bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational and thermodynamic properties of β-HMX: A first-principles investigation
Authors: Wu Zhongqing , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: May 2011

Thermodynamic properties of β-HMX crystal are investigated using the quasi-harmonic approximation and density functional theory within the local density approximation (LDA), generalized gradient approximation (GGA), and GGA + empirical van der Waals (vdW) correction. It is found that GGA well describes the thermal expansion coefficient and heat capacity but fails to produce correct bulk modulus and equilibrium volume. The vdW correction improves the bulk modulus and volume, but worsens the thermal expansion coefficient and heat capacity. In contrast, LDA describes all thermodynamic properties with reasonable accuracy, and overall is a good exchange-correlation functional for β-HMX molecular crystal. The results also demonstrate significant contributions of phonons to the equation of state. The static calculation of equilibrium volume for β-HMX differs from the room-temperature value incorporating lattice vibrations by over 5%. Therefore, for molecular crystals, it is essential to include phonon contributions when calculated equation of state is compared with experimental data at ambient condition.
Efficient laser absorption and enhanced electron yield in the laser-target interaction by using a cone-nanolayer target
Authors: Cao Lihua , Chen Mo , Zhao Zongqing , Cai Hongbao , Wu Sizhong , Gu Yuqiu , Yu Wei , Yu M. Y. , He X. T.
Published: May 2011

A cone-nanolayer target that combines the advantages of the conical and layered geometries for electron acceleration in laser-target interaction is proposed. Two-dimensional particle-in-cell (PIC) simulations show that the cone-nanolayer target can enhance laser absorption and electron yield. With suitable choice of the laser and target parameters, the cone-nanolayer target can be a controllable source of hot electrons at desired energy ranges.
Novel Hamiltonian method for collective dynamics analysis of an intense charged particle beam propagating through a periodic focusing quadrupole lattice
Authors: Startsev Edward A. , Davidson Ronald C.
Published: May 2011

Identifying regimes for quiescent propagation of intense beams over long distances has been a major challenge in accelerator research. In particular, the development of systematic theoretical approaches that are able to treat self-consistently the applied oscillating force and the nonlinear self-field force of the beam particles simultaneously has been a major challenge of modern beam physics. In this paper, the recently developed Hamiltonian averaging technique [E. A. Startsev, R. C. Davidson, and M. Dorf, Phys. Rev. ST Accel. Beams 13, 064402 (2010)] which incorporates both the applied periodic focusing force and the self-field force of the beam particles, is generalized to the case of time-dependent beam distributions. The new formulation allows not only a determination of quasi-equilibrium solutions of the non-linear Vlasov-Poison system of equations but also a detailed study of their stability properties. The corrections to the well-known “smooth-focusing” approximation are derived, and the results are applied to a matched beam with thermal equilibrium distribution function. It is shown that the corrections remain small even for moderate values of the vacuum phase advance συ. Nonetheless, because the corrections to the average self-field potential are non-axisymmetric, the stability properties of the different beam quasi-equilibria can change significantly.
Dielectric function model for p-type semiconductor inter-valence band transitions
Authors: Lao Yan-Feng , Unil Perera A. G.
Published: May 2011

The contributions of inter-valence band (IVB) transitions to the dielectric function (DF) by free holes among the split-off (so), light-hole (lh) and heavy-hole (hh) bands were investigated. A model was developed to determine the DF of two p-type semiconductors, GaAs and Ge1−ySny with the Zinc-blend and Diamond crystal structures, respectively. The IVB transitions dominate the spectral range between 0.1–1eV with respect to the spin-orbit splittings between so-hh and lh-hh bands. In conjunction with inter-band transitions, free-carrier and lattice absorption, a complete DF model allows the determination of optical constants with improved accuracy in the spectral range covering both ultraviolet and infrared regions. The model should be applicable to most of the group III-V and IV materials since their valence band structures resemble the ones under investigation.
Miniature ceramic-anvil high-pressure cell for magnetic measurements in a commercial superconducting quantum interference device magnetometer
Authors: Tateiwa Naoyuki , Haga Yoshinori , Fisk Zachary , Ōnuki Yoshichika
Published: May 2011

A miniature opposed-anvil high-pressure cell has been developed for magnetic measurement in a commercial superconducting quantum interference device magnetometer. Non-magnetic anvils made of composite ceramic material were used to generate high-pressure with a Cu-Be gasket. We have examined anvils with different culet sizes (1.8, 1.6, 1.4, 1.2, 1.0, 0.8, and 0.6 mm). The pressure generated at low temperature was determined by the pressure dependence of the superconducting transition of lead (Pb). The maximum pressure Pmax depends on the culet size of the anvil: the values of Pmax are 2.4 and 7.6 GPa for 1.8 and 0.6 mm culet anvils, respectively. We revealed that the composite ceramic anvil has potential to generate high-pressure above 5 GPa. The background magnetization of the Cu-Be gasket is generally two orders of magnitude smaller than the Ni-Cr-Al gasket for the indenter cell. The present cell can be used not only with ferromagnetic and superconducting materials with large magnetization but also with antiferromagnetic compounds with smaller magnetization. The production cost of the present pressure cell is about one tenth of that of a diamond anvil cell. The anvil alignment mechanism is not necessary in the present pressure cell because of the strong fracture toughness (6.5 MPa m1/2) of the composite ceramic anvil. The simplified pressure cell is easy-to-use for researchers who are not familiar with high-pressure technology. Representative results on the magnetization of superconducting MgB2 and antiferromagnet CePd5Al2 are reported.
Third-order corrections to random-phase approximation correlation energies
Authors: Heßelmann Andreas
Published: May 2011

