bluuebunny/crossref_metadata_2025 huggingface dataset:
RAPID AMMONIUM‐ AND NITRATE‐INDUCED PERTURBATIONS TO CHL a FLUORESCENCE IN NITROGEN‐STRESSED DUNALIELLA TERTIOLECTA (CHLOROPHYTA)1
Authors: Young Erica B. , Beardall John
Published: October 2010

When NH4+ or NO3− was supplied to NO3−‐stressed cells of the microalga Dunaliella tertiolecta Butcher, immediate transient changes in chl a fluorescence were observed over several minutes that were not seen in N‐replete cells. These changes were predominantly due to nonphotochemical fluorescence quenching. Fluorescence changes were accompanied by changes in photosynthetic oxygen evolution, indicating interactions between photosynthesis and N assimilation. The magnitude of the fluorescence change showed a Michaelis‐Menten relationship with half‐saturation concentration of 0.5 μM for NO3− and 10 μM for NH4+. Changes in fluorescence responses were characterized in D. tertiolecta both over 5 days of N starvation and in cells cultured at a range of NO3−‐limited growth rates. Variation in responses was more marked in starved than in limited cells. During N starvation, the timing and onset of the fluorescence responses were different for NO3− versus NH4+ and were correlated with changes in maximum N uptake rate during N starvation. In severely N‐starved cells, the major fluorescence response to NO3− disappeared, whereas the response to NH4+ persisted. N‐starved cells previously grown with NH4+ alone showed fluorescence responses with NH4+ but not NO3− additions. The distinct responses to NO3− and NH4+ may be due to the differences between regulation of the uptake mechanisms for the two N sources during N starvation. This method offers potential for assessing the importance of NO3− or NH4+ as an N source to phytoplankton populations and as a diagnostic tool for N limitation.
UV RADIATION, PHOSPHORUS, AND THEIR COMBINED EFFECTS ON THE TAXONOMIC COMPOSITION OF PHYTOPLANKTON IN A BOREAL LAKE1
Authors: Xenopoulos Marguerite A. , Frost Paul C.
Published: October 2010

We examined how UV radiation and phosphorus (P) affect the taxonomic composition, abundance, and biomass of phytoplankton in an oligotrophic boreal lake. We exposed phytoplankton to three different solar radiation regimes (PAR + UV‐A radiation [UVAR]+ UV‐B radiation [UVBR], PAR + UVAR, and PAR only) and to five levels of P. The biomass of small chrysophytes was reduced by 350% after exposure to PAR + UVAR + UVBR compared with PAR only. No other taxa were found to be negatively affected by exposure to UVBR. Several taxa (e.g. Chry‐ sochromulina laurentiana Kling) were sensitive to UVAR, whereas others (e.g. Tabellaria flocculosa (Roth) Kutzing) were not affected by UV radiation exposure. Principal components analysis ordination separated phytoplankton that were negatively affected by UV radiation and/or positively affected by P treatments (e.g. small chrysophytes, Cryptomonas rostratiformis, T. flocculosa) from those that generally were unaffected by either treatment (e.g. desmids, some Cyanobacteria). Richness, Shannon‐Weaver diversity, and evenness were significantly higher in phytoplankton communities shielded from UVAR and UVBR. The relationship between diversity and richness was positive in all phytoplankton samples except in those exposed to UVBR. Thus, UVBR‐exposed phytoplankton communities were dominated by a few species even though the number of taxa remained relatively unchanged. Consequently, alterations in the UV environments of lakes resulting from climate warming (e.g. drought) and land‐use change (e.g. increased P export) will likely promote shifts in the community composition of lake phytoplankton.
CHOREONEMA (CORALLINALES, RHODOPHYTA): 18S rDNA PHYLOGENY AND RESURRECTION OF THE HAPALIDIACEAE FOR THE SUBFAMILIES CHOREONEMATOIDEAE, AUSTROLITHOIDEAE, AND MELOBESIOIDEAE
Authors: Harvey Adele S. , Broadwater Sharon T. , Woelkerling William J. , Mitrovski Paul J.
Published: October 2010

Phylogenetic analyses of 18S rDNA gene data for Choreonema thuretii (Corallinales, Rhodophyta) and available data for other coralline red algae indicated that Choreonema belongs to the same lineage as other taxa of Corallinales possessing tetra/bisporangial conceptacles with multiporate plates. These results, when integrated with extant morphological/anatomical data, ultrastructural data, and taxonomic data led to the conclusion that all taxa of Corallinales possessing multiporate conceptacles belong to a distinct family, the Hapalidiaceae. Recognition of the Hapalidiaceae as a distinct family was supported both phylogenetically and phenetically. The Hapalidiaceae includes those taxa of Corallinales whose tetrasporangia produce zonately arranged spores and whose tetra/bisporangia are borne in conceptacles, produce apical plugs, and develop beneath multiporate plates. The Hapalidiaceae includes the subfamilies Choreonematoideae, Melobesioideae, and Austrolithoideae, formerly placed in the Corallinaceae sensu lato. The Choreonematoideae lack cell connections between adjacent vegetative filaments and have a multiporate plate that is acellular at maturity, consisting only of a calcium carbonate matrix. The Austrolithoideae and Melobesioideae both have cellular pore plates; taxa of Melobesioideae have cell fusions between cells of adjacent vegetative filaments, whereas taxa of Austrolithoideae lack cellular connections between adjacent vegetative filaments. Inclusion of the Austrolithoideae in the Hapalidiaceae was based entirely on morphological/anatomical evidence; molecular evidence currently is lacking. Relevant historical and nomenclatural data are included.
FLAGELLAR REGENERATION IN SPERMATOZOPSIS SIMILIS (CHLOROPHYTA)
Authors: Schoppmeier Jutta , Lechtreck Karl‐Ferdinand
Published: October 2010

