bluuebunny/crossref_metadata_2025 huggingface dataset:
Early mid‐Holocene SST variability and surface‐ocean water balance in the southwest Pacific
Authors: Duprey N. , Lazareth C. E. , Corrège T. , Le Cornec F. , Maes C. , Pujol N. , Madeng‐Yogo M. , Caquineau S. , Soares Derome C. , Cabioch G.
Published: October 2012

We present early mid‐Holocene records of Sr/Ca,δ18O and δ18Osw from marine archives collected in Vanuatu: two Porites sp. corals (6.7–6.5 ka BP) and a Tridacna maxima giant clam (6.2–6.0 ka BP). Sr/Ca, δ18O, and δ18Osw were used as proxies for sea surface temperature (SST) and sea surface salinity (SSS). The fossil geochemical records were compared to modern Porites sp. and T. maxima records. Reconstructed mean SSTs from the two fossil Porites sp.and from the modern coral are similar, implying that the Western Pacific Warm Pool (WPWP)' southern edge had reached its modern location by 6.7–6.5 ka BP. The post‐glacial SST rise in the Southwest Pacific was thus completed by the early mid‐Holocene. The two early mid‐Holocene corals and the giant clam recorded saltier conditions than modern related to 1) a decoupling between the precipitation regime and the SPCZ due to a northerly position of this climatic feature and 2) an increase of the moisture transport to the extra‐tropics, driven by a strengthened or extended Hadley cell. The longestδ18O coral profile displays an El Niño Southern Oscillation (ENSO) signal reduced by 20–30% compared to the period 1928–1992, in concordance with the reduced ENSO variability observed in the Pacific area during the first half of the Holocene. However, the decoupling between the SPCZ and the precipitation regime may have also contributed to the weak ENSO signal recorded in the early mid‐Holocene coralδ18O profile.
New constraints on the origin of the Sierra Madre de Chiapas (south Mexico) from sediment provenance and apatite thermochronometry
Authors: Witt C. , Brichau S. , Carter A.
Published: October 2012

The timing and source of deformation responsible for formation of the Sierra Madre de Chiapas (south Mexico) are unclear. To address this, apatite fission track and U‐Th‐He thermochronometry, combined with zircon U‐Pb dating, were performed on bedrock and sedimentary samples of the Sierra Madre de Chiapas to discern timing of exhumation and identify sediment source areas. The U‐Pb results show that Paleocene–Eocene terrigenous units outcropping at the northern section of the Sierra were mostly derived from Grenville (∼1 Ga) basement whereas the internal sections of the chain yield mainly Permian to Triassic ages (circa 270–230 Ma) typical of the Chiapas massif complex. Grenville‐sourced sediments are most probably sourced by the Oaxacan block or the Guichicovi complex and were deposited to the north of the Sierra in a foreland setting related to a Laramide deformation front. Other possibly source areas may be related to metasedimentary units widely documented at the south Maya block such as the Baldi unit. The apatite fission track and U‐Th‐He data combined with previously published results record three main stages in exhumation history: (1) slow exhumation between 35 and 25 Ma affecting mainly the Chiapas massif complex; (2) fast exhumation between 16 and 9 Ma related to the onset of major strike‐slip deformation affecting both the Chiapas massif complex and Chiapas fold‐and‐thrust belt; and (3) a 6 to 5 Ma period of rapid cooling that affected the Chiapas fold‐and‐thrust belt, coincident with the landward migration of the Caribbean–North America plate boundaries. These data suggest that most of the topographic growth of the Sierra Madre de Chiapas took place in the middle to late Miocene. The new thermochronological evidence combined with stratigraphic and kinematic information suggests that the left‐lateral strike‐slip faults bounding the Chiapas fold‐and‐thrust belt to the west may have accommodated most of the displacement between the North American and Caribbean plates during the last 6–5 Ma.
Mesenchymal stem cells restore CCl4‐induced liver injury by an antioxidative process
Authors: Cho Kyung‐Ah , Woo So‐Youn , Seoh Ju‐Young , Han Ho‐Seong , Ryu Kyung‐Ha
Published: October 2012

We have investigated BM (bone marrow)‐derived MSCs (mesenchymal stem cells) for the treatment of liver injury. It was hypothesized that MSC‐mediated resolution of liver injury could occur through an antioxidative process. After being injected with CCl4 (carbon tetrachloride), mice were injected with syngenic BM‐derived MSCs or normal saline. Oxidative stress activity of the MSCs was determined by the analysis of ROS (reactive oxygen species) and SOD (superoxide dismutase) activity. In addition, cytoprotective genes of the liver tissue were assessed by real‐time PCR and ARE (antioxidant‐response element) reporter assay. Up‐regulated ROS of CCl4‐treated liver cells was attenuated by co‐culturing with MSCs. Suppression of SOD by adding an SOD inhibitor decreased the effect of MSCs on injured liver cells. MSCs significantly increased SOD activity and inhibited ROS production in the injured liver. The gene expression levels of Hmox‐1 (haem oxygenase‐1), BI‐1 (Bax inhibitor‐1), HGF (hepatocyte growth factor), GST (glutathione transferase) and Nrf2 (nuclear factor‐erythoid 2 p45 subunit‐related factor 20), attenuated by CCl4, were increased up to basal levels after MSC transplantation. In addition, MSCs induced an ARE, shown by luciferase activity, which represented a cytoprotective response in the injured liver. Evidence of a new cytoprotective effect is shown in which MSCs promote an antioxidant response and supports the potential of using MSC transplantation as an effective treatment modality for liver disease.
Dust-ion-acoustic Gardner solitons in a dusty plasma with bi-Maxwellian electrons
Authors: Masud M. M. , Asaduzzaman M. , Mamun A. A.
Published: October 2012