Several random-phase approximation (RPA) correlation methods were compared in third order of perturbation theory. While all of the considered approaches are exact in second order of perturbation theory, it is found that their corresponding third-order correlation energy contributions strongly differ from the exact third-order correlation energy contribution due to missing interactions of the particle-particle−hole-hole type. Thus a simple correction method is derived which makes the different RPA methods also exact to third-order of perturbation theory. By studying the reaction energies of 16 chemical reactions for 21 small organic molecules and intermolecular interaction energies of 23 intermolecular complexes comprising weakly bound and hydrogen-bridged systems, it is found that the third-order correlation energy correction considerably improves the accuracy of RPA methods if compared to coupled-cluster singles doubles with perturbative triples as a reference.
The fine structure constant determines spontaneous emission rates from semiconductors
Authors: Szkopek Thomas
Published: May 2011

The probability of spontaneous emission from a semiconductor, per oscillation of the optical field, is proportional to the cube of the fine structure constant α and the ratio of the semiconductor dipole parameter Ep to hydrogen’s Rydberg energy. Expressions for radiative recombination rates in quantum wells and bulk semiconductors are given, including the bimolecular radiative recombination coefficient B. We show that α sets the natural scale for spectral density of spontaneous emission per square wavelength area of a quantum well. The fine structure constant also sets a physical limit to the Purcell enhancement factor for spontaneous emission.
Unexpected photoreactivation of Vibrio harveyi bacteria living in ionization environment
Authors: Alifano P. , Nassisi V. , Siciliano M. V. , Talà A. , Tredici S. M.
Published: May 2011

Bacteria undergoing environmental effects is extremely interesting for structural, mechanistic, and evolutionary implications. Luminescent bacteria that have evolved in a specific ambient have developed particular responses and their behavior can give us new suggestions on the task and production of luciferina proteins. To analyze the UV interaction under controlled laboratory conditions, we used photoluminescent bacterial strains belonging to a new species evolutionarily close to Vibrio harveyi sampled from a coastal cave with a high radon content that generates ionizing radiation. The survival of the bacterial strains was analyzed, in the light and in the dark, following a variety of genotoxic treatments including UV radiation exposure. The strains were irradiated by a germicide lamp. The results demonstrated that most of the strains exhibited a low rate of survival after the UV exposure. After irradiation by visible light following the UV exposure, all strains showed a high capability of photoreactivation when grown. This capability was quite unexpected because these bacteria were sampled from a dark ambient without UV radiation. This leads us to hypothesize that the photoreactivation in these bacteria might have been evolved to repair DNA lesions also induced by different radiation sources other than UV (e.g., x-ray) and that the luminescent bacteria might use their own light emission to carry out the photoreactivation. The high capability of photoreactivation of these bacteria was also justified by the results of deconvolution. The deconvolution was applied to the emission spectra and it was able to show evidence of different light peaks. The presence of the visible peak could control the photolysis enzyme.
Electric manipulation of electron spin relaxation induced by confined phonons in nanowire-based double quantum dots
Authors: Wang M. , Yin Y. , Wu M. W.
Published: May 2011

We investigate theoretically the electron spin relaxation in single-electron nanowire-based semiconductor double quantum dots induced by confined phonons and find that the electron spin relaxation rate can be efficiently manipulated by external electric field in such system. An anti-crossing, due to the coaction of the electric field, the magnetic field and the spin-orbit coupling, exists between the lowest two excited states. Both energies and spins of the electron states can be efficiently tuned by the electric field around the anti-crossing point. Multiple sharp peaks exist in the electric-field dependence of the spin relaxation rate induced by the confined phonons, which can be ascribed to the large density of states of the confined phonons at the van Hove singularities. This feature suggests that the nanowire-based double quantum dots can be used as electric tunable on-and-off spin switches, which are more sensitive and flexible than the ones based on quantum-well based double quantum dots. The temperature dependence of the spin relaxation rate at the anti-crossing point is calculated and a smooth peak, indicating the importance of the contribution of the off-diagonal elements of the density matrix to the spin relaxation, is observed.
Glassy dynamics and mechanical response in dense fluids of soft repulsive spheres. I. Activated relaxation, kinetic vitrification, and fragility
Authors: Yang Jian , Schweizer Kenneth S.
Published: May 2011