The unicellular green alga Spermatozopsis similis Preisig et Melkonian bears two flagella of unequal length. After deflagellation, cells first regenerated the longer flagellum to about one third of its original length, before the shorter flagellum started to develop. Growth rates were similar for both flagella. Thus, the length difference between both flagella was restored by a lag‐phase during regeneration of the shorter flagellum. To explain the lag‐phase, we have considered a gating mechanism near the flagellar base that controls the entry of precursors into the flagellum. This would allow cells to restrict the time of effective flagellar growth and thereby control flagellar length. Our data indicated that cells are capable of individually regulating flagellar assembly onto basal bodies. We discuss a recent model of flagellar length regulation based on a balance of assembly and disassembly and conclude that flagellar length is controlled by additional factors, including the availability of flagellar proteins and the developmental status of basal bodies.
PHOTOSYNTHETIC FUNCTION IN DUNALIELLA TERTIOLECTA (CHLOROPHYTA) DURING A NITROGEN STARVATION AND RECOVERY CYCLE
Authors: Young Erica B. , Beardall John
Published: October 2010

Phytoplankton can be exposed to periods of N starvation with episodic N resupply. N starvation in Dunaliella tertiolecta (Butcher) measured over 4 days was characterized by slow reduction in cell chl and protein content and chl/carotenoid ratio and a decline in photosynthetic capacity and maximum quantum yield of photosynthesis (Fv/Fm). In the early stages of N starvation, cell division was maintained despite reduction in cellular chl. Chl content was more sensitive than carotenoids to N deprivation, and cellular chl a was maintained preferentially over chl b under N starvation. NO3− resupply stimulated rapid and complete recovery of Fv/Fm (from 0.4 to 0.7) within 24 h and commencement of cell division after 10 h, although N‐replete levels of cell chl and protein were not reestablished within 24 h. Recovery of Fv/Fm was correlated with increases in cell chl and protein and was more related to increases in Fm than to changes in F0. Recovery of Fv/Fm was biphasic with a second phase of recovery commencing 4–6 h after resupply of NO3−. Uptake of NO3− from the external medium and the recovery of Fv/Fm, cell chl, and protein were inhibited when either cytosolic or chloroplastic protein synthesis was inhibited by cycloheximide or lincomycin, respectively; a time lag observed before maximum NO3− uptake was consistent with synthesis of NO3− transporters and assimilation enzymes. When both chloroplastic and cytosolic translation was inhibited, Fv/Fm declined dramatically. Dunaliella tertiolecta demonstrated a capacity to rapidly reestablish photosynthetic function and initiate cell division after N resupply, an important strategy in competing for limiting inorganic N resources.
IN SEARCH OF A PHYSIOLOGICAL BASIS FOR COVARIATIONS IN LIGHT‐LIMITED AND LIGHT‐SATURATED PHOTOSYNTHESIS1
Authors: Behrenfeld Michael J. , Prasil Ondrej , Babin Marcel , Bruyant Flavienne
Published: October 2010

The photosynthesis‐irradiance (PE) relationship links indices of phytoplankton biomass (e.g. chl) to rates of primary production. The PE curve can be characterized by two variables: the light‐limited slope (αb) and the light‐saturated rate (Pbmax) of photosynthesis. Variability in PE curves can be separated into two categories: that associated with changes in the light saturation index, Ek (=Pbmax/αb) and that associated with parallel changes in αband Pbmax (i.e. no change in Ek). The former group we refer to as “Ek‐dependent” variability, and it results predominantly from photoacclimation (i.e. physiological adjustments in response to changing light). The latter group we refer to as “Ek‐independent” variability, and its physiological basis is unknown. Here, we provide the first review of the sporadic field and laboratory reports of Ek‐independent variability, and then from a stepwise analysis of potential mechanisms we propose that this important yet largely neglected phenomenon results from growth rate–dependent variability in the metabolic processing of photosynthetically generated reductants (and generally not from changes in the oxygen‐evolving PSII complexes). Specifically, we suggest that as growth rates decrease (e.g. due to nutrient stress), reductants are increasingly used for simple ATP generation through a fast (<1s) respiratory pathway that skips the carbon reduction cycle altogether and is undetected by standard PE methodologies. The proposed mechanism is consistent with the field and laboratory data and involves a simple new “twist” on established metabolic pathways. Our conclusions emphasize that simple reductants, not reduced carbon compounds, are the central currency of photoautotrophs.
Diversity of Coccoid Algae in Minnesota and North Dakota Lakes
Authors: Fawley M. W. , Fawley K. P. , Hoffman M. J.
Published: October 2010

