bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of the modulated distortions in confined nematic liquid crystals
Authors: Zakharov A. V. , Vakulenko A. A.
Published: December 2013

The peculiarities in the dynamics of the director reorientation in confined nematic liquid crystals (LCs) under the influence of a strong electric field  E have been investigated theoretically based on the hydrodynamic theory including the director motion with appropriate boundary and initial conditions. Analysis of the numerical results for the turn-on process provides an evidence for the appearance of the spatially periodic patterns in confined LC film, only in response to the suddenly applied strong  E. It has been shown that there is a threshold value of the amplitude of the thermal fluctuations of the director over the LC sample which provides the nonuniform rotation mode rather than the uniform one, whereas the lower values of the amplitude dominate the uniform mode. During the turn-off process, the reorientation of the director to the direction preferred by the surfaces is characterized by the complex destruction of the initially periodic structure to a monodomain state.
Fixman compensating potential for general branched molecules
Authors: Jain Abhinandan , Kandel Saugat , Wagner Jeffrey , Larsen Adrien , Vaidehi Nagarajan
Published: December 2013

The technique of constraining high frequency modes of molecular motion is an effective way to increase simulation time scale and improve conformational sampling in molecular dynamics simulations. However, it has been shown that constraints on higher frequency modes such as bond lengths and bond angles stiffen the molecular model, thereby introducing systematic biases in the statistical behavior of the simulations. Fixman proposed a compensating potential to remove such biases in the thermodynamic and kinetic properties calculated from dynamics simulations. Previous implementations of the Fixman potential have been limited to only short serial chain systems. In this paper, we present a spatial operator algebra based algorithm to calculate the Fixman potential and its gradient within constrained dynamics simulations for branched topology molecules of any size. Our numerical studies on molecules of increasing complexity validate our algorithm by demonstrating recovery of the dihedral angle probability distribution function for systems that range in complexity from serial chains to protein molecules. We observe that the Fixman compensating potential recovers the free energy surface of a serial chain polymer, thus annulling the biases caused by constraining the bond lengths and bond angles. The inclusion of Fixman potential entails only a modest increase in the computational cost in these simulations. We believe that this work represents the first instance where the Fixman potential has been used for general branched systems, and establishes the viability for its use in constrained dynamics simulations of proteins and other macromolecules.
Pressure dependence of Kapitza resistance at gold/water and silicon/water interfaces
Authors: Pham An , Barisik Murat , Kim BoHung
Published: December 2013

We conducted non-equilibrium molecular dynamics simulations to investigate Kapitza length at solid/liquid interfaces under the effects of bulk liquid pressures. Gold and silicon were utilized as hydrophilic and hydrophobic solid walls with different wetting surface behaviors, while the number of confined liquid water molecules was adjusted to obtain different pressures inside the channels. The interactions of solid/liquid couples were reparameterized accurately by measuring the water contact angle of solid substrates. In this paper, we present a thorough analysis of the structure, normal stress, and temperature distribution of liquid water to elucidate thermal energy transport across interfaces. Our results demonstrate excellent agreement between the pressures of liquid water in nano-channels and published thermodynamics data. The pressures measured as normal stress components were characterized using a long cut-off distance reinforced by a long-range van der Waals tail correction term. To clarify the effects of bulk liquid pressures on water structure at hydrophilic and hydrophobic solid surfaces, we defined solid/liquid interface spacing as the distance between the surface and the peak value of the first water density layer. Near the gold surface, we found that interface spacing and peak value of first water density layer were constant and did not depend on bulk liquid pressure; near the silicon surface, those values depended directly upon bulk liquid. Our results reveal that the pressure dependence of Kapitza length strongly depends on the wettability of the solid surface. In the case of the hydrophilic gold surface, Kapitza length was stable despite increasing bulk liquid pressure, while it varied significantly at the hydrophobic silicon surface.
Probing the electronic structures of low oxidation-state uranium fluoride molecules UFx− (x = 2−4)
Authors: Li Wei-Li , Hu Han-Shi , Jian Tian , Lopez Gary V. , Su Jing , Li Jun , Wang Lai-Sheng
Published: December 2013

We report the experimental observation of gaseous UFx− (x = 2−4) anions, which are investigated using photoelectron spectroscopy and relativistic quantum chemistry. Vibrationally resolved photoelectron spectra are obtained for all three species and the electron affinities of UFx (x = 2−4) are measured to be 1.16(3), 1.09(3), and 1.58(3) eV, respectively. Significant multi-electron transitions are observed in the photoelectron spectra of U(5f37s2)F2−, as a result of strong electron correlation effects of the two 7s electrons. The U−F symmetric stretching vibrational modes are resolved for the ground states of all UFx (x = 2−4) neutrals. Theoretical calculations are performed to qualitatively understand the photoelectron spectra. The entire UFx− and UFx (x = 1−6) series are considered theoretically to examine the trends of U−F bonding and the electron affinities as a function of fluorine coordination. The increased U−F bond lengths and decreased bond orders from UF2− to UF4− indicate that the U−F bonding becomes weaker as the oxidation state of U increases from I to III.
Three-dimensional transient model for time-domain free-carrier absorption measurement of excess carriers in silicon wafers
Authors: Ren Shengdong , Li Bincheng , Huang Qiuping
Published: December 2013

