bluuebunny/crossref_metadata_2025 huggingface dataset:
The diet of white-chinned petrels Procellaria aequinoctialis, Linnaeus 1758, in years of contrasting prey availability at South Georgia
Authors: Berrow Simon D. , Croxall John P.
Published: December 2007

The diet of breeding white-chinned petrels was studied during the summers of 1996 and 1998 at South Georgia. Krill abundance/availability was high throughout 1996 but apparently low at the beginning of the 1998 breeding season. The diet of white-chinned petrels was similar between years and consistent with previous studies. Krill Euphausia superba (41–42% by weight) was the single most important prey item followed by fish (39–29%) and squid (19–25%). Meal mass was consistent (110 g in 1996, 119 g in 1998) between years but a significant decrease (46%) in feeding frequency in 1998 (0.54 meals day−1 compared to 0.75 meals day−1 in 1996) resulted in 19% less food delivered to chicks in 1998 than in 1996. Breeding success, however, was consistent between years at 44% and similar to that recorded previously at Bird Island. This is in contrast to black-browed and grey-headed albatrosses, both of which experienced almost total breeding failure in 1998. It is suggested that their varied and versatile feeding methods, together with their greater diving ability, capacity to feed at night and extensive foraging range, help white-chinned petrels minimise the effects of krill shortage.
The fish fauna of the Ross Sea, Antarctica
Authors: Eastman Joseph T. , Hubold Gerd
Published: December 2007

The RV Nathaniel B. Palmer was used for bottom trawling at depths of 100–1200 m during two recent cruises in the south-western Ross Sea. Although only 10 of 20 trawls were completely successful, a diverse collection of 979 specimens was obtained representing 47 species (36 notothenioids and 11 nonnotothenioids) and eight families. The collection included four new species, a new colour morph of a known species and eight rare species. The collection also established four new locality records, three second occurrences, three most southerly records and eleven new depth records for fish in the Ross Sea. Good taxonomic coverage for some groups was indicated by collection of all four species of Artedidraco, nine of ten bathydraconids and seven of eight channichthyids occurring in East Antarctica. The most abundant species were Trematomus scotti (29.7%), Bathydraco marri (10.4%), Trematomus eulepidotus (8.7%) and Dolloidraco longedorsalis (6.1%). Fish biomass was determined at two stations. The fish fauna of the Ross Sea south of the 1000-m isobath includes at least 80 species – 54 notothenioids and 26 non-notothenioids, approximately the same number as the Weddell Sea. Species diversity (H′ = 1.88) was higher than both the Weddell Sea and boreal regions. This collection indicates that, even in relatively shallow water, knowledge of specific and intraspecific diversity in the Ross Sea fauna is incomplete.
Active tectonics and morphostructure at the northern margin of central Bransfield Basin, Hurd Peninsula, Livingston Island (South Shetland Islands)
Authors: González-Casado J.M. , López-Martínez J. , Durán J.J.
Published: December 2007

Geophysical, structural, geomorphological, topographical and bathymetric data from the Hurd Peninsula area, Livingston Island, South Shetland archipelago, suggest that an extensional fault system, orientated NW–SE, together with a conjugate group of NE–SW normal oblique-slip faults, control the landforms in this area. These structures separate fault-bounded blocks of different heights, giving rise to a horstgraben structure. The depressed blocks were filled by glaciers and flooded in part by the sea. The recent movement of these faults can be established from the calculated isopachs of a small Quaternary sedimentary basin, related to this extensional fault system, which shows that sedimentary bed thickness is controlled mainly by the NE–SW fault system. Geomorphological analysis also shows that the NW–SE faults control the main morphostructures of this region. The character of the recent stress tensor has been established from fault-slip data, taking into account only those faults that are related to morphostructures. The calculated palaeostress tensor is extensional, with a N46°E main extension direction, and an average stress ratio of 0.17.
Geology, age and origin of the Mount Willing area (Prince Charles Mountains, East Antarctica)
Authors: Mikhalsky E.V. , Laiba A.A. , Beliatsky B.V. , Stüwe K.
Published: December 2007

Mount Willing in the Prince Charles Mountains (East Antarctica) is part of the Fisher Volcano–plutonic complex which formed as part of the global-scale Grenvillian mobile belt system. Mount Willing is composed of four rock complexes: 1) a metamorphic sequence, 2) gabbro intrusions, 3) deformed felsic intrusives, and 4) abundant post-metamorphic dykes and veins. Three rock types constitute the metamorphic sequence: amphibole–biotite felsic plagiogneiss, mafic to intermediate biotite–amphibole schist, and biotite paragneiss. The bulk composition of the mafic schists classifies them as tholeiitic basalts, and rarely as basaltic andesites or andesites. Index mg ranges widely from 47 to 71. Concentrations of TiO2, P2O5, and high-field strength elements are high in some rocks. These rocks are thought to have been derived from enriched (subcontinental) mantle sources. Sm–Nd and U–Pb isotopic data indicate a series of Mesoproterozoic thermal events between 1100 and 1300 Ma. In particular, these events occurred at 1289 ± 10 Ma (volcanic activity), at 1177 ± 16 Ma (tonalite intrusion), at 1112.7 ± 2.4 and at 1009 ± 54 Ma (amphibolite facies metamorphic events). Rb–Sr systematics also indicates a thermal overprint at 636 ± 13 Ma. Mafic schists show low initial 877Sr/86Sr ratios between 0.7024 and 0.7030. Felsic rocks show higher Sri values between 0.7037 and 0.7061. Basaltic andesite metavolcanic and plutonic rocks form a calc-alkaline evolutionary trend, and probably originated from subduction-modified mantle sources in a convergent plate margin environment. An oceanic basin may have existed in central Prince Charles Mountains about 1300 Ma ago and was closed as a result of continental collision around 1000 to 800 Ma.
Dolichiscus spinosetosus n. sp., a new arcturid isopod from the Weddell Sea, Antarctica
Authors: Brandt Angelika
Published: December 2007