The microscopic nonlinear Langevin equation theory of activated glassy dynamics is applied to dense fluids of spherical particles that interact via a finite range Hertzian contact soft repulsion. The activation barrier and mean alpha relaxation time are predicted to be rich functions of volume fraction and particle stiffness, exhibiting a non-monotonic variation with concentration at high volume fractions. The latter is due to a structural “soft jamming” crossover where the real space local cage order weakens when soft particles significantly overlap. The highly variable dependences of the relaxation time on temperature and volume fraction are reasonably well collapsed onto two distinct master curves that are qualitatively consistent with a recent scaling ansatz and computer simulation study. A kinetic vitrification diagram is constructed and compared to its dynamic crossover analog. Intersection of the dynamic crossover and soft jamming threshold boundaries occurs for particles that are sufficiently soft, implying the nonexistence of a clear activated dynamics regime or kinetic arrest transition for such particles. The isothermal dynamic fragility is predicted to vary over a wide range as a function of particle stiffness, and soft particles behave as strong glasses. Qualitative comparisons with simulations and microgel experiments reveal good agreement.
Hydrogenated grain boundaries in graphene
Authors: Brito W. H. , Kagimura R. , Miwa R. H.
Published: May 2011

We have investigated by means of ab initio calculations the structural and electronic properties of hydrogenated graphene structures with distinct grain boundary defects. Our total energy results reveal that the adsorption of a single H is more stable at defect. Further total energy calculations indicate that the adsorption of two H on two neighbor carbons, forming a basic unit of graphane, is more stable at the defect region. Therefore, we expect that these extended defects would work as a nucleation region for the formation of a narrow graphane strip embedded in graphene region.
The use of dynamic light scattering and Brownian microscopy to characterize protein aggregation
Authors: Li Ye , Lubchenko Vassiliy , Vekilov Peter G.
Published: May 2011

Dynamic light scattering (DLS) is often used to monitor aggregation in protein solutions. Here, we explore the veracity of the aggregate sizes, size distribution widths, concentrations, and lifetime resulting from DLS. We use as an example a solution of the protein lysozyme in which dense liquid clusters of radius about 100 nm reproducibly exist. We compare the results of DLS to those of Brownian microscopy. We show that because of the sixth power dependence of the scattered light intensity on the size of the scatterers, DLS overestimates the mean size of the clusters. The factor of overestimation depends on the shape of the size distribution and is ∼1.6 × in the studied solution. The related underestimate of the cluster concentration is ∼10 ×. The CONTIN algorithm, often employed to process DLS data, may, in some instances, produce non-physical results. We put forth an alternative method to determine the aggregates’ sizes, concentrations, and volume fractions. We show that DLS yields a reliable width of the cluster size distribution only if the cluster concentration is above 109 cm−3 and their volume fraction is above 10−6. DLS yields a lower bound of the cluster lifetime, which may be orders of magnitude lower than the real one.
Characteristics of a symmetrical Cockcroft-Walton power supply of 50 Hz 1.2 MV/50 mA
Authors: He Zi-Feng , Zhang Jin-Ling , Liu Yong-Hao , Zhang Yu-Tian , Zhang Yin
Published: May 2011

A 1.2 MV/50 mA symmetrical Cockcroft-Walton (SCW) power supply of over 83% power efficiency, driven by 50 Hz frequency, was developed for an industrial electron beam irradiator. It is constructed by capacitors of 45 nF and 28.13 nF in the coupling column and capacitors of 18.75 nF in the smoothing column. Working status of the rectifier in high power output condition was analyzed, and the conduction angle of the rectifier was calculated. The power factor (PF) of the SCW circuit has been studied, and the equivalent condensance of the circuit has been derived. Measurements were done for the PF compensation. The surge impact during the short circuit transient process was considered in choosing the protection resistance. Test results showed that design specifications of the power supply were achieved, with the non-load voltage being up to 1.32 MV and the ratio of ripple voltage to output voltage as 9.4%.
Cl2O photochemistry: Ultraviolet/vis absorption spectrum temperature dependence and O(3P) quantum yield at 193 and 248 nm
Authors: Papanastasiou Dimitrios K. , Feierabend Karl J. , Burkholder James B.
Published: May 2011

The photochemistry of Cl2O (dichlorine monoxide) was studied using measurements of its UV/vis absorption spectrum temperature dependence and the O(3P) atom quantum yield, $\Phi _{{\rm Cl}_{\rm 2} {\rm O}}^{\rm O} (\lambda)$Φ Cl 2OO(λ), in its photolysis at 193 and 248 nm. The Cl2O UV/vis absorption spectrum was measured over the temperature range 201–296 K between 200 and 500 nm using diode array spectroscopy. Cl2O absorption cross sections, $\sigma _{{\rm Cl}_{\rm 2} {\rm O}} (\lambda {\rm, T})$σ Cl 2O(λ,T), at temperatures <296 K were determined relative to its well established room temperature values. A wavelength and temperature dependent parameterization of the Cl2O spectrum using the sum of six Gaussian functions, which empirically represent transitions from the ground 1A1 electronic state to excited states, is presented. The Gaussian functions are found to correlate well with published theoretically calculated vertical excitation energies. O(3P) quantum yields in the photolysis of Cl2O at 193 and 248 nm were measured using pulsed laser photolysis combined with atomic resonance fluorescence detection of O(3P) atoms. O(3P) quantum yields were measured to be 0.85 ± 0.15 for 193 nm photolysis at 296 K and 0.20 ± 0.03 at 248 nm, which was also found to be independent of temperature (220–352 K) and pressure (17 and 28 Torr, N2). The quoted uncertainties are at the 2σ (95% confidence) level and include estimated systematic errors. ClO radical temporal profiles obtained following the photolysis of Cl2O at 248 nm, as reported previously in Feierabend et al. [J. Phys. Chem. A 114, 12052, (2010)], were interpreted to establish a <5% upper-limit for the O + Cl2 photodissociation channel, which indicates that O(3P) is primarily formed in the three-body, O + 2Cl, photodissociation channel at 248 nm. The analysis also indirectly provided a Cl atom quantum yield of 1.2 ± 0.1 at 248 nm. The results from this work are compared with previous studies where possible.
Effect of pressure-driven MHD instabilities on confinement in reactor-relevant high-beta helical plasmas
Authors: Watanabe K. Y. , Masamune S. , Takemura Y. , Funaba H. , Sakakibara S. , Watanabe F. , Tanaka K. , Ohdachi S. , Toi K. , Narushima Y. ,   LHD Experiment Group
Published: May 2011