A three-dimensional transient model for time-domain (modulated) free-carrier absorption (FCA) measurement was developed to describe the transport dynamics of photo-generated excess carriers in silicon (Si) wafers. With the developed transient model, numerical simulations were performed to investigate the dependences of the waveforms of the transient FCA signals on the electronic transport parameters of Si wafers and the geometric parameters of the FCA experiment. Experimental waveforms of FCA signals of both n- and p-type Si wafers with resistivity ranging 1–38 Ω·cm were then fitted to the three-dimensional transient model to extract simultaneously and unambiguously the transport parameters of Si wafers, namely, the carrier lifetime, the carrier diffusion coefficient, and the front surface recombination velocity via multi-parameter fitting. A basic agreement between the extracted parameter values and the literature values was obtained.
Ozone generation in a kHz-pulsed He-O2 capillary dielectric barrier discharge operated in ambient air
Authors: Sands Brian L. , Ganguly Biswa N.
Published: December 2013

The generation of reactive oxygen species using nonequilibrium atmospheric pressure plasma jet devices has been a subject of recent interest due to their ability to generate localized concentrations from a compact source. To date, such studies with plasma jet devices have primarily utilized radio-frequency excitation. In this work, we characterize ozone generation in a kHz-pulsed capillary dielectric barrier discharge configuration comprised of an active discharge plasma jet operating in ambient air that is externally grounded. The plasma jet flow gas was composed of helium with an admixture of up to 5% oxygen. A unipolar voltage pulse train with a 20 ns pulse risetime was used to drive the discharge at repetition rates between 2–25 kHz. Using UVLED absorption spectroscopy centered at 255 nm near the Hartley-band absorption peak, ozone was detected over 1 cm from the capillary axis. We observed roughly linear scaling of ozone production with increasing pulse repetition rate up to a “turnover frequency,” beyond which ozone production steadily dropped and discharge current and 777 nm O(5P→5S°) emission sharply increased. The turnover in ozone production occurred at higher pulse frequencies with increasing flow rate and decreasing applied voltage with a common energy density of 55 mJ/cm3 supplied to the discharge. The limiting energy density and peak ozone production both increased with increasing O2 admixture. The power dissipated in the discharge was obtained from circuit current and voltage measurements using a modified parallel plate dielectric barrier discharge circuit model and the volume-averaged ozone concentration was derived from a 2D ozone absorption measurement. From these measurements, the volume-averaged efficiency of ozone production was calculated to be 23 g/kWh at conditions for peak ozone production of 41 mg/h at 11 kV applied voltage, 3% O2, 2 l/min flow rate, and 13 kHz pulse repetition rate, with 1.79 W dissipated in the discharge.
Realization of free-standing silicene using bilayer graphene
Authors: Neek-Amal M. , Sadeghi A. , Berdiyorov G. R. , Peeters F. M.
Published: December 2013

The available synthesized silicene-like structures have been only realized on metallic substrates which are very different from the standalone buckled silicene, e.g., the Dirac cone of silicene is destroyed due to lattice distortion and the interaction with the substrate. Using graphene bilayer as a scaffold, a route is proposed to synthesize silicene with electronic properties decoupled from the substrate. The buckled hexagonal arrangement of silicene between the graphene layers is found to be very similar to the theoretically predicted standalone buckled silicene which is only very weakly van der Waals coupled to the graphene layers with a graphite-like interlayer distance of 3.42 Å and without any lattice distortion. We found that these stacked layers are stable well above room temperature.
Highly uniform bipolar resistive switching characteristics in TiO2/BaTiO3/TiO2 multilayer
Authors: Ma W. J. , Lin S. P. , Luo J. M. , Zhang X. Y. , Wang Ying , Li Z. X. , Wang B. , Zheng Yue
Published: December 2013

Nanoscale multilayer structure TiO2/BaTiO3/TiO2 has been fabricated on Pt/Ti/SiO2/Si substrate by chemical solution deposition method. Highly uniform bipolar resistive switching (BRS) characteristics have been observed in Pt/TiO2/BaTiO3/TiO2/Pt cells. Analysis of the current-voltage relationship demonstrates that the space-charge-limited current conduction controlled by the localized oxygen vacancies should be important to the resistive switching behavior. X-ray photoelectron spectroscopy results indicated that oxygen vacancies in TiO2 play a crucial role in the resistive switching phenomenon and the introduced TiO2/BaTiO3 interfaces result in the high uniformity of bipolar resistive switching characteristics.
On the sub-band gap optical absorption in heat treated cadmium sulphide thin film deposited on glass by chemical bath deposition technique
Authors: Chattopadhyay P. , Karim B. , Guha Roy S.
Published: December 2013

The sub-band gap optical absorption in chemical bath deposited cadmium sulphide thin films annealed at different temperatures has been critically analyzed with special reference to Urbach relation. It has been found that the absorption co-efficient of the material in the sub-band gap region is nearly constant up to a certain critical value of the photon energy. However, as the photon energy exceeds the critical value, the absorption coefficient increases exponentially indicating the dominance of Urbach rule. The absorption coefficients in the constant absorption region and the Urbach region have been found to be sensitive to annealing temperature. A critical examination of the temperature dependence of the absorption coefficient indicates two different kinds of optical transitions to be operative in the sub-band gap region. After a careful analyses of SEM images, energy dispersive x-ray spectra, and the dc current-voltage characteristics, we conclude that the absorption spectra in the sub-band gap domain is possibly associated with optical transition processes involving deep levels and the grain boundary states of the material.
A non-adiabatic dynamics study of octatetraene: The radiationless conversion from S2 to S1
Authors: Qu Zexing , Liu Chungen
Published: December 2013

