bluuebunny/crossref_metadata_2025 huggingface dataset:
“Massless” vector field in de Sitter universe
Authors: Garidi T. , Gazeau J.-P. , Rouhani S. , Takook M. V.
Published: March 2008

We proceed to the quantization of the massless vector field in the de Sitter (dS) space. This work is the natural continuation of a previous article devoted to the quantization of the dS massive vector field [J. P. Gazeau and M. V. Takook, J. Math. Phys. 41, 5920 (2000); T. Garidi et al., ibid. 43, 6379 (2002).] The term “massless” is used by reference to conformal invariance and propagation on the dS lightcone whereas “massive” refers to those dS fields which unambiguously contract to Minkowskian massive fields at zero curvature. Due to the combined occurrences of gauge invariance and indefinite metric, the covariant quantization of the massless vector field requires an indecomposable representation of the de Sitter group. We work with the gauge fixing corresponding to the simplest Gupta–Bleuler structure. The field operator is defined with the help of coordinate-independent de Sitter waves (the modes). The latter are simple to manipulate and most adapted to group theoretical approaches. The physical states characterized by the divergencelessness condition are, for instance, easy to identify. The whole construction is based on analyticity requirements in the complexified pseudo-Riemannian manifold for the modes and the two-point function.
Electrical and magnetic properties of (SrMnO3)n∕(LaMnO3)2n superlattices
Authors: Adamo C. , Ke X. , Schiffer P. , Soukiassian A. , Warusawithana M. , Maritato L. , Schlom D. G.
Published: March 2008

We report the magnetic and transport properties of [(SrMnO3)n∕(LaMnO3)2n]m superlattices grown by molecular-beam epitaxy on (100) SrTiO3 with periodicities n=1, 2, 3, 4, 5, 6, 8, and 16. Although the superlattice constituents, LaMnO3 and SrMnO3, are both antiferromagnetic insulators, for small n (n⩽2) the superlattices behave like the ferromagnetic conductor La0.67Sr0.33MnO3. As n increases, the magnetic properties become dominated by the LaMnO3 layers, but the electronic transport properties continue to be controlled by the interfaces.
Core localization and σ∗ delocalization in the O 1s core-excited sulfur dioxide molecule
Authors: Lindgren Andreas , Kosugi Nobuhiro , Gisselbrecht Mathieu , Kivimäki Antti , Burmeister Florian , Naves de Brito Arnaldo , Sorensen Stacey L.
Published: March 2008

Electron-ion-ion coincidence measurements of sulfur dioxide at discrete resonances near the O 1s ionization edge are reported. The spectra are analyzed using a model based upon molecular symmetry and on the geometry of the molecule. We find clear evidence for molecular alignment that can be ascribed to symmetry properties of the ground and core-excited states. Configuration interaction (CI) calculations indicate geometry changes in accord with the measured spectra. For the SO2 molecule, however, we find that the localized core hole does not produce measurable evidence for valence localization, since the transition dipole moment is not parallel to a breaking σ* O–S bond, in contrast to the case of ozone. The dissociation behavior based upon the CI calculations using symmetry-broken orbitals while fixing a localized core-hole site is found to be nearly equivalent to that using symmetry-adapted orbitals. This implies that the core-localization effect is not strong enough to localize the σ* valence orbital.
Early stages of the metal-to-insulator transition of a thin V2O3 film
Authors: Müller C. , Nateprov A. A. , Klemm M. , Wixforth A. , Tidecks R. , Horn S.
Published: March 2008

The metal-to-insulator (MI) transition of a V2O3 thin film is studied, using a surface acoustic wave delay line. The V2O3 film covers not only the sound path but also one of the interdigital transducers (IDTs). The resulting mismatch of the IDTs detunes the delay line, until the film passes through the MI transition. This “self-retuning” behavior makes the device extremely sensitive to the initial changes of the electrical and dielectric properties of the film during the MI transition. Attenuation and sound velocity are measured between 260 and 4.2K. Both suggest a precursor to the MI transition in the paramagnetic metallic regime. The existence of a precursor is consistent with recent extended x-ray absorption fine structure measurements. An oscillatory behavior with steep reductions of the sound velocity is observed during the MI transition. The reductions of the sound velocity probably indicate the recently predicted anomaly at the Mott transition.
Room temperature current oscillations in naturally grown silicon nanocrystallites embedded in oxide films
Authors: Yu Z. , Aceves-Mijares M. , Monfil K. , Kiebach R. , López-Estopier R. , Carrillo J.
Published: March 2008

Current oscillations and other abnormalities in the dark current-voltage characteristics of an aluminum/silicon-rich oxide (SRO)/silicon structure were observed at room temperature. The SRO layers in the devices were fabricated by low pressure chemical vapor deposition and postdeposition thermal annealing. The spikelike current oscillations and other abnormalities are interpreted by an alternative switching between the on and off states of the conduction paths through the Si nanocrystallites at proper biases.
Low- and high-order nonlinear optical properties of Au, Pt, Pd, and Ru nanoparticles
Authors: Ganeev R. A. , Suzuki M. , Baba M. , Ichihara M. , Kuroda H.
Published: March 2008

