and MAG on board ACE to analyze the proton kinetic, thermal, and dynamic characteristics, heavy ion composition, and magnetic field properties of these two fast winds. The comparison shows that: (1) their kinetic, thermal, compositional, and magnetic properties are significantly different at any time during the two minima and (2) they respond differently to the changes in solar activity from cycle 23 to 24. These results indicate that equatorial and polar fast solar wind are two separate subcategories of fast wind. We discuss the implications of these results and relate them to remote-sensing measurements of the properties of polar and equatorial coronal holes carried out in the inner corona during these two solar minima.

  7. Polar and Equatorial Coronal Hole Winds at Solar Minima: From the Heliosphere to the Inner Corona

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Landi, E.

    2014-02-01

    Fast solar wind can be accelerated from at least two different sources: polar coronal holes and equatorial coronal holes. Little is known about the relationship between the wind coming from these two different latitudes and whether these two subcategories of fast wind evolve in the same way during the solar cycle. Nineteen years of Ulysses observations, from 1990 to 2009, combined with ACE observations from 1998 to the present provide us with in situ measurements of solar wind properties that span two entire solar cycles. These missions provide an ideal data set to study the properties and evolution of the fast solar wind originating from equatorial and polar holes. In this work, we focus on these two types of fast solar wind during the minima between solar cycles 22 and 23 and 23 and 24. We use data from SWICS, SWOOPS, and VHM/FGM on board Ulysses and SWICS, SWEPAM, and MAG on board ACE to analyze the proton kinetic, thermal, and dynamic characteristics, heavy ion composition, and magnetic field properties of these two fast winds. The comparison shows that: (1) their kinetic, thermal, compositional, and magnetic properties are significantly different at any time during the two minima and (2) they respond differently to the changes in solar activity from cycle 23 to 24. These results indicate that equatorial and polar fast solar wind are two separate subcategories of fast wind. We discuss the implications of these results and relate them to remote-sensing measurements of the properties of polar and equatorial coronal holes carried out in the inner corona during these two solar minima.

  8. Theoretical studies of the global minima and polarizabilities of small lithium clusters

    NASA Astrophysics Data System (ADS)

    Hu, Han-Shi; Zhao, Ya-Fan; Hammond, Jeff R.; Bylaska, Eric J.; Aprà, Edoardo; van Dam, Hubertus J. J.; Li, Jun; Govind, Niranjan; Kowalski, Karol

    2016-01-01

    Lithium clusters Lin (n = 1-20) have been investigated with density functional theory (DFT) and coupled-cluster (CC) methods. The global minima are located via an improved basin-hopping algorithm. Simulated polarizabilities are in good agreement with the measured data generally. The simulated polarizabilities for Li6, Li12 and Li19 are in reasonable agreement when thermal effects are included, except the Li3 cluster. A linear correlation for the inverse relationship between the CCSD calculated polarizabilities and ionization potential (IP) has been reported to have the linear coefficient of 0.996, which further strengthens our simulations.

  9. Times of Minima and New Ephemerides for Southern Hemisphere Eclipsing Binary Stars Observed in 2015

    NASA Astrophysics Data System (ADS)

    Pavlov, H.; Mallama, A.; Loader, B.; Kerr, S.

    2016-06-01

    Observers from Australia and New Zealand used video equipment to time eclipses of short-period binary stars. The objects were typically south of -20o declination and had periods of less than a day. Many of those systems had very few observations since their discovery and some of them had not been observed for 50 or more years. We present 44 times of minima of 42 stars, provide revised ephemerides for 7 of these systems and characterize an orbital period change for RW PsA.

  10. Times of Minima and New Ephemerides for Southern Hemisphere Eclipsing Binary Stars Observed in 2015

    NASA Astrophysics Data System (ADS)

    Pavlov, H.; Mallama, A.; Loader, B.; Kerr, S.

    2016-04-01

    Observers from Australia and New Zealand used video equipment to time eclipses of short-period binary stars. The objects were typically south of -20o declination and had periods of less than a day. Many of those systems had very few observations since their discovery and some of them had not been observed for 50 or more years. We present 44 times of minima of 42 stars, provide revised ephemerides for 7 of these systems and characterize an orbital period change for RW PsA.

  11. STRUCTURE IN THE 3D GALAXY DISTRIBUTION. II. VOIDS AND WATERSHEDS OF LOCAL MAXIMA AND MINIMA

    SciTech Connect

    Way, M. J.; Gazis, P. R.; Scargle, Jeffrey D. E-mail: PGazis@sbcglobal.net

    2015-01-20

    The major uncertainties in studies of the multi-scale structure of the universe arise not from observational errors but from the variety of legitimate definitions and detection methods for individual structures. To facilitate the study of these methodological dependencies, we have carried out 12 different analyses defining structures in various ways. This has been done in a purely geometrical way by utilizing the HOP algorithm as a unique parameter-free method of assigning groups of galaxies to local density maxima or minima. From three density estimation techniques (smoothing kernels, Bayesian blocks, and self-organizing maps) applied to three data sets (the Sloan Digital Sky Survey Data Release 7, the Millennium simulation, and randomly distributed points) we tabulate information that can be used to construct catalogs of structures connected to local density maxima and minima. We also introduce a void finder that utilizes a method to assemble Delaunay tetrahedra into connected structures and characterizes regions empty of galaxies in the source catalog.

  12. Systematic Phase Diagram of LiSi and LiAl compounds from Minima Hopping Method

    NASA Astrophysics Data System (ADS)

    Romero, Aldo; Marques, Miguel; Botti, Silvana; Sarmiento-Pérez, Rafael; Valencia-Jaime, Irais; Amsler, Max; Goedecker, Stefan

    2014-03-01

    We performed an extensive theoretical exploration of the structural phase diagram of LiSi and LiAl alloys through global structural prediction. These compounds have very interesting properties. For example, LiSi alloys have been considered for high energy density anodes for future rechargeable battery technology, while LiAl alloys are expected to have applications in the field of structural components due to its light weight and maleability. The global structural prediction was performed with the minima hopping method. In this method the low energy structures are obtained by solving a set of dynamical equations of motion that allows efficient visits to local minima on the Born Oppenheimer surface. We found very good agreement between our simulations and previously reported stoichiometries. Moreover, we were able to identify several novel thermodynamically stable compositions that have not been previously synthesized. The ground-state structures were further characterized both structurally and electronically. Our calculations show that global structural prediction is a very powerful tool to predict new thermodynamically stable materials, and that it consistently outperforms other methods commonly used. Support from ACS-PRF #54075-ND10 is recognized.

  13. Enhanced docking with the mining minima optimizer: acceleration and side-chain flexibility.

    PubMed

    Kairys, Visvaldas; Gilson, Michael K

    2002-12-01

    The ligand-protein docking algorithm based on the Mining Minima method has been substantially enhanced. First, the basic algorithm is accelerated by: (1) adaptively determining the extent of each energy well to help avoid previously discovered energy minima; (2) biasing the search away from ligand positions at the surface of the receptor to prevent the ligand from staying at the surface when large sampling regions are used; (3) quickly testing multiple different ligand positions and orientations for each ligand conformation; and (4) tuning the source code to increase computational efficiency. These changes markedly shorten the time needed to discover an accurate result, especially when large sampling regions are used. The algorithm now also allows user-selected receptor sidechains to be treated as mobile during the docking procedure. The energies associated with the mobile side chains are computed as if they belonged to the ligand, except that atoms at the boundary between side chains and the rigid backbone are treated specially. This new capability is tested for several well-known ligand/protein systems, and preliminary application to an enzyme whose substrate is unknown--the recently solved hypothetical protein YecO (HI0319) from Haemophilus influenzae--indicates that side-chains relaxations allow candidate substrates of various sizes to be accommodated. PMID:12395431

  14. A genetic survey of Salvinia minima in the southern United States

    USGS Publications Warehouse

    Madeira, Paul T.; Jacono, C.C.; Tipping, Phil; Van, Thai K.; Center, Ted D.

    2003-01-01

    The genetic relationships among 68 samples of Salvinia minima (Salviniaceae) were investigated using RAPD analysis. Neighbor joining, principle components, and AMOVA analyses were used to detect differences among geographically referenced samples within and outside of Florida. Genetic distances (Nei and Li) range up to 0.48, although most are under 0.30, still relatively high levels for an introduced, clonally reproducing plant. Despite the diversity AMOVA analysis yielded no indication that the Florida plants, as a group, were significantly different from the plants sampled elsewhere in its adventive, North American range. A single, genetically dissimilar population probably exists in the recent (1998) horticultural introduction to Mississippi. When the samples were grouped into 10 regional (but artificial) units and analyzed using AMOVA the between region variance was only 7.7%. Genetic similarity among these regions may indicate introduction and dispersal from common sources. The reduced aggressiveness of Florida populations (compared to other states) may be due to herbivory. The weevil Cyrtobagous salviniae, a selective feeder, is found in Florida but not other states. The genetic similarity also suggests that there are no obvious genetic obstacles to the establishment or efficacy of C. salviniae as a biological control agent on S. minima outside of Florida.

  15. Ultrasound-Assisted Extraction, Antioxidant and Anticancer Activities of the Polysaccharides from Rhynchosia minima Root.

    PubMed

    Jia, Xuejing; Zhang, Chao; Hu, Jie; He, Muxue; Bao, Jiaolin; Wang, Kai; Li, Peng; Chen, Meiwan; Wan, Jianbo; Su, Huanxing; Zhang, Qingwen; He, Chengwei

    2015-01-01

    Box-Behnken design (BBD), one of the most common response surface methodology (RSM) methods, was used to optimize the experimental conditions for ultrasound-assisted extraction of polysaccharides from Rhynchosia minima root (PRM). The antioxidant abilities and anticancer activity of purified polysaccharide fractions were also measured. The results showed that optimal extraction parameters were as follows: ultrasound exposure time, 21 min; ratio of water to material, 46 mL/g; ultrasound extraction temperature, 63 °C. Under these conditions, the maximum yield of PRM was 16.95%±0.07%. Furthermore, the main monosaccharides of purified fractions were Ara and Gal. PRM3 and PRM5 exhibited remarkable DPPH radical scavenging activities and reducing power in vitro. PRM3 showed strong inhibitory activities on the growth of MCF-7 cells in vitro. The above results indicate that polysaccharides from R. minima root have the potential to be developed as natural antioxidants and anticancer ingredients for the food and pharmaceutical industries. PMID:26610456

  16. Annual ionospheric variations of the critical frequency foF2 at the equatorial stations during the solar minima

    NASA Astrophysics Data System (ADS)

    Biktash, Lilia

    2016-07-01

    We have analyzed annual ionospheric variations of the critical frequency foF2 at the equatorial stations during the solar minima. There are essential distinctions between the global TEC (total electron content) and foF2 annual variations during the last two solar minima. Many authors concluded that the annual means of foF2 and the global TEC were reduced, while others investigations no found essential variations as compared with the previous solar minimum. Most if not all of authors suppose that the possible source of this phenomenon is the low level of the EUV (extreme ultraviolet) during the solar minima. The aim of our paper is to amplify these conclusions or to propose new factor which can change ionosphere parameters during the solar minima. We calculated annual variations of foF2 at the equatorial stations and compared these data with Dst annual variations. We found that in addition to low level of the EUV during the solar minima, geomagnetic storms effects have to be included as the influencing factor on annual ionospheric variations.

  17. Absence of multiple local minima effects in intensity modulated optimization with dose-volume constraints

    NASA Astrophysics Data System (ADS)

    Llacer, Jorge; Deasy, Joseph O.; Bortfeld, Thomas R.; Solberg, Timothy D.; Promberger, Claus

    2003-01-01

    This paper reports on the analysis of intensity modulated radiation treatment optimization problems in the presence of non-convex feasible parameter spaces caused by the specification of dose-volume constraints for the organs-at-risk (OARs). The main aim was to determine whether the presence of those non-convex spaces affects the optimization of clinical cases in any significant way. This was done in two phases: (1) Using a carefully designed two-dimensional mathematical phantom that exhibits two controllable minima and with randomly initialized beamlet weights, we developed a methodology for exploring the nature of the convergence characteristics of quadratic cost function optimizations (deterministic or stochastic). The methodology is based on observing the statistical behaviour of the residual cost at the end of optimizations in which the stopping criterion is progressively more demanding and carrying out those optimizations to very small error changes per iteration. (2) Seven clinical cases were then analysed with dose-volume constraints that are stronger than originally used in the clinic. The clinical cases are two prostate cases differently posed, a meningioma case, two head-and-neck cases, a spleen case and a spine case. Of the 14 different sets of optimizations (with and without the specification of maximum doses allowed for the OARs), 12 fail to show any effect due to the existence of non-convex feasible spaces. The remaining two sets of optimizations show evidence of multiple minima in the solutions, but those minima are very close to each other in cost and the resulting treatment plans are practically identical, as measured by the quality of the dose-volume histograms (DVHs). We discuss the differences between fluence maps resulting from those similar treatment plans. We provide a possible reason for the observed results and conclude that, although the study is necessarily limited, the annealing characteristics of a simulated annealing method may not be

  18. Absence of multiple local minima effects in intensity modulated optimization with dose-volume constraints.

    PubMed

    Llacer, Jorge; Deasy, Joseph O; Portfeld, Thomas R; Solberg, Timothy D; Promberger, Claus

    2003-01-21

    This paper reports on the analysis of intensity modulated radiation treatment optimization problems in the presence of non-convex feasible parameter spaces caused by the specification of dose-volume constraints for the organs-at-risk (OARs). The main aim was to determine whether the presence of those non-convex spaces affects the optimization of clinical cases in any significant way. This was done in two phases: (1) Using a carefully designed two-dimensional mathematical phantom that exhibits two controllable minima and with randomly initialized beamlet weights, we developed a methodology for exploring the nature of the convergence characteristics of quadratic cost function optimizations (deterministic or stochastic). The methodology is based on observing the statistical behaviour of the residual cost at the end of optimizations in which the stopping criterion is progressively more demanding and carrying out those optimizations to very small error changes per iteration. (2) Seven clinical cases were then analysed with dose-volume constraints that are stronger than originally used in the clinic. The clinical cases are two prostate cases differently posed, a meningioma case, two head-and-neck cases, a spleen case and a spine case. Of the 14 different sets of optimizations (with and without the specification of maximum doses allowed for the OARs), 12 fail to show any effect due to the existence of non-convex feasible spaces. The remaining two sets of optimizations show evidence of multiple minima in the solutions, but those minima are very close to each other in cost and the resulting treatment plans are practically identical, as measured by the quality of the dose-volume histograms (DVHs). We discuss the differences between fluence maps resulting from those similar treatment plans. We provide a possible reason for the observed results and conclude that, although the study is necessarily limited, the annealing characteristics of a simulated annealing method may not be

  19. MinFinder: Locating all the local minima of a function

    NASA Astrophysics Data System (ADS)

    Tsoulos, Ioannis G.; Lagaris, Isaac E.

    2006-01-01

    A new stochastic clustering algorithm is introduced that aims to locate all the local minima of a multidimensional continuous and differentiable function inside a bounded domain. The accompanying software (MinFinder) is written in ANSI C++. However, the user may code his objective function either in C++, C or Fortran 77. We compare the performance of this new method to the performance of Multistart and Topographical Multilevel Single Linkage Clustering on a set of benchmark problems. Program summaryTitle of program:MinFinder Catalogue identifier:ADWU Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWU Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer for which the program is designed and others on which is has been tested:The tool is designed to be portable in all systems running the GNU C++ compiler Installation:University of Ioannina, Greece Programming language used:GNU-C++, GNU-C, GNU Fortran 77 Memory required to execute with typical data:200 KB No. of bits in a word:32 No. of processors used:1 Has the code been vectorized or parallelized?:no No. of lines in distributed program, including test data, etc.:5797 No. of bytes in distributed program, including test data, etc.:588 121 Distribution format:gzipped tar file Nature of the physical problem:A multitude of problems in science and engineering are often reduced to minimizing a function of many variables. There are instances that a local optimum does not correspond to the desired physical solution and hence the search for a better solution is required. Local optimization techniques can be trapped in any local minimum. Global optimization is then the appropriate tool. For example, solving a non-linear system of equations via optimization, employing a "least squares" type of objective, one may encounter many local minima that do not correspond to solutions, i.e. they are far from zero. Method of solution:Using a uniform pdf, points are sampled from the

  20. Polar cap magnetic field reversals during solar grand minima: could pores play a role?

    NASA Astrophysics Data System (ADS)

    Švanda, Michal; Brun, Allan Sacha; Roudier, Thierry; Jouve, Laurène

    2016-02-01

    We study the magnetic flux carried by pores located outside active regions with sunspots and investigate their possible contribution to the reversal of the global magnetic field of the Sun. We find that they contain a total flux of comparable amplitude to the total magnetic flux contained in polar caps. The pores located at distances of 40-100 Mm from the closest active region systematically have the correct polarity of the magnetic field to contribute to the polar cap reversal. These pores can be found predominantly in bipolar magnetic regions. We propose that during grand minima of solar activity, such a systematic polarity trend, which is akin to a weak magnetic (Babcock-Leighton-like) source term, could still be operating but was missed by the contemporary observers because of the limited resolving power of their telescopes.

  1. Global energy minima of molecular clusters computed in polynomial time with semidefinite programming.

    PubMed

    Kamarchik, Eugene; Mazziotti, David A

    2007-12-14

    The global energy minima of pure and binary molecular clusters with 5-12 particles interacting pairwise are computed in polynomial time as a function of only the two-particle reduced density function (2-RDF). We derive linear matrix inequalities from the classical analogue of quantum N-representability constraints to ensure that the 2-RDF represents realistic N-particle configurations. The 2-RDF reformulation relaxes a combinatorial optimization into a convex optimization that scales polynomially in computer time. Clusters are optimized with a code for large-scale semidefinite programming developed for the quantum representability problem [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)10.1103/PhysRevLett.93.213001]. PMID:18233446

  2. Shear-deformation-potential constant of the conduction-band minima of Si: Pseudopotential calculations

    NASA Astrophysics Data System (ADS)

    Li, Ming-Fu; Gu, Zong-Quan; Wang, Jian-Qing

    1990-09-01

    We have calculated the value of the shear-deformation-potential constant Ξu of the conduction-band minima of Si and its temperature coefficient dΞu/dT. The value of Ξu is 9.0 eV for an ab initio pseudopotential calculation and 10.8 eV by the empirical-pseudopotential method (EPM), in good agreement with our experiment. The EPM calculations of the temperature dependence of Ξu yield the values of (dΞu/dT)||DW=-0.04 meV/K due to the Debye-Waller contribution, and (dΞu/dT)||TE=-0.04 meV/K for thermal expansion. We suspect and suggest that the existing experimental value of dΞu/dT~=+3 meV/K is unreliable due to large experimental uncertainty.

  3. A concept for reducing oceanic separation minima through the use of a TCAS-derived CDTI

    NASA Technical Reports Server (NTRS)

    Love, W. D.; Mcfarland, A. L.; Ludwick, J. S.

    1984-01-01

    A concept for using a cockpit display of traffic information (CDTI), as derived from a modified version of the Traffic Alert and Collision Avoidance System 2 (TCAS 2), to support reductions in air traffic separation minima for an oceanic track system is presented. The concept, and the TCAS modifications required to support it, are described. The feasibility of the concept is examined from a number of standpoints, including expected benefits, maximum alert rates, and possible transition strategies. Various implementation issues are analyzed. Pilot procedures are suggested for dealing with alert situations. Possible variations of the concept are also examined. Finally, recommendations are presented for other studies and simulation experiments which can be used to further verify the feasibility of the concept.

  4. Properties of Supergranulation During the Solar Minima of Cycles 22/23 and 23/24

    NASA Technical Reports Server (NTRS)

    Williams, Peter E.; Pesnell, W. Dean

    2011-01-01

    The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended duration. Among the various fields of study, the evolution of the solar convection zone may provide insight into the causes and consequences of this recent minimum. This study continues previous investigations of the characteristics of solar supergranulation, a convection component strongly linked to the structure of the magnetic field, namely the time-evolution of the global mean of supergranule cell size, determined from spectral analysis of MDI Dopplergrams from the two previous solar minima. Analyses of the global mean of supergranule sizes show a quasi-oscillatory nature to the evolution of this particular supergranule characteristic. Performing similar analyses on realistic, synthetic Doppler images show similar time-dependent characteristics. We conclude that the observed fluctuations are not observational artifacts, and that an underlying trend exists within the evolution of the supergranulation network.

  5. Accurate prediction of interference minima in linear molecular harmonic spectra by a modified two-center model

    NASA Astrophysics Data System (ADS)

    Xin, Cui; Di-Yu, Zhang; Gao, Chen; Ji-Gen, Chen; Si-Liang, Zeng; Fu-Ming, Guo; Yu-Jun, Yang

    2016-03-01

    We demonstrate that the interference minima in the linear molecular harmonic spectra can be accurately predicted by a modified two-center model. Based on systematically investigating the interference minima in the linear molecular harmonic spectra by the strong-field approximation (SFA), it is found that the locations of the harmonic minima are related not only to the nuclear distance between the two main atoms contributing to the harmonic generation, but also to the symmetry of the molecular orbital. Therefore, we modify the initial phase difference between the double wave sources in the two-center model, and predict the harmonic minimum positions consistent with those simulated by SFA. Project supported by the National Basic Research Program of China (Grant No. 2013CB922200) and the National Natural Science Foundation of China (Grant Nos. 11274001, 11274141, 11304116, 11247024, and 11034003), and the Jilin Provincial Research Foundation for Basic Research, China (Grant Nos. 20130101012JC and 20140101168JC).

  6. Comparison of solar activity during last two minima on turn of Activity Cycles 22/23 and 23/24

    NASA Astrophysics Data System (ADS)

    Gryciuk, Magdalena; Gburek, Szymon; Siarkowski, Marek; Podgorski, Piotr; Sylwester, Janusz; Farnik, Frantisek

    2013-07-01

    The subject of our work is the review and comparison of solar activity during the last two solar minima that occurred between recent activity cycles. We use the soft X-ray global solar corona observations covering the two nine-months long time intervals in 1997/98 and 2009. Data from RF15-I multichannel photometer are used for the penultimate minimum. For the last unusually deep and prolonged solar activity minimum in 2009 the data from SphinX spectrophotometer are used. Comparison of measurements from both minima takes place in the overlapping energy range 2-15 keV. We focus on the active region formation, evolution and flaring productivity during respective minima.

  7. Unveiling the nature of the He II λ4686 periodic minima in η Carinae

    NASA Astrophysics Data System (ADS)

    Teodoro, Mairan; Damineli, Augusto; Richardson, Noel; Moffat, Anthony F. J.; St-Jean, Lucas; Russell, Christopher Michael Post; Gull, Theodore R.; Madura, Thomas; Pollard, Karen; Walter, Frederick M.; Coimbra, Adriano; Prates, Rodrigo; Fernández-Lajús, Eduardo; gamen, roberto; Hickel, Gabriel; Henrique, William; Navarete, Felipe; Andrade, Thiago; Jablonski, Francisco; Corcoran, Michael F.; Hamaguchi, Kenji; Groh, Jose H.; Hillier, Desmond John; Gerd, Weigelt; SASER Team Members; Heathcote, Bernard; Luckas, Paul; Locke, Malcolm; Powles, Jonathan; Bohlsen, Terry

    2016-01-01

    η Carinae is known to be a massive binary system, but some of the orbital parameters remain uncertain. The nature of the periodic minima seen in several spectral features are associated with periastron passages near stellar conjunction, but its nature has been interpreted either as a low excitation event or as an eclipse of the hotter secondary star by the dense inner wind of the primary. We conducted an intense spectroscopic monitoring of the He II λ4686 emission line across the 2014.6 event using ground- and space-based telescopes. Comparison with results from the past two events confirmed the stability of the equivalent width and radial velocity of this line, as well as the strict periodicity of its minima. In combination with different other measurements, the orbital period is 2022.7 (±0.3) d. We adopted a power law model in combination with the total opacity in the line of sight to the apex of the wind-wind collision region obtained from hydrodynamic simulations to reproduce the observed He II λ4686 equivalent width curve. We constrained the orbital inclination to 135°-153° and the longitude of periastron to 234°-252°. Periastron passage occurred on T0(2014.6)=2456874.4 (±1.3) d. With these orbital elements, we successfully reproduced both the equivalent width curve observed from our direct view of the central source and the polar view. This suggests that the He II λ4686 minimum is ultimately caused by an increase in the opacity in the line of sight to the emitting region as the secondary star moves behind the primary star and plunges into denser regions of its wind.

  8. Anti-angiogenic Activity and Mechanism of Sesquiterpene Lactones from Centipeda minima.

    PubMed

    Huang, Weihuan; Yu, Xiaobin; Liang, Ning; Ge, Wei; Kwok, Hin Fai; Lau, Clara Bik-San; Li, Yaolan; Chung, Hau Yin

    2016-04-01

    Centipeda minima is a Chinese herbal medicine used in the treatment of various diseases including cancer. An ethanol extract of the herb, its four fractions with different polarities, and two volatile oils prepared by steam distillation (SD) and supercritical fluid extraction (SFE) were investigated for their anti-angiogenic activity in a wild-type zebrafish model using a quantitative endogenous alkaline phosphatase (EAP) assay. The SFE oil displayed potent anti-angiogenic activity. Fifteen sesquiterpene lactones (SLs; compounds 1-15) isolated from the SFE oil were evaluated for their anti-angiogenic effect. Results revealed that pseudoguaianolide type SLs (1-8) inhibited vessel formation in the zebrafish embryos while guaianolide type SLs (9-15) showed little effect. Among the active ones, 6-O-angeloylenolin (1), a major component of SFE oil, possessed the strongest effect by reducing vessel formation in zebrafish embryos to 40% of the control value at 29.7 µM. Further study using the Tg (fli1a:EGFP) y1-type zebrafish model revealed that it blocked both intersegmental blood vessels (ISVs) and subintestinal vessels plexus (SIVs) formation in zebrafish embryos. Real-time polymerase chain reaction assay on the wild-type zebrafish embryos suggested that 6-O-angeloylenolin affected multiple molecular targets related to angiogenesis including VEGF receptor, angiopoietin, and its receptors. Taken together, our findings demonstrate that C. minima possesses anti-angiogenic activity, and 6-O-angeloylenolin is a promising candidate for the development of an anti-angiogenic agent. PMID:27396185

  9. First-year PSA kinetics and minima after prostate cancer radiotherapy are predictive of overall survival

    SciTech Connect

    Cheung, Rex . E-mail: mrcheung@mdanderson.org; Tucker, Susan L.; Kuban, Deborah A.

    2006-09-01

    Purpose: We analyzed whether first-year prostate-specific antigen (PSA) kinetics and minima are predictive of overall survival (OS). Methods and Materials: The data set contained 1,174 patients treated with external beam radiotherapy (RT) from 1987 to 2001. The relative rate of change ({lambda}) in post-RT PSA values during the first year (13.5 months) was computed using regression analysis of ln(PSA) vs. time. We also computed the PSA minimum (mPSA) reached during the same period. Recursive partitioning analysis was used to identify the relevant cutpoints for the factors being investigated for its association with survival: age, pretreatment PSA, radiation dose, relative rate of change in PSA post-RT, and 1-year PSA minimum. For each of the other factors stage, Gleason score and risk group, all possible cutpoints were considered in the multivariate analyses. Significant factors were considered in the multivariate analyses to identify independent predictors for overall survival. Results: The median value of {lambda} was -1.0 years{sup -1} (range, -11.0-5.1 years{sup -1}). The 1-year minimum had a median of 0.8 ng/mL (range, 0.01-30.9 ng/mL). Recursive partitioning analysis and Cox proportional hazards analyses identified the following pretreatment or treatment factors adversely related to OS: age, Gleason score, stage, and dose. First-year mPSA {>=} 4 ng/mL and {lambda} > 0 were post-RT independent prognostic factors for worse OS. Conclusion: First-year post-RT PSA kinetics and minima are early response parameters predictive of overall survival for prostate cancer patients. These factors may be useful in selecting patients for early salvage therapy.

  10. Solar activity during the Holocene: the Hallstatt cycle and its consequence for grand minima and maxima

    NASA Astrophysics Data System (ADS)

    Usoskin, I. G.; Gallet, Y.; Lopes, F.; Kovaltsov, G. A.; Hulot, G.

    2016-03-01

    Aims: Cosmogenic isotopes provide the only quantitative proxy for analyzing the long-term solar variability over a centennial timescale. While essential progress has been achieved in both measurements and modeling of the cosmogenic proxy, uncertainties still remain in the determination of the geomagnetic dipole moment evolution. Here we aim at improving the reconstruction of solar activity over the past nine millennia using a multi-proxy approach. Methods: We used records of the 14C and 10Be cosmogenic isotopes, current numerical models of the isotope production and transport in Earth's atmosphere, and available geomagnetic field reconstructions, including a new reconstruction relying on an updated archeo- and paleointensity database. The obtained series were analyzed using the singular spectrum analysis (SSA) method to study the millennial-scale trends. Results: A new reconstruction of the geomagnetic dipole field moment, referred to as GMAG.9k, is built for the last nine millennia. New reconstructions of solar activity covering the last nine millennia, quantified in terms of sunspot numbers, are presented and analyzed. A conservative list of grand minima and maxima is also provided. Conclusions: The primary components of the reconstructed solar activity, as determined using the SSA method, are different for the series that are based on 14C and 10Be. This shows that these primary components can only be ascribed to long-term changes in the terrestrial system and not to the Sun. These components have therefore been removed from the reconstructed series. In contrast, the secondary SSA components of the reconstructed solar activity are found to be dominated by a common ≈2400-year quasi-periodicity, the so-called Hallstatt cycle, in both the 14C and 10Be based series. This Hallstatt cycle thus appears to be related to solar activity. Finally, we show that the grand minima and maxima occurred intermittently over the studied period, with clustering near lows and highs

  11. Processes controlling mid-water column oxygen minima over the Texas-Louisiana shelf

    NASA Astrophysics Data System (ADS)

    Zhang, Wenxia; Hetland, Robert D.; DiMarco, Steven F.; Fennel, Katja

    2015-04-01

    We investigate distributions of dissolved oxygen over the Texas-Louisiana shelf using spatially highly resolved observations in combination with a regional circulation model with simple oxygen dynamics. The observations were collected using a towed, undulating CTD during the Mechanisms Controlling Hypoxia (MCH) program. Mid-water oxygen minimum layers (dissolved oxygen lower than 3.2 mL L-1) were detected in many transects. These oxygen minimum layers are connected with the bottom boundary layer and follow the pycnocline seaward as a tongue of low oxygen into the mid-water column. T-S diagrams highlighting the low oxygen minima in both observations and simulations imply direct connections between low-oxygen bottom water and the oxygen minimum layer. The dynamics of these oxygen minimum layers in the mid-water column are examined using a three-dimensional hydrodynamic model, based on the Regional Ocean Modeling System (ROMS). Convergence within the bottom boundary layer relative to density surfaces is calculated, results show that there is a convergence in the bottom boundary layer at the location where the pycnocline intersects the bottom. Buoyancy advection forced by bottom Ekman transport creates this convergent flow, and the corresponding low-oxygen intrusion. Similar intrusions of near-bottom water into the pycnocline are observed in other regions. The presence of hypoxia within the bottom boundary layer in the northern Gulf of Mexico creates a unique situation in which these intrusions are also associated with low dissolved oxygen.

  12. Depth-dose equivalent relationship for cosmic rays at various solar minima

    NASA Technical Reports Server (NTRS)

    Badhwar, G. D.; Cucinotta, F. A.; O'Neill, P. M.

    1993-01-01

    Galactic cosmic rays (GCR) pose a serious radiation hazard for long-duration missions. In designing a lunar habitat or a Mars transfer vehicle, the radiation exposure determines the GCR shielding thickness, and hence the weight of spacecraft. Using the spherically symmetric diffusion theory of the solar modulation of GCR, and data on the differential energy spectra of H, He, O, and Fe, from 1965 to 1989, it has been shown that (1) the flux is determined by the diffusion parameter which is a function of the time in the solar cycle, and (2) the fluxes in the 1954 and 1976-1977 solar minima were similar and higher than those in 1965. In this paper, we have extended the spherical solar modulation theory back to 1954. The 1954-1955 GCR flux was nearly the same as that from 1976 to 1977; the 1965 flux values were nearly the same as those in 1986. Using this theory we have obtained the GCR spectra for all the nuclei, and calculated the depth dose as a function of Al thickness. It is shown that the shielding required to stay below 0.5 Sv is 17.5 -3/+8 g/sq cm of Al, and 9 -1.5/+5 g/sq cm to stay below 0.6 Sv. The calculated dose equivalent using the ICRP 60 values for quality factors is about 15 percent higher than that calculated using the ICRP 26 value.

  13. Leaching of lead by ammonium salts and EDTA from Salvinia minima biomass produced during aquatic phytoremediation.

    PubMed

    Núñez-López, Roberto Aurelio; Meas, Yunny; Gama, Silvia Citlalli; Borges, Raúl Ortega; Olguín, Eugenia J

    2008-06-15

    Plant biomass harvested after heavy-metal phytoremediation must be considered as a hazardous waste that should be contained or treated appropriately before disposal or reuse. As a potential method to detoxify the biomass and to convert this material to a suitable fertilizer or mulch, leaching of lead (Pb) from Salvinia minima biomass was studied by testing water, several aqueous ammonium salts, and EDTA solution as lead extractants. The research was carried out in two phases: (i) a leaching study to determine the lead-extraction efficiency of the different leachants, and (ii) a thermodynamic analysis to identify the likely reactions and stable Pb(II) species formed in the leaching systems of the most efficient leachants. Experimentally, lead concentrations measured in leached biomass and in leachates were significantly different among the various leachants. It was determined that the extraction strength of the leachants followed the order: EDTA>ammonium oxalate>water approximately ammonium nitrate>ammonium acetate, achieving Pb extraction efficiencies of 99%, 70%, 7.2%, 6.9% and 1.3%, respectively, in single-stage extractions. The thermodynamic study indicated that the dominant species produced by the leaching process should be the soluble species PbEDTA2- for EDTA system, and the insoluble Pb(COO)2S precipitate for the oxalate system. PMID:18078711

  14. Space climate. On geoeffective solar activity during Maunder and Dalton grand minima

    NASA Astrophysics Data System (ADS)

    Demetrescu, Crisan; Stefan, Cristiana; Dobrica, Venera

    2014-05-01

    The study of geomagnetic phenomena known as geomagnetic activity has long contributed to progress in solar-terrestrial science. The long geomagnetic time series recorded at geomagnetic observatories have provided means to characterize the Sun-Earth interaction at times prior to space era, via geomagnetic indices (e.g. aa, going back to 1868). For times prior to geomagnetic observatory era, we looked for information at the main geomagnetic field model gufm1 (1590-1990) (Jackson et al., 2000). We show first the presence in the time series provided by this model of a solar-activity-related signal, of 10-20 nT. Then the characteristics of this signal for times to 1600 are discussed. A significant geomagnetic activity at the 22-year time scale is found during the the Maunder and Dalton minima. The signal we discuss also corroborates the so-called excursions in the reconstructed sunspot number based on 10Be determinations on polar ice cores (Usoskin et al., 2003).

  15. Coeval dust accumulation minima in Greenland and East Central Europe over 31-23 ka

    NASA Astrophysics Data System (ADS)

    Újvári, Gábor; Stevens, Thomas; Varga, György; Kovács, János; Molnár, Mihály

    2016-04-01

    , together with the bulk loess median grain size (D50bulk) that is considered an integrated proxy of wind strength, dust source distance, aridity and vegetation cover. While an increase of dust flux and D50bulk with time is apparent, such a trend cannot be seen in the quartz grain size measures (D50quartz). This observation may imply that wind speeds were relatively constant in the studied time interval, while the turbulence of the flow may have been extremely varying (i.e. strong/rapid changes in the frequency/magnitude of dust storm events). A striking feature of the MAR record is that accumulation minima in the Dunaszekcsö record are synchronous with the Greenland Interstadials (GI-5.1 to GI-3). Subsequent Ca2+ minima in the NGRIP record at 26.22 and 25.02 ka (b2k) are also coeval with the MAR minima in the studied loess sequence. At the same time, these patterns are barely visible in the bulk and quartz grain size records. We speculate that the synchronous changes in the NGRIP Ca2+ and the Dunaszekcsö MAR records are results of millennial scale variations in the activity of Northern Hemisphere dust emitting regions shown in two archives from different environments. The very similar timing of MAR minima (and also some of the maxima) suggest a rapid aeolian system response in East Central Europe to abrupt climatic changes in the North Atlantic. Although such a synchronicity does not prove a Central European dust source to Greenland, it is consistent with this possibility. This study was supported by the OTKA PD-108639 grant and the Bolyai János Research Fellowship (both to GÚ). [1] Dansgaard, W., et al. (1993). Evidence for general instability of past climate from a 250-kyr ice-core record. Nature 364, 218-220. [2] Johnsen, S.J., et al. (1992). Irregular glacial interstadials recorded in a new Greenland ice core. Nature 359, 311-313. [3] Rasmussen, S.O., et al. (2014). A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three

  16. A gentic survey of Salvinia minima in the southern United States

    USGS Publications Warehouse

    Madeira, Paul T.; Jacono, Colette C.; Tipping, Phil; Van, Thai K.; Center, Ted D.

    2003-01-01

    The genetic relationships among 68 samples of Salvinia minima (Salviniaceae) were investigated using RAPD analysis. Neighbor joining, principle components, and AMOVA analyses were used to detect differences among geographically referenced samples within and outside of Florida. Genetic distances (Nei and Li) range up to 0.48, although most are under 0.30, still relatively high levels for an introduced, clonally reproducing plant. Despite the diversity AMOVA analysis yielded no indication that the Florida plants, as a group, were significantly different from the plants sampled elsewhere in its adventive, North American range. A single, genetically dissimilar population probably exists in the recent (1998) horticultural introduction to Mississippi. When the samples were grouped into 10 regional (but artificial) units and analyzed using AMOVA the between region variance was only 7.7%. Genetic similarity among these regions may indicate introduction and dispersal from common sources. The reduced aggressiveness of Florida populations (compared to other states) may be due to herbivory. The weevilCyrtobagous salviniae, a selective feeder, is found in Florida but not other states. The genetic similarity also suggests that there are no obvious genetic obstacles to the establishment or efficacy of C. salviniae as a biological control agent on S. minimaoutside of Florida.

  17. Coeval dust accumulation minima in Greenland and East Central Europe over 31-23 ka

    NASA Astrophysics Data System (ADS)

    Újvári, Gábor; Stevens, Thomas; Varga, György; Kovács, János; Molnár, Mihály

    2016-04-01

    , together with the bulk loess median grain size (D50bulk) that is considered an integrated proxy of wind strength, dust source distance, aridity and vegetation cover. While an increase of dust flux and D50bulk with time is apparent, such a trend cannot be seen in the quartz grain size measures (D50quartz). This observation may imply that wind speeds were relatively constant in the studied time interval, while the turbulence of the flow may have been extremely varying (i.e. strong/rapid changes in the frequency/magnitude of dust storm events). A striking feature of the MAR record is that accumulation minima in the Dunaszekcsö record are synchronous with the Greenland Interstadials (GI-5.1 to GI-3). Subsequent Ca2+ minima in the NGRIP record at 26.22 and 25.02 ka (b2k) are also coeval with the MAR minima in the studied loess sequence. At the same time, these patterns are barely visible in the bulk and quartz grain size records. We speculate that the synchronous changes in the NGRIP Ca2+ and the Dunaszekcsö MAR records are results of millennial scale variations in the activity of Northern Hemisphere dust emitting regions shown in two archives from different environments. The very similar timing of MAR minima (and also some of the maxima) suggest a rapid aeolian system response in East Central Europe to abrupt climatic changes in the North Atlantic. Although such a synchronicity does not prove a Central European dust source to Greenland, it is consistent with this possibility. This study was supported by the OTKA PD-108639 grant and the Bolyai János Research Fellowship (both to GÚ). [1] Dansgaard, W., et al. (1993). Evidence for general instability of past climate from a 250-kyr ice-core record. Nature 364, 218-220. [2] Johnsen, S.J., et al. (1992). Irregular glacial interstadials recorded in a new Greenland ice core. Nature 359, 311-313. [3] Rasmussen, S.O., et al. (2014). A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three

  18. Rapid sampling of local minima in protein energy surface and effective reduction through a multi-objective filter

    PubMed Central

    2013-01-01

    Background Many problems in protein modeling require obtaining a discrete representation of the protein conformational space as an ensemble of conformations. In ab-initio structure prediction, in particular, where the goal is to predict the native structure of a protein chain given its amino-acid sequence, the ensemble needs to satisfy energetic constraints. Given the thermodynamic hypothesis, an effective ensemble contains low-energy conformations which are similar to the native structure. The high-dimensionality of the conformational space and the ruggedness of the underlying energy surface currently make it very difficult to obtain such an ensemble. Recent studies have proposed that Basin Hopping is a promising probabilistic search framework to obtain a discrete representation of the protein energy surface in terms of local minima. Basin Hopping performs a series of structural perturbations followed by energy minimizations with the goal of hopping between nearby energy minima. This approach has been shown to be effective in obtaining conformations near the native structure for small systems. Recent work by us has extended this framework to larger systems through employment of the molecular fragment replacement technique, resulting in rapid sampling of large ensembles. Methods This paper investigates the algorithmic components in Basin Hopping to both understand and control their effect on the sampling of near-native minima. Realizing that such an ensemble is reduced before further refinement in full ab-initio protocols, we take an additional step and analyze the quality of the ensemble retained by ensemble reduction techniques. We propose a novel multi-objective technique based on the Pareto front to filter the ensemble of sampled local minima. Results and conclusions We show that controlling the magnitude of the perturbation allows directly controlling the distance between consecutively-sampled local minima and, in turn, steering the exploration towards

  19. Blind prediction of SAMPL4 cucurbit[7]uril binding affinities with the mining minima method

    PubMed Central

    Muddana, Hari S.; Yin, Jian; Sapra, Neil V.; Fenley, Andrew T.; Gilson, Michael K.

    2014-01-01

    Accurate methods for predicting protein-ligand binding affinities are of central interest to computer-aided drug design for hit identification and lead optimization. Here, we used the mining minima (M2) method to predict cucurbit[7]uril binding affinities from the SAMPL4 blind prediction challenge. We tested two different energy models, an empirical classical force field, CHARMm with VCharge charges, and the Poisson-Boltzmann Surface Area (PBSA) solvation model; and a semiempirical quantum mechanical Hamiltonian, PM6-DH+, coupled with the COSMO solvation model and a surface area term for nonpolar solvation free energy. Binding affinities based on the classical force field correlated strongly with the experiments with a correlation coefficient (R2) of 0.74. On the other hand, binding affinities based on the quantum mechanical energy model correlated poorly with experiments (R2 = 0.24), due largely to two major outliers. As we used extensive conformational search methods, these results point to possible inaccuracies in the PM6-DH+ energy model or the COSMO solvation model. Furthermore, the different binding free energy components, solute energy, solvation free energy, and configurational entropy showed significant deviations between the classical M2 and quantum M2 calculations. Comparison of different classical M2 free energy components to experiments show that the change in the total energy, i.e. the solute energy plus the solvation free energy, is the key driving force for binding, with a reasonable correlation to experiment (R2 = 0.56); however, accounting for configurational entropy further improves the correlation. PMID:24510191

  20. Mitigating local minima in full-waveform inversion by expanding the search space

    NASA Astrophysics Data System (ADS)

    van Leeuwen, Tristan; Herrmann, Felix J.

    2013-10-01

    Wave equation based inversions, such as full-waveform inversion and reverse-time migration, are challenging because of their computational costs, memory requirements and reliance on accurate initial models. To confront these issues, we propose a novel formulation of wave equation based inversion based on a penalty method. In this formulation, the objective function consists of a data-misfit term and a penalty term, which measures how accurately the wavefields satisfy the wave equation. This new approach is a major departure from current formulations where forward and adjoint wavefields, which both satisfy the wave equation, are correlated to compute updates for the unknown model parameters. Instead, we carry out the inversions over two alternating steps during which we first estimate the wavefield everywhere, given the current model parameters, source and observed data, followed by a second step during which we update the model parameters, given the estimate for the wavefield everywhere and the source. Because the inversion involves both the synthetic wavefields and the medium parameters, its search space is enlarged so that it suffers less from local minima. Compared to other formulations that extend the search space of wave equation based inversion, our method differs in several aspects, namely (i) it avoids storage and updates of the synthetic wavefields because we calculate these explicitly by finding solutions that obey the wave equation and fit the observed data and (ii) no adjoint wavefields are required to update the model, instead our updates are calculated from these solutions directly, which leads to significant computational savings. We demonstrate the validity of our approach by carefully selected examples and discuss possible extensions and future research.

  1. Are both symmetric and buckled dimers on Si(100) minima? Density functional and multireference perturbation theory calculations

    SciTech Connect

    Jung, Yousung; Shao, Yihan; Gordon, Mark S.; Doren, Douglas J.; Head-Gordon, Martin

    2003-08-29

    We report a spin-unrestricted density functional theory (DFT) solution at the symmetric dimer structure for cluster models of Si(100). With this solution, it is shown that the symmetric structure is a minimum on the DFT potential energy surface, although higher in energy than the buckled structure. In restricted DFT calculations the symmetric structure is a saddle point connecting the two buckled minima. To further assess the effects of electron correlation on the relative energies of symmetric versus buckled dimers on Si(100), multireference second order perturbation theory (MRMP2) calculations are performed on these DFT optimized minima. The symmetric structure is predicted to be lower in energy than the buckled structure via MRMP2, while the reverse order is found by DFT. The implications for recent experimental interpretations are discussed.

  2. A population-based evolutionary search approach to the multiple minima problem in de novo protein structure prediction

    PubMed Central

    2013-01-01

    Background Elucidating the native structure of a protein molecule from its sequence of amino acids, a problem known as de novo structure prediction, is a long standing challenge in computational structural biology. Difficulties in silico arise due to the high dimensionality of the protein conformational space and the ruggedness of the associated energy surface. The issue of multiple minima is a particularly troublesome hallmark of energy surfaces probed with current energy functions. In contrast to the true energy surface, these surfaces are weakly-funneled and rich in comparably deep minima populated by non-native structures. For this reason, many algorithms seek to be inclusive and obtain a broad view of the low-energy regions through an ensemble of low-energy (decoy) conformations. Conformational diversity in this ensemble is key to increasing the likelihood that the native structure has been captured. Methods We propose an evolutionary search approach to address the multiple-minima problem in decoy sampling for de novo structure prediction. Two population-based evolutionary search algorithms are presented that follow the basic approach of treating conformations as individuals in an evolving population. Coarse graining and molecular fragment replacement are used to efficiently obtain protein-like child conformations from parents. Potential energy is used both to bias parent selection and determine which subset of parents and children will be retained in the evolving population. The effect on the decoy ensemble of sampling minima directly is measured by additionally mapping a conformation to its nearest local minimum before considering it for retainment. The resulting memetic algorithm thus evolves not just a population of conformations but a population of local minima. Results and conclusions Results show that both algorithms are effective in terms of sampling conformations in proximity of the known native structure. The additional minimization is shown to be

  3. The adventive status of Salvinia minima and S. molestain the southern United States and the related distribution of the weevil Cyrtobagous salviniae

    USGS Publications Warehouse

    Jacono, Colette C.; Davern, Tracy R.; Center, Ted D.

    2001-01-01

    The recent introduction of Salvinia molesta constitutes a serious threat to aquatic systems in the warm temperate regions of the United States. Salvinia minima, the only other member of Salviniaceae present in North America, is considered native by current floras. Evidence is presented which suggests that Salvinia minima was also introduced to North America, probably during the late 1920s and early 1930s. Likely sites of introduction and subsequent range expansions are identified. The accidentally introduced salvinia weevil, putatively Cyrtobagous salviniae, was found to occur widely on S. minima in Florida but is not established in other states. The disparate distribution of this Salvinia herbivore may account for the reduced aggressiveness of S. minima in Florida as compared to its troublesome growth in Texas and LOUisiana, where the weevil is not yet known.

  4. A Novel Approach to Decoy Set Generation: Designing a Physical Energy Function Having Local Minima with Native Structure Characteristics

    PubMed Central

    Keasar, Chen; Levitt, Michael

    2009-01-01

    We suggest a new approach to the generation of candidate structures (decoys) for ab initio prediction of protein structures. Our method is based on random sampling of conformation space and subsequent local energy minimization. At the core of this approach lies the design of a novel type of energy function. This energy function has local minima with native structure characteristics and wide basins of attraction. The current work presents our motivation for deriving such an energy function and also tests the derived energy function. Our approach is novel in that it takes advantage of the inherently rough energy landscape of proteins, which is generally considered a major obstacle for protein structure prediction. When local minima have wide basins of attraction, the protein’s conformation space can be greatly reduced by the convergence of large regions of the space into single points, namely the local minima corresponding to these funnels. We have implemented this concept by an iterative process. The potential is first used to generate decoy sets and then we study these sets of decoys to guide further development of the potential. A key feature of our potential is the use of cooperative multi-body interactions that mimic the role of the entropic and solvent contributions to the free energy. The validity and value of our approach is demonstrated by applying it to 14 diverse, small proteins. We show that, for these proteins, the size of conformation space is considerably reduced by the new energy function. In fact, the reduction is so substantial as to allow efficient conformational sampling. As a result we are able to find a significant number of near-native conformations in random searches performed with limited computational resources. PMID:12742025

  5. Comparison of PSF maxima and minima of multiple annuli coded aperture (MACA) and complementary multiple annuli coded aperture (CMACA) systems

    NASA Astrophysics Data System (ADS)

    Ratnam, Challa; Lakshmana Rao, Vadlamudi; Lachaa Goud, Sivagouni

    2006-10-01

    In the present paper, and a series of papers to follow, the Fourier analytical properties of multiple annuli coded aperture (MACA) and complementary multiple annuli coded aperture (CMACA) systems are investigated. First, the transmission function for MACA and CMACA is derived using Fourier methods and, based on the Fresnel-Kirchoff diffraction theory, the formulae for the point spread function are formulated. The PSF maxima and minima are calculated for both the MACA and CMACA systems. The dependence of these properties on the number of zones is studied and reported in this paper.

  6. cluster: Searching for Unique Low Energy Minima of Structures Using a Novel Implementation of a Genetic Algorithm.

    PubMed

    Kanters, René P F; Donald, Kelling J

    2014-12-01

    A new flexible implementation of a genetic algorithm for locating unique low energy minima of isomers of clusters is described and tested. The strategy employed can be applied to molecular or atomic clusters and has a flexible input structure so that a system with several different elements can be built up from a set of individual atoms or from fragments made up of groups of atoms. This cluster program is tested on several systems, and the results are compared to computational and experimental data from previous studies. The quality of the algorithm for locating reliably the most competitive low energy structures of an assembly of atoms is examined for strongly bound Si-Li clusters, and ZnF2 clusters, and the more weakly interacting water trimers. The use of the nuclear repulsion energy as a duplication criterion, an increasing population size, and avoiding mutation steps without loss of efficacy are distinguishing features of the program. For the Si-Li clusters, a few new low energy minima are identified in the testing of the algorithm, and our results for the metal fluorides and water show very good agreement with the literature. PMID:26583254

  7. Biosynthesis of gold nanoparticles by the living freshwater diatom Eolimna minima, a species developed in river biofilms.

    PubMed

    Feurtet-Mazel, Agnès; Mornet, Stéphane; Charron, Laëtitia; Mesmer-Dudons, Nathalie; Maury-Brachet, Régine; Baudrimont, Magalie

    2016-03-01

    Testing biotransformation capacities of living aquatic microalgae diatoms to naturally synthetize gold nanoparticles (AuNP) from gold salts and assessing aftereffects on their viability by microscope observations is a great challenge. In this work, a laboratory experiment was conducted, which aimed to observe (i) directly by transmission electronic and light microscopy and (ii) through indirect measurements (UV-visible spectroscopy) the periphytic freshwater diatom Eolimna minima exposed to gold salts. This work revealed the capacity of E. minima to intracellularly biosynthetize AuNP and to tolerate it. AuNP synthesis appears as a mechanism of detoxification to protect diatom from gold salt contamination. We also pointed out the risks associated with the spread of diatoms full of AuNP, through the trophic web of freshwater ecosystems. The preponderant part of the diatoms in natural biofilms associated with their position at the basis of the trophic webs in rivers could then make them responsible for the contamination of their consumers (grazer animals) and consequently for the potential release of AuNP through the entire food web. PMID:25628115

  8. Methanolic Extract of Ceplukan Leaf (Physalis minima L.) Attenuates Ventricular Fibrosis through Inhibition of TNF-α in Ovariectomized Rats

    PubMed Central

    Lestari, Bayu; Permatasari, Nur; Rohman, Mohammad Saifur

    2016-01-01

    The increase of heart failure prevalence on menopausal women was correlated with the decrease of estrogen level. The aim of this study is to investigate the effects of ceplukan leaf (Physalis minima L.), which contains phytoestrogen physalin and withanolides, on ventricular TNF-α level and fibrosis in ovariectomized rats. Wistar rats were divided into six groups (control (—); OVX 5: 5-week ovariectomy (OVX); OVX 9: 9-week ovariectomy; treatments I, II, and III: 9-weeks OVX + 4-week ceplukan leaf's methanolic extract doses 500, 1500, and 2500 mg/kgBW, resp.). TNF-α levels were measured with ELISA. Fibrosis was counted as blue colored tissues percentage using Masson's Trichrome staining. This study showed that prolonged hypoestrogen increases ventricular fibrosis (p < 0.05). Ceplukan leaf treatment also resulted in a decrease of ventricular fibrosis and TNF-α level in dose dependent manner compared to without treatment group (p < 0.05). Furthermore, the TNF-α level was normalized in 2500 mg/kgBW Physalis minima L. (p < 0.05) treatment. The reduction of fibrosis positively correlated with TNF-α level (p < 0.05, r = 0.873). Methanolic extract of ceplukan leaf decreases ventricular fibrosis through the inhibition of ventricular TNF-α level in ovariectomized rats. PMID:26941790

  9. Biosynthesis of lead nanoparticles by the aquatic water fern, Salvinia minima Baker, when exposed to high lead concentration.

    PubMed

    Castro-Longoria, E; Trejo-Guillén, K; Vilchis-Nestor, A R; Avalos-Borja, M; Andrade-Canto, S B; Leal-Alvarado, D A; Santamaría, J M

    2014-02-01

    Salvinia minima Baker is a small floating aquatic fern that is efficient for the removal and storage of heavy metals such as lead and cadmium. In this study, we report that lead removal by S. minima causes large accumulation of lead inside the cells in the form of nanoparticles (PbNPs). The accumulation pattern of lead was analyzed in both, submerged root-like modified fronds (here named "roots"), and in its aerial leaf-like fronds ("leaves"). Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) confirmed the biosynthesis of PbNPs by the plant. In both, roots and leaves, PbNPs were found to accumulate almost exclusively at the cell wall and closely associated to the cell membrane. Two types of PbNPs shapes were found in cells of both tissues, those associated to the cell wall were quasi-spherical with 17.2±4.2 nm of diameter, while those associated to the cell membrane/cytoplasm were elongated. Elongated particles were 53.7±29.6 nm in length and 11.1±2.4 nm wide. Infrared spectroscopy (IR) results indicate that cellulose, lignin and pectin are the major components that may be acting as the reducing agents for lead ions; these findings strongly suggest the potential use of this fern to further explore the bio-assisted synthesis of heavy metal nanostructures. PMID:24211828

  10. Methanolic Extract of Ceplukan Leaf (Physalis minima L.) Attenuates Ventricular Fibrosis through Inhibition of TNF-α in Ovariectomized Rats.

    PubMed

    Lestari, Bayu; Permatasari, Nur; Rohman, Mohammad Saifur

    2016-01-01

    The increase of heart failure prevalence on menopausal women was correlated with the decrease of estrogen level. The aim of this study is to investigate the effects of ceplukan leaf (Physalis minima L.), which contains phytoestrogen physalin and withanolides, on ventricular TNF-α level and fibrosis in ovariectomized rats. Wistar rats were divided into six groups (control (-); OVX 5: 5-week ovariectomy (OVX); OVX 9: 9-week ovariectomy; treatments I, II, and III: 9-weeks OVX + 4-week ceplukan leaf's methanolic extract doses 500, 1500, and 2500 mg/kgBW, resp.). TNF-α levels were measured with ELISA. Fibrosis was counted as blue colored tissues percentage using Masson's Trichrome staining. This study showed that prolonged hypoestrogen increases ventricular fibrosis (p < 0.05). Ceplukan leaf treatment also resulted in a decrease of ventricular fibrosis and TNF-α level in dose dependent manner compared to without treatment group (p < 0.05). Furthermore, the TNF-α level was normalized in 2500 mg/kgBW Physalis minima L. (p < 0.05) treatment. The reduction of fibrosis positively correlated with TNF-α level (p < 0.05, r = 0.873). Methanolic extract of ceplukan leaf decreases ventricular fibrosis through the inhibition of ventricular TNF-α level in ovariectomized rats. PMID:26941790

  11. Hybrid functional for correlated electrons in the projector augmented-wave formalism: Study of multiple minima for actinide oxides

    NASA Astrophysics Data System (ADS)

    Jollet, F.; Jomard, G.; Amadon, B.; Crocombette, J. P.; Torumba, D.