The coccoid algae (a.k.a ‘little green balls’) are important primary producers in freshwater communities, but very little is known about their diversity. This lack of knowledge results from the extremely small size and simple morphology of these organisms, which makes identification by light microscopy essentially impossible. However, molecular techniques allow differentiation of taxa at various levels and can ultimately lead to species identification. We have isolated several hundred cultures of coccoid algae from lakes and ponds in Itasca State Park in north‐western Minnesota and Arrowwood National Wildlife Refuge in central North Dakota. Many of these isolates have been examined by light microscopy, 18S rDNA PCR–RFLP analysis, and 18S rDNA sequence analysis. In addition, some taxa with multiple isolates have been examined by rbcL and ribosomal RNA ITS sequence analysis. Our results indicate a high level of diversity, including possible new species of Chlorella, Muriella, Pseudomuriella and Mychonastes, among others. We will discuss the results of our analyses, including implications for identification of taxa and higher level systematics. Supported by National Science Foundation Grants DBI‐00703867, MCB‐0084188 and DEB‐0128952.
New Insights in the Cryptonemiales–Rhodymeniales Complex and Resurrection of the Allied Red Algal Order Nemastomatales Kylin 1925 as Inferred From rbcL Sequence Analysis and Comparative Reproductive Morphology
Authors: Gavio B.
Published: October 2010

In a global molecular phylogeny of florideophycean red algae inferred from chloroplast‐encoded rbcL sequence analysis, a major monophyletic assemblage comprises the Cryptonemiales (=Halymeniales), the Rhodymeniales, the Schizymeniaceae (Schizymenia, Titanophora, Platoma) and the Nemastomataceae (Nemastoma, Predaea). The phylogenetic significance of the auxiliary cell and its interaction with the fertilized egg cell in this assemblage is discussed in relation to established and newly proposed classification schemes. The order Nemastomatales Kylin 1925 is reinstated and emended to contain the nonprocarpic Schizymeniaceae and Nemastomataceae. Unifying characters of the Nemastomatales include fertilized carpogonia that may establish fusions with carpogonial nutritive cells prior to the formation of septate connecting filaments, and simple gonimoblasts developing outwardly from auxiliary cells or from connecting filaments in their vicinity. The auxiliary cell is a transformed vegetative intercalary cell (Sebdeniaceae), that becomes surrounded by either clusters of nutritive cells (Nemastomataceae), involucral filaments (Schizymeniaceae) or by three‐dimensional ampullary filaments (Halymeniaceae including the Corynomorphaceae), or is part of a procarp (Rhodymeniales). The homology of outward gonimoblast initiation and maturation into a simple ball of carposporangia in the Cryptonemiales, Rhodymeniales and Nemastomatales will be illustrated.
Phylogeny of the Conjugating Green Algae (Zygnematales and Desmidiales) Based on Plastid and Mitochondrial Gene Sequences
Authors: McCourt R. M. , Park J. , Hewitt D. A. , Karol K. G.
Published: October 2010

The conjugating green algae (Order Zygnematales and Desmidiales) are charophyceans, that is, they are among the green algae most closely related to land plants. Compared to the five other groups of charophyceans (Mesostigma, Klebsormidiales, Chlorokybales, Coleochaetales, Charales), the conjugating greens are by far the most diverse taxonomically (6 families, about 55 genera, 3–4000 species) and very widespread in distribution (including common species such as Spirogyra, Zygnema, Cosmarium, and Staurastrum). Thallus shape ranges from simple, oblong unicells (saccoderm desmids, or Mesotaeniaceae), to unbranched filaments of cells with smooth walls (Zygnemataceae), to elaborately ornate and deeply incised unicells or filaments made of such cells (placoderm desmids, in four families). Prior analyses of sequences of the chloroplast‐encoded gene rbcL (1354 bp, or 95% of the gene) sampled from all six families showed that two of the traditional families (saccoderms and filamentous forms) are paraphyletic, i.e. they do not form two independent clades, although the component genera may together constitute a monophyletic group. In contrast, three families of placoderm desmids formed three monophyletic groups within a larger clade. New analyses using partial sequences from the mitochondrial gene coxIII (608 bp, or 76% of the gene) for 21 species of conjugating green algae from all six families supported the conclusions of the rbcL analysis, although bootstrap support for each gene along was weak for many branches. The coxIII sequences are more variable than rbcL and have proportionately more parsimony‐informative sites (43% vs. 34%, respectively). Combining the two genes improved the resolution of the resulting tree: (1) bootstrap support increased for all branches, particularly in regards relationships of placoderm desmids; and (2) monophyly of a clade containing filamentous and saccoderm desmids was strongly supported. We conclude that phylogeny of conjugating green algae will be much improved by sampling from additional genes.
Application of optical emission spectroscopy for He I considering the spatial structure of radiation trapping in MAP-II divertor simulator
Authors: Iida Y. , Kado S. , Muraki A. , Tanaka S.
Published: October 2010

The He I optical emission spectroscopy that considers the spatial structure of radiation trapping was proposed by us and was applied to a MAP-II divertor simulator. The spatial distribution of the optical escape factor was calculated from the n P1 (n≥3) state profiles measured by visible spectroscopy. The profile of 2 P1, which is immeasurable by visible spectroscopy, needs to be broader than that of the 3 P1 state. The sensitivity of the 2 P1 profile to the Te value estimated by He I spectroscopy is investigated.
Quiet periods in edge turbulence preceding the L-H transition in the National Spherical Torus Experiment
Authors: Zweben S. J. , Maqueda R. J. , Hager R. , Hallatschek K. , Kaye S. M. , Munsat T. , Poli F. M. , Roquemore A. L. , Sechrest Y. , Stotler D. P.
Published: October 2010

