bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible effects of static electric field on physical vapor growth of lead phthalocyanine crystals
Authors: Sakai Masatoshi , Iizuka Masaaki , Nakamura Masakazu , Kudo Kazuhiro
Published: March 2011

To elucidate the effects of a static electric field on the crystal growth of a molecule with both a molecular dipole and a quadrupole moment, we performed physical vapor growth of monoclinic lead phthalocyanine (PbPc) crystals under quasithermal equilibrium conditions and observed distinct effects of the applied electric field on the drift motion of the molecules that diffused over the substrate surface. The density of crystals grown on the Au electrode with a high electric potential exceeds the crystal density on both an electrically grounded electrode and a glass substrate surface. In addition, this difference in crystal density increases with applied voltage. This biased distribution of crystal growth is explained by the drift motion of diffusing molecules, which is induced by the interaction of the electric field with molecular dipole and quadrupole moments. However, the long-range oriented growth that is clearly seen in the physical vapor growth with an electric field for copper phthalocyanine is not observed in the crystal growth of PbPc; only a locally oriented growth is observed in the vicinity of the Au electrode. For electric-field-sensitive PbPc, it is difficult to maintain quasithermal equilibrium conditions over a wide area because the distribution of the diffusing molecules varies as a function of the spatially nonuniform electric field, which disturbs the long-range oriented growth.
The effect of microcavity laser recombination lifetime on microwave bandwidth and eye-diagram signal integrity
Authors: Wu C. H. , Tan F. , Wu M. K. , Feng M. , Holonyak N.
Published: March 2011

Vertical microcavity surface-emitting lasers employing quantum wells and small aperture buried-oxide current and field confinement are demonstrated with wider mode spacing and faster spontaneous carrier recombination (enhanced Purcell factor), lower threshold current, larger side mode suppression ratio (SMSR), and higher photon density and temperature insensitivity. The result is a microcavity laser that achieves higher microwave modulation bandwidth (f−3dB = 15.8 GHz) at ultra-low power consumption (1.5 mW) with a slope for the modulation current efficiency factor (MCEF) = 17.47 GHz/mA−1/2, as well as a better quality eye diagram in high-speed data transmission. The microwave behavior model for the microcavity laser is used to estimate the enhanced recombination and reduced lifetime.
Optical investigation of InAs quantum dots inserted in AlGaAs/GaAs modulation doped heterostructure
Authors: Khmissi H. , Baira M. , Sfaxi L. , Bouzaïene L. , Saidi F. , Bru-Chevallier C. , Maaref H.
Published: March 2011

Optical properties of InAs quantum dots (QDs) inserted in AlGaAs/GaAs modulation doped heterostructure are investigated. To study the effect of carrier transfer behavior on the luminescence of self-assembled quantum dots, a series of sample has been prepared using molecular beam epitaxy (Riber 32 system) in which we have varied the thickness separating the delta dopage and the InAs quantum dots layer. Photoluminescence spectra show the existence of two peaks that can be attributed to transition energies from the ground state (E1-HH1) and the first excited state (E2-HH2). Two antagonist effects have been observed, a blue shift of the emission energies result from electron transferred from the AlGaAs/GaAs heterojunction to the InAs quantum dots and a red shift caused by the quantum confined Stark effect due to the internal electric field existing In the AlGaAs/GaAs heterojunction.
A Mott polarimeter operating at MeV electron beam energies
Authors: Tioukine V. , Aulenbacher K. , Riehn E.
Published: March 2011

We have developed a Mott electron polarimeter for the Mainzer microtron (MAMI) accelerator in Mainz, Germany. At beam energies ranging between 1.0 and 3.5 MeV two double focusing magnet spectrometers collect elastically backscattered electrons from gold targets. In spite of the small spectrometer acceptance, a sufficient statistical efficiency is achieved to provide very fast measurements if beam currents typical for experiments at MAMI are being used. High reproducibility is achieved, demonstrating that the results of asymmetry measurements are independent of the primary beam current in a range from 0.004 to 45 \documentclass[12pt]{minimal}\begin{document}$\mu \text{A}$\end{document}μA at a level of <1% relative variation. Compared to low energy polarimeters of similar construction an improvement of a factor 2–3 in absolute accuracy seems possible.
Exciton-magnon structure of the optical absorption spectrum of antiferromagnetic MnPS3
Authors: Gnatchenko S. L. , Kachur I. S. , Piryatinskaya V. G. , Vysochanskii Yu. M. , Gurzan M. I.
Published: March 2011

In the region of the A1g6(S6)→A1g4,Eg4(G4) optical transition, the absorption spectrum of the quasi-two-dimensional antiferromagnet MnPS3 has an exciton-magnon structure. It includes a pure exciton line with a wave number of 21223.5cm−1 and an exciton-magnon band with a peak at 21328cm−1 for T=1.7K. The spectra are studied at temperatures ranging from 1.7to80K and with external magnetic fields up to 60kOe. In a magnetic field oriented along the easy axis z, splitting of the exciton line is observed owing to the nonequivalence of the magnetic sublattices with respect to an external field. The behavior of the split components in the region of the spin-orientation transition (35–41kOe) is typical of second order phase transitions.
Electrical resistance of spatially varying magnetic interfaces. The role of normal scattering
Authors: Gurzhi R. N. , Kalinenko A. N. , Kopeliovich A. I. , Pyshkin P. V. , Yanovsky A. V.
Published: March 2011