    2009-12-01

    Exact (Hartree-Fock) exchange for correlated electrons is implemented to describe correlated orbitals in the projector augmented-waves (PAW) framework, as suggested recently in another context [P. Novák , Phys. Status Solidi B 243, 563 (2006)]. Hartree-Fock exchange energy is applied to strongly correlated electrons only inside the PAW atomic spheres. This allows the use of PBE0 hybrid exchange-correlation functional for correlated electrons. This method is tested on NiO and results agree well with already published results and generalized gradient approximation, GGA+U calculations. It is then applied to plutonium oxides and UO2 for which the results are comparable with the ones of GGA+U calculations but without adjustable parameter. As evidenced in the uranium oxide case, the occurrence of multiple energy minima may lead to very different results depending on the initial electronic configurations and on the symmetries taken into account in the calculation.

  12. Complex Orbitals, Multiple Local Minima, and Symmetry Breaking in Perdew-Zunger Self-Interaction Corrected Density Functional Theory Calculations.

    PubMed

    Lehtola, Susi; Head-Gordon, Martin; Jónsson, Hannes

    2016-07-12

    Implentation of seminumerical stability analysis for calculations using the Perdew-Zunger self-interaction correction is described. It is shown that real-valued solutions of the Perdew-Zunger equations for gas phase atoms are unstable with respect to imaginary orbital rotations, confirming that a proper implementation of the correction requires complex-valued orbitals. The orbital density dependence of the self-interaction corrected functional is found to lead to multiple local minima in the case of the acrylic acid, H6, and benzene molecules. In the case of benzene, symmetry breaking that results in incorrect ground state geometry is found to occur, erroneously leading to alternating bond lengths in the molecule. PMID:27232582

  13. Qualitative and quantitative analysis of chemical constituents of Centipeda minima by HPLC-QTOF-MS & HPLC-DAD.

    PubMed

    Chan, Chi-On; Jin, Deng-Ping; Dong, Nai-Ping; Chen, Si-Bao; Mok, Daniel Kam Wah

    2016-06-01

    A high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS) method in both positive and negative ion modes was established to investigate the major constituents in the ethanolic extract of Centipeda minima (EBSC). Twelve common components including flavones and their glycosides, phenolic and polyphenolic acids, and sesquiterpene lactone were identified in ten batches of samples based on comparison with the retention time and accurate mass of external standards (mass accuracy within 3ppm) or the fragmentation patterns of tandem MS. Meanwhile, a simple, accurate and reliable HPLC-DAD method was also developed to determine the content of 10 chemical markers simultaneously. Results obtained from method validations including linearity, accuracy and precision showed that this new method is reliable and robust. Isochlorogenic acid A and brevilin A were found to be the most abundant in the ethanol extract of EBSC and could be served as markers for quality control of EBSC. PMID:27131150

  14. 13,14-seco-Withanolides from Physalis minima with Potential Anti-inflammatory Activity.

    PubMed

    Lin, Ru; Guan, Yu-Zhou; Li, Rui-Jun; Xu, Xiao-Ming; Luo, Jian-Guang; Kong, Ling-Yi

    2016-07-01

    Four new 13,14-seco-withanolides, minisecolides A - D (1 - 4), together with three known analogues 5 - 7, were isolated from the whole plants of Physalis minima. The structures of new compounds were determined on the basis of spectroscopic analysis, including (1) H-, (13) C-NMR, 2D-NMR (HMBC, HSQC, ROESY), and HR-ESI-MS. Evaluation of all isolates for their inhibitory effects on nitric oxide (NO) production was conducted on lipopolysaccaride-activated RAW264.7 macrophages. Compounds 2, 3, 5, and 6 showed inhibitory activities, especially for compound 5 with IC50 value of 3.87 μm. PMID:27258922

  15. Solar Wind Structure at 1 AU: Comparison between Solar Minima 22/23 and 23/24

    NASA Astrophysics Data System (ADS)

    Jian, L.; Russell, C.; Luhmann, J. G.; Galvin, A. B.; Skoug, R. M.; Schroeder, P. C.

    2009-12-01

    The current solar minimum 23/24 has been unusually long and deep, compared with the solar minima in the space era. In order to see the consequence of the extremely quiet Sun on the solar wind, we compare the solar wind structure during the current solar minimum with the last solar minimum 22/23, which represents the case of a short and shallow solar minimum. Based on ACE, Wind, and STEREO in situ plasma and magnetic field observations, we identify and characterize stream interaction regions (SIRs), interplanetary CMEs (ICMEs), interplanetary shocks, sector boundaries, and other structures in the solar wind at 1 AU for 1995 - 1997 and 2007 - 2009. The properties of these structures, such as the occurrence rate, SIR and ICME scale and interaction strength, shock Mach number, correlation between sector boundary and SIR, will be studied. In addition to the statistical study, we will present some case studies of events from this deep solar minimum.

  16. Study of minima of the fluctuations of the order parameter of seismicity using GCMT catalogue in global scale.

    NASA Astrophysics Data System (ADS)

    Christopoulos, Stavros-Richard G.; Sarlis, Nicholas V.; Skordas, Efthimios S.

    2016-04-01

    It has been recently shown [1,2] that earthquakes of magnitude M greater or equal to 7 are globally correlated. The identification of this correlation became possible when studying the variance κ1 of natural time which has been proposed as an order parameter for seismicity[3,4]. In the present study, we focus on the behaviour of the fluctuations of κ1 before major earthquakes using the Global Centroid Moment Tensor catalogue for a magnitude threshold Mthres=5.0 as in Ref.[5]. Natural time analysis reveals that distinct minima of the fluctuations κ1of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than M8.4. This phenomenon corroborates the recent finding [6] that similar minima of seismicity order parameter fluctuations had been observed before all major shallow earthquakes in Japan. Finally, we examine the statistical significance of the results by using ROC graphs [7,8] and the proposed prediction method has a p-value to occur by chance well below 0.1%. The hit rate is 100% with a false alarm rate only 6.67%. An attempt to lower the target earthquake magnitude threshold will be also presented. REFERENCES [1] N. V. Sarlis, Phys. Rev. E 84, 022101 (2011). [2] N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012) [3] P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, Practica of Athens Acad. 76, 294 (2001). [4] P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, Phys. Rev. E 66, 011902 (2002). [5] N.V. Sarlis, S.-R. G. Christopoulos, and E. S. Skordas, Chaos 25, 063110 (2015) [6] N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013) [7] T. Fawcett, Pattern Recognit. Lett. 27, 861 (2006). [8] N. V. Sarlis and S.-R. G. Christopoulos, Comput. Phys. Commun. 185, 1172 (2014).

  17. Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24

    NASA Technical Reports Server (NTRS)

    Williams, Peter E.; Pesnell, W. Dean

    2011-01-01

    Supergranulation is a component of solar convection that manifests itself on the photosphere as a cellular network of around 35 Mm across, with a turnover lifetime of 1 2 days. It is strongly linked to the structure of the magnetic field. The horizontal, divergent flows within supergranule cells carry local field lines to the cell boundaries, while the rotational properties of supergranule upflows may contribute to the restoration of the poloidal field as part of the dynamo mechanism, which controls the solar cycle. The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended length. It is of interest to study whether the convective phenomena that influence the solar magnetic field during this time differed in character from periods of previous minima. This study investigates three characteristics (velocity components, sizes and lifetimes) of solar supergranulation. Comparisons of these characteristics are made between the minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008, respectively. It is found that whereas the lifetimes are equal during both epochs (around 18 h), the sizes are larger in 1996 (35.9 plus or minus 0.3 Mm) than in 2008 (35.0 plus or minus 0.3 Mm), while the dominant horizontal velocity flows are weaker (139 plus or minus m per second in 1996; 141 plus or minus 1 m per second in 2008). Although numerical differences are seen, they are not conclusive proof of the most recent minimum being inherently unusual.

  18. A Change in the Solar He II EUV Global Network Structure as an Indicator of the Geo-Effectiveness of Solar Minima

    NASA Technical Reports Server (NTRS)

    Didkovsky, L.; Gurman, J. B.

    2013-01-01

    Solar activity during 2007 - 2009 was very low, causing anomalously low thermospheric density. A comparison of solar extreme ultraviolet (EUV) irradiance in the He II spectral band (26 to 34 nm) from the Solar Extreme ultraviolet Monitor (SEM), one of instruments on the Charge Element and Isotope Analysis System (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) for the two latest solar minima showed a decrease of the absolute irradiance of about 15 +/- 6 % during the solar minimum between Cycles 23 and 24 compared with the Cycle 22/23 minimum when a yearly running-mean filter was used. We found that some local, shorter-term minima including those with the same absolute EUV flux in the SEM spectral band show a higher concentration of spatial power in the global network structure from the 30.4 nm SOHO/Extreme ultraviolet Imaging Telescope (EIT) images for the local minimum of 1996 compared with the minima of 2008 - 2011.We interpret this higher concentration of spatial power in the transition region's global network structure as a larger number of larger-area features on the solar disk. These changes in the global network structure during solar minima may characterize, in part, the geo-effectiveness of the solar He II EUV irradiance in addition to the estimations based on its absolute levels.

  19. Adults of the Waterfern Weevil, Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae) feed on a Non-Host Plant Salvinia minima Baker, in Louisiana

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The waterfern weevil, Stenopelmus refinasus Gyllenhal, has previously been reported as host-specific, only feeding on plants in the genus Azolla. We report the first observations of S. rufinasus feeding on a non-host plant, Salvinia minima Baker, within the United States....

  20. A ~0.1 bar Rule for Tropopause Temperature Minima in Thick Atmospheres of Planets and Large Moons

    NASA Astrophysics Data System (ADS)

    Robinson, T. D.; Catling, D. C.

    2013-12-01

    Tropopause temperature minima are fundamental for understanding planetary atmospheric structure. A number of shortwave absorbers (e.g., ozone, organic hazes) produce temperature inversions in the stratospheres of Earth, Jupiter, Saturn, Titan, Uranus and Neptune. These inversions lead to temperature minima that, remarkably, all occur near 0.1 bar, despite very different insolation, atmospheric composition, gravity, and internal heat flux. We examined the atmospheric thermal structure of solar system worlds with thick atmospheres using an analytic 1-D radiative-convective model, which assumes gray thermal radiative transfer. Shortwave radiative transfer is divided into a stratospheric channel, which allows for inversions, and a tropospheric channel for solar heating at depth and at the surface. We assume that a convective profile, which is adjusted to account for condensation, sits below the portion of the atmosphere that is in radiative equilibrium. The model ensures that the temperature and upwelling thermal flux are continuous across the radiative-convective boundary. Finally, the model uses a power-law scaling between the gray infrared optical depth and pressure, which is physically justified for tropospheres and lower stratospheres where opacity is dominated by collision-induced absorption and/or strong pressure broadening. For the worlds of the solar system, the tropopause temperature minimum always lies above the radiative-convective boundary. Thus, the shared 0.1 bar tropopause arises from the common physics of infrared radiative transfer. Model fits to solar system worlds show that the gray infrared optical depth where the tropopause minimum occurs is ~0.1. Furthermore, the gray infrared optical depths at a pressure of 1 bar are typically of order a few. These, along with the aforementioned scaling between pressure and infrared optical depth, set the tropopause pressure to be near 0.1 bar. Moving beyond the solar system, we show that the typical gray

  1. Signatures of the Primordial Universe from Its Emptiness: Measurement of Baryon Acoustic Oscillations from Minima of the Density Field

    NASA Astrophysics Data System (ADS)

    Kitaura, Francisco-Shu; Chuang, Chia-Hsun; Liang, Yu; Zhao, Cheng; Tao, Charling; Rodríguez-Torres, Sergio; Eisenstein, Daniel J.; Gil-Marín, Héctor; Kneib, Jean-Paul; McBride, Cameron; Percival, Will J.; Ross, Ashley J.; Sánchez, Ariel G.; Tinker, Jeremy; Tojeiro, Rita; Vargas-Magana, Mariana; Zhao, Gong-Bo

    2016-04-01

    Sound waves from the primordial fluctuations of the Universe imprinted in the large-scale structure, called baryon acoustic oscillations (BAOs), can be used as standard rulers to measure the scale of the Universe. These oscillations have already been detected in the distribution of galaxies. Here we propose to measure BAOs from the troughs (minima) of the density field. Based on two sets of accurate mock halo catalogues with and without BAOs in the seed initial conditions, we demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but it is clearly detected from overlapping voids. The latter represent an estimate of all troughs of the density field. We compute them from the empty circumsphere centers constrained by tetrahedra of galaxies using Delaunay triangulation. Our theoretical models based on an unprecedented large set of detailed simulated void catalogues are remarkably well confirmed by observational data. We use the largest recently publicly available sample of luminous red galaxies from SDSS-III BOSS DR11 to unveil for the first time a >3 σ BAO detection from voids in observations. Since voids are nearly isotropically expanding regions, their centers represent the most quiet places in the Universe, keeping in mind the cosmos origin and providing a new promising window in the analysis of the cosmological large-scale structure from galaxy surveys.

  2. Signatures of the Primordial Universe from Its Emptiness: Measurement of Baryon Acoustic Oscillations from Minima of the Density Field.

    PubMed

    Kitaura, Francisco-Shu; Chuang, Chia-Hsun; Liang, Yu; Zhao, Cheng; Tao, Charling; Rodríguez-Torres, Sergio; Eisenstein, Daniel J; Gil-Marín, Héctor; Kneib, Jean-Paul; McBride, Cameron; Percival, Will J; Ross, Ashley J; Sánchez, Ariel G; Tinker, Jeremy; Tojeiro, Rita; Vargas-Magana, Mariana; Zhao, Gong-Bo

    2016-04-29

    Sound waves from the primordial fluctuations of the Universe imprinted in the large-scale structure, called baryon acoustic oscillations (BAOs), can be used as standard rulers to measure the scale of the Universe. These oscillations have already been detected in the distribution of galaxies. Here we propose to measure BAOs from the troughs (minima) of the density field. Based on two sets of accurate mock halo catalogues with and without BAOs in the seed initial conditions, we demonstrate that the BAO signal cannot be obtained from the clustering of classical disjoint voids, but it is clearly detected from overlapping voids. The latter represent an estimate of all troughs of the density field. We compute them from the empty circumsphere centers constrained by tetrahedra of galaxies using Delaunay triangulation. Our theoretical models based on an unprecedented large set of detailed simulated void catalogues are remarkably well confirmed by observational data. We use the largest recently publicly available sample of luminous red galaxies from SDSS-III BOSS DR11 to unveil for the first time a >3σ BAO detection from voids in observations. Since voids are nearly isotropically expanding regions, their centers represent the most quiet places in the Universe, keeping in mind the cosmos origin and providing a new promising window in the analysis of the cosmological large-scale structure from galaxy surveys. PMID:27176512

  3. Salinity minima, water masses and surface circulation in the Eastern Tropical Pacific off Mexico and surrounding areas

    NASA Astrophysics Data System (ADS)

    Portela, Esther; Beier, Emilio; Godínez, Victor; Castro, Rubén; Desmond Barton, Eric

    2016-04-01

    The seasonal variations of the water masses and their interactions are analyzed in the Tropical Pacific off Mexico (TPOM) and four contiguous areas of on the basis of new extensive hydrographic database. The regional water masses intervals are redefined in terms of Absolute Salinity (SA) in g kg-1 and Conservative Temperature (Θ) according to TEOS - 10. The California Current System Water (CCSW) mass is introduced as an improved description of the former California Current Water (CCW) together with the Subarctic Water (SAW) to describe better the characteristics of the components of the California Current System. Hydrographic data, Precipitation-Evaporation balance and geostrophic currents were used to investigate the origin and seasonality of two salinity minima in the area. The shallow salinity minimum of around 33.5 g kg-1 originated in the California Current System and became saltier but less dense water as it traveled to the southeast. It can be identified as a mixture of CCSW and tropical waters. The surface salinity minimum of 32 - 33 g kg-1 was seen as a sharp surface feature in the TPOM from August to November. It was produced by the arrival of tropical waters from the south in combination with the net precipitation in the area during these months. This result provides new evidence of the presence of the poleward-flowing Mexican Coastal Current and, for the first time, of its seasonal pattern of variation.

  4. Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2–6, and several hexamer local minima at the CCSD(T) level of theory

    SciTech Connect

    Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S.

    2013-01-01

    We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the CCSD(T)/aug-cc-pVDZ level of theory. All five hexamer isomer minima previously reported by MP2 are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n=2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) are found for the librational modes, while uniform increases of ~15 and ~25 cm-1 are observed for the bending and “free” OH harmonic frequencies. The largest differences between MP2 and CCSD(T) are observed for the harmonic hydrogen bonded frequencies. The CCSD(T) red shifts from the monomer frequencies (Δω) are smaller than the MP2 ones, due to the fact that the former produces shorter elongations (ΔR) of the respective hydrogen bonded OH lengths from the monomer value with respect to the latter. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation - Δω = s · ΔR, with a rate of s = 20.3 cm-1 / 0.001 Å. The CCSD

  5. Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2-6, and several hexamer local minima at the CCSD(T) level of theory.

    PubMed

    Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S

    2013-09-21

    We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ~15 and ~25 cm(-1) are observed for the bending and "free" OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (Δω) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (ΔR) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2. Both

  6. Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2-6, and several hexamer local minima at the CCSD(T) level of theory

    NASA Astrophysics Data System (ADS)

    Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S.

    2013-09-01

    We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ˜0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ˜15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ˜15 and ˜25 cm-1 are observed for the bending and "free" OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (Δω) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (ΔR) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2

  7. Variability of surface water dynamics during eccentricity minima interglacials of the last 1 Myr in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Palumbo, Eliana; Emanuele, Dario; Ferretti, Patrizia; Flores, José-Abel; Perugia, Carmen; Petrillo, Zaccaria; Ornella Amore, Filomena

    2014-05-01

    Eccentricity minima occurred only three times during the last 1 Myr in correspondence of Marine Isotope Stages (MIS) 1 (last 11 ka), 11 (425-360 ka) and 19 (791-763 ka). All these stages are characterised by similar orbital configurations and the Pleistocene eccentricity minima interglacials are considered, by several authors, as possible analogues for the Holocene and its future evolution. Surface water dynamics were reconstructed through quantitative analyses performed on coccolithophore assemblages in two key-sites of the North Atlantic: MD03-2699 core, retrieved off Iberian Margin (IM), and IODP Site U1313, located in the upper western flank of the Mid-Atlantic Ridge. Nowadays, IODP Site U1313 is under the influence of a northern ramification of the Gulf Stream, the North Atlantic Current (NAC). This current forms a transitional zone between the productive cold polar system and the oligotrophic warm subtropical system. In addition, the NAC represents the northern boundary of the Portugal Current (PC) system which influences the modern surface oceanography off the IM at MD03-2699 site. Coccolithophore data were carried out by sediments of MD03-2699 core for MIS 11 and MIS 1(Amore et al., 2012; Palumbo et al., 2013a,b) and by IODP Site U1313 for MIS 19 (Emanuele, 2013). The mean sampling resolution for MIS 1 is 140 yrs, for MIS 11 about 400 yrs and for MIS 19 about 220 yrs. The high samples resolution allowed reconstructing long term changes at orbital timescale as well as rapid changes at millennial scale. Data from coccolithophore assemblages were compared with available proxy for the studied cores such as alkenones, lithics, oxygen and carbon isotopes. Coccolithophores belong to phytoplankton group and they are widely used as proxy of surface water dynamics thanks to their attitude to record the smallest paleoclimatic changes and because they directly depend on sea surface temperature and salinity, sunlight and availability of nutrients. Through the use of

  8. New findings on increasing solar trend that can change Earth climate: are we entering new great solar minima?

    NASA Astrophysics Data System (ADS)

    Rozelot, J. P.

    2009-10-01

    Studies of the Sun-Earth relationships during the past years have dramatically changed our view on Solar- Terrestrial Physics. Neither is the interplanetary medium unstructured or quasi-static, nor is it a simple magnetic stratified object. Thus, the interaction of the solar electromagnetic radiation (photons), hot plasma (electrons, protons and other ions), cosmic rays, microscopic dust particles, and magnetic fields (primarily from the Sun) with the upper environment of our Earth leads to a complex physics which is far to be understandable. This new science is growing rapidly, as well as for the physical problems which arise as for its growing impact on our societies. This last case is well illustrated by the emergence of the so-called Space Weather. In spite of a great number of papers and books written on this subject and on a broader one devoted to Solar-Terrestrial links, the different terms deserve to be clarified. In this paper, we will first establish a clear distinction between Space Weather, Space Climate, Space Physics, Sun-Earth connections, and Helioclimatology, this last word being introduced to describe the role of the Sun in the Earth's climate forcing. In a second step, we will emphasize the key role of the ranging time on which the effects may act. We will then underline the necessity to better predict solar activity showing the physical difficulties for such an exercise, yielding the extreme complexity for forecasting specific events. The three dataset, past Earth's temperature (since AD 630), solar shape variability (since AD 1600) and strength of umbral/sunspots magnetic field (since AD 1995) lead all to a Next Grand Minima predictable for 2015-2018. We will conclude by giving some imprints for the future.

  9. Shear-deformation-potential constant of the conduction-band minima of Si: Experimental determination by the deep-level capacitance transient method

    NASA Astrophysics Data System (ADS)

    Li, Ming-Fu; Zhao, Xue-Shu; Gu, Zong-Quan; Chen, Jian-Xin; Li, Yan-Jin; Wang, Jian-Qing

    1991-06-01

    The shear-deformation-potential constant Ξu of the conduction-band minima of Si has been measured by a method which we called deep-level capacitance transient under uniaxial stress. The uniaxial-stress (F) dependence of the electron emission rate en from deep levels to the split conduction-band minima of Si has been analyzed. Theoretical curves are in good agreement with experimental data for the S0 and S+ deep levels in Si. The values of Ξu obtained by the method are 11.1+/-0.3 eV at 148.9 K and 11.3+/-0.3 eV at 223.6 K. The analysis and the Ξu values obtained are also valuable for symmetry determination of deep electron traps in Si.

  10. Ultrastructural studies of the mandibular glands of the minima, media and soldier ants of Atta sexdens rubropilosa (Forel 1908) (Hymenoptera: Formicidae).

    PubMed

    Pavon, Lorena Favaro; Mathias, Maria Izabel Camargo

    2005-01-01

    The mandibular glands of Hymenoptera are structures associated with the mandibles and constitute part of the salivary glands system. Histological studies in workers of Atta sexdens rubropilosa revealed that this gland contains two portions: a secretory and a storage portion or reservoir. Both portions are connected by means of canaliculi. The object of the present work was the study of the ultratructure of the mandibular glands of minima, media and soldier ant of A. s. rubropilosa by TEM techniques. The glands, in the three castes studied, possess a reservoir, constituted by a simple pavementous epithelium surrounded by the cuticular intima and the secretory portion is constituted by cells of rounded shape. The secretory cells, mainly of minima and soldier, were rich in smooth endoplasmic reticulum. The media worker and soldier presented a large number of mitochondria, of varying shape. Well-developed Golgi complexes were also present in the soldiers. The secretory cells in minima, media and soldier were provided with collecting intracellular canaliculi, which were linked to the reservoir through the extracellular portion. The cytoplasm of the canaliculi-forming cell was poor in organelles. In the individuals of the three castes of A. s. rubropilosa, the presence of lipid secretion granules suggested, beyond the other functions, also a possible pheromonal action. The different roles executed by the different insect castes are directly dependent on the glandular products and, consequently, on the secretory cellular characteristics. PMID:15935305

  11. Brachyopa minima (Diptera: Syrphidae), a new species from Greece with notes on the biodiversity and conservation of the genus Brachyopa Meigen in the Northern Aegean Islands.

    PubMed

    Pérez-Bañón, Celeste; Radenković, Snezana; Vujić, Ante; Petanidou, Theodora

    2016-01-01

    An on-going study of the hoverfly fauna of the Northern Aegean Islands (Greece) has revealed the presence of four species of the genus Brachyopa Meigen. During the survey the following species were found: B. bicolor (Fallén), B. quadrimaculosa Thompson in Kaplan & Thompson, B. minima Vujić & Pérez-Bañón sp. nov. and an unidentified species very close to B. pilosa (Collin). Morphological characters and mitochondrial COI barcodes were used to link different life stages of B. minima, and to identify a larval specimen of B. bicolor. In this study adult and larval morphology and habitat preferences for B. minima are described. The description of larval morphology of B. bicolor and Brachyopa sp. aff. pilosa is amended too. An identification key to the adults of the B. quadrimaculosa group sensu Kassebeer (2002) in the Eastern Mediterranean (Greece, Israel and Turkey) is provided. The importance of specific microhabitats for the continued existence of these taxa is discussed. PMID:27395920

  12. Defect mediated room temperature ferromagnetism and resistance minima study in epitaxial ZnGa0.002Al0.02O transparent conducting oxide films

    NASA Astrophysics Data System (ADS)

    Temizer, Namik K.; Nori, Sudhakar; Kumar, D.; Narayan, Jagdish

    2016-09-01

    We report on the micro-structural, transport, optical and magnetic properties in ZnGa0.002Al0.02O (AGZO) films grown by pulsed laser deposition under different growth conditions. AGZO films grown at substrate temperatures of 600 °C show metal-like behavior with a resistivity minima at lower temperatures, whereas films grown at 300 °C and ambient oxygen partial pressure of 1 mTorr show metallic nature with resistivity values on the order of 100 µΩ · cm at room temperature. The most interesting features are the concomitant occurrence of high temperature resistivity minima and room temperature ferromagnetism with a saturation magnetic moment of 1000 A m‑1 and with coercivity in the range 100–240 Oe. The temperature dependent resistivity data has been interpreted in the light of quantum corrections to conductivity in disordered systems, suggesting that the e–e interactions is the dominant mechanism in the weak-localization (WL) limit in the case of films showing resisitivity minima. The simultaneous ferromagnetic ordering coupled with the enhancements in electrical conductivity in AGZO system should have their origin in native point defects in the form of oxygen and zinc vacancies and interstitials and their complexes. We propose that formation of oxygen vacancy–zinc interstitial defect complex (V O–I Zn) is responsible for the enhancement in n-type conductivity, and zinc vacancies (V Zn) for the observed room temperature ferromagnetism.

  13. VizieR Online Data Catalog: TU UMa light curves and maxima, CL Aur minima (Liska+, 2016)

    NASA Astrophysics Data System (ADS)

    Liska, J.; Skarka, M.; Mikulasek, Z.; Zejda, M.; Chrastina, M.

    2016-02-01

    Differential photometry for RR Lyrae star TU UMa in the 1st and 2nd file. The measurements were obtained using 24-inch and 1-inch telescopes, respectively. The observations were performed at the Masaryk University Observatory in Brno (3 nights, 24-inch), and at the private observatory in Brno (16 nights, 1-inch) in the Czech Republic from December 2013 to June 2014. Observing equipments consisted of 24-inch Newtonian telescope (600/2780mm, diameter/focal length) and a Moravian Instruments CCD camera G2-4000 with Stromgren photometric filters vby, and of 1-inch refractor (a photographic lens Sonnar 4/135mm, lens focal ratio/focal length) and ATIK 16IC CCD camera with green photometric filter with similar throughput as the Johnson V filter. Exposures were v - 60s, b - 30s, y - 30s, green - 30s. For the small aperture telescope, five frames were combined to a single image to achieve a better signal-to-noise ratio. The time resolution of a such combined frame is about 170s. CCD images were calibrated in a standard way (dark frame and flat field corrections). The C-Munipack software (Motl 2009) was used for this processing as well as for differential photometry. The comparison star BD+30 2165 was the same for both instruments, but the control stars were BD+30 2164 (for the 24-inch telescope) and HD 99593 (for the 1-inch telescope). The 3rd file contains maxima timings of TU UMa adopted from the GEOS RR Lyr database, from the latest publications, together with maxima timings determined in our study. Times of maxima were calculated from our observations, sky-surveys data (Hipparcos, NSVS, Pi of the Sky, SuperWASP), photographic measurements (project DASCH), and from several published datasets, in which the maxima were omitted or badly determined - Boenigk (1958AcA.....8...13B), Liakos, Niarchos (2011IBVS.6099....1L, 2011IBVS.5990....1L), Liu, Janes (1989ApJS...69..593L), Preston et al. (1961ApJ...133..484P). The 4th file contains minima timings of eclipsing binary CL Aur

  14. Delayed build-up of Arctic ice sheets during 400, 000-year minima in insolation variability confirmed by Chinese loess

    NASA Astrophysics Data System (ADS)

    Hao, Q.; Wang, L.; Oldfield, F.; Peng, S.; Qin, L.; Song, Y.; Xu, B.; Qiao, Y.; Bloemendal, J.; Guo, Z.

    2013-12-01

    The growth and decay of the Northern Hemisphere ice volume led to alternations of glacial and interglacial climate and major changes in sea level during the Quaternary period. Unfortunately, long-term continuous records of ice-sheet variability in the Northern during the Quaternary period Hemisphere only are scarce because benthic δ18O records represent an integrated signal of changes in ice volume in both polar regions. Direct sedimentary records of Northern Hemisphere polar ice sheets exist only for the late Quaternary and longer term records are scarce. However, variations in Northern Hemisphere ice sheets influence the Siberian High (an atmospheric pressure system), so variations in the East Asian winter monsoon (EAWM)--as recorded in the aeolian dust deposits on the Chinese Loess Plateau--can serve as a useful proxy of Arctic climate variability. Here we present an EAWM proxy record using grain-size variations in two parallel loess sections over the past 900 kyr to address the timing of build-up of Northern hemisphere ice sheets around 413 kyr mimina in eccentricity and precessional variability. These periods are regarded as the astronomical analogues of the present interglacial. The results show that during periods of low eccentricity and precessional variability around 400 kyr and 800 kyr ago, the grain-size-inferred intensity of the EAWM remains weak for up to 20 kyr after the end of the interglacial episodes MIS 11, MIS 19 and MIS 21. In contrast, there is a rapid increase in the EAWM after the end of most other interglacials. We conclude that, for these interglacials at 400 kyr intervals, the weak EAWM winds maintain a non-glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records. During these times, the less severe summer insolation minima at 65° N (modulated by 413-kyr eccentricity cycles) would have suppressed ice and snow accumulation, leading to a weak Siberian High and

  15. A study of the properties of the Grand Solar Minima throughout the past 13,000 years and the implications for Space Weather.

    NASA Astrophysics Data System (ADS)

    McCracken, Ken; Beer, Juerg

    2016-04-01

    The intensity of the cosmic radiation reaching the orbit of Earth is primarily controlled by the strength of the heliomagnetic field, which itself is largely determined by the level of solar activity. The paleo-cosmic ray (PCR) record therefore provides the output from a "cosmic magnetometer", and a proxy for solar activity in the past. Using 10Be (ice-cores) and 14C (tree rings) data we investigate the wide variations in the PCR and solar activity that have occurred during the past 13,000 years. In particular, we study the occurrence and properties of "Grand Minima"- the periods of very low solar activity similar to the Maunder Minimum (1645-1715) for which solar and geophysical data are available. There was a sequence of five GM between 950-1830CE; there were three similar sequences of similar duration in the preceding millennia; interspersed with intervals of ~1000 year essentially devoid of GM. The four sequences of GM correspond to the minima of the 2300 y Hallstatt periodicity. The PCR increases by ~50% during "Grand Solar Minima" and we use the PCR intensity to quantify the relative significance of the Grand Minima in the past. On the basis that the terrestrial and heliospheric consequences of a GM will depend on both the amplitude of the change in PCR intensity, and its duration, we have defined a parameter, the GM index, as the product of the amplitude and duration of a GM. We conclude that there have been 22 GM of geophysical significance equal to, or greater than that of the Wolf GM (1230-1350CE). The Sun is in a "Grand Minimum" condition for ~45% of the time during a GM sequence; and for only ~5% of the time in the intervening 1000y intervals of high solar activity. We discuss the implications of these observations in respect of space weather and climate. In conclusion, we speculate that the sun may now be entering one of its extended periods of high activity which will persist for ~1000 y.

  16. Opportunities and challenges to conserve water on the landscape in snow-dominated forests: The quest for the radiative minima and more...

    NASA Astrophysics Data System (ADS)

    Link, T. E.; Kumar, M.; Pomeroy, J. W.; Seyednasrollah, B.; Ellis, C. R.; Lawler, R.; Essery, R.

    2012-12-01

    In mountainous, forested environments, vegetation exerts a strong control on snowcover dynamics that affect ecohydrological processes, streamflow regimes, and riparian health. Snowcover deposition and ablation patterns in forests are controlled by a complex combination of canopy interception processes coupled with radiative and turbulent heat flux patterns related to topographic and canopy cover variations. In seasonal snow environments, snowcover ablation dynamics in forests are dominated by net radiation. Recent research indicates that in small canopy gaps a net radiation minima relative to both open and forested environments can occur, but depends strongly on solar angle, gap size, slope, canopy height and stem density. The optimal gap size to minimize radiation to snow was estimated to have a diameter between 1 and 2 times the surrounding vegetation height. Physically-based snowmelt simulations indicate that gaps may increase SWE and desynchronize snowmelt by approximately 3 weeks between north and south facing slopes, relative to undisturbed forests. On east and west facing slopes, small gaps cause melt to be slightly delayed relative to intact forests, and have a minimal effect on melt synchronicity between slopes. Recent research focused on canopy thinning also indicates that a net radiation minima occurs in canopies of intermediate densities. Physically-based radiative transfer simulations using a discrete tree-based model indicate that in mid-latitude level forests, the annually-integrated radiative minima occurs at a tree spacing of 2.65 relative to the canopy height. The radiative minima was found to occur in denser forests on south-facing slopes and sparser forests on north-facing slopes. The radiative minimums in thinned forests are controlled by solar angle, crown geometry and density, tree spacing, slope, and aspect. These results indicate that both gap and homogeneous forest thinning may be used to reduce snowmelt rates or alter melt synchronicity

  17. Major geophysical events and transitions of heliospheric magnetic field in the beginning, middle and end phase of the Maunder solar minima

    NASA Astrophysics Data System (ADS)

    Casati, Michele; Straser, Valentino; Feron, Alessandro

    2016-04-01

    In recent decades we are moving towards the hypothesis that electromagnetic (EM) processes inside the solar system (not yet fully understood from a physical point of view), may be linked with the energy released during major geophysical events (energy expressed in magnitude or Volcanic Explosivity Index). This research has focused on analysis of the temporal relationship between EM processes inside the solar system and major geophysical events around the crucial phase of the Maunder solar minima (1645-1715). To carry out this study thirty-five limit values of the heliospheric magnetic field strength HMF (minimum and/or maximum) were compared, in terms of time, with twenty-one major geophysical events which occurred between 1600 and 1729. In the solar-terrestrial interaction, the concomitant conditions necessary for the amplification of the energy of the geophysical event, are two: i. low solar activity during a long period (from decades to centuries), for example, the historical solar minima: Wolf, Sporer, Maunder, Dalton, etc. and ii. fast and impulsive EM solar dynamo reorganizations in the short-term (one year or two years), are characteristic in the two periods of the solar cycle border, the incoming or outgoing of the solar minima or solar maximum. The reconstructed intensity of the heliospheric magnetic field (HMF) was the main set of data used to carry out the present study. HMF evaluated by the annual cosmogenic 10Be ice core data from Dye 3 and North GRIP, in Greenland [McCracken;Beer,Sol.Phys.,2015 in press]. Analysis of the data shows that all the major geophysical events, with magnitude and volcanic explosivity index: 8.7

  18. Lead accumulation reduces photosynthesis in the lead hyper-accumulator Salvinia minima Baker by affecting the cell membrane and inducing stomatal closure.

    PubMed

    Leal-Alvarado, Daniel A; Espadas-Gil, Francisco; Sáenz-Carbonell, Luis; Talavera-May, Carlos; Santamaría, Jorge M

    2016-02-01

    Salvinia minima Baker accumulates a fair amount of lead in its tissues; however, no studies have investigated the effect of lead on the physiological processes that affect photosynthesis in this species. The objective of the present study was to assess whether the high amounts of lead accumulated by S. minima can affect its photosynthetic apparatus. The physiological changes in the roots and leaves in response to lead accumulation were analyzed. An exposure to 40 μM Pb(NO3)2 for 24 h (first stage) was sufficient to reduce the photosynthetic rate (Pn) by 44%. This reduction in Pn was apparently the result of processes at various levels, including damage to the cell membranes (mainly in roots). Interestingly, although the plants were transferred to fresh medium without lead for an additional 24 h (second stage), Pn not only remained low, but was reduced even further, which was apparently related to stomatal closure, and may have led to reduced CO2 availability. Therefore, it can be concluded that lead exposure first decreases the photosynthetic rate by damaging the root membrane and then induces stomatal closure, resulting in decreased CO2 availability. PMID:26742090

  19. Cost-effective, species-specific microsatellite development for the endangered Dwarf Bulrush (Typha minima) using next-generation sequencing technology.

    PubMed

    Csencsics, Daniela; Brodbeck, Sabine; Holderegger, Rolf

    2010-01-01

    The dwarf bulrush (Typha minima Funck ex Hoppe) is an endangered pioneer plant species of riparian flood plains. In Switzerland, only 3 natural populations remain, but reintroductions are planned. To identify suitable source populations for reintroductions, we developed 17 polymorphic microsatellite markers with perfect repeats using the 454 pyrosequencing technique and tested them on 20 individuals with low-cost M13 labeling. We detected 2 to 7 alleles per locus and found expected and observed heterozygosities of 0.05-0.76 and 0.07-1, respectively. The whole process was finished in less than 6 weeks and cost approximately USD 5000. Due to low costs and reduced expenditure of time, the use of next-generation sequencing techniques for microsatellite development represent a powerful tool for population genetic studies in nonmodel species, as we show in this first application of the approach to a plant species of conservation importance. PMID:20562212

  20. The difference in the energy spectra of galactic cosmic rays at the minima of the 19th and 20th solar activity cycles

    NASA Technical Reports Server (NTRS)

    Svirzhevskaya, A. K.; Stozhkov, Y. I.; Svirzhevsky, N. S.; Charakhchyan, T. N.

    1985-01-01

    The absorption curves of the cosmic ray charged component for solar minima in 1965 and 1975 to 1977 are analyzed on the basis of daily stratospheric measurements in Murmansk, Moscow, Alma-Ata and Mirny (Antarctic). Two distinct features in the energy spectra of galactic cosmic rays are revealed during these periods. At the 20th solar activity minimum there was the additional short range component of cosmic rays. Additional fluxes in the stratosphere at high latitudes caused by this component are probably protons and He nuclei with the energy 100 to 500 MeV/n. The fluxes are estimates as Approx. 300 sq m/s/sr. At the minimum in 1975 to 1977 the proton intensity in the energy range 1 to 15 GeV is 10 to 15% lower than that in the 1965 solar activity minimum.

  1. Spectroscopic evidence for the coexistence of tetragonal and trigonal minima within the exited state adiabatic potential energy surfaces of hexachlorotellurate and -selenate complexes

    NASA Astrophysics Data System (ADS)

    Cremers, C.; Degen, J.

    1998-11-01

    Coexistence of Jahn-Teller minima resulting from the coupling to different accepting modes within the adiabatic potential energy surface (APES) is not possible within the framework of linear vibronic coupling theory. For the lowest exited triplet state 3T1u of inorganic complexes with s2 electronic ground-state configuration, such a coexistence, due to quadratic coupling effects, is discussed. As a direct experimental evidence two vibronic progressions with different accepting modes in the emission spectra resulting from a single electronic state are observed in the emission spectra of the title compounds. The observation of vibronic finestructure in the emission spectra of [TeCl6]2- is reported for the first time.

  2. Amylase production by Preussia minima, a fungus of endophytic origin: optimization of fermentation conditions and analysis of fungal secretome by LC-MS

    PubMed Central

    2014-01-01

    Background Environmental screening programs are used to find new enzymes that may be utilized in large-scale industrial processes. Among microbial sources of new enzymes, the rationale for screening fungal endophytes as a potential source of such enzymes relates to the hypothesised mutualistic relationship between the endophyte and its host plant. There is a need for new microbial amylases that are active at low temperature and alkaline conditions as these would find industrial applications as detergents. Results An α-amylase produced by Preussia minima, isolated from the Australian native plant, Eremophilia longifolia, was purified to homogeneity through fractional acetone precipitation and Sephadex G-200 gel filtration, followed by DEAE-Sepharose ion exchange chromatography. The purified α-amylase showed a molecular mass of 70 kDa which was confirmed by zymography. Temperature and pH optima were 25°C and pH 9, respectively. The enzyme was activated and stabilized mainly by the metal ions manganese and calcium. Enzyme activity was also studied using different carbon and nitrogen sources. It was observed that enzyme activity was highest (138 U/mg) with starch as the carbon source and L-asparagine as the nitrogen source. Bioreactor studies showed that enzyme activity was comparable to that obtained in shaker cultures, which encourages scale-up fermentation for enzyme production. Following in-gel digestion of the purified protein by trypsin, a 9-mer peptide was sequenced and analysed by LC-ESI-MS/MS. The partial amino acid sequence of the purified enzyme presented similarity to α-amylase from Magnaporthe oryzae. Conclusions The findings of the present study indicate that the purified α-amylase exhibits a number of promising properties that make it a strong candidate for application in the detergent industry. To our knowledge, this is the first amylase isolated from a Preussia minima strain of endophytic origin. PMID:24602289

  3. Molecular and morphological diversity of Narragansett Bay (RI, USA) Ulva (Ulvales, Chlorophyta) populations.

    PubMed

    Guidone, Michele; Thornber, Carol; Wysor, Brian; O'Kelly, Charles J

    2013-10-01

    Macroalgal bloom-forming species occur in coastal systems worldwide. However, due to overlapping morphologies in some taxa, accurate taxonomic assessment and classification of these species can be quite challenging. We investigated the molecular and morphological characteristics of 153 specimens of bloom-forming Ulva located in and around Narragansett Bay, RI, USA. We analyzed sequences of the nuclear internal transcribed spacer 1 region (ITS1) and the chloroplast-encoded rbcL; based on the ITS1 data, we grouped the specimens into nine operational taxonomic units (OTUs). Eight of these OTUs have been previously reported to exist, while one is novel. Of the eight OTUs, all shared sequence identity with previously published sequences or differed by less than 1.5% sequence divergence for two molecular markers. Previously, 10 species names were reported for Ulva in Rhode Island (one blade and nine tube-forming species) based upon morphological classification alone. Of our nine OTUs, three contained blade-forming specimens (U. lactuca, U. compressa, U. rigida), one OTU had a blade with a tubular stipe, and six contained unbranched and/or branched tubular morphologies (one of these six, U. compressa, had both a blade and a tube morphology). While the three blade-forming OTUs in Narragansett Bay can frequently be distinguished by careful observations of morphological characteristics, and spatial/temporal distribution, it is much more difficult to distinguish among the tube-forming specimens based upon morphology or distribution alone. Our data support the molecular species concept for Ulva, and indicate that molecular-based classifications of Ulva species are critical for proper species identification, and subsequent ecological assessment or mitigation of Ulva blooms. PMID:27007320

  4. Ion-Stockmayer clusters: Minima, classical thermodynamics, and variational ground state estimates of Li+(CH3NO2)n (n = 1-20)

    NASA Astrophysics Data System (ADS)

    Curotto, E.

    2015-12-01

    Structural optimizations, classical NVT ensemble, and variational Monte Carlo simulations of ion Stockmayer clusters parameterized to approximate the Li+(CH3NO2)n (n = 1-20) systems are performed. The Metropolis algorithm enhanced by the parallel tempering strategy is used to measure internal energies and heat capacities, and a parallel version of the genetic algorithm is employed to obtain the most important minima. The first solvation sheath is octahedral and this feature remains the dominant theme in the structure of clusters with n ≥ 6. The first "magic number" is identified using the adiabatic solvent dissociation energy, and it marks the completion of the second solvation layer for the lithium ion-nitromethane clusters. It corresponds to the n = 18 system, a solvated ion with the first sheath having octahedral symmetry, weakly bound to an eight-membered and a four-membered ring crowning a vertex of the octahedron. Variational Monte Carlo estimates of the adiabatic solvent dissociation energy reveal that quantum effects further enhance the stability of the n = 18 system relative to its neighbors.

  5. Minima de L'intégrale D'action du Problème Newtoniende 4 Corps de Masses Égales Dans R3: Orbites `Hip-Hop'

    NASA Astrophysics Data System (ADS)

    Chenciner, Alain; Venturelli, Andrea

    2000-09-01

    We consider the problem of 4 bodies of equal masses in R 3 for the Newtonian r-1 potential. We address the question of the absolute minima of the action integral among (anti)symmetric loops of class H 1 whose period is fixed. It is the simplest case for which the results of [4] (corrected in [5]) do not apply: the minima cannot be the relative equilibria whose configuration is an absolute minimum of the potential among the configurations having a given moment of inertia with respect to their center of mass. This is because the regular tetrahedron cannot have a relative equilibrium motion in R 3 (see [2]). We show that the absolute minima of the action are not homographic motions. We also show that if we force the configuration to admit a certain type of symmetry of order 4, the absolute minimum is a collisionless orbit whose configuration ‘hesitates’ between the central configuration of the square and the one of the tetrahedron. We call these orbits ‘hip-hop’. A similar result holds in case of a symmetry of order 3 where the central configuration of the equilateral triangle with a body at the center of mass replaces the square.

  6. Differences in the Effect of Coal Pile Runoff (Low pH, High Metal Concentrations) Versus Natural Carolina Bay Water (Low pH, Low Metal Concentrations) on Plant Condition and Associated Bacterial Epiphytes of Salvinia minima.

    PubMed

    Lindell, A H; Tuckfield, R C; McArthur, J V

    2016-05-01

    Numerous wetlands and streams have been impacted by acid mine drainage (AMD) resulting in lowered pH and increased levels of toxic heavy metals. Remediation of these contaminated sites requires knowledge on the response of microbial communities (especially epiphytic) and aquatic plants to these altered environmental conditions. We examined the effect of coal pile runoff waters as an example of AMD in contrast to natural water from Carolina Bays with low pH and levels of metals on Salvinia minima, a non-native, metal accumulating plant and associated epiphytic bacteria. Treatments included water from two Carolina Bays, one AMD basin and Hoagland's Solution at two pH levels (natural and adjusted to 5.0-5.5). Using controlled replicated microcosms (N = 64) we determined that the combination of low pH and high metal concentrations has a significant negative impact (p < 0.05) on plant condition and epiphytes. Solution metal concentrations dropped indicating removal from solution by S. minima in all microcosms. PMID:26908369

  7. Prevalence and mechanism of polyunsaturated aldehydes production in the green tide forming macroalgal genus Ulva (Ulvales, Chlorophyta).

    PubMed

    Alsufyani, Taghreed; Engelen, Aschwin H; Diekmann, Onno E; Kuegler, Stefan; Wichard, Thomas

    2014-10-01

    Lipoxygenase/hydroperoxide lyase mediated transformations convert polyunsaturated fatty acids into various oxylipins. First, lipoxygenases catalyze fatty acid oxidation to fatty acid hydroperoxides. Subsequently, breakdown reactions result in a wide array of metabolites with multiple physiological and ecological functions. These fatty acid transformations are highly diverse in marine algae and play a crucial rule in e.g., signaling, chemical defense, and stress response often mediated through polyunsaturated aldehydes (PUAs). In this study, green tide-forming macroalgae of the genius Ulva (Chlorophyta) were collected at various sampling sites in the lagoon of the Ria Formosa (Portugal) and were surveyed for PUAs. We demonstrated that sea-lettuce like but not tube-like morphotypes produce elevated amounts of volatile C10-polyunsaturated aldehydes (2,4,7-decatrienal and 2,4-decadienal) upon tissue damage. Moreover, morphogenetic and phylogenetic analyses of the collected Ulva species revealed chemotaxonomic significance of the perspective biosynthetic pathways. The aldehydes are derived from omega-3 and omega-6 polyunsaturated fatty acids (PUFA) with 20 or 18 carbon atoms including eicosapentaenoic acid (C20:5 n-3), arachidonic acid (C20:4 n-6), stearidonic acid (C18:4 n-3), and γ-linolenic acid (C18:3 n-6). We present first evidences that lipoxygenase-mediated (11-LOX and 9-LOX) eicosanoid and octadecanoid pathways catalyze the transformation of C20- and C18-polyunsaturated fatty acids into PUAs and concomitantly into short chain hydroxylated fatty acids. PMID:24915501

  8. Ion-Stockmayer clusters: Minima, classical thermodynamics, and variational ground state estimates of Li{sup +}(CH{sub 3}NO{sub 2}){sub n} (n = 1–20)

    SciTech Connect

    Curotto, E.

    2015-12-07

    Structural optimizations, classical NVT ensemble, and variational Monte Carlo simulations of ion Stockmayer clusters parameterized to approximate the Li{sup +}(CH{sub 3}NO{sub 2}){sub n} (n = 1–20) systems are performed. The Metropolis algorithm enhanced by the parallel tempering strategy is used to measure internal energies and heat capacities, and a parallel version of the genetic algorithm is employed to obtain the most important minima. The first solvation sheath is octahedral and this feature remains the dominant theme in the structure of clusters with n ≥ 6. The first “magic number” is identified using the adiabatic solvent dissociation energy, and it marks the completion of the second solvation layer for the lithium ion-nitromethane clusters. It corresponds to the n = 18 system, a solvated ion with the first sheath having octahedral symmetry, weakly bound to an eight-membered and a four-membered ring crowning a vertex of the octahedron. Variational Monte Carlo estimates of the adiabatic solvent dissociation energy reveal that quantum effects further enhance the stability of the n = 18 system relative to its neighbors.

  9. Tunable reflection minima of nanostructured antireflective surfaces

    NASA Astrophysics Data System (ADS)

    Boden, S. A.; Bagnall, D. M.

    2008-09-01

    Broadband antireflection schemes for silicon surfaces based on the moth-eye principle and comprising arrays of subwavelength-scale pillars are applicable to solar cells, photodetectors, and stealth technologies and can exhibit very low reflectances. We show that rigorous coupled wave analysis can be used to accurately model the intricate reflectance behavior of these surfaces and so can be used to explore the effects of variations in pillar height, period, and shape. Low reflectance regions are identified, the extent of which are determined by the shape of the pillars. The wavelengths over which these low reflectance regions operate can be shifted by altering the period of the array. Thus the subtle features of the reflectance spectrum of a moth-eye array can be tailored for optimum performance for the input spectrum of a specific application.

  10. Quadratic minima and modular forms II

    NASA Astrophysics Data System (ADS)

    Brent, Barry

    We give upper bounds on the size of the gap between a non-zero constant term and the next non-zero Fourier coefficient of an entire level two modular form. We give upper bounds for the minimum positive integer represented by a level two even positive-definite quadratic form. These bounds extend partial results in part I.

  11. High-level ab initio calculations for the four low-lying families of minima of (H2O)(20): 1. Estimates of MP2/CBS binding energies and comparison with empirical potentials

    SciTech Connect

    Fanourgakis, Georgios S.; Apra, Edoardo; Xantheas, Sotiris S.

    2004-08-08

    We report estimates of complete basis set (CBS) limits at the second-order Møller-Plesset perturbation level of theory (MP2) for the binding energies of the lowest lying isomers within each of the four major families of minima of (H2O)20. These were obtained by performing MP2 calculations with the family of correlation-consistent basis sets up to quadruple zeta quality, augmented with additional diffuse functions (aug-cc-pVnZ, n=D, T, Q). The MP2/CBS estimates are: -200.1 kcal/mol (dodecahedron, 30 hydrogen bonds), -212.6 kcal/mol (fused cubes, 36 hydrogen bonds), -215.0 (face-sharing pentagonal prisms, 35 hydrogen bonds) and –217.9 kcal/mol (edge-sharing pentagonal prisms, 34 hydrogen bonds). The energetic ordering of the various (H2O)20 isomers does not follow monotonically the number of hydrogen bonds as in the case of smaller clusters such as the different isomers of the water hexamer. The dodecahedron lies ca. 18 kcal/mol higher in energy than the most stable edge-sharing pentagonal prism isomer. The TIP4P, ASP-W4, TTM2-R, AMOEBA and TTM2-F empirical potentials also predict the energetic stabilization of the edge-sharing pentagonal prisms with respect to the dodecahedron, albeit they universally underestimate the cluster binding energies with respect to the MP2/CBS result. Among them, the TTM2-F potential was found to predict the absolute cluster binding energies to within < 1% from the corresponding MP2/CBS values, whereas the error for the rest of the potentials considered in this study ranges from 3-5%.

  12. Low-Lying Energy Isomers and Global Minima of Aqueous Nanoclusters: Structures and Spectroscopic Features of the Pentagonal Dodecahedron (H2O)20 and (H3O)+(H2O)20

    SciTech Connect

    Xantheas, Sotiris S.

    2012-08-01

    We rely on a hierarchy of methods to identify the low-lying isomers for the pentagonal dodecahedron (H2O)20 and the H3O+(H2O)20 clusters. Initial screening of isomers was performed with classical potentials [TIP4P, TTM2-F, TTM2.1-F for (H2O)20 and ASP for H3O+(H2O)20] and the networks obtained with those potentials were subsequently reoptimized at the DFT (B3LYP) and MP2 levels of theory. For the pentagonal dodecahedron (H2O)20 it was found that DFT (B3LYP) and MP2 produced the same global minimum. However, this was not the case for the H3O+(H2O)20 cluster, for which MP2 produced a different network for the global minimum when compared to DFT (B3LYP). All low-lying minima of H3O+(H2O)20 correspond to hydrogen bonding networks having 9 ''free'' OH bonds and the hydronium ion on the surface of the cluster. The fact that DFT (B3LYP) and MP2 produce different results and issues related to the use of a smaller basis set, explains the discrepancy between the current results and the structure previously suggested [Science 304, 1137 (2004)] for the global minimum of the H3O+(H2O)20 cluster. Additionally, the IR spectra of the MP2 global minimum are closer to the experimentally measured ones than the spectra of the previously suggested DFT global minimum. The latter exhibit additional bands in the most red-shifted region of the OH stretching vibrations (corresponding to the ''fingerprint'' of the underlying hydrogen bonding network), which are absent from both the experimental as well as the spectra of the new structure suggested for the global minimum of this cluster.

  13. Strong Endemism of Bloom-Forming Tubular Ulva in Indian West Coast, with Description of Ulva paschima Sp. Nov. (Ulvales, Chlorophyta)

    PubMed Central

    Bast, Felix; John, Aijaz Ahmad; Bhushan, Satej

    2014-01-01

    Ulva intestinalis and Ulva compressa are two bloom-forming morphologically-cryptic species of green seaweeds widely accepted as cosmopolitan in distribution. Previous studies have shown that these are two distinct species that exhibit great morphological plasticity with changing seawater salinity. Here we present a phylogeographic assessment of tubular Ulva that we considered belonging to this complex collected from various marine and estuarine green-tide occurrences in a ca. 600 km stretch of the Indian west coast. Maximum Likelihood and Bayesian Inference phylogenetic reconstructions using ITS nrDNA revealed strong endemism of Indian tubular Ulva, with none of the Indian isolates forming part of the already described phylogenetic clades of either U. compressa or U. intestinalis. Due to the straightforward conclusion that Indian isolates form a robust and distinct phylogenetic clade, a description of a new bloom-forming species, Ulva paschima Bast, is formally proposed. Our phylogenetic reconstructions using Neighbor-Joining method revealed evolutionary affinity of this new species with Ulva flexuosa. This is the first molecular assessment of Ulva from the Indian Subcontinent. PMID:25329833

  14. Strong Endemism of bloom-forming tubular Ulva in Indian West Coast, with description of Ulva paschima Sp. Nov. (Ulvales, Chlorophyta).