Through the experiment data analysis in the large helical device (LHD), the influence of the global MHD instability and the relatively short wave length MHD instabilities driven turbulence on the confinement performance in reactor-relevant high-beta helical plasmas is studied. The comparison of the energy confinement time between just before global MHD instability disappears and after that, and the estimation of the saturated mode structure by the multi-channel soft x-ray measurement enable us to quantitatively estimate the influence of the global interchange type MHD instability with different saturated mode structures on the confinement performance. According to the comparison between thermal conductivities in experiments and those predicted by theoretical transport models, the transport properties in the peripheral region of high beta LHD plasmas are quite similar with anomalous transport model based on an interchange type MHD instability driven turbulence, and that result is supported by the dependence of the density fluctuation with relatively short wave length on beta value.
Reduced dimensionality spin-orbit dynamics of CH3 + HCl $\rightleftharpoons$⇌ CH4 + Cl on ab initio surfaces
Authors: Remmert Sarah M. , Banks Simon T. , Harvey Jeremy N. , Orr-Ewing Andrew J. , Clary David C.
Published: May 2011

A reduced dimensionality quantum scattering method is extended to the study of spin-orbit nonadiabatic transitions in the CH3 + HCl $\rightleftharpoons$⇌ CH4 + Cl(2PJ) reaction. Three two-dimensional potential energy surfaces are developed by fitting a 29 parameter double-Morse function to CCSD(T)/IB//MP2/cc-pV(T+d)Z-dk ab initio data; interaction between surfaces is described by geometry-dependent spin-orbit coupling functions fit to MCSCF/cc-pV(T+d)Z-dk ab initio data. Spectator modes are treated adiabatically via inclusion of curvilinear projected frequencies. The total scattering wave function is expanded in a vibronic basis set and close-coupled equations are solved via R-matrix propagation. Ground state thermal rate constants for forward and reverse reactions agree well with experiment. Multi-surface reaction probabilities, integral cross sections, and initial-state selected branching ratios all highlight the importance of vibrational energy in mediating nonadiabatic transition. Electronically excited state dynamics are seen to play a small but significant role as consistent with experimental conclusions.
Pilot applications of internally contracted multireference coupled cluster theory, and how to choose the cluster operator properly
Authors: Hanauer Matthias , Köhn Andreas
Published: May 2011

The internally contracted multireference coupled cluster (icMRCC) method allows a highly accurate description of both static and dynamic correlation with a computational scaling similar to single reference coupled cluster theory. The authors show that the method can lose its orbital invariance and size consistency when no special care is taken in the elimination of redundant excitations. Using the BeH2 model system, four schemes are compared which differ in their treatment of linear dependencies between excitations of different rank (such as between singles and doubles). While the energy curves agree within tens of μEh when truncating the cluster operator at double excitations (icMRCCSD), inclusion of triple excitations (icMRCCSDT) leads to significant differences of more than 1 mEh. One scheme clearly yields the best results, while the others even turn out to be not size consistent. The former procedure uses genuine single and double excitations and discards those linear combinations of (spectator) double and triple excitations which have the same effect on the reference function. With this approach, the equilibrium structure and harmonic vibrational frequencies of ozone obtained with icMRCCSDT are in excellent agreement with CCSDTQ. The authors further apply icMRCC methods to potential energy surfaces of HF, LiF, N2, and to the singlet-triplet splitting of benzynes. In particular, the latter calculations have been made possible by implementing the method with the proper formal scaling using automated techniques.
Unoccupied states in Cu and Zn octaethyl-porphyrin and phthalocyanine
Authors: Cook Peter L. , Yang Wanli , Liu Xiaosong , García-Lastra Juan María , Rubio Angel , Himpsel F. J.
Published: May 2011

Copper and zinc phthalocyanines and porphyrins are used in organic light emitting diodes and dye-sensitized solar cells. Using near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the Cu 2p and Zn 2p edges, the unoccupied valence states at the Cu and Zn atoms are probed and decomposed into 3d and 4s contributions with the help of density functional calculations. A comparison with the N 1s edge provides the 2p states of the N atoms surrounding the metal, and a comparison with inverse photoemission provides a combined density of states.
The nature of electron lone pairs in BiVO4
Authors: Payne D. J. , Robinson M. D. M. , Egdell R. G. , Walsh A. , McNulty J. , Smith K. E. , Piper L. F. J.
Published: May 2011