This paper describes the first observations in the National Spherical Torus Experiment (NSTX) [S. M. Kaye et al., Phys. Plasmas 8, 1977 (2001)] of “quiet periods” in the edge turbulence preceding the low-to-high (L-H) mode transition, as diagnosed by the gas puff imaging (GPI) diagnostic near the outer midplane separatrix. During these quiet periods the GPI Dα light emission pattern was transiently similar to that seen during H-mode, i.e., with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of ∼3 kHz for at least 30 ms before the L-H transition, and were correlated with changes in the direction of the local poloidal velocity. The GPI turbulence images were also analyzed to obtain an estimate for the dimensionless poloidal shearing S=(dVp/dr)(Lr/Lp)τ. The values of S were strongly modulated by the quiet periods but did not significantly vary during the ∼30 ms preceding the L-H transition. Since neither the quiet periods nor the shear flow increased immediately preceding the L-H transition, neither of these appears to be the trigger for this transition, at least for these cases in NSTX.
Innovations in optical coupling of the KSTAR electron cyclotron emission imaging diagnostic
Authors: Liang T. , Tobias B. , Kong X. , Domier C. W. , Luhmann N. C. , Lee W. , Yun G. S. , Park H. K.
Published: October 2010

The installation of a new electron cyclotron emission imaging diagnostic for the Korea Superconducting Tokamak Advanced Research (KSTAR) is underway, making use of a unique optical port cassette design, which allows placement of refractive elements inside the cryostat region without adverse effects. The result is unprecedented window access for the implementation of a state of the art imaging diagnostic. A dual-array optical design has been developed, capable of simultaneously imaging the high and low field sides of the plasma with independent features of focal plane translation, vertical zoom, and radial channel spacing. The number of translating optics has been minimized by making use of a zoom lens triplet and parabolic plasma facing lens for maximum channel uniformity over a continuous vertical zoom range of 3:1. The simulated performance of this design is presented along with preliminary laboratory characterization data.
Divertor IR thermography on Alcator C-Mod
Authors: Terry J. L. , LaBombard B. , Brunner D. , Payne J. , Wurden G. A.
Published: October 2010

Alcator C-Mod is a particularly challenging environment for thermography. It presents issues that will similarly face ITER, including low-emissivity metal targets, low-Z surface films, and closed divertor geometry. In order to make measurements of the incident divertor heat flux using IR thermography, the C-Mod divertor has been modified and instrumented. A 6° toroidal sector has been given a 2° toroidal ramp in order to eliminate magnetic field-line shadowing by imperfectly aligned divertor tiles. This sector is viewed from above by a toroidally displaced IR camera and is instrumented with thermocouples and calorimeters. The camera provides time histories of surface temperatures that are used to compute incident heat-flux profiles. The camera sensitivity is calibrated in situ using the embedded thermocouples, thus correcting for changes and nonuniformities in surface emissivity due to surface coatings.
Ultrafast spectroscopy diagnostic to measure localized ion temperature and toroidal velocity fluctuations
Authors: Uzun-Kaymak I. U. , Fonck R. J. , McKee G. R. , Schoenbeck N. , Smith D. , Winz G. , Yan Z.
Published: October 2010

A dual-channel high-efficiency, high-throughput custom spectroscopic system has been designed and implemented at DIII-D to measure localized ion thermal fluctuations associated with drift wave turbulence. A large-area prism-coupled transmission grating and high-throughput collection optics are employed to observe C VI emission centered near λ=529 nm. The diagnostic achieves 0.25 nm resolution over a 2.0 nm spectral band via eight discrete spectral channels. A turbulence-relevant time resolution of 1 μs is achieved using cooled high-speed avalanche photodiodes and ultralow-noise preamplifiers. The system sensitivity is designed to provide measurements of normalized ion temperature fluctuations on the order of δTi/Ti≤1%.
Analysis of the quantum-classical Liouville equation in the mapping basis
Authors: Nassimi Ali , Bonella Sara , Kapral Raymond
Published: October 2010

The quantum-classical Liouville equation provides a description of the dynamics of a quantum subsystem coupled to a classical environment. Representing this equation in the mapping basis leads to a continuous description of discrete quantum states of the subsystem and may provide an alternate route to the construction of simulation schemes. In the mapping basis the quantum-classical Liouville equation consists of a Poisson bracket contribution and a more complex term. By transforming the evolution equation, term-by-term, back to the subsystem basis, the complex term (excess coupling term) is identified as being due to a fraction of the back reaction of the quantum subsystem on its environment. A simple approximation to quantum-classical Liouville dynamics in the mapping basis is obtained by retaining only the Poisson bracket contribution. This approximate mapping form of the quantum-classical Liouville equation can be simulated easily by Newtonian trajectories. We provide an analysis of the effects of neglecting the presence of the excess coupling term on the expectation values of various types of observables. Calculations are carried out on nonadiabatic population and quantum coherence dynamics for curve crossing models. For these observables, the effects of the excess coupling term enter indirectly in the computation and good estimates are obtained with the simplified propagation.
Nonlinear Korteweg–de Vries equation for soliton propagation in relativistic electron-positron-ion plasma with thermal ions
Authors: Saeed R. , Shah Asif , Noaman-ul-Haq Muhammad
Published: October 2010