Two specimens of Dolichiscus spinosetosus were collected by means of an Agassiz trawl and a small dredge in the Weddell Sea, Antarctica. This species is characterized by a large number of strong spines on the dorsal side, some of these possessing tubercular tips. The dorsum is characterized by many smaller and shorter blunt spines and numerous long simple setae all over the body (on spines, pereonites and pleotelson). Dolichiscus acanthaspidus Schultz, 1981 is the taxon most closely related to this new species, but the new species has more setae and tubercular spines on all parts of the body and two caudolateral spines instead of one behind the supraocular ones.
The role of ice in determining mixing intensity in Ellis Fjord, Vestfold Hills, East Antarctica
Authors: Gibson John A.E.
Published: December 2007

Mixing in Ellis Fjord, Vestfold Hills, East Antarctica, is controlled by processes which are influenced by the extent of ice formation. A study of water temperature and salinity at a site near the middle of the fjord was undertaken from May 1994 to February 1995 after a summer (1993–94) in which the ice cover of the fjord was largely retained. Vertical mixing resulting from the exclusion of salt during the limited winter formation of ice was insufficient to mix completely the non-meromictic basins of the fjord. In contrast, a previous study during a winter with far more ice production recorded much stronger vertical mixing throughout the fjord. Warming and freshening of the fjord during the 1994–95 summer, when the ice again did not melt significantly, was attributable to the flow of warmer, less saline water along the fjord. This process was probably related to the formation of tidal jets at the narrow and shallow entrance to the fjord, and was thus influenced by the ice conditions around the entrance. These jets would also have introduced significant amounts of extra-fjord water (along with any resident biota) into the fjord.
Wax esters versus triacylglycerols in myctophid fishes from the Southern Ocean
Authors: Phleger Charles F. , Nelson Matthew M. , Mooney Ben D. , Nichols Peter D.
Published: December 2007

Five species of myctophid fishes were collected by trawl from the Elephant Island region of the Antarctic Peninsula between 60°30′–62°S and 55°–61°30′W. Two species, Gymnoscopelus braueri and Krefftichthyes anderssoni were lipid-rich (406–456 mg g−1 dry weight whole fish) with wax esters (WE) the major lipid class. In three species, G. opisthopterus, G. nicholsi, and Electrona carlsbergii, triacylglycerols (TAG) were the major lipid. All fish had oily bones, with values up to 471 mg g−1 dry weight in the vertebral centra of K. anderssoni. The principal fatty acids of the TAG-rich myctophids included the monoenes 18:1(n-9) and 20:1. There were lower levels of 16:0 and 18:0 saturated fatty acids. Polyunsaturated fatty acids (PUFA) were present at higher abundance in the TAG-rich E. carlsbergii and G. opisthopterus, with lower levels in G. nicholsi. In comparison, the WE-dominated species contained lower levels of PUFA than in the TAG-rich species. The principal fatty acids of the WE-rich myctophids included the monoenes 18:1(n-9), 16:1(n-7), and 18:1(n-7), with lower levels of the saturated acids 16:0 and 18:0. Fatty alcohols were dominated by 16:0 and 14:0 and the monounsaturated 18:1(n-9) with 16:1(n-7), 18:1(n-7), and 20:1(n-9). Based on the fatty acid profiles, the diet of G. opishtopterus and G. nicholsi, previously thought to be mainly Euphausia superba, is suggested to include copepods and other zooplankton with only a minor krill component, possibly consisting of other species than E. superba.
Dynamic age-distributions in a declining population of southern elephant seals
Authors: Pistorius P.A. , Bester M.N. , Kirkman S.P.
Published: December 2007

Estimates of births and standing age-distributions were combined to estimate the size of the southern elephant seal population at Marion Island at various times during its decline. To estimate births each year from 1986 through 1997 we used the number of adult females hauled out on 15 October, which is the peak haulout date for breeding elephant seal females at all breeding sites in the Indian Ocean. A conversion factor (3.15) was derived from the standing age-distributions, and applied to estimates of annual births to yield total population size. The population at Marion Island declined 37.5% overall from 1986–97 at an annual rate of 4.3% from 1986–91 and c. 2.5% yr−1 afterwards.
A new estimate of the adopted gravity value at Rothera Station, Antarctic Peninsula
Authors: Jones Philip C. , Ferris Julie K.
Published: December 2007