The electronic structure of BiVO4 has been studied by x-ray photoelectron, x-ray absorption, and x-ray emission spectroscopies, in comparison with density functional theory calculations. Our results confirm both the direct band gap of 2.48 eV and that the Bi 6s electrons hybridize with O 2p to form antibonding “lone pair” states at the top of the valence band. The results highlight the suitability of combining s2 and d0 cations to produce photoactive ternary oxides.
Electronic states of thiophenyl and furanyl radicals and dissociation energy of thiophene via photoelectron imaging of negative ions
Authors: Culberson Lori Marie , Sanov Andrei
Published: May 2011

We report photoelectron images and spectra of deprotonated thiophene, C4H3S−, obtained at 266, 355, and 390 nm. Photodetachment of the α isomer of the anion is observed, and the photoelectron bands are assigned to the ground X2A′ (σ) and excited A2A″ and B2A″ (π) states of the thiophenyl radical. The photoelectron angular distributions are consistent with photodetachment from the respective in-plane (σ) and out-of-plane (π*) orbitals. The adiabatic electron affinity of α-•C4H3S is determined to be 2.05 ± 0.08 eV, while the B2A″ term energy is estimated at 1.6 ± 0.1 eV. Using the measured electron affinity and the electron affinity/acidity thermodynamic cycle, the C–Hα bond dissociation energy of thiophene is calculated as DH298(Hα–C4H3S) = 115 ± 3 kcal/mol. Comparison of this value to other, previously reported C–H bond dissociation energies, in particular for benzene and furan, sheds light of the relative thermodynamic stabilities of the corresponding radicals. In addition, the 266 nm photoelectron image and spectrum of the furanide anion, C4H3O−, reveal a previously unobserved vibrationally resolved band, assigned to the B2A″ excited state of the furanyl radical, •C4H3O. The observed band origin corresponds to a 2.53 ± 0.01 eV B2A″ term energy, while the resolved vibrational progression (853 ± 42 cm−1) is assigned to an in-plane ring mode of α-•C4H3O (B2A″).
Role of stable and metastable Mg–H complexes in p-type GaN for cw blue laser diodes
Authors: Castiglia A. , Carlin J.-F. , Grandjean N.
Published: May 2011

Secondary ion mass spectroscopy (SIMS) and capacitance-voltage measurements were combined to thoroughly study Mg doping in GaN layers grown by metal organic vapor phase epitaxy. First we found that the Mg steady-state incorporation regime occurs for a surface coverage of 0.3 monolayer. Additionally SIMS indicates that H incorporates proportionally with Mg until a certain [Mg] where [H] saturates. After thermal activation, [H] while being much lower still scales with [Mg]. These results suggest that H combines with Mg to form two different types of Mg–H complexes: a metastable one leading to the Mg acceptor after annealing, the other one (dominating at high [Mg]) being stable and electrically inactive. The obtained results allowed us optimizing doping conditions for blue laser diodes.
Structural and electronic properties of ZrX2 and HfX2 (X = S and Se) from first principles calculations
Authors: Jiang Hong
Published: May 2011

Early transition metal dichalcogenides (TMDC), characterized by their quasi-two-dimensional layered structure, have attracted intensive interest due to their versatile chemical and physical properties, but a comprehensive understanding of their structural and electronic properties from a first-principles point of view is still lacking. In this work, four simple TMDC materials, MX2 (M = Zr and Hf, X = S and Se), are investigated by the Kohn-Sham density functional theory (KS-DFT) with different local or semilocal exchange-correlation (xc) functionals and many-body perturbation theory in the GW approximation. Although the widely used Perdew-Burke-Ernzelhof (PBE) generalized gradient approximation (GGA) xc functional overestimates the interlayer distance dramatically, two newly developed GGA functionals, PBE-for-solids (PBEsol) and Wu-Cohen 2006 (WC06), can reproduce experimental crystal structures of these TMDC materials very well. The GW method, currently the most accurate first-principles approach for electronic band structures of extended systems, gives the fundamental band gaps of all these materials in good agreement with the experimental values obtained from optical absorption. The minimal direct gaps from GW are systematically larger than those measured from thermoreflectance by about 0.1–0.3 eV, implying that excitonic effects may be stronger than previously estimated. The calculated density of states from GW quasi-particle band energies agrees very well with photo-emission spectroscopy data. Ionization potentials of these materials are also computed by combining PBE calculations based on the slab model and GW quasi-particle corrections. The calculated absolute band energies with respect to the vacuum level indicate that that ZrS2 and HfS2, although having suitable band gaps for visible light absorption, cannot be used for overall water splitting as a result of mismatch of the conduction band minimum with the redox potential of H+/H2.
Real-time measurement of Brownian relaxation of magnetic nanoparticles by a mixing-frequency method
Authors: Tu Liang , Jing Ying , Li Yuanpeng , Wang Jian-Ping
Published: May 2011