We investigate diffusive electron transport in conductors with spatially inhomogeneous magnetic properties taking both impurity and normal scattering into account. It is found that the additional interface resistance that arises due to a magnetic inhomogeneity depends fundamentally on its spatial characteristics. The resistance is proportional to the spin-flip time when the magnetic properties of the conducting system vary sufficiently smoothly along the sample. This can be used for direct experimental study of spin-flip processes. In the opposite case, when the magnetic characteristics vary sharply, the additional resistance depends basically on the difference in the magnetic properties far from the interface region on both sides of the interface. The resistance increases as the frequency of electron-electron scattering increases. We consider two types of smooth interfaces: (i) between fully spin-polarized magnets and ordinary magnetic (or non-magnetic) conductors, and (ii) between two fully and oppositely polarized magnetic conductors. It is shown that the interface resistance is very sensitive to an external magnetic field applied to a fully spin-polarized state.
Low-temperature acoustic properties of nanostructured zirconium obtained by intensive plastic deformation
Authors: Vatazhuk E. N. , Pal-Val P. P. , Natsik V. D. , Pal-Val L. N. , Tikhonovsky M. A. , Velikodny A. N. , Khaimovich P. A.
Published: March 2011

The temperature dependences of the logarithmic decrement and dynamic Young’s modulus of polycrystalline coarse-grained and nanostructured Zr are studied at temperatures of 2.5–340K. A nanostructured state of samples with grain sizes on the order of 100nm was produced by intensive plastic deformation (IPD). The measurements were made using a two-component vibrator technique at frequencies of 73–350kHz. A relaxation peak in the internal friction near 250K was discovered in the coarse-grained, annealed Zr which is retained after IPD, but its height increases by roughly a factor of 10 and the localization temperature shifts to lower values. In addition, after IPD a new internal friction peak shows up at moderately low temperatures near 80K. The activation parameters for the observed peaks are estimated and it is shown that they arise from different thermally activated dislocation processes: interactions of dislocations with impurities and kink pair formation in dislocations. It was found that IPD is accompanied by a significant (1–8%) reduction in the Young’s modulus because of quasistatic and dynamic dislocation effects. A glass-like anomaly appears in the temperature dependence of the Young’s modulus of nanostructured Zr at T<20K which may be determined by tunnelling and thermally activated relaxation of quasilocal excitations.
n-type conductivity and phase transition in ultrananocrystalline diamond films by oxygen ion implantation and annealing
Authors: Hu X. J. , Ye J. S. , Liu H. J. , Shen Y. G. , Chen X. H. , Hu H.
Published: March 2011

Ultrananocrystalline diamond (UNCD) films were implanted by oxygen ion and annealed at different temperatures. The electrical and structrual properties of O+-implanted UNCD films were investigated by Hall effects, high-resolution transmission electron microscopy (HRTEM) and uv Raman spectroscopy measurements. The results show that O+-implanted nano-sized diamond grains annealed at 800 °C and above give n-type conductivity to the sample and the UNCD film exhibits n-type resistivity with the carrier mobility of 1∼11 cm2 V−1s−1. With O+ dose increasing from 1015 to 1016 cm−2, diamond phase transits to the amorphous carbon phase accompanied by n-type semiconduction transforming to metallic conduction. In the 1014 cm−2 O+-implanted UNCD film, some amorphous carbon at grain boundaries transits to diamond phase with annealing temperature (Ta) increasing from 500 °C to 800–900 °C, and some of diamond grains are found to be converted to amorphous carbon phase again after 1000 °C annealing. This phase transition is closely relative to the n-type conductivity of the UNCD films, in which n-type conductivity increases with the amorphous carbon phase transiting to diamond phase in the Ta range of 500–900 °C, and it decreases with diamond phase transiting to amorphous carbon phase in the case of 1000 °C annealing. It is indicated that the O+-implanted nano-sized diamond grains dominantly control the n-type conductivity of UNCD film in the Ta range of 800–900 °C, while the grain-boundary-conduction controls the n-type conductivty in UNCD film annealed at 1000 °C. In this case, a novel conduction mechanism that O+-implanted nano-sized diamond grains supply n-type conductivity and the amorphous carbon grain boundaries give a current path to the UNCD films is proposed.
Ionization-induced dynamics of laser-matter interaction in a focused laser pulse: A comparative analysis
Authors: Efimenko E. S. , Kim A. V. , Quiroga-Teixeiro M.
Published: March 2011