The nonlinear propagation of dust-ion-acoustic (DIA) waves in a dusty plasma with bi-Maxwellian electrons, namely, lower and higher temperature electrons (composed of negatively charged stationary dust, inertial ions, and non-inertial two-temperature-electrons) is investigated by deriving the Gardner equation using the reductive perturbation technique. The basic features (amplitude, width, etc.) of the hump (positive potential) and dip (negative potential) shaped DIA solitons (Gardner solitons, i.e., GSs) are found to exist beyond the Korteweg-de Vries (K-dV) limit. These DIA-GSs are qualitatively different from the K-dV and modified K-dV solitons. It is also shown that depending on the parameter σ (where σ=Te1/Te2, Te1 and Te2 being the temperatures of two distinct electrons and Te1≪Te2), the DIA-GSs exhibit hump and dip shape solitary structures. The implications of our results in understanding the localized nonlinear electrostatic perturbations observed in double-plasma machines, rf discharge plasma, noctilucent cloud region in Earths atmosphere, etc., where population of two thermal electrons can significantly dominate the wave dynamics, are also briefly addressed.
A Wang-Landau study of a lattice model for lipid bilayer self-assembly
Authors: Gai Lili , Maerzke Katie A. , Cummings Peter T. , McCabe Clare
Published: October 2012

The Wang-Landau (WL) Monte Carlo method has been applied to simulate the self-assembly of a lipid bilayer on a 3D lattice. The WL method differs from conventional Monte Carlo methods in that a complete density of states is obtained directly for the system, from which properties, such as the free energy, can be derived. Furthermore, from a single WL simulation, continuous curves of the average energy and heat capacity can be determined, which provide a complete picture of the phase behavior. The lipid model studied consists of 3 or 5 coarse-grained segments on lattices of varying sizes, with the empty lattice sites representing water. A bilayer structure is found to form at low temperatures, with phase transitions to clusters as temperature increases. For 3-segment chains, varying lattice sizes were studied, with the observation that the ratio of chain number to lattice area (i.e., area per lipid) affects the phase transition temperature. At small ratios, only one phase transition occurs between the bilayer and cluster phases, while at high lipid ratios the phase transition occurs in a two-step process with a stable intermediate phase. This second phase transition was not observed in conventional Metropolis Monte Carlo simulations on the same model, demonstrating the advantage of being able to perform a complete scan of the whole temperature range with the WL method. For longer 5-segment chains similar phase transitions are also observed with changes in temperature. In the WL method, due to the extensive nature of the energy, the number of energy bins required to represent the density of states increases as the system size increases and so limits its practical application to larger systems. To improve this, an extension of the WL algorithm, the statistical-temperature Monte Carlo method that allows simulations with larger energy bin sizes, has recently been proposed and is implemented in this work for the 3-segment lattice model. The results obtained are in good agreement with the original WL method and appear to be independent of the energy bin size used.
Light-management in ultra-thin polythiophene films using plasmonic monopole nanoantennas
Authors: Yu Binxing , Goodman Sarah , Abdelaziz Alexa , O'Carroll Deirdre M.
Published: October 2012

Deposition of vertical, cone-shaped plasmonic nanorod arrays onto sub-50 nm polythiophene films on Ag substrates is shown to result in significant absorption enhancement (>12 at the polythiophene band edge) and spectral broadening (more than 250 nm increase) relative to polythiophene/Ag films without plasmonic nanorod arrays. Full-field electromagnetic simulations are used to identify the modes of the plasmonic nanorod array/polythiophene/Ag film system. Both gap modes and longitudinal monopole antenna modes give rise to highly localized electric fields in the polythiophene film and are the primary contributors to polythiophene absorption enhancement. This approach is suitable for large area optoelectronic applications where light management in ultrathin active layers is desired.
Thermoelectric properties of n-type Mn3−xCrxSi4Al2 in air
Authors: Funahashi R. , Matsumura Y. , Tanaka H. , Takeuchi T. , Norimatsu W. , Combe E. , Suzuki R. O. , Wang Y. , Wan C. , Katsuyama S. , Kusunoki M. , Koumoto K.
Published: October 2012