The nonlinear propagation of ion-acoustic solitons in relativistic electron-positron-ion plasma comprising of Boltzmannian electrons, positrons, and relativistic thermal ions has been examined. The Korteweg–de Vries equation has been derived by reductive perturbation technique. The effect of various plasma parameters on amplitude and structure of solitary wave is investigated. The pert graphical view of the results has been presented for illustration. It is observed that increase in the relativistic streaming factor causes the soliton amplitude to thrive and its width shrinks. The soliton amplitude and width decline as the ion to electron temperature ratio is increased. The increase in positron concentration results in reduction of soliton amplitude. The soliton amplitude enhances as the electron to positron temperature ratio is increased. Our results may have relevance in the understanding of astrophysical plasmas.
Two-dimensional to three-dimensional structural transition of gold cluster Au10 during soft landing on TiO2 surface and its effect on CO oxidation
Authors: Li Hui , Pei Yong , Zeng Xiao Cheng
Published: October 2010

We investigate the possible structural transition of a planar Au10 cluster during its soft landing on a TiO2 (110) surface with or with no oxygen defects. The collision between the gold cluster and the oxide surface is simulated using the Car–Parrinello quantum molecular dynamics method. Both high-speed and low-speed conditions typically implemented in soft-landing experiments are simulated. It is found that under a high-speed condition, the gold cluster Au10 can undergo a sequence of structural transitions after colliding with a defect-free TiO2 (110) surface. When the TiO2 (110) surface possesses oxygen vacancies, however, chemical bonds can form between gold and Ti atoms if gold atoms contact directly with the vacancies. As a consequence, one oxygen vacancy is capable of trapping one Au atom, and thus can split the Au10 into two parts while bouncing back from the surface. In addition, we study reaction pathways for the CO oxidation based on three isomer structures of Au10 observed in the soft-landing simulation: (1) the precollision two-dimensional structure, (2) a postcollision three-dimensional (3D) structure, and (3) an intermediate (transient) 3D structure that appeared in the midst of the collision. This study allows us to examine the structure-activity relationship using the Au10 as a prototype model catalyst.
Molecular simulation study of cavity-generated instabilities in the superheated Lennard-Jones liquid
Authors: Torabi Korosh , Corti David S.
Published: October 2010

Previous equilibrium-based density-functional theory (DFT) analyses of cavity formation in the pure component superheated Lennard-Jones (LJ) liquid [S. Punnathanam and D. S. Corti, J. Chem. Phys. 119, 10224 (2003); M. J. Uline and D. S. Corti, Phys. Rev. Lett. 99, 076102 (2007)] revealed that a thermodynamic limit of stability appears in which no liquidlike density profile can develop for cavity radii greater than some critical size (being a function of temperature and bulk density). The existence of these stability limits was also verified using isothermal-isobaric Monte Carlo (MC) simulations. To test the possible relevance of these limits of stability to a dynamically evolving system, one that may be important for homogeneous bubble nucleation, we perform isothermal-isobaric molecular dynamics (MD) simulations in which cavities of different sizes are placed within the superheated LJ liquid. When the impermeable boundary utilized to generate a cavity is removed, the MD simulations show that the cavity collapses and the overall density of the system remains liquidlike, i.e., the system is stable, when the initial cavity radius is below some certain value. On the other hand, when the initial radius is large enough, the cavity expands and the overall density of the system rapidly decreases toward vaporlike densities, i.e., the system is unstable. Unlike the DFT predictions, however, the transition between stability and instability is not infinitely sharp. The fraction of initial configurations that generate an instability (or a phase separation) increases from zero to unity as the initial cavity radius increases over a relatively narrow range of values, which spans the predicted stability limit obtained from equilibrium MC simulations. The simulation results presented here provide initial evidence that the equilibrium-based stability limits predicted in the previous DFT and MC simulation studies may play some role, yet to be fully determined, in the homogeneous nucleation and growth of embryos within metastable fluids.
Approximate solutions to second order parabolic equations. I: Analytic estimates
Authors: Constantinescu Radu , Costanzino Nick , Mazzucato Anna L. , Nistor Victor
Published: October 2010

We establish a new type of local asymptotic formula for the Green’s function Gt(x,y) of a uniformly parabolic linear operator ∂t−L with nonconstant coefficients using dilations and Taylor expansions at a point z=z(x,y) for a function z with bounded derivatives such that z(x,x)=x∊RN. Our method is based on dilation at z, Dyson, and Taylor series expansions. We use the Baker–Campbell–Hausdorff commutator formula to explicitly compute the terms in the Dyson series. Our procedure leads to an explicit, elementary, algorithmic construction of approximate solutions to parabolic equations that are accurate to arbitrarity prescribed order in the short-time limit. We establish mapping properties and precise error estimates in the exponentially weighed, Lp-type Sobolev spaces Was,p(RN) that appear in practice.
Active-oxidation of Si as the source of vapor-phase reactants in the growth of SiOx nanowires on Si
Authors: Kim T.-H. , Shalav A. , Elliman R. G.
Published: October 2010

Gold-coated silicon wafers were annealed at temperatures in the range from 800–1100 °C in a N2 ambient containing a low (3–10 ppm) residual O2 concentration. A dense network of amorphous silica nanowires was only observed on samples annealed at temperatures above 1000 °C and was correlated with the development of faceted etch-pits in the Si surface. Comparison with known thermodynamic data for the oxidation of Si and vapor-pressures of reactants shows that nanowire growth is mediated by a vapor-liquid-solid mechanism in which the dominant vapor-phase source of reactants is SiO produced by the active oxidation of Si.
Hydrogen storage and phase transformations in Mg–Pd nanoparticles
Authors: Callini E. , Pasquini L. , Rude L. H. , Nielsen T. K. , Jensen T. R. , Bonetti E.
Published: October 2010