    PubMed

    Bast, Felix; John, Aijaz Ahmad; Bhushan, Satej

    2014-01-01

    Ulva intestinalis and Ulva compressa are two bloom-forming morphologically-cryptic species of green seaweeds widely accepted as cosmopolitan in distribution. Previous studies have shown that these are two distinct species that exhibit great morphological plasticity with changing seawater salinity. Here we present a phylogeographic assessment of tubular Ulva that we considered belonging to this complex collected from various marine and estuarine green-tide occurrences in a ca. 600 km stretch of the Indian west coast. Maximum Likelihood and Bayesian Inference phylogenetic reconstructions using ITS nrDNA revealed strong endemism of Indian tubular Ulva, with none of the Indian isolates forming part of the already described phylogenetic clades of either U. compressa or U. intestinalis. Due to the straightforward conclusion that Indian isolates form a robust and distinct phylogenetic clade, a description of a new bloom-forming species, Ulva paschima Bast, is formally proposed. Our phylogenetic reconstructions using Neighbor-Joining method revealed evolutionary affinity of this new species with Ulva flexuosa. This is the first molecular assessment of Ulva from the Indian Subcontinent. PMID:25329833

  15. High-level ab-initio calculations for the four low-lying families of minima of (H2O)20: II. Spectroscopic signatures of the dodecahedron, fused cubes, face-sharing pentagonal prisms, and edge-sharing pentagonal prisms hydrogen bonding networks

    SciTech Connect

    Fanourgakis, Georgios S.; Apra, Edoardo; De Jong, Wibe A.; Xantheas, Sotiris S.

    2005-04-01

    We report the first harmonic vibrational spectra for each of the lowest lying isomers within the four major families of minima of (H{sub 2}O){sub 20}, namely the dodecahedron, fused cubes, face-sharing pentagonal prisms and edge-sharing pentagonal prisms. These were obtained at the second-order Moeller-Plesset perturbation level of theory (MP2) with the augmented correlation consistent basis set of double zeta quality (aug-cc-pVDZ) at the corresponding minimum energy geometries. The computed infrared (IR) spectra are the first ones obtained from first principles for these clusters. They were found to contain spectral features, which can be directly mapped onto the distinctive spectroscopic signatures of their constituent tetramer, pentamer and octamer fragments. The dodecahedron spectra show the richest structure in the OH stretching region and are associated with the most red-shifted OH vibrations with respect to the monomer. The lowest lying face-sharing pentagonal prism isomer displays intense IR active vibrations that are red-shifted by {approx}600 cm{sup -1} with respect to the water monomer. The zero-point energy corrected MP2/CBS (complete basis set) limit binding energies (D{sub 0}) for the four isomers are -163.1 kcal/mol (face-sharing pentagonal prism), -160.1 kcal/mol (edgesharing pentagonal prism), -157.5 kcal/mol (fused cubes) and -148.1 kcal/mol (dodecahedron).

  16. Observation of Electronic Structure Minima in High-Harmonic Generation

    SciTech Connect

    Woerner, Hans Jakob; Villeneuve, D. M.; Niikura, Hiromichi; Bertrand, Julien B.; Corkum, P. B.

    2009-03-13

    We report detailed measurements of the high-harmonic spectra generated from argon atoms. The spectra exhibit a deep minimum that is shown to be independent of the laser intensity, and is thus a clear measure of the electronic structure of the atom. We show that exact field-free continuum wave functions reproduce the minimum, but plane wave and Coulomb wave functions do not. This remarkable observation suggests that electronic structure can be accurately determined in high-harmonic experiments despite the presence of the strong laser field. Our results clarify the relation between high-harmonic generation and photoelectron spectroscopy. The use of exact continuum functions also resolves the ambiguity associated with the choice of the dispersion relation.

  17. Deciphering Solar Magnetic Activity: On Grand Minima in Solar Activity

    NASA Astrophysics Data System (ADS)

    Mcintosh, Scott; Leamon, Robert

    2015-07-01

    The Sun provides the energy necessary to sustain our existence. While the Sun provides for us, it is also capable of taking away. The weather and climatic scales of solar evolution and the Sun-Earth connection are not well understood. There has been tremendous progress in the century since the discovery of solar magnetism - magnetism that ultimately drives the electromagnetic, particulate and eruptive forcing of our planetary system. There is contemporary evidence of a decrease in solar magnetism, perhaps even indicators of a significant downward trend, over recent decades. Are we entering a minimum in solar activity that is deeper and longer than a typical solar minimum, a "grand minimum"? How could we tell if we are? What is a grand minimum and how does the Sun recover? These are very pertinent questions for modern civilization. In this paper we present a hypothetical demonstration of entry and exit from grand minimum conditions based on a recent analysis of solar features over the past 20 years and their possible connection to the origins of the 11(-ish) year solar activity cycle.

  18. Tunneling from super- to normal-deformed minima in nuclei.

    SciTech Connect

    Khoo, T. L.

    1998-01-08

    An excited minimum, or false vacuum, gives rise to a highly elongated superdeformed (SD) nucleus. A brief review of superdeformation is given, with emphasis on the tunneling from the false to the true vacuum, which occurs in the feeding and decay of SD bands. During the feeding process the tunneling is between hot states, while in the decay it is from a cold to a hot state. The {gamma} spectra connecting SD and normal-deformed (ND) states provide information on several physics issues: the decay mechanism; the spin/parity quantum numbers, energies and microscopic structures of SD bands; the origin of identical SD bands; the quenching of pairing with excitation energy; and the chaoticity of excited ND states at 2.5-5 MeV. Other examples of tunneling in nuclei, which are briefly described, include the possible role of tunneling in {Delta}I = 4 bifurcation in SD bands, sub-barrier fusion and proton emitters.

  19. The 11-year solar cycle continues during prolonged sunspot minima

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2012-12-01

    Streaming into the solar system at nearly the speed of light, galactic cosmic rays (GCRs) are a high-energy mix of protons, electrons, and atomic nuclei. As they pass into reach of the outflowing solar wind, the propagation of GCRs is inhibited. Galactic cosmic rays that make it to Earth interact with the atmosphere, creating a shower of heavy isotopes including beryllium-10. Beryllium-10 isotope concentrations recorded in ice cores provide a long-term, high temporal resolution record of galactic cosmic ray flux.

  20. Grand Minima: Is The Sun Going To Sleep?

    NASA Astrophysics Data System (ADS)

    Mcintosh, S. W.; Leamon, R. J.

    2014-12-01

    We explore recent observational work which indicate that the energetics of the sun's outer atmosphere have been on a steady decline for the past decade and perhaps longer. Futher, we show that new investigations into evolution of the Sun's global magnetic activity appear to demonstrate a path through which the Sun can go into, and exit from, a grand activity minimum without great difficulty while retaining an activity cycle - only losing sunspots. Are we at the begining of a new grand(-ish) minimum? Naturally, only time will tell, but the observational evidence hint that one may not be far off to what impact on the Sun-Earth Connection.

  1. An ab initio method for locating potential energy minima

    SciTech Connect

    Bock, Nicolas; Peery, Travis; Venneri, Giulia; Chisolm, Eric; Wallace, Duane; Lizarraga, Raquel; Holmstrom, Erik

    2009-01-01

    We study the potential energy landscape underlying the motion of monatomic liquids by quenching from random initial configurations (stochastic configurations) to the nearest local minimum of the potential energy. We show that this procedure reveals the underlying potential energy surface directly. This is in contrast to the common technique of quenching from a molecular dynamics trajectory which does not allow a direct view of the underlying potential energy surface, but needs to be corrected for thermodynamic weighting factors.

  2. Two-center minima in harmonic spectra from aligned polar molecules

    SciTech Connect

    Etches, Adam; Gaarde, Mette B.; Madsen, Lars Bojer

    2011-08-15

    We extend a model of two-center interference to include the superposition of opposite orientations in aligned polar molecules. We show that the position of the minimum in the harmonic spectrum from both aligned and oriented CO depends strongly on the relative recombination strength at different atoms, not just the relative phase. We reinterpret the minimum in aligned CO as an interference between opposite orientations, and obtain good agreement with numerical calculations. Inclusion of the first-order Stark effect shifts the position of the interference minimum in aligned CO even though aligned molecules do not posses total permanent dipoles. We explain the shift in terms of the phase that the electron of oriented CO accumulates due to the Stark effect.

  3. VizieR Online Data Catalog: Massive LMC eclipsing binaries minima timings (Zasche+, 2016)

    NASA Astrophysics Data System (ADS)

    Zasche, P.; Wolf, M.; Vrastil, J.; Pilarcik, L.; Jurysek, J.

    2016-04-01

    For the first time, in this study we derived the relatively short periods of modulation in these systems, which relates to third bodies. The orbital periods resulted from 3.6 to 11.3yr and the eccentricities were found to be up to 0.64. This is the first time that this kind of analysis for the set of extragalactic sources has been performed. The Wolf-Rayet system OGLE-LMC-ECL-08823 is the most mysterious one, owing to the resultant high mass function. Another system, OGLE-LMC-ECL-19996, was found to contain a third body with a very high mass (M3,min=26Mȯ). One system (OGLE-LMC-ECL-09971) is suspicious because of its eccentricity, and another one (OGLE-LMC-ECL-20162) shows some light curve variability, with a possible flare-like or microlensing-like event. (2 data files).

  4. Comparing the Internal Structure of the Sun During the Cycle 23 and Cycle 24 Minima

    NASA Astrophysics Data System (ADS)

    Basu, S.; Broomhall, A.-M.; Chaplin, W. J.; Elsworth, Y.; Davies, G. R.; Schou, J.; Larson, T. P.

    2013-12-01

    The Birmingham Solar-Oscillations Network (BiSON) has been collecting helioseismic data for the last three solar cycles. We use these data to determine whether the internal properties of the Sun during the minimum preceding cycle 24 was different compared to that preceding cycle 23.

  5. VizieR Online Data Catalog: Times of minima for 18 LMC eclipsing binaries (Zasche+, 2015)

    NASA Astrophysics Data System (ADS)

    Zasche, P.; Wolf, M.; Vrastil, J.; Pilarcik, L.

    2016-04-01

    New CCD photometry was obtained at the La Silla Observatory in Chile, where the 1.54m Danish telescope with the CCD camera and R filter was used (remotely operated from the Czech Republic). All new times of minimum are given in Table1. (2 data files).

  6. First report of leaf rust of blueberry caused by Thekopsora minima in Mexico

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Blueberry (Vaccinium corymbosum L.) is becoming an important crop in the states of Jalisco and Michoacan in Mexico. As the area under blueberry cultivation increases, new diseases causing severe losses are appearing. Leaf rust is one of the most destructive diseases of blueberry in Mexico. Sori on t...

  7. Radar Inaccuracies and Mid-Air Collision Risk: Part 2 En Route Radar Separation Minima

    NASA Astrophysics Data System (ADS)

    Brooker, Peter

    2004-01-01

    A review of safety targets for en route ATC radar separation suggests that the existing target level of safety (TLS) is over-cautious. If risk budgeting principles are followed consistently, a ‘radar TLS’ of 1·0×10[minus sign]9 fatal aircraft accidents per flying hour is appropriate. This rate is consistent with Joint Aviation Authorities (JAA) guidance on system failure conditions leading to catastrophic accidents. Dynamic and static calculations using published data are compared. The new methodology shows where there are problems with the traditional static calculations, and how to improve the estimation. A further improvement introduces a simple robust model of the controller's decision processes. The focus is not on describing what controllers would generally do, but on setting criteria based on what they could not reasonably be expected to do. This additional ingredient into the calculation adds realism and ensures that attention is focused on hazardous correlated errors. Focused data collection would be an essential component of new risk estimates. The key information required would be on radar performance and the nature and frequency of use of radar separation, including the relative velocities for proximate events at closest point of approach and the frequency of correlated gross errors (through a conditional probability factor). If this factor is not properly taken into account, then the data collection and analysis could be inefficient.

  8. Comparison of Coronal Streamer Properties to Solar Wind Models For The Last Two Solar Cycle Minima

    NASA Astrophysics Data System (ADS)

    Miralles, Mari Paz; Landi, E.; Cranmer, S. R.; Raymond, J. C.; Cohen, O.; Oran, R.

    2013-07-01

    We characterize the physical properties of two coronal streamers during Earth/Ulysses quadrature configurations for the previous two solar minimum periods. Comparisons between coronal remote-sensing observations and in situ measurements of solar wind plasma properties are being used to characterize the origin of slow wind streams. In order to investigate slow solar wind heating and acceleration, we compare the measurements with predictions from MHD models. We aim to use the empirical measurements to distinguish between different proposed physical processes for the slow solar wind. This work is supported by NASA grant NNX10AQ58G to the Smithsonian Astrophysical Observatory.

  9. Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

    NASA Astrophysics Data System (ADS)

    Augustson, Kyle; Brun, Allan Sacha; Miesch, Mark; Toomre, Juri

    2015-08-01

    The 3D MHD Anelastic Spherical Harmonic code, using slope-limited diffusion, is employed to capture convective and dynamo processes achieved in a global-scale stellar convection simulation for a model solar-mass star rotating at three times the solar rate. The dynamo-generated magnetic fields possesses many timescales, with a prominent polarity cycle occurring roughly every 6.2 years. The magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation. The polarity reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. An equatorial migration of the magnetic field is seen, which is due to the strong modulation of the differential rotation rather than a dynamo wave. A poleward migration of magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families. This intermittent dynamo state potentially results from the simulation’s relatively low magnetic Prandtl number. A mean-field-based analysis of this dynamo simulation demonstrates that it is of the α-Ω type. The timescales that appear to be relevant to the magnetic polarity reversal are also identified.

  10. Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo

    NASA Astrophysics Data System (ADS)

    Augustson, Kyle C.; Brun, Allan Sacha; Miesch, Mark; Toomre, Juri

    2015-08-01

    The 3-D magnetohydrodynamic (MHD) Anelastic Spherical Harmonic (ASH) code, using slope-limited diffusion, is employed to capture convective and dynamo processes achieved in a global-scale stellar convection simulation for a model solar-mass star rotating at three times the solar rate. The dynamo generated magnetic fields possesses many time scales, with a prominent polarity cycle occurring roughly every 6.2 years. The magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation. The polarity reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. An equatorial migration of the magnetic field is seen, which is due to the strong modulation of the differential rotation rather than a dynamo wave. A poleward migration of magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families. This intermittent dynamo state potentially results from the simulations relatively low magnetic Prandtl number. A mean-field-based analysis of this dynamo simulation demonstrates that it is of the α-Ω type. The time scales that appear to be relevant to the magnetic polarity reversal are also identified.

  11. VizieR Online Data Catalog: Minima of 41 binaries from entire Kepler mission (Gies+, 2015)

    NASA Astrophysics Data System (ADS)

    Gies, D. R.; Matson, R. A.; Guo, Z.; Lester, K. V.; Orosz, J. A.; Peters, G. J.

    2016-06-01

    We embarked on a search for eclipse timing variations among a subset of 41 eclipsing binaries that were identified prior to the start of Kepler observations (see our first paper, Gies et al. 2012, cat. J/AJ/143/137). Our first paper documented the eclipse times in observations made over quarters Q0-Q9 (2009.3-2011.5). Now with the Kepler mission complete with observations through Q17 (ending 2013.4), we present here the eclipse timings for our sample of 41 binaries over the entire duration of the mission. The associated times given in our first paper were based upon UTC (Coordinated Universal Time) while the current set uses TDB (Barycentric Dynamical Time), and here we report the times in reduced Barycentric Julian Date (BJD-2400000 days). We used the Simple Aperture Photometry (SAP) flux except in the case of KIC04678873. The list of targets appears in Table1. The eclipse timing measurements were made in almost the same way as described in our first paper. Our measurements appear in Table2. (2 data files).

  12. Global Solar Convective Dynamo with Cycles, Equatorward Propagation and Grand Minima

    NASA Astrophysics Data System (ADS)

    Toomre, Juri; Augustson, Kyle C.; Brun, Allan Sacha; Miesch, Mark S.

    2016-05-01

    The 3-D MHD Anelastic Spherical Harmonic (ASH) code, using slope-limited diffusion, is used to study the interaction of turbulent convection, rotation and magnetism in a full spherical shell comparable to the solar convection zone. Here a star of one solar mass, with a solar luminosity, is considered that is rotating at three times the solar rate. The dynamo generated magnetic field forms large-scale toroidal wreaths, whose formation is tied to the low Rossby number of the convection in this simulation which we have labeled K3S. This case displays prominent polarity cycles with regular reversals occurring roughly every 6.2 years. These reversals are linked to the weakened differential rotation and a resistive collapse of the large-scale magnetic field. Distinctive equatorial migration of the strong magnetic wreaths is seen, arising from modulation of the differential rotation rather than a dynamo wave. As the wreaths approach the equator, cross-equatorial magnetic flux is achieved that permits the low-latitude convection to generate poloidal magnetic field with opposite polarity. Poleward migration of such magnetic flux from the equator eventually leads to the reversal of the polarity of the high-latitude magnetic field. This K3S simulation also enters an interval with reduced magnetic energy at low latitudes lasting roughly 16 years (about 2.5 polarity cycles), during which the polarity cycles are disrupted and after which the dynamo recovers its regular polarity cycles. An analysis of this striking grand minimum reveals that it likely arises through the interplay of symmetric and antisymmetric dynamo families.

  13. VizieR Online Data Catalog: Time minima of EP Aur (Li+, 2015)

    NASA Astrophysics Data System (ADS)

    Li, H.-L.; Wei, J.-Y.; Yang, Y.-G.; Li, K.; Zhang, X.-B.

    2015-07-01

    From 2003 December to 2014 January, the photometry of EP Aur was performed by using the 60-cm telescope and the 85-cm telescope at the Xinglong station (XLs) of National Astronomical Observatories of China (NAOC), and the 1.0-m telescope at the Weihai Observatory (WHO) of Shandong University. The three telescopes were equipped with standard Johnson-Cousins UBVRcIc systems. All observed images were reduced by using the IMREDIMRED and APPHOTAPPHOT packages in IRAF in a standard fashion. The multi-color photometry of EP Aur was carried out on 2013 December 1, 2, 3, and 5, 2009 January 3, 4 and 5 using the 60-cm telescope at XLs. TYC 2420-434-1 and TYC 2420-193-1 were taken as the comparison and check stars respectively. (2 data files).

  14. The role of the oceanic oxygen minima in generating biodiversity in the deep sea

    NASA Astrophysics Data System (ADS)

    Rogers, Alex D.

    2000-01-01

    Many studies on the deep-sea benthic biota have shown that the most species-rich areas lie on the continental margins between 500 and 2500 m, which coincides with the present oxygen-minimum in the world's oceans. Some species have adapted to hypoxic conditions in oxygen-minimum zones, and some can even fulfil all their energy requirements through anaerobic metabolism for at least short periods of time. It is, however, apparent that the geographic and vertical distribution of many species is restricted by the presence of oxygen-minimum zones. Historically, cycles of global warming and cooling have led to periods of expansion and contraction of oxygen-minimum layers throughout the world's oceans. Such shifts in the global distribution of oxygen-minimum zones have presented many opportunities for allopatric speciation in organisms inhabiting slope habitats associated with continental margins, oceanic islands and seamounts. On a smaller scale, oxygen-minimum zones can be seen today as providing a barrier to gene-flow between allopatric populations. Recent studies of the Arabian Sea and in other regions of upwelling also have shown that the presence of an oxygen-minimum layer creates a strong vertical gradient in physical and biological parameters. The reduced utilisation of the downward flux of organic material in the oxygen-minimum zone results in an abundant supply of food for organisms immediately below it. The occupation of this area by species exploiting abundant food supplies may lead to strong vertical gradients in selective pressures for optimal rates of growth, modes of reproduction and development and in other aspects of species biology. The presence of such strong selective gradients may have led to an increase in habitat specialisation in the lower reaches of oxygen-minimum zones and an increased rate of speciation.

  15. VizieR Online Data Catalog: HL Aur light curves and minima (Zhang+ 1997)

    NASA Astrophysics Data System (ADS)

    Zhang, R. X.; Fang, M. J.; Zhai, D. S.

    1996-11-01

    Photoelectric observations of HL Aur were carried out with the 60cm reflector of Beijing Astronomical Observatory in 1990 and 1994, and the first photoelectric BV light curves were obtained along with a newly derived ephemeris. The period of the system appears to be constant over the past 65-years. Using the Wilson-Devinney program a photometric analysis of the B and V light curves is performed. It is evident that HL Aur is a near-contact binary with a mass ratio of q=m2/m1=0.722+/-0.011. The primary component of the system is essentially in contact with its Roche lobe, while the secondary is detached but nearly in contact with its lobe. It is found that the components of the system are slightly evolved and located near the terminal-age main sequence. The binary is consistent with the general evolutionary picture for near-contact systems. (3 data files).

  16. Constraints from color and/or charge breaking minima in the supersymmetric standard model with right-handed neutrinos

    SciTech Connect

    Kobayashi, Tatsuo; Shimomura, Takashi

    2010-08-01

    We consider a model where right-handed neutrinos and sneutrinos are introduced to the minimal supersymmetric standard model. In the scalar potential of this model, there exist trilinear and quartic terms in scalar potential that are proportional to Yukawa couplings of neutrinos. Because of these trilinear and quartic terms, color and/or charge breaking (CCB) and unbounded-from-below (UFB) directions appear along which sneutrinos have a vacuum expectation value, making the vacuum of the electroweak symmetry breaking unstable. We analyze the scalar potential of this model and derive necessary conditions for color and/or charge breaking and unbounded-from-below directions to vanish.

  17. Variability of ionospheric TEC during solar and geomagnetic minima (2008 and 2009): external high speed stream drivers

    NASA Astrophysics Data System (ADS)

    Verkhoglyadova, O. P.; Tsurutani, B. T.; Mannucci, A. J.; Mlynczak, M. G.; Hunt, L. A.; Runge, T.

    2013-02-01

    We study solar wind-ionosphere coupling through the late declining phase/solar minimum and geomagnetic minimum phases during the last solar cycle (SC23) - 2008 and 2009. This interval was characterized by sequences of high-speed solar wind streams (HSSs). The concomitant geomagnetic response was moderate geomagnetic storms and high-intensity, long-duration continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map (GIM) software and the GPS total electron content (TEC) database were used to calculate the vertical TEC (VTEC) and estimate daily averaged values in separate latitude and local time ranges. Our results show distinct low- and mid-latitude VTEC responses to HSSs during this interval, with the low-latitude daytime daily averaged values increasing by up to 33 TECU (annual average of ~20 TECU) near local noon (12:00 to 14:00 LT) in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval, the response to HSSs was a maximum of ~30 TECU increases with a slightly lower average value than in 2008. There was a weak nighttime ionospheric response to the HSSs. A well-studied solar cycle declining phase interval, 10-22 October 2003, was analyzed for comparative purposes, with daytime low-latitude VTEC peak values of up to ~58 TECU (event average of ~55 TECU). The ionospheric VTEC changes during 2008-2009 were similar but ~60% less intense on average. There is an evidence of correlations of filtered daily averaged VTEC data with Ap index and solar wind speed. We use the infrared NO and CO2 emission data obtained with SABER on TIMED as a proxy for the radiation balance of the thermosphere. It is shown that infrared emissions increase during HSS events possibly due to increased energy input into the auroral region associated with HILDCAAs. The 2008-2009 HSS intervals were ~85% less intense than the 2003 early declining phase event, with annual averages of daily infrared NO emission power of ~ 3.3 × 1010 W and 2.7 × 1010 W in 2008 and 2009, respectively. The roles of disturbance dynamos caused by high-latitude winds (due to particle precipitation and Joule heating in the auroral zones) and of prompt penetrating electric fields (PPEFs) in the solar wind-ionosphere coupling during these intervals are discussed. A correlation between geoeffective interplanetary electric field components and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms could play important roles in solar wind-ionosphere coupling during prolonged (up to days) external driving within HILDCAA intervals.

  18. On the crossing points of the Lamb modes and the maxima and minima of displacements observed at the surface☆

    PubMed Central

    Veres, István A.; Berer, Thomas; Grünsteidl, Clemens; Burgholzer, Peter

    2014-01-01

    This article elaborates on the crossing points of the frequency–wavenumber branches for the symmetric and anti-symmetric Lamb modes in a homogeneous plate. It is shown both theoretically as well as experimentally that at these crossing points either the normal or the longitudinal components of modal displacement attain an extreme value, i.e. a maximum or it vanishes. This behavior is assessed herein using a method due to Mindlin, who showed that the dispersion curves for a plate with mixed boundary conditions – which are associated with uncoupled shear and dilatational modes – provide bounds to the spectral lines of the free plate. Therefore, a subset of the crossing points of the symmetric and antisymmetric Lamb modes for a free plate coincide with the crossing points for a plate with mixed boundary conditions. PMID:24268025

  19. The GSAM software: A global search algorithm of minima exploration for the investigation of low lying isomers of clusters

    SciTech Connect

    Marchal, Rémi; Carbonnière, Philippe; Pouchan, Claude

    2015-01-22

    The study of atomic clusters has become an increasingly active area of research in the recent years because of the fundamental interest in studying a completely new area that can bridge the gap between atomic and solid state physics. Due to their specific properties, such compounds are of great interest in the field of nanotechnology [1,2]. Here, we would present our GSAM algorithm based on a DFT exploration of the PES to find the low lying isomers of such compounds. This algorithm includes the generation of an intial set of structure from which the most relevant are selected. Moreover, an optimization process, called raking optimization, able to discard step by step all the non physically reasonnable configurations have been implemented to reduce the computational cost of this algorithm. Structural properties of Ga{sub n}Asm clusters will be presented as an illustration of the method.

  20. Pronounced Minima in Tropospheric Ozone and OH above the Tropical West Pacific and their Role for Stratospheric Composition

    NASA Astrophysics Data System (ADS)

    Rex, M.; Wohltmann, I.; Lehmann, R.; Rosenlof, K. H.; Wennberg, P. O.; Weisenstein, D. K.; Notholt, J.; Krüger, K.; Mohr, V.; Tegtmeier, S.

    2014-12-01

    Hundreds of organic species are emitted into the atmosphere mostly from biogenic processes. The rapid breakdown by reactions with OH radicals prevents most of them from reaching the stratosphere. Hence, the omnipresent layer of OH in the troposphere shields the stratosphere from these emissions and is particularly relevant for those species that do not photolyse efficiently. Reactions involving ozone are a strong source of OH in clean tropical air. Hence the OH concentration is closely coupled to ozone abundances. The Western Pacific warm pool is key for troposphere to stratosphere exchange. We report measurements of 14 ozonesondes launched during the Transbrom ship cruise through the center of the warm pool. During a 2500km portion of the ship track between 10S and 15N we found ozone concentrations below the detection limit of the sondes throughout the troposphere. We will discuss the uncertainties of ozonesonde measurements at very low ozone concentrations, the robustness of our observations and the upper limit of the ozone concentration that would be consistent with our raw data. Based on modelling and measurements of OH on the ER-2 during the STRAT campaign we suggest that there also is a pronounced minimum in the tropospheric column of OH over the tropical West Pacific. We show that this increases the lifetime of chemical species and has the potential to amplify the impact of surface emissions on the stratospheric composition. Specifically, we discuss the role of emissions of biogenic halogenated species from this geographic region for stratospheric ozone depletion. Also, we discuss the potential role of increasing anthropogenic emissions of SO2 in South East Asia or from minor volcanic eruptions for the stratospheric aerosol budget.

  1. Binary complexes of ammonia with phenylacetylenes: a combined experimental and computational approach to explore multiple minima on intermolecular potentials.

    PubMed

    Dey, Arghya; Mondal, Sohidul Islam; Patwari, G Naresh

    2013-03-18

    The hydrogen-bonded complexes of phenylacetylene, 4-fluorophenylacetylene, 2-fluorophenylacetylene, and 2,6-difluorophenylacetylene with ammonia are investigated using IR-UV double resonance spectroscopy in combination with high-level ab initio calculations at the CCSD(T)/CBS level of theory. The C-H···N hydrogen-bonded complex, which involves an interaction of ammonia with the acetylenic CH group is the global minimum and is observed in all four cases investigated. In addition, phenylacetylene and 4-fluorophenylacetylene form a quasi-planar cyclic complexes with ammonia incorporating N-H···π and C-H···N hydrogen bonds, wherein the π-electron density of the acetylenic C≡C bond acts as an acceptor to the N-H group of ammonia. A third ammonia complex is observed for 4-fluorophenylacetylene in which ammonia interacts with the fluorine atom once again, leading to the formation of a quasi-planar cyclic complex. The substitution of the fluorine atom on the phenyl ring of phenylacetylene modulates the intermolecular potentials, which are dependent on the position of the substitution. PMID:23281120

  2. HEMISPHERIC ASYMMETRIES IN THE POLAR SOLAR WIND OBSERVED BY ULYSSES NEAR THE MINIMA OF SOLAR CYCLES 22 AND 23

    SciTech Connect

    Ebert, R. W.; Dayeh, M. A.; Desai, M. I.; McComas, D. J.; Pogorelov, N. V.

    2013-05-10

    We examined solar wind plasma and interplanetary magnetic field (IMF) observations from Ulysses' first and third orbits to study hemispheric differences in the properties of the solar wind and IMF originating from the Sun's large polar coronal holes (PCHs) during the declining and minimum phase of solar cycles 22 and 23. We identified hemispheric asymmetries in several parameters, most notably {approx}15%-30% south-to-north differences in averages for the solar wind density, mass flux, dynamic pressure, and energy flux and the radial and total IMF magnitudes. These differences were driven by relatively larger, more variable solar wind density and radial IMF between {approx}36 Degree-Sign S-60 Degree-Sign S during the declining phase of solar cycles 22 and 23. These observations indicate either a hemispheric asymmetry in the PCH output during the declining and minimum phase of solar cycles 22 and 23 with the southern hemisphere being more active than its northern counterpart, or a solar cycle effect where the PCH output in both hemispheres is enhanced during periods of higher solar activity. We also report a strong linear correlation between these solar wind and IMF parameters, including the periods of enhanced PCH output, that highlight the connection between the solar wind mass and energy output and the Sun's magnetic field. That these enhancements were not matched by similar sized variations in solar wind speed points to the mass and energy responsible for these increases being added to the solar wind while its flow was subsonic.

  3. HfO{sub 2} dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

    SciTech Connect

    Zhang, Cheng; Xie, Dan Xu, Jian-Long; Sun, Yi-Lin; Dai, Rui-Xuan; Li, Xian; Li, Xin-Ming; Zhu, Hong-Wei

    2015-10-14

    We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO{sub 2} dielectric and different thickness of high-k HfO{sub 2} dielectric. The results show that transform characteristic (I{sub ds}–V{sub gs}) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO{sub 2} and HfO{sub 2} dielectric (SiO{sub 2}-GFETs and HfO{sub 2}-GFETs). The gate voltage reduces drastically in HfO{sub 2}-GFETs compared with that in SiO{sub 2}-GFETs, and it becomes much smaller with the decline of HfO{sub 2} thickness. The left charge neutrality point in I{sub d}–V{sub g} curves of all HfO{sub 2}-GFETs is negative, compared to the positive ones in SiO{sub 2}-GFETs, which means that there exists n-doping in graphene with HfO{sub 2} as bottom dielectric. We speculate that this n-doping comes from the HfO{sub 2} layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO{sub 2}-GFETs contrast to that in SiO{sub 2}-GFETs. In a series of HfO{sub 2}-GFETs with different HfO{sub 2} dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO{sub 2} film from atomic layer deposition process, the concentration of which varies from the thickness of HfO{sub 2} layer.

  4. In search of radiation minima for balancing the needs of forest and water management in snow dominated watersheds (Invited)

    NASA Astrophysics Data System (ADS)

    Kumar, M.; Seyednasrollah, B.; Link, T. E.

    2013-12-01

    In upland snowfed forested watersheds, where the majority of melt recharge occurs, there is growing interest among water and forest managers to strike a balance between maximizing forest productivity and minimizing impacts on water resources. Implementation of forest management strategies that involve reduction of forest cover generally result in increased water yield and peak flows from forests, which has potentially detrimental consequences including increased erosion, stream destabilization, water shortages in late melt season, and degradation of water quality and ecosystem health. These ill effects can be partially negated by implementing optimal gap patterns and vegetation densities through forest management, that may minimize net radiation on snow-covered forest floor (NRSF). A small NRSF can moderate peak flows and increase water availability late in the melt season. Since forest canopies reduce direct solar (0.28 - 3.5 μm) radiation but increase longwave (3.5-100 μm) radiation at the snow surface, by performing detailed quantification of individual radiation components for a range of vegetation density and and gap configurations, we identify the optimal vegetation configurations. We also evaluate the role of site location, its topographic setting, local meteorological conditions and vegetation morphological characteristics, on the optimal configurations. The results can be used to assist forest managers to quantify the radiative regime alteration for various thinning and gap-creation scenarios, as a function of latitudinal, topographic, climatic and vegetation characteristics.

  5. Curvature and the Visual Perception of Shape: Theory on Information along Object Boundaries and the Minima Rule Revisited

    ERIC Educational Resources Information Center

    Lim, Ik Soo; Leek, E. Charles

    2012-01-01

    Previous empirical studies have shown that information along visual contours is known to be concentrated in regions of high magnitude of curvature, and, for closed contours, segments of negative curvature (i.e., concave segments) carry greater perceptual relevance than corresponding regions of positive curvature (i.e., convex segments). Lately,…

  6. The Local Minima Problem in Hierarchical Classes Analysis: An Evaluation of a Simulated Annealing Algorithm and Various Multistart Procedures

    ERIC Educational Resources Information Center

    Ceulemans, Eva; Van Mechelen, Iven; Leenen, Iwin

    2007-01-01

    Hierarchical classes models are quasi-order retaining Boolean decomposition models for N-way N-mode binary data. To fit these models to data, rationally started alternating least squares (or, equivalently, alternating least absolute deviations) algorithms have been proposed. Extensive simulation studies showed that these algorithms succeed quite…

  7. Emergent phase shift between diurnal transpiration maxima and stream flow minima during base flow as diagnostic of eco-hydrologic interactions in landscapes

    NASA Astrophysics Data System (ADS)

    Zanardo, Stefano; Hilberts, Arno; Foufoula-Georgiou, Efi; Dietrich, William

    2014-05-01

    Diurnal oscillations in river base flow are frequently observed in hydrological datasets, yet have only been examined in a few, exploratory studies. In this work we focus on the oscillation shift between base flow and the forcing signal, which, in the case study at hand, is essentially dominated by the tree transpiration oscillation. This quantity characterizes the propagation time of the forcing throughout the river basin, and will be referred to as Eco-hydrological Phase Shift (EHPS). In principle, it is reasonable to hypothesize that EHPS depends on the combination of hillslope and channel characteristic transport times, however it is unclear whether and how its value varies over a range of spatial scales. This is the central question of the study. We analyzed base flow data collected between 2009 and 2012 in 8 stations within the Eel river basin (Mendocino county, CA), where the typical Mediterranean climate allows for long, undisturbed summer base flow recessions. The drainage areas relative to each gauging station span over four orders of magnitude, ranging from ~10 km2 to ~10000 km2. We found that, despite the wide range of spatial scales, EHPS by late summer tends to a remarkably narrow range of values, between 8 and 11 hours for all the stations considered. This implies that the timing of diurnal oscillations is dominated by hillslope rather than river network processes, even at large spatial scales. We then propose a simple, conceptual model to explore the hillslope controls on EHPS. The framework allows deriving analytical expressions for EHPS under different 'behavioral assumptions' for vegetation water-use. Results show that, within this framework, a delay of 8-11 hours can only be observed if tree roots exclusively use water from the unsaturated zone and variations within that range are due to different signal propagation times in both the unsaturated and the saturated zone. This analysis demonstrates that EHPS represents a scale-invariant signature of river basins and can be used to further explore the eco-hydrological interactions between hillslopes and streams.

  8. Bromine enrichment in marsh sediments as a marker of environmental changes driven by Grand Solar Minima and anthropogenic activity (Caminha, NW of Portugal).

    PubMed

    Moreno, J; Fatela, F; Leorri, E; Araújo, M F; Moreno, F; De la Rosa, J; Freitas, M C; Valente, T; Corbett, D R

    2015-02-15

    A sediment core collected in Caminha tidal marsh, NW Portugal, was used to assess bromine (Br) signal over the last ca. 1,700 years. The Br temporal variability reflects its close relationship with soil/sediment organic matter (OM) and also alterations in Br biogeochemical recycling in marsh environment. The highest Br enrichment in sediments was found during the Maunder Solar Minimum, a major solar event characterized by lower irradiance (TSI) and temperature, increased cloudiness and albedo. The obtained results suggest that those climate-induced changes weakened the natural mechanisms that promote Br biochemical transformations, driven by both living plants metabolism and plant litter degradation, with the ensuing generation of volatile methyl bromide (CH3Br). It seems that the prevailing climate conditions during the Maunder favoured the retention of more Br in marsh ecosystem, ultimately decreasing the biogenic Br emissions to the atmosphere. During the 20th century, the Br pattern in sediments appears to mirror likewise anthropogenic sources. The significant correlation (p<0.05) between Br/OM ratios and Pb contents in sediments after 1934 suggests a common source. This is most probably related with the rise, massive consumption and prohibition of leaded gasoline, where ethylene dibromide was added as lead scavenger to antiknock mixtures. More regionally, the concerted use of flame retardants on forest fire management, covering the 1980s through mid-1990s in the north of Portugal and Galicia, could be responsible for the observed increase of sediment Br (relatively to Pb) pool of this tidal marsh. Although man-made brominated compounds are being phased-out since the inception of the 1992 Montreal Protocol, the Caminha tidal marsh sedimentary record showed that Br levels only started to decline after 2002. PMID:25433387

  9. Temperature minima in the average thermal structure of the middle mesosphere (70 - 80 km) from analysis of 40- to 92-km SME global temperature profiles

    NASA Technical Reports Server (NTRS)

    Clancy, R. Todd; Rusch, David W.; Callan, Michael T.

    1994-01-01

    Global temperatures have been derived for the upper stratosphere and mesosphere from analysis of Solar Mesosphere Explorer (SME) limb radiance profiles. The SME temperature represent fixed local time observations at 1400 - 1500 LT, with partial zonal coverage of 3 - 5 longitudes per day over the 1982-1986 period. These new SME temperatures are compared to the COSPAR International Ionosphere Reference Atmosphere 86 (CIRA 86) climatology (Fleming et al., 1990) as well as stratospheric and mesospheric sounder (SAMS); Barnett and Corney, 1984), National Meteorological Center (NMC); (Gelman et al., 1986), and individual lidar and rocket observations. Significant areas of disagreement between the SME and CIRA 86 mesospheric temperatures are 10 K warmer SME temperatures at altitudes above 80 km. The 1981-1982 SAMS temperatures are in much closer agreement with the SME temperatures between 40 and 75 km. Although much of the SME-CIRA 86 disagreement probably stems from the poor vertical resolution of the observations comprising the CIRA 86 modelm, some portion of the differences may reflect 5- to 10-year temporal variations in mesospheric temperatures. The CIRA 86 climatology is based on 1973-1978 measurements. Relatively large (1 K/yr) 5- to 10-year trends in temperatures as functions of longitude, latitude, and altitude have been observed for both the upper stratosphere (Clancy and Rusch, 1989a) and mesosphere (Clancy and Rusch, 1989b; Hauchecorne et al., 1991). The SME temperatures also exhibit enhanced amplitudes for the semiannual oscillation (SAO) of upper mesospheric temperatures at low latitudes, which are not evident in the CIRA 86 climatology. The so-called mesospheric `temperature inversions' at wintertime midlatitudes, which have been observed by ground-based lidar (Hauschecorne et al., 1987) and rocket in situ measurements (Schmidlin, 1976), are shown to be a climatological aspect of the mesosphere, based on the SME observations.

  10. Quantum chemical and matrix-IR characterization of CH3CN-BCl3: a complex with two distinct minima along the B-N bond potential.

    PubMed

    Wrass, John P; Sadowsky, Daniel; Bloomgren, Kaitlin M; Cramer, Christopher J; Phillips, James A

    2014-08-21

    We have characterized the structural and energetic properties of CH3CN-BCl3via computations and matrix-IR spectroscopy. We find two equilibrium structures of the complex via computations. At the MP2/aug-cc-pVTZ level, the global minimum energy structure has a B-N distance of 1.601 Å, and a binding energy of 12.0 kcal mol(-1). The secondary structure lies 7.1 kcal mol(-1) higher in energy with a B-N distance of 2.687 Å and a binding energy of 4.9 kcal mol(-1). Computational scans of the B-N potential curve using both DFT and post-HF methods indicate that a significant barrier exists between these structures, and that it lies 1 to 2 kcal mol(-1) above the secondary minimum at a B-N distance of about 2.2 Å. We also observed several key, structurally-sensitive IR bands for six isotopic forms of the complex in neon matrices, including: the B-Cl asymmetric stretching band (ν) at 792 cm(-1) and the C-N stretching band (νCN) at 2380 cm(-1) (for the primary isotopomer, CH3C(14)N-(11)BCl3). These frequencies are consistent with computational predictions for the minimum-energy form of the complex. Energy decomposition analyses were conducted for CH3CN-BCl3 and also two related complexes, CH3CN-BF3 and CH3CN-BH3. These provide insight into the trend in Lewis acidity of the BX3 acceptors toward nitriles. Furthermore, these analyses indicate that the barrier along the B-N potential of CH3CN-BCl3 results from Pauli repulsion between the π electrons on the nitrile moiety and the chlorine atoms in BCl3, which is significant at relatively long distances where attractive bonding interactions fail to overcome it. PMID:24984763

  11. He II λ4686 Emission from the Massive Binary System in η Car: Constraints to the Orbital Elements and the Nature of the Periodic Minima

    NASA Astrophysics Data System (ADS)

    Teodoro, M.; Damineli, A.; Heathcote, B.; Richardson, N. D.; Moffat, A. F. J.; St-Jean, L.; Russell, C.; Gull, T. R.; Madura, T. I.; Pollard, K. R.; Walter, F.; Coimbra, A.; Prates, R.; Fernández-Lajús, E.; Gamen, R. C.; Hickel, G.; Henrique, W.; Navarete, F.; Andrade, T.; Jablonski, F.; Luckas, P.; Locke, M.; Powles, J.; Bohlsen, T.; Chini, R.; Corcoran, M. F.; Hamaguchi, K.; Groh, J. H.; Hillier, D. J.; Weigelt, G.

    2016-03-01

    Eta Carinae (η Car) is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He ii λ4686 line increases rapidly in strength, drops to a minimum value, then increases briefly before fading away. To understand this behavior, we conducted an intense spectroscopic monitoring of the He ii λ4686 emission line across the 2014.6 periastron passage using ground- and space-based telescopes. Comparison with previous data confirmed the overall repeatability of the line equivalent width (EW), radial velocities, and the timing of the minimum, though the strongest peak was systematically larger in 2014 than in 2009 by 26%. The EW variations, combined with other measurements, yield an orbital period of 2022.7 ± 0.3 days. The observed variability of the EW was reproduced by a model in which the line flux primarily arises at the apex of the wind-wind collision and scales inversely with the square of the stellar separation, if we account for the excess emission as the companion star plunges into the hot inner layers of the primary’s atmosphere, and including absorption from the disturbed primary wind between the source and the observer. This model constrains the orbital inclination to 135°-153°, and the longitude of periastron to 234°-252°. It also suggests that periastron passage occurred on {T}0=2456874.4\\quad (+/- 1.3 days). Our model also reproduced EW variations from a polar view of the primary star as determined from the observed He ii λ 4686 emission scattered off the Homunculus nebula. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program numbers 11506, 12013, 12508, 12750, and 13054. Support for program numbers 12013, 12508, and 12750 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  12. Exploiting Free-Energy Minima to Design Novel EphA2 Protein-Protein Antagonists: From Simulation to Experiment and Return.

    PubMed

    Russo, Simonetta; Callegari, Donatella; Incerti, Matteo; Pala, Daniele; Giorgio, Carmine; Brunetti, Jlenia; Bracci, Luisa; Vicini, Paola; Barocelli, Elisabetta; Capoferri, Luigi; Rivara, Silvia; Tognolini, Massimiliano; Mor, Marco; Lodola, Alessio

    2016-06-01

    The free-energy surface (FES) of protein-ligand binding contains information useful for drug design. Here we show how to exploit a free-energy minimum of a protein-ligand complex identified by metadynamics simulations to design a new EphA2 antagonist with improved inhibitory potency. PMID:27139720

  13. He II λ4686 Emission from the Massive Binary System in λ Car: Constraints to the Orbital Elements and the Nature of the Periodic Minima

    NASA Astrophysics Data System (ADS)

    Teodoro, M.; Damineli, A.; Heathcote, B.; Richardson, N. D.; Moffat, A. F. J.; St-Jean, L.; Russell, C.; Gull, T. R.; Madura, T. I.; Pollard, K. R.; Walter, F.; Coimbra, A.; Prates, R.; Fernández-Lajús, E.; Gamen, R. C.; Hickel, G.; Henrique, W.; Navarete, F.; Andrade, T.; Jablonski, F.; Luckas, P.; Locke, M.; Powles, J.; Bohlsen, T.; Chini, R.; Corcoran, M. F.; Hamaguchi, K.; Groh, J. H.; Hillier, D. J.; Weigelt, G.

    2016-03-01

    Eta Carinae (η Car) is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He ii λ4686 line increases rapidly in strength, drops to a minimum value, then increases briefly before fading away. To understand this behavior, we conducted an intense spectroscopic monitoring of the He ii λ4686 emission line across the 2014.6 periastron passage using ground- and space-based telescopes. Comparison with previous data confirmed the overall repeatability of the line equivalent width (EW), radial velocities, and the timing of the minimum, though the strongest peak was systematically larger in 2014 than in 2009 by 26%. The EW variations, combined with other measurements, yield an orbital period of 2022.7 ± 0.3 days. The observed variability of the EW was reproduced by a model in which the line flux primarily arises at the apex of the wind-wind collision and scales inversely with the square of the stellar separation, if we account for the excess emission as the companion star plunges into the hot inner layers of the primary’s atmosphere, and including absorption from the disturbed primary wind between the source and the observer. This model constrains the orbital inclination to 135°-153°, and the longitude of periastron to 234°-252°. It also suggests that periastron passage occurred on {T}0=2456874.4\\quad (+/- 1.3 days). Our model also reproduced EW variations from a polar view of the primary star as determined from the observed He ii λ 4686 emission scattered off the Homunculus nebula. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program numbers 11506, 12013, 12508, 12750, and 13054. Support for program numbers 12013, 12508, and 12750 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  14. High Energetic Solar Flares in the Solar Minima Activity in Comparative Study with the Solar Maxima Activity from 1954 to 2014 and Their Effects on the Space Environment

    NASA Astrophysics Data System (ADS)

    Mohamed, Wael

    Solar 11-year cycle of solar activity is characterized by the rise and fall in the numbers and areas of sunspots. On solar maximum activity, many flares and CMEs can affect the near-earth space environment. But on the solar minimum activity, there are sometimes solar proton events, (e.g. High Energetic Solar Proton Flares on the declining phase of solar cycle 22 for M.A.Mosalam Shaltout, 1995), have the same effect for those on the solar maximum activity or more. So, a study must be made for the ascending and descending phases of solar activity for a set of solar cycles (from 1954 to 2014) to confirm the conclusion of Mosalam Shaltout on the light of the present high quality observations from ground and by artificial satellites.

  15. Program of Measurement of the Asymmetry P at the Minima of the Differential Cross Section for Elastic {pi}{sup +}p Scattering

    SciTech Connect

    Beloglazov, Yu.A.; Kovalev, A.I.; Kruglov, S.P.; Novinsky, D.V.; Sumachev, V.V.; Trautman, V.Yu.; Filimonov, E.A.; Shchedrov, V.A.; Alekseev, I.G.; Budkovsky, P.E.; Zhurkin, V.V.; Kanavets, V.P.; Koroleva, L.I.; Morozov, B.V.; Nesterov, V.M.; Ryltsov, V.V.; Svirida, D.N.; Sulimov, A.D.; Bazhanov, N.A.; Bunyatova, E.I.

    2005-03-01

    A program of measurement of the polarization parameter P in elastic {pi}{sup +}p interaction in the resonance region of backward pion scattering is presented. This program is aimed at determining the bifurcation points of the trajectory of zeros of the pion-nucleon amplitude and, hence, at unambiguously reconstructing the amplitude of {pi}N scattering in the second resonance region. It is planned to perform a relevant experiment in a pion beam from the accelerator of the Institute of Experimental and Theoretical Physics (ITEP, Moscow)

  16. New Ulvaceae (Ulvophyceae, Chlorophyta) from mesophotic ecosystems across the Hawaiian Archipelago.

    PubMed

    Spalding, Heather L; Conklin, Kimberly Y; Smith, Celia M; O'Kelly, Charles J; Sherwood, Alison R

    2016-02-01

    Ulvalean algae (Chlorophyta) are most commonly described from intertidal and shallow subtidal marine environments worldwide, but are less well known from mesophotic environments. Their morphological simplicity and phenotypic plasticity make accurate species determinations difficult, even at the generic level. Here, we describe the mesophotic Ulvales species composition from 13 locations across 2,300 km of the Hawaiian Archipelago. Twenty-eight representative Ulvales specimens from 64 to 125 m depths were collected using technical diving, submersibles, and remotely operated vehicles. Morphological and molecular characters suggest that mesophotic Ulvales in Hawaiian waters form unique communities comprising four species within the genera Ulva and Umbraulva, each with discrete geographic and/or depth-related distributional patterns. Three genetically distinct taxa are supported by both plastid (rbcL and tufA) and nuclear (ITS1) markers, and are presented here as new species: Umbraulva kaloakulau, Ulva ohiohilulu, and Ulva iliohaha. We also propose a new Umbraulva species (Umbraulva kuaweuweu), which is closely related to subtidal records from New Zealand and Australia, but not formally described. To our knowledge, these are the first marine species descriptions from Hawai'i resulting from the collaboration of traditional Hawaiian nomenclature specialists, cultural practitioners and scientists. The difficulty of finding reliable diagnostic morphological characters for these species reflects a common problem worldwide of achieving accurate identification of ulvalean taxa using solely morphological criteria. Mesophotic Ulvales appear to be distinct from shallow-water populations in Hawai'i, but their degree of similarity to mesophotic floras in other locations in the Pacific remains unknown. PMID:26987087

  17. Seasonal variations of vegetation patterns and biomass constituents in the rocky eulittoral of Helgoland

    NASA Astrophysics Data System (ADS)

    Munda, I. M.; Markham, J. W.

    1982-06-01

    Seasonal changes in vegetation patterns and biomass of benthic algae were recorded over a 14-month period in the rocky eulittoral of the North Sea island of Helgoland. The area is characterized by the dominance of Fucus serratus throughout most of the eulittoral and this is reflected in higher biomass of F. serratus ranged seasonally from 4.3 kg to 15 kg m-2 in the center of its extensive distribution. Biomass was also recorded monthly, when the plants were present, for Blidingia spp., Enteromorpha spp., Ulva lactuca, Fucus spiralis, F. vesiculosus, Porphyra linearis, P. umbilicalis, Chondrus crispus, Corallina officinalis, Dumontia incrassata, Petalonia fascia, P. zosterifolia and Scytosiphon lomentaria. New generations of several species which reappeared after a destructive winter storm showed a higher protein content than in the previous year. The winter and early spring flora of Helgoland shows several resemblances in species composition to the summer flora of Scandinavia.

  18. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂

    DOE PAGESBeta

    Kim, J. S.; Faeth, B. D.; Wang, Y.; Hirschfeld, P. J.; Stewart, G. R.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.

    2012-07-13

    Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe₀.₉₅₅Co₀.₀₄₅)₂As₂ (Tc = 8 K) and for three overdoped samples Ba(Fe₁₋xCox)₂As₂ (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat γ (∝C/T as T → 0, i.e., a measure of the electronic density of statesmore » at the Fermi energy) as a function of field approximately obeys γ ∝ H0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ≤ 10 T) data show a Volovik-like behavior of γ ∝ H0.3–0.4, followed by an inflection point, followed at higher fields by γ ∝ H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.« less

  19. Specific heat to Hc2: Evidence for nodes or deep minima in the superconducting gap of underdoped and overdoped Ba(Fe1–xCox)₂As₂

    SciTech Connect

    Kim, J. S.; Faeth, B. D.; Wang, Y.; Hirschfeld, P. J.; Stewart, G. R.; Gofryk, K.; Ronning, F.; Sefat, A. S.; Choi, K. Y.; Kim, K. H.

    2012-07-13

    Low-temperature specific heat, C, in magnetic fields up to Hc2 is reported for underdoped Ba(Fe₀.₉₅₅Co₀.₀₄₅)₂As₂ (Tc = 8 K) and for three overdoped samples Ba(Fe₁₋xCox)₂As₂ (x = 0.103, 0.13, and 0.15; Tc = 17.2, 16.5, and 11.7 K, respectively). Previous measurements of thermal conductivity (as a function of temperature and field) and penetration depth on comparable-composition samples gave some disagreement as to whether there was fully gapped/nodal behavior in the under-/overdoped materials, respectively. The present work shows that the measured behavior of the specific heat γ (∝C/T as T → 0, i.e., a measure of the electronic density of states at the Fermi energy) as a function of field approximately obeys γ ∝ H0.5±0.1, similar to the Volovik effect for nodal superconductors, for both the underdoped and the most overdoped Co samples. However, for the two overdoped compositions x = 0.103 and 0.13, the low-field (H ≤ 10 T) data show a Volovik-like behavior of γ ∝ H0.3–0.4, followed by an inflection point, followed at higher fields by γ ∝ H¹. We argue that, within the two-band theory of superconductivity, an inflection point may occur if the interband coupling is dominant.

  20. A close-up view on ITS2 evolution and speciation - a case study in the Ulvophyceae (Chlorophyta, Viridiplantae)

    PubMed Central

    2011-01-01

    Background The second Internal Transcriber Spacer (ITS2) is a fast evolving part of the nuclear-encoded rRNA operon located between the 5.8S and 28S rRNA genes. Based on crossing experiments it has been proposed that even a single Compensatory Base Change (CBC) in helices 2 and 3 of the ITS2 indicates sexual incompatibility and thus separates biological species. Taxa without any CBC in these ITS2 regions were designated as a 'CBC clade'. However, in depth comparative analyses of ITS2 secondary structures, ITS2 phylogeny, the origin of CBCs, and their relationship to biological species have rarely been performed. To gain 'close-up' insights into ITS2 evolution, (1) 86 sequences of ITS2 including secondary structures have been investigated in the green algal order Ulvales (Chlorophyta, Viridiplantae), (2) after recording all existing substitutions, CBCs and hemi-CBCs (hCBCs) were mapped upon the ITS2 phylogeny, rather than merely comparing ITS2 characters among pairs of taxa, and (3) the relation between CBCs, hCBCs, CBC clades, and the taxonomic level of organisms was investigated in detail. Results High sequence and length conservation allowed the generation of an ITS2 consensus secondary structure, and introduction of a novel numbering system of ITS2 nucleotides and base pairs. Alignments and analyses were based on this structural information, leading to the following results: (1) in the Ulvales, the presence of a CBC is not linked to any particular taxonomic level, (2) most CBC 'clades' sensu Coleman are paraphyletic, and should rather be termed CBC grades. (3) the phenetic approach of pairwise comparison of sequences can be misleading, and thus, CBCs/hCBCs must be investigated in their evolutionary context, including homoplasy events (4) CBCs and hCBCs in ITS2 helices evolved independently, and we found no evidence for a CBC that originated via a two-fold hCBC substitution. Conclusions Our case study revealed several discrepancies between ITS2 evolution in the

  1. Circadian Rhythms of Chloroplast Orientation and Photosynthetic Capacity in Ulva123

    PubMed Central

    Britz, Steven J.; Briggs, Winslow R.

    1976-01-01

    Ulva lactuca L. var. latissima (L.) Decandolle and var. rigida (C. Agardh) Le Jolis and U. mutabilis Foyn have a circadian rhythm of chloroplast orientation which results in large changes in the light-absorption properties of the thallus. During the day, the chloroplasts cover the outer face of the cells and absorbance is high. At night, the chloroplasts are along the side walls and absorbance is low. Enteromorpha linza (L.) J. Agardh, E. intestinalis (L.) Link, E. sp., and Monostroma grevillei (Thuret) Wittrock, members of the Ulvales, were not observed to have this rhythmic movement. Chloroplasts, when in the face position, could not be induced to move to the sides by high intensity light up to 80,000 lux. Unrelated to chloroplast position per se and light-absorption efficiency, there is a rhythm of photosynthetic capacity which peaks just before midday and which continues in constant darkness. Images PMID:16659613

  2. Attosecond structures from the molecular cavity in fullerene photoemission time delay

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, Maia; Anstine, Dylan M.; Dixit, Gopal; Madjet, Mohamed El-Amine; Chakraborty, Himadri S.