A silicide material with a good n-type thermoelectric property has been discovered. This silicide possesses a composition of Mn3−xCrxSi4Al2 (0 ≤ x ≤ 0.7) and hexagonal CrSi2 structure. The a- and c-cell parameters decrease with increasing the amount of Cr substitution. The absolute values of Seebeck coefficient and electrical resistivity increase by Cr substitution up to 573 K because of reduction of carrier density. The dimensionless thermoelectric figure of merit ZT reaches 0.21 at 773 K for a non Cr substituted sample at the Mn site and 0.30 at 573 K for a Cr substituted one with x = 0.3. Since oxide passive layer is formed around the surface, electrical resistivity measured at 873 K is constant for 2 days in air, which indicates good oxidation resistance in air of this material. The Mn3−xCrxSi4Al2 is a promising n-type material with a good oxidation resistance in the middle temperature range. A thermoelectric module consisting of 64 pairs of legs has been fabricated using MnSi1.7 and non Cr substituted Mn3Si4Al2 devices as p- and n-type legs, respectively. Output power reaches 9.4 W, which corresponds to 2.3 kW/m2 of power density against surface area of the substrate, for a heat source temperature of 873 K in air.
Optical absorbance of doped Si quantum dots calculated by time-dependent density functional theory with partial electronic self-interaction corrections
Authors: Freitag H. , Mavros M. G. , Micha D. A.
Published: October 2012

The optical properties of Si quantum dots (QDs) with phosphorous and aluminum dopants have been calculated with the recently tested Heyd-Scuseria-Ernzerhof (HSE) density functionals to ascertain the effect of functional corrections to electronic self-interaction. New results have been obtained for 20 crystalline and amorphous structures of Si29 and Si35 quantum dots and are compared to our previous results obtained using the PW91/PW91 functionals. The bandgaps are greater in magnitude and shifted to higher energies in HSE calculations compared to PW91 calculations, and the absorption spectrum is blueshifted in HSE. Trends in the shifts of absorbances due to doping are similar for both sets of calculations, with doped QDs absorbing at lower photon energies than undoped QDs. Consistent with previous results, the bandgaps of QDs are found to decrease as the size of the QD increases, and the absorption spectra of amorphous QDs are redshifted compared to those of crystalline structures. The molecular orbitals involved in the transitions with the largest oscillator strengths show that the electron density moves towards the surface of the quantum dot as the structure is excited. The lifetimes of photoexcited states were found to differ substantially between the two functionals due to their sensitivity to the overlaps of initial and final orbitals. Comparison with available experimental and independent theoretical results supports the conclusion that the HSE functional better matches experimental results due to the partial inclusion of Hartree-Fock exchange.
Thermal imaging diagnostics of high-current electron beams
Authors: Pushkarev A. , Kholodnaya G. , Sazonov R. , Ponomarev D.
Published: October 2012

The thermal imaging diagnostics of measuring pulsed electron beam energy density is presented. It provides control of the electron energy spectrum and a measure of the density distribution of the electron beam cross section, the spatial distribution of electrons with energies in the selected range, and the total energy of the electron beam. The diagnostics is based on the thermal imager registration of the imaging electron beam thermal print in a material with low bulk density and low thermal conductivity. Testing of the thermal imaging diagnostics has been conducted on a pulsed electron accelerator TEU-500. The energy of the electrons was 300–500 keV, the density of the electron current was 0.1–0.4 kA/cm2, the duration of the pulse (at half-height) was 60 ns, and the energy in the pulse was up to 100 J. To register the thermal print, a thermal imager Fluke-Ti10 was used. Testing showed that the sensitivity of a typical thermal imager provides the registration of a pulsed electron beam heat pattern within one pulse with energy density over 0.1 J/cm2 (or with current density over 10 A/cm2, pulse duration of 60 ns and electron energy of 400 keV) with the spatial resolution of 0.9–1 mm. In contrast to the method of using radiosensitive (dosimetric) materials, thermal imaging diagnostics does not require either expensive consumables, or plenty of processing time.
Signal Space Separation method with block matrix inversion for extraction of signals in magnetoencephalography
Authors: Baskaran R. , Janawadkar M. P.
Published: October 2012

Signal Space Separation (SSS) method is a technique utilized to eliminate the contribution of unwanted signals due to external magnetic noise that inevitably get recorded along with the actual magnetic signal due to neuronal currents in the brain. In this paper, the SSS method has been implemented using block matrix inversion. By implementing block matrix inversion along with regrouping of radial terms, it has been possible to extract the true brain signal from the measured magnetic signal which includes the contribution from an external magnetic dipole artifact for measurements from as few as 64 channels. We observe that the minimum root mean square deviation (RMSD) of the signal inferred from block matrix inversion with regrouped terms is around 6 fT when the truncation order is set at L1 = 11 for signals of interest and L2 = 2 for external noise sources and saturates to similar values for higher L1. The RMSD of extracted signal is 50% smaller than the minimum RMSD when the magnetoencephalography signal is extracted by direct pseudoinverse technique and does not have a deep minimum in the truncation order L1 as observed when direct pseudoinverse technique is used.
Non-resonant terahertz field enhancement in periodically arranged nanoslits
Authors: Novitsky Andrey , Ivinskaya Aliaksandra M. , Zalkovskij Maksim , Malureanu Radu , Uhd Jepsen Peter , Lavrinenko Andrei V.
Published: October 2012

We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength λ of the impinging radiation. Two regimes of operation are found. First, when the grating period P≪λ, frequency-independent enhancement is observed, accompanied by a very high transmission approaching unity. With high accuracy, this enhancement equals the ratio of P to the slit width w. Second, when the grating period approaches the THz wavelength but before entering the Raleigh-Wood anomaly, the field enhancement in nanoslit stays close to that in a single isolated slit, i.e., the well-known inverse-frequency dependence. Both regimes are non-resonant and thus extremely broadband for P<λ. The results are obtained by the microscopic Drude-Lorentz model taking into account retardation processes in the metal film and validated by the finite difference frequency domain method. We expect sensor and modulation applications of the predicted giant broadband field enhancement.
Detection of low frequency hurricane emissions using a ring laser interferometer
Authors: Dunn Robert W. , Slaton William V. , Kendall Lauren M.
Published: October 2012