We investigate third- and higher-order nonlinear optical processes in Au, Pt, Pd, and Ru nanoparticles. We measured the nonlinear refractive indices and nonlinear absorption coefficients of the suspensions of these nanoparticles using the 792nm femtosecond and picosecond pulses. The highest values of these parameters were observed in the case of Au nanoparticles (−8×10−14m2W−1 and 1.7×10−10mW−1), when the 210ps pulses were used as a probe radiation. The high-order harmonic generation was studied during the propagation of the 120fs pulses through the plasmas produced on the surfaces containing the nanoparticles. The highest harmonic cutoff (33rd order) was observed in the case of gold nanoparticle-contained plasma. These results were compared with the harmonics generating from the plasma produced on the surfaces of the bulk materials of the same origin. A two- to sixfold enhancement of harmonic yield was observed in the case of nanoparticle-contained plumes with regard to the bulk materials.
New insight brought by density functional theory on the chemical state of alaninol on Cu(100): Energetics and interpretation of x-ray photoelectron spectroscopy data
Authors: Irrera S. , Costa D.
Published: March 2008

In recent years, an increasing interest has been focused on the adsorption of molecules on surfaces due to the importance of technologies based on the interaction of organic systems with metals and oxides for biosensors, catalysis, and molecularly imprinted polymer technology. A particularly attractive area is the study of chiral surfaces, as these can act as heterogeneous catalysts and sensors in the stereochemical industrial processes. This work reports on an ab initio simulation of chemisorption of the D-alaninol on Cu (100). This system has been investigated systematically by using the Vienna ab initio simulation Package (VASP) which performs density functional theory (DFT) calculations in periodic boundary conditions. Molecular dynamics at 300K is performed to explore all the possible geometries, finally, optimized at 0K to obtain the adsorption modes. C 1s, O 1s, and N 1s, core level shift (CLS) calculations of those adsorption modes have been evaluated and compared with x-ray photoelectron spectroscopy experimental data. Energetic and CLS indicate that both chemical functions, the NH2 and the dehydrogenated hydroxyl, are involved in the bonding to the surface at low coverage. Atomic hydrogen coadsorbs in a fourfold hollow site. An atomistic thermodynamics approach suggests that at room temperature under UHV conditions, coadsorbed hydrogen has recombined as H2 and desorbed from the surface.
Characterization of a-plane InGaN multiple-quantum wells grown on maskless lateral epitaxially overgrown a-plane GaN
Authors: Lee Sung-Nam , Paek H. S. , Kim H. , Park Y. M. , Jang T. , Park Y.
Published: March 2008

We investigated the properties of nonpolar a-plane InGaN∕GaN multiple-quantum wells (MQWs) grown on maskless lateral epitaxial overgrowth (LEO) a-plane GaN∕r-sapphire. Many surface defects with asymmetric V-shape were observed on a-plane InGaN MQWs grown on the defective regions which were seed and coalescence regions. In the low defect regions, the surface defect density of a-plane InGaN MQWs was ∼1.0×107∕cm2, which was higher than that of conventional c-plane LEO-GaN, by measuring atomic force microscope and scanning tunneling electron microscope. The cathode luminescence intensity distribution of a-plane InGaN MQWs was significantly dependent on the distribution of surface asymmetric V-defect. Therefore, we suggest that the optical properties of a-plane InGaN active layer were affected by the asymmetric V-defects which were generated by interaction between the epitaxial defects and the limit of InGaN growth kinetics.
The rate constant of polymer reversal inside a pore
Authors: Huang Lei , Makarov Dmitrii E.
Published: March 2008

Translocation of biopolymers through pores is implicated in many biological phenomena. Confinement within a pore often breaks ergodicity on experimental and/or biological time scales by creating large entropic barriers to conformational rearrangements of the chain. Here, we study one example of such hindered rearrangement, in which the chain reverses its direction inside a long pore. Our goal is twofold. First, we study the dependence of the time scale of polymer reversal on the pore size and on the polymer length. Second, we examine the ability of simple one-dimensional theories to quantitatively describe a transition in a system with a complex energy landscape by comparing them with the exact rate constant obtained using brute-force simulations and the forward flux sampling method. We find that one-dimensional transition state theory (TST) using the polymer extension along the pore axis as the reaction coordinate adequately accounts for the exponentially strong dependence of the reversal rate constant on the pore radius r and the polymer length N, while the transmission factor, i.e., the ratio of the exact rate and the TST approximation, has a much weaker power law r and N dependence. We have further attempted to estimate the transmission factor from Kramer’s theory, which assumes the reaction coordinate dynamics to be governed by a Langevin equation. However, such an approximation was found to be inadequate. Finally, we examine the scaling behavior of the reversal rate constant with N and r and show that finite size effects are important even for chains with N up to several hundreds.
Surface plasmon polaritons generated by optical vortex beams
Authors: Tan P. S. , Yuan X.-C. , Lin J. , Wang Q. , Mei T. , Burge R. E. , Mu G. G.
Published: March 2008