Microstructure refinement and synergic coupling among different phases are currently explored strategies to improve the hydrogen storage properties of traditional materials. In this work, we apply a combination of these methods and synthesize Mg–Pd composite nanoparticles by inert gas condensation of Mg vapors followed by vacuum evaporation of Pd clusters. Irreversible formation of the Mg6Pd intermetallic phase takes place upon vacuum annealing, resulting in Mg/Mg6Pd composite nanoparticles. Their hydrogen storage properties are investigated and connected to the undergoing phase transformations by gas-volumetric techniques and in situ synchrotron radiation powder x-ray diffraction. Mg6Pd transforms reversibly into different Mg–Pd intermetallic compounds upon hydrogen absorption, depending on temperature and pressure. In particular, at 573 K and 1 MPa hydrogen pressure, the metal-hydride transition leads to the formation of Mg3Pd and Mg5Pd2 phases. By increasing the pressure to 5 MPa, the Pd-richer MgPd intermetallic is obtained. Upon hydrogen desorption, the Mg6Pd phase is reversibly recovered. These phase transformations result in a specific hydrogen storage capacity associated with Mg–Pd intermetallics, which attain the maximum value of 3.96 wt % for MgPd and influence both the thermodynamics and kinetics of hydrogen sorption in the composite nanoparticles.
The persistence of the magnetocaloric effect in (La1−xAx)0.67Ba0.33Mn1.05O3−δ
Authors: Ancona-Torres C. , Pryds N. , Theil Kuhn L. , Bahl C. R. H. , Linderoth S.
Published: October 2010

Polycrystalline samples of (La1−xAx)0.67Ba0.33Mn1.05O3−δ, with A being a mixture of lanthanides containing 66% La, 22% Nd, 8% Pr, and 4% Ce, were prepared by the glycine-nitrate method, with target compositions of x=0, 0.33, 0.67, and 1. The effect of the mixture of lanthanides on the Curie temperature, TC, and the magnetocaloric properties was investigated. The prepared samples are single phase, with space group R3¯c. The lattice parameters and average A-site ionic radius, rA decrease linearly with x while the size disorder, as characterized by the variance, σ2, increases from 0.014 to 0.017 with x. As x is increased, the increase in σ2 drives a linear decrease in TC. The magnetic entropy change, ΔSM, for a field change of 1 T is obtained by magnetization measurements, giving a maximum value of 1.7 J/kg K, and a relative cooling power of 43 J/kg, independent of x. These results suggest that replacing lanthanum with a mixture of lanthanides is a realistic way to tune the working temperature of magnetocaloric manganites while maintaining a constant magnetocaloric effect.
AlN thin films grown on epitaxial 3C–SiC (100) for piezoelectric resonant devices
Authors: Lin Chih-Ming , Lien Wei-Cheng , Felmetsger Valery V. , Hopcroft Matthew A. , Senesky Debbie G. , Pisano Albert P.
Published: October 2010

Highly c-axis oriented heteroepitaxial aluminum nitride (AlN) films were grown on epitaxial cubic silicon carbide (3C–SiC) layers on Si (100) substrates using alternating current reactive magnetron sputtering at temperatures between approximately 300–450 °C. The AlN films were characterized by x-ray diffraction, scanning electron microscope, and transmission electron microscopy. A two-port surface acoustic wave device was fabricated on the AlN/3C–SiC/Si composite structure, and an expected Rayleigh mode exhibited a high acoustic velocity of 5200 m/s. The results demonstrate the potential of utilizing AlN films on epitaxial 3C–SiC layers to create piezoelectric resonant devices.
Experimental verification of full reconstruction of the near-field with a metamaterial lens
Authors: Morgado Tiago A. , Marcos João S. , Silveirinha Mário G. , Maslovski Stanislav I.
Published: October 2010

It is experimentally verified that a lens formed by tilted metallic wires enables the full reconstruction of the near-field, both in amplitude and phase. It is shown that since the electric field is measured at a significant electrical distance from the object under study the perturbation introduced by the measurement system may be less significant than in the case where the measurements are done in the immediate vicinity of the object, and thus the retrieved near-field may be more accurate. This suggests exciting applications for the tilted wire medium lens in near-field measurement.
Phase diagram of self-assembled rigid rods on two-dimensional lattices: Theory and Monte Carlo simulations
Authors: López L. G. , Linares D. H. , Ramirez-Pastor A. J. , Cannas S. A.
Published: October 2010

Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a two-dimensional system of particles with two bonding sites that, by decreasing temperature or increasing density, polymerize reversibly into chains with discrete orientational degrees of freedom and, at the same time, undergo a continuous isotropic-nematic (IN) transition. A complete phase diagram was obtained as a function of temperature and density. The numerical results were compared with mean field (MF) and real space renormalization group (RSRG) analytical predictions about the IN transformation. While the RSRG approach supports the continuous nature of the transition, the MF solution predicts a first-order transition line and a tricritical point, at variance with the simulation results.
Acoustics at nanoscale: Raman–Brillouin scattering from thin silicon-on-insulator layers
Authors: Lou N. , Groenen J. , Benassayag G. , Zwick A.
Published: October 2010