Because of the lack of a definitive air link to an international gravity base station, the Antarctic Peninsula gravity network was originally, and still is, tied to the Potsdam gravity system via long ship links to South America (Renner 1981, Kennett 1965). An indirect link from the British Antarctic Survey (BAS) scientific station at Rothera to an International Gravity Standardisation Net 1971 (IGSN 71) base station in the UK had previously been made via a link to the BAS gravity station on the Falkland Islands in Port Stanley (McGibbon 1988). Whilst the apparent gravity difference between Port Stanley and the base station in the UK had been calculated via a two-way air tie using a LaCoste and Romberg meter (McGibbon 1988) and later strengthened with three two-way air ties using four LaCoste and Romberg meters (Bassett 1987), the link between Port Stanley and Rothera was based on a one-way tie that included a lengthy ship borne passage (McGibbon 1988). The weakness of this link insured that the adopted gravity value at Rothera continued to be based on the ship ties made by Griffiths et al. (1964) and Kennett (1965). This note describes the strengthening of the gravity link between Rothera and Port Stanley and the subsequent reassignment of the adopted gravity value at Rothera Station.
Aligned growth positions in Pliocene Laternula elliptica (King & Broderip) (Bivalvia: Anomalodesmata: Laternulidae)
Authors: Jonkers H.A.
Published: December 2007

The circum-Antarctic clam Laternula elliptica (King & Broderip 1831) is the largest infaunal bivalve of the Southern Ocean. It mostly lives in water depths of less than 100 m (highest densities from 20–30 m; e.g. Ahn 1994), in soft or semi-consolidated substrates from sandy mud to gravelly sand (Soot-Ryen 1951, Nicol 1966). Animals are deep-burrowing (to >0.5 m; Zamorano et al. 1986) and consequently have large siphons. These are fused, highly muscular and covered by thick, rugose periostracum, and are capable of partial retraction only (Burne 1920). The ecology of L. elliptica was likened by Ralph & Maxwell (1977) to that of Mya arenaria L. in northern temperate and Arctic waters.
Die böse Farbe
Authors: Baudisch Andreas , Hils Martin , Martin-Pizarro Amador , Wagner Frank O.
Published: December 2007

Wir konstruieren einen schlechten Körper der Charakteristik Null. Mit anderen Worten, wir konstruieren einen algebraisch abgeschlossenen Körper mit einem Dimensionsbegriff analog der Zariski-Dimension, zusammen mit einer unendlichen echten multiplikativen Untergruppe der Dimension Eins, so daβ der Körper selbst Dimension Zwei hat. Dies beantwortet eine alte Frage von Zilber.
Water and energy budgets of hurricanes: Case studies of Ivan and Katrina
Authors: Trenberth Kevin E. , Davis Christopher A. , Fasullo John
Published: December 2007

To explore the role of hurricanes in the climate system, a detailed analysis is made of the bulk atmospheric moisture budget of Ivan in September 2004 and Katrina in August 2005 from simulations with the Weather and Research Forecasting (WRF) model at 4 km resolution without parameterized convection. Heavy precipitation exceeding 20 mm h−1 in the storms greatly exceeds the surface flux of moisture through evaporation, and vertically integrated convergence of moisture in the lowest 1 km of the atmosphere from distances up to 1600 km is the dominant term in the moisture budget, highlighting the importance of the larger‐scale environment. Simulations are also run for the Katrina case with sea surface temperatures (SSTs) increased by +1°C and decreased by −1°C as sensitivity studies. For hours 42 to 54 after the start of the simulation, maximum surface winds increased about 4.5 m s−1 (9%), and sea level pressure fell 11.5 hPa per 1°C increase in tropical SSTs. Overall, the hurricane expands in size as SSTs increase, the environmental atmospheric moisture increases at close to the Clausius‐Clapeyron equation value of about 6% K−1 and the surface moisture flux also increases mainly from Clausius‐Clapeyron effects and the changes in intensity of the storm. The environmental changes related to human influences on climate since 1970 have increased SSTs and water vapor, and the results suggest how this may have altered hurricanes and increased associated storm rainfalls, with the latter quantified to date to be of order 6 to 8%.
Water and energy budgets of hurricanes and implications for climate change
Authors: Trenberth Kevin E. , Fasullo John
Published: December 2007

On the basis of simulations of hurricane Katrina in August 2005 with the advanced Weather and Research Forecasting (WRF) model at 4 km resolution without parameterized convection, empirical relationships are computed between the maximum simulated wind and the surface fluxes and precipitation and provide a reasonable fit to the data. The best track data set of global observed tropical cyclones is used to estimate the frequency that storms of a given strength occur over the globe after 1970. For 1990–2005 the total surface heat loss by the tropical ocean in hurricanes category 1 to 5 within 400 km of the center of the storms is estimated to be about 0.53 × 1022 J a−1 (where a is year) (0.17 PW). The enthalpy loss due to hurricanes computed on the basis of precipitation is about a factor of 3.4 greater (0.58 PW), owing to the addition of the surface fluxes from outside 400 km radius and moisture convergence into the storms typically from as far from the eye as 1600 km. Globally these values correspond to 0.33 W m−2 for evaporation, or 1.13 W m−2 for precipitation. Changes over time reflect basin differences and a prominent role for El Niño, and the most active period globally was 1989 to 1997. Strong positive trends from 1970 to 2005 occur in these inferred surface fluxes and precipitation arising from increases in intensity of storms and also higher sea surface temperatures. Confidence in this result is limited by uncertainties in the best track tropical cyclone data. Nonetheless, the results highlight the importance of surface energy exchanges in global energetics of the climate system and are suggestive of the deficiencies in climate models owing to their inadequate representation of hurricanes.
Soil and topographic controls on runoff generation from stepped landforms in the Edwards Plateau of Central Texas
Authors: Wilcox Bradford P. , Wilding Larry P. , Woodruff C. M.
Published: December 2007