A detection scheme for real-time Brownian relaxation of magnetic nanoparticles (MNPs) is demonstrated by a mixing-frequency method in this paper. MNPs are driven into the saturation region by a low frequency sinusoidal magnetic field. A high frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the magnetization of MNPs. These highly sensitive mixing-frequency signals from MNPs are picked up by a pair of balanced built-in detection coils. The phase delays of the mixing-frequency signals behind the applied field are derived, and are experimentally verified. Commercial iron oxide MNPs with the core diameter of 35 nm are used for the measurement of Brownian relaxation. The results are fitted well with Debye model. Then a real-time measurement of the binding process between protein G and its antibody is demonstrated using MNPs as labels. This study provides a volume-based magnetic sensing scheme for the detection of binding kinetics and interaction affinities between biomolecules in real time.
Element-specific study of epitaxial NiO/Ag/CoO/Fe films grown on vicinal Ag(001) using photoemission electron microscopy
Authors: Meng Y. , Li J. , Tan A. , Jin E. , Son J. , Park J. S. , Doran A. , Young A. T. , Scholl A. , Arenholz E. , Wu J. , Hwang C. , Zhao H. W. , Qiu Z. Q.
Published: May 2011

NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film.
Micromachined Fabry–Perot resonator combining submillimeter cavity length and high quality factor
Authors: Malak M. , Pavy N. , Marty F. , Peter Y.-A. , Liu A. Q. , Bourouina T.
Published: May 2011

We demonstrate experimentally optical quality factor of nearly 9000 in a micromachined Fabry–Pérot resonator based on free space propagation of light and direct coupling to optical fibers. This result is obtained on long cavity resonators (L>250 μm), a usually difficult case in terms of power loss, but very useful configuration for experiments requiring either long optical path or enough space for manipulation. The resonator architecture includes two multilayered silicon-air Bragg mirrors of cylindrical shape, combined with a fiber rod lens. The specific stability criteria are derived for the proposed resonator architecture. Dimensions of the fabricated devices are chosen accordingly.
Broadband energy-harvesting using a two degree-of-freedom vibrating body
Authors: Kim In-Ho , Jung Hyung-Jo , Lee Bo Mi , Jang Seon-Jun
Published: May 2011

In this letter, we introduce the concept and describe the realization of a two degree-of-freedom piezoelectric energy-harvesting device. The proposed system consists of a proof mass (i.e., a rigid body) and two cantilever beams; it can utilize both translational and rotational degrees of freedom. Therefore, it exhibits double power peaks and an increased frequency bandwidth, and it can generate power more efficiently than conventional vibration-based single degree-of-freedom devices.
High gain ultraviolet photodetectors based on AlGaN/GaN heterostructures for optical switching
Authors: Martens M. , Schlegel J. , Vogt P. , Brunner F. , Lossy R. , Würfl J. , Weyers M. , Kneissl M.
Published: May 2011

We report on the optoelectronic properties of Al0.25Ga0.75N/GaN-based ultraviolet (UV) photodetectors for the application as a high current, high gain optical switch. Due to an internal gain mechanism combined with the high conductivity of the two-dimensional electron gas at the heterostructure interface, photocurrents in the milliampere-range were obtained with UV illumination. By employing a mesa structure design with meander geometry very low dark currents below 50 nA up to a bias voltage of 100 V were achieved. Optical switching with an on/off-current-ratio of five orders of magnitude was demonstrated. The response time was determined to be 6 ms and persistent photoconductivity was observed. The photodetector is visible-blind with a cut-off wavelength of 365 nm according to the band gap energy of the GaN absorption layer. A high responsivity with a maximum of 70 A/mW at 312 nm and 100 V bias voltage was demonstrated.
Lateral tomographic spatial frequency modulated imaging
Authors: Schlup Philip , Futia Greg , Bartels Randy A.
Published: May 2011

We demonstrate a two-dimensional imaging technique that uses a tomographic image reconstruction algorithm of object projections measured with a single photodetector. By imposing a spatially varying amplitude modulation on the illumination beam, the lateral projections of the object are encoded in the electronic spectrum of the signal from a single-element photodetector.
Polarization-resolved far-field measurement of single-cell photonic crystal lasing modes
Authors: Kang Ju-Hyung , Kim Sun-Kyung , Jeong Kwang-Yong , Lee Yong-Hee , Seo Min-Kyo , Park Hong-Gyu
Published: May 2011

This paper reports the unambiguous identification of lasing modes observed in a single-cell photonic crystal cavity using a solid angle scanning system. The polarization-resolved far-field measurements showed distinctive features of each mode and distinguished it from the other modes in contrast to conventional optical characterization methods. Monopole, quadrupole, and hexapole lasing modes were observed and identified, showing good agreement with numerical simulations. Our understanding of the lasing modes will be useful for determining practical applications as promising light sources in ultracompact photonic integrated circuits.
Rapid confocal Raman imaging using a synchro multifoci-scan scheme for dynamic monitoring of single living cells
Authors: Kong Lingbo , Zhang Pengfei , Yu Jing , Setlow Peter , Li Yong-qing
Published: May 2011

We developed a rapid multifoci-scan confocal Raman microscopy system for label-free molecular imaging of single living cells. A pair of galvo-mirrors were used to raster scan a single laser to generate multifoci excitations and another galvo-mirror synchronously projected Raman scattering from each foci onto a multichannel spectrograph such that multiple spectra were collected simultaneously. The image acquisition time is ∼40 times faster than in conventional point-scan Raman microscopy with diffraction-limited resolution retained. We demonstrated that this system can be used to monitor the germination dynamics of single bacterial spores with about 1.0 min resolution and 2.5 mW power at each focal point.
The Effect of Figural Manipulations on Brightness Differences in the Benary Cross
Authors: Vergeer Mark , van Lier Rob
Published: May 2011