    2015-05-01

    Photoelectron spectroscopy studies earlier probed oscillations in C60 valence emissions, producing a series of minima whose energy separation depends on the molecular cavity. We show here that the quantum phase at these cavity minima exhibits variations from strong electron correlations in C60 , causing rich structures in the emission time delay. Hence, these minima offer unique spectral zones to directly explore multielectron forces via attosecond RABITT interferometry not only in fullerenes, but also in clusters and nanostructures for which such minima are likely abundant.

  3. Alternative electron transports participate in the maintenance of violaxanthin De-epoxidase activity of Ulva sp. under low irradiance.

    PubMed

    Xie, Xiujun; Gu, Wenhui; Gao, Shan; Lu, Shan; Li, Jian; Pan, Guanghua; Wang, Guangce; Shen, Songdong

    2013-01-01

    The xanthophyll cycle (Xc), which involves violaxanthin de-epoxidase (VDE) and the zeaxanthin epoxidase (ZEP), is one of the most rapid and efficient responses of plant and algae to high irradiance. High light intensity can activate VDE to convert violaxanthin (Vx) to zeaxanthin (Zx) via antheraxanthin (Ax). However, it remains unclear whether VDE remains active under low light or dark conditions when there is no significant accumulation of Ax and Zx, and if so, how the ΔpH required for activation of VDE is built. In this study, we used salicylaldoxime (SA) to inhibit ZEP activity in the intertidal macro-algae Ulva sp. (Ulvales, Chlorophyta) and then characterized VDE under low light and dark conditions with various metabolic inhibitors. With inhibition of ZEP by SA, VDE remained active under low light and dark conditions, as indicated by large accumulations of Ax and Zx at the expense of Vx. When PSII-mediated linear electron transport systems were completely inhibited by SA and DCMU, alternative electron transport systems (i.e., cyclic electron transport and chlororespiration) could maintain VDE activity. Furthermore, accumulations of Ax and Zx decreased significantly when SA, DCMU, or DBMIB together with an inhibitor of chlororespiration (i.e., propyl gallate (PG)) were applied to Ulva sp. This result suggests that chlororespiration not only participates in the build-up of the necessary ΔpH, but that it also possibly influences VDE activity indirectly by diminishing the oxygen level in the chloroplast. PMID:24250793

  4. New Family of Ulvan Lyases Identified in Three Isolates from the Alteromonadales Order.

    PubMed

    Kopel, Moran; Helbert, William; Belnik, Yana; Buravenkov, Vitaliy; Herman, Asael; Banin, Ehud

    2016-03-11

    Ulvan is the main polysaccharide component of the Ulvales (green seaweed) cell wall. It is composed of disaccharide building blocks comprising 3-sulfated rhamnose linked to d-glucuronic acid (GlcUA), l-iduronic acid (IdoUA), or d-xylose (Xyl). The degradation of ulvan requires ulvan lyase, which catalyzes the endolytic cleavage of the glycoside bond between 3-sulfated rhamnose and uronic acid according to a β-elimination mechanism. The first characterized ulvan lyase was identified in Nonlabens ulvanivorans, an ulvanolytic bacterial isolate. In the current study, we have identified and biochemically characterized novel ulvan lyases from three Alteromonadales isolated bacteria. Two homologous ulvan lyases (long and short) were found in each of the bacterial genomes. The protein sequences have no homology to the previously reported ulvan lyases and therefore are the first representatives of a new family of polysaccharide lyases. The enzymes were heterologously expressed in Escherichia coli to determine their mode of action. The heterologous expressed enzymes were secreted into the milieu subsequent to their signal sequence cleavage. An endolytic mode of action was observed and studied using gel permeation chromatography and (1)H NMR. In contrast to N. ulvanivorans ulvan lyase, cleavage occurred specifically at the GlcUA residues. In light of the genomic context and modular structure of the ulvan lyase families identified to date, we propose that two ulvan degradation pathways evolved independently. PMID:26763234

  5. Sequences and phylogeny analysis of rbcL gene in marine chlorophyta

    NASA Astrophysics Data System (ADS)

    Shen, Songdong; Li, Yanyan; Wu, Xunjian; Ding, Lanping

    2010-06-01

    The rbcL gene of Ulva pertusa, Enteromorpha prolifera and Monostroma grevillei was amplified, sequenced and analyzed. By comparing the rbcL sequences with seven other Ulvales species retrieved from GenBank, the sequence divergences and the phyletic evolution were analyzed and the phylogenetic tree was constructed. From the phylogenetic tree, it can be found that U. pertusa, E. prolifera and U. californica group in one branch, while E. compressa, U. rigida and U. fenestrata cluster in another clade. Obviously, unlike the Enteomorpha species, the Ulva species do not gather in one branch. Therefore Ulva and Enteomorpha might be affiliates of one genus. E. compressa and E. intestinalis gathered together, which coincided with the morphological characters. However, the thallus of U. pertusa is thick and with many holes, which is different from E. prolifera in morphology. They cluster together in the phylogenetic tree with a genetic distance of 0.005. The results indicate that Ulva and Enteromorpha are not distinguished strictly.

  6. Reconstructing the Phylogeny of Capsosiphon fulvescens (Ulotrichales, Chlorophyta) from Korea Based on rbcL and 18S rDNA Sequences

    PubMed Central

    Sun, Sang-Mi; Yang, Seung Hwan

    2016-01-01

    Capsosiphon fulvescens is a filamentous green algae in the class Ulvophyceae. It has been consumed as food with unique flavor and soft texture to treat stomach disorders and hangovers, and its economic value justifies studying its nutritional and potential therapeutic effects. In contrast to these applications, only a few taxonomic studies have been conducted on C. fulvescens. In particular, classification and phylogenetic relationships of the C. fulvescens below the order level are controversial. To determine its phylogenetic position in the class, we used rbcL and 18S rDNA sequences as molecular markers to construct phylogenetic trees. The amplified rbcL and 18S rDNA sequences from 4 C. fulvescens isolates (Jindo, Jangheung, Wando, and Koheung, Korea) were used for phylogenetic analysis by employing three different phylogenetic methods: neighbor joining (NJ), maximum parsimony (MP), and maximum likelihood (ML). The rbcL phylogenetic tree showed that all taxa in the order Ulvales were clustered as a monophyletic group and resolved the phylogenetic position of C. fulvescens in the order Ulotrichales. The significance of our study is that the 18S rDNA phylogenetic tree shows the detailed taxonomic position of C. fulvescens. In our result, C. fulvescens is inferred as a member of Ulotrichaceae, along with Urospora and Acrosiphonia. PMID:27190985

  7. O-C Analysis of Selected 3-Body Systems

    NASA Astrophysics Data System (ADS)

    Ogłoza, W.; Kreiner, J. M.; Stachowski, G.; Winiarski, M.; Zakrzewski, B.; Doǧru, S.; Aliçavuş, F.; Demircan, O.; Erdem, A.

    2012-04-01

    This paper presents the results of the analysis of (O-C) diagrams of four eclipsing variables. The diagrams are based on times of minima collected in the Cracow database, which contains times of minima found in the literature, from observations at Mt. Suhora and Ulupinar Observatories, or determined using publicly-available photometric surveys (NSVS, ASAS etc).

  8. 75 FR 62639 - Air Ambulance and Commercial Helicopter Operations, Part 91 Helicopter Operations, and Part 135...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-12

    ... in the Federal Register published on April 11, 2000 (65 FR 19477-78) or you may visit http://Dockets..., and alternate airport weather minima. The changes are intended to provide certificate holders and... Weather Minima (Sec. 135.607) ii. IFR Operations at Airports and Heliports Without Weather Reporting...

  9. Kepler-Daten von BR Cyg

    NASA Astrophysics Data System (ADS)

    Pagel, Lienhard

    2015-01-01

    In the Kepler field is the eclipsing binary BR Cyg. He is a BAV program star. In the KIC (Kepler Input Catalogue) he is associated with the identifier kplr009899416 [1]. There have been determined 1084 minima and as many secondary minima. Acknowledgement: This paper makes use of data from the Kepler exoplanetarchive.

  10. Troughs under threshold modeling of minimum flows in perennial streams

    NASA Astrophysics Data System (ADS)

    Önöz, B.; Bayazit, M.

    2002-02-01

    Troughs under threshold analysis has so far found little application in the modeling of minimum streamflows. In this study, all the troughs under a certain threshold level are considered in deriving the probability distribution of annual minima through the total probability theorem. For the occurrence of minima under the threshold, Poissonian, binomial or negative binomial processes are assumed. The magnitude of minima follows the generalized Pareto, exponential or power distribution. It is shown that asymptotic extreme value distributions for minima or the two-parameter Weibull distribution is obtained for the annual minima, depending on which models are assumed for the occurrence and magnitude of troughs under the threshold. Derived distributions can be used for modeling the minimum flows in streams which do not have zero flows. Expressions for the T-year annual minimum flow are obtained. An example illustrates the application of the troughs under threshold model to the minimum flows observed in a stream.

  11. Geometric Frustration of Colloidal Dimers on a Honeycomb Magnetic Lattice

    NASA Astrophysics Data System (ADS)

    Tierno, Pietro

    2016-01-01

    We study the phase behavior and the collective dynamics of interacting paramagnetic colloids assembled above a honeycomb lattice of triangular shaped magnetic minima. A frustrated colloidal molecular crystal is realized when filling these potential minima with exactly two particles per pinning site. External in-plane rotating fields are used to anneal the system into different phases, including long range ordered stripes, random fully packed loops, labyrinth and disordered states. At a higher amplitude of the annealing field, the dimer lattice displays a two-step melting transition where the initially immobile dimers perform first localized rotations and later break up by exchanging particles across consecutive lattice minima.

  12. Glass transition and random walks on complex energy landscapes.

    PubMed

    Baronchelli, Andrea; Barrat, Alain; Pastor-Satorras, Romualdo

    2009-08-01

    We present a simple mathematical model of glassy dynamics seen as a random walk in a directed weighted network of minima taken as a representation of the energy landscape. Our approach gives a broader perspective to previous studies focusing on particular examples of energy landscapes obtained by sampling energy minima and saddles of small systems. We point out how the relation between the energies of the minima and their number of neighbors should be studied in connection with the network's global topology and show how the tools developed in complex network theory can be put to use in this context. PMID:19792062

  13. Impacts of Extended Periods of Low Solar Activity on Climate (Abstract)

    NASA Astrophysics Data System (ADS)

    Denig, W. F.

    2016-06-01

    (Abstract only) There has been great interest in determining the length and amplitude of Solar Cycle 24 in recent years, in part due to increasing speculation that the current solar minimum is anomalously quiet and perhaps signaling the beginning of a decreased period of solar activity in the coming decades. We aim to examine the current solar minimum and compare it to previous solar minima in order to: determine if the current minimum shares characteristics with other historically quiet solar minima (sometimes referred to as grand minima); outline the potential consequences of a grand minimum with respect to climate; and predict the future of Solar Cycle 24.

  14. Geometric Frustration of Colloidal Dimers on a Honeycomb Magnetic Lattice.

    PubMed

    Tierno, Pietro

    2016-01-22

    We study the phase behavior and the collective dynamics of interacting paramagnetic colloids assembled above a honeycomb lattice of triangular shaped magnetic minima. A frustrated colloidal molecular crystal is realized when filling these potential minima with exactly two particles per pinning site. External in-plane rotating fields are used to anneal the system into different phases, including long range ordered stripes, random fully packed loops, labyrinth and disordered states. At a higher amplitude of the annealing field, the dimer lattice displays a two-step melting transition where the initially immobile dimers perform first localized rotations and later break up by exchanging particles across consecutive lattice minima. PMID:26849619

  15. Parametric modeling in distributed optical fiber vibration sensing system for position determination

    NASA Astrophysics Data System (ADS)

    Wu, Hongyan; Wang, Jian; Jia, Bo

    2016-04-01

    Distributed optical fiber vibration sensing system is widely used as a monitoring system in communication cable and pipeline of long distances. When a vibration signal occurs at a particular position along the fiber, the response of the system, in the frequency domain, presents a series of periodic maxima and minima (or null frequencies). These minima depend on the position of the vibration signal along the fiber. Power spectral estimation methods are considered to denoise the power spectrum of the system and determine these minima precisely. The experimental results show higher accuracy of the position using a parametric model with appropriate selection of order p and q than just using fast Fourier transform algorithm.

  16. The Complete Chloroplast and Mitochondrial Genomes of the Green Macroalga Ulva sp. UNA00071828 (Ulvophyceae, Chlorophyta)

    PubMed Central

    Melton, James T.; Leliaert, Frederik; Tronholm, Ana; Lopez-Bautista, Juan M.

    2015-01-01

    Sequencing mitochondrial and chloroplast genomes has become an integral part in understanding the genomic machinery and the phylogenetic histories of green algae. Previously, only three chloroplast genomes (Oltmannsiellopsis viridis, Pseudendoclonium akinetum, and Bryopsis hypnoides) and two mitochondrial genomes (O. viridis and P. akinetum) from the class Ulvophyceae have been published. Here, we present the first chloroplast and mitochondrial genomes from the ecologically and economically important marine, green algal genus Ulva. The chloroplast genome of Ulva sp. was 99,983 bp in a circular-mapping molecule that lacked inverted repeats, and thus far, was the smallest ulvophycean plastid genome. This cpDNA was a highly compact, AT-rich genome that contained a total of 102 identified genes (71 protein-coding genes, 28 tRNA genes, and three ribosomal RNA genes). Additionally, five introns were annotated in four genes: atpA (1), petB (1), psbB (2), and rrl (1). The circular-mapping mitochondrial genome of Ulva sp. was 73,493 bp and follows the expanded pattern also seen in other ulvophyceans and trebouxiophyceans. The Ulva sp. mtDNA contained 29 protein-coding genes, 25 tRNA genes, and two rRNA genes for a total of 56 identifiable genes. Ten introns were annotated in this mtDNA: cox1 (4), atp1 (1), nad3 (1), nad5 (1), and rrs (3). Double-cut-and-join (DCJ) values showed that organellar genomes across Chlorophyta are highly rearranged, in contrast to the highly conserved organellar genomes of the red algae (Rhodophyta). A phylogenomic investigation of 51 plastid protein-coding genes showed that Ulvophyceae is not monophyletic, and also placed Oltmannsiellopsis (Oltmannsiellopsidales) and Tetraselmis (Chlorodendrophyceae) closely to Ulva (Ulvales) and Pseudendoclonium (Ulothrichales). PMID:25849557

  17. The complete chloroplast and mitochondrial genomes of the green macroalga Ulva sp. UNA00071828 (Ulvophyceae, Chlorophyta).

    PubMed

    Melton, James T; Leliaert, Frederik; Tronholm, Ana; Lopez-Bautista, Juan M

    2015-01-01

    Sequencing mitochondrial and chloroplast genomes has become an integral part in understanding the genomic machinery and the phylogenetic histories of green algae. Previously, only three chloroplast genomes (Oltmannsiellopsis viridis, Pseudendoclonium akinetum, and Bryopsis hypnoides) and two mitochondrial genomes (O. viridis and P. akinetum) from the class Ulvophyceae have been published. Here, we present the first chloroplast and mitochondrial genomes from the ecologically and economically important marine, green algal genus Ulva. The chloroplast genome of Ulva sp. was 99,983 bp in a circular-mapping molecule that lacked inverted repeats, and thus far, was the smallest ulvophycean plastid genome. This cpDNA was a highly compact, AT-rich genome that contained a total of 102 identified genes (71 protein-coding genes, 28 tRNA genes, and three ribosomal RNA genes). Additionally, five introns were annotated in four genes: atpA (1), petB (1), psbB (2), and rrl (1). The circular-mapping mitochondrial genome of Ulva sp. was 73,493 bp and follows the expanded pattern also seen in other ulvophyceans and trebouxiophyceans. The Ulva sp. mtDNA contained 29 protein-coding genes, 25 tRNA genes, and two rRNA genes for a total of 56 identifiable genes. Ten introns were annotated in this mtDNA: cox1 (4), atp1 (1), nad3 (1), nad5 (1), and rrs (3). Double-cut-and-join (DCJ) values showed that organellar genomes across Chlorophyta are highly rearranged, in contrast to the highly conserved organellar genomes of the red algae (Rhodophyta). A phylogenomic investigation of 51 plastid protein-coding genes showed that Ulvophyceae is not monophyletic, and also placed Oltmannsiellopsis (Oltmannsiellopsidales) and Tetraselmis (Chlorodendrophyceae) closely to Ulva (Ulvales) and Pseudendoclonium (Ulothrichales). PMID:25849557

  18. Multiple Conformational States of Proteins: A Molecular Dynamics Analysis of Myoglobin

    NASA Astrophysics Data System (ADS)

    Elber, R.; Karplus, M.

    1987-01-01

    A molecular dynamics simulation of myoglobin provides the first direct demonstration that the potential energy surface of a protein is characterized by a large number of thermally accessible minima in the neighborhood of the native structure (for example, approximately 2000 minima were sampled in a 300-picosecond trajectory). This is expected to have important consequences for the interpretation of the activity of transport proteins and enzymes. Different minima correspond to changes in the relative orientation of the helices coupled with side-chain rearrangements that preserve the close packing of the protein interior. The conformational space sampled by the simulation is similar to that found in the evolutionary development of the globins. Glasslike behavior is expected at low temperatures. The minima obtained from the trajectory do not satisfy certain criteria for ultrametricity.

  19. A multidimensional generalization of Heilbronn's theorem on the average length of a finite continued fraction

    SciTech Connect

    Illarionov, A A

    2014-03-31

    Heilbronn's theorem on the average length of a finite continued fraction is generalized to the multidimensional case in terms of relative minima of the lattices which were introduced by Voronoy and Minkowski. Bibliography: 21 titles.

  20. Timing of eclipsing binary V0873 Per: a third body candidate

    NASA Astrophysics Data System (ADS)

    Bogomazov, A. I.; Ibrahimov, M. A.; Satovskii, B. L.; Kozyreva, V. S.; Irsmambetova, T. R.; Krushevska, V. N.; Kuznyetsova, Y. G.; Gaynullina, E. R.; Karimov, R. G.; Ehgamberdiev, S. A.; Tutukov, A. V.

    2016-01-01

    We analyze a set of moments of minima of eclipsing variable V0873 Per. V0873 Per is a short-period low-mass binary star. Data about moments of minima of V0873 Per were taken from the literature and our observations during 2013-2014. Our aim is to test the system on existence of new bodies using timing of minima of eclipses. We found a periodic variation of orbital period of V0873 Per. This variation can be explained by the gravitational influence of a third companion on the central binary star. The mass of the third body candidate is ≈ 0.2 M_{⊙}, and its orbital period is ≈300 days. The paper also includes a table with moments of minima calculated from our observations, which can be used in future investigations of V0873 Per.

  1. Jan Hudde and the Quotient Rule before Newton and Leibniz

    ERIC Educational Resources Information Center

    Curtin, Daniel J.

    2005-01-01

    This article describes some of the work of Jan Hudde who anticipated some results of calculus. Prior to a career as a Burgomaster of Amsterdam, Hudde engaged in mathematics. His method of finding maxima and minima is especially interesting.

  2. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    SciTech Connect

    Kaduchak, Gregory; Ward, Michael D

    2014-10-21

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  3. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    DOEpatents

    Kaduchak, Gregory; Ward, Michael D.

    2011-12-27

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  4. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    DOEpatents

    Kaduchak, Gregory; Ward, Michael D

    2016-05-17

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  5. A simple empirical stream flow prediction model for ungauged watersheds

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Knowledge of streamflow is important for estimating groundwater recharge rates, forecasting floods, and designing hydropower structures and irrigation systems. However, many watersheds throughout the developing world remain ungauged. This fact demands a simple hydrological model that requires minima...

  6. Screw dislocation-induced growth spirals as emissive exciton localization centers in Al-rich AlGaN/AlN quantum wells

    NASA Astrophysics Data System (ADS)

    Funato, Mitsuru; Banal, Ryan G.; Kawakami, Yoichi

    2015-11-01

    Screw dislocations in Al-rich AlGaN/AlN quantum wells cause growth spirals with an enhanced Ga incorporation, which create potential minima. Although screw dislocations and their surrounding potential minima suggest non-radiative recombination processes within growth spirals, in reality, screw dislocations are not major non-radiative sinks for carriers. Consequently, carriers localized within growth spirals recombine radiatively without being captured by non-radiative recombination centers, resulting in intense emissions from growth spirals.

  7. Optical fiber diameter measurement by the diffraction method with digital processing of the light scattering indicatrix

    NASA Astrophysics Data System (ADS)

    Kokodii, N. G.; Natarova, A. O.

    2016-07-01

    Relations between the position of the first diffraction minima and the fiber diameter are derived based on the solution of the problem of electromagnetic wave diffraction on a transparent fiber with a circular cross section. The obtained formulas are used to measure the fiber diameter. The diffraction pattern is recorded with a digital camera. The obtained image is digitally processed to determine the positions of the first two scattering indicatrix minima.

  8. Extreme value statistics of 2D Gaussian free field: effect of finite domains

    NASA Astrophysics Data System (ADS)

    Cao, X.; Rosso, A.; Santachiara, R.

    2016-01-01

    We study minima statistics of the 2D Gaussian free field (GFF) on circles in the unit disk with Dirichlet boundary condition. Free energy distributions of the associated random energy models are exactly calculated in the high temperature phase, and shown to satisfy the duality property, which enables us to predict the minima distribution by assuming the freezing scenario. Numerical tests are provided. Related questions concerning the GFF on a sphere are also considered.

  9. Screw dislocation-induced growth spirals as emissive exciton localization centers in Al-rich AlGaN/AlN quantum wells

    SciTech Connect

    Funato, Mitsuru Banal, Ryan G.; Kawakami, Yoichi

    2015-11-15

    Screw dislocations in Al-rich AlGaN/AlN quantum wells cause growth spirals with an enhanced Ga incorporation, which create potential minima. Although screw dislocations and their surrounding potential minima suggest non-radiative recombination processes within growth spirals, in reality, screw dislocations are not major non-radiative sinks for carriers. Consequently, carriers localized within growth spirals recombine radiatively without being captured by non-radiative recombination centers, resulting in intense emissions from growth spirals.

  10. The complex lightcurve of 1992 NA

    NASA Technical Reports Server (NTRS)

    Wisniewski, Wieslaw Z.; Harris, A. W.

    1994-01-01

    Amor asteroid 1992 NA was monitored during three nights at a large phase angle of -65 deg. The lightcurves obtained did not reveal a repeatable curve with two maxima and two minima. However, some features suggested a periodicity with three maxima and three minima. A satisfactory composite lightcurve of this form was obtained by means of an 'eyeball' fit and by Fourier analysis. Individual and composite lightcurves are presented. The observed colors are consistent with the C class.

  11. Vacuum selection on axionic landscapes

    NASA Astrophysics Data System (ADS)

    Wang, Gaoyuan; Battefeld, Thorsten

    2016-04-01

    We compute the distribution of minima that are reached dynamically on multi-field axionic landscapes, both numerically and analytically. Such landscapes are well suited for inflationary model building due to the presence of shift symmetries and possible alignment effects (the KNP mechanism). The resulting distribution of dynamically reached minima differs considerably from the naive expectation based on counting all vacua. These differences are more pronounced in the presence of many fields due to dynamical selection effects: while low lying minima are preferred as fields roll down the potential, trajectories are also more likely to get trapped by one of the many nearby minima. We show that common analytic arguments based on random matrix theory in the large D-limit to estimate the distribution of minima are insufficient for quantitative arguments pertaining to the dynamically reached ones. This discrepancy is not restricted to axionic potentials. We provide an empirical expression for the expectation value of such dynamically reached minimas' height and argue that the cosmological constant problem is not alleviated in the absence of anthropic arguments. We further comment on the likelihood of inflation on axionic landscapes in the large D-limit.

  12. Photophysical deactivation pathways in adenine oligonucleotides.

    PubMed

    Spata, Vincent A; Matsika, Spiridoula

    2015-12-14

    In this work we study deactivation processes in adenine oligomers after absorption of UV radiation using Quantum Mechanics combined with Molecular Mechanics (QM/MM). Correlated electronic structure methods appropriate for describing the excited states are used to describe a π-stacked dimer of adenine bases incorporated into (dA)20(dT)20. The results of these calculations reveal three different types of excited state minima which play a role in deactivation processes. Within this set of minima there are minima where the excited state is localized on one adenine (monomer-like) as well as minima where the excited state is delocalized on two adenines, forming different types of excimers and bonded excimers of varying but inter-related character. The proximity of their energies reveals that the minima can decay into one another along a flat potential energy surface dependent on the interbase separation. Additionally, analysis of the emissive energies and other physical properties, including theoretical anisotropy calculations, and comparison with fluorescence experiments, provides evidence that excimers play an important role in long-lived signals in adenine oligonucleotides while the subpicosecond decay is attributed to monomer-like minima. The necessity for a close approach of the nucleobases reveals that the deactivation mechanism is tied to macro-molecular motion. PMID:26536353

  13. Random versus Deterministic Descent in RNA Energy Landscape Analysis

    PubMed Central

    Day, Luke; Abdelhadi Ep Souki, Ouala; Albrecht, Andreas A.; Steinhöfel, Kathleen

    2016-01-01

    Identifying sets of metastable conformations is a major research topic in RNA energy landscape analysis, and recently several methods have been proposed for finding local minima in landscapes spawned by RNA secondary structures. An important and time-critical component of such methods is steepest, or gradient, descent in attraction basins of local minima. We analyse the speed-up achievable by randomised descent in attraction basins in the context of large sample sets where the size has an order of magnitude in the region of ~106. While the gain for each individual sample might be marginal, the overall run-time improvement can be significant. Moreover, for the two nongradient methods we analysed for partial energy landscapes induced by ten different RNA sequences, we obtained that the number of observed local minima is on average larger by 7.3% and 3.5%, respectively. The run-time improvement is approximately 16.6% and 6.8% on average over the ten partial energy landscapes. For the large sample size we selected for descent procedures, the coverage of local minima is very high up to energy values of the region where the samples were randomly selected from the partial energy landscapes; that is, the difference to the total set of local minima is mainly due to the upper area of the energy landscapes. PMID:27110241

  14. An Atlas of O-C Diagrams of Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Kreiner, Jerzy M.; Kim, Chun-Hwey; Nha, Il-Seong

    The Atlas contains data for 1,138 eclipsing binaries represented by 91,798 minima timings, collected from the usual international and local journals, observatory publications and unpublished minima. Among this source material there is a considerable representation of amateur astronomers. Some timings were found in the card-index catalogue of the Astronomical Observatory of the Jagiellonian University, Cracow. Stars were included in the Atlas provided that they satisfied 3 criteria: (1) at least 20 minima had been times; (2) these minima spanned at least 2,500 cycles; and (3) the 2,500 cycles represented no fewer than 40 years. Some additional stars not strictly satisfying these criteria were also included if useful information was available. For each star, the Atlas contains the (O-C) diagram calculated by the authors and a table of general information containing: binary characteristics; assorted catalogue numbers; the statistics of the collected minima timings; the light elements (light ephemeris); comments and literature references. All of the data and diagrams in the Atlas are also available in electronic form on the Internet at http://www.as.ap.krakow.pl/o- c".

  15. Molecular phylogeny of the forensically important genus Cochliomyia (Diptera: Calliphoridae).

    PubMed

    Yusseff-Vanegas, Sohath; Agnarsson, Ingi

    2016-01-01

    Cochliomyia Townsend includes several abundant and one of the most broadly distributed, blow flies in the Americas, and is of significant economic and forensic importance. For decades, Cochliomyia hominivorax (Coquerel) and Cochliomyia macellaria (Fabricius) have received attention as livestock parasites and primary indicator species in forensic entomology. However, Cochliomyia minima Shannon and Cochliomyia aldrichi Del Ponte have only been subject to basic taxonomy and faunistic studies. Here we present the first complete phylogeny of Cochliomyia including numerous specimens per species, collected from 13 localities in the Caribbean. Four genes, the mitochondrial COI and the nuclear EF-1α, 28S rRNA, and ITS2, were analyzed. While we found some differences among gene trees, a concatenated gene matrix recovered a robustly supported monophyletic Cochliomyia with Compsomyiops Townsend as its sister group and recovered the monophyly of Cochliomyia hominivorax, Cochliomyia macellaria and Cochliomyia minima. Our results support a close relationship between Cochliomyia minima and Cochliomyia aldrichi. However, we found Cochliomyia aldrichi containing Cochliomyia minima, indicating recent speciation, or issues with the taxonomy of the group. We provide basic information on habitat preference, distribution and feeding habits of Cochliomyia minima and Cochliomyia aldrichi that will be useful for future forensic studies in the Caribbean. PMID:27563274

  16. Molecular phylogeny of the forensically important genus Cochliomyia (Diptera: Calliphoridae)

    PubMed Central

    Yusseff-Vanegas, Sohath; Agnarsson, Ingi

    2016-01-01

    Abstract Cochliomyia Townsend includes several abundant and one of the most broadly distributed, blow flies in the Americas, and is of significant economic and forensic importance. For decades, Cochliomyia hominivorax (Coquerel) and Cochliomyia macellaria (Fabricius) have received attention as livestock parasites and primary indicator species in forensic entomology. However, Cochliomyia minima Shannon and Cochliomyia aldrichi Del Ponte have only been subject to basic taxonomy and faunistic studies. Here we present the first complete phylogeny of Cochliomyia including numerous specimens per species, collected from 13 localities in the Caribbean. Four genes, the mitochondrial COI and the nuclear EF-1α, 28S rRNA, and ITS2, were analyzed. While we found some differences among gene trees, a concatenated gene matrix recovered a robustly supported monophyletic Cochliomyia with Compsomyiops Townsend as its sister group and recovered the monophyly of Cochliomyia hominivorax, Cochliomyia macellaria and Cochliomyia minima. Our results support a close relationship between Cochliomyia minima and Cochliomyia aldrichi. However, we found Cochliomyia aldrichi containing Cochliomyia minima, indicating recent speciation, or issues with the taxonomy of the group. We provide basic information on habitat preference, distribution and feeding habits of Cochliomyia minima and Cochliomyia aldrichi that will be useful for future forensic studies in the Caribbean. PMID:27563274

  17. Time-resolved photoluminescence and excited state structure of Bi3+ center in YAlO3

    NASA Astrophysics Data System (ADS)

    Krasnikov, A.; Lipińska, L.; Mihokova, E.; Nikl, M.; Shalapska, T.; Suchocki, A.; Zazubovich, S.; Zhydachevskii, Ya.

    2014-08-01

    YAlO3:Bi ceramics prepared from the nanopowders synthesized by the sol-gel (Pechini) method are studied at 8-400 K by the time-resolved spectroscopy methods. An intense dominant ultraviolet luminescence of YAlO3:Bi is shown to arise from the radiative decay of the metastable and radiative minima of the triplet relaxed excited state (RES) of Bi3+ centers related to the 3P0, 3P1 levels of a free Bi3+ ion, respectively. At T < 80 K, the radiative transitions from the metastable minima take place. Thermally stimulated nonradiative transitions between the metastable and radiative minima of the triplet RES appear at T > 80 K in the temperature dependences of the emission spectrum and decay kinetics. From these dependences, the energy separation between the radiative and metastable minima, and the rates of the radiative and nonradiative transitions from these minima, are determined. The excitation bands of the ultraviolet emission, located at 4.425, around 5.6 eV and at the energy higher than 6 eV, are ascribed to the 1S0 → 3P1, 1S0 → 3P2, and 1S0 → 1P1 transitions of a free Bi3+ ion, respectively.

  18. Heteroaggregation of microparticles with nanoparticles changes the chemical reversibility of the microparticles' attachment to planar surfaces.

    PubMed

    Shen, Chongyang; Wu, Lei; Zhang, Shiwen; Ye, Huichun; Li, Baoguo; Huang, Yuanfang

    2014-05-01

    This study theoretically investigated detachment of homoaggregates and heteroaggregates attached on the planar surfaces at primary minima during transients in solution chemistry. The homoaggregates were represented as small colloidal clusters with well-defined structures or as clusters generated by randomly packing spheres using Monte Carlo method. The heteroaggregates were modeled as microparticles coated with nanoparticles. Surface element integration technique was adopted to calculate Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies for the homoaggregates and heteroaggregates at different ionic strengths. Results show that attached homoaggregates on the planar surface at primary minima are irreversible to reduction in solution ionic strength whether the primary spheres of the homoaggregates are nano- or micro-sized. Heteroaggregation of nanoparticles with a microparticle can cause DLVO interaction energy to decrease monotonically with separation distance at low ionic strengths (e.g., ⩽0.01M), indicating that the heteroaggregates experience repulsive forces at all separation distances. Therefore, attachment of the heteroaggregates at primary minima can be detached upon reduction in ionic strength. Additionally, we showed that the adhesive forces and torques that the aforementioned heteroaggregates experience can be significantly smaller than those experienced by the microspheres without attaching nanoparticles, thus, the heteroaggregates are readily detached via hydrodynamic drag. Results of study provide plausible explanation for the observations in the literature that attached/aggregated particles can be detached/redispersed from primary minima upon reduction in ionic strength, which challenges the common belief that attachment/aggregation of particles in primary minima is chemically irreversible. PMID:24594038

  19. Hydrocarbon adsorption in an aqueous environment: A computational study of alkyls on Cu(111).

    PubMed

    Montemore, Matthew M; Andreussi, Oliviero; Medlin, J Will

    2016-08-21

    Hydrocarbon chains are important intermediates in various aqueous-phase surface processes, such as CO2 electroreduction, aqueous Fischer-Tropsch synthesis, and aqueous phase reforming of biomass-derived molecules. Further, the interaction between water and adsorbed hydrocarbons represents a difficult case for modern computational methods. Here, we explore various methods for calculating the energetics of this interaction within the framework of density functional theory and explore trade-offs between the use of low water coverages, molecular dynamics approaches, and minima hopping for identification of low energy structures. An effective methodology for simulating low temperature processes is provided by using a unit cell in which the vacuum space is filled with water, employing the minima hopping algorithm to search for low-lying minima, and including dispersion (van der Waals) interactions. Using this methodology, we show that a high coverage of adsorbed alkyls is destabilized by the presence of water, while a low coverage of alkyls is stabilized. Solvation has a small effect on the energetics of hydrocarbon chain growth, generally decreasing its favorability at low temperatures. We studied higher temperatures by running molecular dynamics simulations starting at the minima found by the minima hopping algorithm and found that increased temperatures facilitate chain growth. The self-consistent continuum solvation method effectively describes the alkyl-water interaction and is in general agreement with the explicit solvation results in most cases, but care should be taken at high alkyl coverage. PMID:27544118

  20. Computationally efficient characterization of potential energy surfaces based on fingerprint distances

    NASA Astrophysics Data System (ADS)

    Schaefer, Bastian; Goedecker, Stefan

    2016-07-01

    An analysis of the network defined by the potential energy minima of multi-atomic systems and their connectivity via reaction pathways that go through transition states allows us to understand important characteristics like thermodynamic, dynamic, and structural properties. Unfortunately computing the transition states and reaction pathways in addition to the significant energetically low-lying local minima is a computationally demanding task. We here introduce a computationally efficient method that is based on a combination of the minima hopping global optimization method and the insight that uphill barriers tend to increase with increasing structural distances of the educt and product states. This method allows us to replace the exact connectivity information and transition state energies with alternative and approximate concepts. Without adding any significant additional cost to the minima hopping global optimization approach, this method allows us to generate an approximate network of the minima, their connectivity, and a rough measure for the energy needed for their interconversion. This can be used to obtain a first qualitative idea on important physical and chemical properties by means of a disconnectivity graph analysis. Besides the physical insight obtained by such an analysis, the gained knowledge can be used to make a decision if it is worthwhile or not to invest computational resources for an exact computation of the transition states and the reaction pathways. Furthermore it is demonstrated that the here presented method can be used for finding physically reasonable interconversion pathways that are promising input pathways for methods like transition path sampling or discrete path sampling.

  1. When Gravity Fails: Local Search Topology

    NASA Technical Reports Server (NTRS)

    Frank, Jeremy; Cheeseman, Peter; Stutz, John; Lau, Sonie (Technical Monitor)

    1997-01-01

    Local search algorithms for combinatorial search problems frequently encounter a sequence of states in which it is impossible to improve the value of the objective function; moves through these regions, called {\\em plateau moves), dominate the time spent in local search. We analyze and characterize {\\em plateaus) for three different classes of randomly generated Boolean Satisfiability problems. We identify several interesting features of plateaus that impact the performance of local search algorithms. We show that local minima tend to be small but occasionally may be very large. We also show that local minima can be escaped without unsatisfying a large number of clauses, but that systematically searching for an escape route may be computationally expensive if the local minimum is large. We show that plateaus with exits, called benches, tend to be much larger than minima, and that some benches have very few exit states which local search can use to escape. We show that the solutions (i.e. global minima) of randomly generated problem instances form clusters, which behave similarly to local minima. We revisit several enhancements of local search algorithms and explain their performance in light of our results. Finally we discuss strategies for creating the next generation of local search algorithms.

  2. Nuclear DNA Content Estimates in Green Algal Lineages: Chlorophyta and Streptophyta

    PubMed Central

    Kapraun, Donald F.

    2007-01-01

    Background and Aims Consensus higher-level molecular phylogenies present a compelling case that an ancient divergence separates eukaryotic green algae into two major monophyletic lineages, Chlorophyta and Streptophyta, and a residuum of green algae, which have been referred to prasinophytes or micromonadophytes. Nuclear DNA content estimates have been published for less than 1% of the described green algal members of Chlorophyta, which includes multicellular green marine algae and freshwater flagellates (e.g. Chlamydomonas and Volvox). The present investigation summarizes the state of our knowledge and adds substantially to our database of C-values, especially for the streptophyte charophycean lineage which is the sister group of the land plants. A recent list of 2C nuclear DNA contents for isolates and species of green algae is expanded by 72 to 157. Methods The DNA-localizing fluorochrome DAPI (4′,6-diamidino-2-phenylindole) and red blood cell (chicken erythrocytes) standard were used to estimate 2C values with static microspectrophotometry. Key Results In Chlorophyta, including Chlorophyceae, Prasinophyceae, Trebouxiophyceae and Ulvophyceae, 2C DNA estimates range from 0·01 to 5·8 pg. Nuclear DNA content variation trends are noted and discussed for specific problematic taxon pairs, including Ulotrichales–Ulvales, and Cladophorales–Siphonocladales. For Streptophyta, 2C nuclear DNA contents range from 0·2 to 6·4 pg, excluding the highly polyploid Charales and Desmidiales, which have genome sizes of up to 14·8 and 46·8 pg, respectively. Nuclear DNA content data for Streptophyta superimposed on a contemporary molecular phylogeny indicate that early diverging lineages, including some members of Chlorokybales, Coleochaetales and Klebsormidiales, have genomes as small as 0·1–0·5 pg. It is proposed that the streptophyte ancestral nuclear genome common to both the charophyte and the embryophyte lineages can be characterized as 1C = 0·2 pg and 1n = 6

  3. The emergence of a new chlorophytan system, and Dr. Kornmann's contribution thereto

    NASA Astrophysics Data System (ADS)

    van den Hoek, C.; Stam, W. T.; Olsen, J. L.

    1988-09-01

    In traditional chlorophytan systems the organizational level was the primary character for the distinction of main groups (classes and orders). For instance, in Fott (1971), the flagellate level corresponds with the Volvocales, the coccoid level with the Chlorococcales, the filamentous level with the Ulotrichales, the siphonocladous level with the Siphonocladales, and the siphonous level with the Bryopsidales. The new system presented here is an elaboration and emendation of recently proposed taxonomies and their underlying phylogenetic hypotheses, and it is mainly based on ultrastructural features which have become available over the last 15 years. The following criteria are used for the distinction of classes and orders: (1) architecture of the flagellate cell (flagellate cells are considered as the depositories of primitive characters); (2) type of mitosis-cytokinesis; (3) place of meiosis in the life history and, consequently, the sexual life history type; (4) organizational level and thallus architecture; (5) habitat type (marine versus feshwater and terrestrial); (6) chloroplast type. The following classes are presented: Prasinophyceae, Chlamydophyceae, Ulvophyceae (orders Codiolales, Ulvales, Cladophorales, Bryopsidales, Dasycladales), Pleurastrophyceae (?), Chlorophyceae s.s. (orders Cylindrocapsales, Oedogoniales, Chaetophorales), Zygnematophyceae, Trentepohliophyceae, Charophyceae (orders Klebsormidiales, Coleochaetales, Charales). The new system no longer reflects the traditional hypothesis of a stepwise evolutionary progression of organizational levels in which the flagellate level represents the most primitive lineage, the coccoid and sarcinoid levels lineages of intermediate derivation, and the filamentous, siphonocladous and siphonous levels the most derived lineages. Instead, it is now hypothesized that these levels have arisen over and over again in different chlorophytan lineages which are primarily characterized by their type of flagellate cell

  4. Free energy surfaces from an extended harmonic superposition approach and kinetics for alanine dipeptide

    NASA Astrophysics Data System (ADS)

    Strodel, Birgit; Wales, David J.

    2008-12-01

    Approximate free energy surfaces and transition rates are presented for alanine dipeptide for a variety of force fields and implicit solvent models. Our calculations are based upon local minima, transition states and pathways characterised for each potential energy surface using geometry optimisation. The superposition approach employing only local minima and harmonic densities of states provides a representation of low-lying regions of the free energy surfaces. However, including contributions from the transition states of the potential energy surface and selected points obtained from displacements along the corresponding reaction vectors produces surfaces that compare quite well with results from replica exchange molecular dynamics. Characterising the local minima, transition states, normal modes, pathways, rate constants and free energy surfaces for each force field within this framework typically requires between one and five minutes cpu time on a single processor.

  5. WS-BP: An efficient wolf search based back-propagation algorithm

    NASA Astrophysics Data System (ADS)

    Nawi, Nazri Mohd; Rehman, M. Z.; Khan, Abdullah

    2015-05-01

    Wolf Search (WS) is a heuristic based optimization algorithm. Inspired by the preying and survival capabilities of the wolves, this algorithm is highly capable to search large spaces in the candidate solutions. This paper investigates the use of WS algorithm in combination with back-propagation neural network (BPNN) algorithm to overcome the local minima problem and to improve convergence in gradient descent. The performance of the proposed Wolf Search based Back-Propagation (WS-BP) algorithm is compared with Artificial Bee Colony Back-Propagation (ABC-BP), Bat Based Back-Propagation (Bat-BP), and conventional BPNN algorithms. Specifically, OR and XOR datasets are used for training the network. The simulation results show that the WS-BP algorithm effectively avoids the local minima and converge to global minima.

  6. Registration of range data using a hybrid simulated annealing and iterative closest point algorithm

    SciTech Connect

    LUCK,JASON; LITTLE,CHARLES Q.; HOFF,WILLIAM

    2000-04-17

    The need to register data is abundant in applications such as: world modeling, part inspection and manufacturing, object recognition, pose estimation, robotic navigation, and reverse engineering. Registration occurs by aligning the regions that are common to multiple images. The largest difficulty in performing this registration is dealing with outliers and local minima while remaining efficient. A commonly used technique, iterative closest point, is efficient but is unable to deal with outliers or avoid local minima. Another commonly used optimization algorithm, simulated annealing, is effective at dealing with local minima but is very slow. Therefore, the algorithm developed in this paper is a hybrid algorithm that combines the speed of iterative closest point with the robustness of simulated annealing. Additionally, a robust error function is incorporated to deal with outliers. This algorithm is incorporated into a complete modeling system that inputs two sets of range data, registers the sets, and outputs a composite model.

  7. Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

    NASA Astrophysics Data System (ADS)

    Weiss, N. O.; Tobias, S. M.

    2016-03-01

    In this paper, we argue that the solar activity record, as revealed by telescopic observations and proxy data from the abundances of cosmogenic isotopes, is consistent with the action of a deterministic non-linear chaotic dynamo. In particular, we claim that the long time-scale `supermodulation' apparent in the isotopic record can be ascribed to switching of the dynamo between two different modulational patterns. The first (which is currently in operation) involves deep grand minima and occasional changes in symmetry triggered by these minima. The second, which exhibits only weak modulation and no grand minima, arises as a consequence of symmetry breaking. These processes are demonstrated for highly idealized simple models of the non-linear dynamo equations.

  8. Genetic algorithm optimization of atomic clusters

    SciTech Connect

    Morris, J.R.; Deaven, D.M.; Ho, K.M.; Wang, C.Z.; Pan, B.C.; Wacker, J.G.; Turner, D.E. |

    1996-12-31

    The authors have been using genetic algorithms to study the structures of atomic clusters and related problems. This is a problem where local minima are easy to locate, but barriers between the many minima are large, and the number of minima prohibit a systematic search. They use a novel mating algorithm that preserves some of the geometrical relationship between atoms, in order to ensure that the resultant structures are likely to inherit the best features of the parent clusters. Using this approach, they have been able to find lower energy structures than had been previously obtained. Most recently, they have been able to turn around the building block idea, using optimized structures from the GA to learn about systematic structural trends. They believe that an effective GA can help provide such heuristic information, and (conversely) that such information can be introduced back into the algorithm to assist in the search process.

  9. Comparative modelling of chemical ordering in palladium-iridium nanoalloys

    SciTech Connect

    Davis, Jack B. A.; Johnston, Roy L.; Rubinovich, Leonid; Polak, Micha

    2014-12-14

    Chemical ordering in “magic-number” palladium-iridium nanoalloys has been studied by means of density functional theory (DFT) computations, and compared to those obtained by the Free Energy Concentration Expansion Method (FCEM) using derived coordination dependent bond energy variations (CBEV), and by the Birmingham Cluster Genetic Algorithm using the Gupta potential. Several compositions have been studied for 38- and 79-atom particles as well as the site preference for a single Ir dopant atom in the 201-atom truncated octahedron (TO). The 79- and 38-atom nanoalloy homotops predicted for the TO by the FCEM/CBEV are shown to be, respectively, the global minima and competitive low energy minima. Significant reordering of minima predicted by the Gupta potential is seen after reoptimisation at the DFT level.

  10. Computing Freidlin's Cycles for the Overdamped Langevin Dynamics. Application to the Lennard-Jones-38 Cluster

    NASA Astrophysics Data System (ADS)

    Cameron, M. K.

    2013-08-01

    The large time behavior of a stochastic system with infinitesimally small noise can be described in terms of Freidlin's cycles. We show that if the system is gradient and the potential satisfies certain non-restrictive conditions, the hierarchy of cycles has a structure of a full binary tree, and each cycle is exited via the lowest saddle adjacent to it. Exploiting this property, we propose an algorithm for computing the asymptotic zero-temperature path and building a hierarchy of Freidlin's cycles associated with the transition process between two given local equilibria. This algorithm is suitable for systems with a complex potential energy landscape with numerous minima. We apply it to find the asymptotic zero-temperature path and Freidlin's cycles involved into the transition process between the two lowest minima of the Lennard-Jones cluster of 38 atoms. D. Wales's stochastic network of minima and transition states of this cluster is used as an input.

  11. Heliospheric shocks and catastrophe theory

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.

    1990-01-01

    Various configurations of forward and reverse shocks that occur in the outer heliosphere can be classified using catastrophe theory. The existence of a forward shock is associated with a local maximum of a polynomial, and the existence of a reverse shock is associated with a local minimum of a polynomial. A configuration with N forward shocks and N reverse shocks corresponds to a polynomial with N maxima and N minima. The formation of forward and reverse shocks corresponds to the creation of maxima and minima of a polynomial, which is described by the separatrices of the catastrophes. The coalescence of two forward (reverse) shocks corresponds to the situation when two maxima (minima) of a polynomial have equal values, and the interaction of a forward shock with a reverse shock corresponds to a polynomial with a local maximum equal to a local minimum; these situations are described by the Maxwell sets of the appropriate catastrophes.

  12. Flowing crystals: nonequilibrium structure of foam.

    PubMed

    Garstecki, Piotr; Whitesides, George M

    2006-07-14

    Bubbles pushed through a quasi-two-dimensional channel self-organize into a variety of periodic lattices. The structures of these lattices correspond to local minima of the interfacial energy. The "flowing crystals" are long-lived metastable states, a small subset of possible local minima of confined quasi-two-dimensional foams [P. Garstecki and G. M. Whitesides, Phys. Rev. E 73, 031603 (2006)10.1103/PhysRevE.73.031603]. Experimental results suggest that the choice of the structures that we observe is dictated by the dynamic stability of the cyclic processes of their formation. Thus, the dynamic system that we report provides a unique example of nonequilibrium self-organization that results in structures that correspond to local minima of the relevant energy functional. PMID:16907453

  13. Tight-binding approach to overdamped Brownian motion on a bichromatic periodic potential

    NASA Astrophysics Data System (ADS)

    Nguyen, P. T. T.; Challis, K. J.; Jack, M. W.

    2016-02-01

    We present a theoretical treatment of overdamped Brownian motion on a time-independent bichromatic periodic potential with spatially fast- and slow-changing components. In our approach, we generalize the Wannier basis commonly used in the analysis of periodic systems to define a basis of S states that are localized at local minima of the potential. We demonstrate that the S states are orthonormal and complete on the length scale of the periodicity of the fast-changing potential, and we use the S-state basis to transform the continuous Smoluchowski equation for the system to a discrete master equation describing hopping between local minima. We identify the parameter regime where the master equation description is valid and show that the interwell hopping rates are well approximated by Kramers' escape rate in the limit of deep potential minima. Finally, we use the master equation to explore the system dynamics and determine the drift and diffusion for the system.

  14. Tight-binding approach to overdamped Brownian motion on a bichromatic periodic potential.

    PubMed

    Nguyen, P T T; Challis, K J; Jack, M W

    2016-02-01

    We present a theoretical treatment of overdamped Brownian motion on a time-independent bichromatic periodic potential with spatially fast- and slow-changing components. In our approach, we generalize the Wannier basis commonly used in the analysis of periodic systems to define a basis of S states that are localized at local minima of the potential. We demonstrate that the S states are orthonormal and complete on the length scale of the periodicity of the fast-changing potential, and we use the S-state basis to transform the continuous Smoluchowski equation for the system to a discrete master equation describing hopping between local minima. We identify the parameter regime where the master equation description is valid and show that the interwell hopping rates are well approximated by Kramers' escape rate in the limit of deep potential minima. Finally, we use the master equation to explore the system dynamics and determine the drift and diffusion for the system. PMID:26986305

  15. REVISITED SUNSPOT DATA: A NEW SCENARIO FOR THE ONSET OF THE MAUNDER MINIMUM

    SciTech Connect

    Vaquero, Jose M.; Gallego, M. C.; Usoskin, Ilya G.; Kovaltsov, Gennady A. E-mail: maricruz@unex.es E-mail: gen.koval@mail.ru

    2011-04-20

    The Maunder minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with long-term solar activity evolution. Here, we reconsider the current paradigm of the Grand minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636-1642, i.e., one solar cycle before the beginning of the Maunder minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder minimum, from 60-70 down to about 20, implying a possibly gradual onset of the minimum with reduced activity started two cycles before it. This revised scenario of the Maunder minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.

  16. Differential physiological responses of two Salvinia species to hexavalent chromium at a glance.

    PubMed

    Prado, Carolina; Chocobar Ponce, Silvana; Pagano, Eduardo; Prado, Fernando E; Rosa, Mariana

    2016-06-01

    In plants of Salvinia rotundifolia and Salvinia minima the effect of two Cr(VI) concentrations (5 and 20mgL(-1)) applied for 7days was assessed by measuring changes in biomass, photosynthetic pigments, Cr accumulation, malondialdehyde (MDA), membrane stability index (MSI), thiols (TT, NPT and PBT), and phenolics (SP and IP). Biomass in S. minima was decreased at highest Cr(VI) concentration, but there were no changes in S. rotundifolia. Metal accumulation was different in both species. S. minima accumulates more metal in fronds, but S. rotundifolia accumulates more metal in lacinias. Results also showed that S. minima translocates more Cr to fronds than S. rotundifolia, but at the whole plant level higher accumulation occurred in this last. Tolerance index (Ti) was higher in S. rotundifolia. Chl b and carotenoids were decreased only upon exposure to high Cr(VI) concentration in both species. Cr(VI) treatment did not enhance MDA accumulation. Cr exposure had no impact on MSI values when comparing with Cr-untreated values. Thiols in fronds and lacinias showed different distribution patterns between species. IP and NPT were higher in S. rotundifolia lacinias that accumulate more Cr than S. minima lacinias. Whilst SP and NPT were higher in S. minima fronds compared with S. rotundifolia ones. This may indicate that these species can cope with Cr(VI) toxicity, either through metal complexation and/or metal reduction or by the scavenging of ROS derived from Cr-induced oxidative stress. Based on Cr accumulation and biomass production, S. rotundifolia seems more suitable to remove Cr(VI) from polluted waters. PMID:27061358

  17. Variations of the tropical Atlantic and Pacific SSS minimum zones and their relations to the ITCZ and SPCZ rain bands (1979-2009)

    NASA Astrophysics Data System (ADS)

    Tchilibou, M.; Delcroix, T.; Alory, G.; Arnault, S.; Reverdin, G.

    2015-07-01

    This study focuses on the time-space variability of the low Sea Surface Salinity (SSS) waters extending zonally within 2°N-12°N in the Atlantic and Pacific and within 6°S-16°S in the western third of the Pacific. The analysis is based on a combination of in situ SSS observations collected in the last three decades from voluntary observing ships, TAO/TRITON and PIRATA moorings, Argo floats, and (few) CTD profiles. The mean latitudes of the Atlantic and Pacific low SSS waters appear 1°-3° further poleward than the Evaporation minus Precipitation (E-P) minima linked to the Inter Tropical Convergence Zones (ITCZ) and South Pacific Convergence Zone (SPCZ). At the seasonal time scale, the E-P minima migrate poleward in summer hemispheres, leading the migration of the SSS minima by 2-3 months in the Atlantic ITCZ, Pacific SPCZ, and in the eastern part of the Pacific ITCZ. On the other hand, the seasonal displacements of E-P and SSS minima are in antiphase in the central and western parts of the Pacific ITCZ. At the interannual time scale, the E-P and SSS minima migrate poleward during La Nina events in the Pacific and during the positive phase of the Atlantic Meridional Dipole (AMD) in the Atlantic (and vice versa during El Nino and the negative phase of the AMD). We further document long-term (1979-2009) meridional migrations of the E-P and SSS minima, especially in the SPCZ region, and discuss whether or not they are consistent with documented SST and wind stress trends.

  18. Method and apparatus for thickness measurement using microwaves

    DOEpatents

    Woskov, Paul [Bedford, MA; Lamar, David A [West Richland, WA

    2001-01-01

    The method for measuring the thickness of a material which transmits a detectable amount of microwave radiation includes irradiating the material with coherent microwave radiation tuned over a frequency range. Reflected microwave radiation is detected, the reflected radiation having maxima and minima over the frequency range as a result of coherent interference of microwaves reflected from reflecting surfaces of the material. The thickness of the material is determined from the period of the maxima and minima along with knowledge of the index of refraction of the material.

  19. Photometric geodesy of main-belt asteroids. III. Additional lightcurves

    SciTech Connect

    Weidenschilling, S.J.; Chapman, C.R.; Davis, D.R.; Greenberg, R.; Levy, D.H. )

    1990-08-01

    A total of 107 complete or partial lightcurves are presented for 59 different asteroids over the 1982-1989 period. Unusual lightcurves with unequal minima and maxima at large amplitudes are preferentially seen for M-type asteroids. Some asteroids, such as 16 Psyche and 201 Penelope, exhibit lightcurves combining large amplitude with very unequal brightness for both maxima and both minima, even at small phase angles. An M-type asteroid is believed to consist of a metal core of a differentiated parent body that has had its rocky mantle completely removed by one or more large impacts. 39 refs.

  20. Energy Landscape of Social Balance

    NASA Astrophysics Data System (ADS)

    Marvel, Seth A.; Strogatz, Steven H.; Kleinberg, Jon M.

    2009-11-01

    We model a close-knit community of friends and enemies as a fully connected network with positive and negative signs on its edges. Theories from social psychology suggest that certain sign patterns are more stable than others. This notion of social “balance” allows us to define an energy landscape for such networks. Its structure is complex: numerical experiments reveal a landscape dimpled with local minima of widely varying energy levels. We derive rigorous bounds on the energies of these local minima and prove that they have a modular structure that can be used to classify them.