We study the laser-matter interaction via optical-field ionization of a medium in a focused ultrashort laser pulse by means of the finite-difference-time-domain modeling of Maxwell’s equations. General aspects of the ionization-induced dynamics with TE- and TM-polarized laser pulses are analyzed. It is shown that there are two qualitatively different regimes of the interaction depending on the angle of the laser beam focusing. At comparatively low angles plasma distributions are smooth; however, due to departure from the quasioptical behavior of light rays in self-generated plasma, lateral large-scaled plasma structures can also be produced, leading to additional beam focusing and correspondingly to higher electron densities. At tight focusing, small-scaled plasma structures are generated that strongly influence field distribution, energy deposition, and scattering characteristics. The influence of electron collisions and the Kerr effect are also analyzed.
Measurement of hard x-ray lens wavefront aberrations using phase retrieval
Authors: Guizar-Sicairos Manuel , Narayanan Suresh , Stein Aaron , Metzler Meredith , Sandy Alec R. , Fienup James R. , Evans-Lutterodt Kenneth
Published: March 2011

Measuring the deviation of a wavefront from a sphere provides valuable feedback on lens alignment and manufacturing errors. We demonstrate that these aberrations can be accurately measured at hard x-ray wavelengths, from far-field intensity measurements, using phase retrieval with a moveable structure in the beam path. We induce aberrations on a hard x-ray kinoform lens through deliberate misalignment and show that the reconstructed wavefronts are in good agreement with numerical simulations. Reconstructions from independent data, with the structure at different longitudinal positions and significantly separated from the beam focus, agreed with a root mean squared error of 0.006 waves.
Crystallization of the Lewis–Wahnström ortho-terphenyl model
Authors: Pedersen Ulf R. , Hudson Toby S. , Harrowell Peter
Published: March 2011

Crystallization is observed during microsecond long molecular dynamics simulations of bent trimers, a molecular model proposed by Lewis and Wahnström for ortho-terphenyl. In the crystal, the three spheres that make up the rigid molecule sit near sites of a body centered cubic lattice. The trimer bond angle is almost optimal for this structure. The crystal exhibits orientational disorder with the molecules aligned randomly along the three Cartesian axis, i.e., cubatic orientational order. The rotational and translational mobilities exhibit only modest decreases on crystallization, by factors of 10 and 3, respectively. The rotational relaxation does change from Debye-like in the liquid to large angle jumps in the crystal. We consider the origin of the superior glass forming ability of the trimer over the monatomic liquid.
Tuning optical modes in slab photonic crystal by atomic layer deposition and laser-assisted oxidation
Authors: Kiravittaya S. , Lee H. S. , Balet L. , Li L. H. , Francardi M. , Gerardino A. , Fiore A. , Rastelli A. , Schmidt O. G.
Published: March 2011

The authors experimentally investigate the effects of atomic layer deposition (ALD) and laser-assisted oxidation on the optical modes in GaAs L3 photonic crystal air-bridge cavities, using layers of InAs quantum dots as internal light source. Four distinct optical mode peaks are observed in the photonic bandgap and they show different wavelength-redshifts (0–6.5 nm) as the photonic crystal surface is coated with an Al2O3 layer (0–5.4 nm thick). Numerical finite-difference time-domain (FDTD) simulations can well-reproduce the experimental result and give insight into the origin of the shifts of modes with different spatial profiles. By combining the ALD coating with in situ laser-assisted oxidation, we are able to both redshift and blueshift the optical modes and we attribute the blueshift to the formation of a GaAs-oxide at the expense of GaAs at the interface between GaAs and the Al2O3 layer. This result can be quantitatively reproduced by including a GaAs-oxide layer into the FDTD model. Selective etching experiments, confirm that this GaAs-oxide layer is mainly at the interface between GaAs and Al2O3 layers.
Fusion neutron detector for time-of-flight measurements in z-pinch and plasma focus experiments
Authors: Klir D. , Kravarik J. , Kubes P. , Rezac K. , Litseva E. , Tomaszewski K. , Karpinski L. , Paduch M. , Scholz M.
Published: March 2011

We have developed and tested sensitive neutron detectors for neutron time-of-flight measurements in z-pinch and plasma focus experiments with neutron emission times in tens of nanoseconds and with neutron yields between 106 and 1012 per one shot. The neutron detectors are composed of a BC-408 fast plastic scintillator and Hamamatsu H1949-51 photomultiplier tube (PMT). During the calibration procedure, a PMT delay was determined for various operating voltages. The temporal resolution of the neutron detector was measured for the most commonly used PMT voltage of 1.4 kV. At the PF-1000 plasma focus, a novel method of the acquisition of a pulse height distribution has been used. This pulse height analysis enabled to determine the single neutron sensitivity for various neutron energies and to calibrate the neutron detector for absolute neutron yields at about 2.45 MeV.
Dynamics of small-molecule glass formers confined in nanopores
Authors: Prisk T. R. , Tyagi M. , Sokol P. E.
Published: March 2011

We report a comparative neutron scattering study of the molecular mobility and nonexponential relaxation of three structurally similar glass-forming liquids, isopropanol, propylene glycol, and glycerol, both in bulk and confined in porous Vycor glass. Confinement reduces molecular mobility in all three liquids, and suppresses crystallization in isopropanol. High-resolution quasielastic neutron scattering spectra were fit to Fourier transformed Kohlrausch functions exp[–(t/τ)β], describing the α-relaxation processes in these liquids. The stretching parameter β is roughly constant with wavevector Q and over the temperature range explored in bulk glycerol and propylene glycol, but varies both with Q and temperature in confinement. Average relaxation times 〈τ(Q)〉 are longer at lower temperatures and in confinement. They obey a power law 〈τ(Q)〉 ∝ Q−γ, where the exponent γ is modified by confinement. Comparison of the bulk and confined liquids lends support to the idea that structural and/or dynamical heterogeneity underlies the nonexponential relaxation of glass formers, as widely hypothesized in the literature.
Direct correlation function for complex square barrier-square well potentials in the first-order mean spherical approximation
Authors: Hlushak S. P. , Trokhymchuk A. D. , Sokołowski S.
Published: March 2011