We report on Raman–Brillouin scattering from thin single silicon layers. Starting from a 33 nm silicon-on-insulator structure, a series of layers with progressively decreasing thicknesses was prepared using a chemical treatment consisting of oxide stripping/formation cycles. In order to determine these thicknesses, experimental Raman–Brillouin spectra are compared to calculations performed in the frame of the photoelastic model. We demonstrate that subnanometer changes in the silicon layer thickness can be derived from a proper analysis of the spectral response. It is shown that a 1 nm thick oxide forms during the chemical treatment.
A simultaneous probability density for the intracule and extracule coordinates
Authors: Proud Adam J. , Pearson Jason K.
Published: October 2010

We introduce the intex density X(R,u), which combines both the intracular and extracular coordinates to yield a simultaneous probability density for the position of the center-of-mass radius (R) and relative separation (u) of electron pairs. One of the principle applications of the intex density is to investigate the origin of the recently observed secondary Coulomb hole. The Hartree–Fock (HF) intex densities for the helium atom and heliumlike ions are symmetric functions that may be used to prove the isomorphism 2I(2R)=E(R), where I(u) is the intracule density and E(R) is the extracule density. This is not true of the densities that we have constructed from explicitly correlated wave functions. The difference between these asymmetric functions and their symmetric HF counterparts produces a topologically rich intex correlation hole. From the intex hole distributions (Xexact(R,u)−XHF(R,u)), we conclude that the probability of observing an electron pair with a very large interelectronic separation increases with the inclusion of correlation only when their center-of-mass radius is close to half of their separation.
DNA oxidation by singlet delta oxygen produced by atmospheric pressure microdischarges
Authors: Sousa Joao Santos , Bauville Gerard , Lacour Bernard , Puech Vincent , Touzeau Michel , Ravanat Jean-Luc
Published: October 2010

Arrays of microcathode sustained discharges were developed for the production of singlet delta oxygen (SDO) at atmospheric pressure. SDO densities higher than 3.5×1016 cm−3 have been efficiently produced and transported over distances longer than 50 cm. These arrays appear to be an ideal tool for examining the reactivity of SDO with biological components. Experiments were performed indicating that SDO is able to oxidize 2′-deoxyguanosine, a DNA constituent. It is shown that the 4-OH-8-oxodGuo formation is proportional to the number of SDO molecules while other reactive species could also be involved in the production of the nucleosides dSp and dZ.
Local statistics in natural scenes predict the saliency of synthetic textures
Authors: Tkačik Gašper , Prentice Jason S. , Victor Jonathan D. , Balasubramanian Vijay
Published: October 2010

The visual system is challenged with extracting and representing behaviorally relevant information contained in natural inputs of great complexity and detail. This task begins in the sensory periphery: retinal receptive fields and circuits are matched to the first and second-order statistical structure of natural inputs. This matching enables the retina to remove stimulus components that are predictable (and therefore uninformative), and primarily transmit what is unpredictable (and therefore informative). Here we show that this design principle applies to more complex aspects of natural scenes, and to central visual processing. We do this by classifying high-order statistics of natural scenes according to whether they are uninformative vs. informative. We find that the uninformative ones are perceptually nonsalient, while the informative ones are highly salient, and correspond to previously identified perceptual mechanisms whose neural basis is likely central. Our results suggest that the principle of efficient coding not only accounts for filtering operations in the sensory periphery, but also shapes subsequent stages of sensory processing that are sensitive to high-order image statistics.
Memory T cells persisting within the brain after local infection show functional adaptations to their tissue of residence
Authors: Wakim Linda M. , Woodward-Davis Amanda , Bevan Michael J.
Published: October 2010

The brain is not routinely surveyed by lymphocytes and is defined as an immuno-privileged site. However, viral infection of the brain results in the infiltration and long-term persistence of pathogen-specific CD8+T cells. These cells survive without replenishment from the circulation and are referred to as resident memory T cells (Trm). Brain Trm selectively express the integrin CD103, the expression of which is dependent on antigen recognition within the tissue. After clearance of virus, CD8+T cells persist in tight clusters, presumably at prior infection hot spots. Antigen persistence is not a prerequisite for T-cell retention, as suggested by the failure to detect viral genomes in the T-cell clusters. Furthermore, we show that an intracranial dendritic cell immunization regimen, which allows the transient introduction of antigen, also results in the generation of memory T cells that persist long term in the brain. Brain Trm die rapidly on isolation from the tissue and fail to undergo recall expansion after adoptive transfer into the bloodstream of antigen-challenged recipients. These ex vivo defects imply a dependency on the local milieu for function and survival. Cumulatively, this work shows that Trm are a specialized population of memory T cells that can be deposited in tissues previously thought to be beyond routine immune surveillance.
Heterogeneous myocyte enhancer factor-2 (Mef2) activation in myocytes predicts focal scarring in hypertrophic cardiomyopathy
Authors: Konno Tetsuo , Chen Dan , Wang Libin , Wakimoto Hiroko , Teekakirikul Polakit , Nayor Matthew , Kawana Masataka , Eminaga Seda , Gorham Joshua M. , Pandya Kumar , Smithies Oliver , Naya Francisco J. , Olson Eric N. , Seidman J. G. , Seidman Christine E.
Published: October 2010

