bluuebunny/crossref_metadata_2025 huggingface dataset:
Deactivation of metastable single-crystal silicon hyperdoped with sulfur
Authors: Simmons C. B. , Akey Austin J. , Krich Jacob J. , Sullivan Joseph T. , Recht Daniel , Aziz Michael J. , Buonassisi Tonio
Published: December 2013

Silicon supersaturated with sulfur by ion implantation and pulsed laser melting exhibits broadband optical absorption of photons with energies less than silicon's band gap. However, this metastable, hyperdoped material loses its ability to absorb sub-band gap light after subsequent thermal treatment. We explore this deactivation process through optical absorption and electronic transport measurements of sulfur-hyperdoped silicon subject to anneals at a range of durations and temperatures. The deactivation process is well described by the Johnson-Mehl-Avrami-Kolmogorov framework for the diffusion-mediated transformation of a metastable supersaturated solid solution, and we find that this transformation is characterized by an apparent activation energy of EA=1.7 ± 0.1 eV. Using this activation energy, the evolution of the optical and electronic properties for all anneal duration-temperature combinations collapse onto distinct curves as a function of the extent of reaction. We provide a mechanistic interpretation of this deactivation based on short-range thermally activated atomic movements of the dopants to form sulfur complexes.
Modeling aligning effect of polymer network in polymer stabilized nematic liquid crystals
Authors: Yang Deng-Ke , Cui Yue , Nemati Hossein , Zhou Xiaochen , Moheghi Alireza
Published: December 2013

We developed a phenomenological theory to describe the aligning field of polymer networks in polymer stabilized liquid crystals where sub-micron size polymer networks are phase separated from the liquid crystal in dispersion. The polymer networks are anisotropic and anchor the liquid crystals in their longitudinal direction. They inhibit the liquid crystals reorientation when external stimuli, such as electric field and temperature, are applied and reduce the relaxation time from distorted states. We model the effects produced by the polymer networks as an effective aligning field. We calculate the effective field as a function of the polymer network volume fraction and the lateral size of the network. The theory is compared with experimental results and good agreements were obtained. It is very useful in predicting how much polymer networks change the driving voltage and response time of liquid crystal devices.
Monolithic integration of optical grade GaAs on Si (001) substrates deeply patterned at a micron scale
Authors: Bietti Sergio , Scaccabarozzi Andrea , Frigeri Cesare , Bollani Monica , Bonera Emiliano , Falub Claudiu V. , von Känel Hans , Miglio Leo , Sanguinetti Stefano
Published: December 2013

Dense arrays of micrometric crystals, with areal filling up to 93%, are obtained by depositing GaAs in a mask-less molecular beam epitaxy process onto Si substrates. The substrates are patterned into tall, micron sized pillars. Faceted high aspect ratio GaAs crystals are achieved by tuning the Ga adatom for short surface diffusion lengths. The crystals exhibit bulk-like optical quality due to defect termination at the sidewalls. Simultaneously, the thermal strain induced by different thermal expansion parameters of GaAs and Si is fully relieved. This opens the route to thick film applications without crack formation and wafer bowing.
Conducting and insulating LaAlO3/SrTiO3 interfaces: A comparative surface photovoltage investigation
Authors: Beyreuther E. , Paparo D. , Thiessen A. , Grafström S. , Eng L. M.
Published: December 2013

Surface photovoltage (SPV) spectroscopy, which is a versatile method to analyze the energetic distribution of electronic defect states at surfaces and interfaces of wide-bandgap semiconductor (hetero-)structures, is applied to comparatively investigate heterostructures made of 5-unit-cell-thick LaAlO3 films grown either on TiO2- or on SrO-terminated SrTiO3. As shown in a number of experimental and theoretical investigations in the past, these two interfaces exhibit dramatically different properties with the first being conducting and the second insulating. Our present SPV investigation reveals clearly distinguishable interface defect state distributions for both configurations when interpreted within the framework of a classical semiconductor band scheme. Furthermore, bare SrTiO3 crystals with TiO2 or mixed SrO/TiO2 terminations show similar SPV spectra and transients as do LaAlO3-covered samples with the respective termination of the SrTiO3 substrate. This is in accordance with a number of recent works that stress the decisive role of SrTiO3 and the minor role of LaAlO3 with respect to the electronic interface properties.
Magnetic study of M-type doped barium hexaferrite nanocrystalline particles
Authors: Alsmadi A. M. , Bsoul I. , Mahmood S. H. , Alnawashi G. , Prokeš K. , Siemensmeyer K. , Klemke B. , Nakotte H.
Published: December 2013

Co-Ti and Ru-Ti substituted barium ferrite nanocrystalline particles BaFe12−2xCoxTixO19 with (0≤x≤1) and BaFe12−2xRuxTixO19 with (0≤x≤0.6) were prepared by ball milling method, and their magnetic properties and their temperature dependencies were studied. The zero-field-cooled (ZFC) and field-cooled (FC) processes were recorded at low magnetic fields and the ZFC curves displayed a broad peak at a temperature TM. In all samples under investigation, a clear irreversibility between the ZFC and FC curves was observed below room temperature, and this irreversibility disappeared above room temperature. These results were discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The resistivity data showed some kind of a transition from insulator to perfect insulator around TM. At 2 K, the saturation magnetization slightly decreased and the coercivity dropped dramatically with increasing the Co-Ti concentration x. With Ru-Ti substitution, the saturation magnetization showed small variations, while the coercivity decreased monotonically, recording a reduction of about 73% at x = 0.6. These results were discussed in light of the single ion anisotropy model and the cationic distributions based on previously reported neutron diffraction data for the CoTi substituted system, and the results of our Mössbauer spectroscopy data for the RuTi substituted system.
A comparable study of structural and electrical transport properties of Al and Cu nanowires using first-principle calculations
Authors: Gao N. , Li J. C. , Jiang Q.
Published: December 2013