The rugged Hill Country of Central Texas is part of the extensive Edwards Plateau region. Significant portions of the Texas Hill Country overlie the Glen Rose Formation, which is characterized by a stair‐step topography formed by the weathering of interbedded carbonate materials having different weathering susceptibilities. This process has sculpted the strata into a series of “risers” and “treads” that mimic stairways. In this paper, we document the soil hydrology within the riser–tread catena. Our results are counterintuitive in that we find the highest infiltration and deepest soils on the steep riser slopes. In addition, we find that the riser subsoils are saturated or very wet for extended periods. On the basis of these findings, we suggest that (1) groundwater recharge on these hillslopes is minimal and occurs only in highly fractured zones; (2) the water‐holding capacity of the subsoils is sufficient for supporting the woody vegetation; and (3) runoff generation occurs as a combination of surface and subsurface flow, with the risers serving as sinks or recharge zones and the treads as source areas.
Atlantic meridional overturning circulation and the Southern Hemisphere supergyre
Authors: Speich Sabrina , Blanke Bruno , Cai Wenju
Published: December 2007

The ocean's role in climate manifests itself through its high heat capacity, its own rich internal dynamics and its ability to transport vast quantities of heat and freshwater. Of particular interest is the global ocean circulation associated with the Atlantic meridional overturning (AMOC). Because observations are sparse, the detailed global structure of the AMOC remains poorly understood, particularly the pathways along which water returns to the Atlantic to compensate the export of North Atlantic Deep Water (NADW). Here we provide the first quantitative 3‐dimensional global view of the AMOC using a Lagrangian reconstruction which integrates hundred of thousands water particle trajectories in an ocean model. The resulting pattern elucidates the role of the wind in structuring the pathways of the AMOC. In particular, the Lagrangian analysis reveals a strong link with the three subtropical gyres of the southern hemisphere (SH), which merge into a “supergyre” spanning the three ocean basins. The coupling between the upper ocean wind‐driven circulation and the overturning in the model suggests that changes in the SH winds can alter the pathways of the AMOC, and therefore the water properties and the associated heat and freshwater transports.
Barotropic Rossby wave radiation from a model Gulf Stream
Authors: Miller Arthur J. , Neilson Douglas J. , Luther Douglas S. , Hendershott Myrl C. , Cornuelle Bruce D. , Worcester Peter F. , Dzieciuch Matthew A. , Dushaw Brian D. , Howe Bruce M. , Levin Julia C. , Arango Hernan G. , Haidvogel Dale B.
Published: December 2007

The barotropic Rossby wave field in the North Atlantic Ocean is studied in an eddy‐resolving ocean model simulation. The meandering model Gulf Stream radiates barotropic Rossby waves southward through preferred corridors defined by topographic features. The smoother region between the Bermuda Rise and the mid‐Atlantic Ridge is a particularly striking corridor of barotropic wave radiation in the 20–50 day period band. Barotropic Rossby waves are also preferentially excited at higher frequencies over the Bermuda Rise, suggesting resonant excitation of topographic Rossby normal modes. The prevalence of these radiated waves suggests that they may be an important energy sink for the equilibrium state of the Gulf Stream.
What factors are driving summer phytoplankton blooms in the North Pacific Subtropical Gyre?
Authors: White Angelicque E. , Spitz Yvette H. , Letelier Ricardo M.
Published: December 2007

Annually recurrent summer to fall surface blooms of the dinitrogen (N2) fixing genera Trichodesmium and Richelia have a significant impact on biogeochemical cycling in the North Pacific Subtropical Gyre (NPSG). Yet the environmental determinants of these blooms have not been thoroughly resolved. Here, we combine remote sensing of ocean color, sea surface temperature (SST), sea surface height anomalies (SSHa), wind forcing, and integrated irradiance with the vessel‐based time series of the Hawaii Ocean Time‐series (HOT) program at Station ALOHA (22.75°N, 158.00°W) and mooring data derived from the National Data Buoy Center (NDBC) buoy 51001 (23.42°N, 162.2°W). With these data sets we attempt to constrain the environmental window under which blooms of large cell‐sized N2 fixing organisms increase in abundance in NPSG surface waters using phycoerythrin (PE) as a proxy. For identified blooms, our analyses indicate that these events are confined to the months of June–October, SST in the range of 25°–27°C, and mixed layer depths less than 70 m. Neither wind forcing nor SSHa are correlated (directly or time‐lagged) with increases in PE concentrations. Furthermore, blooms do not consistently result in increases of in situ or remotely sensed chlorophyll a. Additional higher‐resolution data sets of physical forcing, diazotroph abundance, and biochemical properties, sampled on the timescale of bloom development (days‐weeks), will be necessary to the environmental conditions supporting annual summer‐fall blooms.
A comparison of middle atmospheric water vapor as measured by WVMS, EOS‐MLS, and HALOE
Authors: Nedoluha Gerald E. , Gomez R. Michael , Hicks Brian C. , Bevilacqua Richard M. , Russell James M. , Connor Brian J. , Lambert Alyn
Published: December 2007