Simulation of the excited state dynamics of all-trans-1,3,5,7-octatetraene has been performed to investigate the ultrafast radiationless S2 → S1 internal conversion process. Multireference configuration interaction with single excitation method has been employed to optimize the equilibrium structure of the excited states, as well as the S2/S1 conical intersection, and to investigate the non-adiabatic molecular dynamics of the S2/S1 state transition. At the conical intersection, the molecule is found to be distorted from the original planar trans structure to a nearly perpendicular conformation around C3−C4 bond, with the torsion angle being about 107°. Such structural change can result in mutual approaching of states S2 and S1 in energy, and drastically increase the nonadiabatic coupling between the two states by destroying the inter-state symmetry prohibition in the electronic wavefunctions. Surface-hopping molecular dynamics simulations are performed to describe the non-adiabatic process. Upon the Franck-Condon excitation to the S2 state, the molecule quickly twists its C3−C4 bond and approaches the conical intersection region, where it can undergo efficient internal conversion to S1. The decay time constant (τ) of S2 state is estimated to be around 251 fs by fitting the occupation number of average fraction of trajectories using an exponential damping function. This value is reasonably consistent with previous experimental measurements of around 300–400 fs.
Note: Symmetric modulation methodology applied in improving the performance of scanning tunneling microscopy
Authors: Ju Bing-Feng , Zhu Wu-Le , Zhang Wei
Published: December 2013

A symmetric modulation methodology is proposed to combine robust control of external disturbance, rapid response to steep sidewalls with the high speed of a traditional scanning tunneling microscopy. The 1400 × 200 μm2 topography of a comb-like steep sidewalls micro-structure with the depth of 23 μm was acquired at a high scanning speed of 120 μms−1 and the detectable slope angle is up to 85°. The total measuring time was only 17 min. In addition, a 4 × 4 mm2 aluminum dual-sinusoidal array has been successfully measured with a scanning speed up to 500 μms−1. It improved the performance of the normal scanning tunneling microscope and enables efficient and stable measurement of large-area complex micro-structures, and thus can be introduced to engineering applications.
The effect of magnesium added at C60/Rubrene heterointerfaces
Authors: Cheng Chiu-Ping , Lee Cheng-Wei , Chu Yu-Ya , Wei Ching-Hsuan , Pi Tun-Wen
Published: December 2013

This study examines the effect of adding magnesium (Mg) at C60/rubrene heterointerfaces by using synchrotron-radiation photoemission spectroscopy. The heterointerface was obtained by depositing C60 on a 4-Å Mg/rubrene surface. The photoemission spectra showed that the added Mg preferentially interacts with and transfers negative charges to C60. The interfacial dipole potential was significantly enlarged, as was the separation between the lowest unoccupied molecular orbital of C60 and the highest occupied molecular orbital of rubrene. The results demonstrate that the addition of Mg should be an effective method for improving the efficiency of light- and current-generating devices.
A new approach in impurity doping of 4H-SiC using silicidation
Authors: Tin Chin-Che , Mendis Suwan , Tin Michelle T. , Isaacs-Smith Tamara , Williams John R.
Published: December 2013

Oxidation and silicidation have been found to enhance phosphorus diffusion and incorporation in 4H-SiC. Depth profiling by secondary ion mass spectrometry showed significant concentration of phosphorus in the order of 1018–1019 cm−3 in the near-surface region of 4H-SiC in both oxidation and silicidation-assisted phosphorus-diffused samples. However, silicidation was remarkably more effective than oxidation in promoting phosphorus diffusion, producing comparable phosphorus concentration at even greater depth at a temperature of only 900 °C. Specific contact resistance values of the phosphorus-doped samples confirmed feasibility of this method in ohmic contact fabrication on SiC.
Multilevel recording in Bi-deficient Pt/BFO/SRO heterostructures based on ferroelectric resistive switching targeting high-density information storage in nonvolatile memories
Authors: Jiménez David , Miranda Enrique , Tsurumaki-Fukuchi Atsushi , Yamada Hiroyuki , Suñé Jordi , Sawa Akihito
Published: December 2013

We demonstrate the feasibility of multilevel recording in Pt/Bi1-δFeO3/SrRuO3 capacitors using the ferroelectric resistive switching phenomenon exhibited by the Pt/Bi1−δFeO3 interface. A tunable population of up and down ferroelectric domains able to modulate the Schottky barrier height at the Pt/Bi1−δFeO3 interface can be achieved by means of either a collection of SET/RESET voltages or current compliances. This programming scheme gives rise to well defined resistance states, which form the basis for a multilevel storage nonvolatile memory.
Radiative cooling of bulk silicon by incoherent light pump
Authors: Malyutenko V. K. , Bogatyrenko V. V. , Malyutenko O. Yu.
Published: December 2013