We demonstrate that surface plasmon polaritons can be generated by optical vortex beams at normal incidence focused on a metal surface. The surface plasmon resonant angle can be modulated by the radius of the optical vortex beam in the case of different metal/dielectric interface configurations. Our experiments show that the fluorescence in the vicinity of the metal film surface can effectively be excited and detected within the inner ring of the optical vortex beams due to the localized surface plasmon polaritons.
Robustness studies of ignition targets for the National Ignition Facility in two dimensions
Authors: Clark Daniel S. , Haan Steven W. , Salmonson Jay D.
Published: March 2008

Inertial confinement fusion capsules are critically dependent on the integrity of their hot spots to ignite. At the time of ignition, only a certain fractional perturbation of the nominally spherical hot spot boundary can be tolerated and the capsule still achieve ignition. The degree to which the expected hot spot perturbation in any given capsule design is less than this maximum tolerable perturbation is a measure of the ignition margin or robustness of that design. Moreover, since there will inevitably be uncertainties in the initial character and implosion dynamics of any given capsule, all of which can contribute to the eventual hot spot perturbation, quantifying the robustness of that capsule against a range of parameter variations is an important consideration in the capsule design. Here, the robustness of the 300eV indirect drive target design for the National Ignition Facility [Lindl et al., Phys. Plasmas 11, 339 (2004)] is studied in the parameter space of inner ice roughness, implosion velocity, and capsule scale. A suite of 2000 two-dimensional simulations, run with the radiation hydrodynamics code LASNEX, is used as the data base for the study. For each scale, an ignition region in the two remaining variables is identified and the ignition cliff is mapped. In accordance with the theoretical arguments of Levedahl and Lindl [Nucl. Fusion 37, 165 (1997)] and Kishony and Shvarts [Phys. Plasmas 8, 4925 (2001)], the location of this cliff is fitted to a power law of the capsule implosion velocity and scale. It is found that the cliff can be quite well represented in this power law form, and, using this scaling law, an assessment of the overall (one- and two-dimensional) ignition margin of the design can be made. The effect on the ignition margin of an increase or decrease in the density of the target fill gas is also assessed.
Characterization of embedded MgO/ferromagnet contacts for spin injection in silicon
Authors: Uhrmann T. , Dimopoulos T. , Brückl H. , Lazarov V. K. , Kohn A. , Paschen U. , Weyers S. , Bär L. , Rührig M.
Published: March 2008

In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO2 dielectric, on n- and p-doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n-doped and by minority carriers for the p-doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions.
Calibration of lateral force measurements in atomic force microscopy with a piezoresistive force sensor
Authors: Xie Hui , Vitard Julien , Haliyo Sinan , Régnier Stéphane , Boukallel Mehdi
Published: March 2008

We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092to1.24N∕m and lateral stiffness from 10.34to101.06N∕m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to ±12.4% or better. This standard has less error than the commonly used method based on the cantilever’s beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.
Effect of noise on chemical waves in three-dimensional reaction-diffusion systems with gradient
Authors: Lu Xiaochuan , Wang Chunyan , Qiao Chun , Wu Yabi , Ouyang Qi , Wang Hongli
Published: March 2008

The effect of noise on chemical waves in a quasi-three-dimensional reaction-diffusion medium with a gradient in the third dimension is studied using the FitzHugh–Nagumo model [R. FitzHugh, Biophysics J. 1, 445 (1961)]. Numerical simulations reveal that noise of appropriate intensity can postpone the onset of turbulence and stabilize the three-dimensional (3D) waves which would otherwise undergo the gradient-induced collapse. It is also found that the 3D waves can be interrupted by incident irregularities when the noise is not too strong; it can be induced into complete turbulence when the noise is strong enough. A mathematical analysis is given based on the dependence of the oscillation frequency on the control parameter. It agrees qualitatively with our numerical findings.
Generation of ultrasmall nanostructures in oxide layers assisted by self-organization
Authors: Block T. , Pfnür H.
Published: March 2008

We explored the structural limits of unconventional electron-beam lithography by directly writing with an electron beam into ultrathin SiO2 films. The obtained structures were analyzed by tunneling microscopy. The Auger excitation process (Knotek–Feibelman mechanism) necessary for electron-stimulated oxygen desorption allows generation of ultrasmall structures. The subsequent processing step combines thermal desorption of the remaining monoxide and simultaneous etching promoted by thermally activated silicon atoms, which turns out to be a strongly anisotropic process close to step edges. Applying this combination of processes to a regularly stepped Si(557) sample, linewidths close to the resolution of the electron microscope of 5 nm were obtained.
Physics of plasma actuator operating in atmospheric air
Authors: Singh Kunwar Pal , Roy Subrata
Published: March 2008

The physics of plasma actuator operating in the atmospheric air has been numerically investigated. The O−, O2−, O2+, and N2+ ions have been included in the air chemistry to identify their role. For the specific case study, we find the density of positive ions is an order of magnitude higher at the positive peak of the cycle than that at the negative peak of the cycle. This difference in density levels of the species causes the development of the directional bias of the electrodynamic force. Numerical simulations indicate that positive ions play major role in the development of the positive force.
Map of metastable states for thin circular magnetic nanocylinders
Authors: Metlov Konstantin L. , Lee YoungPak
Published: March 2008