  1. Interaction modes between asymmetrically and oppositely charged rods

    NASA Astrophysics Data System (ADS)

    Antila, Hanne S.; Van Tassel, Paul R.; Sammalkorpi, Maria

    2016-02-01

    The interaction of oppositely and asymmetrically charged rods in salt—a simple model of (bio)macromolecular assembly—is observed via simulation to exhibit two free energy minima, separated by a repulsive barrier. In contrast to similar minima in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the governing mechanism includes electrostatic attraction at large separation, osmotic repulsion at close range, and depletion attraction near contact. A model accounting for ion condensation and excluded volume is shown to be superior to a mean-field treatment in predicting the effect of charge asymmetry on the free-energy profile.

  2. Dust Around Herbig Ae Stars: Additional Constraints from their Photometric and Polarimetric Variability

    NASA Technical Reports Server (NTRS)

    Krivova, N. A.; Ilin, V. B.; Fischer, O.

    1996-01-01

    For the Herbig Ae stars with Algol-like minima (UX Ori, WW Vul, etc), the effects of circumstellar dust include: excess infrared emission, anomalous ultraviolet extinction, the 'blueing' of the stars in minima accompanying by an increase of intrinsic polarization. Using a Monte-Carlo code for polarized radiation transfer we have simulated these effects and compared the results obtained for different models with the observational data available. We found that the photometric and polarimetric behavior of the stars provided essential additional constraints on the circumstellar dust models. The models with spheroidal shell geometry and compact (non-fluffy) dust grains do not appear to be able to explain all the data.

  3. Electron-phonon interactions in superconducting La1.84Sr0.16CuO4 films.

    PubMed

    Shim, Heejae; Chaudhari, P; Logvenov, Gennady; Bozovic, Ivan

    2008-12-12

    We have measured quasiparticle tunneling across a junction perpendicular to the superconducting copper oxide planes. The tunneling spectra show peaks in the density of states. There are 11 minima in the second derivative d2I/dV2, where I is the current and V the voltage, suggesting multiple boson-quasiparticle interactions. These minima match precisely with the published Raman scattering data, leading us to conclude that the relevant bosons in superconducting La1.84Sr0.16CuO4 films are phonons. PMID:19113657

  4. Spin–orbit coupling induced magnetoresistance oscillation in a dc biased two-dimensional electron system.

    PubMed

    Wang, C M; Lei, X L

    2014-06-11

    We study dc-current effects on the magnetoresistance oscillation in a two-dimensional electron gas with Rashba spin-orbit coupling, using the balance-equation approach to nonlinear magnetotransport. In the weak current limit the magnetoresistance exhibits periodical Shubnikov-de Haas oscillation with changing Rashba coupling strength for a fixed magnetic field. At finite dc bias, the period of the oscillation halves when the interbranch contribution to resistivity dominates. With further increasing current density, the oscillatory resistivity exhibits phase inversion, i.e., magnetoresistivity minima (maxima) invert to maxima (minima) at certain values of the dc bias, which is due to the current-induced magnetoresistance oscillation. PMID:25932474

  5. Lone pairs: an electrostatic viewpoint.

    PubMed

    Kumar, Anmol; Gadre, Shridhar R; Mohan, Neetha; Suresh, Cherumuttathu H

    2014-01-16

    A clear-cut definition of lone pairs has been offered in terms of characteristics of minima in molecular electrostatic potential (MESP). The largest eigenvalue and corresponding eigenvector of the Hessian at the minima are shown to distinguish lone pair regions from the other types of electron localization (such as π bonds). A comparative study of lone pairs as depicted by various other scalar fields such as the Laplacian of electron density and electron localization function is made. Further, an attempt has been made to generalize the definition of lone pairs to the case of cations. PMID:24372481

  6. Gradient tabu search.

    PubMed

    Stepanenko, Svetlana; Engels, Bernd

    2007-01-30

    This paper presents a modification of the tabu search called gradient tabu search (GTS). It uses analytical gradients for a fast minimization to the next local minimum and analytical diagonal elements of the Hessian to escape local minima. For an efficient blocking of already visited areas tabu regions and tabu directions are introduced into the tabu list (TL). Trials with various well-known test functions indicate that the GTS is a very promising approach to determine local and global minima of differentiable functions. Possible application areas could be optimization routines for force field parameters or conformational searches for large molecules. PMID:17186482

  7. Optical Model and Cross Section Uncertainties

    SciTech Connect

    Herman,M.W.; Pigni, M.T.; Dietrich, F.S.; Oblozinsky, P.

    2009-10-05

    Distinct minima and maxima in the neutron total cross section uncertainties were observed in model calculations using spherical optical potential. We found this oscillating structure to be a general feature of quantum mechanical wave scattering. Specifically, we analyzed neutron interaction with 56Fe from 1 keV up to 65 MeV, and investigated physical origin of the minima.We discuss their potential importance for practical applications as well as the implications for the uncertainties in total and absorption cross sections.

  8. Improved Particle Swarm Optimization for Global Optimization of Unimodal and Multimodal Functions

    NASA Astrophysics Data System (ADS)

    Basu, Mousumi

    2015-07-01

    Particle swarm optimization (PSO) performs well for small dimensional and less complicated problems but fails to locate global minima for complex multi-minima functions. This paper proposes an improved particle swarm optimization (IPSO) which introduces Gaussian random variables in velocity term. This improves search efficiency and guarantees a high probability of obtaining the global optimum without significantly impairing the speed of convergence and the simplicity of the structure of particle swarm optimization. The algorithm is experimentally validated on 17 benchmark functions and the results demonstrate good performance of the IPSO in solving unimodal and multimodal problems. Its high performance is verified by comparing with two popular PSO variants.

  9. Photometric geodesy of main-belt asteroids. III - Additional lightcurves

    NASA Technical Reports Server (NTRS)

    Weidenschilling, S. J.; Chapman, C. R.; Davis, D. R.; Greenberg, R.; Levy, D. H.

    1990-01-01

    A total of 107 complete or partial lightcurves are presented for 59 different asteroids over the 1982-1989 period. Unusual lightcurves with unequal minima and maxima at large amplitudes are preferentially seen for M-type asteroids. Some asteroids, such as 16 Psyche and 201 Penelope, exhibit lightcurves combining large amplitude with very unequal brightness for both maxima and both minima, even at small phase angles. An M-type asteroid is believed to consist of a metal core of a differentiated parent body that has had its rocky mantle completely removed by one or more large impacts.

  10. Anomalous structural feature of LiNbO{sub 3} observed using neutron diffraction

    SciTech Connect

    Fernandez-Ruiz, R.; Bermudez, V.; Martin y Marero, D.

    2005-11-01

    An anomalous structural effect has been observed and analyzed on LiNbO{sub 3} at low temperature by neutron-diffraction experiments. Two minima in the unit-cell volume at 55 and 100 K related with maxima and minima in the volume vibrational isotropic factors of Li and Nb atoms, respectively, and a change in the curve slope of the spontaneous stress at 55 K have been identified. This fact, together with the shortening in distance of the Li and O layers at 55 K, has been related with variations in the Ps factor through the secondary pyroelectric effect.

  11. Energy landscapes for a machine learning application to series data

    NASA Astrophysics Data System (ADS)

    Ballard, Andrew J.; Stevenson, Jacob D.; Das, Ritankar; Wales, David J.

    2016-03-01

    Methods developed to explore and characterise potential energy landscapes are applied to the corresponding landscapes obtained from optimisation of a cost function in machine learning. We consider neural network predictions for the outcome of local geometry optimisation in a triatomic cluster, where four distinct local minima exist. The accuracy of the predictions is compared for fits using data from single and multiple points in the series of atomic configurations resulting from local geometry optimisation and for alternative neural networks. The machine learning solution landscapes are visualised using disconnectivity graphs, and signatures in the effective heat capacity are analysed in terms of distributions of local minima and their properties.

  12. Synergistic air port corrosion in kraft recovery boilers

    SciTech Connect

    Holcomb, Gordon R.

    2001-08-01

    Localized hot corrosion can occur on the cold-side of air-ports in Kraft recovery boilers. Depending on the basicity of the molten salt, either acidic or basic fluxing takes place, with a solubility minima at the transition between the two reactions. For stainless steel, if the basicity of the fused salt is between the iron and chromium oxide solubility minima, then a synergistic effect can occur that leads to rapid corrosion. The products of one reaction are the reactants of the other, which eliminates the need for rate-controlling diffusion. This effect can explain why stainless steel is attacked more readily than carbon steel.

  13. Acoustic concentration of particles in fluid flow

    DOEpatents

    Ward, Michael D.; Kaduchak, Gregory

    2010-11-23

    An apparatus for acoustic concentration of particles in a fluid flow includes a substantially acoustically transparent membrane and a vibration generator that define a fluid flow path therebetween. The fluid flow path is in fluid communication with a fluid source and a fluid outlet and the vibration generator is disposed adjacent the fluid flow path and is capable of producing an acoustic field in the fluid flow path. The acoustic field produces at least one pressure minima in the fluid flow path at a predetermined location within the fluid flow path and forces predetermined particles in the fluid flow path to the at least one pressure minima.

  14. Examination of Bursty Electromagnetic Waves Observed During Intervals of Turbulent Magnetosheath Reconnection

    NASA Technical Reports Server (NTRS)

    Adrian, Mark L.; Wendel, D. E.

    2011-01-01

    We investigate observations of intense bursts of electromagnetic waves in association with magnetic reconnection in the turbulent magnetosheath. These structured, broadband bursts occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic waves and quantify their proximity to X- and O-nulls.

  15. Quasibiennial Periodicity of Solar and Planetary Phenomena

    NASA Astrophysics Data System (ADS)

    Predeanu, Irina

    The quasibiennial oscillation (QBO) of various solar and geophysical parameters is anlysed, taking some planetary configurations as temporal reference points. The incidence of the QBO minima in the proximity of Sun-Mars oppositions is discussed. The increase of this effect when Mars is near the perihelion or Jupiter is conjunct to the Sun is pointed out,

  16. Circulating tumor cell detection using photoacoustic spectral methods

    NASA Astrophysics Data System (ADS)

    Strohm, Eric M.; Berndl, Elizabeth S. L.; Kolios, Michael C.

    2014-03-01

    A method to detect and differentiate circulating melanoma tumor cells (CTCs) from blood cells using ultrasound and photoacoustic signals with frequencies over 100 MHz is presented. At these frequencies, the acoustic wavelength is similar to the dimensions of a cell, which results in unique features in the signal; periodically varying minima and maxima occur throughout the power spectrum. The spacing between minima depends on the ratio of the size to sound speed of the cell. Using a 532 nm pulsed laser and a 375 MHz center frequency wide-bandwidth transducer, the ultrasound and photoacoustic signals were measured from single cells. A total of 80 cells were measured, 20 melanoma cells, 20 white blood cells (WBCs) and 40 red blood cells (RBCs). The photoacoustic spectral spacing Δf between minima was 95 +/- 15 MHz for melanoma cells and greater than 230 MHz for RBCs. No photoacoustic signal was detected from WBCs. The ultrasonic spectral spacing between minima was 46 +/- 9 MHz for melanoma cells and 98 +/- 11 for WBCs. Both photoacoustic and ultrasound signals were detected from melanoma cells, while only ultrasound signals were detected from WBCs. RBCs showed distinct photoacoustic spectral variations in comparison to any other type of cell. Using the spectral spacing and signal amplitudes, each cell type could be grouped together to aid in cell identification. This method could be used for label-free counting and classifying cells in a sample.

  17. Cadophora species as trunk pathogens and wood-infecting fungi of grapevine in North America

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cadophora species, in particular Cadophora luteo-olivacea, are reported from grapevine (Vitis vinifera L.) in California, South Africa, Spain, Uruguay, and Canada. Frequent isolation from vines co-infected with the Esca pathogens (Togninia minima, Phaeomoniella chlamydospora), and confirmation of it...

  18. Geomagnetic detection of the sectorial solar magnetic field and the historical peculiarity of minimum 23-24

    USGS Publications Warehouse

    Love, Jeffrey J.; Rigler, J.

    2012-01-01

    [1] Analysis is made of the geomagnetic-activityaaindex covering solar cycle 11 to the beginning of 24, 1868–2011. Autocorrelation shows 27.0-d recurrent geomagnetic activity that is well-known to be prominent during solar-cycle minima; some minima also exhibit a smaller amount of 13.5-d recurrence. Previous work has shown that the recent solar minimum 23–24 exhibited 9.0 and 6.7-d recurrence in geomagnetic and heliospheric data, but those recurrence intervals were not prominently present during the preceding minima 21–22 and 22–23. Using annual-averages and solar-cycle averages of autocorrelations of the historicalaadata, we put these observations into a long-term perspective: none of the 12 minima preceding 23–24 exhibited prominent 9.0 and 6.7-d geomagnetic activity recurrence. We show that the detection of these recurrence intervals can be traced to an unusual combination of sectorial spherical-harmonic structure in the solar magnetic field and anomalously low sunspot number. We speculate that 9.0 and 6.7-d recurrence is related to transient large-scale, low-latitude organization of the solar dynamo, such as seen in some numerical simulations.

  19. Diffusion of a protein in configuration space

    SciTech Connect

    Garcia, A.E.; Blumenfeld, R.; Hummer, G.; Sobehart, J.

    1995-09-01

    Simulations of biomolecular dynamics are commonly interpreted in terms of harmonic or quasi-harmonic models for the dynamics of the system. These models assume that biomolecules exhibit oscillations around a single energy minimum. However, spectroscopic data on myoglobin suggest that proteins sample multiple minima. Transitions between minima reveal a broad distribution of energy barriers. This behavior has been observed in other biomolecular systems. To elucidate the nature of protein dynamics the authors have studied a 1.2ns molecular dynamics trajectory of crambin in aqueous solution. This trajectory samples multiple local energy minima. Transitions between minima involve collective motions of amino acids over long distances. The authors show that nonlinear motions are responsible for most of the atomic fluctuations of the protein. These atomic fluctuations are not well described by large motions of individual atoms or a small group of atoms, but rather by concerted motions of many atoms. These nonlinear motions describe transitions between different basins of attraction. The signature of these motions manifests in local and global structural variables. A method for extracting Molecule Optimal Dynamic Coordinates (MODC) is presented.

  20. Recycling, Thermodynamics and Environmental Thrift

    ERIC Educational Resources Information Center

    Berry, R. Stephen

    1972-01-01

    Compares the cost, in terms of thermodynamic potential, of manufacturing automobiles from raw mineral resources or from recycled vehicles, and of the production of extended-life products. Uses this as an example for arguing that new technologies, with efficiencies closer to the theoretical themodynamic minima, are needed if a society is to…

  1. Relativistic calculations of angle-dependent photoemission time delay

    NASA Astrophysics Data System (ADS)

    Kheifets, Anatoli; Mandal, Ankur; Deshmukh, Pranawa C.; Dolmatov, Valeriy K.; Keating, David A.; Manson, Steven T.

    2016-07-01

    Angular dependence of photoemission time delay for the valence n p3 /2 and n p1 /2 subshells of Ar, Kr, and Xe is studied in the dipole relativistic random phase approximation. Strong angular anisotropy of the time delay is reproduced near respective Cooper minima while the spin-orbit splitting affects the time delay near threshold.

  2. Analysis of B3LYP and MP2 conformational population distributions in trans-nicotine, acetylcholine, and ABT-594

    NASA Astrophysics Data System (ADS)

    Mora, M.; Castro, M. E.; Niño, A.; Melendez, F. J.; Muñoz-Caro, C.

    This work presents an analysis of the equivalence of MP2 and DFT (B3LYP functional) conformational populations. As a test case, we select three cholinergic agents (trans-nicotine, acetylcholine, and the nicotinic analgesic ABT-594), where the minima on the conformational energy hypersurfaces expand a large range of energies (˜0-30 kJ mol-1). From energetic and structural data obtained in vacuo at the MP2 and B3LYP/cc-pVDZ levels, we build conformational partition functions, including the effect of the conformational kinetic energy and the rotovibrational coupling. Our results at a physiological temperature (37°C) show qualitative agreement in all cases. Quantitative agreement, however, is only found for trans-nicotine and ABT-594. In the first case, energy minima differ by <0.2 kJ mol-1. Therefore, the equivalence of structural results translates in the equivalence of the conformational distribution. For ABT-594, the minima are separated by as much as 8.0 kJ mol-1, and the conformational energy determines the conformational distribution. In this case, the slight relative variation of conformational energy, between B3LYP and MP2, does not affect the population, since the secondary minima are high in energy and very low in population.

  3. The influence of nonstationarity of the solar activity and general solar field on modulation of cosmic rays

    NASA Technical Reports Server (NTRS)

    Zusmanovich, A. G.; Kryakunova, O. N.; Churunova, L. F.; Shvartsman, Y. E.

    1985-01-01

    A numerical model of the propagation of galactic cosmic rays in interplanetary space was constructed for the case when the modulation depth determined by the level of solar activity changed in time. Also the contribution of particle drift in the regular field was calculated, and the agreement with experimental data concerning the ratio of protons and electrons in two solar activity minima is shown.

  4. Computational study of the rovibrational spectrum of CO₂-CS₂.

    PubMed

    Brown, James; Wang, Xiao-Gang; Carrington, Tucker; Grubbs, G S; Dawes, Richard

    2014-03-21

    A new intermolecular potential energy surface, rovibrational transition frequencies, and line strengths are computed for CO2-CS2. The potential is made by fitting energies obtained from explicitly correlated coupled-cluster calculations using an interpolating moving least squares method. The rovibrational Schrödinger equation is solved with a symmetry-adapted Lanczos algorithm and an uncoupled product basis set. All four intermolecular coordinates are included in the calculation. In agreement with previous experiments, the global minimum of the potential energy surface (PES) is cross shaped. The PES also has slipped-parallel minima. Rovibrational wavefunctions are localized in the cross minima and the slipped-parallel minima. Vibrational parent analysis was used to assign vibrational labels to rovibrational states. Tunneling occurs between the two cross minima. Because more than one symmetry operation interconverts the two wells, the symmetry (-oo) of the upper component of the tunneling doublet is different from the symmetry (-ee) of the tunneling coordinate. This unusual situation is due to the multidimensional nature of the double well tunneling. For the cross ground vibrational state, calculated rotational constants differ from their experimental counterparts by less than 0.0001 cm(-1). Most rovibrational states were found to be incompatible with the standard effective rotational Hamiltonian often used to fit spectra. This appears to be due to coupling between internal and overall rotation of the dimer. A simple 2D model accounting for internal rotation was used for two cross-shaped fundamentals to obtain good fits. PMID:24655176

  5. Solitary-wave solutions in binary mixtures of Bose-Einstein condensates under periodic boundary conditions

    NASA Astrophysics Data System (ADS)

    Smyrnakis, J.; Magiropoulos, M.; Kavoulakis, G. M.; Jackson, A. D.

    2013-01-01

    We derive solitary-wave solutions within the mean-field approximation in quasi-one-dimensional binary mixtures of Bose-Einstein condensates under periodic boundary conditions, for the case of an effective repulsive interatomic interaction. The particular gray-bright solutions that give the global energy minima are determined. Their characteristics and the associated dispersion relation are derived.

  6. The Heat Capacity of Ideal Gases

    ERIC Educational Resources Information Center

    Scott, Robert L.

    2006-01-01

    The heat capacity of an ideal gas has been shown to be calculable directly by statistical mechanics if the energies of the quantum states are known. However, unless one makes careful calculations, it is not easy for a student to understand the qualitative results. Why there are maxima (and occasionally minima) in heat capacity-temperature curves…

  7. VizieR Online Data Catalog: Carrier fit analysis of LQ Hya photometry (Olspert+, 2015)

    NASA Astrophysics Data System (ADS)

    Olspert, N.; Kapyla, M. J.; Pelt, J.; Cole, E. M.; Hackman, T.; Lehtinen, J.; Henry, G. W.

    2015-02-01

    The epochs as well as differential magnitudes of primary and secondary minima obtained from the model are presented. The analysis was done for the homogeneous data set D2 as denoted in the paper (photometry obtained with the T3 0.4m APT at the Fairborn Observatory). (1 data file).

  8. 14 CFR 25.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... intensities in overlapping beams, within dihedral angles L, R, and A, and must meet the following requirements... in overlaps may be used with main beam intensities substantially greater than the minima specified in §§ 25.1391 and 25.1393 if the overlap intensities in relation to the main beam intensities do...

  9. 14 CFR 27.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... intensities in overlapping beams, within dihedral angles L, R, and A, and must meet the following requirements... overlaps may be used with main beam intensities substantially greater than the minima specified in §§ 27.1391 and 27.1393, if the overlap intensities in relation to the main beam intensities do not...

  10. 14 CFR 29.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... maximum intensities in overlapping beams, within dihedral angles, L, R, and A, and must meet the following... overlaps may be used with the use of main beam intensities substantially greater than the minima specified in §§ 29.1391 and 29.1393 if the overlap intensities in relation to the main beam intensities do...

  11. 14 CFR 29.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... maximum intensities in overlapping beams, within dihedral angles, L, R, and A, and must meet the following... overlaps may be used with the use of main beam intensities substantially greater than the minima specified in §§ 29.1391 and 29.1393 if the overlap intensities in relation to the main beam intensities do...

  12. 14 CFR 29.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... maximum intensities in overlapping beams, within dihedral angles, L, R, and A, and must meet the following... overlaps may be used with the use of main beam intensities substantially greater than the minima specified in §§ 29.1391 and 29.1393 if the overlap intensities in relation to the main beam intensities do...

  13. 14 CFR 29.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... maximum intensities in overlapping beams, within dihedral angles, L, R, and A, and must meet the following... overlaps may be used with the use of main beam intensities substantially greater than the minima specified in §§ 29.1391 and 29.1393 if the overlap intensities in relation to the main beam intensities do...

  14. 14 CFR 23.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... overlapping beams, within dihedral angles L, R, and A, and must meet the following requirements: (1... with main beam intensities substantially greater than the minima specified in §§ 23.1391 and 23.1393, if the overlap intensities in relation to the main beam intensities do not adversely affect...

  15. 14 CFR 27.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... intensities in overlapping beams, within dihedral angles L, R, and A, and must meet the following requirements... overlaps may be used with main beam intensities substantially greater than the minima specified in §§ 27.1391 and 27.1393, if the overlap intensities in relation to the main beam intensities do not...

  16. 14 CFR 25.1389 - Position light distribution and intensities.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... intensities in overlapping beams, within dihedral angles L, R, and A, and must meet the following requirements... in overlaps may be used with main beam intensities substantially greater than the minima specified in §§ 25.1391 and 25.1393 if the overlap intensities in relation to the main beam intensities do...

  17. Shell corrections, magic numbers, and mean field

    SciTech Connect

    Denisov, V. Yu.

    2007-02-15

    It is shown that the positions of deep local minima of shell corrections associated with magic numbers in the region of superheavy nuclei depend on the parameters of the central and spin-orbit mean-field potentials. The accuracy of nuclear-mass predictions made within various models for superheavy nuclei is analyzed.

  18. Elastic Rod Model of a DNA Loop in the Lac Operon

    NASA Astrophysics Data System (ADS)

    Balaeff, Alexander; Mahadevan, L.; Schulten, Klaus

    1999-12-01

    We use the theory of elasticity to compute the shape of the DNA loop bridging the gap in the crystal structure of the lac repressor-DNA complex. The Kirchhoff system of equations with boundary conditions derived from the crystal structure is solved using a continuation method. This approach can be applied effectively to find coarse-grained conformational minima of DNA loops.

  19. 2. QUANTUM HALL EFFECT: Magnetocapacitance studies of two-dimensional electron systems with long-range potential fluctuations

    NASA Astrophysics Data System (ADS)

    Dorokhova, M. O.; Dorozhkin, S. I.

    2001-10-01

    We report on magnetocapacitance study of the quantum Hall effect (QHE) states. Capacitance minima width was found to be independent of magnetic field and to be the same for even, odd and fractional QHE states when measured as a function of the average electron density. This result indicates that the width of capacitance minima in the samples investigated are governed by long-range carrier density fluctuations. At low temperatures, the amplitudes of the minima decrease linearly with the temperature increase. All our experimental results for the integer QHE states are quantitatively explained by introducing unbroadened magnetic levels and dispersion of the electron density along the sample. The energy gaps at even filling factors obtained from fitting the experimental data are found to be close to the known cyclotron gaps. At odd fillings v = 1, 3, and 5, the energy gaps appear to be enhanced in comparison with the Zeeman splitting, with the enhancement decreasing with filling factor. The capacitance minima are argued to originate from the motion of incompressible regions along a sample caused by the gate voltage variation. We derive the condition for the appearance and motion of such regions for the case of gated samples with long-range fluctuations of density of charged donors. The appearance of narrow magnetocapacitance peaks when a dc current is passed through the sample is reported. We hypothesize that these peaks are due to the current percolation along incompressible regions.

  20. Soil spectra contributions to grass canopy spectral reflectance

    NASA Technical Reports Server (NTRS)

    Tucker, C. J.; Miller, L. D.

    1977-01-01

    The soil or background spectra contribution to grass canopy spectral reflectance for the 0.35 to 0.80 micron region was investigated using in situ collected spectral reflectance data. Regression analysis was used to estimate accurately the unexposed soil spectral reflectance and to quantify maxima and minima for soil-green vegetation reflection contrasts.

  1. The unusual lightcurve of 1990 TR

    NASA Technical Reports Server (NTRS)

    Wisniewski, Wieslaw Z.

    1992-01-01

    Amor asteroid 1990 TR was monitored during three nights shortly after discovery. Obtained lightcurves did not reveal a repeatable curve with two maxima and two minima. However, some features suggest periodicity, and a synodic rotational period P = 6.25 hours was determined. Individual and composite lightcurves are presented. The colors are best represented by the class S.

  2. IDENTIFICATION OF ALGAE WHICH INTERFERE WITH THE DETECTION OF GIARDIA CYSTS AND CRYPTOSPORIDIUM OOCYSTS AND A METHOD FOR ALLEVIATING THIS INTERFERENCE

    EPA Science Inventory

    Fifty-four algal species were tested for cross-reaction in the American Society for Testing and Materials Giardia/Cryptosporidium indirect immunofluorescence assay, and 24 showed some degree of fluorescence. Two species, Navicula minima and Synechococcus elongatus, exhibited a br...

  3. Models for asymmetric hybrid brane

    NASA Astrophysics Data System (ADS)

    Bazeia, D.; Marques, M. A.; Menezes, R.

    2015-10-01

    We deal with relativistic models described by a single real scalar field, searching for topological structures that behave asymmetrically, connecting minima with a distinct profile. We use such features to build a new braneworld scenario, in which the source scalar field contributes to generate asymmetric hybrid brane.

  4. ESTIMATION OF TOTAL DISSOLVED NITRATE LOAD IN NATURAL STREAM FLOWS USING AN IN-STREAM MONITOR

    EPA Science Inventory

    Estuaries respond rapidly to rain events and the nutrients carried by inflowing rivers such that discrete samples at weekly or monthly intervals are inadequate to catch the maxima and minima in nutrient variability. To acquire data with sufficient sampling frequency to realistica...

  5. Roles of starting geometries in quantum mechanics studies of cellobiose

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A relaxed HF/6 31G(d) energy surface was constructed for the fraction of phi,psi space that contains most geometries from crystals of molecules similar to cellobiose. Two regions around other minima were examined with unconstrained B3LYP/6 31+G(d) minimizations, as were two sub regions covered by th...

  6. THE IDENTIFICATION OF ALGAE WHICH INTERFERE WITH THE DETECTION OF GIARDIA AND CRYPTOSPORIDIUM AND A METHOD FOR ALLEVIATING THIS INTERFERENCE

    EPA Science Inventory

    Fifty-four algal species were tested for cross-reaction in the American Society for Testing and Materials Giardia/Cryptosporidium indirect immunofluorescence assay, and 24 showed some degree of fluorescence. Two species, Navicula minima and Synechococcus elongatus, exhibited a b...

  7. Lichtkurve und Periode des RR-Lyrae-Sterns HO Her und GSC 02589-00332, ein W-UMa-Veraenderlicher im Feld

    NASA Astrophysics Data System (ADS)

    Groebel, Rainer

    2015-01-01

    Based on data from the SWASP database and on recent observations 110 maxima and 78 minima timings of the little studied star HO Her could be derived. During the reduction of SWASP data, discrepancies between magnitudes given by series taken simultaneously through different cameras appeared, so that in the present case the reliability of the TAMFLUX correction must be questioned. From the variations in amplitude, a regular secondary cycle could not be derived, but the variations in phase revealed a 17.4 d Blazhko period. Since the discovery, the period remains essentially constant. The ephemeris is improved to HJD (max.) = 2456802.4954(9) + 0.47269795(16) x E One of the comparison stars, GSC 02589-00332 (16:56:31.98 +30:22:22.5) revealed itself as a variable of the W UMa type presenting 0.6 mag. deep total eclipses at primary and 0.5 mag. partial eclipse at secondary minimum. As a variable, it is already known as ROTSE1 J165631.98+302222.0. From SWASP data, 138 minima spreading over 4 years could be derived. The 2014 minima showed positive (O-C) values, indicating a progressive lengthening of the period. The minima timings could be best represented by the quadratic ephemeris HJD (max.) = 2456797.5267 + 0.41111232 x E + 2.625*10 -10 x E^2

  8. "In Situ" Observation of a Soap-Film Catenoid--A Simple Educational Physics Experiment

    ERIC Educational Resources Information Center

    Ito, Masato; Sato, Taku

    2010-01-01

    The solution to the Euler-Lagrange equation is an extremal functional. To understand that the functional is stationary at local extrema (maxima or minima), we propose a physics experiment that involves using a soap film to form a catenoid. A catenoid is a surface that is formed between two coaxial circular rings and is classified mathematically as…

  9. Software for Fermat's principle and lenses

    NASA Astrophysics Data System (ADS)

    Mihas, Pavlos

    2012-05-01

    Fermat's principle is considered as a unifying concept. It is usually presented erroneously as a 'least time principle'. In this paper we present some software that shows cases of maxima and minima and the application of Fermat's principle to the problem of focusing in lenses.

  10. Software for Fermat's Principle and Lenses

    ERIC Educational Resources Information Center

    Mihas, Pavlos

    2012-01-01

    Fermat's principle is considered as a unifying concept. It is usually presented erroneously as a "least time principle". In this paper we present some software that shows cases of maxima and minima and the application of Fermat's principle to the problem of focusing in lenses. (Contains 12 figures.)

  11. AFLP Analysis Provides Strategies for Improvement of Momordica Charantia L. (Bitter Gourd)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Monoecious bitter gourd (Momordica charantia L. var. minima and maxima Williams & Ng), a cucurbit of major economic importance, is widely cultivated in India, China, Africa, and South America. Although the morphology (i.e., growth habit and fruit shape, size, color and surface texture) of Indian bi...

  12. Genetic Diversity Analysis of Indian Bitter Gourd (Momordica Charantia L.) Allows for the Development of Crop Improvement Strategies

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bitter gourd (Momordica charantia L. var. minima and var. maxima) or bitter melon is one of the most economically important cucurbit species worldwide. Although India is the center of origin of bitter melon, and cultivars and landraces of this species are widely cultivated in Asia, a rigorous asses...

  13. Using Cayley's theorem to find the order of a power in a group

    NASA Astrophysics Data System (ADS)

    Dobbs, David E.

    2013-04-01

    It is shown how Cayley's theorem can be used to prove the formula for the order of a power of an element of finite order in a group. Reasoning with disjoint cycles leads to a proof that depends on elementary number theory in some new ways, leading naturally to some new connections involving least common multiples, greatest common divisors and minima.

  14. A measurement by BOOMERANG of multiple peaks in the angular power spectrum of the cosmic microwave background

    NASA Technical Reports Server (NTRS)

    Netterfield, C. B.; Ade, P. A. R.; Bock, J. J.; Bond, J. R.; Borrill, J.; Boscaleri, A.; Coble, K.; Contaldi, C. R.; Crill, B. P.; Bernardis, P. de; Farese, P.; Ganga, K.; Giacometti, M.; Hivon, E.; Hristov, V. V.; Iacoangeli, A.; Jaffe, A. H.; Jones, W. C.; Lange, A. E.; Martinis, L.; Masi, S.; Mason, P.; Mauskopf, P.; Melchiorri, A.; Montroy, T.

    2001-01-01

    This paper presents a measurement of the angular power spectrum of the Cosmic Microwave Background from l = 75 to l = 1025 (10' to 5 degrees) from a combined analysis of four 150 GHz channels in the BOOMERANG experiment. The spectrum contains multiple peaks and minima, as predicted by standard adiabatic-inflationary models in which the primordial plasma undergoes acoustic oscillations.

  15. Detachment of fullerene nC60 nanoparticles in saturated porous media under flow/stop-flow conditions: Column experiments and mechanistic explanations.

    PubMed

    Wang, Zhan; Wang, Dengjun; Li, Baoguo; Wang, Jizhong; Li, Tiantian; Zhang, Mengjia; Huang, Yuanfang; Shen, Chongyang

    2016-06-01

    This study was aimed at investigating the detachment of fullerene nC60 nanoparticles (NPs) in saturated sand porous media under transient and static conditions. The nC60 NPs were first attached at primary minima of Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profiles in electrolyte solutions with different ionic strengths (ISs). The columns were then eluted with deionized water to initiate nC60 NP detachment by decreasing solution IS. Finally, the flow of the columns was periodically interrupted to investigate nC60 NP detachment under static condition. Our results show that the detachment of nC60 NPs occurred under both transient and static conditions. The detachment under transient conditions was attributed to the fact that the attractions acting on the nC60 NPs at primary minima were weakened by nanoscale physical heterogeneities and overcome by hydrodynamic drags at lower ISs. However, a fraction of nC60 NPs remained at shallow primary minima in low flow regions, and detached via Brownian diffusion during flow interruptions. Greater detachment of nC60 NPs occurred under both transient and static conditions if the NPs were initially retained in electrolyte solutions with lower valent cations due to lower attractions between the NPs and collectors. Decrease in collector surface chemical heterogeneities and addition of dissolved organic matter also increased the extent of detachment by increasing electrostatic and steric repulsions, respectively. While particle attachment in and subsequent detachment from secondary minima occur in the same electrolyte solution, our results indicate that perturbation in solution chemistry is necessary to lower the primary minimum depths to initiate spontaneous detachment from the primary minima. These findings have important implications for predicting the fate and transport of nC60 NPs in subsurface environments during multiple rainfall events and accordingly for accurately assessing their environmental risks. PMID

  16. Computationally efficient characterization of potential energy surfaces based on fingerprint distances.

    PubMed

    Schaefer, Bastian; Goedecker, Stefan

    2016-07-21

    An analysis of the network defined by the potential energy minima of multi-atomic systems and their connectivity via reaction pathways that go through transition states allows us to understand important characteristics like thermodynamic, dynamic, and structural properties. Unfortunately computing the transition states and reaction pathways in addition to the significant energetically low-lying local minima is a computationally demanding task. We here introduce a computationally efficient method that is based on a combination of the minima hopping global optimization method and the insight that uphill barriers tend to increase with increasing structural distances of the educt and product states. This method allows us to replace the exact connectivity information and transition state energies with alternative and approximate concepts. Without adding any significant additional cost to the minima hopping global optimization approach, this method allows us to generate an approximate network of the minima, their connectivity, and a rough measure for the energy needed for their interconversion. This can be used to obtain a first qualitative idea on important physical and chemical properties by means of a disconnectivity graph analysis. Besides the physical insight obtained by such an analysis, the gained knowledge can be used to make a decision if it is worthwhile or not to invest computational resources for an exact computation of the transition states and the reaction pathways. Furthermore it is demonstrated that the here presented method can be used for finding physically reasonable interconversion pathways that are promising input pathways for methods like transition path sampling or discrete path sampling. PMID:27448868

  17. Degeneracy in model parameter estimation for multi-compartmental diffusion in neuronal tissue

    PubMed Central

    Jelescu, Ileana O.; Veraart, Jelle; Fieremans, Els; Novikov, Dmitry S.

    2016-01-01

    The ultimate promise of diffusion MRI (dMRI) models is specificity to neuronal microstructure, which may lead to distinct clinical biomarkers using noninvasive imaging. While multi-compartment models are a common approach to interpret water diffusion in the brain in vivo, the estimation of their parameters from the dMRI signal remains an unresolved problem. Practically, even when q space is highly oversampled, nonlinear fit outputs suffer from heavy bias and poor precision. So far, this has been alleviated by fixing some of the model parameters to a priori values, for improved precision at the expense of accuracy. Here we use a representative two-compartment model to show that fitting fails to determine the five model parameters from over 60 measurement points. For the first time, we identify the reasons for this poor performance. The first reason is the existence of two local minima in the parameter space for the objective function of the fitting procedure. These minima correspond to qualitatively different sets of parameters, yet they both lie within biophysically plausible ranges. We show that, at realistic signal-to-noise ratio values, choosing between the two minima based on the associated objective function values is essentially impossible. Second, there is an ensemble of very low objective function values around each of these minima in the form of a pipe. The existence of such a direction in parameter space, along which the objective function profile is very flat, explains the bias and large uncertainty in parameter estimation, and the spurious parameter correlations: in the presence of noise, the minimum can be randomly displaced by a very large amount along each pipe. Our results suggest that the biophysical interpretation of dMRI model parameters crucially depends on establishing which of the minima is closer to the biophysical reality and the size of the uncertainty associated with each parameter. PMID:26615981

  18. What are the consequences of ant-seed interactions on the abundance of two dry-fruited shrubs in a Mediterranean scrub?

    PubMed

    Arnan, Xavier; Rodrigo, A; Retana, J

    2011-12-01

    Strong interactions between dry-fruited shrubs and seed-harvesting ants are expected in early successional scrubs, where both groups have a major presence. We have analysed the implications of the seed characteristics of two dry-fruited shrub species (Coronilla minima and Dorycnium pentaphyllum) on seed predation and dispersal mediated by harvester ants and the consequences of these processes on spatio-temporal patterns of plant abundance in a heterogeneous environment. We found that large C. minima seeds were collected much more (39%) than small D. pentaphyllum seeds (2%). However, not all of the removed seeds of these plant species were consumed, and 12.8% of the seeds were lost along the trails, which increased dispersal distances compared with abiotic dispersal alone. Seed dropping occurred among all microhabitats of the two plant species, but especially in open microhabitats, which are the most suitable ones for plant establishment. The two plant species increased their presence in the study area during the study period: C. minima in open microhabitats and D. pentaphyllum in high vegetation. The large size of C. minima seeds probably limited the primary seed dispersal of this species, but may have allowed strong interaction with ants. Thus, seed dispersal by ants resulted in C. minima seeds reaching more suitable microhabitats by means of increasing dispersal distance and redistribution among microhabitats. In contrast, the smaller size of D. pentaphyllum seeds arguably allows abiotic seed dispersal over longer distances and colonization of all types of microhabitats, although it probably also limits their interaction with ants and, consequently, their redistribution in suitable microhabitats. We suggest that dyszoochory could contribute to the success of plant species with different seed characteristics in scrub habitats where seeds are abundantly collected by seed-harvesting ants. PMID:21643993

  19. Exchange and polarization effect in high-order harmonic imaging of molecular structures

    SciTech Connect

    Sukiasyan, Suren; Ivanov, Misha Yu.; Patchkovskii, Serguei; Smirnova, Olga; Brabec, Thomas

    2010-10-15

    We analyze the importance of exchange, polarization, and electron-electron correlation in high-order harmonic generation in molecules interacting with intense laser fields. We find that electron exchange can become particularly important for harmonic emission associated with intermediate excitations in the molecular ion. In particular, for orbitals associated with two-hole one-particle excitations, exchange effects can eliminate structure-related minima and maxima in the harmonic spectra. Laser-induced polarization of the neutral molecule may also have major effects on orbital structure-related minima and maxima in the harmonic spectra. Finally, we show how exchange terms in recombination can be viewed as a shakedownlike process induced by sudden electronic excitation in the ion.

  20. Elastic tracking versus neural network tracking for very high multiplicity problems

    SciTech Connect

    Harlander, M.; Gyulassy, M.

    1991-04-01

    A new Elastic Tracking (ET) algorithm is proposed for finding tracks in very high multiplicity and noisy environments. It is based on a dynamical reinterpretation and generalization of the Radon transform and is related to elastic net algorithms for geometrical optimization. ET performs an adaptive nonlinear fit to noisy data with a variable number of tracks. Its numerics is more efficient than that of the traditional Radon or Hough transform method because it avoids binning of phase space and the costly search for valid minima. Spurious local minima are avoided in ET by introducing a time-dependent effective potential. The method is shown to be very robust to noise and measurement error and extends tracking capabilities to much higher track densities than possible via local road finding or even the novel Denby-Peterson neural network tracking algorithms. 12 refs., 2 figs.

  1. The sound emission pattern and the acoustical role of the noseleaf in the echolocating bat, Carollia perspicillata.

    PubMed

    Hartley, D J; Suthers, R A

    1987-12-01

    Carollia perspicillata (Phyllostomidae) is a frugivorous bat that emits low-intensity, broadband, frequency-modulated echolocation pulses through nostrils surrounded by a noseleaf. The emission pattern of this bat is of interest because the ratio between the nostril spacing and the emitted wavelength varies during the pulse, causing complex interference patterns in the horizontal dimension. Sound pressures around the bat were measured using a movable microphone and were referenced to those at a stationary microphone positioned directly in front of the animal. Interference between the nostrils was confirmed by blocking one nostril, which eliminated sidelobes and minima in the emission pattern, and by comparison of real emission patterns with simple computer models. The positions of minima in the patterns indicate effective nostril spacings of over a half-wavelength. Displacement of the dorsal lancet of the noseleaf demonstrated that this structure directs sound in the vertical dimension. PMID:3429728

  2. Molecular dynamics study of the mechanical loss in amorphous pure and doped silica

    SciTech Connect

    Hamdan, Rashid; Trinastic, Jonathan P.; Cheng, H. P.

    2014-08-07

    Gravitational wave detectors and other precision measurement devices are limited by the thermal noise in the oxide coatings on the mirrors of such devices. We have investigated the mechanical loss in amorphous oxides by calculating the internal friction using classical, atomistic molecular dynamics simulations. We have implemented the trajectory bisection method and the non-local ridge method in the DL-POLY molecular dynamics simulation software to carry out those calculations. These methods have been used to locate the local potential energy minima that a system visits during a molecular dynamics trajectory and the transition state between any two consecutive minima. Using the numerically calculated barrier height distributions, barrier asymmetry distributions, relaxation times, and deformation potentials, we have calculated the internal friction of pure amorphous silica and silica mixed with other oxides. The results for silica compare well with experiment. Finally, we use the numerical calculations to comment on the validity of previously used theoretical assumptions.

  3. La tasa de decaimiento del ciclo solar como indicador de actividad

    NASA Astrophysics Data System (ADS)

    Buccino, A. P.; Mauas, P. J. D.

    The length of the solar cycle has been linked to solar forcing of global climate. Usually, cycle length is defined as the time difference between consecutive sunspot minima. However, sunspot minima is determined both by the diminishing number of spots of the old cycle and by the increasing number of spots of the new one. Therefore, the date of the minimum depends on the properties of both cycles, and is generally ill defined. Furthermore, changes in solar activity should precede climatic changes. On the other hand, it has been suggested that the length of the cycle is related to changes in the Sun's convective energy transport, through the decay rate of individual sunspots. Here, using the concept of extended activity cycle, we define an activity index based on the decay rate of the cycle, and study its correlation with other indexes.

  4. Methylene blue adsorption on a DMPA lipid langmuir monolayer.

    PubMed

    Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

    2010-07-12

    Adsorption of methylene blue (MB) onto a dimyristoylphosphatidic acid (DMPA) Langmuir air/water monolayer is studied by molecular dynamics (MD) simulations, UV reflection spectroscopy and surface potential measurements. The free-energy profile associated with MB transfer from water to the lipid monolayer shows two minima of -66 and -60 kJ mol(-1) for its solid and gas phase, respectively, corresponding to a spontaneous thermodynamic process. From the position of the free-energy minima, it is possible to predict the precise location of MB in the interior of the DMPA monolayer. Thus, MB is accommodated in the phosphoryl or carbonyl region of the DMPA Langmuir air/water interface, depending on the isomorphic state (solid or gas phase, respectively). Reorientation of MB, measured from the bulk solution to the interior of the lipid monolayer, passes from a random orientation in bulk solution to an orientation parallel to the surface of the lipid monolayer when MB is absorbed. PMID:20544777

  5. Phase retrapping in a φ Josephson junction: Onset of the butterfly effect

    NASA Astrophysics Data System (ADS)

    Menditto, R.; Sickinger, H.; Weides, M.; Kohlstedt, H.; Žonda, M.; Novotný, T.; Koelle, D.; Kleiner, R.; Goldobin, E.

    2016-05-01

    We investigate experimentally the retrapping of the phase in a φ Josephson junction upon return of the junction to the zero-voltage state. Since the Josephson energy profile U0(ψ ) in φ JJ is a 2 π periodic double-well potential with minima at ψ =±φ mod2 π , the question is at which of the two minima -φ or +φ the phase will be trapped upon return from a finite voltage state during quasistatic decrease of the bias current (tilt of the potential). By measuring the relative population of two peaks in escape histograms, we determine the probability of phase trapping in the ±φ wells for different temperatures. Our experimental results agree qualitatively with theoretical predictions. In particular, we observe an onset of the butterfly effect with an oscillating probability of trapping. Unexpectedly, this probability saturates at a value different from 50% at low temperatures.

  6. Effects of nuclear deformation in dinuclear systems: Application to the fission process

    SciTech Connect

    Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.; Ivanova, S. P. Scheid, W.

    2006-02-15

    The relative yields of fission fragments, the mean values of their total kinetic energy, and the variances of their distributions with respect to the total kinetic energy are described within the improved scission-point model. It is shown that, for fixed charge and mass numbers of fragments, the potential energy of the precision configuration as a function of the deformation parameters of the fragments has several minima. The scission at these minima leads to a relative enhancement of the yields of the fragments that have the corresponding values of the total kinetic energy and to the appearance of a fine structure in the mass-energy distribution, this structure being different from that induced by the even-odd effect.

  7. The Nature of Intermolecular Interactions Between Aromatic Amino Acid Residues

    SciTech Connect

    Gervasio, Francesco; Chelli, Riccardo; Procacci, Piero; Schettino, Vincenzo

    2002-05-01

    The nature of intermolecular interactions between aromatic amino acid residues has been investigated by a combination of molecular dynamics and ab initio methods. The potential energy surface of various interacting pairs, including tryptophan, phenilalanine, and tyrosine, was scanned for determining all the relevant local minima by a combined molecular dynamics and conjugate gradient methodology with the AMBER force field. For each of these minima, single-point correlated ab initio calculations of the binding energy were performed. The agreement between empirical force field and ab initio binding energies of the minimum energy structures is excellent. Aromatic-aromatic interactions can be rationalized on the basis of electrostatic and van der Waals interactions, whereas charge transfer or polarization phenomena are small for all intermolecular complexes and, particularly, for stacked structures.

  8. Diatomics-in-Molecules Modeling of Many-Body Effects on the Structure and Thermodynamics of Mercury Clusters.

    PubMed

    Calvo, F; Pahl, E; Schwerdtfeger, P; Spiegelman, F

    2012-02-14

    The stable structures and melting behavior of Hgn clusters, 2 ≤ n < 60, have been theoretically investigated using an updated diatomics-in-molecules (DIM) model initially proposed by Kitamura [Chem. Phys. Lett.2006, 425, 2056]. Global optimization and sampling at finite temperature are achieved on the basis of hierarchical and nested Markov chain Monte Carlo methods, respectively. The DIM model predicts highly symmetric icosahedral global minima that are generally similar to the standard van der Waals atomic clusters, without any indication of distorted or low-coordinated geometries, but also at variance with the global minima found with the pairwise Hg2 potential. The combined influences of surface and many-body effects due to s-p mixing are considerable on the melting point: although the model predicts a bulk melting temperature in fair agreement with experimental results, it is found to decrease with increasing cluster size. PMID:26596612

  9. Antarctic measurements of ozone by SAGE II in the spring of 1985, 1986, and 1987

    NASA Astrophysics Data System (ADS)

    McCormick, M. P.; Larsen, J. C.

    1988-08-01

    This paper presents a three-year (1985, 1986, and 1987) comparison of ozone profiles within the southern polar vortex for September and October, using data obtained by the Stratospheric Aerosol and Gas Experiment II. It was found that, by the first half of October 1986, daily minima in total ozone showed a moderate recovery of 5-7 percent relative to 1985, whereas in 1987, a significant drop of 15 percent from the 1985 minima was observed. The interannual variability of total ozone, temperature, and temperature area or vortex size were found to display a quasi-biennial oscillation (QBO) signal similar to that established by Garcia and Solomon (1987) for Antarctica. Since the 1985 and 1987 years displayed the same QBO phase (westerly) and the 1987 depletion was greater than that of 1985, it is concluded that the long-term secular ozone trend continues to be downward.

  10. Coronene molecules in helium clusters: Quantum and classical studies of energies and configurations

    SciTech Connect

    Rodríguez-Cantano, Rocío; Pérez de Tudela, Ricardo; Bartolomei, Massimiliano; Hernández, Marta I.; Campos-Martínez, José; González-Lezana, Tomás Villarreal, Pablo; Hernández-Rojas, Javier; Bretón, José

    2015-12-14

    Coronene-doped helium clusters have been studied by means of classical and quantum mechanical (QM) methods using a recently developed He–C{sub 24}H{sub 12} global potential based on the use of optimized atom-bond improved Lennard-Jones functions. Equilibrium energies and geometries at global and local minima for systems with up to 69 He atoms were calculated by means of an evolutive algorithm and a basin-hopping approach and compared with results from path integral Monte Carlo (PIMC) calculations at 2 K. A detailed analysis performed for the smallest sizes shows that the precise localization of the He atoms forming the first solvation layer over the molecular substrate is affected by differences between relative potential minima. The comparison of the PIMC results with the predictions from the classical approaches and with diffusion Monte Carlo results allows to examine the importance of both the QM and thermal effects.

  11. Solar activity phase diagram and forecast of the coming 23rd cycle.

    NASA Astrophysics Data System (ADS)

    Pankratov, A. K.; Narmanskij, V. Ya.; Vladimirskij, B. M.

    1998-10-01

    The phase diagram method is used for investigation of relations between planetary dynamics and solar activity variations. It was found that the calculated moments of solar activity maxima/minima are disposed regularly in the coordinates of the difference of heliocentric longitudes of Uranus-Neptune versus the difference of heliocentric longitudes of Saturn-Neptune. There are separate zones containing maxima (minima) of only the northern (or southern) polarity of solar mean magnetic field. There is also a region where only maxima of small amplitudes are concentrated (Rz < 100). The regularities obtained are used for prognosis of the 23rd cycle. The minimum of activity must be observed in 1999±2. The maximum is forecast in 2006±2. The amplitude Rz can be as small as 60±20. Probably there will be no change of the polarity of the mean solar magnetic field.

  12. Ions in solution: Density corrected density functional theory (DC-DFT)

    SciTech Connect

    Kim, Min-Cheol; Sim, Eunji; Burke, Kieron

    2014-05-14

    Standard density functional approximations often give questionable results for odd-electron radical complexes, with the error typically attributed to self-interaction. In density corrected density functional theory (DC-DFT), certain classes of density functional theory calculations are significantly improved by using densities more accurate than the self-consistent densities. We discuss how to identify such cases, and how DC-DFT applies more generally. To illustrate, we calculate potential energy surfaces of HO·Cl{sup −} and HO·H{sub 2}O complexes using various common approximate functionals, with and without this density correction. Commonly used approximations yield wrongly shaped surfaces and/or incorrect minima when calculated self consistently, while yielding almost identical shapes and minima when density corrected. This improvement is retained even in the presence of implicit solvent.

  13. Stability of the complex generalized Hartree-Fock equations

    SciTech Connect

    Goings, Joshua J.; Ding, Feizhi; Li, Xiaosong; Frisch, Michael J.

    2015-04-21

    For molecules with complex and competing magnetic interactions, it is often the case that the lowest energy Hartree-Fock solution may only be obtained by removing the spin and time-reversal symmetry constraints of the exact non-relativistic Hamiltonian. To do so results in the complex generalized Hartree-Fock (GHF) method. However, with the loss of variational constraints comes the greater possibility of converging to higher energy minima. Here, we report the implementation of stability test of the complex GHF equations, along with an orbital update scheme should an instability be found. We apply the methodology to finding the local minima of several spin-frustrated hydrogen rings, as well as the non-collinear molecular magnet Cr{sub 3}, illustrating the utility of the broken symmetry GHF method and some of its lesser-known nuances.

  14. Low-energy electron elastic scattering cross sections for excited Au and Pt atoms

    NASA Astrophysics Data System (ADS)

    Felfli, Zineb; Eure, Amanda R.; Msezane, Alfred Z.; Sokolovski, Dmitri

    2010-05-01

    Electron elastic total cross sections (TCSs) and differential cross sections (DCSs) in both impact energy and scattering angle for the excited Au and Pt atoms are calculated in the electron impact energy range 0 ⩽ E ⩽ 4.0 eV. The cross sections are found to be characterized by very sharp long-lived resonances whose positions are identified with the binding energies of the excited anions formed during the collisions. The recent novel Regge-pole methodology wherein is embedded through the Mulholland formula the electron-electron correlations is used together with a Thomas-Fermi type potential incorporating the crucial core-polarization interaction for the calculations of the TCSs. The DCSs are evaluated using a partial wave expansion. The Ramsauer-Townsend minima, the shape resonances and the binding energies of the excited Au - and Pt - anions are extracted from the cross sections, while the critical minima are determined from the DCSs.

  15. Application of neural networks to range-Doppler imaging

    NASA Astrophysics Data System (ADS)

    Wu, Xiaoqing; Zhu, Zhaoda

    1991-10-01

    The use of neural networks are investigated for 2-D range Doppler microwave imaging. The range resolution of the microwave image is obtained by transmitting a wideband signal and the cross-range resolution is achieved by the Doppler frequency gradient in the same range bin. Hopfield neural networks are used to estimate the Doppler spectrum to enhance the cross- range resolution and reduce the processing time. There is a large number of neurons needed for the high cross-range resolution. In order to cut down the number of neurons, the reflectivities are replaced with their minimum norm estimates. The original Hopfield networks converge often to a local minina instead of the global minima. Simulated annealing is applied to control the gain of Hopfield networks to yield better convergence to the global minima. Results of imaging a model airplane from real microwave data are presented.

  16. An exploration of the ozone dimer potential energy surface

    SciTech Connect

    Azofra, Luis Miguel; Alkorta, Ibon; Scheiner, Steve

    2014-06-28

    The (O{sub 3}){sub 2} dimer potential energy surface is thoroughly explored at the ab initio CCSD(T) computational level. Five minima are characterized with binding energies between 0.35 and 2.24 kcal/mol. The most stable may be characterized as slipped parallel, with the two O{sub 3} monomers situated in parallel planes. Partitioning of the interaction energy points to dispersion and exchange as the prime contributors to the stability, with varying contributions from electrostatic energy, which is repulsive in one case. Atoms in Molecules analysis of the wavefunction presents specific O⋯O bonding interactions, whose number is related to the overall stability of each dimer. All internal vibrational frequencies are shifted to the red by dimerization, particularly the antisymmetric stretching mode whose shift is as high as 111 cm{sup −1}. In addition to the five minima, 11 higher-order stationary points are identified.

  17. RePAMO: Recursive Perturbation Approach for Multimodal Optimization

    NASA Astrophysics Data System (ADS)

    Dasgupta, Bhaskar; Divya, Kotha; Mehta, Vivek Kumar; Deb, Kalyanmoy

    2013-09-01

    In this article, a strategy is presented to exploit classical algorithms for multimodal optimization problems, which recursively applies any suitable local optimization method, in the present case Nelder and Mead's simplex search method, in the search domain. The proposed method follows a systematic way to restart the algorithm. The idea of climbing the hills and sliding down to the neighbouring valleys is utilized. The implementation of the algorithm finds local minima as well as maxima. The concept of perturbing the minimum/maximum in several directions and restarting the algorithm for maxima/minima is introduced. The method performs favourably in comparison to other global optimization methods. The results of this algorithm, named RePAMO, are compared with the GA-clearing and ASMAGO techniques in terms of the number of function evaluations. Based on the results, it has been found that the RePAMO outperforms GA clearing and ASMAGO by a significant margin.

  18. Design of a Kagome lattice from soft anisotropic particles.

    PubMed

    Fejer, Szilard N; Wales, David J

    2015-09-01

    We present a simple model of triblock Janus particles based on discoidal building blocks, which can form energetically stabilized Kagome structures. We find 'magic number' global minima in small clusters whenever particle numbers are compatible with a perfect Kagome structure, without constraining the accessible three-dimensional configuration space. The preference for planar structures with two bonds per patch among all other possible minima on the landscape is enhanced when sedimentation forces are included. For the building blocks in question, structures containing three bonds per patch become progressively higher in energy compared to Kagome structures as sedimentation forces increase. Rearrangements between competing structures, as well as ring formation mechanisms are characterised and found to be highly cooperative. PMID:26212130

  19. The analysis of temporal variations in regional models of the Sargasso Sea from GEOS-3 altimetry

    NASA Technical Reports Server (NTRS)

    Mather, R. S.; Coleman, R.; Hirsch, B.