Over the last decade, large horizontally mounted ring laser interferometers have demonstrated the capacity to measure numerous geophysical effects. In this paper, responses from large ring laser interferometers to low frequency hurricane emissions are presented. Hurricanes create a broad spectrum of noise that extends into the millihertz range. In addition to microseisms, hurricanes with established eyewalls were found to create distinct frequency peaks close to 7 mHz as they came ashore or moved over shallow water. Selected emissions from Hurricanes Katrina, Wilma, and Dean are presented. The exact coupling mechanism between the ∼7 mHz hurricane emissions and the ring lasers remains under active investigation.
Control of current and voltage oscillations in a short dc discharge making use of external auxiliary electrode
Authors: Mustafaev A. S. , Demidov V. I. , Kaganovich I. , Adams S. F. , Koepke M. E. , Grabovskiy A.
Published: October 2012

A dc discharge with a hot cathode is subject to current and voltage plasma oscillations, which have deleterious effects on its operation. The oscillations can be inhibited by installing an auxiliary electrode, placed outside of anode. By collecting a modest current through a small opening in anode, we show that the discharge becomes stable, in a certain pressure range. This method of avoiding current oscillations can be used, for example, for high current stabilizers.
74-fs nanotube-mode-locked fiber laser
Authors: Popa D. , Sun Z. , Hasan T. , Cho W. B. , Wang F. , Torrisi F. , Ferrari A. C.
Published: October 2012

We report an erbium-doped, nanotube mode-locked fiber oscillator generating 74 fs pulses with 63 nm spectral width. This all-fiber-based laser is a simple, low-cost source for time-resolved optical spectroscopy, as well as for many applications where high resolution driven by short pulse durations is required.
Electron spin relaxation in rippled graphene with low mobilities
Authors: Zhang P. , Zhou Y. , Wu M. W.
Published: October 2012

We investigate spin relaxation in rippled graphene where curvature induces a Zeeman-like spin-orbit coupling with opposite effective magnetic fields along the graphene plane in K and K′ valleys. The joint effect of this Zeeman-like spin-orbit coupling and the intervalley electron-optical phonon scattering opens a spin relaxation channel, which manifests itself in low-mobility samples with the electron mean free path being smaller than the ripple size. Due to this spin relaxation channel, with the increase of temperature, the relaxation time for spins perpendicular to the effective magnetic field first decreases and then increases, with a minimum of several hundred picoseconds around room temperature. However, the spin relaxation along the effective magnetic field is determined by the curvature-induced Rashba-type spin-orbit coupling, leading to a temperature-insensitive spin relaxation time of the order of microseconds. Therefore, the in-plane spin relaxation in low-mobility rippled graphene is anisotropic. Nevertheless, in the presence of a small perpendicular magnetic field, as usually applied in the Hanle spin precession measurement, the anisotropy of spin relaxation is strongly suppressed. The spin relaxation channel revealed in this work contributes to spin relaxation around room temperature in rippled graphene with low mobility.
Water plays an important role in osmolyte-induced hairpin structure change: A molecular dynamics simulation study
Authors: Shao Qiang , Gao Yi Qin
Published: October 2012

To investigate how solvent (water) and cosolvent (osmolyte) affect protein structure in various osmolyte solutions, in the present study we used GB1p peptide as the model protein to study its folding process in 2,2,2-trifluoroethanol (TFE)/water and denaturation process in GdmSCN/water solutions, respectively. It was observed that TFE moderately enhances the structure stability of native β-hairpin, consistent with the previous experimental observation that the hairpin conformation population of several polypeptides is increased in TFE/water solution compared to in pure water. More interestingly, the formation of β-hairpin is significantly accelerated in TFE/water solution. The accelerated folding of β-hairpin consists of following sequential events: the accumulation of TFE on protein surface → less water surrounding carbonyl group (easier dehydration of CO) → the formation of CO–NH backbone hydrogen bond. In contrary, the denaturation of hairpin structure of GB1p peptide in GdmSCN/water solution is induced by the accumulation of Gdm+ on protein surface and the hydrogen bonding from water as well as Gdm+. Therefore, this study shows the importance of water in TFE-induced formation and Gdm+-induced denaturation of β-hairpin structure.
Hysteresis effects in the inverse magnetocaloric effect in martensitic Ni-Mn-In and Ni-Mn-Sn
Authors: Titov I. , Acet M. , Farle M. , González-Alonso D. , Mañosa L. , Planes A. , Krenke T.
Published: October 2012