The structural and quantum transport properties of Al and Cu nanowires with diameters up to 3.6 nm are studied using density functional theory combined with Landauer formalism. Contrary to the classical electronic behavior, the conductance of Al wires is larger than that of Cu. This is mainly attributed to the larger contribution of conductance channels from Al-3p, which is determined by the chemical nature. Meanwhile, the stronger axial contraction of Al wires plays a minor role to conductance. This makes Al wires possible candidate interconnects in integrated circuits.
A method to measure nanomechanical properties of biological objects
Authors: Ploscariu Nicoleta , Szoszkiewicz Robert
Published: December 2013

We postulate that one will be able to quantitatively infer changes in the mechanical properties of proteins, cells, and other biological objects (BO) by measuring the shifts of several thermally excited resonance frequencies of atomic force microscopy cantilevers in contact with BOs. Here, we provide a method to extract spring constants and molecular damping factors of BOs in biologically relevant phosphate buffered saline medium and using compliant AFM cantilevers with a small aspect ratio (a ratio of length to width).
Ignition and extinction phenomena in helium micro hollow cathode discharges
Authors: Kulsreshath M. K. , Sadeghi N. , Schwaederle L. , Dufour T. , Overzet L. J. , Lefaucheux P. , Dussart R.
Published: December 2013

Micro hollow cathode discharges (MHCD) were produced using 250 μm thick dielectric layer of alumina sandwiched between two nickel electrodes of 8 μm thickness. A through cavity at the center of the chip was formed by laser drilling technique. MHCD with a diameter of few hundreds of micrometers allowed us to generate direct current discharges in helium at up to atmospheric pressure. A slowly varying ramped voltage generator was used to study the ignition and the extinction periods of the microdischarges. The analysis was performed by using electrical characterisation of the V-I behaviour and the measurement of He*(3S1) metastable atoms density by tunable diode laser spectroscopy. At the ignition of the microdischarges, 2 μs long current peak as high as 24 mA was observed, sometimes followed by low amplitude damped oscillations. At helium pressure above 400 Torr, an oscillatory behaviour of the discharge current was observed just before the extinction of the microdischarges. The same type of instability in the extinction period at high pressure also appeared on the density of He*(3S1) metastable atoms, but delayed by a few μs relative to the current oscillations. Metastable atoms thus cannot be at the origin of the generation of the observed instabilities.
Effect of annealing on SiOx-TiO2 axial heterostructure nanowires and improved photodetection
Authors: Dhar J. C. , Mondal A. , Singh N. K. , Chakrabartty S. , Bhattacharyya A. , Chattopadhyay K. K.
Published: December 2013

Glancing angle deposition technique has been used to synthesize the axial heterostructure SiOx-TiO2 nanowires (NWs) on the Si substrate. The field emission gun scanning electron microscope image shows the formation of perpendicular NWs on Si substrate. A typical transmission electron microscope image confirms the heterostructure NW which consists of SiOx of length ∼130 nm and TiO2 of length ∼170 nm. The amorphous NWs transformed to polycrystalline nature after annealing. The trap assisted radiative recombination process is absent for the annealed NWs. An averagely 1.1 fold enhanced photoabsorption was exhibited by the annealed NWs in the 200–350 nm region and 1.5 fold in the 500–850 nm region. The leakage current (2.6 × 10−8 A/cm2 at −0.5 V) significantly reduced for annealed NWs device. A maximum 1.4 × 103 times enlarged photodetection has been observed for annealed device.
Third order nonlinear optical properties of bismuth zinc borate glasses
Authors: Shanmugavelu B. , Ravi Kanth Kumar V. V. , Kuladeep R. , Narayana Rao D.
Published: December 2013

Third order nonlinear optical characterization of bismuth zinc borate glasses are reported here using different laser pulse durations. Bismuth zinc borate glasses with compositions xBi2O3-30ZnO-(70-x) B2O3 (where x = 30, 35, 40, and 45 mol. %) have been prepared by melt quenching method. These glasses were characterized by Raman, UV-Vis absorption, and Z scan measurements. Raman and UV-Vis spectroscopic results indicate that non-bridging oxygens increase with increase of bismuth content in the glass. Nonlinear absorption and refraction behavior in the nanosecond (ns), picosecond (ps), and femtosecond (fs) time domains were studied in detail. Strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with both ps and fs excitations. In the case of ns pulse excitations, TPA and free-carrier absorption processes contribute for the nonlinear absorption. Two-photon absorption coefficient (β) and the absorption cross section due to free carriers (σe) are estimated by theoretical fit of the open aperture Z-scan measurements and found to be dependent on the amount of bismuth oxide in the glass composition. In both ns and fs regimes the sign and magnitude of the third order nonlinearity are evaluated, and the optical limiting characteristics are also reported.
Effects of flux additives on the characteristics of Y2.95Al5O12:0.05Ce3+ phosphor: Particle growth mechanism and luminescence
Authors: Chiang Chung-Hao , Liu Te-Hsing , Lin Han-Yu , Kuo Hung-Yi , Chu Sheng-Yuan
Published: December 2013