The Benary cross is a classical demonstration showing that the perceived brightness of an area is not solely determined by its luminance, but also by the context in which it is embedded. Despite the fact that two identical grey triangles are flanked by an equal amount of black and white, one of the triangles is perceived as being lighter than the other. It has been argued that the junctions surrounding a test area are crucial in determining brightness. Here, we explored how different aspects influencing perceptual organisation influence perceived figure – background relations in the Benary cross and, with that, the perceived brightness of the triangular patches in our stimuli. The results of a cancellation task confirm that the alignment of contours at junctions indeed has a strong influence on an area's brightness. At the same time, however, the Benary effect is also influenced by the overall symmetry of the cross and its orientation.
Lightness Effects in Delboeuf and Ebbinghaus Size-Contrast Illusions
Authors: Daneyko Olga , Zavagno Daniele , Zanuttini Lucia
Published: May 2011

We examined lightness effects observed in Delboeuf and Ebbinghaus size-contrast illusions. Results of four experiments are reported. Experiment 1 was conducted with Delboeuf-like stimuli and shows that the disk that appears bigger appears either lighter or darker than the disk that appears smaller, depending on the contrast polarity between disks and background. Experiment 2 shows that the direction of these lightness effects is not influenced by the luminance of the size-contrast inducers. Experiment 3 shows that a similar lightness effect is also observed in modified Ebbinghaus size-contrast displays. Experiment 4 tested the presence of the size-contrast illusion in the stimuli used in experiments 2 and 3.
On the Failure of Completion of Lines Passing through the Blind Regions Related to the Optic Disc, and to Scotomas of Migraine Auras
Authors: Storoni Mithu , Hubel David H
Published: May 2011

We compared the appearance of a line passing through the optic-disc blind spot with that of lines passing just medial or just lateral to the blind spot. Though there is no well-defined gap in the line, we see a consistent difference, which is hard to describe. On the other hand, during a migraine aura experienced by one of us, lines passing through scintillating scotomas showed clear sharply defined gaps.
The Effect of Familiarity on Face Adaptation
Authors: Laurence Sarah , Hole Graham
Published: May 2011

Face aftereffects can provide information on how faces are stored by the human visual system (eg Leopold et al, 2001 Nature Neuroscience4 89 – 94), but few studies have used robustly represented (highly familiar) faces. In this study we investigated the influence of facial familiarity on adaptation effects. Participants were adapted to a series of distorted faces (their own face, a famous face, or an unfamiliar face). In experiment 1, figural aftereffects were significantly smaller when participants were adapted to their own face than when they were adapted to the other faces (ie their own face appeared significantly less distorted than a famous or unfamiliar face). Experiment 2 showed that this ‘own-face’ effect did not occur when the same faces were used as adaptation stimuli for participants who were unfamiliar with them. Experiment 3 replicated experiment 1, but included a pre-adaptation baseline. The results highlight the importance of considering facial familiarity when conducting research on face aftereffects.
Graphemes Evoke Synesthetic Colors Even before They are Consciously Recognized
Authors: Ramachandran Vilayanur S , Seckel Elizabeth
Published: May 2011

We showed a grapheme-color synesthete three different examples of stimuli in which the graphemes were ‘hidden’—as in puzzle pictures—and became visible as letters only after prolonged viewing. Intriguingly the subject saw the appropriate colors accurately long before the graphemes became consciously visible—a novel form of blindsight.
Survival, growth and reproduction of non-indigenous Nile tilapia, Oreochromis niloticus (Linnaeus 1758). I. Physiological capabilities in various temperatures and salinities
Authors: Schofield Pamela J. , Peterson Mark S. , Lowe Michael R. , Brown-Peterson Nancy J. , Slack William T.
Published: May 2011

The physiological tolerances of non-native fishes is an integral component of assessing potential invasive risk. Salinity and temperature are environmental variables that limit the spread of many non-native fishes. We hypothesised that combinations of temperature and salinity will interact to affect survival, growth, and reproduction of Nile tilapia, Oreochromis niloticus, introduced into Mississippi, USA. Tilapia withstood acute transfer from fresh water up to a salinity of 20 and survived gradual transfer up to 60 at typical summertime (30°C) temperatures. However, cold temperature (14°C) reduced survival of fish in saline waters ≥10 and increased the incidence of disease in freshwater controls. Although fish were able to equilibrate to saline waters in warm temperatures, reproductive parameters were reduced at salinities ≥30. These integrated responses suggest that Nile tilapia can invade coastal areas beyond their point of introduction. However, successful invasion is subject to two caveats: (1) wintertime survival depends on finding thermal refugia, and (2) reproduction is hampered in regions where salinities are ≥30. These data are vital to predicting the invasion of non-native fishes into coastal watersheds. This is particularly important given the predicted changes in coastal landscapes due to global climate change and sea-level rise.
Long-term effects of different-sized surgically implanted acoustic transmitters on the sciaenid Arygyrosomus japonicus: breaking the 2% tag-to-body mass rule
Authors: Childs A. R. , Næsje T. F. , Cowley P. D.
Published: May 2011