Nanomagnetic systems of artificially shaped ferromagnetic islands recently became a popular subject due to their current and potential applications in spintronics [R. P. Cowburn, Nat. Mater. 6, 255 (2007)], magnetophotonics [A. Garcia-Martin, G. Armelles, and S. Pereira Phys. Rev. B 71, 205116 (2005)], and superconductivity. [D. S. Golubović, W. V. Pogosov, M. Morelle, and V. V. Moshchalkov, Phys. Rev. Lett. 92, 177904 (2004)] When the island size is close to the exchange length of magnetic material (around 15nm), its magnetic structure becomes markedly different. It determines both static and dynamic magnetic properties of elements, but strongly depends on their shape and size. Here, we map this dependence for circular cylindrical islands of a few exchange lengths in size. We outline the region of metastability of C-type magnetic states, proving that they are indeed genuine and not a result of pinning on particle imperfections. A way to create the smallest particles with guaranteed magnetic vortex state at zero field becomes evident. It is expected that the map will help focus the efforts in planning of experiments and devices.
Artificial neural network modeling of reduced glass transition temperature of glass forming alloys
Authors: Cai An-hui , Xiong Xiang , Liu Yong , An Wei-ke , Tan Jing-ying
Published: March 2008

A model based on radial base function artificial neural network (RBFANN) was designed for the simulation and prediction of reduced glass transition temperature Trg of glass forming alloys. Its performance is examined by the influences of different kinds of alloys and elements, large and minor change of element content on the Trg, and composition dependence of Trg for La–Al–Ni ternary alloy system. Moreover, a group of Zr–Al–Ni–Cu bulk metallic glasses is designed by RBFANN. The values of Trg predicted by RBFANN agree well with the experimental values, indicating that the model is reliable and adequate.
A passive all-optical semiconductor device for level amplitude stabilization based on fast saturable absorber
Authors: Nguyen H. Trung , Oudar J.-L. , Bouchoule S. , Aubin G. , Sauvage S.
Published: March 2008

A high-speed saturable-absorber-based device (response time below 2.5ps) providing a significant amplitude stabilization is demonstrated. The experimental results allow estimating that the amplitude fluctuations of the output should be reduced by about 90% compared to the input fluctuations, within the input power range of (5–18μJ∕cm2). This device has been studied in view of its possible use for bit-1 noise reduction. When combined with a state-of-art saturable absorber device, this could provide a simple and compact scheme for the complete reamplification and reshaping regeneration of digital optical signals.
Ultraviolet band-pass photodetectors formed by Ga-doped ZnO contacts to n-GaN
Authors: Sheu J. K. , Chang K. H. , Lee M. L.
Published: March 2008

In this study, Ga-doped ZnO (GZO) films prepared by cosputtering were deposited onto n-GaN films with a low-temperature-grown GaN cap layer to form Schottky barrier photodetectors (PDs). The ultraviolet (UV) PDs exhibited a narrow band-pass spectral response ranging from 340to390nm. The short-wavelength cutoff at around 340nm can be attributed to the marked absorption of the GZO contact layer. With a zero-biased condition, the UV PDs exhibited a typical peak responsivity of around 0.10A∕W at 365nm, which corresponds to the quantum efficiency of around 34%. When the reverse biases were below 10V, the dark currents of the PDs were well below 30pA.
Copia retrotransposons of two disjunctive Panax species: P. ginseng and P. quinquefolius
Authors: Liu X. D. , Zhong X. F. , Ma Y. , Gong H. J. , Zhao Y. Y. , Qi B. , Yan Z. K. , Sun X. B. , Liu B.
Published: March 2008

Sixty highly heterogeneous reverse transcriptase (RT) gene domains, each representing a different copia retrotransposon, were isolated from Panax ginseng and P. quinquefolius, two highly valued medicinal plant species representing classical eastern Asian and eastern North American disjunctive speciation. These RT domains were classifiable into 10 distinct families. While some families contained highly degenerate elements, others were largely composed of intact ones that had been subjected to purifying selection. DNA gel-blot analysis showed that all 10 families existed in both ginseng species, although the copy number of Family 1 showed marked difference between them. All element families appeared heavily methylated in both species, but a difference in cytosine DNA-methylation patterns between the two species was also evident. Thus, the copia retrotransposons in the two ginseng species are diverse and polyphyletic in origin, yet, they all appeared antique and presumably occurred before separation of P. ginseng and P. quinquefolius, followed by genetic and epigenetic differentiation in their respective host genomes.
Floral biology of Australian species of Hierochloe (Gramineae)
Authors: Connor H. E.
Published: March 2008

Four species of Hierochloe R.Br. occur in Australia, with the following three of them endemic: H. fraseri Hook.f. in Tasmania, H. submutica F.Muell. restricted to high alpine sites in south-eastern states, and H. rariflora Hook.f. in three eastern states. The fourth, H. redolens (Vahl) Roemer et Schultes, occurs on the eastern mainland and in Tasmania. Three species are regularly andromonoecious, a pattern common to species in both northern and southern hemispheres; however, Tasmanian H. fraseri is an exception in which, in addition to andromonoecism, male sterility in the two lower florets of the spikelet is not uncommon and produces a mixed floral biology. Compared with other departures from andromonoecism, this is a novel condition in the genus, with its genetic control and its reproductive significance unknown.
Naturally occurring arbuscular mycorrhizal fungi can replace direct P uptake by wheat when roots cannot access added P fertiliser
Authors: Li Huiying , Smith Sally E. , Ophel-Keller Kathy , Holloway Robert E. , Smith F. Andrew
Published: March 2008