The presence of a large inverse magnetocaloric effect around the martensitic transformation in Ni-Mn-Sn and Ni-Mn-In alloys is expected to lead to substantial cooling on applying a magnetic field. However, the occurrence of hysteresis around the transition causes limitations on adiabatic temperature-changes. We study the adiabatic temperature-change in both systems in relation to the hysteresis effects. Ni-Mn-In, having a relatively narrower hysteresis and a greater shift of the characteristic transition temperatures with applied field with respect to Ni-Mn-Sn, shows reversibility in the adiabatic-temperature change related to the inverse magnetocaloric effect when the state of the system is cycled within a minor transitional hysteresis loop. Ni-Mn-Sn does not show reversibility in the inverse magnetocaloric effect under cycling-fields up to 5 T. The reversibility in the adiabatic temperature-change is directly related to the reversibility in the relative amount of austenite and martensite in the sample when the field is cycled.
External electric field induced oxygen-driven unzipping of carbon nanotubes
Authors: Zhao Hongpeng , Xu Wei , Song Liang , Mei Qinggao , Chen Chi , Miao Ling , Jiang Jianjun
Published: October 2012

Based on density functional theory, the mechanisms for oxygen-driven unzipping of carbon nanotubes under electric field are presented. Under the control of external electric field, O adatoms will diffuse along the single-walled carbon nanotube from low potential to the high potential sites. The energy barrier of O adatoms diffusion gets lower while increasing the electric potential, thus enabling the O adatoms to diffuse to the higher potential sites more easily. And with quantities of O adatoms diffusing to the high potential sites, a linear epoxy chain is formed and the single-walled carbon nanotube will be unzipped into graphene nanoribbons automatically.
Electronic scattering of pseudo-magnetic field induced by local bump in graphene
Authors: Yang Mou , Cui Yan , Wang Rui-Qiang , Zhao Hong-Bo
Published: October 2012

We investigated the electronic scattering properties of a local bump strain in graphene sheet in frame of Born approximation. The differential scattering cross section is a function of outgoing and incident angles and has the six-fold rotational symmetry with respect to both angles. The incident plane wave is scattered into two backward fan-waves in different directions in low energy limit and is split into two branches spanning the angle reversely proportional to the incident wavevector k in high energy limit. The total scattering cross section depends on incident wavevector by the form k5 in the former limit, while it is independent of k and sensitive to the incident orientation in the latter limit. We explained these features using the symmetry of the strain-induced pseudo-magnetic field.
Chemical pressure effect on optical properties in multiferroic bulk BiFeO3
Authors: Ramachandran B. , Ramachandra Rao M. S.
Published: October 2012

We have investigated diffuse reflectance spectra of the polycrystalline BiFeO3, Bi0.9Ba0.05Ca0.05FeO2.95, and Bi0.9Ca0.1FeO2.95 samples to demonstrate crystal-field spectroscopy, which enabled us to explore local distortion in the non-centrosymmetric FeO6 octahedron, and also to study chemical pressure effect on the band gap and d-d transition band energies. The energy values of band gap and d-d transition bands of the doped BiFeO3 samples were found to red-shift with the reduced unit cell volume. Absorption spectroscopic studies of the BiFeO3 samples reveal that nature of the band gap is a direct. Raman spectroscopy study also reveals that the softening/hardening of the certain Raman modes in BiFeO3 upon substitution of Ca. The chemical pressure induced changes in the band gap and d-d band energies, and the Raman modes of the Ca doped BiFeO3, which also found to enhance its magnetic and magnetoelectric properties.
Magnetoelectric coupling of multilayered Pb(Zr0.52Ti0.48)O3-CoFe2O4 film by piezoresponse force microscopy under magnetic field
Authors: Xie S. H. , Liu Y. M. , Ou Y. , Chen Q. N. , Tan X. L. , Li J. Y.
Published: October 2012

Multiferroic Pb(Zr0.52Ti0.48)O3-CoFe2O4-Pb(Zr0.52Ti0.48)O3 (PCP) laminated film has been synthesized by sol-gel process and spin coating, with the spinel structure of CoFe2O4 and perovskite structure of Pb(Zr0.52Ti0.48)O3 verified by x-ray diffraction. The good multiferroic properties of PCP film have been confirmed by ferroelectric and magnetic hysteresis loops, with leakage current substantially reduced. The local magnetoelectric coupling has been verified using piezoresponse force microscopy under external magnetic field, showing magnetically induced evolution of piezoresponse and ferroelectric switching characteristics, with piezoresponse amplitude reduced and coercive voltage increased. Such technique will be useful in characterizing local magnetoelectric (ME) couplings for a wide range of multiferroic materials.
Optofluidic random laser
Authors: Shivakiran Bhaktha B. N. , Bachelard Nicolas , Noblin Xavier , Sebbah Patrick
Published: October 2012

Random lasing is reported in a dye-circulated structured polymeric microfluidic channel. The role of disorder, which results from limited accuracy of photolithographic process, is demonstrated by the variation of the emission spectrum with local-pump position and by the extreme sensitivity to a local perturbation of the structure. Thresholds comparable to those of conventional microfluidic lasers are achieved, without the hurdle of state-of-the-art cavity fabrication. Potential applications of optofluidic random lasers for on-chip sensors are discussed. Introduction of random lasers in the field of optofluidics is a promising alternative to on-chip laser integration with light and fluidic functionalities.
Kinetics of color center formation in silica irradiated with swift heavy ions: Thresholding and formation efficiency
Authors: Manzano-Santamaría J. , Olivares J. , Rivera A. , Peña-Rodríguez O. , Agulló-López F.
Published: October 2012