    1978-01-01

    The dense coverage of short pulse mode GEOS-3 altimeter data in the western North Atlantic provides a basis for studying time variations in the sea surface heights in the Sargasso Sea. Two techniques are utilized: the method of regional models, and the analysis of overlapping passes. An 88 percent correlation is obtained between the location of cyclonic eddies obtained from infrared imagery and sea surface height minima in the altimeter models. This figure drops to 59 percent in the case of correlations with maxima and minima of surface temperature fields. The analysis of overlapping passes provides a better picture of instantaneous sea state through wavelengths greater than 30 km. The variability of the Sargasso Sea through wavelengths between 150 km and 5000 km is estimated at + or - 28 cm. This value is in reasonable agreement with oceanographic estimates and is compatible with the eddy kinetic energy of a wind driven circulation.

  20. Multiple nonspherical structures from the extrema of Szekeres scalars

    NASA Astrophysics Data System (ADS)

    Sussman, Roberto A.; Delgado Gaspar, I.

    2015-10-01

    We examine the spatial extrema (local maxima, minima and saddle points) of the covariant scalars (density, Hubble expansion, spatial curvature and eigenvalues of the shear and electric Weyl tensors) of the quasispherical Szekeres dust models. Sufficient conditions are obtained for the existence of distributions of multiple extrema in spatial comoving locations that can be prescribed through initial conditions. These distributions evolve without shell crossing singularities at least for ever expanding models (with or without cosmological constant) in the full evolution range where the models are valid. By considering the local maxima and minima of the density, our results allow for setting up elaborated networks of "pancake" shaped evolving cold dark matter overdensities and density voids whose spatial distribution and amplitudes can be controlled from initial data compatible with standard early Universe initial conditions. We believe that these results have an enormous range of potential application by providing a fully relativistic nonperturbative coarse grained modeling of cosmic structure at all scales.

  1. Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates

    USGS Publications Warehouse

    Barron, John A.; Bukry, David

    2007-01-01

    Cores BAM80 E-17 (27.9° N) and NH01-26 (24.3° N) contain longer-duration cycles of diatoms and silicoflagellates. The early part of Medieval Climate Anomaly (∼ A.D. 900 to 1200) is characterized by two periods of reduced productivity (warmer SST) with an intervening high productivity (cool) interval centered at ∼ A.D. 1050. Reduced productivity and higher SST also characterize the record of the last ∼ 100 to 200 yr in these cores. Solar variability appears to be driving productivity cycles, as intervals of increased radiocarbon production (sunspot minima) correlate with intervals of enhanced productivity. It is proposed that increased winter cooling of the atmosphere above southwest U.S. during sunspot minima causes intensification of the northwest winds that blow down the Gulf during the late fall to early spring, leading to intensified overturn of surface waters and enhanced productivity.

  2. Alien Genetic Algorithm for Exploration of Search Space

    NASA Astrophysics Data System (ADS)

    Patel, Narendra; Padhiyar, Nitin

    2010-10-01

    Genetic Algorithm (GA) is a widely accepted population based stochastic optimization technique used for single and multi objective optimization problems. Various versions of modifications in GA have been proposed in last three decades mainly addressing two issues, namely increasing convergence rate and increasing probability of global minima. While both these. While addressing the first issue, GA tends to converge to a local optima and addressing the second issue corresponds the large computational efforts. Thus, to reduce the contradictory effects of these two aspects, we propose a modification in GA by adding an alien member in the population at every generation. Addition of an Alien member in the current population at every generation increases the probability of obtaining global minima at the same time maintaining higher convergence rate. With two test cases, we have demonstrated the efficacy of the proposed GA by comparing with the conventional GA.

  3. Limits of Predictability of Solar Activity

    NASA Astrophysics Data System (ADS)

    Kremliovsky, M. N.

    1995-07-01

    The study of a nonlinear chaotic map of 11-year cycle maxima evolution recently derived from observations is presented with the purpose of predicting the features of the long-term variability of solar activity. It is stressed that dynamical forecast is limited by the Lyapunov time and a statistical approach can be justified due to the ergodic properties of the chaotic evolution. The Gleissberg variation is described as a chaotic walk and its distribution over length is shown to be broad. The global minima are identified as laminar slots of temporal intermittency and their typical distribution over length is also given. We note that a long sunspot cycle can be used as a precursor of the global minimum and a close sequence of global minima (once in approximately 1500 2000 years) may be responsible for the climatic changes (Little Ice Ages).

  4. On metastable regimes in stochastic Lamb system

    NASA Astrophysics Data System (ADS)

    Freidlin, M. I.; Komech, A. I.

    2006-04-01

    We consider the long time behavior of the coupled Hamilton system of one-dimensional string and nonlinear oscillator, in contact with a heat bath modeled by the white noise. For any temperature the system converges to a statistical equilibrium described by the Boltzmann equilibrium measure. The convergence is caused by radiation provided by the nonlinear coupling. If the oscillator potential has more than one well and the temperature is small, the relaxation time is large, and the system goes through a sequence of metastable states located near local minima of the potential. When both, the temperature and the radiation rate are small, the metastable states are distributions among the minima of the potential.

  5. Chiral effects on helicity studied via the energy landscape of short (d, l)-alanine peptides

    NASA Astrophysics Data System (ADS)

    Neelamraju, Sridhar; Oakley, Mark T.; Johnston, Roy L.

    2015-10-01

    The homochirality of natural amino acids facilitates the formation of regular secondary structures such as α-helices and β-sheets. Here, we study the relationship between chirality and backbone structure for the example of hexa-alanine. The most stable stereoisomers are identified through global optimisation. Further, the energy landscape, a database of connected low-energy local minima and transition points, is constructed for various neutral and zwitterionic stereoisomers of hexa-alanine. Three order parameters for partial helicity are applied and metric disconnectivity graphs are presented with partial helicity as a metric. We also apply the Zimm-Bragg model to derive average partial helicities for Ace-(l-Ala)6-NHMe, Ace-(d-Ala-l-Ala)3-NHMe, and Ace-(l-Ala)3-(d-Ala)3-NHMe from the database of local minima and compare with previous studies.

  6. Coronene molecules in helium clusters: Quantum and classical studies of energies and configurations.

    PubMed

    Rodríguez-Cantano, Rocío; Pérez de Tudela, Ricardo; Bartolomei, Massimiliano; Hernández, Marta I; Campos-Martínez, José; González-Lezana, Tomás; Villarreal, Pablo; Hernández-Rojas, Javier; Bretón, José

    2015-12-14

    Coronene-doped helium clusters have been studied by means of classical and quantum mechanical (QM) methods using a recently developed He-C24H12 global potential based on the use of optimized atom-bond improved Lennard-Jones functions. Equilibrium energies and geometries at global and local minima for systems with up to 69 He atoms were calculated by means of an evolutive algorithm and a basin-hopping approach and compared with results from path integral Monte Carlo (PIMC) calculations at 2 K. A detailed analysis performed for the smallest sizes shows that the precise localization of the He atoms forming the first solvation layer over the molecular substrate is affected by differences between relative potential minima. The comparison of the PIMC results with the predictions from the classical approaches and with diffusion Monte Carlo results allows to examine the importance of both the QM and thermal effects. PMID:26671374

  7. An exploration of the ozone dimer potential energy surface

    NASA Astrophysics Data System (ADS)

    Azofra, Luis Miguel; Alkorta, Ibon; Scheiner, Steve

    2014-06-01

    The (O3)2 dimer potential energy surface is thoroughly explored at the ab initio CCSD(T) computational level. Five minima are characterized with binding energies between 0.35 and 2.24 kcal/mol. The most stable may be characterized as slipped parallel, with the two O3 monomers situated in parallel planes. Partitioning of the interaction energy points to dispersion and exchange as the prime contributors to the stability, with varying contributions from electrostatic energy, which is repulsive in one case. Atoms in Molecules analysis of the wavefunction presents specific O⋯O bonding interactions, whose number is related to the overall stability of each dimer. All internal vibrational frequencies are shifted to the red by dimerization, particularly the antisymmetric stretching mode whose shift is as high as 111 cm-1. In addition to the five minima, 11 higher-order stationary points are identified.

  8. Impact of Mg content on native point defects in Mg{sub x}Zn{sub 1−x}O (0 ≤ x ≤ 0.56)

    SciTech Connect

    Perkins, J.; Foster, G. M.; Myer, M.; Mehra, S.; Chauveau, J. M.; Hierro, A.; Windl, W.; Brillson, L. J.

    2015-06-01

    We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar Mg{sub x}Zn{sub 1−x}O alloys over a wide (0 ≤ x ≤ 0.56) range. Within this wide range, both defect types exhibit strong Mg content-dependent surface segregation and pronounced bulk density minima corresponding to unit cell volume minima, which can inhibit defect formation due to electrostatic repulsion. Mg in ZnO significantly reduces native defect densities and their non-polar surface segregation, both major factors in carrier transport and doping of these oxide semiconductors.

  9. BVR Photometric Analysis of GSC 4277-0586 and GSC 3152-1202

    NASA Astrophysics Data System (ADS)

    Bulut, İ.; Bulut, A.

    2015-03-01

    A detailed light curve analysis of the newly discovered eccentric orbit eclipsing binaries GSC 277-0586 and GSC 3152-1202 are presented for the fist time. For both systems, the B, V and R light curves were secured and also new minima times have been derived. The analysis was made using the Wilson-Devinney program. The absolute dimensions were calculated using mass-luminosity relation for main sequence stars. The O-C diagram of GSC 3152-1202 was also analyzed using all reliable times of minima and the elements of apsidal motion were computed. The apsidal motion period has been found to be 36.6±9.8 years.

  10. Proposal of a checking parameter in the simulated annealing method applied to the spin glass model

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Chiaki

    2016-02-01

    We propose a checking parameter utilizing the breaking of the Jarzynski equality in the simulated annealing method using the Monte Carlo method. This parameter is based on the Jarzynski equality. By using this parameter, to detect that the system is in global minima of the free energy under gradual temperature reduction is possible. Thus, by using this parameter, one is able to investigate the efficiency of annealing schedules. We apply this parameter to the ± J Ising spin glass model. The application to the Gaussian Ising spin glass model is also mentioned. We discuss that the breaking of the Jarzynski equality is induced by the system being trapped in local minima of the free energy. By performing Monte Carlo simulations of the ± J Ising spin glass model and a glassy spin model proposed by Newman and Moore, we show the efficiency of the use of this parameter.

  11. Competitive hopfield network combined with estimation of distribution for maximum diversity problems.

    PubMed

    Wang, Jiahai; Zhou, Yalan; Yin, Jian; Zhang, Yunong

    2009-08-01

    This paper presents a discrete competitive Hopfield neural network (HNN) (DCHNN) based on the estimation of distribution algorithm (EDA) for the maximum diversity problem. In order to overcome the local minimum problem of DCHNN, the idea of EDA is combined with DCHNN. Once the network is trapped in local minima, the perturbation based on EDA can generate a new starting point for DCHNN for further search. It is expected that the further search is guided to a promising area by the probability model. Thus, the proposed algorithm can escape from local minima and further search better results. The proposed algorithm is tested on 120 benchmark problems with the size ranging from 100 to 5000. Simulation results show that the proposed algorithm is better than the other improved DCHNN such as multistart DCHNN and DCHNN with random flips and is better than or competitive with metaheuristic algorithms such as tabu-search-based algorithms and greedy randomized adaptive search procedure algorithms. PMID:19336334

  12. A Theoretical Study of NO2 Complexes with Aluminium and Gallium Based on Topological Analysis of Electron Density and Electron Localization Function

    SciTech Connect

    Panek, Jaroslaw; Latajaka, Zdzislaw

    2000-12-26

    Results of DFT and MP4 calculations on AlNO2 and GaNO2 molecules are presented. One Cs and two C2v structures (two minima and one TS) are found and their energies and vibrational frequencies are reported and discussed. The minima are close in energy and lie ca. 70 kcal mol-1 below reactants (M+NO2). More insight is obtained via topological analysis of electron density and electron localization function (ELF). It is shown that the molecules are bound mainly via electrostatic interactions, and there is a significant charge transfer from metal atom to the NO2 moiety. Detailed analysis of the ELF shows that the loss of stability of gallium complexes with respect to aluminium structures is best explained by (antibonding) influence of gallium semi-cored electrons.

  13. An exploration of the ozone dimer potential energy surface.

    PubMed

    Azofra, Luis Miguel; Alkorta, Ibon; Scheiner, Steve

    2014-06-28

    The (O3)2 dimer potential energy surface is thoroughly explored at the ab initio CCSD(T) computational level. Five minima are characterized with binding energies between 0.35 and 2.24 kcal/mol. The most stable may be characterized as slipped parallel, with the two O3 monomers situated in parallel planes. Partitioning of the interaction energy points to dispersion and exchange as the prime contributors to the stability, with varying contributions from electrostatic energy, which is repulsive in one case. Atoms in Molecules analysis of the wavefunction presents specific O⋯O bonding interactions, whose number is related to the overall stability of each dimer. All internal vibrational frequencies are shifted to the red by dimerization, particularly the antisymmetric stretching mode whose shift is as high as 111 cm(-1). In addition to the five minima, 11 higher-order stationary points are identified. PMID:24985642

  14. Spots and active longitudes on the star V815 Her

    NASA Astrophysics Data System (ADS)

    Savanov, I. S.

    2009-10-01

    An analysis of photometric observations for the starHD166181 (V815Her) is presented. B and V light curves were used to reconstruct temperature inhomogeneities on the stellar surface. The spots on the surface of V815 Her are concentrated at two preferred longitudes separated by 0.5 in phase (180° in longitude). The positions of more and less active regions quasi-periodically “flip-flop,” on time scales of about 600, 950, and 1250 days. The times of active-longitude switches coincide with the maxima and minima of the light curve and the amplitude of the brightness variations, as well as with the minima and maxima of the star’s spottedness.

  15. Rotation Period Determination for 254 Augusta, 465 Alekto 477 Italia, 515 Athalia, and 1061 Paeonia

    NASA Astrophysics Data System (ADS)

    Pilcher, Frederick

    2015-04-01

    Synodic rotation periods and amplitudes have been found for 254 Augusta 5.8949 ± 0.0001 hours, 0.75 to 0.58 magnitudes; 465 Alekto, 10.936 ± 0.001 hours, 0.14 ± 0.02 magnitudes with 3 maxima and minima per cycle; 477 Italia 19.413 ± 0.001 hours, 0.20 to 0.15 magnitudes with 3 very unequal maxima and minima per cycle; 515 Athalia 10.636 ± 0.001 hours, 0.21 ± 0.02 magnitudes; and 1061 Paeonia, 7.9971 ± 0.0001 hours, 1.00 ± 0.05 magnitudes.

  16. Autonomous Mobile Robot Navigation Using Harmonic Potential Field

    NASA Astrophysics Data System (ADS)

    Panati, Subbash; Baasandorj, Bayanjargal; Chong, Kil To

    2015-05-01

    Mobile robot navigation has been an area of robotics which has gained massive attention among the researchers of robotics community. Path planning and obstacle avoidance are the key aspects of mobile robot navigation. This paper presents harmonic potential field based navigation algorithm for mobile robots. Harmonic potential field method overcomes the issue of local minima which was a major bottleneck in the case of artificial potential field method. The harmonic potential field is calculated using harmonic functions and Dirichlet boundary conditions are used for the obstacles, goal and initial position. The simulation results shows that the proposed method is able to overcome the local minima issue and navigate successfully from initial position to the goal without colliding into obstacles in static environment.

  17. A stochastically forced time delay solar dynamo model: Self-consistent recovery from a maunder-like grand minimum necessitates a mean-field alpha effect

    SciTech Connect

    Hazra, Soumitra; Nandy, Dibyendu; Passos, Dário E-mail: dariopassos@ist.utl.pt

    2014-07-01

    Fluctuations in the Sun's magnetic activity, including episodes of grand minima such as the Maunder minimum have important consequences for space and planetary environments. However, the underlying dynamics of such extreme fluctuations remain ill-understood. Here, we use a novel mathematical model based on stochastically forced, non-linear delay differential equations to study solar cycle fluctuations in which time delays capture the physics of magnetic flux transport between spatially segregated dynamo source regions in the solar interior. Using this model, we explicitly demonstrate that the Babcock-Leighton poloidal field source based on dispersal of tilted bipolar sunspot flux, alone, cannot recover the sunspot cycle from a grand minimum. We find that an additional poloidal field source effective on weak fields—e.g., the mean-field α effect driven by helical turbulence—is necessary for self-consistent recovery of the sunspot cycle from grand minima episodes.

  18. On the unlikeliness of multi-field inflation: bounded random potentials and our vacuum

    SciTech Connect

    Battefeld, Diana; Battefeld, Thorsten; Schulz, Sebastian E-mail: tbattefe@astro.physik.uni-goettingen.de

    2012-06-01

    Based on random matrix theory, we compute the likelihood of saddles and minima in a class of random potentials that are softly bounded from above and below, as required for the validity of low energy effective theories. Imposing this bound leads to a random mass matrix with non-zero mean of its entries. If the dimensionality of field-space is large, inflation is rare, taking place near a saddle point (if at all), since saddles are more likely than minima or maxima for common values of the potential. Due to the boundedness of the potential, the latter become more ubiquitous for rare low/large values respectively. Based on the observation of a positive cosmological constant, we conclude that the dimensionality of field-space after (and most likely during) inflation has to be low if no anthropic arguments are invoked, since the alternative, encountering a metastable deSitter vacuum by chance, is extremely unlikely.

  19. Tension in active shapes.

    PubMed

    Papari, Giuseppe

    2014-01-01

    The concept of tension is introduced in the framework of active contours with prior shape information, and it is used to improve image segmentation. In particular, two properties of this new quantity are shown: 1) high values of the tension correspond to undesired equilibrium points of the cost function under minimization and 2) tension decreases if a curve is split into two or more parts. Based on these ideas, a tree is generated whose nodes are different local minima of the cost function. Deeper nodes in the tree are expected to correspond to lower values of the cost function. In this way, the search for the global optimum is reduced to visiting and pruning a binary tree. The proposed method has been applied to the problem of fish segmentation from low quality underwater images. Qualitative and quantitative comparison with existing algorithms based on the Euler–Lagrange diffusion equations shows the superiority of the proposed approach in avoiding undesired local minima. PMID:24235305

  20. Energy spectrum of the recurrent cosmic rays variation during the solar minimum 23/24

    NASA Astrophysics Data System (ADS)

    Gil, Agnieszka; Alania, Michael

    2016-07-01

    We study temporal changes of the power-law energy/ rigidity spectrum of the first three harmonics of the recurrent variation of the galactic cosmic rays (GCR) intensity during the unusual solar minimum 23/24 and compare with four previous minima. We show that the energy spectrum of the amplitudes of the recurrent variation is soft in the minimum 23/24. Moreover, while the energy spectrum of the amplitudes of the first harmonic of the recurrent variation of the GCR intensity practically behaves as during earlier four minima, the energy spectrum of the amplitudes of the second and the third harmonics demonstrate a valuable softening. We attribute this phenomenon to the decrease of an extension of heliosphere caused by the drop of the solar wind dynamic pressure during the solar minimum 23/24.

  1. Electronic structure of small silicon clusters

    SciTech Connect

    Wales, D.J.

    1994-03-01

    Predictions of Stone`s tensor-surface-harmonic theory [Mol. Phys. 41, 1339 (1980)] for bonding in small silicon clusters are tested by {ital ab} {ital initio} calculations. Stable geometries, along with the energies and symmetries of the occupied molecular orbitals, may all be rationalized within the model. For example, local energy minima for Si{sub {ital n}}{sup 2{minus}} clusters are found which are isostructural to the borane and carborane clusters B{sub {ital n}}H{sub {ital n}}{sup 2{minus}} and C{sub 2}B{sub {ital n}{minus}2}H{sub {ital n}}. In particular, both Si{sub 12}{sup 2{minus}} and Si{sub 13}{sup 2+} exhibit icosahedral geometries which are true minima.

  2. Dynamical evolution of domain walls in an expanding universe

    NASA Technical Reports Server (NTRS)

    Press, William H.; Ryden, Barbara S.; Spergel, David N.

    1989-01-01

    Whenever the potential of a scalar field has two or more separated, degenerate minima, domain walls form as the universe cools. The evolution of the resulting network of domain walls is calculated for the case of two potential minima in two and three dimensions, including wall annihilation, crossing, and reconnection effects. The nature of the evolution is found to be largely independent of the rate at which the universe expands. Wall annihilation and reconnection occur almost as fast as causality allows, so that the horizon volume is 'swept clean' and contains, at any time, only about one, fairly smooth, wall. Quantitative statistics are given. The total area of wall per volume decreases as the first power of time. The relative slowness of the decrease and the smoothness of the wall on the horizon scale make it impossible for walls to both generate large-scale structure and be consistent with quadrupole microwave background anisotropy limits.

  3. Resonance Line Pressure as Acceleration Mechanism of Atoms

    NASA Astrophysics Data System (ADS)

    Shestakova, L. I.

    2012-12-01

    Calculations of the solar radiation pressure on atoms and first ions are presented. It is shown that for some of them the light pressure exceeds the action of gravity. Comparison of the results with the values of the ionization potentials shows the coincidence of the maxima of the radiation pressure on neutral atoms and first ions with the minima of the first ionization potential (FIP) and second ionization potential (SIP) consequently. Minima of SIP indicate a number of ions, similar BeII, MgII, CaII and their neighboring elements of large numbers. Thus, a possible mechanism accelerating pickup ions and energetic neutral atoms (ENA) of solar wind, originating from inner sources (zodiacal dust and sungrazing comets) can be radiation pressure in resonance lines.

  4. A Novel Hybrid Statistical Particle Swarm Optimization for Multimodal Functions and Frequency Control of Hybrid Wind-Solar System

    NASA Astrophysics Data System (ADS)

    Verma, Harish Kumar; Jain, Cheshta

    2015-07-01

    In this article, a hybrid algorithm of particle swarm optimization (PSO) with statistical parameter (HSPSO) is proposed. Basic PSO for shifted multimodal problems have low searching precision due to falling into a number of local minima. The proposed approach uses statistical characteristics to update the velocity of the particle to avoid local minima and help particles to search global optimum with improved convergence. The performance of the newly developed algorithm is verified using various standard multimodal, multivariable, shifted hybrid composition benchmark problems. Further, the comparative analysis of HSPSO with variants of PSO is tested to control frequency of hybrid renewable energy system which comprises solar system, wind system, diesel generator, aqua electrolyzer and ultra capacitor. A significant improvement in convergence characteristic of HSPSO algorithm over other variants of PSO is observed in solving benchmark optimization and renewable hybrid system problems.

  5. 500,000-year stable carbon isotopic record from Devils Hole, Nevada

    USGS Publications Warehouse

    Coplen, T.B.; Winograd, I.J.; Landwehr, J.M.; Riggs, A.C.

    1994-01-01

    The record of carbon-13 (??13C) variations in DH-11 vein calcite core from Devils Hole, Nevada, shows four prominent minima near glacial terminations (glacial-interglacial transitions) V to II. The ??13C time series is inversely correlated with the DH-11 oxygen isotope ratio time series and leads it by as much as 7000 years. The ??13C variations likely record fluctuations in the ??13C of dissolved inorganic carbon of water recharging the aquifer. How such variations are transported 80 kilometers to Devils Hole without obliteration by waterrock reaction remains an enigma. The record may reflect (i) global variations in the ??13C of atmospheric CO2 and, hence, the ??13C of continental biomass or (ii) variations in extent and density of vegetation in the southern Great Basin. In the latter case, ??13C minima at 414, 334, 246, and 133 thousand years ago mark times of maximum vegetation.

  6. An algorithm to find minimum free-energy paths using umbrella integration

    NASA Astrophysics Data System (ADS)

    Bohner, Matthias U.; Kästner, Johannes

    2012-07-01

    The calculation of free-energy barriers by umbrella sampling and many other methods is hampered by the necessity for an a priori choice of the reaction coordinate along which to sample. We avoid this problem by providing a method to search for saddle points on the free-energy surface in many coordinates. The necessary gradients and Hessians of the free energy are obtained by multidimensional umbrella integration. We construct the minimum free-energy path by following the gradient down to minima on the free-energy surface. The change of free energy along the path is obtained by integrating out all coordinates orthogonal to the path. While we expect the method to be applicable to large systems, we test it on the alanine dipeptide in vacuum. The minima, transition states, and free-energy barriers agree well with those obtained previously with other methods.

  7. Atlas of reflectance spectra of terrestrial, lunar and meteoritic powders and frosts from 92 to 1800 nm

    NASA Technical Reports Server (NTRS)

    Wagner, Jeffrey; Hapke, Bruce; Wells, Eddie

    1987-01-01

    The reflectance spectra of powdered samples of selected minerals, meteorites, lunar materials and frosts are presented as an aid in the interpretation of present and future remote sensing data of solar system objects. Spectra obtained in separate wavelength regions have been combined and normalized, yielding coverage from 92 to 1800 nm. Spectral features include reflectance maxima in the far UV region produced by valence-conduction interband transitions, and reflectance minima in the near UV, visible and near IR regions, produced by charge transfer and crystal field transitions. Specific maxima and minima are diagnostic of mineral type and composition; additionally, the minerals present in mixtures such as meteorites and lunar samples can be determined.

  8. Influence of the potential range on the heat capacity of 13-atom Morse clusters

    NASA Astrophysics Data System (ADS)

    Moseler, Michael; Nordiek, Johannes

    1999-10-01

    Heat capacity curves as a function of temperature were studied for 13-atom clusters bound by Morse potentials with different range parameters ρ0 ɛ \\{3,4,5,6,14\\} using J-walking Monte Carlo. Decreasing the range of the pair potential (i.e., increasing ρ0) increases the peak of the heat capacity in the melting transition region and decreases the boiling temperature. For ρ0=14 the melting and boiling peaks merge. The short-range potential favors a transition from the catchment region of the icosahedral ground state to the basins of higher minima. On the other hand, clusters bound by the long-range potential (ρ0=3) remain in the ground-state basin even for elevated temperatures, which can be explained by the destabilization of important higher minima for ρ0<4.

  9. Nonlinear plastic modes in disordered solids

    NASA Astrophysics Data System (ADS)

    Gartner, Luka; Lerner, Edan

    2016-01-01

    We propose a theoretical framework within which a robust micromechanical definition of precursors to plastic instabilities, often termed soft spots, naturally emerges. They are shown to be collective displacements (modes) z ̂ that correspond to local minima of a barrier function b (z ̂) , which depends solely on inherent structure information. We demonstrate how some heuristic searches for local minima of b (z ̂) can a priori detect the locus and geometry of imminent plastic instabilities with remarkable accuracy, at strains as large as γc-γ ˜10-2 away from the instability strain γc. Our findings suggest that the a priori detection of the entire field of soft spots can be effectively carried out by a systematic investigation of the landscape of b (z ̂) .

  10. Structural flexibility of 4,4'-methylene diphenyl diisocyanate (4,4'-MDI): evidence from first principles calculations.

    PubMed

    Rodziewicz, Pawel; Goclon, Jakub

    2014-02-01

    A reactant used globally in the production of polyurethane is the molecule 4,4'-methylene diphenyl diisocyanate (4,4'-MDI). The structural flexibility of 4,4'-MDI is one of the most important molecular properties influencing the polymerization process and this property was therefore modeled using density functional theory (DFT) calculations and Car-Parrinello molecular dynamics (MD) simulations. Global and local minima structures were found and confirmed by vibrational analysis. The energy barriers related to rotation of the aromatic rings were estimated by DFT calculations. The stability of global and local minima was verified by Car-Parrinello (MD) runs at finite temperature. The presence of weak C-H⋯π hydrogen bonds was confirmed by atoms in molecules analysis and found to be responsible for the low energy barriers. PMID:24522379

  11. Spin vector and shape of 532 Herculina

    NASA Technical Reports Server (NTRS)

    Kwiatkowski, T.; Michalowski, Tadeusz

    1992-01-01

    Herculina has been observed during 7 oppositions: 1954 (Groeneveld and Kuiper), 1963 (Chang and Chang), 1978 (Harris and Young), 1982 (Drummond et al.; Weidenschilling et al.), 1984 (Taylor et al.), 1985 (Erikson et al.), and 1987 (Lebofsky et al.; Weidenschilling et al.). This asteroid has very unusual lightcurves. They exhibit two maxima and minima in 1978, 1984, and 1987, and only one maximum and minimum in 1954, 1963, and 1982 per rotation cycle of about 9.4 hours. The 1985 lightcurve, which is very close in aspect to those from 1963, shows two maxima and minima. The primary minimum is very similar to a single minimum in 1963, while the secondary one is only 0.06 mag deep. In 1963 no secondary minimum was visible.

  12. Instabilities of microstate geometries with antibranes

    NASA Astrophysics Data System (ADS)

    Bena, Iosif; Pasini, Giulio

    2016-04-01

    One can obtain very large classes of horizonless microstate geometries corresponding to near-extremal black holes by placing probe supertubes whose action has metastable minima inside certain supersymmetric bubbling solutions [1]. We show that these minima can lower their energy when the bubbles move in certain directions in the moduli space, which implies that these near-extremal microstates are in fact unstable once one considers the dynamics of all their degrees of freedom. The decay of these solutions corresponds to Hawking radiation, and we compare the emission rate and frequency to those of the corresponding black hole. Our analysis supports the expectation that generic non-extremal black holes microstate geometries should be unstable. It also establishes the existence of a new type of instabilities for antibranes in highly-warped regions with charge dissolved in fluxes.

  13. Demonstration of the feasibility of a complete ellipsometric characterization method based on an artificial neural network.

    PubMed

    Battie, Yann; Robert, Stéphane; Gereige, Issam; Jamon, Damien; Stchakovsky, Michel

    2009-10-01

    Ellipsometry is an optical technique that is widely used for determining optical and geometrical properties of optical thin films. These properties are in general extracted from the ellipsometric measurement by solving an inverse problem. Classical methods like the Levenberg-Marquardt algorithm are generally too long, depending on direct calculation and are very sensitive to local minima. In this way, the neural network has proved to be an efficient tool for solving these kinds of problems in a very short time. Indeed, it is rapid and less sensitive to local minima than the classical inversion method. We suggest a complete neural ellipsometric characterization method for determining the index dispersion law and the thickness of a simple SiO(2) or photoresist thin layer on Si, SiO(2), and BK7 substrates. The influence of the training couples on the artificial neural network performance is also discussed. PMID:19798371

  14. Effects of scattering area shape on spin conductance in a four-terminal spin-Hall setup

    NASA Astrophysics Data System (ADS)

    Thorgilsson, Gunnar; Erlingsson, Sigurdur I.

    2010-12-01

    We study spin conductance in a ballistic and quasiballistic two-dimensional electron system with Rashba spin-orbit coupling. The system has a four-terminal geometry with round corners at the connection to the leads. It is found that by going from sharp corners to more round corners in the ballistic system the energy-depended spin conductance goes from being relatively flat to a curve showing a series of minima and maxima. It is also found that when changing the size of the terminal area by modifying the roundness of the terminal corners the maxima and minima in the transverse spin conductance are shifted in energy. This shift is due increased (decreased) energy for smaller (larger) terminal area. These results were also found to be reasonably stable in quasiballistic systems.

  15. Real-time obstacle avoidance using harmonic potential functions

    NASA Technical Reports Server (NTRS)

    Kim, Jin-Oh; Khosla, Pradeep K.

    1992-01-01

    This paper presents a new formulation of the artificial potential approach to the obstacle avoidance problem for a mobile robot or a manipulator in a known environment. Previous formulations of artificial potentials for obstacle avoidance have exhibited local minima in a cluttered environment. To build an artificial potential field, harmonic functions that completely eliminate local minima even for a cluttered environment are used. The panel method is employed to represent arbitrarily shaped obstacles and to derive the potential over the whole space. Based on this potential function, an elegant control strategy is proposed for the real-time control of a robot. The harmonic potential, the panel method, and the control strategy are tested with a bar-shaped mobile robot and a three-degree-of-freedom planar redundant manipulator.

  16. Monthly and seasonal occurrences of potential flash flood-producing rains determined from Manually Digitized Radar data

    NASA Technical Reports Server (NTRS)

    Wilson, G. S.

    1980-01-01

    An analysis is conducted of a small 4-year climatological data base of Manually Digitized Radar (MDR) data to infer the monthly and seasonal distributions of the relative frequency of occurrence of potential flash flood-producing rains over the Central and Eastern U.S. Some possible meteorological mechanisms for producing potential flash flooding rains are discussed in terms of the relative maxima and minima in the monthly and seasonal frequency distributions over the MDR network. Frequencies were found to be generally higher in more southern locations and lower farther north in all months and seasons. However, most locations experienced an annual cycle in the frequency of occurrence with maxima in summer and minima in winter. In given seasons and months, local areas of maximum and minimum occurrences may be related to quasi-stationary meteorological processes that trigger and organize intense convection over a common area.

  17. Understanding micro-image configurations in quasar microlensing

    NASA Astrophysics Data System (ADS)

    Saha, Prasenjit; Williams, Liliya L. R.

    2011-03-01

    The micro-arcsecond scale structure of the seemingly point-like images in lensed quasars, though unobservable, is nevertheless much studied theoretically, because it affects the observable (or macro) brightness, and through that provides clues to substructure in both source and lens. A curious feature is that, while an observable macro-image is made up of a very large number of micro-images, the macro flux is dominated by a few micro-images. Micro minima play a key role, and the well-known broad distribution of macro magnification can be decomposed into narrower distributions with 0, 1, 2, 3, … micro minima. This paper shows how the dominant micro-images exist alongside the others, using the ideas of Fermat's principle and arrival-time surfaces, alongside simulations.

  18. Implementing TOPbase/Iron Project: continuous absorption from FeII

    NASA Astrophysics Data System (ADS)

    Cowley, Charles R.; Bautista, Manuel

    2003-06-01

    We discuss implementation of TOPbase and Iron Project opacities for stellar spectral codes. We use a technique employed by Peach, where a Boltzmann-averaged cross-section is calculated for selected temperatures, and the opacity obtained from double interpolation in temperature and wavelength. It is straightforward to include all levels for which cross-sections have been calculated. Boltzmann-averaged cross-sections for FeII show a local maximum between 1700 and 2000 Å. We suggest this feature arises from 3d54snl-> 3d54pnl transitions within FeII. IUE spectra of iron-rich CP stars show local minima in this region. Theoretical calculations of a representative stellar continuum demonstrate that FeII photoionization contributes significantly to the observed minima.

  19. Energies of the X- and L-valleys in In0.53Ga0.47As from electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Greene-Diniz, Gabriel; Fischetti, M. V.; Greer, J. C.

    2016-02-01

    Several theoretical electronic structure methods are applied to study the relative energies of the minima of the X- and L-conduction-band satellite valleys of InxGa1-xAs with x = 0.53. This III-V semiconductor is a contender as a replacement for silicon in high-performance n-type metal-oxide-semiconductor transistors. The energy of the low-lying valleys relative to the conduction-band edge governs the population of channel carriers as the transistor is brought into inversion, hence determining current drive and switching properties at gate voltages above threshold. The calculations indicate that the position of the L- and X-valley minima are ˜1 eV and ˜1.2 eV, respectively, higher in energy with respect to the conduction-band minimum at the Γ-point.

  20. Combustion characteristics in the transition region of liquid fuel sprays

    NASA Technical Reports Server (NTRS)

    Cernansky, N. P.; Namer, I.; Tidona, R. J.

    1984-01-01

    A number of important effects were observed in the droplet size transition region in spray combustion systems. In this region, where the mechanism of flame propagation is transformed from diffusive to premixed dominated combustion, the following effects have been observed: (1) maxima in burning velocity; (2) extension of flammability limits; (3) minima in ignition energy; and (4) minima in NO(x) formation. Unfortunately, because of differences in experimental facilities and limitations in the ranges of experimental data, a unified description of these transition region effects is not available at this time. Consequently, a fundamental experimental investigation was initiated to study the effect of droplet size, size distribution, and operating parameters on these transition region phenomena in a single well controlled spray combustion facility.

  1. Host-Guest Complexes with Protein-Ligand-Like Affinities: Computational Analysis and Design

    PubMed Central

    Moghaddam, Sarvin; Inoue, Yoshihisa

    2009-01-01

    It has recently been discovered that guests combining a nonpolar core with cationic substituents bind cucurbit[7]uril (CB[7]) in water with ultra-high affinities. The present study uses the Mining Minima algorithm to study the physics of these extraordinary associations and to computationally test a new series of CB[7] ligands designed to bind with similarly high affinity. The calculations reproduce key experimental observations regarding the affinities of ferrocene-based guests with CB[7] and β-cyclodextrin and provide a coherent view of the roles of electrostatics and configurational entropy as determinants of affinity in these systems. The newly designed series of compounds is based on a bicyclo[2.2.2]octane core, which is similar in size and polarity to the ferrocene core of the existing series. Mining Minima predicts that these new compounds will, like the ferrocenes, bind CB[7] with extremely high affinities. PMID:19133781

  2. {alpha}-decay hindrance factors: A probe of mean-field wave functions

    SciTech Connect

    Karlgren, D.; Liotta, R.J.; Wyss, R.; Huyse, M.; Vel, K. van de; Duppen, P. van

    2006-06-15

    A simple model to calculate {alpha}-decay hindrance factors (HF) with special emphasis on the shape coexistence in the Pb-Po region is presented. Using deformation values obtained from potential energy surface (PES) calculations as the only input, hindrance factors for the {alpha} decay of Rn and Po isotopes are calculated. The fair agreement between experimental and theoretical hindrance factors suggest that the wave function obtained from the energy minima of the PES calculations contains an important part of the correlations that play a role for the {alpha} decay. The model is applicable to shape coexistence in the Po and Pb region when minima are well defined. The calculated HF that emerge from these calculations render a different interpretation than the commonly assumed n-particle n-hole picture of the intruder states in the Pb region.

  3. Characteristics of Solar Meridional Flows

    NASA Astrophysics Data System (ADS)

    Basu, Sarbani; Antia, H. M.

    2011-01-01

    We have done a ring-diagram analysis of MDI full-disc data to determine the properties of solar meridional flow in the outer 2% of the Sun over the solar cycle 23. The meridional flows show a migrating pattern with higher-velocity flows migrating toward the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of the sunspot butterfly diagram and the zonal flows in the shallow layers. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that during the two minima. We also find that the dominant component of the meridional flows during solar maxima was much lower than that during the minima of solar cycles 23 and 24.

  4. Scattering of light by a film in contact with a modulated dielectric medium

    NASA Astrophysics Data System (ADS)

    Saldaña, Xóchitl I.; Cocoletzi, G. H.; González de la Cruz, G.; Dobrzynski, L.

    1992-12-01

    We present a study of the polariton mode propagation at the interface between a film and a doping modulated semiconductor. The film has a frequency independent dielectric constant while the semiconductor has a periodically modulated dielectric function. We use 'modal theory' to calculate the reflectance and oobtain the dispersion rela- tion of the polariton modes from the reflectance minima. The numerical results of the dispersion relation show a shift of the curves to higher values of the parallel component of the wave vector. The reflectance minima are narrow for low energy of the incident light but evolve in such a way that as the energy increases, the spectra become broader indicating a lost of the excitation of the polariton modes. We consider a film ɛ ƒ= 1.5 and as the modulated medium GaAs.

  5. Convexity at finite temperature and non-extensive thermodynamics

    NASA Astrophysics Data System (ADS)

    Alexandre, J.

    2016-09-01

    Assuming that tunnel effect between two degenerate bare minima occurs, in a scalar field theory at finite volume, this article studies the consequences for the effective potential, to all loop orders. Convexity is achieved only if the two bare minima are taken into account in the path integral, and a new derivation of the effective potential is given, in the large volume limit. The effective potential then has a universal form, it is suppressed by the space time volume, and does not feature spontaneous symmetry breaking as long as the volume is finite. The finite temperature analysis leads to surprising thermal properties, following from the non-extensive expression for the free energy. Although the physical relevance of these results is not clear, the potential application to ultra-light scalar particles is discussed.

  6. Antarctic measurements of ozone by SAGE II in the spring of 1985, 1986, and 1987

    NASA Technical Reports Server (NTRS)

    Mccormick, M. P.; Larsen, J. C.

    1988-01-01

    This paper presents a three-year (1985, 1986, and 1987) comparison of ozone profiles within the southern polar vortex for September and October, using data obtained by the Stratospheric Aerosol and Gas Experiment II. It was found that, by the first half of October 1986, daily minima in total ozone showed a moderate recovery of 5-7 percent relative to 1985, whereas in 1987, a significant drop of 15 percent from the 1985 minima was observed. The interannual variability of total ozone, temperature, and temperature area or vortex size were found to display a quasi-biennial oscillation (QBO) signal similar to that established by Garcia and Solomon (1987) for Antarctica. Since the 1985 and 1987 years displayed the same QBO phase (westerly) and the 1987 depletion was greater than that of 1985, it is concluded that the long-term secular ozone trend continues to be downward.

  7. Data classification using metaheuristic Cuckoo Search technique for Levenberg Marquardt back propagation (CSLM) algorithm

    NASA Astrophysics Data System (ADS)

    Nawi, Nazri Mohd.; Khan, Abdullah; Rehman, M. Z.

    2015-05-01

    A nature inspired behavior metaheuristic techniques which provide derivative-free solutions to solve complex problems. One of the latest additions to the group of nature inspired optimization procedure is Cuckoo Search (CS) algorithm. Artificial Neural Network (ANN) training is an optimization task since it is desired to find optimal weight set of a neural network in training process. Traditional training algorithms have some limitation such as getting trapped in local minima and slow convergence rate. This study proposed a new technique CSLM by combining the best features of two known algorithms back-propagation (BP) and Levenberg Marquardt algorithm (LM) for improving the convergence speed of ANN training and avoiding local minima problem by training this network. Some selected benchmark classification datasets are used for simulation. The experiment result show that the proposed cuckoo search with Levenberg Marquardt algorithm has better performance than other algorithm used in this study.

  8. Fundamental limitations of LIGA x-ray lithography : sidewall offset, slope and minimum feature size.

    SciTech Connect

    Griffiths, Stewart K.

    2004-01-01

    Analytical and numerical methods are used to examine photoelectron doses and their effect on the dimensions of features produced by deep x-ray lithography. New analytical models describing electron doses are presented and used to compute dose distributions for several feature geometries. The history of development and final feature dimensions are also computed, taking into account the dose field, dissolution kinetics based on measured development rates, and the transport of PMMA fragments away from the dissolution front. We find that sidewall offsets, sidewall slope and producible feature sizes all exhibit at least practical minima and that these minima represent fundamental limitations of the LIGA process. The minimum values under optimum conditions are insensitive to the synchrotron spectrum, but depend strongly on resist thickness. This dependence on thickness is well approximated by simple analytical expressions describing the minimum offset, minimum sidewall slope, minimum producible size of positive and negative features, maximum aspect ratio and minimum radius of inside and outside corners.

  9. Variation of solar activity and its effect on climate since the Spoerer Minimum

    NASA Astrophysics Data System (ADS)

    Miyahara, H.; Masuda, K.; Muraki, Y.

    2005-12-01

    This paper presents the evolution of the eleven-year solar cycle since the Spoerer Minimum (1415-1534 AD) deduced from the cosmogenic isotope in tree rings. We have measured the carbon-14 content from 1410 to 1745 AD with annual time resolution, and investigated the modulation of the length of the eleven-year solar cycle associated with the occurrence of the prolonged sunspot minima such as the Spoerer and Maunder minima (1645-1715 AD). A phase transition is found in the waveform of C14 record after the Maunder Minimum. We investigate the global structure of the heliospheric magnetic field during the transition interval. Possible roles of cosmic ray variation in the climate change are also discussed.

  10. Ion morphology in the inner tail of Comet P/Halley

    NASA Technical Reports Server (NTRS)

    Hoban, Susan; Ahearn, Michael F.; Birch, Peter V.; Candy, Michael P.; Martin, Ralph; Klinglesmith, Daniel A., III

    1986-01-01

    Comet Halley CCD images taken in the light of CO(+) and H2O(+) were analyzed. Most of the ionic emission originates in a diffuse component on which the ion ray structure appears to be superimposed. On average, the peak enhancement in the CO(+) rays is 20% over the adjacent minima, where the emission is due to the underlying component. The H2O(+):CO(+) ratio varies by as much as 30% from ray to ray.

  11. Foraging on the potential energy surface: a swarm intelligence-based optimizer for molecular geometry.

    PubMed

    Wehmeyer, Christoph; Falk von Rudorff, Guido; Wolf, Sebastian; Kabbe, Gabriel; Schärf, Daniel; Kühne, Thomas D; Sebastiani, Daniel

    2012-11-21

    We present a stochastic, swarm intelligence-based optimization algorithm for the prediction of global minima on potential energy surfaces of molecular cluster structures. Our optimization approach is a modification of the artificial bee colony (ABC) algorithm which is inspired by the foraging behavior of honey bees. We apply our modified ABC algorithm to the problem of global geometry optimization of molecular cluster structures and show its performance for clusters with 2-57 particles and different interatomic interaction potentials. PMID:23181297

  12. A statistical-based scheduling algorithm in automated data path synthesis

    NASA Technical Reports Server (NTRS)

    Jeon, Byung Wook; Lursinsap, Chidchanok

    1992-01-01

    In this paper, we propose a new heuristic scheduling algorithm based on the statistical analysis of the cumulative frequency distribution of operations among control steps. It has a tendency of escaping from local minima and therefore reaching a globally optimal solution. The presented algorithm considers the real world constraints such as chained operations, multicycle operations, and pipelined data paths. The result of the experiment shows that it gives optimal solutions, even though it is greedy in nature.

  13. Gold Sulfide Nanoclusters: A Unique Core-in-cage Structure

    SciTech Connect

    Jiang, Deen; Walter, Michael; Dai, Sheng

    2010-01-01

    By using a DFT-based basin-hopping method, we found putative global minima for three gold sulfide nanoclusters, observed in mass spectrometry, that all show a symmetric core-in-cage structure: a metallic Au core inside a cage with S as vertices and Au at the edges. This core-in-cage structure is distinct from bulk gold sulfide. This work fills the knowledge gap regarding the structure of gold sulfide nanoclusters of {approx}1 nm.

  14. Inversion of parity splitting in alternating parity bands at high angular momenta

    SciTech Connect

    Jolos, R.V.; Minkov, N.; Scheid, W.

    2005-12-15

    The angular-momentum dependence of parity splitting in ground-state alternating parity bands and especially the sign inversion of parity splitting are considered. It is shown that the complicated odd-even staggering structure of the alternating parity bands can be interpreted as the result of two simultaneously manifesting effects: (1) penetration of the barrier separating two minima with the opposite signs of the reflection asymmetric deformation and (2) alignment of the angular momentum of the intrinsic excitations.

  15. Foraging on the potential energy surface: A swarm intelligence-based optimizer for molecular geometry

    NASA Astrophysics Data System (ADS)

    Wehmeyer, Christoph; Falk von Rudorff, Guido; Wolf, Sebastian; Kabbe, Gabriel; Schärf, Daniel; Kühne, Thomas D.; Sebastiani, Daniel

    2012-11-01

    We present a stochastic, swarm intelligence-based optimization algorithm for the prediction of global minima on potential energy surfaces of molecular cluster structures. Our optimization approach is a modification of the artificial bee colony (ABC) algorithm which is inspired by the foraging behavior of honey bees. We apply our modified ABC algorithm to the problem of global geometry optimization of molecular cluster structures and show its performance for clusters with 2-57 particles and different interatomic interaction potentials.

  16. Training product unit neural networks with genetic algorithms

    NASA Technical Reports Server (NTRS)

    Janson, D. J.; Frenzel, J. F.; Thelen, D. C.

    1991-01-01

    The training of product neural networks using genetic algorithms is discussed. Two unusual neural network techniques are combined; product units are employed instead of the traditional summing units and genetic algorithms train the network rather than backpropagation. As an example, a neural netork is trained to calculate the optimum width of transistors in a CMOS switch. It is shown how local minima affect the performance of a genetic algorithm, and one method of overcoming this is presented.

  17. Functional data analysis of experimental parameters obtained in PVA doped CdCl2 polymer composites

    NASA Astrophysics Data System (ADS)

    Prakash, M. B. Nanda; Urs, Gopal Krishne; Somashekar, R.

    2016-05-01

    Using solution casting method, PVA based polymer composites films with various concentrations of CdCl2 were prepared. Prepared polymer composites films were investigated using XRD. Crystallite size for different concentrations of CdCl2 are computed here using Williamson and Hall plot (WH plot), an in-house program developed by us. To correlate between two independent physical parameters size and conductivity, we have chosen functional data analysis to estimate the maxima and minima in these polymer composites systems.

  18. Illumination system design with multi-step optimization

    NASA Astrophysics Data System (ADS)

    Magarill, Simon; Cassarly, William J.

    2015-08-01

    Automatic optimization algorithms can be used when designing illumination systems. For systems with many design variables, optimization using an adjustable set of variables at different steps of the process can provide different local minima. We present a few examples of implementing a multi-step optimization method. We have found that this approach can sometimes lead to more efficient solutions. In this paper we illustrate the effectiveness of using a commercially available optimization algorithm with a slightly modified procedure.

  19. VizieR Online Data Catalog: Period variations in SuperWASP PCEB (Lohr+, 2014)

    NASA Astrophysics Data System (ADS)

    Lohr, M. E.; Norton, A. J.; Anderson, D. R.; Collier, Cameron A.; Faedi, F.; Haswell, C. A.; Hellier, C.; Hodgkin, S. T.; Horne, K.; Kolb, U. C.; Maxted, P. F. L.; Pollacco, D.; Skillen, I.; Smalley, B.; West, R. G.; Wheatley, P. J.

    2014-05-01

    Times of light curve primary minima for 11 post-common-envelope eclipsing binaries are presented here, as determined from SuperWASP archive photometry, with uncertainties. For each object there are two tables, one giving times selected as reliable and used in period change determinations as described in the paper, and one giving additional times rejected by our code as less reliable and/or with large uncertainties. (23 data files).

  20. Lateral ankle ligament anesthesia significantly alters single limb postural control.

    PubMed

    McKeon, P O; Booi, M J; Branam, B; Johnson, D L; Mattacola, C G

    2010-07-01

    Lateral ankle anesthesia has been used as a model to explore effects of ligament deafferentation related to ankle sprain on single limb postural control with conflicting results. Time-to-boundary (TTB) is a postural control measurement technique found to be sensitive in detecting subtle deficits in postural control in those with chronic ankle instability. The objective of this study was to determine the effects of lateral ankle ligament anesthesia on TTB measures of single limb postural control in healthy adults. Twenty-two healthy adults with no history of lower extremity injury within the past 6 months or balance disorders participated in the study. All subjects received a lidocaine injection to the lateral ankle structures on one of two testing days. On both testing days, subjects performed 3 eyes open and 3 eyes closed, 10-s trials of barefoot single limb stance on a forceplate. The dependent variables were the mean of TTB minima(s) and standard deviation of TTB minima(s) in mediolateral (ML) and anteroposterior (AP) directions. Separate condition (anesthesia, control) by vision (eyes open, eyes closed) ANOVAs with repeated measures were used for each TTB variable to determine the effects of anesthesia on postural control. Alpha level was set a priori at p≤0.05. The anesthesia day TTBAP magnitude (p=0.008) and variability (p=0.044) measures were significantly lower than the control day, regardless of vision. Anesthesia of the lateral ankle ligamentous structures significantly reduced the magnitude and variability of TTBAP measures. These findings are similar to deficits found in those with chronic ankle instability. PMID:20663671

  1. GAUSSIAN 76: An ab initio Molecular Orbital Program

    DOE R&D Accomplishments Database

    Binkley, J. S.; Whiteside, R.; Hariharan, P. C.; Seeger, R.; Hehre, W. J.; Lathan, W. A.; Newton, M. D.; Ditchfield, R.; Pople, J. A.

    1978-01-01

    Gaussian 76 is a general-purpose computer program for ab initio Hartree-Fock molecular orbital calculations. It can handle basis sets involving s, p and d-type Gaussian functions. Certain standard sets (STO-3G, 4-31G, 6-31G*, etc.) are stored internally for easy use. Closed shell (RHF) or unrestricted open shell (UHF) wave functions can be obtained. Facilities are provided for geometry optimization to potential minima and for limited potential surface scans.

  2. Observational Verification of the Limb-Darkening Law Based on Kepler Data

    NASA Astrophysics Data System (ADS)

    Zola, S.; Baran, A.; Debski, B.; Jableka, D.

    2015-07-01

    We present preliminary results obtained from modeling of light curves of a sample of contact binaries observed by the Kepler spacecraft. Our study was aimed at verifying which of the three most commonly used limb-darkening formulations fits the high quality Kepler data the best. We limited our work to twelve binary systems showing flat-bottomed minima, and we found that for ten of them the square root limb-darkening law led to the best fits.

  3. Some possible filler alloys with low vapor pressures for refractory-metal brazing

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1973-01-01

    A compilation of eutectics and melting-point minima for binary combinations of metals having vapor pressures below 10 to the minus 10th power torr at 1500 degrees K and .00005 torr at 2000 degree K is presented. These compositions and others near them on their phase diagrams are potential special brazing fillers for refractory metals. Some possible problems and advantages for fusion bonds of such mixtures are indicated. Evaluations of brazing fillers containing refractory metals are reported.

  4. Morphological stability of the solid‒liquid interface during melt crystallization of Pb1- x Cd x F2 solid solution

    NASA Astrophysics Data System (ADS)

    Fedorov, P. P.; Buchinskaya, I. I.; Chernova, E. V.

    2016-05-01

    The stability function of the solid‒liquid interface for PbF2-CdF2 solid solution with respect to constitutional supercooling is calculated using the phase diagram of the system. The calculated curve is typical of the systems with continuous solid solutions, having minima points in the liquidus and solidus curves. This dependence can be used to estimate the technological parameters of the process which are required for growing crystals with the high optical quality.

  5. Determination of particle size using measurement of scatter

    NASA Technical Reports Server (NTRS)

    Scott, R. L., Jr.

    1978-01-01

    A literature search was conducted to determine the state of the art particle size measurement by the light scatter technique. This technique may involve diffraction pattern analysis, location of minima and maxima in angular dependence of scattered light, magnitude of intensity verses angle, forward lobe scattered intensity ratio using two small angles, forward scatter in a small cone, and total scatter. Some of the more modern recordings and detection systems are video, holographic, and systems using optical processing.

  6. Josephson effect and quasiparticle states in d-wave superconductors

    SciTech Connect

    Tanaka, Yukio; Kashiwaya, Satoshi

    1996-12-31

    A general formula for the Josephson current in a d-wave/insulator/d-wave-superconductor junction is presented by taking account of the zero-energy states formed around the interfaces. For a fixed phase difference between the two superconductors, the current component becomes either positive or negative depending on the injection angle of the quasiparticle. Anomalous temperature dependences are predicted in the maximum Josephson current and in the free energy minima.

  7. A "twist" on the interpretation of the multifluorescence patterns of DASPMI.

    PubMed

    Segado, Mireia; Benassi, Enrico; Barone, Vincenzo

    2015-10-13

    In this computational study, we describe the decay mechanism of DASPMI, providing robust and documented answers to some crucial questions of still open debates on the photophysical behavior of this cationic dye. After the initial excitation, the system evolves along a torsional motion, characterized by a quite flat potential energy surface, which crosses an intramolecular charge transfer (ICT) excited state with higher energy. A nonemissive twisted-ICT (TICT) minimum is populated, and this enhances the radiationless deactivation to the ground state. Additionally, during the twisting motion path toward the TICT minima, the system can emit in a quite wide range of angles, which should lead to a red shift of the locally excited (LE) emission and asymmetric broadening of fluorescence. This picture is fully supported by experimental evidence of the multifluorescence of DASPMI. Three twisted minima are found with different energies (namely, T1, T2, and T3). The extension of the work to charge properties shows that, in the GS, the positive charge of the molecule is mainly localized on the acceptor moiety (i.e., methyl-pyridinium), and after the excitation, the charge delocalizes over the whole molecule with a slight preference for the acceptor moiety. Because of the subsequent deactivation via twisting motions, the positive charge moves from the acceptor to the donor moiety (dimethylaminophenyl moiety) so that in TICT minima the positive charge is localized in the donor part. These large differences between charge localization in LE and TICT minima are responsible for a larger population of twisted forms in solvents of increasing polarity and the enhancement of radiationless deactivation. PMID:26574269

  8. Sobolev gradient approach for the time evolution related to energy minimization of Ginzburg-Landau functionals

    NASA Astrophysics Data System (ADS)

    Raza, Nauman; Sial, Sultan; Siddiqi, Shahid S.