The direct correlation function of the complex discrete potential model fluids is obtained as a linear combination of the first-order mean spherical approximation (FMSA) solution for the simple square well model that has been reported recently [Hlushak et al., J. Chem. Phys. 130, 234511 (2009)]. The theory is employed to evaluate the structure and thermodynamics of complex fluids based on the square well-barrier and square well-barrier-well discrete potential models. Obtained results are compared with theoretical predictions of the hybrid mean spherical approximation, already reported in the literature [Guillen-Escamilla et al., J. Phys.: Condens. Matter 19, 086224 (2007)], and with computer simulation data of this study. The compressibility route to thermodynamics is then used to check whether the FMSA theory is able to predict multiple fluid–fluid transitions for the square barrier-well model fluids.
Interaction-induced negative differential resistance in asymmetric molecular junctions
Authors: Leijnse M. , Sun W. , Nielsen M. Brøndsted , Hedegård P. , Flensberg K.
Published: March 2011

Combining insights from quantum chemistry calculations with master equations, we discuss a mechanism for negative differential resistance (NDR) in molecular junctions, operated in the regime of weak tunnel coupling. The NDR originates from an interplay of orbital spatial asymmetry and strong electron–electron interaction, which causes the molecule to become trapped in a nonconducting state above a voltage threshold. We show how the desired asymmetry can be selectively introduced in individual orbitals in, e.g., oligo(phenyleneethynylene)-type molecules by functionalization with a suitable side group, which is in linear conjugation to one end of the molecule and cross-conjugated to the other end.
Configurational correlations in the coverage dependent adsorption energies of oxygen atoms on late transition metal fcc(111) surfaces
Authors: Miller Spencer D. , İnoğlu Nilay , Kitchin John R.
Published: March 2011

The coverage dependence of oxygen adsorption energies on the fcc(111) surfaces of seven different transition metals (Rh, Ir, Pd, Pt, Cu, Au, and Ag) is demonstrated through density functional theory calculations on 20 configurations ranging from one to five adsorption sites and coverages up to 1 ML. Atom projected densities of states are used to demonstrate that the d-band mediated adsorption mechanism is responsible for the coverage dependence of the adsorption energies. This common bonding mechanism results in a linear correlation that relates the adsorption energies of each adsorbate configuration across different metal surfaces to each other. The slope of this correlation is shown to be related to the characteristics of the valence d-orbitals and band structure of the surface metal atoms. Additionally, it is shown that geometric similarity of the configurations is essential to observe the configurational correlations.
Fourier transform spectroscopy and direct potential fit of a shelflike state: Application to E(4)1Σ+ KCs
Authors: Busevica L. , Klincare I. , Nikolayeva O. , Tamanis M. , Ferber R. , Meshkov V. V. , Pazyuk E. A. , Stolyarov A. V.
Published: March 2011

The paper presents high-resolution experimental study and a direct potential construction of a shelflike state E(4)1Σ+ of the KCs molecule converging to K(42S) + Cs(52D) atomic limit; such data are of interest for selecting optical paths for producing and monitoring cold polar diatomics. The collisionally enhanced laser induced fluorescence (LIF) spectra corresponding to both spin-allowed E(4)1Σ+ → X(1)1Σ+ and spin-forbidden E(4)1Σ+ → a(1)3Σ+ transitions of KCs were recorded in visible region by Fourier transform spectrometer with resolution of 0.03 cm−1. Overall about 1650 rovibronic term values of the E(4)1Σ+ state of 39K133Cs and 41K133Cs isotopologues nonuniformly covering the energy range [16987, 18445] cm−1 above the minimum of the ground X-state were determined with the uncertainty of 0.01 cm−1. Experimental data field is limited by vibrational levels v′ ∈ [2, 74] with rotational quantum numbers J′ ∈ [1, 188]. The closed analytical form for potential energy curve (PEC) based on Chebyshev polynomial expansion (CPE) was implemented to a direct potential fit (DPF) of the experimental term values of the most abundant 39K133Cs isotopologue. Besides analyticity, regularity, correct long-range behavior, and nice convergence properties, the CPE form demonstrated optimal balance on flexibility and constraint for the DPF of a shelflike state aggravated by a limited data set. The mass-invariant properties of the CPE PEC were tested by the prediction of rovibronic term values of the 41K133Cs isotopomer which coincided with their experimental counterparts with standard deviation of 0.0048 cm−1. The CPE modeling is compared with the highly flexible pointwise inverted perturbation approach model, as well as with conventional Dunham analysis of restricted data set v′ ⩽ 50. Reliability of the empirical PEC is additionally confirmed by good agreement between the calculated and experimental relative intensity distributions in the long E(v′) → X(v″) LIF progressions.
Lattice model of glasses
Authors: Cellai Davide , Fima Andrzej Z. , Lawlor Aonghus , Dawson Kenneth A.
Published: March 2011