We investigated the roles of naturally occurring arbuscular mycorrhizal (AM) fungi in phosphorus (P) uptake by wheat (Triticum aestivum L.) in a calcareous, P-fixing soil. Plants grew in a main pot containing autoclaved soil (NM) or autoclaved soil mixed with non-autoclaved soil (to provide inoculum of naturally occurring AM fungi; AM). Granular (GP; monoammonium phosphate) or fluid (FP; ammonium polyphosphate) fertilisers were applied in small compartments (PCs) within a main pot, to which either roots plus hyphae (–Mesh) or hyphae only (+Mesh) had access. Controls received no additional P (NP). Inoculated plants were well colonised by AM fungi. AM growth depressions were observed in –Mesh treatments with NP and GP, but not with FP. Neither AM growth nor P responses were observed in +Mesh treatments. AM plants had much higher P uptake than NM plants, regardless of the P and mesh treatments. Total P uptake by NM plants increased with FP in –Mesh, but was unaffected by either form of P in the +Mesh treatments. Total P uptake by AM plants was similar between –Mesh and +Mesh treatments, regardless of applied P, showing that roots plus hyphae and hyphae alone have the same ability to obtain P. Thus, hyphae can take over the roles of roots in P uptake when roots are not able to access P sources.
Genetic variation in tolerance to the osmotic stress componentof salinity stress in durum wheat
Authors: James Richard A. , von Caemmerer Susanne , Condon A. G. (Tony) , Zwart Alexander B. , Munns Rana
Published: March 2008

Salinity affects plant growth by the osmotic stress of the salt around the roots as well as by toxicity caused by excessive accumulation of salt in leaves. The aim of this study was to determine whether there is significant genetic variation in tolerance to osmotic stress that can be useful in improving the salinity tolerance of crop plants. Durum wheat is a salt-sensitive crop whose yield is reduced by moderately saline soils. Genetic variation in tolerance to osmotic stress in durum wheat was examined in 50 international durum varieties and landraces by measuring the response of stomatal conductance to salt stress before salts built up in the leaf. Stomatal conductance is a sensitive indicator of the osmotic stress because it is reduced immediately with the onset of salinity, and is the initial and most profound cause of a decline in CO2 assimilation rate. Genetic differences of 2–3-fold were found in the magnitude of the response of stomatal conductance to salt-induced osmotic stress. Higher stomatal conductance in salt related to higher CO2 assimilation rate. There was a positive relationship between stomatal conductance and relative growth rate in salt. This study shows the potential for new genetic gains in salt tolerance in durum wheat.
Lack of visible post-pollination effects in pollen grains of two Dendrobium cultivars: relationship with pollinia ACC, pollen germination, and pollen tube growth
Authors: Luangsuwalai Kanjana , Ketsa Saichol , Wisutiamonkul Apinya , van Doorn Wouter G.
Published: March 2008

Dendrobium flowers, pollinated with pollinia from individuals of the same cultivar or other cultivars, usually show rapid post-pollination effects such as floral epinasty, a change in flower colour and early perianth senescence. However, pollination with the pollinia of cv. Karen or cv. Kenny flowers did not produce these effects. We compared these two cultivars with cvv. Pompadour, Willie and Sakura, and tested the hypotheses that the differences were related to levels of 1-aminocyclopropane-1-carboxylic acid (ACC) in the pollinia, ethylene production by the pollinated flower, pollen germination, or pollen tube growth. The pollinia of cvv. Karen and Kenny contained as much ACC as the pollinia of cv. Pompadour, but less than the pollinia of cvv. Willie and Sakura. Ethylene production after pollination with cvv. Karen and Kenny pollinia was much lower than after pollination with pollinia from the other cultivars tested. The pollen grains showed normal germination, but cvv. Karen and Kenny pollen grains exhibited much less tube growth than those of the other cultivars. Pollen tube growth in cv. Pompadour was positively affected by ethylene. Ethylene was required and sufficient for the induction of epinasty, rapid perianth colour changes and early perianth senescence, very similar to the changes after pollination. The absence of these effects after pollination with cvv. Kenny and Karen seems to be due to the low ethylene production induced by the pollinia of these cultivars. This low ethylene production could not be accounted for by the ACC content in the pollinia of cvv. Kenny and Karen.
Photosynthetic maximum quantum yield increases are an essential component of the Southern Ocean phytoplankton response to iron
Authors: Hiscock Michael R. , Lance Veronica P. , Apprill Amy M. , Bidigare Robert R. , Johnson Zackary I. , Mitchell B. Greg , Smith Walker O. , Barber Richard T.
Published: March 2008

It is well established that an increase in iron supply causes an increase in total oceanic primary production in many regions, but the physiological mechanism driving the observed increases has not been clearly identified. The Southern Ocean iron enrichment experiment, an iron fertilization experiment in the waters closest to Antarctica, resulted in a 9-fold increase in chlorophyll (Chl) concentration and a 5-fold increase in integrated primary production. Upon iron addition, the maximum quantum yield of photosynthesis (φ

m

) rapidly doubled, from 0.011 to 0.025 mol C·mol quanta
−1
. Paradoxically, this increase in light-limited productivity was not accompanied by a significant increase in light-saturated productivity (

P
max
b

).