Unknown molecular responses to sarcomere protein gene mutations account for pathologic remodeling in hypertrophic cardiomyopathy (HCM), producing myocyte growth and increased cardiac fibrosis. To determine if hypertrophic signals activated myocyte enhancer factor-2 (Mef2), we studied mice carrying the HCM mutation, myosin heavy-chain Arg403Gln, (MHC
403/+
) and an Mef2-dependent β-galactosidase reporter transgene. In young, prehypertrophic MHC
403/+
mice the reporter was not activated. In hypertrophic hearts, activation of the Mef2-dependent reporter was remarkably heterogeneous and was observed consistently in myocytes that bordered fibrotic foci with necrotic cells, MHC
403/+
myocytes with Mef2-dependent reporter activation reexpressed the fetal myosin isoform (βMHC), a molecular marker of hypertrophy, although MHC
403/+
myocytes with or without βMHC expression were comparably enlarged over WT myocytes. To consider Mef2 roles in severe HCM, we studied homozygous MHC
403/403
mice, which have accelerated remodeling, widespread myocyte necrosis, and neonatal lethality. Levels of phosphorylated class II histone deacetylases that activate Mef2 were substantially increased in MHC
403/403
hearts, but Mef2-dependent reporter activation was patchy. Sequential analyses showed myocytes increased Mef2-dependent reporter activity before death. Our data dissociate myocyte hypertrophy, a consistent response in HCM, from heterogeneous Mef2 activation and reexpression of a fetal gene program. The temporal and spatial relationship of Mef2-dependent gene activation with myocyte necrosis and fibrosis in MHC
403/+
and MHC
403/403
hearts defines Mef2 activation as a molecular signature of stressed HCM myocytes that are poised to die.
A Classification System for Hospital‐Based Infection Outbreaks
Authors: Ganney Paul S. , Madeo Maurice , Phillips Roger
Published: October 2010

Outbreaks of infection within semi‐closed environments such as hospitals, whether inherent in the environment (such as Clostridium difficile (C.Diff) or Methicillinresistant Staphylococcus aureus (MRSA) or imported from the wider community (such as Norwalk‐like viruses (NLVs)), are difficult to manage. As part of our work on modelling such outbreaks, we have developed a classification system to describe the impact of a particular outbreak upon an organization. This classification system may then be used in comparing appropriate computer models to real outbreaks, as well as in comparing different real outbreaks in, for example, the comparison of differing management and containment techniques and strategies. Data from NLV outbreaks in the Hull and East Yorkshire Hospitals NHS Trust (the Trust) over several previous years are analysed and classified, both for infection within staff (where the end of infection date may not be known) and within patients (where it generally is known). A classification system consisting of seven elements is described, along with a goodness‐of‐fit method for comparing a new classification to previously known ones, for use in evaluating a simulation against history and thereby determining how ‘realistic’ (or otherwise) it is.
Generalized Fokker–Planck Theory for Electron and Photon Transport in Biological Tissues: Application to Radiotherapy
Authors: Olbrant Edgar , Frank Martin
Published: October 2010

In this paper, we study a deterministic method for particle transport in biological tissues. The method is specifically developed for dose calculations in cancer therapy and for radiological imaging. Generalized Fokker–Planck (GFP) theory [Leakeas and Larsen, Nucl. Sci. Eng. 137 (2001), pp. 236–250] has been developed to improve the Fokker‐Planck (FP) equation in cases where scattering is forward‐peaked and where there is a sufficient amount of large‐angle scattering. We compare grid‐based numerical solutions to FP and GFP in realistic medical applications. First, electron dose calculations in heterogeneous parts of the human body are performed. Therefore, accurate electron scattering cross sections are included and their incorporation into our model is extensively described. Second, we solve GFP approximations of the radiative transport equation to investigate reflectance and transmittance of light in biological tissues. All results are compared with either Monte Carlo or discrete‐ordinates transport solutions.
Tunnelling magnetoresistance in disordered interacting nanoparticles
Authors: Mao Zhongquan , Chen Xi
Published: October 2010

Tunnelling magnetoresistance (TMR) of three-dimensional disordered ferromagnetic nanoparticles has been studied based on the Monte Carlo (MC) simulations. The dipolar interaction as well as the exchange coupling between the particles are carefully considered. It is found that the maximum TMR is nearly independent of the dipolar interaction, while it decreases with an increasing exchange interaction. The numerical results also reveal that the magnetic field sensitivity of the TMR depends not only on the interactions but also on the distributions of the anisotropy axes.
Novel polarization beam splitter with a tolerance to large random disorder
Authors: Zhou Jie , Shen Yi Feng , Wang Yong Chun , Zhan Yuan , Wu Fang Fang , Guo Chang Qing
Published: October 2010

We propose a design for a simple broad-angle polarization beam splitter (PBS) consisting of two rows of dielectric cylinders with different space periods. The finite-difference time-domain method simulations show that TM polarized light is reflected totally by this PBS but TE polarized light passes through it freely in a broad incident angle range (from −50° to 50°). The PBS can work over a wide frequency range (from 0.22 × (c/a) to 0.28 × (c/a)) with a high efficiency. Moreover, the PBS structure has a novel capability of tolerance to large random disorder, which is very advantageous for practical applications. Even when a random disorder of 15%a (a is space period) is introduced into the radius and position of each cylinder, the PBS structure can still maintain almost the same good performance and high splitting efficiency.