Glass-forming liquids have been extensively studied in recent decades, but there is still no theory that fully describes these systems, and the diversity of treatments is in itself a barrier to understanding. Here we introduce a new simple model that (possessing both liquid-crystal and glass transition) unifies different approaches, producing most of the phenomena associated with real glasses, without loss of the simplicity that theorists require. Within the model we calculate energy relaxation, nonexponential slowing phenomena, the Kauzmann temperature, and other classical signatures. Moreover, the model reproduces a subdiffusive exponent observed in experiments of dense systems. The simplicity of the model allows us to identify the microscopic origin of glassification, leaving open the possibility for theorists to make further progress.
Optical assembly of microparticles into highly ordered structures using Ince–Gaussian beams
Authors: Woerdemann Mike , Alpmann Christina , Denz Cornelia
Published: March 2011

Ince–Gaussian (IG) beams are a third complete family of solutions of the paraxial Helmholtz equation. While many applications of Hermite–Gaussian and Laguerre–Gaussian beams have been demonstrated for manipulation of microparticles, the potential of the more general class of IG beams has not yet been exploited at all. We describe the unique properties of IG beams with respect to optical trapping applications, demonstrate a flexible experimental realization of arbitrary IG beams and prove the concept by creating two- and three-dimensional, highly ordered assemblies of typical microparticles. The concept is universal and can easily be integrated into existing holographic optical tweezers setups.
Plasma absorption effects on collisions of positively charged dust grains in dusty plasmas
Authors: Jung Young-Dae , Hong Woo-Pyo
Published: March 2011

The plasma absorption effects on the collisions of positively charged dust grains are investigated in dusty plasmas. The method of stationary phase and the effective interaction potential containing the attractive part are employed to obtain the scattering cross-section between a pair of positively charged dust grains as a function of the impact parameter, collision energy, electron and ion temperatures, and Debye length. The result shows that the plasma absorption effects on the dust surface strongly suppress the total scattering cross-section. It is also shown that the plasma absorption effects on the scattering cross-section decrease with an increase of the ratio of the electron temperature to the ion temperature. In addition, the plasma absorption effects are found to be decreased with increasing the collision velocity.
Nonlinear effects of the photocurrent in self-assembled InAs/GaAs quantum dots
Authors: Monte A. F. G. , Qu Fanyao
Published: March 2011

We report photocurrent (PC) and its complemented photoluminescence investigations of carrier escape dynamics in multi-layered InAs/GaAs self-assembled quantum dots (QDs) subjected to vertical electric fields. We found a nonlinear dependence of PC on the laser excitation power. This unusual behavior can be tuned by bias voltage. Very well agreement between PC data and theoretical prediction ensures that the accumulation of holes trapped in QDs is responsible for this nonlinearity. It is expected that this laser controlled electronic transport might open many potential applications in optoelectronic devices.
Asymptotic multipolar expansion of collision-induced properties
Authors: Bancewicz Tadeusz
Published: March 2011

The collision-induced (CI) dipole moment, CI polarizability, and CI hyperpolarizability are considered for three \documentclass[12pt]{minimal}\begin{document}$\rm {H}_2$\end{document}H2–rare gas (Rg) pairs (Rg = He, Ne, Ar). In this study, the symmetry-adapted (SA) components, the projection of the CI dipole, polarizability, and hyperpolarizability on an appropriately tailored set of spherical harmonics are calculated. A set of equations for the respective SA components is derived. The Cartesian components of the CI properties calculated by quantum chemistry methods for three intermolecular geometries are used in our calculations as input data. The analytical, multipolar long-range behavior of the CI properties studied is considered within a multipole-induced multipole model. Taking the SA components at large distances, the ab initio SA numerical results and the model semianalytical data were compared. In general, a good agreement has been found. The results of our study are expected to be of value in spectral line shape analysis and in modeling of processes in the Earth's and planetary atmospheres.
Tuning the electronic coupling in a low-bandgap donor–acceptor copolymer via the placement of side-chains
Authors: Oberhumer Philipp M. , Huang Ya-Shih , Massip Sylvain , James David T. , Tu Guoli , Albert-Seifried Sebastian , Beljonne David , Cornil Jérôme , Kim Ji-Seon , Huck Wilhelm T. S. , Greenham Neil C. , Hodgkiss Justin M. , Friend Richard H.
Published: March 2011

We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor–acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine-alt-5,5′-4′,7′,-di-2-thienyl-2′,1′,3′-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor–acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization.
Enhanced photoluminescence around 1540 nm from erbium doped silicon coimplanted with hydrogen and silver
Authors: Naczas Sebastian , Akhter Perveen , Huang Mengbing
Published: March 2011