The dependence of the amount of the BaF2 flux additive on the luminescence of Y2.95Al5O12:0.05Ce3+ phosphors was investigated. The integrated emission intensity of Y2.95Al5O12:0.05Ce3+ prepared without the flux was enhanced by 29% with the addition of BaF2 flux at the optimum amount of 6 wt. %. Such an enhancement can be attributed to the purer phase of Y3Al5O12 and the morphology change from the irregular shape to spherical shape with the smoother surface due to the flux. The morphology and luminescence of Y2.95Al5O12:0.05Ce3+ prepared with the 6 wt. % BaF2 flux additive (Sample II) were further compared with those of Y2.95Al5O12:0.05Ce3+ prepared with the 7 wt. % H3BO3 flux additive (Sample I). The particle size, particle shape, and integrated emission intensity (λex = 450 nm) of the former were found to be larger, more regular, and 6% higher than those of the latter. The difference in the morphology of Samples I and II, which led to the difference in the emission intensity and the external quantum efficiency, were well explained by the particle growth mechanism.
Selective excitation of spin resonance in orthoferrite PrFeO3 with impulsive polarized terahertz radiation
Authors: Song Gaibei , Jiang Junjie , Wang Xinyan , Jin Zuanming , Lin Xian , Ma Guohong , Cao Shixun
Published: December 2013

Single cycle terahertz (THz) pulses were employed to excite coherent spin waves in (110)-oriented PrFeO3 single crystal. The free induction decay radiations at frequency of 0.34 THz (quasi-ferromagnetic mode, FM mode) and 0.41 THz (quasi-antiferromagnetic mode, AFM mode) were observed arising from the coupling of magnetic moment with the impulsive magnetic field of polarized terahertz radiation. These two spin modes in PrFeO3 can be excited and modulated by the magnetic field of THz pulse with a specific polarization with respect to the crystal axis. The extracted complex dielectric permittivity and magnetic permeability dispersion in THz range suggest a higher efficiency of energy transfer from the impulsive THz pulse into the AFM than the FM spin system.
Graphene induced spectral tuning of metamaterial absorbers at mid-infrared frequencies
Authors: Vasić Borislav , Gajić Radoš
Published: December 2013

In order to expand bandwidth of the resonant metamaterial absorbers, we investigate their spectral tuning at mid-infrared frequencies using graphene. We consider the absorbers with square metallic patches, cross-shaped resonators, and split ring resonators. Their resonances can be blue shifted by increasing graphene conductivity. Among these structures, split ring resonators produce the largest electric fields enabling huge spectral shifts, almost 30%. In addition, the tuning can be used for switching the mid-infrared waves at the absorber resonance. Here, the reflectance is zero, so even a small spectral shift of the resonance results in a huge increase of the reflectance.
Nanoscale structural evolution of electrically driven insulator to metal transition in vanadium dioxide
Authors: Freeman Eugene , Stone Greg , Shukla Nikhil , Paik Hanjong , Moyer Jarrett A. , Cai Zhonghou , Wen Haidan , Engel-Herbert Roman , Schlom Darrell G. , Gopalan Venkatraman , Datta Suman
Published: December 2013

The structural evolution of tensile strained vanadium dioxide thin films was examined across the electrically driven insulator-to-metal transition by nanoscale hard X-ray diffraction. A metallic filament with rutile (R) structure was found to be the dominant conduction pathway for an electrically driven transition, while the majority of the channel area remained in the monoclinic M1 phase. The filament dimensions were estimated using simultaneous electrical probing and nanoscale X-ray diffraction. Analysis revealed that the width of the conducting channel can be tuned externally using resistive loads in series, enabling the M1/R phase ratio in the phase coexistence regime to be tuned.
Molecular dynamics simulations of disjoining pressure effect in ultra-thin water film on a metal surface
Authors: Hu H. , Sun Y.
Published: December 2013

Molecular dynamics (MD) simulations are used to examine the disjoining pressure effect of a water thin film adsorbed on a metal surface. The model was validated against experiments and verified against previous MD simulations. The variation of vapor pressure with film thickness was examined for a water thin film adsorbed on a gold surface. The results agree well with the classic disjoining pressure theory without surface charges and show that liquid layering does not affect disjoining pressure. However, surface charges of the gold substrate enhance the disjoining pressure of the water thin film, consistent with experimental evidences for polar liquids.
Forecasting hourly global solar irradiation using simple non-seasonal models
Authors: Pacurar Angel , Stefu Nicoleta , Mares Oana , Paulescu Eugenia , Calinoiu Delia , Pop Nicolina , Boata Remus , Gravila Paul , Paulescu Marius
Published: December 2013

The solar radiation on ground level has cyclic variations due to the rotation and revolution movements of the Earth. This deterministic variation is modulated by weather, which superimposes a random component. The subject of this paper is the forecasting of hourly global solar irradiation using simple statistical models, without exogenous inputs. The study is conducted based on data recorded at Timisoara, Romania, during 2009 and 2010. Since the time series of hourly solar irradiation exhibits a natural seasonality at frequency of 1/24 h, a seasonal decomposition of data is required. First, results referring to the dynamic properties of the seasonal indices are discussed. Second, a comparison of the accuracy of five non-seasonal models applied to seasonally adjusted data was performed. Overall results demonstrate that the random walk model performs best. Third, an adaptive procedure to fit the model parameters (in which the model parameters are refitted for every day) was tested against the standard “frozen parameters” approach (in which the model parameters are obtained by a onetime fitting of the equations on historical data and then used in every forecast in the future). The results show that the proposed adaptive procedure leads to better performance than the frozen parameter approach.
SiGe quantum dots for fast hole spin Rabi oscillations
Authors: Ares N. , Katsaros G. , Golovach V. N. , Zhang J. J. , Prager A. , Glazman L. I. , Schmidt O. G. , De Franceschi S.
Published: December 2013