    2009-04-01

    The Sobolev gradient technique has been discussed previously in this journal as an efficient method for finding energy minima of certain Ginzburg-Landau type functionals [S. Sial, J. Neuberger, T. Lookman, A. Saxena, Energy minimization using Sobolev gradients: application to phase separation and ordering, J. Comput. Phys. 189 (2003) 88-97]. In this article a Sobolev gradient method for the related time evolution is discussed.

  9. Solving the {sup 12}C+{sup 12}C scattering puzzle: is there the '4th elephant'?

    SciTech Connect

    Demyanova, A. S.; Danilov, A. N.; Ogloblin, A. A.; Goncharov, S. A.; Bohlen, H. G.; Khlebnikov, S. V.; Tyurin, G. P.; Maslov, V. A.; Penionzkevich, Yu. E.; Sobolev, Yu. G.; Trzaska, W.

    2010-04-30

    Differential cross sections of the {sup 12}C+{sup 12}C and the {sup 13}C+{sup 12}C elastic scattering were measured at the projectile energies 240 MeV ({sup 12}C) and 250 MeV ({sup 13}C) up to the largest angles. The positions of the 1{sup st} Airy minima known from the former experiments were confirmed.

  10. Sulfur metabolism: different tolerances of two aquatic macrophytes exposed to arsenic.

    PubMed

    Leão, G A; Oliveira, J A; Farnese, F S; Gusman, G S; Felipe, R T A

    2014-07-01

    The toxicity of arsenic (As) and the mechanisms of response to this pollutant were analyzed in two aquatic plant species, one sensitive and one tolerant to the pollutant, Salvinia minima and Lemna gibba, respectively. The plants, grown in nutrient solution at pH 6.5, were exposed to As concentrations of 0.0 and 1.0mgL(-1) for 3 days. Both species accumulated As in their tissues, which resulted in increases in H2O2 production. L. gibba accumulated eleven times more As than S. minima. However, L. gibba was more tolerant, as shown by the absence of cell membrane damage and, despite greater accumulation, smaller growth reduction than S. minima. Indeed, the index of tolerance to As was twenty percent higher in L. gibba than in S. minima, which most likely results from the presence of a more efficient defense system. This defense system in L. gibba is most likely based on sulfate absorption, assimilation and metabolism. L. gibba showed an increase in sulfate absorption and adenosine-5'-triphosphate (ATP) sulfurylase activity (the first enzyme of the inorganic sulfate assimilation pathway) following exposure to As. Consequently, the plant produced greater concentrations of sulfur-containing compounds that are involved in cellular detoxification, such as glutathione and non-protein thiols, and demonstrated greater enzymatic activity of γ-glutamylcysteine synthetase, glutathione S-transferase and glutathione reductase. Therefore, the plant׳s ability to increase absorption, assimilation and metabolism of sulfur are key steps for tolerance to oxidative stress triggered by metals. PMID:24780231

  11. Ring-whizzing in polyene-PtL2 complexes revisited

    PubMed Central

    Oloba-Whenu, Oluwakemi A; Soubra-Ghaoui, Chirine

    2016-01-01

    Summary Ring-whizzing was investigated by hybrid DFT methods in a number of polyene–Pt(diphosphinylethane) complexes. The polyenes included cyclopropenium+, cyclobutadiene, cyclopentadienyl+, hexafluorobenzene, cycloheptatrienyl+, cyclooctatetraene, octafluorooctatetraene, 6-radialene, pentalene, phenalenium+, naphthalene and octafluoronaphthalene. The HOMO of a d10 ML2 group (with b2 symmetry) interacting with the LUMO of the polyene was used as a model to explain the occurrence of minima and maxima on the potential energy surface. PMID:27559391

  12. Denitrification in the Arctic mid-winter 2004/2005 observed by airborne submillimeter radiometry

    NASA Technical Reports Server (NTRS)

    Kleinbohl, Armin; Bremer, Holger; Kullmann, Harry; Kuttippurath, Jayanarayanan; Browell, Edward V.; Canty, Timothy; Salawitch, Ross J.; Toon, Geoffrey C.; Nothol, Justus

    2005-01-01

    We present measurements of unusually low mixing ratios of HNO3 in the exceptionally cold Arctic vortex of late-January and early-February 2005. The measurements were obtained by the airborne submillimeter radiometer ASUR during the polar aura validation experiment (PAVE). The distribution of HNO3 inside the vortex reaches minima below 4 ppbv around 22 km altitude and maxima above 13 ppbv around 16 km altitude, with a considerable spatial variability.

  13. Surface alignment and anchoring transitions in nematic lyotropic chromonic liquid crystal.

    PubMed

    Nazarenko, V G; Boiko, O P; Park, H-S; Brodyn, O M; Omelchenko, M M; Tortora, L; Nastishin, Yu A; Lavrentovich, O D

    2010-07-01

    The surface alignment of lyotropic chromonic liquid crystals can not only be planar (tangential) but also homeotropic, with self-assembled aggregates perpendicular to the substrate, as demonstrated by mapping optical retardation and by three-dimensional imaging of the director field. With time, the homeotropic nematic undergoes a transition into a tangential state. The anchoring transition is discontinuous and can be described by a double-well anchoring potential with two minima corresponding to tangential and homeotropic orientation. PMID:20867479

  14. Ring-whizzing in polyene-PtL2 complexes revisited.

    PubMed

    Oloba-Whenu, Oluwakemi A; Albright, Thomas A; Soubra-Ghaoui, Chirine

    2016-01-01

    Ring-whizzing was investigated by hybrid DFT methods in a number of polyene-Pt(diphosphinylethane) complexes. The polyenes included cyclopropenium(+), cyclobutadiene, cyclopentadienyl(+), hexafluorobenzene, cycloheptatrienyl(+), cyclooctatetraene, octafluorooctatetraene, 6-radialene, pentalene, phenalenium(+), naphthalene and octafluoronaphthalene. The HOMO of a d(10) ML2 group (with b2 symmetry) interacting with the LUMO of the polyene was used as a model to explain the occurrence of minima and maxima on the potential energy surface. PMID:27559391

  15. Near infrared iron absorption bands: Applications to geologic mapping and mineral exploration

    NASA Technical Reports Server (NTRS)

    Rowan, L. C.

    1972-01-01

    A spectroscopic analysis of the difference in reflectance of iron-rich and iron-poor minerals was made. Attempts were made to use these minima contrast in geological mapping and metallic mineral exploration of large areas from near infrared and visible satellite images. Data cover pertinent laboratory spectroscopic investigations, applications of spectral differences to the discrimination of two important metamorphic rock types, and mineral exploration by aircraft in Beartooth Mountains, Montana.

  16. Are rare-gas Cl2 van der Waals molecules linear or T-shaped ?

    NASA Astrophysics Data System (ADS)

    Williams, Jason; Rohrbacher, Andreas; Djahandideh, Daniela; Jamka, Kenneth C. Janda Alan; Tao, Fu-Ming; Halberstadt, Nadine

    Ab-initio potential energy surfaces have been calculated for HeCl , NeCl Moller-Plesset perturbation theory to fourth order (MP4) with a large basis set that includes bond functions. Each surface has local minima for both the perpendicular and the linear configurations, and in each case the linear minimum is the deeper of the two. Low-lying LCAR-IRSAMC, Universite Paul Sabatier et CNRS, 31062 Toulouse Cedex, France

  17. Layers of quasi-horizontally oriented ice crystals in cirrus clouds observed by a two-wavelength polarization lidar.

    PubMed

    Borovoi, Anatoli; Balin, Yurii; Kokhanenko, Grigorii; Penner, Iogannes; Konoshonkin, Alexander; Kustova, Natalia

    2014-10-01

    Layers of quasi-horizontally oriented ice crystals in cirrus clouds are observed by a two-wavelength polarization lidar. These layers of thickness of several hundred meters are identified by three attributes: the backscatter reveals a sharp ridge while the depolarization ratio and color ratio become deep minima. These attributes have been justified by theoretical calculations of these quantities within the framework of the physical-optics approximation. PMID:25322032

  18. The eclipsing binary CW Eridani. [three-color photoelectric observation

    NASA Technical Reports Server (NTRS)

    Chen, K.-Y.

    1975-01-01

    Results of three-color photoelectric observations of CW Eridani are presented which were made with a 30-inch telescope over the three-year period from 1970 to 1973. The times of minima are computed, solutions of the light curves are obtained, and theoretical light curves are computed from the solutions. The period is determined to be 2.72837 days, and the orbital and photoelectric elements are derived from solutions based on the idealized Russell model.

  19. Nonequilibrium Casimir-Polder plasmonic interactions

    NASA Astrophysics Data System (ADS)

    Bartolo, Nicola; Messina, Riccardo; Dalvit, Diego A. R.; Intravaia, Francesco

    2016-04-01

    We investigate how the combination of nonequilibrium effects and material properties impacts on the Casimir-Polder interaction between an atom and a surface. By addressing systems with temperature inhomogeneities and laser interactions, we show that nonmonotonous energetic landscapes can be produced where barriers and minima appear. Our treatment provides a self-consistent quantum theoretical framework for investigating the properties of a class of nonequilibrium atom-surface interactions.

  20. New far infrared observations of the central 30' of the galaxy

    SciTech Connect

    Dent, W.A.; Werner, M.W.; Gatley, I.; Becklin, E.E.; Hildebrand, R.H.; Keene, J.; Whitcomb, S.E.

    1982-05-01

    A 45' x 30' region around the galatic center was mapped with 1' resolution at 55 ..mu..m and 125 ..mu..m using the Kuiper Airborne Observatory. Peaks in temperature of the dust are correlated with centimeter wavelength thermal continuum sources. The distribution of the column density of dust shows minima at the galactic center (Sgr A) and at the position of an HII region complex (G.07+04) 10' to the North.

  1. Visualizing and improving the robustness of phase retrieval algorithms

    SciTech Connect

    Tripathi, Ashish; Leyffer, Sven; Munson, Todd; Wild, Stefan M.

    2015-06-01

    Coherent x-ray diffractive imaging is a novel imaging technique that utilizes phase retrieval and nonlinear optimization methods to image matter at nanometer scales. We explore how the convergence properties of a popular phase retrieval algorithm, Fienup's HIO, behave by introducing a reduced dimensionality problem allowing us to visualize and quantify convergence to local minima and the globally optimal solution. We then introduce generalizations of HIO that improve upon the original algorithm's ability to converge to the globally optimal solution.

  2. Interpretation of the UBV RcIc light variations of the symbiotic binary BF Cyg during its 2006-2014 optical outburst

    NASA Astrophysics Data System (ADS)

    Tomov, N. A.; Tomova, M. T.; Bisikalo, D. V.

    2016-02-01

    It is supposed that the variations of the depth of the orbital photometric minimum of the eclipsing symbiotic binary BF Cyg during its last eruption after 2006 is due to appearance of an accretion disc-like envelope which collimates the stellar wind of the outbursting compact object. The calculated U BV RcIc fluxes of the uneclipsed part of the envelope are in agreement with the observed residual of the depths of the first and second orbital minima.

  3. Cosmological Constant and Axions in String Theory

    SciTech Connect

    Svrcek, Peter; /Stanford U., Phys. Dept. /SLAC

    2006-08-18

    String theory axions appear to be promising candidates for explaining cosmological constant via quintessence. In this paper, we study conditions on the string compactifications under which axion quintessence can happen. For sufficiently large number of axions, cosmological constant can be accounted for as the potential energy of axions that have not yet relaxed to their minima. In compactifications that incorporate unified models of particle physics, the height of the axion potential can naturally fall close to the observed value of cosmological constant.

  4. Ab-initio study of oxygen defects in pure ThO2

    NASA Astrophysics Data System (ADS)

    Ghosh, Partha S.; Gupta, S. K.; Ali, K.; Arya, A.; Dey, G. K.

    2016-05-01

    First principles calculations using projector augmented wave potentials and generalized gradient approximations predicts the structural relaxations due to neutral and positively charged oxygen defects (+1 and +2) in bulk thoria leads to symmetric distortion around the vacancy site. Electronic Density of states (DOS) analysis shows presence of defects states mainly contributed by Th d and f states near the conduction band minima for the double positively charged oxygen vacancy which is having lowest energy of formation.

  5. Outer coronal structure and relative intensity distribution observed during the total solar eclipse on March 9, 1997 in Mohe.

    NASA Astrophysics Data System (ADS)

    Li, Qiusha; Zhang, Bairong

    With a simple video-collecting system, the total solar eclipse on March 9, 1997 has been observed by using Panasonic NV-S88OEN video camera in Mohe. After analyzing the yellow (by adding a GG11 filter) and white coronal observation data, the outer coronal structure and relative intensity distribution outside 1.5 Rsun have been found during the solar minima.

  6. Observation of Coexisting Dissipative Solitons in a Mode-Locked Fiber Laser.

    PubMed

    Bao, Chengying; Chang, Wonkeun; Yang, Changxi; Akhmediev, Nail; Cundiff, Steven T

    2015-12-18

    We show, experimentally and numerically, that a mode-locked fiber laser can operate in a regime where two dissipative soliton solutions coexist and the laser will periodically switch between the solutions. The two dissipative solitons differ in their pulse energy and spectrum. The switching can be controlled by an external perturbation and triggered even when switching does not occur spontaneously. Numerical simulations unveil the importance of the double-minima loss spectrum and nonlinear gain to the switching dynamics. PMID:26722922

  7. Toward New Energy-rich Molecular Systems: From N10 to N60

    SciTech Connect

    Manaa, M R.

    2000-12-01

    The electronic structure calculations locate the local minima for bicyclic N10 and the fullerene analog N60, both as high-energy density species. The bridging N-N bond in N10 is quite remarkably strong yet flexible to allow a facile rotation of one ring with respect to the other. This property could permit N10 to serve as a building block for specific clustering into the nitrogen buckminsterfullerene structure.

  8. Kinetics of atoms in a bichromatic field

    SciTech Connect

    Prudnikov, O. N.; Baklanov, A. S.; Taichenachev, A. V.; Tumaikin, A. M.; Yudin, V. I.

    2013-08-15

    The kinetics of atoms in a bichromatic field is considered. Analytic solutions are obtained for the force, friction coefficient, and diffusion coefficient in the model of a two-level atom without limitations imposed on the intensity of light fields. This effect is observed in the domain of global minima and maxima of the optical potential (i.e., at points where the relative phase of two standing waves is Greek-Phi-Symbol = 0, {pi}/2.

  9. Preheating in bubble collisions

    SciTech Connect

    Zhang Jun; Piao Yunsong

    2010-08-15

    In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that when the bubbles collide, due to the dramatic oscillation of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles. In this sense, the collision of bubbles is actually highly inelastic. The cosmological implications of this result are discussed.

  10. Copernicus spectra of beta Lyrae. [in far UV

    NASA Technical Reports Server (NTRS)

    Hack, M.; Hutchings, J. B.; Kondo, Y.; Mccluskey, G. E.; Plavec, M.; Polidan, R. S.

    1974-01-01

    The observations reported were made in August and September 1973. The principal data were scans in the low resolution mode at phases nearly coincident with the two light minima. Shorter scans were obtained at the two quadrature phases. The data show that the secondary component of beta Lyrae is a hotter object than the visible B8 star. The velocity amplitude of the lines suggests that the secondary is the more massive object, by a factor of several times.

  11. Variable Star and Exoplanet Section of the Czech Astronomical Society

    NASA Astrophysics Data System (ADS)

    Brát, L.; Zejda, M.

    2010-12-01

    We present activities of Czech variable star observers organized in the Variable Star and Exoplanet Section of the Czech Astronomical Society. We work in four observing projects: B.R.N.O. - eclipsing binaries, MEDUZA - intrinsic variable stars, TRESCA - transiting exoplanets and candidates, HERO - objects of high energy astrophysics. Detailed information together with O-C gate (database of eclipsing binaries minima timings) and OEJV (Open European Journal on Variable stars) are available on our internet portal http://var.astro.cz.

  12. Analytic parametrization for nuclear form factors

    SciTech Connect

    Atkin, G.; Dumbrajs, O.

    1982-08-01

    A new analytic parametrization of the nuclear form factor is developed using a factorization theorem. We show that the nuclear form factor can be represented in terms of its real zeros and its asymptotic behavior. The parametrization is applied to nuclear form factor data of /sup 3/He and /sup 4/He. Our results suggest that further diffraction minima can be expected at higher momentum transfer where experiments have not yet been made.

  13. Wave and pseudo-diffusion equations from squeezed states

    NASA Technical Reports Server (NTRS)

    Daboul, Jamil

    1993-01-01

    We show that the probability distributions P(sub n)(q,p;y) := the absolute value squared of (n(p,q;y), which are obtained from squeezed states, obey an interesting partial differential equation, to which we give two intuitive interpretations: as a wave equation in one space dimension; and as a pseudo-diffusion equation. We also study the corresponding Wehrl entropies S(sub n)(y), and we show that they have minima at zero squeezing, y = 0.

  14. Conformations and Coherences in Structure Determination by Ultrafast Electron Diffraction

    PubMed Central

    Lin, Milo M.; Shorokhov, Dmitry; Zewail, Ahmed H.

    2009-01-01

    In this article we consider consequences of spatial coherences and conformations in diffraction of (macro)molecules with different potential energy landscapes. The emphasis is on using this understanding to extract structural and temporal information from diffraction experiments. The theoretical analysis of structural interconversions spans an increased range of complexity, from small hydrocarbons to proteins. For each molecule considered, we construct the potential energy landscape and assess the characteristic conformational states available. For molecules that are quasi-harmonic in the vicinity of energy minima, we find that the distinct conformer model is sufficient even at high temperatures. If, however, the energy surface is either locally flat around the minima or the molecule includes many degrees of conformational freedom, a Boltzmann ensemble must be used, in what we define as the pseudoconformer approach, to reproduce the diffraction. For macromolecules with numerous energy minima, the ensemble of hundreds of structures is considered, but we also utilize the concept of the persistence length to provide information on orientational coherence and its use to assess the degree of resonance contribution to diffraction. It is shown that the erosion of the resonant features in diffraction which are characteristic of some quasi-periodic structural motifs can be exploited in experimental studies of conformational interconversions triggered by a laser-induced temperature jump. PMID:19320469

  15. Non-Axial Octupole Deformations and Tetrahedral Symmetry in Heavy Nuclei

    SciTech Connect

    Mazurek, Katarzyna; Dudek, Jerzy

    2005-11-21

    The total energies of about 120 nuclei in the Thorium region have been calculated within the macroscopic-microscopic method in the 5-dimensional space of deformation parameters {alpha}20, {alpha}22, {alpha}30, {alpha}32 and {alpha}40. The macroscopic energy term contains the nuclear surface-curvature dependence as proposed within the LSD approach. The microscopic energies are calculated with the Woods-Saxon single particle potential employing the universal set of parameters.We study a possible presence of the octupole axial and non-axial degrees of freedom all-over in the ({beta}, {gamma})-plane focussing on the ground-states, secondary minima and in the saddle points. In fact, a competition between axial and tri-axial octupole deformation parameters is obtained at the saddle points and in the secondary minima for many isotones with N > 136. The presence of the tetrahedral symmetry minima is predicted in numerous nuclei in the discussed region, although most of the time at relatively high excitation energies.

  16. Social integration confers thermal benefits in a gregarious primate.

    PubMed

    McFarland, Richard; Fuller, Andrea; Hetem, Robyn S; Mitchell, Duncan; Maloney, Shane K; Henzi, S Peter; Barrett, Louise

    2015-05-01

    Sociality has been shown to have adaptive value for gregarious species, with more socially integrated animals within groups experiencing higher reproductive success and longevity. The value of social integration is often suggested to derive from an improved ability to deal with social stress within a group; other potential stressors have received less attention. We investigated the relationship between environmental temperature, an important non-social stressor, and social integration in wild female vervet monkeys (Chlorocebus pygerythrus), using implanted data loggers to obtain direct measures of core body temperature. Heterothermy (as measured by 24-h amplitude of body temperature) increased, and 24-h minima of body temperature decreased, as the 24-h minimum ambient temperature decreased. As winter progressed, monkeys became increasingly heterothermic and displayed lower 24-h minima of body temperature. Monkeys with a greater number of social partners displayed a smaller 24-h amplitude (that is, were more homoeothermic) and higher 24-h minima of body temperature (that is, became less hypothermic), than did animals with fewer social partners. Our findings demonstrate that social integration has a direct influence on thermoregulatory ability: individual animals that form and maintain more social relationships within their group experience improved thermal competence compared to those with fewer social relationships. Given the likely energetic consequences of thermal benefits, our findings offer a viable physiological explanation that can help account for variations in fitness in relation to individual differences in social integration. PMID:25581128

  17. CHARACTERISTICS OF SOLAR MERIDIONAL FLOWS DURING SOLAR CYCLE 23

    SciTech Connect

    Basu, Sarbani; Antia, H. M. E-mail: antia@tifr.res.i

    2010-07-01

    We have analyzed available full-disk data from the Michelson Doppler Imager on board SOHO using the 'ring diagram' technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius. We find that the dominant component of meridional flows during solar maximum was much lower than that during the minima at the beginning of cycles 23 and 24. There were differences in the flow velocities even between the two minima. The meridional flows show a migrating pattern with higher-velocity flows migrating toward the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of sunspot butterfly diagram and the zonal flows in the shallow layers. A high-latitude band in meridional flow appears around 2004, well before the current activity minimum. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that during the two minima. The different components of the flow have different time dependences, and the dependence is different at different depths.

  18. Global transition path search for dislocation formation in Ge on Si(001)

    NASA Astrophysics Data System (ADS)

    Maras, E.; Trushin, O.; Stukowski, A.; Ala-Nissila, T.; Jónsson, H.

    2016-08-01

    Global optimization of transition paths in complex atomic scale systems is addressed in the context of misfit dislocation formation in a strained Ge film on Si(001). Such paths contain multiple intermediate minima connected by minimum energy paths on the energy surface emerging from the atomic interactions in the system. The challenge is to find which intermediate states to include and to construct a path going through these intermediates in such a way that the overall activation energy for the transition is minimal. In the numerical approach presented here, intermediate minima are constructed by heredity transformations of known minimum energy structures and by identifying local minima in minimum energy paths calculated using a modified version of the nudged elastic band method. Several mechanisms for the formation of a 90° misfit dislocation at the Ge-Si interface are identified when this method is used to construct transition paths connecting a homogeneously strained Ge film and a film containing a misfit dislocation. One of these mechanisms which has not been reported in the literature is detailed. The activation energy for this path is calculated to be 26% smaller than the activation energy for half loop formation of a full, isolated 60° dislocation. An extension of the common neighbor analysis method involving characterization of the geometrical arrangement of second nearest neighbors is used to identify and visualize the dislocations and stacking faults.

  19. Effective Cohesive Behavior of Layers of Interatomic Planes

    NASA Astrophysics Data System (ADS)

    Braides, Andrea; Lew, Adrian J.; Ortiz, Michael

    2006-05-01

    A simple model of cleavage in brittle crystals consists of a layer of material containing N atomic planes separating in accordance with an interplanar potential under the action of an opening displacement δ prescribed on the boundary of the layer. The problem addressed in this work concerns the characterization of the constrained minima of the energy E N of the layer as a function of δ as N becomes large. These minima determine the effective or macroscopic cohesive law of the crystal. The main results presented in this communication are: (i) the computation of the Γ limit E 0 of E N as N → ∞; (ii) the characterization of the minimum values of E 0 as a function of the macroscopic opening displacement; (iii) a proof of uniform convergence of the minima of E N for the case of nearest-neighbor interactions; and (iv) a proof of uniform convergence of the derivatives of E N , or tractions, in the same case. The scaling on which the present Γ-convergence analysis is based has the effect of separating the bulk and surface contributions to the energy. It differs crucially from other scalings employed in the past in that it renders both contributions of the same order.

  20. Photometry of 20 eclipsing and ellipsoidal binary systems

    NASA Astrophysics Data System (ADS)

    Shobbrook, R. R.

    2004-12-01

    A total of almost 2000 V observations of 20 eclipsing and ellipsoidal bright binary stars was collected between 1991 and 2001 for the purpose of determining more recent epoch ephemerides for the light curves than are available in the literature. The original purpose was to provide the Sydney University Stellar Interferometer (SUSI) with orbital periods and particularly the accurate times of minimum separation (light curve minima), so that the SUSI observations need not be used to determine them. This paper provides the periods, the times of primary minima and the phases of secondary minima for the 20 stars at an epoch as near as possible to the year 2000. No attempt has been made in this report to determine other parameters such as {apsidal motion} or stellar radii. Since the program was started in 1991, data for these stars taken in the period from late 1989 to early 1993 has also been available from the Hipparcos satellite; the light curves shown here include both sets of observations.

  1. Photometry of 20 eclipsing and ellipsoidal binary systems

    NASA Astrophysics Data System (ADS)

    Shobbrook, R. R.

    2005-12-01

    ERRATUM: In the published paper the phase diagrams of pi Sco and AL Scl were ommitted. The version reproduced in JAD11, 7 is the complete version. A total of almost 2000 V observations of 20 eclipsing and ellipsoidal bright binary stars was collected between 1991 and 2001 for the purpose of determining more recent epoch ephemerides for the light curves than are available in the literature. The original purpose was to provide the Sydney University Stellar Interferometer (SUSI) with orbital periods and particularly the accurate times of minimum separation (light curve minima), so that the SUSI observations need not be used to determine them. This paper provides the periods, the times of primary minima and the phases of secondary minima for the 20 stars at an epoch as near as possible to the year 2000. No attempt has been made in this report to determine other parameters such as {apsidal motion} or stellar radii. Since the program was started in 1991, data for these stars taken in the period from late 1989 to early 1993 has also been available from the Hipparcos satellite; the light curves shown here include both sets of observations.

  2. Two new species and one new country record of Protaphorura Absolon, 1901 (Collembola: Onychiuridae) from northeast China.

    PubMed

    Sun, Xin; Zhang, Bing; Wu, Donghui

    2013-01-01

    Protaphorura Absolon, 1901 is characterized by the postantennal organ with numerous simple vesicles, the number of chaetae in the distal row of tibiotarsi as 11, the absence of chaeta d0 on the head, the furca reduced to a cuticular pocket with 2+2 dental chaetae, the presence of three or four manubrial rows of chaetae and having anal spines set on distinct papillae (Weiner 1996, Pomorski 1998). Among the 127 species of the genus known in the world (Bellinger et al. 1996-2013), only one species, Protaphorura armata (Tullberg, 1869), has been recorded from China till now (Rusek 1971). During our recent sampling in northeast China, one species new to China (Protaphorura bicampata (Gisin, 1956)) and two new species (Protaphorura changbaiensis sp. nov. and Protaphorura minima sp. nov.) were collected and are described below. One species new to China, Protaphorura bicampata (Gisin, 1956), and two new species, Protaphorura changbaiensis sp. nov. and Protaphorur minima sp. nov., are reported from northeast China. P. changbaiensis sp. nov. is similar to P. ajudagi and P. microcellata, but it can be distinguished from them by absence of a-pso on Th. II tergum. Protaphorura minima sp. nov. is chracterized by its male ventral organ on Abd. VI sternum. It can be separated from other species of the genus with the male ventral organ by the position of the male ventral organ and the dorsal pso formula. PMID:26185845

  3. On the origin of pure optical rotation in twisted-cross metamaterials.

    PubMed

    Barr, Lauren E; Díaz-Rubio, Ana; Tremain, Ben; Carbonell, Jorge; Sánchez-Dehesa, José; Hendry, Euan; Hibbins, Alastair P

    2016-01-01

    We present an experimental and computational study of the response of twisted-cross metamaterials that provide near dispersionless optical rotation across a broad band of frequencies from 19 GHz to 37 GHz. We compare two distinct geometries: firstly, a bilayer structure comprised of arrays of metallic crosses where the crosses in the second layer are twisted about the layer normal; and secondly where the second layer is replaced by the complementary to the original, i.e. an array of cross-shaped holes. Through numerical modelling we determine the origin of rotatory effects in these two structures. In both, pure optical rotation occurs in a frequency band between two transmission minima, where alignment of electric and magnetic dipole moments occurs. In the cross/cross metamaterial, the transmission minima occur at the symmetric and antisymmetric resonances of the coupled crosses. By contrast, in the cross/complementary-cross structure the transmission minima are associated with the dipole and quadrupole modes of the cross, the frequencies of which appear intrinsic to the cross layer alone. Hence the bandwidth of optical rotation is found to be relatively independent of layer separation. PMID:27457405

  4. On the origin of pure optical rotation in twisted-cross metamaterials

    NASA Astrophysics Data System (ADS)

    Barr, Lauren E.; Díaz-Rubio, Ana; Tremain, Ben; Carbonell, Jorge; Sánchez-Dehesa, José; Hendry, Euan; Hibbins, Alastair P.

    2016-07-01

    We present an experimental and computational study of the response of twisted-cross metamaterials that provide near dispersionless optical rotation across a broad band of frequencies from 19 GHz to 37 GHz. We compare two distinct geometries: firstly, a bilayer structure comprised of arrays of metallic crosses where the crosses in the second layer are twisted about the layer normal; and secondly where the second layer is replaced by the complementary to the original, i.e. an array of cross-shaped holes. Through numerical modelling we determine the origin of rotatory effects in these two structures. In both, pure optical rotation occurs in a frequency band between two transmission minima, where alignment of electric and magnetic dipole moments occurs. In the cross/cross metamaterial, the transmission minima occur at the symmetric and antisymmetric resonances of the coupled crosses. By contrast, in the cross/complementary-cross structure the transmission minima are associated with the dipole and quadrupole modes of the cross, the frequencies of which appear intrinsic to the cross layer alone. Hence the bandwidth of optical rotation is found to be relatively independent of layer separation.

  5. The Fraction of the Sun's Lifetime in a Grand Minimum State Estimated from Studies of Solar-Type Stars

    NASA Astrophysics Data System (ADS)

    Lubin, D.

    2011-12-01

    The Maunder Minimum is a key event in climate change research, (1) from the vantage point as a natural control experiment in which greenhouse gas (GHG) abundances were at a pre-industrial constant while solar forcing changed by a magnitude comparable to recent GHG increases, and (2) given recent interest and speculation that a similar grand minimum might occur later this century. To date, periodicity in solar grand minima has been difficult to detect in geophysical proxy data, and an alternative approach involves estimating the frequency of the Sun's lifetime spent in a grand minimum state by searching for evidence of grand minima in solar-type stars. Most often this is done by measuring Ca H and K flux as an indicator of chromospheric activity, or by photometric observations of solar cycles on decadal timescales. Early estimates of grand minimum frequency in solar type stars ranged from 10-30%. However, these early studies inadvertently included many stars that have evolved off the main sequence. This paper discusses how measurements of stellar Lithium abundance, and spectroscopically constrained metallicity, are used as additional constraints on age and main sequence membership, to refine detections of grand minima in solar-type stars. Based on the most recent studies, an estimate emerges of 5-6% for the fraction of the Sun's lifetime spent in a low-activity and reduced luminosity state analogous to the Maunder Minimum.

  6. Understanding diffusion and density anomaly in a coarse-grained model for water confined between hydrophobic walls.

    PubMed

    de los Santos, Francisco; Franzese, Giancarlo

    2011-12-01

    We study, by Monte Carlo simulations, a coarse-grained model of a water monolayer between hydrophobic walls at partial hydration, with a wall-to-wall distance of about 0.5 nm. We analyze how the diffusion constant parallel to the walls, D(∥), changes and correlates to the phase diagram of the system. We find a locus of D(∥) maxima and a locus of D(∥) minima along isotherms, with lines of constant D(∥) resembling the melting line of bulk water. The two loci of D(∥) extrema envelope the line of temperatures of density maxima at constant P. We show how these loci are related to the anomalous volume behavior due to the hydrogen bonds. At much lower T, confined water becomes subdiffusive, and we discuss how this behavior is a consequence of the increased correlations among water molecules when the hydrogen bond network develops. Within the subdiffusive region, although translations are largely hampered, we observe that the hydrogen bond network can equilibrate, and its rearrangement is responsible for the appearance of density minima along isobars. We clarify that the minima are not necessarily related to the saturation of the hydrogen bond network. PMID:22129131

  7. Hybridizing rapidly exploring random trees and basin hopping yields an improved exploration of energy landscapes.

    PubMed

    Roth, Christine-Andrea; Dreyfus, Tom; Robert, Charles H; Cazals, Frédéric

    2016-03-30

    The number of local minima of the potential energy landscape (PEL) of molecular systems generally grows exponentially with the number of degrees of freedom, so that a crucial property of PEL exploration algorithms is their ability to identify local minima, which are low lying and diverse. In this work, we present a new exploration algorithm, retaining the ability of basin hopping (BH) to identify local minima, and that of transition based rapidly exploring random trees (T-RRT) to foster the exploration of yet unexplored regions. This ability is obtained by interleaving calls to the extension procedures of BH and T-RRT, and we show tuning the balance between these two types of calls allows the algorithm to focus on low lying regions. Computational efficiency is obtained using state-of-the art data structures, in particular for searching approximate nearest neighbors in metric spaces. We present results for the BLN69, a protein model whose conformational space has dimension 207 and whose PEL has been studied exhaustively. On this system, we show that the propensity of our algorithm to explore low lying regions of the landscape significantly outperforms those of BH and T-RRT. PMID:26714673

  8. Energy landscape view of phase transitions and slow dynamics in thermotropic liquid crystals

    PubMed Central

    Chakrabarti, Dwaipayan; Bagchi, Biman

    2006-01-01

    Thermotropic liquid crystals are known to display rich phase behavior on temperature variation. Although the nematic phase is orientationally ordered but translationally disordered, a smectic phase is characterized by the appearance of a partial translational order in addition to a further increase in orientational order. In an attempt to understand the interplay between orientational and translational order in the mesophases that thermotropic liquid crystals typically exhibit upon cooling from the high-temperature isotropic phase, we investigate the potential energy landscapes of a family of model liquid crystalline systems. The configurations of the system corresponding to the local potential energy minima, known as the inherent structures, are determined from computer simulations across the mesophases. We find that the depth of the potential energy minima explored by the system along an isochor grows through the nematic phase as temperature drops in contrast to its insensitivity to temperature in the isotropic and smectic phases. The onset of the growth of the orientational order in the parent phase is found to induce a translational order, resulting in a smectic-like layer in the underlying inherent structures; the inherent structures, surprisingly, never seem to sustain orientational order alone if the parent nematic phase is sandwiched between the high-temperature isotropic phase and the low-temperature smectic phase. The Arrhenius temperature dependence of the orientational relaxation time breaks down near the isotropic–nematic transition. We find that this breakdown occurs at a temperature below which the system explores increasingly deeper potential energy minima. PMID:16648269

  9. Eclipsing Binaries: Precise Clocks to Detect Extrasolar Planets

    NASA Astrophysics Data System (ADS)

    Kundra, Emil; Pribulla, Theodor; Vaňko, Martin; Hambálek, Ľubomír

    2014-04-01

    Project Dwarf is a new observing campaign focused on the detection of substellar companions to low-mass (composed of late-type, subdwarf (sd) or/and white dwarf (WD) components) detached eclipsing binaries using minima timing. The crucial condition for the object selection for this campaign is possibility to determine times of the minima with high precision. This is naturally fullfilled for eclipsing binaries with deep and narrow minima or systems hosting a WD component showing fast ingress or egress. The observing project includes three groups of close eclipsing binaries indicating presence of substellar circum-binary components: (i) systems with K or/and M dwarf components (ii) systems with hot subdwarf (sd) and M dwarf components (iii) systems with white dwarf (WD) component(s). The sample of the eclipsing systems have orbital periods in range of 0.1 to almost 3 days and their brightness fits possibilities of small telescopes equipped with a low-end CCD camera and at least VRI filter set. Such kind of telescopes allow us to develop observing network including also amateur astronomers.

  10. Physical Properties and Evolution of the Eclipsing Binary System XZ Canis Minoris

    NASA Astrophysics Data System (ADS)

    Poochaum, R.; Komonjinda, S.; Soonthornthum, B.; Rattanasoon, S.

    2010-07-01

    This research aims to study the eclipse binary system so that its physical properties and evolution can be determined and used as an example to teach high school astronomy. The study of an eclipsing binary system XZ Canis Minoris (XZ CMi) was done at Sirindhorn Observatory, Chiang Mai University using a 0.5-meter reflecting telescope with CCD photometric system (2184×1417 pixel) in B V and R bands of UVB System. The data obtained were used to construct the light curve for each wavelength band and to compute the times of its light minima. New elements were derived using observations with linear to all available minima. As a result, linear ephemeris is HDJmin I = .578 808 948+/-0.000 000 121+2450 515.321 26+/-0.001 07 E, and the new orbital period of XZ CMi is 0.578 808 948+/-0.000 000 121 day. The values obtained were used with the previously published times of minima to get O-C curve of XZ CMi. The result revealed that the orbital period of XZ CMi is continuously decreased at a rate of 0.007 31+/-0.000 57 sec/year. This result indicates that the binary stars are moving closer continuously. From the O-C residuals, there is significant change to indicate the existence of the third body or magnetic activity cycle on the star. However, further analysis of the physical properties of XZ CMi is required.

  11. Stochastic differential equations as a tool to regularize the parameter estimation problem for continuous time dynamical systems given discrete time measurements.

    PubMed

    Leander, Jacob; Lundh, Torbjörn; Jirstrand, Mats

    2014-05-01

    In this paper we consider the problem of estimating parameters in ordinary differential equations given discrete time experimental data. The impact of going from an ordinary to a stochastic differential equation setting is investigated as a tool to overcome the problem of local minima in the objective function. Using two different models, it is demonstrated that by allowing noise in the underlying model itself, the objective functions to be minimized in the parameter estimation procedures are regularized in the sense that the number of local minima is reduced and better convergence is achieved. The advantage of using stochastic differential equations is that the actual states in the model are predicted from data and this will allow the prediction to stay close to data even when the parameters in the model is incorrect. The extended Kalman filter is used as a state estimator and sensitivity equations are provided to give an accurate calculation of the gradient of the objective function. The method is illustrated using in silico data from the FitzHugh-Nagumo model for excitable media and the Lotka-Volterra predator-prey system. The proposed method performs well on the models considered, and is able to regularize the objective function in both models. This leads to parameter estimation problems with fewer local minima which can be solved by efficient gradient-based methods. PMID:24631177

  12. Doping evolution of the superconducting gap structure in the underdoped iron arsenide Ba1 -xKxFe2As2 revealed by thermal conductivity

    NASA Astrophysics Data System (ADS)

    Reid, J.-Ph.; Tanatar, M. A.; Luo, X. G.; Shakeripour, H.; de Cotret, S. René; Juneau-Fecteau, A.; Chang, J.; Shen, B.; Wen, H.-H.; Kim, H.; Prozorov, R.; Doiron-Leyraud, N.; Taillefer, Louis

    2016-06-01

    The thermal conductivity κ of the iron-arsenide superconductor Ba1 -xKxFe2As2 was measured for heat currents parallel and perpendicular to the tetragonal c axis at temperatures down to 50 mK and in magnetic fields up to 15 T. Measurements were performed on samples with compositions ranging from optimal doping (x =0.34 , Tc=39 K) down to dopings deep into the region where antiferromagnetic order coexists with superconductivity (x =0.16 , Tc=7 K). In zero field, there is no residual linear term in κ (T ) as T →0 at any doping, whether for in-plane or interplane transport. This shows that there are no nodes in the superconducting gap. However, as x decreases into the range of coexistence with antiferromagnetism, the residual linear term grows more and more rapidly with applied magnetic field. This shows that the superconducting energy gap develops minima at certain locations on the Fermi surface and these minima deepen with decreasing x . We propose that the minima in the gap structure arise when the Fermi surface of Ba1 -xKxFe2As2 is reconstructed by the antiferromagnetic order.

  13. Transient accretion disc-like envelope in the symbiotic binary BF Cygni during its 2006-2015 optical outburst

    NASA Astrophysics Data System (ADS)

    Tomov, N. A.; Tomova, M. T.; Bisikalo, D. V.

    2015-09-01

    The optical light of the symbiotic binary BF Cyg during its last eruption after 2006 shows orbital variations because of an eclipse of the outbursting compact object. The first orbital minimum is deeper than the following ones. Moreover, the Balmer profiles of this system acquired additional satellite components indicating a bipolar collimated outflow at one time between the first and second orbital minima. This behaviour is interpreted in the framework of the model of a collimated stellar wind from the outbursting object. It is supposed that one extended disc-like envelope covering the accretion disc of the compact object and collimating its stellar wind forms in the period between the first and second minima. The uneclipsed part of this envelope is responsible for the decrease of the depth of the orbital minimum. The calculated U BVR_{ C}I_{ C} fluxes of this uneclipsed part are in agreement with the observed residual of the depths of the first and second orbital minima. The parameters of the envelope require that it is the main emitting region of the line Hα but the Hα profile is less determined from its rotation and mostly from other mechanisms. It is concluded that the envelope is a transient nebular region and its destruction determines the increase of the depth of the orbital minimum with fading of the optical light.

  14. Can cross sections be accurately known for priori?

    SciTech Connect

    Pigni,M.T.; Dietrich, F.S.; Herman, M.; Oblozinsky, P.

    2008-06-24

    Distinct maxima and minima in the neutron total cross section uncertainties were observed in our large scale covariance calculations using a spherical optical potential. In this contribution we investigate the physical origin of this oscillating structure. Specifically, we analyze the case of neutron reactions on {sup 56}Fe, for which total cross section uncertainties are characterized by the presence of five distinct minima at 0.1, 1.1, 5, 25, and 70 MeV. To investigate their origin, we calculated total cross sections by perturbing the real volume depth V{sub v} by its expected uncertainty {+-}{Delta}V{sub v}. Inspecting the effect of this perturbation on the partial wave cross sections we found that the first minimum (at 0.1 MeV) is exclusively due to the contribution of the s-wave. On the other hand, the same analysis at 1.1 MeV showed that the minimum is the result of the interplay between s-, p-, and d-waves; namely the change in the s-wave happens to be counterbalanced by changes in the p- and d-waves. Similar considerations can be extended for the third minimum, although it can be also explained in terms of the Ramsauer effect as well as the other ones (at 25 and 70 MeV). We discuss the potential importance of these minima for practical applications as well as the implications of this work for the uncertainties in total and absorption cross sections.

  15. The first orbital parameters and period variation of the short-period eclipsing binary AQ Boo

    NASA Astrophysics Data System (ADS)

    Wang, Shuai; Zhang, Liyun; Pi, Qingfeng; Han, Xianming L.; Zhang, Xiliang; Lu, Hongpeng; Wang, Daimei; Li, TongAn

    2016-10-01

    We obtained the first VRI CCD light curves of the short-period contact eclipsing binary AQ Boo, which was observed on March 22 and April 19 in 2014 at Xinglong station of National Astronomical Observatories, and on January 20, 21 and February 28 in 2015 at Kunming station of Yunnan Observatories of Chinese Academy of Sciences, China. Using our six newly obtained minima and the minima that other authors obtained previously, we revised the ephemeris of AQ Boo. By fitting the O-C (observed minus calculated) values of the minima, the orbital period of AQ Boo shows a decreasing tendency P˙ = - 1.47(0.17) ×10-7 days/year. We interpret the phenomenon by mass transfer from the secondary (more massive) component to the primary (less massive) one. By using the updated Wilson & Devinney program, we also derived the photometric orbital parameters of AQ Boo for the first time. We conclude that AQ Boo is a near contact binary with a low contact factor of 14.43%, and will become an over-contact system as the mass transfer continues.

  16. The semiannual variation of geomagnetic activity: Phases and profiles for 130 years of aa data

    NASA Astrophysics Data System (ADS)

    Cliver, E. W.; Kamide, Y.; Ling, A. G.

    2001-05-01

    We determined the phases of the maxima (spring, fall) and minima (summer, winter) in the curve of smoothed daily averages of the aa geomagnetic index, available from 1868-1998. The dates we obtained are consistent with the equinoctial hypothesis which has aberration-adjusted theoretical maxima on 25 March (experimentally determined to be 27 March) and 27 September (27 September) and minima on 26 June (26 June) and 26 December (27 December). We also show that the overall shape of the modulation curve throughout the year (broad minima, narrow peaks) bears greater fidelity (r = -0.96) to the solar declination D (the controlling angle for the seasonal variation under the equinoctial hypothesis) than to the solar B angle (r = 0.83; axial hypothesis) or the solar P angle (r = 0.80; Russell-McPherron effect). Lastly, a three-parameter fit of the smoothed annual variation of the aa data with a function consisting of the sum of the smoothed yearly curves for the D, B, and P angles yielded an amplitude of 0.58 for the D component vs. 0.20 for B and 0.16 for P. Generally similar results for each of these analyses (timing, shape, relative contributions) were obtained for shorter intervals of data for the ap and am indices. We conclude that the semiannual modulation of average values of mid-latitude range indices such as aa and ap is primarily controlled by the equinoctial hypothesis.

  17. Energy landscape exploration of sub-nanometre copper-silver clusters.

    PubMed

    Heard, Christopher J; Johnston, Roy L; Schön, J Christian

    2015-05-18

    The energy landscapes of sub-nanometre bimetallic coinage metal clusters are explored with the Threshold Algorithm coupled with the Birmingham Cluster Genetic Algorithm. Global and energetically low-lying minima along with their permutational isomers are located for the Cu(4)Ag(4) cluster with the Gupta potential and density functional theory (DFT). Statistical tools are employed to map the connectivity of the energy landscape and the growth of structural basins, while the thermodynamics of interconversion are probed, based on probability flows between minima. Asymmetric statistical weights are found for pathways across dividing states between stable geometries, while basin volumes are observed to grow independently of the depth of the minimum. The DFT landscape is found to exhibit significantly more frustration than that of the Gupta potential, including several open, pseudo-planar geometries which are energetically competitive with the global minimum. The differences in local minima and their transition barriers between the two levels of theory indicate the importance of explicit electronic structure for even simple, closed shell clusters. PMID:25784077

  18. The 17 GHz active region number

    SciTech Connect

    Selhorst, C. L.; Pacini, A. A.; Costa, J. E. R.; Giménez de Castro, C. G.; Valio, A.; Shibasaki, K.

    2014-08-01

    We report the statistics of the number of active regions (NAR) observed at 17 GHz with the Nobeyama Radioheliograph between 1992, near the maximum of cycle 22, and 2013, which also includes the maximum of cycle 24, and we compare with other activity indexes. We find that NAR minima are shorter than those of the sunspot number (SSN) and radio flux at 10.7 cm (F10.7). This shorter NAR minima could reflect the presence of active regions generated by faint magnetic fields or spotless regions, which were a considerable fraction of the counted active regions. The ratio between the solar radio indexes F10.7/NAR shows a similar reduction during the two minima analyzed, which contrasts with the increase of the ratio of both radio indexes in relation to the SSN during the minimum of cycle 23-24. These results indicate that the radio indexes are more sensitive to weaker magnetic fields than those necessary to form sunspots, of the order of 1500 G. The analysis of the monthly averages of the active region brightness temperatures shows that its long-term variation mimics the solar cycle; however, due to the gyro-resonance emission, a great number of intense spikes are observed in the maximum temperature study. The decrease in the number of these spikes is also evident during the current cycle 24, a consequence of the sunspot magnetic field weakening in the last few years.

  19. Conformational Characteristics of Poly(tetrafluoroethylene) (PTFE) Based Upon Ab Initio Electronic Structure Calculations on Model Molecules

    NASA Technical Reports Server (NTRS)

    Smith, Grant D.; Jaffe, R. L.; Yoon, D. Y.; Arnold, James O. (Technical Monitor)

    1994-01-01

    Conformational energy contours of perfluoroalkanes, determined from ab initio calculations, confirm the well-known spitting of trans states into two minima at plus or minus 17 degrees but also show that the gauche states split as well, with minima at plus or minus 124 degrees and plus or minus 84 in order to relieve steric crowding. The directions of such split distortions from the perfectly staggered states are strongly coupled for adjacent pairs of bonds in a manner identical to the intradyad pair for poly (isobutylene) chains. These conformational characteristics are fully represented by a six-state rotational isomeric state (RIS) model for PTFE comprised of t(+), t(-), g(sup +)+, g(sup +)-, g(sup -) + and g(sup -)-states, located at the split energy minima. The resultant 6 x 6 statistical weight matrix is described by first-order interaction parameters for the g+(+) (ca. 0.6 kcal/mol) and g+- (ca. 2.0 kcal/mol) states, and second order parameters for the g(sup +)+g(sup +)+ (ca 0.6 kcal/mol) and g(sup +)+g(sup -)+ (ca. 1.0 kcal/mol) states. This six-state RIS model, without adjustment of the geometric or energy parameters as determined from the ab initio calculations, predicts the unperturbed chain dimensions and the fraction of gauche bonds as a function of temperature for PTFE in good agreement with available experimental values.

  20. Recent X-ray Variability of eta Carinae: the Quick Road to Recovery

    NASA Technical Reports Server (NTRS)

    Corcoran, M. Francis; Hamaguchi, K.; Pittard, J. M.; Russell, C. M. P.; Owocki, S. P.; Parkin, E. R.; Okazaki, A.

    2010-01-01

    We report continued monitoring of the superluminous binary system eta Car by the Proportional Counter Array on the Rossi X-ray Timing Observatory (RXTE) through the 2009 X-ray minimum. The RXTE campaign shows that the minimum began on 2009 January 16, consistent with the phasings of the two previous minima, and overall, the temporal behavior of the X-ray emission was similar to that observed by RXTE in the previous two cycles. However, important differences did occur. The 2-10 keV X-ray flux and X-ray hardness decreased in the 2.5-year interval leading up to the 2009 minimum compared to the previous cycle. Most intriguingly, the 2009 X-ray minimum was about one month shorter than either of the previous two minima. During the egress from the 2009 minimum the X-ray hardness increased markedly as it had during egress from the previous two minima, although the maximum X-ray hardness achieved was less than the maximum observed after the two previous recoveries. We suggest that the cycle-to-cycle variations, especially the unexpectedly early recovery from the 2009 X-ray minimum, might have been the result of a decline in eta Car's wind momentum flux produced by a drop in eta Car's mass loss rate or wind terminal velocity (or some combination), though if so the change in wind momentum flux required to match the X-ray variation is surprisingly large.

  1. Spectral modulation effect in teleseismic P-waves from DPRK nuclear tests recorded at different azimuths

    NASA Astrophysics Data System (ADS)

    Gitterman, Yefim; Kim, So Gu; Hofstetter, Abraham

    2014-05-01

    Two underground nuclear explosions conducted by North Korea in 2009 and 2013 were recorded by the Israel Seismic Network. Pronounced coherent minima (spectral nulls) at 1.2-1.3 Hz were revealed in the spectra of teleseismic P-waves. For a ground-truth explosion with a shallow source depth (relatively to an earthquake), this phenomenon can be interpreted in terms of the interference between the down-going P-wave and the pP phase reflected from the Earth's surface. A similar effect was observed at ISN stations for the Pakistan nuclear explosion at a different frequency 1.7 Hz indicating a source and not site-effect. Similar spectral minima with about the same frequency were observed in teleseismic P-waves of all three North Korea explosions (including the 2006 test) recorded at network stations and arrays in Kazakhstan (KURK), Norway (NORESS, ARCESS), Australia (Alice Springs, Warramunga) and Canada (Yellowknife), covering a broad azimuthal range. Data of the 2013 test at Warramunga array showed harmonic spectral modulation with several minima, evidencing a clear interference effect. These observations support the above-mentioned interpretation. Based on the null frequency dependency on the near-surface acoustic velocity and the source depth, the depth of the North Korea tests was estimated as ~2 km (different from the value ~1 km reported by USGS for the third test). This unusual depth estimation needs an additional validation based on more stations and verification by other methods.

  2. On the origin of pure optical rotation in twisted-cross metamaterials

    PubMed Central

    Barr, Lauren E.; Díaz-Rubio, Ana; Tremain, Ben; Carbonell, Jorge; Sánchez-Dehesa, José; Hendry, Euan; Hibbins, Alastair P.

    2016-01-01

    We present an experimental and computational study of the response of twisted-cross metamaterials that provide near dispersionless optical rotation across a broad band of frequencies from 19 GHz to 37 GHz. We compare two distinct geometries: firstly, a bilayer structure comprised of arrays of metallic crosses where the crosses in the second layer are twisted about the layer normal; and secondly where the second layer is replaced by the complementary to the original, i.e. an array of cross-shaped holes. Through numerical modelling we determine the origin of rotatory effects in these two structures. In both, pure optical rotation occurs in a frequency band between two transmission minima, where alignment of electric and magnetic dipole moments occurs. In the cross/cross metamaterial, the transmission minima occur at the symmetric and antisymmetric resonances of the coupled crosses. By contrast, in the cross/complementary-cross structure the transmission minima are associated with the dipole and quadrupole modes of the cross, the frequencies of which appear intrinsic to the cross layer alone. Hence the bandwidth of optical rotation is found to be relatively independent of layer separation. PMID:27457405

  3. SOLAR ROTATION RATE DURING THE CYCLE 24 MINIMUM IN ACTIVITY

    SciTech Connect

    Antia, H. M.; Basu, Sarbani E-mail: sarbani.basu@yale.ed

    2010-09-01

    The minimum of solar cycle 24 is significantly different from most other minima in terms of its duration as well as its abnormally low levels of activity. Using available helioseismic data that cover epochs from the minimum of cycle 23 to now, we study the differences in the nature of the solar rotation between the minima of cycles 23 and 24. We find that there are significant differences between the rotation rates during the two minima. There are differences in the zonal-flow pattern too. We find that the band of fast rotating region close to the equator bifurcated around 2005 and recombined by 2008. This behavior is different from that during the cycle 23 minimum. By autocorrelating the zonal-flow pattern with a time shift, we find that in terms of solar dynamics, solar cycle 23 lasted for a period of 11.7 years, consistent with the result of Howe et al. (2009). The autocorrelation coefficient also confirms that the zonal-flow pattern penetrates through the convection zone.

  4. Characteristics of Solar Meridional Flows during Solar Cycle 23

    NASA Astrophysics Data System (ADS)

    Basu, Sarbani; Antia, H. M.

    2010-07-01

    We have analyzed available full-disk data from the Michelson Doppler Imager on board SOHO using the "ring diagram" technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius. We find that the dominant component of meridional flows during solar maximum was much lower than that during the minima at the beginning of cycles 23 and 24. There were differences in the flow velocities even between the two minima. The meridional flows show a migrating pattern with higher-velocity flows migrating toward the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of sunspot butterfly diagram and the zonal flows in the shallow layers. A high-latitude band in meridional flow appears around 2004, well before the current activity minimum. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that during the two minima. The different components of the flow have different time dependences, and the dependence is different at different depths.

  5. Anomalies in high-order harmonic generation at relativistic intensities

    SciTech Connect

    Teubner, U.; Foerster, E.; Pretzler, G.; Eidmann, K.; Witte, K.; Schlegel, Th.

    2003-01-01

    High-order harmonic generation from a solid target surface has been investigated using femtosecond laser pulses focused to intensities greater than 10{sup 18} W/cm{sup 2}. The experiments show that the harmonics are very intense, with a conversion efficiency that is one or two orders of magnitude larger than that of harmonics generated in gases. Beside the observation of presently the shortest wavelength harmonics from femtosecond-laser solid target interaction, i.e., down to 22 nm, an anomaly has been observed in the harmonic spectrum. In contrast to the expected well-known continuous 'roll off' of the high-harmonic orders, the harmonic intensity decreases with the increase of harmonic order, but in between shows minima which are significantly less intense than the neighboring harmonics. Furthermore, the order of the harmonic minima depend on target material. Additional calculations using numerical kinetic particle simulations and a simpler oscillating mirror model show that the physical origin of these modulations is an intricate interplay of resonance absorption and ponderomotive force which leads to a complex electron density profile evolution. Furthermore, this is emphasized by a spectral line analysis of the harmonics. In agreement with the theory, broad lines have been observed and, in particular for the harmonics in the minima, a complex interference structure is present.

  6. Ab Initio and Analytic Intermolecular Potentials for Ar–CH3OH

    SciTech Connect

    Tasic, Uros; Alexeev, Yuri; Vayner, Grigoriy; Crawford, T Daniel; Windus, Theresa L.; Hase, William L.