In contrast to radiative cooling by light up conversion caused exclusively by a low-entropy laser pump and employing thermally assisted fluorescence/luminescence as a power out, we demonstrate light down conversion cooling by incoherent pumps, 0.47–0.94 μm light emitting diodes, and employing thermal emission (TE) as a power out. We demonstrate ≤3.5 K bulk cooling of Si at 450 K because overall energy of multiple below bandgap TE photons exceeds the energy of a single above bandgap pump photon. We show that using large entropy TE as power out helps avoid careful tuning of an incoherent pump wavelength and cool indirect-bandgap semiconductors.
Strain and composition effects on Raman vibrational modes of silicon-germanium-tin ternary alloys
Authors: Fournier-Lupien J.-H. , Mukherjee S. , Wirths S. , Pippel E. , Hayazawa N. , Mussler G. , Hartmann J. M. , Desjardins P. , Buca D. , Moutanabbir O.
Published: December 2013

We investigated Raman vibrational modes in silicon-germanium-tin layers grown epitaxially on germanium/silicon virtual substrates using reduced pressure chemical vapor deposition. Several excitation wavelengths were utilized to accurately analyze Raman shifts in ternary layers with uniform silicon and tin content in 4–19 and 2–12 at. % ranges, respectively. The excitation using a 633 nm laser was found to be optimal leading to a clear detection and an unambiguous identification of all first order modes in the alloy. The influence of both strain and composition on these modes is discussed. The strain in the layers is evaluated from Raman shifts and reciprocal space mapping data and the obtained results are discussed in the light of recent theoretical calculations.
Extracting physical properties of arbitrarily shaped laser-doped micro-scale areas in semiconductors
Authors: Heinrich Martin , Kluska Sven , Hameiri Ziv , Hoex Bram , Aberle Armin G.
Published: December 2013

We present a method that allows the extraction of relevant physical properties such as sheet resistance and dopant profile from arbitrarily shaped laser-doped micro-scale areas formed in semiconductors with a focused pulsed laser beam. The key feature of the method is to use large laser-doped areas with an identical average number of laser pulses per area (laser pulse density) as the arbitrarily shaped areas. The method is verified using sheet resistance measurements on laser-doped silicon samples. Furthermore, the method is extended to doping with continuous-wave lasers by using the average number of passes per area or density of passes.
The effect of bias current asymmetry on the flux-flow steps in the grain boundary YBaCuO long Josephson junctions
Authors: Revin L. S. , Chiginev A. V. , Pankratov A. L. , Masterov D. V. , Parafin A. E. , Luchinin G. A. , Matrozova E. A. , Kuzmin L. S.
Published: December 2013

The current-voltage characteristics and critical current versus magnetic field dependence of long 24°[001]-tilt YBa2Cu3O7−δ bicrystal grain-boundary junctions are studied both experimentally and theoretically. For the opposite magnetic field directions, the flux-flow steps with significantly different height and slope are observed. It is demonstrated that the most probable reason of this discrepancy is recently predicted asymmetry of spatial bias current distribution due to crystallographic anisotropy of bicrystal substrates [Kupriyanov et al., JETP Lett. 95, 289 (2012)].
Creation of quantum entanglement with two separate diamond nitrogen vacancy centers coupled to a photonic molecule
Authors: Liu Siping , Yu Rong , Li Jiahua , Wu Ying
Published: December 2013

We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.
Maximum magnitude in bias-dependent spin accumulation signals of CoFe/MgO/Si on insulator devices
Authors: Ishikawa M. , Sugiyama H. , Inokuchi T. , Tanamoto T. , Hamaya K. , Tezuka N. , Saito Y.
Published: December 2013

We study in detail how the bias voltage (Vbias) and interface resistance (RA) depend on the magnitude of spin accumulation signals (|ΔV| or |ΔV|/I, where I is current) as detected by three-terminal Hanle measurements in CoFe/MgO/Si on insulator (SOI) devices with various MgO layer thicknesses and SOI carrier densities. We find the apparent maximum magnitude of spin polarization as a function of Vbias and the correlation between the magnitude of spin accumulation signals and the shape of differential conductance (dI/dV) curves within the framework of the standard spin diffusion model. All of the experimental results can be explained by taking into account the density of states (DOS) in CoFe under the influence of the applied Vbias and the quality of MgO tunnel barrier. These results indicate that it is important to consider the DOS of the ferromagnetic materials under the influence of an applied Vbias and the quality of tunnel barrier when observing large spin accumulation signals in Si.
Terahertz electrodynamics and superconducting energy gap of NbTiN
Authors: Hong Taeyoon , Choi Kyujin , Ik Sim Kyung , Ha Taewoo , Cheol Park Byung , Yamamori Hirotake , Hoon Kim Jae
Published: December 2013