This work reports on an approach based on coimplantation of hydrogen and silver for improving luminescence around 1540 nm from erbium doped silicon. As a result of H induced nanocavities and their gettering of implanted Ag ions, Ag nanostructures are formed in Si doped with erbium and oxygen. The presence of such nanostructures can lead to an enhancement of more than a factor of 2 in Er photoluminescence, compared to the control sample. In addition, analysis of PL data suggests that both the Er excitation cross section and the Er optical activation are increased by the formation of Ag nanostructures. We discuss possible mechanisms for these findings.
Perturbation theory treatment of pseudorotation in cyclic-N3
Authors: Babikov Dmitri
Published: March 2011

A relatively simple treatment using perturbation theory is proposed to describe spectrum of pseudorotational states in cyclic-N3. The purpose is to develop an analytical expression that could be used to fit the experimentally determined spectrum of cyclic-N3, with purpose of identifying this molecule in the laboratory and deriving parameters of its potential energy surface directly from the experimental data. The perturbation theory expression derived in this work is used to fit the spectrum calculated numerically in the previous work [D. Babikov and B. Kendrick, J. Chem. Phys. 133, 174310 (2010)]. It is found that the second order of perturbation theory works well, giving a very good fit of the spectrum, with the rms deviation of only 0.26 cm−1. Analysis reveals that important characteristics of the potential energy surface, such as equilibrium geometry and pseudorotation barriers, are directly related to the features of spectrum, such as splittings, and can be readily derived from experimental data, when those become available.
Helicity independent optically-pumped nuclear magnetic resonance in gallium arsenide
Authors: Li Yunpu , King Jonathan P. , Peng Le , Tamargo Maria C. , Reimer Jeffrey A. , Meriles Carlos A.
Published: March 2011

We present new phenomenology for optically-pumped nuclear magnetic resonance (OPNMR) of gallium arsenide. When pumping at low irradiation intensity, the OPNMR signal becomes independent of light helicity. The results are consistent with a mechanism in which the bulk signal represents competition between nuclear quadrupolar and electron-nuclear hyperfine relaxation. This mechanism is further supported by the scaling behavior of OPNMR for isotopes with varying hyperfine and quadrupolar interactions. These results indicate the magnitude and sign of nuclear polarization in the sample may be controlled as a function of depth by tuning photon energy and laser intensity, portending submicron scale patterning of nuclear magnetization.
Synchronized time- and high-field-resolved all-optical pump–probe magneto-optical setup based on a strong alternating magnetic field and its application in magnetization dynamics of high coercivity magnetic medium
Authors: Wang Zi-xin , Li Jia-ming , Deng Jun-qi , Chen Zhi-feng , Lai Tian-shu
Published: March 2011

An alternating magnetic field (AMF) apparatus is developed and composed of an electromagnet and driving power supply. The structure of the electromagnet and configuration of the driving supply are described in detail. The apparatus can produce a peak magnetic field up to 9000 Oe and above under a small driving power at its resonance frequency of 1.14 kHz. Based on synchronization between the AMF and the femtosecond laser pulse train, a photomagnetic synchronized time- and high-field-resolved all-optical pump–probe magnetic-optical setup is developed. This setup has the ability to reinitialize any magnetic states between two successive laser pulses so that irreversible magnetization reversal dynamics can be studied. Dynamic Kerr hysteresis loops and magnetization reversal dynamics of high coercivity ferromagnetic TbFeCo and FePt films are demonstrated using this setup, showing importance of this synchronized time- and high-field-resolved all-optical pump–probe magnetic-optical setup in the research of ultrafast magnetization dynamics.
Nonlinear switching in arrays of semiconductor on metal photonic wires
Authors: Milián C. , Skryabin D. V.
Published: March 2011

Using three-dimensional finite element modeling of the time independent Maxwell equations we demonstrate nonlinearity induced suppression of the power transfer in the arrays of nanoscale semiconductor on metal photonic wires. Nonlinear switching of the plasmonic modes can be achieved over few micron propagation distances using few hundred watts of the peak power.
Influence of scrape-off layer on plasma confinement
Authors: Dolan Thomas J.
Published: March 2011

The purpose of this paper is to discuss how plasma phenomena in the scrape-off layer (SOL) can affect the plasma density gradient at the separatrix and hence the plasma behavior inside the separatrix. The parallel flow loss rate and ionization rate in the SOL (related to the electron temperature and neutral gas density) affect the curvature of the electron density profile, which limits the density gradient at the separatrix. This density gradient acts like a boundary condition for plasma inside the separatrix, affecting the ion pressure gradient, radial electric field, and plasma behavior.
Characteristics of mammal communities in Tasmanian forests: exploring the influence of forest type and disturbance history
Authors: Flynn Erin M. , Jones Susan M. , Jones Menna E. , Jordan Gregory J. , Munks Sarah A.
Published: March 2011