We compare middle atmospheric water vapor measurements from the Halogen Occultation Experiment (HALOE), Water Vapor Mm‐wave Spectrometer (WVMS), and Earth Observing System (EOS) Microwave Limb Sounder (MLS) instruments from 40 to 70 km. The ground‐based WVMS measurements shown here were taken at Network for the Detection of Atmospheric Composition Change (NDACC) sites at Mauna Loa, Hawaii (19.5°N, 204.4°E), and Lauder, New Zealand (45.0°S, 169.7°E). A comparison of measurements where HALOE, MLS, and WVMS are all available shows that the average HALOE water vapor retrievals are lower than those from MLS at all altitudes from 40 to 70 km and lower than the WVMS retrievals everywhere except above 64 km at Lauder. The average difference between all coincident WVMS and MLS water vapor profiles is within 0.2 ppmv over almost the entire 40–70 km altitude range, both at Lauder and Mauna Loa. The standard deviation of the difference between weekly WVMS retrievals and coincident MLS retrievals is ∼0.2 ppmv at Mauna Loa and ∼0.3–0.4 ppmv at Lauder. The interannual correlation between water vapor observed by MLS and WVMS is slightly improved by the use of MLS temperature measurements in the WVMS retrievals. The MLS and WVMS profiles at Mauna Loa show particularly good interannual agreement, including a clear QBO signature.
In situ measurements of aerosol mass concentration and radiative properties in Xianghe, southeast of Beijing
Authors: Chaudhry Zahra , Martins J. Vanderlei , Li Zhanqing , Tsay Si‐Chee , Chen Hongbin , Wang Pucai , Wen Tianxue , Li Can , Dickerson Russell R.
Published: December 2007

As a part of the EAST‐AIRE study, Nuclepore filters were collected in two size ranges (coarse, 2.5 μm < d < 10 μm, and fine, d < 2.5 μm) from January to May 2005 in Xianghe, about 70 km southeast of Beijing, and analyzed for aerosol mass concentration, spectral absorption efficiency and absorption coefficient. Twelve‐hour aerosol mass concentration measurements showed an average concentration of 120 μg/m3 in the coarse mode and an average concentration of 25 μg/m3 in the fine mode. To determine how representative ground‐based measurements are of the total column, the mass concentration data was compared with AERONET AOT at 500 nm and AERONET size distribution data. The vertical distribution of the aerosols were studied with a micropulse lidar and in the cases where the vertical column was found to be fairly homogenous, the comparisons of the filter results with AERONET agreed favorably, while in the cases of inhomogeneity, the comparisons have larger disagreement. For fine mode aerosols, the average spectral absorption efficiency equates well to a λ−1 model, while the coarse mode shows a much flatter spectral dependence, consistent with large particle models. The coarse mode absorption efficiency was compatible with that of the fine mode in the NIR region, indicating the much stronger absorption of the coarse mode due to its composition and sizable mass. Single scattering albedo results are presented from a combination between absorption coefficients derived from the filter measurements, from a PSAP and from a three‐wavelength Nephelometer.
Lattice model of equilibrium polymerization. VI. Measures of fluid “complexity” and search for generalized corresponding states
Authors: Douglas Jack F. , Dudowicz Jacek , Freed Karl F.
Published: December 2007

Particle association in “complex” fluids containing charged, polar, or polymeric molecular species often leads to deviations from the corresponding state description of “simple” fluids in which the molecules are assumed to have relatively symmetric interactions and shapes. This fundamental problem is addressed by developing a minimal thermodynamic model of activated equilibrium polymerization solutions that incorporates effects associated with the competition between van der Waals and associative interactions, as well as features related to molecular anisotropy and many-body interactions. As a dual purpose, we focus on thermodynamic signatures that can be used to identify the nature of dynamic clustering transitions and the interaction parameters associated with these rounded thermodynamic transitions. The analysis begins by examining “singular” features in the concentration dependence of the osmotic pressure Π that generically characterize the onset of particle association. Because molecular self-assembly can strongly couple with fluid phase separation, evidence is also sought for associative interactions in the behavior of the second A2 and third A3 osmotic virial coefficients. In particular, the temperatures Tϴ2 and Tϴ3 where A2 and A3, respectively, vanish are found to contain valuable information about the relative strength of the associative and van der Waals interactions. The critical temperature Tc for phase separation, the critical composition φc, and the rectilinear diameter Ad, describing the asymmetry of the coexistence curve for phase separation, along with the average cluster mass Lc and extent of polymerization Φc at the critical point, further specify the relevant interaction parameters of our model. Collectively, these characteristic properties provide a thermodynamic metric for defining fluid complexity and in developing a theoretically based corresponding state relation for complex fluids.
On the formation mechanism of the “pancake” decahedron gold nanoparticle
Authors: Grochola Gregory , Russo Salvy P. , Snook Ian K.
Published: December 2007

We have studied the thermodynamic and kinetic growth mechanisms behind the formation of the “pancake” decahedron (Dh) gold nanoparticle using computer simulation. Free energy calculations showed that the full pancake morphology is thermodynamically unstable across all the nanoparticle size ranges studied. However, from observations of growth simulations we discovered that a kinetic transport mechanism plays a significant contributing role in the formation process through a transfer of adatoms from the top and bottom (111) Dh faces to the side (100) faces. More specifically we observed how diffusing adatoms on the (111) face are at times “pulled” off this face and into the (111)-(100) edge of the Dh, forcing a row of (100) side atoms into a (1×5) hexagonal reconstruction. Subsequently, this row of atoms was observed to buckle and then deconstruct forcing adatoms out onto the (100) side face completing the transfer. This transport mechanism is shown to be the main kinetic driving force behind the growth of the thermodynamically unstable pancake Dh nanoparticle. The observed mechanism has implications for the nonequilibrium morphologies of nanoparticles involving a (100)-(111) surface boundary, especially for systems with surface reconstructions which increase the density of the surface.
Electric field-induced translocation of single-stranded DNA through a polarized carbon nanotube membrane
Authors: Xie Yinghong , Kong Yong , Soh A. K. , Gao Huajian
Published: December 2007