Biotelemetry is an increasingly popular and effective tool to study fish movements. Interpretation of the results relies on the assumption that fish behaviour and physiology is not affected by the presence of the tag. Although the long-term effects of tagging should be evaluated before field telemetry studies, this has rarely been quantified. As a precursor to a long-term telemetry study on Argyrosomus japonicus (Termminck and Schlegel 1843) in South Africa, the effects of surgical implantation of two different-sized tags were assessed in a 256-day experiment. We hypothesised that the larger 13-mm-diameter tags, which exceeded the general 2% tag-to-body mass rule, would have adverse effects on growth, survival and tag retention compared with the smaller 9-mm-diameter tags and an untagged control group. Because no adverse effects in growth were observed among the three groups, nor any long-term tag-related mortality, tag expulsion or internal damage, we suggest that the general 2% tag-to-body mass rule should be regarded only as a broad guide. Further, we conclude that juvenile A. japonicus individuals are well suited for surgical implantation of commercially available 9- and 13-mm-diameter tags and are good candidates for long-term telemetry studies.
Spatial distribution of resting stages (akinetes) of the cyanobacteria Anabaena flos-aquae in sediments and its influence on pelagic populations
Authors: Kravchuk Elena S. , Ivanova Elena A. , Gladyshev Michail I.
Published: May 2011

Recruitment of pelagic populations of cyanobacteria from littoral bottom sediments is assumed to be one of the key factors for the development of harmful blooms. Therefore, it is necessary to obtain more information on the possible factors influencing the spatial distribution of the resting stages in littoral bottom sediments. To test the hypothesis that akinete abundances in littoral bottom sediments are associated with silt and the presence of higher water plants, we sampled spatial and vertical distribution and seasonal dynamics of akinetes of cyanobacterium Anabaena flos-aquae in a small Siberian reservoir. We found that akinetes accumulate in silt at stations located in macrophyte beds. Two experiments were carried out to test if there is relationship between size of inoculum and size of the pelagic population of A. flos-aquae. The proportion of A. flos-aquae in total phytoplankton biomass depended on the initial abundance of akinetes in bottom sediments. The model based on laboratory experiments gave good qualitative description of the field data. These findings can be useful to predict the location of the main akinete accumulation zones in a water body and plan the removal of sediment to prevent the cyanobacterial blooms.
Spatial variability and human disturbance of sponge assemblages associated with mangrove roots in the southern Caribbean
Authors: Guerra-Castro Edlin , Young Paula , Pérez-Vázquez Adriana , Carteron Sophie , Alvizu Adriana
Published: May 2011

Assemblages growing on Caribbean red-mangrove roots are very diverse and characteristically dominated by sponges. The scales of spatial variation of this fauna in the Caribbean region have not been hierarchically quantified, although such information is necessary to understand the relative importance of ecological processes and possible responses to anthropogenic disturbances. We used a hierarchical nested design to identify patterns of spatial variability at different scales, namely among roots, sites, localities and regions within the southern Caribbean. Simultaneously, the sampling considered the relative distance from sources of human disturbance to test the null hypothesis of no difference in sponge diversity among localities as a result of anthropogenic stress. Significant spatial variability in species composition was detected at all spatial scales, especially at the among-root scale. However, there were no differences associated with distance from human disturbance. These results indicate high regional and local β diversity, and also suggest that results from small-scale experiments cannot be scaled up to the entire community. Further, spatial analysis of sponge assemblages is not enough to detect deleterious effects of human disturbances on mangrove areas.
Programmed induction of endoreduplication by DNA double-strand breaks in
Arabidopsis
Authors: Adachi Sumiko , Minamisawa Kazunori , Okushima Yoko , Inagaki Soichi , Yoshiyama Kaoru , Kondou Youichi , Kaminuma Eli , Kawashima Mika , Toyoda Tetsuro , Matsui Minami , Kurihara Daisuke , Matsunaga Sachihiro , Umeda Masaaki
Published: May 2011

Genome integrity is continuously threatened by external stresses and endogenous hazards such as DNA replication errors and reactive oxygen species. The DNA damage checkpoint in metazoans ensures genome integrity by delaying cell-cycle progression to repair damaged DNA or by inducing apoptosis. ATM and ATR (ataxia-telangiectasia-mutated and -Rad3-related) are sensor kinases that relay the damage signal to transducer kinases Chk1 and Chk2 and to downstream cell-cycle regulators. Plants also possess ATM and ATR orthologs but lack obvious counterparts of downstream regulators. Instead, the plant-specific transcription factor SOG1 (suppressor of gamma response 1) plays a central role in the transmission of signals from both ATM and ATR kinases. Here we show that in
Arabidopsis,
endoreduplication is induced by DNA double-strand breaks (DSBs), but not directly by DNA replication stress. When root or sepal cells, or undifferentiated suspension cells, were treated with DSB inducers, they displayed increased cell size and DNA ploidy. We found that the ATM–SOG1 and ATR–SOG1 pathways both transmit DSB-derived signals and that either one suffices for endocycle induction. These signaling pathways govern the expression of distinct sets of cell-cycle regulators, such as cyclin-dependent kinases and their suppressors. Our results demonstrate that
Arabidopsis
undergoes a programmed endoreduplicative response to DSBs, suggesting that plants have evolved a distinct strategy to sustain growth under genotoxic stress.