We report on hole g-factor measurements in three terminal SiGe self-assembled quantum dot devices with a top gate electrode positioned very close to the nanostructure. Measurements of both the perpendicular as well as the parallel g-factor reveal significant changes for a small modulation of the top gate voltage. From the observed modulations, we estimate that, for realistic experimental conditions, hole spins can be electrically manipulated with Rabi frequencies in the order of 100 MHz. This work emphasises the potential of hole-based nano-devices for efficient spin manipulation by means of the g-tensor modulation technique.
Robust relativistic electron mirrors in laser wakefields for enhanced Thomson backscattering
Authors: Mu Jie , Li Fei-Yu , Zeng Ming , Chen Min , Sheng Zheng-Ming , Zhang Jie
Published: December 2013

By adopting an up-ramp density profile, we propose to generate relativistic electron mirrors from laser-driven underdense plasma waves, which are insensitive to finite thermal temperature within a certain range. Along the density ramp, premature wavebreaking due to thermal effects is shown to be well mitigated. Under sufficiently high amplitudes of wake excitation, overcritical dense electron mirrors can pile up when approaching the end of the up-ramp. The consequent mirror speed can be stably driven to the group velocity of the laser propagating in a corresponding uniform plasma. Compared with using purely uniform but thermal plasmas, the present thermal-insensitive mirrors can provide enhanced scattering efficiency and spectral upshift for a counter-propagating probe pulse. These observations are confirmed by multi-dimensional particle-in-cell simulations.
A microelectromechanical system for thermomechanical testing of nanostructures
Authors: Chang Tzu-Hsuan , Zhu Yong
Published: December 2013

We report an integrated microelectromechanical system (MEMS) with an on-chip heater for in-situ mechanical testing of nanostructures from room to elevated temperatures. Multiphysics simulation is used to predict the temperature distribution in air and vacuum conditions. The temperature simulation in air agrees well with the measurement based on Raman spectroscopy. Mechanical testing of single crystalline silicon nanowires is carried out to investigate the brittle-to-ductile transition, demonstrating the efficacy of the MEMS stage. The stage reported here could be applied to investigate the temperature effect on mechanical properties at the nanoscale.
Atomic layer deposition of platinum with enhanced nucleation and coalescence by trimethylaluminum pre-pulsing
Authors: Hwang Yoontae , Nguyen Binh-Minh , Dayeh Shadi A.
Published: December 2013

Conformal coating of metal layers on three-dimensional structures is essential for advanced electronic devices such as storage elements, transistors, and sensors. The quality of atomic layer deposited platinum on oxide surfaces was enhanced by adding pre-deposition pulses of trimethylaluminum (TMA) for improved wetting. With an optimal number of TMA pre-pulses, a 6 nm thick Pt film was perfectly coalesced in contrast to only Pt island formation without TMA pre-pulses. A Pt gate all around Ge/Si nanowire field effect transistor was realized highlighting the potential of this approach for efficient deposition of Pt on 3D nanoelectronic devices.
Tunable metamaterials based on voltage controlled strong coupling
Authors: Benz Alexander , Montaño Inès , Klem John F. , Brener Igal
Published: December 2013

We present the design, fabrication, and realization of an electrically tunable metamaterial operating in the mid-infrared spectral range. Our devices combine intersubband transitions in semiconductor quantum-wells with planar metamaterials and operate in the strong light-matter coupling regime. The resonance frequency of the intersubband transition can be controlled by an external bias relative to the fixed metamaterial resonance. This allows us to switch dynamically from an uncoupled to a strongly coupled system and thereby to shift the eigenfrequency of the upper polariton branch by 2.5 THz (corresponding to 8% of the center frequency or one full linewidth) with a bias of 5 V.
The effects of Co-Ti co-doping on the magnetic, electrical, and magnetodielectric behaviors of M-type barium hexaferrites
Authors: Guan Yujie , Lin Yuanbin , Zou Liangying , Miao Qing , Zeng Min , Liu Zhongwu , Gao Xingsen , Liu Junming
Published: December 2013

Magnetic, electrical and magnetodielectric properties have been studied in Co-Ti co-doped M-type hexaferrite BaCoxTixFe12-2xO19 (x = 0 ∼ 4). With the incorporation of Co-Ti, both their ferromagnetic magnetization and coercivity have been greatly changed. The temperature dependent magnetization curve shows a apparent hump at around 420 K, likely in association with more complicated cycloidal spin ordering, which is closely related to ferroelectric polarization. Interestingly, a significantly enhancement in resistivity (∼3 orders in magnitude) can be obtained in co-doped samples (x > 2), which is beneficial for magnetoelectric properties. The magnetoelectric effect were examined by dielectric tunibility under external magnetic field, which shows apparent tunability up to ∼−3% for sample with x = 2 at 1T magnetic field, further supporting it is a room temperature single phase mutliferroic material.
Electrical transport properties of Si-doped hexagonal boron nitride epilayers
Authors: Majety S. , Doan T. C. , Li J. , Lin J. Y. , Jiang H. X.
Published: December 2013