P
max
b

, maximum Chl normalized productivity, was 1.34 mg C·mg Chl
−1
·h
−1
outside and 1.49 mg C·mg Chl
−1
·h
−1
inside the iron-enriched patch. The importance of φ

m

as compared with

P
max
b

in controlling the biological response to iron addition has vast implications for understanding the ecological response to iron. We show that an iron-driven increase in φ

m

is the proximate physiological mechanism affected by iron addition and can account for most of the increases in primary production. The relative importance of φ

m

over

P
max
b

in this iron-fertilized bloom highlights the limitations of often-used primary productivity algorithms that are driven by estimates of

P
max
b

but largely ignore variability in φ

m

and light-limited productivity. To use primary productivity models that include variability in iron supply in prediction or forecasting, the variability of light-limited productivity must be resolved.
Rifamycin antibiotic resistance by ADP-ribosylation: Structure and diversity of Arr
Authors: Baysarowich Jennifer , Koteva Kalinka , Hughes Donald W. , Ejim Linda , Griffiths Emma , Zhang Kun , Junop Murray , Wright Gerard D.
Published: March 2008

The rifamycin antibiotic rifampin is important for the treatment of tuberculosis and infections caused by multidrug-resistant
Staphylococcus aureus
. Recent iterations of the rifampin core structure have resulted in new drugs and drug candidates for the treatment of a much broader range of infectious diseases. This expanded use of rifamycin antibiotics has the potential to select for increased resistance. One poorly characterized mechanism of resistance is through Arr enzymes that catalyze ADP-ribosylation of rifamycins. We find that genes encoding predicted Arr enzymes are widely distributed in the genomes of pathogenic and nonpathogenic bacteria. Biochemical analysis of three representative Arr enzymes from environmental and pathogenic bacterial sources shows that these have equally efficient drug resistance capacity
in vitro
and
in vivo
. The 3D structure of one of these orthologues from
Mycobacterium smegmatis
was determined and reveals structural homology with ADP-ribosyltransferases important in eukaryotic biology, including poly(ADP-ribose) polymerases (PARPs) and bacterial toxins, despite no significant amino acid sequence homology with these proteins. This work highlights the extent of the rifamycin resistome in microbial genera with the potential to negatively impact the expanded use of this class of antibiotic.
Loss of the inactive myotubularin-related phosphatase Mtmr13 leads to a Charcot–Marie–Tooth 4B2-like peripheral neuropathy in mice
Authors: Robinson Fred L. , Niesman Ingrid R. , Beiswenger Kristina K. , Dixon Jack E.
Published: March 2008

Charcot–Marie–Tooth disease type 4B (CMT4B) is a severe, demyelinating peripheral neuropathy characterized by slowed nerve conduction velocity, axon loss, and distinctive myelin outfolding and infolding. CMT4B is caused by recessive mutations in either myotubularin-related protein 2 (
MTMR2
; CMT4B1) or
MTMR13
(CMT4B2). Myotubularins are phosphoinositide (PI) 3-phosphatases that dephosphorylate phosphatidylinositol 3-phosphate (PtdIns3
P
) and PtdIns(3,5)
P
2
, two phosphoinositides that regulate endosomal–lysosomal membrane traffic. Interestingly, nearly half of the metazoan myotubularins are predicted to be catalytically inactive. Both active and inactive myotubularins have essential functions in mammals and in
Caenorhabditis elegans
. MTMR2 and MTMR13 are active and inactive PI 3-phosphatases, respectively, and the two proteins have been shown to directly associate, although the functional significance of this association is not well understood. To establish a mouse model of CMT4B2, we disrupted the
Mtmr13
gene.
Mtmr13
-deficient mice develop a peripheral neuropathy characterized by reduced nerve conduction velocity and myelin outfoldings and infoldings. Dysmyelination is evident in
Mtmr13
-deficient nerves at 14 days and worsens throughout life. Thus, loss of Mtmr13 in mice leads to a peripheral neuropathy with many of the key features of CMT4B2. Although myelin outfoldings and infoldings occur most frequently at the paranode, our morphological analyses indicate that the ultrastructure of the node of Ranvier and paranode is intact in
Mtmr13
-deficient nerve fibers. We also found that Mtmr2 levels are decreased by ≈50% in
Mtmr13
-deficient sciatic nerves, suggesting a mode of Mtmr2 regulation.
Mtmr13
-deficient mice will be an essential tool for studying how the loss of MTMR13 leads to CMT4B2.
What Is Evolutionary Biology and Where Is It Coming From?
Authors: Lurquin Paul F. , Stone Linda
Published: March 2008