Context With increasing pressure worldwide on forest habitat, it is crucial to understand faunal ecology to effectively manage and minimise impacts of anthropogenic habitat disturbance. Aims This study assessed whether differences in forest type and disturbance history were reflected in small to medium mammal communities found in Tasmania’s production forests. Methods Trapping was conducted in spring and summer, and autumn and winter during 2007–08 at four dry Eucalyptus forest sites (two regenerating after harvest and two in relatively undisturbed forest) in south-east Tasmania, and four wet Eucalyptus forest sites (two regenerating after harvest and two in relatively undisturbed forest) in north-east Tasmania. All sites were embedded within a matrix of mature or older aged regenerating forest. Key results Thirteen mammal species were recorded across all sites. There was no difference in species diversity or richness between forest type or disturbance regime, but species composition differed. Total number of individual animals and captures was influenced strongly by forest type and disturbance history, with most animals captured in the dry disturbed forest sites. Abundance of some species (e.g. bettongs and potoroos) was higher in disturbed sites than undisturbed sites. Brushtail possum numbers (adults and offspring), however, were lower in disturbed sites and populations displayed a male biased adult sex ratio and lower breeding frequency. Habitat structural complexity and vegetation diversity within core sites, and age structure of the forest in the surrounding landscape did not vary significantly, indicating that broad resource (food and refuge) availability was equivalent across sites. Conclusions In general, the small to medium mammals in this study did not appear to be significantly affected by forest harvesting in the medium term. Implications Although past harvesting altered the abundance of some habitat features (e.g. canopy cover, basal area of trees, and tree hollow availability), we suggest that the availability of such features in the surrounding landscape may mitigate the potential effects of disturbance on the species for which such habitat features are important.
An evaluation of hot-iron branding as a permanent marking method for adult New Zealand sea lions, Phocarctos hookeri
Authors: Wilkinson I. S. , Chilvers B. L. , Duignan P. J. , Pistorius P. A.
Published: March 2011

Context Studies of the population and behavioural ecology of pinnipeds require the ability to identify individuals over periods ranging from a single season to an entire lifetime. Aims The aims of this research were to examine the efficacy of hot-iron branding as a permanent marking technique including the legibility of marks over time and comparing estimates of survival for animals marked with brands versus flipper tags. Methods Adult female New Zealand sea lions (n = 135) aged between 4 and 24 years of age were hot-iron branded with four-digit numbers during the austral summer of 2000. Key results Ten years on, 100% of animals still alive could be identified from these brands. Over the 10-year research period, it was observed that the skin of fully healed individual brands could, on occasion, become lacerated due to injuries received from shark bites and/or bites from other sea lions, removing or temporarily reducing the legibility of single characters of some brands. However, these animals were still identifiable when all digits were considered – and scars could become an identifying mark in their own right. Key conclusions Survival estimates derived from branded versus tagged-only individuals were similar, although the variance associated with tagged-only survival estimates was higher, giving less robust estimates. This is likely a result of higher resight probabilities observed for branded individuals. Resighting of tags requires a close approach with a high associated level of disturbance to both the marked animal and those associated with it, especially when considered over the lifetime of the animal, while brands can be read from a considerable distance with little or no disturbance. Implications Thus, hot-iron branding can be an effective method for permanently identifying sea lions that provides robust parameter estimates, causes low disturbance in the resighting process, and does not compromise survival.
Assessment of risks to non-target species from an encapsulated toxin in a bait proposed for control of feral cats
Authors: de Tores Paul J. , Sutherland Duncan R. , Clarke Judy R. , Hill Robert F. , Garretson Sean W. , Bloomfield Lenny , Strümpher Lauren , Glen Alistair S. , Cruz Jennyffer
Published: March 2011

Context The CURIOSITY® bait is the name coined for a variation of the existing sausage-style cat bait, ERADICAT®. The latter is used under experimental permit in Western Australia for research associated with cat control. The CURIOSITY bait differs from ERADICAT by providing a pH-buffered (less acidic) medium and has been proposed to reduce the risk to non-target species by encapsulating a toxin in a pellet. We trialled a prototype pellet proposed for encapsulation of 1080 and/or alternative toxins, with delivery proposed through the CURIOSITY bait. Aim Our aim was to determine whether the pellet was consumed by non-target native species from south-west of Western Australia. Methods Trials involved use of a non-toxic biomarker, Rhodamine B, encapsulated within the pellet and inserted into the CURIOSITY® bait. Uptake of the encapsulated biomarker was assessed in captive trials for the target species, the feral cat (Felis catus) and two non-target species of varanid lizard, Rosenberg’s goanna (Varanus rosenbergi) and Gould’s goanna (V. gouldii) and the non-target mammal species chuditch (Dasyurus geoffroii) and southern brown bandicoot (Isoodon obesulus). Uptake of the encapsulated biomarker was also assessed in field trials for a range of native species. Key results Captive trials demonstrated feral cats will consume the CURIOSITY bait and pellet. However, results from captive and field trials indicated several non-target species also consumed the bait and pellet. We also found the pellet itself was not sufficiently robust for use in a bait. As with previously reported studies, we found Rhodamine B to be an effective biomarker for use in cats. We also developed a technique whereby Rhodamine B can be used as a biomarker in reptiles. However, its use as a biomarker in other mammalian species was confounded by what appeared to be background, or pre-existing, levels of fluorescence, or banding, in their whiskers. Conclusion The prototype pellet is unsuitable in its current form for use with the CURIOSITY bait. We caution that the CURIOSITY bait has non-target issues in south-west of Western Australia and any proposed variations to this bait, or the ERADICAT® bait, need to be rigorously assessed for their potential risk to non-target species and assessed for the level of uptake by cats, irrespective of their suitability/unsuitability as a medium for delivery of an encapsulated toxin. We believe the threat to biodiversity-conservation values from unmitigated feral-cat predation of native fauna poses a significant and real threat and we recommend urgent investment of resources to address the issue of cat predation in a coordinated and collaborative manner within Australia and New Zealand.
Southern brown bandicoots can be successfully returned to the wild after physiological experiments
Authors: Cooper Christine E.
Published: March 2011