We have determined the cross-section σ for color center generation under single Br ion impacts on amorphous SiO2. The evolution of the cross-sections, σ(E) and σ(Se), show an initial flat stage that we associate to atomic collision mechanisms. Above a certain threshold value (Se > 2 keV/nm), roughly coinciding with that reported for the onset of macroscopic disorder (compaction), σ shows a marked increase due to electronic processes. In this regime, a energetic cost of around 7.5 keV is necessary to create a non bridging oxygen hole center-E′ (NBOHC/E′) pair, whatever the input energy. The data appear consistent with a non-radiative decay of self-trapped excitons.
Absence of ferroelectricity in BiMnO3 ceramics
Authors: Goian V. , Kamba S. , Savinov M. , Nuzhnyy D. , Borodavka F. , Vaněk P. , Belik A. A.
Published: October 2012

We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at TC1 = 475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above TC1. Step-like dielectric anomaly observed at TC1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic but only antipolar ferromagnet.
Theory of the suspended graphene varactor
Authors: AbdelGhany M. , Ledwosinska E. , Szkopek T.
Published: October 2012

We report the theory and design equations of the suspended graphene varactor, wherein device capacitance is tuned by the voltage controlled deflection of a suspended graphene membrane. A simple model based on large membrane deflection predicts a capacitor tuning range of 76%, with a membrane pull-in voltage tuneable from 1 V to 30 V. An intrinsic electric quality factor approaching 200 is predicted based on experimentally determined Young's modulus and sheet resistance.
Optimization of antireflective zinc oxide nanorod arrays on seedless substrate for bulk-heterojunction organic solar cells
Authors: Woo Choi Hyung , Lee Kyu-Sung , Alford T. L.
Published: October 2012

We report on the enhanced performance of hybrid photovoltaic devices consisting of poly(3-hexylthiophene), (6,6)-phenyl C61 butyric acid methyl ester, and zinc oxide (ZnO) nanorod arrays grown on seedless indium tin oxide (ITO) glass in aqueous zinc chloride solution. Introduction of optimized-length ZnO nanorod arrays between hole injection and ITO layers increased photocurrent density from 8.0 to 8.8 mA/cm2 and fill factor from 42% to 47%. The absence of a seed layer significantly reduced incident light reflection on the ITO glass and resulted in an overall 10% increase in photocurrent. A photovoltaic device based on a ZnO nanostructure length of 100 nm exhibited a maximum power conversion efficiency of 2.4%, 15% higher than that of an equivalent device without ZnO nanorods.
Hydrogen segregation and lattice reorientation in palladium hydride nanowires
Authors: He J. H. , Knies D. L. , Hubler G. K. , Grabowski K. S. , Tonucci R. J. , Dechiaro L. F.
Published: October 2012

We study palladium hydride nanowires of different sizes and hydrogen concentrations at 300 K using molecular dynamic simulations. Strong surface segregation of hydrogen with a depletion zone behind is observed in the palladium hydride nanowires. We also show that lattice reorientation is controlled by the hydrogen concentration as well as the nanowire size. The interplay of surface stresses and hydrogen induced stresses is responsible for the observations.
Light trapping in solar cells: Analytical modeling
Authors: Boccard Mathieu , Battaglia Corsin , Haug Franz-Josef , Despeisse Matthieu , Ballif Christophe
Published: October 2012

We model analytically light harvesting in realistic solar cells by extending a formalism suggested by Deckman et al. [Appl. Phys. Lett. 42, 110968 (1983)], based on tracing of an average ray of light. Arbitrary light scattering schemes and parasitic absorption are implemented in the model, and we validate our approach by comparing with experimental measurements from microcrystalline silicon devices. The intuitive understanding obtained with this extended model is discussed. This approach enables identifying parasitic absorption as main limitation of state-of-the-art light harvesting schemes, and highlights that a better light trapping requires improving the first scattering events.
Excellent p-n control in a high temperature thermoelectric boride
Authors: Maruyama Satofumi , Miyazaki Yuzuru , Hayashi Kei , Kajitani Tsuyoshi , Mori Takao
Published: October 2012

Polycrystalline samples of YxAlyB14 (x ∼ 0.57) with different fractional occupancies y (0.41 ≤ y ≤ 0.63) were synthesized and their thermoelectric properties investigated. Electrical conductivities generally followed three-dimensional variable range hopping with a rapid delocalization indicated as electrons were increased. Positive Seebeck coefficients were obtained for the Al-poor sample, y = 0.41, which was shifted in the negative direction with increase of y. Maximum Seebeck coefficient values were approximately 400 μV K−1 at 850 K and −200 μV K−1 at 1000 K, for p-type and n-type, respectively. Excellent control of p-n characteristics was achieved in a system with the same crystal structure and consisting of the same elements.
High temperature magnetic properties of SmCo5/α-Fe(Co) bulk nanocomposite magnets
Authors: Rong Chuanbing , Poudyal Narayan , Liu X. B. , Zhang Ying , Kramer M. J. , Ping Liu J.
Published: October 2012