    2006-09-20

    Ab initio calculations at the CCSD(T)/aug-cc-pVTZ level of theory were used to characterize the Ar–CH₃y6tOH intermolecular potential energy surface (PES). Potential energy curves were calculated for four different Ar + CH₃OH orientations and used to derive an analytic function for the intermolecular PES. A sum of Ar–C, Ar–O, Ar–H(C), and Ar–H(O) two-body potentials gives an excellent fit to these potential energy curves up to 100 kcal mol¯¹, and adding an additional r¯¹n term to the Buckingham two-body potential results in only a minor improvement in the fit. Three Ar–CH₃OH van der Waals minima were found from the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ calculations. The structure of the global minimum is in overall good agreement with experiment (X.-C. Tan, L. Sun and R. L. Kuczkowski, J. Mol. Spectrosc., 1995, 171, 248). It is T-shaped with the hydroxyl H-atom syn with respect to Ar. Extrapolated to the complete basis set (CBS) limit, the global minimum has a well depth of 0.72 kcal mol¯¹ with basis set superposition error (BSSE) correction. The aug-cc-pVTZ basis set gives a well depth only 0.10 kcal mol¯¹ smaller than this value. The well depths of the other two minima are within 0.16 kcal mol¯¹ of the global minimum. The analytic Ar–CH₃OH intermolecular potential also identifies these three minima as the only van der Waals minima and the structures predicted by the analytic potential are similar to the ab initio structures. The analytic potential identifies the same global minimum and the predicted well depths for the minima are within 0.05 kcal mol¯1 of the ab initio values. Combining this Ar–CH₃OH intermolecular potential with a potential for a OH-terminated alkylthiolate self-assembled monolayer surface (i.e., HO-SAM) provides a potential to model Ar + HO-SAM collisions.

  7. Understanding density functional theory (DFT) and completing it in practice

    SciTech Connect

    Bagayoko, Diola

    2014-12-15

    We review some salient points in the derivation of density functional theory (DFT) and of the local density approximation (LDA) of it. We then articulate an understanding of DFT and LDA that seems to be ignored in the literature. We note the well-established failures of many DFT and LDA calculations to reproduce the measured energy gaps of finite systems and band gaps of semiconductors and insulators. We then illustrate significant differences between the results from self consistent calculations using single trial basis sets and those from computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Unlike the former, the latter calculations verifiably attain the absolute minima of the occupied energies, as required by DFT. These minima are one of the reasons for the agreement between their results and corresponding, experimental ones for the band gap and a host of other properties. Further, we note predictions of DFT BZW-EF calculations that have been confirmed by experiment. Our subsequent description of the BZW-EF method ends with the application of the Rayleigh theorem in the selection, among the several calculations the method requires, of the one whose results have a full, physics content ascribed to DFT. This application of the Rayleigh theorem adds to or completes DFT, in practice, to preserve the physical content of unoccupied, low energy levels. Discussions, including implications of the method, and a short conclusion follow the description of the method. The successive augmentation of the basis set in the BZW-EF method, needed for the application of the Rayleigh theorem, is also necessary in the search for the absolute minima of the occupied energies, in practice.

  8. Seasonal variations in 35S and Δ17O of sulfate aerosols on the Antarctic plateau

    NASA Astrophysics Data System (ADS)

    Hill-Falkenthal, Jason; Priyadarshi, Antra; Savarino, Joel; Thiemens, Mark

    2013-08-01

    The first reported seasonal Δ17O anomaly in sulfate aerosols and measurements of radioactive 35SO42- activities collected from Dome C, Antarctica, are reported. Δ17O values exhibit minima during summer (as low as 0.91‰) when tropospheric oxidation patterns are dominated by OH/H2O2 mechanisms. Significant enrichment during autumn and spring is observed (up to 2.40‰) as ozone oxidation increases in the troposphere relative to summer and both stratospheric sources and long-range transport become more significant to the total sulfate budget. An unexpected decrease in Δ17O is seen as winter progresses. This decline is concluded to potentially arise due to a reduction in vertical mixing in the troposphere or linked to variations in the long-range transport of sulfur species to Antarctica. 35SO42- activities exhibit maxima during summer (up to 1219 atoms 35S/m3) that correlate with the peak in stratospheric flux and minima during winter (as low as 146 atoms 35S/m3) when the lack of solar radiation substantially reduces photochemical activity. It is shown that 35S offers the potential to be used as an additional tracer to study stratospheric and tropospheric interactions and is used to estimate stratospheric input of sulfur (combination of SO2 and SO42-). Stratospheric sulfur input produces maxima during summer/autumn with an upper limit of 5.5 ng/m3 and minima during winter/spring with an upper limit of 1.1 ng/m3. From these results, it is concluded that the variation in Δ17O is more reliant upon shifts in tropospheric oxidation mechanisms and long-range transport than on changes in the stratospheric flux.

  9. On the Current Solar Magnetic Activity using Its Behavior During the Holocene

    NASA Astrophysics Data System (ADS)

    Inceoglu, Fadil; Simoniello, Rosaria; Faurschou Knudsen, Mads; Karoff, Christoffer; Olsen, Jesper; Turck-Chieze, Sylvaine

    2016-07-01

    Solar modulation potential (SMP) reconstructions based on cosmogenic nuclide records reflect changes in the open solar magnetic field and can therefore help us obtain information on the behavior of the open solar magnetic field over the Holocene period. Using the Greenland Ice Core Project (GRIP) ^{10}Be and IntCal13 ^{14}C records for the overlapping time period spanning between ˜1650 AD to 6600 BC, we first reconstructed the solar modulation potentials and subsequently investigate the statistics of peaks and dips simultaneously occurring in the two SMP reconstructions. Based on the distribution of these events, we propose a method to identify grand minima and maxima periods. We then aim at comparing the Sun's large-scale magnetic field behavior over the last three solar cycles with variations in the SMP reconstruction through the Holocene epoch. To achieve these objectives, we use the IntCal13 ^{14}C data to investigate distinct patterns in the occurrences of grand minima and maxima during the Holocene period. We then check whether these patterns might mimic the recent solar magnetic activity by investigating the evolution of the energy in the Sun's large-scale dipolar magnetic field using the Wilcox Solar Observatory data. The cosmogenic radionuclide data analysis shows that ˜71 % of grand maxima during the period from 6600 BC to 1650 AD were followed by a grand minimum. The characteristics of the occurrences of grand maxima and minima are consistent with the scenario in which the dynamical non-linearity induced by the Lorentz force leads the Sun to act as a relaxation oscillator. This finding implies that the probability for these events to occur is non-uniformly distributed in time, as there is a memory in their driving mechanism, which can be identified via the back-reaction of the Lorentz force.

  10. Past paleoclimatic changes, origin and prediction

    NASA Astrophysics Data System (ADS)

    Mörner, N.-A.; Nevanlinna, H.; Shumilov, O.

    2003-04-01

    In north-western to western Europe, short periods of cold climate are recorded in the decades of 1440-1460, 1687-1703 and 1808-1821. This fits reasonably well with periods of sunspot minima; viz. the Spörer (1420-1500), Maunder (1645-1705) and Dalton (1800-1820) Minima, and a causal connection has been advocated. During these minima, Earth’s rotation experienced a speeding-up leading to a changed ocean circulation pulling down cold Arctic water along the European coasts and concentrating the hot Gulf Stream to the south European region (Mörner, 1995). Via the recording of past changes in aurora frequency and the relation between sunspot activity and aurora frequency, the sunspot activity can be approximated for 1500-2000 years. Even for this period, there seems to be a reasonable correlation between sunspot activity and recorded changes in climate. The combined Schwabe-Gleisberg sunspot cycles provide good correlation with observed changes in climate for the last 300-400 years (Shumilov). The phase of the sunspot cycles and global climate for the period 1860 to 1985 fit exceptionally well (Friis-Christensen &Lassen, 1991). The aa-index and climate fit well for the last 150 years all the way up to 1985 (Pulkkinen et al., 2001). If we extrapolate the combined Schwabe-Gleisberg cycles or the aa-index curve, a new period of cold climate is to be expected in AD 2050-2100. This fact has not yet been included in the IPCC scenarios on future changes in climate, and is quite contrary to their main conclusions.

  11. Global triplet potential energy surfaces for the N2(X(1)Σ) + O((3)P) → NO(X(2)Π) + N((4)S) reaction.

    PubMed

    Lin, Wei; Varga, Zoltan; Song, Guoliang; Paukku, Yuliya; Truhlar, Donald G

    2016-01-14

    This work presents two global triplet potential energy surfaces (PESs) for the high-energy reaction N2(X(1)Σ) + O((3)P) → NO(X(2)Π) + N((4)S)-in particular, for the lowest energy (3)A' and (3)A″ PESs. In order to obtain the energies needed for fitting analytic surfaces, we carried out multireference configuration interaction (MRCI) calculations based on wave functions obtained from state-averaged complete active space self-consistent field calculations for 2280 geometries for the three lowest (3)A″ states and for 2298 geometries for the three lowest (3)A' states. The lowest-energy (3)A' and (3)A″ states at each of these geometries were then improved by applying the dynamically scaled external correlation (DSEC) method to all MRCI points, and the resulting DSEC energies were used for construction of the ground-state PES for each symmetry. The many-body component of the DSEC energies for the three-dimensional (3)A' and (3)A″ PESs was then least-squares fitted in terms of permutationally invariant polynomials in mixed exponential-Gaussian bond order variables. The global and local minima as well as the transition structures of both the (3)A' and the (3)A″ analytic PES were explored. In agreement with previous work, we find that the reverse reaction is barrierless on the (3)A″ surface along the minimum energy pathway. However, we have explored several new local minima and transition structures on the (3)A' PES. Furthermore, based on the newly found minima and transition structures, two independent reaction mechanisms have been illustrated for the reaction path on the (3)A' PES. The analytic surfaces may be used for dynamics calculations of electronically adiabatic reactive scattering and energy transfer. PMID:26772573

  12. Ground-based detectability of terrestrial and Jovian extrasolar planets: observations of CM Draconis at Lick Observatory

    NASA Technical Reports Server (NTRS)

    Doyle, L. R.; Dunham, E. T.; Deeg, H. J.; Blue, J. E.; Jenkins, J. M.

    1996-01-01

    The detection of terrestrial-sized extrasolar planets from the ground has been thought to be virtually impossible due to atmospheric scintillation limits. However, we show that this is not the case especially selected (but nevertheless main sequence) stars, namely small eclipsing binaries. For the smallest of these systems, CM Draconis, several months to a few years of photometric observations with 1-m-class telescopes will be sufficient to detect the transits of any short-period planets of sizes > or = 1.5 Earth radii (RE), using cross-correlation analysis with moderately good photometry. Somewhat larger telescopes will be needed to extend this detectability to terrestrial planets in larger eclipsing binary systems. (We arbitrarily define "terrestrial planets" herein as those whose disc areas are closer to that of Earth's than Neptune's i.e., less than about 2.78 RE.) As a "spin-off" of such observations, we will also be able to detect the presence of Jovian-mass planets without transits using the timing of the eclipse minima. Eclipse minima will drift in time as the binary system is offset by a sufficiently massive planet (i.e., one Jupiter mass) about the binary/giant-planet barycenter, causing a periodic variation in the light travel time to the observer. We present here an outline of present observations taking place at the University of California Lick Observatory using the Crossley 0.9-m telescope in collaboration with other observatories (in South Korea, Crete, France, Canary Islands, and New York) to detect or constrain the existence of terrestrial planets around main sequence eclipsing binary star systems, starting with CM Draconis. We demonstrate the applicability of photometric data to the general detection of gas giant planets via eclipse minima timings in many other small-mass eclipsing binary systems as well.

  13. Nuclear energy surfaces at high-spin in the A{approximately}180 mass region

    SciTech Connect

    Chasman, R.R.; Egido, J.L.; Robledo, L.M.

    1995-08-01

    We are studying nuclear energy surfaces at high spin, with an emphasis on very deformed shapes using two complementary methods: (1) the Strutinsky method for making surveys of mass regions and (2) Hartree-Fock calculations using a Gogny interaction to study specific nuclei that appear to be particularly interesting from the Strutinsky method calculations. The great advantage of the Strutinsky method is that one can study the energy surfaces of many nuclides ({approximately}300) with a single set of calculations. Although the Hartree-Fock calculations are quite time-consuming relative to the Strutinsky calculations, they determine the shape at a minimum without being limited to a few deformation modes. We completed a study of {sup 182}Os using both approaches. In our cranked Strutinsky calculations, which incorporate a necking mode deformation in addition to quadrupole and hexadecapole deformations, we found three well-separated, deep, strongly deformed minima. The first is characterized by nuclear shapes with axis ratios of 1.5:1; the second by axis ratios of 2.2:1 and the third by axis ratios of 2.9:1. We also studied this nuclide with the density-dependent Gogny interaction at I = 60 using the Hartree-Fock method and found minima characterized by shapes with axis ratios of 1.5:1 and 2.2:1. A comparison of the shapes at these minima, generated in the two calculations, shows that the necking mode of deformation is extremely useful for generating nuclear shapes at large deformation that minimize the energy. The Hartree-Fock calculations are being extended to larger deformations in order to further explore the energy surface in the region of the 2.9:1 minimum.

  14. Characterization of Rhynchosia yellow mosaic Yucatan virus, a new recombinant begomovirus associated with two fabaceous weeds in Yucatan, Mexico.

    PubMed

    Hernández-Zepeda, C; Brown, J K; Moreno-Valenzuela, O A; Argüello-Astorga, G; Idris, A M; Carnevali, G; Rivera-Bustamante, R F

    2010-10-01

    Rhynchosia minima (L.) DC. (Fabaceae) plants exhibiting bright golden mosaic symptoms were previously associated with begomovirus infection in Yucatan, México [1]. To characterize the begomovirus infecting these plants, the complete bipartite genome was cloned and sequenced. Sequence comparisons indicated that the virus was distinct from all other begomoviruses known to date, including those previously identified from symptomatic R. minima, and the name Rhynchosia yellow mosaic Yucatan virus (RhYMYuV) is proposed. Pairwise comparisons indicated that RhYMYuV DNA-A [2,597 nt, (EU021216)] and DNA-B [2,542 nt, (FJ792608)] components shared the highest nt sequence identity with Cabbage leaf curl virus (CaLCuV), 87% for component A and 71% for component B. Phylogenetic analysis indicated that both components of RhYMYuV are most closely related to other New World begomoviruses, having as closest relatives immediate outliers to the major Squash leaf curl virus (SLCV) clade. Recombination analysis of the RhYMYuV genome indicated that the DNA-A component has arisen through intermolecular recombination. R. minima plants inoculated with the monomeric clones developed a bright yellow mosaic similar to symptoms observed in naturally infected plants, confirming that the clones were infectious. Nicotiana benthamiana plants biolistically inoculated with monomeric clones developed curling and chlorosis in the newly emerging leaves. RhYMYuV was also detected in symptomatic Desmodium sect. Scorpiurus Benth. (Fabaceae) that were collected near the RhYMYuV-infected plants. PMID:20574644

  15. Detailed Structure of the Tropical Upper Troposphere and Lower Stratosphere as Revealed by Balloon Sonde Observations of Water Vapor, Ozone, Temperature, and Winds During the NASA TCSP and TC4 Campaigns

    NASA Technical Reports Server (NTRS)

    Selkirk, Henry B.; Vomel, Holger; Canossa, Jessica Maria Valverde; Pfister, Leonhard; Diaz, Jorge Andres; Fernandez, Walter; Amador, Jorge; Stolz, Werner; Peng, Grace S.

    2010-01-01

    We report on balloon sonde measurements of water vapor and ozone using the cryogenic frost point hygrometer and electrochemical concentration cell ozonesondes made at Alajuela, Costa Rica (10.0 N, 84.2 W) during two NASA airborne campaigns: the Tropical Convective Systems and Processes (TCSP) mission in July 2005 and the Tropical Composition, Clouds, and Climate Coupling Experiment (TC4), July - August 2007. In both campaigns we found an upper troposphere that was frequently supersaturated but no evidence that deep convection had reached the tropopause. The balloon sondes were complemented by campaigns of 4 times daily high-resolution radiosondes from mid-June through mid-August in both years. The radiosonde data reveal vertically propagating equatorial waves that caused a large increase in the variability of temperature in the tropical tropopause layer (TTL). These waves episodically produced cold point tropopauses (CPTs) above 18 km, yet in neither campaign was saturation observed above approx 380 K or 17 km. The averages of the water vapor minima below this level were 5.2 ppmv in TCSP and 4.8 ppmv in TC4, and the individual profile minima all lay at or above approx 360 K. The average minima in this 360 C380 K layer provide a better estimate of the effective stratospheric entry value than the average mixing ratio at the CPT. We refer to this upper portion of the TTL as the tropopause saturation layer and consider it to be the locus of the final dehydration of nascent stratospheric air. As such, it is the local equivalent to the tape head of the water vapor tape recorder.

  16. Agroecological factors correlated to soil DNA concentrations of Rhizoctonia in dryland wheat production zones of Washington state, USA.

    PubMed

    Okubara, Patricia A; Schroeder, Kurtis L; Abatzoglou, John T; Paulitz, Timothy C

    2014-07-01

    The necrotrophic soilborne fungal pathogens Rhizoctonia solani AG8 and R. oryzae are principal causal agents of Rhizoctonia root rot and bare patch of wheat in dryland cropping systems of the Pacific Northwest. A 3-year survey of 33 parcels at 11 growers' sites and 60 trial plots at 12 Washington State University cereal variety test locations was undertaken to understand the distribution of these pathogens. Pathogen DNA concentrations in soils, quantified using real-time polymerase chain reaction, were correlated with precipitation, temperature maxima and minima, and soil texture factors in a pathogen-specific manner. Specifically, R. solani AG8 DNA concentration was negatively correlated with precipitation and not correlated with temperature minima, whereas R. oryzae concentration was correlated with temperature minima but not with precipitation. However, both pathogens were more abundant in soils with higher sand and lower clay content. Principal component analysis also indicated that unique groups of meteorological and soil factors were associated with each pathogen. Furthermore, tillage did not affect R. oryzae but affected R. solani AG8 at P = 0.06. Lower soil concentrations of R. solani AG8 but not R. oryzae occurred when the previously planted crop was a broadleaf (P < 0.05). Our findings showed that R. solani AG8 concentrations were consistent with the general distribution of bare patch symptoms, based on field observations and surveys of other pathogens, but was present at many sites in which bare patch symptoms were not evident. Management of Rhizoctonia root rot and bare patch should account for the likelihood that each pathogen is affected by a unique group of agroecological variables. PMID:24915426

  17. Rivaling the World's Smallest Reptiles: Discovery of Miniaturized and Microendemic New Species of Leaf Chameleons (Brookesia) from Northern Madagascar

    PubMed Central

    Glaw, Frank; Köhler, Jörn; Townsend, Ted M.; Vences, Miguel

    2012-01-01

    Background One clade of Malagasy leaf chameleons, the Brookesia minima group, is known to contain species that rank among the smallest amniotes in the world. We report on a previously unrecognized radiation of these miniaturized lizards comprising four new species described herein. Methodology/Principal Findings The newly discovered species appear to be restricted to single, mostly karstic, localities in extreme northern Madagascar: Brookesia confidens sp. n. from Ankarana, B. desperata sp. n. from Forêt d'Ambre, B. micra sp. n. from the islet Nosy Hara, and B. tristis sp. n. from Montagne des Français. Molecular phylogenetic analyses based on one mitochondrial and two nuclear genes of all nominal species in the B. minima group congruently support that the four new species, together with B. tuberculata from Montagne d'Ambre in northern Madagascar, form a strongly supported clade. This suggests that these species have diversified in geographical proximity in this small area. All species of the B. minima group, including the four newly described ones, are characterized by very deep genetic divergences of 18–32% in the ND2 gene and >6% in the 16S rRNA gene. Despite superficial similarities among all species of this group, their status as separate evolutionary lineages is also supported by moderate to strong differences in external morphology, and by clear differences in hemipenis structure. Conclusion/Significance The newly discovered dwarf chameleon species represent striking cases of miniaturization and microendemism and suggest the possibility of a range size-body size relationship in Malagasy reptiles. The newly described Brookesia micra reaches a maximum snout-vent length in males of 16 mm, and its total length in both sexes is less than 30 mm, ranking it among the smallest amniote vertebrates in the world. With a distribution limited to a very small islet, this species may represent an extreme case of island dwarfism. PMID:22348069

  18. The shallow donor wavefunction in Si: Corrections to the KL effective mass theory (EMT)

    NASA Astrophysics Data System (ADS)

    Castner, Theodore

    2007-03-01

    The ENDOR data of Hale & Mieher^1 (HM) provides detailed information on &*circ;ψ(Rnnm) at nearly 25 lattice sites for P, As, & Sb. Ivey & Mieher^2(IM) have given the most comprehensive calculation of ψ(r)= σA(k)uk(r)e^ik.r featuring a complex A(k) (and uk(r)) and higher conduction bands. IM could identify most of the sites and reduce the rms error between theory values and experimental results from 60% to 11%. However, the IM results are poor for the (1,1,1) site [shell E] and don't provide clear evidence for subsidiary minima^3 (L1,γ2^ ') from their region IV in the BZ. A reliable calculation of matrix elements is difficult because of the complicated core potential in the central cell. Using the equidistant matched lattice pair data [(3,3,3) & (1,1,5); shells C and Q] provides a good estimate of the % admixture from the L1 minima, somewhat smaller than in [3]. The IM ImA(k) and the L1 minima both provide corrections to the uniaxial strain id parameter^ 4. A data analysis for the odd lattice sites improves the agreement between theory and experiment. Important remaining theoretical issues will be discussed and new ENDOR experiments will be proposed. The corrections to EMT are important, but are smaller than implied in IM. 1) E.B. Hale & R.M. Mieher, Phys.Rev.184, 739, 751 (1969). 2) J.L. Ivey & R.M. Mieher, Phys.Rev.B11, 822 (1975). 3) T.G. Castner, Phys.Rev.B2, 4911 (1970). 4) E.B. Hale & T.G. Castner, Phys.Rev.B1, 4763 (1970).

  19. Secular variation of the aurora for the past 500 years

    SciTech Connect

    Silverman, S.M. )

    1992-11-01

    Direct observations of the Sun exist only since about 1700. Understanding of long-term solar variability thus depends on proxy data, such as visual auroral observations, measurements of magnetic activity, and the radiocarbon record. These also give information on the interaction between the solar wind, interplanetary field, and terrestrial magnetosphere, as well as, for the radiocarbon record, heliospheric conditions. This paper uses a data base of visual auroral observations for a period of about 500 years, from 1450 to 1948, comprising about 45,000 observations, in addition to the well-known sunspot series and the magnetic activity index [ital aa], from 1868 to 1990. The secular variation of the aurora is examined and compared to sunspot data and magnetic activity data. Blackman-Tukey power spectra are used to determine periodicities. The study confirms the variability of the periodicities in frequency and amplitude. The 11.1-year cycle disappears during the Mounder minimum and at the end of the eighteenth and beginning of the nineteenth century. While the 11.1-year period is normally strongly dominant for sunspots, other shorter periods become important for auroras and magnetic activity. Prolonged solar activity minima are clearly evident. In addition to the known Sporer, Mounder, Dalton, and 1901-1913 minima, a previously unrecognized minimum about 1765 is clearly evident in the data. Comparison of the depth of these minima shows that the Dalton minimum may rival the Mounder minimum in importance. Combining the polar data base with that of mid-latitudes provides a globally comprehensive historical record of auroral occurrence. The data provide confirmation of the anticorrelation of auroral occurrence in the polar regions with sunspot activity. The data provide a basis for understanding the variation over time of the general magnetic field of the Sun, in particular the polar field. 59 refs., 29 figs.

  20. Phenylacetylene-water complex: Is it n⋯σ or H⋯π in the matrix?

    NASA Astrophysics Data System (ADS)

    Karir, Ginny; Viswanathan, K. S.

    2016-03-01

    Hydrogen bonded complexes of phenylacetylene (PhAc) and water were studied using matrix isolation infrared spectroscopy and ab initio computations. In this work, we have for the first time identified the n⋯σ complex, in N2 and Ar matrixes. Earlier experiments on the PhAc-H2O system, using molecular beams, had observed only the H⋯π complex, where H2O was the proton donor to the acetylenic π cloud of PhAc, and which was indicated by computations, to be the global minimum. Computations also located two other minima on the PhAc-H2O potential surface. The technique of matrix isolation, which is known to trap local minima, was used to investigate the PhAc-H2O system, in an attempt to observe any of the local minima, which were not observed in the gas phase experiments. Our experiments, using both Ar and N2 matrixes, provided unambiguous evidence for the formation of the n⋯σ complex, a local minimum. Experiments with D2O and phenylacetylene deuterated at the acetylenic hydrogen (PhAcD) were also performed, to confirm the above observation, through the isotopic effect. Rather surprisingly, we were unable to observe any evidence for the global minimum in these experiments. The phenylacetylene-water system was theoretically investigated, employing MP2 and DFT (B3LYP, M06-2X, ωB97XD) methods, with 6-311++G** and aug/cc-pVDZ basis sets. AIM, EDA and NBO analysis were also performed to explore the nature, physical origin and the strength of noncovalent interactions.

  1. Latitudinal Dependence of Coronal Hole-Associated Fast Solar Wind

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Landi, E.

    2014-05-01

    The fast solar wind can have at least two different coronal sources: high-latitude, polar coronal holes (PCH) and low-latitude, equatorial coronal holes (ECH). The in-situ differences in the PCH and ECH winds have not been well studied, nor have the differences in their evolution over the solar cycles. Ulysses' 19 years of observations from 1990 to 2009, combined with ACE observations from 1998 to the present, provide us with measurements of solar wind properties that span two entire solar cycles, which allow us to study the in-situ properties and evolution of the coronal hole-associated solar wind at different latitudes. In this work, we focus on the PCH and ECH solar winds during the minima between solar cycles 22-23 and 23-24. We use data from SWICS, SWOOPS, and VHM/FGM on board Ulysses, and SWICS, SWEPAM, and MAG on board ACE to analyze the proton dynamics, heavy ion composition, elemental abundance, and magnetic field properties of the PCH wind and ECH wind, with a special focus on their differences during the recent two solar minima. We also include the slow and hot, streamer-associated (ST) wind as a reference in the comparison. The comparison of PCH and ECH wind shows that: 1) the in-situ properties of ECH and PCH winds are significantly different during the two solar minima, and 2) the two types of coronal hole-associated solar wind respond differently to changes in solar activity strength from cycle 23 to cycle 24.

  2. Evolution of dark state of an open atomic system in constant intensity laser field

    SciTech Connect

    Krmpot, A. J.; Radonjic, M.; Cuk, S. M.; Nikolic, S. N.; Grujic, Z. D.; Jelenkovic, B. M.

    2011-10-15

    We studied experimentally and theoretically the evolution of open atomic systems in the constant intensity laser field. The study is performed by analyzing the line shapes of Hanle electromagnetically induced transparency (EIT) obtained in different segments of a laser beam cross section of constant intensity, i.e., a {Pi}-shaped laser beam. Such Hanle EIT resonances were measured using a small movable aperture placed just in front of the photodetector, i.e., after the entire laser beam had passed through the vacuum Rb cell. The laser was locked to the open transition F{sub g}=2{yields}F{sub e}=1 at the D{sub 1} line of {sup 87}Rb with laser intensities between 0.5 and 4 mW/cm{sup 2}. This study shows that the profile of the laser beam determines the processes governing the development of atomic states during the interaction. The resonances obtained near the beam center are narrower than those obtained near the beam edge, but the significant changes of the linewidths occur only near the beam edge, i.e., right after the atom enters the beam. The Hanle EIT resonances obtained near the beam center exhibit two pronounced minima next to the central maximum. The theoretical model reveals that the occurrence of these transmission minima is a joint effect of the preparation of atoms into the dark state and the optical pumping into the uncoupled ground level F{sub g}=1. The appearance of the transmission minima, although similar to that observed in the wings of a Gaussian beam [A. J. Krmpot et al., Opt. Express 17, 22491 (2009)], is of an entirely different nature for the {Pi}-shaped laser beam.

  3. Design and implementation of non-linear image processing functions for CMOS image sensor

    NASA Astrophysics Data System (ADS)

    Musa, Purnawarman; Sudiro, Sunny A.; Wibowo, Eri P.; Harmanto, Suryadi; Paindavoine, Michel

    2012-11-01

    Today, solid state image sensors are used in many applications like in mobile phones, video surveillance systems, embedded medical imaging and industrial vision systems. These image sensors require the integration in the focal plane (or near the focal plane) of complex image processing algorithms. Such devices must meet the constraints related to the quality of acquired images, speed and performance of embedded processing, as well as low power consumption. To achieve these objectives, low-level analog processing allows extracting the useful information in the scene directly. For example, edge detection step followed by a local maxima extraction will facilitate the high-level processing like objects pattern recognition in a visual scene. Our goal was to design an intelligent image sensor prototype achieving high-speed image acquisition and non-linear image processing (like local minima and maxima calculations). For this purpose, we present in this article the design and test of a 64×64 pixels image sensor built in a standard CMOS Technology 0.35 μm including non-linear image processing. The architecture of our sensor, named nLiRIC (non-Linear Rapid Image Capture), is based on the implementation of an analog Minima/Maxima Unit. This MMU calculates the minimum and maximum values (non-linear functions), in real time, in a 2×2 pixels neighbourhood. Each MMU needs 52 transistors and the pitch of one pixel is 40×40 mu m. The total area of the 64×64 pixels is 12.5mm2. Our tests have shown the validity of the main functions of our new image sensor like fast image acquisition (10K frames per second), minima/maxima calculations in less then one ms.

  4. Thermodynamic stability in elastic systems: Hard spheres embedded in a finite spherical elastic solid.

    PubMed

    Solano-Altamirano, J M; Goldman, Saul

    2015-12-01

    We determined the total system elastic Helmholtz free energy, under the constraints of constant temperature and volume, for systems comprised of one or more perfectly bonded hard spherical inclusions (i.e. "hard spheres") embedded in a finite spherical elastic solid. Dirichlet boundary conditions were applied both at the surface(s) of the hard spheres, and at the outer surface of the elastic solid. The boundary conditions at the surface of the spheres were used to describe the rigid displacements of the spheres, relative to their initial location(s) in the unstressed initial state. These displacements, together with the initial positions, provided the final shape of the strained elastic solid. The boundary conditions at the outer surface of the elastic medium were used to ensure constancy of the system volume. We determined the strain and stress tensors numerically, using a method that combines the Neuber-Papkovich spherical harmonic decomposition, the Schwartz alternating method, and Least-squares for determining the spherical harmonic expansion coefficients. The total system elastic Helmholtz free energy was determined by numerically integrating the elastic Helmholtz free energy density over the volume of the elastic solid, either by a quadrature, or a Monte Carlo method, or both. Depending on the initial position of the hard sphere(s) (or equivalently, the shape of the un-deformed stress-free elastic solid), and the displacements, either stationary or non-stationary Helmholtz free energy minima were found. The non-stationary minima, which involved the hard spheres nearly in contact with one another, corresponded to lower Helmholtz free energies, than did the stationary minima, for which the hard spheres were further away from one another. PMID:26701708

  5. Centennial eolian cyclicity in the Great Plains, USA: A dominant pattern of wind transport over the past 4000 years?

    USGS Publications Warehouse

    Schwalb, Antje; Dean, Walter E.; Fritz, C. Sherilyn; Geiss, Christoph E.; Kromer, Bernd

    2010-01-01

    Proxy evidence at decadal resolution from Late Holocene sediments from Pickerel Lake, northeastern South Dakota, shows distinct centennial cycles (400-700 years) in magnetic susceptibility; contents of carbonate, organic carbon, and major elements; abundance in ostracodes; and delta18O and delta13C values in calcite. Proxies indicate cyclic changes in eolian input, productivity, and temperature. Maxima in magnetic susceptibility are accompanied by maxima in aluminum and iron mass accumulation rates (MARs), and in abundances of the ostracode Fabaeformiscandona rawsoni. This indicates variable windy, and dry conditions with westerly wind dominance, including during the Medieval Climate Anomaly. Maxima in carbonates, organic carbon, phosphorous, and high delta13C values of endogenic calcite indicate moister and less windy periods with increased lake productivity, including during the Little Ice Age, and alternate with maxima of eolian transport. Times of the Maunder, Sporer and Wolf sunspot minima are characterized by maxima in delta18O values and aluminum MARs, and minima in delta13C values and organic carbon content. We interpret these lake conditions during sunspot minima to indicate decreases in lake surface water temperatures of up to 4-5 degrees C associated with decreases in epilimnetic productivity during summer. We propose that the centennial cycles are triggered by solar activity, originate in the tropical Pacific, and their onset during the Late Holocene is associated with insolation conditions driven by precession. The cyclic pattern is transmitted from the tropical Pacific into the atmosphere and transported by westerly winds into the North Atlantic realm where they strengthen the Atlantic Meridional Overturning Circulation during periods of northern Great Plains wind maxima. This consequently leads to moister climates in Central and Northern Europe. Thus, Pickerel Lake provides evidence for mechanisms of teleconnections including an atmospheric link

  6. What causes geomagnetic activity during sunspot minimum?

    NASA Astrophysics Data System (ADS)

    Kirov, B.; Asenovski, S.; Georgieva, K.; Obridko, V. N.

    2015-12-01

    It is well known that the main drivers of geomagnetic disturbances are coronal mass ejections whose number and intensity are maximum in sunspot maximum, and high speed solar wind streams from low latitude solar coronal holes which maximize during sunspot declining phase. But even during sunspot minimum periods when there are no coronal mass ejections and no low latitude solar coronal holes, there is some "floor" below which geomagnetic activity never falls. Moreover, this floor changes from cycle to cycle. Here we analyze the factors determining geomagnetic activity during sunspot minimum. It is generally accepted that the main factor is the thickness of the heliospheric current sheet on which the portion of time depends which the Earth spends in the slow and dense heliospheric current sheet compared to the portion of time it spends in the fast solar wind from superradially expanding polar coronal holes. We find, however, that though the time with fast solar wind has been increasing in the last four sunspot minima, the geomagnetic activity in minima has been decreasing. The reason is that the parameters of the fast solar wind from solar coronal holes change from minimum to minimum, and the most important parameter for the fast solar wind's geoeffectivity—its dynamic pressure—has been decreasing since cycle 21. Additionally, we find that the parameters of the slow solar wind from the heliospheric current sheet which is an important driver of geomagnetic activity in sunspot minimum also change from cycle to cycle, and its magnetic field, velocity and dynamic pressure have been decreasing during the last four minima.

  7. Properties of a Polar Coronal Hole During the Solar Minimum in 2007

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Bryans, P.; Landi, E.; Miralles, M. P.; Savin, D. W.

    2010-12-01

    We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet-Sun corona. We study the observations above the solar limb in the height range of 1.03-1.20 R sun. The electron temperature T e and emission measure (EM) are found using a geometric mean emission measure method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature T i and the non-thermal velocity v nt using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that the electron density, T e, and T i are comparable in both minima. T e shows a comparable gradient with height. Both minima show a decreasing T i with increasing charge-to-mass ratio q/M. A previously observed upturn of T i for ions above q/M>0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were ~1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole.

  8. Interannual fluctuations in the seasonal cycle of nitrous oxide and chlorofluorocarbons due to the Brewer-Dobson circulation

    NASA Astrophysics Data System (ADS)

    Simmonds, P. G.; Manning, A. J.; Athanassiadou, M.; Scaife, A. A.; Derwent, R. G.; O'Doherty, S.; Harth, C. M.; Weiss, R. F.; Dutton, G. S.; Hall, B. D.; Sweeney, C.; Elkins, J. W.

    2013-10-01

    The tropospheric seasonal cycles of N2O, CFC-11 (CCl3F), and CFC-12 (CCl2F2) are influenced by atmospheric dynamics. The interannually varying summertime minima in mole fractions of these trace gases have been attributed to interannual variations in mixing of stratospheric air (depleted in CFCs and N2O) with tropospheric air with a few months lag. The amount of wave activity that drives the stratospheric circulation and influences the winter stratospheric jet and subsequent mass transport across the tropopause appears to be the primary cause of this interannual variability. We relate the observed seasonal minima of species at three Northern Hemisphere sites (Mace Head, Ireland; Trinidad Head, U.S.; and Barrow, Alaska) with the behavior of the winter stratospheric jet. As a result, a good correlation is obtained between zonal winds in winter at 10 hPa, 58°N-68°N, and the detrended seasonal minima in the stratosphere-influenced tracers. For these three tracers, individual Pearson correlation coefficients (r) between 0.51 and 0.71 were found, with overall correlations of between 0.67 and 0.77 when "composite species" were considered. Finally, we note that the long-term observations of CFCs and N2O in the troposphere provide an independent monitoring method complementary to satellite data. Furthermore, they could provide a useful observational measure of the strength of stratosphere-troposphere exchange and, thus, could be used to monitor any long-term trend in the Brewer-Dobson circulation which is predicted by climate models to increase over the coming decades.

  9. On the periodic variations of geomagnetic activity indices Ap and ap

    NASA Astrophysics Data System (ADS)

    Schreiber, H.

    1998-05-01

    Yearly averages of geomagnetic activity indices Ap for the years 1967-1984 are compared to the respective averages of 2·Bs, where v is the solar wind velocity and Bs is the southward interplanetary magnetic field (IMF) component. The correlation of both quantities is known to be rather good. Comparing the averages of Ap with 2 and Bs separately we find that, during the declining phase of the solar cycle, 2 and during the ascending phase Bs have more influence on Ap. According to this observation (using Fourier spectral analysis) the semiannual and 27 days, Ap variations for the years 1932-1993 were analysed separately for years before and after sunspot minima. Only those time-intervals before sunspot minima with a significant 27-day recurrent period of the IMF sector structure and those intervals after sunspot minima with a significant 28-28.5-day recurrent period of the sector structure were used. The averaged spectra of the two Ap data sets clearly show a period of 27 days before and a period of 28-29 days after sunspot minimum. Moreover, the phase of the average semiannual wave of Ap is significantly different for the two groups of data: the Ap variation maximizes near the equinoxes during the declining phase of the sunspot cycle and near the beginning of April and October during the ascending phase of the sunspot cycle, as predicted by the Russell-McPherron (R-M) mechanism. Analysing the daily variation of ap in an analogue manner, the same equinoctial and R-M mechanisms are seen, suggesting that during phases of the solar cycle, when ap depends more on the IMF-Bs component, the R-M mechanism is predominant, whereas during phases when ap increases as v increases the equinoctial mechanism is more likely to be effective.

  10. Global geometry optimization of silicon clusters described by three empirical potentials

    NASA Astrophysics Data System (ADS)

    Yoo, S.; Zeng, X. C.

    2003-07-01

    The "basic-hopping" global optimization technique developed by Wales and Doye is employed to study the global minima of silicon clusters Sin(3⩽n⩽30) with three empirical potentials: the Stillinger-Weber (SW), the modified Stillinger-Weber (MSW), and the Gong potentials. For the small-sized SW and Gong clusters (3⩽n⩽15), it is found that the global minima obtained based on the basin-hopping method are identical to those reported by using the genetic algorithm [Iwamatsu, J. Chem. Phys. 112, 10976 (2000)], as well as with those by using molecular dynamics and the steepest-descent quench (SDQ) method [Feuston, Kalia, and Vashishta, Phys. Rev. B 37, 6297 (1988)]. However, for the mid-sized SW clusters (16⩽n⩽20), the global minima obtained differ from those based on the SDQ method, e.g., the appearance of the endohedral atom with fivefold coordination starting at n=17, as opposed to n=19. For larger SW clusters (20⩽n⩽30), it is found that the "bulklike" endohedral atom with tetrahedral coordination starts at n=20. In particular, the overall structural features of SW Si21, Si23, Si25, and Si28 are nearly identical to the MSW counterparts. With the SW Si21 as the starting structure, a geometric optimization at the B3LYP/6-31G(d) level of density-functional theory yields an isomer similar to the ground-state- isomer of Si21 reported by Pederson et al. [Phys. Rev. B 54, 2863 (1996)].

  11. Hindered rotor tunneling splittings: an application of the two-dimensional non-separable method to benzyl alcohol and two of its fluorine derivatives.

    PubMed

    Alves, Tiago Vinicius; Simón-Carballido, Luis; Ornellas, Fernando Rei; Fernández-Ramos, Antonio

    2016-04-01

    In this work we present a novel application of the two-dimensional non-separable (2D-NS) method to the calculation of torsional tunneling splittings in systems with two hindered internal rotors. This method could be considered an extension of one-dimensional methods for the case of compounds with two tops. The 2D-NS method includes coupling between torsions in the kinetic and potential energy. Specifically, it has been applied to benzyl alcohol (BA) and two of its fluorine derivatives: 3-fluorobenzyl alcohol (3FBA) and 4-fluorobenzyl alcohol (4FBA). These molecules present two torsions, i.e., about the -CH2OH (ϕ1) and -OH (ϕ2) groups. The electronic structure calculations to build the two-dimensional torsional potential energy surface were performed at the DF-LMP2-F12//DF-LMP2/cc-pVQZ level of theory. For BA and 4FBA the calculated ground-state vibrational level splittings are 429 and 453 MHz, respectively, in good agreement with the experimental values of 337.10 and 492.82 MHz, respectively. In these two cases there are four equivalent wells and the tunneling splitting is the result of transitions between the two closer minima along ϕ1. The analysis of the wavefunctions, as well as the previous experimental work on the system, supports this conclusion. For 3FBA the observed ground-state splitting is 0.82 MHz, whereas in this case the calculated value amounts only to 0.02 MHz. The 2D-NS method, through the analysis of the wavefunctions, shows that this tiny tunneling splitting occurs between the two most stable minima of the potential energy surface. Additionally, we predict that the first vibrationally excited tunneling splitting will also be small and exclusively due to the interconversion between the second lowest minima. PMID:26960818

  12. In-stream biotic control on nutrient biogeochemistry in a forested sheadwater tream, West Fork of Walker Branch

    SciTech Connect

    Roberts, Brian J; Mulholland, Patrick J

    2007-01-01

    A growing body of evidence demonstrates the importance of in-stream processing in regulating nutrient export, yet the influence of temporal variability in stream metabolism on net nutrient uptake has not been explicitly addressed. Streamwater DIN and SRP concentrations in Walker Branch, a first-order deciduous forest stream in eastern Tennessee, show a repeated pattern of annual maxima in summer and biannual minima in spring and autumn. Temporal variations in catchment hydrologic flowpaths result in lower winter and higher summer nutrient concentrations, but do not explain the spring and autumn nutrient minima. Ambient nutrient uptake rates were measured 2-3 times per week over an 18-mo period and compared to daily rates of gross primary production (GPP) and ecosystem respiration (ER) to examine the influence of in-stream biotic activity on nutrient export. GPP and ER rates explained 85% of the variation in net DIN retention with high net NO3- uptake (and lower net NH4+ release) rates occurring during spring and autumn and net DIN release in summer. Diel nutrient concentration patterns were examined several times throughout the year to determine the relative importance of autotrophic and heterotrophic activity on net nutrient uptake. High spring GPP corresponded to daily decreases in NO3- over the illuminated hours resulting in high diel NO3- amplitude which dampened as the canopy closed. GPP explained 91% of the variance in diel NO3- amplitude. In contrast, the autumn nutrient minima was largely explained by heterotrophic respiration since GPP remained low and little diel NO3- variation was observed during the autumn.

  13. Spectral Modulation Effect in Teleseismic P-waves from North Korean Nuclear Tests Recorded in Broad Azimuthal Range and Possible Source Depth Estimation

    NASA Astrophysics Data System (ADS)

    Gitterman, Y.; Kim, S. G.; Hofstetter, R.

    2016-04-01

    Three underground nuclear explosions, conducted by North Korea in 2006, 2009 and 2013, are analyzed. The last two tests were recorded by the Israel Seismic Network. Pronounced coherent minima (spectral nulls) at 1.2-1.3 Hz were revealed in the spectra of teleseismic P -waves. For a ground-truth explosion with a shallow source depth, this phenomenon can be interpreted in terms of the interference between the down-going P-wave and the pP phase reflected from the Earth's surface. This effect was also observed at ISN stations for a Pakistan nuclear explosion at a different frequency 1.7 Hz and the PNE Rubin-2 in West Siberia at 1 Hz, indicating a source-effect and not a site-effect. Similar spectral minima having essentially the same frequency, as at ISN, were observed in teleseismic P-waves for all the three North Korean explosions recorded at networks and arrays in Kazakhstan (KURK), Norway (NNSN), Australia (ASAR, WRA) and Canada (YKA), covering a broad azimuthal range. Data of 2009 and 2013 tests at WRA and KURK arrays showed harmonic spectral modulation with three multiple minima frequencies, evidencing the clear interference effect. These observations support the above-mentioned interpretation. Based on the null frequency dependency on the near-surface acoustic velocity and the source depth, the depth of the North Korean tests was estimated about 2.0-2.1 km. It was shown that the observed null frequencies and the obtained source depth estimates correspond to P- pP interference phenomena in both cases of a vertical shaft or a horizontal drift in a mountain. This unusual depth estimation needs additional validation based on more stations and verification by other methods.

  14. PROPERTIES OF A POLAR CORONAL HOLE DURING THE SOLAR MINIMUM IN 2007

    SciTech Connect

    Hahn, M.; Savin, D. W.; Bryans, P.; Landi, E.; Miralles, M. P.

    2010-12-10

    We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet-Sun corona. We study the observations above the solar limb in the height range of 1.03-1.20 R{sub sun}. The electron temperature T{sub e} and emission measure (EM) are found using a geometric mean emission measure method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature T{sub i} and the non-thermal velocity v{sub nt} using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that the electron density, T{sub e}, and T{sub i} are comparable in both minima. T{sub e} shows a comparable gradient with height. Both minima show a decreasing T{sub i} with increasing charge-to-mass ratio q/M. A previously observed upturn of T{sub i} for ions above q/M>0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were {approx}1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole.

  15. Evolution of dark state of an open atomic system in constant intensity laser field

    NASA Astrophysics Data System (ADS)

    Krmpot, A. J.; Radonjić, M.; Ćuk, S. M.; Nikolić, S. N.; Grujić, Z. D.; Jelenković, B. M.

    2011-10-01

    We studied experimentally and theoretically the evolution of open atomic systems in the constant intensity laser field. The study is performed by analyzing the line shapes of Hanle electromagnetically induced transparency (EIT) obtained in different segments of a laser beam cross section of constant intensity, i.e., a Π-shaped laser beam. Such Hanle EIT resonances were measured using a small movable aperture placed just in front of the photodetector, i.e., after the entire laser beam had passed through the vacuum Rb cell. The laser was locked to the open transition Fg=2→Fe=1 at the D1 line of 87Rb with laser intensities between 0.5 and 4 mW/cm2. This study shows that the profile of the laser beam determines the processes governing the development of atomic states during the interaction. The resonances obtained near the beam center are narrower than those obtained near the beam edge, but the significant changes of the linewidths occur only near the beam edge, i.e., right after the atom enters the beam. The Hanle EIT resonances obtained near the beam center exhibit two pronounced minima next to the central maximum. The theoretical model reveals that the occurrence of these transmission minima is a joint effect of the preparation of atoms into the dark state and the optical pumping into the uncoupled ground level Fg=1. The appearance of the transmission minima, although similar to that observed in the wings of a Gaussian beam [A. J. Krmpot , Opt. ExpressOPEXFF1094-408710.1364/OE.17.022491 17, 22491 (2009)], is of an entirely different nature for the Π-shaped laser beam.

  16. Hyperconjugation in diethyl ether cation versus diethyl sulfide cation.

    PubMed

    Morita, Masato; Matsuda, Yoshiyuki; Endo, Tomoya; Mikami, Naohiko; Fujii, Asuka; Takahashi, Kaito

    2015-09-28

    Ionization of a molecule can greatly alter its electronic structure as well as its geometric structure. In this collaborative experimental and theoretical study, we examined variance in hyperconjugation upon ionization of diethyl ether (DEE) and diethyl sulfide (DES). We obtained the experimental gas phase vibrational spectra of DEE, DES, DEE(+), DES(+), DEE(+)-Ar, and DES(+)-Ar in the wavenumber region of 2500 to 3600 cm(-1). For DEE(+) and DEE(+)-Ar, we observed a greatly red shifted CH stretching peak at 2700 cm(-1), while the lowest CH stretching peaks for DEE, DES, DES(+) and DES(+)-Ar were observed around 2850 cm(-1). For DEE(+), we calculated a drastic red shifted CH stretching peak at 2760 cm(-1), but for DEE, DES, and DES(+) the lowest CH stretching peaks were calculated to be at 2860, 2945, and 2908 cm(-1), respectively. In addition, for DEE, the minima (maxima) geometry in the neutral state becomes a maxima (minima) geometry in the cationic state, while similar minima geometries are seen in neutral and cationic states of DES. These experimental and theoretical findings were rationalized through the natural bond orbital analysis by quantifying the hyperconjugation between the σCH orbital and the ionized singly occupied p orbital of the oxygen (sulfur) in DEE(+) (DES(+)). This study showed how orientation with the ionized orbital can greatly affect the neighboring CH bond strength and its polarity, as well as the geometry of the system. Furthermore, this change in the CH bond strength between DEE(+) and DES(+) is quantified from the energies for intramolecular proton transfer in the two cations. PMID:26300267

  17. Global triplet potential energy surfaces for the N2(X1Σ) + O(3P) → NO(X2Π) + N(4S) reaction

    NASA Astrophysics Data System (ADS)

    Lin, Wei; Varga, Zoltan; Song, Guoliang; Paukku, Yuliya; Truhlar, Donald G.

    2016-01-01

    This work presents two global triplet potential energy surfaces (PESs) for the high-energy reaction N2(X1Σ) + O(3P) → NO(X2Π) + N(4S)—in particular, for the lowest energy 3A' and 3A″ PESs. In order to obtain the energies needed for fitting analytic surfaces, we carried out multireference configuration interaction (MRCI) calculations based on wave functions obtained from state-averaged complete active space self-consistent field calculations for 2280 geometries for the three lowest 3A″ states and for 2298 geometries for the three lowest 3A' states. The lowest-energy 3A' and 3A″ states at each of these geometries were then improved by applying the dynamically scaled external correlation (DSEC) method to all MRCI points, and the resulting DSEC energies were used for construction of the ground-state PES for each symmetry. The many-body component of the DSEC energies for the three-dimensional 3A' and 3A″ PESs was then least-squares fitted in terms of permutationally invariant polynomials in mixed exponential-Gaussian bond order variables. The global and local minima as well as the transition structures of both the 3A' and the 3A″ analytic PES were explored. In agreement with previous work, we find that the reverse reaction is barrierless on the 3A″ surface along the minimum energy pathway. However, we have explored several new local minima and transition structures on the 3A' PES. Furthermore, based on the newly found minima and transition structures, two independent reaction mechanisms have been illustrated for the reaction path on the 3A' PES. The analytic surfaces may be used for dynamics calculations of electronically adiabatic reactive scattering and energy transfer.

  18. A New Scenario for the Production of Weak Bipolar Fields in Space: "Notch" Instabilities Resulting From Electron Velocity Dispersion*

    NASA Astrophysics Data System (ADS)

    Newman, D. L.; Goldman, M. V.

    2007-05-01

    The bipolar signatures of weak (eφmax/Te ≪ 1) electron phase-space holes have now been observed in numerous near-Earth space-plasma environments such as the polar cusp region1 and the solar wind2 at 1 AU. While families of stationary solutions of the Vlasov-Poisson equations consistent with these observations have been found,3 the question of how shallow phase-space density depressions supporting these bipolar fields form remains an open one. While strong bipolar fields associated with deep phase-space holes in Earth auroral downward-current region are consistent with saturated two-stream instabilities resulting from double-layer electron acceleration,4 the weak bipolar fields observed in other space environments may require an alternative generation mechanism. One such mechanism involves the formation of narrow minima in the electron velocity-space distribution resulting from stretching due to velocity dispersion of phase-space density minima that are initially localized in physical space (e.g., constant-density regions with temperatures greater than their surroundings). These velocity-space minima, which become narrower as they are dispersively stretched, eventually cross the threshold condition for a "notch" instability, which saturates by forming an expanding series of shallow phase-space holes and their associated weak bipolar fields. 1-D Vlasov-Poisson simulations show that this process can be a robust mechanism for generating a large ensemble of shallow holes. Simulations with different background electron distributions show that the properties of the holes that form depend sensitively on the characteristics of the embedding plasma environment. * Research supported by NSF, NASA, and DOE. 1 J. R. Franz, et al., JGR, 110, doi:10.1029/2005JA011095 (2005). 2 A. Mangeney, private communication. 3 M. V. Goldman, et al., this meeting. 4 R. E. Ergun, et al., PRL, 87, 045003 (2001); D. L. Newman, et al. PRL, 87, 255001 (2001).

  19. Analysis of serpentinophytes from north-east of Portugal for trace metal accumulation--relevance to the management of mine environment.

    PubMed

    Freitas, H; Prasad, M N V; Pratas, J

    2004-03-01

    In north-east of Portugal, the serpentinized area is about 8000 ha with a characteristic geology and flora. The serpentine plant community and respective soils were analyzed to examine the trace metal budget in different tissues of the plants exhibiting resistance to trace metals. One hundred and thirty five plant species belonging to 39 families and respective soils have been analyzed for total Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Substantial amounts of Ni, Cr, Co and Mn were detected in plant tissues which are listed below: NI: Alyssum serpyllifolium (38105); Bromus hordeaceus (1467); Linaria spartea (492); Plantago radicata (140); Lavandula stoechas (118) and Cistus salvifolius (114); CR: L. spartea (706.7); Ulmus procera (173.4); A. serpyllifolium (129.3); Cistus ladanifer (40.8); L. stoechas (29.5); P. radicata (27.81); Setariopsis verticillata (25.7); Plantago lanceolata (24); Digitalis purpurea (23.4); Logfia minima (23.1); Arenaria querioides (23); Hieracium peleteranum (22.7); Arenaria montana (14.5); CO: A. serpyllifolium (145.1); L. spartea (63.2); P. radicata (10.4); H. peleteranum (7.3); Lepidium heterophyllum (6.9); A. querioides (6.6); C. salvifolius (6.5); C. ladanifer (6.3); L. stoechas (6.1); Anthyllis lotoides (6.1); L. minima (6.1); Euphorbia falcata (5.7) and B. hordeaceus (5.6); MN: A. serpyllifolium (830); L. spartea (339); L. stoechas (187.1); L. minima (182.7); Castanea sativa (125); Spergula pentandra (124); P. radicata (119); Cytisus striatus (115.4); Quercus pyrenaica (110); Teucrium scorodonia (109.4); Fraxinus vulgaris (109); Anthyllis sampaiana (108); Quercus ilex (108). The significance of serpentine flora, need for conservation of these fragile and environmentally invaluable plant resources for possible use for in situ remediation of metalliferous substrates are presented in this paper. PMID:14675842

  20. Synchronous degassing patterns of the neighbouring volcanoes Llaima and Villarrica in south-central Chile: the influence of tidal forces

    NASA Astrophysics Data System (ADS)

    Bredemeyer, Stefan; Hansteen, Thor H.

    2014-10-01

    The neighbouring volcanoes Villarrica and Llaima are two of the most active volcanoes in Chile and both currently degas continuously. We present a semi-continuous time series of SO2 fluxes for Villarrica and Llaima volcanoes. The time series was obtained using five scanning Mini-Differential Optical Absorption Spectrometers (Mini-DOAS, UV spectrometers) over 6 months (13 February to 31 July 2010) and is based on 6,829 scans for Villarrica and 7,165 scans for Llaima. Statistical analyses of the SO2 flux time series reveal a periodicity of degassing maxima about every 7 days, and further a conspicuous synchronicity of the degassing maxima and minima between the two volcanoes. Intra-day variations in SO2 fluxes also show a striking correlation between Villarrica and Llaima. All these patterns correlate well with the trend of the modelled solid Earth tide curves, where the 7-day degassing maxima correspond with both the fortnightly tidal maxima and minima. The intra-day degassing peaks mostly correlate well with the periods of maximum deformation rates during the diurnal tidal cycle, and further with semidiurnal minima in atmospheric pressure, a phenomenon we refer to as "the tidal pump". As there is little time lag between the tidal action and the changes in degassing rates, we infer that degassing at both volcanoes is controlled by conduit convection, involving physical separation between gas and magma at comparatively shallow levels. Variations in daily degassing rates were up to a factor of ca. 12 and 10 for Villarrica and Llaima, respectively, without any noticeable changes in the periodicity. We thus suggest that the described cyclic variations must be taken into account for all comparable volcanoes when using gas monitoring as a tool for volcanic hazard mitigation.