Molecular dynamics simulations based on a novel polarizable nanotube model were performed to study the dynamics in translocation of a single-stranded deoxyribonucleic acid oligonucleotide through a polarized carbon nanotube membrane by an applied electric field. The study revealed a nonlinear dependence of translocation velocity and an inverse quadratic dependence of translocation time on the electric field strength, as well as a threshold electric field below which the translocation process becomes impossible. The translocation rate was found to be pore-size dependent. The polarizable nanotube model developed for this study provides a useful platform for investigating the dynamics of a range of bionanosystems.
Numerical calculation of the combinatorial entropy of partially ordered ice
Authors: Berg Bernd A. , Yang Wei
Published: December 2007

Using a one-parameter case as an example, we demonstrate that multicanonical simulations allow for accurate estimates of the residual combinatorial entropy of partially ordered ice. For the considered case, corrections to an (approximate) analytical formula are found to be small, never exceeding 0.5%. The method allows one as well to calculate combinatorial entropies for other systems.
Collisional quenching at ultralow energies: Controlling efficiency with internal state selection
Authors: Bovino S. , Bodo E. , Gianturco F. A.
Published: December 2007

Calculations have been carried out for the vibrational quenching of excited H2 molecules which collide with Li+ ions at ultralow energies. The dynamics has been treated exactly using the well-known quantum coupled-channel expansions over different initial vibrational levels. The overall interaction potential has been obtained from the calculations carried out earlier by our group using highly correlated ab initio methods. The results indicate that specific features of the scattering observables, e.g., the appearance of Ramsauer-Townsend minima in elastic channel cross sections and the marked increase of the cooling rates from specific initial states, can be linked to potential properties at vanishing energies (sign and size of scattering lengths) and to the presence of either virtual states or bound states. The suggestion is made such that by selecting the initial state preparation of the molecular partners, the ionic interactions would be amenable to controlling quenching efficiency at ultralow energies.
Solving the Schrödinger equation for helium atom and its isoelectronic ions with the free iterative complement interaction (ICI) method
Authors: Nakashima Hiroyuki , Nakatsuji Hiroshi
Published: December 2007

The Schrödinger equation was solved very accurately for helium atom and its isoelectronic ions (Z=1–10) with the free iterative complement interaction (ICI) method followed by the variational principle. We obtained highly accurate wave functions and energies of helium atom and its isoelectronic ions. For helium, the calculated energy was −2.90372437703411959831115924519440444669690537a.u., correct over 40 digit accuracy, and for H−, it was −0.52775101654437719659081456674751138304502a.u. These results prove numerically that with the free ICI method, we can calculate the solutions of the Schrödinger equation as accurately as one desires. We examined several types of scaling function g and initial function ψ0 of the free ICI method. The performance was good when logarithm functions were used in the initial function because the logarithm function is physically essential for three-particle collision area. The best performance was obtained when we introduce a new logarithm function containing not only r1 and r2 but also r12 in the same logarithm function.
Reference interaction site model and molecular dynamics study of structure and thermodynamics of methanol
Authors: Costa D. , Munaó G. , Saija F. , Caccarno C.
Published: December 2007

Thermodynamic and structural properties of various models of liquid methanol are investigated in the framework provided by the reference interaction site model (RISM) theory of molecular fluids. The theoretical predictions are systematically compared with molecular dynamics simulations both at ambient conditions and along a few supercritical isotherms. RISM results for the liquid-vapor phase separation are also obtained and assessed against available Gibbs ensemble Monte Carlo data. At ambient conditions, the theoretical correlations weakly depend on the specific details of the molecular models and reproduce the simulation results with different degrees of accuracy, depending on the pair of interaction sites considered. The position and the strength of the hydrogen bond are quite satisfactorily predicted. RISM results for the internal energy are almost quantitative whereas the pressure is generally overestimated. As for the liquid-vapor phase coexistence, RISM predictions for the vapor branch and for the critical temperature are quite accurate; on the other side, the liquid branch densities, and consequently the critical density, are underestimated. We discuss our results in terms of intrinsic limitations, and suitable improvements, of the RISM approach in describing the physical properties of polar fluids, and in the perspective of a more general investigation of mixtures of methanol with nonpolar fluids of specific interest in the physics of associating fluids.
A particle-particle, particle-density algorithm for the calculation of electrostatic interactions of particles with slablike geometry
Authors: Alireza Ghasemi S. , Neelov Alexey , Goedecker Stefan
Published: December 2007

We present a fast and accurate method to calculate the electrostatic energy and forces of interacting particles with the boundary conditions appropriate to surfaces, i.e., periodic in the two directions parallel to the surface and free in the perpendicular direction. In the spirit of the Ewald method, the problem is divided into a short range and a long range part. The charge density responsible for the long range part is represented by plane waves in the periodic directions and by finite elements in the nonperiodic direction. Our method has computational complexity of O(Nglog(Ng)) with a very small prefactor, where Ng is the number of grid points.
Nuclear spin dynamics using time-dependent projection operators: Application to the saturation of dipolar order in slowly rotating samples
Authors: Charpentier T. , Sakellariou D. , Virlet J. , Dzheparov F. S. , Jacquinot J.-F.
Published: December 2007