The suitability of Si as an n-type dopant in hexagonal boron nitride (hBN) wide bandgap semiconductor has been investigated. Si doped hBN epilayers were grown via in-situ Si doping by metal organic chemical vapor deposition technique. Hall effect measurements revealed that Si doped hBN epilayers exhibit n-type conduction at high temperatures (T > 800 K) with an in-plane resistivity of ∼12 Ω·cm, electron mobility of μ ∼ 48 cm2/V·s and concentration of n ∼ 1 × 1016 cm−3. Temperature dependent resistivity results yielded a Si energy level in hBN of about 1.2 eV, which is consistent with a previously calculated value for Si substitutionally incorporated into the B sites in hBN. The results therefore indicate that Si is not a suitable dopant for hBN for room temperature device applications.
Enhancement in performance of polycarbazole-graphene nanocomposite Schottky diode
Authors: Pandey Rajiv K. , Singh Arun Kumar , Prakash Rajiv
Published: December 2013

We report formation of polycarbazole (PCz)–graphene nanocomposite over indium tin oxide (ITO) coated glass substrate using electrochemical technique for fabrication of high performance Schottky diodes. The synthesized nanocomposite is characterized before fabrication of devices for confirmation of uniform distribution of graphene nanosheets in the polymer matrix. Pure PCz and PCz-graphene nanocomposites based Schottky diodes are fabricated of configuration Al/PCz/ITO and Al/PCz-graphene nanocomposite/ITO, respectively. The current density–voltage (J-V) characteristics and diode performance parameters (such as the ideality factor, barrier height, and reverse saturation current density) are compared under ambient condition. Al/PCz-graphene nanocomposite/ITO device exhibits better ideality factor in comparison to the device formed using pure PCz. It is also observed that the Al/PCz-graphene nanocomposite/ITO device shows large forward current density and low turn on voltage in comparison to Al/PCz/ITO device.
Band gap engineering of In2O3 by alloying with Tl2O3
Authors: Scanlon David O. , Regoutz Anna , Egdell Russell G. , Morgan David J. , Watson Graeme W.
Published: December 2013

Efficient modulation of the bandgap of In2O3 will open up a route to improved electronic properties. We demonstrate using ab initio calculations that Tl incorporation into In2O3 reduces the band gap and confirm that narrowing of the gap is observed by X-ray photoemission spectroscopy on ceramic surfaces. Incorporation of Tl does not break the symmetry of the allowed optical transitions, meaning that the doped thin films should retain optical transparency in the visible region, in combination with a lowering of the conduction band effective mass. We propose that Tl-doping may be an efficient way to increase the dopability and carrier mobility of In2O3.
Nicotine exploits a COPI-mediated process for chaperone-mediated up-regulation of its receptors
Authors: Henderson Brandon J. , Srinivasan Rahul , Nichols Weston A. , Dilworth Crystal N. , Gutierrez Diana F. , Mackey Elisha D.W. , McKinney Sheri , Drenan Ryan M. , Richards Christopher I. , Lester Henry A.
Published: December 2013

Chronic exposure to nicotine up-regulates high sensitivity nicotinic acetylcholine receptors (nAChRs) in the brain. This up-regulation partially underlies addiction and may also contribute to protection against Parkinson’s disease. nAChRs containing the α6 subunit (α6* nAChRs) are expressed in neurons in several brain regions, but comparatively little is known about the effect of chronic nicotine on these nAChRs. We report here that nicotine up-regulates α6* nAChRs in several mouse brain regions (substantia nigra pars compacta, ventral tegmental area, medial habenula, and superior colliculus) and in neuroblastoma 2a cells. We present evidence that a coat protein complex I (COPI)-mediated process mediates this up-regulation of α6* or α4* nAChRs but does not participate in basal trafficking. We show that α6β2β3 nAChR up-regulation is prevented by mutating a putative COPI-binding motif in the β3 subunit or by inhibiting COPI. Similarly, a COPI-dependent process is required for up-regulation of α4β2 nAChRs by chronic nicotine but not for basal trafficking. Mutation of the putative COPI-binding motif or inhibition of COPI also results in reduced normalized Förster resonance energy transfer between α6β2β3 nAChRs and εCOP subunits. The discovery that nicotine exploits a COPI-dependent process to chaperone high sensitivity nAChRs is novel and suggests that this may be a common mechanism in the up-regulation of nAChRs in response to chronic nicotine.
Cross ratio coordinates for the deformation spaces of a marked Möbius group
Authors: Yamamoto Kimiyo , Taniguchi Masahiko
Published: December 2013

We introduce a new kind of coordinate systems for the deformation space of a finitely generated free Möbius group by using cross ratio functions induced by the fixed points of Möbius transformations. As an application, we give a new complete distance on the Schottky space by using such functions, which is not greater than the Teichmüller distance.
The PACT domain, a conserved centrosomal targeting motif in the coiled‐coil proteins AKAP450 and pericentrin
Authors: Gillingham Alison K , Munro Sean
Published: December 2013

AKAP450 (also known as AKAP350, CG‐NAP or Hyperion) and pericentrin are large coiled‐coil proteins found in mammalian centrosomes that serve to recruit structural and regulatory components including dynein and protein kinase A. We find that these proteins share a well conserved 90 amino acid domain near their C‐termini that is also found in coiled‐coil proteins of unknown function from Drosophila and fission yeast. Fusion of the C‐terminal region from either protein to a reporter protein confers a centrosomal localization, and overexpression of the domain from AKAP450 displaces endogenous pericentrin, suggesting recruitment to a shared site. When isolated from transfected cells the C‐terminal domain of AKAP450 was associated with calmodulin, suggesting that this protein could contribute to centrosome assembly.
Brain plasmin enhances APP α‐cleavage and Aβ degradation and is reduced in Alzheimer's disease brains
Authors: Ledesma Maria Dolores , Da Silva Jorge Santos , Crassaerts Katleen , Delacourte Andre , De Strooper Bart , Dotti Carlos G
Published: December 2013