This chapter describes the Darwin-Wallace theory of evolution by natural selection. In particular, it explains the notion of fitness, which underlies the concepts of descent with modification and the appearance of species categorized into clades. It shows that descent with modification is a much better evolutionary theory than the “Great chain of being” model, which implies that evolution is driven toward the production of more perfect and complex life-forms. Finally, it explains how the science of genetics strongly supports evolution through the notions of mutation, gene frequencies in populations, and drift.
Creationist Purpose and Irreducible Complexity Rebutted
Authors: Lurquin Paul F. , Stone Linda
Published: March 2008

This chapter rebuts irreducible complexity and creationism by explaining the reliability of dating techniques as well as sophisticated laboratory techniques that allow researchers to synthesize extinct genes (genetic archaeology, gene resurrection) and study their homology to other genes. These techniques clearly demonstrate that the irreducible complexity of the eye, the immune system, and the bacterial flagellum are subjective impressions. On the contrary, phylogenetic trees based on gene homology show a deep evolutionary link between simple life-forms and complex ones. Finally, the chapter gives several examples of “poor design” that cast doubt on the principle of Intelligent Design.
The Origins of Life and the Cosmos as Evolutionary Themes
Authors: Lurquin Paul F. , Stone Linda
Published: March 2008

This chapter demonstrates that the origin of the universe was probabilistic, not preordained, because Heisenberg's uncertainty principle would have been violated at the level of the Big Bang. The appearance of structure in the universe was made possible by the decoupling of matter and radiation about 400,000 years after the Big Bang. Structure appeared — and continues to appear — without violating the second law of thermodynamics because entropy is not increasing as fast as it could, and this keeps the universe in a state of disequilibrium, not equilibrium. Life appeared as a consequence of this disequilibrium, possibly involving a sequence of events such as formation of an organic prebiotic soup (or synthesis of organic compounds in hydrothermal vents), the appearance of an RNA world, and the formation of lipid-bound hypercycles.
Evolution of the DNA World and the Chance Events That Accompanied It
Authors: Lurquin Paul F. , Stone Linda
Published: March 2008

First life-forms appeared at least as early as 3.5 billion years ago in the form of prokaryotes. Some of these species developed oxygenic photosynthesis, which resulted in the presence of oxygen gas in the atmosphere. Later, eukaryotes appeared and diversified through mutation and gene duplication (including mutation and duplication of master genes), which led to the rewiring of entire gene networks. The chapter shows that there is no fundamental difference between macroevolution and microevolution. It shows that making artificial life in the lab as well as transgenic life-forms would be impossible if the Intelligent Design scenario were correct. Indeed, ID posits that living systems were holistically designed and thus cannot be constructed in a piecemeal fashion.
The Dangers of Creationism
Authors: Lurquin Paul F. , Stone Linda
Published: March 2008

Creationists and some conservative politicians are allies in a culture war that threatens science education in the United States. The threat comes from religious ideologies, such as Intelligent Design, that have never provided a shred of experimental evidence to buttress their claims. This book concludes that the proposition that evolutionary science is against human free will is baseless, and so is the contention that the theory of evolution deprives humans of purpose in life.
Loss of trabeculae by mechano-biological means may explain rapid bone loss in osteoporosis
Authors: Mulvihill Brianne M , McNamara Laoise M , Prendergast Patrick J
Published: March 2008

Osteoporosis is characterized by rapid and irreversible loss of trabecular bone tissue leading to increased bone fragility. In this study, we hypothesize two causes for rapid loss of bone trabeculae; firstly, the perforation of trabeculae is caused by osteoclasts resorbing a cavity so deep that it cannot be refilled and, secondly, the increases in bone tissue elastic modulus lead to increased propensity for trabecular perforation. These hypotheses were tested using an algorithm that was based on two premises: (i) bone remodelling is a turnover process that repairs damaged bone tissue by resorbing and returning it to a homeostatic strain level and (ii) osteoblast attachment is under biochemical control. It was found that a mechano-biological algorithm based on these premises can simulate the remodelling cycle in a trabecular strut where damaged bone is resorbed to form a pit that is subsequently refilled with new bone. Furthermore, the simulation predicts that there is a depth of resorption cavity deeper than which refilling of the resorption pits is impossible and perforation inevitably occurs. However, perforation does not occur by a single fracture event but by continual removal of microdamage after it forms beneath the resorption pit. The simulation also predicts that perforations would occur more easily in trabeculae that are more highly mineralized (stiffer). Since both increased osteoclast activation rates and increased mineralization have been measured in osteoporotic bone, either or both may contribute to the rapid loss of trabecular bone mass observed in osteoporotic patients.
Prevalence of sheep infected with classical scrapie in Great Britain: integrating multiple sources of surveillance data for 2002
Authors: Gubbins Simon
Published: March 2008