Terahertz electrodynamics of superconducting NbTiN has been studied in the spectral range of 8-70 cm–1 above and below the critical temperature of Tc = 14.1 K. Our transmission terahertz time-domain spectroscopy technique allows for independent and accurate determination of both the real part σ1 and the imaginary part σ2 of the optical conductivity σ as a function of frequency ω and temperature T without a Kramers-Kronig analysis. A clear signature of the superconducting energy gap Δ(T) is observed in the real part σ1 of the optical conductivity below Tc, with 2Δ(0) = 36.5 cm−1 corresponding to 2Δ(0)/kBTc = 3.72. No indication of strong-coupling effects was observed in the imaginary part σ2 toward zero frequency. Our results, including the temperature dependence of the penetration depth λ(T), are in excellent quantitative agreement with weak coupling BCS theory and Mattis-Bardeen formula.
Disorder induced interface states and their influence on the Al/Ge nanowires Schottky devices
Authors: Simon R. A. , Kamimura H. , Berengue O. M. , Leite E. R. , Chiquito A. J.
Published: December 2013

It has been demonstrated that the presence of oxide monolayers in semiconductor surfaces alters the electronic potential at surfaces and, consequently, can drastically affect the electronic transport features of a practical device such as a field effect transistor. In this work experimental and theoretical approaches to characterize Al/germanium nanowire Schottky devices by using samples covered with a thin oxide layer (2 nm width) were explored. It was also demonstrated that the oxide layer on Ge causes a weak dependence of the metal work function on Schottky barrier heights indicating the presence of Fermi level pinning. From theoretical calculations the pinning factor S was estimated to range between 0.52 and 0.89, indicating a weak Fermi level pinning which is induced by the presence of charge localization at all nanowires' surface coming from interface states.
Photo-instability of CdSe/ZnS quantum dots in poly(methylmethacrylate) film
Authors: Zhang Hongyi , Liu Yu , Ye Xiaoling , Chen Yonghai
Published: December 2013

The photo-instability of CdSe/ZnS quantum dots (QDs) has been studied under varied conditions. We discussed the main features of the evolution of photoluminescence (PL) intensity and energy at different laser powers, which showed critical dependences on the environment. The PL red shift in a vacuum showed strong temperature dependence, from which we concluded that the thermal activation energy for trapping states of the charge carriers was about 14.7 meV. Furthermore, the PL spectra showed asymmetric evolution during the laser irradiation, for which two possible explanations were discussed. Those results provided a comprehensive picture for the photo-instability of the colloidal QDs under different conditions.
Effect of culture conditions on the growth rate and lipid production of microalgae Nannochloropsis gaditana
Authors: Ren Ming , Ogden Kimberly , Lian Bo
Published: December 2013

Microalgae Nannochloropsis gaditana (CCMP527) is an ideal candidate as a renewable and sustainable alternative oil source to traditional fossil fuel. It has advantages including high oil content, short growth cycle, and high biomass yield. Experimental data showed that with 5% CO2 enriched air and tris-HCl buffered f/2-Si medium, a maximum growth rate of 0.48 day−1 and a lipid yield of 0.32 g/l were achieved. Various carbon and nitrogen sources were investigated to determine the range of substrates that may be feasible for cultivation with minimal impact on productivity. The sources evaluated cover some of the compounds found in fertilizers and groundwater. When glucose was added into the medium, microalgae grew faster mixotrophically but the lipid yield was reduced by 86%. Adding high concentrations of nitrogen, 10 mM N in the form of nitrate, ammonium sulfate, glycine, and urea, resulted in variations in lipid yield from 0.02 g/l to 0.27 g/l. However, the growth rate increased slightly to 0.52 day−1 at the higher nitrogen concentration when nitrate and urea were the nitrogen sources. The major fatty acids were C16:0 and C16:1 regardless of the carbon and nitrogen sources, which are readily converted to fuels. While the amount of nitrogen affects productivity, the types of fatty acids produced are not affected hence making cultivation on impaired waters feasible.
Ultrasonic properties of all-printed piezoelectric polymer transducers
Authors: Wagle Sanat , Decharat Adit , Bodö Peter , Melandsø Frank
Published: December 2013

The ability of producing ultrasonic transducers from screen-printing has been explored experimentally, through printing and characterization of a large number of transducers. In an all-printed test design, 124 transducers with four different electrode sizes ranging from 1 to 4.9 mm2, were printed layer-by-layer on a high performance polyethyleneimine polymer. Inks from ferroelectric and conductive polymers were applied to the active part of a transducer, to provide a good acoustical match between the individual layers. Ultrasonic characterizations of the transducers done by two independent methods provided a broad-banded frequency response with a maximum response around 100 MHz.
Cooperative effect of ultraviolet and near-infrared beams in laser-induced condensation
Authors: Matthews M. , Henin S. , Pomel F. , Théberge F. , Lassonde P. , Daigle J.-F. , Kieffer J.-C. , Kasparian J. , Wolf J.-P.
Published: December 2013

We demonstrate the cooperative effect of near infrared (NIR) and ultraviolet (UV) beams on laser-induced condensation. Launching a UV laser after a NIR pulse yields up to a 5-fold increase in the production of nanoparticles (25–300 nm) as compared to a single NIR beam. This cooperative effect exceeds the sum of those from the individual beams and occurs for delays up to 1 μs. We attribute it to the UV photolysis of ozone created by the NIR pulses. The resulting OH radicals oxidize NO2 and volatile organic compounds, producing condensable species.
Optical properties of hierarchical-nanostructured TiO2 and its time-dependent photo-degradation of gaseous acetaldehyde
Authors: Ahn Kyun , Kim Min-Sun , Kim Soon-Hyun , Hyun Kim Jae , Jeong Se-Young , Kim Jong-Pil , Sung Jin Jong , Cho Chae-Ryong
Published: December 2013