The proteolytic processing of amyloid precursor protein (APP) has been linked to sphingolipid‐cholesterol microdomains (rafts). However, the raft proteases that may be involved in APP cleavage have not yet been identified. In this work we present evidence that the protease plasmin is restricted to rafts of cultured hippocampal neurons. We also show that plasmin increases the processing of human APP preferentially at the α‐cleavage site, and efficiently degrades secreted amyloidogenic and non‐amyloidogenic APP fragments. These results suggest that brain plasmin plays a preventive role in APP amyloidogenesis. Consistently, we show that brain tissue from Alzheimer's disease patients contains reduced levels of plasmin, implying that plasmin downregulation may cause amyloid plaque deposition accompanying sporadic Alzheimer's disease.
The yeast mitotic cyclin Clb2 cannot substitute for S phase cyclins in replication origin firing
Authors: Donaldson Anne D
Published: December 2013

Cyclin‐dependent kinases (CDKs) drive the cell cycle, central to which is the accurate control of chromosome replication. In Saccharomyces cerevisiae, six closely related B‐type cyclins (Clb1–6) drive the events of S phase and mitosis. Either Clb5 or Clb6 can activate early‐firing replication origins, whereas only Clb5 can activate late origins. Clb1–4 are expressed later in the cell cycle. Whether Clb cyclins differ only in timing of expression, or else impart different kinase specificities is under ongoing investigation. This study shows that the expression of Clb2 during S phase in cells lacking Clb5 failed to rescue late origin activation. Early expression of Clb2 in cells lacking both Clb5 and Clb6 did not activate early origins on schedule to restore the correct S phase entry time. Therefore, Clb2 cannot drive timely activation of either early or late replication origins, demonstrating that Clb2‐directed CDK has a specificity distinct from that driven by Clb5 and Clb6.
Mapping of a human centromere onto the DNA by topoisomerase II cleavage
Authors: Floridia Giovanna , Zatterale Adriana , Zuffardi Orsetta , Tyler‐Smith Chris
Published: December 2013

We have mapped the positions of topoisomerase II binding sites at the centromere of the human Y chromosome using etoposide‐mediated DNA cleavage. A single region of cleavage is seen at normal centromeres, spanning ∼50 kb within the centromeric alphoid array, but this pattern is abolished at two inactive centromeres. It therefore provides a marker for the position of the active centromere. Although the underlying centromeric DNA structure is variable, the position of the centromere measured in this way is fixed relative to the Yp edge of the array, and has retained the same position for >100 000 years.
Messenger RNAs that are not synthesized by RNA polymerase II can be 3′ end cleaved and polyadenylated
Authors: Fodor Ervin , Mikulasova Andrea , Mingay Louise J , Poon Leo L M , Brownlee George G
Published: December 2013

The poly(A) tail of influenza virus mRNAs is synthesized by the viral RNA polymerase by reiterative copying of a U5–7 sequence near the 5′ end of the viral RNA (vRNA) template. We have engineered a vRNA molecule by replacing its viral U6 poly(A) site with a negative‐sense eukaryotic polyadenylation signal. The vRNA was transcribed by the viral RNA polymerase and the transcription product was processed by the cellular 3′ end processing machinery in vivo. According to the current model, 3′ end processing of eukaryotic pre‐mRNAs is coupled to cellular RNA polymerase II (pol II) transcription; thus only RNAs synthesized by pol II are believed to be polyadenylated efficiently. Our results show that the cellular polyadenylation machinery is nevertheless able to recognize and process RNA transcripts that are not synthesized by pol II, indicating that synthesis by pol II is not an absolute requirement for 3′ end processing in vivo.
The murine SNF5/INI1 chromatin remodeling factor is essential for embryonic development and tumor suppression
Authors: Klochendler‐Yeivin Agnes , Fiette Laurence , Barra Jaqueline , Muchardt Christian , Babinet Charles , Yaniv Moshe
Published: December 2013

The assembly of eukaryotic DNA into nucleosomes and derived higher order structures constitutes a barrier for transcription, replication and repair. A number of chromatin remodeling complexes, as well as histone acetylation, were shown to facilitate gene activation. To investigate the function of two closely related mammalian SWI/SNF complexes in vivo, we inactivated the murine SNF5/INI1 gene, a common subunit of these two complexes. Mice lacking SNF5 protein stop developing at the peri‐implantation stage, showing that the SWI/SNF complex is essential for early development and viability of early embryonic cells. Furthermore, heterozygous mice develop nervous system and soft tissue sarcomas. In these tumors the wild‐type allele was lost, providing further evidence that SNF5 functions as a tumor suppressor gene in certain cell types.
Phosphorylation disrupts the central helix in Op18/stathmin and suppresses binding to tubulin
Authors: Steinmetz Michel O , Jahnke Wolfgang , Towbin Harry , García‐Echeverría Carlos , Voshol Hans , Müller Dieter , van Oostrum Jan
Published: December 2013

Protein phosphorylation represents a ubiquitous control mechanism in living cells. The structural prerequisites and consequences of this important post‐translational modification, however, are poorly understood. Oncoprotein 18/stathmin (Op18) is a globally disordered phosphoprotein that is involved in the regulation of the microtubule (MT) filament system. Here we document that phosphorylation of Ser63, which is located within a helix initiation site in Op18, disrupts the transiently formed amphipathic helix. The phosphoryl group reduces tubulin binding 10‐fold and suppresses the MT polymerization inhibition activity of Op18's C‐terminal domain. Op18 represents an example where phosphorylation occurs within a regular secondary structural element. Together, our findings have implications for the prediction of phosphorylation sites and give insights into the molecular behavior of a globally disordered protein.
Thyroid hormone regulates the obesity gene tub
Authors: Koritschoner Nicolás P , Alvarez‐Dolado Manuel , Kurz Steffen M , Heikenwälder Mathias F , Hacker Christine , Vogel Frank , Muñoz Alberto , Zenke Martin
Published: December 2013