To find alternative high temperature magnets containing no heavy rare earths for power applications, SmCo5/Fe bulk nanocomposite magnets with enhanced energy density and high thermal stability have been produced by using a ball-milling plus warm-compaction route. Up to 30% of the Fe soft magnetic phase has been added to the composites with grain size <20 nm distributed homogenously in the matrix of the SmCo5 hard magnetic phase. It was observed that the microstructure does not change with temperature up to 500 °C. It is also observed that the thermal stability of bulk nanocomposite samples is closely related to bulk density. Energy products above 11 MGOe have been obtained at 300 °C in fully dense bulk SmCo5/Fe nanocomposite magnets, which is 65% higher than that of a single-phase counterpart at the same temperature.
Localizing trapped charge carriers in NO2 sensors based on organic field-effect transistors
Authors: Andringa Anne-Marije , Christian Roelofs W. S. , Sommer Michael , Thelakkat Mukundan , Kemerink Martijn , de Leeuw Dago M.
Published: October 2012

Field-effect transistors have emerged as NO2 sensors. The detection relies on trapping of accumulated electrons, leading to a shift of the threshold voltage. To determine the location of the trapped electrons we have delaminated different semiconductors from the transistors with adhesive tape and measured the surface potential of the revealed gate dielectric with scanning Kelvin probe microscopy. We unambiguously show that the trapped electrons are not located in the semiconductor but at the gate dielectric. The microscopic origin is discussed. Pinpointing the location paves the way to optimize the sensitivity of NO2 field-effect sensors.
Corrugated flat band as an origin of large thermopower in hole doped PtSb2
Authors: Mori Kouta , Usui Hidetomo , Sakakibara Hirofumi , Kuroki Kazuhiko
Published: October 2012

The origin of the recently discovered large thermopower in hole-doped PtSb2 is theoretically analyzed based on a model constructed from first principles band calculation. It is found that the valence band dispersion has an overall flatness combined with some local ups and downs, which gives small Fermi surfaces scattered over the entire Brillouin zone. The Seebeck coefficient is calculated using this model, which gives good agreement with the experiment. We conclude that the good thermoelectric property originates from this “corrugated flat band”, where the coexistence of large Seebeck coefficient and large electric conductivity is generally expected.
Ontogenetic variability in the habitat associations of Haliotis iris in central New Zealand
Authors: Aguirre J. David , McNaught Douglas C.
Published: October 2012

The drivers of demographic variability in abalone are not well understood. Here, we examine ontogenetic variability in the habitat associations of black-foot abalone (Haliotis iris) populations in central New Zealand to better understand links between habitat variability and demographic variability in abalone. At larger, regional scales, there were west-to-east gradients in juvenile abundance, adult abundance and the size at which H. iris begin to occupy open reef habitats. At smaller, local scales, populations were depth-stratified, and there were two prominent transitions: a deep-to-shallow habitat transition during the juvenile stages; and a shallow-to-deep habitat transition during the adult stages. We also found that associations between abalone abundance and the size of the boulders, as well as associations between abalone abundance and the surface area of the interstitial spaces between boulders, differ among ontogenetic stages. For all stages, abundance was positively associated with crustose coralline algae cover, but negatively associated with articulated coralline algae cover. The relationship between canopy algae and adult abundance was positive, whereas for early juveniles, late juveniles and subadults, the relationship was weakly negative. Last, the association between the cover of understorey algae and abundance was negative for all ontogenetic stages. Overall, habitat variability played a strong, but ontogenetically variable, role in determining the abundance and distribution of H. iris.
Phytotoxic evaluation of Phragmites australis: an investigation of aqueous extracts of different organs
Authors: Uddin Md N. , Caridi Domenico , Robinson Randall W.
Published: October 2012

Phragmites australis is one of the most widespread and invasive plants on earth. Allelopathic interference has been considered as a possible way associated with its invasiveness in wetlands. A series of ecologically realistic experiments was conducted to explore allelochemical phytotoxicity of Phragmites. Germination bioassays using aqueous extracts of different organs (leaf, stem, root and rhizome) of Phragmites were tested with model seeds (Lactuca sativa and Raphanus sativus) and associated plant species (Juncus pallidus and Rumex conglomeratus). These studies showed that leaf and rhizome extracts exhibited strong inhibition on germination, biometric and physiological parameters (all P ≤ 0.001). Dose–response studies confirmed LC50 (4.68% and 11.25%) of Lactuca for leaf and rhizome extracts respectively. Root growth of Juncus and Rumex was inhibited by 75% and 30%, respectively, in leaf leachate-incorporated soil. Chlorophyll content and maximum quantum yield (Fv/Fm) were significantly reduced with leaf and rhizome leachates. The stability and quantity of water-soluble phenolics in anaerobic versus aerobic condition may influence phytotoxic effects to other species. Phragmites organs can be ranked in order of allelopathic potentiality as follows: leaf > rhizome > root > stem. The present study highlighted the potential impacts of allelochemicals on plant recruitment in wetlands invaded by Phragmites.
V-Track: software for analysing and visualising animal movement from acoustic telemetry detections
Authors: Campbell Hamish A. , Watts Matthew E. , Dwyer Ross G. , Franklin Craig E.
Published: October 2012