An extension of the projection operators method is presented by considering explicit time-dependent projection operators. The usefulness of the present formalism is demonstrated by an investigation of nonadiabatic corrections to the evolution of a many-body system under a slow motion. A theoretical and experimental study of the saturation of nuclear spins dipolar order induced by a slow sample rotation is presented. Theoretically, the master equation of the dipolar order beyond the limit of an adiabatic evolution is established. It is shown how the time dependence of the projection operators is related to saturation of the dipolar order. A formal expression of the saturation rate is derived and its dependence upon the angle between rotation axis and external magnetic field is derived. Comparison with experimental data obtained on polycrystalline adamantane validates our theoretical approach.
Reduction of the Rayleigh-Taylor instability growth with cocktail color irradiation
Authors: Otani K. , Shigemori K. , Sakaiya T. , Fujioka S. , Sunahara A. , Nakai M. , Shiraga H. , Azechi H. , Mima K.
Published: December 2007

A novel method for reducing the Rayleigh-Taylor instability (RTI) growth in inertial confinement fusion (ICF) targets is reported. It is well known that high-density compression of ICF targets is potentially prevented by the RTI. Previous studies [K. Shigemori et al., Phys. Rev. Lett. 78, 250 (1997), S. G. Glendinning et al., Phys. Rev. Lett. 78, 3318 (1997), and H. Azechi et al., Phys. Plasmas 4, 4079 (1997)] have indicated that nonlocal electron heat transport enhances the effect on the ablative stabilization of the RTI growth with long wavelength laser irradiation. Planar target experiments, using a small fraction of a long wavelength laser (λ=0.53 or 1.05μm) in addition to the main drive laser (λ=0.35μm), were conducted to verify the RTI reduction by inducing the effect of the nonlocal electron heat transport. The measured RTI growth rate for this “cocktail-color” laser irradiation was clearly reduced from that for the “single-color” short-wavelength laser irradiation. The experimental growth factors are in good agreement with the ablative RTI formula coupled with a one-dimensional Fokker-Planck simulation code.
Analysis of the discharge channel structure upon nanosecond electrical explosion of wires
Authors: Tkachenko S. I. , Barishpoltsev D. V. , Ivanenkov G. V. , Romanova V. M. , Ter-Oganesyan A. E. , Mingaleev A. R. , Shelkovenko T. A. , Pikuz S. A.
Published: December 2007

The structure of the discharge channel during nanosecond wire explosions has been studied using laser probing. Wires of 25μm diameter and 12mm length were exploded in air and vacuum by 10kA current pulse having a 50A∕ns rate of rise. Upon electrical explosion of thin wires in the air, the development of shock waves was observed. The propagation of shock waves was analyzed, and it was possible to draw conclusions on the location of the flow of most of the current in the volume of the discharge channel. This permitted distinguishing between two scenarios (shunting and internal) of the interelectrode gap breakdown development. The scenario depends to a large extent on the properties of the exploding wire material. The same two scenarios are valid upon electrical explosion of wire in vacuum. Moreover, if secondary breakdown develops in the internal scenario, the value of the energy deposition in the wire material during explosion in vacuum may be comparable with that found during explosion in air.
Exchange bias in bulk Mn rich Ni–Mn–Sn Heusler alloys
Authors: Khan Mahmud , Dubenko Igor , Stadler Shane , Ali Naushad
Published: December 2007

An experimental study on the exchange bias properties of bulk polycrystalline Ni50Mn50−xSnx Heusler alloys has been performed. Martensitic transformations have been observed in the alloys for some critical Sn concentrations. The alloys, while in their respective martensitic phases, are found to exhibit exchange bias effect. Shifts in hysteresis loops of up to 225Oe were observed in the 50kOe field cooled samples. The observed exchange bias behavior in Ni50Mn50−xSnx is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system.
Quasiexactly solvable difference equations
Authors: Sasaki Ryu
Published: December 2007

Several explicit examples of quasiexactly solvable “discrete” quantum mechanical Hamiltonians are derived by deforming the well-known exactly solvable Hamiltonians of one degree of freedom. These are difference analogs of the well-known quasiexactly solvable systems, the harmonic oscillator (with∕without the centrifugal potential) deformed by a sextic potential, and the 1∕sin2x potential deformed by a cos2x potential. They have a finite number of exactly calculable eigenvalues and eigenfunctions.
Microcantilever actuation via periodic internal heating
Authors: Lee Jungchul , King William P.
Published: December 2007

This paper reports electrothermal actuation of silicon microcantilevers having integrated resistive heaters. Periodic electrical excitation induced periodic resistive heating in the cantilever, while the cantilever deflection was monitored with a photodetector. Excitation was either at the cantilever resonant frequency, f0, f0∕2, or f0∕3. When the time averaged maximum cantilever temperature was 174°C, the cantilever out-of-plane actuation amplitude was 484nm near the cantilever resonance frequency of 24.9kHz. This actuation was sufficiently large to operate the cantilever in intermittent contact mode and scan a calibration grating of height of 20nm.
Controlling microchannel gas flow rates through time-modulated pressure pulsation
Authors: Chakraborty Suman , Bhalla Amneet Pal Singh
Published: December 2007