Thyroid hormone T3/T4 is a major regulator of energy metabolism in vertebrates, and defects in thyroid status are frequently associated with changes in body weight. It is demonstrated here that thyroid hormone regulates in vivo and in vitro the tub gene, which when mutated in tubby mice causes obesity, insulin resistance and sensory deficits. Hypothyroidism in rats altered tub mRNA and protein in discrete brain areas. These changes could be attributed to thyroid hormone deficiency since T3/T4 treatment restored normal tub expression. T3 also upregulated tub mRNA within 4–6 h in neuronal cells in culture, suggesting that T3 is a positive regulator of tub gene expression. Thus, these results establish a novel pathway of T3 action and provide an important molecular link between thyroid status and the tubby‐associated syndrome.
Sec‐dependent membrane protein insertion: sequential interaction of nascent FtsQ with SecY and YidC
Authors: Urbanus Malene L , Scotti Pier A , Fröderberg Linda , Sääf Annika , de Gier Jan‐Willem L , Brunner Josef , Samuelson James C , Dalbey Ross E , Oudega Bauke , Luirink Joen
Published: December 2013

Recent studies identified YidC as a novel membrane factor that may play a key role in membrane insertion of inner membrane proteins (IMPs), both in conjunction with the Sec‐translocase and as a separate entity. Here, we show that the type II IMP FtsQ requires both the translocase and, to a lesser extent, YidC in vivo. Using photo‐crosslinking we demonstrate that the transmembrane (TM) domain of the nascent IMP FtsQ inserts into the membrane close to SecY and lipids, and moves to a combined YidC/lipid environment upon elongation. These data are consistent with a crucial role for YidC in the lateral transfer of TM domains from the Sec translocase into the lipid bilayer.
Two cyclophilin A homologs with shared and distinct functions important for growth and virulence ofCryptococcus neoformans
Authors: Wang Ping , Cardenas Maria E , Cox Gary M , Perfect John R , Heitman Joseph
Published: December 2013

Cyclophilin A is the target of the immunosuppressant cyclosporin A (CsA) and is encoded by a single unique gene conserved from yeast to humans. In the pathogenic fungusCryptococcus neoformans, two homologous linked genes,CPA1andCPA2, were found to encode two conserved cyclophilin A proteins. In contrast toSaccharomyces cerevisiae, in which cyclophilin A mutations confer CsA resistance but few other phenotypes, cyclophilin A mutations conferred dramatic phenotypes inC. neoformans. The Cpa1 and Cpa2 cyclophilin A proteins play a shared role in cell growth, mating, virulence and CsA toxicity. The Cpa1 and Cpa2 proteins also have divergent functions.cpa1mutants are inviable at 39°C and attenuated for virulence, whereascpa2mutants are viable at 39°C and fully virulent.cpa1 cpa2double mutants exhibited synthetic defects in growth and virulence. Cyclophilin A active site mutants restored growth ofcpa1 cpa2mutants at ambient but not at higher temperatures, suggesting that the prolyl isomerase activity of cyclophilin A has anin vivofunction.
An artificial transcription activator mimics the genome‐wide properties of the yeast Pdr1 transcription factor
Authors: Devaux Frédéric , Marc Philippe , Bouchoux Céline , Delaveau Thierry , Hikkel Immrich , Potier Marie‐Claude , Jacq Claude
Published: December 2013

We analysed the genome‐wide regulatory properties of an artificial transcription activator in which the DNA‐binding domain of the yeast transcription factor, Pdr1, was fused to the activation domain of Gal4 (Pdr1*GAD). This Pdr1*GAD chimera was put under the control of the inducible GAL1 promoter. DNA microarray analyses showed that all the target genes upregulated by the well‐studied native gain‐of‐function Pdr1‐3 mutant were similarly activated by the chimerical factor Pdr1*GAD upon galactose induction. Additionally, this kinetic approach led us not only to confirm previously published targets, but also to define a hierarchy among members of the Pdr1 regulon. Our observations prove, for the first time at the complete genome level, that the DNA‐binding domain of Pdr1 is sufficient to guide its specificity. We propose that this approach could be useful for the study of new transcription factors identified in silico from sequenced organisms. Complete data are available at www.biologie.ens.fr/yeast‐publi.html.
Angiostatin effects on endothelial cells mediated by ceramide and RhoA
Authors: Gupta Nalin , Nodzenski Edwardine , Khodarev Nikolai N , Yu Jianqing , Khorasani Leila , Beckett Michael A , Kufe Donald W , Weichselbaum Ralph R
Published: December 2013

Angiostatin is a cleavage product of plasminogen that has anti‐angiogenic properties. We investigated whether the effects of angiostatin on endothelial cells are mediated by ceramide, a lipid implicated in endothelial cell signaling. Our results demonstrate that angiostatin produces a transient increase in ceramide that correlates with actin stress fiber reorganization, detachment and death. DNA array expression analysis performed on ceramide‐treated human endothelial cells demonstrated induction of certain genes involved in cytoskeleton organization. Specifically, we report that treatment with angiostatin or ceramide results in the activation of RhoA, an important effector of cytoskeletal structure. We also show that treatment of endothelial cells with the antioxidant N‐acetylcysteine abrogates morphological changes and cytotoxic effects of treatment with angiostatin or ceramide. These findings support a model in which angiostatin induces a transient rise in ceramide, RhoA activation and free radical production.
Intermittent recruitment and exploitation pulse underlying temporal variability in a demersal deep-water fish population
Authors: Bergstad Odd Aksel , Øverbø Hansen Hege , Jørgensen Terje
Published: December 2013