The tagging of aquatic and semi-aquatic animals with acoustic transmitters and their detection by passive underwater receivers has gained huge popularity over the past decade. This technology offers researchers the opportunity to monitor the finite- to broad-scale movements of multiple individuals over many years; however, the sheer scale and spatial complexity of these datasets are often beyond the capabilities of routine database and spread-sheet applications. In the present paper, we describe software (V-Track) that greatly facilitates the assimilation, analysis and synthesis of animal-location data collected by underwater passive acoustic receivers. The principal features within V-Track are the behavioural event qualifier (BEQ) and the receiver-distance matrix (RDM) calculator. The BEQ identifies and catalogues horizontal movements from receiver detection data, or vertical movements from transmitter sensor data (depth or temperature). The RDM is generated from the geographical location of the acoustic receivers and is utilised by V-Track to illustrate the behavioural event information in a spatial context. V-Track is a package written within the R-programming language, and a graphical user interface is also provided. Here, we feature two case studies to demonstrate software functionality for defining and quantifying behaviour in acoustically tagged marine and freshwater vertebrates.
Unpredicted ovulations and conceptions during early pregnancy: an explanatory mechanism of human superfetation
Authors: Tarín Juan J. , García-Pérez Miguel A. , Hermenegildo Carlos , Cano Antonio
Published: October 2012

In this bioessay, a literature review on human superfetation was performed in order to find epidemiological variables associated with this phenomenon. Thereafter, an explanatory mechanism of superfetation compatible with the endocrinological, histological and physiological changes undergone by women during early pregnancy is proposed. Superfetation can be defined as the ovulation, fertilisation and implantation of a second or additional embryo(s) during pregnancy. The literature review evidences a small discordance in gestational age between dizygotic twins in humans (range: 2–4 weeks; mean ± s.e.m.: 3.3 ± 0.3 weeks). This difference is compatible with a luteal out-of-phase (LOOP; i.e. atypical increase in E2 levels in the mid-luteal phase)-like event occurring between 1 and 3 weeks after the ovulation that allowed the first pregnancy to take place. The LOOP-like event may allow passive sperm transport from the vaginal fornix to the Fallopian tube ipsilateral to the ovulatory ovary and trigger a LH peak and ovulation. Furthermore, during very early pregnancy, the decidual reaction is not yet completed and at least one proximal Fallopian ostium may be opened, allowing the passage of the spermatozoa ascending to the fertilisation site and the extra embryo(s) descending to the implantation site(s).
Terrestrial vertebrate richness of the inhabited Torres Strait Islands, Australia
Authors: Lavery Tyrone H. , Watson Justin J. , Leung Luke K.-P.
Published: October 2012

Located between New Guinea and Australia, Torres Strait and its islands provide an opportunity to examine the results of recent isolation on the Australo-Papuan fauna. However, records of the modern diversity of terrestrial vertebrates on the islands remained scattered and poorly documented. Analyses of terrestrial vertebrate inventories and physical island variables can provide insight into pre-existing conditions of the Sahul land bridge and useful strategies for conservation efforts. We collated all available records of terrestrial vertebrates from the 17 inhabited islands and supplemented these with our own systematic surveys. We used Spearman’s rank correlation coefficient and nested analysis to determine how species richness relates to physical island variables. We also used cluster analysis to group similar islands based on their vertebrate assemblages. Vertebrate richness is not correlated with Simpson’s habitat diversity but is correlated with total number of habitat types, indicating that rare habitats may contribute disproportionately to richness. The archipelago supports a depauperate Australo-Papuan fauna and the assemblages found on smaller islands are subsets of those on larger islands. Island size is the most effective predictor of species richness, and the analysis reveals that geographically related islands support similar suites of species. The frequency with which our surveys added new records to individual island inventories highlights the need for additional sampling in the region.
Short‐Term Effects of Formalin and Ethanol Fixation and Preservation Techniques on Weight and Size of Fish Eggs
Authors: Frimpong E. A. , Henebry M. L.
Published: October 2012

Preservative‐induced changes in the weight and size of fish eggs distort information in studies of fecundity and egg production, but the nature of changes that occur during short‐term preservation is not well understood. To determine the nature of these effects and to provide a basis for correcting for such changes after sample processing, we examined the short‐term effects of 10% formalin and 70% ethanol on eggs from gravid female white suckers Catostomus commersonii and fantail darters Etheostoma flabellare collected in two tributaries of the New River, Virginia. A sequential treatment with formalin and then ethanol was also tested to simulate effects expected in a typical fixation and preservation schedule when eggs are fixed and preserved within the fish. Formalin resulted in a significant gain (36%) in egg dry weight during the first 12 h of treatment. Ethanol had no detectable effect on egg dry weight after 9 d of fixation and preservation. Eggs that were fixed in formalin and then preserved in ethanol showed dry weights that were equivalent to those of eggs that were fixed and preserved only in ethanol, implying a reversal of the effect of formalin. We hypothesize that the action of ethanol on egg proteins unbinds the formaldehyde, with the effect of reversing formalin‐induced weight gain in eggs that have been fixed with formalin. Reductions in egg diameter were similar (∼17% after drying) between ethanol and formalin treatments, but there was an additional 5.4% shrinkage when eggs were fixed in formalin and then preserved in ethanol. In comparison with changes in egg diameter, changes in egg weight had a wider range among treatments and less variability within treatments. The experimental results indicate that egg weight is a more reliable indicator of preservation‐induced changes and a more consistent characteristic than egg diameter for comparing egg production among fishes.