Context The poor survivorship of animals released into the wild for translocation, reintroduction or rehabilitation may be cited as a reason not to release experimental animals, but there is only limited information available on the fate of ex-research animals returned to the wild. Aims This study tested the hypothesis that there is no difference in the recapture of bandicoots used for physiological experiments and control bandicoots. Methods Six adult male bandicoots were trapped and maintained in captivity for three weeks for physiological experiments, then released at the capture site. Sixteen other bandicoots were captured and released immediately. Seven weeks after the release of the bandicoots used for physiological studies, follow-up trapping was carried out, and the survival, body mass and distance moved of recaptured bandicoots was recorded. Key results Survivorship did not differ statistically between bandicoots used for physiological experiments and control bandicoots, with five of six experimental bandicoots (83%) and 11 of 16 control bandicoots (69%) recaptured. Bandicoots used for physiological experiments lost a significantly greater proportion of body mass than control animals, but this occurred in captivity, not after release. The distance between recaptures for both groups (0–224 m) was consistent with previously published observations. Conclusions My results suggest that bandicoots maintained in captivity for non-invasive physiological experiments can be successfully released, with survivorship at least as high as that of control animals. Implications This study provides researchers, wildlife managers, and animal ethics committees with information to assist with making judgements concerning the fate of ex-research animals.
Physiological response of wild guanacos to capture for live shearing
Authors: Carmanchahi P. D. , Ovejero R. , Marull C. , López G. C. , Schroeder N. , Jahn G. A. , Novaro A. J. , Somoza G. M.
Published: March 2011

Context The use of wild guanacos (Lama guanicoe) through live capture and shearing may contribute to their conservation by providing an economic alternative to rural inhabitants. However, none of the biological impacts of this activity, including the physiological ones, have been addressed. Aims The aim of this work was to characterise the acute response of guanacos to stress after capture and shearing in terms of serum cortisol levels, heart rate, and body temperature. Methods The study was performed during 2006 and 2007 in La Payunia Reserve in western Argentina. In order to determine serum cortisol concentration, 128 blood samples were obtained and the unextracted sera were analysed by radioimmunoanalyses (RIA). Sex, age category, heart rate, body temperature and total restraint time (TRT) were also registered for each animal captured. Key results Serum cortisol levels were higher in guanacos captured and sheared during 2007 than in 2006, and male cortisol levels were consistently lower than female levels. No significant differences were observed in cortisol levels of the different age categories. A positive correlation was observed between TRT and serum cortisol concentration. The analyses of cortisol levels in relation to TRT showed differences between males and females. With handling periods longer than 80 minutes, females showed a delayed stabilisation in cortisol response when compared with males. Heart rate and body temperature showed no differences between year, sex or age categories. Conclusions The present results show that the stress response to capture and shearing in wild guanacos increased significantly with handling time. We recommend avoiding capture of large numbers of animals and keeping roundup duration short to reduce TRT. Implications This work provides new information that can improve guanaco welfare during handling and shearing and may have implications for the conservation of the species.
Intestinal epithelial cells as producers but not targets of chronic TNF suffice to cause murine Crohn-like pathology
Authors: Roulis Manolis , Armaka Maria , Manoloukos Menelaos , Apostolaki Maria , Kollias George
Published: March 2011

TNF plays a crucial role in the pathogenesis of Crohn disease. Dysregulated TNF production in mice that bear the genetic deletion of the TNF AU-rich regulatory elements (ARE) (

Tnf
ΔARE/+

mice) results in TNF receptor I (TNFRI)-dependent spontaneous Crohn-like pathology. Current concepts consider intestinal epithelial cell (IEC) responses to TNF to be critical for intestinal pathology, but the potential contribution of IEC-derived TNF in disease pathogenesis has not been addressed. In this study we examined whether IEC are sufficient as cellular targets or sources of TNF in the development of intestinal pathology. Using IEC-specific reactivation of a hypomorphic

Tnf
ΔAREneo

allele in mice, we show that selective chronic overproduction of TNF by IEC suffices to cause full development of Crohn-like pathology. Epithelial TNF overexpression leads to early activation of the underlying intestinal myofibroblast, a cell type previously identified as a sufficient target of TNF for disease development in the

Tnf
ΔARE

model. By contrast, restricted TNFRI expression on IEC although sufficient to confer IEC apoptosis after acute exogenous TNF administration, fails to induce pathology following chronic specific targeting of IEC by endogenous TNF in

Tnf
ΔARE/+

mice. Our results argue against IEC being early and sufficient responders to chronic TNF-mediated pathogenic signals and suggest that proinflammatory aberrations leading to chronic TNF production by IEC may initiate pathology in Crohn disease.