In this paper, the proposition of obtaining controlled time-periodic mass flow rates of gases through axial pressure pulsations in circular microchannels, within the slip flow regime, is critically investigated. Various types of controlling waveforms are studied through the superposition of time-harmonic solutions corresponding to sinusoidal pulsations, as weighted by the pertinent Fourier coefficients and smoothened by appropriate discontinuity-handling functions. These studies effectively explore the extent to which various input parameters concerned with the slip flow boundary condition can influence the mass flow rate controlling mechanism, with variations in the applied pulsation frequency. Based on these considerations, a signature map is also constructed, which identifies the precise flow controlling parameters as a single valued function of the operating frequency. This generalized map may not only turn out to be useful for developing a fundamental understanding on the effect of frequency variations on mass flow rate controlled gas microflows but can also provide valuable insights into the design of improved microactuators and micropumps.
Identification of a Ni0.5(Al0.5−xMnx) B2 phase at the heterophase interfaces of Cu-rich precipitates in an α-Fe matrix
Authors: Kolli R. Prakash , Mao Zugang , Seidman David N. , Keane Denis T.
Published: December 2007

A phase with the stoichiometry Ni0.5(Al0.5−xMnx) is observed at heterophase interfaces of Cu-rich precipitates in an α-Fe matrix, utilizing atom-probe tomography. First-principles calculations are utilized to determine the substitutional energies, yielding EMn→Ni=0.916eVatom−1 and EMn→Al=−0.016eVatom−1 indicating that the manganese atoms prefer substituting at Al sublattice sites instead of Ni sites. A synchrotron radiation experiment demonstrates that the identified phase possesses the B2 structure.
Is the “out-of-plane” magnetic perturbation always a quadrupole in the Hall-mediated magnetic reconnection?
Authors: Bian N. H. , Vekstein G.
Published: December 2007

The structure of the “out-of-plane” component of the magnetic field is studied from the two-fluid description of magnetic reconnection via resistive tearing instability in a force-free field. Odd parity of the out-of-plane field component signifies a quadrupolar structure, which is usually taken as a signature of the Hall-mediated magnetic reconnection. Here we argue that the structure of the out-of-plane magnetic perturbation is not uniquely specified by the regime of reconnection. Thus, it can be quadrupolar in the standard magnetohydrodynamics (MHD) regime of magnetic reconnection, while being nonquadrupolar in the Hall-MHD regimes.
Optical properties of patterned InAs quantum dot ensembles grown on GaAs nanopyramids
Authors: Liang B. L. , Wong P. S. , Nuntawong N. , Albrecht A. R. , Tatebayashi J. , Rotter T. J. , Balakrishnan G. , Huffaker D. L.
Published: December 2007

We demonstrate the ability to form either coupled or isolated patterned quantum dot (PQD) ensembles on nanopatterned GaAs pyramidal buffers. The coupled PQD “clusters” consist of close-spaced PQDs with inter-QD spacing of 5nm. The isolated PQD “pairs” are comprised of two PQDs well separated by 110nm. The photoluminescence behavior, measured in integrated intensity, linewidth, and emission peak as a function of excitation intensity and temperature, indicates lateral coupling within the QD clusters and an isolated nature for QD pairs. The ability to tailor PQD formation and subsequent carrier recombination characteristic may prove useful in developing PQD-based devices for optical computing applications.
Simultaneous sum-frequency and vibro-acoustography imaging for nondestructive evaluation and testing applications
Authors: Mitri F. G. , Silva G. T. , Greenleaf J. F. , Fatemi M.
Published: December 2007

High-resolution ultrasound imaging systems for inspection of defects and flaws in materials are of great demand in many industries. Among these systems, Vibro-acoustography (VA) has shown excellent capabilities as a noncontact method for nondestructive high-resolution imaging applications. This method consists of mixing two confocal ultrasound beams, slightly shifted in frequency, to produce a dynamic (oscillatory) radiation force in the region of their intersection. This force vibrates the object placed at the focus of the confocal transducer. As a result of the applied force, an acoustic emission field at the difference frequency of the primary incident ultrasound beams is produced. In addition to the difference frequency acoustic emission signal, there exists another signal at the sum frequency, formed in the intersection region of the two primary beams. The goal of this study is to investigate the formation of high-resolution images using the sum frequency of ultrasound waves in VA while concurrently forming the conventional difference-frequency VA image, thereby increasing the amount of information acquired during a single scan. A theoretical model describing the sum-frequency wave propagation, including beam forming and image formation in the confocal configuration, is developed and verified experimentally. Moreover, sample experiments are performed on a flawed fiber-reinforced ceramic composite plate. Images at both the difference and sum frequencies are compared and discussed. Results show that the sum-frequency image produces a high-resolution C scan of the plate by which the flaws and structural details of the plate can be detected.
Suppression of the shear band instability during plastic flow of nanometer-scale confined metallic glasses
Authors: Donohue A. , Spaepen F. , Hoagland R. G. , Misra A.
Published: December 2007

The shear band instability that occurs during plastic deformation of metallic glasses limits the application of these high-strength materials. We show that this instability can be suppressed in nanometer-scale metallic glasses constrained by ultrafine crystalline layers. Free-standing Cu/amorphous Pd0.77Si0.23 multilayers consisting either of 10∕90nm glass/Cu or 100∕100nm glass/Cu were deformed to layer thickness reductions greater than 75% by cold rolling or bending, respectively. Transmission electron microscopy showed uniform reduction in the layer thickness with no shear band formation in the amorphous layers. The mechanisms that allow homogeneous codeformation of metallic glasses with nanoscale crystalline layers at high stresses are discussed.