Estimates for the prevalence of sheep infected with classical scrapie are essential for assessing the efficacy of control strategies that have been implemented in Great Britain (GB). Here a back-calculation approach was used to estimate the prevalence in the GB national flock by integrating data on reported cases and the results of abattoir and fallen stock surveys for 2002. Prevalence estimates ranged from 0.33 to 2.06%, depending on the estimates used for the frequencies of prion protein (PrP) genotypes in the national flock and the stage of incubation at which the diagnostic tests used are able to detect infected animals. The risk of infection was found to be higher than that of clinical disease, especially in those PrP genotypes that have a later age at onset of clinical disease. Moreover, results suggest that a high proportion (more than 55%) of infected animals surviving to disease onset die on farm before clinical signs become apparent, which helps account for the high observed prevalence in the fallen stock compared with the abattoir survey. The analyses indicated that attention needs to be given to identifying the stage of incubation at which diagnostic tests are able to detect infected animals and obtaining better demographic data for the GB national flock.
Adhesion formation of primary human osteoblasts and the functional response of mesenchymal stem cells to 330 nm deep microgrooves
Authors: Biggs M.J.P , Richards R.G , McFarlane S , Wilkinson C.D.W , Oreffo R.O.C , Dalby M.J
Published: March 2008

The surface microtexture of an orthopaedic device can regulate cellular adhesion, a process fundamental in the initiation of osteoinduction and osteogenesis. Advances in fabrication techniques have evolved to include the field of surface modification; in particular, nanotechnology has allowed for the development of experimental nanoscale substrates for investigation into cell nanofeature interactions. Here primary human osteoblasts (HOBs) were cultured on ordered nanoscale groove/ridge arrays fabricated by photolithography. Grooves were 330 nm deep and either 10, 25 or 100 μm in width. Adhesion subtypes in HOBs were quantified by immunofluorescent microscopy and cell–substrate interactions were investigated via immunocytochemistry with scanning electron microscopy. To further investigate the effects of these substrates on cellular function, 1.7 K gene microarray analysis was used to establish gene regulation profiles of mesenchymal stem cells cultured on these nanotopographies. Nanotopographies significantly affected the formation of focal complexes (FXs), focal adhesions (FAs) and supermature adhesions (SMAs). Planar control substrates induced widespread adhesion formation; 100 μm wide groove/ridge arrays did not significantly affect adhesion formation yet induced upregulation of genes involved in skeletal development and increased osteospecific function; 25 μm wide groove/ridge arrays were associated with a reduction in SMA and an increase in FX formation; and 10 μm wide groove/ridge arrays significantly reduced osteoblast adhesion and induced an interplay of up- and downregulation of gene expression. This study indicates that groove/ridge topographies are important modulators of both cellular adhesion and osteospecific function and, critically, that groove/ridge width is important in determining cellular response.
Modal projections for synchronous rotor whirl
Authors: Mahadevan Pradeep , Jog C.S , Chatterjee Anindya
Published: March 2008

We consider the synchronous whirl of arbitrary axisymmetric rotors supported on rigid bearings. Prior computational treatments of this problem were based on adding element-level gyroscopic terms to the governing equations. Here, we begin with a direct continuum formulation wherein gyroscopic terms need not be added on separately and explicitly: all gyroscopic effects are captured implicitly within the continuum elastodynamics. We present two new methods for obtaining the whirl speed, where we project the dynamic equilibrium equations of the rotor on to a few of its non-spinning vibration mode shapes. The first modal projection method is direct and more accurate, but requires numerical evaluation of more demanding integrals. The second method is iterative and involves a small approximation, but is simpler. Both the methods are based on one new insight: the gyroscopic terms used in other treatments are essentially the result of a prestress in the rotor caused by the non-zero spin rate, and may be incorporated as such in the continuum formulation. The accuracy of the results obtained, for several examples, is verified against detailed calculations with a commercial finite-element package, against our own nonlinear finite-element code or against analytical estimates. For further verification and illustration, a closed-form analytical solution for a simple problem, obtained using our method, matches the results obtained with explicit gyroscopic terms.
Analytic solutions to the acoustic source reconstruction problem
Authors: Maury Cedric , Bravo Teresa
Published: March 2008

In this paper, we generalize the recently developed analytical solutions of the radiation modes problem to the determination of closed-form expressions for the singular value expansion of a number of integral operators that map the boundary velocity of a baffled planar structure onto the acoustic pressure radiated in far-field or intermediate regions. Exact solutions to this problem involve prolate spheroidal wave functions that correspond to a set of independent distributions with finite spatial support and maximal energy concentration in a given bandwidth of the transform domain. A stable solution to the inverse source reconstruction problem is obtained by decomposing the unknown boundary velocity into a number of efficiently radiating singular velocity patterns that correspond to the number of degrees of freedom of the radiated field. It is found that the degree of ill-posedness of the inverse problem is significantly reduced, when considering a hemi-circular observation arc with respect to a linear array of sensors, by a factor scaling on the small angular aperture subtended by the observation line. Estimates are derived from the spatial resolution limits that can be achieved in the source reconstruction problem from the dimension of the efficiently radiating subspace.
Radial and circular slit maps of unbounded multiply connected circle domains
Authors: DeLillo T.K , Driscoll T.A , Elcrat A.R , Pfaltzgraff J.A
Published: March 2008

Infinite product formulae for conformally mapping an unbounded multiply connected circle domain to an unbounded canonical radial or circular slit domain, or to domains with both radial and circular slit boundary components are derived and implemented numerically and graphically. The formulae are generated by analytic continuation with the reflection principle. Convergence of the infinite products is proved for domains with sufficiently well-separated boundary components. Some recent progress in the numerical implementation of infinite product mapping formulae is presented.