The TiO2 hierarchical nanostructures (HNs) composed of rutile TiO2 nanowires on anatase TiO2 nanofibers had higher photocatalytic activities of 62% and 48% than the commercial TiO2 nanoparticles (∼21 nm diameter) in the continuous flow mode and closed-circulation mode, respectively, leading to an efficient degradation of gaseous acetaldehyde under UV-light irradiation. This behavior may be attributed to the effective TiO2 HNs with specific surface area of 85.1 m2/g and lower radiative recombination of self-trapped excitons, enabling an effective electron-hole separation.
Efficient, air-stable colloidal quantum dot solar cells encapsulated using atomic layer deposition of a nanolaminate barrier
Authors: Ip Alexander H. , Labelle André J. , Sargent Edward H.
Published: December 2013

Atomic layer deposition was used to encapsulate colloidal quantum dot solar cells. A nanolaminate layer consisting of alternating alumina and zirconia films provided a robust gas permeation barrier which prevented device performance degradation over a period of multiple weeks. Unencapsulated cells stored in ambient and nitrogen environments demonstrated significant performance losses over the same period. The encapsulated cell also exhibited stable performance under constant simulated solar illumination without filtration of harsh ultraviolet photons. This monolithically integrated thin film encapsulation method is promising for roll-to-roll processed high efficiency nanocrystal solar cells.
Slow light enhanced singlet exciton fission solar cells with a 126% yield of electrons per photon
Authors: Thompson Nicholas J. , Congreve Daniel N. , Goldberg David , Menon Vinod M. , Baldo Marc A.
Published: December 2013

Singlet exciton fission generates two triplet excitons per absorbed photon. It promises to increase the power extracted from sunlight without increasing the number of photovoltaic junctions in a solar cell. We demonstrate solar cells with an external quantum efficiency of 126% by enhancing absorption in thin films of the singlet exciton fission material pentacene. The device structure exploits the long photon dwell time at the band edge of a distributed Bragg reflector to achieve enhancement over a broad range of angles. Measuring the reflected light from the solar cell establishes a lower bound of 137% for the internal quantum efficiency.
Conductivity of transparent electrodes made from interacting nanotubes
Authors: Maillaud Laurent , Zakri Cécile , Ly Isabelle , Pénicaud Alain , Poulin Philippe
Published: December 2013

Interactions in carbon nanotube (CNT) dispersions alter the morphology of films made from such dispersions. Weak attractive interactions induce an enhancement of the electrical conductivity. This phenomenon is observed in thin films that lie in a near percolated regime. Strong interactions instead induce a decrease of conductivity. In spite of strong morphological differences, the conductivity of thick films, away from percolated regimes, do not depend on interactions between the CNTs. These experiments support a recent theoretical scenario of the percolation of interacting rods and provide guidance for the optimal formulations of CNT inks in transparent electrode applications.
In situ tensile and creep testing of lithiated silicon nanowires
Authors: Boles Steven T. , Thompson Carl V. , Kraft Oliver , Mönig Reiner
Published: December 2013

We present experimental results for uniaxial tensile and creep testing of fully lithiated silicon nanowires. A reduction in the elastic modulus is observed when silicon nanowires are alloyed with lithium and plastic deformation becomes possible when the wires are saturated with lithium. Creep testing was performed at fixed force levels above and below the tensile strength of the material. A linear dependence of the strain-rate on the applied stress was evident below the yield stress of the alloy, indicating viscous deformation behavior. The observed inverse exponential relationship between wire radius and strain rate below the yield stress indicates that material transport was controlled by diffusion. At stress levels approaching the yield strength of fully lithiated silicon, power-law creep appears to govern the strain-rate dependence on stress. These results have direct implications on the cycling conditions, rate-capabilities, and charge capacity of silicon and should prove useful for the design and construction of future silicon-based electrodes.
Experimental characterization and self-consistent modeling of luminescence coupling effect in III-V multijunction solar cells
Authors: Sogabe Tomah , Ogura Akio , Hung Chao-Yu , Evstropov Valery , Mintairov Mikhail , Shvarts Maxim , Okada Yoshitaka
Published: December 2013

In this paper, we focused on developing an accurate model to describe the luminescent coupling (L-C) effect in multijunction solar cells (MJSC) under light concentration. We present here a transcend current-voltage (I-V) formula combined with a self-consistent simulation algorithm to derive the coupling yield γ dependence on light intensity by including the electrical parameters such as shunt resistance (Rsh) and series resistance (Rs), which were ignored in previous simulation models. The effects of both Rsh and Rs on γ were revealed, and the dependence of γ on the external voltage bias Vbias was investigated. Meanwhile, we have performed experiments to determine coupling yield γ by measuring the I-V curves of individual subcell of InGaP/GaAs/Ge triple junction solar cell under varied light intensity. We found that the measured results are only in good agreement with the simulated data obtained from the model where the resistance parameters were included. Based on these results, we calculated the conversion efficiency of MJSC and found that the efficiency increase due to L-C effect is 0.31% under 1 sun and 1.07% under 1000 suns. Thus the L-C analysis results presented here will work as an additional device optimization criteria for MJSC toward higher efficiency.
A quaternionic construction of 𝐸₇
Authors: Wilson Robert
Published: December 2013