Recent temporal variability in abundance, size and age structure, distribution, and recruitment of the Skagerrak population of the commercially exploited long-lived deep-water demersal macrourid roundnose grenadier (Coryphaenoides rupestris) appeared strongly influenced by a combined effect of a single pronounced recruitment incident in the early 1990s and a subsequent pulse in targeted exploitation a decade later. Fishery-independent annual survey data showed that probably only one strong year class occurred across an almost three-decade period, 1985–present. Recruitment studies in deep-water fish remain few, yet rarity of successful recruitment events may have to be added to life-history characteristics already recognized as limiting the potential for sustainable harvesting of deep-water demersal fish, i.e. extended lifespan, slow growth, high age at first maturity, and low fecundity.
Detection of crayfish plague spores in large freshwater systems
Authors: Strand David A. , Jussila Japo , Johnsen Stein I. , Viljamaa‐Dirks Satu , Edsman Lennart , Wiik‐Nielsen Jannicke , Viljugrein Hildegunn , Engdahl Frederik , Vrålstad Trude
Published: December 2013

Indigenous European freshwater crayfish (ICS) are threatened due to invasive North American freshwater crayfish that are natural carriers of Aphanomyces astaci which causes crayfish plague. Infectious A. astaci zoospores are released from carrier crayfish, but little is known about the spore abundance in water systems that either host non‐indigenous crayfish species (NICS) or experience crayfish plague outbreaks. We tested two large‐scale filtering approaches to generate new insight about the abundance and dynamics of A. astaci spores in natural freshwater systems.

Depth filtration (DF) and dead‐end ultrafiltration (DEUF) followed by A. astaci‐specific quantitative real‐time PCR was used to monitor A. astaci spores in large Nordic lakes hosting A. astaci‐positive Pacifastacus leniusculus, the dominating NICS in Northern Europe. Crayfish and water were sampled together to compare the A. astaci pathogen load in tissues, A. astaci prevalence in the population and the corresponding spore density in water. Samples were also obtained from a river where indigenous noble crayfish suffered from acute crayfish plague. The sensitivity of the filtering techniques was evaluated using simulation of random events.

We detected A. astaci spores in lakes hosting NICS with both filtering methods but predominantly at concentrations below c. 1 spore L−1. We found a significant positive association between A. astaci spore density in water, the A. astaci prevalence in the corresponding NICS population and the tissue pathogen load. Water from the river with the ongoing crayfish plague outbreak contained overall c. 43 times more spores L−1 than water hosting NICS. Both filtering techniques proved suitable and equally sensitive, but simulations suggest that an optimization of the spore recovery could yield a 10‐fold increase in the DEUF‐method sensitivity.

Synthesis and application. Our study demonstrates a low amount of pathogen spores are present in aquatic environments with non‐indigenous crayfish species, emphasizing the need for large‐volume filtering techniques for successful detection. The approach can be used for risk assessments and to improve conservation and management strategies of crayfish in Europe. Applications of this method include targeted disease surveillance, habitat evaluation prior to crayfish re‐stockings and water monitoring that can minimize disease transmission and spread, for example in crayfish farms and prior to fish movements for stocking purposes.
The transmission of world maize price to South African maize market: a threshold cointegration approach
Authors: Abidoye Babatunde O. , Labuschagne Marlene
Published: December 2013

This article seeks to provide an explanation for the relationship between domestic maize price in South Africa and world maize prices in order to evaluate comovement and transmission of world prices to domestic prices in sub‐Sahara African countries. This is done by comparing nested and nonnested models that capture different forms of nonlinearity in the price spread. Adopting a Bayesian approach that allows for comparison of models using Bayes factor, we found that the relationship between South African price and world price for maize indicates the presence of nonlinearity in price transmission with three regimes that is triggered by the price spread in previous period.
Electrocardiography at Diagnosis and Close to the Time of Death in Pulmonary Arterial Hypertension
Authors: Tonelli Adriano R. , Baumgartner Manfred , Alkukhun Laith , Minai Omar A. , Dweik Raed A.
Published: December 2013

Background

Scarce information exits on the electrocardiographic (ECG) characteristics of pulmonary arterial hypertension (PAH) patients close to their death and whether observed abnormalities progress from the time of PAH diagnosis.

Methods

We analyzed the characteristics of the ECG performed at initial diagnosis, during the course of the disease and close to the time of death on consecutive PAH patients followed at our institution between June 2008 and December 2010.

Results

We included 50 patients with PAH (76% women) with mean (SD) age of 58 (14) years. Median heart rate (83 vs 89 bpm, P = 0.001), PR interval (167 vs 176 ms, P = 0.03), QRS duration (88 vs 90 ms, P = 0.02), R/S ratio in lead V1 (1 vs 2, P = 0.01), and QTc duration (431 vs 444 ms, P = 0.02) significantly increased from the initial to the last ECG. In addition, the frontal QRS axis rotated to the right (97 vs 112 degrees, P = 0.003) and we more commonly observed right bundle branch block (5% vs 8%, P = 0.03) and negative T waves in inferior leads (31% vs 60%, P = 0.004). No patient had normal ECG at the time of death.

Conclusions

Significant changes progressively occur in a variety of ECG parameters between the time of the initial PAH diagnosis and close to death.