We give an explicit construction of the simply-connected compact real form of the Lie group of type

E
7

E_7

, as a group of

28
×
28

28\times 28

matrices over quaternions, acting on a

28
28

-dimensional left quaternion vector space. This leads to a description of the simply-connected split real form, acting on a

56
56

-dimensional real vector space, and thence to the finite quasi-simple groups of type

E
7

E_7

. The sign problems usually associated with constructing exceptional Lie groups are almost entirely absent from this approach.
Some toy Furstenberg sets and projections of the four-corner Cantor set
Authors: Oberlin Daniel
Published: December 2013

We give lower bounds for the Hausdorff dimensions of some model Furstenberg sets.
The centrosomal kinase NEK2 is a novel splicing factor kinase involved in cell survival
Authors: Naro Chiara , Barbagallo Federica , Chieffi Paolo , Bourgeois Cyril F. , Paronetto Maria Paola , Sette Claudio
Published: December 2013

NEK2 is a serine/threonine kinase that promotes centrosome splitting and ensures correct chromosome segregation during the G2/M phase of the cell cycle, through phosphorylation of specific substrates. Aberrant expression and activity of NEK2 in cancer cells lead to dysregulation of the centrosome cycle and aneuploidy. Thus, a tight regulation of NEK2 function is needed during cell cycle progression. In this study, we found that NEK2 localizes in the nucleus of cancer cells derived from several tissues. In particular, NEK2 co-localizes in splicing speckles with SRSF1 and SRSF2. Moreover, NEK2 interacts with several splicing factors and phosphorylates some of them, including the oncogenic SRSF1 protein. Overexpression of NEK2 induces phosphorylation of endogenous SR proteins and affects the splicing activity of SRSF1 toward reporter minigenes and endogenous targets, independently of SRPK1. Conversely, knockdown of NEK2, like that of SRSF1, induces expression of pro-apoptotic variants from SRSF1-target genes and sensitizes cells to apoptosis. Our results identify NEK2 as a novel splicing factor kinase and suggest that part of its oncogenic activity may be ascribed to its ability to modulate alternative splicing, a key step in gene expression regulation that is frequently altered in cancer cells.
Structural basis for the regulatory function of a complex zinc-binding domain in a replicative arterivirus helicase resembling a nonsense-mediated mRNA decay helicase
Authors: Deng Zengqin , Lehmann Kathleen C. , Li Xiaorong , Feng Chong , Wang Guoqiang , Zhang Qi , Qi Xiaoxuan , Yu Lin , Zhang Xingliang , Feng Wenhai , Wu Wei , Gong Peng , Tao Ye , Posthuma Clara C. , Snijder Eric J. , Gorbalenya Alexander E. , Chen Zhongzhou
Published: December 2013

All positive-stranded RNA viruses with genomes >∼7 kb encode helicases, which generally are poorly characterized. The core of the nidovirus superfamily 1 helicase (HEL1) is associated with a unique N-terminal zinc-binding domain (ZBD) that was previously implicated in helicase regulation, genome replication and subgenomic mRNA synthesis. The high-resolution structure of the arterivirus helicase (nsp10), alone and in complex with a polynucleotide substrate, now provides first insights into the structural basis for nidovirus helicase function. A previously uncharacterized domain 1B connects HEL1 domains 1A and 2A to a long linker of ZBD, which further consists of a novel RING-like module and treble-clef zinc finger, together coordinating three Zn atoms. On substrate binding, major conformational changes were evident outside the HEL1 domains, notably in domain 1B. Structural characterization, mutagenesis and biochemistry revealed that helicase activity depends on the extensive relay of interactions between the ZBD and HEL1 domains. The arterivirus helicase structurally resembles the cellular Upf1 helicase, suggesting that nidoviruses may also use their helicases for post-transcriptional quality control of their large RNA genomes.
SUMOylation of the polycomb group protein L3MBTL2 facilitates repression of its target genes
Authors: Stielow Christina , Stielow Bastian , Finkernagel Florian , Scharfe Maren , Jarek Michael , Suske Guntram
Published: December 2013

Lethal(3) malignant brain tumour like 2 (L3MBTL2) is an integral component of the polycomb repressive complex 1.6 (PRC1.6) and has been implicated in transcriptional repression and chromatin compaction. Here, we show that L3MBTL2 is modified by SUMO2/3 at lysine residues 675 and 700 close to the C-terminus. SUMOylation of L3MBTL2 neither affected its repressive activity in reporter gene assays nor it’s binding to histone tails in vitro. In order to analyse whether SUMOylation affects binding of L3MBTL2 to chromatin, we performed ChIP-Seq analysis with chromatin of wild-type HEK293 cells and with chromatin of HEK293 cells stably expressing either FLAG-tagged SUMOylation-competent or SUMOylation-defective L3MBTL2. Wild-type FLAG-L3MBTL2 and the SUMOylation-defective FLAG-L3MBTL2 K675/700R mutant essentially occupied the same sites as endogenous L3MBTL2 suggesting that SUMOylation of L3MBTL2 does not affect chromatin binding. However, a subset of L3MBTL2-target genes, particularly those with low L3MBTL2 occupancy including pro-inflammatory genes, was de-repressed in cells expressing the FLAG-L3MBTL2 K675/700R mutant. Finally, we provide evidence that SUMOylation of L3MBTL2 facilitates repression of these PRC1.6-target genes by balancing the local H2Aub1 levels established by the ubiquitinating enzyme RING2 and the de-ubiquitinating PR–DUB complex.
Structural insights into the unique single-stranded DNA-binding mode of Helicobacter pylori DprA
Authors: Wang Wei , Ding Jingjin , Zhang Ying , Hu Yonglin , Wang Da-Cheng
Published: December 2013

Natural transformation (NT) in bacteria is a complex process, including binding, uptake, transport and recombination of exogenous DNA into the chromosome, consequently generating genetic diversity and driving evolution. DNA processing protein A (DprA), which is distributed among virtually all bacterial species, is involved in binding to the internalized single-stranded DNA (ssDNA) and promoting the loading of RecA on ssDNA during NTs. Here we present the structures of DNA_processg_A (DprA) domain of the Helicobacter pylori DprA (HpDprA) and its complex with an ssDNA at 2.20 and 1.80 Å resolutions, respectively. The complex structure revealed for the first time how the conserved DprA domain binds to ssDNA. Based on structural comparisons and binding assays, a unique ssDNA-binding mode is proposed: the dimer of HpDprA binds to ssDNA through two small, positively charged binding pockets of the DprA domains with classical Rossmann folds and the key residue Arg52 is re-oriented to ‘open’ the pocket in order to accommodate one of the bases of ssDNA, thus enabling HpDprA to grasp substrate with high affinity. This mode is consistent with the oligomeric composition of the complex as shown by electrophoretic mobility-shift assays and static light scattering measurements, but differs from the direct polymeric complex of Streptococcus pneumoniae DprA–ssDNA.
The Dictyostelium discoideum RNA-dependent RNA polymerase RrpC silences the centromeric retrotransposon DIRS-1 post-transcriptionally and is required for the spreading of RNA silencing signals
Authors: Wiegand Stephan , Meier Doreen , Seehafer Carsten , Malicki Marek , Hofmann Patrick , Schmith Anika , Winckler Thomas , Földesi Balint , Boesler Benjamin , Nellen Wolfgang , Reimegård Johan , Käller Max , Hällman Jimmie , Emanuelsson Olof , Avesson Lotta , Söderbom Fredrik , Hammann Christian
Published: December 2013

Dictyostelium intermediate repeat sequence 1 (DIRS-1) is the founding member of a poorly characterized class of retrotransposable elements that contain inverse long terminal repeats and tyrosine recombinase instead of DDE-type integrase enzymes. In Dictyostelium discoideum, DIRS-1 forms clusters that adopt the function of centromeres, rendering tight retrotransposition control critical to maintaining chromosome integrity. We report that in deletion strains of the RNA-dependent RNA polymerase RrpC, full-length and shorter DIRS-1 messenger RNAs are strongly enriched. Shorter versions of a hitherto unknown long non-coding RNA in DIRS-1 antisense orientation are also enriched in rrpC– strains. Concurrent with the accumulation of long transcripts, the vast majority of small (21 mer) DIRS-1 RNAs vanish in rrpC– strains. RNASeq reveals an asymmetric distribution of the DIRS-1 small RNAs, both along DIRS-1 and with respect to sense and antisense orientation. We show that RrpC is required for post-transcriptional DIRS-1 silencing and also for spreading of RNA silencing signals. Finally, DIRS-1 mis-regulation in the absence of RrpC leads to retrotransposon mobilization. In summary, our data reveal RrpC as a key player in the silencing of centromeric retrotransposon DIRS-1. RrpC acts at the post-transcriptional level and is involved in spreading of RNA silencing signals, both in the 5′ and 3′ directions.
Improved seamless mutagenesis by recombineering using ccdB for counterselection
Authors: Wang Hailong , Bian Xiaoying , Xia Liqiu , Ding Xuezhi , Müller Rolf , Zhang Youming , Fu Jun , Stewart A. Francis
Published: December 2013

Recombineering, which is the use of homologous recombination for DNA engineering in Escherichia coli, usually uses antibiotic selection to identify the intended recombinant. When combined in a second step with counterselection using a small molecule toxin, seamless products can be obtained. Here, we report the advantages of a genetic strategy using CcdB as the counterselectable agent. Expression of CcdB is toxic to E. coli in the absence of the CcdA antidote so counterselection is initiated by the removal of CcdA expression. CcdB counterselection is robust and does not require titrations or experiment-to-experiment optimization. Because counterselection strategies necessarily differ according to the copy number of the target, we describe two variations. For multi-copy targets, we use two E. coli hosts so that counterselection is exerted by the transformation step that is needed to separate the recombined and unrecombined plasmids. For single copy targets, we put the ccdA gene onto the temperature-sensitive pSC101 Red expression plasmid so that counterselection is exerted by the standard temperature shift to remove the expression plasmid. To reduce unwanted intramolecular recombination, we also combined CcdB counterselection with Redα omission. These options improve the use of counterselection in recombineering with BACs, plasmids and the E. coli chromosome.